Now the interest turns back to keeping a lid on sooty coal fires

Is there really a clean andm efficient way to burn coal? Or do escalating oil prices condemn the United States to a return of the Industrial Revolution's soot and smog?

Some researchers believe they now have the means to leave the worst part of coal emissions behind with history and still make burning of the abundant fuel a profitable undertaking. The hopes of these researchers are pinned on a process known as fluidized bed combustion.

The process itself has been around since the 1920s, used mainly in oil refining. Only since the 1960s, however, has fluidized bed combustion been applied to coal. It was discovered that coal mixed with limestone or similiar material caused most of the dangerous sulfur to be absorbed in the "bed," never making it up the smokestack.

The bed, which contains only about 2 to 6 percent coal, acts like a fluid when air is blasted through it. The oxygen flow allows the to burn at a 75 to 80 percent efficiency rate, which is better than conventional stoker-firing, and less efficient than pulverized coal-firing if the latter is used without smokestack scrubbers.

Is it the perfect solution, one which will make coal king and free industries and utilities from the thralls of OPEC? Not yet. Fluidized bed combustors have yet to prove themselves.

"They're still right on the edge of commercialized development," says Michael O'Hagan, product manager for Combustion Power Company of California. Speaking of industrial application, he adds, "The technology is ready to go, but it'll take a few years to really move." As for utilities, Mr. O'Hagan states, the fluidized bed combustor is still not ready to tackle anything quite that large.

However, Ronald Blank, executive director of corporate development at Curtiss-Wright Corporation in Wood-Ridge, N.J., where the government is sponsoring pilot projects to determine the applicability of the fluidized bed combustor to utilities, predicts it will be the utilities that will be pushed into use of the process. "There hasn't been that much interest on the part of industry," he says. "Industry can choose not to expand or to put a plant elsewhere, where resources are available, so they don't want to take the risk [ of using fluidized bed combustors]."

But utilities, he points out, face constantly growing demand and can't meet that demand from a distant site. However, he adds, "Hundreds of millions of dollars will be necessary for development [of fluidized bed combustors applicable to utilities]. No one's going to put the money up until they're sure about the process."

A lot of federal government money, thus far, has been riding on the process. The Tennessee Valley Authority has carried out several experimental projects and Foster Wheeler Boiler Corporation, with government sponsorship, has installed a modest fluidized bed combustor at Georgetown University.

Says Robert Gamble, manager of the fluidized bed engineering department at Foster Wheeler, "Our intent at Georgetown was to show that coal can be used in an urban setting. We've been burning coal there successfully since July 1979 without complaints about emissions. And we're 20 feet from a tennis court and downhill from an observatory!"

The government will also be sponsoring a project at Great Lakes Naval Training Center in Illinois. There a fluidized bed combustor will be burning a high-sulfur coal and providing steam for kitchens, laundry, and other everyday needs.

At the cutting edge of research at the moment is the pressurized fluidized bed combustor (PFBC), which potentially could allow greater efficiency and cleanliness by keeping the burning chamber under high pressure.

Curtiss-Wright's plant is currently the center of PFBC activity in the United States. There, under Department of Energy sponsorship, a 13-megawatt pilot utility plant, powered by coal burned in a PFBC, is under construction. It is scheduled for completion in 1982.

West Germany and Great Britain are also heavily involved in fluidized bed combustion development, and it is estimated tha t there are now about 30 European installations in use.