2010 AIChE Annual Meeting Salt Lake City, Utah November 7-12, 2010

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

% Lo

ss o

n 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

% Lo

ss o

n 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

% Lo

ss o

n 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