Solar barometric distillation for seawater desalting Part III: Analyses of one-stage and two-stage solar vapour thermo-compression distillation technologies

Solar barometric distillation for seawater desaltingPart III: Analyses of one-stage and two-stage solar vapour

thermo-compression distillation technologies

Mario RealiV. G.B. Angioletti 5, 20151 Milano, Italy

Tel. +39 (02) 452-1488; email: [email protected]

Received 23 March 2006; Accepted 24 June 2006

Abstract

The report concerns design aspects for the recently proposed solar barometric distillation technology for seawaterdesalting (SW–SBD) via underground barometric layout. One-stage and two-stage SW–SBD desalting plants apply-ing a solar vapour thermo-compression distillation technology are specifically analysed. Feed brine at subatmosphericpressure is made to flow in vacuum solar collectors of simple design and construction to absorb solar radiation andto deliver the water vapour which drives a vapour thermo-compression distillation process at operative temperaturesbelow 100°C. The proposed SW–SBD desalting technology has a good energy efficiency and promising technico-economic features. Field research on SW-SBD prototype plants is necessary to bring SW-SBD desalting technologyto its full technological development.

Keywords: Seawater desalination; Solar barometric distillation; Solar vapour thermo-compression; Steam ejectorpump; Energy efficiency

1. Introduction

The technology of seawater desalting via solarbarometric distillation (SW–SBD) concerns arelatively simple sun-driven distillation tech-nology which comprises an underground baro-metric layout and a field of specially designedsolar collectors [1,2]. The introduction andanalysis of various viable SW-SBD schemes, by

means of specific reports, appears necessary toprovide basic information for the design and fieldimplementation of SW–SBD prototype plantsunder rather different conditions as far as desaltedwater daily production capacity, climate, solarradiation, infrastructures, etc., are concerned.Considering the possible range (5×10!3, 5×104)m3/d for fresh water productivity, seven orders ofmagnitude are involved.

Desalination 207 (2007) 304–323

0011-9164/07/$– See front matter © 2007 Published by Elsevier B.V.doi:10.1016/j.desal.2006.06.014

http://dx.doi.org/10.1016/j.desal.2006.06.014

M. Reali / Desalination 207 (2007) 304–323 305

Careful site-specific evaluations of technologi-cal and economical aspects of interest arerequired to single out a possible SW–SBD plantvis-à-vis other technological solutions. Researchwork on the exploitation of solar energy forseawater desalination has a respectable historicalrecord (see, e.g., [3] and related references);mostly, research works and applications havefocused onto small production units (solar stills),but also large scale production plants have beenanalysed [4,5].

Several seawater desalination plants of differ-ing technologies have utilised barometric loops[1]. Solar assisted seawater desalination plantsutilising barometric loops have been presented in[6–10]. Several research projects have in recentyears advanced the state-of-the-art of solar desali-nation. For the sake of brevity and due to lack ofspace and of information, only some of them arementioned here (with apologies to neglectedresearchers).

Reference [11] proposes coupling an advancedsolar concentrating collector technology with amany-effect MED process, in view of developinglarge size desalination plants with potentiallycompetitive distillate cost as compared with grid-powered RO.

Reference [12] introduces an innovative solarstill, of enhanced distillate production, whichwith heat recovery and air mass circulation canreach up to 20 l/(m2 d) and thus substantiallyimproves the economic potential of solar stilldesalination.

Reference [13] introduces a compound solardistiller that has additional side mirrors, greatenergy efficiency, and may produce some 40 L/(m2 d).

Reference [14] considers the environmentalsustainability of desalination due to the largeflowrates of hot brine dissipated into the sea andproposes coupling a solar still plant with anexisting thermal desalination installation so as toimprove the overall desalination process whilemitigating the environmental impact.

Reference [15] presents actual operational datafrom a solar seawater desalination plant ofadvanced technology, utilising vacuum solar col-lectors, a heat storage tank, and an 18-effectMED system.

Reference [16] introduces a solar desalinationstill of enhanced efficiency with separatedevaporator and condenser units.

Reference [17] presents valuable data on asolar multi-effect distillation system with para-bolic troughs installed at Plataforma Solar deAlmeria, Spain.

Reference [18] concerns the development andtesting of a full titanium desalination systemcoupled with a solar pond.

Reference [19] describes a self-regulatingmultistage desalination system coupled with asolar pond.

The interest of developing SW–SBD desaltingtechnology, vis-à-vis the various solar and nonsolar desalting technologies presently available,may be simply referred to the following concepts:C It encompasses several solar desalination

technologies since its vacuum solar collectorscan heat and vaporize salt water solutionsfrom low to even relatively high operatingtemperatures (e.g., 150 C°) with reduced flowpressure drops.

C It exploits an underground barometric layoutwith relatively simple circuits and componentsfor all treated fluids.

C For all SW–SBD schemes, first approximationdesign parameters may be obtained viastraightforward thermodynamic analysis withsimple algebraic equations.

C It has an expected good energy efficiency (interms of electricity kWh per m3 of distillate)which favours potential couplings with elec-tric power generating systems utilizing renew-able energy sources.

C It can provide an efficient distillation sectionfor solar-driven closed-cycle osmotic powerplants for electric power production [20,21]which are of considerable potential interest

M. Reali / Desalination 207 (2007) 304–323306

since salt is theoretically more energetic thanoil [22].The present report introduces and analyses

one-stage and two-stage SW–SBD desaltingplants applying a solar vapour thermocompres-sion distillation technology by means of which asatisfactory exploitation of solar radiation, whichis the driving force of SW–SBD technology, andsmooth plant operation may be achieved. Thefollowing two sections concern operation andthermodynamic features of the proposed desaltingplants, and the last section concerns energy effi-ciency and general aspects of SW–SBD desaltingtechnology

The same type of SW–SBD evacuated solarcollectors introduced in [2] have been assumedfor the present SW–SBD plants. These solar col-lectors are compounded with cylindrical doublewalled transparent glass tubes with closed evacu-ated (Dewar type) interspace: a single flow tube,of ~10.5 m length, ~0.090 m inner diameter,~0.003 m wall thickness, and ~0.110 m outer dia-meter, is made with 4 (~2.6 m long) tubes con-nected in series through plastic/rubber joints andhas an operative sun irradiated surface of~0.90 m2.

The field of SW–SBD evacuated solar col-lectors comprises a suitable number of arrays oftransparent solar collector flow tubes affixedhorizontally on support frames at a preciseoperative height ~1 m above ground level, inlet/outlet manifolds, conduits, flow control valves,and sensors. A typical array has 100 flow tubesthat lie horizontally and adjacent (parallel) to oneanother on the array support frame. All flowtubes are connected by rubber/plastic joints attheir two ends respectively with an inlet manifoldand an outlet manifold which are larger plastictubes perpendicular to them. Rubber/plastic jointsprovide adequate tightened connections betweencomponent glass tubes and between glass tubesand manifolds.

The mass flow rate of the feed brine comingfrom the distillation section is aptly distributed in

the SW–SBD collector flow tubes by means ofpipes which connect all array inlet manifoldsamong themselves. In an analogous way, all arrayoutlet manifolds are connected among themselvesto deliver a sun-heated waste brine/water vapour/air mixture.

2. One-stage SW–SBD plant2.1. Plant operation

A simplified diagram of the proposed plant isillustrated in Fig. 1 where important components,e.g., flow-control valves and temperature/pres-sure/salinity/radiation sensors, are not shown.Feed seawater preheated by waste brine and byproduced distilled water in counter-current heatexchangers is pumped from an underground tankat a depth of ~10 m through a distillation heatexchanger placed at ground level where it is par-tially vaporized by absorbing the change-of-state(latent) heat of water vapour condensing intoproduced distilled water. A feed brine/watervapour/air mixture leaves the distillation heatexchanger and enters into the first vacuum cham-ber from which the water vapour/air mixtureflows to the steam ejector pump while the feedbrine flows through a counter-current heatexchanger to be heated by the waste brinereleased from the second vacuum chamber, andthen to the solar collector field. While flowingthrough the solar collector flow tubes, the feedbrine absorbs solar radiation and is transformedinto a hotter waste brine/water vapour/ airmixture which is released into the second vacuumchamber. From the latter, the waste brine ispumped to a disposal site while the hot pres-surised water vapour/air mixture flows into thesteam ejector pump and, after mixing with thesucked in depressurised water vapour/air mixturecoming from the first vacuum chamber, enters thedistillation heat exchanger where the watervapour is condensed into distilled water while theair is vented by means of a water-jet pump.


Fig. 1. Schematic layout of a one-stage SW-SBD desalting plant utilizing a solar vapour thermo-compression distillationtechnology with water vapour condensing into fresh water at suitable sub-atmospheric pressures and corresponding lowtemperatures.

From the distillation heat exchanger, the pro-duced distilled water is directed to an under-ground storage tank to be delivered to utilizers.Plant operations are regulated by means of acustom-designed control system (not shown).Barometric water columns with suitablycontrolled water levels allow smooth plantfunctioning.

2.2. Plant design parameters

The required evaluations are carried out on thebasis of the following assumption: steady-statesteady-flow production process with fixedoperative parameters (temperatures, pressures,

salinities, sea water composition, mean operativesolar radiation flux, mass flow rates of produceddistilled water, feed sea water, and waste brine).Approximate solutions of mass balance andenergy balance equations are obtained after thetheoretical treatment developed in [2] in order toprovide basic design information for the proposedplant. All thermodynamic simplifications adoptedin [2] have been assumed, in particular, neglect ofdissolved or freed air, water vapour superheat,and gravitational and kinetic energycontributions.

The following quantities are utilized: tem-perature, T (°C); pressure, p (kPa); salinity, σ(mass %); mass flowrate, Ψ (kg/s); specific


enthalpy, h (kJ/kg), mean operative solar radia-tion flux on a horizontal surface, I (kW/m2).Through each heat exchanger, an overall pressuredrop Δp = ~10 kPa (for distributed and localisedlosses), has been assumed. Required thermo-dynamic quantities have generally been obtainedfrom [23]. The enthalpies of seawater solutions atdifferent temperatures and salinities have beenobtained from [24].

Produced fresh water mass flowrate isassumed to have the value Ψd = 1.000 kg/s(~36 m3/d for a ten hour working period). Thefeed seawater mass flowrate, salinity, andtemperature, and the mean operative solar radia-tion flux on a horizontal surface are assumed tohave the values: Ψs = 10.000 kg/s; σs = 3.50; Ts =15°C, and I = 0.3 kW/m2.

The mass of desalted water produced in oneday is roughly proportional to the amount of solarradiation absorbed in the solar collector field [1],so operative flux I represents a suitable dailyaverage of the actual time dependent and sitespecific solar radiation flux which is available atthe plant site and which may be assumed to varysinusoidally from sunrise to sunset [3,25]. For amore refined analysis, if all required data onequipment, components, sensors etc. are avail-able, operative flux I may be represented by ahistogram spanning the whole working period(~10 hours), and all calculations may be repeatedfor various values of I on specified sub-intervalsof the working period.

The steam ejector pump and the distillationheat exchanger represent critical plant compo-nents and require accurate designs. The steamejector pump has been assumed to deliver satu-rated water vapour at 50°C into the distillationheat exchanger. The temperatures of the produceddistilled fresh water and of the feed brine/watervapour/air mixture exiting from the distillationheat exchanger have been assumed to have,respectively, the values 45 and 40°C. For thepurpose of reducing paper length, yet withoutsacrificing clarity, some specific abbreviations

have been adopted: E.B. (Energy balance); M.B.(Mass balance); B.H. (Barometric height);I.M. (Inlet manifolds); O.M. (Outlet manifolds);8 (Top); ² (Left side); 9 (Bottom); and ÷ (Rightside).

2.2.1. Distillation heat exchangerC E.B.:

Ψd10 × hd10 + Ψb8 × hb8 + Ψv8 × hv8 = Ψs7 × hs7

+ Ψv9 × hv9 (1)

C M.B.:

Ψb8 + Ψv8 = Ψs7 (2)

Ψv9 = Ψd10 (3)

σb8 × Ψb8 = σs1 × Ψs1 (4)

C B.H.:

ρd10 × g × Zd = 101.325 kPa ! pd10 (5)

C ÷(7): Seawater:

Ψs7 = Ψs6 = Ψs4 + Ψs5 = Ψs1 = Ψs = 10.000 kg/s;

Ts7 = unknown; ps7 = pv8 + 10 kPa;

σs7 = σs1 = σs = 3.50; hs7 = unknown

C ²(8): Water vapour/air:

Ψv8 = 0.667 kg/s (operative assumption);

Tv8 = 40°C (operative assumption);

pv8 = 7.37 kPa; hv8 = 2574.0 kJ/kg

Feed brine:

Ψb8 = unknown; Tb8 = Tv8 = 40°C

(operative assumption); pb8 = pv8 = 7.37 kPa;

σb8 = unknown; hb8 = unknown


C 8(9): Water vapour/air:

Ψv9 = Ψd = 1.000 kg/s; Tv9 = 50.0°C

(operative assumption); pv9 = 12.33 kPa;

hv9 = 2591.8 kJ/kg

C 9(10): Produced distilled water:

Ψd10 = Ψd = 1.000 kg/s; Td10 = 45.0°C

(operative assumption); pd10 = 9.59 kPa;

hd10 = 188.35 kJ/kg; ρd10 = 990.24 kg/m3;

Zd = unknown

Solution of Eqs. (1)–(2) and (4)–(5) yields:

Ψb8 = 9.333;

σb8 = 3.75;

hb8 = [160.57 ! (160.57!158.32) × 0.75] kJ/kg

= 158.88 kJ/kg;

hs7 = [(10.0)!1× (1.0 ×188.35 + 9.333 ×158.88

+ 0.667 × 2574.0!1.0 ×2591.8)] kJ/kg

= 79.62 kJ/kg

Ts7 = 20°C;

Zd = [(101.325!9.59)×(9.80×0.990)!1] m=9.45 m

2.2.2. First vacuum chamberC E.B.:

Ψv8 × hv8 + Ψb8 × hb8 = Ψv11 × hv11 + Ψb12

× hb12 (6)

hv11 = hv8 (7)

hb12 = hb8 (8)

C M.B.:

Ψv11 = Ψv8 (9)

Ψb12 = Ψb8 (10)

σb12 = σb8 (11)

C B.H.:ρb12 × g × Zb1 = 101.325 kPa!pb12 (12)


Ψv11 = Ψv8 = 0.667 kg/s; Tv11 = Tv8 = 40°C; pv11

= pv8 = 7.37 kPa; hv11 = hv8 = 2574.0 kJ/kg

C ÷(8): Water vapour/air:

Ψv8 = 0.667 kg/s; Tv8 = 40°C; pv8 = 7.37 kPa;

hv8 = 2574.0 kJ/kg;Feed brine:

Ψb8 = 9.333 kg/s; Tb8 = Tv8 = 40°C; pb8 = pv8

= 7.37 kPa; σb8 = 3.75; hb8 = 158.88 kJ/kg

C 9(12): Feed brine:

Ψb12 = Ψb8 = 9.333 kg/s; Tb12 = Tb8 = 40°C; pb12

= pb8 = 7.37 kPa; σb12 = σb8 = 3.75; hb12

= hb8 = 158.88 kJ/kg; ρb12 = 1024.45 kg/m3

Solution of Eq. (12) yields:

Zb1 = [(101.325!7.37) × (9.80×1.024)!1]

m = 9.36 m

2.2.3. Steam-ejector pumpC E.B.:

Ψv17 × hv17 + Ψv11 × hv11 = Ψv9 × hv9 (13)


C M.B.:

Ψv17 + Ψv11 = Ψv9 (14)


Ψv9 = 1.000 kg/s; Tv9 = 50°C

(operative assumption); pv9 = 12.33 kPa;

hv9 = 2591.8 kJ/kg


Ψv17 = unknown; Tv17 = unknown;

pv17 = unknown; hv17 = unknown


Ψv11 = Ψv8 = 0.667 kg/s; Tv11 = Tv8 = 40°C; pv11

= pv8 = 7.37 kPa; hv11 = hv8 = 2574.0 kJ/kg

Solution of Eqs. (13) and (14) yields:

Ψv17 = 0.333 kg/s;

hv17 = [(0.333)!1 × (1.0×2591.8!0.667 × 2574.0)]

kJ/kg = 2627.45 kJ/kg

Tv17 = 70°C

pv17 = 31.11 kPa

2.2.4. Second vacuum chamberC E.B.:

Ψv16 × hv16 + Ψb16 × hb16 = Ψv17 × hv17 + Ψb18 × hb18(15)

hv16 = hv17 (16)

hb18 = hb16 (17)

C M.B.:

Ψv16 = Ψv17 (18)

Ψb16 + Ψv16 = Ψb12 (19)

Ψb18 = Ψb16 (20)

σb16 × Ψb16 = σs1 × Ψs1 (21)

σb18 = σb16 (22)

C B.H.:

ρb18 × g × Zb2 = 101.325 kPa !pb18 (23)


Ψv17 = 0.333 kg/s; Tv17 = 70 °C; pv17 = 31.11 kPa;

hv17 = 2627.45 kJ/kg


Ψv16 = Ψv17 = 0.333 kg/s; Tv16 = Tv17 = 70°C; pv16

= pv17 = 31.11 kPa; hv16 = hv17 = 2627.45 kJ/kg;

Waste brine:

Ψb16 = unknown; Tb16 = Tv16 = 70°C; pb16 = pv16

= 31.11 kPa; σb16 = unknown; hb16 = unknown

C 9(18): Waste brine:

Ψb18 = unknown; Tb18 = Tb16 = 70°C; pb18 = pb16


ρb18 = unknown; Zb2 = unknown

Solution of Eqs. (19)–(23) yields:

Ψb16 = Ψb12 !Ψv16 = 9.000 kg/s

Ψb18 = 9.000 kg/s


σb16 = 3.88

σb18 = 3.88

hb16 = [281.56! (281.56!277.92) × 0.88] kJ/kg

= 278.35 kJ/kg

hb18 = hb16 = 278.35 kJ/kg

ρb18 = 1020.96 kg/m3

Zb2 = [(101.325!31.11) × (9.80 × 1.020)!1]

m = 7.02 m

2.2.5. Waste brine/feed brine heat exchanger

C E.B.:

Ψb19 × (hb19 !hb20) = Ψb13 × (hb14 !hb13) (24)

C M.B.:Ψb14 = Ψb13 (25)

Ψb20 = Ψb19 (26)

σb14 = σb13 (27)

σb20 = σb19 (28)

C 8(14, 19): Feed brine:

Ψb14 = Ψb12 = 9.333 kg/s; Tb14 = 65°C (operative

assumption); pb14 = unknown; σb14 = σb12

= 3.75; hb14 = [261.37 !(261.37!257.94)

× 0.75] kJ/kg = 258.79 kJ/kg;

Waste brine:Ψb19 = Ψb18 = 9.000 kg/s; Tb19 = Tb18 = 70°C;

pb19 = unknown; σb19 = σb18 = 3.88; hb19 = hb18

= 278.35 kJ/kg


Ψb13 = Ψb12 = 9.333 kg/s; Tb13 = Tb12 = 40°C;


= 158.88 kJ/kg;

Waste brine:

Ψb20 = Ψb18 = 9.000 kg/s; Tb20 = unknown; pb20 =unknown; σb20 = σb18 = 3.88; hb20 = unknown;


hb20 = [278.35!(9.333/9.000) × (258.79!158.88)]

kJ/kg = 174.74 kJ/kg; Tb20 = 44EC

2.2.6. Produced fresh water/feed seawaterpre-heating heat exchanger

C E.B.:Ψs3 × (hs5 !hs3) = Ψd3 × (hd5 !hd3) (29)

C M.B.:Ψs5 = Ψs3 (30)

Ψd3 = Ψd5 (31)

σs5 = σs3 (32)

C 8(1, 3): Seawater:

Ψs1 = 10.000 kg/s; Ts1 = Ts = 15°C;

ps1 = unknown; hs1 = 59.55 kJ/kg; σs1 = σs =

3.50;

Ψs3 = 1.000 kg/s (operative assumption); Ts3

= Ts1 = 15°C; ps3 = unknown; σs3 = σs1

= 3.50; hs3 = hs1 = 59.55 kJ/kg;

Produced distilled water:

Ψd3 = 1.000 kg/s; Td3 = 20°C (operative assump-

tion); pd3 = unknown; hd3 = 83.86 kJ/kg


C 9(5): Seawater:

Ψs5 = Ψs3 = 1.000 kg/s; Ts5 = unknown; ps5

= unknown; σs5 = σs3 = 3.50; hs5 = unknown;


Ψd5 = Ψd3 = 1.000 kg/s; Td5 = Td10 = 45°C

(operative assumption); pd5 = unknown;

hd5 = hd10 = 188.35 kJ/kg


hs5 = (59.55 + 188.35!83.86) kJ/kg

= 164.04 kJ/kg;

Ts5 = 41°C

2.2.7. Waste brine/feed seawater pre-heating heatexchanger

C E.B.:

Ψb2 × (hb4 !hb2) = Ψs2 × (hs4 !hs2) (33)

Ψs4 × hs4 + Ψs5 × hs5 = Ψs6 × hs6 (34)

C M.B.:

Ψs2 + Ψs3 = Ψs1 (35)

Ψs4 = Ψs2 (36)

Ψb2 = Ψb4 (37)

σs4 = σs2 (38)

σb2 = σb4 (39)


Ψs1 = 10.000 kg/s; Ts1 = 15°C; ps1 = unknown;

σs1 = 3.50; hs1 = 59.55 kJ/kg

Ψs2 = unknown; Ts2 = Ts1 = 15°C; ps2 = unknown;

σs2 = σs1 = 3.50; hs2 = hs1 = 59.55 kJ/kg;

Waste brine:

Ψb2 = Ψb18 = 9.000 kg/s; Tb2 = unknown; pb2 =

unknown; σb2 = σb18 = 3.88; hb2 = unknown


Ψs4 = unknown; Ts4 = unknown; ps4 = unknown;

σs4 = σs1 = 3.50; hs4 = unknown;

Ψs6 = Ψs1 = 10.000 kg/s; Ts6 = Ts7 = 20°C;

ps6 = unknown; σs6 = σs1 = 3.50; hs6 = hs7

= 79.62 kJ/kg;

Waste brine:

Ψb4 = Ψb18 = 9.000 kg/s; Tb4 = Tb20 = 44°C;


= 174.74 kJ/kg;


Ψs2 = 9.000 kg/s;

Ψs4 = 9.000 kg/s;

hs4 = (9.0)!1 × (10.0 × 79.62!1.0 ×164.04 ) kJ/kg

= 70.24 kJ/kg

Ts4 = 18°C

hb2 = (174.74!70.24 + 59.55) kJ/kg

= 164.05 kJ/kg

Tb2 = 41°C

2.2.8. Solar collector fieldC E.B.:

I×A = Ψb16 × hb16 + Ψv16 × hv16!Ψb15 ×hb15 (40)


C M.B.:

Ψb15 = Ψb16 + Ψv16 (41)

I = 0.3 kW/m2; A = unknown

C I.M.(15): Feed brine:

Ψb15 = Ψb12 = 9.333 kg/s; Tb15 = Tb14 = 65°C

(operative assumption); pb15 = pv17

= 31.11 kPa; σb15 = σb12 = 3.75; hb15 = hb14

= 258.79 kJ/kg

C O.M.(16): Water vapour/air:

Ψv16 = Ψv17 = 0.333 kg/s; Tv16 = Tv17 = 70°C;

pv16 = pv17 = 31.11 kPa; hv16 = hv17

= 2627.45 kJ/kg

Waste brine:

Ψb16 = 9.000 kg/s; Tb16 = Tv16 = 70°C; pb16 = pv16

= 31.11 kPa; σb16 = 3.88; hb16 = 278.35 kJ/kg


A = (0.3)!1 × (9.0 × 278.35 + 0.333 × 2627.45

!9.333 × 258.79) m2 = 3216.0 m2;

With the chosen operative parameters, theone-stage SW–SBD solar vapour thermo-compression desalting plant may be expected toproduce ~36 m3/d of distilled water (in ~10 workhours) with some 36 arrays of solar collectors.

3. Two-stage SW–SBD plant

3.1. Plant operation

A simplified diagram of the proposed plant isillustrated in Fig. 2 where important components,e.g., flow-control valves and temperature/pres-

sure/salinity/radiation sensors, are not shown.Feed seawater preheated by waste brine and byproduced distilled water in counter-current heatexchangers is pumped from an underground tankat a depth of ~10 m through the first distillationheat exchanger placed at ground level where it isheated by absorbing the change-of-state (latent)heat of water vapour condensing into produceddistilled water. It is then further heated byflowing through the second counter-current wastebrine/feed seawater heat exchanger and entersinto the second distillation heat exchanger whereit is partially vaporised by absorbing the change-of-state (latent) heat of water vapour coming fromthe steam ejector pump and condensing intoproduced distilled water. The feed brine/watervapour/air mixture exiting from the second dis-tillation heat exchanger enters into the secondvacuum chamber where it is separated into twostreams: a water vapour/air mixture, directed tothe steam ejector pump and to the first distillationheat exchanger, and a feed brine which is heatedby flowing through a counter-current waste brine/feed brine heat exchanger and then reaches theinlets of the solar collector arrays. The absorptionof solar radiation in the solar collector flow tubestransforms the feed brine into a hotter wastebrine/water vapour/ air mixture which is releasedfrom the solar collector array outlets into thesecond vacuum chamber. From the latter, thewaste brine is pumped to a disposal site while thehot pressurised water vapour/air mixture flowsinto the steam ejector pump and, after mixingwith the sucked in depressurised water vapour/airmixture coming from the first vacuum chamber,enters into the second distillation heat exchangerwhere the water vapour is condensed into distilledwater while the air is vented by means of a water-jet pump.

From the two distillation heat exchangers, theproduced distilled water is directed to an under-ground storage tank to be delivered to utilizers.Plant operations are regulated by means of acustom-designed control system (not shown).


Fig. 2. Schematic layout of a two-stage SW–SBD desalting plant utilizing a solar vapour thermo-compression distillationtechnology with two distillation heat exchangers working in series for condensing water vapour into produced fresh waterat subatmospheric pressures and corresponding low temperatures.

Barometric water columns with suitablycontrolled water levels allow smooth plantfunctioning.

3.2. Plant design parameters

The required evaluations have been carried outafter the treatment developed in [2] and with thesame overall assumptions and thermodynamicsimplifications. The analysis is straightforwardand provides first approximation plant designparameters for the implementation of prototypeplants.

The following quantities have been utilized:temperature, T (°C); pressure, p (kPa); salinity, σ(mass %); mass flowrate, Ψ (kg/s); specific en-

thalpy, h (kJ/kg), mean operative solar radiationflux on a horizontal surface, I (kW/m2). Througheach heat exchanger, an overall pressure dropΔp = ~10 kPa (for distributed and localised los-ses), has been assumed. Required thermodynamicquantities have generally been obtained from[23]. The enthalpies of seawater solutions atdifferent temperatures and salinities have beenobtained from [24].

The produced fresh water mass flowrate, thefeed seawater mass flowrate, salinity, and tem-perature, and the mean operative solar radiationflux on a horizontal surface are assumed to havethe values: Ψd = 1.000 kg/s (~36 m3/d for a tenhour working period); Ψs = 10.000 kg/s; σs =3.50; Ts = 15.0°C; and I = 0.3 kW/m2.


The steam ejector pump and the distillationheat exchangers represent critical plant compo-nents and require accurate designs. The steamejector pump has been assumed to deliver satu-rated water vapour at 60°C onto the second dis-tillation heat exchanger, and the first distillationheat exchanger has been assumed to receivesaturated water vapour at 50°C. The temperaturesof the produced fresh water streams from the firstand from the second distillation heat exchangershave been assumed to have, respectively, thevalues 45 and 55°C. Space saving abbreviations(the same of the previous section) are used.

3.2.1. First distillation heat exchangerC E.B.:

Ψd10 × hd10 + Ψs8 × hs8 = Ψs7 × hs7 + Ψv9 × hv9 (42)

C M.B.:

Ψs8 = Ψs7 (43)

Ψv9 = Ψd10 (44)

σb8 = σs7 (45)

C B.H.:

ρd10 × g × Zd1 = 101.325 kPa !pd10 (46)

C ÷(7): Seawater:

Ψs7 = Ψs6 = Ψs4 + Ψs5 = Ψs1 = Ψs = 10.000 kg/s;

Ts7 = unknown; ps7 = ps8 +10 kPa; σs7 = σs1 = σs

= 3.50; hs7 = unknown

C ²(8): Seawater:

Ψs8 = Ψs7 = 10.000 kg/s; Ts8 = 40°C (operative

assumption); ps8 = ps13 + 10 kPa; σs8 = σs7

= 3.50; hs8 = 159.45;

8(9): Water vapour/air:

Ψv9 = 0.200 kg/s (operative assumption);

Tv9 = 50°C (operative assumption); pv9

= 12.33 kPa; hv9 = 2591.8 kJ/kg


Ψd10 = Ψv9 = 0.200 kg/s; Td10 = 45°C (operative

assumption); pd10 = 9.59 kPa; hd10

= 188.35 kJ/kg; ρd10 = 990.24 kg/m3;

Zd1 = unknown

Solution of Eqs. (42) and (46) yields:

hs7 = [159.45 + (0.2/10.0) × (188.35!2591.8)]

kJ/kg = 111.38 kJ/kg; Ts7 = 28°C;

Zd1 = [(101.325!9.59) × (9.80 × 0.990)!1 ]

m = 9.45 m

3.2.2. Second distillation heat exchangerC E.B.:

Ψd16 × hd16 + Ψb14 × hb14 + Ψv14 × hv14 = Ψs13 × hs13

+ Ψv15 × hv15 (47)

C M.B.:

Ψv15 + Ψv9 = Ψd (48)

Ψv15 = Ψd16 (49)

Ψb14 + Ψv14 = Ψs13 (50)

σb14 × Ψb14 = σs1 × Ψs1 (51)

C B.H.:

ρd16 × g × Zd2 = 101.325 kPa !pd16 (52)


C ÷(13): Seawater:


= pv14+10 kPa; σs13=σs8=3.50; hs13=unknown;


Ψv14 = Ψv15 = unknown (operative assumption);

Tv14 = Tv9 = 50°C (operative assumption); pv14

= pv9 = 12.33 kPa; hv14 = hv9 = 2591.8 kJ/kg;

Feed brine:


= 12.33 kPa; σb14 = unknown; hb14 = unknown;


Ψv15 = unknown; Tv15 = 60°C (operative assump-

tion); pv15 = 19.91 kPa; hv15 = 2609.5 kJ/kg


Ψd16 = unknown; Td16 = 55°C (operative assump-

tion); pd16 = 15.75 kPa; hd16 = 230.16 kJ/kg;

ρd16 = 985.70 kg/m3; Zd2 = unknown


Ψv15 = (1.000!0.200) kg/s = 0.800 kg/s

Ψv14 = 0.800 kg/s

Ψb14 = (10.000!0.800) kg/s = 9.200 kg/s

Ψd16 = 0.800 kg/s

σb14 = (3.50 ×10.0) × (9.2)!1 = 3.80

hb14 = [200.86 !(200.86 !198.14) × 0.80] kJ/kg

= 198.68 kJ/kg

hs13 = [(10.0)!1 × (0.8 ×230.16 + 9.2 × 198.68

+ 0.8 × 2591.8 - 0.8 × 2609.5)] kJ/kg

= 199.78 kJ/kg

Ts13 = 50°C

Zd2 = [(101.325!15.75) × (9.80 × 0. 985)!1]

m = 8.86 m

3.2.3. First vacuum chamberC E.B.:

Ψb14 × hb14 + Ψv14 × hv14 = Ψv17 × hv17 + Ψb18 × hb18

(53)

hv17 = hv14 (54)

hb18 = hb14 (55)

C M.B.:

Ψv17 = Ψv14 (56)

Ψb18 = Ψb14 (57)

σb18 = σb14 (58)

C B.H.:

ρb18 × g × Zb1 = 101.325 kPa !pb18 (59)


Ψv17 = Ψv14 = 0.800 kg/s; Tv17 = Tv14 = 50°C; pv17= pv14 = 12.33 kPa; hv17 = hv14 = 2591.8 kJ/kg


Ψv14 = 0.800 kg/s; Tv14 = 50°C; pv14 = 12.33 kPa;

hv14 = 2591.8 kJ/kg


Feed brine:

Ψb14 = 9.200 kg/s; Tb14 = Tv14 = 50°C; pb14 = pv14

= 12.33 kPa; σb14 = 3.80; hb14 = 198.68 kJ/kg

C 9(18): Feed brine:

Ψb18 = Ψb14 = 9.200 kg/s; Tb18 = Tb14 = 50°C;

pb18 = pb14 = 12.33 kPa; σb18 = σb14 = 3.80; hb18

= hb14 = 198.68 kJ/kg; ρb18 = 1023.34 kg/m3;


Zb1 = [(101.325!12.33) × (9.80 × 1.023)!1]

m = 8.87 m;

3.2.4. Steam-ejector pumpC E.B.:

Ψv26 × hv26 + Ψv19 × hv19 = Ψv27 × hv27 (60)

hv19 = hv17 (61)

hv27 = hv15 (62)

C M.B.:

Ψv26 + Ψv19 = Ψv27 (63)

Ψv9 + Ψv19 = Ψv17 (64)

Ψv27 = Ψv15 (65)


Ψv27 = Ψv15 = 0.800 kg/s; Tv27 = Tv15 = 60°C; pv27

pv15 = 19.91 kPa; hv27 = hv15 = 2609.5 kJ/kg


Ψv26 = unknown; Tv26 = unknown; pv26

= unknown; hv26 = unknown


Ψv19 = unknown; Tv19 = Tv17 = 50°C; pv19 = pv17

= 12.33 kPa; hv19 = hv17 = 2591.8 kJ/kg;

Solution of Eqs. (60), (63), and (64) yields:

Ψv19 = 0.600 kg/s

Ψv26 = 0.200 kg/s;

hv26 = [(0.2)!1 × (0.8 × 2609.5!0.6 × 2591.8)]

kJ/kg = 2662.6 kJ/kg

Tv26 = 91°C

pv26 = 72.85 kPa

3.2.5. Second vacuum chamberC E.B.:

Ψb23 × hb23 + Ψv23 × hv23 = Ψv24 × hv24 + Ψb25 × hb25

(66)

hv23 = hv24 (67)

hb25 = hb23 (68)

C M.B.:

Ψv23 = Ψv24 (69)

Ψb23 + Ψv23 = Ψb18 (70)

Ψb25 = Ψb23 (71)

σb23 × Ψb23 = σs1 × Ψs1 (72)

σb25 = σb23 (73)

C B.H.:

ρb25 × g × Zb2 = 101.325 kPa !pb25 (74)



Ψv24 = Ψv26 = 0.200 kg/s; Tv24 = Tv26 = 91°C; pv24

= pv26 = 72.85 kPa; hv24 = hv26 = 2662.6 kJ/kg


Ψv23 = Ψv24 = 0.200 kg/s; Tv23 = Tv24 = 91°C; pv23

= pv24 = 72.85 kPa; hv23 = hv24 = 2662.6 kJ/kg;

Waste brine:



C 9(25): Waste brine:

Ψb25 = unknown; Tb25 = Tb23 = 91°C; pb25 = pb23

= 72.85 kPa; σb25 = unknown; hb25 = unknown;

ρb25 = unknown


Ψb23 = 9.000 kg/s

Ψb25 = 9.000 kg/s

σb23 = 3.88

σb25 = 3.88

ρb25 = 1017.9 kg/m3

hb23 = [366.54 !(366.54 !361.94) × 0.88] kJ/kg

= 362.49 kJ/kg

hb25 = 362.49 kJ/kg

Zb2 = [(101.325!72.85) × (9.80 × 1.017)!1]

m = 2.85 m

3.2.6. Waste brine/feed brine heat exchangerC E.B.:

Ψb20 × (hb21 !hb20) = Ψb28 × (hb28 !hb29) (75)

C M.B.:

Ψb21 = Ψb20 (76)

Ψb29 = Ψb28 (77)

σb21 = σb20 (78)

σb29 = σb28 (79)


Ψb21 = Ψb18 = 9.200 kg/s; Tb21 = Tb22 = 86°C

(operative assumption); pb21 = unknown; σb21

= σb18 = 3.80; hb21 = [346.27!(346.27

– 341.91) × 0.80] kJ/kg = 342.7 kJ/kg;

Waste brine:

Ψb28 = Ψb25 = 9.000 kg/s; Tb28 = Tb25 = 91°C;


= 362.49 kJ/kg


Ψb20 = Ψb18 = 9.200 kg/s; Tb20 = Tb18 = 50°C; pb20

= unknown; σb20 = σb18 = 3.80; hb20 = hb18

= 198.68 kJ/kg

Waste brine:





hb29 = [362.49!(9.2/9.0) × (342.7!198.68)] kJ/kg

= 215.26 kJ/kg

Tb29 = 54°C

3.2.7. Second waste brine/feed seawater heatexchanger

C E.B.:Ψs11 × (hs12 !hs11) = Ψb11 × (hb12 !hb11) (80)

C M.B.:

Ψs12 = Ψs11 (81)

Ψb11 = Ψb12 (82)

σs12 = σs11 (83)

σb11 = σb12 (84)

C 8(11): Seawater:

Ψs11 = Ψs8 = 10.000 kg/s; Ts11 = Ts8 = 40°C;

ps11 = unknown; σs11 = σs8 = 3.50; hs11 = hs8 =

159.45 kJ/kg

Waste brine:



C 9(12): Seawater:

Ψs12 = Ψs8 = 10.000 kg/s; Ts12 = Ts13 = 50°C;

ps12 = unknown; σs12 = σs8 = 3.50; hs12 = hs13

= 199.78 kJ/kg;

Waste brine:

Ψb12 = Ψb25 = 9.000 kg/s; Tb12 = Tb29 = 54°C;


= 215.26 kJ/kg


hb11 = [215.26!(10.0/9.0) × (199.78 – 159.45)]

kJ/kg = 170.44 kJ/kg; Tb11 = 43°C

3.2.8. Produced fresh water/feed seawaterpre-heating heat exchanger

E.B.:

Ψs3 × (hs5 !hs3) = Ψd3 × (hd5 !hd3) (85)

Ψd5 × hd5 = Ψd10 × hd10 + Ψd16 × hd16 (86)

C M.B.:

Ψs5 = Ψs3 (87)

Ψd3 = Ψd5 (88)

σs5 = σs3 (89)


Ψs1 = 10.000 kg/s; Ts1 = Ts = 15°C; ps1

= unknown; hs1 = 59.55 kJ/kg; σs1 = σs = 3.50;

Ψs3 = 1.000 kg/s (operative assumption); Ts3 = Ts1

= 15°C; ps3 = unknown; σs3 = σs1 = 3.50; hs3

= hs1 = 59.55 kJ/kg


Ψd3 = 1.000 kg/s; Td3 = 20.0°C (operative assump-

tion); pd3 = unknown; hd3 = 83.86 kJ/kg

C 9(5): Seawater:


= unknown; σs5 = σs3 = 3.50; hs5 = unknown;


Ψd5 = Ψd3 = 1.000 kg/s; Td5 = unknown;

pd5 = unknown; hd5 = unknown



hd5 = (0.2 ×188.35 + 0.8 × 230.16) kJ/kg

= 221.79 kJ/kg; Td5 = 53°C

hs5 = (59.55 + 221.79 !83.86) kJ/kg

= 197.48 kJ/kg; Ts5 = 50°C

2.2.9. Waste brine/feed seawater pre-heatingheat exchanger

C E.B.:

Ψb2 × (hb4 !hb2) = Ψs2 × (hs4 !hs2) (90)

Ψs4 × hs4 + Ψs5 × hs5 = Ψs7 × hs7 (91)

C M.B.:

Ψs2 + Ψs3 = Ψs1 (92)

Ψs4 = Ψs2 (93)

Ψb2 = Ψb4 (94)

σs4 = σs2 (95)

σb2 = σb4 (96)


Ψs1 = 10.000 kg/s; Ts1 = 15°C; ps1 = unknown;

σs1 = 3.50; hs1 = 59.55 kJ/kg

Ψs2 = unknown; Ts2 = Ts1 = 15°C; ps2 = unknown;

σs2 = σs1 = 3.50; hs2 = hs1 = 59.55 kJ/kg;

Waste brine:

Ψb2 = Ψb25 = 9.000 kg/s; Tb2 = unknown; pb2

= unknown; σb2 = σb25 = 3.88; hb2 = unknown

9(4): Seawater:

Ψs4 = unknown; Ts4 = unknown; ps4 = unknown;

σs4 = σs1 = 3.50; hs4 = unknown;

Waste brine:

Ψb4 = Ψb25 = 9.000 kg/s; Tb4 = Tb11 = 43°C;

pb4 = unknown; σb4 = σb25 = 3.88; hb4 = hb11 =

170.44 kJ/kg


Ψs2 = 9.000 kg/s

Ψs4 = 9.000 kg/s

hs4 = (9.0)!1 × (10.0 ×111.38!1.0 ×197.48) kJ/kg

= 101.81 kJ/kg; Ts4 = 26°C;

hb2 = (170.44 !101.81 + 59.55) kJ/kg

= 128.18 kJ/kg; Tb2 = 32°C;

2.2.10. Solar collector fieldC E.B.:

I × A = Ψb23 × hb23 + Ψv23 × hv23!Ψb22 × hb22 (97)

C M.B.:

Ψb22 = Ψb23 + Ψv23 (98)

I = 0.3 kW/m2; A = unknown

C I.M.(22): Feed brine:

Ψb22 = Ψb18 = 9.200 kg/s; Tb22 = Tb21 = 86°C

(operative assumption); pb22 = pv26

= 72.85 kPa; σb22 = σb18 = 3.80; hb22

= hb21 = 342.7 kJ/kg


C O.M.(23): Water vapour/air:

Ψv23 = Ψv26 = 0.200 kg/s; Tv23 = Tv26 = 91°C;

pv23 = pv26 = 72.85 kPa; hv23 = hv26

2662.6 kJ/kg;

Waste brine:

Ψb23 = 9.000 kg/s; Tb23 = Tv23 = 91°C; pb23 = pv23

72.85 kPa; σb23 = 3.88; hb23 = 362.49 kJ/kg


A = (0.3)!1 × (9.0 ×362.49 + 0.2 × 2662.6!9.2

× 342.7) m2 = 2140.3 m2

With the chosen operative parameters, thetwo-stage SW–SBD solar vapour thermocom-pression desalting plant may be expected toproduce ~36 m3/d of distilled water (in ~10 workhours) with some 24 arrays of solar collectors.

4. SW–SBD energy efficiency and generalaspects

SW–SBD desalting technology is driven bysolar radiation but electric power is required forpumping all fluids of interest, feed seawater,produced distilled water, and waste brine, and forthe functioning of the deaerator system, of gene-ral services, and of the electronic system whichcontrols all plant operations. The energy effi-ciency of SW–SBD desalting technology is thusrelated to two special topics:C the solar radiation absorption efficiency of

SW-SBD solar collector arraysC the electric energy (kWh) required for the

production of 1 m3 of desalinated water.

The design, construction, and maintenance ofSW–SBD solar collectors have critical impor-tance in view of achieving a suitably large heatcollection efficiency. The electric energy require-

ments of SW–SBD desalting plants are relativelysmall due to the operational advantages providedby underground layouts. All pumps of the pro-posed SW–SBD desalting plants are low headcirculation pumps so that, according to the treat-ment presented in [2], and excluding the electricpower required for pumping feed seawater fromsea intake to plant site, the expected electricenergy efficiency of either plant is about1 kWh/m3.

The performance ratio (defined as the ratiobetween the mass flow rate of product fresh waterand the mass flow rate of heating vapour [26,27]is an important feature of desalting plants inwhich seawater distillation is driven by heatingsteam. The performance ratios of the present one-stage and two-stage SW–SBD desalting plantsare, respectively, (1.000/0.333) = 3.0 and (1.000/0.200) = 5.0: quite promising values consideringthe much lower values of conventional (non-solar) plants.

Without a working SW–SBD prototype plant,no direct quantitative evaluation of SW–SBDdesalting technology can be made. The AbuDhabi plant [15] would be an important referenceplant for useful technology checks. Its 18-effectevaporator is designed for a rated distillate outputof 120 m3/d and a heat accumulator allows con-tinuous (day and night) operation. The actualplant productivity shows large fluctuation, theyearly average distillate production being some80 m3/d. SW–SBD desalting technology appearsto have a simpler design (without a heat accumu-lator system) and a larger energy efficiency.SW–SBD distillate production would depend onthe number of stages which a SW–SBD plantdesign could suitably incorporate.

Waste brine disposal is a potentially criticalenvironment issue for which adequate solutionswill have to be found to achieve satisfactory fieldimplementations of SW-SBD prototype plants.Important research efforts must also be dedicatedto SW–SBD electronic control systems whichmust regulate plant productivity parameters on


available solar radiation flux (which, at anyselected plant site, presents considerable varia-bility during daytime and through the variousseasons), via inputs from several specific sensorslocated at suitable positions. If plate heatexchangers consisting of various sections work-ing in parallel are assumed, it may be feasible tomaintain relatively constant fluid operativetemperatures and pressures while adapting treatedfluid mass flow rates (thus excluding heatexchanger sections when the radiation fluxbecomes too low). The design of SW–SBD heatexchangers should possibly take into account allsuitable alternative operations in view of achiev-ing maximum fresh water productivity. Clearly,field research on prototype plants is required toclarify all technological issues of interest.

The overall good energy efficiency of SW–SBD plants suggests useful couplings with anyavailable renewable energy sources so that SW–SBD desalting technology may be made availablealso at coast sites lacking an electric grid.

5. Symbols

A — Operative area of solar collectorfield, m2

g — Gravitational acceleration, m s!2

h — Specific enthalpy, kJ/kgI — Mean operative solar radiation flux

on horizontal surface, W/m2

p — Pressure, kPaΔp — Fluid pressure drop, kPa T — Temperature, °CZ — Barometric height, m

8 — Top² — Left side9 — Bottom÷ — Right side

Greekρ — Density, kg/m3

σ — Salinity, mass %Ψ — Mass flow rate, kg/s

Subscripts

b — Brine d — Fresh (distilled) water s — Seawater v — Vapour

References

[1] M. Reali, G. Modica, A.M. El-Nashar and P. Marri,Solar barometric distillation for seawater desaltingPart I: Basic layout and operational/technical fea-tures, Desalination, 161 (2004) 235–250.

[2] M. Reali, Solar barometric distillation for seawaterdesalting Part II: Analyses of one-stage and two-stage distillation technologies, Desalination, 190(2006) 29–42.

[3] E.D. Howe, Distillation of sea water, in Solar EnergyTechnology Handbook, Part B, W.C.Dickinson andP.N. Cheremisinoff, eds., Marcel Dekker, New York,1980.

[4] D. Hoffman, The application of solar energy forlarge-scale seawater desalination, Desalination, 89(1992) 115–184.

[5] P. Glueckstern, Potential uses of solar energy forseawater desalination, Desalination, 101 (1995) 11–20.

[6] M. Reali, A refrigerator heat-pump desalinationscheme for fresh water and salt recovery, Energy,9(7) (1984) 583–588.

[7] G. Cavanna, Nuovo impianto dissalatore ad energiasolare, Associazione Termotecnica Italiana, 47°Congresso Nazionale, Parma, Italy, 1992.

[8] G.A. Bemporad and M. Reali, A solar pond desali-nation scheme for fresh water and salt production,2nd Int. Congress on Energy, Environment, andTechnological Innovation, Rome, Italy, 1992.

[9] G.A. Bemporad, Basic hydrodynamic aspects of asolar energy based desalination process, Desali-nation, 54 (1995) 125–134.

[10] S. Al-Kharabsheh and D.Y. Goswami, Analysis of aninnovative water desalination system using low-grade solar heat, Desalination, 156 (2003) 323–332.


[11] D. Sagie, E. Feinerman and E. Aharoni, Potential ofsolar desalination in Israel and its close vicinity,Desalination, 139 (2001) 21–33.

[12] H. Kunze, A new approach to solar desalination forsmall and medium-size use in remote areas,Desalination, 139 (2001) 35–41.

[13] J. de Koning and S. Thiesen, Aqua Solaris — anoptimized small scale desalination system with 40litres output per square meter based upon solar-thermal distillation, Desalination, 182 (2005) 503–509.

[14] A. Cipollina, C. Sommariva and G. Micale, Effi-ciency increase in thermal desalination plants bymatching thermal and solar distillation: theoreticalanalysis, Desalination, 183 (2005) 127–136.

[15] A.M. El-Nashar and M. Samad, A solar asssistedseawater multiple effect distillation plant- 10 years ofoperating performance, Proc. IDA World Conferenceon Desalination and Water Sciences, Abu Dhabi, 5(1995) 451–473.

[16] N.H.A. Rahim, Utilisation of new technique toimprove the efficiency of horizontal solar desali-nation still, Desalination, 138 (2001) 121–128.

[17] L. García-Rodriguez, A.I. Palmero-Marrero andC. Gómez-Camacho, Thermoeconomic optimizationof the SOL-14 plant (Plataforma Solar de Almeria,Spain), Desalination, 136 (2001) 219–223.

[18] G. Caruso and A. Naviglio, A desalination plantutilizing solar heat as a heat supply, not affecting theenvironment with chemicals, Intern. WorkshopDesalination Technologies for Small and MediumSize Plants with Limited Environmental Impact,Rome, Italy, 1998.

[19] T. Szacsvay, P. Hofer-Noser and M. Posnansky,Technical and Economical Aspects of Small ScaleSolar Pond Powered Sea-Water DesalinationSystems, Intern. Workshop Desalination Technolo-gies for Small and Medium Size Plants with LimitedEnvironmental Impact, Rome, Italy, 1998.

[20] M. Reali, Closed cycle osmotic power plants forelectric power production, Energy, 5 (1980) 325–329. Based on Internal Rep. 2750/1 (Aug. 1978),ENEL-DSR-CRIS, V. Ornato 90/14, 20162 Milano,Italy.

[21] M.D. Fraser, S. Loeb and G.D. Mehta, Assessment ofthe potential of generating power from aqueoussaline solutions by means of osmo-hydro powerTM

systems, 13th Intersociety Energy Conversion Engi-neering Conference, San Diego, CA, 1978.

[22] G.L. Wick and J.D. Isaacs, Salt Domes: Is ThereMore Energy Available from Their Salt than fromTheir Oil? Science, 199 (1978) 1436–1437.

[23] N.B. Vargaftic, Tables on the Thermophysical Pro-perties of Liquids and Gases in Normal and Disso-ciated States, Hemisphere Publishing, London, 1975.

[24] L.A. Bromley, A.E. Diamond, E. Salami andD.G. Wilkins, Heat capacities and enthalpies of seasalt solutions to 200°C, J. Chem. Engineer. Data,15(2) (1970) 246–253.

[25] D.J. Close, A design approach for solar processes,Solar Energy, 7 (1967) 112–122.

[26] K.S. Spiegler, Salt-Water Purification, 2nd ed.,Plenum Press, New York, 1977.

[27] H.T. El-Dessouky and M.H. Ettouney, Fundamentalsof Salt Water Desalination, Elsevier, Oxford, 2002.

Documents

Solar barometric distillation for seawater desalting Part III: Analyses of one-stage and two-stage solar vapour thermo-compression distillation technologies