APES 7

7.6: REDUCTION OF AIR POLLUTANTS

Ways to reduce emissions of air pollutants: drive less, conserve electricity, eat more plants, renewable energy

Laws and regulations on air pollutants: clean air act, pollution credits, and Corporate Average Fuel Economy standards

Clean air act: allows EPA to set acceptable levels for criteria air pollutants, monitor emissions levels from power plants and other facilities, and tax/sue/fine corporations that release emissions above levels

Pollution credits: companies that reduce emissions well below EPA-set levels earn pollution credits, and they can sell these to companies that release more than acceptable levels

CAFE standards: requires the entire US fleet of vehicles to meet certain average fuel, requires vehicle manufacturers to work to make more efficient vehicles, which release less air pollutants

2 ways to reduce vehicle air pollutants: vapor recovery nozzle and catalytic converter

Vapor recovery nozzle: captures hydrocarbon VOCs released from gasoline fumes during refueling; separate tube inside nozzle captures vapors and returns them to underground storage tank beneath the gas station, which also reduces benzene (carcinogen) from gas vapors

Catalytic converter: required on all vehicles after 1975, contains metals (platinum and palladium) that bind to NOx and CO, converting NOx, CO, and other hydrocarbons into CO2, N2, O2, and H2O

Crushed limestone: used to reduce SO2 from coal power with crushed coal mixing with limestone before being burned in boiler

How does limestone reduce emission of SO2: calcium carbonate in limestone combines with SO2 to produce calcium sulfate, this calcium sulfate can be used to make gypsum wallboard or sheet rock for home foundations

Fluidized bed combustion: fluidizing jets of air pumped into combustion bed, they bring more O2, making combustion more efficient, bringing SO2 into more contact with calcium carbonate in limestone, and allowing coal to be combusted at lower temperatures, which emits less NOx

Air pollutants that dry/wet scrubbers reduce: NOx, SOx, VOCs, PM (wet scrubbers only)

Dry scrubbers: Large column/tube/pipe filled with chemicals that absorb or neutralize oxides (NOx, SOx, VOCs) from exhaust streams (emissions); an example would be calcium oxide which reacts with SO2 to form calcium sulfate

Wet scrubbers: involves chemical agents that absorb or neutralize NOx, SOx, VOCs, but they also include mist nozzles that trap PM in water droplets

The process of wet scrubbers: mist droplets with pollutants and PM trapped in them fall to bottom of scrubber or get trapped at top by mist eliminator, and sludge collection system traps polluted water for disposal

Ways to reduce PM: Electrostatic precipitator and baghouse filter

How an electrostatic precipitator is used: emissions pass through a device with a negatively charged electrode, giving particles a negative charge, then negatively charged particles stick to positively charged collection plates, trapping them; plates are discharged occasionally so particles fall into collection for disposal

How a baghouse filter is used: large fabric bag filters trapped PM as air from combustion/industrial processes passes through, then the Shaker device knocks trapped particles loose into collection below, taking them to a landfill