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Name: Sarah
Status: Student
Age: N/A
Location: OH 
Country: United States
Date: N/A


Question:
What affect does recovering SO2(g) from smokestacks and installing catalytic afterburners on cars decrease waste and reduce environmental impact? How do these processes work?



Replies:
Sarah,

Let me start off with shortly explaining the combustion process inside of a gasoline engine. Air is sucked (via vacuum) into a pipe, which is then mixed with vaporized gasoline. This air/fuel mixture is then forced into one of several cylinders and then closed off. Once the cylinder is closed off (intake and exhaust sides are sealed), the piston moves up and compresses the air and fuel, at which time the spark plugs spark and ignite the air/fuel mixture. At this point the fuel only has a very short time to combust and in the end you get a mixture of gas that still has come oxygen, some unspent fuel, some fully combusted fuel and some partially combusted fuel. MUCH heat is also a byproduct this this!

Once the air/fuel mixture is ignited, it forces the piston down and then as the piston moves back up, the exhaust valves open and let all of the spent fuel mixture out the opposite side of the engine. The mixture then goes through a pipe and ends up coming out your muffler. Before it gets there, though, it passes through a catalytic converter, which is basically many many fine screens (like a bunch of screen doors stacked ontop of eachother very very close). These screens are coated with a metal catalyst that helps oxidize the fuel that did not get fully combusted as well as turns gases like carbon monoxide into carbon dioxide and water. (This is why when you first start a car, you might notice water trickling from the tail pipe--this is because the car is not warm enough quite yet to combust all of the fuel or hot enough to form steam before it leaves your car.) The formost gas to reduce is carbon monoxide because it can go up into the fair reaches of the atmosphere and react with light to form a radical. Radicals are molecules that are deficient by one electron. When this occurs, it starts a chain of reactions that ends up in depleting ozone from our atmosphere. Ozone is responsible for keeping out the really high energy radiation from the sun!

As far as SO2 (sulfur dioxide) goes, to make a long story short, SO2 can be converted into sulfuric acid (H2SO4) and when this happens acid rain will occur. Acid, will of course, eat the paint off your car and cause a massive wide-spread amount of damage.

Matt Voss


The removal of SO2 gas from the exhaust of vehicles is not an issue since there is virtually no SO2 in gasoline. Its removal from coal fired power plants and municipal waste incinerators is another issue. There are several routes to reducing/eliminating SO2 from these point sources. The first involves "scrubbing" the gaseous effluents with water to form various acids derived not only from SO2 but Cl2, and NOx pollutants as well. The water is then neutralized with some sort of base and disposed of in accordance with regulations set by the Environmental Protection Agency. The solid effluent from the incinerator/power plant is another issue because the acidic residues are in solid form. Here the non-combustible ash residue from the coal and municipal waste is mixed with calcium oxide (CaO = lime) with rapidly reacts with water to form calcium hydroxide (Ca(OH)2 = slaked lime). This reacts with the acid residues to form calcium salts, which are then disposed of in solid waste landfills along with the other non-combustibles. This procedure is not without its own problems, however, because there is usually an excess of CaO (or Ca(OH)2) which raises the pH of the landfill and makes it very alkaline. This in turn causes other problems.

Vince Calder



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