US2791549A - Fluid coking process with quenching of hydrocarbon vapors - Google Patents

Description

c. E. JAHNIG May 7, 1957 FLUID COKING PROCESS WITH QUENCHING OF HYDROCARBON VAPORS Filed Dec. 30, 1953 2 Sheets-Sheet 1 H lGH-T EMPERATU RE VAPORS FIG.|

QUENCH "coKER PRODUCT VAPORS INVENTOR CHARLES E JAH NIG FIG.3

LIQUID QUENCH ATTO RN EY C. E. JAHNIG May 7, 1957 FLUID COKING PROCESS WITH QUENCHING OF HYDROCARBON VAPORS Filed Dec. 30, 1953 2 Sheets-Sheet 2 I-EATING m U m L FLUID COKING BED R KL

A OE

CL CS I S STEAM Charles E. Jahnig Q Inventor FLUID CQKIN G :PROCESS WITH QUENCHING- OF HYDROCARBON VAPORS Charles EiJahnig; RedBank; N. J.-, assignor to Esso Re- Search anWEhgineefing- Company; a corporationot Delaware Application December 30, 1953, Serial No. 401,305 Z' CI'tli'IiIS-Q (Cla19655) This invention relates generally" to the transporting and coolingof hot hydrocarbongases' having atendency to 'forrn coke deposit-son the conduits and equipment containing them; h lore-particularly it relates to methods and means for "transporting and cooling of the hot prod uct; 'gas'es'fr'oni fluid coking operations:

The-fluid coking process for heavy hydrocarbons has reee'ntl ybeen proposed; oil'sare' upgraded by this cokingproce'ss, utilizing the fiilidiza'tion' technique, to'lighter', more valuableprodu'cts by injecting the'oil's into a reactor vessel containing a bed of hot 'fihely dividedfluidized solidsv Pyrolysis of th'e' oil occurs' inthe vessel and carbonaceous residue is -depos'ited on the fluidized solids" and lighter gasiform' hydroe'areons are' -evc'alv'edand withdrawn as product. The-"reaction temperature ofthe bed'is maintainedby continuously"withdrawinga portion of i the" carh'omconta'ini'ng: solids and circul'atingthem to an external heater and' bac 1 One oftheprohlems in fluid coking. is 'the'b'uilding up ofi coke deposits in-th'e system that handles 'the product hydrocarbon gases beforethey are'cool'ed below a critical cokihg=temperature;'i. e., below-700"F; Somewof'the hydrocarbons-in the coker overhead" vapors are' high boiling and Will readilycondense. If condensation occurs-inn critical coking range of about"700"" 1000 R, the condensate" c'okes, causing fouling and plugging of the-equi'pment So long asthe gases rem'ai'n' above the crit i'cal" temperature range; coking will not occur. Bus in cooling thegases; coking will occur while the gases pas's' through this range-if" there" are attendant sunfaces' for the 'coke to form on:

This problern is aggravated somewhat by the fact that the hydrocarbons-in 'this 'overhead productare reactive andmiay te'nd to polymerize. In"this'"way, molecular weight is -raiised and ga'se's} which at first were-at or above their dew point; areconverted to" am'ixtu're 'of part liquid-'and vapor which can condense and cause" coke formations? Particularly trouhl'esomeplaces where" this coking occmsis in the roducttransfr lines fronr'the-fliiid coking reactionwessel to tire uenching (or fractionat'ing) zone and-at the nozzle introducing the vapors info thequench zone.

One method of caring for this difficulty is to add a volume of"superheated" steam'or other" light" inert gas to the reactor 'outl'et products to dilute them. This operates to lower the dew point of the gaseous mixture thereby inhibiting.condensation. This, -howev'er, is costly and leads togreater expense in the recovery of products. 1

This -invention is based upon the 'discoverythat coke epositsby': the gases can. be attributed 'to surfacetemperatures in' af criticalurangew I-fa surface is above the dew point temperature of the gases, condensation and, consequently, coking does not occur. If the temperature is about 600 F, or less, the reaction rate is slow enough so that serious coke deposits do not form. Within a Biiefly stated, hydrocarbon Patented May 7, 1957 2, cri t-ical sufface temperature range of about 700-l000- Fa; there is condensation and sufiicient coking to build up a deposit.-

Aceordingly, anobject of this invention is to prevent coking-and 'foulihgof equipment containing high temperature hydrocarbon vapors. A more specific object is to'pr event carbon'deposition by hot'hydrocarhon gases on the surfaces ofconfining vessels and conduits by judicious control of surface temperatures. Anotherohje'c-t is to provide a-method for cooling hothydrocarbon vapors' to a-temperat'ure below acritical coking temperature without the accompanying formation of coke deposits.- Other objects and advantageswill appear more clearly as the attached drawings, forming a part of this specification; are discussed" in detail.

Generally stated; the objects ofthis invention are attained in a system handling high temperature hydrocarbon v'a'pors -from a reactor by maintaining the temperatur e' of confiiiing surfaces ahove the dew point of the vapors prior to" quenching the vapors, so that condensationiand coking in the liquid phase is avoided; quenohing-r thevapors fr'om -the reaction temperature to about 700-7'5'0 F., in such a manner that the transition through. the critical coke deposition range is in the vapor phas'e'; and thereafter maintaining the temperaturerofi confining surfaces below-about 700 F. Preferably, the surfaces of equipment immediately following the quenching" zone are washed with liquid;

This inventionis concernedwitha novel quenchnozzle depicted i-n the'attacheddrawings, and its use-in such a manner" that problems of' coke deposition by high temperature hydrocarbon' vapors are avoided;

m the drawings;

Figure 1 depicts -in cross-seetiom'a'nozzle arrangement constructed accordin'g' to :the principle of this invention. The; nozzle is used 'to horizont'ally introduce high-tent perature vaporsinto a 'scrubbing 'or 'fracti onatin'gzone:

Figure 2 illustratesanother arrangement for intro ducingrjhot gases into a quench zone.

Figure-3 portraysua conventional quenching arrangem'ent' andwill beused to emphasize the advantagesof the *arrangement of Figure 2.

Figure 4 illustrates the use of this invention in 'a hydrocarbon: oil- :fluid coking.- process.

lnwFi'gure -"l; thef-hot hydrocarbon gases are being transported by; :pipe 2. All surfaces of the equipment i n co'n-' tact with thev gases-priorto' this point are to be unders'tood to' have been maintained' at a temperature above about 900 to=1000t F:

Itis to -be 'understood: that the critical temperature will vary'zwith specific processe's. For example; the dew' point orconden'sation point 05 gases fro'm a-fluid 'c'oker' 'operafl ing at a temperature ofiabout 950 FL; will be *about'QSO F'- For -a :coker operatingzat' a ternperature 'of 900 'Fztlie dew point will be about 900"F;- It is suflicient to keep surface temperatures above this dew" point. Heating means '6 is depicted for keeping Ithe" surface of pipe- '2 above the dew-point of the gases' Astearn coil wrapped aroundthe-pipe -isthe preferred mode 'ofi'hea-t'ing; although other meanscanbe used suohas an 'electric-heat ing-, elem'ent. Insulation can be used to 'help maintain the desiredtemperature: For example; the ""outs'ide of theheating-coil 6 01' "the inside Of! pipe 7*can be=insuiatedi Pipe 2 enters acoolingzone which ca'nbe a'fraetionat ing tower, quenchtank, scrubbing-toweror the like; The gases issue from the pipe and areimmediately mixed-with a downcomingl coolant and cooled in the vapor phase: This coolanfnormally will be a liquid such as water or reflux in a fractionating column in the form of a spray, stream or droplets. However, the cooling can be accomplished by finely divided solid material or by a stream of cool gas such as steam. Suitable solid coolants are shot having about ,6 inch diameter or coke from a fluid coking operation.

For purposes of illustration, the cooling zone is shown as being contained in a vessel 1 with an entrance port constructed of a pipe 5 and flange 4. A flange 3 is aflixed to pipe 2 and matches flange 4. The flanges are held together, with suitable gasketing between them, by bolts (not shown) in holes 9. In this manner, the pipe can be mounted on the vessel 1.

An interior concentric balfle 7 is arranged over the protruding pipe to protect it and the heating means from the coolant. Bleed gas, such as steam, is admitted by line 8 to the annulus formed by the baflle to prevent gases from entering the annulus, due to any surges in the system, and coking.

While the pipe 2 is kept hot, the baflle and the walls of the vessel are kept at a temperature below 700 F. by the coolant so that coke will not form on them. Thus, it can be seen that by this invention, when product hydrocarbon vapors are in a critical coking temperature range, which for a fluid coking vessel is about 780-900 F., there are no equipment surfaces present at this temperature upon which carbon deposition can form. In cases where it is necessary to have a surface temperature in this temperature range, the surface can be blanketed with a purge gas, e. g., steam, as was done to protect zone A of Figure 1.

In Figure 2, a line quench arrangement for the gases is shown. Hot vapors are introduced downwardly into the quench chamber 13 by pipe 11 which protrudes inwardly into the chamber. The pipe 11 is kept at a high temperature by a steam heating coil 12. A spray ring 14, supplied with a liquid coolant by line 15, is mounted just below the end of pipe 11. The gases upon emerging from the pipe are immediately cooled below their coking forming temperature by the liquid quench.

Again, although it is not mandatory, bleed gas is admitted by line 16 to the space around the pipe to prevent hot gases and coolant from surging upwardly and contacting the heating means. Line 17 removes the cooled gases from the quench tank and they are then carried to further processing such as a separation step.

Figure 3 illustrates a conventional method of quenching high temperature product gases from a coker. In the drawing the vapors are being conveyed by line 22 which is heated by element 23 and are cooled by a liquid supplied by line 24. It has been found that an area, B, adjacent to the coolant inlet port has a temperature within the dewpoint of the vapors, even though the pipe is heated up to to this point. Consequently coke deposits build up at this point. Also, on the side of the pipe, C, opposite from the quench port, deposits build up'because the swirling and erratic motion of the liquid and vapors leaves an area having a critical temperature. In the nozzle arrangement of Figure 2, the cooling of the vapors occurs in the vapor phase. The interior walls 18 of the quench chamber 13 are further protected by a liquid film. If the swirling vapors do contact thewall, carbon deposition is prevented by the liquid film.

Thus it can be seen that by the method of this invention, high temperature gases can be effectively cooled without the accompanying formation of coke deposits.

Figure 4 shows the quenching arrangement of this invention as used to handle vapors produced by a hydrocarbon oil fluid coking process. As shown, fluid coking vessel 30 contains a fluid coking bed 32 fluidized by steam supplied by line 29. The coking bed 32 is maintained at a coking temperature. A hydrocarbon oil is injected into the coking bed by line 31. Upon contact with the heated finely divided solids, the oil undergoes vaporization and pyrolysis, depositing coke residue on the solids. Vapors 4 are removed overhead from the coking zone through cyclone 35, and then passed by line 36 to a vapor cooling vessel 40.

According to this invention, line 36 is heated by heating elements 37. The terminal portion of line 36 projecting into vessel 40 is protected by a cylindrical concentric batfle 38. Bleed gas is admitted by line 39 into the annular passageway formed by this cylindrical baflle. Liquid coolant supplied by line 41 is sprayed into the vapors issuing from line 36. Cooled vapors are removed from the upper portion of vessel 40 by line 42 and the liquid coolant, along with any condensed material, is removed by line 43 from the bottom portion of vessel 40.

What is claimed is:

1. In a hydrocarbon oil fluid coking process wherein high temperature hydrocarbon vapors are produced in a coking zone and said hydrocarbon vapors have a propensity to form coke deposits on attendant surfaces, a method of preventing said coke deposits while cooling said hydrocarbon vapors through a critical coke deposition temperature range which comprises withdrawing said hydrocarbon vapors from said coking zone through a gas impervious passageway, maintaining the interior surface temperature of said passageway above the dew point of said hydrocarbon vapors by means of heating elements, injecting said hydrocarbon vapors from said passageway into a gas cooling zone at an interior point removed from the confines of said gas cooling zone, forming a second passageway in said cooling zone about said gas impervious passageway and heating elements extending into said cooling zone, said second passageway terminating and opening into said gas cooling zone at the point of termination of said gas impervious passageway, maintaining the outer confines of said passageway below 780 F., injecting a bleed gas into said second passageway to prevent entrance of hydrocarbon vapors thereto, cooling said vapors below 780 F. in the vapor phase through contact with a finely divided liquid coolant, and withdrawing cooled vapors from said cooling zone.

2. In hydrocarbon oil fluid coking system comprising a reactor vessel, a coking bed of finely divided fluidized solids therein, and a vapor cooling vessel, the improvement comprising a gas impervious cylindrical conduit extending from the upper portion of said reactor vessel and terminating within said vapor cooling vessel adapted for the passage of high temperature hydrocarbon vapors therebetween, concentric heating elements disposed about said gas impervious conduit to maintain the interior surface temperature thereof above the dew point of said high temperature hydrocarbon vapors, a cylindrical concentric baflle in said vapor cooling vessel about said gas impervious cylindrical conduit and said concentric heating elements radially spaced therefrom to form an annular passageway, said passageway opening into said vapor cooling vessel at the terminus of said gas impervious cylindrical conduit, conduit means for injecting a bleed gas into said annular passageway, means in said vapor cooling vessel for dispersing a liquid coolant in the hydrocarbon vapors issuing from said gas impervious cylindrical conduit, and conduit means for withdrawing cooled vapors and liquid from said vapor cooling vessel.

References Cited in the file of this patent UNITED STATES PATENTS -l,892,440 Frankenberg Dec. 27, 1932 2,100,758 Ackeren Nov. 30, 1937 2,391,818 Brandt Dec. 25, 1945 2,557,971 Jacklin June 26, 1951 2,608,527 Holland Aug. 26, 1952 2,719,114 Lefier Sept. 27, 1955

Claims (1)

1. IN A HYDROCARBON OIL FLUID COKING PROCESS WHEREIN HIGH TEMPERATURE HYDROCARBON VAPORS ARE PRODUCED IN A COKING ZONE AND SAID HYDROCARBON VAPORS HAVE A PROPENSITY TO FORM COKE DEPOSITS ON ATTENDANT SURFACE, A METHOD OF PREVENTING SAID COKE DEPOSITS WHILE COOLING SAID HYDROCARBON VAPORS THROUGH A CRITICAL COKE DEPOSITION TEMPERATURE RANGE WHICH COMPRISES WITHDRAWING SAID HYDROCARBON VAPORS FROM SAID COKING ZONE THROUGH A GAS IMPERVIOS PASSAGEWAY, MAINTAINING THE INTERIOR SURFACE TEMPERATURE OF SAID PASSAGEWAY ABOVE THE DEW POINT OF SAID HYDROCARBON VAPORS BY MEANS O F HEATING ELEMENTS, INJECTING SAID HYDROCARBON VAPORS FROM SAID PASSAGEWAY INTO A GAS COOLING ZONE AT AN INTERIOR POINT REMOVED FROM THE CONFINES OF SAID GAS COOLING ZONE, FORMING A SECOND PASSAGEWAY IN SAID COOLING ZONE ABOUT SAID GAS IMPERVIOUS PASSAGEWAY AND HEATING ELEMENTS EXTENDING INTO SAID COOLING ZONE, SAID SECOND PASSAGEWAY TERMINATING AND OPENING INTO SAID GAS COOLING ZONE AT THE POINT OF TERMINATION OF SAID GAS IMPERVIOUS PASSAGEWAY, MAINTAINING THE OUTER CONFINES OF SAID PASSAGEWAY BELO 780*F., INJECTING A BLEED GAS INTO SAID SECOND PASSAGEWAY TO PREVENT ENTRANCE OF HYDROCARBON VAPORS THERETO, COOLING SAID VAPORS BELOW 780*F. IN THE VAPORS PHASE THROUGH CONTACT WITH A FINELY DIVIDED LIQUID COOLANT, AND WITHDRAWING COOLED VAPORS FROM SAID COOLING ZONE.

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