US2088778A - Cracking hydrocarbon oils - Google Patents

Description

H. DIMMIG CRACKING HYDROCARBON OILS Filed. Sept. 8, 1934 2 SheetS-Sheec l INVENTOR.

LOMW M ATTORNEY.

Aug. 3, 1937. H. DIMMIG 2,088,778\r CRACKING HYDROCARBON OILS Filed Sept. 8, 1934 2 Sheets-Sheet 2 BY r www@ i* M ATTORNEY,

Patented Aug. 3, 1937 UNTD `STATE `.mean

PATENT F F i i 2,088,778 oRAoKING HYDRooARBoN oiLs Application September 8, 1934, Serial No. 743,219

1 Claim.

This invention relates to cracking petroleum hydrocarbons into products suitable for motor fuel and pertains more particularly to a method of inhibiting coke deposition in vapor lines employed for transferring hot cracked vaporproducts to other parts of the cracking equipment wherein the cracked products are separated into the desired components.

Although the invention will have a more general application, it is of particular advantage in vapor phase cracking processes, and especially in high temperature cracking processes in which substantially the entire charge becomes vaporized during the cracking operation, in which case the products leaving the cracking zone are essentially in vapor phase.

In such processes operating difliculties have been experienced, dueto c'ke accumulation in passages or conduits employed for transferring the hot cracked vapor products to subsequent equipment wherein separation and purication of the products is accomplished.

Attempts have been made to avo-id coke deposition in the vaporpassages by introducing into the passages a cooler oil of various types and character so as to `reduce the cracked products to a temperature below that at which appreciable coking Will occur. For example it has been proposed to introduce light vaporizable extraneous hydrocarbon oil into thehot vapor conduit and utilize the heat of vaporization of the extraneous oil to coo-l the products. However, inv high temperature cracking processes the relatively large amount of extraneous vapo-rizable oil necessary to bring productsto a temperature below that at which appreciable coking occurs imposes an extra heavy burden on the 'succeeding equipment employed for separation and purification of the products and has a disturbing influence on the temperature control of the succeeding equipment.

It has also been proposed to introduce into the hot cracked vapor pro-ducts a relatively heavy hydrocarbon oil containing substantial amounts of constituents Which will not be vaporized at `the equilibrium temperature of the commingled products, so that the unvaporized liquid constituents o-f extraneous cooling medium may serve to flush or Wash the coke thereafter formed from the conduit.

However, in high temperature vapor phase cracking processes coking troubles are encountered immediately adjacent the point ofintroduction of the relatively heavy residual stock due to the almost instant reversion of the heavier (Cl. ISG-47) constituents to coke when commingled with the high temperature vapor products.

In accordance with my invention, before introducing the relatively heavy residual stock to serve as a cooling and flushing medium for they 5.;

coke or carbon thereafter formed, I rapidly cool the hot vapor products to a'temperature at which the unvaporizable constituents of the residual stock will not substantially revert to coke and,

after the preliminary cooling step, I immediately 10` introduce a heavy residual stock so as to take advantage of the ushing or Washing effect of the unvaporized constituents as soon as possible Without causing rapid reversion of these constituents to coke. In carrying out the process in accordl5 ance with my invention the vapor products need not be preliminarily cooled to below cracking temperature before the introduction of heavy residual stock but need only be cooled to a temperature at which the heavy hydrocarbons intro-v 20 duced will not revert to coke. By Way of example, I may rapidly cool cracked vapor productsV from a temperature of from 850 F'. to 1100" F.

or more to a temperature of from 800 F. to 950 F. and thereafter immediately introduce a 25 relatively heavy stock having a component which will not be vaporized at the last mentioned ternperatures but which will remain in liquid condition and thus serve to flush the vapor passage and Wash aWay any carbon which may thereafter 30 be formed and thus prevent any unobjectionable collectionof carbon or coke in the system.

The initial cooling may be accomplished `by direct or indirect heat exchange with a suitable cooling medium. However, in order to reduce 3 coking diiiiculties Within this preliminary cooling zone the cooling should be effected rapidly so as to require only a relatively short zone through which the hot, dry, cracked vapor products must pass before being intermingled With the heavy 40 residual stock containing the unvaporizable constituents.

With the above and other advantages'in view, which Will be apparent from the more detailed description of the preferred embodiment hereinafter, reference is now made to the accompanying drawings in which:

Figure 1 is a digrammatic view in elevation showing an apparatus for carrying out a cracking process in which my invention may be employed, and i Figure 2 is a sectional view in larger scale of the vapor outlet leading from the reaction chamber. i

Referring to Figure 1 the apparatus shown 55 comprises in general, heating furnaces I0 and II; a reaction chamber I2; a separating chamber I3; a fractionating tower I4; a combined fractionating and distilling tower I5, condensers I6 and II; distillate receiving drums I8 and I9, together `with connecting pipe lines, pumps and other appurtenant equipment for carrying out the process hereinafter described.

Fresh charging oil for the process which is preferably crude petroleum, but which may be a reduced crude or heavy gas oil and which may be preheated by heat exchange with hot products of the process, is introduced into the combined distilling and fractionating chamber I5 through line 20 provided with a charging pump 2|. The charging oil introduced into the chamber I5 is heated to a distilling temperature by direct counter-flow contact with hot vaporized components from residual products withdrawn from the separating chamber I3 through line 22, provided with a pressure-reducing valve 23. The hot residual products from line 22 are discharged after reduction in pressure into the bottom portion of the chamber I5 and are further vaporized by reduction in pressure. Uncondensed vapors formed in the distilling and fractionating chamber kI5 pass overhead through line 24 to condenser I1 wherein a light gasoline distillate is condensed after which the products passY to the separating drum I9 Yfor separation of gases and distillate.

The unvaporized constituents of the fresh charging oil together with the heavier condensed vapors from the residual products and fresh oil are collected in trapout tray 25 andY passed through line 26, provided with a pump 2l, to the heating coil 28 located in the furnace I I wherein the charging oil is heated to a'cracking temperature and maintained for a period adequate toeffect mild conversion and a material reduction in the viscosity of the charging stock. For example the oil duringv its passage through the heating coil 28 may be subjected to a temperature ranging from 800 F. to 850 F. for a period which will 45 convert about 8 or 10 percent of the oil into hydrocarbons within the gasoline range and about 20 or 25 percent into hydrocarbons suitable for vapor phase charging stock for the furnace I0.

The hot products leaving furnace coil 28 pass through line 29 tothe lower portion of the separating chamber I3, preferably without any substantial reduction in pressure. The separator is preferably operated .at a substantial supe-ratmospheric pressure, say for example, between 195 and 215 pounds per square inch. The lighter hydrocarbon products formed in the heating coil 28 are separatedfrom the residual liquid comwardly in such Vform through the separator I3 6o where they commingle with cracked vapor products from the reaction chamber I2. I 'I'he upper section of the separator I3 is provided with suitable fractionating elements such as perforated baffle plates, disc and doughnut, screen-plates, orbubble trays to effect fractionation of the. vapors and condense heavier components thereof. If desired a suitable refluxing agent such as light gas oil collected in the upper trapout tray 30 of the distilling and fracti'onating chamber I5 may be introduced into the upper portion of the separator I3 for knocking down entrained coke particles and heavy vapor constituents. Vapors remaining uncondensed in the separator I3 are withdrawn through vapor, line 3| at a. temperature of, for example, about '750 F. to 760 F. and passed to fractionating tower I4 wherein further separation of the vapors into an overhead vapor fraction containing the gasoline constituents and a clean condensate fraction suitable for vapor phase cracking is effected. To this end the fractionating tower I4 is provided with usual fractionating elements and, if desired, reflux agents such as a light gas oil from the trap-out tray 30 and/or gasoline distillate may be introduced into the upper portion L of the tower through line'32. This fractionating tower I4 is preferably maintained under substantially the same pressure as the separating chamber I3.

Vapors remaining uncondensed in the fractionating tower I4 and containing the gasoline component are withdrawn from thetower through vapor line 33 and passed to the condenser I6 in which the gasoline component is condensed. The products from condenser I6 discharges into a separating and receiving drum I8 in which liquid and gases separate. The temperature at the top of the fractionating tower I4 is controlled so as to produce a gasoline having the desired end point such as 400 F. or thereabouts. The condensate collecting in the bottom of the tower I4, which may be at a temperature of about '700 F., and which may have a specific gravity of about 25 A. P. I., a color corresponding to aboutr3 N. P. A. and a low free carbon content, preferably not over .1 percent by the Conradson test, is Withdrawn through line 34, provided with pump 35 which forces the condensate through the vapor phase cracking coil 36 located in furnace I0 and thence through the transfer line 31 to the lower portion of the reaction chamber or soaking drum I2.

The condensate during its passage through the heating coil 36 and the reaction chamber I2 is subjected to vapor phase cracking conditions, preferably at a temperature in excess of 850 F'. and more desirably Vat a temperature ranging from about 900 to about 950 F. while maintained at moderately low pressures such as from to 225 pounds per square inch. The temperature and time of treatment within the cracking Zonemay be controlled so as to convert from about 15 to 20 or more percent of the condensate stock into gasoline during a single passage of the condensate through the cracking zone. At the temperature and pressure so maintained substantially the entire charging stock is vaporized during the cracking process.

'I'he vapors after being permitted to soak for the desired period within the reaction chamber I2 are'withdrawn through the vapor outlet 38 and cross-fitting 39 andV are passed thence through vapor line 40 to the bottom portion of the separator I3 where they commingle with the vapors liberated from the charge introduced into the separator from the line 29. The combined vapors are subsequently fractionated in the top of the separating chamber I3 and the fractionating tower I4 as hereinbefore described to produce the desired distillate product and reflux condensate.

My invention is not necessarily limited in its application'to the oil cracking process hereinbefore described, this being an example of a type of cracking operation in which my invention has been found to be of advantage. As illustrated, my invention is employed for the purpose of reducing coke difficulties in the vapor outlet 38 leading-from the reaction chamber I2 and the vapor conduit`40 leading to the separating chamber I3.

Referring now to Figure 2, the hot cracked vapors leaving the reaction chamber l2 are preliminarily cooled by a spray of relatively light vaporizable oil introduced into the stream of vapor ,through spray ring il mounted in the reaction chamber ii. immediately adjacent the vapor outlet. As illustrated, a portion of the reux `condensate formed in fractionating tower lll may being entrained in the outgoing vapors. The vaporizable cooling medium may comprise substances other than hydrocarbon oil as before mentioned. The vapor after being preliminarily cooled by the vaporizable oil introduced through spray ring il is immediately commingled with a relatively heavy stock which is introduced into the stream through line d5 which extends through the cross-fitting 39 and terminates in a nozzle 4G. The stock so introduced may be a crude, reduced crude, residual stock from the cracking operation, or any extraneous heavy sto-ck which contains constituents Which will remain in liquid form at the resulting temperature of the mixed products and thus serve to flush the remaining portion of the vapor line 40 of carbon particles.

As illustrated, a` portion of the fresh charging stock such as crude or reduced crude being passed to the viscosity breaking furnace .l l through line 26 may be passed throirgh lines il and t5 to the nozzle 46 or a portion of the cracked residual products from the bottom of the separating chamber i3 may be passed through line 138 to the line 45 and nozzle it. Also if desired a. mixture yof cracked residual stock and crude or reduced crude may be introduced into the stream of vapors through the nozzle @il and the lines above indicated. If desired an extraneous heavy stock co-ntaining unvaporizable constituents may be passed to nozzle t6 through lines @El and 45.

Suitable cooling coils 5l) and 5l may be provided in lines Wand l5 respectively so that the cooling and quenching mediums taken from the system may be cooled to any desired extent before being introduced into the outlet of the chamber through the spray ring il and nozzle l.

Sufficient vapcrizable oil is introduced through the spray ring el to reduce the vapor products to a temperature which Will not cause rapid conversion of the heavier constituents of the charge thereafter introduced through nozzle M5 into ook-e. The temperature need not be reduced, however, to below that at which coke will not subsequently be formed. The amount of oil introduced through the spray ring 4l and the nozzle it Will depend upon the capacity of the unit, the temperature of vapor products and coolv ing medium, so that the exact amount can not be definitely specified. in a specific operation on a unit treating approximately 16,000 barrels of fresh oil per day and wherein the temperature the top ci the soaking drum Was in the Vneighborhood of 885 F., the introduction of substan* tially equal amounts of stock through the spray ring il and through the nozzle t@ at a rate of approximately 60 barrels per hour respectively, was found ample to prevent coking troubles in the transfer line Ml. The'vapors were cooled by the light oil to a temperature approximating 860 F. and thereafter cooled by the heavier stock introduced through nozzle le to a temperature of about 835 F.

To further reduce coking difliculties in the preliminary cooling zone in the vapor outlet it and in the soaking drum or reaction chamber l2 immediately adjacent the vapor outlet Jill' I have shown a plunger 52 (see Figure 2) mounted in the cross tting SS which may be periodically reciprocated in the vapor outlet below the point of introduction of the heavy stock. Fluid actuating mechanism, comprising a cylinder 53 mounted on the cross fitting Se and piston 5ft slidable therein and connected by connecting rod 55 with the plunger 52, is provided for reciprocating the plunger. The cylinder lit is provided with a port at each end which alternately serves as intake and exhaust ports for the actuating fluid. The actuating fluid may be a light hydrocarbon stock which may be subsequently discharged into the transfer line lil as shown.

Although the invention has been described inV connection with a conventional tube and drum type of cracking equipment, it Will be clear that the invention is also applicable in tube cracking processes in which the digesting and soaking of the cracked vapors is accomplished in a coil or is completely dispensed with. in the latter process the preliminary cooling and subsequent introduction or" heavy stock may be accomplished at the outlet of the heating coil or elsewhere in the line leading from the coil to the separati-ng chamber. It will be further appar ent that my invention will und application in other cracking processes and other parts of crack ing equipment wherein hot vapor products above cracking temperature are transferred through a vapor line. For example, my invention will be of particular advantage i-n short-time, high-temperature cracking processes in which the cracking stock is subjected to extremely high crackm ing temperature, such as for example 1.109 F. or more for an extremely short period, measured in seconds or fractions of seconds. In such operations, according to my invention the hot vapor products lat the extremely high cracking temperature is rapidly cooled to a temperature which will not cause rapid conversion of heavy constituents to coke and the vapor products thereafter immediately intermingled with a stock containing unvaporizable constituents before the vapor products pass to subsequent equipment for separation and purification.

Having described the preferred embodiment it is understood that invention embraces such 'other varia-tions and modifications as fall Within the scope and spirit thereof and that the invention is not intended to be limited except as necessary to distinguish from prior art.

I claim:

In the art of cracking hydrocarbon oils Wherein a body of oil vapors is maintained at cracking temperature in an enlarged reaction chamber and vapors are.r Withdrawn from said reaction chlamber through a conduit to a subsequent enlarged zone for fractionation, the improvement which comprises subjecting the vapors passing to the subsequent fractionating zone to a double cooling operation by initially introducing into the hot vapors passing from the enlarged reaction chamber a vaporizable liquid material to the resultant stream of cooled products in the oking therein, but not lower the temperature troduction of said vaporizable liquid medium a below a cracking temperature, and delivering the heavy oil stock of the nature of reduced crude products from the conduit to the subsequent comprising unvaporizable constituents to therefractionatng zone at a, cracking temperature.

by further reduce the temperature ofV the prod- 5 ucts flowing through the conduit and prevent Y HOWARD DIMMIG.

conduit immediately adjaicent the point of n-

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