Enhancing energy output in Iran's natural gas pressure drop stations by cogeneration

Natural gas is transported through transit pipeline at high pressures (5-7 MPa) from production sites to end users. In a place of consumption or at passing into a lower pressure pipeline, the pressure of the gas must be reduced. This pressure reduction takes place in places which are called city gate stations (CGSs). Currently, in all Iran's CGSs, valuable pressure exergy (potential energy) of natural gas flow is destroyed in throttling valves. In the current study, based on a comprehensive programme, inlet and outlet properties of natural gas flow and daily flow rate through seven Khorasan Province (Iran) CGS were measured and recorded for a whole year. Based on these data, the amount of energy which could be generated using a combined heat and power system was calculated. The combined heat and power system consists of a preheat section, a turbo expander and an additional prime mover. The amount of electricity generation for the system has been calculated. The results show that 20.5 MW electrical power can be generated. Based on Iran's average daily natural gas consumption of 336 x 10(6) m(3)/day and assuming the same conditions at all CGSs as at Khorasan, 672 MW electrical power could be generated by cogeneration in all of Iran's CGSs.