(1.4 MB)

(1.4 MB)
Energy Input, Carbon Intensity, and Cost for Ethanol Produced
from Brown Seaweed
by
Aaron Philippsen
B.Eng, University of Victoria, 2010
A Thesis Submitted in Partial Fulfillment of the
Requirements for the Degree of
MASTER OF APPLIED SCIENCE
in the Department of Mechanical Engineering
 Aaron Philippsen, 2013
University of Victoria
All rights reserved. This thesis may not be reproduced in whole or in part, by
photocopy or other means, without the permission of the author.
ii
Supervisory committee
Energy Input, Carbon Intensity, and Cost for Ethanol Produced
from Brown Seaweed
by
Aaron Philippsen
B.Eng, University of Victoria, 2010
Supervisory committee
Dr. Peter Wild, (Department of Mechanical Engineering)
Co-Supervisor
Dr. Andrew Rowe, (Department of Mechanical Engineering)
Co-Supervisor
iii
Abstract
Supervisory committee
Dr. Peter Wild, (Department of Mechanical Engineering)
Co-Supervisor
Dr. Andrew Rowe, (Department of Mechanical Engineering)
Co-Supervisor
Brown macroalgae or brown seaweed is a promising source of ethanol that may avoid the
challenges of arable land use, water use, lignin content, and the food vs. fuel debate associated
with first generation and cellulosic ethanol sources; however, this promise is challenged by
seaweed’s high water content, high ash content, and natural composition fluctuations. Notably,
lifecycle studies of seaweed ethanol are lacking in the literature. To address this gap, a well-towheel model of ethanol production from farmed brown seaweed was constructed and applied to
the case of Saccharina latissima farming in British Columbia (BC), Canada, to determine energy
return on energy invested (EROI), carbon intensity (CI), and near shore seaweed farming
production potential for seaweed ethanol and to examine the production cost of seaweed ethanol.
Seaweed farming and ethanol production were modeled based on current BC farming methods
and the dry grind corn ethanol production process; animal feed was included as an ethanol coproduct, and co-product credits were considered. A seaweed ethanol yield calculation tool that
accounts for seaweed composition was proposed, and a sensitivity study was done to examine
case study data assumptions.
In the case study, seaweed ethanol had lower CI than sugarcane, wheat, and corn ethanol at
10.1 gCO2e/MJ, and it had an EROI comparable to corn ethanol at 1.78. Seaweed ethanol was
potentially profitable due to significant revenue from animal feed sales; however, the market for
seaweed animal feed was limited by the feed’s high sodium content. Near shore seaweed farming
could meet the current demand for ethanol in BC, but world near shore ethanol potential is likely
iv
an order of magnitude lower than world ethanol production and two orders of magnitude lower
than world gasoline production. Composition variation and a limited harvest season make solar
thermal or geothermal seaweed drying and storage necessary for ethanol production in BC.
Varying seaweed composition, solar thermal drying performance, co-product credits, the type of
animal feed produced, transport distances, and seaweed farming performance in the sensitivity
study gave an EROI of over 200 and a CI of -42 gCO2e/MJ in the best case and an EROI of 0.64
and CI of 33 gCO2e/MJ in the worst case. Co-product credits and the type of animal feed
produced had the most significant effect overall, and the worst cases of seaweed composition and
solar thermal seaweed drying system performance resulted in EROI of 0.64 and 1.0 respectively.
Brown seaweed is concluded to be a potentially profitable source of ethanol with climate
benefits that surpass current ethanol sources; however, additional research into seaweed animal
feed value, co-product credits, large scale seaweed conversion, and the feasibility of solar
thermal or geothermal seaweed drying is required to confirm this conclusion.
v
Table of contents
Supervisory committee ................................................................................................................. ii
Abstract ......................................................................................................................................... iii
Table of contents ........................................................................................................................... v
List of tables................................................................................................................................ viii
List of figures ................................................................................................................................ ix
Nomenclature ................................................................................................................................ x
1
2
Background and motivation ................................................................................................. 1
1.1
Ethanol to combat climate change ................................................................................... 1
1.2
Seaweed as an ethanol source .......................................................................................... 1
1.3
Objective .......................................................................................................................... 3
1.4
Outline .............................................................................................................................. 3
Background on seaweed ........................................................................................................ 4
2.1
Seaweed reproduction ...................................................................................................... 4
2.2
Seaweed composition variation ........................................................................................ 6
2.2.1
Seasonal composition variation ................................................................................ 6
2.2.2
Influence of environment on composition ................................................................ 6
2.2.3
Seasonal growth cycle............................................................................................... 9
2.3
General seaweed farming techniques ............................................................................... 9
2.3.1
Near shore seaweed farming ................................................................................... 10
2.3.2
Offshore seaweed farming ...................................................................................... 11
2.3.3
Land based cultivation ............................................................................................ 12
2.4
Near shore farming practices in China and BC .............................................................. 13
2.4.1
2.5
3
Fertilizer application ............................................................................................... 13
Summary ........................................................................................................................ 14
Background on ethanol production ................................................................................... 15
3.1
General ethanol production process ............................................................................... 15
3.1.1
Solar energy capture ............................................................................................... 16
3.1.2
Biomass supply ....................................................................................................... 17
3.1.3
Saccharide extraction .............................................................................................. 17
3.1.4
Hydrolysis ............................................................................................................... 18
3.1.5
Fermentation ........................................................................................................... 18
3.1.6
Ethanol recovery ..................................................................................................... 19
3.1.7
Residue processing.................................................................................................. 19
vi
3.1.8
3.2
Storage .................................................................................................................... 21
3.2.2
Harvest extension .................................................................................................... 21
3.2.3
Additional feedstock ............................................................................................... 21
Seaweed ethanol production........................................................................................... 22
3.3.1
Dealing with seaweed harvest season ..................................................................... 22
3.3.2
Ethanol yield in the literature .................................................................................. 24
3.4
Summary ........................................................................................................................ 25
Seaweed ethanol production model.................................................................................... 26
4.1
Energy inputs, GHG emissions, and co-product credits ................................................ 26
4.1.1
Energy input in seaweed production ....................................................................... 27
4.1.2
Energy input in drying ............................................................................................ 28
4.1.3
Energy input in transport and distribution .............................................................. 29
4.1.4
Energy input in conversion ..................................................................................... 30
4.1.5
GHG emissions ....................................................................................................... 31
4.1.6
Co-product credits ................................................................................................... 32
4.2
Near shore ethanol yield ................................................................................................. 32
4.3
Cost analysis ................................................................................................................... 33
4.4
Model architecture.......................................................................................................... 33
4.4.1
EROI ....................................................................................................................... 34
4.4.2
CI............................................................................................................................. 35
4.4.3
Conversion rate ....................................................................................................... 35
4.4.4
Near shore ethanol yield ......................................................................................... 36
4.4.5
Maximum feedstock cost ........................................................................................ 37
4.4.6
Energy inputs .......................................................................................................... 37
4.4.7
GHG emissions ....................................................................................................... 40
4.4.8
Co-product credits ................................................................................................... 41
4.5
5
Dealing with feedstock harvest season........................................................................... 21
3.2.1
3.3
4
Dry grind corn ethanol production .......................................................................... 21
Summary ........................................................................................................................ 41
BC case study ....................................................................................................................... 42
5.1
Overview ........................................................................................................................ 42
5.2
Energy inputs, GHG emissions, and co-product credits ................................................ 44
5.2.1
Energy input in seaweed production ....................................................................... 44
5.2.2
Energy input in drying ............................................................................................ 46
vii
6
7
8
5.2.3
Energy input in transport and distribution .............................................................. 46
5.2.4
Energy input in conversion ..................................................................................... 47
5.2.5
GHG emissions ....................................................................................................... 49
5.2.6
Co-product credits ................................................................................................... 49
5.3
Near shore ethanol yield ................................................................................................. 50
5.4
Cost analysis ................................................................................................................... 50
5.5
Case study architecture................................................................................................... 51
5.5.1
Maximum drying and delivery cost ........................................................................ 52
5.5.2
Energy inputs .......................................................................................................... 52
5.5.3
GHG emissions ....................................................................................................... 54
5.5.4
Co-product credits ................................................................................................... 55
5.5.5
Cost inputs .............................................................................................................. 55
5.6
Sensitivity study ............................................................................................................. 56
5.7
Summary ........................................................................................................................ 57
Results ................................................................................................................................... 59
6.1
EROI............................................................................................................................... 59
6.2
CI .................................................................................................................................... 60
6.3
Near shore ethanol yield ................................................................................................. 61
6.4
Max feedstock cost and maximum drying and delivery cost ......................................... 62
6.5
Sensitivity Study ............................................................................................................ 64
6.6
Animal feed market limitation ....................................................................................... 65
Discussion ............................................................................................................................. 66
7.1
Seaweed ethanol production in BC ................................................................................ 66
7.2
Benefits from animal feed co-product ............................................................................ 67
7.3
Flexibility in system layout ............................................................................................ 67
7.4
Near shore farming potential .......................................................................................... 68
7.5
The effect of seaweed composition ................................................................................ 68
7.6
The effect of key assumptions........................................................................................ 69
Conclusion ............................................................................................................................ 70
8.1
9
Recommendations .......................................................................................................... 72
References............................................................................................................................. 73
Appendix A - Ideal ethanol yield ............................................................................................... 80
Appendix B - Input data ............................................................................................................. 82
viii
List of tables
Table 4-1: Components of brown seaweed ................................................................................... 36
Table 5-1: Comparison of corn distiller's grains to seaweed distillation residue ......................... 48
Table A-1: Ideal ethanol yield for brown seaweed and corn starch ............................................. 81
Table B-1: Seaweed production .................................................................................................... 82
Table B-2: Drying ......................................................................................................................... 83
Table B-3: Ethanol yield ............................................................................................................... 83
Table B-4: Ethanol conversion input ............................................................................................ 84
Table B-5: Animal feed production and credits ............................................................................ 85
Table B-6: Transportation and distribution................................................................................... 86
Table B-7: Carbon intensity for energy consumed ....................................................................... 87
Table B-8: Global ethanol production .......................................................................................... 87
Table B-9: Cost analysis ............................................................................................................... 88
ix
List of figures
Figure 2-1: Laminaria reproductive cycle....................................................................................... 5
Figure 2-2: Saccharina latissima composition ................................................................................ 7
Figure 2-3: Variation in Saccharina latissima composition, inlet vs. open sea ............................. 8
Figure 2-4: Hanging and horizontal rope seaweed farm systems ................................................. 10
Figure 2-5: Single raft units, raft blocks, and example seaweed farm layout ............................... 11
Figure 3-1: General steps of fermentation based ethanol production ........................................... 16
Figure 3-2: Simplified diagram of ethanol recovery process ........................................................ 19
Figure 3-3: Dry grind corn ethanol process .................................................................................. 20
Figure 4-1: Seaweed ethanol production model. .......................................................................... 27
Figure 4-2: Comparison of seaweed conversion, and dry grind corn ethanol conversion. ........... 30
Figure 5-1: Case study of ethanol production in BC. ................................................................... 43
Figure 5-2: Transport scenarios. ................................................................................................... 45
Figure 6-1: EROI of seaweed ethanol considering feed production and co-product credits. ....... 60
Figure 6-2: CI of seaweed ethanol considering feed production and co-product credits. ............ 61
Figure 6-3: Global near shore ethanol yield compared to current world ethanol production. ...... 62
Figure 6-4: Maximum feedstock cost compared to fresh feedstock cost...................................... 63
Figure 6-5: Maximum drying and delivery cost for dry seaweed. ................................................ 63
Figure 6-6: Sensitivity study results. ............................................................................................ 64
x
Nomenclature
Acronyms
British Columbia
Canadian dollars
Carbon intensity
Coefficient of performance
Dry distiller’s grains with solubles
Energy return on energy invested
Glyceraldehyde-3-phosphate
GHG emission in grams of carbon dioxide equivalent
Greenhouse gas
Global warming potential
Higher heating value
Modified distiller’s grains with solubles
US dollars
Wet distillers grains with solubles
Symbols
Fraction of total dry grind electricity consumption used for feed processing
Seaweed bulk density (kg·m-1)
Ethanol plant capital cost ($)
Maximum drying and delivery cost ($·tonne-1)
Annual feedstock cost ($·yr-1)
Fresh seaweed production cost ($·tonne-1)
Carbon intensity for energy carrier produced (gCO2e·MJ-1)
Ethanol plant annual operating cost less annual feedstock cost ($·yr-1)
Solar thermal system COP
Silo capital cost ($·m-3)
Maximum feedstock cost ($·tonne-1)
Total specific co-product production (kg·MJ-1)
Specific mass of co-product similar to animal feed (kg·MJ-1)
Specific mass of co-product similar to mineral supplements (kg·MJ-1)
xi
Dry grind animal feed production rate (kg·L-1)
Specific mass of co-product i produced (kg·MJ-1)
Specific energy input (MJ·MJ-1)
Electricity input for producing co-product i (MJ·MJ-1)
Fuel input for producing co-product i (MJ·MJ-1)
Electricity consumption in dry grind corn ethanol production (MJ·L-1)
Natural gas consumption in dry grind corn ethanol production (MJ·L-1)
Total energy input for carrier production (MJ)
Total energy carrier output (MJ)
Energy return on energy invested
Fuel use (MJ·tonne-1km-1)
Skiff fuel use at cruising speed (L·km-1)
Skiff fuel use at idle (L·hr-1)
Specific direct GHG emission (gCO2e·MJ-1)
Specific indirect GHG emission (gCO2e·MJ-1)
Ethanol 100 year GWP (gCO2e·g-1)
Total GHG emission for carrier production (gCO2e·MJ-1)
Seaweed water removal heat requirement (MJ·kg-1)
Higher heating value (MJ·kg-1)
Higher heating value, per unit volume (MJ·L-1)
Carbon intensity for energy consumed (gCO2e·MJ-1)
GHG emission credit for co-product i (gCO2e·kg-1)
Total specific GHG emission co-product credit (gCO2e·MJ-1)
Energy credit for co-product i (MJ·kg-1)
Total specific energy co-product credit (MJ·MJ-1)
Coastline length in region i (km)
Horizontal rope seeded per sporeling batch (m·batch-1)
Dry seaweed moisture content
Fresh seaweed moisture content
Inflation correction factor (2012 USD·1999 USD-1)
Operating cost ($·yr-1)
Annual seaweed production (tonne·yr-1)
Sporeling tank electrical power draw (W)
xii
Ethanol plant production capacity (L·yr-1)
Ethanol plant annual ethanol and co-product revenue ($·yr-1)
Seaweed to ethanol conversion rate (kg·kg-1)
2012 CAD/US exchange rate (CAD·USD-1)
Horizontal rope seaweed production rate (kg·m-1)
Rate of fresh seaweed production (kg·batch-1)
Capital cost ($)
Fuel use per unit of fresh seaweed produced (MJ·kg-1)
Wholesale ethanol price ($·L-1)
Wholesale seaweed feed price ($·tonne-1)
Gasoline to ethanol blend equivalence (L·L-1)
Near shore ethanol yield for coastline section x (L·yr-1)
Transport distance (km)
Mass fraction of total seaweed solids for seaweed component i
Mass fraction of co-product i produced
Rate of return
Specific mass flow (kg·MJ-1)
Ethanol vapor loss in distribution (kg·kg-1)
Mass of fertilizer applied per unit fresh seaweed produced (kg·kg-1)
Mass of fresh seaweed (kg)
Sporeling batches produced per number of frond collection trip (batch)
Number of return trips for gathering mature fronds and installing seedlings per unit of
horizontal rope (m-1)
Sporeling batch culture time (weeks·batch-1)
Spore bearing frond collection time (min·batch-1)
Horizontal rope harvesting time (min·m-1)
Total skiff idling time (min·m-1)
Sporeling twine installation time (min·m-1)
Ethanol plant operating life (yr)
Sporeling installation work day (hr)
xiii
Greek
Animal feed production capital cost scaling factor
Ethanol production fuel scaling factor
Energy input cost scaling factor
Conversion efficiency for seaweed component i
Ethanol energy equivalent for fresh seaweed
Ethanol density
Ideal ethanol yield for seaweed component i
Superscripts
Specific quantity. Indicates quantities that are expressed per MJ of ethanol higher
heating value delivered to vehicle fuel tank.
Subscripts
Air compressor
Animal feed production
British Columbia
Sporeling boat fuel
Barge
Coal
China
Typical dry grind animal feed
Drying system electricity
Dry feed
Denaturant
Distillation
Ethanol production electricity
Ethanol production fuel
Ethanol plant energy input
Electricity
Ethanol
Animal feed displacement
xiv
Fermentation capital cost
Gasoline
idling during production operations
Labor, supplies, and overhead
Mineral supplement displacement
Modified feed
Natural gas
Process electricity
Process fuel
Raw materials
Skiff at cruising speed, partial load
Sporeling electricity
Sporeling heating fuel
Skiff at idle
Skiff under full load
Storage and load out system
Support operations
Dry seaweed storage system
Solar thermal system input
Transport fuel
Fuel truck
Train
Transport of mature seaweed, fronds, and sporelings
World coastline
Wet feed
Wastewater treatment capital cost
Coastline in region of interest
1 Background and motivation
1.1 Ethanol to combat climate change
Transportation accounts for 13% of total anthropogenic GHG emissions with 95% coming
from the use of petroleum derived diesel and gasoline [1]. Because of its relative compatibility
with existing infrastructure, bioethanol can be used as a near term replacement for gasoline that
offers a mechanism to reduce transportation emissions; however, replacement of gasoline with
ethanol is limited by the quantity of bioethanol that can currently be produced.
Currently, the majority of bioethanol is produced from ether corn or sugarcane. Known as
first generation ethanol sources, both corn and sugarcane face barriers that limit their production.
Corn production requires arable land, irrigation, and fertilizer, and corn ethanol production has a
potentially negative effect on corn production for human consumption, driving the “food vs.
fuel” debate [2]. Sugarcane does not compete with food production like corn; however, expanded
sugarcane production can contribute to deforestation and wetland destruction [3], and sugarcane
production is limited to specific climates. Cellulosic biomass has been proposed as a solution to
the problems of first generation ethanol sources as it is ubiquitous in the biosphere, it can be
grown in almost any climate, and it typically does not require arable land, irrigation, or fertilizer.
However, cellulosic biomass is difficult to convert to ethanol due to the presence of lignin and
cellulose’s natural resistance to hydrolysis.
1.2 Seaweed as an ethanol source
Macroalgae is a promising source of ethanol that may avoid the challenges of first
generation and cellulosic ethanol sources. Commonly called seaweed, it is free of the food vs.
fuel debate, needs no arable land or fresh water, and lacks lignin [4]; however, it has high water
content (75-90%), high ash content (22-37%) [5], and it experiences significant monthly
fluctuations in fermentable sugar content [6]. Seaweed ethanol has received significant attention
in the literature, but the effect of water content, ash content, and composition variation on the
overall ethanol production system has not been fully addressed.
2
Roesijadi et al. [7], Bruton et al. [5], Reith et al [8], Horn [9], and Hennenberg et al. [10],
provide an excellent review of current research on seaweed in general, seaweed bioenergy
production, and co-product production.
Brown seaweeds are considered the most likely candidates for energy production, and the
brown seaweed Saccharina japonica is the most farmed seaweed by mass, accounting for 33%
of global near shore seaweed production [7]. Apart from water, ash, and a small quantity of
miscellaneous metabolites, brown seaweeds contain seven energy rich biomolecules: laminarin,
mannitol, alginate, protein, cellulose, fucans, and small quantities of lipids [11]. Of these
components, laminarin and mannitol are considered easily fermentable [9], and recent work has
shown that alginate fermentation is possible with genetically modified fermenting organisms
[4][12].
For co-product production, pigment proteins, cellulose, fucans, and metabolite derived
phenolic compounds can be extracted from seaweed and sold to limited markets [7], or the whole
seaweed mass can be anaerobically digested into methane [13], converted into fertilizer, or
potentially made into animal feed. Seaweed fertilizer can act as biostimulant [5], and seaweed
ash contains high amounts of beneficial minerals and trace elements [14] [15] which may
increase its value as animal feed. Feed production is simpler than extraction or digestion,
requiring only dewatering and or drying of whole seaweed, and animal feed is the dominant coproduct in the corn ethanol industry. Replacing conventional animal feed with co-product animal
feed from corn ethanol results in a significant reduction in both greenhouse gas (GHG)
emissions and energy use in the livestock industry, which is accounted to ethanol producers as
co-product credits [16]. Animal feed production and co-product credits have not been considered
for seaweed ethanol systems.
Conversion of seaweed to ethanol has been achieved at lab scale [4] [9][12], and two
studies of bio-ethanol production from seaweed were reviewed by Roesijadi et al. [7]. In the first
study, Aizawa et al. [17] examined ethanol production from seaweed farmed in both coastal and
offshore zones, and estimated resource consumption for cultivation and production. The overall
energy balance was considered similar to that of corn ethanol. Peter et al. [18] examined seaweed
production with juvenile seaweed cultured at a fish hatchery then transferred to ocean farm
structures for a final grow out. Pumping in the culturing stage, boat fuel for maintenance during
3
the growth phase, and ethanol distillation were identified as the largest energy consumers, but no
numerical results were given. Roesijadi et al. concluded that lifecycle analyses for seaweed
biofuel are scarce in the literature, and that additional assessment is necessary to provide an
adequate comparison between seaweed biofuels and conventional biofuels. The effect of
seaweed composition variation and of co-product credits have not been considered, lifecycle
GHG emissions and energy input have not been quantified, and the potential global impact of
seaweed ethanol has not yet been examined.
1.3 Objective
The objective of this thesis is twofold: 1) develop a general well-to-wheel model of
seaweed ethanol production to work towards a comprehensive lifecycle analysis of seaweed
ethanol. 2) Apply the general model to the case of ethanol production from farmed Saccharina
latissima in British Columbia (BC) to determine the effect of high water content, high ash
content, and composition variation on ethanol performance. Both the general model and case
study examine the energy inputs and GHG emissions associated with seaweed ethanol
production, both include an estimate of ethanol production potential based on near shore seaweed
farming, and both address the cost of seaweed ethanol production. The case study also includes a
sensitivity study to determine how ethanol performance is affected by assumed input data.
1.4 Outline
The thesis body is divided into seven chapters. Chapter 2 provides background information
on seaweed reproduction, composition variation, and farming practices. Chapter 3 provides
background information on the ethanol production process and the effect of feedstock harvest
season on the overall production system, and both dry grind corn ethanol production and
seaweed ethanol production are discussed. Chapter 4 describes the well-to-wheel model of
brown seaweed ethanol production including system boundaries and the specific inputs and
outputs considered, and it proposes a tool for estimating ethanol yield from any brown seaweed
based on seaweed composition. Chapter 5 outlines the case study of seaweed ethanol production
in BC, defining the location specific parameters required by the model and outlining a sensitivity
study on case study input data. Chapter 6 presents results from the case study and the sensitivity
study, Chapter 7 gives a discussion of the results, and Chapter 8 gives conclusions from the case
study and recommendations for future work.
4
2 Background on seaweed
This chapter discusses background information on seaweed covering the two basic forms of
seaweed reproduction, the factors that influence seaweed composition, and seaweed farming
techniques. Both seaweed reproduction and seaweed farming techniques affect the inputs
required to produce seaweed biomass, and the variation in seaweed composition can influence
seaweeds ethanol production potential. Seaweed reproduction is discussed in Section 2.1,
composition is discussed in Section 2.2, the general methods used for farming seaweed are
explained in Section 2.3, and near shore seaweed farming practices in China and BC are
explained in Section 2.4.
2.1 Seaweed reproduction
Depending on the species, seaweed propagates through asexual and/or sexual reproduction.
Asexual or vegetative reproduction occurs when fragments of mature seaweed break off the
main body or thallus and grow into new seaweed thallus that is a clone of the original. In
seaweed farming, vegetative reproduction is facilitated by taking cuttings from a mature seaweed
thallus and using them as seed stock for subsequent seaweed crops or by harvesting only part of
the seaweed, leaving the remainder to grow again [14]. Sexual reproduction is more complex to
facilitate then asexual, and it occurs through alternating generations of single chromosome or
haploid cells and double chromosome or diploid cells.
In sexual reproduction, seaweeds alternate between generations of haploid cells and diploid
cells called gametophytes and sporophytes. The haploid form is called a gametophyte because it
will produce gametes (eggs and sperm) that fuse to form the next diploid generation, and the
diploid form is called a sporophyte because it will produce spores that contain new haploid cells.
The large, multicellular structures we recognize as seaweed can be either sporophytes or
gametophytes depending on the species. Many brown seaweed species desirable for energy
production, like the Laminaria species, reproduce through a dominant generation of sporophytes
and a diminutive generation of gametophytes. The gametophytes are microscopic, containing
only a few cells and they exist only to facilitate gamete production, and the sporophytes are
large, multicellular structures that we recognize as seaweed.
5
7
1
Sporophyte
generation
Gametophyte
generation
3
2
6
5
4
Figure 2-1: Laminaria reproductive cycle [19]
The Laminaria reproductive cycle is shown in Figure 2-1. Reproduction begins with the
release of spores from the mature seaweed frond (1). The spores drift through the water and
anchor to the first suitable surface they contact, like bare rock. Once anchored, they mature into
ether a male or a female gametophyte (2). The female gametophytes develop a single egg (3),
and the males produce and release sperm (4) that seek out and fertilize the egg (5). This fertilized
egg is now the first cell of the sporophyte generation (6). The newly formed sporophyte or
sporeling remains attached to the original anchor site where its egg was attached, and the
sporeling matures into what we recognize as seaweed (7). Once mature, the seaweed develops
and releases spores (1) and the cycle repeats. In annual seaweed species like Nereocystis
luetkeana, the mature seaweed only lives for one year, and dying after spore release. In perennial
seaweeds like Macrocystis integrifolia, the mature seaweed can live for many years and produce
several generations of sporelings.
To facilitate sexual reproduction, the spore bearing sections of mature sporophytes must be
harvested before spores are released, and spore release, fertilization, and initial sporeling growth
6
must be facilitated in an illuminated and temperature controlled tank of seawater as detailed in
Section 2.4.
2.2 Seaweed composition variation
Seaweed composition is highly variable; it depends upon the environmental conditions
under which the seaweed grows and can be driven by natural growth cycles in some seaweed.
The seaweed Saccharina latissima is used to illustrate the magnitude of yearly composition
variation, the effect of site selection on composition, and the natural cycle of carbohydrate
storage shown in several seaweed species.
2.2.1 Seasonal composition variation
Freshly harvested seaweed, referred to as fresh seaweed, is typically 85% water by mass,
but its moisture content can range from 70% to 90% [5]. In brown seaweed, the remaining mass
or solids is composed of ash and seven energy rich components: laminarin, mannitol, alginate,
protein, cellulose, fucans, and lipids [11]. Ash content is generally very high, ranging from 22%
to 37%. Laminarin, mannitol, and alginate can be fermented into ethanol [9][12] and the portion
of seaweed solids made of these three components is referred to as the fermentable fraction.
Combined, total solids and fermentable fraction determine the ethanol production potential of a
given mass of fresh seaweed.
Solids content and fermentable fraction can vary significantly throughout the growing
season as illustrated by the seaweed Saccharina latissima. Composition data is provided by
Black [6][20], who studied the composition of several brown seaweed species in Scotland for a
two year period. Samples of Saccharina latissima were taken on a monthly basis from Eilean
Coltair in Loch Melfort, called the inlet location, and at a more open site near Shuna Island,
called the open ocean location. The inlet location is about 38 km from the open ocean location.
Data from the inlet study is shown in Figure 2-2. For the 1947 inlet samples, fermentable fraction
ranged from 25% to 59% throughout the year and solids content ranged from 10% to 21% giving
a significant variation in ethanol production potential.
2.2.2 Influence of environment on composition
Because fermentable fraction and solids content are influenced by local environmental
conditions, ethanol production potential is linked to the site where seaweed is grown. In their
7
60
Solids
Ash
Percent of dry matter by weight
50
Fermentable
fraction [a]
40
Alginate
Mannitol
30
Laminarin
20
Protein
Cellulose [b]
10
0
Dec-46
Celulose,
fuans, lipids
[c]
Mar-47
Jun-47
Sep-47
Dec-47
Mar-48
Jun-48
Sep-48
Figure 2-2: Saccharina latissima composition [6][20]. [a] Fermentable fraction is the sum
of alginate, laminarin, and mannitol content. [b] Cellulose data is for Dec 45 to Nov 46 [20]. [c]
The fraction of dry mass unaccounted for by Black is assumed to be composed of cellulose,
fucans, and lipids as per the typical components of brown seaweed given by Percival [11].
numerical model of Saccharina latissima growth, Broch et. al [21] identified four main factors
that affect growth and composition: water temperature, solar irradiance, water current speed, and
nutrient concentration. They also identified salinity, water turbidity, and light spectral
distribution as potential factors but did not model them due to lack of available data or
potentially low influence. Considering the example of Nereocystis luetkeana, seaweed
composition might also be affected by the hydrodynamic forces that result from farm structure
dynamics and ocean drag. Under natural growing conditions, the seaweed Nereocystis luetkeana
alters its morphology in response to its local hydrodynamic environment [22], changing shape
and structure to accommodate local drag forces.
Comparing Saccharina latissima from the inlet and open ocean locations described in
Section 2.2.1, solids content and fermentable fraction for the inlet location varied by up to 23%
8
and 48% respectively between years for the same month sampled, and they varied by up to 33%
and 26% respectively between the inlet and open ocean location for the same year and month
sampled. Composition for the two sites is compared in Figure 2-3. The variation between
sampling year was likely caused by differences in available sunlight as 1947 was a particularly
good growing year with considerable sunshine and 1948 was a very poor year with considerable
cloud and rain [6]. The difference between sampling locations could have been caused by
differences in local ocean conditions alone. The solar flux and weather conditions experienced at
the two locations were likely similar because the sampling locations were only 38km apart.
60
Fermentable Fraction
(Inlet)
Percent of dry matter by weight
50
Fermentable Fraction
(Open Sea)
Ash
(Inlet)
40
Ash
(Open Sea)
30
Solids
(Inlet)
Solids
(Open Sea)
20
Cellulose
(Inlet) [a]
10
Cellulose
(Open Sea) [a]
0
Dec-46
Mar-47
Jun-47
Sep-47
Dec-47
Mar-48
Jun-48
Sep-48
Figure 2-3: Variation in Saccharina latissima composition, inlet vs. open sea [6][20]. [a]
Cellulose data for Dec 45 to Nov 46.
Because growth environment can influence solids content and fermentable fraction,
seaweed farm site selection could have a significant impact on ethanol production potential and
timing of seaweed harvest. Combined with a model of local weather and ocean conditions, a
9
growth model like that developed by Broch et al. may provide a means to predict seaweed
composition, optimum harvest period, and ethanol production potential for a given seaweed
growth site, and it could be used as a screening tool to select optimum farming sites.
2.2.3 Seasonal growth cycle
Many perennial brown seaweeds, like Saccharina latissima, follow an alternating pattern
of growth and energy storage that is advantageous for ethanol production. In northern and
southern latitudes with reduced daylight in winter months, dissolved ocean nutrient levels are
often maximum in winter when light levels are low but minimum in summer when light levels
peak. This pattern is detrimental to seaweed growth as low light restricts growth in winter when
nutrients are available while low nutrient level restricts growth in summer when light is
available. To deal with this disparity, Saccharina latissima will limit its structural growth in
spring, even if sufficient nutrients are available, and will focus on the production of the
carbohydrates laminarin and mannitol to store energy when light is available. Then in winter
when nutrient levels are high, energy stored in these carbohydrates is used to drive structural
growth and to store additional nutrients, giving the seaweed an advantage the following summer.
This cycle results in a simultaneous peak of solids content, fermentable fraction, and total
biomass at the end of summer that is advantages for ethanol production. In Saccharina latissima
this cycle is likely triggered by fluctuations in day length rather than by fluctuations in ocean
nutrient concentration [23].
2.3 General seaweed farming techniques
Seaweed biomass can be generated in four ways: harvest of natural stocks, near shore
farming, offshore farming, and land based cultivation. For ocean based seaweed production,
natural stocks provide only 6% of global seaweed harvest and offshore farming is still only
experimental, leaving near shore as the dominant form of production [5]. Land based farming is
used at small scale for specialty markets [7]. Near shore farming is labor intensive, and the bulk
of production is done in areas where labor cost is low. Optimum seaweed production technique
varies with the region where seaweed is produced and it influences the cost, energy input, and
GHG emissions associated with seaweed production. Natural stock harvest will likely make a
minor contribution to seaweed ethanol production, therefore, only seaweed farming is considered
10
in the model developed in Chapter 4. Near shore, offshore, and land based farming are discussed
below.
2.3.1 Near shore seaweed farming
Near shore seaweed farming is done with two general methods: hanging kelp rope
systems (Figure 2-4A), and horizontal kelp rope systems (Figure 2-4B). Hanging systems contain
a long floating line (4) that is anchored to the sea floor (1) with anchor lines (2) and suspended
from floats (3), and they have several vertical sections of rope (5) that hang down into the water
to which the seaweed (6) is attached. The ropes are kept vertical by weights attached to their tips
(7). Horizontal systems contain similar anchors (1), anchor lines (2), floats (3), and floating lines
(4), but in these systems, multiple floating lines are connected to each other with horizontal ropes
(8) to which the seaweed is attached. Seaweed species without natural floats like Saccharina
latissima hang vertically from the horizontal ropes due to their own weight.
3
4
8
3
5
2
4
2
6
6
1
7
1
(B) Horizontal rope farm
(A) Hanging rope farm
1) Anchor
3) Float
2) Anchor line 4) Floating line
5) Hanging rope
6) Seaweed
7) Weight
8) Horizontal rope
Figure 2-4: Hanging and horizontal rope seaweed farm systems [19]
Seaweed farms contain both single raft units as shown Figure 2-5A and raft blocks shown
in Figure 2-5B. Single raft units are more stable due to a larger number of anchor points per
floating line and are typically used in more exposed areas to deal with strong currents and wave
action. They can be used as a breakwater to shelter raft blocks from strong currents or waves in
large seaweed farms as shown in Figure 2-5C. Floating line length and spacing between the
single raft units is determined by environmental conditions at the site [19]. Raft blocks are
11
similar to single raft units, but they have a larger number of floating lines per anchor point. Raft
blocks contain 10-40 floating lines each 45-55m long, with a 3-5m horizontal spacing [19], and
(A) Single raft unit
(B) Raft block
(C) Example farm layout
Figure 2-5: Single raft units, raft blocks, and example seaweed farm layout [19]
they contain only a few anchors. Blocks are spaced 30-40m apart for safety and to allow proper
water circulation. Raft block geometry is also determined by site conditions. The floating lines
can support ether hanging kelp ropes or horizontal kelp ropes. In BC, horizontal ropes must be
spaced between 1 and 2 meters from each other for proper water circulation depending on local
currents [24][25]. An example farm layout containing both single raft units and raft blocks is
shown in Figure 2-5C.
2.3.2 Offshore seaweed farming
Offshore seaweed farming covers a range of potential biomass production systems from
near shore farming systems implemented a significant distance away from shore to self contained
12
sporeling production and farming structures with their own power generation and propulsion
systems. Offshore farming systems are reviewed by Bruton et al. [5], Roesijadi et al. [7],
Chynoweth [13], and Aizawa et al. [17]. These systems could open potentially limitless area for
energy production in the open ocean, and oil rigs, offshore wind farms, and emerging wave
energy systems demonstrate the potential feasibly of such structures. However, open ocean
systems are expensive to construct and maintain and seaweed biomass has relatively low value
per unit of ocean structure when ethanol production is considered. Offshore systems could be
combined with offshore wind farms [5] or other existing ocean infrastructure to reduce their
overall cost. Offshore farms are a promising concept, but additional work is required to prove
their feasibility in difficult ocean environments and to prove offshore systems can produce cost
competitive ethanol feedstock.
2.3.3 Land based cultivation
Land based culture of seaweed achieves greater control over growing conditions, but it at
much higher production cost and potentially high energy cost. Roesijadi et al. [7] lists the
advantages of on land systems being 1) ease of seaweed management; 2) use of seaweeds with or
without holdfast structures; 3) ease of nutrient application without dilution; 4) avoidance of open
sea problems such as bad weather, disease, and predation; and 5) possibility of locating farms
near conversion operations. Land based culture is currently used for specialty seaweed products
like food and cosmetics [26], but it is likely difficult to design an affordable system for biofuel
production. For the case study considered in Chapter 5, one tonne of dry seaweed produces $230
worth of ethanol, but the same seaweed could be sold for $48,000 dollars or more in the food
market [25]. Therefore, systems suitable for high value seaweed products like food may not be
cost effective for biofuel production due to the relatively low value of ethanol. In addition to
effecting cost, land based culture systems require energy input for water circulation and lighting
that may degrade lifecycle performance. In their analysis of ethanol production, Peter et al. [18]
found that water circulation in cultivation tanks was a significant contributor to lifecycle energy
input. Because the energy content of fresh seaweed biomass is low due to seaweed’s high ash
and water content, a small amount of energy input per unit of fresh biomass may significantly
increase lifecycle energy inputs and GHG emissions for seaweed ethanol.
13
2.4 Near shore farming practices in China and BC
The culture of Laminaria japonica in Northern China begins with frond collection in midJuly. Spore bearing fronds are partially dried to stimulate spore release and placed in a culturing
tank that is cooled to 8-10°C. The male and female spores anchor to palm fiber mats in the tank
where they generate the next generation of sporelings as described in Section 2.1. The tank is
illuminated by natural light in a greenhouse like structure, and light levels are controlled by
shade cloth. The sporelings grow here for 3 months until they 2-5 cm long, large enough to
transfer to intermediate growing rafts in the ocean. At the intermediate rafts, they grow for an
additional 2-4 weeks until reaching 10-25 cm in length, and they are finally transferred to
permanent growing ropes in the ocean where they mature into a seaweed crop over the next 8
months. Additional cultivation during this growth period can be required. For example, at sites
with significantly turbid waters, the seaweed must be agitated to remove sediment buildup that
can block light and restrict growth [19].
In the seaweed farming system practiced in BC by Cross [24], seaweed production begins
in late September with a similar collection of spore bearing seaweed fronds. The fronds are
placed in a tank of sterilized seawater where spore release is chemically induced. The spores
anchor to lengths of twine and generate sporelings that remain attached to the twine. The tank is
artificially illuminated, electrically heated, and its water is circulated for 6-8 weeks while the
sporelings grow to a length of 1-2mm. The twine segments are then installed on floating ropes at
a farm structure in the ocean, and the sporelings grow into mature seaweeds over the next 7-8
months without additional cultivation. Growth is negligible overwinter, but increases rapidly in
March when light levels increase and the mature seaweeds peaks in biomass content near the end
of July.
2.4.1 Fertilizer application
Fertilizer application has an unknown effect on seaweed production GHG emissions, but it
is only required in Northern China and is not typically required in BC. In Northern China, it is
common to apply nitrogen fertilizer during all stages of seaweed growth in areas where the
natural ocean nitrogen level is low, but no studies examining the GHG emissions of this practice
could be found. In Laminaria japonica production, ammonium nitrate is sprayed in the water
near the seaweed if natural nitrogen levels are less than 100 mg/m3. As seaweeds rapidly absorb
14
this nitrogen and store enough for several days of growth, fertilizer is only applied every few
days [19]. There is potential for this practice to greatly increase the lifecycle emissions of
seaweed ethanol. In corn ethanol production examined by Bremer et al. [16], nitrogen fertilizer
use and associated N2O emissions were responsible for 36% of total GHG emissions. As the
practice of land and ocean fertilization are physically quite different, emission levels per kg of
fertilizer applied on land likely do not translate to ocean application. Seaweed production in
Southern China and in BC does not typically require fertilizer [19][24] as natural ocean nitrogen
levels are sufficient for seaweed growth.
2.5 Summary
As demonstrated in this chapter, seaweed biology can influence seaweed ethanol production
in several ways. Seaweed solids content and fermentable fraction determine ethanol production
potential of seaweed biomass, and both are functions of environmental conditions where the
seaweed grows. They can also vary significantly throughout the year. Seaweed can be farmed
with near shore, offshore, or on land farming systems, and the system chosen will influence
production cost, energy input, and GHG emissions associated with seaweed production. Farming
technique varies depending on the region of seaweed production, and fertilizer use for seaweed
farming is a potentially significant source of GHG emissions that remains to be quantified.
The following chapter deals with farmed seaweed after harvest, giving background
information for the conversion of seaweed biomass into ethanol and giving background
information on ethanol production in general.
15
3 Background on ethanol production
Chapter 3 provides an overview of fermentation based ethanol production and examines the
specific case of fermentation based ethanol production from seaweed biomass. Ethanol is a two
carbon alcohol with a variety of uses which include being a solvent, a beverage, and a high
octane fuel for spark ignition engines. Ethanol can be thermochemically synthesized from syngas
produced from biomass [27], natural gas, coal [28], or almost any other hydrocarbon source. It
can be biologically synthesized from syngas [29], and it can be directly produced and secreted by
genetically engineered photosynthesizing organisms [30]. However, ethanol is most commonly
produced by microbial fermentation of sugars. In this process, sugars are consumed by the
microorganisms as an energy source, and ethanol is excreted as a metabolic byproduct. This
process can be used for a variety of feedstocks with a variety of processes, but most fermentation
based ethanol systems share several common production steps and they are commonly limited by
the natural availability of feedstock. Production is broken into seven steps that are common to
ethanol production from most feedstocks, and the seven steps are illustrated with the case of dry
grind corn ethanol production. Ethanol plants require a nearly year round supply of feedstock,
but fresh feedstock is usually not available. Saccharide crops are often only optimal for ethanol
production during a short period in their natural lifecycle called the harvest season. Three
techniques for ensuring adequate feedstock supply for crops with a short harvest are discussed.
As seaweed can also experience a limited harvest season, the three compensation techniques are
examined in the context of seaweed ethanol production. Ethanol yield from seaweed is also
discussed. Section 3.1 covers the seven steps of fermentation based ethanol production and the
dry grind corn ethanol process, Section 3.2 discusses the techniques used to deal with feedstock
harvest season, and seaweed ethanol is discussed in Section 3.3.
3.1 General ethanol production process
Fermentation based ethanol production contains seven general steps shown in Figure 3-1.
The seven steps of solar energy capture, biomass supply, saccharide extraction, hydrolysis,
fermentation, recovery, and residue processing are explained below, and the process of dry grind
corn ethanol production is illustrated in Section 3.1.8 using these steps.
16
General Steps of Ethanol Production
Solar Energy Capture
Conversion of CO2 and H2O into sugar rich
biomass driven by solar energy
(photosynthesis)
Feedstock Supply
Collection and possibly storage of sugar rich
biomass, and delivery to the conversion
facility. Removal of husks, branches, dirt,
rocks, etc.
Extraction
Mechanical or chemical extraction of
fermentable sugars or polysaccharides from
biomass
Hydrolysis
Breakdown of polysaccharides into
fermentable sugars.
Fermentation
Conversion of sugars into ethanol using
microorganisms
Ethanol Recovery
Separation of ethanol from the output of the
fermentation process, typically through
distillation and molecular sieving.
Residue Processing
Production of valuable co-products from
extraction/hydrolysis/fermentation process
inputs and the non-fermentable components
of the raw biomass.
Figure 3-1: General steps of fermentation based ethanol production
3.1.1 Solar energy capture
Bioethanol production begins with solar energy capture. In this step, photosynthesizing
plants, algae, or bacteria convert the energy in solar radiation to temporary chemical bonds and
perform a series of chemical reactions with that energy to combine water and CO2 into
hydrocarbons. The process of photosynthesis begins with the creation of glyceraldehyde-3phosphate (G3P) which is subsequently used to produce short, energy rich hydrocarbons called
simple sugars or monosaccharides. Common examples include glucose and fructose (both
C6H12O6). Photosynthesizing organisms will often polymerize these monosaccharides through
multiple dehydration reactions. The resulting polysaccharides are used as a dense energy storage
17
mechanism or as structural elements. Examples of polysaccharides made from glucose include
the energy storage polymers amylose and amylopectin (i.e. starch) and the structural polymer
cellulose. Monosaccharides and polysaccharides are referred to generally as saccharides. G3P is
the main target of ethanol production, as fermentation is ultimately a process to convert
saccharides into G3P then to convert G3P to ethanol and CO2.
3.1.2 Biomass supply
In addition to saccharide production, photosynthesizing organisms use the solar energy
stored in G3P and previously produced saccharides to synthesize an assortment of organic
molecules including proteins, lipids, and nucleic acids that make up their overall structure. They
also use that energy to capture an assortment of minerals and elements necessary for life and to
absorb water. This collection of saccharides, organic molecules, and other components is
commonly referred to as biomass. Photosynthesizing organisms like plants are typically spread
over a large area and many only achieve high saccharide composition for a short period each
year.
To facilitate ethanol production, biomass must be harvested, consolidated, pretreated and
delivered to the ethanol production facility. Pretreatment can include removal of husks, branches,
leaves, and other biomass components with a low concentration of targeted saccharides and the
removal of dirt, sand, rocks, or other contaminants that may hinder further processing, and it may
include measures to ensure a year round supply of feedstock to the conversion facility. The issue
of year round feedstock supply is dealt with in detail in Section 3.2.
3.1.3 Saccharide extraction
Once delivered to the ethanol conversion facility, saccharides that will eventually become
ethanol are generally hidden within the larger structure of the delivered biomass, and they must
be extracted before ethanol production can begin. Saccharides are generally extracted into an
aqueous solution in preparation for hydrolysis and fermentation. This process ranges in
complexity from the relatively simple process of crushing sugarcane to extract saccharide rich
juice to the relatively difficult chemical extraction of cellulose from cellulosic biomass [31].
Saccharides usually remain in a mix of non-fermentable biomass components after saccharide
extraction, but if the expense of separation can be justified, proteins, lipids, or other biomass
18
components can be separated from the saccharides as ethanol co-products at this stage in
production. Corn oil is produced this way through the wet grind process [32].
3.1.4 Hydrolysis
Once extracted, monosaccharides can be directly fermented, but polysaccharides must be
depolymerized back into monosaccharides before fermentation. All polysaccharides are formed
by dehydration reactions and they are all depolymerized through hydrolysis reactions. Hydrolysis
can be done biologically using polysaccharide specific enzymes, like cellulase to break down
cellulose or amylase to break down amylose and amylopectin, or it can be done
thermochemically with processes like acid hydrolysis and supercritical water hydrolysis [33]
[34]
3.1.5 Fermentation
Together, saccharide extraction and hydrolysis produce an aqueous solution of
monosaccharides and unfermentable biomass components called mash. Microorganisms are
added to the mash, and they consume the monosaccharides as a source of energy, secreting
ethanol back into the solution as a metabolic by-product. Typical fermentation organisms use the
glycolysis process to divide each monosaccharide into two molecules of G3P and to convert G3P
to pyruvate. This is followed by a two step fermentation reaction to convert pyruvate into CO2
and ethanol. The chosen microorganisms must be appropriate for the feedstock being converted,
as individual microorganisms are limited in the types of monosaccharides they can metabolise
and by the mash environment in which they flourish. For example, glucose and fructose are
commonly fermented by the yeast Saccharomyces cerevisiae at a pH of 4.5 and a temperature
between 27 and 32°C [35], and the seaweed monosaccharides released in alginate hydrolysis can
only be fermented by genetically engineered microorganisms [4][12].
After the monosaccharides have been completely converted to ethanol, the mash is called
beer. As the monosaccharide source is finite and ethanol is toxic to fermenting organisms in
sufficient concentration, fermentation ends when ether the monosaccharide source is depleted or
when ethanol concentration in the mash reaches toxic levels. Final concentration in corn ethanol
production is typically 8-10% ethanol by weight or 10-12% by volume [35], but higher
concentrations have been achieved [36].
19
3.1.6 Ethanol recovery
To be useful as a vehicle fuel, ethanol must be recovered from the beer. Recovery
typically has two stages: distillation to produce a mix of water and 91% ethanol by weight and
molecular sieving to increase the concentration to 99.6% ethanol [35]. If this anhydrous ethanol
is to be used for vehicle fuel, it must be mixed with gasoline to make denatured ethanol that is
legally distinct from ethanol for human consumption. Denatured ethanol is typically 3% gasoline
by volume (2.7% gasoline by mass) [16]. A diagram of the recovery process is shown in Figure
3-2.
Recovery from regeneration cycle
> 90% ethanol vapor
Molecular
sieve system
~45% ethanol vapor
Beer
>99.6% ethanol
Rectifier
Beer
Column
Stripper
Whole stillage
To backset
Figure 3-2: Simplified diagram of ethanol recovery process [35]
3.1.7 Residue processing
After ethanol has been recovered, unfermentable components from the original biomass,
process additives like hydrolysis enzymes, and microorganism biomass generated during the
fermentation process remain as distillation residue. This residual mass of fats, protein, minerals,
and unfermentable saccharides can be processed into a variety of ethanol co-products depending
on the original feedstock composition. In corn ethanol production, whole distillation residue is
commonly dried and sold as an animal feed called distiller’s grains.
20
General Steps of the Dry Grind Corn Ethanol Process
Solar Energy
Capture
Photosynthesis
Produce Starch
Grow Corn Kernels
As the corn plant grows, it captures solar energy though
photosynthesis and produces glucose then amylose and
amylopectin, aka corn starch. The starch is then bound in
unfermentable fiber, protein, and fat within corn kernels.
Feedstock
Supply
Harvest, extraction, storage,
delivery, and cleaning of Corn
Kernels
The corn plant is harvested and the corn kernels are
removed and dried. The dry kernels are stored in grain silos
and are delivered to the ethanol plant as required. Before
extraction, broken kernels, dirt, and other foreign materials
are removed from the kernels by screens and blowers.
Extraction
Grind Corn Kernels into corn
Grains
The kernels are ground into a course flour or grain
containing 0.5-2mm particles to expose the corn starch.
Liquefaction
Convert Starch in corn grains
to soluble Dextrins
The corn grain is mixed with water and the exposed corn
starch is enzymatically decomposed into monosaccharides
through a two stage process. First, the starch is paritially
broken down into to short, water soluble glucose chains
called dextrins with alpha-amylase. This is followed by a
complete breakdown of the dextrins into glucose with betaamylase. The fist process is called liquefaction and it takes
1 hour at 88°C and a pH of 6.5. The second step is called
saccharifaction and it takes 5-6 hours at 60°C and a pH of
4.5.
Hydrolysis
Saccharifaction
Convert Dextrins to Glucose
Fermentation
Convert Glucose to Ethanol
Ethanol
Recovery
Extract fuel grade ethanol
Residue
Processing
Centrifuging and Drying
to produce Distillers Grains
The newly produced glucose is consumed and converted
into ethanol by the yeast S. Cerevisiae. S. Cerevisiae must
be kept between 27-32°C for optimal conversion. The
process takes 46-68 hours and produces a beer containing
10-12% ethanol by volume.
Ethanol in the beer is removed and purified though a
combination of distillation and Molecular Sieving. Distillation
produces at 91% ethanol/water mixture by weight, and
molecular sieving improves the concentration to 99.6%
ethanol.
After ethanol recovery, the residue composed of water,
unfermentable fiber, protein, and fat from the raw corn
kernel, S. Cerevisiae biomass, and processing additives is
commonly dewatered and dried to form a course yellow
animal feed called distiller’s grains.
Figure 3-3: Dry grind corn ethanol process [16][35]
21
3.1.8 Dry grind corn ethanol production
The dry grind process is one of the most common ethanol production processes,
accounting for over 32% of world ethanol production [37]. The seven steps of ethanol production
are shown for the process of dry grind corn ethanol production in Figure 3-3.
3.2 Dealing with feedstock harvest season
Ethanol plants must operate almost year round to maximize the significant capital
investment involved in their construction, but feedstock of acceptable size and fermentable
fraction are typically only available for a few months of the feedstock crop’s natural lifecycle.
Three methods are currently used in the corn and sugarcane ethanol industries to deal with this
discrepancy and maintain an adequate feedstock supply: feedstock storage, harvest extension,
and use of additional feedstock.
3.2.1 Storage
Storage involves drying or otherwise stabilizing ethanol feedstock during its harvest
season and storing the stable feedstock until it is required for ethanol production. In the example
of corn ethanol production, corn kernels are only available for a few months in the fall. The fall
crop is dried and stored in large silos where they remain preserved for a year or more, and dry
kernels are removed from storage and used for ethanol production thought the year as required
3.2.2 Harvest extension
Depending on the crop, it is possible to create an extended harvest season through two
cultivation practices: staggered planting and planting multiple varieties. This is well illustrated
by sugarcane ethanol production which uses both techniques. Sugarcane is broadly classified into
early, mid-late, and late maturing varieties that mature after 12, 14, and 16 months respectively
[38], and a 30:40:40 ratio of the three varieties is typically planted in any given sugarcane
plantation. Each variety is planted in small groups at regular intervals from May until October
[39]. This staggered planting ensures that mature sugarcane is continuously available from April
to December in the following year.
3.2.3 Additional feedstock
If feedstock with acceptable fermentable fraction is not available during part of the year,
and if storage or culturing practices cannot fully compensate, an additional feedstock with ether a
complementary harvest season or better storage characteristics can be used. For example,
22
sugarcane ethanol plants typically shut down for 5 months at the end of December because
harvest extension cannot provide a year round supply of fresh feedstock. As sugarcane and cane
juice are both impractical to store, processing stored corn kernels as an additional feedstock has
been proposed as a method to keep sugarcane ethanol plants operating during this five month
shutdown [40]. Sugarcane saccharide extraction equipment would remain idle, but fermentation
and ethanol recovery equipment could potentially be used for both sugarcane processing and
corn processing.
3.3 Seaweed ethanol production
Both seaweed harvest season and seaweed ethanol yield must be addressed, to understand
seaweed ethanol production, as harvest season can be limited, and yield is significantly
influenced by fluctuations in seaweed composition. For the seaweed Saccharina latissima grown
in BC, storms, low light, and high rainfall in winter and the natural growth cycle discussed in
Section 2.2.3 limits seaweed production to a single crop each year that is optimum for harvest
during a 1-2 month period in summer [24]. Ethanol yield is also an important issue that has
received considerable attention in the literature, but the literature is of limited use for modeling
seaweed ethanol production in general because composition fluctuation is not considered. The
three techniques of storage, harvest extension, and additional feedstock are discussed as they
apply to seaweed to address seaweed harvest season, followed by discussion of seaweed ethanol
yield and proposal of a tool to estimate ethanol yield from any brown seaweed that accounts for
composition variation.
3.3.1 Dealing with seaweed harvest season
Seaweed may suffer the same harvest season limitations of corn and sugarcane, but the
techniques used in corn and sugarcane ethanol could be used to extend harvest season.
Depending on the species, seaweed may only be harvestable for a few months during the year
[19][24], and seaweed begins to decompose within a few days of harvest [5][24]. Feedstock
storage, harvest extension, and/or additional feedstock may be required to provide ethanol plants
with a year round supply of seaweed feedstock. Seaweed can be stored dry or wet, and there may
be opportunity for extended harvest in tropical regions, but the use of additional feedstock is
likely not possible unless combined with the other two techniques.
23
3.3.1.1 Storage
Seaweed is storage stable when dried below 22% moisture, and dry seaweed can be
stored for a year or longer [19]. Drying can be done with a mix of technologies from simply
spreading the seaweed on a flat surface to dry in the sun to sending the seaweed through
multistage steam powered drying systems powered by natural gas or coal. Because seaweeds
typically contain 70-90% water when freshly harvested [5], drying consumes an enormous
quantity of energy per unit of seaweed solids. Bruton et al. [5] noted that mechanical dewatering
could be used to reduce energy use in drying; however, dewatering may result in a significant
loss of fermentable fraction that was not considered. Mannitol and laminarin form a significant
portion of the fermentable fraction in many brown seaweeds, and because both mannitol and
some branched forms of laminarin are water soluble [9], they may be lost during dewatering.
Even rinsing seaweed with fresh water or exposure to rain may reduce mannitol content [6]. Dry
seaweed must be kept in an air tight or low humidity environment as seaweed will rapidly absorb
moisture from the air, rehydrate, and spoil [25].
Fresh seaweed can also be stored in its natural state when combined with a mix of
formaldehyde and methanol called formalin. This mixture can be safely stored for several
months [41]. This eliminates the enormous energy demand of drying, but the toxicity of
formaldehyde and methanol could limit the growth of fermenting organisms during the ethanol
production process. This may be a promising storage method for thermochemical seaweed
conversion processes.
3.3.1.2 Harvest extension
In some tropical regions, seaweed crops can mature in only 35-45 days [14]. Depending
on available ocean nutrients or fertilization it may be possible to produce mature seaweed
throughout the year though staggered planting, similar to the sugarcane planting described in
Section 3.2.2. In higher latitudes, staggered planting is likely not possible because seaweed
growth is limited in winter by low light and poor weather and because fermentable fraction can
be tied to the yearly cycle of day length as described in Section 2.2.3. It may also be possible to
extend seaweed harvest season by planting multiple species or strains of seaweed that mature at
different rates or different times of the year.
24
3.3.1.3 Additional feedstock
Seaweed could be paired with storable feedstocks like corn, wheat, or cellulosic biomass
to achieve year round ethanol production, but seaweed harvest season can be very short, limiting
the use of seaweed in the multi-feedstock arrangement. For example, harvest season is only 1-2
months for Saccharina latissima in BC [24]; therefore, seaweed would produce less than 20% of
total ethanol output. Additional feedstock production may need to be combined with seaweed
feedstock storage or harvest extension if seaweed is to provide a significant percentage of total
ethanol output.
3.3.2 Ethanol yield in the literature
Several studies have shown that ethanol production from seaweed is possible [4] [9][12];
however, ethanol yield estimates in literature are subject to significant uncertainty and are
limited to a small number of seaweed species. Aizawa et al. [17] estimated the ethanol yield from
Japanese Laminaria and from Undaria pinnatifida to be 34 L/tonne and the yield from
Sargassum horneri to be 38 L/tonne. As noted by Roesijadi et al. [7], little background or
reference is given for this estimate. Horn achieved a maximum yield of 0.43 g ethanol per gram
substrate from mix of mannitol and laminarin, and 0.38g/g mannitol alone, giving a conversion
of 0.10 g/g dry seaweed assuming a mannitol content of 25%. Roesijadi et al. reviewed several
studies that estimated a yield from brown and red seaweeds and found values of 0.08 and 0.12
g/g dry seaweed. Roesijadi also calculated a yield of 0.254 g/g dry seaweed or 39L/tonne based
on the work of Reith et al. [8], but comments that Reith’s assumption of 50% conversion of the
seaweed solids to ethanol is "very ambitions and still need research". Recently, Wargacki et al.
[12] achieved an experimental yield of 0.281 g/g dry seaweed, showing that the estimates of
Reith and Aizawa are reasonable.
These conversion estimates do not include composition data for the seaweed samples
examined or details on where and when the samples were taken. As discussed in Section 2.2,
fermentable fraction can range from 25% to 59% of total solids depending on time of harvest. It
is unclear if the samples considered in the above yield estimates were taken while the seaweed
had optimal saccharide content or not; therefore, the above conversion estimates may not
represent ethanol yield from a properly executed seaweed harvest.
25
To deal with the limitations of available ethanol yield values, an alternate method of
ethanol yield calculation is discussed as part of the well-to-wheel seaweed ethanol production
model in Section 4.1.4. Ethanol yield in the context of the model is defined as conversion rate.
3.4 Summary
As discussed in this chapter, seaweed ethanol is produced in a similar manner to
conventional ethanol and it faces similar limitations regarding feedstock supply. Fermentation
based ethanol production commonly requires the seven steps of solar energy capture, biomass
supply, saccharide extraction, hydrolysis, fermentation, recovery, and residue processing, and if
harvest season is limited, the techniques of feedstock storage, harvest extension, and additional
feedstock types can be used to provide year round feedstock supply, as required by large ethanol
plants. Feedstock storage is used to deal with harvest season in corn ethanol production, and the
harvest extending practices of staggered planting and planting multiple crop varieties are used to
deal with harvest season in sugarcane ethanol production. The use of corn as an additional
feedstock is also proposed for sugarcane ethanol production. Dry seaweed storage is promising
for extending harvest season for seaweed in general and harvest extension is promising for
seaweed in tropical areas. Wet seaweed storage is likely problematic for fermentation based
ethanol due to formalin toxicity, but may be helpful in thermochemical seaweed processing
systems. Alternate feedstock is likely not viable unless combined with feedstock storage or
cultivation practices. As ethanol yield values for seaweed are limited to specific species and
subject to uncertainty, an alternate method for calculating ethanol yield was proposed.
The next chapter discusses the well-to-wheel model of seaweed ethanol production that is
the focus of this thesis. The model covers energy inputs, GHG emissions, production potential,
and cost for seaweed ethanol, and it contains the ethanol yield estimation tool discussed in this
chapter.
26
4 Seaweed ethanol production model
This chapter presents a general well-to-tank model for the production of ethanol from
farmed seaweed. The model contains three components: Energy input and emissions, near shore
ethanol yield, and cost analysis, and it produces four performance metrics: Energy Return on
energy Invested (EROI), Carbon Intensity (CI), near shore ethanol yield, and maximum
feedstock cost. EROI for any energy carrier production system is defined as total useful energy
contained in the produced carrier divided by the total energy input required for carrier
production. Similarly, CI for any energy carrier is defined as the total GHG emission during
carrier production divided by the total energy input required to support carrier production. EROI
is used to determine if the process of seaweed ethanol production uses more energy than is
contained in the resulting ethanol, and CI is used to judge climate benefit of replacing gasoline
with seaweed ethanol relative the benefit of replacement by other ethanol sources. Near shore
ethanol yield measures the seaweed ethanol production potential for a given region of coastline if
near shore seaweed farming is used, and maximum feedstock cost gives the maximum cost for
dry seaweed that allows for affordable ethanol production.
The model description is divided into two parts. First, Sections 4.1 to 4.3 describe how the
model is derived. Energy inputs, GHG emissions and co-product credits are discussed in Section
4.1 including a discussion of seaweed-to-ethanol conversion rate in Section 4.1.4. Near shore
ethanol yield is discussed in Section 4.2 and cost analysis is discussed in Section 4.3. Second,
Section 4.4 gives the model itself, covering definition and calculation of the four performance
metrics, then covering calculation of the energy inputs, GHG emissions, and co-product credits.
4.1 Energy inputs, GHG emissions, and co-product credits
As shown in Figure 4-1. Seaweed ethanol production is assumed to require at most five
processes: the production of mature seaweed from young seaweed called sporelings, drying the
seaweed with renewable heat if seaweed storage is required, transporting seaweed feedstock to
the conversion facility, converting seaweed biomass into ethanol, and distributing the ethanol for
final use. These are labeled seaweed production, drying, transport and distribution, and
conversion respectively.
27
Co-product
credits
K’N, K’M
Fertilizer
emissions
G’I,F
Seaweed
production
Sporeling
electricity
E’SE
E’TF
Seaweed
(fresh)
Boat fuel
E’BF
Sporeling
heating fuel
E’SH
Transport
Fugitive ethanol
emissions
G’I,E
Co-product
market
[a]
Co-products
Seaweed
(fresh)
Ethanol
Conversion
Transport
and drying[a]
Ethanol
distribution
Ethanol
Vehicle
fuel tank
Seaweed
(dry)
Process
fuel
Transport fuel Drying system
E’PF
E’TF
electricity
E’DE
Process
electricity
E’PE
E’TF
Figure 4-1: Seaweed ethanol production model. Energy inputs and indirect GHG emissions
are shown with solid arrows, mass flows are shown with dashed arrows, and direct GHG
emissions are omitted for clarity. [a] Depending on the region of production, seaweed may be
delivered fresh for immediate conversion to ethanol or dried and stored at the conversion facility
for later conversion.
The energy inputs, GHG emissions, and co-product credits for each process are divided
into a number of general groups based on energy input type as shown in Figure 4-1. Energy input
includes electricity and various fuels, and it is divided into sporeling electricity, sporeling
heating fuel, boat fuel, drying system electricity, transport fuel, process fuel, and process
electricity. GHG emissions include direct emissions from all energy inputs (omitted from Figure
4-1 for clarity) and indirect emissions from ethanol vapor losses, and they may include indirect
emissions from fertilizer application during seaweed production. Co-product credits may include
both energy and GHG emission credits earned by the conversion facility as explained below. The
treatment of the seven energy inputs is described first followed by emissions and then by coproduct credits.
4.1.1 Energy input in seaweed production
Sporeling electricity, sporeling heating fuel, and boat fuel support the tank based
cultivation of sporelings and the ocean based growth of mature seaweed. Brown seaweed
reproduction is discussed in Section 2.1. Assuming sexual reproduction, seaweed production is
generally facilitated by collecting mature seaweed fronds before spores are released, culturing
28
the spores into sporelings in land based tanks of seawater, and planting the sporelings on ocean
based farm structures. Sporeling electricity is the total electricity input needed for cooling,
lighting, and water circulation during sporeling cultivation, sporeling heating is the total fuel
input (e.g. natural gas, coal) needed to maintain appropriate water tank temperature as the
sporelings mature if heating is required, and boat fuel is the total fuel energy consumed while
collecting seaweed spores, installing mature sporelings on farm structures, applying fertilizer as
the sporelings mature if required, and performing other seaweed cultivation operations if
required. Sporeling electricity and sporeling heating per unit of ethanol produced are calculated
from the total electricity/heat input needed per batch of sporelings, the seaweed yield of mature
seaweed per batch of sporelings, and a seaweed-to-ethanol conversion rate. Boat fuel use per unit
of ethanol produced is calculated using fuel use per unit of seaweed produced and the same
seaweed-to-ethanol conversion rate. Additional details on seaweed production are found in
Section 2.
4.1.2 Energy input in drying
Energy input for seaweed drying is considered cases where feedstock storage is required.
For efficient use of process equipment, ethanol plants require a year round supply of feedstock,
but as discussed in Section 3.3.1, seaweed may not naturally meet this need without feedstock
storage or harvest season extension. Harvest season extension may require additional electricity
or fuel input during seaweed production, and this would be accounted for with sporeling
electricity, sporeling heating fuel, and boat fuel in the preceding section. Due to the very short
shelf life of fresh seaweed, some storage may be needed even when using harvest season
extension. Logistical issues like equipment failure, disease, and storms will likely interrupt the
supply of fresh feedstock, but stored seaweed could be used as backup feedstock supply to
maintain constant ethanol production when fresh feedstock is temporarily unavailable. The case
of pure harvest season extension is shown in Figure 4-1 by the transport pathway. Wet storage is
not considered as the toxicity of formalin would likely inhibit fermentation. As discussed in
Section 3.3.1, dry storage requires moisture content below 22%, and the process of seaweed
drying requires a significant amount of energy.
Because seaweed has a very high water and ash content [5], drying seaweed takes a
greater input of heat energy than the total chemical energy contained in the dry seaweed. If
29
drying heat is produced from fossil fuel combustion, the resulting seaweed ethanol system would
have very poor performance and would likely have an EROI of less than one and a CI higher
than that of the input fossil fuel. In contrast to fossil fuel, renewable heat sources, like solar
thermal and geothermal, are a potentially viable option for dying seaweed because renewable
heat is not included in EROI as an input and because renewable heat sources typically have a
very low CI.
Renewable heat systems often require electricity to operate as they use fluid circulation
pumps, fan motors, and other support systems. This is included in the model as drying system
electricity. The case where electrical input is needed for drying is shown in Figure 4-1 by the
transport and drying pathway. Electricity input for renewable drying systems is characterized by
the ratio of heat output to electricity input called the coefficient of performance (COP). Drying
system electricity is calculated from the required water removal in drying, heat requirement per
unit water removed, and drying system COP. Construction of the heat collection system has
associated indirect energy inputs and GHG emissions, but only electricity input is considered in
the model.
4.1.3 Energy input in transport and distribution
If seaweed drying is not required, fresh seaweed is collected from seaweed farms
distributed over a large area, consolidated for transport, and sent to the conversion facility. If
seaweed drying is required, fresh seaweed is transported to a drying facility, dried, and the
resulting dry seaweed is transported to the conversion facility. Using ether wet or dry seaweed,
the conversion facility produces anhydrous ethanol that is then denatured on site with a small
quantity of gasoline. This denatured ethanol can be transported to specially designed fuel stations
for immediate use, or it can be sent to a blending facility, mixed with additional gasoline, and
distributed as a blended fuel (e.g. E5, E10, E85) [42]. The energy used to transport the gasoline
mixed with denatured ethanol and the gasoline mixed with ethanol blends is not included as an
energy input in the model. Seaweed transport and ethanol distribution requires an array of
vehicles (boats, barges, trains, trucks, etc) determined by geography, locally available
infrastructure, drying heat resource locations (if drying is required), and ethanol plant locations.
Transport fuel energy input is calculated from the total distance traveled, mass flow carried, and
fuel consumption rate for each required vehicle.
30
4.1.4
Energy input in conversion
Process fuel and process electricity are the energy inputs required by the conversion
facility to convert wet or dry seaweed feedstock into ethanol and co-products. Because seaweed
ethanol has only been produced on the experimental scale [4][9][12], data for these process
inputs is not available, and so they must be estimated.
Dry macroalgae
Dry corn grains
Grinding: 1mm particles
Grinding: 0.5-2mm particles
Liquefaction
88°C, pH 6.5, 1 hr
Simultaneous saccharification
and fermentation
25-30°C, pH 7.0, 33 hr
Saccharification
60°C, pH 4.5, 5-6 hr
Fermentation
27-32°C, pH 4.5, 46-68 hr
Ethanol recovery: 4.7% v/v
Ethanol recovery: 10-12% v/v
Residuals processing
Residuals processing
Animal feed
Animal feed (distiller’s grains)
Figure 4-2: Comparison of seaweed conversion, and dry grind corn ethanol conversion.
Ethanol concentration is shown in percent by volume and additional steps added in the seaweed
conversion model are shown with dashed lines.
The conversion experiment conducted by Wargacki et al. [12] is similar to the dry grind
corn ethanol process [35] as shown in Figure 4-2. Based on this similarity, seaweed ethanol
production is assumed to require the same basic energy inputs as the dry grind process: boiler
fuel to provide heat for saccharifaction, fermentation, and distillation and electricity input for
grinding, pumping, and other support operations. Unfermentable seaweed components, like
protein and lipids, can be used to produce a variety of co-products including methane, fertilizer,
and animal feed [7]. Co-product processing in seaweed ethanol production is assumed to require
31
varying quantities of additional fuel and electricity input depending on the type of co-product
produced and quantity of unfermented mass left after ethanol conversion.
Process fuel and process electricity for seaweed ethanol production are simply the sum of
fuel and electricity inputs for both ethanol and co-product production. Energy use in co-product
production is calculated from the energy use per unit of co-product produced, the fermentable
fraction of the seaweed mass processed, and the conversion rate defined below.
Conversion rate is the yield of ethanol per unit of seaweed solids. As discussed in Section
3.3.2, existing estimates for conversion rate are limited to specific seaweed species and do not
provide a mechanism to account for variation in seaweed composition, and as discussed in
Section 2.2.2, total fermentable fraction (i.e. the sum of alginate, laminarin, and mannitol
content) can vary significantly throughout the year, and it can vary with seaweed production
location. Values for conversion rate that do not consider these composition variations may be of
limited value for assessing ethanol production in specific locations or for ethanol production
during specific months of the year. In the model, we propose a conversion rate calculation based
on seaweed composition, ideal ethanol yield from each fermentable component, and conversion
efficiency for each fermentable component to account for variation in seaweed composition.
First, the ethanol yield from each fermentable component is calculated using the ideal ethanol
yield for that component, conversion efficiency for that component, and the mass of that
component present in the seaweed, and then conversion rate is calculated by summing the
ethanol yield from each fermentable component. Ideal ethanol yield is calculated based on the
metabolic path used to convert each component into ethanol as shown in Appendix A and
conversion efficiency is taken from experiments found in the literature.
4.1.5 GHG emissions
GHG emissions include direct emissions for the seven energy inputs described above and
indirect emissions from ethanol vapor loss and fertilizer use. Direct GHG emissions are
calculated for each energy input shown in Figure 4-1 using their corresponding carbon
intensities. Because transport fuel represents the combustion of an array of transport fuels with
potentially different carbon intensities, direct emission for transport is calculated using total
distance traveled, mass flow carried, fuel consumption rate, and fuel carbon intensity for each
vehicle shown in Figure 4-1. Indirect emission for ethanol vapor loss is calculated using the mass
32
of ethanol vapor lost in distribution and the global warming potential (GWP) for ethanol vapor.
The mass lost in delivery is assumed to be small; therefore, the ethanol loss has a negligible
effect on distribution energy input and direct emissions. Indirect emission for fertilizer use is
calculated from the mass of fertilizer applied and an indirect emissions factor. Fertilizer
application is discussed further in Section 2.4.1.
4.1.6 Co-product credits
Co-product credits are negative energy inputs or GHG emissions included in the model to
account for the reduction in energy use or emissions caused by co-product use. The effect of coproducts from conventional ethanol production is typically calculated using the displacement
method [16]. Here, ethanol co-products are assumed to displace a quantity of similar
conventional products. This is assumed to eliminate the production of that quantity of displaced
product, thus reducing energy use and GHG emissions by the amount that would have been
required to produce the displaced products. The displacement method is data intensive. It
requires knowledge of the specific market where the co-products are used to determine what
conventional products are displaced, and it requires knowledge of energy input and GHG
emissions for the production of each product displaced. The energy input reduction and the GHG
emission reduction achieved per unit of co-product produced are called the energy co-product
credit and emissions co-product credit respectively. In the model, credits per unit of co-product
produced must be calculated with additional analysis or taken from the literature. Total coproduct credits are calculated from provided energy and emission co-product credit values and
the total mass of each co-product produced.
4.2 Near shore ethanol yield
Near shore seaweed farming is the dominant form of seaweed production in the current
market (Section 2.3), and it is the most likely seaweed source for ethanol production in the near
term. Installing near shore seaweed farming capacity is a complex issue, and it is beyond the
scope of this work to calculate the true ethanol yield from near shore seaweed farming, but
production potential for a given region is estimated from total available coastline and seaweed
production rate from a representative region.
The process of near shore seaweed farming is explained in Section 2.3.1. Seaweed farming
potential and thus ethanol production potential depends on the total ocean area available for
33
seaweed farming. Because ocean area suitable for near shore seaweed farming generally lies
within a few kilometers of shore, the total area suitable for near shore farming is assumed to be a
function of total available coastline. Ethanol production for near shore farming in a region of
interest or near shore ethanol yield is estimated from total available coastline using the seaweed
production rate per unit of coastline from a representative region, and ethanol conversion rate
explained in section 4.1.4. Seaweed production rate in the representative region is estimated by
dividing total seaweed production from the representative region by the regions total coastline
length, and an average seaweed composition and average conversion rate are assumed for all
seaweed produced and converted.
4.3
Cost analysis
The model addresses the cost of seaweed ethanol production based on an analysis of the
conversion facility. Because seaweed farming cost and seaweed drying cost vary significantly
with the species cultivated, farming method, drying method, and region of production, a
generally applicable cost analysis of seaweed farming and seaweed drying was outside the scope
of this work; therefore, only the cost of the conversion facility is modeled. The cost of
constructing and operating a seaweed conversion plant and the revenue from ethanol and coproduct sales are used to calculate the maximum price that the conversion facility can pay for
dry, delivered feedstock or the maximum feedstock cost. This performance metric gives a
benchmark to determine if a given seaweed farming and drying system can produce and deliver
seaweed at an acceptable cost.
4.4 Model architecture
The model calculates EROI, CI, near shore ethanol yield, and maximum feedstock cost to
characterize the performance of any seaweed ethanol production system. These performance
metrics are calculated using the energy inputs, GHG emissions, and co-product credits shown in
Figure 4-1 and discussed in Sections 4.1 to 4.3 and using the conversion rate discussed in Section
4.1.4 . The four metrics and conversion rate are defined in Sections 4.4.1 to 4.4.5, and the energy
inputs, GHG emissions, and co-product credits required for their calculation are detailed in
Sections 4.4.6 to 4.4.8.
34
4.4.1 EROI
for any energy carrier production system is defined from total carrier energy or
total useful energy output,
, and total energy input required for carrier production,
, as
shown in Eq. (1).
(1)
does not include the primary energy collected that is converted into carrier energy.
Examples of primary energy include biomass chemical energy, petroleum chemical energy, solar
radiation, and wind kinetic energy. In this model, ethanol is the useful carrier produced and
calculation of
includes the co-product credits shown in Figure 4-1.
chemical energy and
is total ethanol
is total co-product credit for energy input.
Energy inputs and co-product credits in the model are calculated per unit of ethanol
higher heating value or as specific quantities. Specific energy input, specific GHG emission,
specific mass flow, and specific co-product credit are noted with prime notation,
, as shown in
Eq. (2).
(2)
Where,
is total quantity, and
is total ethanol chemical energy produced. Specific energy
input, specific GHG emission, specific mass flow, and specific co-product credit quantities are
denoted as
,
,
, and
respectively. Total energy input, total GHG emission, total mass
flow, and total co-product credit are denoted as , ,
, and
respectively.
is calculated using specific quantities with Eq. (3).
(3)
Where
are specific energy inputs for the ethanol system and
credit for energy inputs.
is the specific co-product
35
4.4.2 CI
for any energy carrier system is defined with Eq. (4)
(4)
Where
is total GHGs emitted during carrier production.
For seaweed ethanol,
is measured in grams of carbon dioxide equivalent (gCO2e) per
unit of ethanol produced, and it is calculated from the specific direct emissions, indirect
emissions, and co-product credits shown in Figure 4-1 using Eq. (5).
(5)
Where
are the specific direct emissions associated with direct energy inputs,
indirect emissions, and
are specific
is the total specific co-product credit for emissions.
4.4.3 Conversion rate
Ethanol yield from any mass of fresh brown seaweed,
moisture content and a composition dependent conversion rate,
, can be calculated from its
, using Eq. (6).
(6)
Where
is the mass of fresh seaweed and
is the seaweed’s wet basis moisture content.
is the seaweed conversion rate giving the mass of ethanol produced per mass of seaweed solids
(i.e. seaweed at 0% moisture) processed at the ethanol conversion facility. Conversion rate is
calculated with Eq. (7)
(7)
Where
and
are the conversion efficiency and ideal ethanol yield respectively for
each fermentable seaweed component. Eq. (7) is indexed by the eight primary components of
brown seaweed shown in Table 4-1.
36
Table 4-1: Components of brown seaweed
Component[a]
Composition [%][b]
Index[c]
Alginate
23
1
Laminarin
14
2
Mannitol
12
3
Proteins
12
4
Cellulose
6
5
Fucans
5
6
Lipids
2
7
Ash
24
8
Moisture
88
-
Moisture content is given in wet basis, and the remaining component values are given in
percentage of total solids. [a] Main components of all brown seaweeds [11]. [b] Typical
composition for the Laminaria species [8]. [c] Summation index for Eq. (7), (19), (20), (41), and
(42).
Assuming 90% conversion efficiency for mannitol, laminarin, and alginate, using ideal
ethanol yield from Table A-1 in Appendix A, and using the composition data provided by Reith
et al. in Table 4-1 gives a conversion rate of 0.23 kg per kg of seaweed dry mass which is similar
to the conversion rate estimate of 0.254 kg/kg from Roesijadi et al. [7] referencing Reith et al.
4.4.4 Near shore ethanol yield
Near shore ethanol yield for a given section of coastline,
length for the region of interest,
, is calculated using coastline
, the annual seaweed production in a representative region,
, and seaweed-to-ethanol conversion rate as shown in Eq. (8)
(8)
Where
seaweed, and
is the section of coastline being examined,
is the moisture content of fresh
is the seaweed conversion rate calculated with Eq. (7).
37
4.4.5 Maximum feedstock cost
Maximum feedstock cost,
, is defined as the maximum price the conversion facility
can pay for dry seaweed while still remaining profitable. It is determined using the annual cost of
feedstock,
, calculated with present worth analysis as shown in Eq. (9).
(9)
Where
is the capital cost of the facility in year zero,
facility less the cost of feedstock,
return, and
is the yearly operating cost of the
is annual ethanol and co-product revenue,
is the rate of
is the operational life of the ethanol plant.
is calculated from the annual cost of feedstock and ethanol plant production
capacity,
, using Eq. (10).
(10)
4.4.6 Energy inputs
Specific sporeling electricity input,
, is calculated based on sporeling batch size and
tank power requirements as shown in Eq. (11)
(11)
Where
,
, and
are total electricity input per batch of sporelings for cooling, lighting, and
circulation pumps respectably,
sporelings, and
is the rate of fresh seaweed production per batch of
is the ethanol energy equivalent for fresh seaweed calculated with Eq. (12).
(12)
38
Specific sporeling heating fuel input,
, is calculated with Eq. (13).
(13)
Where,
is the total heating fuel input required per batch of sporelings.
Specific boat fuel input,
, covers sporeling and seaweed transport, support operations,
and boat idling, and it is calculated with Eq. (14).
(14)
Where
is total fuel use per unit of fresh seaweed produced for transporting mature seaweed
fronds and sporelings,
and
total is fuel use per unit of fresh seaweed for other support operations,
is total fuel use per unit of fresh seaweed for vehicle idling during production
operations.
Specific drying system electricity input,
, is calculated from specific water removal,
drying heat required, and system COP using Eq. (15).
(15)
Where
is the drying heat required per unit of water removed from the seaweed,
is the
coefficient of performance for the heating technology (e.g. solar thermal or geothermal) used to
dry the seaweed, and
is the specific mass flow of water removed in drying calculated with
Eq. (16),
(16)
is the moisture content of dry seaweed.
Specific transport fuel input,
, depends on the distance traveled, mass flow, and fuel
use rate for each vehicle in the system examined, and it is calculated using Eq. (17).
39
(17)
Where
is the distance traveled by each vehicle,
vehicle, and
is the specific mass flow carried by each
is the fuel use factor for each vehicle.
Specific process fuel input,
, is the sum of fuel use in ethanol production and fuel use
in co-product processing calculated with Eq. (18).
(18)
Where
is specific fuel input for ethanol production,
product , and
is the fuel input for processing co-
is the specific mass of co-product produced calculated with Eq. (19)
(19)
Where
is the mass fraction of total seaweed solids for component
unfermentable components in the seaweed feedstock,
,
is a subset of
unfermentable seaweed components used to produce co-product , and
is the set of all
containing the
is the total specific co-
product production rate calculated with Eq. (20).
(20)
Eq. (19) and Eq. (20) are indexed by the eight primary components of brown seaweed shown
inTable 4-1.
Specific process electricity input,
, is the sum of electricity use in ethanol production
and electricity use in co-product processing calculated with Eq. (21).
40
(21)
Where
is specific electricity input for ethanol production, and
is the electricity input for
producing co-product i.
4.4.7 GHG emissions
Direct GHG emissions for each energy input,
consumed,
and its respective carbon intensity
, are calculated based on the energy
using Eq. (22)
(22)
Note that
must be defined for every energy source with a unique CI.
Transport fuel GHG emission,
, depends on the CI for the each vehicle used, and it is
calculated with Eq. (23).
(23)
Fugitive ethanol emissions,
, are calculated from the mass of ethanol lost during
ethanol transport as shown in Eq. (24).
(24)
Where
is the mass of ethanol lost in distribution per mass of ethanol produced, and
is the 100 year global warming potential for ethanol.
Indirect fertilizer emissions,
, are calculated from the quantity of fertilizer applied and
a corresponding emission factor as shown in Eq. (25).
(25)
41
Where
is fertilizer applied per unit of fresh seaweed produced and
is indirect GHG
emission per unit of fertilizer applied.
4.4.8 Co-product credits
Specific energy,
, and specific emission,
, co-product credits for a general
collection of co-products are calculated from the specific mass of each co-product produced and
the energy or emission credit achieved by each type co-product produced. They are calculated
with Eq. (26) and Eq. (27).
(26)
(27)
Where
and
are the energy and emissions credits respectively achieved by co-product .
4.5 Summary
In this chapter, a general well-to-wheel model was developed for ethanol production from
seaweed biomass, covering the processes of seaweed production, drying, seaweed transport,
seaweed conversion, and ethanol distribution. A tool was developed to estimate the ethanol yield
from any mass of brown seaweed given its composition, and a tool was developed to estimate the
ethanol production potential of near shore seaweed farming in a given coastal region. Seaweed
drying and storage was included as a possible mechanism to deal with the limited seaweed
harvest season. The model calculates the performance of seaweed ethanol based on the four
metrics EROI, CI, near shore ethanol yield, and maximum feedstock cost.
In the following chapter, the general model is applied to the specific case of seaweed ethanol
production from farmed Saccharina latissima in BC, Canada.
42
5 BC case study
In this chapter, the general seaweed ethanol production model is applied to the specific case
of Saccharina latissima farming in BC. For clarity, the seaweed ethanol production model
described in Chapter 4 is called the general model, and the model discussed here is called the
case study model. BC is an interesting case study for several reasons. It has cold, clean, nutrient
rich waters well suited to seaweed production [24], development of a seaweed industry could
benefit First Nations communities and remote communities in BC, and BC provides a
challenging proving ground for seaweed ethanol production. Seaweed transportation is a
challenge because the main market for ethanol is in southern BC in the greater Vancouver area
while the best areas for seaweed production are in more northern coastal regions, and year round
ethanol production is not possible because of Saccharina latissima’s limited harvest season as
discussed in Section 3.3.
In addition to the four performance metrics in the general model, the case study includes an
additional performance metric coving the specific cost of seaweed drying and delivery, and it
includes a sensitivity study. The case study discussion follows the same basic format as the
seaweed ethanol production model: an overview of simplifications and modeling choices is given
in Section 5.1; energy inputs, GHG emissions and co-product credits are discussed in Section
5.2; near shore ethanol yield is discussed in Section 5.3; cost analysis is discussed in Section 5.4;
Section 5.5 defines the fifth performance metric and gives calculation details for energy inputs,
GHG emissions, co-product credits, and cost; and Section 5.6 outlines the sensitivity study. Input
data for the case study is shown in Appendix B.
5.1 Overview
Seaweed production is modeled after the process currently used by Cross [24] for
Saccharina latissima production in BC. This process requires collection of seaweed spores, land
based spore cultivation to produce young seaweed called sporelings, delivery of the sporelings to
an ocean based farm structure, and ocean based growth into mature seaweed. Collection and
delivery is done with small skiff, and no cultivation is required during the ocean growth phase.
43
Similar to seaweed farming in Southern China [19], fertilizer is not required, as ocean nutrient
levels are sufficient for seaweed production in many areas in BC
Seaweed production
Seaweed transportation
Conversion to ethanol
and co-products
Ethanol distribution
Conversion
facility
Train
loading
site
Seaweed drying
Farm
structure
Drying
facility
d1
d2
d4
dX
Sporeling
culture facility
Sporeling Boat fuel
electricity
E’BF
E’SE
Co-product
market[a]
Drying system
electricity
E’DE
Transport fuel
E’TF
Mass flow: Spore bearing
fronds
Energy input
d3
GHG emission
Blending
facility
K’N K’M
Co-product
credits
E’TF
Process fuel Process
E’PF
electricity
E’PE
Sporeling
Fresh
Dry seaweed
ropes
seaweed (m’Sf)
(m’Sd)
Co-product Credit
Transport
vehicles:
Animal
feed
Skiff
(FSK)
d5
Fuel
station
Fugitive ethanol
emissions
G’I,E
Denatured Ethanol in fuel
ethanol (m’DE) blend (m’E)
Barge
(FBR)
Fuel train
(FTN)
Fuel truck
(FTK)
Figure 5-1: Case study of ethanol production in BC. The boundaries of the five processes
given in the general model (Figure 4-1) are shown with dotted lines and required facilities are
shown with solid lines. Vehicles used for mass transport between each facility are shown with
arrows, and the mass type transported by each vehicle is indicated by an icon above each arrow.
Transportation distances
and
to
are given in Appendix B and illustrated in Figure 5-2
below. Fuel use factors for each vehicle are named in the legend and given in Appendix B.
Direct GHG emissions are omitted for clarity. [a] Transportation of animal feed to the co-product
market is not included as an input as it is included in the calculation of co-product credits.
A schematic of the case study model is shown in Figure 5-1.The model includes a sporeling
culture facility and farm structure that are used for seaweed production, a seaweed drying
facility, an ethanol conversion facility, an ethanol blending facility, and a fuel station. Fresh
seaweed, dry seaweed, and fuel are transported between these facilities by skiff, barge, train, and
truck as indicated in Figure 5-1. Solar thermal drying is used for drying seaweed, and the
electricity consumed by fans and other support equipment at the drying facility is supplied by
44
either a renewable energy source or a diesel generator. Dry seaweed is stored at the conversion
site and taken out of storage as required. Energy inputs and finances for the seaweed conversion
facility are modeled based on the dry grind corn ethanol process and the seaweed conversion
experiments found in literature. The residue remaining after ethanol production is converted into
animal feed as a co-product, and co-product credits for the feed are calculated assuming the feed
it displaces a mix of conventional animal feed and animal mineral supplements.
Transport distances for the case study are taken from three transport scenarios shown in
Figure 5-2. In the minimum transport scenario, seaweed farming, ethanol production, and ethanol
consumption are assumed to occur in a small, local region. In the expected transport scenario,
seaweed production occurs over a wide coastal region and ethanol is distributed a significant
distance inland, but seaweed is dried before long distance delivery. In the wet transport scenario,
the same distances as the expected transport scenario are used, but fresh seaweed is barged
directly to the conversion facility and dried near the conversion facility, greatly increasing the
transported mass. The case study analysis uses the expected transport scenario, and the minimum
and wet scenarios are considered in the sensitivity study.
5.2 Energy inputs, GHG emissions, and co-product credits
The case study model includes six of the seven energy inputs considered in the general
model and only one indirect GHG emission source. The energy input for sporeling heating is
included with sporeling electricity input, as electric heating is used, and the indirect emission
from fertilizer application is not included, as fertilizer is not typically applied in BC. The
treatment of the six energy inputs is described below followed by discussion of GHG emissions
and of co-product credits.
5.2.1 Energy input in seaweed production
Inputs for seaweed production and the assumed growth characteristics are determined
based on the process description in Section 2.4. In this case, a floating farm structure similar to
that shown in Figure 2-4B is used for seaweed production, a sporeling culture facility is used to
prepare young seaweed for the farm structure, and a skiff is used to move materials from the
cultivation facility to the farm, for managing the farm structure, and to collect spore bearing
seaweed fronds. Seaweed biomass reaches a maximum towards the end of July and declines in
45
Farmed Coastline[a]
Prince Rupert
Prince George
Barge routes
Train routes
Prince Rupert
Conversion facilities
Port Hardy
Vancouver
Train loading site
Blending facility
Serviced region[b]
A) Minimum transport scenario
B) Expected transport scenario and
wet transport scenario
Figure 5-2: Transport scenarios. Minimum, expected, and wet transport scenario are
considered in the case study and sensitivity study to explore the effect of transportation distance
on overall system performance and to examine the effect of transporting wet vs. dry seaweed.
Each scenario follows the system schematic shown in Figure 5-1. [a] Regions containing
sporeling culture facilities, farm structures, and drying facilities are shown in black, and the
distances between these three locations are shown in Table B-6 of Appendix B. Farmed coastline
sections in Figure 5-2B follow the distribution of large natural kelp beds found from surveys of
BC’s natural stocks [43]. [b] Barge routes follow the farmed to access drying facilities and farm
sites. [c] The region containing fuel stations serviced by each blending facility is shaded grey. [d]
The wet transport scenario uses the transport distances shown in Figure 5-2B, but wet seaweed is
barged directly to the conversion facility.
the following months [24]. At this point, a portion of the crop is left to develop spores for
producing the next generation of sporelings and the remaining seaweed is harvested manually by
collecting the ropes to which the seaweeds are anchored. Harvest is assumed to occur in July and
August, defining the harvest season.
Total sporeling electricity use is calculated using the average power draw of the sporeling
tank, the time to produce a batch of sporelings, and seaweed production per batch, and total boat
fuel use is calculated from the total distance traveled by the skiff and skiff idling time during the
collection of mature fronds, installation of seedlings, and harvesting of seaweed. Sporeling
electricity use and boat fuel use per unit of ethanol produced are calculating using the conversion
rate for Saccharin latissima collected during the July-August harvest season. As the harvest
46
season occurs during the seaweeds period of maximum biomass content, the composition for
Saccharina latissima in BC during the harvest season is approximated by the composition of
Scottish Saccharina latissima for its period of maximum biomass in September-October as
shown in Figure 2-2.
5.2.2 Energy input in drying
All solar thermal drying systems follow the same basic principle of operation. Solar
radiation is used to heat air to lower the air’s relative humidity, the warm dry air is passed over
the product to be dried, moisture transfers from the product to the warm air, and the now humid
air is rejected to the atmosphere. Heating and circulation of air can be accomplished in many
different ways, and solar thermal drying systems can take a variety of forms [44] from natural
convection based systems driven only by solar energy [45] to complex systems using fans, heat
pumps, and thermal storage that offer increased drying rate at the cost of electricity input [46].
A forced convection system with an electric blower is considered in the case study, and a
heat pump driven system with thermal storage is considered in the sensitivity study. The solar
thermal drying facility is powered by a low emission source of electricity in the case study and
by a diesel generator in the sensitivity study. Drying system electricity input is calculated from
the required water removal during drying, the heat requirement per unit water removed, and the
drying system COP as described in the general model.
5.2.3 Energy input in transport and distribution
Transport fuel is calculated using the transportation and distribution pathway shown in
Figure 5-1 and distances from the expected transportation scenario shown in Figure 5-2B. Fresh
seaweed is transported from the farm structure to a nearby drying facility with a small skiff,
dried, and barged to the conversion facility for storage and conversion to ethanol. Denatured
ethanol (97% by volume [16]) is transported from the conversion facility by barge and train to a
blending facility where it is combined with additional gasoline to produce a 5% by volume
ethanol/gasoline blend (E5). This fuel blend is finally trucked to fuel stations for transfer to
vehicle fuel tanks and final use.
47
Transport fuel energy input is calculated from the total distance traveled, mass carried,
and fuel consumption rate for each required vehicle. As in the general model, the addition mass
from gasoline in denatured and blended ethanol is not included. The energy input needed to
transport co-products from the conversion facility to their point of use is not included in transport
fuel, as the energy input and GHG emission from co-product transport are accounted for in the
data from Bremer et al. [16] used to calculate co-product credits.
5.2.4 Energy input in conversion
Process fuel and electricity for ethanol production are approximated using data from
commercial dry grind corn ethanol plants, and fuel and electricity use in co-product production
are calculated assuming that animal feed is the only co-product. As shown in Figure 4-2, the
seaweed fermentation process used by Wargacki et al. is similar to the standard process of dry
grind corn ethanol production; however, the concentration of ethanol achieved during
fermentation is significantly lower for seaweed ethanol. As lower concentration increases the
energy required for distillation, process fuel for ethanol production is calculated using the fuel
use for dry grind ethanol production and an ethanol production fuel scaling factor. The dry grind
process typically achieves a concentration of 10-12% ethanol by volume [35], but the Wargacki
et al. process only achieves an ethanol concentration of 4.7% by volume [12] which would
double the energy needed in distillation per unit of ethanol distilled relative to dry grind[47]. The
case study assumes a future case where seaweed fermentation processes can achieve the same
ethanol concentration as a typical dry grind process, and the sensitivity study considers
distillation from 4.7% by volume. Electricity input for ethanol conversion is assumed equal to
electricity input for the dry grind process.
Fuel and electricity use in co-product production are calculated assuming animal feed as
the only co-product and assuming the same feed production process used in dry grind corn
ethanol production. The unfermented residue left from seaweed conversion is compared to corn
distiller’s grains as shown in Table 5-1.
48
Table 5-1: Comparison of corn distiller's grains to seaweed distillation residue
Solids mass
fraction
Corn distiller’s grains
with solubles [48]
Ash
5.8% [49]
Seaweed distillation
residue [a]
(non-ash portion)
0%
Seaweed distillation
residue [a]
(whole product)
56%
Protein
25-32%
36%
16%
Fiber
40-44%
32%[b]
14%[b]
Fat
8-10%
11%[c]
4.9% [c]
[a] Unfermentable components of Saccharina latissima from Black [6] September 1947 inlet
sample. [b] Cellulose content for Saccharina latissima from Black [20] September 1946 inlet
sample. [c] Assuming a 2% lipid content in fresh seaweed.
As seaweed residue is similar to corn distiller’s grains and raw seaweed can be used as animal
feed [14], the unfermentable component of seaweed feedstock is assumed to be viable as animal
feed. In the dry grind process, distillation residue is processed to produce a variety of animal feed
products called distiller’s grains. The three main types of distiller’s grains produced are wet
distiller’s grains with solubles (WDGS), modified distiller’s grains with solubles (MDGS), and
dried distiller’s grains with solubles (DDGS) [16]. To produce these products, distillation
residue is first centrifuged, leaving solids rich wet distiller’s grains and water with soluble
nutrients called thin stillage. A portion of the thin stillage is fed back to the fermentation process
and the remainder is passed through an evaporator to supply water for distillation steam. The
concentrated stillage leaving the evaporator is mixed wet distiller’s grains to produce WDGS and
this mixture is dried in a rotary drum drier to produce either MDGS or DDGS [35]. WDGS is
typically 65% moisture, MDGS are dried to 55% moisture, and DDGS are dried to 10%
moisture. It is assumed that seaweed ethanol distillation residue is processed into wet feed,
modified feed, and dry feed using the same process as WDGS, MDGS, and DDGS production
respectively.
The three seaweed feeds are produced in the same ratio as wet/modified/dry distiller’s
grains produced by the collection of US dry grind plants surveyed by Bremer et al. [16], and the
extremes of 100% wet feed and 100% dry feed are considered in the sensitivity study. Process
fuel input for co-product production is calculated from the non-fermentable fraction of seaweed
solids, conversion rate as discussed in the general model, the mass fraction of each type of feed
49
produced, and the natural gas input for drying each type of feed in the dry grind process. As
direct data on electricity use in dry grind feed production was not available and because seaweed
ethanol production produces more feed per unit of ethanol than dry grind ethanol production, the
electricity input for co-product processing is calculated by scaling the electricity input for
distiller’s grain production in the dry grind process by an animal feed production scaling factor
to account for the additional mass of animal feed processed in seaweed conversion.
For calculating conversion rate, seaweed composition is assumed equal to that of Scottish
Saccharina latissima in September-October as described in Section 5.2.1 and shown in Figure
2-2. The ideal ethanol yield for alginate, laminarin, and mannitol were calculated assuming
100% of the input alginate, laminarin, and mannitol was converted to ethanol using the metabolic
processes described by Wargacki et al. [12] for conversion of alginate and Horn [9] for the
conversion of laminarin and mannitol. Additional detail is shown in Appendix A. Equal
conversion efficiency is assumed for all three fermentable components. Wargacki et al. [12]
achieved 80% conversion efficiency for a combination of alginate, laminarin, and mannitol
where 90-94% conversion efficiency is typically achieved for corn ethanol [35]. The case study
model assumes a future case for seaweed ethanol production with 90% conversion efficiency, but
70% to 94% conversion efficiency is considered in the sensitivity study.
5.2.5 GHG emissions
Direct emissions for all inputs are calculated using the six energy inputs shown in Figure
5-1, transport fuel direct emissions are calculated from the total distance traveled, mass flow
carried, fuel consumption rate, and fuel carbon intensity of each required vehicle shown in
Figure 5-1, and indirect emissions from ethanol vapor loss are calculated from the mass of vapor
lost and ethanol vapor GWP. Indirect emissions from fertilizer application are not included as the
seaweed production system discussed in Section 5.2.1 does not require fertilizer.
5.2.6 Co-product credits
Co-product credits are calculated assuming that seaweed animal feed replaces a mix of
animal feed and animal mineral supplements. Because seaweed distillation residue has a
significant ash content, seaweed animal feed is considered to be a mix of pure ash called the ash
portion and a mix of other components called the non-ash portion. As seaweed ash contains
valuable macrominerals and trace elements [14] [15], co-product credits are calculated assuming
50
that the ash portion replaces animal mineral supplements, and as the non-ash portion is
comparable to corn distiller’s grains, the non-ash portion is assumed to replace animal feed. The
product produced at the ethanol plant can be considered an animal feed premixed with mineral
supplements because mineral supplements are often mixed with feed rations before livestock are
fed. Energy and emission co-product credit for the non-ash portion are calculated assuming that
this portion of the seaweed feed will displace the same feed displaced by corn distiller’s grains
and thus achieve similar credits. Credits for the ash portion are assumed to be zero as data for
displacing mineral supplements was not available. Energy and emission co-product credits equal
to those achieved by corn distiller’s grains are considered for the ash portion in the sensitivity
study.
5.3 Near shore ethanol yield
Near shore ethanol yield is estimated for BC and for the total global coastline using China
as a representative region. China is the world’s largest producer of seaweed, accounting for 72%
of global production [7] while possessing only 4% of global coastline. For both BC and the
world coastline, the average fermentable fraction and dry solids content of the seaweed produced
is assumed to be equal to that of the Saccharina latissima sampled by Black [6] for September
1947 as shown in Figure 2-2, and the average conversion rate is calculated as described Section
5.2.4.
In estimating the near shore yield of the entire world coastline, the productivity of China
may be lower than the true seaweed production rate in more tropical areas that can produce
multiple harvests per year [14], which would give an underestimate of global yield. However,
45% of world coastline lies in the Canadian and Russian Arctic where seaweed production
potential is likely lower than that of China despite the subarctic showing some production
potential [50], which may lead to an overestimate of global near shore ethanol yield.
5.4 Cost analysis
Because a true accounting of cost for large scale seaweed ethanol production would require
a full process design outside the scope of this work, annual revenue, capital cost, and operating
cost are approximated using cost data for the dry grind corn ethanol process. Annual revenue is
calculated using the price of raw seaweed animal feed as an approximation for the price of
seaweed animal feed and using the wholesale price of gasoline as an approximation for ethanol
51
price. Based the similarity to the dry grind ethanol process discussed in the general model and
shown in Figure 4-2, the cost of seaweed ethanol production is approximated by scaling the
capital and operating cost of dry grind animal feed processing by the higher feed production rate
of seaweed ethanol, by adding the capital cost of onsite feedstock storage, and by removing the
cost of saccharifaction. The capital cost of animal feed processing equipment is scaled by the
animal feed production scaling factor described in Section 5.2.4.
The energy input cost for both natural gas input and electricity input in animal feed
processing is scaled by the percentage increase in natural gas consumption because data was only
available for combined natural gas and electricity cost. The percentage increase in natural gas
consumption and the percentage increase in electricity consumption due to increased co-product
production were 34% and 37% respectively. Because natural gas use accounts for the majority of
energy input, the error in scaling only by natural gas use was considered acceptable, and a +/50% variation of total energy input cost was considered in the sensitivity study.
The capital cost of feedstock storage is calculated assuming the seaweed ethanol facility
includes enough storage capacity for an entire year of ethanol production. Corn ethanol plants
purchase grain in small batches from grain storage companies and only store enough grain on
site for 8-12 days of operation [35]; however, offsite storage services for seaweed are not
available in BC. The capital cost of seaweed storage is assumed to be similar to that of corn grain
storage. The capital cost of saccharifaction is ignored as the Wargacki et al. process uses
simultaneous saccharifaction and fermentation. Remaining capital and operating costs are taken
directly from the dry grind ethanol process and all capital and operating costs are converted into
2012 Canadian dollars.
5.5 Case study architecture
The case study model calculates the four performance metrics defined in the general model
and an additional performance metric called maximum drying and delivery cost. The five metrics
are calculated using the energy inputs, GHG emissions, and co-product credits, near shore
production scenarios, and the cost scenario discussed in Sections 5.2 to 5.4. EROI, CI, near shore
ethanol yield, and maximum feedstock cost, are defined in Sections 4.4.1 to 4.4.5. Maximum
drying and delivery cost is defined below followed by a four section treatment of the energy
52
inputs, GHG emissions, co-product credits, and cost inputs required to calculate each
performance metric.
5.5.1 Maximum drying and delivery cost
Maximum drying and delivery cost is a simple extension of maximum feedstock cost
defined to highlight the cost of seaweed drying and delivery. Estimates for seaweed production
cost are typical given as the cost of fresh, undelivered seaweed, or fresh cost, and they do not
include the cost of drying seaweed or delivering it to point of use. As the cost of solar thermal
seaweed drying was not available and because calculation of delivery cost was outside the scope
of this work, maximum drying and delivery cost,
, is calculated as a benchmark for combined
drying and delivery systems using Eq. (28).
(28)
Where
is maximum feedstock cost defined in Section 4.4.5 and
is the cost of
producing fresh seaweed.
5.5.2
Energy inputs
Specific sporeling electricity input,
, is calculated with Eq. (29),
(29)
Where
is the average electrical power draw of the sporeling culture tank (electrical heat,
lighting, and pumping),
batch,
is the length of horizontal farm rope of seeded by each sporeling
is the production rate of fresh seaweed per unit of farm rope and
to culture one batch of sporelings, and
calculated with Eq. (12).
is the time required
is the ethanol energy equivalent for fresh seaweed
is a function of seaweed conversion rate,
, which is calculated with
Eq. (7).
Specific boat fuel input,
, is calculated with Eq. (30).
(30)
Where
is the distance from the sporeling culture facility to the farm site shown in Figure 5-1,
is the average fuel use of the planting skiff at cruising speed,
is the average fuel use of
53
the planting skiff while idling,
is the number of return trips made between the support site
and the farm per meter of planted rope for gathering mature fronds and installing seedlings
calculated with Eq. (31),
is higher heating value for boat fuel per unit volume, and
is the total time spend idling calculated with Eq. (32).
(31)
Where
is the number of sporeling batches that can be seeded from one mature frond
collection trip,
structure, and
is the time to required to install a meter of sporeling twine onto the farm
is the time spent installing sporelings per boat trip (the work day).
(32)
Where
is the idling time to required to collect a batch of spore bearing fronds and
is
the idling time required to harvest seaweed from one meter of horizontal growth rope
Specific drying system electricity input,
transport fuel input,
, is calculated with Eq. (15), and specific
, is calculated using Eq. (17) using the mass flow of fresh seaweed, dry
seaweed, and ethanol and using travel distances and fuel use rates from Appendix B. The mass
flow of fresh seaweed,
, and dry seaweed,
are calculated with Eq. (33) and Eq. (34).
(33)
(34)
As in the general model,
and
are fresh seaweed moisture content and dry seaweed
moisture content respectively.
The specific mass flow of pure ethanol within the denatured ethanol,
fuel blend,
is calculated using, and Eq. (35).
, and within the
54
(35)
Specific process fuel input,
, is a function of both distillation fuel input and animal
feed production fuel input as shown in Eq. (36).
(36)
Where
is natural gas use for ethanol production in the dry grind process,
is the ethanol
production fuel scaling factor used to include the effect of low ethanol concentration,
mass fraction of each co-product produced, and
is the
is the natural gas input required for drying
each type of animal feed. i = {WF, MF, DF} for wet feed, modified feed, and dry feed
respectively.
is calculated with Eq. (20).
Specific process electricity input,
, is calculated using the electricity use of the dry
grind process as shown in Eq. (37).
(37)
Where
is the electricity in dry grind ethanol production including typical co-product
processing,
is the fraction of dry grind electricity input accounted to animal feed processing,
and
is the animal feed production scaling factor calculated with Eq. (38).
(38)
Where
is the animal feed production rate for the dry grind process.
5.5.3 GHG emissions
Specific direct emissions for all specific energy inputs are calculated using Eq. (22),
specific transport fuel GHG emissions,
GHG emissions from ethanol vapor,
from fertilizer application,
, are calculated using Eq. (23), and specific indirect
, are calculated with Eq. (24). Indirect GHG emissions
, are not included as no fertilizer is applied.
55
5.5.4 Co-product credits
Specific co-product credits for energy,
, and emissions,
, are calculated with Eq.
(39) and Eq. (40).
(39)
(40)
Where
are the energy and emissions credit for corn distiller’s grains respectively,
and
and
are the energy and emissions credit for animal mineral supplements respectively,
is the specific mass of seaweed residue that is similar to animal feed found with Eq. (41),
and
is the specific mass of seaweed residue that is similar to mineral supplements found with
Eq. (42)
(41)
(42)
Eq. (41) and Eq. (42) are indexed by the eight primary components of brown seaweed shown in
Table 4-1.
5.5.5 Cost inputs
Annual revenue, , is calculated with Eq. (43).
(43)
Where
is the wholesale price of ethanol,
is the price of seaweed animal feed, and
is the ethanol plant production capacity as defined in the general model.
Capital cost,
is calculated using Eq. (44).
(44)
Where
,
,
,
,
,
, and
are the capital costs for feedstock handling,
fermentation, distillation, animal feed production, storage and load out, wastewater treatment,
56
and air compression respectively, and
is the capital cost of the seaweed storage system,
calculated with Eq. (45).
(45)
Where
is the cost per unit of silo capacity, and
Annual operating cost,
is the bulk density of dry seaweed.
, is calculated with Eq. (46)
(46)
Where
,
,
and
are the annual operating costs for raw materials, denaturant,
energy input, and labor/supplies/overhead respectively, and
is the energy input scaling factor
calculated with Eq. (47).
(47)
Where
is natural gas use in distiller’s grain production for the dry grind process.
The conversion between 1999 US dollars and 2012 Canadian dollars is given by equation
Eq. (48).
(48)
Where C is capital or operating cost in 2012 Canadian dollars,
cost in 1999 US dollars,
is the CAD to USD exchange rate, and
is capital or operating
is the 1999 to 2012 US
inflation correction factor.
5.6 Sensitivity study
All inputs to the model were individually varied by +/- 50% to determine their effect on the
three performance metrics EROI, CI and maximum feedstock cost. Any input that produced less
than a +/-5% variation in all three performance metrics was discarded. Individual expected
ranges were determined for all the remaining inputs, and the sensitivity study was run again to
57
measure the effect of each expected range on the three metrics. Energy use data for the dry grind
corn ethanol process was considered sufficiently certain and was not included in the study.
Unless otherwise defined, all cases considered in the sensitivity study are for composition equal
to the inlet location sample of Saccharina latissima in Sept 1947 from Figure 2-2.
To give a more meaningful result, the effect of transportation system layout and the effect of
seaweed composition were examined through the simultaneous variation of multiple inputs. In
the case of transportation system layout, the distances
to
shown Figure 5-1 are varied
together according to the minimum transport scenario and wet transport scenario shown in
Figure 5-2A and Figure 5-2B respectively. In the wet scenario,
expected scenario, but seaweed is not dried and
to
is transported over both
are the same as in
and
.
In the case of seaweed composition, three separate composition sensitivity studies are
considered. In each study, the case study model is run multiple times, the EROI, CI, and
maximum feedstock cost are recorded for each run, the run results are sorted, and the maximum
and minimum values for EROI, CI, and maximum feedstock cost are recorded as the extremes of
the given sensitivity study. In each run, the dry weight mass factions of alginate, laminarin, and
mannitol and fresh seaweed moisture content are varied to match the Saccharina latissima
composition given by Black [6] and described in Section 2.2.1 for a given month and location
(E.g. September 1947, inlet location). In the monthly composition study, the case study model is
run for each month of composition data given for the inlet location for 1947. In the seaweed farm
location study, the model is run for the Sept 1947 open sea composition to show how farm
location can affect the three metrics, and in the seaweed production year study, the model is run
for the Sept 1948 composition show how production year can affect the three metrics. Aside
from transport scenario, monthly composition variation, seaweed farm location, and seaweed
production year, all other sensitive inputs are varied individually by the ranges shown in
Appendix B
5.7 Summary
This chapter discussed the case of ethanol production from Saccharina latissima in BC.
Ethanol system performance was analyzed using case study specific choices and simplifications
applied to the general model from Chapter 4. Seaweed farming was modeled after the production
58
process used by Cross [24] for Saccharina latissima production in BC. Solar thermal drying was
chosen to deal with the need for seaweed drying and storage. Additional feedstock storage was
included to compensate for lack of a seaweed storage network in BC. Energy input and cost for
the ethanol conversion plant were both estimated using data for the dry grind ethanol process and
a comparison between the dry grind process and the seaweed conversion processes used by
Wargacki et al. [51], and three transportation system configurations were defined. Animal feed
was assumed to be a viable co-product due to seaweeds current use as animal feed and the
similarity between seaweed ethanol distillation residue and corn ethanol co-product feed. Animal
feed production energy input and production cost were modeled based on corn ethanol animal
feed production, and co-product credits were calculated assuming that seaweed animal feed
displaces a mix of mineral supplements and conventional animal feed
The following chapter presents results from the case study model, giving EROI, CI, near
shore ethanol production potential, maximum feedstock cost, and maximum drying and delivery
cost for BC, and giving the near shore ethanol production potential of the world coastline. It also
includes a simple calculation of animal feed market size.
59
6 Results
This chapter presents results from the BC case study calculated using data form Appendix B.
The chapter is divided into four main sections: the first three cover EROI, CI, and near shore
ethanol yield, and the fourth section covers maximum feedstock cost and maximum drying and
delivery cost. It also includes a section for the sensitivity study and a section addressing the
market for seaweed animal feed. Because animal feed drying energy, animal feed co-product
credits, and ethanol plant energy carbon intensity resulted in significantly more variation in
EROI, CI, and maximum feedstock compared the other inputs considered in the sensitivity study,
the variation caused by these four inputs is presented with the main results in the first four
sections. The results for EROI, CI, and near shore ethanol yield are presented in Sections 6.1,
6.2, and 6.3 respectively; maximum feedstock cost and maximum drying and delivery cost are
presented in Section 6.4; the sensitivity study is presented in Section 6.5, and animal feed market
size is addressed in Section 6.6.
6.1 EROI
Shown in Figure 6-1, seaweed ethanol has an EROI of 1.78 which is slightly higher than
the EROI of corn ethanol. Varying the feed production mix from 100% dry feed to 100% wet
feed and varying the energy co-product credit from zero to the maximum level calculated by
Bremer et al. [16] gives a minimum EROI of 1.33 and a maximum EROI of over 200. This
extremely high EROI value indicates that the total energy co-product credit is nearly equal to the
total energy input required for ethanol and co-product production.
60
5
249
4.5
Max credits
4
Typical credits
3.5
No credits
EROI
3
2.5
2
Corn ethanol [52]
1.5
Break even
1
0.5
0
100% dry 100% wet Typical feed
animal feed animal feed mix (dry
grind)
Figure 6-1: EROI of seaweed ethanol considering feed production and co-product credits.
EROI varies with the energy input required to dry animal feed and with the energy input coproduct credits assumed for the animal feed. Kim [52]
6.2 CI
Shown in Figure 6-2, seaweed ethanol has a CI of 10.1 gCO2e·MJ-1, lower than the CI of
all conventional ethanol sources shown. Varying the feed production mix and the varying the
emissions co-product credit gives a maximum CI of 32.9 gCO2e·MJ-1 and a minimum CI of 42.4 gCO2e·MJ-1. The maximum CI is still lower than all conventional ethanol sources shown. If
coal is used for process fuel and if coal fired generation is used for process electricity, CI ranges
from 37.8 to 65.3 gCO2e·MJ-1and is lower than the CI of corn ethanol produced with coal for the
full range considered.
61
Gasoline, E10
equivilent [a]
130
Carbon intensity [gCO2·MJ-1]
110
Gasoline, E100
equivilent [b]
90
70
Corn, coal [55]
50
Corn, natural gas [16]
Wheat [53]
Sugar cane [c]
30
10
Max credits
-10
Typical credits
-30
No credits
-50
100% dry
100% wet Typical feed
animal feed animal feed
mix (dry
grind)
High CI, typ credits
Figure 6-2: CI of seaweed ethanol considering feed production and co-product credits.
The first three co-product credit cases consider natural gas as the fuel for both ethanol production
and animal feed drying and the high CI case considers coal as heating fuel and coal based
electricity input. [a],[b] The top comparison lines represent the specific GHG emissions
eliminated by replacing 1L of gasoline with 1L of ethanol in an E10 fuel blend and as E100
respectively. Emission reduction is calculated using the CI of gasoline in BC [53] and the
equivalence ration given by Macedo et al. [54]. = 1.0 for ethanol blends upto E10, = 0.75
for neat ethanol (E100).
. This accounts for both lower energy
content of ethanol and the improvement in combustion efficiency achieved with ethanol fuel
blends. [c] Domestic use of sugarcane ethanol is approximated by replacing transportation
emissions for delivery from Brazil to Canada with domestic delivery emissions for Canadian
corn ethanol [53].
[55] For coal [16] for natural gas, and [53] for wheat
6.3 Near shore ethanol yield
Near shore ethanol yield for BC is approximately 1.3 billion liters per year. Processing
this volume of ethanol would require 7 ethanol plants with a typical production capacity of 200
ML·yr-1 [56]. For comparison, current ethanol consumption in BC is 240 million liters per year,
as required to meet the mandatory 5% ethanol content in all gasoline consumed in BC. Near
shore ethanol yield for the entire global coastline is approximately 18.4 billion liters per year,
and would require 90 typical ethanol plants. As shown in Figure 6-3, global near shore yield is
62
an order of magnitude lower than current global ethanol production and two orders of magnitude
lower than global gasoline production.
World gasoline production: 32.4 EJ/yr [58]
World near shore ethanol
potential: 0.4 EJ/yr
World ethanol production:
2.0 EJ/yr [57]
Figure 6-3: Global near shore ethanol yield compared to current world ethanol
production. Near shore seaweed farming could significantly increase global ethanol production,
but it is likely that open ocean seaweed farming would be required for seaweed ethanol to
replace more than a few percent of global gasoline consumption. [57] For gasoline [58] Ethanol
reference
6.4 Max feedstock cost and maximum drying and delivery cost
Maximum feedstock cost is shown in Figure 6-4 along with fresh cost values from the
literature. Maximum cost is $743 per tonne for the case study and it ranges from $188 per tonne
for zero co-product revenue to $987 per tonne for maximum co-product revenue. Maximum
feedstock cost is lower than the fresh cost of current BC farming methods and lower than the
high end cost of offshore seaweed farming for zero co-product revenue, but it is higher than fresh
cost in all other cases.
Maximum drying and delivery cost is shown in Figure 6-5. It is negative for all cases considering
the current fresh cost of seaweed production in BC, it is negative for the high end fresh cost for
offshore farming combined with zero co-product revenue, and it is positive for all other cases.
Maximum drying and delivery cost ranges from $223 to $965 per tonne of dry seaweed if coproduct revenue is considered and from $46 to $166 dollars per tonne for the positive cases with
zero co-produce revenue.
63
Current BC
cost [25]
Maximum feedstock cost [$·tonne-1]
1400
1200
800
Maximum drying
and delivery cost at
offshore high
production cost
600
Offshore high [a]
1000
400
Offshore low [a]
Near shore high [b]
200
Near shore low [b]
0
Max
Average
Zero
Animal feed revenue
Figure 6-4: Maximum feedstock cost compared to fresh feedstock cost. Price of fresh
seaweed is shown with dashed lines. [a] Bruton et al. [5] citing Chynoweth [13]. [b] Roesijadi et
al. [7]. Production cost is adjusted for inflation and converted to Canadian dollars [59][60]. [25]
For BC
Cost
Maximum drying and delivery cost
[$·tonne-1]
1200
1000
Raw seaweed cost
800
Near shore low
600
Near shore high
400
Offshore low
200
Offshore high
0
-200
-400
Max
Average
Co-product revenue
Zero
Figure 6-5: Maximum drying and delivery cost for dry seaweed. The maximum cost for
solar thermal drying and boat/barge delivery of one unit of dry seaweed feedstock is most
significantly affected by the revenue from animal feed sales and by the cost of fresh seaweed
production. Maximum drying and delivery cost is calculated using Eq. (28) and data from Figure
6-4.
64
Figure 6-6: Sensitivity study results. Transport scenario, seaweed composition, seaweed
farm location, and seaweed production year indicate simultaneous variation in multiple inputs as
explained in Section 5.6. Comparison values for corn ethanol EROI, sugarcane ethanol CI, and
offshore seaweed production cost are taken from Figure 6-1, Figure 6-2, and Figure 6-4
respectively.
6.5 Sensitivity Study
The sensitivity study results are shown in Figure 6-6 along with EROI, CI, and maximum
feedstock cost values for comparison. EROI shows the most significant variation of the three
performance metrics. It is most affected by solar thermal system COP and seaweed composition,
dropping below 1 for both inputs. Farm location, production year, ethanol production fuel scaling
factor, and conversion efficiency each produce an EROI that is less than or equal to that of corn
ethanol, but greater than 1. Transport scaling factor and horizontal rope seaweed production rate
both decrease EROI but not below that of corn ethanol. Sporeling tank electrical power draw
increases EROI to 2.0. CI shows the largest relative variation of the three outputs, but the
absolute value of CI remains below that of all current ethanol sources. Solar thermal system
input CI and ethanol production fuel scaling factor have the largest relative effect, increasing CI
by 21 gCO2e·MJ-1 and 11 gCO2e·MJ-1 respectively. Maximum feedstock cost shows the least
sensitivity of the three metrics, and it remains greater than the cost of offshore seaweed farming
65
in all cases. Variation in seaweed composition gives the lowest and highest maximum feedstock
cost values of $683 and $955 per tonne respectively. The increase in maximum feedstock cost is
caused by a higher unfermentable fraction leading to greater animal feed production and higher
co-product revenue.
6.6 Animal feed market limitation
The seaweed feed produced in the model has an average ash content of 56% and the
seaweed animal feed production rate for the case study was 1.21 kg of dry mass per liter of
ethanol produced. With seaweed ash containing 12% sodium or more by weight [15] and cattle
tolerating feed with a maximum sodium content of 0.1% of total feed dry mass [61], the
maximum amount of seaweed feed that can be included in cattle rations or inclusion rate for is
0.83% of total cattle feed dry mass. Assuming a 0.83% inclusion rate for beef, dairy, and swine
and assuming a US feed market size equal to that considered by Bremer et al. [16], the US feed
market could accept seaweed feed from 890 million liters of ethanol production per year. This
would require 17 million tonnes of fresh Saccharina latissima per year, roughly equal to current
global seaweed production [7], and it would require 4-5 ethanol plants with a typical production
capacity of 200 ML·yr-1 [56]. For comparison, Bremer et al. calculated that US beef, dairy, and
swine have maximum theoretical feed inclusion rates of 45%, 30%, and 27% respectively for
corn ethanol animal feed and that the US feed industry can accept animal feed from 69 billion
liters of corn ethanol production per year.
This chapter gave the results of the case study, presenting EROI, CI, near shore ethanol
yield, maximum feedstock cost, and maximum drying and delivery cost for seaweed ethanol in
BC, and showing the effect of animal feed production energy input, co-product credits, coproduct revenue, and on these five performance metrics. It also included a sensitivity study
showing the sensitivity of EROI, CI, and maximum feedstock cost to transportation, solar
thermal seaweed drying, seaweed composition, seaweed farming, and seaweed to ethanol
conversion.
The next chapter discusses the above results, the implications they have for seaweed ethanol
production in BC, and their implications for seaweed ethanol production in general.
66
7 Discussion
This chapter discusses several exciting possibilities that emerge from the case study results
documented in the previous chapter. The discussion is divided into six sections. The first covers
points of interest specific to the BC case, the next four sections discuss points of interest for
seaweed ethanol production in general, and the final section address the effect of key
assumptions made in the case study model. Seaweed ethanol production in BC is discussed in
Section 7.1 followed by discussions of animal feed production in Section 7.2, transportation
system layout in Section 7.3, near shore farming potential in Section 7.4, seaweed composition in
Section 7.5, and key assumptions in Section 7.6.
7.1 Seaweed ethanol production in BC
Seaweed ethanol production in the BC case is promising, but only if farming cost can be
reduced and if adequate renewable drying systems can be designed. Despite the challenges of
high water content, high ash content, and limited harvest season, the produced ethanol had very
low CI and good EROI. Total near shore ethanol yield is equal to 28% of total BC gasoline use
by volume, and BC’s current ethanol demand could be supplied using 1-2 typically sized ethanol
plants and farming 18% of the BC coastline at the same rate as China. Considering the minimal
effect of the wet seaweed transport scenario shown in the sensitivity study, it may be feasible to
transport farmed seaweed from any location on the coast to a central ethanol plant. Such a plant
could be located in Bella Coola near geothermal resources [62] or in Kitimat near potential waste
heat resources from an aluminum smelter. Both heat sources could replace fossil fuel for process
heat and improve EROI and CI [63][64]. BC farming cost will need to be reduced as maximum
drying and delivery cost was negative for all cases, but current farming systems are for small
scale, artisanal seaweed production, and there is significant room for cost reduction [25]. Solar
thermal seaweed drying may be an issue due to the high rainfall and humidity often experienced
on the BC coast; however, seaweed is harvested during the summer months where rainfall is
generally lower and solar resources are generally higher. Geothermal heat may be an option for
continuously available drying heat as the BC coast has considerable geothermal resources [62].
67
7.2 Benefits from animal feed co-product
Animal feed may be a promising way to start the seaweed ethanol industry and to reduce
energy input and GHG emissions through co-product credits, but feed distribution and feed
market size may be a challenge. In the case of average co-product revenue and high near shore
seaweed production cost, if both capital cost and operating cost are tripled, and seaweed
production cost is doubled, the maximum drying and delivery cost is still $321 per tonne, thus
animal feed revenue may be able to absorb the high cost of developing a first-of-a-kind seaweed
ethanol plant. Because seaweed ethanol production may be possible without any animal feed
sales for the ethanol plant cost considered in the case study, it may be possible to construct a
large number of n-th of a kind seaweed ethanol selling low value co-products like methane or
fertilizer if the seaweed feed market becomes saturated.
In addition to cost reduction, animal feed provided significant co-product credits in the case
study. Co-product credits had the most significant influence of all the factors varied in the
sensitivity study, and they may make it possible for seaweed ethanol to have negative carbon
intensity and an EROI higher than most other biofuels. Additional research must be done to
determine the true value of seaweed animal feed, feed inclusion rate in animal rations, and
seaweed animal feed market size.
As the US feed market may only support 4-5 ethanol plants with the levels of sodium found
in seaweed feed, a single seaweed ethanol plant may need to market and distribute feed to a large
geographical area to find a market large enough to take its total feed output. Removing sodium
from the feed could reduce the minimum distribution area required, and it would allow the feed
market to sustain a larger number of ethanol plants. Methods to remove sodium from seaweed
animal feed and the true value of co-product credits should also be investigated.
7.3 Flexibility in system layout
The flexibility in transportation distance shown in the sensitivity study opens up several
opportunities for optimum system design regarding process heat sources and co-product
production. Ethanol production facilities could be located near sources of geothermal heat [64] or
industrial waste heat which could be used to reduce ethanol production fuel use and animal feed
drying fuel use [63], and seaweed drying facilities could be located near good solar/geothermal
resources or near low CI electricity sources to improve drying system COP and input CI.
68
Production facilities could be located in near sources of natural gas and low carbon electricity to
avoid the use of coal which results in a significant increase in ethanol CI. Ethanol plants could
also be located near livestock farming operations to increase the use of wet or modified animal
feed which can significantly improve CI and EROI. These process improvement strategies
should be considered for the design of seaweed ethanol production systems in the future.
7.4 Near shore farming potential
It is likely that ethanol production from near shore seaweed farming will be a valuable
industry but a minor contributor to global biofuel production, and ocean fertilization may be
required for substantial seaweed production. Near shore ethanol yield could be on the order of
billions of liters per year, but it is two orders of magnitude lower than global gasoline
consumption, therefore, open ocean seaweed farming may be required for seaweed ethanol to
replace more than a few percent of global gasoline use. Fertilization may be required for some
near shore farming regions to reach their full seaweed production potential, as is the case in
Northern China [19], and fertilization may be needed for open ocean farming. Seaweed fertilizer
emissions factors must be determined to determine the effect of fertilization on ethanol CI. As
the case study production estimate is only a rough approximation of production potential, region
specific studies of near shore seaweed production potential should be conducted.
7.5 The effect of seaweed composition
Seaweed composition has a significant influence on ethanol production, but additional work
may be required to accurately predict its effect. Composition variation determines the length of
the harvest season and thus determines if seaweed storage is required, and in the case study,
composition variation resulted in EROI less than one. Accurate prediction of seaweed ethanol
performance may require accurate prediction of seaweed composition as it varies throughout the
year and as it varies between farm sites. A seaweed growth model similar to that given by Broch
et al. [21] combined with a detailed model of local current, nutrient levels, weather, and farm
structure geometry supply such a prediction, and this combination could be used as a screening
tool for locating optimum seaweed farm sites.
69
7.6 The effect of key assumptions
The results of the case study depend on key assumptions in co-product credits, the cost and
feasibility of renewable seaweed drying, and the future case of ethanol concentration and
conversion yield. Because of the significant variation in CI and EROI caused by co-product
credits, a study of credits similar to Bremer et al. [16] may be required to determine an accurate
value of CI and EROI for seaweed ethanol. Ethanol performance is significantly affected by the
performance of the solar thermal drying system. For solar thermal drying as considered in the
case study, seaweed ethanol EROI matched that of corn ethanol for a COP of 14. Using a diesel
generator to power a system with a COP of 14 raises CI from 10.1 gCO2e·MJ-1 to 49.2
gCO2e·MJ-1. A drying system with a COP of 14 or higher and with input energy CI of 140
gCO2e·MJ-1 or lower is required to produce seaweed ethanol with a CI below 30 gCO2e·MJ-1.
The conservative case for ethanol concentration and conversion yield considered in the
sensitivity study did not significantly affect ethanol performance. CI and maximum feedstock
cost were not significantly affected, and EROI was reduced to 1.5 for the worst case. It may be
possible to make low cost seaweed ethanol with a low CI without significant improvement in
ethanol concentration or conversion yield if EROI can be improved. This could be done by using
some amount of renewable heat for ethanol production or co-product production.
As discussed in this chapter, the case study results bring up several interesting points of
discussion. Seaweed could meet the current need for ethanol in BC, but farming cost must be
reduced and renewable drying systems must be proven feasible. Animal feed is a promising coproduct, potentially compensating for high production costs and significantly improving EROI
and CI through co-product credits. System layout is flexible due to low transportation energy
use. Near shore farming production potential is small relative to current ethanol production and
gasoline use. Seaweed composition variation has a significant influence of ethanol production,
and solar thermal drying system COP and input CI have a significant effect on EROI and CI
The following chapter gives a summary of the general seaweed ethanol model, the case
study, and thesis objectives, it gives a review of the most important results and discussion points,
and it presents the conclusions of the thesis and recommendations for future work.
70
8 Conclusion
In this thesis, a general well-to-wheel model of seaweed ethanol was developed and applied
to the case of ethanol production from Saccharina latissima farmed in BC, Canada. The
objective was to contribute to a full lifecycle analysis of seaweed ethanol with a well-to-wheel
model and to examine the well-to-wheel performance of seaweed ethanol through the BC case.
To meet these objectives, the general model included a seaweed ethanol yield estimation tool to
account for seaweed composition, and the case study included a model of large scale seaweed
ethanol production based on the dry grind ethanol process. The case study also included revenue,
energy input credits, and GHG emission credits from animal feed as a co-product, and it included
a sensitivity study on input data.
Despite the challenges of high water content, high ash content, and limited harvest season,
seaweed ethanol is a promising biofuel with low CI, good EROI, and promising finances for the
BC case study. Ethanol in the scenario considered had a CI of 10.1 gCO2e·MJ-1 and EROI of
1.78. Considering a natural gas powered production facility, a range of co-product credits, and
various levels of animal feed drying, CI ranged from -42 to 33 gCO2e·MJ-1, and EROI ranged
from over 200 to 1.33. Considering a coal powered ethanol production facility with these same
ranges, CI varied from 37.8 to 65.3 gCO2e·MJ-1. The ethanol yield from near shore seaweed
farming was estimated at 1.3 billion liters per year for BC and at 18.4 billion liters per year for
total global coastline. This would require 7 and 90 typically sized ethanol plants respectively,
and in the BC case, it is equal to 28% of provincial gasoline demand by volume. Maximum
feedstock cost was $188 per tonne of dry seaweed without co-product revenue, and it ranged
from $743 per tonne to $987 per tonne with co-product revenue Maximum drying and delivery
cost was negative for current BC seaweed farming costs and for the case of high offshore
farming cost with no co-product revenue. It ranged from $46-166 per tonne of dry seaweed in the
other cases without co-product revenue, and it ranged from $223-965 per tonne with co-product
revenue. Seaweed animal feed has sodium content on the order of 12% of total dry mass which
limits its inclusion rate in animal feed to the order of 0.8% of total feed dry mass. At this
71
inclusion rate, the entire US cattle and swine feed markets could only accommodate the annual
feed production from 4-5 typically sized ethanol plants.
The case study and sensitivity study revealed several interesting points of discussion relating to
production in BC, animal feed production, seaweed transportation, seaweed farming, seaweed
composition, and seaweed drying.

Seaweed ethanol production is promising in BC, but seaweed farming costs must be
reduced and solar thermal or geothermal seaweed drying must be proven feasible.

Animal feed production significantly improves the finances of seaweed ethanol and may
help start the seaweed ethanol industry by absorbing the cost of a first-of-a-kind seaweed
ethanol plant. Maximum drying and delivery cost would still be significantly positive if
seaweed ethanol conversion facilities were triple the cost of dry grind conversion and
near shore farming cost double the value given in literature.

Energy and emissions in transportation are relatively small, allowing long transportation
distances and flexibility in locating ethanol plants, drying sites, and farms.

Near shore seaweed farming appears to have significant ethanol production potential, but
offshore seaweed farming may be required for seaweed ethanol to significantly impact
global fossil fuel consumption.

Seaweed composition varies significantly depending on time of year, environmental
conditions, and seaweed’s natural growing cycles, and it has a significant influence on
EROI

Seaweed drying is necessary to support ethanol production in regions like BC and
northern China that have a limited seaweed harvest season, and drying system COP and
input CI have a significant effect on EROI and CI.
Seaweed ethanol shows promise as an outstanding, low emission biofuel that may be
affordable to produce even in regions that require seaweed drying and storage, and that animal
feed revenue may compensate for the additional cost of developing a first-of-a-kind seaweed
ethanol plant; however, this analysis is preliminary in nature and significant additional analysis is
required to validate these conclusions.
72
8.1 Recommendations
To enhance the model and to confirm the conclusions of the case study, the following
improvements are recommended.

Determine the true revenue from seaweed animal feed and seaweed animal mineral
supplements, and determine maximum inclusion rates and seaweed feed market size.

Investigate the removal of sodium from seaweed ethanol co-products to increase
inclusion rates, feed value, and feed market size.

Conduct a co-product credit study similar to Bremer et al. [16] for seaweed animal feed,
seaweed mineral compliments, and seaweed fertilizer to determine accurate credit values
and thus accurate CI and EROI values for seaweed ethanol.

Create a more accurate model of the seaweed conversion facility for cost and energy use
that more accurately accounts for process differences and considers the effect of seaweed
salt content on conventional ethanol processing equipment, and create a more accurate
model of bulk seaweed storage that considers the effect of salt content, seaweeds
propensity to rehydrate in the presence of humid air, and differences in material handling
between corn grains and bulk seaweed.

Examine the COP, input CI, and cost for solar thermal and geothermal seaweed drying in
regions that require seaweed storage, considering local weather, solar or geothermal
resources, cost of labor, and existing infrastructure.

Develop a farm site specific seaweed production model to calculate seaweed composition
and analyze farm performance based on a growth model like that of Broch et al. [21], and
conduct region specific studies of seaweed farming potential and ethanol production
potential.

Determine GHG emission factors for ocean application of fertilizer as they currently
unknown and fertilizer application may be required in many seaweed production regions.

Examine solar and geothermal drying for animal feed production and examine
geothermal heat for the ethanol conversion plant to improve EROI and CI in the BC case
73
9 References
[1]
US EPA, "Global Emissions," [Online]. Available:
http://epa.gov/climatechange/ghgemissions/global.html. [Accessed Nov 2012].
[2]
D. Graham-Rowe, "Agriculture: Beyond food versus fuel," Nature, vol. 474, no. 7352, pp.
S6-S8, 2011.
[3]
L. A. Martinelli and S. Filoso, "Expansion of sugarcane ethanol production in Brazil:
environmental and social challenges," Ecological Applications, vol. 18, pp. 885-898, 2008.
[4]
H. Takeda, F. Yoneyama, S. Kawai, W. Hashimoto and K. Murata, "Bioethanol production
from marine biomass alginate by metabolically engineered bacteria," Energy &
Environmental Science, vol. 4, no. 7, p. 2575, 2011.
[5]
T. Bruton, H. Lyons, Y. Lerat, M. Stanley and M. B. Rasmussen, "A review of the
potential of marine algae as a source of biofuel in Ireland," Sustainable Energy Ireland,
Dublin, 2009.
[6]
W. Black, "The seasonal variation in weight and chemical composition of the common
British Laminariaceae," Journal of the Marine Biological Association of the United
Kingdom, vol. 29, no. 1, pp. 45-72, 1950.
[7]
G. Roesijadi, S. B. Jones, L. J. Snowden-Swan and Y. Zhu, "Macroalgae as a Biomass
Feedstock: A Preliminary Analysis," Pacific Northwest National Laboratory under contract
DE-AC05-76RL01830 for USDE, 2010.
[8]
J. H. Reith, E. P. Deurwaarder, K. Hemmes, A. Curvers, P. Kamermans, W. Brandenburg
and G. Zeeman, "Bio-offshore: grootschalige teelt van zeewieren in combinatie met
offshore windparken in de Noordzee," Energy research Centre of the Netherlands, 2005.
[9]
S. Horn, "Bioenergy from brown seaweeds," Norwegian University of Science and
Technology, Department of Biotechnology, Trondheim, 2000.
[10] K. J. Hennenberg, U. Fritsche, R. Herrera, A. Eggert, M. Renato, S. Hunt and B. Bunnag,
"Aquatic Biomass: Sustainable Bioenergy from Algae," Institute for Applied Ecology,
2009.
[11] E. Percival, "The polysaccharides of green, red and brown seaweeds: Their basic structure,
biosynthesis and function," British Phycological Journal , vol. 14, no. 2, pp. 103-117,
1979.
[12] A. J. Wargacki, E. Leonard, M. N. Win, D. D. Regitsky, C. N. S. Santos, P. B. Kim, S. R.
Cooper, R. M. Raisner, A. Herman, A. B. Sivitz, A. Lakshmanaswamy, Y. Kashiyama, D.
Baker and Y. Yoshikuni, "An Engineered Microbial Platform for Direct Biofuel
Production from Brown Macroalgae," Science, vol. 335, no. 6066, pp. 308-313, 2012.
74
[13] D. Chynoweth, "Review of Biomethane from Marine Biomass," Department of
Agricultural and Biological Engineering, University of Florida, Gainsville, 2002.
[14] D. J. McHugh, "FAO Fisheries Technical Paper 441: A guide to the seaweed industry,"
Food and Agriculture Organization of the United Nations, Rome, 2003.
[15] P. Ruperez, "Mineral content of edible marine seaweeds," Food Chemistry, vol. 79, no. 1,
pp. 23-26, 2002.
[16] V. Bremer, A.J.Liska, T. Klopfenstein, G. E. Erickson, H.S.Yang, D. Walters and K.
Cassman, "Emissions savings in the corn-ethanol lifecycle from feeding co-products to
lifestock," Journal of Environmental Quality, no. 39, pp. 472-482, 2010.
[17] M. Aizawa, K. Asaoka, M. Atsumi and T. Sakou, "Seaweed bioethanol production in
Japan – The Ocean Sunrise Project," Oceans, Vancouver, 2007.
[18] A. L. S. Peter and M. Pietrak, "Life Cycle Assessment of Macro Algae as a Bio-Fuel
Feedstock Source," AIChE Spring Meeting, San Antonio, 2010.
[19] FAO, "Culture of Kelp (Laminaria japonica) in China," Training Manual 89/5
(RAS/86/024), 1989. [Online]. Available:
http://www.fao.org/docrep/field/003/AB724E/AB724E00.htm#TOC.
[20] W. Black, "The seasonal variation in the cellulose content of the common Scottish
Laminariaceae and Fucaceae," Journal of the Marine Biological Association of the United
Kingdom, vol. 29, no. 2, pp. 379-387, 1950.
[21] O. Broch and D. Slagstad, "Modelling seasonal growth and composition of the kelp
Saccharina latissima," Journal of Applied Phycology, vol. 24, no. 4, pp. 759-776, 2012.
[22] M. Denny and B. Cowen, "Flow and flexibility. II. The roles of size and shape in
determining wave forces on the bull kelp Nereocystis luetkeana," Journal of experimental
biology, vol. 200, no. 24, p. 3165, 1997.
[23] K. Luning, "Environmental and internal control of seasonal growth in seaweeds,"
Hydrobiologia, vol. 260, no. 1, pp. 1-14, 1993.
[24] S. Cross, Personal communication, 2011-2012.
[25] L. Druehl, Personal communication, 2011-2012.
[26] "Acadian Seaplants," [Online]. Available: http://www.acadianseaplants.com/. [Accessed
Nov 2012].
[27] S. Phillips, A. Aden, J. Jechura, D. Dayton and T. Eggeman, "Thermochemical Ethanol via
Indirect Gasification and Mixed Alcohol Synthesis of Lignocellulosic Biomass - Technical
Report NREL/TP-510-41168," National Renewable Energy Laboratory, Golden, Colorado,
2007.
75
[28] D. J. Wilhelm, D. R. Simbeck, A. D. Karp and R. L. Dickenson, "Syngas production for
gas-to-liquids applications: technologies, issues and outlook," Fuel Processing
Technology, vol. 71, no. 1-3, pp. 139-148, 2001.
[29] K. Liu, H. K. Atiyeh, R. S. Tanner, M. R. Wilkins and R. L. Huhnke, "Fermentative
production of ethanol from syngas using novel moderately alkaliphilic strains of
Alkalibaculum bacchi," Bioresource Technology, vol. 102, pp. 336-341, 2012.
[30] J. Fortman, S. Chhabra, A. Mukhopadhyay, H. Chou, T. S. Lee, E. Steen and J. D.
Keasling, "Biofuel alternatives to ethanol: pumping the microbial well," Trends in
Biotechnology, vol. 26, no. 7, pp. 375-381, 2008.
[31] Bioweb, "Ethanol from Cellulose Resources," [Online]. Available:
http://bioweb.sungrant.org/Technical/Biofuels/Technologies/Ethanol+Production/Ethanol+
from+Cellulose+Resources/Default.htm. [Accessed Nov 2012].
[32] Bioweb, "Ethanol - wet grind process," [Online]. Available:
http://bioweb.sungrant.org/Technical/Biofuels/Technologies/Ethanol+Production/Ethanol+
Wet+Grind+Processes/Default.htm. [Accessed Nov 2012].
[33] Z.-Y. Sun, Y.-Q. Tang, T. Iwanaga, T. Sho and K. Kida, "Production of fuel ethanol from
bamboo by concentrated sulfuric acid hydrolysis followed by continuous ethanol
fermentation," Bioresource Technology, vol. 102, no. 23, pp. 10929-10935, 2011.
[34] M. Sasaki, B. Kabyemela, R. Malaluan, S. Hirose, N. Takeda, T. Adschiri and K. Arai,
"Cellulose hydrolysis in subcritical and supercritical water," The Journal of Supercritical
Fluids, vol. 13, no. 1-3, pp. 261-268, 1998.
[35] BioWeb, "Ethanol - dry grind process," [Online]. Available:
http://bioweb.sungrant.org/At-aGlance/Biofuels/Technologies/Ethanol+Production/Ethanol+Dry+Grind+Process/Default.
htm. [Accessed 18 Nov 2011].
[36] K. Thomas and W. Ingledew, "Production of 21%(v/v) ethanol by fermentation of very
high gravity (VHG) wheat mashes," Journal of Industrial Microbiology & Biotechnology,
vol. 10, no. 1, pp. 61-68, 1992.
[37] U.S. Department of Energy Office of Biomass Programs, "Current State of the U.S.
Ethanol Industry," [Online]. Available:
http://www1.eere.energy.gov/biomass/pdfs/current_state_of_the_us_ethanol_industry.pdf.
[Accessed Aug 2012].
[38] Netafim, "Agronomic Practices – Improved Varieties," Netafim Agriculture Department,
[Online]. Available:
http://www.sugarcanecrops.com/agronomic_practices/improved_varieties/. [Accessed Aug
2012].
76
[39] Netafim, "Agronomic Practices – Planting time," Netafim Agriculture Department,
[Online]. Available: http://www.sugarcanecrops.com/agronomic_practices/planting_time/.
[Accessed Aug 2012].
[40] M. Cordonnier, "Brazilian Mill Can Utilize Sugarcane or corn to Produce Ethanol,"
Commodities street journal, [Online]. Available:
http://commoditiesstreetjournal.com/blog/2012/03/16/brazilian-mill-can-utilize-sugarcaneor-corn-to-produce-ethanol/. [Accessed Mar 2012].
[41] D. J. McHugh, " Chapter 2 - Production and Utilization of Products from Commercial
Seaweeds," FAO Fisheries Technical Paper 288, 1987. [Online]. Available:
http://www.fao.org/docrep/X5822E/x5822e04.htm.
[42] Worldwatch Institute, Biofuels for transport, global potential and implications for
sustainable energy and agriculture, London: Earthscan, 2006.
[43] BC Ministry of Agriculture, "Historical Kelp Inventory," [Online]. Available:
http://www.agf.gov.bc.ca/fisheries/commercial/Historical_Kelp_Inventory.htm#REPORT
S. [Accessed Nov 2012].
[44] A. Fudholi, K. Sopian, M. Ruslan, M. Alghoul and M. Sulaiman, "Review of solar dryers
for agricultural and marine products," Renewable and Sustainable Energy Reviews, vol.
14, no. 1, pp. 1-30, 2010.
[45] A. Ayensu, "Dehydration of food crops using a solar dryer with convective heat flow,"
Solar Energy, vol. 59, no. 4, pp. 121-126, 1997.
[46] Y. Xie, L. Song and C. Liu, "Analysis of a Solar Assisted Heat Pump Dryer with a Storage
Tank," in ASME Solar Energy Division International Solar ENergy Conference, Denver,
Colorado, 2006.
[47] R. Katzen, P. Madson and G. M. Jr., "Ethanol distillation: the fundamentals," in The
Alcohol Textbook: A reference for the beverage, fuel and industrial alcohol industries,
1999.
[48] K. Tjardes and C. Wright, "Feeding Corn Distiller’s Co-Products to Beef Cattle," 2002.
[Online]. Available:
http://pubstorage.sdstate.edu/AgBio_Publications/articles/ExEx2036.pdf.
[49] M. J. Spiehs, M. H. Whitney and G. C. Shurson, "Nutrient database for distiller’s dried
grains with solubles produced from new ethanol plants in Minnesota and South Dakota,"
Journal of animal science, vol. 80, no. 10, pp. 2639-2645, 2002.
[50] G. Sharp, A. L. M. Allard, R. Semple and G. Rochefort, "The potential for seaweed
resource development in subarctic Canada; Nunavik, Ungava Bay," Journal of Applied
Phycology, vol. 20, no. 5, pp. 491-498, 2008.
77
[51] A. J. Wargacki, E. Leonard, M. N. Win, D. D. Regitsky, C. N. S. Santos, P. B. Kim, S. R.
Cooper, R. M. Raisner, A. Herman, A. B. Sivitz, A. Lakshmanaswamy, Y. Kashiyama, D.
Baker and Y. Yoshikuni, "Supporting Online Material for An Engineered Microbial
Platform for Direct Biofuel Production from Brown Macroalgae," Jan 2012. [Online].
Available: www.sciencemag.org/cgi/content/full/335/6066/308/DC1.
[52] S. Kim and B. Dale, "Life cycle assessment of fuel ethanol derived from corn grain via dry
milling," Bioresource technology, vol. 99, no. 12, pp. 5250-5260, 2008.
[53] "GHGenius Version 4.01," 2012. [Online]. Available: http://www.ghgenius.ca/.
[54] I. C. Macedo, J. E. A. Seabra and J. E. A. R. Silva, "Green house gases emissions in the
production and use of ethanol from sugarcane in Brazil: The 2005/2006 averages and a
prediction for 2020," Biomass and Bioenergy, vol. 32, no. 7, pp. 25-40, 2008.
[55] Average British Columbia Fuel Carbon Intensity Information Bulletin RLCF-002,
Victoria: BC Ministry of Energy and Mines, 2012.
[56] "Biorefinery Locations," Renewable Fuels Association, [Online]. Available:
http://www.ethanolrfa.org/bio-refinery-locations/. [Accessed Oct 2012].
[57] "Petrol Consumption per day," Hydrogen Ambassadors, [Online]. Available:
http://www.hydrogenambassadors.com/background/petrol-consumption-per-day.php.
[Accessed Oct 2012].
[58] J. Urbanchuk, "Current State of the U.S. Ethanol Industry," U.S. Department of Energy
Office of Biomass programs, Washington, DC, 2012.
[59] "Inflation Calculator," [Online]. Available:
http://www.dollartimes.com/calculators/inflation.htm. [Accessed October 2012].
[60] "Bank of Canada USD-CAD Noon Rate," [Online]. Available:
http://www.bankofcanada.ca/. [Accessed August 2012].
[61] C. Hale and K. Olson, "Mineral Supplements for Beef Cattle," University of Missouri,
Department of Animal Sciences, [Online]. Available:
http://extension.missouri.edu/p/G2081. [Accessed Oct 2012].
[62] BC hydro, "Resource Options Report," 2010.
[63] BlueFlint Ethanol, "Process Description," [Online]. Available:
http://www.blueflintethanol.com/index.cfm?show=10&mid=29. [Accessed Nov 2012].
[64] A. Chiasson, "Geothermal energy utilization in ethanol production," Geo-Heat Center,
2007.
[65] B. Alberts, D. Bray, K. Hopkin, A. Johnson, J. Lewis, M. Raff, K. Roberts and P. Walter,
Essential cell biology, New York: Garland Science, 2012.
78
[66] S. M. Read, G. Currie and A. Bacic, "Analysis of the structural heterogeneity of laminarin
by electrospray-ionisation-mass spectrometry," Carbohydrate research, vol. 281, no. 2,
pp. 187-201, 1996.
[67] Food and Agriculture Organization of the United Nations, "Compendium of Food Additive
Specifications. Addendum 5," 1997. [Online]. Available:
http://www.fao.org/docrep/W6355E/w6355e04.htm.
[68] "Mako Pro 17 Skiff Test Results," BoatTEST.com, 2012. [Online]. Available:
http://www.boattest.com/boats/boat_video.aspx?id=2660#bt-Overviews.
[69] S. Hallsson, "Drying of seaweeds by geothermal heat in Iceland," Geothermics, vol. 21,
no. 5-6, pp. 717-731, 1992.
[70] F. Mei, "Mass and energy balance for a corn-to-ethanol plant," Washington University
Department of Chemical Engineering, Saint Louis, Missouri, 2006.
[71] A. McAloon, F. Taylor, W. Yee, K. Ibsen and R. Wooley, "Determining the cost of
producing ethanol from corn starch and lignocellulosic feedstocks," National Renewable
Energy Laboratory Report, 2000.
[72] "IPCC Fourth Assessment Report: Climate Change 2007: Working Group I: The Physical
Science Basis," [Online]. Available:
http://www.ipcc.ch/publications_and_data/ar4/wg1/en/ch2s2-10.html. [Accessed Oct
2012].
[73] 0. Gulbrandsen, "FAO Working Papers - BOBP/WP/27: Reducing the Fuel Costs of Small
Fishing Boats," 1986. [Online]. Available:
http://www.fao.org/docrep/007/ad967e/ad967e00.HTM.
[74] "National Inventory Report 1990–2008—Part II," Environment Canada, 2008.
[75] "Unit conversions, emissions factors, and other reference data," US EPA, 2004.
[76] "Electricity Intensity Tables," Environment Canada, 2010. [Online]. Available:
http://www.ec.gc.ca/ges-ghg/default.asp?lang=En&n=EAF0E96A-1#section11.
[77] "The State of World Fisheries and Aquaculture," FAO Fisheries and Aquaculture
Department, Rome, 2012.
[78] "CIA World Factbook," [Online]. Available: https://www.cia.gov/library/publications/theworld-factbook/fields/2060.html. [Accessed Oct 2012].
[79] "The National Atlas of Canada - Facts about Canada - Coastline," Natural Resources
Canada, [Online]. Available:
http://nides.bc.ca/Assignments/France/Paper11/Coastline.htm. [Accessed Nov 2012].
79
[80] "Average Wholesale (Rack) Prices for Regular Gasoline," Natural Resources Canada,
2012. [Online]. Available:
http://www2.nrcan.gc.ca/eneene/sources/pripri/wholesale_bycity_e.cfm.
[81] "Qingdao CoDo International Limited, Seaweed Powder," [Online]. Available:
www.tootoo.com/s-ps/seaweed-powder-kelp-powder-laminaria-powder-algae-powderfeed-grade--p-2096927.html. [Accessed Oct 2012].
[82] "Böd Ayre Products, Animal feed seaweed meal," [Online]. Available:
http://www.seaweedproducts.co.uk/p/48/animal-feed-seaweed-meal. [Accessed Oct 2012].
[83] "MSDS: ASL Kelp Meal or Flour," 2004. [Online]. Available:
http://files.tlhort.com/msds_labels/10486-acadian_kelp_meal_707.pdf.
[84] "Steel tanks and corrugated metal bins," [Online]. Available:
www.michigan.gov/documents/Vol1-27GrainBinsandTanks_120836_7.pdf. [Accessed Oct
2012].
[85] J. Dexter and P. Fu, "Metabolic engineering of cyanobacteria for ethanol production,"
Energy & Environmental Science, vol. 2, no. 8, p. 857, 2009.
80
Appendix A - Ideal ethanol yield
The ideal yield is calculated from net result of the metabolic process used to convert each
fermentable component into ethanol assuming that 100% of fermentable component is converted.
The conversion process and the molar ideal ethanol yield for mannitol, laminarin, and alginate
are described below.
Mannitol
Mannitol is a simple sugar alcohol (C6H14O6). In ethanol production, mannitol is first
converted to fructose-6-phosphate then converted to pyruvate via glycolysis or the EntnerDoudorof pathway [9]. Pyruvate is then converted to ethanol via fermentation. Unlike the
fermentation of glucose, mannitol fermentation does not result in a redox balance. Oxygen and
an active electron transport chain, H2 production, or transhydrogenase enzymes are required to
effect a balance which limits the number of microorganisms that can metabolize mannitol
(Horn). Each molecule of mannitol yields 2 molecules of ethanol and 2 molecules of CO2.
Laminarin
Laminarin is a polymer of glucose (C6H12O6) and a small quantity of mannitol. It is
largely polymers of glucose that terminate in a single mannitol molecule, but it also includes
some polymers of pure glucose. Both have varying degrees of branching and varying chain
lengths. In ethanol production, laminarin is enzymatically decomposed into free glucose and
mannitol molecules. The glucose is converted first into pyruvate via glycolysis and then into
ethanol through fermentation [65], and the mannitol is converted as described above. Each
glucose and each mannitol molecule yield 2 ethanol molecules and 2 CO2 molecules.
Read et al. [66] found the composition of laminarin from the brown seaweed Laminaria
digitata to be 73% chains of 20-30 glucose units that terminated in a mannitol molecule and 27%
chains of 20-28 glucose units without mannitol. Based on the composition computed by Read et
al., the laminarin sample was 3% mannitol and 97% glucose by weight giving an ideal ethanol
yield of 0.5679 gEtOH·gLaminarin-1. Because data on the exact composition of laminarin from
other species of brown seaweed was unavailable, ideal yield is approximated assuming that
81
laminarin contains only glucose. Applying this assumption to conversion of the sample examined
by Read et al. gives a yield of 0.5683 gEtOH·gLaminarin-1, only 0.05% higher than the true
ideal yield.
Alginate
Alginate is a polysaccharide of mannuronate and guluronate with varying
mannuronate:guluronate ratio, varying degrees of branching, and molar mass ranging from
10,000 to 600,000 g·mol-1 [67]. Because mannuronate and guluronate have identical molecular
formulae and identical ethanol yield per mole, the ideal yield from alginate can be calculated
considering alginate to be a polymer of the form (C6H8O6)n. Following the metabolic pathway
described by Wargacki et al. [12], each C6H8O6 monomer yields 2 ethanol molecules and 2 CO2
molecules.
Results
Ideal ethanol yield per unit mass,
, for mannitol, laminarin, and alginate is calculated
using Eq. (0.1) with input data and results shown in Table A-1.
(0.1)
Where
is the molar mass of ethanol, and
is the subunit molar mass of feedstock i.
Table A-1: Ideal ethanol yield for brown seaweed and corn starch
Polysaccharide/
monosaccharide
Alginate
Sub unit
structure
[C6H8O6]n
Subunit ethanol
yield [mol·mol-1]
2[a]
Subunit molar
mass [g·mol-1]
176.12
Ideal ethanol
yield, [gEtOH·g-1]
0.523
Laminarin[c]
[C6H10O6]n
2[b]
162.14
0.568
Mannitol
C6H14O6
2[b]
182.17
0.506
2
162.14
0.568
2
180.16
0.511
Amylose/Amylopectin [C6H10O6]n
(corn starch)
Glucose
C6H12O6
[a] From metabolic path given in Wargacki et al. [12]. [b] From metabolic path given by Horn
[9]. [c] Laminarin is largely composed of glucose but contains a small amount of mannitol. Ideal
yield is calculated assuming that laminarin contains only glucose which results in negligible
error. Ethanol yield assuming pure glucose is only 0.05% higher the true ethanol yield calculated
using the composition of laminarin samples analyzed by Read et al. [66]
82
Appendix B - Input data
Model parameters are broken into nine groups: seaweed production, drying, ethanol yield,
animal feed production and credits, transportation and distribution, CI, global ethanol
production, and cost analysis. Each contains the values used in the main analysis and expected
ranges considered in the sensitivity study as shown in Table B-1 to Table B-9. Expected ranges
were not determined for non-sensitive inputs.
Table B-1: Seaweed production
Name
Value
Range
Units
Source
300
50-300[a]
W
[24]
Sporeling batch culture time
8
-
weeks·batch-1
[24]
Horizontal rope seaweed
18.5
-
kg·m-1yr-1
[24]
600
-
m·batch-1
[24]
Skiff fuel use at cruising speed
0.271
-
L·km-1
[68]
Skiff fuel use at idle (700 RPM)
0.757
-
L·hr-1
[68]
Sporeling rope installation time
0.75
-
min·m-1
[24]
Installation work day
8
-
hr
[24]
Spore bearing frond collection time
10
-
min·batch-1
[24]
Sporeling batches produced per
10
-
batch·trip-1
[24]
0.1
-
min·m-1 [b]
[24]
Sporeling tank electrical power
Symbol
draw
production rate
Horizontal rope seeded per
sporeling batch
frond collection trip
Horizontal rope harvesting time
[a] The current system power draw is considered in the model and a future case of reduced
power consumption is considered in the sensitivity study. [b] 2 minutes to collect one 20m
horizontal rope of kelp
83
Table B-2: Drying
Name
Symbol
Dry seaweed moisture content
Value
Range
Units
Source
0.22
-
-
[19]
4.0
-
MJ·kg-1
[25][69]
30
5.4-30
-
[a]
(wet basis)
Seaweed water removal heat
requirement
Solar thermal system COP
[a] COP lower bound is for the a heat pump based system with thermal storage described by Xie
et al. [46], and the upper bound is an approximation for simple seaweed drying systems using
only an air circulation fan.
Table B-3: Ethanol yield
Name
Conversion efficiency
Symbol
Value
Range
Units
Source
0.9
0.7-
-
[12][35]
0.94
Ideal ethanol yield
Dry weight mass fraction[b]
Fresh seaweed moisture content
0.523
-
-
[a]
0.568
-
-
[a]
0.506
-
-
[a]
0.131
[c]
-
[6]
0.18.5
[c]
-
[6]
0.201
[c]
-
[6]
0.808
[c]
-
[6]
(wet basis)[b]
[a] Appendix B. [b] Values are shown for September 1947 composition as an example. The case
study model is run for the composition in September 1947 and again for composition in October
1947, and the results are averaged. [c] September 1947 is used for all calculations in the
sensitivity study aside from the seaweed composition cases discussed in Section 5.6.
84
Table B-4: Ethanol conversion input
Name
Value
Range
Units
Source
1
1-2[a]
-
[47]
4.91
-
MJ·L-1
[16]
0.634
-
MJ·L-1
[16]
0.40
-
-
[70]
Dry grind animal feed drying fuel[b]
4.44
-
MJ·kg-1
[16]
Dry grind animal feed production
0.632
-
kg·L-1
[16]
100
-
106 L
[71]
Ethanol production fuel scaling
Symbol
factor
Natural gas consumption in dry
grind ethanol production
Total electricity consumption in
dry grind ethanol production
Fraction of total dry grind
electricity consumption used for
feed processing
rate
Ethanol plant production capacity
[a] As the maximum ethanol concentration achieved through fermentation decreases from the
typically achieved 12% by volume [35] to 4.7% by volume [12], energy consumption in
distillation doubles [47]. [b] Energy required for drying the average mix of wet, modified, and
dry distiller’s grains with solubles produced by the dry grind ethanol plants reviewed by Bremer
[16].
85
Table B-5: Animal feed production and credits
Name
Value
Range
Units
Source
Wet feed mass fraction
0.01[a]
0-1
-
[16]
Modified feed mass fraction
0.32[a]
-
-
[16]
Dry feed mass fraction
0.67[a]
0-1
-
[16]
Wet feed drying fuel[b]
0
-
MJ·kg-1
[16]
Modified feed drying fuel[b]
2.59
-
MJ·kg-1
[16]
Dry feed drying fuel[b]
5.41
-
MJ·kg-1
[16]
Feed displacement energy credit[c]
3.27
0-5.06
MJ·L-1
[16]
Feed displacement emissions
19.9
0-28.3
gCO2e·L-1
[16]
0
0-5.06
MJ·L-1
[16]
0
0-28.3
gCO2e·L-1
[16]
credit[c]
Mineral supplement displacement
energy credit
[c]
Mineral supplement displacement
emissions credit[c]
[a] The average mix wet, modified, and dry distiller’s grains with solubles produced by dry grind
ethanol plants surveyed by Bremer et al. [16]. The case of
,
and the case of
,
give the extremes of the feed production type study. [b] Fuel input
calculated for a typical grains production rate of 0.632 kg·L-1. [c] All four co-product credit
values are varied together in the sensitivity study. All credits equal to zero and all credits equal to
the maximum indicated value give the extremes of the co-product credit study.
86
Name
Table B-6: Transportation and distribution
Symbol Value
Range
Units
Source
Ethanol vapor loss in distribution
0.05
-
kg·kg-1
[52]
Ethanol 100 year GWP
1.3
-
gCO2e·g-1
[72]
Skiff fuel use factor, full load
15.0
-
MJ·tonne-1km-1
[73]
Barge fuel use factor
0.566
-
MJ·tonne-1km-1
[53]
Train fuel use factor
0.219
-
MJ·tonne-1km-1
[53]
Fuel truck fuel use factor
2.09
-
MJ·tonne-1km-1
[53]
10
-
km
-
Farm structure to drying facility
1.5
1.5-0.6[a][b]
km
-
Drying facility to conversion
200
68-200[b]
km
-
720
0-720[b]
km
-
620
0-620[b]
km
-
25
12.5-25[b]
km
-
Transportation and distribution distances
sporeling culture facility to farm
structure
facility
Conversion facility to train
loading site
Train loading site to blending
facility
Blending facility to fuel station
[a] For the wet transport scenario shown in Figure 5-2B, fresh seaweed is transported 0.6km by
skiff before being loaded onto the barge. [b] Simultaneously varied distances for the minimum
transport scenario shown on the left, distances for the wet transport scenario shown on the right
87
Table B-7: Carbon intensity for energy consumed
Name
Symbol
Value
Range
Units
Source
Natural gas
50
-
gCO2e·MJ-1
[74]
Coal
97.3
-
gCO2e·MJ-1
[75]
Electricity[a]
5.6
5.6-244
gCO2e·MJ-1
[76]
Gasoline
90.2
-
gCO2e·MJ-1
[55]
Barge fuel
104
-
gCO2e·MJ-1
[53]
Train fuel
106
-
gCO2e·MJ-1
[53]
Fuel truck fuel
92.9
-
gCO2e·MJ-1
[53]
Solar thermal system input[b]
5.6
5.6-275
gCO2e·MJ-1
[76]
[a] BC grid electricity and coal heavy Alberta grid electricity are considered as extremes. [b] The
solar thermal system is assumed to be powered by renewable electricity similar in CI to BC grid
electricity or by a diesel generator (34% efficient, 93.3 gCO2e·MJ-1 input fuel).
Table B-8: Global ethanol production
Name
Symbol
Value
China annual seaweed production
11.1
World coastline length
356,000
BC coastline length
25,725
China coastline length
Gasoline to ethanol blend
Range
-
Units
6
Source
-1
10 tonne·yr
[77]
km
[78]
-
km
[79]
14,500
-
km
[78]
1
-
L·L-1
[54]
equivalence[a]
[a] Gives the quantity of gasoline replaced by one liter of ethanol in an E10 blend for the same
distance driven.
88
Table B-9: Cost analysis
Name
Symbol
Value
Range
Units
Source
Rate of return
0.20
-
-
-
Ethanol plant operating life
10
-
yr
[71]
Wholesale ethanol price[a]
0.83
-
$·L-1
[80]
Wholesale seaweed feed price[b]
1250
0-1900
$·tonne-1
[81][82]
2012 CAD/USD exchange rate
0.993
-
CAD·USD-1
[60]
Inflation correction factor
1.38
-
2012 USD·
[59]
1999 USD-1
Seaweed bulk density
0.6
-
kg·m-3
[83]
Silo capital cost[c]
21
-
$·m-3
[84]
Feedstock handling
3.56
-
106 $
[71]
Fermentation
6.30
-
106 $
[71]
Distillation
7.26
-
106 $
[71]
Animal feed production
14.39
-
106 $
[71]
Storage and load out
2.06
-
106 $
[71]
Wastewater treatment
1.37
-
106 $
[71]
Air compressor
0.14
-
106 $
[71]
Raw materials
2.19
-
106 $·yr-1
[71]
Denaturant
0.82
-
106 $·yr-1
[71]
Energy input
5.48
-
106 $·yr-1
[71]
Labor, supplies, and overhead
4.25
-
106 $·yr-1
[71]
Ethanol plant capital costs[d]
Ethanol plant operating costs[d]
[a] Average for Vancouver for Jan-Sept 2012. [b] Chosen price is average of the maximum and
minimum kelp animal feed prices found online, 600 $·tonne-1 and 1900 $·tonne-1 respectively.
[c] Converted to 2012 CAD [59][60]. [d] For 95 ML·yr-1 capacity.
Was this manual useful for you? yes no
Thank you for your participation!

* Your assessment is very important for improving the work of artificial intelligence, which forms the content of this project

Download PDF

advertisement