Study On Basic Characteristics Of Sludge During Its Drying Process And Sludge Drying Technology

The water content of municipal sewage sludge is about 80%. Water content makes disposal and treatment of sludge difficult. Drying is a necessary step of sludge treatment. Study on mass transmission, heat transmission and viscosity of sludge during the drying process are made in this paper. And impacts of these properties on drying process are studied.Research on the viscosity is made in this papar using rotary viscosimeter and self-made viscosimeter. Results show that water content has influence on the viscosity. As water content decreases, the viscosity increases at first and then decreases. The sticky region of sludge is 50%-55%. The viscosity of this kind of sludge is highest when the water content is 50%-55%. The heat conduction speed becomes lower when the water content becomes less. The heat conduction is above 0.195W/(m·K) when water content is below 40%. If drying process is continued and water content is less, the heat conduction is slow. This means when the water content is less, drying efficiency is low and more heat is needed.Mass transmission is studied by TG-DTA analysis technology. Results show that mass transmission rate becomes lower as water content decreases. When the temperature is below 100℃, the water content decreases slowly. Weight loss is apparent when temperature is near 100℃that is just close to the boiling point of water. When the water content is above 60%, mass transmission rate is quick (0.08mg/s-0.09mg/s). When the water content is below 50%, mass transmission rate becomes slow. Endothermic peak appears when the temperature reaches to 105℃. More energy is needed when the water content is less.The results show that drying efficiency is high when mass transmission is quick, heat transmission is high and viscosity is low. Semi-drying process is suggested.