US2763601A

US2763601A - Conversion of hydrocarbons

Info

Publication number: US2763601A
Application number: US357752A
Authority: US
Inventors: Homer Z Martin; Harvey E W Burnside; Frank T Barr; Robert W Krebs
Original assignee: Exxon Research and Engineering Co
Current assignee: ExxonMobil Technology and Engineering Co
Priority date: 1953-05-27
Filing date: 1953-05-27
Publication date: 1956-09-18
Anticipated expiration: 1973-09-18

Description

Sept. 18, 1956 H. z. MARTIN ET A1.

CONVERSION oF HYDRocARBoNs Filed May 27, 1955 STEAM gUnited States Patent O CONVERSION F HYDROCARBONS Horner Z. Martixn Cranford, Harvey W. Burnside, -Locusnand Frank T. Barr, Summit, N. J., and `Robert W. Krebs, `liaton Rouge, La., assignors to Esso Research and Engineering Company, a corporation of Delaware ApplicationMay 27, 'l1-953, Serial No. 357,752

3 Claims. (Cl. 196-55) This invention relates Vto a `process for treating hydrocarbons `and more `particularly relates to the `cracking or coking of heavy residual oils to produce lower boiling `hydrocarbons and coke.

The hydrocarbon residual oilwhich is to ^be cracked according to 'the present process is a high boiling 4hydrocarbon voil which cannot `be vaporized at ordinary ,pressures without cracking the high 'boiling constituents. The residual oil may be that produced by distilling crude petroleum oil at ordinary Aatmospheric pressure or under subatmospheric pressure such as `vacuum distillation. The present process may also `be used for cracking or coking shale oils, pitches, tars, etc.

Processes are known in the prior art for cracking or coking residual oils in the presence of nely divided inert or substantially inert solids maintained as a `liuidized u bed.

in the present process a dense iluidized. bed `of iinely divided inert solids such as sand, coke, etc. is .used and the preheated residual oil is introduced into the dense liuidized bed of nely dividedsolids maintained at Ireaction temperature. Vaporous products of coking are taken overhead and further treated as desired to recover lower boiling hydrocarbon fractions. During coking more coke is formed and some coke may 'be withdrawn from the process as ,product coke. Coke particles from the coking zone or reactor are stripped 4to remove volatile hydrocarbons therefrom. Some of the strippedlcoke particles 4may be withdrawn as product coke and the rest of the cokeparticles are vpassed to a burner where Vthey are preferably maintained ina dense fluidized condition and contacted with air or other oxygen-containing "gas to burn some of thecoke particles and to `supply heat to the coke particles. Or a Vtransfer line burner may be used in which the superciallgas velocity is between `about l0 `and 6() feet per second. The heated coke particles are then returned to the .cokingzone to supply heat there- One of the problems inthe uid coking of residual or other heavy oil feeds-is the deposition of coke in the overhead systennthat is, `in that partof `the process .where hot products of `coking leave the coking zone or afterthey leave the coking zone. The hot products .ofrcokingleaving the dense uidized bed `in the reactor contain .entraincdcoke particles and most `of these particles are removed bypassing the productsof'coking through a-deoil :feed ron the `hot inert solids. 4desirable to `feed `or. sprayttheoil` feed into ther dilute phase 2,763,601 Patented Sept. 18, 1956 ICC present process by injecting or introducing hot adsorbent finely divided lsolid -particles into the cyclone separator inlet when `the `cyclone separator is located within the lcolcing zone. If the cyclone separator is located outside the coking zone it is preferred to introduce the hot adsorbent particles into the outlet of the coking zone leading to the cyclone separator. In some cases it may also be desirable to introduce hot adsorbent finely divided particles into the outlet line from the cyclone separator at Vone or more spaced points to maintain the products of coking at coking temperature or higher.

The hot adsorbent particles to be used comprise `hot coke particles withdrawn asa separate stream or streams from the burning Zone. AIn some cases it `may be -desirable to increase the surface area of the cokeparticles to be used .as the hot adsorbent yparticles and this is preferably done by treating the particles with steam at high temperatures.

In the drawing the ligure represents one form of apparatus adapted .for carrying out the process of the `present "invention Referring `now to the drawing, the reference character 1l) `designates a `reactor or .coking Vzone containing auidzed dense bed 12 of solid finely `divided inert particles such as coke ortthe like. The dense bed -12 has `a level 'indicated at 14 with a dilute .or disperse phase 16 thereabove. The inert -solids of .thefluidized bed :12 `have a particle size ,betweenabout `20 ,and 10100 `microns prefera'oly `between about 5() and 400 microns and maycomprisepetroleum icoke, orotber coke, .coke formed in the process, spent crachingcatalysts, .purnice, Carborundum, .aluminaor other` materials refractory `under the `operation conditions.

The riiui'dized .bed 12 is maintained at a :temperature between .aboutr800 and 1600" F. When .looking -to produce .motor `fuel such .as gasoline, `terriperatures -in the .lower Vrange .of about-800 to about l200 .F., preferably about ,900 to .1.100" will `beused whereas `when `colting tat. extremely `high temperatures .to `produce chemicals such as 4.unsaturated hydrocarbon gases and-aromatic -hydrocarbons, temperatures in :the higher `range `of about 1.200"` torabout l600 F.`,ypreferably about 1250 ito 1450 will `be used.

The oil feed to be converted is ,introduced :into the dense uidizedhighly `turbulent bed 12 in the reactor lvia `feed line ..18 provided with nozzles 22 for `distributing the :In `some `cases it :may be .1-6-above therdense :bed level 14. The oil feed is pref- .erably preheated in `any suitable -manner to a tempera- .turetbetween about-600 and 800 F. beforebeing intro- .duced 1into the reactor 10. The preheating is done to reducefthe `low :temperature viscosity of theoil and render itruid. The Aoil feedmay be high boiling hydrocarbon oils, comprising `a residual petroleum oil `such as tar,

t .pitch, `,crude residuum, heavy bottoms or other similar vice such as a cyclone separator orthe-like for .separating solid ,particles from `the hot products of `coking. One -por more stages of cyclone separators zmay be .usedandthey may be `arranged ,inside the ,cokingzone at Vthe top there- `olor outside the `Coking zone. Deposition of coke occurs in the `cyclone separator and causes Vthe `pressure drop through tthe cycle separator to build upto such an extent that the cokingunithas to bezshutfdown for `cleanirigtdue `to ,thisfcause Deposition of coke valso occurs inthellines leading :to and `from `the cyclone separator.

stool; havingagravity between about 10 and 20 API, "aConradsonrcarbonbetween about 5 and 50 wt. and

an initial boiling point between about 850 and `1200o 1F. Steam may be `introduced at one or more "points 24 tto assist in maintainingthe "bed iin fluidized condition or -steam"may be added with the oilfeed in .line IS.

The fluidized bed 12 is maintained as such `by the uprflowing hydrocarbon gases and vapors formed by the 4ficial `velocity ofabout l to 2 feet per second, the` density The problem of coke `deposition Iis avoided in the of 'theiuidizedbed willbe about 4() lbs.` per cu. ft. but

may vary between about 15 and 60 lbs. per cu. ft. depending on the gas velocity and particular particle size range selected.

Vaporous products of coking leave the bed 12 and pass overhead into inlet 26 of cyclone separator 28 arranged at the top interior of the reactor 10. The vaporous products contain entrained solids and the cyclone separator 28 or other gas-solids separating device is used to separate or recover the entrained solids and return them through dip leg 32 of the cyclone separator to the dense bed 12. More than one cyclone separator in stages may be used. The separated vapors pass overhead from the cyclone separator 28 through line 34 for further treatment in a recovery system.

Deposition of coke on the walls of the outlet line 34 and cyclone separator 28 has caused premature shutdowns of the coking unit. These coke deposits are believed to be formed through polymerization of unstable reaction products and have been shown to be greatly reduced and substantially eliminated by maintaining the effluent stream of vaporous products of coking at a high temperature, either substantially at the reactor temperature, or at a temperature which steadily increases from the reactor to the point of quenching. The natural tendency due to the endothermic reactions taking place is for the temperature to fall steadily as soon as the vaporous products of coking leave the dense bed 12. As the cooling takes place in the line 34 and cyclone separator 28, high boiling materials deposit on the walls and polymerization causes coke deposits.

Cooling of the vaporous reaction products and hence deposition of coke can be prevented according to this invention by introducing hot solid particles into the eluent stream from the reactor 10. The hot particles are preferably added at the inlet 26 to the cyclone separator and/ or at one or more points along outlet line 34. This prevents coke deposition because of the introduction of large quantities of surface in the form of solid adsorbent materials. The most convenient source for the hot adsorbent coke solids is from the burner vessel 36 later to be described in greater detail. Ordinarily, coke particles of reasonably small particle size will contribute considerable surface, but this can be greatly enhanced by treating coke to be injected into the stream of vaporous overhead products of coking with steam at high temperatures. This has the effect of activating the coke particles and producing a porous structure through chemical reaction of the steam with the carbon.

Introduction of the hot adsorbent solids prevents or substantially reduces deposition of coke in the outlet line or lines and equipment associated with the reactor in that it heats the vaporous reaction products and prevents liquid separation due simply to condensation; any condensed liquid would go to coke because of the temperature. The introduced solid particles also have a scouring eifect so that any coke which has been deposited previously can be removed. In addition the introduced adsorbent solid particles adsorb easily coked materials and prevent them from forming coke on equipment surfaces. The easily coked materials also tend to condense easily and by removing them from the vaporous reaction product effluent stream, they are prevented from fouling the apparatus. At least some of the adsorbent solids added to the inlet 26 of cyclone separator 28 and containing the easily coked materials as adsorbed materials are returned to the coking reactor to further crack or coke these materials.

Hot coke particles from burner vessel 36 are passed through line 38 alone into the inlet line 26 of cyclone separator 28 or through line 38 and line 42 and/or line 44 to outlet line 34 from the cyclone separator 28. More or less points of addition of hot adsorbent solids may be used as found necessary. Y

The hot vaporous reaction products are passed through vessel or the bottom of a fractionating tower (not shown). The hot vaporous products have their temperature reduced to about 500 F. to 900 F. by the introduction of a quench medium through line 48. The quench medium may be any suitable liquid such as oil or water. Condensed liquid plus some scrubbed-out solids is withdrawn from the bottom of quench vessel 46 through line 52 and may be recycled to reactor 10 through feed line 18 or may be withdrawn from the process and discarded or disposed of in any desired manner. The reaction vapors leave the top of quench vessel 46 through line 54 and are preferably fractionated to recover chemical raw materials and/or motor fuel, gas oil cracking stock, a recycle oil fraction and gases. Instead of fractionating the vapors from line 54 they may be treated as desired to recover desired hydrocarbon fractions.

Returning now to the reactor 10, coke or coked particles are withdrawn downwardly from the dense bed 12 into stripping zone or vessel 56 which is shown as having a smaller diameter than reactor 10 and which depends from reactor 10. Steam or other suitable stripping gas is introduced through line or lines 58 into the bottom of stripping zone 56 to'remove volatile hydrocarbons from the coke in the stripping zone and pass them into the dense fluidized bed 12 in reactor 10.

During the coking process, coke is formed so that some of the coke particles are preferably withdrawn from the bottom of the stripper 56 or through line 60 from line 62 leading from the bottom of stripper 56. The withdrawn coke particles are cooled and sent to storage or otherwise disposed of. Fluidizing gas may be introduced into line 62 through one or more lines 64. Line 62 is formed as a U-bend and the solids therein are maintained in a uidized condition. A process showing the use of U- bends is described in Packie Patent No. 2,589,124, granted March 1l, 1952. Gas such as steam or air in a small amount is added at the bottom of the U-bend 62 as at 66 to maintain uidity of the solid particles. The upflow leg 67 of the U-bend is provided with a controllable restriction such as a valve or an orice at 68 to assist in control of the circulation of solids and to provide a safety shut-off. The principal control, however, is usually effected by controlling the amount of gas introduced in the riser portion 67 of the U-bend system, through one or more ports 72. The greater the flow of gas to the riser, within limits, the greater the solids flow rate. Increasing the flow of gas decreases the density on this leg of the U-bend and therefore increases the pressure differential driving force. Other methods of controlling the circulation and transport of hot tluidized solids may be used. The upow leg 67 empties into the bottom portion of the burner vessel 36 before referred to. Additional air is preferably introduced through line 74 and nozzles 76 into the lower portion of burner vessel 36 to burn coke from the solid particles and also to maintain the solid particles as a dense uidized highly turbulent bed 78 having a level designated at 82 and a disperse or dilute phase 84 thereabove. Combustion gases leaving the disperse phase 84 contain entrained solids which are removed by passing the combustion gases through cyclone separator 86, the separated solids being returned to the dense bed 78 through dip leg 88 and the denuded combustion gases passing to the atmosphere through outlet line 92 or to additional separation devices and heat recovery systems if desired. Preferably 2 or 3 stages of cyclone separator are used on the burner side to remove solids from gases leaving through line 92.

During combustion of the coke particles in burner vessel 36, the particles are heated to a temperature higher than that in the reactor 10 so that when the particles are recirculated to the reactor they will contain sufficient heat to supply the heat of vaporization and cracking of the feed oil introduced into the reactor. The temperature in the burner vessel 36 will be about 50 line 34 to a quench zone 46 which may be a separate 75 tQ 509 F- highef than. 'fhfdtin the reactor 10Y aanstaan [In the rbottom ofiburner vessel 36 satwell194 tis provided by `short vertical fpartition '96 from which lrot burned coke particles areremovedithrou gh line 98zwhich may sbc provided with a uidizinglinevortlines i102. :One portion of the withdrawn hot coke or other isolid Iparticles :is passed through a second U-bend 104 provided with an aerating orfluidizing line 106 at =its `lower porltion and a control restriction u1.08 similar :to restriction 68 above described. Upow leg 112 of U-bend.104 communicates with reactor vessel `10 below the level 14 of 'the dense fluidized bed therein. Steam or other gas introduced through line 114 located above control restriction 108 controls the rate of ow of solids through U-bend 104 and to the reactor 10. The major portion of the hot coke particles from burner vessel 36 will pass through U-bend 104 and this may amount to about 75 to 99%, usually about 90 to 98% of the total withdrawn from burner 36 through line 98.

In addition to and shown as arranged above U-bend 104 is a third U-bend 116 which is also connected to burner withdrawal line 98 shown at a location above U- bend 104. The positioning and arrangement of

U-bends

104 and 116 may be changed, if desired. U-bend 116 is also provided with an aeration line 118, control restriction 122 and gas inlet 124 for controlling the rate of low of hot solids through U-bend 116 which are similar to the parts described in connection with U-bend 104, The upflow leg 126 of U-bend 116 is a line which provides hot solid particles to be supplied to the cyclone separator inlet 26 and outlet line above described. Line 126 forms a continuation of line 38 above described.

In cases where the hot coke particles or other inert solid particles being passed through line 38 alone or line 38 and/or line 42 and/ or line 44 for preventing coke deposition in the outlet line and cyclone separator have a low surface area, the coke particles may have their surface area increased by passing them through a steam activation zone 128. Superheated steam is introduced into zone 128 through line 132 and gaseous reaction products are taken overhead through line 134. During activation the coke particles may be maintained as a dense tluidized bed. The temperature during activation is between about 1100 and 1600 F. with about 1200 to 1400 F. being preferred. The time of activation may vary between about to 100 minutes. With this treatment coke particles having a surface area of about l to 10 square meters per gram may have their surface arca raised to about 100 to 1000 square meters per gram. In some cases it may be desirable to obtain the high temperatures needed for this reactivation reaction by introducing some air with the steam or ahead of the steam, although less appreciation in surface area will result through the introduction of the air.

Line 136 is a by-pass for line 126 around the steam activation zone 128.

Lines

42 and 44 lead ot from line 38 but may lead olf from line 136 where no steam activation is practiced.

In cases where more heat is required than is being produced by burner vessel 36 or where it is more desirable to withdraw product coke than burn it, oil or gas or other fuel may be introduced into vessel 36 through line 138.

In a specific example about 100 barrels per day of residual oil having an API gravity of 10 and a Conradson carbon of 18 and an initial boiling point of about 1150 F. and about 7000 lbs/day (or 20 wt. percent of feed) .of steam were added to the reactor 10 at three longitudinally spaced points with most of the steam being added through lines 24. The oil feed was injected through nozzles into the lluid bed 12 in the reactor. The solids lto feed oil ratio by weight to the reactor was about 15 to l. 4The temperature in the reactor was 1000 P. and in the burner was ll50 F. About 2 to 3 gallons per hour of oil avere injected into the burner 36 through line 138.

The circulating solid was coke having a particle size ofiabout 20.`20l);standard mesh .with `the :majority `of fthe particles rbeing between about `48 land 80 mesh. The superficial velocity of .thegas inthe-.reactor 10 `wasabout `l A.ft/sec. .at the Abottom `of `the `cylindrical .portion andthe density of the dense fluidized bed l2 was about 45 lbs./cu. ft. 'The superficial velocity of the fgas in .the burner 3,6 was about `3 ,ft./sec. and the density of the dense iluidized "bed 78 was about 40 `lb.s./cu. ft.

The .overhead products `from 4line 34 were quenched in quench zone 46 `to `a temperature of about 400 il?. with a quench oil consisting of condensed liquid product boiling above about F.

In the stripper 56 temperature was about 995 F. and the superficial velocity of the uptiowing gas in the stripper was about 1.0 ft./sec.

The yields obtained are as follows:

Ca, wt. percent 6.5 C4., vol. percent 2.8 C5, 430 F., vol. percent 15.0 430, 650 F., vol. per cent 10.7 650, 1050 F., vol. percent 30.0 1050 F. -l, vol. percent 30.0 Coke, wt. percent 10.0

About lbs. of coke per hour are withdrawn as product through line 60 and as losses 'through

lines

52 and 92.

In the system shown on the drawing with only one cyclone separator 28 on the reactor size and in order to maintain the temperature from dropping in cyclone separator 28 and outlet line 34, about 210,000 to 40,000 lbs/day of coke from line 38 at a temperature of about 1100 F. would have to be introduced into cyclone separator 28. In order to obtain more nearly isothermal conditions it is desirable to distribute this coke among

lines

38, 42 and 44. If this is not done, for simplicity, some additional coke should be added to line 38.

Operating the process as described above eliminates coking problems heretofore encountered when cracking heavy residual oils.

What is claimed is:

1. A method of cracking oils which contain constituents unvaporizable at ordinary pressures without cracking which comprises contacting hydrocarbon oil with a dense fluidized highly turbulent bed of nely divided solids in a cracking zone maintained at a temperature above about 800 F. to produce lower boiling hydrocarbons while depositing coke on the solids, said cracking zone containing a disperse phase above the turbulent bed, removing coke-containing solids from said cracking zone and passing them to a separate combustion zone where oxygen-containing gas is introduced to burn the coke and heat the solid particles to a temperature above that existing in said cracking zone, separately recovering ue gas from said combustion zone, returning at least part of the hot solids from said separate combustion zone to the turbulent bed of said cracking zone to supply heat thereto, removing a stream of vaporous reaction products overhead from said cracking zone through a gas-solids separating stage, and introducing through an auxiliary injection means another portion of the hot solids as a discrete stream from said combustion zone into the stream of vaporous reaction products in the disperse phase passing into said gas-solids separating stage to prevent deposition of coke from said vaporous reaction products.

2. A method according to claim l wherein the other portion of solid particles from said combustion zone to be passed to the vaporous reaction products stream is steam activated to increase their surface area before being introduced into the stream of vaporous reacting products passing overhead from said cracking zone.

3. A method of coking oils which contain constituents unvaporizable at ordinary pressures without cracking which comprises converting an oil in a dense uidized 7 bed of finely divided solids in a lower portion of an enlarged zone provided with a gas-solids separation stage in the upper dispersed phase portion, said fluidized bed being maintained at a coking temperature, to produce lower boiling hydrocarbons while depositing coke on the solids, removing and passing solids from said dense bed to a separate combustion zone to burn coke and heat the solid particles to a temperature above said coking temperature, separately recovering ue gases from said separate combustion zone, returning heated solids from said combustion zone to said dense uid bed to supply heat thereto, and introducing another portion'of heated solids as a discrete stream from said combustion zone into said 5 gas-solids separation stage.

References Cited in the file of this patent UNITED STATES PATENTS 2,445,328l Keith July 20, 1948

Claims

1. A METHOD OF CRACKING OILS WHICH CONTAIN CONSTITUENTS UNVAPORIZABLE AT ORDINARY PRESSURES WITHOUT CRACKING WHICH COMPRISES CONTACTING HYDROCARBON OIL WITH A DENSE FLUIDIZED HIGHLY TURBULENT BED OF FINELY DIVIDED SOLIDS IN A CRACKING ZONE MAINTAINED AT A TEMPERATURE ABOVE ABOUT 800* F. TO PRODUCE LOWER BOILING HYDROCARBONS WHILE DEPOSITING COKE ON THE SOLIDS, SAID CRACKING ZONE CONTAINING A DISPERSE PHASE ABOVE THE TURBULENT BED, REMOVING COKE-CONTAINING SOLIDS FROM SAID CRACKING ZONE AND PASSING THEM TO A SEPARATE COMBUSTION ZONE WHERE OXYGEN-CONTAINING GAS IS INTRODUCED TO BURN THE COKE AND HEAT THE SOLID PARTICLES TO A TEMPERATURE ABOVE THAT EXISTING IN SAID CRACKING ZONE, SEPARATELY RECOVERING FLUE GAS FROM