AN ABSTRACT OF THE THESIS OF
Rungsun Pianpucktr for the degree of Master of Science in Chemical Engineering
presented on September 21, 1995.
Title: Formation of NO During Pyrolysis and
Combustion of Kraft Black Liquc
Redacted for Privacy
Abstract approved:
Kristiina Iisa
Nitrogen evolution during black liquor pyrolysis and black liquor combustion
were studied using a laminar entrained-flow reactor. The experimental conditions were
700-1100°C and 0.3-2.2 seconds residence time. The pyrolysis experiments were
performed in a pure nitrogen atmosphere. The oxygen concentrations during the
combustion of black liquor experiments were 4 and 21% oxygen in a nitrogen
atmosphere, and 3 and 15% oxygen in a helium atmosphere. The black liquor used was
a southern pine liquor with 0.09 wt.% nitrogen on dry basis.
During black liquor pyrolysis, volatile species release and nitrogen release
increased as residence time increased. Part of the released nitrogen formed NO. The
NO formation depended on residence time and temperature. A maximum in the amount
of NO formed was observed in the residence time range studied at 700 and 900°C. At
1 100 °C, there was a maximum in the NO formation at a residence time below the
shortest residence time studied, 0.3 seconds. NO destruction mechanisms dominated
NO formation at long residence times and high temperatures. The NO formation data
seemed to fit fairly well with a simple pyrolysis model developed by lisa et al. The
model included three stages: instantaneous release of N, oxidation of volatilized N to
NO and reduction of NO to N2. It was suggested that the model could be improved by
using a more complicated reduction model.
During black liquor combustion, total mass loss and nitrogen release increased
as residence time and temperature increased as well. The total mass loss and the
nitrogen release were higher during combustion than during pyrolysis. Volatile and
char combustion began earlier at higher temperatures. At 700°C and 4% oxygen, there
was no combustion, at 1100°C and 21%, combustion was complete at the shortest
residence time. The amount of NO formed was higher during combustion than during
pyrolysis. NO formation increased with increasing residence time except at long
residences times when NO reduction was evident. During complete combustion, 90%
of mass, 98% of nitrogen were released and the maximum NO formed was 49% of fuel
nitrogen.
Thermal and prompt NO formation occurred during black liquor combustion
when pyrolysis occurred along with volatile and char combustion. During char
combustion alone, there was no thermal NO formed.
Formation of NO
During Pyrolysis and Combustion of Kraft Black Liquor
by
Rungsun Pianpucktr
A THESIS
submitted to
Oregon State University
in partial fulfillment of
the requirements for the
degree of
Master of Science
Completed September 21, 1995
Commencement June, 1996
Master of Science thesis of Rungsun Pianpucktr presented on September 21, 1995
APPROVED:
Redacted for Privacy
Major Professor, representing Chemical Engineering
Redacted for Privacy
Chair of D artment of Chemical Engineering
Redacted for Privacy
Dean of Grad
I understand that my thesis will become part of the permanent collection of Oregon
State University libraries. My signature below authorizes release of my thesis to any
reader upon request.
Redacted for Privacy
Rungsun Pianpucktr, Author
Acknowledgments
I would like to express my sincere appreciation to the following:
Dr.Kristiina Iisa, my major professor, who gave many valuable
comments and recommendations throughout the research.
Dr.William James Frederick who provided many suggestions.
Dr.Terry Beaumariage, Dr.Skip Rochefort, Dr.Joseph Zaworski who
were my committee members
Vichien Tangpanyapinit, Udom Techakijkajorn, Viboon Srichareonchaikul,
Varut Phimolmas, Victor and Caren Reis, Kai Wag and Yan Lu for their
coorperation during the experiments.
Scott Sinquefield who built the laminar entrained-flow reactor and solved
the problems of laminar entrained-flow reactor during the experiments.
My parents who supported and encouraged me.
Thanaporn Bansantrakul, my girl friend, who encouraged me and
was always there.
Rangsi Yokubol who helped me type some parts of the thesis.
Varong Pavarajarn who was my English counselor during the night.
Punnchalee Laothamathat and Kawin Suvatte who lent me the computer.
This research is being sponsored by the U.S. Department of Energy, ABB
Combustion Engineering, Ahlestrom Recover Inc., and Gotaverken Energy Systems.
TABLE OF CONTENTS
Page
1. Introduction
1.1 Kraft Recovery Process
1
1
1.2 NOx Air Pollution
4
1.3 Formation of NOx
5
1.3.1 Thermal NOx
1.3.2 Prompt NOx
1.3.3 Fuel NOx
5
7
8
2. Thesis Objectives
10
3. Literature Review
11
3.1 Black Liquor Combustion
11
3.2 Formation of NOx During Black Liquor Pyrolysis
11
3.3 Formation of NOx During Black Liquor Char Combustion
17
3.4 Formation of NOx During Black Liquor Combustion
18
4. Experimental Methods
23
4.1 Laminar Entrained-Flow Reactor (LEFR)
23
4.2 Analytical Methods
27
4.2.1 Chemiluminescence NO-NOx Gas Analyzer
4.3.2 Nitrogen Content
4.3 Experimental Conditions for Pyrolysis and Combustion of
Black Liquor Experiments
4.3.1 Material
4.3.2 Temperature
27
28
29
29
30
TABLE OF CONTENTS (Continued)
Page
4.3.3 Residence Time
4.3.4 Gas Atmosphere
4.3.5 Particle Heating Rate
30
30
33
4.4 Black Liquor Char Combustion
34
5. Results and Discussions
5.1 Black Liquor Pyrolysis
5.1.1 Char Yield
5.1.2 Nitrogen Remaining in Char
5.1.3 Nitrogen Release
5.1.4 NO Formation
5.1.5 Comparison of Nitrogen Release and NO Formation
5.1.6 Model for Formation of NO During Pyrolysis
5.2 Black Liquor Combustion
5.2.1 Char Yield
5.2.2 Nitrogen Remaining in Char
5.2.3 Nitrogen Release
5.2.4 NO Formation
5.2.5 Comparison of Nitrogen Release and NO Formation
35
35
35
37
38
41
46
48
50
50
55
57
60
68
5.3 Black Liquor Combustion in Helium Atmosphere
73
5.4 Black Liquor Char Combustion
77
5.5 Sources of Error
78
6. Conclusions
81
7. Recommendations for Future Work
84
Bibliography
85
Appendices
88
LIST OF FIGURES
Figure
1.1
Schematic Diagram of Kraft Recovery Cycle
Page
2
1.2
Recovery Boiler Furnace
3
1.3
Nitrogen Cycling in Atmosphere
6
1.4 Fates of Nitrogen Contained in Coal
3.1
The Behavior of Fuel Nitrogen During Black Liquor Pyrolysis
9
13
3.2 Pyrolysis Model for Carangal's Results
16
3.3 Fuel Nitrogen Conversion Pathways
19
Experimental Set-Up Diagram
23
4.1
4.2 Schematic Diagram of the Laminar Entrained-Flow Reactor
25
4.3 Cyclone Assembly
27
4.4 Chemiluminescence Reaction and Detection
28
4.5
Particle Temperature as a Function of Residence Time
33
5.1
Char Yield as a Function of Residence Time During Black Liquor
Pyrolysis
36
5.2 Char Nitrogen Content by Weight as a Function of Residence Time
During Black Liquor Pyrolysis
38
5.3 Nitrogen Release as a Function of Residence Time During Black
Liquor Pyrolysis
39
5.4 NO Formation as a Function of Residence Time During Black
Liquor Pyrolysis
41
5.5 NO Formation as a Function of Temperature During Black
Liquor Pyrolysis
44
LIST OF FIGURES (Continued)
Figure
Page
5.6 Nitrogen Release and NO Formation as a Function of Residence Time
During Black Liquor Pyrolysis
5.7 Pyrolysis Model of NO Formation
47
49
5.8 Char Yield as a Function of Residence Time During Pyrolysis and
Combustion of Black Liquor at Reactor Temperature 700°C
51
5.9 Char Yield as a Function of Residence Time During Pyrolysis and
Combustion of Black Liquor at Reactor Temperature 900°C
51
5.10 Char Yield as a Function of Residence Time During Pyrolysis and
Combustion of Black Liquor at Reactor Temperature 1100°C
52
5.11 Char Yield as a Function of Residence Time During Black Liquor
Combustion in 4 % Oxygen
53
5.12 Char Yield as a Function of Residence Time During Black Liquor
Combustion in 21 % Oxygen
53
5.13 Char Nitrogen Content as a Function of Residence Time During
Black Liquor Combustion in 4 % Oxygen
56
5.14 Char Nitrogen Content as a Function of Residence Time During
Black Liquor Combustion in 21 % Oxygen
56
5.15 Nitrogen Release as a Function of Residence Time During Black
Liquor Combustion in 4 % Oxygen
58
5.16 Nitrogen Release as a Function of Residence Time During Black
Liquor Combustion in 21 % Oxygen
58
5.17 NO Formation as a Function of Residence Time During Pyrolysis and
Combustion of Black Liquor at Reactor Temperature 700°C
61
5.18 NO Formation as a Function of Residence Time During Pyrolysis and
Combustion of Black Liquor at Reactor Temperature 900°C
61
LIST OF FIGURES (Continued)
Figure
Page
5.19 NO Formation as a Function of Residence Time During Pyrolysis and
Combustion of Black Liquor at Reactor Temperature 1100°C
62
5.20 NO Formation as a Function of Residence Time During Black Liquor
Combustion in 4 % Oxygen
64
5.21 NO Formation as a Function of Residence Time During Black Liquor
Combustion in 21 % Oxygen
64
5.22 NO Formation as a Function of Temperature During Black Liquor
Combustion in 4 % Oxygen
67
5.23 NO Formation as a Function of Temperature During Black Liquor
Combustion in 21 % Oxygen
67
5.24 Nitrogen Release and NO Formation as a Function of Residence
Time During Pyrolysis and Combustion of Black Liquor at Reactor
Temperature 700°C
69
5.25 Nitrogen Release and NO Formation as a Function of Residence
Time During Pyrolysis and Combustion of Black Liquor at Reactor
Temperature 900°C
69
5.26 Nitrogen Release and NO Formation as a Function of Residence
Time During Pyrolysis and Combustion of Black Liquor at Reactor
Temperature 1100°C
70
5.27 Nitrogen Release and NO Formation as a Function of Residence Time
During Black Liquor Combustion in 4 % Oxygen
71
5.28 Nitrogen Release and NO Formation as a Function of Residence Time
During Black Liquor Combustion in 21 % Oxygen
71
5.29 NO Formation in Nitrogen and Helium Atmosphere During Black
Liquor Combustion at Reactor Temperature 700°C
74
LIST OF FIGURES (Continued)
Figure
Page
5.30 NO Formation in Nitrogen and Helium Atmosphere During Black
Liquor Combustion at Reactor Temperature 900°C
74
5.31 NO Formation in Nitrogen and Helium Atmosphere During Black
Liquor Combustion at Reactor Temperature 1100°C
75
5.32 NO Formation in Black Liquor and Black Liquor Char Combustion
at Reactor Temperature 900°C and 2.2 seconds
77
LIST OF TABLES
Table
Page
4.1
Elemental Compositions of the Black Liquor Solids
29
4.2
Experimental Conditions for Nitrogen Atmosphere Experiments
31
4.3
Experimental Conditions for Helium Atmosphere Experiments
32
5.1
Reaction Rate Coefficients of the Pyrolysis Model
49
LIST OF APPENDICES
Page
Appendices
Appendix A Analysis of Data Procedures
A.1 Actual Black Liquor Solids Input
A.2 Total Nitrogen Input
A.3 Total NO
A.4 Conversion of Fuel N to NO
A.5 Char Yield
A.6 Total Nitrogen Remaining in Char
A.7 Nitrogen Release
A.8 Possible Maximum Relative Error in Nitrogen Release
Appendix B Experimental Data and Results
88
89
90
90
91
91
91
92
92
92
95
LIST OF APPENDIX TABLES
Table
Page
B.1 Experimental Data and Results for Black Liquor Pyrolysis and
Combustion in Nitrogen Atmosphere
96
B.2 Experimental Data and Results for Black Liquor Combustion in
Helium Atmosphere.
B.3 Experimental Data and Results for Black Liquor Char Combustion
109
112
Formation of NO
During Pyrolysis and Combustion of Kraft Black Liquor
Chapter 1
Introduction
1.1 Kraft Recovery Process
Kraft pulping recovery process destroys toxic waste, recovers chemicals from
the pulping process, and also produces energy for the pulping process. Kraft pulping is
the most widely practiced method of pulping. A schematic diagram of the Kraft
recovery cycle is shown in Figure 1.1.
Wood chips are mixed with white liquor and cooked in the cooking process.
White liquor, which contains the active pulping chemicals, NaOH and Na2S, dissolves
lignin from cellulose fiber in the wood. Then, in the washing process, the fiber is
washed in order to separate it from the spent liquor. The fiber after washing, called
pulp, is the material for making paper. The spent liquor, called weak black liquor,
consists of dissolved material and 12-15% solids (1). The weak black liquor is then
evaporated in multiple effect evaporation. The evaporated black liquor, called strong
black liquor, now contains 65-75% solids (1).
In the combustion process, the strong black liquor is used as a fuel in the Kraft
recovery furnace to generate energy. A schematic diagram of the Kraft recovery
2
furnace is shown in Figure 1.2. The residual from the bottom of the furnace, called the
molten smelt, is then dissolved to become green liquor. After that, the green liquor is
passed through the causticizing process to form white liquor and reused in the cooking
process again. In the causticizing process, NaCO3 in the green liquor is converted to
NaOH and CaCO3 by Ca(OH)2. CaCO3 is separated from the white liquor and then
calcined together with some make up CaCO3 to form reburnt lime (CaO). CaO then
reacts with water to form Ca(OH)2 which is reused in the causticizing process.
Wood chips
White liquor
NaOH, Na2S
PI
oi
Cooking
Pulp
Washing
Weak black liquor
(12 15% solids)
Condensate
Evaporation
Strong black liquor
Salt cake make up
(65-75% solids)
Combustion I
Energy
Na, S losses
Molten smelt
Dissolving
Green liquor
., NaCO3
Causticizing
Ca(OH)2
CaCO3
CaCO3 make up
Slaking
4Water
CaO
01 Calcining
Figure 1.1 Schematic Diagram of the Kraft Recovery Cycle (2)
3
GAS OUTLET
-Or
Er'
T RTIART
AIR
CYCLONE
*INDICES
SPRAY
OSCILLATORS
it
SECONDARY
AIR
11.
'JIMMIES
11
PRIMARY
AIR ­
MINIMA
SMELT
SPOUTS
STEAM COIL
AIR HEATER
SMELT
SISSOLYINS
TANK
CYCLONE
RECIRCULATING
PUMPS
FUEL AND
POPPER
FLOSS
FORCED
DRAFT FUN
GREEN LIMIER
RE C IF CULATINC
PUMPS
PUMP:,
Figure 1.2 Recovery Boiler Furnace (1)
4
1.2 NOx Air Pollution
Air pollution is air borne waste remaining from producing goods, transportation,
and generating energy. The major cause of air pollution is combustion, and combustion
is essential to human life. Impurities in fuel and incomplete combustion cause the
formation of such side products as carbon monoxide (CO), sulfur oxides (SOx), unburnt
hydrocarbons (HC), and nitrogen oxides (NOx)
all are pollutants.
There are seven forms of oxides of nitrogen. These are nitric oxide (NO),
nitrogen dioxide (NO2), nitrogen trioxide (NO3), nitrous oxide (N20), dinitrogen
trioxide (N203), dinitrogen tetraoxide (N204), and dinitrogen pentaoxide (N205). The
two most important of oxides of nitrogen with respect to pollution are NO and NO2,
generally called NOx. In the United States, NOx are emitted at a rate of about 20
million metric tons per year (3). Of this, about 11 million metric tons per year is due to
stationary source fuel combustion. NO is the main oxide of nitrogen formed during the
combustion in stationary sources, about 95% of total oxides of nitrogen (4).
NOx together with hydrocarbons in high concentration can cause photochemical
smog, the grayish haze seen over urban areas, which impairs vision. In daylight NOx
and the hydrocarbons react with sunlight to produce ozone (03). Ozone in high
concentration reduces visibility. In the lower troposphere, NOx can result in the
formation of ozone which is a greenhouse gas. N20 is a greenhouse gas as well. High
concentrations of greenhouse gases increase the global temperature and this is called the
greenhouse effect.
5
NOx itself never reaches the upper troposphere and stratosphere. The major
source of NOx in the upper troposphere and stratosphere is the oxidation of nitrous
oxide (N20). The presence of NOx in the upper troposphere and stratosphere
contributes to the depletion of ozone. The depletion of ozone will allow more UV
radiation to earth which causes human skin cancer and climate change. NOx along with
SOx are responsible for acidity in rain and snow. Dry deposition of NOx on the ground
level is also reported. Inhalation of NOx in high concentrations can affect directly to
human health. Cycling of nitrogen in the environment is shown in Figure 1.3.
The U.S. Clean Air Act Amendments of 1990 (CAAA 90) require the
Environmental Protection Agency (EPA) to identify alternative control technologies for
all categories of stationary sources of volatile organic compounds (VOC) or NOx that
have the potential to emit 25 tons per year or more of either pollutant (5).
1.3 Formation of NOx
The formation of NOx during the combustion is generally attributed to several
mechanisms.
1.3.1 Thermal NOx
Thermal NOx is formed according to the Zeldovich mechanism (7), in which
NOx is formed by reactions between nitrogen and oxygen in the combustion air. It
consists of three reactions:
6
ozone layer
03
NO+02->NO2+0,
ozone
long range transport
depletion
stratosphere/upper troposphere
troposphere
NO2+0H->11NO3
/
2NO2+H20->HNO,+HNO2
NO2+NO+H20->2HNO2
NO+OH->HNO2
0
lightning
"I
atmospheric NO, NO2 and N20
NO +H02 <- >NO2 +OH
R02+NO->R0+NO2
NO2->N0+0
0 +02->0
/
deposition
//
/
/
/
//
/
/
dry
wet
fertilizer/
manure
s21
power micro
stations/ ac ivity
industry
ornass
burning
Ili 4,
4/34/
4/ 4/ 4)
acidification
°
F1
groundwater
leaching
Figure 1.3 Nitrogen Cycling in Atmosphere (6)
0 + N2
<=>
NO + N
(1.1)
N + 02
<=->
NO + 0
(1.2)
N + OH
<=>
NO + H
(1.3)
Reactions 1.1 and 1.2 are the most significant in the Zeldovich mechanism. The
reactions occur at high temperatures, normally above 1300°C. The formation of NOx
by this mechanism increases rapidly with rising temperature. The rate of formation of
7
thermal NOx is also affected by the concentration of oxygen atoms and OH radicals in
flame. It may be assumed that the fuel combustion reactions (between C, H and 0) are
in equilibrium; hence, equilibrium equations can describe the concentrations of 0, H
and OH.
1.3.2 Prompt NOx
Prompt NOx formation was originally described by Fenimore in 1971 (8). In
the prompt NOx mechanism, hydrocarbon radicals originating from the fuel combine
with nitrogen in the combustion air and generate nitrogen containing hydrocarbons
(such as HCN) and nitrogen atoms.
N2 + CH
(1.4)
HCN + N
Hydrogen cyanide (HCN) can be converted to NO or N2 by these reactions (8):
NO
HCN --' NCO
NH,' N2
/
(1.5)
N ENO
N2
Nitrogen atoms may react with molecular oxygen or hydroxyl radicals (reaction
1.2 or 1.3) to form NO. Consequently, the degree of conversion of prompt NOx
8
depends on the hydrocarbon radicals concentrations and the rate of formation of the
nitrogen containing hydrocarbon compounds. The reaction rates depend on temperature
and pressure as well, normally they occur at low temperature and low pressure.
Compared to the total NOx quantity in most combustion processes, prompt NOx is of
minor importance.
1.3.3 Fuel NOx
The formation of NOx from fuel bound nitrogen is significant to the total NOx
formation in most combustion processes. Fuel NOx can account for over 50% of the
total NOx. (9) Nitrogen contained in the fuel is oxidized to form NOx. However, the
reaction mechanisms are complex and not fully known.
During the combustion process, the volatile part of fuel bound nitrogen is
converted to HCN (formed from aromatic compounds) and NH3 (formed due to
amines). Similar to prompt NOx formation, HCN and NH3 are converted to chemical
radicals containing nitrogen atoms which react rapidly with oxygen carrying
components.
Hydrogen cyanide can be converted to NO or N2 as in reaction 1.5. Similar
reactions seem to be likely for ammonia (NH3).
In coal combustion, the possible reaction paths are shown in Figure 1.4. The
rate of formation of NOx in char reactions is dependent on flame temperature, air/fuel
ratio and char characteristics. In gas phase reactions resulting from volatile fraction of
9
hydrocarbon and nitrogen compound (R-N), the reaction rates are highly dependent
upon the air/fuel ratio and gas phase nitrogen concentration. Contrast to thermal NOx,
temperature changes do not seem to affect the reaction rates (10).
Path A
Volatile
fraction R-N
Reduced in heat
release zone
Path B
To flue gases
(Oxidized)
Coal
Reduction in
Char
N
Oxidize at
particle surface
boundary layer
Escape from
boundary layer
Ash
free
Figure 1.4 Fates of Nitrogen Contained in Coal (11)
0
10
Chapter 2
Thesis Objective
The study of NOx emissions from recovery boilers is presently of interest since
new regulations require lower NOx emissions. There have been several studies of NO
formation during black liquor pyrolysis. However, there are only few studies of black
liquor combustion. This thesis is the study of NO formation during pyrolysis and
combustion of black liquor using a laminar entrained-flow reactor. The objectives of
this study are:
to obtain and compare nitrogen evolution data during pyrolysis and
combustion of black liquor
to determine the effect of residence time and temperature on nitrogen
evolution during black liquor pyrolysis and black liquor combustion
to investigate the effect of oxygen concentration on nitrogen evolution
during combustion of black liquor
to study the effect of prompt and thermal NO formation during black liquor
combustion
to examine char combustion separate from pyrolysis and pyrolysis
products combustion
11
Chapter 3
Literature Review
3.1 Black Liquor Combustion
Black liquor combustion involves four stages -- drying, devolatilization, char
burning and smelt coalescence (1). Drying occurs immediately when heat is transferred
from the surroundings to the particles and water is evaporated from the particles.
During devolatilization, volatile gases are released from the fuel particles due to the
rapid destruction of the organic macromolecules in the liquor, which is called pyrolysis,
and then the volatile gases react with oxygen in combustion air, which is called volatile
combustion. After pyrolysis, black liquor is swollen and has become a porous char.
During char combustion, carbon is oxidized to CO and CO2. After char combustion, the
residue, mainly sodium salts, melts and coalesces.
3.2 Formation of NOx During Black Liquor Pyrolysis
Aho et al. (12,13) conducted two pyrolysis studies. In their experiments, a
single droplet of black liquor was suspended on a platinum hook, lowered into a reactor
and removed after 300 seconds. The reactor was in an argon environment. The furnace
temperature was varied between 300°C and 900°C. The nitrogen compounds, NO and
NH3, released during the experiments were measured.
12
In the first study (12), the pyrolysis of one soft wood liquor and one hard wood
liquor were studied at different temperatures in an oxygen free environment. The
results indicated that very little or no HCN was formed during black liquor pyrolysis, or
that all of the HCN formed might have been converted to NH3. The major fixed
nitrogen gas released during pyrolysis of black liquor was ammonia. Only small
amounts of NO were detected. They also found that fixed nitrogen (NIX), referring to
HCN, NH3, and NO, was released during the pyrolysis stage after drying. About 15­
20% of the nitrogen originally present in the black liquor was released as MI, during
pyrolysis of black liquor. The rate of Nth released increased with rising temperature. A
maximum yield of Nth, released was observed at temperatures between 600-800°C. At
higher temperatures, NIX decreased probably due to secondary pyrolysis reactions, in
which Nfix is converted to molecular nitrogen.
In the second study (13), the same experiments were conducted at two
temperatures, 600°C and 800°C, with different types of black liquor samples. Most of
Nfix was ammonia in these experiments as well. At 800°C, the NO formation was less
than at 600°C. The amount of NO was about the same for all black liquor samples.
However, the amount of Nfix released during pyrolysis of black liquor increased with
increasing nitrogen content in the black liquor sample. The conversion of fuel nitrogen
in black liquor to Nth, was roughly 10-30%; about 7-28% was NH3, and about 1-2% was
NO. The total NIX released was linearly proportional to the fuel nitrogen content in the
liquor. Aho et al. found that 20-60% of fuel nitrogen was released during pyrolysis of
black liquor at 400°C. Based on this estimate of nitrogen release, approximately halfof
13
the nitrogen release was Nfix and Aho et al. assumed that the rest was molecular
nitrogen. A schematic of the behavior of fuel nitrogen during black liquor pyrolysis as
suggested by Aho et al. is illustrated in Figure 3.1.
Figure 3.1. The Behavior of Fuel Nitrogen During Black Liquor Pyrolysis (13)
The level of Nfix during black liquor pyrolysis was similar to the levels observed
in Kraft recovery boilers. Assuming that all fixed nitrogen is converted to NOx in the
recovery furnace, Aho et al. concluded that the nitrogen released in the pyrolysis stage
may be the most significant source of NO in Kraft recovery boiler.
Forssen et al. (14) conducted more pyrolysis experiments in the same reactor as
Aho et al. The nitrogen remaining in the char and char yield were measured. The
results showed that the char nitrogen decreased as temperature was increased during
300-500°C, was constant during 500-900°C, and then decreased at 1000°C. The
14
average char nitrogen at 500-900°C was approximately 20-30% of nitrogen originally
present in black liquor. At 1000°C, the char nitrogen was significantly lower. The
average char yield was 50% of black liquor solids at furnace temperatures 500-800°C.
At 900-1000°C, the char yields decreased to below 20% of black liquor solids. It was
suggested that at 900°C, the nitrogen still remained in the residues while most of char
mass had devolatilized.
Experiments of black liquor pyrolysis in a laminar entrained-flow reactor were
conducted by Carangal (15). Black liquor solids with particle size of 90-125 [tm and 0.11
wt.% nitrogen (dry basis) were used in the experiments. The reactor and the experimental
methods were the same as in our pyrolysis experiments (and are described in chapter 4).
Ammonia was measured by an absorption method. However, the ammonia data were
scattered and no conclusion could be reached. The results indicated that NO formation
during black liquor pyrolysis was dependent on the reactor temperature. At a constant
residence time, the conversion of fuel nitrogen to NO increased with increasing
temperature and reached a maximum, after which the NO level decreased. As a function
of residence time, the NO formation increased as residence time increased, and again
decreased at long residence times. A maximum in the formation of NO was observed at
0.8 seconds for 800°C and 0.5 seconds for 900°C. However, there was no maximum in
NO observed at 700°C. It was suggested that the NO destruction mechanisms dominated
at high temperature and/or long residence time. Carangal suggested that the destruction
of NO may have been due to homogeneous reactions of NO with other gas species, or
heterogeneous reactions of NO with char or fume.
15
The nitrogen content in the char was approximately constant at an average of
0.10 wt.% for all experiments. The char yield decreased with increasing residence time
and temperature. At 0.3 seconds which was the shortest residence time of the
experiments, the char yield was approximately 60% of black liquor solids. It was
implied that the volatile species were released significantly before the 0.3 seconds
residence time. This agreed with Frederick (16) who stated that major devolatilization
is complete at a residence time less than 0.1 seconds.
From the results of Carangal, a model of nitrogen volatilization was developed
by Iisa et al. (17). The model assumed that the nitrogen in black liquor pyrolysis was
involved in three stages: release of nitrogen from black liquor, oxidation of nitrogen
released to NO, and reduction of NO.
Nbls
Nyot
(3.1)
NO
(3.2)
Nred
(3.3)
ko,
Nyol
kred
NO
The nitrogen release (Noi) was assumed to be instantaneous. The oxidation and
reduction reactions were assumed to be irreversible and first order. The reaction rate
coefficients are denoted as ko, and kred respectively. Thus, the NO concentration can be
calculated by the following equation.
[NO] = [Nvoi
(e-krcdt
ko,
k
e-k,t
(3.4)
where t is the residence time and [NOdo is the initial concentration of N1.
16
The model fitted reasonably with the pyrolysis experiments at 800 and 900°C
with different residence times. The fitted values were; at 800°C, kox 0.84 1/s, kred 1.09
1/s, and at 900°C, 1(0, 1.97 1/s, kred 2.56 1/s. By subtracting the time at which NO
started forming from the residence time, the model fitted better. The results of the fits
to NO formation are shown in Figure 3.2. The reduction rate coefficient kred from the
model was of the same order of magnitude as the char reduction rate coefficient, while
it was five orders of magnitudes faster than the fume reduction rate coefficient.
Therefore, it was suggested that the reaction of NO by char was significant in the
pyrolysis of black liquor.
700°C
25
C5
800°C
900°C
20
0
.*
15
A
111
-
A
10
_
A
Z
A
5
0
0.0
0.5
1.0
1.5
Resident time, s
Figure 3.2 Pyrolysis Model for Carangal's Results
2.0
17
3.3 Formation of NOx During Black Liquor Char Combustion
Forssen et al. (14) conducted experiments of black liquor char combustion. The
reactor and experimental methods were the same as described in pyrolysis experiments
by Aho et al. (section 3.2). The NO and CO2 concentrations were measured during the
experiments. The black liquor droplet was devolatilized for 100 seconds in a nitrogen
atmosphere, then a combustion gas mixture (N2 and 02) was instantaneously
introduced. The results showed that at 700 and 800°C in 1% oxygen, CO2 formation
occurred in the beginning of the char burning, while NO formation occurred in the end.
At 900°C in 1% oxygen, there were two peaks of CO2 and NO formation, one in the
beginning and one in the end of the char burning. Maxima of CO2 and NO were
observed at the same time at 900°C in 1% oxygen. At 1000°C and I% oxygen, there
were maxima in CO2 and NO formation in the beginning of the char burning, after
which NO and CO2 gradually decreased. At 700°C in 1-10% oxygen, the major part of
NO formation again occurred in the beginning of the char burning. It was suggested
that when NO formation started to increase, char burning had ended. In order to verify
this, Forssen et al. performed a series of experiments by changing the oxygen mixture to
pure nitrogen for some times after the CO2 formation was complete, then switching
back to the oxygen mixture again. In the pure nitrogen atmosphere, there were few
small peaks of CO2 formation but no NO formation was observed. After reintroducing
the oxygen mixture, no CO2 formation occurred while the NO level increased similar to
the earlier oxygen mixture experiments. From these results, Forssen et al. concluded
18
that part of nitrogen remained in the residual salt and oxidized to NO after all the
carbon in the char had been consumed.
In 1% oxygen, the conversion of nitrogen to NO was much lower than the
conversion of carbon to CO2 at temperatures below 900°C. At higher temperatures, the
fraction of NO released was about the same as the fraction of CO2 released. The NO
level in 1% oxygen at 700-900°C was 10 mg N / 100 g BLS which is about two thirds
of the char nitrogen. At 1100°C in 1% oxygen, the amount of NO was 30 mg N / 100 g
BLS which is double the amount of nitrogen in the char. It was suggested that during
black liquor char combustion experiments above 950°C, the NO formed might be partly
thermal NO.
The NO formation pathways were suggested by Forssen et al. as shown in
Figure 3.3. The nitrogen released during the pyrolysis was about 70% of black liquor
nitrogen. Approximately 30% of nitrogen remained in the char. Two thirds of nitrogen
remaining in the char might form NO in an oxidative environment. It was suggested
that under oxygen free, char nitrogen would remain in inorganic residues and could be
carried out from the furnace along with the smelt.
3.4 Formation of NOx During Black Liquor Combustion
Nichols and Lien (18) conducted experiments of black liquor combustion. The
objective of the first part of the study was to understand how fuel NOx and thermal
NOx contribute to the total NOx emitted from recovery furnaces. Their reactor
19
NO
N2
NH3
35%
35%
Fuel-N
30%
N2
Nchar
NO
N2
Nsmeli
NO
Ngreen
Figure 3.3 Fuel Nitrogen Conversion Pathways (14)
consisted of a vertical tube furnace placed above a char bed furnace. Black liquor
droplets were fed from the top into the tube furnace and they fell down through the
furnaces with a gas flowing upward. A comparison was made between the combustion
of black liquor in air and in synthetic air (21% 02 in Ar). However, they found that
there was an air leakage to the system during the synthetic air experiments. The N2
content was thus reduced from 79% in air to 16% in the synthetic air experiments. The
results indicated that the NOx concentration average was about 50 ppm both in air and
20
in synthetic air. If thermal NOx was generated during these combustion experiments,
this change in N2 content should have affected the total NOx. Therefore, Nichols and
Lien concluded that thermal NOx had no significant effect during the combustion of
black liquor, and all the NOx formed was concluded to be fuel NOx.
From the simplified expression for the maximum of thermal NOx formation,
Nichols and Lien concluded that temperatures from 1430 to 1530°C require residence
times of 2.0-0.1 seconds to generate 10 ppm of thermal NOx (19). The highest
temperature in a recovery furnace, reported by Whitten et al., was 1320°C (20). It is not
high enough to produce significant amounts of thermal NOx.
The results of NOx measurements at different heights from the char bed showed
that 40% of the maximum NO (28 ppm average) was produced near the char bed. The
rest of the NO was produced during the in-flight burning. The in-flight burning was
mainly devolatilization. Thus, the major part of NOx was formed during the
devolatilization stage. The NO level first increased with increasing distance and
reached a maximum at the second farthest point from the char bed. The maximum NO
level average was 78 ppm. The NO level then decreased to an average of 50 ppm at the
farthest point from the char bed. The reason may be that NO reacts with other species.
The possibilities are NOx reduction by particles and char, or gas phase reactions.
A second study was conducted in order to compare NOx formation in black
liquor combustion with two different nitrogen contents, a mill liquor and a low nitrogen
synthetic liquor, and to study the effect of temperature change on NOx formation in
black liquor combustion. For this study, Nichols and Lien used another reactor, a tube
21
furnace reactor. The results indicated that higher nitrogen contents in black liquor gave
higher NOx levels. Therefore, it was concluded that the NOx formed during black
liquor combustion was fuel NOx. The conversion of fuel nitrogen to NOx in the lower
nitrogen liquor was higher than in the higher nitrogen liquor which agreed with the
finding of Bowman (21) for other fuels. The NOx concentration increased as the
temperature was increased from 800°C to 900°C. The reason for the increase in NOx
concentration when the temperature was changed from 800 to 900°C was suggested to
be that more nitrogen was released during pyrolysis at the higher temperature. There
was no change in the NOx level when the temperature was further increased to 1000°C.
From these experiments, the NOx formed during black liquor combustion is not highly
sensitive to temperature. This agreed with the results of Pershing and Wendt (22) for
fuel NOx in coal combustion.
Forssen et al. (23) also conducted experiments of combustion of single black
liquor droplet at 900°C in 10% oxygen. The reactor and experimental method were the
same as in the pyrolysis experiments by Aho et al. (as described in section 3.2). Two
peaks of NO formation were observed during the combustion experiments. Forssen et
al. suggested that the first peak was due to release of nitrogen during pyrolysis. The
second peak was the NO formation after the char combustion complete as described in
section 3.3. From this suggestion, the average pyrolysis NO was 60% of the total NO
formed for 17 liquors. The total NO formation average was 45% of the black liquor
nitrogen. The data were converted to corresponding to NO emissions from recovery
boilers. The total NO emission levels base on the experiments were 120-180 ppm. The
22
NO emission level from formation of NO during pyrolysis and volatile combustion was
70-120 ppm which agreed well with typical NO emission from the recovery boilers.
Forssen et al. concluded that recovery boiler NO emission originated from fuel
nitrogen.
23
Chapter 4
Experimental Methods
4.1 Laminar Entrained-Flow Reactor (LEFR)
The pyrolysis and combustion of black liquor solid experiments were conducted
in a laboratory scale laminar entrained-flow reactor equipped with a cyclone and a
chemiluminescence NO-NOx analyzer. The experimental set-up diagram is shown in
Figure 4.1.
Primary flow
LEFR
Secondary flow
o.
Quench flow
to exhaust
Cyclone/filter
NO-NOx analyzer
to exhaust
exhaust
Figure 4.1 Experimental Set-Up Diagram
24
Figure 4.2 shows a schematic diagram of the laminar entrained-flow reactor.
The LEFR consists of two cylindrical mullite tubes. The smaller mullite tube has an
inside diameter of 70 mm. There is a three heating zone furnace outside the mullite
tubes, each zone is 12 inches long. The maximum furnace temperature is 1200°C. The
temperature of the furnace is controlled by an Omega CN76000 Micro-processor Based
Temperature/ Process Controller capable of ramping to its set point temperature at a
maximum heating rate of 300°C/hr.
The reactor operates with a high temperature gas flowing downward at laminar
conditions. There are primary and secondary gas streams entering the reactor. There is
another gas stream, a quench gas stream, entering through the collector. All gas flows
are controlled by Omega FMA5600 Electronic Mass Flow Meter (MFM).
The particles are entrained by the primary gas stream from the feeder, and flow
through the injector into the center of the inner mullite tube. To prevent change of
particle temperature before entering the reaction zone, the primary gas stream is kept
cool throughout the injector by cooling water. The secondary gas stream is preheated
when flowing upward through the annular space between the mullite tubes. The
secondary gas stream then flows downward into the inner tube through a flow
straightener. The primary and secondary flows merge together to form a single laminar
flow entering the reaction zone. The particles are instantly exposed to the high
temperature of the secondary gas stream and the hot reactor wall when they enter the
reaction zone. The heating rate of small particles is very rapid (>104°C/sec).
25
primary gas flow
cooling water
C
injector
flow straightener
MFM #5
C:::,
Zone I
(-OE-
Zone 1
particle
feeder
REACTOR
Zone 2
MFM #I
<ZD
Zone 2
feed as
MFM #2
Zone 3
Zone 3
MIX
V'
feed gas 2
0
N1FM 43
secondary gas flow
4
secondary gas flow
-1
MFM #4 feed 20s 3
COLLECTOR
is.
feed gas 4
roclmeter for collator tip
MFM 46
cooling %pier
<
quench gas flow
to CYCLONE
1-1
quench gas feed
rota:neer for collector body
Figure 4.2 Schematic Diagram of the Laminar Entrained-Flow Reactor
26
After the particles and gas streams pass through the reactor, they are cooled
down by the quench gas stream which enters through the collector. Most of the quench
gas stream enters near the tip of collector, called the tip quench stream, to rapidly
decrease the temperature of the particles. The rest, called the wall quench stream, flows
through the porous wall of the collector to prevent deposition of particles on the wall
and further decrease the temperature. The residence times of the particles can be
controlled by changing the reactor pathlenght (moving collector up or down) or by
changing the primary and secondary gas flows. The residence times were calculated by
a predictive model based on Flaxman's computational fluid dynamic algorithm. (25)
In the long residence time experiments, a small fixed collector was used. The
collector cannot be moved. Thus, the reactor pathlenght was fixed at the maximum
pathlenght of 41 inches. However, the residence times could still be controlled by
changing the gas velocity.
The particles and the gas stream then enter the cyclone. The cut size of the
cyclone is 3 mn. Most of the gas stream flows through the exhaust duct. The rest
flows through a filter of 2.2 pm pore size into the chemiluminescence NO-NOx
analyzer for NO measurement. A schematic diagram of the cyclone assembly is shown
in Figure 4.3.
27
incoming gas
from collector
cyclone
to exhaust
L
cyclone compartment
for char collection
f lter 2
j
filter 1
to NO-NOx analyzer
Figure 4.3 Cyclone Assembly
4.2 Analytical Methods
4.2.1 Chemiluminescence NO-NOx Gas Analyzer
The NO concentration is determined by measuring light emitted from the
chemiluminescence reaction of NO with 03 in the reaction chamber. Figure 4.4
illustrates the analytical technique based on this principle.
28
Chemiluminescence Reaction
NO + 03 -> NO2 + 02
NO2 + ho (photons)
Signal is proportional to [NO]
d[photons]
oc
dt
[03] [NO]
Figure 4.4 Chemiluminescence Reaction and Detection (24)
The light emission is measured through an optical filter by a high sensitivity
photomultiplier. The output from the photomultiplier is directly proportional to the NO
concentration.
For NOx (NO and NO2) measurement, there is a converter for quantitatively
reducing NO2 to NO before entering the chemiluminescence reaction chamber.
4.2.2 Nitrogen Content
The nitrogen content in black liquor solids and black liquor char was analyzed
by the Plant Analysis Lab in the Department of Soil Science, Oregon State University.
The analytical method was the Kjeldahl analysis.
In the Kjeldahl method, the sample is digested by a strong acid at a high
temperature to convert nitrogen to ammonia. The ammonia is then distilled and back
titrated with an acid. The total moles of nitrogen are equivalent to the moles of
ammonia.
29
4.3 Experimental Conditions for Pyrolysis and Combustion of Black Liquor
Experiments
4.3.1 Material
Black liquor solids obtained by drying a southern pine kraft black liquor and
grinding to fine particle sizes were used in all experiments. The particle size of 90-125
pm was used to minimize temperature gradient and external mass transfer effects, and
to obtain uniform feeding rate with minimum plugging. The composition of the black
liquor solids is shown in Table 4.1.
Table 4.1 Elemental Compositions of the Black Liquor Solids
Element
Wt. %
Carbon
35.70
Hydrogen
3.05
Sodium
22.65
Sulfur
2.85
Potassium
0.62
Chloride
0.67
Nitrogen
0.09
Oxygen­
34.37
* obtained by difference
30
4.3.2 Temperature
The effect of temperature on pyrolysis and combustion was investigated. The
temperatures of the reactor in the experiments were 700, 900 and 1100°C. This
temperature range was chosen because it is the same range as in a recovery boiler.
4.3.3 Residence Time
The effect of residence time on pyrolysis and combustion was studied. The
residence times ranged from 0.3 to 2.2 seconds. The residence times were calculated by
Flaxman's computational fluid dynamic and heat transfer model for particles in laminar
entrained-flow reactors (25). The model accounts for momentum transport, gas particle
slip, and convective and radiative heat transfer between gas, reactor wall and particles.
The residence times were adjusted by changing the reactor pathlenght and/or changing
the gas stream flow rates.
4.3.4 Gas Atmosphere
Most of the experiments were run in nitrogen with different oxygen
concentrations. The oxygen contents were 0% oxygen for pyrolysis experiments, 4%
and 21% oxygen for combustion experiments. Some helium environment experiments
with 2.9% and 15.4% oxygen were run at residence times of 0.3 and 2.2 seconds to
31
verify the effect of prompt and thermal NOx formation in the combustion experiments.
Tables 4.2 and 4.3 illustrate the experimental conditions of the experiments.
Table 4.2 Experimental Conditions for Nitrogen Atmosphere Experiments
Pyrolysis 0% 02
Temperature (°C)
Residence Time
(sec)
700
900
1100
0.3
x
x
x
0.6
x
x
x
1.1
x
x
x
1.6
x
x
x
2.2
x
x
x
Combustion 4% 02
Temperature (°C)
Residence Time
(sec)
700
900
1100
0.3
x
x
x
0.6
x
x
x
1.1
x
x
x
1.6
x
x
x
2.2
x
x
x
32
Table 4.2 Experimental Condition for Nitrogen Atmosphere Experiments (continued)
Combustion 21% 02
Residence Time
Temperature (DC)
(sec)
700
900
1100
0.3
x
x
x
0.6
x
x
x
1.1
x
x
x
1.6
x
x
x
2.2
x
x
x
Table 4.3 Experimental Conditions for Helium Atmosphere Experiments
Combustion 2.9% 02
Temperature (°C)
Residence Time
900
1100
0.3
x
x
2.2
x
x
(sec)
700
Combustion 15.4% 02
Temperature (°C)
Residence Time
(sec)
700
0.3
2.2
x
900
1100
x
x
x
x
33
4.3.5 Particle Heating Rate
The particle temperature was calculated by Flaxman's model (25). It was
estimated that the particle heating rates were in excess of 104 °C/sec. Figure 4.5 shows
plots of particle temperature with time at 700, 900 and 1100°C. The plot of particle
temperature with time indicates that the particle temperature reached the reactor
temperature within 0.2 seconds after injection into the reaction zone.
1200
1000
800
-
600
400
200
Temp 700°C
Temp 900°C
Temp 1100°C
0
0
0.4
0.8
1.2
1.6
2
Residence time (sec)
Figure 4.5 Particle Temperature as a Function of Residence Time
34
4.4 Black Liquor Char Combustion
Two experiments were performed by using black liquor char as the feeding
materials. The objective of the char combustion experiments was to investigate char
combustion separated from pyrolysis and pyrolysis products combustion and to test
thermal NOx formation during char combustion.
The char was prepared by pyrolysis in nitrogen at 1100°C reactor temperature
and 2.2 second residence time. The char then was ground to fine particles and used as
the feeding material. The experimental conditions for char combustion experiments
were 900°C reactor temperature, 2.2 seconds residence time and 21% oxygen. One
experiment was in nitrogen environment, the other was in helium environment.
35
Chapter 5
Results and Discussions
5.1 Black Liquor Pyrolysis
5.1.1 Char Yield
Figure 5.1 shows char yield as a function of residence time during black liquor
pyrolysis. The char yield decreased as residence time increased. At 700°C, the char
yield was 82% at 0.3 seconds, and it quickly decreased to 65% at 0.6 seconds. At
residence times above 0.6 seconds, the char yield gradually decreased to 53% at 2.2
seconds. This indicates that the black liquor solids were volatilized rapidly until the
residence time of 0.6 seconds, after which they were volatilized more gradually.
At 900 and 1100°C, the char yields decreased during the residence times
studied, 0.3-2.2 seconds. At the shortest residence time studied, 0.3 seconds, the char
yield was 60% at 900°C and 50% at 1100°C. This implies that substantial amounts of
volatile species in the black liquor solids were released at residence times below 0.3
seconds. The lowest char yield in this study was 20% at 1100°C and 2.2 seconds, i.e.
80% of black liquor solids were released as gas species. This indicates that
considerable amounts of inorganic material in addition to C, H, and N vaporized.
36
Temp 700°C, 02 0%
100
Temp 900°C, 02 0%
90
Temp 1100°C, 02 0%
80
70
60
50
40 _
30 _
20
10
0
0
0.5
1
1.5
2
2.5
Residence time (sec)
Figure 5.1 Char Yield as a Function of Residence Time
During Black Liquor Pyrolysis
At higher temperature, the char yields were lower. This indicates that the
amounts of volatile species released increases as temperature increases. This is in
accordance with the finding of Frederick and Hupa (26), Carangal (15), and
Forssen et al. (14).
In Carangal's experiments (15) with the same liquor, at temperatures between
700 and 1100°C, the char yields were 35-60% at 0.85 seconds. This agrees well with
our results, which show that the char yields were 30-65% at residence times between
0.6-1.1 seconds in the same temperature range. The char yields at 2.2 seconds, the
longest residence time studied, were compared to those in the study by Forssen et al.
37
(14) in which the pyrolysis times were long. The results agree well, in both studies the
char yields decreased from 50 to 20% as temperature increased from 700 to 1100°C.
5.1.2 Nitrogen Remaining in Char
The plots of char nitrogen content (by weight) versus residence time during
pyrolysis of black liquor are shown in Figure 5.2. At 700°C, the nitrogen content in the
char decreased with increasing residence time. The average of char nitrogen content at
700°C was 0.075% by weight. At 900 and 1100°C, the char nitrogen contents were
roughly constant at an average of 0.77% by weight. This indicates that at 700°C,
nitrogen is released from the black liquor faster than other volatile materials. At 900
and 1100°C, a constant nitrogen content indicates that nitrogen is released at the same
rate as other volatile materials. At residence times of 1.6 and 2.2 seconds, the nitrogen
content of the char at 700°C was even lower than at 900 and 1100°C. Because the
amount of nitrogen in the char was very low and only one sample for each point was
analyzed, there may be considerable error in the analysis. Carangal who used the same
laboratory for nitrogen measurement found that the error in the analysis was ±0.01 wt.%
nitrogen (15). In Carangal's data (15), the char nitrogen contents were approximately
constant in all pyrolysis experiments which agreed with our results at 900 and 1100°C.
Thus, all the nitrogen contents measured may have been the same.
38
0.09
I
0.08
0.07
0.06
0.05
0.04
Temp 700°C, 02 0%
0.03
Temp 900°C, 02 0%
Temp 1100 °C, 02 0%
0.02
0.01
0
0
0.5
1
1.5
2
2.5
Res idence time (sec)
Figure 5.2 Char Nitrogen Content by Weight as a Function of Residence Time
During Black Liquor Pyrolysis
5.1.3 Nitrogen Release
Figure 5.3 shows nitrogen release as a percentage of nitrogen originally present
in the black liquor solids as a function of residence time during black liquor pyrolysis at
the three furnace temperatures. The fraction of nitrogen released from black liquor was
calculated by subtracting the amount of nitrogen that remained in the char from the total
nitrogen in the black liquor solids that was fed to the reactor. The detailed calculation
is described in Appendix A.7. At 0.3 seconds, fractions of nitrogen released were 22%
of fuel nitrogen at 700°C, 46% of fuel nitrogen at 900°C, 58% of fuel nitrogen at
1100°C. The fraction of nitrogen released increased as residence time increased. At
39
100
90
80
70
-
60
50
40 _
-
A
Temp 700°C 02 0%
Temp 900°C, 02 0%
30
Temp 1100°C, 02 0%
20
10
0
0
0.5
1
1.5
2
2.5
Residence time (sec)
Figure 5.3 Nitrogen Release as a Function of Residence Time
During Black Liquor Pyrolysis
700°C, the amount of nitrogen released increased rapidly to 50% of fuel nitrogen at 1.1
seconds, then increased more gradually and reached 55% of fuel nitrogen at 2.2
seconds.
At 900 and 1100°C, the amount of nitrogen released increased gradually during
the residence time range studied, 0.3-2.2 seconds. This agrees well with the char yield
as discussed in section 5.1.1. The lowest char yield in this study was 20% at 1100°C
and 2.2 seconds, i.e. 80% of black liquor solids were released to gas species. This
concurs with the amount of nitrogen release which is also 80% of black liquor nitrogen.
The nitrogen release increased with rising temperature as well, except at 700 and
40
900°C, when it was about the same at residence times 1.6-2.2 seconds. The results
agree with the experiments of Carangal (15).
From the data, it can be concluded that the nitrogen release was 20-60% of black
liquor nitrogen at 700°C, 45-70% of black liquor nitrogen at 900°C, and 60-80% of
black liquor nitrogen at 1100°C. Carangal (15) found that at 0.85 seconds and
temperatures 700-1100°C, the nitrogen release was 40-60% of black liquor nitrogen.
This agrees with our experiments that at 0.6-1.1 seconds and 700-1100°C, the nitrogen
release was 40-70% of fuel nitrogen in black liquor.
However, Forssen et al. (14) reported considerably higher nitrogen release for
liquors with nitrogen contents of 0.06-0.09 wt.%. They found that at 600-900°C, the
fraction of nitrogen remaining in the char was constant at an average of 20-30% of fuel
nitrogen (which corresponds to 70-80% of black liquor nitrogen released). Almost all
of the nitrogen in black liquor was released at 1100°C. The results may be different
from ours due to different types of the black liquor used, or different experimental
methods. In the experiments of Forssen et al., the pyrolysis time was much longer than
in our experiments (hundreds of seconds versus a couple of seconds). Thus, more of the
volatile nitrogen in the black liquor might be released in their experiments. In our
experiments, the nitrogen release continued at 2.2 seconds. The nitrogen release at 300
seconds based on our experiments should be higher than the value we measured and
could well be the same as Forssen et al. found. We believe that our values for nitrogen
release are more representative for the conditions in a recovery boiler, since in them
char combustion typically begins in a couple of seconds.
41
5.1.4 NO Formation
Figure 5.4 shows the conversion of nitrogen originally present in black liquor
solids to NO during black liquor pyrolysis as a function of residence time at
temperatures 700, 900, and 1100°C. The results indicate that NO formation is
dependent on residence time and the temperature. At 700 and 900°C, the NO level
initially increased with increasing residence time, and then decreased as residence time
further increased. The maximum in the amount of NO formed was at a residence time
between 1.1 and 2.2 seconds at 700°C, and at 900°C the maximum was between 0.3 and
1.1 seconds. The highest NO conversion was roughly 12% of the nitrogen originally
present in the black liquor solids at both 700 and 900°C.
Temp 700°C, 02 0%
A
Temp 900°C, 02 0%
Temp 1100 °C, 02 0
0
0.5
1.5
2
2.5
Residence time (sec)
Figure 5.4 NO Formation as a Function of Residence Time
During Black Liquor Pyrolysis
42
At 1100°C, the NO level decreased with increasing residence time and in the
residence time range studied, 0.3-2.2 seconds, no maximum in the amount of NO formed
can be observed. Since there is no NO formed at 0 second residence time, there must be
a maximum in the amount of NO formed at a residence time below or near 0.3 seconds.
The highest amount of fuel nitrogen in black liquor that was converted to NO was 15%
at the shortest residence time studied, 0.3 seconds. The NO level decreases at long
residence times because NO destruction takes place and the rate of NO destruction is
higher than the rate of NO formation. At 1100°C, the destruction of NO probably
already dominates at the shortest residence time studied. The NO destruction may be
due to homogeneous reactions of NO with other gas species and/or heterogeneous
reactions of NO with fume or char to form molecular nitrogen. Based on the simple
model of black liquor pyrolysis developed by Iisa et al. (17), it was suggested that the
dominating NO destruction mechanism is the reduction of NO by char.
In the similar pyrolysis experiments of Carangal (15), the maximum NO level at
900°C was observed at 0.5 seconds. At 700°C, the highest NO formation measured was
at 1.7 seconds which was the longest residence time in her experiments. The NO level
only slightly increased from 1.4 to 1.7 seconds which may imply that there was a
maximum in the amount of NO formed near 1.7 seconds. The highest amount of NO
formed was approximately 16% of fuel nitrogen at 700°C and 19% of fuel nitrogen at
900°C in Carangal experiments (15). This indicates that the results from both black
liquor pyrolysis experiments agree well. The slight difference in the amount of NO
formed may have been due to the fact that in our experiments, only 5 residence times
43
were used, thus the actual maximum NO level might have been higher at other
residence times. The other reason may be differences in the black liquor solids.
Although the black liquor was the same, they were dried at different batches and at
different times. For instance, the nitrogen content of black liquor solids in our
experiments was 0.09% by weight, and 0.11% by weight in Carangal's experiments.
The decrease in nitrogen content from 0.11 to 0.09% by weight was probably because
more volatile nitrogen was lost and thus it is reasonable that the NO formed during
pyrolysis was lower for the 0.09% nitrogen liquor. The study of Aho et al. (12,13)
found that the fuel nitrogen released as Nfix (NH3, NO and HCN) is higher for a black
liquor that has a higher nitrogen content.
At 700°C, very little (0.09% of fuel nitrogen) NO formed at the shortest
residence time of 0.3 seconds, and at 900°C the NO formation was 5% of fuel nitrogen.
At 1100°C the NO formation was 15% of fuel nitrogen at this residence time. This
indicates that at higher temperature, fuel nitrogen in black liquor starts to form NO at
shorter residence times during black liquor pyrolysis.
The same NO formation data are shown as a function of temperature in Figure
5.5. At a residence time of 0.3 seconds, the NO level increased with increasing
temperature. At 0.6 and 1.1 seconds, there was a maximum in the amount of NO
formed at reactor temperatures between 700 and 1100°C. At 1.6 and 2.2 seconds, the
NO formation decreased as temperature increased. Since there is no NO formed at
room temperature, there must be a maximum in the amount of NO formed at
temperatures below 700°C. Thus, at very short residence times the net amount of NO
44
16
14
12
o
10
0.3 seconds
0.6 seconds
8
1.1 seconds
6
1.6 seconds
4
2.2 seconds
700
800
900
1000
1100
1200
Temperature (°C)
Figure 5.5 NO Formation as a Function of Temperature
During Black Liquor Pyrolysis
formed increases as temperature is increased, but at longer residence times, there is a
maximum in the formation of NO and NO destruction is dominating at higher
temperatures. The data also suggests that the longer the residence time, the lower the
temperature at which the maximum is located. At residence times longer than 1.6
seconds, the NO destruction has exceeded NO formation in the whole temperature
range studied. Carangal (15) found that in her experiments at 0.85 seconds, there was a
maximum in NO formation at 800°C. This agrees well with our results. In the
experiments of Aho et al. (12) the fixed nitrogen species released during pyrolysis of
black liquor increased with increasing temperature to some extent at low temperatures,
then decreased at higher temperatures.
45
The maximum in the amount of NO formed in our experiments was 12-15% of
nitrogen originally present in black liquor. In the black liquor pyrolysis experiments of
Aho et al. (13), the level of fixed nitrogen released from pine liquor (the same type as
our experiments) was 11-14% of fuel nitrogen in black liquor. Thus, the maximum NO
formed in our experiments and the fixed nitrogen in the experiments of Aho et al. were
approximately equal. Aho et al. stated that conversion of this amount to NO would
yield the same levels of NO as typical NO emissions from recovery boilers. Therefore,
Aho et al. suggested that NO formed during pyrolysis stage may be the major source of
NO emissions from recovery boilers. However, the operating temperature in a recovery
furnace is normally 1000-1200°C. Due to exothermic combustion and turbulent
fluctuations, the actual local temperature can be much higher (>1400°C) (19). At these
temperatures in our experiments, the NO level during pyrolysis is obviously affected by
the NO destruction mechanisms. Consequently, the amount of NO formed during
pyrolysis stage is probably lower than the emission level of NO in recovery boilers.
The results were also compared with the study of Forssen et al. (23). Their
experiments were performed in an oxidative atmosphere. Two peaks of NO formation
were observed. Forssen et al. assumed that the first peak of NO resulted from the
pyrolysis of black liquor and volatile combustion. The total average NO formed was
45% of nitrogen originally present in black liquor. About 60% of the amount of NO
formed originated from the pyrolysis and volatile combustion, which gave as the
pyrolysis NO average 27% of black liquor nitrogen. The higher amount of NO formed
in the Forssen et al. experiments is probably because some of NO formed in the first
46
peak originated from other nitrogen gas species reacting with oxygen in the combustion
gas or because of a different type of black liquor.
5.1.5 Comparison of Nitrogen Release and NO Formation
Figure 5.6 illustrates the fraction of nitrogen released and NO formation at
different residence times during black liquor pyrolysis. As discussed previously, at 0.3
seconds, the NO formation increased as temperature increased. The nitrogen release
increased as well. At residence times 0.6-1.1 seconds, the nitrogen release still
increased with increasing temperature but the NO formation decreased as temperature
increased from 900 to 1100°C. At residence times 1.6 and 2.2 seconds, the nitrogen
release was approximately the same at 700 and 900°C, but higher at 1100°C. However,
the NO formation clearly decreased with rising temperature. This supports the previous
discussion that the NO level is highly affected by NO destruction mechanisms at higher
temperatures and longer residence times.
At 700°C and 0.3 seconds, the nitrogen release was about 21% of the nitrogen in
black liquor, but only little NO formation was observed. At 900 and 1100°C and the
shortest residence time studied, 0.3 seconds, the amounts of nitrogen release were 46
and 58% of black liquor nitrogen respectively. Therefore, a significant amount of
nitrogen was released at the short residence time. Nevertheless, the NO levels were
only 5 and 15% of fuel nitrogen. This suggests that part of nitrogen released forms NO.
47
* N release includes shaded and black area
Figure 5.6 Nitrogen Release and NO Formation as a Function of Residence Time
During Black Liquor Pyrolysis
At the maximum NO level observed at 700 and 900°C, the NO level was 12% of
black liquor nitrogen whereas the nitrogen release was 56% of nitrogen in black liquor.
At the maximum NO level, the fractions of NO formed were 21-26% of the nitrogen
released. At its lowest, the fraction of the nitrogen release that had formed NO was
0.4% at 700°C and 0.3 seconds.
48
5.1.6 Model for Formation of NO During Pyrolysis
A simple pyrolysis model was developed by Iisa at al. (17). The details of the
model were explained in chapter 3.1. The amount of NO formed can be calculated by
this equation:
[NO] = [Nvoil
k"
kw( kd
e -k red
t.
e -k ox
t.)
(5.1)
The model was fitted to the amount of NO formed during black liquor pyrolysis
at 700, 900 and 1100°C. As a modification from Iisa et al., the time used in the model
was the residence time subtracted by the times at which it was estimated that NO started
forming, which were 0.3, 0.2 and 0 seconds for 700, 900 and 1100°C respectively. The
[Nvoik, used were the amounts of nitrogen released at 0.3 seconds, which were 22, 46,
58% of fuel nitrogen for 700, 900 and 1100°C respectively. The ko, and kred were
adjusted to minimize the sum of square of errors in the amount of NO formed using a
Marquardt optimization routine.
The results of the fits to NO formation are shown in Figure 5.7. The fitted
values of k0 and kd are shown in Table 5.1. The model seemed to fit fairly well.
However, when the amount of NO formed decreased, there was a slight difference
between the model and the experiments. The model assumed that only the NO formed
reacted to Nd. Other possible reactions during the reduction of NO are that Nv01 is
converted to Nred directly and Nvoi reacts with NO to form Nred. It is believed that the
model will fit better by using a more complicated reduction model.
49
Temp 700°C
16
Temp 900°C
14
Temp 1100°C
12
10
8
6 -­
4
2
0
0.0
0.5
1.0
1.5
2.0
2.5
Residence time, sec
Figure 5.7 Pyrolysis Model of NO Formation
Table 5.1 Reaction Rate Coefficients of the Pyrolysis Model
Temperature (°C)
k0 (1/s)
kred (1/s)
700
0.86
0.90
900
1.62
2.84
1100
9.0E+06
4.32
900*
2.90
3.27
* from Iisa et al. results using modified time
The values of ko, and kred obtained here at 900°C are close to the values from the
fits to Iisa et al. results. The kred is of the same order of magnitude as kchar which was
4.7 1/s (17). This indicates that NO reduction by char is one of the significant NO
reduction reactions during black liquor pyrolysis.
50
5.2 Black Liquor Combustion
5.2.1 Char Yield
Figures 5.8, 5.9 and 5.10 show the char yields at constant temperatures during
black liquor pyrolysis and black liquor combustion. At 700°C, the char yields in black
liquor combustion were about the same at all oxygen levels at all other residence times,
except at 1.6 and 2.2 seconds in 21% oxygen, when they were lower. This suggests that
only pyrolysis occurs, except at 1.6 and 2.2 seconds in 21% oxygen, when the char
remaining after pyrolysis started to burn. Another possibility is that the volatile species
ignited between 1.1 and 1.6 seconds, and increased the temperature of particles. Due to
the higher temperature, the volatiles release was increased. It is difficult to distinguish
between the two without measurements of the carbon content of the char or visual
observation for the phase of a flame during the combustion of the particles. In this
thesis, we refer char burning and/or gas phase burning as combustion. At 900°C, the
char yields in black liquor combustion were lower at residence times above 1.1 seconds
in 4% oxygen and above 0.6 seconds in 21% oxygen which indicates that combustion
starts at these points. At 1100°C, the char yields in combustion of black liquor were
lower than in pyrolysis of black liquor, except at 0.3 seconds in 4% oxygen. This
suggests that in oxidative atmospheres at 1100°C the combustion occurs except at 0.3
seconds in 4% oxygen.
51
A
100
Temp 700°C, 02 0%
90
Temp 700°C, 02 4%
80
Temp 700°C, 02 21%
70
60
7)
as"
^
50
40
30
20
10
0
0
0.5
1
1.5
2
2.5
Residence time (sec)
Figure 5.8 Char Yield as a Function of Residence Time
During Pyrolysis and Combustion of Black Liquor at Reactor Temperature 700°C
Temp 900°C, 02 0%
100
Temp 900°C, 02 4%
90
Temp 900°C, 02 21
80
70
0
e.
60
7:J
.1
50
tt"
40
(5
30
20
10
0
0
0.5
1.5
2
2.5
Residence time (sec)
Figure 5.9 Char Yield as a Function of Residence Time
During Pyrolysis and Combustion of Black Liquor at Reactor Temperature 900°C
52
Temp 1100°C, 02 0%
100
Temp 1100°C, 02 4%
90
Temp 1100°C, 02 21%
80
70
60
7)
>,
50
40
U
30
20
10
0
0
0.5
1.5
2
2.5
Residence time (sec)
Figure 5.10 Char Yield as a Function of Residence Time
During Pyrolysis and Combustion of Black Liquor at Reactor Temperature 1100°C
Figures 5.11 and 5.12 show the same char yield data as a function of residence
time in 4 and 21% oxygen respectively. The volatile yields approach a constant value
at the longer residence time. In 4% oxygen at 700°C, there is only pyrolysis going on,
no combustion as discussed earlier. The char yield decreased rapidly until 0.6 seconds,
after which the char yield started to level off at the pyrolysis level. At 900°C, the char
yield decreased rapidly beyond 0.3 seconds and continued to some extent even at the
longest residence time, 2.2 seconds. This indicates that combustion starts and
continues until the end of measurements. At 1100°C, the char yield first decreased
sharply during 0.3-0.6 seconds and then leveled off at a value of 15%. The
combustion is near completion at the same time.
53
100
Temp 700°C, 02 4%
90
Temp 900°C, 02 4%
80 -
Temp 1100°C, 02 4%
70 _
60
a.)
50 _
40 _
-
30
20
10 _
0
0
0.5
1.5
2
2.5
Residence time (sec)
Figure 5.11 Char Yield as a Function of Residence Time
During Black Liquor Combustion in 4% Oxygen
Temp 700°C, 02 21%
100
90
Temp 900°C, 02 21%
80
Temp 1100°C, 02 21%
70
60
50
40
30
20
10
0
0
0.5
1
1.5
2
2.5
Residence time (sec)
Figure 5.12 Char Yield as a Function of Residence Time
During Black Liquor Combustion in 21% Oxygen
54
In 21% oxygen at higher temperatures, the loss of materials from black liquor
solids approaches a constant value at shorter residence times. A constant value implies
that volatile combustion is complete or that char burning is complete as well. The char
yield at 700°C decreased from 75 to 60% when the residence time increased from 0.3 to
0.6 seconds, then there was a very slight decrease as the residence time further
increased to 1.1 seconds. At residence times between 1.1 and 1.6 seconds, the char
yield decreased rapidly to 30% and then there was no change as the residence time
further increased to 2.2 seconds. During 0.3-1.1 seconds, char yield show the pyrolysis
behavior as discussed earlier. There is a sharp decrease between 1.1 and 1.6 seconds
due to either increased pyrolysis because of a higher temperature as a result of gas
ignition or char burning, after which the char yield remained constant. At 900°C, the
char yields decreased quickly during residence times 0.3-0.6 seconds, then gradually
decreased. This indicates that combustion begins during 0.3-0.6 seconds. At 1100°C,
the char yield was 12% at the shortest residence time, 0.3 seconds, and very slowly
decreased after that. This indicates that combustion was already complete at 0.3
seconds.
In both 4 and 21% oxygen, the char yields decreased with increasing
temperature as well. In other words, the amounts of volatile species released depends
on temperature.
From the data, it can be concluded that complete combustion occurs at 1.6
seconds at 900°C in 21% oxygen, 1.1 seconds at 1100°C in 4% oxygen, and 0.3
seconds at 1100°C in 21% oxygen. This suggests that at 1100°C in 21%, the black
55
liquor combustion is complete at very short residence times. At lower temperatures and
lower oxygen concentrations, the combustion of black liquor requires longer residence
time for completion. The char yields were on average 11% when the combustion was
complete. This indicates that the maximum loss of mass from black liquor solids is
approximately 89% under these conditions. It can be observed that the residue from the
combustion of black liquor is inorganic salts.
5.2.2 Nitrogen Remaining in Char
Figures 5.13 and 5.14 illustrate the nitrogen remaining in the char (by weight)
versus residence time in 4 and 21% oxygen. In both oxygen concentrations, the char
nitrogen content decreased as a function of residence time during 0.3-1.6 seconds.
During 1.6-2.2 seconds, the nitrogen content in the char seemed to be constant or
slightly decrease. The nitrogen remaining in the char decreased as temperature increased
at all residence times. In 4% oxygen, the char nitrogen contents were relatively close
(0.073-0.09% by weight) at the shortest residence time, 0.3 seconds, whereas in 21%
oxygen, the nitrogen contents in the char were close at 700 and 900°C but considerably
lower at 1100°C. The lowest char nitrogen content, 0.013% by weight, was observed at
2.2 seconds both in 4 and 21% oxygen.
56
Temp 700°C, 02 4%
0.09
Temp 900°C, 02 4%
0.08
Temp 1100°C, 02 4%
0.07
-A
0.06
-
0.05
0.04
0.03
0.02
0.01
0
0
0.5
2
1.5
2.5
Residence time (sec)
Figure 5.13 Char Nitrogen Content as a Function of Residence Time
During Black Liquor Combustion in 4% Oxygen
A
0.09
Temp 700°C, 02 21%
Temp 900°C, 02 21%
0.08
Temp 1100°C, 02 21%
0.07
0.06
0.05
0.04
0.03
0.02 _
0.01
0
0
0.5
1.5
2
2.5
Residence time (sec)
Figure 5.14 Char Nitrogen Content as a Function of Residence Time
During Black Liquor Combustion in 21% Oxygen
57
It is worth to note that there is considerable uncertainty in the nitrogen content
measurements as discussed earlier in section 5.1.2. Hence, it is believed that the
nitrogen content at 900°C in 21% oxygen is better presented by a smooth decline in
nitrogen content than a curve linking the individual data points.
5.2.3 Nitrogen Release
Figures 5.15 and 5.16 illustrate the plots of nitrogen release versus residence
time in 4 and 21% oxygen. The nitrogen releases are consistent with the char yields
which represent the mass releases. In 4% oxygen, at 700°C when only pyrolysis
occurs, the nitrogen release increased quickly at residence times 0.3-0.6 seconds, then
increased more slowly as the residence time further increased. At 900°C, the nitrogen
release increased in the whole residence time range studied and continued to increase at
2.2 seconds. This is because combustion still continues. At 1100°C, at residence times
longer than 1.1 seconds, almost all the nitrogen in black liquor was released. This
coincides with complete combustion as discussed previously. The release of nitrogen
increased with rising temperature as well.
In 21% oxygen, at 700°C the nitrogen release increased rapidly during 0.3-0.6
seconds, and there was a slight decrease as the residence time further increased to 1.1
seconds. This shows the pyrolysis behavior. During 1.1-1.6 seconds, there was a sharp
58
100
90 -
80 _
.­
70
60
50
40
A
Temp 700°C, 02 4%
30
Temp 900°C, 02 4%
20
Temp 1100°C, 02 4%
10
0
0
0.5
1
1.5
2
2.5
Residence time (sec)
Figure 5.15 Nitrogen Release as a Function of Residence Time
During Black Liquor Combustion in 4% Oxygen
100
90
80
70
60
A Temp 700°C, 02 21%
50
Temp 900°C, 02 21%
40
Temp 1100°C, 02 21
30
20
10
0
0
0.5
1
1.5
2
2.5
Residence time (sec)
Figure 5.16 Nitrogen Release as a Function of Residence Time
During Black Liquor Combustion in 21% Oxygen
59
increase in the nitrogen release again. This coincides with the beginning of
combustion. At 900°C, the amount of nitrogen release increased rapidly from 50 to
90% of fuel nitrogen as the residence time increased from 0.3 to 0.6 seconds. There
was a slight increase with increasing residence time and the nitrogen release remained
almost constant at 1.1-2.2 seconds. This is consisten with the char yield data which
indicates that combustion starts at short residence times and is complete at longer
residence times. At 1100°C in the residence time range studied, the release of nitrogen
was extremely high. At 0.3 seconds, the amount of nitrogen released was 95% of fuel
nitrogen, then it was average 98% of fuel nitrogen during 0.6-2.2 seconds. At this
temperature, combustion was complete at very short residence times.
At 900°C in 21% oxygen, the nitrogen release data show a decrease in the
amount of nitrogen released at 1.6 seconds. This is clearly impossible and shows that
the earlier assumption of an error in the nitrogen content analysis under these conditions
is valid. Thus, a smooth curve is used to present the nitrogen release data at this
temperature as well.
Comparing to char yield data, the nitrogen releases showed the same pattern as
the mass releases. This indicates that the nitrogen in black liquor is lost simultaneously
with total mass loss. At the complete combustion points discussed previously, the
amount of nitrogen released was 98% of fuel nitrogen, and the volatile yield was 89%.
60
5.2.4 NO Formation
Figures 5.17, 5.18, and 5.19 show the NO formation as a function of residence
time at temperatures 700, 900, and 1100°C respectively. Both pyrolysis and
c( -nbustion data are included. At 700°C in the residence time range 0.3-1.1 seconds,
the NO level was about the same at all three oxygen concentrations. At 1.6-2.2
seconds, the NO formation in 21% oxygen was slightly higher than in 0 and 4%
oxygen. This indicates that at 700°C in 4% oxygen, the NO formation originates from
black liquor pyrolysis and is not affected by possible reaction of oxygen with other
nitrogen gas species or char combustion. In 21%, at 0.3-1.1 seconds, the NO formation
is the result of pyrolysis of black liquor as well. After that the NO formation is higher
probably due to the other nitrogen gas species that were released from black liquor, i.e.
NH3, HCN, reacting with oxygen in the combustion gas and/or due to the char burning.
This agrees well with the char yield and the nitrogen release which showed that the
combustion starts at 1.6 seconds in 21% oxygen, otherwise only pyrolysis occurs.
At 900°C at 0.3 seconds, the NO level was approximately the same during
pyrolysis and combustion of black liquor. During 0.6-2.2 seconds, the NO formation
was higher in black liquor combustion than in black liquor pyrolysis, except at 0.6
seconds in 4% oxygen. This indicates that at the shortest residence time studied, 0.3
seconds, the NO formation in black liquor combustion originates from pyrolysis. The
NO formation in 4% at 0.6 seconds is probably the result of black liquor pyrolysis as
61
Temp 700°C, 02 0%
Temp 700°C, 02 4%
Temp 700°C, 02 21%
16
14
12
10
0
0.5
1
1.5
2
2.5
Residence time (sec)
Figure 5.17 NO Formation as a Function of Residence Time
During Pyrolysis and Combustion of Black Liquor at Reactor Temperature 700°C
50
45
40
35
30
25
Temp 900°C, 02 0%
20
Temp 900°C, 02 4%
15
Temp 900°C, 02 21%
10
5
0
0
0.5
1.5
2.5
Residence time (sec)
Figure 5.18 NO Formation as a Function of Residence Time
During Pyrolysis and Combustion of Black Liquor at Reactor Temperature 900°C
62
60
50
40
30
Temp 1100°C 02 0%
Temp 1100°C, 02 4%
20
Temp 1100°C, 02 21 %'
10
0
0.5
1
1.5
2
2.5
Residence time (sec)
Figure 5.19 NO Formation as a Function of Residence Time
During Pyrolysis and Combustion of Black Liquor at Reactor Temperature 1100°C
well. This is in accordance with the previous discussion in the char yield and the
nitrogen release section. In 4% at 1.6 and 2.2 seconds, and in 21% oxygen at 0.6-2.2
seconds, the NO formation was much higher than in black liquor pyrolysis. This could
be due to reactions of the other nitrogen gas species with oxygen in the combustion gas,
char combustion and thermal or prompt NO formation. Thermal and prompt NO
formation will be discussed later in section 5.3. At 1.1 seconds in 4%, the amount of
NO formed was slightly higher than in pyrolysis of black liquor. This indicates that the
reactions described above just started. A higher amount of NO formed indicates that
the reactions are more complete. This agrees with the char yield and the nitrogen
release which showed that at longer residence times, the combustion is more complete.
At 0.6-2.2 seconds, the NO level in 21% oxygen was higher than in 4% oxygen.
63
Consequently, the formation of NO in black liquor combustion at 900°C is dependent
on the oxygen concentration at these residence times.
At 1100°C, the NO formation at 0.3 seconds in 4% oxygen was about the same
as in black liquor pyrolysis, thus it originates from the pyrolysis. At 0.3-1.1 seconds in
4%, the NO formation increased and was higher than in black liquor pyrolysis. This
shows that the combustion starts at 0.3-0.6 seconds. At 1.1-2.2 seconds in 4% oxygen
and 0.3-2.2 seconds in 21% oxygen, the NO level is much higher than during pyrolysis,
and combustion is complete as discussed earlier. At 0.6 seconds, the NO formation in
4% oxygen was lower than in 21% oxygen but about the same at long residence times.
This indicates that black liquor combustion depends on oxygen concentration at 0.6
seconds, at longer residence times the combustion is complete which yields
approximately the same NO levels.
The conversions of fuel nitrogen in black liquor to NO at 700, 900, and 1100°C
in 4 and 21% oxygen are shown in Figures 5.20 and 5.21. In 4% oxygen, maxima in
NO formation were observed at residence times between 1.1 and 2.2 seconds at all the
three furnace temperatures. The maxima in NO indicate that the amount of NO formed
during combustion of black liquor at 2.2 seconds in 4% oxygen is affected by the NO
destruction as in pyrolysis of black liquor. At 700°C, the NO level was almost zero at
the shortest residence time studied, 0.3 seconds. The conversion of fuel nitrogen to NO
slightly increased with increasing residence time during 0.3-1.6 seconds, then decreased
at 2.2 seconds. The highest amount of NO formed was 12% of nitrogen originally
present in black liquor solids at 1.6 seconds. At 900°C, the NO level increased slightly
64
A
60
Temp 700°C, 02 4% 1
Temp 900°C, 02 4%
Temp 1 100 °C, 02 4%!
50
-
40
30
20
10
-'
0
0.5
1.5
2
2.5
Residence time (sec)
Figure 5.20 NO Formation as a Function of Residence Time
During Black Liquor Combustion in 4% Oxygen
50
45
40
35
Temp 700°C, 02 21')/0
30
Temp 900°C, 02 21%
25
Temp 1100°C, 02 21
20
15
10
5
0
0.5
1.5
2
25
Residence time (sec)
Figure 5.21 NO Formation as a Function of Residence Time
During Black Liquor Combustion in 21% Oxygen
65
during 0.3-0.6 seconds. Then the combustion starts and the NO formation increased
rapidly from 8 to 39% of fuel nitrogen in black liquor as the residence time increased
from 0.6 to 1.6 seconds. At 1.6-2.2 seconds, the level of NO was almost constant. At
1100°C, the conversion of fuel nitrogen to NO increased significantly during 0.3-1.1
seconds. The amount of NO formed at 1.6 seconds was barely higher than at 1.1
seconds. At 0.3-1.6 seconds, the NO formation in black liquor combustion increases as
residence time increases due to continuing combustion. The NO level decreased from
49 to 37% of black liquor nitrogen when the residence time further increased from 1.6
to 2.2 seconds.
At 700°C, the NO formation in 21% oxygen shows the same trend as in 4%
oxygen. The highest amount of NO formed was 15% of fuel nitrogen. At 900°C in
21% oxygen, the conversion of fuel nitrogen to NO increased dramatically during 0.3­
0.6 seconds, then increased gradually as the residence time further increased to 1.1
seconds. The NO formation in black liquor combustion at 700 and 900°C in 21%
oxygen is dependent on the residence time as in 4% oxygen. At 900°C, a maximum in
the amount of NO formed was observed between 1.1 and 2.2 seconds. The highest NO
level was 49% of nitrogen in black liquor at 1.6 seconds. At 1100°C, the combustion is
complete as discussed earlier. The amount of NO formed decreased slightly between
0.3 and 2.2 seconds from 48 to 43% of fuel nitrogen. The reduction in NO seemed to
be more pronounced at longer residence times. There is no char left due to complete
combustion, and probably little reducing species for homogeneous reactions. The
66
possible source of NO reduction is the reduction of NO by fume. It can be concluded
that at complete combustion, 49% of fuel nitrogen is converted to NO.
Figures 5.22 and 5.23 show the same NO formation data as a function of
temperature in 4 and 21% oxygen respectively. The NO level increased with increasing
temperature, except at 1.6 seconds in 21% oxygen and at 2.2 seconds in 4 and 21%
oxygen, when it remained approximately constant or even slightly decreased from 900
to 1100°C. In other words, the NO formation in black liquor combustion increases as
temperature increases, except at long residence times and high oxygen concentrations.
In 4% oxygen, the net rate of NO formation was higher at low temperatures than at
higher temperatures for 0.3-1.1 seconds. At 1.6 and 2.2 seconds, the net NO formation
rate was lower at higher temperatures. It implies that when the combustion of black
liquor approaches completion, the net rate of NO formation decreases. The NO level
was lower at 2.2 seconds than at 1.6 seconds. This indicates that the NO destruction
mechanisms start to dominate at the long residence time as well. At 2.2 seconds, the
NO level at 900-1100°C was nearly constant. This may indicate that the NO formation
due to temperature increase is as the same as increase in the NO destruction, and thus
the net rate of NO formation is zero.
In 21% oxygen, the net conversion of fuel nitrogen to NO was lower at higher
temperatures at all other residence times, except at 0.3 seconds, when it was higher at
higher temperatures. This indicates that at 0.6-2.2 seconds, the net rate of NO
formation decreases due to the combustion of black liquor approaching completion at
higher temperatures. At 1.6 and 2.2 seconds, the formation of NO reached a maximum
67
50
45
2-,
40
Z
35
z
30
0.6 seconds
25
1.1 seconds
C
C)
O
0
20
0.3 seconds
1.6 seconds
-°
2.2 seconds
10
0
5
0
600
700
800
900
1000
1100
1200
Temperature (°C)
Figure 5.22 NO Formation as a Function of Temperature
During Black Liquor Combustion in 4% Oxygen
60
50
O
0.3 seconds
40
0.6 seconds
30
1.1 seconds
1.6 seconds
20
10
0
600
700
800
900
1000
1100
1200
Temperature (°C)
Figure 5.23 NO Formation as a Function of Temperature
During Black Liquor Combustion in 21% Oxygen
68
between 700 and 1100°C. This indicates that the combustion of black liquor was
complete at the temperature around 900°C at residence times above 1.6 seconds. At
longer residence times, NO destruction mechanisms result in a lower amount of NO
formed at 2.2 seconds.
The results were compared to combustion experiments of Forssen et al. (23).
Their experiments were done at 900°C in 10% oxygen. Forssen et al. found that the
amount of NO formed was approximately 45% of black liquor nitrogen for seven
liquors. In our experiments at 900 in 4 and 21% oxygen, the amounts of NO formed
were 38-40% of nitrogen original in black liquor. The results agree rather well.
Nichols and Lien (18) found that in 21% oxygen, the amount of NO formed
increased when the temperature was increased from 800 to 900°C and remained
constant when the temperature was further increased to 1000°C. This agrees well with
our experiments in 21% oxygen at long residence times.
5.2.5 Comparison of Nitrogen Release and NO Formation
The nitrogen release and NO formation during the black liquor pyrolysis and
black liquor combustion at each temperature are shown in Figures 5.24, 5.25 and 5.26.
When the NO formation in combustion of black liquor was at the same level as in
pyrolysis of black liquor, the nitrogen releases were rather near each other as well. This
supports the previous discussion that at all these points, the NO formations in black
69
A
100
Nrelease, 02 0%
Nrelease, 02 4°/0
90
Nrelease, 02 21%
80
NO, 02 0%
70
60
o
NO, 02 4%
0
NO, 02 21%
50
40
0
30
20
10
0.5
1.5
1
2
2.5
Residence time (sec)
Figure 5.24 Nitrogen Release and NO formation as a Function of Residence Time
During Pyrolysis and Combustion of Black Liquor at Reactor Temperature 700°C
A
100
Nrelease, 02 0%
Nrelease, 02 4%
90
Nrelease, 02 21%
.. -­
80
.
70
60
.1'
A
NO, 02 0%
o
NO, 02 4%
O
NO, 02 21%
50
40
30
20
10
0
0
0.5
1.5
2
2.5
Residence time (sec)
Figure 5.25 Nitrogen Release and NO formation as a Function of Residence Time
During Pyrolysis and Combustion of Black Liquor at Reactor Temperature 900°C
70
I
100
90
80
70
60
Nrelease, 02 0%
Nrelease, 02 4%
Nrelease, 02 21%
o NO, 02 0%
o NO, 02 4%
o NO, 02 21%
A
1
50
40
30
20
10
0
0
0.5
1.5
2
2.5
Residence time (sec)
Figure 5.26 Nitrogen Release and NO formation as a Function of Residence Time
During Pyrolysis and Combustion of Black Liquor at Reactor Temperature 1100°C
liquor combustion are the result of pyrolysis of black liquor only. It is good to note that
there is more uncertainty in the nitrogen release data than the NO data due to the
uncertainty in the measurements of the char nitrogen content. The results also indicate
that when the amounts of NO formed in black liquor combustion were higher than in
black liquor pyrolysis, more nitrogen was released. This suggests that at these points,
the increase in the amount of NO formed originates from combustion.
Figures 5.27 and 5.28 show the amount of nitrogen released and NO formed as a
function of residence time in 4% and 21% oxygen respectively. In 4% oxygen at 0.3-1.6
seconds, the release of nitrogen increased as residence time increased, and the formation
71
* N release includes shaded and black area
Figure 5.27 Nitrogen Release and NO Formation as a Function of Residence Time
During Black Liquor Combustion in 4% Oxygen
* N release includes shaded and black area
Figure 5.28 Nitrogen Release and NO Formation as a Function of Residence Time
During Black Liquor Combustion in 21% Oxygen
72
of NO increased as well. This indicates that part of the nitrogen released reacts with
oxygen in the combustion gas and forms NO. At 1.6-2.2 seconds, the nitrogen release
still increased at 700 and 900°C and was constant at 1100°C but the NO formation
decreased. This shows that the amount of NO formed is affected by NO destruction.
In 21% oxygen, at 700 and 900°C, the nitrogen release and the NO formation
show the same pattern as in 4% oxygen, i.e. at short residence times both the nitrogen
release and the NO formation increased, but at long residence times the nitrogen
release increased whereas the NO formation decreased. At 900°C and 1.6 seconds in
21% oxygen, 1100°C and 1.6 seconds in 4% oxygen, and 1100°C during 0.3-1.6
seconds in 21% oxygen, the release of nitrogen was almost 100% of black liquor
nitrogen, and the formation of NO was approximately 49% of black liquor nitrogen.
At these points, the combustion of black liquor is complete as discussed earlier. It can
be concluded that when the combustion of black liquor is complete, all the nitrogen in
black liquor solids is released and half of the nitrogen released forms NO. The rest
should be molecular nitrogen. At 2.2 seconds, at 900°C in 21% oxygen, and 1100°C
in 4 and 21% oxygen, the combustion of black liquor is complete as well. However,
the amount of NO formed was lower probably because part of the NO formed was
converted to molecular nitrogen (N2).
73
5.3 Black Liquor Combustion in Helium Atmosphere
Black liquor combustion experiments in helium atmosphere were conducted in
2.9 and 15.4% oxygen in order to compare the effect of the nitrogen in the combustion
gas on NO formation. The experiments were done in slightly lower oxygen
concentrations than those in the nitrogen atmosphere because of a miscalculation in the
helium flow.
Figures 5.29, 5.30, and 5.31 show the amount of NO formed in nitrogen and
helium environments at 700, 900, and 1100°C respectively. At 700°C in helium with
15.4% oxygen, the NO level was 0.5% of black liquor nitrogen, whereas in nitrogen with
21% oxygen it was 5.6% of black liquor nitrogen. Therefore, the amount of NO was
considerably lower in helium than in nitrogen. In nitrogen atmosphere in 4% oxygen the
NO formation was 3.1% of fuel nitrogen, so only small part of the difference in NO
could possibly be attributed to differences in oxygen concentration. Thus the difference
must mainly come from nitrogen in combustion gas being converted to NO. At 700°C,
the temperature is too low for thermal NO formation. The higher amount of NO formed
in the nitrogen atmosphere is probably due to prompt NO formation.
At 900°C and 0.3 seconds, all the NO formations were approximately the same,
though slightly lower. As discussed previously, the NO formation originates from the
pyrolysis and there is very little volatile combustion. This indicates that the nitrogen in
the combustion gas does not much affect the amount of NO formed during the pyrolysis
stage. The NO formation in helium at 2.2 seconds was higher than at 0.3 seconds.
74
Figure 5.29 NO Formation in Nitrogen and Helium Atmosphere
During Black Liquor Combustion at Reactor Temperature 700°C
III in N2, 4% 02
El in He, 2.9% 02
111 in N2, 21% 02
in He, 15.4% 02
Figure 5.30 NO Formation in Nitrogen and Helium Atmosphere
During Black Liquor Combustion at Reactor Temperature 900°C
75
in N2, 4% 02
in He, 2.9% 02
El in N2, 21% 02
0 in He, 15.4% 02
Figure 5.31 NO Formation in Nitrogen and Helium Atmosphere
During Black Liquor Combustion at Reactor Temperature 1100°C
However, at 2.2 seconds the amount of NO formed in the helium atmosphere was
considerably lower than in nitrogen atmosphere. Some prompt NO was evidently
formed like at 700°C. The difference in the NO formation was, however, significantly
greater than at 700°C. Prompt NO formation is not highly sensitive to temperature.
Therefore, there was probably thermal NO formation as well. Thermal NO formation
normally occurs only at temperatures above 1300°C (17) which is much higher than
900°C. Nevertheless, it has been reported by Frederick and Hupa (26) that at furnace
temperature 800°C in 21% oxygen, the gas temperature surrounding black liquor
droplets during volatile ignition of black liquor was very high (almost 2000°C). Reis
(27) also calculated that the temperature of small black liquor particles like in our
76
experiments during combustion at a furnace temperature 900°C was around 1300°C.
Thus, thermal NO can be formed.
At 1100°C, the NO formation in helium environment was lower than in nitrogen
environment, except at 0.3 seconds in the low oxygen concentration when it was higher.
At 0.3 seconds and 4% oxygen, the NO formation during black liquor combustion in
nitrogen atmosphere is the result of black liquor pyrolysis. This indicates that the
combustion in helium atmosphere may start at shorter residence times than in nitrogen
atmosphere. This is a reasonable assumption since the thermal conductivity of helium
is higher than that of nitrogen and thus the particles will heat up faster in helium than in
nitrogen. At all other points, the combustion of black liquor is complete as discussed
previously, and the amount of NO formed was lower in helium than in nitrogen. This
indicates that part of NO formed during combustion of black liquor in nitrogen
atmosphere is prompt and thermal NO. At 2.2 seconds in 15.4% oxygen in helium, the
amount of NO formed was obviously lower than at 0.3 seconds. This indicates that the
NO destruction mechanisms dominate during black liquor combustion in helium
atmosphere as well.
77
5.4 Black Liquor Char Combustion
The NO formation in the combustion of black liquor and char at 900°C and 2.2
seconds is shown in Figure 5.32. The NO level in char combustion was at the same level
for 21% oxygen in nitrogen and 15.4% oxygen in helium. This indicates that in char
combustion, the nitrogen in the combustion gas does not affect the amount of NO
formed, i.e. there is no prompt and thermal NO.
Figure 5.32 NO Formation in Black Liquor and Char Combustion
at Reactor Temperature 900°C and 2.2 seconds
78
The NO level in black liquor combustion in helium atmosphere was
significantly lower than in nitrogen atmosphere, it was lower than in char combustion as
well. The higher value of NO in nitrogen during black liquor combustion is probably
due to both prompt and thermal NO formation as discussed previously. During char
burning in helium atmosphere, there was, however, no prompt and thermal NO
formation. As discussed earlier, during black liquor combustion, the gas temperature is
very high due to volatile ignition. During char burning, there is no volatile combustion,
and the temperature should be lower than during black liquor combustion when
pyrolysis, volatile combustion and char burning occur. Thus there may be thermal NO
formation during volatile combustion but not during char burning. The reason for the
lower NO during black liquor combustion in helium than during char burning alone
may be related to temperature. During black liquor combustion, temperature is high
due to the volatile combustion and causes high NO reduction. During char burning,
temperature is lower and the reduction of NO should be lower as well. Consequently,
the amount of NO formed in char burning alone in helium is higher than in black liquor
combustion. However, there might be some other reasons and further experiments are
needed.
5.5 Sources of Error
The variations in the char yields may be due to the mass loss in the feeding
system. Particles accumulated in transport tubes and the injector. After each
79
experiment, the system was flushed with a high flow rate of primary nitrogen gas, and
the cyclone catch from flushing was collected. However, there still were some particles
accumulated in the injector that needed to be flushed by a higher flow rate of nitrogen
and these particles could not be collected. The weight of the particles collected in the
cyclone was assumed to be 60% of the black liquor solids that were not fed. This
assumption may not be true. In the worst case, the maximum relative error in the
weight of the actual black liquor input is estimated to be 20%. This causes a 20%
relative error in the char yield. However, the average relative difference in the char
yields from duplicate runs was less than 3%.
The nitrogen analysis was a source of error in the nitrogen content in char. The
nitrogen content in the char samples was very low and close to the detection limit of
Kjeldahl method. Because the amount of char was small, the char samples from
duplicate experiments were combined and only one analysis for each condition was
done. Therefore, the accuracy was not very good. Carangal (15) who used the same
laboratory for nitrogen analysis found that the difference in the same sample was as
high as 0.01 wt.% of nitrogen. By assuming constant absolute error, the relative errors
were 10-100% depending on the nitrogen content. At the highest char nitrogen content,
0.09 wt.%, the relative error was 10%. At the lowest char nitrogen content, 0.012 wt.%,
the relative error was 100%.
Sources of error in the nitrogen release were the mass loss in the feeding system
and the nitrogen analysis. The relative error depends on the amount of nitrogen
released. At the lowest nitrogen release, 16% of fuel nitrogen, the maximum relative
80
error is about 160% and the maximum absolute error is about 25% of fuel nitrogen. At
the second lowest nitrogen release, 20% of fuel nitrogen, the maximum relative error is
about 115% and the maximum absolute error is about 23% of fuel nitrogen. At the
highest nitrogen release, 98% of fuel nitrogen, the maximum relative error is about 2%
and the maximum absolute error is about 2% of fuel nitrogen. This indicates that the
relative error decreases rapidly when the nitrogen release increased. Nevertheless, the
highest relative difference in duplicate experiments was only 20%. The detailed
calculations are described in Appendix A.B.
The errors in the NO formation may be due to the mass loss in the feeding
system and the measurement of NO concentration. The relative error in the mass loss is
about 20%. The chemiluminescence NO-NOx analyzer was calibrated with NO
standard gas before and after each experiment. The difference from calibration was less
than 1%. The maximum relative difference between the NO formation in duplicate
experiments was 20% which was probably due to the mass loss in the feeding system.
The average relative difference in the NO formation from duplicated runs was less than
5%.
81
Chapter 6
Conclusions
The conclusions of nitrogen evolution during black liquor pyrolysis are as
follows:
At short residence times (at 700°C up to 0.6 seconds, at 900 and 1100°C up to 0.3
seconds) the volatile release increased rapidly, at longer residence times it increased
more gradually. The volatile release increased with increasing temperature as well.
Nitrogen release increased with increasing residence time and temperature, except at
700 and 900°C at long residence times when it was about the same.
Nitrogen and volatile species were released at the same rate.
At all temperatures studied, there was a maximum in the amount of NO formed as a
function of residence time. At short residence times, the NO formation increased
with increasing temperature. At longer residence times and higher temperatures,
NO destruction controlled the net NO formation.
The pyrolysis model developed by Iisa et al. (26) for NO formation seemed to fit the
NO formation data fairly well. It is believed that an improved fit could be obtained
by using a more complicated reduction model.
82
The conclusions of nitrogen evolution during black liquor combustion are as
follows:
The nitrogen release and the mass release showed the same pattern of increasing
with increasing residence time and temperature. The higher the nitrogen release, the
higher the amount of NO formed.
The char nitrogen content decreased as residence time increased at short residence
times and it was approximately constant or slightly decreased at 1.6-2.2 seconds.
At 700°C the NO formation was the result of pyrolysis only, except at high oxygen
concentration and long residence time.
At 900 and 1100°C, the NO formation was the result of pyrolysis, volatiles
combustion and char burning. The combustion was complete at 1.6 seconds at
900°C in 21% oxygen, at 1.1 seconds at 1100°C in 4% oxygen, and all the residence
times studied at 1100°C in 21% oxygen.
When the combustion was complete, the nitrogen release was 98% of nitrogen
originally present in black liquor, and the maximum amount of NO formed was
49% of nitrogen originally present in black liquor.
The amount of NO formed increased with increasing temperature, except at long
residence times and high temperatures when it was constant or slightly decreased.
NO destruction mechanisms dominated at the longest residence time 2.2 seconds in
all combustion experiments.
83
There was prompt and thermal NO formation during the combustion of black liquor.
However, the thermal NO formation occurred only when pyrolysis, volatile
combustion and char burning occurred together.
The data suggest that NOx emissions from recovery boilers could be reduced by
increasing the residence time of black liquor in recovery furnaces.
84
Chapter 7
Recommendations for Future Work
Other nitrogen gas species (e.g. NH3, HCN) should be measured for better
understanding of nitrogen evolution during black liquor pyrolysis.
A model of the NO formation during pyrolysis of black liquor should be
modified to account for more complex reduction reactions.
A global model of NO formation during black liquor combustion needs to
be developed.
The effect of the nitrogen content in black liquor solids on the evolution of
nitrogen during black liquor pyrolysis and black liquor combustion should be
determined.
The effect of particle size in black liquor solids should be studied.
More experiments of black liquor combustion in helium atmosphere
should be made.
Char combustion experiments should be done in the entire range of residence
time and temperature.
Gasification of black liquor using a laminar entrained-flow reactor should
be studied.
85
Bibliography
(1)
Frederick, W.J., and Adams, T.N., "Kraft Recovery Boiler Physical and
Chemical Processes", American Paper Institute, NY, 1988.
(2)
Boonsongsup, L., M.S. Thesis, Oregon State University, September, 1993.
(3)
U.S.Environmental Protection Agency, National Air Pollution Emission
Estimates, 1940-1990, Research Triangle Park, NC, 1991.
(4)
U.S.Environmental Protection Agency, Control Techniques for Nitrogen Oxide
Emissions from Stationary Sources (revised 2nd ed.), Research Triangle Park,
NC, 1993.
(5)
Office of Air and Radiation, U.S.Environmental Protection Agency, "The Clean
Air Act Amendments of 1990, Summary Material",1990.
(6)
Sloss, L.L., et al., "Nitrogen Oxide Control Technology Fact Book", Noyes Data
Corporation, NJ, 1992.
(7)
Zeldovich, J, "The Oxidation of Nitrogen in Combustions and Exposions", Acta
Physicochimica U.S.S.R., Moscow, 1946.
(8)
Fenimore, C.P., "Formation of Nitric Oxide in Premixed Hydrocarbon Flames",
Thirteenth Symposium (International) on Combustion Institute, PA, 1971.
(9)
Schneider, T.,and Grant, L., "Air Pollution by Nitrogen Oxides", Elsevier
Scientific Publishing Company, NY, 1982.
(10) Pershing, D.W., Martin, G.B., and Berkan, E.E., Influence of Design Variables
on the Production of Thermal and Fuel NO from Residential Oil and Coal
Combustion, American Institute of Chemical Engineers Symposium series, 1975.
(11) Cooper, C.D., and Alley, F.C., "Air Pollution Control: A Design Approach,
Waveland Press, Inc., 1994.
(12) Aho, K., Hupa, M., and Vakkilainen, E., "Fuel Nitrogen Release During Black
Liquor Pyrolysis , Part I: Laboratory Measurements at Different Conditions",
Tappi Journal, Vol.77, No.5, p.121, 1994.
86
(13)
Aho, K., Hupa, M., and Nikkanen, S., "Fuel Nitrogen Release During Black
Liquor Pyrolysis , Part II: Comparisons Between Different Liquors", Tappi
Journal, Vol.77, No.8, p.182, 1994.
(14) Forssen, M., Hupa, M., Petterson, R., and Martin, D., "Nitrogen Oxide Release
During Release During Black Liquor Char Combustion and Gaastification",
Proceedings of International Chemical Recovery Conference, Tappi Press, 1995.
(15) Carangal, A., M.S. Thesis, Oregon State University, September , 1994.
(16) Frederick, W.J., "Combustion Process in Black Liquor Recovery: Analysis and
Interpretation of Combustion Rate Data and Engineering Design Model ", U.S.
DOE Report, No.ACO2-83CE40637, 1990.
(17) Iisa, K., Carangal, A., Scott, A., Pianpucktr, R., and Tangpanyapinit, V.,
Proceedings of International Chemical Recovery Conference, Tappi Press, 1995.
(18) Nichols, K.M., and Lien. S.J., "Formation of Fuel NOx During Black Liquor
Combustion", Tappi Journal, Vol.76, No.3, P.185, 1993.
(19) Nichols, K.M., Thomson, L.M., and Empie, H.J., "A Review of NOx Formation
Mechanisms in Recovery Furnaces", Tappi Journal, Vol.76, No.1, P.119, 1993.
(20) Whitten, P.G., Barna, J.L., Ivie, L., and Abbot, S.R., "Application of Acoustic
Temperature Measurement to Optimize Recovery Boiler Furnace Operation",
Proceedings of the 1989 International Chemical Recovery Conference, Tappi
Press, 1989.
(21) Bowman, C.T., "Chemistry of Gaseous Pollutant Formation and Destruction.",
Fossil Fuel combustion: A Source Book (W. Bartok and A.F. Sorofim, Eds.),
John Wiley & Sons, NY, 1991.
(22) Pershing, D.W., and Wendt, J.O.L., Sixteenth Symposium (International) on
Combustion, Combustion Institute, PA, 1977.
(23) Forssen, M., Hupa, M., and Hellstrom, P., "Liquor-to-Liquor Differences in
Combustion and Gasification Process: Nitrogen Oxide Formation Tendency",
Proceedings of Tappi Engineering Conference, 1995.
(24) Boubel, R.W., Fox, D.L., Turner, D.B., and Stern, A.C., -Fundamentals of Air
pollution", Academic Press, NY, 1994.
87
(25) Flaxman, R.J., and Hal let, L.H., "Flow and Particle Heating in an Entrained flow
Reactor", Fuel, Vol.66, p.607, 1987.
(26) Frederick, W.J., and Hupa, M., "Combustion Properties of Kraft Black Liquors",
U.S. DOE Report, No.DE-FG02-90CE40936, 1993.
(27) Reis, V.V., Frederick, W.J., Wag, K.J., Iisa, K., and Sinquefield, S.A., "The
Effects of Temperature and Oxygen Concentration on Potassium and Chloride
Enrichment During Black Liquor Combustion", Submitted for Publication to
Tappi Jounal, 1995.
88
APPENDICES
89
Appendix A
Analysis of Data Procedures
90
A.1 Actual Black liquor Solids Input
The black liquor solids were weighed before and after the experiments in order
to calculate the amount of black liquor input. It was found that there were some black
liquor solids accumulated in the feeding system during the experiments. After the
experiments, the particle feed line was flushed by pure nitrogen at a very high flow rate.
The cyclone catch from the flushing was collected and weighed.
The char from the flushing was assumed to be 60% of the black liquor solids
that accumulated in the system. The actual black liquor input was calculated by
subtracting the amount of accumulated black liquor from the black liquor feed.
BLSactual
=
BI-Steed
BLSactual
BLSked
CHARfiush =
BLSbefore
BLSafter
CHARtlush / 0.6
Actual black liquor solids input weight, g
BLSbefore -BLSafter, g
Flushing char weight, g
Black liquor solids weight before the
experiments, g
Black liquor solids weight after the
experiments, g
A.2 Total Nitrogen Input
The total nitrogen input weight is given by:
Ninput
0.09/100 x BLSactual
91
A.3 Total NO
The total NO is calculated from Chemiluminescence NO-NOx data by:
-(1\10, +NO,:
NO total =
Concentration of NO at time i, ppm
NO,
=
t,
= Time, s
A.4 Conversion of Fuel N to NO
The amount of NO formed is given by:
(
( NO total
g N as NO
g Fuel N
106 x 60;
P(Qs +QJ(14
RT
x100%
x100%
N
NOtotai
Q,
gN
mol NO)
=
Qq
Ninput
Total NO from Chemiluminescence NO-NOx
analyzer. ppm.s
Reactor pressure, 1 atm
Secondary gas stream flow rate, 1 /min
Secondary gas stream flow rate, 1/min
Gas constant, 0.08205 1.atm/ mol.K
Room temperature, K
Total nitrogen input weight, g
A.5 Char Yield
The char yield is given by:
Char yield x 100%
=
Char weight
BLS actual
x 100%
92
A.6 Total Nitrogen Remaining in Char
The total nitrogen remaining in char is given by:
=
Nchar
Char N content / 100 x Char weight
A.7 Nitrogen Release
The nitrogen release is calculated by subtracting the nitrogen remaining in the
char from the total nitrogen input:
g N Release
g Fuel N
x100%
X
100%
Ninput
= 100%
Nchar
N char
N Input
=
Char N content
x Char yield %
BLS N content
Total nitrogen remaining in the char, g
A.8 Possible Maximum Relative Error in Nitrogen Release
The possible maximum relative error in the nitrogen release is calculated by:
Error,,,,,, in N release
AN release
x 100%
N release
Char yield x AChar N content
BLS N content x N release
X
100%
Char N content x AChar yield
x 100%
BLS N content x N release
93
AN release
N release
Char yield
AChar N content
Char N content
AChar yield
Absolute error in N release, %
Nitrogen release, %
Char yield at the same point as N release, %
Absolute error in char nitrogen content at the
same point as N release, wt.%
Char nitrogen content at the same point as N
release, wt.%
Absolute error in char yield at the same point as
N release, ')/0
BLS N content
Total nitrogen content in black liquor solid,
0.09 wt.%
At the lowest nitrogen release, 16% of fuel nitrogen
Char yield
AChar N content
Char N content
AChar yield
=
=
=
=
84%
0.01 wt.%
0.09 wt%
20/100x84% = 16%
Therefore,
Errormax in N release
84 x 0.01
0.09 x 16
x 100% +
0.09 x 16
0.09 x 16
x 100%
= 160%
At the second lowest nitrogen release, 20% of fuel nitrogen
Char yield
AChar N content
Char N content
AChar yield
=
=
=
=
80%
0.01 wt.%
0.08 wt.%
20/100x80% = 16%
Therefore,
Errormax in N release
80 x 0.01
0.09 x 20
= 115%
x 100% +
0.08 x 16
0.09 x 20
x 100%
94
At the highest nitrogen release, 98% of fuel nitrogen
Char yield
AChar N content
Char N content
AChar yield
=
=
=
=
10%
0.01 wt.%
0.012 wt.%
20/100x10% = 2%
Therefore,
Errormax in N release
10 x 0.01
0.09 x 98
= 2%
x100% +
0.012 x 2
0.09 x 98
x 100%
95
Appendix B
Experimental Data and Results
96
Table B.1 Experimental Data and Results for Black Liquor Pyrolysis and Combustion
in Nitrogen Atmosphere
PCO26
PCO27
PCO28
4/5/95
4/5/95
4/5/95
4
21
21
4
41
-).?
41
-.) ?
...._
41
41
41
700
700
0.121
13.79
13.79
4.96
4.96
0.121
13.75
11.16
2.59
5.00
5.00
100
100
285.50
150.61
18.0554
16.3527
1.7027
0.2031
1.3642
0.0012
17.4923
16.6173
244.61
3.6256
108.28
3.2908
0.7250
53.14
0.063
0.00046
37.20
62.80
0.3709
55.75
0.069
0.00026
42.74
57.26
EXPERIMENT NO.
PCO24
Date
Oxygen Content (%)
Reactor Path Length (inches)
Residence Time (sec)
Reactor Temperature (°C)
4/5/95
PCO25
4/5/95
0
/./
700
2.7
700
0.125
13.69
0.118
0.120
13.81
13.69
13.81
4.94
4.94
5.01
5.01
13.78
11.20
2.58
5.00
5.00
100
120.12
100
250.62
100
156.54
17.4969
16.9118
0.5851
0.0330
0.5301
0.0005
18.8863
17.3019
1.5844
0.1558
1.3247
0.0012
17.0685
16.2546
0.8139
0.0348
0.7559
0.0007
142.33
384.61
5.8925
107.02
2.8674
0.4063
30.67
0.062
0.00025
21.13
78.87
0.3486
46.12
0.069
0.00024
35.36
64.64
2.2
700
GAS FLOW
Primary Flow (1/min)
Secondary Flom, l /min)
N2 (1/min)
Air (1/min)
Quench Flow (1/min)
Tip (1 /min)
Wall (1/min)
NOx Meter Scale
Total Running Time (sec)
BLACK LIQUOR DATA
BLS Before (g)
BLS After (g)
BLS Input Weight (g)
Flush Char Weight (g)
Actual BLS Input Weight (g)
Total Fuel N Input (g)
NO DATA
Total NO Released (ppm.$)
g N as NO / g Fuel N ( %)
CHAR DATA
Char Weight (g)
Char Yield (%)
N Content in Char (`)/0 by wt)
Total Char N (g)
g Char N / g Fuel N (%)
g N Release / g Fuel N (%)
NOTE:
0.8750
0.1258
0.6653
0.0006
5.3944
0.1555
29.33
0.061
0.00009
19.88
80.12
97
Table B.1 Experimental Data and Results for Black Liquor Pyrolysis and Combustion
in Nitrogen Atmosphere (Continued)
EXPERIMENT NO.
PCO29
PC030
PC031
PC032
PCO33
Date
Oxygen Content (%)
Reactor Path Length (inches)
Residence Time (sec)
Reactor Temperature (°C)
4/6/95
4/6/95
4/6/95
4/6/95
4/7/95
0
4
21
4
0
41
41
41
41
41
2.2
900
2.2
900
2.2
900
2.2
900
2.2
1100
0.095
11.48
11.48
0.104
11.43
0.101
11.52
0.083
9.77
9.77
4.98
4.98
9.26
2.17
4.96
4.96
11.52
4.93
4.93
0.099
11.49
9.26
2.23
4.95
4.95
10
100
100
100
10
252.27
178.40
300.93
263.26
122.97
17.2170
15.9094
1.3076
0.1776
1.0116
0.0009
17.1449
15.9359
1.2090
0.1272
0.9970
0.0009
16.8299
14.6415
2.1884
0.2121
1.8349
0.0017
16.9141
15.2039
1.7102
0.1986
1.3792
0.0012
17.4529
16.9123
0.5406
0.0525
0.4531
0.0004
82.62
1.4498
2051.16
36.3640
4288.66
41.4632
3058.51
39.3163
21.57
0.7537
0.4986
49.29
0.075
0.00037
41.07
58.93
0.2673
26.81
0.033
0.00009
9.83
90.17
0.1618
8.82
0.012
0.00002
0.3885
28.17
0.019
0.00007
5.95
94.05
0.0925
20.41
0.074
0.00007
16.79
83.21
GAS FLOW
Primary Flow (1/min)
Secondary Flow (1/min)
N2 (1/min)
Air (1/min)
Quench Flow (1/min)
Tip (1/min)
Wall (I/min)
NOx Meter Scale
Total Running Time (sec)
BLACK LIQUOR DATA
BLS Before (g)
BLS After (g)
BLS Input Weight (g)
Flush Char Weight (g)
Actual BLS Input Weight (g)
Total Fuel N Input (g)
NO DATA
Total NO Released (ppm.$)
g N as NO / g Fuel N (%)
CHAR DATA
Char Weight (g)
Char Yield ( %)
N Content in Char (% by wt)
Total Char N (g)
g Char N / g Fuel N ( %)
g N Release / g Fuel N (%)
NOTE:
1.18
98.82
4.91
4.91
98
Table B.1 Experimental Data and Results for Black Liquor Pyrolysis and Combustion
in Nitrogen Atmosphere (Continued)
PC042
4/11/95
PCO41
4/25/95
4
21
0
4
41
41
41
41
41
2.2
1100
2.2
1100
2.2
1100
1.1
1.1
700
700
0.085
9.79
9.79
0.085
9.73
7.85
0.082
9.77
0.279
0.280
32.31
32.31
1.88
9.77
4.90
4.90
15.00
15.00
32.41
26.19
6.22
20.32
20.32
EXPERIMENT NO.
PC036
PC037
PC039
Date
Oxygen Content ( %)
Reactor Path Length (inches)
Residence Time (sec)
Reactor Temperature (°C)
4/10/95
4/10/95
0
4/25/95
GAS FLOW
Primary Flow (1/min)
Secondary Flow (1/min)
N, (1/min)
Air (1/min)
Quench Flow (I/min)
Tip (1/min)
5.03
5.02
5.02
5.03
10
100
241.39
17.6854
15.8963
Wall (1/n-iin)
NOx Meter Scale
Total Running Time (sec)
BLACK LIQUOR DATA
BLS Before (g)
BLS After (g)
BLS Input Weight (g)
Flush Char Weight (g)
Actual BLS Input Weight (g)
Total Fuel N Input (g)
NO DATA
Total NO Released (ppm.$)
g N as NO / g Fuel N (%)
CHAR DATA
Char Weight (g)
Char Yield (%)
N Content in Char (% by wt)
Total Char N (g)
g Char N / g Fuel N (%)
g N Release / g Fuel N (%)
NOTE:
100
100
194.43
100
159.01
300.88
300.93
0.2391
1.3906
0.0013
18.2136
17.1428
1.0708
0.0226
1.0331
0.0009
17.5817
16.6141
0.9676
0.0094
0.9519
0.0009
18.6099
16.5262
2.0837
0.1407
1.8492
0.0017
18.2453
16.3435
1.9018
0.0790
1.7701
0.0016
14.39
0.1653
2281.58
35.1523
2583.14
42.9299
242.67
6.6953
175.46
5.6366
0.1709
0.3245
16.54
23.34
0.014
0.082
0.00027 0.00002
2.57
21.26
97.43
78.74
Data Acq.
0.0611
6.42
0.012
0.00001
0.86
99.14
1.0942
59.17
0.075
0.00082
49.31
50.69
0.9774
55.22
0.074
0.00072
45.40
54.60
1.7891
PC035
99
Table B.1 Experimental Data and Results for Black Liquor Pyrolysis and Combustion
in Nitrogen Atmosphere (Continued)
EXPERIMENT NO.
PC043
PC045
PC053
PC054
PC055
Date
Oxygen Content (%)
Reactor Path Length (inches)
Residence Time (sec)
Reactor Temperature (°C)
4/25/95
4/26/95
4/29/95
4/29/95
4/29/95
21
0
0
21
41
41
41
4
41
1.1
1.1
1.1
1.1
1.1
700
900
1100
1100
1100
0.282
32.38
0.237
27.02
27.02
0.204
23.14
23.14
0.204
23.18
18.76
4.42
19.98
0.203
23.11
41
GAS FLOW
Primary Flow (1/min)
Secondary Flow (1/min)
N2 (1/min)
Air (1/min)
Quench Flow (1/min)
Tip (1/min)
Wall (1/min)
NOx Meter Scale
Total Running Time (sec)
BLACK LIQUOR DATA
BLS Before (g)
BLS After (g)
BLS Input Weight (g)
Flush Char Weight (g)
Actual BLS Input Weight (g)
Total Fuel N Input (g)
NO DATA
Total NO Released (ppm.$)
g N as NO / g Fuel N ( %)
CHAR DATA
Char Weight (g)
Char Yield (%)
N Content in Char (% by wt)
Total Char N (g)
g Char N / g Fuel N (%)
g N Release / g Fuel N ( %)
NOTE:
19.98
23.11
20.10
20.10
100
100
100
72.11
250.29
299.46
301.49
0.0013
17.9664
17.5449
0.4215
0.0124
0.4008
0.0004
17.4325
15.9680
1.4645
0.0668
1.3532
0.0012
17.6674
15.5650
2.1024
0.1380
1.8724
0.0017
18.0044
15.9217
2.0827
0.1337
1.8599
0.0017
150.88
5.7917
83.64
10.5786
89.24
3.0866
1902.69
47.2976
1878.94
47.0764
0.8557
58.13
0.2143
53.46
0.071
0.00015
42.18
57.82
0.4308
31.84
0.073
0.00031
25.82
74.18
0.3305
0.1985
10.67
0.023
0.00005
2.73
97.27
32.38
20.02
20.02
19.99
19.99
20.26
20.26
100
10
309.95
17.8054
16.0366
1.7688
0.1780
1.4721
0.071
0.00061
45.86
54.14
17.65
0.020
0.00007
3.92
96.08
100
Table B.1 Experimental Data and Results for Black Liquor Pyrolysis and Combustion
in Nitrogen Atmosphere (Continued)
EXPERIMENT NO.
PC060
PC064
PC065
PC066
PCO67
Date
Oxygen Content (%)
Reactor Path Length (inches)
Residence Time (sec)
Reactor Temperature (°C)
5/4/95
5/11/95
5/12/95
5/12/95
4
0
0
5/12/95
4
41
11
11
11
11
1.1
1100
0.6
700
0.6
700
0.6
700
0.6
700
0.198
23.17
18.76
0.122
13.79
13.79
0.120
13.77
13.77
0.120
0.119
13.80
21
GAS FLOW
Primary Flow (1/min)
Secondary Flow (1/min)
N2 (1/min)
Air (1/min)
Quench Flow (1/min)
Tip (I/min)
Wall (1/min)
NOx Meter Scale
Total Running Time (sec)
BLACK LIQUOR DATA
BLS Before (g)
BLS After (g)
BLS Input Weight (g)
Flush Char Weight (g)
Actual BLS Input Weight (g)
Total Fuel N Input (g)
NO DATA
Total NO Released (ppm.$)
g N as NO / g Fuel N ( /o)
CHAR DATA
Char Weight (g)
Char Yield ( %)
N Content in Char (% by wt)
Total Char N (g)
g Char N / g Fuel N ( %)
o N Release / g Fuel N (%)
NOTE:
13.81
11.17
2.64
18.50
12.30
6.20
18.44
12.26
6.18
18.48
12.29
6.19
13.80
18.43
12.26
6.17
100
10
10
10
10
299.13
165.88
143.76
100.43
180.92
17.6653
15.6343
2.0310
0.1817
1.7282
0.0016
17.6426
16.9367
0.7059
0.0751
0.5807
0.0005
17.6511
16.8293
0.8218
0.0903
0.6713
0.0006
17.7323
17.3270
0.4053
0.0501
0.3218
0.0003
17.8431
16.8291
1.0140
1842.70
49.6638
54.16
3.2476
61.00
3.1564
30.96
3.3502
78.75
3.1613
0.2947
0.2921
50.30
0.074
0.00022
41.36
58.64
0.4339
64.64
0.084
0.00036
60.33
39.67
0.1931
60.01
0.078
0.00015
52.01
47.99
0.5430
4.41
20.02
20.02
17.05
0.015
0.00004
2.84
97.16
0.0889
0.8658
0.0008
62.71
0.079
0.00043
55.05
44.95
101
Table B.1 Experimental Data and Results for Black Liquor Pyrolysis and Combustion
in Nitrogen Atmosphere (Continued)
EXPERIMENT NO.
PC068
PCO71
PC074
PC075
PC077
Date
Oxygen Content ( %)
5/13/95
5/15/95
5/17/95
5/17/95
5/18/95
21
0
4
21
0
11
11
11
11
11
0.6
900
0.6
900
0.6
900
0.6
900
0.6
1100
0.105
12.09
0.106
12.06
0.105
12.03
12.03
0.090
12.06
0.107
12.10
12.10
16.16
10.78
5.38
100
63.54
16.17
10.78
5.39
100
300.61
16.24
10.81
5.43
100
196.96
13.92
9.30
105.41
0.0114
0.4654
0.0004
17.7064
17.5307
0.1757
0.0260
0.1324
0.0001
17.3259
15.5866
1.7393
0.1660
1.4626
0.0013
17.2354
16.0759
1.1595
0.0047
1.1517
0.0010
17.4259
17.0701
0.3558
0.0273
0.3103
0.0003
538.74
35.3162
45.58
10.4795
652.28
13.5960
1434.16
37.9651
65.69
5.5523
0.0659
0.0622
46.99
0.072
0.00004
37.59
0.8787
60.08
0.073
0.00064
48.73
51.27
0.1339
0.1423
45.86
0.085
0.00012
43.31
56.69
Reactor Path Length (inches)
Residence Time (sec)
Reactor Temperature ( °C)
GAS FLOW
Primary Flow (1/min)
Secondary Flow (1/min)
N2 (1 /min)
Air (1/min)
Quench Flow (1/min)
Tip (1/min)
Wall (1/min)
NOx Meter Scale
Total Running Time (sec)
BLACK LIQUOR DATA
BLS Before (g)
BLS After (g)
BLS Input Weight (g)
Flush Char Weight (g)
Actual BLS Input Weight (g)
Total Fuel N Input (g)
NO DATA
Total NO Released (ppm.$)
g N as NO / :_z Fuel N (%)
CHAR DATA
Char Weight (g)
Char Yield (%)
N Content in Char (% by wt)
Total Char N (g)
g Char N / g Fuel N (%)
g N Release / g Fuel N (%)
NOTE:
12.09
16.20
10.80
5.40
100
108.86
17.7343
17.2499
0.4844
14.16
0.046
0.00003
7.24
92.76
62.41
11.63
0.046
0.00006
5.94
94.06
10.40
10.40
4.62
10
,
102
Table B.1 Experimental Data and Results for Black Liquor Pyrolysis and Combustion
in Nitrogen Atmosphere (Continued)
EXPERIMENT NO.
PC078
PC079
PC080
PCO81
PC082
Date
Oxygen Content (%)
Reactor Path Length (inches)
Residence Time (sec)
Reactor Temperature ( °C)
5/18/95
5/18/95
5/22/95
5/22/95
5/22/95
4
21
0
21
4
11
11
22
22
22
0.6
1100
0.6
1100
1.1
1.1
1.1
900
900
900
0.089
0.090
10.33
8.36
1.07
13.84
9.26
4.58
100
10.33
0.111
12.69
12.69
0.111
12.69
0.110
12.86
10.40
2.46
GAS FLOW
Primary Flow (1/min)
Secondary Flow (1/min)
N2 (1/min)
Air (1/min)
Quench Flow (1/min)
Tip (1/min)
Wall (1/min)
NOx Meter Scale
Total Running Time (sec)
BLACK LIQUOR DATA
BLS Before (g)
BLS After (g)
BLS Input Weight (g)
Flush Char Weight (g)
Actual BLS Input Weight (g)
Total Fuel N Input (g)
NO DATA
Total NO Released (ppm.$)
g N as NO / g Fuel N (%)
CHAR DATA
Char Weight (g)
Char Yield (%)
N Content in Char (% by wt)
Total Char N (g)
g Char N / g Fuel N (%)
g N Release / g Fuel N ( %)
NOTE:
98.97
13.80
9.26
4.54
100
170.54
17.00
11.30
5.70
100
168.74
12.69
16.96
11.27
5.69
100
298.91
17.9129
17.5085
0.4044
0.0250
0.3627
0.0003
17.6674
16.9081
0.7593
0.0508
0.6746
0.0006
18.2754
17.3259
0.9495
0.0628
0.8448
0.0008
17.7912
15.9731
1.8181
0.1261
1.6079
0.0014
17.8492
15.8741
454.72
32.6754
1245.06
48.0251
284.59
10.7857
2053.17
40.8291
961.31
17.3308
0.0949
26.16
0.033
0.00003
9.59
0.0758
11.24
0.022
0.00002
2.75
97.25
0.4517
53.47
0.077
0.00035
45.74
54.26
0.2428
0.8193
45.85
0.063
0.00052
32.10
67.90
90.41
10.33
15.10
0.058
0.00014
9.73
90.27
17.01
11.30
5.71
100
299.18
1.9751
0.1130
1.7868
0.0016
103
Table B.1 Experimental Data and Results for Black Liquor Pyrolysis and Combustion
in Nitrogen Atmosphere (Continued)
EXPERIMENT NO.
PC083
PC084
PC085
PC086
PCO88
Date
5/24/95
5/24/95
5/24/95
5/25/95
0
5/24/95
4
21
0
21
9
9
9
9
9
0.3
700
0.3
700
0.3
0.3
0.3
700
900
900
0.252
28.74
28.74
0.247
28.57
0.222
25.30
25.30
0.219
25.18
25.41
12.65
0.248
28.70
23.21
5.49
38.55
25.67
12.88
10
10
300.16
Oxygen Content (%)
Reactor Path Length (inches)
Residence Time (sec)
Reactor Temperature (°C)
GAS FLOW
Primary Flow (1 /min)
Secondary Flow (1/min)
N2 (1/min)
Air (1/min)
Quench Flow (1/min)
Tip (1/min)
Wall (1/min)
NOx Meter Scale
Total Running Time (sec)
BLACK LIQUOR DATA
BLS Before (g)
BLS After (g)
BLS Input Weight (g)
Flush Char Weight (g)
Actual BLS Input Weight (g)
Total Fuel N Input (g)
NO DATA
Total NO Released (ppm.$)
g N as NO / g Fuel N ( %)
CHAR DATA
Char Weight (g)
Char Yield ( %)
N Content in Char ( °A by wt)
Total Char N (g)
g Char N / g Fuel N (%)
g N Release / g Fuel N (%)
NOTE:
22.66
25.18
33.95
22.67
11.25
11.28
10
10
10
300.06
300.39
200.54
141.43
18.0093
15.7101
2.2992
0.3734
1.6769
0.0015
17.6267
15.5017
2.1250
0.3752
1.4997
0.0013
18.5106
16.4442
2.0664
0.2624
0.0015
17.8876
16.5899
1.2977
0.1502
1.0474
0.0009
17.6694
16.9778
0.6916
0.1190
0.4933
0.0004
2.07
0.0889
1.95
0.0943
1.82
0.0811
82.93
5.0559
56.14
7.2575
1.3726
81.86
0.086
0.00118
78.22
21.78
1.2573
83.84
0.090
0.00113
83.84
16.16
1.2153
74.60
0.085
0.00103
70.46
0.6329
60.43
0.080
0.00051
0.2799
56.74
29.54
46.29
38.06
28.57
38.73
25.76
12.97
1.6291
33.91
53.71
0.081
0.00023
51.07
48.93
104
Table B.1 Experimental Data and Results for Black Liquor Pyrolysis and Combustion
in Nitrogen Atmosphere (Continued)
EXPERIMENT NO.
PC089
PC090
PCO91
PC092
PC095
Date
Oxygen Content ( %)
Reactor Path Length (inches)
Residence Time (sec)
Reactor Temperature (°C)
5/25/95
5/25/95
5/25/95
5/25/95
5/31/95
4
0
4
21
21
9
9
9
32
0.3
0.3
900
1100
0.3
1100
9
0.3
1100
700
0.220
25.38
20.57
0.190
21.84
21.84
0.189
21.81
0.130
14.74
14.74
19.76
13.18
6.58
1.6
GAS FLOW
Primary Flow (1/min)
Secondary Flow (1/min)
N2 (1/min)
Air (1/min)
Quench Flow (1/min)
Tip (1/min)
Wall (1/min)
NOx Meter Scale
Total Running Time (sec)
BLACK LIQUOR DATA
BLS Before (g)
BLS After (g)
BLS Input Weight (g)
Flush Char Weight (g)
Actual BLS Input Weight (g)
Total Fuel N Input (g)
NO DATA
Total NO Released (ppm.$)
g N as NO / g Fuel N ( %)
CHAR DATA
Char Weight (g)
Char Yield (%)
N Content in Char (`)/0 by wt)
Total Char N (g)
g Char N / g Fuel N (%)
g N Release / g Fuel N (%)
NOTE:
0.191
21.86
17.64
4.22
4.81
33.85
22.62
11.23
29.30
19.50
9.80
29.21
19.45
9.76
21.81
29.18
19.43
9.75
10
10
10
100
10
299.57
300.55
180.71
289.02
180.98
17.5900
15.5610
2.0290
0.3638
1.4227
0.0013
17.1570
15.3972
1.7598
0.1901
1.4430
0.0013
17.7355
16.6237
1.1118
0.1301
0.8950
0.0008
17.5292
15.5480
1.9812
0.1531
1.7260
0.0016
17.7847
16.7089
1.0758
0.0700
0.9591
0.0009
164.36
7.3794
389.25
14.8772
228.26
14.0468
1503.34
47.8940
372.53
14.4507
0.9802
68.90
0.7281
50.46
0.074
0.00054
41.49
58.51
0.4327
48.35
0.073
0.00032
39.22
60.78
0.2093
0.2931
30.56
0.064
0.00019
21.73
78.27
0.081
0.00079
62.01
37.99
12.13
0.035
0.00007
4.72
95.28
105
Table B.1 Experimental Data and Results for Black Liquor Pyrolysis and Combustion
in Nitrogen Atmosphere (Continued)
EXPERIMENT NO.
PC096
PC097
PC098
PCO99
PCO100
Date
Oxygen Content ( %)
Reactor Path Length (inches)
Residence Time (sec)
Reactor Temperature (°C)
5/31/95
5/31/95
5/31/95
5/31/95
5/31/95
0
4
0
4
21
32
32
1.6
32
1.6
1.6
1.6
32
1.6
700
700
900
900
900
0.129
0.111
12.62
12.62
0.110
0.111
12.66
19.86
13.22
6.64
0.128
14.80
11.97
2.83
19.82
13.20
6.62
10
10
299.62
104.14
16.99
11.30
5.69
100
163.35
17.8886
15.7234
2.1652
0.1644
1.8912
0.0017
17.2513
16.6436
0.6077
0.0457
0.5315
0.0005
633.26
12.5014
1.0490
55.47
0.070
0.00073
43.14
56.86
32
-,
GAS FLOW
Primary Flow (1/min)
Secondary Flow (1/min)
N2 (1/min)
Air (1/min)
Quench Flow (1/min)
Tip (1/min)
Wall (1/min)
NOx Meter Scale
Total Running Time (sec)
BLACK LIQUOR DATA
BLS Before (g)
BLS After (g)
BLS Input Weight (g)
Flush Char Weight (g)
Actual BLS Input Weight (g)
Total Fuel N Input (g)
NO DATA
Total NO Released (ppm.$)
g N as NO / g Fuel N (%)
CHAR DATA
Char Weight (g)
Char Yield ( %)
N Content in Char (% by wt)
Total Char N (g)
g Char N / g Fuel N (`)/0)
g N Release / g Fuel N (%)
NOTE:
14.76
14.76
12.79
10.36
2.43
17.08
11.33
5.75
100
12.66
16.97
11.28
5.69
100
300.50
298.96
17.4374
16.5976
0.8398
0.0522
0.7528
0.0007
17.8171
15.9084
1.9087
0.2157
1.5492
0.0014
17.8540
15.8668
1.9872
0.1923
1.6667
0.0015
174.16
12.2330
70.85
3.0053
1878.44
39.0583
2544.12
48.7753
0.2820
53.05
0.070
0.00020
41.26
58.74
0.3561
0.4941
31.89
0.036
0.00018
12.76
87.24
0.2283
13.70
0.022
0.00005
3.35
96.65
47.30
0.081
0.00029
42.57
57.43
106
Table B.1 Experimental Data and Results for Black Liquor Pyrolysis and Combustion
in Nitrogen Atmosphere (Continued)
PC0104 PC0105
EXPERIMENT NO.
PC0101
PC0102
PC0103
Date
Oxygen Content ( %)
Reactor Path Length (inches)
Residence Time (sec)
Reactor Temperature (°C)
5/31/95
5/31/95
5/31/95
6/1/95
6/1/95
0
-­32
4
21
4
4
-,-)
..)..
32
11
11
1.6
1.6
1.6
1100
1100
1100
0.6
900
0.6
900
0.095
10.98
0.095
0.096
0.105
11.01
11.01
12.15
10.98
8.92
2.09
14.70
9.80
4.90
100
301.05
0.104
12.10
9.77
2.33
14.67
9.79
4.88
100
300.45
10
10
229.86
205.42
1.7679
0.1925
1.4471
0.0013
17.6634
15.5479
2.1155
0.2070
1.7705
0.0016
17.6997
15.7339
1.9658
0.1265
1.7550
0.0016
17.3310
15.8458
1.4852
0.1305
1.2677
0.0011
17.9892
16.6798
1.3094
0.1620
1.0394
0.0009
52.20
0.9990
3174.80
49.7176
3044.56
48.0440
333.38
8.0373
262.14
7.6998
0.3714
25.67
0.080
0.00030
0.2566
14.49
0.012
0.00003
22.81
1.93
77.19
98.07
0.2181
12.43
0.015
0.00003
2.07
97.93
0.6680
52.69
0.079
0.00053
46.25
53.75
0.5949
57.23
0.074
0.00044
47.06
52.94
GAS FLOW
Primary Flow (1/min)
Secondary Flow (1/min)
N2 (1 /min)
Air (I/min)
Quench Flow (1/min)
Tip (1/min)
Wall (1 /min)
NOx Meter Scale
Total Running Time (sec)
BLACK LIQUOR DATA
BLS Before (g)
BLS After (g)
BLS Input Weight (g)
Flush Char Weight (g)
Actual BLS Input Weight (g)
Total Fuel N Input (g)
NO DATA
Total NO Released (ppm.$)
g N as NO / g Fuel N ( %)
CHAR DATA
Char Weight (g)
Char Yield (%)
N Content in Char (% by wt)
Total Char N (g)
g Char N / g Fuel N (%)
g N Release / g Fuel N ( °A)
NOTE:
14.70
9.80
4.90
10
258.64
17.1781
15.4102
11.01
9.82
2.33
16.19
10.79
5.40
16.21
10.80
5.41
107
Table B.1 Experimental Data and Results for Black Liquor Pyrolysis and Combustion
in Nitrogen Atmosphere (Continued)
EXPERIMENT NO.
Date
Oxygen Content (%)
Reactor Path Length (inches)
Residence Time (sec)
Reactor Temperature (°C)
PC0106
PC0107 PC0108 PC0109 PC0110
6/2/95
6/2/95
6/3/95
6/3/95
6/3/95
4
4
4
4
22
4
22
41
41
41
1.1
1.1
900
900
2.2
900
2.2
1100
2.2
1100
0.109
12.68
0.112
12.68
10.28
2.40
0.102
0.086
9.75
7.87
0.086
9.82
7.95
1.88
1.87
4.91
4.91
GAS FLOW
Primary Flow (1/min)
Secondary Flow (1/min)
N2 (1/min)
Air (1/min)
Quench Flow (1/min)
Tip (I/min)
Wall (1/min)
NOx Meter Scale
Total Running Time (sec)
BLACK LIQUOR DATA
BLS Before (g)
BLS After (g)
BLS Input Weight (g)
Flush Char Weight (g)
Actual BLS Input Weight (g)
Total Fuel N Input (g)
NO DATA
Total NO Released (ppm.$)
g N as NO / g Fuel N (%)
CHAR DATA
Char Weight (g)
Char Yield (%)
N Content in Char (% by wt)
Total Char N (g)
g Char N / g Fuel N (%)
g N Release / g Fuel N (%)
NOTE:
10.28
2.40
17.02
11.30
5.72
100
16.95
11.27
5.68
100
89.36
239.91
18.0951
17.8468
0.2483
0.0115
0.2291
0.0002
11.41
9.23
2.18
4.98
4.98
4.99
4.99
100
299.56
100
100.62
111.05
17.6895
16.2367
1.4528
0.1132
1.2641
0.0011
18.0728
16.1565
1.9163
0.0939
1.7598
0.0016
17.7458
17.3160
0.4298
0.0071
0.4180
0.0004
17.6656
17.1930
0.4726
0.0107
0.4548
0.0004
124.98
17.4702
722.86
18.2718
3731.18
37.4757
977.58
37.1789
1086.66
37.9573
0.0695
30.33
0.070
0.00005
23.59
76.41
0.4444
35.15
0.055
0.00024
21.48
78.52
0.5040
28.64
0.035
0.00018
0.0452
0.014
0.00001
0.0532
11.70
0.014
0.00001
1.68
1.82
98.32
98.18
100
11.14
88.86
10.81
108
Table B.1 Experimental Data and Results for Black Liquor Pyrolysis and Combustion
in Nitrogen Atmosphere (Continued)
EXPERIMENT NO.
Date
Oxygen Content (%)
Reactor Path Length (inches)
Residence Time (sec)
Reactor Temperature (°C)
PCO112
PC0129
6/3/95
7/10/95
21
0
41
41
2.2
900
2.2
900
0.102
11.46
0.230
GAS FLOW
Primary Flow (1/min)
Secondary Flow (1/min)
N2 (1/min)
Air (1/min)
Quench Flow (1/min)
Tip (1/min)
Wall (1/min)
NOx Meter Scale
Total Running Time (sec)
BLACK LIQUOR DATA
BLS Before (g)
BLS After (g)
BLS Input Weight (g)
Flush Char Weight (g)
Actual BLS Input Weight (g)
Total Fuel N Input (g)
NO DATA
Total NO Released (ppm.$)
g N as NO / g Fuel N (%)
CHAR DATA
Char Weight (g)
Char Yield (%)
N Content in Char (% by wt)
Total Char N (g)
g Char N / g Fuel N (%)
g N Release / g Fuel N (%)
NOTE:
10.71
10.71
11.46
4.93
4.93
4.97
4.97
100
10
151.54
291.38
18.0532
17.2611
0.7921
0.0102
0.7751
0.0007
19.2360
17.3816
1.8544
0.1067
1.6766
0.0015
1722.49
39.2795
179.92
1.8146
0.0760
0.5913
35.27
0.083
0.00049
32.53
67.47
9.81
0.024
0.00002
2.61
97.39
109
Table B.2 Experimental Data and Results for Black Liquor Combustion in Helium
Atmosphere
EXPERIMENT NO.
Date
Oxygen Content (%)
Reactor Path Length (inches)
Residence Time (sec)
Reactor Temperature (°C)
PCO117 PCO118
PC0119 PC0120 PCO121
6/27/95
15.4
6/27/95
2.9
15.4
6/27/95
2.9
41
41
9
9
9
1.1
1.1
0.3
1100
1100
900
0.3
900
0.3
1100
0.200
30.34
26.49
3.85
0.199
31.38
26.56
4.82
0.220
36.44
35.40
1.04
0.221
34.63
29.28
5.35
0.191
31.26
30.37
0.89
14.61
14.64
14.64
49.57
33.05
49.57
33.06
42.57
28.32
16.52
16.51
6/16/95
6/16/95
12.7
GAS FLOW
Primary Flow (1/min)
Secondary Flow (I/min)
He (1/min)
02 (1/min)
Quench Flow (1/min)
Tip (1/min)
Wall (1/min)
NOx Meter Scale
Total Running Time (sec)
14.61
100
100
10
10
14.25
100
300.12
155.05
108.65
299.89
286.16
BLACK LIQUOR DATA
BLS Before (g)
BLS After (g)
BLS Input Weight (g)
Flush Char Weight (g)
Actual BLS Input Weight (g)
Total Fuel N Input (g)
NO DATA
17.8694
15.6672
2.2022
0.1560
1.9422
0.0017
18.1655
17.0739
1.0916
0.0892
0.9429
0.0008
18.0358
17.5013
0.5345
0.0708
0.4165
0.0004
18.5975
16.0635
18.4838
16.3690
2.1148
0.6124
Total NO Released (ppm.$)
g N as NO / g Fuel N (%)
1272.12
31.7506
587.39
30.9158
28.21
90.71
6.2824
6.0409
313.46
22.8104
0.3861
19.88
0.1710
0.2118
50.85
0.070
0.00015
39.55
60.45
1.0254
75.20
0.067
0.00069
55.98
44.02
0.7366
67.32
0.049
0.00036
36.65
63.35
CHAR DATA
Char Weight (g)
Char Yield (%)
N Content in Char (% by wt)
Total Char N (g)
18.13
g Char N / g Fuel N ( %)
g N Release /g Fuel N (%)
NOTE:
Char loss Char loss
2.5340
0.7023
1.3635
0.0012
1.0941
0.0010
110
Table B.2 Experimental Data and Results for Black Liquor Combustion in Helium
Atmosphere (Continued)
EXPERIMENT NO.
PC0122 PC0123
PC0124 PC0125 PC0126
Date
Oxygen Content (`)/0)
6/27/95
6/27/95
6/29/95
15.4
15.4
9
Reactor Path Length (inches)
Residence Time (sec)
Reactor Temperature (°C)
6/29/95
15.4
6/29/95
2.9
9
41
41
41
0.3
0.3
1100
1100
2.2
700
2.2
900
2.2
900
0.190
29.78
25.18
4.60
42.82
28.43
14.39
0.191
29.74
0.249
16.47
13.90
2.57
7.20
7.20
0.231
15.45
14.98
0.47
7.15
7.15
0.232
100
100
10
100
100
15.4
GAS FLOW
Primary Flow (1/min)
Secondary Flow (1/min)
He (1/min)
02 (1/min)
Quench Flow (1/min)
Tip (1/min)
Wall (1/min)
NOx Meter Scale
Total Running Time (sec)
25.14
4.60
42.59
28.34
14.65
12.39
2.26
7.14
7.14
14.25
171.59
299.35
158.18
299.89
264.58
BLACK LIQUOR DATA
BLS Before (g)
BLS After (g)
BLS Input Weight (g)
Flush Char Weight (g)
Actual BLS Input Weight (g)
Total Fuel N Input (g)
NO DATA
18.1510
17.1750
0.9760
0.2042
0.6357
0.0006
18.2363
15.8887
2.3476
0.3552
1.7556
0.0016
18.0086
16.8918
1.1168
0.1644
0.8428
0.0008
17.7991
15.2670
2.5321
0.1951
2.2069
0.0020
18.2407
16.2036
2.0371
0.1712
1.7518
0.0016
Total NO Released (ppm.$)
g N as NO / g Fuel N ( %)
243.00
29.9296
695.17
30.8867
17.07
0.5170
1250.37
13.8085
928.82
12.4595
CHAR DATA
Char Weight (g)
Char Yield (%)
N Content in Char (% by wt)
Total Char N (g)
0.2050
32.25
0.034
0.00007
0.4172
23.76
0.037
0.00015
9.77
90.23
0.2292
27.20
0.4202
0.3066
19.04
0.033
17.50
0.021
0.00014
6.98
93.02
0.00006
4.08
95.92
g Char N / g Fuel N ( %)
g N Release /g Fuel N (%)
NOTE:
12.18
87.82
0.051
0.00012
15.41
84.59
111
Table B.2 Experimental Data and Results for Black Liquor Combustion in Helium
Atmosphere (Continued)
EXPERIMENT NO.
Date
Oxygen Content (%)
Reactor Path Length (inches)
Residence Time (sec)
Reactor Temperature (°C)
PC0127 PC0128
6/29/95
2.9
6/29/95
41
41
2.2
1100
2.2
1100
0.210
13.72
13.32
0.40
7.18
7.18
0.209
100
100
184.50
84.31
17.3954
15.7825
1.6129
0.0462
1.5359
0.0014
17.7681
16.9248
0.8433
957.01
14.0439
462.80
13.1140
0.1642
0.0529
6.94
15.4
GAS FLOW
Primary Flow (1/min)
Secondary Flow (I/min)
He (1/min)
02 (1/min)
Quench Flow (I/min)
Tip (1/min)
Wall (1/min)
NOx Meter Scale
Total Running Time (sec)
BLACK LIQUOR DATA
BLS Before (g)
BLS After (g)
BLS Input Weight (g)
Flush Char Weight (g)
Actual BLS Input Weight (g)
Total Fuel N Input (g)
NO DATA
Total NO Released (ppm.$)
g N as NO / g Fuel N (`)/0)
CHAR DATA
Char Weight (g)
Char Yield (%)
N Content in Char (')/0 by wt)
Total Char N (g)
g Char N / g Fuel N (c1/0)
g N Release /g Fuel N (%)
NOTE:
10.69
0.035
12.88
10.88
2.00
7.15
7.15
0.0486
0.7623
0.0007
0.00006
4.16
95.84
Not
enough
char
112
Table B.3 Experimental Data and Results for Black Liquor Char Combustion
EXPERIMENT NO.
Date
Environment
Oxygen Content ( %)
Reactor Path Length (inches)
Residence Time (sec)
Reactor Temperature (°C)
GAS FLOW
Primary Flow (1/min)
Secondary Flow (1 /min)
He or N2 (1/min)
02 (1/min)
Quench Flow (1/min)
Tip (1/min)
Wall (1/min)
NOx Meter Scale
Total Running Time (sec)
BLACK LIQUOR DATA
BLS Before (g)
BLS After (g)
BLS Input Weight (g)
Flush Char Weight (g)
Actual BLS Input Weight (g)
Total Fuel N Input (g)
NO DATA
Total NO Released (ppm.$)
g N as NO / g Fuel N ( %)
CHAR DATA
Char Weight (g)
Char Yield (%)
N Content in Char (% by wt)
Total Char N (g)
g Char N / g Fuel N (%)
g N Release / g Fuel N (%)
NOTE:
PCO131
7/25/95
He
15.4
PC0132 PC0133
7/26/95
He
7/26/95
15.4
21
N2
41
41
41
7.7
2.2
2.2
900
900
900
0.231
14.67
12.42
2.25
7.23
7.23
0.230
14.66
12.40
2.26
7.15
7.15
0.230
100
100
100
45.58
130.92
89.96
12.3112
12.2354
0.0758
0.0053
0.0670
0.0001
12.1568
11.6722
0.4846
0.0100
0.4679
0.0004
12.4371
12.1936
79.97
30.5819
616.30
33.5905
415.00
32.3480
0.0230
34.35
0.1883
40.24
0.035
0.00007
15.65
84.35
0.0428
18.26
Not
enough
char
10.72
8.50
2.22
4.90
4.90
0.2435
0.0055
0.2343
0.0002
Not
enough
char