JP2604164B2 - Catalytic combustion device - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a catalyst deterioration countermeasure, and more particularly, to a catalytic combustion device capable of detecting a combustion temperature in a catalyst layer and controlling the temperature to a certain temperature or less.

[Conventional technology]

Catalytic combustion is a method of burning combustibles in gas using a noble metal oxidation catalyst such as platinum (pt) or palladium (pd).
Technology that can be burned under low-calorie gas and low-O ₂ conditions compared to conventional gas-phase combustion, and has features such as low NOx. It is. As its application, catalytic burners, gas turbines, household fan heaters, and the like are being studied.

The structure of the catalyst carrier for catalytic combustion is based on the premise that the honeycomb structured carrier is formed of a thin-walled cell with a large geometric surface area and a small pressure loss. It is supported by a method such as impregnation and used as a honeycomb catalyst layer.

The catalytic combustion device preheats a honeycomb catalyst layer to several hundred degrees Celsius, mixes a combustible gas such as methane or propane with air, flows into the catalyst layer, and burns the catalyst in contact with the catalyst. However, as shown in FIG. 11, when the temperature in the honeycomb catalyst layer exceeds a certain temperature, the noble metal oxidation catalyst rapidly agglomerates or evaporates,
The decrease (deterioration) of the activity is accelerated, and the life is remarkably reduced. When such catalyst deterioration progresses, combustion becomes extremely unstable, and energy saving, which is a feature of catalytic combustion,
Pollution-free combustion cannot be achieved. In particular, in the case of household fan heaters, the influence on the human body due to the generation of NOx and CO may be a serious social problem.

As described above, there is a problem of deterioration of the catalyst as the temperature of the catalyst increases. However, in a catalytic combustion device, the higher the temperature, the more stable combustion is possible. Therefore, the operating conditions (combustion amount / air amount) are set at a temperature relatively close to the deterioration temperature.
However, even if the conditions are kept constant in this way, in a normal apparatus, the surrounding environmental conditions change, and the temperature in the catalyst layer easily changes by several tens degrees Celsius due to a slight change in the amount of fuel or air,
This has caused the life of the catalyst to be shorter than expected.

As a safety device for the catalyst in the conventional catalytic combustion device, a temperature detection element is installed upstream of the catalyst layer to indirectly monitor the temperature of the catalyst and to alert when abnormal combustion such as backfire or blow-off occurs. There has been proposed a system in which a fuel supply system is shut off by issuing an alarm. Further, a honeycomb sensor for purifying exhaust gas for automobiles is also provided with a temperature sensor in the vicinity of an exhaust gas outlet, and employs a system that issues a temperature alarm when the temperature exceeds a certain temperature. All of these methods indirectly estimate the temperature of the catalyst and are mainly based on the protection of the entire system and safety aspects, and do not deal with catalyst deterioration due to routine combustion monitoring of the system. Was.

[Problems to be solved by the invention]

Difficulty in countermeasures for catalyst deterioration is as follows: (1) The position of the maximum temperature in the catalyst varies considerably depending on the distribution of the catalyst activity in the catalyst layer and the space velocity of the fuel, and there is no means for easily detecting the maximum temperature. That is, since thermocouples and temperature sensors can measure only the temperature at a certain point, if it is intended to detect the maximum temperature in the honeycomb catalyst layer, a number of temperature sensors are attached to each position in the layer and the maximum value is measured. Need to ask. (2) When the temperature in the catalyst layer exceeds a set value, there is no method for immediately lowering the temperature to near the set value.

An object of the present invention is to provide a catalytic combustion device having means for detecting a combustion temperature in a catalyst layer and controlling the temperature of the catalyst so as not to exceed a set temperature at which the temperature of the catalyst deteriorates.

[Means for solving the problem]

In order to achieve the above-mentioned object, the present invention forms a catalyst layer by supporting a noble metal oxidation catalyst on a monolithic carrier having a large number of through-holes, and flows a combustible gas mixed with air through the catalyst layer to increase the temperature. In a catalytic combustion device that performs contact combustion at a temperature, a temperature detecting element that is inserted into a through hole of a catalyst layer and detects the temperature, and a unit that controls a combustion temperature by adjusting a flow rate of air with a signal from the temperature detecting element. It is configured to be provided.

[Action]

According to the present invention, by inserting the temperature detecting element into the catalyst layer of the catalytic combustion device, the combustion temperature at which the catalyst starts to deteriorate can be detected, and the air amount is adjusted by the signal of the temperature detecting element to control the combustion temperature. Is done.

〔Example〕

A first embodiment of the present invention will be described with reference to FIG.

As shown in FIG. 1, a catalyst layer, for example, a honeycomb catalyst layer 1 is formed by supporting a noble metal oxidation catalyst on an integrally-structured carrier having a large number of through holes, and air is passed through a rectifying plate 6 to the catalyst layer. And a combustible gas which flows through the combustible gas and performs catalytic combustion at a high temperature, a temperature detecting element 2 which is inserted into a through hole of the catalyst layer and detects a temperature at which the temperature starts to deteriorate, This is a configuration including means for adjusting the flow rate of air by a signal to control the combustion temperature, that is, a control unit 3, a fuel supply unit 4, and a fan 5.

The temperature in the honeycomb catalyst layer is detected by a temperature detecting element having a structure in which a semiconductor such as a ZrO ₂ element having a negative temperature coefficient of resistance and a large temperature coefficient is sandwiched between conductive materials in the combustion temperature range. By adjusting the amount of air blown into the bed when the temperature of the catalyst reaches or exceeds the temperature at which the catalyst starts to deteriorate, the temperature can be reduced to or below the set temperature.

FIG. 6 shows the relationship between the amount of air and the temperature distribution in the catalyst layer. By increasing the amount of air by about 5%, the combustion temperature in the catalyst layer can be reduced by about 30 ° C. It can be seen that the combustion temperature can be controlled by appropriate adjustment.

FIG. 7 shows the relationship between the amount of air supplied from the fan and the temperature in the layer. There is a good correspondence between the air amount and the combustion temperature, and it is possible to set the in-layer temperature with high accuracy.

The air amount is controlled by changing the opening ratio of the damper based on the detected current value, or the inverter that changes the power frequency of the fan so that the detected current value does not exceed the set current value corresponding to the deterioration temperature By performing the control or the like, it is possible to prevent overheating in the catalyst layer.

A second embodiment of the present invention will be described with reference to FIG.

As shown in FIG. 2, the structure of the temperature detecting element is such that a ZrO ₂ —CaO solid solution of a semiconductor 7 is disposed in the center, and this is sandwiched between conductive ceramics 8 of a conductive material 8 connected to an electrode wire 9. It is a laminated body joined to. The dimensions are
It is very small, such as 0.4 × 0.4 mm ^{2 to} 2 × 2.4 mm ² .

The principle by which the temperature detecting element can detect the temperature distribution in the honeycomb catalyst layer is shown in FIG. That is, the temperature detecting element has a structure in which a semiconductor such as a ZrO ₂ -based element having a negative temperature coefficient of resistance and a large temperature coefficient in a combustion temperature range is sandwiched between conductive materials. The semiconductor in the middle shows a characteristic that the resistance is remarkably reduced when the temperature rises, as shown in the example of the ZrO ₂ -based semiconductor in FIG. Therefore, when such a material is inserted into the honeycomb catalyst layer, the resistance is minimized at the portion where the temperature is highest. Therefore, if a voltage is applied between the semiconductor and the conductive material, the resistance is preferentially increased. Current flows in a small portion of the layer, and by detecting this current, the temperature in the layer can be detected. By using such an element, the maximum temperature can be detected even if the position indicating the maximum temperature changes.

As an example, the conductive properties of the ZrO ₂ —CaO solid solution are as shown in FIG. 9, but the properties required of the semiconductor are (1) a combustion temperature range (800 to 1000 ° C.) and a negative temperature coefficient of resistance. Yes, and the absolute value of the coefficient is large (the resistance value is thermally sensitive). (2) Thermally stable characteristics. The following two points are required.

As a material that satisfies this condition, there is stabilized zirconia stabilized by adding CaO, MgO, and Y ₂ O _{3. In} this case, the resistance characteristics can be changed depending on the stabilizing component to be dissolved and its amount. Spinel type semiconductor such as CoO-Al ₂ O ₃ In addition to this can also be applied which satisfies the above conditions.

On the other hand, it is necessary that the conductive material has at least 100 times or more the conductivity in the combustion range as compared with the semiconductor and that the bonding property with the semiconductor and the coefficient of thermal expansion are close. FIG. 10 shows the resistance characteristics of typical conductive ceramic materials.
Most of them are made of base ceramics such as SiC or ZrO ₂ and ZrB ₂ , TiN
And a mixture of TiC conductive ceramics, the resistance characteristics of which change with the ratio of both.

The laminated body of the semiconductor and the conductive material is obtained by superimposing at the stage of the green compact and sintering it integrally, and cutting this into a short shape as shown in FIG. And

As a structure of the temperature detecting element, in addition to such a laminated type, a structure in which an electrode wire 9 having heat resistance and corrosion resistance such as Pt as shown in FIG. 4 may be embedded. In this case, it can be manufactured by embedding the electrode wire 9 in the molded body of the temperature detecting element and firing it.

When a voltage is applied to the temperature detecting element having the above-described structure, the resistance is greatly reduced at the highest temperature portion in the honeycomb catalyst layer, and a current flows. The maximum temperature is estimated based on this current value, the amount of air by the fan is controlled so as not to exceed the current value corresponding to the deterioration temperature, and the combustion temperature in the layer can be maintained at a certain value or less.

The relationship between the temperature in the honeycomb catalyst layer and the output current of the temperature detecting element differs depending on the shape of the temperature distribution in the layer, and this causes an error. For example, if the width of the distribution doubles, the resistance value will be 1/2
And the current value doubles. However, in practice, the difference between the distribution shapes near the maximum temperature is at most 20 even when the catalyst loading state, air excess ratio and space velocity are experimentally changed.
%. Further, in the case of a product, since the conditions are relatively constant, the error is very small at most 5% or less. As an example, FIG. 5 schematically shows the relationship between the temperature and the output current when the distribution width differs by 20%. In the case of B, which is 20% wider than the standard distribution A, the output current is 20% higher when the maximum temperature matches. Therefore, the error in estimating the temperature based on the output current depends on the temperature coefficient of resistance (the rate of increase of the output current with respect to the temperature...). The larger the temperature coefficient of resistance, the smaller the estimation error. Actual calculation of the temperature detecting element using the ZrO ₂ -CaO solid solution shown in FIG.
２2%, which means that there is almost no problem in practical use.

〔The invention's effect〕

According to the present invention, by inserting the temperature detecting element into the through hole of the catalyst layer of the catalytic combustion device, it becomes possible to detect and control the combustion temperature, and to prevent the deterioration of the catalyst. Further, if this system is used, an alarm at the time of backfire or blowout and safety measures can be performed at the same time, and the reliability of the device is improved.

[Brief description of the drawings]

FIG. 1 is a sectional view showing a first embodiment of the present invention, FIG. 2 is a sectional view of a temperature detecting element showing a second embodiment of the present invention, and FIG. 3 is a perspective view showing a method of manufacturing the temperature detecting element. FIG. 4 is a perspective view showing another method of manufacturing the temperature detecting element, FIG. 5 is a graph showing an error of the temperature detecting element, FIG. 6 is a graph showing the temperature with respect to the position of the honeycomb catalyst layer due to an increase in the amount of air, FIG. 7 is a graph showing the temperature in the honeycomb catalyst layer with respect to the increase and decrease of the air amount, FIG. 8 is a graph showing the principle and operation of the temperature detecting element of the present invention, FIG. 9 is a graph showing the characteristics of the temperature detecting element,
FIG. 10 is a diagram showing the characteristics of the conductive ceramics, and FIG. 11 is a graph showing the deterioration characteristics of the catalyst. 1 ... (honeycomb) catalyst layer, 2 ... temperature detection element, 3 ... control unit, 4 ... flammable gas, 5 ... fan (air), 7 ... semiconductor, 8 ... conductive material.

Claims (2)

(57) [Claims] 1. A catalyst in which a noble metal oxidation catalyst is supported on a monolithic carrier having a large number of through-holes to form a catalyst layer, and a combustible gas mixed with air flows through the catalyst layer to contact and burn at a high temperature. In the combustion device, a temperature detection element inserted into the through hole of the catalyst layer and detecting the temperature thereof, and a means for adjusting a flow rate of the air by a signal of the temperature detection element and controlling a combustion temperature are provided. And a catalytic combustion device. 2. A semiconductor wherein the temperature detecting element has a negative temperature coefficient of resistance in a combustion temperature range and has a large temperature coefficient of resistance.
2. The catalytic combustion apparatus according to claim 1, wherein said apparatus comprises a conductive material which is joined to both sides of said semiconductor and connected to an electrode wire.