for Sulfur Air Pollutants Fuel Desulfurization Oil by gcVRYVj

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




SOx Control processes
                        1
                    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]




                                                                   2
          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)
                                          3
 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



                                             4
    Effects
• Human Health (as well as animals)

• Plants

• Corrosion

• Acid Rain




                                      5
   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)




                                                              6
                    Effects on Plants
 Sulfur dioxide* can enter leaf
 stomata, causing:

• Necrosis – morphological
changes due to cell death
(produces brown or black spots)                               Necrosis (above)
                                                              Chlorosis (below)
• Chlorosis – “bleaching” of
leaves, producing a yellow or
white discoloration
*These effects can happen with other air pollutants as well


                                                                                  7
                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

                                                      8
             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


                                           9
Acid Rain –
The process




              10
          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

                                         11
Control Measures for Sulfur Air Pollutants
Main Option       Suboption              Examples of Processes
Do not create SO2 Desulfurize the fuel   Oil desulfurization, Coal
                                         cleaning
                  Low-sulfur fuel
Dispersion        Build tall stacks
SO2 scrubbing:
  Throwaway       Wet scrubbing          Lime, Limestone, Dual alkali,
                                         Mitsubishi, Bischoff, Forced
                                         oxidation (w/ gypsum
                                         disposal)
                  Dry scrubbing          Lime spray drying, Lime
                                         injection, Trona, Nahcolite
  Regenerative    Wet processes          Absorption with water
                                         (smelters), Wellman-Lord,
                                         MgO, Citrate, Aqueous
                                         carbonate, SULF-x,
                                         CONOSOx, Forced oxidation
                                         (w/ gympsum sales)
                  Dry processes          Activated carbon adsorption,
                                         Copper oxide adsorption
                                                                         12
   Fuel Desulfurization
Coal
Mineral sulfate  wash away

Organic sulfur + O2  SO2  SO2 removal

Oil & natural gas
               
R  S  H 2 cataly ticreaction H 2 S  R
Claus process

H 2 S  3 O2  H 2O  SO2
         2
               reaction
2H 2 S  SO2 cataly tic  2 H 2O  3S
                                             13
      SO2 Removal
High concentration (e.g. smelting)
  Absorbing SO2 to make H2SO4

Low concentration (< 2000 ppm)
   Flue gas desulfurization


                                     14
           Limestone Scrubbing
CaCO3 ( s)  H 2O  2SO2  Ca 2  2 HSO3  CO2 ( g )
CaCO3 ( s)  2 HSO3  Ca  2  2CaSO3  CO2 ( g )  H 2O

             Lime Scrubbing
CaO  H 2O  Ca OH 2
SO2  H 2O  H 2 SO3
H 2 SO3  Ca (OH ) 2  CaSO3  2 H 2O
CaSO3  2 H 2O  0.5O2  CaSO4  2 H 2O

                    Dual Alkali
                                             2
                                 
Na2 SO3 / NaOH  SO2  Na   xSO4 2  ySO3  0.5H 2O
                          2
                  2
CaO / CaCO3  xSO4  ySO3  Na   0.5H 2O
  xCaSO4  yCaSO3  NaOH (recycled)
                                                            15
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)

                                                                                         16
             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)

                      Ca2+                  CaO
      Ca2+


SO2                                   CaO

                     CaSO4                        CaSO4

                                                          17
     Wellman-Lord (W-L) process
(1) Flue gas pretreatment: (venturi prescrubber) to remove
    particulates, SO3 and HCl
(2) SO2 absorption by Na2SO3 solution
   Na2 SO3  SO2  H 2O  2 NaHSO3
   Na2 SO3  0.5O2  Na2 SO4
   2 Na2 SO3  SO3  H 2O  Na2 SO4  2 NaHSO3
(3) Purge treatment: centrifuge the slurry to remove solids
(4) Na2SO3 regeneration
               
               
    2 NaHSO3 heat Na2 SO3  SO2  H 2O
    Na2CO3  SO2  Na2 SO3  CO2
                         (average, 1 mole Na2SO3 for 42 moles of SO2)

                 MgO process
Similar to lime/limestone scrubbing                                     18
     Citrate scrubbing process
SO2 ( g )  H 2O  H 2 SO3
H 2 SO3  H   HSO3
   3             2                      3
Ci  H  HCi                            Ci : citrate ion
HCi 2  H   H 2Ci 
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
                                                           19
      Westvaco process
SO2  H 2O  0.5O2  H 2 SO4
                     activatedcarbon


H 2 SO4  3H 2 S  4S  4 H 2O
               activatedcarbon



          CuO process
CuO  SO2  0.5O2  CuSO4

                                       20
AIR POLLUTION CONTROL WITH LIME SLUDGE

    SO2 + CaCO3  CaSO3 + CO2
Typical water treatment
process with lime softening

  Ca(OH)2
  Lime
        
        
        



            Lime sludge
SETTLING
LAGOON DEWATERING
STOCKPILING
Reuse Applications in Power Plants




           ISU Power Plant
CONTROL
OF POWER
PLANT AND
EMISSIONS




            RESULTS:
            ENCOURAGING
      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




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