Abstract:
An injection assembly for introducing a plurality of laterally spaced sprays of a normally liquid hydrocarbon feedstock into the cracking zone of a carbon black furnace.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to a carbon black producing feedstock injection apparatus for use in the oil furnace process for the production of tread grade rubber reinforcing carbon black. 
     2. Description of the Prior Art 
     The oil furnace process for obtaining high abrasion resistant carbon blacks for rubber reinforcing applications, particularly automotive tires, known in the relevant industry as the HAF, ISAF and SAF types, basically consists of contacting atomized droplets of a normally liquid hydrocarbon feedstock with an extremely turbulent mass of combustion products resulting from burning a mixture of fuel gas and excess pre-heated air. In accordance with the foregoing method, a major portion of the feedstock is pyrolytically dissociated in a partial oxidation reaction to provide a substantial yield of carbon black in the form of an aerosol from whence pulverulent carbon black is recovered and then pelleted. Beyond the particle size requirement of the respective grades of carbon black mentioned, there are other important quality standards that must be met, foremost of which is structure. Structure is essentially the inherent tendency of the nascent carbon black particles to agglomerate to form chain-like units or clusters of the particles during and immediately subsequent to the completion of the pyrolysis reaction. The structure characteristic is very important insofar as it relates directly to certain critical properties exhibited by cured carbon black reinforced rubber compositions. It will suffice to say, however, that the carbon black manufacturing art as presently practiced is highly sophisticated and thus those skilled in this art are well aware of the combination of processing parameters needed to provide a quality product. 
     Lately, however, an additional quality standard for tread grade rubber reinforcing carbon black has been assuming importance. Such concerns the particle size distribution of the resultant product. Essentially the improvement being sought in this regard is to produce a product composed of more uniform particle sizes and particularly, the elimination of the larger particle size component associated with the heretofore standard products. In this connection, particle size refers to the size of the resultant agglomerates. These new products are referred to as high tint blacks, named so because of the empirical test method utilized to measure this property. 
     It is known in the art that the manner whereby the feedstock is injected into the furnace, specifically at or near the center of the situs of maximum turbulency of the cracking gases, leads to the formation of high tint black. However, this expedient results in a product having unacceptably low structure properties. In order to increase structure, the feedstock injector can be moved upstream of the high turbulence zone to provide for a broader feedstock spray pattern as it enters the high turbulence zone. This unfortunately attenuates tint by increasing the agglomerate size distribution, so to compensate the reaction time must be shortened. This practice, however, reduces yield and calls for an expensive drying operation to rid the final product of unreacted oil so that the carbon black will meet the stain test imposed by the consuming rubber industry. It is accordingly, the object of this invention to provide a feedstock injector whose use in the oil furnace process facilitates the production of high tint carbon black without experiencing the shortcomings mentioned above. 
     SUMMARY OF THE INVENTION 
     In accordance with the present invention an injection assembly is provided which is adapted to permit the introduction of a normally liquid hydrocarbon feedstock into a carbon black furnace as a variably spaced array of individual sprays thereof. The contemplated assembly, from the standpoint of design, basically comprises a pipe housing or shroud containing a plurality of axially aligned feedstock supply tubes connected to a common source of the feedstock. The individual feedstock supply lines are adjustable as a unit with respect to said shroud to permit projections thereof from the shroud which in operation remains as a stationary part of the assembly affixed to the upstream closure end of the furnace. In the main, the supply tube projections are thereupon adjustable to extend same radially. The injection assembly design is such that in operation both of the aforementioned adjustments permitting the longitudinal and radial displacement of the feedstock supply tubes are accomplished from without the furnace. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is an overall isometric view of the feedstock injection assembly; 
     FIG. 2A is a sectional view, partly in elevation, along plane 2A--2A of FIG. 1; 
     FIG. 2B is a sectional view, partly in elevation, along plane 2B--2B of FIG. 1; 
     FIG. 3 is a diagrammatic end-on view of feedstock supply tube spreader plate 10 of FIG. 2B; and 
     FIG. 4 is a diagrammatic illustration of the placement of the feedstock injection assembly of FIG. 1 in a carbon black furnace utilizing a choke section for developing turbulent effluent flow conditions therein. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     For the purpose of describing how the feedstock injector of this invention is intended to be used in practice, it would be firstly desirable to discuss generally but briefly the furnace design commonly utilized in the production of the abrasion resistant types of rubber reinforcing carbon blacks. While operational variants such as feedstock rate, air pre-heat temperature and rate, duration of the reaction, as well as the composition of the feedstock are important in implementing the production of abrasion resistant blacks, the design of the furnace nevertheless remains as the most important factor. Essentially all of the commercial furnaces of the type under consideration are composed of two main structural parts; the first or upstream portion being the combustion chamber wherein a mixture of a fuel, preferably natural gas, and an excess of combustion supporting gas, generally air, is combusted. The combustion chamber is invariably of tubular design having a diameter substantially larger than the length thereof. The other structural component of the furnace consists of the reaction zone wherein the carbon producing feedstock is for the most part dissociated into carbon black. This part of the furnace is in direct communication and centrally aligned with the downstream end of the combustion chamber. The reaction zone is likewise tubular but having a diameter substantially smaller than the length thereof. The reaction zone is provided with quench ports at various distances longitudinally removed from the upstream opening thereof whereby quench water can be introduced to terminate the cracking reaction after the desired duration. 
     The modes of effluent flow are applicable in the operation of the aforedescribed furnace design. In one mode of operation the combustion air and fuel are introduced tangentially into the combustion chamber. The combusted gas accordingly enters into the reaction zone in an inwardly spiralling pattern and in so doing leads to the formation of extremely turbulent conditions therein especially near the upstream opening. 
     The other effluent flow pattern observed is that of axial flow whereby the combustion air and fuel are burned in the combustion chamber and introduced into the reaction zone in a generally linear manner. This type of flow does not create the highly turbulent conditions within the reaction zone as does the tangential flow method and therefore the upstream extremity of the reaction zone is provided with a choke or a venturi configuration in order to realize the degree of turbulency required. 
     The linear flow method of operation is preferred in the utilization of this invention. A particularly suitable design for operating in the foregoing manner is the type of furnace generally illustrated in FIG. 4. Complete details with respect to this design of a furnace and the operation thereof can be found in U.S. Pat. No. 3,060,003. 
     With reference to FIG. 4 preheated combustion air is introduced into the plenum 20 and flows axially within conduit 21 to combine with the fuel gas from jets 22. The flame and the resultant combustion products are directed radially outwardly by the deflector element 23. The hot combustion gases thereupon flow generally axially within the combustion chamber 24 near the peripheral extent thereof and then proceed radially downwardly along the downstream end of the combustion chamber and into the choke 25. Accordingly, the velocity as well as turbulency of the combustion gases are maximized in the choke section. The reactor effluent then flows into the enlarged reaction zone or tunnel and is quenched downstream by introducing sprays of water into the tunnel. 
     As further shown in FIG. 4, the individual feedstock supply tube discharge ends of the injection assembly of FIG. 1 are positioned contiguous to and in axial alignment with the upstream opening of the choke. Desirably, the injection assembly is designed so that the discharge ends of the radially extendible feedstock supply tubes will, when the latter are fully extended, lie within and adjacent to the periphery of the choke opening. In this position the tint and structure of the resultant carbon black will be maximized. In the event less structure is desired the radially extended portion of the supply tubes can be adjusted inwardly to the degree which provides the level of structure desired, without reducing tint. 
     As it is apparent from the foregoing discussion, the feedstock injector is positioned within the furnace where it is subjected to intense heat exposure, generally in the order of 2800° F. or more. Accordingly, it is essential that the unit be compact in order to minimize the area exposed to the high heat environment and to permit it to be removed from the furnace for periodic servicing through gate valve 26 without the necessity of shutting down the furnace. Compactness in itself, however, will not serve to protect the injector for any extended period let alone maintain the feedstock below cracking temperature and therefore the unit must be provided with cooling means as a practical expedient, all as will be set forth in connection with the detailed description of the invention given below. 
     For a detailed description of the injector assembly of FIG. 1 reference will now be had to FIGS. 2A and 2B. Feedstock supply pipe 1 connects to feedstock distribution chamber or manifold 2 fabricated from pipe fitting piece 3 and header piece 4. Feedstock supply pipe 1 can acceptably be 1/2 inch SCH 80 black pipe. Six segments of metal flex tubes 5 of 1/4 inch ID equally spaced on a 3/4 inch diameter circle are brazed into the header 4. Likewise, a 1/4 inch ID metal feedstock supply tube 6 positioned centrally with respect to flex tubes 5 is brazed into the center of header 4. Feedstock supply extension tubes 7 are brazed into the ends of flex tubes 5 and extend to about the length of said centrally positioned feedstock supply tube 6. 
     The integral combination of feedstock supply pipe 1, manifold and feedstock supply tubes 6 and 7 are positioned within pipe shroud 8 via feedstock supply pipe locking mechanism 18 by means of packing gland 9. Pipe shroud 8 can be acceptably a 1  inch SCH 40 pipe which is provided with closure member or spreader plate 10 drilled to accommodate freely the longitudinal positioning of said feedstock supply tubes. Pipe shroud 8 is of sufficient length so as to allow the ends of feedstock supply tubes 6 and 5 to be pulled back substantially flush with the outside face of tube spreader plate 10. Shroud 8 is appropriately provided with an interior shoulder as shown in FIG. 2B with which pipe fitting piece 3 abuts to prevent retraction of the feedstock supply tubes through spreader plate 10 into the shroud. 
     As previously mentioned, it is necessary to provide means for cooling the portion of the injection assembly disposed within the furnace. With reference to FIGS. 2A and 2B, such is accomplished in the depicted injector by providing the downstream part thereof with a water-cooled jacket generally shown at 11. The water jacket can be permanently affixed to the shroud member or constitute a removable part as shown, connected to the assembly by means of packing gland 12. The water-cooled jacket is preferably fabricated from heat resistant stainless steel and is appropriately connected at the upstream end thereof to a cooling water manifold shown generally at 13. Cooling water manifold 13 is composed of two sections. Inlet section 14 is adapted for introducing the cooling water and outlet section 15 is adapted for discharging same. The inlet section 14 of the manifold communicates directly with the interior of the cooling jacket by means of quadrantly spaced tubes 16 which extend longitudinally to near the downstream extremity of the jacket thereby permitting the cooling water to discharge into the jacket at this location and to return and exit through outlet section 15 of the manifold. Insofar as there is a tendency for blow back to occur within the downstream interior of the shroud member, it is desirable to provide additional cooling means in order to prevent the tube spreader plate 10 and the adjacent portions of the feedstock supply tubes from overheating. This can be readily accomplished by introducing compressed air in the inlet section 17 of the locking mechanism 18, such cooling air exiting through the spreader plate 10. 
     The operation of the present injector will next be described and in so doing reference will be had to FIG. 3 in particular. The novel feature of the present invention is that by simply rotating the feedstock supply pipe 1 relative to the stationary tube spreader plate 10, the latter shown in detail in FIG. 3, the action of the segment of flex tube coupled with manner in which spreader plate exit holes are designed causes each tube extension 7 projecting beyond the spreader plate to take an outwardly angular position relative to the centrally disposed feedstock supply tube 6. The net result is an equally spaced circular pattern of the discharge ends of said feedstock supply tubes 7. The diameter of the circular pattern depends upon the length of the projection of the indicated feedstock supply tubes beyond the spreader plate and the relative degree of rotation of feedstock supply pipe 1. 
     The tube spreader plate 10 serves to permit supply tube extensions 7 to assume a given angular position upon rotation of the feedstock supply pipe 1. As illustrated in FIG. 3, this is accomplished by the manner in which the holes 19 of the spreader plate 10 are provided. Firstly, holes having a diameter slightly larger than that of the tubing to be accommodated are drilled perpendicular to the face of the spreader plate. Next superimposed drillings are effected at an acute angle with respect to the face of the spreader plate and along an axis inclined toward the periphery of said plate.