Development of a compressor for gas network simulation

Abstract

In this thesis the development of a compressor for a gas network simulation will be discussed. The modelled compressor is a centrifugal compressor and this compressor is common to use when compressing gas. At first the equations to describe a centrifugal compressor and an ex- ample parameter set are given. These equations will be used in an algorithm to calculate either the suction pressure, the discharge pressure or the volume flow. A compressor can only operate when it is in a feasible area. This feasible area is defined by both a surge and choke line as well as the minimum and maximum rotation speed.
The gas network considered consists of a compressor plus a pipeline in front and after the compressor. To model a pipeline the Weymouth pressure-drop equation is used. The pipe- compressor system can be described as a system of seven equations. There are seven unknown variables and two given variables. The given variables are the pressure at the beginning of the first pipeline and the pressure at the end of the second pipeline. To solve the system of equations a nonlinear solver is used. The Newton method is an ex- ample of such a nonlinear solver and will be discussed for scalar equations and a system of equations. Solving the system of equations as part of a simulation, a function in Python called fsolve will be used. This function uses a more robust algorithm to get the solution quickly. The numerical behaviour of the solver will be considered during multiple simulations. Fur- thermore a parameter study has been done to understand what kind of pipelines are needed for a certain pressure ratio. Finally two examples are discussed briefly.