The purpose of this paper is to discuss the effects of compressor station constraints on pipeline modeling and optimization results. Compressor definitions within pipeline models contain constraints which limit their region of operation. These constraints can include maximum and minimum speeds, compression ratios, cylinder clearances and powers. Operation of centrifugal compressors is also limited by their surge and sonic flows. These constraints are used to reflect either actual compressor limitations or to limit the regions of operation to more efficient areas. In the field, compressors temporarily need to violate some of these constraints during startup and shutdown sequences. In optimization algorithms, enforcing minimum constraints can sometimes cause sub-optimal answers because they produce "holes" in the feasible space which can lead to local minima. This paper will investigate a methodology for visualizing the effects of various constraints that a gas pipeline must satisfy for feasible operation. It will also lay out the problems associated with using steady state compressor models containing minimum constraints within pipeline simulation and optimization software.
The effect of compressor constraints on simulation results will be studied by examining how they impact the maximum and minimum pressure envelopes. The value of this approach is that it makes it easier to visualize how different pipeline constraints impact the available range of pipeline operation. This paper will also alert modelers to the issues associated with using minimum constraints on compressor stations during pipeline simulation and optimization.
