Prof. Jiakuan Yang Huazhong University of Science and Technology Air Pollution Control Engineering

Lecture 11 Lecture 11 Control of Sulfur Oxides Particulate pollutants Volatile Organic Compounds (VOCs) Sulfur Oxides Nitrogen Oxides The four major air pollutants

Lecture 11 Lecture 11 Control of Sulfur Oxides Particulate pollutants Volatile Organic Compounds (VOCs) Cyclone, ESP, filter, leakage control, vapor capture, condensation Mostly Physical process Sulfur Oxides Nitrogen Oxides Mostly chemical process

Lecture 11 Lecture 11 Control of Sulfur Oxides Ⅰ Harmful effects of Sulfur Oxides Ⅱ Sources of sulfur pollution Ⅲ Removal of Reduced Sulfur compound (H 2 S) from Petroleum and Natural Gas Stream Ⅳ Removal of SO 2 from the Rich Waste Gases Ⅴ Removal of SO 2 from Lean Waste Gases Ⅵ Alternatives to Sulfur Control

Ⅰ Harmful effects of Sulfur Oxides Strong respiratory irritants Secondary Particles and impairing visibility, PM 10, PM 2.5 Acid rain, Acid deposition

Ⅱ Sources of sulfur pollution Reduction Elemental form Oxidation First step Oxidation Second step Reaction with water Reaction with NH 4 + or other cations N2N2 NO NO 2 HNO 3 NH 3 Nitrate particles S SO 2 SO 3 H 2 SO 4 H2SH2S sulfate particles

Sources of sulfur pollution H2SH2S Petroleum and natural gas streams SO 2 Rich Waste Gases Copper, lead, zinc, and nickel smelters SO 2 Lean Waste Gases Coal-burning electric power plant H 2 SO 4 sulfate particles Secondary Particles S 、 CaSO 4 harmless

Ⅲ Removal of Reduced Sulfur compound (H 2 S) from Petroleum and Natural Gas Stream Feed gas in Cleaned gas out Absorber Loaded solvent Heat exchanger Solute gas out Stripper Stripped solvent Reboiler Figure 10.15

Ⅲ Removal of Reduced Sulfur compound (H 2 S) from Petroleum and Natural Gas Stream Using water as the scrubbing agent, The required liquid flow rate is 148kg/s Using monoethanolamine (MEA, 乙醇胺 ), HO(CH 2 ) 2 NH 2 as the scrubbing agent, The required liquid flow rate is 6.1kg/s H 2 S(gas) H 2 S(dissolved in water)H + + HS - H 2 S(gas)+ 0.5 O 2 S + H 2 O

Ⅳ Removal of SO 2 from the Rich Waste Gases Page 405 The SO 2 concentrations in off-gases from the smelting of metal sulfide ores depend on which process is used and vary with time within the batch smelting cycle. However, they generally range from 2 ~4% SO 2. SO O 2 SO 3 +H 2 O H 2 SO 4

Economic Problem metal sulfide ores melting plant Sulfuric acid plants Phosphate fertilizer plant

Ⅴ Removal of SO 2 from Lean Waste Gases Coal-burning or oil-burning facilities. SO 2 content of the exhaust gas is about 0.1 percent. Flue gas desulfurization (FGD) The most widely used procedure for controlling SO 2 emissions from these sources is scrubbing with water containing finely ground limestone. CaCO 3 + SO O 2 CaSO 4 + CO 2 limestone

(1) Problems of SO 2 Removal by river water It requires a large amount of water. SO 2 will emit from the waste water back into the atmosphere. SO 2 undergoes oxidation reaction, removing most of the dissolved O 2 in the river.

The first SO 2 Removal process with river water Ⅴ Removal of SO 2 from Lean Waste Gases Power plant scrubber limestone Thames River Settling tank Cleaner gas 1933~1940

(2) SO 2 Removal by NaOH Solution CO 2 (gas)CO 2 (dissolved)+H 2 O H 2 CO 3 H + +HCO 3 - SO 2 (gas)SO 2 (dissolved)+H 2 O H 2 SO 3 H + +HSO 3 - SO 2 forms much stronger acid than does CO 2. We must be careful to control the pH of our solution so that it is acid enough to exclude CO 2 but not acid enough to exclude SO 2. CO 2 will use up NaOH alkali. The cost of NaOH alkali is high.

(3) Forced-Oxidation Limestone Wet Scrubbers Page 415, Figure 11.6

FGD

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(3) Forced-Oxidation Limestone Wet Scrubbers Development problems with limestone scrubbers. Corrosion Solid deposition( 结垢 ) Entrainment separator plugging Poor reagent utilization Poor solid-liquid separation

(4) Other SO 2 Removal Processes Page 420, Table 11.4 Reagents Processes CaCO 3 Limestone Ca(OH) 2 Hydrated lime quicklime Na 2 CO 3 NaHCO 3 Regenerable adsorbents Wet LimestoneLime throwaway scrubbing Double alkali Dry BoilerBoiler lime Boiler or flue throwaway Limestone injection Wet-dry Spray dryers Regenerative Many kinds

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Ⅵ Alternatives to Sulfur Control (Pollution prevention) Change to a Lower Sulfur Control Fuel Remove Sulfur from the Fuel Modify the Combustion Process Don’t Burn at all

Summary Page 430

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This Lecture and the Next Lecture  This Lecture:  Chapter 10 page 395~430  The Next Lecture:  Chapter 12 page 439~464

Exerciser 1. What are the major development problems with Limestone Wet Scrubbers? 2. Please present other approaches of removal of SO 2 from LEAN waste gases except for Limestone Wet Scrubbers?

DISCUSSION Topics about Air pollution:  Introducing yourself  Interesting news or information about air pollution your having read or heard  Your opinions on this Air Pollution course  Your suggestions for Chinese Air Pollution  Other familiar issues about Air Pollution