JPS61293532A - Prevention method for catalyst poisoning in shut-down period of catalytic denitration apparatus - Google Patents

Abstract

PURPOSE:To prevent the poisoning of a catalyst in a shut-down period of a catalytic denitration apparatus by keeping a denitration catalyst layer in <=70% relative humidity and preventing an alkaline content contained in dust stuck on the catalyst from penetrating into the catalyst. CONSTITUTION:In a catalytic denitration apparatus 1, after the inside of the apparatus 1 is purged with air so that raw gas does not remain in the inside of the apparatus when a combustion installation is stopped, the ducts of the inlet and outlet parts of the apparatus are closed with the dampers and an exhaust vent 6 provided to a top of the apparatus 1 is opened to perform the moisture control of the inside of the apparatus. The relative humidity of the inside of the apparatus is controlled in 50-<=70% by providing a moisture sensor 7 near to the exhaust vent 6, detecting the relative humidity of the inside of the apparatus and actuating a heater 5 for air heating. In such a way, the poisoning of the catalyst due to the alkaline content contained in the dust stuck on the catalyst is prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) This invention describes a system for catalytically denitrifying nitrogen oxides (NOx) in combustion exhaust gas in the presence of ammonia (NH). This invention relates to a method for preventing catalyst poisoning.

(Conventional technology) Conventionally, nitrogen oxides (NOx) contained in exhaust gas from point, diesel, municipal waste incinerators, and sintering furnaces were converted into nitrogen and water using a catalyst in the presence of ammonia (NH). There is an exhaust gas treatment method that decomposes it to the point where it becomes harmless. The shape of the catalyst used can be roughly divided into two types: honeycomb shape and pellet shape. The catalyst is poisoned by the adhesion of alkaline components such as Na and other substances contained in the dust in the exhaust gas.
Since performance deteriorates over time, it is necessary to replace the catalyst or regenerate the catalyst when the performance falls below expected performance.

Furthermore, since the catalyst layer is the so-called heart of the exhaust gas treatment device, the entire device must be stopped when replacing the catalyst, and the cost of replacing the catalyst is high, so it is necessary to avoid catalyst poisoning as much as possible.

(Problems to be solved by the invention) By the way, catalyst poisoning due to the above-mentioned adhesion of alkaline components is
When the relative humidity is high due to the influence of moisture (relative humidity is 7
0% or more, the effect appears strongly), and it progresses significantly,
It has been found that in cases where the catalytic denitrification equipment is repeatedly started and stopped during operation, the temperature inside the catalytic reactor decreases and the relative humidity of the atmospheric gas increases when the catalytic denitrification device is stopped, causing a problem in which the catalyst is significantly poisoned.

Therefore, the present invention attempts to avoid catalyst poisoning by adjusting the humidity when the catalyst denitrification device is stopped.

(Means for Solving the Problems) The present invention is a method for preventing poisoning of a denitrification catalyst, which is characterized by maintaining the denitrification catalyst layer at a relative humidity of 70 degrees or less when the catalytic denitrification equipment is stopped. The denitration catalyst to be used uses a ceramic material such as titanium oxide or copillite as a carrier, and vanadium oxide, tungsten oxide, iron oxide, chromium oxide, etc. alone or in combination as an active ingredient. Note that the humidity in the denitrification catalyst layer can be reduced, for example, by slightly blowing heated air.

(Function) The method for preventing catalyst poisoning of the present invention will be explained in detail based on the catalytic denitration apparatus shown in FIG.

The combustion exhaust gas containing NOx, that is, the raw gas G, is sent to the catalytic denitrification device 1. When passing through the gas, NOX is removed and the gas becomes clean. A catalytic denitrification device 1 is filled with a catalyst 2. Before the raw gas G1 enters the catalytic denitration equipment t, NO
NH3 is used as a reducing agent for x, NH, supply equipment 3. From the spray nozzle 4. When the mixed gas of the raw gas G passes through the catalyst 2, NOx and gas undergo the following reaction to decompose into N2 and H, and NOx is rendered harmless.

4NO+ ANH1+ O, → 4N, + 6H,0・
・・・・・・・・・・・・・・・・・・・・・ (1)6
NO, +8N)1. → 7N, + 128,0...
・・・・・・・・・・・・・・・・・・ (2) Furthermore,
The ash is discharged through the rotary valve 8 at the bottom of the catalytic denitrification device t.

When the combustion equipment is stopped, the catalyst denitration equipment is also stopped in parallel, but on the contrary, the catalyst poisoning prevention equipment according to the present invention is started. In other words, when the combustion equipment is stopped, the inside of the catalytic denitrification equipment is purged with air to prevent raw gas from remaining inside the equipment, and after minimizing residual moisture, the inlet and outlet of the catalytic denitrification equipment are Close the duct with a damper and catalytic denitration equipment 1. A humidity sensor 7 is installed above the catalyst 2 near the exhaust vent 6 to detect the relative humidity inside the device.
Activate the air heater 5 to lower the relative humidity inside the device to 50.
Control to 70 inches or less (preferably 50% or less). The air heater 5 is of an electric type, or when using gas or oil combustion, indirectly heats the air to prevent introduction of moisture as much as possible when heating the air.

(Example) A catalytic denitrification device was filled with a honeycomb type catalyst consisting of 90% Tie as a carrier and 10% V2O as an active metal to treat exhaust gas from a municipal waste incinerator. The operation of the catalytic denitrification apparatus was stopped in a state in which the collected ash from the exhaust gas adhered to the catalyst in an amount equal to the volume of the catalyst. The room temperature was 20°C. The relative humidity of the atmospheric gas in the catalyst layer is O~
The catalyst was forcibly poisoned by changing 100%.
As can be seen from Figure 2, the denitrification performance after poisoning was measured against the denitrification performance of the fresh catalyst measured in advance, and the decrease in activity during that time was illustrated in relation to relative humidity. When the relative humidity exceeds 50 degrees, catalyst deterioration occurs.1
Deterioration becomes noticeable at 70% or more.

From this, the relative humidity of the atmospheric gas in the catalyst layer is set to 70%.
It has been found that catalyst poisoning due to alkali content in the dust adhering to the catalyst when the equipment is stopped can be prevented by adjusting the ratio to preferably 50% or less. This figure shows the change in the degree of catalyst deterioration by comparing cases in which catalyst poisoning prevention equipment is installed and not installed during repeated shutdowns of the catalyst denitrification equipment. It turns out that prevention is important.

(Effect of the invention) When the equipment is shut down, the relative humidity inside the catalyst denitrification equipment is adjusted to a low level, so the alkali content in the dust attached to the catalyst does not enter the catalyst9, and poisoning of the catalyst can be prevented. .

[Brief explanation of drawings]

Fig. 1 is a conceptual diagram of a catalytic denitrification device equipped with means for carrying out the catalyst poisoning prevention method of the present invention, and Fig. 2 shows the degree of deterioration of the catalyst when the relative humidity of the denitrification catalyst layer is changed. FIG. 3 is a diagram showing the relationship between relative humidity and the degree of catalyst deterioration, assuming the operation of a denitrification treatment device for exhaust gas from a municipal waste incinerator. Sub-agents 1) Meifuku agent Ryo Hagiwara - Sub-agent Atsuo Anzai Figure 1 Figure 2 Relative humidity (5) Figure 3 Operating time

Claims (1)

[Claims] When the catalytic denitrification equipment is stopped, the denitrification catalyst layer is kept at a relative humidity of 70%.
A method for preventing poisoning of a denitrification catalyst, characterized by maintaining the following: