US1782056A - Art of cracking hydrocarbons - Google Patents

Description

Nov. 18, 1930. J. E. BELLE-r AL 1,782,055

ART oF GRACKING HYDROCARBONS Filed Nov. l2, 1924 3 Sheets-Sheet 1 INVENTOR 5 Jo f BE//a/:dfa/Ward iff/i002 BY l A4/aw ATTORNEYS Nov. 1s, 1930.

l.l.'l:. BELL ET AL 1,782,056

ART OF CRACKING HYDROCARBONS IPE/70x TUWER TAR 4- 'l INVENTORS gulli, Quan/M MM 'ATTORNEY 3 Sheets-Sheet 3 Nov. 18, 1930. J. E. BELL l-:T AL

ART 0F QRACKING HYDRocARBoNs Filed Nov. 12, 1924 Patented Nov. 18, 1930 UNI-TED s'rA'ras `PATENT OFFICE JOHN E 1sE1.LOr` nnOOxLYN, AND EDWARD W. rsou, OE LOCUs'r VALLEY, NEW YORK, yAssiofNoas To sINCLAIn'nErININe COMPANY, or CHICAGO, ILLINOIs, A CORPORA- TION OF IAINE ART or CnA'cxING HYDBOCARBONS ppliotion filed November 12, 1924. Serial No. 749,402.

This invention relates to improvements in cracking heavier hydrocarbon oils, such as gas oil, for the production of lighter hydrocarbon oils, such as gasoline or pressure distillate, bydistillation under pressure. This application is in part a continuation of our copending application Serial No. 437,662,-

iled January 17, 1921, which has issued as PatentpNo. 1,547 ,993.

In' cracking hydrocarbonl oils by distillation under pressure, the Oil is heated to a cracking temperature under pressure and the heavier oil, or a portion thereof, is broken down or cracked with the formation of lighter oils which are vapori'zed and driven off. The cracking operation takes place gradually and progressively, part of the cracked constituents escapin as pressure distillate and part of the heavier cracked constituents remaining and mixing with the charge of oil in the pressure still. A small amount of asphaltic, or pitch-like vconstituents, or heavy tar is also formed by the cracking operation. This tar remains in the charge and gradually accumulates due to the vaporization of cracked constituents and to the progressive formation of tar constituents. This tar accumulatingin the oil in the still tends to deposit on the eating surfaces of the still and 1n contact therewith tends to form a carbonaceous deposit thereon closely adhering thereto. Such carbonaceous materials ,and the heavy tar accumulating in the still charge are poor conductors Aof heat and when deposited on the heating surfaces of the vstill which `are externally exposed to heating gases interfere wlth heat transfer and insulate the wall from the' protection afforded -by the Oil so that the walls of the still are apt to become Overheated the temperature of the metal of the heat transferring wall increasing over that of the oil to an extent dependent upon the thickness of the deposit and the amount of heat externally delivered to the Wall from the heating gases.' As a conseuence the pressure still must frequently be s iut down for cleaning or the temperature of the heating gases must be reduced below that which is most efficient. There is also considerable danger involved due to possible bursting of the heat transferring walls at overheated points. The heating surfaces over which heatin gases are first circulated are exposed to the ighest temperature of the heating gases and absorb the greatest amount of heat, and vthese surfaces are most apt to suffer. Heating surfaces immediately adjacent the furnace em loyedv to heat the pressure still may also a sorb large amount of heat by direct radiation from the furnace.

'According to the present invention, the vaors from the cracking operation vare sub- ]ected to a reiuxing operation indirect contact with fresh oil and the reflux and admixed fresh oil are employed to\protect the heating surfaces of the pressure still while at the same time the reflux and admixed fresh oil are subjectedy to advantageous cracking conditions. All of the refiuxed constituents have been vaporized from the charge of oil in the still and are substantially free from tar constituents, and the fresh oil and admixed refiuxed constituents; when admixed with the still charge, or a part thereof, assist vin reducing the concentration of tar constituents and in maintaining the concentration ofl tar constituents below saturation therein. A According to the present invention, the relflux and admixed -fresh oil are first brought .intoheat exchanging relation with the heatmg gases at their ighest tem erature before they are passed over other eating surfaces of the pressure still, and, as the light cracked constituents are va orized and the Oil loses its content of crac able hydrocarbons and as the concentration of tar constituents increases, the oil isbrought into heat exchan 'ng relation with heatinof gases which ave been tempered and re uced in temperature by heat exchange with the reflux and. admixed fresh oil by passing the Oil of increased tar content over more remote'heating surfaces of the pressure still. The heatingv gases while at highest temperature are thus passed over heatin surfaces which are in contact with oil relatively free of tar constituents, or in which the concentration of tar is least, and as the tar concentration increases the oil is passed over heating surfaces in contact with progressively tempered and cooler heating gases. The lighter crack-r able constituents of the reflu'xand admixed fresh oil are also subjected to advantageous cracking condition by heat exchangewith the hottest heating. gases. The heating surfaces of the pressure still most apt'to suffer are thus protected by absorption of the heat transferred therethrough in heating and cracking the oil constituentsof the reflux and admixed fresh oil and this heat available at high temperature is advantageously employed in a useful crackin operation rather than in the further crac ing of tar constituents while a. reduced concentration of tar constituents is maintained in theI oil in contact with these [initial heating surfaces preventin or materially reducing the formation o carbonaceous deposits thereon. The heat available in the heating gases, the temperature of which has been lowered by the heat absorbed in heating and cracking the reflux and admixed fresh oil, is then further employed to advantage in cracking the oil as tar constituents accumulate therein.

In carrying out the invention, the heating surfacesf the pressure still may be further protected and theV heating of the pressure still charge equalized by providing `progressively increased areas of heat transfer between the oil and the heating gases as the tar content of the oil increases and as the temperature of the heatingl gases decreases. The heating eil'ect is thus equalized by increasing the area of heat transfer as the temperature of the heating gases decreases while an increased area of heating surface is provided in contact with the oil containing an increased tar content where deposition is most likely to occur. Additional fresh oil may also be passed overA the initial heating surfaces together with the reiux and admixed fresh oil returned from the refluxing operation. The tar content of the pressure still charge may also be controlled and reduced by withdrawing tar from one or more portions of the still charge where the tar tends to accumulate.

The present invention is of s cial value and-application in connection with cracking operations in which directed circulation of the still charge is maintained over the heating surfaces of the pressure still. Circulation may be maintained by convective action, or by mechanical forcing means such as a pum or pumps, or by the introductionof suita le gases. Circulation further assists'in preventing or materially reducing the forma'- tion of carbonaceous deposits on the heating surfaces and assists in carr 'ng tar constituents with the circulating oily.l Circulation of the oil over the heatin motes the heat transfer om the heating surface to the oil and further rotects the heating surface in this way. irected circulawhich the re surfaces also protion may be maintained either in the initial heating stagesor in the later heating stagesor in both. l Th'e process of the invention may also with advantage be carried out in a series of stages or cycles, with circulation of the oil in each stage or cycle froma body of the oil in heat exchanging relation with the heating gases and back tothe body, and transferring oil to successive stages as its tar content increases, circulating heating gases in heat exchanging relation with the oil in the stages or cycles successively in the order of increasing tar content, and returning reflux and admixed fresh oil from. the refluxing operation to which the vapors from the cracking operation are subjected to the stage or cycle in which the oil is subjected to heat exchange with the heating gases of highest temperature.

In one aspect, the process of the present invention ma be considered a process in ffiix and admixed fresh oil are first subjected to a more or less. intense cracking treatment and then, as tar and carbon accumulate in the oil, to a digestion treatment in which the cracking temperature'is maintained by employing the heating gases from the initial cracking treatment.

While the invention is of particular advantage where the same stream of heating gases 1s employed for heating t-he oil in the successive stages of the process as the temperature of the heating gases is progressively reduced, certain advantages of the invention may be obtained by em loying heating gases of separately regulate temperature in the successi-.ve stages, employing hotter heating gases for initially heatin and cracking the reflux and admixed fres oil and progressively cooler heating gases for heating thel oil of progressively increasing tar content in the successive stages.

The process of the invention may be carried out in different types of apparatus. The reflux and admixed fresh oil may be returned through a tubular heater arranged to be heated by the heating gases as they first leave the furnace and arranged to discharge the oil into a shell or drum, or digestion chamber, for further treatment of the tar containing oil. The shell or digestion' chamber may be arranged to be heated directly by the heatinggases which have assed over the heater through which the re ux and admixed fresh oil is circulated, or the oil in the shell or di- I' gestion chamber may be'heated b `bein circulated from and back to the she l or igestion chamber throu h a .tubular heater arranged for heat eisrcange with the heating gases from the first heater. The successive heaters may also all be tubular in character or a divided pressure still may be arranged to maintainpa series of bodiesof the oil in a. series of compartments with a separate heater ,connected to each compartment with means form of apparatus adapted for carrying out the process of the invention.` The apparatus illustrated is described and claimed inan application filed Jan'. 17, '1921, Serial Number 437 ,662 andthe process of, the present invention is of special value and application in connection with'pressure stills of this general character. The pr'ocess of the invention may,-

however, be carried out in other and different apparatus. v

In the accompanying drawings:

Fig. y1 represents a pressure still, in elevation and section with parts broken away,

`adapted for carrying out the process of the invention,

Fig. 2 is a section on line 2-2 of Fig. 1 wiih a condenser diagrammatically shown, an

. Fig. 3 is a fragmentary section on line 3-3 of Fig. 1.

The pressure stillillustratedcomprises a drum 4 and a series of tubular heating elements communicating therewith arranged `in the heating Hue of a furnace 5. .The heating Hue comprises a series of connected vertical Hues 6, 7, 8. and 9, the Hue 6 also.con. necting with the furnace 5 and the Hue 9 4with a stack Hue 10. The Huesare arranged so that the heating gases from the furnace are passed successively therethrough tothe stack. A draft tube 11 is arranged for withdrawing waste heating gases from a point adjacent the exitl of the heating Hue 9 and returning them to the Hue 6 fortempering the heating gases fresh from the furnace 5 in the Hue 6. The draft 'tube may be .operated by a steam jet or other suitable forcing means. By re turningwaste heating gases inthis way, the heating gases are tempered in thez first heating Hue, the volume and rate of circulation of the heating gases through the heating Hues is increased,-and the available heat in the recycled gases may be further utilized. By- passes 12 and 13 provided with regulating dampers 14 and 15 are provided for further controlling the distribution of heat in the several Hues.

The still drum 4 is provided internally with a seriesof partitions 16, -17 and 18 dividing the drum into a series .of compartments A, B, C and D and a corresponding series of heating elements separately communicating with each of these compartments arel arranged in the heating Hues. The heating elementconnected to compartment A is arranged in Hue 6, that is the Hue through diottest heating gases.

which the heating gases are Hrst passed, the heating element of the next compartment B in the next Hue 7, and so on, the heating element connectedto the last compartment D being arranged in -the plast heating Hue 9 through which vthe coolest heating gases are circulated. The partitions in thedrum do not completely shut olf the compartments from each other but extend a. short distance above the normal liquid level therein leaving a common vapor space iii-the upper part of the drum. OverHow pipes 19, 20 and 21 are arranged for progressively .transferring oil to successive compartments in the series, and these pipes-are provided with bell caps to prevent transfer of surface scum and froth to successive compartments.

' Each of the heating elements connected to the respective compartments comprises these" v similar groups of heating tubes.v Eachy of' these groups comprises an outHow header 22,.

a series of upwardly inclined .tubes y23 arranged through the heating Hue for heat exchange with the -heating ases therein, connecting headers 24, anotier series of." up wardly inclined tubes25 arranged through the heating Hue,and an inHow header v26. I n order to facilitate cleaning and repair-the headers are arranged outside of the heating Hues and are formed-with'plugged hand holes in alignment with the heating tubes. In order to equalize 'the heating effect inthe several heaters and to provide .an increased area of heat transfer as the tar content of thev oil increases, as will presently appear in more detail,vthe heat transferring vareapf the several heaters is progressively increased as the temperature of the heating gases declines.- -In the apparatus illustrated, the heater connected to the first compartment A lon to compartment V4B eight tubes, that 'connected to vcompartment C twelve tubes and that connected to the last compartment D sixteen tubes.` l

Arranged above the drum 4 .is a rcHux tower 27 adapted to receive vapors from the vapor space of the drum 4 and to discharge ref-lux and admixed oil into the first compartment A connected to the heating element arranged in heat exchanging relation with theA A connection 28 is provided for introducing fresh oil into the upper part of the reflux tower over the baHles.

therein and vin direct contact with the vapors therein. A connection 29 discharging into the iirst compartment A is providedfor the introduction of supplementary or additional fresh oil. The vapors escape from the-re- Hux tower through vaporl line 30 to a condenser -diagrammatically illustrated at 31.

The pressure inthestill may be reduced and controlled by a/regulating valve 32 arrangedV between the reflux tower and the condenser or bya-valve 33 arranged beyondthe condenser. In order to provide for drainage, and for Withdrawal of tar during the cracking operation the lower ends of the inflow headers in each heating element are connected to a manifold 34 having a valved outlet 35,

the outlet from the last compartment D being designated 35. 'u

The reflux tower and the still drum may, with advantage, be covered or protected with suitable heat insulation, such as an asbestos or mineral wool jacket.

In carrying out the process of the invention in the apparatus illustrated, the` still is initially charged with oil, through connection 29 the oil successively overflowing into the adjacent compartments as the preceding compartments are filled, and brought to the cracking temperature and pressure in the usual way. The pressure employed may differ with different charging stocks and for theproduction of different pressure distillates. With gas oil character charging stocks for the production of gasoline character distillates, pressures in the neighborhood of 90 to 1,25 pounds per square inch-or more may be employed. In cracking a kerosene character charging stock to produce a gasoline character distillate, considerably higher pressures maybe used, for example, pressures up to 300 pounds per square inch or more may be employed.

After the still charge is broughtto the cracking temperature and pressure, the cracked vapors rise from the several compartments and pass upwardly through the reflux tower27, and the introduction of fresh oil through connection 28 is be n. In the reflux tower the fresh oil is intimately contacted with the vapors from the still, refluxing the heavier vapors and preheating the fresh oil, and the reflux and admixed fresh oil are returned to compartment A. As the reflux and admixed fresh oil are introduced into compartment A, oil from thisfirst compartment which has been deprived of a part of its Vcrackable constituents and contains some tarconstituents overflows into the second compartment B where it is further cracked and a further part of its components are,

vaporized. In the same Way oil'is trans#l ferred from compartment B to compartment C and from compartment C to compartment D asthe cracked constituents are vaporized and as the tar accumulates, the oil in the successive compartments containing less and less of the original oil constituents and more and more heavy tarry constituents. t

Tar may also be withdrawn from one or more of the successive compartments," and.

with particular advantage from the last compartment D through connection 35. The introduction of fresh oil into the reflux tower is controlled to regulate the refluxing operation. Where no tar, or only a relatively small amount of tar is Withdrawn, the

amount of fresh oil introduced intothe reflux tower may correspond approximately to the amount of distillate taken off or may be somewhat in excess of this amount. Where larger amounts of tar are withdrawn, the still charge is maintained by the introduction of an increased amount of fresh oil, and

that in the second compartment B to a somewhat lower temperature, and so on. The heat absorbed by the oil in the first compartment A is employed to crack the oil constituents of the reflux and admixed fresh oil and this oil is circulated over the heating surfaces protecting them against the highest temperature of the heating gases, and as the tar content of the oil increases it is transferred to successive compartments where it is Subjected to heat exchange with heating gases of progressively lower temperature. At the same time the heating effect in the successive compartments is equalized by the progressively increased area of heat transfer provided, and the difliculties and dangers incident to the formation of carbonaceous deposits are materially reduced due both to the decreased temperature of the heating gases and the increased area of heat transfer and consequent reduction in the rate of heat transfer per unit of area. In all of the heating elements the absorption of heat bythe circulating oil protects the heating surfaces, particularly in the first where the heating element is exposed to the hottest heating gases and where the circulating oil contains the reflux and admixed fresh oil and the least content of tar. i

y It will thus be seen that .the present in` 'vention provides an improved method of cracking hydrocarbon oils by distillation under pressure in externally heated pressure stills in which fresh oil is supplied to the cracking operation and in which the, fresh oil 'is first employed to promote and control a refluxing operation to which the vapors from the pressuregstill are subjected and then, in admixture with the reflux, to-protect the heating surfaces of the pressure still subjected to heat `exchange with the hottest .heating gases while the lighter-crackable heating pors from said .conv

tillate,

the'heatin gases or otherwiser- Another portant a vantage of the invention is that 1t enablesan improved applicationbfithe,

gases to the crackingloperation sothat both the eiiciency and t e capacity of the pressure still may be increased.l

Weclaim: L'An improved method of cracking hydrocarbonfoils, which comprises heating' the oil to a cracking temperature under pressure lin a series o stages.- and circulating the oil to successive stages Vas the tar content of the oil increases, circulating heating gases in heat exchanging vrelation successively with the oilin vthe stages in the order in which the oil ,is-circulated there-v through, maintaining progressively 'increas-v ing areas of heat-transfer betweenfthe heating gases and the oil in the successive stages in the same order,`. 'subjecting the vapors from the cracking operation` to a refluxing j t=fwith1j fresh oil,

operation in -direct contac and returning the reiiux a oil to the 4irst stagelin d inxed fresh #new mcentration is least.'

2. /A process for-crac khydrocarbons comprising passing the oil thronghf'a heating coil wherein it is raisedftoja ccnversionitemperature, l discharging "th enlarged conversion cham phlegmation-and co unvaporized oil from-Sal zone than thatin .whichiis'aidf heating coil;

version temperature, in discharging the heated oil into anV enlarged conversion `chanu` ber, in passing the vapors issuing roxnsaid- .'converslon chamber to a dephlegmatonrin Vreturning refiux condensate from. the de-v phlegmator to said heating coil, inl condensmater `and ina-collecting .the resulting disin circulating the unvaporized oil from said conversion chamber through an independent heating element wherein it is subjected to a lower tempjraturethan the oil Ein said coil and bac tc 4the conversion chamber', Y and in .maintainingfa superatmosphe'ric pressure on the oil undergoing conversion.

4. A process for cranking hydrocarbons comprising passing the oil through a heating A coil wherein it is raised to a conversion temperature, discharging the heated voil into an enlarged conversion chamber, taking off vars from said conversion chamber and reuxing the vapors in heat exchanging relation with resh oil', circulating unvaporized oil from said conversion chamber through ducing fresh oil to the deph cracking hydrocarbon oil,

that inw ch said heating coil 1s positioned and 'back to the conversion chamber, and supplying the fresh oil from the refluxing zone totheheatingcoil.- A

5. A process of cracking h drocarbon oil consisting in passin the oil t rough aheatlng coil wherein it 1s subjected to a conversion temperature, in discharging the heated oil into an enlarged conversion chamber, in passin the vapors issuinl fromsaid conversionl c amber to a dep egmator, in introcontact with'thevapors therein, 1n returning ref iux condensate and admixed fresh oil from the dephlegmator to said heating coil, in condensing the vapors issuln from the dephlegmator and in collecting t e resulting distillate, in circulating the unvaporized oil from said conversion chamber throu h an indeendentl heating element wheremit is' suh-l jected to `a lower temperature than the oil' 1n said coil and back to the conversion chamber, and in maintalning a superatmospheric- "pressure onthe oil undergoing conversion.

6'. A n improved methodof cracking hydro` carbon oils, which comprises ycirculatin the oil in each of a series of cycles from a ed of Vtheoil in heat -exchanging relation wit heating gases' and back tothe' body, transf erringi the oil to successive-c cles as vthe ta content of the oil increases, eating the oil to a cracking temperature under pressure by ber through a cooler portion of the heating -circulating'heating gases in heat exchanging l .relation successively with the oilin the cycles is positioned and back to. said 1conversion inthe order of increasing tar content, maintaining progressively increasing areas of heat transfer between the heating gases and the oil in the successive cycles in the same order, subjecting the vapors from the cracking operation to a reiuxing operation, and returning the reflux to the first cycle in which the tar concentration is least. Y

:` 7. A process of cracking hydrocarbon oil, consisting in passing the oil through a-heating coil wherein it is subjected to a converfsion i temperature, in discharging the heated voil anto an enlarged converslon chamber, in `passing the vapors issuing from said conversion chamber to a de phlegmator, in returning reflux condensate from the dephle ator to said heatingcoil, in condensing t e vapors issuing from the dephle mator` and in jcollecting 4the resulting disti late, in circulating the unvapxorized o1l from said conversion chamber t rough an independent heating element wherein v1t is subjected to a lower temperature than'the oil in said coil and back to the conversion chamber, in preventingthe return of unvaporized oil which has passed through said independent heating element to said heating coil, and in maintainmg'a superatmospheric pressuregon the oil undergoing conversion.

8. A process of cracking hydrocarbon oil,

egmator in direct consisting in passing the oil through a heating coil wherein it is subjected to a conversion temperature, in discharging the heated' oil into an enlarged conversion chamber, in passing the vapors issuing from said conversion chamber to a dephlegmator, in returning refiux condensate from the dephlegmator together with additional fresh oil to said heating coil, in condensing the vapors issuing from the dephlegmator and in co1- lecting the resulting distillate, in circulating the unvaporized oil from said conversion chamber through an independent heating element wherein 1t is subjected to a lower telnperature than the oil in said coil and back to the conversion chamber, in preventing the return of unvaporized oil which has passed through said independent heating element to said heating coil, and in maintaining a superatmospheric pressure on the oil undergoing conversion.

In testimony whereof we ax our signatures.

JOHN E. BELL. EDWARD W. ISOM.

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