JPH10216459A - NOx reduction method and apparatus for combustion exhaust gas - Google Patents

Abstract

[PROBLEMS] To appropriately set and control the NH ₃ / NOx molar ratio in a denitration catalyst, maintain high denitration efficiency, and reduce equipment maintenance load. SOLUTION: A catalyst 28 for converting NH ₃ to NOx, N
The Ox reduction catalyst 29 and the NOx analyzer 30 are combined, the slip NH ₃ equivalent concentration 31 and the insufficient reducing agent concentration 32 are obtained by the calculator 33, and the flow rate of the NH ₃ addition device 35 of the denitration catalyst is calculated from the values by the signal converter 34. Control valve 3
6 and flow control valve 3 of NH ₃ addition device 37 of desulfurization equipment
8 is controlled. The control signal converts the deviation from the set value into an opening change signal for the flow control valves 36 and 38, and adjusts the NH ₃ flow rate so that the deviation becomes a minimum amount.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for reducing NOx in combustion exhaust gas by selectively contacting a nitrogen oxide (NOx) in a combustion exhaust gas with a reducing agent (NH ₃ or the like) in a catalytic reaction layer and performing a denitration treatment. It concerns the device. Especially,
The present invention relates to a method and apparatus for indirectly measuring the NH ₃ concentration and appropriately setting and controlling the concentration ratio between NH ₃ and NOx (hereinafter referred to as “NH ₃ / NOx molar ratio”) using the measured value. .

[0002]

2. Description of the Related Art Catalyst-based denitrification and reduction supply technology: The selective catalytic reduction method using a catalyst is one of the general technologies of flue gas denitration, and it depends on the type of catalyst and reaction conditions divided by temperature and space velocity. (SV), linear velocity (LV), reducing agent, etc. are appropriately selected according to the required efficiency of the process, exhaust gas components, etc.
Designed.

Here, SV = (processing gas flow rate) / (catalytic reaction layer volume), LV = (processing gas flow rate) / (catalyst reaction layer flow path cross-sectional area) FIG. FIG. 1 is a conceptual diagram showing an apparatus for performing the above. When the exhaust gas 39 is guided to the duct 40 and passes through the catalyst layer 42 incorporated in the denitration reaction layer 41, NOx 43 in the exhaust gas is reduced by NH 3 of the reducing agent blown from a nozzle 44 provided at the entrance of the denitration reaction layer 41. _It is mixed with 345 and reduced on the surface of the catalyst layer 42 to become N ₂ 46 and H ₂ O 47, detoxified and sent to the chimney 48.

[0004] The type of the reducing agent and the charging method are also set in consideration of costs and equipment restrictions, and the charging amount is generally adjusted and controlled so as to be supplied without excess or depletion during denitration. NH ₃ is used as a reducing agent. As the reducing agent can also be used like in addition to urea or hydrogen sulfide NH _3, most NH ₃ are used. Hereinafter, the reducing agent will be described as NH ₃ .

As a general technique for adjusting the input amount of NH ₃ (reducing agent), a processing gas flow rate and a NOx concentration are measured,
A method in which a required flow rate is set by calculation and mixed into a processing gas via a flow rate setting device and a control valve (Japanese Patent Laid-Open No. 1-1483)
No. 33; method for supplying a reducing agent for denitration, JP-A-5-15
No. 4340; a method for denitration of exhaust gas from a sintering machine, Japanese Patent Publication No. 2-579805, and a disclosure of an ammonia injection amount control device, etc.) are known.

In general, adjustments such as confirmation of the concentration after addition and feedback control of the addition amount are not performed because the analysis of the reducing agent is complicated. In general, it is rare that slip of the reducing agent (excess of the reducing agent) occurs from the previous step of the denitration treatment process. Therefore, even if the charging amount and the concentration ratio of the reducing agent are adjusted by the above-described means, the operation is not improved. No problem.

However, in a process in which the reducing agent slips from the upper step in the denitration processing gas, and a process in which the slip concentration fluctuates, it is impossible to continuously and quantitatively grasp the slip concentration. , Quantitative injection method ". This is because continuous measurement of the concentration of the slip reducing agent in the processing gas has problems such as being complicated and lacking in stability, and the measured value cannot be used as it is as a flow control signal.

[0008] Regarding NH ₃ gas analysis technology: continuous N
The H ₃ analyzer includes, for example, an ultraviolet (UV) absorption analyzer in a dry system, and is a method of quantifying a concentration from a spectral characteristic value such as NH ₃ . In the wet method,
Japanese Patent Application No. -90994 discloses a measuring instrument using an ion electrode method.

[0009] However, maintenance of gas pretreatment (for example, countermeasures such as condensation in a sampling conduit, trapping or separation and separation of compounds, etc.) are required for covering, fouling and deterioration of the sensor due to impurities and deposits in the analysis gas. processing)
Is too poor for online devices because it is too complicated.

The NH ₃ analysis includes an indophenol method (JIS K-0099) called a wet method and a simple detector tube (Gastec etc.), all of which are batch analyses, and include analysis time and accuracy. From becoming an online analyzer.

As a technique for indirectly analyzing NH ₃ in a gas, Japanese Patent Publication No. 56-32580 and Japanese Patent Laid-Open Publication No.
Publication No. -114666 is the NH ₃ in the oxidation catalyst to convert to NO, discloses a proposal that the concentration difference is the NH ₃ concentration in the schematic. This makes use of the fact that NH ₃ / NO reacts almost equimolarly.

FIG. 4 is a system diagram showing the configuration of an apparatus for performing analysis of NH ₃ in gas disclosed in Japanese Patent Publication No. 56-32580. As shown in FIG. 4, after performing SOx treatment 50 on the exhaust gas 49 in advance, the distribution route is branched into two, one of which is a direct route 51 and the other of which is a temperature controller 5.
2. NO through NH ₃ oxidizer 53 and NO converter 54
Guided to a route with x analyzer 55. These two routes are automatically switched by the solenoid valve 56. 2 obtained here
And a NH ₃ equivalent amount of NOx concentration difference of the route.

Regarding a process in which the concentration of the reducing agent fluctuates: FIG. 5 is a system diagram showing a configuration of an apparatus for performing a conventional sintering exhaust gas treatment at a steel mill. As shown in FIG. 5, dust 5 in the combustion exhaust gas 58 generated by the sintering machine 57
9. In an exhaust gas treatment process for purifying SOx60 and NOx61 by a dust collector 62, a desulfurization facility 63 and a denitration facility 64, a wet desulfurization method using an absorbent 65 for desulfurization is advantageous in terms of desulfurization efficiency, and the liquid after absorption is It is used as an absorbing solution for absorbing NH ₃ 67 in COG 66 which is a by-product gas in the chemical processing of an adjacent coke.
The liquid that has absorbed H ₃ is circulated through a circulation pump 68 as an absorption liquid for desulfurization of the sintering exhaust gas.

In the wet desulfurization equipment, the processing gas is guided to a reaction tower, and SOx in the gas is absorbed while making gas-liquid contact with the absorbing liquid in the tower. The reaction tower 69 has a cooling stage 7 from the upstream.
0, an absorption stage 71, a dilution stage 72, a purification stage 73, and a demister 74. The liquid sprayed from the nozzle 75 in each stage is circulated into and out of the system by a pump 76.

The basic reaction formula in this reaction tower is as follows. SO ₂ + (NH ₄ ) ₂ SO ₃ + H ₂ O → 2 (NH ₄ ) H
SO ₃ : production of ammonium acid sulfite Here, (NH ₄ ) ₂ SO ₃ : absorption liquid.

FIG. 6 is a graph showing the slip characteristics of SOx and NH _{3 in} a conventional wet flue gas desulfurization reaction and the like. As shown in FIG. 6, when the pH of the purified solution corresponding to the final stage of the absorption tower is shifted to the alkali side, the denitration efficiency is improved,
On the other hand, the slip NH ₃ increases. Since the desulfurization efficiency is usually controlled, the operation is performed in a balance where slip NH ₃ of a certain concentration level is always generated from the process design.

The slip concentration of the reducing agent (NH ₃ ) from the above step is determined by adjusting the balance of the absorbent in the desulfurization process (NH in the chemical process).
₃ Absorption). However, in the actual desulfurization operation, the properties of the absorbing solution and p
H and the like are adjusted. The adjustment function adjusts the balance by the coke oven gas processing amount in the NH ₃ absorption process in chemical processing, the liquid extraction amount for ammonium sulfate production, the NH ₃ addition amount in the system, and the like.

[0018]

Adjustment of the amount of reducing agent (NH ₃ ) added: In the selective catalytic reduction method using a catalyst, a NOx reducing agent (mainly NH ₃ , urea, hydrogen sulfide, etc. can be used) The setting and control of the concentration ratio are extremely important in terms of efficiency management, running cost and environmental management. That is, if the operation is performed at an appropriate concentration ratio or less, the denitration efficiency is reduced due to the shortage of the reducing agent, while if the operation is excessive, the amount of the reducing agent slipping through the denitration reaction layer is increased, and the cost of the reducing agent is increased, as well as the post-process. (E.g., heat exchanger blockage, corrosion, etc.) and the problem of environmental pollution during chimney discharge.

In the process of adding the reducing agent only in the denitration process, if there is an accurate measurement value of the processing gas flow rate and the NOx concentration, an appropriate reducing agent addition flow rate can be obtained by calculation and can be controlled by the flow rate control valve. .

FIG. 7 is a system diagram showing the configuration of an apparatus for controlling the flow rate of a reducing agent (NH ₃ ) added for wet flue gas desulfurization disclosed in Japanese Patent Application Laid-Open No. 5-154340. As shown in FIG. 7, the concentration of NOx 79 and the processing gas flow rate 80 in the combustion exhaust gas 78 discharged from the sintering 77 are changed by the NOx in the inlet duct 83 of the reaction layer 82 of the nitrate denitration 81.
Meter 84 and a flow meter, and the catalyst inlet NH ₃
Is calculated by the computing unit 86. However, in a process in which the reducing agent slips from the previous step of denitration and the concentration of the reducing agent fluctuates, in order to set the appropriate reducing agent concentration at the entrance of the denitration catalyst, the slip concentration is usually continuously measured and the slip concentration is usually measured. A method is required in which the shortage amount is calculated by calculation, and the flow rate of the reducing agent is adjusted and added. for that purpose,
Along with the measurement of the denitration gas flow rate and the NOx concentration, a highly accurate concentration analysis of the slip reducing agent is required.

Concerning continuous analysis of reducing agent (NH ₃ ) and concentration ratio (molar ratio) control: Online analysis of NH ₃ used as a main reducing agent for denitration is carried out in a sintering exhaust gas containing many impurities such as SOx dust. In the target, the sensor is affected by blockage due to dust and precipitates in the gas sampling conduit and pretreatment device, drain condensation and trapping, etc., and as a result, sensor deterioration and accuracy deterioration due to adhesion and coating to the sensor part and corrosion May occur, and the reliability is poor as an online measuring device.

[0022] suppression of the concentration variation of the slip reducing agent (NH _3), the supply-demand balance of the desulfurization efficiency maintaining and absorption solution (between sinter / Chemical) many limitations in terms of adjustment, slip NH ₃ concentration for its Has to be the result of operations.

For the desulfurization and denitration of exhaust gas, a heat exchanger is generally provided from the viewpoint of energy saving. In particular, when the flow rate of the processing gas is large, a rotary heat storage type heat exchanger (for example, Jungstrom) is used. , SOx in exhaust gas
(Mist, Fume-like), ammonium sulfate ((NH ₄ ) ₂
As SO ₄ ] or ammonium acid sulfate [(NH ₄ ) HSO ₄ ], sulfide precipitates and gasifies on the surface of the heat exchanger element (corrugated plate) in a certain temperature range, and a part of the slip NH ₃ Since absorption and separation occur, the presence of these facilities upstream of the denitration catalyst causes fluctuations in the NH ₃ concentration even within the facilities.

However, the absorption and separation of NH ₃ is not a uniform occurrence, but depends on the gas temperature, NH ₃ concentration, slip SOx concentration, NH ₃ / NOx molar ratio, the shape of the heat exchanger element and the state of blockage. Because it is affected, it is difficult to grasp the phenomenon quantitatively.

NOx and a reducing agent (NH
Appropriate control of the molar ratio with ₃ ) is important in terms of maintaining denitration efficiency, preventing corrosion and blockage of equipment, stabilizing catalyst activity, and reducing exhaust gas. However, slip NH ₃
Without continuous analytical values with accurate concentration, it is difficult to control the molar ratio.

Further, in the actual process, there are not only cases where the amount of NH _{3 is} excessive but also cases where the amount is insufficient. In this case, the catalyst efficiency is reduced almost in proportion to the insufficient concentration. Therefore, it is very important to know the amount of the reducing agent. That is, in controlling the molar ratio of the reducing agent, it is indispensable to measure and grasp the excess or shortage (concentration) of the reducing agent in the gas.

SOx and NOx in combustion exhaust gas such as sintering
When processing, desulfurization when the absorption liquid in a wet contains NH _3, NH ₃ in the absorption liquid in the subsequent stage of the denitration process is mixed with the slip. NOx and reducing agent N in denitration catalyst
Setting the molar ratio with H ₃ is an important item for efficiency management and equipment maintenance.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and an object of the present invention is to maintain and maintain a high denitration efficiency by appropriately setting and controlling the NH ₃ / NOx molar ratio in a denitration catalyst. It is another object of the present invention to provide a method and an apparatus for reducing NOx in combustion exhaust gas, which can reduce the load of equipment maintenance.

[0029]

According to the first aspect of the present invention, there is provided a method for reducing NOx of combustion exhaust gas, wherein a desulfurization facility and a facility having a denitration catalyst reaction layer are used in a flow path of the combustion exhaust gas, and NH ₃ is used as a reducing agent. In the NOx reduction method for combustion exhaust gas, wherein nitrogen oxides (NOx) contained in the combustion exhaust gas are selectively reduced in the denitration catalyst reaction layer by using the same, the excess / deficiency of the NH ₃ concentration of the combustion exhaust gas at the outlet of the denitration catalyst reaction layer is measured. To determine the NH ₃ / NOx molar ratio, and from the difference between the determined molar ratio and the set molar ratio, determine the opening of the NH ₃ input flow rate control valve of each of the denitration catalyst reaction layer and the desulfurization equipment to adjust the opening. into a signal, by adjusting the introduced NH ₃ flow rate of the denitration catalyst reaction layer and the desulfurization by said signal, controlling the child the molar ratio of NH ₃ / NOx of the denitration catalyst reaction layer to a predetermined appropriate value Those having features to.

The NOx of the flue gas of the invention according to claim 2
The reduction method uses desulfurization equipment and denitration catalyst in the flue gas flow path.
Using a facility having a medium reaction layer, NH_ThreeUsing
To remove nitrogen oxides (NOx) contained in the combustion exhaust gas.
N of combustion exhaust gas which is selectively catalytically reduced in the nitrate catalyst reaction layer
In the Ox reduction method, the fuel at the outlet of the denitration catalyst reaction layer
The flue gas is passed through a route with an oxidation catalyst and
The route through which the flue gas passes, and the reduction catalyst
And distributing into three flow paths with a route having
In the above, the combustion exhaust gas is oxidized by the oxidation catalyst.
The amount of NOx after the combustion was measured and
The amount of NOx in the exhaust gas was measured and
The combustion exhaust gas contains a predetermined amount of NH._ThreeTo the reduction catalyst
Therefore, the NOx amount of the combustion exhaust gas after reduction is measured.
The measured value of the NOx amount of the route and the N of the route
Excess NH due to the difference from the measured Ox amount_ThreeCalculate the concentration and
NOx measured value of the funnel and NOx amount of the route
Insufficient NH due to difference from measured value _ThreeCalculate the concentration
NH_ThreeConcentration and lack of NH_ThreeFrom the calculated value of the concentration,
NH in the catalytic reaction layer_Three/ NOx molar ratio is calculated,
From the calculated value of the ratio, the denitration catalyst reaction layer or the desulfurization
One or both input NH_ThreeCalculate the quantity and calculate
Amount of NH_ThreeOf the denitration catalyst reaction layer and the desulfurization equipment
By adding to one or both, the denitration catalytic reaction
Characterized by controlling the molar ratio of the layers to a predetermined value
It is.

According to a third aspect of the present invention, in the first aspect of the present invention, the operations of the NH ₃ introduction flow rate control valve of each of the denitration catalyst reaction layer and the desulfurization equipment can be switched mutually, and the obtained NH ₃ When the value of the difference between the / NOx molar ratio and the set molar ratio is within a predetermined control range, the NH ₃ supply flow rate control valve of the denitration catalyst reaction layer is operated to supply NH ₃ to the denitration catalyst reaction layer. , Outside the prescribed control range,
The method is characterized in that the NH ₃ supply flow rate control valve of the desulfurization facility is operated to supply NH ₃ to the desulfurization facility, thereby controlling the NH ₃ supply flow rate of the denitration catalyst reaction layer and the NH ₃ supply rate of the desulfurization facility. .

NOx in the flue gas of the invention according to claim 4
The reduction device has a desulfurization facility and a denitration catalyst reaction layer in a flow path of the flue gas, and uses NH ₃ as a reducing agent to selectively reduce nitrogen oxides (NOx) contained in the flue gas in the denitration catalyst reaction layer. in the NOx reduction apparatus of the combustion exhaust gas, the denitration catalyst outlet connected to the root of the reaction layer, the root and three flue gas passage route, and NH ₃ oxidation catalyst provided in the route provided in the route A predetermined amount of NH ₃ addition device, a NOx reduction catalyst downstream of the addition device, a NOx concentration meter for measuring the NOx concentration in the route, the route and the flow path of the route, and a value of the NOx concentration meter Oyo excess NH ₃ concentration and a calculator for calculating a shortage NH ₃ concentration, the excess NH ₃ concentrations and under NH ₃ from said concentration denitration catalyst reaction layer NH ₃ flow rate control valve from And a signal converter for generating a signal for controlling the NH ₃ flow control valve of the desulfurization facility.

In a nitrogen oxide reduction facility equipped with a degassing facility and a denitration facility (denitration catalyst), the concentration of the reducing agent (NH ₃ ) in the processing gas at the inlet of the denitration catalyst depends on the precipitation of ammonium sulfate and the like, gas separation, and drainage. It fluctuates due to fluctuations in the condensation trap, desulfurization operation, and improper mixing of the input NH ₃ , and changes over time. Therefore, in the present invention, the NH ₃ concentration at the inlet of the denitration catalyst having a large fluctuation is not measured, and the excess (slip) at the outlet of the denitration catalyst (catalyst reaction layer) is not measured.
The NH ₃ concentration and the insufficient NH ₃ concentration are obtained by an indirect method, and the values are used as a reducing agent addition flow rate control signal in the NH ₃ input amount control method. The reason why the exhaust gas analysis is performed at the outlet of the denitration catalyst is that the catalyst reaction layer of the denitration catalyst functions as a gas mixer, and a state in which mixing and uniformity are relatively achieved.

First, a method of continuously measuring the indirect NH ₃ concentration and the insufficient NH ₃ concentration will be described. The combustion exhaust gas (analytical gas) at the outlet of the denitration catalyst (catalyst reaction layer) is transferred from the main duct to _three routes: a route (NH ₃ oxidation catalyst installed), a route (untreated line) and a route (NOx reduction catalyst installed). The flow is switched by means of a timer to the branched three routes, and the exhaust gas is made to flow alternately. Each processing route is continuous NO
Connected to gas suction pump via x-meter. A certain amount of gas is sucked by the suction pump.

In the route, almost all of the slip NH ₃
Is converted to equimolar NOx, so that the difference in NOx concentration from the value of the route gas cooler alone is approximately equal to the slip N
H ₃ concentration.

In this case, in the route, the reducing agent (NH
_{Since 3} ) is sufficiently supplied, there is no difference in NOx concentration due to the presence or absence of specially added NH ₃ , and the indicated value is almost in the range of the set value (<2 ppm). That is, utilizing a high-efficiency conversion oxidation catalyst and a high-temperature reaction without poisoning and precipitation effects,
NH ₃ to grasp indirectly NH ₃ concentration by equimolar converted to NOx rather than direct (mostly NO).

Next, each route will be described. About the route: In the route, oxidation of the reducing agent (conversion from NH ₃ to NO) is performed, and the amount of excess (slip) NH ₃ is measured.

Structure: gas indirect heater (exhaust gas is 800 to
Can be heated to 1000 ° C), NH ₃ oxidation catalyst reaction layer (P
t-Rh noble metal catalyst, about 10% Rh), a gas cooler, a switching valve, and a NOx analyzer. By heating the exhaust gas at the outlet of the denitration catalyst (catalyst reaction layer) above the precipitation temperature of salts such as ammonium sulfate and acidic ammonium sulfate, the maintenance load on the analytical gas conduit and pretreatment equipment is reduced, and accurate analysis and measurement can be performed. Achieved.

Function: Oxidation of NH ₃ in exhaust gas (conversion from NH ₃ to NO). The reaction formula is as follows. 4NH ₃ + 5O ₂ → 4NO + 6H ₂ O Here, it is basically considered as equimolar NO conversion.

Measured value: The measured value is the total concentration of residual NO in the exhaust gas and NO converted from the reducing agent (NH ₃ ).
The absolute value of this concentration varies depending on the concentration of NO and excess (slip) NH ₃ at the outlet of the denitration catalyst (catalytic reaction layer). Further, even if the efficiency of the denitration catalyst is constant, the NOx concentration in the gas before the treatment changes due to an operation fluctuation of the exhaust gas purification process and the like.

Route: On the route, raw exhaust gas (NOx at the outlet of the denitration catalyst) flows, and the standard NOx concentration in the exhaust gas is measured.

Structure: A gas cooler, a switching valve and a NOx analyzer. Function: Measures only the NOx concentration in the exhaust gas. Analytical obstacle components are removed by a drain trap.

Measured value: The measured value is the NOx concentration of the gas at the outlet of the denitration catalyst (catalyst reaction layer). In the method of the present invention, excess (slip) or insufficient NH at the outlet of the denitration catalyst is used.
It becomes the reference value for ₃ quantity judgment. Thereby, the NOx concentration fluctuation in the denitration-untreated gas and the efficiency of the denitration catalyst of this facility are grasped.

About the route: In the route,
Reduction of unreacted NO (NH _{3 in} gas and specially added NH ₃
To reduce unreacted NO). In addition, the performance of the denitration catalyst is checked and the amount of the insufficient reducing agent (NH ₃ ) is measured.

Configuration: gas indirect heater (exhaust gas is about 300
° C), high performance denitration catalyst reaction layer (Ti-V-
W system), gas cooler, switching valve and NOx analyzer.
You. Furthermore, specially added NH_ThreeProcess gas
During the distribution period, specially added NH _ThreeWith or without the addition of
Create a state.

(A) Slip NH ₃ and NO of NOx removal catalyst (catalytic reaction layer)
And a reduction reaction is performed. The reaction formula is as follows.

4NO + 4NH ₃ + O ₂ → 4N ₂ + 6H ₂ O (ii) The reduction reaction of the present catalyst slip NO is carried out in a state where there is no shortage of reducing agent due to the specially added NH ₃ .

(A) No special addition of NH _{3 When} the reducing agent (NH ₃ ) at the outlet of the denitration catalyst (catalytic reaction layer) is excessive (abundant), the difference is zero. On the other hand, the reducing agent (N
H ₃ ) If there is a shortage, a gap occurs.

(B) With special addition of NH ₃ Addition of excess reducing agent at outlet of denitration catalyst (catalytic reaction layer)
In such cases, the disparity is zero. On the other hand, the disparity is also zero when the reducing agent is insufficient.

The difference between the two measured values; the difference between the two measured values (a) and (b) is the absolute value of the insufficient concentration of the reducing agent (NH ₃ ) in the present denitration catalyst.

Next, a method for measuring the NH ₃ deficiency concentration in the route will be described. After the exhaust gas is heated to about 300 ° C. by an indirect gas heater, a predetermined amount of NH ₃ (special addition NH ₃ ) is added for a fixed period of time (concentration setting enabling complete reduction). Next, a NOx reduction catalyst reaction layer (Ti-VW system)
And then enter the NOx analyzer. At this time, NOx with no special addition of NH ₃ (reduction in raw exhaust gas)
The concentration difference becomes the insufficient NH ₃ concentration.

The reduction reaction of NO with the specially added NH ₃ is as follows:
It is as follows. 4NO + 4NH ₃ + O ₂ → 8N ₂ + 6H ₂ O When there is no slip NH ₃ , there is no difference in NOx concentration between the NH ₃ oxidation catalyst outlet (route) and the untreated gas (route), so the required amount of NH ₃ is further insufficient. If you do
The difference obtained here (route) can be grasped as the NH ₃ deficiency.

The efficiency of the denitration catalyst and the molar ratio of the reducing agent are as follows. The general catalyst denitration efficiency is about 70 to 90% in view of regulatory values, economy and catalyst performance.

At the inlet of the denitration catalyst (catalyst reaction layer), NH ₃ /
Although the NO molar ratio depends on the type of catalyst and reaction conditions, it is usually 1.
Set to 0-1.2. NH ₃ / NO on catalyst efficiency
The general form of the molar ratio characteristic is as shown in FIG. Even if the NH ₃ / NO molar ratio is 1.0 in an equimolar reaction, the catalyst efficiency is 80%.
%, Unreduced NOx and NH ₃ equivalent to 20% remain.

Next, information obtained from the gas analysis values of the three channels (routes to) will be described. FIG. 9 is a system diagram illustrating a method for measuring the molar ratio of the reducing agent. First, the information obtained from the gas analysis values of the three routes is
Define as follows.

[0056] Route of NOx values: NOx-a route NOx values: Special NH ₃ added without NOx value of the NOx-b route: Special NH ₃ addition there NOx value of the NOx-c route: NOx-d method (a): Oxidation catalyst outlet exhaust gas (NOx-
Disparity between a) and the raw gas (NOx-b) in the route (NO conversion amount of slip NH _{3 at} oxidation catalyst outlet) Excessive reduction (NH ₃ ) in denitration catalyst
Case: ΔNOx route and route (NOx-a)-(NOx-b)> (NOx-b) * K
1 where K1: oxidation catalyst conversion efficiency (K1 = 0.9-0.
95) In case of ideal equimolar reaction; ΔNOx route and route (NOx-a)-(NOx-b) = (NOx-b) * K
1 In case of insufficient reducing agent; ΔNOx route and route (NOx-a)-(NOx-b) <(NOx-b) * K
1 Control deviation (required NH ₃ concentration) = ΔNH ₃ is as follows.

ΔNH ₃ = (NOx−b) − ｛(NOx−
a)-(NOx-b)｝ / K1 (ΔNH ₃ >0; insufficient, ΔNH ₃ = 0; equimolar ratio, ΔN
(H ₃ <0; excess) However, the condition is satisfied under the precondition that NH ₃ and NOx react equimolarly.

Method (b): Difference between the special addition of NH _{3 at the} outlet of the reduction catalyst at the route and the addition of NH _{3 When} the reducing agent in the denitration catalyst is excessive (abundant); (NOx−c) = (NOx−d) (NOx−c) = (NOx−b) * (1−K2) where K2: conversion rate of the reduction catalyst (K2 = 0.95 to 0.95)
0.99) In the case of ideal equimolar reaction; (NOx-c) = (NOx-d) (NOx-c) = (NOx-b) * (1-K2) In the case of insufficient reducing agent; NH ₃ = ｛(NOx−b) − (N
Ox-c)｝ / K2 Catalyst required NH ₃ amount (ΔNH ₃ ) = ｛(NOx-c)-
(NOx-d)｝ / K2 Control deviation in the balance of NH ₃ deficiency (required NH ₃ concentration)
= ΔNH ₃ is as follows.

ΔNH ₃ = {(NOx−c) − (NOx−d)} / K2, where K2: conversion rate of the reduction catalyst (ΔNH ₃ >0; insufficient, ΔNH ₃ = 0; equimolar ratio or excess) The reason why the above two methods (a) and (b) are used together is as follows.

The method (a) is based on the premise that NH ₃ and NO are equimolar reactions. However, since oxygen coexists in a non-catalytic state in the process of obtaining the catalytic reaction temperature, the following oxidation reaction and Partial reduction reaction occurs (error factor).

4NO + 4NH ₃ + O ₂ → 4N ₂ + 6H ₂ O 4NH ₃ + 5O ₂ → 4NO + 6H ₂ O 4NH ₃ + 3O ₂ → 2N ₂ + 6H ₂ O Since the above reaction varies depending on the concentration and temperature of NH ₃ , NO and O ₂ , etc. However, the method (a) cannot always be limited to an equimolar reaction.

In the method (b), the reaction is carried out under a reaction condition without catalyst poisoning.
Analysis, and there is no intermediate reaction seen above.
Relatively accurate judgment is possible. However, equimolar ratio or more
NH _ThreeWhen there is, there is no gap.

Therefore, the method (b) is used for correcting an error of the method (a) in a region where the ratio of the reducing agent is equal to or more than equimolar.
The use of the analysis values and disparities is as follows.

The slip concentration of NH ₃ at the outlet of the denitration catalyst (catalyst reaction layer) was measured, and the deviation from the set value was determined. The deviation was determined for each of the desulfurization equipment and the denitration catalyst reaction layer of the present nitrogen oxide reduction facility. It is used as a valve opening adjustment signal for the NH ₃ input amount adjustment valve.

In the region from excess reducing agent (slip NH ₃ ) to equimolar, the difference of the method (a) is used. However, it is assumed that the disparity of the method (b) is “zero”. In the area where the reducing agent is insufficient, the disparity of the method (b) is used. The method of utilization depends on the control of the molar ratio of the reducing agent (NH ₃ ) of the present denitration catalyst (deviation from the set molar ratio). Then, the gas concentration after the catalytic reaction is analyzed and the difference from the set value is determined by the N 2
This is a control signal for adjusting the H ₃ input amount.

Next, a method of adjusting the reducing agent concentration ratio (NH ₃ / NOx molar ratio) of the denitration catalyst according to the present invention will be described. Adjustment of the reducing agent concentration ratio is performed by controlling the NH ₃ input amount of the NH ₃ flow rate control valve (two-stage adjustment method) in the desulfurization facility and the denitration catalyst reaction layer of the nitrogen oxide reduction facility. That is,
2-step adjustment method, a two-stage NH ₃ addition of NH ₃ addition and denitration catalyst reaction layer desulfurization. The method is by adjusting (increasing or narrowing) the opening of the NH ₃ flow control valve).

(A) Control range of desulfurization equipment: (Slip N
H ₃ Concentration <When 50 ppm); increased or, (slip NH ₃ concentration> when 250 ppm); refinement.

(B) Control range of the denitration catalyst reaction layer: 50 p
pm ≦ slip NH ₃ concentration ≦ 250 ppm. Desulfurization slip NH ₃ concentration and concentration at the inlet of the denitration catalyst (untreated heat exchanger outlet, that is, before the addition of the denitration catalyst reaction layer NH ₃ ): The inlet concentration of the denitration catalyst reaction layer is 0.7 to 0.75 (desulfurization slip). N
H ₃ concentration). This deposits on the element surfaces of the heat exchanger and is captured, reducing the concentration.

Method of adjusting NH ₃ concentration ratio: When slip NH _{3 of the} denitration catalyst is excessive than the set value, (a) NOx obtained by switching the switching valve (electromagnetic valve)
The concentration difference ΔNOxA (ppm) (root) and the setting N set from the viewpoint of the performance and activity maintenance of the denitration catalyst
The deviation from Oxo (ppm) is determined.

If the value of ΔNOxA is ΔNOxA> NOxo
In the range from ΔNOxA = {NOxo−20 ppm}, the NH ₃ flow rate control valve of the denitration catalyst is set to ΔNOxA =
Adjust to become NOxo.

(B) Even if the NH ₃ flow rate control valve of the denitration catalyst is squeezed, if ΔNOxA> (NOxo + 20 ppm) (ie, slip NH ₃ ), the NH ₃ adjusting function is provided from the denitration catalyst reaction layer to the denitration catalyst reaction layer. Move to flow control valve.

However, the above-mentioned action is performed by a different system NO.
NOx depending on whether or not a predetermined amount of NH ₃ addition (special addition NH ₃ ) is added to the exhaust gas reduction route (route), which is x information
It is assumed that the disparity satisfies the condition within 2 ppm.

When NH _{3 of the} denitration catalyst is less than the set value, (a) when ΔNOxA <(NOxo−20 ppm) and the NOx disparity in the reduction route is 2 ppm or more,
In the denitration catalyst (catalytic reaction layer), NH _{3 is} insufficient.

(B) In this case, the difference in NOx concentration at the outlet of the reduction catalyst due to the presence / absence of addition of a predetermined amount (concentration setting capable of complete reduction) of NH ₃ (special addition NH ₃ ) directly becomes an NH ₃ deficiency amount. Until the disparity is within 2 ppm, NH ₃ equivalent to the disparity is added to the denitration catalyst to increase the amount. Since the NH ₃ supply capacity of the denitration catalyst is designed to be able to cope with even zero NH ₃ slip from the upstream, this action may be one operation.

The gas sampling cycle is about 5 to 6 minutes / time,
The deviation control action is performed by calculating and using the average difference value for 20 to 30 minutes.

[0076]

Next, an embodiment of the present invention will be described with reference to the drawings. FIG. 1 shows a reducing agent (NH) at the outlet of a catalytic reaction layer (denitration catalyst) according to an embodiment of the present invention.
₃ ) It is a system diagram showing a device configuration for performing a slip concentration measurement.

In the apparatus shown in FIG. 1, NOx ₃ and NH ₃ 4 flow at a predetermined concentration ratio through the denitration catalyst 2 incorporated in the denitration reaction layer 1 to cause a selective catalytic reduction reaction on the catalytically active surface. NOx3 is reduced to the N ₂ 5 and H ₂ O6.
The reduction reaction formula is as follows.

4NO + 4NH ₃ + O ₂ → 4N ₂ + 6H ₂ O In the exhaust gas at the outlet of the catalytic reaction layer 1, unreduced NOx corresponding to the denitration efficiency of the catalyst and excessive NH _{3 in the} reduction reaction may remain. General. Here, the ideal reaction is equimolar, but in an actual reaction layer, it is usual to add a reducing agent (NH ₃ ) in excess of about 10 to 50% due to the gas residence time and the like.

The exhaust gas is branched from an exhaust gas duct 8 by a gas suction pump 7 and separated into three gas processing routes 11 (gas detection tubes) by switching valves (electromagnetic valves) 10 at the outlets of the respective gas coolers 9.

In the three processing routes, the exhaust gas flows alternately by the action of the timer 12. The first processing route (route) is an indirect gas heater for oxidation 1
3, an arrangement of the NH ₃ oxidation catalyst reaction layer 14 and the gas cooler 9. Note that the NH ₃ oxidation catalyst using Pt-Rh-based noble metal catalyst, the set temperature of the gas heater is about 800 to 10
Set to 00 ° C. The second route (route) includes only the gas cooler 9. Further, the remaining third route (route) includes an indirect gas heater 15 for reduction treatment, an NH ₃ gas quantitative injection valve 16 into a gas processing line upstream thereof, and a constant NH ₃ (special addition NH ₃ ) injection timer for operating the valve. NH ₃ adding device 18 provided with
It is composed of an iVW-based denitration catalyst reaction layer 19.
As described above, the denitration catalyst of this reduction route includes Ti-V-
The heater temperature is adjusted to be constant at about 300 ° C. using a W system.
Further, a simple dust collector 20 is installed before branching of the gas processing route according to the dust concentration of the analysis gas. The analysis gas 21 at the outlet of the gas cooler 9 is collected and the NOx analyzer 22
And the NOx concentration is measured. At this time, the NOx of the gas on the second route (route) is converted into raw NOx 23, and the NOx of the gas that has passed through the NH ₃ oxidation catalyst on the first route (route).
x is converted NOx 24, and the time average value of the concentration difference a25 is calculated by the calculator 26.

In the NH ₃ selective catalytic reduction of the combustion exhaust gas, since it is considered that the reaction is approximately equimolar, the concentration of the difference a25 can be said to be approximately the concentration of the slipping reducing agent (NH ₃ ).

If the reducing agent (NH ₃ ) is not supplied at a sufficient molar ratio in the denitration catalyst 2 (ie, the reducing agent (NH ₃ ) is insufficient), the concentration difference tends to decrease, and finally reaches the level where the difference disappears. . This level is completely reduced (N
H ₃ ) Shortage. As a countermeasure in such a case, in order to estimate the amount of the reducing agent deficiency, a change in the NOx concentration at the outlet of the denitration catalyst in the analysis route is determined by adding or not adding quantitatively added NH ₃ (specially added NH ₃ ).
(27) is detected. Since this difference can be said to be approximately the insufficient concentration of the reducing gas, the computing unit 26 can similarly grasp the insufficient amount.

The exhaust gas at the outlet of the denitration catalyst 2 is analyzed by the above-mentioned means, and the schematic flow of adjusting the addition amount of the reducing agent and controlling the molar ratio using the difference is shown in FIG. As shown in FIG.
Conversion catalyst 28 from NH ₃ to NOx, NOx reduction catalyst 2
9 and the NOx analyzer 30, the slip NH ₃ equivalent concentration 31 and the insufficient reducing agent concentration 32 are determined by the calculator 33, and the signal converter 34 adjusts the flow rate of the NH ₃ addition device 35 of the denitration catalyst reaction layer based on the calculated values. The valve opening of the valve 36 and the flow control valve 38 of the NH ₃ addition device 37 of the desulfurization facility is controlled.

As the control signal, the deviation from the set value is converted into an opening change signal for the flow control valves 36 and 38, and the deviation is determined as Mi.
n. (Minimum amount) The flow rate of the added NH ₃ is adjusted. When the slip NH ₃ concentration is excessive, first, the control valve 36 of the denitration catalyst reaction layer is narrowed, and when the control valve 36 becomes full, the next action is to perform a two-stage control in which the control valve 38 of the desulfurization facility is narrowed.

The reducing agent (N) in the denitration catalyst reaction layer 1
In the case where the concentration of H ₃ ) is insufficient, the NH ₃ equivalent concentration 31 becomes “zero”, so that the NH ₃ addition valve operates in the opening direction.

This NH ₃ increase action can be dealt with by the control valve 36 because the NH ₃ supply capacity of the denitration catalyst reaction layer is sufficient. The denitration efficiency change pattern when the reducing agent is supplemented is sharp, and the followability controlled by this action is sufficient.

[0087]

Next, the present invention will be described with reference to embodiments. An example of a method and an apparatus for enabling a proper molar ratio operation of NOx and a reducing agent (NH ₃ ) in a denitration catalyst will be described with reference to a sintering flue gas denitration process of an ironworks.

The NH ₃ / NO molar ratio setting and control conditions of the denitration catalyst were as shown below. (A) From the viewpoint of catalyst efficiency and poisoning, the NH ₃ / NO molar ratio was set as follows. NH ₃ / NO molar ratio =
1.1 ± 0.1 (b) The NO concentration of the denitration-untreated gas is 170 ± 20 on average.
ppm.

C) The NH ₃ concentration at the inlet of the denitration catalyst is NO
The x concentration was in the range of 170 to 204 ppm at 170 ppm. The above is based on the premise that the set value and the control range of the above-described method (a) are −17 ± 17 ppm, and the disparity of the method (b) is 0.

The operation specifications of the sintering exhaust gas treatment were as shown below. Sintered exhaust gas flow rate: 1150 kNm ³ / h (hour) NOx concentration in exhaust gas; 150 to 170 ppm Desulfurization; wet denitration; selective catalytic reduction of NH ₃ by catalyst Catalytic reaction temperature: about 300 ° C Catalyst SV: about 3000 (l / h) ) Outflow slip SOx; <2 ppm First, as a comparative example, denitration by a conventional method will be described.

The slip NH ₃ from the desulfurization process is 30
３５０350 ppm, the fluctuation pattern is a gentle wave shape, usually from peak to peak (pe
ak to peak) for about 4-5 hours.

At the time of manual intervention by the operator, the variation range of the slip NH ₃ concentration can be suppressed to about 80 to 150 ppm (however, only when there is an alarm or the like). NH ₃ reaching the inlet of the denitration catalyst (catalytic reaction layer)
Concentration is about 65-70% of the normal desulfurization slip NH _3, 30 to 35% in the middle of the heat exchanger is ammonium sulfate is trapped in the form of salts such as acid ammonium sulfate.

The fluctuation range of the NH ₃ / NO molar ratio of the denitration catalyst is 0.9 to 1.9. In the case of shortage, it is dealt with by operator intervention. Next, examples of the present invention will be described.

A method for estimating slip NH ₃ concentration from the NOx concentration difference of the gas composition by converting NOx from the denitration catalyst slip NH ₃ with a Pt-Pd oxidation catalyst, and calculating the difference between NH ₃ and NH _3.
Depending on the method used for controlling the opening of the charging flow control valve, the NH ₃ / NOx molar ratio at the inlet of the denitration catalyst is 1.1 ± 0.1.
Denitration efficiency fluctuation due to molar ratio fluctuation of about ± 3%
Could be controlled within. Since the reaction temperature of the oxidation catalyst (Pt-Rh system) for converting NH ₃ to NOx is set and maintained at a high temperature by the gas heater, the effect of poisoning substances in the exhaust gas was avoided, and a stable reaction was maintained. As described above, it was possible to maintain the efficiency of the denitration catalyst and reduce troubles such as corrosion and clogging caused by slip NH _{3 of the} denitration catalyst.

The breakdown of the economic effects obtained through the examples is as follows. The NH ₃ concentration reduction that slips through the denitration catalyst reaction layer is an average of 60 ppm. Therefore, ΔNH ₃ (60 ppm) * 1150 kNm ³ / h = 69
In terms of Nm ³ -NH ₃ / h, it can save about 0.2 billion yen a year in terms of cost.

Regarding the stable maintenance of the denitration efficiency, the fluctuation range of the catalyst denitration efficiency could be maintained within ± 3%. Therefore, a great saving of energy cost (fuel + electric power) can be achieved. Troubles such as corrosion and blockage of the denitration equipment are reduced, and equipment repair costs can be saved.

The life can be extended by reducing the NOx poisoning.

[0098]

As described above, according to the present invention, the molar ratio of the reducing agent at the inlet of the denitration catalyst reaction layer is controlled at an appropriate level. As a result, the cost of the reducing agent is reduced, and the poisoning of the catalyst and the equipment is reduced. High accuracy and stable measurement value reduce the maintenance burden by reducing troubles such as clogging and corrosion, and configuring the measuring device with NH ₃ oxidation catalyst and NOx meter when measuring reducing agent (NH ₃ ). Thus, an industrially useful effect is obtained.

[Brief description of the drawings]

FIG. 1 is a system diagram showing a configuration of an apparatus for measuring a reducing agent (NH ₃ ) slip concentration at an outlet of a denitration catalyst according to an embodiment of the present invention.

FIG. 2 is a system diagram showing an apparatus configuration for implementing a reducing agent flow control incorporating a concentration measuring apparatus according to an embodiment of the present invention.

FIG. 3 is a conceptual diagram showing an apparatus for performing flue gas denitration according to the related art.

FIG. 4 is a system diagram showing the configuration of an apparatus for performing analysis of NH ₃ in gas according to a conventional technique.

FIG. 5 is a system diagram showing an apparatus configuration for performing a conventional steelworks sintering exhaust gas treatment.

FIG. 6 shows SO in a conventional wet flue gas desulfurization reaction and the like.
₃ is a graph showing slip characteristics of x and NH ₃ .

FIG. 7 is a system diagram showing a configuration of an apparatus for performing a flow rate control of a reducing agent (NH ₃ ) addition in wet flue gas desulfurization according to a conventional technique.

FIG. 8 is a graph showing a general form of NH ₃ / NO molar ratio characteristic given to catalyst efficiency.

FIG. 9 is a system diagram illustrating a method for measuring the molar ratio of a reducing agent according to the present invention.

[Explanation of symbols]

DESCRIPTION OF REFERENCE NUMERALS 1 denitration reaction layer 2 denitration catalyst 3 NOx 4 reducing agent (NH ₃ ) 5 N ₂ 6 H ₂ O 7 gas suction pump 8 exhaust gas duct 9 gas cooler 10 switching valve (electromagnetic valve) 11 gas processing route 12 timer 13 indirect gas heater for oxidation 14 NH ₃ oxidation catalyst reaction layer 15 Indirect gas heater for reduction treatment 16 NH ₃ gas constant injection valve 17 Fixed NH ₃ injection timer 18 NH ₃ addition device 19 Ti-V-W system denitration catalyst reaction layer 20 Dust collector 21 Analysis gas 22 NOx analyzer 23 Raw NOx 24 Converted NOx 25 Concentration difference a 26 Operation unit 27 Concentration difference b. Reference Signs List 28 NOx oxidation catalyst (NH ₃ → NOx conversion catalyst) 29 NOx reduction catalyst 30 NOx analyzer 31 Slip NH ₃ equivalent concentration 32 Insufficient reducing agent NH ₃ concentration 33 Arithmetic unit 34 Signal converter 35 NH ₃ addition device for denitration catalyst 36 NH ₃ flow rate adjusting valve 37 NH ₃ addition device 38 NH ₃ flow rate control service 39 exhaust gas 40 duct 41 denitration reaction layer 42 catalyst layer 43 NOx 44 nozzle _{45 NH 3 46 N 2 47 H} 2 O 48 chimney 49 exhaust gas 50 SOx process desulfurization 51 direct line 52 temperature controller 53 NH ₃ oxidation device 54 NO diverter 55 NOx analyzer 56 solenoid valve 57 sintering machine 58 flue gas 59 dust 60 SOx 61 NOx 62 dust collector 63 desulfurization 64 denitrification equipment 65 absorbing solution 66 COG 67 NH ₃ 68 circulation pump 69 reactor 70 cooled stage 71 intake Stage 72 lean stage 73 purification stage 74 demister 75 spray nozzle 76 pump 77 sintered 78 flue gas 79 NOx 80 process gas flow 81 denitration catalyst 82 reaction layer 83 of the inlet duct 84 NOx meter 85 catalyst inlet must NH ₃ 86 calculator

Claims (4)

[Claims] An apparatus having a desulfurization facility and a denitration catalyst reaction layer in a flow path of combustion exhaust gas, wherein NH ₃ is used as a reducing agent and nitrogen oxides (NOx) contained in the combustion exhaust gas are used for the denitration catalyst reaction layer in the NOx reduction process of the combustion exhaust gas of selective catalytic reduction, to measure the excess or deficiency of the NH ₃ concentration in the combustion exhaust gas in the denitration catalyst reaction layer outlet in NH ₃
/ NOx molar ratio is determined, and from the difference between the determined molar ratio and the set molar ratio, the opening of each of the denitration catalyst reaction layer and the NH ₃ input flow control valve of each of the desulfurization equipment is obtained and converted into an opening adjustment signal. And adjusting the NH ₃ / NOx molar ratio of the denitration catalyst reaction layer to a predetermined appropriate value by adjusting the input NH ₃ flow rate of the denitration catalyst reaction layer and the desulfurization equipment according to the signal. NOx reduction method of exhaust gas. 2. A denitrification catalyst reaction layer using a desulfurization facility and a denitration catalyst reaction layer in a flow path of the combustion exhaust gas and using NH ₃ as a reducing agent to reduce nitrogen oxides (NOx) contained in the combustion exhaust gas. In the NOx reduction method for combustion exhaust gas which is subjected to selective catalytic reduction in the above, the combustion exhaust gas at the outlet of the denitration catalyst reaction layer has a route having an oxidation catalyst, a route through which the combustion exhaust gas passes without any catalyst, and a reduction catalyst. Distributed in three flow paths with the route, in the route, measuring the NOx amount after oxidizing the combustion exhaust gas by the oxidation catalyst, in the route, measuring the NOx amount of the combustion exhaust gas, in the route,
A predetermined amount of NH ₃ is added to the flue gas and the NOx amount of the flue gas after reduction by the reduction catalyst is measured, and the measured NOx amount of the route and the NOx amount of the route are measured.
The excess NH ₃ concentration is calculated from the difference from the measured Ox amount, and the insufficient NH ₃ concentration is calculated from the difference between the measured NOx amount of the funnel and the measured NOx amount of the route, and the excess NH ₃ concentration and the insufficient NH ₃ concentration are calculated. NH ₃ calculates the NH ₃ / NOx molar ratio of the concentration the denitration catalyst reaction layer from the arithmetic value, from the calculation value of the molar ratio, the charged amount of NH ₃ of one or both of the denitration catalyst reaction layer or the desulfurization And calculating the calculated amount of NH ₃ into one or both of the denitration catalyst reaction layer and the desulfurization facility to control the molar ratio of the denitration catalyst reaction layer to a predetermined value. NOx reduction method. 3. The denitration catalyst reaction layer and the desulfurization facility
Each NH_ThreeSwitching the operation of the input flow control valve between each other
Possible and required NH_Three/ NOx molar ratio and set molar ratio
When the difference value is within a predetermined control range, the denitration catalyst
NH of reaction layer _ThreeActivating the input flow control valve to activate the denitration catalyst
NH to reaction layer_ThreeIs out of the specified control range
Is the NH in the desulfurization facility_ThreeActivate the flow control valve
NH to desulfurization equipment_ThreeAnd put the denitration catalyst reaction layer and
And NH in the desulfurization facility_ThreeSpecially designed to control the input flow rate
2. The method for reducing NOx of combustion exhaust gas according to claim 1, wherein: 4. A desulfurization facility and a denitration catalyst reaction layer in a flow path of the combustion exhaust gas, and a nitrogen oxide (NOx) contained in the combustion exhaust gas is selectively contacted in the denitration catalyst reaction layer by using NH ₃ as a reducing agent. In the NOx reduction device for reducing combustion exhaust gas, a route connected to the outlet of the denitration catalyst reaction layer, a route, and three combustion exhaust gas channels, an NH ₃ oxidation catalyst provided in the route, A device for adding a predetermined amount of NH ₃ and a NOx reduction catalyst downstream of the device, a NOx concentration meter for measuring the NOx concentration in the route, the route and the flow path of the route, and a NOx concentration meter for measuring the NOx concentration. and computing unit for computing the excess NH ₃ concentrations and under NH ₃ concentration from the values, NH ₃ flow rate control valve of the denitration catalyst reaction layer from the excess NH ₃ concentrations and under NH ₃ concentration Contact Fine wherein desulfurization of the NH ₃ flow rate signal conversion for emitting a signal for controlling the control valve unit and the NOx reduction apparatus of the combustion exhaust gas, characterized in that it consists of.