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Viable alternative to incineration.

A new technique - reverse - burn gasification - looks better than conventional incinerators fortreating some of the most stubborn hazardous wastes. The process (patented as ChemChar) treats wastes in the form of solids, liquids, sludge, and soils. Operations of several laboratory-scale reactors based on the process have demonstrated its versatility and usefulness successfully.

Wastes that are treated most effectively by reverse-burn gasification are chemical sludges (specifically those containing polychlorobenzenes or PCBS), heavy metals, contaminated soils, and sewage sludge, according to Stanley E. Manahan, professor of chemistry, University of Missouri-Columbia. "The gasification process is especially useful for destroying mixed waste [chemical waste mixed with radioactive materials]."

In reverse-burn gasification, waste constituents are destroyed by conversion to a combustible gas and dry, inert carbonaceous solid, which either is nonhazardous or readily can be mixed with cement to prevent leaching of its toxic components. "Conventional incineration suffers some severe disadvantages in the thermochemical [heat] treatment of wastes, particularly in the areas of emissions and by-product generation."

Gasification offers distinct advantages over incineration. Instead of an exhaust gas that must be treated to control emissions, it emits a combustible gas that can be burned under carefully controlled conditions to destroy any remaining traces of wastes. The process produces nonhazardous water and inorganic salts and gases as the only by-products.

The ChemChar process involves mixing solid wastes with char; gasification of the char/waste mixture; removal from the gas stream of aqueous waste products; and final combustion of the gas stream. The method allows for recovery of the spent activated char without unacceptable loss of mass, absorptive capacity, or physical integrity.
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Title Annotation:reverse-burn gasification
Publication:USA Today (Magazine)
Date:Jun 1, 1993
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