Using a hybrid heating system to increase the biogas production of household digesters in cold areas of China: An experimental study

In rural areas of China, household-scaled biogas digester plays an important role in improving rural production and living conditions, impelling energy conservation and emission reduction, and thus protecting the environment. To date, household digester has become the largest biomass energy industry in China. However, when operating in the cold winter, low slurry temperature of the digester often results in a relatively low efficiency or even a suspension in the fermentation process. This paper proposes a hybrid heating system which integrates the advantages of solar energy heating system and biogas boiler heating system, as a solution. An experimental setup including three digesters was built to investigate the performance of the heating system. Continuous tests on the operational status of the three digesters were conducted, and the slurry temperatures and the biogas production rates were compared. Results show that, employing the hybrid heating system, the slurry temperatures of the two heated digesters could be maintained around 19.82 °C and 23.50 °C, and the average production rate could be increased to 0.389 m³/(m^-3 d) and 0.472 m³/(m^-3 d). Additionally, an economic and sensitivity analysis shows that yet the increased the initial and maintenance cost notwithstanding, the hybrid system benefits greatly from more net production of biogas during lifetime employment.