Desalination Using Ambient Air- Simulation and Energy Optimization

ELSEVIER Desalination 175 (2005) 247-257

DESALINATION

www.elsevier.corn/locate/desal

Desalination using ambient air: simulation and energy optimization

Ahmad Hama&*, Mohammed Abdu l -Kar im b

~Chemical Engineering Department, Qatar University, PO Box 2713, Doha, Qatar Tel. +974 4851117; email: [email protected]

bChemical Engineering Department, United Arab Emirates University, Al-Ain, United Arab Emirates

Received 23 September 2003; accepted 16 September 2004

Abstract

This work applies to process design, simulation, analysis, and optimization to minimize the energy requirements for producing desalinated water using ambient air (humidification and dehumidification process). The only operating cost is for the use of air blower to supply air flowrate of 65-70 kmol/h. The production rate is 1 gpm of desalinated water per 2.25 gpm of saline water. By using process simulation and applying energy optimization concepts, the process parameters were manipulated and analyzed so that the feed saline water to the column is used to cool the exit air stream. The proposed approach reduced the solar energy requirement by 65%, and the cooling energy is eliminated. A case study is pursued to show the effectiveness of using process simulation and energy optimization concepts.

Keywords: Desalination; Humidification; Dehumidification; Energy minimization

1. Introduction

The shortage of potable water in the Arab Peninsula calls for new cost-effective methodo- logies for water desalination. The population is increasing rapidly and new industrial firms are increasing while resources of potable water are scarce. Hence, desalination of seawater and brackish water is becoming the main source for producing potable water in these parts of the

*Corresponding author.

world. For example, 65% of worldwide plants are operating in the Arabian Gulf states [ 1 ]. There are several technologies used for water desalination. In this part of the world, multi-stage flash (MSF) units and multi-effect distillation (MED) are mainly the processes used. Usually, these plants are connected to power plants. Reverse osmosis (RO) is widely used to desalinate brackish water.

There have been many of attempts to reduce energy costs in all types of desalination plants. Just to mention a few, Schwarzer et al. [2]

0011-9164/05/$- See front matter 2005 Elsevier B.V. All rights reserved doi: 10.1016/j. desa1.2004.09.028

248 A. Hamad, M. AbduI-Karim / Desalination 175 (2005) 247-257

discussed the use of heat recovery combined with solar energy to produce 25 L/mVd of desalinated water. Mesa et al. [3] discusses the design of maximum energy efficiency desalination plants. A1-Nashar [4] applies automatic set point control to optimize MSF plants. Slesarenko [5] discusses the use of heat pumps to minimize energy requirements in seawater desalination plants. Geisler et al. [6] uses pressure-exchange systems to optimize energy demands in reverse osmosis units. AI-Sofi et al. [7] discusses the optimization of integrated seawater desalination plants. Beckman et al. [8] introduced the idea of dewvaporation tower. They used ambient air to desalinate water. The vapor is then heated and returned to the outside surface of the tower. Hence, the vapor will heat the column as it cools down and the water condenses.

Process simulators are becoming very valuable and powerful tools in design and optimization. In this work, process simulation and optimization tools are used to minimize the operating cost and the performance of the proposed air desalination unit. The operating conditions will be identified so as to minimize the operating cost of the unit.

2. Schematic description of the proposed process

A simplif ied schematic diagram of the proposed process is presented in Fig. 1. The process is simple and is similar to the humidification- dehumidification desalination process. In this work, the system set up and the operating conditions are optimized. The top feed of the column is the saline water and the ambient air is fed from the bottom. The saline water could be seawater, brackish water or the reject from a reverse osmosis plant. The air leaving the column is assumed to be at the saturation limit at the exit temperature. Packing could be needed to guarantee enough contact time and enough surface area between air and water. The air stream is cooled in a heat exchanger to condense the product water.

Discharged / . . - -~ i r out Fo~t Air ~y~ ~)~'y -' ]

Condensed Water

Water in

yin

F~ P Air in Water out

Fig. 1. Simple representation of the system.

3. Process model

A simplified model will be developed. This model will be used to identify important design parameters and then study their effect on the process performance. The unit can be designed to recover a specific amount of water. The outlet air leaving the top of the column is assumed to be saturated. The column is assumed to run at atmo- spheric pressure. The flowrate of air can be manipulated with a blower and a flow meter. The amount of water removed (WR) from saline water can be estimated using the following equation:

WR = F~y "t -Fray ~ (1)

where Fou t and F~ are the flowrates of outlet and inlet air streams, respectively, yOUr and ym corres- pond to outlet and inlet water compositions in the air stream, respectively. The water inlet composition (ym) can be easily determined by ambient air humidity. The outlet composition is assumed to be the saturation limit at exit temperature, which can be easily determined using a temperature sensor. The overall material balance of the system is presented by:

A. Ht~nad, M. Abdul-Karim / Desalination 175 (2005) 247-257 249

Fo., = WR + (2)

Substituting Eq. (2) in Eq. (1) and solving for WR, the following equation is obtained:

WR=Fi .(y~-.yi~)/(1-y~t) O)

Eq. (3) shows that water removed is a function of inlet air flowrate, inlet water composition in air, and outlet water composition in air. The exit water composition in air is assumed to be at saturation and hence it becomes a function of temperature. Since the system is countercurrent, the exit air temperature is affected by the water inlet temperature. The higher the water inlet temperature, the higher the air exit temperature.

When the exit air is cooled, water will condense. Conden~d water represents water product (WP) in this process and can be calculated as follows:

WP= Fo~ .yOUr _ Fa . ya~ (4)

where/~'~ and y~S are the discharged air flowrate and water composition in discharged air respectively. To reduce Eq. (4) in terms of Fi~ ~, the following set of equations is used.

Substitute Eq. (3) in Eq. (2) to obtain:

( Y~----Y~nl-E ( l -Yml Fo~t=F~n 1"t 1 yO~t ) - in - ~ , l -y ~t ) (5)

Fd,s - WP (6)

Substituting Eqs. (5) and (6) in Eq. (4) and with some rearrangements, the following equation is obtained:

I WP=F n 1+ 1- 1 -y ~' ) 1 yin yOUr ydiS (7)

Eq. (7) is the model equation for this process that has all the inlormation on the parameters that affect the quantity of water recovered from the saline water feed.

4. Design parameters

Eq. (7) provides a comprehensive picture for the design parameters that influence the performance of the process shown in Fig. 1. These design parameters are as follows.

4.1. Flowrate of inlet air, E m

As the inlet air flowrate increases, the water removed by air increases. Air flowrate has a major impact on the volume of the system and the loads of the blower (fan) and condenser used in the process. Inlet air flowrate can be reduced by increasing inlet air temperature, as will be illustrated by the case study. However, for the same water recovery, the lower the flowrate of air, the lower the capital cost of the system. This is due to smaller columns and smaller heat exchangers.

4.2. Outlet air composition, yOUr, and temperature, To~

The outlet water composition in air (y~) from the column is assumed to be the saturation composition at the exit air temperature (T~). The higher the exit air temperature (T ~) the higher y~, and hence, more water is removed by the inlet air stream. T ~ can be increased by increasing the inlet water temperature aud/or increasing the inlet water flowrate if the inlet water is fed to the column at a high temperature. This suggests that the temperattu-e profile inside the column should be as high as possible to increase the value ofy ~t [see I!k t. (7)].

4.3. Discharged air composition, ya~, and temperature, T a~

The condensation temperature (/t~) determines the water discharged composition (yaS) in air. The

250 A. Hamad. M. Abdul-Karim /Desalination 175 (2005) 247-257

lower the condensation temperature, the lower the discharged composition. The lower the discharged air composition, the more the water that is condensed from the air stream.

4.4. lnlet air composition, yi,

The inlet air composition determines the amounts of water and dry air in the inlet air stream. The higher the water composition of inlet air, the lower the amount of dry air that is entering the system. This has a negative impact on the process performance because lower dry air flowrate means that less water will be carried out at saturation. Hence, the removal efficiency per unit air is reduced. This parameter will not be analyzed since y'" will be determined by ambient conditions which are beyond our control.

5. Analysis of design parameters

Among all the above design parameters, your (water composition in air leaving the column) is the most process-oriented parameter. In other words, it is directly affected by process operating conditions. Inlet air flowrate and composition are more likely to be determined by design and/or ambient conditions, yd~ is likely to be determined by the amount of cooling applied and by the capacity of available cooling utility. However, y~t depends on process conditions such as flowrate of air, flowrate of water, inlet air temperature, inlet water temperature, and pressure inside the column. Thus, yd~, plays a major role in determining the amount of water condensed. The lower the y~, the higher the amount of water condensed. The effects of yOUt and yd~ on process performance are analyzed.

Consider the system presented in Fig. 2. At a constant inlet airflow and constant inlet air composition, the target discharged air temperature at various values ofy ut to achieve the desired water production rate is investigated. For each case, the required cooling duty of the condenser to achieve the target temperature is identified using simulation. At a fixed inlet flowrate, 1000 kmol/h, and a

Discharged Air : ,~Ai r out o.t y~ ~ Y

I I Stripping Water I [ Column Product ~

Air in y~

Fig. 2. Illustration of design parameters (3, refers to water composition in associated stream).

f~ed inlet water composition, y~" = 0.01, Eq. (7) was solved to calculate y~S for various values of ):out so as to obtain the desired water production (PIP). Then, a simplified process is developed using Hysys simulation software. The software is used to calculate the duty of the condenser, Q (kW), and the outlet temperatures, T ut and/~s. Tables 1, 2 and 3 contain the design parameters for water production rates of 10, 20, and 30 kmol/ h, respectively.

When the air flowrate (F~,) is reduced (Table 4) for the same water recovery (Table 1), the condenser duty increased and discharge temperature decreased. This may lead to using more expensive refrigerants but capital cost could be lower due to smaller equipment. This parameter will be further investigated in the case study later in the paper.

Table 1 Design parameters for WP = 10 kmol/h, F~, = 1000 kmol air/h, yin = 0.01

yO~, z ~'(oc) y~ r ~(oc) Q(kW) 0.02 17.7 0.01 7.5 207.0 0.03 24.3 0.02 18.0 174.5 0.04 29.2 0.03 24.6 160.1 0.05 33 0.04 29.5 151.8 0.06 36.4 0.05 33.5 146.3 0.07 39.2 0.06 36.8 142.4 0.08 41.8 0.07 39.6 139.3 0.09 44 0.08 42.1 136.9 0.1 46 0.09 44.4 135.0

A. Hamad, M. Abdul-Karim /Desalination 175 (2005) 247-257 251

Table 2 Design parameters for WP = 20 kmol/h, F~, = 1000 kmol air/h,y ~"= 0.01

yO~t /o~t (oC) y~ /~ (C) Q (kVO

0.03 24.3 0.01 7.9 384.0 0.04 29.2 0.021 18.5 334.1 0.05 33.1 0.031 24.9 319.5 0.06 36.4 0.042 29.8 304.8 0.07 39.2 0.052 33.8 293.1 0.08 41.8 0.062 37.1 284.3 0.09 44 0.073 40 278.4 0.1 46 0.083 42.4 278.4

Table 3 Design parameters for WP = 30 kmol/h, Fi, = 1000 kmol air/h, 3?" = 0.01

yO. zo.(oc) y~S ~s(oc) Q(kW) 0.04 29.2 0.011 8.6 545.2 0.05 33.1 0.022 19.2 483.6 0.06 36.4 0.032 25.4 466.0 0.07 39.2 0.043 30.4 442.6 0.08 41.8 0.053 34.3 430.9 0.09 44 0.064 37.6 422.1 0.1 46 0.075 40.4 416.2

Table 4 Design parameters for WP = 10 air/h, yi, = 0.01

kmol/h, Fi. = 750 kmol

yO~t z '(oc) y~S #'(oc) QO~W) 0.02 17.7 0.007 1.857 220.8 0.03 24.3 0.017 15.31 178.6 0.04 29.2 0.027 22.81 162.2 0.05 33 0.038 28.16 153.1 0.06 36.4 0.048 32.36 147.2 0.07 39.2 0.058 35.85 143.0 0.08 41.8 0.069 38.83 139.8 0.09 44 0.079 41.45 137.3 0.1 46 0.089 43.79 135.3

higher the exit air temperature (at saturation), the lower the condensation duty. Also, when the discharged temperature (/~s) increases, low cost cooling utilities can be utilized and that would reduce the costs of the system. In addition, air flowrate can be used to manipulate the performance of the system.

6. Temperature prof'fle inside the column

As illustrated above, increasing temperature profile inside the column (yO,t) can increase the water recovery ratio. Beckman et al. [8] proposed the return of hot vapor to the outside surface of the column to heat water inside the column. In this work, the following scenarios are considered to increase the temperature profile inside the column and hence increase yO,t. These scenarios consider only capital cost with no operating cost. Heating inlet saline water. This task can be

achieved by either of the following methods: - Use solar energy. This is a very important

source of energy in the Middle East, Asia, and Africa and should be utilized accordingly. This option requires only capital cost.

- Use hot process stream. Any stream in this process (i.e. exit air stream) that needs to be cooled is a potential heating source and can be used to heat the feed water stream. In addition, if this unit is built in a chemical/ manufacturing plant, a low pressure steam or a hot process stream that needs to be cooled, could also be used to heat the feed water. This option includes only a capital cost. This option could be the most cost- effective option.

Increasing inlet air temperature. This task also can be achieved using the same methods used for heating inlet saline water.

5.1. Summary of results

Tables 1-4 show that as yO,t increases, y~US increases, and Q decreases. This means that the

7. Energy requirements

By inspecting Fig. 1, the only energy requirement is cooling energy that is needed to condense

252 A. Hamad. M. Abdul-Karim /Desalination 175 (2005) 247-257

water from the outlet air stream. However, heating energy can be used to enhance the performance of the system. Heating energy can be used to increase the temperature profile inside the column. This can be achieved in two ways: 1. Heating feed water 2. Heating feed air

Accordingly, the following is a list of streams that can utilize cooling/heating energy.

Hot streams that need to/can be cooled Exit air stream

- The exit air stream must be cooled to recover the desired amount of water.

- Cold streams that need to/can be heated Inlet air stream

- Heating inlet stream can be heated to increase your

Inlet water stream - Heating inlet stream can be heated to in-

crease yO~t

8. Energy optimization

There is only one stream that needs to be cooled but two streams that can be heated. The- question is what streams to match? Using the inlet

air stream to the column to remove heat from the exit air stream from the column will not be sufficient and will be more costly. This is because: 1. Both streams have same flowrate of dry air

but the exit stream has higher moisture content 2. Cooling the exit stream requires removal of

latent heat of condensation 3. Air-air exchangers are larger and more ex-

pensive than air-water exchangers for the same duty and the same air flowrate (exit air stream). - Consequently, energy optimization strategy

requires using inlet feed water to the column to remove heat duty from the air stream leaving the column. Heating inlet air stream to the column can be used to enhance the system performance.

- To minimize energy in the system, cooling energy should be provided completely by the feed water stream.

9. System structure

Based on the process analysis and energy optimization strategies, the system structure presented in Fig. 3 is developed. The features of this structure are as follows:

Discharged Air ~ ~ ~

"~ Condensed ' Water

Air in y

l Water Discharge

Fresh Saline Water

Fig. 3. Proposed structure for energy minimization.


1. No external cooling utility is needed 2. Solar energy is used to further heat the water

feed to enhance the performance of the system (increase yOUr).

3. Water is discharged to prevent salt accumu- lation in the system

4. Condensed water flowrate is predetermined.

10. Problem formulation

Using the above proposed structure, the objective of this work becomes to minimize the solar energy requirements for the system for a fixed water recovery amount. Solar energy is used to enhance the performance of the system. Water recovery ratio can be tackled by placing an upper limit to reduce water discharge with respect to fresh saline water. The problem can be represented as follows: Objective function: Minimize solar energy requirements

Subject to: Cooling energy requirements = 0 Flowrate of recovered water = fixed value Temperature of feed water stream < maximum value

Solar energy is used to maintain temperature of feed water at fixed temperature

Water discharge flowrate < maximum value Air discharge temperature > minimum value

II. Solution approach

The following steps will be followed to identify the optimal system structure to solve the above optimization problem. 1. Identify ambient conditions 2. Set water recovery flowrate 3. Set process constraints 4. Apply process analysis to optimize energy

Manipulate process design parameters to eliminate the usage of external cooling utility and to minimize solar energy requirements.

11.1. Process analysis

Process sensitivity analysis supported by process simulation will be pursued to accomplish the above optimization task (part 4). The following process design parameters that were identified from Eq. (7) will be manipulated in this analysis: 1. yUt/(T"t): exit air composition (water)/temp-

erature 2. y~s/(T~is): discharged air composition (water)/

temperature after condensation 3. Ft." inlet air flowrate

Having high yOU, and lower F could lead to smaller equipment and lower costs. However, these parameters have to guarantee that no external cooling energy is needed. The analysis will be illustrated in the case study.

12. Case study: designing a unit in the Arabian Gulf

The objective of this case study is to illustrate the above mentioned solution methodology. The Arabian Gulf (AG) has a very hot and humid climate, especially in summer. Even in winter, temperatures stay in the range of 20-30C. In addition, potable water resources inAG are scarce and the region depends mainly on desalination plants to produce the needed potable water. This process can be used in remote areas; it can be used to complement existing desalination plants to enhance water recovery; and it can be used in industrial plants. Designing of this unit is analyzed here to produce a small scale of potable water. The following parameters are used in the design: Production rate of water: 1.0 gallon/min (gpm) Saline water (brackish water) is available at

30C Inlet air is fed at 30C Water composition of air is y~ = 0.015 (mole

fraction) Water can be heated using solar energy up to

70C

254 A. Hamad, M. Abdul-Karim /.Desalination 175 (2005) 247-257

Lowest discharge temperature is assumed to Discharged be 18C Air ql

Maximum water discharge is 1 gpm (brine 18c solution). 0.0204 water

12.1. Base design

As a basis for analysis and comparison, the following design is assumed to be the base design (Fig. 4). The base case relies on using the lowest possible discharge temperature (18C) and producing 1 gpm of product water. The base case has the following design parameters: inlet water flowrate 5.3 gpm; outlet water (brine) temperature: 19.2C; Fi: 7514 kmolfh; 7~ut: 19.3C;y ut= 0.022; y~S= 0.020; T ~s= 18C; Q (condenser): 231 kW.

12.2. Energy minimization

Fig. 5 represents the exit air stream (saturated) and the feed saline water to the column in terms of inlet/outlet temperatures and energy requirements. Energy can be transferred from the air stream to the water stream in the region where the air stream is above the water stream on this diagram. Fig. 5 shows that there is some energy that can be exchanged between the two streams, but still external cooling energy is needed to completely cool the exit air stream. This is against the design objectives of this work. Both streams are shown as dotted lines because the flowrate of each stream can be manipulated to enhance the performance of the unit and meet the design objectives. Maximizing the heat exchanged between feed water and exit air stream will minimize or eliminate the use of external cooling utility and will reduce the amount of solar energy.

However, to be able to use exit air stream in heating the feed water to the column, the final temperature of the air stream should be higher than that of the inlet fbed water by at least a minimum allowable difference (driving force). Similarly, the final water temperature should be lower than that of the inlet air by at least the driving force. In this

Air out ~ 19"3C

231 kW

Condensed Water 1 gpm

Water

L - - 5.3 gpm 30C

Air in y Water out 7514 kmol/h * 1 gpm

19.2C 30C 0.015 water

Fig. 4. Base design for case study.

80 Feed water stream ~

,~.,,..,~o~:'::~'~xit air stream 50i

30~ ~* 20

|0 0 . . . . . . . . . . . . . . . . . . . ............................. ~ . . . . . . . .

0 50 100 ! 50 2oo 250

Heal exchanged, kW

Fig. 5. Thermal representation of the water and air streams.

study, 3C is used as the minimum allowable difference (driving force).

The following structure guidelines are used to realize the objective of the unit design. 1. Using solar energy as the second source of

heating. Hence, the water feed temperature is always 70C.

2. Heat duty needed to heat feed water in the first stage (before using solar energy) is equal to the heat duty removed in the condenser.

3. The target temperature for heating the feed water is lower than T ~ut minimum by 3C.

4. Fresh water flowrate is increased and air flowrate is reduced to achieve points 2 and 3. The


preference is given to reducing air flowrate since the water can be recycled due to the advantages mentioned earlier for reducing the air flowrate.

12.3. Process analysis and final design

As the air flowrate decreases and water fow- rate increases, exit temperatures of air and water

Table 5 Unit design parameters when heating feed water

increase. In this case, the exit air temperature ( T "t) approaches 70C (the temperature of solar-heated water). Table 5 includes air flowrates that guarantee cooling the air stream completely by the feed water (point 2 in the structure). The Hysys model used in this study is shown in Fig. 6.

The following design features can be seen from Table 5:

Air flowrate, kmol/h 56 60 Water feed, gpm ~45.1 35.7 Fresh water, gpm 2.47 2.37 Exchanged heat duty, kW* 159.3 161.7 Solar heat duty, kW 100.7 86.3 /o~, o C 66.7 64.8 /~s, o C 49.6 46.2 Driving force, C 3.0 3.0

65 70 75 85 32 29.4 28.1 26.7 2.25 2.39 2.42 2.55

163 164.4 165.2 166.2 81 78.8 79.4 84 63.3 62.0 61 59.3 44.4 42.8 42.2 41.3 3.0 3.0 3.0 3.0

*Exchanged heat between exit air stream and feed water

84,74 L~t, I I

I~"V4

Fig. 6. Hysys representation of the proposed structure.

i

L* .Ti

T;~ -

256 A. Hamad, M. Abdul-Karim /Desalination 175 (2005) 247-257

1. All designs have no external cooling utility. 2. Going lower than the air flowrate of 56 kmol/h

is not feasible since this will violate point 2 in the structure approach.

3. As air flowrate increases, a. heat exchanged between the two streams

increases b. total feed water flowrate to the column

decreases c. the column outlet temperature and the dis-

charged temperature go down 4. Fresh saline water and solar energy require-

ments go through optimum values between air flowrates of 65-70 kmol/h.

The optimum design parameters lay within the range of air flowrate 65-70 kmol/h.

12.4. Potential improvement by heating inlet air

As mentioned earlier, increasing the inlet air temperature can be used to enhance the performance of the system. This is shown in Table 6.

Table 5 shows that increasing the air temperature has a negligible effect on the air flowrate and feed water flowrate. Actually, it can hinder the performance of this unit. This is because it causes the exit water temperature to increase and hence reduce the amount of heat duty that can be exchanged with the exit air stream. In addition, the

Table 6 Design parameters when heating inlet air

Air flowrate, kmol/h 65 65 Air temperature, C 50 70 Water feed, gpm 38 38 Fresh water, gpm 2.38 2.69 Exchanged heat duty, kW 160 160.4 Solar heat duty, kW* 106.7 108.6 /~, C 66.8 67.4 /~, C 52.0 53.2 Driving force, C 4.2 3.3

*Includes energy needed to heat feed air

amount of energy needed to heat the air stream raises energy requirements for the system. Hence, heating the inlet air stream is not pursued in the final design of this unit.

The final solution of the proposed process is presented in Fig. 7.

13. Conclusion

The energy requirements for the proposed solar-aided desalination unit are minimized using simulation-aided simulation and energy optimization strategies. The feed saline water is used to cool the saturated air stream leaving the column to condense water, and hence the need for cooling utility is eliminated. Solar energy is used to further heat feed saline water to 70C to enhance the water recovery. Solar energy is reduced by more than 65 % by the proposed energy optimization scenario. A case study was discussed in detail to produce 1 gpm of potable water. The process analysis showed that solar energy and fresh saline water requirements go through optimum values as air flowrate increases.

14. Symbols

F - - Molar flowrate of air Q - - Heat duty T - - Temperature WR - - Molar flowrate of water removed from

saline water feed WP - - Molar flowrate of product potable water y - - Water molar composition

Subscripts

in - - In to the column out - - Out of the column

Superscripts

dis - - Discharged after condensation in - - In to the column out - - Out of the column


Discharged Air, 44~ ~ u t

Condgnsed Water 1 gpm

Air in 65 kmol/hr 30C

32 gpm 70oc

Solar Unit

81 kW

Water 2.25 gpm 30C

Water Discharge 1 gpm Fig. 7. Final design.

References

[ 1 ] S. AI-Mutaz, The continued challenge of capacity building in desalination, Desalination, 141 (2001) 145-156.

[2] K. Schwarzer, M.E. Vieira, C. Faber and C. Muller, Solar thermal desalination system with heat recovery, Desalination, 137 (2001) 23-29.

[3 ] A.A. Mesa, C.M. Gomez and R.U. Azpitarte, Design of maximum energy efficiency desalination plant (PAME), Desalination, 108 (1996) 111-116.

[4] A.M. E1-Nashar, Optimization of operating parameters of MSF plants through automatic setpoint control, Desalination, 116 (1998) 89-107.

[5] V.V. Slesarenko, Heat pumps as a source of heat

energy for desalination of seawater, Desalination, 139 (2001) 405-410.

[6] P. Geisler, W. Krumm and T. Peters, Optimization of the energy demand of reverse osmosis with a pressure-exchange system, Desalination, 125 (1999) 167-172.

[7] M. A1-Sofi, A. Hassan, O. Hamed, A. Dalvi, M. Kither, G. Mustafa and K. Bamardouf, Optimization of hybridized seawater desalination process, Desalination, 131 (2000) 147-156.

[8] J.R. Beckman, B.M. Hamieh and M.D. Ybarra, Experimental study with economical analysis of a dewvaporation tower, Energy and the Environment Proceedings, AIChE Annual Meeting, November 2000, pp. 316--333.

Documents

Desalination Using Ambient Air- Simulation and Energy Optimization