GARBAGE POWER

The oil vampires now face a new opponent. Playboy has come down from the lofty heights of mons Veneris to charge that the oil companies are not interested in power from refuse because "they haven't got a franchise on our garbage dumps as yet."

Apart from sinking gas wells into garbage dumps to recover the methane produced by organic rotting matter, there are several ways of harnessing the energy contained in solid wastes. The simplest is to burn the trash in special incinerators designed to recover the heat, usually by heating a boiler. Such a plant in Hempstead, N.Y., produces 68,000 kg of steam per hour, part of which is used for desalination of sea water. A Chicago plant produces 454,000 kg/day of steam this way, and a large facility in Nashville, Tenn., will provide steam for yearround heating or air conditioning of 32 adjacent government office buildings, thus recycling garbage in more than one sense.

A second method is to process trash and compact it into supplementary fuel for power plants. The biggest system of this type is now in operation in St. Louis, Mo. The trash is shredded, ferrous metals are magnetically removed for recycling, and an air classification system removes the remaining noncombustibles. The remainder compacts under its own weight and is shipped to a nearby power plant, where it provides 10 to 15% of the fuel for two coal-fired 135 MW boilers. The cost of the refuse preparation is around $5 per ton, far cheaper than coal (let alone oil at its decontrolled value).

A third way is to convert the garbage, after shredding and removing non-combustible matter, to gas and oil by pyrolisis - heating in an oxygen-free atmosphere.

The heat value of the gas is more than sufficient to sustain the pyrolisis process, and the oil is low-sulfur with heat content some 75% of orthodox heating oil. Pilot projects are operated by the US Bureau of Mines, the Garrett Co., a subsidiary of Occidental Petroleum, and Union Carbide. A related, but different system of high-temperature incineration will be used in a 900 ton/day plant now under construction in Baltimore, Md.

A fourth system, now being developed by Combustion Power Co of Menlo Park, Ca., attempts to make garbage combustion directly usable for electric cower generation in already existing hardware. The idea is to power a gas turbine directly with the hot gases resulting from burning trash, after the particulates have been removed.

For details, see IEEE Spectrum, September 1974; however, the reader should not uncritically accept some of the article's comments. In all of these systems, energy and resource recovery are additional and very welcome benefits in solving the main problem, which is garbage disposal. The caption under a photo of trash cans claiming that "society's continued affluence may well depend on efficient use of the humble contents" is bunk: Even if it were possible to collect and process every last bit of the 180 million tons of trash produced annually in the US, the resulting energy would amount only to about 1% of the total consumption.