Using Digital Models for Condition Based Maintenance of High Pressure Pumps in SWRO Desalination Plants

Condition based maintenance (CBM) is a very useful technique built around the concept of monitoring the operation of assets. This allows performing diagnostics, troubleshooting and determining the proper maintenance action. Conventional CBM programs are solely built around analyzing sensors’ data collected from physical systems. Incorporating simulation data collected from digital replica of the system with sensors’ data can lead to more optimization for operation and maintenance. This paper focuses on demonstrating the role of digital models in implementing effective condition based maintenance on high pressure pumps in SWRO desalination plants. Two digital models have been developed for the high pressure pump experiencing cavitation condition. The first digital model is a 3-D fully turbulent Computational Fluid Dynamic (CFD) model. Based on the pressure distribution obtained from the CFD model, pressure pulsation due to impeller-diffuser interaction is studied and used to analytically model the exciting forces affecting the rotor. The second digital model is a pump rotordynamic model which is used to predict the rotor vibration response to exciting forces at both normal and faulty operating conditions. Results obtained from the digital models are validated using an experimental test rig of a small centrifugal pump. Using this concept, a pump faulty operation can be simulated to provide complete understanding of the root cause of the fault. Additionally, digital models can be used to simulate different corrective actions that would restore the normal operation of the pump. Introduction Fresh water shortage is threatening development and prosperity in many Arab countries. In just ten years about two thirds of the Arab countries are expected to suffer from acute water scarcity. Sea Water Reverse Osmosis (SWRO) desalination is fast becoming a dominant technology for facing water shortage threats by cost effective production of fresh water for multiple purposes. The high pressure pump is the heart of any Reverse Osmosis desalination plant. The role of the high pressure pump is to raise the pressure of the feed flow to allow for the permeation process through the RO membranes. Typical pressures for SWRO are in the range of 40 – 80 bar. Accordingly, the high pressure pump consumes most of the electric energy supplied to the SWRO desalination plant. Common problems experienced by a centrifugal high pressure pump may be attributed to one or several probable causes. Low flowrate or low pressure problem can be attributed to either air leaks in inlet piping or faulty mechanical seal. Pump cavitation can lead also to the same problem. Other common problems are excessive lateral or axial vibration and noise which can be attributed to either pump cavitation or to pump rotor misalignment or excessive axial thrust. Cavitation can be considered as a major cause for pump failures. In the first phase of cavitation, vapor bubbles are formed in areas of relatively low pressure around the impeller of the pump. While in the second phase of the cavitation, the collapse of these bubbles triggers intense shockwaves leading to high speed fluid Amr A. Abdel Fatah, Ph.D. Mechanical Engineering Department Centre of Excellence in Predictive Maintenance, The British University in Egypt El Sherouk City , Cairo, Egypt amr.abdelkader@bue.edu.eg Mohamed Lotfy, Ph.D. Department of Mechanical Engineering, Faculty of Engineering, Suez Canal University, Ismailia, Egypt Centre of Excellence in Predictive Maintenance, The British University in Egypt, El Sherouk City, Cairo, Egypt mohamed.lotfy@bue.edu.eg Mohammed A. Hassan, Ph.D. Department of Electrical Engineering, Fayoum University, Fayoum, Egypt. Centre of Excellence in Predictive Maintenance, The British University in Egypt El Sherouk City , Cairo, Egypt. hassanm@fayoum.edu.eg Antoine S. Dimitri, Ph.D. Mechanical Design and Production Department Faculty of Engineering Cairo University Giza, Egypt adimitri@eng.cu. edu.eg