Study on municipal sludge physical-chemical properties and pyrolysis characteristics

The pyrolysis process of sludge was studied under isothermal and non-isothermal heating conditions. The pyrolysis characteristics and physical and chemical characteristics of the sludge were analyzed using TGA, XRD, FTIR and SEM. The reaction mechanism was revealed by using the distributed activation energy model and the apparent dynamic parameters. The results show that under non-isothermal condition, the differential thermogravimetric curves move to the high temperature side, with the increase of heating rate, the maximum mass loss rate increases, and the peak temperature shifts. At the same time, the thermal inertia occurs, which is conducive to the precipitation of volatiles. The distributed activation energy model is suitable for kinetic analysis in the range of conversion α≤0.8. The activation energy increases first and then decreases with the increase of conversion α; SiO2 and SiS2 exist in the mineral composition of sludge, while AlPO4 and α-HgS are detected. Under isothermal conditions, with the increase of pyrolysis time and temperature, the surface functional groups decrease, and the release of the volatiles promotes the development of pore structure. The collapse of the carbon frame and the melting of the channel during pyrolysis show that the disorder degree and vitrification of the micro-morphology increase. © 2021, Central South University Press. All right reserved.