Research And Application Of Pressure Energy Recovery In Natural Gas Pressure Regulation Process In Urban Gate Station

With the increase of the proportion of natural gas in the primary energy consumption structure, China has accelerated the construction of gas pipeline network, and the gas pressure continues to be increased. In general, the pressurized natural gas need to be depressurized in the distribution stations (pressure regulating stations) and gate stations before being supplied to the users, and the depressurize process will lead to a great pressure exergy loss. In order to improve the energy efficiency and the operation economy of the natural gas pipeline network, the worldwide research achievements are investigated and referred to study the pressure energy recovery and utilization of pressurized natural gas in the distribution stations. An energy recovery process of utilizing turbo expander to regulate the natural gas pressure and pressurize to liquefy the natural gas is proposed in this paper, and economical evaluation is carried out to assess the practical process improvement project. The main achievements are:(1) Discussed and analyzed the natural gas pressure energy utilization in both here and abroad and summarized the development in these processes.(2) Analyzed the thermodynamic characteristics of the throttle valve and the expander, and developed their exergy loss mathematical model. Their ability of achieving low temperature exergy and consuming high pressure exergy are calculated and compared. The study result indicates that the effect of the turbo expander using the low temperature exergy and high pressure exergy is better than the throttle valve.(3) The "post-booster liquefaction process " is proposed and evaluated in this paper. By using the soft Unisim to set the parameters of the key facilities'model (such as compressor, throttle, gas-liquid separator, expander and heat exchanger, etc.), the influence of parameters' variety (incoming pressure and temperature) on the out coming of the process is calculated and analyzed. The results demonstrated that the post-booster liquefaction process shows a better performance under the condition of higher gas pressure, higher storage pressure, higher heat exchanger condensing temperature, or lower gas temperature. The post-booster liquefaction process is suitable for the pressure liquefaction in the disti'ibution stations and gate stations with relatively high incoming pressure.(4) The "pre-booster liquefaction process" is introduced and improved in this research. By using the software Unisim, the influence of the parameters (such as incoming pressure and temperature) to the result of the processes has been calculated and analyzed. The result indicated that the pre-booster liquefaction process can behave better under the condition of higher incoming pressure, higher LNG storage pressure, higher condensation temperature of the heat exchanger or lower income temperature. And the performance of the pre-booster liquefaction process is better than the post-booster liquefaction process over a particular range of pressure. The Pre-booster liquefaction process is suitable for the pressure liquefaction in the distribution station and the gate station with a lower incoming pressure.(5) The study result has been referred and utilized to perform the pressure energy utilizing process reformation in a distribution station and a gate station. The overall liquefaction rate after the process reformation is proved to be 20%, and the overall investment yield rate of the reform project can be as high as 18.1%. This practical result demonstrated the feasibility and economical efficiency of the two processes introduced in this paper.