US2708621A

US2708621A - Injection means for hydrocarbon cracking

Info

Publication number: US2708621A
Application number: US203105A
Authority: US
Inventors: James H Shapleigh
Original assignee: Hercules Powder Co
Current assignee: Hercules Powder Co
Priority date: 1950-12-28
Filing date: 1950-12-28
Publication date: 1955-05-17
Anticipated expiration: 1972-05-17

Description

May 17, 1955 J. H. sHAPLElGH INJECTION MEANS FOR HYDROCARBON CRACKING Filed Dec. 28, 1950 2 Sheets-SheecI l JAMES H. sHAPLElsH.

1N V ENTOR.

AGENT.

Unite States Patent O INJECTION MEANS FR HYDROCARBON CRACKNG James H. Shaplegh, Wilmington, Del., assignor to Hercules Powder Company, Wilmington, Del., a corporation of Delaware Application December 28, 1950, Serial No. 203,105

1S Claims. (Cl. 23-284) This invention relates to the treatment of fluid reactants and more particularly to an injection assembly for introduction of lluid reactants into the reaction zone.

In the treatment of lluid hydrocarbons, there is an ever present problem of avoidance of detrimental carbonization either before or during the actual cracking step especially in the treatment of normally liquid hydrocarbons and unsaturated hydrocarbons. Tube-type apparatus utilizing injection assemblies for the hydrocarbon have been found particularly advantageous in reducing carbon formation during the treatment of unsaturated hydrocarbons and normally liquid hydrocarbons. However, even in such apparatus the desired degree of reaction control is often difficult to obtain.

In the most successful tube-type apparatus, the fluid hydrocarbon, usually admixed with a gas such as steam or air, is introduced into the reaction zone of the cracking tube through a concentrically disposed injection tube which projects a considerable distance into the interior of the exteriorly heated tube. The steam, air, or other gas is normally introduced into the cracking tube as a secondary stream substantially above the injection end of the injection tube and is caused to flow concurrently, but out of contact, with the primary stream of hydrocarbon in the injection tube. The hydrocarbon is normally preheated prior to its entry into the injection tube. If the hydrocarbon treated is liquid, it is desired that it be in as fully a Vaporized state as is possible at the point of injection without bringing about thermal decomposition and carbon formation prior to flash-heating to cracking temperature. At the same time, the concurrently llowing or secondary stream must itself be heated to a temperature which, when mixed with the hydrocarbon at the mouth of the injection tube, will flash-heat the hydrocarbon to near reaction temperature. The resulting mixture is then quickly raised to reaction temperature by the heat from the Wall of the cracking tube. Such immediate dash-heating in the cracking tube is essential to minimize ,thermal decomposition and carbon formation prior to cracking, whether such reaction is thermal or catalytic. Consequently, it will be seen that positive temperature control in an injection assembly is essential to the successful treatment of duid hydrocarbons without detrimental carbonization.

The object of the present invention, therefore, is an injection assembly for introducing fluid reactants into a reaction zone wherein the necessary positive temperature control can be more easily exercised and detrimental carbonization thus more easily prevented.

A further object of the invention is an injection assembly for introducing fluid reactants into a reaction zone wherein a secondary stream of fluid medium may be heated to desirably high temperatures prior to admixture with a primary stream of fluid reactant without causing detrimental carbonization of the fluid reactant.

An additional object of the invention is an injection assembly for introducing fluid reactants into a reaction 2,708,621 Patented May 17, 1955 rice zone which is characterized by more efficient and more easily controlled heat transfer characteristics.

Generally described, the present invention is an injection assembly for introduction of fluid reactants into a reaction zone having in combination a hollow, thinwalled, externally heated outer refractory member, and injection means concentrically disposed within the outer member, said injection means comprising a body member containing longitudinally thereof a centrally located passageway for fluid medium, a substantial portion of the outermost surface of said body member being positioned in close spaced relationship with the inner surface of the externally heated outer member to provide an elongated, restricted passageway therebetween for liuid medium.

According to the preferred embodiment of the invention, the injection assemblies of the invention are employed in conjunction with tube-type reaction apparatus. When so employed, the outer member will normally be the upper portion of an externally heated cracking tube. However, the injection assemblies in accordance with the invention may be employed with other than tube-type apparatus. For example, the assemblies may be employed in the controlled introduction of olens and air to an insulated, unheated reaction zone to form acetylene, the only heat supplied being applied to the injection assembly itself.

The injection assemblies of the invention may be formed from any desired number of separate elements as long as the resulting structure has an elongated, annular passageway for restricted flow of fluid medium disposed just within a thin-walled, externally heated outer member and as long as said passageway is spaced a substantial distance from the concentrically located longitudinal perforation of the injection means. For example, the assembly may be formed from an outer tube and a concentrically positioned injection tube of greatly smaller diameter. A hollow casing or channeling member may then be disposed about the injection tube for a substantial portion of its length. The wall of this casing or channeling member is positioned in close spaced relationship with the inner Wall of the externally heated outer tube. ln this embodiment, it is preferred that the casing or channeling be of corrugated construction. Such corrugated structure provides a greater metal surfacefor heat transfer and promotes turbulence in the ow of fluid medium through the annulus between the corrugated member and the cracking tube. Such turbulence together with the increased mass velocity due to restricted ilow results in more efficient heating of the fluid medium. Furthermore, the corrugated member may be of light, flexible construction which renders the injection means more readily removable from the outer member.

When the injection means comprises an injection tube surrounded by a separate hollow body member, one end of the body member must be in substantially uid-impervious relationship with the injection tube. lt is preferred that the upper end be open or vented and that the lower end be closed except for a very small bleeder hole which will allow a slow llow of steam through the interior of the member. It is within the scope of the invention that the top of the annular body member be closed and that the bottom of the member be open. However, this particular construction is not normally preferred since under some conditions of reaction some backflow of iluid reactant into the interior of the body member may occur. It has also been found desirable in some instances to lill the annular space within the body member either partially or completely with insulatory packing material.

According to a further embodiment of the invention, a jacket may be disposed about the injection tube within the elongated, hollow body member. In this embodiment, the lower end of the jacket will normally be sealed to the injection tube and the upper portion will be vented. The lower end of the body member will be sealed either' to the lower end of the jacket or to the injection tube below the jacket. Vents are then formed in the outer periphery ot the hollow body member near the upper end thereof Cooling steam is led to the bottom of the jacket, preferably through a pipe disclosed within the hollow body member or Within the jacket itself. This pipe may be insulated if desired, The cooling steam passes upward out of the jacket, into the interior of the hollow body member, and out of the vents to join the secondary steam and thus be heated as it passes downward through the annulus between the body member and the wall of the cracking tube.

According to an additional embodiment, an operable injection assembly may comprise an externally heated outer refractory tube and a centrally oriticed body of refractory, ceramic material concentrically disposed within the metallic tube. The body of refractory, ceramic material is so formed that its outer surface is in close spaced relationship with the inner wall of the tube to provide the restricted passageway for fluid medium which characterizes the assemblies of the invention. Preferably the outer surface of the refractory body will be irregular to promote turbulence.

Having generally described the invention, more specific illustration of several embodiments is described with reference to the accompanying drawings wherein like symbols refer to like parts wherever they occur.

In the drawings, Fig. l is a part sectional, part elevational view of a preferred embodiment of the injection assembly of the invention. Fig. 2 is a part elevational, part sectional bottom view of the injection apparatus of Fig. l taken along line 2-2 Figs. 3 and 4 are fragmentary, part sectional, part elevational view of additional embodiments of the invention. Fig. 5 is a part elevational, part sectional view of a further embodiment of the invention.

In Figs. l and 2 a cracking tube 10 is suspended through a furnace 11. Projecting concentrically within the cracking tube is an injection tube 12 equipped at its leading extremity 13 with spraying means. A thermocouple well 14 is concentrically disposed within the injection tube 12. An inlet 15 for fluid medium passes into the injection tube 12. An inlet 16 for fluid medium leads into cracking tube 10 above the furnace hearth. A corrugated metal body member 17 is disposed about a substantial portion of the injection tube 12. The lower end of the corrugated body member or casing 17 is welded in fluid-impervious relationship to the injection tube 12 adjacent the nozzle 13. A supporting strap 13 secures the upper end of the body member in position about the injection tube 12. The annulus between the injection tube 12 and the corrugated body member 17 is filled with insulatory packing 19. A small bleeder hole 2t) allows a very slow iiow of the secondary stream through the insulatory packing 19.

The structure illustrated in Figs. l and 2 is particularly effective in treating fluid hydrocarbons and steam and operates as follows: The furnace 11 is tired by any suit able means known to the art and the temperatures of the various portions of the cracking tube 10 are brought to predetermined levels. The Fluid hydrocarbon to be treated is preferably in admixture with steam and is introduced into the injection tube 12 through the inlet 1S. A secondary stream of steam is simultaneously introduced into the cracking tube 10 through the inlet 16. The secondary steam passes downwardly through the annulus between the wall of the cracking tube 1d and the corrugated body member tube 17. The corrugations of the member 17 cause turbulence in the steam flow and thus promote better heating of the steam in the annulus. In addition, the corrugation gives a greater metal surface for improving transfer of heat to the stream of secondary steam in the annulus between the corrugated tube 17 and the cracking tube 1). Depending on the character of the insulation employed, a small portion of the secondary steam may pass slowly downward through the interior of the body member 17, through the packing 19 and out the bleeder hole 20 into the annulus between the shielding tube 17 and the cracking tube 1). When only a trickle of steam passes through the interior of the corrugated tube 17, the only substantial effect is theremoval of occluded air from the packing 19, thus enhancing the safety of the process. Where the insulatory packing is more loosely packed, however, a relatively greater flow of secondary steam through tube 17 will also have a cooling eiect. The desired amount of ow can be positively controlled by Varying the size of the bleeder hole 26 and/ or the nature of the packing 19. This steam is introduced into the iiow of the now superheated secondary steam prior to its entry into the flash-heating zone below the end 13 of the injection tube 12. The hydrocarbon-steam mixture in the injection tube 12 is maintained at a temperature that,

normally liquid, the hydrocarbon is in as nearly a completely vaporized state as possible without carbonization as it emerges from the end 13 of the injection tube 12. Due to the fact that the heated secondary steam is out of contact with the injection tube 12, and insulated therefrom by the insulation 19, higher metal temperatures may be employed to heat the secondary steam to a desirably high temperature without causing carbonization in the injection tube 12. When the vaporized hydrocarbon is injected into the cracking tube 1%, it is therefore projected into and adrnixed with a moving wall of snperheated steam which can be at such elevated temperatures that it is instantaneous Hash-heated to near cracking temperature without detrimental carbon deposition. Furthermore, the annular curtain of steam flowing from the annulus between the corrugated body member 17 and the cracking tube 1t) minimizes the impingement of hydrocarbon on the hot metal surface of the cracking tube 1t). Such impingement will normally result in substantial carbonization at the metal temperatures employed. The .steam-hydrocarbon mixture is then quickly brought to cracking temperature by the heat externally applied to the cracking tube. The mixture is then passed through the cracking zone of the cracking tube 111 which may or may not contain catalyst, depending on the nature of the cracking process. The products of the reaction are removed from the bottom of the cracking tube 10 and treated according to known procedures.

In Fig. 3, an injection assembly is shown wherein an injection tube 12 projects into a cracking tube 10 as in the apparatus of Figs. l and 2. In the assembly of Fig. 3, however, a cylindrical body member 31 is concentrically disposed about the injection tube 12 and in close proximity to the inner wall of the cracking tube 10. An annular disc 32 is welded in huid-impervious relationship into the annulus between the injection tube 12 and the body member 31. The lower end of the tube 31 is open and is held in position by positioning studs 33.

The structure of Fig. 3 operates in essentially the same manner as that of Fig. 1. The cylindrical body tube 31 forces the superheated steam to flow through a narrow annulus adjacent the cracking tube wall and thus provides for more efcient heating of the secondary stream. Since no insulation is present within the tube 31, however, the amount of heat transfer to the injection tube 12 is greater. With this particular apparatus, therefore, it is preferred to use less hydrocarbon preheat and/ or increase the rate of hydrocarbon ow through the injection tube 12. Insulation may be employed within the tube 31, if desired, but in this event, the lower end of the tube 31 must contain a suitable supporting member.

In Fig. 4, an injection tube 12 projects into a cracking tube 1t) as in the structures shown in Figs. l, 2 and 3. A jacket 40 is disposed about a portion of the injection tube 12. An annular disc 41 is welded into the annulus agresser between the lower end of the jacket 40 and the injection tube 12 to form a Huid-impervious joint. The upper end of the jacket 40 is open and is held in its concentric position by studs 42. A corrugated metallic body member 43 is disposed about the jacket 40 and an additional portion of the injection tube 12 and is positioned in close spaced relationship with the inner wall of the cracking tube 10. The lower end of the corrugated body member 43 is welded in Huid-impervious relationship to the lower end of the jacket 40. An annular disc 44 is welded in the annulus formed by the upper end of the corrugated body member 43 and the injection tube 12 to form a huid-impervious joint. Vents 4S are formed in the end of the corrugated member 43 adjacent the disc 44. An insulated conduit 46 for uid medium passes through the disc 44 and extends into the lower portion of the jacket 40.

The operation of the assembly of Fig. 4 is again similar to that of the assemblies of Figs. 1 and 3. The hydrocarbon or hydrocarbon-steam mixture is introduced into the upper end of the injection tube 12 and superheated steam is introduced into the upper end of the cracking tube 10, and the two uid streams flow as before. Cooling steam is introduced through conduit 46 into the bottom of the jacket 4t) to maintain the hydrocarbon temperature in the injection tube 12 at the desired level. This cooling steam passes upward from the jacket 4t) into the interior of the corrugated body member 43 and out of vents 45 into the downward flow of superheated steam. ln this manner the cooling steam is not wasted and is heated prior to its entry into the cracking zone below the injection assembly.

ln Fig. 5 an annular body member of refractory, ceramic material 50 is concentrically disposed within an outer annular metallic tube 51. The outer surface of the refractory body 50 is of corrugated construction and is disposed in close spaced relationship with the inner surface of the tube 51 to form an annular passageway 52. The refractory body Sti has a longitudinal passageway 53 formed therein. An inlet conduit 54 is in communication with one end of passageway 53. The inlet conduit 54 is secured in the perforation 53 of the refractory body 50 in a fluid-impervious joint by means of a sealing bushing 55. The other end of passageway 53 leads to the interior of a reaction chamber 56 formed by refractory material 57. A second inlet conduit 58 enters the tube 51 above the body of refractory material 50. The ceramic body 50 is suspended in the outer tube 51 by means of members 59 and is concentrically positioned by studs 60. An outlet 61 for reaction products is located in the wall 57 of the reaction chamber 56.

The apparatus of Fig. 5 is especially adapted to such reaction as the formation of acetylene from oleiins and air. The gaseous hydrocarbon is introduced into the reaction chamber 55 through inlet conduit 54 and passageway 53 while air is introduced into the reaction chamber 55 by way of inlet conduit 58 and annulus 52. The tube 51 is externally heated to bring the air to any desired temperature. The hydrocarbon may be preheated as desired. The olefin and air mix in chamber S5 and react exothermally to form acetylene which is withdrawn through outlet 60.

The beneficial results obtained with the apparatus in accordance with the invention may be illustrated by comparing the performance of an apparatus similar to that shown in Figs. 1 and 2 with the performance of a standard apparatus. In the apparatus of the invention, the cracking tube is 8 inches in inner diameter and the injection tube extends 7 feet into the cracking tube. The casing 17 is spaced M: inch from the cracking tube wall. The standard apparatus is identical except for omission of the casing 17 and the insulation 19. When a secondary stream of steam is introduced into both cracking tubes at 240 F. at a rate of 122 pounds of steam per hour; when the top of each tube is maintained at 1090 F.; and when d the injection level of each tube is maintained at 1575 F., the secondary steam temperature at injection level is about l335 F. in the apparatus of Fig. 1 but only about 830 F. in the standard apparatus. This substantial increase in steam temperature in the apparatus in accordance with the invention insures greatly improved flash mixing and is obtained without any detrimental carbonization in the injection tube.

As heretofore indicated, the outermost surface of the injection assembly, body member, or casing, as the case may be, is disposed in close, spaced relationship with the inner wall of the hollow, thin-walled, externally heated cracking tube or outer member. The width of the annulus between these two members will depend upon the desired rise in temperature of the secondary stream of gaseous medium, and the through-put of the gaseous medium of the secondary stream. The higher the mass velocity through the annulus, the higher will be the temperature rise. Whereas, with the 8 inch tube of the above example, an annulus of one quarter inch width was used, a different diameter tube would use the same or a different width annulus to suit the objective.

The combination as set forth herein, for example, enables high snperheat temperature to be reached which is reasonably close to the metal wall temperature at the injection tube exit level. in the example, inlet steam temperature was 240 F. The inlet temperature may be at any suitable degree of superheat, the outer member at any temperature consistent with the type refractory used, as for instance metal or quartz, and the attained temperature of the secondary stream much higher than the l335 F. of the example.

The temperatures and rates of ilow of the fluid reactants and inert gas such as steam will, of course, vary with the type of reaction and the particular reactants ernployed. The optimum conditions are known to the art. The improved injection assemblies of the invention a1- low these known conditions to be used and controlled with greater ease and accuracy, thus eliminating detrimental formation ot carbon in the cracking apparatus. Furthermore, injection assemblies in accordance with the invention will allow considerably higher secondary steam temperatures to be employed than has heretofore been deemed possible without causing detrimental carbonization of hydrocarbons prior to cracking.

The cracking tubes, injection tubes, jackets, and the various body members are preferably made of metals such as stabilized stainless steel except in the type apparatus shown in Fig. 4. The use of metal is not essential to operability, however', since one or more of the structural elements may be constructed of equivalent refractory materials known to the art which exhibit the desirable structural strength at the temperatures to be employed.

While the primary purpose ot the body members and jackets employed in accordance with the invention is to provide a means whereby the secondary stream of lluid medium may be heated to desirably high temperatures without causing detrimental thermal decomposition of the fluid reactant in the injection tube, the regulated flow of heat through the body members may, if de sired, be employed to raise the temperature level of the fluid reactant within the injection tube.

Structures other than those specifically illustrated are also within the scc-pe of the invention. For example, desirable features of the structures shown in Figs. l and 4 can be combined for even more efficient control of ternperature in the injection tube. For example, the lower portion of the corrugated tube 43 of Fig. 4 can be lilled with insulatory packing maintained in position by a suitable supporting member disposed at or below the open end of the jacket 4d. Thus, the combined benefits of cooling steam within the jacket and insulatory packing within the corrugated tube may be obtained. There- 7 fore, it is intended that the invention be limited only by the scope of the appended claims.

What I claim and desire to protect by Letters Patent 1s:

1. Apparatus for introducing iiuid reactants into a reaction zone having in combination an injection assembly disposed in a heat generating zone, means associated with the heat generating zone and separate from the injection assembly for externally heating the injection assembly, said assembly comprising a hollow, thin walled, outer refractory member externally heated by the heating means, and internally centered and longitudinally extending within the outer member, an inner injection means having longitudinally thereof a central passageway for uid reactants, at least part of the outer surface of the injection means being disposed in close spaced relationship with the inner surface of the outer member to provide an elongated, restricted outer passageway for uid reactants therebetween, said outer passageway being disposed around the central passageway of the injection means to enable the fluid reactants in the outer passageway to be highly heated by the outer member of the assembly while flowing concurrently but out of contact with the fluid reactant in the injection means.

2. Apparatus according to claim l in which the injection means is a single, centrally perforated body of refractory ceramic material, the diameter of said perforation constituting only a minor portion of the diameter the ceramic body.

3. Apparatus according to claim 1 in which the injection means comprises a metallic injection tube for uid medium concentrically disposed in a hollow, elongated, metallic body member.

4. Apparatus according to claim 1 in which the portion of the surface of the body member which is disposed in close spaced relationship withr the outer member is irregular.

5. Apparatus for treating fluid reactants having in combination a refractory walled reaction furnace, an elongated metallic cracking tube disposed in the furnace, heating means associated with the furnace to apply heat to the exterior of the cracking tube, an injection tube for fluid reactants extending longitudinally into the interior of the cracking tube, and an elongated casing disposed substantially concentrically about at least a portion of the injection tube adjacent the end thereof disposed within the cracking tube, said casing being disposed in close spaced relationship with the inner wall of the cracking tube to -form an elongated, annular passageway therebetween for vliuid reactants, said annular passageway being disposed around the injection tube to enable the uid reactants in the annular passageway to be heated by the cracking tube while flowing concurrently but out of contact with the tiuid reactants in the i injection tube.

6. Apparatus in accordance with claim 5 wherein one end of the casing is in uid-impervious relationship with the injection tube and the cracking tube.

7. Apparatus in accordance with claim 5 wherein the end of the casing disposed opposite the injection end of the injection tube is in communication with the interior of the cracking tube, and the end of the casing adjacent the injection end of the injection tube is vented to permit restricted ilow of fluid medium through said casing.

8. Apparatus in accordance with claim 5 wherein both ends of the elongated casing are sealed to the injection tube in duid-impervious relationship and vents are located in the wall of the said member.

9. Apparatus in accordance with claim 5 wherein the elongated casing is of corrugated construction.

l0. An injection assembly for introduction of fluid reactants into a reaction zone having in combination an externally heated cracking tube; an injection tube for fluid medium projecting longitudinally into the interior of the cracking tube; a metallic jacket disposed about a portion of the injection tube adjacent the end thereof projecting into the cracking tube, the end of the jacket adjacent the end of the injection tube being sealed to the injection tube and tr e opposite end of the jacket being open; means for introducing fluid medium into the jacket adjacent the sealed end thereof; and an elongated, metallic casing disposed about the jacket and injection tube, one end of said casing being sealed to the injection tube beyond the open end of the jacket, the opposite end of said casing being sealed to the jacket adjacent the end of the injection tube, said casing being vented adjacent the end thereof sealed to the injection tube; said casing being disposed in ciose spaced relationship with the inner wall of the cracking tube to form an elongated, annular passageway therebetween for uid medium.

11. An assembly according to claim 10 wherein the casing is of corrugated construction.

12. An injection assembly for introduction of fluid reactants into a reaction zone having in combination an externally heated cracking tube; an injection tube for uid medium projecting longitudinally into the interior of the cracking tube; and an elongated, metallic casing disposed substantially concentrically about a portion of the injection tube adjacent the end thereof projecting within the cracking tube; at least one end of said casing being sealed to the injection tube in fluid-impervious relationship; insuiatory material disposed within the space between the injection tube and the casing; the wall of the casing being disposed in close spaced relationship with the inner wall of the cracking tube to form an elongated, annular passageway therebetween for iiuid medium.

13. An assembly according to claim l2 wherein the casing is of thin-walled corrugated construction.

14. An assembly according to claim l2 wherein the end of the casing opposite the injection end of the injection tube is open and the opposite end thereof is sealed to the injection tube.

15. An assembly according to claim 12 wherein thc end of the casing opposite the injection end of the injection tube is open and the opposite end thereof is sealed to the injection tube, said casing being vented adjacent its sealed end to permit restricted ilow of fluid medium therethrough.

Ret'erences Cited in the le of this patent UNITED STATES PATENTS 324,005 BurrellV Aug. 1l, 1885 1,339,709 Mohn May 11, 1920 1,340,902 Lundgaard May 25, 1920 1,773,002 Hunt Aug. 12, 1930 1,857,364 De Rachat May 10, 1932 2,059,527 Kaplan Nov. 3, 1936 2,071,721 Bagley et al. Feb. 23, 1937 2,366,670 Maude Ian. 2, 1945 2,457,505 Soiem Dec. 28, 1945 2,512,587 Stengel June 20, 1950 FOREIGN PATENTS 839,528 France Apr. 5, 1939

Claims

1. APPARATUS FOR INTRODUCING FLUID REACTIONS INTO A REACTION ZONE HAVING IN COMBINATION AN INJECTION ASSEMBLY DISPOSED IN A HEAT GENERATING ZONE, MEANS ASSOCIATED WITH THE HEAT GENERATING ZONE AND SEPARATE FROM THE INJECTION ASSEMBLY FOR EXTERNALLY HEATING THE INJECTION ASSEMBLY, SAID ASSEMBLY COMPRISING A HALLOW, THINWALLED, OUTER REFRACTORY MEMBER EXTERNALLY HEATED BY THE HEATING MEANS, AND INTERNALLY CENTERED AND LONGITUDINALLY EXTENDING WITHIN THE OUTER MEMBER, AN INNER INJECTION MEANS HAVING LONGITUDINALLY THEREOF A CENTRAL PASSAGEWAY FOR FLUID REACTANTS, AT LEAST PART OF THE OUTER SURFACE OF THE INJECTION MEANS BEING DISPOSED IN CLOSE