JP2004006405A - Hydrogen purification apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a hydrogen purification apparatus capable of detecting the concentration of carbon monoxide contained in gas which is passed through a purification part. <P>SOLUTION: The hydrogen purification apparatus is equipped with the purification part having a catalyst layer showing activity to methanation of carbon monoxide and a temperature detector detecting gas temperature on at least the downstream side of the purification part, and the concentration of the carbon monoxide of gas which is passed through the purification part is detected with a signal of the temperature detector, and the flow rate of oxygen-containing gas supplying to the purification part is controlled according to the concentration of the carbon monoxide. <P>COPYRIGHT: (C)2004,JPO

Description

The present invention relates to a gas concentration detector and a hydrogen purification device. More specifically, a device for detecting a CO concentration 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 purification device About.

Conventionally, hydrogen used in fuel cells and the like has been produced 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, and heating. It is generated by contact with.
Usually, the hydrocarbon fuel is reformed at a temperature of about 500 to 800 ° C, and the alcohol or ether fuel is reformed at a temperature of about 200 to 400 ° C. CO is generated at the time of reforming, but as the reforming is performed at a higher temperature, the concentration of generated CO increases. 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%.

Furthermore, in the case of a fuel cell that operates 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 reformed gas contains the Pt catalyst used for the electrode. Since the reformed gas may be poisoned by the 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. Therefore, a CO purification unit filled with a catalyst is provided in a hydrogen purification device, and CO is removed by methanation or selective oxidation by adding a small amount of air.
When CO is removed by selective oxidation using a CO purification catalyst, a noble metal catalyst such as Pt, Ru, Rh or Pd is mainly used. In order to sufficiently remove CO, about 1 to 3 times as much oxygen as CO is required.
Here, when the amount of hydrogen supplied to change the amount of power generation of the fuel cell system changes, or when the catalyst activity is slightly reduced by operating the apparatus for a long time, the CO concentration in the reformed gas changes. Therefore, in order to control the amount of oxygen to an optimal value, it is necessary to detect the CO concentration.

However, the method of detecting the CO concentration from the absorption of the infrared wavelength light by CO or detecting the CO concentration from the change in the resistance value due to CO adsorption, which is generally performed, is stable in the reformed gas. It is currently difficult to apply because it does not work or is expensive.
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 reformed gas to the reactor.

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. .

In order to achieve the above object, the present invention includes a purification unit having a catalyst layer that is active in methanation of carbon monoxide, and a temperature detector that detects a gas temperature at least downstream of the purification unit, A signal from the temperature detector detects a carbon monoxide concentration of the gas after passing through the purification unit, and controls a flow rate of the oxygen-containing gas supplied to the purification unit in accordance with the carbon monoxide concentration. A hydrogen purification device is provided.
It is preferable that the temperature of the carbon monoxide purifying unit is further controlled in accordance with the carbon monoxide concentration.
A gas supply unit configured to supply a reformed gas containing hydrogen, carbon monoxide, and carbon dioxide to the purification unit, and by setting the temperature of the catalyst layer to 80 ° C. or more and 250 ° C. or less, the temperature detector It is preferable to detect the carbon monoxide concentration of the gas after passing through the catalyst layer by the signal of

In this hydrogen purifier, it is effective that the temperature of the purifier 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, it is effective that the catalyst layer contains at least Pt, Ru, Rh, Pd or Ni as an active component.

According to the present invention, the CO concentration in the reformed gas can be detected by detecting the temperature of the catalyst.

Hereinafter, embodiments of the present invention will be described 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. The signal is sent to the signal processing device 8 and processed, and then output as the CO concentration.
The temperature of the reaction chamber 2 is maintained at a constant temperature by the heater 4. Here, a case of a reformed gas (CO concentration is 10 to 1000 ppm, carbon dioxide concentration is about 20%, and the balance is hydrogen) obtained when steam reforming natural gas is described. However, there is no substantial difference in the effect obtained by using the gas concentration detector of the present invention, even if the composition is other than the above, 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 heat of reaction at this time is about 200 kJ per mole of CO, 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 constant relational expression, the CO concentration can be detected by creating 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 the detection of the CO concentration becomes difficult. In this case, if the temperature of the reaction chamber 2 is increased, the CO conversion can be increased, and the detection limit concentration can be increased.

However, since carbon dioxide is methanated at high temperatures, it must be used at a temperature that 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, depending on the type of the catalyst.
Conversely, when the CO concentration is low, the calorific value on the catalyst becomes small, so that the change in the temperature difference becomes small, and it becomes difficult to detect the CO concentration. In this case, a lower concentration of CO can be detected by cutting off the heat radiation to the outside of the reaction chamber 2 or increasing the calorific value on the catalyst by increasing the flow rate of the reformed gas.

The catalytically active component used in the catalyst layer 3 is one that is selectively active against methanation of CO, that is, active only in the hydrogenation reaction of CO among carbon dioxide and CO in the reformed gas. Or those exhibiting high selectivity for the hydrogenation reaction of CO.
Examples of such a catalyst component include metals such as Pt, Ru, Rh, Pd, and Ni. In particular, it is preferable that at least Ru, Rh or Ni is contained as a 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. Examples of such a material include alumina, silica, silica alumina, magnesia, titania, zeolite, and the like.
As the base material used for the catalyst layer 3, a 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 communication 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 preferably 250 ° C. or lower, at which the reaction of carbon dioxide hardly occurs. However, since the calibration curve is created at the operating temperature under conditions including side reactions, the operating temperature can be determined according to the application.

In addition, 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, and it is preferable to perform sufficient heat insulation and adjust the temperature to a constant temperature. .
Here, a heater is used for temperature control, but a cooling system 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.
Although a thermocouple is used to detect the temperature of the catalyst layer in FIG. 1, 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 are detected. However, when the temperature of the supplied reformed gas 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 shift section and the purification section, the concentration of carbon monoxide flowing into the purification section and the gas flowing out of the purification 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 a gas temperature detector is installed downstream of the CO purification catalyst, the same effect as when installed upstream is achieved by controlling the amount of air so that the CO concentration downstream of the purification catalyst does not increase. can get.

Furthermore, 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 is detected by a signal from the gas temperature detector. If the CO concentration is high, the fuel cell is poisoned by CO 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. Can be prevented.

Furthermore, at the time of startup, since it is possible to detect that the CO has been sufficiently removed by the hydrogen purifier, there is no need 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 applies 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 caused by 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.

Hereinafter, the gas concentration detector according to the present invention will be described more specifically with reference to examples. 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. A reformed gas containing CO was supplied such that the CO concentration in the reformed gas became 5 ppm, 20 ppm, 100 ppm, 500 ppm, 900 ppm, 1200 ppm, and 2000 ppm, 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.).

<< Example 2 >>
In Example 1, the flow rate of the reformed gas was increased to 0.3 liter per minute, and CO was mixed and supplied so that the CO concentration became 1 ppm, 4 ppm, 20 ppm, 100 ppm, 180 ppm, 240 ppm, and 400 ppm. Then, the temperatures of the first thermocouple and the second thermocouple were measured. Table 2 shows the results.

<< Example 3 >>
CO was mixed and supplied so that the CO concentration became 0 ppm, 5 ppm, 20 ppm, 100 ppm, 500 ppm, 900 ppm, 1200 ppm, and 2000 ppm in the same manner as in Example 1 except that Rh was supported instead of Ru. The temperatures of the thermocouple and the second thermocouple were measured. Table 3 shows the results.

<< Example 4 >>
CO was mixed and supplied so that the CO concentration became 0 ppm, 5 ppm, 20 ppm, 100 ppm, 500 ppm, 900 ppm, 1200 ppm, and 2000 ppm in the same manner as in Example 1 except that Ni was supported instead of Ru. The temperatures of the thermocouple and the second thermocouple were measured. Table 4 shows the results.

It is a schematic diagram showing the composition of one embodiment of a gas concentration detector concerning the present invention. It is a figure showing the characteristic of the gas concentration detector of the present invention.

Explanation of reference numerals

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

Claims (3)

A purifying unit having a catalyst layer that is active in the methanation of carbon monoxide, and a temperature detector that detects a gas temperature at least downstream of the purifying unit, and after passing through the purifying unit according to a signal from the temperature detector. A hydrogen purification apparatus, wherein the concentration of carbon monoxide is detected and the flow rate of the oxygen-containing gas supplied to the purification unit is controlled in accordance with the concentration of carbon monoxide. 3. The hydrogen purifier according to claim 2, further comprising controlling the temperature of the carbon monoxide purifying unit in accordance with the carbon monoxide concentration. A gas supply unit that supplies a reformed gas containing hydrogen, carbon monoxide, and carbon dioxide to the purification unit, and by setting the temperature of the catalyst layer to 80 ° C. or more and 250 ° C. or less, the signal of the temperature detector The hydrogen purification apparatus according to claim 1, wherein the concentration of carbon monoxide after passing through the catalyst layer is detected by the method.

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