Investigating the possibility of using the turbo-expander for natural gas pressure reduction stations

Using a turbo-expander instead of a regulator, the output temperature will be reduced. Reducing the gas temperature to the freezing temperature of the water within gas can damage the station equipment. In the present work, the gas flow is simulated in a turbo-expander under the real conditions of natural gas pressure reduction stations and the amount of gas temperature reduction during this process is predicted. The equations of continuity, Navier-Stokes, energy, and k−ε turbulence model are solved with the help of CFD. Simulation results for twelve real cases, including three different input pressures, two different output pressures, and two different input temperatures are obtained. Results show that almost for every 9 psi pressure reduction, the temperature decreases by 1 °C. Also, the highest temperature drop occurs in the middle part of the outlet. Results show that due to a very low temperature of outlet gas, using a turbo-expander in the case of high-pressure stations is not recommended. In the case of medium pressure stations, a turbo-expander may be used with a heater. In the case of low-pressure stations, as the temperature at the center of outlet is lower than at the other points, installing a flow mixer can solve the freezing problem.