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
Thermal
Desalination
MSF
MED
Membrane
Desalination
EDR
RO
Energy
consumption
kWh/m3
Feed TDS
(mg/L)
Product
TDS
(mg/L)
Required
space
10.3 – 13
20,000
–
500,000
<10
Very large
6.5 – 8.5
20,000
–
500,000
<10
Large
0.6 – 4.2
3,000
–
12,000
<10
Small
3.5 – 3.8
5,000
–
50,000
<500
Small
•Ettouney, H.M ., El-Dessouk y, H.T., Faibish, R.S., et. al., “Evaluating the Econom ics of Desalination”,
Chem ical Engineering P rogress, pp. 32 – 39, Decem ber 2002
•I DA W orldw ide Desalting P lants I nventory Report No 18; published by W angnick Consulting 2004
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 40%
95%
48%
Raw
Seawater
Filtered
Seawater
Filtered
NF
Seawater
Product
95%
70%
MF
NF
50%
60%
Potable
water
RO
MF Retentate
NF Retentate
Salt Crystals
MDC
Brine
Heat source
Potable water
Concentrate
MD
Heat source
ECONOMICAL INVESTIGATION
ECONOMICAL INVESTIGATIONS
Reference values for cost analysis
MF Membrane cost
90 $/m2
NF and RO Membrane cost
30 $/m2
Membrane life
6.7 years
Electricity cost
0.03 $/kWh
Steam cost
7 $/ton
Plant capacity
24,000 m3/day
ECONOMICAL INVESTIGATIONS
FLOW & WATER COST
Feed
3000
Concentrate
2506
1.27
1.2
1.14
Flow (m3/h)
2105
2000
0.8
1506
1500
0.62
1250
1191
1124
1000 0.51
1068
1000
0.4
500
250
68
0
MF-RO MF-NF-RO
MD
131
14
MF-NF-RO MF-NF-RO MF-NF-RO
+MC+MC +MD+MD
+MC+MD
0
.
2500
1.29
1.27
Total Water Cost ($/m3)
Water cost
SENSITIVITY STUDY
1.
2.
3.
4.
5.
Water Recovery (Yield)
Feed Concentration
Membrane Cost
Electricity Cost
Steam Cost
SENSITIVITY STUDY
1. WATER RECOVERY (YIELD)
RO Recovery in MF-NF-RO
-10
0
1.2
8
0
0.6
-8
0.5
-20
-10
0
10
20
Without ER
With ER
8
1.0
0
0.8
-8
0.6
-16
45
50
55
RO water recovery (%)
60
2.0
16
10%
Water cost ($/m3)
With ER
Water cost variations (%)
Without ER
0.7
40
MD water recovery variations (%)
RO water recovery variations (%)
20
16
10%
Water cost ($/m3)
10
-16
50
60
RO water recovery (%)
ER=Energy Recovery; HR=Heat Recovery systems
70
-20
-10
0
10
20
16
10%
Without HR
With HR
1.8
Water cost ($/m3)
-20
Water cost variations (%)
Water recovery variations (%)
0.8
MD Recovery in MD
alone
8
6%
1.6
0
1.4
-8
1.2
Water cost variations (%)
RO Recovery in MF-RO
-16
1.0
70
80
90
MD water recovery (%)
SENSITIVITY STUDY
2. FEED CONCENTRATION
MD PLANTS
.
1.4
0.7
Without ER
1.8
15%
With ER
Without HR
Without ER+HR
0.5
16%
0.4
NO CHANGES
1.2
1.1
Seawater
Brackish
Water cost ($/m3)
Seawater
With ER+HR
1.3
.
0.6
Water cost ($/m3)
With HR
.
Water cost ($/m3)
INTEGRATED SYSTEM
1.6
3%
Brackish
0.3
1.0
20
Seawater
1.2
Brackish
10
2%
1.4
.
MF-NF-RO PLANTS
.
.
30
40
Feed Concentration (g/L)
50
1.0
10
20
30
40
Feed Concentration (g/L)
ER=Energy Recovery; HR=Heat Recovery systems
50
10
20
30
40
Feed Concentration (g/L)
50
SENSITIVITY STUDY
3. MEMBRANE COST
MF-NF-RO PLANTS
MD PLANTS
INTEGRATED SYSTEM
8
8
4
0
.
0
6%
With HR
.
5%
With ER
4
Water cost variations (%)
Without HR
Without ER
Water cost variations (%)
8
Water cost variations (%)
Reference: MF=90 $/m2, NF & RO=30 $/m2
Reference value
MF = 90 $/m2
NF and RO = 30 $/m2
-4
Reference value
MD = 90 $/m2
-4
-8
-8
-20
-10
0
10
Membrane cost variations (%)
20
Without ER+HR
With ER+HR
4
2%
0
Reference value
MF and MD = 90 $/m2
NF and RO = 30 $/m2
-4
-8
-20
-10
0
10
20
MD membrane cost variations (%)
ER=Energy Recovery; HR=Heat Recovery systems
-20
-10
0
10
Membrane cost variations (%)
20
SENSITIVITY STUDY
4. ELECTRICITY COST
MF-NF-RO PLANTS
MD PLANTS
INTEGRATED SYSTEM
8
1.4
8
3%
.
0
With HR
Reference value
electricity cost = 0.03 $/kWh
-4
1.3
NO CHANGES
1.2
1.1
-20
-10
0
10
Electricity cost variations (%)
20
2%
0
Reference value
electricity cost = 0.03 $/kWh
-4
-8
1.0
-8
With ER+HR
4
.
4
Water cost variations (%)
With ER
Without ER+HR
Without HR
5%
Without ER
Water cost ($/m3)
Water cost variations (%)
Reference: Electricity cost=0.03 $/kWh
-20
-10
0
10
Electricity cost variations (%)
ER=Energy Recovery; HR=Heat Recovery systems
20
-20
-10
0
10
Electricity cost variations (%)
20
SENSITIVITY STUDY
5. STEAM COST
Reference: Steam=7 $/ton
INTEGRATED SYSTEM
MD PLANTS
8
With HR
6
0
Reference value
steam cost = 7 $/ton
-6
-12
Without ER+HR
With ER+HR
4
5%
0
.
12%
Water cost variations (%)
Without HR
.
Water cost variations (%)
12
Reference value
steam cost = 7 $/ton
-4
-8
-20
-10
0
10
20
Steam cost variations (%)
ER=Energy Recovery; HR=Heat Recovery systems
-20
-10
0
10
Steam cost variations (%)
20
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
attractive for satisfying the ZLD concept
very
THANK YOU
ECONOMICAL INVESTIGATIONS
Assumptions
Plant availability, f
Plant capacity, QP
Plant life, n
Membrane life
Interest rate, i
90 %
24,000 m3/day
20 years
6.7 years
5%
Fluxes
UF flux = 90 L/m2 h
NF flux = 28 L/m2 h
RO flux = 15 L/m2 h
MD flux = 8.2 L/m2 h
MC flux = 6.8 L/m2 h
Efficiencies
Pumps-motor combined efficiency = 0.75
Pressure exchanger efficiency = 0.95
Heat exchanger efficiency = 0.8
Costs
Cost of MF membranes
Cost of NF and RO membranes
Electricity cost
Steam cost
90 $/m2
30 $/m2
0.03 $/kWh
7 $/ton