Study On Low-temperature Pyrolysis And Pyrolysis Charaeteristics Of Municipal Sewage Sludge

Sludge are main by-products from municipal sewage treatment plant,and the yield of sludge are ever-increasing due to the rapid urbanization and higher environmental protection criteria implemented in recent decades. How to dispose of tremendous sewage sludge to eliminate the potential hazardous effect on environment has become an important issue of environmental protection. Pyrolysis is receiving more attention as an economical efficiency and environmental friendly route to waste treatment. Pyrolysis of sewage sludge is a promis- ing thermal conversion technology aiming at sludge reduction,stabilization, detoxification and recycle. This paper study on pyrolysis characteristics and products character of sewage sludge from Xi'an business water limited corporation.The pyrolysis characteristics of sludge was studied by thermogravimetric analyzer, effects of sample partical size and heating rate on the pyrolysis characteristics of sludge were investigated, and the kinetic parameters of pyrolysis reaction were calculated respectively by Coats-Redfern integration method. The results showed that the sludge pyrolysis TG and DTG curves have the same variation trend under different experimental conditions. The laws of the coke combustion, water and volatile volatilize were same basically. In each stage, The starting temperature, final temperature and temperature of maximum reaction rate increased in different degree with the increase of particle size and heating rate, while the main reaction region decreased. Heating rate had little influence on activation energy of sludge pyrolysis reaction. The reaction rate is proportional to heating rate. The sludge particle size had little effect on the reaction rate. When the heating rate was 10℃/ min, the reaction stage number of optimum kinetic fitting equation for three kinds of particle size sludge were 2.5. When the heating rate was 20℃/ min or 30℃/ min , the reaction stage number of optimum kinetic fitting equation for three kinds of particle size sludge were 1.Low temperature pyrolysis experiments of sludge by using two-stage tubular and Fischer-Schrader assay respectively. The results showed that the yields of tar oil was largest by using two-stage tubular reactor. The optimum process conditions of sludge pyrolysis with two-stage tubular reactor were as follows: the heating rate was 7℃/min, the sludge particle size was 120 mesh, the final temperature was 550℃, and the reaction time was 20 min. The yield of semi-coke, liquid and gas were 47%, 41% and 11% respectively, where the yield of tar oil was 33%.Three kinds of pyrolytic products have been detected. The results indicated that the main components of tar oil were single-ring benzene compounds, nitrogen compounds, alkane, acid esters and the experimental condition had great influence on the content of main components of the tar oil. The pyrolysis gas can not burn when the final pyrolysis temperature was lower than 300℃; The heat value of semi-coke was the highest at the pyrolysis temperature of 350℃. During the low-temperature pyrolysis process of sludge, the heavy metal in the sludge was almost fixed in the semi-coke.