Thermal treatment of organic contaminated solids and waste : experiment, model and mass balance

A number of processes can be used to remediate contaminated soils. The thermal technologies for remediation of contaminated soils are summarized in this study. Each of these treatment process along with their system components are identified and described. Waste applicability is included for each treatment technology. A detailed list of feasible treatment processes is presented with descriptions of site demonstration results to aid ill selection of a given process. Technology status is summarized to provide current information on the processes. Energy components are discussed for cost requirement and safety considerations in thermal treatment applications. It is determined that the heat loss from kiln shell to environment demands the major fraction (56 percent) of the energy requirements in the bench scale thermal desorber. However, only 6 percent of total energy requirement is due to this heat loss to environment in a full scale desorber. The major heat required in a full scale desorber is used for treatment of water which consumes approximately 48 percent of the energy. Data on concentrations of PCDD/F in the feed, and in the effluent from modern Municipal Solid Waste Incinerators (MSWI) are surveyed and evaluated to determine if more PCDD/F are destroyed than formed in the Municipal Solid Waste (MSW) incineration process. Tile results show that a range of 0.8 to 87 pg(I-TE)/g or 0. 16 - 17.4 grams(I-TE) PCDD/F in 2 x 10 8 kg waste is present in the feed to a MSW incinerator. For 7.2 g(I-TE) PCDD/F in the feed to a MSW incinerator per year; the output in the combined gas and solid streams ranges from 0. 11 to 12 g(I-TE) per year. This data indicates that input and output levels of PCDD/F in modem, efficient municipal solid waste incineration are of similar magnitude. A bench scale rotary kiln thermal desorber was constructed and tested. Operation parameters such as kiln temperature, solid residence time, kiln tilt, kiln rotary speed, soil feed rate, and purge gas flowrate are varied to quantify their effects and determine optimum conditions. Results show that the thermal desorber system is highly effective in removing semivolatile organics from field contaminated soils. Temperature and solid residence time are two primary parameters affecting the desorption results. Higher temperatures and longer residence times result in higher removal efficiency. The result of mass balances for carbon illustrated that most of carbon recovery ranged from 45 to 115 percent in 20 experimental runs. A detailed heat and mass transfer model for thermal desorption of contaminants in/on soils has been developed for application in a rotary kiln thermal desorber. The heat balance and the heat flow between soil, gas and kiln wall are incorporated. Temperature profiles of gas and soil are calculated using the fourth order Runge-Kutta method. Evaporation rates of moisture and organic contaminants derived by Wendt et al. is applied for the mass balance calculation. A comparison of modeling results with experimental data for gas and soil temperature profiles as well as the mass flow rates of moisture and organic contaminants with experimental data is in reasonable agreement. Improvements in the model development are recommended