Study On The Municipal Sewage Sludge Thermal Drying Characteristics And Energy Consumption

As the increasing of China's urban sewage treatment rate over the years, the number of city sewage treatment plant and sludge production are sharply increasing. Therefore sludge treatment and disposal has become an urgent problem. Difficulties in the sludge treatment lies in its high moisture content. Reducing the moisture content of sludge has become a key step for the sludge treatment and disposal. Thermal drying of sludge is a best way to reduce the moisture of sludge. At present, thermal drying of sludge are more applications in Europe and America. The applications are also increasing year by year in China. Thermal drying of sludge is currently not enough for research, especially in terms of the characteristics of the sludge itself reveals the characteristics of sludge thermal drying and the law of thermal drying energy research is very little.In this paper, the physical and chemical characteristics of sludge, the characteristics of sludge thermal drying and sludge thermal drying energy consumption were tested, with focus on physical and chemical properties, such as moisture content, organic matter content, liquid limit and plastic one, bound water content; and thermal drying of sludge characteristics on different drying conditions and integrated TG-DTA thermal analysis, thermal drying heat loss. By comprehensive analysing of the above study , this paper comes to the following conclusions:①Because influencing factors of sludge thermal drying are very complex, and because of the interaction of sludge pre-treatment, physical and chemical properties, thermal drying characteristics and heat drying energy consumption, comprehensive research and analysis of sludge thermal drying is a need.②Plasticity indexs of sludges from Beibei,Jiguanshi,Tangjiaqiao are less than 0.73 (WL-20), of a high plastic sticky or silty organic soils.And liquid limit more than 50%, plasticity index greater than 26, of higher liquid limit soil, It is not easy to dehydrate.this seriously restricted the follow-up of sludge processing.③Sludge drying temperature the higher, the faster rate of thermal drying, the shorter the time of thermal drying required, Test found that at 105℃, the constant drying period is the longest, about 20% of the drying time, and at 80℃, 130℃, the constant speed zone are shorter, about about 10% of the whole drying time. This phenomenon shows that at every drying temperature, there should be a relatively best sludge dispersion (size), and sludge samples of the dispersion constant sludge drying period is the longest at this temperature.At this point, the internal and external control conditions of sludge drying achieve a better balance.④The relevance of sludge organic matter content, water distribution and sewage sludge dewatering performance are obvious. The higher organic matter content, the greater bound water content,and the worse dehydration performance.⑤The study found that when the bound water content of sludge samples were 1.16 (g/g dry basis), 1.37 (g/g dry basis), 2.67 (g/g dry basis), the sludge drying heat consumption has, respectively, an increase of 8.4%, 10.7% and 13.3% than the theoretical heat consumption. Their correlation coefficient is 0.936, with a certain degree of positive correlation between them. Therefore, the measures to reduce the combined water content will help reduce sludge thermal drying energy consumption.