Optimization of a large gas transmission pipeline results in reduced fuel consumption or higher capability and improves pipeline operation. In the current study, we have done an extensive research to optimize the operation of a huge NPS 56 pipeline system using gas cooling. This gas transmission line (the 4th major gas transmission pipeline of the National Iranian Gas Company, NIGC, or IGAT4) is designed to move over 110 MMSCMD (4.0 BCFD) of natural gas from the Assaluyeh Gas Refinery. This gas refinery which in turn receives gas from the huge gas reservoir of the South Pars Field (Iranian off-shore) is located in the south of Iran. The length of this system is over 800 kms (500 miles) with over 700 MW of compression power and aerial coolers at all compressor stations. This system passes through a very tortuous terrain with significant changes in elevation and ambient temperature which makes the optimization process even more challenging. The main objective of this project was to develop a customized tool to optimize the operation (energy consumption) of this gas transmission pipeline with all the existing system variables. The emphasis was on the impact of gas cooling (effective operation of aerial coolers) on the optimization process which in turn leads to the fuel minimization or higher capability. In this process, the impact of ambient temperature, soil temperature throughout the entire route of the pipeline, cost of electricity & fuel gas, heat transfer and Joule-Thompson effect were carefully considered. The tool was finally developed and was successfully tested on this gas transmission system which resulted in extremely accurate results. This tool could be further generalized to be used for other transmission systems.

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