JPH031053B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a denitrification device for drying a denitrification medium in a denitrification reactor.

For example, in a denitrification device that targets combustion exhaust gas from boilers, etc., the exhaust gas is passed through a denitrification reactor with a built-in denitrification catalyst, and then injected into the upstream side of the denitrification reactor.
_NH3 converts NOx in exhaust gas into harmless nitrogen ( _N2 )
and water (H ₂ O).

Figure 1 shows a typical flue system of a boiler equipped with a denitrification device.

The combustion air in the air duct 1 is pressurized by a forced draft fan (hereinafter referred to as FDF) 2, heated by the exhaust gas from the exhaust gas duct 4 in an air preheater (hereinafter referred to as A/H) 3, and then heated by the exhaust gas from the exhaust gas duct 4. It is supplied from box 5 to boiler 6.

On the other hand, the exhaust gas combusted in the boiler 6 is denitrated by the denitration catalyst 8 of the denitration reactor 7 through the exhaust gas duct 4, and then the exhaust heat is recovered by the A/H 3.

Thereafter, the exhaust gas is pressurized by an electric precipitator 9 and an induced draft fan (hereinafter referred to as IDF) 10, and is released into the atmosphere from a chimney 11.

However, the denitrification catalyst 8 in the denitrification reactor 7 deteriorates over time, and
The cause of deterioration is sulfur oxides (SOx) in the exhaust gas.
) and those caused by alkali metals such as sodium (Na) and potassium (K) in the duct.

For example, poisoning by SOx occurs when the exhaust gas temperature is approximately 250
It occurs in a low temperature section below ℃, and SO ₃ and H ₂ O in the exhaust gas react with the added NH ₃ on the surface of the denitrification catalyst 8 to form acidic ammonium sulfate (NH ₄ SO ₄ ) and ammonium sulfate [(NH ₄ ) ₂ SO ₄ ], ammonium sulfite [(NH ₄ ) ₂ SO ₃ ], and other ammonium sulfate ammonium salt products are generated, which are adsorbed into the catalyst pores of the denitrification catalyst 8 and cause capillary condensation. or cover the surface of the denitrification catalyst 8 to reduce catalytic activity.

However, this poisoning of the denitrification catalyst by SOx is caused by the temperature of the exhaust gas from the boiler 6, and the temperature of the exhaust gas at the outlet of the boiler 6 is 360°C at full load.
℃, 310℃ at 1/2 load and 270℃ at 1/4 load
This is because the temperature decreases depending on the load.

As a means of increasing the temperature of the exhaust gas flowing into the denitrification reactor 7 due to load fluctuations, the temperature of the exhaust gas is increased by causing the exhaust gas to bypass the economizer (not shown) of the boiler 6, which is a so-called economizer bypass. Therefore, poisoning of the denitrification catalyst 8 by SOx is prevented.

On the other hand, the denitrification catalyst 8 deteriorates due to alkali metals, which deteriorates slowly during normal operation of the boiler 6 and does not pose a particular problem.

However, if a tube breakage accident occurs in the boiler 6, the boiler 6 will be stopped immediately, and the boiler 6 itself will be unilaterally forcibly cooled by the combustion air from the air duct 1 using the FDF 2. The steam and water leaking from the tube are entrained in the exhaust gas discharged from the boiler 6 and become highly humid gas. At temperatures below about 100°C, water is entrained in the denitrification reactor 7 placed downstream. catalyst 8
However, the mist causes a sudden drop in performance.

This is because when mist (or water) adheres to the surface of the denitrification catalyst 8 due to a tube breakage accident, Na and K in the dust that had previously adhered to the surface of the denitrification catalyst 8 enter the pores of the denitrification catalyst 8 using the mist as a medium. This is to get into.

Therefore, if the performance of the denitrification catalyst 8 deteriorates due to such a tube breakage accident of the boiler 6,
As shown in FIG. 2, the denitrification catalyst 8 was washed with water.

In FIG. 2, 12 is a water washing line.

That is, after the operation of the boiler 6 is stopped, the denitrification catalyst 8 is sprayed with water from the water washing line 12 to thoroughly wash away the poisonous components that have entered the pores of the denitrification catalyst 8, and then the denitrification catalyst 8 is thoroughly washed away with water. The boiler 6 is started up using fuel with few duct components, and the exhaust gas is passed through the denitration catalyst 8 of the denitration reactor 7 to dry the denitration catalyst 8. After drying the denitration catalyst 8, the boiler 6 is returned to normal operation. A method was taken to bring it back.

However, in the conventional drying method using a fuel with low duct components such as light oil, the upstream exhaust gas duct 4 of the denitrification reactor 7 is used for drying by directly using the exhaust gas duct 4 after the boiler 6 has stopped operating. The dust that had accumulated inside the denitrification catalyst 8 was accompanied by the exhaust gas during drying and reattached to the denitrification catalyst 8, and even though the poisonous components were washed with water, the dust that had accumulated during the drying process reattached and reattached to the denitrification catalyst 8. This has the disadvantage that it is poisoned and the cost of light oil fuel for the drying process increases.

The present invention attempts to eliminate such conventional drawbacks, and its purpose is to dry the denitrification catalyst that has been washed with water using heated air, thereby saving the fuel cost for drying the denitrification catalyst. It is something.

In order to achieve the above-mentioned object, the present invention provides a first denitrification reactor with a built-in catalyst and a first air preheater along the gas flow direction of the first exhaust gas duct, and a first air preheater is covered with the first air preheater. A first air duct is connected to the heating section side, and a second denitration reactor with a built-in catalyst and a second air preheater are installed along the gas flow direction of the second exhaust gas duct. The object is a denitrification device in which a second air duct is connected to the heated part side, and a water washing line for washing the catalyst in the reactor with water is connected to the first denitrification reactor and the second denitrification reactor, respectively. be.

A first drying air pipe extending from the first air preheater outlet side of the first air duct to the second denitrification reactor inlet side of the second exhaust gas duct is connected to the second air pipe of the second air duct. A second drying air pipe extending from the preheater outlet side to the first denitrification reactor inlet side of the first exhaust gas duct is connected, and the catalyst is dried from the operating air duct of the air ducts to the stopped exhaust gas duct. The apparatus is characterized in that it is configured to supply high-temperature air for drying through the drying air piping.

Embodiments of the present invention will be described below with reference to FIG.

FIG. 3 shows a case where the boiler 6 has two air systems and two exhaust gas systems, and numerals 1 to 12 are the same as those in the conventional system. The denitrification device 7 is one that is alternately washed with water, and those that are in operation are distinguished by an A after the code, and those that have stopped operating and are being washed with water are distinguished by a B after the code.

13 is an exhaust gas bypass duct that connects the exhaust gas ducts 4A and 4B, and 14A and 14B are drying units that supply high-temperature air for drying the denitrification catalysts 8A and 8B from the air duct 4A to the denitrification device 8B and from the air duct 1B to the denitrification device 7A, respectively. air piping, 15A,
15B, 16A, 16B are inlet dampers and outlets of the denitrification devices 7A, 7B, 17A, 17B are air dampers of the drying air pipes 14A, 14B, 18 are exhaust gas dampers of the exhaust gas bypass duct 13, 19
A, 19B, 20A, 20B are water washing lines 12
A, 12B inlet and outlet valves.

In such a structure, during normal operation of the boiler 6, the inlet valves 19A, 19B and the outlet valves 20A, 20 of the water washing lines 12A, 12B are closed.
B. Exhaust gas damper 1 of exhaust gas bypass duct 13
8 and the air dampers 17A, 17B of the drying air pipes 14A, 14B are closed, and the other dampers 15
A, 15B, 16A, 16B are open and boiler 6
The exhaust gas flows into the exhaust gas ducts 4A and 4B.

Next, a case will be described using as an example a case in which the upper half with A after the symbol in FIG. 3 is in operation, and the lower half with B after the symbol is stopped to wash and dry the denitrification catalyst 8B.

First, when washing the denitrification catalyst 8B with water, the inlet damper 15B of the denitrification reactor 7B is closed to block the flow of exhaust gas to the exhaust gas duct 4B, and the exhaust gas is passed from the exhaust gas bypass duct 13 to the exhaust gas duct by opening the exhaust gas damper 18. Flow exhaust gas only to 4A. and
The operation of FDF2B also stops.

In this way, close the inlet damper 15B and
By stopping the exhaust gas duct 4B and air duct 1B in the lower half of FIG.
A: It is completely disconnected from the air duct 1A.

And the inlet valve 19 of the flush line 12B
B. Open the outlet valve 20B and flush the water line 12.
The alkali metal on the denitrification catalyst 8B is washed with water from B and removed.

Next, the denitrification catalyst 8B that has been washed with water is transferred to the water washing line 12.
The inlet valve 19B and outlet valve 20B of B are closed for drying, but in the present invention, this water-washed denitrification catalyst 8B is dried by high-temperature air from the drying air pipe 14A.

In other words, the air damper 1 of the drying air pipe 14A
7A is opened, a part of the combustion air heated to 250 to 350°C by A/H3A is diverted from the air duct 1A to the drying air pipe 14A, and the denitrification reactor 7
The denitrification catalyst 8B supplied to B and washed with water is dried.

When the drying of the denitrification catalyst 8B is completed, the air damper 17A is closed, the inlet damper 15B is opened, and the FDF 2B is operated to return to normal operation.

In this way, the water-washed denitrification catalyst 8B can be dried with the drying air from the other system A/H3A that is in steady operation, so that dust does not re-adhere to the water-washed denitration catalyst 8B during drying. Therefore, the cost of fuel (light oil) for drying the denitrification catalyst 8B can be reduced.

The one in FIG. 4 shows another embodiment of FIG. 3, and the one in FIG. 3 has two systems of air ducts 1A, 1B and exhaust gas ducts 4A, 4B. The explanation was based on the case where the side is in normal operation and the air duct 1B and exhaust gas duct 4B are rinsing and drying the denitrification catalyst 8B, but in the case shown in Figure 4, both air ducts 1A and 1B were damaged due to an accident in boiler 6. This is an example of a case where the program is stopped.

In FIG. 4, only the A system of FIG. 3 is shown for convenience of explanation.

In FIG. 4, 21A is a denitrification bypass gas duct, and 22A is a damper of the denitrification bypass gas duct 21A.

For example, if a tube breakage accident occurs in the boiler 6, in order to prevent the denitration catalyst 8A from deteriorating,
The inlet damper 15A of the denitrification reaction 7A is closed, and the damper 22A is opened to allow the exhaust gas to flow to the exhaust gas duct 4A, the denitration bypass gas duct 21A, and the exhaust gas duct 4A.

High-temperature air from the in-house boiler or another adjacent plant is supplied to the drying air pipe 14B, and the water-washed denitrification catalyst 8A is dried by the high-temperature air from the other plant. The explanation is the same as that in FIG.

In the present invention, a drying air pipe for drying the catalyst is provided from the air duct in operation to the exhaust gas duct in the stopped operation, so that the catalyst washed with water can be dried by this drying air. Re-poisoning due to re-deposition of dust is prevented, and fuel costs for drying the denitrification catalyst can be reduced.

[Brief explanation of the drawing]

Figure 1 is a system diagram showing the boiler smoke duct system.
FIG. 2 is a system diagram showing the water washing and drying steps of a conventional denitrification catalyst, and FIG. 3 is a system diagram showing the water washing and drying steps of the present invention. FIG. 4 is a system diagram showing another embodiment of FIG. 3. 1A, 1B...Air duct, 3A, 3B...
A/H, 4A, 4B...Exhaust gas duct, 7A, 7
B...Denitration reactor, 8A, 8B...Denitrification catalyst, 1
2A, 12B...Washing line, 17A, 17B...
...Air piping for drying.

Claims (1)

[Claims] 1. Along the gas flow direction of the first exhaust gas duct,
A first denitrification reactor containing a catalyst and a first air preheater are provided, and a first air preheater is provided on the side to be heated of the first air preheater.
The air duct is connected, and a second denitrification reactor with a built-in catalyst and a second air preheater are installed along the gas flow direction of the second exhaust gas duct. In the denitrification device, two air ducts are connected, and a water washing line for washing the catalyst in the reactor is connected to the first denitrification reactor and the second denitrification reactor, respectively, the first air preheating of the first air duct. A first drying air pipe extending from the outlet side of the denitrification reactor to the inlet side of the second denitrification reactor of the second exhaust gas duct is connected to the first drying air pipe extending from the outlet side of the second air preheater of the second air duct to the A second drying air pipe extending to the inlet side of the denitrification reactor is connected, and high-temperature air for drying the catalyst is passed from the operating air duct of the air ducts to the stopped exhaust gas duct through the drying air pipe. A denitrification device configured to supply