Experimental Study On Integrated Incineration Technique For Sewage Sludge In Circulating Fluidized Bed

Among numerous methods of sludge disposal, incineration is considered as the most thorough way to realize the reduction, stabilization and harmlessness of sewage sludge. Sewage sludge incineration after being dried has been given the priority in China. For the most techniques of sewage sludge, the systems of drying and incineration are separated, which means the disposal system is complex. In this thesis, experimental research on the integrated incineration technique for sewage sludge in circulating fluidized bed was conducted.The experiments were carried out in exploratory test system and a large scale cold experimental system in order to investigate the key parameter of the technique and regulating characteristics of pneumatic distribution valve(PDV) which is the core part of the system. The main work processes, including sewage sludge drying characteristics in a bubbling fluidized bed and the escape rate of fine powders were carried out in the experimental system for fluidized bed sewage sludge drying. Based on100t/d integrated incineration system for sewage sludge in circulating fluidized bed, the performance test was carried out and economic analysis was made by theory and practice. Theoretical analysis and calculation were conducted about a new integrated incineration technique for sewage sludge in circulating fluidized bed with condensing drying.Exploratory test system and large scale cold experimental system were designed and established; the technique process was verified, the flow characteristics and the control characteristic of PDV were obtained as well. The results show that the key factor which influences the system's safe and steady operation is the coupling performance of pressure in combustion circuit and drying circuit at pressure balance pipe. Main bed fluidization velocity has influences on flow rate of the system and regulating rate of PDV' both sides. Pressure distortion appears at pressure balance pipe when the flow rate of system or pressure fluctuation at dense phase region of main bed is excessive. Compared with the fluidization number at III region of PDV, the regulating scope of fluidization number at IV region of PDV is wider and regulating effect is better. The maximum mass flux of dryer side and the pressure range which cause the fluctuation of PDV's regulation on the top of the dryer are obtained. Experimental results of sewage sludge drying characteristics in a bubbling fluidized bed with heat conducting oil reveal that the more the sludge pellets in the mixture of river sands and sludge, the smaller the average heat transfer coefficient between the heat conducting oil pipes and bed will be. The average heat transfer coefficient reaches to its maximum187W/(m2·K) with the increase in fluidization velocity. The particle size of the dried product decreases when the fluidization velocity and residence time of materials increase. The escape rate of fine powders decreases when the dried sludge in the mixture increases, and at given condition, first order exponential growth model can fulfill well the relations between them.Performance test results on100t/d integrated incineration system for sewage sludge in circulating fluidized bed show that temperature distribution is even and the combustion efficiency is over98%in the incinerator. In the compound dryer, temperature distribution is even with the sludge being dried well, and the process of fluidized drying is safe. The test results of flue gas emission indicate that smoke concentration and the concentration of CO, Hg, Cd, Pb, NOx, SO2and dioxin-like pollutants is lower than the emission standard limit. The leaching toxicity of heavy metal in solid materials is also tested and proven that all the leaching toxicity is lower than the identification standards for hazardous wastes, and the fly ashes could be utilized or disposed as general waste.On the basis of operation data, economic analysis of the integrated incineration technique for sewage sludge in circulating fluidized bed is made. It is found that the technique is effective for energy-saving and consumption-reducing. Compared with the typical system that separates drying and incineration, the integrated technique has its advantages with distinctly reliable process and economic operation.A new integrated incineration technique for sewage sludge in circulating fluidized bed with condensing drying is proposed, and theoretical analysis and calculation are conducted as well.