Process parameter optimization of urban biowaste carbonization

Abstract

About 75% of municipal solid waste (MSW) collected around Sri Lanka is organic biomass. It has created a huge potential in converting urban biowaste into value-added component like biochar, thus resolving the problems associated with MSW management. In this study, torrefaction is identified as the most viable technology available for the conversion of organic MSW into biochar and the study mainly focuses on developing a 3D computational fluid dynamics (CFD) model of a continuous packed-bed torrefaction reactor and then optimizing the process variables and the geometry. A mathematical model including heat, mass & energy transfers, and chemical reactions is firstly developed and then converted to a numerical model, which subsequently simulated using OpenFOAM. The torrefaction reactor is optimized for inlet gas temperature and residence time and then the geometry of the reactor is optimized for the optimum inlet gas temperature and residence time. The optimum values for inlet gas temperature, residence time and column aspect ratio are 573 K, 13000 s and 24/6 respectively. For the optimum conditions, biochar yield is 55.7% while ash content is 19.1%. Further In dry basis, 95.9% of biomass is decomposed and the total weight loss based on the initial wet biomass is 86.6%.