JPS5814247B2 - Hi-enshiyorihouhou - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides a highly efficient and practical method for removing nitrogen oxides and sulfur oxides from flue gas from factories and the like.

It is well known that it is necessary to reduce both nitrogen oxides and sulfur oxides in flue gas from factories, but there is no highly efficient and practical method available at the current technological level. It's not too much to say.

There is absolutely no way to reduce and remove both nitrogen oxides and sulfur oxides using simple principles.

The current status of methods for reducing and removing nitrogen oxides and sulfur oxides in flue gas is as follows.

That is, most of the reduction/removal treatment methods are currently implemented for each of nitrogen oxides and sulfur oxides, and most of the methods reported and proposed are for each of them individually.

The reason for this is thought to be related to the fact that domestic laws and regulations were first made for sulfur oxides, and more recently for nitrogen oxides.

The individual technical levels are as follows.

Nitrogen oxides are currently in the complete development stage.
There are no devices in actual operation that target large amounts of smoke exhaust.

Sulfur oxides have been developed to some extent, and wet methods are often used to treat flue gas.

In other words, it is a method of absorbing sulfur oxides using milk of lime or an aqueous solution of sodium hydroxide, etc., and although it has been put into practice, it is still difficult to use for product treatment and wastewater treatment when dealing with large amounts of flue gas. There are many unresolved problems.

Based on the above, the present inventors have studied a new method of performing both denitrification and desulfurization at the same time, based on sufficient experience with the respective desulfurization methods and denitrification methods, and have arrived at the present invention.

Before arriving at the present invention, we thoroughly considered all aspects such as equipment cost, equipment scale, operation, and personnel costs.

The gist of the present invention is as follows.

Ammonia is mixed into the flue gas in an amount equivalent to the content of nitrogen oxides in the flue gas, and the flue gas is heated to 150 to 450°C.
After the nitrogen oxides in the flue gas are reduced, ammonia is mixed again to convert the sulfur oxides in the flue gas into ammonium compounds, and the flue gas is reduced to 15
A flue gas treatment method, characterized in that the ammonium compound is precipitated by cooling to 0° C. or lower and collected by a dust collector or the like.

Nitrogen oxides and sulfur oxides, which are considered to be a particular problem in smoke exhaust and are regulated by law, cannot be treated by simply arranging the current single devices (although there are problems) in series as described above. In terms of cost, equipment scale, operation, and personnel costs,
Not practical.

The present inventors have studied in detail the so-called ammonia reduction denitrification method, and have published Japanese Patent Application No. 49-135-119 (Japanese Unexamined Patent Publication No. 51-6069).
6), Japanese Patent Application No. 50-9873 (Japanese Unexamined Patent Publication No. 51-84771)
) and other inventions.

In the course of this study, we gained a wide range of knowledge and experience regarding the denitrification rate, the behavior of ammonia, the behavior of sulfur oxides, etc., which led us to the present invention.

In the ammonia reduction denitrification method, the catalysts used are platinum metal (US Patent No. 2975025), nickel, cobalt, and iron oxides (America Patent No. 30087).
96), oxides of vanadium, molybdenum, and tungsten (US Pat. No. 3,279,884), manganese oxides (JP-A No. 50-17368), oxides of iron and vanadium (JP-A-49-129691), etc. Proposed.

Nitrogen oxides in general flue gas are mostly NO and are thought to contain a small amount of NO, but according to the following formula, N2 and H2
It is thought that it is reduced to 0 and processed.

This reaction is relatively stoichiometric and is superior to the ammonium compound production reactions (4) and (5) described below.

On the other hand, ammonia itself decomposes according to the following formula at a catalyst bed temperature of about 300° C. or higher, although this varies depending on the catalyst used.

In addition, although the reactions of formulas (1) and (2) are dominant, ammonia is in excess, the reaction of formula (3) does not proceed much, and when sulfur oxides coexist, sulfur oxides and (4 ), (5
) ammonium sulfate or ammonium sulfite (hereinafter abbreviated as ammonium compound) is formed according to the formula.

? The sulfur oxides in general flue gas are SO and S03.
O.

It is thought that there are more. Also, depending on the catalyst, S0
2 may be oxidized to SO3.

The present invention is based on the above results obtained with the ammonia reduction denitrification method, and has invented a new method for denitrification and desulfurization, targeting both denitrification and desulfurization.

An explanatory diagram of the method of the present invention is shown in FIG.

In Figure 1, 1 is an arrow indicating that exhaust smoke is introduced, and exhaust smoke can be heated to a temperature of 150 to 450 if necessary.
It is said to be ℃.

2 is a first ammonia mixer, and if necessary, a device for improving mixing is placed at a position where the ammonia is mixed into the exhaust gas.

3 is a catalytic reactor.

4 is a second ammonia mixer, and if necessary, a device for improving mixing is placed at a position where the ammonia is mixed into the exhaust gas, as in 2.

5 is an ammonium compound collector.

6 is an arrow indicating that flue gas is discharged, and the flue gas is normally then led to a chimney and finally discharged.

In other words, the exhaust gas containing nitrogen oxides and sulfur oxides can be heated to 150% by heating with a burner, etc., as indicated by the arrow 1.
~450°C, and ammonia is mixed in by the ammonia mixer 2 and reaches the catalytic reactor 3, (1), (2)
Denitrification is carried out according to the formula.

After the denitrification is finished, ammonia is mixed into the exhaust gas exiting the catalytic reactor 3 again from the second ammonia mixing device 4 (4).
, (5), the sulfur oxide in the flue gas becomes an ammonium compound.

This ammonium compound is precipitated from the gas phase by lowering the temperature of the flue gas, so it can be separated and collected from the flue gas using a bag filter, electrostatic precipitator, etc., or it can be collected by wet dust collection such as washing the flue gas with water. Separate and collect by using a container.

The flue gas from which nitrogen oxides and sulfur oxides have been removed is guided to the chimney and disposed of (after being heated if necessary).

What is characteristic of the above is that the amount of ammonia added during denitrification is limited to the amount necessary to carry out the denitrification reaction (according to equations (1) and (2)).

As mentioned above, the inventor believes that the denitrification reactions (1) and (2) take precedence over the ammonia decomposition reactions (3) and the ammonium compound production reactions (4) and (5) in the temperature range of 150 to 450°C. In this case, if too much ammonia is added, the ammonia will be decomposed in the reaction (3) at temperatures above about 300° C., depending on the catalyst used, and will be lost.

Similarly, at temperatures below about 300°C, excessive ammonia is added, and if sulfur oxides are present, ammonium compounds according to (4) and (5) will precipitate on the catalyst layer itself, although this will depend on the catalyst used. It is generally believed that there is a risk of clogging the catalyst layer.

In any case, since the purpose of this catalytic reactor 3 is denitrification, it is only necessary to add the required amount of ammonia from the first ammonia mixing device 2, but adding an excessive amount has disadvantages as described above. So, use the first and second ammonia mixers. A feature of the present invention is that only the amounts required for each reaction are added.

In principle, the amount of ammonia added from the first ammonia mixer can be determined from equations (1) and (2).

As mentioned above, most of the nitrogen oxides in general flue gas are NO, and the NO content is relatively small. However, nitrogen dioxide (NO
Considering the removal of 2), and also taking into consideration safety in the case of insufficient or uneven gas mixing, a slight margin was taken, and the content equivalent to the content of nitrogen oxides in the flue gas was set. I decided to add ammonia.

In addition, the temperature of the flue gas 1 is set to 150 to 450°C by burner heating or electric heating as necessary, and this temperature is necessary for carrying out the denitrification reaction, (4) In order to separate and precipitate the ammonium compound produced according to the formula (5) from the gaseous phase of flue gas, experiments have shown that the temperature must be lower than 150°C to separate and precipitate, and it cannot be collected in a solid state.

That is, the exhaust gas after the catalytic reactor 3 needs to be at a temperature of 150° C. or lower before reaching the ammonium compound collector 5.

In order to reduce the flue gas temperature to 150℃ or less, air cooling, external air cooling, external water cooling, internal air cooling, internal water cooling, air blowing, water blowing, etc. can be considered, but the blowing of ammonia can also be expected to have a cooling effect, albeit to a small extent. .

The present invention will be supplementarily explained below.

As the catalyst in the reactor 3 of the catalyst 13 in FIG. 1, since the object of the present invention is exhaust gas containing both nitrogen oxides and sulfur oxides, it is desirable to use a denitrification catalyst for ammonia reduction that is not affected by sulfur oxides. .

As a catalyst suitable for the purpose, one or more oxides, chlorides, and sulfides of vanadium, iron, chromium, molybdenum, and tungsten are supported on a catalyst carrier mainly composed of aluminum oxide by impregnation method. Something is desirable.

Figure 2 shows the results of a study on the temperature of flue gas when ammonium compounds produced according to formulas (4) and (5) are separated and precipitated from flue gas.Sulfur oxides are collected as ammonium compounds. It shows the relationship between the rate (%) and the temperature (°C) of flue gas at the time of collection.

This experiment was conducted as follows. That is, in a quartz reaction tube (inner diameter L 2 mm, length 200 mm), 4 cc of vanadium oxide and aluminum oxide catalyst (diameter 1.4 to 2
．． A spherical catalyst with a diameter of 0 mm and a γ alumina catalyst carrier with the above diameter impregnated with vanadyl oxalate and calcined at 600° C. were filled.

This quartz reaction tube was placed in an electric furnace that was split in two, a gas introduction tube was provided at the top of the quartz reaction tube, and an ammonia introduction port was provided in the gas introduction tube near the quartz reaction tube.

A gas exhaust pipe is provided at the bottom of this quartz reaction tube. At the same time as the tube was connected to a glass tube cyclone, an ammonia inlet was installed in the middle.

A glass cyclone with an inner diameter of 70 mm and a height of 80 mm was used, and the gas temperature could be measured at the center of the cyclone.

Gas: NO 300ppm, SO2 500ppm
, 0.15%, and other N2 gases were fed into the reaction tube at a flow rate of 120 L/hour, and ammonia equivalent to 300 ppm was added just in front of the reaction tube inlet.

The temperature of the catalyst layer was set at 350° C., and ammonia equivalent to 1200 ppm was further added between the reaction tube and the glass cyclone to investigate the collection of ammonium compounds.

In the collection experiment, the above reaction conditions were kept constant, and the collection temperature was changed by air-cooling and water-cooling the discharge pipe from the reaction tube and the cyclone. This study investigated the relationship between collection rate (%) and collection temperature.

According to the results shown in FIG. 2, it was found that if the collection temperature was set to 140° C. or less, the collection rate was 85% or more.

When flue gas is led to a chimney, if the temperature is too low, the discharge rate will be reduced, but at 110 to 140°C, there is no need for afterburning, and it is a sufficiently practical collection temperature.

Figure 3 shows the results of an experiment investigating the relationship between catalyst layer temperature and denitrification rate and desulfurization rate in a quartz reaction tube, and the experiment was carried out in exactly the same manner as above.

However, the collection temperature was 110° C., and the denitrification rate and desulfurization rate were determined by the following equations (7) and (8).

According to the results shown in FIG. 3, it was found that in the method of the present invention, a catalyst bed temperature of 150 to 450°C is good for both the denitrification rate and the desulfurization rate.

At temperatures below 150°C and above 450°C, both the denitrification rate and the desulfurization rate decrease, but the decrease in the desulfurization rate is significant.

Furthermore, in the results shown in Figure 3, both the denitrification rate and the desulfurization rate are 90%.
The most desirable temperature range is 200°C to 35°C.
It was found that the temperature was 0°C.

The ammonium compound collected above is a white powder, relatively free-flowing, and water-soluble. Although ammonium sulfate was identified in the X-ray diffraction analysis results, other X-ray diffraction peaks remained that could not be analyzed.

This diffraction peak does not match the X-ray diffraction peak of a general standard substance.

This white powder can be collected using regular dust collectors, electrostatic precipitators,
A bag filter can suffice, and it is also natural to consider absorbing water or an aqueous solution or using a wet dust collector.

Hereinafter, the present invention will be explained in more detail based on Examples.

Example 30 tons of vanadium pentoxide-gamma alumina spherical catalyst (v205 content 8%) prepared by the impregnation method was packed in a stainless steel box-shaped reaction tank (40 x 40 x 50 cm each), and sintering furnace exhaust gas (average composition 02: 15%, NO :200ppm1CO:
2%, SO2: 300ppm 1CO2: 12%, remainder:
N2 (after dehydration) was flowed at a flow rate of 300 m'/hour, and ammonia was added in an amount equivalent to 200 ppm from a cylinder at the inlet of the reaction tank.

A small high-voltage electrostatic precipitator was connected to the outlet of the reaction tank via a water cooling device, an inlet was provided just before the precipitator, and ammonia equivalent to 1000 ppm was added from a cylinder.

The temperature of the reaction tank was 350°C, and the temperature inside the small high voltage electrostatic precipitator was 100°C.

Gas analysis was performed at the inlet of the reaction tank and the outlet of the electrostatic precipitator, and the denitrification rate and desulfurization rate were determined according to the following equations (9) and (10).

The results are shown in Figure 4.

In a continuous experiment of 1000 hours, both the denitrification rate and the desulfurization rate were 90% or higher, showing good results.

The material collected in the small electrostatic precipitator was grayish white, and its properties and analysis results were similar to those collected in the glass cyclone as described above.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram of the method of the present invention. FIG. 2 shows the experimental results of the present invention, and is a diagram showing the relationship with the collection rate (%) of sulfur oxide as an ammonium compound. FIG. 3 shows the experimental results of the present invention, and is a diagram showing the relationship between the denitrification rate (%), the desulfurization rate (%), and the catalyst layer temperature (° C.). Figure 4 shows the results of an example of the present invention, showing the denitrification rate (%).
) and the relationship between desulfurization rate (%) and elapsed time (hours). ■ indicates the denitrification rate, and ■ indicates the desulfurization rate. 1...Arrow indicating that flue gas is introduced, 2...1st ammonia mixer, 3...catalytic reactor, 4...2nd ammonia mixer,
5... Ammonium compound collector, 6... Arrow indicating that exhaust smoke is discharged.

Claims (1)

[Claims] 1. Mix ammonia in the flue gas in an amount equivalent to the content of nitrogen oxides in the flue gas, and make the flue gas
After the nitrogen oxides in the flue gas are reduced by passing through a catalyst layer and the nitrogen oxides in the flue gas are reduced, ammonia is mixed in again to convert the sulfur oxides in the flue gas into ammonium compounds, and the flue gas is cooled to below 150 °C. A flue gas treatment method characterized in that the ammonium compound is precipitated and collected by a dust collector or the like.