HIGH VACUUM THERMAL STUDIES ON MLLW

摘要

This study investigated the use of an indirectly heated, high temperature (900℃), high vacuum (28” Hg)rnrotary kiln, developed and patented by Raduce, Inc. (a subsidiary of Sepradyne Corp.), to treat a dioxin contaminatedrnincinerator ash classified as mixed waste. This process differs from conventional thermal processing systemsrn(e.g., direct-fired incinerators and indirect heated thermal desorption units) primarily because of the combination ofrna high vacuum and rotary mixing action achieved by means of a proprietary rotating vacuum seal. This high vacuumrnresults in compounds being volatilized from the contaminated matrix at much lower temperatures than normallyrnencountered. This vacuum is an essential component of the treatment process. Treatment in the absence of anrnoxidative environment distinguishes the technology from conventional techniques and eliminates products ofrnincomplete combustion. A 500 cm3 bench-scale rotary vacuum thermal desorption and destruction unit (DDU) wasrnused at Brookhaven National Laboratory (BNL) to demonstrate this thermal treatment process. Dioxins and furansrnwere successfully decomposed at both low (450℃) and high (700-800℃) temperature regimes. Dioxin homologuernconcentrations in the untreated ash ranged between 30 and 565 ppb and furan homologue concentrations rangedrnbetween 78 and 267 ppb. After thermal treatment dioxin/furan homologue concentrations were close to nondetectablern(the highest dioxin concentration was reported at 0.067 ppb and the highest furan concentration wasrn0.119 ppb) for samples treated at both 450℃ and 750℃. In addition, substantial volume and mass reduction of thernash was achieved. Stabilization of the nonvolatile residues by a post-treatment encapsulation process will bernrequired to reduce the leachability of Resource Conservation and Recovery Act (RCRA) metals to below the EPArnToxicity Characteristic Leaching Procedure (TCLP) requirements.