Improved combustion in wood stoves

Improved combustion in wood stoves
Reduksjon av utslipp i vedovner
Mario Ortega
Master of Science in Product Design and Manufacturing
Submission date: August 2008
Supervisor:
Johan Einar Hustad, EPT
Norwegian University of Science and Technology
Department of Energy and Process Engineering
Problem Description
Background and objective.
Norway uses approximately half of the bioenergy consumption in wood stoves and fireplaces. An
amount of approximately 7 TWh is consumed in such units. Old stoves have been a source to large
particle emissions, and in 1998 new regulations came into force which limits these emissions.
However,to reduce these emissions further, new and improved combustion principles have to be
developed. SINTEF in co-operation with the Norwegian industry are running a project financed
partly by the Research Council emphasizing new technology developments in this field.
The Master thesis will take part in these studies developing new and improved technology for
emission reductions.
The following questions should be considered in the project work:
1. Literature studies on different technologies and methods for measurements and emission
reduction in wood stoves and fireplaces.
2. Suggest experimental tests for studying measurements in stack and dilution tunnel. The
experimental test setup shall be explained and give the reason for.
3. Do testing in accordance with the suggested experimental test setup.
4. Discuss the results and give an explanation of the obtained results
5. Discuss and give suggestions of the best way for measuring and testing emissions from wood
stoves and fireplaces.
Assignment given: 01. February 2008
Supervisor: Johan Einar Hustad, EPT
Preface
This Master’s Thesis report is the result of Mario Ortega’s work in the Department of Energy
and Process Engineering of the Norwegian University of Science and Technology (NTNU).
The project was developed within the Sócrates-Erasmus program during the spring of 2008.
This project has greatly increased my interest and motivation within the field of biomass
combustion and has improved my knowledge about emission reduction in small-scale wood
burning appliances.
I would like to thank my supervisors Prof. J.E. Hustad and M.Sc. Edvard K. Karlsvik for
their continuous guidance and help. Also, I would like to thank the NTNU and my home
university, the ETSI of Bilbao, for giving me the great opportunity of studying this year in
Norway in the fantastic city of Trondheim.
Special thanks go to my family and friends.
Mario Ortega Cela
Spring 2008
1
Abstract
There are two main ways of measuring particle emission from wood combustion. Firstly,
particles can be sampled directly in the chimney. Secondly, a dilution tunnel can be used,
thus cooling the flue gases parallel to diluting. The purpose of this work is to investigate the
differences between both measurements and establish which is the best method to measure
particle emission from wood combustion. The approach is to perform particle emission measurements in the chimney and in a dilution tunnel simultaneously during the combustion of
wood in a small-scale appliance. Moreover, Flame Ionization Analysis will be carried out to
understand the contribution of condensed organic compounds to the total particulate matter
emission.
The particle emission measured in the dilution tunnel was between 5 and 12 times higher
than in the chimney. The more unfavourable combustion conditions, the larger the difference
between both measurements was seen. The results also show a factor of about 2,5 between
both particle emission measured in the stack and Total Hydrocarbon content in the flue gas
and particle emission measured in the dilution tunnel, indicating that about 35 % of the
hydrocarbons measured in the stack with the Flame Ionization Detector condense along the
dilution tunnel accounting for approximately 85 % of the total particle emission found at this
location.
3
Contents
List of Figures
12
List of Tables
14
1 Introduction
15
2 Wood Combustion
17
2.1
Wood composition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
17
2.2
The combustion process . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
18
2.3
Firing habits in Norway . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
19
3 Emissions from Wood Combustion
3.1
3.2
21
Emissions from complete combustion . . . . . . . . . . . . . . . . . . . . . .
22
3.1.1
Carbon dioxide (CO2 ) . . . . . . . . . . . . . . . . . . . . . . . . . .
22
3.1.2
Particle emissions from complete combustion (ashes) . . . . . . . . .
22
Emissions from incomplete combustion . . . . . . . . . . . . . . . . . . . . .
22
3.2.1
Carbon Monoxide (CO) . . . . . . . . . . . . . . . . . . . . . . . . .
23
3.2.2
Volatile Organic Compounds (VOC) and Polycyclic Aromatic Hydrocarbons (PAH) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
24
Particle emissions from incomplete combustion . . . . . . . . . . . . .
26
3.2.3
5
CONTENTS
6
3.3
Influence of particle sampling . . . . . . . . . . . . . . . . . . . . . . . . . .
27
3.4
Particulate Matter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
28
3.5
Particulate matter effects on Human health . . . . . . . . . . . . . . . . . .
29
3.6
Measures for particle emission reduction . . . . . . . . . . . . . . . . . . . .
30
4 The Standards
4.1
31
EN-13240 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
32
4.1.1
Description of performance test at nominal heat output . . . . . . . .
33
4.1.2
Requirements for performance test at nominal heat output . . . . . .
33
4.2
German - Austrian particle test method . . . . . . . . . . . . . . . . . . . .
34
4.3
United Kingdom particle test method . . . . . . . . . . . . . . . . . . . . . .
36
4.4
CEN tasks for a common particle emission test method . . . . . . . . . . . .
37
4.5
U.S.A particle test method . . . . . . . . . . . . . . . . . . . . . . . . . . . .
38
5 The Stove: Jøtul F3
41
5.1
Main features of the stove . . . . . . . . . . . . . . . . . . . . . . . . . . . .
41
5.2
Activation zone . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
43
5.3
Stove’s air vents . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
43
5.4
Wood consumption and nominal heat output
44
. . . . . . . . . . . . . . . . .
6 The Test Facility and the Measurements
47
6.1
The test facility . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
47
6.2
The measurements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
48
6.2.1
CO, CO2 and O2 measurements in the stack . . . . . . . . . . . . . .
50
6.2.2
CO and CO2 measurements in the dilution tunnel . . . . . . . . . . .
51
CONTENTS
7
6.2.3
Particle measurements in the stack and dilution tunnel . . . . . . . .
52
6.2.4
Hydrocarbons measurement in the stack . . . . . . . . . . . . . . . .
53
The Norwegian Standard . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
54
6.3.1
The fuel . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
54
6.3.2
The different burn rate categories . . . . . . . . . . . . . . . . . . . .
55
6.4
Running a test according to the Norwegian Standard . . . . . . . . . . . . .
56
6.5
Running a test according to the EN-13240 Standard . . . . . . . . . . . . . .
57
6.3
7 Results and Discussion
59
7.1
Fuelsim - Transient . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
59
7.2
Emission factors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
60
7.3
Problems during testing . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
60
7.4
Appropriate use of the Flame Ionization Analyzer . . . . . . . . . . . . . . .
61
7.5
Combustion conditions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
61
7.6
Particle emission . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
62
7.7
Efficiencies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
64
7.8
Comparison between stack and dilution tunnel . . . . . . . . . . . . . . . . .
66
7.9
Accuracy and Reliability . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
73
8 Conclusions
75
Bibliography
77
CONTENTS
8
A Calculations
81
A.1 Gas meter volume . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
81
A.2 Particulate concentration . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
82
A.3 Particulate emission rate . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
82
A.4 Adjusted particulate emission rate
. . . . . . . . . . . . . . . . . . . . . . .
82
A.5 Particulate Emission Requirements . . . . . . . . . . . . . . . . . . . . . . .
83
A.6 Calculation of weighted particulate emission . . . . . . . . . . . . . . . . . .
83
B Norwegian Standard Graphs
C EN-13240 Graphs
85
117
List of Figures
2.1
Two-staged air combustion . . . . . . . . . . . . . . . . . . . . . . . . . . . .
19
3.1
CO emission as a function of the excess air ratio λ . . . . . . . . . . . . . . .
24
3.2
Influence of combustion temperature in PAH emission . . . . . . . . . . . . .
25
3.3
Hydrocarbons from wood burning (%weight) . . . . . . . . . . . . . . . . . .
26
4.1
Flue draught values
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
34
4.2
Sampling train according to VDI 2066 . . . . . . . . . . . . . . . . . . . . .
35
4.3
Filter system according to VDI 2066 . . . . . . . . . . . . . . . . . . . . . .
35
4.4
Test facility used in The United Kingdom . . . . . . . . . . . . . . . . . . .
36
4.5
CEN proposed test facility . . . . . . . . . . . . . . . . . . . . . . . . . . . .
37
4.6
CEN proposed sampling train . . . . . . . . . . . . . . . . . . . . . . . . . .
38
4.7
Test Facility used in EPA method 5G (USA) . . . . . . . . . . . . . . . . . .
39
5.1
Air flow pattern inside the stove . . . . . . . . . . . . . . . . . . . . . . . . .
42
5.2
Secondary air system . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
42
5.3
Front view of Jøtul F3 with both air vents . . . . . . . . . . . . . . . . . . .
44
6.1
Test facility according to the Norwegian standard . . . . . . . . . . . . . . .
48
6.2
Measurements in the stack . . . . . . . . . . . . . . . . . . . . . . . . . . . .
48
9
LIST OF FIGURES
10
6.3
Measurements in the dilution tunnel . . . . . . . . . . . . . . . . . . . . . .
49
6.4
Stack flue gas measuring unit . . . . . . . . . . . . . . . . . . . . . . . . . .
51
6.5
Sampling unit for particle measurements . . . . . . . . . . . . . . . . . . . .
52
6.6
Filter holder . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
53
6.7
Size of the standard test fuel . . . . . . . . . . . . . . . . . . . . . . . . . . .
54
6.8
Damper used during EN-13240 tests . . . . . . . . . . . . . . . . . . . . . . .
57
7.1
Norwegian Standard - Particle emission related to burning rate . . . . . . . .
63
7.2
EN Standard - Particle emission related to burning rate . . . . . . . . . . . .
64
7.3
Norwegian Standard - PMs , Total Hydrocarbon content in the flue gas and PMd 67
7.4
Norwegian Standard - Comparison of PM emission in stack and dilution tunnel 67
7.5
Norwegian Standard - Ratio between PM in the dilution tunnel and PM in
the stack . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
68
Norwegian Standard - Ratio between THC + PM in the stack and PM in the
dilution tunnel . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
68
Norwegian Standard - Percentage of hydrocarbons measured with the FID
found as particles in the dilution tunnel . . . . . . . . . . . . . . . . . . . . .
69
Norwegian Standard - Percentage of total PM measured in the dilution tunnel
consisting of condensed organic matter . . . . . . . . . . . . . . . . . . . . .
69
Norwegian Standard - Ratio PMd /PMs related to combustion conditions . .
70
7.10 EN Standard - Comparison of PM emission in stack and dilution tunnel . . .
71
7.11 EN Standard - Ratio between PM in the dilution tunnel and PM in the stack
72
7.12 Typical look of the filters after performing the tests . . . . . . . . . . . . . .
73
B.1 Test 16 - Graphs (a)-(c) . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
87
B.2 Test 16 - Graphs (d)-(f) . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
88
7.6
7.7
7.8
7.9
LIST OF FIGURES
11
B.3 Test 16 - Graphs (g)-(h) . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
89
B.4 Test 17 - Graphs (a)-(c) . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
90
B.5 Test 17 - Graphs (d)-(f) . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
91
B.6 Test 17 - Graphs (g)-(h) . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
92
B.7 Test 18 - Graphs (a)-(c) . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
93
B.8 Test 18 - Graphs (d)-(f) . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
94
B.9 Test 18 - Graphs (g)-(h) . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
95
B.10 Test 19 - Graphs (a)-(c) . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
96
B.11 Test 19 - Graphs (d)-(f) . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
97
B.12 Test 19 - Graphs (g)-(h) . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
98
B.13 Test 20 - Graphs (a)-(c) . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
99
B.14 Test 20 - Graphs (d)-(f) . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
100
B.15 Test 20 - Graphs (g)-(h) . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
101
B.16 Test 21 - Graphs (a)-(c) . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
102
B.17 Test 21 - Graphs (d)-(f) . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
103
B.18 Test 21 - Graphs (g)-(h) . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
104
B.19 Test 22 - Graphs (a)-(c) . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
105
B.20 Test 22 - Graphs (d)-(f) . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
106
B.21 Test 22 - Graphs (g)-(h) . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
107
B.22 Test 23 - Graphs (a)-(c) . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
108
B.23 Test 23 - Graphs (d)-(f) . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
109
B.24 Test 23 - Graphs (g)-(h) . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
110
B.25 Test 30 - Graphs (a)-(c) . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
111
LIST OF FIGURES
12
B.26 Test 30 - Graphs (d)-(f) . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
112
B.27 Test 30 - Graphs (g)-(h) . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
113
B.28 Test 31 - Graphs (a)-(c) . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
114
B.29 Test 31 - Graphs (d)-(f) . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
115
B.30 Test 31 - Graphs (g)-(h) . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
116
C.1 Test 35 - Graphs (a)-(c) . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
119
C.2 Test 35 - Graphs (d)-(f) . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
120
C.3 Test 36 - Graphs (a)-(c) . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
121
C.4 Test 36 - Graphs (d)-(f) . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
122
C.5 Test 37 - Graphs (a)-(c) . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
123
C.6 Test 37 - Graphs (d)-(f) . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
124
C.7 Test 38 - Graphs (a)-(c) . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
125
C.8 Test 38 - Graphs (d)-(f) . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
126
C.9 Test 39 - Graphs (a)-(c) . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
127
C.10 Test 39 - Graphs (d)-(f) . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
128
C.11 Test 40 - Graphs (a)-(c) . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
129
C.12 Test 40 - Graphs (d)-(f) . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
130
List of Tables
2.1
Main constituents of the wood . . . . . . . . . . . . . . . . . . . . . . . . . .
17
3.1
Immision limit values for PM10 . . . . . . . . . . . . . . . . . . . . . . . . .
29
4.1
Carbon monoxide emission requirements . . . . . . . . . . . . . . . . . . . .
33
4.2
Efficiency requirements at nominal heat output . . . . . . . . . . . . . . . .
34
4.3
Average wood consumption rates for method 5G (USA) . . . . . . . . . . . .
39
5.1
Technical data according to EN-13240
. . . . . . . . . . . . . . . . . . . . .
44
5.2
Recommended fuel size . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
45
6.1
Measuring equipment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
49
6.2
Location of thermocouples . . . . . . . . . . . . . . . . . . . . . . . . . . . .
50
6.3
Gas analyzers used in the stack . . . . . . . . . . . . . . . . . . . . . . . . .
51
6.4
Gas analyzers used in the dilution tunnel . . . . . . . . . . . . . . . . . . . .
52
6.5
Flame Ionization Detector (FID) . . . . . . . . . . . . . . . . . . . . . . . .
53
6.6
Moisture content of the test fuel . . . . . . . . . . . . . . . . . . . . . . . . .
55
6.7
Burn rate categories according to the Norwegian Standard . . . . . . . . . .
55
7.1
Norwegian Standard - Combustion conditions . . . . . . . . . . . . . . . . .
62
13
LIST OF TABLES
14
7.2
EN Standard - Combustion conditions . . . . . . . . . . . . . . . . . . . . .
62
7.3
Norwegian Standard - Adjusted particle emission . . . . . . . . . . . . . . .
63
7.4
Norwegian Standard - Efficiencies . . . . . . . . . . . . . . . . . . . . . . . .
65
7.5
EN Standard - Data according to EN-13240 . . . . . . . . . . . . . . . . . .
65
7.6
Norwegian Standard - Comparison between stack and dilution tunnel . . . .
66
7.7
EN Standard - Comparison between stack and dilution tunnel . . . . . . . .
71
A.1 Particulate emission requirements in Norway . . . . . . . . . . . . . . . . . .
83
Chapter 1
Introduction
Wood is a renewable energy source considered to be CO2 -neutral with respect to the global
carbon cycle, i.e. provided that we do not fell more timber than what it grows, the combustion
of wood does not contribute globally to the greenhouse effect. Annually, the growth in
Norwegian forests exceeds the felling of trees. Therefore, in Norway, the forests will actually
benefit from human activities.
These are powerful reasons to increase the use of wood as an environmentally sustainable
fuel for heat and power generation, especially with the current prices of oil and natural gas.
Nevertheless, a further propagation of wood combustion may be hindered by the disadvantage
of its high particle emissions.
Since restrictions on particulate matter in the atmosphere are getting stricter due to its
adverse effects on human health, it will be neccesary to reduce sources of particulate matter
to the air. Biomass combustion is a relevant source of fine particles, especially in small-scale
applications like wood stoves. To assist the development of environmentally friendly wood
stoves it would be desirable to have a common standard for particle emission testing and
appliance certification. However, there are many kinds of methods used for this purpose and
there is no common standarized method within Europe.
One of the main differences between the various methods available is the location of the measurement. There are two main ways of measuring particle emission from wood combustion.
Firstly, particles can be sampled directly in the hot flue gases (in the chimney). Secondly, a
dilution tunnel can be used, thus cooling the flue gases parallel to diluting, simulating what
happens as the flue gas from the chimney goes out to the ambient air.
15
CHAPTER 1. INTRODUCTION
16
The aim of this project is the comparison between particle sampling in the stack and in a
dilution tunnel during wood combustion, to quantify the difference between both measurements and investigate which location is more representative of what truly happens when the
flue gases reach the atmosphere.
The approach is to perform particle emission measurements in the chimney and in a dilution
tunnel simultaneously during the combustion of wood in a small-scale appliance. Moreover,
Flame Ionization Analysis will be carried out to understand the contribution of condensed
organic compounds to the total particulate matter emission.
Firstly, the main characteristics of wood combustion will be explained briefly. Secondly, the
emissions from wood combustion will be described, followed by the presentation of the main
methods currently available for measuring particle emission from wood combustion. The
stove used during the tests will be presented next. In chapter 6, the test facility used and
the different measurements are described. Finally, the results are presented and discussed.
The main findings will be summarized in the conclusion.
Chapter 2
Wood Combustion
In this project, the combustion of wood as a batch process is of interest. During combustion,
the photosynthetic energy stored in the wood is released and converted into heat, infrared
radiation, light and other forms of energy.
2.1
Wood composition
The main components of wood are cellulose, hemicellulose and lignin. They are all made of
carbon, hydrogen and oxygen atoms. Wood is similar in structure to fiberglass. The fibrous
part of wood that is similar to glass fibers is called cellulose. The cellulose is embedded in
a material called lignin, which acts like the resin in fiberglass. Wood also contains a large
amount of water, as well as minerals, oils and other compounds.
The main constituents of the wood that will be used during the tests are presented in Table
2.1. The water content of the wood is not included. Being a very important factor, it will be
measured for each test fuel.
Wood
Spruce
Birch
Carbon
47,25 %
47,12 %
Hydrogen
6,3 %
6,22 %
Oxygen
46,38 %
46,55 %
Nitrogen
0,07 %
0,11 %
Table 2.1: Main constituents of the fuel [30]
17
CHAPTER 2. WOOD COMBUSTION
2.2
18
The combustion process
Every combustion requires three elements: the fuel, an oxidizer and a source of heat. When
these three elements are combined in the appropriate environment, combustion will occur. If
any of the elements is removed, combustion stops. In wood combustion, wood is obviously
the fuel, air is the oxidizer and the initial source of heat is usually the flame from a match or a
lighter. When burning wood for heat production it is desired to have a complete combustion.
This means that all the hydrogen in the wood is converted to water and all the carbon is
transformed to carbon dioxide.
The combustion of wood can be divided in three main processes:
• Pre-heating and evaporation: The wood is heated to evaporate and drive off moisture.
Since vaporization robs heat energy from the combustion process, it lowers the temperature in the combustion chamber, which slows down the combustion process [7].
This makes the water content in the wood a very important factor. Wood with a high
moisture content is hard to ignite.
• Devolatilization/Gasification: When heated to temperatures over 300 ºC wood turns
into gaseous components (volatile components like CO, H2 , CH4 and others) and solid
carbon (char). At 500 ºC about 85% by weight of the wood substance is converted into
gaseous compounds [14]. This gaseous compounds contain between 50 and 60 percent
of the heat value of the wood.
• Combustion: After volatile gases are released, the remaining material is charcoal. When
the temperature is high enough, the flaming combustion of the released volatile gases
and the char oxidation take place. In batch combustion applications there will be a
distinct separation between a volatile and a char combustion phase, in both position
and time.
In most modern wood stoves air staged combustion with primary and secondary air inlet is
used. The wood is gasified with primary air before the combustible gases and the char are
oxidized with secondary air. Through the separation of the devolatilization and the gas and
char combustion the mixing of the fuel with air is improved, the combustion temperature is
increased and the emission of unburnt pollutants is reduced. The two-staged air combustion
is shown in Figure 2.1.
CHAPTER 2. WOOD COMBUSTION
19
Figure 2.1: Two-staged air combustion [2]
For the gasification process primary air should be added in an under stochiometric level
λ1 < 11 . Otherwise the oxidation takes place with primary air where the mixture is not
homogenous [2]. During the combustion it is very important that the fuel/air ratio is optimized. The optimum excess air is usually between 1,5 and 2 [14]. Higher excess ratios will
decrease the combustion temperature while lower excess air ratios will result in inadequate
mixing conditions. If there is too little excess air the carbon monoxide emissions increase
considerably as a result of the local shortage of oxygen.
2.3
Firing habits in Norway
Norwegians have always used wood as a source heat. However, the firing habits have changed.
In the past the houses were poorly insulated and there was always somebody at home that
could take care of the fire. Nowadays, nobody can take care of the fire through the night and
from the morning to the evening the members of the family are either at school or at work.
Furthermore, houses are now well insulated and usually made of wood. Therefore, to get a
confortable temperature at home, less heat output is needed. The tendency is then to fill
the stove with a big load of wood and nearly close the air supply so that the average wood
consumption is low and the fire lasts longer. This results in low efficiency, high pollutant
emission and coating of the chimney with risks of chimney fire [3]. This is the main reason
why emissions from wood combustion have become an increasing problem in Norway.
1
λ: Excess air ratio = effectively supplied air/stoichiometric amount of air
Chapter 3
Emissions from Wood Combustion
There are numerous pollutants resulting from wood combustion. However, in this chapter,
only the ones considered relevant for our project will be discussed. Apart from the pollutants
described later in detail, emissions from wood combustion can be also found as nitrogen
oxides (NOx ), nitrous oxide (N2 O), sulphur oxides (SOx ), heavy metals, PCDD/PCDF1 , etc.
Emissions from wood combustion can be divided into two groups: emissions from complete combustion (oxidized pollutants) and emissions from incomplete combustion (unburnt
pollutants). All the pollutants listed above belong to the first of this groups.
As it will be shown later, particle emissions can originate from both complete and incomplete combustion. When the combustion is efficient, almost all organic material is converted
to carbon dioxide and water, and few particles are formed (mostly inorganic particles). In
contrast, during poor combustion conditions, a lot of particles from incomplete combustion
are originated increasing drastically the total amount of emitted particles (now mostly condensed organic matter). This is a significant problem for residential wood combustion, since
this kind of appliances are usually poorly operated.
Besides the particles emitted directly from the combustion process (primary particles), secondary particles can originate in the atmosphere as a result of physical or chemical transformations from precursors emitted as gaseous pollutants. The four primary precursors of
secondary particles are sulphur dioxide, nitrogen oxides, ammonia and volatile organic compounds (VOCs).
1
Polychlorinated dibenzodioxin and dibenzofuran
21
CHAPTER 3. EMISSIONS FROM WOOD COMBUSTION
3.1
3.1.1
22
Emissions from complete combustion
Carbon dioxide (CO2 )
Like happens with any other carbon-containning fuel, CO2 is an important product of the
combustion of wood. However, emissions from wood combustion are considered to be CO2 neutral regarding the global carbon cycle. This is because the CO2 emitted during the
combustion of wood is considered to be equal to the CO2 absorbed by the trees during
the photosynthesis and similar to the amount of pollutant that would be emitted during
the natural decay of the wood. This is considered to be the main environmental benefit of
biomass combustion and the main advantage of biomass compared to fossil fuels.
3.1.2
Particle emissions from complete combustion (ashes)
Ashes are formed during the combustion or gasification of the inorganic material in the wood.
They can leave the combustion system as bottom ashes (that stay in the ash pan), fly-ashes
or vapour. If not avoided, fly-ashes leave the combustion chamber as particle emissions.
Fly-ashes consist of [7]:
• Coarse fly-ashes (particles with a diameter larger than 1 µm), which result from the
entrainment in the flue gas of ash and fuel particles from the fuel bed
• Aerosols (particles with a diameter smaller than 1 µm), which are formed from compounds (e.g. salts like KCl, NaCl, K2 SO4 )
3.2
Emissions from incomplete combustion
Complete combustion would only be possible under ideal conditions. In practice, this never
happens and incomplete combustion always occurs to some extend, resulting in added emissions. The main possible causes of incomplete combustion in biomass applications are [7]:
• Inadequate mixing of combustion air and fuel in the combustion chamber, which originates local fuel-rich combustion zones, i.e. local shortage of oxygen
• Overall lack of available oxygen
CHAPTER 3. EMISSIONS FROM WOOD COMBUSTION
23
• Too low combustion temperatures
• Too short residence times
Therefore, optimizing this factors will improve the combustion process resulting in less emissions from incomplete combustion2 . When sufficient oxygen is available, the combustion
chamber temperature is the most important factor due to its exponential influence on the
reaction rates as described by the Arrhenius equation:
Ea
k = A · exp −
R·T
k
rate constant of an elementary reaction
T
absolute temperature
R
gas constant
Ea
activation energy
A
pre-exponential factor
(3.1)
Small-scale wood burning appliances like wood stoves are usually poorly operated, being the
high level of emissions from incomplete combustion their main environmental problem.
3.2.1
Carbon Monoxide (CO)
CO is an intermediate product of the conversion of fuel carbon to CO2 . Oxidation of CO
to CO2 comes late in the reaction, after the original fuel and the intermediate hydrocarbons
have been consumed and if oxygen is available. Only under ideal conditions, with an excess
of oxygen and optimal burning conditions, is carbon completely oxidized to carbon dioxide
[10]. The oxidation of CO to CO2 also requires high combustion temperatures and sufficient
retention time, being carbon monoxide a later intermediate than hydrocarbons.
2
Later also referred as primary measures for emission reduction
CHAPTER 3. EMISSIONS FROM WOOD COMBUSTION
24
The amount of carbon monoxide emitted during a combustion process depends on how complete or incomplete the combustion is. This is determined by the excess air ratio λ. From
the stoichiometrical point of view a complete combustion is achieved when λ is above 1. As
shown in Figure 3.1 CO emission is lowest at a specific excess air ratio (usually between 1,5
and 2). Higher excess ratios will decrease the combustion temperature while lower excess air
ratios will result in inadequate mixing conditions [7].
Figure 3.1: CO emission as a function of the excess air ratio λ
CO is usually used as an indicator of the combustion quality. High values of CO emitted
during a combustion process indicates poor combustion conditions.
3.2.2
Volatile Organic Compounds (VOC) and Polycyclic Aromatic
Hydrocarbons (PAH)
This section includes all unburnt hydrocarbons except some heavy hydrocarbons that are
included in the following section as particle emission because they condense forming tar.
Hydrocarbons are intermediate products in the conversion of fuel carbon to CO2 and fuel
hydrogen to H2 O. They originate before CO in the reaction, which means they have lower
emission levels. Unburnt hydrocarbons are a consequence of local flame extinction caused
by strain or flame extinction at walls and gaps. VOCs are organic chemicals that evaporate
easily whereas PAHs are polycyclic (“many ringed”) hydrocarbons with carcinogenic effects.
As for CO, emissions of VOC and PAH are a result of too low combustion temperatures, too
short residence time, or lack of available oxygen [7].
Within the aliphatic compounds, methane is the main product. During wood combustion,
methane is considered to be formed either by the decarboxylation reaction of acetic acid (see
Equation 3.2) or by the decarboxylation reaction of acetaldehyde (see Equation 3.3) [6].
CHAPTER 3. EMISSIONS FROM WOOD COMBUSTION
25
CH3 COOH −→ CH4 + CO2
(3.2)
CH3 CHO −→ CH4 + CO
(3.3)
Incomplete combustion of methane may lead to the formation of higher molecular species,
such as ethylene and acetylene [6].
The influence of the combustion temperature in the PAH emission level is ilustrated in Figure
3.2. If the temperature is low, the formation of PAH is low, and if the combustion temperature
is high enough, the formed PAHs are oxidized in the flame [14].
Figure 3.2: Influence of combustion temperature in PAH emissions [7]
The results from a study [5] of non-methane hydrocarbons (C2 - C8 ) emissions from wood
burning in a wood stove and in a small-scale model (a pot), are ilustrated in Figure 3.3. The
proportions of the different hydrocarbons are presented in %weight of total non-methane hydrocarbons. The first two columns correspond to the emissions from a wood stove firing birch
for initial flaming combustion and during smouldering conditions. The rest of the columns
correspond to emissions from the ceramic pot, both burning birch and pine. The study reveals that hydrocarbons are emitted in similar proportions from hardwood and softwood.
Moreover, prominent proportions of benzene, which is highly carcinogenic, were found.
CHAPTER 3. EMISSIONS FROM WOOD COMBUSTION
26
Figure 3.3: Hydrocarbons from wood burning (%weight)
All hydrocarbons contribute indirectly to the greenhouse effect through the formation of
ozone (O3 ). Furthermore, methane (CH4 ) is a direct greenhouse gas with a global warming
potential of 213 . Hydrocarbons also cause negative effects on the human respiratory system.
3.2.3
Particle emissions from incomplete combustion
Particle emissions from incomplete combustion can be found as soot, char or condensed heavy
hydrocarbons (tar droplets). Soot is an agglomeration of carbon particles, which is a result
of a local lack of oxygen in the flame zone and/or local flame extinction. Char particles
may be entrained in the flue gas due to their very low specific density, especially at high
flue gas flow rates. Condensed organic matter is an important, and in some cases the main,
contributor to the total particle emission level in small-scale biomass combustion applications
such as wood stoves. Their contribution is even higher during poor combustion conditions.
3
Calculated over 100 year time horizon
CHAPTER 3. EMISSIONS FROM WOOD COMBUSTION
27
As for CO, emissions of particles may be a result of low combustion temperatures, short
residence times or lack of available oxygen. However, due to the diversity of particle emission
components, reducing particle emission levels by primary measures is not as straightforward
as it is for CO, except for particles consisting of condensed heavy hydrocarbons [7]. A higher
combustion temperature, for example, reduces the density of the particles. This makes easier
for the them to leave the combustion chamber entrained in the flue gases.
3.3
Influence of particle sampling
The particle emissions may consist of a filterable (solid fraction) and a condensable fraction.
Especially under unfavourable combustion conditions in wood burning appliances, the flue
gas contains organic compounds which condense at ambient temperature originating new
particles. In this situations, the amount of particle emission measured depends on the location
of the measurement, i.e. the state of the flue gas at that location.
There are two main ways of measuring particle emission from wood combustion:
• Sampling particles on a heated filter, from undiluted hot flue gas in the chimney (above
the dew point of the gas)
• Sampling particles after cooling and diluting the flue gas using a dilution tunnel (below
the dew point of the gas), resulting in condensation of organic tar compounds.
The lower the temperature in the sampling point is, the more compounds will condense
to liquid phase originating new particles (liquid particles) that will be also collected in the
filter. Thus, more compounds will be found in liquid phase at sampling in the dilution tunnel
compared with sampling in the hot flue gas and higher particle emission is expected at this
location.
Sampling in the chimney means collecting only the liquid particles with a dew point above
the measurement point, which are really few since the temperature of the flue gases in this
measurement point is high. In order to detect both the filterable and the condensable fraction
the measurement should be done after diluting and cooling the flue gas.
CHAPTER 3. EMISSIONS FROM WOOD COMBUSTION
3.4
28
Particulate Matter
Particulate Matter (PM) describes the sum of airborne solid particles and droplets. The
main sources of atmospheric particulate matter in Europe are residential wood combustion
and transport (especially diesel engines), but particles also originate from road abrasion (especially during the winter due to the use of spikes), handling of raw materials, etc. However,
fine particles are mostly originated through combustion processes. EPA4 groups particle
pollution into two categories:
• “Coarse Particles” (PM10-2.5 ) such as those found near roadways and dusty industries
range in diameter from 2,5 to 10 µm. The existing “coarse” particle standard (known as
PM10 ) includes all particles and droplets with an aerodynamic diameter smaller than
10 µm. EPA has proposed replacing this standard with one that includes only particles
between 10 and 2,5 µm in size (PM10-2.5 ).
• “Fine Particles” (PM2.5 ) such as those found in smoke and haze have diameters less
than 2,5 µm. PM2.5 is referred to as “primary” if it is directly emitted into the air as
solid or liquid particles, and is called “secondary” if it is formed by chemical reactions
of gases in the atmosphere.
Since particulate matter with a diameter smaller than 10 µm penetrates into the human
thorax (PM10 is considered as the inhalable fraction) the European Community has established limits for PM10 in the air (Directive 1999/30/EC) that became effective in 2005 within
its member states (see Table 3.1). In the first phase the limit for the yearly average is 40
µm/m3 and for the daily average (24 hour mean) 50 µm/m3 . The daily average can not
be exceeded more than 35 times per year. In the second phase, starting in 2010, the yearly
average restriction will be 20 µm/m3 and the allowed number of yearly exceedances for the
daily average will be reduced to 7.
In Norway the limit for the yearly average is set to 35 µm/m3 whereas the daily average limit
is also 50 µm/m3 . To meet these clean air requirements, authorities will have to promote
measures to reduce the different sources of particulate matter to the air.
Residential wood combustion is an important source of particulate matter to the air, especially in the Nordic countries where it contributes to a large share of the total PM emissions.
4
USA Environmental Protection Agency
CHAPTER 3. EMISSIONS FROM WOOD COMBUSTION
Annual limit
value (µm/m3 )
24 hours limit
value (µm/m3 )
EC (phase 1)
40
50
EC (phase 2)
20
50
Norway
35
50
29
Allowance for 24
hours limit value
35 exceedances per
year
7 exceedances per
year
Table 3.1: Immision limit values for PM10 [4]
Most of the particles emitted from wood combustion are fine particles with a diameter smaller
than 1 µm, usually in the range of 30 to 300 nm [19]. Nowadays, PM10 is used as air quality
indicator. However, due to its adverse effects on human health, future restrictions also on
PM2.5 are expected.
3.5
Particulate matter effects on Human health
Atmospheric particulate matter causes serious effects on human health. Several epidemiological studies show a relation between long-term exposure to particulate matter and: increased
hospitalization for respiratory and heart disease, lung cancer death rates, reduced lung function, exacerbation of asthma, etc. Particles are also carriers of toxic substances like benzene
or PAH, with carcinogenic effects.
The main determinant of health effects is the particle size. PM10 is considered to be the
inhalable fraction, since larger particles are usually filtered in the nose or throat. However,
the smallest particles (PM2.5 ) are of most concern, since they can penetrate deeply into the
human respiratory system inflaming the lungs alveoli. Fine particles (PM2.5 ) are strongly
associated with mortality and hospitalization for cardio-pulmonary disease [WHO5 ]. Fine
particles also remain longer in the atmosphere. This means that the size distribution of the
emissions is different from that of the exposure, because the most dangerous fractions are
more persistent.
5
World Health Organization
CHAPTER 3. EMISSIONS FROM WOOD COMBUSTION
3.6
30
Measures for particle emission reduction
The measures for particle emission reduction in biomass combustion applications can be
divided into two groups:
• Primary measures: optimizing the combustion conditions with respect to combustion
temperature, mixing and residence time generally contributes to a reduction in the
emissions from incomplete combustion.
• Secondary measures: filtration devices like baghouse filters or ESPs6 could be use to
reduce the emissions further. However, this measures are not cost-effective for smallscale applications yet.
Furthermore, consumer information promoting adequate operation and maintainance of the
appliance, as well as the use of quality fuel, is fundamental in the task to reduce particle
emissions from wood combustion.
6
Electrostatic precipitators
Chapter 4
The Standards
European clean air requirements are getting stricter on particulate matter, forcing the European countries to reduce its different sources to meet this requirements. Since residential
wood combustion is a relevant source of particulate matter to the air , further development
of wood stoves is necessary in order to reduce their particle emissions.
The standards and test procedures are fundamental in the task to get low emission stoves.
Several countries have already introduced national standards for emission testing and certification of wood stoves. However, these standards are very different in the way the emissions
are measured, the test facility used, etc. This makes difficult to compare the emission results
from tests performed according to different standards and it can result in confusion regarding the environmental evaluation and acceptance of stoves. Different standards, laboratories and measurements can result in different evaluations and conclusions of the emissions
from the same stove [9]. The introduction of a common European standard for emission
testing of wood stoves would help to solve this problems, supporting the development of
environmentally-friendly appliances.
In this chapter the situation in Europe regarding this matter will be explained, focusing on
particle emission measurement methods. The main test methods for this purpose will be
described and the differences between them will be addressed.
Firstly, the EN-13240 standard will be presented. Although this standard does not deal with
particle emission measurements and requirements, it establishes the basic emission requirements that every stove has to fulfil to enter the market in Europe.
31
CHAPTER 4. THE STANDARDS
32
Nowadays, there are three official methods for measuring particle and dust emissions in
Europe:
• The combined Austrian-German method (see 4.2)
• The Norwegian method (see 6.3)
• The UK method (see 4.3)
A country without a national method for this purpose can choose to apply any of this three
methods. Secondly, the combined Austrian-German method and the UK method will be
described.
It seems difficult to reach an agreement to obtain a common European method for particle
emission testing of wood stoves from the different methods provided by the national documents of those countries that have their own method. The CEN1 tasks for this purpose will
be presented next.
Finally, the EPA method for paticle emission testing will be described.
4.1
EN-13240
The European standard for roomheaters fired by solid fuel is the most commonly used method
for stove testing and certification in Europe. It establishes the basic requirements that
a stove has to fulfil to enter the market. The main requirements are efficiency and CO
emission but stoves must be also safe and sound, have thorough instruction manuals and be
labelled with the efficiency, heat output and CO emission on each recommended fuel. Type
tests are performed at nominal heat output and constant flue draught pressure following the
manufacturer’s recommendations regarding the test fuel, the burning rate and the combustion
controls settings to be used to achieve the claimed nominal heat output during the test. The
standard allows individual states to add extra requirements, for instance for higher efficiency
or smoke reduction, if they wish.
1
European Committee for Standardization
CHAPTER 4. THE STANDARDS
4.1.1
33
Description of performance test at nominal heat output
The test consists of three test periods preceded by a pre-test. The refuelling interval between
these three test periods should not be less than 45 minutes and the fuel load for each of this
three test periods is calculated with the following equation [20] :
Bf l = 360.000 ×
(Pn × tb )
(Hu × η)
(4.1)
Where:
Bf l
is the mass of fuel load, in kg
Hu
is the lower calorific value of the test fuel, on a fired basis, in kJ/kg
η
is the minimum efficiency according to this appliance standard or a higher value
declared by the manufacturer, in %
Pn
is the nominal heat output, in kW
tb
is the minimum refuelling interval, in hours, or duration as declared by the manufacturer
4.1.2
Requirements for performance test at nominal heat output
• Carbon monoxide emission: the mean carbon monoxide contents of the dry combustion
gases shall be less than 1 % (related to 13% oxygen content in the flue gases).
Requirements on appliances with closed doors
Class % CO emission class limits (at 13% O2 )
1
≤ 0.3
2
> 0.3 ≤ 1.0
Table 4.1: Carbon monoxide emission requirements [20]
• Efficiency at nominal heat output: the average thermal efficiency calculated from the
mean of at least two test results at nominal heat output shall be higher than 50 %.
CHAPTER 4. THE STANDARDS
34
Requirements on appliances with closed doors
Class
Efficiency class limits (%)
1
≥ 70
2
≥ 60 < 70
3
≥ 50 < 60
Table 4.2: Efficiency requirements at nominal heat output [20]
• Flue draught: The flue draught (the static pressure to be applied in the measurement
section) shall be 12 Pa for stoves with nominal heat output smaller than 25 kW. The
flue static pressure shall be kept within ±2 Pa of the specified value.
Figure 4.1: Flue draught values
4.2
German - Austrian particle test method
Germany has no requirements on dust emissions from wood stoves. However, during EN13240 type tests, dust measurements are often performed on a voluntary basis according to
the specifications of the German quality label “DIN plus” with measurements according to
the VDI2 2066 part 1 (gravimetric measurements from undiluted exhaust gas). This method
uses the sampling train shown in Figure 4.2 to withdrawn a sample of the flue gas directly
from the chimney (without using a dilution tunnel) and collect the particles from that sample
in a glass fibre filter.
2
Verein Deutscher Ingenieure
CHAPTER 4. THE STANDARDS
35
The filter system is shown in Figure 4.3. The temperature in the filter area shall be maintained
at 70 ºC to avoid the dew point of the sampled gas. The test is carried out at nominal heat
output.
Figure 4.2: Sampling train according to VDI 2066 [24]
Figure 4.3: Filter system according to VDI 2066 [24]
Austrian laws demand to measure particle emissions from wood stoves at nominal heat output
and to report them as mg/MJ. The method used in Austria also measures the particles
directly in the chimney according to the German method VDI 2066. The filter can be fitted
CHAPTER 4. THE STANDARDS
36
either inside or outside the chimney. If the filter is placed outside the chimney its temperature
shall be maintained at 70 ºC.
4.3
United Kingdom particle test method
UK has restrictions if an appliance is submitted for consideration towards exception for use
in smoke control areas under Clean Air Act 1993, which laid down requirements regarding
emissions from solid fuel burning appliances. The Department of Environment would require
it to lie within the smoke emission limits set out in the British Standards document PD 6434
[9]. The document deals with the design and testing of smoke reducing solid fuel burning
domestic appliances. Smoke is here defined as “including soot, ash, grit, gritty particles and
fume emitted in smoke”. PD 6434 sets a smoke emission limit that can be expressed as 5 g/h
+ 0,1 g/h per 0,3 kW of the corresponding mean heat output (wood with 12-16% moisture
content) [27]. As shown in Figure 4.4 a small electrostatic precipitator fitted in the top of
the chimney is used to collect and measure the smoke from domestic appliances tested under
laboratory conditions. Moreover, the optical density of the smoke is monitored during the
whole test run.
Figure 4.4: Test facility used in The United Kingdom [9]
CHAPTER 4. THE STANDARDS
4.4
37
CEN tasks for a common particle emission test method
Since the EN-13240 Standard does not include particle emission measurements the CEN has
been working lately in a common European standard for the test method to be used for this
purpose. The most important features of this method will be presented next. The method
is based on gravimetric particulate emission measurement collecting the entire flue gas flow
under constant volume sampling (CVS) conditions by means of a dilution tunnel [19]. The
proposed test facility is shown in Figure 4.5. The test would be carried out parallel to an EN13240 type test. The flue gas coming out from the stack is collected in a movable telescope
type cowl and diluted with ambient air before entering the dilution tunnel. A bypass supplies
the dilution tunnel with the extra ambient air needed to achieve the required dilution ratios.
Figure 4.5: CEN proposed test facility
The required draft in the stack (according to the EN-13240) can be roughly obtained, during
the pretest, changing the gap between the cowl and the top of the stack and can be adjusted
afterwards changing the inclination of the damper fitted in the air bypass duct. In the
bottom of the dilution tunnel a sample of the diluted gases is withdrawn at constant flow
into a sampling train (see Figure 4.6) so that particles from that sample can be collected in a
filter unit for subsequent gravimetric analysis. An extraction fan fitted after the particulate
matter measurement section carries the diluted gases from the cowl to the exhaust, evacuating
them outside the test facility.
The dilution tunnel gas flow should be maintained in the range of 3 to 10 m/s to meet the
required dilution ratios of between 10 and 20 for the different burning rates [19]. Therefore,
it should be possible to regulate the speed of the fan controlling the flow rate in the dilution
CHAPTER 4. THE STANDARDS
38
Figure 4.6: CEN proposed sampling train [19]
tunnel to meet the required dilution ratio at the respective burning rate. The ratio of the
dilution tunnel gas flow and the appliance flue gas flow shall be obtained from the CO2
concentration in both sides. The ratio of the CO2 concentration in the dilution tunnel and
in the flue gas in the stack defines the dilution ratio.
4.5
U.S.A particle test method
Wood burning stoves to be sold in the United States must be certified by the U.S. Environmental Protection Agency (EPA). Certification is required before a wood-burning stove
model line can be offered for sale. For the EPA to certify a wood-burning stove, the stove
must be tested for emissions by an EPA-accredited testing laboratory. The EPA method
5G is used for determination of particle emissions from wood stoves. The test facility used
is shown in Figure 4.7. The measurements are done using a dilution tunnel and the firing
procedures are determined by method 28. Testing consists of sampling air emissions during
the burning of four separate fuel loads, each burned at a different burning rate. The measurements done at four different average wood consumptions provide information about the
emissions from the stove at the whole range of firing rates (from low to high firing rates). The
filter system used for collecting the particles should be maintained at a temperature below
32 ºC [25].
CHAPTER 4. THE STANDARDS
39
Figure 4.7: Test Facility used in EPA method 5G (USA) [25]
There are substantial differences between the U.S. EPA emissions standard and those found
in most European countries, especially as compared to the Deutsch Industry (DIN) test standards. However, the U.S method has many things in common with the Norwegian method
and emission results from both standards should be comparable. The method gives four
values of particle emissions measured in g/h. Each of these measurements shall be within
one of the different average wood consumption rates shown in Table 4.3.
Category
Average wood
consumption (kg/h)
1
2
3
4
< 0,8
0,8 – 1,25
1,25 – 1,9
> 1,9
Table 4.3: Average wood consumption rates for method 5G (USA) [26]
From these four values a weighted value of particle emission is calculated. The particle
emission limit is 4,1 g/h (dry basis) for catalytic stoves/fireplaces and 7,5 g/h (dry basis) for
non-catalytic stoves/fireplaces. The state of Washington has a lower limitation of 4,5 g/h.
Chapter 5
The Stove: Jøtul F3
In this chapter the stove used during the tests will be presented. The catalog name of the
stove is Jøtul F3. Jøtul AS is a Norwegian company that since 1853 manufactures wood
stoves and fireplaces. Jøtul AS works closely with Sintef and NTNU to develop measures
for emission reduction from wood combustion. The company supported the project with a
new Jøtul F3. Jøtul F3 is an improved version (including a secondary combustion system)
of Jøtul 3, that has been in use in Norway since it was first produced in the 80’s.
5.1
Main features of the stove
Jøtul F3 is a cast iron stove. The stove is equipped with a glass door leading to heat losses
through radiation and resulting in a lower temperature in the combustion chamber. The
stove is wider than long. The dimensions of the combustion chamber are 0.21 x 0.48 x 0.21
m3 giving a chamber volume of 0.02117 m3 . The desired wood weight ranges between 2.14 kg
and 2.6 kg according to the Norwegian Standard, which states that the fuel charge density
must be within (112 ± 11) kg/m3 of the test fuel usable firebox volume [21].
The stove benefits from the advantages of a two-staged combustion. The combustion process
is divided in two stages; gasification of the wood with primary air and oxidation of the
combustible gases with secondary air. The air flow pattern inside the stove is shown in
Figure 5.1. The primary combustion air is coming from the top of the door allowing a better
heat exchange and keeping the glass door clean. The air goes first down toward the wood
and moves then out of the stove across the secondary air system leading to a longer retention
41
CHAPTER 5. THE STOVE: JØTUL F3
42
Figure 5.1: Air flow pattern inside the stove
time of the gases in the stove. The secondary combustion system brings secondary air from
the back of the stove to the combustion chamber.
As shown in Figure 5.2 the secondary air is getting into the stove from two rows of holes,
each row with 25 holes with a diameter of 3 mm making a total area of secondary air of
0.00035343 m2 .
Figure 5.2: Secondary air system
Thanks to this secondary air, the flue gases and toxic particles that would otherwise go up
the chimney can be ignited again leading to a better burnout and lower particle emission.
The dual “clean burn” system converts up to 90% of the gases and particles in the smoke
into heat and increases the efficiency by 40% [29].
CHAPTER 5. THE STOVE: JØTUL F3
5.2
43
Activation zone
Jøtul F3 is wider than long. The reason for this design is that the customer can easily watch
the fire through the glass door. The design of the stove influences the burning characteristics.
The activation zone is the zone where the burning takes place. This zone starts in the front
of the stove (where the primary air inlet is) and moves slowly toward the end of the stove.
The wood burns fast in the part close to the front of the stove since the air can easily reach
the wood. However, the further back the activation zone moves toward the end of the stove
the lower the burning rate becomes due to the difficulties for the air to get to the rear part
of the stove. Due to this feature, most of the charcoal can be found in the back of the stove.
For the same reason more ash will be found in the front part of the stove than in the back.
The activation zone in this kind of stove is bigger than in a stove longer than wide, resulting
in higher burning rates for Jøtul F3. Thus, it is more difficult to achieve low burning rates
for wider stoves. The primary air supply has to be lower for wider stoves in order to get the
same low burning rate as for the longer stoves. Therefore, since at low burning rates the air
coming in will be less, the oxygen supply will be lower and there will be more emissions. The
particle emission will be higher at low burning rates for Jøtul F3 than for longer than wide
stoves.
5.3
Stove’s air vents
As shown in Figure 5.3 the product has two vents: the “air vent” and the “ignition vent”.
The “air vent” regulates the primary combustion air. It is used to control the combustion
rate of the wood, i.e. the burning rate. Opening the “air vent” will allow more air to the
combustion chamber and the burning rate will increase. Thus, the wood will burn faster.
The “ignition vent” is only used during the ignition phase, helping the ignition process by
feeding air directly to the fire.
CHAPTER 5. THE STOVE: JØTUL F3
44
Figure 5.3: Front view of Jøtul F3 with both air vents
5.4
Wood consumption and nominal heat output
The technical data of the stove is presented in Table 5.1. Jøtul F3 has a nominal heat output
of 6,0 kW. To achieve the claimed nominal heat output, the manufacturer recommends the
use of wood with a nominal heat emission of approx. 2 kg/h, opening the air vent almost
completely [28].
Flue dimension
Operating range
Nominal heat output
Flue gas mass flow
Recommended chimney draught
Efficiency
CO emission (13% O2 )
Flue gas temperature
Operational mode
Ø 150 mm/ 177 cm2 cross section
3,4 – 9,0 kW
6,0 kW
5,3 g/sec
11 Pa
78% at 6,8 kW
0,05 %
328 ºC
Intermittent
Table 5.1: Technical data according to EN-13240 [28]
CHAPTER 5. THE STOVE: JØTUL F3
45
The recommended fuel consists of logs of birch or spruce with a water content of approx. 20
%. The amount of energy produced by 1 kg of quality wood is about 3,8 kWh [28]. A very
important factor for the correct consumption of the fuel is that the logs have the correct size.
According to the manufacturer the size of the logs should be as described in Table 5.2.
Kindling
Length
20-30 cm
Diameter
2-5 cm
Amount per fire
6-8 pieces
Firewood (split logs)
Length
30 cm
Diameter
8 cm
Intervals for adding wood approx. every 60 min.
Size of the fire
2 kg
Amount per load
2 pieces
Table 5.2: Recommended fuel size [28]
Chapter 6
The Test Facility and the Measurements
In this chapter the test facility and the measuring equipment will be described. Some figures
will clarify where and how the different measurements were performed. Furthermore, the
main features of the Norwegian Standard will be presented, along with the description of
the procedure for running a test according to this standard. Some tests were also performed
following the requirements of the EN-13240. Finally, the peculiarities of this tests will be
shown.
6.1
The test facility
The test facility stands in the Laboratory of Thermal Energy of the Department of Energy
and Process Engineering and was built according to the Norwegian Standard requirements
(see Figure 6.1). It consists of a scale where the oven stands, the stack and the dilution
tunnel. The stack consists of an insulated steel pipe with an interior diameter of 20 cm and
approx. 4,5 m of height. The flue gases coming out from the stack are collected in a hood,
where they are diluted by mixing with ambient air. After crossing the dilution tunnel, the
diluted and cooled gases are evacuated from the test rig.
47
CHAPTER 6. THE TEST FACILITY AND THE MEASUREMENTS
48
Figure 6.1: Test facility according to the Norwegian standard [22]
6.2
The measurements
Figure 6.2 and Figure 6.3 show the most relevant measurements performed in the stack and
in the dilution tunnel.
Figure 6.2: Measurements in the stack
CHAPTER 6. THE TEST FACILITY AND THE MEASUREMENTS
49
Figure 6.3: Measurements in the dilution tunnel
The measuring equipment consists of several thermocouples, two continuous infrared analyzers (IR-analyzers), an oxygen analyzer, a Flame Ionization Detector, a pressure gauge, a
pitot tube and an electronic scale.
Measurement
Device
Output
Signal
Effective
Range
Temperature
Thermocouple
0 – 50 mV
0 – 1200 ºC
Weight
Pressure in
the chimney
Mettler PE 240
0 – 10 V
0 – 240 kg
Measurement
accuracy
± 1.5 ºC
(-40 -375ºC
±0.004*T,
over 375 ºC)
± 10 g
PC
0 – 10 V
0 – 1 mbar
± 0.01 mbar
Table 6.1: Measuring equipment
To measure the negative pressure in the flue gas outlet, a probe has been introduced inside
the stack at approx. 17 cm from the top surface of the stove. The probe is connected to a
pressure gauge. A pitot tube has been fitted in the top of the dilution tunnel (see velocity
measurement section in Figure 6.1) to measure the velocity of the diluted flue gas in the
tunnel, which mean value has to be 3,33 m/s according to the Norwegian standard [22]. This
value is achieved regulating the speed of the small fan fitted at the end of the dilution tunnel.
CHAPTER 6. THE TEST FACILITY AND THE MEASUREMENTS
50
The fan extracts the gases from the dilution tunnel making possible to achieve the required
velocity and the appropriate dilution rate. The location of the thermocouples is shown in
Table 6.2.
Thermocouples
Inside stove (above the fuel)
Back surface stove
Top surface stove
Bottom surface stove
Right surface stove
Left surface stove
Top dilution tunnel
Bottom dilution tunnel
Gas watch sampling train
Pitot tube
Bottom of the stack (flue gas)
Top of the stack
Filter holder stack
Filter holder dilution tunnel
Room temperature
Table 6.2: Location of thermocouples
Every device sends a signal to an “implog box” that converts the signal and forwards it to
the PC. The different measurements have been recorded each minute during the test run.
6.2.1
CO, CO2 and O2 measurements in the stack
A sample of the flue gases is withdrawn from the stack through a steel probe. As it can be
seen in Figure 6.4 the flue gas goes through several devices before reaching the analyzers.
Firstly, the water is removed in a condenser. Secondly, the gas is dried with silica gel and
filtered by means of a filter located in the top of the gas dryer. Finally, after going through
the pump the flue gas reaches the analyzers.
CHAPTER 6. THE TEST FACILITY AND THE MEASUREMENTS
51
Figure 6.4: Stack flue gas measuring unit
The silica gel and the filter have to be changed from time to time. The characteristics of the
flue gas analyzers used in the stack are shown in Table 6.3.
Measurement
Volume
fraction O2
Volume
fraction CO2
Volume
fraction CO
Device
Sybron Taylor
Servomex, OA
500
Hartmann Braun
Uras 10 E
Hartmann Braun
Uras 10 E
Output
Signal
Effective
Range
Measurement
accuracy
0 – 10 V
0 – 25 vol%
± 0.25 vol%
0 – 10 V
0 – 20 vol%
± 0.4 vol%
0 – 10 V
0 – 5 vol%
± 0.1 vol%
Table 6.3: Gas analyzers used in the stack
6.2.2
CO and CO2 measurements in the dilution tunnel
CO and CO2 measurements in the dilution tunnel are performed similarly as in the stack.
The only difference is that the analyzer has to be more accurate (as it can be observed in
Table 6.4) because in the dilution tunnel the flue gas is diluted approx. 10 times and this
means that the quantity of CO and CO2 will be more or less 10 times lower than in the stack.
In fact, the dilution ratio has been obtained from the relation between the concentration of
CO2 in the stack and in the dilution tunnel.
CHAPTER 6. THE TEST FACILITY AND THE MEASUREMENTS
52
Moreover, the dilution ratio has been used to calculate the velocity of the flue gases in the
stack, dividing the velocity of the flue gases in the dilution tunnel (obtained from the pitot
tube) by the average dilution ratio. The equipment used to withdrawn the flue gas is similar
to the one shown in Figure 6.4 but without the condenser.
Measurement
Device
Volume
fraction CO2
Volume
fraction CO
Hartmann Braun
Uras 10 E
Hartmann Braun
Uras 10 E
Output
Signal
Effective
Range
Measurement
accuracy
0 – 20 mA
0 – 5 vol%
± 0.1 vol%
0 – 20 mA
0 – 500 ppm
± 10 ppm
Table 6.4: Gas analyzers used in the dilution tunnel
6.2.3
Particle measurements in the stack and dilution tunnel
The equipment used for this purpose is the same for the stack and for the dilution tunnel.
The gas is withdrawn proportionally from the flue gas by means of a pump that forces it
to go through the filter holder where a glass fibre filter collects the particles for subsequent
analysis. After being dried, the withdrawn gas is recorded in the gas meter. The filters are
weighed before and after the test run to obtain the mass of pasticles collected. The sampling
train is shown in Figure 6.5.
Figure 6.5: Sampling unit for particle measurements
An electrical trace have been fitted around the stack’s filter holder keeping it at an average
temperature of approx. 170 ºC during the test run, avoiding condensation of organic matter.
CHAPTER 6. THE TEST FACILITY AND THE MEASUREMENTS
53
Since we are measuring the hydrocarbons separately with the Flame Ionization Detector, if
condensation is allowed we would be measuring them twice. Furthermore, according to the
Norwegian standard the dilution tunnel filter holder gas temperature shall be kept below 35
ºC [22], to ensure that condensable organic matter is sampled.
Figure 6.6: Filter holder
6.2.4
Hydrocarbons measurement in the stack
For measuring the hydrocarbons in the flue gas a Flame Ionization Detector (FID) has been
used. The device gives the Total Hydrocarbon Content (THC) in the flue gas expressed in
ppm of propane (C3 H8 ) equivalents but does not give any specific information about the separate constituents. The measurement is continuous (each minute). The measurement system
consists of a heated sample line, a heated filter to remove particles from the sample and a
Flame Ionization Detector. Both sample line and filter are heated up to 180 ºC, protecting
the system against the formation of tar.
Measurement
Device
Output
Signal
Effective
Range
Measurement
accuracy
Total Hydrocarbon
Content in the
chimney
Signal Model 3000
Hydrocarbon
Analyzer
0 – 10 V
0 – 100 ppm
± 2 ppm
Table 6.5: Flame Ionization Detector (FID)
CHAPTER 6. THE TEST FACILITY AND THE MEASUREMENTS
6.3
54
The Norwegian Standard
In Norway measurements of particle emissions from wood stoves are done according to the
Norwegian Standard. A test is always preceded by a pretest, which is used to achieve the
basic firebed in the stove and to heat up the stove to facilitate a thermal balance during the
test run. The difference between the mean value of the wood heater surface temperature at
the beginning and completion of the test run shall not be greater than 70 ºC [21]. The pretest
has to last at least for one hour and the air supply opening has to be the same as the one
that will be used afterwards fo the test. The weight of the charcoal pieces from the pretest
shall be within 20 to 25 % of the fuel charge to be loaded at the start of the test [21]. The
test is carried out under natural chimney draught over one big load of wood. The particle
emission is measured isokinetically in a dilution tunnel, calculated as an average from four
test runs at different wood consumptions and reported as gram emission per kilogram of fuel
on dry basis (g/kg). Since 1997 it is required that all stoves installed in Norway have been
tested for particle emission according to the Norwegian Standard and fulfil its requirements.
6.3.1
The fuel
The standard test fuel (see Figure 6.7) is made of Norwegian spruce pieces with a cross section of 49 mm x 49 mm stitched together with two wood spacers.
Figure 6.7: Size of the standard test fuel
CHAPTER 6. THE TEST FACILITY AND THE MEASUREMENTS
55
The moisture content of the test fuel, which is determined with an electrical resistance meter,
shall be within the range shown in Table 6.6.
Moisture in spruce (%)
Dry basis
Wet basis
19 - 25 %
16 - 20 %
Table 6.6: Moisture content of the test fuel [21]
6.3.2
The different burn rate categories
The reported particle emission value (g/kg) is calculated as a weighted mean value of the
emission results from four test runs (see Equation A.6 in the Appendix), each of which has
to belong to one of the burn rate categories shown in Table 6.7 which values are given in kg
of consumed wood (dry basis) per hour and are calculated as an average value dividing the
weight of the fuel before the test (minus the water content) by the length of the test run.
The weighing factors applied in Equation A.6 were obtained from a study of the firing habits
in Norway. Therefore, the emission results should represent real use of the appliance within
the country.
Burn rate category
Grade 1
Grade 2
1
< 0,80
< 1,25
2
0,80 - 1,25
1,25-1,90
3
1,26-1,90
1,91-2,80
4
>1,90
>2,80
Table 6.7: Burn rate categories according to the Norwegian Standard [21]
The grade of the stove is determined according to its lowest achievable burn rate, i.e. if the
stove can not achieve a burn rate lower than 0,80 kg/h it is classified as grade 2. Grade 1
stoves are used for heating of small rooms whereas grade 2 stoves are used for space heating
of larger rooms. Jøtul F3 is a Grade 2 stove.
CHAPTER 6. THE TEST FACILITY AND THE MEASUREMENTS
6.4
56
Running a test according to the Norwegian Standard
In this section the procedure for running a test according to the Norwegian Standard will
be described. Performing a test involves many tasks. Therefore, it usually takes the whole
morning to finish a single test. The whole test run could be divided in four parts: (1) tasks
before the pretest, (2) pretest, (3) test and (4) tasks after the test.
Before the pretest can start, several tasks need to be done. First, the standard spruce should
be prepared and its moisture recorded. The test fuel width is determined by the spacers.
This dimension was constant in our tests, because we have always used spacers of 17 cm.
However, the test fuel length was adjusted so that the fuel fulfils the requirement already
mentioned in Section 5.1. According to this requirement, the test fuel weight has to lie within
2,1 and 2,6 kg.
The stove must be cleaned from the charcoal and ashes from the previous test. The gas
analyzers should be calibrated before each test run. New glass fibre filters are weighed and
introduced in their respective filter holders. One of the filter holders is placed in the stack
before the pretest and the heating trace is connected and fitted around it so that it has
enough time to reach the adequate temperature for the test.
Just before the pretest, the scale is set to zero. The stove is loaded with approx. 2,5 kg of
birch. The wood is ignited and the door is left slightly opened for a few minutes to help the
ignition process. During the pretest, the air vent opening must be the same as the one that
is planned to be used during the test. The pretest ends when the required charcoal bed is
achieved and at least one hour has elapsed.
Before loading the test fuel all the pumps for the gas analyzers are turned on and the scale
is set to zero again. Furthermore, the labview program must be running and sending data
to the excel file. After ranking the charcoal pieces the standard fuel is loaded. The pumps
for the particle filters must be turned on immediately after loading the stove. The door was
left slightly opened for 5 minutes to help the ignition of the test fuel. The test ends when
the scale shows zero, indicating that the total mass of test fuel has been combusted. Right
after that, the pumps for the particle filters should be turned off.
After the test, everything is turned off, the filters are weighed and the gas watches reading
is noted. Moreover, the silica gel and the filters for the gas dryers must be changed and a
leak check should be performed from time to time. Before leaving the laboratory, the stove
should be cleaned so that the extraction fan can be turned off.
CHAPTER 6. THE TEST FACILITY AND THE MEASUREMENTS
6.5
57
Running a test according to the EN-13240 Standard
Most of the tests were performed according to the Norwegian Standard. However, in order
to compare the emission results, a few tests were performed following the requirements of
the EN-13240 regarding test fuel and chimney draft. The procedure for running a test under
this conditions is very similar to the one described above. There are only some peculiarities
that will be presented next.
The tests must be conducted at nominal heat output (in accordance with EN-13240 section
A.4.7). To obtain the required constant draft in the chimney (12±2 Pa) an adjustable damper
(see Figure 6.8) was fitted in the top of the stack and a rope was attached to it so that the
draft could be regulated from below during the entire test run.
Figure 6.8: Damper used during EN-13240 tests
The tests were performed following the manufacturer intructions to achieve the claimed
nominal heat output (see Section 5.4). Instead of performing the test over one big load, the
test run is divided into three test periods. During each of this periods a small amount of
wood is loaded. The refuelling interval should not be less than 45 minutes. The amount of
wood for each test period must be calculated using Equation 4.1 and the technical data of
the stove (see Table 5.1). From this calculation, the fuel load for each of the three periods
was set to 1,5 kg. The test fuel used during the EN-13240 tests was birch.
Chapter 7
Results and Discussion
In this chapter, the results are presented. The discussion will be focused on the Norwegian
Standard results. The purpose of the EN-13240 tests was performing some measurements
following the standard requirements regarding chimney draft and fuel, to see how these
modifications could influence the results. However, it has to be clear that no EN-13240 test
was performed as such, since, among other things, our test facility was built according to
the Norwegian Standard. Furthermore, due to a problem with the FID, only two of these
tests were performed with hydrocarbon measurements. The EN results were calculated as
an average of three tests periods.
7.1
Fuelsim - Transient
Fuelsim - Transient is a relatively simple, but useful, mass, volume and energy balance
spreadsheet mostly used for batch combustion applications. The solid fuel is converted to a
fuel gas mixture of O2 , CO, NO, NO2 , UHC (unburnt hydrocarbons), SO2 , N2 O, H2 , NH3 ,
HCN, Tar, CO2 , N2 , Ar and H2 O [30]. The program was used to calculate the efficiencies
and to convert the hydrocarbon content in the wet flue gas (as measured by the FID) to the
reported hydrocarbon content in the dry flue gas. Moreover, the reported average emission
values of CO, CO2 and THC (total hydrocarbons) were also obtained with this program.
59
CHAPTER 7. RESULTS AND DISCUSSION
7.2
60
Emission factors
Emission factors are representative values which attempt to relate the quantity of a pollutant
released to the atmosphere with an activity associated with the release of that pollutant
[EPA]. In wood combustion, emission factors are expressed as weight of the pollutant divided
by energy, volume or weight of the activity emitting the pollutant. Particle emission factors
from wood combustion are strongly influenced by the measurement technique. Therefore,
data from emission inventories have to be analyzed carefully to consider, not only the emission
results, but also the sampling and measurement procedure. In countries with compulsory
measurements in the dilution tunnel, emission factors are persistently higher than in those
where the measurements are performed directly in the chimney. This is even more remarkable
in Norway, where compulsory measurements are also performed at low thermal output with
throttled air supply.
In this report, most of the emission results are presented as mg pollutant per megajoule fuel
supplied (mg/MJ). The used upper heating value of the wood (MJ end energy contained in
the fuel) was 19,122 MJ/kg dry wood for spruce and 18,964 MJ/kg dry wood for birch.
7.3
Problems during testing
Obviously, not all the tests were successful. It took a long time to get everything ready and
the first tests were performed just to get used to the burning rates, the analyzers, the stove,
etc. The main problems found during testing are presented next.
In the beginning, the heating trace used in the stack’s filter holder was not working properly.
The insulating fabric that covers the resistance was broken and we had to find a new one.
Furthermore, the small fan fitted at the end of the dilution tunnel was clogged, not being
able to dilute the flue gases properly. It was full of soot and we had to change it. However,
a lot of tests were carried out with the fan in this conditions and all of them were refused.
Some tests where also rejected because the pretest was not long enough.
The FID was not always available. Moreover, it was difficult to use the appropiate range
during the whole test run. Tests 14 and 15 were not considered for this reason.
CHAPTER 7. RESULTS AND DISCUSSION
7.4
61
Appropriate use of the Flame Ionization Analyzer
It is not recommended to use the FID at low burning rates. During poor combustion conditions, the emission of unburnt heavy hydrocarbons increases. These hydrocarbons can
condense along the sampling duct forming tar, which could clog the system or originate misleading results. We have used the CO content in the flue gas as an indicator of the combustion
quality. High values of CO indicates poor combustion conditions. Therefore, the FID was
not used when high values of CO were expected. Since we are interested in using the FID,
our project has been focused in the high burning rate range. However, some tests where
performed at low air supply to establish the differences between high and low burning rates.
These tests were carried out without using the hydrocarbon analyzer.
7.5
Combustion conditions
Table 7.1 shows the combustion conditions during each test performed according to the
Norwegian Standard. Tests 16 - 19 belong to burn rate category 4 (see Table 6.7). These
four tests resulted in burning rates between 2,87 and 4,34 kg dry wood/h. The CO2 content
in the flue gas was 6,64 - 7,56 Vol% and the measured CO was 1427 - 1498 mg/MJ.
Tests 20 - 23 and 31 belong to burn rate category 3. During this group of tests, the burning
rate was 2,50 - 2,61 kg dry wood/h, CO2 was 5,48 - 8,20 Vol% and CO was 1777 - 3555
mg/MJ.
Test 30 belongs to burn rate category 2. In this case, the burning rate was 1,44 kg dry
wood/h, CO2 was 5 Vol% and CO was 9042 mg/MJ wood supplied. Although the resulting
average wood consumption was not the intended, tests 30 and 31 were performed at low
air supply to study how the results change during poor combustion conditions. Therefore,
as explained in the previous section, these tests were performed without the hydrocarbon
analyzer. Test 31 will not be used for further analysis because it is the only one that does
not fulfil the requirement stated in Section 6.3. The difference between the mean value of the
stove surface temperature at the beginning and completion of the test was greater than 70 ºC.
CHAPTER 7. RESULTS AND DISCUSSION
Test
16
17
18
19
20
21
22
23
31
30
Moisture
content of
the wood
(%)
17,5
17,5
18,0
17,5
17,5
20,0
16,3
19,3
16,0
16,0
Burning
rate (kg
dry
wood/h)
2,87
3,12
3,28
4,34
2,50
2,61
2,52
2,59
2,50
1,44
62
T inlet
chimney
(ºC)
O2 in dry
flue gas
(Vol %)
CO2 in dry
flue gas
(Vol%)
390
386
385
386
338
332
363
384
268
231
13,1
14,0
13,5
14,1
14,6
13,8
13,5
12,4
15,2
15,3
7,56
6,76
7,25
6,64
6,13
6,93
7,15
8,20
5,48
5,00
CO in dry
flue gas
(ppm at
11 % O2 )
2577
2598
2587
2465
3630
3078
3334
3395
6213
16377
Dilution
ratio
11
8
8
8
13
11
12
15
18
17
Table 7.1: Norwegian Standard - Combustion conditions
Table 7.2 shows the combustion conditions during each test performed following the EN13240 method. During the EN tests, the burn rate was 0,92 - 1,72 kg dry wood/h, CO2 was
3,19 - 8,67 Vol% and CO was 643 - 7585 mg/MJ.
Test
35
36
37
38
39
40
Moisture
content of
the wood
(%)
18,1
19,0
16,8
18,0
17,3
18,4
Burning rate
(kg dry
wood/h)
T inlet
chimney
(ºC)
O2 in dry
flue gas
(Vol%)
CO2 in dry
flue gas
(Vol%)
CO in dry
flue gas (ppm
at 11 % O2 )
1,72
1,38
0,92
1,43
1,32
1,52
318
286
178
286
288
297
12,1
17,7
15,2
13,4
13,2
13,6
8,67
3,19
5,27
7,30
7,60
7,20
1091
3212
13942
2830
2415
1919
Table 7.2: EN Standard - Combustion conditions
7.6
Particle emission
Table 7.3 shows the adjusted particle emission results from the Norwegian Standard tests
(particle emission measured in the dilution tunnel). These particulate emission values were
obtained following the procedure described in NS 3058-2 (see calculations in Appendix A).
CHAPTER 7. RESULTS AND DISCUSSION
63
During the Norwegian Standard tests 1,4 - 37 grams particulate matter/kg dry wood were
measured in the dilution tunnel.
Test
16
17
18
19
20
21
22
23
31
30
Moisture
content of
the wood
(%)
17,5
17,5
18,0
17,5
17,5
20,0
16,3
19,3
16,0
16,0
Burning rate
(kg dry
wood/h)
2,87
3,12
3,28
4,34
2,50
2,61
2,52
2,59
2,50
1,44
Adjusted
particle
emission
Ead (g/h)
4,02
8,73
10,01
9,69
10,54
5,94
6,27
4,13
24,72
53,44
Adjusted
particle
emission
Ead (g/kg)
1,40
2,80
3,05
2,24
4,21
2,28
2,49
1,59
9,88
37,06
Adjusted
particle
emission
Ead (mg/MJ)
73
146
159
117
220
119
130
83
516
1938
Table 7.3: Norwegian Standard - Adjusted particle emission
The relation between particle emission and burning rate is ilustrated in Figure 7.1. The
amount of particles emitted into the air usually increases with decreasing average wood
consumption [3]. Since most of our tests were carried out at high burning rates, the results
do not show this trend clearly. However, it can be noticed that if the burning rate goes below
2 kg/h the particle emission increases rapidly.
Figure 7.1: Norwegian Standard - Particle emission related to burning rate
CHAPTER 7. RESULTS AND DISCUSSION
64
During the EN tests, 2 - 43 grams particulate matter/kg dry wood were found in the dilution
tunnel. It must be explained that, since the EN Standard does not consider particle emission,
these values were also calculated following the Norwegian Standard method. The relation
between particle emission and burning rate for the EN tests is ilustrated in Figure 7.2. EN13240 tests must be performed at nominal heat output. However, test 37 was performed at
low air supply to prove the increasing particle emission with lower burning rates.
Figure 7.2: EN Standard - Particle emission related to burning rate
The particle emission results were compared with other measurements like for example [17],
a certification test according to the Norwegian Standard carried out on the old version of
Jøtul F3.
7.7
Efficiencies
The average efficiencies were calculated using Fuelsim and are based on the EHV (Effective
Heating Value) of the wood. The resulting values from the Norwegian Standard tests are
presented in Table 7.4.
CHAPTER 7. RESULTS AND DISCUSSION
Test
16
17
18
19
20
21
22
23
31
30
Moisture
content of
the wood
(%)
17,5
17,5
18,0
17,5
17,5
20,0
16,3
19,3
16,0
16,0
65
Burning rate
(kg dry
wood/h)
T inlet
chimney
(ºC)
Thermal
efficiency
(EHV)
Combustion
efficiency
(EHV)
Total
efficiency
(EHV)
2,87
3,12
3,28
4,34
2,50
2,61
2,52
2,59
2,50
1,44
390
386
385
386
338
332
363
384
268
231
0,63
0,60
0,62
0,59
0,63
0,67
0,65
0,66
0,69
0,74
0,97
0,96
0,96
0,97
0,95
0,96
0,96
0,97
0,95
0,89
0,60
0,56
0,59
0,56
0,58
0,63
0,61
0,63
0,64
0,63
Table 7.4: Norwegian Standard - Efficiencies
As demanded by the EN-13240 Standard, the values of CO content in the flue gas, efficiency
and heat output are presented in Table 7.5. The selected net heat output from Fuelsim is
based on the EHV (Effective Heating Value) of the wood. As it can be noticed, even following
the recommendations of the manufacturer, it was difficult to obtain the claimed nominal heat
output. However, most of the tests fulfil the EN requirements on CO emission and efficiency
(see Section 4.1).
Test
35
36
37
38
39
40
CO in dry
flue gas
(Vol%)
0,095
0,096
0,785
0,213
0,178
0,143
Total
efficiency
(EHV)
0,72
0,34
0,69
0,70
0,71
0,69
Heat Output
(KW)
6,0
2,7
3,1
4,8
4,7
5,1
Table 7.5: EN Standard - Data according to EN-13240
CHAPTER 7. RESULTS AND DISCUSSION
7.8
66
Comparison between stack and dilution tunnel
Table 7.6 shows the particle emission measured both in the stack and in the dilution tunnel
during the Norwegian Standard tests. Furthermore, the Total Hydrocarbon content in the
flue gas is also included. As explained before, tests 30 and 31 were carried out without using
the FID. Factor F1 corresponds to the ratio between PM measured in the dilution tunnel
and PM measured in the stack whereas factor F2 corresponds to the ratio between both PM
measured in the stack and hydrocarbon content in the flue gas and PM in the dilution tunnel.
Some figures presented afterwards will clarify this relations.
Test
16
17
18
19
20
21
22
23
31
30
Burning
rate (kg
dry
wood/h)
2,87
3,12
3,28
4,34
2,50
2,61
2,52
2,59
2,50
1,44
CO
(mg/MJ)
stack
filter
(mg)
1498
1498
1493
1427
2068
1777
1922
1965
3555
9042
4,5
6,1
7,8
4,3
13,6
5,6
7,0
4,5
52,8
258,3
Particles
in the
stack filter
(mg/MJ)
11,8
19,6
28,9
22,1
20,9
17,9
15,5
9,7
75,7
162
DT
THC
filter
(mg/MJ)
(mg)
185,6
367,2
345,6
278,6
522,7
294,8
306,0
217,7
4,4
11,2
12,3
8,5
18,0
7,1
9,1
5,3
49,5
220,5
Particles
in the DT
filter
(mg/MJ)
73
146
159
117
220
119
130
83
516
1938
F1
F2
6,2
7,5
5,5
5,3
10
6,6
8,4
8,6
6,8
12
2,7
2,6
2,3
2,6
2,5
2,6
2,5
2,7
Table 7.6: Norwegian Standard - Comparison between stack and dilution tunnel
During the group of tests belonging to burn rate category 4, 12 - 29 mg particulate matter/MJ
was measured in the chimney (flue gas temperature between 385 and 390 ºC) and 73 - 159
mg particulate matter/MJ was measured in the dilution tunnel. The hydrocarbon content in
the flue gas was between 186 and 367 mg/MJ. During the group of tests belonging to burn
rate category 3, measurements resulted in 10 - 76 mg particulate matter/MJ in the chimney
(at 268 - 384 ºC) and 83 - 516 mg particulate matter/MJ in the dilution tunnel. In this
case, the hydrocarbon content in the flue gas was between 218 and 523 mg/MJ. Finally, test
30 gave 162 mg particulate matter/MJ in the chimney (at 231 ºC) and 1938 mg particulate
matter/MJ in the dilution tunnel. The difference between the particle emission in both
measurement points is ilustrated in Figure 7.3, were the hydrocarbon content in the flue gas
is also included.
CHAPTER 7. RESULTS AND DISCUSSION
67
Figure 7.3: Norwegian Standard - PMs , Total Hydrocarbon content in the flue gas and PMd
As shown in Figures 7.4 and 7.5, the particle emission measured in the dilution tunnel was
between 5 and 12 times higher than the particle emission measured in the chimney. Since
soot is already formed in the flames and should be stable between both sampling points [15],
the higher particle emission found in the dilution tunnel is due to the potential contribution
of condensed of organic matter.
Figure 7.4: Norwegian Standard - Comparison of PM emission in stack and dilution tunnel
CHAPTER 7. RESULTS AND DISCUSSION
68
Figure 7.5: Norwegian Standard - Ratio between PM in the dilution tunnel and PM in the
stack
The ratio between both particles in the stack and THC measured in the flue gas and particles
in the dilution tunnel is ilustrated in Figure 7.6. The results show a persistently constant
factor of around 2,5 between both measurements, indicating that, obviously, not all the
hydrocarbons condense in the dilution tunnel. This is probably due to the difference in
type and volatility between the different organic compounds present in the flue gas. This
constituents include simple hydrocarbons (C1-C7) which exist as gases or volatilize at ambient
conditions and complex heavy substances which condense at ambient temperature.
Figure 7.6: Norwegian Standard - Ratio between THC + PM in the stack and PM in the
dilution tunnel
CHAPTER 7. RESULTS AND DISCUSSION
69
Assuming that all the extra particle emission found in the dilution tunnel originates from
condensed organic matter, the results show that about 35 % of the hydrocarbons measured
in the stack with the Flame Ionization Detector condense along the dilution tunnel forming
liquid particles that are subsequently measured as particle emission. Furthermore, the results
also reveal that these condensed tar compounds account for approximately 85 % of the total
particle emission found at this location. These percentages are ilustrated in Figures 7.7 and
7.8.
Figure 7.7: Norwegian Standard - Percentage of hydrocarbons measured with the FID found
as particles in the dilution tunnel
Figure 7.8: Norwegian Standard - Percentage of total PM measured in the dilution tunnel
consisting of condensed organic matter
CHAPTER 7. RESULTS AND DISCUSSION
70
Figure 7.9 ilustrates the influence of the combustion quality on the ratio PMdiltution tunnel /
PMstack . The results show a general trend of increasing difference between both measurements
with increasing CO content in the flue gas. This is due to the higher emission of unburnt
hydrocarbons from incomplete combustion during poor combustion conditions.
Figure 7.9: Norwegian Standard - Ratio PMd /PMs related to combustion conditions
The presented results are consistent with other studies. In [15], parallel measurements of
particle emission in the chimney according to the Swedish method and in a dilution tunnel
according to the Norwegian method were performed during the combustion of wood logs in a
stove. Different combustion conditions were achieved by firing wood at different burn rates.
Four tests belong to burn rate category 2 of the Norwegian Standard and another four to
burn rate category 3 (see Table 6.7). The test fuel used was the same standard spruce used
during our tests. In this study, the particle emission measured in the dilution tunnel was
between 2 and 10 times higher than the particle emission value measured in the chimney.
The corresponding CO emission was 4100 - 7600 mg/MJ. The report also reveals the larger
difference between both measurement methods during poor combustion conditions.
Another study performed in Switzerland following the CEN proposed method for particle
emission measurements parallel to EN-13240 type testing (see Section 4.4), also shows a
similar trend. The stove used for this study was also a Jøtul F3. The results showed that
particle emissions measured in the dilution tunnel were between 40% and 160% higher that
if they were sampled directly from the stack using a heated filter [16]. The study also points
to a relation between this ratio and the combustion efficiency.
A survey on measurements and emission factors from biomass combustion carried out by the
International Energy Agency (IEA) also deals with this topic. The survey gathers emission
CHAPTER 7. RESULTS AND DISCUSSION
71
data from several countries. For wood stoves, all measurements performed with throttled
air supply resulted in a factor of 2,5 - 10 between particle emission measured in the dilution
tunnel and particle emission measured directly in the hot flue gases [4].
The comparison between stack and dilution tunnel for the EN tests is presented next. During
these tests, 11 - 194 mg particulate matter/MJ was measured in the chimney (flue gas temperature between 178 and 318 ºC) and 108 - 2252 mg particulate matter/MJ was measured
in the dilution tunnel. The results are shown in Table 7.7.
Test
35
36
37
38
39
40
Burning
rate (kg
dry
wood/h)
1,72
1,38
0,92
1,43
1,32
1,52
CO
(mg/MJ)
stack
filter
(mg)
643
1730
7585
1648
1405
1121
27,9
33,4
351,9
33,4
28,3
25,3
Particles
in the
stack filter
(mg/MJ)
10,9
18,9
194,2
14,95
16,43
13,28
THC
(mg/MJ)
48,9
743,2
DT
filter
(mg)
12,8
19,1
438,5
26,4
20,9
14,32
Particles
in the DT
filter
(mg/MJ)
108
157
2252
211
170
123
F1
F2
9,9
8,3
11,6
14,1
10,4
9,3
0,5
4,8
Table 7.7: EN Standard - Comparison between stack and dilution tunnel
As shown in Figures 7.10 and 7.11, the EN results also corroborate the higher particle emission
found when measurements are performed after cooling and diluting the flue gas. The particle
emission measured in the dilution tunnel was between 8 and 14 times higher than the particle
emission measured in the chimney.
Figure 7.10: EN Standard - Comparison of PM emission in stack and dilution tunnel
CHAPTER 7. RESULTS AND DISCUSSION
72
Figure 7.11: EN Standard - Ratio between PM in the dilution tunnel and PM in the stack
Unfortunately, due to a problem with the FID, not enough EN tests were carried out including
hydrocarbon measurements. Therefore, is not possible to establish any further conclusions
in this sense. As shown in Table 7.7, only two tests were performed with the FID, leading to
contradictory results. Especially during test 35, some mistake must have been made when
measuring the hydrocarbon content, either with the range of the FID or during the conversion
with Fuelsim. However, the results were carefully reviewed and no error was found.
[18] was used as guidance during the EN tests. In this report, measurements of the total
hydrocarbon content in the flue gas were performed on a Jøtul F3 parallel to an EN-13240
type test. The test results are also based on a mean value of the three test periods. The mean
value of the THC (Total Hydrocarbon Content) in the flue gas was 172 ppm (as methane
equivalent) and the CO content 0,113 (% at 13 % O2 ). The efficiency during the test was
68% and the heat output 5,8 kW.
CHAPTER 7. RESULTS AND DISCUSSION
73
The typical look of the filters after performing the tests is shown in Figure 7.12. In the stack
filter most of the particles consist of soot, with its characteristic black color. In contrast, the
brown color found in the dilution tunnel is due to the organic compounds, which condense
forming tar.
(a) stack filter
(b) dilution tunnel filter
Figure 7.12: Typical look of the filters after performing the tests
7.9
Accuracy and Reliability
The accuracy of the measuring equipment is presented in the previous chapter. Several factors
like moisture, ignition or colocation of the fuel in the stove influence greatly the emission
results. Considering the influence that these factors have in the combustion process, the
obtained results from the Norwegian Standard tests appear to be rather constant. Being
similar to the ones presented in other studies, the results are found to be quite reliable.
Chapter 8
Conclusions
The difference between measuring particle emission directly in the stack and in a dilution
tunnel has been analyzed. For the Norwegian Standard tests, the particle emission measured
in the dilution tunnel was between 5 and 12 times higher than in the chimney. For the EN
tests, this factor was between 8 and 14. The more unfavourable combustion conditions, the
larger the difference between both measurements was seen. The higher particle emission
found in the dilution tunnel is due to condensed organic compounds. Therefore, particle
emission inventories including only solid particles may underestimate the real contribution
of wood combustion to atmospheric particulate matter.
The Norwegian Standard results also show a factor of about 2,5 between both particle emission measured in the stack and Total Hydrocarbon content in the flue gas and particle
emission measured in the dilution tunnel, indicating that about 35 % of the hydrocarbons
measured in the stack with the Flame Ionization Detector condense along the dilution tunnel
accounting for approximately 85 % of the total particle emission found at this location.
The obtained factors may be useful to compare different measurements and to roughly predict
what would be, for example, the particle emission measured in the dilution tunnel if emission
data on particle emission measured in the stack is available.
From this work, it can be concluded that the best way to measure particle emission from
wood combustion is by using a dilution tunnel, thus cooling the flue gases, thus allowing
condensation of organic compounds. This method mimics what truly happens when the flue
gases reach the atmosphere. However, measuring only solid particles directly in the stack is
cheaper and faster and still provides useful information about the environmental performance
of an appliance.
75
CHAPTER 8. CONCLUSIONS
76
Since condensables from wood combustion have been identified as highly toxic [4], a separate
measurement of condensables and solid particles could also be interesting. Furthermore,
measuring at several average wood consumptions will provide more realistic emission results
than measuring only at one average wood consumption.
Further research is necessary to investigate the influence of certain important combustion
parameters on the obtained results. New measurements could be carried out with different
fuel, different moisture content, shorter ignition period, etc.
Bibliography
[1] Øyvind Skreiberg. Theoretical and experimental studies on emissions from wood combustion. PHD thesis, The Norwegian University of Science and Technology, Trondheim,
Norway. Faculty of Mechanical Engineering, Department of Thermal Energy and Hydropower, 1997.
[2] Thomas Nussbaumer. Wood combustion. In Advances in Thermochemical Biomass Conversion, Pages 575-589, 1994.
[3] Edvard Karlsvik, Johan E. Hustad and Otto K. Sønju. Emissions from wood stoves and
fireplaces. In Advances in Thermochemical Biomass Conversion, Pages 690-707, 1994.
[4] Thomas Nussbaumer, Claudia Czasch, Norbert Klippel, Linda Johansson and Claes
Tullin. Particulate Emissions from Biomass Combustion in IEA Countries, Survey on
Measurements and Emission Factors, January 2008.
[5] Gunnar Barrefors and Göran Petersson, Volatile hydrocarbons from domestic wood burning. In Chemosphere, Vol. 30, No. 8, pp. 1551-1556, 1995.
[6] C.K.W. Ndiema, F.M. Mpendazoe and A. Williams. Emission of pollutants from a
biomass stove. In Energy Conversion and Management, Vol. 39, No. 13, pp. 1357-1367,
1998.
[7] International Energy Agency. The Handbook of Biomass Combustion & Co-firing, 2002.
[8] Danish Environmental Protection Agency. Comparison of measuring results between
solid fuel stoves tested in accordance with EN-13240 and NS-3058, December 2006.
[9] International Energy Agency, Task X, Combustion. Round Robin Test of a Wood Stove
– Emissions, February 1995.
[10] Marquita K. Hill. Understanding Environmental Pollution, Chapter 5: Air Pollution,
January 2004.
77
BIBLIOGRAPHY
78
[11] Nordic Ecolabelling. Swan labelling of Closed Fireplaces, Version 2.0, March 2006.
[12] Edvard Karlsvik. Comparison of Test Standards from Various Countries.
[13] Aerosols from Biomass Combustion, International Seminar in Zurich, June 2001.
[14] T. Nussbaumer and J. E. Hustad. Overview of Biomass Combustion, October 1996.
[15] Linda Johansson, Lennart Gustavsson, Claes Tullin, Daniel Ryde and Marie Rönnbäck,
SP Technical Research Institute Sweden. Comparison of particle sampling in chimney
and dilution tunnel during residential combustion of wood logs.
[16] Christian Gaegauf and Timothy Griffin, University of Applied Science Bale/Muttenz.
Comparison of in-stack and dilution tunnel measurement of particulate emission, April
2007.
[17] SINTEF Energi - Norges branntekniske laboratorium, Jøtul 3 R Prøvingsrapport, October 1997.
[18] Stefan Österberg, Energy Technology, SP Swedish National Testing and Research Institute. Testing a residential roomheater fired by wood, Jøtul F3 Report, April 2005.
[19] European Committee for Standardization. Up-to-date draft of EN TS on particulate
emission test method, January 2007.
[20] European Standard EN 13240: Roomheaters fired by solid fuel, Requirements and test
methods, April 2001.
[21] Norwegian Standard NS 3058-1: Enclosed wood heaters smoke emission, part 1: Test
facility and heating pattern, June 1994.
[22] Norwegian Standard 3058-2: Enclosed wood heaters smoke emission, part 2: Determination of particle emission, June 1994.
[23] Norwegian Standard NS 3059: Enclosed wood heaters smoke emission – requirements,
October 1994.
[24] VDI 1066 - Sheet 2: Measurement of particulate matter; manual dust measurement in
flow gases; gravimetric determination of dust load.
[25] Environmental Protection Agency (EPA), Method 5G: Determination of particulate matter emissions from wood heaters (dilution tunnel sampling location), February 2000.
BIBLIOGRAPHY
79
[26] Environmental Protection Agency (EPA), Method 28: Certification and auditing of wood
heaters, February 2000.
[27] British Standard document PD 6434: Recommendations for the design and the testing
of smoke reducing solid fuel burning domestic appliances.
[28] Jøtul AS, Jøtul F3 Installation Instructions with Technical Data and General Use and
Maintenance Manual (English Version).
[29] Jøtul AS web page, www.jotul.com.
[30] Øyvind Skreiberg. Fuelsim - Transient v1.0, The Norwegian University of Science and
Technology, Institute of Thermal Energy and Hydropower, August 2002.
Appendix A
Calculations
The following calculations shall be used to calculate the particulate emission rate according
to the Norwegian Standard:
A.1
Gas meter volume
Vm(norm) =
KI × Vm × Y × Pbar
Vm × Y × Tnorm × Pbar
=
Tm × Pnorm
Tm
(A.1)
Where:
Vm(norm)
is the gas volume from the sample measured by dry gas meter or similar measuring
equipment and correlated to standard conditions, in dm3 (273 K and 760 mm Hg).
Vm
is volume of gas sample measured by dry gas meter or similar measuring equipment, in dm3 .
Y
is the gas meter or similar measuring equipment calibration factor.
Tnorm
is 273 K.
Pbar
is air pressure at the sampling site, in mm Hg.
Tm
is average dry gas meter temperature during the measuring period, in K.
Pnorm
is 760 mm Hg.
KI
is 0,3858 K/mm Hg.
81
APPENDIX A. CALCULATIONS
A.2
82
Particulate concentration
Cs =
mn
1000 × Vm(norm)
(A.2)
Where:
Cs
is the concentration of particulate matter in the flue gas on dry basis, correlated
to standard conditions, in g/dm3 (273 K and 760 mm Hg).
mn
is the total amount of particulate matter collected, in mg.
Vm(norm)
is the gas volume from the sample measured by dry gas meter or similar measuring
equipment and correlated to standard conditions, in dm3 (273 K and 760 mm Hg).
A.3
Particulate emission rate
E = CS × Qad
(A.3)
Where:
E
is the particulate emission rate, in g/h.
Qad
is the average gas flow rate in the dilution tunnel, in dm3 /h (273 K and 760 mm
Hg).
Cs
is the concentration of particulate matter in the flue gas on dry basis, correlated
to standard conditions, in g/dm3 (273 K and 760 mm Hg).
A.4
Adjusted particulate emission rate
Particulate emission results shall be adjusted for reporting purposes using Equation A.4:
Ead = 1, 82 × E 0,83
(A.4)
APPENDIX A. CALCULATIONS
83
Where:
Ead
is the particulate emission rate adjusted to reported emission, in g/h.
E
is the particulate emission rate, in g/h.
To obtain the particulate emission rate in g/kg dry wood for an individual test:
Ead (g/kg) =
Ead
b
(A.5)
Ead (g/kg) is the particulate emission rate adjusted to reported emission, in g/kg dry wood.
Ead
is the particulate emission rate adjusted to reported emission, in g/h.
b
is the burn rate of the test, in kg dry wood/h.
A.5
Particulate Emission Requirements
The particle emission requirements in Norway are shown in Table A.1.
Stove with catalyst
Stove without catalyst
Maximum for each
test
10 g/kg
20 g/kg
Maximum weighted
mean value
5 g/kg
10 g/kg
Table A.1: Particulate emission requirements in Norway [23]
A.6
Calculation of weighted particulate emission
EV =
n X
E(ad)i
Ki ·
mi
i=1
n
X
Ki
i=1
EV
is the weighted particulate emission from the tests in g/kg dry wood.
(A.6)
APPENDIX A. CALCULATIONS
n
is the total number of tests.
Pi
is the probability for burn rate category for test i.
Ki
is the weighted factor of the test which is Pi+1 − Pi−1 .
E(ad)i
is the weighted particulate emission in g/h from the test i.
mi
is the mean burn rate on dry basis in kg/h for test i.
84
Appendix B
Norwegian Standard Graphs
The subtitles of the following graphs correspond to:
(a)
Fuel burnt against time
(b)
Surface temperatures of the stove against time
(c)
CO2 and O2 content in the dry flue gas in Vol% and excess air ratio against
percentage of dry fuel burnt
(d)
Total hydrocarbon content in the dry flue gas in ppm and CO content in the dry
flue gas in Vol% against percentage of dry fuel burnt1
(e)
Combustion, Thermal and Total Efficiencies against percentage of dry fuel burnt
(f)
Combustion chamber and chimney inlet temperatures against percentage of dry
fuel burnt
(g)
Stack and dilution tunnel filter temperatures against percentage of dry fuel burnt
(h)
Pitot and chimney negative pressures against percentage of dry fuel burnt
1
Tests 30 and 31 were performed at low air supply. Since it is not recommended to use the FID in this
circumstances, the graphs only ilustrate the CO content.
85
APPENDIX B. NORWEGIAN STANDARD GRAPHS
(a)
(b)
(c)
Figure B.1: Test 16 - Graphs (a)-(c)
87
APPENDIX B. NORWEGIAN STANDARD GRAPHS
(d)
(e)
(f)
Figure B.2: Test 16 - Graphs (d)-(f)
88
APPENDIX B. NORWEGIAN STANDARD GRAPHS
(g)
(h)
Figure B.3: Test 16 - Graphs (g)-(h)
89
APPENDIX B. NORWEGIAN STANDARD GRAPHS
(a)
(b)
(c)
Figure B.4: Test 17 - Graphs (a)-(c)
90
APPENDIX B. NORWEGIAN STANDARD GRAPHS
(d)
(e)
(f)
Figure B.5: Test 17 - Graphs (d)-(f)
91
APPENDIX B. NORWEGIAN STANDARD GRAPHS
(g)
(h)
Figure B.6: Test 17 - Graphs (g)-(h)
92
APPENDIX B. NORWEGIAN STANDARD GRAPHS
(a)
(b)
(c)
Figure B.7: Test 18 - Graphs (a)-(c)
93
APPENDIX B. NORWEGIAN STANDARD GRAPHS
(d)
(e)
(f)
Figure B.8: Test 18 - Graphs (d)-(f)
94
APPENDIX B. NORWEGIAN STANDARD GRAPHS
(g)
(h)
Figure B.9: Test 18 - Graphs (g)-(h)
95
APPENDIX B. NORWEGIAN STANDARD GRAPHS
(a)
(b)
(c)
Figure B.10: Test 19 - Graphs (a)-(c)
96
APPENDIX B. NORWEGIAN STANDARD GRAPHS
(d)
(e)
(f)
Figure B.11: Test 19 - Graphs (d)-(f)
97
APPENDIX B. NORWEGIAN STANDARD GRAPHS
(g)
(h)
Figure B.12: Test 19 - Graphs (g)-(h)
98
APPENDIX B. NORWEGIAN STANDARD GRAPHS
(a)
(b)
(c)
Figure B.13: Test 20 - Graphs (a)-(c)
99
APPENDIX B. NORWEGIAN STANDARD GRAPHS
(d)
(e)
(f)
Figure B.14: Test 20 - Graphs (d)-(f)
100
APPENDIX B. NORWEGIAN STANDARD GRAPHS
(g)
(h)
Figure B.15: Test 20 - Graphs (g)-(h)
101
APPENDIX B. NORWEGIAN STANDARD GRAPHS
(a)
(b)
(c)
Figure B.16: Test 21 - Graphs (a)-(c)
102
APPENDIX B. NORWEGIAN STANDARD GRAPHS
(d)
(e)
(f)
Figure B.17: Test 21 - Graphs (d)-(f)
103
APPENDIX B. NORWEGIAN STANDARD GRAPHS
(g)
(h)
Figure B.18: Test 21 - Graphs (g)-(h)
104
APPENDIX B. NORWEGIAN STANDARD GRAPHS
(a)
(b)
(c)
Figure B.19: Test 22 - Graphs (a)-(c)
105
APPENDIX B. NORWEGIAN STANDARD GRAPHS
(d)
(e)
(f)
Figure B.20: Test 22 - Graphs (d)-(f)
106
APPENDIX B. NORWEGIAN STANDARD GRAPHS
(g)
(h)
Figure B.21: Test 22 - Graphs (g)-(h)
107
APPENDIX B. NORWEGIAN STANDARD GRAPHS
(a)
(b)
(c)
Figure B.22: Test 23 - Graphs (a)-(c)
108
APPENDIX B. NORWEGIAN STANDARD GRAPHS
(d)
(e)
(f)
Figure B.23: Test 23 - Graphs (d)-(f)
109
APPENDIX B. NORWEGIAN STANDARD GRAPHS
(g)
(h)
Figure B.24: Test 23 - Graphs (g)-(h)
110
APPENDIX B. NORWEGIAN STANDARD GRAPHS
(a)
(b)
(c)
Figure B.25: Test 30 - Graphs (a)-(c)
111
APPENDIX B. NORWEGIAN STANDARD GRAPHS
(d)
(e)
(f)
Figure B.26: Test 30 - Graphs (d)-(f)
112
APPENDIX B. NORWEGIAN STANDARD GRAPHS
(g)
(h)
Figure B.27: Test 30 - Graphs (g)-(h)
113
APPENDIX B. NORWEGIAN STANDARD GRAPHS
(a)
(b)
(c)
Figure B.28: Test 31 - Graphs (a)-(c)
114
APPENDIX B. NORWEGIAN STANDARD GRAPHS
(d)
(e)
(f)
Figure B.29: Test 31 - Graphs (d)-(f)
115
APPENDIX B. NORWEGIAN STANDARD GRAPHS
(g)
(h)
Figure B.30: Test 31 - Graphs (g)-(h)
116
Appendix C
EN-13240 Graphs
The subtitles of the following graphs correspond to:
(a)
Fuel burnt against time
(b)
CO2 and O2 content in the dry flue gas in Vol% against time
(c)
Total hydrocarbon content in the dry flue gas in ppm and CO content in the dry
flue gas in Vol% against time1
(d)
Combustion chamber and chimney inlet temperatures against time
(e)
Stack and dilution tunnel filter temperatures against time
(f)
Pitot and chimney negative pressures against time
1
Only Tests 35 and 36 include Total hydrocarbon content
117
APPENDIX C. EN-13240 GRAPHS
119
(a)
(b)
(c)
Figure C.1: Test 35 - Graphs (a)-(c)
APPENDIX C. EN-13240 GRAPHS
120
(d)
(e)
(f)
Figure C.2: Test 35 - Graphs (d)-(f)
APPENDIX C. EN-13240 GRAPHS
121
(a)
(b)
(c)
Figure C.3: Test 36 - Graphs (a)-(c)
APPENDIX C. EN-13240 GRAPHS
122
(d)
(e)
(f)
Figure C.4: Test 36 - Graphs (d)-(f)
APPENDIX C. EN-13240 GRAPHS
123
(a)
(b)
(c)
Figure C.5: Test 37 - Graphs (a)-(c)
APPENDIX C. EN-13240 GRAPHS
124
(d)
(e)
(f)
Figure C.6: Test 37 - Graphs (d)-(f)
APPENDIX C. EN-13240 GRAPHS
125
(a)
(b)
(c)
Figure C.7: Test 38 - Graphs (a)-(c)
APPENDIX C. EN-13240 GRAPHS
126
(d)
(e)
(f)
Figure C.8: Test 38 - Graphs (d)-(f)
APPENDIX C. EN-13240 GRAPHS
127
(a)
(b)
(c)
Figure C.9: Test 39 - Graphs (a)-(c)
APPENDIX C. EN-13240 GRAPHS
128
(d)
(e)
(f)
Figure C.10: Test 39 - Graphs (d)-(f)
APPENDIX C. EN-13240 GRAPHS
129
(a)
(b)
(c)
Figure C.11: Test 40 - Graphs (a)-(c)
APPENDIX C. EN-13240 GRAPHS
130
(d)
(e)
(f)
Figure C.12: Test 40 - Graphs (d)-(f)