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Show Introduction Under the sponsorship of the Office of Research and Development of the U.S. Environmental Protection Agency (EPA), the EPA Mobile Incineration System (MIS) was designed and constructed to demonstrate high-temperature incineration of hazardous wastes [1]. The system, shown in Figure 1, consists of a refractory-lined rotary kiln, followed by a cyclone, a secondary combustion chamber (SCC), and an air pollution control system. The air pollution control system consists of a quench system, followed by a wet electrostatic precipitator, a packed bed scrubber and a mist eliminator [2]. During the past year, the EPA Mobile Incineration System (MIS), has processed a brominated sludge material, which had high concentrations of chromium and trace quantities of other heavy metals. Because the brominated sludge contained high concentrations of chromium, there was a concern that the emissions of heavy metals from the stack could produce a significant health risk during the incineration of the material. To address this concern stack testing for heavy metals was conducted in September, 1988. The metal emissions of concern, measured6by the stack tests, were arsenic (As), cadmium (Cd), hexavalent chromium (Cr+ ), total chromium (Cr), lead (Pb) and mercury (Hg). Beryllium, antimony, barium, silver and thallium were not measured because their occurence is rare. The results of the stack testing were compared with the Tier II emission rates given in the draft version of the proposed incinerator regulation amendments [3]. The Tier II emission rates are conservative screening limits whic~ insure that the maximum increased cancer risks do not exceed 1 x 10- for the aggregate of the heavy metals emissions. The results of the two stack tests showed that the metals emissions from the MIS complied with the proposed incinerator amendments. The stack testing also provided the opportunity to explore the fate of the heavy metals as they were partitioned to the various residue streams generated by the MIS. Concentrations of the metals of concern were measured in the waste feed, kiln ash, cyclone ash, separator sludge (containing particulates removed by process water in the air pollution control system) and process water. Mass balances were performed for each metal species to supplement concentration data and the behavior of lead was examined by analyzing its occurence in various particle size ranges for the kiln ash, cyclone ash, and separator sludge. The results showed that Pb, Hg and Cd were depleted in the kiln and cyclone ash agd were enriched in the separator sludge and stack particulates and that Cr+ occurred mainly in the cyclone ash with trace quantities in the separator sludge. The data and the conclusions derived from the data are discussed in greater detail below. MIS Operating Conditions Process operating conditions for the heavy metals tests are summarized in Table 1. As shown in the table, operating conditions were consistent for the two tests. The sludge was fed at 1630 lb/hr, with about a 17000F average kiln temperature, a 2IOOoF SCC temperature, a I750F stack gas temperature, a 6.25% (wet) excess kiln oxygen and a solids residence time of 27 minutes (O.S rpm). 1 |