Cleaning Up Coal Smoke

Though the U.S. is running short of oil and natural gas, it has enough coal to last for hundreds of years. But environmental laws forbid burning much of the nation's available coal because it contains large quantities of sulfur. When the high-sulfur coal is burned, it gives off sulfur dioxide (SO2), an invisible gas that kills plants, corrodes metals and injures human health.

Now General Motors reports a new process that reduces SO2 emissions by 90%. Tested successfully for 14 months in a pilot installation at the Chevrolet plant in Parma, Ohio, GM's process starts with a trap to take dust particles out of coal smoke. Then the gases are routed into a device called a scrubber, where they bubble through a caustic-soda solution; chemical reaction between the SO2 and the soda produces two salts, sodium sulfite and sodium sulfate, that are pumped from the scrubber in waste liquids into tanks. There, lime and calcium carbonate are added. The resulting calcium salts settle to the bottom of the tanks, are removed and buried as safe landfill. The remaining liquid flows into another tank where it is treated with chemicals to create more caustic-soda solution for the scrubber--and the process begins anew.

GM is expanding its system to serve the entire Chevrolet-Parma plant. That will cost $3,000,000. But the process will pay for itself by allowing GM--or any other industrial user--to burn the cheapest and most abundant of all fuels: high-sulfur coal.

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