Development and application of screw expander in natural gas pressure energy recovery at city gas station

Highlights: • The natural gas screw expander keeps running below its critical speed. • Mechanical seal with cryogenic materials was adopted and proved to be reliable. • Rolling bearing can be simply selected due to its low rotation speed. • Stable performance under variable gas conditions can be guaranteed easily. • The natural gas screw expander is suitable for energy recovery in CGS. There is a tremendous energy loss in the process of natural gas delivery by pipes. The energy lost in the pressure reduction process can be first transformed into mechanical energy and then further converted into electricity by a generator. In this study, an oil free twin screw expander was designed and applied for the nature gas energy recovery at a city gas station for the first time. And the critical speed of the rotors, the seals and bearings were discussed and presented in the design, which was proved that the system designed with the twin screw expander is much simpler without challenges of the sealing and bearing selection facing in the traditional turbine expander used in the CGS. Finally, the feasibility and simplicity of using the screw expander in natural gas energy recovery and power generation were proved through its stable running performance at site. The twin screw expander, therefore, could make up for the defects of the traditional turbine expander at a high rotation speed applied in the samilar area, and turned out to be an effective way to recover the pressure energy from the natural gas.