155 South 1452 East Room 380 SO 3 Formation During Oxy- Coal Combustion Salt Lake City, Utah 84112 ...
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Transcript of 155 South 1452 East Room 380 SO 3 Formation During Oxy- Coal Combustion Salt Lake City, Utah 84112 ...
155 South 1452 East Room 380
SO3 Formation During Oxy-Coal Combustion
Salt Lake City, Utah 84112
1-801-585-1233
Jiyoung Ahn1, Dana Overacker1, Ryan Okerlund1, Andrew Fry2 and Eric G.Eddings1
1Dept. of Chemical Engineering , University of Utah 2Reaction Engineering International
Outline
•Background•Methodology and Equipment
- Controlled Condensation Method- Pilot-Scale Combustor (L1500)
•Equilibrium Calculations•Experimental Results- SO3 Concentration- Mass of SO3 emitted- Effect of Temperature- Effect of Staged Combustion
Background : SO3 in Combustion
- In general, only a small percentage of the sulfur in fuel is oxidized to sulfur trioxide (SO3). - Negative effects of SO3 on plant operations: 1) The potential for corrosion of metallic surfaces 2) The increased emission of acid aerosols, which create visible plumes and cause acid rain.- The increased amount of O2 in oxy-fuel combustion has a higher chance of affecting the oxidation of SO2 to SO3.
- Considering the effects of SO3 on the environment, and the possibility of increasing SO3 emissions in oxy-fuel combustion, it is important to investigate the behavior of sulfur compounds in oxy-fuel combustion.
Method of Measurement
- The Controlled Condensation Method ( ASTM D 3226-73T) is used to measure SO3 and SO2.- It takes advantage of the difference between the dew point of water and acid to selectively collect SO3.
Controlled Condensation Method
- SO3 is condensed into a sulfuric acid mist in the condenser. Temperature in the condenser was kept between 167F and 185F.- The first two impingers contain a hydrogen peroxide solution that captures SO2.
- The heated quartz filter removes particulate matter.
Titration Methodology- The amount of SO3 and SO2 present in the condensed acid and hydrogen peroxide solutions is quantified through a titration using barium perchlorate with thorin indicator (EPA Method 8A). - Due to subtle color changes during titrations, various concentrations of dilute sulfuric acid were used to make standards for comparison.
Pilot-Scale Combustor
- The 5 million Btu/hr furnace has a 3.2 ft2 internal cross section and is approximately 46 feet in length. - Gas was sampled at three different locations to investigate the effect of temperature on the formation of sulfur oxides during air- and oxy-fired coal combustion.
Equilibrium Behavior of SO3
- At higher temperatures (>1273K/1832F), equilibrium favors SO2 formation, not SO3. - The equilibrium is shifted toward the formation of SO3 at lower temperatures, with a maximum value at around 900 K (1160 F).
Equilibrium calculations of oxyfiring Illinois 6 coal
0 500 1000 1500 2000 25000.00E+00
5.00E+02
1.00E+03
1.50E+03
2.00E+03
2.50E+03 SR1.2 Oxygen 20%SR1.2 Oxygen 25%SR1.2 Oxygen 30%
Temperature (K)
mole fractio
n of SO3 (ppm
)
0 500 1000 1500 2000 25000
500
1000
1500
2000
2500
Temperature (K)
mol fractio
n of SO2 (ppm
)
(b) SO2 ppm(a) SO3 ppm
SO3 Measurement Challenges
1) If the gas is sampled at too high a temperature-> It may be prior to the maximum formation of SO3.
2) If the gas is sampled at too low a temperature-> Some SO3 may have condensed out prior to sampling
It is important, therefore, to sample for SO3 in an optimal temperature window to account for the formation that takes place, but to also sample prior to any SO3 condensation.
Experiment Results: Coal Analyses
Ultimate and Proximate analyses of PRB, Utah, and Illinois 6 coal*HHV=higher heating value
CoalLoss on drying Ash C H N S O
Volatile Matter
Fixed Carbon HHV*
[wt. %] [wt. %] [wt. %] [wt. %] [Btu/lb]
PRB 23.69 4.94 53.72 6.22 0.78 0.23 34.11 33.36 38.01 9078
Utah 3.18 8.83 70.60 5.41 1.42 0.53 13.21 38.60 49.39 12606
Illinois 6
9.65 7.99 64.67 5.59 1.12 3.98 16.65 36.78 45.88 11598
Experiment Result : Coal analyses
Ash Composition from PRB, Utah, and Illinois 6 coal (wt%)
Coal Al Ca Fe Mg Mn P K Si Na S Ti Al2O3 CaO Fe2O3 MgO MnO P2O5 K2O SiO2 Na2O SO3 TiO2
PRB 14.78 22.2 5.20 5.17 0.01 1.07 0.35 30.46 1.94 8.83 1.30Utah 14.52 6.11 5.09 1.39 0.02 0.59 0.57 60.89 1.41 2.33 0.88Illinois
617.66 1.87 14.57 0.98 0.02 0.11 2.26 49.28 1.51 2.22 0.85
Experiment Results: SO2
SO2 concentration (ppm) measured in the pilot scale experiments
500 600 700 800 900 1000 11000
500
1000
1500
2000
2500Oxy fuel, Illinois 6Air fuel, Illinois 6Oxy fuel, UtahAir fuel, UtahOxy fuel, PRBAir fuel, PRB
Gas temperature at the point of measurement (K)
SO2 concentratio
n (ppm
)
Because of the recycling of the flue gas, the amount of SO2 was much higher in oxy-coal combustion than in air-fuel combustion, ranging from twice as much (PRB) to almost six times as much (Illinois 6) at all temperatures.
Experimental Results: SO3
SO3 concentration (ppm) measured in the pilot scale experiments
500 600 700 800 900 1000 11000
1
2
3
4
5
6
7
8
9
10 Oxy fuel, Illinois 6Air fuel, Illinois 6Oxy fuel, UtahAir fuel, UtahAir fuel, PRB
Gas temperature at the point of measurement (K)
SO3 concentration (ppm
)
- For Illinois 6 coal, which had the highest sulfur composition, the concentration of SO3 at the optimum sampling temperature (755.2K/900F) increased up to 5 times for oxy- fuel combustion compared to air-fuel combustion. - At higher sampling temperatures, limited difference was found between oxy- and air-fuel combustion for Illinois 6 coal.
Experimental Results: SO3
800 805 810 815 820 825 830 835 840 845 8500
10
20
30
40
50
60
Oxy fuel, Illinois 6
Gas temperature at the point of measurement (K)
SO3 Concentration (ppm
)
0 500 1000 1500 2000 2500 30000.00E+00
2.00E-03
4.00E-03
6.00E-03
8.00E-03
1.00E-02
1.20E-02
0
10
20
30
40
50
60SR1.1, Oxygen 20%SR1.1, Oxygen 25%SR1.1, Oxygen 30%Oxy fuel, Illinois 6
Temperature (K)
mole fractio
n of SO3
Measured SO
3 Concentration
(ppm
)
SO3 concentration (ppm) measured in a small range of temperatures and comparison with the equilibrium calculations
- An increase in temperature of 40K in the critical sampling zone can decrease the SO3 concentration by 10-15 ppm- The data from Illinois 6 is in the region of very steep gradients in the equilibrium predictions. However, for Utah coal, small changes in the same temperatures didn’t affect SO3 concentration as greatly
Experimental Results: SO3
400 500 600 700 800 900 1000 1100 1200 1300 14000
0.002
0.004
0.006
0.008
0.01
0.012
0.014
0.016
0.018
0.02 Oxy-fuel, Illinos 6Air-fuel, Illinois 6Oxy fuel, UtahAir fuel, UtahAir fuel, PRB
Gas temperature at the point of measurement (K)
SO3 concentration (lb/MMBtu)
SO3 concentration (lb/MMBtu) from the pilot scale experiments
When actual furnace exhaust emissions are computed on a mass basis, mass of SO3 per million Btu is lower for oxy-fuel than air-fuel fired conditions, due to the reduced volume of flue gas.
Experimental Results: SO3
20.00% 25.00% 30.00% 35.00%0
10
20
30
40
50
60
Measured at 800KMeasured at 842K
Overall oxygen concentration (wt%)
SO3 Concentration ( ppm )
20.00% 25.00% 30.00% 35.00%0
0.005
0.01
0.015
0.02
0.025
0.03
0.035
Overall oxygen concentration (wt%)
SO3 Concentration
(lb/M
MBtu)
SO3 concentration of Illinois 6 coal measured in oxy-fuel combustion
- An increase in temperature of 40K in the critical sampling zone can decrease the SO3 concentration by 10-15 ppm, and by 0.01 0.015 lb/MBtu.- SO3 concentration shows an inverse relationship with overall oxygen concentration in oxy-fuel combustion.
(a) Molar concentration (ppm) (b) Mass concentration (lb/MMBtu)
Experimental Results: SO3
SO3 concentrations measured with Illinois #6 coal under staged and unstaged air- and oxy-fired combustion
- Because SO3 formation is favored at lower temperatures, it is anticipated that SO3 is formed primarily downstream of the burner.→ It is unlikely that the concentration of SO3 would be affected by staged combustion.- The figure does not indicate any significant correlation between SO3 concentration and staged or unstaged combustion.0.5 0.6 0.7 0.8 0.9 1 1.1 1.2
0
10
20
30
40
50
60 Oxy fuel at 800KAir fuel at 800K
Burner stoichiometric ratio
SO3 Concentration (ppm
)
Conclusions
- - Temperature at the point of - measurement has a strong impact on- the amount of SO3 captured in the - sample.
- Measurements of SO3 taken around 800 K (980.6F) during combustion of a high-sulfur coal showed that the SO3 concentration was three to five times higher during oxy-coal combustion as compared to air-fired conditions, but the difference was strongly coal- or S-content-dependent.- At higher sampling temperatures (922K/1200F), roughly the same amount of SO3 was measured in both air- and oxy-fired combustion.
Future Work- More detailed investigation of the effects of O2and CO2 concentration on the amount of SO3 formed for both air- and oxy-fired combustion - Development of fundamental understanding of the chemistry of N2 and CO2 and associated effects on the formation of SO3
- Investigating the influences of limestone (CaCO3) on SO3 formation
Acknowledgments
This material is based upon work supported by the U.S. Department of
Energy under Award Numbers DE-NT0005015 and DE-NT0005288.
Questions?