Switch to coal as fuel revives potential for long-haul slurry pipelines

The newest form of energy transportation, one which works like an ice slush pumped through a soda straw, now has more of a future than once thought. The idea that pipelines could cheaply carry a slurry of water mixed with crushed coal over long distances has been waiting in the wings for years as King Coal slowly returned to the energy stage.

The biggest block to coal slurry development has been water availability in america's dry but coal-rich West. The slurry industry is confident of securing enough water rights at least to get started, but just how many lines can be accommodated remains uncertain.

But new research into waterless coal pipelines and ways of directly burning coal-water mixtures could fundamentally change the future of the slurry business.

The fact that there are now nine proposals to build coal slurry pipelines to utilities indicates just how promising this new type of transport may be in helping the US tap its most abundant nonrenewable resource.

The possibility of slurry pipelines offering healthy competition to coal-carrying railroads has enticed utilities, coal rpducers, and government energy planners to lobby lately on the pipelines' behalf.

And the present legal barriers to the ability of pipelines to cross private and public lands -- including railroad rights-of-way -- are expected to be resolved later this year or early in 1981 as Congress considers granting powers of eminent domain to the industry. Such powers will be given to the coal slurry industry as a quid pro quom for benefits given to railroads in the rail deregulation legislation taking shape, report congressional aids.

Considered by most analysts to be cheaper than rail transport for large and consistent coal-users far from the mines, slurry pipelines are expected to start coming on line by 1985, predict industry leaders.(A small one already exist in Arizonia.)

The National Coal Association estimates that total coal production east of the mississippi River will increase 33 percent from 554 billion tons in 1979 to 736 billion tons in 1990. Western coal production, however, will jump some 140 percent from 216 billion tons last year to 514 billion tons in 1990.

Just how much of this increase goes to either rail or slurry could depend to a large part on what comes out of experiments under way in many laboratories.

"In the next five years it will have to be coal-water slurries," says Robert Faddick, civil engineering professor at the Colorado School of Mines. "But possibly in the next decade, we would be looking at alternative carriers."

These alternatives include using liquefied carbon dioxide synthetic liquid fuels made from coal, compressed air, or even treated sewage as a substitute for water in coal slurries.

Each of these, however, may have its own problems, adds Dr. Faddick, a coal slurry consultant.

The most advanced and perhaps most promising is a liquid CO[2] process patented this year by A.D. Little Inc., a Cambridge consulting firm. Carbon dioxide is available from burning coal at a mine site and can be pressurized to transport crushed coal under low viscosity. At the end of the pipeline, the CO[ 2] could be recycled for use in enhanced oil recovery, a process now used in oil fields. But, cautions Dr. Faddick, the liquid's flow properties still need study and there is a possible problem in dry ice crystals forming on the coal.

Transporting coal with compressed air so far only works for short distances, says Dr. Faddick. Use of liquefied coal as a pipeline medium seems unlikely because the water needed in liquefaction may be more than the water needed for a slurry pipeline in most cases. Using conventional oil in a coal slurry requires either an oil filed near a coal mine, which is very rare, or tapping into an oil pipeline passing through a coal site. And burning such a mixture is not yet attractive.

Officials in Omaha, Neb., are studying the idea of using sewage as a carrier of coal. But the extra cost of shipping it to the Wyomming coal fields could possibly prohibit the practice. One benefit: the sewage receives partial threatment in the enclosed coal slurry.

Using less water and more coal in a slurry pipeline has been tried in the past without success. But in July, the idea got a strong boost.Atlantic Research Corp. of Alexandria, Va., announced that its engineers had developed a slurry able to be pumped with 62 percent coal. Current pipelines on the drawing boards use one ton of water for every ton of coal.

What's more, said Atlantic officials, a specially developed cornstarch added to the slurry makes it burnable in furnaces which rely on No. 6 oil, largely used in industry. The coal combustion quickly evaporates the water, whcih actually helps the burning by providing hydrogen. The price of a coal-water fuel would be about half the price of oil at $25 a barrel and about one-twentieth the cost of liquied coal, claims atlantic vice-president Charles B. Henderson.

Backed partially by the US Department of Energy (DOE), the project gives hope to utilities and industries resisting a switch to coal, which requires expensive storage and handling equipment. "Bringing coal back to utilities is almost an impossibility these days. but having a tank filled with a coal-water slurry is much easier," says Doe official William Fedarko.

Pumping coal directly from a mine, through a water pipeline and into a furnace had attractive possibilities to DOE. It eliminates the high cost of separating the water from the coal. "We could end up burning it in homes again, " suggests Mr. Fedardo

But direct combustion of coal slurry with 38 percent water still has a long way to go before it is widely used. Mr. Fedarko says the Soviet Union recently claimed coal burning with 50 percent water.

Using less water may reduce much of the water problem for slurry pipelines, "but it won't alleviate the emotional aspect of battles for water rights," says Dr. Faddick.