Worldwide energy crisis makes it necessary to optimize consumption. One of the fundamental ways to reduce energy consumption is recovery from wasted energy. This can be applied in oil, gas and petrochemical industries in which large amounts of energy waste occur. We can refer to gas transportation when there is a pressure reduction at natural gas pressure reducing stations. In common classic methods, this reduction is accomplished through regulators or throttle valves which the great amount of energy existing in pipelines lost by them. In this paper, it has been suggested to use expansion turbine for achieving pressure reduction, as well as energy recovery goals. In this regard, Tehran City Gate Station No.2 which is one of the large natural gas pressure reducing stations in Iran (both from capacity and inlet pressure perspectives), has been selected as a case study. In first step waste of energy was calculated by using exergy analysis and in second step, by using expansion turbines that are used parallel in the station for achieving the goals of gas reduction pressure and power recovery was simulated in four scenarios by Thermoflow1 software. The results show undeniable fact that the Energy loss at this station has been 38,443,578 KWhr for a year. As a result of using turboexpander, the exergy recovery will be 96%. At the final step, one scenario was selected as the best which its period of payback was about 2 years.

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