SO x Control processes

1. AE/CE 524B J. (Hans) van Leeuwen SOxControl processes

2. Legislation In March 2005, the U.S. EPA finalized the Clean Air Interstate Rule (CAIR). CAIR caps emissions of sulfur dioxide (SO2) and nitrogen oxides (NOx) in the eastern United States.[1] The rule includes three separate cap and trade programs, including annual SO2 and NOx reduction programs to limit fine particulate matter formation (PM2.5), and a seasonal NOx reduction program to decrease ozone formation.[2]

3. Sources of SOx • The majority of sulfur • oxides come from • power generation • sources: • - coal • oil • S + O2 SO2 • Other sources include: • - other industry such as paper mills • - mobile sources • - natural sources (e.g. volcanoes)

4. Specific Pollutants Involved • While SO2 is the main sulfur-containing pollutant, there are various others: • SO3 (the other “oxide”) SO2 + ½ O2 SO3 • H2S (rotten egg smell) • Various mercaptans (decaying garbage) • H - S - R or R’- S - R

5. Effects • Human Health (as well as animals) • Plants • Corrosion • Acid Rain

6. Human Health Effects • Lung and throat irritation • Worse symptoms for those with bronchitis • Weakening of the immune system • Sulfur oxides in combination with other air pollutants seem affect health even more: • €SOx with acid aerosols can product chronic cough • and difficulty breathing • € SOx with PM has produced some of the worst air pollution disasters (Meuse Valley 1930, Donora 1948, London 1952)

7. Effects on Plants Sulfur dioxide* can enter leaf stomata, causing: • Necrosis – morphological changes due to cell death (produces brown or black spots) • Chlorosis –“bleaching” of leaves, producing a yellow or white discoloration Necrosis (above) Chlorosis (below) *These effects can happen with other air pollutants as well

8. Corrosion • Apart from acid rain, sulfur-containing gases can directly corrode metals • H2S is most notorious for corrosion, but sulfur oxides and mercaptans can also corrode. Many times, corrosion is actually due to microbial activity acting on the sulfur Gas pipeline Stainless Steel

9. Acid Rain Sulfur oxides are not the only contributor to acid rain, but they are a primary cause. The chemistry is: SO2 + hν SO2* SO2* +O2  SO3 + O SO3 + H2O  H2SO4

10. Acid Rain – The process

11. Problems with Acid Rain • Increased acidity in bodies of water • Destruction of vegetation in forests • Corrosion of paints • Deterioration of building materials • Deterioration decorative materials • (e.g. stone on statues) • Decreased visibility • Deterioration of human health

12. Control Measures for Sulfur Air Pollutants

13. Fuel Desulfurization Coal Mineral sulfate  wash away Organic sulfur + O2 SO2 SO2 removal Oil & natural gas Claus process

14. SO2 Removal High concentration (e.g. smelting) Absorbing SO2 to make H2SO4 Low concentration (< 2000 ppm) Flue gas desulfurization

15. Limestone Scrubbing Lime Scrubbing Dual Alkali (recycled)

16. Scrubbing with a basic solid or solution • SO2 is an acid gas – sorbent slurries used to remove SO2 from flue gases alkaline. • Wet scrubbing using a CaCO3 (limestone) slurry produces CaSO3 (calcium sulfite): • CaCO3 (solid) + SO2 (gas) → CaSO3 (solid) + CO2 (gas) • Ca(OH)2 (lime) slurry, the reaction also produces CaSO3 (calcium sulfite): • Ca(OH)2 (solid) + SO2 (gas) → CaSO3 (solid) + H2O (liquid) • Mg(OH)2 (magnesium hydroxide) slurry produces MgSO3 (magnesium sulfite): • Mg(OH)2 (solid) + SO2 (gas) → MgSO3 (solid) + H2O (liquid) • To partially offset the cost of the FGD, in some designs, the CaSO3 (calcium sulfite) is oxidized to produce marketable CaSO4·2H2O (gypsum) by forced oxidation: • CaSO3 (solid) + H2O (liquid) + ½O2 (gas) → CaSO4 (solid) + H2O • A natural alkaline usable to absorb SO2 is seawater. The SO2 is absorbed in the water, and oxygen is added to react to form sulfate ions SO4- and free H+. • The surplus of H+ is offset by the carbonates in seawater pushing the carbonate equilibrium to release CO2 gas: • SO2 (gas) + H2O + ½O2 (gas)→ SO42- (solid) + 2H+ • HCO3- + H+ → H2O + CO2 (gas)

17. Lime-spray drying Same as lime scrubbing except the water evaporates before the droplets reach the bottom of the tower Dry scrubbing Direct injection of pulverized lime or limestone, also trona (natural Na2CO3) or nahcolite (natural NaHCO3) CaO Ca2+ Ca2+ SO2 CaO CaSO4 CaSO4

18. Wellman-Lord (W-L) process (1) Flue gas pretreatment: (venturi prescrubber) to remove particulates, SO3 and HCl (2) SO2 absorption by Na2SO3 solution (3) Purge treatment: centrifuge the slurry to remove solids (4) Na2SO3 regeneration (average, 1 mole Na2SO3 for 42 moles of SO2) MgO process Similar to lime/limestone scrubbing

19. Citrate scrubbing process US Bureau of Mines process SO2 is reduced with H2S to S in a liquid phase reaction Flakt-Boliden process Use steam to strip SO2 off the liquid. The SO2 can then be processed further to S via a Claus rdn or to H2SO4 by oxidation and absorption

20. Westvaco process CuO process

21. AIR POLLUTION CONTROL WITH LIME SLUDGE SO2 + CaCO3 CaSO3 + CO2

23. Typical water treatment process with lime softening Ca(OH)2 Lime    Lime sludge

24. SETTLING

25. LAGOON DEWATERING

27. STOCKPILING

28. Reuse Applications in Power Plants ISU Power Plant

29. CONTROL OF POWER PLANT AND EMISSIONS RESULTS: ENCOURAGING

30. Flue Gas Scrubbing with Fly Ash and Oxidant with Production of a New Wastewater Treatment Chemical NaClO3 + 3H2O + 3SO2 3SO42- + 6H+ + Na+ + Cl- Fe2O3 + 6H+ + 6e  3H2O + 2Fe3+ Al2O3 + 6H+ + 6e  3H2O + 2Al3+ 2Fe3+ + (3-n/2)(SO42-) + n (OH-)  Fe2(OH)n(SO4)3-n/2 2Al3+ + (3-n/2)(SO42-) + m (OH-)  Al2(OH)m(SO4)3-m/2