Development, Optimization and Implementation { of the Design for a Centrifugal Reverse-Osmosis Desalination System ACCEPTHU rsUV.lATF STUOUib by EACUtTY of GaAuUAit * ......- Peter Martin Wild ^ / / p University of British Columbia, 1983 A Dissertation Submitted in Partial Fulfillment of the Requirements for the Degree of DOCTOR OF PHILOSOPHY in the Department of Mechanical Engineering We accept this dissertation as conforming to the required standard. Dr. ((j/w. Vickers, Co-supervisor (Mechanical Engineering) Dr. N Dirlali, Co-supervisor (Mechanical Engineering) Dr. 6. Tabarrok, Member (Mechanical Engineering) Dr. A. Doi^^Merr^er (Mechanical Engineering) Dr. A. ^ fin sk i, Member (Electrical Engineering) Dr. R. Venter, External Examiner (University of Toronto) ©Peter Martin Wild, 1994 University of Victoria All rights reserved. The dissertation may not be reproduced in whole or in part, by photocopying or other means, without permission of the author. Abstract ii (( A new method of sea water desalination, Centrifugal Reverse-Osmosis (CRO), is developed from concept to patented design and functional prototype of capacity 11,355 litres of fresh water per day. CRO is shown to have significant benefits relative to the leading existing desalination technology, conventional reverse-osmosis. These benefits include: lower energy consumption, reduced initial and replacement membrane costs, lower noise levels and improved reliability. CRO is projected to show increasing cost efficiency as plant capacity increases. For a relatively large CRO plant, 65lm^ fresh water per day, the total cost of desalinated water is projected to be 25.9% lower than the total cost of water produced by a conventional RO plant of equivalent capacity. The current patented design requires further development in order to realize this potential. Toward this end, a computational and experimental study of rotor windage losses and an experimental study of fluid flow losses through the rotor are conducted. In addition a new method for the analysis of stresses in a filament wound rotor shell under combined centrifugal and pressure loading is developed. Examiners: Dr. G/W. Vickers, Co-supervisor (Mechanical Engineering) Dr. NrDiiTaliv'Co-supervisor (Mechanical Engineering) d (\ B. Tabarrok, Member (Mechanical Engineering) Dr. A. Doige, ivjetf^gr (Mechanical Engineering) Dr. A. ZielijliS^Member (Electrical Engineering) Dr. R. Venter, External Examiner (University of Toronto) iii Table Of Contents Abstract..........................................................................«.......................................i Taole Of Contents........................................ ........................................................ii List of Tables ................................................................................................viii List of Figures ........................................................................................ ix Nomenclature Table ....................................................................................xiv Acknowledgements..............................................................................................xxiii Chapter 1 Introduction - Existing Desalination Technologies and the Potential of Centrifugal Reverse-Osmosis 1.0 The Growing Demand for Desalination ................................................................1 1.1 Conventional Reverse-Osmosis Desalination .......................................................4 1.1.1 Cross-Flow Filtration ....................................................................................4 1.1.2 Membrane Types ...........................................................................................5 1.1.3 Reverse-Osmosis ........................................................................................... 6 1.1.4 Concentration Polarisation ........................................................................... 7 1.1.5 RO Membranes and RO Membrane Packaging .......................................... 9 1.1.6 Conventional Reverse Osmosis System Design and Operation .................10 1.2 Centrifugal Reverse Osmosis (CRO) Desalination .............................................. 14 1.2.1 Conceptual Design of a CRO System ......................................................... 14 1.2.2 The Potential Benefits of CRO .................................................................... 15 1.3 Survey of Relevant Literature ................................................................................19 1.4 Scope of the Dissertation ................................. ..................... .......................... 20 Chapter 2 A Practically Feasible Design for CRO Incorporating Novel Design Solutions 2.0 Preliminary Feasibility Study ................................................................................ 25 2.1 Survey of Literature Relevant to Centrifuge Design ....................................25 iv 2.2 Membrane Configurations for CRO ....................................................................26 2.2.1 Pressure Gradient Within a Centrifuge Rotor .............................................. 28 2.2.2 Forces Associated With Centripetal Acceleration ......................................29 2.2.3 Rotor Balance ................. 31 2.2.4 The Influence of Centripetal Acceleration on Concentration Polarisation and Fouling .........................................................................................31 2.2.5 Volumetric Efficiency of Membrane Configurations for CRO ..................34 2.3 Ideal Energy Savings of CRO Relative to RO ......................................................36 2.4 Sources of Non-Ideal Power Losses in CRO ........................................................ 42 2.4.1 Rotor Windage ........................................................................................44 2.4.2 Fluid Flow Losses ..........................................................................................49 2.5 Novel Design Solutions Enabling CRO Feasibility .............................................. 52 2.5.1 Provision of a Uniform Pressure Differential .............................................. 52 2.5.2 Rotor Windage Abatement ............................................................................ 54 2.5.3 Fresh Water Removal Means .................................... 60 2.6 Assessment of CRO Feasibility ..............................................................................62 Chapter 3 Development and Testing of First and Second Prototype CRO Systems 3.0 Prototype Development ........................................................................................... 66 3.1 The First and Second Prototype Designs ................................................................66 3.1.1 Prototype System Specifications ................................................................... 67 3.1.2 Sea Water Flow Paths ...................................................................................69 3.1.3 Structure to Restrain Pressure Vessels Against Forces of Rotation ............71 3.1.4 Pressure Vessel Design ..................................................................................72 3.1.5 Materials and Corrosion ................................................................................75 3.1.6 Bearing and Seal Configurations .................................................................. 76 3.1.7 Vacuum Systems.................................................................. 77 3.1.8 Rotor Drive and Unit Instrumentation ..........................................................78 3.2 Performance of the First and Second Prototypes ...................................................79 3.2.1 Permeate Salinity and Flow Rates ................................................................79 3.3.2 Power Consumption Due to Windage ...........................................................82 3.3.3 Fluid Flow Losses Through the Rotor ..........................................................87 3.3.4 Total Power Consumption ............................................................................88 3.3.5 Rotor Balance .................................................................. 90 3.3.6 Noise Levels .................................................................................................. 92 3.4 Assessment of First and Second Prototype and Potential for Further Development .................................................................................................... 93 V Chapter 4 An Experimental and Computational Investigation of Windage Losses Associated with a Rotating, Enclosed and Immersed Cylinder 4.0 Introduction ............................................................................................................. 96 4.1 Review of Relevant Literature ............................................................................... 97 4.1.1 The Similarity Argument .............................................................................. 98 4.1.2 Flow Regimes, Transitions and Stability ..................................................... 100 4.1.3 Theoretical, Empirical and Semi-Empirical Functional Torque Relations ............................................................................................... .................. 103 4.2 Experimental Apparatus ..........................................................................................108 4.3 Computational Analyses ....................................................................................