US2943994A - Chemicals coking quenching system - Google Patents

Description

July 5, 1960 w. D. MCCAIN, JR 2,943,994

CHEMICALS COKING QUENCHING SYSTEM Filed Feb. 14, 1958 L- sEPARATgRJ 38 in Q I23 REACTOR 1.. I 37 FIGURE I GASIFORM PRODUCTS FIGURE II William 0. McCain, Jr. Inventor By W Attorney United States atent CHEMICALS COKING QUENCHING SYSTEM William David McCain, In, Baton Rouge, La., assignor to Esso Research and Engineering Company, a corporation of Delaware Filed Feb. 14, 1958, Ser. No. 715,294 13 Claims. c1. 208-48 The present invention is concerned with the quenchingiof hot gasiform products of a transfer line chemicals c'oker. More particularly, it deals with cooling prod uct vapors so as to arrest after-cracking while minimizing coke deposition in the overhead equipment.

In recent years, there has been an increasing demand for converting heavy end, relatively low valued petroleum hydrocarbons into light unsaturates, such as ethylene and propylene, suitable for use as chemicals raw material.

Towards this end,'the dispersed solids phase thermal cracking process, more commonly referred to as transfer line chemicals coking, has been developed. Basical ly;-athe process comprises introducing a suitable preheatedhydrocarbon oil feed into a rapidly moving (greater than 20 ft./sec.)', gaseous suspension of hot inert solids. Theoil, upon contacting the solids which are at temperatures of at least 1200". F., is converted into light gasiform material and carbonaceous matter which deposits on the solids surfaces. After, or even before, passing through a' solids separation, the gasiform reaction products are quenched to arrest further thermal cracking. Separated solids are normally passed to a combustion zone wherein oxidation of the carbonaceous residue deposited upon them during the reaction serves to heat them to a temperature 50 to 400 F. above that of the reaction zone. If desired, an extraneous fuel may be added to the combustion zone. The thus heated s'olidsare then recirculated to the reaction zone so as to supply requisite thermal energy for conversion.

,Among solids suitablefor use are sand, coke particles, ceramic :or metallic solids, etc. The solids ordinarily range from about 20 to 800 microns in size.

r-A wide variety of hydrocarbon oil fractions may be utilized asfeed. For example, reduced crudes, asphalts, tar,shale oil fractions, gas oils, etc. are readily cracked in the transfer line chemicals coking system. Generally, the feed has an initial boiling point above 600 F., an A.P.I. gravity of about to 20, and a Conradson carbon content of about 5 to40 wt. percent.

-One ,of the serious problems encountered in transfer line coking 'for chemicals is the deposition of carbonaceous-matter" in the overhead equipment e.g. conduits downstream of the solids separator and the quench point. In addition to light unsaturates, the reaction product stream contains heavy materials such as unconverted feed and high molecular weight unsaturates. In practical operation, it has heretofore been found that upon quenchin g'the reactor products from about 1300" F. to approximately 500 F. by conventional means, a mist or fog of heavy hydrocarbons is formed. Dew point cooling and condensation occur in the high velocity gas stream thus causing formationtof the mist of heavy material.

mist or fog upon contacting the surfaces of the equipment condenses thereon, resulting in deleterious carbonaceous deposits on the structural surfaces. These carbon deposits may continuously build up to such levels as ,tointerfere with the flow of overhead vapors, ultimately causing shutdown of the entire system.

The present invention sets forth means whereby heavy hydrocarbon mist formation is' avoided, coke deposition minimized and improved operating realized.

More particularly, in accordance with the present invention the reactor gasiform efliuent is passed through a plurality, preferably three or. more, quenching stages, each of which reduces the stream temperature by a substantially equal amount. Quenching liquid is introduced into each stage in suflicient amounts to be only partially vaporized while cooling the stream to the desired degree. The normal 800-900 F. temperature drop of reactor vapors is thus broken up into steps of about 200 to 300 F. The temperature drop of 200 to 300 F. in each quenching stage is low enough to prevent the major portion of the niain gas stream from reaching its dew point, while condensing enough of the heavy, high boiling material so as to lower the dew point of the gasiform stream leaving the stage to below the temperature the stream will reach in the subsequent stage. Thus heavy material is removed from the reactor efiluent in a stepwise manner, diluted and washed away by unvaporized quench liquid without forming the undesirable mist which characterized prior art systems.

In preferred embodiments, the quenching stages are placed immediately after the solids separator and operate at progressively greater residence periods. In this manner, equal temperature change occurs in the several stages without requiring excessively increasing amounts of quenching liquid to offset the decreasing temperature differential between the gasiform stream and the quenching medium. 7

It should be clearly understood that the present invention does not consist in mere multiple quenching of reactor vapors. Basically, it teaches quenching by the use of a series of stages, each of the stages cooling the stream flowing therethrough to give a substantially equal temperature drop. Heavy materials are thus condensed in a stepwise manner without cooling the major portions of the stream below its dew point.

By way of clarification, the terms gases and vapors are used synonymously. The phrase reaction time denotes the time between the first contact of oil feed and hot solids and the subsequent solids-gas separation.

The various aspects and modifications of the present invention will be made more clearly apparent by reference to the following description, examples and accompanying drawings.

Figure I illustrates a transfer line chemicals coking process employing the present quenching features.

Figure II depicts a preferred type of multi-equal temperature drop quenching stages.

Turning to Fig. I, there is shown a transfer line conversion system comprising essentially reactor 10, burner 11,'solids separator 12 and multi-quenching units 28, 29 and 30.

Reactor 10 is an elongated, conduit-like reaction unit conventionally referred to as a transfer line reactor. Hot solids, e.g. sand, are withdrawn from the heater vessel or burner 11 and passed upwardly through reactor 10 in the form of a dilute gas-solids suspension i.e. density of approximately 5 lbs./ft.

Requisite thermal energy for conversion is normally supplied by the combustion of the carbon deposited on the solids during the courseof the thermal cracking reaction. As will further be described, contact solids are separated from the reactor gasiform efiiuent and passed to burner 11 through conduit 15. As shown, a mass of contact solids is maintained within the burner in the form of a relatively dense fluidized bed 13. Air, or other oxygen-containing media, passing upwardly through the bed, serves to oxidize the carbonaceous matter on the solids surfaces while providing fluidization of the solids 22 disposed about the reactor 1! are normally disposed circumferentially andlon'gitudinally aboutthe reactionzone so as to ensure goodsolidsoil contact and provide a convenient means of altering reaction residencetimes. Residence times of" about 0.2"" to 1.0 second,f e1;g.;0.30 sec., are normally employed. V

- diameter conduit may be employedfor this purpose.

mass. desired, an extraneous fuel such. as. the heavy end material separated from the reactor'efiluent, refinery sur plusage and the like may be added to the burner by means, not shown. This type, of operation is advantage ously. employed. when insufiic'ient carbon. is deposited Steam may beadded for further fluidization. If L 2,943,994 v 7 a f I may be supplied, in part or in total, by fractionationof the transfer line eflluent. Alternatively an, extraneous gas oil having the desired boiling point characteristics may be used, either independently or in conjunction with a' recycle fraction. The quench liquid consists of low boiling material for cooling the flowing stream togetherwith on the contact solids'during thconvefsion step: to'supply required fuel needs or when it is desiredztorecover can hon-containing solids as such. 'While a fluid bed burner is illustrated, other heating units such asa' transfer line burner; fixedbed combustion zone, etc; may alternatively be employed. H

Hot, Combustion gases, after having entrained solids separated therefrom in cyclone 16: andreturned to bed I 13, are withdrawnoverhead. Their latent heat may p then be recovered: and utilized for providing heat for-the" system e'.g.? preheating of reactor fueli high, boiling material which is unvaporized during the quench operation. A portion" of the heavy material'in.

the reactor etfiuent condenses and is dilutedwith the -higher boiling constituents of the quench liquid, thus providing against coke deposition. The major portion. of thereactor vapiform stream is maintainedabove'its dew' point and leaves quench unit '28 after a residence interval'of x 0.018 second therein in the gaseous state." I The ,stream then flows into quench unit 29.

The unvaporized quench liquid, which serves to wash j theequipment surfaces and protect "them against carbon Hot solids at" a temperature of about 1500 'F. are

Withdrawn 'from the burner through conduit 18 and passed to reactor 10'. Propelling gases, such'as steam,

light hydrocarbons; or the like, injected by means of taps 19 and 20serve to carry the solids and'forrn a rapidly moving gas-solidssuspension. passing through the reactor 7 at about 3O ft./sec.

A hydrocarbon oil feed, such as a South Louisianareduced crude preheated to a temperature of about-600 F, is injected inoverall amount of: 100'barrels per'day into-the hot'so'lidsstream by means ofinlets 21 and/or The feed injectors Upon contact with the hot solids stream, thermal cracking of the feed takes place at atemperature of 1350" F.

tog've light unsaturates (ethylene, propylene, etc.)"to'-" gether with other'hydrocarbon fractions while depositing carbonaceous residue upon the surface of the contact solids.

Theentire-reactor efiluent, e.g. solids, conversion products, unconverted feed,"propelling steam, etc., are withdrawn overhead and rapidly subjected to' a solids separa-' tion step in separator 12. This separationunit normally consists of one or more cyclones, although vane separators or the like may alternatively be employed; Sepa rated solids are recirculated back to burner 11 by conduits 24' and 15. Stripping gas is advantageously introduced countercurrent to the separated solids by inlet 25; i occluded hydrocarbon thus being removed from thesolids surfaces and recovered overhead with the reactor gasiform products. In order to maintain a constant mass inventory within the system, solids may be withdrawn through outlet 26 positioned inline 24. 1 Solids may, of

course, be withdrawn from other parts of their circulation solids back. to burner 11'.

Up to this point, the description has: dealt largely with features Well known in the art.

creasing volume isillustrated varying len gth of aconstant Referring to .unit'28, aquench liquid such as a'recycle product fraction; boiling in the 'range' of 38010 710 'F.

is introduced bythe dine 31 at a rate of '20 lbsJhrE/barrel per day; of feed so.as to cool thereaction vapors fromfa temperatureof-lZTS? 'E; to.1025 F. The quench liquidpath; Aeration'tap27 serves tosmoothly convey the deposit, together with the condensed heavy material from" 'the reactor eflluent stream are withdrawn by outlet '34r1 While individual exit systems for the various. quench stages may be employed, it'is advantageous-to utilizezla j common exit conduit 37 intowhich. each of the quench;

units discharge their liquid material bylines 3.4-, 35i-andi= 1 '36 respectively. a r,

Units 29 and 30 operate in afsimilarmanrien toithat'ii 7 described in reference to quenclrstage 28. Quenclrliquidil introduced through'inlets 32'and33 respectivelyareOn Y-T V partially vaporized'as they cool the 'flowingrgasifornri stream, condensed heavy ends :and unvaporized .quenchz medium being. withdrawn through outlet: 351 and 36-.

The gaseous effluent of unit 28 enters unit' 29 at amperature of about 1025 F. and leaves it ata temperature of approximately 775 F., heavy, material being-condensed? therein. The condensation of heavy. ends inthe i 2 stage serves to lower the dew point of the materialpassingi t i into the second stage by some 300'F;, andzsoithemajoriz portion of the reaction productstream remainsunconai: densed. In an analogous manner, the gaseous;efi'iueut"of: unit 29 is thereafter quenchedto atemperature ofQSZS F., in unit 33, the thus cooled g'asiform reactor products A being withdrawn therefrom through line :38; 'lhe gaseous stream may'then be further cooled, sent to' fractiona tion, or processed in other manners as desi ed; 1 Y

Vapor residence of approximately 0.031 and 0.079 1 seconds are employed in the second and third stages. respectively, the rate atwhich quench liquid is introduced" thereto being substantially the same as that'employedr in unit 28. The overall residence period inthe plurality of quench stages described is less. than 0.2 second;

While three stages" are shown in the drawingssladdi t tional quench stages may be desired, as fore'xamplef when very high temperature reactionproductsf-ezg. 15,011? I 5., are to becooled to relatively lowgtemper'aturesiega Turning to FigureH, thereis shown a particularlyide -lu V sirable apparatus configuration for quenching; in accord-e ancewith the present invention. Basically, itillustratesz-z the use of aplurality: .of pipe sectionsmlntegrally-zctin- ,nectedto each other and havinga common longit udinali? central, axis. The diameters of the quench conduib sem tionsv are of increasingly greater value. Eor;example,..;

when solid separator exit conduit is3- inches'indiam eter, the diameters of sections 101, 102,, and-i103: are;

4, 5, and ,6 inches, respectively. 7 The lengths .Offfliti dividual sections may, be. approximatelyv the: Samoa-erg 1.5 ft.,.or may vary so as; to givea furthcnvaporresin dence difierential among the. several quenchingrstagess.

Hot reaction vapors flow into the succesivegquenchingi? 7 stages through conduit 100, and are' quenchedbyrstegy wise reduction of temperature of about 200'300.-F;--. in each quenchsection. As. described in Fig.. I, quench oil inlets 105, 106, and 197' are provided: near the errtrance sections of the successive quenching sections: The quencheconduits preferably slope downwards, thus pro-; motingdrainage of condensed 1 heavy materials" and" vaporized quench liquid into liquid-gas separator '104. Cooled gases, e.g. at temperature of about300-600 F., are withdrawn from the separator by line 109, while heavy liquid hydrocarbons are removed by exit 108. The system of Figure H provides for effective stepwise quenching by means of a simple and cheap configuration of pipes of varying diameters. a p

The following table sets forth a compilation of data applicable to the systems heretofore described:

Table I Broad Range Preferred Range Reaction Conditions:

Average Size of Solids, microns. 20800 50-500 Density of Solids-Gas Suspen- 0.5-15 1.0-5.0

sion, Lbs/Cu. Ft.

Velocity of Solids-Gas Suspen- 20-100 25-60 51011 FtJSec.

Reaction Temperature, F 1,200-1,600 1,2001,400

Reaction Time, Sec 0.1-2.0 0. 20-1.0

Quenching Conditions:

Average Temperature of Reactor 1,200-1,600 1,200-1,400

Vapors Prior to Quenching F.

Temperature Drop across Each 100-400 200-300 Quenching Stage, F.

Quantity of Quench Liquid Intro- 18#lhr./b.ld. feed 20 to 25 duced into Each Quenching to 30#/hr./b.ld. Stage (base on feed). e

Volumetric Ratio of First Three 1:2:3 1:1.6:2.3

Quenching Stages.

Overall Temperature Drop across 6001,200 7001, 000

Quenching Stages, F.

Final Vapor Temperature after 200-700-.-; 300-600 Passing through Stages, F.

tively small, there is a decreased tendency of cooling and condensation of vapors on upstream pipe walls. The use of a multi-stage arrangement allows equilibrium, and hence fractionation of vapors, to be more nearly approached as compared with a single large temperature drop quench operation.

What is claimed is:

1. In the coking of hydrocarbons wherein a gas-solids rapidly moving gaseous suspension of inert solids at a temperature above 1200 F. is passed through an elongated, conduit-like reaction zone at a velocity greater than 20 ft./sec., wherein a hydrocarbon oil feed is introduced into said solids suspension and upon contact with said solids is converted into lighter gasiform material and carbonaceous residue which deposits on said solids, and wherein said gasiform materials and said hot solids are separated in a gas-solids separation zone, the improvement which comprises subjecting separated gasiform material leaving said separation zone to a plurality of quenching stages in succession, injecting quenching liquid into each of said stages in sutficient amounts to be only partially vaporized While lowering the temperature of the gasiform material passing through each of the said stages by substantially equal amounts of about 200 to 300 F., said quenching liquid thus condensing out only high boiling material in said stream and diluting and washing away the condensed high boiling material while maintaining the major portion of said gasiform material above its dew point.

2. The process of claim 1 wherein said separated gasiform materials are at a temperature of about 1200 to 1400 F. prior to quenching, and are ultimately quenched to a temperature in the range of 300-600 F. in at least three stages of substantially equal temperature drops.

3. The process of claim 1 wherein the residence times of the gasiform materials is progressively greater in said plurality of quenching stages, the overall residence time in said plurality of quenching stages being less than 0.2

second.

4. The process of claim 1 wherein the quantity of quenching liquid used in each stage ranges between 18 to 30 lbs/hr. per barrel per day of feed.

' 5. In a transfer line chemicals coking process wherein.

a suitably preheated oil feed is introduced into a disperse phase, rapidly flowing, inert solids stream maintained carbonaceous material which deposits on said solids and wherein said gasiform product stream' after being separated from said inert solids is at a'temperature of about 1200 to 1400" F;, the improvement which comprises passing said separated gasiform product stream through three quenching stages of successively increased'residence 7 periods, injecting quenching liquid into each of said quenching stages in amounts suificient to be only partially vaporized while cooling said product stream by about 200 to 300 F. in each of said stages, the heavier ends of said gasiform product stream being. thus condensed while maintaining the major portion of said gasiform product stream above its dew point and said unvaporized quenching liquid acting to dilute and wash away condensed high boiling hydrocarbons in each stage.

6. The apparatus of claim 7 wherein said plurality of quenching chambers comprising several successive conduits integrally connected to each other, said conduits having a common longitudinal central axis, and wherein the diameters of said conduits are of successively greater size.

7. An apparatus adapted for carrying out hydrocarbon conversion operations, which includes in combination, a vertically arranged reaction vessel having an'inlet and an outlet, a gas-solids separating unit, a pipe connecting said reaction vessel outlet with said gas-solids separating unit for passing reaction product eflluent from said reaction vessel to said separating unit, a plurality of separate quenching chambers arranged in succession and in spaced relation and spaced from said separating unit, a pipe for conducting separated gasiform reaction products from said separation unit to the first of said quenching chambers, tubular means for connecting said quenching chambers in succession whereby gasiform products to be cooled are passed through said quenching chambers in series, said quenching chambers being of successively larger volume in the direction of flow of gasiform products therethrough, inlet means opening into the top of each of said quenching chambers for introducing a quenching medium into each of said quenching chambers and outlet meanscommunicating with the bottom portions of said quenching chambers for withdrawing liquid collecting in said quenching chambers.

8. An apparatus adapted for carrying out hydrocarbon conversion operations, which includes in combination, a vertically arranged reaction vessel having an inlet and an outlet, a gas-solids separating unit, a pipe connecting said reaction vessel outlet with said gas-solids separating unit for passing reaction products effluent from said reaction vessel to said separating unit, a plurality of quenching chambers arranged in succession and spaced from said separating unit, a pipe for conducting separated gasiform reaction products from said separation unit to the first of said quenching chambers, tubular means for connecting said quenching chambers in succession whereby gasiform products to be cooled are passed through said quenching chambers in series, inlet means for introducing a quenching medium into the top of each of said quenching chambers and outlet means communicating with the bottom portions of said quenching chambers for withdrawing liquid collecting in said quenching chambers.

9. An apparatus according to claim 7 wherein said tubular means includes pipes for spacing and connecting said quenching chambers, and saidoutlet means includes a pipe leading from each quenching chamber,

; for withdrawing liquid'from each of said quenching chambers.

IIOI -Af i'Qeessacebrding to 1 wherein the separat'ecP- gasiftSTmmateflal is passed'through a confined passageway leading-from said gas-solids separation zone V wsaiclr first quenching stage spaced laterally-from said separatidngon'and liquid is withdrawn from the bottom of 'saictjquencliingstages. '7

V i'lxA- processracqordin'glto claim 1 whereinithe separated 7 gasifbr'm material is :passed through a confined passageway ieaaing fronifs aid' gas-solids separation zones" V tQ -Siiiffiit qHenChingstagE' Spat ted laterally from said separation ibne landf liqiiicl' is separately: withdrawn from A n qq s a c rd n claim 5awilsrein r sn d heavy end's are withdrawn" from the bottom 9f said q} h m en a ew d w QHWQh iEf sQ 1 I V V a V References Cited in'the, file n fthi; fia tent 13. Apr'oeess accor in'g' tq g in} 5' whereinieendensqF s pa e ys m, he b tqmvf V team-Ma w,

Claims (1)

1. IN THE COKING OF HYDROCARBONS WHEREIN A GAS-SOLIDS RAPIDLY MOVING GASEOUS SUSPENSION OF INERT SOLIDS AT A TEMPERATURE ABOVE 1200* F. IS PASSED THROUGH AN ELONGATED, CONDUIT-LIKE REACTION ZONE AT A VELOCITY GREATER THAN 20 FT./SEC., WHERIN A HYDROCABON OIL FEED IS INTRODUCED INTO SAID SOLIDS SUSEPNSION AND UPON CONTACT WITH SAID SOLIDS IS CONVERTED INTO LIGHTER GASIFORM MATERIAL AND CARBONACEOUS RESIDUE WICH DESPOSITS ON SAID SOLIDS, AND WHERIN SAID GASIFORM MATERIALS AND SAID HOT SOLIDS ARE SEPERATED IN A GAS-SOLIDS SEPARATION ZONE, THE IMPROVEMENT WHICH COMPRISES SUBJECTING SEPERATED GASIFORM MATERIAL LEAVING SAID SEPERATION ZONE TO A PULRALITY OF QUENCHING STAGES IN SUCCESSION, INJECTING QUENCHING LIQUID INTO EACH OF SAID STAGES IN SUFFICENT AMOUNTS TO BE ONLY PARTIALLY VAPORIZING WHILE LOWERING THE TEMPERATURE OF THE GASIFORM MATERIAL PASING THROUGH EACH OF THE SAID STAGES BY SUBSTANTIALLY EQUAL AMOUNTS OF ABOUT 200 TO 300*F., SAID QUENCHING LIQUID THUS CONDENSING OUT ONLY HIGH BOILING MATERIAL IN SAID STEAM AND DILUTING AND WASHING AWAY THE CONDENSED HIGH BOILING MATERIAL WHILE MAINTAINING THE MAJOR PORTION OF SAID GASIFORM MATERIAL ABOVE ITS DEW POINT.

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