JPS6166009A - Combustion device - Google Patents

Abstract

PURPOSE:To improve radiation efficiency and the variable width of a combustion quantity by a method wherein the device is provided with a combustion body having the catalytic substance of the platinum series for a heat-resistant material having many combustion holes, means to supply the mixture of fuel gas and air to the combustion body and a heat permeating plate provided on the surface opposed to the upstream surface of the combustion body. CONSTITUTION:Premixing gas is burnt at the upstream surface 3b of the combustion body 3 and the upstream portion A of combustion holes 3a. The combustion body 34 is heated by above heat of combustion and radiation heat is discharged out of an upstream surface 3b. Further, the heat of exhaust gas after combustion is transferred to the combustion body 3 at the downstream portion (b) of the combustion hole 3a. The temperature of the upstream surface 3b is more risen by this heat and the radiation heat is discharged efficiently. The radiation heat is radiated to the body to be heated through the premixing gas layer and the heat permeating plate 2 by the heat permeating plate 2 provided in the direction of the upstream surface 3b. According to this method, the temperature in the combustion chamber 1l does not cause to ascend abnormally, therefore, backfire does not cause and the variable width of the combustion quantity may be increased even if the temperature of the upstream 36 become high temperature as the premixing gas is not preheated abnormally.

Description

DETAILED DESCRIPTION OF THE INVENTION FIELD OF INDUSTRIAL APPLICATION The present invention relates to a combustion device used in heating appliances, drying devices, and the like.

Conventional Structures and Problems Conventionally, two types of combustion devices for obtaining high radiation have been known: a fuel bank burner and a catalytic combustion burner.

In particular, the Schwunk burner is common as a burner for the purpose of radiation, but this Schwunk method has two drawbacks. Firstly, there is a limit to the emissivity, and secondly, the amount of combustion cannot be adjusted.

These two drawbacks are basically caused by one reason, namely the flashback phenomenon. In the Schwank system, in order to completely prevent backfire, the combustion hole of the combustion body is made extremely small in diameter, and the flow velocity is maintained within the combustion hole at a rate higher than the combustion speed of the air-fuel mixture. occurs downstream of If the speeds become unbalanced, the flame will propagate upstream, causing what is called a flashback. For these reasons, it has been difficult to change the flow rate of the air-fuel mixture, and it has been difficult to completely change the combustion amount. At the same time, since flame is always generated on the downstream side of the combustion body, combustion heat is not sufficiently transmitted to the combustion body and is dissipated as waste heat. This is the reason why the radiation efficiency of the Schwank method is limited to approximately 30 to 40%.

A second conventional example that has been studied extensively in recent years in order to eliminate such drawbacks is the decomposer combustion method.

An example of a typical catalytic combustion system will be explained below.

The combustion body is a non-woven fabric made of heat-resistant fibers such as alumina.
A combustion catalyst is supported. The premixed gas flowing from upstream is combusted in this combustion body.

Due to the action of the catalyst, combustion begins upstream of the combustion body, where the temperature is relatively low, and combustion is completed downstream of the combustion section. This method has the characteristic of being less likely to cause backfires because it can be burned at a low temperature due to the action of a catalyst. Therefore, it is possible to change the amount of combustion. In addition, compared to the Schwank method where combustion occurs only on the downstream side of the combustion body, the catalytic combustion method where combustion occurs throughout the combustion body allows the heat of combustion to heat the combustion part better and improve radiation efficiency. There is a radiation efficiency of about 50%. However, despite these advantages of the catalytic combustion method, the reason why the Schwank method is still the mainstream radiant heating source for home and industrial use is that the increase in radiant efficiency is small even though it uses an expensive catalyst. In addition, the variable range of combustion amount is not very wide, resulting in poor cost performance.

OBJECT OF THE INVENTION The object of the present invention is to drastically improve the radiation efficiency and the total change in combustion amount of a combustion device using a catalyst.

Structure of the Invention In order to achieve the above object, the combustion device of the present invention includes a combustion body in which a platinum group catalyst such as platinum or palladium is supported on a heat-resistant material having a large number of combustion holes through which gas passes in the thickness direction; The apparatus includes means for supplying a mixture of fuel gas and air to the combustion body, and a heat-permeable plate provided on a surface facing the upstream surface of the combustion body.

DESCRIPTION OF EMBODIMENTS Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.

In the figure, 1 is a combustion box, and the front and rear surfaces are open. 2 is a heat permeable plate provided to close the front opening of the combustion box 1 from the inside, and 3 is a combustion body provided to close the rear opening of the combustion box 1 from the inside.
It is made of a heat-resistant material such as cement, and has a large number of combustion holes 3a of arbitrary shapes such as round or square in the thickness direction, and a platinum metal catalyst such as platinum or palladium is supported on the surface. The amount of catalyst supported on the combustion body is large on the heat permeable plate side (upstream surface 3b side) and small on the opposite side ψ (downstream surface 3c side). A premixer 4 mixes the gaseous fuel or liquid fuel flowing through the fuel pipe 5 with the air blown by the blower 6 to generate a premixed gas. Note that, when liquid fuel is supplied, the premixer 4 has a built-in heater for vaporization or a device for atomization, such as an ultrasonic vibrator. 7 is a premixing tube that connects the premixer 4 and the combustion box 1, and the premixed gas generated in the premixer 4 passes through the premixing tube T and passes through the hole provided in the bottom of the combustion box 1. 9 and is supplied between the heat permeable plate 2 and the combustion body 3 in the combustion box 1 . 1Q is an electric heater wound around the combustion body 3,
The combustion body 3 is heated in advance to a predetermined catalyst activation temperature. Reference numeral 11 denotes a heat reflecting plate disposed substantially parallel to the downstream surface 3C of the combustion body 3, and an exhaust passage is formed between the heat reflection plate 11 and the combustion body 3.

In the above configuration, at the time of ignition, the combustion body 4 is heated in advance to a predetermined catalyst activation temperature by the electric heater 10 provided in the combustion body 4. After reaching a predetermined temperature, fuel is sent from the fuel pipe 5 and air is sent from the blower 6, and the premixed gas generated in the premixer 4 is supplied into the combustion box 1 through the premixing pipe 7, and combustion is started completely. .

Due to the action of the catalyst, combustion starts from the upstream surface 3b of the combustion body 3, continues to burn within the combustion hole 3a, and ends by the time it reaches the downstream surface 3C. In tactile combustion, the oxidation reaction occurs microscopically on the surface of the catalyst, resulting in so-called flameless combustion. Therefore, the downstream face 3 of the combustion body 3
The unburned components flowing further downstream from c are hardly oxidized because there is no so-called external flame. For this reason, in this apparatus, the reaction must be completed before the downstream surface 3c of the combustion body 3, and the air amount of the premixed gas must be set to an air-fuel ratio that is greater than the required amount in advance.

Next, the reason why this device has high radiation efficiency and a wide variable range of combustion amount will be explained with reference to FIG.

The premixed gas is combusted on the upstream surface 3b of the combustion body 3 and the upstream portion a of the combustion hole 3a. This combustion heat heats the combustion body 3 and emits radiant heat from the upstream surface 3b.

Furthermore, the heat of the exhaust gas after combustion is transferred to the combustion body 3 already downstream of the combustion hole 3a. This heat further increases the temperature of the upstream surface 3b and efficiently releases the radiant twist.
Exit in direction c. Further, in this device, a heat permeable plate 2 is provided in the direction of the upstream surface 3b, and the radiant heat passes through the premixed gas layer and the heat permeates through the plate 2, and is radiated to the object to be heated. This structure is completely different from the conventional Schwunk method or catalytic combustion method, that is, the structure obtains radiation from the upstream surface 3b of the combustion body 3. In the conventional method in which radiation is taken from the downstream surface of the combustion body, exhaust gas whose temperature is higher than that is always generated from the high-temperature radiation surface, and a large amount of heat is lost as exhaust temperature. In contrast, with this device, the radiation emitted from the high-temperature radiation surface
High-temperature exhaust gas is converted back into radiation through heat exchange,
High radiation efficiency is achieved because the remainder is released as low-temperature exhaust gas.

Furthermore, since the main radiation surface is the upstream side surface and the radiation passes through the heat-transmissive plate 2, the temperature inside the combustion chamber 1 will not rise abnormally. The heat transmitting plate 2 is made of a material with high heat transmittance, such as quartz glass, silicate glass, or mica. Since the premixed gas is not preheated abnormally in this way, flashback will not occur even if the temperature of the upstream surface 3b increases. This is the reason why the variable width in this device increases.

Incidentally, even if the catalyst surface becomes high temperature, the premixed gas does not easily ignite. As is well known, if a premixed gas is heated to a high temperature, it will spontaneously ignite. Also, if a flame comes into contact with the mixed gas, it will catch fire. Because the catalyst performs flameless combustion, it may ignite the premixed gas but not cause it to catch fire. However, the platinum group catalyst used in this device in particular has a high temperature on the catalyst surface. However, it is difficult to ignite the premixed gas that comes into contact with it. This is a fact known as the ignition suppressing effect of catalysts.

This effect is one of the reasons for the expansion of the variable range. In this way, this device has a structure that prevents the premixed gas from being overheated, and the structure that suppresses ignition of the catalyst makes it difficult to cause backfire.Furthermore, the action of the platinum group catalyst, which maintains catalytic activity at low temperatures, reduces the amount of combustion. This allows the variable range of small combustion amount to be expanded.

Furthermore, as mentioned above, combustion in the combustion body 3 starts from the upstream surface 3b of the catalyst regardless of the concentration and speed of the premixed gas, but if the flow speed increases, combustion will gradually become more intense in the direction of the downstream surface 3C. It's coming.

The oxidation reaction naturally begins upstream when the premixed gas and catalyst come into contact, but the main reaction zone tends to move downstream according to the flow velocity. These phenomena occur when the flow velocity of the combustion hole 3a exceeds the flame propagation velocity of the premixed gas.

However, as described above, this device has a configuration that makes it difficult to cause flashback, so there is no need to apply a high flow rate to prevent flashback. A high emissivity can be achieved by making the flow velocity in the combustion hole 3a smaller than the flame propagation velocity of the premixture, and by setting the main combustion region at the upstream surface 3b. In general, if re-combustible premixed gas comes into contact with such a high-temperature surface, it will ignite.
In this case, a phenomenon called backfire occurs and the device becomes extremely dangerous, but as mentioned above, this does not occur with this device unless it burns at an extremely high density. Therefore, by providing a low flow rate, the upstream surface 3b is heated to a high temperature, and high radiation efficiency can be obtained due to the heat exchange action. Note that the above-mentioned air-fuel mixture flow rate of the combustion hole 3a is a value obtained by dividing the amount of air-fuel mixture by the average area of the combustion hole 3a of the combustion body 3.

Further, the distribution of the amount of catalyst supported in the combustion body 3 is narrower in the upstream and smaller in the downstream, and catalytic combustion is performed mainly only in the upstream face 3b and the upstream direction of the combustion hole 3a. Therefore, there is basically no need for a catalyst downstream of the combustion hole 3a whose main purpose is to recover exhaust heat. Therefore, by using a catalyst only in the upstream direction, the amount of catalyst can be saved. Alternatively, if the same amount of catalyst is used, the catalytic combustion characteristics will be improved if the catalyst is supported on the upstream side. Basically, a catalyst is not required in the downstream direction, but it is better to support a small amount of it to purify unburned components such as trace amounts of C○ that were not completely combusted upstream. Different loadings are sufficient.

In addition, the radiant heat emitted from the upstream surface 3b of the combustion body 3 passes through the heat-transmissive plate 2 and heats the object to be heated, but a part of the radiation is absorbed or reflected by the heat-transparent plate 2. and head in the opposite direction, that is, downstream.

Radiation radiated in the opposite direction through the combustion hole 3a,
The radiation generated from the downstream surface 3c of the combustion body 3 is directed in the opposite direction to the object to be heated.

However, due to the heat reflecting plate 11 provided substantially parallel to the combustion body 3, the radiation directed downstream is returned to the front through the combustion hole 3a. A part of this returned heat is also transferred to the heat transmitting plate 2,
Although mutual reflection is repeated between the combustion body 3 and the heat reflection plate 110,
Since the heat permeable plate 2 always transmits a portion of the radiation, the temperature inside the combustion box 1 does not become abnormally high and backfire is unlikely to occur. or,
The heat reflecting plate 11 may be a mirror surface made of aluminum, stainless steel, etc., and may be made of a material with high reflectivity or a material with high absorption rate, and is configured not to dissipate heat from the back surface, so that it does not dissipate heat toward the downstream direction. Any material that has the function of returning upstream energy by reflection or secondary radiation may be used. Radiation is emitted forward in a concentrated manner by the heat reflecting plate 11, effectively heating the object to be heated.

Note that the heat permeable plate 11 is made of a transparent material with a low coefficient of thermal expansion and weak strength such as glass, and it is difficult to maintain airtightness with the combustion box 1 made of metal, for example. A large amount of sealing material, etc. must be used. If the O-seal is bad, the premixed gas will leak, causing odor and other hygienic conditions.
The pressure inside the combustion box 1 is made negative by the natural draft force caused by
By creating a negative pressure inside, the premixed gas will not leak even if there are some gaps.

Effects of the Invention As is clear from the above explanation, according to the present invention, an extremely high radiation efficiency can be obtained, and therefore a comfortable heating effect or a strong drying effect can be obtained using infrared rays, and the combustion amount can be varied over a wide range. , the convenience of adjusting the combustion amount as needed, the safety of lowering the exhaust temperature, etc. are improved.

[Brief explanation of the drawing]

FIG. 1 is a partially cutaway perspective view of a combustion device showing an embodiment of the present invention, FIG. 2 a is a sectional view of the same essential part, and FIG. FIG. 3 is a sectional view of another main part of the same combustion apparatus, and FIG. 10 is a sectional view of the main part of another embodiment of the present invention. 2... Heat permeable plate, 3... Combustion body, 3a...
... Combustion hole, 3b... Upstream surface, 3C...
...Downstream surface, 12...Heat reflecting plate.

Claims (5)

[Claims] (1) A combustion body in which a platinum group catalyst is supported on a heat-resistant material having a large number of combustion holes; a means for supplying a mixture of fuel and air to the combustion body; A combustion device equipped with a heat permeable plate provided on the surface. (2) The combustion device according to claim 1, wherein the flow velocity of the mixture in the combustion hole of the combustion body is lower than the combustion velocity of the mixture. (3) The combustion device according to claim 1 or 2, wherein the amount of catalyst supported on the combustion body is large on the upstream side and small on the downstream side. (4) The combustion device according to claim 1, wherein a heat reflecting plate is provided substantially parallel to the downstream surface of the combustion body, and an exhaust passage is formed between the two. (5) The combustion device according to claim 1, wherein the air-fuel mixture path is configured to have a negative pressure with respect to the atmosphere.