JP2004352528A - Hydrogen production system - Google Patents

Abstract

An object of the present invention is to provide a hydrogen production system capable of uniformly heating a reaction tube with a combustion gas, uniforming a temperature distribution in a reformer, and stably performing a steam reforming reaction on the entire catalyst layer.
A plurality of reaction tubes filled with a reforming catalyst are provided with a hydrogen permeable portion separated by a hydrogen separation membrane, and a combustion gas passage for heating the reaction tubes is provided. A hydrogen separation type reformer comprising: a multitubular reaction section; a combustion section for generating combustion gas for heating the multitubular reaction section; and a combustion exhaust gas inlet for introducing combustion exhaust gas in the vicinity of the combustion section. And a flue gas circulation line for circulating a part of the flue gas discharged from the hydrogen separation type reformer through a blower and returning the flue gas from the flue gas inlet to the reformer. .
[Selection diagram] Fig. 1

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a hydrogen production system, and more particularly to a hydrogen production system suitably used when a hydrogen separation type reformer has a convection heat transfer type multi-tube reactor.
[0002]
[Prior art]
In a hydrogen production system using a hydrogen separation type reformer, a raw material gas consisting of hydrocarbons such as methane and methanol and oxygenated hydrocarbons is mainly decomposed into hydrogen and carbon dioxide by a steam reforming reaction and a CO shift reaction. The separated hydrogen is selectively separated through a hydrogen separation membrane built in the reformer. As the hydrogen separation membrane, for example, a membrane made of palladium, a palladium alloy, or the like is used.
[0003]
In a conventional hydrogen production system, combustion exhaust gas discharged from a reformer is exhausted by a vent after being used for preheating a source gas (for example, see Patent Document 1).
A multiplex cylindrical reformer is also known as a hydrogen production system, but is a device that performs heating mainly by radiant heat transfer (for example, Patent Document 2).
[0004]
[Patent Document 1]
Japanese Patent No. 3035038 [Patent Document 2]
JP-A-7-109104 [0005]
In the case of a multi-cylindrical reformer, heat input cannot be expected because the thickness of the inner cylinder increases as the shape increases, and the heat transfer area cannot be increased in the reformer.
On the other hand, there is a reformer using a multi-tube type reaction tube.However, when a reformer having a convection heat transfer type multi-tube type reaction tube is used in such a conventional system, the high temperature from the combustion section is high. The combustion gas locally heats a part of the reaction tube, and the temperature of the reaction tube in the vicinity of the combustion part may exceed 700 ° C., for example. The hydrogen separation membrane constituting a part of the reaction tube needs to be used at a temperature of 600 ° C. or less, preferably 550 ° C. or less in view of the durability of the membrane, and cannot withstand locally generated heating.
On the other hand, if the combustion is performed so that the temperature of the reaction tube in the vicinity of the combustion section is suppressed to 700 ° C. or less, the steam reforming reaction proceeds only in a part of the reaction tube, and the reaction efficiency is significantly reduced. On the other hand, when the high-temperature combustion gas is diluted using secondary air that does not participate in combustion, the thermal efficiency of the system decreases even if the temperature decreases.
[0006]
[Problems to be solved by the invention]
In view of the above problems, the present inventors have found that, in a hydrogen production system having a multitubular reaction tube, in particular, the reaction tube is uniformly heated by the combustion gas, and the temperature distribution in the reformer is made uniform to perform steam reforming. We studied diligently to develop a hydrogen production system that can stably carry out the reaction over the entire catalyst layer and improve the thermal efficiency of the system.
As a result, the present inventors have found that the above problem can be solved by introducing the combustion exhaust gas into the reformer again through a circulation line using a blower or the like. The present invention has been completed from such a viewpoint.
[0007]
[Means for Solving the Problems]
That is, the present invention provides a hydrogen separation type reformer, and a combustion exhaust gas circulation line that circulates a part of the combustion exhaust gas from the hydrogen separation type reformer via a blower and returns the combustion exhaust gas from the combustion exhaust gas inlet to the reformer. And a hydrogen production system including the same. In the hydrogen separation type reformer of the present invention, a plurality of reaction tubes filled with a reforming catalyst are provided with a hydrogen permeable portion separated by a hydrogen separation membrane, and a combustion gas passage is provided for heating the reaction tubes. A multitubular reaction section, a combustion section for generating combustion gas for heating the multitubular reaction section, and a combustion exhaust gas inlet for introducing combustion exhaust gas in the vicinity of the combustion section. In this reformer, since the combustion exhaust gas inlet is provided near the burner, which is a combustion section, local heating of the reaction tube near the burner can be effectively prevented. In this system, a part of the combustion exhaust gas discharged from the reformer is recycled and circulated to the reformer by using a blower, thereby making the temperature distribution in the reformer uniform.
[0008]
In the hydrogen-separated reformer, the combustion gas emitted from the combustion section is mixed with the combustion exhaust gas and the combustion gas supplied from the combustion exhaust gas introduction section at a stage before reaching the multitubular reaction section. Can be provided. Various forms of the combustion mixing section are conceivable, for example, inside the reformer, a mode in which a porous partition plate is divided into a multitubular reaction tube section and a combustion mixing section, or a combustion exhaust gas mixing apparatus is separately installed, From there, the mixed gas is supplied to the reaction section.
[0009]
In addition, the hydrogen production system of the present invention can further include a boiler that introduces and combusts a part of the hydrocarbon gas used for the steam reforming reaction together with air, and heats water to produce steam. Here, the heating gas used in the boiler can be added to the flue gas circulation line as a part of the flue gas.
In addition, the hydrogen production system of the present invention may further include a gas-liquid separator that cools off gas discharged from the hydrogen separation type reformer and separates a water component and a gas component in the off gas.
[0010]
Further, in the hydrogen production system of the present invention, (1) a mode including a heat exchanger for preheating air to be burned in the combustion section with heat of off-gas discharged from the hydrogen separation type reformer, (2) the hydrocarbon gas And a heat exchanger for preheating a mixed gas obtained by mixing steam produced by the boiler with heat of the combustion exhaust gas discharged from the hydrogen separation type reformer. (3) The air separated by the boiler is subjected to the hydrogen separation. A form including a heat exchanger for preheating with the heat of the hydrogen gas from the mold reformer, or (4) a heat exchanger for preheating the water heated by the boiler with the heat of the hydrogen gas coming from the hydrogen separation type reformer. And the like can be used.
The thermal efficiency of the hydrogen production system can be improved by utilizing the thermal energy of the off-gas, the combustion exhaust gas, and the generated hydrogen gas from the reformer for preheating the components supplied to the reformer or the boiler. The combustion exhaust gas (about 500 ° C) from the reformer is used for preheating the process gas (mixed gas), and the product hydrogen gas (about 500 ° C) from the reformer exchanges heat with the water and combustion air supplied to the boiler. Preheating is preferred.
[0011]
According to the hydrogen production system of the present invention, in a system having a multitubular reaction tube, the reaction tube is uniformly heated by the combustion gas, the temperature distribution in the reformer is made uniform, and the steam reforming reaction is performed on the entire catalyst layer. And can be implemented stably. Then, there is no hot spot where the temperature locally rises in the reformer, and the device life of the reformer is extended.
In addition, in this system, it is possible to improve the thermal efficiency of the entire system by circulating the combustion exhaust gas, and the gas flow velocity is increased by increasing the amount of the combustion gas, and the convection heat transfer can be promoted. is there.
[0012]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, the hydrogen production system of the present invention will be described in detail.
The present invention provides a method for producing hydrogen by a steam reforming reaction using hydrocarbons such as city gas and steam as raw materials, and using a hydrogen separation membrane that selectively permeates only hydrogen to produce high-purity hydrogen. A separate reformer system is provided. As the raw material gas, city gas, methane, propane, kerosene, hydrocarbon such as dimethyl ether is used as the raw material gas.
The system of the present invention is a hydrogen production system combining a hydrogen separation type reformer and a combustion exhaust gas circulation line that circulates a part of the combustion exhaust gas from the hydrogen separation type reformer through the blower and returns it to the reformer. is there.
[0013]
FIG. 1 schematically shows a hydrogen production system of the present invention.
Reference numeral 1 denotes a hydrogen separation type reformer. Each reaction tube constituting a multitubular reaction tube section has a reforming catalyst layer 11 and a hydrogen separation membrane 12. Steam is mixed with the hydrocarbon as the raw material of the reformer 1 to form a mixed gas. The mixed gas is preheated in the heat exchanger 16 and heated to around the reaction temperature. The preheated mixed gas is introduced into the catalyst layer 11 of the hydrogen separation type reformer 1 as a process gas.
[0014]
In the reforming catalyst layer 11, hydrogen, carbon monoxide, and carbon dioxide are generated from the mixed gas by a steam reforming reaction. For example, when methane is used as a raw material, a steam reforming reaction is performed according to the following reaction formula.
CH ₄ + H ₂ O → 3H ₂ + CO (Endothermic reaction) (1)
CO + H ₂ O → CO ₂ + H ₂ (exothermic reaction) (2)
Usually, this reaction is performed at 500 ° C. or higher, and is performed under a steam-rich condition in which the S / C (steam / carbon ratio), which is a molar ratio of water and carbon C of methane, is 2 or more. Since the reaction of the above (1) is an endothermic reaction, a higher temperature promotes the reaction.
On the other hand, as described above, the operating temperature of the hydrogen separation membrane 12 needs to be suppressed to 600 ° C. or lower, preferably 550 ° C. or lower. Therefore, the catalytic reaction is usually performed in the range of 500 to 600 ° C.
[0015]
Of the gas generated by the reformer 1, only the hydrogen gas is separated into the permeable portion 14 through the hydrogen separation membrane 12 made of palladium, a palladium alloy or the like. The hydrogen gas stored in the permeation section 14 is taken out of the system as high-purity hydrogen gas.
The remaining gas mainly composed of carbon dioxide from which hydrogen has been taken out is recovered as an off-gas, cooled with cooling water or the like, introduced into the combustion unit 13 together with air, and burned to be used as fuel for the hydrogen separation reformer 1. The combustion gas introduced into the hydrogen separation type reformer 1 from the combustion unit 13 passes through a combustion exhaust gas passage 15 near the reaction tube and supplies thermal energy for reacting to the catalyst layer 11.
[0016]
After that, a part of the flue gas is sent to the flue gas a circulation line after leaving the reformer 1, and the remaining flue gas is discharged through the heat exchanger 16. The exhaust gas is circulated by providing a blower 17 in the circulation line. The proportion of the flue gas sent to the circulation line can be arbitrarily determined according to the operating conditions, but is usually at least 50% by volume, preferably at least 60% by volume, more preferably at least 70% by volume. The higher the ratio, the lower the temperature of the flue gas that has passed through the downstream heat exchanger 16.
This increases the rate of heat circulation in the system and improves the thermal efficiency of the system. It is preferable that the entire tube is heated in the range of usually 500 to 600 ° C. by the thermal energy of the combustion gas and the combustion exhaust gas.
[0017]
The combustion exhaust gas sent to the circulation line returns to the reformer 1 again from the inlet (introduction line) of the reformer. At this time, the ratio between the combustion gas introduced from the combustion unit 13 of the reformer 1 and the combustion exhaust gas to be circulated and reused can be arbitrarily determined depending on the operating conditions and the system configuration. When the exhaust gas introduction port is provided, it is possible to use a combustion gas of primary air: combustion exhaust gas = 1: 1 to 10, preferably 1: 2 to 8, for example 1: 5.
In the system of the present invention, the high-temperature combustion gas burned by the burner as the combustion unit 13 is diluted by using a part of the combustion exhaust gas discharged from the reformer 1, and the temperature is lowered before the multitubular reaction unit (11). , 12), the temperature distribution in the reformer 1 becomes uniform and stable.
[0018]
FIG. 2 shows a hydrogen separation type reformer 1 in which the hydrogen production system of the present invention is suitably used. FIG. 2A is a cross-sectional view as viewed from the side, and FIG. 2B is a diagram illustrating a cross-section as viewed from the front of the same reformer.
In the reformer 1, a plurality of reaction tubes 20 are filled with a reforming catalyst and provided with a hydrogen permeable portion separated by a hydrogen separation membrane, thereby forming a multitubular reaction portion. In the vicinity of the reaction tube 20, a combustion gas passage 24 for heating the reaction tube is provided. A combustion gas is sent from a line burner 22 (combustion unit) provided at a lower portion of the reformer 1 to a reaction tube in a multitubular reaction unit at an upper portion thereof. At the same time, in the lower part of the reformer 1, near the line burner 22, there are provided secondary air introduction lines 21 having combustion exhaust gas introduction ports in every other row. In addition, the burner installed in the combustion part 13 is not limited to a line burner, and various burners such as a high flow rate burner and a flat frame burner can be used.
[0019]
In the reformer shown in FIG. 2, a partition plate 25 is provided below the multitubular reaction section. The lower portion of the partition plate 25 becomes a combustion exhaust gas mixing section. In this combustion exhaust gas mixing section, the combustion gas emitted from the combustion section (line burner) 22 is mixed with the combustion exhaust gas supplied from the combustion exhaust gas inlet 21 before reaching the multitubular reaction section. As a result, the temperature of the mixed gas passing through the upper reaction tube is made uniform, and the high temperature combustion gas can be reliably prevented from directly reaching the reaction tube 20. Then, the catalyst layer can be evenly heated to the reaction temperature, and the reaction can proceed in the entire reaction tube 20.
[0020]
3 and 4 show an example of a system in which the present invention is suitably used.
In the system shown in FIG. 3, the steam supply water is preheated by the heat of the hydrogen gas generated by the reformer 1 and then sent to the boiler 2. By the preheating of the heat exchanger 9, the supply water is heated in a preceding stage of the boiler. In the boiler 2, the supply water is evaporated by the heat of burning a part of the hydrocarbon gas and the air to produce steam. The steam becomes high temperature under pressure, and the temperature of the steam at the boiler outlet is about 185 ° C. The steam is sent to the mixed gas preheater 6 (heat exchanger), is introduced together with the hydrocarbon as the raw material gas, and is preheated as a mixed gas by the combustion exhaust gas discharged from the reformer 1.
The preheated mixed gas is introduced into the catalyst layer 11 of the hydrogen separation reformer 1 as a process gas. The preheating is performed in this way because the reformer 1 needs to perform the reforming reaction at 500 to 600 ° C.
[0021]
In the hydrogen separation reformer 1 used in the present system, a reaction tube is filled with a reforming catalyst 11 for performing a steam reforming reaction using hydrocarbon gas and steam as raw materials. This reaction tube is provided with a hydrogen permeable section 14 separated by a hydrogen separation membrane 12. A combustion section 13 is provided outside the reaction tube, for example, at a lower portion or an upper portion, and a combustion gas passage 15 is provided.
Hydrogen gas generated by the steam reforming reaction in the catalyst layer 11 is extracted through the hydrogen separation membrane 12 to the permeation section 14. The hydrogen gas stored in the permeation section 14 is discharged from the reformer 1 as high-purity hydrogen gas. Since the separated hydrogen gas has a high temperature of about 500 ° C., it is cooled through a heat exchanger at the subsequent stage.
At this time, the hydrogen gas passes through a boiler air preheater 8 (heat exchanger) in order to preheat air for combustion in the boiler 2. Next, the hydrogen gas passes through a water preheater 9 (heat exchanger) to preheat the water supplied to the boiler. The hydrogen gas is passed through a cooling heat exchanger 10 through which cooling water is passed, if necessary, in order to make the temperature of the product hydrogen gas (for example, 40 to 50 ° C.) appropriate.
[0022]
On the other hand, in the system of the present embodiment, in the off-gas recovery step, after the off-gas discharged from the hydrogen production step is cooled, the water component and the gas component in the off-gas are separated into gas and liquid, and then only the gas component is produced by hydrogen. It can also be used for combustion in the process.
Specifically, the temperature of the off-gas of about 500 ° C. that has exited the catalyst layer 11 is reduced to about 100 ° C. by preheating the primary air sent to the combustion section 13 with the burner air preheater 3 (heat exchanger). Lower. The off-gas is further cooled to about 70 to 80 ° C. through the cooling heat exchanger 4 through which cooling water passes. Next, water and gas components are separated in the gas-liquid separator 5 at about 50 ° C. The water component becomes water supply or drainage to the boiler, and the remaining gas component is sent to the combustion unit 13 as a combustion component for heating the reformer 1.
In the system according to the present embodiment as described above, the thermal efficiency of the entire system can be improved by effectively using the waste heat generated in the system.
Further, in the system shown in FIG. 4, the exhaust gas from the boiler 2 is also used for the heat of the reformer 1, so that the thermal efficiency can be improved.
[0023]
【The invention's effect】
According to the system of the present invention, in a system having a multitubular reaction tube, the reaction tube is uniformly heated by the combustion gas, the temperature distribution in the reformer is made uniform, and the steam reforming reaction is stabilized throughout the catalyst layer. It can be implemented in practice. In addition, by using a system for circulating combustion exhaust gas, waste heat can be effectively recovered, so that the overall system has high thermal efficiency.
[Brief description of the drawings]
FIG. 1 is a system diagram schematically showing a configuration of a hydrogen production system of the present invention.
FIG. 2 is a configuration diagram showing an example of a hydrogen separation type reformer having a multitubular reaction section suitably used in the system of the present invention.
FIG. 3 is a configuration diagram schematically showing an example of the hydrogen production system of the present invention.
FIG. 4 is a configuration diagram schematically showing another example of the hydrogen production system of the present invention.
[Explanation of symbols]
1 Hydrogen separation type reformer 2 Boiler 3 Burner air preheater (heat exchanger)
4 heat exchanger 5 gas-liquid separator 6 mixed gas preheater (heat exchanger)
7 heat exchanger 8 air preheater for boiler (heat exchanger)
9 Water preheater (heat exchanger)
Reference Signs List 10 Heat exchanger 11 Reforming catalyst layer 12 Hydrogen separation membrane 13 Combustion unit (burner)
14 Hydrogen permeable section 15 Combustion gas passage 16 Heat exchanger 17 Blower 20 Reaction tube 21 Secondary air introduction line (combustion exhaust gas inlet)
22 Line burner (combustion unit)
23 gas line 24 combustion gas passage 25 partition plate

Claims (4)

A plurality of reaction tubes filled with the reforming catalyst are provided with a hydrogen permeable portion separated by a hydrogen separation membrane, and a combustion gas passage is provided for heating the reaction tubes. Generating a combustion gas that heats the multitubular reaction section, a combustion section, and a combustion exhaust gas introduction port for introducing combustion exhaust gas in the vicinity of the combustion section, a hydrogen separation type reformer, and
A flue gas circulation line for circulating a part of the flue gas discharged from the hydrogen separation type reformer through a blower and returning the flue gas from the flue gas inlet to the reformer;
A hydrogen production system comprising: In the hydrogen separation type reformer, a combustion exhaust gas and a combustion gas supplied from a combustion exhaust gas inlet are mixed at a stage before a combustion gas exiting from a combustion unit reaches a multitubular reaction unit. The hydrogen production system according to claim 1, further comprising: 3. The fuel cell system according to claim 1, further comprising a boiler for introducing a part of the hydrocarbon gas used in the steam reforming reaction together with the air, burning the air, and heating the water to produce steam. Hydrogen production system. The gas-liquid separator according to any one of claims 1 to 3, further comprising, after cooling off-gas discharged from the hydrogen separation type reformer, separating a water component and a gas component in the off-gas. The hydrogen production system as described.

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