JPH0842814A - Catalytic burning method - Google Patents

Abstract

PURPOSE:To provide a catalytic burning method wherein the thermal problems of a catalyst are avoided by lowering the combustion temperature of the catalytic part, and the emission of air pollutant is controlled and obtain a high thermal efficiency by employing the aforesaid method in the combustion apparatus such as boiler and combustion furnace. CONSTITUTION:A catalytic burning method comprises supplying a premixed gas adjusted to an air ratio of less than one to a catalytic reaction part C with a catalyst 12, generating the partially reactive gases containing the combustible components such as HC hydrocarbon, CO and H2 from the fuel in the premixed gas by the action of the catalyst 12 of the catalytic reaction part C and introducing the partially reactive gases into a flame burning part F with a secondary air introducing means A, whereby a secondary air is introduced into the partially reactive gases from the catalytic reaction part C by the secondary air introducing means A to effect the flame burning. The aforesaid method further comprises setting a total of the amounts of the air in the premixed gas and of the secondary air and the amount of fuel in the premixed gas at an air ratio of at most 1.5.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a novel combustion method using a combustion catalyst.

[0002]

2. Description of the Related Art With the recent increase in global environmental problems, social demands for reducing the emission of air pollutants from industrial heat equipment have become more severe. In particular, the current state of air pollution due to NO _x , despite various exhaust gas regulations,
No improvement, especially in metropolitan areas, NO
Measures to reduce _x are being strengthened.

In the combustion equipment used for industrial heat equipment such as a boiler or a combustion furnace, it is the most energy efficient combustion to burn the fuel at the theoretical air amount, but in reality, the fuel and air are not mixed. It is general to supply and burn a slightly larger amount of air than the theoretical air amount due to completeness or combustion delay. Therefore, in flame combustion close to such a theoretical air amount, the combustion reaction region becomes high temperature, and in this high temperature region, N ₂ in the air is oxidized and thermal NO _x (ther
mal NO _x ) is generated. In particular, NO generated by the combustion of kerosene, gas fuel, etc. in which the nitrogen content in the fuel is extremely small
Most of _x is the above-mentioned thermal NO _x , and it is known that the production of this thermal NO _x can be suppressed by lowering the combustion temperature. However, in combustion that generates a normal flame, there is a trade-off relationship in which, when the combustion temperature is lowered in order to reduce NO _x (especially the above-mentioned thermal NO _x ), the amount of CO is increased on the contrary. Although the generation of NO _x and CO can be suppressed to some extent by the improvement of the method, the essential solution has not been reached.

[0004]

Various measures for reducing air pollutants in combustion equipment have been proposed so far, and as one of them, a catalytic combustion method is in the limelight. That is, it is known that in the catalytic combustion method, by utilizing the catalyst surface reaction, the combustion temperature can be lowered and the NO _x generation amount can be reduced without increasing the CO generation amount. However, precious metals such as Pt and Pd, C
Catalysts that carry rare earth elements such as e, La, and Y, or a mixture of both, have high low-temperature activity, but volatilize at high temperatures (current catalysts of 1,000 ° C or higher), and solid-phase reactions tend to occur.
There is a problem in thermal stability, that is, heat resistance. Therefore, these low-temperature highly active catalysts are used for boilers or combustion equipment for combustion furnaces.
That is, when applied to a burner, a method of controlling the heat load of the catalyst within an appropriate range is required. Conventionally, as a method of controlling the heat load of the catalyst, the catalyst combustion temperature is lowered by setting the air ratio of the premixed gas introduced to the catalyst to 2 or more,
Further, there has been proposed a catalytic combustion burner in which fuel is added to combustion gas by a catalyst to perform flame combustion and the air ratio in the entire combustion device is set to 1.5 or less.

As described above, in the method of introducing a premixed gas having a high air ratio (air ratio of 2 or more) into the catalyst in order to maintain the combustion temperature of the catalyst below the heat resistant temperature of the catalyst, the following four points are particularly important. It's a problem. First, the first problem is that the volume of the premixed gas passing through the catalyst becomes relatively large and the space velocity becomes large. In this case, the contact time between the catalyst and the premixed gas becomes short, and it is difficult to completely carry out the catalytic reaction. Also, because the volume of the premixed gas increases,
The pressure loss in the catalyst layer increases. The second problem is that the amount of heat required for preheating when starting catalytic combustion increases. That is, when starting the catalytic combustion, it is necessary to preheat the catalyst or the premixed gas to a predetermined temperature or higher. However, as described above, the air ratio of the premixed gas is high, and the air is mixed with the fuel. When the amount is large, when the catalyst is preheated, the catalyst is likely to be cooled by a large amount of premixed air, and when preheating the premixed air, it is necessary to preheat a large amount of air in addition to the fuel. is there. The third problem is that there is a high risk that the catalyst combustion temperature will fluctuate toward the high temperature side. That is, when the amount of air forming the premixed gas is reduced and the air ratio is reduced to 2 or less, the catalyst temperature is rapidly increased, which causes thermal deterioration and burnout of the catalyst. The fourth problem is that the NO _x reduction effect is limited. That is, when the secondary fuel is supplied to the combustion gas by the catalyst for flame combustion, the mixing distance is short, and
The volume ratio of the combustion gas and secondary fuel by the catalyst can not be achieved sufficiently mixed because of such a large, inhibits locally shading of fuel is formed NO _x reduction.

Therefore, the technical problem to be solved by the present invention is to control the reaction temperature in the catalyst to avoid the thermal problem of the catalyst, to suppress the emission of air pollutants, and to further improve the boiler and the combustion furnace. It is intended to provide a catalytic combustion method which can be applied to a combustion device such as the above to obtain high thermal efficiency.

[0007]

The present invention has been made in view of the above-mentioned problems, and supplies a premixed gas having an air ratio adjusted to less than 1 to a catalytic reaction part equipped with a catalyst, The fuel in the premixed gas is converted into H
A partial reaction gas containing combustible components such as C (hydrocarbon), CO, and H ₂ is generated, and the partial reaction gas is introduced into a flame combustion section equipped with a secondary air introducing means, and the partial reaction gas from the catalytic reaction section is introduced. Firstly, flame combustion is performed by introducing secondary air into the reaction gas by the secondary air introducing unit.
In addition, the total air amount of the air in the premixed air and the secondary air and the fuel amount in the premixed air are set to be 1.5 or less in air ratio. A second characteristic is a catalyst burner.

[0008]

In the catalytic combustion method according to the present invention, the premixed gas with the air ratio adjusted to less than 1 (fuel excess) is introduced into the catalytic reaction section (C), and the catalyst (12) is used to remove the fuel in the premixed gas. A partial reaction gas containing combustible components such as HC (hydrocarbon), CO, and H ₂ is used. Then, in the flame combustion section (F) downstream of the catalytic reaction section (C), secondary air is added to this partial reaction gas for combustion. In the flame combustion section (F), the relatively high temperature partial reaction gas containing almost no NO _x and the secondary air are rapidly mixed and gas-phase combusted. Therefore, the temperature of the combustion gas in the flame combustion section (F) becomes substantially uniform as a whole, and the high temperature region that causes NO _x generation becomes small.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A concrete embodiment in which the present invention is applied to a burner will be described in detail below with reference to the drawings. 1 is an explanatory view schematically showing the cross-sectional structure of one embodiment of the catalytic combustion burner to which the catalytic combustion method according to the present invention is applied.

In the catalytic combustion method according to the present invention, the premixed gas whose air ratio is adjusted to less than 1 is supplied to the catalytic reaction section, and the fuel in the premixed gas is converted into hydrocarbon and CO by the action of the catalyst in the catalytic reaction section. , H _{2 and the} like into a partial reaction gas containing a combustible component, the partial reaction gas is introduced into the flame combustion section, and secondary air is introduced into the partial reaction gas by the secondary air introduction means in the flame combustion section. By doing so, the flame is burned.

Therefore, the illustrated catalytic combustion burner (B) is
The premixed gas introducing means (P) for supplying the premixed gas and the fuel in the premixed gas are used as HC (hydrocarbon), CO,
A catalytic reaction part (C) that decomposes into a partial reaction gas containing combustible components such as H ₂ and secondary air for combustion from the secondary air introduction means (A) to the partial reaction gas from the catalytic reaction part (C). And a flame combustion unit (F) for supplying and performing flame combustion. The premixed gas introduction means (P) is configured by providing a premixed gas supply port (11) at the upstream end of the inner cylinder (10). The catalytic reaction part (C) is configured by mounting a catalyst (12) on the downstream side of the inner cylinder (10). This catalyst (12) uses the combustion air to burn the fuel in the premixed gas as an HC with a small molecular weight.
It decomposes into partial reaction gases containing combustible components such as (hydrocarbons), CO, and H ₂ . Examples of the catalyst (12) include a catalyst made of a carrier made of ceramic or the like and a precious metal such as Ag, Pt, or Pd, a rare earth element such as Ce, La, or Y, or a mixture thereof, or a metal. An oxide catalyst or a composite oxide catalyst is used. Then, in order to cause a catalytic reaction with this catalyst (12), as described above, the catalyst (12) itself or the premixed gas is raised to a temperature (for example, 300 to 350 ° C) at which catalytic combustion starts. It is necessary to heat it, and it is preferable to attach a preheating means therefor to the catalytic reaction section (C) or the premixed gas supply means (P).

The secondary air introducing means (A) includes the inner cylinder (1
It is configured by arranging an outer cylinder (20) around the outer circumference of (0). In addition, in this embodiment, the outer cylinder (20) is arranged at a predetermined interval so as to form an air flow path (21) between the outer cylinder (20) and the inner cylinder (10). In this example,
Combustion flowing into the air flow path (21) by arranging the air introduction pipe (22) further outside the outer cylinder (20) and rapidly changing the flow of air at the upstream end of the outer cylinder (20). The secondary air for use is rectified. A diaphragm plate (24) is provided on the outer periphery of the upstream end of the outer cylinder (20) to narrow the flow path between the outer cylinder (20) and the air introduction pipe (22). That is, the throttle plate (24) prevents uneven flow of the secondary air for combustion from the air introduction pipe (22) into the outer cylinder (20).

The flame burning section (F) is formed on the downstream side of the flaming flame holder (30) attached to the tip of the inner cylinder (10). This flame holder (30) has holes (31) that penetrate the front and back of the flame holder.
Are perforated. Further, on the downstream side of the flame stabilizer (30), a baffle plate (23) extending from the tip of the outer cylinder (20).
Has been arranged. This baffle plate (23) is provided with the flame stabilizer (3
The baffle plate (23) has an inner diameter that is set so as to slightly cover the downstream end opening of the flame stabilizer (30). There is. A flame arrester (13) for preventing flashback is attached on the upstream side of the catalyst (12) in the inner cylinder (10).

The operation of the catalytic combustion burner having the above construction will be described below. In the examples below, the catalyst
It is described as a configuration in which the catalytic reaction is started by preheating (12). First, the catalyst (12) in the catalytic reaction section (C)
Is preheated to a temperature (for example, about 300 to 350 ° C.) at which the catalytic reaction starts by an appropriate heating means.
In this state, the premixed gas introducing means (P) supplies the premixed air, and at the same time, the secondary air introducing means (A) introduces the secondary air for combustion. At this time, the air ratio of the premixed gas supplied by the premixed gas introducing means (P) is adjusted to less than 1, and the amount of secondary air supplied by the secondary air introducing means (A) is The air ratio is adjusted to 1.5 or less (preferably 1.1 to 1.3) when mixed with air. The amount of fuel contained in the premixed air is determined by the amount of heat generated by the catalytic combustion burner.

The excess fuel premixture flows through the inner cylinder (10), passes through the flame arrester (13), and passes through the preheated catalyst (12). The fuel in the air-fuel mixture reacts with air, and the fuel is decomposed into combustible components such as HC (hydrocarbon), CO, H ₂ having a smaller molecular weight. In the catalytic reaction at this time, part of the premixed gas may be decomposed into H ₂ O and CO ₂ , and the fuel may remain unreacted. Since heat is generated during the decomposition reaction of the fuel by the catalyst (12), the partial reaction gas (partial combustion gas) rises to a predetermined temperature. 1,200
Since it reacts at (° C or lower), almost no thermal NO _x is generated. Then, the partial reaction gas is the catalyst in this state.
It flows from (12) into the flame combustion part (F).

The secondary combustion air from the secondary air introduction means (A) is supplied to the flame combustion section (F). That is, the secondary air for combustion, after flowing into the air introduction pipe (22), flows toward the upstream side of the air flow path (21) inside the outer cylinder (20), and the throttle plate (24). After being rectified by the air flow, the air flows into the air flow path (21). And this air flow path (2
It circulates from 1) toward the flame stabilizer (30) and is ejected from the plurality of holes (31) to the flame combustion section (F). In the flame combustion section (F), secondary air for combustion is supplied to the partial reaction gas generated in the catalytic reaction section (C). Here, since the partial reaction gas is heated to a predetermined temperature by the decomposition reaction by the catalyst (12), the combustion reaction starts when the secondary air for combustion is supplied, and a flame is formed. Burn. In order to increase the certainty of ignition of the partial reaction gas in the flame combustion section (F), a known ignition means, for example, a spark ignition means such as a spark plug is preferably used. In the combustion reaction in this flame combustion section (F), the partial reaction gas is at a relatively high temperature, and mainly HC (hydrocarbon) C
Since it is composed of combustible components such as O and H ₂ , the combustion reaction is promoted and complete combustion is easily performed. Therefore, CO is burned almost completely without being left behind and changed into CO ₂ , and the temperature of the combustion gas becomes substantially uniform as a whole, and it is difficult to form a local high temperature region, so that thermal NO _x is generated. The quantity is also small.

As described above, in the catalytic combustion method according to the present invention, since the air ratio of the premixed gas is less than 1, the space velocity of the premixed gas in the catalyst (12) is small and the catalyst reaction time is reduced. Can be long Therefore, the amount of heat required for preheating the catalyst itself or the premixed gas can be reduced as compared with the conventional method. Furthermore, the pressure loss in the catalyst layer can be reduced,
The stability of catalytic combustion can be improved. Further, in the conventional method of controlling the catalyst combustion temperature by setting a large air ratio of the premixed gas, the catalyst temperature rises sharply due to the decrease in the air flow rate,
It causes thermal deterioration and burning of the catalyst. However, according to the method of the present invention, by controlling the catalyst temperature in the excess fuel region, a change in the theoretical flame temperature due to a change in the air ratio of the premixed gas and a change in the reaction rate at the catalyst due to a change in the space velocity are caused. Since they work in antagonism, it is possible to reduce the change in the catalyst combustion temperature and reduce the thermal deterioration and burnout of the catalyst. For example, although the catalyst combustion temperature decreases as the air amount decreases (air ratio decreases), the rapid decrease in the catalyst reaction temperature can be suppressed by increasing the reaction ratio in the catalyst due to the decrease in space velocity. On the contrary, when the air amount increases, the catalytic combustion temperature tends to rise because it approaches the theoretical air ratio (1), but since the fuel reaction ratio in the catalyst decreases due to the increase in space velocity, the catalyst combustion temperature increases too much. Without, it is hard to exceed the heat resistance limit of the catalyst. Therefore, in the catalytic combustion method according to the present invention, it is possible to stabilize the reaction temperature of the catalyst, avoid thermal problems of the catalyst, and suppress emission of air pollutants.

Further, in the above description, a gas fuel is used, but in the catalytic combustion method according to the present invention, a liquid fuel such as kerosene may be used in addition to the gas fuel. When it is used, it is advantageous to vaporize it and use it in a gaseous state for catalytic combustion.

[0019]

As described above, according to the catalytic combustion method of the present invention, the final NO _x concentration in the combustion exhaust gas can be significantly reduced, and thus, the NO _x and C
Since it is possible to reduce air pollutants such as O, it is possible to contribute to the prevention of air pollution and reduce the adverse effects of combustion exhaust gas on the human body.

Further, in the conventional method, the catalyst combustion temperature was controlled to be equal to or lower than the heat resistant temperature of the catalyst by setting the air ratio to a large value, but in the catalytic combustion method according to the present invention, since the air ratio is set to 1 or less, Since the space velocity of the premixed gas introduced becomes small and the catalytic reaction time of the premixed gas can be extended, the amount of catalyst used can be reduced. Further, the amount of heat required for preheating the catalyst or the premixed gas can be reduced. Moreover, the pressure loss in the catalyst layer can be reduced, and the stability of catalyst combustion can be improved.

Further, in the conventional method, the fluctuation of the air ratio of the premixed gas causes thermal deterioration and burnout of the catalyst.
In the catalytic combustion method according to the present invention, the catalyst temperature is controlled by setting the air ratio to less than 1 (fuel excess), so that the change of the catalyst temperature due to the change of the air ratio (air supply amount) of the premixed gas is suppressed. Since the amount is small, thermal deterioration and burnout of the catalyst can be effectively prevented.

As described above, according to the present invention, the advantage of low NO _x due to the catalytic reaction can be effectively utilized, and the highly efficient catalytic combustion that solves the problem of the thermal durability of the conventional combustion catalyst is solved. A method can be provided.

[Brief description of drawings]

FIG. 1 is a diagram illustrating a schematic configuration of a catalytic combustion burner to which a catalytic combustion method according to the present invention is applied.

[Explanation of symbols]

 (A) Secondary air introduction means (C) Catalytic reaction part (F) Flame combustion part (12) Catalyst

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Natsuhiko Ninomiya 7 Horie-cho, Matsuyama-shi, Ehime Prefecture Miura Laboratory Co., Ltd.

Claims (2)

[Claims] 1. The operation of the catalyst (12) of the catalytic reaction section (C), wherein a premixed gas having an air ratio adjusted to less than 1 is supplied to the catalytic reaction section (C) equipped with the catalyst (12). The fuel in the premixed gas is caused to generate a partial reaction gas containing combustible components such as HC (hydrocarbon), CO and H ₂ , and the partial reaction gas is equipped with a secondary air introducing means (A) in a flame combustion section. (C), characterized in that flame combustion is carried out by introducing secondary air into the partial reaction gas from the catalytic reaction section (C) by the secondary air introduction means (A). Method. 2. The total air amount of the air and secondary air in the premixed air and the fuel amount in the premixed air are set so that the air ratio is 1.5 or less. The catalytic combustion method according to claim 1.