present and future trends in thermal desalination with possible solar application
TRANSCRIPT
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.
