Mechanism And System Integration Based On Thermochemical Utilization Of Biogas And Solar Energy

With the long-term and large-scale utilization of fossil energy,the energy shortage,environmental pollution and climate change have become major problems that people urgently need to solve.The gradual replacement of fossil energy by renewable energy is one of the important directions for the future transformation of the international energy structure.The huge amount of solar energy and biomass resources and the wide distribution of characteristics have attracted widespread attention and research.At present,solar thermal utilization is the most common solar energy utilization technology.After years of development,it still faces problems such as low efficiency,high cost,difficulty in energy storage and unstable energy supply,which has seriously restricted its development.Anaerobic digestion is an effective way to clean and efficiently treat organic waste such as kitchen waste.The main advantage is that biogas production is stable.The main problems are small scale and low efficiency of biogas utilization.Through the deep complementary use of solar energy and biogas,it has the prospect of simultaneously improving the utilization level of biogas and promoting the development of solar energy utilization technology.However,the existing biogas and solar energy complementary use are mostly limited to the thermal complementary mode to compensate for the time instability of solar energy,and less research is carried out from the perspective of improving energy utilization efficiency.Based on the National Natural Science Foundation of China and the National Key Research and Development Program,this paper explores the thermodynamic theory of biogas and solar thermal chemical complementary utilization,and proposes a distributed energy system based on the new method,and explores the energy conversion law.The experimental platform of the key thermochemical reaction was developed,and the energy conversion mechanism was experimentally verified.The main contents and conclusions of this paper are as follows:(1)Taking the complementary advantages of biogas and solar energy as a breakthrough,the thermochemical conversion mechanism of biogas and solar energy is revealed.The physical models of biogas steam reforming and solar heat collection were established.Based on the energy concept,the energy conversion mechanism were studied.The analytical expression of comprehensive lifting coefficients was deduced from both biogas and solar utilization aspects.The further studies show that the low steam-carbon molar ratio combined with the appropriate reaction temperature contributes to the improvement of the comprehensive lifting coefficients.The complementary method was extended to the system level,and to show the effects of thermochemical reaction on cold,heat and power supply.Combined with the reaction carbon deposition analysis,the optimum performance intervals were theoretically given based on the maximum benefit of the system.(2)The experimental platform of biogas steam reforming process was developed,and the reaction characteristics were studied.The effects of reaction temperature and steam-to-carbon molar ratio on biogas conversion and composition of products were revealed.The energy conversion mechanism of the complementary method based on the experimental reaction process was discussed,and the theoretical energy conversion mechanism was validated.On this basis,the total performance improvement and the cold,heat and electric power supply based on partial experiment of the key reaction process were studied,and the average relative error between the experimental and simulated values was less than 8%.The above studies validate the feasibility of biogas and solar thermochemical complementary methods,and provide a complete theoretical basis f'or subsequent system integration.(3)Based on the proposed method by synthetic use of biogas and solar energy,a distributed energy system based on the new method is proposed.Compared with the current advanced biogas-driven trigeneration and dish solar Stirling power generation system,the studies indicates the performance advantages of the new system from the first and second law of thermodynamics.Furthermore,the influence of thennochemical unit on the perf'ormance of the new system was analyzed,and the optimal reaction parameters of the new system were given.The conclusions from the mechanism analysis were verified from the side:the low water-carbon ratio combined with suitable reaction temperature contributes to the improvement of comprehensive system income.Considering the energy consumption of the biogas production process,the power,cooling capacity and heat output of the new system were investigated throughout the year,and its thermal performance,economic performance and environmental performance were analyzed and compared.The researches indicated that the new system has a greater advantage than the comprehensive performance of the reference system.Further analysis of the impact of biogas project scale on the performance of new systems indicated that the development of large-scale biogas projects in China in the future will help to further improve the comprehensive performance of the new system.(4)The characteristics of various energy needs of a sewage treatment plant were first studied.Based on supply and demand matching,the multi-objective and multi-parameter optimization for the system was conducted by genetic algorithm.Through optimization,the optimal system installed capacity and the key design parameters(hydraulic residence time)of the biogas tank based on the optimal integrated performance are obtained,and the effects of the two f-actors on the integrated performance of the system was explored.Based on the optimal performance,The purchased electricity and natural gas were analyzed and compared monthly,indicating that the new system only has a silighter advantages on the aspects of thermal performance and environmental performance.But in terms of economic performance,the new system has an absolute advantage.Finally,the potential to further improve the performance was revealed by studying the waste heat instribution over the whole year.By recovering the waste heat,the integrated performance can be improved by 6.2%.