Investigation of Thermal Performance of a Solar Assisted Anaerobic Digestion System Integrated With Solar Thermal Energy Storage Packed With Phase Change Material

Abstract

Anaerobic digestion is a promising technology for the treatment of organic wastes, since it produces renewable energy (biogas) and valuable digestate as fertilizer. Temperature is an important factor that can affect the performance of anaerobic digestion systems. The amount of gas produced increases with digester temperature. To keep the anaerobic digestion process at higher temperature than ambient air, external source of heating is required. Solar energy can be used as a heating source, but it is intermittent. Solar energy storage system is a key issue to be addressed to allow the intermittence of solar energy. The objective of this study was to investigate the thermal performance of a solar assisted anaerobic digestion system, which is composed of anaerobic digester, flat plate collector and latent heat thermal energy storage. The digester was used to ferment cow dung and designed to produce 100 peoples average daily energy consumption for their cooking application. Water is used as a heat transfer fluid and spherical capsules of encapsulated paraffin n-Triacontane are used as phase change material. Transient one-dimensional heat transfer models are developed, and solve iteratively using finite difference scheme. Results from a numerical simulation performed with meteorological data from Adama shows that 3 m3 of phase change material and 31 units of flat plate collectors can satisfy the heat required for the designed digester.