Dynamic simulation of gas flow within the yard piping of a compressor station requires mathematical modelling of the dynamic behaviour of the various piping elements and the compressor itself. Such models consist of large systems of non-linear partial differential equations describing the pipe flow together with non-linear algebraic equations describing the quasi-steady flow through various valves, constrictions and compressors and their drivers. In addition, the models also include mathematical descriptions of the control system which consists of mixed algebraic and ordinary differential (mad) equations with some inequalities representing controllers' limits. A computer program has been developed that deals with these two levels of computations:
the gas dynamic behaviour, and
the associated control loops' response.
This paper briefly describes the mathematical models, the applied numerical methods used and their properties, and presents simulation results and comparison with actual field measurements of three case histories:
blowdown of the yard piping at a three-unit compressor station;
simulation of a compressor surge protection control process;
slow transient of a compressor station responding to changes in the discharge pressure set point.
Good agreement between simulation results and field measurements is demonstrated.
The technology relating to gas pipeline transient flow simulation is mature. Today, transient models of large gas pipeline networks for off-line purposes are generalized to the point that almost any practical network or straight line system can be readily simulated. Examples of the application of transient modelling are found in leak detection, size and location [I]o,p eration planning and line pack/inventory analysis [2], blowdown [3], line rupture [4,51, pipeline integrity monitoring [6], and generally in the design of such networks [71. The literature contains a vast amount of papers dealing with the subject of dynamic simulation of compressible as flow in pipes. main categories; slow or rapid transients, for which formulations of the mathematical models are slightly different. Several different methods of solution for the pertinent one-dimensional conservation equations have been developed. The choice of a particular method is partly dependent upon the requirements of the system such as the degree of accuracy, size of the system, imposition of boundary conditions, variation of wave speed and the type of transient. A good review paper on the various numerical methods applied is by Thorley and Tiley [8], while others [9,10,11] presented actual numerical comparison between various methods. Additional unique techniques were also used such as the variational method [12], the finite element method [13], a combined implicit finite difference with the method of characteristics [14], the concept of thermodynamic path [15], together with error estimation in the simulation [16]. From an analysis point of view, these papers may be divided into two The dynamic behaviour of the gas flow within a compressor station not only depends on the dynamic behaviour of each piping element, includin the compressor itself, but also interacts strongly with the station dynamic simulation includin control systems are scarce.
