United Nations Development Programme
BIOMASS ENERGY FOR CEMENT PRODUCTION:
OPPORTUNITIES IN ETHIOPIA
Contributions By:
CDM Capacity Development
in Eastern and Southern Africa
Yisehak Seboka
Mulugeta Adamu Getahun
Yared Haile-Meskel
FOREWORD
Biomass and biomass residues, if sourced in an environmentally and socially
sustainable fashion, represent a vast – and largely untapped – renewable energy
source for the countries of sub-Saharan Africa. This guide, jointly developed by UNDP
and UNEP Risoe Centre, seeks to outline the potential, taking the Ethiopian cement
sector as a specific example of how biomass energy might be deployed in practice.
Many of the issues covered, such as the need for biomass pre-treatment and
densification, the problems of biomass availability in space and time, and the
importance of appropriate on-site storage and handling facilities, are equally
applicable to other countries of the region and, indeed, other manufacturing sectors.
It is hoped that the guide will assist policy makers, industrial operators and the
technical community to engage with the opportunities and challenges presented by
the use of biomass energy, particularly in the context of the financing opportunities
provided by the Clean Development Mechanism.
The guide is based on three studies conducted by acknowledged Ethiopian experts:
Yisehak Seboka, Ethiopian Ministry of Mines & Energy; Mulugeta Adamu Getahun,
energy consultant; and Yared Haile-Meskel, industrial consultant. The views
expressed by the authors are those of the authors alone.
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CHAPTER ONE: SOURCING & TREATMENT OF BIOMASS FOR ENERGY
APPLICATIONS IN THE CEMENT INDUSTRY
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BACKGROUND
OBJECTIVES
SOURCES OF BIOMASS / BIOMASS RESIDUES TO BE USED AS AN ENERGY
SOURCE IN THE ETHIOPIAN CEMENT INDUSTRY
TECHNOLOGIES FOR BRIQUETTING OF BIOMASS & BIOMASS RESIDUES
SPATIAL PROXIMITY OF BIOMASS TO CEMENT FACTORIES
THERMAL ENERGY CHARACTERISTICS
TEMPORAL AVAILABILITY OF BIOMASS
COST OF BIOMASS
FRAGMENTATION OF SUPPLY
CURRENT USES OF THESE BIOMASS RESIDUES
PRE-TRANSPORT PROCESSING
LOGISTICAL COSTS AND REQUIREMENTS OF TRANSPORTING BIOMASS TO
ETHIOPIAN CEMENT FACTORIES
PRICE ELASTICITY OF DEMAND FOR BIOMASS
GENERAL BARRIERS TO USING BIOMASS RESIDUES IN THE CEMENT INDUSTRY
BENEFITS
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CHAPTER TWO: BIOMASS ENERGY FOR THE CEMENT INDUSTRY IN ETHIOPIA
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ABSTRACT
INTRODUCTION
CEMENT PRODUCTION PROCESS AND ENERGY USE
CO2 GENERATED IN CEMENT PLANTS AND REDUCTION MEASURES
EXPERIENCES OF USING ALTERNATIVE FUELS IN CEMENT PLANTS
TECHNICAL OPTIONS RELATING TO THE USE OF BIOMASS ENERGY IN THE
CEMENT INDUSTRY
OPTIONS FOR BIOMASS UTILISATION IN CEMENT PLANTS IN ETHIOPIA
CONCLUSIONS
RECOMMENDATIONS
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CHAPTER THREE: ENVIRONMENTAL & ECONOMIC BENEFITS OF BIOMASS
FUEL USE IN CEMENT CLINKER PRODUCTION
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INTRODUCTION
CEMENT CHEMISTRY AND IMPACT ON THE ENVIRONMENT
THE CHEMICAL REACTION OF CLINKER PRODUCTION
BENEFITS OF USING BIOMASS AND ALTERNATIVE FUELS
TECHNOLOGY
ECONOMIC AND ENVIRONMENTAL JUSTIFICATION FOR USING BIOMASS IN
ETHIOPIA
CONCLUSIONS
SUMMARY
REFERENCES – PAGE 73
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CHAPTER ONE
SOURCING & TREATMENT OF BIOMASS FOR
ENERGY APPLICATIONS IN THE CEMENT
INDUSTRY
YISEHAK SEBOKA
Contact: yseboka@yahoo.com
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1. BACKGROUND
Agricultural and agro-industrial residues constitute 15% of the total energy
consumed in Ethiopia. Residues are mostly used in the domestic sector for cooking
and baking, using very low efficiency devices. Residue supply is seasonal and residue
use as fuel is also seasonal.
In different parts of the country, various types of crops are cultivated and, as a
result, a considerable volume of crop residues is also produced. Generally, for use as
fuel, crops with a higher residue-to-seed ratio provide the largest volume of
potential biomass. However, it is often not desirable, socially and environmentally
acceptable or, indeed, economically viable to divert all types of biomass residue for
fuel.
Agricultural residues have different uses. Residues from wheat and maize, for
example, may be left on the ground or burned in the field to recycle soil nutrients;
some parts are used as animal feed, as building materials and as cooking fuel. The
fraction that is available for fuel, either for direct use or further processing, is
therefore limited and varies from crop to crop.
In the small (subsistence) scale farming context, residues are generally better used
for ecological, agricultural or construction purposes than for fuel. However, in large
commercial farms and in agro-industries a large proportion of the residue available
cannot be used on-site due to limited demand in the immediate vicinity. As a
consequence, residue tends to be disposed of wastefully.
Crop and agro-industrial residues have low bulk and energy density, and for these
reasons cannot be transported far from production sites without some form of
processing. Residues from large commercial farms and agro-industries can be
converted to relatively high-quality and high-energy density fuels for use in the
domestic, commercial and industrial sectors through a number of physical, biological
and thermo-chemical conversion processes.
Cement factories can potentially use alternative fuels, including biomass and
biomass residues, to heat their kilns. The substitution of fossil fuel by biomass and
biomass residues qualifies, in principle, for CDM carbon crediting. Biomass can
substitute for approximately 20% of process heat requirements without the need for
major capital investment.
Throughout this Guide, reference will be made to Mugher Cement plant as an
indicative example of the opportunities and challenges Ethiopian cement operators
can expect to encounter should they decide to utilize biomass energy in their
operations. Mugher Cement plant is a large, state-owned cement factory located 105
km west of Addis Ababa. Currently, the plant produces 900,000 tonnes of cement
per year - Ordinary Portland Cement (OPC) and Portland Pozzolana Cement (PPC) –
and plans are being implemented to expand its capacity to 2.3 million tonnes/year.
5
The production process of cement clinker is energy-intensive and requires a large
amount of fuel. Table 1 shows the increase in fuel consumption experienced by
Mugher Cement plant over time.
1999
2000
2001
2002
2003
Table 1. Furnace Oil Consumption by Mugher Cement Plant, 1999-2000
(Taddele, 2008)
Fuel Consumed
Fuel
Year
(litres)
(Birr)
57,614,478
88,645.635
57,673,490
97,095.467
58,303,321
123,116.129
59,080,215
129,527.180
61,080,215
134,291.435
2. OBJECTIVES




To replace 20% of Heavy Fuel Oil (HFO) or other fossil fuel with agroindustrial wastes such as coffee husks, cotton stalks, saw dust, castor husks
or chat stem. This will significantly reduce the fossil fuel usage required to
produce cement.
To introduce alternative fuels into the cement-making process without
compromising the clinker quality or quantity.
To reduce the amount of imported fossil fuel used for cement production.
To achieve greenhouse gas emission reductions through partial substitution
of fossil fuels with alternative fuels in cement manufacture.
3. SOURCES OF BIOMASS/BIOMASS RESIDUES TO BE USED AS AN
ENERGY SOURCE IN THE ETHIOPIAN CEMENT INDUSTRY
3.1. COFFEE HUSK
Coffee is a major commodity export-earner for Ethiopia, accounting for 61% (by
value) of the country’s annual commodity exports. It is estimated that the total area
covered by coffee is approximately 400,000 hectares, with a total production of
200,000 tonnes of clean coffee per year (Gemechu, 2009).
3.11 COFFEE PROCESSING
There are essentially two ways of processing coffee beans from the freshly picked
red cherries of the coffee plant: wet and dry processing. Each process produces a
different quality of “green coffee” and residues with very different characteristics.
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3.1.2
SUN-DRIED (UNWASHED) COFFEE RESIDUES
In the dry process, the red cherries, which initially contain approximately 65%
moisture content, are sun-dried until they reach approximately 10-12% moisture
content. After the cherries are dry, they are put through a dry mechanical pulping (or
decorticating) process in which the green coffee bean is separated from the outer
residue material (skin and husk) of the cherry. The dry process removes the upper
hard cover (the husk) and the inner skin (parchment) in the milling process. This
residue material is generally blown out of the rear of the processing plant, where it
accumulates during the processing season and eventually composts due to ingress of
moisture. Heat generated during the composting of this waste occasionally
spontaneously ignites the dry layers of recently added materials, commonly resulting
in slowly smouldering heaps next to the processing plants.
A mass of 100 kg of red cherries picked at 65% moisture content will result in
approximately 40 kg of sun-dried coffee cherries delivered to the processing plant.
Of this mass, about 17 kg will become sun-dried coffee beans while the remaining 23
kg will end up as residue at the processing plant.
3.1.3
WASHED COFFEE RESIDUES
In the wet (washed coffee processing) process the fresh cherries are milled using wet
pulping machines to remove the outer skin and some of the mucilage. The processed
cherry is then left to ferment in tanks for a specified period of time and the removal
of the remaining mucilage is effected while the parchment is left intact.
As a result of the washed processing method, two distinct types of residue are
generated. The first is the wet coffee pulp, which consists of the epicarp that is
removed at the washing plants in the coffee growing regions. For 100 kg of ripe
cherries delivered to a washing plant, 60% by mass ends up as washed coffee pulp
with the remaining 40% consisting of the green bean and endocarp (parchment). Of
this 60% washed coffee pulp, only 20 kg remains after sun-drying of the bean and
parchment. This is then shipped to the washed coffee processing facility in Addis
Ababa where the parchment is removed. The result is 16 kg of washed coffee beans
ready for export and 4 kg of parchment as residues.
The average residue production per tonne of wet red cherry is about 600 kg or,
based on green coffee bean production, the residue potential would be 1.4 times the
mass of green beans produced (ESMAP, 1986).
3.1.4
RESIDUE AVAILABILITY
Most of the coffee production areas and processing plants in Ethiopia are found in
the southern and eastern parts of the country, notably in the Southern Nations,
Nationalities and People’s Region (SNNPR) and in Oromia, which each host more
than 500 coffee processing plants.
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In the case of dry processing of coffee, all residues are effectively available at the
processing plant; in wet processing, about 14% of the residue (the parchment) is
available at about 10 central processing stations (Addis Ababa). Currently, 84% of the
coffee arriving at the central auction stations in Addis Ababa and Dire Dawa are dryprocessed. Wet processing results in a better quality of coffee products, however,
and its share of the market is growing.
3.1.5
POTENTIAL OF COFFEE RESIDUES: COFFEE PULPING AND HULLING PLANTS
These are concentrated in the major towns of the coffee growing areas of the
country. In the Dilla area, for example, there are more than a hundred such
establishments. Residue pulp is mostly dumped in streams, although a small amount
of it is sold as fuel or for ‘tea’ making in rural areas.
With increasing participation of the private sector both in production and export, the
production of coffee and coffee arrivals at coffee processing stations has increased
over recent years. The total volume of coffee supply to the official market is
estimated to be about 160,000 tonnes per year. However, it is estimated that a
considerable amount of coffee is also traded illegally and total coffee production
could be as high as 250,000 tonnes per year. Considering the lower production
figure, the corresponding annual coffee residue production would be at least
200,000 tonnes.
Currently, the wet pulp is discharged into local streams and rivers where it tends to
clog, forming a putrescent mass and producing a highly acidic effluent which pollutes
the water, destroying aquatic life and generating an offensive odour. Recovery of
this pulp for industrial fuel use would require collecting the residues as they are
discharged from the pulping machine and processing them to greatly reduce the
moisture content.
Husks represent over 90% of the coffee residues produced. However, the extremely
low bulk density (approximately 50-80 kg/m3) of the husks produced precludes their
economic transport to cement factories 300-500 km distant. Densifying or pelleting
this material to a density of 500-600 kg/m3 would greatly reduce transport, handling
and storage costs and facilitate its use as industrial fuel.
The regional distribution of coffee residues is indicated in Table 2 below.
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Table 2. Regional Distribution of Coffee Residues (Kebede, 2001)
Location
Process
Dry Process
Wet Process
Grand Total
3.1.6
Green Coffee
(tonnes/yr)
Coffee Residue
(tonnes/yr)
Regional total
SNNPR
Oromiya
Gambela
Others
130,350
35,060
94,145
1,033
112
184,024
49,496
132,911
1,458
158
Regional total
SNNPR
Oromiya
Gambela
Others
25, 019
16,533
6,959
1,519
8
155,369
30,275
20,006
8,421
1,838
10
214,299
No. of
Processing
Plants
113
273
2
309
189
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BRIQUETTE PRODUCTION POTENTIAL
Coffee residues have very low bulk density, 50-80 kg/m3, and are difficult to handle
and transport. Coffee residue is generally not used as a significant fuel source in the
regions where coffee is produced and, presently, has very little financial value.
Residues, however, could be effectively used for the production of fuel briquettes as
substitutes to fuelwood, coal and fuel oil in cement factories.
3.2. POTENTIAL OF COTTON RESIDUES
State farm plantations, mostly concentrated in the Awash River Basin, dominate
cotton production in Ethiopia. Some private cotton cultivators are also active in
these areas and others. At present, the residues are not utilised but are burnt in the
field to control pathogen and insect infestation of the following crops and are then
ploughed under.
The bulk density of cotton stalk residues collected in the field is approximately 140
kg/m3. The cotton-producing state farms in Awash are approximately 300 km from
Addis Ababa. Economic transport and use of the cotton stalk residues would require
that the material be densified. Cotton stalk and other residues from the farms can be
densified directly, or charred and then densified, to make domestic and commercial
fuel. Proven technologies are available.
Based on studies conducted by the Ethiopian Rural Energy Development &
Promotion Centre (EREDPC, 2000), the total volume of residues from cotton
plantations(state farms) is estimated to be 89,000 tonnes per year. The national
distribution of the residues is indicated in Table 3.
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Table 3. National Annual Cotton Stalk Production and Areas Planted for 1997/98
from State Farms
Area
Residues
Region
Location
Cultivated
(tonnes)
(ha)
AFAR
Middle Awash Cotton
4,782
18,170
Plantation
3,242
12,318
 Melka Warer
1,440
5,472
 Melka Sedi
100
380
 Middle Awash Banana &
Cotton Plantation
Tendaho Cotton Plantation
7,350
27,930
4,000
15,200
 Dufti
3,350
12,730
 Ditbara
Tigray
Hummera (and others in Tigray) 11,260
42,822
Total
23,392
88,922
Table 4. Regional Distribution of Cotton Plantation at the State Farms
(MoARD, 2009)
Region
Area Under Production (ha)
Residues (tonnes)
Afar
14,132
53,702
Tigray
11,435
43,453
SNNPR
3,800
14,440
Oromiya
2,888
10,975
Gambella
1,000
3,800
Total
33,255
126,370
According to Hiwot (2007), the potential total area agro-ecologically conductive for
cotton production in Ethiopia is estimated to be 2,575,810 ha. However, in spite of
high-potential areas existing in the country, actual current production does not
exceed 125,000 ha.
Cotton production in Ethiopia (from 2003-2006) is indicated in Table 5. As this table
shows, the production of cotton is increasing annually, implying that cotton residues
are also increasing – which can be promising for the production of an industrial
biomass energy resource.
Table 5: Cotton Production and Residues in Ethiopia from Smallholder, Private and
Public Farms (Hiwot, 2007)
Year
Area Under Cotton Total Production
Cotton Residues
(ha)
(Tonnes)
(Tonnes)*
2003
110,000
136,000
374,680
2004
125,000
137,000
377,435
2005
120,000
144,000
396,720
2006
122,000
145,300
400,301.5
Total
477,000
662,300
1,549,136.5
*Residue to product ratio is 2.755 at 12% moisture content (Bhattacharry et al, 1990)
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3.3. SAW DUST POTENTIAL OF ETHIOPIA
The total number of saw mills in Ethiopia is approximately 39, with a total of 5-10
factories involved in the production of plywood. A total of 200-300 joinery and
furniture factories also operate in different parts of the country.
Most of the saw mills are located in the southern and south-western parts of the
country. The total number of sawmills and their log-intake capacities is relatively low
(at about 3,500 solid cubic metre/year, single shift); moreover, due to the low
availability of wood-logs, most mills operate below their nominal capacity.
Sawmill residue is estimated to total about 25,000 tonnes per year. Residues
generated in sawmills located in remote areas of the country have insignificant
economic value and are usually dumped or piled up and allowed to rot. Although no
recent surveys have been conducted at national level, EREDPC conducted one in
some of the saw mills in the Oromia region in 2000. According to this survey, the
average annual log (wood) processed in these mills varies from as little as 1,000 m3
to a high of 3,500 m3/year. The total residue potential from the four saw mills
included in Table 6 below is about 4,600 tonnes/year.
At Tiro Botor Betcho and Ethio Plywood Enterprise (Jimma), the off-cuts and slabs
are used for firing the boilers, while saw dust is disposed of into the river or piled up
in fields; at the Ethio Plywood Enterprise in Jimma, the saw dust is freely given to
workers.
Some of the sawmills located in remote areas (away from large towns) might
nonetheless be of interest as these mills have already piled up a considerable
amount of residue for lack of alternative uses.
Table 6. Sawmill Residues from Selected Saw Mills in Oromia Region, 1990/2000
(Kebede, 2001)
Location
Logs – Input
Estimated Residue (tonnes)
3
(m )
Tiro Botor Betcho (Jimma Zone)
1,000
500
Ethio Plywood Enterprise (Arusi)
1,182
591
Sigmo wood Enterprise
3,500
1,750
Ethio Plywood Enterprise (Jimma
3,500
1,750
Zone)
Total
9,182
4,591
Chat is among the most important cash crops grown and consumed in Ethiopia,
particularly in the eastern and southern parts of the country. Chat is also one of the
major crops exported to neighboring countries, earning significant amounts of
foreign currency for the country. Total land under chat in 2004/05 was over 120,000
hectares, up by 8% on preceding years (CSA, 2005). Cultivation of chat trees and
consumption of chat has recently expanded to the northern part of the country
where, until recently, it was little known or used.
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A study conducted to assess Harrar coffee production (Woldu et al, 2002), found that
in the past three decades chat has become one of the major crops grown in a
separate field, or integrated with coffee trees, by farmers in the “two *eastern and
western] zones of Harrarge as well as some pocket areas of the neighbouring Somali
and Harar regional states.”
In 2000/01, chat farms in the two zones of Harrarge, Dire Dawa Administrative
Council and part of the regional state of Somali was 154,400 hectares. Over 74% of
these chat farms are located in the two zones of Harrage, where the reported total
chat production volume for 2000/01 was 157,700 tonnes.
Table 7. Estimated Gross Chat Residue Generation in Addis Ababa
(Kebede and Seboka, 2006)
2004
2005
2006
Addis Ababa
Chat inflow (tonnes/year)
10,134
12,181 9,440
Chat residue generated (tonnes/year)
7,094
8,526 6,608
Air-dry chat residue (tonnes/year)
3,547
4,263 3,304
Gross charcoal production potential
887
1,066
826
(tonnes/year)
3.5. RESIDUES FROM THE BIOFUEL SECTOR
3.5.1
JATROPHA
The Jatropha plant is widely distributed in Ethiopia, existing in many low-lying areas
of the country (North Shewa, Wello, Benishangul-Gumuz, Gambela, Welayita, Bale
and others). Large volumes of residue are expected to be available from the biofuel
processing industry over the coming years. The husk (outer cover) of the Jatropha
seed has high fibre content and may be used as fuel – in briquette form – in the
same way as coffee husks.
The Ethiopian Government is promoting Jatropha as an alternative fuel source to
help reduce the country’s dependence on costly imported fossil fuel. Increasing the
bio-diesel blend will require processing of more Jatropha seeds, resulting in a
corresponding increase in the volume of waste that can be tapped for biomass
briquetting. Promoting production and use of briquettes in this way will help people
realise profit from Jatropha waste.
In medium- and large-scale processing plants, the depulping of Jatropha fruit may be
done at processing sites to ensure the quality of kernels. In large processing plants
depulping will be by mechanical means. Residue pulp will be substantial and can be
another source of income for the processing plants.
The Jatropha fruit is 40% pulp, 30% kernel and 30% oil. About 0.4 tonnes of pulp will
be available from 1 tonne of seed processed. A small (3 tonnes per day), processing
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plant will produce 1.2 tonnes of pulp per day while a large (130 tonnes per day)
processing plant will generate 50 tonnes of residue per day. If used properly, this
represents a significant energy source. But it can also pose serious disposal and
environmental problems if it is not.
3.5.2
CASTOR
The castor bean is native to Ethiopia. The castor plant grows in diverse climates but
favours warm, dry climates (600-700mm of rain; 1,600-2,600 masl altitude). It
requires moist, deep and well-drained soils for optimal yields. It can tolerate saline
or alkaline soils and is also drought resistant. Since yield depends on soil moisture,
there may be a requirement for irrigation in arid zones.
There is a large castor plantation planned in the adjacent area to the Mugher cement
factory (near Woliso town). A significant source of castor husks is also available in
Southern Region around Wolayita Zone, from an enterprise called Global Energy.
3.6. INVASIVE SPECIES THAT HAVE NO FUNCTIONAL VALUE
3.6.1
PROSOPIS JULIFLORA
Prosopis is a wild tree / shrub that grows across hundreds of hectares of the Afar and
Somali regions. It was introduced to Ethiopia some three decades ago for the
purpose of soil conservation. However, with time it has developed into a real
nuisance as a weed, fast growing and coming to dominate cultivated lands along the
middle and lower Awash valley of Afar region.
Pastoralists cut and remove the upper stem and branches of the plant, leaving the
root and the main stem undisturbed and causing the tree to regenerate at a faster
rate. They use the prosopis wood as fuelwood and for fence and house construction.
The Afars have continuously appealed for the eradication of this noxious plant,
complaining of the injuries they suffer from the thorns of the plant. Because it has
formed thick forest, prosopis also serves as shelter for warthogs and hyenas that
have been blamed for attacking gardens and people. The economic and social
benefits of using prosopis wood or branches as a fuel energy for industry are quite
evident.
3.7. BAMBOO
Bamboo is native to Ethiopia, which has possibly the largest bamboo growing area in
Africa. Bamboo is a rapidly renewable natural resource and can represent a
sustainable source for industrial fuel. Increased use of bamboo would significantly
reduce pressure on local timber resources and contribute to afforestation and soil
conservation efforts. Greater use of bamboo would act to offset current
deforestation of other tree species; this in turn would lead to the conservation of
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trees and the rebuilding of the natural resource wealth of the country and the
environment.
Bamboo in Ethiopia has the potential of improving the livelihoods of countless
families. Although bamboo is wood, it differs in one important respect in that it can
be harvested annually, despite being a perennial plant. Such annual harvests (or
even monthly harvests), if undertaken sustainably, do not affect the health of the
plant or its future growth and productivity. This on-demand harvest potential
provides the material for use when needed, and the income when needed – not just
annually but even monthly.
Region
Amhara
Benishangul Gumuz
Oromiya
SNNPR
3.7.1
Table 8. Major Bamboo Areas in Ethiopia
Specific Area
Covered Area (ha)
Injibara
Hinde
Asosa
Bambesi
Begi
Demi
Dibate
Guba
Kamashi
Pawe
Agaro
Gera
Bale mountains
Shenen, Jibat mountain
Gimbi
Guten
Gera bamboo forest
Gera-Lola
Agere Selam- Bore
Chencha
Indibir-Jembero
Jima-Ameya
Mizan Teferi- Kulish
Wushwush- Bonga
Bonga-Ameya
Masha
Shashemene
8,670
77,947
64,245
21,509
27,612
14,200
7,757
33,723
53,830
56,851
1,774
29,125
6,044
1,052
34,493
7,997
18,652
4,183
ESTIMATION OF NET RESIDUE AVAILABILITY
Residues may have one or multiple uses, including use as fertilizer, as animal fodder,
as building material and as cooking fuel. The availability of certain types of
agricultural or process residue also depends on its accessibility and ease of collection
and transportation.
14
For example, while the bulk of cotton stalks produced in large farms are burned onsite as a means of disposal, other agricultural residues, such as coffee husks and
sawmill residues produced in urban areas, are used as household fuels.
Figure 1. Factors Determining Gross Potential & Net Residue Availability
(Kebede, Seboka & Yilma, 2002)
15
Table 9. Summary of Potential Bio-Residues in Ethiopia (tonnes)
(State Enterprise Development Supervisory Authority, 2009)
Location
Tigray
Afar
Amhara
Oromiya
Somali
Benshangul
SNNPRs
Gambela
Harari
Addis Ababa
Dire Dawa
Others
Total
1
Coffee
residue
141,322
69,503
3,298
2
Cotton stalk
42,822
46,100
3
Prosopis juliflora
(ha)
4
Bamboo tree
waste (ha)
5
Saw
dust
1.9m
700,000
7.4m
10.6m
4m
0.12m
0.02m
0.04m
168
214,299
88,922
700,000
1,000,000
24.1m
1 includes: coffee husk, parchment and pulp.
Total cotton residues are undoubtedly an underestimate in light of ever-increasing cotton production.
4 TECHNOLOGIES FOR BRIQUETTING OF BIOMASS AND BIOMASS
RESIDUES
The system and equipment needed for the use of biomass energy in cement
production includes alternative fuel storage, waste transportation and collection
systems, and fuel feeding and burning systems. As agro-industrial wastes have lower
heating values than heavy fuel oil, adjustment to a cement factory’s airflow and
furnace design may also be required.
To transform the low-density biomass into a useful energy substitute for cement
production, it would have to be densified under high pressure and temperature to
form wood-like logs known as briquettes.
The following process flow diagram, Figure 2, presents the activities that would need
to be undertaken in the production of briquettes from agricultural and process
residues.
16
Figure 2. Schematic Flow Diagram for Simple Briquetting Process
(Kebede, Seboka & Yilma,2002)
Aside from the problems of transportation, storage, and handling, the direct burning
of loose biomass in conventional grates is associated with very low thermal
efficiency and widespread air pollution. In addition, a large percentage of unburnt
carbonaceous ash has to be disposed of. Briquetting of the biomass residues could
mitigate these pollution problems while at the same time making use of an
important industrial energy resource.
4.1 MAJOR EQUIPMENT REQUIRED
i.
ii.
iii.
iii.
iv.
v.
vi.
Biomass chopper
Briquetting Plant Equipment
Hammer mill
Piston briquettor
Screw press briquettor
Bagging station
Other
Table 10. Estimated Prices for Briquetting Plants:
Construction and Equipment Costs
Construction
US$
Site preparation
5,000
Buildings
100,000
Total
105,000
Type of machine
Biomass chopper
3,500
Hammer mill crusher
3,400
Briquetting Machine
Piston Briquettor
100,000
Screw press
70,000
Collection /storage equipment
10,000
Conveyors
30,000
17
Silos
40,000
Electrical
30,000
Bagging station
10,000
Workshop equipment
35,000
Spares
50,000
Transport and Delivery
45,000
Engineering and Installation
70,000
Sub-total
496,900
Other/Miscellaneous
30,095
Total
631,995
Source: http://www.satglobal.com/briqplant.htm; personal communications
5 SPATIAL PROXIMITY OF BIOMASS TO CEMENT FACTORIES
Cement factories will need to utilise surplus agricultural residues that are readily
available and in close proximity to them. Regarding Mugher cement factory, such
residues would include castor husks from around the factory area, coffee husks
(around Awassa – 300km distance), cotton stalk and prosopis (around Melka Sedi –
350km distance).
6 THERMAL ENERGY CHARACTERISTICS
Table 11. Properties of common biomass residues (Da Silva, Kutty & Kucel, 2006)
Residue
LHV
Ash content
Volatile matter
Moisture
(MJ/kg)
(%)
(%)
content (%)
Coffee
16.4
11.4
69.4
11.4
husk
Saw dust
18.8
58.4
80.1
1.6
Cotton
17.4
3.3
75.8
12.0
stalk
Cotton
19.1
3.2
N.A
5.9
stalk
briquette
7 TEMPORAL AVAILABILITY OF BIOMASS
Agricultural residues such as cotton stalk, coffee husk and others are seasonal (not
available all year round). Collection and storage of residues during the months of
availability will be necessary; alternatively, different residues could be sourced at
different times of the year.
18
Table 12. Seasonal Availability of Selected Biomass Residues
Biomass Type
Season (months) of Availability
Coffee husk
September to January
 Washed coffee pulp
December to July
 Sun-dried coffee
November to February
Cotton stalk
8 COST OF THE BIOMASS
Table 13. Average Cost of Biomass and Biomass Briquettes
Biomass Type
Cost of Biomass
Total Cost of Biomass
($/tonne)
Briquette
($/tonne)
Cotton stalk
10
114
Coffee husk
20
106
Chat stalk
20
80-90
Jatropha/castor husk
15
95
Prosopis juliflora
30
90-110
Bamboo
40
100-130
Sources: http://www.hedon.info/BP12; Kebede, Seboka & Yilma, 2002.
Table 14. Distance and Delivered Costs of Briquette to End-Use Site (Mugher)
(UNDP/World Bank, ESMAP, 1986)
Production Site
Distance
Delivered Cost of
(km)
Briquettes
(US$/tonne)
Coffee Husk
Mugher (430)
88.97
(Dilla)
Cotton stalk
Mugher (370)
126.75
(Awash)
Average 108
9 THE FRAGMENTATION OF SUPPLY
In Ethiopia, biomass residues are distributed over a large area in small quantities:
farms are scattered. But for some wastes, such as coffee husks, a few large-scale
suppliers (coffee processing plants) are available.
19
10 THE CURRENT USES OF THESE BIOMASS RESIDUES
Crop and agro-industrial residues have low bulk and energy density and, for these
reasons, cannot be transported far from production sites. Where residue supply
exceeds local demand, residues are usually disposed of wastefully and harmfully
(typically burnt in the field or at agro-industrial sites, or dumped into streams).
Crop residues such as teff, wheat and barley are important sources of animal feed
and are additionally used for soil nutrient recycling.
11 PRE-TRANSPORT PROCESSING
Prior to densification, agricultural residues have to undergo a number of stages
including collection, storage, cleaning, drying, size reduction and feeding. Depending
on the residue, each of the above stages will require a certain expenditure on
equipment, materials and labour.
11.1. COLLECTION
Depending on the agricultural residue, collection can be a major component of the
densification process. For example, materials such as cotton stalks tend to be widely
dispersed in the fields and must be collected and transported to a central location.
Alternatively, materials such as coffee husks are produced at central locations and
do not present a major collection effort.
11.2. STORAGE
The type of storage required will depend on the residue and the environmental
conditions it is subjected to. Usually, the residue will be stored in an open-air heap, a
shed, a bin or within retaining walls or fences. If the collected residue is dry and
open-air storage would result in the accumulation of moisture, then closed or
sheltered storage is necessary. Conversely, wet residue can be reduced in moisture
content through carefully managed open storage.
11.3. CLEANING
Cleaning is necessary if the residue contains foreign materials (such as stones, soil or
metal) that could damage the processing and densifying equipment. Cleaning can
usually be achieved with pneumatic, mechanical and / or magnetic screens.
11.4. DRYING
In general, most extrusion-type densification equipment requires that the feedstock
be in the range of 10-20% moisture content on a wet basis (% mcwb). If the moisture
content of the feedstock is too high (above 20% mcwb) the excess water becomes a
superheated liquid because of the high pressure required for densification and the
20
resultant frictional heat build-up. The water will flash to steam as it exits the
densifier and the pressure is lowered, usually exploding the briquette or pellet.
Stored at moisture contents above 20% for extended periods, any biomass will begin
to decompose, reducing its calorific value and posing a risk of spontaneous
combustion. Because of this, drying of the residue prior to densification is required if
the material as received is above 20% mcwb. The method of drying will depend on
several factors, including environmental conditions, the initial moisture content of
material, the level of throughput, the size of material, the type of densifying
equipment, etc.
11.5. SIZE REDUCTION
Most densification equipment requires that the maximum particle size of the
incoming feedstock be no more than 25% of the diameter of the resulting briquette
or pellet. For example, a piston extruder producing briquettes 50 mm in diameter
has a maximum particle size constraint of 12 mm. Feedstock size reduction is usually
achieved with a hammer mill. With the exception of saw dust and other materials of
similar size, all other materials should be crushed to 6-8 mm size with 10-20% fines
to achieve optimum briquetting results. While many types of crushing and grinding
equipment are available on the market, for biomass materials hammer mills are
considered the most suitable. These are available in various sizes, from a few kg/hr
to 10-15 tonnes per hour.
11.6. DENSIFICATION, BRIQUETTING/PELLETING
There are essentially four main types of extrusion densification process:




Piston press briquettors
Screw press briquettors
Roll briquettors;
Pellet mills
There follows a brief description of each of these processes.
11.6.1
PISTON PRESS BRIQUETTING
In this process, a reciprocating piston forces the feed material into a die, where
pressure and friction heat the feedstock to 150-300°C before it is extruded through a
die 25-100 mm in diameter. In most cases, the die is water-cooled to reduce wear.
The briquettes then enter a cooling line which, by friction, provides a back pressure
on the material exiting the dies so that the cooling takes place with gradually
diminishing pressure. A sudden pressure drop can cause the high temperature water
to flash to steam, exploding the briquettes. The back pressure can often be adjusted
to allow optimum production for fuels with varying moisture contents. As they exit
the cooling line, briquettes may be cut or broken off at any desired length.
21
Capacity ranges from 150kg-1.5 tonnes per hour. Piston press briquetting is
characterised by high capital costs (US$500,000) and moderate operating costs
($130,000)
11.6.2



11.6.3




11.6.4
SCREW PRESS BRIQUETTING
Low production capacity (750-1,000kg) per hour
High labour cost ($7.2/tonne) and high capital cost per tonne of output
($15).
High amount of friction heating by the screw, resulting in higher die
temperatures and increased wear on the screw and die head.
ROLL BRIQUETTING
Feedstock is pre-compressed with a screw feeder and compacted between
two rollers with opposing cavities to form pillow-shaped briquettes 25-50
mm in size.
This method requires little energy input since there is little friction heating
of the material.
Maintenance requirements are lower.
Rolled briquettes are generally less durable than extruded products unless a
binder is used.
PELLET MILL
In a pellet mill, a hard steel die, cylindrical or disc-shaped, is perforated with a
dense array of holes 5-15 mm in diameter, and a press roller forces the biomass
through the holes. As the pellets are extruded from the holes they may be cut off
at a specified length, usually less than 30 mm.
The unique characteristics of the pellet – its small size, smooth rounded edges,
high bulk density and durability – make it most suitable for bulk storage and
handling.
Pellets have a lower tendency to bridge in hoppers and are easily handled by
screw conveyers which often have difficulty with larger briquettes or cubes. In
addition, pellets are the only densified form that can be handled pneumatically.
One negative consequence of the small size is that the feedstock particle size
must be smaller as well, which can increase the cost of pre-processing. Another
significant aspect of pelletising is the high production capability of pellet mills,
from 2-10 tonnes per hour. High output can result in lower labour costs and
lower capital costs per tonne of output. (Joint UNDP/World Bank, ESMAP 1986).
22
Table 15. Estimated Range of Densification Costs for Extrusion Processes
(UNDP/World Bank ESMAP, 1986)
Equipment
Capacity
Equipment
Energy
Maintenance
Labour
type
(tonnes/hr)
Cost
Consumption
Cost
requirements
(US$ 000) (kWh/tonne) (US$/tonne) (Man-hour/
tonne)
Piston
0.15-1.50
40-100
30-80
2-3
3-0.5
Press
briquettor
Screw
0.1-1.0
20-70
60-120
3-5
3-0.5
Press
briquettor
Roll
1.0-10.0
75-300
12-25
0.5-1.0
1.0-0.2
briquettor
Pellet mill 4-6
130-300
20-35
1-2
0.5-0.2
12 LOGISTICAL COSTS AND REQUIREMENTS OF TRANSPORTING
BIOMASS TO ETHIOPIAN CEMENT FACTORIES
Table 16. Potential Industrial Briquette Demand of Mugher Cement Plant at 20% of
Heavy Fuel Oil Replacement by Biomass
Fuel oil consumption (litre/year) 60,000,000 (100% HFO)
Cost of modification (US$)
600,000-1,000,000
Fuel oil displaced (litre/year)
12,000,000 (20% replacement by biomass)
Fuel oil savings (US$/year)
6,000,000
Briquette demand (tonnes/year) 50,000
Cost of briquettes (US$/year)
5,400,000
1litre fuel oil cost =$0.5; 1-tonne briquette cost = $108
12.1 SPECIAL STORAGE OR TRANSPORT REQUIREMENTS OF THE BIOMASS
The raw material that is collected should be stored near to the briquetting site. All
agricultural residues feeds are relatively light, with bulk densities ranging from 0.050.08 g/cc (50-180 kg/m3). Because of their bulky nature, such residues are usually
stored in the open; when the location lies in a heavy-rainfall region, the residues
should be stored in ground-level bins that can be covered by heavy waterproof
sheets or, alternatively, a side-open shed could be provided.
Depending upon the reliability of supply, feed material for a 15 day-3 month period
should be stored at the plant site. It should be stored in such a manner that the
heaps are naturally aerated and heavy wind effects are minimized. Approximately 34 m2 of open space is needed to store one tonne of material.
23
13 PRICE ELASTICITY OF DEMAND FOR PARTICULAR SOURCES OF
BIOMASS / BIOMASS RESIDUE
If demand for a biomass residue increases (e.g. from the cement sector), the price of
the residue will tend to increase. Establishing plantations of fast-growing trees
around the cement factory to provide a guaranteed, stable source of biomass supply
can help to address this problem.
14 GENERAL BARRIERS TO USING BIOMASS RESIDUES IN THE CEMENT
INDUSTRY
14.1 INFORMATION / EDUCATION
Fostering the use of biomass or biomass residues in Ethiopian cement factories will
require a focused informational and educational programme aimed at potential
users. Emphasis will need to be placed on convincing both managerial and technical
personnel of the economic advantage of converting to the use of biomass briquettes.
Measures should be identified for overcoming or dealing with some of the
disadvantage of briquettes, such as the relatively high ash content, the greater
generation of particulates, the necessity to isolate briquettes from direct contact
with water, etc.
14.2 LOCAL TECHNICAL ASSISTANCE
Currently, no organised means to provide technical assistance to cement factories
willing to convert to biomass briquettes exists. Technical assistance, both for
conversion and during the initial periods of briquette use, will ensure efficient and
proper use of the product.
14.3 CAPITAL FOR CONVERSION
Cement factories that require modification of equipment and / or additional facilities
in order to use biomass briquettes will require upfront capital. If the availability of
capital to the cement sector is limited it would act to constrain potential conversion.
14.4 RELIABILITY OF SUPPLY
Cement plants that make a capital investment to covert to biomass briquettes will be
concerned about the reliability of the biomass supply. Also, the uniformity of
briquette quality, given process needs, may be a concern for cement plants with no
previous experience with this kind of fuel.
Biomass availability is subject to seasonal fluctuations due to the vagaries of nature.
Hence, although sufficient quantity of surplus biomass is estimated, in the long run
24
continuous supply of sufficient quantities of biomass fuels is not assured and risk
mitigation measures must be put in place.
This problem of supply is compounded by the sheer volume of biomass that would
be required: biomass energy conversion efficiency is very low compared with fossil
fuel energy conversion efficiencies. Further, the storage of biomass materials
presents additional problems. The characteristics of biomass fuels can change quickly
within short time-periods. Most importantly, the calorific value decreases due to the
loss of volatiles and deterioration of the biomass, which affects the performance of
the kiln. Hence, biomass materials cannot be stored for long periods.
15 BENEFITS
15.1 LOCAL BENEFITS
Use of biomass by Ethiopian cement factories would provide financial benefits to
farmers / pastoralists.
15.2 NATIONAL BENEFITS
Use of nationally-sourced biomass would help to retain foreign exchange that would
otherwise have been spent on imported fossil fuels.
15.3 GLOBAL BENEFITS
Global benefits from the implementation of biomass usage instead of heavy fuel oil
would be the reduction of greenhouse gas (GHG) emissions. Provided the biomass or
biomass residues are sourced sustainably, biomass is considered to be a zeroemission fuel.
25
CHAPTER TWO
BIOMASS ENERGY FOR THE CEMENT INDUSTRY
IN ETHIOPIA
MULUGETA ADAMU GETAHUN
Contact: mage@ethionet.et
26
1. ABSTRACT
Cement production is an energy-intensive process. Conventional fuels used in the
cement industry, such as coal, petcoke and furnace oil, are notoriously polluting to
the environment in terms of greenhouse gas emissions. With suitably designed
feeding and combustion systems, biomass fuels can be used in cement factories in
considerable proportions, thereby replacing polluting fossil fuels with carbon-neutral
biomass fuels. Switching to biomass fuels is attractive for the cement industry from
both environmental and financial perspectives. In some cement factories in Ethiopia,
with minor plant modification, it is possible to replace 15-20% of the fossil fuels
currently used. In the longer term, with more rigorous plant redesign and
modification, a greater proportion of biomass fuel use is possible in some cement
factories. New, upcoming cement factories have ample opportunity to incorporate
into their design the provision for utilization of biomass fuels in considerable
proportions.
2. INTRODUCTION
Conventional fuels used in cement factories, such as coal, petcoke and furnace oil,
can be partially replaced by biomass fuels. The financial and environmental benefits
of fuel switching are attractive for most cement factories. Switching to biomass fuels
of 15-20% in the short term, and a greater percentage in the longer term, is a
feasible option for some cement factories in Ethiopia. Switching to biomass fuels will
have financial benefits arising from the reduced cost of fuels. The factories can also
benefit from added revenue from the Clean Development Mechanism (CDM), as
biomass fuels can reduce CO2 emissions from cement plants substantially. At the
national level, there are benefits such as foreign exchange savings and job creation.
In this chapter, the key issues that must be considered by any cement factory
wishing to partially switch to biomass fuels and biomass-based waste fuels are
discussed. The attempt here is only to indicate some critical issues that must be
given due attention when fuel-switching is anticipated by a cement factory.
In order to be able to explain the issues clearly, the case of Mugher cement factory is
considered in a number of instances as an example. Some of the critical issues
discussed with reference to Mugher cement factory are, however, generic and can
also be applied to other factories.
3. CEMENT PRODUCTION PROCESS AND ENERGY USE
3.1
CEMENT PRODUCTION
The production process of cement starts with raw material supply, which involves
such activities as blasting of rocks, transporting the raw material from quarries by
dump trucks, crushing the rock on-site and transporting it to the cement plant by
27
conveyer belts. The raw material transported to the plant is stored and homogenized
at the plant storage facilities. Raw meal is obtained by grinding the homogenized raw
material. The raw meal is pre-heated in cyclone heaters, calcined and sent to the
kilns.
The kilns used in cement production are of two types. These are: the small-scale
vertical type of kilns that are predominantly used in developing countries; and the
large-size horizontal rotary type of kilns widely used in industrialized countries.
Large-scale rotary kilns are more energy-efficient (Taylor et al, 2006).
In the kiln, a flame of 2,000°C heats the raw material to about 1,500°C. After air
cooling, clinker is obtained. Clinker is the principal ingredient in cement production
and is a mixture of approximately 80% limestone and 20% clay (Lafarge, 2008). The
clinker formation process has four stages (Karstensen, 2006):

Stage 1: Drying and pre-heating, which releases free and chemically-bound
water, takes place in a temperature range of 20-900°C.

Stage 2: Calcination, which is the stage of CO2 release in the initial reactions
associated with formation of clinker minerals and the intermediate phase.
This stage occurs in a temperature range of 600-900°C.

Stage 3: Sintering or clinkerisation, which is essentially the stage of
formation of calcium silicates and the liquid phase. This stage takes place in a
temperature range of 1,250–1,450°C.

Stage 4: Kiln internal cooling, in which crystallisation of calcium aluminates
and calcium ferrite occurs in the temperature range of 1,350-1,200°C.
3.2 CEMENT TYPES
Cement is produced by fine grinding the clinker with gypsum. Portland cement, for
instance, is produced by grinding 95% clinker with 5% gypsum. Various other
additives can be introduced to obtain blended cement. The most commonly used
additives are fly ash and blast furnace slag. Fly ash is produced as a result of burning
coal in coal power plants. Fly ash contains vitreous silica, alumina, iron oxide and
lime. It has hydrophilic properties and can substitute for clinker. Slag is obtained
from iron smelting blast furnaces. Slag has hydraulic properties similar to clinker and
is a suitable additive for cement. Blended cement that has high proportion of slag
reduces the setting speed of concrete. Fly ash-blended cement, on the other hand,
improves mechanical resistance (Lafarge, 2008).
28
Table 1: Composition Of Different Cement Types (Taylor et al, 2006)
Cement types
Cement type
Portland
Portland fly
Blast furnace
Activated
cement (%)
ash cement
cement (%)
slag cement
(%)
(%)
Clinker
95
75
30
Fly ash
25
45
Blast
furnace
65
slag
Synthetic slag
45
Water glass
10
Gypsum
5
5
Different types of cement are produced, depending upon the contents of the cement
additive materials. The most common types of cement obtained by various additives
are exhibited in Table 1.
3.3 ENERGY USE IN CEMENT PRODUCTION
Cement production is an energy-intensive process. Pyroprocessing – the process of
clinker production in the pre-heaters / pre-calciners, kilns and coolers – is a
particularly energy-intensive system. Energy consumption of the pyroprocessing
system is, however, dependent upon the technology of the production process.
There are fundamentally five basic technologies of cement production: namely, the
wet process, the dry process, the semi-wet/semi-dry process, the dry process with
pre-heaters, and the dry process with pre-heaters and pre-calciners.
A considerable amount of energy is wasted at various stages of the pyroprocessing
system. Depending upon the type of clinker production process, 7-38% of the energy
consumption in the pyroprocessing system is wasted in the evaporation of moisture.
Some of 13-27% of the energy is carried away with exit gas, and 5-12% of the energy
is wasted by the kiln shell. The typical energy losses in pyroprocessing systems are
indicated in Table 2.
29
Table 2: Thermal Energy Balances of Clinker Production In Process Kilns
(Choate, 2003)
Energy Use Area
Theoretical Requirement
Exit Gas Losses
Evaporation of Moisture
Dust in Exit Gas
Clinker Discharge
Clinker Stack
Kiln Shell
Calcination of Waste Dust
Unaccounted Losses
TOTAL
Wet Kiln
MJ/tonne
1,783.0
752.3
2,236.7
11.3
56.7
189.9
677.3
40.7
88.9
5,840.8
Dry Kiln
%
30.5
12.9
38.3
0.2
1.0
3.3
11.6
0.7
1.5
100
MJ/tonne
1,825.2
1,382.1
300.7
13.0
61.2
590.8
606.7
18.5
192.0
4,994.6
Pre-heater Kiln
%
36.6
27.7
6.0
0.3
1.2
11.8
12.1
0.4
3.8
100
MJ/tonne
1,761.9
496.9
235.3
1.3
65.8
614.0
175.1
6.2
173.0
%
50
14
7
0
2
18
5
0
5
3,612.5
100
Specific energy consumption for various production processes is depicted in Table 3.
It is evident from this table that wet processes are more energy-intensive and
wasteful than dry processes. The dry process with rotary kiln and pre-heaters and
pre-calciners is the most energy-efficient pyroprocessing system.
Table 3: Specific Thermal Energy Consumption of Different Clinker Production
Processes (Tokheim, 2007)
Process type [MJ/t clinker]
Specific energy
consumption
Wet process long kilns
5,000-6,000
Dry process long kilns
up to 5,000
Semi-dry/semi-wet processes (Lepol kilns)
3,300-4,500
Dry process kilns equipped with cyclone pre-heaters
Dry process rotary kilns equipped with multi-stage
cyclone pre-heaters and pre-calcinerkilns
3,100-4,200
3,000
A substantial capacity increase can be obtained with pre-calciner kilns with a second
combustion device between the rotary kiln and the pre-heater section. In the precalciner, up to 60% of the total fuel of the kiln system can be burnt. At an exit
temperature of about 880°C, the hot meal is calcined to a degree of around 90%
when entering the rotary kiln. Kiln systems with 5 or 6 stage cyclone pre-heater and
pre-calciners are considered
Standard technology for new plants today, as the extra cyclone stages improve
thermal efficiency (Karstensen, 2006).
4. CO2 GENERATED IN CEMENT PLANTS AND REDUCTION MEASURES
CO2 emissions from cement plants originate from two sources. The first, and major,
source of CO2 emission is the de-carbonisation of the raw material at high
temperature:
30
CaCO3  CaO + CO2
The second source of CO2 emissions is the combustion of carbon fuels in the kiln
according to the following simplified form of chemical reaction:
C+O2  CO2
With regard to the first source of CO2 emissions, those deriving from decarbonisation of the calcinaceous raw material, such emissions can be reduced in
two ways:
1. By reducing the proportion of clinker in the cement mix by blending the
clinker with additives such as fly ash, gypsum or slag. The use of these
materials will serve to reduce carbon emissions originating from the use of
lime in proportion to the amount of lime that is displaced.
2. By using alternative raw materials for clinker production that do not contain
carbonates. Examples include waste ash from fuel consumption in thermal
power plants, blast furnace slag, anhydrite or fluorite.
With regard to the second source of CO2 emissions, such emissions can be reduced in
two ways:
4.1 FUEL-SWITCHING
Since it is only the combustion of carbon that generates CO2, fuels with relatively
high hydrogen content, such as natural gas, generate lower energy-specific emissions
of CO2. Fuels, such as coal and petcoke, with lower hydrogen content, have higher
energy-specific CO2 emissions. For example, coal has an energy-specific CO2
emission factor of 96kg/GJ, whereas natural gas has a CO2 emission factor of
56kg/GJ (Tokheim, 2007). Therefore, by switching from pure coal-firing to pure
natural gas, a 40% reduction of CO2 emissions can be achieved. The main
impediment here, however, is that natural gas can rarely be used for pyroprocesing
because it is an expensive fuel compared with other fossil fuels.
Some alternative biomass fuels have lower energy-specific CO2 emissions than coal;
others have higher emissions. Hence, absolute carbon content does not provide the
rationale for switching from coal to biomass. Rather, the critical aspect of biomass in
this regard is that it can, in certain circumstances, be regarded as a net zero-emission
fuel-source, even if CO2 is liberated during its combustion. If biomass, or biomass
residues, is/are cultivated sustainably – that is, if the rate of biomass extraction is
not higher than the rate of biomass re-planting or replenishment – then the biomass
is considered to be ‘carbon-neutral’. The logic is that the biomass grown to replace
the combusted biomass is considered to absorb CO2 from the atmosphere while
growing, thereby in effect ‘cancelling out’ the CO2 emissions associated with the
combustion of the cultivated biomass: the net effect on the atmospheric carbon
balance is zero. Sustainably-cultivated biomass has, in effect, an emission factor of
31
zero. It is evident, then, that fuel switching, particularly to carbon-neutral biomass,
can significantly reduce net CO2 emissions.
CO2 emissions from the combustion of some commonly-used and alternative fuels
are shown in Table 4.
Table 4. CO2 Emissions of Commonly-Used and Alternative Fuels In the Cement
Industry (Tokheim, 2007)
Fuel
Coal
Petcoke
Waste oil
Plastic
Solid hazardous
waste
Liquid hazardous
waste
Refuse-derived
fuels
1
CCA waste wood
Animal meal
Wood
Lower
Heating
Value
(GJ/t)
29.3
33.9
34.0
37.7
14.9
Gross CO2
emission
factor
(kg/GJ)
96.0
92.8
74.0
75.0
74.0
100%
100%
100%
100%
100%
Net Co2
emission
factor
(Kg/GJ)
96.0
92.8
74.0
75.0
74.0
Net
emission
factor
(tco2/t)
2.8
3.1
2.5
2.8
1.1
15.7
1.2
100%
74.0
1.2
87.0
1.2
10%
8.7
0.1
110.0
88.0
110.0
1.4
1.5
1.7
0%
0%
0%
0.0
0.0
0.0
0.0
0.0
0.0
Gross CO2
emission
factor(tco2/t)
Fossil
fraction
2.8
3.1
2.5
2.8
1.1
74.0
13.5
12.6
16.8
15.7
4.2 ENERGY EFFICIENCY
Net CO2 emissions are proportional to the energy consumption of the
pyroprocessing system (expressed in GJ/tonne of cement) and to the net emission
factor (expressed in kgCO2/GJ). Improving the efficiency of the pyroprocessing
system can reduce energy consumption and hence CO2 emissions (tCO2/t)
considerably. Measures to improve energy efficiency in cement production can
include (Choate, 2003):
a) Lower kiln exit gas losses
 Install devices to provide better conductive heat transfer from the
gases to the materials (e.g. kiln chains).
 Operate at optimal oxygen levels (control combustion air input) and
optimize burner flame shape and temperature.
 Improve or add pre-heater capacity.
b) Reduce moisture absorption opportunities for raw meal and fuels (avoiding
the need to evaporate adsorbed water).
c) Reduce dust in flue gases by minimizing gas turbulence. (Dust carries energy
away from the kiln where it is captured in dust collectors. The dust is recycled
into the raw meal and fed into the kiln where it is re-heated.)
1
Chromated Copper Arsenate treated wood
32
d) Lower the clinker discharge temperature (retaining more heat within the
pyroprocessing system).
e) Lower the clinker cooler stack temperature:
 Recycle excess cooler air.
 Reclaim cooler air by using it for drying raw materials and fuels or preheating fuel or air.
f) Lower kiln radiation losses by using the correct mix and more energy efficient
refractory to control kiln temperature zones.
g) Lower cold air leakage:
 Close unnecessary openings.
 Provide more energy-efficient seals.
 Operate with as high a primary air temperature as possible.
h) Optimize kiln operations to avoid process disruptions and downtime.
i) Upgrade existing technology: the addition of pre-heater sections, precalcination sections or more efficient clinker coolers serves to maximize heat
recovery.
j) Adopt new technology: large-scale fluidized-bed kilns (200 tonnes/day of
clinker) have been developed and have demonstrated significant energy
savings. It is estimated that a full-scale fluidized-bed (3,000 tonnes/day)
system will consume approximately 3,000 MJ/tonne of clinker – as efficient
as the most advanced kiln utilizing a pre-heater and pre-calciner Fluidizedbed systems are estimated to have capital costs equivalent to 90% of the
capital costs of a modern cement facility and operating costs equivalent to
75% of a modern cement facility’s operating costs (Choate, 2003).
k) Cogeneration: large industrial thermal energy demand offers opportunities
for cogeneration of electricity and/or steam production, particularly if the
cogeneration system is part of the initial plant design. Some cement
manufacturing plants in the USA co-generate electricity on-site.
5. EXPERIENCES OF USING ALTERNATIVE FUELS IN CEMENT PLANTS
The conventional fuels used in the cement industry are coal, petcoke, heavy furnace
oil and natural gas. Recently, there has been a trend to substitute conventional fuels
with alternative fuels derived from industrial waste, urban waste and biomass.
Cement kilns are well-suited for waste combustion because of their high process
temperature and because the clinker product and limestone feedstock act as gascleaning agents. Used tyres, wood, plastics, chemicals and other types of waste can
be co-combusted in cement kilns in large quantities. Some cement factories in
33
Belgium, France, Germany, the Netherlands and Switzerland have reached
substitution rates ranging from 35% to more than 70% of the total energy used.
However, very high substitution rates can only be accomplished if a tailored pretreatment and surveillance system is in place. Municipal solid waste, for example,
needs to be pre-treated to obtain homogeneous calorific values and feed
characteristics (Taylor et al, 2006).
Most waste-derived fuels have heating values lower than those of fossil fuels such as
coal, oil and gas. Typically, waste-derived fuels contain relatively high levels of
moisture and ash. The moisture increases the gas flow in the system, which means
that extra thermal energy has to be added to achieve the correct operational
temperatures in the system. Hence, a kiln system applying a high percentage of lowcalorific fuels tends to have high specific thermal energy consumption – and, as a
consequence, higher absolute CO2 emissions.
This is a drawback of using high waste-fuel blends. However, from a greenhouse gas
perspective, this drawback is more than outweighed by the advantage of reduced
CO2 emissions when the fuels used are CO2-neutral (for example, sustainablysourced biomass residues). Although the gross emissions may increase, the net
emissions will decrease. The indirect effect of reduced waste disposal is another
positive effect of utilizing waste fuels in the cement kiln system. This is true for all
types of waste fuels, whether they are CO2-neutral or not.
The emissions from cement kilns using alternative fuels are no different than those
from traditional cement plants. Nor is the quality of the cement affected by the use
of alternative fuels.
Some experiences of using alternative fuels in the cement industry are outlined
below:

In France, bone meal has been used as a substitute fuel since 1998. It is
instantly destroyed when placed into the kiln’s flame at 2,000°C, with no
detrimental impact on the environment (Lafarge, 2008).

In Norway, the Norcem plant in Brevik carried out an extensive
modernization project in 2004-5, and, as a result of this, the plant uses about
100,000 tonnes of CO2-neutral waste fuels every year, originating from
different types of waste (Tokheim, 2007).

In Uganda, the Hima cement plant has reduced fossil fuel consumption by
30% by using coffee bean husks as an alternative fuel. After harvesting and
drying, the coffee grains are separated from their husks, which were formerly
treated as waste. Instead, they are now transported to the cement plant,
where they are burned in the furnaces, in a system developed especially for
this purpose (Lafarge, 2008).
34

In Malaysia, part of the coal used in the cement plants of Rawang and
Kanthan has been replaced by biomass (palm kernel shells). This is said to
have saved over 60,000 tonnes of CO2 per year and uses by-products from
the local production of palm oil which would otherwise be wasted. This
initiative was approved as a Clean Development Mechanism (CDM) project in
April 2007 (Lafarge, 2008).

In Brazil, a waste management joint venture, Eco-Processa, supplies plants
with substitute fuels. In some cement plants in Brazil, 42% of the fuel used
comes from biomass or waste, which reduced emissions of 156,000 tonnes of
CO2 in 2007 (Lafarge, 2008).

In the USA, at the Atlanta cement plant, scrap tyres are used as an alternative
fuel. They are placed whole in the kiln at 2,000°C, which allows them to be
completely destroyed and avoids dispersing black smoke. Furthermore, the
material is homogeneous and has a high calorific value, which makes it a very
effective fuel for cement plants. The cement industry in the United States
burns 53 million used tyres each year (Taylor et al, 2006).
In Japan, around 200 kilo-tonnes (kt) of used tyres, 450 kt of waste oil, 340 kt
of wood chips and 300 kt of waste plastic were burnt in cement factories in
2005. This is equivalent to approximately 42 PJ of energy from alternative
sources (Taylor et al, 2006).


In the UK, the Cauldon plant was the first cement plant in the country to use
scrap tyres as an alternative to petcoke and coal. Over the last ten years, it
has used approximately two million tyres a year, allowing an annual saving of
24,000 tonnes of fossil fuel (Lafarge, 2008).
6. TECHNICAL OPTIONS RELATING TO THE USE OF BIOMASS ENERGY IN
THE CEMENT INDUSTRY
Among the alternative fuels available for fuel switching in cement plants, biomass is
the only carbon-neutral fuel. The following technical options are available when
using biomass in cement plants:
a) Direct combustion of biomass in pre-heaters / pre-calciners and in the kiln by
part-replacing the fossil fuel used in raising the temperature of the raw meal.
This can happen in two ways:

By mixing crushed and pulverized biomass with coal or petcoke for
use in the kiln.

By direct feeding of biomass in solid lump form (such as pellets and
briquettes) into the rotary kiln and / or pre-heater/pre-calciner
combustion chamber.
35
b) Transforming biomass into producer gas (also known as ‘synthesis gas’ or
‘syngas’) and co-firing it in the kilns using a gas burner.
Each of the options has its own advantages and disadvantages, which will be
discussed in detail in the following sections.
6.1 DIRECT COMBUSTION OF SOLID BIOMASS IN PRE-HEATERS, PRE-CALCINERS
AND KILNS
The technical implications of using biomass in the pyroprocessing system of cement
plants are challenging. Biomass fuels have to be cleaned, prepared, dried and
homogenized to have uniform heating value. Biomass fuels prepared in pieces of up
to 150 mm diameter or in pellet or in briquette form can be directly burned in
combustion chambers arranged between pre-heaters / pre-calciners and the kiln.
Modification of the kiln and the pre-heaters / pre-calciners, particularly the
combustion chamber, is mostly necessary to be able to use biomass fuels in the
pyroprocessing system. Fuel preparation and cleaning units have to be designed and
integrated into the plant.
Biomass can be utilized in pulverized or in lump solid form. The fuel-feed system and
plant modification have to be designed according to the form of solid biomass.
6.1.1 PULVERIZED BIOMASS FUELS
Biomass fuels in crushed, ground and pulverized forms can be used in cement plants.
This is the case, for instance, if charcoal residue, sawdust, coffee husk and similar
types of biomass fuels are considered.
After they are delivered to the plant, these types of biomass fuels should be stored
in dry locations within the factory. Pulverized biomass should be cleaned, dried and
transferred by mechanical or pneumatic conveyors to intermediate silos in the plant.
Pulverized biomass can be suitably utilized mixed with coal or petcoke. Careful
metering, proportioning and mixing have to be conducted in the fuel preparation
section.
As the heating value of biomass fuels is approximately half that of coal and petcoke,
the feed rate of biomass-coal or biomass-petcoke mixture has to be increased
proportionally to compensate for the lower heating values of biomass fuels. For
example, for a 10% biomass and 90% coal or petcoke blend, the feed rate has to
increase by approximately 10%. The precise feed rate has to be calculated on the
basis of the heating values of the mixture and that of the original fuel.
6.1.2 LUMP SOLID BIOMASS FUELS
Biomass fuels in solid form, such as wood chips, pellets, briquettes and the like, can
be burned in combustion chambers arranged in pre-heaters / pre-calciners or can be
36
co-combusted in rotary kilns.These types of fuels are less suitable for vertical shaft
kilns.
Generally, to use lump-solid biomass in the kilns (rotary or vertical shaft kilns) is
problematic due to uncontrolled mixing of fuel ash in the clinker. In vertical shaft
kilns, the most common fuel, petcoke, is ground into small granules and is mixed
with raw meal and fed into the kilns.
Biomass fuels, particularly waste-derived fuels, require a lot of prior cleaning, drying
and preparation (cutting to size, making pellets or briquettes) so that efficient
combustion can be achieved without affecting the clinker production process.
The cleaning and fuel preparation has to take place in biomass storage houses, which
should preferably be located outside of the plant premises, due to the large space
requirement. Ready-to-use solid biomass can be transported to the plant by
mechanical conveyors and should be chute-fed to the combustion chambers or kilns.
6.2 GASIFICATION OF BIOMASS AND WASTE
Gasification is a process of converting carbonaceous materials by partial oxidation
into gaseous fuels (producer gas) of low heating value, containing carbon monoxide,
hydrogen, methane and traces of higher hydrocarbons such as ethane (Cioni et al,
2002).
All biomass fuels can be converted into producer gas for use in cement plants.
Gasification of urban solid waste creates particular convenience due to the
difficulties of directly combusting such material. Producer gas can be co-fired with
fuel oil (furnace oil) in the rotary kilns. New plants can incorporate into their design
producer gas co-firing systems. However, existing plants have to be modified by
adding a gasification reactor and a gas injection and firing system into the kiln.
Although challenging, it is a technically feasible option. Producer gas can also be
conveniently used in pre-calciners.
The most utilized gasification technology for industrial-scale applications is the
fluidized bed gasifier. Fluidized bed technology offers the following benefits (Cioni et
al, 2002):





Relatively simple construction and operation
Tolerance to different particle size, feedstock heating value and composition
High carbon conversion and good quality of raw gas produced (low tar and
particle content)
Good temperature control and high reaction rate
Feasibility of retrofitting in existing plants
Silica sand is usually used as the fluidizing material and air as the oxidizing agent; the
typical operating temperature is 800-850°C and gasification occurs in isothermal
conditions. The high thermal capacity due to the inert bed and the high mass
37
transfer rate due to the good mixing of the solid phase leads to carbon conversion
approaching 100% within the bed.
The main disadvantage of the technology is the carry-over of fine particles produced
from the elutriation2 of ash and fuel, which enriches the gas with solids that must be
removed. In a Circulating Fluidized Bed (CFB) gasifier, the fluidizing velocity is high
enough to let the gas entrain some of the fine particles, both sand and fuel. The
cyclone separates the raw gas from the solid particles, which are recycled back to the
bed. Ashes are discharged from the bottom of the gasifier in solid form and, to
reduce the content of fine particles in the bed, by bleed from the bottom part of the
cyclone.
Worldwide, there are a number of examples of using producer gas for
pyroprocessing systems in cement plants. One such example is in Germany, at
Rüdersdorfer Zement GmbH cement plant (Greil et al, 2002). The plant underwent a
major modification, with a new kiln with a capacity of 5,000 tonnes of clinker per
day. The kiln was designed with high flexibility for utilizing secondary raw materials
and alternative fuels for cement production without compromising the quality of the
cement product and without adversely affecting the environment.
As the most feasible option for its specific technical requirements, the plant installed
a fluidized bed gasification reactor between the raw mill and the kiln. This made it
possible to convert a variety of residues, such as those containing carbon with high
mineral proportions and fuels with high or low heating values, into producer gas. The
gas is fed without any treatment to the calciners of the cement kiln where two-thirds
of the total fuel demand of the kiln plant is supplied. As secondary fuel, shredded
used wood and light recycling materials are principally used. Four different types of
materials and feeding system are employed with the gasification reactor. These are:




Materials that can be blown, by directly blowing them into the gasification
reactor by means of pneumatic conveyors.
Lump fuels that can be conveyed into the gasification reactor by means of
mechanical conveyors.
Mineral residues with upstream drying by means of mechanical conveyors to
the seal pot.
Residues that are difficult to handle or lumpy fuels by means of mechanical
conveying into the sealed pot.
The burnt out ash is conveyed through an ash cooler into the raw mill, where it is
accurately metered into the raw mill as a feed component. By using a fluidized bed in
this plant, it is possible to completely convert waste into a resource material for
cement production, in the form of both energy and as feed material (Greil et al,
2002).
2
The separation of finer lighter particles from coarser heavier particles in a mixture by means of a
usually slow upward stream of fluid so that the lighter particles are carried upward.
38
In Italy, one cement plant is using producer gas. The Grève-in-Chianti gasification
plant has been operating since 1992 and is based on TPS (Thermal Processing
System) technology. It consists of a bubbling fluidized bed combined with a second
circulating fluidized bed used as a cracking reactor where catalyst is added. The
specific configuration of this plant provides for a single circulating fluidized bed
whose bottom part operates as a bubbling bed (Cioni et al, 2002).
The Grève-in-Chianti plant processes 200 tonnes of RDF (Refuse-Derived Fuel) per
day. The plant is comprised of two CFB gasifiers, each of 15 MWth fuel capacity. The
gasifiers operate at close to atmospheric pressure and approximately 850°C,
employing air as the gasification / fluidizing agent. The gasifiers are able to handle
relatively large-sized fuel particles: the maximum length of the RDF pellets delivered
to the plant is 150 mm (Lundberg and Morris, 2008).
The plant represents a simple application of the gasification technology as the raw
gas from the gasifiers is not required to be cleaned before it is fed to either the
adjacent cement kiln or to a dedicated boiler.
7. OPTIONS FOR BIOMASS UTILIZATION IN CEMENT PLANTS IN ETHIOPIA
7.1 THE ETHIOPIAN CEMENT INDUSTRY
There are seven cement factories already operating in Ethiopia and around 39 new
factories are at various stages of investment, planning and development. When the
planned plants are completed there will be approximately 46 cement factories in
total.
Only three of the operating cement factories, namely Mugher, Mosobo and National,
have rotary kilns with five-stage pre-heaters. None of these factories currently has
pre-calciners, although the new, third, line of Mugher cement factory is anticipated
to have pre-calciners.
Mugher cement factory uses furnace oil while National and Mosobo use imported
coal. The other cement factories, Abissinya, Dashen, Jemma and Koka, which use
vertical shaft kilns without any pre-heaters, use petcoke.
Furnace oil, petcoke and coal are all notoriously polluting to the environment,
particularly in terms of greenhouse gas emissions. Using biomass-based alternative
fuels in these cement plants would have obvious benefits from the perspective of
reducing greenhouse gas emissions.
Biomass-based alternative fuels, such as coffee husks, can be considered for use in
Ethiopian cement plants. The logistics and costs of transporting these fuels to the
plant sites can be minimised by using cement delivery trucks (which deliver cement
to local markets) to transport coffee husks back to the plants on their return trips.
39
Such trucks typically make their return trip to cement plants empty, without any
load.
Table 5: Technology and Fuel Use in Ethiopian Cement Plants
Cement plant
Capacity (tonnes/day Technology
Fuel
of cement)
Mugher cement
2,000
Rotary kiln with 5-stage
Furnace oil
cyclone pre-heaters
Mosobo cement
2,000
Rotary kiln with 5-stage
Furnace oil,
cyclone pre-heaters
coal
National cement
300
Rotary kiln
Coal
Abissinya
300
Vertical shaft kiln
Petcoke
Jemma cement
150
Vertical shaft kiln
Petcoke
Dashen cement
300
Vertical shaft kiln
Petcoke
Koka cement
300
Vertical shaft kiln
Petcoke
Source: Information gathered by the author
Table 6: Planned Future Investment in Cement Plants in Ethiopia
(Ethiopian Investment Agency)
Name of Investor
Region of Investment
Abkit Construction material factory Plc
Acces Capital service share Company
Amhaf Cement Industries PLC
B.M Cement Technology PLC
Chamu Industrial PLC
Chen Genfu
DARER RUIYA PLC
Derba Midroc Cement PLC
Emaar-Pak Cement Factory PLC
Ethio Cement PLC
Ethio Cement PLC
Ethio Cement PLC
Ethio-Korean Development
Falath Pertoluem/Ethiopian Branch/
Fa-Nur Cement PLC
Gulfmeera General Business Development PLC
Gulfmeera General Business Development PLC
Hilmat PLC
Hua Yi Cement PLC
Ismaile Kassa
Jatish Manilal Patel
Lafarge Cement Ethiopia PLC
Lafarge Cement Ethiopia PLC
Makarus Filotheso Farag Wassef
Melake Mikiru
Mohaned Osman Mahamed Mhamoud
Mugher Cement Enterprise
Oromia
Oromia
Oromia
Dire Dawa
Oromia
Dire Dawa
Dire Dawa
Oromia
Dire Dawa
Oromia
Oromia
Oromia
Dire Dawa
Dire Dawa
Dire Dawa
Oromia
Oromia
Oromia
Oromia
Amhara
Multiregional
Oromia
Oromia
Multiregional
SNNPR
Multiregional
Oromia
3
1 USD = 11.13 Ethiopian Birr (March, 2009)
40
Capital (x1,000)
3
US$
1,332.3
31,166.1
2,131.6
133.2
46,630.6
23,981.5
13,323.0
322,819.6
6,661.6
71,838.9
124,056.5
124,056.5
257,775.2
124,710.6
261,264.5
8,393.5
8,393.5
7,549.6
7,993.9
532.9
9,992.3
452,982.7
452,982.7
6,661.6
2,131.6
6,661.6
193,589.8
Murtadha A. Abduljalil
Myk Cement Industries PTE LTD (Ethiopian
Branch)
P &F General Business PLC
Peacock Oil PLC
Rina International Investment (ETH) PLC
Samuel Langano Deno
Sri Sai Flora PLC
Sunrise Industrial Activities Construction &
Trading Service Ethiopia PLC
Super Sunrise Industrial PLC
T.N.T.M Industrial PLC
Ture Dire Dawa Cement Factory S.C.
Universal Cement PLC
Multiregional
Multiregional
6,661.6
93,261.1
Oromia
Oromia
Oromia
SNNPR
Multiregional
Oromia
2,131.6
19,984.6
175,981.1
134.6
7,546.1
1,106,558.6
Oromia
Oromia
Dire Dawa
Multiregional
1,263,164.3
599,536.1
41,023.5
1,332.3
The cement plants that are under various stages of planning and investment are far
greater in number than the ones that are operational. Around 39 investors intending
to establish cement factories in Ethiopia have already received their investment
licences. These plants have ample opportunity to incorporate into their design a
provision for flexible fuel use so that they can use biomass-based fuels in greater
proportion. In the longer term, new plants can plan to use biomass from dedicated
energy forestry plantations that can be established as integral components of the
cement plants. Though they are not using it for energy purposes, Hima cement plant
in Uganda is planting trees in old quarries to reclaim the natural beauty of the land.
7.2 CANDIDATE CEMENT PLANTS FOR BIOMASS UTILIZATION
Some of the cement plants in Ethiopia face favourable circumstances for partially
switching to biomass fuels. The plants that have the greatest opportunities for using
biomass-based fuels – because of their proximity to the resources and because of
their current utilization of fuels such as petcoke and coal – are indicated in Table 6
below.
Table 7: Proposed Alternative Biomass Fuels for Ethiopian Cement Plants
Cement
Plant
Location
Abissinya
Chancho
Dashen
Dejen
National
Jemma
Drie
Dawa
Muketuri
Mossobo
Type of
kiln
Vertical
Shaft
Vertical
shaft
Rotary
Production
Capacity
(tonnes /day)
300
Petcoke
300
petcoke
300
Coal
300
Petcoke
Fuels used
currently
Mekelle
Vertical
shaft
Rotary
2,000
coal
Mugher
Mugher
Rotary
2,000
Furnace oil
Koka
Cement
Koka
Vertical
shaft
300
41
Petcoke
Proposed alternative
biomass fuels
Coffee husk, urban
waste
Energy forestry
Cotton stalk, energy
forestry
Coffee husk, urban
waste
Cotton and sesame
stalk, energy forestry
Coffee husk, urban
waste and energy
forestry
Coffee husk, urban
waste and energy
forestry
7.3 TECHNICAL OPTIONS FOR BIOMASS UTILIZATION
As with cement plants elsewhere, Ethiopian cement factories wishing to use biomass
–based fuels have two options for biomass utilisation: to use solid biomass by
directly feeding it into pre-heaters / pre-calciners and the kilns, or to convert the
biomass into producer gas and use the gas in a co-combustion system.
7.3.1 DIRECT COMBUSTION IN THE PRE-HEATERS AND PRE-CALCINERS
In principle, the preferred option for combusting solid biomass is in the pre-heaters /
pre-calciners, where more than 60% of the energy input is used. For this, a speciallydesigned combustion chamber has to be arranged in between the pre-heater / precalciner and the kiln.
However, it must be noted that, at the moment, no plants in Ethiopia have precalciners. The third line of Mugher cement factory, which is currently under
construction, is anticipated to incorporate pre-calciners in its pyroprocessing system.
Solid biomass fuels can be utilized in the pre-calciners of this third line by
incorporating into the design a suitable combustion chamber. The other option
would be to modify the first two lines to include a pre-calciner unit. However, this
option would require a major plant redesign and modification.
7.3.2 DIRECT COMBUSTION IN THE KILN
The other option of using biomass is to directly combust it in the rotary kilns. Vertical
shaft kilns (VSK) are not suitable for using lump solid biomass. Solid biomass use in
vertical shaft kilns is possible only by pulverizing it and mixing it with petcoke, the
fuel mostly used in VSK.
Direct combustion of solid biomass fuels, particularly urban waste-derived fuels, in
the rotary kilns is the preferred option from the perspective of safer disposal of the
waste, as the high kiln temperature enables complete combustion and minimizes the
risk to the environment from un-combusted fuel. High temperatures and longer
retention times in the kilns offer greater energy-efficiency when combusting the fuel.
In the Ethiopian context, urban waste, particularly household waste, is by and large
composed of biomass and contamination from release of chromium, lead, mercury
and chlorine rarely occurs. Industrial waste can contain these metals, though not in
substantial quantities.
The feeding of solid biomass fuels into rotary kilns can be performed by chute
feeding into the raw meal inlet section of the kilns. Alternatively, solid biomass can
be chute-fed into the burner end of the kiln. Feeding at the transition section,
though not preferred, is also possible for these kinds of fuels. Depending upon the
feeding point, care has to be taken to make a controlled feed of biomass so that the
optimum operational temperature profile of the kiln is not disturbed. In addition,
42
controlling the feeding system fuel homogeneity with uniform heating value and
moisture content is vital for maintaining the correct kiln temperature profile.
Little modification is required in the case of feeding biomass fuel at the ends of the
kilns. However, the kilns have to be modified considerably if the feed point is to be in
the transition section.
A major challenge, when considering direct combustion of biomass fuels in clinker
kilns, is the amount and nature of fuel ash produced in the kilns. Some fuel ash can
be added to the raw meal without any problems arising. However, the content of the
fuel ash is crucial in determining the amount that can be added. For instance, a high
content of minerals in fuel ash would substantially influence the quality of the
resulting cement product (Greil, 2002). The final composition of Portland cement, for
example, consists of 50% tricalcium silicate (Ca3SiO5 or 3CaO•SiO2), 25% dicalcium
silicate (Ca2SiO4 or 2CaO•SiO2), 10% tricalcium aluminate (Ca3Al2O6 or 3CaO•Al2O3),
10% tetracalcium aluminoferrite (Ca4Al2Fe2O10 or 4CaO•Al2O3•Fe2O3) and 5%
gypsum (CaSO4•2H2O), (Choate, 2003). This composition has to be maintained in
order to obtain a good-quality cement product. In using biomass fuel ash in raw
meal, care has to be taken not to significantly affect the chemical composition of the
final product.
7.3.3
USING PRODUCER GAS
The other option of using biomass in cement plants in Ethiopia is to generate
producer gas from biomass fuels using circulating fluidized bed gasifiers. With this
technology a variety of biomass fuels, such as urban waste-derived fuels, agricultural
waste and residues (for example coffee husks and cotton stalks, forest residues and
solid wood from energy forestry) can all be transformed into producer gas. The gas
so produced can be used, often with minimum need for cleaning, in pre-heaters /
pre-calciners and as a secondary fuel in the rotary kiln. The advantage of this system
compared with the use of solid biomass is that it enables easy control of a number of
parameters that can otherwise affect the pyroprocessing system.
The gasification reactor can be located outside the cement plant in the raw biomass
fuel storage house, where fuel cleaning, preparation and storage is performed. Fuel
conveyance to the plant and feeding can be performed through sealed gas pipes.
Producer gas can be combusted in a controlled manner in a combustion chamber
arranged at the pre-heaters / pre-calciners or can be co-combusted in the clinker
kiln.
The system of producer gas supply can be kept autonomous in case of system
disturbance in the pyroprocessing unit. The plant designs or modification designs
should allow operation with 100% of the original fuel when the need to close the
producer gas supply system (for maintenance or other reasons) occurs.
43
7.4 THE NEED FOR PLANT REDESIGN AND EQUIPMENT ACQUISITION FOR BIOMASS
UTILIZATION
Biomass-based alternative fuels tend to have lower heating values than the fossil
fuels typically used.
Taking the case of Mugher cement factory as an example, and assuming the
minimum specific energy consumption of the pyroprocessing system to be 4.2 MJ/kg
of cement and the heating value of furnace oil to be 42 MJ/litre, daily fuel
consumption of Mugher cement factory, with a production capacity of 2,000 tonnes
per day, is estimated at 200,000 litres of heavy furnace oil. Replacing 20% of the
furnace oil consumption would require about 120,000-160,000 kg (equivalent to
286m3-381m3 stacked4 wood) of biomass-based alternative fuel (assuming a heating
value of 14 GJ/m3). This is a considerable amount of fuel to handle on a daily basis.
Due to the bulky nature of biomass fuels, properly designed fuel storage, cleaning
and preparation units have to be designed and built outside the cement plant, as
considerable space is require for biomass storage. The fuel preparation unit should
consist of: storage halls, a cleaning-and-separation of foreign materials unit, drying
and crushing / grinding facilities (for pulverized fuels), and a pelletizing and / or
briquette-making facility.
The ready-to-use biomass fuel then has to be conveyed by mechanical conveyors (if
in lump form) or pneumatic conveyors (if in pulverized form) into an intermediate
silo in the plant, from where it can be directly fed to the combustion chambers of
pre-heaters / pre-calciners or the kilns.
During storage and preparation, care has to be taken that deterioration of the
biomass does not lead to methane emissions. Storage of wet and damp biomass
fuels has to be avoided. If the plant does receive biomass fuel with high moisture
content, it must be immediately dried with the flue gas from the plant. Failure to do
this can result in emission of gases such as methane.
Cement plants opting to use biomass have to consider a number of options.
First, they must decide what type of biomass they will use. This decision is made
largely on the basis of availability in the vicinity of the plant. For instance, Mugher,
Abyssinia and Jemma cement factories can consider using coffee husks and urban
waste-derived biomass fuels because of their proximity to the resource bases of
these fuels. Mossobo and National cement can consider using cotton and sesame
stalks for the same reason. In the longer term, all cement factories can consider
utilizing biomass from dedicated energy forestry. Some cement plants can consider
using existing wood plantations. In this regard, Dashen plant at Dejen, for instance,
can consider immediately utilizing woody biomass from existing plantations near the
4
3
1m stacked wood ~ 420kg
44
plant with a contingent plan to reforest the utilized forest land and develop new
energy forestry with fast-growing trees for future use.
Second, once the decision on the type of biomass to be utilized is reached, a detailed
study has to be conducted by the plant to consider the technology suitable for the
particular type of biomass chosen. The options to be considered are:

To use solid lump fuels such as woody biomass, briquettes or pellets in the
kilns.

To use biomass in pulverized form mixed with petcoke, particularly in the
kilns (suitable for vertical shaft kilns) or mixed with coal for use in rotary kilns.

To transform biomass into producer gas and use it in the pyroprocessing
system.
For all of these options, plant redesign and equipment acquisition is necessary. This
will be further elaborated in the following sections.
7.4.1
SOLID LUMP BIOMASS FUELS
In the case of using solid lump fuels in pre-heaters / pre-calciners, which is applicable
in today’s Ethiopian context only for the upcoming Mugher third line, the
combustion chambers have to be arranged in between the pre-heaters / precalciners and the kilns have to be designed, so that biomass combustion can be
performed without any problems such as fuel feeding and un-controlled ash mixing
with clinker.
If biomass fuels are to be used in the kilns, the feed system (chute feed) and feeding
rate monitoring system have to be designed for fuel feed at the inlet and firing ends
of the rotary kiln and have to be installed. A major redesign and modification will be
required if the fuel is to be fed into the transition section of the rotary kiln.
Using solid biomass fuels, particularly in the kilns, requires undertaking the following
plant modification and construction:

Depending upon the type of fuel, the moisture content of the fuel and the
content of undesirable material, the fuel warehouse has to have fuel-cleaning
and fuel-drying sections equipped with the necessary facilities. The design of
this section is dependent on the particular situation of each plant and the
nature of the biomass fuel.

Particular consideration should be given to whether or not to receive wet or
damp fuels. Fuels supplied to the cement plant can preferably be dried at the
site of resource base. This will minimize the space requirement at the plant
for drying fuels. If drying is absolutely necessary, the plant should consider
designing the drying facility using the flue gas heat from the plant. When
45
using flue gas for drying, due consideration has to be given to environmental
issues to prevent undesirable emission of particles and gases.

The need and method of cleaning is dictated by the biomass being used.
Manual cleaning and sorting can suffice for certain types of woody biomass.
Magnetic separation of foreign metallic materials will be required in the case
of urban waste-derived fuels. Cleaning of fuels is very important for two
reasons: to prevent or minimize undesirable material that can alter the
quality of clinker and result in corrosion of the kilns, and to avoid the release
of environmentally-damaging substances such as chromium, lead, chlorine
and mercury. Fuel cleaning is, therefore, an important task that should be
designed carefully on the basis of the nature and content of the fuel.

Fuel preparation is another important task that has to be undertaken with
care. Fuel preparation consists of homogenizing the fuel to obtain uniform
heating value and preparing it to the required size. Urban waste-derived
fuels, agricultural waste and agricultural residues have to be pelletized and /
or briquetted to increase their density and energy content per unit volume. If
the fuels have to be transported over a long distance, pelletizing and / or
briquette-making can be conducted at the resource site in order to reduce
transportation cost and create convenience in handling and transportation.
However, the pellets and briquettes can also be made at the cement plant.
The economics, health and environmental issues will determine which option
is best suited for a particular cement plant. If it is chosen to make pellets
and/or briquettes at the plant, the pellet/briquette press has to be installed
as an additional section of the fuel preparation and storage facility.

The finished ready-to-use fuel has to be stored in a clean, dry place separate
from the ‘raw’ (unprocessed) biomass. The ready-to-use fuel can be conveyed
to the plant using mechanical conveyors and delivered to a buffer silo in the
plant. From the buffer silo, the fuel can be chute-fed to the combustion
chambers of the pre-heaters / pre-calciners or the kilns at a pre-determined
rate.
The feed rate is determined by the energy requirement. For instance, a 20% fuel
oil replacement at Mugher will require a daily feed rate of approximately
120,000-160,000kg of biomass. Adjustment and fine tuning of the rate can be
done in initial test runs and in the course of repeated usage.
The equipment required for solid biomass utilization consists of:




Fuel cleaning facility – including magnetic separation of metallic elements
if required
Fuel drying facility – drying bed and flue gas duct, flue gas Induced Draft
Fan (IDF)
Cutting, shredding and / or crushing and sizing equipment
Pellet or briquette-making equipment (if required)
46




7.4.2
Conveyor to the plant – bucket conveyors and / or belt conveyors
Buffer silo
Chute feed
Combustion chamber at the pre-heaters / pre-calciners (if required)
PULVERIZED FUELS
All of the tasks and facilities indicated above for solid lump fuels also apply for
pulverized fuels.
In addition, due to the particular nature of pulverized fuels, the conveyance system
and fuel preparation system have to be designed in a different manner. After
cleaning and drying, the biomass fuel crushing and / or grinding has to be done in a
separate area.
Pulverized fuels are preferably used in vertical shafts, mixed with petcoke in predetermined proportions. Pulverised biomass can also be used in rotary kilns mixed
with coal. The mixture fuel can then be pneumatically conveyed to an intermediate
silo in the plant from where it can again be pneumatically conveyed to the kiln
combustion point. Care has to be taken when blowing pulverized fuel mixture,
particularly in rotary kilns, so that backfiring and explosions do not occur. In the case
of using pulverised fuels in rotary kilns, the blowing air pressure has to be sufficiently
higher than the pressure in the kilns.
The equipment required for utilization of pulverized biomass mixed with coal or
petcoke consists of:








Cleaning facility – magnetic separation of metallic materials if required
(manual cleaning is possible for some biomass-types)
Fuel-drying system using the flue gas from the plant
Shredding, crushing and / or grinding mill
Fuel metering and mixing facility
Pneumatic conveyors – to the silo in the plant and from the silo to the kilns
Intermediate silos
High-pressure blowers
Piping for fuel transport and flue gas ducts for drying
Based on the foregoing, a suggested biomass fuel feed and combustion system
that could be constructed at Mugher cement plant is indicated in the figure
below. The addition of a biomass combustion chamber at the pre-heaters / precalciner using the hot gas from the kiln and clinker cooler is one suggested
modification for Mugher cement factory. The other alternative modification is
the arrangement of biomass feed system at the inlet end of the kiln.
47
Figure 1: Proposed Biomass Fuel Feed and Combustion Points
at Mugher Cement Factory
7.4.3
BIOMASS ENERGY IN THE FORM OF PRODUCER GAS
Transforming biomass into producer gas using a Circulating Fluidized Bed gasification
reactor is the most convenient means of using biomass fuels in the cement industry.
The efficiency of utilization, from raw biomass to process heat, is lower than other
alternatives because of the heat loss at the gasification reactor. However, converting
biomass into producer gas has many advantages:

A variety of biomass fuels, such as urban waste-derived fuels, agricultural
residues, forest residues and forest waste, woody biomass from energy
forestry etc., can all be utilized for producer gas generation with little
requirement for drying, cleaning and fuels preparation.

Relatively large sizes of up to 150 mm pieces of biomass fuel can be utilized
without any need for significant size reduction.

Fuel ash can be conveniently disposed without any disturbance to clinker
production. If desired, measured quantities of fuel ash can be added to the
raw meal.

Flexibility: the cement plant can be designed to use a high proportion of
producer gas in the fuel mix but can also retain the flexibility of using 100%
fossil fuel if the need arises.
Bubbling fluidised bed gasification reactors can be used in combination with
circulating fluidised bed gasification reactors. The first reactor enables full
gasification of carbonaceous materials and the second reactor facilitates the cracking
48
of tar. The combined effect of these two reactors is that they act like one single
circulating fluidised bed gasification reactor with bubbling bed. This type of
gasification reactor enables the utilization of a variety of biomass fuels with different
carbonaceous mineral contents, size and moisture contents.
The gas from the gasification reactor can be utilized without cleaning or with little
cleaning at the pre-heaters / pre-calciners, in the case of the third line at Mugher, or
as a secondary fuel in rotary kilns. The fuel ash can be cooled, the contents checked
by laboratories and, if found suitable, can be added into the raw meal, thereby
displacing a considerable amount of raw material for clinker production.
7.5 INVESTMENT
Little information is available on the magnitude of additional investment
requirement. Knopf (1995) indicates that the additional investment costs for
combustion of 22 kilo-tonnes of municipal solid waste (MSW) in a kiln with a capacity
of 500 kt clinker per year is in the region of EURO 750,000 (EUR 35/t MSW) and the
additional operational and maintenance costs are EUR 220,000 (EUR 10/t MSW) (De
Feber and Gielen, 2000).
Using this information, the estimated investment cost for 20% biomass fuel
switching at Mugher cement factory (which would amount to 48,000 tonnes of
biomass fuel per year) would be about EUR 2.16 million. This estimated plant
modification cost in Ethiopian Birr would be about Br 24 million5.
7.6 RUNNING COSTS
Running costs are related to the fuel preparation process and the fuel feed process.
The running costs consist of:




Biomass fuel cost at the source site
Labour cost for fuel cleaning and preparation
Utilities such as electricity and water
Transportation
All of these cost components add to the raw material cost and give the total cost of
biomass fuels. The average cost of solid biomass fuel delivered at the factory gate is
estimated at Birr 1.25/kg (this is simply an estimate and each factory will face
different costs). This cost is deliberately taken on the high side to account for any
contingencies – for example, so that cement factories can set attractive prices for
third-party biomass supply companies if cement producers choose to opt out of
direct sourcing themselves. The current fuel wood cost in Addis Ababa is
approximately Birr 0.5/kg.
5
1 EUR ~ Birr 11 (May, 2009)
49
7.7 FINANCIAL BENEFITS OF FUEL SWITCHING
7.7.1
FUEL DISPLACEMENT
The benefits of using biomass fuels to displace fossil fuels used in the cement
industries are financial and environmental. The financial benefits are the difference
in unit cost of useful thermal energy of the fossil fuels and that of the substitute
biomass fuels. To displace a litre of fuel oil, 3-4 kg of biomass fuel will be required.
The biomass fuel requirement will be on the higher side, about 4 kg, if the producer
gas route is used because of energy losses in the gasification reactor.
Taking the Mugher case as an example, 20% fuel oil replacement would represent
160,000 kg per day of biomass fuel. Assuming the average biomass fuel cost to be
Birr 1.25 /kg, the total daily biomass fuels cost would, therefore, be approximately
Birr 200,000.
The price of furnace oil fluctuates between 7.02 birr/litre to 5.47 birr/litre. For our
calculation here, the higher furnace oil price is taken. The cost of 20% of the daily
consumption of furnace oil at Mugher cement factory is approximately Birr 240,000.
The estimated net saving from fuel replacement is, therefore, Birr 40,000/day. This
amounts to a total saving of about Birr 12 million (US$1.1 million) per annum (300
working days) from fuel displacement alone.
The investment cost for plant modification for 20% biomass fuel switching would be
approximately Birr 32 million. The investment cost could, therefore, be recovered in
less than 30 months from savings in the fuels cost alone.
7.7.2
REVENUE FROM CDM
Cement factories opting for biomass fuel switching can reduce their CO2 emissions
considerably. This reduction in CO2 emissions can enable them to apply for revenue
from the CDM (Clean Development Mechanism).
Taking again Mugher Cement as an example, it can be noted that with 20% fuel
switching, about 40,000 litres of furnace oil can be displaced. Assuming an average
300 working days per year, this quantity translates into about 12 million litres per
year.
The CO2 emission factor of heavy furnace oil is about 92kg/GJ and the average
heating value of heavy furnace oil is 42 MJ/litre. The estimated CO2 emission
reduction would, therefore, be about 46,368 tonnes per year.
With this reduction, revenue from the CDM (at US$14/tonne of CO2) would be about
US$650,000 (approximately Birr 7.15 million) per year.
50
7.8 OUTSOURCING BIOMASS SUPPLIES
In the preceding section, the estimated cost of ready-to-use biomass fuel is taken to
be Birr 1.25 per kg. This price is on the high side. Some sources indicate that the
biomass fuel price may, in reality, be nearer Birr 0.5/kg.
Cement operators may not be interested in becoming involved too deeply in the task
of fuel sourcing and preparation. The alternative for such plants is to out-source the
supply of biomass to other companies.
Biomass fuel supply companies can enter into contracts to prepare and supply
biomass fuels from known and agreed sources with pre-specified homogeneity, form
and moisture content. The biomass supply companies can also enter into
agreements to observe certain environmental norms in their production and
processing.
By out-sourcing biomass fuel supply, cement factories will also be saved the space
requirements for fuel drying and preparation. Another positive aspect of outsourcing is that a number of companies may emerge and may compete to supply
cement factories with biomass fuels from a variety of sources, including agricultural
residues, forest waste, urban waste and energy forestry. As a first step, in the initial
phases of planning for biomass fuels switching a cement factory can issue tenders for
the supply of biomass fuels.
8. CONCLUSIONS
Fuel switching, from conventional fossil fuels to biomass, is a feasible and attractive
option for Ethiopian cement plants. Biomass fuel switching of even 20% can be
financially rewarding, with the financial benefits accruing from the reduced cost of
fuel and the revenue from the CDM.
Biomass fuel switching in the cement industry, in addition to the financial revenues
flowing to the cement factories, has nationwide benefits such as:


Reduced foreign exchange requirements
The creation of considerable job opportunities in biomass fuel development,
preparation and transportation
Mugher Cement has a unique opportunity to switch to biomass fuels, especially in
the third line where pre-calciners will be added. Similarly, most new cement
factories have ample opportunity to incorporate into their design pre-calciners fitted
with special combustion chambers for biomass fuel utilization.
51
9. RECOMMENDATIONS
The financial and other benefits of switching to biomass fuels in cement plants are
evident from the discussion in the preceding section. Cement plants in Ethiopia have
to consider the option of utilizing biomass fuels and thereby replacing some portion
of the fossil fuels they are currently using.
Cement factories need to study what types of biomass fuels are available in their
locality and what can effectively be utilized in the short term to replace 15-20% of
the conventional fuels they are using. In the longer term, they need to study all
options for switching to higher-percentage biomass fuel utilization. In these studies,
they must consider plant modification requirements and the option of developing
new dedicated energy plantations (possibly in old quarries or other disused land) so
that they can supply themselves with a considerable portion of their biomass fuel
requirement.
Mugher Cement factory especially, which faces the possibility of switching to
biomass fuel in the first two production lines and particularly in the new third line,
should pursue a biomass fuel-switch policy. Similarly, all upcoming cement factories
should consider in their design a flexible fuel use so that they can exercise the option
of using biomass in greater proportions.
52
CHAPTER THREE
ENVIRONMENTAL & ECONOMIC BENEFITS OF
BIOMASS FUEL USE IN CEMENT CLINKER
PRODUCTION
YARED HAILE-MESKEL
Contact: yarhm@aol.com
53
1. INTRODUCTION
Biomass refers to biological materials derived from living or recently dead biological
materials, encompassing materials from both plants and animals. It includes plant
tissues such as wood, charcoal and yarns; farm wastes such as coffee husks, teffe
and chat; animal wastes, such as animal fat, dung, meats and bones; and household
or industrial biological degradable wastes. These materials are primarily composed
of carbon-based organic matter, which releases energy when it reacts or combusts
with oxygen. When cultivated or sourced in a sustainable manner (such that the total
stock of the resource does not diminish in size), biomass can be regarded as a form
of renewable energy. (Nicholls, Monerud and Dykstra, 2008).
Although fossil fuels are also made from the remains of dead animals and plants,
fossil fuels are not considered renewable on any scale of time that matters to
humans (Shafiee and Topal, 2009).
1.1. BIOMASS AS AN ENERGY SOURCE
Biomass is the oldest source of energy, in use since mankind first harnessed fire and
used wood as a source of heat, light, and power. For centuries before the invention
of the steam and internal combustion engines, most of the world’s energy came
from biomass. The advent of industrialisation created the need for a large quantity,
and more concentrated source, of energy. This led to large-scale exploration and
utilisation of fossil fuels (Winandy et al, 2008). Nonetheless, biomass still accounts
for 10 percent of global energy use, which is approximately five times more than the
energy generated from hydroelectric power (IEA, 2006). In the United States alone,
about eleven gigawatts (GW) of electrical power are generated from bioenergy
sources. This makes biomass the second-largest US renewable energy source next to
hydropower (94 GW), and more significant than wind energy (5 GW) and geothermal
(2.7 GW) (Nicholls et al, 2008).
In the Less Developed Countries (LDCs), biomass accounts for almost one-third of all
energy consumption. In fact, in sub-Saharan countries biomass accounts for more
than 80 percent of all energy needs, and is primarily used for cooking, lighting and
heating (Palz and Kyramarios, 2000). Figure 1 shows world energy demand by
source.
With the growing realisation of the impact of fossil fuels on global warming, coupled
with volatile energy prices and an emerging energy security agenda, there is a
renewed interest in using biomass as a carbon-neutral and cost-effective alternative.
For example, Nicholls et al (2008) state that wood energy could potentially supply up
to 10 percent of U.S energy demand. Currently it is below four percent and is
expected to grow to five percent by 2020. As shown in Table 1, Wright (2006) put US
biomass consumption at a lower level of 2.8 percent in 2005 and Brazil at 27.2
percent.
54
2007
World
EnergyDemand
Demand by
by Source
Source (IEA, 2006)
Figure 1: 2007
World
Energy
Nuclear, 6.30%
Hydroelectric,
2.20%
Biomass & Waste,
10.00%
Petroleum, 35.00%
Geothermal, Solar
& Wind, 0.50%
Coal , 25.30%
Natural Gas,
20.70%
Biomass can be used as an energy source in a variety of ways: as a direct combustion
feedstock in home stoves, thermal power plants, furnaces and boilers (possibly in
combination with coal or other fossil fuels); or as a feedstock for pyrolysis,
gasification, charcoal production, briquetting, transesterification or fermentation
(the latter two for producing biodiesel and bio-ethanol (Kelly, 2009).
Table 1. Biomass Consumption by Country (Wright, 2006)
Country
Total (EJ6)
Biomass (EJ)
Biomass %
Brazil
7.3
1.98
27.2
China
45.5
7.5
16.4
Canada
13.1
1.77
13.5
Sweden
2.2
0.34
15.9
Denmark
0.83
0.098
11.8
EU-25
70.5
2.75
3.9
U.S
103.4
2.92
2.8
UK
9.48
0.06
0.6
1.2. PURPOSE
The purpose of this chapter is to evaluate the opportunities, barriers and costs
associated with utilising biomass for thermal combustion in cement factories. It
seeks to address the following questions:


6
Is it possible to use biomass / biomass residues in cement plants?
How is cement produced and where can biomass be used?
18
EJ – exajoule = 10 joules
55







What engineering modification or redesign of cement plants is required to
burn solid biomass in cement kilns?
What are the experiences of the global cement industry and available
technologies?
What preparation methods are needed to make biomass acceptable in an
industrial application, such as size reduction and drying?
What are the benefits?
o Environment
o Economical
o Social
What are the barriers for use of biomass in cement kilns?
o Cost
o Environmental, regulatory and legal issues
o Technical, perception and skills
What are the environmental and health and safety risks?
Finally, recommendations are put forward, highlighting the potential benefits
of using biomass in Ethiopia’s cement factories.
2. CEMENT CHEMISTRY AND IMPACT ON THE ENVIRONMENT
Cement production is a large user of fossil fuels and producer of greenhouse gases
(GHGs) (Worrell et al, 2001). In cement production, there are three sources of
greenhouse gases.
1. The first source comes from the inherent nature of cement production. Cements
are made from limestone, which predominantly contains more than 90 percent
calcium carbonate (CaCO3). As shown in chemical equation 1, when heat is applied to
CaCO3 it dissociates into calcium oxide, which is the main ingredient for cement, and
carbon dioxide, which is a greenhouse gas.
CaCO3
CaO + CO2 …………. (1)
Heat ~850°C
For every 100 grams of calcium carbonate heated in a kiln above 750°C, about 44
grams of carbon dioxide and 56 grams of calcium oxide are produced. In effect, for
every 56 grams of calcium oxide that is used by the construction industry, about 44
grams of carbon dioxide are released into the atmosphere. According to the
European Cement Association (2009a), approximately 525kg CO2 per tonne of
‘clinker’ is produced. (Clinker is a solid intermediary cement product that is formed
at high temperature through total or partial fusion of cement raw materials). In 2007
alone about 2.77 billion tonnes of cement were produced globally, which means up
to 1.45 billion tonnes of CO2 were released from de-carbonisation of CaCO3 alone
into the atmosphere.
56
Table 2. 2007 World Cement Production by Region
(European Cement Association, 2009a)
Cement Production
Percentage [ % ]
Asia
70.1
China
48.7%
Japan
2.4%
India
6.1%
Other Asia
12.9
USA
3.4
Other America
6.2
European Union 27
9.7
Africa
4.4
Oceania
0.4
CIS
2.4
2. The second source of greenhouse gases comes from the combustion of carboncontaining fossil fuels such as methane, furnace fuel, coal or alternative fuels such as
biomass, re-ground tyres, and household and industrial wastes.
The mechanism by which carbon-containing fuel burns to give off carbon dioxide is
given in equation 2 using the smallest hydrocarbon compound, methane (CH4).
CH4 + 2 O2 →
CO2 + 2 H2O
………………(2)
The European Cement Association (2009a) estimates that overall carbon dioxide
production from combustion of fuel in the kiln is approximately 335 kg of CO2 per
tonne of cement.
3. The third source of carbon dioxide derives from the use of electricity produced by
power stations that are burning fossil fuels. This accounts for approximately 50 kg of
CO2 per tonne of cement produced (European Cement Association, 2009a).
Countries, such as Ethiopia, that generate a significant fraction of their electricity
from hydroelectric power stations do not produce large quantities of carbon dioxide
from the use of electrical motors. However, cement plants in these countries do, of
course, produce carbon dioxide from the first two sources.
When all the carbon dioxide produced from the three sources is added together, the
cement industry releases about 0.8 tonne of carbon dioxide into the atmosphere per
tonne of cement produced. This makes cement production one of the largest sources
of greenhouse gases, producing 5 percent of global emissions (Worrell et al, 2001).
This is more than the emissions from the global steel industry. According to the
Intergovernmental Panel on Climate Change (IPCC), the steel industry accounts for
between 3 to 4 percent of total world greenhouse gas emissions (World Steel
Association, 2007).
57
Carbon dioxide (CO2) from decarbonisation of limestone can be reduced by diluting
cement clinker with raw, thermally untreated rocks such as pumice7, gypsum8,
pozzolan9 or ground furnace slag10. For example, pumice rock can be added up to 15
percent with some compromise on physical properties, strength or setting time of
cement for less critical constructions (Hossain, 2003). Hence, carbon dioxide from
decarbonisation of limestone can be reduced – but cannot be fully eliminated – as
long as cement is made from CaCO3. There is ongoing research into the development
of ‘eco-cement’ made from magnesium oxide (MgO) which can absorb carbon
dioxide and water to set and harden (Harrison, 2009). But the chemistry of cement
per se (as opposed to the energy sources used to make the cement) is beyond the
scope of this chapter and will not be considered further.
However, CO2 from the burning of fossil fuels can be reduced and, even more
importantly, can be made carbon-neutral with the utilisation of biomass as an energy
source for pyroprocessing.
To understand how this can be achieved, it is important to understand how cement
is produced and the types and amounts of energy needed to make cement.
2.1 CEMENT PRODUCTION PROCESS
Cement manufacturing starts with the quarrying of more than one raw material to
provide a source of necessary metallic oxides, such as calcium oxide from limestone,
iron and aluminium oxides from clay and silicon oxide from sand. Big rocks blasted
from quarries are crushed into gravel to facilitate transportation, blending and
milling into powder.
As shown in Figure 2, there are two processes of raw material grinding and blending.
Those are known as the ‘wet’ process and the ‘dry’ process. In the wet process, the
materials are ground and homogenised as slurry. This method was traditionally
preferred to achieve homogeneity of feedstock, but following improvements in dry
mixing and blending of powder materials most modern cement factors now use the
dry process because it requires less energy per tonne of clinker.
Using the dry or wet process, different types of cement are made for various
applications. The most common cement used in civil construction today is Ordinary
Portland Cement (OPC), but there are specialist cements such as rapid heat cement,
high alumina cement, oil-well cement, quick set cement, etc. For example, the raw
material for Portland Cement needs to be predominantly calcareous, rich in calcium
oxide (CaO) and with smaller amounts of siliceous (SiO2), aluminous (Al2O3) and ironrich (Fe2O3) content. Most often, between 70-99 percent of this calcareous
component comes from limestone deposits. Clay, sand or other minerals are also
7
Pumice is a volcanic rock.
Gypsum is a very soft mineral composed of calcium sulfate dihydrate.
9
Pozzolan is a siliceous rock which react with calcium hydroxide to form calcium silicates.
10
Ground granulated blast furnace slag is a by-product of iron and steel making.
8
58
milled with limestone in the correct proportions to achieve the following proportion
in the cement clinker (Chatterjee, 1983):
CaO
Al2O3
Fe2O3
SiO2
Trace amounts
63-67 %
4- 7%
2-4 %
21-24%
2-3%
Figure 2. Cement Production Steps in the Dry and Wet Process
(European Cement Association, 1998)
Once the correct proportions of these chemical compounds are achieved, the
material is fed into pre-heating cyclones to be heated to decompose some of the
CaCO3 and prepare it for further reactions that will take place. In the kiln, as shown
in Figure 3, the temperature of the material reaches around 1,450°C and the air
temperature is as high as 2,000°C. During this process of chemical reactions, a
black/grey solid mass is formed through partial or total fusion of the raw materials.
This is known as clinker (Peter, 2001).
59
Figure 3. Temperature Profile of Pre-Heating Cyclones and Kiln (Hansen, 1990)
3. CHEMICAL REACTION OF CLINKER PRODUCTION
The pre-heated material in the cyclones is dropped into the kiln for complete
reaction. As shown in Figure 4, most modern cement kilns are rotary shafts with a
diameter ranging from 3.5m to 5.5m and a length of between 50 to 200m. Coal, gas,
fossil fuels or alternative fuels are continuously injected into the kiln to burn and
produce heat of about 1,450°C in the clinker production zone.
A typical Portland cement clinker consists of at least two-thirds mass of calcium
silicates (CaO)3SiO2 and (CaO)2SiO2 and the remainder consists of aluminium oxide
(Al2O3), iron oxide (Fe2O3) and other oxides (Peter, 2001). Once the clinker is formed
it drops into a cooler where air is blown in at one end to remove the heat from the
partly-softened and molten material and turn it into small pebbles. The clinker is
then ground in a cement mill – with or without “extender minerals” such as pumice,
gypsum, pozzolan or ground furnace slag – to produce cement.
To carry out these operations a large amount of electrical and fossil fuel energy is
used, which will be discussed in the next section.
60
Figure 4. Kiln Source
3.1 ENERGY CONSUMPTION OF THE CEMENT INDUSTRY
Cement production is one of the largest users of fossil fuels. According to energy
consumption benchmarking carried out in Canada, the energy cost of cement
production is between 25-35 percent of the total direct cost of cement production. A
similar analysis carried out in Poland estimated energy costs to be between 30-40
percent of the total costs of cement production (Mokrzycki, Uliasz-Bochenczyk and
Sarna, 2003). Messebo Cement factory in Ethiopia reports that it spends up to 60
percent of its total cost of production on imported furnace fuel, which is
exceptionally high compared with the industry standard (Addis Fortune, 2007). This
figure is probably distorted by cheap labour and other costs. Nonetheless, this high
proportion of energy cost has been a major driver for the industry to search for costeffective and alternative fuels.
Fuel consumption at a cement plant depends on the type of process the plant uses.
As shown in Table 3, total energy consumption used during the wet cement
production process is much higher than in the dry kiln process.
Table 3. Typical Fuel Consumption of Three Kiln Types
(Energy Innovation Initiative in Canada, 2001)
Kiln Type
Average Fuel Consumption
GJ/tonne clinker
Wet Kilns
6.0
Dry Kilns – Single stage pre-heater
4.5
Dry Kilns – Multi-stage pre-heater
3.6
Ruth et al (2000) estimate that the most efficient and modern kilns could use as little
as 3,200 MJ of energy per tonne of clinker produced. Assessing the Polish cement
industry, Mokrzycki (2003) derived average energy consumption of Polish factories
61
at around 4,100MJ per tonne of clinker. On average, Mokrzycki (2003) states that the
energy required for the production of one tonne of cement is about 120 kg of coal.
Another study carried out in Pakistan suggests that about 85 kg of furnace oil is used
to produce a tonne of cement (Kazmi, 1996). Ethiopia’s cement factories use
imported furnace fuel, probably with similar energy efficiency to that of Pakistan.
The scope of this report is to assess the use of fuel directly injected into the rotary
kiln to generate flame and heat of around 1,450°C. This heat activates the
decomposition of calcium carbonate and facilitates solid state reactions between
aluminium, iron, silicon and calcium oxides to produce a new chemical structure
substance called clinker. To achieve these reactions, three types of fuels are
commonly used.
3.2 TYPES OF FUELS USED IN CEMENT KILNS
In the context of the cement industry, there are three sources of fuels used in kilns.
These are fossil fuels, biomass, and non-renewable wastes.
1. Fossil Fuels: Fossil fuels represent the main sources of energy used in cement
production. Principal fossil fuels used are coal, petcoke and petroleum-based
fuels such as natural gas and heavy furnace fuel.
2. Biomass: These materials are, in principle, ‘renewable’ because they can be regrown at a rate equal to, or greater than, the rate of harvesting; they are
‘carbon-neutral’ because plants absorb carbon dioxide as they grow. Biomass
waste such as forest products, fuelwood, foliage, shavings, agricultural crops,
cotton stokes, rice straw, sugarcane, flower farm waste and wheat straw are
widely used as renewable and carbon-neutral fuels. Industrial-scale animal
wastes, such as bones, fats, meats and other animal wastes, also fall under the
biomass category.
3. Non-renewable wastes: These materials are wastes or materials at the end of
their service lives. They can be burnt in the cement kiln to recover energy and
conserve fossil fuels that would have otherwise been used. Some, such as
plastics and rubber wastes, can also cause environmental hazards when dumped
in landfills. Rubber tyres, plastics, hydraulic oil, grease and hydrocarbon-based
household or industrial wastes can be used as an energy source in cement
factory kilns.
The European Cement Association (1998) states that “*w+aste is used in cement
manufacturing as an alternative fuel and raw material, thereby providing a
significant contribution to waste management. Unlike incinerators, the cement
manufacturing process “absorbs” all of the elements present in the burnt waste.
In this way, it cuts both its production costs and global greenhouse gas
emissions. Today, on average, alternative fuels provide about 17 percent (up to
72 percent in some regions) of thermal energy consumption in European
cement plants” (European Cement Association, 1998).
62
Though there are no clear specifications for determining what would be a good
waste fuel, Lafarge Cement, for example, has developed the following
specifications to protect the environment and conserve the efficiency of their
cement kilns (Mokrzycki et al, 2003):





Calorific value – over 14.0 MJ/kg (weekly average)
Chlorine content – less than 0.2 percent
Sulphur content – less than 2.5 percent
Polychlorinated Biphenyls (PCB) content – less than 50ppm
Heavy-metal content – less than 2,500 ppm, out of which:
 Mercury (Hg) – less than 10ppm, and
 Total cadmium (Cd) and thallium (Tl) less than 100ppm
Most hydrocarbon-based materials are safe to burn in the kiln to provide energy as
long as they meet the above guidelines. Results in Table 4 give a rough range of
calorific values for different cement fuels materials.
Table 4: Calorific Values of Different Fuels (Source: Hansen, 1990)
Low Heat Value
High Heat Value
(LHV)
(HHV)
MJ/kg
MJ/kg
Coal
27.8
29
Coal Fines
20.4
21.5
Petroleum Coke
29.7
32.8
Liquid Hazardous Waste22.6
25.8
Derived Fuel
Waste Tyre
31.5
33.0
Wood
19.7
20.7
Hog Fuel Sawdust
19.7
21.2
Municipal Waste
13.2
15.1
As a result of these calorific value differences, the fuels cannot be replaced by each
other at a one-to-one ratio. An adjustment has to be made to compensate for the
loss of calorific value. For example, an approximate 1:1.4 coal-to-wood ratio is
needed to replace coal with wood to achieve similar heat energy in the kiln.
Though the scope of this chapter is principally interested in the use of biomass, it
discusses non-renewable waste materials as a source of fuels in the cement industry
for two reasons:
First, finding a sustainable supply of biomass with uniform calorific value could be
challenging from a supply as well as a logistical perspective. This may discourage
cement factories from investing in modifications of their systems to burn biomass
fuels only.
63
Second, the cost of biomass could be higher and there may not be clear cost
benefits. Alternative waste fuels are often free, except the cost of collection,
transportation and processing of these materials. In some cases, waste may even be
‘negative cost’, where waste producers pay cement factories to take away their
wastes.
3.3 REAL-LIFE EXAMPLES OF BIOMASS USE IN CEMENT KILNS
Burning biomass in cement kilns is occurring more often due to volatile energy prices
and environmental benefits. The following are a few examples reported in various
publications.

Kenya: A cement firm operating in Kenya and Uganda claims to have cut its
“annual carbon dioxide emission by reducing its use of fossil fuels in cement
making by 20 percent. The company, which is partly owned by Lafarge Cement,
plans to reduce its use of coal by using wood from its own plantations as well as
coffee, rice and cashew nut husks. It is targeting a reduction of 132,000 tonnes
of CO2 per annum by 2010.” (Reuters, March 11, 2008; Lafarge, 2007).

Uganda: Uganda’s Hima cement factory burns coffee husks as a CDM project.
This project is expected to save the factory about $3.1 million in foreign
exchange per annum (Cement World, 21 May, 2008).

Malaysia: Investigations performed to evaluate the feasibility of using biomass
fuels as a substitute for fossil fuels in Malaysia’s cement industry have reached
the following conclusions (Evald and Majidi, 2004):
o The economic feasibility of using biomass in the cement industry is very
good, with a 263 percent financial internal rate of return (FIRR)
o The cement sector is an obvious choice for the use of solid biomass
because of the ease of replacement of coal.
o For the cement industry, the combination of a very large volume of fuel
substitution involving a relatively small investment cost allows for
significant savings from the use of alternative fuels.

Germany: Heidelberg Cement claims to have increased the use of alternative
fuels up to 78 percent in one of its plants and 66 percent in another. It uses
tyres, plastics, paper residues, animal meal, grease and sewage sludge to replace
fossil fuels. It states that the company had to invest EURO 8 million in one plant
and another EURO 4 million on storage equipment, homogenization and dosing
installations for flexible use of alternative fuels (Hridelberg Cement, 2009a).

Indonesia: Heidelberg Cement’s Indonesian subsidiary was approved as the first
CDM project in Indonesia in 2005. The company claims to have increased the
use of alternative fuels, in particular rice husks and residues from palm oil
production, replacing coal (Hridelberg Cement, 2009b).
64

Poland: Six cement plants in Poland currently use alternative fuels. Lafarge
Poland Ltd. has been using combustible fractions of municipal wastes, liquid
crude-oil derived wastes, car tyres, waste products derived from paint and
varnish production, expired medicines from the pharmaceutical industry, bone
meal provided from meat processing plants, coke from the chemical industry
and emulsified oil from a refinery (Mokrzychi et al, 2003)..

India: Cement companies in India are using non-fossil fuels including agricultural
wastes, sewage, domestic refuse and used tyres, as well as a wide range of
waste solvents and other organic liquids (Bernstein and Roy, 2007). The Indian
Cement firm ACC is using cow dung, old shampoo, soap, plant sludge and
municipal waste as alternatives to fossil fuels (Cement World, 2008).

USA: In the United States, approximately 5 percent of fuel used in the cement
industry comes from renewable and non-renewable waste fuels such as wood,
tyres and other non-hazardous and hazardous materials. Various sources
suggest the availability of millions of tonnes of wood that could be used in
cement factories to reduce greenhouse gas emissions and minimise forest fires
(Mackes and Lightburn, 2003).

UK: Cemex cement factory in Rugby uses alternative fuels such as tyres and
‘climafuel’, which is derived from household and commercial wastes. The
‘climafuel’ can contain at least 50 percent biomass, displacing nearly 180,000
tonnes of fossil fuel CO2 (Cemex, 2009; Cement News, January 2009). The
Lafarge plant at Hope uses bone meal (MBM) which is expected to reduce
30,000 tonnes of CO2 emissions per year (Cement World, October 2008).

Austria: Austria’s cement factories were amongst the earliest to start burning
tyres (since the 1980s), and have been burning solid waste such as plastics,
paper, textile and composite materials since 1993. All nine cement plants in
Austria use solid waste to various degrees (European Cement Association, 2009).
One of the factories, Wietersdorfer & Peggauer cement plant, claims to have
used alternative fuels substituting up to 70 percent of fossil fuels (Zieri, 2007).

Tunisia: A feasibility study carried out to study the use of municipal solid waste
(MSW) as a replacement for natural gas in the cement industry was found to be
unattractive economically due to the high cost involved in collection and sorting
of the MSW and government subsidies on natural gas imports (Lechtenberg,
2008).

Canada: St. Mary Cement in Ontario, Canada, wants to replace 13 percent of its
fuel consumption with wastes such as paper sludge left over from recycling and
plastic films. A factory in British Colombia uses renewable synthesis gas products
from its gasifier, enabling it to replace 6 percent of its fossil fuel consumption
(Dufton, 2001)
65

Portugual: Cement producer Cimpor Cimentos de Portugal is using hazardous
hydrocarbon waste in its plant in Souselas, Central Portugal (Cement World,
2008).
The list of cement factories using biomass and waste fuels is longer, but the above
diverse examples are sufficient to strengthen the argument that:
1. Biomass and alternative fuels can be used in the cement industry.
2. Biomass, as well as non-renewable waste fuels, can be an economical
alternative to fossil fuels.
3. There is well-established materials preparation, feeding and burning technology
that can be purchased by cement factories to adopt a co-firing technology.
It is clear that using biomass in the cement industry is possible and achievable. In the
following section some of the benefits are discussed.
4. BENEFITS OF USING BIOMASS AND ALTERNATIVE FUELS
The use of renewable biomass can generate environmental and economic benefits.
4.1 ENVIRONMENTAL
Biomass is a renewable energy resource that can be replaced by growing trees, crops
or other vegetation to maintain the level of sequestered carbon in the environment.
In addition to capturing carbon dioxide, planting vegetation protects land fertility,
prevents solid erosion, reduces sedimentation at dams and water reservoirs,
provides ecosystems for wildlife and insects, and, of course, produces wood for highvalue timber use as well as biomass.
4.1.1
HOW BURNING BIOMASS HELPS THE ENVIRONMENT
Plants absorb carbon dioxide during photosynthesis. This cycle continues as long as
trees are planted to absorb carbon dioxide, to ‘cancel out’ the carbon dioxide
released from combustion of the cultivated biomass. That is why sustainable
biomass is considered to be carbon-neutral, with no net increase of carbon dioxide
into the atmosphere.
4.2 BENEFITS OF USING ALTERNATIVE WASTE FUELS
The use of waste as alternative fuels in the cement industry has numerous
environmental benefits, such as:

Alternative fuels reduce the use of fossil fuels.
66
 Contributes towards lowering emissions of greenhouse gases from materials
that would otherwise have to be incinerated (with corresponding emissions) or
left in the landfill to decompose (and generate methane).

Maximises the recovery of energy from waste. All the energy is used directly in
the kiln for clinker production.

Maximises the recovery of the non-combustible part of the waste and
eliminates the need for disposal of slag or ash, as the inorganic part is
incorporated into the cement.

Improves waste management and public health. High temperatures in the kilns,
long residence times and the ability to absorb inorganic residue/ash allow the
complete destruction of combustible hazardous waste while recovering the
energy they contain in an environmentally sound manner (Hansen, 1990; Van
Loo, 2006). For these reasons, the cement industry is recognised by some
European governments as an essential part of their waste management policy
(European Cement Association, 1998).

The only viable means of safe, permanent disposal of this combustible waste is
by thermal treatment. Cement kilns are not only ideally suited for the safe
disposal of this material, but they also can recover the energy to reduce use of
fossil fuel.
4.3
ECONOMIC BENEFITS OF USING BIOMASS AND ALTERNATIVE WASTE FUELS

Between 30-40 percent of the total cost of cement production is accounted
for by energy needs. This means a significant reduction in cost can be
achieved by using renewable and waste fuels. For example, the study carried
out in Malaysia estimates that a 263 percent FIRR can be achieved (Evald and
Majidi 2004). Hence, burning biomass and waste as a source of energy could
save significant costs.

Burning biomass and waste can save foreign currency by replacing imported
fuels.

Provides energy security for land-locked countries such as Ethiopia and
hedges against volatile global energy markets.
5. TECHNOLOGY
Biomass burning in cement kilns is a well-established technology, which can be
purchased or custom-made in developing countries. Existing feeding systems of
alternative fuels into kilns are robust and it is possible to feed in biomass ranging
from small pellets to full-sized tyres. For ease of handling and achieving uniform
calorific input into the kiln, it is important to reduce biomass materials to
67
manageable sizes. For example, solid woody biomass needs to be chipped into small
sizes, pre-dried, and unwanted materials such as stone and metal bits removed
(Nicholls et al, 2008).
Figure 5: Rubber Tyre Feeding System through Bottom of Pre-Calcination Region
(Derksen, 2009)
Alternative and biomass materials can be fed in 3 principal ways:
1. As shown in Figure 5, large-size biomass and alternative waste fuels such as
tyres can be fed into the kiln in specially-made gates at the bottom of the precalcining region.
2. It is possible to grind wood along with cement raw materials to feed as
pulverised fuel. However, this process may cause two potential problems
(Mackes and Lightburn, 2003):

Due to the low ignition temperature of wood, fire may start during the
milling process unless special precautions are put in place.

It may also affect the efficiency of the mill if the moisture content of the
wood is high. Though it may make it easier to feed into the kiln, grinding
the biomass adds to costs.
3. Companies that use coal as a main source of energy can blend biomass or
alternative materials with coal to feed it into the kiln using a coal-feeding
system.
Of the three methods described, feeding through specially-made gates at the precalcination region is the safest choice. There are already rotary valves or screw
feeders on the market that can be easily installed. The screw feeder has certain
advantages over the rotary valve as coarse materials can easily be pushed into the
pre-calcining region and the feed rate of the biomass can be regulated by the speed
of the screw. Figures 6a and 6b shows examples of large and small screw feeders.
68
Figure 6: Example of Screw Conveyor to Feed the Whole Tyre
(Skidmore, 2008)
Conveyer belts are used to transport biomass materials from storage to feeding
hoppers. From the hoppers, a screw conveyor feeds the biomass into the precalcination region.
5.1 POTENTIAL BARRIERS
Burning alternative fuels is beneficial to cement companies as well as the
environment. But there are barriers to successful utilisation of biomass in the
cement industry:

Supply: obtaining a constant and sufficient amount of biomass.

Consistency: the variability in calorific value of biomass may affect the
efficiency and output of kiln production.

Harvesting: although extensive biomass resources are available in many
countries, often such biomass is spatially dispersed and difficult to aggregate
together.
69

Cost: the capital costs for the preparation and densification of biomass at
harvesting sites, as well as modifications of the cement factory, may not
justify biomass use.

Accessibility: infrastructure barriers, roads, and transportation.

Skill barriers. Mulugeta (2008) states that despite wood-based fuels being
used by more than 90 percent of the population in Ethiopia, there are no
biomass research centres in the country that study sustainable biomass
development, help to upgrade skills, or that can replenish stocks.

Scepticism: Management and decision-makers may regard burning
household waste in modern factories with some degree of scepticism. Hence,
champions are needed to overcome this resistance to change.

Unwanted materials: Biomass often contains unwanted materials, such as
metal wastes that may damage machines and that need to be removed using
metal detectors. The European Cement Association (2009a) also classify
nuclear waste, infectious medical waste, entire batteries, and untreated
mixed municipality waste as unsuitable for the cement industry and public
health.
5.2 ADVERSE EFFECTS ON THE ENVIRONMENT

Deforestation: Industrial-scale usage of biomass may add to already-present
stresses on biomass resources, thereby inadvertently encouraging
deforestation (Mangoyana, 2009).

Hazardous substance release: In many developing countries, there may not
be stringent regulations, or enforcement of regulations, regarding air quality.
This may invite companies to take a less responsible approach to burning
chlorine-containing wastes such as PVC pipes and PVC packaging that may
lead to formation of toxic dioxins (polychlorinated dibenzo-p-dioxins and
polychlorinated dibenzofurans) or industrial wastes containing toxic metals
such as mercury, cadmium or chromium (Court, 2005; WHO, 2007).

Health: In the absence of proper treatment, transportation of household and
industrial waste could spread germs and disease.
6. ECONOMIC AND ENVIRONMENTAL JUSTIFICATION FOR USING
BIOMASS IN ETHIOPIA
A total of 24 companies have permits to invest in cement production in Ethiopia, out
of which 13 have begun installation and construction work (All African News, April
70
2008). By 2011, the total amount of cement production in Ethiopia is estimated to be
17 million tonnes per annum (Taye, 2008). This is going to increase the competition
and price pressure on cement factories, squeezing their profit margins. This volume
will enable the country to jump from its current position of 78 th in the world ranking
of cement producers to one of the top 30, placing it above the UK, Canada and
Australia.
This will exert considerable pressure on energy supply in the country. The country
will probably have 24 cement factories within a short time, increasing cement
production from the current level of approximately 1.6 million tonnes to 17 million
tonnes. That means the country will have to import approximately 1.4 million tonnes
of furnace fuel. At the current market price of US$400 per tonne, the country may
need to spend billions of dollars on furnace fuel alone. This is simply unaffordable in
the context of a total national export value of US$1.5 billion dollars per year.
6.1 STRATEGIES AND BENEFITS IN ETHIOPIA
1. Farm Wastes: Coffee waste, cotton, oil processing, chat, sugarcane, flower
farms and processing plants can be used as seasonal sources of biomass.
2. Commercial Plantations: Cement factories can start commercial plantations
of trees on their own lands. The factories’ land could be used to plant trees at
the commercial level to harvest for cement production. According to
Ethiopian investment law, land for tree plantation is free and no lease fee is
paid on it.
3. High-value products: In addition to biomass fuel, high-value timber can be
sold to maximise the return on investment.
4. Public Health: The capital city, Addis Ababa, has no proper waste
management system. Household as well as industrial waste is dumped on
open land, causing environmental problems and health risks. Heavy pollution
of Koka Lake is a result of waste influx from tanneries, flower farms, industrial
facilities and household waste (Aljazeera, February 21, 2009). Having the
capability to burn alternative waste could encourage municipalities to invest
in waste-processing plants and industries to collect and supply hydrocarbonbased wastes to the cement industry. This would contribute to public health,
reduce methane emissions and save energy costs.
5. Hazard management: Liquid hazardous wastes that are often generated from
industrial hydraulics and automotive lubricant can be blended with furnace
oil to be burnt in the kiln, preventing the pollution of drinking water and
poisoning of aquatic life (Hansen, 1990).
6. Financial incentives: As international concern over global warming and
greenhouse gases arise, government and international organisations may
provide financial support for the utilisation of biomass, reducing the burden
71
on the industry. Biomass-switching in the cement industry also has a rich
pedigree in the Clean Development Mechanism (CDM).
7. CONCLUSIONS
The use of biomass and waste fuels is a growing area based on sound economic and
environmental benefits. Biomass fuel-switching is possible, achievable and beneficial
to the environment and companies that are willing to embrace it. Once
implemented, companies can also benefit from the generation of carbon credits
through the Clean Development Mechanism. Countries such as Ethiopia could save
foreign currency, create jobs and start a sustainable biomass industry. This would
help to reduce deforestation and soil erosion, while simultaneously offering social
benefits to rural communities.
8. SUMMARY
With the growing realisation of the impact of fossil fuels on global warming, there is
a renewed interest in the utilisation of biomass as a renewable and carbon-neutral
energy source. This chapter reviews the available literature with regard to the use of
biomass in clinker production in the cement industry, which is one of the largest
sources of greenhouse gases. The chapter reports experiences of different countries
that are using biomass and non-renewable waste fuels in cement production plants.
The technology of preparation, feeding, and burning of biomass in cement kilns is
widely available and could be purchased to implement a co-firing of biomass along
with fossil fuels.
Taking Ethiopia as an example, the chapter makes recommendations for formulating
a strategy for integrated biomass technology to achieve not only economic benefits
but also to deliver long-term energy security and sustainable development.
Published data confirms that this investment is economically justifiable and
environmentally beneficial.
72
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CDM Capacity Development in Eastern and Southern Africa
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by the United Nations Development Programme
1 UN Plaza, New York, New York, 10017, USA
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