Oxygen generators

An oxygen generator comprising a housing and a chemical core within the housing, the chemical core being capable on ignition of producing oxygen by chemical reaction. An ignition apparatus within the housing is for igniting the chemical core, and a collection apparatus within the housing collects oxygen produced by the chemical core. The ignition apparatus comprises an ignition handle accessible from outside the housing, the ignition handle being arranged to be rotatable by hand, and an ignition block disposed within the housing, the ignition block being arranged, when rotated in contact with the chemical core, to ignite the chemical core. A thermal isolator between the ignition handle and the ignition block is arranged to transmit rotational force from the ignition handle to the ignition block.

FIELD OF THE INVENTION

The present invention concerns oxygen generators. More particularly, but not exclusively, the present invention concerns portable oxygen candles that are used to provide breathable oxygen for medical use.

BACKGROUND OF THE INVENTION

Oxygen candles are well-known. Oxygen candles are devices that produce on demand a supply of oxygen by means of a chemical reaction. (The term “chemical reaction” is used herein to exclude electrolytic decomposition and other methods requiring an external source of energy.) An example of an oxygen candle is disclosed in WO 2009/030921 A2 (Molecular Products Group PLC) published 12 Mar. 2009.

A typical oxygen candle comprises a chemical core of an oxygen-containing substance, for example an alkali metal chlorate or perchlorate, in admixture with a catalyst that facilitates lower temperature decomposition of the chemical to oxygen and residual solids. The catalyst may be manganese dioxide or cobalt dioxide, for example, both of which reduce the temperature at which alkali metal chlorates decompose. The chemical core often also comprises a fuel such as iron.

A typical oxygen candle will comprise an ignition apparatus, which is used to trigger the production of oxygen by the device. The ignition apparatus may for example be a spring-loaded shaft with a head coated with a friction-ignitable substance such as phosphorus. When a supply of oxygen is required, the head of the spring-loaded shaft is driven into the surface of the chemical core. When the phosphorus on the head of the spring-loaded shaft is bought into contact with the chemical core, an exothermic reaction is generated. The exothermic reaction initiates the chemical reaction that releases the oxygen the chemical core contains. Alternatively, the ignition apparatus may be an explosive-type ignition, in which a pyrotechnic chemical reaction initiates the release of oxygen from the chemical core.

While the catalyst reduces the temperature at which the chemical reaction can occur, nevertheless the reaction is exothermic, and the exterior of the chemical core typically reaches very high temperatures of the order of 600-1200° C. For this reason the chemical core of the oxygen candle will be surrounded by insulation, and housed within a housing. Considerable efforts have been made to provide portable oxygen candles that can be safely held and used, despite the high temperatures the chemical core reaches when undergoing the chemical reaction.

A problem with known oxygen candles is that the ignition devices can be complicated. This can result in them being unreliable in operation. A particular problem with explosion-type ignition apparatuses is that they can introduce impurities generated during the ignition explosion into oxygen supply. Even if the impurities do not necessarily present a risk, they are nevertheless toxic gases, and their presence may be detectable as an odour in the oxygen supply, which can cause undue concern to users.

The invention seeks to solve or mitigate some or all of the above-mentioned problems. Alternatively and/or additionally, the invention seeks to provide an improved oxygen generator.

SUMMARY OF THE INVENTION

In accordance with a first aspect of the invention there is provided an oxygen generator comprising:

a housing;

a chemical core within the housing, the chemical core being capable on ignition of producing oxygen by chemical reaction;

an ignition apparatus within the housing for igniting the chemical core;

a collection apparatus within the housing for collecting oxygen produced by the chemical core;

wherein the ignition apparatus comprises:

an ignition handle accessible from outside the housing, the ignition handle being arranged to be rotatable by hand;

an ignition block disposed within the housing, the ignition block being arranged, when rotated, to ignite the chemical core;

a thermal isolator between the ignition handle and the ignition block, the thermal isolator being arranged to transmit rotational force from the ignition handle to the ignition block.

The thermal isolator allows the oxygen candle to be triggered by rotation of the ignition handle, as it causes the ignition block to rotate causing the chemical core to ignite. However, the use of the thermal isolator advantageously transmits at most only a very small amount of heat from the ignition block to the ignition handle. Further advantageously, the ignition apparatus does not require the use of any chemicals such as are required in an explosive-type ignition apparatus, minimising the introduction of impurities into the generated oxygen supply.

Preferably, the chemical core comprises metal chlorate or perchlorate. Preferably, the chemical core further comprises a catalyst and a fuel. The catalyst may be manganese dioxide or cobalt dioxide. The fuel may be iron. Alternatively, the fuel may be magnesium.

Advantageously, the thermal isolator comprises an insulating mineral material, optionally in composite form together with a binder. Such materials have been found to have good insulating properties, while also being strong enough to transmit the required rotational force without breaking. Suitably, the mineral is provided in sheet or particulate form, together with a binder. Any suitable binder, for example a polysiloxane, a polyurethane or an epoxy resin may be used. In a preferred embodiment, the mineral is mica, and the binder is a polysiloxane, for example methyl polysiloxane. Such composites suitably contain at least 80, for example at least 85, % wt of mineral, for example mica, the residue being binder together with optional small quantities of additives, for example lubricants or fillers. A preferred material for the thermal isolator is a composite comprising 89% wt mica, 10% wt methylpolysiloxane, and 1% wt silicon dioxide. Such a composite is commercially available from the Cogebi of the Netherlands.

Preferably, a first end of the thermal isolator is positioned within a slot in the ignition handle, and a second end of the thermal insulator opposite the first end is positioned within a slot in thermal block. This provides a convenient way for the thermal isolator to transmit the rotational force, by at each end pushing against the inner surface of the slots (in a similar way to a flat-blade screwdriver). Preferably, the thermal isolator is a rectangular slab. This makes the thermal isolator easy to manufacture.

Preferably, the ignition block comprises a body with an ignition surface arranged to come into contact with the chemical core. The body may be made of brass. Preferably, the ignition surface comprises phosphorus.

Advantageously, an outer surface of the body of the ignition block has a screw-thread which engages with a corresponding screw-threaded interior surface within the housing, so that rotation of the body of the ignition block in a first direction moves the ignition block towards chemical core. This allows the rotational movement to cause the ignition block to move towards the chemical core. This improves the ignition process, as in addition to a frictional force caused by the rotation of the ignition block against the chemical core, there is an additional compressive force of the ignition block moving towards the chemical core. Further, it allows the oxygen generator to be provided for use with the ignition block positioned a distance away from the chemical core, which reduces the risk of accidental ignition. The screw-threaded interior surface may be on interior surface of the housing, or of a separate ignition block holder within the housing, for example. Advantageously, a coarse screw thread is used, as this allows the ignition block to be moved a large distance with a smaller amount of rotation. It also makes the oxygen generator easy to use as it is ignited by means of a simple rotation rather than a corkscrew action being required.

Advantageously, the oxygen generator further comprises an insulating disk positioned around the thermal isolator between the ignition handle and the ignition block. This reduces the amount of heat transmitted from the chemical core to the ignition handle and surrounding housing. In particular, the insulating disk prevents radiated heat. The insulating disk may be circular. Preferably, the thermal isolator passes through a hole in the insulating block.

Advantageously, the oxygen generator further comprises a removable locking pin to prevent the ignition handle being rotated. Advantageously, the housing comprises a removable cover to prevent access to the ignition handle from outside the housing. Both these features reduce the risk that the chemical core is ignited accidentally.

Advantageously, the collection apparatus comprises a cooling chamber having an inlet through which oxygen produced by the chemical core enters into the cooling chamber, and an outlet through which oxygen in the cooling chamber leaves the cooling chamber, and wherein the interior of the cooling chamber has at least one wall arranged in the path of oxygen flowing from the inlet to the outlet. The oxygen expands as it passes through the cooling chamber, causing it to cool. By having walls in the path of the oxygen, its passage through the cooling chamber is delayed. This gives the oxygen a longer time to expand and cool. Further, by having the walls in the path of the oxygen, it has been found that this results in more efficient cooling than is the case if the oxygen is simply made to flow along an extended path. This allows the cooling chamber to be more compact. It has also been found that the walls do not need to be sealed in order for the efficient cooling to be achieved. The use of such a cooling chamber can in certain embodiments of the invention allow a portable oxygen generator to be provided in which the oxygen passing from the outlet is sufficiently low in temperatures, for example below 70° C., that standard oxygen tubing can be fixed to the outlet and the tubing will not melt. This is advantageous as it means that special tubing does not need to be used with the oxygen generator. This is particularly advantageous for oxygen tubing, which is manufactured with a star-shaped hole in the middle so that the oxygen it supplies will not be cut off if the tubing is sharply bent. Because of its unusual construction with a star-shaped hole, special heat-resistant oxygen tubing would be particularly expensive to provide.

Preferably, the at least one wall defines a plurality of paths from the inlet to the outlet. Advantageously, a first path and second path of the plurality of paths are arranged so that a stream of oxygen flowing along the first path is directed into a stream of oxygen flowing along the second path. The direction of the first and second paths into each other acts to slow down the movement of the oxygen in the cooling chamber. The walls may be arranged concentrically. Advantageously, the oxygen generator comprises at least a first and a second wall having gaps on opposite sides of the cooling chamber. This forces the oxygen to travel from one side of the cooling chamber to the other as it passes through the cooling chamber, so increasing the time it takes to pass through the cooling chamber.

Advantageously, the cooling chamber is formed by a depression in a first cooling chamber piece and a corresponding depression in a second cooling chamber piece. This makes the cooling chamber easy to manufacture. An O-ring may be provided between the first cooling chamber piece and the second cooling chamber piece, to provide a gas-impermeable seal. The walls in the cooling chamber can advantageously be formed by walls extending from the inner surface of first cooling chamber piece into corresponding grooves in the second cooling chamber piece. As the walls are intended to provide a single elongated path they do not need to be completely gas-impermeable, and so no special seal is required between the walls of the first cooling chamber piece and the grooves of the second cooling chamber piece. This simplifies the construction of the cooling chamber. Preferably, the inlet is in the first cooling chamber piece, and the outlet is in the second cooling chamber piece. This allows the first cooling chamber piece to be positioned with its external surface facing the chemical core, and the second cooling chamber piece to be positioned with its external surface facing the outside of the oxygen generator, providing a simple and compact construction. Advantageously, the inlet is positioned apart from the outlet. For example, the inlet may be positioned in centre of cooling chamber, and the outlet at one edge of the cooling chamber. This again forces the oxygen to travel a further distance across the cooling chamber as it passes through the cooling chamber, so increasing the time it takes to pass through the cooling chamber.

Preferably, the outlet is arranged to be receive a standard oxygen tube pressure fitting. This means standard oxygen tubing can be used. A particular advantage of this is that if an excess of pressure builds up due, for example, to the oxygen tubing being blocked, the pressure fitting will simply be forced off the outlet, so allowing the oxygen to be released.

DETAILED DESCRIPTION

An oxygen candle in accordance with a first embodiment of the invention is now described with reference toFIGS. 1 to 8.

An exploded view of the oxygen candle is shown inFIG. 1, and a cross-sectional view is shown inFIG. 2. The oxygen candle1comprises a tube-shaped housing2, and has an ignition end1a(the top end) and an oxygen-release end1b(the bottom end).

Inside the housing1is a cylindrical insulating body3, comprising top insulating block4and bottom insulating block5of solid insulating material at the top and bottom ends of the insulating body3, with a tube formed from further insulating material between the top4and bottom5insulating blocks. A chemical core6for ignition to produce oxygen is positioned within the insulating body3between the top4and bottom5insulating blocks. Each of the top4and bottom5insulating blocks has a central passage through which gas can pass between the chemical core6and the exterior of the insulating body3at the top and bottom ends respectively.

An ignition block holder10is positioned at the ignition end1aof the oxygen candle1, within the insulating body3between the top insulating block4and the chemical core6. An ignition block11, described in more detail below, is positioned within the ignition block holder10. For clarity, the chemical core6, ignition block holder10and ignition block11are shown alone inFIG. 6. As can be seen in particular inFIG. 7, in which for clarity the ignition block holder10is shown alone, the ignition block holder10comprises a body10awith a threaded inner surface, and at the bottom end a flange10b.

As can be seen in particular inFIG. 8, there is further at the ignition end1aof the oxygen candle1a thermal isolator12and insulating disk13. For clarity, the ignition block11, thermal isolator12and insulating disk13are shown alone inFIG. 8. The ignition block11is made of brass, and has a threaded exterior surface11awhich engages with the threaded interior10aof the ignition block holder10. The bottom end of the ignition block11comprises an ignition layer11bof phosphorus. The top end of the ignition block11comprises a slot11c, in which is positioned a thermal isolator12. The thermal isolator12is a rectangular slab of mica/polysiloxane composite containing 89% wt mica, 10% wt methyl polysiloxane, and 10% wt silicon dioxide, with dimensions roughly 20 mm by 25 mm and thickness 5 mm. The insulation disk13has a central slot13athrough which the thermal isolator12passes.

A close-up of the ignition end1aof the oxygen candle1is shown inFIG. 3. An ignition handle15is positioned within a lid portion16, which has a hinged lid16awhich can cover the ignition handle16. The ignition handle15is circular with a bar passing diametrically across its centre, providing means by which the ignition handle15can be rotated by a user. As shown inFIGS. 1 and 2, the ignition handle15is mounted upon a circular insulation block14. The bottom face of the circular insulation block14provides a slot into which the thermal isolator12is positioned.

At the oxygen-release end1bof the oxygen candle1, in contact with the bottom of the insulating body3, is a first cooling chamber piece7. A second cooling chamber piece8is positioned below the first cooling chamber piece7. An O-ring9is positioned between the first cooling chamber piece7and second cooling chamber piece8to create a cooling chamber as described in more detail below. The O-ring9creates a gas-impervious seal between the first cooling chamber piece7and the second cooling chamber piece8at the outside edge of the cooling chamber.

The first cooling chamber piece7is shown in more detail inFIGS. 4aand 4b. The first cooling chamber piece7has on the top side shown inFIG. 4a, in other words the side facing the insulating body3, a central hole7a. The first cooling chamber piece7has on the bottom side shown inFIG. 4ba circular depression, in which there is a first circular wall7barranged concentrically outside the hole7a, and a second circular wall7carranged concentrically outside the first circular wall7b. Each of the first circular wall7band second circular wall7chas a gap, arranged respectively on opposite sides of the first cooling chamber piece7.

The second cooling chamber piece8is shown in more detail inFIGS. 5aand 5b. The second cooling chamber piece8has on the top side shown inFIG. 5a, in other words the side facing the first cooling chamber piece7, a circular depression corresponding to the circular depression of the first cooling chamber piece7. In the circular depression there is an offset hole8apositioned towards a side of the second cooling chamber piece8, a first circular groove8bpositioned to receive the top edge of the first circular wall7b, and a second circular groove8cpositioned to receive the top edge of the second circular wall7c. The offset hole8ais positioned outside the second circular groove8c, on the opposite side from the gap in the corresponding second circular wall7c. The offset hole8aof course passes through to the bottom side of the second cooling chamber piece8shown inFIG. 5b. The second cooling chamber piece8is formed on the bottom side around the offset hole8ato provide a standard oxygen pressure valve, to receive a standard oxygen tube fitting.

Thus, as can be seen in particular inFIG. 2, the circular depressions of the first cooling chamber piece7and second cooling chamber piece8together form a circular cooling chamber, with the first circular wall7band second circular wall7bbeing positioned between the central hole7ain the first cooling chamber piece7and the offset hole8ain the second cooling chamber piece8.

Before use, the oxygen candle1will be provided with the ignition block11positioned within the ignition block holder10so that the ignition layer11bis a suitable distance away from the chemical core6to prevent accidental ignition, say a distance of 10 mm. The lid16aof the lid portion16will be closed, and the entire oxygen candle1may be provided within a material bag which can be opened at each end.

When used, oxygen tubing will be fitted to the standard oxygen pressure valve round the offset hole8aat the oxygen-release end1bof the oxygen candle. The oxygen tubing may be standard oxygen tubing which has a central hole of star-shaped cross-section, and may at the other end have a face mask, for example.

To ignite the oxygen candle1, first the lid16aof the lid portion16is opened to allow access to the ignition handle15. The ignition handle15is then rotated in a clockwise direction. This causes the circular insulation block14to rotate, which in turn rotates the thermal isolator13, which in turn rotates the ignition block11. As the ignition block11is screw-threaded within the ignition block holder10, the rotation causes the ignition block11to move towards the chemical core6. After a sufficient amount of rotation the ignition layer11bof the ignition block11will come into contact with the chemical core6. The friction of the phosphorus of the ignition layer11brotating against the surface of the chemical core6will then trigger the chemical reaction of the chemical core6.

As mentioned above, the chemical reaction causes a considerable amount of heat. However, while the thermal isolator13allows rotational force to be passed from the ignition handle15to the ignition block11, due to its insulating properties it nevertheless only conducts a very small amount of heat. The insulation disk13and insulation block14further help prevent more than a very small amount of heat passing from the chemical core6to the ignition handle15, or to the ignition end1aof the oxygen candle generally.

As the chemical core6undergoes the chemical reaction, it of course releases oxygen. The oxygen is not able to pass through the insulating body3or the ignition end1aof the oxygen candle1, but is instead forced through the central hole7aof the first cooling chamber piece7into the cooling chamber formed by the circular depressions in the first cooling chamber piece7and second cooling chamber piece8. The oxygen first collects in the centre of the cooling chamber within the first circular wall7b. It then passes through the gap in the first circular wall7binto the area of the cooling chamber between the first circular wall7band second circular wall7c. The oxygen then travels between the first circular wall7band second circular wall7cin both directions from the gap in the first circular wall7b. The oxygen then passes through the gap in the second circular wall7cinto the area of the cooling chamber between the second circular wall7cand the outside edge of the chamber, as defined by O-ring9between the first cooling chamber piece7and second cooling chamber piece8. Similarly to before, the oxygen then travels between the second circular wall7cand the outside edge of the cooling chamber in both directions from the gap in the second circular wall7c, until it reaches the offset hole8a. It then passed through the offset hole8ainto the oxygen tubing.

As the oxygen travels through the cooling chamber from the central hole7ato the offset hole8ait expands, causing it to reduce in temperature. Importantly, the first circular wall7band second circular wall7cdo not provide a single extended path through the cooling chamber. Rather, after passing through each gap the oxygen travels in two streams in opposite directions to the other side of the cooling chamber, where the streams meet and pass through the next gap or offset hole8a. The meeting of the streams of oxygen arriving from opposite directions slows the passage of the oxygen through the cooling chamber, increasing the time the oxygen has to expand and cool before leaving the cooling chamber.

Whilst the present invention has been described and illustrated with reference to particular embodiments, it will be appreciated by those of ordinary skill in the art that the invention lends itself to many different variations not specifically illustrated herein.