Thermodynamic Modeling and Exergy-Based Optimization of Natural Gas Pressure Energy Recovery Systems

Abstract Traditional natural gas (NG) pressure reduction relies on throttling, causing significant exergy destruction and energy-intensive heating to counteract the Joule-Thomson effect. To address these issues, an integrated pressure energy recovery system coupling a turboexpander with an air-source heat pump (ASHP) was proposed. Two configurations, pre-heating and post-heating, were simulated and optimized using rigorous exergy analysis. Results identify a “thermodynamic sweet spot” for both architectures. The pre-heating configuration achieves a peak system exergy efficiency of 74.81% (3557.94 kW) at an optimized compressor discharge pressure of 1.8 MPa, driven by minimized energy-grade mismatch between the R134a refrigerant and the NG stream. Conversely, the post-heating scheme delivers a superior net power output of 3829.21 kW with an exergy efficiency of 60.44%, benefiting from reduced ASHP parasitic work at lower temperature lifts. Critically, both systems honor a strict safety constraint, maintaining NG exhaust above 8°C to prevent hydrate formation. Sensitivity analysis across seasonal variations (263.15 K–298.15 K) demonstrates the system's robust operability, where R134a phase-change characteristics ensure stable performance even in cold climates. This research provides a theoretical framework for designing high-performance, carbon-free energy recovery units for global NG distribution networks.