desalination systems powered by solar energy

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

[email protected]

© 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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4

Grid connected systems Stand alone systems

Introduction

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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


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


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)!!!


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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


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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

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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


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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


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13


c

Solar energy for

desalination

Large scale but also small

units are available


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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

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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


c

Solar energy for

desalination

Technologies which are adapted

particularly to solar thermal low

grade heat supply


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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


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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


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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


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22

q

Driving force: Difference of water vapor pressure between both membrane boundary layers


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permeate

outlet

evaporator inlet evaporator outlet

condenser outlet condenser inlet

distillate outlet

external heat source


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permeate

outlet



distillate outlet


1. preheating of cold feed water

kWTTcmQ pfeedrec 15)( 12


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permeate

outlet



distillate outlet



2. temperature gain by external energy

kWTTcmQ pfeedin 3)( 23


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permeate

outlet



distillate outlet


concept of internal heat recovery GOR~ 3-8


2. temperature gain by external energy

3. evaporation through membrane into permeate gap

cooling by latent heat of vaporisation and sensible heat losses


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Test cell for the investigation of:

Membrane performance

Channel configurations

Validation of single node simulation

models


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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


Ready installed MD System

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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)


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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)


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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


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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

desalination systems powered by solar energy

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