JPS6049605B2 - Double pipe for high temperature pyrolysis of hydrocarbon-containing materials - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to the provision of a double pipe for a reactor used for thermal decomposition and reforming of hydrocarbons.

When liquid or gaseous hydrocarbons are subjected to a chemical reaction of thermal decomposition or reforming using a catalyst at high temperature and high pressure, precipitation of solid carbon occurs, and this precipitated solid carbon is absorbed into the reactor. It is known that these substances accumulate on the side of the tubes that undergo chemical reactions (the inner side will be explained as an example).

If this solid carbon precipitation is left unattended, it will obstruct the flow of fluid containing hydrocarbons, and at the same time, it will be necessary to supply reaction heat from the outer surface of the tube to carry out the chemical reaction of thermal decomposition or reforming. When removed, the overall heat transfer coefficient decreases significantly, creating a problem that makes it difficult to continue operating the reactor.
The materials conventionally used for this type of reactor are the so-called Fe-Cr-Ni system, which is common as a material for high-temperature equipment and contains a large amount of -Ni)Cr in order to adapt to the high temperature and high pressure operating conditions. It is an austenitic heat-resistant steel,
In particular, as the operating conditions become higher, the amount of N in the heat-resistant steel for pipes increases.
It was customary to increase the amount of i. However,
When this Fe-Cr-Ni austenitic heat-resistant steel is used, solid carbon deposits inevitably adhere to the inner surface of the tube, and as a result, reactors that are designed for continuous operation cannot be used for a period of time. The plant has no choice but to stop its operation and periodically carry out work to remove this precipitated carbon (so-called decoking) using various methods.

It is known that this tendency becomes more pronounced as the steel contains more Ni, and in that case, solid carbon precipitates on the inner surface of the tube in a short period of time, and the amount of solid carbon deposited increases even more rapidly. , there was a problem that the frequency with which the above-mentioned removal work was required further increased. As a result of intensive research and consideration regarding this solid carbon precipitation phenomenon, the present inventor found that the Ni content in the Fe-Cr-Ni austenitic heat-resistant steel material constituting the reactor tube and the amount of solid carbon precipitated are They discovered that there is a correlation between the Ivy. Based on such technical considerations, in order to prevent the precipitation and adhesion of solid carbon when using this type of reactor tube, it is necessary to coat the inner surface of the tube, which comes into contact with hydrocarbon-containing materials, with a Ni-free or Ni-containing material. It is known that an effective countermeasure can be to coat the Fe-Cr-Ni heat-resistant steel material that makes up the reactor tube body with a different type of heat-resistant material with a lower content to prevent it from coming into contact with hydrocarbons. It is being

That is, for this type of reactor application, Fe-Cr-Nj type austenitic heat-resistant steel is used as the constituent material of the tube body, and the inner surface that comes into contact with hydrocarbons is made of Fe-Cr-Ni type steel that does not contain N1. It can be said that it is suitable to use a double pipe coated with a different type of material such as. The easiest way to meet this purpose would be to use a double-walled pipe made by centrifugal casting. However, in the case of centrifugal cast products, there are problems in the weldability of the inner and outer layers and non-uniformity of welding in the longitudinal direction, and there is also a high risk of defects such as slags at the joints. It is. In addition, when using the centrifugal force casting method, if we try to ensure weldability, welding tends to be excessive on the inner surface of the outer layer.As a result, when the heat-resistant steel mentioned above is used for the outer layer, its original characteristics change. There is a great risk of doing so. Furthermore, when casting the inner layer, consideration must be given to the welding with the outer layer and its castability. In the case of casting, a casting defect occurs on the innermost surface of the inner layer, and this portion must be removed by turning, which is a disadvantage in terms of yield and cost. In view of these problems, the present invention provides a tube (so-called cracking tube, reflow march tube) used for high-temperature pyrolysis and reforming of hydrocarbon-containing materials, in place of the centrifugally cast double tube, To provide a double-walled pipe having a new configuration that guarantees uniformity and integration of the inner and outer layers, allows the outer layer or inner layer to be made thinner, and can be manufactured at a high yield and at low cost. It is a thing and its characteristics. In this process, a raw tube made of Fe-Cr-Ni austenitic heat-resistant steel and a thin-walled raw tube made of Fe-Cr steel are concentrically polymerized by inserting one tube into the inner tube and the other outer tube. (in some cases, the former is an outer layer tube and the latter is an inner layer tube, and in some cases, the former is an inner layer tube and the latter is an outer layer tube), and a metal with excellent thermal conductivity and easy plastic processing is used between the two. The main feature is that it is integrated by pressure bonding with powder or metal foil interposed therebetween.

The double pipe of the present invention will be explained below along with its manufacturing method.

Therefore, first, a base pipe 1 made of Fe-Cr-Ni austenitic heat-resistant steel as shown in Fig. 1 is used as an outer layer pipe, and F
An example of a double-walled tube constructed by integrally bonding the thin-walled tube 2 made of e-Cr-Ni steel as an inner layer tube will be described below. In order to obtain such a double pipe,
First, a raw tube 1 of Fe-Cr-Ni austenitic heat-resistant steel is formed into a predetermined shape and dimensions, and a thin-walled tube 1 of Fe-Cr steel
Prepare the base tube 2.

In this case, it is preferable to use a normal centrifugally cast steel pipe with an inner surface machined finish for the base pipe 1, while for the thin wall base pipe 2, for example, a drawn pipe of 18Cr128Cr steel with a finished inner surface. It is suitable for use. As shown in FIG. 2, the inner surface of the raw tube 1 has Cu
A mixture of one or more metal powders 3 with excellent thermal conductivity and easy plastic deformation such as metal powder or AI powder is coated, and the thin-walled blank tube 2 is inserted into the inner surface of the coating. As shown in FIG. 3, the thin-walled blank tube 2 is concentrically superimposed within the blank tube 1 with the metal powder 3 interposed therebetween.

Although the above example describes the use of metal powder 3, metal foil may be used instead of metal powder as long as it has excellent thermal conductivity and is easily plastically deformable. It's working. Further, the metal powder (or the metal foil) 3 is
As shown in FIG. 3, it is only necessary to interpose the material tube 1 and the thin-walled material tube 2 in a concentrically superimposed state, and therefore, the inner surface of the material tube 1 is coated in advance as shown in FIG. In addition to this, it is also possible to coat (or wrap) the outer surface of the thin-walled tube 2 to be inserted. As mentioned above, the thin-walled raw tube 2 is concentrically superposed inside the raw tube 1 with the metal powder (or metal foil) 3 interposed therein, and the thin-walled raw tube that forms the inner layer tube is produced by plug drawing processing, explosive pressure welding, etc. 2 is expanded and integrated with the base tube 1 via metal powder (or metal foil) 3 by pressure bonding. FIG. 4 shows an example of plug drawing processing, in which a plug 4 is inserted and held 5 at one end of the polymerized raw pipe, and the other end is fastened to a chuck 8 and pulled in the direction of the arrow in the figure. The pipes are then expanded by the plug 4 and crimped and integrated. At this time, the plug 4 is
It is preferable to use rollers 7, 7 to hold and regulate the outer surface of the raw tube 1, which corresponds to the tube expansion position. Thus, as shown in FIG. 1, a raw tube 1 made of Fe-Cr-Ni type austenitic heat-resistant steel is used as an outer layer tube, a thin-walled raw tube 2 made of Fe-Cr-Nj type steel is used as an inner layer tube, and metal powder (or metal foil) is used. A double tube is obtained in which the two are crimped and integrated via 3.

Here, to explain the constituent material of the double tube, Fe-C is used as the outer layer tube that makes up the main wall thickness of the double tube.
Specifically, the r-Ni-based austenitic heat-resistant steel includes Cr2O to 30%, Nil 5 to 40%, CO. 2~
0.6%, Si2.5% or less, Mn2.5% or less, NO
．． 3% or less (each % by weight), the remainder being substantially Fe or a part of Fe in MO. ．． W,. One or two of Nb
Examples of Fe-Cr-N1-based steels used as inner layer tubes that coat the inner surface of double-layered tubes include alloys substituted with 18Cr-type or more (total amount of 8% by weight or less). Examples include Cr-based stainless steels that do not contain Ni, such as 28Cr-based stainless steels, and in particular those with a low C content (less than CO.1%, preferably less than 0.01%) from the viewpoint of plastic workability. is selected.

That is, the former is selected from the viewpoint of heat resistance suitable for the operating conditions of the reactor tube, while the latter is selected because it does not contain Ni to prevent solid carbon precipitation and is easy to plastically work. Therefore, these do not preclude variations in the above-mentioned component ranges, etc., as long as the technical purpose of the present invention is not changed. In addition, the base pipe 1 constituting the outer layer pipe
The metal powder or metal foil (3) interposed between the thin-walled tube 2 constituting the inner layer tube contributes to the crimp integration of the outer and inner layer tubes as will be described later, and also improves the heat transfer properties of the outer and inner layer tubes. From this point of view, it is necessary to have particularly excellent thermal conductivity and easy plastic working.

In the case of a double pipe with such a configuration, the inner surface is covered with a thin-walled raw pipe 2 made of Fe-Cr steel that does not contain N1, so during operation, it is protected from fluids containing hydrocarbons. The precipitation phenomenon of solid carbon can be reliably suppressed.

In addition, the thin-walled tube 2 that forms the inner layer is made of Fe-C, which has excellent malleability.
Since it is made of R-series steel, when it is expanded and brought into close contact with the base pipe 1 that forms the outer layer pipe by plug-pulling processing, etc.
The wall thickness has been made even thinner (A). (can be changed arbitrarily within the range of about 1 to 5 gourds), thereby maintaining almost the same design state as conventional single-layer pipes (in contrast, When using a centrifugally cast double-walled tube, the thickness of the inner layer must be increased, so in order to ensure the reaction rate, the operating temperature must be increased in accordance with the increase in wall thickness. It will also be necessary to change the heat-resistant steel to a higher-grade material.) In addition, when directly crimping the raw pipe 1 forming the outer layer pipe and the thin-walled raw pipe 2 forming the inner layer pipe, it is difficult to reach a metallurgical adhesion (welding) state with the processing degree of normal plug pipe expansion processing. However, in the case where metal powder (or metal foil) 3 is interposed as described above, this may be compressed between the two after the tube expansion process. The raw pipe 1 and the thin-walled raw pipe 2 are completely crimped and integrated via the compressed metal powder (or metal foil) 3.

If a low melting point metal such as Cr or A1 is used for the metal powder (or metal foil) 3, the raw tube 1 can be The thin-walled tube 2 can be substantially metallurgically integrated using the metal powder (or metal foil) 3 as a medium. Moreover, the metal powder (or metal foil) 3 has excellent thermal conductivity, and in addition, the thin-walled tube 2 forming the inner layer tube can be formed with an extremely thin wall.
In the end, it is possible to maintain the same overall heat transfer coefficient as in the case of a single-layer pipe (therefore, there is no need to change the design in this respect either, and the problem of "high-grade heat-resistant steel for the outer layer pipe and increase in operating temperature" can be avoided. ).Next, as shown in Fig. 5, Fe-Cr-N
An example of a double-walled pipe constructed by integrally crimping a raw pipe 1 made of i-type austenitic heat-resistant steel as an inner layer pipe and a thin-walled raw pipe 2 made of Fe-Cr type steel as an outer layer tube will be described.

Due to today's deteriorating trend in petroleum fuel, the demand for such applications will continue to expand in the future for those whose outer surfaces are coated with Fe-Cr steel, that is, double pipes that prevent the precipitation of solid carbon on the outer surface. It is expected that To obtain such a double-walled pipe, first coat or wrap metal powder or metal foil 3 on the outer surface of the raw pipe 1 as shown in Fig. 6, and fit the thin-walled raw pipe 2 therein (or 1 into the thin-walled blank tube 2), and as shown in FIG. 7, the blank tube 1 is concentrically overlapped within the thin-walled blank tube 2 with metal powder or metal foil 3 interposed therebetween.

Then, as shown in FIG. 8, this polymerized raw pipe is subjected to tube shrinking using dies 8, 8 or rolls, as shown in FIG. 8, to obtain the desired double-walled pipe shown in FIG. The double pipe thus obtained has substantially the same effect as the double pipe example described above, which has a completely opposite configuration.

As described above, in the double pipe of the present invention, the required inner or outer surface of the base pipe made of Fe-Cr-Nl austenitic heat-resistant steel, which constitutes the main part of the pipe wall thickness, has thermal conductivity. Because it is made by crimp-bonding a thin-walled Fe-Cr steel tube with a metal powder or metal foil that has excellent properties and is easy to plastically process, the inner or outer surface of the tube can be adjusted based on the coating of the thin-walled tube. The precipitation phenomenon of solid carbon is reliably prevented.

Further, in the double pipe according to the present invention, the thickness of the thin-walled pipe to be coated and crimped can be made extremely thin, and the integrity and uniformity of the pipe can be improved by interposing the metal powder or metal foil. Since it is possible to ensure the This has the advantage that design conditions similar to those of conventional single-layer pipes can be secured due to good adhesion and good thermal conductivity of the inclusions.

Therefore, the double tube according to the present invention can be used as a reactor tube for high-temperature thermal decomposition and reforming of hydrocarbon-containing materials, instead of the conventional Fe-
This is an excellent alternative to Cr-Ni single layer tubes or centrifugally cast double tubes.

[Brief explanation of drawings]

FIG. 1 is a sectional view showing an embodiment of a double pipe according to the present invention, and FIGS. 2, 3, and 4 are sectional views showing the manufacturing process thereof. FIG. 5 is a sectional view showing another embodiment of the double pipe according to the present invention, and FIGS. 6, 7, and 8 are sectional views showing the manufacturing process thereof. 1...Main tube made of Fe-Cr-Ni austenitic heat-resistant steel, 2...Fe-
Thin-walled tube made of Cr-based steel, 3...Metal powder or metal foil, 4...Plug, 5...
Holding rod, 6...Chucking, 7...
Roller, 8...Dice.

Claims (1)

[Claims] 1 A raw tube made of Fe-Cr-Ni austenitic heat-resistant steel and a thin-walled raw tube made of Fe-Cr steel are concentrically overlapped by inserting one as an inner layer tube into the other outer layer tube, and A double pipe for high-temperature pyrolysis of hydrocarbon-containing materials, characterized in that the two are integrally crimped with a metal powder or metal foil having excellent thermal conductivity and easy plastic processing interposed therebetween.