US2543884A

US2543884A - Process for cracking and coking heavy hydryocarbons

Info

Publication number: US2543884A
Application number: US768197A
Authority: US
Inventors: Weikart John
Original assignee: Standard Oil Development Co
Current assignee: Standard Oil Development Co
Priority date: 1947-08-12
Filing date: 1947-08-12
Publication date: 1951-03-06
Anticipated expiration: 1968-03-06

Description

March 6, 1951 J. wElKART 2,543,884

PROCESS FOR CRACKING AND COKING HEAVY HYDROCARBONS Filed Aug. l2, 1947 INVEN TOR. Jw Mmm/P7' BYQ.

f Patented 6, 1951 PROCESS FORERACKING AND COKING HEAVY HYDBYOCARBONS .nim wiiiiri, Elizabeth, N. 1.,-mimoito sianai i ard Oil lDevelopment Company, a corporation of Delaware Application August 12, 1947, Serial No. 768,197

This invention relates to an improved process for the production of valuable distillates by the coking of heavy hydrocarbon fractions obtained from crude petroleum or from synthetic oils. More particularly, it relates to a process for preparing high-grade gasoline and gas oils suitable as catalytic cracking feed stocks from residue,

petroleum residues or pressure tars, part or all` of the nely divided coke produced in the op eration being used as the heat transfer medium. It relates especially to a-method comprising a first rapid cracking step wherein the vapor contact time is very short and a second step wherein the more refractory fractions of the residuum are allowed a considerably greater residence time inthe reaction zone to transform them into coke and relatively lowboiling con-l stituents.

Economic considerations and increased demands for distillate fuels are constantly stimulating the efforts of the oil industry in its search for methods allowing the best possible conversion of crude petroleum into high-grade products. One of the major problems to be solved in this connection is to improve the conversion of heavy residues into high yields of valuable distillates, such conversion consisting essentially of separating the heavy and/or refractory cokeforming fractions present in the residues in such a manner as to obtain optimum yields of gasoline and of gas oils suitable for catalytic cracking andcoking rtheheavy fractionA in such a manner that the resulting coke interferes as little as possible with the continuous operation of the process.

Prior to appliants invention, the conventional methods of processing residues were operations known in the art by the names' of de-asphalting, viscosity breaking and delayed cokingrespectively. These processes, however, were usually characterized by the fact that they had to be interrupted atintervals to remove the formed coke.

It has also been proposed to coke `heavy residual oils in a continuous manner by spraying the oil unto a continuously moving'mass of highly heated solids. For example, according to one mode of operation, a relatively cool re' I siduum is sprayed over'and passed downwardly through a hot rabbled bed of lump coke. The top temperature of the bed may. for example, be of the' order of 1000 F. The oil on contacting vthe hot coke is subjected to partial vaporization and the unvaporized constituents of the residual oil are maintained on the coke lumps for a period materially greater' than the vaporized portion.

wniie this operation has certain advantages,

.it is subject to other inherent limitations. For

example, the mechanism for rabbling the-hot coke is subject to frequent failures due tn the high temperature conditions maintained in the coking zone. Also the operation requires the use of an extremely heavy residual oil which contains a minimum amount of vaporizable constitp uents in order to-minimize the amount .of heat required for the coking operation.A 'It has also been found that when coking heavy residual oils containing substantial amounts oi* sulfur, the sulfur is retained in the coke which makes the resulting coke inferior, particularly for such specialty products as metallurgical coke and coke used for makingcarbon electrodes.

It is the object of this invention toprovide an improved method for converting heavy or residual hydrocarbon oils, which are characterized by the widely different refractoriness'or resistance to cracking of their several constituents, into high; yields of gasoline and feed stock suitable for catalytic cracking. Another object is to devise a process for, cokinggresiduu'm oils in such a manner as to reduce or control the extent to whichthe resulting 'vapors Vreci'ack' or polymerlze. A further object is to provide a' continuous -iiuidized process for coking residuum oils in such a manner that the coke produced thereby is partially used for supplying the necessary heat of reaction. Another object is to .design an apparatus adapted 'for coking heavy petroleum fractions employing a two-stage fluidized technique so as to obtain the greatest pos-y sible yield of useful. distillate andv to produce-a coke of relatively low sulfur content. Still other' objects will become apparent from the subsequent description.

The present invention is concerned with a process in .which the heavy residual oils to be converted into lighter components are initially mixed with a stream of hot -nely divided coke particles; The temperature of the particles and the amount of particles introduced into the re-' sidual oil are suiiicient to effect at least a partial vaporization of the oil to thereby form a suspenf sion of oil vapors, finely :divided coke .particles and unvaporized oil residue. The resulting suspension is then passed through a conduit wherein the oil may be subjected to further heating and wherein mild cracking of the less refractory components of the feed may be carried out; 'I'he resulting products following the heat treatment are `3 passed into a separating zone wherein the vapors formed during the vaporization and cracking treatment are separated from the coke particles and the unvaporized portion of the residual feed. The mixture of coke and unvaporized residue is then introduced into a coking chamber. According to one of the specific phases of this invention. the coking chamber is immersed in a body of carbon particles undergoing combustion by passing an oxidizing gas upwardly through the combustion zone at such a rate as to maintain a relatively dense fiuid turbulent layer of coke particles in the bottom of the combustion zone. A stream of non-oxidizing gas is also introduced into the bottom portion of the coking zone and passes upwardly therethrough at such a rate as to maintain the coke particles therein in a similar dense 4 tinuously removed from the combustion vessel I phase iiuidized condition. The relatively dense iiuldized layer of coke particles in the combustion zone and in the cooking chamber serves to transfer heat from the combustion' zoneto the coking zone and tends to maintain the coking zone at a substantially uniform temperature throughout. Furthermore, the gas passing upwardly through the coking chamber accelerates the removal of vapors formed from the residual oil during the coking treatment. As a result. such vapors are retained in the coking chamber for a relatively short period of time, thus materially reducing the amount of recracking of such materials in the coking zones. The vapors removed from the coking zone are rapidly cooled and thereafter subjected to suitable fractionation to recover the desired distillate products therefrom.

In order that the invention may be better understood, reference is made to the attached drawing which forms a part of the specification and which is a schematic illustration of an apparatus suitable for carrying out the invention.

Referring to the drawing, a stream of air, oxygen or other suitable oxidizing gas intermixed with iinely divided coke particles is introduced into a combustion vessel I through line 2 which enters the combustion vessel at point 3 below a perforated grid 4. The perforated grid I may extend over a substantial portion of the combustion vessel I or over a rather` restricted portion, as

.shown in the drawing. In the latter case, an upwardly extending vertical partition 5 is provided having its lower end connected to the bottom ofthe vessel and its upper end connected to the perforated grid l to form a distributing zone below the perforated grid I. 'I'he mixture of oxidizing gas and coke particles passes' upwardly through grid 4 into the main body of the combustion vesseLI wherein the velocity of the oxidizing vgas is reduced to cause the carbon particles to segregate into arelatively dense layer in the bottom portion of the combustion vessel which is maintained in a relatively vdense turbulent state bythe gases rising therethrough. The superficial v velocity of the gas will depend upon the size of the carbon particles in the combustion vessel. The size of the carbon particles may vary over an extended range, such as from 5 microns up to 1A" or more. When using extremely fine carbon particles, suchl as those ranging from 5 to 150 microns in diameter, the superficial velocity of the rising gas will be of the order of from .5 to 3 feet per second. The term "superficial velocity as here employed means the velocity that the gases would assume in the absence of any solid material in the combustion space.

Under properly controlled conditions a relatively dense layer\of particles undergoing combustion is maintained in the lower portion of the combustion vessel having a relatively well-defined upper level as shown by numeral 6.

The amount of air introduced into the combustion vessel Il is sufficient to burn a portion of the carbon introduced and to supply sufficient heat thereby for carrying out the process. 'I'he temperature within the combustion vessel I may be maintained within the range of from 1000 F. to -1400 F. andadvantageously between the temperatures of from 1l00 F. to 1200 F.

A stream of heated carbon particles is conthrough standpipe 1, which communicates with the residuum feed line 8. The standpipe is provided with a control valve'9 .adapted to regulate the ilowof coke into line 8 for admixture with the residuum. Also, it-may be desirable to introduce an aerating gas through line I0 near the bottom of the standpipe 1, to prvent packing of the -particles and to facilitate their flow. The gas used for aerating the coke in the standpipe may advantageously be an oxygencontaining gas such as air and/or flue gas so as to supply additional heat to the system by combustion in subsequent steps, but others may prefer to use a nonoxidizing stripping gas, such as steam, nitrogen or carbon dioxide so as to prevent undesirably high quantities of oxygen from entering feed line 8. 'Ihe heavy residual oil to be coked which may ycause a substantial vaporization of the feed so as to form a suspension of coke particles and hydrocarbon vapors, the density of this dispersion being advantageously kept below 10 lbs./cu. ft. preferabiywithin the range of about 0.1 to 2 lb./ cu. it. 'Ihis mixture or dilute dispersion, is then passed through the high-temperature transfer line i2,

immersed in the relatively dense layer of iluidized coke in combustion chamber I..

However, instead of causing vaporization of the feed-by means of the heat content of the coke particles admixed to the feed, the vaporization may be caused at least in part by the heat exchange between conduit I2 and the combustion vessel I. In this manner the resulting hydrocarbon vapors are maintained at a temperature of about 850 to 1200 F.V or higher. preferably at about 900 to 1100 F. The contact time of the suspension in the transfer line I2 should be between 1/2 second to 50 seconds, advantageously from l to 10 seconds, with the result that very little true coking takes placein this step. 'I'he mixture from line I2 containing cracked products fromthe less refractory feed fractions is then carried into separating means I3 which for purposes of illustration is assumed to be a cyclone separator. The vapor stream which may contain small amounts of coke particles is withdrawn from the Iseparatorvmeans through line Il. tothe heat exchanger I I wherein the incoming feed may be conveniently used as the cooling medium. However, instead 4of the heat exchanger n, it is also possible to w01 the' vapors by injecting cold fresh feed into line Il, the feed stock being withdrawn from the bottom of one of the fractionation towers and then introduced into line 8 for admixture withk the i hot coke. Finally, the products are transferred through line I5 to suitable recovery equipment which may be advantageously an atmospheric amasar.

vacuum distillation tower `V. .Thencerthe final distillate products are withdrawn. A substantial proportion of these products is very well suited as a catalytic cracking feed stock while another pro portion consists. of high octane gasoline. The bottom 'fraction obtainedfin the fractionation towers will normally contain a 4small amount of coke and may be used for fuel purposes or a portion of it'may be 'recycled to the process for further treatment. v

'I'he hot coke particles are. admixed to the feed in a suillcient proportion to lavoid `the formation of a. separate liquid phase in conduit I2. In other words, the coke particles become coatedby the more refractory high-boiling materials present in the feed during their passage through hot transfer line I2.f The cokeparticles containing the unvaporized oil absorbed thereon separated in cyclone I3 arepassed vinto Vcoking vessel I6, which consists of an upper section Il and a lower section IB. In this Areactor the particles are maintained at a suitablereaction temperature above 850 F.. preferably' between` 900 F. and 1200 F., as adense fluidized massl having an upper level I9. The fiuidized mass of coke particles continuously passes downwardly from section II` into the lower stripping section I8. A gaseous stripping medium such as steam, nitrogen or carbon dioxide is introduced near the bottom of the stripping section I8 through nozzles 20.

This stripping medium passes` upwardly `throughl the stripper and reactor at such a rate that .the

coke particles are maintained as a dense turbulent fluidized mass. The stripping medium also serves to sweep the hydrocarbon vapors formed i in the reactor through separating means 2| and line 22 to line I4 where they merge with the vapors therein. In some cases it is of advantage to subject the vapors from the-coking vessel to separate fractionation independently of the vapors formed during initial vaporization and version. 4

The coke particles separated in cyclone 2I are returned to the iiuidized reactor bed through dip line 23 which preferably extends below particle level I9. After passing through the coking vessel I6, the coke particles, which consist essentially of the. original coking particles mixed intothe feed stock plus addriyional coke formed during the coking operatic l are withdrawn from bottom of stripper section .l through standpipe 24 providedwith aI controlvalve 25 adapted to regulate the rate of withdrawal of the coke particles therefrom.` The particles withdrawn from standpipe 24 Vare pickedup by a streamA of oxygen-containing gas passing;through line 3 and are thus carriedback into'combustion vessel I for further combustion to supply the necessary process heat as described previously. The flue .gasresulting from the burning of the coke in vessel I is removed overhead through line 26, part of the ilue gas being useful for recycling through line 3.

Sincethe coke produced from this vprocess is usually more than enough tomake up forthe coke burned up for process heat, leg 21 containing a 75 control valve 2l-is provided through which excess coke may bewithdrawn from thevsystem... A This must.becooled `lueforevbeing withdrawn or it will burn on contact with air. l

x The unitv illustrated inthe drawing has the high temperature conduit I2 and coking vessel I6 within the combustion vessel I. This arrangement is advantageous'in that considerable heat loss is thus saved,v especially when operating at extremely high temperatures. However, it is also practicable to operatea process according to the present invention using `equipment/where thel conduit I2 and vessel ISare located outside of the said combustion vessel and Where all the necessary heat of reaction including heat losses to the atmosphere, is supplied exclusively bythe coke particles which are mixed with the `oillto be treated.l Also, while the high temperature conduit I2 is shownl-discharginginto cyclone I3 above thecoking vessel IIS, the conduit I2 may discharge directly into reactor vessel I6 above level I9 so that vapors from conduit I2 would pass through separator 2i together with the vapors formed inthe reactor I6. Also, it will be". readily understood thatvwhereasthe unit shown.

in the drawing discharges vexcess coke from the combustion chamber I, this excess coke may be withdrawn from a dierentpart of the system, for instance, from coking vessel I 6.

In cases where it is desired to briquette the excess coke formed in the process, it is of advantage to withdraw the `excess coke either from the upper portion of thecoking vessel IG or directly from the dip leg leading from the separator I3. This latter materialwill have a substantial quantityv of tarry matter which may serve as a bindel in forming the .briquettes l The particles of the circulated coke can be lof a wide size range, for instance, 5 to 160 microns or even as large as 1A since vthe larger particles tend to break up intovsmaller ones by attrition or otherwise. The 'coke produced in the process is very desirable for many purposes `in view of its very low ash content and maybe .prepared for Y.

marketing by briquetting or balling up the nely divided discharged particlesin a rotary kiln using heavy pitch in a manner which, is well known per se. With certain feed stocks it willalso be found that the resulting coke will have'a sufli.

I have found a novel and efficient process for producing optimum yields ofvaluable distillate oils including catalyticcracking feed stocksand gasoline, and Valso a readily'. marketable highegrade coke lfrom a cheap starting material.A The specific description, however, is intended for purposesv of illustration only and; my invention is .not to be limitedvfto any specific. embodiment pre` sented herein.

I claim. asmy invention:

l. A processv forthe "production of valuable products from heavy residual hydrocarbon .oils which comprises contacting said heavy residual hydrocarbon Voils with hot finely divided coke in cracking and vaporization of the less refractory l portions of the oils but for an insufficient time to eii'ect extensive coking of said oils, segregatingand recovering the vapors from said initial conversion zone. passing the coke particles and unvapo- 2.`A process i'or the production of valuable I products fromheavy residual hydrocarbon oils which comprises contacting said heavy residual hydrocarbon oils with hot nely divided coke in an initial conversion zone at a temperature above 900 F. and for a period or time between l/2' second to 50 seconds to cause mild cracking and vaporization of less refractory portions of the feed stock, segregating and recovering the vapors from the initial conversion zone, passing the coke particles and unvaporized portion of said oil into a coking zone at a temperature of at least 850 F. and allowing the oil to remain in contact with the coke for a period of time of from 1 to l0 minutes to convert said unvaporized portion 'of the oils into vapors and coke and withdrawing a, stream `of the vapors and a relatively high grade of coke from said coking zone.

3. A process for the production o! valuable products from heavy residual hydrocarbon oilsiwhich comprises contacting said heavy residual hydrocarbon oils with hot finely divided coke in an initial conversion zone at a temperature above 900 F. and for a period of time of between 1 to 10 second to cause mild cracking and vaporization of less refractory portions o1' the feed stock, segregating and recovering the vapors from the initial conversion zone, passing the coke particles and unvaporized portion of said oil into a coking zone at a temperature oi' at least 850 F. and allowing the oil to remain in contact with the coke for a period of time of from 1 to 3 minutes to convert said unvaporized portion of the oils into vapors and coke and withdrawing a stream of the vapors and a relatively high grade of coke from said coking zone.

4. A process for the productionofvaluableproducts from heavy residual hydrocarbon oils which comprises contacting said residual hydrocarbon oils with nely divided coke for a relatively short period of time in an initial conversion zone at a temperature suiiicient to effect a partial vaporization of the oil but foran insumcient time to effect extensive coking of said oil, segregating and recoveringv the vapors from said initial conversion zone, passing the coke particles and unvaporized portion oi said oil into a coking zone at substantially the same temperature and allowing said coke particles and unvaporized portion of the oil to remain in contact in said coking zone for a substantially longer period of time than the period of residence in the reaction zone and suilicient to convert said unvaporized portion of the oil into vapors and coke and withdrawing a stream of hydrocarbon vapors and relatively high grade coke from said coking zone.

5. A process for converting heavy residual oils into coke and lower boiling products, comprising mixing the heavy oils with a suicient quantity of hot nely divided coke particles to vaporize a substantial proportion of said oil, subjecting the resulting mixture to a relatively brief period of treatment in a high temperature conversion zone to vaporize and convert a portion of the oil into lower boiling hydrocarbon compounds but insunlcient to effect extensive coking, separating the mixture issuing from the said zone into a hydrocarbon vapor stream and a stream comprising coke particle and unvaporized oil, introducing the last named stream into a hot coking zone, passing a iluidizing gas upwardly through the coking zone at a rate controlled to maintain the coke particles as a dense, turbulent bed in the lower portion of said coking zone, maintaining the said bed at a temperature between 850 and 1200 F. for a substantially longer period of time until the said components become coked on the coke particles, and the particles become dry, withdrawing an overvhead stream containing cracked vapors from the coking zone, quenching said cracked vapor stream and recovering valuable distillates therefrom, transferring the dry coke particles including the coke formed in the process from the coking zone to a combustion zone, passing an oxidizing gas upwardly through the combustion zone to maintain the coke particles as a dense iluidized burning mass in the lower portion ot said combustion zone, removing a stream of hot coke particles from the combustion zone for admixture with additional heavy oil feed, withdrawing excess coke from the process subsequently to the coking of the said heavy components, and removing combustion gases as an overhead stream from the combustion zone.

6. A process for the production of gas oil and gasoline from a petroleum residue boiling substantially above the gas oil range which comprises charging nely divided coke particles into a combustion zone, passing an oxygen-containing gas upwardly through the combustion zone at a rate controlled to maintain the coke particles as a burning, dense, turbulent bed in the lower portion of said combustion zone, withdrawing a stream of combustion gases from the upper portion of the combustion zone, removing a stream of hot coke particles from the dense bed of the combustion zone and mixing them with a petroleum residue in a proportion suincient to vaporize a substantial portion of the said fraction, passing the resulting mixture of coke and hydrocarbons through a coni-ined high-temperature zone contained within the combustion zone at a rate to provide only a relatively brief period of residence and to avoid extensive coking, separating a vapor stream from the mixture issuing from the high-temperature zone, passing the said stream to a recovery zone and separating distillate product therefrom; also, separating from the mixture issuing from the high-temperature zone, a stream comprising coke particles and unvaporized residue and passing the last named stream downwardly through a coking zone which is maintained in indirect heat exchange relation with the combustion zone, passing a stripping gas upwardly through the coking zone in counter-current with the stream of coke particles whereby the particles are maintained as a hot, dense, turbulent moving bed within the said coking zone, maintaining the unvaporized residual oil in the hot coking zone for a substantially longer period of time than the period of residence in the conned hightemperature zone and for a time suiiicient to convert said oil into vapors and coke, withdrawing an overhead vapor stream from the coking zone, passing the stream to a recovery zone and separating distillate products therefrom; wit'ndrawing stripped coke particles from the bottom of the coking zone and mixing them with additional oxygen-containing gas for further combustion in the combustion zone; and separately withdrawing a stream of excess coke from the combustion zone.

JOHN WEIKART.

l0 REFERENCES CITED The following references are of record in the le of this patent:

UNITED STATES PATENTS Number Name Date Kuhl Jan. 25, 1944 Hemminger Nov. '1, 1944 Eastwood et a1 Dec. 9, 1947 Blanding Feb. v17, 1948 Keith July 20, 1948

Claims

1. A PROCESS FOR THE PRODUCTION OF VALUABLE PRODUCTS FROM HEAVY RESIDUAL HYDROCARBON OILS WHICH COMPRISES CONTACTING SAID HEAVY RESIDUAL HYDROCARBON OILS WITH HOT FINELY DIVIDED COKE IN AN INITIAL CONVERSION ZONE AT A TEMPERTURE ABOVE 900* F. FOR A RELATIVELY SHORT PERIOD TO CAUSE MILD CRACKING AND VAPORIZATION OF THE LESS REFRACTORY PORTIONS OF THE OILS BUT FOR AN INSUFFICIENT TIME TO EFFECT EXTENSIVE COKING OF SAID OILS, SEGREGATING AND RECOVERING THE VAPORS FROM SAID INITIAL COVERSION ZONE, PASSING THE COKE PARTICLES AND UNVAPO-