Pyrolysis characteristics and kinetics of sewage sludge by thermogravimetry Fourier transform infrared analysis

The characteristics and gas product properties of pyrolyzing sewage sludge were determined, aiming to utilize efficiently the waste for energy recovery. The pyrolysis of two predried sludge materials (S1 and S2) was conducted in a thermogravimetry analyzer (TGA). It was found that the pyrolysis mainly occurred at about 150 - 550 degrees C, with two and one reaction stages found respectively for S1 and S2. Using the global reaction kinetic model, the activation energy was calculated at similar to 30 kJ mol(-1) in the first reaction stage for all the selected heating rates, and the pre-exponential factors increased with the increasing heating rate. The kinetic parameters calculated explained well the pyrolysis characteristics observed. In the meantime, the gas products released under different pyrolysis conditions were analyzed online using Fourier transform infrared (FTIR) spectroscopy; the results showed that the gas composition was highly dependent on temperature, and the releasing of the gas species was consistent with the weight loss of sludge in pyrolysis. Thermodynamic simulation using Outokumpu HSC Chemistry version 4.1 was conducted to predict the thermodynamically predominant gas species at different temperatures. A further analysis by dividing the whole pyrolysis of sludge into 5 temperature regions revealed preliminarily the sludge pyrolysis mechanisms. This fundamental study provides a basic insight into the sludge pyrolysis, which would benefit the efficient utilization of sewage sludge as an energy source.