KR100387945B1 - Low NOx combustion method and combustor using catalytic combustion and catalyst bed with swirl - Google Patents

Abstract

The present invention relates to a low NOx combustion method and a combustor combining a catalyst combustion and a swirl generation of a catalyst layer, and an object thereof is a catalyst that can simultaneously overcome the problems of the flue gas treatment and the combustion treatment techniques by using catalytic combustion. It is to provide a flame supported combustion method and a flame combustor device.

The present invention is a combustion method for suppressing NOx generated from a high load combustor, wherein a part of the mixer 1 is catalytically burned by a catalyst surface reaction in the catalyst layer 2 to heat the mixer 1 with heat generated at this time. To increase the combustion speed of the mixer, and to burn the mixer by swirling it in the wake, and to burn the remaining lean mixer (1) heated in the flame combustion chamber (3) installed at the rear of the catalyst bed (2). A combustion method and apparatus for exhausting NOx-reduced exhaust gas through a flame combustion step of stably combusting at speed are the subject of the invention.

Description

Low NOx combustion method and combustor using catalytic combustion and catalyst bed with swirl}

The present invention relates to a low NOx combustion method that combines catalytic combustion and swirl generation of a catalyst bed and a combustor. In particular, the high load combustor of the present invention can be used in combustors for boilers, gas turbines, hot air generators, and the like.

Existing techniques for suppressing NOx generated from high load combustors can be roughly classified into flue gas treatment and combustion treatment techniques.

The flue gas treatment technique is a technique of treating NOx generated during combustion before discharging it into the atmosphere, and includes a wet method and a dry method. The method of removing NOx by passing exhaust gas directly through an aqueous solution is called a wet method, and the technique of directly reducing NOx to nitrogen as a stabilizer using a catalyst is called a dry method.

Until now, dry methods have been widely used due to economical efficiency and process simplicity. There are various methods of the dry method, but the most selective catalytic reduction method (SCR), in which flue gas and a reducing agent are passed through the catalyst layer to selectively reduce NOx in the flue gas to nitrogen and water vapor, is most commonly used.

However, the selective catalytic reduction method has a problem in that the operating cost is excessive because of the large amount of ammonia used as a reducing agent.

The combustion treatment technology is a technique of suppressing generation of NOx by improving combustion conditions or improving a combustion device in order to reduce NOx.

The improvement of the combustion conditions is a method of suppressing the NOx production reaction in the combustion zone by reducing the flame temperature, the oxygen concentration, and the residence time of the combustion gas, which are factors influencing NOx production.

The core of the combustion treatment technology is to reduce the temperature of the flame through lean combustion, thereby suppressing the generation of thermal NOx, which is absolutely dependent on the flame temperature.

However, lean combustion has a problem that combustion becomes unstable as the mixer becomes thinner.

Therefore, the method of suppressing nitrogen oxide by lean combustion has a limitation.

SUMMARY OF THE INVENTION An object of the present invention for solving the above problems is to provide a flame combustion method and a flame combustor device that supports catalytic combustion that can simultaneously overcome the problems of the flue gas treatment and combustion treatment technology using catalytic combustion. have.

The catalytic combustion enables stable combustion even in ultrathin conditions by utilizing the surface reaction of the catalyst. Stable combustion is possible by using catalytic combustion even in lean conditions where stable combustion is difficult with flame combustion alone.

In this way, it is possible to lower the flame temperature to a lower temperature where thermal NOx does not occur, thereby fundamentally solving the generation of NOx.

Several design concepts are possible to apply catalytic combustion to practically high load combustors.

The first is to burn all the mixtures of fuel and air in the catalyst bed. In this case, the temperature of the catalyst layer increases to a high temperature up to the adiabatic flame temperature of the mixer, so it is necessary to use a high temperature catalyst that can withstand a high temperature of 1000 ° C or higher.

Secondly, only a part of the fuel is supplied to the catalyst bed to be completely combusted by the catalytic reaction, and the remaining fuel is supplied to the rear of the catalyst bed to be treated with flame combustion. In this manner, the catalyst bed temperature can be appropriately controlled by adjusting the amount of fuel supplied to the catalyst bed.

Third, all of the fuel and air mixers are supplied to the catalyst bed to burn only a part of the mixer in the catalyst bed, and the remainder is completely burned in a flame combustion chamber installed at the rear of the catalyst bed. This is called a flame combustor with catalytic combustion.

In this method, there is an advantage that the temperature of the catalyst layer can be properly adjusted by burning only a part of the mixer in the catalyst layer.

The object of the present invention is thus achieved by providing a combustion method and apparatus according to the third method.

1 is a schematic structural diagram of a flame combustor supported with catalytic combustion;

2 is a graph showing the relationship between the temperature of the mixer entering the flame combustion chamber and the flame propagation rate (air-methane mixer, fuel concentration (fuel / air): 2.94%),

3 is a structural diagram of a metal honeycomb,

4 is a metal honeycomb without the inclination of the bent thin plate,

5 is a metal honeycomb with a slope of the bent sheet,

6 is a graph showing a stable combustion region of a lean mixer supported by catalytic combustion (mixer speed: 23.2 m / sec; catalyst layer: 2.0 wt% Pd (52 mm) + 2.0 wt% Pt (26 mm), 300 cell / in ² ceramics Honeycomb, diameter 50 mm, length 78 mm),

7 is a graph showing the emission concentration of NOx emitted from a flame combustor supported with catalytic combustion.

<Description of the symbols for the main parts of the drawings>

(1): Mixer (2): Catalyst Layer

(3): flame combustion chamber (4): exhaust gas

(5) Corrugated sheet (6): Flat metal

(7): bent thin plate (8): bent thin plate

The present invention provides a combustion method for suppressing NOx generated from a high load combustor, wherein in the catalyst layer (2), a part of the mixer (1) is catalytically burned by a catalyst surface reaction to produce a lean mixer (1) as heat generated at this time. A catalytic combustion step of heating and increasing the combustion speed of the mixer, and rotating the mixer in the wake to inflame it;

Combustion method of exhausting NOx-reduced exhaust gas through a flame combustion step of stably burning the remaining heated lean mixer (1) in the flame combustion chamber (3) installed at the rear of the catalyst layer (2) by the increased combustion speed of the mixer. to be.

In addition, the present invention is a combustor for suppressing NOx generated from a high load combustor, a catalyst layer (2) for raising a part of the mixer by the combustion reaction by the catalytic reaction, and a mixer having a temperature rise at the rear end of the catalyst layer to flame combustion It consists of the flame combustion chamber 3 which combusts by fire.

Hereinafter, the present invention will be described in detail with reference to the accompanying drawings.

FIG. 1 is a schematic structural diagram of a flame combustor supported by catalytic combustion. The flame combustor supported by catalytic combustion includes a catalyst layer 2 and a flame combustion chamber 3.

In the catalyst layer 2, a part of the mixer 1 is combusted by the catalyst surface reaction, and the mixer 1 is heated as heat generated at this time. The heated mixer enters the flame combustion chamber 3 installed at the rear end of the catalyst bed, generates flame combustion, completes combustion, and is then discharged into the exhaust gas 4. The role of the catalyst layer 2 serves to maintain the temperature of the mixer at a high temperature of 800 ° C. or more so that flame combustion can be stably maintained at the rear end of the catalyst layer. The higher the temperature of the mixer entering the flame combustion chamber 3, the higher the flame propagation speed (combustion rate) of the mixer.

2 is a result of calculating the flame propagation velocity according to the change of the temperature of the mixer entering the flame combustion chamber when the fuel concentration is 2.94% lean concentration.

As shown, the flame propagation velocity is below 1 m / sec at mixer temperatures below 600 ° C, but increases exponentially to 1.9 m / sec at 875 ° C, 9.0 m / sec at 1023 ° C, and 30.8 m / sec at 1106 ° C. do. The temperature of the mixer entering the flame combustion chamber is determined according to the degree of surface reaction of the mixer in the catalyst layer 2. In the flame combustion chamber 3 the flame is stabilized at the point where the mixer speed and flame propagation speed are in equilibrium.

In high load combustors such as boilers and gas turbine combustors, the speed of the mixer is usually very high, typically 10-30 m / sec. However, the flame propagation velocity of the mixer at room temperature is 1 m / sec or less as shown in FIG. Therefore, in order to achieve stable combustion by supplying a mixer at room temperature, an additional flame retarder is required. In particular, as the concentration of the mixer becomes thinner, the combustion rate decreases dramatically, making the flame more difficult to stabilize.

Therefore, in lean combustion developed as one of the low NOx technologies, combustion becomes very difficult without the support of catalytic combustion.

The present invention is a catalytic combustor composed of the catalyst layer (2) and the flame combustion chamber (3) serves to increase the temperature of the mixer by the catalytic reaction so that the flame combustion is stable.

The catalyst used for the catalyst layer 2 generally uses many ceramic honeycombs.

However, in the present invention, a metal honeycomb using a metal instead of ceramic is used as a support for the catalyst.

Figure 3 shows the structure of the metal honeycomb used in the present invention. The metal support can withstand high temperatures, and especially has a strong thermal shock effect compared to the ceramic.

The metal honeycomb is preferably in the presence of aluminum in the metal component so that a catalytic material such as platinum or palladium can be coated well.

There may be various methods for making honeycomb shapes using metal, but the most effective method is a method of assembling the flat plate 6 and the flexible thin plate 5 as shown in FIG. 3.

In the assembly method, when the curved thin plate 5 is combined on the metal flat plate 6 and wound into a cylindrical shape, it becomes a honeycomb shape.

The metal honeycomb is coated with a catalyst to be used as a catalyst layer.

The catalyst layer carries a noble metal or metal oxide catalyst.

In addition, in the present invention, when assembling the metal honeycomb as shown in FIG. 3, the direction of the hole passing through the mixer is inclined with the direction of the combustor.

4 shows the case of the bent thin plate 7 without inclination, and FIG. 5 shows the case of the bent thin plate 8 with inclination.

When the curved thin plate is inclined, when the honeycomb as shown in FIG. 3 is molded, the direction of the mixer flow is inclined in the direction of the combustor. This allows the mixer to swing in the wake of the metal honeycomb.

If turning occurs after the catalyst body, the flame flame function can be improved by turning. The flame stability is enhanced by adding flame retardation by catalytic combustion and swing.

In order to stably burn the lean premixer, flame burning with catalytic combustion support is used, and the stability of the flame can be further increased by adding turning to the mixer coming out of the catalyst bed.

This allows the combustion of lean mixers that are not capable of stable combustion without the support of catalytic combustion, thereby enabling low NOx combustion.

Hereinafter is a preferred embodiment of the present invention.

"Example"

The catalyst-supported combustor used in this experiment was equipped with a catalyst bed at the front and a flame combustion chamber at the rear of the catalyst bed as shown in FIG.

The inner diameter of the combustor was 52 mm and the outside was insulated (50 mm thick) using a ceramic insulator (130 kg / m ³ ) to insulate the combustor.

The catalyst layer was tested by combining a catalyst carrying 56 mm of Pd (2.0 wt%) in the front and a catalyst carrying 26 mm of Pt (2.0 wt%) in the rear. The total size of the catalyst layer was 78 mm in length and 50 mm in diameter.

The flow rate of the combustion air was controlled by a mass flow controller, and an electric heater was used to preheat the combustion air.

LNG was used as gas fuel (CH ₄ 90.2%, C ₂ H ₆ 6.5%, C ₃ H ₈ 2.3%, etc.) and a porous nozzle was used to mix with the preheated air.

The flow rate of the gas was controlled using a mass flow controller.

A rectifier mixer was used for uniform mixing of air and gas.

A flame combustion chamber of 1300 mm length was installed at the rear end of the catalyst layer.

300 cell / in ² honeycomb (diameter 50 mm, cordierite 50%, mullite 50%) was used as a catalyst carrier to be used in this experiment.

The film on the surface of the honeycomb and the support of the catalyst material were simultaneously carried out.

First, Pd (NO ₃ ) ₂ and the coating agent γ-Al ₂ O ₃ sol were mixed together as a catalyst material, followed by stirring for 12 hours.

Al (NO ₃ ) ₃ .9H ₂ O was added to the sol as a binder in order to coat the catalyst material and the coating agent on the honeycomb surface.

The prepared honeycomb was immersed in the sol mixed with the catalyst material and the coating agent, and then taken out, and the excessively agglomerated portion in the honeycomb cell was blown off with an air gun.

The honeycomb coated with the catalyst material and the coating agent was then dried at 100 ° C. for 12 hours in a drier.

The dried honeycomb was calcined again at 600 ° C. for 6 hours in a kiln.

The content of the coating agent (alumina) and the catalytic material (palladium) coated on the honeycomb was 20% and 2.0% based on the honeycomb, respectively.

After the firing was completed, the honeycomb was subjected to aging at 1200 ° C. for 24 hours.

On the other hand, the platinum catalyst was prepared using H ₂ PtCl ₆ as a catalyst and the others were carried out in the same manner as the preparation of the palladium catalyst.

The platinum content was 2.0% based on the honeycomb basis.

FIG. 6 shows the results of measuring conditions under which the catalytic reaction is extinguished in the catalyst bed and conditions under which flame is extinguished in the flame combustion chamber when the mixer speed is supplied at 23.2 m / sec.

Flame extinguishing in the flame retardant chamber has been shown to be greatly influenced by the fuel concentration of the mixer.

For example, at a fuel concentration of 2.9%, the flame was extinguished at the preheat temperature of the mixer at 670 ° C. When the preheating temperature of the mixer was above 670 ° C, a stable flame was maintained, and below 670 ° C, the flame was extinguished.

As the fuel concentration increased to 4.2%, the fire extinguishing temperature decreased significantly to 320 ° C.

On the other hand, catalytic reaction digestion in the catalyst bed was not significantly affected by the fuel concentration.

For example, at 2.9% fuel concentration, the catalyst bed was digested at 460 ° C in the preheat temperature of the mixer, and at 400 ° C when the fuel concentration increased to 4.2%.

In order to stably combust the mixer through the catalytic combustion-supported combustor, the catalytic reaction must be maintained in the catalyst bed, and the flame combustion must be maintained in the flame combustion chamber.

These stable combustion conditions are indicated by the stable combustion region in FIG.

As shown, the stable combustion region A is the result obtained by using a ceramic honeycomb having no turning action.

The stable combustion zone A is determined by the conditions under which the flame is extinguished at a fuel concentration of 3.7% or lower, and by the conditions under which the catalytic reaction is extinguished at a fuel concentration of 3.7% or higher.

It is economical to achieve stable combustion under conditions where the preheating temperature of the mixer is as low as possible in a combustor supported on catalytic combustion.

It can be seen from FIG. 6 that there is room to improve the stable combustion region A to the stable combustion region B indicated by the dotted line in the region having a fuel concentration of 3.7% or less.

In order to improve the stable combustion region A to the stable combustion region B, a method of suppressing the extinguishing of the flame in the flame combustion chamber is required.

That is, there is a need for a method in which the preheating temperature at which the flame is extinguished in the flame combustion chamber is lower than the preheating temperature at which the catalytic reaction is extinguished at a fuel concentration of 3.7% or less.

These methods include increasing the combustion rate of the mixer in the flame combustion chamber or improving the flame flame function of the flame.

Since the combustion rate of the mixer has been sufficiently increased by the catalytic reaction of the catalyst bed, there remains a method of improving the flame flame function.

In the present invention, the apparatus as shown in FIG. 5 was invented in such a way as to turn the flow of the mixer in the catalyst bed.

The mixer passing through the catalyst bed undergoes catalytic reaction in the catalyst bed, and at the same time, turning occurs in the mixer, thereby improving flame flame function at the rear of the catalyst bed.

When the flame retardant function by turning in the catalyst layer is added, it is possible to improve from the stable combustion region A to the stable combustion region B. FIG.

7 is a result of measuring the amount of NOx generated from the flame combustor supported by catalytic combustion. When the concentration of fuel was maintained at 2.0 ~ 4.0%, NOx emission was very low as 2.0 ppm (15% oxygen).

Considering that the lower combustion limit of methane is about 5.0%, the catalytically supported combustor can operate stably at 2.0 to 4.0% lower than the lower combustion limit, and the amount of NOx generated is less than 2.0 ppm. Showed very low values.

As described above, the combustor supporting the catalytic combustion of the present invention can operate stably at a condition lower than the lower combustion limit, and the amount of NOx generated at this time is very low, and its effectiveness when used in a combustor for a boiler, a gas turbine, a hot air generator, and the like. This is expected to have a high effect.

Claims (5)

In the combustion method for suppressing NOx generated from a high load combustor, In the catalyst layer 2, part of the mixer 1 is catalytically burned by the catalyst surface reaction, and the heat generated at this time is used to heat the lean mixer 1 to increase the combustion speed of the mixer, and to rotate the mixer afterwards to inflame the flame. Catalytic combustion step, Combustion method of exhausting NOx-reduced exhaust gas through a flame combustion step of stably burning the remaining heated lean mixer (1) in the flame combustion chamber (3) installed at the rear of the catalyst layer (2) by the increased combustion speed of the mixer. A low NOx combustion method combining catalyst combustion and swirl generation of a catalyst layer, characterized in that. In the combustor for suppressing NOx generated from the high load combustor, A catalyst layer 2 for raising a temperature of a part of the mixer by combustion by a catalytic reaction, A low NOx combustor combining the combustion of catalyst combustion and the catalyst layer, characterized by comprising a flame combustion chamber (3) which burns a temperature-rise mixer at the rear end of the catalyst layer by flame combustion. The catalyst layer (2) according to claim 2, wherein the catalyst layer (2) uses a metal honeycomb, and a catalyst containing at least one selected from a precious metal and a metal oxide catalyst is used. burner. 4. The catalytic combustion and the turning of the catalyst layer according to claim 3, wherein the metal honeycomb is formed by combining a curved thin plate 5 on a flat plate 6 and winding it in a cylindrical shape so that the passage of the mixer becomes spiral with respect to the central axis. Low NOx combustor combining generation. 5. The low NOx combustor according to claim 4, wherein the curved thin plate (5) is a curved thin plate with an inclination.