Modelling of high-pressure gas transmission lines

Gas flow in a transmission line is described by a set of three coupled partial differential equations (PDE) expressing conservation of mass, momentum and energy; the gas properties are described by a non-ideal equation of state. A technique is introduced which reduces the energy equation into a single parameter in the mass equation without the assumption of isothermal or isentropic flow.The remaining set of PDEs is solved by two different techniques. An accurate but time-consuming technique consists of applying the method of characteristics, for which an improved representation of the friction term is presented. The second way consists of a finite-difference implementation with a second-order truncation error on an analogue computer. Both the physical assumptions and the numerical approximations are checked against data obtained from experiments in the main transport system of Gasunie.Guidelines on the analogue modelling of pipeline systems and the interpretation of simulation results conclude the paper.