Thermal Analysis And Experimental Research Of Solar Heated Straw Biogas Fermentation System

It is a key energy policy in China that developing biogas technology is to crack energy short problem in its rural areas, requiring to promote the comprehensive utilization of waste and renewable energy development and utilization technology in suitable areas. At present, our country common household with biogas digesters are mostly of natural fermentation and the fermentation temperature varies with the environment, so the efficiency of fermentation and gas production is not stable, especially in the winter, the gas production is very small or without gas production due to low temperature fermentation, which has become a bottleneck of restricting household biogas technology promotion. To solve this problem, the solar heated straw biogas fermentation system with phase change heat storage device is developed to utilize the abundant straw resources in this area effectively and achieve a high efficient and stable biogas production applied to rural areas in the middle and lower reaches of the Yangtze RiverThe main research work of this paper is as follows:Firstly, the principle and influence factors of two-phase anaerobic fermentation are introduced, and then the solar heated straw biogas fermentation system based on two-phase anaerobic fermentation device is put forward. Then this paper introduces the composition of the experimental platform, and builds the physical and mathematical models of phase change thermal storage water tank which is helped to describe the design basis of it.Secondly, thermal performances of heat collection, heat storage and heat supply subsystem are analyzed. This paper obtains the necessity of combining solar thermal collector with photovoltaic device and the winter's compensation heat change characteristics of phase change energy storage tank's paraffin layer through winter historical meteorological data of demonstration base of project located in Hexian. We also analyze the heat transfer coefficient variation of heating coils whose floating range is small, indicating that heat supply subsystem can make inlet and outlet water temperature maintain relatively stable and enter the state of stable heating quickly, but there is still space for further improvement of it.Thirdly, according to the experimental results of solar heated straw biogas fermentation system's continuous operation experiment in the winter period of demonstration base of project located in Hexian, the fermentation temperature of biogas production tank can be maintained at 32?35? which means maintain the state of mesophilic biogas fermentation. The average daily biogas production is 1.03m3,and the volume gas productivity is 0.64m3/(m3·d), average methane content of bilogas is 67%. Paraffin layer can maintain state of phase transition most of time, and water temperature in phase change heat storage water tank remains constant approximately which is not lower than 55? when this system runs stablely under the average daily ambient temperature is 4.7?, indicating that it achieves the effect of stable heat storage. The experimental results show that solar heated straw biogas fermentation system's heat utilization efficiency is 42.3% in winter.Finally, the net present value of this system is positive after 20 years through quantitative-analysis method according to the experimental results under the winter conditions and demonstration unit cost, indicating the investment is economical in the return period of 20 years. Meanwhile, this system can save 642kg of standard coal, and its emission reduction of CO2 and SO2 is 510kg and 8.6kg, respectively. So it is benefical to the air quality in the middle and lower reaches of the Yangtze River and straw waste resource utilization through developing and generalizing this kind of solar heated straw biogas fermentation system.