Research On Optimization Of Integrated Energy System Coupling And Compressing CO₂ Energy Storage

As problems such as energy depletion and greenhouse effect caused by traditional fossil fuels have become increasingly intensified,countries around the world are actively exploring new ways of using energy.Among them,the integrated energy system is an important way to achieve carbon neutrality and has broad development prospects.However,due to the unstable power generation,large output fluctuations,and unsustainable supply of new energy sources such as wind power and photovoltaics,a large number of integrated energy systems still use natural gas as the main energy source.However,the price of natural gas is relatively high,and combustion will produce a large amount of carbon dioxide.How to make it operate economically and environmentally has become a key research content.With the increasing development of carbon capture technology and compressed gas energy storage technology in recent years,compressed carbon dioxide energy storage systems have gradually become a key solution to the above problems.The compressed carbon dioxide energy storage technology can not only recycle the carbon dioxide generated by natural gas combustion,but also realize the functions of peak shaving,valley filling,fluctuation suppression,and demand response in the process of system load supply.It is one of the most promising energy storage technologies.This paper focuses on the optimization of the integrated energy system operation and the compressed carbon dioxide energy storage system and has carried out the following work:(1)Using the Energy Hub method,a comprehensive energy system model including a compressed carbon dioxide energy storage subsystem was established to describe the coupling relationship between equipment and energy in the system.And based on the different working principles,a detailed mathematical model is established for the main components of the system to describe the energy conversion process.(2)Combining the integrated energy system model and the non-dominated sorting genetic algorithm,the integrated energy system operation optimization model is established.Taking typical daily energy purchase costs and carbon dioxide emissions as the objective function,the power range of the equipment is the upper and lower limits of output,and the balance of load supply and demand is the energy balance constraint.After20,000 iterations,a Pareto solution set(Pareto)containing 57 schemes is obtained.According to the Euclidean distance rule,the optimal value is selected.The final result is a daily energy purchase cost of 5,156.40 yuan and a daily carbon dioxide emission of4,097.74 kg.And extract the typical daily equipment hourly scheduling strategy corresponding to the optimal target value as a typical daily equipment scheduling plan.The results show that the overall performance of the electric refrigerator is better,as the main equipment for supplying cooling load;the Rankine cycle belongs to the waste heat recovery work process,and its performance is better than that of the electric boiler,which always maintains the minimum load state.(3)In order to recover the carbon dioxide produced by natural gas combustion,thermodynamic models of advanced adiabatic compressed carbon dioxide energy storage system(AA-CCS)and pre-expansion compressed carbon dioxide energy storage system(PH-CCS)were established based on the difference of reheating methods.The efficiencies under AA-CCS and PH-CCS design conditions are 0.32 and 0.47,respectively.And with the system cycle efficiency as the goal,the influence of the compressor and expander related thermodynamic state parameters on the system performance is studied.The results show that the compressor inlet pressure and expander inlet pressure are the key parameters that affect the cycle efficiency of the system,which lays the foundation for the subsequent optimization work.(4)Based on the results of the sensitivity analysis,the compressor inlet pressure,the first-stage compressor pressure ratio,and the second-stage compressor pressure ratio are taken as decision variables,and the system cycle efficiency is taken as the optimization target,and the thermal performance of PH-CCS with higher efficiency is carried out.optimization.The optimization results show that the optimal value of the compressor inlet pressure is 7.049 MPa,the pressure ratio of the two-stage compressor is both 2,and the corresponding optimal efficiency is 0.55.And the main components exergy loss analysis of PH-CCS optimal working conditions.The results show that the components with the largest exergy loss are the first-stage reheater and the second-stage expander,accounting for 39.42% and 30.15%,respectively.Among them,the main reason for the large loss of the primary reheater exergy is the large temperature difference between the cold and hot streams of the heat exchanger,which causes a large energy loss.The main reason for the large exergy damage of the secondary expander exergy is that the exhaust gas at the outlet still has a high temperature of 292°C,and a large amount of thermodynamic energy is wasted,which causes large exergy damage of the secondary expander exergy.