International Conference on Renewable Energy Desalination
Tunis, 11.06.2012
Desalination systems powered by
solar energy
Dr. -Ing. Joachim Koschikowski Fraunhofer Institute for Solar Energy Systems ISE Heidenhofstr. 2, 79110 Freiburg [email protected]
e Dipl.-Ing. Marcel Wieghaus
SolarSpring GmbH
Hanferstr. 28, 79108 Freiburg
© Fraunhofer ISE
Outline
Introduction
Solar driven desalination
PV-RO
CSP-MED
Small thermally driven units
Membrane distillation
Conclusion
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Decrease of fresh water
resources due to:
Deepwelling ground water
levels
Intrusion of salt water
Draining of fossil ground
water reservoirs
Pollution of surface water
Introduction
Potential of solar energy e.g. 6kWh/(m²d)0.6 l oil /(m² d)220 l oil /(m² y)
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Challenging approach because:
Energy supply is not
constant during the course
of a year, during day and
night time and during
daytime even within seconds
intensity can change
Qualified technical staff for
operation and maintenance
is not available
Stand alone systems
Introduction
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6
Different approaches for the utilization of solar energy as the prime mover for desalination processes
RO: Reverse Osmosis
ED: Electro Dialysis
MSF: Multi stage flash
MED: Multi Effect Distillation
c
VC: Vapor Compression
STIL: Simple Solar Stil
MEH: Multi Effect Distillation
MD: Membrane Distillation
Solar energy for
desalination
Solar driven desalination
UF
MF
UV
Filtration and
Disinfektion
Desalination
Pumping Well / circul.
Efficiency high low
low
high
Com
ple
xity
Correlation between
efficiency and complexity:
As higher the efficiency as
higher the complexity of the
system
Solar driven desalination
Correlation between energy
costs and system efficiency:
As higher the costs of energy are
as higher the efficiency
(investment costs) can be
Energy costs high low
low
high
Syste
m e
ffic
iency
Solar energy is not for free because of significant investment costs !!!
Costs for water distribution must be considered (savings for distributed systems)!!!
Solar driven desalination
© Fraunhofer ISE
Different approaches for the utilization of solar energy as the prime mover for desalination processes
RO: Reverse Osmosis
ED: Electro Dialysis
MSF: Multi stage flash
MED: Multi Effect Distillation
c
VC: Vapor Compression
STIL: Simple Solar Stil
MEH: Multi Effect Distillation
MD: Membrane Distillation
Solar energy for
desalination
Modular technology for wide
range of capacities and
different applications
Solar driven desalination
© Fraunhofer ISE
10
PV-RO - stand alone system configuration
Systeme solar
Challenging approach
under development at ISE:
stand alone PV-RO
systems without batteries
Solar driven desalination – PV-RO
Advanced pressure
exchangers
© Fraunhofer ISE
Development of PV-driven
stand alone RO-systems
without batteries an
chemical pre-treatment
Capacity: 5 m³/d from seawater
28Tppm
Location of pilot plant : Cyprus
Number of RO mudules: 3
Pre-treatment: UF
No of PV-modules : 34
PV peak power = 7.65 kWp
Solar driven desalination – PV-RO
© Fraunhofer ISE
Advantages of PV-RO
High performance density
low energy demand with pressure recovery (3.5 -6 kWh/m³ for SWRO)
Modular set up applicable for a wide range of capacities
PV and RO system can be separated for “long” distances
Comprehensive R+D on RO membranes, modules and system components
Disadvantages of PV-RO
Significant sensitivity of RO-membranes against scaling and fouling
Limitation in salt concentration
Operation with alternating energy supply is not proven
Batteries as energy storage are expensive and very limited in lifetime
Product water quality is poor in single stage systems
Solar driven desalination – PV-RO
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13
Different approaches for the utilization of solar energy as the prime mover for desalination processes
c
Solar energy for
desalination
Large scale but also small
units are available
Solar driven desalination
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Concentrating solar power combined with MED:
Vapor of 60 to 69°C from the steam turbine is condensed in
the first stage of the MED plant
Solar driven desalination – CSP-MED
Fischer Ecosolutions 20 -100m³/day MED
plant
Source: Veolia Source: Fischer Ecosolutions
Fraunhofer ISE: System simulations
© Fraunhofer ISE
Advantages of CSP-MED
Utilization of low grade waste heat from CSP or other industrial sources
“Low” thermal energy demand is possible with a certain number of effects
Very robust system design
Components for large scale systems are state of the art
Product water is of very high quality
Disadvantages of CSP-MED
Energy demand is high compared to RO (1.5-2.5 kWhel/m³ +~60kWhth/m³)
Limitation in salt concentration due to scaling and corrosion
Cooling is necessary - air cooling for inland locations is inefficient
Mismatch of geographical and metrological site conditions for CSP and MED
Efficiency of the power plant is reduced by about10%
Solar driven desalination – CSP-MED
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16
Different approaches for the utilization of solar energy as the prime mover for desalination processes
c
Solar energy for
desalination
Technologies which are adapted
particularly to solar thermal low
grade heat supply
Solar driven desalination
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Simple solar still
Systems without heat recovery
loose the latent heat to the ambient
very low efficiency <~4 l/m² day
Solar driven desalination – small thermal
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Simplified Solar thermally driven MED system
developed by Soalrinstitut Jülich
6 -10 effects recover latent heat,
All effects are operated at ambient pressur
GOR ~3
Output about 10 -15 l/m²
Solar driven desalination – small thermal
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Solar driven desalination – small thermal
Multi Effect Humidification unit MEH
Developed by ZAE Bayern, TAS
and Tinox-MAGE
Range of
operation
The performance
of solar thermal
collectors is
decreasing with
operation
temperature, the
performance of
thermally driven
desalination
processes is
increasing
Performance optimization
Solar driven desalination – small thermal
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Advantages of adapted thermally driven small and medium size systems
Potential for good compromise between low complexity and good efficiency
Adapted system design for transient operation
Robustness
Up and downscaling is possible
Disadvantages of adapted thermally driven small and medium size systems
No “real” long term experience
Expensive compared to output (Solar system is about 50% of total costs)
Still not perfect match between complexity and efficiency
Development does not profit from improvements in large scale technology
Market for small units is not developed yet
Solar driven desalination – small thermal
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22
q
Driving force: Difference of water vapor pressure between both membrane boundary layers
Membrane distillation
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permeate
outlet
evaporator inlet evaporator outlet
condenser outlet condenser inlet
distillate outlet
external heat source
Membrane distillation
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permeate
outlet
evaporator inlet evaporator outlet
condenser outlet condenser inlet
distillate outlet
external heat source
1. preheating of cold feed water
kWTTcmQ pfeedrec 15)( 12
Membrane distillation
© Fraunhofer ISE
permeate
outlet
evaporator inlet evaporator outlet
condenser outlet condenser inlet
distillate outlet
external heat source
1. preheating of cold feed water
2. temperature gain by external energy
kWTTcmQ pfeedin 3)( 23
Membrane distillation
© Fraunhofer ISE
permeate
outlet
evaporator inlet evaporator outlet
condenser outlet condenser inlet
distillate outlet
external heat source
concept of internal heat recovery GOR~ 3-8
1. preheating of cold feed water
2. temperature gain by external energy
3. evaporation through membrane into permeate gap
cooling by latent heat of vaporisation and sensible heat losses
Membrane distillation
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Test cell for the investigation of:
Membrane performance
Channel configurations
Validation of single node simulation
models
Membrane distillation
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Development of MD-pilot-
desalination systems for sea and
brackish water using solar or waste
heat
Membrane distillation
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MD Compact system
Process design: Solar driven systems
Collector area: 6.8m²
Capacity: 150 l/day
Specific capacity: 17-22 l/m² d
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Nuber of Modules: 12 Hot Water Storage: Volume 12m³
Collector Area: 225 m²
Target Capacity: ~5000 l/d
Installation at Etosha Basin – North
Namibia
Membrane distillation
Ready installed MD System
© Fraunhofer ISE
Waste heat driven MD system in Pantelleria, Italy
Start of operation October 2010
Prime mover: Waste heat from power plant
Target capacity: 5m3/day
Raw water source: Sea water 28.000ppm
Operation mode: 24h / day (no heat storage)
Membrane distillation
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Solar thermally driven MD system in Gran Canary, Spain
Start of operation, March 2011
Prime mover: Solar only (180m² flat plate collectors)
Target capacity: 3.5 m3/day
Raw water source: Sea water 35.000ppm
Operation mode: <16h / day (with heat storage)
Membrane distillation
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Advantages of Membrane Distillation MD
Good compromise between efficiency and complexity
Feed temperature, depending on MD configuration, can be between
50 and 90°C low grade waste heat or solar thermal collectors can be used
Low sensitivity against fouling and scaling due to membrane properties and flow
configuration
Transient operation in temperature and flow rate is possible in a wide range
High salinities can be treated depending on system configuration (zero liquid
discharge)
Disadvantages of Membrane Distillation MD
Specific energy demand is high compared to RO (2kWh/m³el, 80kWh/m³th)
Specially developed MD – membranes are not available
Long lifetime is still not proven
No large scale industrial systems in the market today
Solar driven desalination
© Fraunhofer ISE
All desalination technologies have advantages and disadvantages and
must be chosen with respect to particular boundary conditions
Small and medium size-, in particular stand alone solar driven desalination
systems, are still in the developing ore pilot phase
Long term experience for realistic life time estimations must be conducted
also with respect to the calculation of realistic water production costs
Today solar driven desalination systems are almost not on the market
because they are considered as “too expensive” but there is already a huge
demand
Cost savings due to decentralized production (no transportation, no grid,
no subsidies for conventional energy) must be considered more carefully
for the comparison of water production costs
Conclusion