 |
Description  |
|
|
This invention relates to a gas generator. More particularly, this
invention relates to a gas generator disposed in a solid form with stable
properties until use and with properties of generating a gas, and
particularly oxygen, without also generating hazardous or harmful
chemicals. The invention also particularly relates to an oxygen generator
which is capable of generating a considerably greater amount of oxygen per
unit of stored volume than any of the generators of the prior art.
It is desirable in a number of different applications to generate oxygen,
carbon monoxide or carbon dioxide. For example, a supply of oxygen is
often desirable on a controlled basis for life-saving purposes such as for
resuscitating patients or for sustaining patients who have had heart
attacks. Oxygen is also desired in industrial applications such as
equipment for welding, brazing, smelting or heat treating different
materials. Oxygen is also desired for instituting, generating or
sustaining combustion of various materials including wood, coal, coke,
petrochemicals or paper products. Gases such as carbon monoxide or carbon
dioxide are further desired to inflate articles such as rafts or slides
for aircrafts, life vests, balloons and underwater inflation devices.
Although different types of gas generators are available, generators in the
form of solid candles have certain inherent advantages. They are fairly
compact and light in weight and generate significant amounts of oxygen per
unit of volume. They do not generate noxious or hazardous fumes while
being stored and they do not present any problems of instability so as to
be explosive while being stored. In view of these advantages, oxygen
generators in the form of solid candles can be easily transported and
stored until placed into use.
The oxygen generators now in use in solid form generally include a
fiberglas as a binder, iron powder as a fuel and a chlorate such as sodium
chlorate as an oxidizer. The fiberglas has certain disadvantages as a
binder. It is somewhat hydrophyllic so that it tends to retain moisture
during the formation of the generator and to attract moisture after the
formation of the generator. It tends to have a relatively low green
strength when moist and to retain the fuel in clumps in the generator
rather than allowing the fuel to be dispersed evenly throughout the
generator. When the fuel in the generator burns to produce heat and to
provide for the liberation of oxygen by the generator, the fiberglas tends
to melt and to flow, thereby preventing the oxygen from being liberated on
a controlled basis at a uniform rate. Furthermore, when the fuel in the
generator burns, the moisture in the generator vaporizes and thereby
inhibits the combustion. As will be seen from the subsequent discussion,
the moisture also tends to react with other materials in the generator to
produce hazardous or harmful chemicals.
The oxygen generators now in use include iron powder as the fuel. This is
disadvantageous for certain important reasons. As the oxygen generator
ages, the iron powder rusts. Iron powder as a fuel is advantageous because
it can combust to the ferrous or ferric forms to generate heat and thereby
liberate the oxygen in the chlorate. However, when the iron powder rusts,
it becomes converted to the ferric form (Fe.sub.2 O.sub.3) and is no
longer combustible. The rusting of the iron powder in the oxygen
generators of the prior art has been accelerated by the inclusion of
moisture in the generator, particularly since the iron powder and the
moisture have been included in the presence of a strong oxidizer such as
sodium chlorate. As a result, the oxygen generators in solid form have had
only a limited shelf life.
A chemical has generally been included in the oxygen generators now in use
to inhibit the generation of noxious fumes. This catalyst has been
primarily barium peroxide (BaO.sub.2). However, when the oxygen generator
of the prior art has been formed, some water has been mixed with the other
chemicals to facilitate the formation of the oxygen generator. The water
has reacted with the barium peroxide to form barium hydroxide
(Ba(OH).sub.2). The barium hydroxide in turn has reacted with additional
molecules of water to form barium hydroxide octahydrate (Ba(OH).sub.2
.multidot.8H.sub.2 O).
The water in the barium hydroxide octahydrate can only be removed at a
relatively high temperature in the order of 550.degree. C. This
temperature is considerably higher than the temperature (approximately
245.degree. C.) at which the mixture of the fuel (iron powder) and the
chlorate in the oxygen generator decomposes exothermically or, in other
words, autoignites. As a result, if any attempt should be made to
eliminate the water molecules from the barium hydroxide after the
formation of the oxygen generator, the oxygen generator would be comsumed.
The barium peroxide has been included in the oxygen generators of the prior
art to react with free chlorine liberated from the sodium chlorate during
the combustion of the fuel in the generator. Actually, because of the
entrapment of the water molecules in the barium hydroxide and the
conversion of the barium peroxide to barium hydroxide octahydrate, the
barium peroxide has not been able to react chemically with the free
chlorine. What has actually happened has been the decomposition of the
sodium chlorate to sodium chloride (NaCl) and oxygen and the melting of
the sodium chloride (NaCl) at a temperature of approximately 248.degree.
C. and the vaporization of the sodium chloride at a temperature of
approximately 1414.degree. C. The vaporization of sodium chloride is
produced at the points of combustion of the fuel and the oxygen liberated
from the chlorate even though the average temperature in the reaction zone
is in the order of 700.degree. C. to 800.degree. C. When the sodium
chloride becomes vaporized, it reacts with water released from the barium
hydroxide octahydrate as follows:
NaCl + H.sub.2 O.fwdarw.HCl + NaOH. (1)
as is well known, hydrochloric acid (HCl) is noxious. Since the
temperatures are quite high, the hydrochloric acid vaporizes so that it is
breathed by the people in the vicinity of the oxygen generator.
Furthermore, heat is absorbed in such a reaction so as to inhibit the
continued liberation of oxygen from the generator. The heat absorbed is in
the dehydration of the barium peroxide octahydrate to make water molecules
available for reaction with the sodium chloride. Since this heat is
absorbed at the combustion zone, it decreases the heat available to
decompose the sodium chlorate.
When the water molecules are released from the barium hydroxide octahydrate
at a temperature of approximately 550.degree. C., the water molecules tend
to produce a vapor at the surface of the oxygen generator. This tends to
inhibit further combustion of the fuel (iron powder) and the oxygen
liberated from the sodium chlorate. Furthermore, the high heat capacity
and heat vaporization of the water reduce the net enthalpy resulting from
the heat liberated by the decomposition of the sodium chlorate to sodium
chloride and free oxygen and the combustion of the fuel with the free
oxygen. This reduction in the net enthalpy may be so great as to cause the
oxygen generator to become extinguished or even to prevent the fuel in the
generator from becoming ignited.
Manganese powder has sometimes been used as the fuel in oxygen generators.
In the presence of moisture such as water or a fine spray or as a vapor
(steam) added during the mixing process, manganese exhibits dangerous
properties. This may be seen from the following chemical reaction:
Mn + H.sub.2 O.fwdarw.MnO + H.sub.2. (2)
the liberation of hydrogen in the presence of atmospheric oxygen sometimes
produces an explosive gas mixture. The explosive reaction of the hydrogen
and the oxygen is facilitated by the heat liberated from the exothermic
reaction of manganese and water.
The production of the oxygen generators specified above has generally
occurred in the presence of a significant amount of water. This
significant amount of water has been as high as 5% of the weight of the
oxygen generator. For the reasons discussed above, the water has been
retained in the oxygen generator even though there has been a conscious
desire, and even attempt, to remove such moisture from the generator.
This invention provides an oxygen generator which overcomes the above
difficulties. The oxygen generator includes a binder which is not
hydrophyllic and which has the properties of remaining in solid form even
while the fuel in the generator is being combusted. The binder has the
properties of retaining the fuel dispersed throughout the binder rather
than being bunched as in the prior art. The binder provides good strength
even while green. By "green" is meant the moist, undried or uncured state
of the freshly pressed or consolidated candle ingredients. The binder can
be mixed with the fuel and the oxidizer by the addition of a minimal
amount of water so that a minimal amount of water is retained in the
oxygen generator after the formation of the generator. Steps can be taken
to remove this water, without combusting the fuel, after the generator has
been formed.
The oxygen generator of this invention also includes a fuel which is not
hazardous and which does not emit noxious fumes when combusted. The fuel
is provided in the form of relatively large particles which are uniformly
dispersed in the binder in isolated relationship to one another. In this
way, combustion of the fuel occurs at isolated or localized positions with
the production of concentrated heat and high temperatures at these
isolated or localized positions. This prevents a continuous liquid
interface of molten sodium chloride from being produced between the
combustion zone and the decomposed candle. Molten sodium chloride is still
produced in this invention at random positions but the molten sodium
chloride has an opportunity to cool and solidify at these positions after
the fuel has been consumed at these positions.
By providing for the production of the combustion of the fuel at the
isolated or localized positions, the combustion is also sustained on a
controlled basis such that the combustion can be interrupted at any time
desired. This can be accomplished by bending or breaking the candle along
the surface of the combustion. Furthermore, the combustion occurs at a
slower rate in certain embodiments of the generators of this invention
than in the generators of the prior art so that a generator of minimal
weight can be provided for a reaction intended to continue over a
predetermined period of time.
In other embodiments of the generator of this invention, combustion can be
produced at a faster rate that in the prior art. This can be an advantage
in producing an increased rate of heat flux for such operations as
brazing. The increased rate of oxygen flow in these embodiments is useful
in cutting or burning the metal by combustion with the excess oxygen
provided by the generator.
The amount of fuel used in the oxygen generator of this invention is less
than the amount of fuel included in oxygen generators of the prior art.
The combined embodiment of fuel, binder and catalyst used in the oxygen
generator of this invention is also less than that in the prior art. In
this way, the amount of oxidizer included in the generator of this
invention is substantially increased.
In the drawings:
FIG. 1 is a curve showing the rate of combustion of the fuel in an oxygen
generator in relation to the amount of fuel in the generator.
A suitable clay such as bentonite is preferably used as the binder in the
oxygen generator of this invention. Bentonite constitutes a hydrous
aluminum silicate found, for example, in Wyoming. It may be defined as a
colloidal clay of the montmorillonite mineral group. It swells in water or
with the addition of water and carries sodium as its predominant
exchangeable ion. It may be classified nominally as Na.sub.2
O-CaO-6Al.sub.2 O.sub.3 -36SiO.sub.2 -O.7Fe.sub.2 O.sub.3. A typical
percentage by weight of the different materials in bentonite is as
follows:
______________________________________
Material Percentage (%)
______________________________________
Silica (SiO.sub.2)
69.76
Alumina (Al.sub.2 O.sub.3)
16.84
Ferric Oxide (Fe.sub.2 O.sub.3)
3.51
Lime (CaO) 1.80
Magnesia (MgO) 0.97
Soda (Na.sub.2 O) 1.95
Potash (K.sub.2 O)
0.20
______________________________________
It will be appreciated, however, that different bentonite deposits will
have different compositions from that specified above. Bentonite having a
relatively high percentage of sodium may be used as the binder in oxygen
candles. The igniters for charcoal briquettes may use either sodium
bentonite or calcium bentonite or a mixture of various bentonites to
provide desired properties of processing or cured strength.
A clay such as bentonite begins to soften at about 1037.degree. C., and
fusion occurs at 1337.degree. C. to form a refractory matrix material.
When the oxygen candle is ignited, the bentonite binder tends to lose
slightly less than 6% of its weight through vaporization of chemically
held water and other causes. Since the clay binder may represent 7% of the
candle formula, the chemically held water may be less than 0.5% of the
candle weight.
Bentonite has a good thermal conductivity so as to transfer heat between
the different localized hot spots as the fuel in the generator is
combusted. Actually, the bentonite has a better thermal conductivity than
sodium chlorate, which is included as the oxidizer in the generator. In
this way, the clay such as bentonite tends to sustain the combustion of
the fuel after such combustion has been initiated.
Bentonite has other desirable properties of some importance. It provides a
high green strength such that the oxygen generator of this invention is
strong even before it is dried or cured. Furthermore, the high green
strength of the bentonite causes it to position and retain the fuel and
the oxidizer even while it is wet. This insures that the fuel will be
thoroughly dispersed throughout the binder.
Since it is essentially a refractory material, bentonite does not melt or
flow even when subjected to high temperatures such as occur when the fuel
in the generator is combusted. A clay such as bentonite offers the further
advantage of quiet and ready release of water at temperatures below the
boiling point of water, with negligible retention of molecules of water.
It is easily mixed uniformly with the fuel and the oxidizer to form a
homogeneous mixture.
Preferably the clay such as bentonite is retained in the mixture in the
range of 7% to 10% by weight when the generator is used as an oxygen
candle or as an igniter for charcoal briquettes. However, the bentonite
can be included in the range of 4% to 20% by weight, particularly when it
is used for other purposes than as an oxygen candle or as an igniter for
charcoal briquettes. As the percentage of bentonite in the generator is
increased, the combustion of the fuel becomes correspondingly inhibited
since the bentonite tends to isolate the different fuel particles.
Lignin may also be used as the binder. The lignin may be used alone or in
combination with bentonite or a suitable material such as calcium
carbonate or both the bentonite and the calcium carbonate. When lignin is
used in combination with calcium carbonate, the sodium lignol sulfonate
(lignin) combines with the calcium carbonate to form calcium sulfate and
sodium carbonate. By way of illustration, the mixture may include as the
binder a combination of approximately 5% to 10% by weight of bentonite,
approximately 1% to 5% by weight of lignin and approximately 1% to 3% by
weight of calcium carbonate.
The fuel preferably comprises finely granulated particles of coke or
charcoal. The coke is commercially designated as fluid coke, which is
solid carbonaceous residue. Such a carbonaceous residue is produced by
fractional distillation of petroleum in a reducing atmosphere to remove
the volatile fractions, leaving only the fixed carbon and the ash content
after the water and the volatile matter are removed. This material
constitutes essentially pure carbon with an ash content dependent upon the
petroleum from which the coke is derived. Coke breeze may also be used
instead of fluid coke. Coke breeze has a compositon similar to that of
fluid coke.
Depending upon the use to be made of the oxygen generator, sea coal may
also be used. For example, when the oxygen generator is to be used to
ignite charcoal briquettes to obtain the combustion of the briquettes in
an outdoor barbeque, sea coal is preferably used as the fuel because it
contains volatile hydrocarbons in solid forms. These hydrocarbons are
ignited relatively easily by the flame from a match or by striking the
generator on a phosphorous strip. When the hydrocarbons are ignited, they
fuel the generation of heat and oxygen for igniting the briquettes.
Although bentonite requires a temperature of 1337.degree. C. for fusion,
local temperatures greater than 1400.degree. C. are produced at the
localized positions of combustion of the fuel. This may be seen from the
fact that a salt fog (or vapor) of sodium chloride is produced at the face
of the oxygen generator. Sodium chloride vaporizes at a temperature in
excess of 1411.degree. C. When the oxygen generator is used as an oxygen
candle, the salt fog is removed by filtering because the salt fog tends to
make the flame yellow.
Generally, not all of the fuel is consumed in the combustion process. One
reason is that the coke or charcoal or sea coal is diluted somewhat by the
ash content of the fuel. Another reason is that the coke or charcoal or
sea coal is encapsulated by the binder such as the bentonite. Since the
combustion occurs on a localized basis, not all of the fuel is accessible
to the combustion because of the encapsulation by the clay.
Preferably the particles of fuel should not be too small, such as in a
finely divided powder. When a finely divided powder such as carbon black
or lamp black is used, the entire combustion zone is liquefied to such a
depth as to cause flow of the molten sodium chlorate. This flow tends to
extinguish the combustion, particularly since the flow is often away from
the area of combustion. The use of a finely dispersed powder as the fuel
is particularly undesirable when the generator is to be used as a free
standing candle.
Coke burns more slowly than sea coal. However, it tends to produce a hotter
fire than sea coal, partly because it combusts to carbon dioxide. Another
reason is that it produces no water as it burns. This is advantageous
because water acts as a coolant or heat sink in the combustion zone.
Therefore, coke tends to utilize oxygen more efficiently within the
confines of the oxygen generator than sea coal. Since some uses of the
oxygen generator are to provide an efficient liberation of oxygen, the use
of coke as the fuel is preferable in such instances. For example, when the
oxygen generator is used as an oxygen candle to produce as much oxygen as
possible for a given weight and volume of the candle, the use of coke as
the fuel is preferable. Under such circumstances, the coke preferably has
a range by weight in the order of (11/2%) to 4% in the candle. However,
coke in a range of approximately 1% to 5% can be used. This means that the
oxidizer in the candle has a weight as high as 92% in the candle. It
further means that most of the oxygen in the oxidizer can be liberated
without being consumed by combustion with the fuel.
The heat from the igniter should be controlled within certain limits when
the generator is used as an oxygen candle. If the heat from the igniter is
too great, the oxygen candle will melt below the combustion zone and flow
away from the zone, thereby causing the combustion zone to become
extinguished.
When the oxygen generator is used as an oxygen candle, it provides
insulation except at the surface where it is being combusted. For example,
the oxygen candle can be manually handled by grasping it at a position a
fraction of an inch removed from the surface of combustion. Furthermore,
the candle can be extinguished by placing it on its side and cutting or
breaking the ash from the parent material. This causes the ash to fall
away from the remainder of the material in the candle and the remainder of
the material to be saved for a subsequent combustion.
As previously explained, the use of sea coal is desirable when the oxygen
generator is used to ignite such difficult material as charcoal
briquettes. The use of sea coal is desirable because it will ignite more
readily, than will fluid coke or other fuels, from a match or other
convenient source of heat and flame. This results in part from the
inclusion of the volatile material in the sea coal, as explained above.
The sea coal may be ASTM Classification II, Bituminous, Group 5, high
volatile C.
The amount of fuel in oxygen generator for use in igniting charcoal
briquettes is preferably higher than in other applications. For example,
an amount of sea coal as high as 15% or 20% can be used. Preferably, the
amount of fuel in an oxygen generator for igniting charcoal briquettes is
in the order of 7%. When a fuel level of approximately 7% is used in
igniting charcoal briquettes, an excess of oxygen is assured for
hypergolic oxidation of the briquettes in the ignition process. As will be
appreciated, if the heat from the ignition is not sufficient, the charcoal
briquettes will not be ignited.
When the oxygen generator is used to ignite charcoal briquettes, the oxygen
generator can be activated by striking it on the strip included on match
books for igniting matches. The heat generated by the friction between the
match strip and the oxygen generator is sufficient to ignite the fuel in
the oxygen generator. This occurs through the following chemical reaction:
P + NaClO.sub.3 .fwdarw.P.sub.2 O.sub.5 + NaCl (3)
As will be appreciated, the phosphorous in the above chemical reaction is
obtained from the match strip. The heat generated by the above reaction
causes oxygen to be released by the sodium chlorate. This oxygen in turn
reacts with the fuel in the generator to produce combustion and generate
additional heat. By generating excess oxygen, heat is liberated and the
oxygen is freed to combust with the charcoal briquettes. In addition,
relatively little salt fog is produced to inhibit combustion.
Sea coal having a weight as high as approximately 20% in the mixture has
been used with a binder having a weight as high as approximately 20% to
ignite charcoal briquettes. In such a mixture, the predominantly carbon
fuel becomes combusted to carbon monoxide and hydrogen. These combustible
gases then undergo secondary combustion with atmospheric oxygen to produce
water and carbon dioxide. Such combustion causes temperatures in excess of
1800.degree. C. to be produced. Although the charcoal or other combustible
fuel is enveloped in a reducing atmosphere, the heat transfer is more than
adequate to raise such combustibles above their auto ignition
temperatures. This causes the combustibles to ignite and sustain
combustion with atmospheric oxygen after the igniter is consumed. However,
salt fog tends to be produced. The salt fog tends to inhibit the surface
of the combustible fuel from direct contact with the atmospheric oxygen
that it needs to support ignition and combustion. As a result, the use of
a relatively high percentage of fuel in an igniter for charcoal briquettes
is not as desirable as those igniters which provide a reduced amount of
fuel and which generate oxygen.
In an igniter for charcoal briquettes, an increased amount of binder offers
certain advantages. It improves the plasticity of the wet mixture for ease
of molding the mixture into a desired shape such as a slender rod. As will
be appreciated, a slender rod is desirable because it distributes the heat
over an expanded area or volume and ignites an increased mass of the
charcoal briquettes with a particular weight of the igniter material.
Furthermore, by increasing the weight of the binder in the igniter
material, the freshly molded rods are provided with an enhanced green
strength and the strength of the rods is enhanced after the rods have been
cured. The cost of the rods is reduced by increasing the percentage of
weight of binder in the rods.
The oxidizer described above has certain advantages in addition to those
set forth above. For example, a percentage by weight as high as 92% for
the oxidizer is considerably greater than that provided for the oxidizer
in the generators of the prior art. Furthermore, since the amount of fuel
is relatively low in the generator of this invention and since the
combustion of the fuel is quite efficient, particularly when coke (as
distinguished from sea coal) is used, a considerably larger percentage of
oxygen is available in the generator of this invention for subsequent use
than in the generators of the prior art.
The technical grade of sodium chlorate used in the oxygen generator
preferably has a minimum purity of 99.5%. The sodium chlorate preferably
has a maximum content of 0.12% of sodium chloride by weight and a maximum
content of 0.20% of water by weight. It is preferably produced by
electrolysis of an aqueous solution of technically pure sodium chloride.
Preferably a generator to be used as an oxygen candle has a cylindrical
shape similar to that of an ordinary candle and a generator to be used as
an igniter for charcoal briquettes has the shape of a cylindrical rod,
which may be approximately 4 inches long and may have a diameter of
approximately one half inch. All portions of the candle or rod form a
uniform mixture. Although the igniter for the charcoal briquettes is
preferably in the form of a cylindrical rod, other shapes such as discs
and spheres may also be used. The generator may also be in other shapes
than cylindrical when it is used as an oxygen candle.
When fluid coke (or coke breeze) is used as the fuel in candles designed
for closed pressure vessel combustion, burning times ranging from 5
minutes per inch to 2 minutes per inch are generally produced as the fuel
content is varied from 1.25% to 2.5%. FIG. 1 illustrates the increase in
the proportional ratio, substantially linear, of fuel content to burning
time. This substantially proportional relationship has been maintained in
tests with fuel to 15% by weight in the candles.
The tests in FIG. 1 were made at atmospheric pressure on a candle having an
outer diameter of approximately 11/8 inches. It has been found that the
diameter of the candle influences the ability of the candle to sustain
combustion. As the diameter of the candle is increased, the percentage of
fuel required to sustain combustion becomes correspondingly decreased.
This results from reduced heat loss as the diameter is increased, the
reduced heat loss resulting from the increase in cross sectional area
relative to the circumference of the candle.
Candles approximately 4 inches in length and approximately 7/8 inch in
diameter have also been produced with a burning time greater than 15
minutes for each candle. Six of these candles and eight igniters have a
net weight of less than 1 pound and provide an oxygen supply for
approximately 11/2 hours for a torch tip of approximately 0.052 inch in
diameter.
By varying the fuel ratio so as to progressively increase the oxygen output
per unit of time with a corresponding reduction in burning time, one pound
of oxygen candles will supply the oxygen required for various sizes of
torch tips as follows:
______________________________________
Tip Diameter in Inches
Burn Time in Minutes/Pound
______________________________________
0.052 90+
0.065 66+
0.070 60+
0.080 50+
0.085 45+
0.100 30+
______________________________________
It has also been found that six candles, each having an axial length of
approximately 25/8 inches and a diameter of 11/8 inches, and seven
igniters weigh less than 1 pound. It has been further found that the
candles, when ignited by the igniter, will supply oxygen for at least 1
hour. According to the regulations of the United States Government, if
oxidizing material can be packed in a package of less than 1 pound and if
multiple packages can be packed in a container with the net weight of
oxygen-generating material not exceeding 25 pounds, the container is
exempt from labelling as hazardous. Because of this, the container is
exempt from a premium type of shipping and can illustratively be made from
styrene. In contrast, the prior art has required 11/2pounds to 2 pounds of
material to obtain a supply of oxygen for at least 1 hour. As a result,
the prior art has had to ship its material on a premium basis in metal
containers with stringent labelling requirements and with no assurance
even then that the material will operate properly when placed into use by
the recipient.
One practical limit of fuel would be the stoichiometric properties for
converting all carbon to carbon dioxide. This may be of interest in some
applications as a hot gas generator. A formula for producing such
conversion is as follows:
6C + 4NaClO.sub.3 .fwdarw.4NaCl + 6CO.sub.2 (4)
when the binder constitutes approximately 10% of the generator and when
allowance is made for ash residue in the fuel, fuel having a weight of
approximately 15% in the generator is needed to achieve this stoichiometry
with approximately 75% by weight of sodium chlorate.
The upper practical limit of fuel would be the stoichiometric proportion to
convert all of the oxygen in the generator to carbon monoxide. This may be
seen from the following chemical reaction:
6C + 2NaClO.sub.3 .fwdarw.2NaCl + 6CO (5)
again, allowing for about 10% by weight of binder and for about 10% by
weight of ash content in the fuel, the fuel would have a weight of about
25% and the sodium chlorate would have a weight of about 65%. This
stoichiometry would provide a maximum number of molecules of gas from the
generator relative to the weight of the reactants in the generator.
One application for a generator such as described in the previous paragraph
would be for emergency gas generation, such as inflating a life raft, a
life vest, a tire or a slide in an airplane. Another application is for
use in a welding torch where a combustible gas such as carbon monoxide is
mixed with oxygen to produce a very hot flame for welding and brazing. As
will be appreciated, the carbon monoxide can be produced by a generator
such as specified in the previous paragraph and can be mixed with oxygen
obtained from an oxygen candle. This eliminates the need for bottled fuel
gases such as propane or methyl acetylene propadiene (MAPP).
The gas generators are formed by volumetrically proportioning the different
ingredients as a first step. The proportional ingredients may be
transferred by a conveyer belt and then thoroughly mixed with ambient
temperatures to form a homogeneous blend. Water may then be introduced to
the homogeneous mixture in the form of a vapor, as steam or as a finely
dispersed spray. The amount of water introduced to the mixture may be as
little as 1.5% by weight. From a practical standpoint, as small an amount
of water as possible is introduced to the mixture. The material is then
pressed into tablet or rod form or into the form of an oxygen candle.
The material is then dried by directing hot air or forced air past the
tablets, rods or candles. Chemical desiccants such as calcium chloride and
mechanical desiccants such as molecular sieves may also be employed to
remove water vapor from the recirculated hot air in the drying process and
to assure complete drying of the product. The drying of the product is
facilitated because the characteristics of the binder offer the further
advantage of quiet and ready release of the process water at temperatures
below the boiling point of water, with negligible retention of molecular
water.
By limiting the amount of process water to a weight as low as 1.5%, the
material constitutes a damp powder which will flow. This is in contrast to
the prior art which adds water in an amount of 5% during the processing
operations and accordingly produce a wet powder which flows poorly.
Furthermore, the addition of water in an amount of only 1.5% to the
material of this invention enhances the green strength of the material and
reduces breakage of the undried material. It also minimizes the energy
required to subsequently dry the material.
Although this application has been disclosed and illustrated with reference
to particular applications, the principals involved are susceptible to
numerous other applications which will be apparent to persons skilled in
the art.
* * * * *
|
|
 |
|
 |
Description |
|
