WATER WALL INCINERATION

The method has been in use in Europe since the 1950's, but has only recenty been introduced in this country. Its great, and probably only, advantage is that there is little or no need to process the wastes before they are burned. Only very large items are removed from it, the rest is burned unprocessed, and the ash water quenched; incombustibles such as metals may be recovered from the ash afterwards.

Almost any other aspect of the method is disadvantageous: Capital costs are high, and so are operating costs, mainly due to maintenance of the grates and tubes that corrode quickly with this type of fuel. It is also difficult to maintain a uniform rate of steam production, since the heat content and burning rate of wastes fluctuate with different batches.

But perhaps most disappointing, the steam cannot be used for large power plant turbines, Since it is at low pressure and temperature (600 psi, 500 degreesF). The processor sells the steam for district heating, for industrial process heat, or for use in small power plants.

The best known US system of this type is operating in Saugus, Mass., with a capacity of 1,200 tons of wastes per day; another, with 2,000 tons/day capacity, is to go into operation later this year in Hempstead, N.Y. In both cases the uses of steam include generation of electric power.