Design and experimental validation of a thermal model for anerobic digester for consistent biogas production

Anaerobic digestion is highly sensitive to temperature fluctuations, leading to seasonal variations in biogas output and posing challenges to stable electricity generation. To ensure consistent performance, maintaining a constant digester temperature through heating is essential. This study presents a validated thermal model to estimate the energy required for temperature regulation in biogas digesters under varying ambient conditions. The model calculates heat losses and gains, including feedstock preheating and biogas enthalpy, and is validated using an underground digester with electric heating. Through simulation and experimental validation, the study first establishes the importance of temperature control for biogas stability. A biogas-based energy system is then analyzed using Typical Meteorological Year (TMY) data to assess the annual performance of a heated digester. Results show that a 3100 m3 heated digester can increase annual energy output by 29 %, reduce required digester volume by 24 %, and deliver electricity at a competitive levelized cost of $ 0.045/kWh. However, heating becomes economically unviable for systems below 21 m3 or in climates exceeding 36.4 °C. The study offers a practical framework for designing constant-temperature biogas digesters, providing key design insights for optimizing performance and ensuring reliable, year-round biogas-based power generation.