GB1569449A - Catalytic storage battery cap - Google Patents

Description

(54) A CATALYTIC STORAGE BATTERY CAP (71) We, NIPPON TELEGRAPH AND TELEPHONE PUBLIC CORPORATION, a Japanese Company of No. 1-6 Uchisaiwai - cho l-chome, Chujoda - Ku, Tokyo, Japan and JAPAN STORAGE BATTERY COMPANY LIMITED a Japanese Company of No. 1 Kisshoin Nishinosho Inobabacho, Minami-ku, Kyoto-shi, Kyoto Japan, do hereby declare the invention for which we pray that a Patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention relates to a catalytic storage battery cap.

Catalytic caps containing a hydrogen-oxygen recombining catalyst have been previously used in stationary storage batteries to reduce the frequency of water replenishment and to prevent the discharge of acid fumes and explosive gases. None of these prior art caps have been suitable for large capacity storage batteries, however, because any attempts to increase their water recycling efficiencies have resulted in extreme catalyst temperature increases and attendant reductions in their safety factors. It is therefore an object of this invention to remedy and/or alleviate this defect.

According to the invention, a catalytic storage battery cap includes a casing having an opening in the bottom thereof for the introduction of hydrogen and oxygen gases released by the battery and the discharge of condensed water vapours back into the battery, and a vent in the top thereof for discharging unreacted gases, at least one porous, anti-explosive catalyst container mounted within the casing so that at least one face of the container is directly presented to the casing without being separated therefrom by an interior cover, said container containing a charge of hydrogen-oxygen recombining catalyst and the amount of catalyst and the physical dimensions of the porous catalyst container being selected so that the maximum catalyst temperature rise is limited to 220"C.

In the accompanying drawings, Figure 1 shows a vertical sectional view of a catalytic storage battery cap in accordance with a first example of the invention, Figure 2 shows a vertical sectional view of a conventional catalytic battery cap, Figure 3 shows an experimentally derived plot of maximum catalyst temperature rise versus water recycling efficiency, Figure 4 shows an experimentally derived plot of the maximum catalyst temperature rise attained as a function of the amount of the catalyst and the shape of the catalyst container, Figures 5 through 8 show vertical sectional view of catalytic caps according to second to fifth examples respectively of the invention, Figure 9 shows a plan view of part of Figure 8, Figure 10 shows an experimentally derived plot of the height-to-diameter ratio of the catalyst container versus the maximum catalyst temperature rise attained and the maximum recombining current, and Figure 11 shows a plot of the particle size of the material constituting the catalyst container versus the maximum catalyst temperature rise attained and the maximum recombining current.

Referring to Figure 1, reference numeral 1 designates a cap casing, 2 is an opening for introducing gases generated in the battery and for returning condensed water vapor, 3 is a vent, 4 is a hydrogen-oxygen recombining catalyst such as palladium adhered to a y-alumina carrier, 5 is a porous, anti-explosive catalyst container comprising sintered particles of an inorganic substance or a synthetic resin material and 6 is a support pedestal made of a moulded, heat resistant material such as ebonite for mounting the catalyst container within the casing 1.

The structure of the conventional catalytic cap shown in Figure 2 is similar to the example shown in Figure 1 with regard to components 1 through 6, but differs in that an interior cover 7 is provided to limit the gas flow to a predetermined amount, the cap has a relatively large volumetric capacity, and the saturation temperature is quite high. A more detailed description of this prior art cap is given in our U.S. Patent No. 4,002,496.

In operation, hydrogen and oxygen gas generated during battery charging, particularly if the battery is overcharged, flow into the casing 1 through the opening 2, pass through the porous walls of the container 5, and thus contact the catalyst 4. These gases are converted to water vapour by chemical recombining and are discharged back through the container walls, whereupon they contact the interior surface of the casing 1, condense, and return to the battery cell through the opening 2 via passages (not shown) between the casing 1 and the pedestal 6. The remaining, unreacted gases are discharged to the atmosphere through the vent 3.

If the structure of the catalyst container and the amount of the catalyst are suitably selected, optimum reaction conditions can be achieved whereby the amount of gas recombined reaches a saturation value. By disposing such a catalyst container(s) within a casing provided with an appropriate bottom opening and gas vent, a catalytic cap having a desired reaction capacity can be constructed. This relationship has been tested, and Table 1 shows the experimental results obtained in one practical embodiment in which the catalyst container employed had an internal diameter of 22 mm and an internal height of 25 mm Table 1 Amount of Maximum Maximum temperature Maximum temper Catalyst (g) Recombining rise of the catalyst ature rise of the Current (A) container catalyst ( C) ( C) 0.3 5.0 50 65 2.5 11.5 100 130 4 13.0 125 160 7 16.5 165 210 As can be seen from Table 1, the amount of catalyst which results in a maximum catalyst container temperature rise of about 120 to 1700C, considering the catalyst deterioration and wetting factors, is 3 to 7 g.

The maximum catalyst temperature rise versus the water recycling efficiency has also been determined, and the results are plotted in Figure 3. This test shows that rather than the dimensions of the cap casing or the amount of catalyst, the temperature rise of the catalyst most directly affects the efficiency of the water recycling or reconversion. An efficiency of 90So, which is required for most practical applications, can be achieved with a maximum catalyst temperature rise of less than about 220"C. Furthermore, a maximum temperature rise of 220"C is favourable with respect to preventing the deterioration of a water-repellent usually a silicone which exhibits a good water repelling property at temperatures up to about 250"C) used for preventing the wetting of the catalyst and the catalyst container, thereby prolonging the life of the catalyst.

Figure 4 shows the relation between the amount of the catalyst and the maximum catalyst temperature rise attained for various catalyst container shapes. Curve A was obtained using a tall catalyst container; curve B using a medium-height container; and curve C using a short container.

Thus, there are various combinations of catalyst amounts and container shapes which limit the maximum temperature rise to 220"C. For example, the amount of catalyst in the tall container (curve A) was 5g, and in the short container (curve C) the amount was 10g.

The empirical formula for the relation between the maximum catalyst temperature rise and the amount of catalyst, the shape of the catalyst container, etc., has been generally determined to be as follows: 4W 0.5 Tmax = K (pD + 0.225 god) (4alp irk3) 0.065, Where: Tmax is the maximum catalyst temperature rise attained in "C; K is a constant determined by parameters including the material and thickness of the catalyst container and the degree of activity of the catalyst; W is the weight of the catalyst in grams; p is the apparent density of the catalyst; and D is the inside diameter of a cylindrical catalyst container in centimeters.

As may be seen from the above equation, there are various combinations which will limit the catalyst temperature rise to 220"C, and if the amount of the catalyst is first selected, the shape (the diameter and height in the case of a cylindrical container) of the required container is unequivocally determined.

Experimental results comparing a catalytic cap according to the invention with a contentional catalytic cap are presented in Table 2.

Invention Conventional Cap Cap Outer Shape Diameter 70 110 Dimensions (mm) Height 100 150 Volume of Cap 1.4 Casing (liters) 0 4 1.4 Nominal capacity for a water recycling efficiency 10 10 of 90% (A) Maximum catalyst temperature rise 200 360 attained (OC) This table readily shows that the catalytic cap of the invention is small in size and yet has a high safety factor as compared with the prior art.

In the above example the maximum catalyst temperature rise within the container is limited to 220"C by properly selecting the amount of catalyst and the structure and dimen sions of the container on the basis of the Tmax equation given above.

Figures 5 to 8 show second to fifth examples respectively of the invention which are similar to the example shown in Figure 1 with regard to the structural components 1 through 6, but which involve the following modifications.

In the second example shown in Figure 5, the maximum catalyst temperature rise is limited to 220"C by making the inside height of the container 5 less than 0.3 times its inside diameter.

Experimental results showing the effect of varying the shape (height/diameter) of the catalyst container on both the maximum temperature rise attained and the maximum recom bining current are plotted in Figure 10. In each case, the catalytic cap used was of the general structure shown in Figure 5, and had a catalyst container having a capacity of 10 cc and containing the same weight of catalyst. As will be seen from Figure 10 the maximum recombining current can be decreased by flattening the shape of the container, although tends to stabilize at a height-to-diameter ratio of less than 0.3.

In the third example shown in Figure 6, a shield member 7 is disposed around the catalyst container. With this structure sufficient recombination takes place before the volume of gas flow reaches a given limit value, and when the volume exceeds this limit the flow of gas to the catalyst is shielded to thereby prevent the catalyst temperature rise from exceeding 220"C.

The shield 7 may be disposed surrounding the side walls and bottom of the catalyst container, or it may be dimensioned to shield all or part of just the side walls or just the bottom portion of the container.

In the fourth example shown in Figure 7, the catalyst temperature rise is limited to 2200C by increasing the particle size of the inorganic substance or synthetic resin material from which the catalyst container is formed. Figure 11 shows a plot of experimental results indicating the relationship between the particle size of the container material and both the maximum temperature rise to be restricted to an upper limit of 220"C. A suitable support pedestal 6 for a plurality of such stacked but spaced catalyst containers is shown in plan view in Figure 9. The pedestal 6 includes four equiangularly spaced vertical columns which support a plurality of vertically spaced platforms, each of which is shaped to receive a respective catalyst container.

WHAT WE CLAIM IS: 1. A catalytic storage battery cap including a casing having an opening in the bottom thereof for the introduction of hydrogen and oxygen gases released by the battery and the discharge of condensed water vapours back into the battery, and a vent in the top thereof for discharging unreacted gases, at least one porous, anti-explosive catalyst container mounted within the casing so that at least one face of the container is directly presented to the casing without being separated therefrom by an interior cover, said container containing a charge of hydrogen-oxygen recombining catalyst and the amount of catalyst and the physical dimensions of the porous catalyst container being selected so that the maximum catalyst temperature rise is limited to 2200C.

2. A catalytic storage battery cap as defined in claim 1, wherein the amount of catalyst and the physical parameters of the cylindrical container are selected in accordance with the following expression; 4W 0.5 4W 0.065 Tmax = K (pD + 0.225 D) (pD 3) Where; Tmax is the maximum catalyst temperature rise attained in "C, K is a constant determined by parameters including the material and thickness of the catalyst container, and the degree of activity of the catalyst; W is the weight of the catalyst in grams, P is the apparent density of the catalyst, and D is the inside diameter of the container in centimeters.

3. A catalytic storage battery cap as claimed in claim 1, claim 2 wherein the cylindrical container inside height is less than 0.3 times its inside diameter.

4. A catalytic storage battery cap as claimed in any one of the preceding claims, and further comprising a gas-impermeable shield concentrically disposed around the container and spaced therefrom.

5. A catalytic storage battery cap as claimed in any one of the preceding claims, wherein there are a plurality of catalyst charged containers within the casing and spaced apart from each other.

6. A catalytic storage battery cap as claimed in any one of the preceidng claims, wherein the particle size of the container material is large so as to decrease the porosity of the container and assit in limiting the catalyst temperature rise to 220"C.

7. A catalytic storage battery cap as claimed in claim 1 comprising the combination and arrangements of parts substantially as hereinbefore described with reference to and as shown in Figure 1 or any one of Figures 5 to 8 of the accompanying drawings.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (7)

**WARNING** start of CLMS field may overlap end of DESC **. in Figure 9. The pedestal 6 includes four equiangularly spaced vertical columns which support a plurality of vertically spaced platforms, each of which is shaped to receive a respective catalyst container. WHAT WE CLAIM IS:

1. A catalytic storage battery cap including a casing having an opening in the bottom thereof for the introduction of hydrogen and oxygen gases released by the battery and the discharge of condensed water vapours back into the battery, and a vent in the top thereof for discharging unreacted gases, at least one porous, anti-explosive catalyst container mounted within the casing so that at least one face of the container is directly presented to the casing without being separated therefrom by an interior cover, said container containing a charge of hydrogen-oxygen recombining catalyst and the amount of catalyst and the physical dimensions of the porous catalyst container being selected so that the maximum catalyst temperature rise is limited to 2200C.

2. A catalytic storage battery cap as defined in claim 1, wherein the amount of catalyst and the physical parameters of the cylindrical container are selected in accordance with the following expression; 4W 0.5 4W 0.065 Tmax = K (pD + 0.225 D) (pD 3) Where; Tmax is the maximum catalyst temperature rise attained in "C, K is a constant determined by parameters including the material and thickness of the catalyst container, and the degree of activity of the catalyst; W is the weight of the catalyst in grams, P is the apparent density of the catalyst, and D is the inside diameter of the container in centimeters.

3. A catalytic storage battery cap as claimed in claim 1, claim 2 wherein the cylindrical container inside height is less than 0.3 times its inside diameter.

4. A catalytic storage battery cap as claimed in any one of the preceding claims, and further comprising a gas-impermeable shield concentrically disposed around the container and spaced therefrom.

5. A catalytic storage battery cap as claimed in any one of the preceding claims, wherein there are a plurality of catalyst charged containers within the casing and spaced apart from each other.

6. A catalytic storage battery cap as claimed in any one of the preceidng claims, wherein the particle size of the container material is large so as to decrease the porosity of the container and assit in limiting the catalyst temperature rise to 220"C.

7. A catalytic storage battery cap as claimed in claim 1 comprising the combination and arrangements of parts substantially as hereinbefore described with reference to and as shown in Figure 1 or any one of Figures 5 to 8 of the accompanying drawings.