A clean and green way to reduce acid rain has been developed by Chang Yul Cha of the University of Wyoming in Laramie. The process cuts sulphur dioxide and nitrogen oxides from coal-fired smokestacks using char and microwaves (Science, Vol 257 No 5076). The gases are absorbed as they pass through a bed of porous char. The char is microwaved to stimulate a reaction between the gases and carbon atoms in the char that results in the release of nitrogen and carbon dioxide. The sulphur is cooled in a spray chamber and can be collected and sold. If powdered coal is added to the char-gas mix, it gets converted into more char that can be used repeatedly. After about 40 cycles, the char can be used for filtration in waste water treatment plants. The process is cheaper and more effective than the limestone scrubbers now used to clean smokestacks.
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