The Control Of Variable Speed Pumps In Parallel Operation

Abstract

The features are discussed of a PLC based control scheme that was developed for a multipump pumping station to be used to supply oil field produced liquids (crude oil and associated water) from tanks through a dehydration facility to dewatered crude storage. The hydraulic resistance characteristic of this system exhibits substantial variation and the required flow is variable and covers a wide range from initial startup conditions to the eventual peak capacity requirement. The avoidance of unnecessary energy input to the product was of special importance, since it would promote the formation or stabilization of emulsion of the produced fluids, thereby complicating the dehydration process. The control scheme developed is applicable to any variable-speed, parallel pump station. With the optimum pump number fixed in this way, pump speed is simply controlled to provide the desired overall flow. As a minimum, values of Q and N (or excitation frequency) have to be measured and input to the control scheme. The individual values of Q/N, besides providing the basis of pump number optimization, also permit protection against excessively high or low flow, Additional practical aspects are discussed.