Contribution of combustion air preheating to operation of an industrial waste treatment plant

In a water-cooled rotary stoker combustor (WRC) used in industrial waste treatment, the effect of the preheating temperature of the combustion air on clinker generation and the concentrations of lead, zinc, and chromium in the incineration residue was examined. First, the temperatures and gas components in the WRC were measured. It was confirmed that the vapor phase temperature rises rapidly near the WRC outlet when the combustion air temperature is room temperature, whereas this rapid rise is eliminated when the combustion air temperature is 180°C. By eliminating the high temperature field and forming a relatively mild combustion field, the interval between occurrences of clinker trouble at the combustion air temperature of 180°C could be extended to about twice that at room temperature. Next, the mass balance of ash, lead, zinc, and chromium in the waste throughout the process was examined, and reasonable results were obtained. Comparison of the concentrations of the three heavy metals in the incineration residue and fly ash further revealed increasing migration of the metals from waste to fly ash with increasing preheated air temperature. This was explained in relation to the measured temperature distribution in the WRC.