Study On Thermal Treatment Of Hazardous Wastes In Rotary Kilns

Hazardous wastes should be safely treated for their imperilment to both human being and environment. Thermal treatment of hazardous wastes, represented by incineration technology, has been widely used and well developed. Incineration in Rotary kiln is one of the most popular treatments of hazardous wastes.Comprehensive study on thermal treatment of industrial hazardous wastes beside medical wastes was made in this paper. The thermogravimetric characteristics of typical hazardous wastes were studied using thermobalance. The thermogravimetric processcan be described as a gas-solid reaction equation, da/dt = K(1-α)~n, within the practicalrange of error. The apparent kinetics parameters of typical hazardous wastes were calculated using Coats-Redfern integral method and they fitted well with experimental values.Electroplating sludge is not suitable for incineration solely for lacking of combustible content. But incineration of the electroplating sludge can get remarkable mass decreasing rates as more than 68% for original sludge and more than 30% for exsiccated sludge and high temperature can effectively reduce the lixiviation of heavy metals, but even the lowest lixiviation of Chromium is much higher than the national standard. Nickel is the only heavy metal which does not migrated out of the slag. The migration of Zinc, Copper and Lead increase with higher incineration temperature, and that of Chromium increase slightly with longer incineration time.For those hazardous wastes with high heat values, such as dye residue, it is proved that the incineration process can maintain steady when a is more than 0.4 and temperature between 600-900℃. But a> 0.6 and enough residence time in the incineration chamber is needed for the burn out of carbon. Desulfurizing and dechlorinating are essential and gasification can reduce the release of NOx than pyrolysis condition. Good mixing with air is necessary for high DRE of hazardous wastes with high heat value.Experiments on mean residence time (MRT) in rotary kiln were executed and model of axial transport in rotating drum was built. Feed rate was firstly introduced into the practical equation for MRT when the holdup is less than 10%. It is proved that the model including the factor of feed rate is more accurate than others especially in conditions of low rotating speed and can predict the MRT effectively.