US2599981A - Carbon black - Google Patents

Description

Patented June 10, 1952 CARBON BLACK Wesley C. Ekholm, Monroe, La., assigner to Columbian Carbon Company, New York, N. Y., a

corporation of Delaware Application December 22, 1949, Serial No. 134,520

(Cl. 2li-209.4)

7 Claims. 1

The present invention relates to the manufacture of carbon black and particularly to the process involving the thermal decomposition of a hydrocarbon by separately injecting it intoa turbulent stream of hot furnace gases.

In the Wiegand and Braendle Patent No. 2,378,055 there is described an improved process of the type just noted in which a combustible mixture of a fluid hydrocarbon fueland air is blasted into one end of an elongated, unobstructed chamber to form a turbulent stream of hot blast flame gases. This turbulent stream of blast flame gases courses through the furnace chamber and, at a point removed from the point of entry of the combustible mixture to the furnace chamber, the hydrocarbon to be decomposed is separately and forcefully injected into the turbulent stream of gases.

The present invention provides an improvement in the method of operation just noted and particularly an improved method of effecting the mixing of the hydrocarbon to be decomposed with the hot blast flame gases.

In operations such as specifically illustrated in the patent, the hydrocarbon to be decomposed is injected radially into the furnace chamber, advantageously as relatively small, high velocity streams positioned directly'opposite one another. Difficulty has been experienced in this type of operation where the diameter of the furnace chamber has been too greatly increased. Rectangular furnace chambers have been extensively used in large commercial sized installations, but here, too, it has been found desirable to limit the width of the chamber to not in excess of about 2 feet, and preferably not greater than about 1 foot, in order to maintain a uniform pattern of the streams of hydrocarbon to be decomposed so as to get uniform mixing of the hydrocarbon with the blast flame gases.

One difficulty of the type noted which has been experienced is that of spacing the make gas tubes so as to prevent channelling of blast flame gases through the chamber in between the streams of the hydrocarbon to be decomposed. This difculty has been minimized by close spacing of the make tubes. However, in commercial installations, this solution has introduced new problems. The increased number of tubes requires a complicated manifolding systeml which is serviced with great difficulty. Deposition of carbonaceous residues in the tubes, or in the manifold, tends to disrupt the distribution of make gas to the tubes and results in some tubes being overloaded, while others are underloaded.

The present invention provides an improved method of operation whereby much of the difficulty heretofore experienced in effecting rapid, uniform mixing of the hydrocarbon to be decomposed With the blast flame gases is avoided.

I have found that these channels of inadequately mixedrblast llame gases may be avoided and, at the same time,'the number of make gas streams reduced by using a reaction chamber of circular section, injecting the combustible mixture into the reaction chamber as streams moving at high velocity in a substantially circumferential, or tangential, direction and separately, downstream from the point of injection of the combustible mixture, forcefully injecting the hydrocarbon to, be decomposed into the chamber in a substantially radial direction.

By this method of operation, it appears that the blast flame gases tend to follow a more or less helical path through the chamber and, therefore, a path of much greater length, so that for av given time within a reaction chamber of a given length much higher blast gas velocities may be maintained than would be possible if the blast flame gases were passed axially through the chamber. Accordingly, the requirement of careful coordination between furnace diameter and mass velocities is materially relaxed and much greater leeway in the ratio of blast flame gases to hydrocarbons to be decomposed is permissible.

It appears, therefore, that an advantage of the tangential injection of the blast flame gases is that it permits much higher velocities of the blast flame gases than is practical where the blast fiame gases flow substantially longitudinally through the chamber.

These higher blast flame velocities make it practical to increase the make gas injection velocities. By reason of the latter, the make gas injection tubes may be maintained at a lower temperature and a richer make gas may be used without encountering serious coking problems in the tubes. Further, by the use of higher make gas injection velocities, the number of make gas injection tubes may be reduced which further simplifies construction and maintenance problems.

A still further advantage of the tangential injection of the blast flame is that thereby the blast flame in the region of its initial development, is in closer contact with the furnace walls than where longitudinal blast flame injection is employed. The advantages of surface combustion are, in part at least, attained and the permissible' range of ratios of air to natural gas in the combustible mixture is materially broadened.

The improved process is applicable to operations in which natural gas, or other normally gaseous hydrocarbons, is decomposed to form the carbon black. It is, however, especially advantageous in operations adapted to form the carbon black by decomposing a higher molecular weight hydrocarbon, for instance, a petroleum distillatel A particularly desirable heavier hydrocarbon is a 3 distillate of the type resulting from the cracking of petroleum and comprising around 20-60%, usually in the range of Bil-50% by Weight of aromatic constituents, as determined `by the ytest method D-875-46T of the American Society for Testing Materials. ltshould most suitably have an aniline cloud point as determined by the method prescribed by the said society and designated D-6lll6T, within the range of 10 to 125 F. Its end point should not exceed 725F. 'and preferably should be somewhat lower.

These higher molecular Weight .hydrocarbons appear to be more readily thermally decomposed than is natural gas, for example, and should be mixed uniformly with the blast name gases proportionately more rapidly. It is desirable, therefore, to accelerate in some way the mixing of the hydrocarbon with the blast gases. This is accomplished in accordance with the present invention by intensifying the blast gas velocity and turbulence by blasting the combustible mixture into the furnace tangentially, or substantially so, and separately injecting the hydrocarbon to be decomposed substantially radially into the resultingswirling mass of blast flame gases advantageously at a point Vnear the perimeter of the whirling gas stream, i. e., adjacent the furnace wall,VV thus insuring the Adesired rapid Vand uniform mixing of the heavier hydrocarbon with the blast name gases.

In orderfurther to expedite 'the complete dispersion of theheavier hydrocarbon in the blast 'flame gases, I have found it --especiall-y advantageous to dilute the vaporized heavier hydrocarbon by mixing steam, air, or other diluent,

therewith, advantageously in proportions within the range-of 1 to 2 volumes of steam for each volume of `oil vapor. Mixing of steam with the hydrocarbon to be decomposed has been found particularly beneficial in carrying out the-present process, especially where -it is desired to produce carbonblack of the type used inthe compounding -of rubber of the tire tread type.V

`According to a preferred aspect of my invention, afpetroleum distillate of the aromatic type just described is vaporized and the vapors mixed with steam in proportions within the range of vabout .1 'to V2 volumes of steam per volume of :hydrocarbon vapors (eachmeasured at 60 F. and

'760 ,millimeters of mercury) and this mixture is separately `and forcefully injected directly into therapidly swirling flame gases in a substantially radial direction, With respect to the swirling-motion of the blast name gases, and is :thereby substantially instantaneously dispersed in those blast flame gases and further diluted and thereby heated to the decomposition itemperature of the hydrocarbon.

`Instead of using steam along `as a diluent for the heavier hydrocarbon, natural gas may be used, either together with steam, or alone, as a diluentffor the heavier hydrocarbon. Or, in place of the steam, Va substantially inert' gas,

'such as carbon dioxide, or nitrogen, may be employed. `The use of air as a diluent has also been found advantageous` in certain types of operation.

The invention will be `further described and illustrated by reference -to Athe accompanying Adrawings which'show conventionally andv somewhat diagrammatically apparatus found particularly useful in carrying out the process and of which:

Figure 1 is a longitudinahsectional vview in elevation of a reaction chamber, together with reaction chamber along the lines 3--3 of Figure 1.

In Ythe apparatus shown, the reference nu- Vm'erall .indicates a cylindrical, elongated reaction and-cooling 4chamber opening at one end into a vertical cooler 2. At the lefthand end,

the reaction .chamber is closed by the end block 3, and extending axially through this block is a conduit@ adapted to the introduction of secondary air into the furnace chamber, as desired.

The chamber I -is formed 4by the cylindrical wall -5 of highly refractory material which, .in turn, is covered externally vby layers 6 and 1 .of heat insulating material.

Extending through the layers of heat insulating material 'and the furnace wall Vand substantially normal to the longitudinal axis of the chamber, thereare four blast burner ports 8, eachenteringv the furnace chamber in a circumferential direction, vas more clearly shown in-Figure -2 of the drawings. The apparatus shown is provided with two substantially identical sets of these blast burner ports positioned at different distances from the end block 3.

"Further downstream, the furnace chamber is provided with a set of four radially extending tubes 9V spaced90 apart and extending through the layers of insulating material and the furnace -Wall as lmore clearly shown in Figure 3 of the drawings. These tubes are provided for the injection .into the furnace chamber of the hydrocarbon tombe decomposed and will normally be positioned with their inner ends flush with the inner walls of the furnace chamber. Still further downstream, the furnace is provided with asecond 4set of hydrocarbon injection tubes 9 substantially identical with that just described.

These hydrocarbon injection tubes should be fabricated from highly refractory material, for instance, Carbofrax, Alundum, or the like. The burner ports 8 shouldbefabricated of or lined -with .a similar refractory material.

'.Spacedalong the vertical .cooler `2 are water sprays In for assisting in cooling `thehot-eflluent furnace gases. Similar sprays kmay be positioned in thedownstream portion of chamber I adjacent the vertical cooler.

In ,'operation, a combustible mixture of a fluid hydrocarbon fueland air is blasted at high velocity through the circumferential blast burner ports 8, Iis ignited and burned Within the chamber to formra hot, highly turbulent mass of blastflame gases -rapidly swirling through-the furnace chamber in a more or less helical path. This Ycombustible mixture may -be injected into a zone of .the chamber more or less removed from the end block by selection of one or the other ofthe sets of blast burner ports. The hydrocarbon to -be decomposed -is injected into the `chamber through the radial tubes 9 and, as previously described, is extremely rapidly and uniformly mixed with the swirlingfstreamof blast flame gases,and is heated thereby and decomposed to form carbon 'black in suspension in the .furnace gases. As the suspension continues through thedownstream fend of Vthe chamber and through the vertical cooler, it is cooled by-'contact with the water sprays l0. Any unvaporizedwater fromthese sprays, :together with any-carbon knocked uout-of the suspension, passes downwardly throughthe vertical cooler into the sump Il and cooled suspension passes from the upper end of the vertical cooler through conduit I2 to conventional separating and collecting apparatus, as well understood in the art. y

The number and diameter of the circumferential blast burner ports have not been found to be critical so long as they have the capacity for lling the furnace chamber with the violently turbulent blast flame gases. With a furnace chamber approximating 1 foot in diameter, I have found that a ring of four blast ports, each 2 inches I. D. and positioned 3 to 6 inches from the inner face of the end block 4 to be adequate for this purpose.

Similarly, the number and size of the hydrocarbon injection tubes are subject to some variation. Four Carbofrax tubes, 1/2 inch I. D., positioned as shown in the drawings and located 1 to 4 feet downstream from the blast burner ports have been found highly satisfactory.

In using higher molecular weight hydrocarbons, such as herein described, I have found that the period of time during which the hydrocarbon anddecomposition products thereof should remain in the reaction chamber at reaction temperaturea'in order to result in a carbon black having certain desirable rubber compounding characteristics, is less than the so-called contact. time. where natural gas is used as themake 'I'his contact time, i. e., the period of time between injection of the hydrocarbon and the quenching of the product to below the reaction temperature, may be varied by providing a number of spray heads along the downstream portion of chamber I and selecting the proper spray, or sprays, so as to cool the suspension at the proper time to below the reactive temperature.

It will be understood, of course, that the contact time is arrived at by calculation and cannot otherwise be more positively determined in the absence of more precise information as to the exact path of the gases through the chamber. Contact time so calculated has been found to be a rather dependable guide in practical operation.

In general, contact time at temperatures above 2,000 F. should not exceed 0.5 second. Satisfactory operation has been obtained with contact time within the range of 0.02 to 0.3 second. In these operations, water spray was used to quench the suspension. It will be understood, however, that waste gases from the process, natural gas or any convenient fluid of relatively low oxidizing potential may be used to effect cooling of the suspension.

The blast port velocities at which the combustible mixture enters the furnace chamber is of primary importance. Velocities within the range of approxmiately 60 feet per second to 180 feet per second have been successfully employed. However, port velocities of about 80 feet per second have been found highly satisfactory in commercial operations.

In the apparatus shown in the drawing, the burner ports are shown to lie in a plane perpendicular to the longitudinal axis of the chamber.

AIt will be understood, however, that thesev ports may be directed somewhat downstream without departing from the spirit of this invention, pro- -vided thexentering combustion mixture is injected into the furnace chamber in a direction substantially circumferential with respect to the chamzbel.;

Likewise, the hydrocarbon injection tubes may be .inclined somewhat from the transverse plane of the furnace chamber so long as they are directed substantially at the longitudinal axis of the chamber. In the usual operation of my process, the tube 4 for injection of secondary air is not employed. However,'operating conditions within the furnace may at times be more satisfactorily controlled by injecting a relatively small proportion of the air requirement into the chamber axially through conduitI 4.

'The process will be further illustrated by the following specific examples:

Example I The invention has been utilizedA in a furnace constructed as shown in the drawing, and comprising a cylindrical reaction chamber 12 inches I. D. and 771/2 feet long, discharging into a vertical spray cooler and having a set of four blast burner ports 2 inches I. D. positioned G-inches downstream from the inlet end of the furnace and a second identical set of blast burner ports located 9 inches downstream from the first. A ring of four hydrocarbon injection tubes 1/2 inch I. D. was positioned l foot downstream from the second set of blast burner ports and a further identical ring'of hydrocarbon injection tubes was positioned 3 feet 6 inches downstream from the second set of burner ports. In this operation, the blast air and blast gas was distributed uniformly to two side burners of the rst set and the top and bottom burners of the second set and was supplied at a total rate of 37,000 C'. F. H. of blast air and 3060 C. F. H. of blast gas, the ratio of blast air to blast gas being 12.2. Secondary air was supplied through the conduit 4 at the rate of 2800 C. F. H. Highly aromatic oil was supplied in vapor form at the rate of 40 gallons per hour and diluted by mixing with steam at the rate of 860 C. F. H. and injected into the furnace through the first set of tubes 9. In this operation, the yield was 2.4 pounds per gallon of oil.

The blast gas, i. e., fuel gas, used was natural gas of 960 B. t. u. The furnace temperature at a point about 2 feet downstream from the end block was 2,620 F. The hydrocarbon oil to be decomposed had the following properties:

In substantially identical apparatus, the process was carried on under the conditions and with the results set forth in the following tabulation, the temperatures T-l, T-2, T-3, and T4, being taken at the points approximately l foot, 2 feet 6 inches, 4 feet 6 inches, and 6 feet, respectively, from the inner face of the end block. --In each of these runs, the hydrocarbon to be decomposed was injected through the tubes of the rst set only and evenly distributed, the number of tubes of the set used in each instance being as indicated in the tabulation. f

Example II VIII Numbercf Tubes Total Blast-Axf-C. E; H SecondaryAirfGjE. H. Total Blast Gas-0. F. H. BlastqRatio-Air: Gas.. l Oil-GalL/Hr Steam-Lbs/Hr Steam-Pery GentotOil Vapor Blast Port Ve1octy-ft.lsec. :it 60 F. Make Stream Velocity-It/sec, at 60 Make Stream,Velocityfmsceatl600" F Temperatures F.:

-4 Contact time to spray-seconds Yieldv-.Lba/Gal. of Oil Rubber Properties:

Gure.Time.,-minutes Modulus at 300% elongation- Tensile Strength Elongation. Hardness- Electrical Resistivity, Log R .Rebound-:.(Optimum Cure) The, rubber properties Ygiven'in the4 foregoing tabulation are those obtained byl compounding therespective blackswith "low temperature polymer synthetic rubber by the formula indicatedbelow and vulcanizingthe rubber composition asindicated.

LTP 100.000 Black 50.000 Zincioxide 3.5 Paraux 4-.0 Circosol (2XI-I) 4.0 Stearic acid 2.0 Santocure 1*.125 Sulphur 2.0

As illustrative of aromatic hydrocarbonv distillateswhich have been used with outstanding.` advantages, there may be noted two types of. oils, the characteristics ofwhich are set forth in the following tabulation.

Sample #1 #2 Gravity (Afl.) 24:5 24.7 AnilinezCloud Point-"F 60. 1 w108 Distillation IBPn 348 '480 10% Point.. 406 508 50% Poin '463 '530 90% Point 537 568 End Point 622 588 Recovery, percent. 98.*5' 99.0 Residue, percent 1. 4 0.8 Loss, percent 0.1 0. 2 ASTM D875-46T-Test Percent Naphthencs and Paraiins 32. 32 40. 40 Percent Aromatics- 46.97 40. 71 Percent Olefns 20.71: 1S. 89

A@ distillate, such as. sample, 1J was used in;v the foregoing Examples IVl V,.and VI and-a.- distillate, such as sample 2, was used-in-,ExamplesIL III, and VII.

Depending somewhat upon the desiredchar.- acteristics of the carbon black product, the relative=` proportions of-theblast air, the-hydrocar bon fuel, `the separately injected` hydrocarbon and the secondary air usedlmay bevariedsorne what as illustrated by-the foregoing exam-ples. It will` be understood, of course; that'in alllinstances, the proportion ofoxygen:supp'liedwill be substantially `less than that` requiredtorr the combustion of the -fuelgas -andthelseparatelyinjected hydrocarbon.A The invention. Ycontemplates operations inwhich theproportion'- offair and gasin the combustiblemixtureLtangentially injected into the chamber; aresuchI as-to-produce eitherffan-oxidiaing, a neutral, or'a.reducing-blast name. The proportions-fof blastlamegases-to the separately njectedi hydrocarbon, `or mixture of` hydrocarbon, steam, and 'the like, maylilcewise be varied somewhat. Theproportion should, ofcourse, in each instancezbe'suchfthait; upon mixing, thev temperature off the: resultant mixturewill be atleast suiciently high to veffect the thermal decomposition: off' the; hydrocarbon to carbon black. Wherethe operationaisrsuch as .to produce anoxidizing. Lblastfiiarne,v ,.someiadditional heat may-.be generated upon mixinavr'ith the separately -inj ected' hydrocarbon by the )come bustionof` a portion thereof.

Itis partieularlyvdesirable that thed-istance between the blast flame injection point andthe makegas injection point' be-so--correlatedwdth the -ightA angle ofi thelspiralling.- gaslstreaxn, that the respective-make' gasets are directlyin. the path of a fully-developed streamr of. theV blast gases andi thatA there/be little or no overlapping of thefmake-gas streams. Thisit'endsftoreduce unevenconcentrations: of? the make easn insthe spirallinggasstream.

In" a preferred method@ ofl operation, vaporized fuel-oil, such as No. 2 cycle oilv from' af catalytic cracking'operation, isfvaporized and diluted with steam, usually inthe-ratio of.' 100to200`per cent, and; normally 125 to 150' percent; bywoluma assuming lf-tcubic feetof; vapors`per-gallonfof the, oil. The. injected' steam vappears tov have severaldesirable effects. In the first placmthe presence of steam appears materially, to. reduce thetendency. for carbon depositstdformon vthe heater; wall` and within. the .make gasl injection tubes-and. lines leading, theretoI Secondly,.tl1`e steam, appears` to. act. as an inert diluent. By regulating. the proportion. of steam,.the. neness of.. the resultant carbon ,particles masa.A to some extent, be controlled. A third.. advantage de.- r-ived.- from thef usefofsteam` is' that .itV provides means-fon controlling thetraj ectoryfof.- thefmake gas-:streamss i. e.,' the; extent:- of.. penetration into carbon is the petroleum distillate of the type elsewhere herein described in detail.

By modifying operating conditions, the characteristics of the resultant carbon black may be varied over a range extending, for instance, from a normal HMF carbon having a surface area of ve acres per pound, to a furnace black having a surface area in excess cf eleven acres per pound. As normally produced, these blacks, when compounded with an elastomer, produced stocks of very high modulus and unusually high wear resistance. The resultant black, then, as normally produced, is characterized by a very fine particle size with high modulus, or stiffness characteristics.

The invention, in its broader aspect, is independent of contact time. However, in normal operation, a value of about 0.06 second has been found adequate for complete reaction, where normally liquid hydrocarbon is used as the primary make, and further time does not appear to be necessary.

` Iclaim:

1. I'he process for producing carbon black comprising in combination the following steps, blasting into one end of an elongated cylindrical reaction chamber a combustible mixture of a fluid hydrocarbon fuel and air in a direction substantially tangential to the inner wall of the chamber, burning the combustible mixture within the chamber to form a swirling stream of blast flame gases passing through the furnace chamber at a temperature in excess of that at which hydrocarbons are decomposed to form carbon black, separately and forcefully injecting into the swirling gases, at a point downstream from the point of entry of the combustible mixture to the chamber and in a zone near the periphery of the swirling gas stream and in a substantially radial direction, a stream of hydrocarbons, and thereby immediately subjecting the said stream of hydrocarbons as it enters the furnace chamber to the impact and shearing forces of the swirling gas stream, whereby the hydrocarbons thereof are rapidly mixed with the blast flame gases and decomposed by heat absorbed therefrom to form carbon black in suspension in the furnace gases, cooling the suspension, and separating and recovering the carbon black therefrom.

2. The process of claim 1 in which the combustible mixture is blasted into the chamber at a velocity within the range of feet to 180 feet per second.

3. The process of claim 1 in which the combustible mixture is blasted into the chamber at a velocity of about feet per second.

4. The process of claim 1 in which the radially injected hydrocarbon is a normally liquid hydrocarbon and is injected into the chamber in a vaporized state in admixture with steam.

5. The process of claim 4 in which the steam and hydrocarbon vapors are used in proportions of l to 2 parts of steam for each part of hydrocarbon vapors by volume.

6. The process of claim 4 in which the injected hydrocarbon is a petroleum distillate composed of aromatic hydrocarbons to the extent of at least 50% by weight.

7. The process of claim 4 in which the injected hydrocarbon has an end point not less than 725 F. and an aniline cloud point within the temperature range of 10 to 125 C.

WESLEY C. EKHOLM.

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

UNITED STATES PATENTS Number Name Date 2,163,630 Reed June 27, 1939 2,375,795 Krejci May 15, 1945 2,378,055 Wiegand et al June 12, 1945 2,440,424 Wiegand et al. Apr. 27, 1948

Claims (1)

1. THE PROCESS FOR PRODUCING CARBON BLACK COMPRISING IN COMBINATION THE FOLLWOING STEPS, BLASTING INTO ONE END OF AN ELONGATED CYLINDRICAL REACTION CHAMBER A COMBUSTIBLE MIXTURE OF A FLUID HYDROCARBON FUEL AND AIR IN A DIRECTION SUBSTABTIALLY TANGENTIAL TO THE INNER WALL OF THE CHAMBER, BURNING THE COMBUSTIBLE MIXTURE WITHIN THE CHAMBER TO FORM A SWIRLING STREAM OF BLAST FLAME GASES PASSING THROUGH THE FURNACE CHAMBER AT A TEMPERATURE IN EXCESS OF THAT AT WHICH HYDROCARBONS ARE DECOMPOSED TO FORM CARBON BLACK, SEPARATELY AND FORCEFULLY INJECTING INTO THE SWIRLING GASES, AT A POINT DOWNSTREAM FROM THE POINT OF ENTRY OF THE COMBUSTIBLE MIXTURE TO THE CHAMBER AND IN A ZONE NEAR THE PERIPHERY OF THE SWIRLING GAS STREAM AND IN A SUBSTANTIALLY RADIAL DIRECTION, A STREAM OF HYDROCARBONS, AND THEREBY IMMEDIATELY SUBJECTING THE SAID STREAM OF HYDROCARBONS AS IT ENTERS THE FURNACE CHAMBER TO THE IMPACT AND SHEARING FORCES OF THE SWIRLING GAS STREAM, WHEREBY THE HYDROCARBONS THEREOF ARE RAPIDLY MIXED WITH THE BLAST FLAME GASES AND DECOMPOSED BY THE HEAT ABSORBED THEREFROM TO FORM CARBON BLACK IN SUSPENSION IN THE FURNACE GASES, COOLING THE SUSPENSION, AND SEPARATING AND RECOVERING THE CARBON BLACK THEREFROM.

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