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Presented at the EuroMed 2004 conference on Desalination Strategies in South Mediterranean Countries: Cooperation
between Mediterranean Countries of Europe and the Southern Rim of the Mediterranean. Sponsored by the European
Desalination Society and Office National de lEau Potable, Marrakech, Morocco, 30 May2 June, 2004.
0011-9164/04/$ See front matter 2004 Elsevier B.V. All rights reserved
Desalination 165 (2004) 393408
Visual basic computer package for thermal and membranedesalination processes
Hisham EttouneyDepartment of Chemical Engineering, College of Engineering and Petroleum, Kuwait University,
PO Box 5969, Safat 13060, Kuwait
Fax: +965 483-9498; email: hisham@kuc01.kuniv.edu.kw
Received 23 February 2004; accepted 3 March 2004
Abstract
A visual basic computer package was developed for the design and analysis of thermal and membrane desalinationprocesses. The package includes conventional processes, i.e., reverse osmosis, single-effect mechanical vaporcompression, multiple-effect evaporation with/without thermal or mechanical vapor compression, and multi-stage flashevaporation. The models for these systems provide detailed design data that include flow rates, stream salinity,temperatures, heat transfer or membrane area, ejector dimensions, and bundle dimensions. The model predictions are
based on detailed energy and material balances and well tested correlations for the heat transfer coefficient, thermo-dynamic losses, and physical properties of the seawater and water vapor. The visual basic interface provides displaysfor profiles of system variables across the effects, stages, or membrane modules, which may include salinity, flow rates,etc. Also, displays for the process flow diagram and design results are generated simultaneously. The design resultsinclude the unit product cost, process capital, performance ratio or specific power consumption, the flow rate of coolingwater, the heat transfer or the membrane area, and a number of thermodynamic losses.
Keywords: Desalination; Modeling; Computer simulation; Thermal desalination; Membrane separation; Economics
1. Introduction
In arid and semi-arid regions around the globe,the desalination industry has proved to be the
most viable solution to provide a sustainable
source for water. This is because natural sources
of fresh water are not evenly distributed. It is
common to have massive annual floods in oneregion and prolonged draughts in others. At
present more than half the worlds population is
experiencing water shortages. Moreover, many
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conventional water resources have limited capa-city and are difficult and expensive to expand.
This is manifested in the cost of water trans-
portation over long distances, destructive effects
of water dams on the delicate environment up and
down river bodies, and limited resources of
ground water [1].
Desalination processes have developed rapidly
since its start where the unit production capacity
was limited to 100 m3/d. Also, all processes were
thermally based and had a submerged tube con-
figuration. Subsequently, new and more efficientprocesses emerged, especially the multistage flash
(MSF) evaporation, single- and multiple-effect
evaporation (MEE), and reverse osmosis (RO)
membrane desalination. The size of these units
increased rapidly to reach much larger capacity,
close to 100,000 m3/d [2]. In many arid regions
around the world, desalination of sea and brack-
ish water is the main source of fresh water for
urban and industrial applications. Examples
include the Gulf States, several Mediterranean
and Caribbean Islands, Spain, and southern Italy.
In the US desalination of low-salinity water using
RO is found on a very large scale to produce
high-purity water for boiler houses and the
electronics industry.
The desalination industry is expanding con-
stantly. In this regard, large producers areincreasing their desalination capacity to meet theever-increasing demands. Several new countries
are also adopting desalination as the mostpractical solution for water shortages. During theperiod 19962002, the desalination capacity in
Spain has doubled. As a result, Spain became theleading producer in Europe with more than a 30%share of the installed desalination capacity on the
continent. Currently, the desalination capacity inSpain is approaching 1.5106m3/d [3,4]. Anotherexample is found in Saudi Arabia, which
currently stands at 5106 m3/d and is expected todouble this capacity by the year 2020. Similarscenarios are also found in Oman, Kuwait, andUnited Arab Emirates [5].
Modeling, simulation, and costing of thermaland membrane desalination processes are essen-
tial for better understanding, efficient and
accurate process design, troubleshooting of
operational difficulties, performance analysis,
process control, and cost estimation. Several
studies in the literature can be cited for modeling
of various thermal and membrane desalination
processes. A summary of most of these studies
can be found in El-Dessouky and Ettouney [5].
On the other hand, attempts to develop a simu-
lation package have ben rather limited. Simu-lating desalination plants using commercial
packages for a simulation of chemical process
plants is rather difficult and might not produce
accurate results. This is because of a lack of
models for thermodynamic losses or specific heat
transfer functions for seawater.
Attempts to develop simulation packages forthermal and membrane desalination processes
include the studies by Ettouney et al. [6], Herreroet al. [7], and Jernqvist et al. [8]. The simulator byJernqvist et al. [8] is modular and includes basic
modules forming thermal desalination processesincluding vapor compressors, evaporators, con-densers, and preheaters. The simulator also
includes a database for physical properties ofwater as a function of temperature and salinity.Other features include a specialized correlation
for the heat transfer coefficient on different sur-faces as well as thermodynamic losses and atemperature drop caused by demisters, trans-
mission lines, and condensers.The simulator by Uche et al. [7] focused on
the design and analysis of dual-purpose powerand desalination plants. The developed software
allows for the graphical design of plant layout,
calculation of the heat and mass balances,
thermo-economic analysis, and a parametric
analysis. This software remains under develop-
ment by Uche et al. [8].
The DEEP economic simulator focuses on
evaluation of the unit product cost of MSF, MEE,
or RO combined with various types of co-
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generation power plants, which include nuclear aswell as fossil fuel [9]. The DEEP simulator does
not perform simulation of the desalination plant;
instead, it utilizes input data provided by the user
such as the performance ratio, capacity, and other
parameters for the power plant to determine the
required process capital, unit product cost, and
other economic parameters.
The simulator presented in this study was
previously developed by Ettouney et al. [6]. The
previous simulator focused on an analysis of a
conventional thermal desalination process inaddition to a number of novel configuration, i.e.,
absorption and adsorption single-effect evapo-
ration, MSF with vapor compression. The
development presented in this study focuses on
conventional thermal and membrane desalination
processes. The new additions to the simulator
include calculations of the unit product cost,
number of tubes and evaporator dimensions, and
detailed design of the steam jet ejector. Also, new
displays are added to the simulator, including
system profiles, cost analysis, performance results
and a flow chart.
Another important addition to the simulator
presented in this study is the design and analysis
of the RO process. Several RO simulators are
available for downloading from sites of RO
manufacturing companies. These commercial
simulators focus on specific system design, which
is based on the membranes produced by the
manufacturing company. The RO simulator
developed in the package presented here is more
general and allows the user to define the mem-
brane characteristics, i.e., salt rejection andrecovery. In addition, cost calculations determine
the unit product cost and required capital.
The following sections include a description
of conventional thermal and membrane desali-
nation processes, features of the simulation pack-
age, a case study of the MEE process, a model of
the MEE process, cost analysis model, and
package results.
2. Conventional desalination process
Conventional thermal and membrane desali-
nation processes (Fig. 1) include the following:
C single-effect mechanical vapor compression
(MVC)
C multiple-effect evaporation with/without ther-
mal vapor compression (MEE and MEE-TVC)
C multiple-effect evaporation with/without
mechanical vapor compression (MEE and
MEE-MVC)
C once-through multi-stage flashing (MSF-OT)
C brine circulation multi-stage flashing (MSF)C reverse osmosis (RO) with options for single
stage, two stages, and two passes.
The thermal desalination processes (MVC,
MEE, MEE-MVC, MEE-TVC, and MSF-OT, and
MSF) operate only on seawater feed. On the other
hand, the RO process operates on low-salinity
river water, brackish water, and seawater. Market
share among these processes differs considerably.
As for seawater desalination, the MSF process
accounts for more than 60%, while the RO
market share may exceed 30%; other thermal
desalination process accounts for less than 10%.
These shares differ when desalination of low-
salinity and brackish water is taken into con-
sideration. In this case, the RO market share is
almost identical to the MSF process, and both
processes account for a total of 94%, while other
thermal desalination processes account for 6%
[10].
Schematics of the four conventional desali-
nation processes are shown in Fig. 2, which
include MVC (a), MEE (b), MSF (c), and RO (d).The MVC process is characterized by being
driven solely by electric current, which is used to
drive the mechanical vapor compressor. Start-up
of the MVC process requires use of an external
heating source, i.e., heating steam. The MVC pro-
cess presents a viable choice for water desali-
nation in remote areas and for small populations.
The system capacity remains limited below
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Fig. 1. Conventional thermal and membrane desalination processes.
5000 m3/d for single-effect configurations. The
system is operated at low temperatures, below
70C, and is characterized by low specific power
consumption, which may range between 5
8 kWh/m3 [11]. However, actual field data report
a much higher specific power consumption of
14 kWh/m3 [12]. Further details of the MVC
system, field data, and model can be found in thestudy by Ettouney et al. [13].
The MEE system, which is shown in Fig. 2b,
includes three main configurations. The first is
MEE without vapor compression. The second and
third are those for thermal or mechanical vapor
compression. The stand-alone system, evapo-
ration is driven in the first effect by low-
temperature heating steam. This results in
formation of a smaller amount of vapor, which is
used to drive evaporation in the second effect.
This process continues throughout all subsequenteffects, which may vary from two effects up to
12. The vapor formed in the last effect is then
condensed in the down condenser against the feed
and cooling seawater stream. System operation in
a stand-alone mode provides a performance ratio
of 8 for a 12-effect system. Operation in the
thermal vapor compression mode increases the
performance ratio to a range of 1416. As for the
MEE system combined with mechanical vapor
compression, its specific power consumption
remains the same as single-effect mechanical
vapor compression where it will vary over a
range of 58 kWh/m3. Use of the MEE-MVC
system is thought to increase the production capa-
city of the system rather than to reduce the
specific power consumption [14].
The MSF system shown in Fig. 2c is the work-horse of seawater desalination and, in particular,
the desalination industry in the Gulf States. The
MSF process dates back to the 1950s. Since then
the process has progressed considerably and a
large amount of field experience has been accu-
mulated in system design, construction, commis-
sioning, operation, maintenance, and cleaning.
Currently, MSF operation has been continuous
for periods varying from 2 to 5 years. This is
achieved in part by developments in antiscalents,
adoption of an on-line ball cleaning system,frequent acid cleaning, and progress in material
selection [15].
The RO process accounts for more than 45%
of the entire desalination market, which includes
low-salinity river water, brackish, and seawater.
The RO process requires an increase of the feed
pressure to 60 bars for the case of seawater
desalination; however, desalination of low-
salinity river water requires operation at much
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Fig. 2. Schematics of conventional desalination processes. (a) MVC, (b) MEE, (c) MSF, and (d) RO.
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lower feed pressures that may not exceed 10 bars.The RO process requires extensive feed pretreat-
ment, which is necessary to prevent scaling or
fouling of the membrane surface. Failure to
operate the feed pretreatment process properly
may have adverse effects on the membrane. This
might result in an increase of the operating cost
expressed in terms of down-time as well as
increased frequency of membrane replacement
and cleaning. Large-scale RO seawater desali-
nation plants are becoming more visible.
Examples include the plants: Trinidad, with acapacity of 135,000 m3/d [16]; Cyprus, with a
capacity of 45,000 m3/d [16]; and Florida, USA,
with a capacity of 94,625 m3/d [2]. Adoption of
such large capacities is thought to reduce the unit
product cost, which is currently reported at a
range of $0.5/m3.
3. Features of the computer package
Development of a comprehensive computer
package seeks ease of use, flexibility, and accu-racy of the results. Features of the visual basic
desalination computer package include the
following:
C Ability to design and perform cost estimate for
conventional desalination processes including
single-effect mechanical VC, MEE with/with-
out VC, MSF and RO.
C Ability to select and adjust the design and cost
parameters used in the calculations.
C The computer codes check and limit the value
of input parameters within practical ranges.C Several displays are used to present the design
and cost results. These displays include per-
formance results, profiles, flow diagram, and
cost results.
C Availability of help and tutorial files.
C Capability to print forms and results data file.
C Capability for handling of various errors.
The process selection feature includes six
choices: MVC; MEE and MEETVC; MEE and
MEE-MVC; MSF-OT; MSF; and RO with op-tions for single stage, two stages, and two passes.
Fig. 3 shows a flow diagram of the computer
package, which includes help files, process selec-
tion, adjustment of input design data, calcula-
tions, view of various displays, and print of forms
or output results.
4. Multiple effect evaporation: a case study
The following case study illustrates the mainfeatures of the simulation package through the
analysis of the MEE system. The illustration
includes model assumption, model equations,
process economics, and results of the simulation
package. Details of other processes will be
presented in subsequent publications.
4.1. Mathematical model
The MEE mathematical model includes the
following assumptions and features:
C Steady-state operation, which is valid for theentire operating regime except for start-up,
shut-down, or change of the operating con-
ditions to a new set. The latter condition is
caused by variations in the production capa-
city as dictated by product demand.
C There is no temperature gradient within
various phases in each effect. Irrespective of
this, temperature differences between vapor
and liquid, which are caused by boiling point
elevation, non-equilibrium allowance, and
other thermodynamic loss, are included in themodel.
C All physical properties of the vapor stream are
evaluated as a function of the stream temp-
erature. Also, all physical properties of the
liquid stream are evaluated as a function of
water temperature and salinity.
C The heat transfer coefficients for seawater
flowing inside the tubes, the falling film of
seawater on the outside surface of the evapo-
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Fig. 3. Elements of computer package.
rator tubes, or the condensing vapor inside or
outside the tubes are obtained from well testedcorrelations. The correlations depend on the
stream salinity and temperature as well as the
stream physical properties, which include
specific heat at constant pressure, viscosity,
thermal conductivity, and density.
C The heat transfer area is the same in all
effects. This is standard practice in the indus-
try, which reduces the cost of spare parts,
initial construction, and maintenance.
The mathematical model of the MEE system
includes the following set of system variables:C Brine flow rates in effects 1 through n, which
are defined byB1,B2, ,Bn!1,Bn. This gives
n unknowns.
C Feed flow rates in effects 1 through n, which
are definedF1,F2, ,Fn!1,Fn. This gives n
unknowns.
C Distillate flow rate due to brine evaporation in
effects 1 through n, which are defined byD1,
D2, ,Dn!1,Dn. This gives n unknowns.
C Distillate flow rate due to brine flashing in
effects 2 through n, which are defined by d2,d3, .. , dn!1, dn. This gives n!1 unknowns.
C Distillate flow rate due to distillate flashing in
effects 2 through n, which are defined by
. This gives n!1 unknowns.
C Temperature of evaporating brine in effects 1
through n!1, which are defined by T1, T2, ,
Tn!1. This gives n!1 unknowns.
C The flow rate of the heating steam, which is
defined byMs.
C The flow rate of the cooling seawater, which
is defined byMcw.C The heat transfer area in each evaporation
effect, which is defined byAe.
C The condenser heat transfer area of the con-
denser, which is defined byAc.
This gives a total of (6n+1) variables, which
requires simultaneous solution of (6n+1) equa-
tions. These equations include the following:
C Total mass balance for each effect, which
gives n equations.
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(5)
C Salt balance for each effect, which gives nequations.
C Energy balance for each evaporator, which
gives n equations.
C Heat transfer rate for each evaporator, which
gives n equations.
C Energy balance for brine flashing in effects 2
to n, which gives n!1 equations.
C Energy balance for distillate flashing in effects
2 to n, which gives n!1 equations.
C Energy balance and heat transfer rate for the
condenser, which gives two equations.C Constraint on the total distillate flow rate,
which gives one equation.
A summary of the system model is given
below:
C Total mass balance in the first effect:
F1 =D1 +B1 (1)
C Total mass balance in effects 2 to n:
Fj
+ Bj!
1
=Dj
+ Bj
(2)
C Salt balance in the first effect:
Xcw F1 =Xbj Bj (3)
C Salt balance in effects 2 to n:
Xcw Fj + Xbj!1Bj!1 =Xbj Bj (4)
C Constraint on the total distillate flow rate:
C Energy balance in the first effect:
Ms8s =F1Cp (Tb1!Tcw) +D18v1 (6)
C Energy balance in the second effect:
D18c1 =F2Cp (Tb2!Tcw) +D28v2 (7)
C Energy balance in the effects 3 to n:
(8)
C Heat transfer rate in the first effect:
Ms8s = U1A (Ts!Tb1) (9)
C Heat transfer rate in the second effect:
D18c1 = U2A (Tc1!Tb2) (10)
C Heat transfer rate in effects 3 to n:
(Dj!1 + dj!1 + ) 8cj!1 = UjA (Tcj!1!Tbj) (11)
C Flow rate of vapor formed by brine flashing ineffects 2 to n
Bj!1Cp (Tbj!1!Tbj) = dj8vj (12)
C Flow rate of vapor formed by distillate flash-
ing in effects 2 to n
(13)
C Evaporation temperature in effects 1 to n:
Tvj = Tbj!BPEj!NEAj (14)
C Condensation temperature in effects 2 to n:
Tcj = Tvj!
)Tpj!
)Ttj!
)Tcj (15)
C Condenser energy balance:
(Mf + Mcw) Cp (Tf!Tcw) =Mu8cn (16)
C Condenser heat transfer rate:
(17)
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(18)
C Mass balance of entrained and un-entrained
vapor by the steam jet ejector in vapor com-
pression mode:
Mev + Mu = (dn + +Dn) (19)
C
Entrainment ratio by the steam jet ejector:
w = Mev/Mm (20)
C Performance ratio:
PR = Md/Mm (21)
C The specific flow rate of cooling water:
sMcw = Mcw/Md (22)
C The conversion ratio:
CR = Md/Mf (23)
C The specific heat transfer area:
sA = (Ac + n Ae)/Md (24)
4.2. Process economics
Calculations of the product unit cost dependon process capacity, site characteristics, and
design features. System capacity specifies the
heat transfer area, size of various pumping units,
and dimensions of the evaporation effects. Site
characteristics considerably affect the process
capital, i.e., construction on a new site is quite
different from construction on a site that has older
desalination units. In the latter case, the new
installation can benefit from a common intake
piping system, discharge lines, and pretreatmentunits. The heating steam temperature dictates the
type of antiscalent used, material of construction,
deaerator capacity, and capacity of a non-con-
densable gas removal system. In a low-temp-
erature ME system where the heating steam
temperature is below 70C, the condenser/
evaporator tubes are constructed from 90/10
Cu/Ni alloys, titanium, or aluminum brass alloys.
Costs include direct capital, indirect capital,
and operations. The direct capital cost includes
land, well construction, process and auxiliaryequipment and buildings. The land cost is usually
greatly reduced because most of the desalination
plants are owned by governments or munici-
palities. The cost of process equipment includes
evaporators, instrumentation, controllers, pipe-
lines, valves, pumps, and treatment equipment.
The auxiliary equipment includes intake lines,
transmission pipes, storage tanks, generators, and
transformers. Buildings include the control
rooms, laboratories, workshop, storage space, and
offices. Indirect capital cost is expressed as
percentage of the total direct capital cost or the
cost of materials and labor. Insurance and con-
tingency may account for up to 15% of the total
direct capital costs. Other indirect capital costs
include construction overhead, which may
account for up to 15% of the material and labor
cost.
Operating costs cover all expenditures in-
curred after plant commissioning and duringactual operation. These include labor, energy,chemical, spare parts, and miscellaneous costs.
Energy costs include heating steam and elec-tricity. Electricity cost varies over a range of$0.040.09/kWh. Estimating the heating steam
cost depends on the features of the co-generationfacility and type of power plant production. Also,demand for electric power affects the estimated
cost of the heating steam, i.e., high vs. lowdemand periods. The maintenance and spare partscosts account for up to 2% of the annual direct
capital cost. Another important operating cost
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item is the chemicals cost, which includes acids,alkali, chlorine, and antiscalent.
The following illustration gives the required
parameters and calculation steps of the unit
product cost. The following system parameters
are used in the calculations:
C Production capacity (Md) is set at 12,000 m3/d
C Plant life (n) is set at 30 years
C Electricity cost (ce) is set at $0.05/kWh
C Steam heating cost (cs) is set at $1.5/MkJ
C Performance ratio (PR) is set at 16 kg product/
kg steamC Latent heat of heating steam at 70C is equal
to 2333.9 kJ/kg
C Specific cost of operating labor (cl) is set at
$0.1/m3
C Interest rate (i) is set at 5%
C Plant availability (f) is set at 0.9.
C Production efficiency (g) is set at 0.9.C Maintenance annual cost, expressed as a per-
centage of the direct annual cost (x), is set at
0.01.
C Direct capital cost (cd
) = $27.5106
C Specific consumption of electric power (w) =
3 kWh/m3
C Specific chemicals cost (ck) = $0.025/m3
The results of the calculations are:
C Amortization factor:
C Annual fixed charges:
A1 = (a) (cd) = (0.065051) (27.5106)
= $1788902.5/y
C Annual heating steam cost:
A2 = (cs) (8)(f) (g) (Md) (365)/[(1000) (PR)]
= (1.5) (2333.9) (0.9) (0.9) (12,000) (365)/
[(1000)(16)] = $776,269.7/y
C Annual electric power cost:
A3 = (ce) (w) (f) (g) (Md) (365)
= (0.05) (3) (0.9) (0.9) (12,000) (365)
= $532,170/y
C Annual chemicals cost:
A4 = (ck) (f) (g) (Md) (365)
= (0.025) (0.9) (0.9) (12,000) (365)
= $88,695/y
C Annual labor cost:
A5 = (cl) (f) (g) (Md) (365)
= (0.1) (0.9) (0.9) (12,000) (365)
= $354,780/y
C Annual maintenance cost:
A6 = (x) (a) (cd) = (0.01) (0.065051) (27.506
)= $17,889/y
C Total annual cost:
At =A1 +A2 +A3 +A4 +A5 +A6 = 1,788,902.5
+ 776,269.7 + 532,170 + 88,695 + 354,780
+ 17,889 = $3,558,706.2/y
C Unit product cost:
As = At/[(f) (g) (Md) (365)] = (3558706.2)/( 0.9)
(0.9) (365) (12,000) = $1.003/m3
The above value for the unit product cost is
within limits of the reported field data, which
may vary over a range of $0.8/m3 up to $1.5/m3.
Such variations depend on the plant capacity,
energy cost, labor experience in operation and
maintenance, plant life, efficiency of chemical
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Table 1
Summary of previous economic data for multiple effect evaporation in stand-alone and vapor compression modes
Reference Process Capacity,
m3/d
Capital,
$
Unit capital
cost, $/(m3/d)
Unit energy
cost, $/m3Unit chemical
cost, $/m3Unit product
cost, $/m3
Matz and
Fisher (1981)
MVC 1,000 8.94105 894 0.52 0.02 1.51
Veza (1995) MVC 1,200 1.586106 1322 1.057 3.22
Leitner (1992) MEE 37,850 70.4106 1860 0.08 0.024 1.08
Wade (1993) MEE 32,000 67.2106 2100 1.147 0.207 1.31
Morin (1993) MEE 22,730 35.05106 1562 0.49 0.0606 1.24
Morin (1993) MEE-TVC 22,730 34.65106
1524 0.785 0.0606 1.55
treatment, etc. A summary for some results of the
field data are shown in Table 1. Additional data
and analysis of the economics of thermal and
membrane desalination processes can also be
found in the study by Ettouney et al. [17].
4.3. Package results
Results of the MEE process are shown inFigs. 48. The illustration includes the following:
C design data display, shown in Fig. 4
C results display, shown in Fig. 5
C profiles display, shown in Fig. 6
C flow diagram display, shown in Fig. 7C cost display, shown in Fig. 8.
The design data display (Fig. 4) allows the
user to define the following variables:C number of effects (n), set equal to 12
C compression ratio (Cr), set equal to 4
C pressure of motive steam (Pm), set equal to1500 kPa
C heating steam temperature (Ts), set equal to
70CC rejected brine temperature (Tn), set equal to
40C
C feed salinity (Xf), set equal to 36,000 ppmC feed temperature (Tf), set equal to 30C
C intake seawater temperature (Tcw), set equal to
25C
C plant capacity (Md), set equal to 12,000 m3/d
C brine salinity leaving each effect (Xbj), set
equal to 52,000 ppm.
Other input design parameters include dimen-
sions and properties of the evaporator or con-
denser tubes as well as the specifications of the
evaporator demister:
C wall thickness of evaporator tubes (te), set
equal to 5 mmC outer diameter of evaporator tubes (deo), set
equal to 31.75 mm
C wall thickness of condenser tubes (tc), set
equal to 5 mm
C outer diameter of condenser tubes (dco), set
equal to 31.75 mm
C thermal conductivity of evaporator tubes (ke),
set equal to 0.042 kW/mC
C thermal conductivity of condenser tubes (kc),
set equal to 0.042 kW/mC
C
fouling resistance in the evaporator (Rfe), setequal to 0.1 m2 C/kW
C fouling resistance in the condenser (Rfc), set
equal to 0.1 m2 C/kW
C velocity of the falling film in the evaporator
(Vf), set equal to 1.5 m/s
C length of the condenser tubes (Lc), set equal to
10 m
C length of the condenser tubes (Le), set equal to
10 m
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Fig. 4. Display of design
data.
Fig. 5. Display of perfor-
mance results.
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Fig. 6. Display of process profiles, which include temperatures, flow rates, heat transfer coefficients, and losses.
Fig. 7. Display of flow chart showing the design data of the steam jet ejector.
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Fig. 8. Display of cost data and results.
C thickness of the falling film in the evaporator
(tfe), set equal to 1 mm
C vapor velocity in the demister (Vp), set equal
to 5 m/sC demister thickness (Lp), set equal to 0.2 m
C demister density (Dp), set equal to 300 kg/m3
Performance results shown in Fig. 5 give the
following main features for the MEE and MEE-
TVC:
C specific heat transfer areas of 767.4 m2/(kg/s)
and 757.9 m2/(kg/s) for the MEE and MEE-
TVC, respectively
C performance ratios of 9.5 and 14.7 for the
MEE and MEE-TVC, respectively
C specific flow rates of cooling water of 7.17
and 3 for the MEE and MEE-TVC, respect-ively
C shell diameter for each evaporator of 3.38 m
and number of tubs in each evaporator, 8706
The system profiles shown in Fig. 6 show the
following behavior:
C Mass flow rate of distillate vapor varies
between 12.9 kg/s to 10.4 kg/s from effect 1 to
effect 12.
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C The overall heat transfer coefficient variesbetween 2.487 kW/m2 C to 2.253 kW/m2 C
from effect 1 to 12.
C The sum of the BPE and the non-equilibrium
allowance from effects 1 to 12 varies between
1.6C and 1.8C.
The flow diagram of the process is shown in
Fig. 7. The flow diagram includes the 12 effects,
the steam jet ejector, the condenser, as well as
blocks for various streams. The display shows the
design results for the steam jet ejector. Thisspecific condition requires use of two ejectors in
series in order to achieve the required vapor
compression. The design data include dimensions
of nozzles and diffuser, flow rates of entrained
vapor, compressed vapor, and motive steam. Each
block in the flow diagram includes design results
for the block, which may include heat transfer
coefficient, area, flow rates, temperatures, or
pressures.
The cost display is shown in Fig. 8, and it
includes the input parameters, which can be
adjusted by the user. The cost parameters include
plant life, plant factor, production efficient,
production capacity, performance ratio, interest
rate, and various cost elements. The plants capa-
city and performance are the same as those used
in the system design. However, the user can
adjust these values. The display also includes the
cost results, which indicate that the unit product
cost is equal to $1.016/m3. This value is con-
sistent with field data shown in Table 1.
5. Conclusions
This paper summarizes the developments in
the visual basic simulation package of thermal
and membrane desalination processes. Several
additions have been made in the packages includ-
ing cost estimation, simulation of the RO process,
calculations of effect dimensions, and a detailed
design of the steam jet ejector for vapor com-
pression. The development process was necessaryto improve the capabilities of the simulator. The
simulator proved to be highly useful in teaching
desalination and engineering training.
The simulator gives the user efficient tools for
system design or simulation. Results give the user
the means to have a better understanding of the
desalination systems. Further modification and
additions are underway, which are based on feed-
back of users in other colleges and the industry.
The package integrates well with other literature
attempts focusing on developing a package forprocess simulation or cost estimation.
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Recommended