US2847366A - Steam cracking process - Google Patents

Description

Aug. 12, 1958 w. w. BOISTURE- 2,847,366

' STEAM CRACKING PROCESS Filed March 4, 1955 2': a? a- W LIGHTER X 2'0- 2'2 mmsrsn LINE m OUENCH ZONE e 2 CRACKING -ra sum; 5 COIL 5 5: I: VAPORIZEDSEI OIL 2s WATER FRACTIOIIATOR- TAR smu WORTH W. BOISTURE INVENTOR BY 5M ATTORNEY United States Patent STEAM CRACKING PROCESS Worth William Boisture, Baton Rouge, La., assignor to Esso Research and Engineering Company, a corporation of Delaware Application March 4, 1955, Serial No. 492,273

3 Claims. (Cl. 196-63 This invention relates toa process for converting hydrocarbons, particularly petroleum naphthas and gas oils. It is more particularly concerned with an improved steam cracking process wherein the cracked products are rapidly cooled in a fluidized solids cooling system of special design.

In brief compass, the present invention is directed to an improvement of a steam cracking process wherein an oil such as a gas oil is diluted with steam and subjected to cracking temperatures in the order of 1300 F. in a cracking coil to obtain chemicals and chemical intermediates. The improvement comprises introducing the high temperature eflluent from the cracking coil into a transfer line quench zone which contains relatively cool particulate. solids. The eflluent is thereby quenched to a temperature in the range of about 800 to 1000 F. and a small amount of liquid residue or tar is deposited on the solids. Solids are separated from the cooled vapors in a cyclone. The vapors may then be further cooled by quenching with a relatively cool quench oil. The separated solids are. passed to a cooling zone. The cooling zone contains a bed of fluidized solids and a coolant such as water is circulated in'indirect'heat transfer relationship with the bed tov maintain the temperature of of the bed at about 100 to 300 F. below the temperature in the transfer line quench zone. Cool solids are circulated from this fluid bed to the quench zone to cool further amounts of the cracking coil eflluent.

The process of steam cracking of selected petroleum fractions is well known by the art. In this process a petroleum fraction having a boiling range withinthe limits of about 350 to 900 F. is vaporized, diluted with steam, and cracked in a coil at a temperature in a range of about 1200" to 1600 F. Residence timesare'relatively short being in the range of about 0.5 to 5.0 seconds. The products are immediately quenched to a temperature below about 700 F. to arrest further reactions and to prevent undue loss of the primary conversion products. This quenching is customarily accomplished by injecting water or a cooled oil such as a cycle stock into the high temperature cracked mixture.

Until now, there has not been a satisfactory method developed for quenching the efliuent from the steam cracking coil without forming coke deposits in the lines containing the vapors. Coke deposits form at the-point of quenching and beyond. Such coke deposits rapidly cause blockage and shut down of the equipment. To

circumvent this difliculty, it is the current practice to use line 11.

into the fluid bed to extract heat therefrom and to supply 6 ice and others. A more particular object is to develop a Referring now to the drawing, an oil such as a light gas oil, which in this case has been previously vaporized, 1

although this is not necessary, is admitted to the process by line 1 and is admixed with a substantial amount of. steam supplied by line 2. The resulting mixture "is passed through a cracking coil 3 and heated toa high temperature. The eflluent therefrom in line 4 is 'im-' mediately admitted to a transfer line quench zone 5 and contacts cool solids which quickly quench the mixture to temperatures below cracking temperatures.

'Any convenient particulate solid may be used in the practice of thisinvention such as sand, finely divided mullite, pumice, kieselguhr, spent catalyst, coke and similar materials. The cool solids are supplied to the quench zone in amounts suflicient to. absorb substantially all of the tar or. heavy liquid residue in the cracked products. The amount of material condensed is small, amounting to about 1 to 5% on fresh feed. The amount of solids is suificient to absorb these heaviermaterials while still remaining relatively free flowing;

The contents of the quench zone are discharged into a cyclonic separator 6 or an equivalent separator, e. g.,

-are further cooled at this point by injecting a cooled quench and wash oil supplied by line 8 into the vapors. The separated solids are transferred via dipleg 9 to a cooling zone 10. i i

A fluid bed of the solids is maintained in the cooling zone 10 in a manner known in the art. Fluidizing gas, 7, e. g., steam is supplied to the base of zone 10 by line 11.

This fluidizing gas may be used to extract some of the heat from the fluidized solids. Thus low temperature steam or wet steam may be injected into the vapor via In some cases water may be'directly injected fluidizing gas thereto. 1

The vapors emerging from the fluid bed are passed through cyclone 1 2, which may be located .interiorly withinvessel 10 or exteriorly as shown. Entrained solids are removed "in the cyclone and returned to the bed via dipleg 13. The spent gases are vented from the cyclone via line ,14. v It is 'preferred to remove v by maintaining a cooling coil 15 inthe.,bed.. n A coolant such as-water is'circulated-through this coil to remove heat from the bed. Alternatively,-steam may be generated in this cooling coil or the oil feed to the process may conveniently be preheated or vaporized in this coil. As coke deposits on the solid particles, it is necessary in most cases to provide means for burning off this coke or for removing it from the process. If a cheap material such as sand is used, a portion of the circulating solids can be discharged from the system and fresh feed particles added. It is preferred, however, to remove these coke deposits from the solids by burning. Thus a small portion of the circulating solids can be passed to an external buming vessel wherein the coke deposits are burnt ofi. Alternatively, air or a free oxygen containing gas may be supplied to vessel 10 via line 24 as shown,,such that the burning and regeneration of the solids will take place in Patented Aug. 12, 1958;

of the heat from the} fluidized solids the cooling zone. This air, is preferably, injected into the bedabove'the cooling coils, and "vessel "has, preferably, a large length to diameter ratio such that a temperature gradient exists,

coolsolidsare circulated from the cooling,.zone by line. 16to the-quench; zoneina manner wellknown. in the art. Anaerating gassuch as steam is supplied to the base of the riserby line 17 to assist in the circulation of the solidsr A vap orizable coolant,flsuch'as water, can be injectedjinto. line 16,"a s.by line23f, to further cool the'solids, if desired.

'Theconversion products aretransferred by line 7 to a separationzone orfractionator 18. As shown, arelatively simple separation is made. A heavy tar is removed fromthe base of the fractionator by line 19 as product. An-intermediate boiling range. fraction. which may boil fr'omab'out 400,F. up to about 600 F. is removed from the fractionator byline 20.1 This material is cooled in heatexchanger 21 and is then passedto the cyclone separator 6 by line 8." Instead of using a recycle stream as a quench oil, other quench media such as water or catalytic cycle stocks can be used. Alternatively, a-bottoms fraction alone can be separated in fractionator 18 'and'used as a quench medium.

The-lighter products .from the steamcracking operation boiling below about 430 F. areremoved .from they fractionation tower by line22 and are subjected to further conventional processing. For example, the vapors may be compressedand .an, aromatic distillate separated therefrom. The vaporsthen may-be scrubbed with caustic, dehydratedand then passed. through a de-methanizer, deethanizer, de-propanizer system and a butane-pentane fractionatorto, recover the desired chemicals andfchemical intermediates.

ThefollowingTable I summarizes the pertinentoperating conditions applicable to the processdepicted in the figure and presentsa specific example; I

TABLE I Operating conditions Range Example:

Feed-Boiling Range, F.- 350 to 700 light gas oil. APT 35. Steam-Cracking Coll:

0utlet.Pressure, 17.18.. 1. gm. o 25--. Outlet Temperature, F 1,200-t0 l,600 1,360. Con'vgrslon to C 'and lighter, wt; perto 0.

cen v Mol percent steam, based on feed to 82. Oilresidence time, secs c- 0.5 to 6.0' 3. Transten LnieJQuenchZone:

Outlet Temperature, F 800 to 1,000 n. 900. Outlet Pressure, 1). s. i. g 4 to 20; 8. Solids/feed ratio, lbs/1b. feed.-- l0.to:2 ,3. Particle-size:

Maximum; 30% '011'45 mesh; Minimum ,97%.on 150.

mesh. Density of mixture, lbsJtt; w 2 to 10- Average solids residence time, to 7. 3. Inlet temperature of solids, F 700 150950 750. Fluid iBed .Cooling; Zone:

Temperature, F 800 to 1,000-"- 850. Pressure at cycloneoutlet, p. s. 1 10 to 30 15. Superficial fiuidizinggas ,velocity 0.5 to-4.0. 1. 0.

. protected by Letters Patent is' succinctly set forth in the following claims;

What is claimed is:

l. -In a now catalytic, steam cracking process wherein an oil isdiluted with steam and subjected tocracking temperatures in the range of 1200 to 1600 F. in a cracking coil, the improvement'which comprises introducing the high temperature effluent from said coil into a transfer line quench zone containing a dispersed suspension of flowing relatively cool particulate solids, the solids-feed ratio being in the range of 10-2, the density of the resultant mixture being in the range of '2-10 lbs/ft. and the average solids residence time in the transfer line quench zone being in the range of 1 to 7 seconds whereby said eflluent is quench to a temperature in the range of 800 to 1000 F. and liquid residue in an amount of from 1 to 5%. on oil feed is deposited on said solids, separating solids and vapors from the eflluent so quenched. in a separationzone, further cooling said vapors by injecting a relatively cool quench oil, passing solidsfrom .said separation zone to a cooling zone containing a fluid bed of solids,

circulating a coolant inindirect heat transfer relationship with said fluid bed tomaintain the, temperature'thereof at least F. below the temperature of said transfer line quench zone, and circulating. cool solidsfrom said fluid bed tosaid transfer linequench. zone.

2. The process of claim 1 wherein the separated and further cooledvapors areseparated to. obtain a tar product, a cycle oil having a boiling point in the range of 400 to,600 F. and lighter fractions, and said cycle oil iscooled and used as said quench oil.

3. The process of claim-1 Whereina free oxygen containing, gas isinjected into said fluid bed to further dry and partially combust the solids therein.

References Cited in the file of this patent UNITED STATES PATENTS 1,492,305 Murrie Apr. 29, 1924 2,340,814 Lidov Feb. 1, 1944 2,363,903 Smith Nov. 28, 1944 2,376,190 Roetheli May 15, 1945 2,443,210 Upham JunelS, 1948 2,485,315' Rex eta1. Oct. 18, 1949 UNITED STATES PATENT OFFlCE CERTIFICATE 0F '(JORRECEHIQN Patent Nov 2,847,366 August 12, 1958 Worth William Boisture It is hereby certified that error appears in theprinted specification of the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 4, line 12, for "now catalytic read m non-=-oatalytic line 23, for "quench read -v--- quenched -u Signed and sealed this 18th day of November 1958 (SEAL) Attest:

KARL AXLINE ROBERT c. WATSON Attesting Oflicer Commissioner of Patents

Claims (1)

1. IN A NOW CATALYTIC, STEAM CRACKING PROCESS WHEREIN AN OIL IS DILUTED WITH STEAM AND SUBJECTED TO CRACKING TEMPERATURES IN THE RANGE OF 1200* TO 1600*F. IN A CRACKING COIL, ATHE IMPROVEMENT WHICH COMPRISES INTRODUCING THE HIGH TEMPERATURE EFFEUENT FROM SAID COIL INTO A TRANSFER LINE QUENCH ZONE CONTAINING A DISPERSED SUSPENSION OF FLOWING RELATIVELY COOL PARTICULATE SOLIDS, THE SOLIDS-FEED RATIO VEING IN THE RANGE OF 10-2. THE DENSITY OF THE RESULTANT MIXTURE BEING IN THE RANGE OF 2-10 LBS./FT. AND THE AVERAGE SOLIDS RESIDENCE TIME IN THE TRANSFER LINE QUENCH ZONE BEING IN THE RANGE OF 1 T0 7 SECONDS WHEREBY SAID EFFLUENT IS QUENCH TO A TEMPERATURE IN THE RANGE OF 800* TO 1000*F. AND LIQUID RESIDUE IN AND AMOUNT OF FROM 1

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