Energy optimisation of the control of motors used for water boosting applications

Abstract

The use of pumps for water boosting is a common application in process cooling systems within industrial plants. In the past, the control side of such pumping systems simply used to be a Direct On Line (DOL), Open Loop (OL) system that required additional manpower to control the flow mechanically. As time passed, such systems were replaced by a Closed Loop (CL) system that made use of a Variable Frequency Drive (VFD) and a number of sensors such that the system is fully automated and therefore requires minimal human intervention. Therefore, the aim of this project was to investigate and go through a commissioned process cooling system, and identify areas where the system could operate in a more efficient manner. This was carried out by implementing a simulation model on Matlab/Simulink and investigating several operating scenarios which are currently being applied within the process cooling system, and also propose additional changes which would result in an improved efficiency of the system. The simulations carried out included a comparison between the operation of pump using DOL or a VFD, and also a comparison between the operation as currently implemented and the proposed change of adding a common header to the process cooling system. From the results achieved it was concluded that by operating using a VFD surely is much more efficient than DOL. Moreover, the change which proposes an additional common header is advantageous at certain operating points and therefore to make full use of this change the control system must also be updated. Finally, the effect of changing the pump rating from 11kW to 7.5kW was explored and the results yielded show that by changing to 7.5kW is advantageous as the pumps are correctly sized.