US2033473A - Process for the treatment of hydrocarbon oils - Google Patents

Description

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Marh 10, 1936. P. c. KEITH, JR

PROCESS FOR THE TREATMENT OF HYDROCARBON OIL Filed Feb. 8, 1934 ATTORNEY Patented Mar. l0, 1935 UNITED PATENT OFFICE PROCESS FOR THE TREATMENT OF HYDROCARBON OILS Percival C. Keith, Jr., Peapack, N. J., assigner to Gasoline Products Company, Inc., Newark,

1 Claim.

This invention relates to processes for the treatment of hydrocarbon oils, and pertains more particularly to processes for producing relatively light low boiling point oils such as gasoline from heavier higher boiling point oils.

It is an object of my invention to provide an improved process for forming relatively light low boiling point oils such as gasoline from heavy higher boiling point oils such as gas oil, crude oil, reduced crude or the like, according to which novel interlocking heat exchange steps are provided whereby highly efficient operation results.

In accordance with my invention fresh relatively heavy charging stock, such for example, as gas oil or other clean stock, or a relatively dirty stock such as crude or reduced crude, is passed in heat exchange relation with condensate withdrawn from a fractionating Zone, then in indirect heat exchange relation with vapors 'withdrawn from a flashing operatic-n, next in heat exchange with tar withdrawn from the hashing operation, and is iinally introduced either into the fractionating zone mentioned, or into an evaporating zone from which vapors pass to the fractionating Zone; reflux condensate is withdrawn from the fractionating zone, combined with distillate from the flashing operation, and subjected to a cracking operation, the resulting cracked products being introduced into the evaporating zone, from which tar is drawn off and introduced into the flashing Zone. According to another feature of my invention, a portion of the composite charging stock is diverted before passing to the cracking furnace and is passed in indirect heat exchange relation with liquid in the base of a stabilizing tower through which condensate, formed by condensing the fractionated vapors, e. g. gasoline is passed. This charging stock is returned to the cracking furnace after passing through the indirect heat exchanger.

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

In the drawing the single gure represents diagrammatically 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 is forced by -pump 2. The charging stock passes through indirect heat exchanger 2 having control valve 65 and also through indirect heat exchanger 3, having control valve 4, and heat exchanger 5 having control valve 6, either through branch line 1 into evaporating section 8 of combination evaporator fractionator tower II, or through branch line 9 into fractionating section Ill of the combination tower, or into both sections simultaneously if desired. In case the fresh charging stock is a clean cracking stock such as gas oil or the like, the point of introduction of the charge may be at 9, in which case the charging stock would be collected with the reflux condensate formed by the fractionating operation. However heavy dirty stock may be introduced through line 9 into the fractionating section I0 when it is not desired to subject the composite liquid from the base of that section to a very drastic cracking operation. The clean gas oil may also be introduced into the evaporator section if desired, for cooling or any other purpose.

If relatively heavy dirty charging stock such as crude oil or reduced crude is used, the point of introduction is preferably at 1, so that -the heavy dirty stock is subjected to a distilling operation in the evaporating section. Resulting vapors pass upwardly through the stand pipe I2 into the fractionating section I0 wherein they I are subjected to fractionation with the resulting formation of reflux condensate, which collects on the trap-out tray I3, while the unvaporized portion of the charging stock collects in the base of the evaporator section 8. The reflux condensate collecting on trap-out tray I3 is removed through line i4 to accumulator or mixing tank I5, which is provided With a vent line I6 for returning any vapors formed therein to the fractionating section I6 of the combination tower II. Composite cracking stock is removed from the mixing tank Iii through line I1 and forced by pump i8 through the coils of cracking furnace or heater I9, wherein it is raised to a cracking temperature and subjected to conversion. The i resulting hot products pass to reaction chamber 2@ wherein they are subjected to additional conversion by their contained heat in the well known manner. The majority of the conversion may take place in the reaction chamber, or a part of L it may be effected in the cracking furnace and another part in the reaction chamber. Alternatively the reaction chamber may be omitted if desired. The hot cracked products pass from4 reaction chamber 28 through line ZI into the evaporating section 8 of the combination tower EI, preferably below the liquid level therein.

The pressure in the evaporating section 8 is preferably kept considerably lower than that in the reaction chamber 20, for example by acyz Cil tion of pressure control valve 22. In the evaporating section the introduced cracked products separate into vapors and liquid residue, the vapors passing upwardly through the tower around baiiie plates or similar devices 23, through stand pipe l2 and then upwardly through the fractionating section l0, wherein they undergo fractionation in the well known manner by contact with bubble trays or other similar fractionating elements. The fractionated vapors, having the desired boiling characteristics, pass off from the top of the fractionating section, through line 24 and condenser 25, the resulting condensate being collected in gas separator 2E, having the usual gas draw-off line 21. In this gas separator xed gases separate from the liquid distillate, e. g. gasoline, this distillate passing through line 'I4 and pressure reducing valve I5 into secondary gas separator 78, which is held under a still lower pressure. In the secondary gas separator additional xed gases and light vapors are separated and pass off through line 11, while the remaining liquid is removed through line 28 and forced by pump 29 through heat exchanger 3U, wholly or in part, depending upon the setting of bypass valve 3l, into an intermediate point in stabilizer tower 32, through any one of the several branch lines 33. Fixed gases and light vapors from the gas separator 26 may be passed through line 12, under control of valve 73, into the base of flash tower 50 if desired, as will be explained hereinafter. In this stabilizer tower, which preferably operates at considerably higher pressure than gas separator 16 the undesirably light constituents, including any xed gases present, are separated from the final gasoline distillate, these light constituents passing off from the top of the tower through line 34 and condenser 35, resulting condensate being collected in the reflux drum 35 from which liquid is pumped back through line 3l as a refluxing medium, all of this operation being carried out in the well-known manner. The stabilized distillate collects in the base of the stabilizer tower and is withdrawn through lines 38, indirect heat exchanger 30, and cooler 39, to storage. Heat is supplied to the base of the stabilizer tower by withdrawing a quantity of liquid from a trap-out tray 4D located near the base of the tower, passing this through an indirect heat exchanger 4|, and returning the resulting heated liquid to the base of the stabilizer tower through line 42. Heat is supplied to the heat exchanger 4! by withdrawing a quantity of hot oil from the accumulator or mixing tank l5 and passing it through line 43 to the heat exchanger and back to the mixing tank through line 44, by action of pump 45. Reference numeral 46 indicates a control valve whereby a portion of the circulating liquid may be by-passed around the heat exchanger. Forty-seven (4l) indicates another control valve for regulating the amount of liquid being circulated through the entire line.

Liquid residue collecting in the base of the evaporating section 8 of combination tow-er Il, is withdrawn through line 48 having therein reducing valve 49 and is introduced into flash tower 50, which is held at a pressure considerably lower than that maintained on the evaporator section 8. In this flash tower, as the result of the reduction in pressure, the lighter constituents of the residue are separated as vapors, and passed upwardly through the fiash tower undergoing partial fractionation by contact with baille plates or similar devices 5 I, and bubble trays or other fractionating elements 52. The vapors remaining uncondensed pass off the top of the ash tower through line 53, indirect heat exchanger 54, and indirect heat exchanger 3, wherein the vapors are partially condensed, then through the final cooler or condenser 55, the resulting condensate being collected in receiving drum 56 which is provided with the usual gas draw-off line 51. Flash distillate so collected is removed from the receiving drum and forced through line 58, under pressure generated by pump 59, a portion being returned to the flash tower 5 through valve line 88, as reiiuxing medium while another portion thereof passes through indirect heat exchanger 54, this latter portion in turn being sub-divided so that a part thereof passes through valved branch line 6| into the lower part of the fractionating section l0 as a refluxing medium, another portion passes through valved branch line 62 onto baiiie plate 23 in the evaporating section 8, while the remainder is directed through valved line 63 into the mixing tank l5, to form a portion of the composite charging stock for passage through the cracking furnace I9.

Additional separation or stripping of lighter constiutents from the liquid residue collecting in the base of the ash tower 50 may be insured by passing fixed gases and light vapors from separator 26 through pipe 12 into the liquid residue. The pressure of the separator 26 will ordinarily be considerably higher than that of the ash tower so as to cause the ow of gas.

Reflux condensate is supplied to the top of the fractionator section IS by removing condensate from an upper tray in the fractionator section by means of line 64 and passing it through the indirect heat exchanger 2 in quantities controlled bythe adjustment of by-pass valve 65, and returning the cooled liquid to the top of the fractionating column, the circulation being effected by pump 65. The total amount of condensate so circulated may be controlled by valve 61.

When treating certain corrosive types of charging stocks it is desirable to add caustic or similar neutralizing agent to the stock as it is charged to the process. This may be accomplished by the aid of branch line 68 through which a caustic solution withdrawn from supply tank 89 is forced by pump 10, the quantity being controlled by valve 1l. The amount of caustic so mixed with the fresh charging stock prior to its passage through the cracking process depends upon the .corrosive character of that charging stock, The ..f

greater the corrosive character of the stock, the more caustic solution necessary to effect neutralization. In general, it may be said that a quantity of the order of a few pounds of dry caustic per barrel of charging stock, will be suiiicient. The dry caustic may be rendered uid for pumping purposes either by mixture with water or oil to form a solution, suspension or emulsion.

Operation In operation fresh charging stock, which may be either a relatively clean distillate charging stock such as gas oil, or a relatively dirty charging stock containing residual products such as crude oil or reduced crude, is introduced through the line l and heat exchangers 2', 3 and 5, either into the evaporator section B or fractionator section I0 of combination tower Il, or may be introduced at both levels. In the case ci a clean charging stock, the point of introduction would preferably be in the fractionating section lo, while in the case of a dirty oil such as crude oil or reduced crude, the point of introduction would preferably be in the evaporator section 8, when it is desired to operate the cracking furnace I9 at relatively high cracking per pass. On the other hand, even the heavy dirty oil might be charged to the fractionator section IIB if the cracking per pass in the furnace I9 be kept low enough to prevent deleterious coke formation. An alternative method of operation would be to introduce quantities of the charging stock into both the evaporator and into the fractionator.

The fresh charging stock in the combination tower is heated by rising hot cracked vapors and subjecting to partial vaporization, the vapors passing upwardly through the fractionating tower and the fractionated vapors, having the desired boiling characteristics, being removed through the vapor line 24 and condenser 25 and the resulting distillate being collected in the primary gas separator 26. In this gas separator a` quantity of fixed gases and light vapors are separated and pass off through line 21 or through line 12, leaving liquid oil which travels through pipe 14 and reducing valve 15 into the secondary gas separator which is held under substantially lower pressure and wherein additio-nal fixed gases and light vapors separate. The xed gases and light vapors pass off through line 11 and the remaining distillate is pumped into stabilizer tower 32 after being preheated in heat exchanger 36.

Reiiux condensate from the fractionating operation, together with any unvaporized portions of the fresh charging stock, if that be introduced through pipe 9, is withdrawn through line I4 to the accumulator tank I5, from which it is removed and passed through the cracking furnace I9 and reaction chamber 20 to cause any desired amount of cracking thereof. 'I'he cracking in the furnace I9 and reaction chamber 26 is preferably carried out at a pressure of several hundred pounds per square inch, for example, about 700 or 800 pounds per square inch and at a temperature suiiicient to cause the desired conversion per passage of the oil through the cracking apparatus. This amount of conversion would, of course, be dependent upon the coking tendency of the stock charged to the furnace. A relatively clean stock such as the gas oil and reflux condensate from the fractionating operation could be subjected to a higher temperature than a stock containing residual components, such as reduced crude. In general, it may be said that the temperature may range from 850 to 950 F., an average value for clean stock being about 925 F. In the combination tower, to the evaporating section 8 of whichthe cracked products pass through line 2I, a pressure considerably lower than that in the cracking furnace and reaction chamber is most desirably maintained.v The control of this pressure is effected by means of pressure reducing valve 22. 'Ihe pressure in the evaporating section may be, for example, about 150 pounds per square inch and that of the primary gas separator 26 may be about the same value, while the secondary gas separator 16 is held under a considerably lower pressure such as 30 pounds per square inch. The pressure on the stabilizer 32 is preferably higher, for example, 250 pounds per square inch. In the evaporating section separation of the introduced cracked products into vapors and liquid residue takes place, the vapors rising upwardly through the tower past the baflie plates or similar devices 23 and through the fractionating section I0, wherein it undergoes fractionation in the manner set forth hereinbefore.

The liquid residue collects in the base of the evaporating section and is passed through line 48, having reducing valve 49 into flash tower 50, which is held under a still lower pressure, for example about pounds per square inch. In this fiash tower separation of vapors fromliquid residue takes place by the contained heat of the introduced residue, as well as by action of fixed gases and light vapors from gas separator 26, which are introduced in desired quantities through line 12. The vapors pass upwardly through the flash tower, undergoing partial fractionation and the vapors remaining uncondensed at the top of the tower pass through the heat exchangers 54 and 3, giving up heat to the flash distillate and fresh charge respectively, then through condenser 55, the resulting condensate being collected in the accumulator tank 56. The liquid residue remaining in the base of the flash tower is withdrawn, for example, as fuel oil through line 18 under control of valve 19. The lighter fractions which tend to remain in the liquid residue may be removed by injecting fixed gases and light vapors, from gas separator 26, into the residue by way of line 12, the quantity being controlled by valve 13. Distillate is removed from the receiving drum 56 and pumped back to the top of the flash tower through line 66 in quantities necessary to assure the desired characteristics of the vapors leaving that tower, while other portions of the distillate pass through heat exchanger 54 and thereafter may be introduced either into the fractionating section Ill or evaporating section 8, of the combination evaporating and fractionating tower II, or may be introduced into the mixing tank or accumulator l5, or it may be introduced into all of these several places simultaneously. The quantity introduced into the evaporator tower is preferably only sufcient for reiiuxing purposes, while the remainder is diverted either through the line 6I into the lower part of the fractionating column or into the mixing tank I5. Where the quantity of distillate available is relatively large it would be more suitable to introduce only part of this distillate through the line 6I so as not to interfere with the eiiiciency of the fractionating operation, the rest being passed directly to the mixing tank I5 for` cracking in the furnace I9.

A part of the composite stock is removed from the accumulator I5 and passed through the heat exchanger 4I wherein the contained heat is used for reboiling condensate collected in the stabilizer tower 32, the composite stock being thereafter returned to the mixing tank. It has been proposed heretofore to remove reflux condensate from the fractionating column and utilize it for reboiling the stabilizer bottoms, the cool stock being returned to the fractionating column, but the present operation of utilizing stock from the mixing tank I5 has the advantage over the process just mentioned of avoiding any disturbance to the fractionating operation. The condensate removed from the stabilizer tower and passed through the heat exchanger coil 4I is preferably withdrawn from a trap-out tray such as 4B, and returned, after being heated, above the level of the liquid in the base of the stabilizer tower, this operation resulting in heating the removed condensate and separating lighter fractions therefrom as vapors before the returned stock is commingled with the liquid collected in the base of the stabilizer tower.

The caustic, which may be introduced with the fresh charging stock through line 68, is preferably injected in the form of a slurry of caustic with Water or oil, the amount of caustic so introduced preferably being only a small percentage of the amount of charging stock. The exact amount introduced would of course depend upon the corrosive character of the charging stock, some stocks requiring only a Very little caustic, whereas others might require many times as much. In general it may be said that not more than a few pounds of caustic per barrel of charging stock need ordinarily be used.

While I have described a particular embodiment of my invention for the purposes 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 claim.

I claim:

The process of treating hydrocarbon oil which comprises passing charging stock through a cracking zone wherein it is raised to a cracking temperature and subjected to conversion, introducing the resulting cracked products into an evaporating zone wherein vapors separate from liquid residue, removing vapors from said evaporating zone and passing them to a fractionating zone wherein fractional condensation thereof occurs, removing fractionated vapors from said fractionating zone and condensing them as a desired product, removing liquid residue from said evaporating zone and subjecting it to reduced pressure in a ashing zone, removing vapors from said ashing zone and condensing them, removing unvaporized products from said flashing zone, transferring heat from hot vapors near the top of said fractionating zone to cooler fresh charging stock so as to provide reiiux for said fractionating zone and heat said charging stock, passing the resulting partially heated charging stock in indirect heat exchange with hot vapors removed from said flashing zone, then in indirect heat exchange with unvaporized liquid removed from said ashing zone and iinally introducing the preheated fresh charging stock into direct contact with vapors separated from the hot cracked products introduced into the evaporating zone, condensing vapors removed from said flashing zone subsequently to the passage thereof in indirect heat exchange with said fresh charging stock, passing resulting condensate in indirect heat exchange with vapors removed from said ashing zone prior to the passage of said vapors in indirect heat exchange With said charging stock and then introducing the heated condensate into direct countercurrent contact with vapors separated from the hot cracked products introduced into the evaporating zone.

PERCIVAL C. KEITH, JR.

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