Combustion behavior and kinetic characteristics of a city sewage sludge

The pyrolysis and combustion characteristics of a city swage sludge were studied by analysing the TG, DTG and DSC curves from a thermogravimetry. The combustion and pyrolysis TG curves are similar before 250℃, suggesting that the loss rate of weight is controlled mainly by the decomposition of organic matter, and the action of combustion is less. The DTG curve of combustion presents a “W” shape peak, the first peak is in a good agreement with the pyrolysis DTG curve. The weight loss rate has a rapid acceleration after 410℃. Based on the Coats-Redfern integral method, some reaction models are tested to fit the combustion process, and the results show that the burning process with two DTG peaks has a complicated mechanism. It can be concluded that the volatile burning in the initial combustion stage is controlled by the chemical reaction rate, while with the rising of temperature the combustion rate of the residual volatile and fixed carbon is controlled gradually by the diffusion. According to the mechanism, a four-parallel reactions model is brought out to simulate the burning process, which better fits the experimental data.