Heating mode of biogas plant in alpine region based on underground water source heat pump

Temperature is one of the key factors affecting anaerobic fermentation。In the alpine region of China，due to the cold weather in winter, it is necessary to strictly control the temperature of the anaerobic fermentation, taking appropriate heating and insulation measures to ensure that biogas plants are perennial and stable and that they maintain a constant and efficient rate of gas production. However, it requires energy consumption and associated environmental pollution to heat the anaerobic fermentation liquid. An energy saving equipment with better heating mode was needed to solve that problem in the alpine region. Due to the energy-saving and environmental-protection characteristics of heat pump technology, this research used a groundwater source heat pump to heat the anaerobic fermentation system. It used the heat source method, the anaerobic fermentation liquid temperature within the reactor, ambient temperature, water temperature difference and flow between supply and return water heating pipelines, as well as measurements of various electricity consumption parameters, to test the running performance and the effect of groundwater source heat pump system. The experimental site was in Jixi City, Heilongjiang Province, and the biogas plant handled 20 t a day of manure. The test from January 1, 2010 to January 1, 2012 showed that fermentation liquid temperature in the reactor can be maintained between 33 ~ 35℃, even in the coldest weather. It validated that a groundwater source heat pump system cloud maintained the stable operation of an anaerobic fermentation system. The average energy efficiency ratio (EER) of the heat pump unit was 4.39, its primary energy ratio (PER) was 1.27, and the average energy efficiency of the heating system was 2.71 by calculating the heat pump unit energy consumption, almost doubled compared to the direct coal-fired boiler heating mode. Meanwhile, through the real-time tracking and monitoring of the heating system from September 29, 2010 to February 25, 2011, the actual energy consumption of the system was 4.79 × 108 kJ, primary energy 44%. Total savings in standard coal consumption was 10.8 t, and carbon dioxide emissions were reduced 25.9 t compared with the direct heating method using coal-fired boilers. The results indicated that the heating system with groundwater source heat pump was feasible as a heating mode for the biogas plants, and it had many advantages, such as high effectiveness and energy savings, stable working ability, and reduced CO2 emissions.