JP5630987B2 - Carburizing gas supply device - Google Patents

Description

  The present invention relates to a carburizing gas supply device for supplying a carburizing gas containing carbon monoxide gas to a carburizing furnace for carburizing a processing material such as a steel material part, and in particular, heating a raw material gas containing a hydrocarbon gas. When the carburizing gas containing the carbon monoxide gas obtained by conducting the catalytic reaction of this raw material gas is supplied to the carburizing furnace, the carburizing gas is generated. This is characterized in that the soot generated in the catalyst layer is appropriately removed while maintaining the amount, and the carburizing gas can be stably supplied to the carburizing furnace.

  Conventionally, in order to increase the strength of steel parts such as low carbon steel and low alloy steel, carburizing treatment for diffusing and penetrating carbon from the surface to the inside has been performed.

  And in carburizing treatment materials such as steel parts in this way, various methods are used. For example, as shown in FIG. 1, the treatment material 1 is introduced into the carburizing treatment furnace 2, A heating process in which a carburizing gas containing carbon monoxide gas is supplied from the carburizing gas supply apparatus 3 into the carburizing furnace 2 and the treatment material 1 is heated in the carburizing furnace 2, and the treatment thus heated A carburizing step of imparting carbon to the material 1 and carburizing, a diffusion step of diffusing the carbon imparted to the treatment material 1 in this way so that the surface carbon concentration becomes a required value, and this Thus, carburizing treatment of the processing material 1 is performed through the temperature-falling process which lowers the temperature of the processing material 1 in which carbon was diffused inside.

  Here, as the carburizing gas supply device 3 for supplying the carburizing gas containing carbon monoxide gas to the carburizing treatment furnace 2 as described above, generally, a Ni catalyst, Rh, Pt or the like is provided in the heat-resistant reaction cylinder 3a. A catalyst layer 3b containing a noble metal catalyst such as the like is provided, and an exterior body 3c using a heat insulating material is provided on the outer peripheral side of the reaction cylinder 3a, and an electric heater is provided between the exterior body 3c and the reaction cylinder 3a. A heating means 3d is provided, and the catalyst layer 3b is heated by the heating means 3d.

  In the conventional carburizing gas supply apparatus 3, generally, a hydrocarbon gas such as LNG or LPG and air are used as the source gas, and the hydrocarbon gas guided by the first source gas supply pipe 3e, The air guided by the raw material gas supply pipe 3f is mixed by the gas mixer 3g, and the mixed raw material gas is introduced into the reaction cylinder 3a through the raw material gas supply pipe 3h.

  Then, this raw material gas is reacted with the catalyst through the catalyst layer 3b heated as described above to generate a carburizing gas containing carbon monoxide, and the carburizing gas thus generated is used for carburizing. The gas is supplied into the carburizing furnace 2 through the gas supply pipe 3i.

  Here, when the raw material gas is reacted with the catalyst through the heated catalyst layer 3b as described above to generate a carburizing gas containing carbon monoxide, the raw material gas is reduced in temperature when the temperature of the catalyst layer 3b decreases. There was a problem that the gas reaction was not sufficiently performed, soot was generated, and the soot was clogged in the catalyst layer 3b, and the carburizing gas could not be produced stably.

  Further, conventionally, the carbon monoxide gas concentration in the carburizing gas is increased to about 40 to 57% by volume, the carburizing rate for the processing material 1 is increased, and the processing time is shortened. It has been studied to obtain a carburizing gas in which the concentration of carbon monoxide gas is increased by using an oxidizing gas such as carbon dioxide gas or oxygen gas instead of air.

  However, when generating a carburizing gas containing carbon monoxide gas at a high concentration using a raw material gas that uses carbon dioxide gas instead of air as described above, the reaction between hydrocarbon gas and carbon dioxide gas Since it is an endothermic reaction, the catalyst layer 3b is not sufficiently heated only by heating with the heating means 3d provided on the outer peripheral side as described above, and the temperature in the catalyst layer 3b is lowered and the raw material gas is heated. There was a problem that the reaction was not sufficiently performed, soot was more likely to be generated in the catalyst layer 3b, and the carburizing gas could not be produced stably.

  For this reason, in recent years, a raw material gas obtained by mixing hydrocarbon gas, carbon dioxide gas, and oxygen gas outside the explosive gas mixture range (for example, see Patent Document 1), or hydrocarbon gas is used. When introducing a raw material gas mixed with carbon dioxide gas and oxygen into the nickel catalyst layer and reacting it, oxygen gas is introduced in the middle of the nickel catalyst layer to use an exothermic reaction (for example, Patent Document 2), and a catalyst layer having a double tube to increase heating efficiency (for example, refer to Patent Document 3) have been proposed.

  However, even in the case as described above, the carburizing gas having a high concentration of carbon monoxide gas due to the generation and deposition of soot still cannot be stably produced, and after a short operation, There was a problem that had to be stopped.

JP 2000-256824 A JP 2001-152313 A JP 2005-290509 A

  The present invention provides a carburizing gas supply apparatus for supplying a carburizing gas containing carbon monoxide gas, particularly high-concentration carbon monoxide gas, to a carburizing furnace for carburizing a processing material such as steel parts. The problem is to solve the problem.

That is, in the present invention, the raw material gas containing hydrocarbon gas and carbon dioxide gas is led to the catalyst layer provided in the reaction cylinder heated by the heating means, and the high concentration obtained by catalytic reaction of this raw material gas When supplying the carburizing gas containing carbon monoxide gas to the carburizing furnace, while maintaining the amount of carburizing gas produced, the soot generated in the catalyst layer is appropriately removed to the carburizing furnace. An object of the present invention is to enable stable supply of carburizing gas.

In this invention, in order to solve the above problems, a raw material gas containing hydrocarbon gas and carbon dioxide gas is led to a catalyst layer provided in a reaction cylinder heated by a heating means, and this raw material gas is In a carburizing gas supply apparatus for supplying a carburizing gas containing carbon monoxide gas obtained by catalytic reaction at a high concentration of 40 to 57% by volume to a carburizing treatment furnace, a plurality of reaction cylinders heated by heating means are provided. Supply gas switching means is provided in each gas supply pipe for supplying gas to the catalyst layer provided in each reaction cylinder in parallel, and by this supply gas switching means, the catalyst layer provided in the reaction cylinder through the gas supply pipe is provided. The gas to be supplied is switched to the raw material gas and the soot removal gas, and a guide path switching means is provided in a guide pipe for guiding the gas led out from each reaction cylinder through the catalyst layer. By means, since only the carburizing gas source gas is derived from the reaction tube supplied was then supplied to the carburizing furnace is.

  In the carburizing gas supply apparatus, when the gas supplied through the gas supply pipe to the catalyst layer provided in each reaction cylinder is switched between the raw material gas and the soot removal gas by the supply gas switching means. It is preferable that the reaction cylinders to which the soot removal gas is supplied are sequentially changed, and the number of reaction cylinders to which the raw material gas is supplied is made constant.

Here, in the carburizing gas supply apparatus, the soot removing gas may be any gas that can burn and remove soot generated in the catalyst layer provided in the reaction cylinder. Alternatively, an oxidizing gas such as CO ₂ or O ₂ can be used.

Like the carburizing gas supply apparatus in this invention, the raw material gas containing hydrocarbon gas and carbon dioxide gas is led to the catalyst layer provided in the reaction cylinder heated by the heating means, and this raw material gas is subjected to catalytic reaction. In order to obtain a carburizing gas containing carbon monoxide gas at a high concentration of 40 to 57% by volume , if a plurality of reaction tubes heated by heating means are provided in parallel, the diameter of each reaction tube is reduced. Thus, the catalyst layer provided in the reaction cylinder can be sufficiently heated by the heating means.

In addition, when the gas supplied through the gas supply pipe to the catalyst layer provided in each reaction cylinder as described above is switched between the source gas and the soot removal gas by the supply gas switching means, the source gas is supplied. In the reaction cylinder, the raw material gas is catalytically reacted in the catalyst layer, and a carburizing gas containing carbon monoxide gas at a high concentration of 40 to 57% by volume is appropriately generated. On the other hand, in the reaction cylinder to which the soot removal gas is supplied, soot generated in the catalyst layer in the reaction cylinder is burned by the soot removal gas and removed from the catalyst layer.

  Then, only the carburizing gas derived from the reaction cylinder supplied with the raw material gas is supplied to the carburizing furnace by the guide path switching means, and the soot removal derived from the reaction cylinder supplied with the soot removal gas is performed. The soot removal gas is not supplied to the carburizing furnace.

In this way, in the reaction cylinder supplied with the raw material gas containing hydrocarbon gas and carbon dioxide gas, the raw material gas is catalytically reacted in the sufficiently heated catalyst layer, and the carbon monoxide gas is 40 to 57 volumes. The carburizing gas contained at a high concentration of% is appropriately generated and the generation of soot in the catalyst layer is also suppressed. On the other hand, in the reaction cylinder supplied with the soot removal gas, soot in the catalyst layer is combusted by the soot removal gas and appropriately removed.

As a result, in the carburizing gas supply apparatus according to the present invention, carbon monoxide gas is generated in the catalyst layer in each reaction cylinder while maintaining the amount of carburizing gas that is contained at a high concentration of 40 to 57% by volume. By removing the soot appropriately, the carburizing furnace can be stably supplied with a carburizing gas containing carbon monoxide gas at a high concentration of 40 to 57% by volume .

Further, when the gas supplied to each reaction cylinder through the gas supply pipe is switched to the source gas and the soot removal gas by the above supply gas switching means, the reaction cylinder to which the soot removal gas is supplied is sequentially installed. In the case where soot in the catalyst layer is removed sequentially in each reaction cylinder, and then the raw material gas is supplied to the reaction cylinder, the raw material gas is appropriately converted into a catalyst in the catalyst layer. By being reacted , a carburizing gas containing carbon monoxide gas at a high concentration of 40 to 57% by volume is appropriately generated.

  Further, if the number of reaction cylinders to which the raw material gas is supplied is made constant by the supply gas switching means, the amount of carburizing gas generated is constant, and a constant amount of carburizing gas is stably supplied to the carburizing treatment furnace. It becomes possible to supply.

It is the schematic explanatory drawing which showed the state which supplies the carburizing gas to the carburizing process furnace with the conventional gas supply apparatus for carburizing. In the carburizing gas supply apparatus according to one embodiment of the present invention, heating means are respectively provided on the opposing outer surfaces of the reaction container so as to sandwich the six pairs of reaction tubes provided in the reaction container. It is transverse cross-sectional explanatory drawing which showed the state which attached the exterior body so that it might cover. It is a longitudinal cross-sectional explanatory drawing along the arrangement direction of said reaction cylinder which shows the state which supplies the carburizing gas to the carburizing process furnace with the carburizing gas supply apparatus which concerns on said embodiment. FIG. 6 is a longitudinal sectional explanatory view showing a state in which two reaction cylinders that are paired are arranged in the case where the carburizing gas is supplied to the carburizing treatment furnace by the carburizing gas supply device according to the embodiment. In the carburizing gas supply apparatus according to the embodiment of the present invention, it is a partial cross-sectional explanatory view showing an example of supplying a raw material gas and soot removal gas to a catalyst layer provided in a reaction cylinder through a gas supply pipe.

  Hereinafter, a carburizing gas supply apparatus according to an embodiment of the present invention will be specifically described with reference to the accompanying drawings. In addition, the carburizing gas supply apparatus according to the present invention is not limited to the one shown in the following embodiment, and can be implemented with appropriate modifications within a range not changing the gist of the invention.

  In the carburizing gas supply apparatus in this embodiment, as shown in FIG. 2, six pairs of heat-resistant reaction cylinders 10 in which a catalyst layer 11 using a noble metal catalyst such as a Ni catalyst or Rh, Pt is provided are provided. (10A to 10F), a total of 12 reaction cylinders 10 are provided so as to penetrate through the inside of the reaction container 12 formed of a hollow box. And the heating means 13 which consists of an electric heater etc. is provided in the outer surface which the reaction container 12 opposes so that these 6 pairs of reaction cylinders 10A-10F may be pinched | interposed, and a heat insulating material may be covered so that said reaction container 12 may be covered The exterior body 14 using is attached.

  Here, when a plurality of reaction cylinders 10 are provided so as to penetrate through the inside of the reaction container 12 in this way, the diameter of each reaction cylinder 10 can be reduced and provided in each reaction cylinder 10. Further, the catalyst layer 11 can be sufficiently heated by the heating means 13 described above. In addition, as said each reaction cylinder 10, the thing of a diameter about 25A-40A can be used, for example.

Then, as shown in FIGS. 3 and 4, the catalyst layer 11 in each pair of reaction cylinders 10 </ b> A to 10 </ b> F provided in the reaction container 12 is passed through the gas supply pipe 21 and from the source gas supply pipe 21 a. The feed gas switching means 22 supplies the raw material gas Ga containing the hydrocarbon gas to be supplied and the soot removal gas Gb supplied from the soot removal gas supply pipe 21b. Note that as the soot removal gas Gb, an atmosphere for burning and removing soot generated in the catalyst layer 11 as described above, or an oxidizing gas such as CO ₂ or O ₂ is used.

  Here, the gas to be supplied to the catalyst layer 11 provided in each pair of reaction cylinders 10A to 10F through each gas supply pipe 21 by the supply gas switching means 22 is the above-described raw material gas Ga and soot removal gas Gb. In switching, the carburizing gas supply apparatus of this embodiment is provided with switching valves 22a and 22b in the raw material gas supply pipes 21a and the soot removal gas supply pipes 21b, respectively.

  And with respect to the reaction cylinder 10 which supplies raw material gas Ga, while switching valve 22a provided in the raw material gas supply pipe 21a is opened, the switching valve 22b provided in the soot removal gas supply pipe 21b is closed, and raw material is supplied. The source gas Ga supplied from the gas supply pipe 21 a is supplied to the reaction cylinder 10 through the gas supply pipe 21. On the other hand, for the reaction cylinder 10 that supplies the soot removal gas Gb, the switching valve 22b provided in the soot removal gas supply pipe 21b is opened, while the switching valve 22a provided in the source gas supply pipe 21a is closed. The soot removal gas Gb supplied from the soot removal gas supply pipe 21 b is supplied to the reaction tube 10 through the gas supply pipe 21.

  Here, in the reaction cylinder 10 supplied with the raw material gas Ga, the raw material gas Ga undergoes a catalytic reaction in the catalyst layer 11 of the reaction cylinder 10 to generate a carburizing gas Gc containing a high concentration of carbon monoxide gas. Become so. On the other hand, in the reaction cylinder 10 to which the soot removal gas Gb is supplied, soot in the catalyst layer 11 of the reaction cylinder 10 is burned by the soot removal gas Gb and removed from the catalyst layer 11. .

  The carburizing gas Gc generated in the reaction cylinder 10 supplied with the source gas Ga as described above, and the soot removal gas Gd after soot removal generated in the reaction cylinder 10 supplied with the soot removal gas Gb, Are guided to the respective guide tubes 23 connected to the respective reaction cylinders 10, and the route for guiding the carburizing gas Gc and the soot removal gas Gd guided to the respective guide tubes 23 is switched by the guide route switching means 24. I have to.

  Here, in switching the route for guiding the carburizing gas Gc and the soot removal gas Gd guided to the respective guide pipes 23 by the guide route switching means 24, in the carburizing gas supply device of this embodiment, The carburizing gas guide pipe 23a that guides the carburizing gas Gc guided to the guide pipe 23 to the carburizing furnace 2, and the soot removal gas guide pipe 23b that guides the soot removal gas Gd guided to the guide pipe 23 to the outside. In addition to branching, the carburizing gas guide pipe 23a and the soot removal gas guide pipe 23b are provided with switching valves 24a and 24b, respectively.

  In the reaction cylinder 10 in which the raw material gas Ga is supplied and the carburizing gas Gc is guided to the guide tube 23, the switching valve 24a provided in the carburizing gas guide tube 23a is opened, while the soot removal gas guide tube 23b is opened. The provided switching valve 24b is closed, and the carburizing gas Gc guided to the guide pipe 23 is supplied to the carburizing treatment furnace 2 through the carburizing gas guide pipe 23a. On the other hand, in the reaction cylinder 10 in which the soot removal gas Gb is supplied and the soot removal gas Gd is guided to the guide tube 23, the switching valve 24b provided in the soot removal gas guide tube 23b is opened while the carburizing gas guide tube is provided. The switching valve 24a provided at 23a is closed, and the soot removal gas Gd guided to the guide pipe 23 is led outside the carburizing furnace 2 through the soot removal gas guide pipe 23b.

  In this way, in the reaction tube 10 supplied with the raw material gas Ga containing the hydrocarbon gas, the raw material gas Ga undergoes a catalytic reaction in the sufficiently heated catalyst layer 11 and contains a high concentration of carbon monoxide gas. The carburizing gas Gc is appropriately generated and the generation of soot in the catalyst layer 11 is suppressed.

  In the reaction cylinder to which the soot removal gas Gb is supplied, soot in the catalyst layer 11 is combusted by the soot removal gas Gb and appropriately removed. When the soot in the catalyst layer 11 is thus combusted by the soot removal gas Gb and appropriately removed, when the source gas Ga is supplied to the reaction tube 10 next, the catalyst layer 11 The raw material gas Ga is appropriately catalyzed without hindering the gas flow by the soot inside, and the carburizing gas Gc containing the high-concentration carbon monoxide gas is appropriately generated.

  Here, in the carburizing gas supply apparatus of this embodiment, when switching the gas supplied to each reaction tube 10 through the gas supply pipe 21 to the source gas Ga and the soot removal gas Gb as described above, If the reaction cylinders 10 to which the gas Gb is supplied are made different one after another, soot in the catalyst layer 11 of each reaction cylinder 10 will be removed one after another, and the carburizing gas Gc will be more stable. Can be generated. Further, when the number of reaction cylinders 10 to which the raw material gas Ga is supplied through the gas supply pipe 21 is constant, the amount of carburizing gas Gc generated is constant, and a constant amount of carburizing gas Gc is stabilized in the carburizing treatment furnace 2. Can be supplied.

  For example, in the six pairs of reaction cylinders 10A to 10F, initially, the soot removal gas Gb is supplied to the pair of reaction cylinders 10F, and the soot in the catalyst layer 11 of the pair of reaction cylinders 10F is burned and removed. On the other hand, the raw material gas Ga is supplied to the remaining five pairs of reaction cylinders 10A to 10E, and the carburizing gas Gc is generated and supplied to the carburizing treatment furnace 2. Next, when the source gas Ga and the soot removal gas Gb supplied to the six pairs of reaction cylinders 10A to 10F are switched by the supply gas switching means 22, the pair of reaction cylinders 10E different from the first are used for soot removal. The gas Gb is supplied and the soot in the catalyst layer 11 of the pair of reaction cylinders 10E is burned and removed, while the raw material gas Ga is supplied to the remaining five pairs of reaction cylinders 10A to 10D, 10F, and the carburizing gas Gc. Is generated and supplied to the carburizing furnace 2. Then, the pair of reaction cylinders 10A to 10F that supply the soot removal gas Gb in this way are sequentially changed to burn and remove soot in the catalyst layer 11, and the source gas Ga is removed from the remaining five gas cylinders. When the source gas Ga is supplied to the pair of reaction cylinders 10A to 10F to generate the carburizing gas Gc, soot in the catalyst layer 11 of each reaction cylinder 10 is sequentially removed as described above. The amount of carburizing gas Gc generated by these reaction cylinders 10 is also constant, and a constant amount of carburizing gas Gc can be stably supplied to the carburizing treatment furnace 2.

  Further, in supplying the source gas Ga and the soot removal gas Gb to the catalyst layer 11 provided in each reaction cylinder 10 through the gas supply pipe 21 as described above, as shown in FIG. A support pipe 15 through which the gas supply pipe 21 inserted into the gas pipe 21 is inserted is provided, and a catalyst layer is provided between the outer periphery of the tip of the gas supply pipe 21 protruding upward from the support pipe 15 and the inner periphery of the reaction tube 10. 11 is preferably provided with a protect ring 16 for holding the catalyst 11a. In this way, the catalyst 11a is prevented from entering between the outer periphery of the distal end portion of the gas supply pipe 21 and the inner periphery of the reaction tube 10, and the raw material gas Ga and the soot removal gas enter the catalyst layer 11 as described above. In the case where Gb is supplied for reaction, the catalyst 11a that has entered between the outer periphery of the tip of the gas supply pipe 21 and the inner periphery of the reaction cylinder 10 during expansion and contraction due to temperature changes of the reaction cylinder 10 and the gas supply pipe 21. This prevents the reaction tube 10 and the gas supply pipe 21 from being deformed or damaged. Further, as shown in the figure, when the tip surface of the gas supply pipe 21 protruding upward from the protect ring 16 is inclined, the hole of the gas supply pipe 21 is blocked by the catalyst 11 a in the catalyst layer 11. Thus, the source gas Ga and the soot removal gas Gb can be appropriately supplied from the gas supply pipe 21 to the catalyst layer 11.

  Although not shown, a cooling device (not shown) such as water cooling is provided in the guide tube 23 for guiding the carburizing gas Gc and the soot removal gas Gd generated in the reaction cylinder 10. The guided carburizing gas Gc and soot removal gas Gd can also be cooled.

2 Carburizing furnace 10 (10A to 10F) Reaction cylinder 11 Catalyst layer 11a Catalyst 12 Reaction container 13 Heating means 14 Exterior body 15 Support pipe 16 Protecting ring 21 Gas supply pipe 21a Raw material gas supply pipe 21b Soot removal gas supply pipe 22 Supply gas switching means 22a, 22b Switching valve 23 Guide pipe 23a Carburizing gas guide pipe 23b Soot removal gas guide pipe 24 Guide path switching means 24a, 24b Switching valve Ga Raw gas Gb Soot removal gas Gc Carburizing gas Gd Soot removal gas

Claims (5)

The raw material gas containing hydrocarbon gas and carbon dioxide gas is led to a catalyst layer provided in a reaction cylinder heated by a heating means, and carbon monoxide gas obtained by catalytic reaction of this raw material gas is 40 to 57 volumes. In a carburizing gas supply apparatus for supplying a carburizing gas contained at a high concentration of 1 % to a carburizing furnace, a plurality of reaction cylinders heated by heating means are provided in parallel, and gas is supplied to a catalyst layer provided in each reaction cylinder. Supply gas switching means is provided in each gas supply pipe for supplying the gas, and the gas supplied to the catalyst layer provided in the reaction cylinder through the gas supply pipe is supplied to the above-mentioned raw material gas and soot removal gas by the supply gas switching means. And a guide path switching means is provided in the guide tube for guiding the gas led out from each reaction cylinder through the catalyst layer, and the guide path switching means leads out from the reaction cylinder supplied with the raw material gas. Carburizing gas supply device, characterized in that only carburizing gas be supplied to the carburizing furnace. 2. The carburizing gas supply apparatus according to claim 1 , wherein the gas supplied through the gas supply pipe to the catalyst layer provided in each reaction cylinder is switched between the source gas and the soot removal gas by the supply gas switching means. In this case, the carburizing gas supply apparatus is characterized in that the reaction cylinders to which the soot removal gas is supplied are sequentially changed. 3. The carburizing gas supply apparatus according to claim 1 , wherein the gas supplied through the gas supply pipe to the catalyst layer provided in each reaction tube by the supply gas switching means is a raw material gas and a soot removal gas. A gas supply apparatus for carburizing, characterized in that the number of reaction cylinders to which the raw material gas is supplied is made constant when switching to the above. The carburizing gas supply device according to any one of claims 1 to 3 , wherein a support pipe for inserting the gas supply pipe is provided in the reaction cylinder, and the tip of the gas supply pipe protruding from the support pipe The carburizing gas is characterized in that a protective ring for holding the catalyst in the catalyst layer is provided between the outer periphery of the reaction part and the inner periphery of the reaction cylinder, and the front end surface of the gas supply pipe protruding from the protective ring is inclined. Feeding device. For carburizing containing carbon monoxide gas obtained by conducting a raw material gas containing hydrocarbon gas and carbon dioxide gas to a catalyst layer provided in a reaction cylinder heated by a heating means and catalytically reacting this raw material gas In a carburizing gas supply apparatus for supplying gas to a carburizing furnace, a plurality of reaction cylinders heated by heating means are provided in parallel and supplied to each gas supply pipe for supplying gas to a catalyst layer provided in each reaction cylinder. Gas switching means is provided, and by this supply gas switching means, the gas supplied to the catalyst layer provided in the reaction cylinder through the gas supply pipe is switched to the raw material gas and the soot removal gas and each reaction through the catalyst layer. A guide path switching means is provided in the guide tube for guiding the gas derived from the cylinder, and only the carburizing gas derived from the reaction cylinder supplied with the raw material gas is carburized by the guide path switching means. Together so as to supply, the support pipe is provided for inserting the gas supply pipe to the reaction cylinder, between the inner periphery of the outer peripheral reaction tube of the distal end portion of the gas supply pipe projecting from the support pipe, A carburizing gas supply apparatus comprising a protect ring for holding a catalyst in a catalyst layer, and a tip end surface of a gas supply pipe projecting from the protect ring being inclined.

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