Patent Grant
8142726
This patent application claims the benefit of priority from PCT application Ser. No. PCT/NL02/00506 filed Jul. 25, 2002, the contents of which are incorporated herein by reference.
This invention relates to a chemical oxygen gas generator.
Chemical oxygen (pyrotechnic) gas generators have been developed and used already for long periods. Self-controlled, continuously ready to operate for many years without any verification tests, easy activation from low-power electric sources, small size, safe, a rather high yield of oxygen on a per-unit volume and unit mass and a number of other advantages make them irreplaceable in case of emergencies and in accidents. They are used and applied, for instance, for the emergency supply of oxygen to the passengers in aircraft in case of cabin depressurization, in submarines if the other emergency oxygen supply systems fail, in space stations in case of emergency if the basic oxygen supply systems fail, and in many other conceivable emergency cases. A typical example of the use of oxygen generators on-board aircraft is presented in U.S. Pat. No. 4,840,171.
An operational application is the supply of oxygen for firefighters. Other cases to provide oxygen to satisfy operational requirements are e.g. for divers, or for driving rocket engines on-board spacecraft. In all these cases oxygen has to be provided independently of the ambient or surroundings.
In general, oxygen may be provided from oxygen stored in bottles or from oxygen generators. The latter in many cases are lighter and less voluminous for the same amount of oxygen than bottles. Chemical oxygen generators are the subject of this invention. Chemical oxygen generators are well known to those versed in the art. As a rule, chemical compounds, which release oxygen during thermal decomposition, are used in chemical oxygen generators. The following compounds are commonly used:
Special additives are used in small amounts to assure self-sustained decomposition (combustion) while releasing oxygen. These additives also control the reaction rate, and form a heat resistant slag with a high-melting point and scavenge harmful gases (i.e. impurities, e.g. chlorine, its compounds and others) that may be released by side reactions.
Typical Examples of These Additives Are:
U.S. Pat. No. 6,126,854 mentions a number of combinations and specifically mentions magnesium oxide to control the decomposition reaction, suppress chlorine formation, improve the rheology and facilitate the mixing. One reason for improving the rheology and the mixing, is the way in which the oxygen candle according to U.S. Pat. No. 6,126,854 has been made. The present invention avoids several of these difficulties. U.S. Pat. No. 3,868,225 discusses another oxygen generator (or oxygen candle). Materials, like asbestos, which are presently considered a health hazard, are used in this patent to obtain oxygen of breathing quality. The cool oxygen gas generator which is subject of this invention does not use asbestos.
U.S. Pat. Nos. 5,336,470 and 5,322,669 discuss means to control the mass flow rate of the oxygen. This is done by introducing barriers of various shapes. These barriers on one hand create a specific path for the decomposition front, but also specifically serve to absorb heat from the decomposition reaction. This is certainly required if the chemical oxygen generator has to provide oxygen for breathing purposes. For example, the decomposition of sodium chlorate is according to the reaction:
2NaClO3→2NaCl+3O2+101 kJ
To maintain the decomposition reaction, fuel like iron (Fe) is added to the mixture. The decomposition temperature of the mixture is in the order of 1500 K. In a classical chemical oxygen generator heat is absorbed by the additives and the housing, but insulation material is required to prevent the outside of the housing becoming too hot and additional heat sinks to cool the oxygen to acceptable temperatures. U.S. Pat. No. 3,868,225 uses glass fiber as insulating material and a double wall through which coolant air may pass. Nevertheless, oxygen temperatures of 370° C. (700° F.) are reported. It is obvious that if the oxygen is to be used directly for breathing, it must be cooled down further, which usually is done by large heat capacity filters. These serve the purpose of filtering the oxygen gas from particulate material and polluting chemicals, if present, but especially to cool the oxygen. Therefore, these filters are much larger and heavier than would be the case if the only purpose was to filter and cleanse the oxygen. In fact, the filters are counterproductive for mass and volume reduction. The importance of low mass is specifically stressed in U.S. Pat. No. 6,007,736.
The present invention circumvents the problems of the prior art, by making use of a technology that has been described in the Russian patent 2108282 and the International patent application PCT/NL00/00696, publication Number WO 0123327. Here the hot decomposition gas is passed through the not reacted material, thereby raising the temperature of the virgin material and cooling the produced gas. However, to accomplish this it is necessary to make a porous charge that remains integer during the decomposition when oxygen is released. If that were not the case, particulate material might clog the porous charge and functioning of the gas generator would be impaired. U.S. Pat. No. 4,981,655 teaches a chemical oxygen generator where also the hot oxygen passes through the virgin material. However, this virgin material consists of loose pellets held together and compressed by a spring load. The pellets themselves are specially manufactured and consist of a cylindrical center body and two hemispherical end caps. The cylindrical part can even be of a different chemical composition than the hemispherical end caps. Although the dimensions of the pellets are not given in U.S. Pat. No. 4,981,655, it can be inferred from the drawings that they are of macroscopic dimensions; therefore the specific surface area for contact with the hot oxygen is much smaller than the specific surface of the porous virgin material that is subject of the present invention.
The object of the invention is a chemical gas generator providing oxygen of low temperature, such as below 50° C., preferably below 30° C., preferably also of very high purity. The main object of the invention is a special oxygen-generating material and the technology of manufacturing the porous, gas-permeable, mechanically strong charges of this material. When receiving a defined amount of (externally provided) heat, these charges are able to decompose exothermally (burn) while generating oxygen. They are also capable to pass hot oxygen through their own body without destruction or volumetric burning. The charge is placed in the gas generator in such a way that the oxygen generated in the reaction passes through the porous virgin charge in the same direction as the reaction front under a pressure difference. Because of this process, the oxygen is cooled down to the ambient temperature due to heat exchange with the charge. At the same time, the oxygen heats the charge near the reaction front up to the temperature required to sustain this reaction.
The slag formed after the reaction consists of substances with high melting and boiling points and remains within the gas generator.
To achieve an efficient exchange of heat and an unobstructed path for the oxygen, the charge has a porosity (ερ) ranging from 41% to 61% and a relatively large specific surface Spc=(13±2)·108 m2/kg. (The porosity is defined as ερ=1−ρch/ρc, where ρch is the charge density and ρc is a charge composition density).
The charge is composed of fine-granules as an oxygen source; the main ingredients are compounds from the groups:
Small amounts of special substances are introduced into the charge composition to:
To achieve the proper burning and cooling characteristics, it is preferred that the porous material has a very high specific surface. It is important that at the substantial porosity and relatively high specific surface of the pores, a rather high charge strength is assured (the minimum compression strength is at least 0.67 MPa and the modulus of elasticity is over 50 MPa). These mechanical characteristics assure when assembling, operating and transporting the gas generator, that the charge does not deform, remains integer and doesn't crack or crumble.
The selection and amount of special binder material and the process of charge manufacturing is an important aspect of this invention. It is an aspect of the invention that the amount of binder material is less than 3.0 wt. % of the charge, thereby assuring a high purity, while at the same time maintaining sufficient porosity. It provides a sufficient level of mechanical properties at a substantial porosity of the charge with a very small amount of binder in the composition. The binder is selected from the following group:
In case organic binders are used, and this is preferred, the amount thereof is preferably less than 1.5 wt. %.
According to the method to generate cool gases (Russian Patent No2108282) the charge design and its arrangement in the generator must create a decomposition front and ensure that the generated oxygen flows through the charge in the direction: from the igniter to the vent. In relation to this, the design and shape of the charge are limited only by the fact they must provide a suitable propagation of decomposition front and oxygen flow through the charge.
Vibration-tamping the granular mass into a processing die is used to manufacture the porous charges. This technology involves the following main stages:
Preparation of the solid ingredients involves:
Preparation of the Binder Involves:
Mixing of the mass involves the following: thorough agitation of the binder solution (or parts of it) and mixing of the dry powdered ingredients in the required ratios.
Granulation comprises manufacturing of solid granules of defined sizes from the obtained mass such that it guarantees the required porosity and specific surface area of the charge pores. The granules are moistened with the binder solution in the intermediate processing solvent or directly with the intermediate processing solvent and are molded by vibration tamping into a processing die of the required dimensions and shape. Vibration tamping is carried out to provide homogenous density, porosity and strength of the complete charge. The charge, cast into a processing die, is subjected to solidification.
One part of the invention is that the housing of the gas generator has one or more filters. These filters are installed between the charge and the vent of the gas generator. The filters have the following objectives:
Another part of this invention is a thermal protection on the oxygen generator housing to prevent heating of its outer surface during the burning of a charge.
This thermal protection may be applied on the inner side or the outer side of the housing or on both sides.
The inner thermal protection may be made of glass or silicon fibers impregnated with the same binder as used in charge.
Alternatively, the housing itself, if that is made of composite and low heat-conducting material, may serve as a thermal protection material.
If there is no thermal protection on the housing, the outer side of the charge may be provided with a thermal protection, or the outside surface of the charge itself may serve as thermal insulation. The outside of charge with a thickness ˜1.5 mm adjacent to the wall of the housing will not burn due to cooling by the wall and then serves as a thermal insulator.
All these approaches may also be used in combination.
The chemical cool oxygen generator (
In one of the preferred embodiments, the housing is protected from the heat of the decomposing charge by a thermal protection 5, preferably made from silica or glass fiber impregnated with the same binder as used for the charge 2. In another preferred embodiment, the charge 2 itself provides the thermal protection of the housing. In this case a layer of ˜1.5 mm thickness adjacent to the wall of the housing does not burn due to cooling of the outside of the charge by the wall of the housing, 4.
In the preferred embodiment, the housing, 4, is made of metal such as steel, aluminum or titanium. In another preferred embodiment, the housing, 4, is made of a composite material (plastic composite).
Between the charge, 2, and the vent, 6, a filter, 3, is installed. The given filter serves:
Filter, 3, can consist of four separate filters: the first is for preventing carrying particles away with the oxygen, 11, the second is for removing harmful gaseous impurities, the third is for converting any CO into CO2, the fourth filter is for additional oxygen cooling.
Sand can be a material of the filter to cool the very last portion of the oxygen, 11. In a second preferred embodiment, all the filter functions are combined in two or three separate filters, 3. In another preferred embodiment, the various filter functions are combined in one filter, 3.
In other preferred embodiment the number of filters is reduced, as in many cases no filters or only specific filters are required. If no additional cooling is required, the sand filter is omitted.
In another preferred embodiments, the sand filter combines the functions of cooling and preventing any particle matter to be expelled with the oxygen.
The housing, 4, in a preferred embodiment has handles or grips for easy transportation. In another preferred embodiment, the housing, 4, has attachment fixtures, that provide easy mounting of the oxygen generator in different devices. Such fixtures encompass threaded ends, flanges, screw connections or other standard connections that are known in the field.
In the preferred embodiment, the oxygen releasing composition involves chemicals selected from the following list as oxygen sources:
The chemicals from the following list are added in small proportion (up to 5%) to the composition to maintain the self-sustaining decomposition of the oxygen releasing material, to control the reaction rate, to form a slag with a high melting point, and to remove impurities (i.e. harmful gases) that can be formed as a result of side reactions:
Metals:
The binder for the oxygen generating composition is selected from the following group of materials:
In the preferred embodiment, the porous charge of oxygen generating composition has a specific surface area of 11·108−15·108 m2/kg, a porosity within the range from 41% to 61%, a compression strength over 0.67 MPa, a modulus of elasticity more than 50 MPa and a density between 1020 to 1150 kg/m3.
In the first preferred embodiment, the charge has the following composition:
The measured characteristics of the decomposition products (without a filter) are:
Composition of the Gas:
The gas temperature (at the exit of the gas generator) is 293.degree K (20.degree.C.).
In the second preferred embodiment, the charge has the following composition:
The measured characteristics of the decomposition products (without a filter) are:
Composition of the Gas:
The gas temperature (at the exit of the gas-generator) is 293.degree K (20.degree.C.).
The technology of vibration-tamping the granular mass of the oxygen generating composition in a processing die is used to manufacture porous charges. The technology involves the following main stages: preparation of ingredients, mixing of the mass, granulation of the mass, molding the granular mass and solidification of the charge.
The preparation of solid ingredients involves drying, grinding and separation to separate out fractions with particles of specific sizes. Subsequently, the powdered ingredients are agitated in the required ratio until a homogeneous mixture is obtained.
The mixing of the mass is obtained by agitation of the binder (or a part of it) with the dry powdered ingredients and an intermediate solvent in the required ratio.
Granulation involves the manufacturing of solid grains from the obtained mixture with well-defined sizes, that guarantees the required porosity and specific surface area of the pores in the charge. The grains are moistened with a mixture consisting of a part of the binder and the intermediate processing solvent, or they are only moistened with processing solvent. They are molded by vibration-tamping into a processing die of the required dimensions and shape of the charge. Vibration-tamping is carried out to provide a homogenous density, porosity, and strength through the complete body of the charge. After this, the charge in the processing die is left to harden at the appropriate solidification temperatures.
After solidification the charge is removed from the processing die and placed in the housing of a chemical gas generator. In some cases, the processing die itself can be a part of the generator housing and after the solidification, the charge can be connected with the other generator elements.
In accordance with the method to generate cool gases by decomposition in porous charges, according to the Russian Patent No2108282, the design of a charge and its installation in the gas generator provides a proper propagation of the decomposition front and oxygen flow through the porous-charge body.
It is understood that the foregoing description is that of the preferred embodiments of the invention and that various changes and modifications may be made thereto without departing from the spirit and scope of the invention as defined in the appended claims.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2001121023 | Jul 2001 | RU | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/NL02/00506 | 7/25/2002 | WO | 00 | 6/25/2004 |
| Publishing Document | Publishing Date | Country | Kind |
|---|---|---|---|
| WO03/009899 | 2/6/2003 | WO | A |
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|---|---|---|
| 1 099 904 | Sep 1955 | FR |
| Number | Date | Country | |
|---|---|---|---|
| 20050053527 A1 | Mar 2005 | US |
