Thermodynamic Performance Analysis And Optimization Design Of Solar And Biogas Hybrid Heating System In Livestock Breeding Rural Areas Of Northwest China

At present,there are still problems with high operating costs and high carbon emissions in winter clean heating methods in northern China.The vast rural areas are rich in solar energy resources and have a natural advantage in utilizing solar heating.Solar building heating has good energy-saving and environmental protection benefits.However,the inherent fluctuation and discontinuity of solar energy cause poor reliability of solar heating alone,and other energy sources need to be selected to supplement heating.Rural residents generate a large amount of biomass resources during the agricultural production process.The use of anaerobic fermentation technology can convert agricultural biomass waste into clean and renewable biomass fuel biogas,and the use of biogas for supplementary heating can compensate for the heating instability of individual solar systems.The increasingly mature technology of solar energy and biogas fermentation has made it possible to promote the application of solar energy and biogas,two renewable energy sources,for combined heating in rural areas.The combined heating system will maximize the utilization of renewable energy,help improve the environment,and solve the energy shortage problem in rural areas.Based on the present situation of resources and the characteristics of technology application in farming villages and towns in northwest China,this study proposes a solar and biogas hybrid heating system.Based on the first and second laws of thermodynamics,the mathematical model of the main equipment in the combined heating system and the thermodynamic analysis and evaluation model of the system are established by analyzing the thermodynamic process of the system.Based on MATLAB / Simulink simulation platform,the program of thermodynamic dynamic simulation model of solar and biogas hybrid heating system is developed.The thermal performance of the combined heating system is analyzed and evaluated by means of numerical simulation,including system energy and exergy flow process analysis,system thermal performance evaluation,system dynamic operation performance analysis and thermal performance comparison analysis of the system under different equipment capacities.Secondly,by analyzing the key design parameters of system capacity matching,the capacity matching optimization model of solar and biogas hybrid heating system is established with the optimization goal of heating cost.The genetic algorithm is used to optimize the joint system,and the optimization results are analyzed by single factor test and optimization results.In addition,five typical cities in Northwest China are selected for a large number of optimization calculations,and the optimization results of the capacity configuration of the solar and biogas hybrid heating system are obtained,and the heating guarantee rate of the system under the optimization results are analyzed.Finally,based on a large number of optimization calculation results,a simplified design method for capacity matching of solar and biogas hybrid heating systems in different regions is summarized.The main findings are as follows:(1)The energy and exergy efficiency analysis results of solar and biogas hybrid heating system show that the system has high energy efficiency but low exergy efficiency.The analysis of the energy and exergy flow process of the system shows that the solar collector,biogas fermenter and biogas boiler are the components with the lowest exergy efficiency in the system,and the key to improving the exergy efficiency is the cascade utilization of high-grade energy.The dynamic operation performance analysis of the system shows that the heating reliability of the hybrid system can be significantly improved by adding energy storage devices and using biogas combined with solar energy for heating.(2)Compared to the independent solar or biogas system,the solar and biogas hybrid heating system has greater potential to improve the renewable energy guarantee rate as the capacity of the equipment system increases.In terms of life cycle cost and payback period,the solar and biogas hybrid system is more advantageous than a single solar or biogas heating system in scenarios with high renewable energy guarantee rates.(3)The optimization results of the solar and biogas hybrid heating system show that for the three regions of Jiuquan,Xining and Yinchuan with good solar energy resources,the guaranteed renewable energy rate reaches more than 80 % under the condition of good biomass resources,and the application conditions of the combined heating system are better.For Xi’an and Urumqi regions with general solar energy resources,the economic advantages of developing solar and biogas hybrid heating systems under better biomass resources are not obvious.(4)Based on the engineering problems and design application requirements of solar and biogas hybrid heat source heating system,based on some traditional solar and biogas system design methods,based on a large number of optimization calculations,and according to the characteristics of engineering design,the simplified design and calculation process of solar and biogas hybrid heating system is summarized,and a complete set of simplified design methods for solar and biogas hybrid heating system is proposed.This research proposes a solar and biogas hybrid centralized heating system applied in villages and towns and corresponding thermodynamic analysis and optimization design methods,which can effectively improve the comprehensive utilization rate of renewable energy and thermal performance of the heating system.The research results will provide a theoretical basis for the design and operation of a solar and biogas hybrid heating system.