Optimal detailed design and performance assessment of natural gas pressure reduction stations system equipped with variable inlet guide vane radial turbo-expander for energy recovery

The turbo-expander system is utilized instead of the pressure regulator to avoid exergy destruction occurring in gas pressure reduction systems. However, due to the variation of natural gas input conditions such as mass flow rate, the sustainable performance of this technology is challenging. In this study, at first, the optimal system design of gas pressure reducing station equipped with radial expansion turbine is performed. It is based on economic and exergy analyses as well as considering geometric, fluid, thermodynamic constraints of components and the systematic constraints. To do so, detailed design models of main components including mean-line design model of radial turbine, mathematical model of heat exchanger and design model of fired heater are developed. Then, the annual proficiency of the optimal system in dynamic conditions was evaluated according to the strategies considered for having stable production. One of the solutions is to improve the turbine efficiency by adjusting the angle of nozzle blades regarding the changes in mass flow rate. Therefore, our developed mean-line off design model of the turbine is applied to adjust inlet guide vane angle in the off-design situation to improve continuous electricity generation. The results of the design section show that the exergy efficiency on this occasion can achieve up to a maximum of 40%. Compared with fix inlet guide vane (IGV), applying variable IGV improves efficiency of turbine up to 60% at off-design condition. The Levelized cost of electricity (LCOE) and payback period of selected optimal design are about 0.0236 $/kWh, and 4 years, respectively. It indicates that this technology could be the economic option compared to other power generation systems. •Maximum exergy efficiency of gas reduction station with turboexpander is 40%.•A mean-line off-design turbine model is proposed to set the angle of nozzle blades.•Applying variable IGV in turboexpander rises its off-design efficiency up to 60%.•LCOE of gas reduction station with turboexpander is about 0.024 $/kWh.•The payback period of gas reduction station with turboexpander is about 4 years.