Aspen Plus Simulation of Power Generation Using Turboexpanders in Natural Gas Pressure Reduction Stations

This paper investigates the economic feasibility of installing a turboexpander in parallel with the throttling valve of a city gate station for the purpose of distributed electricity generation through exergy recovery from pressurized natural gas. The preheating requirements for preventing hydrate formation due to pressure reduction are provided by the combustion of a small fraction of the outlet natural gas stream. As a case study, the simulation of Tehran No.2 City Gate Station demonstrates an exergy loss of more than 36.5 million kWh per year for the present throttling valves. Thermoeconomic analyses gives the optimum operating conditions for electricity generation through a turboexpander. Optimization of preheating temperature leads to an exergy recovery of >60%, cost to generate electricity of <$0.04/kWh, and discounted payback period of around ~4 years. Simulation results can be used for designing an automatic preheating temperature control system to optimize exergy recovery via turboexpander under the variable operating conditions of a pressure reduction station.