Kinetic Study on Pyrolysis of Sewage Sludge

The sewage sludge is a complex heterogeneous mixture of organic and inorganic materials, and large amounts of sewage sludge are produced from the relevant industry, which can be exploited and utilized for energy. In this work, bio-oils from pyrolysis of sewage sludges obtained from relevant industry including refineries, power plants and pharmaceutical factories were analyzed by a Thermogravimetric Analysis(TGA) instrument and the corresponding Differential Thermal Analysis(DTA). The TGA curves were obtained at the heating rate of 15 degrees C/min and with temperature range from 32 degrees C to 1000 degrees C. The results indicated that the pyrolysis of sewage sludges included three stages: dehydration, volatilization of light fraction organics together with decomposition reaction, and decomposition of heavy nonpolar organic compounds. More importantly, between the temperature range of 175 degrees C and 725 degrees C, by using the Coats-Redfern equation, correlation coefficients of different reaction models describing the bio-oil from pyrolysis of sewage sludge were predicted, and the best-fit models for different stages of pyrolysis were found. The activation energies as well as frequency factors( A) from the best-fit models were calculated.