Experimental Investigation of the Use of Expander–Generator Pressure Regulators in Small-Scale Natural Gas Pressure-Reduction Stations

Natural gas pressure-reduction stations dissipate a significant portion of the gas pressure energy during conventional throttling. The recovery of this energy at small-capacity stations remains challenging due to low gas flow rates and variable operating conditions. This study investigates the application of a volumetric expander–generator regulator based on a vane-type positive-displacement expander as a combined pressure control and energy recovery device for small natural gas pressure-reduction stations. A mathematical model of gas-dynamic processes in the expander–generator regulator was developed and verified using experimental data obtained from a laboratory-scale compressed-air test facility. Experimental investigations were carried out within four pressure-drop ranges of 25–65, 45–105, 75–175, and 125–285 kPa under both rotor-speed stabilization and outlet-pressure stabilization modes. Based on the experimental results, second-order regression models were developed to describe the dependence of rotor speed on operating pressures and were subsequently used to estimate annual energy recovery. The results indicate that outlet-pressure stabilization provides higher energy recovery than rotor-speed stabilization across the investigated operating ranges. Depending on operating conditions, the estimated annual recovered energy ranged from 83 to 2265 kWh, which is sufficient to cover the auxiliary power demand of cabinet-type pressure-reduction stations and cathodic protection systems. The experimental validation presented in this study was performed using compressed air as the working medium. Therefore, the obtained quantitative results should be regarded as a laboratory-scale assessment of the feasibility of the proposed approach rather than a direct validation of a natural-gas expander–generator system. The results suggest the potential applicability of volumetric expander–generator regulators for energy recovery at small-scale gas pressure-reduction stations operating under variable flow conditions.