Proposal and analysis of a coupled power generation system for natural gas pressure reduction stations

With the increased use of natural gas, it is valuable to study energy recovery ratio in the natural gas pressure reduction stations (PRSs). This paper focused on recovering the energy in PRSs as well as low-grade waste heat by a coupled power generation system (CPGS). The CPGS integrates a natural gas expansion (NGE) subsystem and an organic Rankine cycle (ORC) subsystem driven by low-temperature waste heat. Firstly, a comparative analysis is carried out between the separated natural gas expansion system and the separated ORC system. Then, the effects of heat source conditions, upstream pressure of natural gas and the isentropic efficiency of the natural gas expander are investigated. At last, working fluids selection is conducted with respect to two different pressure ranges of natural gas. The results show that there is an optimal temperature and mass flow rate of the heat source that maximizes the system exergy efficiency. With the increase of the upstream pressure of natural gas, the net power output and waste heat recovery factor increase while the system exergy efficiency has an optimal point. Furthermore, the isentropic efficiency of the natural gas expander has a great influence on the net power output of the system.