JPS61186704A - Catalytic burning process - Google Patents

Abstract

PURPOSE:To improve ignitability in low temp. and prevent deterioration by heat at the same time by using catalysts and forming cross sectional area of flow paths at a catalyst vessel in such a manner that catalyst having superior low temp. activity but inferior heat resistance at the upper stream part and catalyst having superior heat resistance but low temp. activity at the down stream part and the former cross sectional area of flow path is determined to be smaller than the latter one. CONSTITUTION:Catalyst forming a catalyst layer 21A of the upper stream part is made by adding catalyst such as platinum or palladium, etc. to gamma-alumina catalyst carrier and has superior low temp. activity and on the other hand, catalyst forming a catalyst layer 21B is made by adding catalyst such as platinum to catalyst carrier such as alumina, zirconium and silicon carbide, etc. and has superior heat resistance. At the start time operation, preheated temp. of fuel gas by a preheater 14 is set up to be higher than ignition temp. of catalyst forming catalyst layer 21A and then burning reaction takes place only in the catalyst layer 21A of the upper stream part and by its burning heat, temp. of the catalyst layer 21B of the down stream part becomes higher than its ignition temp. When the flow rate is increased consecutively, fire extinction takes place at the catalyst layer 21A of the upper stream part and burning starts at the catalyst layer 21B of down stream part because gas flow velocity in the catalyst layer 21A of the upper stream part is larger than that in the catalyst layer 21B of the down stream.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to a catalytic combustion method, and particularly to a catalytic combustion method that has excellent ignition performance at startup and is suitable for high-temperature combustion.

[Background of the invention]

In recent years, many attempts have been made to downsize boilers and wood combustors by using the so-called catalytic combustion method, in which combustion reactions are promoted by catalysts. In this catalytic combustion method, the volumetric combustion rate (Kcat/rrl-h), which is the calorific value per unit volume and time, is several tens of times larger than that of the conventional flame combustion method, and the furnace volume is several tens of times larger than that of the conventional flame combustion method.
In addition, nitrogen oxides (
It also has the advantages of being difficult to generate NOx)Y and being able to burn completely at low oxygen concentrations.

However, in the above catalytic combustion method, (1) When used under high load conditions, the catalyst deteriorates due to combustion heat.

■ In order to start sustained combustion (ignition), catalyst 7
It is necessary to preheat, which requires a large-capacity preheater.

There were two problems, which were major obstacles to practical application. That is, although carriers with excellent heat resistance are being used as catalysts, the ignition temperature of the resulting catalysts also increases accordingly, which tends to be disadvantageous in terms of preheating described in (2) above. On the other hand, the catalytic body! Although it has been effective to lower the ignition temperature (i.e. improve low-temperature activity) and improve initial activity by making it porous and highly dispersing noble metals such as platinum and palladium, which are active ingredients, Once such catalyst bodies are exposed to high temperatures, they undergo significant thermal deterioration.
A deactivation phenomenon occurs in which the activity of the catalyst itself is lost, and when a catalyst body containing platinum, palladium, etc. as an active component is used, the maximum continuous use Wff is at most 1200 to 1300°C.

That is, the challenges of improving the heat resistance of the catalyst and lowering the ignition temperature are incompatible with each other. In other words, if the content of active ingredients is increased in order to lower the ignition temperature, the probability of contact between the active ingredients increases and sintering between the active ingredients becomes easier. Reducing the probability of component contact (reducing the active component content leads to a decrease in relative activity, making it impossible to fully utilize the catalytic action).

In this way, to date, catalyst bodies with excellent heat resistance and low-temperature ignition properties have been obtained.The problems in ① and ② above have been solved in terms of the structure and operating method of catalytic combustion equipment. Therefore, there is a need for a catalytic combustion method that has excellent low-temperature ignitability and is suitable for high-temperature load combustion.

[Purpose of the invention]

The present invention was developed in view of the above-mentioned problems, and its purpose is to provide a catalytic combustion method that has excellent low-temperature ignition properties and is capable of high-temperature, high-load combustion.

[Summary of the invention]

In order to solve the above-mentioned problems, the inventors investigated the catalytic combustion phenomenon in detail and found that both low-temperature ignitability and prevention of thermal deterioration were achieved! In order to achieve this goal, we have come to the conclusion that it is best to use different catalysts that have excellent characteristics, and this has led us to the present invention. The points of view and principles are shown below.

FIG. 11 shows a catalytic combustion device in which a catalyst layer 3 filled with a catalyst having excellent low-temperature activity but poor heat resistance is formed in the upstream part of a catalyst tank 2 through which fuel gas 1 is introduced, and in the downstream part thereof. FIG. 2 is a diagram showing a system in which four catalyst layers are formed filled with a catalyst having excellent heat resistance but poor low-temperature activity, and the former is utilized during startup, and the latter is utilized during high-load combustion. However, in the catalyst tank 2 shown in FIG.
During both startup and high-load combustion, the combustion reaction proceeds only in the upstream catalyst layer 3, which has poor heat resistance, and the temperature distribution is as shown by the solid line and broken line in FIG.
(The solid line shows the temperature distribution in the catalyst tank when the catalytic combustion equipment is started, and the broken line shows the temperature distribution in the catalyst tank at high load.) Catalyst A in the upstream section was thermally degraded after one use, resulting in a significant rise in ignition temperature. ; One of the main objectives of the present invention is to prevent this increase in ignition temperature. The inventors discovered that in catalytic combustion, as shown in Figure 13, when the flow rate of fuel gas passing through the catalyst tank is increased and the cylinder velocity is gradually increased, the combustion rate rapidly decreases. Focusing on the fact that a misfire phenomenon occurs due to blowout, if the cylinder velocity of the fuel gas flowing in the upstream catalyst layer 3 is made higher than that in the downstream catalyst layer 4, the fuel gas at startup can be reduced. While the amount is small, combustion occurs in the upstream section, but when the gas amount increases as the load increases, the gas flow velocity in the upstream catalyst layer 3 enters the misfire region and misfire occurs, and the downstream catalyst layer 4 Sometimes the heat of combustion is high enough for the combustion reaction to continue here. As a result, the catalyst tank 2 exhibits a temperature distribution shown by the dashed line in FIG. 12, and the upstream catalyst layer 3 used for ignition is protected from thermal deterioration by decreasing to almost the inlet gas temperature during high-load combustion. The present invention is based on the following aspects. In addition, in order to misfire only the upstream catalyst layer, in addition to making the flow velocity of the fuel gas in the catalyst tank different between the upstream and downstream parts as described above, it is also possible to misfire the fuel gas in the upstream catalyst layer. This can also be achieved by making the contact surface area smaller than that of the downstream catalyst layer.

In addition, Figure 14 shows the ignition and misfire temperatures by repeatedly raising and lowering the temperature after flowing methane gas (concentration: 4 cm) through a catalyst layer in which platinum is supported on mullite and then filled with a catalyst. , In this figure, the solid line shows the first ignition and misfire, the dashed line shows the second ignition and misfire, and the broken line shows the third ignition and misfire. It is. The characteristic phenomenon shown in the 14th factor is that by repeatedly increasing and decreasing the temperature, the combustion start temperature of methane gas at the time of temperature increase, the so-called ignition temperature, gradually increases due to thermal deterioration of the catalyst body, but the characteristics when the temperature decreases are There is almost no change.

This cannot be explained if it is considered that catalytic combustion occurs only due to the catalytic action of platinum. In other words, although it is thought that repeated temperature rises cause the platinum particles to sinter, reducing their activity and raising the ignition temperature, when the temperature falls, combustion continues below the ignition temperature, and the temperature at which misfire occurs is due to the heat of combustion. This behavior is contrary to the usual predictions regarding catalytic activity, which is that it is almost unaffected by deterioration.

The conclusion obtained by analyzing this phenomenon is that the functions of the catalyst in a catalytic combustion reaction are to promote combustion through the catalytic action of the active component, and to efficiently transfer combustion heat to fuel through heat conduction within the catalyst that forms the catalyst layer. There is a combustion promoting effect by intensifying preheating by transmitting it to the gas inlet direction, and the former plays a dominant role at the start of combustion (at the time of ignition), and the latter plays a dominant role during sustained combustion. Therefore, after ignition, there is no need for the catalyst to have a catalytic action.In other words, even if a heat conductive member that can efficiently transfer combustion heat in the gas inflow direction is used instead of the catalyst, the above-mentioned It can be expected to have a combustion promoting effect.

The inventors focused on this point, and by separating and using the above-mentioned two functions of the catalyst body, the present invention! This is what led to the eggplant.

The catalytic combustion method according to the present invention is a method of burning combustible gas with a combustion catalyst, in which a low-temperature active catalyst zone consisting of a catalyst layer with excellent low-temperature activity is provided on the upstream side of a combustible gas flow path, and the Providing a combustion zone made of a heat-resistant material layer with better heat resistance than the upstream catalyst layer, and causing ignition and misfire in the upstream catalyst zone by changing the cylinder velocity of combustible gas in the low-temperature active catalyst zone. It is characterized by igniting in the upstream catalyst area where it is easy to ignite, causing misfire in the upstream catalyst area as the load increases, and continuing combustion in the downstream combustion area which has excellent heat resistance. Because there are
It has excellent ignitability and is suitable for high-temperature, high-load combustion.

[Embodiments of the invention]

Next, examples of the present invention will be described.

FIG. 1 is a diagram showing a first embodiment of a catalytic combustion apparatus used in the method according to the present invention.

In this figure, fuel is supplied to the mixer 5 through a fuel injection pipe 6, and air is also supplied via an air intake pipe 7, a fan 8, and an air injection pipe 10, and the fuel is supplied to the mixer 5. 2, the fuel gas is mixed with air to become a fuel gas with an appropriate air-fuel ratio, and is led from the duct 12 to the preheater 14 to be preheated, and further led to the catalyst tank 20 by the duct 16, where it comes into contact with the catalyst body in the catalyst tank 20. It is designed to burn. Further, the combustion gas is led through a duct 28 to a device (not shown) for the purpose of heat utilization.

The catalyst tank 20Vi is divided into an upstream part 20A and a downstream part 20B, and the flow passage cross-sectional area of the upstream part 20A is configured to be smaller than that of the downstream part 20B, and the ratio is such that the catalyst tank 20 is filled with Although it varies somewhat depending on the catalyst body used and the type of fuel used, the former is a few to several tenths of the latter.
It is set between i, Upstream section 20 of catalyst tank 20
A and the downstream portion 20BK are filled with a catalyst body having a non-nicam structure in which a catalyst is supported on a carrier to form catalyst layers 21A and 21B, respectively. Upstream catalyst layer 21A
i The catalyst body to be formed uses γ-alumina as a support, and supports a catalyst such as platinum or palladium on it, and has excellent low-temperature activity.On the other hand, the downstream catalyst layer 2
The catalyst body that forms 1B'Y is α-alumina, zirconia,
A catalyst such as platinum is supported on a support having excellent heat resistance such as carbonized cane.

At startup, the preheating temperature of the fuel gas by the preheater 14 is set higher than the ignition temperature of the catalyst formed in the upstream catalyst layer 21A', and the flow rate of the fuel scum is set to several minutes at a steady load (high load). It can be suppressed to one to several tenths of that. The air-fuel ratio in the case is such that the adiabatic combustion temperature is the upstream catalyst 421A'Ij! r: below the allowable temperature limit of the catalyst body to be formed, and the downstream catalyst layer 21
The temperature is selected so that the temperature is higher than the ignition temperature of the catalyst that forms BY. Under these conditions, the combustion reaction occurs only in the upstream catalyst layer 21A, and the downstream catalyst layer 21B is heated to above its ignition temperature by the heat of combustion.

When the air-fuel ratio is maintained as it is and the flow rate of fuel gas is increased, the gas flow velocity in the upstream catalyst layer 21A is higher than that in the downstream catalyst layer 21B, so the gas flow rate in the upstream catalyst layer 21A is increased. Along with the misfire, combustion starts in the downstream catalyst layer 21B. If the air-fuel ratio is lowered in this state, the combustion temperature in the downstream catalyst layer 21B will rise. However, the upstream catalyst layer 21A misfires and remains in a cold state, and the temperature decreases to the preheating temperature, causing the upstream catalyst layer 21A to misfire.
-Y forming catalysts are protected from thermal deterioration.

As described above, according to this embodiment, it is possible to use the catalyst for ignition and the catalyst for high-load combustion depending on the shape and operation of the catalyst tank 20, and this reduced ignition temperature can be significantly reduced compared to the conventional method. can be lowered to

Therefore, the preheater 14'lk can be of small capacity. For the catalyst for high-load combustion that forms the downstream catalyst layer 21BY, a catalyst with high high-temperature activity can be used, so if a catalyst with excellent heat resistance is used, the maximum combustion temperature will be lower than that of conventional catalysts. can be made higher.

FIG. 2 shows the upstream portion 20A of the catalyst layer 20, the downstream portion 20A of the catalyst layer 20, The specifications of the upstream catalyst layer 21A and the downstream catalyst layer 21B formed in the section 20B are shown in Table 1, and the combustion conditions at startup and during high-load combustion are shown in Table 2.

In the Table 1 test, the temperature of the preheater 14 was gradually increased,
When combustion starts in the upstream catalyst layer 21A, the temperature is maintained at that temperature, and then high-load combustion is started according to the operating procedure shown in the first embodiment.

In addition, in FIG. 2, the ○ mark indicates the case of this example,
On the other hand, the mark Δ indicates that the upstream portion 20A and downstream portion 20B of the catalyst tank 20 are in the same cross section, that is, the upstream catalyst layer 21A and the downstream catalyst layer 21B have the same cross-sectional area. It shows.

As is clear from this Figure 2, in the conventional example, the temperature was approximately 600°C.
The ignition temperature was approximately 350° C. in this example, and it can be seen that this example has better low-temperature ignition properties.

FIG. 3 is a diagram showing a second embodiment of the catalytic combustion apparatus used in the method according to the present invention.

In FIG. 3, the catalyst tank 3o of the catalytic combustion device is the upstream part 3.
It is divided into 0A and downstream part 30B, and the cross-sectional area of the upstream part 30A and downstream part 30B is formed to be the same size, but the upstream part 30A is filled and the upstream catalyst layer 31AY is formed, which has excellent low-temperature activity. The particle size of the secondary catalyst is larger than the particle size of the secondary catalyst, which is filled in the downstream section 30B and forms the downstream catalyst layer 31B, which is characterized by excellent heat resistance. The surface area is different between the upstream catalyst layer 31A and the downstream catalyst layer 31B, and the flow rate of fuel gas!
By increasing the amount, the upstream catalyst layer 31A causes a misfire and the downstream catalyst layer 31B performs high-temperature combustion.The rest is the same as the first embodiment, so the same reference numerals are given. Possibly an explanation〉
Omitted.

According to this second embodiment, since the outer surface area per unit volume of the upstream side catalyst layer 31A is smaller than the outer surface area per unit volume of the downstream side catalyst layer 31B, when the flow rate of fuel gas is increased, the upstream side Although the catalyst layer 31A misfires, high-temperature combustion can be performed in the downstream catalyst layer 31B, so low-temperature ignitability is good and high-temperature, high-load combustion can be achieved.

FIG. 4 shows a third embodiment of a catalytic combustion apparatus used in the method according to the present invention. The second embodiment (third embodiment)
(see figure), the particle size of the catalyst bodies forming the catalyst layers 31A and 31BY is made different between the upstream part and the downstream part, and the upstream catalyst layer 3
1A and the downstream catalyst layer 31B are configured to have different outer surface areas per unit volume, but in this third embodiment, each catalyst layer is provided with a honeycomb structured catalyst body in the upstream portion 40A and downstream portion 40B of the catalyst layer 40. 41A and 41B are formed, and the cell diameter of the honeycomb structure of the upstream catalyst layer 41A is larger than that of the downstream catalyst layer 41B, making it the runner-up. The rest is the same as the second embodiment, and the explanation thereof will be omitted by giving the same reference numerals.

Also in this embodiment of fli, 3, the outer surface area per unit area of the upstream catalyst layer 41A is smaller than that of the downstream catalyst layer 41B, and the same effect as in the second embodiment can be obtained.

FIG. 5 shows a fourth embodiment of a catalytic combustion apparatus used in the method according to the present invention.

In FIG. 5, an upstream portion 4OA of the catalyst tank 40 is filled with a catalyst having a nine-Nicum structure having excellent low-temperature activity to form an upstream catalyst layer 42A, and a downstream portion 40B of the catalyst layer 40.
A downstream catalyst layer 42B is formed by filling a catalyst body with a honeycomb structure with excellent heat resistance. In the middle of the duct 16 that guides the fuel gas from the preheater 14 to the catalyst tank 40,
A bypass 43 is provided extending between the upstream portion 4OA and the downstream portion 40B of the catalyst tank 40, and is provided at a branch point of the duct 16 so that the flow direction of the fuel gas can be switched by a switching valve 44. . This switching valve 44 is configured so that the flow rate of the fuel gas flowing through the duct 16 is determined by a gas flow rate detector (not shown) installed in the duct 16 to a predetermined value (
When the fuel gas flow rate in the upstream catalyst layer 42A reaches a value equal to or higher than that corresponding to the value immediately before a misfire occurs, the gas flow path is switched and the fuel gas is passed through the bypass 43' to the catalyst tank 4.
It is designed to supply within 0. The other parts are the same as those in the third embodiment, and the explanation thereof will be omitted by giving the same reference numerals.

In the first to third embodiments, the shapes of the catalyst tanks are made different between the upstream and downstream parts (see FIG. 1), or the upstream catalyst layers 31A, 41A and the downstream catalyst layers 31B, 41
Make the outer surface area different from B (see Figures 3 and 4)
This causes misfire in the upstream catalyst layers 31A, 41A and transfers the combustion reaction to the downstream catalyst layers 31B, 41B. In this fourth embodiment, the gas flow rate detector, the switching valve 44, Since the combustion reaction is transferred to the downstream catalyst layer 42B by the bypass 43, in addition to the same effect as in the third embodiment, the catalyst layer 42
A, 42B9 has the advantage that the honeycomb structure of the catalyst body can be made of the same size. Note that the switching valve 44 may be operated by a gas flow rate detector or a temperature sensor installed in the catalyst tank 40 instead of the gas flow rate detector.

FIG. 6 shows a fifth flow diagram for use in the method according to the invention.

In this figure, nine fuels are introduced into the mixer 45 by a fuel injection pipe 46, an air intake pipe 47, and a fan 4.
8. The rL air introduced through the air injection pipe 50 is mixed with fuel gas having an appropriate air-fuel ratio, and the resulting fuel gas is led to the preheater 54 through the duct 52. After being heated by the preheater 54, the duct 56 into the catalyst tank 60, where it comes into contact with the catalyst filled in the catalyst tank and is combusted. In addition, the combustion gas is transferred to duct 6
8 leads to a device (not shown) for the purpose of heat utilization.

The catalyst tank 60 is divided into an upstream section 60A and a downstream section 60B, and the cross-sectional area of the upstream section 60A is a fraction of the cross-sectional area of the downstream section 60B. has been done. The upstream portion 60A is filled with a catalyst body having a honeycomb structure having excellent low-temperature activity to form a catalyst layer 61.
On the other hand, the downstream portion 60BK is filled with a honeycomb-structured ceramic body having excellent heat resistance to form a heat conductive layer 62. For the catalyst body forming the catalyst layer 61'Y, alumina, mullite, cordierite, etc. are used as a carrier,
A catalyst active in promoting combustion reactions such as platinum or palladium is supported on the mullite, and from the viewpoint of low ignition temperature, good pressure loss and heat resistance, it is preferable to support palladium on mullite. The primary catalyst body may have a granular structure instead of a honeycomb structure. On the other hand, it is desirable that the ceramic body forming the heat conductive layer 62 has both high thermal conductivity and high melting point, and cane carbide and α-alumina are preferable, but other heat-resistant ceramics may be used.

Further, the shape of the ceramic body is desirably a honeycomb structure in order to improve heat transfer efficiency, but it may also be an aggregate structure of molded bodies in the shape of a vibrator or a granular structure.

At startup, the preheating temperature of the fuel gas by the preheater 54 is set higher than the ignition temperature of the catalyst body forming the catalyst layer 6, and the flow rate of the fuel gas is reduced by several times the temperature at a steady load (high load). It is suppressed to one to several tenths. The air-fuel ratio is selected so that the adiabatic combustion temperature is lower than the allowable temperature limit of the catalyst body forming the catalyst layer 61. Due to this condition, a combustion reaction occurs in the catalyst layer 61. The heat of combustion causes the heat conductive layer 62 to reach a temperature higher than its ignition temperature. Subsequently, while maintaining the air-fuel ratio as it is and increasing the flow rate of the fuel gas, the flow rate of the fuel gas in the catalyst layer 61 or the heat conductive layer 6 increases.
Since it is larger than that of No. 2, a misfire occurs in the catalyst layer 61 and combustion starts in the heat conductive layer 62. If the air-fuel ratio is lowered in this state, the combustion temperature in the heat conductive layer 62 will rise. In this heat conductive layer 62, as shown in FIG. 7, a heat flux as shown by arrow A is transmitted upstream from the combustion part 64 of the fuel gas through the ceramic body forming the heat conductive layer 62. A preheating section 66 for preheating the fuel gas is formed, and the preheating section 66 strengthens the preheating of the fuel gas.The preheating section 66 strengthens the preheating of the fuel gas, which causes combustion within the heat conductive layer 62. It happens.

Therefore, it is not necessary to take into account the reduction in activity due to heat, which is a problem in the case of catalytic combustion. Furthermore, the combustion promotion effect by strengthening the preheating of the heat conductive layer 62 shown in FIG. 7 is more effective as the temperature rise due to combustion heat increases, so the smaller the heat conductive layer 62 is, the more suitable it is for high-load, high-temperature combustion. I can say that. Note that during this high-load combustion, the catalyst layer 61 formed in the upstream part of the catalyst tank 60 is in a misfired state, so the catalyst layer 61 is lowered to the preheating temperature by the preheater 54, and the catalyst layer 61 is formed. The catalytic converter is not adversely affected by the high temperature combustion in the thermally conductive layer 62.

8 and 9 show the catalytic combustion system fIt shown in FIG.
This is a diagram showing the results of a combustion test conducted using a conventional combustion engine in comparison with a conventional example. are Example 5A and Example 5B, and the conventional examples are Conventional Example 1 and Conventional Example 2.
are shown in each column.

Table 3 Table 4 The combustion test was conducted repeatedly by starting - high load combustion - stopping. During the test, the temperature of the preheater 54 was gradually increased and the combustion start temperature (ignition temperature) was measured. , the procedure for increasing the load and performing high-load combustion is adopted.

Figures 8 and 9 show changes in ignition temperature and combustion rate under high fuel load conditions when the above test was repeated. The mark is Example 5
In case B, 0 mark and ◇ mark respectively indicate the conventional example 1.2t. As can be seen from these figures, Examples 5A and 5
In the case of B, the ignition temperature increases only slightly even with repeated high-load combustion, and it ignites at about 350°C, and the combustion rate during high-load combustion also maintains about 100% Y, making it a good choice.

On the other hand, when palladium, which has excellent ignition performance but poor heat resistance, is supported on mullite and is used alone as a catalyst (conventional example 1), the first high-load combustion causes the inlet part of the catalyst layer to It melted, making the next test impossible.

In addition, when palladium is supported on α-alumina, which has excellent heat resistance, and is used alone in the friend catalyst 7 (Conventional Example 2), the ignition temperature is higher than the initial one, and increases even more with repeated combustion tests. After that, even if heated to 700℃, sustained combustion could not be started.

In this way, in this embodiment, at the time of startup, ignition and combustion occur in the upstream catalyst layer 61 made of a catalyst having excellent low-temperature activity.
When the load is high, the upstream catalyst layer 61 causes a misfire, and the downstream part is configured to cause high-temperature combustion with the thermally conductive layer 62 made of a highly heat-resistant and solid ceramic body. High-temperature, high-load combustion is possible. Furthermore, since the heat conductive layer 62, which burns at a high temperature, is formed of a heat-resistant ceramic body, it is possible to burn at a high temperature of 1200° C. or higher.

Furthermore, since this embodiment enables combustion in a high temperature range of 1200° C. or higher, it can be applied not only to low-calorie gas combustors but also to general combustors such as heating furnaces and boilers.

FIG. 10 shows a main part Y of yet another embodiment of the apparatus for the method YtE according to the present invention, in which the catalyst tank 70 is formed in a cylindrical shape with the same inner diameter in the direction of flow of fuel gas,
The upstream part 70A of the catalyst tank 70 is filled with a catalyst body having excellent low-temperature activity to form a catalyst layer 71, and the downstream part 70B is filled with a ceramic body having excellent heat resistance to form a heat conductive layer 72. ing. The outer surface area per unit volume of the catalyst layer 71 is set to be smaller than the outer surface area per unit volume of the heat conductive layer 72, for example, when the catalyst body and the ceramic body forming both have a granular structure. In this case, the particle size of the catalyst body is made larger than the particle size of the ceramic body, and when both the catalyst body and the ceramic body have a nicum structure, the cell diameter of the catalyst body is made larger than that of the ceramic body. It is designed to cause a misfire in the upstream catalyst layer 71 when the flow rate Z of the fuel gas increases.

Since the other parts are the same as the structure of the apparatus already explained and shown in FIG. 5, the explanation thereof will be omitted by giving the same symbols.

〔Effect of the invention〕

As is clear from the above description, according to the present invention, it is possible to achieve excellent low-temperature ignitability and high-temperature, high-load combustion.

[Brief explanation of the drawing]

Fig. 1 is a schematic diagram of a first embodiment of the catalytic combustion device used in the method according to the present invention, Fig. 2 is a t diagram showing changes in the ignition temperature, and Fig. 3 is a diagram of the second embodiment. 4 is a schematic diagram of the third embodiment, FIG. 5 is a schematic diagram of the fourth embodiment, FIG. 6 is a schematic diagram of the fifth embodiment, and FIG. 7 is a schematic diagram of the fifth embodiment. An explanatory diagram of the preheating strengthening effect of the heat conductive layer. Figure 8 shows the change in ignition temperature due to fc. Figure 9 shows the change in combustion rate under high load conditions. Figure 10 shows the change in combustion rate under high load conditions. A schematic diagram of the sixth embodiment, FIG. 11 is a vertical cross-sectional view of a catalyst tank of a conventional catalytic combustion device, FIG. 12 is a diagram showing the temperature distribution in the catalyst tank, and FIG. 13 is a misfire phenomenon of catalytic combustion. Figure 14 showing
The figure is a diagram showing a combustion deterioration phenomenon of a catalyst in a catalyst tank of a conventional catalytic combustion device. 5.45...Mixer, 14.54...Preheater,
20.30,40. Full h60.70...Catalyst tank, 20
A, 50A, 40A, 60A, 70A...upstream part of the catalyst tank, 20B, 50B, 40B, 608°70B...downstream part of the catalyst tank, 21A,! +1A, 41A. 42A, 61.71...Upstream catalyst layer, 21B, 31
B, 41B, 42B...Downstream catalyst layer, 44...Switching valve, 43...Bypass, 62.72...Heat conductive layer.

Claims (4)

[Claims] (1) In a method of burning flammable gas with a combustion catalyst,
A low-temperature active catalyst region made of a catalyst layer having excellent low-temperature activity is provided on the upstream side of the combustible gas flow path, a combustion region made of a heat-resistant material layer having better heat resistance than the upstream catalyst layer is provided on the downstream side, and the A catalytic combustion method characterized in that ignition and misfire in the upstream catalyst region are performed by changing the cylinder velocity of combustible gas in the low temperature active catalyst region. (2) The catalytic combustion method according to claim 1, wherein the downstream heat-resistant material layer is a catalyst layer with excellent heat resistance. (3) The catalytic combustion method according to claim 1, wherein the downstream heat-resistant material layer is a heat conductive layer made of ceramic. (4) Let u_1 and u_2 be the respective flow velocities of the combustible gas flowing in the catalyst layer on the upstream side and the heat-resistant material layer on the downstream side, and the respective units of the catalyst layer on the upstream side and the heat-resistant material layer on the downstream side Assuming the outer surface area per volume as S_1 and S_2, u_1/S_
The catalytic combustion method according to any one of claims 1 to 3, characterized in that the conditional expression 1>u_2/S_2 is satisfied.