How do you remove sulfur dioxide and nitrous oxides from a smokestack?
Expensively, say utility executives.
The cost of a ''scrubber'' - a device that uses limestone and water to convert the gaseous SO2 into solid gypsum - can run well beyond $100 million for a single 500 megawatt plant.
Since it requires about one ton of limestone for every ten tons of coal, it also produces a major sludge problem. Richard Grant, manager of environmental affairs for the Central Illinois Public Service Company, says the scrubber on a Jasper County plant produces 1,500 tons of waste per day, which is buried in landfills.
And that process doesn't touch the nitrous oxides.
Now, however, a process developed jointly in Massachusetts and Japan offers hope. Known as the electron-beam dry scrubber, it mixes flue gas with ammonia and bombards the mix with electrons.
The result: solid ammonium sulfate and ammonium nitrate, two principal compounds used in producing fertilizers.
Dr. Ven H. Shui of Avco Everett Research Laboratory in Everett, Mass., says the process, which has been under development since 1970 and is still several years from full-scale testing, will undercut the costs of conventional scrubbers. ''We figure we can save something like 40 percent'' on capital costs, he says. The process, which should cost about as much as a conventional scrubber to run but will produce a saleable by-product, was the subject of a paper delivered at the summer meeting of the American Institute of Chemical Engineers in Cleveland.
The idea may be greeted with caution, however. In the utility industry, Mr. Grant says, ''You rarely go to a new idea until it's been proven on at least a 100 megawatt power plant.''