SOLID FUEL FROM WASTES

The wastes are first shredded into particles 3 to 5 ins in size. These shreds are then separated by weight: An airstream makes paper and plastic shreds rise to the top, while metals, glass and sand fall through to the bottom. The heavy fraction can be recycled, leaving only 10% to 20% of the original waste to go to the landfill. The light fraction is further shredded into shreds of 1 to 2 ins. This is the "solid RDF" (refuse derived fuel) with 4,000 to 7,000 BTU per pound (coal has about 13,000 at very roughly the same dollar cost per pound).

The fuel can be burned at the processing plant to produce steam for sale, or it can be sold to other users, including electric utilities. A power plant cannot burn it as primary fuel, because the chemicals in it (particularly chlorides) can cause corrosion at high temperatures. However, it can be mixed as a supplementary fuel with coal or oil and burned in boilers designed for coal firing..

To date, no significant corrosion has been found when the fuel is so used, but long term corrosion effects are still one of the unknowns in the energy from wastes business, now under investigation at Wisconsin Eleetric's Oak Creek station in a joint research project by the Electric Power Research Institute (EPR1), Wisconsin Electric, and Combustion Engineering.

Solid refuse derived fuel is now being manufactured in a number of cities and sold to the local utility (usually below cost, at the price of competitive fuel). The largest such facility now in operation seems to be in Milwaukee, Wisc., run by the City and American Can Co., with a capacity of 1,600 tons/day; but plants with capacities of 2,000 tons/day are under construction or planned in Rochester, N . Y ., Norfolk, Va., and St. Petersburg, Fla.

However, in all of these cases, it is the City that needs help from the utility in getting rid of its garbage; not the utility that prefers the fuel for price or any other reason (except good public relations) over coal or other fossil fuel.

[More: "Municipal Waste Problem or Opportunity," EPRI Journal, Nov. 1977; on pyrolysis: Study by Southern California Edison Co., Rosemead, Calif., April 1977.]