JP2005162581A - Hydrogen refining unit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a hydrogen refining unit in which CO content in reformed gas at the outlet of a cleaning part is surely reduced. <P>SOLUTION: In this unit, a cleaning catalyst 5 and an alumina ball 6 are mixed in the cleaning part 3, and in the upstream region of the cleaning part 3 in the direction of the reforming gas passing, the packing density of the cleaning catalyst 5 is made low, and the packing density is heightened towards the downstream region, thus oxygen is not consumed up in the upstream region, by the hydrogen in the reforming gas, and reaches the downstream region, and the CO concentration in the reforming gas at the outlet of the cleaning part 3 can be surely reduced. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a hydrogen generator. More specifically, the present invention relates to an apparatus that removes CO (carbon monoxide) in a hydrogen-rich gas produced by a reforming reaction and produces hydrogen used for fuel such as a fuel cell.

  A fuel cell cogeneration system with high power generation efficiency and high overall efficiency has attracted attention as a distributed power generator that effectively uses energy.

  Many fuel cells, such as phosphoric acid fuel cells that have been put to practical use and solid polymer fuel cells that are being developed, generate power based on hydrogen. However, since hydrogen is not provided as infrastructure, it must be generated at the site where the system is installed.

  In order to generate hydrogen, it contains an organic compound composed of at least hydrogen and carbon typified by hydrocarbon fuels such as methane, propane, gasoline, kerosene, alcohol fuels such as methanol, or ether fuels such as dimethyl ether. This is done by mixing the raw material with water vapor and bringing it into contact with a heated reforming catalyst. Usually, hydrocarbon fuel is reformed at a temperature of about 500 to 800 ° C., and alcohol fuel and ether fuel are reformed at a temperature of about 200 to 400 ° C.

  During reforming, CO is generated, and the concentration of generated CO increases as reforming is performed at a higher temperature. In particular, when a hydrocarbon fuel is used, the CO concentration is around 10% by volume (dry gas base). Therefore, the CO concentration is reduced to about several thousand ppm to several volume% by providing a shift portion containing a shift catalyst that causes CO and water vapor to contact each other to advance the water gas shift reaction.

  Furthermore, in the case of a fuel cell that operates at a low temperature of 100 ° C. or less, such as a polymer electrolyte fuel cell used for in-vehicle use or home use, the Pt (platinum) catalyst used for the electrode is replaced with hydrogen-rich gas. Since it is poisoned by the contained CO, it is necessary to remove the CO concentration to 100 ppm or less, preferably 10 ppm or less before supplying the reformed gas to the fuel cell.

  In order to reduce the CO concentration in the reformed gas to 100 ppm or less, a purification unit filled with a purification catalyst is provided after the shift unit, and a configuration is often adopted in which a small amount of air is added to oxidize CO. .

  In addition, when oxidizing by adding air, the reformed gas temperature rises due to the heat generated by the reaction, so that oxygen in the supplied air is promoted to oxidize hydrogen in the reformed gas, so that the amount of generated hydrogen is not reduced. In addition, it has been proposed that an inert substance that does not contribute to the oxidation reaction, such as glass beads and ceramic particles, is mixed to release heat from the reaction (see, for example, Patent Document 1).

Further, for the same purpose as the invention described in Patent Document 1, the vent opening is provided so that the reformed gas and the air do not pass through the purification catalyst in the upstream region but go to the purification catalyst in the downstream region. (For example, refer to Patent Document 2).
JP-A-10-72202 JP-A-11-102608

  However, simply by mixing, the amount of the purification catalyst particularly in the downstream region may be uncontrollable because it may be less than the reformed gas flow rate, and CO may not be reliably reduced.

  In addition, the method described in Patent Document 2 has a problem that it is not applicable to various configurations of the purifying unit, and mixing of the reformed gas and air is difficult to proceed.

  In order to solve the above-mentioned problems, the hydrogen purifier of the present invention has a purifying section filled with a purifying catalyst that oxidizes CO in the reformed gas using an oxidizing gas, and is inactive against the oxidation reaction. An inert substance and a purification catalyst are mixed and filled in the purification unit, and the contact area between the reformed gas and the purification catalyst increases as the reformed gas moves from the upstream region to the downstream region in the direction of passing through the purification unit. The purification unit is configured so that

  With this configuration, it is more reliable to reduce the CO concentration in the reformed gas at the purification section outlet.

  As described above, according to the hydrogen purification apparatus of the present invention, since oxygen in the air supplied to the downstream region of the purification unit can be reached, CO in the reformed gas at the outlet of the purification unit is 100 ppm or less. It becomes more reliable to reduce to.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

(Embodiment 1)
FIG. 1 is a configuration diagram of a hydrogen purification apparatus according to the first embodiment of the present invention. In FIG. 1, the reforming unit 1 includes a fuel and steam containing an organic compound composed of at least carbon and hydrogen, such as natural gas, city gas, hydrocarbons such as propane, alcohols such as methanol, or ethers. And a reforming catalyst (not shown) for generating hydrogen-rich reformed gas by reacting with air.

  The shift unit 2 stores a shift catalyst (not shown) that promotes a water gas shift reaction between CO and water vapor in the reformed gas.

  The purification unit 3 is filled with a purification catalyst 5 that oxidizes the oxygen in the air supplied to the reformed gas that has passed through the shift unit 2 by the air supply unit 4 and the CO in the reformed gas. Further, as an inert substance that is not reactive with CO in the reformed gas, the alumina sphere 6 is mixed with the purification catalyst 5 and filled, and the upstream region in the direction in which the reformed gas passes through the purification unit 3. In this case, the filling ratio of the purification catalyst 5 is lowered and the filling ratio is increased toward the downstream region.

  In the present embodiment, the purification catalyst 5 is a Pt / alumina catalyst in which Pt is supported on a spherical alumina carrier.

  According to such a configuration, the CO concentration in the reformed gas after passing through the shift unit 2 is about several thousand ppm to several percent.

  By supplying air from the air supply unit 4 into the reformed gas after passing through the shift conversion unit 2, oxygen in the air oxidizes CO in the reformed gas on the surface of the purification catalyst 5 and reduces CO. be able to.

  However, in the upstream region in the direction in which the reformed gas passes, since the filling ratio of the purification catalyst 4 is low, oxygen in the air passing through the surface of the alumina sphere 6 does not oxidize CO and hydrogen of the reformed gas. Head downstream.

  In the downstream region, since the filling ratio of the purification catalyst 5 is high, the CO remaining in the reformed gas can surely react with oxygen that has passed through the upstream region, and reforming at the outlet of the purification unit 3 The CO concentration in the gas can be reduced to 100 ppm or less.

  In the upstream region of the purification unit 3, all the oxygen in the supplied air is not consumed by the oxidation reaction of CO and hydrogen, so that the number of oxidation reactions of the purification catalyst 5 existing in the upstream region can be reduced. Further, there is an effect that the durability of the purification catalyst 5 can be improved and the selective oxidation property with respect to CO can be maintained.

  Further, the disturbance of the flow of the reformed gas caused by filling the purification catalyst 5 and the alumina sphere 6 promotes the mixing of CO and oxygen in the reformed gas, so that CO is more effectively oxidized. Can do.

  Further, as shown in FIG. 1, it is preferable that the upstream is a mixed layer and the most downstream is a 100% purification catalyst. This is because heat generation is reliably prevented upstream of the purification catalyst, and downstream, which leads to improved reactivity of the carbon monoxide selective oxidation reaction.

  In this embodiment, a Pt / alumina catalyst is used as the purification catalyst 5, but a catalyst prepared by supporting another noble metal or metal, or a mixture of two or more kinds of noble metals or metals supported by alloying. A catalyst prepared by doing so may be used. Moreover, you may use the catalyst prepared using the other metal oxide support | carrier.

  In this embodiment, alumina spheres are used as the inert substance, but the same effect can be obtained by using a substance that is not reactive to an oxidation reaction such as silica.

  In this embodiment, the purification catalyst 5 and the alumina sphere 6 are spherical, but the shape is not limited.

(Embodiment 2)
FIG. 2 is a configuration diagram in the present embodiment. In FIG. 2, the same components as those in FIG.

  In FIG. 2, the purification unit 11 is filled with the purification catalyst 5.

  The purification unit 11 has a configuration in which the flow path cross-sectional area is narrowed in the upstream region through which the reformed gas passes, and the flow channel cross-sectional area increases toward the downstream region, and passes through the purification unit 11. The speed in the flow direction in which the reformed gas contacts the purification catalyst 5 decreases from the upstream region toward the downstream region.

  According to such a configuration, since the contact speed between the purification catalyst 5 and the reformed gas is high in the upstream region of the purification unit 11, the oxygen in the supplied air has priority over oxidizing CO, It is difficult to be used to oxidize hydrogen. Therefore, oxygen can reach the downstream region of the purification unit 11 without consuming all the oxygen in the air supplied in the upstream region.

  Since the contact speed between the purification catalyst 5 and the reformed gas is slow in the downstream region of the purification unit 11, the oxygen that has passed through the upstream region of the purification unit 11 reliably oxidizes the CO remaining in the reformed gas. It is possible to more reliably reduce the CO concentration in the reformed gas to 100 ppm or less at the outlet of the purification unit 11.

  In the upstream region of the purification unit 11, since all of the oxygen in the supplied air is not consumed by the oxidation reaction of CO and hydrogen, there is an effect that the durability of the purification catalyst 5 can be improved and the selective oxidation property against CO can be maintained. .

  In this embodiment, a Pt / alumina catalyst is used as the purification catalyst 5, but a catalyst prepared by supporting other noble metals or metals, or two or more kinds of noble metals or metals mixed or alloyed and supported. A catalyst prepared by doing so may be used. Moreover, you may use the catalyst prepared using the other metal oxide support | carrier.

  As in the first embodiment, the purifying unit 11 is further filled with an inert substance that is not reactive to the oxidation reaction of CO typified by alumina spheres and the purifying catalyst 5. The effect of reducing CO is improved.

(Embodiment 3)
FIG. 3 is a configuration diagram in the present embodiment. 3, the same components as those in FIGS. 1 and 3 are denoted by the same reference numerals, and description thereof is omitted.

  In FIG. 3, the purification section 21 has a conical blocking section 22 that narrows the cross-sectional area of the upstream region in the direction in which the reformed gas passes and increases the cross-sectional area of the flow path toward the downstream area. The purification catalyst 5 is filled so as to surround the periphery of the obstruction part 22.

  According to such a configuration, since the cross-sectional area of the flow path through which the reformed gas passes is small in the upstream region of the purification unit 21, the contact speed between the purification catalyst 5 and the reformed gas is increased. For this reason, oxygen in the supplied air is preferentially used for oxidizing CO, and is difficult to use for oxidizing hydrogen in the reformed gas. As a result, oxygen can reach the downstream region of the purification unit 21 without consuming all the oxygen supplied in the upstream region.

  Since the contact speed between the purification catalyst 5 and the reformed gas is slow in the downstream region of the purification unit 21, the oxygen that has passed through the upstream region of the purification unit 21 reliably oxidizes the CO remaining in the reformed gas. It is possible to reduce the CO concentration in the reformed gas to 100 ppm or less at the outlet of the purification unit 21.

  In the upstream region of the purification unit 21, all the oxygen in the supplied air does not contribute to the oxidation reaction of CO and hydrogen, so that there is an effect of improving the durable life of the purification catalyst 5.

  In this embodiment, a Pt / alumina catalyst is used as the purification catalyst 5, but a catalyst prepared by supporting other noble metals or metals, or two or more kinds of noble metals or metals mixed or alloyed and supported. A catalyst prepared by doing so may be used. Moreover, you may use the catalyst prepared using the other metal oxide support | carrier.

  As in the first and second embodiments, the purifying unit 21 is further filled with an inert substance that is not reactive to the oxidation reaction represented by alumina spheres and the purifying catalyst 5, thereby further reducing CO. There is a reduction effect, and the durability of the catalyst is also improved.

  The obstructing portion 22 is not limited to a conical shape, and the contact between the reformed gas and the purification catalyst 5 is such that the flow passage cross-sectional area in the upstream region of the purification portion 21 is narrowed and the flow passage cross-sectional area increases toward the downstream region. Any configuration may be used as long as the speed decreases toward the downstream region.

  Further, the blocking unit 22 may be provided inside the purification unit 11 described in the second embodiment to narrow the flow passage cross-sectional area in the upstream region, and the flow passage cross-sectional area may be increased toward the downstream region.

(Embodiment 4)
FIG. 4 is a configuration diagram in the present embodiment. 4, the same components as those in FIG. 1 are denoted by the same reference numerals, and description thereof is omitted.

  In FIG. 4, a metal oxide 36 is a substance that releases oxygen into the reformed gas when it comes into contact with the reformed gas, and fills the purifying unit 3 together with the purifying catalyst 5.

  In the present embodiment, spherical ceria is used as the metal oxide 36.

  The ceria used as the metal oxide 36 is reduced by hydrogen in the reformed gas as shown in the following (Chemical Formula 1) and releases oxygen into the reformed gas.

  In particular, when the amount of oxygen supplied into the reformed gas decreases, oxygen is easily released.

  When the amount of hydrogen generated by the hydrogen purifier is increased, the flow rate of the reformed gas supplied to the purification unit 3 is increased. At that time, the amount of oxygen relative to CO in the reformed gas becomes small, and the CO concentration in the reformed gas cannot be reduced to 100 ppm or less at the outlet of the purification unit 3 in some cases.

  However, when the amount of oxygen decreases, the metal oxide 36 is reduced by hydrogen in the reformed gas to release oxygen, and the released oxygen is purified catalyst in the same manner as oxygen in the air supplied from the air supply unit 4. 5 CO is oxidized on the surface. For this reason, even when the reformed gas flow rate is increased, the CO concentration in the reformed gas can be reliably reduced to 100 ppm or less at the outlet of the purification unit 3.

  When the ratio of the amount of oxygen to the amount of CO in the reformed gas becomes high, the reduced metal oxide 36 is oxidized as shown in the following (Chemical formula 2) so that oxygen can be released again. Become.

  In the present embodiment, ceria is used as the metal oxide 36. However, the metal oxide 36 is a substance that undergoes a redox reaction in a reformed gas such as iron oxide or magnesia and releases oxygen into the reformed gas. It doesn't matter if it exists.

  The metal oxide 36 may not be spherical.

  As described above, the hydrogen purifier of the present invention has the effect of more reliably reducing CO in the reformed gas at the outlet of the purifier to 100 ppm or less, and is supplied from the hydrogen purifier. It is useful for a fuel cell system using hydrogen.

Configuration diagram of a hydrogen purifier in Embodiment 1 of the present invention Configuration diagram of a hydrogen purification apparatus in Embodiment 2 of the present invention Configuration diagram of a hydrogen purification apparatus in Embodiment 3 of the present invention Configuration diagram of a hydrogen purifier in Embodiment 4 of the present invention

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Reforming part 2 Metamorphic part 3 Purifying part 4 Air supply part 5 Purifying catalyst 6 Alumina sphere 11 Purifying part 21 Purifying part 22 Interference part 36 Metal oxide

Claims (8)

A reformed gas supply unit for supplying a reformed gas containing at least CO, an oxidizing gas supply unit for supplying an oxidizing gas into the reformed gas, and oxidizing the CO in the reformed gas using the oxidizing gas A purification unit filled with a purification catalyst, wherein the purification unit is configured such that a contact area between the reformed gas and the purification catalyst increases from upstream to downstream. Hydrogen purification equipment. The purifying unit is a mixture of an inactive substance that is not active with respect to an oxidation reaction and a purifying catalyst, and the mixing ratio of the inactive substance decreases from upstream to downstream of the purifying unit. The hydrogen purifier according to claim 1. A reformed gas supply unit that supplies a reformed gas containing at least CO, an oxidizing gas supply unit that supplies an oxidizing gas into the reformed gas, and a purification that oxidizes CO in the reformed gas by the oxidizing gas. A purification unit filled with a catalyst, wherein the purification unit is configured such that a contact speed between the reformed gas and the purification catalyst decreases from upstream to downstream. apparatus. The hydrogen purification unit according to claim 3, wherein the purification unit is configured such that a cross-sectional area of a flow path through which the reformed gas passes through the purification catalyst increases from upstream to downstream of the purification unit. apparatus. The purification unit has an obstruction part that does not allow the reformed gas to pass inside, and a purification catalyst is filled around the obstruction part, and the volume of the obstruction part decreases as it goes from upstream to downstream of the purification part, The hydrogen purifier according to claim 3 or 4, wherein the purification catalyst is configured so that a filling volume thereof is increased. The hydrogen purifier according to any one of claims 1 to 5, wherein the purification unit is further mixed with a metal oxide that generates oxygen in contact with the reformed gas in the purification catalyst. The hydrogen purification apparatus according to claim 1, wherein the purification catalyst has a particle shape. The hydrogen purifier according to any one of claims 1 to 9, wherein the inert substance has a particle shape.

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