US2126472A - Process for the treatment of hydrocarbon oil - Google Patents

Description

1933- Y P.. c. KEITH, JR 2,126,472

PROCESS FOR THE TREATMENT OF HYDROCARBON OIL Filed Jan.. 25, 19:55 4 Sheets-Sheet 1 FIG-@- owl/vs 145 103 FUR/VICE INVENTOR. PE/rc/mL c KE/THw:

ATTORNEY Aug. 9, 1938. P. c. KEITH. JR 2,126,472

PROCESS. FOR THE TREATMENT HYDROCARBON OIL Filed Jan. 25, 1955 4 Sheets-Shee 2 FlG.1b.

. V4100? PHASE H a i.

' IN V EN TOR. PE/PC/ML C. KEN/Ian ATTORNEY I Aug. 9, 1938. P. c. KEITH. JR 7 PROCESS FOR THE TREATMENT OF HYDROCARBON OIL Filed Jan. 25, 1935 4 Sheets-Sheet 3 FlGJc.

IN V EN TOR. PEEK/ML C hE/I'Hm BY 7 ATTORNEY- product.

Patented Aug. 9, 1938 UNITED STATES PATENT. OFFICE- rnocrss ron 'rnn DROCARBON OIL TREATMENT or nr- Percival 0. Keith, Jr., Peapack, N. L, assl or to Gasoline Products Company, Inc.,

ewark,

N. J., a corporation of Delaware Application January 25, 1935, Serial No. 3,401

18 Claims.

) cracking, a distilled stock suitable for charging to a major cracking operation, this stock being subsequently treated under cracking conditions of heat and pressure to produce the desired gasoline acter it has usually been customary to separate various oil fractions and to regard them somewhat in the nature of by-products which are more suitably treated in independent operations, or even classified as marketable products without further processing. For example, a well known method is to separate from raw crude oil a gas oil charging stock which is thereafter subjected to cracking in a separate operation, complete in itself, to produce gasoline. This gasoline in many cases has been of such character as'to require further processing, such as reformation and stabilization, to form a final gasoline product complying with the desired specifications. Likewise in many instances it has been found desirable, prior to the separation of the gas oil, to top the raw crude and subject the resulting unvaporized portion to a light cracking operation of a viscosity breaking nature, whereby the content of gas oil may be increased. Various additional steps in the processing of crude oil for the production of gasoline have also been undertaken independently.

It is an object of my invention to provide a unitary process for the treatment of raw crude oil whereby all the operations necessary to produce a maximum amount of gasoline of final desired end point and characteristics, may be cariied out at the same time in a series of interlocking steps so related one to the other that a minimum amount of heat and attention are necessary, and high efficiency results. By combining all of the various steps which have heretofore been performed individually or in some incomplete combination one with the other, it is possible to utilize more advantageously heat which might otherwise be wasted, and also keep at a low figure the amount of labor and supervision necessary in the operation of a system to carry out the process.

More specifically it is an object of myinvention to combine in a single unitary process for the treatment of raw crude oil, the steps of topping the raw crude, viscosity breaking the topped crude, cracking a clean condensate stock, reforming any necessary portion of the gasoline pro- In carrying on a process of this charduced to raise its anti-knock value to the desired point, and stabilizing gasoline distillate resulting from these operations to give a final desired product of the proper end point and vapor pressure.

.Among the objects of my invention is to provide a process of the character mentioned wherein the heavier constituents of the charging stock,

as well as heavier relatively dirty condensatev formed in the process, may be subjected to conversion into lighter relatively clean cracking stock, by treatment in what may be called a primary cracking or viscosity breaking stage, while the lighter clean cracking stock derived from the crude charging stocks and from the primary or viscosity breaking operation, is subjected to conversion in a separate cracking stage, which may be operated in the vapor phase, the arrangement being such that cracked tars resulting from the two cracking operations may be separately withdrawn from the process, and that any lighter constituents formed in the viscosity breaking stage are passed to the vapor phase cracking stage for further conversion, while any heavier constituents formed in the vapor phase cracking stage are passed to the viscosity breaking stage for further conversion. g

In accordance with my invention the fresh heavy charging stock, preferably crude oil, although it may be alternatively any heavy stock containing lighter constituents, is preheated by passing in, indirect heat exchange relation with hot products derived from other portions of .the system, the thus preheated oil being further raised in temperature if desired by passage through a directly fired coil located, for exam ple, in one of the cracking furnaces handling stocks separated during the carrying out of the process. The resulting heated charging stock, having a temperature suficient to cause the distillation therefrom of the desired lighter constituents, is introduced into a crude flashing tower wherein partial vaporization thereof occurs, and wherein fractionation of the evolved vapoi'stakes place, The vapors remaining uncondensed after passage through the crude flash tower are removed from the top thereof and constitute straight-run gasoline, which is collected for depropanization, after which it may be used in the final desired gasoline distillate blend. A cut of kerosene may likewise be removed from the crude flash tower, as well as a cut of naphtha and a cut of gas oil. The heavy naphtha preferably comprises the heavy constituents of gaso-k line, such as require reformation, in order to increase the anti-knock value thereof, and the naphtha so obtained is subsequently reformed, if

ther cracked, and the same is true of the gas oil derived from the crude flash tower. The reduced crude remaining unvaporized in the crude trap-out tray, wherein it passes downwardlyagainst a rising stream of vapors and is thereby further distilled and additionally heated. The portion remaining unvaporized, in mixture with condensed fractions of the rising vapors, is removed from trap-out tray mentioned and passed through a primary or viscosity breaking furnace wherein it is raised to a moderate cracking temperature and subjected to conversion sufllcient to cause the formation of a considerable amount of clean gas oil charging stock, which can be subjected to a separate vapor phase cracking operation. The amount of cracking which takes place in the viscosity-breaking heater will be dependent upon the exact character of stock passing therethrough but should be, preferably, as great as possible without deleterious coke deposition in the coils of the heater.

The resulting cracked products are passed from the viscosity breaking heater into the base of the second tower just mentioned, which constitutes the viscosity breaking evaporator. In this evaporator the cracked products separate into vapors and liquid residue, the former rising through the tower and constituting a source.

of the vapors mentioned, which contact with the reduced crude from the crude flasher, while the liquid residue may be withdrawn for use as fuel oil without dilution or may be blended with lighter stocks from other sources, as fuel oil. The vapors remaining uncondensed in their passage upwardly through the viscosity breaking evaporator, which is supplied with bubble trays or other contact devices of any well known type, are removed and condensed to form gasoline distillate. This distillate may be used by itself or may be subjected to additional distillation or refformation. One desirable method of operation is to object this viscosity breaker gasoline to redistillation in the main bubble tower of the vapor phase cracking unit, as will be described more fully hereinafter.

A side stream of gas oil is preferably withdrawn from the viscosity breaking evaporator and utilized as refluxing oil in various portions of the unit While the remainder of the gas oil so withdrawn is preferably introduced into the bubble tower of the vapor phase cracking unit to be recycled through that unit and further cracked in the vapor phase. By this method the light gas oil, which is very well suited for vapor phase cracking and which has been formed in the viscosity breaking furnace by the cracking reaction carried on therein, is transferred to the vapor phase cracking side of the unit and subjected to more drastic conversion therein.

Reflux condensate from the bubble tower of the vapor phase cracking portion of the sys tern, including gas oil derived from the viscosity breaking evaporator and any heavy ends contained in the viscosity breaker gasoline, if that be introduced into the said bubble tower, are removed as a mixture and passed through the coils of the vapor phase heating furnace wherein the oil is raised to vapor phase cracking temperature and subjected to conditions such as to cause relatively mark-ed conversion' thereof into products in the gasoline boiling range. The resulting cracked products may be passed into a soaking drum for further conversion without additional heat, and then be introduced into a high pressure evaporator, or if desired may be passed directly to the high pressure evaporator without previous soaking thereof in the drum. In this high pressure evaporator, which is separate from the viscosity breaker evaporator, separation of the-highly heated cracked products into vapors and liquid residue takes place, the former passing upwardly through the tower and undergoing partial fractionation therein, the remaining cracked products not condensed in the high pressure evaporator passing out through the vapor line into the bubble tower already mentioned and therein undergoing fractional condensation.

The vapors remaining uncondensed pass off from the top of the said bubble tower and from there may be condensed and collected as a desired product but instead are preferably subjected to passage through bodies of clay, in the vapor phase, whereby beneficial polymerization L of certain unstable constituents thereof occurs. After their treatment by contact with the clay the vapors are subjected to final fractionation in an after-fractionator wherein constituents thereof heavier than desired for inclusion in the final gasoline distillate are condensed, while the uncondensed and fractionated vapors passing off from the top of the after -fractionator are condensed as a desired distillate. This distillate is then preferably subjected to a stabilizing operation whereby undesirably light constituents thereof are removed with the resulting formation of a final desired stabilized distillate.

Polymers formed in the clay treating operation may be withdrawn from the process but are preferably introduced into the viscosity breaker evaporator wherein they are subjected to partial vaporization and are thereby segregated into light and heavy condensates for treatment in the proper portions of the system. The reflux condensate formed in the after-fractionator is preferably introduced into the main bubble tower of the vapor phase cracking system. Or the polymers and/or after-fractionator reflux condensate may be introduced directly into the transfer line of the vapor phase cracking heater as a fiuxing medium.

Liquid residue is removed from the vapor phase evaporator and introduced into a fuel oil flash tower, under a considerably lower pressure, whereby partial vaporization thereof occurs by agency of its contained heat. The resulting vapors are introduced into 'the viscosity breaker evaporator at a low point, whereby they are subjected to further fractionation with the result that lighter and heavier constituents thereof are recycled through the process for further conversion in the proper crackingcoil. Liquid tar is removed from the fuel oil flash tower and may be used alone as fuel oil or may be blended with fuel oil withdrawn from the base of the viscosity breaker evaporator, or if desired either or both of these fuel oils may be cut back with a lighter condensate withdrawn from another portion of the system, e. g., with reflux condensate formed in the main bubble tower.

The gasoline resulting from the viscosity breaking cracking operation is usually of somewhat lower anti-knock value than that produced by the vapor phase cracking step, and to counteract this breaking cracking operation, it is desirable to subject to a reforming operation the heavy naphtha derived from-the stripping of the crude charging stock so as to form added high antiknock constituents. To this end the heavy naphtha from the crude charging stock is passed through a separate reforming coil wherein the naphtha is raised to a cracking temperature and subjected to reformation with an attendant increase in the anti-knock value thereof, the re-- suiting reformed products being introduced,

preferably, into the'vapor phase evaporator along with the vapor phase cracked products. Any heavypolymers formed by the reforming step col- .lect with the liquid residue in the base of the vapor phase evaporator and are passed down into the fuel oil'fiash tower, wherein lighter constituents present vaporize and travel to the viscosity breaker evaporator for fractional condensation therein and recycling to the proper cracking coil. Since the reforming heating coil is preferably operated on a once-through basis without recycling, it is possible and sometimes highly desirable, to pass through the reforming coil considerably heavier stock than would ordinarilybe subjected to a reformingoperation or to a drastic cracking step. To accomplish this, relatively light gas oil and/or kerosene may be blended with the heavy naphtha and passed through the reforming coil,

jected to a relatively drastic cracking operation,

which can be of a more violent nature than is possible where cycle stock is present, without the deleterious formation of coke, and with the attendant formation of relatively high anti-knock gasoline constituents. In order further to in crease the anti-knock value of the final desired distillate part or all of the viscosity breaker gasoline may be passed through the reforming coil in mixture with the heavy naphtha. Or if desired the viscosity breaker gasoline alone might be reformed.

The straight-run gasoline derived from the distilling of the crude oil is desirably subjected to a depropanizing step, which consists in partial distillation, to remove undesirably light fractions thereof including propane, but without removing heavier desirable constituents in the nature of butane and higher boiling point'hydrocarbons. It is also desirable to recover certain suitably heavy constituents from the gases derived from the depropanizing operation and from the stabilizing operation, and this may be done by passing these gases under increased pressure through the clay towers with the vapors from the main bubble tower. In efiectin'g the depropanizing and stabilizing steps it is intended to use waste heat derived from other portions of the process in a beneficial manner such that a heat balance of high eificiency is obtained. if it is wished to dispense with the separate depropanining'of the virgin light naphtha, this material may be passed to the stabilizing operation with the other gasoline distillate.

The various cracking coils for the operation may separate cracking tubes in the furnace, but [hey be of any known type.

The above-mentioned and further objects and advantages of my inventionand the manner of attaining them will be explained morefully in the following description. taken in conjunction with the accompanying drawings.

Figs. 1a, 1-b, and 1c of the drawings, when joined together, illustrate diagrammatically an oil cracking system embodying my invention.

Fig. 2 is a simplified flow diagram.

Referring more particularly to the drawings reference numeral I indicates a charging line through which passes fresh relatively heavy charging stock, preferably crude -oil, although alternatively reduced crude or other stock containing both light and heavy constituents, under pressure generated by pump 2, this charging stock traversing indirect heat exchangers 3 and' 4, or alternatively heat exchangers 5, 6, and l, or part of the charging stock traversing heat exchangers 3 and 4 and part traversing heat exchangers 5, 6, and I, with the result that the charging stock is raised in temperature considerably while supplying cooling to those parts of the apparatus which require it. The control of the flow of the charging stock to one series or the other of the indirect heat exchangers mentioned, being efiected by means of valves 8 and t. The line by which'the charging stock passes to the two heat exchangers first-mentioned is indicatcd by reference numeral III while the lineleading to the heat exchangers last-mentioned is indicated by reference numeral H. The preheated charging stocks now preferably pass through a directly fired coil in the convection section l2 of furnace It. The flow through this furnace may be in two parallel paths as indicated by reference numerals l4 and i5, each path comprising a separate bank of tubes and the two banks being symmetrically disposed in the convection section i 2, although a single tube bank may be used if desired. In these coils the oil is further heated so that the final temperature is sufllc ent to cause the desired distillation of the oil. The resulting hot oil, at distilling temperature, is passed through line it into the lower portion of crude stripping tower ll, wherein partial vaporization thereof occurs as a result of its contained heat. In the crude flash tower ll 1 the vapors separate from liquid residue, the former passing upwardly through baflle plates or other contact elements wherein fractionation thereof occursin the well known manner, while the liquid residue passes downwardly into the base of the tower preferably over similar battle plates or contacting devices, andmay be additionally stripped by the introduction of steam, hot gas or other stripping medium introduced by way of line it, or may be stripped by indirect heat exchange brought about by a reboiier, not shown. The vapors remaining uncondensed after passage through the crude flash tower it pass off from the top thereof through vapor lines it, are condensed in condenser it, and resulting condensate is collected in the receiver it, this condensate being straight-run gasoline, preferably of a relatively low end point. ,A; portion of this gasoline so obtained may be pumped back into the top of the crude flash tower by way of line 22, under pressure generated by pump 23, for refluxing purposes. The remaining gasoline distillate may be withdrawn from the receiver and from the process by way of draw-off line 24 having float control valve 25, but instead is preferably diverted Ebb bill

fill

through pipe 26, under regulation of automatic level responsive valve 21 into the upper portion of a depropanizing tower 28 wherein the dis conduit 32 and may be cooled and passed to storage for use alone, or for blending purposes. The flow of depropanized gasoline from the column 26 is most suitably under the control of an automatic level responsive valve 33. Additional heat for the carrying out of the depropanizing step in the column 26 may be supplied by indirect heat exchanger or reboiler 54, through which a hotter fluid is circulated via line. 35, as will be explained more fully hereinafter.

From the crude flash tower H a plurality of side cuts may be withdrawn, including heavy naphtha, kerosene and gas oil. The heavy naphtha draw-oil. line is indicated by reference numeral 3! and the draw-off line for the kerosene and light gas oil are identified by reference numerals 36 and 38 respectively. The naphtha and kerosene are preferably subjected to stripping operations in the separate strippers 40 and 4!, which are shown as superimposed in the drawing, under the influence of steam or other suitable stripping agents injected through lines 42 and 43 respectively. The vapors resulting from the stripping operation are desirably returned to the crude flash tower by way of vapor lines 44 and 45 respectively. Pipes 46, 41 and 48 are furnished whereby the naphtha, kerosene and light gas oil respectively, either individually or in any desired mixture may be introduced into the accumulator tank 49. The kerosene and light gas oil may be cooled if necessary before introduction into the accumulator, this being accomplished by coolers 60 and 5| respectively.

Ordinarily it is more desirable to remove the kerosene from the crude flash tower as a marketable product and to pass the naphtha into the accumulator 49, and with this in mind the accumulator last mentioned is designated the naphtha charge accumulator. The naphtha so obtained constitutes a source of supply for a reforming operation which will be described more fully hereinafter. In order to insure that the supply will at all times be suflicient a liquid level responsive valve 52 is furnished, which serves to introduce into the naphtha accumulator light gas oil from the line 39,'should the level in the naphtha accumulator fall below the selected mark. Similar control valves of the level responsive type are connected in the conduits 31 and 38 and are identified by reference'numerals 53 and 54. Forty-nine prime (49') indicates a vent line for passing vapors from the accumulator 49 to the flash tower ll.

The reduced crude liquid residue is Withdrawn from the base of the crude flash tower and forced by pump 55 through conduit 56 into an upper intermediate level in the viscosity breaker combination evaporator-fractionator 51, wherein it travels downwardly over bubble trays or baiiies or other suitable contacting means against a rising stream of hot vapors. The hot vapors are derived from a source which will be explained hereinafter, As a result of this countercurrent contact of the reduced crude and the hot rising vapors, additional portions of the reduced crude are vaporized including any virgin gas oil suitable for use as clean cracking stock and not previously removed in the crude flash tower l I, and heavier fractions of the rising vapors are condensed, the unvaporized reduced crude and condensed portions of the vapors collecting on trap-out tray 58 and constituting a source of charging stock for the viscosity breaking heater. Oil is withdrawn from the trap-out tray 58 through pipe 59, after having been stripped of any dissolved lighter constituents by the introduction of steam or other stripping medium through pipe 60, and is forced by pump 6i through the heating coils of the primary cracking furnace or viscosity breaking furnace 62, wherein the oil is raised to a cracking temperature and sub-. jected to conversion sufficient to cause the formation of a considerable amount of relatively light clean gas oil, suitable for use as vapor phase cracking stock, the amount of cracking permitted being limited to prevent deleterious deposition of coke in the heating tubes.

The preferred type of heating furnace shown in the drawings is provided with parallel heating paths, the stream of oil to be cracked being divided into two similar portions and passed simultaneously through parallel heating coils. The

-oil is preferably first passed through heating tubes located in the radiantiy heated portion of the furnace, in order to raise the temperature 1 thereof to a cracking value relatively quickly, and is subsequently passed through convectively heated tubes in the convection portion of the furnace, wherein the oil is subjected to additional cracking. The resulting highly heated cracked products travel through transfer line 63 into the base of the evaporator section 63 of the viscosity breaker tower 51, wherein they undergo separation into vapors and liquid residue, the vapors passing upwardly through the tower and constituting a source of the hot vapors already mentioned, while the liquid residue is withdrawn from the evaporator through line 64, and passed from the system as fuel oil, either alone or as a blend with a suitable cut-back medium, preferably a relatively light condensate stock derived from the vapor phase bubble tower by way of line 65, as will be explained more fully hereinafter. Reference numeral 66 indicates a valved connecting line whereby the light condensate oil from conduit 65 may be mixed with the residue withdrawn through line 64.

Part of the residue from 64 may be forced through line 61 and cooler 68, by action of pump 69 and be introduced into the transfer line 63 of the viscosity breaking heater, in quantities controlled by valve 10, so as to reduce the temperature of the products in the transfe line and in the base of the viscosity breaker evaporator 5'! to inhibit deleterious coke deposition. To a similar end a quantity of heavy gas oil condensate may be collected on trap-out tray II, this condensate being removed by way of pipe 12 and forced by pump 13 through indirect heat exchanger 4, auxiliary cooler 14 and valved line l5, into the transferline 63. An additional quantity of this heavy condensate may be introduced into the evaporator 51 above bafile plate 1'6 located below the trap-out tray 1 I, as well as above baflie plates 17 and above bubble trays 18, by

vapor phase evaporator M wherein the products cracking coils.

means of-valved pipes I9, 80, and 8| respectively, in quantities sufllcient for refluxing purposes. These baflie plates and bubble trays serve to aid in the fractionation of the rising vapors, which fractionation is also assisted by the introduced refluxing oil. According to one desirable method of operation the level of the condensate collected on the trap-out tray 'l l is prevented from rising above a desired value by means of a level re-' sponsive valve 82 located in the line 80 whereby the amount of refluxing oil introduced into the tower through lines 19 and Bi may be maintained constant, while the amount of condensate collected on the trap-out tray 8i is-determined by the amount of cooled stock returned thereto through line 80, the greater the amount of cooled stock returned, the higher the level in the tray and vice versa.

Another trap-out tray 93 is positioned in the fractionator section 83' of the combination tower 51, near the top thereof, and serves to collect relatively light gas oil suitable for vapor phase cracking stock. The gas oil is withdrawn through line 84 and collected in gas oil accumulator ft. The greater part of the gas oil so collected is forced by pump 86 through line Bl into an intermediate point in the vapor phase bubble tower or fractionator 88, wherein it serves as a refluxing medium and may be partialiy re distilled. The main object in introducing this gas oil into the vapor phase fractionator is to insure its passage through the vapor pe cracking coil. The line'tll therefore provides a path whereby relatively clean gas oil condensate derived from the viscosity breaking operation may be transferred to the vapor phase cracking side of the process.

Reflux condensate collected in the base of the fractionator 88, including liquid constituents of clean gas oil condensate introduced thereinto through line 81 from the viscosity breaker fractionator, is removed through conduit it and is forced by pump 90 through the vapor phase cracking coils of the furnace I3, wherein the clean condensate stock is raised to a vapor phase cracking temperature and subjected to conversion, the resulting cracked products being passed through transfer line 9| into vapor phase soaking drum d2, wherein additional conversion thereof takes place without the addition of heat from an extraneous source. The vapor phase cracked products then travel through the line 93 into the undergo separation into vapors and liquid residue, the former passing upwardly through the tower, past the baffle plates 95 and bubble trays 96, while the liquid residue is withdrawn from the base thereof, through draw-off line 91, and is introduced into the fuel oil flash tower 98. If desired the soaker 92 may be eliminated so that the highly heated cracked products will pass directly into the evaporator from the vapor phase Virgin gas oil from the crude flash tower might also be included directly with the vapor phase charging stock, being introduced directly into line 89, or into fractionator 88.

In the fuel oil flash tower vapors, including any naphtha fractions present, separate from liquid residue, the former passing through line 91' to the lower portion of vis-breaker tower 51 while the latter is withdrawn from the process through draw-off line 98'. The vapors are thereby subiected to further fractionation and treatment with the vapors'in the tower 51. By this arrangement part of the flashed vapors form condensate which is collected in the gas oil accumulator 85. Separate elimination of tar from the vapor phase cracking operation is also permitted. And the tar drawn off from the base of the flash tower 98 may be cut back with lightcondensate from line 65, if desired, similarly to the tar from the combination tower.

The heating of the oil to vapor phase cracking temperature may be accomplished in any well.

known manner, but by preference the particular type of furnace shown is used, wherein the stream of oil to be cracked is divided into'two portions which travel through separate parallel banks of heating tubes in the furnace, the oil of each stream first entering a radiant heating coil and then passing through a bank of convectively heated tubes which arelo'cated in the convection section of the furnace. The separate banks of tubes located in the radiantly heated portions of the furnace are indicated by reference numerals t9 and lilil while the banks of tubes subjected to convection heat are indicated by reference numerals till and ma; From this it will be seen that the cracking furnace has two separate combustion chambers Hi3 and tilt and a common convection section it, the heating gases being generated in the combustion chambers by burning of any desired fuel, and the combustion products passing upwardly through thecombustion chamber and downwardly through the common convection section.

In the evaporator 94 the rising vapors are subjected to partial dephlegmation and then pass off through the vapor connection H into the lower portion of the fractionator 88-, above bubble trays Hi6, but below the other bubble trays or baffle plates. These vapors move upwardly through the fractionator and are subjected to fractional condensation in the usual Well known manner, the fractionated vapors, comprising essentially fractions in the gasoline boiling range, being removed from the top of the fractionator through vapor line Hi1 and being subjected to treatment in one or several clay towers H18. In

- this clay tower the vapors are subjected to beneficial polymerization with resulting gum stabilization, resulting polymers being removed as liquid from the base of the tower through pipe I09, and collected in the receiver Mil/from which the polymers may be passed through line iii into the viscosity breaker evaporator above the trap-out tray 1i. Clay treated vapors are removed fromthe lower portion of the clay tower, above the liquid level therein, and transferred through line H2 into a low level in the afterfractionator H3. In the after-fractionator the vapors are subjected to the usual fractional condensation, the fractionated vapors having the desired boiling characteristics passing off through the vapor line'lM, indirect heat exchanger H5 and condenser H6 into the distillate receiver Hill. The necessary cooling may be supplied to the fractionator H3 by returning to the top thereof a portion of the distillate from receiver Ill, through the agency of conduit H8 and pump H9.

The distillate collected in the receiver II! will have the end point desired for the final product and may be withdrawn directly from the receiver for use, but preferably this distillate is subjected to stabilization to remove undesirably light fractions therefrom and reduce the vapor pressure thereof to the desired value. This may be done by passing the distillate through conduit I and heat exchangers i2l,l22 and H5 into an intermediate point in the stabilizer column I24, the necessary pressure being supplied by pump I23. By passage throughthe heat exchangers mentioned the distillate is raised in temperature sufllclently to volatilize the undesirably light constituents as well as some of the desirably heavy fractions, the vapors separating from any unvaporized portions in the stabilizer tower, the former passing upwardly and the latter downwardly through the usual bubble trays or other contact devices inside of the tower. In their passage upwardly through the tower the vapors are subjected to partial condensation with the result that only undesirably light vapors and gases pass off from the top of the tower through the vapor pipe I and cooler I26 into the receiver I21, In this receiver a portion of the products may be collected as liquid and some or all of this liquid may be returned to the top of the stabilizer "olumn as a refluxing medium, by agency of pipe I28 and pump I29. The uncondensed gases may 'be removed from the accumulator I21 through conduit I30, for use as fuel or for any other desired purpose. A similar gas removal line I3I is connected -to the top of the distillate receiver I I! for venting the gases therefrom. The liquid gasoline constituents gravitate downwardly through the tower I24 and are subjected to the stripping action of the rising vapors, the distillate collecting in the base of the stabilizer tower being a desired stable product, which may be withdrawn from the process by way of draw-off connection I32. The stabilizingaction is aided by supplying heat to the base of the stabilizing column by means of indirect heat exchanger I 33. A stream of the distillate is circulated from trap-out tray I of the tower through the indirect heat exchanger I33 and back to the tower through conduit 83d, under pressure generated by a pump not shown.

By preference the distillate withdrawn from the stabilizer column is secured from a point above the liquid level in the base thereof, and the heated distillate returned to the tower is injected at a point above the liquid level in the base thereof but below the trap-out tray from which it is removed. The heat transferred through the indirect heat exchanger I33 is desirably'supplied from reflux condensate formed in the bubble tower or fractionator 88, and to this end a quantity of the reflux condensate formed in the fractionator is withdrawn from trap-out tray it through pipe I31 and is forced by the pump tail through the indirect heat exchanger I33, next,

, if desired, through pipe 36 and indirect heat exchanger 34 in the base of the depropanizer column 28, and then through indirect heat exchanger 8, wherein it is passed in indirect heat exchange relation with the fresh charging stock. The resulting cooled condensate may be used for several different purposes around the unit, a portion being passed through an auxiliary cooler I39 and into several different levels in the evaporator 94, through valved connection I40, Ni and I42, the first mentioned connection serving to supply the cooled condensate to the liquid collected in the base of the evaporator and thereby to inhibit the formation of coke therein while the two latter connections provide means whereby refluxing oil may be supplied to -the bubble trays or other contact elements in the evaporator. Another quantity of the cooled condensate is passed through conduit I43 and valved connections I44 and '55, into a spray ring adjacent the vapor outlet of the soaker 92, and into the vapor passage through the indirect heat exchanger 6 may pass through the cooler I41 and conduit I48 into the fractionator 88 at an intermediate point, above certain of the contact elements therein, while a crossover-line I49 is furnished so that condensate from the cooler I41 may be diverted to the evaporator 94, or on the other hand, cooled condensate from cooler. I39 may be passed through this cross-over line into the fractionator 88. If additional cooling oil other than that passing through the indirect heat exchanger I33 is necessary for use in the fractionator 88, the evaporator 94, or the soaker 92, an additional quantity of the reflux condensate withdrawn from tray I36 may be passed from the outlet of pump I38 through connection I50 and indirect heat exchanger I to both of the coolers I41 and I39. A portion of the hot condensate from tray I36 may also be forced through indirect heat exchanger I5I, so as to supply heat to the base of the after-fractionator M3, the transfer being effected by withdrawing a side stream of oil from the base of the afteriractionator and passing it through the indirect heat exchanger I 5|, after which it is returned to the base of the after-fractionator. In addition to this reboiling action or as an alternative thereto, steam or hot gases may be supplied to the base of the after-fractionator through pipe 852. Reflux condensate from the base of the after-fractionator H3, comprising fractions heavier than those desired for the final product and polymers resulting from clay treatment, are forced through conduit I53 under pressure generated by pump i5 4, into an intermediate point in the fractionator 88 wherein they are again subjected to partial vaporization and fractional condensation, the heavier constituents collecting in the base of the fractionator and passing through the vapor phase cracking zone again.

The fractionated vapors remaining uncondensed after passage through the combination evaporator and bubble tower 57 of the vis-breaker are removed from the top of the tower through pipe 455 and condenser E58, resulting condensate being collected in receiver t5! and constituting mainly gasoline of substantially the desired end point, although optionally of higher end point. A portion of this gasoline distillate may be re-- turned to the top of the bubble tower by way of line Nit under pressure of pump I553, for refluxing purposes. This gasoline is preferably subjected to redistillation in the bubble tower or fractionator 88 of the vapor phase portion of the system, being introduced thereinto through con-= duits 5,636 and Hit, the flow being effected by pump 562. The via-breaker gasoline from the receiver. introduced into the fractionator 38 through pipe ESI, may be additionally cooled by means of cooler E83, whereby it serves as an efficient refluxing medium, preferably being intro duced into the iractionator 88 at an intermediate or upper level, through the branch lines Q64 and t in desired quantities. In this fractionator the gasoline is revaporized and subjected again to fractionation, the desirably light fractions passing off through the vapor line it]? with the other vapors in the manner already mentioned. Any heavier constituents gravitate downwardly I through the fraction'ator 8 8,- are collected with iii the reflux condensate in the base thereof and recirculated through the vapor phase cracking furnace for further conversion.

Alternatively part or all of the via-breaker gaso'line collected in the fecelver I51 may be transferred through cross over line I66 to pipe I61,

through which naphtha from the accumulator M is forced by pump I68, to be reformed, as

will be explained more fully hereinafter. Or vis-f breaker gasoline may be diverted from the process through draw-oif connection I66. Instead of reforming the entire range of vis-breaker gasoline only the heavier ends thereof might be reformed, either alone or in mixture with stock from accumulator db. I

Additional cooling for the top of the fractionatorrtt may be provided by withdrawing a portion of the condensate from one of the upper trays, cooling it and returning it to the upper portion of the tower. in the drawings the means for doing this is shown, reference numeral ltd referring to the conduit by which the condensate is withdrawn from one of the upper trays, this condensate passing through indirect heat er:- changer b in indirect heat exchange relation with the fresh cool charging stools, thence through an auxiliary cooler lib, if desired, thereafter being returned by pump iii to the top of the bubble tower, the amount of distillate so returned being regulated by temperature controller I12, which is adapted to open the temperature control valve i it responsive to a rise in the temperature of the vapors passing through the vapor line lbi, thereby to supply more cooling to the top of the fractionator and establish balanced conditions, and vice versa, in the well lrnown manner.

A relatively light condensate falling in the light gas oil or kerosene boiling range is removed from one or several trap-out trays in the fractionator ti, these trays being indicated generally by reference numeral l'iti,'and is passed through the conduit i'iii into the stripper ilfi wherein the condensate gravitates downwardly through bubble trays or other contacting elements and is subjected to the stripping action of steam or other stripping fluid introduced at the base of the stripper. The result is that the lighter constituents of the condensate are volatilized and pass ofi from the top of the stripper, preferably being returned to the bubble tower through the vent line ill. The stripper condensate is removed from the base of the stripper through conduit lit and cooler I19 and may be used as a source of the light condensate used for cutting back the liquid residue ontar from the base of the viscosity breaker evaporator, as already mentioned, being passed thereto through conduit 65. Or part or all of the condensate from the stripper I16 may be withdrawn from the process as furnace oil through the pipe I80, being commingled, if desired, with kerosene or other light distillate withdrawn from the base of stripper 4|, to which a connection is made by way of pipe I8I. The steam for stripping the furnace oil in the stripper H6 may be admitted through conduit I82.

Portions of the gas oil collected in the gas oil accumulator 85, after removal from the trapout tray 83 of the viscosity breaker bubble tower,

may be passed, by way of pipe I83, into the top of the fuel oil flash tower 88 as a refluxing medium, in quantities suflicient to cause the desired refluxing effect, while additional quantities thereof may be directed through the pipe I84 and be forced by pump I85 into the transfer line from the reforming furnace, as will bejexplained more fully hereinafter. Another portion of the gas oil may be returned through pipe I" to the viscosity breaker combination tower Bl as a refluxing medium, the point of return being below the trap-out tray 83 from which the gas oil is removed.

Gases from the via-breaker gasoline accumulator I81, as well as gases from the straight-run moved through drain We and returned to the vis-- breaker gasoline receiver ib'i, or may be diverted from the process through line its, while the gases are drawn oil" through pipe lit and forced by compressor ibi either into the base of the fractionator iii to serve as a stripping medium, or into the vapor outlet line lti from the top of the fractionator, or both. Conduit ltd is provided for passing the gases to the base of the fractionator while conduit lit performs the function of conducting the gases to thevapor line it'i. Ordinarily a portion oi 'the gases would be introduced into the base of the fractionator while the remainder would pass through the vapor line ib'l, although all of the gases might be passed through either one path or the other. in any event the gases pass off through the vapor line it'll and likewise through the clay tower ltd with the vapors, and therein undergo beneficial treatment of a polymerizing nature, which serves to clean up and improve the color of any of the gasoline constituents present .in the gases or formed therein while passing through the clay bed. Any gasoline constituents present in the gases from the dry drum are by this means continuously recovered for admixture with the dual gasoline distillate.

The relatively heavy naphtha, constituting the heavier ends of the straight-run gasoline, collected in the accumulator it, is removed therefrom and forced by the pump lltt through conduit ltl into reforming heating coils located in the furnace it, wherein thenaphtha is raised to a cracking temperature and subjected to reformation so as to increase the anti-knock value thereof, the resulting reformed products passing through the transfer line ltd into the baseof the evaporator til in mixture with the vapor phase cracked products. This transfer line is preferably fluxed by the introduction of gas oil from the gas oil accumulator t5, which is conducted to the transfer line by way of pipe ltd and pump I85, as already mentioned. The introduction of this flux oil serves to inhibit the deleterious deposition of coke in the transfer line. Polymers fromthe clay tower may be used as flux for the naphtha reformer transfer line, in place of, or in addition to the gas oil mentioned. Cross over line 300 and valves 3M and 302 are provided so that desired quantities of polymers from drum Ilfl may be passed to line ltd. The polymers and after-fractionator bottoms may be used for fluxlng the visbreaker and vapor phase transfer lines,'if'desired. Alternatively in place of, or in addition to the gas oil from accumulator 85 vis-breaker gasoline from conduit ISI may be introduced into the reformer transfer line I94, as a fluxing medium, since the gasoline is a good cooling agent and since it is desired to pass it eventually to the fractionator 88. A pressure reducing valve I95 is preferably introduced ahead of this reducing valve as shown on the drawings.

The heating of the naphtha which may be either virgin heavy naphtha, or vls-breaker naphtha or mixtures of these with each other, or of either or both of them with virgin kerosene and/or light gas oil, to reforming temperature may be carried out in any well known way and in any desired type of heating coll, but preferably the stream is divided into two portions, each of which is passed through a separate heating coil in a radiant portion of the heating furnace, after having first passed through a heating coil located in the convection portion of the furnace. Referring to the drawings, reference numerals I96 and I 91 indicate the two banks of heating tubes in the convection section .of the furnace, and reference numerals I98 and I99 to the banks of heating tubes located in the radiantly heated portions of the furnace. The naphtha to be reformed passes first through the coils I96 and I9! then through c the coils I99 and I99 and finally through separate coils 200 and IN which overlap both the radiantly heated portion of the furnace and the convection portion of the furnace.

Reference numeral 20I' indicates a valved cross-over line whereby naphtha or gas oil flowing in line I" may be by-passed to line 09 or vice versa. As already stated hereinbefore the charging stock for the reforming furnace is most desirably mainly heavy naphtha derived from the crude oil flash tower, but may also comprise virgin kerosene or virgin light gas oil from the crude flash tower, as well as gasoline or heavy naphtha derived from the viscosity breaker accumulator I51, or any desired mixture of these'oils. When operating on any of the stocks derived from the crude flash tower the reforming operation may be relatively. drastic, since all of the constituents are of a virgin nature. Likewise when operating on the gasoline derived from the accumulator I51 or heavy naphtha from tower 51, the reforming may likewise be carried out under drastic conditions since the stockto be treated is relatively light and of slight carbon forming tendencies.

Since three separate streams of oil pass through separate heating paths in the vapor phase and naphtha reforming furnace i9 it is highly desirable that some special form of heating control be Provided so that the outlet temperatures of the several oil streams may be kept at the desired values. Referring more particularly to the furnace it will be noted that the combustion is carried out in the two separate combustion chambers containing the coils 99 and I00, the source of heat being represented by gas or oil burners 202 and 203, and the burners in each combustion chamber being supplied by a separate feed line under control of separate valves. Numerals 204 and 205 refer to the feed lines, while 206 and 201 indicate the controlling valves therefor. These valves are of the temperature responsive type and are adapted to be actuated by a temperature responsive element located in the outlet of the radiant section of the heating tubes located in the combustion chamher in which the burners are situated. The valve 206 is connected by means of any well known mechanism, indicated diagrammatically by reference numeral 208, with a temperature responsive element 209, which is responsive to the temperature of the oil leaving the radiantly heated vapor phase cracking coil 99 and traveling to the coil IOI located in the convection portion of the furnace, the connection being such that upon a rise in the temperature of the oil passing the point 209, above a predetermined desired value, the fuelvalve 206 is slightly closed so as to reduce the temperature or quantity of the combustion gases in the combustion chamber in which the heating coil 99 is located, so as to bring the temperature of the oil at the point 209 down to the correct value; When the temperature at 209 falls below the desired value valve 206 is automatically opened somewhat to give a correcting effect. Reference numeral 2I0 indicates a similar connection by means of which the valve 201 is.

.. desired value by adjusting the amount of naphtha flowing through the reformer coil. Since the amount of heat generated in the combustion chambers will be dependent upon the outlet temperature of the oil leaving the radiantly heated vapor phase cracking coil the quantity of naphtha passing through the naphtha reforming coil must always be suflicient to keep the outlet temperature of the naphtha leaving the reformer coil at the desired low value. To make sure a suflicient supply of oil will always be available in the naphtha charge accumulator, the automatically controlled valve 52 is provided, so that when the level of the liquid in the naphtha charge accumulator 49 falls below the selected value the valve 52 will be automatically opened by any well known form of liquid level responsive mechanism, and permit light gas oil from one or several trapout trays in the lower portion of the crude flash tower I! to flow through line 48 into the accumulator 49 and make up the deficiency of oil therein. There is'then no danger of the naphtha charge pump I69 pumping the charge accumulator 49 dry. The amount of fresh charging stock passing through the preheating coils I l and I5 is preferably regulated and maintained at a constant value by flow controllers 2H3 and 2H.

While automatic controllers have been indicated for regulating certain of the heating operations taking place in the furnace these might be dispensed with and control be obtained manually. Or the several controllers mentioned might be used in connection with other than the coils mentioned.

The primary cracking or viscosity breaking furnace 62, is, as stated hereinbefore, provided with two parallel heating paths, each of which comprises a bank of heating coils located in the radiant section of the furnace and a bank of coils located in the convection section of the furnace, the oil passing first through the radiant section of the furnace, and then through the convection section thereof. In the drawings reference numeral 2 I8 indicates a series of burners located in the combustion chamber of the furnace which generate combustion gases, these passing upwardly through the combustion chamber and to the right, as shown in thedrawings, over the top of the bridge wall and downwardly through the convection section. The fuel supplied to the burners 2I8 is regulated in quantity by temperabeing about 925 F. The pressure may range from afew pounds per square inch to several hundred pounds per square inch, most suitably falling within the range of 100 to 400 pounds per square inch, a preferable value about 240 pounds per square inch. In the case of the vapor phase cracking coil the temperature preferably is caused to increase, even after the oil leaves the radiantly heated portion of the furnace, the temperature attained at the outlet of the radiantly heated coil being, for example, about 865 F. while the final temperature is in the neighborhood of 925 F. after the passage of the oil through the con-, vectively heated portion of the coil. The pressure maintained in the soaking drum 92 is desirably about the 'same as that at the outlet of the vapor phase heating coil, but this may be held at a lesser value if desired. The pressure in the evaporator 94 is likewise substantially the same as that at the' outlet of the vapor phase heating coil being, for example, about 200 pounds per square inch. This same pressure, minus any drop due to pipe friction, may be held in the bubble tower or fractionator 88 and in the distillate receiver lll. Alternatively a lower pressure may be held on the evaporator 94 than in the soaking drum 92, if desired; The amount of conversion to products in the gasoline boiling range per pass of the oil through the vapor phase cracking coil may be held in the range of 10% to 25% per pass or more, being most suitably about 20% per pass. With a very clean stock the amount of conversion per pass might exceed the highest value mentioned.

In the reforming heating coil the naphtha is .subjected to suificiently drastic conversion conditions to insure the production of the desired amount of relatively high anti-knock gasoline constituents, the greater the anti-knock value generally the more drastic the conditions required. The outlet temperature may, for example, fall in the range of 950 F. to 1050 F., being most desirably about 975 F., while the pressure usually may profitably be held higher than that at the outlet of the vapor phase coil, ranging as high as 700 or 800 pounds per square inch or more, but preferably this pressure is about 240 pounds per square inch, this value necessitating a pressure reduction upon introduction of the reformed products into the evaporator 94. The percentage of gasoline constituents in the stream of naphtha leaving the reforming coil with respect to the amount of naphtha entering the reformer coil will necessarily depend upon the end point and general character of the stock charged to the reformer coil, as well as the characteristics of the desired product. -Where the end point of the naphtha charged to the reformer coil is about 450? F. this percentage may be about 75% to or thereabouts; while when the end point is raised by the addition of kerosene or light gas oil the percentage will decrease depending upon the amount of such stock so added. Since the kerosene and light gas oil which may be added to the naphtha charge for the reforming coil from the crude fiash tower are of a virgin nature the amount of conversion in the reforming coil can still be kept at a relatively high value, even if these heavier stocks are blended with the naphtha.

The temperature in the base of the evaporator 94 which accommodates the vapor phase cracking products and reformed products should be kept sufliciently low to prevent undersirable coking and may be, for example, about 800 F. more or less, the temperature being somewhat dependent upon the pressure used. The temperature in the base of the viscositybreaker evaporator 51 may be about the same or perhaps slightly higher, for example about 820 F. These desirably low temperatures'in the evaporators may be attained by proper introduction of cooling oils through the lines shown on the drawings.

With the connections shown the pressure in the fuel oil flash tower 98 will necessarily have to be at least as high as the pressure in the lower portion of the viscosity breaker evaporator 51, in order to insure the fiow of vapors from this flash tower to the evaporator. This pressure is suitably about 27 pounds per square inch, when the pressure in the vis-breaker evaporator is about 25 pounds per square inch. If desired, the pressure in the fuel oil flash tower may be held lower than that in the viscosity breaker evaporator and in this event the vapors passing overhead from the fuel oil flash tower may be ,condensed and the.

condensate may be pumped into the viscosity breaker evaporator, the condensing and pumping being carried out by means not shown on the drawings.

While I have described a particular embodiment of my invention for the purposes of illustration, it should be understood that various modifications and adaptations thereof may be made within the spirit of the invention as set forth in the appended claims.

I claim:

.1. The process of treating hydrocarbon oil which comprises passing relatively heavy oil through a cracking zone wherein it is raised to a cracking temperature and subjected to conversion, introducing the resulting cracked products into a first separating zone wherein vapors separate from liquid residue, subjecting said vapors to fractional condensation in a first fractionating zone to form a clean condensate cracking stock, introducing condensate so obtained into a second fractionating zone wherein it is subjected to contact with hot vapors, removing reflux con-.

densate, including unvaporized portions of the said clean condensate stock, from said second fractionating zone, passing it through a second cracking zone wherein it is raised to a cracking temperature and subjected to conversion, introducing the resulting cracked products into a. second separating zone wherein vapors separate from liquid residue, passing said vapors into said second fractionating zone, removing said liquid residue from said second separating zone, introducing residue so removed into a low-pressure flashing zone wherein a further separation of the vapors from unvaporized residue takes place, introducing constituents so vaporized in said flashing zone into contact with vapors separated in said separating zone first-mentioned for further treatment therewith, withdrawing unvaporized residue from said flashing zone and removing fractionated vapors from said second fractionating zone and condensing them as a desired product.

2. A process in accordance with claim 1 wherein relatively heavy charging oil is introduced into contact with vapors separated in said first separating zone, whereby said heavy oil is raised in temperature anda portion of said vapors are condensed, resulting heated oil and condensed portions of the vapors are removed, free from residual constituents resulting from the firstmentioned cracking step, and oil so removed is utilized as saidheavy oil first-mentioned.

ture responsive valve 2I8 which is interconnected by a suitable means of any well known type, 220, to a temperature responsive means 22I which is adapted to measure the temperature of the 011 passing from the radiantly heated coil to the coil located in the convection section of the furnace, and to serve as a controller for the adjustable valve 2H, whereby when the temperature of the oil passing through 22l rises beyond the desired value, the valve 2 l9 will be closed somewhat to reduce the furnace temperature and establish equilibrium, and vice versa. coils representing the parallel paths through which pass the divided streams of viscosity breaker charging stock, are located in a common combustion chamber only a single control mechanism H9, 220, MI is necessary.

The back pressure on the coils of the primary cracking furnace 62 may be regulated by means of control valve 222, which is adapted to serve as a pressure reducer whereby the pressure at the outlet of the convection furnace can be held higher than the pressure maintained in the viscosity breaker evaporator if desired. A similar control valve 223 is arranged in the transfer line leading from the. vapor phase heating coil to the vapor phase soaking drum 82 whereby the back pressure on that heating coil can be controlled with respect to the pressure maintained in the soaking drum. The valve I95 performs a similar function for the naphtha reforming coils.

While ordinarily the stabilized gasoline may be drawn directly from the base of the tower through line l3? for use bydtself or as a; blending constituent, it may be desirable to separate this stabilized gasoline into light and'heavy naphtha, so as to be able to form, by blendingthese separate constituents, gasoline having certain specific characteristics. This may be accomplished by withdrawing stabilized gasoline from the base of the stabilizer tower 22% through line 225 and passing it into a lower level in a naphtha flash tower 224% wherein separation thereoi into vapors and unvaporized heavy naphtha takes place, under a reduction in pressure brought about by pressure reducing valve 22?. The amount i pressure reduction depends upon the separation of the gasoline into light and heavy naphtha, desired. Ordinarily, if the pressure in. the stabilizer 22 i is about 350 pounds per square inch, the pressure in the naphtha flash tower may be about 70 pounds per square inch. The light naphtha passes upwardly through the naphtha flash tower in vapor form around baffle plates or other contacting elements of a well known character, whereby partial fractionation thereof occurs. The resulting fractionated light naphtha vapors are removed from the top of the flash tower through vapor line 228 and passed through condenser 22& into receiver 230, a portion of the resulting distillate being returned to the top of the fiash tower through the agency of line 23i and pump 232, as a refluxing medium. The remainder of the distillate may be withdrawn through conduit 233 to storage for blending or any other desired use. Any light vapors or gases collecting in the receiver 230 pass 0d through gas vent pipe 234 and may pass to the fuel gas line of the system. The heavy naphtha collects in the base of the naphtha flash tower and is removed therefrom through connection 235 and indirect heat exchanger I2I to storage for blending or for any other desired use.

The final desired gasoline distillate is preferably formed by blending the depropanized gas- Since both of the oline derived from the base of the depropanizing tower 28 with light and heavy naphtha from the draw- oil lines 233 and 235, the relative quantitles of the distillate making the blend, being selected to give the desired characteristics.

Various valves on the drawings not specifically referred to are for obvious control purposes. Additional lines may be provided for adding stocks or withdrawing them from various parts of the system to establish balanced operating conditions.

The actual operating conditions maintained in operating the system as described herelnbefore, will obviously depend upon the character of the charging stock and the character of the desired final products. As a general rule the crude oil, in passing through the indirect heat exchangers and through the preliminary heating coil in the furnace I3, is raised only to a distilling temperature without being subjected to cracking, whereby any of the constituents removed from the crude flash tower will be of a virgin nature. The temperature of the oil after being preheated and at the point of introduction into the crude flash tower may be, for example, in the neighborhood of 600 F. more or less, and the pressure thereon is usually relatively low, e. g. less than 100 munds per square inch, say about pounds per square inch, but it may be higher than 160 pounds. The temperature and the pressure of the crude oil may vary considerably from the values given, the temperature being raised or lowered depend ling on the amount of vaporization desired to take place in the crude flash tower, and the pressure being varied accordingly. In the primary cracking or viscosity breaking furnace the cracking conditions of temperature, pressure and time are so selected as to prevent deleterious deposition of coke in the heating coils and these conditions will therefore depend upon the exact character of the charging stock passing through the heating coils. However, as a rule, it is desirable to maintain the amount of cracking to products in the gasoline boiling range per pass, in the neighborhood of 6% to 15%, more or less, for exam-- ple about 10%, the outlet temperature of the heated oil may be varied considerably while still obtaining this percentage, the higher the outlet temperature, the shorter the time oi contact necessary. The outlet temperature may U 885 F. prior to the passage thereof into the final coil located in the convection section of the furnace, wherein the temperature may drop somewhat. The outlet pressure on the viscosity breaking heater is preferably relatively low, varying, for example, from substantially atmospheric to several hundred pounds per square inch, but preferably being about pounds per square inch. In the viscosity breaker combination tower ill the pressure is preferably about the same or somewhat lower than that at the outlet of the viscosity breaking furnace, and may be, for example, 25 pounds per square inch, or thereabouts.

The cracking conditions in the vapor phase heating coil of the furnace i3 are likewise subject to variation depending upon the character of the stock and the character of the desired products. As an example the outlet temperature may vary from 850 F. to 1000 F. more or less, preferably 14. The. process of treating hydrocarbon oil which comprises passing relatively heavy chargingoil through a first cracking zone wherein it is raised to a cracking temperature and subjected to conversion, introducing the resulting cracked products into a first separating zone wherein vapors separate from liquid residue, fractionating resulting vapors in a first fractionating zone to separate a gasoline distillate, a relatively light clean gas oil cracking stock, and a heavier gas oil stock, introducing said clean gas 011 stock into a second fractionating zone and recycling said heavy gas oil stock to said first cracking zone, withdrawing reflux condensate from said second iractionating zone, passing it through a second cracking zone wherein it is raised to a cracking temperature and subjected to conversion, introducing resulting cracked products into a second separating zone wherein vapors separate from liquid residue, passingresulting vapors from said second separating zone into said second fractionating zone, combining clean virgin gas oil cracking stock with aforesaid gasoline distillate and passing the mixture once-through a third cracking zone without recycling, wherein it is raised to a relatively high cracking temperature and subjected to conversion, introducing resulting cracked products into said second separating zone, and removing fractionated vapors from said second fractionating zone and condensing them to form a desired gasoline distillate.

15. The process of treating hydrocarbon oil which comprises passing relatively heavy charging oil through a first cracking zone wherein it is raised to a cracking temperature and subjected to conversion, introducing the resulting cracked products into a first separating zone wherein vapors separate from liquid residue, fractionating resulting vapors in a first fractionating zone to separate a gasoline distillate, a relatively light clean gas oil cracking stock, and a heavier gas oil stock, introducing said clean gas oil stock into a second fractionating zone and recycling said heavy gas oil stock to said first cracking zone, introducing aforesaid gasoline distillate into the second fractionating zone as a refluxing medium, withdrawing reflux condensate from said second iractionating zone, passing it through a second cracking zone wherein it is raised to a cracking temperature and subjected to conversion, introducing resulting cracked products into a second separating zone wherein vapors separate from liquid residue, passing resulting vapors from said second separating zone into said second fractionating zone, passing a clean virgin gas oil cracking stock once-through a third cracking zone without recycling, wherein it is raised to a relatively high cracking temperature and subjected to conversion, introducing resulting cracked products into said second separating zone, and removing fractionated vapors from said second fractionating zone and condensing them to form a desired gasoline distillate.

16. The process of treating hydrocarbon oil that comprises introducing crude petroleum into a stripping zone wherein lighter constituents separate as vapors from heavier liquid residual constituents, fractionating the separated vapors to form a clean condensate cracking stock, passing residual constituents of the crude derived from the stripping zone to a first cracking zone wherein the residual constituents are heated at a cracking temperature and subjected to conversion, introducing the resultant cracked products into a first separating zone wherein separation of vapors from residue takes place, fractionating the separated vapors in a first iractionating zone to separate out clean gas oil constituents, passing said clean condensate cracking stock from the crude stripping zone to a once-through cracking zone wherein it is heated at a cracking temperature and subjected to cracking without recycling, introducing the resultant cracked products into a second separating zone wherein separation of vapors from residue takes place, fractionating the separated vapors in a second fractionating zone to separate out a final desired distillate from higher boiling constituents, combining higher boiling constituents thus obtained with gas oil constitu-- ents from the first iractionating zone and passing the combined constituents to a recycling cracking zone wherein they are heated at a cracking temperature and subjected to cracking, separating the resultant cracked products into vapors and residue and fractionating the separated vapors in aioresaid second iractionating zone.

17. The [process of treating hydrocarbon oil that comprises introducing crude petroleum into a stripping zone wherein lighter constituents separate as vapors from heavier liquid residual constituents, fractionating the separated vapors to form a clean condensate cracking stock, passing residual constituents of the crude derived from the stripping zone to a first cracking zone wherein the residual constituents are heated at a cracking temperature and subjected to conversion, introducing the resultant cracked products into a first separating zone wherein separation of vapors from residue takes place, tractionating the separated vapors in a first iractionating zone to separate out heavy gas oil condensate and lighter gas oil constituents, recycling said heavy gas oil condensate to the first cracking zone, passing said clean condensate cracking stock from the crude stripping zone to a once-through cracking zone wherein it is heated at a cracking temperature and subjected to cracking without recycling, introducing the resultant cracked products into a second separating zone wherein separation of vapors from residue takes place, fractionating the separated vapors in a second fractionating zone to separate out a final desired distillate from higher boiling constituents, combining higher boiling constituents thus obtained with lighter gas oil constituents from thefirst iractionating zone and passing the combined constituents to a recycling cracking zone wherein they are heated at a cracking temperature and subjected to cracking,

separating the resultant cracked products into vapors and residue and fractionating the separated vapors in aforesaid second fractionating zone.

18. A process in accordance with claim 16 wherein gases are separated from distillate from the first i'ractionating zone and gases thus separated are combined with the fractionated vapors removed from the second i'ractionating zone and passed through a bed of solid adsorbent material and the'final desired distillate is formed from the resulting treated products.

PERCIVAL C. KEITH, JR.

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