JPS58109589A - Reaction tube for thermal cracking/reforming of hydrocarbon - Google Patents

Abstract

PURPOSE:To prevent separated solid carbon from depositing on the surface of a reaction tube and to give excellent high-temp. characteristics, by forming the inner layer of the tube wall from Fe/Cr-base heat-resistant steel, etc. and the outer layer from high-Ni Fe/Cr/Ni-base heat-resistant steel. CONSTITUTION:The inner layer of a tube wall is formed from Fe/Cr-base heat- resistant steel composed of 0.01-1.5wt% C, not more than 2.5wt% Si, not more than 2wt% Mn, 13-30wt% Cr, not more than 0.15wt% N and the balance of Fe, or of Fe partially replaced by not more than 5wt% Mo, W, Nb, etc., or of Fe/Cr/Ni-base heat-resistant steel contg. not more than 10wt% Ni, and the outer layer is formed from Fe/Cr/Ni-base heat-resistant steel composed of 0.1- 0.6wt% C, not more than 2.5wt% Si, not more than 2wt% Mn, 20-30wt% Cr, 18-40wt% Ni, not more than 0.15wt% N and the balance of Fe, or of Fe partially replaced by not more than 5wt% Mo, W, Nb, etc., to form the titled reaction tube.

Description

DETAILED DESCRIPTION OF THE INVENTION This invention [is a reaction tube used in a thermal decomposition e-reforming reaction of hydrocarbons, in particular, a reaction tube in which precipitated solid carbon accompanying a chemical reaction of hydrocarbons is deposited on the surface of the reaction tube. (=Regarding a reaction tube that can prevent J deposition accumulation.

The reactor for thermal decomposition and reforming of hydrocarbons is tubular, and liquid or gaseous hydrocarbons are passed through the tube at high temperature and under pressure, and a catalyst layer is or is not allowed to exist. The material for the reaction tube constituting the reactor E3 is Fe-C, which contains a large amount of Nl and Cr and is commonly used as a material for high-temperature equipment.
r-Ni-based austenitic high-temperature steel is used, and as the operating conditions become higher in temperature, it is common to use steel with a further increased N1 content.

This thermal decomposition and reforming reaction of hydrocarbons is accompanied by the precipitation phenomenon of solid carbon, but these reactions can be carried out using the Fe-Cr-Ni austenitic type 1 secondary heating steel reaction tube described above.
If this is continued, the inner wall i1 of the reaction tube (the surface against which chemical reaction 9 occurs). In this case, the above-mentioned precipitated solid carbon inevitably accumulates.If this solid carbon precipitate is left unattended, it will only obstruct the flow of the fluid containing hydrocarbons in the pipe. This results in a significantly low F of the l+ coefficient, making it difficult to continue operating the reactor.1 For this reason, long-term continuous operation is difficult. The reactor unit, which is in trouble with Kim, has also temporarily suspended operations and removed carbon deposits using six different methods.
It is necessary to periodically carry out so-called decoking.

In the past, in response to the above-mentioned problems, we continued intensive research on the precipitation phenomenon of solid carbon in Takemuro surface. The reason for this significant deposition is that the Ni contained in the pipe acts as a 'S melting medium on the pipe surface that promotes carbon precipitation from the hydrocarbons in contact with it, and solid carbon There is a certain correlation between the precipitation of carbon and the Ni content in the control phase, and by reducing the Ni content of The knowledge of the city.

This invention was completed on the basis of twofold knowledge, and when the reaction zone is used as a reaction zone, the inner wall surface (inner layer) in contact with the hydrocarbons of the reaction tube )
is Fe-Cr which does not contain Ni. The inner layer is made of high-temperature equipment paulownia material, such as Fe-Cr, which is a conventional pipe material.
- Provides a reaction tube coated with a laminated outer layer made of Ni-based austenitic heat-resistant steel, and by having such a double laminated structure, it can be used in high areas and under pressure in fields. While maintaining the necessary characteristics as a reaction tube, we have successfully suppressed and prevented the precipitation of solid carbon accompanying the reaction and ensured stable operation over a long period of time without the need for decoking.

This invention will be explained in detail below.

The reaction tube of this invention has an inner layer in contact with hydrocarbons, an F
e-Cr type ferritic or martensitic heat-resistant steel, or Ni content of approximately 10% or less (DFe-C
It is made of r-Ni ferrite, ferrite-austenite type or martensitic type heat resistant steel.

As a specific example of the above Fe-Cr heat-resistant steel, Cr
13-30% (weight %, same hereinafter), CO, 01% or more, less than 1.5%, Si 2.5% or less, Mn 2.0% or less, NO, 15% or less, the balance consisting of Fe, or In order to further improve the material properties, a portion of Fe was
．． MoXW in the range of 0% or less.

Examples include those substituted with one or more elements selected from Nb. It should be noted that as the C content of the inner layer alloy that comes into contact with hydrocarbons increases, the amount of carbon deposited on its surface tends to increase. The outer layer alloy material deteriorates due to the diffusion of carbon into the outer layer. In order to avoid these disadvantages, it is advantageous for the inner layer alloy to have a lower C content. Therefore, in this invention, the C content of the inner layer alloy is set to less than 1.5%.

When forming the tube inner layer using a Fe-Cr-Ni heat-resistant steel containing Ni instead of the Fe-Cr heat-resistant steel described above, specifically, part of the Fe in the Fe-Cr steel composition is A material having a component composition in which Ni is substituted with Ni may be used, but the Ni content needs to be within a range of about 10% or less.

FIG. 1 shows Fe-Cr-Ni heat-resistant steel (Cr 18%).

C008%, Si1.5%, Mn1.1%, NO,05
%.

The amount of solid carbon deposited (Mf
/crV) and Ni content (%). (Experimental conditions: Ecun supply N400 cc/min, s/c
1.5, temperature 900°C).

As shown in the figure, the amount of precipitation increases as the Ni content of the arm material increases. By the way, the Ni content of the Fe-Cr-Ni heat-resistant steel conventionally used as reactive bone phase PI is 35%, and significant accumulation of solid carbon can be avoided.
This corresponds to the fact that there was no such thing. This is because, as described above, Ni on the surface of the tube wall exhibits a catalytic effect on the precipitation of solid carbon.

In this invention, in order to suppress and prevent solid carbon precipitation as much as possible,
The upper limit of N1 content I: is set to about 10.0%, more preferably about 5.0% or less.

Regarding the Fe-Cr system and Fe-Cr-Ni system mentioned above, it is important to note that the chemical composition of the hot steel must be determined by taking into account the properties necessary for use in hydrocarbon chemical reactors. However, the above component composition is an example, and as long as the purpose of the present invention is not lost, the amount of each component element may be slightly increased or decreased beyond the above composition range, or small amounts of other component elements may be added or deleted, etc. as appropriate. Purification/alteration is equally useful.

The reaction tube of the present invention has an inner layer made of the above-mentioned Fe-Cr type heat-resistant steel or Fe-Cr-Ni type heat-resistant steel with 10.0% or less Ni.
-It has a double laminated structure coated with Cr-Ni type iJ heat steel. This outer layer is formed by the following heat steel:
Fe-Cr is conventionally used as a pipe material for this purpose.
-Ni-based austenitic heat-resistant steel can be used. Specific examples include Cr2O~30%, Ni1
8-40%, C0.1-0.6%, Si2.5% or less,
Mo in a steel composition in which Mn is 2.0% or less, NO is 15% or less, and the balance is Fe, or a part of Fe is 5.0% or less.

Examples include steel compositions crystallized with one or more elements selected from W and Nb. Of course, as long as the purpose of the present invention is not lost, various component compositions in which the amount of each element is slightly increased or decreased, new additions or deletions are made are similarly useful.

By making such a double laminated tube, the precipitation of solid carbon on the inner wall surface of the reaction tube is effectively suppressed, and at the same time, the Fe=Cr-Ni austenitic structure of the outer layer is suppressed. The added mechanical properties of hot steel, such as high temperature strength and high temperature creep rupture strength, make it even more preferable for reactions and compatibility when used at high temperatures and high pressures.

1. The reaction tube of the present invention having a double-layered structure is preferably manufactured by a centrifugal casting method. In order to cast a reaction tube by centrifugal force casting using heat-resistant steels having the above chemical components as alloys for the inner layer and outer layer, first, the alloy for the outer layer (Fe-Cr-Ni of high Ni content) is used. Immediately after injecting the molten metal of the inner layer alloy (F-based heat-resistant steel) to form an outer layer with a desired thickness and solidifying up to the inner wall surface, the inner layer alloy (F
e-Cr system or Fe-Cr with NilOlO% or less
- It is sufficient to form an inner layer of a desired thickness by casting a molten metal of Ni-based heat-resistant steel), thereby obtaining a double-laminated pipe in which the inner and outer layers are metallurgically joined together at the boundary ( In this case, the composition of each layer alloy (principally, it is preferable to use a mixture of C and J within the specified range) so that the inner layer alloy has a lower melting point than the outer layer alloy.
. There are no particular restrictions on the casting conditions of the pond; for example, the molten metal casting temperature of each layer may be adjusted to a temperature higher than the melting point of each layer, for example, by about 150°C, as is the case with conventional methods. A suitable slagging agent may be administered in a conventional manner to protect the inner surface of the outer layer from air oxidation.

In order for the double-laminated tube obtained by centrifugal casting to fully demonstrate its characteristics, it is essential that the alloys in each layer do not mix with each other during casting and that a predetermined layer thickness is ensured. Furthermore, each layer is metallurgically completely adhered and strongly bonded at the boundary, and the fused layer at the boundary has a strong bond ((minimum thickness required). From this point of view, in conventional centrifugal casting of double-layered pipes, if the inner layer alloy is injected after solidifying up to the inner surface of the outer layer, fusion at the boundary between the two layers can be prevented. Due to concerns that the inner layer may be insufficient, it is common practice to cast the inner layer while the inner surface is in an unsolidified state.In that case, the adhesion between both layers is sufficient, but on the other hand, the adhesion between the two layers is There is a drawback that the molten metal mixes excessively, and it is difficult to form a good double-layer structure.However, in the centrifugal casting double-layer structure of the present invention, the inner layer is cast after the inner surface of the outer layer is solidified. Nevertheless, the adhesion between both layers is excellent.The reason for this is that if the melting point of the inner layer alloy is lower than that of the outer layer alloy, the inner layer molten metal in contact with the solidified inner surface of the outer layer will solidify immediately. This is because it is possible to form an appropriately thick fusion layer on the interface.Moreover, in that case, the outer layer is unnecessarily SI [iIf between the two layers because it does not melt] of the alloy. No mixing occurs, and the double fusion layer thickness remains at the minimum necessary to obtain a strong bond, forming an ideal double laminate structure.

The double laminated structure can be formed by using a method similar to 1.1, for example, by using a combination of casting and thermal spraying to produce a cast pipe made of a predetermined alloy, and then coating the surface with the predetermined alloy by thermal spraying. However, if you use the centrifugal casting method,
As mentioned above, not only can the bonding between both layers be reliably obtained, but also the layer thickness of each layer can be arbitrarily controlled to be thick or thin as desired.
There is also the advantage that the chemical composition of the alloy used can be freely selected depending on the desired paulownia wood characteristics.

To give an example of a reaction tube having a double-layered structure formed by centrifugal casting, in a high-frequency induction melting furnace, Fe-Cr-Ni thread surface/j hot steel molten metal (C0,4
5%, Si1.2%, Mn1.1%, Cr26.5%,
Ni35.5%, NO, 06%, balance Fe), Fe-Cr series alloy as the splintered inner layer alloy] hot steel molten metal (C1,2%)
, Si 1.2%, Mn 1.0%, Cr 18.5%, balance Fe) were melted, and 35 kg of molten alloy for the old model outer layer was cast by centrifugal force casting, and the outer diameter was 134 mm.
Immediately after forming an outer layer with a thickness of 25 mm and a length of 500 mm, and solidifying the inner surface, 1 oka of molten alloy for the inner layer was formed.
A reaction tube was obtained which consisted of two concentric layers in which there was no mixing of the inner and outer layer alloys and both layers were metallurgically bonded together by forming an inner layer with a wall thickness of 10 mm.

Furthermore, to give another example, Fe-Cr having a chemical composition similar to that of the above example is used as an alloy for the outer layer.
-Ni-based molten steel (C0.43%, Si1.3%, M
n 1°1%, Cr26.0%, Ni35.8%, N
O, 04%, balance Fe) 35kg, and the inner layer alloy is Fe-10.0% or less Ni.
Cr-Ni type extremely hot steel molten metal (C0.8%, Si1.2%,
Mn1.1%, Cr24.5%, Ni7.5%, balance F
e) Mixing of the inner and outer layer alloys by using lOkq and forming an outer layer with the same dimensions as in the previous example using centrifugal force a, and casting the inner layer immediately after the inner surface has solidified. A reaction tube was obtained in which both layers were metallurgically bonded together.

In addition, in the double explanation, we took as an example a reaction tube used under conditions where the inner wall surface of the reaction tube comes into contact with hydrocarbons, but a reaction tube where the outer wall surface of the reaction tube comes into contact with hydrocarbons is used as an example. In the case of pipes, contrary to the above example, the outer layer is made of Fe-Cr or N
Fe-Cr-Ni system metathermal heat of less than i1O, 0% (ifl
Needless to say, if the inner and outer surfaces of the pipe are to be used in contact with hydrocarbons, the above copper phase should be used for the outer and inner layers. At the same time, a triple laminated structure in which conventional Fe-Cr-Ni austenitic high-temperature steel is interposed in the middle gate of both layers is suitable.

In either case, it can be manufactured by centrifugal casting.

As described above, in the reaction tube of the present invention, the surface in contact with hydrocarbons is made of Fe-Cr type heat-resistant steel or Fe-Cr-Ni type heat-resistant steel with a limited amount of Ni. Precipitation and deposition of solid carbon accompanying chemical reactions of hydrocarbons can be effectively suppressed and prevented. Moreover, this Fe-
Because it is reinforced by a Cr-based or Fe-Cr-Ni-based heat-resistant layer, or a layer of Cr-Ni-based heat-resistant steel with unbonded high Ni content, it can withstand high temperatures of over 500°C. , has high-temperature properties that can withstand use under pressures higher than atmospheric pressure.

Therefore, the reaction tube of the present invention is suitable for thermal decomposition into low molecular weight carbides, etc., which is carried out by mixing hydrocarbons with water vapor, oxygen-containing gas, etc. under double high temperatures and high pressures, or When used to produce a gaseous mixture containing hydrogen, carbon oxide, etc., precipitation and deposition of solid carbon can be suppressed and stable operations can be maintained over a long period of time.

[Brief explanation of drawings]

FIG. 1 is a graph showing the relationship between the Ni content of the reaction tube material and the amount of solid carbon deposited on the tube surface. Agent: Patent Attorney Shinhebe Miyazaki (111A) Continuing from page 1 - Inventor Junichi Sugitani 1-2-1 Nakamiya Oike, Hirakata City Kubota Ironworks Co., Ltd. Hirakata Cast Steel Inside the factory [stock] / Inventor Takeshi Torigoe 1-2-1 Nakamiya Oike, Hirakata-shi Kubota Iron Works Co., Ltd. Hirakata Casting Steel Factory Applicant Kubota Iron Works Co., Ltd. 2-47 Shikitsu Higashi-chome, Naniwa-ku, Osaka City

Claims (2)

[Claims] (1) The inner layer of the tube wall, C00O1~1.5% (wt%)
, hereinafter the same), Si 2.5% or less, Mn 2.0% or less,
One or more elements selected from Mo, W, and Nb in a composition range of 13 to 30% Cr, 15% or less NO, and the balance is Fe or a part of Fe is 5.0% or less Fe-Cr ferritic type or martensitic type one-body thermal steel substituted with or C0,0
1 to 1.5%, Si 2.5% or less, Mn 2.0% or less,
Cr 13-30%, Ni 10.0% or less, NO, 15
% or less, and the remainder is Fe, or a part of Fe is Mo, W, and N in a range of 5.0% or less.
Fe'-Cr-Ni-based ferrite substituted with one or more elements selected from b, 7-elite-
It is made of austenitic or martensitic heat-resistant steel, and the outer layer of the tube wall contains CO, 1 to 0.6%, Si25
% or less, Mn 2.0% or less, Cr 20-30%, Ni
1. A tube for thermal decomposition and reforming reactions of hydrocarbons, characterized in that it is made of Fe-Cr-Ni austenitic type surface/j-heat steel substituted with one or more elements selected from Nb and Nb. (2) A tube for pyrolysis/reforming reaction of hydrocarbons according to claim (1), wherein the outer layer and the inner layer of the tube wall are formed by centrifugal casting.