Numerical Simulation Of Solar Assisted Biogas Production And Comprehensive Utilization System

The energy and environment are increasingly severe in the moment, so biomass energy and solar energy utilization with the high efficient and low cost are very important for changing the structure of energy constitute, improving living environment and promoting the economic development in the rural areas. In addition, the biogas thermoelectric system which can provide gas, electricity and heating to user and recycle the waste heat in the biogas plant is a green eco-energy pattern with energy efficiency and economic benefits increased.The cattle manure which has higher volatile solids is one of the rural common solid wastes. Anaerobic fermentation experiments use the cattle manure as a raw material. The effect of different temperature(room temperature, 35 ℃ and 55 ℃) and different concentration inoculums(10%, 30% and 50%) on the daily bio-gas production, total bio-gas production, pH of the feed solution and methane content were studied. The results showed that the thermophilic fermentation had a shorter acidification period and more gas production, but the methane content was only 52.52% and the methane content of the mesophilic fermentation was 57.82%. Besides, the inoculums concentration of 50% was more accessible to enter the methanogen stage, and the daily bio-gas production was more at the beginning, but the total bio-gas production was less than the 30% inoculums concentration. What’s more, the methane content was only 52.63%. In contrast, the 30%inoculums concentration was more suitable for manure fermentation.Based on referring to the studies of the solar heated biogas fermentation system and biogas utilization system, a system combined solar energy with biogas boiler aided biogas production and utilization is established. And the dynamic mathematical model of the system was built by lumped parameters method depending on a principle of the balance of the energy and mass. The modularized simulation of the system was made with the Matlab/Simulink,building mathematical equations of the biogas production rate and the heat loss of the bioreactor with the insulation thickness increasing to confirm the suitable hydraulic time HRT and the rigid polyurethane insulation thickness. Effects of the ambient temperature, the solar collector area, the continuous cloudy, the sequence feed on performances of the system(the biogas production mainly) were analyzed. Meanwhile,the operating performance of this system in the heating season, summer, spring and autumn without heating and January were compared. The simulation results indicated that the better rigid polyurethane insulation thickness was 100 mm, and the lower temperature,the less collector area, the continuous cloudy increasing and the sequence fee, the biogas production of the system and effective volume of the bioreactor must be increased.What’s more, the annual average collection efficiency of the collector is about 0.522, and the annual biogas consumption, the annual generating capacity, the annual heating and the annual biogas consumed by the users were 8594.19 kg, 4934 kWh, 15067.1kWh and439.2kg, respectively. The total energy efficiency was 51.5%, and the payback period is approximately8 years, decreasing2876.4m3 CO2 releasing.