Analysis And Optimization Of The Power Generation System With A Gas Heat Pump In The Natural Gas Regulating Station

The natural gas regulating and power generating station is a new type of natural gas regulating and pressurizing door station which can recover the natural gas pressure energy for power generation.In order to prevent ice plugging of natural gas,huge preheating energy consumption is required before decompression.At present,the research is mainly limited to using electric driving heat pump to replace the traditional gas-fired boiler,but it still facing of the problems such as low patial load efficiency and poor economy.Therefore,this article puts forward a new type of natural gas regulating and power generating(NGHP)system based on gas heat pump,which using gas engine driven heat pump instead of sacrificing electric,at the same time using the engine cylinder and exhaust smoke waste heat to further enhance the temperature of the natural gas.In this study,theory model and exergy loss model of the system are builded,the optimized operation strategy and the ratio of power equipment under partial load are calculated,the model was validated by gas heat pump test bench,the variable condition and partial load characteristic of the system are explored,a comparison between the the heat pump driven by gas engine and traditional electric are constructed with a actual cases.The specific research contents are as follows:The NE-NGHP system model construction and exergic analysis: On the basis of thermodynamic analysis,the theoretical modeling of gas expansion unit and heat pump unit are carried out.Based on the test,the performance prediction model of the gas engine,generator and waste heat recovery are built.The dynamic simulation model of the whole system is obtained by coupling the related parameters of each component.An optimization scheme is proposed for the partial load operation strategy of NE-NGHP system: With engine thermal efficiency as the optimization goal,in accordance with the engine optimum torque curve,the system partial load operation mode could be divided into two kinds according to different compressor speed range,and solving the corresponding optimal transmission ratio,in order to realize the rational matching of compressor and engine and the improving of the system partial load efficiency.The gas heat pump unit in NE-NGHP system was studied by experiment: In experiment study,the heating characteristics,heating efficiency and the engine torque,efficiency and fuel consumption characteristics under different load are explored.The error between simulation and experimental results are within ±10%,which verifing the reliability of the model.The efficiency of the engine and motor always remain above 0.255 and 0.88,which verifing the effectiveness of the system control strategy optimization.Analysis of the system performance under variable conditions: the influence of different gas inlet parameters on the system performance is explored.The results show that,under the same operation mode,when the gas pressure into the system increases,the total output electrical power and preheating gas loss rate of the system increase,while the exergic efficiency and heat pump COP of the system decrease accordingly.As the temperature of natural gas entering the system rises,exergic efficiency,total output power and COP of the system increase as well as the preheating gas loss rate decreases.Generally,the system efficiency is greatly affected by the inlet pressure of natural gas,followed by temperature.Comparison of partial load performance between The system equipped with engine driven(NE-NGHP)and electric driven heat pump: When the natural gas flow at the inlet of the system decreases,the preheating load rate decreases,and the NE-NGHP system COP increases,increasing by 48% compared with the electric driven system,the total output power decreases,which increases by 41.9% compared with the electric driven system.Exergic efficiency gradually increased,which increases by 8.65% compared to the electric driven system.The preheating gas loss rate decreases gradually and the mean value is only 0.7% of the electric driven system.Case study: Combined with the annual natural gas pressure regulation parameters of the actual door stations,the performance difference between the engine driven heat pump and the electric driven heat pump applied to the natural gas expansion power generation system is explored.The results show that the NE-NGHP system mainly operates in mode A in spring and summer,and operates in mode B in autumn and winter.Compared with the traditional electric driven system,the annual power output per unit natural gas flow of the fire drive system is Increased by 34.77%,COP is increased by 41%,Overall exergic efficiency was increased by11.6%,and the exergic efficiency of the fire drive system in autumn and winter is 7.65% lower than that in spring and summer.The annual preheating gas loss rate is only 0.8% of the electric driven system.In addition,in autumn and winter,when the natural gas temperature is low and the flow rate is large,the performance difference between them is particularly significant.