Study On Sewage Sludge Drying In Paddle Dryer With Solar Assisted

A solar assisted paddle dryer for sewage sludge drying was designed and studied in this paper. And the emission characteristics in the drying process of sewage sludge was also analyzed.The way for sludge disposal and utilization, the development of sludge drying study, and the characteristics of solar energy utilization are discussed to determine the research contents and build the solar assisted system. There were two key points in building this solar assisted system:(1) oil heated by the solar energy; (2) making the upper cover of the paddle dryer transparent, to let the solar radiation in.A small scale oil circuit was built to conduct the experiments of heating oil by the solar radiation. The result indicated that the temperature of the oil can reach the temperature scope of 60℃to 80℃, to insure the mid-temperature utilization. The temperature rising rate, the relationship between the temperature rising rate and the oil volume, and the relationship between the temperature rising rate and the oil flowing rate were analyzed. The efficiency of the solar collectors was calculated in both winter and summer.Based on the temperature rising rate, a solar assisted paddle dryer was built. Comparing the drying condition in paddle dryer with solar assisted, without solar assisted and in solar drying cabinet, it is found that the water evaporation rate in the solar assisted paddle dryer is the highest of all. The temperature in the dryer, the energy consumption and the condensed water quality were also studied.At last, the drying characteristics of sludge, emission characteristics of flue gases and condensed water quality were analyzed. The result indicated that three kinds of volatile compounds, i.e., ammonia, volatile fatty acid (CHCOOH, CH₃CH₂COOH) and alkane (heptane) were found in the thermal drying process. The drying rate of sludge, the concentration of volatile compounds, pH value and COD value were influenced by drying temperature. The concentration of volatile compounds was measured before and after condensing. It was found that condensing could markedly reduce the emission of gaseous pollutants.