JPH0218898B2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Field] The present invention relates to a method for supplying a reducing agent to combustion exhaust gas, and more specifically, to reduce the amount of NO contained in combustion exhaust gas discharged from combustion equipment such as boilers and industrial furnaces. This invention relates to a method for supplying a reducing agent to combustion exhaust gas containing NO _x , in which the reducing agent supplied to remove nitrogen oxides (NO _x ) such as NO ₂ is uniformly dispersed and mixed in the exhaust gas.

[Prior art and its problems] Many processes have been developed to remove nitrogen oxides from combustion exhaust gas, but a selective reduction method using NH ₃ as a reducing agent in the presence of a titanium oxide catalyst has been developed. It has become mainstream. In this method, as shown in FIG.
The NO _x in _the combustion exhaust gas sent to the
and NH ₃ mixed with the dispersion air sent via the dispersion air blower 6 and released from the header 7
Then, the reaction 4NO+4NH ₃ +O ₂ →4N ₂ +6H ₂ O 6NO ₂ +8NH ₃ →7N ₂ +12H ₂ O takes place in the titanium oxide catalyst layer 8, converting it into harmless N ₂ and H ₂ O, which are then used in the heat exchanger. The air is discharged into the atmosphere from a chimney 11 via a blower 10 and a chimney 11.

In this way, the selective reduction method is based on the premise that NO _x contained in exhaust gas at a dilute concentration reacts with the reducing agent NH ₃ in the presence of a catalyst. is in exhaust gas
It is necessary to sufficiently disperse and mix NH ₃ .

However, with such conventional reduction methods, it has been impossible to supply the reducing agent over a short distance so that it is uniformly dispersed and mixed in the exhaust gas. Therefore, if the exhaust gas reaches the catalyst layer with an uneven reducing agent concentration distribution, in the exhaust gas portion where the reducing agent concentration is higher than the NO _x concentration, the excess reducing agent passes through the catalyst layer unreacted. On the other hand, in the exhaust gas portion where the reducing agent concentration is lower than the NO _x concentration, excess NO _x passes through the catalyst layer unreacted, causing a decrease in the denitrification rate.
Furthermore, the unreacted reducing agent often causes various troubles in equipment downstream of the catalyst bed, such as precipitation of acidic ammonium sulfite, resulting in blockage, or corrosion. On the other hand, if the distance from the reducing agent injection position to the catalyst layer is increased to ensure uniform dispersion and mixing, the exhaust gas piping or duct will become longer, increasing the construction cost of the equipment and requiring a larger site area. There will be economic disadvantages such as

For this reason, a method has been proposed (Japanese Patent Laid-Open No. 1902-1983) in which a movable baffle rod or baffle plate for ammonia mixing is installed near the wake of an ammonia supply nozzle to achieve dispersive mixing. However, this method requires separate means, increases pressure loss, and because the baffle rods and baffle plates are movable, it is very difficult to seal the attachment part to the exhaust gas pipe wall or duct wall. There are many problems.

Furthermore, in the selective reduction method, it is essential to be able to easily follow changes in the load of the boiler etc. from the viewpoints of maintaining the denitrification rate, economic efficiency of the reducing agent, operability of equipment downstream of the catalyst bed, etc. However, conventional methods merely provide separate dispersion means such as baffles in the duct that increase pressure loss, and mechanically movable parts that tend to cause the above-mentioned failures.

[Object of the Invention] The present invention has been made to solve the above-mentioned drawbacks of the prior art. That is, an object of the present invention is to be able to uniformly disperse and mix a reducing agent in combustion exhaust gas over a short distance without using a separate dispersion means and without causing an increase in pressure loss, and in which a reducing agent can be dispersed and mixed in combustion exhaust gas over a short distance. It is an object of the present invention to provide a method for supplying a reducing agent to combustion exhaust gas that can easily follow load fluctuations.

[Means for Solving the Problems] In the first invention of the present application, in order to solve the above problems, in a method for supplying a reducing agent to combustion exhaust gas, a fluid containing a reducing agent is introduced into a header, and a fluid containing a reducing agent is introduced into a header. A reducing agent-containing fluid is ejected into the combustion exhaust gas from a nozzle located upstream of the combustion exhaust gas in a direction intersecting the flow of the combustion exhaust gas and tracing a trajectory that collides with the header.

Furthermore, in the second invention of the present application, in addition to the steps of the method of the first invention, the reducing agent dispersion fluid is adjusted in response to fluctuations in the load of the flue gas or fluctuations in the concentration of the substance to be reduced in the flue gas. At least one of the flow rate and the supply amount of the reducing agent is controlled to correspond.

[Operation of the invention] In the first invention, since the reducing agent-containing fluid is ejected from the nozzle in a direction intersecting the flow of the combustion exhaust gas, the reducing agent-containing fluid ejected into the combustion exhaust gas collides with the header. During this period, a part of it is effectively dispersed and mixed into the combustion exhaust gas. In addition, most of the remaining reducing agent-containing fluid is actively collided with the header together with the exhaust gas, thereby significantly disturbing the flow of the exhaust gas and extremely effectively dispersing and mixing the reducing agent-containing fluid and the exhaust gas. As described above, according to the first invention, the exhaust gas and the reducing agent-containing fluid are uniformly distributed in the trailing part of the header due to the combination of dispersive mixing up to the time when the header collides with the header and dispersive mixing due to the collision with the header. Therefore, the reducing agent can be uniformly dispersed and mixed into the combustion exhaust gas over a short distance.

According to the second invention, in addition to the effects of the first invention, when the flow rate of the exhaust gas and the concentration of the substance to be reduced in the exhaust gas fluctuate due to fluctuations in the load of the exhaust gas generator such as a boiler, these The flow rate of the reducing agent dispersion fluid and the supply amount of the reducing agent are respectively controlled according to the fluctuations. Therefore, according to the second invention, in response to load fluctuations in a boiler, etc., load fluctuations in the flue gas or reducible substances in the flue gas can be reduced without making any changes to equipment factors such as the shape of the nozzle. It is possible to follow the concentration fluctuations by simply changing the flow rate of the reducing agent-containing fluid.

[Summary of the Invention] Since the trajectory of the reducing agent-containing fluid ejected from the nozzle in the exhaust gas flow changes depending on various factors, the first and second inventions are characterized in that the reducing agent-containing fluid collides with the header. In order to draw such a trajectory, it is necessary to control the factors that change the trajectory using an appropriate method. The main factors that change the trajectory of the reducing agent-containing fluid are the exhaust gas flow rate,
The flow rate of the reducing agent-containing fluid, the shape and installation angle of the nozzle, the distance between the nozzle and the header, and the diameter of the exhaust gas piping or duct are factors that change the above trajectory and are interrelated in a complex manner. Their values cannot be unambiguously specified because they cause collisional trajectories to be drawn.

However, among these, the standard value for the exhaust gas flow rate is determined by the design conditions of the exhaust gas generating device such as a boiler, so the diameter of the exhaust gas piping or duct is also set to a predetermined value accordingly. Ru. In addition, preferred standard values can be set for the reducing agent supply amount and the reducing agent-containing fluid flow rate in accordance with the respective standard values of the exhaust gas flow rate and the concentration of NO _x in the exhaust gas. Based on this, the configuration of the reducing agent supply device, such as the shape and installation angle of the nozzle, and the distance between the nozzle and the header, is adjusted so that the reducing agent-containing fluid ejected from the nozzle draws a trajectory that collides with the header in the exhaust gas. can be designed.

In this way, it is possible to design an apparatus that can implement the method of the present invention based on the design conditions of the exhaust gas generator, and the exhaust gas generator is operated under the same conditions as the design conditions (steady state). In this case, the reducing agent supply device designed as described above should be configured to draw a trajectory in which the reducing agent-containing fluid ejected from the nozzle in a direction intersecting the flow of exhaust gas always collides with the header. Can be done.

However, boilers etc. are not always operated under the same steady state as the design conditions mentioned above, and the exhaust gas flow rate and the concentration of the reductant in the exhaust gas may change depending on load fluctuations, fuel type, etc.
NO _x concentration fluctuates. As mentioned above, the trajectory of the reducing agent-containing fluid changes depending on various factors that are intricately related to each other. By simply changing the flow rate of the reducing agent-containing fluid without making any changes to the equipment factors such as
It can be followed.

That is, in response to fluctuations in the exhaust gas flow rate, by adjusting the amount of reducing agent to correspond to fluctuations in the amount of NO _x according to the detected exhaust gas flow rate, and controlling the flow rate of the dispersion fluid that carries the reducing agent, It is possible to create a trajectory in which the reducing agent-containing fluid always impinges on the header.

Next, regarding fluctuations in NO _x concentration in exhaust gas,
Only the amount of reducing agent supplied is controlled in response to fluctuations in the amount of NO _x . That is, in order to efficiently react the reducing agent with NO _x contained in the exhaust gas at a dilute concentration, the reducing agent must be sufficiently uniformly dispersed in the exhaust gas. To do this, the dispersion fluid carrying the reducing agent is sprayed into the exhaust gas at a flow rate several tens of times higher than the standard value of the reducing agent supply amount, with the reducing agent pre-dispersed in the dispersion fluid. . Comparing this to the case where the reducing agent is directly supplied into the exhaust gas, the flow rate of the reducing agent-containing fluid is supplied into the exhaust gas at a flow rate several tens of times that of the case where the reducing agent is directly supplied into the exhaust gas, so the dispersion of the reducing agent into the exhaust gas is effective. It will be held in Therefore, even if the supply amount of the reducing agent is changed in accordance with the fluctuations in _NO Since the supply amount is almost the same as before the change, the reducing agent-containing fluid ejected from the nozzle can be made to follow a trajectory that collides with the header in the same way as before the change in the reducing agent supply amount.

Furthermore, if the exhaust gas flow rate and NO _x concentration change simultaneously, the control of the flow rate of the dispersion fluid and the control of the reducing agent supply amount can be performed separately as described above, so these two types of control can be combined. By doing so, the reducing agent-containing fluid ejected from the nozzle can draw a trajectory such that it always collides with the header.

In the present invention, air, nitrogen, combustion exhaust gas, inert gas, etc. can be used as the fluid for dispersing the reducing agent, but it is usually convenient to use air. In addition, the nozzle that spouts the reducing agent-containing fluid is
A branch pipe may be provided on the header and the pipe may be attached to the tip thereof, or it may be attached directly to the header. Preferably, the nozzle is provided at an angle so as not to face the flow of the exhaust gas, that is, at an angle that allows the reducing agent-containing fluid to be ejected in a direction intersecting the flow of the exhaust gas. Further, in order to further promote the dispersion mixing function of the header, it is also possible to attach projections such as fins to the header as long as the pressure loss is within the allowable pressure loss for the exhaust gas.

[Explanation based on Experimental Examples] Next, in order to better understand the method of the present invention, a dispersion state observation experiment conducted using model gases as both the reducing agent-containing fluid and the exhaust gas will be described.
In this experimental example, air was used as the exhaust gas, and white smoke generated by a smoke tube was used as the reducing agent.

Air is passed through a visible wind tunnel, white smoke is introduced into a header together with dispersion air, and a fluid containing white smoke is introduced into the air through a branch pipe installed in the header and from a nozzle located near the tip of the branch pipe. The state of dispersion of the white smoke was observed.

In the present invention, as described above, when the reducing agent is supported in the dispersing fluid and is ejected from the nozzle into the exhaust gas as a reducing agent-containing fluid, the flow rate of the dispersing fluid is several tens of tens of times lower than the standard amount of the reducing agent. It is doubled.
Therefore, in this experimental example as well, the flow rate of dispersion air was set to be several tens of times higher than that of white smoke. Therefore, the state of dispersion of white smoke can be considered to be almost the same as the state of dispersion of the actual reducing agent.

FIG. 2 shows the experimental results based on the above. Arrows indicate the direction in which air flows through the wind tunnel.
The device includes a header 14, a direction perpendicular to the air flow on the upstream side of the air flow with respect to the header,
For example, it includes a nozzle 15 disposed in a direction perpendicular to the flow of exhaust gas.

In this experimental example using the apparatus with the above configuration,
White smoke passes from the header 14 through the branch pipe 16 to the nozzle 1.
5 into the air in a direction perpendicular to the air flow. The white smoke emitted from the nozzle is
The white smoke is pushed downstream by the air flow, and some of the white smoke is dispersed and mixed in the air as it collides with the header, and when the white smoke collides with the header, the flow is significantly disturbed there. The white smoke was effectively dispersed and mixed into the air. When white smoke is ejected in a direction perpendicular to the air flow and collides with a header, the white smoke and air are extremely effectively dispersed through dispersive mixing up to the time of collision and dispersive mixing due to collision with the header. Mixing could be achieved, and the air and white smoke were uniformly mixed at the wake of the header. Therefore, it has been confirmed that according to the present invention, white smoke can be uniformly dispersed and mixed in the air over a short distance.

Figures 3 and 4 show different experimental results. In Figure 3, the insertion direction of the header is changed by 90 degrees compared to the case in Figure 2, and the nozzle is the same as in Figure 2. Similarly, it is oriented in a direction perpendicular to the air flow in order to emit white smoke in a direction that crosses the air flow. In addition, FIG. 4 shows an example in which two headers are provided. In both cases of Fig. 3 and Fig. 4, dispersive mixing of white smoke and air can be performed extremely effectively by dispersive mixing up to the time of collision and dispersive mixing due to collision with the header. It was confirmed that white smoke could be uniformly dispersed and mixed in the air over a short distance.

Moreover, FIGS. 5, 6, and 7 show the results of comparative experiments.

In FIG. 5, the nozzle 15 is arranged on the downstream side of the air flow with respect to the header, and the white smoke is ejected parallel to the air flow, but the white smoke simply flows downstream. They are not uniformly distributed within the distance range of this observation experiment.

In FIG. 6, white smoke is ejected from a nozzle 15 disposed on the downstream side of the header 14 with respect to the air flow in a direction perpendicular to the air flow. As a result, they are only pushed downstream and are not evenly dispersed within the distance range of this observation experiment.

In FIG. 7, white smoke is ejected from the nozzle 15 disposed upstream of the header 14 in a direction perpendicular to the air flow, but the flow rate of the dispersion air is inappropriate. Therefore, the white smoke does not collide with the header 14 and is not uniformly dispersed within the distance range of this observation experiment.

As is clear from the observation of the dispersion state in the above experiments, according to the method of the present invention, the nozzle is located upstream with respect to the header, and the reducing agent-containing fluid is directed from the nozzle in a direction that crosses the flow of combustion exhaust gas. It can be seen that the reducing agent can be uniformly dispersed and mixed in the combustion exhaust gas over a short distance by ejecting it into the combustion exhaust gas so as to draw a trajectory such that it hits the header.

Figures 8 and 9 show the experimental results when the air flow rate was reduced to half of the air flow rate in the experiment shown in Figure 4. Figure 8 shows the dispersion carrying white smoke. When the dispersion air flow rate was controlled and decreased so that the white smoke collided with the header 14, Fig. 9 shows the dispersion air flow rate carrying white smoke compared to the dispersion air flow rate in the experiment shown in Fig. 4. The experimental results are shown when the same amount was maintained without any particular control. In the case of Fig. 8, the white smoke is evenly dispersed in the air by colliding with the header 14, just as in the case of Fig. 4, but in the case of Fig. 9, the white smoke is It does not collide with the header 14 and is not uniformly dispersed in the air. As is clear from this experiment, according to the present invention, even if the exhaust gas flow rate fluctuates due to load fluctuations in the boiler, etc., it can be easily followed by simply controlling the dispersion air flow rate.

[Explanation based on Examples and Comparative Examples] Examples and comparative examples will be shown in which a reducing agent was actually supplied to remove nitrogen oxides contained in combustion exhaust gas.

Example 1 Exhaust gas at 350℃ containing 180ppm NO _x
10000N ^-3 /hour in the presence of titanium oxide catalyst
Treated with _NH3 . An overview of the equipment used is shown in Figures 10A and 10B.

The two headers 14 are inserted from the outside into portions of the horizontally installed side wall of the duct 13 at a height of 1/4 and 3/4 from the upper end. The two headers 14 communicate with each other outside the duct 13,
An inlet 12 for the reducing agent-containing fluid is located in the center of the communication part.
is provided. A total of four branch pipes 16, two from each header 14, are provided on the upstream side of the exhaust gas flow with respect to the header 14, and a total of four nozzles 15 are arranged at the tip of each branch pipe 16. It is set up. Regarding the mounting direction of the nozzles, the nozzle of the upper branch pipe is vertically downward, and the nozzle of the lower branch pipe is vertically upward.

The cross section of the duct 13 is 1000 mm square, the nominal diameter of the header 14 is 100 mm, the nominal diameter of the reducing agent-containing fluid inlet 12 is 100 mm, the length from the inlet 12 to the tip of the header 14 is 1000 mm, and from the header 14 to the nozzle 15 The length between the branches 16 was 500 mm, and the distance from the nozzle 15 to the catalyst layer 8 was 2000 mm.

First, from the reducing agent-containing fluid inlet 12,
NH ₃ 1.8N ^-3 /hr mixed with air 80N ^-3 /hr
NH ₃ -containing air was introduced, passed through the header 14 and the branch pipe 16, and was ejected from four nozzles 15 into the exhaust gas. Then, at a position 500mm downstream of the catalyst layer 8, the heights in the duct are 100mm, 300mm, 500mm, 700mm and
The exhaust gas was sampled at five points of 900 mm, and the NO _x concentration was measured using the NO _x concentration detector 17. The measurement results are shown in Figure 11, and the outlet NO _x concentration is about 10 ppm at any height.
It is clear that the method of Example 1 allows substantially uniform dispersion and mixing of NH ₃ into the exhaust gas.

[Comparative Example] Exhaust gas was treated using a device in which a nozzle was disposed downstream of the flow of exhaust gas with respect to the header. The composition, flow rate, etc. of the exhaust gas and NH ₃ -containing air were the same as in Example 1. An overview of the equipment used is given in Section 12.
A and 12B, 13A and 13B, and 14A and 14B. 12th A and 12B
The figures are the same as Figures 10A and 10B of the apparatus of Example 1, except that the nozzles are arranged as described above, and Figures 13A and 13B show the nozzle arrangement method and the distance from the nozzle to the catalyst layer. 14A and 14B.
The figure shows how to arrange the nozzles, and how four headers are provided, and each header is provided with four branch pipes each having a nozzle at its tip, increasing the number of nozzles to 4 times that of Example 1, or 16. , device No. 10A of Example 1
and 10B.

In the exhaust gas after treatment carried out in the same manner as in Example 1
The measurement results of NO _x concentration are shown in Figure 15. 1st
In Figure 5, ● marks indicate when the apparatus shown in Figs. 12A and 12B are used, 〇 marks indicate when the apparatuses shown in Figs. 13A and 13B are used, and △ marks indicate when the apparatuses shown in Figs. 14A and 14B are used. ing.

The results of the comparative example (Fig. 15) are compared to Example 1 of the present invention.
When compared with the result (marked with ○ in Figure 11), when the number of nozzles and the distance from the nozzle to the catalyst layer are both under the same conditions (marked with ● in Figure 15), the NO _x concentration distribution is similar to that of Example 1 of the present invention. There is a large variation compared to that, and even when the number of nozzles is the same as in Example 1 but the distance from the nozzle to the catalyst layer is twice (marked with a circle in Figure 15),
From Example 1 of the present invention, there was variation in the NO _x concentration distribution, indicating that NH ₃ was not sufficiently dispersed. In addition, when the number of nozzles is four times that of Example 1 and the distance from the nozzle to the catalyst layer is the same (first
Figure 5 (△ mark) shows almost the same results as Example 1, and the concentration distribution was almost as uniform as Example 1 of the present invention, indicating that NH ₃ was sufficiently dispersed. It has been shown that From the above results,
A part of the NH ₃ -containing air is dispersed in the exhaust gas by blowing out the NH ₃ -containing air so as to cross the flow of the exhaust gas, and the NH ₃ -containing air is made to collide with the exhaust gas against the header to achieve sufficient uniform dispersion. Therefore, it was found that in Example 1, the mixing distance could be reduced to about half and the number of nozzles to be reduced to about 1/4 compared to the comparative example.

Example 2 Exhaust gas treatment was performed by reducing the combustion exhaust gas flow rate and the NH ₃ supply amount to one half. in exhaust gas
The NO _x concentration and equipment configuration were the same as in Example 1.

Here, we will compare the case where the dispersion air flow rate is controlled and decreased according to the decrease in the exhaust gas flow rate so that the NH ₃ -containing air ejected from the nozzle traces a trajectory that collides with the header, and the case where the dispersion air flow rate is decreased according to the decrease in the exhaust gas flow rate. A comparison was made between the flow rate of the dispersing air and the case where the flow rate was the same and not controlled. FIG. 16 shows the measurement results of the NO _x concentration in the exhaust gas after treatment conducted in the same manner as in Example 1. When the dispersion air flow rate is controlled (marked with a circle in Figure 16),
The NO _x concentration distribution was uniform, indicating that NH ₃ was sufficiently dispersed, but if the dispersion air flow rate was not controlled (● mark in Figure 16), the NO _x concentration distribution would vary. This indicates that the mochi NH ₃ was not sufficiently dispersed. That is, it can be seen that by the method of the present invention, fluctuations in the exhaust gas flow rate can be easily followed by simply controlling the reducing agent supply amount and the dispersion air flow rate.

[Field of Application of the Invention] Since the present invention has the above-mentioned configuration and the many excellent features described above, it can be used when supplying a reactant in a dry flue gas desulfurization method, etc. It can also be applied to

[Effects of the Invention] As is clear from the above, according to the present invention, the following particularly remarkable effects can be achieved.

According to the first aspect of the invention, the exhaust gas and the reducing agent-containing fluid are uniformly mixed in the trailing portion of the header through a combination of dispersive mixing up to the time when the header collides with the header and dispersive mixing due to the collision with the header. Therefore, the reducing agent can be uniformly dispersed and mixed into the exhaust gas over a shorter distance than before. This eliminates the need for separate dispersion means that would increase pressure loss, as has been proposed in the past, or for mechanically moving parts that are prone to failure and are extremely difficult to seal at the installation part. Alternatively, since the duct can be shortened and the number of nozzles can be significantly reduced, the structure of the device can be simplified. Therefore, the site area can be saved and equipment costs and operating costs can be reduced.

In particular, according to the second invention, fluctuations in the flow rate of exhaust gas and the amount of the substance to be reduced can be very easily followed by simple control of the flow rate of the reducing agent dispersion fluid and the amount of reducing agent supplied. As a result, a high removal rate of the substance to be reduced can be obtained at all times, so that the reducing agent can be used effectively, and troubles such as clogging and corrosion in equipment downstream of the catalyst layer can be prevented. Therefore, economical and stable operation can be performed without requiring special skilled workers.

[Brief explanation of drawings]

FIG. 1 is a system diagram showing an apparatus for implementing the selective reduction method, FIGS. 2, 3, 4 and 8 are schematic diagrams showing the experimental results of the present invention, and FIGS. 5 and 6.
Figures 7 and 9 are schematic diagrams showing the results of comparative experiments, Figure 10A is a front view of the apparatus of the embodiment of the present invention, Figure 10B is a side view of the apparatus of Figure 10A, and Figure 11. and FIG. 16 are graphs showing the results of Examples of the present invention, FIGS. 12A and 12B, and FIG.
Figures 3A and 13B and Figures 14A and 14B are Figures 10A and 10B, respectively, showing devices of comparative examples.
FIG. 15, which is similar to the figure, is a graph showing the results of a comparative example. 12... Reductant-containing fluid inlet, 13... Exhaust gas piping or duct, 14... Header, 15... Nozzle, 16... Branch pipe, 17... NOx concentration detector.

Claims (1)

[Scope of Claims] 1. In a method for supplying a reducing agent to combustion exhaust gas, a reducing agent-containing fluid is introduced into a header, and the reducing agent-containing fluid is supplied to the combustion exhaust gas from a nozzle located upstream of the combustion exhaust gas. A method for supplying a reducing agent to combustion exhaust gas, characterized in that the reducing agent is ejected into the combustion exhaust gas in a direction that intersects the flow of the exhaust gas and draws a trajectory that collides with the header. 2. In a method for supplying a reducing agent to combustion exhaust gas, a reducing agent-containing fluid made by mixing a reducing agent dispersion fluid and a reducing agent is introduced into a header, and the reducing agent is supplied from a nozzle located upstream of the combustion exhaust gas to the header. The reducing agent-containing fluid is ejected into the combustion exhaust gas in a direction that intersects the flow of the combustion exhaust gas and draws a trajectory that collides with the header, thereby controlling the load fluctuation of the combustion exhaust gas or the fluctuation in the combustion exhaust gas. A method for supplying a reducing agent to combustion exhaust gas, the method comprising controlling at least one of the flow rate of the reducing agent dispersion fluid and the supply amount of the reducing agent to respond to changes in the concentration of a substance to be reduced. 3. When the concentration of the substance to be reduced in the combustion exhaust gas changes without changing the flow rate of the combustion exhaust gas, only the supply amount of the reducing agent is changed without changing the flow rate of the reducing agent dispersion fluid. 3. The method for supplying a reducing agent to combustion exhaust gas according to claim 2, wherein the reducing agent is adjusted to correspond to concentration fluctuations of the substance to be reduced. 4. When only the flow rate of the combustion exhaust gas changes and the concentration of the substance to be reduced in the combustion exhaust gas does not change, the supply amount of the reducing agent is made to correspond to the fluctuation in the flow rate of the combustion exhaust gas, and the reducing agent The method for supplying a reducing agent to combustion exhaust gas according to claim 2, characterized in that the flow rate of the dispersion fluid is controlled. 5. When both the flow rate of the combustion exhaust gas and the concentration of the substance to be reduced in the combustion exhaust gas fluctuate, controlling the supply amount of the reducing agent and controlling the flow rate of the reducing agent dispersion fluid. A method for supplying a reducing agent to combustion exhaust gas according to claim 2.