JPS6193307A - Heating element utilizing combustion catalyst - Google Patents

Abstract

PURPOSE:To enable to obtain a relatively large calorific value to a shape while a combustion temperature is being kept comparatively low, by a method wherein a combustion catalyst layer is provided on the surface of a carrier made of porous ceramics and a wall surface of continuous voids, fuel gas and air are made to flow in naturally, and flameless combustion of them is made to perform on the combustion catalyst layer. CONSTITUTION:A large number of continuous voids 4 are existing in gaps among carrier particles 3, 3... of a cylindrical pipe wall 2 made of porous ceramics and catalyst content is carried on the carrier particles 3, 3.... Fuel gas flows in a flow path 1 along the direction of an arrow A and soaks and diffuses further in the direction of an arrow B through a natural inflaw to the voids to be formed among the carrier particles 3, 3.... Air is soaked and diffused in the direction of an arrow C to the voids 4 and an air-fuel gas mixture layer is formed on the surface of a combustion reaction sphere. When ignition is performed within the sphere L1, flameless combustion through the catalyst is performed and exhaust gas is discharged in the direction of an arrow D or through the pipe wall 2. A combustion temperature does not become so high as compared with that obtainable when mixing is made to perform forcibly, life of the catalyst is improved, an area of the reaction sphere per volume of an element is increased and a large calorific value can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to a heating element using a combustion catalyst, and particularly to the heating element device suitable for being incorporated into a relatively small-sized heating device.

(Problems with the Prior Art) Heating or combustion devices using catalysts have been known for a long time, and various combustion catalysts have been proposed and implemented for this purpose. Such catalysts are widely used for secondary combustion to purify industrial exhaust gas, automobile exhaust gas, etc., and have also been used in catalytic body warmers for a long time due to their flameless combustion. It is.

More recently, LS1. When processing delicate electronic components such as VLSIs, gas-heated soldering irons are being reconsidered as an alternative to conventional electric soldering irons, which have the risk of damaging the workpiece due to electrical discharge or dielectricity. Various combustion catalysts have also been proposed. By the way, in such a gas soldering iron, it is necessary to raise the combustion temperature to a high temperature in order to transmit the temperature necessary for heat processing to the iron tip. For this reason, attempts have been made to forcibly introduce air into the fuel gas for combustion, but in this case the temperature of the combustion catalyst element often locally reaches a high temperature of approximately 1300°C.

However, among the currently known practical combustion catalysts, about 1
There are few materials that can withstand high temperatures of over 1,000°C for long periods of time; for example, cordierite ceramic carriers used as automobile exhaust gas catalysts have a temperature of about 800°C or higher.
oo°C, and asbestos and glass fibers as catalyst carriers for platinum body warmers melt or break at around 1000°C, and the supported catalyst components permeate into the carrier and lose their activity.

The present inventor had previously proposed a device that uses a heating element in which a platinum group (Pt-Rh) metal catalyst is supported on an alumina ceramic carrier as a device that can withstand such high temperatures (Japanese Patent Application No. 1983-1999). No. 219498).

When this heating element is used, for example, as a heating tip of a gas soldering iron, the life of the catalyst is greatly improved compared to the conventional one, and excellent mechanical and thermal strength can be obtained.

However, even with this improved heating element, the catalyst life is still only about 60 to 80 hours depending on the operating temperature conditions, and there is still room for practical improvement. In this case, controlling the flow rate of the fuel gas (and air) makes it possible to suppress the exothermic temperature to some extent. However, since the area of the combustion reaction region of the catalyst formed on the carrier surface is constant and limited, reducing the gas flow rate will inevitably reduce the amount of heat required for thermal processing transferred to the chip. Therefore, proper temperature control by adjusting the flow rate is actually not easy.

Furthermore, with the soldering irons used to process electronic components such as recent LSIs and VLSIs, it has become essential to make the soldering irons smaller and lighter so as not to burden the precision processing work. The catalyst element portion is often required to have a diameter on the order of a millimeter (approximately 2 mm outer diameter, 0.8 mm inner diameter).

When designing a gas soldering iron to meet these conditions, the amount of heat generated by the heating element itself will be extremely small, and losses due to heat dissipation and transmission to the outside will be relatively increased. The effective amount of heat available at the tip tip is significantly reduced due to flow rate.

temperature control becomes extremely unstable. Therefore, in order to obtain the required processing temperature, it is essential to raise the combustion temperature on the element side to a certain degree, but this inevitably reduces the catalyst life due to the high temperature and requires complicated element replacement. This is one of the reasons that prevents the use of gas soldering irons in continuous production lines.

Furthermore, such high-temperature combustion requires a mechanism such as an ejector to sufficiently mix combustion air into the fuel gas, as described above, and requires the installation and control of precise flow control valves. Since a high degree of skill is required for the heating, the structure of the small-sized heating device becomes complicated and its operation becomes difficult.

(Object of the Invention) An object of the present invention is to provide a heating element using a combustion catalyst that can maintain a relatively low combustion temperature while also obtaining a relatively large calorific value compared to its shape. .

(Summary of the Invention) The object of the invention is to consist of a porous ceramic carrier having air permeability and a combustion catalyst layer supported on the surface of the carrier and on the walls of continuous pores in the carrier. On the other hand, this is achieved by a heating element using a combustion catalyst, characterized in that fuel gas and air are allowed to naturally flow in each at normal pressure, and are mutually diffused and mixed to cause flameless combustion on the catalyst layer. .

The present invention will be explained in more detail below.

(Structure of the Invention) The porous ceramic carrier having air permeability used in the heating element of the present invention is preferably alumina or a carrier having a composition mainly composed of alumina and containing silica. Specifically, for example, alumina, Alumina-based ceramics such as mullite, aluminumite, and mullite-zircon are used.

In the present invention, it is essential that the ceramic carrier is porous and has air permeability. Generally, the porosity of a ceramic carrier can be adjusted by adjusting the temperature during firing of the carrier and the addition of a binder. Firing temperature (1
000° C. to 700° C.), the porosity increases, and as the combustion temperature increases, the ceramic structure becomes denser and the porosity decreases. Furthermore, binders such as PVA and CMC1 starch are used when burning ceramics, and the more they are used, the more the area of continuous pores in the fired ceramic increases. Furthermore, as is known in the art of manufacturing ceramic filters, it is also possible to control the pore size by incorporating a specific mesh of organic combustible material and dissipating it during firing. The porous ceramic used only needs to have a porosity that allows fuel gas and air to easily flow in and out at normal pressure, and in practice, such porosity is calculated by converting it into the water absorption rate of the sintered ceramic body. can be determined.

In the present invention, the water absorption rate is preferably in the range of 8 to 20 m2. If the water absorption rate is less than 8%, the natural flow of gas and air into the carrier, which will be described later, will be insufficient, while if it is more than 20%, the mechanical and thermal strength of the carrier will be impaired, which is not preferable.

Furthermore, the heating element of the present invention has a thermal conductivity of 0.
It is preferable to set it as 003-0.006 cal/cm/sec degreeC. 0.006 cal/cm/sec”
If it is 0 or more, the heat at the ignition point when the element is ignited is easily taken away, and the time to reach the reaction start temperature (approximately 180°C) becomes longer. It is difficult to manufacture and has low mechanical strength. Since the thermal conductivity of the carrier is approximately inversely proportional to the porosity, a preferable value can be obtained by adjusting the manufacturing conditions while taking into consideration the conditions described above regarding the porosity.

Regarding the ceramic carrier, the above-mentioned Japanese Patent Application No. 57-21949
As described in No. 8, it is preferable to form a γ-alumina coating on the surface and pore walls in advance by impregnating with aluminum chloride and firing to prevent the catalyst components from melting or the like.

In the heating element of the present invention, a layer of a combustion catalyst is supported on the surface of the porous ceramic carrier as well as on the walls of continuous pores within the carrier by conventional impregnation, firing, etc. The catalyst preferably has a composition containing platinum as the main component and other platinum group metals such as rhodium and ruthenium.In particular, in order to shorten the time from ignition to the start of the reaction, platinum 80-98: rhodium 2-10 (
% by weight) is preferred.

The above-mentioned platinum group catalyst is basically disclosed in the above-mentioned Japanese Patent Application No. 57-219.
It can be prepared by the method described in No. 498.

In the present invention, the porous ceramic carrier supporting the catalyst component is prepared by allowing combustion gas and air to naturally flow into the continuous pores of the carrier at normal pressure, and to phase them and diffuse and mix them into the catalyst layer. - It is used as a heating element for flameless combustion. Depending on the specific structure of the device that uses the heating element, such a form may include:
For example, any shape such as a hollow cylinder or a flat plate as shown in the embodiments is possible.

(Function of the Invention) FIG. 1 is a model diagram showing a longitudinal section of a heating element of the present invention formed into a hollow cylindrical shape.

In the figure, the heating element consists of a cylindrical porous ceramic carrier having a gas flow path 1 extending in the axial direction in the center, and carrier particles 3.3-- inside the cylindrical wall 2. A large number of fine pores 4 are present in the gap 1-, which are continuous from the inner surface to the outer surface 4 of the cylindrical wall 2. A combustion reaction region is formed by carrying a catalyst component on the inner and outer surfaces of the cylinder wall 2 and on the surface of the carrier particles inside. In other countries, 5 is the support part of the heating element.

:51 In the carrier shown in FIG.
It permeates and diffuses in the direction of arrow B by natural inflow into the pores 4 formed between the carrier particles 3.3----- inside the carrier particles. On the other hand, the air outside the carrier similarly permeates and diffuses in the direction of arrow C from the outer surface of the cylinder wall 2 to the inner pores 4, forming a mixed layer with the fuel gas on the surface of the combustion reaction region. Here, the concentration of fuel gas is determined in the region L1. shown along the axial direction of the cylinder wall 2. It is the highest, and decreases in the order of L2 and L3. In the central region L2, fuel gas and air are mixed at an appropriate ratio, and the exothermic reaction is most active during combustion.

When ignition is performed in the region Ll, a combustion reaction occurs first in the region L1, and this occurs in the reciprocal region L2. At L3, the entire catalyst becomes in a predetermined combustion operating state in a short period of time.

The naturally flowing fuel gas and air diffuse into the combustion reaction area of the pores 4 inside the cylinder wall at normal pressure and undergo flameless combustion by the catalyst, and the exhaust gas (HO, Go, , ) is released into the gas flow path 1.
It is discharged to the outside of the element in the direction of the arrow or through the cylindrical wall 2.

Here, it is conceivable that more complicated aspects actually exist regarding the inflow and outflow of the fuel gas, air, and exhaust gas. However, according to one basic experiment conducted by the present inventors, when liquefied gas cylinders are connected to both ends of a cylindrical heating element and ignited, the element immediately becomes red hot and flameless combustion continues. has been confirmed. In this case, unlike the case of a normal gas soldering iron, there is no active suction mechanism for air using an ejector, so all the gas necessary for combustion comes from naturally evaporated gas from the cylinder and from air. It seems that the external air from around the element flows into the continuous pores due to almost natural pressure, and is obtained by mutual diffusion and mixing. Furthermore, in this experiment, no active exhaust path was provided for the combustion exhaust gas, so it is thought that the fuel gas was burned in the pores and gradually turned into exhaust gas and naturally flowed out from the outer surface of the element. Here, even when a high-temperature flame was brought close to the outer peripheral surface of the element, no flaming combustion occurred, confirming that the combustion gas was almost completely combusted by the action of the catalyst inside and on the surface of the porous ceramic carrier. It was done.

(Effects of the Invention) In the case of the heating element of the present invention, fuel gas and air are naturally introduced into the heating element using a porous ceramic carrier at normal pressure, and are diffused and mixed with each other. Burned under catalytic action. Therefore, if a sufficient amount of air is forcibly mixed in advance, as in a conventional gas soldering iron, the combustion temperature in the reaction region will not rise too high, and the life of the catalyst can be greatly improved.

Particularly in this case, the reaction region is formed not only on the inner and outer surfaces of the cylindrical wall 2 of the cylindrical carrier but also on the wall surface of the continuous pores inside the cylindrical wall 2 (the surface of the carrier particles 3). By increasing the area of the reaction region, a large amount of heat can be obtained, and by exchanging it, the required amount of heat can be obtained. The size of the support to obtain the S content can be significantly reduced. As described above, in the heating element of the present invention, a large amount of heat is obtained as a whole due to the porous structure of the phase body.
At a soldering temperature of about 0° C., the combustion temperature does not have to be very high to transfer the required amount of heat, and the catalyst life can be significantly increased.

Furthermore, since the fuel gas and air supplied to this heating element are provided by natural inflow at normal pressure as described above,
There is no need for an air suction mechanism such as an ejector as in the prior art, and the structure is extremely simplified, thereby making it easier to downsize the heating device as a whole.

In addition, since the heating element of the present invention has a much larger calorific value than the conventional surface combustion type element, changes in the flow rate affect the temperature change of the tip even when controlling the temperature by adjusting the flow rate. The influence is not so deliberate, and stable temperature control can be easily performed.

Hereinafter, the heating element of the present invention and a specific heating device to which such a heating element is applied will be further explained.

Example of manufacturing a heating element A raw material prepared by mixing approximately 0.1 w% of CMC as a binder with mullite ceramic (3Al O, 2S102) powder was fired at a temperature of 900°C for 3 hours to reduce the outer diameter. ■, inner diameter 0.8■, length 50mm, water absorption rate 16%, apparent specific gravity 2.8, thermal conductivity 0.003 cal/cm/sec
A hollow cylindrical porous ceramic carrier of "c" was manufactured by iA. This carrier was impregnated with a 5z aluminum chloride aqueous solution under reduced pressure, then immersed in a 5t ammonia aqueous solution, and water-soluble salts were removed with running water. 3 hours at 90℃, then 11
It was dried at 5° C. for 2 hours, and then fired at 800° C. for 3 hours to form a γ-alumina coating on the inner and outer surfaces of the carrier cylinder wall and on the internal pore surfaces. This carrier was impregnated with a solution containing 1-2z of rhodium chloride in a 1z aqueous solution of chloroplatinic acid, air-dried, and heated at 200°C to 300°C in a hydrogen reduction furnace.
The temperature was raised to 0.degree. C. to support the platinum catalyst on the surface of the cylindrical wall and the internal pores of the carrier.

The heating element of the present invention can be effectively applied to heating devices such as gas soldering irons that require relatively high temperatures, and since combustion is a flameless type unique to catalytic combustion, it is difficult to handle. It is also suitably used as a heat source for portable heating or heat-retaining equipment that requires ease and safety.

Example 1 FIG. 2 shows an example in which the heating element of the present invention is applied to heating a gas soldering iron using liquefied butane gas as a heat source.

In the figure, reference numeral 11 denotes a hollow cylindrical carrier made of porous mullite ceramic formed according to the manufacturing example described above, and is housed and fixed in an outer cylinder 13 made of a material with high thermal conductivity by means of a support member 12 and the like. . The outer circumferential surface of the outer cylinder 13 is provided with a slit 14 for air intake from its base to its tip.
14--1, and slits 16 and 1[3--1 for exhausting combustion gas are formed at the most distal end near the chip 15, respectively. A conduit 17 that introduces gas from a liquefied butane gas tank (not shown) into the gas flow path of the carrier 11 is fitted into the support member of the outer cylinder 13 . In other countries, 1B is a heat transfer ring 19 for an ignition heater, and 20 is an ignition switch.

The valve of the butane gas tank (not shown) is opened and butane gas is introduced from the conduit 17 into the gas flow path of the carrier 11 at a rate of 100 mJ.
When flowing at a rate of L/min, this gas flows along the cylindrical wall of the carrier 11, during which time it naturally flows into the internal pores at normal pressure, and diffuses and permeates therein. On the other hand, the slit 14.1 of the outer cylinder 13
4--In the same way, air diffuses and permeates into the pores inside the carrier 11 by natural flow, and is mixed with butane gas in the combustion reaction region (see FIG. 1).

In this state, when the switch 20 is closed and the heater 19 is heated, this part of the carrier 11 is heated, and after about 1 to 3 seconds, the mixture with the butane gas starts a catalytic combustion reaction, and the entire heating element reaches about 800°C. heated to a temperature of

This heat is transferred by the carrier 11 itself, which has good thermal conductivity.
Furthermore, the heat is transmitted to the iron tip 15 through the outer cylinder 13 by the heat transfer ring 18 interposed between the carrier 11 and the outer cylinder 13, and the temperature is maintained at about 300°C.

The soldering iron of this example did not show any deterioration in its catalytic action even after continuous use of JiI for about 1000 hours.

For comparison, the results obtained when the heating element was used in a forced air mixing method similar to a conventional gas soldering iron are shown.

The heating element of the present invention was attached to a conventional soldering iron that allows a mixture of butane gas and air forced into it, which is ejected at high pressure from a liquefied butane gas tank by an ejector, to flow into a catalytic reaction area. The butane gas flow rate was 100 mJL/■in, and when ignited with an electric heater, the catalyst temperature rose to 1000-130 shortly after the exothermic reaction started.
The temperature reached 0°C. When used continuously in this state, the heating element did not lose its catalytic function and the reaction stopped after about 80 hours. In this case, it was observed that the catalyst metal was semi-melted or penetrated into the pore walls of the carrier.

Example 2 The heating element of the present invention has a relatively small size, can generate a large amount of heat, and has a long life, so it can be suitably used as a heating element for general heating or heat retention equipment.

FIG. 3 shows an example in which the heating element prepared in Example 1 is incorporated into a flameless heating type cooking gas stove. In the figure, a pump 22 of liquefied butane gas as a heat source is built into the bottom of a casing 21 of the gas stove, and the liquefied gas from the pump is sent from a supply valve 23 through a supply pipe 24 to the cooking section above. . The heating cooking section includes a supporting frame 25 provided on the upper surface of the casing 21 and a heating element 28 supported by the frame 25. The heating element 26 is ignited by turning the ignition switch 2 using the battery 27 as a power source. In other countries, 29 is a knob for opening and closing the supply valve 23 attached to the outer surface of the casing 21, and 30 is a cap with a set screw provided on the bottom of the pump 22.

The heating element 28 shown in FIG. 3 is constructed by inserting and fixing a large number of cylindrical elements 31 through the frame 25 so that they are arranged on substantially the same plane, as shown in FIG. Heat-resistant rubber tube 32 such as fluorine rubber is connected to both opening ends of
is formed by sequentially connecting every other one. In other countries, 33 is an ignition heater attached to a part of the catalyst element 31.

In the gas stove, liquefied butane gas vaporized from the pump 22 flows into the gas supply passage inside the heating element 26 at approximately normal pressure by opening the valve 23 and diffuses outward through the internal pores of the 4+i porous ceramic body of the element 26. I'll go. On the other hand, along with this, air from the L side of the casing 21 is similarly diffused into the inside of the element 26, and a mixed layer with butane gas is formed on the reaction region of the catalyst supported on the pore surface.

When the heater 33 is ignited in this state, combustion by the catalyst is started in the reaction area, and the entire heating element 26 is sequentially heated to red heat for cooking.

Since the gas stove of this example performs almost flameless combustion due to the catalytic action, it can be used safely even in places where the use of ordinary gas stoves has recently become a regulation 1 for disaster prevention reasons. Further, since the air for combustion is simply supplied by natural inflow from above the casing, there is no need to provide an air mixing amount adjustment 04M as in the conventional case, and the operation thereof is extremely simple.

Although a hollow cylindrical heating element is used in this example, the shape is not limited to the cylindrical shape but may be any shape as long as the fuel gas is diffused and mixed with air in the heating element. You can also.

For example, as shown in FIG. 5 and FIG.
Rectangular plate-shaped heating elements 3B, 36-- are provided in each lattice frame of
- to - may be fitted and supported to form an integrated planar heating plate as a whole. In this case, the fuel gas supplied from the gas pump etc. is supplied to the casing 34 as shown in FIG.
It flows from a passage 37 provided therein through a communication hole 38 into a supply chamber 33 provided below the heating plate, and from there permeates and diffuses upward into the heating element 36 at normal pressure.
The outside air for force preheating permeates and diffuses into the heating element 3B from above the casing 34 and is mixed with the fuel gas, and in this state flameless combustion is performed by the catalyst.

Example 3 FIG. 7 shows an example in which the heating element of the present invention is incorporated into a thermos flask and heated at any time to further ensure its heat retention effect.

In the figure, 41 is a casing of a thermos bottle, 42 is a liquid container, and 43 is a cap thereof. A liquefied gas pump 44 is provided in the space below the casing 41. gas supply valve 45,
A supply pipe 46, a heating or heat retaining section 47 consisting of a heating element, a battery 48, an ignition switch 49, etc. are built-in, and their configuration and a 11 are basically the same as in Example 1. Further, a through hole 50 for outside air and exhaust is provided in the lower peripheral wall of the casing 41.

When it is necessary to maintain infant milk or the like at a constant temperature for a relatively long period of time, such as when traveling, the milk is often carried in a thermos bottle.

In such cases, the heat retention effect of the thermos bottle alone is insufficient and rewarming is often required. In this example, the built-in heating element can be activated at any time to heat the liquid storage container 43 from its lower surface. Furthermore, if a bimetal is used as the heating element and its temperature-sensitive operating part controls the opening and closing of the valve of the cylinder, the inside of the thermos bottle can be automatically maintained at a constant temperature at all times. Furthermore, in this embodiment, a cylinder for supplying the amount of gas required for heating to this extent may be a cylinder for a normal gas lighter, and its handling is extremely safe and easy.

[Brief explanation of drawings]

Fig. 1 is a model diagram showing the principle of the present invention, Fig. 2 is a schematic longitudinal sectional view of a gas soldering iron to which the present invention is applied, and Fig. 3 is a schematic longitudinal sectional view of a gas soldering iron to which the present invention is applied.
The figure is a schematic vertical cross-sectional view showing another application example of the heating element of the present invention, FIG. 4 is a plan view of the heating element used in the application example,
FIG. 5 is an f-plane view showing another form of the heating element, FIG. 6 is a VI-VI sectional view of FIG. 5, and FIG. 7 is a further example of application of the heating element of the present invention. FIG. 8 is a schematic cross-sectional view. ■... Gas flow path 2... Cylinder wall 3... Carrier grains F4... Pores 11... However, body 13... Outer cylinder 14.1
6... Slit 15... Chip 17... Conduit 18... Heat transfer ring 19... Ignition heater

Claims (1)

[Claims] 1. Consisting of a porous ceramic carrier having air permeability and a combustion catalyst layer supported on the surface of the carrier and on the walls of continuous pores in the carrier, 1. A heating element using a combustion catalyst, characterized in that fuel gas and air are allowed to naturally flow in each other at normal pressure, and are mutually diffused and mixed to cause flameless combustion on the catalyst layer. 2. The heating element according to claim 1, wherein the porous ceramic has a porosity of 8 to 20% in terms of water absorption. 3. The heating element according to claim 1, wherein the porous ceramic is an alumina ceramic, and the combustion catalyst is a platinum group metal catalyst. 4. The heating element according to claim 1, wherein the fuel gas is a hydrocarbon gas supplied from a liquefied gas source. 5. The porous ceramic has a thermal conductivity of 0.003 to 0.
．． 0.006 cal/cm/sec°C.