Process Simulation And Multi-objective Optimization Of Biomethane Production System

Biomass waste via anaerobic digestion to biomethane can achieve energy saving,CO2 reduction and pollutant reduction simultaneously,hence has been accepted as a hot spot in the research fields of environment and renewable energy.At present,the research on biomethane technology mainly focus on the development and optimization of unit technology.However,multi-objective optimization for biomethane production system with respect to economic and environmental performance has not been reported.Thus,models of energy consumption,economic performance,green degree and biogas yield were established in this work for each processing section.Afterwards,the economic and environmental performance of biomethane production system were optimized and analyzed.Based on the optimization results,the influence of production scale on energy-environment-economy indicators was studied.The work provides scientific basis for the large application of biomethane technology and has important practical and theoretical significance.The main results of this thesis are as follows:(1)A biomethane network system including 9 kinds of feedstocks,3 kinds of heat supply technologies and 4 kinds of decarbonization technologies was designed in this work.Mathematical models of energy consumption,economic benefit,green degree and biogas yield,were established for important processing sections based on literature and experiment data.Based on process simulation results,empirical models of key parameters has been established for decarbonization technologies.It provides model bases for simulation and optimization of biomethane production system.(2)We established a multi-objective optimization model for biomethane production system with net present value(NPV)and green degree(GD)as objective functions and technology combinations and process parameters as decision variables.Non-dominated Sorting Genetic Algorithm ?(NSGA-?)was applied to solve the model,from which Pareto solutions were obtained.Afterwards,we analyzed the optimal technology combinations as well as the distribution of investment cost,energy consumption and green degree.The results showed that the biomethane production system after optimization has relative high economic and environmental feasibility.The most expensive equipment is anaerobic digester;the mostexpensive section is anaerobic digestion;the most energy consuming section is anaerobic digestion,followed by decarbonization and waste management.Processing sections of anaerobic digestion and waste management has positive green degree while other sections presents negative green degree values.(3)Based on the optimization results,we analyzed energy-environment-economy performance of biomethane production system under two digestion temperature and seven process scales.The results showed that the increase of biomethane production can improve the energy efficiency and specific green degree,and decrease the cost of methane production and digestion liquid processing.Energy efficiency increases with digestion temperature while production cost decreases.Compared with mesophilic digestion,the energy efficiency of thermophilic digestion increased by 7.4%,the methane production cost decreased 3%,the specific green degree decreased 10%.