Present and Future Trends in
Thermal Desalination with Possible
Solar Application
Mohamed Darwish
Qatar Environment and Energy Research
Institute, Doha, Qatar
www.qeeri.org.qa KAUST, 2013
Content
• Current large capacity Thermal Desalting systems
• MSF and TVC/ME Thermal Energy consumption
• Recent advances in MSF and TVC/ME
• Raising the TBT for MSF by Nano filtration
• Modifying TVC/ME by raising TBT and number of effects
• Using MVC in place of TVC
• Feasibility of solar applications
Large capacity thermal desalting systems
• Multi Stage Flash (MSF), most used in GCC.
• Reliable, mature, more than 50y experience in
design, operation, material selection, maintenance.
• Largest unit capacity 20 MIGD, (in Ras Al Khaiir)
• Thermal Vapor Compression (TVC) combined with
conventional Multi Effect (TVC/ME)
• Up to 8 MIGD capacity, TBT = 70 C
First MSF unit was one MIGD in Kuwait in 1960
Capacity reached 20 MIGD/unit, GR = D/S = 89,
Specific thermal energy, Q/D = 260 MJ/m3, TBT = 90 112C
Requires steam at 117oC saturated T.
Pumping energy 3.5-4 kWh/m3
One of 8 MSF units for the Ras Al Khair , SA , total cost $ 1.76 B
Capacity/unit = 91,000 t/d (20 MIGD), $11M/MIGD
123 m (l)x33.7 m (w), weighs 4,150 t
Distillate water
Vapor
Seawater
Brine
D = 200.2 [kg/s]
B6 = 400.4 [kg/s]
D1 = 24.62 D2 = 23.59 D3 = 23
D1 = 24.62 D2 = 23.59 D3 = 23
D4 = 21.48 D5 = 19.13 D6 = 17.21
Df = 10.15 [kg/s]
Ds = 12.3 [kg/s]
T1 = 62.8
T1 = 62.8 T2 = 59
T2 = 59 T3 = 55.2
T3 = 55.2
T4 = 51.4 T5 = 47.6 T6 = 43.8
F = 600.7 [kg/s]
Mc = 1031 [kg/s]
t1. = 55.2
t1. = 55.2
t2. = 51.4
t2. = 51.4
Ds = 12.3 [kg/s]
Ated = 333.7 [m2/kg/s]
GR = 8.139
MIGD = 3.803
Qd = 300.6 [kJ/kg]
Ad = 76.71 [kJ/kg]
Flow sheet diagram of Al-Taweelah A1 ME-TVC desalination plant
GR= D/S = 8-10
LP Steam Supply 2.5-3 Bar (started with boiler and at 20 bar)
Pumping power 2 KWh/m³, compared to 4 for MSF
26-Apr-15 10
• No MSF units built outside GCC for long time
• Shuaiba Barge, 52,000 m3/day (14 MGD) SWRO
• 2-pass, 5,656 (8” elements), output TDS <100 ppm
• Hamma SWRO in Algiers, 200,000-m3/d,
Recovery ratio 40% 44.5%.
• Perth SWRO in Australia, 143,000 m3/d, Wind
operated plant by 83 MW wind farm. (48 WT)
• 11 SWRO plants planned in California, 1.117
Mm3/d.
26-Apr-15 13
MSF and TVC/ME Consumed Energy
• In MSF and ME, steam supplied few T 7oC above TBT,
say at 117oC
• TVC can be at higher T as steam operate ejector
• Better generate steam at HP and T (as in PP), expands it in
ST, producing work before inlet to DS units at relatively LP
• This saves about 50% of fuel energy
• Required thermal energy 240-300 kJ/kg
• Expressed as Gain ratio D/S
• 4 kWh/m3 for MSF and 2 kWh/m3 for TVC/ME
B: Pressure, Bar
H: Enthalpy, kJ/kg
T: Temperature, oC
m: mass flow rate, kg/s
G
G
HP
DrumDe-aerator
STEAM TURBINE GENERATOR(1 UNIT)
GAS TURBINE GENERATOR
(1 OF 3 UNITS)
AF
GT Comp.
3 HP EJECTORS
3 MSF UNITS
ST 215.7 MW
215.5 MW
Make up water
HEAT RECOVERY STEAN GENERATOR
(1 OF 3 UNITS)
CONDENSATE RETURNFROM DESAL PLANT
CONDENSATE
PUMPS
BRINE
HEATERS
DESALINATION PLANTS
BLOWDOWN
1%
DUMP
CONDENSER
BFP
625.8 T
591.5 m
75 B 560 T
3550.7 H 293.58 m
6.8 B 142.3 T599.3 H 101.33 m
183.1 T
591.5 m
13 B 118 T496.7 H 293.58 m
IP PROCESS STEAM
LP PROCESS STEAM
30.3 B 449.3 T
3342.7 H 7.5 m2.8 B 158.8 T
2781.5 H 286.08 m
13 B 115.8 T486.7 H 98.25 m
87.2 B 142.3 T603.9 H 3.47 m
15 B 30 T127.1 H 3.08 m
13 B 60 T252.2 H 1.167 m
CEP
HRSG # 2
HRSG # 3
HRSG # 2
HRSG # 3
B
HRSG # 2
HRSG # 3
B
87.2 B 142.3 T603.9 H 10.41 m
2.8 B 137 T2734.6 H 2.91 m
2.5 B 135 T
2733.1 H 293.58 m
GTCC Steam extracted
Energy consumption calculations
• Steam from ST to DS at 2.8 bar, 158oC, 2781.5 h,
• de-superheated to enter DS at 2.5 bar, 135C, 2733 h
• S =293.6, D=2368 kg/s, D/S=8.06, 3 MSF (45
MIGD)
• Wde (lost work or equivalent) = ms (hMSF – h cond)
• = 293.7 (2781 -2345.5)/1000 = 127.8 MW
• 127.8 MW work (eq) to Q=657 MW supply to DS
• (14.6 MW Q/MIGD and 2.84 MW Weq/MIGD
• 54 kJ/kg D, 15 kWh/m3, adding 4 kWh/m3 pumping,
• Total consumed W(eq) 19 kWh/m3 for MSF
• Total consumed W(eq) 17 kWh/m3 for TVC/ME
• Wangnick, reported 4 kWh/m3 for pumping and 14 kWh/m3 for thermal, total 18 kWh/m3.
• Hamed, [8] of SWCC analysis shows MSF plants inherited exergy loss in range of 15.2 23.7 kWh/m3,
Desalted water fuel cost by work loss method
• Extracted steam to MSF can produce EE if not extracted,
• No cheap or wasted energy as claimed
• Coupling MSF with steam turbines reduces energy 50% compared with boiler operated MSF
• Still, much very high compared with SWRO
• MSF combined with steam turbine consume at least 20-kWh/m3 or 5 times that of SWRO.
• MSF widespread in GCC is due to low calculated fuel cost as compared with international fuel cost
E-146
P-52
Treatment
Brine Heater Heat Recovery SectionHeat Rejection
Section
Recirculaion Steam
Brine
Blow Down
Distillate
Cooling
Water Mc
Feed
Mc-F
Condensate
Steam
Figure 1 Recirculation Multi Stage Flash Desalting System
Thermal
Energy to
BH
Pumping
Energy to
move
streams
Relation between
GR, n number of
stages and specific
heat transfer area.
2012
8
20
33.5
Ras Al
Khair
Improving Prospects of MSF by its
combination with NF Pretreatment
• No doubt that MSF system is simple, highly reliable,
robust, and has higher capacity/unit than SWRO
• MSF can deal with worst seawater quality and produces
almost pure water.
• There are concerns on reliability of SWRO
• This is not excuse to avoid the SWRO use and
development, same way MSF developed with many
failures at the beginning
• New suggested MSF improvement:
• Pre-treat its feed water, fully or partially by NF
• NF as pretreatment for SWRO and MSF suggested and
extensively studied in S.A.
• Awerbuch [10] showed its benefits of removal of scale
elements from seawater, and suggested using NF
permeate for partial feed to thermal process.
• NF pre-treatment lowers significantly the concentration
of hard scale elements in seawater such as Ca2+, Mg2+,
SO4, and HCO3-
• This permits raising the TBT and recovery ratio of MSF
26-Apr-15 29
• The maximum (TBT), at which sulfate scale
begins to precipitate, is shifted to 120, 135 and
145oC when the NF-treated portion increased
from 10, 25 and 50%, respectively.
• Combination of the MSF unit with NF
pretreatment is not free.
26-Apr-15 30
• MSF D-output flashing range, (TBT– Tn).
• TBT Increase from 110C 135C gives 35% D
increase, i.e 7.29.72 MIGD,
• 2.52 MIGD increase.
• Minimum specific mechanical energy for the modified
case is 27.33 kWh/m3 (22.7 for heat and 4.625 for
pumping).
26-Apr-15 31
Figure 3: Influence of NF on sulfate scale potential in BR-MSF plant
26-Apr-15 32
26-Apr-15 33
Case 1: Using SWRO system to augment the
existing MSF
E-146
P-52
Treatment
Brine Heater Heat Recovery SectionHeat Rejection
Section
Recirculaion Steam
Brine
Blow Down
Distillate
Cooling
Water Mc
Feed
Mc-F
Condensate
Steam
Figure 1 Recirculation Multi Stage Flash Desalting System
Thermal
Energy to
BH
Pumping
Energy to
move
streams
PLUS
26-Apr-15 34
• The maximum (TBT), at which sulfate scale
begins to precipitate, is shifted to 120, 135 and
145oC when the NF-treated portion increased
from 10, 25 and 50%, respectively.
• Combination of the MSF unit with NF
pretreatment is not free.
Thermal vapor compression (TVC) and Multi
effect (ME), i.e. TVC/ME
Forward feed multi-effect desalting unit
with pre-feed heaters
Multi-effect thermal vapor desalting unit.
Ratio of
S/Dr for
different
expansio
n Ps/Pn
and
Pd/Pn
compres
sion
ratios
ALBA ME-TVC
plant (
Schematic diagram similar to Al-Jubail (MARAFIQ) ME-
TVC unit, 6.5 MIGD.
The increase of unit
size capacity of ME-
TVC desalination
systems.
The increase in the gain output ratio of new ME- TVC projects
• Logic question, why thermal compressor is used in TVC/MED.
• Mechanical vapor compressor (MVC) is more efficient, energy wise
• This fact is illustrated first, and then the obstacles of using the MVC are studied.
15نيسان، 26 45
F
Dis
till
ate
D
B= F - D
Compressed vapor D
D
evapora
tor
Multi - flow heat
exchanger
Compres
sor
Feed F
Dat
To
B at To
Feed F
F
Dis
till
ate
D
B= F - D
Compressed vapor D
D
Figure 2: Single Effect Mechanical Vapor desalting unit
evapora
tor
Multi - flow heat
exchanger
Compres
sor
Feed F
Dat
To
B at To
Feed F
• Work loss due to steam extraction to TVC/MED is similar to that of MSF
• 54 kJ/kg D, 15 kWh/m3, adding 2 kWh/m3
pumping , total eq. energy is 17 kWh/m3
• Twice energy reported by leading MVC manufacturer of 8 kWh/m3 for units producing 3000 m3/d, and expected to be 7.5 kWh/m3 for 4000 and 5000 m3/d for newly designed units.
26-Apr-15 49
• MSF D-output flashing range, (TBT– Tn).
• TBT Increase from 110C 135C gives 35% D
increase, i.e 7.29.72 MIGD,
• 2.52 MIGD increase.
• Minimum specific mechanical energy for the modified
case is 27.33 kWh/m3 (22.7 for heat and 4.625 for
pumping).
26-Apr-15 50
Comparison between augmenting MSF
with SWRO, or modifying it with NF
26-Apr-15 51
Case 1: Using SWRO system to augment the
existing MSF
E-146
P-52
Treatment
Brine Heater Heat Recovery SectionHeat Rejection
Section
Recirculaion Steam
Brine
Blow Down
Distillate
Cooling
Water Mc
Feed
Mc-F
Condensate
Steam
Figure 1 Recirculation Multi Stage Flash Desalting System
Thermal
Energy to
BH
Pumping
Energy to
move
streams
PLUS
26-Apr-15 52
Unmodified 7.2 MIGD MSF+SWRO unit will produce:
• MSF output 10.752 Mm3/y (if CF = 0.9), and consumes
EE of: 216.12 GWh (20.1 kWh/m3).
• SWRO 2.52 MIGD (11.456×103 m3/d) produce 3.76
Mm3/y (CF = 0.9), and consumes:
• EE 15.05 GWh (based on 4 kWh/m3) EE .
• A total EE consumption of 231.65 GWh, .
• A total EE consumption of 231.65 GWh,
• fuel energy consumption of 2.3165 MGJ (0.38 Mbbl)
based on 10,000 kJ/kWh heat rate, and at a cost of $M
26.58.
• When the fuel energy represents 70% of the EE cost,
the EE cost is $M37.97.
• The capital cost of the SWRO system is in the range of
$750/(m3/d), and the 2.52 MIGD will cost $M8.592
Case 2
26-Apr-15 55
• Case 2:
• Modified MSF unit by raising its TBT from 110135oC to produce
• 9.72 MIGD or 14.515 Mm3/y, and consumes:
• 396.7 GWh (27.33 kWh/m3) EE.,
• fuel energy consumption of 3.967 MGJ
• 0.6503 Mbbl at a cost of $M 45.522, and
• EE cost of $M 65.032.
26-Apr-15 56
• The annual consumed electric energy in case 2 is more 165.05 GWh than case 1, and its electric energy cost is $M 27.062 more than case 1.
• The saving of the energy cost when an SWRO is added to the unmodified MSF unit compared to modifying the MSF unit in one year is $M27.062, which is more than 3 times the cost of adding the SWRO unit.
Suggested ISCC using PTC and Desalination
• Co-generation Power Desalting Plants (CPDP)
using CC,
• and integrated with Multi Stage Flash (MSF) or
Multi Effect Distillation (MED)
• Examples are: Shuaiba North in Kuwait,
• Jabal Ali in United Arab Emirates (UAE), and
• Ras Girtas, and Mesaieed in Qatar.
Examples of the ISCC in operation or under
construction • Kureimat (Egypt), 140 MW, and 20 MW,
• Hassi R'Mel (Algiers), 130 MW, 25 MW,
• Ain Beni Mathar (Morocco), 472 MW, 20 MW,
• Yazd (Iran), 430 MW, 67 MW,
• Martin solar, Florida (USA), 480 MW, and 75 MW,
• Agua preta (Mexico), 480 MW, and 31 MW,
• Victorville, California (USA), 563 MW and 50 MW, and
• Palmdale, California (USA), 617 MW, and 62 MW.
• Suggested here;
Gas Turbine Generators
3 × 215.5 MW
HEAT RECOVERY
STEAM GENERATOR
Steam Turbine Generator
1 × 215.7 MW
DESALINATION PLANTS
Air
inlet
Fuel
Air
inlet
Fuel
Air
inlet
Fuel3 HP EJECTORS
3 × 15 MIGD MSF UNITS
Shuaiaba CC3 GT×215.5 MW each + 3 HRSG + 1 BPST×215.7 MW + 3
MSF of 15 MIGD each
B: Pressure, Bar
H: Enthalpy, kJ/kg
T: Temperature, oC
m: mass flow rate, kg/s
G
G
HP
DrumDe-aerator
STEAM TURBINE GENERATOR(1 UNIT)
GAS TURBINE GENERATOR
(1 OF 3 UNITS)
AF
GT Comp.
3 HP EJECTORS
3 MSF UNITS
ST 215.7 MW
215.5 MW
Make up water
HEAT RECOVERY STEAN GENERATOR
(1 OF 3 UNITS)
CONDENSATE RETURNFROM DESAL PLANT
CONDENSATE
PUMPS
BRINE
HEATERS
DESALINATION PLANTS
BLOWDOWN
1%
DUMP
CONDENSER
BFP
625.8 T
591.5 m
75 B 560 T
3550.7 H 293.58 m
6.8 B 142.3 T599.3 H 101.33 m
183.1 T
591.5 m
13 B 118 T496.7 H 293.58 m
IP PROCESS STEAM
LP PROCESS STEAM
30.3 B 449.3 T
3342.7 H 7.5 m2.8 B 158.8 T
2781.5 H 286.08 m
13 B 115.8 T486.7 H 98.25 m
87.2 B 142.3 T603.9 H 3.47 m
15 B 30 T127.1 H 3.08 m
13 B 60 T252.2 H 1.167 m
CEP
HRSG # 2
HRSG # 3
HRSG # 2
HRSG # 3
B
HRSG # 2
HRSG # 3
B
87.2 B 142.3 T603.9 H 10.41 m
2.8 B 137 T2734.6 H 2.91 m
2.5 B 135 T
2733.1 H 293.58 m
Mass and heat balance diagram of Shuaiba North GTCC Power- Desalination Plant.
Superheater Evaporator Economizer
CT o6254
CT o
steam 560
CT osat 7.290.
CT ostuck 183
CT ofeed 142
CT ogpp 7.310
CT opp 20
Gas and steam-water temperature profile of the HRSG
GE912FA Gas turbine, GT
3 No. of units
Natural Gas Type of fuel
215.5 Gross output, MW
50 Ambient temperature, oC
Natural
circulati
on
HRSG, Type
3 No. of HRSG
3 Integral de-aerator
1 blow down, %
BPST Steam Turbine, ST
1 No. of ST
215.7 Gross capacity, MW
MSF Desalination
3×15 MIGD #unitsx Capacity
Gas turbine combined cycle,CC of 862.2 MW Gross output,
Desalination units
• Steam flow rate to one MSF = 97.86 kg/s, 1/3 of
BPST discharged
• D = 15 MIGD (789 kg/s). This gives:
• GR = 789/97.86 = 8
• Turbine work loss = 42.57 MW equivalent to the heat = 218.68 MW supplied to the MSF unit.
• 2.5 MW is added for steam supply to ejector
• Total 45.1 MW, 45100/789=57.16 kJ/kg = 15.9 kWh/m3
• Shuaiba CC equivalent power output for:
• 3 GT (3×215.5 MW = 645.5 MW) +
• 1 BPST of 215.7 MW +
• 3 MSF producing 45 MIGD
• Equivalent to
• CC of 3 GT (3×215.5 MW) + 1 ST of 350.7 MW = 997.2 MW
• So Qatar needs at least similar units by 2020
Final combination of the solar field with the CC
ISCC
• ISCC consists of CC PP connected to Solar Field.
• Heat to HRSG and solar field to generate steam operating one ST
• Solar field produce heat to produce steam.
• Solar collectors heat exchangers (called SSG)
• Solar steam from SSG integrated either at high, or medium, or low T
section of HRSG to oversized ST
• This ST (designed): larger than ST of original CC, but same GTs
• Operating with no solar steam, ST operate at part load
• With solar steam, ST operate at full load.
• For 350 MW ST as in Shuaiba CC, and adding 50 MW
capacity by solar steam,
• ST Load range 350 MW(87.5%) to 400 MW (100%)
• Usually, ST have almost at 85% to 100% of nominal
load.
• If solar Capacity limited to 15%, part load negative
effect is negligible.
Sizing solar collectors
• (Carnot) =1 – (320/539.2)= 0.4065; (Cycle)
=0.5x0.9=0.36
• (collector)=heat gained by SSG/incident solar
energy)0.5
• Solar capacity = 54 MW equivalent work (Power+
Desalting)
• Heat input by solar steam = 54/0.18 = 150 MWt
• 54 MW equivalent work is assumed, to be checked later
after sizing solar field delivering 150 MW to the SSG.
• (SPP) Electricity to solar efficiency equal 18%.
• Required incident solar energy 300 MWt,
• [300,000/(0.95)]x1.2 = 378,947 m2, or 7,017 m2/MW,
Compared to Hassi R'mel ISCC in Algiers, (25 MW and
183,860 m2, 7,354 m2/MW
• Solar field parallel solar collector assemblies (SCA).
• Each 4 SCA form single circuit (loop)
• SCA example: 150 m length and 5.45 m aperture width,
area = 817.5 m2/SCA,
• Required SCA # = 378,947/817.5 = 463.5. The number
of SCA can be taken as 364, for 4 SCA per loop, the #
loops 116 loops
Solar collector assembly (SCA),
loop width = 4x aperture 36 m, length=2x 150 m, + 10 m
from each side or 330 m, area= 11,880 m2.
total loops area (solar field) = 11,880×116 =1,378,080 m2
Final combination of the solar field with the CC
Final ISCC with Desalination
• Q(SSG) = 150×1000 = MS× (2765 – 593), MS=
69.06 kg/s.
• Ms (solar) delivered/HRSG = 23.02 kg/s each HRSG.
• new steam flow rate to steam turbine is: 3×91.73 +
69.06 = 344.25 kg/s
• Original mass flow rate of 293.58 kg/s to the steam
turbine,
• Steam turbine power output 17% or from 215.7 MW
252.4 MW, or 36.67 MW increase.
• Increase of desalination output is 7.65 MW.
• Now the new CC plant consisting of 3GT×215.5 MW + 1 ST of 252.4 MW + MSF units producing 51.75 MIGD is equivalent to:
• 3GT×215.5 MW + 1 ST of 252.4 MW + 51.75 ×3 (MW/MIGD), or
• 3GT×215.5 MW + 1 ST of 407.65; total equivalent output of 1054.15 MW.
• Compared with original CC of total 997.2 MW before adding the solar field, or
• 56.95 MW equivalent power output increase
• 36.7 MW for ST and
• 6.75MIGD ×3=20.25 MW for desalting plant
Conclusion
• Kuwait and the GCC should stop installing MSF units
• They consume at least 4 times energy than SWRO
• No such thing as waste or cheap heat source
• MSF system drains country energy resources.
• EE cost by MSF in 1 year reached $M2233
• It would have been $M 361.6 if SWRO was used.
• MSF Improvements by NF to raise its capacity 35%
lead to increase of energy cost more than 3- times cost
of adding simple SWRO system to produce the same
amount of water obtained by modifying the MSF unit.