successfully specify three phase separators 2
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Successfully pecifyThree-PhaseSeparators
t is often necessaryo separatewoimmiscible liquids, the light andheavy phases,and a vapor.A typi-cal example in petroleum refining
is the separationofwater, and a hydro-carbon liquid and vapor. Little hasbeen published on three-phase(liq-uid/liquid/vapor) separarion, withmost information available only incorporate design files. This articleattemptsto alleviate this situation bycovering he basicsofthree-phasesep-arator design. The authors provide a
Step-by-Step procedure and workedout examples. Further, the examplesoffer guidance n makingassumptionsfor the calculations.
Selectinghree.phare eparatoreAs with two-phase designs, three-
phaseunitscan be eitherverticalor hor-izontal,although hey typically arehori-zontal (seeFigures and2). The verti-cal orientation.Figure 1, s only used fthere is a large amount of vapor to beseparated rom a small amount of the
light and heavy liquid (< l0-207o byweight). Unfortunately, there are nosimple rules for separator selection.Sometimes,both configurationsshouldbe evaluated o decide which is moreeconomical. Further, the available plotspace footprint) may be a factor.
The designof three-phaseseparatorsis similar to their two-phasecounter-parts, except that the liquid sectiondif-fers. For the vertical type, a baffle com-monly keeps the liquid separation
r t -v T -
1,488g,fi(p, pr)( l )
18F
where 1,488converts iscosityof the
sectioncalm to promote the separation.There are different variations of hor-
izontal three-phasevapor-liquid separa-tors. The liquid separationsection isusuallya variationof a device o provideinterface level control, which mayincludea boot or a weir.A boot typical-ly is specifiedwhen he volumeof heavyliquid is not substantial < l5-207o oftotal liquid by weight), while a weir isused when the volume is substantial.Thesehorizontal separators re llustrat-ed in Figure 2. The bucket-and-weirtype design s usedwhen interface evelcontrol may be difficult, such as withheavy oils or when large amountsof anemulsionor a paraffinare present 1).
$tokos'law pplieeSeparatinga vapor from a light liquid
(two-phaseseparation)hasbeencoveredin a previous article (2) and will not bediscussed ere.However,all necessaryinformation for performing this part ofthe calculation s providedhere.The fol-lowing discussion overs he separationof light and heavy liquids.
The flow of rising light droplets inthe heavy liquid phaseor settling heavydroplets n the ight liquid phase s con- ,sidered laminar and is soverned bvStokes'law:
Heresastepwise
procedurefordesigning
liquid/Iiquid/vapor
separutors.
Wayne .Monnery ndWilliamY.Svrcek,
UniversityfCalgary
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M U L T I P H A S E F L O W
+ D -
1 - n .vent
H"l "rg"I
Baffle
HoldupLisht iq.
+r'-\l H '
lnterfaceheavy iquid
Vapornozzle
Wire mesh
Feednozzle
Maximuml i q u i dlevel
il - *A
Baffle o provide
ca lming one srecommended
SectionA-A
I
Heavyl iquidnozzle
^.[-Lioht r-t iq"uiOnozzle
_THr l
J
I Figure l.Vertical three-phaseseparalors are used with high
vapor loadings
is more diffi-
c u l t ( r e q u i r e s
more time) to set-
tle the droplets
out of the contin-uous phase with
the greater vis-
cosity,since U. is
lower. Practically
speaking, U, is
typically limited
i n c a l c u l a t i o n s
t o 1 0 i n . / m i n
maximum.
For vefiical sep-
arators, he diame-
ter required for
vapor disengage-ment is calculated
as in our previous
article (2). In siz-
ing a separator,he
heightsof the light
and heavy liquids
are assumed,and
the settlingveloci-
ties and settling
t i m e s a r e t h e n
calculated.
The residence imes of the light and
heavy iquids are determinednext.Forthe liquids to separate, he residence
time of the light liquid must be greater
than the time required for the heavy
droplets o settleout of the light liquid
phase; and the residence ime of the
heavy liquid must be greater han the
time required for the light liquid
droplets o rise out of the heavy iquid
phase.fthese conditions renot satis-
fied, then liquid
separation s con-
trolling and the
vessel diametermust be increased.
Holdup time for
liquids must be
added o residence ...
time. The height
of the vertical
three-phase sepa-
rator is calculated
in the same man-
ner as for-the two-
phase ase.
For horizontal separators with a
given diameter, he heights of the light
and heavy liquids are assumedso that
the cross-sectionalareacan be calcu-
lated. With the vapor disengagementarea set by guidelines, the lengths
required by holdup requirementsand
vapor/liquid separationare calculated.
Then, with the assumedheightsof the
light andheavy liquids and calculated
values of settling velocities, the set*
tling times are calculated.
The actual residence imes for the
light and heavy liquids are subse-
quently calculatedandcomparedwith
the required settling times. as in the
vertical case. If the residence times
are not greater than the required set-tling times, then either the diameter
should be increased or. for a given
diameter, the length should be
increased liquid separations con-
trolling). In the subsequentdesign
procedures, the laner approach is
used, along with the procedures dis-
cussed in our previous paper for
vapor/liquid separation 2).
The following desi-rn procedures
and heuristics are a result of a review
of literature sources and accepted
industrial design guidelines.Horizontal designproceduresarepre-
sented for the four separator types
shown in Figure l. The horizontal
design procedures incorporate opti-
mizing the diameter and length by
minimizing the approximate weight
of the shell and heads.To adda degree
of conservatism o the design, he vol-
ume available n the heads s ignored.
oi austi,or causiic
continuousphase rom lb/(ft)(s) to cP.
Simplifying Eq. 1 and convertingthe units of the terminal settling
velocity to in./min from fUs results n:
r r 2 .0615 l x l } - s | f ,QH-pL), r = T
(2)
whereDo is in microns 1 micron=
3.28084 106 eet) andU7, n./min.Eq.2 maybe rewrittenas:
r t kt(Pu - Pr)ur=---T
where
ks=2.0615tl \-sf i .
Values of ft, are given for some sys-
tems n Table 1.
From Eqs. 1-3, it can be seen hat
the settling velocity of a droplet is
inverselyproportional o the viscosi-
ty of the continuousphase.Hence, t
(3 )
Methylethyletonesec-ButyllcoholMethylsobutyletoneNonyl lcohol
FurfuralWaterWaterWaterWater
0is3'0.i630.1630.1630.163
1218989898g8989
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3. Interface ontrolwith weir
Feedin let
l , v
Heavyl iquidoutlet
,* l N , l
' l^n.* * u,n. l
Lightl iquidoutlet
* L N I * -- l
2. InterJaceontrolwith boot 4. Bucket ndweir
Heavy Lightl iquid l iquidoutlet outlet
Heavy iquid
| - t - t - t - l
I L , l L z l L s l L 4 l
Note:N= 112 7,1+6in.
drv=Nozzle ia'
outlet
t - L -
Min.12 n.
Min.12 n.
Vapor
outlet
Light iquidholdu/surge
Vapor
outlet
I Figure 2. Basic designs of horizontal three-phase separators,
Vertical design.procedur€Refer to Figure 1 for dimensions:1. Calculate the verlical terminal
vapor velocity:
U- = ylPt - Pvr t t2 (4)Pv
Calculate he K value, using one ofthe methods n Thble 2 and set Uu =
A.l5Ur for a conservative esign.2. Calculate the vapor volumetric
flow rate:
Q v = 3,600pu(s)
internal. Calculate the vesseldiameter,Dur:
140-,\" 'D""= l# | (6 )
\nu,
If there is a mist eliminator, add 3-6in. Io D, to accommodatea supportring and round up to the next 6-in.
increment to obtain D; if there is nomist eliminator,D = Dur.
4. Calculate the setting velocity ofthe heavy iquid out of the light liquidusingStokes'law(themaximum s 10
in./min):
r t - k t (Pn -P r ) 0 \v H L -
l t r
whereft, is obtained rom Table 1 or is
calculated seeEq. 3) .
5. Similarly, calculate the risingvelocity of the light liquid out of theheavy liquid phaseusing Stokes' aw:
r r - k t ( P r - P t )u u.J
ILH
6. Calculate the light and heavyliquid volumetric flow rutes, Q* and
QnL:
w--o - . - " L L ( 9 )wrL_
60pL
n - W r tunr- 60pa
(8)
WV(10)
7. Assume Hr = I ft (minimum)
and calculate the settling time for the
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M U L T I P H A S E
"=,{*t#d)where " s n t.
Note: micron3.2808410{ t
heavy iquid droplets o settle hrough
thisdistance 12 s a conversionactor
for ft to in.):
g. Use Table 3 to determineAo lA.
h. CalculateA= (nl4)D2.
i. CalculateAr.j. Select he argervalueofAr.
k. Calculate the area of the baffle
plate - settling areafor the light liq-
u i d ; A . - A - A o .
10. Calculate the residence ime
of eachphasebasedon the volumes
occupied by the light and heavY
phases:
basedon the requiredholduP
( 1 1 )
8. Assume Hn = | ft (minimum)
and calculatethe settling time for the
light liquid droplets to rise through
this distance:
LzH,(12)
t - ---:,LH -
TIu L H
9. If there is a baffle Plate, calcu-
late the area:
a. Calculate P. - P).b. Assume11*(use9 in. as a mini-
mum) and calculateHt+ H^.
c. Use Figure 3 to obtain G.
d. CalculateAr:
SeeEq. 3) in thebox.
e. Assume Wo = 4 in.
f. CalculateWD/D.
If eLL< tu, or Iur 1 trr, \tctease
the diameterandrepeat he procedure
from Step7 (liquid separation s con-
trolling).Note thatAn= A.
11. Calculate the height of the
light liquid above the outlet (holdup
(1s)
Checkthis r-alueu'ith that assumed
in Step9b to ensure hat the assumed
value is reasonable.ft- surge is not
specified, calculate the surge height
basedon surge ime:
(eu*eo)r,Hs=\---TL
(16)
The minimum is 6 in.
12. Calculate the vessel height
using he guidelines:
He= 6 in. minimum.
H aio h d. + greaterof (2 ft or /1t
+ 0.5 0.
Ho=0.5D or a minimumof :
3 6 i n . + V z d r w i t h o u t m i s t
eliminator),or
24 in.+ t/zd* lwith misteliminator):
H.=+l2H,
t - ----------=,HL_U, ,
s*=w (I4a)
(14b) - HuAuvHL-
Qr t
^ (t.+aeal\/oo,in{0- 0rl\a,=
l-r,
I--T-/\----G-/) Equation13
Ur=0'313
I EquationEl
=2.14ftJs
Q v =415.000lb/h =165.32ft' ls
3.600 /h 0.69731VfflEquation E2
^ 1TVT4STFIs -r-\o=V --irISHs - r0.13tlEquation E3
16.5000lb/hou -
60 minthx 53.95btftt
a EquationE4
= 5.10 t'lmin
l,3o0lb/hvnr=ffi
lEquation E5
= 0.35 t'lmin
53.95 0.6973
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10,000
9,000
8,000
2. Calculatehe rapor ' r r lurr - t r i "
flow rate,seeEq. El in thebor.
3. Calculatehe vesselnnerdiam-
eter, eeEq. E3 in thebox.Use1J= 10.5 i.4 . C a l c u l a t eh c : e t t l i n ge l o c i l r r l
theheavy iquid out of the ight iqLridphase.Using Table l , f ts = 0.163Then:
Um = 0.163(62.11 53.95)/0.630= 2.11 n. /min
5. Calculatehe sett l ing elocitl of
the ight iquid out of theheavy iquiclphase:
U ra= 0 .163(62 .1153 .95 ) /0 .761= l.l4 tn.lmin
6. Calculate he l ight and hearIiquid volumetric flow rates.seeEq.E4 andE5 in the box.
7. AssumeHr= 1ft andcalculatethe tirne fbr the heavy iquid to sertleout of the ight iquid phase:
tn , .= 12) 1 .0 )2 . l1 = 5 .7mi n8. AssumeHn = 1 fi andcalculate
the ime lbr thelight liquid to
rise out of theheavy liquidphase:
t r H = ( 1 2 ) ( 1 . 0 )
l l . l J = 6 . 9 m i n
9. Calculatei i l i t i - : , r - r ' : '1 : r i - i1 f - ;1:
r _ r _ i l , ) < r l n t l l l _ i l ) S
lL. t '. . \ : > . r1 . ' t - = I ) i n . .Hr+ Hn= 24
in. L ' . : rg Fr ,rLrre1.G = 9.800 ph/f tz.{ . =
- j r_cal i i t ' r r60 inih) 5.10
- o.-1-iii ' 9..\00gph/iir = 0.25 t2. . \ . . . l l t i l l = J j p . .
\ \ . ,D -1 l r1 l 10 .5) 0 .0317
.an, =Hn+ H, +HR+O^ Ufii
It ' a mist eliminatorpad is used,-,-riional eight s added sshown n
: - - l r e .
Example
Sizea verticalseparator ith a baf'-' : : l l tc andwire-meshmist elimina-: i,.rseparatehe mixture given in
. -,rleJ. Theoperating ressures 165'.., : , rrild t is necessaryo have a
Jr'(rcarboniquid holdup ime of 25:: and a surge ime of only 5 min.1. Calculate he vertical erminal
- .iitr '. Using Table 2, calculateK- ' i t he York Demis te r q r r r t i ons .
. . . Eq .E1 n thebox ., :nJL'1= 0.75 2.14= 2.05 t ls.
co_
oFc
-
-oG
G
r. i
24 in .
/= 4.0184a8
. = _J.9 t64 t
= - i .801705
= l 1.i5348
t. \, to H/D+= HID= \/.\r
= 0.00153756' = 16.787101= 1.299201
: - i.2.923932
. = 1.1.353518'= 11.844824
- = -36.999376
: = 10.529572: = 9.892851
:.luivalentxpressions,uch sH',/D
pr- pu,lblft3
^=#6ft3ls
60,fF;
1oa,r= r+A,
Q , - r , .T t : 2
- v u :
4u ,
High iquid evelabove nterface
I Figure 3. G is found rom the downconterallowable low.
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M U L T I P H A S E F L O W
Experienced 1.0
Trained 1.2
Inexperienced 1.5
Well nstrumented 1. 0
Standardnstrumented 1.2
Poorlvnstrumented 1. 5
F Fuel as nock-outrum
ZOt.ilug n he ncominguelgas ine etween Ltand igh evel hutdown
G.Flare nock-outru m20 o 30min o Hll
Mult ip ly y he ol lowingactorsoptionall:
Personnel Factor Instrumentation Factor
. Using Table 3, AD/A= 0.0095:
1= (nl4)(10.5 t)2= 86.59 tz
A, = (0.0095) 86.59 t2)= g.g21r2
. UseA, = 0.82 ft2.
A, = 86.59 0.82 = 85.11 t210. Calculate he residence ime of
eachphase:
0r. = (1.0 fI) (85.77 112115.10
ft3lmin= 16.8min
lnr = (1.0 f0 (86.59 ftz)10.35
ft3lmin = 241 4 min
11. Calculate he height of the light
liquid above the outlet, based on
holdup:
tlo = (5.10 t3imin)(25 min)/85.77
ftz = 1.5 t
/1s = (5.10 + 0.35)(ft3/min) 5
min)i86.59 t2 = 0.31 tUse I/r = 0.5 ft .
12. Calculate d, according to
Table5:
)"= Qrl(Qr + Q) = (5.10 +
0.35Y(5.10 0.35+ 165.32 60) =
0.0006
Use Eq. E6 (seebox) to calculate
Prpu = pLX+ pll - l.) = (54.55)
(0.0006)+ (0.6913) (l - 0.0006) =
0.730
Qu = 165.32+ (5.10+ 0.35)/60=
165.4I t3/sUseEq. E7 (seebox) to calculated*
dN > 2l in.; use dt = 24 in.
Calculate Ho'.
Ho = 0.5 (10.5)= 5.25 t or
Ho = 24 + 2412= 36 in. = 3.0 ft(minimum)
Use11,= 5.5 ft. From Figure 1, 1t= I ft ands = 0.5 ft. Calculate lur:
Hsw='/,(2.0 f0 + 2 ft = 3 ft
Set11, = 0.5 ft. Final dimensions:
D = 10.5 t, HH= I.0 ft^ HL = 1.0 t,
Hn= 1.5 r, Ho = 0.5 ft. HB.,= 3.0 t,
andHo = 5.5ft. Add 1.5 t for the misteliminator.
Hr= l4'0 ft
H I D = 1 4 . 0 i 1 0 . 5 = 1 . 3
Add 2 ft to H, (Hp = 2.0 ft, Ho =
7.0 f0 so that HlD = 1.52 (HlD
shouldbe n the rangeof 1.5 o 6.0).
Horizontaldesignprocedure:no boot or weir
1. Calculate the vapor volumetric
flow rate,Qu,usingEq. 5.
p,=## x53.es+ffi x62.It 54.55btft3
l EquationE6
)'''= .rr ,
I EquationE7
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2. Calculate the light and heavyliquid volumetric flow rates, Q' and
O711,sing Eqs.9 and 10.
3. Calculate the vertical terminal
velocity,Ur, using Eq. 4. (selecta Kr alue from Table 2) and set Uu =
0.75Ur.
4. Select holdup and surge timest-romTable 6 and calculate he holdupandsurge olumes,V, atd Vr, (unless
surge s otherwisespecified, uchas a>lusvolume):
'= - " {trrQ* tntQ,
e * ' ( h - A v - o * )
Qrr=I A , - A , - A u , l L 1 ? q r\ ' ' . 1 \ . / |
5. Obtain an UD from Table 7 andinitially calculate the diameteraccordingo:
(20)
Calculate the total cross-sectionalilea:
(2r)6. Set the vapor space height, 11,
, rhe larger of 0.2D or 2 ft; I ft if:.-,eres no mist eliminator. Using1 ,/D n Table3, obtainAr/A, andcal---llateAu .
7. Set he heightsof the heavy and
;ht liquids,Hrrand Hr,8. Find (AnL+ AL)lAr, using (I1",
- fl -tlD inTable3,andcalculateA*
9. Calculate he minimum length to
-- -,rmmodatehe iquid holdup/surge:
r _L _
V, +V,(22)
10. Calculate the liquid dropout-:a:
I = H,./L't Q3)
| [. Ca]culate the actual vapor
velocity:
Uw= Qr/Av( ) L \
12. Calculate he minimum lengthrequiredfor vaporiliquid separation:
Lum= UvlQ (2s)
13. If L 1 Lr,,,r, then set L = Lr,*(here, vapor/liquid separationcon-trols). This simply results in someextra holdup and residence ime. If I11 Lr,*, then increaseHu and recal-culate Au, and repeat, starting fromStep 9. If L > L*n, the design isacceptable or vapor/liquid separa-tion. If L )) Lr,,., liquid holdupcon-trols). can onlr,be reducedand .rrr.increased f H,, is reduced.F1, ma1'only be reducedf it is _ureaterhan heminimum specified n Step 6. (With
reduced 11* recalculateAu and repeattheprocedurerom Step9.) Note: Forthis and other calculations, "much
greater than" (>>) and "much lessthan" (<<) meana varianceof greater
than 20Vo.
14. Calculate he settling velocitiesof the heavy iquid out of the light liq-uid phaseand he ight liquid out of theheavy iquid phase,U". and U.o, usingEqs.7 and 8 (find ft, from Thble 1).
15. Calculate he settling imes ofthe heavy iquid out of the ight phase
and the light liquid out of the heavyphase:
tur= 12 (D - Hv- HH)IUHL
tro= 12 HHL/ULH
16. Calculate he residenceof the light and heavy iquids:
0ur= AorLlQu,
(26)
(21)
times
(28)
17.If gHL< tL Hincrease he vessel
arationcontrols):
Q,,
or 0,-, < t", thenlength(liquid sep-
(30)
18. CalculateUD.If UD << 1.5,decrease (unless t is alreadyat its
minimum), and if UD >> 6.0 thenincreaseD; repeat rom Step5.
19. Calculate the thickness of theshell and headsaccording to Table 8.
20. Calculate surface area of theshell and headsaccording o Table8.
21.Calculateheapproximatees-sel weight according o Table8.
22. Increaseor decrease he vesseldiameter by 6-in. increments an drepeat the calculations :until the UDratio ran-eesrom 1.5-6.0.
23. Using the optimum vesselsize
(minimum wei-eht). alculate he nor-mal andhigh liquid levels:
Hau= D - H, (3 )
Anrr= (Am+ Arr) + Vo/L (32)
Obtain 11r.. using Table 3 with thevalue of A*ro/Ar.
Horizontaldesignprocedure:heavy iquid boot
1. Calculate the vapor volumetric
flow rate,Q, usingEq. 5.2. Calcrilate the light and heavy
liquid volumetric flow rates, Q* and
Qnr,perEqs.9 and 10.
3. Calculate the vertical terminalvelocity, Ur, using Eq. 4 (the K value
comes from Table 2) and set Uu =
0.15 Ur.4. Select holdup and surge times
from Table 6 and calculate he holdupand surge volumes, V, and Vr, fromEqs. 18 and 19 (unlesssurge s other-
Vo= To Q,
V s = T s Q r
(18)
( 1 9 )
A _ TED'
4
t r -Au_ (our* ,4 r r )
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M U L T I P H A S E F L O W
wisespecified, uchas slug volume).
5. Obtain UD from Table 7 and
initially set he diameteraccording o:
/ ? \
Then calculate the total cross-sec-
tional area,A, usingEq. 21.
6. Set the Yapor spaceheight, F1*
to the larger of 0.2D or 2 ft (l ft if
there is no mist eliminator). Using
HutD in Table 3, obtainAv/Ar andcal-
culateAu.
7. Set he light liquid heights n the
vesseland boot, HrN andHrrt.8. Calculate the cross-sectional
areaof the light liquid above he bot-
tom of the vessel,Ar., using Hrtt/D
in Table 3.
9. Calculate he minimum length to
accommodatehe liquid holdup/surge:
'=(t+
(,q,,- ,)rou=
eu(36)
DishedHeads
Approximate
(34)
10. Calculate the liquid droPout
time, $, usingEq. 23.
1L. Calculate the actual vaPorvelocity,Uuo, singEq.24.
12. Calculate he minimum length
required or liquid/vaporseparation.
Lrr*, usingBq.25.
13. If L 1 Lr,*, then set L = Lr,*
(vapor/liquid separation controls).
This simply results in some extra
holdup and residence time. If I
11Lr,*, then increaseH, and ecalcu-
lateAr, then epeat rom Step9.If L>
Lr,*, the design is accePtable for
vapor/liquid separation. f L >> LMrN,
liquid holdup controls. I can only bereduced atd L*,* increased f I1u is
reduced.Humay only be reduced f it
is greater han the minimum specified
in Step6.
With reduced Hu, recalailate A,
and repeat rom Step 9.
14. Calculate the settling velocity
of the heavy iquid out of the light liq-
uid phase, U"., using Eq. 7 (obtain ks
from Table1).
15. Calculate the settling time of
V., +V"f - n o
" - A r - A u - A r N
the heavy iquid out of the light liquid
phase:
tm= 12 (Hrrn + D - H)IUHL Q5)
16. Calculate he residence ime of
the ight liquid:
19. Calculate the thickness of the
shell and headsaccordingto Table 8.
20. Calculate the surface area ofthe shell and headsaccording o Table
8 .
21. Calculate the aPProximate
weight of the shell and headsaccord-
ing to Table 8.
22.Increaseor decreasehe vessel
diameter by 6-in. increments and
repeat the calculations until 1,/D
ranges rom 1.5-6.0.
23. With the optimum vessel size
(minimum weight), calculatethe nor-
mal andhigh liquid levels:
Hnu= D - Hu (38)
Attrr= Arru + VrlL (39)
DetermineH*rrusingTable 3 from
A*r/Ar.
24. Design the heavy liquid boot:
Set the height of the heavY liquid,
Hur; calculate the rising velocity of
the light liquid out of the heavy iquid
phase,Uru, using Eq. 8 (find ft, from
Note: This volume of light liquid
ignores the light liquid volume in the
boot.
I7. If 1LL< to, then increasethevessel ength (liquid separation on -
trols):
(37)
18. CalculateUD.If UD << 1. 5
then decreaseD (unless t is alreadyat
a minimum) and if UD >> 6.0 then
increaseD; rcpeat rom SteP5.
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Table 1); set U, - 0.15 ULHicalculatethe heavy liquid boot diameter:
Then calculate he settling time of thelight liquid out of the heavy liquidphase:
ttr= l2Hu1/Us1
Calculate he residence ime of theheavy iquid:
the light liquid comparlment usingEq. 44 or read t from Table 9.
(4r) Htu= 0.5D + 1 (44)
whereD is in feet andHrrrin inch-es (roundup to nearestn.). If D < 4.0ft, then Hrm= 9 in. Using HoytD inTable 3, CalculateArrr.
8. Calculate he weir heisht:
tru= l2Hrx/Uro (4e)
14. Calculate minimum I, to facil-itate liquid-liquid separation as thelarser of:
A -ndH*"ut - 4en
( ,,o-,=maxl : f f\ n ur
trrQrr\ (50),A,, I
If eHr < tru, thendiameter.
(42)
the boot
Horizontaldesignprooedure:weir
1. Calculate the vapor volumetricflow rate,Qu,using Eq. 5.
2. Calculate the light and heavl'liquid volumetric flow rates,Qu and
Q11y.aserEqs.9 and 10.
3. Calculate the vertical terminalvaporvelocity, Ur, using Eq. 4 (find Ktiom Table2) and set Uv = 0.l5Ur.
4. Select holdup and surge timestiom Table6, and calculate he holdupand surge volumes, V, and V., fromEqs.18 and 19 (unless urge s other-ir sespecified, uchas a slugvolume).
5. Obtain UD from Table 7 andinitially calculate the diameteraccordingo:
Then calculate he total cross-section-
" larea. . . usingEq.2l .
6. Set he vaporspace eight.Hu .ro the larger of 0.2D or 2 ft (1 ft iflhere is no mist eliminator). UsingH../D in Table3, obtainAu/A, and cal-;ulateAu .
H w = D - H v (4s)
If Hw< 2 ft, increaseD, and repeatthe calculationsrom Step6.
9. Calculate he minimum lengthof the light liquid compartment toaccommodate holdup/surge, 1,. inFigure 2 :
V n + V ,Ar - A r . - AuL
Round to the nearest 7: ft. Theminimum for Lr= d, + 12 in.
10. Set the interface at the heightH,*12, obtaining the heights of theheavy and ight liquids, Hrrand Hrr.
11. For the liquid settling com-partment,calculate he cross-section-al area of the heavy liquid, usingHr/D in Table 3 and calculate thecross-sectionalreaof the ight liquidfrom:
(43) Ar r= Ar - A , - A* (4',7)
12. Calculate the settling velocityof the heavy iquid out of the light liq-uid phase,Uur, and he light liquid outof the heavy liquid phase,U"r, usingEqs 7 and 8 (find ft, from Table 1).
13. Calculate the settling times ofthe heavy iquid out of the light liquidphase and the light liquid out of theheavy iquid phase:
tur= l2Hr1/U*
L1
Round to the nearest% ft.15. Find l,:
L = L t + L z (s1)
16. Calculate the liquid dropouttime, Q,using Eq. 23.
17. Calculate the actual vaporvelocity.U,,.,. singEq.24.
18. Calculate he minimum lengthrequired for vapor/fliquid separation,
1.,rr,.. sing Eq. 25.19. lf L ( Zr'.r- then set L = L*r
(vapor/liquid separation controls).This simply results in some extraholdup and residence time. If L <<Lr,*, then increase Hr, recalatlate A,and repeat he calculations from Step6. If L > L*,r, the design s acceptablefor vapor/liquid separation. If Z >>.Lrr, (liquid separation and holdupcontrol), Z can only be reducedandLr,* increased f Hv is reduced. //umay only be reduced if it is greater
than the minimum specifled n Step 9.With reduced Hr, recalculate A, andrepeat rom Step9.
20. CalculateUD.If UD << 1.5,then decreaseD (unless t is already ata minimum) and repeat from Step 6.If UD >> 6.0, then increase D andrepeat rom Step 5.
21. Calculate he thicknessof theshell and headsaccording to Table 8.
22. Calculate the surfacearea of theshell and headsaccordins to Table 8.
(-+6)
(48). Calculate he low liouid level
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M U L T I P H A S E F L O W
23. Calculate he approximate ves-
sel weight according to Table 8.
24. Increaseor decrease he diam-
eter by 6-in. incrementsand repeat he
calculations untiT UD ranges from
1.5-6.0.
25. With the optimum vessel size
(minimum weight), calculatenormal
and high liquid levels:
Hnu=D-H , (52 )
Atrrr= Arrr+ V,1L, (53)
Obtain Hr' using Table 3 with
ANLL|Ar.
Horizontaldesignprocedure:bucket and weir
1. Calculate he vapor volumetric
flow rate,Qu,usingEq. 5.
2. Calculate the light and heavy
liquid volumetric flow rates,Q, and
Qnr,perEqs.9 and 10.
3. Calculate the vertical terminal
vapor velocity, Ur, using Eq. 4 (flnd K
from Table2) and set Uv= 0.75 Ur.
4. Select esidence imes for light
and heavy liquids, 0r, and 0o.. For
sour water stripper feed drums, 0o. =
there is no mist eliminator). Using
Hr/D inTable 3, obtainAu/Arand cal-
culateAu.
7. Calculate ,:
(o,e,,+o-,e-,1, ' . ' ' . ]
60 min for reflnery service,or 10-15
min for chemical-plantservice.For
amine regeneratoreed drums, 0o. =
10-15 min.5. Obtain UD from Table 7 and
initially set he diameteraccording o:
(s4)
0J0n(r1r)
Then calculate he total cross-section-
al area. . usingEq.21
6. Set the vapor spaceheight, 11u,
to the larger of 0.2D or 2 ft. (1 ft if
, = (+(e,,0,,re,,,O,,
f -L l -
1 5 5 )
Ar-4,
8. Calculate the liquid dropout
time,Q,usingEq. 23.
9. Calculate he actualvaporveloc-
Uuo, singEq.24.
10. Calculate the minimum length
required for vapor/liquid separation,
L*,r, using Eq. 25
ll.If Ll 1 Lr,*, then set Lt = Luru
(vapor/liquid separation controls).This simply results in some extra
holdup and residence ime. lf Lt <<
LM,N, h.enncrease lr,. recalculateAu
and repeat he calculations from Step
1. If Lt ) Lr,*, the design s accept-
able or vapor/liquid eparation.
12. Calculate he light liquid layer
thicknessbasedon the heavy liquid
settlinsout:
g,,= 235'ooolblh =343.5'7t3/s3.600 /hx 0.190b/ff
I EquationE8
o,,=45'ooorblh -=18.52ft'lmin
60min/h 40.5 b/ft'I Equation E9
o-, = 7'5oo b/h =2.y2ft'lmin60 min/hx62.0lblfr'
I Equation810
Ur=0'175
I Equation811
, , - ( 4r27r .80 " ' ' -\0.6ru t.7xr/i)
= 11'15t'use1'0 t
I EquationE12
4 = f f i = 1 4 . 5 4 f t- Equation813
tutQrt - 2.0 min x2.02ft3hn1n=0.45 tA,,
I Equation814
s.% t
trrQo - 2.0 min x 18.52 t3lmin =2.41 tALL
I Equation E15
r r Q uure=T
=
I Equation816
rs.02ff
343.51f ls = 4.83 tls7r.08e
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prop€r-
engli
l ne
w,D,tlni
of Western
degreesn
u 0.00128e'(AsG)Dprr i6 ,V,'
,.hereD" is in microns.13. Calculate the differenc- rl
:rsht between he light and he;:,,.,quidweirs:
i o . r :_ \ H = H r r l l - X l- \
Pu
1-1. esign he ight iquidbucker:': the op of light l iquid u eir '= D
, lssumehe bottonr s at 0.1l5Dl. . r t t ie a holdup/surge t1,prcal l r .' . -i min.); assumeHLL is 6 in., rrl the weir height andLLL is 6 in.
i e the bottom of the bucket.. r,c Table 3 with HrrrlD and
D. calculate Au' and Arr.r.-ulateL,:
:,=
il;::T:1",,-*lllllJli,'
^- =
:#, ?:light
l iquid bor.eesselor -
l:==,1'l
:-i;iliill,1l11;1",,'7\=il,,l,l,1l;;,'.;l:l'"'.'"
D = resseliemeler."r ' l lu'
3' = lJli';,il ,. rmicronsD , = r3prlr 'J isengagementia. . r
t =
; : : ]o.oLoint
eff ic iency. imension-
-' = cfa\ i tar ional onstant, 2.17 r , /sr
6 = baffle iquid toad.gph/fr)
H = heighr. t
H.. = liquid level above baffle, in. or ft
HB,. = liquid height from abor.ebaffle to
leed nozzle. t
H;, = disengagement eight. i
H. = htrldupheisht. i
H- = tei ,sht r . .= l i ; . : : i : : : : :=: : i i l i
: , z z : : . '
0 = volumetr ic iow. l r /sor l t r /min
S - vesselml ler ia l stress alue. s i
ASu = 5psqif gravity differenceberween
Nomenclbture
) l r ' - : -
li. l';L
;JL:
L, L;
LL L
1/
.\ I
I
TC
TH
tut
ttu
1s
TH
TS
Y:,HL
u,.,ou to f heavy iqu id , n . im in
Un = mixture velocity, tVs
Up = boot velocitr'. n.lmin
f = l c f rn i l r J lg l 6 . 1_1 .i . ' . r i n . / r r i n
L = \ i-Lpi \rel . rc i t r . Ll :
,a ,
= - - - . - . - : . : . : '
= : : - : : a i l r denaa t ime. min
- ::'.:::,i:. liquid ifact ion
= l \ : . : : : \ . - P
= : : : . : : : . l b r ' f t ]
= : , : : i r L r l ou i t ime- s
I ighrandheavy iquidr
= '*ftJil],."',0,'o,"0,",,out ol l ight iquid 'min
rprels ul iiii,r;:i::';i'J'
*'=;5.,ff::;l= \u rge rmr .m in .
= al lor lable or izorrnl c loci t l . rl s
= se t t l i nqe loc i t v f he rv r i ou id
dropleis Lrr f l ighr iquid. n.tmin
= ris ingveloci t)of l ighr iquiddroplers
T _ lro+r,)9,,(58)
(Ar,'r_Arr,')
\ssume1., s the argerof D/l2i n .
Design he heavy iquid com-rnt: Set he top of theheavy iq-. - i r '= D - Hv- A11; ssume:r \Lrr_setypically, 5-15 min);: HLL is about6 in. below the:r,ght and LLL is about 6 in..h- bottomof thevessel. sing: v,trh Hrrr/D andHr,,y/D, ca7-i . ..andAr_r...- LLl . i te ., :
i: -.
H,, ;
H , , -
H,. .
H,,,u
HP.
Hsg
n v
H,,,
fts
l
K
L
L*,*
;'':liilr,r-Hj
- - - : - : - - - . . ' -_ - .
= :: : : : : : : - : : : : ,: -= heiSi:t i,'::r iiir:
fle. 11
= i r r r oe he i ohr r i
= totai verticalsepararor eight. i
= vapordisengagement reaheighi. r
= weir height. ft
= heighldrf lerence el i ieen ighi un J
heavy iquid weirs. n.
= Stokes' au. erminal elocirr con-
srant. n. /min)r Pr i t lb/ fr
= terminal eloci tyconsLanl.r , is
= vessel engrh. t
= vapor,4iquideparar ion irrrrnum: .
l
t 6 ,
I - , ; i
: . : : : l ; ; i r i , l ;evei
i : i : i . ; ; i r i t i
: , , . r r q l i i i e re l
r - : . I l i . ' , ' i , l l - . ^ l
' , : a . t I
I _(r, + rr)9,,
(5e)
lAorr- Arrr)
17.Calculate = L, + Lr+ L. + L^.18. Calculate D.I f UD << 1.5.
thendecre seD trnd epeat i'onlStep5 Ii UD >> 6.0. hen ncrease an drepeat i'omStep 5.
19. Calculate he thickness f th eshel1 ndheads ccordingo Table8.
20. Calculate l're surf'ace rea of
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M U L T I P H A S E F L O W
shell and headsaccording o Table8.21. Calculatehe approximate es -
sel weight according to Table 8.
22. Increaseor decrease he diam-eter by 6-in. incrementsand repeat he
calculations until UD ranges fromt.5-6.0.
Example2Design a three-phasehorizontal
separatorwith a weir to separate hemixture in Table 10. The operatingpressureand temperature are 25 psig
and 100, espectively, nd t is neces-sary to havea liquid holdup and surgetime of 15 min.
1. SeeEq. E8, box, p. 382. SeeEqs.E9 andE10,box,p. 38
3. K = 0.175 (the Gas Processors
Suppliers'Associationvalue n Table
2 was divided by 2 since here s no
mist eliminator).
SeeEq.E11,box,p. 38
Uv=0 .75x2 .55 = 1 .91 t l s4. Holdup + surgeas specified= 15
min.
Vu+ V, = (15 min) (18.52 t3lmin)= 211.80 t3
Assume 10 min holdup, 5 minsurge.
5. Assume D = l. l .
SeeEq. El2, box,p. 38Ar=n/4 (11.0 | 'z = 95.03 t2
6. Since the mass ate of vaoor is
where : = des ignressurendD= drum ia ,
about 27o f the oading, etF1yo bemuch greater han the minimum.Assume v = 0.70D (0.70)(1.0 0= 7.70 ft. UsingTable3, Av/Ar =
0.148, v= 71.08t27,Hrr r= 0.5) (11.0)7 =I2 .5 in . ,
use 3 n.Hrr/D = 13/(11.0 12)= 0.098UsingTable ,ALLrj/Ar 0.051Aur= (0.051X95.03P)= 4.95112
8. H, = 11.0 1 10= 3.30 t9. SeeEq.El3, box,p. 38Use ,r = 15.0 t.10.HHL- Hrr= 3.3012 1.65 tll. HH//D= 1.65111.00.150FromTable , AH/A, = 0.094Aur= (0.094X95.03t2)= 8.93 t2Au=95.03 71.08 8.93 15.02t l12.FromTable1, ks= 0.333Uur= (0.333)(62.040.5)/0.24
29.83n./minUse10 n./min maximum)Uro= (0.333)(62.040.5)10.682
10.50n./minUse10 n./min maximum)13, tHL= Q2 in./ft)(1.65 t)ilo
in./min= 1.98min, use2.0minstr, = tnr = 2.0 min14. SeeEqs.E14 andE15.box,
p .38Use r = 3.0 t.15 . = 3.0+ 15.0 18.0t16.0 = '7.10
ftll.gI ftls= 4.03s17.See q.El6,box. .38
18. LurN = (4.83 ftls)(4.03 s ) =
19.5 r
19. SinceL 1 Lr,*, set L= 19.5 t(setZ, = 16.0 t, lr = 3.5 t)
20. UD = 19.5/11.0 L78
21. Assume dished heads per
Table11 .
AssumeE = 0.85
Use SA-516 70 carbon steel,design emperature= 650o
S = 17,500psi; from Ref. (3).Corrosionallowance= Vrs n.
P = 2 5 + 3 0 = 5 5 p s i g
SeeEq. E17,box on thispage.
Use r, - 7s n.
SeeEq. E18, box on this page.
Use /" = Vz in; use = Vz n.
22. As = ?I(11.0 0 (19.5 f0 =
673.81 tz
Au= (0.842) 11.0 O'z 101.88 t2
23. SeeEq. E19,box on thispage.
24. In this example, calculationswere performed for only one diame-
ter. However, nearly the minimumUD corcesponded o a diameter of
11.0 fU therefore. he next diameter
should be smaller, resulting in a
laryerUD. Also, calculationsshould
be performed using a diameter of
I 1.5 t .
25. For the light liquid compartment:
Hnrr= Hw= 3'3 ft - 3 ft, 4 in'
AxLr=4.85 185.20116.016.43fP
A*t/Ar= 16.43/95.03 0.713
Using Table 3, HNLrt/D 0.229
Htrrr= (0.229) 11.0)= 2.52 t - 2
ft, 6 in.HLLL=13 n'
Comment: Due to the smal l
amount of heavy liquid and large
amount of vapor, a better design
would have used a boot. A vertical
vessel should be comoared. as
we11.
To eceive freecopyof his article,
send n heReadernquiry ard n his
issue ith henumber 53 ircled,
@
1 _ 55x I32
" - 2 x l 7 M*l|rc=0.307 n.
I Equation 817
r . . = , =0.- -8=81l f 1?? -- *r ,160.495n.H2x 17.5000.850.1x 55
I EquationE18
t =ff' ltff#(on.at
rt22x 0r.88')= 7.s20tbI EquationE19
40 . sEpTEMBER994 CHEMTCALNGTNEERTNGRocnEss