Abstract
The natural gas which is supplied to the Khangiran gas refinery comes from a high-pressure natural gas transmission pipeline and passes through a metering and reducing station, sometimes referred to as the pressure drop station. The gas at this reduced pressure enters the refinery for internal uses. It is at the pressure drop station that a lot of energy is wasted, as the pressure of the natural gas is reduced by an expansion-type ball valve. But, the design of the ball valve does not allow any of the energy from the compressed natural gas to be recovered, as it regulates from a higher pressure to a lower pressure. If this energy loss can be captured, it can be converted into electricity. In this study, a comprehensive program has been carried out to record and measure natural-gas properties and flow rates at Khangiran pressure drop station for a year. Based on these data and an accompanying exergy analysis, the amount of available work that can be produced from capturing natural-gas pressure exergy from the station has been calculated. To produce work, a system which consists of preheating and a turbo expander has been proposed and studied. The effect of preheating temperature and turbo expander exergetic efficiency on amount of obtainable work has been studied. The results show that the amount of available energy can meet all electrical demand of the refinery.