JP2008114115A - Harmful substance reduction system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a harmful substance reduction system which reduces a toxic substance efficiently without restriction to the function and combustion control of a gas generation source. <P>SOLUTION: The harmful substance reduction system is provided with a gas generation source 1 from which the composition of the gas to be discharged and the temperature are changed, a gaseous properties adjustment means 2 to adjust the composition and temperature of oxygen, nitrogen oxide and carbon monoxide of the gas to a predetermined concentration ratio and a predetermined temperature respectively, which is installed at the downstream of the gas generation source 1 and a catalyst 3 to reduce the concentration of carbon monoxide and nitrogen oxide by a first reaction to oxidize the carbon monoxide and a second reaction to reduce the nitrogen oxide by the carbon monoxide, which is installed of the gaseous properties adjustment means 2. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a harmful substance reduction system that reduces nitrogen oxides and carbon monoxide in a gas discharged from a gas generation source such as an exhaust gas boiler.

  This kind of harmful substance reduction system is known from US Pat. The system of Patent Document 1 uses a catalyst that oxidizes carbon monoxide and reduces nitrogen oxides to reduce carbon monoxide and nitrogen oxides in the exhaust gas from the incinerator. Then, the combustion of the incinerator, which is a gas generation source, is controlled, specifically, fuel rich combustion is performed to adjust the gas composition of the exhaust gas.

JP 2003-275543 A

  Since the technique described in Patent Document 1 controls the combustion state of a gas generation source, it is restricted by the original function of the gas generation source, or is desirable for the gas properties required by the catalyst. There is a problem that it cannot be controlled.

  The problem to be solved by the present invention is to efficiently reduce harmful substances without being restricted by the function of the gas generation source and the combustion control.

  This invention was made in order to solve the above-mentioned subject, and the invention according to claim 1 is provided downstream of this gas generation source, the gas generation source in which the composition and temperature of the gas to be discharged fluctuate, A gas property adjusting means for adjusting the composition and temperature of oxygen, nitrogen oxide and carbon monoxide in the gas to a predetermined concentration ratio and a predetermined temperature, respectively, and provided downstream of the gas property adjusting means to oxidize carbon monoxide It is characterized by comprising a catalyst for reducing the concentration of carbon monoxide and nitrogen oxides by the first reaction and the second reaction of reducing nitrogen oxides with carbon monoxide.

  According to a second aspect of the present invention, in the first aspect, the gas property adjusting unit includes a gas property detecting unit that detects the gas composition, the gas flow rate, and the gas temperature, and oxygen, nitrogen oxides of the gas, and An adjuster for adjusting the composition and temperature of carbon monoxide, and a controller for controlling the adjuster based on the detection value of the gas property detecting means to control the composition and temperature of the gas to a predetermined concentration ratio and a predetermined temperature, respectively. It is characterized by comprising.

  According to the first and second aspects of the invention, it is possible to control the properties of the gas without limiting the function of the gas generation source and the combustion control, and to maximize the function of the catalyst. In addition, it is possible to control the properties of the gas and effectively reduce harmful substances.

According to a third aspect of the present invention, the gas property adjusting means according to the first or second aspect is such that the concentration ratio of carbon monoxide, nitrogen oxide and oxygen contained in the gas is expressed by the following formula (1): It is characterized by adjusting to satisfy.
([NOx] +2 [O ₂ ]) / [CO] ≦ 2.0 (1)
(In the formula (1), [CO], [NOx] and [O ₂ ] indicate the carbon monoxide concentration, nitrogen oxide concentration and oxygen concentration, respectively, and satisfy the condition [O ₂ ]> 0.)

  According to the third aspect of the invention, in addition to the effect of the first or second aspect, the nitrogen oxide concentration in the gas after passing through the catalyst is substantially zero, and the carbon monoxide concentration is There exists an effect that it can reduce.

  According to a fourth aspect of the present invention, in the first to third aspects, the gas after passing through the catalyst is guided to an exhaust gas boiler to perform heat recovery.

  According to the invention of claim 4, in addition to the effects of claims 1 to 3, the heat generated by the gas property adjusting means and the catalyst can be recovered by the exhaust gas boiler, so energy saving There is an effect that the system can be provided.

  According to the present invention, harmful substances can be effectively reduced without limiting the function of the gas generation source and the combustion control.

  Before describing embodiments of the present invention, terms used in the present application will be described. The gas includes a gas in the combustion reaction (combustion process) and a gas in which the combustion reaction is completed, and can be referred to as a combustion gas. The combustion-in-combustion gas means a gas in the combustion reaction, and the combustion-completed gas means a gas in which the combustion reaction is completed, and is referred to as exhaust gas in the present application. Further, the harmful substance is a concept including at least nitrogen oxide and carbon monoxide.

  Next, an embodiment of the present invention will be described. The present invention is particularly preferably implemented in a harmful substance reduction system that reduces nitrogen oxides and carbon monoxide contained in a gas discharged from a gas generation source such as a diesel engine.

  An embodiment of the present invention includes a gas generation source in which the composition and temperature of a gas to be discharged vary, and a composition and temperature of oxygen, nitrogen oxide, and carbon monoxide of the gas provided downstream of the gas generation source. Gas property adjusting means for adjusting to a predetermined concentration ratio and a predetermined temperature, respectively, a first reaction for oxidizing carbon monoxide and a second reaction for reducing nitrogen oxide with carbon monoxide provided downstream of the gas property adjusting means And a catalyst for reducing the concentration of carbon monoxide and nitrogen oxides.

  In an embodiment of the present invention, gas is discharged from the gas generation source. The composition and temperature of oxygen, nitrogen oxide and carbon monoxide in the gas vary depending on the load of the gas generation source, etc., but the gas property adjusting means adjusts the composition to a predetermined concentration ratio, The temperature is adjusted to a predetermined temperature. By this adjustment, the catalyst reduces nitrogen oxide and oxidizes carbon monoxide with high efficiency. As a result, the nitrogen oxide concentration in the gas after passing through the catalyst can be reduced to a value close to zero of 5 ppm or less. In addition, the concentration of carbon monoxide in the gas after passing through the catalyst can be reduced.

  Here, components of the embodiment of the present invention will be described. The gas generation source is preferably a device in which the composition and temperature of the oxygen, nitrogen oxide and carbon monoxide of the exhaust gas varies, that is, a gas turbine for a power generation device, a diesel engine, a gas engine, etc. It is not limited to this. For example, a combustion apparatus such as a boiler having a burner as the gas generation source, an incinerator, or the like can be used. It should be noted that the gas discharged from the gas generation source usually contains oxygen and carbon monoxide, but a gas generation source that does not include it is also included in this embodiment.

The gas property adjusting means preferably detects the composition and temperature of the gas, and the concentration ratio of carbon monoxide, nitrogen oxide and oxygen contained in the gas from the gas generation source is represented by the following formula (1): And the temperature of the gas is adjusted to a predetermined temperature.
([NOx] +2 [O ₂ ]) / [CO] ≦ 2.0 (1)
(In the formula (1), [CO], [NOx] and [O ₂ ] indicate the carbon monoxide concentration, nitrogen oxide concentration and oxygen concentration, respectively, and satisfy the condition [O ₂ ]> 0.)

  The gas property adjusting means includes a gas property detecting means for detecting the composition and temperature of the gas discharged from the gas generation source, and an adjustment for adjusting the concentration ratio and temperature of the carbon monoxide, nitrogen oxide and oxygen of the gas. And a controller that controls the regulator based on the detection value by the gas property detection means so that the concentration ratio satisfies the equation (1) and the temperature becomes a predetermined temperature. It is configured to include.

  The gas property detection means includes an oxygen concentration sensor, a carbon monoxide sensor, and a nitrogen oxide sensor for adjusting the gas composition. The nitrogen oxide sensor can be omitted when the nitrogen oxide concentration is lower than the carbon monoxide and oxygen concentrations. As these sensors, known sensors can be used.

  The gas property detection means for adjusting the gas temperature includes a flow rate sensor for detecting a gas amount (air volume) per unit time from the gas generation source, and a gas temperature sensor. As these sensors, known sensors can be used.

  The gas property detection means is preferably provided at two locations, between the gas generation source and the regulator and between the regulator and the catalyst, but only between the gas generation source and the regulator. be able to. In addition, the detecting means is provided on the downstream side of the catalyst, and the set values of the nitrogen oxide concentration, the carbon monoxide concentration and the temperature are determined, and the adjuster can be controlled so that these set values are obtained. In this case, control is performed in consideration of control response delay.

The regulator has a function of regulating the concentration ratio and temperature of carbon monoxide, nitrogen oxide and oxygen. The concentration ratio is adjusted by adjusting the concentration ratio of carbon monoxide, nitrogen oxide, and oxygen, and is preferably adjusted by adjusting the concentration ratio of carbon monoxide and oxygen. In particular, when the concentration of nitrogen oxide with respect to the concentration of carbon monoxide and oxygen in the gas flowing into the regulator is lower by one digit or more, the concentration ratio adjustment between the carbon monoxide and oxygen can be easily performed. This preferable concentration ratio adjustment and temperature adjustment can increase carbon monoxide concentration by incomplete combustion (carbon monoxide concentration adjustment) and increase O ₂ concentration by high O ₂ combustion (oxygen concentration adjustment). It can be realized by a burner.

  The adjuster, the density adjustment function, and the temperature adjustment function can be configured to be performed by different means. For example, the temperature adjustment function can be performed by a heating mechanism such as an electric heater, and the concentration adjustment function can be performed by a carbon monoxide supplier such as a carbon monoxide cylinder and an oxygen supply means such as an oxygen cylinder. Further, when the temperature of the exhaust gas from the gas generation source is stable and the temperature adjustment is unnecessary, the temperature adjustment function of the regulator can be omitted.

The catalyst is a catalyst having a function of reducing the concentration of carbon monoxide and nitrogen oxides by a first reaction for oxidizing carbon monoxide and a second reaction for reducing nitrogen oxides by carbon monoxide. It is set as the structure which apply | coated the catalytically active substance to the base material which has. As the substrate, a metal such as stainless steel or ceramic is used, and a surface treatment is performed to increase the contact area with the gas. As the catalytically active substance, platinum is generally used, but noble metals represented by platinum (Ag, Au, Rh, Ru, Pt, Pd) or metal oxides can be used depending on the implementation.

  It is considered that the action of reducing harmful substances by this catalyst is performed as follows. In the catalyst, as a main reaction, a first reaction for oxidizing carbon monoxide and a second reaction for reducing nitrogen oxide with carbon monoxide are generated. In the reaction in the catalyst (catalytic reaction), in the presence of oxygen, the first reaction is superior to the second reaction, and based on the first reaction, carbon monoxide is consumed by oxygen, After the concentration is adjusted, nitrogen oxides are reduced by the second reaction. This description is simplified. Actually, the first reaction is a competitive reaction with the second reaction. However, since the reaction between carbon monoxide and oxygen occurs apparently faster than the second reaction in the presence of oxygen, the first reaction is performed in the first stage. It is considered that carbon oxide (first reaction) is performed and nitrogen oxides are reduced (second reaction) in the second stage.

In short, in the catalyst, in the presence of oxygen, oxygen is consumed by the first reaction of CO + 1 / 2O ₂ → CO _{2, and} by the second reaction of 2CO + 2NO → N ₂ + 2CO ₂ using the remaining CO. Reduce nitrogen oxides by reducing nitrogen oxides.

Here, [NOx] in formula (1) is nitric oxide: [NO] and nitrogen dioxide concentration is the total concentration of the [NO _2]. In the description of the above reaction formula, NO is used without using NOx. The composition of the produced nitrogen oxide in the high temperature field is NO as the main component, and NO ₂ is only a few percent. This is because it can be described approximately. Even if NO ₂ is present, it is considered that it is reduced by CO in the same manner as NO.

In the case of the value of ([NOx] +2 [O ₂ ]) / [CO] (concentration ratio value) 1, theoretically, the oxygen concentration, nitrogen oxide concentration and carbon monoxide concentration discharged from the catalyst Can be zero. However, experiments have shown that a small amount of carbon monoxide is emitted. ([NOx] +2 [O ₂ ]) / [CO] = 1 is theoretically derived from the first reaction and the second reaction based on the experimental results.

  When the value of the concentration ratio is smaller than 1, the concentration of carbon monoxide is higher than the concentration necessary for the reduction of the nitrogen oxides, so the exhaust oxygen concentration is zero and the gas after passing through the catalyst Carbon monoxide remains. It is preferable to further provide an oxidizing means for oxidizing the residual carbon monoxide. This oxidation means can be configured to provide a catalyst separate from the catalyst and oxidize carbon monoxide by introducing oxygen.

  The concentration ratio value 2.0 in equation (1) in this embodiment is an experimentally obtained value, which is considered to be due to the following reason. The reaction occurring in the catalyst has not been completely elucidated, and it is considered that a side reaction occurs in addition to the main reaction of the first reaction and the second reaction. As one of the side reactions, when the carbon monoxide concentration is high, hydrogen is generated by the reaction between the steam and carbon monoxide, and the nitrogen oxide and oxygen are reduced by this hydrogen.

  As described above, the value of the concentration ratio may be slightly changed due to a reaction other than the main reaction in the catalyst. Therefore, considering the main reaction that is surely occurring, the function of the gas property adjusting means can be expressed as follows.

That is, the gas property adjusting means has a function of adjusting the concentrations of carbon monoxide, nitrogen oxide and oxygen contained in the gas to a predetermined relationship, and the carbon monoxide concentration on the primary side of the catalyst is The carbon monoxide concentration reduced in the catalyst by the first reaction and the carbon monoxide concentration reduced in the catalyst by the second reaction are approximately equal to or higher than the value.

  In this expression, paying attention only to the main reaction, “the concentration of carbon monoxide on the primary side of the catalyst is reduced in the catalyst by the first reaction and the catalyst by the second reaction. Is approximately equal to or greater than the sum of the carbon monoxide concentration reduced within the range. " Therefore, in the above formula (1), an embodiment in which the value of the concentration ratio slightly fluctuates due to a side reaction and does not satisfy the above formula (1) is also included in the embodiment of the present invention by this expression.

  In this embodiment, the gas that has passed through the catalyst and has reduced harmful substances is preferably supplied to an exhaust gas boiler as a heat recovery means. This exhaust gas boiler has at least a heat exchanger such as a water pipe for recovering heat from the gas after passing through the catalyst. The exhaust gas boiler can preferably include a blower that forcibly flows the gas to the heat exchanger, a reheating burner that burns when the required amount of heat cannot be obtained by the recovered heat amount, and the like. The heat recovery means may be an economizer instead of an exhaust gas boiler.

  Further, in this embodiment, the gas generation source, the exhaust gas boiler, the gas property adjusting means, the catalyst, the economizer are arranged in this order, or the gas generation source, the gas property adjusting means, the exhaust gas boiler are arranged. , The catalyst, and the economizer. In this case, the economizer can be omitted if necessary.

  Next, Embodiment 1 of the hazardous substance reduction system of the present invention will be described with reference to the drawings. FIG. 1 is a schematic configuration diagram of a hazardous substance reduction system according to the first embodiment.

  The harmful substance reduction system according to the first embodiment includes a gas turbine 1 serving as an exhaust gas generation source in which the composition and temperature of exhaust gas vary, and a downstream of the gas turbine 1. A gas property adjusting means 2 for adjusting the composition and temperature of carbon monoxide to a predetermined concentration ratio and a predetermined temperature, respectively, and a first reaction and nitrogen oxide provided downstream of the gas property adjusting means 2 for oxidizing carbon monoxide As a main part, a catalyst 3 for reducing the concentration of carbon monoxide and nitrogen oxides and an exhaust gas boiler 4 provided on the downstream side of the catalyst 3 are provided. The components of the first embodiment will be described below.

  In the gas turbine 1, the composition and temperature of the oxygen, nitrogen oxide, and carbon monoxide of the exhaust gas vary depending on the load.

  The gas property adjusting means 2 includes a first detection means 5 for detecting the composition and temperature of the exhaust gas discharged from the gas turbine 1, and concentrations of carbon monoxide, nitrogen oxides and oxygen of the exhaust gas before flowing into the catalyst 3. By the burner 6 for adjusting the ratio and temperature, the second detection means 7 for detecting the composition and temperature of the exhaust gas whose concentration and temperature are adjusted by the burner 6, and the first detection means 5 by the second detection means 7 Based on the detected value, the controller 8 controls the combustion of the burner 6 so that the concentration ratio satisfies the following formula (1) and the temperature of the exhaust gas becomes a predetermined temperature at which the catalyst 3 is activated. It is comprised including.

More specifically, the concentration ratio of carbon monoxide, nitrogen oxide and oxygen contained in the exhaust gas before flowing into the catalyst 3 is adjusted to satisfy the following formula (1), and the temperature of the exhaust gas is set to a predetermined value. It is comprised so that it may adjust to temperature (150 degreeC-500 degreeC which is the activation temperature of the catalyst 3 of this Example 1).
([NOx] +2 [O ₂ ]) / [CO] ≦ 2.0 (1)
(In the formula (1), [CO], [NOx] and [O ₂ ] indicate the carbon monoxide concentration, nitrogen oxide concentration and oxygen concentration, respectively, and satisfy the condition [O ₂ ]> 0.)

  The first detection means 5 and the second detection means 7 are respectively an oxygen concentration sensor and a carbon monoxide sensor for adjusting the gas composition, and a flow rate sensor and a gas temperature sensor for adjusting the gas temperature (both not shown). ).

The burner 6 is a premixed burner having a function of adjusting the concentration ratio and temperature of carbon monoxide and oxygen of the exhaust gas. The adjustment of carbon monoxide and oxygen by the burner 6 is configured to increase the carbon monoxide concentration by incomplete combustion of the burner 6 and to increase the O ₂ concentration by high O ₂ combustion. Further, the gas temperature is adjusted by changing the combustion amount of the burner 6.

  The burner 6 is provided with a fuel valve 9 as a gas fuel supply amount adjusting means and a blower 10 capable of rotating speed control as a combustion air supply amount adjusting means. By controlling the rotation speed of the blower 10, the concentration ratio and the temperature are adjusted.

  The control by the controller 8 is realized by a gas property adjustment program stored in advance. This adjustment program includes a difference signal between the first detection value of the first detection means 5 and the set value of the concentration ratio (for example, carbon monoxide concentration: 4000 ppm, oxygen concentration: 2000 ppm) and the first detector. Based on a difference signal from a predetermined temperature, a first control signal is sent to the fuel valve 9 and the blower 10 to perform rough adjustment, and a second detection value of the second detection means 7 and a set value of the concentration ratio are set. Based on the difference signal and the difference signal between the second detection value and the temperature set value, a second control signal is sent to the fuel valve 9 and the blower 10 to perform fine control. That is, this control mainly controls the combustion of the burner 6 based on the detection value of the first detection means 5 upstream of the burner 6, and the second detection means 7 downstream of the burner 6. The main control is corrected based on the detected value. Preferably, the second detection means 7 is made to function as a backup sensor when the first detection means 6 fails. In this case, the burner 6 is controlled based on a backup program.

  The catalyst 3 is composed of a CO oxidation catalyst having a function of reducing the concentration of carbon monoxide and nitrogen oxides by a first reaction for oxidizing carbon monoxide and a second reaction for reducing nitrogen oxides by carbon monoxide. The catalytically active material is applied to a base material having air permeability. In the first embodiment, stainless steel is used as the base material, and surface treatment is performed to increase the contact area with the gas. Platinum is used as the catalytically active substance.

  The gas turbine 1 and the catalyst 3 are connected by a first gas passage 11. The catalyst 3 and the exhaust gas boiler 4 are connected by a second gas passage 12.

  The operation of the first embodiment having the above configuration will be described. First, the gas turbine 1 is operated and exhaust gas is discharged. In the gas turbine 1, the composition and temperature of oxygen, nitrogen oxides, and carbon monoxide in the exhaust gas change due to load fluctuations and the like. Now, the composition and temperature of oxygen, nitrogen oxide and carbon monoxide in the exhaust gas during high load operation are set to 1900 ppm, 100 ppm, 2000 ppm and 300 ° C., respectively. Under this exhaust gas condition, the left side of the equation (1) is calculated to be 1.95. Therefore, since the formula (1) is satisfied and the set temperature of the catalyst 3 is satisfied, the adjustment by the exhaust gas property adjusting means 2 is unnecessary.

  It is assumed that the composition and temperature of oxygen, nitrogen oxide, and carbon monoxide become 3000 ppm, 100 ppm, 2000 ppm, and 100 ° C., respectively, due to the load fluctuation of the gas turbine 1. Under this exhaust gas condition, the left side of the equation (1) is calculated to be 3.05. Since the equation (1) is not satisfied and the set temperature of the catalyst 3 is not satisfied, the adjustment by the exhaust gas property adjusting means 2 is performed.

  This adjustment controls the combustion of the burner 6 such that the oxygen concentration is decreased, the carbon monoxide concentration is increased, and the gas temperature is increased to the set temperature. In order to reduce the oxygen concentration, the burner 6 is burned using oxygen in the gas from the gas generation source. To increase the carbon monoxide concentration, incomplete combustion is performed. The temperature of the gas is determined by combustion of the burner 6 accompanying the composition adjustment. These specific controls can be performed based on experimentally obtained change characteristics of the combustion state and oxygen and carbon monoxide concentrations in advance by experiments.

  The exhaust gas adjusted by the gas property adjusting means 2 is in contact with the catalyst 3 by flowing into and contacting the catalyst 3. In this catalyst 3, as the main reaction, the first oxidation of carbon monoxide is performed. A reaction and a second reaction in which the nitrogen oxides are reduced with carbon monoxide occur. Based on the first reaction, carbon monoxide is consumed by oxygen and the concentration is adjusted, and then the nitrogen oxide is reduced by the second reaction. As a result, the nitrogen oxide concentration and the carbon monoxide concentration after passing through the catalyst 3 are made substantially zero.

  The exhaust gas whose harmful substances have been reduced by the catalyst 3 is recovered by the exhaust gas boiler 4. That is, the combustion heat generated by the burner 6 and the heat generated by the oxidation in the catalyst 3 are recovered. The exhaust gas after passing through the exhaust gas boiler 4 has a low temperature and contains almost no harmful substances.

  According to the first embodiment, it is possible to provide an energy saving system which is low in pollution and hardly contains nitrogen oxides and carbon monoxide and which does not waste heat wastefully.

  Next, Embodiment 2 of the present invention will be described with reference to FIG. FIG. 2 is a schematic configuration diagram of the hazardous substance reduction system according to the second embodiment. In the following description, the same components as those in the first embodiment are denoted by the same reference numerals and the description thereof is omitted.

  The second embodiment is different from the first embodiment in that the first embodiment uses the first detection means 5 and the second detection means 6 to adjust the concentration ratio and temperature. In the second embodiment, the second detection means 7 is not used, and the first detection means 5 is used for control.

  Since the operation of the second embodiment is basically the same as that of the first embodiment, the description thereof is omitted.

It is a schematic block diagram of Example 1 of this invention. It is a schematic block diagram of Example 2 of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Gas generation source 2 Gas property adjustment means 3 Catalyst 4 Exhaust gas boiler 5 First detection means (gas property detection means)
6 Burner (regulator)
7 Second detection means (gas property detection means)
8 Controller

Claims (4)

A gas generation source in which the composition and temperature of the gas to be discharged fluctuate;
A gas property adjusting means which is provided downstream of the gas generation source and adjusts the composition and temperature of oxygen, nitrogen oxide and carbon monoxide of the gas to a predetermined concentration ratio and a predetermined temperature, respectively;
A catalyst that is provided downstream of the gas property adjusting means and that reduces the concentration of carbon monoxide and nitrogen oxides by a first reaction that oxidizes carbon monoxide and a second reaction that reduces nitrogen oxides by carbon monoxide; A hazardous substance reduction system characterized by comprising:   The gas property adjusting means includes: a gas property detecting means for detecting the gas composition, the gas flow rate and the gas temperature; a regulator for adjusting the composition and temperature of oxygen, nitrogen oxide and carbon monoxide of the gas; 2. The controller according to claim 1, further comprising a controller that controls the regulator based on a detection value of the gas property detection means to control the composition and temperature of the gas to a predetermined concentration ratio and a predetermined temperature, respectively. Hazardous substance reduction system. The gas property adjusting means adjusts the concentration ratios of carbon monoxide, nitrogen oxide, and oxygen contained in the gas so as to satisfy the following formula (1). The hazardous substance reduction system described in 1.
([NOx] +2 [O ₂ ]) / [CO] ≦ 2.0 (1)
(In the formula (1), [CO], [NOx] and [O ₂ ] indicate the carbon monoxide concentration, nitrogen oxide concentration and oxygen concentration, respectively, and satisfy the condition [O ₂ ]> 0.)   The harmful substance reduction system according to claim 1, wherein the gas after passing through the catalyst is guided to an exhaust gas boiler to perform heat recovery.

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