a comparison of particle size distribution, composition, and combustion efficiency as a function of...
TRANSCRIPT
A Comparison of Particle Size Distribution, Composition, and Combustion Efficiency
as a Function of Coal Composition
2010 AIChE Annual Meeting Salt Lake City, Utah
November 7-12, 2010
William J. MorrisDunxi Yu
Jost O. L. WendtDepartment of Chemical Engineering
University of Utah, Salt Lake City, UT 84112
Outline
• 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 ChemistryCoal Analysis (on an as-received basis)
Sample LOD Ash C H N S O (diff) VolatileMatter
FixedCarbon
HHVBTU/lb
% % % % % % % % %
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
Ash Analysis
Alas Al2O3
Caas CaO
Feas Fe2O3
Mgas MgO
Mnas MnO
Pas P2O5
Kas K2O
Sias SiO2
Naas Na2O
Sas SO3
TiAs
TiO2
% % % % % % % % % % %
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
Coal Firing Rates and Combustion Conditions
Coal Coal feed rate (kg/h) Coal firing rate (kW)
36.64PRB 6.26
Illinois Bituminous 4.89
Sampling Systems
Bulk Ash Sampling (LOI) Black Carbon and PSD sampling
Laboratory CombustorPrimary
Coal feeder
3.8 m
Secondary
1.2 m
Heat exchanger #1 - 8
Flue gas1. Maximum capacity: 100 kW2. Representative of full scale units:
1. Self sustaining combustion2. Similar residence times and
temperatures3. Similar particle and flue gas
species concentrations3. Allows systematic variation of
operational parameters
Sampling port
Particle Size Distribution
10 100 1000 10000 10000010
100
1000
10000
100000
1000000
1% O2 Flue Gas Comparison
PRB 1% O2Illinois 1% O2
Dp (nm)
dM/d
logD
p (u
g/m
3 of
flue
gas
)
Particle Size Distribution
10 100 1000 10000 100000100
1000
10000
100000
1000000
3% O2 Flue Gas Comparison
PRB 3% O2Illinois 3% O2
Dp (nm)
dM/d
logD
p (u
g/m
3 of
flue
gas
)
Black Carbon (Soot) Emission by Photoacoustic Analysis
0 0.5 1 1.5 2 2.5 3 3.50
2000
4000
6000
8000
10000
12000
14000
16000
Black Carbon Emissions
PRBIllinois
Percent Oxygen in Flue Gas
BC u
g/m
3
Ultrafine and BC Comparison
0 0.5 1 1.5 2 2.5 3 3.5100
1000
10000
100000
Illinois Air
Ultrafine Concen-tration
Black Carbon Concentration
% O2 in Flue Gas
ug/m
3
0 0.5 1 1.5 2 2.5 3 3.51000
10000
100000
PRB Air
Ultrafine Concentra-tionBlack Carbon Concentration
% O2 in Flue Gas
ug/m
3
Note that the ultrafine concentration and black carbon concentration of both coals show correlating trends.
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 ~15-650nm.
Illinois Ash Composition by ICP-MS
0.01 0.1 1 100.1
1
10
100
1000
10000
100000
1000000
Illinois Air Fired
Na2OMgOAl2O3P2O5K2OCaOTiO2MnOFe2O3As2O3
Aerodynamic Particle Diameter (um)
dM/D
logD
p (u
g/m
3)
PRB Ash Composition by ICP-MS
0.01 0.1 1 100.1
1
10
100
1000
10000
100000
1000000
PRB Air
Na2OMgOAl2O3P2O5K2OCaOTiO2MnOFe2O3As2O3
Aerodynamic Particle Diameter (um)
dM/D
logD
p (u
g/m
3)
Comparison of Iron Emissions
0.01 0.1 1 101000
10000
100000
1000000
Iron as Fe2O3
PRB Fe2O3Illinois Fe2O3
Aerodynamic Particle Diameter (um)
dM/D
logD
p (u
g/m
3)
Comparison of Calcium Emissions
0.01 0.1 1 101000
10000
100000
1000000
Calcium as CaO
PRB CaOIllinois CaO
Aerodynamic Particle Diameter (um)
dM/D
logD
p (u
g/m
3)
Comparison of Sodium Emissions
0.01 0.1 1 101000
10000
100000
1000000
Sodium as Na2O
PRB Na2OIllinois Na2O
Aerodynamic Particle Diameter (um)
dM/D
logD
p (u
g/m
3)
Comparison of Arsenic Emissions
0.01 0.1 1 1010
100
1000
10000
Arsenic as As2O3
PRB As2O3Illinois As2O3
Aerodynamic Particle Diameter (um)
dM/D
logD
p (u
g/m
3)
Ignition Loss
0 0.5 1 1.5 2 2.5 3 3.50
2
4
6
8
10
12
14
16
Loss on Ignition Comparison
PRBIllinois
% Oxygen in Flue Gas
% L
oss
on Ig
nitio
n
Ignition Loss
-1 -0.5 0 0.5 1 1.5 2 2.5 3 3.50
1
2
3
4
5
6
7
PRB
Air Fired
% Oxygen in Flue Gas
% L
oss
on Ig
nitio
n
-1 -0.5 0 0.5 1 1.5 2 2.5 3 3.50
2
4
6
8
10
12
14
16
Illinois
Air Fired
% Oxygen in Flue Gas
% L
oss
on Ig
nitio
n
The PRB ignition loss begins to rise again at higher S.R.
The Illinois coal ignition loss is reduced as S.R. increases.
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