JP7626802B2 - Hydrogen storage alloy tank - Google Patents

Description

This invention relates to a cylindrical tank filled with a hydrogen storage alloy that can be used vertically.

In recent years, hydrogen storage alloy tanks have come to be used in stationary hydrogen storage facilities that gradually absorb hydrogen produced using surplus renewable energy and gradually release large amounts of stored hydrogen. More recently, there is expected to be demand for a cylinder or tank delivery and distribution system similar to the currently widely used LPG tanks.

When considering the delivery and distribution method for this hydrogen storage alloy tank, it is desirable to make it as light as a conventional LPG cylinder. Furthermore, as with conventional LPG cylinders, it is desirable to use a cylindrical tank placed upright, as this will reduce the installation area required during transportation and operation and will increase portability.

However, when using a normal cylindrical hydrogen storage alloy tank, the repeated expansion and contraction of the alloy powder due to the absorption and release of hydrogen causes the powder to become finely aggregated, and in this state, the expansion caused by hydrogen absorption causes localized stress increase in the tank casing near the powder aggregates, so as a general rule, it should not be used upright.

In particular, with conventional alloys, the powder itself becomes finer as it absorbs and releases hydrogen, and as the powder agglomerates, new surfaces are created, and the powder eventually solidifies into a porous shape. This creates a stronger expansion force, which can lead to the destruction of the tank casing.

On the other hand, if the alloy itself is not finely divided, the fine agglomeration will reach a certain limit, and the expansion force will no longer increase. Therefore, whether the tank casing can withstand the external force caused by the expansion when the alloy has fully agglomerated to a certain extent determines whether it can maintain long-term durability.

If the yield point of the tank material is exceeded before it is completely agglomerated, the residual strain will increase with each repetition, and the permanent strain will continue to increase. Even if the yield point is not reached, if the stress is not kept within the fatigue limit, it will not be able to withstand permanent use against repeated hydrogen absorption and release. Therefore, even with alloy powder that is not finely divided, it is necessary to increase the material strength of the tank casing in order to achieve long-term use as a vertical tank, which results in the use of expensive metals and increased plate thickness, resulting in a heavy tank and reduced delivery workability.

The force exerted in the direction of the tank's internal pressure due to the alloy expansion becomes greater the higher the aspect ratio. A large aspect ratio results in a large weight per unit cross-sectional area, which means that the entire alloy filling layer cannot be pushed up in response to the expansion, and instead acts as an external force that increases the tank's internal pressure. In some cases, the alloy may locally agglomerate in the middle of the tank's length, which can lead to increased local stress.

In particular, in the case of alloys in which the hydrogen absorption and release causes the particles to become finer and new surfaces to be generated, the increase in the self-weight load per unit area due to the high aspect ratio promotes the porous solidification of the alloy powder. Therefore, it is necessary to consider an internal structure that prevents agglomeration in the weight direction of the alloy in response to the hydrogen absorption and release (expansion and contraction) of the alloy.

This hydrogen storage alloy tank requires a mechanism for removing the reaction heat generated when the alloy absorbs and releases hydrogen. The heat removal methods are roughly divided into water-cooled and air-cooled. In the water-cooled type, a heat transfer medium path is provided on the outer periphery or inside of the tank, and the alloy reaction heat is removed by heat exchange with the heat transfer medium. In the air-cooled type, the alloy reaction heat is removed mainly by heat exchange between the tank and the atmosphere. In both types, a heat transfer material is generally provided in the alloy-filled part inside the tank to efficiently remove the heat. As shown in Figures 10 and 11 , the inside of the tank 20 is divided by radiating fins 21, and hydrogen storage alloy powder 22 is filled in the tank, which has been commercialized as a horizontal stationary type.

In such hydrogen storage alloy tanks, several countermeasures have already been developed to prevent stress increases due to alloy agglomeration. The one described in Patent Document 1 is a hydrogen storage tank in which a hydrogen storage alloy is filled into multiple capsule containers housed with gaps between them, and these capsule containers are elastically deformable in response to the expansion of the storage alloy when it absorbs hydrogen and the contraction of the alloy when it releases hydrogen.

Patent document 2 describes a hydrogen storage tank in which a small chamber separated by radial fins inside the tank housing has a partially contractible space that contracts when the alloy expands, thereby suppressing the internal pressure on the tank housing.

JP 2005-9549 A JP 2009-222200 A

The device in Patent Document 1 requires that multiple capsule containers be provided in the tank with gaps between them, and that each capsule container be filled with hydrogen storage alloy, resulting in a complex structure and time-consuming process for filling the hydrogen storage alloy. The device in Patent Document 2 separates the tank container into multiple small chambers with radial fins, and further provides a contractible space in part of each small chamber, resulting in a complex structure and time-consuming process for manufacturing.

The present invention focuses on the above points and aims to provide a hydrogen storage alloy tank that has a simple structure, can be filled with hydrogen storage alloy powder easily and quickly, does not cause the hydrogen storage alloy powder to aggregate finely, and can be placed vertically.

The invention of claim 1 is a hydrogen storage alloy tank having an outer diameter that is 80% or more of the inner diameter of the tank casing, a central hollow portion in the center, and a spiral-shaped fin having spring properties that is formed continuously in the longitudinal direction of the tank alone within a cylindrical pipe tank casing, with a hydrogen storage alloy filled between the spiral-shaped fins.

The invention of claim 2 is a hydrogen storage alloy tank as described in claim 1, in which the pitch of the spiral fins is less than twice the outer diameter of the tank casing.

The invention of claim 3 is a hydrogen storage alloy tank as described in claim 1 or 2, in which the length of the spiral fin is at least 2/3 of the length of the tank.

Furthermore, the invention of claim 4 is a hydrogen storage alloy tank as described in claim 1, in which the spiral-shaped fin is made of a thermally conductive material.

According to the invention of claim 1, the shape of the heat transfer fins that have been used conventionally is made into a continuous spiral shape, and the hydrogen storage alloy is filled between the spiral fins. Therefore, even when the hydrogen storage alloy tank is placed vertically, there are multiple partitions in the direction of gravity, and it is possible to prevent the hydrogen storage alloy from expanding and contracting when it absorbs and releases hydrogen, and also to prevent the formation of fine agglomerations at the bottom of the tank due to its own weight.

When a conventional tank with radiating fins is placed vertically, the aspect ratio of the small chambers formed by the partitions of the radiating fins is large, and in some cases exceeds 20. However, in this invention, the fins are spirally shaped and the spaces between the spirally shaped fins are filled with hydrogen storage alloy, so that the alloy-filled section is formed in a tube shape with a low cross-sectional aspect ratio that spirals vertically from the bottom. This filling shape significantly reduces the force in the direction of gravity per unit cross-sectional area of the alloy-filled layer. Therefore, even when the tank of this invention is placed vertically, although it is a cylindrical tank, the alloy-filled layer can be created in the shape of a horizontally placed tube.

In addition, when the tank of this invention is placed vertically, the continuous partition structure of the spiral fins causes the expansion force of the alloy to act as opposing component forces on the upper and lower surfaces of the partition, generating a shear force between the upper and lower layers of the alloy layer between the spiral pitches, separating the layers of the alloy and preventing excessive aggregation.

Even if the expansion force increases due to partial refinement of the alloy layer in the fin pitch, the spring deformation of the spiral fin allows the expansion force to escape vertically, preventing excessive alloy expansion force from acting in the direction of the tank's internal pressure.

As described above, the invention of claim 1 has a much simpler structure than the conventionally developed products that take measures to prevent the formation of fine agglomerations at the bottom of the tank caused by the relationship between expansion, contraction, and the tank's own weight during hydrogen absorption and release, and can accommodate a variety of aspect ratios as long as the tank is cylindrical. Furthermore, since no completely independent small chambers are provided in the vertical direction, it is possible to fill the alloy from the top after inserting the spiral fins, making the tank highly mass-producible. Also, as described above, the alloy expansion force can be significantly reduced, eliminating the need to consider excessive stress on the tank casing, which contributes to reducing the weight of the tank casing. Therefore, it can also be applied to the tank delivery system.

Furthermore, according to the invention of claim 2, the pitch of the spiral fin is set to a length less than twice the outer diameter of the tank housing, thereby ensuring a certain length of the tube-shaped alloy layer, and the force in the direction of gravity per unit cross-sectional area of the alloy-filled layer is greatly reduced, ensuring the effect.

Furthermore, according to the invention of claim 3, the length of the spiral fin is set to at least 2/3 of the length of the tank, thereby ensuring that the length of the tube-shaped alloy layer is at least a certain length, and the force in the direction of gravity per unit cross-sectional area of the alloy-filled layer is significantly reduced, ensuring the effect.

Furthermore, according to the invention of claim 4, the spiral-shaped fin is formed of a thermally conductive material, so that the reaction heat of the hydrogen storage alloy can be transferred from the spiral-shaped fin to the outer wall of the tank, thereby improving heat exchange with the atmosphere.

1 is a longitudinal sectional view of a hydrogen storage alloy tank according to a first embodiment of the present invention placed vertically. 1 is a front view of a hydrogen storage alloy tank according to a first embodiment of the present invention placed vertically with an upper cap removed. FIG. 1 is an enlarged cross-sectional view of a hydrogen storage alloy tank according to a first embodiment of the present invention placed vertically. FIG. 1 is an enlarged partial vertical cross-sectional view of a hydrogen storage alloy tank according to a first embodiment of the present invention placed vertically. 1 is an image diagram of a tube-shaped alloy layer formed by a spiral fin in a hydrogen storage alloy tank according to a first embodiment of the present invention; FIG. 4 is an image diagram of the force acting on the alloy layer by the spiral fin of the hydrogen storage alloy tank according to the first embodiment of the present invention. FIG. FIG. 1 is a graph showing the results of repeated hydrogen absorption and release tests of a conventional hydrogen storage alloy tank, where (a) shows the stress versus hydrogen amount for the first absorption and (b) shows the stress versus hydrogen amount for the tenth absorption. FIG. 1 is a graph showing the results of repeated hydrogen absorption and release tests of a hydrogen storage alloy tank according to a first embodiment of the present invention, in which (a) shows the stress versus hydrogen amount for the first absorption and (b) shows the stress versus hydrogen amount for the tenth absorption. FIG. 11 is a longitudinal sectional view of a hydrogen storage alloy tank according to a second embodiment of the present invention placed vertically. FIG. 1 is a longitudinal sectional view of a conventional hydrogen storage alloy tank placed vertically. FIG. 1 is an enlarged cross-sectional view of a conventional hydrogen storage alloy tank placed vertically.

(Embodiment Example 1)
A hydrogen storage alloy tank A according to a first embodiment of the present invention will be described with reference to FIGS.

First, as shown in Figure 1, hydrogen storage alloy tank A has a cylindrical tank housing 1 with a spiral fin 2 formed continuously in the longitudinal direction and having an outer diameter of at least 80% of the inner diameter of the tank housing 1 inside. As shown in Figure 3, this spiral fin 2 has a circular hole formed in the center when viewed from above, which forms a central cavity 3 from the upper end to the lower end of the spiral fin 2. Powder of hydrogen storage alloy 4 filled in the tank housing 1 fills the gap partitioned by the spiral fin 2 and the central cavity 3 (see Figure 4). In addition, a valve knob 5 for storing and releasing hydrogen is provided at the upper end of the tank housing 1.

The spiral fins 2 are made of a heat conductive material such as steel. The pitch of the spiral fins 2 is preferably equal to or less than the outer diameter of the tank housing 1, but in order to ensure that the length of the tube-shaped alloy layer is at least a certain length, it is sufficient that the pitch is equal to or less than twice the outer diameter of the tank housing 1. The length of the spiral fins 2 is set to at least 2/3 of the length of the tank body 1, thereby ensuring that the length of the tube-shaped alloy layer is at least a certain length.

When the hydrogen storage alloy tank A is placed vertically, the hydrogen storage alloy 4 is filled between the spiral fins 2, so that the alloy-filled section forms a tube shape with a low cross-sectional aspect ratio that spirals vertically from the bottom, as shown in Figure 5. In addition, due to the continuous partition structure of the spiral fins 2, the expansion force of the alloy 4 acts as opposing component forces at the upper partition 2a and the lower partition 2b, as shown in Figure 6, so that a shear force is generated between the upper and lower layers of the alloy layer between the spiral pitches, and by separating the layers of the alloy 4, excessive aggregation can be prevented.

In addition, when the hydrogen storage alloy tank A is placed vertically, the spiral fins 2 provide the alloy powder filled in the tank housing 1 with multiple partitions in the direction of gravity, greatly reducing the force in the direction of gravity per unit cross-sectional area of the alloy layer, and preventing fine agglomeration at the bottom of the tank housing 1 caused by the alloy's expansion and contraction during hydrogen absorption and release, as well as its own weight.

Figures 7 and 8 show the results of repeated hydrogen absorption and release tests conducted on the hydrogen storage alloy tank A of the present invention and a conventional product in a vertical position. In the test, hydrogen was filled into the hydrogen storage alloy tank at a pressure of 1 MPa, and after it was fully filled, all of the hydrogen was released, repeatedly. The test results were obtained by measuring the stress at regular intervals along the length of the tank. The conventional product was a delivery tank with radial fins, with the same external dimensions as the hydrogen storage alloy tank (for delivery) of the present invention, 1210 mm long x 139.8 mm in diameter, and a tank weight of 65 kg (45 kg of which was alloy filling amount).

With the conventional radial fin structure, the stress amplitude acting on the tank increases with each repetition, and as shown in Fig . 7 (b), it was confirmed that after 10 repetitions, the stress amplitude exceeded the yield point at 230 MPa. On the other hand, with the hydrogen storage alloy tank A of the present invention, as shown in Fig . 8 (b), the stress amplitude remained constant at about 20 MPa even after 10 repetitions, the same as the initial stress amplitude ( Fig. 8 (a)). It was also confirmed that while the conventional product had a large stress variation (over 100 MPa) at the longitudinal position of the tank, the present invention had an extremely small stress variation of only 5 MPa.

In addition, the stress amplitude value of 20 MPa is close to the stress value when an internal pressure of 1 MPa acts on the tank, which indicates that in this invention, the alloy expansion force is not acting on the tank internal pressure side, and the effect of mitigating the alloy expansion force due to the spiral fin structure was confirmed.

(Embodiment 2)
Second Embodiment Next, a hydrogen storage alloy tank B according to a second embodiment of the present invention will be described with reference to FIG .

9, this hydrogen storage alloy tank B has mesh plates 9 spaced apart in the longitudinal direction within a tank casing 1 , dividing the tank casing 1 into multiple stages, with the spiral fins 2 provided within each partition 10, and the hydrogen storage alloy 4 filled between the spiral fins 2 within each partition 10, with each mesh plate 9 allowing hydrogen gas to pass through but not allowing the hydrogen storage alloy 4 to pass through. The other configuration is the same as that of the first embodiment.

As mentioned above, the hydrogen storage alloy tanks A and B of this invention can be used in a vertical position, but they can also be used in a horizontal position. These tanks can be either air-cooled or water-cooled. The hydrogen storage alloy powder to be filled can be either an alloy that becomes fine by repeated hydrogen absorption and release, or an alloy that does not become fine. The illustration of the spiral fin 2 in the figure is a schematic drawing.

A Hydrogen storage alloy tank B Hydrogen storage alloy tank 1 Tank housing 2 Spiral fin 2a Top partition 2b Bottom partition 3 Central cavity 4 Hydrogen storage alloy 5 Valve knob 9 Mesh plate
10 Partition

Claims (4)

A hydrogen storage alloy tank, characterized in that the tank has an outer diameter that is 80% or more of the inner diameter of a cylindrical tank casing, has a central hollow portion in the center, and has spiral-shaped fins formed continuously in the longitudinal direction and having spring properties alone in the longitudinal direction of the tank , with a hydrogen storage alloy filled between the spiral-shaped fins. The hydrogen storage alloy tank according to claim 1, characterized in that the pitch of the spiral fins is less than or equal to twice the outer diameter of the tank housing. The hydrogen storage alloy tank according to claim 1 or 2, characterized in that the length of the spiral fin is at least 2/3 of the length of the tank. 2. The hydrogen storage alloy tank according to claim 1, wherein the spiral fin is made of a heat conductive material.

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