Study On The Co-combustion Characteristics Of Coal And Sewage Sludge

With the increasing of handling capacity of urban sewage treatment, the situation of urban sewage sludge treatment and disposal became more and more urgent. Sewage sludge contains many pollutants. If there is no timely and effective treatment and disposal, people's life will be threatened due to the pollution from air, groundwater and food chain. So the treatment and disposal of sewage sludge should be paid attention as high as sewage treatment. Currently, incineration is the way can thoroughly achieve the objective of shrinkage, stability and harmlessnization of urban sludge treatment. Due to the lower heat value of dry sludge, if it is combusted directly as fuel, there would be bad combustion stability and more power consumption. Mixed the sewage sludge and coal as fuel in coal fired power plants can not only solve the problem of sewage sludge treatment and disposal, it also can make sludge get resource-oriented utilization.This research is based on the renovation project of co-combustion of coal and sewage sludge in a 420 t/h tangentially fired boiler. Firstly, the expermental investigation was carried out to analyse the element composition of samples mixed by different ratios of coal and sewage sludge with different moisture content ratio. Then, through the thermogravimetric experiment, the combustion and slagging characteristics of the samples were studied. Finally, exergy balance analysis was used to study the exergy efficiency and exergy losses of the samples, and it was also compared with the thermal balance calculation to verify the experimental results.The experimental results revealed that the burnout temperature of the mixture is a little bit lower than single coal, but burnout peroid was shorter than either of single coal or single sludge. If the ration of mixture was not great than 1:4, the ignition performance was almost the same as that of coal; the combustion and slagging characteristics was similar to coal. That would improve the ignition condition,enhance combustion, reduce internal exergy losses and increase combustion exergy efficiency under the situation of good slagging and burnout performance and the mixed ratio of single is not too large. Theoretical analysis and experimental investigation showed that the combustion characteristics of coal mixed with proper ratio of sludge is better than that of single coal or single sludge in some ways. The mixed ratio of 1:4 is recommended as reference.