US2016948A - Conversion of hydrocarbon oils - Google Patents

Description

Get, 8, R935. R. F, TROW CONVERSION OF HYDROCARBON OILS Filed May 19, 1951 E/CHHED E TEOW INVENTOR BY W H/S ATTORNEY Patented Oct. 8, 1935 UNITED STATES PATENT OFFICE Richard F. Trow, Port Arthur, Tex., assignor' to The Texas Company, New York, N. Y., a corporation of Delaware Application May 19,

V 11 Claims. This invention relates to the conversion of higher boiling hydrocarbon oils into lower ones and relates particularly to a method of distilling a clean cracking stock from a relatively dirty charge oil and cracking the clean stock, a reflux condensate which is formed in the process and the residue from the distillation step, in which the maximum practicable yield of a desirable light product having a high anti-knock value from the charge stock with a minimum yield of gas and carbon is obtained.

The invention broadly contemplates a method of crackingpetroleum oils in a coil and drum type of apparatus, where a relatively dirty higher boiling oil such as unclean gas oil or topped crude is separated by distillation into a clean vaporous gas oil fraction and a' residual fraction in the presence of hot vapors evolved in the process, the vapors are dephlegmated, a resultant clean condensate is heated to a conversion temperature in the coil, the residual fraction of the charge is commingled with the heated clean fraction and the mixture is transferred to a plurality of reaction Vessels where it is further cracked and vaporized.

The invention is especially adapted to a conversion process in which substantially no liquid is carried in the reaction vessels. This process, popularly known as low liquid level cracking, is one in which both liquid phase and vapor phase cracking is effected simultaneously in the same zone. It is capable of being practiced at a higher temperature than is ordinarily employed in liquid phase cracking, and accordingly yields a product having a much higher anti-knock value. It is also capable of being practiced at somewhat lower temperature than true vapor phase cracking and avoids high gas losses which usually attend the latter.

It has been found that the class of charge stock which is suitable for cracking in the liquid phase tends to precipitate and deposit coke in the heater coil at the higher temperature employed in low liquid level operation. Therefore one of the main objects of the present invention is to develop within the system a stock cleaner than that charged to the ordinary liquid phase cracking process from a relatively dirty charge stock. The present invention makes it possible to charge any petroleum oil containing an appreciable amount of crackable or gas oil constituents to a cracking system and evolve therefrom a clean desirable cracking stock, and crack the stock under such conditions as to produce a desirable yield of superior quality motor fuel.

1931, Serial No. 538,589

It is not desirable to discharge an appreciable quantity of crackable constituents of the charge oil from the system, even tho it is quite unclean, before it has been subjected to appropriate cracking conditions. Thus a further object of 5 my invention is to subject the residual fraction of the charge oil to suitable cracking conditions so as to effect such conversion of it into lighter products as is practicable.

These and other objects and advantages of my invention will be better understood by referring to the following description, taken in connection with the accompanying drawing the single figure of which illustrates in diagrammatical elevation I a preferredform of apparatus for practicing the 1.5 invention.

I is a furnace; 2, 3, and 4 are reaction vessels,

5 is a combination reaction vessel and scrubber,

6 is a dephlegmator, l is a reflux condenser, 8 is a final condenser and S is an accumulator drum. A line l5 may conduct the fresh charge oil to preheater coils I6 and I l which are situated in the reflux condenser l and the dephlegmator 6, respectively, or by-pass either or both of them by manipulation of valves 20, 2|, 22, and 23, and in to the upper portion and/or lower portion of the vessel 5. I

A vapor line connects the upper portion of vessel 5 with the lower portion of dephlegmator 6. A pump 32 takes suction thru a line 3! 30 from the bottom of dephlegmator 6 and discharges thru a line 33 into a heater coil 35 situated in the furnace l. A branch line 34 connected to the discharge side of the pump 32 serves to conduct a regulated quantity of reflux 3 or scrubbing oil to the uppermost portion of the vessel 5.

A transfer line leads from the outlet of th heater coil 35 to the upper portion of the reaction vessel 2 and lines 4| 42, and 43 connect the lower 40 portions of vessels 2 and 3, the upper portions of vessels 3 and 4, and the lower portions of vessels 4 and 5, respectively. A pump 45 takes suction on the bottom of vessel 5 thru a line 46 and discharges into the transfer line all thru a line 41 45 while drain lines 50, 5E, 52, and 53 lead from the bottoms of the vessels 2, 3, 4, and 5 to a common header 55.

A vapor line 68 connects the upper portion of the dephlegmator t with the reflux condenser l while a condensate run-back line 6| is provided also interconnecting the two vessels. A final vapor line 62 conveys vapor from the condenser 7 thru the final condenser coil 8 to the accumulator 9 which has a liquid outlet 63 and a gas outlet 64.

When beginning to operate a sufiicient amount of clean oil may be drawn thru a pipe 29 from a source not shown and pumped into the heater 35. After operating conditions are established a switch may be made to the fresh charge oil.

In a preferred mode of operation a fresh charge oil, which may be a relatively dirty gas oil or a topped crude, is charged thru the preheaters I6 and I7 and emerging therefrom at a temperature of approximately 700 F. is split between the upper and lower portion of the vessel 5. That portion of the fresh charge oil which is delivered to the bottom of the vessel 5; is introduced below the surface of the small body of liquid carried therein which is ordinarily only enough to insure a liquid seal so that no vapors are withdrawn from this vessel. That portion of the charge which is discharged to the upper portion of the vessel 5 is delivered at about a midpoint of a series of baffle plates which serve to distribute the liquid in a film-like manner to effect maximum contact with the hot vapors moving upward towards the outlet pipe 38.

Vapors leaving the vessel 5 at .a temperature of about 810 F. are conducted thru the line 3i! into the dephlegmator 6 where dephlegmation is effected to produce an overhead vapor and a reflux condensate. The reflux condensate, which is cooled somewhat in the lower portion of the dephlegmator 6 by heat interchange with the charge oil being passed thru the preheater section ll, is withdrawn therefrom at a temperature of about 750 F. and pumped into the heater coil 35 where the temperature is raised to about 960 F.

Such portions of oil as are condensed out and as remain liquid in the vessel 5 are withdrawn therefrom at a temperature of approximately 800 F. by the pump 45 and are discharged into the transfer line 49 near the outlet from the heater coil.

The thus combined highly heated clean charging stock and somewhat cooler residue from the vessel 5, having an average temperature of about 880 F. is delivered into the upper portion of the vessel 2. A large portion of the products remaining liquid at the entry to the vessel 2 are immediately flashed into vapor. Some atomization of the liquid also occurs due to the vaporization and rapid separation of portions of the oil from the main stream being introduced into the vessel 2. A pressure of about 400 pounds per square inch is preferably maintained in the first vessel and throughout the remainder of the system.

The vapors and entrained or suspended finely divided liquid particles are passed thru the vessels 2, 3, and s and into 5 by the connecting lines 4|, 42, and 43 while liquid portions being deposited in the bottoms of vessels 2, 3, and 4 are preferably drawn off as they are deposited. In some cases it may be desirable to maintain such an amount of liquid in the vessel 2 as to overflow small quantities of it thru the line 4| to the vessel 3; In the vessels 3' and 4, however, it will ordinarily be preferable to carry only enough liquid to insure that no vapors are withdrawn from those vessels.

The hot vapors entering the vessel 5 move upwardly encountering that portion of the fresh charge which is dropping down from the baflies above.- Cooling and condensation of the vapors and heating and vaporization of the fresh charge is effected by the interchange of heat between the hot vapors and cooler charge oil.

After encountering the charge oil, the upwardly moving vapors encounter the clean scrubbing oil which is delivered to the uppermost of the baffies thru the line 34, as previously described, and are still further cooled and cleansed and finally emerge substantially free of carbonaceous or dirty material thru the line 38. Altho no specific provision is made for such it may be found desirable to cool the scrubbing oil delivered to the top of the vessel 5 after it leaves the pump 32 and before it is discharged into the vessel in order to reduce the amount of oil to be handled.

That portion of the oil which fails to vaporize and that which remains condensed in the vessel 5 is deposited in the bottom thereof in contact with that portion of the cooler fresh oil being delivered thereto. The amount of cooling supplied here should be at least sufficient to lower the temperature of the combined oils below where advanced cracking or cracking to pitch or coke of the least refractory constituents occur. It is in fact preferable to maintain only a temperature at which cracking of the heavier less refractory constituents begins and at which substantially all of the lighter more refractory constituents of the oil will have become vaporous at the pressure employed.

The vapors developed from the charge oil delivered to the bottom of the vessel are added to those moving upwardly to the top of the vessel while the remaining liquid is withdawn thru the line 46, as previously described.

The warm vapors conveyed thru the line 30 to the dephlegmator 5 are subjected therein to any conventional method of fractionation in the first stages of which heat is interchanged between them and the fresh charge which is being passed thru the preheater coil ill. The fractionated vapors .are passed thru the reflux condenser E, where the heaviest portions are condensed by heat interchange with the fresh charge which is being passed thru the coil IS. The final vapor is con-- ducted thru the line 62 to the final condenser 8 and to storage while a portion condensed in the condenser 1 is returned to the upper portion of the dephlegrnator 6 thru the line 6| as a reflux coolant.

In the mode of operation which is described herein the approximate temperatures given are well above the economical and practicable operating limits of a liquid phase cracking operation, that is one where sizable bodies of liquid are maintained in reaction vessels such as 2, 3, 4, and 5 By maintaining temperatures of these higher orders it is possible to produce an ultimate distillate which has a relatively high anti-knock value and because of the shorter times of reaction in the reaction vessels of a combined vapor and finely divided suspended liquid particles, as compared with only bodies of liquid, no secondary or advanced cracking in which pitchy or coky bodies and non-condensable gases are ordinarily formed has time to occur. On the other hand, as the rate of cracking is greater at these higher temperatures, a yieldof lighter products based on the fresh charge will be obtained which is as good economically speaking as that obtained from an average liquid phase conversion.

It is pointed out, however, that in order to maintain these desirable high temperatures it is necessary to provide a cracking stock, that is, the oil passed thru the heater coil 35, which is much cleaner than the usual charge oil for a coil heater in a coil and drum type apparatus where cracking in the liquid phase. This is because a relatively unclean cracking stock contains constituents which are not capable of being subjected to the higher order of temperatures maintained in my coil without readily precipitating cokey particles which deposit in the coils and greatly shorten the timerof a single continuous operation.

' Theformation of these bodies is believed to be due largely to advanced or secondary cracking of the less refractory of the heavier constituents of the dirtier oils and be also due to some substance which may be present in the oil tending to promote the formation of coke at the rapid rate of reaction that occurs in the coil at the higher temperature employed.

In my invention the high temperature to which the clean cracking stock is heated in the coil is immediately quenched or lowered by the addition of a somewhat 'c'ooler'oil which includes the previously referred to somewhat less refractory constituents which have been separated from the cleaner fractions of the fresh charge oil. This temperature is only lowered however to one at which a desirable further reaction of all of the oil being treated will continue at a somewhat slower rate and the combined oil thus undergoing treatment is delivered into the reaction vessels for further time of digest as has been previously described.

The addition of the further crackable somewhat cooler material to the hotter material, which whenin the coil is being decomposed at a faster rate, serves not only to lower the temperature and thus reduce the rate of decomposition but also acts as a solvent it is believed for incipient pitchy or cokey particles and gas which may be present in the highly heated oil from the coil and which would doubtless evidence itself positively in the reaction vessels if this quenching solvent oil were not added at a stage before additional secondary reaction begins. I

A suitable clean cracking stock for passing heating coil 35 may be a gas oil having a straw or light straw color or an oil of 15-20 on the cell, Lovibond scale; however, the use in this stage of other relatively clean cracking stocks is not precluded.

While a preferred mode of operation has been described herein in detail it is to be understood that neither this form nor the approximate temperatures given are intended to serve as a limitation to the spirit and scope of my invention which is believed to be adequately defined and limited by the appended claims.

I claim:

1. The process of cracking hydrocarbon oil that comprises subjecting a condensate oil to high cracking temperature in transit through a heating coil to eifect a high rate of cracking adapted to cause the formation of constituents of high anti-knock quality, passing the resultant cracked products into an enlarged reaction zone maintained at cracking temperature under superatmospheric pressure wherein cracking is continued and separation of vapors from liquid occurs, passing the separated vapors at a cracking temperature into a distilling chamber wherein separation into vapors and liquid occurs, passing the latter vapors at a cracking temperature to a fractionating tower wherein the vapors are subjected to fractionation to form a condensate, conducting said condensate to aforesaid heating coil, passing fresh charging stock in indirect heat exchange with vapors in a higher temperature section of said fractionating tower and introducing the charging stock thus preheated into said distilling chamber wherein the charging stock is subjected to distillation at a temperature withinthe cracking range, withdrawing resultant liquid residue from said distilling chamber and combining it with the highly heated products 5 discharged from aforesaid heating coil so that the combined products are in contact in said enlarged reaction zone to thereby increase the rate of cracking on the constituents of said liquid residueand decrease the rate of cracking 1 on the constituents from said heating coil and limiting the time of reaction on the residual constituents of said liquid residue by withdrawing liquid from said enlarged reaction zone at a rate adequate to prevent the accumulation of liquid 15 vapors at a cracking temperature to a fractionat- 301 ing tower wherein the vapors are subjected to fractionation to form a condensate, conducting said condensate to aforesaid heating coil, heating fresh charging stock to a temperature approximating a mild cracking temperature and intro- 35 duoing it thus preheated into said distilling chamber wherein it is subjected to distillation at a temperature within the cracking range, withdrawing resultant liquid residue from said distilling chamher and combining it with the highly heated prod- 4o ucts discharged from aforesaid heating coil so that the combined products are in contact in said enlarged reaction zone to thereby increase the rate of cracking on the constituents of said liquid residue and decrease the rate of cracking on the constituents from said heating coil and limiting the time of reaction on the residual constituents of said liquid residue by withdrawing liquid from said enlarged reaction zone at a rate adequate to prevent the accumulation of liquid therein. 50 3. The process of cracking hydrocarbon oil that comprises subjecting a condensate oil to high cracking temperature in transit through a heating coil to eiTect a high rate of cracking adapted to cause the formation of constituents of high 55.,

anti-knock quality, passing the resultant cracked products into an enlarged reaction zone maintained at cracking temperature under superatmospheric pressure wherein cracking is continued and separation of vapors from liquid occurs, pass ing the separated vapors at a cracking tempera-' ture into a distilling chamber wherein separation into vapors and liquid occurs passing the latter vapors at a cracking temperature to a fractionating tower wherein the vapors are subjected to fractionation to form a condensate, conducting said condensate to aforesaid heating coil, heating fresh charging stock to a temperature approximating a mild cracking temperature, dephlegmating vapors in said distilling chamber with the charging stock thus preheated whereby downflowing unvaporized portions thereof are subjected to increasing temperatures within the cracking range, withdrawing resultant liquid residuefrom said distilling chamber and comsaid enlarged reaction zone at a rate adequate to prevent the accumulation of liquid therein.

4. The process of cracking hydrocarbon oil that comprises subjecting a condensate oil to high cracking temperature in transit through aheat ing coil toeffect a high rate of cracking adapted to cause the formation of constituents of high anti-knock quality, passing the resultant cracked products into an enlarged reaction zone maintained at cracking temperature under superatmospheric pressure wherein cracking is continued and separation of vapors from liquid occurs, passing the separated vapors at a cracking temperature into a distilling chamber wherein separation into vapors and liquid occurs, passing the latter vapors at'a cracking temperature to a fractionating' tower wherein the vapors are subjected to fractionation to form a condensate, passing fresh charging stock in indirect heat exchange with vapors in a higher temperature section of said fractionating tower and introducing the charging stock thus preheated into said distilling chamber wherein the charging stock is subjected to distillation at a temperature within the cracking range,

withdrawing resultant liquid residue from said "distilling chamber and combining it with the highly heated products discharged from aforesaid heating coil so that the combined products are in contact in said enlarged reaction zone to therebyincrease the rate of cracking on the constituents of said liquid residue and decrease the rate of cracking on the constituents from said heating coil and limiting the time of reaction on the residual constituents of said liquid residue by withdrawing liquid from said enlarged reaction zone at a rate adequate to prevent the accumulation of liquid therein while permitting the separated vapors a further time of digest at a cracking temperature before delivering them to said distilling chamber.

, 5. The process of cracking hydrocarbon oil that comprises introducing charging stock into a cracking and'distilling zone to dephlegmate vapors therein and subjecting the products therein to distillation to effect a separation into vapors and a residue, maintaining a cracking temperature throughout said cracking and distilling zone involving a temperature of the order of 800 F. to which the residue is subjected therein, passing the separated vapors to a fractionating zone and subjecting them to fractionation therein to form a condensate, passing said condensate through a heating coil wherein the condensate oil is subjec ted to a high cracking temperature to effect a high rate of cracking, withdrawing said residue from the cracking and distillingzone and bringing the withdrawn residue, without further heating or digestion, directly into contact with the stream of heated condensate oil passing from said heating coil to intimately commingle the residue with the hot products from the heating coil in a contacting zone, maintaining the contacting zone at a high cracking temperature of an order adapted for the formation of constituents of high anti-knock quality and at which conversion of residual constituents into coke would ordinarily occur, limiting the time of reaction-on-such residual' constituents by rapidly withdrawing the resi-' due 'as a liquid from' the contacting zone so that no substantial conversion to coke occurstherein and'passing evolved vapors from the contacting zone to aforesaid distilling and cracking zone:

6. The process of cracking hydrocarbon oil that comprises introducing charging stock into a. cracking and distilling zone to dephelgmate vag pors therein and subjecting the products therein to distillation to efiect a separation into vaporsand a residue, maintaininga cracking temperature throughout said cracking and distilling-zone, passing the separated vapors to a fractionatlng zoneand subjecting them to fractionation therein to form'a condensate; passing said condensate through a heating coil wherein the condensate oil is subjected to a high cracking temperature to effect a high rate of cracking, withdrawing said residue from the cracking and distilling zone and-20 bringing the withdrawn residue, without further heating or digestion, directlyinto contact with the stream of heated condensate oil passing from said heating'coil to intimately commingle the residue with the hot products from the heating coil in a contacting zone, maintaining the contacting zone at a high cracking temperature adapted for that type of cracking characteristic of temperatures of the order of 880 F. resulting in the formation of constituents of high antiknock quality, maintaining a material superatmospheric pressure in the contacting zone, rapidly withdrawing liquid constituents from the contacting zone so as to prevent the accumulation of a body of liquid therein while permitting the evolved vapors a further time of reaction at said high cracking temperature and passing the vapors to aforesaid distilling and crackingzone. 7. The process of converting higher boiling hydrocarbon oils into lower boiling ones that comprises heating a condensate oil to high cracking temperature in transit through a heating coil, discharging the heated oil from the heating coil and passing it at a high cracking temperature into an enlarged cracking zone maintained at 5 cracking temperature wherein separation 'of vapors from liquid occurs, introducing oil into said enlarged cracking zone at a temperature lower than that of said condensate oil discharged from said heating coil to thereby lower the'temperature' of reaction therein as Well as subject the cooler oil to cracking therein, withdrawing separated liquid from the enlarged cracking zone at a rate adequate to prevent the accumulation of abody of liquid therein, passing separated vapors to a secondary cracking zone wherein the vaporsare maintained at a cracking temperature to eifect further cracking of the vaporous constituents, bringing liquid oil into contact with vaporous constituents undergoing cracking to dephlegmate the vapors while still maintaining them at cracking temperature, passing thevapors to a fractionating zone and subjecting them to fractionation therein to separate out a final light distillate and a reflux condensate and conducting said fromliquid occurs,introducing oil into said en- 7 5 larged cracking zone at a temperature lower than that of said condensate oil, discharged from said heating coil to thereby lower the temperature of reaction therein as well as subject the cooler oil to cracking, withdrawing separated liquid from the enlarged cracking zone at a rate adequate to prevent the accumulation of a body of liquid therein, passing the separated vapors to a secondary cracking zone comprising a plurality of chambers through which the vapors undergoing cracking pass successively, introducing liquid oil into contact with the vapors in the last of said cracking chambers to dephlegmate the vapors therein maintained at cracking temperature,

" passing the vapors to a fractionating zone and subjecting them to fractionation therein to separate out a final light distillate and a reflux condensate and conducting said reflux condensate to said heating coil.

9. The process of converting higher boiling hydrocarbon oils into lower boiling ones that comprises heating a condensate oil to high cracking temperature in transit through a heating coil, discharging the heated oil from the heating coil and passing it at a high cracking temperature into an enlarged cracking zone maintained at cracking temperature wherein separation of vapors from liquid occurs, introducing oil into said enlarged cracking zone at a temperature lower than that of said condensate oil discharged from said heating coil to thereby lower the temperature of reaction therein as well as subject the cooler oil to' cracking, withdrawing separated liquid from the enlarged cracking zone at a rate adequate to prevent the accumulation of a body oi. 5

liquid therein, passing separated vapors to a secondary cracking zone wherein the vapors are maintained at a cracking temperature to effect further cracking of the vaporous constituents, bringing liquid oil into contact with vaporous constituents undergoing cracking to dephlegmate the vapors while still'maintaining them at cracking temperature, passing the vapors to a fractionating zone and subjecting them to fractionation therein to separate out a final light distillate and a reflux condensate, conducting said reflux condensate to said heating coil, and withdrawing liquid from said secondary cracking zone and conducting it to said enlarged cracking zone.

10. The-process according to claim 7 in which the lower temperature oil introduced to said enlarged cracking zone is charging stock heated to a moderate cracking temperature.

11. The process according to claim '7 in which the lower temperature 011 introduced to said enlarged cracking zone is liquid oil resulting from the dephlegmation of the vaporous constituents undergoing craoldng in said secondary cracking zone.

RICHARD F. TROW.

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