Thermodynamic Characteristtics And Economics Of Carbon Dioxide Transcritical Heat Pump Energy Storage System

With the continuous development of global economy and science and technology,the power generation industry is facing great pressure of energy consumption.The application of energy storage technology can increase the proportion of renewable energy in the power generation process,reduce the consumption of fossil energy,and contribute to the completion of the dual-carbon goal.In the aspect of energy storage,the heat pump energy storage system has the advantages of being free from regional restrictions and high flexibility of scale.Among them,CO₂transcritical heat pump energy storage system（CT-PTES）is a promising technology,but related research is still very limited.In order to comprehensively study and optimize the CT-PTES system,this study mainly explores its thermal economic performance in depth and draws the following conclusions:Firstly,thermodynamic and economic model of CO₂ transcritical heat pump energy storage system（CT-PTES）is established,and the single/multi-objective optimization is carried out by genetic algorithm.The results show that the round-trip efficiency of CO₂ transcritical single/dual stage heat pump energy storage system（CTO/T-PTES）can reach 32.65%and 33.69%respectively after single objective optimization.After multi-objective optimization,average energy storage cost（LCOS）of CTO/T-PTES can reach 0.3862$/（k W·h）and 0.3845$/（k W·h）,respectively,and the corresponding round-trip efficiency is 26.93%and 27.30%,respectively.On this basis,when the power consumption of the compressor is 10MW,the LCOS of CTO/T-PTES are 0.2002$/（k W·h）and 0.2022$/（k W·h）,respectively.Secondly,based on the optimization results of CT-PTES,this paper proposes a CO₂transcritical heat pump energy storage coupled heating system（CTO-PTES-H）to solve the problems of high temperature of heat storage fluid and serious energy waste after energy release.The thermodynamic model of the system is established,and the influence of key parameters on the system performance is studied.The results show that:（a）For CTO-PTES-H,the influence order of key parameters on system performance sensitivity is:heat pump evaporation temperature,compressor inlet temperature,high pressure of heat pump side and high pressure of heat engine side.（b）For CTT-PTES-H,the influence order of key parameters on system performance sensitivity is as follows:heat pump evaporation temperature,low pressure stage compressor inlet temperature,high pressure of heat engine side and double stage high pressure of heat pump side.The energy utilization rate of both systems can reach more than 100%.Then,based on the thermodynamic model of CT-PTES,the influence law of key parameters on the thermodynamic performance of the system is studied.The results show that:（a）For CTO-PTES,the influence order of key parameters on the sensitivity of thermodynamic performance of the system is as follows:heat pump evaporation temperature,compressor inlet temperature and heat pump side high pressure.The round-trip efficiency first increases and then decreases with the increase of the high pressure on the side of the heat engine and the condensation temperature of the heat engine.（b）For CTT-PTES,the order of influence of key parameters on the sensitivity of thermodynamic performance of the system is as follows:evaporation temperature of heat pump,inlet temperature of low-pressure stage compressor.With the increase of the high pressure on the side of the two-stage heat pump,the high pressure on the side of the heat engine and the condensation temperature of the heat engine,the round-trip efficiency first increases and then decreases.Finally,based on the economic model of CTT-PTES,the influence law of the key parameters of the system on the economic performance of the system is studied.The results show that:（a）For CTO-PTES,the influence order of key parameters on the sensitivity of system economic performance is:heat pump evaporation temperature,compressor inlet temperature and heat engine side high pressure.As the high pressure at the heat pump side of the system and the condensation temperature of the heat engine increase,the LCOS decreases first and then increases.（b）For CTT-PTES,the influence order of key parameters on the sensitivity of system economic performance is as follows:inlet temperature of low-pressure stage compressor and high pressure on heat engine side.As the evaporation temperature of the system heat pump,the high pressure on the side of the two-stage heat pump and the condensation temperature of the heat engine increase,the LCOS decreases first and then increases.