JP4123297B2 - Nitrogen oxide containing gas treatment method - Google Patents

Description

  The present invention relates to a method for treating a nitrogen oxide-containing gas applied to a water tube boiler, a regenerator of an absorption chiller, and the like.

  In general, as a principle for suppressing the generation of NOx, suppression of flame (combustion gas) temperature, shortening of residence time of high-temperature combustion gas, and the like are known. There are various NOx reduction technologies that apply these principles. For example, a two-stage combustion method, a concentration combustion method, an exhaust gas recirculation combustion method, a water addition combustion method, a steam injection combustion method, a flame cooling combustion method using a water tube group, and the like have been proposed and put into practical use.

  By the way, the influence on the environment is increasing even for a relatively small capacity NOx generation source such as a water tube boiler, and a further reduction in NOx has been demanded. In this reduction in NOx, if the generation of NOx is reduced, the amount of CO emissions increases, so it is difficult to simultaneously reduce NOx and CO.

  The cause is that there is a technical problem in which low NOx and low CO are contradictory. That is, if the combustion gas temperature is drastically lowered to promote low NOx and suppressed to a low temperature of 900 ° C. or less, a large amount of CO is generated and the generated CO is discharged without being oxidized, resulting in an increase in CO emission. End up. Conversely, if the combustion gas temperature is suppressed to be high in order to reduce the amount of CO emission, the amount of NOx produced will be insufficiently suppressed.

  In order to solve this problem, the applicant has developed a low NOx and low CO technology that suppresses the combustion gas temperature so as to minimize the amount of CO generated with the reduction of NOx and to oxidize the generated CO. Proposed and commercialized (see Patent Documents 1 and 2). However, the NOx reduction techniques described in Patent Documents 1 and 2 actually have a generated NOx value of only about 25 ppm.

  As a solution to this problem, the applicant performs a NOx reduction step that suppresses the combustion gas temperature and lowers the generated NOx value to a predetermined value or less so that the suppression of NOx generation takes precedence over the reduction of the exhausted CO value. In addition, a low NOx combustion method is proposed in which a CO reduction step in which the exhaust CO value from the NOx reduction step is set to a predetermined value or less (see Patent Documents 3 and 4). According to the techniques described in Patent Documents 3 and 4, it is possible to reduce NOx below 10 ppm, but it is difficult to achieve NOx below 5 ppm. This is because the production of NOx of 5 ppm or more is inevitable due to the characteristics of combustion.

  And the NOx reduction technology described in Patent Documents 3 and 4 belongs to a so-called high air ratio combustion region Z1 having an air ratio of 1.38 or more as shown in FIG. On the other hand, in the combustion zone Z2 where the air ratio is 1.1 or less (hereinafter referred to as “low air ratio”), the amount of nitrogen oxide generated increases, making it difficult to achieve both low NOx and low CO, and the air ratio. Since it is difficult to control stable combustion, such as causing a backfire when it becomes 1 or less, the low air ratio combustion region Z2 has hardly been the subject of research and development so far. In FIG. 15, lines F and E schematically show the NOx characteristics and CO characteristics on the primary side by the combustion apparatus of the present invention, respectively, and lines U and J respectively show NOx on the catalyst secondary side by the combustion apparatus of the present invention. The characteristics and CO characteristics are schematically shown. The techniques for reducing NOx in Patent Documents 3 and 4 basically suppress NOx generation by burning a burner in a high air ratio region Z1, and are generated in an oxidation catalyst (Patent Documents 3 and 4). This is a technique for removing CO.

  On the other hand, as the background of the times, there has been a demand for further NOx reduction in boilers and a low air ratio operation that saves energy.

  The inventors of this application have been researching and developing a combustion method that can reduce nitrogen oxides to near zero using an oxidation catalyst.

  By the way, Patent Document 5 is known as a method for treating a nitrogen oxide-containing gas generated by combustion of a burner.

  In the exhaust gas treatment method of Patent Document 5, the burner is burned at an air ratio of less than 1.0, so that the combustion exhaust gas does not contain oxygen, contains unburned components of CO and HC (hydrocarbon), and nitrogen. In the oxidation-reduction catalyst, nitrogen oxides are reduced by unburned components to purify the nitrogen oxides, and air is added to the exhaust gas after the purification, and the unburned components are purified by the oxidation catalyst.

  The processing method of Patent Document 5 does not reduce carbon monoxide and nitrogen oxides in the presence of oxygen. According to Patent Document 5, since a large amount of unburned hydrocarbon is discharged, it is difficult to make the exhaust nitrogen oxidation concentration and the exhaust carbon monoxide concentration substantially zero by the oxidation catalyst. In addition, an oxidation catalyst having such a characteristic that the efficiency of reduction of nitrogen oxides decreases in the presence of hydrocarbons cannot be used. Moreover, since the reduction step of nitrogen oxides and the oxidation step of unburned components are performed using different catalysts, the processing becomes complicated.

  Patent Document 6 discloses a method for purifying nitrogen oxide-containing gas from a gas engine. This Patent Document 6 purifies nitrogen oxides and carbon monoxide using a three-way catalyst, but the existence of hydrocarbons in the gas is essential, and a gas having a theoretical air ratio without excess oxygen. Only applicable to Therefore, the processing method of patent document 6 is not suitable for the combustion gas processing of combustion apparatuses, such as a boiler which arises by combustion of a burner and contains excess oxygen.

  Further, Patent Document 7 discloses a technique for reducing nitrogen oxide in exhaust gas from an incinerator with carbon monoxide using an oxidation catalyst. In the technique of Patent Document 7, since the reduction of nitrogen oxides does not proceed when oxygen is present in the exhaust gas, the exhaust gas is in an oxygen-free state by burning the fuel richly (less than 1 in the air ratio) in the primary combustion. It is what. In this patent document 7, since it is restricted by fuel rich combustion, it is difficult to apply to a combustion apparatus that contains oxygen in exhaust gas such as a boiler using a burner.

Japanese Patent No. 3221582 US Pat. No. 5,353,748 JP 2004-125378 A US Pat. No. 6,792,895 JP 2001-241619 A Japanese Patent Laid-Open No. 5-38421 Japanese Patent Laid-Open No. 2003-275543

  The problem to be solved by the present invention is to reduce the emission amount of nitrogen oxide and carbon monoxide contained in a gas containing oxygen to a value close to zero by an easy method using an oxidation catalyst, or The object is to provide a method for treating a nitrogen oxide-containing gas that can be reduced to an acceptable range.

As a result of intensive studies to solve the above-mentioned problems, the inventors of this application have made almost no research so far on boilers equipped with an oxidation catalyst for reducing carbon monoxide described in Patent Documents 3 and 4. In the burner combustion region (region Z2 in FIG. 15) at a low air ratio close to 1, which has not been performed, a point was found at which the emission amounts of nitrogen oxides and carbon monoxide were substantially zero. As a result of pursuing the cause of the fact that the emission amounts of nitrogen oxides and carbon monoxide could be substantially zero, the concentration ratio of oxygen, nitrogen oxides and carbon monoxide on the primary side of the oxidation catalyst was determined as a reference predetermined concentration. By setting the ratio, the emission amount of nitrogen oxides and carbon monoxide can be reduced to almost zero using an oxidation catalyst, and by adjusting the concentration ratio in the vicinity of the reference predetermined concentration ratio, harmful substances can be obtained. A new finding was obtained that the emission amount of (nitrogen oxide and carbon monoxide) can be reduced to substantially zero or an allowable value. The present invention has been completed based on this finding. According to the present invention, not only the emission concentration of harmful substances can be made substantially zero, but also this can be realized at an air ratio close to 1.0, so that significant energy saving can be realized.
Hereinafter, when simply referred to as the concentration ratio, it means the concentration ratio of oxygen, nitrogen oxide and carbon monoxide on the primary side of the oxidation catalyst. The oxidation catalyst may be a known oxidation catalyst or a novel oxidation catalyst.

  In other words, as described in Patent Document 7, the inventors of this application break the technical common sense that oxygen is an obstacle to reducing nitrogen oxides with carbon monoxide under the action of oxidation catalyst. By using oxygen, the above-mentioned problem is achieved by adopting a novel technical means for adjusting the relationship of oxygen, nitrogen oxide and carbon monoxide concentrations on the primary side of the oxidation catalyst to a predetermined relationship (predetermined concentration ratio). It came to solve.

  The problem has the following sub-tasks. The first sub-problem is that hydrocarbons that inhibit the reduction of harmful substances (NOx and CO) of the oxidation catalyst are not included in the gas produced by the burner. This can be solved without using hydrocarbon removal means by using combustion without rapid cooling as in an internal combustion engine.

  The second sub-task is how to set the gas concentration ratio to the reference predetermined concentration ratio. The reference predetermined concentration cannot be obtained simply by burning the burner. For this sub-task, adjustment using the concentration ratio characteristic of the burner, adjustment using the concentration ratio characteristic of the burner and the endothermic means for absorbing heat from the burner, and auxiliary adjustment in addition to these adjustments The problem can be solved by adjusting the density ratio by means of an auxiliary means.

  As described above, the present invention is not only remarkable in the harmful substance reducing effect, but also an epoch-making solution that can easily solve the above-described problems by the technical means of adjusting the concentration ratio using a conventional burner and an oxidation catalyst. It is an invention.

  The present invention is not limited to a boiler, and can be applied to a method for treating a nitrogen oxide-containing gas generated by a burner.

The invention according to claim 1 is a method for treating a nitrogen oxide-containing gas, wherein a gas generated by burning fuel in a burner is brought into contact with an oxidation catalyst to reduce nitrogen oxide contained in the gas. A combustion step in which a hydrocarbon-containing fuel is burned in the burner to produce a gas that does not contain hydrocarbons and contains oxygen, nitrogen oxides, and carbon monoxide; and contacts the gases with an oxidation catalyst. A harmful substance reducing step of oxidizing carbon monoxide contained in the gas with oxygen and reducing nitrogen oxide with carbon monoxide; and oxygen, nitrogen oxide and carbon monoxide in the gas on the primary side of the oxidation catalyst. And a density ratio adjusting step for adjusting the density ratio K to a predetermined density ratio, wherein the predetermined density ratio satisfies the following expressions (1) and (2).
([NOx] +2 [O2]) / [CO] = K (1)
K ≦ 2.0 (2)
(In Equation (1), [CO], [NOx] and [O2] indicate the CO concentration, NOx concentration and O2 concentration, respectively, and satisfy the condition [O2]> 0.)

  Here, the nitrogen oxide concentration being substantially zero is preferably 5 ppm, more preferably 3 ppm, and still more preferably zero. The carbon monoxide concentration is substantially zero is 30 ppm, more preferably 10 ppm. Further, in the following description, the oxygen concentration substantially zero is 100 ppm or less, but is preferably less than the measurement limit value. Furthermore, the nitrogen oxide concentration and the carbon monoxide concentration below the predetermined values mean below the emission standard concentration determined in each country and each region, but it is preferable to set the values to almost zero as much as possible. Needless to say. Thus, in the meaning of the emission standard value, “predetermined value” or less can be referred to as “allowable value” and “emission standard value”.

According to the first aspect of the present invention, in the adjustment step using the oxidation catalyst, the concentration ratio of the gas is set to the predetermined concentration ratio. By effectively utilizing the oxidizing action, the carbon monoxide concentration is adjusted, the nitrogen oxide concentration on the secondary side of the oxidation catalyst is substantially zero or below a predetermined value, and the carbon monoxide concentration is substantially zero or predetermined. It can be reduced below the value. Further, since the combustion in the combustion step is combustion that does not discharge hydrocarbons in the gas, combustion control can be easily performed as compared with a method of burning so as to discharge hydrocarbons as in Patent Document 7. . Further , since the gas flowing into the oxidation catalyst does not contain hydrocarbons, nitrogen oxides and carbon monoxide are effectively reduced by the oxidation catalyst without using a complicated technique as in Patent Document 5. In addition, the concentration ratio K can be easily adjusted without considering the reaction due to hydrocarbons. Further, in the concentration ratio adjusting step, the concentration ratio of the gas is set to the predetermined concentration ratio, so that the oxidation of carbon monoxide by oxygen is effectively utilized in the harmful substance reduction step, and the carbon monoxide concentration is reduced. It is possible to adjust the exhaust nitrogen oxide concentration to be substantially zero by using the oxidation catalyst, and to reduce the exhaust carbon monoxide concentration to substantially zero or a predetermined value or less.

According to a second aspect of the present invention, there is provided a method for treating a nitrogen oxide-containing gas, wherein a gas generated by burning fuel in a burner is brought into contact with an oxidation catalyst to reduce nitrogen oxide contained in the gas. A combustion step in which a hydrocarbon-containing fuel is burned in the burner to produce a gas that does not contain hydrocarbons and contains oxygen, nitrogen oxides, and carbon monoxide; and contacts the gases with an oxidation catalyst. A harmful substance reducing step of oxidizing carbon monoxide contained in the gas with oxygen and reducing nitrogen oxide with carbon monoxide; and oxygen, nitrogen oxide and carbon monoxide in the gas on the primary side of the oxidation catalyst. and a concentration ratio adjusting step of adjusting a concentration ratio K, the concentration ratio adjusting step, the concentration ratio K is decreased to substantially zero concentration of nitrogen oxides and carbon monoxide concentration of the oxidation catalyst secondary side Adjustment 0 for adjusting to a quasi-predetermined concentration ratio K0, a first predetermined concentration ratio in which the concentration ratio K is substantially zero in the nitrogen oxide concentration on the secondary side of the oxidation catalyst and the carbon monoxide concentration is below a predetermined value. Adjustment 1 for adjusting to K1, the concentration ratio K is adjusted to a second predetermined concentration ratio K2 in which the carbon monoxide concentration on the secondary side of the oxidation catalyst is substantially zero and the nitrogen oxide concentration is not more than a predetermined value. The equation for determining the reference predetermined concentration ratio K0, which is one of the adjustments 2, is the following equation (3) that satisfies the following equation (4), and the first predetermined concentration ratio K1 is smaller than the reference predetermined concentration ratio K0: A method for treating a nitrogen oxide-containing gas, wherein the second predetermined concentration ratio K2 is larger than the reference predetermined concentration ratio K0.
([NOx] +2 [O2]) / [CO] = K (3)
1.0 ≦ K = K0 ≦ 2.0 (4)
(In Formula (3), [CO], [NOx] and [O2] are the carbon monoxide concentration,
Nitrogen oxide concentration and oxygen concentration are shown, and the condition of [O2]> 0 is satisfied. )

According to the second aspect of the present invention, in the concentration ratio adjusting step, the adjustment 0, that is, the concentration ratio K of the gas is set to the reference predetermined concentration ratio K0, thereby exhausting nitrogen oxides using the oxidation catalyst. Concentration and emission carbon monoxide concentration can be substantially zero. Further, the adjustment 1, that is, by setting the gas concentration ratio K to the first predetermined concentration ratio K1, the exhaust nitrogen oxide concentration is made substantially zero using the oxidation catalyst, and the exhaust carbon monoxide concentration is predetermined. It can be less than or equal to the value. Further, by adjusting the concentration ratio of the gas to the second predetermined concentration ratio, the exhausted carbon monoxide concentration is made substantially zero using the oxidation catalyst, and the exhausted nitrogen oxide concentration is less than a set value. It can be. Furthermore, even Oite other effects according to claim 2 to claim 1 can be obtained in the same manner.

The invention described in claim 3 is characterized in that, in the invention described in claim 1 or 2, the adjustment of the concentration ratio K is performed by changing the air ratio of the burner and burning .

According to the invention described in claim 3 , in addition to the effect of the invention described in claim 1 or 2 , the concentration ratio adjustment is performed using combustion by changing the air ratio of the burner. Therefore, there is an effect that a means for adjusting the concentration ratio is not required separately.

According to a fourth aspect of the present invention, in any one of the first to third aspects, the air ratio of the burner is 1.1 or less .

According to invention of Claim 4 , in addition to the effect by the invention of any one of Claims 1-3 , there exists an effect that energy saving is realizable.

Invention of claim 5, Oite to the invention of claim 1 or claim 2, adjustment of the concentration ratio K is, together with utilizing be burned by changing the air ratio of the burner, the It is characterized in that it is carried out by using an auxiliary adjusting means that is arranged between the burner and the oxidation catalyst and adjusts the concentration ratio as an auxiliary.

According to the invention described in claim 5 , in addition to the effect of the invention described in claim 1 or 2 , the concentration ratio adjustment is performed in addition to the combustion by changing the air ratio of the burner. Since the adjustment means is used, there is an effect that the range of the burner and the heat absorption means to which the present invention can be applied can be expanded.

Further , the tenth invention is a nitrogen oxide which is produced by combustion of a burner and reduces the concentration of exhaust nitrogen oxide and exhaust carbon monoxide by contacting a gas containing nitrogen oxide and carbon monoxide with an oxidation catalyst. A method for treating a contained gas, wherein oxygen is included in the gas, and the concentration ratio of nitrogen oxide, carbon monoxide and oxygen on the primary side of the oxidation catalyst in the gas is adjusted to a predetermined concentration ratio, The emission concentration of the nitrogen oxide and carbon monoxide is substantially zero or a predetermined value or less.

According to the tenth aspect of the invention, the concentration ratio of nitrogen oxide, carbon monoxide and oxygen is adjusted by the presence of oxygen. Therefore, the predetermined concentration ratio can be easily adjusted, and the oxidation catalyst is used. The emission concentrations of nitrogen oxides and carbon monoxide can be made substantially zero or less than a predetermined value easily.

  According to the present invention, the emission amounts of nitrogen oxides and carbon monoxide can be reduced to a value close to zero as much as possible, or can be easily reduced to a predetermined value or less within an allowable range.

Next, an embodiment of the present invention will be described. Before describing the embodiments of the present invention, terms used in this application will be described. “Gas” refers to a gas from the burner until it has passed through an oxidation catalyst (which can be referred to as an oxidation / reduction catalyst; hereinafter simply referred to as “catalyst”). It is called “exhaust gas”. Therefore, 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. Here, when the catalyst is provided in multiple stages along the gas flow, “gas” refers to the gas until it has passed through the final stage catalyst, and “exhaust gas” refers to the final stage catalyst. The gas after it is done.

  The “primary side of the catalyst” is the side on which the burner is provided with respect to the catalyst. Unless otherwise specified, the gas immediately before passing through the catalyst, and the “secondary side of the catalyst” The opposite side of the primary side.

  Also, “not containing hydrocarbons” does not mean that no hydrocarbons are produced in the course of the combustion reaction, but some hydrocarbons are produced in the course of the combustion reaction, This means that the gas that flows into the catalyst, that is, the gas flowing into the catalyst is substantially free of hydrocarbons that reduce nitrogen oxides (below the measurement limit).

Further, the air ratio m is defined as m = 21 / (21− [O ₂ ]). However, [O ₂ ] represents the oxygen concentration in the exhaust gas on the secondary side of the oxidation catalyst, but [O ₂ ] used when determining the air ratio represents the excess oxygen concentration in the oxygen excess region and in the fuel excess region. The deficient oxygen concentration required for burning unburned gas such as carbon monoxide at an air ratio m = 1 is expressed as a negative value.

  Next, an embodiment of the present invention will be described. The present invention is applied to a combustion apparatus (which may be referred to as a thermal device or a combustion device) such as a water tube boiler such as a small once-through boiler, a water heater, or a regenerator of an absorption refrigerator.

(Embodiment 1)
A combustion apparatus such as a boiler to which an embodiment of the method for treating a nitrogen oxide-containing gas of the present invention is applied typically has a burner and a heat absorption means for performing heat absorption from the gas generated by the burner. A can body including a heat transfer tube (water tube) group and a gas containing oxygen, nitrogen oxide and carbon monoxide after passing through the heat transfer tube group in a predetermined concentration ratio are in contact with each other to oxidize carbon monoxide. An oxidation catalyst for reducing nitrogen oxides, fuel supply means for supplying gaseous fuel to the burner, combustion air supply means for supplying combustion air to the burner and premixing combustion air and fuel, and A sensor for detecting the oxygen concentration downstream and a controller for inputting a signal from the sensor or the like to control the fuel supply means, the combustion air supply means, and the like are provided as main parts.

  Embodiment 1 of the present invention suitably implemented in such a combustion apparatus is a nitrogen oxide contained in the gas by contacting a gas generated by burning fuel with a burner and an oxidation catalyst. Is a method for treating a nitrogen oxide-containing gas, wherein a hydrocarbon-containing fuel is burned by the burner to generate a gas containing oxygen, nitrogen oxides, and carbon monoxide without containing hydrocarbons. A step of reducing the harmful substances by contacting the gas with an oxidation catalyst to oxidize carbon monoxide contained in the gas with oxygen and reducing nitrogen oxide with carbon monoxide, and in the gas on the primary side of the oxidation catalyst; The concentration ratio of oxygen, nitrogen oxides, and carbon monoxide of the catalyst is such that the nitrogen oxide concentration on the secondary side of the oxidation catalyst is substantially zero or a predetermined value or less, and the carbon monoxide concentration is substantially zero or a predetermined value or less. Na Characterized in that it comprises a concentration ratio adjusting step of adjusting the predetermined concentration ratio.

(Embodiment 2)
The first embodiment of the present invention can be expressed by the following second embodiment. Embodiment 2 of the present invention is a method for treating a nitrogen oxide-containing gas in which a gas generated by burning fuel in a burner is brought into contact with an oxidation catalyst to reduce nitrogen oxide contained in the gas. A combustion step in which a hydrocarbon-containing fuel is burned in the burner to produce a gas that does not contain hydrocarbons and contains oxygen, nitrogen oxides, and carbon monoxide; and contacts the gases with an oxidation catalyst. A harmful substance reducing step of oxidizing carbon monoxide contained in the gas with oxygen and reducing nitrogen oxide with carbon monoxide; and oxygen, nitrogen oxide and carbon monoxide in the gas on the primary side of the oxidation catalyst. A density ratio adjusting step for adjusting the density ratio K, wherein the density ratio adjusting step is any one of the following adjustment 0 to adjustment 2.
Adjustment 0: The reference predetermined concentration ratio K0 is set so that the nitrogen oxide concentration and the carbon monoxide concentration on the secondary side of the oxidation catalyst are substantially zero.
Adjustment 1: The concentration ratio K is adjusted to a first predetermined concentration ratio K1 in which the nitrogen oxide concentration on the secondary side of the oxidation catalyst is substantially zero and the carbon monoxide concentration is a predetermined value or less.
Adjustment 2: The concentration ratio K is adjusted to a second predetermined concentration ratio K2 in which the carbon monoxide concentration on the secondary side of the oxidation catalyst is substantially zero and the nitrogen oxide concentration is not more than a predetermined value.

  When the adjustment 0 is performed, the catalyst makes the nitrogen oxide concentration and the carbon monoxide concentration on the catalyst secondary side substantially zero, and when the adjustment 1 is performed, the nitrogen oxidation on the catalyst secondary side is performed. When the adjustment 2 is performed, the carbon monoxide concentration on the secondary side of the oxidation catalyst is made substantially zero and the nitrogen oxide concentration is made substantially zero. It has the characteristic of being below a predetermined value.

In the second embodiment, the concentration ratio means a mutual relationship between the carbon monoxide concentration, the nitrogen oxide concentration, and the oxygen concentration. The reference predetermined density ratio K0 in the adjustment 0 is preferably determined by the determination formula of the following expression (1), and preferably satisfies the following expression (2), and the first predetermined concentration ratio K1 is set to the reference predetermined density. The second predetermined density ratio K2 is set to be smaller than the ratio K0 and larger than the reference predetermined density ratio K0.
([NOx] +2 [O ₂ ]) / [CO] = K (1)
1.0 ≦ K = K0 ≦ 2.0 (2)
(In the formula (1), [CO], [NOx] and [O ₂ ] indicate a carbon monoxide concentration, a nitrogen oxide concentration and an oxygen concentration, respectively, and satisfy the condition of [O ₂ ]> 0.)

  The reference predetermined concentration ratio K0 is defined as the oxygen, nitrogen oxides and monoxide on the primary side of the oxidation catalyst in which the oxygen concentration, nitrogen oxide concentration and carbon monoxide concentration on the secondary side of the oxidation catalyst are substantially zero, respectively. It is the concentration ratio of carbon. The equation (1) is a determination equation for determining the reference predetermined concentration ratio K0, and the equation (2) represents the oxygen concentration, nitrogen oxide concentration, and carbon monoxide concentration on the secondary side of the oxidation catalyst, respectively. The condition for substantially zero is shown. Theoretically, each concentration can be made zero under the condition of K0 = 1.0. However, according to the experimental results, it has been confirmed that each concentration is substantially zero within the range of the formula (2). However, the upper limit of K0 is 2.0 depending on the characteristics of the catalyst. It is conceivable to take a value greater than zero.

  The concentration ratio K on the primary side of the oxidation catalyst is adjusted so as to be lower than the value of the reference predetermined concentration ratio K0, that is, the first predetermined concentration ratio K1 that is smaller than K0 in the equation (1) ( In the adjustment 1), the oxygen concentration and the nitrogen oxide concentration on the secondary side of the oxidation catalyst become substantially zero, and the carbon monoxide concentration becomes a predetermined value or less. The predetermined value of the carbon monoxide concentration is preferably set to an emission standard value or less (this value varies depending on the country and can be changed for each country). When the predetermined value is determined, the first predetermined concentration ratio K1 can be determined experimentally. Specifically, the adjustment of the concentration ratio K such that the value of the concentration ratio K becomes the first predetermined concentration ratio K1 smaller than K0 is, specifically, the ratio of the oxygen concentration to the carbon monoxide concentration on the primary side of the oxidation catalyst. This can be realized by reducing the ratio of the oxygen concentration to the carbon monoxide concentration satisfying the reference predetermined concentration ratio K0.

Further, when the concentration ratio K on the primary side of the oxidation catalyst is adjusted so that the concentration ratio K becomes the second predetermined concentration ratio K2 larger than K0 (adjustment 2), the primary side of the oxidation catalyst is adjusted. The carbon oxide concentration becomes substantially zero and the nitrogen oxide concentration becomes a predetermined value or less. In this case, the oxygen concentration on the secondary side of the oxidation catalyst is a predetermined concentration. The predetermined value of the nitrogen oxide concentration is a value different from the predetermined value of the carbon monoxide concentration, and is preferably equal to or less than the emission standard value determined in each country. When this predetermined value is determined, the second concentration ratio K2 can be determined experimentally. Specifically, the adjustment of the concentration ratio K to obtain the second predetermined concentration ratio K2 is performed by adjusting the ratio of the oxygen concentration to the carbon monoxide concentration on the primary side of the oxidation catalyst so as to satisfy the reference predetermined concentration ratio K0. This can be realized by increasing the ratio of the oxygen concentration to the carbon concentration.

  In Embodiment 1 of this processing method, first, in the combustion step, the burner contains nitrogen oxides and carbon monoxide, and a gas not containing hydrocarbons is generated. The concentration ratio K of oxygen, nitrogen oxides, and carbon monoxide in the gas on the primary side of the catalyst is determined by any one of the adjustment 0, the adjustment 1, and the adjustment 2 by the concentration ratio adjustment step. The reference predetermined density ratio K0, the first predetermined density ratio K1, and the second predetermined density ratio K2 are adjusted. In the harmful substance reduction step, the gas comes into contact with the catalyst, carbon monoxide is oxidized by oxygen in the gas, and nitrogen oxides are reduced by carbon monoxide. The role of oxygen in the hazardous substance reduction step when the adjustment 0 or the adjustment 1 is performed is necessary to adjust the concentration of carbon monoxide, that is, to reduce the nitrogen oxide to make the concentration substantially zero. It consumes and reduces the amount of carbon monoxide present above a certain amount. By this harmful substance reduction step, the emission amount of nitrogen oxide in the gas is substantially reduced to zero, and the emission amount of carbon monoxide is substantially reduced to zero or below a predetermined value.

The reference predetermined density ratio K0 of the adjustment 0 and the first predetermined density ratio K1 of the adjustment 1 are expressed by being included by the following equation (3). That is, when the expression (3) is satisfied, the nitrogen oxide concentration on the secondary side of the catalyst is substantially zero, and the carbon monoxide concentration is substantially zero or reduced. In order to reduce the carbon monoxide concentration below the predetermined value, the concentration ratio K on the primary side of the oxidation catalyst is adjusted so that the value on the left side of Equation (3) is smaller than K0, and the first One predetermined concentration ratio K1.
([NOx] +2 [O ₂ ]) / [CO] ≦ 2.0 (3)
(In Expression (3), [CO], [NOx] and [O ₂ ] indicate the CO concentration, NOx concentration and O ₂ concentration, respectively, and satisfy the condition of [O ₂ ]> 0.)

The reduction action in the harmful substance reduction step will be further described. This reduction action is considered to be performed as follows. In the oxidation 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. Then, Oite the reaction (catalysis) in the oxidation catalyst, in the presence of oxygen, the first reaction is predominant than the second reaction, the carbon monoxide on the basis of the first reaction 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 is oxidized (first reaction), and nitrogen oxides are reduced (second reaction) in the second stage.

In short, in the oxidation catalyst, in the presence of oxygen, the _{CO + 1 / 2O 2 → CO} 2 comprising the first reaction, oxygen is consumed, with the remaining _{CO, 2CO + 2NO → N 2} + 2CO 2 becomes the second reaction To reduce nitrogen oxides and reduce exhaust nitrogen oxide concentration.

Here, the value of ([NOx] +2 [O ₂ ]) / [CO] (value of the concentration ratio) is 2.0 or less as described above, but preferably 1.5 or less. Further, [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.

When the value of ([NOx] +2 [O ₂ ]) / [CO] (value of the concentration ratio K) is 1.0, theoretically, the concentration of oxygen discharged from the catalyst, the concentration of nitrogen oxides, and The carbon monoxide concentration 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 in consideration of the experimental results.

Here, how [(NOx] +2 [O ₂ ]) / [CO] = 1 is derived will be described. Since this expression typically satisfies the reference predetermined density ratio K0, it is referred to as a reference predetermined density sufficient expression.

In the catalyst, it is known that the first reaction (I) occurs as a main reaction.
CO + 1 / 2O ₂ → CO ₂ (I)

Further, in the catalyst using a noble metal catalyst such as Pt, the NO reduction reaction by CO in the second reaction (II) proceeds in an atmosphere in which no oxygen exists.
CO + NO → CO ₂ + 1 / 2N ₂ (II)

  Therefore, paying attention to the concentration of the substance contributing to the reaction of the first reaction (I) and the second reaction (II), the reference concentration satisfaction formula was derived.

That is, assuming that the CO concentration, NO concentration, and O ₂ concentration are [CO] ppm, [NO] ppm, and [O ₂ ] ppm, respectively, the oxygen concentration that can be removed by CO from the above formula (I) is the following formula (III): It is represented by
2 [O ₂ ] = [CO] _a (III)

Further, in order to cause the reaction of the above formula (II), an equal amount of NO is required for CO, and the relationship of the following formula (IV) can be said.
[CO] _b = [NO] (IV)

When the reactions of the formulas (I) and (II) occur continuously in the catalyst, the concentration relationship of the following formula (V) obtained by adding the formula (III) and the formula (IV) is necessary. It becomes.
[CO] _a + [CO] _b = 2 [O ₂ ] + [NO] (V)

Since [CO] _a + [CO] _b is the same component, it can be expressed by [CO] as the CO concentration in the gas on the catalyst secondary side.
Therefore, the standard predetermined concentration ratio satisfaction formula,
That is, the relationship of [CO] = 2 [O ₂ ] + [NO] can be derived.

  When the value of the concentration ratio K is smaller than 1.0, the concentration of carbon monoxide is higher than the concentration necessary for the reduction of the nitrogen oxides, so that the exhaust oxygen concentration is zero and after passing through the catalyst. Carbon monoxide remains in the gas.

  Further, 2.0 which exceeds 1.0 of the value of the concentration ratio K 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 these side reactions, hydrogen is generated by the reaction between steam and carbon monoxide, and a reaction in which nitrogen oxides and oxygen are reduced by this hydrogen can be considered.

The combustion step is performed by burning a hydrocarbon-containing fuel in the burner, and a gas containing nitrogen oxides, carbon monoxide, and oxygen is generated without containing hydrocarbons. This combustion is combustion performed in a normal combustion apparatus such as a boiler, and does not involve rapid cooling as in an internal combustion engine, so the exhaust gas does not contain hydrocarbons. And preferably, the said air ratio shall be 1.1 or less. Thereby, energy saving is realized by low air ratio combustion.

  The burner is a combustion device that continuously supplies fuel and combustion air and continuously burns it, and does not include an internal combustion engine. Internal combustion engines such as automobile engines perform discontinuous supply and combustion of fuel and combustion air, so a large amount of hydrocarbons and carbon monoxide are generated as unburned components and are contained in the exhaust gas. Therefore, it is not suitable for the nitrogen oxide-containing gas treatment method of the present invention.

  The burner is preferably an all-primary air premix burner that premixes and burns gas fuel. In order to effectively cause the first reaction and the second reaction to occur in the catalyst, the concentration ratio K as shown in the above formulas (2) and (3) relating to oxygen, nitrogen oxides, and carbon monoxide is adjusted. is important. By making the burner a premixed burner, the reference predetermined concentration ratio K0 can be obtained relatively easily in a low air ratio region. However, oxygen, nitrogen oxides, and carbon monoxide in the gas on the primary side of the catalyst are uniformly mixed, and the respective concentrations are controlled to the predetermined concentration ratio, thereby performing a partial premix burner other than the premix burner. Or a premixed burner.

  The concentration ratio adjusting step is a step of adjusting the concentration ratio K on the primary side of the oxidation catalyst to the reference predetermined concentration ratio K0, the first predetermined concentration ratio K1, or the second predetermined concentration K2. It can be performed using first to fourth concentration ratio adjusting means.

  The first concentration ratio adjusting means adjusts the concentration ratio K using the concentration ratio characteristic of the burner. This first concentration ratio adjusting means is preferably performed by setting the air ratio of the burner. When the density ratio K is adjusted using the first density ratio adjusting means, no density ratio adjusting means other than the burner is required, so that the configuration of the apparatus can be simplified. The concentration ratio characteristic of the burner is a characteristic in which the amount of carbon monoxide and the amount of nitrogen oxide generated are changed by burning the burner while changing the air ratio.

In this first concentration ratio adjusting means, carbon monoxide is injected into the burner or fuel is partially injected into the burner, and as a result, the concentration of carbon monoxide in the gas is increased. Therefore, the concentration ratio K can be adjusted.

  The second concentration ratio adjusting means uses the concentration ratio characteristic of the burner to adjust the concentration ratio K, and also adjusts the concentration ratio characteristic of an endothermic means that is disposed between the burner and the oxidation catalyst and absorbs heat from the gas. In other words, using the concentration ratio characteristics of the burner and the endothermic means. This concentration ratio characteristic is a characteristic in which the amount of carbon monoxide and the amount of nitrogen oxide after passing through all or a part of the heat absorption means generated by burning the burner while changing the air ratio are changed. The concentration ratio characteristic is basically determined by the concentration ratio characteristic of the burner, and the endothermic device typically changes or maintains the concentration ratio characteristic of the burner. Has the function of When the endothermic means is the first aspect, the carbon monoxide concentration is increased and the nitrogen oxide concentration is suppressed. When the endothermic means is the second aspect, typically, the concentration ratio characteristic by the burner is held with almost no change.

The said heat absorption means can be made into the water pipe group which comprises cans, such as a boiler. This heat absorption means is preferably a water tube group constituting a can such as a boiler. As a form of this heat absorption means, there is a first aspect (corresponding to Patent Documents 1 to 4) in which there is almost no combustion space in the immediate vicinity of the burner and a water tube group is arranged in the combustion space, and the burner and the water pipe. And a second configuration having a combustion space between the groups. When the endothermic means is the first aspect, the carbon monoxide concentration is increased and the nitrogen oxide concentration is suppressed. When the endothermic means is the second aspect, typically, the concentration ratio characteristic by the burner is held with almost no change. The water pipe group is a plurality of water pipes that exchange heat with the gas from the burner, but a plurality of water pipes can be configured by meandering one water pipe like a water pipe of a water heater.

  The endothermic means can have a function of adjusting the concentration ratio K by suppressing the concentration of generated nitrogen oxides by suppressing the combustion gas temperature of the burner. Further, the endothermic means suppresses the rise of the gas temperature to about 900 ° C. or more, suppresses the oxidation of carbon monoxide, and does not change the concentration ratio of the gas from the burner. It is configured to adjust K. The endothermic means absorbs heat from the gas generated by the burner and uses the heat, and the temperature of the gas is higher than the activation temperature of the oxidation catalyst and prevents thermal degradation. The function to suppress can be given below.

  When the concentration ratio K is adjusted using the second concentration ratio adjusting means, no concentration ratio adjusting means other than the burner and the endothermic means is required, so that the configuration of the apparatus can be simplified. Moreover, the temperature of the gas can be suppressed by the endothermic means, and the durability of the oxidation catalyst can be improved.

  The third concentration ratio adjusting means uses the concentration ratio characteristic of the burner to adjust the concentration ratio K, and is arranged between the burner and the oxidation catalyst to assist in adjusting the concentration ratio. It is performed using means.

  The auxiliary adjusting means is between the burner and the oxidation catalyst (including the middle of the endothermic means), and injects carbon monoxide or adsorbs and removes oxygen, thereby monoxide with respect to the oxygen concentration. It has a function of assisting the adjustment by increasing the ratio of the carbon concentration. As this auxiliary adjusting means, a CO generator or an auxiliary burner capable of adjusting the amount of oxygen or CO in the exhaust gas can be used.

  When the density ratio K is adjusted using the third density ratio adjusting means, the density ratio adjustment is performed using the auxiliary adjusting means in addition to the density ratio characteristics of the burner. The application range of the burner can be expanded without being limited to the burner.

  The fourth concentration ratio adjusting means uses the concentration ratio characteristics of the burner and an endothermic means that absorbs heat from the gas and is disposed between the burner and the oxidation catalyst to adjust the concentration ratio K. This is performed using the auxiliary adjusting means arranged between the burner and the oxidation catalyst.

  When the concentration ratio is adjusted using the fourth concentration ratio adjusting means, the concentration ratio adjustment is performed using the auxiliary adjusting means in addition to the concentration ratio characteristics of the burner and the endothermic means. The application range of the burner and the heat absorbing means can be expanded without being limited to the burner having the structure.

The catalyst is a catalyst having a function of efficiently reducing the nitrogen oxides in a state where hydrocarbons are not contained in the gas, and is provided in the downstream of the endothermic means or in the middle of the endothermic means and has air permeability. A structure in which a catalytically active substance is supported on a substrate is provided, and the structure is not limited to a specific one. As the base material, a metal such as stainless steel or ceramic is used, and a surface treatment is performed to increase the contact area with the exhaust 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. When the catalyst is provided in the middle of the endothermic means, the catalyst can be provided in a gap between a plurality of endothermic means, or a heat-absorbing means such as a water pipe can be used as a base material and a catalytically active substance can be supported on the surface.

  Next, an embodiment in which the combustion apparatus of the present invention is applied to a steam boiler will be described with reference to the drawings. 1 is an explanatory view of a longitudinal section of the steam boiler according to the first embodiment, FIG. 2 is a sectional view taken along the line II-II in FIG. 1, and FIG. FIG. 4 is a diagram illustrating a configuration of a main part viewed from the flow direction, FIG. 4 is a diagram illustrating air ratio-NOx / CO characteristics of the first embodiment, and FIG. 5 is a damper position adjusting device of the first embodiment. FIG. 6 is an explanatory diagram of a partial cross section of the damper position adjusting device in use, and FIG. 7 is a burner, heat absorption means characteristics and catalyst of the first embodiment. FIG. 8 is a diagram for explaining the output characteristics of the sensor of the first embodiment, and FIG. 9 is a diagram for explaining the motor control characteristics of the first embodiment. 10 is a diagram illustrating the NOx and CO reduction characteristics of Example 1. FIG.

  First, the steam boiler according to the first embodiment will be described. The steam boiler includes a burner 1, a can body 3 including a heat transfer tube (water tube) group 2 as heat absorption means for absorbing heat generated from the burner 1, and oxygen and nitrogen after passing through the heat transfer tube group 2. Gases containing oxides and carbon monoxide at predetermined concentration ratios pass through each other to oxidize carbon monoxide and reduce nitrogen oxides (hereinafter also simply referred to as “catalyst”). 4, fuel supply means 5 for supplying gaseous fuel to the burner 1, combustion air supply means 6 for supplying combustion air to the burner 1 and premixing combustion air and fuel, and oxygen downstream of the catalyst 4 The main part is a sensor 7 for detecting the concentration, and a controller 8 as a boiler controller for inputting signals from the sensor 7 and controlling the fuel supply means 5 and the combustion air supply means 6. Eteiru.

  The burner 1 is a complete premix burner having a flat combustion surface (a premixed gas ejection surface). This burner 1 has the same configuration as the burner described in Patent Document 1.

  The can body 3 includes an upper header 9 and a lower header 10, and a plurality of inner water tubes 11, 11,... Constituting the water tube group 2 are disposed between the headers. And, as shown in FIG. 2, a pair of water pipe walls 14, 14 configured by connecting outer water pipes 12, 12,... With connecting members 13, 13,. A first gas passage 15 through which the gas from the burner 1 flows almost linearly is formed between the water pipe walls 14 and 14 and the upper header 9 and the lower header 10. The burner 1 is provided at one end of the first gas passage 15, and a second gas passage (smoke) 17 through which exhaust gas flows is connected to the exhaust gas outlet 16 at the other end. In the first embodiment, the burner 1 and the can 3 are known ones.

  The second gas passage 17 includes a horizontal portion 18 and a vertical portion 19, and the catalyst 4 is attached to the horizontal portion 18. A feed water preheater 20 as an exhaust heat recovery device is mounted on the vertical portion 19 so as to be located downstream of the catalyst 4, and the sensor 7 is disposed between the catalyst 4 and the feed water preheater 20. ing.

The components from the burner 1 including the burner 1 and the front water pipe group 2 to the catalyst 4 (particularly, the main part of the burner 1 and the water pipe group 2) have the concentration ratio K in the gas on the primary side of the catalyst 4 It functions to adjust the predetermined concentration ratios K0 and K1. That is, the air ratio-NOx / CO characteristic shown in FIG. 4 is obtained when the air ratio adjusting means 28 described later adjusts the air ratio. The air ratio-NOx / CO characteristic is obtained by controlling the air ratio adjusting means 28 to change the air ratio and burning the primary side air ratio-NOx / CO characteristic of the catalyst 4 (hereinafter, referred to as "the air ratio-NOx / CO characteristic"). Called primary characteristics). The catalyst 4 has a secondary air ratio-NOx / CO characteristic (hereinafter referred to as a secondary characteristic) of the catalyst 4 obtained by bringing the gas having the primary characteristic into contact with the catalyst 4. is doing. The primary characteristic is a concentration ratio characteristic due to components from the burner 1 to the catalyst 4, and the secondary characteristic is a characteristic due to the catalyst 4. The primary characteristic is that the NOx concentration and carbon monoxide concentration on the secondary side of the catalyst 4 are substantially zero when the set air ratio is adjusted to 1.0. At this time, the reference predetermined concentration ratio K0 in the primary gas of the catalyst 4 becomes the specific reference predetermined concentration ratio K0X (see FIG. 7).

  FIG. 4 is a schematic diagram in which the low air ratio region Z2 in FIG. 15 is extended, although the vertical axis and the horizontal axis are differently scaled. In FIG. 4, a first line (characteristic line) E indicates the CO concentration on the primary side of the catalyst 4, and a second line F similarly indicates the NOx concentration on the primary side. The third line J indicates the CO concentration on the secondary side of the catalyst 4. When the air ratio is 1.0 or more, the CO concentration becomes substantially zero, and the concentration rapidly increases as the air ratio becomes smaller than 1.0. It has an increasing characteristic. The fourth line U indicates the NOx concentration on the secondary side of the catalyst 4, and the NOx concentration becomes substantially zero in a predetermined region where the air ratio is 1.0 or less, and as the air ratio exceeds 1.0, It has a characteristic that the concentration increases substantially from zero and eventually becomes equal to the concentration on the primary side of the catalyst 4. A region where the secondary NOx concentration of the catalyst 4 is equal to or lower than the air ratio where the secondary side NOx concentration is equal to the primary side concentration is referred to as a NOx / CO reduction region. The lower limit of the NOx / CO reduction region can be an air ratio at which the CO concentration on the secondary side of the catalyst 4 is 300 ppm (Japanese CO emission standard). The air ratio-NOx / CO characteristic in this low air ratio region is a novel characteristic that has not been studied so far.

  The catalyst 4 has a function of oxidizing nitrogen monoxide (second reaction) as well as oxidizing carbon monoxide contained in the gas not containing hydrocarbons after passing through the water tube group 2 (second reaction). In Example 1, a catalyst in which the catalytically active substance is platinum is used. As described in the section of “Best Mode for Carrying Out the Invention”, the gas and the catalyst satisfying the concentration ratio formula of the formula (3) when theoretically considered in consideration of the experimental results. It is considered that the first reaction for mainly oxidizing carbon monoxide and the second reaction for reducing nitrogen oxides with carbon monoxide are caused by contact with the catalytically active material No. 4. Whether or not the reaction proceeds in the first reaction is determined depending on the oxygen concentration. In the catalyst 4, the first reaction is considered to be superior to the second reaction.

  The catalyst 4 will be described more specifically. This catalyst has a structure as shown in FIG. 3 and is formed as follows, for example. A large number of fine irregularities are formed on the surfaces of both the stainless steel flat plate 21 and the corrugated plate 22 as the base material, and a catalytically active material (not shown) is carried on the surfaces. Next, the flat plate 21 and the corrugated plate 22 having a predetermined width are superposed and then wound spirally to form a roll. The roll-shaped material is surrounded and fixed by the side plate 23. Platinum is used as the catalytically active material. FIG. 3 shows only a part of the flat plate 21 and the corrugated plate 22.

  This catalyst 4 has oxidation activity in a low temperature region, is the horizontal portion 18 in the middle of the second gas passage 17, and has an exhaust gas temperature of about 100 ° C to 350 ° C, preferably about 150 ° C to 350 ° C. Placed in position. The catalyst 4 is detachably attached to the second gas passage 17 so that it can be replaced when the performance deteriorates.

  The fuel supply means 5 includes a gas fuel supply pipe 24 and a flow rate adjusting valve 25 for adjusting the fuel flow rate provided in the gas fuel supply pipe 24. The flow rate adjusting valve 25 has a function of controlling the fuel supply amount to a high combustion flow rate and a low combustion flow rate.

  The combustion air supply means 6 adjusts the amount of combustion air flowing through the air supply passage 27 and the air supply passage 27 for supplying combustion air from the air blower 26 to the burner 1. An air ratio adjusting means 28 for adjusting the air ratio is included. The gas fuel supply pipe 24 is connected to the supply passage 27 so as to eject the fuel gas.

  The air ratio adjusting means 28 includes a damper 29 as a flow rate adjusting means for adjusting the opening degree (flow passage sectional area) of the air supply passage 27, and a damper position adjusting device for adjusting the opening position of the damper 29. 30 and the controller 8 for controlling the operation of the damper position adjusting device 30.

  As shown in FIG. 5, the damper position adjusting device 30 includes a drive shaft 32 that is detachably connected to a rotating shaft 31 of the damper 29, and the drive shaft 32 is connected to a motor 34 via a speed reducer 33. And can be rotated. As the motor 34, a motor capable of arbitrarily adjusting the rotation stop position is used. In this embodiment, a stepping motor (pulse motor) is used.

  The drive shaft 32 is connected to the rotary shaft 31 of the damper 29 via a coupling 35 so that the drive shaft 32 can rotate integrally on substantially the same axis. The coupling 35 has a stepped columnar shape, and a small diameter hole 36 and a large diameter hole 37 are formed in the center thereof so as to penetrate in the axial direction. The drive shaft 32 is inserted into the small-diameter hole 36, and the drive shaft 32 is integrated with the coupling 35 with a mounting screw 38. On the other hand, the rotary shaft 31 of the damper 29 can be inserted into the large-diameter hole 37, and the rotary shaft 31 can be rotated integrally with the coupling 35 by a key 39. For this purpose, key grooves 40 and 41 are formed in the large-diameter hole 37 of the rotary shaft 31 and the coupling 35, respectively.

  Such a coupling 35 is rotatably held by the outer case 43 of the damper position adjusting device 30 at the other end via a bearing 42 with the drive shaft 32 inserted at one end. In the outer case 43, the speed reducer 33 and the motor 34 are held at one end, and the large diameter hole 37 with the key groove 41 of the coupling 35 is exposed at the other end. 35 and the rotation abnormality detecting means 44 are sealed inside.

  The rotation abnormality detection means 44 includes a detection plate 45 and a detector 46. The detection plate 45 is fixed to the stepped portion at the axially central portion of the coupling 35 so as to extend radially outward. The detected plate 45 is provided concentrically with the coupling 35 and the drive shaft 32. A slit forming region 48 in which a large number of slits 47, 47... Are formed at equal intervals in the circumferential direction is provided in a part of the outer peripheral portion of the detection plate 45. In the present embodiment, the slit forming region 48 is provided for a quarter arc (90 degrees). The slits 47 formed in the slit forming region 48 have the same shape and size. In this embodiment, elongated rectangular grooves along the radial direction of the plate 45 to be detected are formed by punching at equal intervals along the circumferential direction.

  The detector 46 for detecting the slit 47 is fixed to the outer case 43. The detector 46 is formed of a transmissive photo interrupter, and is attached in a state where the outer peripheral portion of the detection plate 45 is interposed between the light emitting element 49 and the light receiving element 50. By interposing the detection plate 45 between the light emitting element 49 and the light receiving element 50 of the detector 46, a position corresponding to the detector 46 (an optical path from the light emitting element 49 to the light receiving element 50). Whether or not light is received from the light emitting element 49 in the light receiving element 50 is switched depending on whether or not the slit 47 of the plate 45 to be detected is disposed at a position corresponding to. Thereby, the opening position of the damper 29 can be detected.

  In the damper position adjusting device 30, the damper 29 is connected to the air supply passage in a state where the clockwise end slit 51 of the slit forming region 48 in FIG. 6 is disposed at a position corresponding to the detector 46. 27 is positioned so as to be fully closed, and is attached to the rotating shaft 31 of the damper 29.

  Since the slit forming region 48 is formed by 90 degrees of the detection plate 45, the end slit 51 in the clockwise direction of the slit forming region 48 is disposed at a position corresponding to the detector 46. In this state, the damper 29 fully closes the air supply passage 27 as described above, while the counterclockwise end slit 52 of the slit forming region 48 is disposed at a position corresponding to the detector 46. In this state, the damper 29 fully opens the air supply passage 27.

  In the damper position adjusting device 30, the motor 34 and the detector 46 are connected to the controller 8 so that the rotation of the motor 34 can be controlled while monitoring the rotation abnormality of the damper 29. It is configured. That is, in order to control the motor 34, the damper position adjusting device 30 has a control signal generation circuit including a drive pulse for the motor 34, and can output the generated control signal to the motor 34. is there. Thus, the rotation angle of the motor 34 is arbitrarily controlled in accordance with the forward rotation or reverse rotation and the drive amount, that is, the number of drive pulses. In addition, the rotation speed can be controlled by changing the interval (feed speed) of the drive pulses.

  When actually controlling the opening and closing of the damper 29, the controller 8 first performs an origin detection operation in order to set the fully closed position of the damper 29 as the origin. First, in FIG. 5, the detected plate 45 is rotated counterclockwise. Now, assuming that the detector 46 is disposed in the slit forming region 48 of the detection plate 45, the detector 46 periodically detects the slit 47 as the detection plate 45 rotates. Therefore, the detection pulse is input to the controller 8 as a detection signal. When the detection plate 45 is rotated until the detector 46 is disposed outside the slit forming region 48, no pulse is detected. If the pulse is not detected for a predetermined time, the controller 8 recognizes that the detector 46 is outside the slit forming region 48 and switches the rotation direction to the reverse direction. That is, in this embodiment, the detected plate 45 is reversed in the clockwise direction, and the position where the pulse (clockwise end slit 51) is first detected is set as the origin. The origin confirmation by the clockwise rotation is performed at a lower speed than the counterclockwise rotation before the rotation direction is switched.

  Since the origin detected in this way corresponds to the fully closed position of the damper 29, the controller 8 outputs a drive signal to the motor 34 based on this state, and the damper 29 is turned on. Open / close control is possible. When the controller 8 drives the motor 34 to open and close the damper 29, the detection signal of the slit 47 is acquired as a pulse from the detector 46 accordingly. Therefore, the controller 8 can monitor the rotation abnormality of the damper 29 by comparing the detection signal from the detector 46 with the control signal to the motor 34. Specifically, a control signal composed of a drive pulse to the motor 34 and a detection signal composed of a detection pulse of the slit 47 by the detector 46 are compared to monitor the presence / absence of rotation abnormality.

For example, when a detection pulse is not detected from the detector 46 even though a drive pulse is sent to the motor 34, the controller 8 determines that the rotation is abnormal. At this time, since the detection pulse from the detector 46 is usually different from the frequency of the drive pulse to the motor 34, it is controlled in consideration of this difference. For example, if no pulse of the detection signal is detected even after the time corresponding to a predetermined pulse of the drive signal has elapsed, the control is performed so as to determine that the rotation is abnormal only. When it is determined that the rotation is abnormal, the controller 8 performs measures such as notification of abnormality or stopping combustion. On the contrary, even when a drive pulse is not sent to the motor 34, a rotation abnormality can be detected even when a pulse is detected from the detector 46.

The controller 8 is configured so that the air ratio of the burner 1 becomes the set air ratio (first control condition) based on the detection signal of the sensor 7 according to the air ratio control program stored in advance, and the set air ratio. , The motor 34 is controlled so that the concentration ratio K of the gas on the primary side of the catalyst 4 satisfies the following expression (3) (second control condition).
([NOx] +2 [O ₂ ]) / [CO] ≦ 2.0 (3)
(In Formula (3), [CO], [NOx], and [O ₂ ] indicate a carbon monoxide concentration, a nitrogen oxide concentration, and an oxygen concentration, respectively, and satisfy the condition of [O ₂ ]> 0.)
In the first embodiment, the first control condition is directly controlled, and the second control condition is automatically satisfied by satisfying the first control condition. . This point will be described below with reference to FIGS.

  The air ratio-NOx / CO characteristics of FIG. 4 are expressed based on the primary characteristics of the components including the burner 1 and the water pipe group 2 and the secondary characteristics of the catalyst 4. FIG. Is expressed based on the primary characteristics of the constituent elements and the characteristics of the catalyst 4 with respect to the oxygen concentration on the primary side of the catalyst 4.

As shown in FIG. 7, the characteristics of the catalyst 4 are as follows: a fifth line L (secondary side [NOx] = 0, [CO] = 0 line) relating to the reference predetermined concentration ratio K0 on the primary side of the catalyst 4; It represents its characteristics. In the fifth line L, when the concentration ratio K on the primary side of the catalyst 4 is positioned (placed) on that line, the nitrogen oxide concentration and the carbon monoxide concentration on the secondary side of the catalyst 4 are substantially increased. The line is zero, that is, the line satisfies the reference predetermined density ratio K0. The fifth line L corresponds to the case where the predetermined concentration ratio of the formula (3) is 1. That is, the fifth line L is a line representing the following expression (3A).
[NOx] +2 [O ₂ ] = [CO] (3A)

  Here, since [NOx] is about 1/30 to 1/50 of [CO] as shown in FIG. 10, in FIG. 7, the NOx concentration characteristic with respect to the oxygen concentration is omitted, and the equation (3A) [NOx] can be ignored. In the fifth line L, when the primary oxygen concentration is X1, the primary carbon monoxide concentration Y1 is Y1 = 2X1 + [NOx]. The reference predetermined concentration that makes the nitrogen oxide concentration and the carbon monoxide concentration on the secondary side of the catalyst 4 substantially zero in the range of the concentration ratio K to 2.0 exceeding 1.0. Since it has been confirmed that the ratio K0 can be obtained, the fifth line L is not limited to the illustrated line L, and can be a line that satisfies the equation (2).

  The reference predetermined concentration ratio K0 of oxygen, nitrogen oxide, and carbon monoxide at the intersection of the sixth line M representing the primary characteristic curve of the burner 1 and the water pipe group 2 and the fifth line L is a singular reference. The predetermined concentration ratio (hereinafter referred to as a specific reference concentration ratio) is referred to as K0X. The catalyst 4 has a characteristic that the nitrogen oxide concentration and the carbon monoxide concentration on the secondary side of the catalyst 4 are substantially zero when the concentration ratio K on the primary side is the reference concentration ratio K0X. is doing. The adjustment to the reference density ratio K0X corresponds to the adjustment 0 of the present invention.

The catalyst 4 has a concentration corresponding to the difference between the primary oxygen concentration and the reference oxygen concentration on the secondary side of the catalyst 4 when the primary oxygen concentration is set higher than the reference oxygen concentration SK corresponding to the specific reference concentration ratio K0X. Is detected, the carbon monoxide concentration on the secondary side of the catalyst 4 is made substantially zero, and the nitrogen oxide concentration on the secondary side of the catalyst 4 is reduced by the reduction reaction. It has the characteristic to reduce more. A region in which oxygen is detected on the secondary side of the catalyst 4 and the concentration is lower than the nitrogen oxide concentration on the primary side is referred to as a secondary NOx leakage region R1. The secondary NOx leakage region R1 is a region that realizes the adjustment 2 of the present invention, and the air ratio of the burner 1 exceeds 1.0.

  Further, when the primary oxygen concentration is made lower than the reference oxygen concentration SK, carbon monoxide having a concentration corresponding to the difference between the primary oxygen concentration and the reference oxygen concentration SK is detected on the secondary side of the catalyst 4, and predetermined In this range, the nitrogen oxide concentration on the secondary side of the catalyst 4 is substantially zero. A region where carbon monoxide is detected on the secondary side of the catalyst 4 and the nitrogen oxide concentration is substantially zero is referred to as a secondary CO leakage region R2. This secondary side CO leakage region R2 is a region for realizing the adjustment 1 of the present invention, and the air ratio of the burner 1 is less than 1.0. Even when the air ratio of the burner 1 is set to be less than 1.0, it is set in a range including oxygen on the primary side of the catalyst 4 without containing hydrocarbons. A region obtained by combining the secondary NOx leakage region R1 and the secondary CO leakage region R2 is referred to as a NOx / CO reduction region R3.

  The characteristics of the catalyst 4 shown in FIG. 7 are consistent with the air ratio-NOx / CO characteristics shown in FIG. As apparent from FIG. 7, the oxygen concentration and / or carbon monoxide concentration on the secondary side of the catalyst 4 is detected, and the air ratio adjustment is performed so that the oxygen concentration and / or carbon monoxide concentration becomes zero. When the means 28 is controlled, the concentration ratio K on the primary side of the catalyst 4 is controlled to the specific reference concentration ratio K0X, and the nitrogen oxide concentration and carbon monoxide concentration on the secondary side of the catalyst 4 are substantially zero. Can be controlled. Thus, when the first control condition is satisfied, the second control condition is satisfied.

  If the first control condition is not satisfied, unburned components such as hydrocarbons are generated. In this case, energy is lost and NOx reduction in the catalyst 4 is not effectively performed.

The second control condition is a condition necessary for making the exhaust nitrogen oxide concentration substantially zero. In order to make the nitrogen oxide concentration and the carbon monoxide concentration on the secondary side of the catalyst 4 zero, from the first reaction and the second reaction, ([NOx] +2 [O ₂ ]) / [CO] It has been found from experiments and theoretical considerations that the concentration ratio K is approximately 1.0. However, it has been confirmed that even if the concentration ratio K is 1.0 to 2.0, which is 1 or more, the exhausted nitrogen oxide concentration can be made substantially zero.

  As the sensor 7, a zirconia air-fuel ratio sensor having a good response with a resolution of exhaust oxygen concentration of 50 ppm and a response time of 2 seconds or less is used. As shown in FIG. 8, the output characteristic of the sensor 7 is an output related to the oxygen concentration on the positive side and an output related to the carbon monoxide concentration on the negative side. That is, the air ratio m is calculated from the measured oxygen concentration (oxygen excess region), carbon monoxide concentration, etc. (fuel excess region), and a current or voltage output corresponding to the air ratio m is obtained. In FIG. 8, Q1 indicates an oxygen concentration detection zone, and Q2 indicates a carbon monoxide concentration detection zone.

  The air ratio control program controls the air ratio m of the burner to be the set air ratio m0 based on the output signal of the sensor 7. Specifically, the air ratio control program is configured as follows. Has been. That is, as shown in FIG. 9, the feed speed V (drive amount per unit time) of the motor 34 is changed according to the difference between the output value E from the sensor 7 and the set value corresponding to the set air ratio m0. The first control zone C1 and the second control zones C2A and C2B that set the feed speed V to the first set value V1 and the second set value V2 respectively outside the first control zone C1 are provided. A control procedure for controlling the drive amount is included. In FIG. 9, P1 indicates a damper open region, and P2 indicates a damper closed region.

  The set range of the first control zone C1 is set by an oxygen concentration N1 (for example, 100 ppm) and a carbon monoxide concentration, etc., N2 (for example, 50 ppm), and the air ratio is substantially set air m0 (the reference oxygen concentration is 1). It corresponds to SK).

The feed speed V in the first control zone C1 is calculated by the following equation (4). The feed speed V is a driving amount per unit time. The rotation angle by one step of the motor 34 of the first embodiment is 0.075 degrees, which corresponds to a fluctuation of about 30 ppm when converted to O ₂ .

V = K × ΔX (4)
(However, K is a gain, and ΔX is a difference between (the output value of the sensor 7) − (the set value).)

  Next, the operation of the steam boiler having the above configuration will be described. First, regarding the schematic operation of the steam boiler, the combustion air (outside air) supplied from the blower 26 is premixed in the supply air passage 27 with the fuel gas supplied from the gas fuel supply pipe 24. The premixed gas is ejected from the burner 1 toward the first gas passage 15 in the can body 3. The premixed gas is ignited by an ignition means (not shown) and burns. This combustion is performed at a low air ratio near 1.0.

  The gas generated by this combustion crosses the upstream water tube group 2 and is cooled, and then exchanges heat with the downstream water tube group 2 to absorb heat to become a gas of about 100 ° C. to 350 ° C. This gas does not contain hydrocarbons, contains oxygen, nitrogen oxides, and carbon monoxide, and is treated with the catalyst 4 so that the nitrogen oxide concentration and the carbon monoxide concentration are substantially zero, and then, as exhaust gas. The gas is discharged from the second gas passage 17 into the atmosphere.

  Next, air ratio control by the air ratio adjusting means 28 will be described. The boiler of the present embodiment is operated by switching between high combustion and low combustion. Therefore, the damper 29 is positioned by selecting either the high combustion air volume position or the low combustion air volume position.

  The position adjustment of the damper 29 is performed by the damper position adjusting device 30 according to a command from the controller 8. That is, the controller 8 inputs a selection signal of high combustion or low combustion and an output value corresponding to the air ratio detected by the sensor 7, and outputs a drive signal of the motor 34, so that the damper 29 Adjust the opening position of. The controller 8 stores the set opening position of the damper 29, which is a set value corresponding to each set air ratio m0 at the time of high combustion and low combustion, as an initial value by the number of pulses from the origin.

  First, control during high combustion will be described. The controller 8 must control the current opening position of the damper 29 to the opening side (side to be controlled in the closing direction) or the closing side (opening direction) with respect to the set opening position. And the number of drive pulses of the motor 34 is calculated. In addition, in FIG. 9, it is determined whether the output value belongs to the first control band C1 or the second control band C2A or C2B.

  When belonging to the second control zone C2A, the motor 34 is driven at the first set feed speed V2 and the calculated drive pulse, and the damper 29 is closed at a high speed. When belonging to the second control zone C2B, the motor 34 is driven at the second set feed speed V1 and the calculated drive pulse, and the damper 29 is opened at a high speed. In this way, when it is relatively far from the set value corresponding to the reference set air ratio m0, the output value corresponding to the detected air ratio is controlled to approach the set value corresponding to the reference set air ratio m0 at a high speed. Air ratio control with good responsiveness can be performed.

  Further, when belonging to the first control zone C1, after determining the rotation direction, the feed rate of the motor 34 is calculated based on the equation (4), and the calculated feed rate and the calculated drive pulse are used. The motor 34 is driven. In the control in the first control zone C1, the feed speed is increased as the distance from the set value corresponding to the reference set air ratio m0 increases. By such control, it is possible to quickly approach the set value corresponding to the target reference set air ratio m0. In addition, the stepping motor is capable of reliably performing the rotational position control, and the control is performed to reduce the feed rate as the output value corresponding to the detected air ratio approaches the set value corresponding to the reference set air ratio m0. Thus, overshoot and hunting of the air ratio in the vicinity of the set value corresponding to the reference set air ratio m0 can be suppressed.

By such air ratio control, the air ratio of the burner 1 is set to a low air ratio m0 close to 1.0, and the variation range of the concentration ratio of the gas on the primary side of the catalyst 4 is controlled so as to stabilize the equation (2). Can be satisfied. As a result, the nitrogen oxide concentration on the secondary side of the catalyst 4 can be made substantially zero, and the carbon monoxide concentration can be reduced to almost zero. When the set air ratio m0 is less than 1.0, the nitrogen oxide concentration on the secondary side is made substantially zero, and the carbon monoxide concentration is reduced to a predetermined value or less within the practical range.
(Experimental example 1)

Can body 800kg of per evaporation unit time 3: (applicant of the manufacturing model can bodies called SQ-800), is burned in the combustion amount 45.2m ³ N / h of premixed burner 1, a catalyst An experimental result in the case of a catalyst having a volume of 10 L and an inner diameter of 360 mm carrying Pt at a rate of 2.0 g / L as an active substance will be described. When the reference set air ratio m0 is 1, the carbon monoxide concentration, the nitrogen oxide concentration, and the oxygen concentration on the primary side of the catalyst 4 (before passing through the catalyst 4) are 2295 ppm and 94 ppm, respectively, on average for 10 minutes. The concentration was adjusted to 1655 ppm, and the respective concentrations on the secondary side of the catalyst 4 (after passing through the catalyst 4) were less than 13 ppm, 0.3 ppm, and 100 ppm on average for 10 minutes. Here, the oxygen concentration of 100 ppm on the secondary side of the catalyst 4 is an oxygen concentration measurement limit. The gas temperatures before and after the catalyst 4 were 302 ° C. and 327 ° C., respectively. In the present Experimental Example 1 and the following Experimental Examples 2 and 3, the catalyst 4 is disposed slightly upstream of the feed water preheater 20, and measuring devices are disposed before and after the catalyst 4. The temperature of the gas was measured using PG-250 manufactured by Horiba, Ltd., and each concentration before passing was measured using COPA-2000 manufactured by Horiba, Ltd. Of course, even if the catalyst 4 is disposed at the position shown in FIG.
(Experimental example 2)

  When the same burner 1 and can body 3 as in Experimental Example 1 are used, the combustion amount is the same as in Experimental Example 1, and a catalyst having a volume of 10 L and an inner diameter of 360 mm carrying Pd at a rate of 2.0 g / L as a catalytically active substance FIG. 10 shows values at each concentration ratio K of carbon monoxide concentration, nitrogen oxide concentration, and oxygen concentration. Here, since the oxygen concentration after passing through the catalyst was measured using the same oxygen concentration sensor as in Experimental Example 1, even if the value was actually 100 ppm or less, it was indicated as 100 ppm. The gas temperatures before and after the catalyst 4 were about 323 ° C. to 325 ° C. and about 344 ° C. to 346 ° C., respectively.

  According to the first embodiment, the oxygen ratio on the primary side of the catalyst 4 is controlled by controlling the air ratio to 1.0 by the damper position adjusting means (air ratio adjusting means) 30 that adjusts the ratio of combustion air and fuel. , The concentration ratio of nitrogen oxides and carbon monoxide can be controlled to the specific reference concentration ratio K0X (adjustment 0), and the exhaust NOx concentration and exhaust CO concentration can be reduced to substantially zero. Therefore, compared with the NOx reduction technology by water / steam addition and the NOx reduction technology by introduction of a denitration agent, low NOx and low CO can be realized with a simple configuration using the air ratio adjusting means and the catalyst.

Further, since the air ratio is substantially 1.0, energy saving operation can be performed. By the way, comparing the operation of an ordinary boiler with an oxygen concentration of 4% (air ratio about 1.235) and an operation with an oxygen concentration of 0% (air ratio of about 1.0), the boiler efficiency is increased by about 1 to 2%. Can be achieved. In recent years when countermeasures against global warming have been screamed, the achievement of increased boiler efficiency has great industrial value.

  Further, since the sensor 7 is provided on the secondary side of the catalyst 4 to control the air ratio, the control is stabilized as compared with the control by providing a sensor on the primary side of the catalyst 4. Can do. In addition, since the air ratio is controlled with a resolution of oxygen concentration of 100 ppm or less, the air ratio control in a region where the amount of CO is large and the CO increase rate in the air ratio-CO characteristic is high is responsive and stable. be able to.

  Another embodiment 2 of the present invention will be described with reference to FIGS. In Example 2, the sensor 7 for detecting the oxygen concentration is provided not on the secondary side of the catalyst 4 but on the primary side. This sensor 7 is a sensor that detects only the oxygen concentration. The control characteristics of the motor 34 based on the sensor 7 are shown in FIG. Hereinafter, only differences from the first embodiment will be described, and description of common portions will be omitted.

In Example 2, the sensor 7 detects the primary side oxygen concentration of the catalyst 4 so that the reference set air ratio m0 is 1.0 (the secondary side oxygen concentration of the catalyst 4 is zero). Thus, the air ratio is indirectly controlled. Based on various experimental results, when the oxygen concentration O ₂ on the primary side of the catalyst 4 is controlled to a value of 0% <O ₂ ≦ 1.00%, the above equation (2) is satisfied and the secondary of the catalyst 4 It has been found that the oxygen concentration on the side can be made substantially zero, that is, the air ratio can be made almost 1.

  Therefore, in the air ratio control program of the second embodiment, as shown in FIG. 12, based on the detected value E (oxygen concentration signal) from the sensor 7, the difference between the detected value and the set oxygen concentration value is determined. The first control band C1 for changing the feed speed V (drive amount per unit time) of the motor 34 and the feed speed V outside the first control band C1 are set to a first set value and a second set value, respectively. A control procedure for providing a second control zone C2A, C2B and controlling the drive amount of the motor 34 is included.

  The setting range of the first control zone C1 is controlled so as to be within the range set by the oxygen concentration N1 and the oxygen concentration N2. The feed speed V in the first control zone C1 is calculated by the equation (4) as in the first embodiment.

  The third embodiment is an example in which the set air ratio is set to a value at which the NOx concentration in the secondary characteristic substantially exceeds zero and is lower than the NOx concentration in the primary characteristic, as shown in FIG. . This value is the air ratio of the secondary side NOx leakage region R1 of the secondary characteristic where the set air ratio substantially exceeds 1.0. The adjustment of the density ratio K in Example 3 is the adjustment 2.

In the first control zone C1 in Example 3, the center of the control range (target air ratio) is an air ratio of 1.005 (O ₂ concentration: about 1000 ppm), and the left end is substantially lower than the air ratio of 1.0. the value of the region, the right end is an air ratio 1.01: a (O ₂ concentration: about 2000 ppm). This will be explained with reference to FIG. 7. The air ratio control is performed in the secondary NOx leakage region (region where the adjustment 2 is realized) R1 in which the oxygen concentration on the primary side of the catalyst 4 is higher than the reference oxygen concentration. become.

(Experimental example 3)
In Example 3, when the experiment was performed under the same conditions (excluding the set air ratio) as in Experimental Example 1, the CO concentration, NOx concentration, and O ₂ concentration on the primary side of the catalyst 4 (before passing through the catalyst 4) were respectively The average values for 10 minutes were adjusted to 1878 ppm, 78 ppm, and 3192 ppm, and the respective concentrations on the secondary side of the catalyst 4 (after passing through the catalyst 4) were 0 ppm, 42 ppm, and 1413 ppm for the average value for 10 minutes.

  As is apparent from Experimental Example 3, according to the air ratio control of Example 3, the reduction effect of the catalyst 4 reduces the exhaust NOx concentration to a value lower than the NOx concentration of the primary characteristic, The exhaust CO concentration will be reduced to zero.

  In the third embodiment, the first control zone can be freely set within the range of the secondary NOx leakage region R1. The closer the first control zone C1 is to the air ratio 1.0, the greater the NOx reduction effect and the energy saving effect. However, since the concentration of CO to be treated is high (the gradient may be steep), CO is likely to leak, difficult to control, and requires a large amount of catalyst. Therefore, if the first control zone is set on the right side so as to be away from the air ratio 1, control becomes easy and the amount of the catalyst 4 can be reduced.

  Specifically, the left end of the first control zone C1 can be set to an air ratio of 1.0 instead of the air ratio of 1.0 or less in the third embodiment (FIG. 13). It is also possible to set the left end of the first control zone C1 to a value exceeding the air ratio 1.0.

  In the fourth embodiment, referring to FIG. 14, the air ratio control means 28 includes a blower motor 52 for driving the blower 26 and an inverter 53 for controlling the rotational speed of the motor 52. It is. In the fourth embodiment, the air ratio control and the concentration ratio constant control are not performed using the damper 29 but are performed using the inverter 53. The control of the blower motor 52 by the controller 8 can be control for suppressing overshoot and hunting shown in FIG. 9 of the first embodiment. The damper 29 lowers the opening at the time of ignition, and increases the opening when performing steady combustion after ignition, and performs air volume control for high combustion and low combustion. Although this air volume control can be performed using the inverter 53, the present invention is not limited to this, and the air volume control at the time of ignition or the like is performed by any one of the damper 29 and the inverter 53. Can do. In the fourth embodiment, since the other configuration is the same as that of the first embodiment, the description thereof is omitted.

  The present invention is not limited to the first to fourth embodiments. For example, the air ratio-NOx / CO characteristics shown in FIGS. 4 and 13 have different curves and concentration values depending on the structure of the burner 1 and the can body 3 of the combustion apparatus, and therefore different characteristics can be used. . In the first and second embodiments, the set air ratio is set to 1.0 or more. However, the air ratio can be set to a value lower than 1.0 within a range in which the combustibility is not impaired and hydrocarbons are not generated.

In the second embodiment, the sensor 7 is an O ₂ concentration sensor, but can be a CO concentration sensor. The structure of the damper position adjusting device 30 can be variously modified. Further, the motor 34 may be a gear motor (not shown) other than the stepping motor. Further, the damper position adjusting device 30 is controlled by a single controller (a controller for boiler control) 8. Separately from this controller 8, another controller for the damper position adjusting device 30 ( (Not shown), and this controller, the front sensor 7 and the controller 8 can be connected to perform air ratio control.

It is explanatory drawing of the longitudinal cross-section of the steam boiler of the present Example 1. FIG. It is sectional drawing which follows the II-II line of FIG. It is a figure which shows the principal part structure which looked at the oxidation catalyst of FIG. 2 from the flow direction of exhaust gas. It is a figure which shows the air ratio -NOx * CO characteristic of the present Example 1. FIG. It is explanatory drawing of the partial cross section of the use condition of the damper position adjustment apparatus of the present Example 1. FIG. It is sectional explanatory drawing of the principal part of the damper position adjustment apparatus. It is a schematic diagram explaining the characteristic of the burner of this Example 1, an endothermic means, and the characteristic of an oxidation catalyst. It is a figure explaining the output characteristic of the sensor of the present Example 1. It is a figure explaining the motor control characteristic of the present Example 1. FIG. It is a figure explaining the NOx and CO reduction characteristic of the present Example 1. It is explanatory drawing of the longitudinal cross-section of the steam boiler of the present Example 2. It is a figure explaining the motor control characteristic of the present Example 2. It is a figure explaining the air ratio control using the air ratio-NOx * CO characteristic of the third embodiment. It is explanatory drawing of the longitudinal cross-section of the steam boiler of the present Example 4. It is a figure explaining the NOx * CO primary characteristic and secondary characteristic by this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Burner 4 Oxidation catalyst 7 Sensor 8 Controller 28 Air ratio adjustment means 29 Damper 30 Damper position adjustment device 34 Motor

Claims (5)

A method for treating a nitrogen oxide-containing gas, wherein a gas generated by burning fuel in a burner is brought into contact with an oxidation catalyst to reduce nitrogen oxide contained in the gas,
A combustion step of burning a hydrocarbon-containing fuel in the burner to produce a gas that does not contain hydrocarbons but includes oxygen, nitrogen oxides, and carbon monoxide;
A harmful substance reducing step of contacting the gas with an oxidation catalyst to oxidize carbon monoxide contained in the gas with oxygen and reduce nitrogen oxide with carbon monoxide;
A concentration ratio adjusting step of adjusting the concentration ratio K of oxygen, nitrogen oxide and carbon monoxide in the gas on the primary side of the oxidation catalyst to a predetermined concentration ratio,
The method for treating a nitrogen oxide-containing gas, wherein the predetermined concentration ratio satisfies the following expressions ( 1) and (2) .
([NOx] +2 [O ₂ ]) / [CO] = K ( 1 )
K ≦ 2.0 (2)
(In the formula ( 1 ), [CO], [NOx] and [O ₂ ] indicate the CO concentration, NOx concentration and O ₂ concentration, respectively, and satisfy the condition of [O ₂ ]> 0.) A method for treating a nitrogen oxide-containing gas, wherein a gas generated by burning fuel in a burner is brought into contact with an oxidation catalyst to reduce nitrogen oxide contained in the gas,
A combustion step of burning a hydrocarbon-containing fuel in the burner to produce a gas that does not contain hydrocarbons but includes oxygen, nitrogen oxides, and carbon monoxide;
A harmful substance reducing step of contacting the gas with an oxidation catalyst to oxidize carbon monoxide contained in the gas with oxygen and reduce nitrogen oxide with carbon monoxide;
A concentration ratio adjusting step for adjusting a concentration ratio K of oxygen, nitrogen oxide and carbon monoxide in the gas on the primary side of the oxidation catalyst,
The concentration ratio adjustment step includes:
Adjustment 0 for adjusting the concentration ratio K to a reference predetermined concentration ratio K0 that makes the nitrogen oxide concentration and carbon monoxide concentration on the secondary side of the oxidation catalyst substantially zero,
Adjustment 1 for adjusting the concentration ratio K to a first predetermined concentration ratio K1 in which the nitrogen oxide concentration on the secondary side of the oxidation catalyst is substantially zero and the carbon monoxide concentration is a predetermined value or less.
Adjustment 2 for adjusting the concentration ratio K to a second predetermined concentration ratio K2 in which the carbon monoxide concentration on the secondary side of the oxidation catalyst is substantially zero and the nitrogen oxide concentration is a predetermined value or less.
Either
The equation for determining the reference predetermined concentration ratio K0 is the following equation (3) that satisfies the following equation (4), the first predetermined concentration ratio K1 is smaller than the reference predetermined concentration ratio K0, and the second predetermined concentration ratio K2 is A method for treating a nitrogen oxide-containing gas, wherein the treatment ratio is greater than the reference predetermined concentration ratio K0.
([NOx] +2 [O2]) / [CO] = K (3)
1.0 ≦ K = K0 ≦ 2.0 (4)
(In Formula (3), [CO], [NOx] and [O2] are the carbon monoxide concentration,
Nitrogen oxide concentration and oxygen concentration are shown, and the condition of [O2]> 0 is satisfied. ) Method of processing nitrogen oxide-containing gas according to claim 1 or claim 2, characterized in that the adjustment before Kiko intensity ratio K is performed by burning by changing the air ratio of the burner. The method for treating a nitrogen oxide-containing gas according to any one of claims 1 to 3 , wherein an air ratio of the burner is 1.1 or less. The adjustment of the concentration ratio K uses combustion by changing the air ratio of the burner, and uses auxiliary adjustment means that is arranged between the burner and the oxidation catalyst and that adjusts the concentration ratio as an auxiliary. The method for treating a nitrogen oxide-containing gas according to claim 1 or 2, wherein the method is performed.