US2119409A - Process for the treatment of hydrocarbon oil - Google Patents

Description

May 31, 1938.

R. L. ZIMMERMAN PROCESS FOR THE TREATMENT OF HYDROCARBON- OIL Filed April 1B, 1954 d-m m10 OIL CHICK/IVG FUHNACE Patented May 31, 1938 UNETED STATES Z,li9,409

PATENT cerise PROCESS FOR THE TREATMENT OF HY- DROCARBON OIL Application April 18, 1934, Serial No. 721,070

3 Claims.

This invention relates to processes for producing gasoline or other relatively light distillates from relatively heavy charging stock such as crude oil, reduced crude, or the like.

5 It is an object of my invention to provide an improved process for the production of gasoline or other light distillates from crude petroleum oil according to which the crude oil is rst subjected to a stripping operation wherein any virgin gasoline, gas oil, and any other desired light products may be removed, leaving reduced crude; the reduced crude is subjected to a viscosity breaking cracking operation to form a relatively large amount of clean cracking stock and a small amount of gasoline; the light clean gas o-il cracking stock is subjected to a separate cracking operation to form a relatively large amount of gasoline or other light distillate, and the heavy tar resulting from these cracking operations is subjected to a flashing operation to form a heavy flash distillate which is also separately subjected to a cracking operation to form lighter products, including gasoline or other light distillates and relatively light clean cracking stock which is subjected to further cracking in the unit. When reduced crude or the like is charged the preliminary stripping step may be omitted.

In accordance with my invention fresh charging stock, such as crude petroleum oil, is rst preheated, for example by heat exchange with products of subsequent cracking, and then introduced into a crude flashing zone wherein the lighter products contained in the crude, such as gasoline and gas oil, are separately removed and 5 condensed and the remaining liquid reduced crude is withdrawn and passed through a viscosity breaking heater or furnace wherein it is raised to a cracking temperature and subjected to a moderate degree of cracking sufli'cient to form a relatively large amount of clean cracking stock, without at the same time causing deleterious coking. The resulting products of conversion are then introduced into an evaporating zone wherein vapors separate from liquid residue; these vapors are then removed and subjected to fractionation to form the desired final distillate, e. g. gasoline, and a reilux condensate which is clean and suitable for cracking to produce more gasoline, for example in the vapor phase. This condensate is passed through its own individual cracking furnace wherein it is raised to a cracking temperature and subjected to conversion to produce a relatively large amount of products in the desired boiling range, for example, in the gasoline boiling range, and the resulting cracked products are then introduced into the evaporating zone with the products from the viscosity breaking operation. The liquid residue remaining unvaporized in the evaporating zone is withdrawn and introduced into a zone of low pres- 5 sure wherein flashing thereof takes place with the resulting separation of the tar into lighter vaporous products and heavier unvaporized residue. The vapors are removed and condensed and passed through an individual cracking furnace wherein they are subjected to the proper cracking conditions for their conversion into lighter products, including relatively light distillate such as that forming the nal product, and a heavier but still clean distillate suitable for cracking with the condensate formed in the fractionating operation already mentioned. The resulting products of conversion are introduced into the evaporating zone with the viscosity broken products and the vapor phase cracked products.

By operating in this manner the heavy flash distillate, derived from the liquid tar removed from the evaporating zone, may be separately treated under conditions adapted for its conversion into lighter products, without serious trouble from the formation of coke. By separately treating this objectlonably dirty stock of marked coke forming tendencies, it is possible to maintain the unit on stream for a longer period of time and with greater ei'ciency of operation than would be possible if this relatively heavy flash distillate were combined with the vapors from the evaporating zone already mentioned, for fractionation. When the flash distillate derived from the flashing of the tar from the evaporating zone is combined with the light clean distillate formed by fractionating of the vapors from the evaporating Zone the resulting mixture must be more lightly cracked than is possible when the clean distillate from the fractionating zone alone is treated, since the heavy flash distillate derived from the tar has stronger coke forming tendencies than the light clean distillate formed by the fractionating operation. By eliminating this heavy flash distillate from the cracking zone and treat- 45 ing the relatively light clean condensate it is possible to extend the period of operation of the unit and also increase its output. A further advantage is that the anti-knock value of the final desired distillate may be increased by operating in this manner.

The above mentioned and further objects and advantages of my invention and the manner of attaining them will be explained more fully in the following description taken in conjunction with the accompanying drawing:

In the drawing the single figure represents dlagrammatically an oil cracking system embodying my invention.

Referring more particularly to the drawing reference numeral I indicates a charging line through which fresh charging stock, such as crude petroleum oil, is forced by pump 2 after having been preheated in some suitable manner, as, for example, by passage through heat exchange coils, such as 3 and fl, in other parts of the system, and then introduced into the crude flash tower 5, wherein the preheated charging stock separates into vapors and liquid residue. The vapors travel upwardly through the tower, those of lighter character passing off from the top thereof through vapor line 6 and condenser 'I and the resulting condensate being collected in receiving drum 8. This condensate may be, for example, gasoline. An intermediate condensate, such for example, as clean gas oil suitable for cracking in the vapor phase, is withdrawn from an intermediate point in the crude flash tower through line 9, and passed into gas oil receiving drum I0, from which it is withdrawn through line II and forced by pump I2 to other parts of the system, as will be explained more fully hereinafter, The unvaporized liquid reduced crude is Withdrawn from the base of the crude flash tower 5 through line I3 and is forced by pump I4 through the coils of viscosity breaking heater or furnace I5, wherein it is subjected to a preliminary light cracking operation of a viscosity breaking nature, such as produce light clean gas oil relatively free from coke forming tendencies, with only a relatively small accompanying production of products in the gasoline boiling range, for example 5% to 12% of the latter products per pass. The temperature of the oil emerging from the heater is preferably about 850 F. and the pressure thereon preferably about 230 lbs. to 400 lbs. per square inch. The hot cracked products pass through line I6 into evaporator I1, or alternatively may be rst subjected to further cracking or digestion in reaction chamber I8, by proper manipulation of valves I9, 20, and 2|.

lin the vessel I 1, which may be held at the same or a lower pressure than the coils of the heater i5, the hot cracked products separate into vapors which pass off overhead, and a liquid residue. This residue is removed through line 22, having reducing valve 23 and introduced into ilash drum or tower 24, which is held under considerably lower pressure, for example substantially atmospheric pressure. Partial vaporization of the residue takes place in the drum 24 as a result of the reduced pressure, and the vapors move upwardly through the tower, cooling being supplied in any suitable manner, for example by means of cooling coil 25, to give the desired refluxing action. The amount of cooling supplied by the coil 25 or in any other corresponding manner is preferably kept relatively low, so that the amoimt of distillate flashed off overhead from the liquid residue will be relatively great, leaving a very heavy tar-like residue in the bottom of the flash tower. The amount of cooling supplied can be regulated to give the desired characteristics to the residue remaining unvaporized in the bottom of the fiash tower or drum. It is possible when operating with a system in accordance with the present invention to ash off a greater amount of stock than would be possible where all of the flash distillate is subjected to cracking in a common coil with some lighter other oil of lesser coke forming tendencies, the reason being that the heavy flash distillate in the present case is subjected to cracking in its own separate cracking zone under conditions which may be regulated to give the desired conversion without deleterious coke formation. The flashed vapors pass off overhead through vapor line 26 and condenser 21, the resulting condensate being collected in receiving drum 28, which is provided with the usual gas draw-off line 29 and liquid draw-off line 30. The liquid residue remaining in the bottom of the fuel oil flash tower 24 may be withdrawn through valved line 3|, and diverted from the process.

The vapors separated in the evaporator I'I pass upwardly therethrough and are subjected to any desired amount of refluxing, in the usual manner, by cooling supplied through the agency of indirect cooling coil fi, and/or by refluxing liquid introduced through line 32, as will be explained more fully hereinafter. The vapors remaining uncondensed pass olf from the top of the evaporator through vapor line 33 into the fractionator 3/5, wherein they undergo fractionation in the usual manner, the vapors passing upwardly through bubble trays or other suitable fractionating elements, against a downwardly flowing stream of reflux condensate formed by the cooling action of indirect cooling coil 3, and/or by the introduction of reiluxing liquid through line 35. The vapors remaining uncondensed pass off from the top of the fractionator through the vapor line 3S and condenser 3l', the resulting condensate collecting in receiver 38, which is provided with the usual gas draw-off line 39 and distillate draw-ofi line 40. The distillate so collected is a iinal desired product, for example, gasoline. Reflux condensate formed in the fractionator 3d collects in the bottom thereof and is removed through line iiI and forced by pump 42 through the coils of light gas oil cracking furnace 44.

In the cracking furnace 4l! the clean condensate oil is subjected to any conventional type of cracking operation, but is preferably subjected to cracking in the vapor phase, for example at a temperature of less than l050 F. and more than 900 F., most desirably about 925 F. to- 975 F. and at a pressure of from 100 to 400 lbs. per square inch, most desirably to 225 lbs. per square inch. The cracking to gasoline per pass is preferably in the neighborhood of 15% to 20%, the vgreatest part of this conversion being effected at temperatures above 850 F. These moderate cracking conditions are advantageous since they have been found to produce a relatively high anti-knock gasoline without the simultaneous formation of excessively large amounts of fixed gas or heavy products such as tar or coke; however, other cracking conditions may be utilized as mentioned hereinbefore, for example such as to produce from 25% to 30% of gasoline per pass. The resulting cracked products may be passed directly through line 45 into evaporator II, but preferably additional cracking is obtained by passing the cracked products from the furnace 44 through line 46 into reaction chamber 41 wherein further soaking and conversion takes place. This method of operation may be obtained by proper manipulation or control valves $8, A9, and 50.

The evaporator Il is preferably maintained under substantially the same pressure as that oi' the soaking drum or reaction chamber [il and a singledistillate which would then be pumped through the cracking furnace 53, similarly to the single product from the receiving drum 28 as shown.

The segregation might be still further carried out by adding separate fractionators which would treat the vapors removed from each of the additional evaporators, the reflux condensate from the several fractionators being combined in any desired ratio and the overhead vapors being condensed to form a common blended distillate. It might also be desirable in certain cases to reform the natural gasoline collected in the receiver 8 or to reform merely the heavier ends thereof, this being effected by passing the gasoline or its heavier ends through a conventional reforming furnace wherein it is subjected to a reforming temperature adapted to increase its anti-knock value, the resulting reformed products being introduced into the evaporator Il along with the cracked products from the furnaces 44, 53, and I5. In other instances it might be desirable to treat reduced crude derived from an external source, the crude flash tower E in that case not being necessary. The system would then operate in the same manner as described hereinbefore except that reduced crude from an external source would be charged to the viscosity breaking furnace I5 and the necessary cooling for the operation of the evaporator Il" and fractionator 34 would be supplied by other means than the gas oil introduced through lines 32 and 35. In this case the heat exchange coils 4 and 3 might be relied upon exclusively for the cooling effect or additional cooling fluid could be introduced in the well known manner from any source.

Operation In operation fresh charging stock, such as crude petroleum oil, or other equivalent oil having light and heavy constituents, is introduced through line I into crude flash tower 5, after having been preheated to a distilling temperature, for example by passage through heat e-xchange coils 3 and 4 in the fractionator 34 and evaporator I'I respectively. In the crude flash tower the introduced crude oil is separated into vapors and liquid residue or reduced crude. 'I'he vapors pass upwardly through the tower and undergo partial fractionation therein, the fractionated vapors having the'desired boiling characteristics passing olf through the condenser 'I and being collected as a desired distillate, e. g. gasoline, in the receiver 8, while a portion of the vapors are `removed in the form of a condensate through line 9, as gas oil charging stock which is suitable for treatment in a vapor phase cracking operation.

The reduced crude is Withdrawn from the base of the flash tower through line I3 and passed through viscosity breaking furnace I5, and if desired reaction chamber IS, wherein cracking of a viscosity breaking nature, e. g. such as to produce from 5% to 12% of products in the gasoline boiling range per pass, takes place and the resulting cracked products are introduced into the evaporator Ii. The reduced crude charged to the viscosity breaking furnace I5 may have, for example, a gravity of about 22 A. P. I. 'I'he cracking conditions in the heater I5 may be such as to give to the oil leaving the heater a temperature of from 840 to 880 F., preferably about 850 F., and the pressure at the outlet of the heater may be from lbs. to 400 lbs. per square 25% to 30% gasoline per pass.

inch, preferably about 230 lbs. per square inch or more. In the evaporator, which may be held at the same or a lower pressure than that of the heater by action of pressure control valve 12, the products separate to 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 the-reof and transferred to the flash drum 2li. The partially fractionated vapors pass through the vapor line 33 into the fractionator 3d, wherein they are completely fractionated in the usual manner, the fractionated vapors passing off from the top thereof and condensed, resulting condensate being collected in receiver 38 as a gasoline distillate suitable as a nal desired product or for blending with other distillates to form a final desired product. rI"he residue introduced into the fuel oil flash tower 24 undergoes vaporization therein by its contained heat, as a result of the reduction of pressure thereon, and the resulting vapors are passed upwardly through the tower, those remaining uncondensed at the top being collected in the form of a distillate in receiver 20. The characteristic of this distillate may be adjusted by controlling the amount of cooling supplied to the top of the fuel oil flash tower, as well as by the adjustment of the pressure reduction by means of valve 23.

The reflux condensate withdrawn from the base of the'fractionator 3ft is a relatively light clean gas oil cracking stock. This condensate is passed through the light gas oil cracking furnace It which preferably operates under vapor phase cracking conditions. In this heater the condensate is subjected to cracking, preferably at a temperature of less than 1050 F. and more than 9000o F., most desirably 925 to 975 F., and a pressure of from 100 lbs. to 400 lbs. per square inch, most desirably 195 lbs. to 225 lbs. per square inch. The cracking to gasoline, per pass, is preferably in the neighborhood of 15% to 20%, the greatest part of this conversion being effected at temperature abo-ve 850 F. These moderate cracking conditions are preferable since it has been found that they produce a relatively high anti-knock gasoline without the simultaneous formation of excessively large amounts of fixed gas or heavy products such as tar or coke. However, other cracking conditions may be used if desired, for example such as to produce from The anti-knock rating of the gasoline produced can be increased by increasing the temperature or the percentage of cracking of gasoline per pass. may be effected entirely in the heater M but preferably part of the conversion is carried out in the heater and the rest in the reaction chamber 47. In the event that the reaction chamber is used the greater part of the cracking would ordinarily be taking place in the cracking furnace and the smaller proportion in the reaction chamber. The resulting cracked products are introduced into the evaporator Il and therein separate into vapors and liquid residue similarly to the products from the viscosity breaking furnace I5.

The heavy flash distillate collected in the receiver 28 is removed and passed through line 30 into the coils of heavy recycle gas oil cracking furnace 53, wherein they are subjected to cracking conditions of temperature and time, to cause conversion to a degree as great as possible without the formation of deleterious quantities of coke. The conditions selected for cracking in the furnace 53 will be dependent upon` the character of The cracking furnace 44, but may be held under considerably lower pressure if desired, this pressure reduction being effected by aid of pressure reducing valve 5I. In the evaporator I1 the hot cracked products from the furnace 44 undergo separation into vapors and liquid residue, similarly to the products from the viscosity breaking furnace I5, constituents thereof being blended with the light final distillate collected in the receiver 38, with the reflux condensate collecting in the base of fractionator 34, and with the liquid tar passed t the fuel oil flash drum through line 22.

Heavy flash distillate is removed from the receiver 28 and passed by action of pump 52 through line 3i] and the coil of heavy recycle gas oil cracking furnace 53, wherein it is subjected to a moderate amount of conversion intermediate that taking place in the viscosity breaking furnace I and that taking place in the light gas oil cracking furnace 44. The conditions to which this heavy flash distillate stock may be subjected in the cracking furnace 53 is dependent upon the degree of flashing taking place in the flash drum 2d. Where the liquid residue introduced into the flash drum or tower is subjected to a drastic flashing operation such as would attend a very great decrease in pressure, for example to an atmospheric value, with only a relatively small amount of reflux, the condition in the cracking furnace 53 must be more moderate, in order to carry out cracking without deleterious coke formation, than would be the case where the flashing in the llash tower 2-'5 is less drastic. Under most conditions the heavy flash distillate passing through the cracking furnace 53 will have characteristics such that it can be subjected to a degree of conversion intermediate that taking place in the viscosity breaking furnace I5 and that taking place in the light gas oil cracking furnace 44, for example, the amount of conversion per pass, to products in the gasoline boiling range, may be from to 15%, for example about 12%, the temperature necessary to produce this conversion depending upon the character of the stock. The temperature may be, by way of illustration, from 850 F. to 950 F. or thereabouts, and the pressure under which the cracking takes place ls most suitably substantially the same as that being held on the evaporator I1.

The products of conversion pass from the heater 53 through line 54 having control valve 55, directly into the evaporator I1, or alternatively the hot cracked products from the furnace 53 may be directed through line 56 into reaction chamber 5'1 wherein further conversion thereof takes place in the well known manner. This method of operation may be effected by proper manipulation of valves 58, 59, and 5i). The resulting digested products then pass into the evaporator I1 for separation into vapors and liquid residue, similarly to the products from the cracking furnace 44 and viscosity breaking furnace I5.

According to a modified form of my invention the cracking furnace 53 and chamber 51 may be operated to carry out a coking operation on the heavy flash distillate from the receiver 28. In this instance the temperature to which the distillate is heated in passing through the furnace 53 would be considerably higher than that mentioned, the temperature attained being sufficient to cause the desired amount of coking to take place after the hot oil is introduced into the chamber 51, which would then act as a coke drum. The temperature to which the oil is heated in the furnace 53 may be from 900 to 975 F., for example. Additional heat may be supplied to the chamber 51, from an auxiliary source if desired, to carry on the coking operation. The vapors resulting from the coking operation pass off through the line 54 into the evaporator I1 and are therein treated in a similar manner to those from the other cracking coils. Other conventional types of coking operations may be carried out, if desired, the resulting vapors being treated as set forth hereinbefore.

The virgin gas oil removed from the crude flash tower 5 and collected in the receiver I0 is passed through pipe II, by action of pump I2, into the fractionator 34 and the evaporator I1, as refluxing medium. The amount of gas oil so returned to the evaporator I1 through line 32 is only that necessary to maintain the desired temperature at the top of that vessel, and the remainder is introduced into the fractionator 3:4, either by way of line 35 or by way of line 5 I, or both. The amount returned through line 35 is that suillcient to supply the necessary amount of reflux at an intermediate point in the fractionator, and the remainder is preferably returned to the fractionator through line 5I, the bottom part of the fractionator acting as an accumulator drum from which the composite charging stock, including the reflux formed in the tower and the gas oil introduced through lines 35 and 6I, is pumped to the cracking furnace 44, as described hereinbefore. Valves 02, 53, and 64 provide the necessary ccntrol for the distribution of the gas oil.

If desired, the gasoline distillate from the receiver 3B may be combined with the distillate from the receiver 8, cross-over line 65 being provided for this purpose. Reference numeral 66 indicates a line whereby distillate may be drawn off from the receiver 8 separately.

Valved lines 61, 68 and 69 are provided so that when desired gas oil from receiver IIJ, flash distillate from receiver 28, or reflux condensate from fractionator 315 may be diverted from the system in any desired quantities to establish a predetermined balance of operating conditions.

Reference numeral 10 indicates a line whereby' liquid residue may be drawn off from the reaction chamber 41 from time to time if desired. This line would not ordinarily be used when the reaction chamber is operating as a vapor phase soaking drum. Valved line 1I is provided for drawing off any desired amount of reaction products from the reaction chamber 51, when that vessel ls operating in such manner as to produce a liquid residue.

The apparatus shown on the drawing is believed to be all that is necessary to illustrate the invention and for sake of simplicity other apparatus, which might be used, has not been shown. For example, when furnace 53 is opating in connection with a coking process a plurality of drums 51 might be arranged in parallel so that when one drum is full of coke another drum may be used. Likewise it might be advantageous in some cases to provide for the separate segregation of tar from the three cracking operations and this might be done by furnishing two more evaporators which would serve to treat the cracked products from the cracking furnace 53 and cracking furnace I5 respectively, only the cracked products from furnace 44 then passing to evaporator I1. Separate fuel oil flash drums would also be needed for these two additional evaporators and in event that such an arrangement is used the flashed vapors from the several flash towers would be combined to form the. stock passing therethrough, but under ordinary conditions it may be said that a temperature of` from 850 to 900 F. is suitable. The pressure under which cracking is carried out is most desirably the same as thatin the evaporator I1, approximately, although higher pressures may be used if desired, control being eiected by means ci pressure reducing valves` 55. In passing through the cracking furnace 53 andthe reaction chamber l, if that chamber be used, the amount of conversion per pass may be, by way of example, from to 15%, although this would be subject to some variation depending upon the character of the stock selected in the iiashing operation carried out in flash tower 24.

In the alternative method of operation according to which furnace 53 and reaction chamber 5l are utilized to carry out a coking operation, the temperature to which the oil is raised in the heating furnace 53 would be considerably higher than that mentioned hereinbeiore, for example 9G0 F. to 975 F. or thereabouts, in order to store up in the oill enough heat to cause the desired coking eiect to take place in the coke drum 51 or additional heat may be supplied to the coke drum '57 from an auxiliary source to aid in carrying out the coking operation. When operating in this manner the pressure is preferably relatively low, for example about the same as that maintained in the evaporator i'i, to which the vapors from the coking operation pass through line 54. The coking operation is preferably carried out in the manner just mentioned but it may alternatively be effected in any well known manner, for example in an ordinary red shell still, the vapors passing therefrom to the evaporator ill as described.

The iinal distillate collected in receiving drum 33 may be combined with that collected in the receiver ii, if desired, by way of line E55, or the distillates may be drawn. ofi separately through line d@ and @t respectively. Quantities of the reflux condensate from the iractionator 311 may be diverted from the process through linev 59 to establish any desired balance of conditions. Similarly portions of the ash distillate collected in receiver 28 may be diverted through line 68 and gas oil :from the receiver I0 may be diverted through line 'i. Gas oil from receiver il) is preferably passed through line 32 into the top of evaporator il in any necessary quantities to effect the desired temperature control. The indirect cooling coils 4 may be removed if desired. The amount of gas oil introduced through line 3E into the fractionator 34 between the fractionating plates is adjusted to effect the necessary cooling action. The remainder of the gas oil is introduced through line iii into the base of the fractionator, which serves as a mixing drum o1' accumulator tank from which the composite charge is withdrawn and passed through line 42 into the coils of light gas oil cracking furnace 44.

Heavy charging oil not requiring preliminary hashing or stripping such as reduced crude, heavy gas oil or the like, may be charged directly to viscosity breaking furnace I5, after first having been preheated, for example by passage through heat exchange coils 3 and li, the crude flash tower 5 then being unused.

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

and condensing them as a desired product, re-

moving reux condensate from said fractionating zone and passing it through a cracking Zone wherein it is raised to a cracking temperature and subjected to a relatively large amount of conversion per pass, introducing the resulting cracked products into said separating zone in mixture with the cracked products from the viscosity breaking cracking operation, withdrawing liquid residue from said separating zone and subjecting it to reduced pressure in a flashing zone wherein vapors separate from liquid tar-like residue, condensing resulting vapors independently of the vapors from thel cracked products rst mentioned to form a heavy flashed distillate containing the heaviest constituents oi the flashed vapors, heating said heavy flashed vdistillate in an independent heating Zone to a coking temperature, delivering the heated iiashed distillate into a coking zone, maintaining the products therein at a coking temperature to effect conversion into a coke residue, withdrawing evolved vapors from the coking zone and passing them into said separating zone.

2. The process of treating hydrocarbon oil which comprises passing relatively heavy hydrocarbon oil through a cracking Zone wherein it is raised to a cracking temperature and subjected to conversion to products of a lighter nature, l

introducing the resulting cracked products into a separating zone wherein separation of vapors from liquid residue takes place, removing separated vapors from said separating zone and forming a desired product therefrom, withdrawing liquid residue from said separating zone and subjecting it to reduced pressure in a hashing zone wherein vapors separate from liquid tar-like residue, condensing resulting vapors independently of the vapors from the cracked products iirst mentioned to form a heavy flashed distillate containing the heaviest constituents of the flashed vapors, heating said heavy ilashed distillate in an independent heating zone to a coking temperature and maintaining it in an independent coking Zone at a coking temperature to effect conversion into a coke residue, withdrawing evolved vapors from the coking zone and passing them into said separating zone.

3. The process of treating hydrocarbon oil which comprises passing relatively heavy hydrocarbon oil through a cracking zone wherein it is raised to a cracking temperature and subjected to conversion to products of a lighter nature, introducing the resulting cracked products into a separating Zone wherein separation of vapors from liquid residue takes place, subjecting the separated vapors to fractionation in a fractionating Zone to form a reflux condensate and a desired distillate product, passing said reflux condensate through a cracking zone wherein it is raised to a cracking temperature and subjected to cracking, directing resultant cracked products ing said heavy liashed distillate in an independent heating zone to a coking temperature and maintaining it in an independent coking Zone at a coking temperature to effect conversion into a coke residue, withdrawing evolved vapors from 5 the coking zone and passing them into said separating zone.

RUSSELL L. ZIMMERMAN.

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