JPH01208609A - Catalytic combustion apparatus and method therefor - Google Patents

Abstract

PURPOSE:To achieve a stable and uniform combustion without continuous preheating, by burning a gas mixture mixed in a mixer at the gas-mixture injection orifices of a burner to preheat a catalyst layer and thereafter directing the gas mixture to the catalyst layer to carrying out a catalytic combustion on the preheated catalyst layer. CONSTITUTION:A pipe burner 7 is provided with a plurality of injection orifices 14 each having an flame hole load of 20 to 100kcal/mm<2>, which face a catalyst layer 6 and arranged in three rows along the longitudinal direction of the pipe burner. Fuel 3 is fed to a mixer 13 at which fuel is mixed with air to produce a combustible gas mixture 15. The gas mixture is introduced into the pipe burner 7 and then injected through the orifices 14 into a combustion apparatus 5. Actuation of a timer 11A caused the pipe burner 7 to be ignited so that the catalyst layer 6 is preheated. A preparation time for changing a combustion mode is preset at a timer 11B. Upon termination of the preparation time preset at the timer 11B, the previous pipe burner combustion mode is changed over to a catalytic combustion mode, whereupon fuel 3 is fed through the mixer and the combustible gas mixture 15 is directed to the catalyst layer 6. This system prevents occurrence of dangerous back-fire and guarantees safe and easy actuation for changing-over of the combustion mode.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a catalytic combustion device and a combustion method thereof, and in particular a self-thermal combustion type suitable for performing stable and uniform combustion without providing a preheating device. This invention relates to a catalytic combustion device and its combustion method.

[Conventional technology]

Conventionally, combustion using a burner is well known as a method of burning gaseous fuel. In this burner combustion method,
Fuel and air are mixed in advance or at the tip of the burner, and the mixture ratio of air and fuel is adjusted to maintain a flame and stable combustion continues. Therefore, there is an appropriate air-fuel ratio depending on the type of fuel; for example, the air-fuel ratio for methane and propane is approximately 1.
．． 0 to 1.2, and the air-fuel ratio of -carbon oxide is approximately 1.0 to
It is 2.0. In addition, in order to maintain the flame, self-combust, and achieve stable combustion, the calorific value of the fuel must be at least 800 to 10
It is necessary that it is 00 kcal/mN or more. Furthermore, since flame is generated during combustion, there is a drawback that a large amount of NOx is generated.

On the other hand, in recent years, a so-called catalytic combustion method in which catalytic combustion is performed using a catalyst has been proposed, and has been put into practical use as a purifying catalyst for automobiles and the like. This catalytic combustion method consists of (1) 100-2
Possible to burn low calorie gas of less than 00 k c a I /rrrN, (2) Possible to burn in low oxygen (theoretical 0.) and in a wide range of air-fuel ratios, (3) No flame and NO
It has excellent features such as low x.

FIG. 12 is a flow diagram of a catalytic combustion device according to the prior art. In the figure, fuel 3 is mixed with air l preheated by a heat exchanger 28 to form an air-fuel mixture 15 that is combusted in a catalyst layer 6. During combustion, the temperature 26-1 of the air-fuel mixture 15 upstream of the catalyst layer is measured, and the flow rate of the heating medium 24 supplied to the heat exchanger 28 is adjusted by the control device 27-1 to achieve the optimum air-fuel mixture temperature. The heating of the air 1 is controlled as follows, the temperature 26-2 of the exhaust gas downstream of the catalyst layer is measured, and the control device 27-2
The flow rate of the fuel is adjusted to obtain a mixture with an optimal air-fuel ratio.

In such a catalytic combustion device, Japanese Patent Application Laid-Open No. 58-86314
No. 1, JP-A-58-106315, JP-A-Sho 57
As shown in Japanese Patent Application No. 21716, etc., when the temperature of the air-fuel mixture 15 is lower than the combustion start temperature, so-called preheating to raise the temperature to the combustion start temperature is essential. Mixture 1
Preheating in step 5 is performed by heating with a heating burner, an electric heater, mixing high temperature gas, recirculating exhaust gas, or the like.

However, in such a method, especially in the case of large-sized equipment, the preheating equipment is also large-sized, takes time to start up, and has the disadvantage that equipment costs are high. Furthermore, when a heating burner or the like is used, if uneven heating occurs on the catalyst surface, local blow-through occurs due to the difference in pressure loss within the catalyst, causing incomplete combustion.

For small equipment such as water heaters, self-thermal combustion devices have been proposed that use the heat held by the catalyst to raise the temperature of the air-fuel mixture and continue combustion without preheating. It is necessary to increase the cross-sectional area to continue combustion. Furthermore, with larger equipment, it is difficult to uniformly preheat the entire catalyst surface and to mix and disperse gas uniformly during startup, and localized blow-through due to uneven preheating can occur, causing incomplete combustion.
In addition, there have been problems such as a shortened catalyst life due to abnormally high local catalyst temperatures due to uneven mixing and dispersion, catalyst damage due to thermal stress generated from combustion temperature differences, and backfire caused by fuel concentration distribution.

[Problem that the invention seeks to solve]

An object of the present invention is to provide a self-thermal combustion type catalytic combustion system that eliminates the drawbacks of the prior art, has a short start-up time, does not require constant preheating, and can obtain stable and uniform combustion regardless of the size of the device. An object of the present invention is to provide an apparatus and a combustion method thereof.

[Means for solving problems]

The first aspect of the present invention is a mixer that mixes fuel and air, and a plurality of flame holes and combustible mixture supply holes (hereinafter simply referred to as ``mixture supply holes'') that are installed in one or more in the combustor. A pipe burner type preheating burner/mixing/distributor (hereinafter simply referred to as "vibe burner J") with a flame hole load of 20 to 100 kcal/mmz (hereinafter simply referred to as "vibe burner J"), and a catalyst layer provided in the combustor opposite to the vibe burner. It is characterized by having the following.

A second aspect of the present invention is that when performing combustion in the catalytic combustion device, the mixture mixed in the mixer is combusted in the mixture supply hole to preheat the catalyst, and then the combustion of the mixture is catalytically It is characterized in that the catalyst preheating, the switching from the catalyst preheating to the catalytic combustion, and the catalytic combustion according to the required capacity are performed by controlling the supply amounts of the fuel and air.

In the present invention, the radiant heat from the catalyst layer is absorbed and efficiently radiated to the combustible mixture, improving the combustibility of the catalyst and expanding the self-combustion region with respect to the flow rate passing through the catalyst. It is best to install a radiant heat receiver at the front, for example at a position of 30 to 60 mm. As these radiant heat receivers, ceramic honeycombs, porous ceramics, metal materials such as wire mesh and punched metal are preferably used.

In addition, in the present invention, when a plurality of pipe burners are provided, a partition wall is provided for each pipe burner to minimize damage caused by flame propagation in the event of an abnormal phenomenon such as backfire or explosion. It is also preferable because the fuel supply amount can be adjusted for each compartment.

The catalyst used in the present invention is a catalyst used in conventional catalytic combustion devices, such as a catalyst in which approximately 0.5% of a metal such as PL (platinum) is supported on a β-alumina carrier.

Further, fuels used in the present invention include methane, hydrogen,
Examples include kerosene and propane.

[Effect]

FIG. 10 is a diagram showing the relationship between the flow rate of a mixture of fuel (methane) and air passing through the catalyst layer and the required preheating temperature. At low passing flow rates, there is a range in which preheating is not required, and as the passing flow rate increases to a certain extent, the required preheating temperature increases.

FIG. 11 is a diagram showing the temperature distribution near the catalyst layer with respect to the distance from the catalyst layer inlet due to the difference in air-fuel mixture flow velocity. The temperature of the catalyst surface at high passing flow rates is only about 10 to 50°C higher than the preheating temperature of the mixture;
500~ at low passing flow velocity (0-0, 2m/s)
A temperature increase of 600°C was observed. If the catalyst layer is heated above the required temperature in advance, even if a non-preheated mixture at room temperature is supplied, the combustible mixture will be preheated by heat radiation to the inlet side of the catalyst layer, and the catalyst will be heated. It was found that combustion could continue using only the self-heat of the layer.

This self-thermal combustion reduces the surface load of the catalyst (combustion capacity kcal/h/cal) to 25xto' to 3, regardless of the scale of the device.
．． This can be achieved by setting it to 5X10' kca I/%h, but in the case of large equipment, flashback phenomenon often occurs under this condition. This phenomenon occurs when a local high fuel concentration area is formed due to poor mixing and dispersion of air and fuel, and when this high fuel concentration area overlaps with a high area of uneven temperature distribution during catalyst bed preheating, Or it occurs when switching from catalyst bed preheating to catalytic combustion. However, this problem has been solved by using a pipe burner, which is installed parallel to the inlet cross section of the catalyst layer and has multiple air-fuel mixture supply holes, to act as a burner during catalyst preheating and as a combustible mixture feeder during catalytic combustion. Use one or more pipe burners depending on the cross section of the bed inlet, and set the flame hole load of the pipe burner to 20 to 100.
k c a l/m+n” (cross-sectional load in the pipe 1.5
~1Okca 17mm”).

At startup (when preheating the catalyst layer), this vibrator burner forms a uniform short flame through the numerous air-fuel mixture supply holes provided throughout the length of the pipe burner and burns, preheating the catalyst layer. Therefore, temperature unevenness (preheating unevenness) does not occur in the catalyst layer. In addition, the uniformly shortened flame allows the pipe burner to be placed close to the catalyst layer, minimizing the space through which the combustible mixture passes during catalytic combustion, and minimizing damage from abnormal phenomena such as backfire. . Furthermore, after the catalyst preheating is completed, the vibrator burner is used to supply a combustible air-fuel mixture.

The range of conditions (air-fuel ratio, hole jet flow velocity) under which a pipe burner can stably maintain a flame is narrow, and during catalytic combustion, the air-fuel mixture is supplied under conditions that do not produce a flame in the burner, so a vibrator burner does not form a flame. .

In addition, these combustible mixtures are further mixed and dispersed by the orifice effect in the pipe and at the time of injection from the supply hole.
Since the uniformity is improved, shortening of catalyst life due to abnormally high temperature of the catalyst locally, loss of catalyst due to thermal stress caused by differences in combustion temperature, and evolution phenomena caused by fuel concentration distribution do not occur.

Furthermore, since the jet flow velocity of the combustible mixture in the supply hole can be made faster than the flame propagation velocity, backfire into the burner can be prevented.

[Example] - Hereinafter, the present invention will be explained in detail with reference to Examples.

FIG. 1 is a side cross-sectional view of a catalytic combustion apparatus showing an embodiment of the present invention, FIG. 2 is a cross-sectional view taken along arrows -■ in FIG. ■-■ Cross-sectional view as seen from the arrows,
FIG. 4 is an enlarged side view of the pipe burner in FIG. 1.

This device includes a mixing mold 13 that mixes air 1 and fuel 3 supplied from an air header 2 and a fuel header 4, and a plurality of pipes provided in a combustor main body 5 connected to the mixer 13L. A burner 7 , a large number of air-fuel mixture supply holes 14 provided in the pipe burner 7 , a catalyst layer 6 provided in the combustor main body 5 in parallel to the pipe burner 7 , and a connection between the catalyst layer 6 and the pipe burner 7 . It consists of a radiant heat receiving body 8 provided in the middle, and partition walls 17 (FIG. 2) provided for each of the pipe burners 7.

Incidentally, the pipe burners 7 are equally divided into a plurality of 15 pipe burners and arranged according to the size of the inlet cross-sectional area of the catalyst layer 6. Further, the mixture supply holes 14 are arranged in three rows facing the catalyst layer in the longitudinal direction of the pipe burner 7 and have a flame hole load of 20 to 100 kc.
a l/+nn".Also, 1
Reference numeral 6 denotes a heat insulating material provided on the side wall of the combustor main body 5 other than the catalyst layer surface.

In such a configuration, air 1 is introduced into air header 2 , distributed and supplied to mixer 13 , and fuel 3 is introduced into fuel header 4 , distributed and supplied from fuel nozzles 18 to mixer 13 . Ru.

The air 1 and fuel 3 mixed in the mixer 13 become a combustible mixture 15, which is supplied to the pipe burner 7 of the combustor body 5, and is injected into the combustor body 5 from the mixture supply hole 14. During catalyst preheating during startup, this combustible mixture becomes combustion gas and a flame is formed, but during catalytic combustion, the combustible mixture 15 is introduced into the catalyst layer 6 through the radiant heat receiver 8, and the catalyst is heated. Combustion takes place.

During catalyst preheating and catalytic combustion, and switching from catalyst preheating to catalytic combustion is performed by controlling the mixing ratio of fuel and air. The combustion control method will be specifically explained below.

FIG. 5 is a flow diagram showing the catalytic combustion method of the catalytic combustion apparatus shown in FIG.

In the figure, an air pipe 21 that supplies air 1 to the combustor main body 5 is equipped with air shutoff valves 9A, 9B and an air manual valve 10 for flow rate adjustment, and a fuel pipe 21 that supplies fuel 3 to the fuel device main body 5 is installed. The piping 20 includes a combustion cutoff valve 1 for adjusting the flow rate.
9B and a fuel manual valve 20B, a full fuel cutoff valve 19A provided downstream of these, and a fuel manual valve 20A provided downstream of the fuel rudder 4 to adjust the flow rate of each fuel. Also provided are timers 11A, 11B and push button switches for controlling these cutoff valves and manual valves.

Activation of the catalytic combustion device begins with preheating of the catalyst layer by the pipe burner 7. The preheating time to the required preheating temperature by the pipe burner is known in advance, and the preheating time is set by timer I.
IA is set, and furthermore, the fuel cut time when switching from pipe burner combustion to catalytic combustion is set in timer 11B. The preheating temperature of the catalyst layer varies depending on the type of fuel, but is usually 600 to 900°C at the catalyst inlet surface.
Usually, the time required to fill the fuel tank is about 2 to 10 seconds. Next, the manual air valve 10 whose required opening degree has already been adjusted is opened and air is supplied. Shutoff valve 9 at that time
A and 9B are closed. Then, turn on the push button switch 12.
What, Thailand? -Activate 11A. The fuel cutoff valve 19A is opened by the operation of timer IIA, and the fuel manual valve 2 is opened.
Fuel 3 is supplied through the OA, the pipe burner is ignited, and the catalyst layer 6 is preheated. The amount of fuel supplied to the pipe burner during preheating should be the minimum combustion amount (low combustion) during catalytic combustion to ensure flashback safety, and the air-fuel ratio for pipe burner combustion should be approximately 1.1 to 1.2. It is preferable.

When the timer 11A times up, preheating is completed, the fuel cutoff valve 19A closes, and the pipe burner is extinguished.
At the same time, the air cutoff valves 9A and 9B are opened, and the switching timer IIB is activated.

When timer IIB times up, preparations for switching from pipe burner combustion to catalytic combustion are completed, and combustion cutoff valves 19B and 1
9A is opened, the fuel 3 is supplied, the combustible mixture 15 is supplied from the pipe burner 7 to the catalyst layer 6, and the combustion is switched to catalytic combustion. Such switching avoids flashback conditions and allows for safe and easy combustion switching.

The catalyst combustion capacity is controlled by opening and closing a shutoff valve. That is, during high combustion, the air manual valve 10 and the shutoff valves 9A and 9B are opened to maximize the air supply amount,
Further, the manual fuel valve 20B and the fuel cutoff valve 19B are opened to maximize the amount of fuel supplied, and operation is performed. On the other hand, during low combustion, the air manual valve 10 and the air cutoff valve 9A
is opened, the air cutoff valve 9B is closed to reduce the air supply amount, the manual fuel valve 20B is opened, the air cutoff valve 19B is opened, and the fuel supply amount is reduced to the amount of fuel supplied during pipe burner combustion. will be held. Even if the amount of fuel supplied during pipe burner combustion and during catalytic combustion is the same (low combustion), the amount of air during catalytic combustion is approximately twice as much, so the jetting speed from the mixing supply hole 14 is approximately twice, Flame formation is possible, and flashback into the pipe does not occur due to the increased flow rate.

The air-fuel ratio during catalytic combustion is 1.5 in order to supply a combustible mixture to the catalyst layer without forming a flame in the pipe burner.
It is preferable to set it to 3.0. If the air-fuel ratio exceeds 5, the pipe burner will no longer be able to form a flame and will blow out.

In this embodiment, the air and fuel supply amounts were adjusted by a two-stage switching operation, but it goes without saying that the present invention can also be adjusted by a two-stage or more switching operation.

FIG. 6 is a side sectional view of a catalytic combustion device showing another embodiment of the present invention, showing a case where fuel 3 and air 1 are supplied from the center of the long side of the pipe burner 7. In such a catalytic combustion device, the operation and effect are similar to those of the catalytic combustion device shown in FIG. Compared to the gas flow rate of the catalytic combustion device shown in Fig.
2, and the pipe cross-sectional area can be reduced to 1/2.

FIG. 7 is a side cross-sectional view of a catalytic combustion device showing still another embodiment of the present invention, FIG. 8 is a cross-sectional view of the pipe burner in FIG. It is a side enlarged sectional view of the pipe burner in a figure. The difference between this device and that shown in FIG. 1 is that a fuel supply nozzle 18 having a fuel supply hole 19 is inserted into the pipe burner 7 to mix air 1 and fuel 3 within the pipe burner 7. . At this time, the air 1 and the fuel 3 are introduced facing each other, and a plurality of fuel supply holes 19 provided in the fuel supply nozzle 18 are arranged in the longitudinal direction at the centers of the air-fuel mixture supply holes 14 . The action and effect of this catalytic combustion device are similar to those of the catalytic combustion device shown in Fig. 1, and since fuel-air mixing is performed in a pipe burner, backfire within the pipe burner is less likely to occur.
＜, Safety is increased.

〔Effect of the invention〕

According to the present invention, even when a large catalyst layer is used, self-thermal combustion can be performed without causing flashback or local abnormal combustion. Therefore, there is no need to install a special preheating device to perform constant preheating, which is economical, and allows stable catalytic combustion to continue safely and easily, making it possible to easily suppress the generation of NOx. .

[Brief explanation of the drawing]

FIG. 1 is a side sectional view of a catalytic combustion device showing one embodiment of the present invention, FIG. 2 is a sectional view taken along the line ■-■ in FIG. 1, and FIG.
The figure is a cross-sectional view taken along the line ■-■ in Figure 1, Figure 4 is an enlarged side view of the pipe nose in Figure 1, and Figure 5 is a
Flow diagram showing the catalytic combustion method of the catalytic combustion device shown in Fig. 6.
7 is a side sectional view of a catalytic combustion device showing another embodiment of the present invention, FIG. 8 is a side sectional view of a catalytic combustion device showing still another embodiment of the present invention, and FIG. 9 is an enlarged side sectional view of the pipe burner in FIG. 7, and FIG. 10 is a diagram showing the relationship between the flow velocity of fuel and air through the catalyst layer and the required preheating temperature. , FIG. 11 is a diagram showing the temperature distribution near the catalyst layer with respect to the distance from the catalyst layer inlet due to the difference in flow velocity, and FIG. 12 is a flow diagram of a catalytic combustion apparatus according to the prior art. ■...Air, 2...Air header, 3...Fuel, 4
...Fuel header, 5...Combustor body, 6...Catalyst layer, 7...Pipe burner, 8...Radiation heat receiver, 9A
, 9B... Air cutoff valve, 10... Air manual valve, II
A, IIB...Timer, 12...Push button switch, 1
3...Mixer, 15...Flammable mixture, 16...Insulating material, 17...Partition plate, I...Fuel nozzle, 19A
, 19B...Fuel cutoff valve, 20A, 20B...Fuel manual valve, 20...Fuel piping, 21...Air piping. Agent Patent Attorney Takeshi Kawakita 1t A, t+B: Timer 12: Push button switch

Claims (2)

[Claims] (1) A mixer for mixing fuel and air, and one or more pipes installed in the combustor with a flame hole load of 20 to 100 kcal/mm^2 and having multiple flame holes and combustible mixture supply holes. A catalytic combustion device comprising: a burner type preheating burner/mixing/dispersing device; and a catalyst layer provided in the combustor opposite to the pipe burner type preheating burner/mixing/dispersing device. (2) A mixer for mixing fuel and air, and one or more pipes installed in the combustor with a flame hole load of 20 to 100 kcal/mm^2 having multiple flame holes and combustible mixture supply holes. When performing combustion in a catalytic combustion device consisting of a burner type preheating burner/mixing/dispersing device and a catalyst layer provided in the combustor opposite to the pipe burner type preheating burner/mixing/distributing device, the mixer mixes the The mixture is combusted in the flame hole and combustible mixture supply hole to preheat the catalyst, and then the mixture is combusted in the catalyst layer, and the preheating of the catalyst and switching from the preheating to catalytic combustion are performed. , and catalytic combustion according to the required capacity by controlling the supply amounts of the fuel and air.