Modelling Self-Heating in Compost Piles: Application of Reaction Engineering Approach

Abstract

Spontaneous combustion in compost piles is the main cause of fires at compost facilities or landfill sites. Hence, the increase in temperature in compost piles, known as self-heating phenomenon, has to be considered thoroughly for safety aspect at the facilities. One of the most reliable methods for estimating the safety aspect is modelling the self-heating in compost piles. In this study, a new model is proposed to better represent self-heating phenomenon. The proposed model incorporates simultaneous heat and mass transfer coupled with biological and chemical heat generations. For better accuracy of the modelling, the evaporation term implementing the Reaction Engineering Approach (REA) is used here to yield a set of heat and mass conservation which consists of mass balance of water vapor, liquid water, oxygen, and heat balance. The set of partial differential equations is solved using finite element solver Comsol Multiphysics to generate the spatial profiles of concentration of oxygen, water vapor, water liquid, and heat balance inside the compost piles. Benchmarks against the experimental data indicate that the results of the modelling match well with the experimental data. Therefore the proposed model can be implemented to predict safe storage of compost piles under various configurations.