| Sludge is the main byproduct of sewage treatment. It contains a large types of organic pollutants and some potential toxic ingredients such as bacteria, heavy metals and carcinogens .Sludge also has a foul odor. It has been the main secondary pollution sources. The treatment and disposal of sludge has become a worldwide problem. It's an important approach to make the sludge steady, harmless and quantitative reduction with drying technique.The characteristics of sludge drying process was experimentally investigated. On this basis, the integrated multi-effect plate dryer system was studied and developed. The structure, transmission system, operating conditions and automatic control system of integrated multi-effect palte dryer were designed. Furthermore, a drying process model was constructed in ASPEN PLUS. This model was used to simulate the whole drying process for optimizing the process parameters.The existence form of water contained in the sludge and the process of sludge drying were analysed with the drying curve obtained by sludge drying experiments. The experiments also showed that the drying characteristics of sludge during the drying process was effected by the drying temperature, the surface area and the thickness of the sludge and the mixing ratio of dry sludge, etc. Some preferable process parameters were suggested, i.e. the temperature of 140 to 180℃, depth of 30mm and 30% mixing ratio of dry sludge..The mass and heat transfer, structure and transmission system of the integrated multi-effect plate dryer were studied. The heat exchange area, structure, material and machining of the drying disc were determined. The transmission and stirring systems were designed, which optimized the structure of the equipment and the process parameters.The automatic control system of the dryer was designed, which had PLC and electric control units. The valves, thermoscope and attemperator were used to make the multi-effect drying with the secondary steam successfully working.The model constructed in ASPEN PLUS was used to simulate the whole drying process and optimize the process parameters with the tools of Sensitivity Analysis and Design Optimization. Some process data were determined by 56kg/h steam flow, 13.51m2 the heat exchange area,1.2kW compressor power,which is significant to the dryer manufacture, component selection and process optimization.The whole sludge dryer system including hot steam,dry sludge, condensate , exhaust gas was experimentally investigated.The mass and the energy of the sludge were analysed,and the way to how to save energy was given. |
