US1823922A - Process for converting hydrocarbons - Google Patents

Description

Sept. 22, 1931. c. w. WATSON PROCESS FOR CONVERTING HYDROCARBONS Filed June 26, 1928 044km. QSXUSQD Patented Sept. 22, 1.931

PATENT oFFlc. f

CLAUDEW. WATSON, or PORT ARTHUR, TEXAS, AssIeNon To THE TEXAS F yNEW YORK, N. Y., A CORPORATION 0F DELAWARE y `23.0(211185 FOB COIhTVERflINGr HYDROGARBONS v Application led June 26,

The present invention relates to cracking processes wherein reflux condensate formed in the `course of fractionation of the devell oped vapors is returned to the cracking zone for retreatment, and contemplates the removal from the reflux condensate certain of its lower boiling components before it is returned to the cracking zone.

The invention has in view particularly u dephlegmating or fractionating vapors from a cracking still to form an overhead vaporous roduct, which is condensed to fo'rm a gasoine or other light distillate, and a` plurality of reflux condensates, the heavier condensates being returned to thersame cracking zone for retreatment. l

In a preferred embodiment of the invention the evolved vapors from a cracking still may be subjected to fractionation to form a 2o final vapor fraction which is condensed to yield gasoline or other light distillate desired, a heavy'reflux condensate substantially free from light components which is returned to the cracking zone, -and alight intermediate 26 component or reflux condensate which is removed from the system.

My process, therefo're,has` particular reference to that part of lcracking systems commonly known as fractionators, separators,

:o dephlegmators or bubble towers which will hereinafter be called fractionators. I It is into these parts of the apparatus that the vaporous roducts of the cracking reaction are led, and) wherein they are separated or fractionated, the lighter from theheavier components. A n i In the practice of my processl preferably employ two fractionators, although it is to be understood that'` more than two fractionators may be employed" if desired, for the present invention contemplates'removing certain components fromA the system whose presence tends to retard or interfere with the conversion process. The,vaporous products from the cracking zone entering the first fractionator are partially condensed therein and precipitating to theb'ottom of said irst fractionator are subject tez-withdrawal there- A from, preferably for recycling throu h .the system, while the lighter uncondense com,-

1928. Serial No. 288,410.

ponents pass off overhead in vaporous form preferebly to the second fractionator forv fur ther fractionation therein. The heavier components of the vaporous products conducted overhead from the first fractionator are condensed in the second fractionator and precipitating to the bottom thereof are subjected to withdrawal preferably for discharge from the system while the lighter comp onents in vaporous form pass off overhead to suitable condensing means and then to storage.

.l have in mind producing refined hydrocarbons'on a commercialscale and in the present invention contemplate the practice of an important improvement in the previously known methods of converting the higher boiling hydrocarbons into lower boiling ones. Generally speaking the art of cracking' is now well known to the petroleum industry. It is also known that, according to` the method of treatment, a varying amount of decomposition and rearrangement of the Y hydrocarbon molecules of the oil under treatment may take place, when converting higher boiling hydrocarbons into lower boil- -ing ones. This is especially noticeable when practicing a process or method whereincertain components of the products of conversion, formed during the period of decomposiao tion and rearrangement are recirculated or recycled through the system for treatment.

-For example if a crude petroleum from the well be fractionally-distilled atsubstan-` tially atmospheric pressure the'components. evolved maybe gas, gasoline, kerosene, gas oil, lubricating stock and fuel oil stock.. The crude or virgin gasoil thus derived may have an'initial boiling point of say 450" ,F.and may form an excellent charging stock for cracking stills wherein it may be subjected to cracking conditions including Va pressure of say 300 ounds per square inc and a ternperature o about 825 F.

As the gas oil undergoes cracking it may be subjected to continuous withdrawal from the cracking zone while other gas oil may be conducted to the cracking zone at the rateY thetreatedl oil is withdrawn.. Thus the oil undergoingtreatment is being renewed con- 100 tinuously and at a constant rate whereby the time of treatment or conversion is xed.

With the decomposition or breaking down of the relatively high boiling oil thus undergoing treatment there is set up a rearrangement of the atoms and a completely different product or products are formed. This newly formed product, from the standpoint of physical characteristics, may be said to resemble in a lgeneral way crude petroleum in that it maybe fractionally distilled much as the crude oil previously mentioned. The v fractional products of thesaid'newly formed products may be classified as gas, gasoline, a product of rather wide distillation range resembling gas oil and a heavy residue suitable for fuel oil stock.

In the continuous conversion of a relatively high boiling gas oil charging stock 2. into lower boiling products a certain fraction is formed which, as has been explained, may resemble the virgin gas oil charging stock. It has also been explained that the said fraction has a rather wide distillation range. Previous to my invention this entire fraction of evolved gas oil, in a cracking operation, has ordinarily been withdrawn in condensed form from a fractionator in the system and has been recycled through the cracking zone for retreatment.

When this fraction or evolved gas oil is processed underl similar converting conditions but separately and in comparison with the original'virgin .gas oil from which the fraction was evolved, ithas been found that the yield of gasoline from the evolved gas oil is relatively less than the yield of gasoline from the virgin gasoil. However when the evolved gas oil is itself separated into two fractions and the two fractions thereof, the lighter and the heavier, are similarly processed, that is using the same pressures and temperatures, in comparison with each other and in comparison with said virgin gas oil, it has been found that the heavier fraction shows much better gasoline yields than the lighter fraction and etter gasoline yields than the total evolved gas oil comprising both ofY said fractions,

i though a still slightly poorer gasoline yield than the original virgin gas oil charge.

It has thus been found in many cases thatl a considerable percentage of thevirgin' charge is converted into a lighter gas oil fraction that is relatively difficult to crack,

and the recycling of said lighter fraction' v together with the heavier fraction amounts to 1the continuous recycling of a product which at best maybe only slightly affected by the vcracking'conditions employed which are sev lected as most effective to the bulk of the prod`- f uct undergoin treatment.r While I do not attempt to exp ain what causes this differencev it is well recognized that lighter components such as light gas oil and kerosene having rela- 1,sas,922 y tively low critical temperatures are extremely diitcult to crack.

Experiments in processing have established that the heavier fraction of the evolved gas oil lrespondsrelatively well to theY cracking conditions best suited for the conversion of. the virgin as oil into lower boiling products; therefore the evolved heavy gas oil forms a good recycle stock from astandpoint of yields, while onv the other hand the evolved light gas oil or fraction of the converted product responds slowly to the converting conditions whichmay be found to be most productive in the conversion of the virgin gas oil. In other words it is necessary to recycle the evolvedyheated gas oil through the cracking zone a number of times to accom plish any appreciable amount of conversionA due to its content of lighter fractions. This is expensive and unprotitable, therefore it would be better to remove the evolved light gas oil from the system continuously as evolved.

In the regular operation of apparatus wherein higher boiling hydrocarbons are being converted into lower boiling ones, the evolved product, which I have previously described as a newly formed product, it being a product of cracking and resembling in a vague way a crude petroleum, is subjected to the rst step in the separation or fractionation of its components in the cracking zone, wherein the residual unvaporized fraction settles to the bottom of the stills and is regularly withdrawn therefrom.

An overhead vapor which may have a temperature of approximately 790 F. and comprising the remaining components ofv the product of cracking; namely,' the gas, gasoine and evolved gas oil, are delivered into a -fractionator wherein these components Iare subjected to further separation or fractionation, the evolved gas oil being condensed and precipitated to the bottom ofthe fractionator while-the gas and a gasoline distillate of approximately 400 F. end point are takenl off overhead in vapor form.

As hasalready been pointed out, prior to my invention it has been the re lar practice to remove all of the intermediate fractions lll -namely those boiling above the gasoline range from the fractionating "zone in condensed f0rm this condensate being the total evolved gas oil component formed, and to recycle said fractions through the systemwith the fresh charge of virgin gas oil.'

' According to the present irvention, as reviously stated, I preferably employ two ractionators and among other objects eectingy in the first fractionator a close fractional 18B tion ofthe vaporous roducts of conversion issuing from the crac 'ng or reaction zone, whereb only the heaviest fraction-or the evolve heavy gas oil component of the vaporous product will be condensed and collected in the bottom of the first fractionator. An overhead vapor composed of the evolved light gas oil, the gasoline and the gas components, will then be passed to a second fractionator for further separation by condensing thereinl the evolved light'gas oil and withdrawing overhead in-vapor form the evolved p gasoline and gas components.

For example, I have previously disclosed,

that a fresh stock or gas oil having an initial boiling point of say 450o F. may be converted.

Then in the practice of my invention it would be preferable to condense in thelirst fractionating zone all fractions of the vaporous products of conversion from the cracking zone having an initial boiling point of^ approximately 450 F. and make them available therein for recycling for further conversion.

It would accordingly be preferable to remove overhead in vaporous form all of the evolved lighter fractions or components having an end point of approximately 450 F. Where superatmospheric pressure is employed in the conversion it might be found advantageous to somewhat reduce the pressure within the first fractionator. The lighter components having an end oint of approximately 450 F., leaving the rst fractionator in vaporous form would preferably be delivered into a second fractionator. All of thegas and v gasoline components, namely those having an be folind desirable to maintain a still further reduced pressure from that maintained in the first fractionator.

These objects of my invention as well as others may be betterunderstood from the following description and the accompanying drawing which illustrates in diagrammatic elevation the preferred embodiment of an apparatus adapted for carrying out my process as described herein, although it will be understood that any form of suitable apparatus may be employed for practicing the process.

` Referrin to the drawing:

Fresh oito undergo treatment is forced into the system preferably under'several atmospheres of pressure and entering through the pipe 1 may pass through the closed coil 2 in heat exchange with the warm vaporous products in the top of fractionator 97 whereby the fresh oil is slightly preheated. It is then conducted through the heat insulated pipe 3 and is passed through the closed coilV 4 in heat exchange with the wariner vaporous products in the top of the fractionator 90 whereby the said preheated oil is further heated.

The preheated oil passing through the heatl insulated pipe 5 then enters the preheater coil 10, and is highly heated in transit therel through.

Upon emerging from the preheater coil the highly heated oil may be returned immediately tothe heating zone for still further heating entering the heating coil 16 through a bypass pipe 11, the valve 12 therein being open and the valves 13 and 14 being closed. Preferably, however, the valve 12 1s closed and valves-13 and 14 are open so that the oil leaving the coil 10 is conducted through the heat insulated pipe 15and passed through the closed coil in contact with a body of oil maintained in the bottom of thefractionatorf90 imparting a part of its heat to the said body of oil.

The oil, now somewhat reduced in temperature,`emerging through the heat insulated pipe 21 from the coil 20 may be returned to the heating zone, a bypass line 22 being provided for this purpose with a valve 23 which will then be open while valves 24 and 25 will be closed. Preferably, however, the

`oil leaving coil 20 is conducted through the closed coil in contact with a body of oil maintained in the bottom of the fractionator 97, imparting a part of its heat to the said body of oil. When operating in this way the valve 23 will be, closed and valves 24 and 25 open.

The oil, somewhat further reduced in temperature but still quite hot, is returned through the heat insulated pipe to the heating coil 16 and the temperature of the oil is rapidly raised to the cracking point` in transit therethrough. It is then passed through the heat insulated pipe 17 and is delivered to the stills 50 and 51 through the pipe connections 40 and 41. I may wish to extend the pipe 41-in future operation to effect a hot oil entry in to the stills 52 and 53 also.

A series connection near the top between stills 50, 51, 52 and 53 is effected by means of the- pipes 54, 55, 56, 57, 58V and 59.- The said connections permit the free liow of fluids, both liquids and vapors, from the stills and 51` to 52 and 53.

within tht-,stills 5o, 51, 52 and 5s as the de'- i composition of the oil dergoing conversion progresses and the rearrangement of the molecules takes lace, all that vhea component hereinbe ore described as residueor fuel oil settles out and, maybe withdrawn by means of the pipe 78 connecting with the stills by means of branch pipes and'valves 70, 71, 72, 73, 74,75, 76 and 77.

A vapor line 60 is provided for conducting all vaporous components of the converte product from the cracking zone. It is to be uurl remembered that the evolvedvaporous coinponents have been hereinbefore described as an 'evolved heavy gas oil, an evolved light gas oil, evolved gasoline and gas.

The vaporous components entering the fractionator 90 through the pipe 60, preferably under super-atmospheric pressure, may

be subjected -to a reduction of pressure before 'entering the fractionator 90 and accordingly the pressure regulating valve 61 is provided in the vapor line 60. It is preferable, however, to provide a fractionator suitable to withstand the maximum operating pressure of the system for I'contemplate practicing my invention, at different times, depending upon various factors, either by reducing the pressure in the fractionators or by maintaining a lsubstantially equal pressure in the systhe top of the fractionator.

Where in the practice ofmy invention the coil 20 is provided submerged in the body of condensate in the bottom of fractionator 90 and where the highly heated oilfromtheheating coil 10 is passed therethrough the lighter vapors which might have been condensed and precipitated or otherwise mechanically held in solution are kept boiled off, and in consequence there may be regularly withdrawn, by means of the pipe 91 controlled by the valve 92, a heavy gas oil, such for example as one having an initial boiling point of approximately 450 F. `Preferably said evolved heavy gas oil is recycled to the system by forcing it into the heatingcoil 16 at a suitable intermediate point by means of the hot oil pump 93. v

The coil 4 provided in the top of the frac- `tioator 90 by virtue of the relatively cool fresh oil'charge passing therethrough in regulated flow imparts a regular amount of cooling to the warmer vapors in the top of the fractionator 90 whereby all the components falling 'within certain boiling limits may be condensed or knocked back, for example all components such as may boil above approxivmately :450 F.

At the same time there may be withdrawn overhead in vaporous form from the fractionator 90 all of the lighter components which may boil oi at a predetermined end point such for example as all those boiling o below approximately 450 F.

- It is to be understood that the top of the fractonator 90, in the practice of my invention, is balanced with the bottom. In other words while withdrawing overhead said ap- 05 proximately 450 F. end-point components there may be withdrawn from the bottom of the fractionator a recycle gas oil relatively free of both the heavy residue or fuel oil, and

those lighter components which are intended to be passed overhead including all of thev components from the lightest'gases to the components somewhat heavier than gasoline but lighter than the original charging stock and also lighter than the recycle gas oil.

As hereinbefore disclosed it has been found Toward this end it is quite desirable t0 determine before a run when changing to a new type of charging Istock,.tl1e best operating condition with reference to temperature, pressure, and time and to predetermine the characteristics of the recycle gas oil which may be advantageously evolved.'` Considerable advantage may be realized'in regularly making small scale "test runs of the various.

stocks for this purpose.

The vapors from the fractionator arel conducted through the vapor line into the fractionator 97, entering the latter at about the midpoint. Herein the entering vapors are subected to al fractionatinga action simiiar to thatin the fractionator` 90, in that the heavier components of the vapor` are cndensed and precipitated toward the botto of said fractionator, forming a body of con ensate therein. It may be desired, when deviating from operating the entire system at balanced pressure, to'reduce the pressure in the fractionator '97 below that existent in the fractionator 90, and for this purpose a pressure regulating va1ve`96 may be placed in the vapor line 95. y

A s I have previously disclosed herein the evolved light gas oil component of the total evolved product from the cracking or converting treatment may not be suited for recvcling for further treatmentinder the conditions foundA most favorable for the charging stock used. Sometimes the amount of the light gas oil of this nature which is evolved may be relatively small and again it may be relatively large.

Depending primarily upon the nature of the gasollne component evolved which may be approximately 400 F.; and second by the fact that the end point of the light gas oil is predetermined and remains constant, it being substantially of the order of the predetermined initial boiling point of the heavy evolved gas oil, such for example as approximately 450 F. Since the evolved light gas oil is generally not adapted to crack readily at the calculated operating conditions maintained for the original charge, it is preferable to remove it entirely from the system for its presence in any amount tends to hamper the speed and economy of cracking. Itis to be understood however that it must not be regarded as a waste product since it vmay form a very desirable charging stock for a different method of treatment or may be cracked sep` arately under more favorable conditions, such as under higher temperatures and pressuresv or in 'a vapor phase cracking process.

To aid in effecting close fractionation in the fractionator 97 'there is provided the previously mentioned coil 30 submerged in the body of condensate collecting in the bottom of the fractionator, and by regulatively passing the hotter oil from coil 20 through the coil 30 such gasoline components as may. have been improperly condensed or dissolved are kept boiled off. This serves to produce at the bottom of this fractionator a light gas oil fraction which for example may have an initial boiling point of approximately 400 F. `and an end point of approximately 450 F. Preferably this will be regularly withdrawn xfrom the system by means of a pipe 99 and valve 98.

The lighter vapors passing upwardly in the fractionator 97, encounter progressively lower temperaturesv and are subjected to a cooling in the top of the said fractionator by virtue of the coil 2, through which the oold oil charge is passed in entering the system. The light gas oil components, such for examle as those boiling above a proximately 400 are condensed or knoc ed back and the lighter components, namely gasoline and gas, which may have an end point of approximately 400 F., are withdrawn in vapor form. l

The emerging vapors from the fractionator 97 are conducted through a pipe 100 and ut through a condensing coil 101. Emero- 1ng from the condenser 101 the cooled products are passed through a pipe 102, provided with a pressure regulating valve 103, interposed between the condenser and a collectin tank 104.

rom the collecting tank 104 the gasoline` struction have been set forth it should be understood that many variations may be effected without departing materially from the s irit and scope of the invention as de-Y fined y the appended claim. l

What I claim is:

An oil conversion process which comprises heating a high boiling oil in a coil to a conversion tem erature and permitting cracking to produce vapors of lower boiling oils, passing the vapors to a fractionator to effect separation between a high boiling condensate having substantially the same characteristics as said high boiling oil and a vapoi` of lower boiling constituents, returning the condensate to said coil, passing saidvapor to Va second fractionator to eiect further separation, eliminating fromthe system the condensate so formed, passin partially heated oil withdrawn from said eating coll in heat exchange with'the condensate in the bottoms of said ractionators to re-boil said condensates, returning said heated oil to the coil for further heating, and condensing .the vapors leaving said second fractionator to form a desired final distillate.

In witness whereof I have hereunto set my hand this 18th day of June, 1928. CLAUDE 'W. WATSON.

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