Technion - Israel Institute of Technology
Grand Water Research Institute
Rabin Desalination Laboratory
Chemical Engineering Department
ENERGY ISSUES
IN DESALINATION TECHNIQUES
Dmitry Lisitsin, David Hasson and Raphael Semiat
Energy Forum - Energy in the Water Sector
Technion, November 2008
TOPICS
What is the energy demand for
water desalination? Can we reduce
it dramatically?
Desalination wastes energy and
pollutes the environment?
REVERSE OSMOSIS
Product tank
Feed
water
Low pressure pump
Pre-treatment
MembranesPost Treatment
Product water
High pressure pump
To concentrate
disposal
Energy recovery unit
Concentrate
By now, RO is still the most cost effective & the least
energy consuming technique for water desalination
Sea water RO desalination is limited by the high osmotic
pressure of the concentrate
Brackish water RO desalination is limited by the precipitation of
scaling salts on the membrane surface
Power usage in RO seawater plant with partial
second stage
High pressure pumps, 1st
pass, 80.6%
High pressure pumps,
2ndt pass, 3.8%
Product transfer pumps, 6.7%
Pretreatment
system, 2.6%
Seawater supply,
4.5%
Miscellaneaus, 1.8%
ENERGY DEMAND FOR DESALINATION
Reverse Osmosis
High pressure pumps comprise most of the energy demand for sea
water RO desalination
Source Technique
Heat requirements
KWh/m3
(Thermal)
Electricity
required
KWhe/m3
TOTAL
demand
KWhe/m3
Blank et al. (2006)
RO - 4-6 4-6
MSF 40-120 (Thermal) 2.5-5 12-58
MED 30-120 (Thermal) 2-2.5 8-58
El-Sayed (2001) MSF variations 34-102 2-2.2 17-47
Ophir & Lukiec (2007) MED 4.8 1.2 6
Glueckstern, (2004)
MED 6-12
MSF 10-16
RO 3.8
Wilf (2004) RO 3-4
ENERGY DEMAND FOR DESALINATION
Comparison of different desalination techniques
100 KWhe = 21 kg Gas
= 18 kg Gasoil
= 19 kg Heavy fuel
= 25 kg Coal
Dramatic cost reduction of desalinated water in last
20 years was mostly governed by the reduced specific
power consumption and plant size increase.
CAN WE FURTHER REDUCE THE
ENERGY CONSUMPTION?
Can we reduce power consumption further by 50%,
75% or even more?
RO case
CAN WE FURTHER REDUCE THE
ENERGY CONSUMPTION?
Current energy
consumption
~ 4 kWhe/m3
Minimal energy needed to separate a
component from binary solution.
For 50% recovery sea water desalination:
1.09 kWhe/m3
Energy requirements besides the
separation process: sea water supply,
product transfer, pretreatment etc.
RO case
Irreversible energy losses (can be reduced
by better process design, pressure exchange
units, improved membrane performance)
Desalination wastes energy and pollutes the environment
ENERGY “WASTED” BY DESALINATION
CoalHeavy
fuelGasoilGas
45.25.64.7kWhe/kgfuel
For large power plant
1.21.51.61.3m3
water/kgfuel
For large desalination plant
What can I do with energy “wasted” to produce 1 m3 of
desalinated sea water?
I can drive for 2-6 km (depends on car fuelconsumption)
I can operate my AC for 1.4 hr (2.5 kWh single
room air conditioner)
ENERGY “WASTED” BY DESALINATION
Household Energy Consumption
A typical Israeli family consumes:
water at a rate of 18 m3/month
1200 kWh of electricity /month
160 liter Gasoil/month (by driving 1500 km/month)
~ 150 kWht (fuel value)
~ 2670 kWht (fuel value)
~ 1500 kWht
ENERGY EQUIVALENT
Can we save 3.4% in our household energy consumption?
Assuming desalination water usage for household…
Energy “wasted” by desalination/ total energy consumption - 3.4%
ENERGY “WASTED” BY DESALINATION
Compared to overall Israel energy demand
500 MCM/year of desalinated water production will
comprise more than 20% of overall Israel water demand.
In terms of kilo watts: ~ 200 MW (3.5 kWh/m3)
~ 2% of maximal electricity production capacity
Less than 5% of Israel average energy demand
CONCLUSIONS
RO is the most cost effective & the least energy
consuming technique for desalination
Only marginal energy reductions are attainable in
RO.
Future renewable energy sources would be
environmentally beneficial also for desalination.
RO is affordable economically and
energetically
Q U E S T I O N S ?
14
Solar Desalination
Aqaba Jordan
Sept 2005
SOLAR ENERGY IN SEA WATER DESALINATION
Power production cost –
Reaches affordable values
Investment cost –
Still too high
Steam taken from power
plant for thermal desalination
Simplified diagram of steam engine for electricity production
Condensated steam from
thermal desalination plant
Energy utilized by thermal desalination plant,
otherwise available for electricity production
