JP2001343341A - Gas concentration detector, hydrogen refiner and fuel cell system including the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a CO concentration detector functioning stably in reformed gas and a hydrogen refiner capable of making a CO cleaning catalyst fulfill its function and rapidly supplying the reformed gas to a fuel cell on starting. SOLUTION: This detector is provided with a temperature detector provided with a gas supplying part for supplying a gas containing hydrogen and carbon monoxide and a reaction chamber equipped with a catalyst layer on the downstream side from the gas supplying part to detect the temperature of the catalyst layer or the gas temperature after passing through the catalyst layer. The concentration of the carbon monoxide is detected by a signal from the temperature detector.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a gas concentration detector and a hydrogen purifier. More specifically, an apparatus for detecting the concentration of CO in a reformed gas containing hydrogen used as a main component in fuel such as a fuel cell and containing carbon monoxide (hereinafter referred to as “CO”), and a hydrogen purifier About.

[0002]

2. Description of the Related Art Conventionally, hydrogen used in fuel cells and the like is obtained by mixing steam with hydrocarbon fuels such as methane, propane, gasoline and kerosene, alcohol fuels such as methanol, or ether fuels such as dimethyl ether. It is generated by contact with a heated reforming catalyst.
Normally, hydrocarbon fuel is reformed at a temperature of about 500 to 800 ° C, and alcohol and ether fuels are reformed at a temperature of about 200 to 400 ° C. CO is generated during the reforming, but the higher the temperature is, the higher the concentration of the generated CO becomes. In particular, when a hydrocarbon fuel is used, the CO concentration of the reformed gas is about 10% by volume. Therefore, CO and hydrogen are reacted using a CO shift catalyst to reduce the CO concentration to about several thousand ppm to several volume%.

Further, in the case of a fuel cell operating at a low temperature of 100 ° C. or less, such as a solid polymer electrolyte fuel cell used for vehicles or for home use, the Pt catalyst used for the electrode is reformed. Since there is a possibility of being poisoned by CO contained in the gas, 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. for that reason,
A CO purification section filled with a catalyst is provided in the hydrogen purification device,
Is removed by methanation or selective oxidation with the addition of traces of air to remove CO. When CO is removed by selective oxidation using a CO purification catalyst, Pt, Ru,
A noble metal catalyst such as Rh or Pd is mainly used. In order to sufficiently remove CO, 1 to 1
About three times as much oxygen is required. Here, the CO concentration in the reformed gas changes when the amount of hydrogen supplied to change the power generation amount of the fuel cell system changes, or when the catalyst activity is slightly reduced by operating the apparatus for a long time. for that reason,
In order to control the oxygen amount to the optimum value, it is necessary to detect the CO concentration.

[0004]

However, as is generally done, the absorption of light of infrared wavelengths by CO
The concentration is detected, and from the change in resistance due to CO adsorption, C
The technique of detecting the O concentration does not function stably in the reformed gas or is expensive, and thus is difficult to apply at present. For this reason, it has been difficult to keep the amount of oxygen supplied to the CO purification catalyst always optimal. Further, at the time of starting the fuel cell system, it is difficult to determine that the reformed gas can be supplied to the fuel cell even after the CO is sufficiently removed by the hydrogen purifier.

As described above, in the prior art, since there was no inexpensive and reliable means for detecting the concentration of CO effective in the reformed gas, the function of the CO purification catalyst could not be fully exhibited, , A long standby operation was required to start supplying the reformed gas to the fuel cell. Therefore, an object of the present invention is to provide a means capable of inexpensively and reliably detecting the CO concentration in a reformed gas and a hydrogen purifying apparatus capable of sufficiently exerting the function of a CO purification catalyst. .

[0006]

In order to achieve the above object, the present invention provides a gas supply unit for supplying a gas containing at least hydrogen and carbon monoxide, and a catalyst provided downstream of the gas supply unit. A reaction chamber having a catalyst layer and a temperature detector for detecting the temperature of the catalyst layer and / or the temperature of the gas after passing through the catalyst layer. Provided is a gas concentration detector for detecting a carbon oxide concentration. In this gas concentration detector, it is effective that the temperature of the reaction chamber is controlled to be constant. It is effective that a first temperature detector is provided on the upstream side of the catalyst layer and a second temperature detector is provided on the downstream side of the catalyst layer. Further, the catalyst layer may include at least Pt, Ru, Rh, Pd
Alternatively, it is effective to use Ni as an active component.

Further, according to the present invention, a gas temperature detector is provided upstream or downstream of a carbon monoxide purifying unit provided with a purifying oxygen-containing gas supply unit, and the gas temperature detector receives the signal from the gas temperature detector. Provided is a hydrogen purifying apparatus characterized by detecting a concentration of carbon monoxide of a gas after passing through a purifying unit, and controlling a flow rate of the purifying oxygen-containing gas in accordance with the concentration of carbon monoxide. In this hydrogen purifier, it is effective to further control the temperature of the carbon monoxide purifying section in accordance with the carbon monoxide concentration. Further, the present invention provides
A fuel cell system comprising a hydrogen purifier and a fuel cell, wherein a gas temperature detector is provided between the hydrogen purifier and the fuel cell, and a gas introduced into the fuel cell by a signal of the gas temperature detector. A gas flow path connecting the purifying unit and the fuel cell is switched according to the carbon monoxide concentration, so that the gas is not introduced into the fuel cell. Also provide.

[0008]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a schematic diagram showing a configuration of a gas concentration detector according to an embodiment of the present invention. In FIG. 1, a reformed gas supplied from a reformed gas inlet 1 is sent to a reaction chamber 2, reacted in a catalyst layer 3, and then discharged from a reformed gas outlet 7. The upstream temperature and the downstream temperature of the catalyst layer are measured by the first thermocouple 5 and the second thermocouple 6, respectively,
After this signal is sent to the signal processing device 8 and processed, C
Output as O concentration. The temperature of the reaction chamber 2 is maintained at a constant temperature by the heater 4. here,
Reformed gas obtained when steam reforming natural gas (C
O concentration is 10 to 1000 ppm, carbon dioxide concentration is about 2
0%, the balance being hydrogen). However, there is no substantial difference in the effect obtained by using the gas concentration detector of the present invention, even if other compositions are used, as long as there is an excess of hydrogen with respect to CO.

Next, the operation principle of the gas concentration detector according to the present invention will be described. In the catalyst layer 3, carbon monoxide and hydrogen in the reformed gas react with each other to generate methane and steam. The reaction heat at this time is about 200 k per mole of CO.
J, and the calorific value on the catalyst changes according to the CO concentration. Then, the CO concentration is measured by detecting a temperature change due to the heat generation. FIG. 2 shows the relationship between the temperature difference detected by the first thermocouple 5 and the second thermocouple 6 and the CO concentration in the reformed gas. As shown by the solid line, in a region where the CO concentration and the temperature difference can be expressed by a certain relational expression, the CO concentration can be detected by forming a calibration curve. When the CO concentration is extremely high, the conversion ratio of CO decreases, so that the change in the temperature difference with respect to the CO concentration becomes small, and it becomes difficult to detect the CO concentration. In this case, the reaction chamber 2
By increasing the temperature of, the CO conversion can be increased and the detection limit concentration can be increased.

However, since carbon dioxide is methanated at a high temperature, it must be used at a temperature which does not affect the heat generated by methanation of carbon dioxide. For this reason, the temperature of the reaction chamber 2 is preferably set to about 250 ° C. or lower, although it depends on the type of catalyst. Conversely, when the CO concentration is low, the calorific value on the catalyst is small, so that the change in the temperature difference is small and the CO
It becomes difficult to detect the density. In this case, by lowering the heat release to the outside of the reaction chamber 2 or increasing the flow rate of the reformed gas to increase the calorific value on the catalyst, a lower concentration of CO can be obtained.
Can be detected.

The catalytically active component used in the catalyst layer 3 is one that selectively shows activity against CO methanation, ie, carbon dioxide and CO in the reformed gas.
Those which show activity only for the hydrogenation reaction of CO or those which show high activity for the hydrogenation reaction of CO are used. Such catalyst components include Pt, Ru, Rh,
Metals such as Pd and Ni can be exemplified. In particular, it is preferable to contain at least Ru, Rh or Ni as the catalytically active component.

The catalyst carrier used for the catalyst layer 3 is not particularly limited as long as it can support the active component in a highly dispersed state. As such,
Alumina, silica, silica alumina, magnesia, titania, zeolite and the like can be exemplified. As the base material used for the catalyst layer 3, a base material that can sufficiently secure the contact area between the catalyst and the gas in the reaction chamber is used. As such a material, a honeycomb-shaped or foam-shaped substrate having communicating holes is preferable, and a pellet-shaped substrate may be used. Further, the temperature of the catalyst layer is preferably 80 ° C. or higher at which CO can sufficiently react, and the upper limit is 250 ° C., at which reaction of carbon dioxide hardly occurs.
C. or less is preferred. However, since the calibration curve is created at the operating temperature under the conditions including the side reaction, the operating temperature can be determined according to the application.

Further, in order to accurately detect heat generation on the catalyst, it is preferable that the temperature of the reaction chamber 2 is not affected by the external environment, sufficient heat insulation is performed, and the temperature is adjusted to a constant temperature. Is preferred. Here, a heater is used for temperature control, but a cooling method using a cooling fan or a heat medium such as oil may be used. If the application does not need to detect the CO concentration with high accuracy, there is no need to adjust the temperature. Further, in FIG. 1, a thermocouple is used to detect the temperature of the catalyst layer, but other detecting means such as a thermistor may be used as long as the temperature can be detected. Further, here, the temperatures on the upstream side and the downstream side of the catalyst layer were detected. However, when the temperature of the reformed gas to be supplied is constant, the CO concentration can be accurately measured by measuring only the downstream side of the catalyst layer. Can be measured.

The gas concentration detector using the gas temperature detector as described above can be applied to a hydrogen purifier and a fuel cell system. For example, by adopting a similar configuration not only in the above-described reforming reaction chamber but also in the metamorphic section and the purifying section, the concentration of carbon monoxide flowing into the purifying section from the denaturing section and the gas flowing out from the purifying section can be detected. can do. For example, by installing a gas temperature detector upstream of the CO purification catalyst and controlling the CO concentration detected by the signal of the gas temperature detector to supply an appropriate amount of air, wasteful hydrogen consumption is achieved. , And an increase in the CO concentration downstream of the purification catalyst due to a shortage of air can be avoided. Therefore, when used in a fuel cell system, its efficiency can be improved and stable operation can be ensured. Also, when the gas temperature detector is installed on the downstream side of the CO purification catalyst, by controlling the amount of air so that the CO concentration on the downstream side of the purification catalyst does not increase, the same effect as when the gas temperature detector is installed on the upstream side is obtained. can get.

Further, when the above gas concentration detector is applied to a fuel cell system including a hydrogen purifier and a fuel cell, the gas temperature detector is installed between the hydrogen purifier and the fuel cell, and When the CO concentration detected by the signal is high, the gas flow path is closed by closing the gas flow path so that the reformed gas is not introduced into the fuel cell, or by switching the gas flow path so that the reformed gas is discharged out of the fuel cell. To prevent poisoning.

Further, at the time of start-up, since it is possible to detect that the CO has been sufficiently removed by the hydrogen purifier, it is necessary to perform a standby operation until the temperature of the purification catalyst reaches a steady-state operation at which the CO can be reliably removed. Power can be generated quickly. Further, since the catalyst used here uses the function of the CO purification catalyst as a gas concentration detector, the CO concentration can also be detected by detecting the temperature of a part of the CO purification catalyst. If the temperature change other than the change due to the change in the CO concentration is large, the CO concentration cannot be detected with sufficient accuracy, and thus it is preferable that the change in the flow rate of the reformed gas and the temperature is small.

[0017]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a gas concentration detector according to the present invention will be described more specifically with reference to embodiments. However, the present invention is not limited only to these. Example 1 An alumina pellet having a diameter of 1 mm and a length of 1 mm and carrying 5% by weight of Ru was charged into the reaction chamber 2 of the gas concentration detector shown in FIG. A reformed gas containing 20% by volume of carbon dioxide and the remainder being hydrogen is supplied from the reformed gas inlet at a flow rate of 0.1 liter per minute, and the temperature of the first thermocouple is set to 150 ° C. by the heater 4. Adjustments were made. CO concentration in the reformed gas is 5ppm, 20ppm,
100 ppm, 500 ppm, 900 ppm, 1200
A reformed gas mixed with CO at a concentration of 2000 ppm and 2000 ppm was supplied, and the temperatures of the first thermocouple and the second thermocouple were measured. Table 1 shows the results of the CO concentration (ppm) and the temperature difference between upstream and downstream (° C.).

[0018]

[Table 1]

Example 2 In Example 1, the flow rate of the reformed gas was increased to 0.3 liter per minute, and
ppm, 4 ppm, 20 ppm, 100 ppm, 180
ppm, 240 ppm, and 400 ppm of CO
Were supplied as a mixture, and the temperatures of the first thermocouple and the second thermocouple were measured. Table 2 shows the results.

[0020]

[Table 2]

Example 3 The same procedure as in Example 1 was carried out except that Rh was used instead of Ru to reduce the CO concentration to 0 ppm and 5 ppm.
ppm, 20 ppm, 100 ppm, 500 ppm, 9
CO was mixed and supplied so as to be 00 ppm, 1200 ppm, and 2000 ppm, and the temperatures of the first thermocouple and the second thermocouple were measured. Table 3 shows the results.

[0022]

[Table 3]

Example 4 A CO concentration of 0 ppm, 5 ppm and 5% was obtained in the same manner as in Example 1 except that Ni was used instead of Ru.
ppm, 20 ppm, 100 ppm, 500 ppm, 9
CO was mixed and supplied so as to be 00 ppm, 1200 ppm, and 2000 ppm, and the temperatures of the first thermocouple and the second thermocouple were measured. Table 4 shows the results.

[0024]

[Table 4]

[0025]

As is clear from the evaluation results of the gas concentration detectors of the above embodiments, according to the present invention, it is possible to detect the CO concentration in the reformed gas by detecting the temperature of the catalyst. it can.

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing a configuration of an embodiment of a gas concentration detector according to the present invention.

FIG. 2 is a diagram showing characteristics of the gas concentration detector of the present invention.

[Explanation of symbols]

 Reference Signs List 1 reformed gas inlet 2 reaction chamber 3 catalyst layer 4 heater 5 first thermocouple 6 second thermocouple 7 reformed gas outlet 8 signal processor

Continued on the front page (51) Int.Cl. ⁷ Identification FI FI Theme Court II (Reference) // H01M 8/10 H01M 8/10 (72) Inventor Kunihiro Ukai 1006 Kadoma Kadoma, Kadoma City, Osaka Matsushita Electric Industrial Co., Ltd. F term (reference) 2G040 AA02 AB12 BA23 BB09 CA02 CA10 CB02 CB04 DA03 DA13 EA02 EB02 EC07 ZA05 4G040 FA04 FB04 FC07 FE01 5H026 AA06 5H027 AA06 BA01 BA17 KK44 MM12

Claims (5)

[Claims] 1. A gas supply unit for supplying a gas containing at least hydrogen and carbon monoxide; a reaction chamber including a catalyst layer provided downstream of the gas supply unit; and a temperature and / or temperature of the catalyst layer. A temperature detector for detecting a gas temperature after passing through the catalyst layer, and detecting a carbon monoxide concentration of the gas after passing through the catalyst layer by a signal of the temperature detector. . 2. The gas concentration according to claim 1, wherein a first temperature detector is provided on an upstream side of the catalyst layer, and a second temperature detector is provided on a downstream side of the catalyst layer. Detector. 3. A temperature detector for detecting a gas temperature is provided upstream and / or downstream of the carbon monoxide purifier provided with the purifying oxygen-containing gas supply unit, and a signal from the gas temperature detector is provided. Detecting the concentration of carbon monoxide in the gas after passing through the purifying section, and controlling the flow rate of the purifying oxygen-containing gas in accordance with the concentration of carbon monoxide. 4. The hydrogen purifier according to claim 3, wherein the temperature of the carbon monoxide purifier is further controlled in accordance with the concentration of carbon monoxide. 5. A fuel cell system including a hydrogen purifier and a fuel cell, wherein a gas temperature detector is installed between the hydrogen purifier and the fuel cell, and the fuel cell is operated by a signal from the gas temperature detector. Detecting the concentration of carbon monoxide gas introduced into, the gas flow path connecting the purifier and the fuel cell is switched according to the carbon monoxide concentration,
A fuel cell system, wherein the gas is not introduced into the fuel cell.