Research On The New Process Of Dewatering And Incineration Of Municipal Sludge

Municipal sludge is the product of municipal sewage treatment, and its production increased year by year, and it has been a serious problem of environment, so how to dispose it safely and economically is the urgent thing. The process which we study contains thermal hydrolysis, drying, incineration and classification of multi-effect evaporation. We take the mechanical dewatering sludge of Dalian sewage plant as the research object. The content of thermal hydrolysis contains the effect of the temperature and the reaction time on the properties of sludge dewatering. It is concluded that the higher thermal hydrolysis temperature, sludge moisture content after mechanical filter is lower, and the sludge’s dewatering effect to improve above 190℃ is not very obvious, and the energy consumption is increased, so the best thermal hydrolysis temperature is around 190 ℃, and the sludge moisture content after the filter falls and then rises with the reaction time going on, and the moisture content rised after 60 minutes, so the best reaction time is around 60 minutes.Then research on fluidization character of the sludge after thermal hydrolysis and filtration. And analysis of the effects of fluidization medium velocity, fluidization medium temperature and sludge particle diameter on drying velocity. We find the least velocity of fluidization is 1.0031m/s, and the higher the fluidization medium temperature and the smaller the sludge particle size, the larger the drying velocity, and the velocity of the medium does not effect the drying velocity effectively.As to the treatment of the filtered fluid, we put forward the new idea of multi-effect evaporation, and verify its feasibility, and simulate multi-effect evaporation by AspenPlus. According to the practical situation of industry, we stipulate the total evaporation is 90%, and the temperature difference is 10 ℃, and we find that the five effect evaporation is advisable, and we get the amount of every evaporation capacity and and experimental parameters, and then we conduct the multi-effect evaporation experiment according to the results of simulation, then we mesure the chemical oxygen demand (COD) value of the distillation from every effect by the potassium dichromate method, and get the rule of COD value. It is found that the COD values, respectively, are around 4500,500,400,500 and 2500 mg/L, and the value rises first and then reduces. The substrate’s COD value is about 410000 mg/L, so it can be treated by grading. We can mix the distillates from one effect, five effect and the substrate, and mix distillates from the second effect, three effect and four effect are mixed, and the cost of one ton filtered fluid is 0.73 yuan, and it has a good economy.Finally we construct a new process which is based on thermal hydrolysis, drying and incineration and multi-effect evaporation, and we have realized the energy recycle, and we study its economy. Through the calculation of mass balance and heat balance, we find that the process can keep the energy balance oretically, and the treatment cost of one ton sludge is less heavily than that of traditional process, so it has a good economy.