Heating system of biogas digester by ground-source heat pump

Biogas is one of the renewable energies which is suitable for rural area in China. For improving the lower biogas production in winter, with several heating method analyzed, a heating system of biogas digester was developed, in which the heat energy was supplied by hot water from ground-source heat pump. An experiment?was carried out at a medium scale pig farm. The research results showed that this system could guarantee the fermentation temperature at (32±2)℃, and the biogas productivity at 0.6 m3/(m3·d), sometimes even at 1.1 m3/(m3·d). During the experiment, the average coefficient of performance (COP) of the ground-source heat pump unit was about 3.6, the average COP of the overall heating system about 2.7, and the primary energy ratio could reach 0.84. Compared with electrothermal film heating system, it could save 63% of electricity and the present value of investment benefit was increased to 40 188.5 yuan. And compared with hot-water boiler which burns fossil fuels, a better environment could be guaranteed without pollution. Therefore this system was feasible in technology and economy, simultaneously in favor of environmental protection and energy saving. In all, this system has the potential to develop.