JPH06343828A - Waste gas treatment - Google Patents

Abstract

PURPOSE:To attain the improvement of dust collecting efficiency, the prevention of pressure loss and the improvement of economization, etc., to also attain a sufficient application to existing equipment, to efficiently remove nitrogen oxide from waste gas, and to also easily make a bag filter. CONSTITUTION:A reducing agent for nitrogen oxide and a reducing catalyst are injected from a reducing agent jetting device 4 and a reducing catalyst jetting device 5 to waste gas on the upstream side of a bag filter installed in a waste gas filter 6 to reduce the nitrogen oxide in the waste gas until the reducing catalyst reaches filter cloth of the bag filter, and the reducing catalyst is collected by the bag filter. The nitrogen oxide in the waste gas which has not been reduced before it reaches the filter cloth is reduced by the catalyst collected by the filter cloth and discharged in the air. Thus, nitrogen oxide is removed from waste gas by using filter cloth currently in use without a special treatment being newly made on the filter cloth.

Description

Detailed Description of the Invention

[0001]

[Field of Industrial Application] The present invention purifies exhaust gas generated from a boiler of a power plant, an incinerator of municipal solid waste, an incinerator of industrial waste, a sinter of iron making, etc., containing acid gas, nitrogen oxides, and dust. Exhaust gas treatment method.

[0002]

2. Description of the Related Art Conventionally, in order to purify this kind of exhaust gas, for example, a method shown in the system diagrams of FIGS. 3 to 5 is known.

Explaining one example thereof, as shown in FIG. 3, first, high temperature exhaust gas generated from the incinerator 31 is guided to a cooling device 32 and cooled to a temperature suitable for exhaust gas treatment. Next, the acidic gas absorbent is sprayed from the acidic gas absorbent spraying device 33 to the exhaust gas, and the acidic gas such as HCl and SOX in the exhaust gas is absorbed by the acidic gas absorbent and removed. Next, the exhaust gas is guided to the exhaust gas filtering device 34, and the bag filter removes soot and dust from the exhaust gas. Although the acidic gas and the soot and dust are removed in this manner, the exhaust gas in which the nitrogen oxides have not been treated is exhausted to the atmosphere by the exhaust device 35 including a chimney, an exhaust fan, and the like.

As another conventional example, as shown in FIG. 4, a reducing agent of a nitrogen oxide is injected from a reducing agent spraying device 36 into a high temperature exhaust gas generated from an incinerator 31 to perform high temperature reduction, After that, as in the above-described conventional example shown in FIG. 3, the acidic gas in the exhaust gas and soot and dust are removed, and the air is exhausted to the atmosphere by the air exhaust device 35.

As another conventional example, as shown in FIG. 5, the exhaust gas cooled by the gas cooling device 32 is sprayed with an acidic gas absorbent from an acidic gas absorbent spraying device 33,
The acid gas in the exhaust gas is removed, then the exhaust gas is guided to the exhaust gas filtering device 34, the dust filter in the exhaust gas is removed by the bag filter, and a denitration device 37 is additionally provided as an environmental measure, and a reducing agent injection device is provided. The exhaust gas from which the reducing agent has been injected from 36 is guided to the denitration device 37 to remove nitrogen oxides in the exhaust gas, and the exhaust gas from which acid gas, soot dust and nitrogen oxides have been removed is exhausted to the atmosphere by the exhaust device 35.

However, in the treatment method of FIG. 3, no nitrogen oxide is treated, which causes environmental pollution. Further, in the treatment method of FIG. 4, nitrogen oxide can be reduced and removed to some extent, but since no catalyst is used, the removal rate is low, which still causes environmental pollution. The treatment method shown in FIG. 5 is the most desirable from the viewpoint of preventing environmental pollution, but there is a problem that not only the construction cost and maintenance cost of the denitration device 37 become expensive, but also a wide site is required.

In order to solve the above conventional problems,
Japanese Patent Publication No. 3-69570, Japanese Patent Laid-Open No. 1-293123.
Recently, as described in Japanese Patent Publication No. 1993-242, etc., an acidic gas absorbent and a reducing agent of nitrogen oxides are recently injected into cooled exhaust gas, and the produced reaction product and the residual acidic gas absorbent are reduced together with other soot dust. There has been proposed an exhaust gas treating apparatus and a treating method in which a catalyst is collected by a bag filter previously loaded, and nitrogen oxide is brought into contact with a reducing catalyst to be reduced by a reducing agent.

[0008]

However, in the prior art as described above, it is necessary to use a thick filter cloth to support the catalyst on the filter cloth, and the pressure loss of the exhaust gas passing through this filter cloth is Compared with the case of ordinary filter cloth, it becomes significantly larger. Further, in order to support the catalyst on the filter cloth, after dipping the filter cloth in the liquid mixed with the catalyst powder, the filter cloth is pulled out from the solution to perform surface treatment curing, and the filter cloth after curing is adjusted with another adjusting liquid. It is dipped in, and dried and baked. As a result, the catalyst is carried on the filter cloth with its eyes closed, so that the pressure loss of the exhaust gas passing through the filter cloth is further increased.
Moreover, it is significantly more expensive than the commonly used filter cloth. Further, when the catalyst is exposed to exhaust gas for a long time, the catalytic activity is lost due to impurities in the exhaust gas, but as described above, the catalyst is supported on the filter cloth and is not newly replenished. The reduction efficiency gradually decreases. In order to prevent this, the entire bag filter carrying the catalyst must be replaced relatively often, which is not economically disadvantageous, and exhaust gas treatment cannot be performed during that time, so replacement work is not possible. Subject to time constraints. In addition, the filter cloth, when used for a certain period of time, has its surface covered with soot and dust in the exhaust gas and causes a large pressure loss of the exhaust gas, so it is necessary to perform backwashing as appropriate. The existing catalyst peels off and falls off, reducing the reduction efficiency of nitrogen oxides. Furthermore, the catalyst carried on the filter cloth easily falls off when the filter cloth is bent or rubbed, so considerable care must be taken when manufacturing the bag filter, and not only is it troublesome to manufacture. There are problems such as becoming expensive.

The present invention solves the above-mentioned conventional problems, and collects dust on a filter cloth constituting a bag filter,
The optimum material can be selected only by considering the pressure loss of exhaust gas and the price, and moreover, the pressure loss of the ordinary bag filter can be prevented, thus improving the dust collection efficiency and pressure loss. Can be applied to existing equipment, and the efficiency of nitrogen oxide reduction by the catalyst can be improved without the need for frequent bag filter replacement. Therefore, the nitrogen oxides can be efficiently removed from the exhaust gas, and the bag filter can be easily handled during manufacturing. Therefore, the bag filter can be manufactured easily and at low cost. It is an object of the present invention to provide an exhaust gas treatment method made possible.

[0010]

The technical means of the present invention for achieving the above object is to inject a reducing agent for nitrogen oxides and a reducing catalyst for nitrogen oxides into the exhaust gas on the upstream side of the bag filter. Reduce the nitrogen oxides in the, the reducing catalyst is collected by the bag filter, the nitrogen oxides in the exhaust gas that was not reduced before reaching the bag filter is the catalyst collected by the bag filter. It is designed to be reduced.

In the above technical means, a reducing agent for nitrogen oxides such as ammonia is injected into the exhaust gas in a gas state, and vanadium oxide, titanium oxide, tungsten oxide, chromium oxide, iron oxide, copper oxide, oxide A nitrogen oxide reduction catalyst composed of one or more manganese can be injected into the exhaust gas in the form of powder or slurry.

[0012]

According to the present invention, the reducing agent for nitrogen oxides and the reducing catalyst are injected into the exhaust gas on the upstream side of the bag filter to reduce the nitrogen oxides, and the reducing catalyst is provided on the filter cloth constituting the bag filter. Since the filter cloth is not carried in advance, the filter cloth is optimal considering only dust collection, pressure loss of exhaust gas and price without deteriorating the function conventionally used and without new special processing. The material can be selected, and the pressure loss of a normal bag filter can be prevented from exceeding. Moreover, it is possible to constantly replenish a new reducing catalyst to maintain the catalytic activity,
Moreover, since the reduction reaction of nitrogen oxides can proceed while the reduction catalyst is floating in the exhaust gas, the reduction efficiency of nitrogen oxides by the reduction catalyst can be improved without requiring frequent replacement of the bag filter. Can be made. Further, since the reducing catalyst is not previously loaded on the bag filter, the handling at the time of manufacture becomes easy.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a system diagram showing an exhaust gas treatment method in one embodiment of the present invention, and FIG. 2 is an explanatory diagram showing a filtration method by the exhaust gas treatment method.

As shown in FIG. 1, first, high-temperature exhaust gas generated from the incinerator 1 and containing acid gas, nitrogen oxides, and soot is guided to a gas cooling device 2 and cooled to a temperature suitable for exhaust gas treatment.

Next, the exhaust gas from the gas cooling device 2 is sprayed with an acidic gas absorbent such as calcium hydroxide, calcium carbonate, calcium oxide, magnesium hydroxide, magnesium carbonate, magnesium oxide from the acidic gas absorbent spraying device 3. The acidic gas such as HCl and SOX in the exhaust gas is absorbed and removed by the acidic gas absorbent.

Next, a reducing agent injection device 4 and a reducing catalyst injection device 5 sequentially inject a reducing agent of nitrogen oxides and a reducing catalyst of nitrogen oxides into the nitrogen oxide-containing exhaust gas from which the acidic gas has been removed and inject them. To do. As the reducing agent, for example, ammonia is used, and as the reducing catalyst, for example, vanadium oxide, titanium oxide, tungsten oxide, chromium oxide,
Iron oxide, copper oxide, and manganese oxide are used alone or as a selective mixture. At this time, the reducing agent is injected into the exhaust gas in a gas state, and the reducing catalyst is injected into the exhaust gas in a powder or slurry state. By this injection, while the reducing catalyst is suspended in the exhaust gas, a part of nitrogen oxides such as NOX in the exhaust gas is reduced by the reducing agent and is guided to the exhaust gas filtering device 6. As shown in FIG. 2, the exhaust gas filtering device 6 includes a bag filter 8 which has been conventionally used.

Then, as shown in FIG. 2, the exhaust gas G1 passes through the filter cloth 9 of the bag filter 8. At this time, the dust in the exhaust gas G1, the acidic gas reaction product generated after the acidic gas absorbent is injected, the remaining acidic gas absorbent 10 and the reduction catalyst 11 are collected by the filter cloth 9. Nitrogen oxides in the exhaust gas G1 that have not been reduced before reaching the filter cloth 9 by the reducing agent and the reduction catalyst injected on the upstream side of the bag filter 8 pass through the layers collected by the filter cloth 9, Reduction catalyst 11 in that layer
And is easily reduced by the reducing agent that has reached with the exhaust gas. The exhaust gas G that has passed through the filter cloth 9 in this way
No. 2 is purified by removing acidic gas, nitrogen oxides and dust.

Next, the purified exhaust gas is discharged into the atmosphere by an exhaust device 7 including a chimney, an exhaust fan and the like.

The reducing catalyst may be injected into the exhaust gas together with the acidic gas absorbent. In addition, the present invention can be variously modified without departing from the basic technical idea thereof.

[0020]

As described above, according to the present invention, a nitrogen oxide reducing agent and a reducing catalyst are injected into the exhaust gas on the upstream side of the bag filter to reduce the nitrogen oxides. The filter cloth does not have a reducing catalyst pre-loaded on it, so the filter cloth does not lose its conventional function and does not undergo new special processing. The optimum material can be selected by considering only the price and the price, and the pressure loss of the usual bag filter can be prevented from being exceeded. Therefore, the dust collection efficiency can be improved, the pressure loss can be prevented, the economical efficiency can be improved, and the present invention can be sufficiently applied to the existing equipment. Moreover, it is possible to constantly replenish a new reducing catalyst to maintain the catalytic activity,
Moreover, since the reduction reaction of nitrogen oxides can proceed while the reduction catalyst is floating in the exhaust gas, the reduction efficiency of nitrogen oxides by the reduction catalyst can be improved without requiring frequent replacement of the bag filter. Can be made. Therefore, nitrogen oxides can be efficiently removed from the exhaust gas. Further, since the bag filter does not carry the reduction catalyst in advance, the handling at the time of manufacture is simplified, and therefore the bag filter can be manufactured easily and at low cost.

[Brief description of drawings]

FIG. 1 is a system diagram showing an exhaust gas treatment method according to an embodiment of the present invention.

[Fig. 2] When performing exhaust gas treatment by the same exhaust gas treatment method,
Explanatory drawing showing a state in which a catalyst or the like is collected on a filter cloth and formed into a layer

FIG. 3 is a system diagram showing an example of a conventional exhaust gas treatment method.

FIG. 4 is a system diagram showing another example of a conventional exhaust gas treatment method.

FIG. 5 is a system diagram showing still another example of a conventional exhaust gas treatment method.

[Explanation of symbols]

 1 Incinerator 2 Gas Cooling Device 3 Acid Gas Absorption Spraying Device 4 Reducing Agent Injection Device 5 Reduction Catalyst Injection Device 6 Exhaust Gas Filtration Device 7 Exhaust Air Device 8 Bag Filter 9 Filter Cloth 10 Acid Gas Absorbent etc. 11 Reduction Catalyst

Claims (2)

[Claims] 1. A nitrogen oxide reducing agent and a nitrogen oxide reduction catalyst are injected into the exhaust gas on the upstream side of the bag filter to reduce the nitrogen oxide in the exhaust gas, and the reduction catalyst is collected by the bag filter. The exhaust gas treatment method is characterized in that the nitrogen oxides in the exhaust gas that have not been reduced before reaching the bag filter are reduced by the catalyst collected by the bag filter. 2. A nitrogen oxide reducing agent comprising ammonia or the like is injected into an exhaust gas in a gas state to comprise one or more of vanadium oxide, titanium oxide, tungsten oxide, chromium oxide, iron oxide, copper oxide and manganese oxide. The exhaust gas treatment method according to claim 1, wherein the reduction catalyst for nitrogen oxides is injected into the exhaust gas in a powder or slurry state.