US2114671A - Process for the treatment of hydrocarbon oil - Google Patents

Description

R. v. SHANKLAND ET AL 2,114,671

April 19, 1938.

PROCESS FOR THE TREATMENT OF HYDROCARBON OIL Filed May 25, 1934 INVENTORS llwllfy (W/1M0 BY RALPH H. PRICE ATTQRNEY Patented Apr. 19, 1938 2,1

UNITED STATES PATENT OFFICE PROCESS FOR THE TREATMENT OF HYDRO- CARBON OIL Rodney V. Shankland, Hammond, Ind., and Ralph H. Price, Galveston, Te'x., assignors to Standard Oil Company (Indiana), Chicago, 111., a corporation of Indiana Application May 23, 1934, Serial N0. 727,045

7 Claims. (Cl. 196-49) This invention relates to processes and appastock suitable for further cracking, preferably ratus for the treatment of hydrocarbon oil and under low pressure in the vapor phase, and a more particularly to the production of lower boilfinal distillate. The reduced crude is simultaing point oil from higher boiling point oil. neously subjected to a preliminary viscosity It is an object of our invention to provide an breaking cracking operation, such as to produce 5 improved plural stage cracking process for proclean gas oil with only a. relatively small accomducing gasoline of high anti-knock value from panying production of products in the gasoline heavier hydrocarbon oil, whereby the heavy oil boiling range, e. g. 8% to 20% per pass. The reto be treated is first subjected to a preliminary suiting cracked products are separated into-heavy 10 distilling operation wherein light clean gas oil, tar-like residue, a clean gas oil suitable for vapor 10 relatively free from coke-forming tendencies, is phase cracking and gasoline. A heavier gas oil, separated from heavier products, any gasoline not suitable for vapor phase cracking, may also constituents present in the heavy oil also being be separated if desired, and be recycled to the segregated in this operation; the light gas oil viscosity breaking cracking operation. The clean is subsequently subjected to a single pass cracking gas oil derived from the viscosity breaking oper- 15 step wherein a relatively large percentage of conation, mixed with the intermediate condensate version to products in the gasoline boiling range stock derived from the primary drastic cracking takes place rapidly under relatively high temoperation, is subsequently cyclically cracked to perature and high pressure conditions, and the completion in the vapor phase in a secondary resulting cracked products are separated into a zone at a relatively high temperature and,at 20 light final distillate and an intermediate conrelatively low pressure, the amount of cracking densate stock; the heavy residual products from to products in the gasoline boiling range, per pass, the preliminary distilling operation are subjected being lower than that taking place in the prito a viscosity breaking cracking operation wheremary zone.

in clean gas oil is produced; and this gas oil The vapor phase cracked products are either 25 in mixture with the intermediate condensate fractionated to produceaflnal distillate, and constock from the single pass cracking step, is theredensate for further recycling through the vapor after cyclically cracked to completion at relaphase cracking zone, or are combined with the tively low cracking per pass in a separate low primary or high pressure stage cracked products pressure high temperature cracking operation. for fractionation therewith. In the event that 30 If desired a heavy gas oil out may also be segrethe vapor phase or low pressure cracked products gated from the products formed by the viscosity are separately fractionated, the final distillate breaking operation, and returned, in mixture with may be combined with that produced by the a similar cut of heavy gas oil derived from the fractionation of the high pressure cracked prodsingle pass cracking step, to the viscosity breakucts resulting from the once-through cracking 5 ing operation for further conversion. operation, the gasoline derived from the viscosity In accordance with our invention the heavy breaking cracking operation, and the gasoline oil to be treated, for example crude oil, is first derived from the distilling operation, or if desubjected to a preliminary distilling operation sired other blends of the light final distillates wherein gasoline constituents, light clean gas may be made to produce a final product of de- 40 oil, and reduced crude are separated. The light sired characteristics. clean gas oil is then subjected to a drastic crack- Important conditions of this invention are that ing operation, by being passed once through a the gas oil separated in the preliminary distilprimary cracking zone at a relatively high temling operation should be so light as to be relaperature and under a relatively high pressure, tively free from coke forming tendencies, e. g., 45 whereby a large amount of conversion to products of a maximum end point in the neighborhood of in the gasoline boiling range takes place quickly, 675-700 F., the heavier ends of the charging for example, such as to produce 30% or more of stock being treated by the viscosity breaking 420 E. P. gasoline. The cracked products from operation; and that the temperatures and presthis once-through operation are thereafter passed sures of the primary and secondary cracking 50 to an evaporator tower wherein the lighter prodzones, and time of passage of the oil thereucts are separated as vapors from liquid tar-like through, should be selected to produce high residue, these lighter products being subsecracking per pass in the primary single pass quently fractionated in a bubble tower or similar zone and relatively low cracking per pass in the device to produce an intermediate condensate secondary recycling zone. The values to be used 55 depend upon the characteristics of the charging stock, the temperatures of the primary single pass zone being, for example, from 850 to 985 F., or even higher where a very clean stock, e. g., a redistilled low end point stock, is used, and the pressure being from 500 to 2000 pounds per square inch, or more. The secondary recycling zone may operate under a temperature of from 875 to 1100 F., and a pressure of from 50 to 400 pounds per square inch. The viscosity breaking cracking zone is operated under such conditions of temperature, pressure and time as to cause only a relatively small amount of conversion to products in the gasoline boiling range, per pass, while at the same time causing the cracking of the relatively heavy charging stock to produce relatively large quantities of clean gas oil cracking stock suitable for cracking in the vapor phase cracking zone. For example, the temperature may be from 840 to 890 F., preferably about 850 F., and the pressure is most suitably in the range of from 150 pounds per square inch to 300 pounds per square inch, preferably about 230 pounds per square inch. The viscosity breaking cracking operation serves to form a relatively large percentage of clean gas oil which is suitable as charging stock for the vapor phase cracking operation carried out in the secondary or vapor phase recycling cracking zone. This gas oil and also any gasoline formed are removed from the cracked products directly upon the discharge thereof from the viscosity breaking cracking zone so that in the event recycling is carried out only heavy gas oil is returned for further cracking in the viscosity breaking zone.

As a result of the drastic cracking in the primary single pass zone under high temperature and high pressure, of the light clean gas oil separated in the preliminary distilling operation, a final distillate gasoline is produced having a high anti-knock value, and the mixture of clean gas oil from the viscosity breaking operation and the intermediate condensate stock from the primary single pass cracking operation, when cyclically cracked to completion in the secondary cracking zone under high temperature and low pressure, produces a final distillate gasoline also of high anti-knock value, which may be blended with the distillate first mentioned. The anti-knock value of the final product can be increased still more by reforming virgin heavy naphtha, viscosity breaker naphtha or both, and blending resulting gasoline distillate with the other distillates mentioned.

The above mentioned and further objects and advantages of our invention, and the manner of attaining them, will be more fully explained in the following description taken in comunction with the accompanying drawing.

In the drawing, the single figure is a diagrammatic view of an oil treating system embodying our invention.

Referring more particularly to the drawing, reference numeral I indicates a charging line throughwhich fresh charge, such as Mid-Continent crude, reduced crude, heavy gas oil, or the like, is forced by pump 2, traveling through heat exchange 00115 3 and 4 having the usual control valves, into stripping tower 5, of any well known type, wherein the heavy charge is distilled in the well known manner to segregate gasoline constituents and light clean gas oil as vapors, from liquid reduced crude, or other heavy liquid oil where the charging stock is not crude oil. The gasoline vapors pass off from the top of the tower through vapor line 6 into condenser I from which the resulting condensate passes to receiver 8. The light clean gas oil, relatively free from coke forming tendencies, is condensed and collected on trap-out tray 9, to form a distillate having an end point of, preferably, from 675 to 700 F. or thereabouts, from which it is removed through pipe Ill and forced by pump H through the coils of high pressure heater l2, leaving them preferably at a temperature of about 950 F. and a pressure approximating 750 pounds per square inch, and traveling through pipe l9 into reaction chamber l4. After being soaked in the reaction chamber, the resulting cracked products pass through a conduit l5 into the base of evaporator I6, wherein separation of the cracked products takes place with the result that lighter vapors pass overhead through a vapor line H into fractionator ll, tar residuum being withdrawn through line 19. The evaporator I6 may be supplied with ballle plates or similar devices 20 which serve to prevent entrainment'of tar in the evolved vapors and with a trapout tray 2| which serves to collect heavy gas oil such asTrequires viscosity breaking treatment. The heat exchange coil 4 serves to provide cooling for refluxing purposes, or other suitable conventional refluxing means may be used if desired. This evaporator is most desirably operated at a pressure lower than that of the reaction chamber I, for example pounds per square inch, the reduction in pressure being insured by pressure reducing valve 22 located in the conduit l5 connecting the evaporator and reaction chamber. If desired the reaction chamber may be by-passed by proper manipulation of valves 23, 24, and 25. I

In the fractionator I! the vapors are separated into a light vaporous portion, e. g. gasoline vapors, which passes overhead through vapor line 29 and condenser 21, resulting condensate being collected in receiver 28, and intermediate condensate stock which is drawn oil from the bottom of the tower through a conduit 29 for treatment in the secondary cracking zone.

Reduced crude or other heavy unvaporized stock is withdrawn from the bottom of stripper 5 through pipe 30 and is forced by pump 3| through the coils of viscosity breaking heater 32. In this heater the heavy stock is subjected to cracking of a viscosity breaking nature, such, for example, as to cause a. conversion to products in the gasoline boiling range, of 8% to 20% per pass. The temperature of the oil emerging from the heater is preferably about 850 F., and the pressure thereon preferably about 230 pounds per square inch, these conditions corresponding to cracking of about 8% to 10% per pass. Higher temperature, such as 875890 F., and/or longer times of contact or heatings will be necessary to secure cracking per pass at a value as high as 20%. In the heating steps the times of passage of the oil through the heating coils are preferably such that little or no coke will be deposited therein.

The hot cracked products pass through the line 33 and control valve 34 into evaporator 25, which may be equipped with fractionating elements, such as baffles 36, or the like, the necessary reflux being supplied by any suitable means, for example, cooling coil 31. In this vessel, which may be held at the same or lower pressure than the coils of viscosity breaking heater 92, the hot cracked products separate into vapors which pass off overhead through vapor line 38 into fractionator 39, and liquid residue which is withdrawn through line 40. In the fractionator 39 the introduced vapors are subjected to fractionation in the usual well known manner, vapors of the desired end point, e. g. gasoline, passing overhead through line 4| into condenser 42 and resulting condensate being collected in receiver 43. Cooling for refluxing purposes may be supplied in any suitable manner, for example by means of the heat exchange coil 44. Reflux condensate, being clean gas oil, is withdrawn from the base of the fractionator 39 through pipe 45 and is forced by pump 46 through the coils of secondary vapor phase heater 41, in mixture with the intermediate condensate withdrawn from the base of fractionator l8 through pipe 29. The hot cracked products emerge from the coils of the secondary va-- por phase heater 41 at a vapor phase cracking temperature of preferably more than 900 F., for example 950 F., under a relatively low pressure such as 175 pounds per square inch, and pass through transfer line into reaction chamber or digester 56, preferably under substantially the same pressure. The amount of cracking per pass through the secondary vapor phase cracking zone is preferably lower than that in the primary cracking zone, most suitably around 18%, although it may range from 10% to 25%. Part or all of this cracking may take place in the heater 41 itself, the digester 56 being by-passed if desired, by operation of valves 51, 58, and 59. The digested products pass from the reaction chamber through vapor line and reducing valve 5| into evaporator 62. The evaporator is preferably maintained at a pressure considerably lower than that of the reaction chamber, for example, 50 pounds per square inch. The evaporator 35 may be provided with a trap-out tray 41 for collecting heavy gas oil which should be subjected to further viscosity breaking treatment. This condensate is withdrawn through line 48 and forced by pump 49 through the coils of viscosity breaking heater 32, in mixture with the reduced crude from stripper 5, and also heavy condensate withdrawn from trap-out tray 2| of evaporator I5, by way of conduit 50 having pump 5|. If desired additional viscosity breaking cracking may be accomplished by means of a reaction chamber 52 which may be placed in operation by proper adjustment of valves 34, 53, and [4. This reaction chamber is particularly useful in obtaining the higher percentages of cracking per pass mentioned hereinbefore.

Light vapors pass off from the top of the evaporator 62 through vapor line 63, which introduces them into the base of fractionator 64, while liquid tar residue collecting in the bottom of the evaporator is withdrawn through draw-off line 55. In the fractionator 64 the vapors are separated into a light vapor fraction of the desired end point, e. g. gasoline, which passes through the vapor line 66 into condenser 61, the resulting condensate being collected in receiver 68, and reflux condensate which collects in the base of the fractionator. Distillate deposited in the receiver 68 has the desired end point and may either be used separately or be blended with the distillate from the receivers 8, 28, and 43, or some of them, the lines 69, 10, II, and 12 being provided for this purpose, resulting blended distillate being collected in storage drum 13 if desired. Draw-off lines 14, I5, 16, and 11 are furnished so that the several distillates may be drawn oif individually. Reflux condensate is withdrawn from the base of the fractionator 64 through conduit 18 having pump 19, preferably being forced through the coils of the secondary heater 41, along with charge introduced either through line 45 or line 29 or through both, this recycling of the reflux condensate serving to cause additional cracking thereof.

Reference numerals 80, 9|, and 82 indicate draw-off lines whereby, if desired, quantities of condensate collecting in the iractionators I8, 39, and 64, respectively, may be diverted from the process in order to establish any selected balance of conditions. These condensates are suitable as distillate fuel oil, or may be used in cutting tars drawn off from the process, to desired viscosity for use as fuel oil. In place of the cooling coils in the various towers or in cooperation with the coils, direct cooling may be employed by pumping back distillate or other cooling mediums in the-customary manner, by suitable means (not shown). Cross-over line 84 and valves 85 and 86 are provided so that the evaporator 35 and fractionator 39 may be cut out of circuit, the cracked products from the viscosity breaking zone being passed directly to the evaporator l5, if desired. This flow, which may be accomplished by closing valve 85 and opening valve 85, results in the liquid residues and heavy gas oils and light gas oils from the primary high pressure cracking operation and viscosity breaking cracking operation being combined and treated as a mixture. No further description of this alternative method of operation seems necessary. In like manner the fractionator 39 alone may be eliminated, evaporator 35 still being used, by closing valve 95 and opening valve 96 incross-over line 91, thereby directing the vapors from evaporator 35 into fractionator l8.

Instead of utilizing two difierent fractionators for the primary high pressure and the secondary vapor phase portions of the systems a single fractionator alone may be used, cross-over line 81 being provided so that vapors from the evaporator 62 can be directed into fractionator l8. When this manner of operation is desired valve 88 is closed and valve 89 is opened. When operating in this manner the final distillates from both the primary high pressure system and the secondary vapor phase system are collected together in the receiver 28. Even more apparatus may be eliminated if separate residue draw-off lines are not desired, by introducing the digested products from reaction chamber 56 directly into evaporator Hi, this operation being effected by means of crossover line 90 and valves 9| and 6|. Upon closure of valve 6|, and opening of valve 9| the vapor phase digested products are diverted into the evaporator l6. This manner of operation causes the mixing of the residues from both the secondary vapor phase cracking operation and the primary high pressure cracking operation, the mixed residue being withdrawn through line |9.

Additional light clean oil for cracking in the primary high pressure heater I2 may be supplied through charging line 93, this oil being for example, a light virgin gas oil from an external source. Additional heavy oil may be supplied to the viscosity breaking operation from an external source through line 94,

In order to obtain increased anti-knock value of the final gasoline distillate of the process, a cut of heavy virgin naphtha may be removed from the stripper 5, after having been collected on trap-out tray I00, and passed by way of line |0| through a separate reforming coil located in the secondary vapor phase furnace 41, in which it is subjected to a conventional reforming operation,

for example one carried out at a temperature in excess of 950 F. and a pressure of, for example, 700 pounds per square inch or more. The resulting reformed products may be passed into the evaporator 52 through line I having pressure control valve I05. If desired vis-breaker naphtha may be collected on a trap-out tray I02 in the fractionator 39 and passed through line I03 into the reforming coil in the furnace 41, either alone or in mixture with virgin heavy naphtha collected on the trap-out tray I00 of the stripper I. The illustrative temperature and pressure given for the reforming operation are not intended to be taken as invariable since different conditions of temperature and pressure may be used for producing different degrees of reformation. The reforming coil might also be located in either of the furnaces l2 or 32, or in a separate furnace if desired, the only requisite being that the necessary temperature be attained. Alternatively the reforming coil might discharge into one of the other evaporators of the system.

Operation In operation heavy charging stock such as crude oil, reduced crude or heavy gas oil, e. g., 37 A. P. I. Mid-Continent crude, is preheated 'to a distilling temperature in any suitable manner, for example by passage through the heat exchange coils 3 and 4 in fractionator I5 and evaporator l6, respectively, and is then subjected to a conventional stripping operation, for example in a tower such as 5, with the resulting segregation of the crude or other charging stock, into reduced crude or other liquid residue, which collects in the base of the stripper tower 5, a light clean gas oil condensate, preferably having an endpoint of from 675-700 R, which collects on trap-out tray 9 and may be introduced directly into the primary high-pressure heater i2 by way of line i0, and a light distillate of lower boiling characteristics than desired for treatment in the high-pressure heater. This light distillate, which is collected in receiver 3, would fall in the gasoline boiling range.

The reduced crude or liquid residue collecting in the base of the stripper tower 5 is withdrawn through line 30 and introduced into the coils of viscosity breaking heater 32. In this heater the heavy reduced crude is cracked sufliciently to produce from 8% to 20%, e. g., 8% to 10%, of products in the gasoline boiling range, and resulting cracked products are introduced into the evaporator 35, after passage through the reaction chamber 52, or not, as desired. The cracking conditions in the heater 32 may be a temperature of from 840 to 890 F., preferably about 850 F., and a pressure of from 150 to 300 pounds per square inch, preferably about 230 pounds per square inch. The desired amount of cracking may be accomplished partially in the viscosity breaking heater and partially in the reaction chamber 52, or wholly in the heater alone, the reaction chamber being by-passed and correspondingly higher temperatures being employed in heater 32. In the evaporator, which may be held at the same or a lower pressure than that of the heater, the roducts separate into vapors and a liquid residue, the former passing upwardly through the tower and being partially fractionated therein, while the latter is withdrawn from the bottom of the tower through line 40. The partially fractionated vapors pass through vapor line 38 into fractionator 39, wherein they are completely fractionated in the usual manner, the

fractionated vapors passing off from the top thereof and being collected in receiver 43 as a gasoline distillate suitable for blending to produce a final desired product. A side out of heavy gas oil collects on trap-out tray 41' and is preferably recycled through the viscosity breaking heater 32 for further conversion.

The light clean gas oil withdrawn as a side stream from stripper 5 passes through the primary high pressure cracking heater l2, which operates on a once-through basis without recycling. Inthis heater the oil is subjected to a high temperature, preferably in excess of 900 F., e. g., 950 F., under a high pressure such as 750 pounds per square inch, and the heated products are then transferred to the reaction chamber I wherein additional conversion takes place, the conditions of temperature and pressure already mentioned being regulated to cause cracking to an extent of from 35% to 55%, or more, per pass through the heater and reaction chamber, or heater alone if the reaction chamber .be bypassed, for example 45 or After leaving the reaction chamber the cracked products pass to the evaporator IS, the pressure in the evaporator being held at a lower value, which may approximate 125 pounds per square inch, by action of pressure reducing valve 22 in the transfer pipe l5 through which the products travel from the reaction chamber to the evaporator.

In the evaporator the introduced products, being under lower pressure and at a suitable temperature such as 800 to 825 F., separate into a vapor portion which passes overhead through vapor line H into fractionator i8, and a,liquid residue portion which is drawn of! through pipe is. The fractionator II is provided with bubble plates and caps or similar fractionating devices, and serves in the well known manner to separate the vapors into an intermediate reflux condensate suitable for further cracking which collects in the base of the fractionator, and a light vapor portion, e. 8. gasoline, having the desired boiling characteristics, which passes overhead and is then condensed and collected in receiver 28.

The intermediate condensate oil is drawn off through the conduit 29 and, in mixture with reflux condensate from the base of fractionator 39, is passed through secondary vapor phase cracking heater 41, wherein it is raised to a temperature preferably in excess of 900 F., for example 950 F., under a relatively low pressure such as 175 pounds per square inch, which is preferably the same as that prevailing in the digester into which the cracked products are subsequently introduced. The amount of cracking per pass through the vapor phase system is relatively low, preferably around 18%, although the conversion may range from 10% to 25%. The hot cr'acked products pass from the secondary vapor phase heater into digester or reaction chamber 55, and

there undergo further conversion, the digested products being passed through line into evaporator 52. which is maintained at a still lower pressure, such as 50 pounds per square inch, by action of the pressure reducing valve Si. Alternatively digester 56 may be bypassed by opening valve 53 and closing valves 51 and 59. Light vapors travel from the evaporator through vapor line 63, which introduces them into the bottom of fractionator 64, while the liquid tar residue collecting in the base of the evaporator is removed through line 55.

In the fractionator 5| the vapors are separated into a light fraction of the desired boiling characteristics, which passes of! from the top thereof and is collected as a distillate of desired end point, or of desired blending characteristics, e. g. gasoline, in receiver 68, and a reflux condensate that collects in the base of the fractionator. This reflux condensate is preferably recycled through line 18 for further cracking in the heater 41.

Additional heavy charging stock may be introduced through line 9| and additional light clean charging stock may be introduced through line 93, if desired, both of these stocks being derived from external sources. Likewise, portions of the reflux condensate from fractionators I8, 88, and 64 may be diverted from. the process through lines 80, 8|, and 82 to effect any desired balance of operating conditions. The several light gasoline distillates formed in the different parts of the combined process may be withdrawn seperately or may be blended to produce a gasoline of predetermined characteristics, the blending being accomplished by way of lines 88, 18, 1|, and 12, the blended distillate being collected in gasoline storage drum 18.

Instead of using separate evaporators and fractionators for the secondary vapor phase stage as assumed in the preceding description of the operation. valve 8| may beclosed and valve 9| opened thereby directing all of the products into evaporator ii. In this event all of the gasoline from both of these stages would be collected in receiver 28. Instead of using a single evaporator, the secondary vapor phase products may be permitted to pass into evaporator 82 and the vapors therefrom may be diverted into the fractionator I8 by the closing of valve 88 and opening of valve 89. This latter method of operation would eliminate one fractionator and its accessories, while permitting the drawing of! of tar'separately from each stage. A further reduction in the quantity of apparatus used may be effected by diverting the viscosity breaker products into the evaporator i8, this being accomplished by closing valve 88- and opening valve 88. Alternatively the evaporator 85 may be utilized and the fraotionator 88 eliminated, by closing valve 95 and opening valve 98. This arrangement of crossover pipes and valves permits flexible operation of the system, enabling separation and fractionation to be carried out inseparate towers or permitting the viscosity broken products to be treated with the high pressure cracked products and with the vapor phase cracked products, or enabling the viscosity broken products to be treated separately and the high pressure cracked products and the vapor phase cracked products treated together.

The tar withdrawn from the several evaporators through draw-off lines i9, 40, and 85 may be cut back with condensate stock withdrawn through any of draw-off lines 80, 8i, and 82, if desired, the condensate withdrawn through line 82 from the base of fractionator 8| being particularly suitable for this purpose. When operating in this manner heavier tars may be produced in the evaporators i8, 35, and 52, while still permitting the formation from these heavy tars of fuel oil of desired viscosity. Alternatively the condensate stocks withdrawn may be used sepa rately as light distillate fuels.

If desired heavy virgin naphtha from trap-out tray I in stripper or heavy via-breaker naphtha from trap-out tray I02 of fractionator 89 may be subjected to reformation either individually or in mixture, by passage through the reforming coil located in one of the several furnaces shown, for example-in furnace ",or in a separate furnace if desired. In passage through this reforming coil the naphtha is raised to a suitable reforming temperature, for example, a temperatureof from 950 to 1050" F., under a pressure of, for example, 500 pounds to 1000 pounds per square inch, more or less, the resulting reformed products being introduced into the evaporator 82, after having been reduced in pressure if desired, by action of reducing valve I05. Alternatively, the reformed products might be introduced into one of the other evaporators.

Our invention as described hereinbefore permits the production from relatively heavy charging stock having. marked coke-forming tendencies, of a relatively large quantity of high antiknock gasoline, the preliminary distilling step serving to produce a relatively clean cracking stock of small coke-forming tendencies suitable for very high cracking per pass in the primary high pressure stage wherein, since the cracking is carried out under high pressure and high temperature gas production is minimized as a result. Likewise as the cracking is done rapidly tar does not have much chance to form. In the subsequent cracking of the intermediate condensate from the high pressure stage, in the following secondary vapor phase stage, tar formation'is still further retarded and, since a large part of the lighter products produced has already been removed in the high pressure operation, the total loss of desired distillate due to the secondary cracking is small, being essentially only that which occurs in the low pressure cracking operation. The viscosity breaking step permits the heavy residual stock which is undesirable from a coke-forming viewpoint for treatment in the primary high pressure heater, to be converted into cracking stock suitable for further conversion in the vapor phase in mixture with the intermediate condensate from the primary cracking operation.

The expression. "cracking per pass used throughout this specification refers to the percentage of conversion to end point gasoline of the stock passing into the conversion zone, in a single pass therethrough.

This specification describes certain specific embodiments of our invention but the scope of the invention is not intended to be limited thereto except as set forth in the accompanying claims.

Thus, we may obtain higher cracking per pass.

in the primary cracking stage than that set forth, particularly when using higher pressure, such as pressures of 1500-2000 lbs. per square inch. These high degrees of conversion are a distinctive feature of our invention and to them we ascribe in large measure the success of the process.

We claim:

1. The process of treating hydrocarbon oil which comprises heating crude oil to a distilling temperature to cause vaporization of lighter constituents thereof and leave liquid reduced crude, fractionally condensing the vaporized lighter constituents to segregate a heavy naphtha condensate, and a light clean gas oil condensate relatively free from coke-forming tendencies, heating said clean gas oil condensate to a relatively high cracking temperature in a primary cracking zone under relativelyhigh pressure, for a sumcient length of time to cause a high degree of cracking thereof, separating resulting cracked products into vapors and a liquid residue, in a first separating zone, fractionatlng said vapors to 15 form a desired gasoline distillate and an intermediate gas oil condensate, preventing the return of said intermediate condensate to said hightemperature cracking zone, simultaneously pass ing said reduced crude first-mentioned through a viscosity breaking cracking zone wherein it is raised to a moderate cracking temperature and subjected to a viscosity breaking cracking operation, separating the resulting lightly cracked products into vapors and a liquid residue, fractionating said vapors to form a desired gasoline distillate and reflux condensate, combining said intermediate condensate and said reflux condensate, and passing the mixture through a secondary vapor phase cracking zone wherein it is raised to a vapor phase cracking temperature and subjected to a moderate amount of cracking per pass, introducing the resulting moderately cracked products into a second separating zone wherein separation thereof into vapors and a liquid residue occurs, fractionating said vapors to form a desired gasoline distillate and a reflux condensate, returning said refiux last-mentioned to said secondary vapor phase cracking zone for further cracking, simultaneously passing said heavy naphtha condensate through a separate reforming zone wherein it is raised to a cracking temperature and subjected to reformation, and introducing the resulting reformed products into said second separating zone.

2. The process of treating hydrocarbon oil which comprises heating crude oil to a distilling temperatureto cause vaporization of lighter constituents thereof, including light clean gas oil, and leave liquid reduced crude, condensing said light clean gas oil to form a clean charging stock, relatively free from coke-forming tendencies, heating said clean charging stock to a relatively high cracking temperature in a primary cracking zone, under relatively high pressure, for a sufiicient length of time to cause a high degree of cracking thereof, separating resulting cracked products into vapors and a liquid residue, in a first separating zone, fractionating said vapors in a first fractionating zone to form a desired gasoline distillate and an intermediate gas oil condensate, preventing the return of said intermediate condensate to said high-temperature cracking zone, simultaneously passing said reduced crude first-mentioned through a viscosity breakingcracking zone wherein it is raised to a moderate cracking temperature and subjected to a viscosity breaking cracking operation, separating the resulting lightly cracked products into vapors and a liquid residue, in a second separating zone, fractionating said vapors in a second fractionating zone to form a desired gasoline distillate, ,a heavy naphtha condensate and a clean gas oil condensate, combining said intermediate condensate and said clean gas oil condensate and passing the mixture through a secondary vapor phase cracking zone wherein itis raised to a vapor phase cracking temperature and subjected to a moderate amount of cracking per pass, separating the resulting moderately cracked products into vapors and a liquid residue in a third separating zone, fractionating said vapors in a third fractionating zone to form a desired gasoline distillate and a reflux condensate, and simultaneously passing said heavy naphtha condensate through a separate reforming zone wherein it is raised to a cracking temperature and subjected to reformation and introducing the resulting cracked products into said third separating zone.

3. The process of treating hydrocarbon oil which comprises passing a relatively light clean gas oil through a primary cracking zone wherein it is raised to a relatively high cracking temperature and subjected to conversion, introducing the resulting cracked products into a separating zone wherein vapors separate from liquid residue, passing resulting vapors to a first fractionating zone wherein fractional condensation thereof occurs and constituents heavier than desired in the final product are condensed as a reflux condensate, removing the fractionated vapors and condensing them as a desired product, simultaneously passing a relatively heavy oil, not suitable for use as clean cracking stock, through a viscosity breaking 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 the resulting vapors into a second fractionating zone wherein fractional condensation occurs with the formation of a heavy naphtha condensate and a gas oil condensate, removing the fractionated vapors and condensing them as a desired product, removing reflux condensate from said first fractionating zone and gas oil from said second fractionating mne, combining them and passing the mixture through a secondary cracking zone wherein it is raised to a cracking temperature and subjected to conversion, introducing the resulting cracked products into a third separating zone wherein vapors separate from liquid residue, fractionating the resulting vapors to form an additional quantity 01' final desired distillate, and simultaneously passing said heavy naphtha condensate through a separate reforming zone wherein it is raised to a cracking temperature and subjected to conversion, and introducing the resulting reformed products into said third separating zone.

4. A process in accordance with claim 3 wherein the vapors separated in said third separating zone are fractionated in a fourth fractionating zone.

5. A process in accordance with claim 3 wherein the vapors separated in said third separating zone are fractionated in said first fractionating zone.

6. A process in accordance with claim 3 wherein the vapors separated in said third separating zone are fractionated in a third fractionating zone wherein a refiux condensate is formed and said reflux condensate is recycled through said secondary cracking zone for further conversion.

7. A process in accordance with claim 3 wherein during the fractionation of the vapors separated in the first separating zone a relatively heavy condensate is formed and this condensate forms a source of the relatively heavy oil passed through the viscosity breaking cracking zone.

RODNEY V. SHANKLAND. RALPH H. PRICE.

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