DESALINATION

ELSEVIER Desalination 180 (2005) 217-229

www.elsevier.com/locate/desal

Integration of seawater desalination with power generation*

Ismat Kamal
Fluor Enterprises, Inc.. One Fluor Daniel Drive, Aliso Viejo, CA 92698, USA
Tel. +1 (949) 349-4537; Fax +1 (949) 349-3149; email: lsmat.Kamal@fluor.com

Received 14 September 2004; accepted 4 February 2005

Abstract
The economic benefits of integrating seawater desalination with power plants are discussed, starting from the
first principles of thermodynamics. The concepts of the "fuel-use performance ratio" and the "power loss" method
are described in the context of their usage for thermal cycle evaluation and desalination process selection, both with
conventional steam cycles and with combined cycle power plants. A thermo-economic model is introduced to
evaluate water and power costs and rates of return in dual-purpose power/desalination applications. The future of
integrated power and desalination plants is discussed with reference to the growing role of seawater reverse osmosis
(SWRO) in the desalination arena. A case study is presented to evaluate the benefits of integrating SWRO with
existing power/desalination plants in the Middle East. Subject to the assumptions of the study, it is concluded that
repowering and retrofitting would result in a nearly three-fold increase in the power generating capacity and an
over six-fold increase in the water output, without requiring any expansion of the seawater intake system. Based on
natural gas fuel, the repowered plant would also result in a 70% increase in the fuel efficiency of the station and a
drastic reduction in the cost of water production. For a privatization scenario, an economic analysis is used to show
that attractive rates of return would be obtained if a developer were to purchase and refurbish the existing plant,
selling the products on a build own and operate (BOO) basis, in preparation for this promising application, the need
for pilot plant testing at existing power/desalination stations, together with research and development work in
membrane technology for high temperature operation, is emphasized.
Keywords: Seawater desalination; Power generation; Reverse osmosis; Multistage flash distillation; Thermo-
economic modeling; Dual-purpose plants; Fuel-use performance ratio; Power loss; Repowering;
Membrane techniques; Power cost; Water cost; Rate of return; BOO plants; IWPPs

* An abridged version of this paper was presented at

the Water and Waste Water Conference in Fira Barce-
lona, Spain, May 26, 2004, organized by the Pennwell
Corporation.

001 i-9164/05/$- See front matter © 2005 Elsevier B.V. All rights reserved
doi: 10.1016/j.desal.2005.02.007
218 L Kamal / Desalination 180 (2005) 217-229

I. Introduction lowering of the energy cost of seawater desali-

The integration of seawater desalination in- nation, as illustrated in the next section. Simplified
volving the utilization of extraction or back- schematics of an isolated single-purpose multi-
pressure steam as the source of heat for thermal stage desalination plant (MSF) and MSF plants
desalination was one of the first innovations in integrated with power generation are shown in
desalination technology. It resulted in a significant Figs. 1-3.

Pressure HP steam to air eiectors

~ reducer
Boiler
Desuperheater

MSF SW intake
desalination SW reject
plant
Condensate Product
return
[ ~ Blowdown

Fig. I. Self-containedsingle purpose MSF plant.

HP steam to air ejectors

LP steam MSF ~-- SW intake

y

desalination ~ SW reject
plant Product
Boiler t [ ~ Blowdown
~" Condensateretum to feed heaters
J

Condensate
return from
MSF plant
brine heaters
I Feedwater
heaters I
Fig. 2. Dual-purpose plant with extraction
steam.
 I. Kamal / Desalination 180 (2005) 217-229 219

HP steam to air ejectors

+
LP steam SW intake
MSF
desalination SW reject
plant
Product
Boiler
[ - - - ~ Btowdown

Condensate return to feed heaters

....Feedwater
heaters
Fig. 3. Dual-purpose plant with backpressure steam.

2. Quantification of benefits minimum energy requirement for separation of

pure water from seawater at its normal concentra-
In order to quantify the benefits of combined
tion. For boiling at atmospheric pressure, Tb =
power and water production in dual-purpose
373°K and L b = 2257 kJ/kg. This gives the boiling
plants, it would be useful to start with an overview
point elevation for seawater desalination at its
of the energy requirements of thermal desalination
normal concentration as
processes. Thermodynamically, the difference be-
tween saline water and pure water is the difference
ATh = 2.8 × 373/2257 = 0.46°K
in free energy. One of the physical phenomena in
which this difference manifests itself is the boiling In a real, continuous distillation process, the
point elevation, and it has been shown [1 ] that the concentration increases as the water is removed.
two are related by the equation If the mean brine concentration is assumed to be
twice that of seawater, the free energy difference
increases to approximately 2AG ° or 5.6 kJ/kg. This
would result in ATb= 0.92°K.
where L b is the latent heat o f evaporation at the
boiling point, Th is the boiling temperature of pure
water and AT~ is the boiling point elevation. A G O
2.1. Energy consumption in single-purpose ther-
is the free energy difference per unit mass of water
mal desalination plants
and, in physical terms, represents the work that
would be necessary in order to remove unit mass The energy consumption in thermal desali-
o f water from solution by means o f an ideal nation processes can be derived from first prin-
irreversible process. For seawater boiling at atmo- ciples by considering a simple reversible engine
spheric pressure, A G Ois 2.8 kJ/kg and gives the where heat Q is absorbed at Tb+ A T (where z~Tjp
220 L Kamal / Desalination 180 (2005) 217-229

Heat input Q Feed we may denote as A,. Eq. (4) can then be rewritten
at Tb + A T,,j, seawater
as

Q = A G o + Lh (ATb + A,)/AT,,p (5)

IDEAL THERMAL
HEAT DESALINATION In practice, the value of Ai has been found to
ENGINE AGo PLANT
be a minimum of 5°C, so that

Q = 5.6 + 5.92 x 2320 / 70 = 202 kJ/kg

I I

Heat reject Fresh

" Brine This corresponds to a performance ratio of 5 kg
Q-AGo al Th water
distillate produced per 1000 kJ or 11.5 Ib per
Fig. 4. Ideal desalinationprocess with heat energyinput. 1000 Btu. In practice, the performance ratio used
in commercial plants is considerably lower, based
on an optimization between capital costs and
is the operating temperature range) and heat Q - energy costs.
AG o is rejected at T~, as shown in Fig. 4. Thermal desalination plants use additional
The work done by the engine is given by energy in the form of pumping power and medium
pressure steam for removing non-condensable
a< =oaro /( + aro,,) (2) gases by means of steam-jet air ejectors. To take
all energy inputs into account, a re-defined per-
Also, since we are at the boiling point,
formance ratio was proposed in 1980 at the Am-
sterdam Panel on Energy Usage in Desalination
Q-AGo=L ~ (3)
[2]. This was called the fuel-use performance ratio
The heat input necessary to bring about the (FPR) and defined as the quantity of water
separation is obtained by rearranging Eq. (2) as produced, in kg, per kJ of the heat content of the
fuel used. The FPR is applicable to all kinds of
Q : A G o ( T h +AT,,r)IAT,,p=AG,,TblATo, +AGo desalination processes, including reverse osmosis,
and enables us to make a direct energy-use com-
Substituting from Eq. (1), we get parison among the different processes for seawater
desalination. In calculating the FPR, requirements
Q = AG O + LhATh / ATop (4) such as ejector steam, pumping power, etc., are taken
into account, together with the efficiency of con-
In an idealized process working over a range version of fuel to the appropriate energy form.
of 110°C-40°C, where the average latent heat is Taking as an example a single-purpose multistage
2320 kJ/kg, the heat energy requirement would flash (MSF) desalination plant with a performance
be ratio of 5 kg product/1000 kJ of heat input to the
brine heater, and assuming that the steam
Q -- 5.6 + 2320 x 0.92 / 70 = 36 kJ/kg
requirements are met by a boiler with an efficiency
In a real thermal desalination process the of 0.85, and pumping power requirements are met
irreversibilities which invariably occur due to by a diesel generator with an efficiency of 0.3,
finite temperature difference requirements for heat the overall energy inputs are shown in Table 1.
transfer, pressure drop on the vapor side and non- Therefore, the total energy requirement of this
equilibrium losses, add to the resistance created plant, in terms of the heat content of fuel, is
by the boiling point elevation by a quantity which approximately 294 kJ/kg of product, corres-
 L Kamal / Desalination 180 (2005) 217-229 221

Table 1
Energy requirements in a single-purpose MSF plant, PR = 5 kg product/1000 kJ heat input to the brine heater

Requirements, kJ/kg Fuel conversion efficiency Heat from fuel, kJ/kg

Heat to brine heater 200 0.85 235.3
Ejector steam 6 0.85 7.1
Electrical energy 15.6 0.30 52.0

Table 2
Energy requirements in a dual-purpose MSF plant, PR = 3 kg product/1000 kJ heat input to the brine heater

Requirements, kJ/kg Fuel conversion efficiency Heat from fuel, ld/kg

Heat to MSF plant, including ejector steam 120.4 0.92 130.9
Electrical energy 14.25 0.32 44.5

ponding to an FPR of 3.4 kg/1000 kJ heat content bination, the concept of the FPR was used for a
of fuel (HCF). real case, a large-sized power desalination plant
located in the Middle East [2]. The station can be
run either as a power-only plant, or as a dual-
2.2. Energy consumption in dual-purpose ther-
purpose plant with steam extraction at 2.5 bar for
mal desalination plants
the MSF distillation plant. The unit capacity is
The energy consumptions discussed in the 22,000 ton/d at a performance ratio (PR) of 3 kg
previous section are very high when compared per 1000 kJ heat input to the brine heater. Each
with power-consuming processes such as reverse power plant steam turbine supplies extraction
osmosis, even when we take into account the steam at 2.5 bar to two desalination units.
efficiency of conversion from thermal to electrical Under two different operating conditions, for
power for the latter. However, distillation pro- a gross power output of 98.705 MWe in each case,
cesses using heat as the energy input possess an the boiler heat consumption (BHC) is 1006.88x
advantage in that they do not require the thermal 106 kJ/h w h e n p r o d u c i n g p o w e r o n l y and
input to be at a very high temperature, and can 1,227.66x106 kJ/h when producing both power
make use of thermal energy extracted from other and water. Hence the excess BHC chargeable to
operations. The most common arrangement is a the desalination plant is 220.78× 106 kJ/h. As the
dual-purpose plant using back pressure or extrac- distillate production from two units is 1.8333×
tion steam from a power plant steam turbo- 106kg/h, the heat to the brine heater is 120.4 kJ/kg
generator, as shown in Figs. 2 and 3. of distillate produced.
Operating a steam turbine at a back-pressure The efficiency of the power-only cycle is 0.35,
higher than its normal condensing pressure, or and the boiler efficiency is 0.92. The pumps are
extracting steam from a steam turbine, causes ~ driven by electrical motors, and the fuel conver-
reduction in the power output, and the heat charge- sion efficiency for pumping power is 0.35 × 0.92
able to desalination is the heat required to make or 0.32. The overall energy requirements are shown
up for the power loss. in Table 2. Hence the total heat required from fuel
In order to indicate the benefit of the corn- is about 175 kJAtg.
222 L Kamal / Desalination 180 (2005) 217-229

Table 3
Energy requirements in a dual-purpose MSF plant, PR = 5 kg product/1000kJ heat input to the brine heater

Requirements,kJ/kg Fuel conversionefficiency Heat from fuel, kJ/kg

Heat to MSF plant, includingejector steam 72.3 0.92 78.6
Electrical energy 15.6 0.32 48.8

If the dual-purpose plant had been designed In this model, the energy consumption for the
with an MSF evaporator PR of 3 instead of 5, the different processes is evaluated on the basis of
plant output for the same energy consumptionwould the "power loss method", introduced in a paper
have been 3.0555 x 106 kg/h, and the heat charge- presented at the 3rd International Symposium on
able to the desalination plant would be 72.3 kJ/kg, Fresh Water from the Sea at Dubrovnik in 1970
with the overall energy requirements shown in [8]. In this paper, the energy cost o f MSF
Table 3. desalination in a dual-purpose plant based on a
Thus the total heat chargeable to the desali- heavy water nuclear power reactor was equated
nation plant is approximately 127 kJ/kg, which is to the value of the power 'lost' owing to the
less than half the energy requirement evaluated withdrawal of steam for process use plus the
in the previous section for a single-purpose MSF power consumed by the process pumps. The total
plant with the same performance ratio. The bene- power equivalent of the MSF plant's energy con-
fits are greater when the steam for the desalination sumption at a plant capacity of 1 million gallons
plant is extracted at a lower pressure, such as in per day and a performance ratio of 10 was deter-
the low temperature multiple-effect distillation mined as 2.40 MWe, which is equivalent to
process, as quantified in a paper presented at an 15.2 kWh/m 3 product. This shows good agree-
International Atomic Energy Agency (IAEA) ment with our recent results based on the more
seminar in Algiers [3]. sophisticated tools now available and mentioned
in the preceding paragraph. The relationships
between the 'power loss' method and the FPR
3. Thermo-economie modeling of dual-purpose
methods of evaluating energy consumption have
power/desalination plants
been discussed in an earlier paper [9].
A thermo-economic model has been developed
[4,5] to simulate the performance and cost eco-
nomics of dual-purpose plants for steam cycle and 4. The future of integrated power and desalina-
combined cycle power plants, both for proposed tion plants
new stations as well as for the repowering of Owing to significant reductions in membrane
existing stations with the addition of thermal or costs, improved energy recovery devices and due
reverse osmosis desalination plants. The model attention to adequate pretreatment, reverse
uses thermal cycle simulation programs, such as osmosis has become the process of choice for
GateCycle ® [6], SteamMaster®, GTMaster ®and desalination plants being built in Europe and the
ReMaster® [7], together with a financial model to Americas. Once the reliability issues have been
evaluate the power and water cost and the rate of addressed, it is likely that reverse osmosis will
return for given power and water costs in dual- gain the overwhelming share of the market in the
purpose applications. The model can also be used Middle East as well. Integrated plants with SWRO
for desalination process comparison and selection. as the desalination process have synergies as
 1. Kamal / Desalination 180 (2005)217-229 223

substantial as obtained for thermal desalination repowering and retrofitting typical steam turbine/
combinations. This has been demonstrated in a MSF based dual-purpose units in the Middle East.
number of studies based on new and repowered Two options were initially considered in this study
plants for Southern California and Rosarito, for the desalination process:
Mexico [10-17]. The SWRO feed would be drawn (a) Option A, based on refurbishing and retaining
from the power plant condenser cooling-water the existing MSF units and adding an RO plant
return, reducing the water cost by lowering the drawing its feed from the cooling water
operating pressure due to increased flux at the returning from the power plant condensers and
higher operating temperature. There is also an the MSF plant heat rejection sections, and
excellent opportunity to increase power and water (b) Option B, based on dismantling the MSF units
supplies in the Middle East through repowering and adding an RO plant drawing its feed from
and integration of SWRO with existing power/ the MSF plant seawater intake system and the
desalination plants, and the next section will be cooling water returning from the power plant
devoted to a case study conducted to illustrate the condenser.
benefits of this application.
5.1. Base power plant characteristics
5. Integration of reverse osmosis with existing
For the purposes of the study, the base power
dual-purpose plants
plant selected for repowering was assumed to be
There was a spate of construction activity in a two-unit coastal station, each unit consisting of
the field of dual-purpose power/desalination a conventional natural gas-fired boiler, a 118 MWe
plants in the Middle East during the late 1970s non-reheat steam turbo-generator (STG) with six
and early 1980s [18]. Most of these plants were feed water heaters, a seawater-cooled condenser
based on conventional boilers with steam turbines and balance of plant equipment. The typical steam
for power generation and MSF distillation for turbine has a high pressure (HP) stage group with
seawater desalination. While the steam turbines throttle conditions of 81 bar and 503°(;. Each STG
and some of the desalination units are still per- provides extraction steam at 2.5 bar to the brine
forming satisfactorily, many of the boilers asso- heaters of two 22,000 m3/d MSF units, each with
ciated with these plants are close to the end of a PR of 3 kg/1000 kJ heat input to the brine heater.
their useful life. At the same time, increasing Motive steam for the MSF plant's steam jet air
demand calls for substantial additions to the power ejectors is drawn from the high pressure header
generation and water desalination capacity of the and is used after letdown to appropriate con-
region. ditions. The existing cooling water system delivers
High-efficiency combined cycle plants based approximately 12,800 m3/h seawater to each
on combustion turbines with heat recovery steam power block (for a total of 25,600 m3/h) with
generators and steam turbines provide an excellent design temperatures of 32°C and 39°C respectively
means of obtaining a dramatic increase in the gross at condenser inlet and outlet. Fig. 5 shows a
power plant capacity and the fuel efficiency simplified flow diagram of the existing steam
through repowering. At the same time reverse cycle. The second column of Table 4 shows the
osmosis can be used to supplement the MSF units performance data for the existing plant. As
of these plants, greatly increasing the capacity and demonstrated in an earlier paper with the help of
efficiency of desalination. the Mollier chart [4], the withdrawal of low pres-
The study presented in the following section sure steam for MSF process use imposes a severe
evaluates technical and economic aspects of penalty on the efficiency of the conventional steam
224 L Kamal / Desalination 180 (2005) 217-229

Steam to MSF plant air ejectors

2,5 bar steam to MSF

I ~ a n t brine heaters

Boiler ~ 2 ~

*~' ~' ~ Ixll8MW

Extraction steam
Condensate for feed heaters
return from
MSF plant . ~
brine heaters
J ~ Feedwater
heaters I
Fig. 5. Original steam cycle (1 of 2 power blocks).

Table 4
Steam cycle performance summaryfor the existing and repowered plant, natural gas fuel, 30°(] ambient temperature

Existing plant Repoweredplant,

MSF units retained
Number of power blocks 2 1
CTGs per power block 0 3
STGs per power block 1 2
Total CTG gross power output, kWe 0 459,768
Total STG gross power output,kWe 236,106 198,749
Total gross power output, kWe 236,106 658,517
Power block auxiliary loads, kWe 9,444 16,463
Net power output, kWe 226,662 642,054
Fuel heat input to boiler or CTG, millionkJ/h LHV 2,951 4,71 I
Fuel heat input to duct burner, million kJ/h LHV 0 189
Total fuel heat input, kJ/h LHV 2,951 4,900
Heat rate based on net power output,kJ/kWh LHV 13,020 7,631
Efficiency based on power output, % 27.7 47.2

cycle. The resultant heat rate for the base power repowered by replacing the two existing boilers
plant is 13,020 kJ/kWh LHV, corresponding to a with three heat recovery steam generators
power-production efficiency of 27.7%. (HRSGs) utilizing exhaust heat from three
advanced combustion turbines in a 3 on 2 power
5.2. Repowering strategy with MSF units retained block configuration. Our study was based on GE
The repowering strategy adopted for this 7241 FA turbines with dry low NOx combustors,
option assumes that the two steam turbines are but similar results would be obtained with other
 I. Kamal / Desalination 180 (2005) 217-229 225

equivalent machines available in the market. meet the requirements of two MSF units. With
Thermoflow software, STEAMPro ®, REMaster~ the additional steam withdrawn for feed heating,
and GTMaster ® [7] were used to simulate the only 150 ton/h at approximately 0.09 bar flows to
existing steam cycle and the re-powered combined the condenser as exhaust steam. The condenser is
cycle at an average ambient temperature of 30°C. designed for a 7°C temperature rise for this con-
Duct firing is required in order to make maximum densing pressure and exhaust flow.
possible use of the capability of the existing STG, For one of the off-design conditions of the
condenser and cooling water systems. However existing steam turbine, the power output is
since the existing ports supplying extraction steam 99 MWe with athrottle HP steam flow of 394 ton/h
to the feed heaters must be plugged, the power with zero extraction for desalination. At this
output of the STG is lowered to approximately condition, the condenser pressure rises to 0.16 bar
99 MWe in order to maintain acceptable exhaust and the cooling water temperature rise increases
steam flows without exceeding the design sea- to about 13°C in order to accommodate the higher
water temperature rise. A simplified flow diagram exhaust flow of 293 ton/h. However, a temperature
for the repowered combined cycle is shown in Fig. 6. rise higher than 7°C would not be allowed on a
Expected steam cycle performance data for this long-term basis owing to environmental consider-
option is shown in the third columns of Table 4. ations. Therefore, throttle steam flow would need
The repowering increases the net power output to be curtailed in the absence of extraction for the
of the plant to approximately 642 MWe, and MSF units, effectively de-rating the STG to an
improves the net power production efficiency to output of approximately 50% of the original de-
47.2%. sign capacity. For this reason, the option was not
considered any further.
5.3. Repowering option with MSF units dis-
mantled 5.4. Capacity and design o f desalination units
Out of the 560 ton/h throttle steam flow in the Table 5 shows the potential desalination plant
original steam cycle, 279 ton/h is withdrawn to capacity based on the feed seawater available from

,~ 2.5 bar steamto MSF plant brine heaters

Steam to
second STG l Steamto MSF plant
~ t e fi'om
T. -
air eiectors

A
~ _ secondcondenser
Condensatereturnfrom
MSF plant brineheaters
3 x 153 MWe
............ New
:....!
. . " v " "-...E 3x ~
,- CTG 3xHRSG Existing
%°.°...... ~ , , . . . . . . . . . i ~ . . . . . . . "'og, . . . . . . o . . . . . , . . . . . . . . . . . . . Fig. 6. Repoweredsteam cycle.
226 I. Kamal / Desalination 180 (2005) 217-229

Table 5
Capacity of desalination units

Cooling seawater usage for power plant condenser,m3/h 25,600

Cooling seawater usage for thermal desalinationplant heat rejection, ma/h 35,440
Cooling seawater usage for thermal desalinationplant make up, m3/h 11,520
Net cooling seawater available from thermal desalinationplant, m3/h 23,920
Total seawater available for RO feed, m3/h 49,520
Maximum RO feed supply temp., °C 39
Potential RO plant capacity at 45% recovery, m3/d* 500,296
Design RO plant capacity, m3/d 500,000
MSF desalination plant capacity,m3/d 88,000
Total desalination plant capacity, m3/d 588,000
*with allowance for backwash and waste

the existing cooling water system. The maximum Table 6

feed supply temperature for reverse osmosis is Main inputs for economic analysis
39°C. This is well within the temperature tolerance
o f advanced membranes which have been deve- Fuel cost, S/millionkJ 1.5
Power selling price, S/kWh 0.03
loped for seawater reverse osmosis. The potential Water selling price, $/m3 0.65
SWRO plant capacity with the existing MSF units Interest rate,% 7
retained is 500,000 m3/d. The conceptual design Annual inflation rate, % 4
of the RO plant, built in blocks of 125,000 m3/d, Owner's equity, % 25
has been described in an earlier paper [ 19]. Loan repayment period, years 15
Plant life, years 30
Purchase price for existing plant and land, 300
million $
5. 5. Economic analysis Owner's cost as % age of total EPC cost 10
Contingencyas % age ofEPC + owner's cost 10
The financial model referred to in section 4 was
used to conduct an economic analysis, assuming
that the plant will be purchased and refurbished
by a developer on a build, own and operate (BOO)
5.6. The need for pilot plant testing
basis. The purchase price for the existing 227 MWe/
88,000 m3/d plant was assumed to be $300 million. Unlike the cool seawater temperatures of the
The main assumptions for the economic analysis Pacific coast, seawater temperatures prevailing in
are listed in Table 6. the Middle East would present specific challenges
Results of the economic analysis are shown in when used in the manner proposed in this paper.
Table 7. The water plant cost shown in Table 7 Membrane replacement costs and general opera-
includes the cost for refurbishment of the existing tional costs are likely to increase at elevated temp-
MSF plant in addition to the cost o f the new eratures. Although membranes stable at tempera-
500,000 ma/d RO plant. Table 7 shows that high tures of up to 50°C are available, there is a need
rates of return would be obtained if the refurbish- for pilot plant testing at existing power/desalina-
ment is carried out by an Independent Water and tion plants in order to establish long-term per-
Power Producer (IWPP) on a BOO basis. f o r m a n c e at elevated t e m p e r a t u r e s and to
 I. Kamal / Desalination 180 (2005)217-229 227

Table 7
Economic analysis

Plant characteristics
Power plant net output, MWe 642
Power plant net fuel efficiency, % 47.2
Thermal desal plant capacity, m3/d 88,000
SWRO plant capacity, m3/d 500,000
Net saleable power, MWe 540.2
Power plant annual O&M costs (2003), million $ 25.3
Water plant annual O&M costs (2003), million $ 33.4
Power plant engineering and construction period, months 36
Water plant engineering and construction period, months 36
Construction start date January 2005
Construction completion date December 2007
Economic evaluation basis
Fuel cost (2003), S/million kJ 1.5
GDP inflation rate, post 2003, % 4
Power plant net capacity factor 0.9
Water plant net capacity factor 0.81
Plant life, years 30
Owner's equity at in-service date, % 25
Water selling price (2003), $/cu m 0.65
Power selling price (2003), S/kWh 0.03
Year of pricing 2003
Interest rate, % 7
Loan repayment period, years 15
Capital costs, million $
Purchase price for existing plant 300.0
Power plant Water plant
EPC contract 437 415.3
Owner' s cost 43.7 41.5
Owner's contingency 48.1 45.7
Total construction cost 528.8 502.5
Interest during construction 56.5 53.7
Totals 585.3 556.2 1.141.5
Total capital as spent 1,441.5
Economic evaluation results
Discount rate, % NPV, million $
10.0 714.3
20.0 12.9
30.0 -129.4
Pre-tax IRR 20.5

incorporate improvements in membrane techno- potential benefits would easily justify the invest-
logy based on feed back from the test results. The ment in the research and development work.
228 L Kamal / Desalination 180 (2005) 217-229

6. Conclusions nation, InternationalAtomic energyAgency,Algiers,

1991.
The integration o f seawater desalination with [4] I. Kamal and G.V. Sims, Thermal cycling and
repowering and retrofitting o f existing dual- financial modeling for the optimization of dual-
purpose plants in the Middle East could provide purpose power-cum-desalinationplants, Proc. IDA
dramatic increases in the power and water supplies World Congresson Desalinationand WaterSciences,
and drastic reductions in the cost of water and Abu Dhabi, 3 (1995)427.
power. Subject to the assumptions made, our [5] 1. Kamal, Thermo-economic modeling of dual-
studies show that for a plant capacity of 240 MWe/ purpose power/desalination plants: steam cycles,
Proc. IDA World Congress on Desalination and
88,000 m3/d for an existing plant
WaterReuse, Madrid, Spain, October 1997, 4 (1997)
• the net power output can be increased nearly 193.
three times to approximately 640 MWe, [6] Enter Software, Inc., Menlo Park, CA, USA, Design
• the water output can be increased nearly seven and Simulation Software.
timesto 588,000 m3/d without any addition to [7] Thermoflow,Inc., Wellesley,MA, CA, USA, Design
the existing seawater intake system, and Simulation Software.
• the fuel efficiency o f power production can be [8] I. Kamal, Design of a million-gallons-per-day MSF
increased from the current 27.7% to 47.2%, desalination plant for combinationwith a 456 MWth
heavy-water nuclear power reactor, Proc. 3rd
and International Symposium on Fresh Water from the
• attractive rates of return would be obtained if Sea, Dubrovnik, 3 (1970) 285.
the refurbishment is carried out by an IWt'P [9] I. Kamai, A uniform basis for desalination energy
on a BOO basis. cost comparisonin dual-purposepower/desalination
plants, presented at the IDA World Congress on
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