GB2290410A - Device for catalytic combination of hydrogen and oxygen eg. produced during operation of storage batteries in an enclosed space - Google Patents

Abstract

The device comprises activated carbon (2) carrying a catalytically active metal, the activated carbon being in a pouch of perforate material of good thermal conductivity eg. a metal, preferably aluminium. The pouch preferably comprises two sheets (3, 4), one (3) larger than the other (4), edges of the larger sheet being crimped around edges of the smaller sheet to form the pouch. A large number of devices according to the invention may be mounted between grooved aluminium rails. The pouch provides the catalyst mat with mechanical protection, ensures uniform distribution of hydrogen, limits catalyst activity in the event of oversupply of gas and prevents local overheating. <IMAGE>

Description

DEVICE FOR CATALYTIC COMBINATION OF HYDROGEN AND OXYGEN The present invention relates to a device for catalytic combination of hydrogen and oxygen. In particular, but not exclusively, the invention relates to a device for catalytic recombination of hydrogen and oxygen produced during operation, i.e. charging, storage and discharge, of one or more electrical storage batteries in an enclosed space.

Low-maintenance operation of modern storage batteries requires efficient devices for recombination of gaseous hydrogen and oxygen produced both during charging and storage and during discharge of the batteries. Such recombination devices are usually arranged on top of a casing of the battery and above a vent orifice or alternatively may conveniently be incorporated in sealing plugs. One well-tried recombination device according to EP-0 066 676, comprises a two-ply mat made from a polytetrafluoroethylene/activated carbon mixture, one ply containing finely divided palladium as catalyst.

It is also necessary to eliminate hydrogen from a gaseous mixture containing oxygen as well as hydrogen in enclosed spaces which accommodate storage batteries and must be entered by maintenance personnel. Such enclosed spaces include accommodation space of submarines.

DE-OS 34 37 479 describes a recombination device for such applications and which is in tablet form and has an activated carbon/polytetrafluoroethylene core containing palladium and an absorbent layer compressed around the core.

A catalyst comprising metal layers is known from DE-OS 38 26 503, in which catalyst a metal sheet acting as support is provided on both sides with a catalytically active Pd Ni Cu-surface layer with an interposed layer of a transition metal.

An object of the present invention is to provide a device for catalytic combination of hydrogen and oxygen and which, at the low hydrogen concentrations usually prevailing in battery rooms, effects the safe and reliable combination of the hydrogen with oxygen to yield water, and which also functions in the event of a temporary oversupply of hydrogen gas.

In accordance with the present invention there is provided a device for catalytic recombination of hydrogen and oxygen produced during the operation of one or more storage batteries in an enclosed space, comprising a mat, sheet or layer (hereinafter referred to as a "mat") of activated carbon carrying a catalytically active metal, the activated carbon being in a pouch of perforate sheet metal of good thermal conductivity.

It has been found that the object of the invention is achieved by use of activated carbon impregnated with a catalytically active metal in a pouch-like container which is shaped from a perforate sheet of material of good thermal conductivity.

The metal of good thermal conductivity is preferably a metal selected from iron, stainless steel, copper, brass and aluminium. Of these metals aluminium is most preferred because of its low relative density. Aluminium also has a comparatively high thermal conductivity, which is approximately half that of copper, which is more than four time denser.

Enclosing the mat of activated carbon within the pouch of perforate material ensures that the activated carbon is readily accessible to the ambient atmosphere and that the heat of recombination is rapidly dissipated by the highly thermally conductive material.

Enclosure of the mat of activated carbon in the pouch allows the catalytically active metal used to be a highly active catalyst which can function at very low hydrogen concentrations to effect combination of hydrogen and oxygen. Such concentrations occur for example in the interior of submarines, where the hydrogen concentration is normally only 0.1 to 0.3% H2.

Highly sensitive catalysts have the disadvantage of overheating or even igniting themselves or their carrier at elevated hydrogen concentrations. This danger is, however, eliminated by means of the pouch of perforate sheet material, because the activated carbon is largely covered up. When approximately 70% of the geometric or outer surface area of the mat of activated carbon is covered the available hydrogen is not entirely reacted especially in the event of overload, but partially passes by the pouch, such that the rate of reaction is limited and the rate of evolution of heat is less.

The outer surface of the pouch may be smooth. The optionally increased gas throughput promoted by the smooth surface is inevitably accompanied by a greater supply of hydrogen, but this cannot, however, be completely reacted due to the reduced catalyst activity caused by the covered surface. In this manner, the hydrogen supply and catalyst activity cancel each other out with regard to recombination capacity, such that the rate of recombination surprisingly remains substantially stable. Irrespective of this, the greater gas throughput brings about improved cooling of the catalyst and reduces the recombination temperature.

Preferably the carbon is in firm contact with the highly conductive material of the pouch and the mass of the material of the pouch exceeds that of the mat by many times. In such a device the tendency of extensive flat catalyst arrangements, such as activated carbon mats, to local overheating is suppressed because the perforate sheet material of the pouch or cover distributes the hydrogen over the entire surface of the catalyst (i.e. the activated carbon carrying the catalytically active metal) and unimpeded dissipation of heat is ensured due to the firm contact of the carbon with he highly thermally conductive material.

In order to prevent highly localised overheating in the area of the open catalyst surface, the selected perforation size should not be too large.

Preferably the perforations of the pouch have a diameter in the range from 1 mm to 3 mm, and more preferably the diameter is about 2 mm.

The invention is further described below by way of example with reference to the accompanying drawings, wherein: Figure 1 is a front view, partly cut away, of a device according to the invention.

Figure 2 is a cross-section of the device along line A-A of Figure 1; and Figure 3 is a view of an apparatus including a plurality of devices as shown in Figures 1 and 2.

Referring to Figure 1 of the drawings, a perforated sheet metal pouch 1 is formed from aluminium sheet of approximately 1 mm thickness, the diameter of the perforations being 2 mm. The perforations are arranged regularly over the sheet at a spacing between centres of approximately 3.5 mm.

The perforated sheet metal pouch is produced by placing together two shells 3,4 made from the perforated sheet metal with an interposed catalyst mat 2 and bonding the shells together along their edges, which extend beyond the mat, for example by spot welding or crimping.

The shells comprise flat metal sheets 3 and 4 of differing sizes, the edges of the larger sheet 3, as may be seen from Figure 2, being crimped around the edges of the smaller sheet 4.

The dimensions of a perforated sheet metal pouch may be selected as desired.

Perforated aluminium pouches of a size of 80 mm x 170 mm have proved most successful in practice.

Due to their bead-like periphery, perforated pouches described above may readily be inserted between grooved metal rails and thereby fixed. Figure 3 shows an apparatus in which two aluminium rails 5 form a mounting for a plurality of perforated sheet aluminium pouches 1. In this arrangement, the catalyst mats or sheets are maintained at a precise spacing and the dissipation of heat to a casing (not shown) enclosing the entire apparatus is promoted.

Used catalyst mats or sheets may be replaced easily and rapidly. The snug fit of the mats or sheets in the perforated sheet metal pouches protects them from damage by shock and prevents small particles from flaking off over extended use.

The invention may be summarised as follows: 1. Device for the catalytic recombination of hydrogen and oxygen produced during the operation of storage batteries in enclosed spaces, characterised in that the recombination unit (1) consists of an activated carbon mat (2) provided with a catalytically active metal, which mat is arranged in a pouch (2, 3) made from perforated sheet metal with good thermal conductivity.

2. Device according to Summary 1, characterised in that the sheet metal material is formed from one of the metals iron, stainless steel, copper, brass or aluminium.

3. Device according to either of Summaries 1 or 2, characterised in that the perforated sheet metal pouch may be fixed in grooved rails.

4. Device according to any of Summaries 1 to 3, characterised in that the perforated sheet metal pouch comprises two shells (3, 4) made from perforated sheet metal, the edges being firmly bonded together by crimping.

5. Device according to any of Summaries 1 to 4, characterised in that the perforated sheet metal pouch has a regular distribution of the perforations, which are spaced at centres of approximately 3.5 mm.

6. Device according to Summary 5, characterised in that the diameter of the perforations is 1 mm to 3 mm, preferably 2 mm.

From the foregoing description it will be understood that a device (1) for the catalytic recombination of hydrogen and oxygen in accommodation areas located in the vicinity of batteries provides the arrangement of an activated carbon mat (2) impregnated with a catalyst metal in a pouch (3, 4) made from perforated sheet metal with good thermal conductivity, preferably aluminium.

The perforated cover provides the catalyst mat with mechanical protection ensures uniform distribution of hydrogen, limits catalyst activity in the event of oversupply of gas and prevents local overheating. The perforated sheet metal pouch, produced by crimping a larger sheet of metal (3) around the edges of a smaller sheet of metal (4), may be fixed between grooved aluminium rails and mounted in large numbers.

Claims (10)

1. A device for catalytic recombination of hydrogen and oxygen produced during the operation of one or more storage batteries in an enclosed space, comprising a mat sheet or layer (hereinafter referred to as a "mat") activated carbon carrying a catalytically active metal, the activated carbon being in a pouch of perforate sheet metal of good thermal conductivity.

2. A device according to claim 1, wherein the material of good thermal conductivity is iron or steel, copper, brass or aluminium.

3. A device according to claim 1 or 2, wherein the pouch comprises two perforate shells having respective edges fastened together by crimping.

4. A device according to any of claims 1 to 3, wherein the pouch has a regular distribution of perforations spaced at centres of approximately 3.5 mm.

5. A device according to claim 4, wherein the diameter of the perforations is 1 mm to 3 mm.

6. A device according to claim 5, wherein the diameter of the perforations is about 2 mm.

7. A device for catalytic combination of hydrogen and oxygen, substantially as described herein with reference to and as illustrated in Figures 1 and 2 of the accompanying drawings.

8. Apparatus comprising one or more devices according to any preceding claim and located in grooves in rails.

9. Apparatus according to claim 8, wherein a pair of the rails are spaced apart and opposite edge portions of the or each device are located in respected grooves in the rails.

10. Apparatus according to claim 8, substantially as described herein with reference to and as illustrated in Figure 3 of the accompanying drawings.