2nd CSP Training series : solar desalination (1/2)

Dr. JuliDr. Juliáán Blancon Blanco
Plataforma Solar de AlmeriaPlataforma Solar de Almeria
julian.blanco@psa.esjulian.blanco@psa.es
SOLAR DESALINATIONSOLAR DESALINATION
TECHNOLOGIESTECHNOLOGIES
Solar Desalination Webinar #1Solar Desalination Webinar #1
14 October 201014 October 2010

SOLAR DESALINATION TECHNOLOGIES
LEONARDO WEBINAR, 14 OCTOBER 2010
1. DESALINATION FUNDAMENTALS
2. LOW PRODUCTION SOLAR
DESALINATION TECHNOLOGIES
3. MULTI-EFFECT DISTILLATION
WITH SOLAR ENERGY
4. HYBRID SOLAR-GAS MED
DESALINATION SYSTEMS
5. CASE STUDY DESIGN
PRESENTATION PROGRESSPRESENTATION PROGRESS

DESALINATION
PROCESSES
Thermal energy
Mechanic energy
Evaporation
Chemical energy
Multi-Stage Flash Distillation (MSF)
Thermal Vapor Compression (TVC)
Solar Distillation
Freezing
Reverse Osmosis (RO)
Mechanical Vapor Compression (MVC)
Membrane distillation
Multi-Effect Distillation (MED)
Hydrate formation
Electrodialysis (ED)
Ionic exchange
Crystallization
Filtration and evaporation
Evaporation
Selective filtrationElectric energy
Filtration
Exchange
DESALINATION PROCESSESDESALINATION PROCESSES

THERMAL DISTILLATIONTHERMAL DISTILLATION
Parameters to measure energy efficiency of thermal
distillation processes:
Gain Output Ratio (G.O.R.): kg of distillate produced for
every kg of steam supplied to the distillation unit
Performance Ratio (PR): kg of distillate produce for every
2326 kJ of thermal energy supplied to the distillation unit

3 3
MJ kWh
10 232 64.6
m m
PR = = =

China
4.0%
Qatar
3.0%
Japan
2.0%
Libya
2.0%
Rest of the world
29.0%
USA
13.0%
Saudi Arabia
17.0%
Algeria
4.0%
UAE
13.0%
Spain
8.0%Kuwait
5.0%
Source: GWI (2008)
Five countries (Saudi Arabia, UAE, United
States, Spain and Kuwait) have, today,
56% of the total share of world desalted
water production.
WORLDWIDEWORLDWIDE CAPACITYCAPACITY

DISTRIBUTION BYDISTRIBUTION BY PROCESSPROCESS
Source: GWI (2006)

DISTRIBUTION BYDISTRIBUTION BY PROCESSPROCESS
Thermal Distillation
37.0%
Reverse Osmosis
56.0%
ED and others
7.0%
Source: GWI (2008)

The desalination mechanism of a solar still is similar to that of nature.
A shallow pool of brackish or seawater absorbs solar energy and as a result vapor
of fresh water is formed in the space above the water.
Vapor condenses on the inside of the glass cover and is collected in a side trough.
A conventional solar still has a simple geometry. The still is formed of a square
or rectangular box, which is equipped with a sloped glass cover.
The top cover is transparent to allow passage of solar energy (radiation).
SOLAR STILLS
The walls and base of the box must be
made from materials that can withstand
the environmental influences (wood,
plastic, or tolerant metal).

Advantages
Simple Design
Affordable Investment
Proven technology
Obstacles
Relatively low efficiency
High ground area demand
Limited system capacity (100 l/d)
SOLAR STILLS
1970: U.S. Dept. of the Interior, Office of Saline Water R&D Report. “Manual on solar distillation
of saline water” (S.G.Talbert, J.A.Eibling and G.O.D.Löf)
Average production: 3.26 l·m-2·day-1 → ~ 1.2 m3·m-2·year-1

In 1870 the first American patent on solar distillation by Wheeler and Evans,
describing the basic operation of the solar stills.
In 1872 Carl Wilson designed and built the first large solar still in Las
Salinas, Chile.
Effluents from a saltpeter (KNO3)
mine, (salinity 140g/kg).
64 bays, 4450 m2 surface, 7896
m2 of land
22.7 m3/day. Operated for 40
years.
Wood and timber frameworks.
from: Delyannis, Solar Energy 75, 357-366, 2003
SOLAR STILLS

SOLAR STILLS
The efficiency of the solar still is low as a result of the loss of
latent heat of condensation through the cover.
Even when the latent heat is reused (multi-effect stills) the
performance is relatively low.
Daily production rate not larger than 3-5 l/m3·day
Large durable-type, glass-covered solar stills could produce
water on a consistent, dependable basis for a cost between 0.8
and 1.1 $/m3
Thermal inefficiencies can be reduced by separating these
functions into different components
→ humidification-dehumidification desalination

The H-DH (Humidification-Dehumidification) processes are based on the fact that
air can be mixed with important quantities of vapor. The vapor carrying capability
of air increases with temperature, i.e., 1 kg of dry air saturated with vapor can carry
additional 0.26 kg of water vapor (about 208 kJ/kg) when its temperature increases
from 30°C to 80°C.
0.5974 kg/m³169.4 J/g2256.3 J/g419.0 J/g101.32 kPa100 °C
0.4232 kg/m³165.5 J/g2282.6 J/g376.6 J/g70.10 kPa90 °C
0.2931 kg/m³161.5 J/g2307.7 J/g334.6 J/g46.12 kPa80 °C
0.1979 kg/m³157.3 J/g2332.9 J/g292.7 J/g31.15 kPa70 °C
0.1300 kg/m³153.0 J/g2357.6 J/g250.8 J/g19.90 kPa60 °C
0.08285 kg/m³148.7 J/g2381.4 J/g209.0 J/g12.33 kPa50 °C
0.05107 kg/m³144.2 J/g2404.9 J/g167.2 J/g7.370 kPa40 °C
0.03036 kg/m³139.7 J/g2427.9 J/g125.6 J/g4.242 kPa30 °C
0.01728 kg/m³135.1 J/g2450.9 J/g83.8 J/g2.536 kPa20 °C
0.009398 kg/m³130.5 J/g2473.5 J/g42.0 J/g1.227 kPa10 °C
0.004845 kg/m³126.0 J/g2496.5 J/g0.00 J/g0.612 kPa0 °C
ρ of vapor∆vapW∆vapHH of liquidPressureTemp.
0.5974 kg/m³169.4 J/g2256.3 J/g419.0 J/g101.32 kPa100 °C
0.4232 kg/m³165.5 J/g2282.6 J/g376.6 J/g70.10 kPa90 °C
0.2931 kg/m³161.5 J/g2307.7 J/g334.6 J/g46.12 kPa80 °C
0.1979 kg/m³157.3 J/g2332.9 J/g292.7 J/g31.15 kPa70 °C
0.1300 kg/m³153.0 J/g2357.6 J/g250.8 J/g19.90 kPa60 °C
0.08285 kg/m³148.7 J/g2381.4 J/g209.0 J/g12.33 kPa50 °C
0.05107 kg/m³144.2 J/g2404.9 J/g167.2 J/g7.370 kPa40 °C
0.03036 kg/m³139.7 J/g2427.9 J/g125.6 J/g4.242 kPa30 °C
0.01728 kg/m³135.1 J/g2450.9 J/g83.8 J/g2.536 kPa20 °C
0.009398 kg/m³130.5 J/g2473.5 J/g42.0 J/g1.227 kPa10 °C
0.004845 kg/m³126.0 J/g2496.5 J/g0.00 J/g0.612 kPa0 °C
ρ of vapor∆vapW∆vapHH of liquidPressureTemp.
H-DH DESALINATION PROCESS

Air heated
HDH system
Water heated
HDH system
Air-heated systems have higher energy consumption than water-heated systems,
because energy can be recovered from water in the humidifier but not from the air

Natural air convection is normally preferred as air
flowrate has an insignificant effect on unit productivity.
Water flowrate is important on unit performance.
Thermal storage and a 24-h operation of the units is
required to improve productivity.

Courtesy of TiNOX GmbH
(Munich, Germany)
GOR of experimental units without
thermal storage were between 3 and
4.5
Pilot plants with direct flow through the
collectors has been working almost
without any maintenance or repair for
more than 7 years on Canary Islands
of Fuerteventura (TINOX).
At laboratory conditions a GOR higher
than 8 at steady-state conditions was
achieved (ZAE Bayern).
Typical daily distillate production is: 10
to 20 L/m2 (of solar collector) and day.
20 to 30 L/m2 if 24-h run and thermal
storage is implemented

Membrane Distillation is an
evaporative process in which water
vapour, driven by a difference in
vapour pressure, permeates through
a hydrophobic membrane, thus
separating from the salt water phase.
The separation effect of these
membranes is based on the
hydrophobicity of the polymer
material constituting the membrane.
Molecular water in the form of steam
can pass through the membrane.
Once the vapour has passed through
the membrane, it can be extracted or
directly condensed in the channel on
the other side of the membrane.
MEMBRANE DISTILLATIONMEMBRANE DISTILLATION

Membrane distillation system with internal heat recovery

A possible design for a MD module is
the formation of channels by spiral
winding of membrane and condenser
foils to form a spiral wound module.
• 30x40 cm, height 85 cm
• Thermal consumption: 90-200 kWh/m3
• Distillate production: 10-30 L/h (80º C and 300 L/h feed flow)
• Wide range of operation temperatures (50-85ºC)
• Favor behavior under dynamic operation conditions
• No pre-treatment of feed water
• High quality of distillate (5-50 µS/cm)
• Modular set-up. Systems from 100-20000 L/day
COMMERCIAL MD SYSTEMSCOMMERCIAL MD SYSTEMS

Good potential to solar driven stand-alone operating desalination systems.
Advantages of MD process:
Process operating temperature in the range of 60 to 80°C.
Alternative energy sources such as solar energy/waste heat, possible.
Chemical feed water pre-treatment is not necessary.
Intermittent operation of the module is possible. Contrary to RO, there is no
danger of membrane damage if the membrane falls dry.
100% theoretical salt rejection.
No operating pressure is required.
The membranes used in MD are tested against fouling and scaling.
Less space and equipment requirements compared to those of thermal
processes that result in capital savings.
Theoretically system efficiency and high product water quality are independent
from the salinity of the feed water.

Main disadvantages to be overcome:
High thermal consumption (inefficiencies) bigger solar collector area.
Lack of specific membranes designed for MD purposes (currently used
designed for microfiltration)
Possible wetting lower distillate quality
Experimental Membrane
Distillation facility at PSA

Source: García-Rodríguez, Desalination 143 (2002), pp. 103-113
WORLDWIDE EXPERIENCESWORLDWIDE EXPERIENCES

External thermal energy is supplied to the evaporator resulting in a partial
evaporation of the seawater.
The vapor goes to the condenser, where it turns into liquid (distillate) production and
the latent heat released is transferred to the refrigerant fluid. Feed water is used as
refrigerant (at ambient temperature) to reduce the external heat supply.
The PR is around 1 and most of the energy supplied to the evaporator is released to
the environment in the condenser.

Abu Dhabi, UAE
MED Plant (18 effects)
120 m3/day
Solar collectors: evacuated tube
Useful absorption area: 1862 m2
Thermal storage: 300 m3 (water)
Performance Ratio = 12.4
WORLDWIDE EXPERIENCESWORLDWIDE EXPERIENCES

CIEMAT (Spain) and DLR (Germany) decided in 1987 to develop an
efficient solar thermal desalination system, thus initiating the so-called
Solar Thermal Desalination (STD) Project carried out at the Plataforma
Solar de Almería (PSA) until 1994.
A solar desalination system was implemented at the PSA, composed by:
A 14-effect Multi-Effect Distillation (MED) plant
A solar parabolic-trough collector field
A thermocline thermal energy storage tank
The system operates with a synthetic oil (Santotherm 55) as heat transfer
fluid. The solar energy is thus converted into thermal energy in the form
of sensible heat of the oil, and is then stored in the thermal oil tank.
Hot oil from the storage system provides the MED plant with the required
thermal energy.
PLATAFORMA SOLAR STD PROJECTPLATAFORMA SOLAR STD PROJECT

The solar collector field consists of one-axis tracking parabolic trough
collectors with a total aperture area of 2672 m², model Acurex-3001. The
daily thermal energy delivered by the collector field is about 6.5 MWth·h,
but the daily thermal energy requirement of the desalination plant is less
than 5 MWth·h for 24-hour daily operation.

The distillation plant installed at the PSA is a
forward-feed, vertically-stacked, multi-effect
distillation unit with 14 effects.

PerformancePerformance Ratio: 9.4Ratio: 9.4 –– 10.410.4

PerformancePerformance Ratio: 12Ratio: 12 -- 1414

AQUASOL SYSTEM COMPONENTSAQUASOL SYSTEM COMPONENTS
14 effects
MED plant
(150 kWth, 2.5
m3/h distillate
prod.)
Stationary
CPC solar
collector field
Thermal
storage
system (water,
24 m3 )
Double-effect
(LiBr-H2O)
absorption
heat pump
Smoke-tube
gas boiler
Main sub-system
components are:

Three desalination system operating modes are possible depending on
where the desalination unit energy supply comes from:
Solar-only mode: energy to the first distillation effect comes
exclusively from thermal energy from the solar collector field.
Fossil-only mode: the double-effect heat pump supplies all of the
heat required by the distillation plant.
Hybrid mode: the energy comes from both the heat pump and the
solar field. Two different operating philosophies are considered:
The heat pump works continuously 24 hours a day with a 30%
minimum contribution.
Start-up and shutdown of the pump when requested,
depending on the availability of the solar resource.
PSA MED OPERATING MODESPSA MED OPERATING MODES

MED OPERATION: SOLAR MODEMED OPERATION: SOLAR MODE

MED OPERATION: FOSSIL MODEMED OPERATION: FOSSIL MODE

MED OPERATION: HYBRID MODEMED OPERATION: HYBRID MODE

The solar field is made up of 252 stationary solar collectors (CPC Ao Sol 1.12x)
with a total surface area of 500 m2 arranged in four rows of 63 collectors.
CPC SOLAR COLLECTOR FIELDCPC SOLAR COLLECTOR FIELD

The thermal storage system is made up of two interconnected 12-m3-capacity water
tanks. This storage volume is based on the response time required by the gas boiler
and the DEAHP to reach nominal operating conditions
THERMAL STORAGE TANKSTHERMAL STORAGE TANKS

150 kW
78 kW
2 kW
70 kW
ABSORPTION HEAT PUMPSABSORPTION HEAT PUMPS

The inclusion of a
Double Effect
Absorption Heat
Pump make
possible a
reduction up to
50 percent of the
overall energy
consume with
respect to
conventional MED
plants. However, it
requires higher
steam
temperature
(180ºC)

70 kW
M.E.D. Plant
78 kW 150 kW
72 kW
Heat Pump
35 65 180
Temperature [ºC]
M.E.D. Plant
Heat Pump
35 65 180
Temperature [ºC]
M.E.D. PlantM.E.D. Plant
Heat PumpHeat Pump
35 65 180
Temperature [ºC]
2 kW
70 kW
78 kW 150 kW
72 kW
Heat PumpHeat Pump
35 65 180
Temperature [ºC]
Heat PumpHeat Pump
35 65 180
Temperature [ºC]
Heat PumpHeat Pump
35 65 180
Temperature [ºC]
2 kW
The double effect absorption heat pump increases the energy efficiency of the
distillation process by making use of the 35ºC saturated steam produced in the last
MED plant effect, which otherwise involve the loss of the energy in the evacuation of
the cooling fluid used for its condensation.

LiBrLiBr--HH22O THERMODYNAMIC CYCLEO THERMODYNAMIC CYCLE
Qg = 72 kW (gas)
Qe = 78 kW (LP steam)
Qa + Qc = 150 kW (MED)

EXPERIMENTAL RESULTSEXPERIMENTAL RESULTS
Day 1 Day 2

Distillate
production
and global
thermal
energy
consumed
by
AQUASOL
plant in
SOLARSOLAR--
ONLYONLY
MODEMODE
Average
PR = 10.07
SOLARSOLAR--ONLY MODEONLY MODE

Distillate
production
and global
thermal
energy
consumed
by
AQUASOL
plant in
FOSSILFOSSIL--
ONLYONLY
MODEMODE
FOSSILFOSSIL--ONLY MODEONLY MODE

Performance ratio of the AQUASOL
plant in Fossil-only mode
PERFORMANCE RATIOPERFORMANCE RATIO

TVC-MED Plant
Unit capacity = 14.400 m³/day
Number of units = 4
Annual availability = 95%
Overall annual production = 19.972.800 m³
GOR = 11.3
Number of effects = 11
Heat supply: superheated steam at 330°C and 4.56 bar
DESIGN OF DESALINATION PLANTDESIGN OF DESALINATION PLANT

LOCATION AND PARAMETERSLOCATION AND PARAMETERS
Annual direct normal irradiation = 1990 kWh/m² year

Live steam enthalpy (330°C, 4.56 bar) = 3127.56 kJ/kg
First effect temperature: 70°C
Saturated liquid water = 293.02 kJ/kg
(GOR) = 11.3
Unit capacity = 14.400 m³/day
41.81MWin out
MED
h h
P CAP
GOR
−
= × =
4 167.23MWu MEDP P= × =
DESIGN OF DESALINATION PLANTDESIGN OF DESALINATION PLANT
Power consumption:
1.2 kWh/m³
Chemical pretreatment: Antifoaming, Antiscaling Acid cleanings

Solar field temperature
Oil inlet temperature =
250°C
Oil outlet temperature =
350°C
Geographical coordinates
Latitude = 37.2406° N
Longitude = 1.7899° W
DESIGN OF THE SOLAR SYSTEMDESIGN OF THE SOLAR SYSTEM
Solar (Euro)trough field:
- Collectors per row = 33
- Number of rows = 171171
- Total aperture area = 279,585 m279,585 m22
Incidence angle at design point
ϕ = 13.92°
Meteorological data at design point
Normal direct irradiance = 886
W/m²
Ambient temperature = 32°C

SOLAR THERMAL MED PLANTSOLAR THERMAL MED PLANT

Thermal
oil/water heat
exchanger
Generator
Degasifier
Steam Turbine
Vapor at 97 bar/395 ºC
Vapor at 17 bar/225 ºC
G
Water at 70ºC
Vapor at 70ºC
Oil at 295 ºC
Oil at 400 ºC
Oil expansion
deposit
50 mbar
35ºC
0,3 bar
70ºC
Distilled Seawater
Brine
ThermalStorage
SolarCollectorField
Auxiliary
boiler
SOLAR THERMAL DUAL PLANTSOLAR THERMAL DUAL PLANT

ThankThank
you veryyou very
much formuch for
youryour
attentionattention

2nd CSP Training series : solar desalination (1/2)

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