Patent Application
20050019233
The present invention relates to systems and apparatuses for stabilizing the high-temperature process tubes of a fired heater, furnace, heat exchanger or other device utilizing high-temperature process tubes. More specifically, the present invention relates to systems and apparatuses for stabilizing reactor tubes within their housing device by limiting their movement. Most specifically, the present invention relates to systems and apparatuses for stabilizing reactor furnace tubes by using a framework of structural components to limit their movement and thereby reduce harmful stresses on the tubes, extend the useful life of the tubes, increase the efficiency and safety of reaction processes and allow for the streamlining the design of the tubes.
The present invention relates to systems and apparatuses for stabilizing the high-temperature process tubes of a fired heater, furnace, heat exchanger or other device that utilizes high-temperature process tubes. However, systems and apparatuses used in accordance with the present invention are particularly well suited and advantageous to the reactor tubes of furnaces used for the cracking of a variety of hydrocarbon feedstocks by pyrolysis to ethylene and other valuable olefinic gases. Accordingly, by way of illustration, but not limitation, the present invention will be described and explained in the context of that process.
Cracking furnaces long have been used in the process of cracking a variety of hydrocarbon feedstocks to ethylene and other valuable olefinic gases. There are at least several thousand such furnaces located in world refineries and petrochemical plants. U.S. Pat. Nos. 2,671,198, 3,407,789, 3,671,198, 4,342,642, 4,499,055 and 5,427,655 describe basic designs of short-residence time/high temperature cracking furnaces. In general, cracking furnaces vary in size and style but all contain reactor tubes, which transport the feedstock being heated and processed. The sensible heat and the heat of cracking are supplied by radiant heat from burners located on the floor and/or walls of the firebox of the furnace. This heat transfers through the reactor tubes into feedstock that flows therewithin.
Given the relatively high temperatures to which the reactor furnace tubes are exposed, metallic materials have been preferred for construction of reactor lines. Recent conventional reactor lines have been constructed of nickel-containing alloys, however, varying the materials used for reactor lines are found in the prior art. See, e.g., Winkler et al., U.S. Pat. No. 2,018,619, describing an apparatus that uses reactor tubes made from silicon powder; and European Patent Application EP 1 018 563 A1 describing constructing a portion of a heating furnace tube with a material comprising a rare earth oxide particle dispersion (“ODS”) iron alloy.
The length of reactor furnace tubes varies and generally may range from about 10 feet to about 400 feet in length. Further, reactor furnace tubes may take many shapes. Although the present invention is particularly well suited and advantageous to reactor furnace tubes that are coiled in a serpentine shape or comprised of a series of u-shaped tubes, other configurations are within the contemplated scope of the present invention. Among the problems relevant to the present invention associated with reactor furnace tubes is the movement of the tubes due to harmonics, fluid momentum, thermal expansion and/or other forces. Such movement is sometimes referred to “swing.” Movement of the tubes introduces harmful stresses in the tubes and their welds, which distort the shape of the tubes, reduce the useful life of the tubes and create a safety risk of tube or weld breakage. Such movement also disturbs the alignment of the tubes with the burners of the furnace, which is sometimes referred to as “shadowing,” i.e., one tube blocking the radiant heat from reaching another tube. Misalignment also can reduce the efficiency of the process by allowing the reactor tubes to get too close or too far from the burners thereby causing inconsistent heat transfer. In addition, misalignment of the reactor furnace tubes can cause an increase in coke formation, a deleterious by-product of the process, within the tubes. The deposition of coke on the insides of the reactor furnace tubes constricts the flow path for the feedstock, causing an increased system pressure drop, and a decrease in the furnace capacity. Additionally, the coke deposition on the inside of reactor furnace tubes decreases the heat transfer of the radiant heat from the radiant burners through the tube wall to the hydrocarbons flowing through the tubes, which results in a decrease in the cracking yield. Coking in conventional reactor furnace tubes is major cause of furnace shutdown.
To date, manufacturers have welded locator pins to the return bends of u-shaped reactor furnace tubes in an attempt to limit their movement. Despite such efforts, the problems of “swing,” “shadowing,” misalignment and their adverse effects continue and there is no prior art that teaches or suggests systems or apparatuses for stabilizing reactor furnace tubes using a framework of structural components that effectively limits the movement of the reactor furnace tubes.
The present invention concerns systems and apparatuses for stabilizing the high-temperature-process tubes of a fired heater, furnace, heat exchanger or other device utilizing high-temperature process tubes. Thus, it is an object of the present invention to provide systems and apparatuses to reduce the movement of high-temperature-process tubes due to harmonics, fluid momentum, thermal expansion or other forces.
It is still another object of the present invention to provide systems and apparatuses to reduce harmful stresses in reactor furnace tubes and their welds. Such stresses distort the shape of the tubes, reduce the useful life of the tubes and create a safety risk of tube or weld breakage.
It is still a further object of the present invention to provide systems and apparatuses that, in the case of a reactor furnace, maintain the alignment of reactor furnace tubes to the burners of the furnace thereby allowing consistent heat transfer and concomitantly increasing the efficiency of the reaction processes within the tubes and/or reducing coke formation within the tubes.
It is still another object of the present invention to provide systems and apparatuses that allow for streamlining the design of the reactor furnace tubes by eliminating the need for locator pins and the like.
It is still a further objective of the present invention to provide systems and apparatuses that may be used in the construction of a new fired heater, furnace, heat exchanger or other device utilizing high-temperature process tubes and/or retrofitted to an existing such device.
These and other objects are achieved by the present invention, which relates to systems and apparatuses for stabilizing high-temperature process tubes in devices utilizing such process tubes comprising surrounding a portion of said reactor tubes with at least one apparatus comprising at least two rods, having at least two spacers attached thereto, at least one rod retaining means on said rod wherein said rods and spacers are comprised of temperature-resistant material.
The following detailed description of present invention is provided to illustrate the present invention and is not to be construed to limit the scope of the appended claims in any manner whatsoever.
The apparatus depicted in
In the depicted embodiment, the rods 1 are cylindrical and solid and may have an outer diameter ranging from about 0.5″ to about 2.0″. In addition, the length of the rods may range from about 3′ 0″ to about 15′ 0″, depending upon, inter alia, the furnace size and the number of tubes to be stabilized. In the depicted embodiment, u-shaped pins 4 serve as the retaining means.
In other embodiments, the rods need not be cylindrical and/or solid and may be of any dimensions known to those skilled in the art. Further, the length of the rods may vary based, for example, on the number of the reactor tubes to be stabilized and the number of apparatuses the user desires to apply in stabilizing the tubes. The longer the rods, the fewer number of apparatuses will be needed. In addition, the dimension of the pins may vary based upon the size of the openings in the rods. Further, the pins need not be u-shaped but may take the form of cotter pins. In addition, any means known to those skilled in the art may be used to as the means of retaining the outermost spacers on the rods.
In still other preferred embodiments, bending a length of ODS rod material in half or in any other manner such that the rods are parallel and integrally attached at one end 5 may form the rods. Such embodiments are depicted in
Referring again to
The rods 1, spacers 2 and retaining means 4 of the present invention are comprised of a high strength, high-temperature resistant material. The materials used for the apparatuses should be able to withstand at least the same temperatures as the reactor tubes being stabilized. Preferred materials include the nickel alloys used to construct conventional reactor lines, ceramics or ODS materials, or any combination thereof. Especially preferred materials for the rods and spacers are ceramics or ODS, or a combination thereof. The use of ceramics or oxide dispersion strengthened materials is preferred for their ability to resist carburization at the high temperatures in the furnace. Where pins are used as the retaining means, an especially preferred material for their construction is ODS alloy wire.
The ceramic materials useful in the process of the present invention for constructing the spacers and the rods are any of the known ceramic materials that can be fashioned into the desired shape and include, but are not limited to, silicon-carbide materials such as a direct sintered silicon-carbide (typically abbreviated DSSiC, DSSC, alpha and beta bond phases). Examples of DSSiC materials include, but are not limited to, those sold under the trade name, Hexoloy SA by Saint-Gobain, Advanced Ceramics (formerly Carborundum) and under the trade name Halsic-S by W. Haldenwanger Technische Keramik GmbH & Co. KG. Further, the spacers and/or rods may be constructed of a wide variety of other SiC-based ceramic materials including, by way of example, materials taken from the group consisting of alpha silicon carbide, reaction bonded silicon carbide, silicon nitride, alumina, alumina/silicon carbide composites and composites based on silicon carbide. In addition, other useful ceramic materials may present themselves to those skilled in the art. See, for example, Jones, Divakar et al., U.S. Pat. No. 5,589,428, Tenhover et al., U.S. Pat. No. 5,616,426; Divakar et al., U.S. Pat. No. 5,635,430; Eiermann, U.S. Pat. No. 5,813,845. Other families of ceramic materials useful in the preparing the apparatuses of the present invention can be found at the web site having the URL address of http://www.scprobond.com/tech_corner.asp, wherein an excerpt of Metzger et al., “Understanding Silicon Carbide Types—Having the Right Tool for the Job” from the February 2000 issue of World Coal Magazine is reprinted.
Another useful material for constructing apparatuses in accordance with the present invention is what is commonly known as ODS materials. An exemplary ODS material useful in the practice of the present invention is a rare earth oxide dispersion strengthened ferrous alloy sold under the trade name Super Alloy Incoloy® MA956 by Specialty Metals Corporation; a virtually equivalent material is sold under the trade name PM 2000 by Plansee. However, the apparatuses may be constructed of a wide variety of other useful ODS materials including, by way of example, a rare earth oxide dispersion strengthened ferrous alloy which contains from about 17% to about 26% of Cr by weight and about 2% to about 6% of Al by weight.
Other useful ODS materials for constructing apparatuses in accordance with the present invention may suggest themselves to those skilled in the art in light of the present description. Non-limiting descriptions of ODS materials useful in the practice of the present invention can be found in an article by I. G. Wright, C. G. McKamey, B. A. Pint and P. J. Maziasz, of Oak Ridge National Laboratory, entitled “ODS Alloys for High-Temperature Applications;” in Yamamoto et al., European Patent Application No. EP 1 018 563 A1; and in the paper by Tassen et al., entitled “High Temperature Service Experience and Corrosion Resistance for Mechanically Alloyed ODS Alloys,” Heat-Resistant Materials, Proceedings of the First International Conference, Fontana, Wis., 23-26 Sep. 1991.
With regard to the systems of using the apparatuses to stabilize the movement of the reactor furnace tubes, reference is first had to
With reference to
Although the systems and apparatuses of the present invention have been described in certain preferred embodiments, all variations obvious to one skilled in the art are intended to fall within the spirit and scope of the invention, including the appended claims. For example, the number, shape, size and configuration of the rods, spacers, retaining attachment means and/or retaining means could be varied in numerous ways that may present themselves to those skilled in the art. Such variations are within the full-intended scope of the present invention. All of the above-referenced patents, patent applications and publications are hereby incorporated by reference in their entirety.
