Design and construction of a rotary kiln simulator for use in studying the incineration of hazardous waste

Rotary kilns have been used extensively in the cement industry to calcine limestone. In the past few years, the technology has been viewed as a possible option for the incineration of hazardous waste materials, especially for the disposal of solid wastes and the cleanup of contaminated soils and transformers.1 The technology is promising for incineration of hazardous waste for several reasons. First, it is flexible,2 i.e., many different types of solids and liquids can be fed into a single facility. Second, in some cases, incineration greatly reduces the volume of solid waste streams. Finally, there are many existing facilities that could be retrofitted for use in hazardous waste incineration. The kiln is used to drive the hazardous compounds into the gas phase, and an afterburner is used to destroy the gaseous compounds by exposing them to the required time/temperature history. Incineration success is measured by the destruction and removal efficiency (DRE), for each toxic component, which is defined as DRE = (Massin - Massou! )/Massin X 100% . (1) Generally, a DRE of at least 99.99% is required by the EPA. Facilities have been determined to be successful as long as these criteria are been satisfied. Whether a smaller or lower temperature facility could have produced the same results is generally not known, because the tests are often done on already existing facilities. The ambiguous nature of DRE also prevents success from being accurately measured; 99.99% DRE of a component with a high initial concentration in a waste is considerably easier to measure accurately than 99.99% DRE of a compound initially present in small amounts. Because of the rising costs and legal liabilities associated with hazardous waste disposal, there is now considerable interest in optimizing the disposal options. In order to mitigate the costs involved in hazardous waste incineration, it is necessary to define the temporal and thermal requirement for a particular application by testing the specific waste stream to establish its suitability for rotary kiln incineration. Each waste stream has its own particular properties and thus its own particular problems associated with incineration.3 Small-scale testing is desirable to determine the feasibility of incinerating a particular waste stream in a rotary kiln. Such testing can aid in the design and sizing of the kiln, in defining the optimum operating conditions, and determining whether or not rotary kiln incineration is appropriate for that particular waste stream.