Research On High Pressure Natural Gas Energy Recovery At Pressure Regulating Process

Petrochina had constructed a gas pipeline from Xinjiang province to Shanghai which is named West East Pipeline Project since 2000. This pipeline will transport natural gas from Western China to developed area of Eastern China. WEPP is the first long distance natural gas pipeline with high pressure and large flow. Petrochina has constructed and planed the other natural gas pipeline from the Eleventh Five Year Plan, such as WEPP II, WEPP III, WEPP IV. By 2020, it will reach more than 420 billion Nm3/a of natural gas transported by pipeline.All of the gas pipelines that have been completed and are building are operated above 7MPa. It will be de-pressure in the sub transmission station before the high pressure gas is transported to the city gate stations or industrial users. In order to meet the needs of downstream users, the pressure regulating skid is widely used which is a throttling device. There is bigger economic benefit if we can recycle the pressure energy that is loss during regulating pressureIn this paper, it was presented to recycle the energy by using a single screw to generate power. And it was also presented the cold energy utilization proposal to achieve energy saving purposes.In this paper, It was first analyzed the pressure energy recycle plan by thermodynamic analysis. The exergy analysis method is used to calculate the pressure energy recovery and power generation system. To recovery the low temperature natural gas, it was put forward the scheme of the comprehensive utilization of cold energy in this paper.It was analyzed comprehensively to the pressure energy recovery device, such as turbo expander, double screw expander and single screw expander. Considering the gas pipeline station core mission which is to ensure the equipment running safely and smoothly, single screw expansion has become the preferred equipment for the pressure energy recovery. Mainly because that single screw expansion has the advantages of simple structure and less maintenance. Meanwhile, the paper defines the technology specific of main equipment and system on pressure energy recovery system including all the necessary reference standards and specifications, system configuration, technical requirements, alarm and protection etc. for single screw expander, generators, air heat exchanger and control system.It can satisfy the system requirements of pressure energy recovery according to the performance test data of single screw expander.It has big benefit in accordance with the recommendations of the pressure energy recovery system design combined with the price of equipment when the gas flow low to 100,000 Nm3/d. Finally, the paper prospects the pressure energy recovery and cold energy utilization in long distance natural gas pipeline transportation with high pressure. Pressure energy recovery and utilization of cold energy has significant social benefits in saving energy and green natural gas pipeline construction and operation.