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Патент USA US2404677

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July 23, 1194s,"
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_ 2,404,611
Patented July 23, 1946
Warren C. Wilson, Rahway, N. J., assignor to
Standard Oil Development Company, a corpo
ration of Delaware
Application October 29, 1941, Serial No; 416,980
9 Claims.
(Cl. 19d-94,)
This invention relates to the fractionation of `
and in this way provides the necessary liquid re
vapor mixtures >and more particularly relates `to
. controlling the temperature .of the top of a frac
flux for fractionating the hydrocarbon vapors.
tionating tower by controlling the temperature
of the reflux liquid introduced into the top of the
fractionating tower.
olf and run through heat exchanger equipment
and the recovered. heat is transferred to the fresh
In my process the liquid sidestream is drawn
In the fractionation of vapors containing dif
ferent constituents such as hydrocarbon vapors
`it is usual practice to control the temperature at
feed. In this manner the heat is recovered from
the top of the tower. With my `invention itis
desirable to circulate the maximum quantity of
liquid from the tower in order to increase the
the top of the fractionatîng tower by regulating
the quantity of reflux liquid introduced into th‘e
top of the fractionating tower. The reflux liquid
~ Also, it is desirable to transfer as much heat as
heat transfer coeñ‘lcient of the h'eat exchangers.
possible from the liquid to the fresh feed in order
may be cooled in various ways but if the rate of
to secure maximum efliciency.
reiiuxing is held constant and the temperature
is controlled by regulating the quantity of waterpassed to the coolers there is danger of vaporiza
move the correct amount of heat, however, it is
tion of the water and by loss of water due to
vaporizatîon corrosion of the heat exchange coil
In order to re
. necessary to provide a cooler or coolers in addi
tion to the heat exchangerl equipment so that
when the amount cf h'eat transferred `from the
hot liquid to thev fresh feed is not sutlicient to
Water used in these cool
give the required fractionation inthetower, the
ers is in many cases salt water which is more cor
rosive at h'igher temperatures.
20 additional heat may be removed by the cooler.
or surface will result.
According to my invention, the reflux liquid is
This means then that as the temperature` of the
fresh feed is increased or as the heat exchanger
equipment becomes fouled the load on the cooler
withdrawn from the fractionating tower at a
constant rate and passed in indirect heat ex
change with fresh feed and another medium to 25 If all of the liquid after passing `through the
heat exchangers were to be passed to the cooler,
recover heat and then the partially cooled reflux
it would then be necessary to regulate the quan
liquid is passed to another heat exchanger where
is increased.
cooling water is‘used. When using the reflux
tity of Vwater going to the coolers. This could
Y recovered from the reflux and put into the fresh
_cient water is always, flowing through the> cooler
either be done by hand or by anautomatic con
liquid as a heat exchange medium, it is desirable
to obtain maximum heat recovery before 'cooling 30 trol valve in th‘e water line. However, if this
were done there would be times when very little if
with water.
_any heat would have to be removed from the
According to my invention, the danger` of va
cooler and under` that condition the valve con
porization of the cooling water and resultant cor
trolling the water to the cooler would be closed
rosion of parts of the heat exchanger is avoided
and without replenishing the supply of water the
by holding substantially constant the quantity of 35 temperatureof
the water in the cooler would
water passing to the cooler or coolers and regu
gradually rise until it reached th'e vaporization
'lating the temperature of the reflux liquid by
temperature of water and it wouldv then be evap
lay-passing a portion of the partly cooled reflux
orated. With such a condition there would be
liquid around th'e heat exchangers or coolers.
40 severe corrosion of the cooler. In order to pre
According to my invention maximum heat is
vent this the equipment is laid out so that suñi
feed without running the danger of operating the
cooler at salt water temperatures considerably
to take care ofthe maximum heat load. Then
if less than that maximum heat load is required
in excess of those required to prevent corrosion. k45 the reflux liquid is by-passed around the cooler
In order to fractionate the vapors it is `necessary
which means `that very little if any temperature
to vaporize the feed stock in the bottom of the
rise would `occur onA the water going thrcugh the
tower and then remove heat somewhere up the
cooler and at no time would the temperature of
tower. This heat removal can be accomplished
the water reach the vaporization point and there
by condensing vapors and refluxing the condensed 50 by start corrosion.
liquid, but according to my invention, the heat is
In the drawing:
l .
» ,
removed by removing a sidestream of hot liquid,
Figure 1 represents one form of apparatus which
cooling this liquid outside the tower, and then
may be used to carry out my invention; and
reinjecting it. The reinjected cooled‘liquid con
Figure 2 represents one form-of control valve
»denses a part of the vapors coming up the tower 55
whichmay loe-used.
through line 84 is the lightest fraction separated
Referring now to the drawing, the reference
from the liquid feed.
character ID designates a line through which the J
Returning now to the reflux liquid withdrawn
liquid to be fractionated is passed by pump I2.
from top trap-out tray 5ft, the reflux liquid is
Where hydrocarbon liquids are to be fractionated,
the oil feed comprises light naphtha or heavy 5 passed through line 64 by pump 85 and then
through valved line 86 through the -heat eX
naphtha or any other desired hydrocarbon frac~
changers I6 and 24, previously described, where
tion from lwhich it is desired to separate suitable
vthe reñux liquid is cooled by indirect îcontact with
fractions. V«Ii'iqu'id Y mixtures ‘other lthan hydro
lthe liquid feed introduced through line I0. If
carbon mixtures may be fractionated according to
. 10 ^desired, the refiux liquid may be in part or all
my invention.
v`“by-passed around the heat exchangers IB and
`‘1`2llîthrough Icy-pass line 88 having a valve 9B.
The cooled reflux liquid is then passed through
I8 and through another coil 22 in a second heat
line‘g‘SZ; and! through cooler 94 for cooling the
exchanger 24 for preheating the vliq'uidifeed."P Dur
ing passage through the C'CîlS l4'ar`1d'~22, the liq- 15 'reflux Yliquid to the desired temperature. The
cóoler'Ss is preferably a closed cooler. The tem
uid feed is indirectly contacted with reflux liq
The liquid feed is passed through coil Ill‘in
heat exchanger I6 and then passed -throughv :line
.fperature responsive device 63 in line $5, herein
uid withdrawn from a fractionating tower@ .to> be
hereinafter described. If desired, onlyioneheat
before described, is connected by a line 95 to a
control valve 95 in line S8 which communicates
exchanger may be used or the feed may be passed
through other heat exchangers for additional 2O with line V92. Device 6-8 may control valve 96 by
Nheating. Ái’I-‘he“preheated- >liquidy *feed is 'passed `~velectrical'rnean's, by air "pressure or,` in any suit
A‘able mannerfïñ‘or example, thé temperature at
through ‘linetZIìl andï‘through the -heating coilv 2B
“in 'aheater 32/‘to'bring`the'liquid-‘feed‘toî the de
i -sired'temperatura
il Geein line "56 is transmitted-‘to a temperaturecon
v‘trol instrument ‘ such . as a` Leeds- and' Northrup
i ‘Inlet line "IU'is provided with a *valve-¿'¿Sârand 25 “fMicromaxjy which in turn controls'the pressure
on the diaphragm valve 96. Byï~regulating the
-"outlet‘linè’25 -is`provided» with a> valve .42 for by»
1 air pressure on the diaphragmfofvalve'ßß in re
f passingrthe Lheat exchangers~` ‘I t `and` 24Min which
v"eveht'the ~liquid'feed` is passed through k„by-pass
' sponse‘to temperature'changes,ï'the valve iseither
"“jlinerëiic having a valve ‘42. ’ The ‘heated ‘liquid
*raised-or lowered and this in `turn :regulates 'the
"feed-fromithe"heatingcoil‘Zß'is introducedinto» 30 ' flow: through linè S3. ' Other controfm'eans‘may
-`"the'ilowerfportion oi" aA fractionating “tower M
be fused. VV‘These control ‘valves andL associated
""The‘ fractionating'ßtower
trays'äßj'EZ ‘and"54. ‘44
'îvheatedivapor's‘from the liquid feed “pass” upward
' parts'are` well known equipment available on the
v7market and- furtherV detailed description ofthe
equipment is not believed necessary.
' ".ti'onated` ‘to‘L separate llighterA 'constituents from
""heavier"constituents, " The Vfractionatingv tower
`:mayhe’ofïiany’suitable construction'such as a
'» Asshown in the drawing,"the temperature re
sponsive device 63‘is a bulb or the like >containing
vM13/“through” the‘fractionating‘ tower ` ‘and’ 'are Afrac~ y 35
aïliduid or liquids having desired vapor pressures
` at'~"the"cperating temperatures. `An> increase in
temperature‘in line Alili _results in ari‘increase in
trays are-'provided 'so "that dif- 40 pressure' in‘devi’ce S8 which is transmitted through ,
line 95 to the pressure responsive valve-‘SBSVThe
"ferent 'fractions :may be `removed‘from :the‘frac
“L tionating'towerîßd The 'fraction having the’high„
f valve~ 96Y and 'associated parts- shown- irî'Figure 2
" -estlooiling range` is“ withdrawn from "thetrap-out
ï will now v'be described.
The control` valve 9G comprises a valve housing
Vtray 48. ..A lighter fraction is withdrawnffrom
“the-next higher" trap-‘out""tray "52 and~- a lighter' 451- saiaßvaivefmc and a vaiveïseat mar- valve’ioo
M"fraction is withdrawn from thetop traplo'ut‘trav
‘ thas a '-»valveïstem'iIM "passingi'through agland
“T545 "The unva'porized heavier 'constituents lcoln
'packing H36. ‘f The> upper 'end of‘stem ’I F34’ :is Íse
*""le‘ctthe'bottomi‘ofthe fractionating tower ¿i4
~~ cured to a‘m-ovable f member ror'ïdiaphragm * : I B8
""at ‘I I2. *Positioned >between'‘idiaph'ragm I-ß8`and
«packing ‘I'êliik is a spring:surrounding'stem "IIL
"»is‘witlîdrawn’throu'gh’line 53 and may beA further
"treated to .separate desired constituents theree
."Lfrom. "Iïhe'" fraction 'withdrawn 'from trap-out
tray '52 is 'passed‘through ,line'iiZ and maybe fur-_l
The diaphragm housing II 5 has a fixed-»rear wall
l il 81 and «sidefwall» I 22‘forrningA a cup‘shaped
:cham-ber to which the-»diaphragm‘ïl‘ßß is secured.
>»Housing IIS is lrigidly secured, to the Valve hous
Alîth'er’treated 4Las‘ 'desired Vto separate" desired con-“ 55«ing199 bymembersv I24andY-l26. Tube -or line'Sä
f .communicates withthe housing I I6.
‘ >From the above it will be seen thatias the: tem
» .peratureat ßßiincreasesithe liquid intemperature
"’stituent's therefrom. " The relatively lightfraetion
""cbllectingfon ïi the top trap-outßtray '54 is" with
-¿drawn ‘through'liné ‘64 and is cooled as will be
responsive device Will have .its temperaturefin
hereinafter'moré fully' described- to provide cool
I.reflux-liquid,for'the' fra'ctionating tower TM.
@F0` creasedrandl the pressure incline 95` williincrease.
"The .'uncon'dens'ed vapors ¿forming the" lightest
." The’. increaseinepressure will move§diaphragm
portion' of‘théliquid feed pass overlfi'eadv through
->line 65"which.' is'lprovided with. atemp‘erature
Y ‘Y or paiîtlyfclose valve |00 and this will causel'the
¿|08 down against the action ofspring IIIIA to close
liquid to be passed through lineÍISU and cooling
" "responsive ’deviceJEB for controlling.’A the-tempera
ture 'of ‘the’ reflux -liquid introduced into’- the frac
' vtiona'tin‘g'tower'êli'as'willbe hereinafter described
‘ r'irrgreater detail. " The overhe'ad'vapors arep'assed
5 couilaz inthe cooler’ s4 .to reduœ‘tne tempera
ture of thereñux liquid.
The cooled liquid from the coil îI32`îis`- then
>passed through line ’§34 where it join’s‘the'r’eflux
` v'through' heat “exchangers 'I2 vand "I4" where' Vthey
'liquid by-’passed around the'coolerf'fSlI andjpass
nfares" indirectly -contacted' Awith îcooling water to
condense and cool the vanors.‘1"The condensed 70"ing"through' line- 93. 'The' reñuxîi'quid‘ìs" then
and cooled vapors are passedthrough‘line "I6 to
' ~ a `> gas'"separatorl "18Minu 'which ’ thefgases'jare“ sep
aratedf fromf'"liuuidl~ zthe ‘gases’ passing kf'overh‘ead
‘ <^ through linel "82 - andr` the‘liduidvv being with-drawn
through bottom line `IM.
” passedA through line l|36 and introduced ‘into the
top \ portion "of" the fractionatingLtowe?’flllîiabove
vvthe-top trapáout 'tray' `~54, ’ Preferably, thef'rela
tively“ `cooled-reflux' 'liquid 'ist' introduced' ‘into’ a
ferential pressure valve |38, hereinafter described
example of fractionating hydrocarbon oils will
in greater detail, to insure satisfactory operation
in housing ||6 on control valve 96 will decrease
and spring ||4 will force the diaphragm |08 up
beV given. A hydrocarbon mixture such as a
heavy naphtha having an A. P. I. gravity of
about 50° and having an initial boiling point of
about 200° F. and a final boiling point of 435° F.
is passed through the heater 28 and heated to a
wardly to open valve |00.
temperature of about 625° F. while maintained
of the control valve 96.
If the temperature at 68 decreases the pressure
The cooling water for the cooler 94 is intro
duced through line |42A and overflows through
line |44. According to my invention, the amount
of water passing to the cooler 94 is not regulated
under pressure of about 50 lbs. per square inch
gauge. The vapors are fractionated in the frac
tionating tower 44. Unvaporized residual oil
withdrawn from the bottom ofthe fractionating
or controlled but the cooler is kept full of water
tower 44 through line 56 has a boiling range of
all of the time by using an excess of the maxi
about 560° F. to about '100° F. and has an
mum requirement. In this way corrosion of the
A. P. I. gravity of about 26°.
apparatus due to vaporization of the water is 15
The hydrocarbon fraction withdrawn from the
eliminated. The temperature of the reflux liquid
lowest trap-out tray 48 has an A. P. I. gravity
is controlled by ley-passing the cooler 94. In
of about 36° and an initial boiling point of about
order'to obtain the desired temperature, all or
400° F. and a final boiling point of about 620° F.
a portion of the reflux liquid is by-passed around
This fraction is withdrawn at a temperature of
the cooler 94.
about 360° F. The fraction withdrawn from the
The cooling >water used in the cooler 94 is pref
trap-out tray 52 has an A. P. I. gravity of about
erably ñrst used for cooling overhead vapors from
44.2°, an initial boiling point of about 275° F.
the fractionating tower 44, The cooling water
and a final boiling point of about 390° F. The
may comprise any available water such as salt
lighter fraction withdrawn from the trap-out
water, well water, etc. The cooling water is
tray 52 is at a temperature of about 310° F. The
passed through line | 46 by pump |48 and through
reflux liquid withdrawn from the `topitrap-out
the heat exchangers 14 and 12 where the cooling ’
tray 54 has an A. P. I. gravity of about 60°, an
initial boilingpoint of about 100° F. and a final
boiling point of about 320° F. The reñux liquid
withdrawn through line `64 is at a temperature
water indirectly contacts the vapors passing
through line 66. During this heat exchange, the
cooling water has its temperature raised a small
amount. The cooling water is then passed
through line |52 and introduced into the cooler
94 through line |42 as above described.
If desired, the Ifractionating tower 44 at its
lower portion may be provided with a reboiler.
of about 225° F.
tower are at a temperature -of about 225° F. and
after being condensed by passing through the
coolers and'condensers 12 and 14, the distillate
collected in the separator 13 forms the lightest
Diiferential pressure valve |38 will now be de
Two pressure conneotions |60 and |62
are taken as indicated, one on each side of cooler
94, 'I’hese pressure connections are connected by
lines |64 and |66 to a differential pressure regu
lator instrument, such as is manufactured by the
American Meter Company or the Foxboro Meter
Company, and which is shown diagrammatically
as including pressure chambers |68 and |10 con
nected by a line |12, Line |12 communicates
with a valve memberI |14 into which air is sup»
plied by line |16. The air under pressure sup
plied through valve member |14 depends on the
differential pressures in chambers |68 and |10
and is passed through line |18 to control valve
|38. This control instrument regulates the air
pressure on` diaphragm valve |38 either raising
or lowering the valve in order to maintain a con
stant differential pressure across the cooler 94.
The vapors leaving the top of the fractionating
fraction of the naphtha, This light distillate
has an A. P. I. gravity of 62°, an initial boiling
point of about 60° F. and a final boiling point of
about 290° F. In order to maintain the tempera*
ture of the top of the tower at about 225° F. and
further to obtain the desired amount of frac
tionation, the reflux liquid is returned to the top
of the tower and the splash pan |31 at a tem
perature of about 150° F. The ratioof the re
flux to the vapors passing overhead is about 4 to
l b-y weight.
The cooling water is introduced into the cooler
64 at a substantially constant rate to maintain
50 the cooler full of cooling water.
The reflux liquid lis'passed through heat ex
Ichangers i6 and 24 to recover heat from the
reflux liquid.V The reflux liquid has its tempera
This differential pressure regulator is preferably 55 ture reduced to about 200° F. after having passed
through the heat exchangers I6 and 24. In this
used in order to take care of the wide range in
-way the maximum amount of heat is recovered
from the reflux liquid. 'I‘he temperature of the
|32 when only a very small part of the total liquid
-reflux liquid is controlled by the temperature
being circulated is run through the cooling coil
responsive device 68 in the outlet line 66 from
|32 and when the major portion of the liquid is
being run through the cooler. In order to operate 60 the fractionating tower 44. If the vapors passing
overhead through line 66 from the fractionating
valve 96 properly there must be a fairly constant
tower 44 are at too low a temperature, the re
differential pressure across the cooling coil.
flux liquid is too cold and the temperature re
When a large portion of the stock is going
sponsive device 68 moves the control valve 96
through the cooling coil a pressure drop is builtl
toward open position to permit by-passing of
up by the resistance to the flow of this liquid.
the reñux‘liquid through lines 98 and |36 around
However, when only a small portion is going
the cooler 94.
through the cooling coil there would be practi
If the vapors passing overhead through line
cally no resistance and therefore no pressure
66 are at too high a temperature, the reflux
drop. Valve |38 merely holds this differential
pressure constant. Other means may be used to " liquid temperature is too high in which event
the temperature responsive device 68 effects
accomplish this result.
While the apparatus may be used generally
movement of the control valve 90 in line 98 to
ward closed >position and more of the reflux
for the fractionation of liquid mixtures, it is es
pecially adapted for the separation of hydro
liquid is passed through line |30 and coil |32 in
carbon mixtures into desired fractions. One 75 cooler 94,
pressure drop which may occur acrosscooling coil .
trolled Vbythe ,temperature in the `upper -portion
' The side streams taken through lines 58 and
52 may be passed to separate stripping towers
of said fractionating Zone,
to separate lighter constituents therefrom which
3. A method of fractionating liquids compris
ing mixtures of different constituents which `com
prises heating a liquid feed andintroducing it
are .preferablyA returned to the fractionating
tower 44.
If desired, instead of controlling the process
with a temperature responsive device at the top
ofthe tower 44, a similar arrangement may be
into a lfractionating zone, fractionating the va
pors to separate lower boiling constituents from
higher boiling constituents, passing vapors of» low
er boiling constituents overhead, withdrawing a
used to regulate the temperature at any place in
the tower where the stock is to be circulated
through a water cooler.
relatively light liquid from the upper portion- of
said vfractionating zone atV a constant rate, pass
ing the withdrawn relatively light liquid through
Other hydrocarbon mixtures may be fraction
ated as for example hydrocarbon mixtures re
a cooler, supplying a cooling medium to said cool
sulting from the cracking o-f hydrocarbon oils
er at a substantially constant rate in excess of
the maximum cooling required, by passing at least
or heavier oils may be fractionated to separate
a portion of the relatively light liquid around said
them into desired fractions and my invention
cooler, returning ‘the combined cooled relatively
may be used in fractionating lthese mixtures.
light liquid at a constant rate to said fractionat
Or,V other mixtures may be fractionated.
ing zone as reflux liquid, and controlling the rela
>While one form of apparatus has been shown
for carrying out my invention and one Specific 20 tive amounts of the relatively light liquid passing
through and >around said cooler bythe tempera
example has been disclosed, it is to be under
ture in the upper portion of said fractionating
stood that these are by way of illustration only
and various changes and modifications may be
made without departing from the spirit of the
4. A method according to‘claim 1 whereinîthe
reflux liquid withdrawn from' the upper portion
of said fractionation zonelis passed in indirect
heat exchange with fresh liquid feed of said frac
I claim:
1. In the fractionation of mixed vapors in a
fractionating Zone to separate desired constitu
ents, the steps of removing reflux liquid from the
upper portion of said fractionating zone at a con
stant rate, passing the reflux liquid through a
cooler, passing a cooling medium through said
cooler at a substantially constant rate in excess
of the maximum cooling required and regulating
tionation zone, before it ispassed through said
5. A method according to claim 1 whereinv the
differential pressure across said cooler vis kept
substantially constant independent of the amount
of reflux liquid passed through said cooler.
6. A method according to claim 3 wherein the
the temperature of the reflux liquid to be re 35 relatively light liquid withdrawn from the upper
turned at a constant rate to saidy fractionating
portion of said fractionating zone is ypassed* in
tower by by-passing at least a portion of the re
indirect heat exchange with the liquid feedbefore
flux liquid around said cooler, the relative flow
itis passed through said cooler to obtain maxi
of the reflux liquid through and around said cool
mum heat recovery from the relatively light
er being controlled by the temperature in the 40
upper portion of said fractionating zone.
’7. A method according to claim 3 wherein the
2,'In the fractionation of mixed vapors in a
relatively light liquid withdrawn from the'upper
fractionating zone to separate desired constitu
portion of said fractionating Zone is passed in
ents, the steps of removing reflux liquid from
indirect heat exchange with the liquid feed before
the upper portion of said fractionating zone at a
itis passed through said cooler and wherein fur
ther thecooling medium is water and the'water
before being passed to said cooler is passed in
indirect heat exchange with the overhead vapors
constant rate, passing the reflux liquid in heat
exchange relation with the liquid .feed passing
to said iractionating zone to obtain maximum
heat recovery from the reflux liquid, then passing
from said fractionating zone to cool and. con
the partly cooled reflux liquid through a water 50 dense the overhead vapors.
cooler, passing water through said cooler at a
8.- A method according to claim 1 wherein hy
substantially constant rate in excess of the maxi
drocarbon mixtures are fractionated to separate
mum cooling required and regulating the temper
lower »boiling hydrocarbons from condensate oil.
ature of the reflux liquid to be returned at a con
9. A method according to claim 2 wherein hy
stant rate to said fractionating tower by by-pass 55 drocarbon mixtures are fractionated to separate
ing at least a portion of the reflux liquid around
lower boiling .hydrocarbons from condensate oil.
said cooler, the relative flow of the reflux liquid
through and around said Water cooler being con
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