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Патент USA US2283832

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May19, 1942. K
Y c. l.. THOMAS
Filmfan. 9, 1940
. Ill’rl’l
1111111; ".
Patented May 19, 1942 '
` 2,283,832
rnEaMrcoA'raLrrrc aaaorroNs
Charles L. 'l‘liomaav Chicago, lll., assignor` to Uni
versal 'Oil Products Company, Chicago, lll., a v corporation of Delaware .
' application' Febreary 9. 1_940, serial No. :5,113,098
The invention particularly relates to an im
proved method and means of controlling the
place for `a substantial body or pool of liquid in
which,- according to conventional practice, said
temperature ofsimultaneously conducted endo'
thermic and exothermicl reactions. whereby heat
tubes or other elements are immersed or bathed. ‘_
Preferably, in accordance' with the provisions ’
>of the present invention, any of the liquid heat
liberated in the exothermic step is advantageous'
ly supplied to the endothermic step through the
' transfer' medium which remains -unvaporized in
ñowing> over the surface'of the catalyst contain
>er in which the exothermic reaction is taking
p1ace,»as well as the condensate which._forn_is on
medium of vliquid which is vaporized by'indirect
heat exchange with-the materials in .the exo
thermic relation zone »and condensed _by indirect
heat exchange with' the materials in the endo
thermic reaction zone.
the surface ofthe catalyst 'container in which
ro ’the
endothermic reaction is'taking place, i‘lows
. The usual method of controlling temperatures
from the lower portion of the reactor to> a small
in l simultaneously conducted endothermic and
" accumulating drum or the like wherefrom it is'
- pumped back to the reactor and sprayed or oth
exothermic reactions, wherein a vaporizing and
condensing fluid is employed‘as the „heat trans-~ :l54 erwise distributed overïthe surface of the catalyst
fer medium, is to employ separate interconnected '
reactors of-the heat exchanger type each’contain- '
'container in which Jthe exothermic reaction is
>taking place.` Thus, when-the operation is dis
continued for anyv reason and the circulatingl
ing tubular- elements or'the `like'wherein the de
lpump is stopped, the liquid drains to the accu
sired conversion reaction takes place, the tubular
elements wherein the exothermic reaction is tak, 20, mulator, leaving the reactor substantially dry.
This is particularly- advantageous when a heat
ing piace being .disposed in a body of liquid which
is vaporized by the heat evolved. the vapors thus-- - transfer fiuidwhich solidifies at normal tempera
ture is employed, since, by the elimination of a
generated being conducted to the other reactor
body of such'material in the reactor,- its solidifi
wherein they are condensed by contact with the
tubular elements wherein the endothermic re
action is taking place and the condensed liquid
being returned therefrom to the -body of liquid
cation therein and the attendant diillculties are. ,
' obviated.
Thus, the -reactor may be Areadily
_opened for inspection, repair or the like, after
the operationisdiscontinued andthe> apparatus
in the >first reactor,
is cooled, and in order to melt the heat trans
-,The present invention obviates the use of sep
arate reactors inv this type of system'by dispos-y 30 fer material in preparation for starting the op
ing the tubes or other elements wherein the en
' _' eration, it is only necessary to supply ,-heat ex
dothermic and exothermic reactions occur within- ' ternally. or otherwise. ,to vthe relatively small.
a common shell` or housing comprising a single re- ' . mass of such material in the accumulator..
The invention is adapted to be advantageously
actor and spraying or washing the surface of the
utilized for controlling temperatures in awide '
zone in which the exothermic reaction is taking.`
' variety of catalytically promoted orcatalytically
place with the heat transfer liquid which is there
by vaporized and condenses on the surface ofthe .' retarded reactions and although, _as previously
explained, it is particularly advantageous >as ap
zone in which the endotherniic reaction is taking
plied to simultaneously conducted endothermic
place. This also obviates maintaining a substan
tial body or a pool of liquid about the zone where' 40 `and exothermic reactions of the class in which
the zones ofxendothermic and exothermiereac
lin the exothermic reaction occurs and is par
tion are periodically shifted, it is not limited to
ticularly advantageous in operations wherein the
catalytic reactions so long as- the operation in,
i -zones of endothermic and exothermic reactions
volves the transfer of heat from a zone wherein
are periodically shifted from one set of tubes to
another, since the shift may be accomplished 45 it is liberated' to one in which it is absorbed
without'transferring a substantial body or pool i through the medium of a vaporlzing and condens
ing vfluid employed in the- manner herein pro
-of liquid from one reactor. to another.
~Another advantage results from the fact that,
The most common example of an operation of
with the improved 'apparatus and mode of opera->
tion herein provided, the quantity of heat trans 50 the general type in’which the zones' of endo
thermic and exot-hermic reaction are periodical-fer fluid required for an installation of any given
capacity is materiallytreducedI by virtue of the t ly shifted, is one in which the activity of a mass
of catalytic material employed to promote or re,
` substitution of a sheet orillm of4 evaporating
tard one` of the reactions decreases with such
liquid on the surface of the tubes or other ele
ments wherein the exothermic reaction . takes 55 rapidity and to such an 'extent that frequent
' 2
and in which the improved process of the inven
periodic reviviñcation for reactivation of the
catalyst is required. This occurs in such endo
thermic processes as the catalytic cracking and
tion may be conducted. The shell of the re
actor is illustrated in cross-section and other
portions of the apparatus are shown in elevation.
catalytic dehydrogenation of hydrocarbons,
wherein heavy carbonaceous conversion products 5
Referring to the drawing, the outer shell I
deposit on and foul the surface of the catalyst
particles, reactivation of the catalyst being an
exothermic reaction and involving burning of the
of the reactor. in the particular case here illus
trated, is cylindrical in form and is provided with
an upper head 2 and a lower head1. ’I'he in
carbonaceous materials from the catalyst'in a
terior of the shell is divided into compartments,
stream of hot oxidizing gas. The catalytic Í 10 A-and A', B and B',’C, D and D' by means of
polymerization of hydrocarbons and catalytic
the horizontal partitions l and 5, the lower sub
stantially cone-shaped partition 6 and the ver
hydrogenation are examples of other exothermic'
reactions which may comprise the exothermic
tical partitions 'I- and 8. An inlet nozzle 9 in the
step of a process embodying the features provided VUpper head 2 communicates with compartment
by the invention and in such instances the en 15 A and compartments A and D communicate
dothermic step may comprise, forA example, pre
through the tubular elements I0 extending there
heating of the reactants forl the exothermic step, '
between, an outlet nozzle II in the lower
the generation of steam, the heating or vaporiza
head 3 - communicating with compartment D.
On the opposite side of a vertical planepassing
tion of oil or any other fluid for any desired pur
pose or it may comprise a pyrolytic or catalytic 20 through partitions] and 8, an inlet nozzle S'in
conversion reaction such as thermal or catalytic
the upper head communicates with compartment
cracking, dehydrogenation, isomerization, cy
-A' and the latter communicates with compart
clization or the like or a combination of such op
' ment D' through the tubular elements I0’ ex
erations. These examples are typical of conver
sion operations encountered in modern hydro
carbon oil renning. The invention will find fur
ther application in many other chemical indus
tending therebetween, an outlet nozzle II' com
municating with compartment D' being provided
in the lower head 3.
tries andgits broad features are in no way limited
to the s'peciilc reactions involved.
Any heat transfer medium may be employedl
which will substantially vaporize at 'a tempera
ture within the range of that desired for the ex
othermic reaction and 'which will be substantial
ly condensed at a temperature within the range
suitable for conducting the endothermic reaction.
Atmospheric or substantially atmospheric pres
Compartments B and B’ each communicate
with compartment: C through a plurality of suit
able orifices or spray nozzles, such` as indicated,
for example, at I2, which are provided in parti
tion 5 about each of the tubular elements I0 and
I Il'. The purpose of these openings l2 is to spray
liquid from zone B over the surface of tubes Il
l or the liquid from ‘zone B' over the surface of
tubes III'. whichever tubes comprise thezone in
which the exothermic reaction is taking place, as
sure may be employed in the zone wherein vap
will be later explained.
orization and condensation of the heat transfer
medium employed occurs, or, when required, the
Vapors generated on> the surface of the zone
in which the exothermic reaction is »taking place
' boilingpoint of the heat transfer «medium em
are totally or partially condensed on the surface
, ployed may _be modified by the use of . sub-at
of the zone in which the endothermic reaction is ,
mospheric-or superatmospheric pressure in this
zone. The specific heat transfer medium em
taking piace. Thus, an emclent transfer of heat4
from the exothennlc to the endothermic reaction
ployed in any given case may be selected to ful
' ñll the above requirements and may range from
relatively low-boiling liquids or readily condensi
’ 1s obtained.
. Condensate formed on the surface of the zone
in which the _endothermic reaction is taking
place islremoved from the lower portion of the
water, alcohol and the like through the many
reactor through line I3, together with any quan
heavier liquids such as hydrocarbon oils, aliphatic
tity of vapors generally in excess of those re
~ and aromatic ethers and glycols to and includ vto quired to supply the desired heat to the endo#
ing normally solid materials such as molten salts
thermic reaction.- When only liquid condensate
and mixtures thereof (eutectic or otherwise) low`
is thus removed from the lower portion of the
' melting point metals and alloys. Wherever pos
reactor, it may be supplied from line _I3 4through
sible, the‘heat> transfer medium selected should>
line I4, valve I 5 and line I9 to accumulator 2li or>
be non-corrosive and otherwise chemically inert 55 it may be passed, all or inl part, from line I3
to metals which are not injured by and exert
through valve IB, cooler I 1, line I 8 and valve I9
‘ ble normally gaseous materials such as propane,
no detrimental effect on the endothermic and ex
to theaccumulator. In case vapors are with-H
othermic reactions involved but, when no heat
drawn with the liquid from the reactonthe mix
transfer medium which fulfills all of these re
ture is preferably passed, as' above described,
quirements is available,- the shell and tubular 60 through cooler I1 to the accumulator.
elements or catalyst containers of the reactors
' The function of coolerl I‘I is to 4condense any ‘
may be constructed of a metal or an alloy which
.vaporous components of» the convective medium
- is not adversely effected by a heat transfer medi
_ removed from the reactor and to reduce the
um which possesses the required physical char
temperature of the convective medium, when
acteristics, while the tubes or other elements of 65 this is required. It may be of any suitable con
the reactor, which form the zones wherein'thc
ventional form and, in the particular case here
endothermic and exothermic reactions occur,
illustrated, comprises a heat exchanger to which '
may be coated or lined `with another suitable
suitable cooling fluid is directed through line
metal, alloy or other protective coating which
`2I, passes through the cooler in indirect heat
does not; adversely affect and is not adversely 70 exchange relation with the >convective medium
affected by the _reactants and the catalyst,`in case
and is removedtherefrom through line 22. Thus.
a catalyst is employed.
only liquid is collected in the accumulator and'
The accompanying drawing diagrammatically
is preferably kept at such a temperature that
illustrates one specific form of apparatus em
' it may be returned therefrom to the reactor and
bodying the features provided by the invention 75 sprayed over the surface of the ‘tubularelements
. -
2,983,832 `
in which the exothermic reaction is taking fplace l
at a temperature close to its vaporization' point,
line 2i, although this is not illustrated in the
allowing for radiation losses’ froml the„circulating equipment, This temperature adjustment
may be accomplished'by the operation of cooler
-Theftubes Il andthe tubes Il' comprise sep- '
arate zones in which contact- material such'as a
`catalyst for promoting the de's'ziredv reaction may
bev disposed and in which the'desired‘fendother- ‘
' I1 and valve l5 in by-p'assq-line Hf or by adjust
` ment of the amount and/or temperature of 'cool
ing fluid passed through cooler I1. `
, j mic reaction and’exothermic reviviilcation of the
catalyst may be alternately conducted. Any suit
able means of conventional form maybeïem
' Liquid from accumulator 20> is directed through
line 23 to pump 24 wherefrom itis fed through, 10 ployed for switching the ilow of the stream "of
line 25 and’it may ordinarily be _directedwthere
reactants and reactivating gasesl with respect to
from, all or in part, through line `28> and Avalve
21 back to zone B or to zone'lB’y without addi
tional heating or cooling. However, in case ad
ditional heating of the recirculated convective
partially spent revivifying gases from zones D
zones A and A’ and the separate tube banks and ,
for diverting the outgoing reaction products and «
and D', each to the desired subsequent equip
liquid is required to obtain a closer approach to
The specific form of such> means -'em
ployed do not Jconstitute part of the invention
its vaporization point lnzones y13 and B', with
out allowing any appreciable quantity of va
pors to collect in the accumulator, all or a- regu
Vand since several suitable forms are nowïwell
known in the industry they lare not'illustrated
lated portion of the convective `liquid-'is _recir 20
culated to zones B and B' through heater 2l
by manipulatingl valve 21 in line 2t, valve 29
in the’drawlng.
_It will be apparent from the _above that -the
invention takes advantage'of the latent heat of
vaporlzation and the latentfheat of` condensa- tion. of a circulating heat- transfer fluid for con- "
in line 25 and'valve 23 in line'32. "From the
.junction oflines 32 and 28,jthe reheated or u_n
reheated liquid from‘accumulator 20 is direct 25 trolling `the temperature of simultaneously con
ducted endothermic and exothermic reactionsiand
~ed through line 34 and valve 35 to zo'n'e'B orl
through line 3l' and A35' to zone> B' and -~from
zone B -or zone B', as lthe case- may. be, itis l
again caused to pass' 4over the surface of the
vtubular elements in which the exothermic reac 30
'tionis taking place.
that, with the apparatus provided, this may be
accomplished with a relatively small quantity '
of heat transfer-'fluid and ¿without maintaining
a substantial bo'dy or pool of vaporizing heat
transfer liquid about the zone in which the ex
- Heater 28 maybe of any suitable conventional ' 'othermic reaction is taking place, thereby accom
form and, in the particular _case here illustrated, - 1 plishing the improvements mentioned prior. to
comprises a heating coil 30 disposed in a s_uit
the description' of` the'drawing. -Furthermore,
to 'generate hot combustion gases4 inv-the -i'ur- 'A
exothermic reaction are periodically ‘shifted and
able furnace 3I to which a regulated quantity 35.' the process adapts‘itself-to operations of the
.of fuel and air are, supplied throughburner 3l ' type in whichv the zones ’of .endothermic and-
all of the desirable features'of-the‘processfmay
beA accomplished in an apparatus oi'rrelativellfv
nace and supply the desired quantity of_- heat
therefrom to the convective fluid passing through
coil 30.
Instead of ,serving as a tempering‘zone where
simple form. ~ .`
.It _wm be understood, of course, that the se#
in any required small additional quantity of heat - >
companying 4drawing illustrates only one of the
may besupplied to the convective liquid recircu- ' .many specific forms of apparatus in which the »
improved process provided bythe invention may
' heater28 may, in accordance with another mode .45 be conducted and should, therefore, not be con
strued as a limitation. For example, insteadv of
of operation of 'the process, serve as a zone
wherein a regulated quantityoi the recycled l comprising tubes, the zone- in which the endo
' thermic and exothermic reactions occur'may'be
convective liquid may beA revaporized >at sub
_stantially the temperature prevailing'in space y formed between spaced metallic 'sheets 'or plates
C of the reactor and supplied to the latter zonel 50i of any desired contour and any other well known
to augment, to any ldesired degree, the quantity> ' means of spraying or otherwise distributing the
lated from the accumulator to zones B and B', -
the surface of the zone in which the exothermic' .
heat transfer liquid over >the surface upon which
it is vaporized by heat evolved in the exothermic
reaction is Ataking place. 'When this -mode of
reaction may be- employed within the scope of the '
through valve 29 inline 25 to> and'through heat
down-flow may becemployed within .the "zones
. of vapors evolvedfrom the convective liquid on '
’operation is employed, regulated quantities of; 55 -invention in place of the specific means illus-I
the liquid from- accumulator 20 are directed Y trated in the,y drawing. Also, -either up-flow or
wherein _the endothermic- and exothermic reac
tions occur and the direction of flow isnot neces
'which they are thence directed through line 22,
line 31. and valve 38 into space C of the reactor. ' ' sarily-the‘, same in both zones. For example, an
ing' coil 30 wherein they are vaporized andl from>
“wherein they commingle with thevap'ors evolved
endothermic reaction such as dehydrogenation, _
' from> the convective fluid inthis zone and, by v
catalytic cracking or the likemay be»accom-
- condensation on the surface of the tubes in which
plished by passing a stream of heated hydrocar-` `
bons upwardly through the zone of le'ndotherrriic
they endothermic reaction lis takingplace, sup
ply to the latter any-heat required for conduct 65 reaction in contact with a bed of catalytic mate-l
ing-'the endothermic reaction in excess of that ~ -rial disposed therein, countercurrent to the di'
.' evolved in the exothermic reaction.' ' »'
-In caseA heater 28 is utilizedv inthe manner
last described and it is also necessary to supply
some additionalheat to the convective liquid
recirculated from Athe accumulator to zones B
and B', a. separate heater of any conventional _
form suitable for supplying the required addi
rectlon of flow of the tllmor sheet of condensed
- e» heat transfer fluid flowing downward »over the
outer surface of the walls of this zone, while the
catalytic material in the zonefof exothermic re
action is being reactivated by passing a stream
of hot oxygen-containing gases downwardly
through this zone in contact with the catalyst,
concurrent to the film or sheet of vaporizing
tional heatv to the convective liquid recirculated
to the zones B and B' ‘is preferably provided in 75 heat transfer ñuid flowing downwardly over the
' 2,288,832
mercury, we lind that only about 196 pounds per
exterior surface of the walls ofv this zone,` or,
hour of mercury vapor need be condensed on
the surface' of the tubes in which the cracking
when desired, this procedure may be exactly re
versed or concurrent or countercurrentñow, with
reaction is taking place to satisfy the heat re
quirements `(i. e., 25g000 divided by 127.5 `equals
respect to the‘illms `or sheets of heat transfer
fluid ilowing downwardly over the surface of the
196+). „ Therefore, no liquid/mercuryis allowed
walls of theexothermic and endothermic 4reac
`tion zones may be employed in both zones.
to accumulate in the` reactor` and approximately
31 pounds per hour of mercury vapor is passed
applied to the apparatus illustrated in the draw
with the liquid mercury from the reactor through
ing, this means that nozzles Il and Il' may be
employed as inlet rather than outlet connections, 10. the _condenser tothe accumulator,- the mixture
of mercury vapor and liquid being cooled in the
while` nozzles Á9 and 9' are employed as outlet
condenser to such a temperature that, allowing
rather than inlet connections or their usel as
for radiation losses in the recirculating lines, the
inlet and outlet connections may be alternated.
resulting liquid mercury is returned to the reactor
As an example of one speciiic operation of the>
at a temperature of about 980° F. '
process provided by the invention as applied ‘tov
The figure above given for the pounds of mer
`the catalytic cracking of Ahydrocarbon oil (the( l
cury circulated through" the system per 100
endothermic reaction) with .periodic vreactivation
Vpounds of oil treated per hour is not to be taken
of the catalyst (the exothermic reaction)„as it
as indicative of the quantity of mercury required
may be conducted in an apparatus of the char
acterillustrated, we will assume that the catalyst 20 within the system, since the rate of circulation
preferably is relatively high so that the total
employed comprises preformed granules-or rela
mercury required within the system 4may be, for
tively small pellets 'of substantially uniform size
example, only ’fio to- lí[email protected] or less of the iigure
and shape consisting essentially of alumina, silica
above given (i. e., approximately 2 to 20 pounds l.
and zirconia in the proportion of approximately
100 mols of ,SiOz to 2 mols of A120: to 5 mols of~ 25 per 100 pounds of oil cracked per hour).
We will also assume that the oil to be
I claim as my invention:
cracked is `substantially completely vaporized and
heatedto a temperature of approximately 950°
.F. -prior to its contact with the active cracking
catalyst and that, in addition to theheat thus
supplied to the oil, an additional ¿250 B. t..u.’s per
pound is required to effect the desired cracking
reaction in contact with the catalyst. `We will
1. The method of , controlling the temperature
of endothermic and exothermic reactions simul
taneously` conducted in separate reactionv zones
¿having heat-conductive walls, comprising the
steps of `contacting a heat transfer medium in
the form of a flowing film- or sheet of liquid at
a` temperature‘closely approaching its vaporiza
further assume that approximately 2% by weight A tion point with the heat-conductive walls of said
,of the oil is converted to heavy carbonaceous ma- 35 -exothermic reaction zone to substantially vapor
terial which is deposited on the catalyst and’that
ize said iluid and absorb therein the latent heat
of.vaporization, causing resulting evolved vapors
approximately 290 B. t. u.’s per pound of oil
cracked are evolved during reactivation of the'
- catalyst, reactivation being accomplished by pass
ing a stream of heated oxygen-containing gases
to -contact the heat-conductive’ walls of the en
dothermic reaction zone and substantially con
40 dense thereon to liberate the latent heat of con
densation, collecting liquid thus' condensed from
the vaporized heat transfer medium and return
in contact with the catalyst bed upon which said
carbonaceous material has been deposited during
the preceding crackingphase of the operating
ingthe same in regulated quantities as said iilm
Thus, theheat generated in the _exo
or` sheet of liquid into contact with said walls
thermic step exceeds the heat required in the 4 GI of the exothermic reaction zone.
endothermic step by 40B. t. u.’s per pound of oil
2. The method defined in claim 1, wherein the
N cycle.
>heat content of said vapors is controllably in
creased prior totheir contact with said walls of
In this particular instance, mercury is utilized
as the convective medium for controlling the
the endothermic Vreaction zone.
temperature Yof the reactions.v It is desired to 50
3. The method deñned- in claim 1, wherein the
conduct the cracking reaction at a` temperature
heat content of said ‘vapors is controllably in
creased‘prior to their contact with said walls
of approximately 950° F. and reactivationof the
of the endothermic` reaction zone by commingling
catalyst is so conducted that the average tem
perature in the catalyst bed during reactivationV _a regulated additional quantity of hot vapors of
- is approximately 1050° F.- The mercury is sup
. plied to the zone of the reactor from which it is
A said heat transfer medium therewith.
4. The method defined 1n claim 1, wherein a
regulated quantity of said evolved vapors are pre
sprayed over the surface‘of the tubular elements
in which the exothermic reaction is taking place
vented from contacting and condensing on said
at a temperature of approximately 980° F. and a
walls of the endothermic reaction zone.
superatmospheric pressure of approximately 2501`
5. The method deiinedv in claim ,1, wherein a
regulated quantity of` said evolved vapors are
.prevented from contacting and condensing on
`pounds per square inch is employed `in the
mercury vaporizing and condensing space of the
reactor. At this pressure, the mercury vaporizes
ata temperature of approximately 1000cl F. yThe
circulating pump is operated at such a rate that
approximately 227 pounds per hour of mercury
are circulated through the system per 100 pounds
A»of oil cracked per hour. This figure is derived
by dividing the heat evolved during regenera
tion, per 100 pounds of oil cracked,` by the heat
o! vaporization of mercury which is approxi
mately 127.5 B. t. u.’s per pound (i. e., 29,000
divided by 127.5V equals 227+). However, when
we divide ,the B. t. u.’s required to crack ,100’
said walls of the endothermic reaction zone, said
lregulatedquantity of vapors being separately
condensed and the resultingeondensate returned
with the other liquid components of said heat
v.transfer medium into contact with said walls of » ,
the exothermic reaction zone.
6. The method defined in claim 1, wherein the
temperature of said heat transfer medium is
readjustedLot the desired value prior to each
successive contact. thereof with said walls of the
_l exothermic reaction zone.
7. An apparatus 'of the class described com
pounds of oil by the heat of condensation of 75 prising an endothermic reaction zone and an exo
- 2,283,832
`thermic reaction zone, both having heat-con
ductive walls, means for contacting the walls‘of
said exothermic zone with a ñowing ñlm of a
heat transfer liquid at a temperature closely ap
proaching its vaporization point, means for con`
tacting vapors of said liquid with the walls of
said endothermic zone, means for _collecting con
densate condensed on the last-named walls, and
means for returning regulated quantities of said
condensate into contact with the walls of the exo
thermlc zone.
8. The apparatus as defined in claim 7 further
characterized in the provision of means for in
creasing the heat content of said vapors prior
to their contact with the walls of the endother
mic zone.
9. An apparatus of theclass described com
prising an endothermic reaction zone and an
exothermic reaction zone, both having heat-con
ductive walls, means for contacting the walls of
said exothermic zone with a ñowing ñlm of a
heat transfer liquid at a temperature closely ap
proaching its vaporization point, whereby vapors
' are evolved from said liquid, said endothermic
and exothermic reaction zones being enclosed in a
common vessel whereby vapors evolved from said
10 liquid contact with and condense on >the walls
of the endothermic zone, an accumulator exterior
of said vessel and means for supplying thereto
condensate formed on the last-named walls, and
means for returning liquid from the accumulator
15 to said vessel and into contact with the walls of
the exothermic zone.
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