US1776985A - Process of decomposing relatively high-boiling point oils into relatively low-boiling point oils - Google Patents

Description

S14/vanto@ A. L. STROUT PROCESS OF DECOMPOSING RELATIVELY HIGH BOILING POIN OILS INTO RELATIVELY LOW BOILING POINT OILS Filed April 25, 1927 'Sept'. 30, 1930.

I Halloran and Archle Patented Sept. 30, 1930.

UNITED STATES PATENT OFFICE i L. STROUT, OF BERKELEY, CALIFORNIA, ASSIGI'NOR TO STANDARD OIL COM- PANY OF CALIFORNIA, OF SAN FRANCISCO, CALIFORNIA, A CORPORATION OF DELA- PROCE'SS 0F DECOMPOSING RELATIVELY IGH-BOILING- POINTOILS INTO RELATIVELY LOW-BOILING POINT OILS Application led April 25,

l This invention relates to the art of decomposing orcracking oils, such as petroleum oils, and has to do more particularly with a cracking process commonly known as the vaporization type wherein the charging stock, after passage through the heating zone in which the oil is raised to the desired cracking temperature, is passed into an enlarged reaction chamber where vaporizationtakes place for the separation of the lower' boiling point constituents from those of higher boiling point.

Heretofore, in the practice of the vaporization method of cracking oils as above outlined, there has been evolved from the vaporization chamber not only those constituents comprising the desired low boiling point or gasolinelike products,` but in addition thereto, so much of the heavier or higher boiling point ingredients that there is left in the vaporization chamber either only coke or a yheavy liquid residuum of low A. I. I. gravit usually at about 9 A. P. I. gravity or suc as to make it of suit-able fuel oil viscosity. When the process is thus practiced the total vaporized material from thevaporization chamber is passed to a dephlegmating tower in which the heavier vapors are condensed from the gasoline-like or desired low boiling point ingredients, and such heavy constituents therefrom recycled as va reflux from the tower back .through the heating coils and into the vaporization chamber.

In the co-pending a plicationlof Ralph A. Strout, filed October 6, 1927, Serial No. 176,990, process of decomposing relatively high boiling point oils into relatively low boiling point oils, there is described a ltype of cracking process of the vaporization type in which, in order to secure a substantial reduction in the uantity of coke formed in the rocess and a su stantial reduction in the se iment content of the 11qu1d residuum produced in the process as well as other advantages, the liquid in the vaporization Vso chamber is maintained at an A. P. I. gravity several degrees higher than thegravity. of the residuum to be formed inthe system and in fact but slightly less in A. P. I. gravity than that of the feed oil charged to the system. In order to obtain a high'yield of gasoline-like 1927. Serial No. 186,307.

are contained within'this liquid thus with-` drawn from the vaporization chamber, and which are useful for further cracking, be distilled therefrom and recycled through the process. It is the practice of said co-pending application thus to separate and use such lower boiling point constituents from this liquid withdrawn from the vaporization chamber.

In order to distinguish between the two stages of distillation which take place in la system of this type it will be understood that throughout this specification the vaporization chamber refers to the chamber into which the oil is discharged from the heating zone of the system and wherein the produced low boiling point or gasoline-like constituents are evolved as vapors. Of necessity there' will be evolved along with said vapors the vapors of certain heavier constituents, thus making it necessary to fractionate these vapors so that the gasoline-like constituents, may be separated from the heavier constituents. The term dephlegmator as used herein will be restricted to refer only to the fractionating equi ment wherein this separation takes place. he term reflux will be restricted to the condensate obtained in said dephle ator and returned to the heating zone. he material obtained by the condensation of vapors evolved during the distillation of the liquid withdrawn from the aforesaid vaporization chamber will be referred t o as cycle stock .and the va ors condensed to give said cycle stock will e termed cycle stock vapors. (It will be noted that .both the said cycle stock and the said reliux Atermed `residuum as distinguished from the bottoms withdrawn from the aforesaid vaporization chamber which latter material will be design ated as heavy liquid from the vaporization chamber.

In order to completely condense the cycle stock vapors, it is enerally necessary that they be cooled to a out 150 to 250 F. In order to provide lan economical operation so A' loo of the cracking process in the use of heat, which economy will be reflected in fuel saving, it is necessary to conserve the heat of vaporization of the cycle stock vapors and to utilize this heat for the purpose of preheating the fresh feed oil to the cracking process.

Heretofore, in attempts to preheat feed oil o f a cracking s stem, the common practice has been to uti ize as far as practical heat exchangers so constructed that the liquid feed oil to be heated passes through closed passages in contact with the opposite walls of which is the medium to be cooled. Heat exchangers for this purpose are expensive to build and maintain. Furthermore, the temperature to which the fresh oil may be preheated is often limited by the economical conditions existing at the unit, and asa result comparatively few heat exchangers are successfully employed to effect economy in connection with cracking apparatus.

An object of thegpresent invention is to provide a method or process for recovering the useful heat in a vaporized oil which is to be condensed and recycled to a cracking process, and a particular object of the present invention is to provide a method by which the recovery of the heat of the cycle stock vapors may be accomplished by transfer of heat to the fresh feed stock to be processed. Another object of the present invention is to provide a method for efficiently recovering the heat of the cycle stock vapors, which will eliminate the difficulties experienced with the usual heat exchangers, which method employs direct contact between the vapors of the oil to be recycled and the fresh oil.

Another object of the present invention is to provide a method for condensing and recovering th'e heat of the cycle stock vapors by which the greater part of both the cycle stock and the fresh feed oil may be brought to a comparatively high temperature before being fed into the heating zone of the system, while at the same time the recovery of said heat leaves available a quantity of'comparatively cold oil for use in the dephlegmating tower of the system.

Another object of the invention is to provide a method for condensing and recovering the heat of the cycle stock vapors by which either the entire quantity or suitable portions of both cycle stock and fresh feed oil may be commingled and brought tofa comparatively high temperature and at the same time' be suitable for use subsequent thereto in obtaining the desired reflux in the dephlegmating tower of the system.

In order to maintain economical operation it is necessary not only that the heat of the cycle stock vapors be preserved, but it is also necessary to conserve the heat in the vapors from which the reflux material is formed in the dephlegmator. In order tolform the desired amount of reflux it is necessary that there be employed a cooling medium, the temperature of which may vary within certain limits depending upon the quantity ofmaterial so used. The present invention comprehends a process in which the heat of the cycle stock vapors may be recovered and-imparted to the feed oil while at the same time using the heated feed oil and the resulting cooled cycle stock material, or different portions thereof, to maintain a cooling medium in the dephlegmator sufficient to form the desired reflux. An embodiment of the invention therefore comprehends the splitting of the feed oil into a plurality of parts, contacting the cycle stock vapors progressively with said portions of the feed oil so that each' of such successive portions of the feed oil encounters the residual vapors of the preceding contacting step and admixing any or all of the resulting portions of commingled cycle stock and feed oil for application as a cooling medium to the'dephlegmator. By so applying all such resulting portions of commingled material the cooling medium to the dephlegmator willbe at a relatively high temperature but this is compensated for by the increased quantity of such material so that the desired amount of reflux may be obtained. 'Alternatively by admixing fewer of such portions of commingled material a smaller quantity of cooling medium but at a lower temperature may be made available for coolingpurposes required in the dephlegmator. In the preferred form of the invention the feed oil to the system is split usually into three portions thus providingI three stages for the cooling and condensation of the cycle stock vapors by a contacting and commingling operation. The residual vapors remaining after each such condensation operation are passed to the succeeding condensation or commingling operation and there contacted with a different portion of the feed oil.. lHence each portion of the fresh feed oil thus contacted with the vapors is heated to a different temperature, the last portion so contacted being at the coolest or lowest temperature. In each instance by admixing proper portions of the resulting intermingled liquid a cooling medium is obtained suitable in quantity and temperature to produce the required amount of reflux in the dephlegmator. The process may also comprehend that not all of the feed oil may be so employed for the cooling and condensation of the cycle stock vapors but that a portion of the fresh feed oil may, if desired, be diverted from such action and passed directly to the dephlegmator where it may serve as a cooling medium either of itself or in conjunction with portions of admixed feed oil and cycle stock material from the aforesaid' intermingling and condensation operation. It will be understood that the process is not limited tothe use of threeI stages of the intermingling and condensation operationy but that any desired .number of such operations may be employed. In some instances it may be desirable to employ only one such stage.

The present invention may be better understood and comprehended in its various aspects in connection with the description of a process comprising an embodiment of the linvention, by reference to the accompanying drawing which illustrate an apparatus in which` a process embodying the invention may be performed. For this purpose there is hereinafter described a process embodying the present invention ascarried out with the apparatus illustrated in the accompanying drawing.

In the drawing the apparatus is illustrated in diagrammatic elevation,

In the drawing, 1 represents a feed line through which fresh feed stock from storage or'other suitable source may enter the system from where it is finally passed by means of pump 2, and line 4, into heating coils 8 which are provided in al suitable furnace 9 where the oil receives its heat and is raised to the desired decomposing temperature. Any decomposing temperature may be employed, a particularly suitable temperature being from 850 to 890 F. when processing a gas oil fraction of a California base oil. The temperature may be modified, depending upon the character of oil processed as well as the quantity and quality of the products to be produced.V The oil is then passed through line 10 into a vaporization and reaction chamber ll. y i

The pressure employed within the vaporization chamber will depend on the oil treated and the amount of decomposition and vaporization of the heavy oils desired, but will generally range from 200:#- upwards, per

square 1nch. From the vaporization chamber 11 the vapors pass through vapor line 12 into a dephlegmating ltower 13 which may be one of several different and suitable types. In this dephlegmating -tower the desirable lighter or gasoline-like constituents will be. separated from the heavier constituents and will pass in vapor form through line 14 and` thence through suitable condensing apparatus such, for example, as condenser coil 16. The condensate thus formed then passes through line 17 into receiving drum 18 where any relatively fixed or incondensable gas is permitted to separate therefrom. This gas may be led olf through valve 19 and line 20 and conducted from the system. The condensed gasoline-like or low-boiling point constituents will pass through line 21 provided with valve 22 for further treatment or to suitable storage (not shown in the diagram).

The liquid oil withdrawn from evaporator 11 passes through pressure release valve 24 thence through line 25 and is discharged into vessel 26. The release of pressure through valve 24 is as a rule suiiicient to permit of the vaporization from the hot liquid residuum, immediately upon its discharge into vessel 26, of a substantial quantity of the volatile ingredients thereof. The vapors thus .evolved will comprise a quantity ofmaterial beyond the condensing equipment on line 47,l

the necessar valves being also provided on the liquid raw-off lines. By varying the pressure on vessel 26 the quantity of vapors evolved and the consequent grade of fuel oil residuum withdrawn from the system may be varied and controlled. The residuum thus formed is withdrawn through line 45 provided with valve 44. It will be understood that heat may be applied in any suitable manner to the material under oing vaporization in vessel 26 and that if esired open steam may also be employed therein to assist in the evolution of the cycle stock vapors and that vacuum may also be employed, if desired. Means for supplying heat to the vessel 26 or for supplying open steam or for maintaining the vessel 26 under vacuum are not shown in the drawin In the met od of the present invention these cycle stock vapors are passed through line 27 thence through a series of condensation vessels 28, 29 and 30 in which they are progressively contacted with different portions of the feed oil, thus effecting the condensation of successive portions of these vapors to give the necessary cycle stock for recycling to the heating coils 8 and reaction chamber 11. To this end the feed oil in line 1 is shown as preferably split into a plurality of portions which are passed to the separate condensation vessels 28, 29 and 30 throuvh lines 31, 32 and 33 respectively, controlled by valves 33, 34 and 35 respectively. The resulting portions of admixed feed oil and condensate thus formed in the condensation units 28,29 and 30 are passed through lines 36, 37 and 40 respectively, provided respectively with pumps 5, 6 and 38, whereby through suitable operation of the valves of a simple (manifold arrangement such as that shown in`the drawing, one or all o an intervening number of such portions o admixed feed oil and condensate may either be sent through line 41 and `employed as a cooling medium to obtain the desired reflux in the dephlegmator 13 or ma be sent through line 4 directly to the heating coils 8. For example, if it is esired to use in the 'dephlegmator 13 a relatively small quantity of such cooling medium but with the same at a relatively low temperature, only the admiX- ture from condensation vessel 30 may be sent through line 41 to the dephlegmator, the remaining portions being fed direct to the heating system. On the other hand by passing the admixture from all or a number of such condensation vessels through line 41 there is provided in the dephlegmator 13 a cooling medium of relatively higher temperature but one having a correspondingly larger volume so that the desired amount of reflux is again obtained. It is understood that while there is disclosed three different units of such condensation vessels for the cycle stock vapors any desired number may be so employed. In each instance the cooling medium obtained thereby for reflux purposes in the dephlegmator may range from a small quantity at a relatively low temperature to a materially larger quantity at a correspondingly higher temperature but with sufficient cooling power to provide adequate reflux. Valve 42a and line 42 are provided so that a portion of the fresh feed oil may be diverted from contacting with the cycle stock vapors and used expressly as a cooling medium in the dephlegmator 13 when it is desired to employ the minimum quantity of oil as a cooling medium at the lowest available temperature. While the operating conditions may vary widely in the process, as an example of the operation of the present invention, when operating the reaction chamber 11 at a pressure ranging from 250 to 600# per square inch and while withdrawing oil therefrom at approximatelv 850 F. and then reducing the pressure in the distillation chamber 26 to atmospheric; the vapors will pass off from the chamber 26 at a temperature of about 690 F. These vapors will comprise the equivalent in quantity of about of the feed oil charged to the system. When charging to the system feed oil at a temperature of about 70 F. and by passing approximately 20% of such feed oil into the condensation vessel 28, approximately 30% of the cycle stock vapors will be condensed and the resulting admixture of feed oil and condensate will have a temperature of approximately 550 F. By passing approximately 25% of the feed oil into the second condensation vessel 29 approximately 50% of the total cycle stock vapors arecondensed forming an admixture of oil at about 425 F. in temperature. By passing approximately 55% of the fresh feed into the last condensation vessel 30 the balance of the heavy vapors or about 20% of the total cycle stock vapors will be condensed forming a liquid at a temperature of about 170 F.

' The refiux together with the cooling oil charged into the dephlegmator 13 are passed therefrom through line 43 where they joined the balance of the stock passing through pump 2 and line 4 tothe heating coil 8.

, from the system Thereby, both the cycle stock material from chamber 26 and the reflux formed in the dephlegmator 13 are 'recycled through the apparatus for further treatment.

An important advantage in the present invention resides in that all of the heat of the vapors to be recycled in the process is conserved without the necessity of employing the expensive and inefficient closed coil type of heat exchangers for this purpose. Moreover, this is accomplished by separating all of the material to be used as cycle stock from the tarry or residuent matter withdrawnfrom the system and used as fuel oil residuum or otherwise disposed of. It will, therefore, be seen that while this heat is imparted to the feed oil so that the furnace 9 is relieved of a material burden, provision is made for the Vuse of this feed oil in any desired and convenient quantity but at a temperature not too high to give the required reflux. At the same time the heavy liquid oil withdrawn from the reaction chamber 11 is so distilled as to produce a heavy residuum in the chamber 26 which may be Withdrawn and used as a satisfactory liquid fuel oil. This fuel oil is found to be remarkably free from sediment.

It will be understood that there may be employed in this process in conjunction with distillation element 26 any equipment which will aid in obtaining the desired cycle stock vapors such as any conventional fractionating equipment, as more fully explained in the co-pending case of Halloran and Strout hereinbefore referred to. In another copending application filed by myself September 26, 1927, Serial No. 221,920, there is describedl a modification of the present invention by which the cycle stock vapors to be condensed are partially cooled before entering the contacting and heat conservation elements which comprise an embodiment of the present invention.

While the formof process herein described is well adapted for 'carrying out the objects of the present invention, it is understood that various modificationsand changes may be made without departing from the invencluding therewith the vapors of the produced relatively low boiling point oils passing said vapors to a dephlegmating zone, removing from said `vaporization chamber part of the oils as liquid having an A. P. I. gravity higher than the residuum ultimately to be leo formed bythevprocess, vaporizing from said withdrawn liquid its more volatile' constituents for the production of a. cycle stock material to be returned to the heating system, splitting the feed oil to the system into different portions and progressively contacting the cycle stock vapors with different portions of the feed oil wherebyin each succeeding contacting step feed oil encounters the residual vapors not condensed by the preceding step and whereby several mixtures of feed oil with condensates at different temperatures are obtained, and passing one of such er than the residuum ultimately to be formed -by the process, vaporizing from said withdrawnliqu-id and lat a pressure less thanthat maintained in said vaporization chamber its more volatile constituents' for the production of a cycle-stock material to be returned to the heating system, splitting the feed oil to the system into different portions and progressively contacting the cycle stock vapors'with' different portions of the feed oil whereby in each succeeding contacting step feed oil encounters the residual vapors not condensed by the preceding step and whereby several mixtures of feedoil with condensates at' different temperatures are obtained, and passing one of such mixtures of feed oil and condensate as a reiu'xing agent to said dephlgmating zone. v

densed by the preceding step and passing a .portion of the feed oil with its commingled` portion of cycle stock material as a refluxing agent to said dephlegmator, returning to the heating-zone the -balance of such feed oil and cyclev stock, together fwith unvaporized oil from said dephlegmator.

4. A process of decomposing oils into relatively low boiling point constituents which includes -heating the oils to a decomposing temperature, passing the cils into a vaporization chamber, removing from said vaporization chamber part of the oils as vapors including therewith the vapors of the produced relativelyflow boiling point oils, passing said vapors to aI dephlegmator, removing from said vaporization chamber part of the oils as liquid having an A. P. I. gravity higher than Vthe residuum ultimately rto be formedby the process, vaporizing from said. withdrawn liquid and at a pressure less than that maintained in said4 vaporization chamber its more volatile constituents for the production of a cycle stock material to be returned to the heating zone, splitting the feedoil to the system into different portions, progressively contacting the cycle .stock vapors with di'erent portions of the feed oil whereby in each successive contacting step feed oil encounters the residual vapors not condensed by thevpreceding step and passing a cooler portion of feed oil with its commingled portion of cycle stock material as a reluxinggent of said dephlegmator, returning to the heating zone a warmer portion of said feed oil and cycle stock, together with unvaporized oil from sald deghlegmator.

igned at San Francisco, California, this 9th day of April, 1927.

- v ARCI-IIE 'L STROUT.

v3. A process of decomposing oils intorelatively low boiling point constituents which includes heating the oils to Aa decomposing temperature, passing the oils into a vaporiza.- tion chamber, removing from said vapor1 zation chamber part of the' oils as vapors 1ncluding therewith the vapors ofthe produced relatively low boiling point oils, passingsaid vapors to a dephlegmator, removing from said vaporization c'hamber'part of the oils as liquid having an A. PII. gravity higher than the residuum ultimately to be formed by the process, vaporizing from said withdrawn liquid its more volatile constituents for the productionof a cycle stock material to be returned to the heating zone, splitting the feed oil to the system into different portions, progressively contacting the cycle stock vapors 'with different portions of the feed oil Whereby in each successive contacting step feed oil encounters the residual vapors not-con-

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