Optimization of a pipe-line for the natural gas transportation

Abstract This paper deals with the problem of optimizing the management of a natural gas transportation pipe-line. The system is formed by m compressing stations linked by pipe-legs. Each station Si is equipped with Ni centrifugal turbocompressors; its behaviour is characterized by the actual number ni of operating turbocompressors and by the values of the machine flow-rate and of the suction and discharge pressures and temperatures. A fraction of the gas passing through the station is used for the feeding of the turbocompressors (fuel-gas). For each station Si it is necessary to find the optimal values of ni and of the discharge pressure so as to minimize the total amount of fuel-gas (inclusive of the quantity needed for turbocompressors start-stop operations), taking into account the constraints on the pressures and temperatures in the stations and along the pipe-legs. Sophisticated simulation models of the stations and of the pipe-legs are presented and justified by means of experimental tests. An algorithm based on a dynamic programming formulation of the problem is proposed; the algorithm utilizes dominance criteria and lower bounds in order to reduce the total number of states. Extensive computational results referring to a set of real situations are given in order to evaluate the saving with respect to the current manual management of the system. The results reported in this article have been applied to the gas transportation pipe-line that is operated by OeMV (Austria) and SNAM (Italy).