Feasibility study on energy recovery at Sari-Akand city gate station using turboexpander

Saving energy is a significant issue in the oil and gas industries because of the high cost of global energy sources. Turboexpanders are generally used to recover pressure energy of gas at city gate stations. The present study examined the challenges to turboexpander installation at gas station. These include fluctuations in natural gas (NG) flow and the high cost of installing new heating devices. The first line at Sari-Akand city gate station was simulated using HYSYS software for a nominal capacity of 120,000 SCMH. The NG pressure energy lost at the regulator was calculated using exergy analysis. The results showed that the pressure energy of NG lost during regulation was 7.1 GWh annually. Two scenarios were analyzed to find the suitable plan of turboexpander installation at the gas station. The scenario for installation of one turboexpander instead of one regulator had lower payback period than the scenario where one turboexpander was installed in place of two regulators. NG fluctuation resulted in inability to use the turboexpander for five months of the year and decreased electricity production 8.3% in the other seven months. The annual turboexpander electricity production was computed to be 3.2 GWh. The payback period for turboexpander installation was calculated as 12.9 years to account for the significant 2-fold increase in dollar price in Iran. A feasibility study for implementing a similar plan in England had a payback period of 2.2 years because of the higher price of electricity and lower interest rate in comparison with Iran. The connection of lines 1 and 2 increased annual turboexpander electricity production 54%, which resulted in an annual increase in revenue of $53,400. This decreased the payback period to approximately 8 years in Iran and 1.7 years in England. It is predicted that implementation of similar arrangement at the three other stations will significantly increase revenue about $160,000 annually.