JPS6250723B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] This invention relates to a low nitrogen oxide catalytic combustion device using a catalyst.

[Conventional technology]

FIG. 3 is a schematic diagram showing a conventional catalytic combustion device. In the figure, 1 is a combustion air blower, 2 is a fuel supply device such as gas, and 3 is a porous body made of palladium, platinum, etc., foamed metal, honeycomb, etc. Oxidation catalyst coated on ceramic fiber etc. 4 is ignition electrode, 5
is a temperature detector embedded in the oxidation catalyst 3, and 6 is the combustor main body.

A conventional catalytic combustion device is configured as described above.
Fuel is supplied from the fuel supply device almost simultaneously with the operation of the blower 1, and the air-fuel mixture is ignited on the surface of the catalyst 3 by the ignition electrode 4. Thereafter, the catalyst receives heat from the flame and its temperature gradually rises, and combustion progresses within the catalyst one after another until it reaches a steady state. The temperature of the catalyst is detected by a detector 5 to confirm combustion.

Catalytic combustion takes place on the surface of a catalyst carrier such as a porous body, metal foam, or honeycomb ceramic, or within narrow pores, so the flame temperature is low, and due to the reducing effect of the catalyst and combustion intermediate products, it is a typical harmful exhaust gas. Extremely low nitrogen oxides (NOx) (〓
1ppm). Carbon monoxide (CO) is also oxidized on the surface of the catalyst, so its emissions are extremely low.

[Problem that the invention seeks to solve]

Conventional catalytic combustion devices such as those described above have the problem that a large amount of unburned fuel (HC) and carbon monoxide (CO) are emitted during ignition, as shown in the example of exhaust gas measurement in Figure 4. . In other words, at the moment when a flame is formed on the catalyst surface during ignition, HC and CO,
Each concentration of CO ₂ shows a sharp peak, and then as the catalyst layer temperature T ₁ increases due to heat received from the flame, combustion begins to proceed within the catalyst.

However, at this point, the catalyst layer is still at a low temperature, so the reaction does not proceed sufficiently and the fuel is discharged unburnt, resulting in a large amount of HCCO being emitted, and conversely, the CO ₂ concentration is low. After that, when the temperature of the catalyst layer rises to a temperature sufficient for reaction, the HCCO concentration decreases rapidly.
CO ₂ increases to a steady value.

In the conventional example, since the HCCO concentration is high at the beginning of ignition, countermeasures have been taken such as preheating the catalyst layer with an electric heater or the like, or providing a second catalyst layer with a small heat capacity downstream. In addition, since it is an all-primary type that supplies several times the amount of air required for combustion and uses the mixture with gas fuel, the required amount of air is large. Moreover, since the pressure loss in the catalyst layer is large, an air supply means such as a blower is indispensable. In addition, since the combustion reaction is determined by the catalyst bed temperature and catalyst activity, a safety device is required to prevent a decrease in the amount of supplied air and catalyst deterioration, and there are also problems such as difficulty in adjusting the combustion amount with a single burner. The point was hot.

This invention was made to solve this problem, and although NOx emissions are higher than the conventional all-primary type, it prevents transient HCCO emissions during ignition and is highly safe against catalyst deterioration. The object of the present invention is to obtain a catalytic combustion device that can adjust the amount of combustion.

[Means for solving problems]

The catalytic combustion device according to the present invention includes a combustor that is provided with a throat that takes in the fuel supplied from the fuel supply nozzle and the amount of air that is less than the amount of air required for combustion sucked in by the jet ejector action of the fuel. A catalyst layer is disposed in the combustor so as to react a mixture of air and air, and an auxiliary combustion plate having a large number of holes surrounds the catalyst layer, and an ignition electrode ignites the mixture. It is equipped with the following.

[Effect]

In this invention, air less than the amount of air required for combustion is sucked in using the action of the gas fuel ejector, and after partial combustion is performed within the catalyst layer,
The unburned substances are diffused and burned with the air in the atmosphere.

〔Example〕

FIG. 1 is a sectional view showing an embodiment of the present invention, and FIG. 2 is a cross-sectional plan view taken along the line shown in FIG. 1.
3 to 6 are the same as those of the conventional catalytic combustion device described above. 7 is a gas fuel supply nozzle, 8 is a catalyst layer 3
9 is the throat of the combustor that takes in the gas fuel and air from the supply nozzle 7; 10 is the catalyst layer 3; The pressure equalizing plate 11 provided on the air-fuel mixture inflow side is an ion electrode for detecting the ion current of the flame.

In the catalytic combustion device configured as described above, when gas fuel is supplied from the nozzle 7, the throat 9 is
Air in an amount less than the amount of air required for combustion (less than theoretical air) is drawn into the chamber, and the mixture of this air and gas fuel is ignited by the discharge of the ignition electrode 4, and this ignition causes an ionic current flowing through the ion electrode 11. This is confirmed by the rectified waveform of

At the time of ignition, the catalyst layer temperature is low and the pressure loss is small, so the suction air amount can be set to an air ratio (supply air amount / theoretical combustion air amount) of about μ〓0.8, and a stable plane flame is formed on the catalyst layer. A secondary flame is formed around the burner.

After ignition, when the catalyst layer 3 receives heat from the flame and rises in temperature, the catalytic reaction begins to take place actively.
At the same time, the pressure loss of the catalyst layer 3 increases, so the amount of suction air decreases and reaches a steady state at about μ=0.6 to 0.7.

Since a secondary flame is always formed from the above-mentioned ignition to the steady state, HC and CO emitted at the beginning of the catalytic reaction are burned by this secondary flame and are extremely reduced. Furthermore, when the catalyst activity deteriorates, the rate of catalytic reaction simply decreases and the rate of combustion in the secondary flame increases, and there is no danger of harmful CO being emitted. Therefore, since it is not necessary to strictly control the temperature of the catalyst layer, stable combustion can be obtained even if the combustion amount is changed, and the combustion amount can be adjusted.

Furthermore, since the diffusion flame on the auxiliary flame hole plate 8 provided around the catalyst layer has a relatively high flame temperature, the diffusion flame from the secondary flame is
It has the effect of suppressing CO generation. Further, since the pressure loss of the auxiliary flame hole plate 8 is small and does not change much from the time of ignition to the steady state, it also plays the role of reducing fluctuations in the amount of air sucked from the throat 9 of the combustor.

In addition, although the illustrated example shows the case where gas fuel is used, it goes without saying that the same effect can be obtained using vaporized gas of liquid fuel such as kerosene.

〔Effect of the invention〕

As described above, according to the present invention, the catalyst layer disposed in the combustor is surrounded by the auxiliary flame hole plate, and the air ratio μ<
1.0 achieves catalytic combustion, (i) prevents transient HC and CO emissions during ignition, (ii) eliminates the need for a blower, and (iii) prevents catalyst activity from deteriorating or reducing intake air volume. (iv) The amount of combustion can be adjusted, and (v) Performance is greatly improved compared to conventional catalytic combustion devices.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram of a catalytic combustion device according to an embodiment of the present invention, FIG. 2 is a cross-sectional plan view taken along the line of FIG. 1, and FIG. 3 is a schematic diagram of a conventional catalytic combustion device.
FIG. 4 is a graph showing temporal changes in exhaust gas concentration and catalyst temperature due to the catalytic combustion. In the figure, 3 is a catalyst layer, 4 is an ignition electrode, and 6 is a catalyst layer.
is a combustor, 7 is a fuel supply nozzle, 8 is an auxiliary flame hole plate, and 9 is a throat of the combustor. In addition, in the figure,
The same reference numerals indicate the same or equivalent parts.

Claims (1)

[Claims] 1 A combustor having a throat that takes in the fuel supplied from the fuel supply nozzle and the amount of air sucked in by the jet ejector action of the fuel in an amount less than the amount of air required for combustion, and reacts the mixture of fuel and air. a catalyst layer provided in the combustor so as to cause the combustor to ignite, an auxiliary combustion plate having a large number of small holes surrounding the catalyst layer, and an ignition electrode for igniting the air-fuel mixture;
Catalytic combustion device equipped with.