JP5088674B2 - Combustion equipment - Google Patents

Abstract

It is possible to suppress concentration of the exhausted nitrogen oxide upon a combustion start or combustion shift regardless of an external fluctuation such as an outside air temperature. A combustion device includes: a burner (1); heat absorbing means (2); a catalyst (4) for oxidizing carbon monoxide in a gas after passing through the heat absorbing means (2) and reducing nitrogen oxide in the gas; flow rate regulating means (29) for regulating an air ratio by changing the ratio between the combustion air amount and/or a fuel amount of the burner (1); a sensor (7) for detecting the air ratio of the burner (1); and control means (8) for controlling the air ratio of the burner (1) by controlling the flow rate regulating means (29) according to a detection signal from the sensor (7) so as to adjust the concentration ratio of the oxygen, the nitrogen oxide, and the carbon monoxide in the gas of the primary side of the catalyst (4). The control means (8) stores a control value of the flow rate regulating means (29) as a set air ratio during combustion under a predetermined combustion condition with the set air ratio and controls the flow rate regulating means (29) according to the stored control value upon combustion resumption.

Description

  The present invention relates to a combustion apparatus 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 NOx reduction and CO reduction 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 Document 1). However, the NOx reduction technology described in Patent Document 1 actually has 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 priority over the reduction of the exhausted CO value, and thereafter A low NOx combustion method that performs a low CO reduction step in which the CO emission value from the low NOx reduction step is set to a predetermined value or less has been proposed (see Patent Document 2). According to the technique of Patent Document 2, 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.

  The low NOx technology described in Patent Document 2 belongs to a so-called high air ratio combustion region having an air ratio of 1.38 or more. On the other hand, in the combustion region 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. Since stable combustion control is difficult, such as causing a backfire when the air ratio is 1 or less, the low air ratio combustion area has been hardly the subject of research and development until now.

  As a result of extensive research, the inventors of this application have found that nitrogen oxide emissions are almost as low as zero in a combustion region with a low air ratio as close to 1 as there has been little research so far. The invention of the industry's first combustion method that can reduce the carbon monoxide emission to an acceptable range and can realize energy saving with a low air ratio was filed earlier (Japanese Patent Application No. 2005-300343).

  This patented invention uses an oxidation catalyst that reduces nitrogen oxides using carbon monoxide, and oxidizes by adjusting the concentration ratio of oxygen, nitrogen oxides, and carbon monoxide in the primary gas of the oxidation catalyst. The nitrogen oxide concentration on the secondary side of the catalyst can be made substantially zero.

  In the process of practical application of the combustion apparatus according to the present invention, the air ratio changes due to fluctuations in the outside air temperature, fuel gas pressure, temperature and properties (hereinafter referred to as external fluctuations), and the set air ratio is obtained. Since the position of the corresponding flow rate adjusting means fluctuates, if the flow rate adjusting means is controlled to the initial setting value at the start of combustion or at the time of combustion transition, appropriate control is not achieved. As a result, the present inventors have found a problem that carbon monoxide is discharged before appropriate control is performed.

Japanese Patent No. 3221582 (corresponding US Patent: US Pat. No. 5,353,748) JP 2004-125378 A (corresponding US patent: US Pat. No. 6,792,895)

  The problem to be solved by the present invention is to keep the carbon monoxide concentration low at the start of combustion and at the time of transition to combustion, regardless of external fluctuations such as outside air temperature.

The present invention has been made to solve the above-mentioned problems. The invention according to claim 1 is directed to a burner, a heat absorbing means for absorbing heat from the gas generated by the burner, and after passing through the heat absorbing means. An oxidation catalyst that oxidizes carbon monoxide in the gas and reduces nitrogen oxides, a flow rate adjusting unit that controls an air ratio by changing a ratio of combustion air amount and / or fuel amount of the burner, and A sensor for detecting the air ratio of the burner, and based on the detection signal of this sensor, the air ratio of the burner is controlled by the control of the flow rate adjusting means, and oxygen and nitrogen in the gas on the primary side of the oxidation catalyst A combustion apparatus comprising control means for adjusting a concentration ratio of oxide and carbon monoxide,
The control means performs concentration ratio adjustment for adjusting the concentration ratio K of oxygen, nitrogen oxide and carbon monoxide in the gas on the primary side of the catalyst by controlling to the set air ratio,
The concentration ratio adjustment is
The concentration ratio K is determined by the following equations (1) and (2) in which the nitrogen oxide concentration on the secondary side of the catalyst means is substantially zero or a predetermined value or less, and the carbon monoxide concentration is substantially zero or a predetermined value or less. Configured to adjust to a predetermined concentration ratio satisfying 2),
Storing the correction value of the flow rate adjusting means for said set air ratio in the combustion operation in a given combustion conditions at the set air ratio, controls the flow rate adjusting means based on the correction value stored during the combustion operation resuming It is characterized by that.
([NOx] +2 [O ₂ ]) / [CO] = K (1)
K ≦ 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.)

According to the first aspect of the present invention, when the combustion operation is resumed, the flow rate adjusting means can be quickly controlled to a correction value reflecting external fluctuations such as the outside air temperature, and the production of carbon monoxide can be suppressed. There is an effect. Further, in addition to the above effects, the nitrogen oxide concentration on the secondary side of the catalyst means can be made substantially zero, and the carbon monoxide concentration can be made substantially zero or a predetermined value or less.

The invention according to claim 2 is a burner, an endothermic device that absorbs heat from the gas generated by the burner, and oxidizes carbon monoxide in the gas after passing through the endothermic device and also converts nitrogen oxides. An oxidation catalyst to be reduced, a flow rate adjusting means for controlling an air ratio by changing a ratio of a combustion air amount and / or a fuel amount of the burner, a sensor for detecting the air ratio of the burner, and detection of the sensor Control means for controlling the air ratio of the burner by controlling the flow rate adjusting means based on the signal to adjust the concentration ratio of oxygen, nitrogen oxide and carbon monoxide in the gas on the primary side of the oxidation catalyst; A combustion device comprising:
The control means performs concentration ratio adjustment for adjusting the concentration ratio K of oxygen, nitrogen oxide and carbon monoxide in the gas on the primary side of the catalyst by controlling to the set air ratio,
The concentration ratio adjustment is
Adjustment 0 for adjusting the concentration ratio K to a reference predetermined concentration ratio K0 in which the nitrogen oxide concentration and the carbon monoxide concentration on the secondary side of the catalyst are 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 catalyst secondary side 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 catalyst secondary side is substantially zero and the nitrogen oxide concentration is a predetermined value or less.
Adjust to one of the
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 Greater than the reference predetermined concentration ratio K0,
The correction value of the flow rate adjusting means to be the set air ratio is stored during a combustion operation under a predetermined combustion condition at the set air ratio, and the flow rate adjusting means is controlled based on the correction value stored when the combustion operation is resumed. It is characterized by that.
[NOx] +2 [O ₂ ]) / [CO] = K (3)
1.0 ≦ K = K0 ≦ 2.0 (4)
(In the formula (1), [CO], [NOx] and [O ₂ ] are the carbon monoxide concentration,
Nitrogen oxide concentration and oxygen concentration are shown, and the condition of [O ₂ ]> 0 is satisfied. )

According to the second aspect of the present invention, when the combustion operation is resumed, the flow rate adjusting means can be quickly controlled to a correction value reflecting external fluctuations such as the outside air temperature, and the production of carbon monoxide can be suppressed. There is an effect. Further, in addition to the above effect, the adjustment 0 makes the nitrogen oxide concentration and the carbon monoxide concentration on the secondary side of the catalyst means substantially zero, and the adjustment 1 makes the nitrogen oxide on the secondary side of the catalyst means The concentration is substantially zero and the carbon monoxide concentration is set to a predetermined value or less, and the adjustment 2 causes the carbon monoxide concentration on the secondary side of the catalyst means to be substantially zero.
In addition, there is an effect that the nitrogen oxide concentration can be set to a predetermined value or less.

  According to the present invention, when the combustion operation is resumed, the flow rate adjusting means can be quickly controlled to a control value reflecting external fluctuations such as the outside air temperature, and the production of carbon monoxide can be suppressed.

  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 the gas from the burner to the end of passing through the oxidation catalyst, and the gas after passing through the oxidation catalyst is referred to as “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 oxidation catalyst is provided in multiple stages along the gas flow, “gas” refers to the gas that has passed through the final stage oxidation catalyst, and “exhaust gas” refers to the final stage oxidation catalyst. The gas after passing through the catalyst.

In addition, the “primary side of the oxidation catalyst” is the side where the burner is provided with respect to the oxidation catalyst, and unless otherwise specified, means the gas immediately before passing through this oxidation catalyst. “Side” refers to the opposite side of the primary side of the oxidation catalyst. Further, the air ratio m is defined as m = 21 / (21− [O ₂ ]). However, [O _2] is an oxygen concentration in the exhaust gas, is used in determining the air ratio [O _2] represents the excess oxygen concentration in the oxygen-excess region, non such as carbon monoxide in the fuel excess region The deficient oxygen concentration required for burning the fuel gas at the air ratio m = 1 is expressed as a negative value. In addition, “does not contain hydrocarbons” does not mean that hydrocarbons (HC) are not produced at all in the course of the combustion reaction, but some hydrocarbons are produced in the course of the combustion reaction, This means that the combustion reaction is completed, that is, the gas flowing into the oxidation catalyst is substantially free of hydrocarbons that reduce nitrogen oxides (below the measurement limit).

  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)
In the first embodiment, a burner, an endothermic means that absorbs heat from the gas generated by the burner, and carbon monoxide in the gas after passing through the endothermic means are oxidized and nitrogen oxides are reduced. An oxidation catalyst (hereinafter referred to as a catalyst), a flow rate adjusting means for controlling the air ratio by changing the ratio (ratio) of combustion air amount and / or fuel amount of the burner, and for detecting the air ratio of the burner And the ratio of oxygen, nitrogen oxides, and carbon monoxide in the gas on the primary side of the catalyst by controlling the air ratio of the burner by controlling the flow rate adjusting means based on the detection signal of the sensor. And a control unit that adjusts the flow rate adjusting unit that sets the correction value of the flow rate adjusting unit to the set air ratio during a combustion operation under a predetermined combustion condition at a set air ratio. And 憶 a combustion apparatus, characterized by controlling the flow rate adjusting means based on the correction value stored during the combustion operation resumed. Here, “correction value” means a predetermined opening when the flow rate adjusting means is a damper, and a predetermined output when the flow rate adjusting seed means is an inverter that controls the rotation speed of the blower. Means frequency.

  In the first embodiment, the burner burns at the set air ratio under the predetermined combustion condition by the air ratio control by the flow rate adjusting means, and receives the endothermic action by the heat absorbing means to adjust the predetermined A gas containing oxygen, nitrogen oxides, and carbon monoxide is generated at a concentration ratio. In this gas, carbon monoxide is oxidized and nitrogen oxides are reduced by contact with the catalyst.

Although the control of the set air ratio is performed by the control of the flow rate adjusting means, the initial set value (initial value) of the flow rate adjusting means corresponding to the set air ratio can be adjusted during the first combustion operation. . This adjustment is performed by feedback control, but actually, the adjustment is not performed with the initial value as the center, but is adjusted with the actual operation value slightly deviating from the initial value. The setting of the initial value is not always necessary, and the initial value can be controlled using control by the first control band and the second control band described later without using the initial value.

  The actual operation value is a value reflecting external fluctuations such as outside air temperature, but the control means stores the actual operation value as a correction value. When the combustion operation is resumed, the control means controls with the correction value when the combustion is resumed under the predetermined combustion condition. As a result, the flow rate adjusting means is quickly adjusted to a correction value that reflects external fluctuations such as outside air temperature. By such quick adjustment, the amount of carbon monoxide produced due to the deviation of the air ratio can be suppressed.

  The first embodiment of the present invention is preferably implemented in the following second and third embodiments.

(Embodiment 2)
In the second embodiment, the nitrogen oxide and carbon monoxide concentrations are reduced by the catalyst. In the second embodiment, the control means sets the concentration ratio of oxygen, nitrogen oxide and carbon monoxide in the gas on the catalyst primary side, and the nitrogen oxide concentration on the catalyst secondary side is substantially zero or predetermined. The carbon monoxide concentration is adjusted to a predetermined concentration ratio that is substantially zero or less than a predetermined value below the value.

  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”.

(Embodiment 3)
In Embodiment 3, the control means performs concentration ratio adjustment for adjusting the concentration ratio K of oxygen, nitrogen oxide, and carbon monoxide in the gas on the primary side of the catalyst. , Adjustment 1 and Adjustment 2 are configured.
Adjustment 0: The concentration ratio K is adjusted to a reference predetermined concentration ratio K0 in which the nitrogen oxide concentration and carbon monoxide concentration on the catalyst secondary side 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 catalyst secondary side 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 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 catalyst is substantially zero and the nitrogen oxide concentration is predetermined. It has the characteristic of being below the value.

In the third embodiment, the concentration ratio means a mutual relationship among the carbon monoxide concentration, the nitrogen oxide concentration, and the oxygen concentration. The reference predetermined density ratio K0 in the adjustment 0 is preferably
It is determined by the determination formula of the following formula (1), and preferably satisfies the following formula (2), the first predetermined concentration ratio K1 is smaller than the reference predetermined concentration ratio, and the second predetermined concentration ratio K2 is set to the reference It is set to be larger than the predetermined concentration ratio.
([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 predetermined reference concentration ratio K0 is a ratio of oxygen, nitrogen oxides, and carbon monoxide on the primary side of the catalyst, where the oxygen concentration, nitrogen oxide concentration, and carbon monoxide concentration on the catalyst secondary side are substantially zero, respectively. Concentration ratio. The equation (1) is a determination equation for determining the reference predetermined concentration ratio K0, and the equation (2) substantially represents the oxygen concentration, the nitrogen oxide concentration, and the carbon monoxide concentration on the catalyst secondary side. This shows the condition of zero. 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 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) (see above). In the adjustment 1), the oxygen concentration and the nitrogen oxide concentration on the secondary side of the 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. The adjustment of the concentration ratio K such that the value of the concentration ratio K is the first predetermined concentration ratio K1 smaller than K0, specifically, the ratio of the oxygen concentration to the carbon monoxide concentration on the primary side of the 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 catalyst is adjusted so that the concentration ratio K becomes the second predetermined concentration ratio K2 larger than K0 (the adjustment 2), carbon monoxide on the catalyst secondary side The 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 catalyst becomes 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 setting the ratio of the oxygen concentration to the carbon monoxide concentration on the primary side of the catalyst to carbon monoxide satisfying the reference predetermined concentration ratio K0. This can be realized by increasing the ratio of the oxygen concentration to the concentration.

  In the third embodiment, preferably, the concentration ratio K is controlled so as to keep the concentration ratio K constant at the predetermined concentration ratios K0, K1, and K2.

In the third embodiment, first, the burner burns to generate a gas containing oxygen, nitrogen oxides, and carbon monoxide but not hydrocarbons. Then, the concentration ratio K of oxygen, nitrogen oxides, and carbon monoxide in the gas on the primary side of the catalyst is adjusted by the concentration ratio adjustment, by the adjustment 0, the adjustment 1, or the adjustment 2, respectively. The reference predetermined density ratio K0, the first predetermined density ratio K1, and the second predetermined density K2 are adjusted. 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 harmful substance reduction action when the adjustment 0 or the adjustment 1 is performed is necessary to adjust the carbon monoxide concentration, 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. Due to the action of reducing harmful substances after the adjustment 0 and the adjustment 1, the emission amount of nitrogen oxide in the gas is substantially reduced to zero, and the emission amount of carbon monoxide is substantially zero or less than a predetermined value. Reduced to Further, the emission of carbon monoxide in the gas is made substantially zero by the harmful substance reducing action after the adjustment 2, and the nitrogen oxide concentration is reduced to a predetermined value or less. Furthermore, by the concentration ratio constant control, fluctuations in the values of the predetermined concentration ratios K0, K1, and K2 are suppressed, and the effect of reducing the nitrogen oxide emission amount and the carbon monoxide emission amount can be ensured. In particular, in the adjustment 0, in order to make the nitrogen oxide emission amount substantially zero, the concentration ratio constant control is important.

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 catalyst is adjusted so that the value of the concentration ratio K is smaller than K0, and the first predetermined concentration The ratio is K1.
([NOx] +2 [O ₂ ]) / [CO] = K ≦ 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 action of reducing harmful substances by the catalyst will be further described. This reduction action is considered to be performed as follows. In the catalyst, as a main reaction, a first reaction for oxidizing carbon monoxide and a second reaction for reducing nitrogen oxide with carbon monoxide are generated. In the reaction in the catalyst (catalytic reaction), in the presence of oxygen, the first reaction is superior to the second reaction, and based on the first reaction, carbon monoxide is consumed by oxygen and has a concentration. After the adjustment, the nitrogen oxide is 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 catalyst, in the presence of oxygen, oxygen is consumed by the first reaction of CO + 1 / 2O ₂ → CO _{2, and} by the second reaction of 2CO + 2NO → N ₂ + 2CO ₂ using the remaining CO. Reduce nitrogen oxides by reducing nitrogen oxides.

Here, [NOx] in formula (2) 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 concentration ratio K is 1.0, the oxygen concentration, nitrogen oxide concentration, and carbon monoxide concentration discharged from the catalyst can theoretically 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 substances 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), it is necessary to have the same amount of NO as 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 is considered.

Next, components of the first to third embodiments of the present invention will be described.
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. Further, when the oxygen concentration O ₂ on the primary side of the catalyst is 0% <O ₂ ≦ 1.00% under the condition of satisfying the above formulas (2) and (3), the air ratio is almost 1, and the exhaust concentration is In addition to low NOx and low CO that are close to zero, energy saving is realized, and a low-pollution and energy-saving combustion apparatus can be provided.

  The heat absorbing 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 embodiment having a combustion space between the groups. In the first aspect, the combustion reaction proceeds in the gap between the water tubes. 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 absorbs heat from the gas generated in the burner and uses the heat, controls the temperature of the gas close to the activation temperature of the catalyst, and prevents the thermal deterioration or less. In other words, the gas temperature can be effectively caused to cause the first reaction and the second reaction, the deterioration due to temperature can be suppressed, and the temperature can be controlled in consideration of durability. In addition, the endothermic means is prevented from increasing the temperature of the gas to about 900 ° C. or more, thereby suppressing the oxidation of carbon monoxide and functioning as a means for preventing the concentration ratio of the gas from the burner from changing. Can do.

  The concentration ratio adjustment by the burner and the concentration ratio adjustment by the endothermic means are performed by obtaining an air ratio-NOx / CO characteristic based on experimental data. In this concentration ratio adjustment, the concentration ratio K of oxygen, nitrogen oxides, and carbon monoxide on the primary side of the catalyst is determined based on the concentration ratio characteristics of the burner and the endothermic means. By controlling to the predetermined concentration ratio using an air ratio adjusting means for adjusting the ratio of the catalyst, the nitrogen oxide concentration on the secondary side of the catalyst is substantially reduced from zero to a predetermined value, and the carbon monoxide concentration is substantially reduced. Is adjusted from zero to a predetermined value or less. In this concentration ratio adjustment, the concentration ratio K on the primary side of the catalyst is adjusted to the reference predetermined concentration ratio K0, the first predetermined concentration ratio K1, and the second predetermined concentration K2. The second concentration ratio adjusting means can be used. In the present invention, any of the adjusting means adjusts the concentration ratio by the air ratio adjusting means for adjusting the ratio of the combustion amount to the burner and the combustion air amount.

  The first concentration ratio adjusting means uses the characteristics of the burner to adjust the concentration ratio K, and uses the characteristics of the endothermic means disposed between the burner and the catalyst to absorb heat from the gas, That is, it is performed using the concentration ratio characteristics of the burner and the endothermic means. This concentration ratio characteristic is a characteristic in which the carbon monoxide concentration and the nitrogen oxide concentration 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 means typically changes part of the concentration ratio characteristic of the burner or changes its concentration ratio characteristic. Has the function of holding. When the endothermic means is the first aspect, cooling of the gas during the combustion reaction causes an increase in the carbon monoxide concentration and suppresses the nitrogen oxide concentration. When the endothermic means is the second aspect, typically, the concentration ratio characteristic by the burner is held with almost no change.

  When the concentration ratio K is adjusted using the first 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 effect that the durability of the catalyst can be improved can be achieved.

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

  The auxiliary adjustment means is between the burner and the catalyst (including the middle of the endothermic means), and injects carbon monoxide or adsorbs and removes oxygen to remove carbon monoxide with respect to the oxygen concentration. It has a function of assisting the adjustment by increasing the concentration ratio. 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 adjusting the concentration ratio using the second 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 a burner having a specific structure.

  The concentration ratio adjustment by the concentration ratio adjusting means is performed by adjusting the carbon monoxide concentration in the gas on the primary side of the catalyst to be reduced in the catalyst by oxidation of carbon monoxide and carbon monoxide. It can be expressed as an adjustment that is approximately equal to or higher than the value obtained by adding the concentration of carbon monoxide reduced in the catalyst by the reduction by the above. When this concentration ratio adjustment is impossible, it can be configured to perform adjustment by carbon monoxide injection or oxygen injection.

  In this concentration ratio, it is preferable to achieve energy saving if the air ratio is controlled to a low air ratio of substantially 1.0. In addition, this concentration ratio adjustment preferably suppresses the amount of nitrogen oxide and carbon monoxide to a predetermined amount or less by adjusting the combustion temperature, and does not reduce the concentration of carbon monoxide obtained by maintaining the gas temperature. Is done. Since carbon monoxide is easily oxidized when the gas temperature is about 900 ° C. or higher, the burner and the endothermic means are preferably configured so that the gas temperature on the primary side of the catalyst is maintained at 600 ° C. or lower. The

  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. The base material has a catalytically active substance supported thereon. 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, it can be provided in a gap between the endothermic means such as a plurality of water pipes, or the endothermic means can be used as a base material and a catalytically active substance can be supported on the surface. .

  The air ratio adjusting means includes a flow rate adjusting means, a motor as a position adjusting means for driving the flow rate adjusting means, and a control means for controlling the motor. The flow rate adjusting means is a means for adjusting the air ratio of the burner by changing either or both of the combustion air amount and the fuel amount of the burner to change the ratio of both. In the case of adjusting the amount of combustion air, a damper (including a valve meaning) is preferable. As the structure of this damper, a rotary type that changes the opening degree of the flow path by a valve body that rotates around a rotation axis, and a slide type that changes the opening degree of the flow path by sliding with respect to the cross-sectional opening of the flow path. Can be.

  In the case where the flow rate adjusting means changes the amount of combustion air, it is preferably provided in the air flow path between the blower and the fuel supply means, but is provided on the suction inlet side of the blower such as the suction inlet of the blower. be able to.

  The motor is preferably means for driving the flow rate adjusting means, and is a motor capable of controlling the opening degree of the flow rate adjusting means in accordance with the drive amount and adjusting the drive amount per unit time. This motor constitutes a part of mechanical control means for stably controlling the air ratio. The phrase “the amount of opening can be controlled according to the amount of driving” means that when the amount of driving is determined, the opening of the flow rate adjusting valve can be controlled to stop at a specific position. Further, “the drive amount per unit time can be adjusted” means that the responsiveness of the position control can be adjusted.

The motor is preferably a stepping motor (which can be referred to as a step motor), but may be a gear motor (which may be referred to as a geared motor), a servo motor, or the like. In the case of the stepping motor, the driving amount is determined by a driving pulse, and the opening position of the flow rate adjusting means is moved from the reference opening position by an amount corresponding to the number of driving pulses for an arbitrary purpose. It can be controlled to the stop position. Further, in the case of the gear motor or the servo motor, the driving amount is the opening / closing driving time, and the opening position of the flow rate adjusting means is arbitrarily opened and closed by an amount corresponding to the opening / closing driving time from the reference opening position. The target stop position can be controlled.

  The flow rate adjusting means of the air ratio adjusting means can control the motor of the blower with an inverter. A known inverter can be used for this inverter. Even when this inverter is used, it can be controlled by the air ratio control program used for damper control.

  The sensor represents an excess oxygen concentration in an oxygen excess region, and a deficient oxygen concentration necessary for burning unburned gas such as carbon monoxide at an air ratio m = 1.0 in a fuel excess region as a negative value. The oxygen concentration meter to represent can be used suitably. Further, as the sensor, an oxygen ratio sensor and a carbon monoxide concentration sensor can be combined to obtain an air ratio approximately. The mounting position of the sensor as described above is preferably the secondary side of the catalyst, but is not limited thereto, and an exhaust heat recovery device is provided on the primary side of the catalyst or on the downstream side of the catalyst. When provided, it can be on the downstream side.

  The control means inputs the detection value of the sensor based on a prestored air ratio control program, feedback controls the driving amount of the motor, and the concentration of carbon monoxide in the gas on the primary side of the catalyst is The carbon monoxide concentration reduced in the catalyst by the oxidation and the carbon monoxide concentration reduced in the catalyst by the reduction are approximately equal to or greater than the value, or the equation (2) The air ratio is controlled to a set air ratio of 1.0 so as to satisfy (3).

  Preferably, the air ratio control program changes a driving amount per unit time of the motor (which can be expressed as a time per driving unit) according to a difference between the detected air ratio and the set air ratio. A first control zone and a second control zone having a fixed predetermined value for the driving amount per unit time outside the first control zone are provided to control the driving amount of the motor. This control constitutes an electrical control means for controlling the detected air ratio so as to be within a set range centered on the set air ratio. The air ratio control program is not limited to this control method, and can be various PID controls.

  The control amount in the first control zone can be controlled by the product of the difference between the detected air ratio and the set air ratio and the set gain. By such control, it is possible to quickly control the set air ratio, and it is possible to achieve an effect that control with less overshoot and hunting can be performed.

  Further, the air ratio control program is configured to perform the following operations. That is, the set air ratio corresponds to the correction value of the flow rate adjusting means. The control of the set air ratio by the control means is performed by the control of the flow rate adjusting means. During the first combustion operation, the flow rate adjusting means aims at the initial value or the control band corresponding to the set air ratio. Done. This adjustment is performed by feedback control. Actually, the adjustment is not performed by the initial value, but is adjusted by the actual operation value slightly deviating from the initial value.

This actual operation value is a value reflecting external fluctuations such as outside air temperature, but the control means stores the actual operation value when the combustion operation is stopped as a correction value. The actual operation value to be stored is an instantaneous value or an average value for a predetermined time. When the combustion operation is resumed, the control means resumes combustion under the predetermined combustion condition, but this time controls the flow rate adjustment means aiming at the stored correction value.

  The initial value and the correction value are set for each predetermined combustion condition of the combustion device. When the predetermined combustion conditions of the combustion device include a first combustion condition with a small amount of combustion (low combustion) or a second combustion condition with a large amount of combustion (high combustion), the first combustion condition and the second combustion condition, respectively. The initial value and the correction value are set for. Further, the predetermined combustion condition includes a third combustion condition that suppresses generation of carbon monoxide at the time of transition from the first combustion condition to the second combustion condition or from the second combustion condition to the first combustion condition. If so, the initial value and the correction value are set for the third combustion condition. As described above, the detection value of the sensor can be controlled to be within the first control zone without using the initial value.

(Embodiment 4)
The present invention is not limited to Embodiments 1 to 3 of the invention described above, and can be applied to Embodiment 4 in which the following combustion start control is performed. Embodiment 4 includes a burner that generates gas by combustion, an endothermic means that absorbs heat from the gas, a catalyst that oxidizes at least carbon monoxide in the gas after passing through the endothermic means, and a primary side of the catalyst And a control means for controlling the combustion of the burner to the first set condition at the start so that the carbon monoxide concentration in the gas at the start becomes a first set value at the start, wherein the control means comprises: A combustion apparatus that performs combustion start control that suppresses generation and / or emission of carbon monoxide at the start of combustion of the burner.

  In the fourth embodiment, the combustion start control is preferably performed so that the carbon monoxide concentration on the primary side of the catalyst becomes a second start set value lower than the start first set value. The combustion is controlled to the second setting condition at the start, and thereafter, the combustion shifts to the combustion by the first setting condition at the start. The start first setting condition and the start second setting condition are changed by changing the air ratio of the burner. Here, the first setting condition at the start time and the second setting condition at the start time correspond to the predetermined combustion conditions of the present invention, and the initial value and the correction value are respectively set for each as in the first to third embodiments. Is set. The second air ratio of the start second setting condition is set to a value higher than the first set air ratio of the start first setting condition.

  Further, the present invention includes a mode in which the concentration ratio adjustment by the burner and the endothermic means is performed by an element constituting a gas passage from the burner to the catalyst other than the endothermic means and an element included in the gas passage. .

  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. FIG. 1 is an explanatory view of a longitudinal section of the steam boiler of this embodiment, FIG. 2 is an explanatory view of a section taken along the line II-II of 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 view of a partial cross section of the damper position adjusting device according to the first embodiment, and FIG. 7 is an explanatory view of the burner of the first embodiment. FIG. 8 is a diagram for explaining output characteristics of the sensor of the first embodiment, and FIG. 9 is for explaining motor control characteristics of the first embodiment. FIG. 10 is a diagram for explaining the NOx and CO reduction characteristics of the first embodiment, and FIG. 11 is a graph showing the variation in combustion amount of the first embodiment. FIG. 12 is a table for explaining changes in various values of the combustion amount change time control according to the first embodiment, and FIG. 13 is a table showing a control procedure according to the first embodiment. It is a flowchart figure explaining a part.

  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 from gas generated in the burner 1, and oxygen and nitrogen oxidation after passing through the water tube group 2. And a gas supply containing gas and carbon monoxide in contact with each other, a catalyst 4 for oxidizing carbon monoxide and reducing nitrogen oxides, and a fuel supply means 5 for supplying gaseous fuel to the burner 1 A combustion air supply means 6 for supplying combustion air (combustion air) to the burner 1 and premixing the combustion air and fuel, a sensor 7 for detecting the oxygen concentration downstream of the catalyst 4, and the sensor 7 And a controller 8 as a boiler controller for controlling the fuel supply means 5 and the combustion air supply means 6 by inputting signals such as.

  The burner 1 is a complete premix burner having a flat combustion surface (a premixed gas ejection surface). This burner is a 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 is provided between the water pipe walls 14, 14 and the upper header 9 and the lower header 10. The gas during combustion reaction and the combustion completion gas from the burner 1 flow almost linearly. Is forming. 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) are the predetermined concentration ratio K in the gas on the primary side of the catalyst 4. Is adjusted to the predetermined concentration ratio K0, 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. This air ratio-NOx / CO characteristic is obtained by controlling the air ratio adjusting means 28 to substantially adjust the nitrogen oxide concentration on the secondary side of the catalyst 4 when the air ratio is adjusted to a set air ratio of 1.0. The air ratio on the primary side of the catalyst 4 that is essentially zero—the NOx / CO characteristic (hereinafter referred to as the primary characteristic). 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. doing. The primary characteristic is the 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 concentration ratio K0X (see FIG. 7).

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 is substantially zero. When the air ratio is less than 1.0, the concentration rapidly increases. Has increasing properties. 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, The concentration increases from essentially zero,
Eventually, it has a characteristic that it 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. Here, the low air ratio is an air ratio of 1.1 or less, preferably 1.05 or less, and this air ratio region is referred to as a low air ratio region.

  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”, when theoretically considered based on experimental results, the gas and the catalyst 4 satisfying the concentration ratio formula of the formula (3) are described. 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 the contact with the catalytically active substance. 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.

  The catalyst 4 has oxidation activity in a low temperature region, and is disposed in a horizontal portion 18 in the middle of the second gas passage 17 at a position where the exhaust gas temperature is about 100 ° C. to 350 ° C. 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 the first 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. The outer case 43 holds the speed reducer 33 and the motor 34 at one end, and the coupling 35 with the large diameter hole 37 with the keyway 41 of the coupling 35 exposed at the other end. The rotation abnormality detecting means 44 is 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). Each slit 47 formed in the slit forming region 48 has 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.

  A 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 detected plate 45 between the light emitting element 49 and the light receiving element 50 of the detector 46, the position corresponding to the detector 46 (corresponding to the optical path from the light emitting element 49 to the light receiving element 50). The presence or absence of light reception 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 the position. Thereby, the opening position of the damper 29 can be detected.

  In the damper position adjusting device 30, in the state where the clockwise end slit 51 of the slit forming region 48 in FIG. 6 is arranged at a position corresponding to the detector 46, the damper 29 is connected to the air supply passage 27. 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. 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, control is performed so as to determine that the rotation is abnormal for the first time. 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 controls the motor by an air ratio control program stored in advance. The air ratio control program includes a basic control program (first program) for controlling the concentration ratio so that the nitrogen oxide concentration on the secondary side of the catalyst 4 is substantially zero, and combustion start of the burner 1. And a combustion start control program (second program) for controlling the motor so as to prevent the emission of a large amount of carbon monoxide, and the combustion of the burner 1 from low combustion to high combustion or from high combustion to low combustion When switching to, a combustion amount change control program (third program) for controlling the motor so as to prevent a large amount of carbon monoxide emission, a large amount of when the function of the catalyst 4 is reduced and the sensor 7 is abnormal And an abnormal-time control program (fourth program) for preventing carbon monoxide emission. The second program and the third program are configured to include the first program. The description of the second program is omitted in the first embodiment. In addition, the fourth program is not directly related to the present invention, and therefore its description is omitted.

  First, the basic control program will be described. In the following description, the controller 8 is configured so that the air ratio of the burner 1 becomes the first set air ratio ratio λ11, λ21 (= 1.0) based on the detection signal of the sensor 7 (first control). And the motor 34 is controlled so that the concentration ratio of the gas before flowing into the catalyst 4 satisfies the following expression (3) (second control condition) at the first set air ratios λ11 and λ2. It is configured as follows.

([NOx] +2 [O ₂ ]) / [CO] ≦ 2.0 (3)
(In Formula (3), [CO], [NOx], and [O ₂ ] indicate the carbon monoxide concentration, nitrogen oxide concentration, and oxygen concentration, respectively, and satisfy the condition of [O ₂ ]> 0.)

  In the first embodiment, it is the first control condition that is directly controlled. When the first control condition is satisfied, the second control condition is automatically satisfied. 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. This 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 (3).

  And 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 tube group 2 and the fifth line L is the unique The reference concentration ratio is 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 specific reference concentration ratio K0X. Have. The adjustment to the reference density ratio K0X corresponds to the adjustment 0.

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 where the adjustment 2 is realized, 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 the predetermined oxygen concentration is determined. 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, it is ([NOx] +2 [O ₂ ]) / [CO] from the first reaction and the second reaction. It was found from experiments and theoretical considerations that the concentration ratio should be approximately 1. However, it has been confirmed that the exhaust nitrogen oxide concentration can be made substantially zero even if the concentration ratio is 1 or more and 1 to 2.0.

  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 or the like 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.

  The air ratio control program controls the burner so that the air ratio of the burner becomes the set air ratio based on the output signal of the sensor 7. Specifically, the air ratio control program is configured as follows. Yes. That is, as shown in FIG. 9, the first change of the feed speed V (drive amount per unit time) of the motor 34 according to the difference between the output value from the sensor 7 and the set value corresponding to the set air ratio. A control band C1 and second control bands C2A and C2BB are provided outside the first control band C1 so that the feed speed V is a first set speed V2 and a second set speed V1, respectively. A control procedure to control is included. In FIG. 9, P1 indicates a damper open region, and P2 indicates a damper closed region.

The setting range of the first control zone C1 is set by an oxygen concentration N1 (for example, 100 ppm) and a carbon monoxide concentration such as N2 (for example, 50 ppm), and is controlled so that the air ratio is substantially 1.0.

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 in one step of the motor of Example 1 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 combustion amount changing control program will be described with reference to FIGS. This program is configured to feedback control the damper 29 so that the air ratio detected by the sensor 7 becomes the set air ratio.

  First, at the time of low combustion, the first set air ratio λ11 combustion at the time of low combustion is performed. The amount of air and the amount of fuel supplied to the burner 1 at this time are A1 and F1, respectively, and the carbon monoxide concentration on the primary side of the catalyst 4 is C1. During high combustion, combustion is performed at the first set air ratio λ21 during high combustion. The amount of air and the amount of fuel supplied to the burner 1 at this time are A2 and F2, respectively, and the carbon monoxide concentration on the primary side of the catalyst 4 is C3.

  When changing from low combustion to high combustion, the controller 8 commands combustion based on the second set air ratio λ22 during high combustion (> first set air ratio λ21 during high combustion). The air amount and fuel amount of λ22 are A3 (> A2) and F2, respectively, and the carbon monoxide concentration on the primary side of the catalyst 4 is C4 (<C3). Thereafter, the controller 8 shifts to the first set air ratio λ21 during high combustion.

  When changing from high combustion to low combustion, the controller 8 sets the second set air ratio λ12 at the time of switching from high combustion to low combustion at the time of low combustion (> second set air ratio λ11 at the time of low combustion). Command based combustion. The air amount and fuel amount of λ12 are A4 (> A1) and F1, respectively, and the carbon monoxide concentration on the primary side of the catalyst 4 is C2 (<C1). Thereafter, the controller 8 shifts to combustion with the first set air ratio λ11 during low combustion. In the first embodiment, the air ratio λ11 and the air ratio λ21 are set to an air ratio of 1.0, and the air ratio λ12 and the air ratio λ22 are determined in advance by experiments so as to belong to the second control zone C2A.

  As shown in FIG. 12, with respect to the set air ratios λ11, λ12, λ21, and λ22. Initial values P11, P12, P21, and P22 are set, respectively. The initial value is an initial set position of the damper 29 corresponding to the set air ratio controlled by the damper position adjusting means 30 during the first combustion operation.

  The controller 8 is shown in the control procedure of FIG. That is, the correction values M11, M12, M21, and M22 are stored for the respective set air ratios during the combustion operation at the set air ratios λ11, λ12, λ21, and λ22, and these correction values are stored when the operation is resumed. The damper 29 is controlled. The correction value means an actual operation position of the damper 29 corresponding to the set air ratio controlled by the damper position adjusting means 30 during combustion operation (the position of the opening is adjusted around this position). .

  The initial value and the correction value are stored as the number of driving pulses of the motor 34, which is how much the motor 34 is driven from the origin of the damper position adjusting device 30. The correction values M11, M12, M21, and M22 are actual operation positions when the combustion operation is stopped (including immediately before the stop).

  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 3. The premixed gas is ignited by an ignition means (not shown) and burns. This combustion takes place at a low air ratio.

  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 and contains oxygen, nitrogen oxides and carbon monoxide, and is oxidized and reduced by the catalyst 4 so that the nitrogen oxide concentration becomes almost zero and the carbon monoxide concentration is discharged. After being reduced to a concentration below the reference value, the exhaust gas is discharged from the second gas passage 17 into the atmosphere as exhaust gas.

(Operation by the basic control program)
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 the set air ratio at the time of high combustion and low combustion, as an initial value with 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. At the same time, it is determined whether the output value belongs to the first control zone or the second control zone A or B in FIG.

  When belonging to the second control zone C2A, the motor 34 is driven at the first set speed V2 and with 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 speed V1 with the calculated drive pulse, and the damper 29 is opened at a high speed. Thus, when the set values corresponding to the first set air ratios λ11 and λ21 are relatively far from each other, the output value corresponding to the detected air ratio is controlled to approach the set value corresponding to the set air ratio at a high speed. Therefore, 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 rate is increased as the distance from the set value corresponding to the set air ratio increases. By such control, it is possible to quickly approach the set value corresponding to the target set air ratio. In addition, by using a stepping motor that can reliably perform rotational position control, and by setting the output value corresponding to the detected air ratio to be slower as the set value corresponding to the set air ratio approaches the set value, Overshoot and hunting of the air ratio in the vicinity of the set value corresponding to the set air ratio can be suppressed.

By such air ratio control, the air ratio on the primary side of the burner 1 is set to a low air ratio close to 1, and the concentration ratio change width of the gas on the primary side of the catalyst 4 is controlled to be small. Can be met. 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 a practical range value.

(Experimental example 1)
It burns with a premix burner 1 with a combustion amount of 45.2 m ³ N / h in a can body 3 (applicant's manufacturing model: can body called SQ-800) with an evaporation amount of 800 kg per unit time, and Pt The experimental results when the catalyst 4 having a volume of 10 L and an inner diameter of 360 mm supported at a rate of 2.0 g / L is used will be described. When the set air ratio is 1.0, the carbon monoxide concentration, the nitrogen oxide concentration, and the oxygen concentration on the primary side of the catalyst 1 (before passing through the catalyst 4) are 2295 ppm, 94 ppm as average values for 10 minutes, respectively. The concentration was adjusted to 1655 ppm, and the respective concentrations on the secondary side of the catalyst 1 (after passing through the catalyst 1) 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 1 is the measurement limit of the oxygen concentration. The gas temperatures before and after the catalyst 4 were about 302 ° C. and 327 ° C., respectively. In the present Experimental Example 1 and the following Experimental Examples 2 and 3, the catalyst 4 is arranged slightly upstream of the feed water preheater 20, and measuring devices are arranged before and after it, and each concentration after passing through the catalyst 4 is , PG-250 manufactured by HORIBA, Ltd. was used, 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)
The same burner 1 and can 3 as in Experimental Example 1 were used, the combustion amount was the same as in Experimental Example 1, Pd was used as the catalytically active substance and the catalyst 4 having a volume of 10 L and an inner diameter of 360 mm supported at a rate of 2.0 g / L FIG. 10 shows values in the respective concentration ratios 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 to 325 ° C. and about 344 to 346 ° C., respectively.

(Operation by the control program at the time of combustion amount transition)
Next, the operation at the time of changing the combustion amount of the burner 1 will be described with reference to FIGS. First, the operation when changing from low combustion to high combustion will be described. During low combustion, combustion is performed at the first set air ratio λ11 during low combustion. The controller 8 controls the motor 34 based on the signal from the sensor 7 to rotate the damper 29 toward the initial value P11 corresponding to the air ratio λ11, and the flow rate adjusting valve 25. To the low combustion position. As shown in FIG. 12, the oxygen amount, the fuel amount, and the carbon monoxide concentration on the primary side of the catalyst 4 are A1, F1, and C1, respectively, as shown in FIG. Similarly, during high combustion, combustion is performed with the first set air ratio λ21 during high combustion. The oxygen amount, the fuel amount, and the carbon monoxide concentration on the primary side of the catalyst 4 are A2, F2, and C3, respectively, during combustion at the first set air ratio λ21 during high firing.

  Here, the rotation control of the damper 29 to the initial value P11 corresponding to the air ratio λ11 will be described with reference to FIG. Although the same control is performed for the air ratios λ12, λ21, and λ22, the description thereof is omitted.

  The control of the first set air ratio λ11 by the controller 8 is performed by position control of the damper 29. In S11, it is determined whether or not the low combustion is the first combustion operation. In the initial operation, the process proceeds to S12, and the controller 8 adjusts the position of the damper 29 with the damper position adjusting means 30 aiming at the initial value P11 corresponding to the first set air ratio λ11. This position adjustment is performed by feedback control, and as described above, the position control is performed so as to be within the range of the first control zone C1.

  The control target position of the damper 29 is the initial value P11. Actually, however, the position is not adjusted around the initial value P11, but the actual operation position slightly deviated from the initial value P11. Is adjusted around. This deviation occurs because the air ratio fluctuates due to external fluctuations such as the outside air temperature.

  When it is determined in S13 that the combustion operation is stopped, the controller 8 stores the actual operation position at the time of the stop as the correction value M11. This correction value M11 can be said to be a position reflecting external fluctuations.

  When the operation is resumed after completion of the combustion operation, NO is determined in S11, and the damper position adjusting means 30 is controlled based on the correction value M11 in S15. When the combustion operation ends, in S14, a correction value based on the actual operation position is calculated, and the correction value is updated.

  Referring to FIG. 12, when the combustion amount is switched from low combustion to high combustion, the controller 8 controls the motor 34 so that the second set air ratio λ22 during high combustion is obtained. The rotational position of the damper 29 is controlled to a position corresponding to the air ratio λ22 having a larger opening than the high combustion position, and the flow rate adjusting valve 25 is controlled to the high combustion position. The air ratio λ22 is larger than the first set air ratio λ21, and combustion is performed with a low carbon monoxide concentration on the primary side of the catalyst 4. As shown in FIG. 12, the oxygen amount, the fuel amount, and the carbon monoxide concentration on the primary side of the catalyst 4 during combustion at the second set air ratio λ22 during high firing are respectively A3 (> A2), F2, C4. (<C3).

  Thereafter, when the movement of the damper position adjusting device 30 to the position corresponding to the second set air ratio λ22 is confirmed by the function, the controller 8 commands the combustion of the first set air ratio λ21. As a result, due to combustion at the air ratio λ21, the concentration ratio of the gas on the primary side of the catalyst 4 satisfies the equation (3), and the nitrogen oxide concentration on the secondary side of the catalyst 4 is substantially zero. be able to.

  Since the operation at the time of changing from high combustion to low combustion is performed in the same manner as the change from low combustion to high combustion, detailed description thereof will be omitted. When changing from high combustion to low combustion, first, combustion is performed with the first set air λ11 during low combustion after the combustion with the second set air ratio λ12 during low combustion. As shown in FIG. 12, the oxygen amount, the fuel amount, and the carbon monoxide concentration on the primary side of the catalyst 4 are A4 (> A1), F1, and C2, respectively, as shown in FIG. (<C1).

  According to the control at the time of changing the combustion amount of the first embodiment, since the air ratio is once controlled to a high value and then controlled to the set air ratio, a large amount of carbon monoxide is discharged when the combustion amount is changed due to the deviation of the air ratio. It is prevented.

  Further, since the initial value corresponding to the set air ratio is controlled in place of the correction value reflecting external fluctuations such as outside air temperature, it can be quickly controlled to a predetermined set air ratio. As a result, the production of carbon monoxide can be suppressed.

  Further, according to the first embodiment, the concentration ratio ratio K of oxygen, nitrogen oxides and carbon monoxide on the primary side of the catalyst 4 is determined by the air ratio adjusting means 28 for adjusting the ratio of combustion air and fuel. The concentration ratio K0X can be controlled (adjustment 0), and the exhaust NOx concentration and exhaust CO concentration can be reduced. 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 can be stably performed with good responsiveness.

  Another embodiment 2 of the present invention will be described with reference to FIGS. In the second embodiment, a sensor 7 for detecting an oxygen concentration or the like 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. And the control characteristic of the said motor based on this sensor 7 is shown in FIG. Hereinafter, only differences from the first embodiment will be described, and description of common portions will be omitted. In the second embodiment, the same combustion amount change time control as that in the first embodiment is performed.

In Example 2, the primary oxygen concentration of the catalyst 4 is detected so that the first set air ratios λ11 and λ21 are 1.0 (the oxygen concentration on the secondary side of the catalyst 4 is zero). And indirectly control the air ratio. Based on the results of various experiments, 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% under the condition that the formula (3) is satisfied, the catalyst 4 It has been found that it is possible to make the oxygen concentration on the secondary side of the gas substantially zero, that is, to make the air ratio almost 1.

  Therefore, in the air ratio control program of the second embodiment, based on the detection value (oxygen concentration signal) from the sensor 7, the motor feed rate is set according to the difference between this detection value and the set value of the set oxygen concentration. A first control zone C1 that changes V (amount of drive per unit time), and a second control zone C2A that sets the feed speed V to the first set speed V2 and the second set speed V1 outside the first control band C1, respectively. , C2B, and a control procedure for controlling the drive amount of the motor 34 is included.

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

  In Example 3, the first set air ratios λ11 and λ21 are set to values at which the NOx concentration in the secondary characteristic substantially exceeds zero and lower than the NOx concentration in the primary characteristic, as shown in FIG. This is an example of setting. Since other configurations are the same as those of the first embodiment, the description thereof is omitted. 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 third embodiment, the same combustion amount change time control as that in the first embodiment is performed.

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 right end of the region value is 1.01 (O ₂ concentration: about 2000 ppm). This will be described 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 SK. It will be.

(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 C1 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, 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, when the first control zone C1 is set on the right side so as to be away from the air ratio 1, the 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 an air ratio of 1.0 or less. 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. 17, the air ratio control means 28 includes a blower motor 54 for driving the blower 26 and an inverter 55 for controlling the rotational speed of the motor 54. 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 55. The control of the blower motor 54 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 when ignited, 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 55, 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 55. 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, in the first embodiment, as shown in FIG. 12, the initial values P11, P12, P21, and P22 are set and controlled, but this initial value is not set and the set air ratio is supported. The first control zone C1 and the detection signal of the sensor 7 can be controlled.

  Further, although the sensor 7 is an oxygen concentration sensor, it can be a carbon monoxide concentration sensor. 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 catalyst of FIG. 2 from the flow direction of waste 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 explanatory drawing of the principal part cross section 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 a 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 a time chart explaining the control of the first embodiment. It is a table | surface explaining the change of the various values of the control at the time of combustion amount change of the present Example 1. FIG. It is a flowchart figure explaining a part of control procedure of the present Example 1. FIG. 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 which shows the air ratio -NOx * CO characteristic of the present Example 3. It is explanatory drawing of the longitudinal cross-section of the steam boiler of the present Example 4.

Explanation of symbols

1 Burner 4 Catalyst 7 Sensor 8 Controller 28 Air Ratio Adjusting Means 29 Damper 30 Damper Position Adjusting Device 34 Motor

Claims (2)

A burner, an endothermic means for absorbing heat from the gas generated in the burner, an oxidation catalyst for oxidizing carbon monoxide in the gas after passing through the endothermic means and reducing nitrogen oxides, The flow rate adjusting means for controlling the air ratio by changing the ratio of the combustion air amount and / or the fuel amount, the sensor for detecting the air ratio of the burner, and the detection signal of the sensor, the flow rate adjusting means Control means for controlling the air ratio of the burner by control to adjust the concentration ratio of oxygen, nitrogen oxides and carbon monoxide in the gas on the primary side of the oxidation catalyst,
The control means performs concentration ratio adjustment for adjusting the concentration ratio K of oxygen, nitrogen oxide and carbon monoxide in the gas on the primary side of the catalyst by controlling to the set air ratio,
The concentration ratio adjustment is
The concentration ratio K is determined by the following formulas (1) and (2) in which the nitrogen oxide concentration on the secondary side of the catalyst means is substantially zero or a predetermined value or less, and the carbon monoxide concentration is substantially zero or a predetermined value or less. Configured to adjust to a predetermined concentration ratio satisfying 2),
Storing the correction value of the flow rate adjusting means for said set air ratio in the combustion operation in a given combustion conditions at the set air ratio, controls the flow rate adjusting means based on the correction value stored during the combustion operation resuming Combustion device characterized by that.
([NOx] +2 [O ₂ ]) / [CO] = K (1)
K ≦ 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.) A burner, an endothermic means for absorbing heat from the gas generated in the burner, an oxidation catalyst for oxidizing carbon monoxide in the gas after passing through the endothermic means and reducing nitrogen oxides, The flow rate adjusting means for controlling the air ratio by changing the ratio of the combustion air amount and / or the fuel amount, the sensor for detecting the air ratio of the burner, and the detection signal of the sensor, the flow rate adjusting means Control means for controlling the air ratio of the burner by control to adjust the concentration ratio of oxygen, nitrogen oxides and carbon monoxide in the gas on the primary side of the oxidation catalyst,
The control means performs concentration ratio adjustment for adjusting the concentration ratio K of oxygen, nitrogen oxide and carbon monoxide in the gas on the primary side of the catalyst by controlling to the set air ratio,
The concentration ratio adjustment is
Adjustment 0 for adjusting the concentration ratio K to a reference predetermined concentration ratio K0 in which the nitrogen oxide concentration and the carbon monoxide concentration on the secondary side of the catalyst are 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 catalyst secondary side 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 catalyst secondary side is substantially zero and the nitrogen oxide concentration is a predetermined value or less.
Adjust to one of the
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 Greater than the reference predetermined concentration ratio K0,
The correction value of the flow rate adjusting means to be the set air ratio is stored during a combustion operation under a predetermined combustion condition at the set air ratio, and the flow rate adjusting means is controlled based on the correction value stored when the combustion operation is resumed. Combustion device characterized by that .
[NOx] +2 [O ₂ ]) / [CO] = K (3)
1.0 ≦ K = K0 ≦ 2.0 (4)
(In the formula (1), [CO], [NOx] and [O ₂ ] are the carbon monoxide concentration,
Nitrogen oxide concentration and oxygen concentration are shown, and the condition of [O ₂ ]> 0 is satisfied. )

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