JPH0259363B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application This invention relates to a heat exchange device, and more specifically,
By integrating the combustion zone and the heat transfer zone, we have achieved an extremely compact equipment configuration, and by uniformly burning the mixed fuel supplied to the combustion heat transfer zone, we are able to eliminate nitrogen oxides (NOx). ), carbon monoxide (CO), etc., and the generation of unburned substances, thereby effectively preventing air pollution, and relates to a heat exchange device with excellent heat transfer efficiency.

Prior Art A water heater or other steam boiler that circulates water in a heat transfer tube and heats the heat transfer tube from the outside to supply hot water is a type of heat exchange device that exchanges heat in a heat transfer section. Generally, fuel combustion gas is often used as a heating source, but in this case, if a cold heat transfer tube with circulating water is brought into direct contact with a flame in which a combustion reaction is progressing in the combustion chamber, it will immediately become incomplete. Combustion occurs and produces unburned hydrocarbons (UHC).
Therefore, in this type of water heater or steam boiler, there is always a space between the combustion chamber and the heat transfer chamber located above it, and a heat transfer tube such as a coiled pipe is installed in the heat transfer chamber. It's getting old.

That is, heat exchange is performed by allowing a combustion reaction accompanied by a flame to proceed in the combustion zone, guiding the high-temperature combustion gas after the reaction to the heat transfer zone, and bringing the combustion gas into contact with the heat transfer tube. In this way, the combustion space is divided into the combustion zone, where combustion reactions are promoted, and the heat transfer zone, where high-temperature combustion gas passes through and heat exchange takes place. The space became large, and therefore there was a limit to miniaturization.

In addition, with conventional heat exchange equipment, it is difficult to achieve uniform combustion in the combustion space, and there are locally high and low temperature areas, resulting in the production of nitrogen oxides (NOx) and monoxide as combustion byproducts. carbon (CO),
Other unburned hydrocarbons (HUC) tend to be generated easily. For this reason, as emissions regulations have been tightened from the standpoint of administrative pollution prevention, efforts have been made to reduce NOx, such as switching to fuels with lower sulfur and nitrogen content and installing flue gas denitrification equipment. However, it is currently difficult to achieve the regulated values due to equipment costs and other technical issues.

Problems to be Solved by the Invention Such so-called "thermal NOx" is produced by the reaction of nitrogen and oxygen in the air during fuel combustion, but as the combustion temperature increases, the reaction becomes more intense. , and therefore its maximum temperature determines the thermal NOx emissions. In normal flame combustion, the temperature distribution is not constant, so locally high temperatures (for example, 1400
℃), which is the cause of increased thermal NOx generation.

Furthermore, the generation of carbon monoxide (CO) and unburned hydrocarbons (UHC) is also closely related to the combustion temperature of combustion gas, and according to catalytic combustion experiments using catalysts described below, the combustion temperature is below 900℃
CO and UHC increase rapidly, and above 1000℃,
It has been confirmed that almost no CO or UHC is generated. Such thermal NOx, CO, UHC
Since this is closely related to the combustion temperature, catalytic combustion methods using high-performance catalysts have been recently researched. We have a track record of effectively and significantly reducing the

However, the problem with applying the catalytic combustion method using this catalyst to heat exchange equipment such as boilers is that a catalyst that can maintain a long life in a high-temperature region has not yet been developed, and there are Since a high-performance catalyst is extremely expensive, it is not worth it in terms of running cost.

Purpose of the Invention In view of the current situation, the inventor has developed a system that has excellent heat transfer efficiency, a compact structure, and a thermal NOx
As a result of our efforts in research and prototyping to obtain a new heat exchange device that can suppress the generation of CO, UHC, etc., we constructed a combustion heat transfer block using a so-called breathable solid with a sufficiently large porosity. If a heat transfer medium serving as a heat load is interposed in the heat block, and a mixed fuel consisting of a mixture of fuel gas and air is combusted in this combustion heat transfer block, air-permeable solids can be used as described later. Due to the large surface area (heat transfer area),
A nearby gas has almost the same temperature as the solid,
On the other hand, the temperature distribution between solids is smoothed due to the exchange of strong radiation, resulting in uniform combustion. As a result, the generation of thermal NOx is suppressed, and the unburned matter also comes into contact with the hot thin wire and re-burns, resulting in CO It was found that the occurrence of UHC was suppressed. Moreover, since the combustion zone and the heat transfer zone are integrated, the overall structure becomes extremely compact, and as a result of combustion being carried out in a so-called breathable solid, which will be described later, a large amount of solid radiant heat is generated, which improves heat transfer. It has also been found that the rate can be increased all at once.

Means for Solving the Problems In order to overcome the above-mentioned problems and achieve the intended purpose, the present invention provides an air-permeable solid material having a sufficiently large porosity on the opening side of a pipe body for supplying fuel gas and oxygen-containing gas. In a heat exchange device configured to connect a combustion heat transfer block consisting of a combustion heat transfer block and interposing a heat transfer medium as a heat load in the combustion heat transfer block, there is a gap between the opening side of the tube body and the combustion heat transfer block. , a rectifying means for uniformly dispersing and circulating the fuel gas and oxygen-containing gas is interposed, and on the combustion gas discharge side of the combustion heat transfer block, the porosity is smaller than that of the air-permeable solid constituting the block. It is characterized by a breathable solid being placed in contact with it.

Another invention of the present application is to connect a combustion heat transfer block made of an air-permeable solid with a sufficiently large porosity to the opening side of a pipe body for supplying fuel gas and an oxygen-containing body through an air-permeable solid with a small porosity. A heat transfer medium constituting the heat load is interposed in this combustion heat transfer block, and a permeable solid having a smaller porosity than the permeable solid constituting the block is provided on the combustion gas discharge side of the combustion heat transfer block. It is characterized by being connected and arranged.

In addition, in the present invention, the so-called breathable solid is
Because it occupies an extremely important weight,
Before describing preferred embodiments, an overview of this breathable solid will be provided. In this specification, the so-called breathable solid refers to heat-resistant materials such as metals and ceramics that are formed into various shapes such as net, honeycomb, and fiber to provide air permeability and that are difficult for light and other heat rays to pass through. It can be defined as a solid medium of thickness.

This is considered to be composed of a large number of thin wires or fine grains, and its substantial surface area is extremely large. Since the radiation emitting ability of a solid is sufficiently higher than that of a gas, when the combustion gas is passed through the air-permeable solid, the sensible heat of the combustion gas comes into contact with the solid with an extremely large surface area, resulting in highly efficient heat exchange. is carried out, generating a large amount of solid-state radiant heat. A solid heat transfer element having such characteristics is called a breathable solid. Note that this breathable solid has the characteristic that even if it removes heat through heat exchange downstream of the combustion gas, it has almost no effect on the upstream side.

Regarding the radiant heat emission state of the breathable solid S,
To explain using the schematic diagram shown in FIG. 1, since the breathable solid S has a thickness X in the direction of flow of the combustion gas G, when the combustion gas G passes through the solid S, convective heat transfer takes place within the layer. A temperature gradient shown by curve C results. Then _{, in} each _{layer x 1 ...} , of this solid radiant heat, y ₄ , y ₅ and z ₁ ,
z ₂ is shielded and attenuated according to the thickness of the breathable solid S in the front-rear direction, and as a result, most of the radiant heat R is emitted to the upstream side (y) of the combustion gas G.

Embodiments Next, the heat exchange device according to the present invention will be described in detail below by giving preferred embodiments and referring to the accompanying drawings. FIG. 2 shows one embodiment of the device of the present invention, in which fuel gas (for example, city gas,
A fuel mixture MF consisting of a mixture of air and combustible gas (natural gas, top waste gas, etc.) is pressurized from a fuel supply source (not shown) and fed to the fuel mixture supply pipe 10. It's becoming like that. Note that if the combustion exhaust gas is sucked from the combustion gas exhaust side using a suction fan or the like, it is not necessary to pressurize and supply the humid fuel MF. Further, the fuel mixture MF may be mixed with fuel gas and air immediately before flowing into a block body to be described later. In the figure, reference numeral 12 indicates a suitably three-dimensional block made of an air-permeable solid with a sufficiently large porosity, and combustion of fuel and heat transfer are performed inside this block 12 as will be described later. Hereinafter, this will be referred to as a combustion heat transfer block. The mixed fuel supply pipe 10 has an elongated opening 14 as shown in the figure, and a combustion heat transfer block 12 made of an air-permeable solid having a sufficiently large porosity is arranged and connected to the opening side. In this case, a rectifying means 16 such as a rectifying grid made of a ceramic plate with a large number of holes is interposed between the opening 14 of the supply pipe 10 and the combustion heat transfer block 12. After uniformly dispersing the mixed fuel MF supplied from the combustion block 12, it is configured to be sent into the combustion block 12.

The porosity of the air permeable solid constituting this combustion heat transfer block 12 is preferably 99% or more (in other words, the filling ratio is 1% or less). Suitable examples of suitable solids include blocks made of heat-resistant thin metal wires agglomerated into flocculent shapes, multi-laminates of heat-resistant wire mesh, and porous objects made by foaming and solidifying other ceramic materials in the form of pumice. Ru. In this case, the question is how much porosity the breathable solid should have to be considered "sufficiently large", but it is better to make a judgment based on the optical thickness rather than the number of meshes as in the case of wire mesh. It is most appropriate to do so.

Here, "optical thickness" is a variable that represents the degree of attenuation of radiation, and its measurement is performed by interposing an air permeable solid object between the light source and the illumination meter, and determining how much light is transmitted. This is done by determining how much energy is being absorbed using the illuminance meter, and at this time, the diameter of the thin metal wire and other absorption coefficients are taken into consideration. In the case of this embodiment, as the breathable solid constituting the combustion heat transfer block 12, an agglomerate of fine metal wires having an optical thickness in the range of 1 to 10 depending on the size of the combustion heat transfer block 12 is used. Good results were obtained.

In the combustion heat transfer block 12, there is a heat transfer medium 18 (for example, a water pipe for evaporation generation) constituting the heat load.
is interposed by burial or other means. As the heat transfer medium 18, a heat transfer tube such as the above-mentioned water tube is typically used, but depending on the purpose, a solid rod of metal wire with a large heat capacity may be used to store heat as a heat storage medium. Also, heat dissipation may be performed. Furthermore, in order to increase the heat transfer area between the heat transfer medium 18 and the combustion heat transfer block 12,
Preferably, the heat transfer medium 18 is meandered or spirally wound within the block.

Further, a gas permeable solid 22 having a smaller porosity than the gas permeable solid constituting the block 12 is connected to the combustion gas discharge side of the combustion heat transfer block 12. The porosity of this breathable solid 22 is 90 to 95%.
or more (in other words, the filling rate is preferably 10 to 5% or less). Further, the combustion heat transfer block 12 and the air permeable solid 22 are surrounded by a fire-resistant heat insulating material 20, except for the upstream side where the mixed fuel flows in and the downstream side where the combustion gas is discharged, to prevent radiant heat from the outer periphery of the block. It is constructed to shield the escape of

FIG. 3 shows another embodiment of the invention according to the present application, in which the combustion gas upstream side and the downstream side of the combustion heat transfer block 12 have a porosity lower than that of the air permeable solid constituting the block 12, respectively. A small air permeable solid body 24 is connected and arranged. The porosity of this air-permeable solid 24 is preferably 90 to 95% or more (in other words, the filling rate is 10 to 5% or less). In this embodiment, the opening 14 of the fuel mixture supply pipe 10 is connected to one of the air permeable solids 24, and the fuel mixture fed under pressure from the supply pipe 10 passes through this air permeable solid 24. Since the liquid is uniformly dispersed during passage, there is no need to separately provide a rectifying means 16 as in the embodiment shown in FIG. However, the combustion heat transfer block 12 and the breathable solid 2
Similar to the embodiment shown in FIG. 2, it is surrounded by a fire-resistant heat insulating material 20 as shown in the figure for the purpose of shielding radiant heat from escaping from the outer periphery of the parts 4 and 24.

Effects of the Embodiment Next, the effects of the heat exchange device according to the embodiment configured as described above will be explained below. In the embodiment shown in FIG. 2, the mixed fuel MF is
When supplied, the flow of this mixed fuel is adjusted by the rectifying means 16 and is uniformly dispersed.
is fed into the combustion heat transfer block 12. code 26
When the fuel mixture is ignited by an ignition means (e.g. a heater or spark plug), combustion is initiated in a confined space within the air-permeable solid block 12. As mentioned earlier, air permeable solids have an extremely large practical specific surface area, and the radiation emission ability of solids is sufficiently higher than that of gas, so the high temperature combustion gas after the combustion reaction is transferred to air permeable solids. Highly efficient heat exchange occurs by contacting the combustion gas, and the sensible heat in the combustion gas is converted into a large amount of solid radiant heat. In addition, since the air permeable solid 22 is connected to the combustion gas discharge side of the combustion heat transfer block 12, the high temperature combustion gas further flows into the air permeable solid 22, and highly efficient heat exchange is performed here as well. Sensible heat in the combustion gas is converted into a large amount of solid radiant heat. Moreover, most of the obtained large amount of radiant heat is on the upstream side of the combustion gas, that is, in the combustion heat transfer block 12.
Since the heat is emitted toward the block 12, the radiant heat in the block 12 is further increased, and the heat transfer efficiency in the heat transfer medium 18 is further promoted.

At this time, due to the effect of solid contact, the low temperature parts of the combustion gas are pulled up, and the high temperature parts are suppressed, so the overall temperature becomes flat and uniform combustion is obtained (in normal flame combustion, the flame (localized high or low temperature areas occur on the surface). As a result of the temperature being made uniform in this way, the generation of thermal NOx is reduced.
This is because thermal NOx reacts more intensely with nitrogen and oxygen as the combustion temperature increases, but in the device according to the preferred embodiment, there is no local temperature rise that would cause this. Also, normal thermal NOx
By lowering the combustion temperature to reduce CO
However, in the device of the present invention, unburnt substances such as CO and UHC are generated because the unburned substances are combusted by contact with a breathable solid such as a high-temperature thin metal wire. There is no risk of it occurring and polluting the atmosphere.

Moreover, conventionally, when a heat transfer medium 18 such as a heat transfer tube is interposed in the combustion zone, incomplete combustion occurs immediately and causes the generation of CO and UHC. As mentioned above, it was necessary to separately secure a heat transfer space for heat transfer by the combustion gas.
However, in the example device, a heat transfer medium was interposed in the combustion zone, so even if unburned components were produced, they would come into contact with the permeable solid heated to a high temperature and be completely combusted. This eliminates the need for separate combustion zones and heat transfer zones.

That is, the block body 12 made of breathable solid
The combustion zone and heat transfer zone are integrated, making the structure extremely compact.
In this combustion heat transfer block 12, high-temperature combustion gas contacts a heat transfer medium 18 (for example, a water pipe) to exchange heat, and a large amount of solid radiant heat is obtained in the air permeable solid constituting the block 12. As a result, extremely efficient heat exchange is achieved.

In the embodiment shown in FIG. 3, air permeable solids 24 are connected to each other on both sides of the combustion heat transfer block 12. Since the combustion of the mixed fuel MF is carried out in the combustion heat transfer block 12 as in the embodiment shown in FIG. It will be present in block 12. Therefore,
The high temperature combustion gas generated in the block 12 is
When the sensible heat in the gas is converted into a large amount of solid radiant heat by flowing into each air permeable solid 24, the obtained radiant heat is transferred to the combustion conductor on the upstream side of the combustion gas, similar to the embodiment shown in FIG. It will be injected towards the thermal block 12. Moreover, in the case of this embodiment, since the radiant heat is emitted from both sides of the block 12, the heat transfer efficiency to the heat transfer medium 18 is the best.

Effects of the Invention As described above, according to the heat exchange device according to the present invention, mixed fuel can be combusted with a uniform temperature distribution, so generation of unburned components such as thermal NOx, CO, and UHC can be suppressed. is possible. Furthermore, even if a temperature-reducing element such as a heat transfer tube is present in the combustion zone, no unburned matter is generated due to uniform combustion.
It becomes possible to integrate the combustion zone and the heat transfer zone, and a heat exchange device with an extremely compact configuration can be obtained. Furthermore, since a large amount of radiant heat can be obtained, there are many beneficial effects such as further improvement in heat exchange efficiency.

In the preferred embodiment described above, a case has been described in which a mixture of fuel gas and air is sent to the combustion heat transfer block through a common fuel mixture supply pipe, but the fuel gas supply pipe and Air supply pipes may be provided independently, and each supply pipe may be connected to the combustion heat transfer block, so that the fuel gas and air are mixed and combusted in the combustion heat transfer block. Further, the gas mixed with the fuel gas before entering the combustion heat transfer block or in the combustion heat transfer block is generally air, but other gases containing oxygen may be used as appropriate.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram showing a radiant heat emission state of a breathable solid, FIG. 2 is a schematic diagram of a heat exchange device according to the present invention, and FIG. 3 is a schematic diagram of a heat exchange device according to another invention. . 10... Air mixture fuel supply pipe, 12... Combustion heat transfer block, 14... Opening, 16... Rectifying means, 1
8... Heat transfer medium, 20... Fire-resistant heat insulating material, 22,
24... Breathable solid, 26... Ignition means.

Claims (1)

[Scope of Claims] 1. A combustion heat transfer block made of an air-permeable solid having a sufficiently large porosity is connected to the opening side of a pipe body for supplying fuel gas and oxygen-containing gas, and a heat load is applied to the combustion heat transfer block. In the heat exchange device configured to have a heat transfer medium interposed therebetween, a rectifying means for uniformly distributing and circulating fuel gas and oxygen-containing gas between the opening side of the tube and the combustion heat transfer block. A heat exchange device characterized in that a gas permeable solid having a lower porosity than the gas permeable solid constituting the block is connected and arranged on the combustion gas discharge side of the combustion heat transfer block. 2. A combustion heat transfer block made of an air permeable solid with a sufficiently large porosity is connected to the opening side of the tube for supplying fuel gas and oxygen-containing gas via an air permeable solid with a small porosity, and this combustion heat transfer block A heat transfer medium constituting a heat load is interposed therein, and a permeable solid having a smaller porosity than the permeable solid constituting the block is connected and arranged on the combustion gas discharge side of the combustion heat transfer block. Features of heat exchange equipment.