JPH10245202A - Purification of hydrogen gas - Google Patents

Abstract

PROBLEM TO BE SOLVED: To solve the problems of a batch process for the purification of hydrogen gas comprising the increase in the initial discharging amount, the lowering of the recovery of hydrogen and the unstable purging amount and the problems of flow process comprising the increase in the hydrogen content of the purge gas caused by the constant purging in the absorbing step to deteriorate the hydrogen recovery. SOLUTION: This hydrogen purification process comprises the absorption operation to introduce hydrogen gas containing impurity gases into a hydrogen recovery vessel 4 to cause the occlusion of the hydrogen gas in a cooled hydrogen-occlusion alloy M, the releasing operation to stop the introduction of hydrogen gas and release the hydrogen gas rich in the impurity gas from the hydrogen recovery vessel to the outer atmosphere while keeping the pressure in the hydrogen recovery vessel 4 to a level exceeding the dissociation equilibrium pressure of hydrogen gas, the repetition of the absorption operation plural times interposing the releasing operation therebetween, the purging operation to release the occluded hydrogen by heating the hydrogen- occlusion alloy M and discharge the hydrogen gas rich in impurity gas from the hydrogen recovery vessel 4 and the recovering operation to stop the purge and recover the high-purity hydrogen gas released from the heated hydrogen-occlusion alloy M.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for purifying hydrogen gas for obtaining high-purity hydrogen gas by removing impure gas from hydrogen gas containing impure gas.

[0002]

2. Description of the Related Art As a conventional hydrogen gas purifying method, a batch type and a flow type are known. A conventional batch type of this type is disclosed in, for example, Japanese Patent Application Laid-Open No. 7-26760.
No. 7 is known. In this hydrogen gas purification method, hydrogen from a hydrogen source is guided to a hydrogen recovery container and stored in a cooled hydrogen storage alloy in the hydrogen recovery container. In the absorption step of storing hydrogen in the hydrogen storage alloy, the impurity gas gradually accumulates around the hydrogen storage alloy while being concentrated. When sufficient hydrogen has been absorbed by the hydrogen storage alloy, supply from the hydrogen source is stopped, and then the hydrogen storage alloy in the hydrogen recovery container is heated to release hydrogen from the hydrogen storage alloy. At the beginning of the hydrogen release, the impurity gas in the container is purged using the pressure at which hydrogen is released from the hydrogen storage alloy.

However, in such a conventional batch-type hydrogen gas purification method, since the impurity gas is purged while heating the hydrogen storage alloy without fail, the initial release amount increases and the hydrogen recovery rate decreases. There is a tendency. In addition, the amount of hydrogen released during heating varies depending on the capacity of the hydrogen storage alloy, and there is a technical problem that the amount of purge is unstable. In addition, the hydrogen storage alloy has a property that, in the absorption step of storing hydrogen, when the impurity gas gradually accumulates around the hydrogen storage alloy and the purity of the surrounding hydrogen decreases, the amount of hydrogen storage decreases. . As a result, the hydrogen absorption capacity of the hydrogen storage alloy is not fully utilized, and as a result, it is necessary to switch the hydrogen storage alloy from the cooling state to the heating state at an early stage. The purification takes a long time.

[0004] As a conventional flow method, Japanese Patent Publication No.
What is described in -49561 is known.
In this hydrogen gas purification method, in the absorption step of storing hydrogen in the hydrogen storage alloy, while introducing hydrogen containing an impure gas from the hydrogen source into the hydrogen recovery container, the impurity is continuously passed through the pores from the outlet of the container. Release hydrogen containing gas,
Thereafter, hydrogen gas is desorbed.

However, in such a conventional flow-type hydrogen gas purification method, in the absorption step of cooling the hydrogen storage alloy, the impurity gas is always purged, so that the hydrogen content in the purge gas increases. In addition to the tendency, the hydrogen recovery rate is inferior, and the structure becomes complicated due to the necessity of a throttle pipe or the like for forming pores.

[0006]

SUMMARY OF THE INVENTION The present invention has been made in view of such conventional technical problems, and has the following configuration. According to the first aspect of the present invention, the hydrogen recovery container 4 is configured to supply hydrogen gas containing impurity gas from the impurity hydrogen gas line 10.
Then, an absorption operation for storing hydrogen in the cooled hydrogen storage alloy M in the hydrogen recovery container 4 is performed, and then the introduction of hydrogen gas from the impure hydrogen gas line 10 is stopped. Is maintained at a pressure exceeding the hydrogen gas dissociation equilibrium pressure, a discharge operation of discharging hydrogen gas containing a large amount of impurity gas in the hydrogen recovery container 4 from the purge gas line 12 to the outside is performed, and the absorption operation is performed at least with the discharge operation interposed therebetween. After the plurality of passes, the hydrogen storage alloy M in the hydrogen recovery container 4 is heated to release the hydrogen stored in the hydrogen storage alloy M, and the hydrogen gas containing a large amount of the impurity gas in the hydrogen recovery container 4 is purged. A purge step of releasing the gas from the line 12 to the outside is performed. Thereafter, the release from the purge gas line 12 is stopped, and the high purity hydrogen released from the hydrogen storage alloy M in the heated state is removed. It is hydrogen gas purification method, characterized in that to release recovered hydrogen gas from the purified gas line 11. Claim 2 is provided with a pressure detecting means 7 for detecting the pressure in the hydrogen recovery container 4, and starts the discharge operation after the pressure in the hydrogen recovery container 4 reaches a predetermined set value, and a predetermined time elapses. The method for purifying hydrogen gas according to claim 1, wherein the method is continued.

[0007]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows a hydrogen gas purifying apparatus according to one embodiment of the present invention. In the figure, reference numeral 1 denotes a hydrogen utilization device as a hydrogen source, which uses high-purity hydrogen gas and discharges impure hydrogen gas to be purified after use. The impure hydrogen gas discharged from the hydrogen utilization device 1 contains an impure gas, for example, nitrogen, carbon dioxide, oxygen, methane, and the like. The hydrogen outlet 1a of the hydrogen utilization device 1 has:
An impure hydrogen gas line 10 having a first valve AV1 having an opening / closing function allows a hydrogen recovery container 4 composed of an MH container
Is connected. The hydrogen inlet 1b of the hydrogen utilization device 1
Is connected to a hydrogen outlet of the hydrogen recovery container 4 by a purified gas line 11 having a second valve AV2 having an opening / closing function.

Further, a purge gas line 12 having a third valve AV3 having an opening / closing function is connected to a hydrogen outlet of the hydrogen recovery container 4. This purge gas line 12
Is open to the atmosphere, but can be connected to another container to collect the impure gas.

Hydrogen recovery container 4 using hydrogen storage alloy M
Contains hydrogen storage alloy M (metal hydride) inside,
A heating device 5 for heating the hydrogen storage alloy M and a cooling device 6 for cooling are provided. 7 is a pressure detecting means (pressure gauge)
Thus, the pressure in the hydrogen recovery container 4 can be detected. The pressure detecting means 7 detects that the pressure in the hydrogen recovery container 4 has risen to a set value. This setting is
Normally, the hydrogen absorption of the hydrogen storage alloy M substantially reaches saturation, and the pressure in the hydrogen recovery container 4 is set to substantially match the pressure in the hydrogen utilization device 1. The heating device 5 is generally configured by introducing hot water into the heat medium passage, and the cooling device 6 is generally configured by introducing cold water into the heat medium passage. The hydrogen storage alloy M reacts with hydrogen gas and reversibly absorbs or releases hydrogen gas. This reaction is performed based on a hydrogen equilibrium pressure-temperature characteristic (PT characteristic) in a plateau region, and hydrogen dissociation occurs. From the temperature condition at the equilibrium pressure, hydrogen gas is occluded when cooled to a low temperature by the cooling device 6, and hydrogen gas is released when heated to a high temperature by the heating device 5. On the other hand, when the temperature is constant, hydrogen gas is released under a pressure lower than the hydrogen dissociation equilibrium pressure (plateau pressure).

Next, a method for purifying hydrogen gas will be described. Since impure hydrogen gas is generated in the hydrogen in the hydrogen utilization device 1, the absorption process is performed periodically. The absorption step consists of an absorption operation and a release operation. In the absorption operation, the first valve AV1
Is opened, and the other second and third valves AV2 and AV3 are closed. Thereby, the impure hydrogen gas in the hydrogen utilization device 1 flows into the hydrogen recovery container 4 through the impure hydrogen gas line 10 and the first valve AV1. At this time, by operating the cooling device 6 to cool the hydrogen storage alloy M, hydrogen is stored in the hydrogen storage alloy M, and the impurity gas gradually accumulates in the voids around the hydrogen storage alloy M.

By performing this absorption operation, impurity gases such as nitrogen and carbon dioxide gradually accumulate around the hydrogen storage alloy M,
As the hydrogen absorption amount decreases, the pressure in the hydrogen recovery container 4 increases. This pressure increase is detected by the pressure detecting means 7, and when the pressure in the hydrogen recovery container 4 reaches a predetermined set pressure, the first valve AV1 is closed, and the third valve AV3 is opened for a predetermined time, so that hydrogen is removed. A discharge operation of discharging hydrogen gas containing a large amount of impurity gas in the recovery container 4 from the purge gas line 12 to the outside is performed. At that time, the cooling device 6
It is desirable to continue the operation to continue cooling the hydrogen storage alloy M and to reliably prevent the hydrogen gas from being released from the hydrogen storage alloy M as the pressure is reduced. However, the cooling device 6 is temporarily stopped. It is possible. On the other hand, the heating device 5
Shall remain inactive. In short, the release of hydrogen from the hydrogen storage alloy M is suppressed while the hydrogen storage alloy M is kept at a pressure exceeding the hydrogen dissociation equilibrium pressure (plateau pressure).

As a result, the relatively high-pressure impurity gas collected around the hydrogen storage alloy M is discharged from the purge gas line 12 to the outside (atmosphere), and the pressure in the hydrogen recovery container 4 is reduced by the gas purge amount. When discharging the impure gas from the purge gas line 12 to the atmosphere, the impure gas is purged for a predetermined time from a state where the pressure inside the hydrogen recovery container 4 reaches the set pressure and a constant differential pressure between the atmospheric pressure and the pressure. The outflow of the purge gas is stabilized. The reason why the purge gas amount for purifying the hydrogen gas is stabilized is that the constant differential pressure between the set pressure in the hydrogen recovery container 4 and the atmospheric pressure is not affected by the hydrogen processing ability of the hydrogen storage alloy M.

When a predetermined time has elapsed since the third valve AV3 was opened and the pressure in the hydrogen recovery container 4 decreased, the third valve AV3 was closed to finish the discharge operation, and the first valve AV1 was opened again. The cooling device 6 continues to operate.
Thereby, the absorption operation is performed again in a state where the impurity gas around the hydrogen storage alloy M is reduced. If the pressure in the hydrogen recovery container 4 increases to the set pressure again by the continuation of the absorption operation, the above-described hydrogen recovery container 4
After performing the operation of releasing the impurity gas in the inside, the hydrogen storage alloy M is caused to perform the hydrogen storage, that is, the absorption operation. Thus, the operation of discharging the impure gas prevents the hydrogen storage capacity of the hydrogen storage alloy M from gradually decreasing due to the influence of the surrounding impurity gas, thereby ensuring a stable hydrogen storage function of the hydrogen storage alloy M. In addition, the performance of the hydrogen recovery container 4 is hardly reduced. When sufficient hydrogen has been occluded in the hydrogen storage alloy M in this way, the cooling device 6 is stopped, the first valve AV1 is closed, the absorption process is completed, and the process proceeds to the purge process. The fact that sufficient hydrogen was stored in the hydrogen storage alloy M
It can be known from the fact that the pressure in the hydrogen recovery container 4 has risen to the set pressure.

In the purging step, the heating device 5 is operated, and the third valve AV3 is opened to release hydrogen from the hydrogen storage alloy M, and the impurities accumulated around the hydrogen storage alloy M without being absorbed are collected. Purging gas line 12
From the outside (atmosphere). The impurity gas around the hydrogen storage alloy M is pushed out from the hydrogen recovery container 4 while the hydrogen is released from the hydrogen storage alloy M by the operation of the heating device 5. When the impurity gas in the hydrogen recovery container 4 has been sufficiently released in this way, the third valve AV3 is closed, and the process proceeds to the discharging step.

In the discharging step, while the heating device 5 is operated, the second valve AV2 is opened, and pure hydrogen released from the heated hydrogen storage alloy M is led to the purified gas line 11, and hydrogen is supplied from the hydrogen inlet 1b to the hydrogen inlet 1b. It flows into the use device 1.
When the pure hydrogen is sufficiently released from the hydrogen storage alloy M in this way, the heating device 5 is stopped and the second
The valve AV2 is closed, and the discharging step ends. The fact that the hydrogen has been sufficiently released from the hydrogen storage alloy M can be known from a decrease in the pressure in the hydrogen recovery container 4.

As described above, the hydrogen gas discharged from the hydrogen utilization device 1 can be returned to the original hydrogen utilization device 1 after purification, and of course can be returned to another hydrogen utilization device 1 after purification. Further, the hydrogen gas having the impure gas can be introduced from another hydrogen source instead of the hydrogen utilization device 1.

Table 1 shows that each valve AV1 and valve AV
2, the opening / closing operation of the valve AV3 and the operation of the pressure detecting means 7, the heating device 5 and the cooling device 6 are shown. The black painted portion indicates that the valves AV1, AV2, and AV3 are open and the hydrogen recovery container 4
The inside indicates the set pressure and the operating state of the heating device 5 or the cooling device 6, and the white portions indicate the valves AV 1, AV 2, A
V3 indicates a closed state, the inside of the hydrogen recovery container 4 indicates a pressure lower than a set pressure, and the heating device 5 or the cooling device 6 indicates a non-operating state. As can be seen from the table, in the absorption step, an absorption operation (shown in Table 1) is performed by opening only the first valve AV1 while operating the cooling device 6 to cool the hydrogen storage alloy M. Thereby, the impure hydrogen gas in the hydrogen utilization device 1 passes through the impure hydrogen gas line 10 and the first valve AV1,
And is absorbed by the cooled hydrogen storage alloy M, and the impurity gas gradually accumulates around the hydrogen storage alloy M.

[0018]

[Table 1]

When the impurity gas accumulates around the hydrogen storage alloy M and the pressure detecting means 7 detects that the set pressure has been reached, a discharging operation (shown in Table 1) is performed. That is, while the cooling device 6 is operated, the first valve AV
1 is closed and the third valve AV3 is opened. By performing this release operation for a predetermined period of time, the hydrogen recovery container 4
If the internal pressure decreases, perform the absorption operation again. In the example of Table 1, the absorbing operation is performed three times and the discharging operation is performed twice, but the absorbing operation may be performed at least a plurality of times with the discharging operation interposed therebetween. Instead of performing the discharging operation for a predetermined time, the discharging operation can be terminated when the pressure detecting means 7 detects that the set pressure has reached the lower limit. In this case, the discharge operation may be started when the pressure detecting means 7 detects that the set pressure has reached the upper limit.

Table 2 shows a method of operating a flow type hydrogen gas purifying apparatus as a comparative example. A black portion indicates that each of the valves AV1, AV2, and AV3 is open and the heating device 5 or the cooling device 6 is in an operating state. A white portion indicates that each of the valves AV1, AV2, and AV3 is closed and the heating device 5 or the cooling device. The device 6 indicates an inactive state. As can be seen from the table, in the absorption step, the first and third valves AV1 and AV1 are operated while cooling the hydrogen storage alloy M by operating the cooling device 6.
3 is opened, and the second valve AV2 is closed. However, the third valve AV3 is provided with a function as an aperture. Thereby, the impure hydrogen gas in the hydrogen utilization device 1 flows into the hydrogen recovery container 4 through the impure hydrogen gas line 10 and the first valve AV1, is absorbed by the cooled hydrogen storage alloy M, and Impurity gas accumulated around M is continuously discharged from the purge gas line 12 to the outside (atmosphere).

[0021]

[Table 2]

In the subsequent purging step, the cooling device 6 is stopped and the heating device 5 is operated, and only the third valve AV3 is opened to a large extent, so that the pool is not absorbed by the hydrogen storage alloy M but absorbed. The entrained impurity gas is discharged from the purge gas line 12 to the outside (atmosphere).
As a result, the impurity gas around the hydrogen storage alloy M is pushed out from the hydrogen recovery container 4 while the hydrogen is released from the hydrogen storage alloy M heated by the heating device 5. When the impurity gas in the hydrogen recovery container 4 has been sufficiently released in this way, the third valve AV3 is closed, and the second valve AV2 is opened to shift to the discharging step. In the release step, pure hydrogen released from the heated hydrogen storage alloy M is led to the purified gas line 11 while the heating device 5 is operated, and is caused to flow into the hydrogen utilization device 1 from the hydrogen inlet 1b. If pure hydrogen is sufficiently released from the hydrogen storage alloy M,
The heating device 5 is stopped, the second valve AV2 is closed, and the discharging step is completed.

[0023]

As will be understood from the above description,
According to the hydrogen gas purification method of the present invention, the following effects can be obtained. (1) In a single absorption step having an absorption operation and a release operation, the hydrogen storage alloy can absorb more hydrogen gas than the conventional batch type, and the hydrogen purification processing capacity can be increased. . That is, the impurity gas collected around the hydrogen storage alloy is released by performing the releasing operation in accordance with the absorbing operation of storing the hydrogen in the hydrogen storing alloy. A decrease in the hydrogen storage capacity of the hydrogen storage alloy caused by the impurity gas accumulated around the alloy is suppressed. As a result, a state is obtained in which the hydrogen absorbing ability of the hydrogen storage alloy is effectively utilized. As a result, a large amount of hydrogen can be absorbed by the hydrogen storage alloy without significantly increasing the time required for the absorption step performed while cooling. In addition, it is not necessary to switch the hydrogen storage alloy from the cooling state to the heating state at an early stage, so that not only the thermal efficiency is excellent but also the entire time required for purifying the hydrogen gas can be shortened.

(2) The discharging operation is performed by releasing the hydrogen gas containing a large amount of impurity gas in the hydrogen recovery container from the purge gas line to the outside while keeping the hydrogen storage alloy at a pressure exceeding the hydrogen gas dissociation equilibrium pressure. There is no need to heat the hydrogen storage alloy. Therefore, the amount of purge accompanying the release operation is determined by the pressure difference between the pressure in the hydrogen recovery container and the external pressure to be released, and is not related to the capacity of the hydrogen storage alloy. Become In addition, since there is no need to perform heating during the discharging operation, an increase in the amount of hydrogen released due to the discharging operation is suppressed, and a decrease in the hydrogen recovery rate is prevented. (3) Since the impurity gas is purged by the discharging operation,
As compared with the conventional batch method, the impurity concentration in the hydrogen recovery container at the completion of one absorption step is reduced. As a result, not only the amount of hydrogen release required for purging the impurity gas in the subsequent purging step is reduced, but also the time required for the purging step is shortened.

(4) Compared with the conventional flow-type hydrogen gas purification method in which impurity gas is constantly purged during the absorption step, the hydrogen storage alloy is only kept at a pressure exceeding the hydrogen gas dissociation equilibrium pressure by the release operation. In addition, since the impurity gas is intermittently purged by the discharge operation and the purge step, an increase in the hydrogen content in the purge gas can be suppressed by using a hydrogen gas purifier having a simple structure. As a result, the hydrogen recovery rate is excellent. (5) According to the second aspect, since the impurity gas is purged for a predetermined time when the pressure reaches the set pressure, not only the operability is excellent but also the purge amount of the impurity gas is further stabilized, and the hydrogen gas is accordingly reduced. Recovery efficiency is improved.

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing a hydrogen gas purifying apparatus according to one embodiment of the present invention.

[Explanation of symbols]

1: hydrogen utilization device, 4: hydrogen recovery container, 5: heating device,
6: Cooling device, 7: Pressure detecting means, 10: Impure hydrogen gas line, 11: Purified gas line, 12: Purge gas line, AV1: First valve, AV2: Second valve, AV
3: Third valve, M: hydrogen storage alloy.

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Yuichi Wakisaka 4 Chazu-cho, Muroran-shi, Hokkaido Japan Steel Works Co., Ltd.

Claims (2)

[Claims] 1. A hydrogen gas containing an impure gas is led from an impure hydrogen gas line (10) to a hydrogen recovery container (4), and hydrogen is added to the cooled hydrogen storage alloy (M) in the hydrogen recovery container (4). Perform an absorption operation to occlude, then stop the introduction of hydrogen gas from the impure hydrogen gas line (10),
A discharge operation of releasing hydrogen gas containing a large amount of impurity gas in the hydrogen recovery container (4) from the purge gas line (12) to the outside while keeping the pressure inside the hydrogen recovery container (4) at a pressure exceeding the hydrogen gas dissociation equilibrium pressure is performed. After performing the absorption operation at least a plurality of times with the discharge operation interposed therebetween, the hydrogen storage alloy (M) in the hydrogen recovery container (4) is heated to remove the hydrogen stored in the hydrogen storage alloy (M). Performing a purge step of releasing hydrogen gas containing a large amount of impurity gas in the hydrogen recovery container (4) from the purge gas line (12) to the outside;
After that, the discharge from the purge gas line (12) is stopped, and the high-purity hydrogen gas released from the heated hydrogen storage alloy (M) is released and recovered from the purified gas line (11). Purification method. 2. A pressure detecting means (7) for detecting the pressure in the hydrogen recovery container (4) is provided, and the discharging operation is started after the pressure in the hydrogen recovery container (4) reaches a predetermined set value. 2. The method according to claim 1, wherein the processing is continued until a predetermined time elapses.
Hydrogen gas purification method.