SOx Control processes - Air Pollution - Lecture Slides, Slides of Ecology and Environment

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SOx

Control processes

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Legislation

In March 2005, the U.S. EPA finalized the

Clean Air Interstate

Rule (CAIR).

CAIR caps emissions of sulfur dioxide (SO

) and 2

nitrogen oxides (NOx) in the eastern United States.

[1]^ The rule

includes three separate cap and trade programs, including annualSOand NOx reduction programs to limit fine particulate matter^2 formation (PM2.5), and a seasonal NOx reduction program todecrease ozone formation.

[2]

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Specific Pollutants Involved While SO

is the main sulfur-containing 2 pollutant, there are various others:• SO(the other^3

“oxide”

) SO+^2

½^ O^2

SO^3

• HS (rotten egg smell)^2 • Various mercaptans (decaying garbage)H - S - R or R

’- S - R

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

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Effects on Plants

• Necrosis -^ morphological changes due to cell death(produces brown or black spots)• Chlorosis -^ “bleaching

”^ of

leaves, producing a yellow orwhite discoloration

Necrosis (above)Chlorosis (below)

Sulfur dioxide* can enter leafstomata, causing: *These effects can happen with other air pollutants as well

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Corrosion

• Apart from acid rain, sulfur-containinggases can directly corrode metals• HS is most notorious for corrosion, but^2 sulfur oxides and mercaptans can alsocorrode. Many times, corrosion is actuallydue to microbial activity acting on the sulfur^ Gas pipeline

Stainless Steel

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Acid Rain

The process

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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

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Fuel DesulfurizationOil & natural gas

RSH HSR

    ^

2 reactioncatalytic 2 Claus process

SOH

SOSH

SOOH OS H

(^32)

(^322)

2 reactioncatalytic (^22)

(^22) 2 2

     Coal^ Mineral sulfate 

^ wash away Organic sulfur + O

^ SO^2 ^ SO^ removal^2

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SORemoval^2 High concentration (e.g. smelting)^ Absorbing SO

to make H 2

SO 24

Low concentration (< 2000 ppm)^ Flue gas desulfurization

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Scrubbing with a basic solid or solution SOis an acid gas – alkaline sorbent slurries used to remove SO^2

from flue gas 2

Wet scrubbing

using a CaCO

(limestone) slurry produces CaSO 3

(calcium sulfite): 3

CaCO(solid) + SO^3

(gas)^ →^ CaSO 2

(solid) + CO 3

(gas) 2

Ca(OH)^ (lime) slurry, the reaction also produces CaSO^2

(calcium sulfite): 3

Ca(OH)^ (solid) + SO^2

(gas)^ →^ CaSO 2

(solid) + H 3

O (liquid) 2

Mg(OH)(magnesium hydroxide) slurry produces MgSO^2

(magnesium sulfite): 3

Mg(OH)(solid) + SO^2

(gas)^ →^ MgSO 2

(solid) + H 3 O (liquid) 2

To partially offset the cost of the FGD, in some designs, the CaSO

(calcium sulfite)^3

is oxidized to produce marketable CaSO

·2H^ O (gypsum) by 42

forced oxidation

CaSO(solid) + H^3

O (liquid) + ½O 2

(gas)^ →^ CaSO 2

(solid) + H 4

O 2

A natural alkaline usable to absorb SO

is seawater. The SO 2

is absorbed in the 2

water, and oxygen is added to react to form sulfate ions SO

• and free H 4

+^.

The surplus of H

+^ is offset by the carbonates in seawater pushing the carbonate equilibrium to release CO

gas: 2 SO(gas) + H^2

O + ½O(gas) 22

2-^ → SO(solid) + 2H 4

+

-^ +^ HCO+ H^3

→^ H^ O + CO^2

(gas) 2

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Lime-spray drying Same as lime scrubbing except the water evaporatesbefore the droplets reach the bottom of the tower

Dry scrubbing Direct injection of pulverized lime or limestone, alsotrona (natural Na

CO) or nahcolite (natural NaHCO 23

) 3

2+ Ca SO 2

2+Ca CaSO^4

CaO CaSO

4

CaO

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Citrate scrubbing process

   

 ^ CiHH HCi

Ci HCiH Ci

HSOH SOH

SOH OH gSO

ioncitrate :

)( US Bureau of Mines process SOis reduced with H 2

S to S in a liquid phase reaction 2 Flakt-Boliden process^ Use steam to strip SO

off the liquid. 2 The SO^2 can then be processed further to S via a Claus rdn or to H

SO^ by oxidation and absorption 24

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Westvaco process

OH S

SH SOH

SOH

O OH SO

2 carbonactivated 2 (^42)

(^42) carbonactivated 2 (^22)

(^44)

3

(^5). 0

  ^

  

 ^

   

CuO process

4 2 2

(^5). 0

CuSO O SO CuO^

  

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