Post on 01-Jun-2018
transcript
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Continuous ColumnDistillation
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Column diagram
feed
F, xF
bottomsB, xB
boilupV, yB
reuxL, xR
distillateD, xD
feedstage
total condenser
reux drum(accumulat
or)
VL
li!uid"#apor streams
inside t$e column o%counter¤t in directcontact %it$ eac$ ot$er
partial reboiler
xR ' xD
yB xB
xD xB t e m p e r a t u r e
all t$ree externalstreams (F, D, B) can be
li!uids (usual case) for a binarymixture, t$ecompositions xF, xD,
xB all refer to t$e
more #olatile
component to *eep t$e li!uid o%rate constant, part of t$edistillate must be returnedto t$e top of t$e column asreux
t$e partial reboiler is t$e laste!uilibrium stage in t$e system
e n r i c
$ i n g s e c t i o n
s t r i p p i n g
s e c t i o n
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+xternal mass balance
-B. F ' D / B
C-B. F xF ' D xD / B xB
for speci0ed F, xF, xD, xB,t$ere are only 1un*no%ns (D, B)
B ' F &D
feedF, xF
bottoms
B, xB
d
istillateD, xD
D = x F − x
B
x D− x
B
÷÷F
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+xternal energy balance
• assume column is %ell&insulated, adiabatic
feedF, xF
bottoms
B, xB
distillateD, xD
+B. F $F / 2C / 2R
' D $D / B $B
F, $F are *no%n
D and B are saturated li!uidsso $D, $B are also *no%n
un*no%ns. 2C, 2R
need anot$er e!uation
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Balance on condenser
distillate
D, xD
reuxL3, xR
#aporV4, y4
45 -ass balance
-B. V4 ' D / L3
C-B. y4 ' xD ' xR (doesn6t $elp)
un*no%ns. V4, L3
specify external reux ratio R ' L3"D
V4 ' D / (L3"D)D ' (4 / R)D
15 +nergy balance
V474 / 2C ' (D / L3)$D ' V4$D
2C ' V4($D 8 74)
t$en calculate 2R from column energy balance
$D 9 742C : 3
2R 9 3
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;plits;ometimes used instead of
specifying compositions in productstreams5
-ost #olatile component (-VC) isben=ene.
xF ' 35?@FRMVC
= x DD x F F
= 0.99D0.46F
FRLVC
=(1− x
B)B
(1− x F
)F = 0.98D0.54F
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Calculating fractionalreco#eries
B ' F 8 D ' @13 & 1A4 '
FRMVC
= x DD
x F F
= 0.99(281)0.46(620)
= 0.975
FRLVC
=(1− x
B)B
(1− x F )F
= 0.98(339)0.54(620)
= 0.992
D = x F − x
B
x D− x
B
÷÷F =
0.46−0.020.99−0.02
÷F =
0.44
0.97(620) = 281
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#aporV4, y4
distillateD, xD
;tage&by&stage analysisLe%is&;orel met$od
reuxL3, x3
V1y1
L4x4
stage 4
onsider t$e top of t$e distillation column.
V4, V1 are saturated #apors
L3, L4 are saturated li!uids
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Relations$ips for stage 4
-B. L3 / V1 ' L4 / V4C-B. L3x3 / V1y1 ' L4x4 / V4y4
+B. L3$3 / V171 ' L4$4 /
V474
VL+. 4(4,) ' y4"x4
#aporV4, y4
distillateD, xD
reuxL3, x3
V1y1
L4x4
stage 4
$ere are 4? #ariables.? o% rates (L4, V1, L3,
V4)
? compositions (x4, y1,
x3, y4)
? ent$alpies ($4, 71, $3,
74)
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Relations$ips for stage 1
-B. L4 / V ' L1 / V1C-B. L4x4 / Vy ' L1x1 / V1y1
+B. L4$4 / V7 ' L1$1 / V171
VL+. 1(1,) ' y1"x1
can sol#e for ? un*no%ns (L1, x1, V,y)
V1,y1L4,x4
and so on proceed do%n t$e column to t$e reboiler5 Verytedious5
;implifying assumption.Gf λi (latent $eat of #apori=ation) is not a strong function ofcomposition, t$en eac$ mole of #apor condensing on agi#en stage causes one mole of li!uid to #apori=e5
stage 1
V,yL1,x1
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Constant molal o#ero%
-B. L4 / V ' L1 / V1
C-H. V & V1 ' L1 & L4 ' 3
V ' V1 ' V
L1 ' L4 ' L
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Rectifying column
B, xB
D, xD
F, xF
Feed enters at t$e bottom, as a
#apor5
Eo reboiler re!uired5
Can gi#e #ery pure distillateI butbottoms stream %ill not be #erypure5
-ass balance around top of
column, do%n to and includingstage J.
L, xR
stage J
V J/4,y J/4 L J,x JC-B. V J/4y J/4 ' L Jx J / DxD
C-H. y J/4 ' (L"V) x J / (D"V) xD D ' V & L
y J/4 ' (L"V) x J / (4 & L"V) xDRelates com ositions of assin strea
L i l i f tif i
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Le%is analysis of rectifyingcolumn
45 Kssume C-H (V J ' V J/4 ' VI L J ' L J&4 ' L)
15 Eeed speci0ed xDI xD ' y4
5 ;tage 4. use VL+ to obtain x4
x4 ' y4" 4(4,)?5 se mass balance to obtain y1
y1 ' (L"V) x4 / (4 & L"V) xD
M5 ;tage 1. use VL+ to obtain x1
x1 ' y1" 1(1,)
@5 se mass balance to obtain y
y ' (L"V) x1 / (4 & L"V) xD
N5 Continue until x ' xB
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Orap$ical analysis of rectifying column
ation of t$e operating line.
(L"V) x / (4 & L"V) xD
pe ' (L"V)ays positive (compare to fash drum
otting t$e operating line.
t ' (4 & L"V) xD
ll. xD ' xR ' x3I t$e passing stream is y4
perating line starts at t$e point (x3,y4)
perating line gi#es t$e compositions of all passing streams (x J,y J/4)
!nd a second point on theoperating line"
y ' x ' (L"V) x / (4 & L"V) xD ' xDplot xD on y ' x
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y ( M e O H )
x(MeOH)
V L +
yint
o p5 l i n
e
xD 'x3(x3,y4
)
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-cCabe&$iele analysis. rectifyingcolumn
45 lot VL+ line (yi #s5 xi)
15 Dra% t$e y ' x line
5 lot xD on y ' x
?5 lot yint ' xD (4 8 L"V)
L"V ≡ internal reux ratio, usually not speci0edinstead, t$e external reux ratio (R) is speci0ed
M5 Dra% in t$e operating line@5 ;tep oP stages, alternating bet%een VL+ andoperating line,
starting at (x3
,y4
) located at y ' x ' xD
, until you
reac$ x ' xB
L
V =LDV
D
=LD
(L +D)
D
= RR +1
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y ( M e O H )
x(MeOH)
+x5. -eH7&71H rectifying column
V L +
y ' x
yint
o p5 l i n
e
(x4,y4)
(x1,y1)
(x,y)
(x4,y1)
(x1,y)
xB
15 Dra% y'x line
5 lot xD on y'x
?5 lot yint ' xD (4 & L"V)
@5 ;tep oP stages from xD to xB
N5 Count t$e stages
tifying column %it$ total condenser
ci0cations. xD ' 35A, R ' 1 E re!uired to ac$ie#e xB ' 354
L"V ' R"(R/4) ' 1"yint ' xD(4 & L"V)' 35A" ' 351@
E+V+R Qstep o#er t$e VL+ line5
lo%est xB possible for t$is op5 line
45 lot VL+ line
M5 Dra% in operating line
xD' x3(x3,y4)
stage 4
stage 1
stage
E '
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y ( M e O H )
x(MeOH)
Limiting cases. recti0cation
xD' x3(x3,y4)
V L +
y ' x
stage 4(x4,y4)
eci0cations.
' 35A, #ary R ' L"D
3' L"D 3 EH R+FLSV 3
L"V ' 3Eo reuxT
istance bet%een VL+ and op5 lineeparation on eac$ e!uil5 stage
ponds to Emin, but no distillateT
L"V ' 4 otal reuxT
3' L"D ∞ HKL R+FLSV ' R"(R/4) 467Upital6s Rule)
ating line is y'x
Column operates li*e asingle e!uilibriumstage5()
3 L"V 43 R ∞
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y ( M e O H )
x(MeOH)
-inimum reux ratio
V L +
y ' x
peci0cations.D ' 35A, #ary R
L"V ' 3
$e number of stages Ere!uired to reac$ t$e VL+&
op5 line intersection pointis ∞5
L"V ' 4
3 L"V 4
3 R ∞
xB ,min for t$is R
$is represents xB,min for a
particular R5
Gt also represents Rmin for t$is #alue of xB5
xD' x3(x3,y4)
Rmin for t$is xB
Gncreasing R ' L"DDecreasing DDecreasing xB (for 0xed E)
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Hptimum reux ratio
c o s
t " l b
external reux ratio, R
Rmin Ropt
operating (energy) cost
Rule&of&t$umb.453M R
opt
"Rmin
451M
Ractual can be speci0ed as a multiple of Rmin
W s t a g e s
min5 $eatre!uired
capital cost
total cost
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;tripping column
B, xB
D, xD
F, xF
Feed enters at t$e top, as a
li!uid5
Eo reux re!uired5
Can gi#e #ery pure bottomsI butdistillate stream %ill not be #erypure5
-ass balance around bottom of
column, up to and includingstage *.
stage *
C-B. L*&4x*&4 ' V*y* / BxB
V*,y*L*&4,x*&4
C-H. y* ' (L"V) x*&4 & (B"V) xB L ' V / B
y* ' (L"V) x*&4 / (4 & L"V) xB
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Orap$ical analysis of stripping column
s t$e partial reboiler> Designate t$is as stage E/4, %it$ xE/4 ' xB5
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y ( M e O H
)
x(MeOH)
V L +
o p
5 l i n
e
xB ' xE(xE/4,yE/1)
uation of t$e operating line.
' (L"V) x / (4 & L"V) xB
pe ' L " Vways positive
plotting the operating line"y ' x ' (L"V) x / (4 & L"V) xB ' xBplot xB on y ' x
ding the operating line slope"
call V"B is t$e boilup ratio)
Coordinates of t$e reboiler. (xE/4,yE/4)
(xE/4,yE/4
)R
LV = V +BV =1+ BV
b $i l l i i i
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-cCabe&$iele analysis. strippingcolumn
45 lot VL+ line (yi #s5 xi)
15 Dra% t$e y ' x line
5 lot xB on y ' x
?5 Dra% in t$e operating line
M5 ;tep oP stages, alternating bet%een VL+ and
operating line,starting at (xE/4,yE/1) located at y ' x ' xB, until
you reac$ x ' xD
@5 Count t$e stages5
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y ( M e O H )
x(MeOH)
+x5. -eH7&71H stripping column
V L +
y ' x
(35N,4)
(xE&1,yE&1)stage 1
15 Dra% y'x line
5 lot xB ' xE/4 on y ' x
?5 Dra% op5 line
5 ;tep oP stages starting at R
@5 ;top %$en you reac$ x ' xD
olumn %it$ partial reboilerpeci0cations.
B ' 353N,
ind E re!uired to ac$ie#e xD ' 35MM
N5 Count t$e stages5
(xE/4,
yE/4)
(xE,yE/4)R
(xE,yE) (xE&4,yE)
(xE&4,yE&4)
xD,max for t$is
boilup ratio
stage
E+V+R step o#er t$e VL+ line5
(xE&1,yE&1)
stage 4
xB' xE/4(xE/4,yE/1)
45 lot VL+ line
xD
V /B = 2
L /V =1+B /V =1.5
y =1=1.5 x −0.05 x =1.05/1.5 = 0.7
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y ( M e O H )
x(MeOH)
Limiting cases. stripping
V L +
y ' x
eci0cations.
' 353N, #ary boilup ratio
istance bet%een VL+ and op5 lineeparation on eac$ e!uil5 stage
ponds to Emin5 But no bottoms productT
Be$a#es as if t$ecolumn %asn6t e#en
t$ere5()
xB' xE/4
R
45
EH BHGL
3
rating line is y'x
HKL BHGL
EH BHGL
HKL BHGL
V /B
1≤ L /V ≤ ∞
∞ ≥V /B ≥ 0
L /V = ∞
L /V =1
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0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1
y ( M e O H )
x(MeOH)
-inimum boilup ratio
V L +
y ' x
eci0cations. ' 353N, #ary boilup ratio
$e number of stages Ere!uired to reac$ t$e VL+&
op5 line intersection pointis ∞5
G n c r e a
s i n g b o i l u
p r a t i
o
D e c r e
a s i n g
B
G n c r e a
s i n g x D
( f o r 0
x e d E )
yD ,max fort$is boilup ratio
$is represents yD,max for
a particular boilup ratio5
Gt also represents t$eminimum boilup ratio for t$is #alue of yD5
xB' xE/4
R
Eo boilup
otal boilup
1≤ L /V ≤ ∞ L /V = ∞
L /V =1
∞ ≥V /B ≥ 0
- C b $i l l i
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y ( M e O H )
x(MeOH)
-cCabe&$iele analysisof complete distillation column
V L +
y ' x
stage 4
45 Dra% y'x line
15 lot xD and xB on y'x
5 Dra% bot$ op5 lines
?5 ;tep oP stages startingat eit$er end, using ne%op5 line as you cross t$eirintersectionM5 ;top %$en youreac$ t$e ot$erendpoint
otal condenser, partial reboiler;peci0cations.xD ' 35A, R ' 1
xB ' 353N,
Find E re!uiredLocate feed stage
@5 Count stages
R
stage 1
xB
xD
t o p
o p 5 l i n
e
Feed enterson stage 1
E+V+R stepo#er t$e VL+line5
N5 Gdentif feed sta e
V /B = 2
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• Gf t$e feed enters as a saturated li#uid,
t$e li!uid o% rate belo% t$e feed
stage %ill increase.
• Gf t$e feed enters as a saturated vapor ,
t$e #apor o% rate abo#e t$e feed stage
%ill increase.
Feed condition
• C$anging t$e feed temperature
aPects internal o% rates in t$e
column
VLfeed
F
VL
and
• Gf t$e feed as$es as it enters t$e feed stage
to form a two$phase mixture, M3 X li!uid,
bot$ t$e li!uid and #apor o% rates %ill
increase.
L = L+F
V =V +F
F +L +V = L +V
L = L+0.5F V =V +0.5F
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Feed !uality, !
+B.
rearrange.
-B.
su%stitute.
com%ine terms.
de!ne.! ≡ mol sat6dli!uid
generated on
FhF +LhL +V&V = LhL +V&V
FhF + (V −V )&
V = (L −L)h
L
V −V = L −L −F
FhF + (L −L−F )&
V = (L −L)h
L
(L −L)(&V −hL) = F (&V −hF )
L −L
F
=&V −h
F
&V −hL≡ #
DiPerent types of feed
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DiPerent types of feed!uality
saturated li!uid feed ! ' 4
feed as$es to form 1&p$ase 3: ! : 4
mixture, !X li!uid
and
subcooled li!uid feed! 9 4
& some #apor condenses on feed plate
super$eated #apor ! :3
saturated #apor feed ! '3
L = L+F
L = L+#F
# ≡L − LF L = L+#F V =V + (1−#)F
V =V +F
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+!uation of t$e feed line
rectifying section C-B.
and
stripping section C-B.
intersection of top andbottom operating lines.
substitute.
e!uation of t$e feed line.
Vy ' = Lx
' −1−Bx B
Vy (+1 = Lx ( +Dx D
(V −V ) y = (L −L) x − (Bx B +Dx D)
y = −L −L
V −V
÷ x +
F) F
V −V
Bx B+Dx
D= F)
F
L −L = #F V −V = (1−#)F
y = − #
(1−#) x + ) F
1−#
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lotting t$e feed line
%$ere does t$e feed line intersect y'x>
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y ( M e O H )
x(MeOH)
V L +
y ' x' =F
feed type ! slope, msatYd li!uid !'4 m ' ∞satYd #apor !'3 m ' 3
1&p$ase li!"#ap 3:!:4m : 3
subcooled li! !94 m 9 4
super$eated #ap !:3 3:m:4
=F
s a t Y d
l i !
satYd #apor
1 & p $ a
s e
s u b
c o o l e
d l
i !
s u p e r $ e a t e d
# a p
y = − #(1−#) x + ) F
1−# x = − #
(1−#) x + ) F
1−#
x 1+
#
(1−#) ÷=
) F
1−#
x
1−#= ) F
1−#
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+x5. Complete -eH7&71H column
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y ( M e O H
)
x(MeOH)
y ' x
45 Dra% y'x line
15 lot xD, xB and =F on y'x
5 Dra% feed line, slope ' &35M
M5 Dra% bottom op5 line(no calc5 re!uired)
@5 ;tep oP stages startingat eit$er end, using ne%op5 line as you cross t$efeed line5
otal condenser, partial reboiler
peci0cations.D ' 35, xB ' 353?, =F ' 35M, R'4
eed is a 1&p$ase mixture, M3X li!5ind E and EF,opt5
5 Dra% top op5 line, slope ' L"V ' 35M
xB
xD
=F
4
@
1
M
?
Hperatinglinesintersecton stage ?5
$is isEF,opt5
*sing a non$optimal +eed location reduces
E ' @ / R
R
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y ( E t O H )
x(EtOH)
Knot$er type of pinc$ point
V L +
y ' x
45 Dra% y'x line
15 lot xD, xB and =F on y'x
5 Dra% feed line, slope ' !"(!&4)
M5 Don6t cross t$e VL+lineT
+t$anol&%ater
xD ' 35A1, xB ' 353N=F ' 35M, ! ' 35M
Find Rmin
?5 Dra% top op5 line to
intersect %it$ feed line onVL+ line
xB
xD
=F
@5 Redra% top operatingline as tangent to VL+5
pinc$point
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Kdditional column inputs"outputs
bottomsB, xB
distillateD, xD
VL
feed 1
F1, =1, !1
V[L[
feed 4F4, =4, !4
VL
distillateD, xD
bottoms
B, xB
feedF, =
VL
side&stream;, x; or y;V[L[
VL
Column
%it$ t%ofeeds.
Column %it$
t$reeproducts.
mediate input"output stream c$anges t$e mass balance, re#uiring a new oper
=1 9 =4and"or!1 9 !4
side&streamsmust be
saturatedli!uid or#apor
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-ultiple feedstreams
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1
y ( M e O H )
x(MeOH)
V L +
y ' x
45 Dra% y'x line
15 lot xD, =4, =1 and xB on y'x
5 Dra% bot$ feed lines
@5 Dra% bottom operatingline (no calc5 re!uired)
N5 ;tep oP stages starting
at eit$er end, using ne% op5line eac$ time you cross an
5 Dra% top op5 line, slope ' L"V
4
R
1
M
?
Hptimumlocation for feed4 is stage M5Hptimumlocation for feed1 is stage 5
tal condenser, partial reboilereci0cations. ' 35, xB ' 353N, =4 ' 35?, =1'35@
me speci0ed !alues' 45 Find E, EF4,opt, EF1,opt
xB
xD
=1
=4
M5 Calculate slope of
middle operating line, L["V[, and dra% middleoperating line
=4 ' =1
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;lope of middle operating line1&feed mass balances.-B. F
1 / V[ ' L[ / D
C-B. F1=1 / V[y J/4 ' L[x J / DxDmiddle operating line e!uation.
y ' (L["V[)x / (DxD & F1=1)"V[
btain slope from.
L[ ' F1!1 / L ' F1!1 / (R)(D) V[ ' L[ / D 8 F1
feed 1F1, =1, !1
D, xD
V[L[
stage J
side&stream;, x; or y;
D, xD
V[L[
stage J
iddle operating line e!uation.y ' (L["V[)x / (DxD / ;x;)"V[
side&stream ≡ feed&stream %it$ 8#eo% rate sat6d li! y ' x ' x;
sat6d #apor y ' x ' y;side&stream mass balances.
-B. V[& L[' D / ;C-B. V[y J/4 & L[x J ' DxD / ;x;
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-cCabe&$iele analysis of side&streams
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1
y ( M e O H )
x(MeOH)
V L +
;aturated li!uid side&stream, xs ' 35@?
xB
x
D
x;
=
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1
y ( M e O H )
x(MeOH)
;aturated #apor side&stream, ys ' 35
V L +
xB
x
D
y;
=
;ide&stream must correspond exactly to stage position5
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0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1
y ( M e O H )
x(MeOH)
artial condensers
K partial condenser can be used%$en a #apor distillate is desired.
D, yD
VL
L, x3
V, y4
partial condenser is an e!uilibrium stage5
B. Vy J/4 ' Lx J / DyD
erating line e!uation.
y ' (L"V)x / DyD ' (L"V)x / (4 & L"V)yD
yD
C
4
1
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0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1
y ( M e O H )
x(MeOH)
otal reboilers
K total reboiler is simpler (less
expensi#e) t$an a partial reboilerand is used %$en t$e bottomsstream is readily #apori=ed.
K total reboiler is not ane!uilibrium stage5
xB,yB R
E
E&4
B, xB
V L
stage .
V, yB
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;tage e\ciency
nder real operating conditions, e!uilibrium is approac$ed but
not ac$ie#ed. Eactual 9 Ee!uil
o#erall column e\ciency. +o#erall ' Ee!uil"Eactual
+\ciency can #ary from stage to stage5
Reboiler e\ciency tray e\ciency
%$ere yn] is t$e e!uilibrium #apor
composition (not actually ac$ie#ed) onstage n.
Can also de0ne -urp$reeli!uid e\ciency.
x J] ' y J " J
-urp$ree #apor e\ciency.
/ML
= x n− x
n−1
x n* − x
n−1
/MV
= y n− y
n+1
y n * − y n+1
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0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1
y ( M e O H
)
x(MeOH)
y ' x
xB
xD
=
R
+x5. Vapor e\ciency of -eH7&71H column
otal condenser, partialreboiler
;peci0cations.xD ' 35, xB ' 353N, = ' 35M,
! ' 35M,R ' 4, +-V,R ' 4, +-V ' 35NM5
Find E and EF,opt5
45 Dra% y'x line
15 lot xD, =, and xB on y'x
5 Dra% feed line
M5 Dra% bottom operating
line (no calc5 re!uired)@5 Find partial reboiler
5 Dra% top op5 line, slope ' L"V
N5 ;tep oP stages, using+-V to adJust vertical step
si=e5A5 Label real stages5
1
A
@
?M
4
N
E ' A / R
EF,opt ' @
o use +LV, adJust hori)ontal step si=e instead5
Gntermediate condensers and
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Gntermediate condensers andreboilers
Gntermediate condensers"reboilers can
impro#e t$e energy e\ciency of columndistillation.
45 by decreasing t$e $eat t$at must besupplied at t$e bottom of t$ecolumn, pro#iding part of t$e $eatusing an intermediate re%oiler instead
& use a smaller (c$eaper) $eatingelement at t$e bottom of t$e column, orlo%er temperature steam to $eat t$eboilup
15 by decreasing t$e cooling t$at mustbe supplied at t$e top of t$e column,pro#iding part of t$e cooling using anintermediate condenser instead
5 & use a smaller (c$eaper) cooling elementat t$e top of t$e column, and"or a $ig$ertemperature coolant for t$e intermediate
distillateD, xD
bottomsB, x
B
feed
F, =
VL
VL
V[L[
;, x;
intermediatereboiler
y; ' x
;
c$ column section $as its o%n operating line5
V[[L[[
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V1 L4
L3, x3
V4, y4
D, xD
stage 0
;ubcooled reux
Gf t$e condenser is located belo% t$e
top of t$e column, t$e reux stream$as to be pumped to t$e top of t$ecolumn5
+B. V171 / L3$3 ' V474 / L4$4
%$ere 74 ≈ 71 ' 7, but $3 $4 ' $
(V1 8 V4)7 ' L4$ & L3$3
c7 ' (L3 / c)$ & L3$3 ' L3($ & $3) / c
ere L3"V4 ' (L3"D)"(4 / L3"D) ' R"(R / 4)
C-H is #alid belo% stage 45 Find L"V' L4"V1>
V4 ' V1 & c and L4 ' L3 / c
cumping a saturated li!uiddamages t$e pump, by causingca#itation5 $e reux stream (L3)
s$ould be subcooled5 $is %illcause some #apor to condense5
;ubcooled reux causes L"V toincrease5
!3 ≡ !uality of reuxc =
h−h0
& −hL
0
= (1−#0
)L0
L1
V 2
=L0+c
V 1+c
=L0+ (1−#
0)L
0
V 1+ (1−#
0)L
0
=2−#
0( ) L0 /V 11+ (1−#
0)L
0/V
1
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Hpen steam distillation
B, xB
D, xDmostly -eH7
;, y;
L, xR
stage J
V J/4,
y J/4
L J,
x J
-eH7"71H
feedF, =
bottomsB, xB
Gf t$e bottoms stream is primarily%ater, t$en t$e boilup is primarilysteam5
Can replace reboiler %it$ directsteam heating (;)5
op operating line and feed lines
do not c$ange5
Bottom operating line is diPerent.
-B. V / B ' L / ;
C-B. V y J/4 / B xB ' L x J / ;
y;
usually 3
Hperating line e!uation.
y ' (L"V) x & (L"V) xB xint. x ' xB
C-H. B ' L
mostly 71H
+ H t di till ti f - H7"7 H
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+x5. Hpen steam distillation of -eH7"71H
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1
y ( M e O H )
x(MeOH)
V L +
y ' x
45 Dra% y'x line
15 lot xD and =F on y'x
5 Dra% feed line, slope ' !"(!&4)
@5 Dra% bottom op5 line(no calc5 re!uired)
N5 ;tep oP stages startingat eit$er end, using ne%op5 line as you cross t$eir
intersection
M5 Dra% top op5 line, slope ' L"V
xB
xD
=F5 lot xB on x&axis
4
@
1
M
?
Kll stages are on t$ecolumn (no partialreboiler)5E ' @ EF,opt '
?
peci0cations.
D ' 35, xB ' 353N, =F ' 35Meed is a 1&p$ase mixture, M3X li!5tal condenser, open steam, R ' 45
ind E and EF,opt5
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Column internals
• Klso called a perforated tray• ;imple, c$eap, easy to clean• Oood for feeds t$at contain suspended solids• oor turndown performance (lo% e\ciency %$en operated belo%
designed o% rate)I prone to Qweeping
;ie#e tray
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D
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Do%ncomers
Dual&pass tray
Gn large diameter columns, use multi&
pass trays to reduce li!uid loading indo%ncomers
Cross&o% tray (single pass)
# e r t i c a l d
o % n c
o m e r
a l t e r n a t e
s s i d e
s
Bot$ li!uid and #apor pass t$roug$ $oles Earro% operating range
Dual&o% tray (no do%ncomer)
\ i
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ray e\ciency
e \ c
i e n c y
#apor o% rate
%eeping"dumping
ooding i n e \
c i e n t
m a s s
t r a n s f e r
e x c e s s i # e
e n t r a i n m e n t
design
point
•
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Column distillation #ideos
Eormal column operation.$ttp.""%%%5youtube5com"%atc$>#'22gtcE=
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C l i i
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Column si=ing
45 Calculate #apor ood #elocity, ufood (ft"s)
%$ere Csb,f is t$e capacity factor, from empirical correlation %it$ o%
parameter, F
%$ere
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ray spacing
C l i i t
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Column si=ing, cont5
Relations$ip bet%een net area for #apor o%, Knet, in ft1,
and column diameter, D, in ft.
%$ere η is t$e fraction of t$e cross§ional area a#ailable for #aporo% (i5e5, not occupied by t$e do%ncomer)
$e re!uired column diameter, D, in ft, is also.
ired column diameter c$anges %$ere t$e mass balance c$anges5build column in sections, %it$ optimum diameter for eac$ section, orbuild column %it$ single diameter.
if feed is saturated li!uid, design for t$e bottom
if feed is saturated #apor, design for t$e topbalance section diameters (1&ent$alpy feed, intermediate condenser"re
3net
= π D2η
4
D =4V M2
V ( )3600πηρ
V uop
≈ 4V 3600πη u
op
R4
1
* d l
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ac*ed columns
larger surface area, for better contact bet%een li!uid and #apor preferred for column diameters : 15M[ pac*ing is considerably more expensi#e t$an trays c$ange in #apor"li!uid composition is continuous (unli*e staged column) analysis li*e a staged column. 7+ (' 7eig$t +!ui#alent to a $eoreticallate"ray)
structuredpac*ing.
randompac*ing.