ACHIEVING THE ZLD TARGET USING INTEGRATED MEMBRANE SYSTEM FOR SEAWATER DESALINATION Sulaiman AL-OBAIDANI Mechanical and Industrial Engineering Department Sultan Qaboos University
CONTENTS 1 OVERVIEW OF THE DESALINATION TECHNOLOGIES 2 THE ROLE OF MEMBRANE DISTILLATION IN THE INTEGRATED MEMBRANE SYSTEM 3 ECONOMICAL INVESTIGATION & SENSITIVITY STUDY 4 CONCLUSIONS AND REMARKS
DESALINATION TECHNOLOGIES Process Energy consumption kwh/m 3 Feed TDS (mg/l) Product TDS (mg/l) Required space 2, Thermal Desalination MSF 13 13 MED 65 85 5, 2, 5, <1 Very large <1 Large Membrane Desalination EDR 6 42 RO 35 38 3, 12, 5, 5, <1 Small <5 Small Ettouney, HM, El-Dessouky, HT, Faibish, RS, et al, Evaluating the Economics of Desalination, Chemical Engineering Progress, pp 32 39, December 22 IDA Worldwide Desalting Plants Inventory Report No 18; published by Wangnick Consulting 24
MEMBRANE DISTILLATION (MD) Emerging separation technology Transport of vapor through hydrophobic membrane Based on vapor-liquid equilibrium Driving force is temperature difference
LIMITATIONS OF THE DESALINATION TECHNOLOGIES Low efficiency Environmental impact Water quality Product water cost Can be improved by combining several desalination processes in one integrated system
RESEARCH OBJECTIVE To perform economical investigations and sensitivity study for evaluating several combinations of the integrated membrane system
INTEGRATED MEMBRANE SYSTEM Total system recovery 4% 95% 48% Raw Seawater 95% MF Filtered Seawater 7% NF Filtered NF Seawater Product 5% 6% RO Potable water MF Retentate NF Retentate Brine Salt Crystals Potable water MDC Heat source Concentrate MD Heat source
ECONOMICAL INVESTIGATION
ECONOMICAL INVESTIGATIONS Reference values for cost analysis MF Membrane cost 9 $/m 2 NF and RO Membrane cost 3 $/m 2 Membrane life 67 years Electricity cost 3 $/kwh Steam cost 7 $/ton Plant capacity 24, m 3 /day
ECONOMICAL INVESTIGATIONS FLOW & WATER COST 3 Feed Concentrate Water cost 127 129 127 Flow (m 3 /h) 25 2 15 1 215 1 51 256 156 62 125 114 1124 168 1191 12 8 4 Total Water Cost ($/m 3 ) 5 25 MF-RO MF-NF-RO MD MF-NF-RO +MC+MD 68 14 MF-NF-RO +MC+MC 131 MF-NF-RO +MD+MD
SENSITIVITY STUDY 1 Water Recovery (Yield) 2 Feed Concentration 3 Membrane Cost 4 Electricity Cost 5 Steam Cost
SENSITIVITY STUDY 1 WATER RECOVERY (YIELD) RO Recovery in MF-RO RO Recovery in MF-NF-RO MD Recovery in MD alone Water cost ($/m 3 ) 8 7 6 5 Water recovery variations (%) -2-1 1 2 Without ER 1% 1% With ER 16 8-8 Water cost ($/m 3 ) 12 1 8 6 RO water recovery variations (%) -2-1 1 2 Without ER With ER 16 8-8 Water cost ($/m 3 ) 2 18 16 14 12 MD water recovery variations (%) -2-1 1 2 6% 1% Without HR With HR 16 8-8 4 45 5 55 6 RO water recovery (%) -16 5 6 7 RO water recovery (%) -16 1 7 8 9 MD water recovery (%) -16 ER=Energy Recovery; HR=Heat Recovery systems
SENSITIVITY STUDY 2 FEED CONCENTRATION MF-NF-RO PLANTS MD PLANTS INTEGRATED SYSTEM Water cost ($/m 3 ) 7 6 5 4 16% Without ER With ER 15% Seawater Water cost ($/m 3 ) 14 13 12 11 Without HR With HR NO CHANGES Brackish Seawater Water cost ($/m 3 ) 18 16 14 12 3% Without ER+HR With ER+HR 2% Seawater 3 Brackish 1 2 3 4 5 Feed Concentration (g/l) 1 1 2 3 4 5 Feed Concentration (g/l) 1 Brackish 1 2 3 4 5 Feed Concentration (g/l) ER=Energy Recovery; HR=Heat Recovery systems
SENSITIVITY STUDY 3 MEMBRANE COST Reference: MF=9 $/m 2, NF & RO=3 $/m 2 8 4-4 MF-NF-RO PLANTS MD PLANTS INTEGRATED SYSTEM Without ER With ER 5% Reference value MF = 9 $/m 2 NF and RO = 3 $/m 2 8 4-4 Without HR With HR 6% Reference value MD = 9 $/m 2 8 4-4 Without ER+HR With ER+HR 2% Reference value MF and MD = 9 $/m 2 NF and RO = 3 $/m 2-8 -2-1 1 2 Membrane cost variations (%) -8-2 -1 1 2 MD membrane cost variations (%) -8-2 -1 1 2 Membrane cost variations (%) ER=Energy Recovery; HR=Heat Recovery systems
4 ELECTRICITY COST SENSITIVITY STUDY Reference: Electricity cost=3 $/kwh MF-NF-RO PLANTS MD PLANTS INTEGRATED SYSTEM 8 14 8 4-4 Without ER With ER 5% 3% Reference value electricity cost = 3 $/kwh Water cost ($/m 3 ) 13 12 11 Without HR With HR NO CHANGES 4-4 Without ER+HR With ER+HR 2% Reference value electricity cost = 3 $/kwh -8-2 -1 1 2 Electricity cost variations (%) 1-2 -1 1 2 Electricity cost variations (%) -8-2 -1 1 2 Electricity cost variations (%) ER=Energy Recovery; HR=Heat Recovery systems
SENSITIVITY STUDY 5 STEAM COST Reference: Steam=7 $/ton MD PLANTS INTEGRATED SYSTEM 12 6-6 Without HR With HR 12% Reference value steam cost = 7 $/ton 8 4-4 Without ER+HR With ER+HR 5% Reference value steam cost = 7 $/ton -12-2 -1 1 2 Steam cost variations (%) -8-2 -1 1 2 Steam cost variations (%) ER=Energy Recovery; HR=Heat Recovery systems
CONCLUSIONS & REMARKS The pressure-driven membranes were very sensitive to the changes in the feed concentration and the cost of electricity MD was very sensitive to changes in the steam costs The best tolerance to the variation of these parameters was obtained when using the integrated membrane system The integrated membrane system was very attractive for satisfying the ZLD concept
THANK YOU
ECONOMICAL INVESTIGATIONS Assumptions Plant availability, f 9 % Plant capacity, Q P 24, m 3 /day Plant life, n 2 years Membrane life 67 years Interest rate, i 5 % Fluxes UF flux = 9 L/m 2 h NF flux = 28 L/m 2 h RO flux = 15 L/m 2 h MD flux = 82 L/m 2 h MC flux = 68 L/m 2 h Efficiencies Pumps-motor combined efficiency = 75 Pressure exchanger efficiency = 95 Heat exchanger efficiency = 8 Costs Cost of MF membranes 9 $/m 2 Cost of NF and RO membranes 3 $/m 2 Electricity cost 3 $/kwh Steam cost 7 $/ton