US1949656A - Art of cracking hydrocarbons - Google Patents

Description

March 6, 1934. H. L.. PELzl-:R

ART OF CRACKING HYDROCARBONS original'Filed June 13, 1927 INVENTOR Har/yf Z. Pe /zer' ATTORNEYS Patented Mar. 6, 1934 PATENT OFFICE ART F CRACKING HYDBOCARBONS Harry L. Pelzer,Y Houston, Tex.,

assignor to Sinclair Refining Company, New York, N. Y., a

corporation of Maine original application .inne 1s, 1927, serial No. 198,621. Divided and this application July 1s,

1933, Serial No. 680,905

1 Claim.Y

This invention relates to improvements in the cracking of heavier and higher boiling hydrocarbon oils for the production of lighter and lower boiling hydrocarbon oils. In particular, the in- 5 vention relates to improvements in such operations Where the heavier or higher boiling oil isv cracked While in the vapor phase and subjected to treatment with an absorbent material While in the vapor phase.

The invention is of special value and application in the production of gasoline or motor fuels having a relatively high critical compression or having anti-knock properties when burned in the usual type of internal-combustion gasoline engine. This application is a division of my application Serial No. 198,621,1iled June 13,1927.

Certain oils, such as kerosene and light' gas oil, are more refractory with reference to cracking than are other heavier or higher boiling cils,'sueh as heavier gas oil, and usually must be subjected to more intense or more severe cracking conditions for effective cracking than is necessary with such less refractory oils. The products of operations in which more intense or more severe cracking conditions are maintained include, if the conditions are appropriate, constituents of special value as components of motor fuels. Such more intense or more severe cracking conditions, however, tend to promote objectionable overcracking with excessive formation of gases incondensible at ordinary temperatures and pressures and excessive formation of carbon and tarry matter.

The products of a cracking operation are closely related to the temperature to which the oil is sub- ?.5 jected and to the time duringwhich the oil is subjected to the cracking temperature, both as to the amount of lighter or lower boiling constituents produced and as to the character of such constituents. In the production of a cracked oil for use as or in a motor fuel of relatively high critical compression, it is advantageous to subject the heavier or higher boiling oil to a high cracking temperature for a substantial period of time. With many of the more refractory stocks, such as mentioned above, the more advantageous range of cracking temperatures lies above the critical temperature of the stock so that the operation must be carried out substantially in the vapor phase. With heavier or higher boiling and less refractory stocks the more advantageous range of cracking temperatures may not exceed the critical temperature of the stock, but even in such cases the pressures necessary to maintainA any substantial part of the stock in liquid phase are usually extremely high.

The products obtained from vapor phase cracking operations generally contain a relatively large percentage of unstable unsaturated constituents and, with most stocks, undesirable sulphur compounds which are not desirable as components of motor fuels. The removal of such objectionable constituents by ordinary refining methods involves several difficulties. These diiiculties may bevlargely overcome by treating such cracked products with fullers earth or treated clay or l similar absorbent material While in the vapor phase, in accordance with the present invention.

In carrying out my present invention, the heavier or higher boiling oil is maintained in the vapor phase,substantially completely, throughout u' the cracking operation proper. Small amounts of tarry matter or carbonaceous matter may be formed during the cracking operation or very small amounts of very heavy constituents of the stock may be carried in the oil-vapor mixture u as a fog or mist, but the predominating proportion of the oil is in the vaporphase.

Several difficulties are involved in heating oil in the vapor phase to a high cracking temperature and more diiculties are involved in maintaining it at a high cracking temperature, among which may be mentioned difficulties involved in eilicient and effective heat transfer and in excessive formation of gases and carbon and tarry matter. This invention provides several improvements 06 which assist in eliminating or minimizing such diiiculties.

The invention also includes improvements in the complete operation and in the handling and treatment of the products of the cracking opera.- 00 tion proper and of the stocks supplied to the operation.

According to the present invention, a stream of the stock to be cracked is heated and vaporized, the vapors are then heated to a high cracking 9i temperature, and the hot vapors are then maintained at a cracking temperature for a substantial period of time. The stock may be heated and vaporized and the vapors then heated to a high cracking temperature in a continuous heating conduit or a series of conduits arranged in a single heating furnace, or the stock may be vaporized in one operation and the vapors from this operation heated to an appropriate cracking temperature in a separate operation. To promote eiiicient and effective heat transfer, the vapors advantageously may be heated to a high cracking temperature by heat exchange with heating gases at a substantially higher temperature. After being brought to an appropriate lio cracking temperature, the vapors advantageously may be maintained at a cracking temperature by heat exchange or by being maintained in heat exchanging relation with heating gases at 5 a temperature notl substantially higher than that of the vapors, to avoid or reduce excessive formation of gases and carbon and tarry matter.

Digestion of the vapors for a substantial period of time at a cracking temperature, in accordance With the invention, improves the yield oil constituents.

0 pors during the digesting operation may be somewhat higher or somewhat lower as an average than that at which the vapors are supplied to the digesting operation. Generally counter-current or generally concurrent ow relations may be maintained between the heating gases and oil vapors which are in heat exchanging relation during the digesting operation. The cracking temperature may be maintained substantially the same throughout the digesting operation, or

the cracking temperature may be reduced somewhat during or toward the end of the digesting operation. Each of these modes of operation has certain advantages.

The cracked vapors discharged from the di- /gesting operation may be subjected to suitable 6017 ply of such scrubbing agents may be reiiuxing or fractionating operations, and, before final condensation, the vapors are subjected to refining treatment. The vapors, for example, may be subjected to a fractionating operation or to a. reuxing operation for separation of heavier and higher boiling constituents suitable for further treatment. in the cracking operation. Such reux condensate may be returned while hot to the cracking operation together with fresh stock, or it may be cooled and then returned with fresh stock. Likewise, fresh stock exclusively may be supplied to the cracking operation. The vapors may also be subjected to a suitable fractionating operation for the direct production of a product of T the desired boiling range.

Before the vapors from the digesting operation are subjected to such refluxing, fractionating or treating operations, it is advantageous to subject the vapors to a scrubbing treatment for the separation of any tarry or carbonaceo-us matter mechanically carried With the vapors, for example, with fresh stock or with condensate from some subsequent refluxing or fractionating operation or With mixtures of such stocks. The supregulated so .that the scrubbing agent is vaporized substantially completely to pass on with the vapors from the cracking operation, or, where the stock supplied to the operation, or part of it, contains S1tarry or carbonaceous matter, such stock may be supplied to the scrubbing treatment for the separation of such tarry or carbonaceous matter therein together with tarry and carbonaceous matter carried by the. vapors from the cracking 0 operation. The vapors from the digesting operation may also be passed through a body of collected tar constituents to promote the removal of mechanically entrained tarry or carbonaceous matter. Such tarry or carbonaceous matter is separated from the vapors, or from stock supplied to the scrubbing treatment, and withdrawn without again being supplied to the cracking operation.

Stocks containing tarry or carbonaceous constituents may alsoy be supplied to such scrubbing treatment for separation therefrom of such constituents together with the tarry or carbonaceous matter separated from the vapors from the cracking operation proper. Raw stock containing tarry or carbonaceous matter, for example, may be introduced into the scrubbing treatment and the balance of the stock vaporized therein leaving behind such tarry or carbonaceous matter, this raw stock at the same time serving as a scrubbing agent. The vaporized part of the stock, or such portions of it as are appropriate to be supplied to the cracking operation proper, may then be condensed in some subsequent fractionating or refluxing operation from which condensate is returned to the cracking operation proper. Crude petroleum or topped crude oil, for example, may be supplied to the scrubbing operation and tarfree components of the crude oil supplied to the cracking operation proper as a condensate from some subsequent fractionating or refluxing operation.

The invention provides for close control of the boiling range of the stock supplied to the cracking operation proper. The stock supplied to the cracking operation proper may be fractionated, Y l

as part of the complete operation, so that the stock forced through the heating and vaporizing and digesting operations is of advantageous character. The boiling range of the stock supplied to the cra-cking operation proper, including raw stock as Well as reluxed stock, may thus be made narrow and Within such limits as may be desired. Raw stock may be supplied to one or more of the reuxing or fractionating operations, heavier components may be separated and discharged l fromthe operation, components appropriate to be supplied tothe cracking operation proper may be separated in one or more of the reuxing or fractionating operations, in a refluxing or fractionating operation subsequent to any in which heavier components are separated, and lighter components may be stripped from the stock without being supplied to the cracking operation proper. Similar components of the vapors from the cracking operation proper may be handled in the same Way in the same refluxing or fractionating operations. Condensates from subsequent fractionating operations, for example, may be returned to preceding refluxing or fractionating operations for stripping of lighter components therefrom, and at the same time may serve as refluxing or condensing mediums. A heart cut from crude petroleum or from a topped crude oil, for example, may be supplied to the cracking operation proper by introducing the crude oil into the scrubbing treatment and condensing from the resulting vaporized fraction the intermediate components comprising the heart cut in a subsequent refluxing or fractionating operation and returning this condensate to the cracking operation proper. The stock so supplied to the cracking operation proper may include in admixture similar components condensed from the vapors from the cracking operation proper. By stripping stocks supplied to the cracking operation proper of light components, such as those desirable as components of the cracked product, overcracking of such components is avoided.

The cracked product is subjected to refining treatment before condensation so that the vapors Lemons forming the product are subjected to treatment while fresh from the cracking operation. The process heat, or part oi it, may thus also beutilized for effecting or promoting the rening treatment. The vapors, for example, are passed through a body of ullers earth or similar absorbent earth or clay while still at elevated temperature. LThe cracked product may thus be stabilized, chemically and physically, as part of the complete operation by direct fractionation and treatment. A part of the vapors may be condensed in the rening treatment and such condensate may include heavy polymerized constituents. This condensate may be returned to preceding reiiuxing or fractionating operations. If this condensate includes polymerized constituents of a tarry character or tending to form tarry constituents, it may be supplied to the scrubbing treatmentr for separation of such constituents therein.

The heat for the heating and vaporizing operations and the digesting operation may be supplied by heating gases from a common nrebox. The heating gases may be supplied to the heating operation at a temperature initially substantially higher than that at which the oil vapors are discharged from the heating opera'- tion and the heating gases may be supplied to the digesting operation at a temperature intermediate this initialV temperature and the temperature at which the heatinggases escape from the heating operation. The heating gases, for example, may be supplied to the heating operation and to the digesting operation from a common ire-box and the heating gases supplied to the digesting operation tempered to a lower temperature than that at which the heating gases enter the heating operation. This tempering may be effected by admixing with the heating gases from the firebox a portion of the heating gases escaping from the heating operation or from the digesting operation or from both of these operations. The heating gases supplied to the heating operation from the common rebox may also be tempered, to a lesser degree, by admixing therewith a portion of the heating gases escaping from the heating operation or from the digesting operation or a mixture of the heating gases escaping from both operations. Remaining heating gases escaping from either the heating operation or the digesting operation or both may he utilized to preheat air for combustion in the lrebox. However, separate heating furnaces may be used for the heating operation and the digesting operation.` Where such separate heating furnaces are used, the heating gases supplied to each operation may also be tempered, as ljust described, by admixing therewith heating gases escaping from either or both of the operations.

Further features and advantages of the invention will be apparent as the 'description proceeds.

The invention will be further described in connection with the accompanying drawing which represents, partly in elevation and partly in section, and partly by diagram only, one arrangement of apparatus adopted for the practice of the invention, but it is intended and will be understood that this further description and illustration are for the purpose of exemplication and that the invention is not limited thereto.

Referring to the drawing, a stream of the stock to be cracked is heated and vaporized and the vapors are then heated to a high cracking temj perature in the heating conduit 1 arranged ina heating flue in the heating furnace and the hot vapors discharged from this heating conduit are maintained at a. cracking temperature for a substantial period of time while flowing in succession through the drums, or digesting chambers, 5, 6, 7 and 8.

The heating conduit 1 may comprise a tube or a bank of tubes through which the stock passes but once and arranged in a suitable furnace structure.

The digesting drums 5, 6, 7 and 8 are with advantage vertically arranged in heating flues (not shown). These drums are connected in series and the connections are arranged so that the vapors are required to pass through substantially the entirelength of each drum. Manholes may be arranged to provide access to the interior of each drum for cleaning, inspection or repair..

Y The tower 38 may be provided interiorly with baies, best in its upper part. The tower 39 may be of any construction suitable for refluxing or fractionating the vapors. For example, it may be an ordinary baffle tower. The tower 40 may be of any construction suitable for 1accurate l' fractionation of the vapors. For example, it may be an ordinary bubble tower. The tower 41A is of any suitable construction adapted to hold a body of a refining agent, such as fullers earth or a treated clay, and to provide for passage of the vapors therethrough. These towers, particularly towers 38, 39 and 40, may with advantage be thoroughly lagged or thermally insulated to prevent or reduce heat loss.

In carrying out the invention in the apparatus illustrated, a stream or" oil is heated and vaporized and the vapors are heated to a high cracking temperature in the heating conduit l, the hot vapors discharged from the heating conduit are maintained at a cracking temperature for a substantial period of time while flowing through the drums 5, 6, '7 and 8, and the vapors discharged from the drums are passed in succession through towers 38 and 39 by means of connections 42, 43 and 44. The vapors from tower 38 may also pass directly to tower 40 or tower 41 through by-pass connections 51 or 51 and 52. Raw stock' from tank 45 is supplied by means of pump 46 directly tothe heating conduit, through connections 47, or, wherev the vapors from the digesting operation are su jected to a refluxing operation in tower 39, to the upper part of tower 39 andA there introduced into direct contact with the vapors owing therethrough, through connections 48 and 50, or to the upper part of tower 38 and there introduced v,

into direct contact with the vapors flowing therethrough, through connections 48 and 49 orthe fresh stock may be supplied in part directly to the heating conduit and in part to either or bothY of towers 38 and 39. Where the vapors are subjected to a refluxing operation in tower 39, the condensate therefrom, together with any admixed unvaporized portions of stock introduced into the upper end of the tower, may be returned to the heating conduit, in whole or in part, through connection 53. 'I'his condensate or condensate mixture may be so returned hot or cold or at an intermediate temperature.

The scrubbing treatment effected in tower 38 and the refluxing or fractionating operations carried out in towers 39 and 40 may be effected or controlled by the regulated introduction of stocks or mixtures of stocks of appropriate character'and at appropriate temperature. The fresh stock supplied to the cracking operation may be introduced into one or more of these towers to assist in effecting or controlling the scrubbing or refiuxing or fractionating operation carried out therein, and at the same time may be preheated and subjected to fractionating treatment for the separation of components heavier or lighter than desired to be supplied to the cracking operation proper. Similarly, the condensates or condensate mixtures from tower 39 or tower 40 or both of these towers may be reintroduced into either or both of these towers to assist in effecting or controlling the refluxing or fractionating operations carried out therein, and at the same time components of these condensates or condensate mixtures heavier or lighter than desired to be supplied to the cracking operation proper may similarly be separated therefrom. Either or both of towers 39 or 40 may be operated as a refluxing or as a fractionating tower, that is all or part of the condensate or condensate mixture produced in either tower may be supplied to the cracking operation proper or may be discharged from the operation.

Where the vapors from tower 38, including vapors from the cracking operation proper and any vaporized compo-nents of stock introduced into tower 38, are subjected to a reiiuxing operation in tower 39, this refluxing may be controlled by supplying raw stock through connections 48 and 50 and by regulating the rate at which raw stock is so supplied. Reflux condensate, together with any admixed unvaporized raw stock, discharged from tower 39 through connection 54 may be supplied to the heating conduit 1 directly through connection 53 by means of hot oil pump 55. Part of this hot oil mixture may be supplied to the upper part of tower 38 through connection 49. Part of the raw stock supplied to the operation may also be supplied to the upper part of tower 38 through connections 48 and 49. Condensate, together with any admixed unvaporized raw stock, discharged from tower 39, may be passed through cooler 56, in whole or in part, and then supplied, in whole or in part, to the heating conduit 1 through connections 57 and 53 by means of pump 58. Part of this condensate or condensate mixture, or all of it where the vapors from tower 38 are subjected to a fractionating operation rather than a reiiuxing operation in tower 39, may be so cooled and then discharged to tank 59 through connection 60. Part of such cooled condensate or condensate mixture may be supplied to the upper part of tower 38 through connections 6l and 49. The operation in tower 38 may thus be controlled or effected by the condensate mixture discharged from tower 39 through connection 54 either while hot or after cooling. For example, such of this oil mixture as is returned to the heating conduit l may be returned directly while hot and another part of the oil mixture may be introduced into the upper part of tower 33 after cooling. Where condensate or condensate mixture is not returned from either tower 39 or tower 40 to the heating conduit l, all of the raw stock may be supplied directly to the heating conduit through connection 47, or where condensate or condensate mixture from either tower 39 or 40 is returned to the heating conduit the raw stock, or part of it, may be supplied to tower 38 through connections 48 and 49. Where raw stock is not introduced into the upper part of tower 39, or where the amount introduced is insufficient to effect the desired condensation, the operation in this tower may be eifected or controlled with advantage by introduction oi' condensate or part of the condensate from tower 40 or 41, or by introduction of part of the final product, or by introduction of mixtures of these oils. For example, cooled condensate from tower 40 may be introduced into the upper part of tower 39 through connections 62, 63 and 50 and cooler 64 by means of pump 65; or condensate from tower 4l may be introduced into the upper part of tower 39 through connections 66, 67 and 50 and cooler 68 by means of pump 69; or part of the final condensate may be introduced into the upper part of tower 39 through connections 70, 7l and 50 by means of pump 72. Likewise, part of the oil mixture discharged from tower 39 through connection 54 may be returned to the upper part of the tower, after cooling or partial cooling, through connections 57, 73 and 50 or through connections 74 and 50 by means of pump 58, to assist in effecting or controlling the operation in the tower. The condensate mixture, or part of it, from tower 40 may be introduced hot into the upper end of tower 38 or tower 39 through connection 63 by means of hot oil pump 75, and the condensate mixture, or part of it, from tower 4l may similarly be introduced into the upper end of tower 38 or tower 39 through connection 67 by means of hot oil pump 76.

In tower 38, the hot vapors discharged from the digesting drums 5, 6, 7 and 8 through connection 42 are subjected to treatment for the separation of any tarry or carbonaceous matter mechanically carried with the vapors. This material usually separates as a heavy residue or tar which is fluid while hot. Connection 77 is provided for the discharge of such fluid tars or residues from tower 38 to tank 78. Except for reintroduction into tower 38 as a scrubbing medium, this material is not returned to the system. Cooler 79 may be provided in connection 77 to cool the tar or residue to a temperature below its ignition point when exposed to air. It is advantageous to maintain a body of this hot tar or residue in the lower part of tower 38 and to discharge the hot vapors from the digesting drums into this liquid body below its surface. The operation in tower 38 may be controlled or effected as has been described; by the introduction of raw stock into the upper part of the tower through connections 48 and 49, or by the introduction of condensate or condensate mixture from one or more of the towers 39, 40 and 4l, or by introduction o-f mixtures of these stocks. The supply of such oil mixtures, that is raw stock or condensate or condensate mixtures from subsequent refluxing or fractionating or rening operation, or mixtures thereof, is advantageously regulated so that substantially all of the oil mixture introduced is vaporized and escapes with the vapors from the digesting operation through connection 43. Where fresh stock initially containing tarry or carbonaceous matter is to be cracked, it may with advantage be supplied to tower 38 through connection 49 to separate such constituents with the tar and residue collected in tower 38 before the fresh stock is supplied to the heating conduit 1, the vaporized components of the raw stock, or those desired to be supplied to the heating conduit, then being condensed in tower 39 or tower 40 and supplied to the heating conduit as condensate or one or the other of these towers. To assist or to effect the scrubbing treatment carried out in tower 38, a part of the tar or residue discharged through connection 77 may be reintroduced into the tower through connection 80. This reintroduced tar or residue may be returned hot by means of pump 81 or after cooling by means of pump 82. In such operation, where fresh stock or condensate or condensate mixtures from one or more of the subsequent refiuxing or fractionating or renning operations or mixtures thereof is also introduced into tower 38, such reintroduced tar or residue is advantageously introduced into tower 38 at a point lower than that at which such other stock is introduced, for example, through connection 83.

Where it is desired to produce directly, for redistillation, a low end point product, the vapors from tower 39 are passed through connections 85 and 87 to tower 40. This tower may, for example, be a bubble tower of any standard construction. The fractionation of the vapors therein may be effected or controlled by returning a part of the nal condensate and introducing it into the upper part of the tower through connections and 88 by means of pump v72. Constituents heavier or higher boiling than desired as components of the final product are condensed in this tower and discharged through connection 62 while the vapors remaining uncondensed escape through connection 89. As previously explained, the condensate or part of the condensate from tower Ll0 may be used to assist in effecting or controlling the operation in tower 38 or in tower 39. Storage tank 90 is provided for condensate from tower 40.

In the apparatus illustrated, the vapors escaping from tower 39, with or without intermediate fractionating in tower 40, may be subjected to treatment with fullers earth or treated clay or similar absorbent material in the tower 41. In this tower, the vapors are passed upwardly while still at elevated temperature through a body of iullers earth or the like suitably supported in the tower. Part of the objectionable constituents is absorbed and part collects as a condensate in the lower part of the tower. This condensate may be discharged through connection 66 and cooler 68 to the tank 91. Where this condensate or part of this condensate is supplied to the upper part of tower 39, as previously described, heavier or higher boiling constituents thereof may be returned to the heating conduit 1 with condensate from tower 39 or with condensate from tower 40. if the condensate from tower 41 includes polymerized constituents of a tarry character or tending to form tarry constituents, it may be introduced into tower 38 through connections 66, 67 and 49 for separation of such constituents with the tar or residue separated in tower 38. Where the cracked product is subsequently to be redistilled, and in particular where such redistillation is in conjunction with the redistillation of other light oils or distillates of such character as not to require any different further refining treatment than the cracked fraction, the vapors from tower 39 may be passed directly to tower el through connections 85, 52 and 92. By passing the vapors from tower 39 through both the fractionating or reiiuxing tower 40 and the treating tower lil, however, only the lighter vapors are subjected to the treating operation and the capacity of the treating tower is accordingly increased.

The cracked product is condensed in condenser 84 and the condensate is separated from gases and any vapors remaining uncondensed in separator and receiver 93. This separator and receiver is advantageously provided with baies, as illustrated,A above the point or discharge of the connection from the condenser Se, to promote a clean separation between condensate and the gases and vapors remaining uncondensed. The condensate is discharged through connection 94, for example to tank 95, and the gases and luncondensed vapors are discharged through connection 96. The gas-vapor mixture discharged through connection 96 may be subjected to any suitable treatment for the recovery of condensible constituents, for example, it may be subjected to a scrubbing operation with an absorbent oil and. the absorbed constituents distilled from the oil.

The several towers 38, 39 and 40 may be combined in operation to control the boiling range oi the stock supplied to the heating conduit 1. The towers through which the vapors from the digesting operation are passed, for example, are advantageously operated to prevent the return to the heating conduit of any very light components, particularly those suitable as components of the desired product. Condensate or condensate mixture from tower 40, for example,

ymay with advantage be reintroduced into tower 38 or tower 39 to be revaporized and recondensed to strip from it any such light components, the heavier components being condensed and returned to the heating conduit in the condensate from tower 39. Tower 39 may be operated as a fractionating tower rather than as a reflux tower to separate from raw stock or condensates or condensate mixtures introduced into it components heavier than desired to be returned to the heating conduit l, and the vaporized stock then condensed in tower 40' and returned to the heating conduit from this tower through connections 62 and 63. Crude petroleum, for example, may be introduced into tower 38, the tar free components of the crude oil vaporized in this tower, and these vaporized components condensed in tower 39 or 49 and returned to the heating conduit 1 in the condensate from either or both of these towers. ponente of the crude oil may be separated and discharged from the opera-tion. For example, the operation of tower 39 may be regulated so that only those components desired to be supplied to the heating conduit are condensed therein and the lighter components may then be discharged from the operation in condensate from tower 49 or with the final condensate. A heart cut from crude petroleum or from a topped crude oil may thus be supplied to the heating conduit 1 by introducing the crude oil into tower 38 and condensing from the resulting vaporized fraction the intermediate components comprising the heart cut in tower 39 and supplying this condensate to the heating conduit. The condensate or condensate mixture, or part of it, may be returned from any one or more of the towers 39, 40 and 41 to the heating conduit 1 either while hot or after cooling; from tower 39 through connection 53 by means of pump 55 or pump 58, from tower 40 through connection 63 by means of pump or pump 65, and from tower 41 through connection 67 by means of pump '76 or pump 69.

It will be appreciated that one raw stock or raw stock mixture or several separate raw stocks or raw stock mixtures can be handled advantageously in carrying out the present invention. For example, a gas oil or a light gas oil stock may be supplied to the heating conduit 1 or in part to the heating conduit l and in part to tower 39 and a crude oil or topped crude oil supplied At the same time, lighter comto tower 38 in the same operation. Similarly, a Y

duit 1 and in part to the tower 39 and a naphtha cut containing gasoline components may be supplied to the tower 39 together with such part of the gas oil or light gas oil as is supplied thereto in the same operation. In this respect, the inadvantageously just sufficient to maintain flow through the apparatus.

I claim: A method of cracking hydrocarbon oils, comprising owing a stream of the oil in succession through a heating operation, a digesting operation, a tar separating operation, a refluxing operation, a fractionating operation, a treating operation and a condensing operation, heating the oil in the vapor phase to a high cracking temperature in the heating operation, maintaining the hot vapors discharged from the heating operation at a cracking temperature for a substantial period of time in the digesting operation, discharging separated tar from the tar separating operation Without permitting it again to enter the system, returning condensate from the reluxing operation to the heating operation, separating as a condensate constituents heavier than desired as components of the product in the fractionating operation, contacting the oil in vapor phase with an absorbent earth in the treating operation and condensing the cracked product in the condensing operation.

HARRY L. PELZER.

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