JPS60137420A - Process for supplying reducing agent to combustion waste gas - Google Patents

Abstract

PURPOSE:To disperse and mix a reducing agent uniformly in waste gas without increasing pressure drop in a process for supplying a reducing agent to combustion waste gas contg. NOx by injecting the reducing agent from a nozzle so as to collide with a header. CONSTITUTION:NH3-contg. air is introduced from an introducing port 12 for fluid contg. a reducing agent, and the air is ejected into waste gas from four nozzles through a header 14 and a branch pipe. The nozzles are provided to the upstream side of the flow of the waste gas than the header, and the reducing agent ejected from the nozzle is deflected by the flow of the waste gas toward the downstream side and is dispersed and mixed in the waste gas and collides in this state with the header, where it is dispersed and mixed uniformly and effectively. Following-up to the variation of the flow rate of the waste gas is performed easily by only controlling the flow rate of the reducing agent correspondingly.

Description

[Detailed Description of the Invention] [Technical Field to which the Invention Pertains] The present invention relates to a method for supplying a reducing agent to combustion exhaust gas, and more specifically, to a method for supplying a reducing agent to combustion exhaust gas, and more specifically, to supply a reducing agent to combustion exhaust gas such as a boiler, an industrial furnace, etc. The present invention relates to a method for supplying a reducing agent to a combustion exhaust gas containing No.sub.2, in which a reducing agent supplied to remove nitrogen oxides (NO) such as No. 2 is uniformly dispersed and mixed in the exhaust gas.

[Prior Art] Many processes have been developed to remove nitrogen oxides from combustion exhaust gas, but the mainstream is a selective reduction method that uses NH3 as a reducing agent in the presence of a titanium oxide catalyst. There is. As shown in FIG. 1, this method converts NO in the flue gas that is sent from a flue gas generator 1 such as a boiler to a reduction device @3- via a heat exchanger 2.
The NH3 supplied from the NH3 supply source 4 is further mixed with the dispersion air sent through the dispersion air flow control valve 5 and the dispersion air valve 0, and is released from the header 7, and the titanium oxide catalyst N8. 4NO+4NH3+02→4N2+6H206N○2,0008NH3→7N2+12H2゜The reaction is carried out to convert into harmless N2 and H2O, which are then transferred to heat exchanger 9 and blower 1o.
The gas is discharged into the atmosphere from the chimney 11 through the chimney 11.

In this way, the selective reduction method is based on the premise that No contained in exhaust gas at a dilute concentration reacts with the reducing agent NH3 in the presence of a catalyst, but in order to carry out this reaction efficiently, It is necessary to sufficiently disperse and mix NH in the exhaust gas.

3 However, with such conventional reduction methods, it has been impossible to supply the reducing agent so as to uniformly disperse and mix it in the exhaust gas over a short distance. For this reason, the exhaust gas has an uneven reducing agent concentration distribution. Upon reaching the Il decoy, in the exhaust gas portion where the reducing agent concentration is higher than the NOx concentration, the excess reducing agent passes through the catalyst layer unreacted, while in the exhaust gas portion where the reducing agent concentration is lower than the NOx concentration, Excess NO passes through the catalyst layer unreacted, causing a decrease in the denitrification rate, and furthermore, the unreacted reducing agent causes various kinds of trouble, such as acidic sulfite, to the downstream equipment of the catalyst layer. This often results in the precipitation of ammonium and the resulting 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, there is a method of installing a movable baffle bar or baffle plate for ammonia mixing near the wake of the ammonia supply nozzle to achieve dispersive mixing (Japanese Patent Laid-Open No. 57-19020), but this requires a separate dispersion means. This will increase the pressure loss and hinder the rod.

Since the baffle plate is movable, there are many problems, including the fact that it is very difficult to seal the attachment portion to the exhaust gas pipe wall or duct wall.

Furthermore, in the selective reduction method, it is essential to be able to easily follow the load fluctuations of the boiler etc., to maintain the denitrification rate, to use the reducing agent economically, to to operate the equipment downstream of the catalyst bed, etc. However, conventional methods merely provide a separate dispersion means such as a baffle plate in the duct that increases pressure loss, and mechanically movable parts that are likely to cause the above-mentioned failure.

[Object of the Invention] The present invention has been made to solve the above-mentioned drawbacks of the prior art. That is, the object of the present invention is to be able to uniformly disperse and mix the reducing agent in the combustion exhaust gas over a short distance without using a separate dispersion means or without causing an increase in pressure loss, and to reduce the load fluctuations of boilers, etc. 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 the above.

[Summary of the Invention] The present invention provides a method for supplying a reducing agent to combustion exhaust gas, in which a reducing agent-containing fluid is introduced into a header, and the reducing agent-containing fluid is introduced from a nozzle located upstream of the combustion exhaust gas in the header. This is a method for supplying a reducing agent to combustion exhaust gas, characterized in that the reducing agent-containing fluid is ejected into the combustion exhaust gas so as to draw a trajectory such that the fluid collides with the header.

Since the present invention has the above-described configuration, the reducing agent-containing fluid ejected from the nozzle is pushed toward the downstream side of the exhaust gas by the flow of the exhaust gas, is dispersed and mixed in the exhaust gas, and collides with the header together with the exhaust gas, where the fluid flows. The exhaust gas and the reducing agent-containing fluid are uniformly mixed at the downstream part of the header, so that the reducing agent is uniformly mixed into the combustion exhaust gas over a short distance. can be dispersed and mixed.

In addition, if the exhaust gas flow rate and NOa degree in the exhaust gas change due to changes in the load of the exhaust gas generator such as a boiler,
These can be easily followed by simply controlling the flow rate of the reducing agent dispersion fluid and the supply amount of the reducing agent, respectively, which will be explained next.

The trajectory of the reducing agent-containing fluid ejected from the nozzle in the exhaust gas flow changes depending on various factors, so in order to draw a trajectory that collides with the header, which is a feature of the present invention, it is necessary to The factors that change the trajectory need to be controlled by an appropriate method.a 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, and the nozzle size. and the header, and the diameter of the exhaust gas piping or duct, but these are factors that change the above trajectory in a complex manner, so in order to draw a trajectory that collides with the header, these values must be adjusted. It cannot be uniquely identified. 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. 2 in the exhaust gas. Based on the shape and shape of the nozzle
The configuration of the reducing agent supply device, such as the angle and the distance between the nozzle and the header, can be designed such that the reducing agent-containing fluid ejected from the nozzle follows a trajectory that impinges on the header in the exhaust gas. In this way, it is possible to install a device capable of implementing 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). If you are
With the reducing agent supply device designed as described above, the reducing agent-containing fluid ejected from the nozzle can draw a trajectory such that it always collides with the header.

However, boilers and the like are not always operated under the same steady state as the above-mentioned design conditions, and the exhaust gas flow rate and No' in the exhaust gas fluctuate depending on changes in load, type of fuel, etc. As mentioned above, the trajectory of the reducing agent-containing fluid changes depending on various factors that are intricately related to each other.
In the method of the present invention, it is possible to follow the flow rate of the reducing agent-containing fluid by simply changing the flow rate of the reducing agent-containing fluid without making any changes to equipment factors such as the shape of the nozzle.

That is, in response to fluctuations in the exhaust gas flow rate, the amount of reducing agent is adjusted to correspond to fluctuations in the amount of No. 2 according to the detected exhaust gas flow port, and the flow rate of the dispersion fluid carrying the reducing agent is controlled.
l], it is possible to draw a trajectory in which the reducing agent-containing fluid always collides with the header.

Next, for a 1 degree fluctuation in the exhaust gas, N
Only the amount of reducing agent supplied is controlled in response to variations in the amount of o. In other words, the NO contained in the reducing agent and the exhaust gas at a dilute concentration
In order to react efficiently, the reducing agent must be sufficiently uniformly dispersed in the exhaust gas. To achieve this, the dispersion fluid that carries the reducing agent must have a flow opening several tens of times larger than the standard value of the reducing agent supply amount, and the reducing agent must be pre-dispersed in the dispersion fluid before being ejected into the exhaust gas. let

Comparing this to the case where the reducing agent is directly supplied into the exhaust gas, 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 reduced. done effectively. Therefore, even if the supply amount of the reducing agent is changed according to the fluctuation of NO, the flow rate of the dispersion fluid, which accounts for the majority of the reducing agent-containing fluid, does not change. Since the 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. fluctuate at the same time, the control of the dispersion fluid flow rate and the reducing agent supply amount can be performed separately as shown in -F, 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 j-base agent, but it is usually convenient to use air. Further, the reducing agent-containing fluid ejection nozzle may be attached to the header by providing a branch pipe thereto, or may be directly attached to the header. Furthermore, the nozzle can be installed so as to face the flow direction of the exhaust gas, but in this case, the exhaust gas directly hits the nozzle nozzle, which may cause the nozzle to become clogged with dust contained in the exhaust gas. be. To prevent this, the nozzle is preferably provided at an angle so as not to face the flow of exhaust gas. Further, in order to further promote the dispersion and moisture dispersion ability of the header, it is also possible to attach protrusions such as fins to the header as long as the pressure loss against the exhaust gas is within the allowable range.

[Explanation based on Experimental Examples] Next, a dispersion state observation experiment conducted using Monal gas as both the reducing agent-containing fluid and the exhaust gas will be described in order to improve the beating of the method of the present invention.

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 flowed 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 the reducing agent-containing fluid, the flow rate of the dispersing fluid is set to the standard amount of the reducing agent - It is assumed to be 1 times.

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.

This device includes a header 14 and a nozzle 15 disposed on the upstream side of the header in a direction perpendicular to the direction of the air flow.

In this experimental example using the apparatus configured as described above, white smoke is ejected from the header 14 through the branch pipe 16 into the air through the nozzle 15 in a direction perpendicular to the air flow. The white smoke ejected from the nozzle is pushed downstream by the air flow, and while being dispersed and mixed in the air, it collides with the header with the air, where the flow is violently disturbed, resulting in extremely effective dispersion and mixing. It was confirmed that since the air and white smoke are heated uniformly in the downstream part of the header, the white smoke can be uniformly dispersed and mixed in the air over a short distance.

Figures 3 and 4 show different experimental results. Figure 3 shows the insertion direction of the header changed by 90 degrees compared to the case of Figure 2, and Figure 4 shows the header inserted 2 times. In both cases, it was confirmed that by colliding with the header together with the air, the white smoke could be uniformly dispersed and mixed in the air over a short distance, as in Fig. 2.

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

In Fig. 5, the nozzle 15 is arranged downstream 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. Therefore, it is 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. They are simply 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, in the method of the present invention, the nozzle is located upstream of the header, and the reducing agent-containing fluid is ejected from the nozzle so as to collide with the header. This allows the reducing agent to be uniformly dispersed and mixed into the combustion exhaust gas over a short distance.

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 results of the dispersion carrying white smoke. When the dispersion air flow rate is controlled and decreased so that the white smoke collides with the header 14, FIG.
The experimental results are shown in which the dispersion air flow rate in the experiment shown in the figure was kept at the same Q as that without any particular control. In the case of FIG. 8, just as in the case of FIG. 4, the white smoke hits the header 14 and is evenly dispersed in the air, but in the case of FIG. 9, the white smoke hits the header 14. They do not collide and are not evenly dispersed in the air. As is clear from this experiment, according to the present invention, even if the exhaust gas flow port 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] Practical examples and comparative examples in which a reducing agent was actually supplied to remove nitrogen oxides contained in combustion exhaust gas will be shown.

Example 1 Exhaust gas 10 at 350'C containing 180 ppm of No.
．． 00ON TIl'/h were treated with N, 1-13 in the presence of titane oxide catalyst. 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 one quarter and three quarters from the upper end. The two headers 14 are connected to the duct 1
An inlet 12 for a reducing agent-containing fluid is provided at the center of the communicating portion. Each header 14
A total of four branch pipes 16, two from each, are provided on the upstream side of the flow of exhaust gas with respect to the header 14, and a total of four nozzles 15 are arranged at the tip of each branch pipe 16. There is. The nozzles are attached in such a way that the nozzles on the upper branch pipe face vertically downward, and the nozzles on the lower branch pipe face vertically upward.

The cross section of the duct 13 is 1000 mm square, the nominal diameter of the header 14 is 100 m, the nominal diameter of the reducing agent-containing fluid 19 is 100 m, and the length from the inlet 12 to the tip of the header 14 is 100 mm. The length to nozzle 15 is 450 mm, the length between branches 16 is in order of 500, nozzle 1
The distance from 5 to catalyst layer 8 was 200011111.

First, from the reducing agent-containing fluid inlet 12, NH31, 8N
+n'/hour mixed with 8ON air+n3/hour NH3
Contained air is introduced and passed through the header 14 and the branch pipe 16 to the 4
It was ejected into the exhaust gas from the nozzles 15. The height inside the duct is 100t at a position 500m downstream of the catalyst layer 8.
ra, 300mm, 500mm.

Exhaust gas was sampled at five points at 700 yvn and 900 m, and NoX concentration was measured using the NoX concentration detector 17. The measurement results are shown in Figure 11, and the outlet No. concentration is about 10 ppm at any height.
It was revealed that the method of Example 1 enabled substantially uniform dispersion and mixing of NH3 into the exhaust gas.

Exhaust gas was treated using a device in which a shell counterfeit nozzle was placed downstream of the exhaust gas flow with respect to the header. The composition of exhaust gas and NH3-containing air, flow G, etc. were the same as in Example 1. An outline of the apparatus used is shown in FIGS. 12A and 12B, 13A and 13B, and 14A and 14B. 12th
Figures A and 12B are the same as Figures 10A and 10B of the device of Example 1, except that the nozzles are arranged as described above, and Figures 13A and 13B show how the nozzles are arranged and how the catalyst layer is separated from the nozzles. The distance to
00 Oboro, and Figures 14A and 14B show the nozzle arrangement method and the number of nozzles by providing four headers and four branch pipes each with a nozzle at the tip. In Example 1, the number was 4 times 1, that is, 16.
10A and 10B.

The measurement results of the No 2 concentration in the exhaust gas after the treatment performed in the same manner as in Example 1 are shown in FIG. In Fig. 15, the O mark is when the apparatus shown in Figs. 12A and 12B is used, the O mark is when the apparatus shown in Figs. 13A and 13B is used, and the Δ mark is the
The cases in which the apparatuses in Figures A and 14B are used are shown, respectively.

The results of the comparative example (Fig. 15) are compared with the results of Example 1 of the present invention (Fig.
When the number of nozzles and the distance from the nozzle to the catalyst layer are both the same (marked in Figure 15), the No i15 degree distribution is lower than that in Example 1 of Akira Mizumoto. If the number of nozzles is the same as in Example 1 but the distance from the nozzle to the catalyst layer is twice (Fig. 15)
Even in Example 1 of the present invention, there was variation in the No. 1 degree distribution, indicating that NH3 was not sufficiently dispersed. Furthermore, 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 (indicated by △ in Fig. 15), almost the same results as Example 1 are observed, and the results are similar to those of Example 1 of the present invention. The concentration distribution is almost uniform, and NH3
It is shown that the dispersion of the particles had occurred well in advance. From the above results, it can be seen that the NH3-containing air collides with the header together with the exhaust gas and is sufficiently uniformly dispersed in Example 1.
In this case, it was possible to reduce the mixing distance to about 1/2 and the number of nozzles 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 NH3 supply amount to one half. The No 2 concentration in the exhaust gas and the configuration of the device were the same as in Example 1.

Here, we will discuss the case where the dispersion air flow rate is controlled and decreased in accordance with the decrease in the exhaust gas flow rate so that the N l-13-containing air ejected from the nozzle draws a trajectory that collides with the header, and the example A comparison was made between the dispersion air flow m of No. 1 and the case where the flow rate was the same and was not controlled.

FIG. 16 shows the measurement results of the No 2 concentration in the exhaust gas after the treatment performed in the same manner as in Example 1. When the dispersion air vl■ was controlled (○ mark in Figure 16), the No. 1 degree distribution was uniform, indicating that NH3 was sufficiently dispersed, but when the dispersion air meteor was not controlled. In this case (marked O in Fig. 16), the NO concentration distribution varied, indicating that NH3 was not sufficiently dispersed. It can also be seen that by the method of the present invention, fluctuations in the exhaust gas flow rate can be easily followed by controlling the reducing agent supply amount and the dispersion air flow rate.

"Effects of the Invention" As is clear from the above, the present invention can produce the following particularly remarkable effects.

First, it is possible to ensure uniform dispersion and mixing of the reducing agent into the exhaust gas over a shorter distance than in the past. 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 made more efficient. Therefore, the site area is saved and
Equipment costs and operating costs can be reduced.

Next, it is possible to very easily follow the fluctuations in the exhaust gas flow rate and NOx by simply controlling the cause of the reducing agent dispersion fluid and the reducing agent supply amount. As a result, a very high denitrification rate can be obtained, so that the reducing agent can be used effectively, and troubles such as blockage and corrosion in the catalyst bed flow insulator can be prevented. Therefore, economical and stable operation can be performed without requiring special skilled workers.

[Field of Application of the Invention] The present invention has the above-mentioned structure and the many excellent features described above, and is therefore applicable to cases where a reactant is supplied in a dry flue gas desulfurization method, etc. It can also be applied to

[Brief explanation of drawings]

Figure 1 is a system diagram showing an apparatus for implementing the selective three-binary method;
3, 4, and 8 are schematic diagrams, FIG. 5, and FIG. 6, respectively, showing experimental results of the present invention. 7 and 9 are schematic diagrams showing the results of comparative experiments, FIG. 10A is a front view of the apparatus according to the embodiment of the present invention, and FIG.
Figure B is a side view of the device in Figure 10A, Figures 11 and 16.
12A and 12B, 13A and 13B, and 14A and 148 are graphs showing the results of the example of the present invention, and FIGS.
FIG. 15, which is similar to FIG. 0B, is a graph showing the results of a comparative example. 12...Reducing agent-containing fluid inlet, 13...Exhaust gas piping or duct, 14...Header, 15...Nozzle, 1
Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6

Claims (1)

[Claims] 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 collides with the header from a nozzle located upstream of the combustion exhaust gas of the header. 1. A method for supplying a reducing agent to combustion exhaust gas, the method comprising jetting the reducing agent-containing fluid into the combustion exhaust gas as shown in FIG.