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155 South 1452 East Room 380

1-801-585-1233. 155 South 1452 East Room 380 . Salt Lake City, Utah 84112 . SO 3  Formation During Oxy-Coal Combustion. Jiyoung Ahn 1 , Dana Overacker 1 , Ryan Okerlund 1 , Andrew Fry 2 and Eric G.Eddings 1 1 Dept. of Chemical Engineering , University of Utah

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155 South 1452 East Room 380

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  1. 1-801-585-1233 • 155 South 1452 East Room 380 • Salt Lake City, Utah 84112 SO3 Formation During Oxy-Coal Combustion Jiyoung Ahn1, Dana Overacker1, Ryan Okerlund1, Andrew Fry2 and Eric G.Eddings1 1Dept. of Chemical Engineering , University of Utah 2Reaction Engineering International

  2. 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

  3. 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.

  4. 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.

  5. 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.

  6. 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.

  7. 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.

  8. Equilibrium Behavior of SO3 Equilibrium calculations of oxyfiring Illinois 6 coal (b) SO2 ppm (a) SO3 ppm • - 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).

  9. 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.

  10. Experiment Results: Coal Analyses Ultimate and Proximate analyses of PRB, Utah, and Illinois 6 coal *HHV=higher heating value

  11. Experiment Result : Coal analyses Ash Composition from PRB, Utah, and Illinois 6 coal (wt%)

  12. Experiment Results: SO2 SO2 concentration (ppm) measured in the pilot scale experiments 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.

  13. Experimental Results: SO3 SO3 concentration (ppm) measured in the pilot scale experiments • 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.

  14. Experimental Results: SO3 • 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

  15. Experimental Results: SO3 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.

  16. Experimental Results: SO3 SO3 concentration of Illinois 6 coal measured in oxy-fuel combustion (a) Molar concentration (ppm) (b) Mass concentration (lb/MMBtu) • 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.

  17. 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 • SO3concentration and staged or • unstaged combustion.

  18. 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 • SO3concentration 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.

  19. Future Work • More detailed investigation of the effects of O2and • CO2 concentrationon 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

  20. Acknowledgments This material is based upon work supported by the U.S. Department of Energy under Award Numbers DE-NT0005015 and DE-NT0005288.

  21. Questions?

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