Energy and environmental analysis of a natural gas pressure reduction station equipped with turboexpander, solar collector, and storage tank

Abstract

The pressure of natural gas in the transmission pipelines is high, and it is not suitable for urban consumptions. Therefore, it should be decreased to a certain lower amount in the pressure reduction stations near the urban area by the pressure reducing valves. Recently, for recovering the energy losses in these valves and generating electricity, turboexpanders are utilized. However, the pressure decrease in the turboexpander results in a sudden decrease in temperature, which leads to the formation of hydrates. To prevent the hydrate formation, preheating is required, which is conventionally done by a line heater. In this study, the required energy for preheating the natural gas entering the station is supplied from the solar energy and an auxiliary line heater for a case study of Mashhad city (Iran). Parabolic trough thermal collectors are used for the absorption of the solar radiant energy. The collector was modeled through one-dimensional implicit finite-difference method and using discretization of energy balance equation between the working fluid, the absorbent pipe, and the glass envelope. The reduction in natural gas consumption and the produced CO2 emission are computed for the pressure reduction station with a thermal collector and a storage tank. The results reveal that the presence of the thermal collector and the storage tank reduces the consumption of fuel and consequently the generation of pollutant about 90%.