US2731400A

US2731400A - Conversion of hydrocarbons

Info

Publication number: US2731400A
Application number: US229584A
Authority: US
Inventors: Charles E Jahnig; Harvey E W Burnside; James W Brown
Original assignee: Standard Oil Development Co
Current assignee: Standard Oil Development Co
Priority date: 1951-06-02
Filing date: 1951-06-02
Publication date: 1956-01-17
Anticipated expiration: 1973-01-17

Description

C.E..JAHN1G ETAL 2,731,400

CONVERSION OF HYDROCARBONS Jan. 17, 1956 Filed June 2, 1951 3 Sheets-Sheet l 42- Co2: 5A. 52

A-A- Nv* AQ QM@ Aa,V w F E@ @uw /Zi TI @ri Jan. 17, 1956 c. E. JAHNIG ETAL 2,731,400

q CONVERSION OF' HYDROCARBONS Filed June 2, 1951 5 Sheets-Sheet 2 Clbtowzeceg Jan. 17, 1956 c. E. JAHNIG ET AL O 2,731,400

CONVERSION OF HYDROCARBONS Filed June 2, 1951 5 Sheets-Sheet 3 '244% i| 255 l x 4 l I 12,2 f f- Q'gf El nl I /igo Y? 242 ft, i94^- :P184 FUEL. GAS '258 JMG i92,:J--1L--- Anz *r Mory 222 Pos1. 226

United States Patent O CONVERSION F HYDROCARBONS Charles E. Jahnig, Red Bank,` Harvey E. W. Burnside,

Rumson, and James W. Brown, Elizabeth, N. J., assignors to Standard Oil Development Company, a corporation of Delaware Application June 2, 1951, Serial No. 229,584

6 Claims. (Cl. 202--14) This invention relates to a process for treating hydrocarbons and more particularly relates to the conversion of heavy residual petroleum oil to produce lower boiling hydrocarbons.

The petroleum oil residuum or residual oil which is to be converted according to the present process is a high boiling hydrocarbon oil which cannot bey vaporizedat ordinary pressures without cracking the high boiling constituents. At present relatively large volumes of reduced crude or heavy bottoms are available because lower grade crude oil feedstocks are being processed which leave more residue and because there is a larger demand for motor fuel such as gasoline and other petroleum oil products such as heating oil which means` processing more crude oil to leave more residue.

It is known in theprior art to `crack or coke heavy residual oils in the presence of finely divided inert solid particles maintained as a uidizedbed. Visbreaking is a short time cracking operation in which the purpose is to make an additional amount of gas oilfeedstock and not much gasoline. In visbreaking, about `to 15% gasoline isproduced when the temperature is at about 800 to 950 F. Higher temperatures are inoperable due to cok- In coking, the temperature can be ing in the heater coil. much higher and the cracking more drastic. In coking at high severity, about`5-50% gasoline is made which has a higher octane number than the gasoline produced when visbreaking. During coking the final products are gasoline, some gas oil, gas and coke. Unlikevisbreaking, the products from coking are withdrawn as vapors and solids rather than primarily as a liquid. Thepresent invention can` be used for high temperature and low` temperature cracking of residual oils.

According to the `present invention heat is suppliedto a dense uidized bed of particles in a cokingbed by indirect heat transfer to the solid particles. The use `of indirect heat exchange is important in supplying `heat to a fluid coking bed because the coking may be carried out at a relatively high pressure while the combustion supplying the heat for the particles is carried out at low pressure, substantially atmospheric, and therefore requires little air compression.` Efforts to develop heat exchange inside the coke bed have met with considerable mechanical `or construction diculties due to thermal `expansion and strength of material problems especially around the relatively high temperatures of 1100` F. and above, and relatively high i pressures. i

According `to the presentrinvention the coke or other` particles from the coking bed` are` circulated through U- bend transfer lines which hang from the bottomof the coking vessel. Heat is` supplied to the U-shaped transfer lines in a plurality of ways.

In one form of the present invention the U-bend heat transfer lines are arranged in a fired furnace.

In another form of the invention the U-bend heat transfer `tubesare arranged in a heating vessel packed with .inert or ceramic spheres or the like which may contain a ice combustion catalyst and heat is supplied to such spheres by burning a fuel in contact therewith.

In another form of the invention the U-bend heat transfer tubes are arranged in a vessel containing a uid ized bed of finely divided inert solids. The heated solids are removed from the vessel, heated outside the vessel with fuel gas and air and the heated particles then returned to the tluidized heated bed to supply heat to the U-shaped heat transfer tubes. A combustion catalyst such as an oxide or oxides ofchromium, iron, etc. may be incorporated with the heat transfer solid.

In the drawings:

Fig. l represents one form of apparatus for carrying out the process of the present invention in which the U- bend heat transfer tubes depending from the bottom of Athe coking vessel are arranged in a tired furnace and the heat transfer tubes are heated by radiant and convection heat in the tired furnace; i

Fig. 2 represents another form of apparatus in which the `U-shaped heat transfer tubes depending from the coking vessel are arranged in a heating vessel provided with inert or ceramic spheres which are packed around the tubes and hot combustion gases are used for supplying the heat to the ceramic spheres and the heat transfer tubes; and i Fig. 3 represents another form of apparatus in which the depending heat transfer tubes arranged below the coking vessel are submerged inta uidized bed of inert solids which are removed from the fluid bed, heated by burning a fuel gas in the presence of the removed solids and the heated inert solids arethen returned to the tluidized bed for supplying heat to the heat transfer tubes. In some cases it may be preferable to heat the circulating solids by contacting with hot flue gas from a separate burner.

Referring now to Fig. l of the drawings, the reference character 10 designates VAa line through which residual hydrocarbon oil to be coked is pumped by pump 12. The residual oil may compriseA atmospheric or vacuum residnum petroleum oil, reduced crude oil, tar, pitch, heavy cycle oil, clarified oil from catalytic cracking, the clarified oil being a high boiling aromatic fraction. The oil is heated to a temperature of about 400.950 F., preferably above 600 F. by being passed through the coil 14 in furnace 16 and the heated oil is then passed through line 18 into or onto a fluidized solids bed 22 arranged in coking vessel 24 and maintained at a temperature of about 800 to 13S0 F. Line 26 is provided for injecting steam into the heated feed oil passing through line 18. While only one inlet line 18 is used as shown in the drawing for supplying the heated residual oil to the coking bed, it is preferred to introduce the heated oil at a number of places into the coking bed, especially where the coking vessel is a large piece of equipment. Also, sprays or nozzles may be used at the outlet end of the line or lines 18.

The lluidized coking bed 22 has a level indicated at 28 above which is a dilute phase 32 where the uplowing gasiform material contains only a small amount of entrained `solid particles. The gasiform material is passed `through a gas-solids separating device such as a cyclone separator 34 arranged at the top of colting vessel 24 and provided with a dip leg 36 for returning separated solids to the dense lluidized bed 22. Gasiform reaction products pass overhead through line 38 and tnay be further treated as desired to recover hydrocarbon products or fractions. The. coking bed 22 is maintained in a dense luidized highly turbulent condition by upflowing gases as will be hereinafter described in greater detail. For starting up solids forming the initial bed in the coking vessel sand, finely diivded petroleum coke, pumice, kieselguhr, carborundum or other similar refractory materials may be used. During coking, more coke is formed along the actual number of U-bendV tubes will be given.

vection heating section 46. The furnace is preferably formed of a 'cylindrical' shell provided with burners 48 arranged in concentric circles for supplying radiant heat to the radiant heating section. The furnace is fired from the bottom by burners 48 and' combustion gases pass upwardly in the radiant'v heating section. The furnace isprovided Vwith a central' refractory wall 5,2 which is preferably circular in cross section and which is shorter Y in height than the. height of the furnace to provide a passageway for the hot combustion gasesfrom the radiant heating section to the convection heating section 4'6 formed by the refractory Wall 52.

Arranged'within the radiant heating section 44 ofthe red furnace 42, is a4 plurality of U-bend' heat transfer lines 54V arranged in a circle whichhang from the bottom of the coking vessel 24 and have their upper ends in communication with the bottom of` the coking vessel 2'4. With the U-bend construction2 mechanical problems caused byfthermal expansion. are avoided; The U-bend lines 54' are shown in the drawing in a position to show the U-tube arrangement, but preferably the U-bend lines are arranged at-right angles tothatshown in the drawing sothat-one circle oftubes is formedv and so that radiant heatl will beV supplied to both sides of the tubes.

They heat transfer tubes 54 are fired on both, sides by the VburnersY 48' which are arrangetl'inY concentric circles. Only aV few of" these U-shaped heat transfer tubes have Y been shown in the drawingfbutl it will be understood that there are a'la'rge number-'of them an'd'when the specific apparatus will be described' for one form of apparatus The U-bend tubes permitV dense iluidized coke or other inert particles to pass down one legV 55i and then steam is introduced into the lower portion of the other leg S8 beyond' the bend as at 56 to lower the density of the' mixture therein and to-cause circulation of the particles through the U-bend heat transfer tube. i

This same operation occurs in each of the U-bend heat rtransfer tubes.l The fluidizinggasv is preferably' steam which is. passed linto the upow leg 58 of the U-bend transfer tube 54 by means of manifold line 62. Steam for tluidization is preferably generated by. utilizing heat from the combustion gases'leav'ing' the furnace aswill be hereinafter described. The outletV endv of the upflow leg of each U-bend heat transferl tube may be arranged'at about the-.same level as: the point 'of connection of the downcoming leg from-fthe,- coltingvessel 24.

Another set of heat transfer-tubes is provided for the convection heating sectionwhere for simplicity, only a single U-shaped heat transfer tube 64l is shown. again steam ory other fluidizing gasis introduced by means oflinex66 into the upow leg 68 of the U-tube to cause circulation of theV solid particles in the U-tube in the convection heating section to supply heat to the solid particles from the coking bed 22.

The rate of flow of the solids in the downiow leg 55 of the U-tube heat transfer elements 54 may be between aboutk 1; feet, per second and 10v feet per second,

about 50" and 500 B. t. u. per hour'per square Vfoot perf F. With this method-of 'heat transfer using the U-shaped elements and having a temperature of` 850 F., for` ex.v ample, in the fluidized.v coking bed. 22, the solids ternperature- 'in' the coking bedi2 2 will4 be. maintained within,

Herev about' 110"l `of the desired 850 F. Also,A highV circulation rate through these U-shaped tubes will maintain the smallest difference of temperature between the tube wall' and the coke or other solid passing through the tube.

By reducing the solids circulation rate in the U-bend transfer tubes the coke particles may be heated to a temperature substantially higher than 850 F., if desired, for the purpose of drying the Ycoke particles or completing the reaction on the coke: particles. This method of heating solids` may be used in the` desorption of the char and regeneration ofthe char in iuid charcoal adsorption processes. Y

The hot combustion gases pass from the radiant heating section 44 over the top of the bridge wall 52 into the high velocity convection heating sectionl 46 from whence the combustion gases pass outwardly through line 70 to a stack. The hot combustion gases are preferably passed through a waste heat boiler or suitable heat `exchange device 71 for, recovering some of. the Yheat from these gases. Water or steam is` passed through line 72. and' waste heat boilerA 71' to supply superheated steam under pressure which is supplied to manifold 62 by line 73 and passesv into coking bed. 22. or part of Vthe superv heated steam may be4 withdrawn through line 73 Vand used' as uidizing gas for the cokihg bed 22.215. will. be

referred to presently. High velocity jets canv be used in` below' theY radiant heating section and' the transfer tubesv in the convection heating section. extend below the floor ofthe main' furnace orbelowthe level ofthe radiant heating section so that' the pointsofv connection are` not exposed to the burner flames. As above stated coke is formedv during the coking operation and finely divided coke particles are withdrawn from the dense uidized bed 22 throughline 74 to maintain the level 28 constantand are, preferably` cooled by quenching with water or other means and then recovered as such for use asfuel or for other uses.

VAn annular gridfor steam distribution is arranged at the bottom of the iluidized bed 22 in vessel 24 as shown at 76.'V The uidized bed 22is maintained as a dense fiuidized' highly` turbulent bed by steam or other fluidizinglgas introduced below the grid member 76 through line 77 and also bygas introduced into the upowingelegs of the U-bendheattransfer tubes. coking bed have a size of about 2'5 microns to 500 microns, preferably about 80200 microns, and the superficialv velocity 'ofthe' gasiform. material passing upwardly through the` col'ting bed22 is between about 0.3 andv 5 feet'persecond. y

Specific' details for a commercial size' fluid' coker of the typeV disclosed in Fig. 1 will now be given.V The hyr drocarbon residuum feedlselectedhas an'API gravity of about 5 and a Conradson carbon ofA about 22 wt. percent. The gravity of the residual oil treated, however, may varybetween about" -:1.0and 20`API gravity and the Conradson mayrvarybetween about 5 and 3'5`wt. percent.' 'Ihe` feed tothe cokingvesselalso contains-recycle` oil from cokingoperation. The vaporous crackedproductsv from coking' zone 22 Aand the fresh residual oil feed are introduced into the bottom of the fractionator (not shown)V of the recovery system and bottornsfrom the fractionaton are used" as feedforfthis specic example.

Theresidual oil feed is` thereby prelieated'and'picks upv residual coke-.particles aswellias the-heavy oil product which is to be recycled. Y Y

In .thepresent-case', about V2300Cl2barrels per operating day of residualoilplus# 6;900"batrels' per operating day of. recycle-Stockton bottomswas heated l to a` .temperature oftabut T55"- E. and thenfp'ased throughthe-heater" V14;

The particles in the about 89 feet deep and using coke as the inert fluidized i particles has a density `of about 30 lbs. per cubic foot. The coke particles have a size between about 80 and 200 microns. The superficial velocity of the steam plus vapors passing upwardly through the fluidized bed is about` 3 feet per second.

The line corresponding to line 18 in Fig. l is an 8 line and in the design under discussion thereare 12 connections from this arranged around thecircumference of the vessel 24 to supply feed oil at a `plurality of points. Steam under pressure is introduced through line 26 into each of these feed lines 18. About 1 `to 5% by Weight f steam on feed may be used.` t

The total vapor products going overhead through line 38 are as follows:

10.7 MMISCF/SD c3-gas 230 a/sll...` CtH 230 B/sD ClHm 4,370 B/SD C-430 F. 6,320 B/sD 43o-650 F. 8,620 a/SD...` n-950 F. 6,900 n/sD 950 R+ 1Million standard cubic feet per stream day.

Forthe size coking vessel shown in Fig. 1, there are 21 U -bend transfer tubes (or 42 single tubes) arranged in a circle in the radiant heating section 44 of the fired furnace 42. The tubes have a diameter of 6" and a length of 17 feet within the radiant heating section 44, that is, that portion of the tubes between the top and bottom wall of the radiant heating section 44. The circleof the U- shaped heat transfer tubes 54 in thepreferred arrangement above referred to has a diameter of about 13 1". The size and number and arrangement of the tubes can be varied. i

In the convection heating section 46 there are 44 single heattransfer tubes of 4` diameterformed from 22 U- bends with steam injection near the bottom of each U- bend. The heated length of `the tubes in the convection heating section is about 17'.

Steam at about 850 F. and 50 lbs. per square inch gage in the amount of 20,000 lbs.` per `hour is passed to manifold 62 and is supplied to the upow legs `of each U- bend heat transfer tube. The furnace 42 is cylindrical and has a diameter of about 23 feet.

The radiant heating section is `maintained atfa temperature of about 2160 F. while the convection heating section 46 is maintained at a temperature of about l330 F. The combustion gases passing to the stack through line 70 are at a temperature of about 900 F. About 880 tons per standard day of finely divided coke are removed via line 74 from fluid bed 22. t

, Referring now to Fig. 2 of the drawing, the reference character 102 designates a coking vessel provided with a fluidized bed of solids 104 having a level indicated at 106 with a dilute suspension or dilute phase 108 thereabove. A cyclone separator or other similar gas-solids separating device 112 is arranged in the upper portion `of the coking vessel 102 for separating entrained solids from gasiform products going overhead, Ithe solid being returned to the lluidized bed 104 through dip pipe 114 andthe gasiform products passing overhead through line 116 to a suitable product recovery system.

into the uidized bed 104 in the coking vessel 102. In the commercial design unit twelve feed lines like line 122 are provided for supplying the preheated residual oil feed to the lluidized bed at a plurality of points around the circumference of the coking vessel.

ln the form of the invention shown in Fig. 2 U-bend heat transfer tubes 124 hang from the bottom of the coking vessel 102 and have their upper ends in open communication with the bottom of the coking vessel so that finely divided solid particles from the lluidized bed 104 can be circulated down one leg 125 of the U-tube and up the other leg 125' of the U-tube and back into the liuidized bed. The U-shaped tubes are arranged in a heating vessel for supplying heat to the fluidized bed 104 in the coking vessel and` for maintaining the temperature of the fluidized bed 104 between about 800 and 1400 F. and under a pressure of about atmospheric to 200 lbs. per sq. in. In the drawings only a few of the heat transfer tubes are shown but in a commercial unit having a construction such as shown in Fig. 2, there will be 332 Such tubeshaving a diameter of 4 inches and connected to form 166 U-bends spaced about approximately 13 apart on equilateral triangles where the upper ends of the tubes connect into the bottom of the coking vessel 102. A steam line 126 is provided for injecting steam or other iluidzed gas into the upllow leg of each of the heat transfer tubes 124, for causing circulation through the tubes.

The heat transfer tubes are arranged in a shell 1.28 provided with an internal insulation lining and in the commercial design the shell will have a diameter of about 13 feet and the insulation will be about 8 thick. The shell 128 is packed to about the level 132 with 1 diameter refractory spheres made of silica, alumina, carborundum, zirconia, etc. Instead of ceramic material, other materials such as metals may be used. In this form of coking apparatus the refractory spheres provide a fixed bed of heating material. For heating the heat transfer tubes during starting up, fuel gas is supplied through line E34 and air through line 136 to an auxiliary burner 138 and air heated to about 1500 F. then leaves the burner through line 142 and is passed to the duet 144 which extends into the center of the heating shell 128. At its inner end the duct 144 connects into a 30" diameter axial distributor 146 which comprises a hollow cylindrical tube extending from the exterior of the bottom of coking vessel 102to the bottom of shell 128, the tube being per forated to permit the passage of gas.

After the vessel 128 is heated up the flow of fuel gas and air through burner 138 is stopped but air continues to ow to axial distributor 146. Fuel gas is then intro duced into the stationary packing 133 in shell 128 through a plurality of perforated pipes or tubes 148 arranged in the packing in one or more circles substantially concentric with said distributor 146. By arranging the tubes in this way overheating is avoided. lf all the fuel were added to the entire air stream in the packed bed heater 123 the combustion would give theoretical flame temperatures of roughly 3600 F. which would give exceedingly high heat transfer rates.

However, in many cases there is the possibility of the heat `transfer tubes becoming plugged on the inside and with flame temperatures of 3600o F. a plugged tube would l immediately result in tube failure since the metal would `Residual oil feed of the type above `described heated line and introduced through one or more lines 122 toatemperatureof about`800-950" F. is passed through heat up approaching flame temperatures'.

This would canse a shutdown of the plant and in order to avoid this possibility it is advisable to limit the llame temperature around the tubes to 1500 F. This is done by spaced fuel injection by the perforated tubes 148. rlhat is, the fuel is added in increments to the total air stream. The air from distributor 146 flows radially outward through the packed bed 133 surrounding the U-shaped heat exchange tubes 124. Thus, for example, when the gas containing air flowing across the tubes has cooled to say 1400" F. t

enough fuel gas is added to raise the temperature of the gas to about 1600* F. This incremental addition of the fuel gas is effected. by the perforated pipes 148. Thermocouplesare provided to facilitate this control. To prevent coking of. the fuelthe perforated or porous tubes maybe insulated For example, one-half inch of insulation on the outside of the tubes will preventV excessive temperaturesl on the fuel gas passing therethrough.

As shown in Fig. 2 of the drawings, the air from the distributor 146 flows radially outward' from the openings kin the distributor and through the packed bed 133 and in. this way also provides increased contact time just be" fore the gases leave the packing whereby complete con bustion of the fuel gas is assured.

The packed bed 133 may be made up of refractory material such as silica, alumina, carborundum, zirconia, etc., or metals or other material and should preferably be porous with aV high surface area to promote combus tion. yIf* desired, a combustion catalyst may be used in connection with the refractory packing.

In a Vcommercial design unit of the modification shown inv Fig. 2 of the drawings, the U-tubes 124 have a height of about 28 feet. There are 100 equally spaced one inch perforated pipes 148V for this design. The packed bed 133 is maintained atV a temperaturel of about 1500" F. and under a pressure of about one pound per square inch gage.

Coke produced in the form of finely divided particles is withdrawn from the iiuidized bed 104 through line 152 and may be cooled or quenched and then stored or used as such.

The hot combustion gases leaving the heating` shell 12S passupwardlythrough line 154 through waste heat boiler 156 and then through. water preheater 158 before passing' to the stack through line 162; After passing through the Waste heat boiler 156 the combustion gases are at a temperature of about 600 F. and after leaving the preheater 158 the gases are at about a temperature of about 300 F.

In the commercial design such as shown in Fig. 2 the twelve feed lines 122 have a diameter of about 3 for supplying the oil feed at about 870 F. to the coking vessel 102. Theoil feed comprises 23,000 barrels per operating dayV of reduced crude having an API gravity of to 10 and a Conradson carbon of about 20 weight per cent and an initial boiling point of about 11.00 F. The oil feed also includes 6240 barrels per operating day of recycle oil from the process.

The tluidized bed of coke 104 in the coking vessel 102 is about feet deep and' has a density of about 30 lbs.

per cubic foot where the coke particles have a size between about 20 and 400 microns. The coking vessel 102 has an inside diameter of about 11.5 feet and a straight side of about feet. The coking iluidized bed 1'04- .is maintained at a temperature of about 1100 F. and under a superatmospheric pressure of about 110 lbs. per sq. in. gage.

Instead of passing the air through axial distributor 146, it may be introduced below a distribution grid member (not shown) arranged at the lower portion of the heating shell 128 to support the bed 133 and the air distributed across the area of the heating shell in this way.V The rate offilow of solids through U'bend tubes 124 may be the same as that in U-bend tubes 54-described above in connection-with Fig; 1.

The technique of supplying heat to a uid bed by circulation of solids through hot U-bend tubes is especially and the heated oill is introducedv through line 201 intoV the iiuidized bed of solids 188v maintained at a coking temperaturebetweenabout- 800 and4 1400 F. in the cok ing lvessel 180. Coking vessel 180V may be maintained at a pressure betweenl aboutV 0 and- 200 lbs. per sq. in. Steam is preferably added tothe heated oil through line 202. While one lineV 201 isshown for feeding the heated oil toI thev coking'vessel 180, in the large commercial design it is preferred to have 12 such lines feeding the oil into the fluid. bed? in a plurality of places. Coke is formed during the eokingprocess and iluidized-coke product is removed from the tluidized-bed 188 through line 204 and may be treatedy as hereinbefore described in connectionwith other forms` ofthe invention.

In the form of the invention shown in Fig. 3 the U- bendheat transfer ,tubes are heated by being submerged in a iiuidized bed of inert solids, the solids beingremoved from the bed, heated and returned to the iluidized heat'- ing bed. Surrounding a portion of the lower'end of` the'y coking vessel 180 is a heating4 vessel 206 having an enlarged upper portion or dome 208. A dense bed of highly turbulent inert solids of about -200 mesh is located theV vessel 206 as shown at 212 having a level valuable whenthe solids are to be heated under'pressure. At low pressure the, solids can often be heated by direct with al separating means such asl'a cyclone separator 182 at 214. Theinert solids may be made of metallic material suchas iron spheres but ,silica gel or other similar materials such as carborundum,l clay, alumina, silica, etc. are preferred.

U-bend heat transfer tubes 214l are provided having a down` flow leg.216V and anupow leg 218 which hang from the bottom of coking vessel- 100. The upper ends of the U-tube openr into thebottom portion of the dense bed 188y in coking; vessel 180. Steam or other liuidizing gas is introduced into'the lower portion of the upflow leg 218 ofthe U-bend by line 220 for causing circulation of the solidsv through the U-bend heatv transfer tube. Steam from upfiow, legs 218 is used to, uidize coking bed 188. The superficial fluidizing-,gasvelocity is betweenY about 0.1 and 5 ft. per second in fluid bed 188. While only' Y a few of the U-bend tubes are shown in the drawing, it is toibe understood that ina commercial design unit where about 12 feet.

Some. fuel. gas or. other fuel isy introduced through manifold 222` to. lines4 224 which. feed the fuel gas into the bottom of the fluidized bed 212 in the heatingy vessel206l the iluidized bed 212 is. 5 feet per second and may be varied between l foot per second and l0 feetper second. Additional fuel and .air to supply heat to the inert particles 0f the uidized bed 2712 is utilized outside heating y vesself 206 as will be hereinafter described.

As the gases pass upwardly into the enlargeddome`208 their velocity is decreased and some of the particles en.-

trained' by thegases are dropped' back intol the. fluidized. bed 212.V Additional airis added near the top of the n fluidized bed 212 through one or more lines 230 to con-` trol the solids circulation rate. Thus a higher air rate will increase the entrainment and increase the solids circulation.

Near the top of the heating vessel 206 and leading from the enlarged dome 208 is a line 232 for carrying solids from the heating vessel 206 in suspension. These solids i are heated and then returned to the heating vessel 206. For heating these solids at startingup only a burner 234 is provided into `which air is introduced at 236 and fuel at 23S, the fuel preferably being a gas. `The gas and air are introduced into the upper portion `of the burner 234 and in burning raise the temperature of the gas to about 150031?. `After the unit is heated up, flow of gas through line 238 may be turned oi and fuel gas passed through line 242 into transfer line heater 246. When the auxiliary `burner is in use, the hot gases from line 244 and the suspended solids in line 232 are mixed and the mixture passed through the upow heater 246 for heating the suspended solids to a temperature between about 1000" F. and 2000 F., preferably about 1600" F. In the transfer line heater 246 the mixture is maintained-in a highly turbulent condition and extremely good contact and heating are obtained. The suspension is then introduced into a solids-gas separating means such as a cyclone separator 248 for separating the heated solids from the hot gases and the heated solids ata temperature between about l000 F. and 2000 F., preferably about 1600 F. are passed through standpipe 252 provided witha control valve 254 to the lower portion of the fiuidized bed 212 in the heating vessel 206.

The hot gases separated in the separator 248 pass overhead through line 256 and are passed to waste heat boiler 258 and water preheater 262 before being passed to the stack at about 300 F. p r t In a commercial unit it is preferred to use three sets of equipment including the uptlow heater 246,` cyclone separator 248 and standpipe 252 and associated parts to avoid the use of oversized equipment. A single starting up burner 234 is used but the outlet from this burner will be divided into three parts with each part going to an upiiow heater similar to 246. The outlet from the standpipe 252 may be at one point or each of the three sets of equipment above referred to may have a single standpipe associated with it for delivering the hot solids to three different bottom portions of the heating vessel 206, preferably equally spaced to promote uniform ow distribution.

In a commercial design unit the twelve feed connections 201 will be 3" diameter pipes and the coking bed 188 will be maintained at a temperature of about 1100 F. and under a superatmospheric pressure of about 110 lbs. p` s. i. g. The fluidized bed 188 will be about 20 feet deep and using coke particles having a size of 20 to 400 microns the density will be about 30 lbs. per cubic ft. The coking vessel has an internal diameter of about 11.5 feet and will be 35 feet on the straight side. The supercial velocity flowing up through the coking bed will be about 3 ft./sec.

The enlarged dome will have an internal diameter of about 15.5 feet and a straight side of about 3 feet. The air connections 230 will be about 4" in diameter and there will be six of these connections. The air connections 228 at the bottom of the` heating bed will be 6 inches in diameter and there will be 12 of these air connections.

The auxiliaryburner will have an outlet of 46 internal diameter. Line 244 will have an internal diameter of about 30". The upiiow vertical heating element 246 for p heating the suspension will be about l5 ft. long and will have an internal diameter of about 54 inches. Three cyclone separators will preferably be used, one for each set of equipment above referred to. Standpipe 252 will have an internal diameter of about 18".

From the above description of Fig. 3 it will be seen that part of the air and fuel gas are added to the heat transfer bed 212 in heating vessel 206 to provide good iiuidization of the solids and provide efficient heat transfer. It is impractical to put all the combustion air into the tluidized i bed 212 and `therefore most of the burning for supplying the heat is carried out outside the bed 212 in upflow heating vertical tubular member 246. If all the air were added to the bed, the velocity of the air would be too high to give adequate bed density for good heat transfer in the heating vessel 206.

To increase the circulation of solids through bed 212 more airis added near the top of the heat transfer bed 212 as at 230 whereby more solids are carried olf from the bed 212 in suspension without otherwise affecting conditions in the heat transfer bed 212. The superficial velocity of t the combustion gases passing upwardly through vertical heater 246 is between about l0 and 60 ft./sec., preferably about 20-30 ft./ sec.

One or two stages of cyclone separators may be used wherever they are used in the designs above described.

Heat transfer may be improved by using baflies or stationary packing in the fluidized heating bed 212 to give a temperature gradient from the bottom to the top of the bed thereby improving the temperature differential for heat transfer at constant heating solids removal temperature.

The coke holdup in the coking zones corresponds to about 7.9 Weight of oil per hour per weight of coke based on total feed but may be varied between about l and l0 w./hr./ W. when using high temperatures. For lower temperatures the w./hr./w. may be between about 0.1 and 3.

The amount of heat input can be controlled by regulating the amount of fuel added to the external heater 246. Also heat transfer in the uidized heating bed 212 can be changed independently by adjusting the air rate introduced into the bed 212 through lines 22S` At very low velocity, uidization and heat transfer are poor but as the velocity of the upflowing gas is increased heat transfer first improves sharply and then decreases gradually and finally falls off sharply as bed density is lost.

The rate of Circulation of solids through the external heating zone 246 may be controlled by changing the amount of `air introduced at the top of the bed 212 through lines 230. The entrainment of the solids in the line 232 leaving the heating vessel 206 depends on the total air iiow and this can be varied without changing conditions in the iiuidized bed 212.

Instead of using the U-tube shaped sections, other forms may be used as for example, a tubular member may be divided by a vertical partition stopping above the bottom of the tubular member so that the solids can go down the tubular member on one side of the partition and up the tubular member on the other side of the partition, thus in effect constituting one form of U-tube. Or con centric tubes or pipes may be used for similar U-tube type iiow in which the solids go down through the central tube and up through the outer tube or vice versa.

What is claimed is:

l. In a process wherein high boiling residual petroleum hydrocarbons which contain constituents unvaporizable at ordinary pressures without cracking are converted into lower boiling hydrocarbons in contact with a dense fluidized bed of finely divided coke maintained at a coking temperature of about 800 to 1400" F. in a coking zone and wherein vapors of said lower boiling hydrocarbons are removed overhead from said eoking zone while coke product is withdrawn from the dense bed, the improvement in supplying heat to said coking zone which cornprises downwardly withdrawing a multiplicity of individual confined narrow streams of said finely divided coke in dense phase from the bottom of said bed, circulating each withdrawn` stream along a U-shaped conned path back into a bottom portion of said bed, injecting an inert gas into the bottom portion of the upliow leg of each said U-shaped paths to control the circulation rate of the coke, maintaining said colte in said confined U-shaped paths within a heating zone in indirect heat exchange relation with anotherl dense bed of finely divided solid heat carrie;

particles having a disperse phase of heat carrier particles of less than about 10ft/sec., said heating` zone beingear range beneath said? coking zone and being maintained @at Y a tempera-ture above said coking temperature and within the range of about 1000 to 1500 F. and at substantially' atmospheric pressure, continuously withdrawing'a portion of said disperse phase containing heat carrier particles from an upper portion of said heating zone, heating the Withdrawn disperse phase Vto a temperature not in excess of 2000o F. by mixing it ina confined elongatedk burner zone with hot gases at a superficial gas velocity of about toV 60 ft-./sec., separating hot heat carrier solidsfrom said disperseI phase, and returning said` hot separated'. solids to said dense bed in the heating zone.

v2. A process according to claim 1 wherein said hot gases in the,v burner Zone` contain combustible fuel and wherein an oxygen-containing gas is added' to thel upper portion of the heating zone so as to regulate entrainrnent of heat carrier solids from the dense bed of the heating zone to the elongated burner zone.

3. A process according to claim 2 wherein the .fluidizy ing gas passing upwardly throughthe densey bedv of, the

Yheating zone contains a burning'mixture of hydrocarbon fuel and air and wherein the heat transfer coefficient to the VU-shaped streams is' regulated by adjusting the velocity of said iluidizing gas in said dense bed of the heating zone.

4. Avprocess according to claim 2 wherein the coking zone is maintained atan elevated' pressure up to about 200 lbs; per sq. in. and at a temperature of about 1100V to 1400 and the heating zone is maintained at substantially atmospheric pressure and at a temperature higher than said coicingzone temperature.

5. A process according to claim 1 wherein the liuidizing gas passing upwardly through the dense bed of the heating zone contains Va burning mixture of'combustible fuel and oxygen-containing gas. l

' Y6. An apparatus for the conversion of hydrocarbons including in Vcombination a coking vessel adapted to con tain a iiuidized bed of inert solids, means for introducing oil to be converted into said coking vessel, means for removing', vaporiieed reaction products and coked-.particles from-said vessel; lil-shaped tubeshanging-from thelower end'of said vesselv with the upper ends of the'U-shaped tubesin communication with the lower portion ofj said vessel? whereby solid particles from' said vessel maybe circulated down through one leg and upA through another leg ot'eaeh U-shaped tube, means for'introducing a gas into-the upow legot each U-tube to assist in the circulation of solids, a heating chamber surrounding said U-s'haped" tubes including* the lowermostA portions thereof, said heating chamber being adapted to contain a dense uidized bed of inert solidi particles superimposed by a dilute ,suspension of solids, means for introducing fuel and air intol aj lowen portion ofv saidheating chamber for `burn ing therein and` for supplying uidizing gas for said; bed, au outletline at th'eupper portiono said heating chamber forrernovingcombustion gases andl entrainedY solids therefrom, separating meansassociated with' said-outlet line for separating'entrained solids fromgases and pipe means for returning separated solids from saidl separating ,means toV a lowerportion of said heating chambenymeans for introducing aicontrolled amount'of-gas into the upper portioneot saidi heating chamber forreg'ulating the entrainment from the fluidizedi bed andthereby 'regulating the circulation'` of solidsV through-V said" outlet line,` `and pipe means` for'introduci'ng fuel intosaid outlet line for supplying additional heat to the circulating; solids.

, aefeme'eec'itedi inthe are of this, patent' VUNI-TED STATES PATENTS VSchutte i Dec. 23, 1952

Claims

1. IN A PROCESS WHEREIN HIGH BOILING RESIDUAL PETROLEUM HYDROCARBONS WHICH CONTAIN CONSTITUENTS UNVAPORIZABLE AT ORDINARY PRESSURES WITHOUT CRACKING ARE CONVERTED INTO LOWER BOILING HYDROCARBONS IN CONTACT WITH A DENSE FLUIDIZED BED OF FINELY DIVIDED COKE MAINTAINED AT A COKING TEMPERATURE OF ABOUT 800 TO 1400* F. IN A COKING ZONE AND WHEREIN VAPORS OF SAID LOWER BOILING HYDROCARBONS ARE REMOVED OVERHEAD FROM SAID COKING ZONE WHILE COKE PRODUCT IS WITHDRAWN FORM THE DENSE BED, THE IMPROVEMENT IN SUPPLYING HEAT TO SAID COKIN ZONE WHICH COMPRISES DOWNWARDLY WITHDRAWING A MULTIPLICITY OF INDIVIDUAL CONFINED NARROW STREAMS OF SAID FINELY DIVIDED COKE IN DENSE PHASE FROM THE BOTTOM OF SAID BED, CIRCULATING EACH WITHDRAWN STREAM ALONG A U-SHAPED CONFINED PATH BACK INTO A BOTTOM PORTION OF SAID BED, INJECTING AN INERT GAS INTO THE BOTTOM PORTION OF THE UPFLOW LEG OF EACH SAID U-SHAPED PATHS TO CONTROL THE CIRCULATION RATE OF THE COKE, MAINTAINING SAID COKE IN SAID CONFINED U-SHAPED PATHS WITHIN A HEATING ZONE IN DIRECT HEAT EXCHANGE RELATION WITH ANOTHER DENSE BED OF FINELY DIVIDED SOLID HEAT CARRIER PARTICLES HAVING A DISPERSE PHASE OF HEAT CARRIER PARTICLES AND GAS THERABOVE, PASSING A FLUIDIZING GAS UPWARDLY THROUGH THE LAST-NAMED DENSE BED AT A SUPERFICIAL VELOCITY OF LESS THAN ABOUT 10 FT./SEC., SAID HEATING ZONE BEING ARRANGE BENEATH SAID COKING ZONE AND BEING MAINTAINED AT A TEMPERATURE ABOVE SAID COKING TEMPERATURE AND WITHING THE RANGE OF ABOUT 1000 TO 1500* F. AND AT SUBSTANTIALLY ATMOSPERIC PRESSURE, CONTINUOUSLY WITHDRAWING A PORTION OF SAID DISPERSE PHASE CONTAINING HEAT CARRIER PARTICLES FROM AN UPPER PORTION OF SAID HEATING ZONE, HEATING THE WITHDRAWN DISPERSE PHASE TO A TEMPERATURE NOT IN EXCESS OF 2000* F. BY MIXING IT IN A CONFINED ELONGATED BURNER ZONE WITH HOT GASES AT A SUPERFICIAL GAS VELOCITY OF ABOUT 10 TO 60 FT./SEC., SEPARATING HOT HEAT CARRIER SOLIDS FROM SAID DISPERSE PHASE. AND RETURNING SAID HOT SEPARATED SOLIDS TO SAID DENSE BED IN THE HEATING ZONE.

6. AN APPARATUS FOR THE CONVERSION OF HYDROCARBONS INCLUDING IN COMBINATION A COKING VESSEL ADAPTED TO CONTAIN A FLUIDIZED BED OF INERT SOLIDS, MEANS FOR INTRODUCING OIL TO BE CONVERTED INTO SAID COKING VESSEL, MEANS FOR REMOVING VAPORIZED REACTION PRODUCTS AND COKED PARTICLES FROM SAID VESSEL, U-SHAPED TUBES HANGING FROM THE LOWER END OF SAID VESSEL WITH THE UPPER ENDS OF THE U-SHAPED TUBES IN COMMUNICATION WITH THE LOWER PORTION OF SAID VESSEL WHEREBY SOLID PARTICLES FROM SAID VESSEL MAY BE CIRCULATED DOWN THROUGH ONE LEG AND UP THROUGN ANOTHER LEG OF EACH U-SHAPED TUBE, MEANS FOR INTRODUCING A GAS INTO THE UPFLOW LEG OF EACH U-TUBE TO ASSIST IN THE CIRCULATION OF SOLIDS, A HEATING CHAMBER SURROUNDING SAID U-SHAPED TUBES INCLUDING THE LOWERMOST PORTIONS THEREOF, SAID HEATING CHAMBER BEING ADAPTED TO CONTAIN A DENSE FLUIDIZED BED OF INERT SOLID PARTICLES SUPERIMPOSED BY A DILUTE SUSPENSION OF SOLIDS, MEANS FOR INTRODUCING FUEL AND AIR INTO A LOWER PORTION OF SAID HEATING CHAMBER FOR BURNING THEREIN AND FOR SUPPLYING FLUIDIZING GAS FOR SAID BED, AN OUTLET LINE AT THE UPPER PORTION OF SAID HEATING CHAMBER FOR REMOVING COMBUSTION GASES AND ENTRAINED SOLIDS THEREFROM, SEPARATING MEANS ASSOCIATED WITH SAID OUTLET LINE FOR SEPARATING ENTRAINED SOLIDS FROM GASES AND PIPE MEANS FOR RETURNING SEPARATED SOLIDS FROM SAID SEPARATING MEANS TO A LOWER PORTION OF SAID HEATING CHAMNER, MEANS FOR INTRODUCING A CONTROLLED AMOUNT OF GAS INTO THE UPPER PORTION OF SIAD HEATING CHAMBER FOR REGULATING THE ENTRAINMENT FROM THE FLUIDIZED BED AND THEREBY REGULATING THE CIRCUALTION OF SOLIDS THROUGH SAID OUTLET LINE, AND PIPE MEANS FOR INTRODUCING FUEL INTO SAID OUTLET LINE FOR SUPPLYING ADDITIONAL HEAT TO THE CIRCULTING SOLIDS.