Process for utilizing low calorific value off-gases and simultaneous

Abstract

A process is disclosed in which any off-gas generated in a wastewater treatment plant, which off-gas has a low calorific (or BTU) value about one-tenth of that of natural gas, and usually even less, may be profitably burned in a multiple hearth furnace if the off-gas is first wet-scrubbed to a temperature below about 90.degree. F., then pre-heated by passing it through the center shaft of a multiple hearth furnace, before the pre-heated gas is burned. Such cooling of the off-gas by wet-scrubbing has the effect of lowering the moisture content of the wet-scrubbed gas sufficiently so that it may be advantageously pre-heated in the center shaft of the furnace and recycled to the hearths to assist in the combustion of sludge. In addition to providing desirable savings in auxiliary fuel usage, wet-scrubbed off-gas is unexpectedly cleansed of a sufficient amount of its corrosive components so as to permit ducting the wet-scrubbed gas in mild steel or cast iron equipment. Further, burning an odorous gas conveniently deodorizes it. The greater opening efficiency thus achieved provides more economical operation of a wastewater treatment facility. The process is most profitably utilized with decant tank off-gas ('DTO') which is generated in an amount about equal to the normal cooling gas capacity ('CG') of the furnace's center shaft, and which DTO is about equal to the volume of combustion air ('CA') which would be required to burn the sludge.