Method for the purification of hydrogen

Abstract: Hydrogen gas from an generator (1) is occluded in a hydrogen recovery container (20), thereafter, in the initial stage during which hydrogen gas is released from the hydrogen recovery container (20), initially purged hydrogen gas containing much amount of impure gas is introduced from the hydrogen recovery container (20) to a gas tank (2) and saved therein, then, hydrogen gas having high purity released from a hydrogen absorbing alloy in the hydrogen recovery container (20) is refluxed to the generator (1), and this process comprising absorbing and releasing of hydrogen gas in the hydrogen recovery container (20) and saving in the gas tank (2) is repeated once or several times, successively, the hydrogen gas containing much amount of impure gas saved in the gas tank (2) is introduced in the hydrogen recovery container (20) and occluded therein, thereafter, in the initial stage during which hydrogen gas is released from the hydrogen recovery container (20), the hydrogen gas containing much amount of impure gas is discharged outside, then hydrogen gas having high purity released from the hydrogen absorbing alloy in the hydrogen recovery container (20) is refluxed to the generator (1).

Description: The present invention relates to a process for improving hydrogen purity. A conventional hydrogen purity improving method is the batch system described in JP-A-3-27110 and 7-267607. According to such a system, while hydrogen is actively recovered from an impure gas source from a generator so that it may be reused, a remaining amount of impure gas is discharged to the atmosphere whereby improvement in the hydrogen purity is conducted effectively. The apparatus described in JP-A-3-271101 is characterized in that a hydrogen-utilizing unit comprising a generator and a hydrogen recovery container equipped with a heating unit, a cooling unit and a hydrogen absorbing alloy therein are connected with a pipe for absorption having a first pressure-controlling valve. In addition, the hydrogen recovery container employs a purging gas line having a second pressure-controlling valve activated with respect to a pressure corresponding to the internal pressure of the hydrogen recovery container. A product gas line having the first valve and a discharging gas line having the second valve are respectively connected with the hydrogen recovery container. According to this hydrogen purity improving apparatus, in a case where hydrogen purity is improved by a batch system, firstly, hydrogen gas in the hydrogen-utilizing unit is sufficiently absorbed in a hydrogen absorbing alloy in the hydrogen recovery container. Next, in releasing hydrogen gas from the hydrogen recovery container, hydrogen gas including a substantial amount of impure gas from the hydrogen recovery container is momentarily released from the releasing gas line. Thereafter, hydrogen gas having a high purity released from the hydrogen absorbing alloy is returned to the hydrogen-utilizing unit through the product gas line. Since this apparatus is equipped with only one hydrogen recovery container, the construction of the apparatus is simple, which results in a low cost, and the maintenance of the apparatus is reasonable. However, the technical problem of a low hydrogen recovery may arise. Namely, after introducing hydrogen gas in the hydrogen-utilizing unit into the hydrogen recovery container according to the batch manner, hydrogen gas including a substantial amount of impure gas from the hydrogen recovery container is released outside through the releasing gas line in the initial stage where hydrogen is released from the absorbing alloy. Thus, hydrogen included in the impure gas cannot be recovered. On the other hand, the hydrogen purity improving apparatus described in JP-A-7-267607 is characterized by a hydrogen-utilizing unit comprising a generator connected in parallel with plural hydrogen recovery containers. Each hydrogen recovery container employs a hydrogen absorbing alloy absorbing hydrogen as a hydride, a cooling unit and a heating unit. A first valve and a second valve each having a switch function are provided at the hydrogen inlet side of each parallel hydrogen recovery container. In addition, a third valve and a fourth valve are provided at the hydrogen outlet side of each hydrogen recovery container each having a switch function. A recycling pipe is connected in line with each hydrogen recovery container and equipped with valves arranged in series and having a switch function. Burging gas lines having a purging valve are connected with each hydrogen recovery container at the hydrogen outlet side thereof. According to this conventional hydrogen purity improving apparatus, hydrogen can be recovered from the purged gas from one hydrogen recovery container and reused. Thus, hydrogen recovery is improved. However, hydrogen gas including a substantial amount of impure gas is introduced into another hydrogen recovery container in which the impure gas-containing hydrogen gas is absorbed again in the hydrogen absorbing alloy. Therefore, plural hydrogen recovery containers having a complicated structure are required, which results in a high cost. Further, since oxygen which is harmful to the hydrogen absorbing alloy comes into contact with the hydrogen absorbing alloy for a longer period of time, deterioration of the hydrogen absorbing alloy is increased within a short time even though a substantial amount of the hydrogen absorbing alloy is contained in the plural hydrogen recovery containers. JP-A-9-286601 discloses a method for improving hydrogen purity using a single hydrogen recovery container connected to a hydrogen-utilizing apparatus and a gas tank which is connected to the hydrogen recovery container via a tank tubing system with a pressure-adjusting valve. The present invention has been achieved with a view of overcoming the conventional technical problems. The present invention provides a method for improving hydrogen purity by using an apparatus comprising a hydrogen-cooling type generator (1), a hydrogen recovery container (20) containing a hydrogen absorbing alloy and a gas tank (2) connected with the hydrogen recovery container (20) said method comprising the steps of: a) feeding hydrogen gas from a hydrogen-cooling type generator (1) into the hydrogen recovery container (20); b) absorbing hydrogen as a hydride in the hydrogen absorbing alloy; c) releasing hydrogen gas from the hydrogen absorbing alloy contained in the hydrogen recovery container (20) and introducing, in the initial stage during which said hydrogen gas is released, initially purged hydrogen gas containing a substantial amount of impure gas from the hydrogen recovery container (20) into the gas tank (2) to store therein a first impure hydrogen gas; d) refluxing hydrogen gas having high parity released from the hydrogen absorbing alloy contained in the hydrogen recovery container (20), to the generator (1); e) optionally repeating steps (a) to (d) at least once; a') introducing the first impure hydrogen gas stored in the gas tank (2) into the hydrogen recovery container (20); b') absorbing hydrogen as a hydride in the hydrogen absorbing alloy; c') releasing hydrogen gas from the hydrogen absorbing alloy contained in the hydrogen recovery container (20) and discharging, in the initial stage during which hydrogen gas is released from the hydrogen recovery container (20), initially purged hydrogen gas containing a substantial amount of impure gas outside the apparatus; and d') refluxing hydrogen gas having high purity released from the hydrogen absorbing alloy in the hydrogen recovery container (20), to the generator (1). Preferred embodiments of the present invention are set forth in the sub-claims. Fig. 1 is a schematic drawing showing a hydrogen purity improving apparatus which may be used in the present invention. One embodiment of the present invention will be explained below by way of Fig. 1. In the drawing, 1 represents a hydrogen-cooling type turbine generator discharging impure gas including a hydrogen component having been used. 20 represents a hydrogen recovery container which contains a hydrogen absorbing alloy absorbing hydrogen as a hydride (metal hydride), equipped with a heating unit 7 for heating the hydrogen absorbing alloy and a cooling unit 8 for cooling the same, and a pressure gage 21 for detecting the internal pressure. The cooling unit 8 cools the hydrogen absorbing alloy so that the alloy may absorb hydrogen. For example, the cooling unit 8 may be a cold water supply. A heating unit 7 heats the hydrogen absorbing alloy so that the alloy may release hydrogen. For example, the heating unit 7 may be a hot water supply or an electric heater. The hydrogen absorbing alloy reacts with hydrogen gas to reversibly absorb or release the hydrogen gas. This reaction proceeds depending upon the hydrogen equilibrium pressure-temperature characteristics in a plateau region. According to temperature conditions at a hydrogen equilibrium pressure, hydrogen gas is absorbed by cooling to a low temperature and it is released by heating to a high temperature. The usual heating unit 7 in the hydrogen recovery container 20 releases hydrogen gas by heating the hydrogen absorbing alloy at around 50 to 98°C. Alternatively, by using steam, hydrogen gas can be released by heating to around 100 to 170°C. The pipe for absorption 10 connected at one end thereof with the hydrogen outlet part of the generator 1 is sequentially equipped with a deoxygen column 25, a condenser 26, and a dehumidifier 27 as well as a first valve 11 having a switch function. Another end thereof is connected with the hydrogen recovery container 20. The condenser 26 and the dehumidifier 27 constitute a dehumidifying treatment unit. A product gas line 28 equipped with a second valve 12 having a switch function is connected with the hydrogen recovery container 20 at one end thereof and at another end, it is connected with the hydrogen inlet part of the generator 1. One end of a tank pipe 29 is connected with the hydrogen recovery container 20. Specifically, it is connected with the product gas line 28 between the hydrogen recovery container 20 and the second valve 12. Further, a purging gas line 30 equipped with a third valve 13, i.e., purging valve, having a switch function is connected with the hydrogen recovery container 20. Specifically, with a middle part of the tank gas pipe 29. Still further, at another end of the tank pipe 29 a gas tank 2 for recycling is connected and equipped with a fourth valve 14 for storing hydrogen gas containing a substantial amount of impure gas. The gas tank 2 can be constructed as a usual tank or with an accumulator. As a matter of course, the gas tank 2 does not contain a hydrogen absorbing alloy. Next, the function of the above-described hydrogen purity improving apparatus will be explained below. The hydrogen purity inside the generator 1 is improved and maintained by using the hydrogen recovery container 20 according to a batch system. Namely, while opening the first valve 11, the second valve 12 through the fourth valve 14 are all closed. Further, by cooling the hydrogen recovery container 20 by means of the cooling unit 8, hydrogen gas having relatively low purity in the generator 1 is introduced into the hydrogen recovery container 20. The hydrogen gas having relatively low purity in the generator 1 is passed through the pipe for absorption 10. In the course of passing, oxygen harmful to the hydrogen absorbing alloy is removed by the deoxygen column 25 and water harmful to the hydrogen absorbing alloy is removed by the condenser 26 and the dehumidifier 27. The water removed by the condenser 26 is discharged outside. Thus, with flowing hydrogen gas from the generator 1 to the hydrogen recovery container 20, the hydrogen is sufficiently absorbed in the hydrogen absorbing alloy in the hydrogen recovery container 20. At the time of finishing this portion of the hydrogen absorbing process, the pressure inside the hydrogen recovery container 20 is temporarily raised by the occupation of the hydrogen recovery container 20 with hydrogen gas. This rise in pressure is detected by a pressure gage in the hydrogen recovery container 20 and depending upon the detected signal, the first valve 11 is closed. The first valve can also be closed by time control. In such a case, a given time having passed after opening the first valve 11 is detected by a timer, thereafter, the valve may be closed. Next, the hydrogen absorbing alloy in the hydrogen recovery container 20 is heated by the heating unit 7 so that hydrogen may be released. In this case, in the initial stage of releasing hydrogen, the fourth valve 14 is momentary opened without fail to effect initial purging. By momentary opening the fourth valve 14, hydrogen gas containing a substantial amount of impure gas which was not absorbed and, therefore, present within the hydrogen recovery container 20 is introduced into the gas tank 2 through the piping for the tank 29. During the initial purging of hydrogen gas containing a substantial amount of impure gas, this gas is introduced into the gas tank 2 which does not contain the hydrogen absorbing alloy. According to such a construction, the impure gas is prevented from contacting the hydrogen absorbing alloy for a long time in comparison with the case where hydrogen gas containing a substantial amount of this impure gas is introduced into the hydrogen recovery container comprising the hydrogen absorbing alloy. Thus, early deterioration of the hydrogen absorbing alloy contained in the hydrogen recovery container is prevented as well as lowering of the treating capacity for keeping hydrogen purity and hydrogen recovery (variability) can be suppressed. Thereafter, simultaneously with closing the fourth valve 14, the second valve 12 is opened, whereby hydrogen gas having high purity, released from the hydrogen absorbing alloy in the hydrogen recovery container 20, is refluxed to the generator 1 through the product gas line 28. According to such a construction, the apparatus is operated at a given interval at a hydrogen purity of, for example, about 99.98 % in the generator 1, and the operation is appropriately stopped so that the given hydrogen purity (about 99.98 %) can be substantially maintained. Thus, by using only one hydrogen recovery container 20 and employing a batch system, hydrogen gas purity can be improved and maintained. By conducting the above-described process for improving and maintaining hydrogen gas purity once or several times, a given amount of hydrogen gas containing a substantial amount of impure gas is collected in the gas tank 2, which can then be discharged therefrom. That is, upon closing the first to third valves 11 to 13, the fourth valve 14 is opened, whereby the hydrogen gas containing a substantial amount of impure gas stored in the gas tank 2 is absorbed in the hydrogen recovery container 20. At that time, the hydrogen absorbing alloy in the hydrogen recovery container 20 is cooled by the cooling unit 8. After sufficiently flowing out the hydrogen gas containing a substantial amount of impure gas from the gas tank 2, the fourth valve 14 is closed. Thereafter, hydrogen gas is released from the hydrogen recovery container 20 by heating the hydrogen absorbing alloy in the hydrogen recovery container 20 by means of a heating unit 7. In the initial stage of releasing hydrogen gas from this hydrogen recovery container 20, the third valve 13 is momentary opened so that the hydrogen gas containing a substantial amount of impure gas which was not absorbed and, therefore, present within the hydrogen recovery container 20, is discharged outside through the purging gas line 30. Simultaneously with closing the third valve 13, the second valve 12 is opened, whereby high purity hydrogen gas released from the hydrogen absorbing alloy is refluxed to the generator 1. According to such a manner, by using one hydrogen recovery container 20 and gas tank 2, the amount of purged gas discharged to the atmosphere can be decreased while still improving hydrogen recovery. By repeating the above process, the purity of hydrogen in the generator 1 is improved or kept substantially constant. An additional process also can be effected. As shown by a hypothetical line in Fig. 1, an auxiliary gas tank 2' is connected to the hydrogen recovery container 20 through recycling pipe 31 equipped with a fifth valve 15 having a switch function. Actually, regarding the hydrogen recovery container 20, the recycling pipe 31 is arranged nearer than the fourth valve 14 provided in the tank pipe 29. The hydrogen gas containing a substantial amount of impure gas,supplied from the gas tank 2 and collected around the hydrogen absorbing alloy within the hydrogen recovery container 20, is stored in the auxiliary gas tank 2' by opening the fifth valve 15 instead of discharging outside through the purging gas line 30. The auxiliary gas tank 2 ' has the same structure as that of the gas tank 2. Thereafter, high purity hydrogen gas released from the hydrogen absorbing alloy is refluxed to the generator 1. This process is effected once to several times. Thereafter, hydrogen gas containing a substantial amount of impure gas stored in the auxiliary gas tank 2' is introduced into the hydrogen recovery container 20 and adsorbed therein. Then, in the initial stage during which hydrogen gas is released from the hydrogen recovery container 20, the third valve 13 is opened so that hydrogen gas containing a substantial amount of impure gas may be purged outside through the purging gas line 30. Thereafter, high purity hydrogen gas released from the hydrogen absorbing alloy is refluxed to the generator 1. According to such a construction, the amount of the hydrogen gas containing a substantial amount of impure gas discharged to the atmosphere can be noticeably decreased. Thus, hydrogen recovery can be further improved. The hydrogen gas containing a substantial amount of impure gas supplied from auxiliary gas tank 2' and collected around the hydrogen absorbing alloy in the hydrogen recovery container 20 can also be stored in still another gas tank without discharging outside through the purging gas line 30. Thereafter, the hydrogen gas containing a substantial amount of impure gas in still another gas tank is introduced into the hydrogen recovery container 20, and the hydrogen gas containing a substantial amount of impure gas within the hydrogen recovery container 20 can be purged outside through the purging gas line 30. The term "outside" as used herein includes the atmosphere and another gastank. As can be seen from the above-explanation, according to the hydrogen purity improving method of the present invention, the following effects can be achieved. According to the present invention, in the initial stage during which hydrogen gas is released from a hydrogen recovery container, initially purged hydrogen gas containing a substantial amount of impure gas is introduced from the hydrogen recovery container into a gas tank and stored therein. Thereafter, the hydrogen gas containing a substantial amount of impure gas stored in the gas tank is introduced into the hydrogen recovery container and absorbed therein. Then, in the initial stage during which hydrogen gas is released from the hydrogen recovery container, the hydrogen gas containing a substantial amount of impure gas is discharged outside. After that high purity hydrogen gas released from the hydrogen absorbing alloy in the hydrogen recovery container is refluxed to the generator. According to such a construction, the number of hydrogen recovery containers containing a hydrogen absorbing alloy can be decreased and, therefore, the apparatus has a simple construction providing a low cost and the maintenance thereof is excellent. Further, hydrogen recovery can be sufficiently improved as well. Additionally, since hydrogen gas containing a substantial amount of impure gas which was not absorbed in a hydrogen absorbing alloy in the hydrogen recovery container is introduced into a gas tank which does not contain a hydrogen absorbing alloy, harmful contact between oxygen or water and the hydrogen absorbing alloy is reduced compared with a case where hydrogen gas containing a substantial amount of impure gas is introduced into the hydrogen recovery container comprising the hydrogen absorbing alloy. According to this construction, early deterioration of the hydrogen absorbing alloy contained in the hydrogen recovery container can be reduced as well as lowering the treating capacity for keeping hydrogen purity and hydrogen recovery (variability) can be suppressed. According to the present invention, hydrogen gas containing a substantial amount of impure gas stored in a gas tank is introduced into a hydrogen recovery container and absorbed therein. Thereafter, in the initial stage during which hydrogen gas is released from the hydrogen recovery container, the hydrogen gas containing a substantial amount of impure gas is stored in another gas tank. Thereafter, the hydrogen gas containing a substantial amount of impure gas stored in the other gas tank is introduced into the hydrogen recovery container and absorbed therein. Then in the initial stage during which hydrogen gas is released from the hydrogen recovery container, the hydrogen gas containing a substantial amount of impure gas is discharged outside. Thereafter, hydrogen gas having high purity released from a hydrogen absorbing alloy in the hydrogen recovery container is refluxed to a generator. According to such a construction, hydrogen recovery can be further improved.

Claims: A method for improving hydrogen purity by using an apparatus comprising a hydrogen-cooling type generator (1), a hydrogen recovery container (20) containing a hydrogen absorbing alloy and a gas tank (2) connected with the hydrogen recovery container (20) said method comprising the steps of: a) feeding hydrogen gas from a hydrogen-cooling type generator (1) into the hydrogen recovery container (20); b) absorbing hydrogen as a hydride in the hydrogen absorbing alloy; c) releasing hydrogen gas from the hydrogen absorbing alloy contained in the hydrogen recovery container (20) and introducing, in the initial stage during which said hydrogen gas is released, initially purged hydrogen gas containing a substantial amount of impure gas from the hydrogen recovery container (20) into the gas tank (2) to store therein a first impure hydrogen gas; d) refluxing hydrogen gas having high purity released from the hydrogen absorbing alloy contained in the hydrogen recovery container (20), to the generator (1); e) optionally repeating steps (a) to (d) at least once; a') introducing the first impure hydrogen gas stored in the gas tank (2) into the hydrogen recovery container (20); b') absorbing hydrogen as a hydride in the hydrogen absorbing alloy; c') releasing hydrogen gas from the hydrogen absorbing alloy contained in the hydrogen recovery container (20) and discharging, in the initial stage during which hydrogen gas is released from the hydrogen recovery container (20), initially purged hydrogen gas containing a substantial amount of impure gas outside the apparatus; and d') refluxing hydrogen gas having high purity released from the hydrogen absorbing alloy in the hydrogen recovery container (20), to the generator (1). The method of claim 1 characterized in that said discharging the hydrogen gas in step (c') is conducted by introducing the gas into an auxiliary gas tank (2') to store therein a second impure hydrogen gas. The method of claim 2, further comprising the steps of: f) optionally repeating steps (a) through (d') at least once; a") introducing said second impure hydrogen gas stored in the auxiliary gas tank (2') into the hydrogen recovery container (20); b") absorbing hydrogen as a hydride in the hydrogen absorbing alloy; c") releasing hydrogen gas from the hydrogen absorbing alloy contained in the hydrogen recovery container (20) and discharging, in the initial stage during which said hydrogen gas is released, initially purged hydrogen gas containing a substantial amount of impure gas from the hydrogen recovery container (20) outside; and d") refluxing hydrogen gas having high purity released from the hydrogen absorbing alloy in the hydrogen recovery container, to the generator. The method of claim 3, characterized in that said discharging the hydrogen gas in step (c") is conducted by introducing the hydrogen gas containing a substantial amount of impure gas into still another gas tank to store therein a third impure hydrogen gas.

Inventors: NISHIMURA YUSAKU, SATO JUNICHI, SATO SHOICHI, SATO YUKIO, TAKEDA HARUNOBU, WAKISAKA YUICHI, NISHIMURA, YUSAKU, SATO, JUNICHI, SATO, SHOICHI, SATO, YUKIO, TAKEDA, HARUNOBU, WAKISAKA, YUICHI, Nishimura, Yusaku, The Kansai Elec. Power Com. Inc, Sato, Junichi, The Kansai Electric Power Com. Inc., Sato, Shoichi, c/o The Japan Steel Works, Ltd., Sato, Yukio, c/o The Japan Steel Works, Ltd., Takeda, Harunobu, c/o The Japan Steel Works, Ltd., Wakisaka, Yuichi, c/o The Japan Steel Works, Ltd.
Applicants: JAPAN STEEL WORKS LTD, KANSAI ELECTRIC POWER CO, THE JAPAN STEEL WORKS, LTD., THE KANSAI ELECTRIC POWER CO., INC.
Application year: 1997
Main classification: C01B3
IPC codes: C01B3