Sewage sludge and phytomass co-pyrolysis and the gasification of its chars: A kinetics and reaction mechanism study

Abstract

This paper presents the kinetics and mechanisms of pyrolysis and gasification processes of sewage sludge and phytomass blends as well as their application in gas conversion. Sewage sludge is a type of combustible waste substance that constitutes a renewable energy source. Mixing sewage sludge with another type of waste biomass can have a beneficial effect on the quality of the fuel produced and may improve the conversion efficiency. Pyrolysis and gasification processes are considered sustainable methods for the production of combustible gas. The two-stage gasification process combining co-pyrolysis and the gasification of “hot” char were studied using a thermogravimetric analyser and a fixed-bed reactor coupled with gas chromatography. The pyrolysis of sewage sludge and Salix viminalis as well as their mixture was performed below the temperature of 900 °C at low heating rates under a nitrogen atmosphere and in non-isothermal conditions. The char gasification experiments were carried out at temperatures of 700, 800 and 900 °C in an atmosphere of air. The effect of the percentage share of Salix viminalis in the tested blends on the pyrolysis process and on the reactivity of “hot” char in the gasification process were investigated. For the tested blends, the kinetic parameters of co-pyrolysis and gasification were determined.