Study On The Co-pyrolysis Characteristics Of Sawdust And Excess Activated Sludge From Domestic Sewage Treatment Plant

Excess activated sludge is the residue in the process of the urban sewage treatment,which contains a large amount of organic matter.The rational use of excess activated sludge can effectively realize reduce,harmless,and utilize the sludge resource.Although,the traditional pyrolysis process can efficiently and cleanly convert sludge resource,there are some problems,such as low yield and low quality of pyrolysis syngas.The addition of sawdust can improve the thermochemical conversion process and promote the pyrolysis reaction.In this paper,the co-pyrolysis characteristics of sludge and sawdust were studied.The weight loss law,the optimal co-pyrolysis conditions and the co-pyrolysis synergistic effects of sludge and sawdust were emphatically analyzed.Firstly,thermogravimetric analysis was used to study the thermogravimetric characteristics of the co-pyrolysis of sludge and sawdust.Through the analysis of thermogravimetric results,it was found that with the heating rate increased,the initial temperature and the termination temperature of the pyrolysis reaction moved toward the high temperature,and the maximum weight loss rate increased significantly.The addition of sawdust changed the shape of weight loss peaks in the volatilization stage.As the amount of sawdust increased,the volatilization stage gradually changed from a form of two broad overlapping peaks to a form of a shoulder peak and a maximum pyrolysis peak.The initial temperature,the termination temperature of pyrolysis characteristic curve and the reaction interval all moved toward the high temperature.The maximum weight loss rate increased and the weight loss of the entire pyrolysis process increased remarkably.Secondly,the co-pyrolysis experiment of sludge and sawdust was carried out in a fixed bed pyrolysis furnace to determine the optimum co-pyrolysis conditions.The results of pyrolysis experiments showed that increasing the moisture content of sludge and the amount of sawdust could significantly increase the yield of pyrolysis syngas and solid products,while the yield of pyrolysis oil was significantly reduced.As the moisture content of the sludge increased,the contents of CO and H₂ in the pyrolysis syngas increased.As the amount of sawdust increased,the CH₄ and CO contents in the pyrolysis syngas increased significantly.Comprehensive analysis of pyrolysis syngas yield and calorific value,it was determine that the optimal pyrolysis process conditions,that was,the pyrolysis temperature of 800?,the sludge moisture content of 20wt%and the The corresponding calorific value and yield of pyrolysis syngas calorific value and yield were 14.07MJ/m³and 23.17wt%,respectively.Finally,the co-pyrolysis synergistic effect of sludge and sawdust was analyzed combined with the experimental results of co-pyrolysis of sludge and sawdust from the perspectives of weight loss during the volatilization stage,the yield of solid product,and the calorific value and the yield of pyrolysis syngas during the whole pyrolysis process.It was found that the co-pyrolysis synergistic effect of sludge and sawdust at lower pyrolysis temperature was stronger while the amount of sawdust added was less.The co-pyrolysis synergistic effect of sludge and sawdust at higher temperature was stronger while the amount of sawdust added was large.