US2436282A

US2436282A - Surface combustion cracking furnace

Info

Publication number: US2436282A
Application number: US480705A
Authority: US
Inventors: Edwin O Bennett
Original assignee: Continental Oil Co
Current assignee: ConocoPhillips Co
Priority date: 1943-03-26
Filing date: 1943-03-26
Publication date: 1948-02-17
Anticipated expiration: 1965-02-17

Description

Feb. 17, 1948. E. o. BENNETT 2,436,282

SURFACE COMBUSTIION CRCKING FURNACE Filed Maron ze, 194s Patented Feb. 17, 1948 UNITED STATE:

SURFACE COMBUSTION CRACKING FURNACE Edwin O.Y Bennett, Ponca City, Okla., assigner to` Continental Oil Company, Ponca'. City, Okla., a

rcorporation of Delaware ApplicationMarch 2s, 1943, serial 10,480,705 Y.

5 canna,`

1 o My invention relates broadly to 'improvements in a method of and apparatusfor cracking fluids, and more particularly to a method of and appa' ratus for cracking a hydrocarbon uid into its constituent parts of carbon and hydrogen to produ-ce a superior grade of carbon black.

Carbon black isv made by heating a hydrocarbon fluid in the absence of air. Heretofore carbon black has been almost-entirely made by either one of two processes. One of these processes, commonly known as the channel process, consists of burning hydrocarbon gas withinsuliicient air in a smoky flame. This operation is conducted in an apparatus having cold Ametall surfaces upon which the flame impinges. Carbon deposited by the ame on the metal surfaces is scraped'off and recovered as carbon black'. v

The other process consists of alternately passing hydrocarbon gas through a pair v of refractory furnaces which heats the 'gas in the absence of air. In operation it ishecessary to heat'the refractory of one furnace while the'gas is being cracked in the other. A reversing switch is provided in the gas supply line which automatically reversesthe iiow of gas when the temperature of the cracking furnace becomes -too low.

Both of the above processes are inefficient and expensive. The channel process yields approximately 1.5 lbs. of carbon black .per 1,000 cubic feet of gas. The second process is vmore eflicient, but it is also more expensive. It yields from 8 to 9 lbs. of carbon black per 1,000 cubic feet of gas. However, large amountsof fuel are required to heat the huge mass of refractory. Therefractory must be large in order to. minimize the temperature drop in the furnace during the cracking cycle. Also the reversing switch is com,l plicated and expensive. The yield is far .below the theoretical maximum due to burning of carbon by oxygen which enters the furnace during the heating cycle. Y l' .An important object of myinvention is kto pro-y vide a cracking furnace that isparticularly suitable for making carbon black. r 1

Another object of my invention' is to provide a furnace of the above mentioned character that will maintain the cracking chamber at'a constant temperature under oxygen-free conditions.

Still another objectof' my invention is to provide a cracking furnace of the above 'mentioned character wherein heat is supplied tojth'ei combustion chamber in such away aste prevent the, y cracked materials from depositing-,on the chamberwalls.,

Y other objects and advantages of my invention:

(Cl. 23-277) n f 2 l will be apparent during the course of the following description.

In the drawings forming a part of this specication, and wherein.V like numerals are employed to designate like parts throughout same,

Fig. 1 is a vertical section Yof a surface combustion cracking furnace embodying my invention with the control Amechanism shown in elevation and in smaller scale,

the line 2-2 of Fig. 1, and

Fig.3 is a transverse sectional theline 3--3 of Fig. 1, 4

In its broader aspects,- the invention consists of passing hydrocarbon gas longitudinally through a porous tube of refractory material, the passage through which the gas flows being heated by surface combustion.

A combustible mixture under pressure is supplied to a .confined annular space around the tube. This mixture passes through the tube to the inside thereof where it is ignited and forms a fire-lining covering the inner surfaceof the tube. ,Combustion is complete within a short distance of the surface, depending upon the porosity of the tube and differential pressure within and outside the tube.- vIn appearance the inner surface ofthe tube is incandescent and no llame, as such, appears to be present. The mixture is 3.0 regulated. so that all oxygen is consumed by combustion. No free oxygen entersthe vtube to mix with the fluid being cracked. Temperatures up to 3600 F. are obtainedby this method of combustion. Y A.

The iiow of fluid through -the tubeis regulated so that the fluid is completely broken up into its component parts. As they pass through the tube, the cracked products are'prevented from adhering to or depositing onthe tube by the continu- 40 ously moving fire-lining. VThese components are easily separatedand collected r`at thedisoharge end -of the tube., The carbon. recovered by this method is a superior carbon black for use in making synthetic rubber. c

More particular1y,rthe invention comprises a surface combustion cracking furnace having a verticaltube l0 of a refractory material such as Carborundum. The middle Vportion Ia of the tube is porous, and the ends |0b and Ic are pref- 59 erably impervious. The vends of thetube may be madeimpervious by any suitable means, such as dipping them in a Carborundum sealing cement. v Surrounding tube l0 is a metal housing I l, carried by a suitable supporting structure comprising legs A, a horizontal supporting plate B and view taken on Fig. 2 is a transverse sectional View taken onl triangular gussets C based on the supporting plate and against the sides of the housing H. The housing ll is of greater diameter than the tube and supportsthe tube adjacent its upper end. The top la ol.' the housing has a vertical extension or collar lib, which surrounds the projecting end of tube lll. "Packing lf2' retained in the annular space between'the tube and the collar by the threaded locking ring I3, provides a pressure tight seal between the tube and the upper end of the housing. l v

Expansion and contraction of tube modated by an expansion joint assembly on the lower end of the housing. Tubes IPD and l-I areclosed at the bottom by means of an assembly congisting of a plate l5, retaining ring I6 and a slidable sleeve Il. pansion and contraction of the inner refractory To compensate for uneven eX- tube lll and outer metallic tube il, there is provided a diaphragm expansion joint I8. The lower half lea of the expansion joint-is welded to sleeve il and the upper half l8b is welded to tube Il.v

To solidly iifx the lower end of' tube l0 within the cup-shaped portion oiplate l a .bonding material, such 'as' a 'refractory ceramic mortar, nils the space within the :disc surrounding the tube and when set, lxedly holds the tube within the disc. Retaining ring i6 `is threaded to sleeve ll and sets against a shoulder portion of the disc l5 in order 'to hold fthe assembly together. 4In operation, elongation or shortening of either of. the tubes Hl Vor Il different fromv theother tube will be compensated for by this expansion joint.

A combustible mixture, preferably fuel gas and air, is charged Vunder pressure to .the annular space 20 between tube il! and Vhousing Il. Air.

passes through pipe 2l controlled by valve 22 and pressure regulator 23, and gas passes through.

In the form of :the invention shown in Fig. 1,.

ain-opening a iis provided in plate `l5 through which ian ignition torchfc'an be inserted to ignite the combustible Ivapors 'within thetube.. Opening ia is normally closed by a pivoted plate 33. It

is necessary that isuicient pressure be applied to the combustible mixture -iin lannular 'space 20 to force it inwardly'through"tube 'l 0 `at fa 'rategreater than the velocity or *flame 'propagation'outwardly through the tube. If this iis done, fall danger oi backfire and explosion is eliminated. .i

When thefurnaceisred the combustible mixture permeati'ng the "porous vportion lDa of tubel i0 burns at T-the inner surfaceof the tube, whichv becomes incandescent. Actuallylnoame as such appears within the ltube. This lislrnown assurface ''co'rnbustiorlr Surface combustlonv'in a furnace of this type develops :a higher temperature than can'be obtained by yany other method. This is due to the completenessof combustion 4and the intense preheat y-tof which=the air-gas'mixture in annular "space T 'is subjected.` Ai-temperature. as

high as 360o F. ihes'ibeen obtained in the iur-- nace illustrated-in the Adrawings. Y

Fluid lto be cracked passesthroughpipe 34 `irito the lower Vend-loitube-itil. li'pe "34 is controlled by valves V'arid lsoperated by pressure regulators 31 and 38; `.As indicated by the double lead line for each "of the

reference numerals

30 and 34, the` said pipes indicated thereby extend continuously to the annular chamber 20 and to the interior of conduit i0 respectively, without opening to the atmosphere. Y

The temperature to which the iiuid will be raised is controlled or regulated by adjusting the amount of combustible mixture supplied to the ratio of combustible mixture to the fluid must be accurately regulated. This is done automatically by the'diiferental pressure regulator 39 in pipe 4D, which connected at its ends to pipes 3 0 and 34.' Dierential pressure regulator 39 operates valve 4l vin pipe 30 to pass an amount of fuel to 4the combustion tube proportioned to the quantity of `fluid to be .cracked The temperature to which the iluid will be raised is also dependent upon the time required topass it through tube Hl. 'I-Iowever, the rate of ilow of the iluidA through the tube is automatically .regulated by the pressure. `at which it enters the furnace and by the length of the i'lrekv zone of tube i0. It is obvious *that Vthe.preS S\1.-rc,at Ywhich the fluid enters the 1f uijnzaqx; as well` as ythe vratio of iluid tol combustible mixture be accurately and automatically controlledy by the pressure regulaters and meters controlling flow through the re- Snectve Supply 1.11185- YSince the combustible mixture iS Supplied t0 the inside `ofntube vi l) .from the outside thereof, the Viluid Passing through the tube has n0 effect upon the burning action of the mixture. Furthermore, the fluid is prevented from adhering to or depositing o n the inner suriac'e of tube lil bythe continuouslymoving..rirelining As the fluid passes through the tube itis Cracked or `physically disrupted into lts-component parts. The cracked fluid together with the products :of combustion pass' out `of .the furnacethrough stack 42 bolted to the topgofi housing li. The gases entering stack 42 are :cooled by the water jacket 43 and -quenching iluids "such asstearri `.or Water introduced intdtire stack through .lateral pipes 44 andc45. Anyv suitable means may be provided to recover and separate the :cracked components of the -iluid. When vthej-urnace-is used to produce carbon. black, the free carbon vis preferably recovered byimeans of :an electrostatic :precipitator or by vsuitable ii'lters which are connected to thev discharge end-.of the .furnace shown as the stack 42.. The 'facilities l:for controlling the temperature Yandfcornliustion :condition permit the manufacture -of la fcarbon 1black particularly adapted for yuse 'in` rubber manufacture, `.either natural or synthetic.

.It is. to be 'understood thatthe Vform of the invention herewith shown and describeclris to be taken as` 2a :preferred example for fthe same, and that ivariouschanges .in itheisize', shape and arrangement of parts 'may be :resorted to Ywithout departing .from `ithefspirit of my :invention or the scope .ofithefappendedeclaims. For example, .a plurality of furnaces inay 'be-aeiciently yoperated as a unit landifor lcertain .zpurposesdt may benacessary orfdesirable' .to falter :the size -or shape of the `respective parts.

:Havingthus :described my :inventiom I l claim:

f1. (A surface-:combustion:crackingfurnace iconiprising fatlporouslrefractory tubeproviding :an interior surface for surface combustion deningr'a reactionfspece conduittor thesupplyofihydrocarbon gas to be cracked opening into an end portion of said tube, an outlet from the opposite end portion of said tube, a housing surrounding said tube and spaced therefrom to provide a chamber therebetween, the walls of said housing being otherwise sealed against passage of gas except through said porous refractory tube to the interior of the latter, a gaseous mixture supply conduit opening into said chamber, two branched -conduits connected to said gaseous mixture supply conduit for the supply under pressure of air and fuel gas respectively to said supply conduit, means for proportioning the ratio of air to fuel gas passing from said branched conduits to said supply conduit to form a gaseous combustible mixture in the latter in which the amount of oxygen is not in excess of that required for surface combustion of the fuel gas in the said combustible mixture, a pressure regulating valve for controlling the pressure of the said gaseous combustible mixture, an additional flow controlling valve between said pressure regulating valve and said chamber, and regulating means for said flow controlling valve eiective to control the flow of gaseous combustible mixture to said chamber in accordance with the pressure of hydrocarbon gas in said firstmentioned conduit, whereby suiicient pressure difference is maintained between said chamber and the interior of said tube to force the said gaseous combustible mixture from said chamber inwardly through the pores of said tube at a velocity greater than that of flame propagation outwardly through the pores of said tube, and the said gaseous combustible mixture burns by surface combustion providing an incandescent lining at the interior surface of said tube while the hydrocarbon gas passes longitudinally through said tube within the incandescent lining and is cracked by the heat of said surface combustion.

2. A surface combustion cracking furnace according to claim 1, wherein the said refractory tube has impervious end portions and a porous central portion, and sealing means between the impervious end portions of said tube and said housing.

3. A surface combustion cracking furnace according to claim 1, wherein said tube is vertical, said inlet is at the lower end of said tube, said Aoutlet is at the upper end of said tube, and an expansion joint between said housing and the lower end of said tube.

4. A surface combustion cracking furnace according to claim 1, including a cooling jacket surrounding said outlet, and an inlet for direct injection of a quenching iiuid into said outlet.

5. A surface combustion cracking furnace according to claim l, wherein said tube is vertical, a supporting plate for the lower end of said tube receiving said inlet, a sleeve slidably receiving the lower end of said housing, a retaining ring clamping said plate and sleeve together, an expansion joint between said housing and said sleeve, said plate having an opening therethrough communieating with the interior of said tube, and a removable closure for said opening.

EDWIN O. BENNETT.

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

UNITED STATES PATENTS Number Name Date 1,348,175 Hidden Aug. 3, 1920 1,364,157 Thrane 1 Jan. 4, 1921 1,909,163 Brownlee May 16, 1933 1,019,392 Weintraub Mar, 5, 1912 1,891,859 Winter Dec. 20, 1932 2,062,358 Frolich Dec. 1, 1936 2,196,767 Hasche Apr. 9, 1940 834,257 Brunler Oct. 30, 1,906 1,895,284 Hay Jan. 24, 1933 1,592,474 Szarvasy July 13, 1926 2,212,606 Klinker Aug. 27, 1940 2,197,904 Terry Apr. 23, 1940