US2160872A - Cracking hydrocarbon oils - Google Patents

Description

June 6, 1939. L. c. KEMP CRACK'ING HYDROCARBON OILS Original Filed March 24, 1936 BY 'u/M, 1 www ATTORNEY Patented June 6, 1939 vPATENT OFFICE CRAC/KING HYDE()CARBON OILS Lebbeus C. Kemp, 'Port Arthur, Tex., assigner to The Texas Company, NewYork, N. Y., a corporation of Texas Original application March 24, 1936, Serial No.

Divided and this application February 25, 1939, Serial No. 258,387

3 Claims.

V This application is a division of the pending application Serial No. 70,628, filed March 24, 1936. This invention relates to the manufacture of gasolineof superior'anti-knock quality and contemplates aunitary process in which higher-boiling oil is converted into lower-boiling oils within the gasoline boiling-point range and gasoline constituents of insufficiently high anti-knock quality are subjected to reforming to increase the antiknock quality thereof.

The invention is` particularly adapted for the processing of heavy stocks, such as reduced crude or crude petroleum containing large proportions of. heavy residual constituents. In accordance with the invention, heavy or highly viscous stocks may be subjected to moderate conditions of cracking to effect viscosity-breaking of the stocks and to thereby form relatively large quantities of gas oil or intermediate constituents adapted for high temperature cracking and a smaller proportion of gasoline, which, due to having been formed under viscosity-breaking conditions, may be of relatively inferior anti-knock quality.y The gas oil or intermediate constituents may be subjected to high-temperature cracking conditions conducive to the formation of gasoline constituents of high'anti-knock quality, and the relatively low anti-knock gasolinel constituents derived from Y the viscosity-breaking operation may be subjected .to reforming to increase the anti-knock quality thereof.

An important feature ofthe invention consists in taking the residual fraction derived from the viscosity-breaking operation and bringing such residual fraction into contact with high-temperature products undergoing reaction in the reforming zone or in the high-temperature cracking zone and effecting a short-time cracking of the heavy fraction. In other words, heavy residual fractions from the viscosity-breaking operation which are not well adapted for ordinary drastic crackingV operations may,in accordance with the invention, be combined with a'stream of highlyheated, cracked or reformed products and subjected to an intensive cracking operation conducive to the formation of high anti-knock gasoline constituents, but. under conditions in which the extent of cracking. of the residual constituents of the heavy fraction may be appropriately limited, so that over-cracking, which would produce coking difficulties, may be avoided.

. In order to more completely disclose the invention, reference will now be had to the accompanying drawing, which is a flow diagram illustrating apparatus adapted for the practice of the invention.

The drawing shows a cracking coil I and a reforming coil I I installed in suitable furnaces and communicating with a reaction chamber I2 provided with fractionating towers I3 and I4, and a viscosity-breaking coil i5 disposed in a suitable furnace and discharging into an evaporator I6, provided with a fractionating tower I l. In prac-` ticing the invention, the charging stock may be introduced by a pump I8 through a charging line I9 which may be provided with connections to Va heat exchange coil 2E positioned in the dephlegmator id. The charging line is branched, one branch 2I leading into the primary dephlegmator I3, so that charging stock, or a portion thereof, may be introduced directly into the tower to be contacted with the vapors therein, and the other branch 22 leading to the viscosity-breaking coil I5. A line 23 is provided for conducting bottoms from the dephlegmator I3 to line 22 for introduction to the viscosity-breaking coil I5.

As stated, the viscosity-breaking coil I 5 discharges into the evaporator I6. The evaporator is shown provided with a fractionating section 211 and a trap-out tray 25 for removing a heavy cut; A vapor line 23 extends to the fractionat- I ing tower Il. A condenser coil 2'! serves for condensing the overhead vaporsirom the towerV Il, the condensate being collected in receiving drum 2B. Reflux condensate from the tower III is drawn through line 29 and directed by pump 3E? through line 3I tothe high-temperature cracking coil I0. Reflux condensate from tower Irl is drawn through line 32 and directed by pump 33 through line 34 to the cracking coil I0. The charge to the cracking coil Ill may-thus comprise reflux condensateV from either or both of the towers I4 and I'I. l

The products from the cracking coil I0 pass through a transfer line 35- .to the enlarged reaction chamber I2. The residue separated out from the viscosity-broken products in evaporator I5 may constitute'the heavy fraction which is brought into contact with the highly heated products discharging from, thel cracking .coil II) for short-timer` reaction therewith, and for the purpose of carrying out such operation, a line 36 leads from the evaporator I6 to a pump 13'? which forces the residue through line 38 to transfer 'line 35 for introducing the heavy stock intothe reaction chamber I 2. In addition to using the residue from the evaporator I6 as the heavy fraction to be introduced into the cracking chamber I2 the heavy condensate collected` in trap-outv 55 tray may be so employed. For this purpose, a line 39 leads from the trap-out tray 25 to a pump 40 by which the heavy condensate may be pumped through line il to line 38 for introduction to the transfer line 35. In cases where it is not desired to introduce this condensate into the reaction chamber I2, the condensate may, in accordance with the invention, be cycled to the viscosity-breaking coil I5, as through the branch lines 42. Thus in accordance with the invention, the heavy residue, which is not suited for ordinary high-temperature, high cracking per pass operations, may be directed to the transfer line to be subjected to intensive cracking conditions, due to the contacting with the products from the high-temperature cracking coil, while the heavy gas oil from tray 25 is cycled to the viscositybreaking coil I5. Y

As indicated in the drawing, the transfer line 35 preferably enters the reaction chamber I2 at the upper end thereof, so as to thus provide for down-flow in the reaction chamber. A vapor line 43 is shown for conducting separated vapors from the cracking chamber I2 to the primary fractionating tower I3, and a tar or residue line IM is indicated for withdrawing tar or residue from the cracking chamber. In practicing the invention, residual material is not permitted to accumulate in the reaction chamber I2, the tar or residue being withdrawn at such a rate as to effectively prevent the accumulation of liquid therein. Thus, in accordance with the invention, the heavy stock from the viscosity-breaking operation is brought into intimate contact with f the high-temperature products from the cracking coil IIJ, to thus subject the heavy stock to intensive cracking conditions conducive to the formation of constituents of high anti-knock quality, and due to the rapid separation of liquid constituents from vapors in the reaction chamber I2, and by reason of the fact that the liquid constituents are not permitted to accumulate therein, the over-cracking of residual constituents into coke is largely prevented. In this way heavy stocks from theV viscosity-breaking operation, which are not well adapted for ordinary hightemperature cracking, may be utilized to produce an additional yield of gasoline without any material sacrifice of anti-knock quality in the ultimate product.

The vapors which pass through vapor line 43 are subjected to fractionation in the primary and secondary towers I3 and I4. The heavy condensate separated out in tower I3 or, in the event that charging stock is introduced into this tower,

the compositefraction of reflux condensate and unvaporized constituents of the charging stock, is withdrawn through line 23 for introduction to the viscosity-breaking coil I5, and the secondary condensate, which is well adapted for high-temperature, high cracking Vper pass cracking, is cycled to theV high-temperature cracking coil I0. The overhead vapors from the tower I4 are condensed in condenserY coil 45, the distillate being collectedin receiving drum or gas separator 46. The distillate thus collected inV receiving drum 46 constitutes a gasolinerstock of high anti-knock value. Y

The fractionation of the vapors evolved in the evaporator I6 and tower I 'I is advantageously car-v ried out in such a way as to separate out a heavy condensate in the trap-out tray l25, anY intermediate condensate in thelbottom-of the tower I'I, and a light distillate collected in the receiving drum 28. Thus the'fractionation may be so conducted as to segregate in the trap-out tray 25 a highly viscous condensate or a stock containing a very high percentage of waxy constituents. The stock thus segregated in the trap-out tray 25 may be either cycled to the viscosity-breaking coil for further cracking under viscosity-breaking conditions or directed through line 4I to the transfer line 35 to be thus subjected to an intensive cracking conducive to the formation of superior'anti-knock quality gasoline constituents.

The fractionation of the vapors remaining uncondensed after the segregation of the heavy gas oil cut may be so conducted as to separate out a light stock adapted for vapor phase cracking or to segregate a particular gasoline fraction which it is desired to subject to reforming. Thus the fractionation may be so conducted as to separate out a fraction collected at the bottom of the tower II which will include the gasoline constituents which it is desired to reform. This cut may be designated as a heavy naphtha or light gas oil cut, and will contain a large proportion of constituents in the gasoline boiling range. The

` initial boiling point of this cut will generally be from about 200 to 300 F. The overhead vapors from the tower I 'I may be subjected to condensation in the coil 21 and collected as a light gasoline distillate in the receiving drum 28. In case it is desired to subject to reforming the entire gasoline cut, it is unnecessary to fractionate the gasoline into a light and heavy cut.

In accordance with a modification of the invention the vapors evolved in the evaporation of the viscosity-broken products may with advantage be fractionated to segregate a light gas oil cut adapted for vapor-phase cracking and a gasoline cut to be reformed. In carrying out this type of operation, a separate reforming coil II is provided and thus a light gas oil stock adapted for vapor-phase cracking for conversion into lower boiling or gasoline constituents may be withdrawn from tower I1 through line 29 and directed to the high-temperature cracking coil ID, and, as shown in the drawing, the fractionating tower I1 may be provided with a trap-out tray 41 with a line V48, pump 49, and line 5I! for introducing the desired gasoline cut rto the reforming coil Il. A branch line 5 is indicated for withdrawing distillate from the receiving drumZB, in the event it is desired to subject to reforming the distillate collected in receiving drum 28. Thus, in accordance with the invention, a light gas oil cut adapted for high cracking per pass or more particularly for vapor phase cracking for conversion into gasoline'may be withdrawn from the tower I'I through line 29 and directed by pump 30 through line 3l to the high-temperature cracking coil III, while a gasoline stock introduced by the pump 49 to the reforming coil II is'subjected to reforming conditions to increase its antiknock quality;

In one modification contemplated by the invention the gasoline stock to be reformed is collected in the bottom of the fractionating tower Il, with or without the addition of some higherboiling constituents, and this gasoline-containing stock is directed by pump 30through line 3| and a branch line 52 to, line 5I!Y and :thence tothe reforming coil II, while the Vstock directed to the high-temperature cracking coil I0 may consist of the cyclev condensate withdrawn from towerV I4 and introduced by pump 33. t Y

In practicing .the invention, the charging stock or commingled `charging stock and` reflux condensate from the tower I3 may be subjected to mod- 4o to, includingthe heavyfraction from the viscoserateconditionsof crackingin the AcoilIS adapt- ,ed Vfon-effecting a. reduction in Vthe viscosity Vof theaoibandfor producing arelatively largeyield .ofrconstituents suitable for further conversion into :gasoline and aA relatively vsmaller yield of gasoline... The bestv temperature conditionsy for quality.,

this -operation involve@ temperatures of about ,S-880 F. under vcondi tions, lof k,a cracking `per pass of aboutv 8-15%, usually about V1 0-12%. Practical. operating pressures are about 200-,400 lbs. lThe vpressureflflflay `with advantage-.be reducedin the evaporator I 6 to loW super-atmospheric pressures or to pressures approximating atmospheric.

4ingper pass, such as a crackingA per pass of.2 0%

and higher, so thatthe conversion therein will be under conditions in` which gasoline of high anti-,knockfcharacter is formed. Temperatures of the order of 900 F. or 1000 F. may berecolmmended, although higher temperatures adapted for intensive cracking under relatively short time conditions may beemployedwith advantage. In the event .that the cracking coiliiiis also used for reforming ga'soiine constituents introduced thereto, the temperatures vemployed should be Within a range adapted for accomplishing reforming. I.

Itis an object o fltherinvention to maintainv cracking temperaturesin the reaction chamber I2 ofthe commingled products'introduced thereitybreaking operation, sufiiciently high to maintain conditions of conversion therein capable of sustaining a rate of cracking per pass adapted to produce high anti-knock gasoline. A temperature Vof 850? F. is approximately. the minimum temperature adaptedforv this purpose., At the same `time Athe temperature must not. exceed a .range adapted for sustaining a condition of liquidity adjacent the pointat 'which residual constituents are Withdrawn from the chamber. It may be pointed out that Within Vcertain temperature ranges the heavyv stock introduced into the reaction chamber I2 yinto contact With the highly heated products from either or both of the high temperature cracking'coils I 0 and I2 actually serves to preventcoking under conditions Where liquid is withdrawn at a. rate adequate to prevent the accumulation of liquid in the chamber. The upper limit of this temperature range is approximately 930 F. Thus the temperatures maintained in the reaction chamber I2 should exceed 850 F. in order to maintain conversion conditions therein adapted for the production of anti-knock gasoline, but should not exceed about 930 F. While the pressures employed may vary considerably and still facilitate an efficient operation, pressures of about 200 lbs. to 400 lbs. are to be recommended for the reaction chamber I2.

In one modification contemplated by the invention, the gasoline constituents from the viscosity-breaking operation,` which-it is desired to reform, may be directed by pump 49 through line Y 'Ihetemperature the reforming Icoil I I f shouldnotbeunder 850 F., andnto obtain best transfer line'35 for introduction into the reaction chamber -.I2. In this way the gasoline constituents to be reformed are brought into contact With the highly heated products from the cracking coil I0, aswell as in contact with the heavyor residual stockv from the viscosity-breaking operation introduced through line 38 and the reformation ofthe gasoline constituents is accomplished in the transfer line 35 and reaction cham'- berl ,I2l wherein reforming A conditions are maintained.

-The residue Withdrawn from the reaction lchamber I2 through line 44 may be Withdrawn to storage orto a tar flashingunit A'11n-one method of operation:contemplatedby the invention, the heavyoil from the viscositybreaking operation., instead of kbeing introduced into Ythe transfer line from the cracking and reforming c oils or into thereaction chamber, may be introduced into the latter portion of either the reforming coill or the cracking coil, ora portion of such heavy;oi1 may be introduced into the latter section 4of' the cracking coil and anotherl portion of the heavy oil introduced into alatter portion of the reforming coil, the commingledl products passing thence through the transfer line into the reaction chamber. Inanoth'er modification contemplated by the invention, the highly heated products from the cracking coil or from both the cracking coil and reforming coil may, before being introduced into the reaction chamber I2, be: passed into a soaking or reaction zone, preferably in the form of a coilinsulated or moderately heated to prevent loss of heat, and the.

heavy stock from the viscosity-breaking operation passing through the line `38 may also be vintroduced into this'soaking section. In this Way the heavy stock may be subjected to a further eX- tent of cracking than when introduced directly into the transfer line 35 or into the reaction chamber-I2. The cracking and reforming reactions `may be continued on the 'commingled products upon,4 being introduced into the reaction chamber I2, but by preventing the accumulation of liquid therein the undue cracking ofy liquid or residual constituents is prevented. In this method of operation both the soaking zone and the reaction chamber should be maintained at a cracking temperature adequate to sustain reactions Ayielding products of high anti-knock quality.

Obviously many modications and variations I rof the invention, as hereinbefore set forth, may

be made Without departing from the spirit and scopethereof, and therefore, only such limitations should be imposed as are indicated in the comprises passing hydrocarbon oil through a cracking coil to subject the oil to cracking therein, directing resultant cracked products into a reaction chamber maintained at a cracking temperature in which separation of vapors from liquid occurs and from which liquid is Withdrawn at a rate adequate to prevent the accumulation of liquid therein, passing separated vapors to a primary fractionating zone, introducing charging stock 'comprising residual constituents of crude petroleum into contact with vapors therein and forming a composite fraction therein separate from said liquid being Withdrawn from the reaction chamber and comprising resultant reflux condensateand unvaporized constituents of the charging stock, passing uncondensed vapors to a secondary fractionating zone wherein fractionation is carried on to separate out a gasoline distillate and a reflux condensate, directing reflux condensate thus obtained to said crackingl coil, passing said composite fraction from the primary fractionating zone through a heating coil and subjecting the oil therein to moderate cracking conditions to Vproduce viscosity-breaking thereof, subjecting the viscosity-broken products to distillation in a separate distilling zone to effect separation into a residue and vapors, fractionatingY separated vapors in a separate fractionating zone to separate out a gasoline-containing stock, directing said gasoline-containing stock to said cracking coil, maintaining temperature conditions in said cracking coil adequate to effect the reformation of gasoline constituents, and directing said residue into contact with the cracked products discharged from said cracking coil to effect the Ycracking thereof in said reactionV chamber.

j 2. The process of 'cracking hydrocarbons that comprises passing hydrocarbon oil through a cracking coil to subject the oil to cracking therein, directing resultant cracked products into a reaction chamber maintained at a cracking temperature in which separation of vapors from liquid occurs and from which liquid is withdrawn at a rate adequate to prevent the accumulation of liquid therein, passing separated-vapors to a primaryfractionating zone, introducing charging stock comprising residual constituents of crude petroleum into contact with vapors therein and forming a composite fraction therein separate from said liquid being withdrawn from the reaction chamber and comprising resultant reux condensate and unvaporized constituents of the charging stock, passing uncondensed vapors to a secondary fractionatingv Zonel wherein fractionation is carried cn to separate out a gasoline distillate and a reflux condensate, directing reflux condensate thus obtained to said cracking coil, passing said composite fraction from the primary fractionating zone through a heating coil and subjecting the oil therein to moderate cracking conditions to produce viscosity-breaking thereof, directing the resultant viscosity-broken products to a separating Zone wherein separation of vapors from residue takes place, passing the separated vapors to a separate fractionating zone wherein the vapors are fractionated to form a lighter fraction comprising gasoline constituents and a higher boiling reflux condensate, directing said higher boiling reiiuX condensate to said heating coil wherein the oil is subjected to viscositybreaking conditions, subjecting said lighter fraction`fcomprisingA gasoline constituents to conditions" of Atemperature to effectv the reforming thereof into constituents of increased anti-knock quality, directing the products of such reforming into aforesaid reaction chamber, and introducing said-residue into saidv reaction chamber to be contacted therein with the products of said reforming and the products discharged from said Yare subjected to fractionation to form a heavy reiiux condensate, passing uncondensed vapors from the primary fractionating zone to a secondary fractionating `Zone wherein fractionation is vcarried on to separate out a gasoline distillate and reflux condensate, directing reux condensate thus obtained from ythe secondary fractionating zonel to saidv cracking oil, combining charging stock comprising `residual constituents of crude petroleum with heavy reflux condensate formed in the primary fractionating zone and directing the constituentsjthus combined to a viscositybreaking zone wherein said constituents are heated at a cracking temperature and subjected to cracking conditions to 'effect' viscosity-breaking, directing the resultant viscosity-broken products to a separating zonewherein separation of vapors from residue takes place, passing the separated vapors to aseparate fractionating zone wherein the vapors are fractionated to form a lighter fraction comprising gasoline constituents, an intermediate reux condensate and a higher boiling reflux condensate, directing said higher boiling reux condensate to'said Viscosity-breaking zone, passing said intermediate reuX condensate to aforesaid cracking coil, subjecting said lighter fraction containing gasoline constituents to conditions of temperature to effect reforming thereof into constituents of increased anti-knock quality, directing the products of such reforming into aforesaid reaction chamber, and introducing said residue into said reaction chamber to be contacted thereinwith the products of said reforming and the products discharged from said cracking coil'.

LEBBEUS C. KEMP.

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