ELSEVI ER Desalination 138 (2001) 111-119 DESALINATION
www.elsevier.com/locate/desal Mul ti -effectstillfor
hybridsolar/fossildesalinationo fsea- andbrackish water Frieder
Gr~iter*, MichaelDiirrbeck, J0rgen Rheinlander Centre for Solar
Energy and Hydrogen Research, Baden-Wiirtemberg (ZSW),
Heflb~'hlstr. 21c, D-70565 Stuttgart, Germany Tel. +49 (711)
7870-239; Fax +49 (711) 7870-200; email:[email protected]
Received 6 February 2001; accepted 20 February 2001 Abstract The
evaporationprocessinafour-effect still for the desalination of sea
and brackish water wasexperimentally investigatedfor typical
operationconditionsinZSW'sthermalprocesslaboratory.Different
operationmodes and configurationsofthe testfacilitywere
examined:heat recovery,naturalandforced convectioninthedistillation
chambers (effects). The results show that heat recovery from the
outlet mass flows ofconcentrate and distillate has only
alittleeffect
ondistillateoutputbutthegainedoutputratio(GOR)increasesconsiderably.Withblowersand
intermediate screens, installed inside the distillation effects,
the distillate yield can be increased by more than 50% and the GOR
by 60% related to resultsofa configuration without heat recovery
and blowers.This reduces the specific thermal power requirement and
thus the required solar collector area and boiler capacity.
Keywords:Desalination;
Multi-effect-still;Distillaterate;Experimental;Solar energy;
De-centraldesalination; Hybrid solar/fossil systems 1. I n t r o d
u c t i o nFor smal ldesalination applications ( . . . . ~. . . . .
. ' . . . . .I i , > L . < i " i/ i ~ , " ~ , " - / !i / ~ i
. ./ !1 . 0 . . . . . . . a : ~ : ~ . . . . . . . . . . . . . . . .
i . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . i
................................... I,/[/~i1 i 0 . 5 . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . i . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ~ . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . .
.5060708090I00 H e a t i n g i n l e t t e m p e r a t u r e [aC]
Fig.3.a. Di sti l l ateoutput and GORas function o frelation
brine-in/distillate,b.GORas function o fheatingand cool i ng inlet
temperatures (tu andtc ) .wi t ht heheat i ngi nl ettemperaturet ot
hemaxi -mu mo f G O R =2. 3(tu =9 6 C) and decreasesfor hi gherc o
o l i ng i nl ettemperatures. Thevari ati on o ft heGORatt c = 2 0
Ci sattributedt odi f f erentheat l os s e s int heheat
recoverycycl e.Foroperat i onmo de 2, t hevari at i ono f t he heat
i ng i nl et temperature wi t houtheatrecoveryi s s ho wninFi g.
4aandcomparedwi t ht heresul t s o f operat i onmo de 1f orconst
ant c o o l i ng i nl et temperatureso ftc=20 C( s e e al s oFi g.
2a) . The 116 . cl m 3 o2 .iJ t OC ~F.Grater et aL /Desalination138
(2001)111-119 0 50 t c = 2 0 * C.......l q. . . . . . . D i s t i l
l a t e o u t p u tw i t h o u t h ~ a t r e c o v e r y #~ . . . .
. . ~ - ~ D i s t i l l a t e o u t p u t w i t h .............~. .
. . . . . . . . . . . . . . . . .h e a t r e c o v e r y ~_
..................................................t -
..................................................................
I6 0 7 0 8 0 9 0 I 0 0? ~ i . 51.0 0 . 55 0 6 0 7 0 8 0 9 0H e a t
i n g i n l e t t e m p e r a t u r e [ * C ]t c=20~C 2. 5
.....................F- "F. . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . [. . . . . . . . . . . . . . . . . . . . .
. . . T. . . . . . . . . . . . . . . . . . . . . . . . . . . . ~".
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
.I"'~--GORwithheatrecovery Q,~.GOR withoutheatrecovery 2 . 0
.............................i
....................................................................i
.............. ,ii . . . i : ; ' ? ' * ...................... i .~i
!.......................................................~
;~*~.....................i............................i...............................
,,< ..........h(i ................. ~/'i_ I i , , t : f ' ' " ~
. . . . . . . . . . . . . . . . . . . . . . i. . . . . . . . . . .
. . . . . . . . . . . . . . . . .j , " i ii t ~. . . . . . . . . i
~i 0 ~H e a t i n g i n l e t t e m p e r a t u r e [ * C ]Fig.
4.a. Distillateoutput asfunctiono fheatinginlet temperatures
(tz).b. GOR as functiono fheatinginlet temperatures ( t . ) and two
operationmodes. t e = 2 0* C8 . . . . . . . . . . . . . . . . . . .
. . . . . T . . F . . . . .:iT . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . I . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . I. . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . .I+,,Blowersa~26WandIia iheatr e c o v e r y
!l --~!.....n:Blowersat8 Nandi 6 i . . . heat=~.coveryI I / +. . .
. . .i . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . r - - - - - - ~ . . . . . . . . . . . . . . . . . . i~ ~'
........&--BlowersatIWand/+//~ {heatrecoveryF- - / ~i "~/,[/La
/i i i I I . / / . A i .i I I...,,..~. s.:...i.~. I /.~/ / z i Ii i
.....* ' . ~ J . . . ~ " ! !- , - 4 ~ 2 . . . . . ~ . . . . . . . .
. . . ; : ~ " " ' ; . . . . . . . . . . . . . . . . . . . : ~ , ".
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . 4. . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . .i + . . i............t ~ . . . ! ....t. , 4 i I icl0
5 0 6 0 7 0 B 0 901 0 0H e a t i n g i n l e t t . e m p e r a t u
r e [*C] I nt e f f e c t ; t c = 2 0 * Cj - , - t ~ - 5 8 " c I i
b i1 2 0 ,. . . . . . . . . . . . . . . . . . . . . . . . I
...................................................r
................................................... o' i - * - t "
' ~ 6 I i _ _ . _ - - - Z ,~ , - ' ~ 8 0 . . . . . . . . . tH-96C .
. . - . ~ . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . I ~ 4 o i . . . . . . . . . . . . . . . . Z . - . - . ~ . ~ .
. . . . . . . . . . . . . . . . . . . . . . . ~ . . . . . . . . . .
. . . . . . . . . . . . . . . . . i i . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . : : : : :
: : : : : : : : : : : : : : : : : : : : : : . . . . . . . . . . . .
. . .. . . . . . . . . . . . . . . . . . . . . . . . . . . i. ~ 0"
- " 0~ ' - 4 o i0 l O 2 0 3 0B l o w e r w a t t a g e [W] Fig. 5.
a. Distillate output as functiono fheatinginlet temperatures (t.
)and different blower wattage,b. Relativeincrease o
fdistillateoutput asfunctiono fblower wattageand heatinginlet
temperatures in thefirst effect. heat r e c o v e r y f r o mt he
di s t i l l at e andconcent rat e ma s s f l o w s has l i t t l
ei mpa c t o n t het ot al di s t i l l at e out put . Th ea v e r
a g e evaporat i ons ur f ac et e mpe r a-t uresi nt hes e ve r al
s t age s o f t hef o ur - e f f e c t st i l larenot i nc r e as e
dbyt heheat r e c ove r y.Thema i nadvant ageof theheatrecovery
systemistheconsiderableimprovementofthe GOR by decreasing demand
for primary heating of thefirsteffect(seeFig.4b).TheGOR i nc r e as
e s by upto80% with heat recovery from F.Grdter
etal./Desalination138(2001)111-119117 t c = 2 0 * C~8[
................[. . . . . . . . . .
1......................................................................................................
1 ......+......Blowers a t 26 W a n d a N iheatr e c o v e r
y!.......M : . - - S c r e e n , n a t . c o n y .~ 6 ia n d h e a
t r e c o v e r y . . . . . . . . . . . . . . . . . . . . .
i........ A . O .......... i ....O.-..-lleat r e c o v e r y // . .
. . . O ~ N O h e a t recoveryl/ i / :/ ,
X......................................i , ~L
