US2406312A

US2406312A - Cracking and coking of hydrocarbon oils

Info

Publication number: US2406312A
Application number: US467176A
Authority: US
Inventors: Barron Joseph Mason
Original assignee: Texaco Inc
Current assignee: Texaco Inc
Priority date: 1942-11-28
Filing date: 1942-11-28
Publication date: 1946-08-27
Anticipated expiration: 1963-08-27

Description

Patented Aug. 27. 1946 OILS Joseph Mason Barron, Port Arthur, Tex., assignor to The Texas Company, New York, N. Y., a corporation of Delaware Application November 2 This invention relates to certain improvements in the cracking and coking of hydrocarbon oils. The invention is concerned with the coking of residual constituents from a pressure cracking operation and contemplates a combination cracking and coking process in which a condensate stock is subjected to a cracking temperature in a heating zone and the heated eiiluenttherefrom subjected to counter-current contact with a heavy or residualstock in a reaction chamber wherein separation of vapors from liquid residue occurs and in'which the residue is flashed to coke by means of its contained heat..

By having the heated condensate stock and the heavy or residual oil in counter-current contact in the reaction chamber a sufliciently high temperature may be maintained therein that the residue may be flashed to coke solely by its contained heat. Moreover, the refluxing to which the vapors are subjected while undergoing cracking in the countercurrent cracking chamber functions to prevent the delivery to the subsequent fractionator of certain heavy potential carbonforming polymers with the result that the reflux condensate produced in the subsequent fractionator is suitable as charging stock to a recycling cracking zone. It is' not necessary to subject the overhead vapors from the reaction chamber to any dephlegmating operation ahead of the fractionating zone in which the cycle condensate is formed. The overhead vapors from the reaction chamber may be subjected to fractionation to separate from the gasoline or naphtha distillate a higher boiling reflux condensate having a sufliciently low 90% 'A. S. T. M. distillation point and carbon residue that it may be subjected in a heating coil to high cracking temperatures and high rates of cracking per pass without encountering coking difficulties therein so as to effect conversion into high anti-knock gasoline constituents.

In accordance with the invention the condensate stock is passed through a heating coil and delivered to the lower portion of a reaction chamber into the upper portion of which a heavy oil or residual stock is introduced for cracking in counter-current contact with the rising vapors therein. Separation of vapors from liquid residue occurs in the reaction chamber and the vapors and residue are separately withdrawn. The reaction chamber is maintained at a high cracking temperature sufiicient that upon the flashing of the residue a conversion to coke will occur. Liquid is prevented from accumulating in the reaction chamber by rapidly withdrawing it and des, 1942, Serial No. 467,176

4 Claims. (01. 19649) livering it to the coking zone wherein the pressure is lowered and the residue flashed to coke.

In the prior art practice coking has been accomplished with the aid of considerable 'quan tities of hot vapors and gases and one of the principal difficulties encountered has been that occasioned by the priming of the coking drum.

In this priming, potential coke-forming constituents are carried with the'effluentvapors from the coking drum and create coking difficulties in vapor line and in the dephlegmating or fractionating portion of the system. In order to avoid this difliculty it has been necessary in the past to operate with relatively low charging rates to the coking drum and to maintain relativelyhigh outage gauges therein, the outage gauge being the height of the" space in the drum'above the coke level. In accordance with the present invention, since the material directed to-the coking chamber is essentially a liquid, the quantity of vapors and gases evolved from the coking chamber is greatly reduced with a consequent material diminution in priming tendencies. The practics of the invention thus makes possible the maintenance of high charging rates to the coking drum and high levels therein while avoiding priming, with the result that a maximum amount of coke is produced per coke drum cycle.

In practicing the invention the vapors from the counter-current reaction chamber are subjected to fractionation to obtain a reflux condensate which is cycledto the heating coil wherein it is subjected to cracking temperature and the heated effluent is discharged into the lower portion of the reaction chamber. The separated residue is withdrawn at temperatures adequate to support autogenous coking and is delivered into a lower pressure zone wherein it is coked by means of its contained heat. The vapors from the coking operation are subjected to a separate primary dephlegrnation to form a heavy tarry condensate which is of highly aromatic character well adapted for fuel oil. This heavy condensate is either withdrawn as the product of the process or is combined with the hot residue withdrawn invention reference is had to the accompanying and heat-insulated. As illustrated, the transfer line extends within the lower portion of the repipe or section [4 through which the heated products are discharged in an upward direction against a bafile l5. In practice with a three-inch transfer line the element [4 maybe composed of; a six-inch pipe. The products passing from the. coil H) to'the'reaction chamber l3 will consist; largely of vapors'and gases and upon being discharged through the enlarged pipe I'd against? the baflle l5 an efficient diffusion of the vapors and gases is accomplished. A' black oil' orresidual stock isintroducedto an upper portion of the reaction chamber 13 ,througha line 16 which extends within the reaction chamber and 'termi-. I nates in a distributororspray' nozzle ll. The

spray ll'is arranged to spray the liquid'oil-ina downward direction through 'the chamber 50 as to bring the liquid oil into intimate contact with the rising vapors. V obstructed space between the distributor l5 and It is desirable to have an unspray'nozzle ll free from baflles" or any other contact elements, since it is contemplated to maintain such elevated temperatures therein that injurious coking would take place if surfaces were presented upon'which coke deposition could occur.

Separation of vapors from liquid residue takes place in the reaction chamber E3. The separated;

vapors pass'thr-ough a vapor line It to a fractionating. tower I 9. This tower is provided with suitable vapor-liquid contact elements suchas bubble trays and with suitable cooling andfrefiuxing means. The vapors are fractionatedin the tower l9 to separate the desired naphtha or gasoline fractions from higher boiling reflux con dens'ate. This reflux condensate is recycled by a adapted for the practice of the inven- In th apparatus illustrated the heating coil I action chamber and terminates in an enlarged pump 20 through a line 2| to the heating coil H1. The 'gasoline or naphtha fractions pass from the tower l9 as a vapor to a condenser'22 thence to a distillate receiver or gas separator 23; Y

Liquid is prevented from accumulating in the reaction chamber I3 bythe rapid withdrawal of liquid residue therefrom. In practice a} very 3 slight amount of vapor may be withdrawhwith Y I theliquid, an amount merely sufficient toinsure that no liquid level is maintained in the reaction chamber. The'residue is withdrawn through a 1 line 24 and pressure-reducing valve 2 5 to a cok- 1 ing drum 26 wherein it is converted to coke by means of its contained heat. In practice a plu- I'he vapor line 2? limited amount of cooling is supplied to the de- 1 rality of coking drums are employed so that while one is' 'on stream the other or others may be down for cokeremoval or cleaning and thus con- 5 tinuity in the complete process maintained. 1 The coking drums are suitably heat-insulated. 1 a The vapors from the coking drum pass through a Vapor line 21 to a primary dephlegmating' zone. 1 As illustrated, a tower 28 is provided having a 5 lower section 29 and an upper section 30 sepa- 1 rated bya trap out tray 3|. 1 communicates with the lower section 29 wherein Q the vapors'from the coking operation are sub- 5 jected to aseparate primary dephlegmation; A

the temperature and so as to' obtain a condensate consisting of extremely high boiling constituents collected as a tarry condensate in the bottom of the dephlegmator. The tarry condensate is withdrawn through a line 32 and a portion thereof is continuously circulated by a pump33 and 7 line 34 back to the dephlegmating zone 29 so as to establish and maintain a continuous flow of liquid through the dephlegmating zone over bafiles or vapor-liquid contact elements therein the dephlegmating zone which will prevent coking. I V The dephlegrnated vapors pass upwardly from th primar dephlegmating zone 29 to secondary,

dephlegmating zone 39 into which charging stock, such as crude petroleum or topped or reduced crude,,isintroduced by a pump 35 through a line 36. 'Iheresultant mixture of reflux condensate and unvaporized charging stock is withdrawn from the tray 3| througha line 37 and is directed by' a pump 38 and line 39 thence through line Is to the upper portion of the reaction chamber I3. unvaporized charging stock may be directed through a branch line 4%? and heating coil 4! which may be conveniently disposed in the, fur nace H. -In the coil4l the oil, is subjectedto a cracking temperature and the heated effiuent is "passed througha transfer line 42*tothe line l6 for introduction'to the reaction chamber 13.

Primary dephlegmate obtained from the coke still vapors may be withdrawn as'a fuel oil product of the process.- This product is of a high aromatic character and due to its solvent properties is particularly-well adapted for blending purposes in the preparation of fuel oils. Instead V of being utilized as fuel oil the primary dephleg mate may be directed by a pump 53 and line 44 to the'coking drum 26 onto the transfer line 24 so as to' combine it with'the mixture of vapors and-liquid which is passed from the reaction chamber-l3 to the coking drum, r c I r Naphtha or gasoline fractions are removedas vapors from the fractionating section 313 and passed to-a' condenser 45 thence to a receiving drum or gas separator 46.

In practicing the invention the cycle condensate is subjected 'to cracking temperature such as 1000 R4030? F in the heating coil l0 and discharged into the reaction chamber l 3 wherein the cracked products are contacted with the downflowing residual stock. Superatmospheric pressures, such as 200-600 p. s. i.; with cracking temperatures upwards 01 900. F. are maintained peratures of 920 F.-'925 F. are recommended for the residue passing from the reaction chamber through the transfer line 24. ducted under reduced pressures approximating atmospheric pressure, preferably not over about .50 p. s.*i. and at temperatures of about 850 F. 7

Separated vapors from the reaction chamber If desired this mixture of condensate and The coking is coni I3 pass through the vapor line I'B'at a temperature of 900 F.91'0 F. and the vapors are fractionated in the tower IB un'der approximately the same pressure as obtains in the reaction chamber or, if desired, under a somewhat lower superatmospheric pressure. For example, with a pressure of 400 lbs. in the reaction chamber the fractionation may be conductedat approximately that pressur or the pressure may be reduced to an intermediate pressure such as 200-300 lbs. The fractionation is conducted so as to take overhead a distillate fraction of desired end point, such as a 400 F. end point fraction, and obtain a reflux condensate comprising the higher boiling constituents which is cycled to the cracking coil In the dephlegmator 29 only a relatively small amount of cooling is supplied which can be accomplished, for example, by cooling a small amount of the reflux condensate from tower l9 and refluxing it in the dephlegmator 29/ It is desired to condense in this primary dephlegmator only the extremely high boiling contsituents so that the bulk of the vapors will remain uncondensed and pass to the secondary fractionating section 30. Temperatures of about 800 F.-8l0 F. are maintained at the bottom of the dephlegmat irlg zone 29 without coking due to the hot circulation accomplished by the pump 33. Due to the relatively small amount of reflux supplied to the dephlegmator 29 and to the circulation of the hot oil by the pump 33 there is a minimum temperature differential through the dephlegmator so that the uncondensed vapors pass to the dephlegmating section 30 at temperatures approaching 800 F. The residual charging stock introduced by the pump 35 is preferably passed in heat exchange with the hot products of the system rior to introduction to the dephlegmator 3E and the mixture of reflux condensate and unvaporized charging stock is withdrawn from the tray 3! at temperatures of about 750 F.-780 F. This mixture is either passed directly to the reaction chamber I3 through line H5 or is passed through the heating coil 4!: wherein it is heated to temperatures of the order of 800 F.-900 F. before being introduced into the reaction chamber.

In the prior practice when using, for example, coke drums 40 ft. by 10 ft. in size it was necessary to maintain the coke drum outage gauge at about 23-24 ft., that is coke depths of 16-17 feet, in order to prevent priming and consequent coking in the primary dephlegmator. By means of the present invention the outage gauge may be reduced to as low as -1? feet, that is the coke depths increased to 23-25 feet, with a consequent increase in fresh charge capacity of some 30-50%.

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

I claim:

I. In the combination cracking and coking of hydrocarbon oils the process that comprises passing a condensate stock through a heating coil wherein it is subjected to a high cracking temperature, delivering the heated stream into the lower portion of a Vertically disposed reaction chamber wherein separation of vapors from liquid residue takes place, introducing a stream of heated residual stock into an upper portion of the reaction chamber, subjecting resultant down-flowt 6 ing liquid and upwardly rising vapors to countercurrent'contact in. an unobstructed zone within the reaction chamber at cracking temperatures of upwards of 900 F. under 200-600 pounds pressure, withdrawing the separated vapors from an upper portion of the reaction chamber at a temperature of the order of 900 F., withdrawing the liquid residue from the lower portion thereof at a temperature of the order of 920 F. at a rate adequate to prevent the accumulation of liquid residue therein, delivering the withdrawn residue to a coking zone wherein the pressure is reduced to a low pressure not exceeding about 50 pounds and wherein a temperature approximating 850 F. is maintained by means of the hot residue introduced to thereby effect coking solely by the contained heat of the residue subjecting said vapors withdrawn from the reaction chamber to fractionation to separate lighter products from higher boiling reflux condensate, cycling said reflux condensate to the aforesaid heating coil, subjecting evolved vapors from the coking zone to dephlegmation with a residual charging stock to form a resultant mixture of reflux condensate and unvaporized residual changing stock, passing said mixture of reflux condensate and unvaporized residual charging stock through a heating coil wherein it is heated to a temperature of the order of BOO-900 F. and

directing the heated mixture to the upper portion of the aforesaid reaction chamber as the residual I stock introduced therein.

2. In the combination cracking and coking of hydrocarbon oils the process that comprises passing a condensate stock through a' heating coil wherein it is subjected to a high cracking temperature, delivering the heated stream into the lower portion of a vertically disposed reaction chamber wherein separation of vapors from liquid residue takes place, introducing a stream of heated residual stock into an upper portion of the reaction chamber, subjecting resultant downflowing liquid and upwardly rising vapors to countercurrent contact in an unobstructed zone within the reaction chamber at cracking temperatures of upwards of 900 F. under 200-600 pounds pressure, withdrawing the separated vapors from an upper portion of the reaction chamber at a temperature of the order of 900 F., withdrawing the liquid residue from the lower portion thereof at a temperature of the order of 920 F. at a rate adequate to prevent the accumulation of liquid residue therein, delivering,

reaction chamber to fractionation to separate lighter products from higher boiling reflux eondensate, cycling said reflux condensate to the aforesaid heating coil, subjecting evolved vapors from the coking zone to dephlegmation with a residual chargingstock to form a resultant mixture of reflux condensate and unvaporized residual charging stock, passing said mixture of reflux condensate and unvaporized residual charging stock through a heating coil wherein it is heated to a temperature of the order of 800-900 F. and directing the heated mixture to the upper portion of the aforesaid reaction chamber as the residual stock introduced therein.

3. In the combination cracking'and coking of hydrocarbon oils the process that comprises passing a condensate stock through a heating coil wherein it is subjected to a high cracking tem-' 'perature, delivering the heated stream into the lower portion of a vertically disposed reaction chamber wherein separation of vapors from liquid residue takes place, introducing a stream of I heated high boiling constituents, formed as hereinafter specified, into an upper portion of 1 the reaction chamber, subjecting resultant downflowing liquid and upwardly rising vapors .to

' jecting said vapors withdrawn from the reaction chamber to fractionation to separate lighter products from higher boiling reflux condensate, cycling said reflux condensate to the aforesaid heating coil, subjecting the evolved vapors from hydrocarbon oils the process that comprises passing condensate stock through a heating coil wherein it is subjected to a, high cracking temperature deliveringthe heated stream into the lower portion of a vertically disposed reaction chamber wherein separation of vapors from liquid residue takes place, introducing a stream of heated high boiling constituents, formed as hereinafter specified, into an upper portion of the reaction chamber, subjecting resultant downflowing liquid and upwardly rising vapors to countercurrent contact in an unobstructed zone within th reaction chamber at cracking temperatures of upwards of 900.F. under 200-600 lbs. pressure, withdrawing the separated vapors from the upper portion of the reaction chamber I at a temperature of the order of 900 F., withthe coking zone to a separate dephlegmation in a primary-dephlegmating zone to form a heavy tarry condensate, subjecting resultant dephlegmated Vapors to dephlegmation with a residual charging stock to form a resultant mixture ;of reflux condensate and unvaporized residual charging stock; passing said mixture of reflux condensate and unvaporized residual charging stock through a heating coil wherein-it is heated to temperatures of the order of 800-900 F. and

directingthe resultant heated products to the upper portion of the reaction chamber to con- 'stitute the aforesaid high boiling constituents v introduced thereinto.

4. In the combination cracking and coking of drawing the liquid residue from the lower portion thereof at a temperature of upwards of 920 F. and at a rate adequate to prevent the accumulation of liquid residue 'therein, delivering the withdrawn residue toa coking zone wherein the pressure is reduced and wherein coking is effected solely by the contained heat of the residue, subjecting said vapors withdrawn from the reaction chamber to fractionation to separate lighter products from higher boiling reflux condensate, cycling said reflux condensate to the aforesaid heating coil, subjecting evolvedvapors from the coking zone to dephlegmation with aresidual charging stock to form a resultant mixture of reflux condensate and unvaporized residual charging stock, passing said mixture of reflux condensate and unvaporized V residual charging stock through a heating coil wherein it is heated to a temperature of the order of BOO-900 F. and directing the resultant heated products to the upper portion of the reaction chamber to constitute the aforesaid high boiling 40 constituents introduced thereinto.

' JOSEPH MASON BARRON. f