JPS63252530A - Ammonia reduction and denitration device and denitration method - Google Patents

Abstract

PURPOSE:To eliminate the necessity of providing a damper and its controller and enhance denitration performance by providing a bypass flow channel and a primary reactor catalyst layer in the gas flow direction in a manner to equal ize the exhaust gas pressure drops and providing a secondary reactor post- stream. CONSTITUTION:A partition plate 2 is installed along the flowing direction of untreated gas on the inlet side of casing 7 of a denitration reactor, and an exhaust gas flow channel 2A with a primary reactor 4 and a bypass flow channel 2B are demarcated by said partition plate 2. A NH3 injecting device 1 is provided on the pre-stream side of the primary reactor 4 inside the partition plate 2, and a dispersion plate 5 for bypass gas is provided on the outlet side of the bypass flow channel 2B, while a secondary reactor 8 is installed on the post-stream side of the dispersion plate. A denitration treatment can be carried out at low cost and high performance by regulating the bypassing quantity for the purpose of eliminating the necessity of a damper by means of a resistance element 9 to equalize the exhaust gas pressure drops of the bypass flow channel 2B and the primary reactor 4.

Description

[Detailed Description of the Invention] Industrial Application Field] The present invention relates to an ammonia reduction and denitrification device and a denitrification method, and in particular to a method for removing nitrogen oxides (NOx) from combustion exhaust gas discharged from a combustion device such as a boiler. Regarding equipment.

[Conventional technology]

In recent years, with the tightening of regulations on NOx emission concentrations, in addition to improvements in conventional combustion methods, ammonia (hereinafter referred to as NH3)
An increasing number of plants are installing denitrification equipment using a dry catalytic reduction method, which performs the denitrification reaction in the presence of a catalyst using denitrification as a reducing agent. In this method, the injection molar ratio (ratio of NOx / NH3) is limited so that the concentration of NH3 discharged from the denitrification equipment is as low as possible in consideration of the impact on downstream equipment. . However, on the other hand, such an operation prevents the effective use of the catalyst, so the inventors of the present invention used the catalyst effectively to improve the denitrification performance and to reduce the amount of catalyst, even in the previous operation to limit leaked NH3. proposed a method to reduce this (Japanese Patent Application No. 61-26950). In this method, the denitrification reactor is divided into primary and secondary denitrification reactors along the flow direction of the process gas, and a bypass flow path is provided for the primary denitrification reactor on the upstream side. High molar ratio, low S
By operating under V (low gas pressure) conditions, the activity of the catalyst in the primary denitrification reactor is increased, and the overall denitrification performance of the primary and secondary reactors is increased.

Hereinafter, the conventional reactor structure will be explained using FIG. 6. This device includes a casing 7 and a partition plate 2
a plurality of exhaust gas passages divided and formed by a plurality of exhaust gas passages; ammonia injection nozzles IA and primary denitrification reactor 4 provided in every alternate row among the plurality of exhaust gas passage rows; and exhaust gas passages other than the said divided rows. The denitrification reactor 9 includes a mixing chamber 6 and a secondary denitrification reactor 8 provided downstream of the primary denitrification reactor. Note that 1 is a pipe of an ammonia inflow device.

In the denitrification apparatus configured in this manner, when exhaust gas is introduced into the casing 7, it is separated into treated gas that passes through the primary denitrification reactor 4 and untreated gas that passes through the bypass flue 3. The bypass amount of untreated gas is adjusted by damper 9 to an optimum value. The exhaust gas introduced into the primary denitrification reactor 4 is mixed with NH3, and a denitrification reaction is performed in the primary denitrification reactor 4. Primary denitrification reactor 4
The unreacted NH3 contained in the exhaust gas that has passed through the bypass flue 3 and the unreacted exhaust gas that has passed through the bypass flue 3 are mixed in the mixing chamber 6, and then introduced into the secondary denitrification reactor 8 for denitrification. A reaction takes place, NOx in the gas is removed, and the gas is guided to the outlet of the casing 7.

[Problem that the invention seeks to solve]

Although the above conventional technology can control the amount of bypass and adjust the optimum amount of bypass by changing the opening/closing degree of the damper 9, it is possible to control the amount of bypass and adjust the optimum amount of bypass by changing the degree of opening/closing of the damper 9. , control equipment, power sources, and other equipment are required, which not only increases the cost but also makes the control itself complicated.

In addition, in the conventional reactor, the mixing effect of the denitrified gas and the untreated gas in the mixing chamber provided between the primary reactor and the secondary reactor is not sufficient, resulting in high concentrations in some parts. There was a problem in that the glue NH3 was discharged from the secondary reactor and the denitrification performance deteriorated.

An object of the present invention is to provide an ammonia reduction and denitrification device and a denitrification method that can omit the damper provided in the bypass flow path of the primary denitrification reactor and eliminate the need for related control equipment. be.

[Means for solving problems]

The denitrification device of the present invention includes a plurality of exhaust gas flow paths divided by a partition plate, an ammonia injection nozzle and a primary denitrification reactor provided in a predetermined flow path among the plurality of exhaust gas flow paths, and a A resistor provided as necessary in a bypass flow path other than the flow path, a gas dispersion means provided at the outlet thereof, and a secondary denitrification reactor provided downstream of the primary denitrification reactor. It is characterized by having.

Specifically, the apparatus of the present invention includes a partition member provided along the flow direction of the untreated gas on the inlet side of the denitrification reactor casing, and a catalyst is placed in at least one gas circulation space defined by the partition member. arranged to constitute a primary reactor,
At least one other gas circulation space is a bypass flow path, an ammonia injection means is provided on the upstream side of the primary reactor inside the partition member, and a bypass gas distribution plate is provided on the outlet side of the bypass flow path. A secondary denitrification reactor is placed on the downstream side of the dispersion plate.

Further, in the denitrification method of the present invention, the pressure loss when the bypass gas passes through the bypass flow path is equal to the pressure loss that occurs when the exhaust gas passes through the primary denitrification reactor at a preset speed. The feature is that the pressure loss of the bypass flow path is set as follows. More specifically, the pressure loss of each reactor is adjusted so that the gas velocity of the primary denitrification reactor is the same as the gas velocity of the secondary reactor when a predetermined amount of exhaust gas is bypassed through the bypass flow path. and then setting the pressure loss in the bypass flow path so that the pressure loss when the gas passes through the primary denitrification reactor at the gas velocity is equal to the pressure loss in the bypass flow path.

[Effect]

In the present invention, the bypass amount, which was conventionally set by opening and closing a damper, is set by providing a resistor so that the pressure loss of the exhaust gas passing through the bypass flow path is equal to the pressure loss of the primary reactor catalyst layer. , the conventional damper is no longer necessary, and the bypass gas is dispersed by the gas dispersion plate installed on the downstream side of the bypass flow path and is sufficiently mixed with the denitrification processing gas of the primary reactor, so that the denitrification equipment is Performance can be improved.

〔Example〕

FIG. 1 is an explanatory diagram showing one embodiment of the present invention. This device includes a plurality of exhaust gas flow paths divided by a partition plate 2, an ammonia injection nozzle IA provided in a predetermined flow path 2A among the plurality of exhaust gas flow paths, and a primary denitrification reactor 4.
and a resistor 9 provided in the exhaust gas flow path 2B (also referred to as a bypass flow path or a bypass flue) other than the predetermined flow path.
and a gas dispersion plate 5 disposed at the outlet thereof, a mixing chamber 6 and a secondary denitrification reactor 8 provided downstream of the primary denitrification reactor 4. The difference from the prior art shown in FIG. 6 is that the damper 9 in the bypass flow path 2B is omitted and a resistor 9 is provided in its place, and that the cross-sectional area of the bypass flow path is reduced compared to the conventional technology. This is because a V-shaped gas distribution plate 5 is provided at the downstream portion of the bypass flow path.

The pressure loss of the resistor provided in place of the damper is set as follows.

(1) Determine the optimum amount of bypass under the load conditions under which the denitrification equipment (primary and secondary reactors 4.8) will be used for the longest time.

(2) When bypassing the above-mentioned amount of bypass, the primary reactor is set so that the gas velocity passing through the catalyst layer of the primary reactor 4 is the same as the gas velocity passing through the catalyst layer of the secondary reactor 8. Select the cross-sectional area or length of the catalyst layer in step 4.

(3) The pressure loss in the bypass flue 2B is set so that the pressure loss when gas passes through the catalyst layer of the primary reactor 4 at the above speed is equal to the pressure loss in the bypass flue.

(4) Set the bypass outlet gas flow velocity to a moderate value (approximately 15 m/s for gas containing dust), and select a resistor having the pressure loss set in (3) at this velocity. At this time, it is desirable that the length of the resistor be matched to the length of the catalyst layer.

As the resistor to be used, a material having a shape such as a plate-like structure or a honeycomb structure and having high abrasion strength is suitable.

The gas dispersion plate 5 has the function of dispersing the bypass gas ejected at high speed from the outlet of the bypass flue 2B. It is installed on its center line at the exit section. As for the shape, it is preferable to use a member having a widening portion toward the gas downstream side (for example, a 7-shaped cross section as shown in FIG. 1), and it is also desirable to select a material with high abrasion strength. The mixing effect of the untreated gas from the bypass flue 2B and the gas that has passed through the catalyst in the primary reactor is affected by the flow velocity ratio of the two, the width of the bypass flue, etc., so it depends on each denitrification reactor. It is desirable to select the gas distribution plate that has the greatest mixing effect.

Although not shown, it is also possible to provide a rectifying member in the mixing chamber 6 for rectifying the exhaust gas introduced into the secondary reactor 8. This is convenient when the distance between the primary reactor 4 and the secondary reactor 8 is insufficient and the exhaust gases mixed in the mixing chamber 6 are not naturally rectified.

As mentioned above, the gas flow rates in the primary reactor 4 and the secondary reactor 8 are set to be the same, but this rate is selected to be the most efficient flow rate at the planned load. The denitrification reaction will be carried out efficiently in both the primary and secondary reactors.

On the other hand, we will discuss whether the denitrification performance can be maintained with the device of the present invention, that is, with the bypass amount fixed constant and the damper omitted, when the load changes and the exhaust gas conditions such as gas amount and temperature change.

FIG. 3 shows the change in the optimum bypass ratio of the primary reactor with respect to the load change. The bypass ratio here represents the ratio of the amount of gas passing through the bypass flue 3 to the total amount of gas passing through the primary reactor 4. As can be seen from this figure, the optimal bypass ratio is almost constant except in the low load range.

Figure 4 shows two bypass control methods for load changes.
The comparison was made using the NOx concentration at the outlet of the secondary reactor. Optimal bypass ratio control is a method of controlling the amount of bypass to achieve the optimal bypass ratio shown in Figure 3, and corresponds to the conventional technology using a damper.
This control method sets the optimum bypass ratio at 00% load and keeps this bypass ratio constant even when the load changes, and corresponds to the method of the present invention. From the figure, the secondary reactor outlet N by this recontrol method
The Ox values are almost the same. Even in the low load range, the third
Despite the difference between the two control values shown in the figure, the reason why almost the same performance is obtained in the low load range shown in Figure 4 is because the gas amount decreases at low loads, so the bypass ratio changes. This is because the change in bypass amount is small even if therefore,
It can be seen that even when the load changes, according to the fixed bypass ratio control used in the present invention, performance equivalent to the optimum bypass ratio can be obtained. On the other hand, also in Figure 4, even when the load changes, the outlet NOx9 degree is almost constant,
The denitrification performance can be considered to be almost constant, but this is because when the load decreases, the negative effect of the decrease in exhaust gas temperature on catalyst performance is offset by the positive effect of the decrease in exhaust gas volume, etc. The behavior is the same as that of denitrification performance.

Next, FIGS. 5A and 5B illustrate the effect of the gas distribution plate 5 at the outlet of the bypass flue 2B. 1
The gas flow rate within the catalyst layer of the next reactor 4 is determined by the dust concentration in the exhaust gas, but is generally 4 to 8 m/
It is in the range of about S. On the other hand, the bypass gas flow rate is about 15 m/s as described above. In the absence of this molecule &Fi5, as shown in (B), the bypass gas ejected from the duct with a high speed and narrow cross-sectional area protrudes in the downstream direction and takes a long distance to mix with the process gas from the catalyst layer. It takes. On the other hand, when the dispersion plate 5 is provided (B), the bypass gas is ejected diagonally downward and diffused, so that the gases can be mixed over a short distance, and the capacity of the mixing chamber 6 can also be small.

Next, FIG. 2 shows another embodiment of the present invention, in which the cross-sectional area of the bypass flue 3 is extremely reduced to increase the gas pressure loss, and the resistor 9 used in FIG. is omitted. According to this embodiment, the bypass flue 3
The width of the bypass gas is narrow, for example, several tens of meters, and the bypass gas flow velocity ranges from about 40 to 50 m/s, so it is preferably used for clean exhaust gas that does not contain dust. According to this embodiment, the cross-sectional area of the reactor is narrowed to the extent that the resistor can be omitted.
Also, the structure can be simplified and simplified.

〔Effect of the invention〕

According to the present invention, the damper conventionally provided in the bypass flue of the primary reactor can be omitted, and the accompanying equipment including the gas amount detector for controlling the damper can be omitted. can.

Further, by providing a simple gas distribution plate, the exhaust gas itself can mix the gases, and a suitable mixing effect can be obtained, so that the mixing distance can be shortened and the apparatus can be made more compact. Furthermore, the denitrification performance of the entire device can also be improved by uniform NH3 dispersion. As described above, by using the present invention, a high-performance denitrification device can be provided at a low cost.

[Brief explanation of drawings]

FIG. 1 is a sectional view of a denitrification device showing an embodiment of the present invention, and FIG. 2 is a sectional view of a denitrification device showing another embodiment of the invention.
Figure 3 is an explanatory diagram illustrating the optimum bypass ratio of the primary reactor with respect to load changes, and Figure 4 is an explanatory diagram illustrating the optimum bypass ratio of the primary reactor with respect to load changes.
Next, an explanatory diagram comparing two bypass ratio control methods using the reactor outlet NOx concentration. Figures 5 (A) and (B) are diagrams explaining the effect of the gas dispersion slope. Figure 6 is a diagram comparing the two bypass ratio control methods using the reactor outlet NOx concentration. 1 is a cross-sectional view of a denitrification device according to the technology; FIG. 1...N H3 injection device, 2...Partition plate, 2A...
・Exhaust gas flow path, 2B...Bypass flow path, 3...Bypass flue, 4...Primary reactor, 5...Bypass gas distribution plate, 6...-Mixing chamber, 7... Casing, 8...
-Secondary reactor, 9...resistor. Agent Patent Attorney Takenaga Kawakita Figure 1 Figure 2 Figure 3 Figure 4 Load ('/,)

Claims (2)

[Claims] (1) A plurality of exhaust gas flow paths divided by partition plates,
An ammonia injection nozzle and a primary denitrification reactor provided in a predetermined flow path among the plurality of exhaust gas flow paths, and a resistor and its outlet provided as necessary in a bypass flow path other than the predetermined flow path. a gas dispersion means disposed in the above-mentioned 1;
An ammonia reduction denitrification device comprising a secondary denitrification reactor provided downstream of the secondary denitrification reactor. (2) a plurality of exhaust gas flow paths, an ammonia injection nozzle provided in a predetermined flow path among the plurality of exhaust gas flow paths;
A secondary denitrification reactor, a resistor provided as necessary in a bypass flow path other than the predetermined flow path, and a gas dispersion means provided at the outlet thereof, and a gas dispersion means provided downstream of the primary denitrification reactor. When operating a denitrification device having a secondary denitrification reactor, the pressure loss when the exhaust gas passes through the bypass flow path and when the exhaust gas passes through the primary denitrification reactor at a preset speed. A denitration method characterized by setting the pressure loss of the bypass flow path so that the pressure loss of the bypass flow path is equal to the pressure loss of the bypass flow path.