Configuration Optimization Of Power Generation System Utilizing LNG Cold Energy And Deep Geothermal Energy

Based on the development demand of "Carbon Peak,carbon neutral",the demand of natural gas in China is increasing rapidly.At present,domestic natural gas can not meet the needs of our natural gas consumption.So there is a need to buy vast quantities of liquefied natural gas(liquefied natural gas)from abroad and to speed up the construction of LNG terminal infrastructure.A large amount of cold energy will be released from LNG during gasification,but this part can not be fully utilized because of the imperfect theory and technical system of cold energy utilization.In addition,the LNG gasification process needs to consume a lot of heat energy(such as the heat energy of gas-fired boilers)to meet the gas transportation temperature requirements of the gas pipeline network downstream users.At present,the Organic Rankine cycle system is the main way of LNG Cold Energy Utilization.The singlestage Rankine cycle system will result in a large irreversible loss due to the large temperature rise during LNG gasification.Therefore,a multi stage Organic Rankine cycle system utilizing LNG cold energy will help to improve the thermal performance of the system and reduce the irreversible loss of the thermal process.Based on the above problems,three types of power generation systems using LNG cold energy and mid-deep geothermal energy are proposed in this paper according to the geothermal energy and LNG cold energy cascade utilization principle.The first process is the Organic Rankine cycle series system.The second process is the three stage Organic Rankine cycle system with a heater.The third process is the three stage Organic Rankine cycle system with a temperature rising absorption heat pump.In this paper,the system model is established and the Organic Rankine cycle working medium(R32)is screened out.The effect and benefit of using geothermal energy and LNG cold energy step by step are studied by theoretical research and numerical calculation,and then the optimal allocation law of power generation system using LNG Cold Energy and mid-deep geothermal energy is revealed.The results show that with the increase of geothermal water supply temperature,the designed flow rate of heat medium circulating water decreases correspondingly.And the design temperature of natural gas at the condenser outlet of the last stage Organic Rankine cycle system in processes II and III increases accordingly.Compared with single-stage Rankine cycle system,system thermal efficiency and product efficiency of process III can be increased by 5%～7% and11%～14% respectively when the temperature of geothermal water supply is 60°C～80°C.Compared with process I and II,the system thermal efficiency and product efficiency of process III can be increased by 1%～2% and 2%～4% respectively.The geothermal load and exergy loss of system three increases with the increase of geothermal water supply temperature,but the capacity ratio of the main equipment in the system changes little.Compared with conventional coal-fired thermal power generation system,the power generation system using LNG Cold Energy and mid-deep geothermal energy has greater energy-saving and emission reduction potential.Compared with process I and II,the energy-saving potential of System III can be increased by 11.27% and 0.71% respectively.Among the three systems,the cost of power generation and the payback period of investment are the smallest,and the rate of return of fixed assets is the largest.For the third process,the system thermal efficiency,product efficiency,cost of power generation are 17.23%,28.76%,0.478yuan/kW·h at 70°C.And its payback period and the rate of return on fixed assets are 4.29 years and 17.33% respectively when the selling price is 1 yuan/kW·h.To sum up,the third system technology has the best energy,environmental and economic benefits,so its energy transfer and conversion technology is more advanced and the system configuration is better.For system process 3,the capacity of water-water heat exchanger and heat pump is about 773.29 kw and 233.05 kw,respectively,when geothermal water temperature is 70 ° C and LNG gasification per unit.The condenser capacities of the three-stage Organic Rankine cycle are about 246.20 kW,248.03 kW,209.41 kW and 117.80 kW respectively.The technology of three-stage Organic Rankine cycle power system with heat pump provides a new idea and scheme for developing and utilizing LNG cold energy and medium-deep geothermal energy.