This research focuses on the development of a quasi-isothermal pressure regulator based on the principle of flow mixing after energy separation. Currently, no established methods exist for designing pressure reduction devices that utilize energy separation effects, and this study aims to fill this gap. The paper presents experimental results on the performance of a pressure reduction device operating based on the Hartmann–Sprenger effect. This study investigated the hypothesis that by selecting the size of resonators, relative distances, and their mutual location, it would be possible to realize pressure regulation, simultaneously providing both the maintenance of a significant effect and the full provision of the functions of pressure regulators operating in non-stationary conditions. The experiments involved three resonators (45.5 mm, 70.5 mm, and 97.5 mm) in regurgitant mode. The findings revealed that the smallest resonator demonstrated the highest rate of temperature increase, with an average value of 2.36 K/s. The medium resonator exhibited the highest reliability under non-stationary conditions, while the largest resonator provided the highest temperature, with a maximum excess of 102 K over the temperature in front of the nozzle. The primary goal of this study was to develop technology suitable for installation at a pressure reduction station, considering mass and dimensional constraints.

The present paper provides a brief overview of the existing methods for energy separation and an analysis of the possibility of the practical application of the Hartmann–Sprenger effect to provide quasi-isothermal pressure reduction of natural gas at the facilities within a gas transmission system. The recommendations of external authors are analyzed. A variant of a quasi-isothermal pressure regulator is proposed, which assumes the mixing of flows after energy separation. Using a numerical simulation of gas dynamics, it is demonstrated that the position of the resonators can be determined on the basis of calculations of the structure of the underexpanded jet without taking into account the resonator and, accordingly, without the need for time-consuming calculations of the dynamics of the processes. Based on the results of simulating the gas dynamics of two nozzle–resonator pairs installed in a single flow housing, it is shown that, in order to optimize the regulator length, the width of the passage between the two nearest resonators should be greater than or equal to the sum of diameters of the critical sections of the nozzles. Numerical vibroacoustic analysis demonstrated that the most dangerous part of the resonator is the frequency of its natural oscillations.

When transporting and storing hydrocarbons, one of the main operational problems is the external and internal corrosive wear of the metal. A frequent cause of accidents in main and technological gas pipelines due to their stress corrosion cracking is the enrichment of the pipe body with hydrogen. Literature experimental data on the effect of hydrogen on the hardness of iron and low-carbon steels during their electrolytic saturation with hydrogen are analyzed. It is noted that the curves of changes in hardness in all the analyzed sources for all these materials have a similar form: at the initial stage of hydrogenation, the hardness increases, reaching its maximum, and then it declines to values close to the initial level follows. At the same time, the time to reach the maximum hardness decreases with the introduction of promoters into the electrolyte solution, which can be Na2S, As. Increasing the current density during electrolysis increases the value of the maximum hardness. The time to reduce the hardness to the initial level is approximately the same as the hydrogenation time required to achieve maximum hardness. Possible explanations of the regularities obtained by the authors are given.

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.