Air Emissions TreatmentAir Emissions Treatment

Because air pollutants vary in size many orders of magnitude, Because air pollutants vary in size many orders of magnitude, many different types of treatment devices are required for many different types of treatment devices are required for emissions treatment.emissions treatment.

Air pollutant devices can be treated as black box separators, like Air pollutant devices can be treated as black box separators, like we studied in Chapter 3. Recovery efficiency can be described by we studied in Chapter 3. Recovery efficiency can be described by the equation:the equation:

RR11 = (x = (x11/x/x00) x 100) x 100

RR11 = recovery of component 1, % = recovery of component 1, %

xx11 = amount of pollutant collected by the device per = amount of pollutant collected by the device per

unit time, kg/sec unit time, kg/sec x x00 = amount of pollutant entering the device per = amount of pollutant entering the device per

unit unit time, kg/sectime, kg/sec

ExampleExample

An air pollution control device removes a particulate that is being emitted at a An air pollution control device removes a particulate that is being emitted at a concentration of 125,000 concentration of 125,000 g/mg/m33 at an air flow rate of 180 m at an air flow rate of 180 m33/sec. The device /sec. The device removes 0.48 metric toms per day. What are the concentration of the removes 0.48 metric toms per day. What are the concentration of the emission and the recovery of collection?emission and the recovery of collection?

Pollution control Pollution control devicedevice

FeedFeed

xx00

EscapedEscaped

xx22

RemovedRemoved xx11

At steady state the mass balance is:At steady state the mass balance is:

Rate of particulates in = rate of particulates outRate of particulates in = rate of particulates out

Rate of particles in = rate of particles removed + rate of particles escapingRate of particles in = rate of particles removed + rate of particles escaping

Particulates in:Particulates in:

180 m180 m33/sec x 125,000 /sec x 125,000 g/mg/m33 x 10 x 10-6-6 g/g = 22.5 g/secg/g = 22.5 g/sec

Particles Particles collected:collected:

0.48 tons/day x 100.48 tons/day x 1066 g/ton x 1 hr/3600 sec x 1 day/24 hr = 5.5 g/sec g/ton x 1 hr/3600 sec x 1 day/24 hr = 5.5 g/sec

Mass Mass balance:balance:

22.5 = 5.5 + particles that escape22.5 = 5.5 + particles that escape

Particles that escape = 17 g/secParticles that escape = 17 g/sec

Emission Emission concentration:concentration:

(17 g/sec x 10(17 g/sec x 1066 g/g)/ 180 mg/g)/ 180 m33/sec = 94,000 /sec = 94,000 g/mg/m33

Recovery:Recovery:

R = (xR = (x11 x 100)/x x 100)/x00 = (5.5 x 100)/22.5 = 24% = (5.5 x 100)/22.5 = 24%

Treatment DevicesTreatment Devices

Settling ChambersSettling Chambers

The simplest of treatment devices. Wide spot in the exhaust flue The simplest of treatment devices. Wide spot in the exhaust flue that allows particles to settle out. Only very large particles (> 100 that allows particles to settle out. Only very large particles (> 100 m) will settle effectively.m) will settle effectively.

CyclonesCyclones

Bag Filter or Bag HouseBag Filter or Bag House

Spray Tower or ScrubberSpray Tower or Scrubber

Electrostatic PrecipitatorsElectrostatic Precipitators

Electrostatic PrecipitatorsElectrostatic Precipitators

Process SelectionProcess Selection

A)A) Settling ChamberSettling Chamber

B)B) Simple CycloneSimple Cyclone

C)C) High-efficiency High-efficiency CycloneCyclone

D)D) Electrostatic Electrostatic PrecipitatorPrecipitator

E)E) Spray Tower wet Spray Tower wet scrubberscrubber

F)F) Venturi ScrubberVenturi Scrubber

G)G) Bag FilterBag Filter

Control of Gaseous PollutantsControl of Gaseous Pollutants

Wet ScrubbersWet ScrubbersAdsorptionAdsorptionIncineration or flaringIncineration or flaring

Catalytic CombustionCatalytic Combustion

Wet ScrubberWet Scrubber

Venturi ScrubberVenturi Scrubber

Wet ScrubbersWet Scrubbers

AdsorptionAdsorption

Carbon Adsorption SystemCarbon Adsorption System

Incineration and FlaringIncineration and Flaring

Control of Sulfur Oxides (SOControl of Sulfur Oxides (SOxx))Emission of SOEmission of SOxx one of the major causes of acid precipitation one of the major causes of acid precipitation

Major source of SOMajor source of SOxx is coal-fired power plants is coal-fired power plants

Several options for control:Several options for control:

Change to Low-sulfur fuelChange to Low-sulfur fuel

Desulfurize the coalDesulfurize the coal

Sulfur in coal is either organic (usually about 60%) or Sulfur in coal is either organic (usually about 60%) or inorganic (about 40%). The inorganic form is iron inorganic (about 40%). The inorganic form is iron pyrite (FeSpyrite (FeS22) that can be removed from the coal by ) that can be removed from the coal by

washing.washing.

The removal of organic sulfur requires a chemical The removal of organic sulfur requires a chemical reaction that is accomplished best if the coal is reaction that is accomplished best if the coal is gassified first. Gasified coal is like natural gas.gassified first. Gasified coal is like natural gas.

SOSOx x Control Options (continued)Control Options (continued)

Tall StacksTall Stacks

Flue-Gas DesulfurizationFlue-Gas Desulfurization

Contact with limeContact with lime

SOSO22 + CaO + CaO CaSO CaSO33

Contact with limestoneContact with limestone

SOSO22 + CaCO + CaCO33 CaSO CaSO44 + CO + CO22

Calcium sulfite (CaSOCalcium sulfite (CaSO33) and calcium sulfate (CaSO) and calcium sulfate (CaSO44) )

are solids that have low solubilities so they can be are solids that have low solubilities so they can be removed from the water by settling, but then there is removed from the water by settling, but then there is a disposal problema disposal problem