A heat-transfer analysis of fixed-dome biogas plants

Abstract A steady-state heat transfer analysis has been carried out for fixed-dome biogas plants (Chinese type). The analysis takes into account heat losses from the surface of the slurry inside the digester as well as the heat losses to the surrounding earth. Results indicate that methods such as hot-charging or greenhouse heating can increase the digester temperature by a maximum of 5–7°C, and that burning part of the gas to heat the digester does not result in a net energy-gain. The heating requirements are proportionally much lower for higher-size plants. The heating requirements are reduced by insulating the dome, but no further significant reduction is achieved by adding insulation to the side walls.