A Comparison of Particle Size
Distribution, Composition, and
Combustion Efficiency as a Function of
Coal Composition
William J. Morris
Dunxi Yu
Jost O. L. Wendt
Department of Chemical Engineering
University of Utah, Salt Lake City, UT 84112
2010 AIChE Annual Meeting
Salt Lake City, Utah
November 7-12, 2010
Outline
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Objectives
Coals examined
Furnace, sampling, and analysis
Particle Size Distribution
Soot Emissions
Chemical Composition
Loss on Ignition
Discussion
Conclusions
Objectives
• Provide a comparison of two different coal
aerosols for use in deciding whether fuel
switching is the best alternative for meeting EPA’s
interstate sulfur emissions targets.
• Examine aerosol emissions.
• Use aerosol chemistry to provide information for
those who wish to make predictions of
fouling/slagging within the furnace.
• Examine coal burnout performance when
switching coals in a given furnace.
Coal Chemistry
Coal Analysis (on an as-received basis)
Sample
Volatile Fixed
HHV
Matter Carbon BTU/lb
LOD
Ash
C
H
N
S
O (diff)
%
%
%
%
%
%
%
%
%
PRB
23.69
4.94
53.72
6.22
0.78
0.23
34.11
33.36
38.01
9078
Illinois
9.65
7.99
64.67
5.59
1.12
3.98
16.65
36.78
45.58
11598
K
as K2O
Si
as SiO2
Na
as Na2O
S
as SO3
Ti
As
TiO2
Ash Analysis
Al
as
Al2O3
Ca
as CaO
Fe
as
Fe2O3
%
%
%
%
%
%
%
%
%
%
%
PRB
14.78
22.19
5.2
5.17
0.01
1.07
0.35
30.46
1.94
8.83
1.3
Illinois
17.66
1.87
14.57
0.98
0.02
0.11
2.26
49.28
1.51
2.22
0.85
Mg
Mn
P
as MgO as MnO as P2O5
Coal Firing Rates and Combustion
Conditions
Coal
Coal feed rate (kg/h)
Coal firing rate (kW)
PRB
6.26
36.64
Illinois Bituminous
4.89
Sampling Systems
Bulk Ash Sampling (LOI)
Black Carbon and PSD sampling
Laboratory Combustor
Coal feeder
Primary
Secondary
1.2 m
3.8 m
1. Maximum capacity: 100 kW
2. Representative of full scale units:
1. Self sustaining combustion
2. Similar residence times and
temperatures
3. Similar particle and flue gas
species concentrations
3. Allows systematic variation of
operational parameters
Heat exchanger #1 - 8
Sampling port
Flue gas
Particle Size Distribution
1% O2 Flue Gas Comparison
dM/dlogDp (ug/m3 of flue gas)
1000000
100000
10000
1000
PRB 1% O2
Illinois 1% O2
100
10
1
1
10
100
1000
Dp (nm)
10000
100000
Particle Size Distribution
3% O2 Flue Gas Comparison
dM/dlogDp (ug/m3 of flue gas)
1000000
100000
10000
1000
PRB 3% O2
Illinois 3% O2
100
10
1
1
10
100
1000
Dp (nm)
10000
100000
Black Carbon (Soot) Emission by
Photoacoustic Analysis
Black Carbon Emissions
30000
25000
BC ug/m3
20000
15000
PRB
Illinois
10000
5000
0
0
0.5
1
1.5
2
Percent Oxygen in Flue Gas
2.5
3
3.5
Ultrafine and BC Comparison
Illinois Air
100000
Note that the ultrafine
concentration and black carbon
concentration of both coals show
correlating trends.
1000
Ultrafine
Concentration
100
10
Black Carbon
Concentration
1
0
0.5
1
1.5
2
2.5
3
3.5
% O2 in Flue Gas
PRB Air
100000
For the PRB coal, the ultrafine tracks
the black carbon, while the Illinois
black carbon mirrors the ultrafine
concentrations. Here ultrafines are
defined as particles with an
aerodynamic diameter of ~15650nm.
10000
ug/m3
ug/m3
10000
1000
Ultrafine
Concentration
100
10
Black Carbon
Concentration
1
0
0.5
1
1.5
2
% O2 in Flue Gas
2.5
3
3.5
Illinois Ash Composition by ICP-MS
Illinois Air Fired
1000000
dM/DlogDp (ug/m3)
100000
Na2O
MgO
10000
Al2O3
P2O5
1000
K2O
100
CaO
TiO2
10
MnO
1
Fe2O3
As2O3
0.1
0.01
0.1
1
Aerodynamic Particle Diameter (um)
10
PRB Ash Composition by ICP-MS
PRB Air
1000000
100000
dM/DlogDp (ug/m3)
Na2O
MgO
10000
Al2O3
1000
P2O5
K2O
100
CaO
TiO2
10
MnO
Fe2O3
1
As2O3
0.1
0.01
0.1
1
Aerodynamic Particle Diameter (um)
10
Comparison of Iron Emissions
Iron as Fe2O3
dM/DlogDp (ug/m3)
1000000
100000
PRB Fe2O3
Illinois Fe2O3
10000
1000
0.01
0.1
1
Aerodynamic Particle Diameter (um)
10
Comparison of Calcium Emissions
Calcium as CaO
dM/DlogDp (ug/m3)
1000000
100000
PRB CaO
Illinois CaO
10000
1000
0.01
0.1
1
Aerodynamic Particle Diameter (um)
10
Comparison of Sodium Emissions
Sodium as Na2O
dM/DlogDp (ug/m3)
1000000
100000
PRB Na2O
Illinois Na2O
10000
1000
0.01
0.1
1
Aerodynamic Particle Diameter (um)
10
Comparison of Arsenic Emissions
Arsenic as As2O3
dM/DlogDp (ug/m3)
10000
1000
100
PRB As2O3
Illinois As2O3
10
1
0.01
0.1
1
Aerodynamic Particle Diameter (um)
10
Ignition Loss
Loss on Ignition Comparison
18
16
% Loss on Ignition
14
12
10
PRB
8
Illinois
6
4
2
0
0
0.5
1
1.5
2
% Oxygen in Flue Gas
2.5
3
3.5
Ignition Loss
PRB
7
The PRB ignition loss begins to rise
again at higher S.R.
5
4
3
Air Fired
2
1
Illinois
0
-1
0
1
2
3
4
16
% Oxygen in Flue Gas
The Illinois coal ignition loss is
reduced as S.R. increases.
14
% Loss on Ignition
% Loss on Ignition
6
12
10
8
Air Fired
6
4
2
0
-1
0
1
2
% Oxygen in Flue Gas
3
4
Discussion
• Sulfur emissions are obviously reduced when switching from Illinois to PRB
coal due to coal chemistry.
• Black Carbon, or soot emissions are reduced using the higher rank Illinois
coal, which is an important consideration due to black carbon aerosol’s
effects on climate change as well as having significant health effects.
• Residence time is important in ignition loss effects, and is likely
responsible for the increased LOI at high S.R. for the PRB coal. Since more
mass of PRB coal has to be fired to generate the same heat value,
residence time in the furnace is decreased.
• Iron emissions are very similar between the two coals. However, the PRB
coal produces much more Na and Ca emissions which provide a sticky
surface for Fe particles to attach to on boiler tubes thus affecting slagging
and deposition within the furnace.
• Arsenic emissions are much higher for the Illinois coal than the PRB coal,
indicating there may be some health effects benefits from blending or
switching to PRB coals.
Conclusions
• The high sulfur Illinois coal reduced black carbon
emissions.
• The PRB coal, known for high burnout, may not achieve
optimum combustion completion in a furnace designed
for Illinois coal due to the increased mass feed rate.
• Ultrafine particle concentration is heavily dependent
upon soot, and is also influenced by sulfates and
mineral matter.
• Future regulation of soot and black carbon aerosols
may present conflicting solutions for current scheduled
SO2 emission regulations.
Acknowledgements
• Financial support from the Department of
Energy under Awards DE-FC26-06NT42808
and DE-FC08-NT0005015
• David Wagner, Ryan Okerlund, Brian Nelson,
Rafael Erickson, and Colby Ashcroft Institute
for Clean and Secure Energy, University of
Utah