JPH07257902A - Heat transfer method in heat exchanger type reformer - Google Patents

Abstract

(57) [Summary] [Structure] A fuel containing hydrogen and carbon monoxide as main components by using a reformer having a bayonet type double-tube catalyst tube and supplying natural gas and steam to the reformer. In a method for obtaining a reformed gas for a battery, a heat transfer promoting means A surrounding the catalyst tube is provided outside the central portion of the catalyst tube, and a sleeve surrounding the catalyst tube outside the base portion of the catalyst tube, the sleeve and the catalyst. The heat transfer promoting means B arranged in the gap between the tubes is provided, and the combustion gas for heating introduced into the shell side is discharged through the gap. [Effect] The flow of the combustion gas on the shell side in the can is made uniform, and the plurality of catalyst tubes arranged in the can can be heated uniformly. Further, since the combustion gas flows at high speed in the vicinity of the base of the catalyst tube, the heat transfer efficiency in the base of the catalyst tube is improved.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to promoting heat transfer in a reformer for producing a reformed gas for a fuel cell. More specifically, the present invention relates to a method for improving heat utilization efficiency in a heat exchanger type reformer having a bayonet type double tube type catalyst tube, and the reformer used in such a method.

[0002]

2. Description of the Related Art Fuel cell power generation has been attracting attention as a power generation method that has high power generation efficiency and little influence on the environment. In principle, a fuel cell continuously supplies hydrogen and oxygen to a fuel electrode (hydrogen electrode) and an air electrode (oxygen electrode),
By arranging an electrolyte between both electrodes, a direct current is taken out to an external circuit connected to both electrodes.

In the fuel cell, alkaline type (AFC) and phosphoric acid type (PAF) are used depending on what is used as the electrolyte.
C), molten carbonate type (MCFC) and the like. These are the same in that hydrogen (pure hydrogen or crude hydrogen) is supplied to the fuel electrode, but differ in whether or not carbon dioxide or carbon monoxide can be mixed in the hydrogen. That is, in the case of the alkaline type, carbon dioxide deteriorates the function of potassium hydroxide as an electrolyte, and carbon monoxide poisons platinum used as a catalyst, so that the performance of the fuel cell deteriorates. It will be allowed and mixing is not allowed. For this reason, this type has a drawback that substantially pure hydrogen must be used as the fuel gas. On the other hand, in the case of the phosphoric acid type, carbon monoxide poisons platinum, which is also used as a catalyst, so mixing is not allowed, but mixing of carbon dioxide is not a problem, so carbon monoxide is converted to carbon monoxide. Crude hydrogen can be used by reacting it with steam in a vessel to convert it to carbon dioxide and hydrogen. Further, in the case of the molten carbonate type, since no platinum catalyst is used, any mixing is not a problem at all, and carbon monoxide generates hydrogen by the water produced at the fuel electrode and the carbon monoxide shift reaction. Therefore, it can be effectively used as fuel. Since the molten carbonate type has many other economical advantages, it is regarded as a promising alternative to small- and medium-sized thermal power generation. Other than the above, solid electrolyte type (SOFC) and polymer type (PFC) are known as fuel cells, and each has its own characteristics, but both are the same in that hydrogen is supplied to the fuel electrode. Is.

Crude hydrogen supplied to the fuel electrode of a phosphoric acid type or molten carbonate type fuel cell is generally produced by reacting steam with natural gas (main component is methane) as a raw material.
The reaction at this time is considered to follow, for example, the following formula (1) or (2). CH ₄ + H ₂ O → CO + 3H ₂ (1) CH ₄ + 2H ₂ O → CO ₂ + 4H ₂ (2) These reactions are endothermic reactions and are usually 600 ° C to 1000 ° C in the presence of a catalyst. Done in. The apparatus for performing the above reaction is a reformer, and generally has a structure in which a raw material gas (natural gas and steam) is circulated in a reaction tube filled with a catalyst and heated from outside by a burner or a high temperature fluid by catalytic combustion. .

As the reformer, one having a bayonet type double tube type catalyst tube has been often used conventionally. The outline of the typical structure is shown in FIG. In FIG. 1, raw material natural gas and steam are introduced into a can body from a source gas inlet 2 at one end (the top in the figure) of the can body 1 and an inner tube 3 which constitutes a bayonet type double tube type catalyst tube. It flows through the tubular space between the outer tubes 4. The reforming catalyst 5 is filled in the space, and the natural gas and steam react with each other during this period to form a reformed gas containing hydrogen. Next, the generated reformed gas passes through the inner pipe 3 and is supplied from the manifold 6 to the fuel cell (not shown) through the reformed gas outlet 7. Can body 1
A combustion gas supply portion is provided at the other end (bottom portion in the drawing) of, and is composed of, for example, a combustion chamber 8, a combustion device 9, a combustion gas dispersion plate 10 and the like as shown in FIG. The combustion gas flows outside (shell side) of the outer pipe 4, heats the catalyst 5 from the outside, and is then discharged from the combustion exhaust gas outlet 11. Inner tube 3
Is supported by a manifold 6 and the outer tube 4 is a tube plate 12
Since the two tubes are supported by each other and the positional relationship between the two tubes is not fixed, stress due to the difference in the degree of thermal expansion between the outer tube and the inner tube (generally the outer tube becomes hotter) can be released. This is one of the merits of adopting the bayonet type catalyst tube in the reformer for a fuel cell, which requires frequent start-stop and load changes. As the gas to be burned in the combustion device, exhaust gas from the fuel electrode side of the fuel cell is usually used (unused hydrogen remains because not all hydrogen supplied can be used in the cell reaction). However, when the hydrogen content is low and the calorific value is low, it is difficult to cause self-combustion, so catalytic combustion is used instead of normal burner combustion.

As described above, the heat required for the reforming reaction is supplied from the combustion device. High temperature (1000 ℃ ~ 1500
(° C) combustion gas is diffused and rectified by the dispersion plate and flows through the shell side inside the can body, heating the outer tube of the bayonet-type catalyst tube from the outside. Generally, the heat transfer efficiency between the combustion gas and the catalyst tube is Since it is not so high, various means have been conventionally used to increase the heat transfer efficiency. For example, it has been conventionally practiced to provide a heat transfer promoting means such as an orifice baffle and a wire net near the outer tube shell side of the base portion of the catalyst tube (closer to the tube plate and farther from the combustion gas supply portion). These heat transfer promotion means generate turbulence in the combustion gas flow by obstructing the flow of the combustion gas, and have solid surface radiation by having a large surface area and being heated to a high temperature by the combustion gas. However, the catalyst tubes are efficiently heated by their contributions.

[0007]

However, the above heat transfer promoting means is an obstacle to the gas flow, and on the other hand, since there is a gap between the orifice baffle and the inner wall of the can, the combustion gas flow can There is a tendency to channel along the inner wall, which causes a problem that the catalyst tubes arranged in the can are not heated uniformly. That is,
Since the flow of the combustion gas gathers in the peripheral portion of the can, heat is not sufficiently transferred to the catalyst tube (particularly the base portion) arranged in the center of the can. As described above, although it is preferable to provide the heat transfer promoting means around the catalyst tube to improve the heat transfer efficiency, in that case, the flow of the combustion gas in the can is made uniform with respect to the can cross section. Various challenges are raised.

[0008]

SUMMARY OF THE INVENTION The present invention uses a reformer having a bayonet type double tube type catalyst tube, and supplies natural gas and steam to the reformer to mainly supply hydrogen and carbon monoxide. In a method of obtaining a reformed gas for a fuel cell as a component, a heat transfer promoting means A surrounding the catalyst tube outside the central portion of the catalyst tube.
And a sleeve surrounding the catalyst tube and a heat transfer promoting means B arranged in the gap between the sleeve and the catalyst tube outside the base of the catalyst tube, and the combustion gas for heating introduced to the shell side is provided in the gap. The above-mentioned problems are solved by discharging the gas after passing through.

[0009]

In the present invention, the heat transfer promoting means is provided at the central portion and the base portion of each catalyst tube (referred to as "heat transfer promoting means A" and "heat transfer promoting means B"), respectively, whereby turbulence is caused in the gas flow. A flow is generated to promote convective heat transfer, and radiative heat transfer due to solid radiation is used to improve heat transfer efficiency from the combustion gas to the catalyst tube. In this case, since there is no heat transfer promoting means for obstructing the gas flow in the vicinity of the inner wall of the can, and a straight flow path is easily secured along the wall, the combustion gas easily flows along the inner wall of the can. For this reason, in the present invention, by providing a sleeve surrounding each catalyst tube base and substantially leaving only the gap between the sleeve and the catalyst tube as the outlet of the combustion gas, even if the combustion gas flows along the inner wall of the can, it is discharged as it is. Combustion gas must always pass through the gap around each catalyst tube at the end. This reduces the tendency for the gas flow to gather around the inside of the can, and as a result, the flow of combustion gas is made uniform over the cross section of the can.

Further, according to the present invention, the flow of the combustion gas is concentrated in the gap between the sleeve and the base of the catalyst tube (that is, near the catalyst tube) and passes at a high speed. Therefore, convective heat transfer in the base of the catalyst tube is more effective than before. The heat transfer efficiency from the combustion gas to the base of the catalyst tube is remarkably improved because the radiant heat transfer effect by the solid radiation from the heat transfer promoting means provided in the gap is added.

[0011]

EXAMPLE Since the sleeve surrounding the base of the catalyst tube concentrates the flow of combustion gas in the gap, the outside of the sleeve must have a structure in which combustion gas does not substantially pass through. . For example, as shown in FIG. 2, a partition plate 14 that supports the sleeve 13 is provided separately from the tube plate 12 that supports the outer tube 4 of the catalyst tube, and the combustion gas outlet chamber 15 is formed by the tube plate 12 and the partition plate 14. Doing is the preferred embodiment. As another aspect, the combustion gas inlet side of the sleeve 13 is supported by the partition plate 14 as shown in FIG.
The length L of the sleeve 13 by using two partition plates 14 as shown in
You may form the perforated-plate structure of thickness equal to. The length L of the sleeve is preferably 1/5 to 1/2 of the length of the catalyst outer tube, and particularly preferably 1/4 to 1/3. The width D of the gap between the sleeve and the catalyst tube is 7.5 to 40 m.
m is preferable, and 15 to 30 mm is particularly preferable.

The heat transfer promoting means A provided outside the central portion of the catalyst tube has an action of disturbing the gas flow to generate a turbulent flow, and has a large heat transfer surface area and is heated by the combustion gas to generate solid radiation. It is preferable to have a combination of action and
For example, an orifice baffle having a large disturbing effect on the gas flow and a wire net having a large surface area may be provided in combination. The orifice baffle is, for example, as shown in FIG. 5, a ring-shaped flat plate made of a corrosion-resistant metal such as stainless steel, which is connected with a certain number of tie rods at predetermined intervals. The wire net is a mesh-like sheet made of stainless steel wire or the like, and those having 10 to 60 mesh can be preferably used. Those having 20 to 40 mesh are particularly preferable. As shown in FIG. 6, it is a preferred embodiment that the wire net is provided so as to surround the catalyst tube and the orifice baffle is provided so as to surround the catalyst tube. The heat transfer promoting means A is preferably provided in the central portion of the catalyst tube at a length of 1/5 to 1/2 of the length of the catalyst outer tube, and is provided at a length of 1/4 to 1/3. Particularly preferred.

On the other hand, as the heat transfer promoting means B provided in the gap between the base of the catalyst tube and the sleeve, the convective heat transfer from the combustion gas to the catalyst tube is already sufficiently promoted because the high-speed gas flow flows near the catalyst tube. Therefore, it is more important to have a large heat transfer surface area so that the combustion gas heats it to a higher temperature. Therefore, for example, a wire net or the like suitably used as the heat transfer promoting means A can also be suitably used as the heat transfer promoting means B. Heat transfer promotion means B
Is provided in the gap between the catalyst tube and the sleeve, and is appropriately selected so as not to give an extremely large resistance to the combustion gas flow in relation to the length of the sleeve and the width of the gap. The heat transfer promoting means B is preferably provided over the entire length of the gap.

As shown in FIG. 7, it is a particularly preferred embodiment that the same wire net 16 is used as the heat transfer promoting means A and the heat transfer promoting means B, and they are integrally formed. In that case, as shown in FIG. 7, the same wire net integrally surrounds the central portion and the base portion of each catalyst tube. The orifice baffle 17 is provided at the central portion and the sleeve 13 is provided at the base portion. It is provided outside of.

[0015]

According to the present invention, in the heat exchanger type reformer in which the heat transfer promoting means is provided outside the bayonet type double tube type catalyst tube, the flow of the combustion gas on the shell side in the can is made uniform. Thus, the plurality of catalyst tubes arranged in the can can be heated evenly. Further, since the combustion gas flows at high speed in the vicinity of the base of the catalyst tube, the heat transfer efficiency in the base of the catalyst tube is improved.

[Brief description of drawings]

FIG. 1 shows a conventional reformer.

FIG. 2 shows an example of a structure for supporting a sleeve.

FIG. 3 shows another example of a structure for supporting a sleeve.

FIG. 4 shows still another example of the structure for supporting the sleeve.

FIG. 5 shows an example of an orifice baffle.

FIG. 6 shows a preferred configuration example of a heat transfer promoting means A.

FIG. 7 shows a preferred embodiment of the reformer of the present invention.

[Explanation of symbols]

 1 can body 2 raw material gas inlet 3 inner pipe 4 outer pipe 5 reforming catalyst 6 manifold 7 reformed gas outlet 8 combustion chamber 9 combustor 10 combustion gas dispersion plate 11 combustion exhaust gas outlet 12 tube plate 13 sleeve 14 support plate 15 combustion gas Outlet chamber 16 Wire net 17 Orifice baffle

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Maki Hayasaka 2-12-1, Tsurumi Chuo, Tsurumi-ku, Yokohama-shi, Kanagawa Chiyoda Kako Construction Co., Ltd. (72) Toshihiro Horie Chuo, Tsurumi-ku, Tsurumi-ku, Yokohama-shi, Kanagawa Chome 12-1 Chiyoda Kako Construction Co., Ltd.

Claims (7)

[Claims] 1. A reformer for a fuel cell, which uses a reformer having a bayonet-type double-tube catalyst tube and supplies natural gas and steam to the reformer to contain hydrogen and carbon monoxide as main components. In the method for obtaining gas, heat transfer promoting means A surrounding the catalyst tube is provided outside the central portion of the catalyst tube, and a sleeve surrounding the catalyst tube is provided outside the base portion of the catalyst tube, and a gap between the sleeve and the catalyst tube is provided. A method comprising: providing a heat transfer promoting means B arranged, and discharging the combustion gas for heating introduced to the shell side through the gap. 2. The method according to claim 1, wherein said heat transfer promoting means A comprises an orifice baffle and a wire net, and said heat transfer promoting means B comprises a wire net. 3. The method according to claim 2, wherein the heat transfer promoting means A comprises an orifice baffle surrounding the catalyst tube and a wire net disposed in a gap between the orifice baffle and the catalyst tube. 4. The method according to claim 3, wherein the wire net forming the heat transfer promoting means A and the wire net forming the heat transfer promoting means B are integrally formed around the catalyst tube. 5. A heat exchanger type reformer having a bayonet type double tube type catalyst tube in a can body, wherein a heat transfer promoting means A consisting of a wire net and an orifice baffle is provided outside the central portion of the catalyst tube. A heating combustion introduced into the shell side, having a sleeve surrounding the catalyst tube on the outer side of the base of the catalyst tube, and having a heat transfer promoting means B composed of a wire net in the gap between the sleeve and the catalyst tube. A reformer, characterized in that the gas is configured to be discharged through the gap. 6. The reformer according to claim 5, wherein the heat transfer promoting means A comprises an orifice baffle surrounding the catalyst tube and a wire net disposed in a gap between the orifice baffle and the catalyst tube. 7. The reformer according to claim 6, wherein the wire net forming the heat transfer promoting means A and the wire net forming the heat transfer promoting means B are integrally formed around the catalyst tube.