JPS5827975B2 - Flue gas denitration method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for removing nitrogen oxides from exhaust gas containing nitrogen oxides by a catalytic reduction reaction method, particularly for efficiently removing nitrogen oxides from the exhaust gas containing oxygen and dust. It is about the method.

Imada: As fossil fuel usage increases and plants become larger, the concentration of nitrogen oxides (NOx) in the atmosphere increases, causing photochemical smog and oxidants.

Therefore, NOx emissions are legally regulated, and
Even if measures are taken to remove or suppress Ox, if the above-mentioned emissions do not fall below the regulation value, the operation of NOx generating sources such as combustion devices is no longer permitted.

Nitrogen oxides (NOx, NO2, N2O5, etc.)
Most of the answers are NO.

The main sources of NO (which will also be explained mainly in this invention) are:
Petroleum combustion equipment, such as power generation boilers, industrial furnaces for chemical conversion, sintering furnaces, cement machines, internal combustion engines, as well as nitric acid plants that use nitric acid and pickling lines at steel works, etc.

Conventionally, many NOx reduction measures have been proposed for each of the above-mentioned generation sources.

Measures for reducing NOx can be roughly divided into suppression methods and removal methods.

The suppression method is a method to reduce the production of NOx by improving combustion by improving burners and exhaust gas recirculation methods.

However, this method has a limit to its reduction rate, and
Not only is it not possible to completely eliminate the generation of , but there are also problems such as the fact that improved burners cannot be applied to sintering machines and the like.

In addition, the removal method is effective in that it can purify more than 90% of NOx, but the removal method has the following advantages: ■ The treatment cost is low, and ■ Long-term stable operation is possible with simple operation. Conditions are imposed, such as (1) not interfering with the operation of main equipment such as boilers, and (2) not causing secondary pollution, and the following problems remain.

First, removal methods are broadly divided into wet methods and dry methods.

The wet method is a method in which No is brought into contact with an oxidizing agent by some method to be converted into higher-order oxides such as NO2, and the oxides are absorbed and removed by water or an absorbing liquid.

This method has problems, such as that the NO oxidizing agent is expensive and that the solution that has absorbed NOx is a secondary pollution component as wastewater, so it must be treated.

The dry method is a method in which NOx is reduced to nitrogen (N2) using some kind of reducing agent in the presence of a catalyst, and this reduction method includes a non-selective catalytic reduction method and a selective catalytic reduction method.

The non-selective catalytic reduction method is a method that uses hydrocarbons (HC), carbon monoxide (CO), etc. as a reducing agent, and when using this method, the oxygen (02) present in the exhaust gas must be eliminated in advance. The reducing agent does not react with NOx but preferentially performs a combustion reaction with 02.

Therefore, the scope of application is narrow because the required amount of reducing agent to be added is equivalent to NOx+02, the combustion reaction heat is high, and the reactor must have heat resistance.

In addition, the selective catalytic reduction method is a method that uses NH3 as a reducing agent, and the amount of NH3 added is
x equivalent is sufficient and is expressed by the following reaction formula.

6NO+4NH3→5N2+6H20 This selective catalytic reduction method also has the following problems.

That is, the exhaust gas to which the denitrification method is applied includes so-called dirty exhaust gas fueled by heavy oil or coke, and various substances present in the exhaust gas have an effect on the catalyst.

For example, sulfur oxides (SOx) and halogen compounds as poisonous substances cause a decrease in catalyst activity, and dust causes clogging of a catalyst bed-passing reactor due to pellet filling.

This problem of catalyst activity deterioration is being solved by imparting poison resistance to the catalyst, but the problem of blockage of the reactor due to dust can be solved by using an electrostatic precipitator, Methods of removing dust using a bag filter, etc., and methods of preventing clogging by increasing the size of the catalyst or moving the catalyst have been adopted.

On the other hand, as a method for providing dust countermeasures in the reactor itself, there is a method in which pellet-shaped catalysts are arranged in a plate shape and brought into contact with the catalyst in a parallel flow, or a method in which a honeycomb-shaped catalyst is used. A method is proposed.

Since the former uses a pellet catalyst, it is economically no different from the above-mentioned catalyst layer passing type reactor, while the latter requires extrusion molding and high-temperature treatment, so it is larger. It is economically disadvantageous because it is inconvenient to use a collection of small pieces because it cannot be processed, and because it is not active as it is and requires the application of a more active phase substance.

Furthermore, a common drawback of both is that the regeneration method at high temperatures cannot be applied because the carrier is a sintered body such as alumina or cordierite.

The present invention improves the method using a honeycomb-shaped catalyst as a dust countermeasure among the selective catalytic reduction methods described above, and relates to a denitrification method using a catalyst using a honeycomb formed from asbestos paper as a carrier. .

That is, the present invention provides a method for selectively reducing and removing nitrogen oxides to nitrogen by adding ammonia as a reducing agent to nitrogen oxide-containing exhaust gas in the presence of a catalyst substance, in which asbestos paper is used as a base material as the catalyst. The gist of this paper is a dry flue gas delithification process characterized by the use of a honeycomb-shaped catalyst.

The process of forming asbestos I paper into a honeycomb shape does not require high-temperature treatment unlike ordinary ceramic carriers, and compared to glass fiber, asbestos paper is difficult to form due to its inherent weakness as a material. It has the advantage of being easy to remove, can be manufactured in a large size, and can significantly simplify the work of transporting the catalyst during use.

In general, catalysts require active ingredients (e.g. ferric sulfate, etc.) to be supported on carrier materials (e.g. alumina, titania, etc.), and in the field of dry flue gas denitrification, glass fibers, mullite, etc. Whereas inorganic fibers require the application of the carrier material, asbestos paper does not require the presence of a carrier material, reducing catalyst production costs and being economical.

Furthermore, in the step of applying a cold cloth or impregnating the active ingredient etc. onto the base material, the water retention rate (as one of the physical properties of the base material) is
It is desirable that the asbestos paper has a high water absorption rate (or water absorption rate), which is about 60% for asbestos paper, and about 3% for general inorganic fibers.
Although it is about 0%, it is significantly higher and makes it easier to support the catalyst component.

The catalyst used in the method of the present invention contains asbestos fibers of 0.05
The most common material is a paper-like material or non-woven fabric, that is, asbestos paper, with a thickness of ~0.2 mm, and the asbestos paper is formed into a laminated state of a flat plate 1 and a corrugated plate 2 as shown in Figure 1A. However, the first modification is
As shown in Figure B, strength can also be improved by filling part 3 of the corrugated plate 2 with asbestos fibers.

The dimensions of the flute are 1 to 1 in diameter or height and width.
A dimension of 5 mm is preferred.

Further, the thickness of asbestos fibers is not particularly specified as long as it can be made into asbestos paper.

In addition, the no-nikum shape used in the method of the present invention is shown in Fig. 1A.
Needless to say, the shape is not limited to the shape of a polygon, and includes various shapes such as a polygon and a circle, and the shape thereof is not particularly defined.

In the method of the present invention, the above-mentioned catalyst is used in such a manner that an active substance of a conventional dry denitrification catalyst, such as iron sulfate, is supported as an active substance.

In the method of the present invention, the catalyst has a reactor temperature of 300 to
It is preferable to use it under the conditions of 400° C. and exhaust gas velocity of 1.5 to 5 m/sec.

This is because when the reactor temperature is below 300°C, compounds of SOx and NH3, such as ammonium sulfate, are formed on the catalyst.
This is because liquids and solids such as ammonium bisulfate and ammonium bisulfite precipitate, which not only hinders the reaction but also causes blockages, and the effectiveness remains unchanged even at temperatures above 400°C.

Furthermore, if the exhaust gas velocity is less than 0.5 m/sec, dust will increase on the gas inlet side of the catalyst, increasing pressure loss.
Further, if the time is 5 1 seconds or more, dust will not adhere, but this is because the pressure loss from the beginning is large.

Further, in the method of the present invention, it is preferable that the reactor in which the catalyst is arranged is placed vertically so that the exhaust gas flows perpendicularly to the earth's surface.

This installation mode can prevent the above-mentioned SOx and NH3 compounds from adhering to the catalyst.

When the activity of the above-mentioned catalyst decreases due to adhesion of the above-mentioned compound or dust, the activity can be restored by washing with water or the like.

In this case, cleaning at a high temperature is extremely effective, and the cleaning method can also involve taking out the deactivated catalyst and cleaning it, but as shown in Figure 2A, a part of the catalyst layer 4 is )) while continuing the denitrification operation.
An effective method is to wash the remaining portion with washing water introduced from line 5.

During this cleaning operation, the catalyst layer 4 is rotated as shown by arrow α.

Note that FIG. 2B shows a part of the plan view of FIG. 2A, and the same reference numerals as in FIG. 1 indicate the same parts as in FIG. 1.

Next, one embodiment of the method of the present invention will be explained along the flow sheet of FIG.

The exhaust gas discharged from the NOx-containing exhaust gas generation source (1) is added with NH3 from line 2 while passing through line 1, and is introduced into reactor H in which the above-mentioned catalyst is arranged.

The catalyst in the reactor (2) is arranged so as to be rotatable as shown by the arrow α.

The exhaust gas that has completed the denitrification reaction in the reactor (2) passes through the line 3, the air heater (3), and is discharged from the line 4 to the flue.

In the air heater (2), the combustion air introduced from the line 5 exchanges heat with the exhaust gas, and then is supplied from the line 6 to the NOx-containing exhaust gas generation source I.

Examples of the present invention will be given below.

Example 1 Iron sulfate F e 2 (SO4
) Denitration treatment was carried out in accordance with the flow sheet shown in FIG. 3 using a material containing 5% S and a C heavy oil-fired boiler as the source of NOx-containing exhaust gas.

The composition of the exhaust gas discharged into line 1 from boiler ① was as shown in Table 1.

In addition, the denitrification reaction conditions in reactor ■ are shown in the table below. to 2 It was as shown.

The results are shown in Figure 4.

As is clear from FIG. 4, if the temperature of the reactor is set from 300°C to 400°C, it is possible to remove 90% or more of NOx.

Example 2 A long-term test was carried out in exactly the same manner as in Example 1 except that the exhaust gas velocity of the reactor (■) was set to 0.5 m/sec and 3 m/sec, and the change in pressure loss of the catalyst layer was measured and the results were reported. It is shown in FIG.

In Figure 5, graph a shows the case where the exhaust gas velocity is 0.5 m/sec.
Graph b shows exhaust gas velocity of 3 m.

This is the case for seconds.

As can be seen from this figure, when the exhaust gas velocity is 0.5 m/sec, after 1000 hours, the amount of dust attached to the gas inlet side of the catalyst layer increases slightly, and the pressure loss increases slightly.
In the case of 3 m 1 sec, no pressure loss phenomenon due to adhesion of dust was observed.

Example 3 Example 1 except that the exhaust gas velocity of reactor ■ was variously changed.
Denitration treatment was carried out in exactly the same manner.

The results are shown in Figure 6.

As is clear from this figure, when the exhaust gas velocity is increased, the adhesion of Das I is eliminated, but the pressure loss from the beginning becomes large, and it can be seen that the optimum value is 1.5 to 5 m/sec.

Example 4 In Example 1, when the reactor ■ is placed vertically and the exhaust gas flows perpendicularly to the earth's surface, a, and when the reactor ■ is placed horizontally and the exhaust gas flows parallel to the earth's direction. We conducted a long-term test on this.

The results are shown in FIG.

In FIG. 7, graph a is for the above case a, and graph b is for the above case.

As can be seen from this figure, compounds of SOx and NH3 are more difficult to adhere to in case a, and a high denitrification rate can be obtained.

Example 5 In case a of Example 4, when the NOx removal rate fell below 80%, water washing was performed by the method shown in FIG. 2a.

Table 3 shows the amount of water that restores the activity of the catalyst.

In addition, for comparison, the catalyst was taken out, and water and 10% water at room temperature were added.
Table 3 also shows the amount of water required when washing with 0°C warm water.

As is clear from Table 3, washing with hot water using the method shown in Figure 2a shows the best effect.

As shown in each of the above embodiments, according to the method of the present invention, it is possible to regenerate the catalyst without being affected by dust, and when the activity of the catalyst has deteriorated, while performing denitrification treatment.

Furthermore, if the activity of the catalyst in the method of the present invention does not recover after washing with water, the active material can be carried through the line 5 by the method shown in FIG.

[Brief explanation of drawings]

Figures 1A and B are diagrams showing an example of the shape of the catalyst used in the method of the present invention, Figure 2 is a diagram showing an example of the method of cleaning the catalyst used in the method of the present invention, and Figure 3 is a diagram showing an example of the catalyst shape used in the method of the present invention. FIG. 4 is a flow sheet showing one embodiment; FIG.
The figure is a chart showing the relationship between exhaust gas velocity and pressure loss when the method of the present invention is implemented for a long period of time, Figure 6 is a chart showing the influence of exhaust gas velocity on pressure loss in the method of the present invention, and Figure 7 is a chart showing the relationship between exhaust gas velocity and pressure loss when the method of the present invention is implemented for a long period of time. It is a chart showing the influence on the denitrification rate by the installation mode of the reactor in the method.

Claims (1)

[Claims] 1. In a method of selectively reducing and removing nitrogen oxides to nitrogen by adding ammonia as a reducing agent to nitrogen oxide-containing exhaust gas in the presence of a catalyst substance, the catalyst is a honeycomb-shaped catalyst based on asbestos paper. A dry flue gas denitrification method characterized by using.