JP2009031080A - System for reducing harmful substance and combustion device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To enhance safety by performing the self-diagnosis of a carbon monoxide concentration sensor. <P>SOLUTION: This system for reducing harmful substance is equipped with: an oxidizing catalyst 4 for oxidizing carbon monoxide contained in the gas from a gas producing source 1 by oxygen and for reducing nitrogen oxide by carbon monoxide; and a carbon monoxide concentration sensor 32 for detecting the concentration of carbon monoxide in the gas on the secondary side of the oxidizing catalyst 4. Also, the system is equipped with: a diagnosing gas contact means 33 for bringing the carbon monoxide concentration sensor 32 into contact with a diagnosing gas; and a judge means 8 for judging the abnormality of the carbon monoxide concentration sensor 32 when the output of the carbon monoxide concentration sensor 32 during the contact with the diagnosing gas is a set value or below. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a combustion apparatus applied to a harmful substance reduction system for purifying harmful substances in exhaust gas from a gas generation source such as a gas turbine, a water pipe boiler, a regenerator of an absorption refrigeration machine, or 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.

  And the NOx reduction technique described in Patent Document 2 belongs to a so-called high air ratio combustion region Z1 having an air ratio of 1.38 or more as shown in FIG. On the other hand, in the premixed combustion region Z2 having an air ratio of 1.1 or less (hereinafter referred to as “low air ratio”), the amount of nitrogen oxide generated increases, making it difficult to achieve low NOx and low CO, and the air ratio. Since it is difficult to control stable combustion, such as causing a backfire when it becomes 1 or less, the low air ratio combustion region Z2 has hardly been the subject of research and development so far. In FIG. 16, lines F and E schematically show the NOx characteristics and CO characteristics on the primary side by the combustion apparatus of the present invention, respectively, and lines U and J show NOx characteristics on the secondary side of the catalyst by the combustion apparatus of the present invention. And schematically show the CO characteristics. The technique for reducing NOx in Patent Document 2 is basically a technique for suppressing NOx generation by burning a burner in a high air ratio region Z1 and removing generated CO with an oxidation catalyst.

  As a result of intensive studies to solve the above-mentioned problems, the applicant of the present invention has so far conducted almost no research on a boiler provided with an oxidation catalyst for reducing carbon monoxide described in Patent Document 2. In the burner combustion region (region Z2 in FIG. 16) at a low air ratio as close to 1 as possible, a point was found at which the emissions of nitrogen oxides and carbon monoxide were substantially zero. As a result of pursuing the cause of the fact that the emission amounts of nitrogen oxides and carbon monoxide could be substantially zero, the concentration ratio of oxygen, nitrogen oxides and carbon monoxide on the primary side of the oxidation catalyst was determined as a reference predetermined concentration. By setting the ratio, the emission amount of nitrogen oxides and carbon monoxide can be reduced to almost zero using an oxidation catalyst, and by adjusting the concentration ratio in the vicinity of the reference predetermined concentration ratio, harmful substances can be obtained. A new finding was obtained that the emission amount of (nitrogen oxide and carbon monoxide) can be reduced to substantially zero or an allowable value. Based on this knowledge, the amount of nitrogen oxide emissions can be reduced to almost zero in the combustion region with a low air ratio as close to 1 as possible with little research, and carbon monoxide emissions are allowed. The invention of the industry's first combustion apparatus that can achieve energy savings with a low air ratio can be created, and this was filed earlier (Japanese Patent Application No. 2005-300343).

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)

By the way, in the invention of the previous application, there is a possibility that high concentration of carbon monoxide leaks to the secondary side of the oxidation catalyst due to deterioration of the oxidation catalyst or the like.
The problem to be solved by the present invention is to improve safety by performing a self-diagnosis of a carbon monoxide concentration sensor.

  The present invention has been made to solve the above problems, and the invention according to claim 1 is an oxidation catalyst for oxidizing carbon monoxide contained in a gas with oxygen and reducing nitrogen oxide with carbon monoxide. And a harmful substance reduction system comprising a carbon monoxide concentration sensor for detecting a carbon monoxide concentration in a gas on the secondary side of the oxidation catalyst, wherein the diagnosis is made to contact the carbon monoxide concentration sensor with a diagnostic gas. It is characterized by comprising gas contact means and determination means for judging that the carbon monoxide concentration sensor is abnormal when the output of the carbon monoxide concentration sensor is equal to or less than a set value upon contact with the diagnostic gas.

  According to the first aspect of the present invention, since the carbon monoxide concentration sensor performs self-diagnosis by bringing the carbon monoxide concentration sensor into contact with a diagnostic gas, a sensor abnormality is detected and carbon monoxide leakage is detected. Therefore, it is possible to provide a highly safe hazardous substance reduction system.

  Invention of Claim 2 is a combustion apparatus provided with the carbon monoxide concentration sensor which detects the carbon monoxide concentration in the gas produced | generated in a burner, Comprising: The said carbon monoxide concentration sensor and diagnostic gas are included. Diagnostic gas contact means for contacting, and determination means for determining that the carbon monoxide concentration sensor is abnormal when the output of the carbon monoxide concentration sensor is equal to or less than a set value when in contact with the diagnostic gas. Yes.

  According to the second aspect of the present invention, since the carbon monoxide concentration sensor performs self-diagnosis by bringing the carbon monoxide concentration sensor into contact with a diagnostic gas, a sensor abnormality is detected and carbon monoxide leakage is detected. Can be prevented, and a highly safe combustion apparatus can be provided.

  Invention of Claim 3 burns hydrocarbon-containing fuel, and produces | generates the gas containing oxygen, nitrogen oxide, and carbon monoxide, The air ratio adjustment means which adjusts the air ratio of the said burner, An oxidation catalyst for oxidizing carbon monoxide contained in the gas with oxygen and reducing nitrogen oxide with carbon monoxide, an air ratio sensor for detecting the air ratio of the burner, and a gas on the secondary side of the oxidation catalyst A carbon monoxide concentration sensor for detecting a carbon monoxide concentration in the gas, and the burner has oxygen, nitrogen oxides and monoxide in the gas on the primary side of the oxidation catalyst when the air ratio is a set air ratio. The concentration ratio of carbon has a predetermined concentration ratio, and the oxidation catalyst has a nitrogen oxide concentration on the secondary side of the oxidation catalyst substantially zero or a predetermined value when the concentration ratio is the predetermined concentration ratio. The carbon monoxide concentration is A diagnostic gas contact means for contacting the carbon monoxide concentration sensor with a diagnostic gas during NOx reduction combustion in which the burner burns at the set air ratio qualitatively having a characteristic of zero or less than a predetermined value; And determining means for determining that the carbon monoxide concentration sensor is abnormal when the output of the carbon monoxide concentration sensor is equal to or lower than a set value when in contact with the diagnostic gas.

  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 discharge reference value, “predetermined value” or less can be referred to as “allowable value”.

  According to the third aspect of the present invention, since the NOx and CO emissions are substantially zero or less than or equal to a predetermined value, it is possible to provide a combustion apparatus that reduces the emission of harmful substances. In addition, when the carbon monoxide concentration sensor is brought into contact with a diagnostic gas during NOx reduction combustion, self-diagnosis of the carbon monoxide concentration sensor is performed, and when the output of the carbon monoxide concentration sensor detects a set value or less, Since the carbon monoxide concentration sensor is determined to be abnormal, a highly safe combustion apparatus can be provided.

  According to a fourth aspect of the present invention, in the third aspect, when the determination means determines an abnormality, the burner is burned at a higher air ratio than the NOx reduction combustion and a sensor abnormality is reported. It is characterized by.

  According to the invention of claim 4, in addition to the effect of the invention of claim 3, when the carbon monoxide concentration sensor is determined to be abnormal, the burner has a higher air ratio than the NOx reduction combustion. Since combustion is performed at an air ratio, the combustion apparatus can be operated while ensuring safety without stopping the combustion of the burner. Furthermore, since the abnormality of the sensor is notified, there is an effect that the cause of the abnormality can be pursued based on the notification information.

  The invention according to claim 5 is characterized in that, in claim 3, when the determination means determines abnormality, combustion of the burner is stopped and sensor abnormality is notified.

  According to the fifth aspect of the invention, in addition to the effect of the third aspect of the invention, when the carbon monoxide concentration sensor is determined to be abnormal, the combustion of the burner is stopped and the abnormality of the sensor is determined. Since the notification is made, it is possible to perform combustion with high safety and to pursue the cause of the abnormality based on the notification information.

  A sixth aspect of the invention is characterized in that, in the third to fifth aspects, the diagnostic gas is a part of the gas on the secondary side of the oxidation catalyst.

  According to the invention described in claim 6, in addition to the effect of the invention described in claims 3-5, there is an effect that the diagnostic gas can be easily obtained.

  A seventh aspect of the invention is characterized in that, in the sixth aspect, the carbon monoxide concentration sensor is a catalytic combustion type CO sensor.

  According to the invention described in claim 7, in addition to the effect of the invention described in claim 6, there is an effect that the carbon monoxide concentration detection of the high-temperature gas can be performed easily and inexpensively.

  According to the present invention, a highly safe hazardous substance reduction system or combustion apparatus can be provided by performing self-diagnosis of a carbon monoxide concentration sensor.

  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 (which can be referred to as “oxidation / reduction catalyst”, hereinafter referred to as “catalyst”). Gas is called "exhaust gas". Therefore, the gas includes a gas in the combustion reaction (combustion process) and a gas in which the combustion reaction is completed, and can be referred to as a combustion gas. Here, when the catalyst is provided in multiple stages along the gas flow, “gas” refers to the gas until it has passed through the final stage catalyst, and “exhaust gas” refers to the final stage catalyst. The gas after it is done.

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

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

Further, the air ratio m is defined as m = 21 / (21− [O ₂ ]). However, [O _2] is an oxygen concentration in the exhaust gas of the catalyst secondary side, used to obtain the air ratio [O _2] represents the excess oxygen concentration in the oxygen-excess region, one in the fuel excess region The deficient oxygen concentration required to burn unburned gas such as carbon oxide at an air ratio m = 1 is expressed as a negative value.

  Next, an embodiment of the present invention will be described. The present invention relates to a harmful substance reduction system for purifying harmful substances in exhaust gas from a gas generation source such as a gas turbine, or a combustion apparatus such as a water tube boiler such as a small once-through boiler, a water heater, a regenerator of an absorption refrigeration machine, etc. (It may be referred to as thermal equipment or combustion equipment.)

(Embodiment 1)
Embodiment 1 of the present invention includes an oxidation catalyst that oxidizes carbon monoxide contained in a gas with oxygen and reduces nitrogen oxides with carbon monoxide, and carbon monoxide in a secondary gas of the oxidation catalyst. A harmful substance reduction system comprising a carbon monoxide concentration sensor for detecting a concentration, wherein the carbon monoxide is in contact with the diagnostic gas contact means for bringing the carbon monoxide concentration sensor into contact with the diagnostic gas. A harmful substance reduction system comprising: a determination unit that determines that the carbon monoxide concentration sensor is abnormal when the output of the concentration sensor is equal to or less than a set value. The above-mentioned “sensor output is less than or equal to the set value” can be rephrased as “sensor output does not increase beyond the set value”.

  According to the first embodiment, in order to perform self-diagnosis of the carbon monoxide concentration sensor, the diagnostic gas is brought into contact with the carbon monoxide concentration sensor by the diagnostic gas contact means. Then, the determination means determines that the carbon monoxide concentration sensor is abnormal when the output of the carbon monoxide concentration sensor is equal to or less than a set value. When it is determined that the sensor is abnormal, an abnormality notification can be performed.

  In the first embodiment, the carbon monoxide concentration sensor is preferably a catalytic combustion type CO sensor that detects the concentration of carbon monoxide in a gas generated by combustion of a burner. This contact combustion type CO sensor has higher temperature durability and is less expensive than a semiconductor type CO sensor, a constant potential electrolysis type CO sensor, and a non-dispersive infrared absorption type CO sensor. It is suitable as a sensor for detecting the concentration of carbon monoxide.

  When a contact combustion CO sensor is used, the diagnostic gas is a gas containing carbon monoxide and oxygen, or a gas containing the combustible gas and oxygen.

  The diagnostic gas contact means has a function of bringing the carbon monoxide concentration sensor into contact with the diagnostic gas. Preferably, the diagnostic gas contact means includes a guide pipe for guiding the diagnostic gas to the carbon monoxide concentration sensor and a valve provided in the guide pipe. Consists of including. If necessary, the diagnostic gas contact means can include an oxygen introduction pipe for containing oxygen in the diagnostic gas in addition to the guide pipe. The self-diagnosis of the carbon monoxide concentration sensor is performed in a state where the carbon monoxide concentration sensor contains almost no carbon monoxide.

(Embodiment 2)
The hazardous substance reduction system according to the first embodiment can be applied to the next combustion apparatus as the second embodiment. The second embodiment includes a burner for burning a hydrocarbon-containing fuel to generate a gas containing oxygen, nitrogen oxides, and carbon monoxide, an air ratio adjusting means for adjusting the air ratio of the burner, and An oxidation catalyst that oxidizes carbon monoxide contained in the gas with oxygen and reduces nitrogen oxide with carbon monoxide, an air ratio sensor that detects an air ratio of the burner, and a secondary gas in the oxidation catalyst A carbon monoxide concentration sensor for detecting a carbon monoxide concentration, and the burner has a ratio of oxygen, nitrogen oxides and carbon monoxide in the gas on the primary side of the oxidation catalyst when the air ratio is a set air ratio. The oxidation catalyst has a characteristic that the concentration ratio is a predetermined concentration ratio, and the oxidation catalyst has a nitrogen oxide concentration on the secondary side of the oxidation catalyst substantially zero or a predetermined value or less when the concentration ratio is the predetermined concentration ratio. The carbon monoxide concentration is real Diagnostic gas contact means for bringing the carbon monoxide concentration sensor into contact with the diagnostic gas during NOx reduction combustion in which the burner burns at the set air ratio, and the diagnostic gas And a determination unit that determines that the carbon monoxide concentration sensor is abnormal when the output of the carbon monoxide concentration sensor is equal to or lower than a set value.

  According to the second embodiment, combustion of the burner generates a gas containing oxygen, nitrogen oxides, and carbon monoxide, but not hydrocarbons. The concentration ratio of oxygen, nitrogen oxide and carbon monoxide in the gas on the primary side of the catalyst is adjusted based on the characteristics of the burner by controlling the set air ratio by the air ratio adjusting means. The Then, in the catalyst, the gas comes into contact with the catalyst, carbon monoxide is oxidized by oxygen in the gas, nitrogen oxides are reduced by carbon monoxide, and the concentration of nitrogen oxides on the catalyst secondary side Is substantially zero or below a predetermined value, and the carbon monoxide concentration is substantially zero or below a predetermined value. In this NOx reduction combustion, self-diagnosis of the carbon monoxide concentration sensor is performed. That is, the diagnostic gas is brought into contact with the carbon monoxide concentration sensor by the diagnostic gas contact means. Then, the determination means determines that the carbon monoxide concentration sensor is abnormal when the output of the carbon monoxide concentration sensor is equal to or less than a set value.

  In the second embodiment, the carbon monoxide sensor and the diagnostic gas contact means can be configured in the same manner as in the first embodiment. When the catalytic combustion CO sensor is used, a part of the gas on the primary side of the catalyst is preferably used as the diagnostic gas, but can be a gas containing the combustible gas and oxygen. The self-diagnosis of the carbon monoxide concentration sensor is performed in a state where the carbon monoxide concentration sensor contains almost no carbon monoxide.

In the second embodiment, when a sensor abnormality is determined, the air ratio adjusting means is configured to perform the next sensor abnormality control. This sensor abnormality control is a control in which the burner is burned at an air ratio having a higher air ratio than the NOx reduction combustion and at the same time a sensor abnormality is notified.

  In the second embodiment, the sensor abnormality time control may be a control for notifying the sensor abnormality while stopping the combustion of the burner. According to the latter control when the sensor is abnormal, when the sensor abnormality is determined, the burner is immediately stopped without performing the rated-time combustion, and a sensor abnormality alarm is issued. According to the latter control when the sensor is abnormal, it is possible to perform control giving priority to safety, but it is disadvantageous compared to the former control when the sensor is abnormal in that it is economically damaged by the stop of combustion.

(Embodiment 3)
The second embodiment is preferably applied to the following third embodiment. The third embodiment includes a burner, a fuel supply means capable of changing the fuel supply amount so as to change the combustion amount of the burner, a combustion air supply means including a blower for supplying combustion air to the burner, The air ratio adjusting means for adjusting the air ratio of the burner, an inverter for changing the rotational speed of the blower, and a sensor for detecting the air ratio of the burner, wherein the air ratio adjusting means comprises the following normal combustion A combustion apparatus characterized by performing time control. This normal combustion control is based on a signal from the sensor, and controls the inverter so as to achieve the set air ratio (NOx reduction combustion air ratio, hereinafter referred to as a reduction air ratio) by feedback control. NOx reduction combustion control (hereinafter referred to as reduction control but also referred to as steady control) and rated combustion air ratio higher than the reduction air ratio (hereinafter referred to as rated air ratio) It is possible to select rated combustion control (hereinafter referred to as rated control but also referred to as change control) for controlling the inverter so that the air ratio can be changed). . In the third embodiment and the fourth to eighth embodiments described below, the fuel supply means can be configured to change the combustion amount stepwise or continuously. In the third embodiment and the fourth to eighth embodiments described below, the self-diagnosis of the carbon monoxide concentration sensor and the control at the time of abnormality when a sensor abnormality is determined are performed as in the second embodiment. In the following description, the description is omitted.

  In the third embodiment, the rated time control is preferably performed when the combustion air amount corresponding to the change in the combustion amount is changed, and the reduction time control is performed after the change in the combustion air amount. The shift to the reduction time control after the change is preferably after a predetermined time after the change is completed. With such a configuration, when the burner combustion amount is changed, for example, when changing from high combustion to low combustion or from low combustion to high combustion, the air ratio adjusting means performs the rated time control, The burner is burned at the rated air ratio having a high ratio, and generation of carbon monoxide due to unstable combustion when changing the combustion amount can be prevented. Further, when the change of the combustion amount is completed, preferably, after a predetermined time has elapsed, the air ratio adjusting means performs the control at the time of reduction, burns the burner at the air ratio at the time of reduction when the air ratio is low, and reduces the reduction. The air ratio is kept constant by feedback control. This prevents the generation of carbon monoxide due to fluctuations in the air ratio. The air ratio during reduction is preferably 1.1 to 1.0, and more preferably 1.0. The rated-time control in the third embodiment and the following fourth to fourth embodiments is preferably performed by feedback control, but may be configured not to perform feedback control. When feedback control is applied, it takes time to accelerate / decelerate, but by not applying feedback control, the acceleration / deceleration time can be shortened, and the amount of NOx discharged before the air ratio is reduced can be reduced.

The third embodiment is typically applied to the combustion apparatus according to the fourth embodiment. In the fourth embodiment, a hydrocarbon-containing fuel is burned to generate a gas containing oxygen, nitrogen oxides, and carbon monoxide, and the fuel supply amount is changed so as to change the combustion amount of the burner. Fuel supply means made possible, a blower for supplying combustion air to the burner, and a combustion air supply means including an inverter for changing the rotation speed of the blower, and carbon monoxide contained in the gas oxidized with oxygen and nitrogen A catalyst for reducing oxides with carbon monoxide; air ratio adjusting means for adjusting the air ratio of the burner; and a sensor for detecting the air ratio of the burner, wherein the burner reduces the air ratio when air is reduced. The ratio of oxygen, nitrogen oxide and carbon monoxide in the gas on the primary side of the catalyst has a predetermined concentration ratio, and the catalyst has the concentration ratio as the predetermined concentration ratio. The catalyst was less secondary side substantially zero or a predetermined value of nitrogen oxide concentration, a combustion apparatus characterized by having the property of substantially a zero or a predetermined value or less carbon monoxide concentration. In the fourth embodiment, the air ratio adjusting means reduces the concentration ratio to a predetermined concentration ratio by controlling the inverter so that the reduced air ratio is set by feedback control based on a signal from the sensor. It is possible to select the time control and the rated time control for controlling the inverter so that the rated air ratio is higher than the reduced air ratio. The fourth embodiment includes the following three fifth to seventh embodiments.

(Embodiment 5)
In the fifth embodiment, a burner that burns hydrocarbon-containing fuel to generate a gas containing oxygen, nitrogen oxides, and carbon monoxide, and the fuel supply amount are changed so as to change the combustion amount of the burner. Fuel supply means made possible, a blower for supplying combustion air to the burner, and a combustion air supply means including an inverter for changing the rotation speed of the blower, and carbon monoxide contained in the gas oxidized with oxygen and nitrogen A catalyst for reducing oxides with carbon monoxide; air ratio adjusting means for adjusting the air ratio of the burner; and a sensor for detecting the air ratio of the burner, wherein the burner reduces the air ratio when air is reduced. The ratio of oxygen, nitrogen oxide and carbon monoxide in the gas on the primary side of the catalyst has a reference predetermined concentration ratio K0, and the catalyst uses the concentration ratio K as the reference. A combustion apparatus characterized by having the property of substantially zero concentration of nitrogen oxides and carbon monoxide concentration of the catalyst secondary side when a constant concentration ratio K0. In the fifth embodiment, the air ratio adjusting means controls the inverter so as to obtain the reduced air ratio by feedback control based on a signal from the sensor, thereby setting the concentration ratio K to the reference predetermined concentration ratio. The control at the time of reduction set to K0 and the control at the time of rating that controls the inverter so that the rated air ratio is higher than the air ratio at the time of reduction can be selected.

(Embodiment 6)
In the sixth embodiment, a burner that burns a hydrocarbon-containing fuel to generate a gas containing oxygen, nitrogen oxides, and carbon monoxide, and a fuel supply amount so as to change the combustion amount of the burner. The fuel supply means that can be changed, the blower that supplies combustion air to the burner, and the combustion air supply means that includes an inverter that makes the rotation speed of the blower variable, and the carbon monoxide contained in the gas is oxidized by oxygen And a catalyst for reducing nitrogen oxide with carbon monoxide, an air ratio adjusting means for adjusting the air ratio of the burner, and a sensor for detecting the air ratio of the burner, wherein the burner is configured to reduce the air ratio to the air ratio. When the reduced air ratio is lower than the reduced air ratio of the fifth embodiment, the concentration ratio K of oxygen, nitrogen oxides, and carbon monoxide in the gas on the primary side of the catalyst is the first predetermined concentration ratio K1. When The catalyst has a nitrogen oxide concentration on the secondary side of the catalyst substantially zero and a carbon monoxide concentration below a predetermined value when the concentration ratio K is the first predetermined concentration ratio K1. It is a combustion apparatus characterized by having the characteristic of In the fifth embodiment, the air ratio adjusting means controls the inverter so as to obtain the reduced air ratio by feedback control based on a signal from the sensor, thereby adjusting the concentration ratio K to the first constant concentration. The control at the time of reduction to be the ratio K1 and the control at the time of rating to control the inverter so that the air ratio at the time of rating higher than the air ratio at the time of reduction can be selected.

(Embodiment 7)
In the seventh embodiment, a burner that burns hydrocarbon-containing fuel to generate a gas containing oxygen, nitrogen oxides, and carbon monoxide, and a fuel supply amount so as to change the combustion amount of the burner. Including a fuel supply means having a fuel adjustment valve that can be changed, an inverter that makes the rotational speed of the blower variable, a blower that supplies combustion air to the burner, and an inverter that makes the rotational speed of the blower variable An air supply means, a catalyst for oxidizing carbon monoxide contained in the gas with oxygen and reducing nitrogen oxide with carbon monoxide, an air ratio adjusting means for adjusting an air ratio of the burner, and an air ratio of the burner And the burner has an acid in the gas on the primary side of the catalyst when the air ratio is a reduced air ratio that is higher than the reduced air ratio in the fifth embodiment. , Nitrogen oxide and carbon monoxide concentration ratio K is a second predetermined concentration ratio K2, and the catalyst has a secondary side when the concentration ratio K is the second predetermined concentration ratio K2. The combustion apparatus is characterized in that the nitrogen oxide concentration of the carbon dioxide is not more than a predetermined value and the carbon monoxide concentration is substantially zero. In the sixth embodiment, the air ratio adjusting means controls the inverter so as to obtain the set air ratio by feedback control based on a signal from the sensor, thereby setting the concentration ratio K to the second constant concentration. The ratio is K2.

That is, the reference predetermined concentration ratio K0, the first predetermined concentration ratio K1, and the second predetermined concentration ratio K2 are set such that the reduced air ratio is changed to the reference set air ratio, the first set air ratio, and the second set air ratio, respectively. By controlling, the following adjustments are made.
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 first predetermined concentration in which the concentration ratio K is lower than the reference predetermined concentration ratio K0, the nitrogen oxide concentration on the secondary side of the catalyst is substantially zero, and the carbon monoxide concentration is not more than a predetermined value. Adjust to the ratio K1.
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 these Embodiments 5 to 7, the concentration ratio K means the relationship between the carbon monoxide concentration, the nitrogen oxide concentration, and the oxygen concentration. The reference predetermined density ratio K0 in the adjustment 0 is determined by a determination formula of the following formula (1), and preferably satisfies the following formula (2), and the first predetermined density ratio K1 is determined from the reference predetermined density ratio K0. The second predetermined density ratio K2 is set to be smaller than the reference predetermined density ratio K0.
([NOx] +2 [O ₂ ]) / [CO] = K (1)
1.0 ≦ K = K0 ≦ 2.0 (2)
(In 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. )

  That is, the reference predetermined concentration ratio K0 is such that the oxygen concentration, nitrogen oxide concentration, and monoxide concentration 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. It is the concentration ratio of carbon. The equation (1) is a determination equation for determining the reference predetermined concentration ratio K0, and the equation (2) 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 Embodiments 4 to 7 described above, first, a gas containing oxygen, nitrogen oxides, and carbon monoxide and not containing hydrocarbons is generated by combustion of the burner. And the concentration ratio K of oxygen, nitrogen oxide and carbon monoxide in the gas on the primary side of the catalyst is controlled based on the characteristics of the burner by controlling the air ratio at the time of reduction by the air ratio adjusting means. They are adjusted to the reference predetermined density ratio K0 and the first predetermined density ratio K1, respectively. In the catalyst, 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 when the adjustment 0 or the adjustment 1 is performed is more than the amount necessary to adjust the carbon monoxide concentration, that is, to reduce the nitrogen oxides so that the concentration becomes substantially zero. The amount of carbon monoxide to be consumed is reduced. Due to the contact between the gas after the adjustment 0 and the adjustment 1 and the catalyst, 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 It is reduced below a predetermined value. Further, due to the contact between the gas after the adjustment 2 and the catalyst, the emission amount of carbon monoxide in the gas is substantially zero, and the nitrogen oxide concentration is reduced to a predetermined value or less. Further, since the control at the time of reduction is feedback control, fluctuations in the values of the predetermined concentration ratios K0, K1, and K2 are suppressed, and the reduction effect of the nitrogen oxide emission amount and the carbon monoxide emission amount is stabilized. It can be demonstrated. In particular, in the adjustment 0, the reduction control is important in order to make the nitrogen oxide emission substantially zero.

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 on the left side of Equation (3) is smaller than K0, and the first The predetermined concentration 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 value of ([NOx] +2 [O ₂ ]) / [CO] (concentration ratio value) is preferably 1.5 or less. The nitrogen oxide concentration ([NOx]) is the total concentration of the nitric oxide concentration ([NO]) and the nitrogen dioxide concentration ([NO ₂ ]). Further, the concentration ratio of the carbon monoxide concentration, the nitrogen oxide concentration, and the oxygen concentration satisfying the expression (3) is referred to as a predetermined concentration ratio.

When the value of the predetermined concentration ratio is 1, theoretically, the oxygen concentration, nitrogen oxide concentration, and carbon monoxide concentration discharged from the catalyst can be made zero. However, experiments have shown that a small amount of carbon monoxide is emitted. ([NOx] +2 [O ₂ ]) / [CO] = 1 in the formula (1) is theoretically derived from the first reaction and the second reaction in consideration of 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), an equal amount of NO is required for CO, and the relationship of the following formula (IV) can be said.
[CO] b = [NO] (IV)
When the reactions of the formulas (I) and (II) occur continuously in the catalyst, the concentration relationship of the following formula (V) obtained by adding the formula (III) and the formula (IV) is necessary. It becomes.
[CO] a + [CO] b = 2 [O ₂ ] + [NO] (V)
Since [CO] a + [CO] b is the same component, it can be expressed as [CO] as the CO concentration in the gas on the catalyst secondary side.
Therefore, the reference predetermined concentration ratio satisfaction formula, that is, the relationship of [CO] = 2 [O ₂ ] + [NO] can be derived.

  When the value of the predetermined concentration ratio is smaller than 1, the concentration of carbon monoxide is higher than the concentration necessary for the reduction of the nitrogen oxides, so the exhaust oxygen concentration is zero and the gas in the gas after passing through the catalyst Carbon monoxide remains on the surface. For this reason, the lower limit of the concentration ratio in the formula (3) is not provided. When carbon monoxide is contained after passing through the catalyst, it is preferable to further provide an oxidizing means for oxidizing the residual carbon monoxide. The oxidation means can be configured to provide a catalyst separate from the catalyst and oxidize carbon monoxide by introducing oxygen upstream of the catalyst.

  Moreover, although the value of the concentration ratio exceeds 1.0 and reaches 2.0, it is an experimentally obtained value, which is considered to be due to the following reason. The reaction occurring in the catalyst has not been completely elucidated, and it is considered that a side reaction occurs in addition to the main reaction of the first reaction and the second reaction. As one of these side reactions, hydrogen is generated by the reaction between steam and carbon monoxide, and a reaction in which nitrogen oxides and oxygen are reduced by this hydrogen can be considered.

(Embodiment 8)
The fourth embodiment can be expressed by the following eighth embodiment. In the eighth embodiment, a hydrocarbon-containing fuel is burned to generate a gas containing oxygen, nitrogen oxides, and carbon monoxide, and the fuel supply amount is changed stepwise. The fuel supply means that can be changed, the blower that supplies the combustion air to the burner, and the combustion air supply means that includes an inverter that makes the rotation speed of the blower variable, and the carbon monoxide contained in the gas is oxidized by oxygen A catalyst for reducing nitrogen oxides with carbon monoxide, a sensor for detecting the air ratio of the burner, and an air ratio adjusting means for controlling the burner to a set air ratio based on a detection signal of the sensor. When the air ratio is adjusted to the reduced air ratio by the air ratio adjusting means, the burner makes the nitrogen oxide concentration on the catalyst secondary side substantially zero or a predetermined value or less. A predetermined concentration ratio of oxygen, nitrogen oxides, and carbon monoxide on the primary side of the catalyst that is substantially zero or less than a predetermined value, and the air ratio adjusting means is Based on the signal from the sensor, the inverter is controlled so as to obtain the reduced air ratio by feedback control, thereby reducing the concentration ratio to a predetermined concentration ratio, and the rated air ratio higher than the reduced air ratio. The combustion apparatus is characterized in that the control at the rated time for controlling the inverter can be selected.

  In the above Embodiments 4 to 8, the reduced air ratio is preferably controlled to a set air ratio of 1.0, but as a result of the reaction with the catalyst, the set air ratio of 1.0 can be satisfied. The air ratio may be controlled so that the oxygen concentration on the primary side of the catalyst becomes a predetermined concentration.

  Here, the action of reducing harmful substances (nitrogen oxides and carbon monoxide) in Embodiments 4 to 8 will be described in more detail. This reduction action is considered to be performed as follows. In the gas not containing HC (hydrocarbon), in the catalyst, as the main reaction, a first reaction for oxidizing carbon monoxide and a second reaction for reducing nitrogen oxide with carbon monoxide are generated. In the reaction in the catalyst (catalytic reaction), in the presence of oxygen, the first reaction is superior to the second reaction, and based on the first reaction, carbon monoxide is consumed by oxygen, After the concentration is adjusted, nitrogen oxides are reduced by the second reaction. This description is simplified. Actually, the first reaction is a competitive reaction with the second reaction, but the reaction between carbon monoxide and oxygen occurs apparently faster than the second reaction in the presence of oxygen. It is considered that the first reaction is performed and the second reaction is performed 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, in the description of the above reaction formula, NO is used without using NOx. The composition of the generated nitrogen oxide in a high temperature field is NO as the main component, and NO ₂ is several 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.

  Next, density ratio adjusting means for performing the adjustment 0, the adjustment 1 and the adjustment 2 will be described. The concentration ratio adjusting means can be configured to adjust the concentration ratio K of oxygen, nitrogen oxides, and carbon monoxide on the primary side of the catalyst using only the concentration ratio characteristics of the burner. Based on the concentration ratio characteristics of the burner and the endothermic means, the nitrogen ratio on the secondary side of the catalyst is controlled from substantially zero to a predetermined value by controlling the predetermined concentration ratio using the air ratio adjusting means of the burner. Below the value, the carbon monoxide concentration is adjusted from substantially zero to a predetermined value or less. The density ratio adjustment can be performed using the following first and second density ratio adjusting means. Any of the adjusting means preferably adjusts the concentration ratio by the air ratio adjusting means.

  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 amount of carbon monoxide and the amount of nitrogen oxide after passing through all or part of the heat absorbing means generated by burning with the air ratio of the burner changed. The concentration ratio characteristic is basically determined by the concentration ratio characteristic of the burner, and the endothermic device typically changes or maintains the concentration ratio characteristic of the burner. It has the function to do. When the endothermic means is the first aspect described later, the carbon monoxide concentration is increased and the nitrogen oxide concentration is suppressed. When the endothermic means is a second embodiment described later, typically, the concentration ratio characteristic by the burner is held with almost no change.

  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 located between the burner and the catalyst and assists the adjustment by increasing the ratio of the carbon monoxide concentration to the oxygen concentration by injecting carbon monoxide or removing oxygen by adsorption. It has the function to perform automatically. 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.

  Next, the components of the embodiment of the present invention will be further 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 as shown in the equations (2) and (3) relating to oxygen, nitrogen oxides, and carbon monoxide is important. is there. By using the premix burner as the burner, the predetermined concentration ratio can be obtained relatively easily in a low air ratio region. However, if oxygen, nitrogen oxides, and carbon monoxide in the gas on the primary side of the catalyst are uniformly mixed and each concentration can be controlled to the predetermined concentration ratio, a burner other than the premix burner is used. be able to.

In addition, when the oxygen concentration O ₂ on the primary side of the catalyst is 0% <O ₂ ≦ 1.00% under the condition that the expression (3) is satisfied, the air ratio is almost 1, and the exhaust concentration is close to zero. Energy saving is realized in addition to low NOx and low CO, 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 and 2) 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 water pipe. And a second embodiment having a combustion space between the groups. 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 catalyst is a catalyst having a function of efficiently reducing the nitrogen oxides in a state where HC is not contained in the gas, and is provided in the downstream of the water pipe group or in the middle of the water pipe group and has air permeability. The structure is such that a catalytically active substance is supported on a substrate, and the structure is not limited to a specific one. As the base material, a metal such as stainless steel or ceramic is used, and a surface treatment is performed to increase the contact area with the exhaust gas. As the catalytically active substance, platinum is generally used, but noble metals represented by platinum (Ag, Au, Rh, Ru, Pt, Pd) or metal oxides can be used depending on the implementation. When the catalyst is provided in the middle of the water pipe group, it can be provided in a gap between a plurality of water pipes, or the water pipe can be used as a base material and a catalytically active substance can be supported on the surface thereof.

  This catalyst has the following characteristics. That is, as shown in the schematic diagram of FIG. 6, the catalyst has a concentration ratio characteristic line L (secondary side [NOx] = 0, secondary side [CO] = 0 line) on the primary side of the catalyst. When the concentration ratio K on the primary side of the catalyst is located on the line L, the nitrogen oxide concentration and the carbon monoxide concentration on the secondary side of the catalyst become substantially zero. The line L theoretically corresponds to the predetermined concentration ratio K of the equation (3) being 1.0 (K0 = 1.0 in the equation (2)). In FIG. Expression (3) when K is 1.0 is illustrated. However, as described above, the nitrogen oxide concentration and the carbon monoxide concentration on the secondary side of the catalyst are substantially zero in the range where the predetermined concentration ratio K is experimentally in the range up to 2.0 exceeding 1.0. Therefore, the line L is not limited to the line shown in FIG.

  Then, the concentration ratio K of oxygen, nitrogen oxide, and carbon monoxide at the intersection of the primary characteristic line M of the burner and the endothermic means and the line L is assumed to be a specific reference predetermined concentration ratio (hereinafter referred to as a specific reference concentration). Called ratio). When the concentration ratio K on the primary side of the catalyst is adjusted to the specific reference concentration ratio K0X (the adjustment 0), the nitrogen oxide concentration and the carbon monoxide concentration on the secondary side of the catalyst are substantially zero. . Then, when the primary oxygen concentration is set higher than the reference oxygen concentration SK corresponding to the specific reference concentration ratio K0X (the adjustment 2), that is, when the primary oxygen concentration is increased by the air ratio adjusting means, the catalyst secondary side A concentration of oxygen corresponding to the difference between the primary oxygen concentration and the reference oxygen concentration is detected, the nitrogen oxide concentration on the secondary side of the catalyst is lower than the nitrogen oxide concentration on the primary side, and the secondary side The carbon monoxide concentration becomes substantially zero. Further, when the primary oxygen concentration is made lower than the specific reference concentration ratio K0X (adjustment 1), carbon monoxide having a concentration corresponding to the difference between the primary oxygen concentration and the reference oxygen concentration is detected on the secondary side of the catalyst. In addition, the nitrogen oxide concentration on the secondary side of the catalyst becomes substantially zero, and the carbon monoxide concentration on the secondary side is reduced.

  By utilizing the characteristics of the catalyst and the primary characteristics of the premix burner and the water tube group, the oxygen concentration and / or carbon monoxide concentration on the secondary side of the catalyst is controlled to zero, that is, the air ratio is set to 1. By controlling to 0.0, the exhaust NOx concentration and the exhaust CO concentration can be easily controlled to substantially zero. That is, by controlling the oxygen concentration and / or carbon monoxide concentration on the secondary side of the catalyst, super energy saving by burning at an air ratio of 1.0, and the exhaust NOx concentration and the exhaust CO concentration exceed substantially zero. Low pollution can be achieved at the same time.

  Further, by controlling the oxygen concentration and / or carbon monoxide concentration on the secondary side of the catalyst in the vicinity of zero, the exhaust NOx concentration is close to zero until it cannot be substantially zero. It can be reduced to a low value.

  The air ratio sensor represents an excess oxygen concentration in an oxygen excess region, and a deficient oxygen concentration required to burn unburned gas such as carbon monoxide at an air ratio m = 1 in a fuel excess region. 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 air ratio adjusting means preferably includes a blower that blows combustion air to the burner, a motor that drives the blower, an inverter that controls the rotation speed of the motor, and a control means that controls the inverter. . In this case, the air ratio of the burner is adjusted by changing the ratio of the combustion air amount to the burner fuel amount by controlling the inverter.

  The air ratio adjusting means is not limited to the one in which the rotation speed of the blower is controlled by an inverter, and the amount of combustion air to the burner can be adjusted by a damper.

  The control means controls the air ratio of the burner based on an air ratio control program stored in advance. This air ratio control program is configured to perform normal combustion control and sensor self-diagnosis control. The normal combustion time control is based on a signal from the sensor, and the inverter is controlled so that the air ratio at the time of reduction is controlled by feedback control, thereby reducing the control at the time of reducing the concentration ratio to a predetermined concentration ratio by controlling the inverter. It is possible to select the rated time control for controlling the inverter so that the rated air ratio is higher than the rated air ratio. The rated time control is performed before and after the change of the combustion air amount corresponding to the combustion amount change, and the reduction time control is performed after the combustion air change. The rated time control in the third to eighth embodiments is preferably feedback control, but may be configured not to perform feedback control.

  In the sensor self-diagnosis control, when the control at the time of reduction is performed, the carbon monoxide concentration sensor and the diagnostic gas are contacted by the diagnostic gas contact means, and the carbon monoxide concentration at the time of contact is determined by the determination means. When the output of the sensor is less than or equal to the set value, the carbon monoxide concentration sensor is determined to be abnormal. And when the said determination means determines abnormality, the following sensor abnormal time control can be performed. The sensor abnormality control is configured to combust the burner at an air ratio that is higher than the NOx reduction combustion and to notify the sensor abnormality.

The air ratio at the time of reduction in Embodiments 2 to 8 is preferably 1.1 to 1.0, and more preferably 1.0 from the viewpoint of energy saving. The rated air ratio is preferably 1.27 (exhaust gas O ₂ : 4.5%) or more, but is not limited thereto.

  The feedback control by the air ratio adjusting means is preferably a well-known PID control, but is not limited to this. Further, the supply of the frequency output to the motor can take the following two modes. In the first aspect, an oxygen concentration signal from the sensor is directly input to the inverter, an operation amount is calculated in the inverter, converted into a frequency output, and supplied to the motor. In a second aspect, an oxygen concentration signal from the sensor is input to the controller, an operation amount is calculated in the controller, converted into a frequency command signal, output to the inverter, and the inverter Supplies the frequency output to the motor.

(Embodiment 9)
The present invention is not limited to the first to eighth embodiments, and includes the following ninth embodiment. The ninth embodiment is a combustion apparatus including a carbon monoxide concentration sensor for detecting a carbon monoxide concentration in a gas generated by a burner, and bringing the carbon monoxide concentration sensor into contact with a diagnostic gas. Combustion comprising diagnostic gas contact means and determination means for determining that the carbon monoxide concentration sensor is abnormal when the output of the carbon monoxide concentration sensor is equal to or less than a set value when in contact with the diagnostic gas Device.

  The ninth embodiment is an embodiment in which it is not a requirement to reduce harmful substances by the catalyst.

  In addition, the present invention is not limited to a combustion apparatus in which the fuel supply means is configured to change the fuel supply amount so as to change the combustion amount of the burner stepwise, but also to continuously change the combustion amount of the burner. Further, the present invention can be applied to a combustion apparatus configured to be able to change the fuel supply amount.

  Further, in the first to ninth embodiments, the self-diagnosis of the CO sensor is performed as a diagnosis (first self-diagnosis) using CO or a diagnostic gas containing combustible gas and oxygen. In addition to this diagnosis, It is possible to determine whether or not the detection value of the CO sensor in a state where the combustible gas concentration is zero is within a set range, and to add a second self-diagnosis that determines that the sensor is abnormal when it is not within the set range. Even when the sensor abnormality is determined by the second self-diagnosis, it is possible to perform the sensor abnormality control similar to the first self-diagnosis.

  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 the first embodiment, FIG. 2 is a sectional view taken along line II-II in FIG. 1, and FIG. 3 is a flow of exhaust gas through the catalyst in FIG. FIG. 4 is an explanatory diagram of an enlarged cross section of the main part of FIG. 1, and FIG. 5 is a diagram for explaining the air ratio-NOx / CO characteristics of the first embodiment. FIG. 6 is a schematic diagram for explaining the characteristics of the burner and endothermic means and the catalyst of the first embodiment, and FIG. 7 is a diagram for explaining the output characteristics of the sensor of the first embodiment. 8 is a time chart illustrating air ratio control in normal combustion control according to the first embodiment. FIG. 9 is a flowchart illustrating the operation of sensor self-diagnosis control according to the first embodiment. FIG. 11 is a view for explaining the NOx and CO reduction characteristics of Example 1, and FIG. It is a figure explaining a CO primary characteristic and a secondary characteristic.

  First, the steam boiler according to the first embodiment will be described. The steam boiler includes a burner 1, a can body 3 including a heat transfer tube (water tube) group 2 as heat absorption means for absorbing heat generated from the burner 1, and oxygen and nitrogen after passing through the heat transfer tube group 2. A catalyst (hereinafter simply referred to as “catalyst”) 4 that allows gas containing oxides and carbon monoxide to pass through in contact with each other to oxidize carbon monoxide and reduce nitrogen oxides, and the above. The fuel supply means 5 for supplying gas fuel to the burner 1, the combustion air supply means 6 for supplying combustion air to the burner 1 and premixing the combustion air and fuel, and the oxygen concentration on the secondary side of the catalyst 4. An air ratio sensor 7 to be detected and a controller 8 as a boiler controller that inputs signals from the air ratio sensor 7 and controls the fuel supply means 5 and the combustion air supply means 6 are provided as main parts. To have.

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

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

  The second gas passage 17 includes a horizontal portion 18 and a vertical portion 19, and the catalyst 4 is attached to the horizontal portion 18. A feed water preheater 20 as an exhaust heat recovery device is mounted on the vertical portion 19 so as to be located downstream of the catalyst 4, and the air ratio sensor 7 is interposed between the catalyst 4 and the feed water preheater 20. Has been placed. In the conventional general gas, the second gas passage 17 is divided into a plurality of parts, and the divided parts are integrated by flange connection. However, in the first embodiment, there is a possibility that the concentration in the exhaust gas flowing through the second gas passage 17 may be increased during abnormal combustion, so that the exhaust gas leakage does not occur as an integral structure by welding. .

  The components from the burner 1 including the burner 1 and the front water pipe group 2 to the catalyst 4 (particularly, the main part of the burner 1 and the water pipe group 2) have the concentration ratio K in the gas on the primary side of the catalyst 4 It functions to adjust the predetermined concentration ratios K0 and K1. That is, the air ratio-NOx / CO characteristic shown in FIG. 5 is obtained when the air ratio adjusting means 28 (described later) adjusts to the set air ratio. The air ratio-NOx / CO characteristic is obtained by controlling the air ratio adjusting means 28 to change the air ratio and burning the primary side air ratio-NOx / CO characteristic of the catalyst 4 (hereinafter, referred to as "the air ratio-NOx / CO characteristic"). Called primary characteristics). The catalyst 4 has a secondary air ratio-NOx / CO characteristic (hereinafter referred to as a secondary characteristic) of the catalyst 4 obtained by bringing the gas having the primary characteristic into contact with the catalyst 4. is doing. The primary characteristic is a characteristic due to components from the burner 1 to the catalyst 4, and the secondary characteristic is a concentration ratio 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 a specific reference predetermined concentration ratio (hereinafter referred to as a specific reference concentration ratio) K0X (see FIG. 6).

  FIG. 5 is a schematic diagram in which the low air ratio region Z2 of FIG. 16 is extended. In FIG. 5, a first line (characteristic line) E indicates the CO concentration on the primary side of the catalyst 4, and a second line F indicates the NOx concentration on the primary side. The third line J indicates the CO concentration on the secondary side of the catalyst 4. When the air ratio is 1.0 or more, the CO concentration becomes substantially zero, and the concentration rapidly increases as the air ratio becomes smaller than 1.0. It has an increasing characteristic. The fourth line U indicates the NOx concentration on the secondary side of the catalyst 4, and the NOx concentration becomes substantially zero in a predetermined region where the air ratio is 1.0 or less, and as the air ratio exceeds 1.0, It has a characteristic that the concentration increases substantially from zero and eventually becomes equal to the concentration on the primary side of the catalyst 4. A region where the secondary NOx concentration of the catalyst 4 is equal to or lower than the air ratio where the secondary side NOx concentration is equal to the primary side concentration is referred to as a NOx / CO reduction region. The lower limit of the NOx / CO reduction region can be an air ratio at which the CO concentration on the secondary side of the catalyst 4 is 300 ppm (Japanese CO emission standard). This air ratio-NOx / CO characteristic is a novel characteristic in a low air ratio region that has not been studied so far.

The catalyst 4 has a function of oxidizing nitrogen monoxide (second reaction) as well as oxidizing carbon monoxide contained in the gas not containing hydrocarbons after passing through the water tube group 2 (second reaction). In Example 1, a catalyst in which the catalytically active substance is platinum is used. As described in the section of “Best Mode for Carrying Out the Invention”, when theoretically considered based on experimental results, the gas and the catalyst 4 satisfying the concentration ratio formula of the formula (3) are described. Contact with the catalytically active substance of
It is considered that a first reaction that mainly oxidizes carbon monoxide and a second reaction that reduces nitrogen oxides by carbon monoxide occur. 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 the horizontal portion 18 in the middle of the second gas passage 17 at a position where the exhaust gas temperature is about 100 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 fuel adjustment valve 25 for adjusting the fuel flow rate provided in the gas fuel supply pipe 24. The fuel adjustment valve 25 has a function of controlling the fuel supply amount to a high combustion flow rate and a low combustion flow rate. The fuel adjustment valve 25 can be composed of a single valve or a plurality of valves connected in parallel to each other. In the first embodiment, the latter low fuel valve and high fuel valve (both not shown) are connected in parallel.

  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 controls the inverter 26 for controlling the rotational speed of the blower 26, a motor 29 for driving the blower 26, a motor 29 for driving the blower 26, and the air blower 26. And the control means 8 to be configured. The air ratio adjusting means 28 is provided with a damper 31 for assisting in controlling the amount of combustion air.

  Further, in the first embodiment, the carbon monoxide concentration sensor (hereinafter referred to as a CO sensor) 32 for detecting the carbon monoxide concentration on the secondary side of the catalyst 4 and the burner 1 burn at the set air ratio. Diagnostic gas contact means 33 for bringing the CO sensor 32 into contact with the diagnostic gas during NOx reduction combustion (during the reduction control), and when the output of the CO sensor is below a set value when in contact with the diagnostic gas, the CO sensor Is determined as an abnormality (configured as part of the control procedure of the controller 8).

The mounting structure of the CO sensor 32 will be described with reference to FIG. A gas detector 34 is formed on the upstream side of the feed water preheater 20 in the vertical portion 19 of the second gas passage 15. The gas detector 34 includes a gas inlet 35 formed on the wall surface of the vertical portion 19, a detection box 36 mounted so as to cover the gas inlet 35, and a wall surface of the detection box 36 on the side opposite to the gas inlet And a guide plate 39 that forms a detection gas flow path 38 so as to guide the secondary gas 37 flowing through the vertical portion 19 to the CO sensor 32. The guide plate 39 preferably has one end protruding inward of the vertical portion 19 and the tip bent downward as shown in the figure. Thereby, the intake of the secondary gas 37 is effective, that is, the gas flow to the CO sensor 32 is effectively generated.

  The diagnostic gas contact means 33 causes the primary side of the catalyst 4 and the detection box 35 to guide the primary side gas 40 flowing on the primary side of the catalyst 4 of the horizontal portion 18 to the upstream part of the detection gas flow path 37. , A diagnostic gas introduction control electromagnetic valve 42 provided in the middle of the guide pipe 41 and an orifice 43 as a flow rate adjusting means. The diagnostic gas in the first embodiment is a gas containing carbon monoxide and oxygen on the secondary side of the catalyst 4. The opening of the orifice 43 is such that when the solenoid valve 42 is opened during reduced combustion when the CO sensor 32 is in a normal state, the value detected by the CO sensor 32 becomes a value higher than a set value by a predetermined value. In addition, it is obtained and set in advance by experiments.

The controller 8 controls the air ratio of the burner 1 based on a prestored air ratio control program. This air ratio control program performs normal combustion control as shown in FIG. 8 and sensor self-diagnosis control as shown in FIG. In the normal combustion control, based on the signal from the air ratio sensor 7, the concentration ratio K is reduced to the reference predetermined concentration ratio K0 by controlling the inverter 30 so as to obtain the reduced air ratio by feedback control. The time control and the feedback control are not performed, and the rated time control for controlling the inverter so that the rated air ratio is higher than the reduced air ratio can be selected. In the first embodiment, the reduced air ratio is 1.0, and the rated air ratio is preferably 1.27 (exhaust gas O ₂ : 4.5%).

  Further, in the sensor self-diagnosis control, in the control at the time of reduction, first, the diagnostic gas contact means 33 is operated, that is, the electromagnetic valve 42 is opened, and the determination means determines whether the detected value of the CO sensor 32 is equal to or less than the set value. Judgment by When the detected value is less than or equal to the set value, the CO sensor 32 is determined to be abnormal, and the burner 1 is burned as a rated air ratio that is higher than the reduced air ratio. It is comprised so that abnormality may be alert | reported. This control procedure is shown in FIG.

  The notification of the sensor abnormality is configured to be performed by a notification device 44 attached to the controller 8. The sensor abnormality notification signal is transmitted to a management device other than the controller 8 (not shown), a terminal of a maintenance manager of a boiler owner, a terminal of a maintenance worker of a maintenance manager, and an alarm. It can be configured to provide inspection instructions.

  The sensor self-diagnosis may be configured such that after the NOx reduction combustion is performed for a predetermined time, the electromagnetic valve 42 is opened and the CO sensor 32 is diagnosed. The predetermined time is a time required to determine whether or not there is any CO leakage from the catalyst 4 during this period, and self-diagnosis is performed after this predetermined time. The sensor self-diagnosis interval is once every several hours, but is not limited thereto.

The reduction control is control in which the gas concentration ratio K on the primary side of the catalyst 4 satisfies the following expression (3).
([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.)
This reduction control will be described below with reference to FIGS.

The air ratio-NOx / CO characteristics in FIG. 5 are expressed based on the primary characteristics and the secondary characteristics of the components including the burner 1 and the water pipe group 2, and FIG. 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. 6, the characteristics of the catalyst 4 are the fifth line L (secondary side [NOx] = 0, secondary side [CO] = 0 line for the reference predetermined concentration ratio K0 on the primary side of the catalyst 4). ) 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. 9, the NOx concentration characteristic with respect to the oxygen concentration is omitted in FIG. [NOx] is 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 carbon monoxide concentration on the secondary side of the catalyst 4 substantially zero within a range of the predetermined concentration ratio value exceeding 1.0 exceeding 2.0. 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. In the secondary NOx leakage region R1, the air ratio of the burner 1 exceeds 1.0.

  Further, when the primary oxygen concentration is made lower than the reference oxygen concentration SK, carbon monoxide having a concentration corresponding to the difference between the primary oxygen concentration and the reference oxygen concentration SK is detected on the secondary side of the catalyst 4, and predetermined In this range, the nitrogen oxide concentration on the secondary side of the catalyst 4 is substantially zero. A region where carbon monoxide is detected on the secondary side of the catalyst 4 and the nitrogen oxide concentration is substantially zero is referred to as a secondary CO leakage region R2. This secondary side CO leakage region R2 is a region for realizing the adjustment 1, 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.

The characteristics of the catalyst 4 shown in FIG. 6 are consistent with the air ratio-NOx / CO characteristics shown in FIG. As is clear from FIGS. 5 and 6, the oxygen concentration and / or carbon monoxide concentration on the secondary side of the catalyst 4 is detected, and the air concentration is adjusted so that the oxygen concentration and / or carbon monoxide concentration becomes zero. When the ratio adjusting means 28 is controlled, the concentration ratio K on the primary side of the catalyst 4 is controlled.
Is controlled to the specific reference concentration ratio K0X, and the nitrogen oxide concentration and the carbon monoxide concentration on the secondary side of the catalyst 4 can be controlled to substantially zero. Thus, the reduction control is realized.

  As the air ratio sensor 7, a zirconia air-fuel ratio sensor having a good response 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. 7, the output characteristic of the air ratio sensor 7 is an output related to the oxygen concentration on the positive side and an output related to the carbon monoxide concentration on the negative side. That is, the air ratio m is calculated from the measured oxygen concentration (oxygen excess region), carbon monoxide concentration, etc. (fuel excess region), and a current or voltage output corresponding to the air ratio m is obtained. In FIG. 7, Q1 represents an oxygen concentration detection zone, and Q2 represents a carbon monoxide concentration detection zone.

  The air ratio control program causes the air ratio m of the burner 1 to become the air ratio during reduction (reference air ratio) m0 based on the output signal of the air ratio sensor 7 during the reduction time control. In addition, the inverter 30 is feedback-controlled. In the rated time control, the air ratio m is controlled to be the rated air ratio.

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

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

(Normal combustion control)
Next, air ratio control in normal combustion control by the air ratio adjusting means 28 will be described with reference to FIG. FIG. 8 illustrates a stage after a “main trie” control stage (hereinafter referred to as a stage) described later. The boiler according to the first embodiment operates by switching between high combustion and low combustion. For this purpose, the damper 29 is switched between H with a large opening and L with a small opening by selecting either a high combustion air flow position or a low combustion air flow position.

  First, in the “pre-purge” stage, the motor 29 is turned on, the output frequency from the inverter 30 is set to the frequency corresponding to the rated air ratio, the feedback control is turned off, the damper is set to H, and the known pre-purge is performed. Done.

  Next, at the “pre-ignition” stage, the damper 31 is set to L and an ignition transformer (not shown) is driven. Thereafter, a pilot valve (not shown) is turned on to ignite the pilot valve. When ignition is completed, the operation of the ignition transformer is stopped and the process proceeds to the “pilot only” stage. Thereafter, when there is a combustion request for the burner 1, the low fuel valve is opened and a "main try" stage is performed.

  As described above, since the control at the rated time is performed between “pre-purge” and “main trie”, the combustion control similar to the conventional one is performed without any trouble.

  Referring to FIG. 8, when the “low combustion” stage is entered after the “main trie” is completed, T1 (T1 is detected by temperature detection) from the start of this stage until the temperature of the catalyst 4 reaches about 150 ° C. or more. The control at the rated time is continued, and then the controller 8 switches to the control at the time of reduction. This reduction control is performed by feedback control in response to a signal from the air ratio sensor 7. That is, the controller 8 outputs a signal to the inverter 30 so as to maintain the reduced air ratio m0. Since the output signal of the air ratio sensor 7 changes as shown in FIG. 7, the controller 8 receives this signal, and the controller 8 performs feedback control so that the air ratio m converges to m0. A signal is output to the inverter 30. By the control at the time of reduction by this feedback control, fluctuations in the air ratio due to fluctuations in the outside air temperature can be minimized. As a result, the generation of carbon monoxide prevents the catalyst 4 from exceeding its processing capacity, and carbon monoxide and nitrogen oxides are prevented from leaking out of the boiler, thus ensuring a stable harmful substance reduction effect. . In particular, in the first embodiment, since the air ratio 1 is set to 1.0, there is a possibility that a large amount of carbon monoxide is generated even if the air ratio is slightly changed. Is big.

  Next, when a request for high combustion is received, the "high combustion" stage is controlled. First, the controller 8 issues a command to turn off the feedback control and change the output frequency of the inverter 30 from the reduced air ratio m0 to the rated air ratio. As a result, the inverter 30 outputs a gradually increasing frequency as shown in FIG. 8 so that the trip does not occur. When a predetermined time T2 has elapsed from the start of the "high combustion" stage and the frequency corresponds to the rated air ratio, first, the high combustion valve is opened, and a predetermined time is delayed, that is, the predetermined time T3 from the start of the "high combustion" stage. When the time has elapsed, the damper 29 is set to H. Then, after the “high combustion” stage is started, the high fuel holding by the control at the rated time is performed for a predetermined time T4, and then the control at the time of reduction is switched.

  When the low combustion request is received again, the controller 8 controls the “low combustion” stage. The feedback control is turned off, and a command is issued so that the output frequency of the inverter 30 is changed from the reduced air ratio m0 to the rated control air ratio. As a result, the inverter 30 outputs a gradually increasing frequency as shown in FIG. When the predetermined time T6 has elapsed from the start of the “low combustion” stage and the frequency corresponds to the rated air ratio, first, the damper 29 is set to H, and the predetermined time T5 from the start of the “low combustion” stage is delayed by a predetermined time. When the time has elapsed, the high combustion valve is closed. Then, after the low fuel holding by the rated time control is performed for a predetermined time T7 from the start of the “low combustion” stage, the control is switched to the reduction time control in which the feedback control is turned on.

  In the air ratio control by the inverter 30 described above, it is generally considered that the inverter control is less responsive than the damper. The reason for this is to reduce the increase / decrease gradient of the output frequency when the operation amount causing slipping is large. However, in the control in which the operation amount is small in the vicinity of the air ratio of 1.0 as in the first embodiment, it is not necessary to reduce the increase / decrease gradient, so that there is no difference in responsiveness compared to the damper.

Here, the harmful substance reduction effect by the reduction control will be described.
(Experimental example 1)
The catalyst is burned with a premix burner 1 having a combustion amount of 45.2 m ³ N / h in a can 3 having an evaporation amount of 800 kg per unit time (model manufactured by Applicant: SQ-800). An experimental result in the case of a catalyst having a volume of 10 L and an inner diameter of 360 mm carrying Pt at a rate of 2.0 g / L as an active substance will be described. When the reference air ratio m0 is 1, 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 about 327 ° C., respectively. In the present Experimental Example 1 and the following Experimental Examples 2 and 3, the catalyst 4 is disposed slightly upstream of the feed water preheater 20, and measuring devices are disposed before and after the catalyst 4. The temperature of the gas was measured using PG-250 manufactured by Horiba, Ltd., and each concentration before passing was measured using COPA-2000 manufactured by Horiba, Ltd. Of course, even if the catalyst 4 is disposed at the position shown in FIG.

(Experimental example 2)
When the same burner 1 and can 3 as in Experimental Example 1 are used, the combustion amount is the same as in Experimental Example 1, and the catalyst is a catalyst having a volume of 10 L and an inner diameter of 360 mm carrying Pd at a rate of 2.0 g / L as a catalytically active substance. FIG. 10 shows values at each concentration ratio K of carbon monoxide concentration, nitrogen oxide concentration, and oxygen concentration. Here, since the oxygen concentration after passing through the catalyst was measured using the same oxygen concentration sensor as in Experimental Example 1, even if the value was actually 100 ppm or less, it was indicated as 100 ppm. The gas temperatures before and after the catalyst 4 were about 323 ° C. to 325 ° C. and about 344 ° C. to 346 ° C., respectively.

(Sensor self-diagnosis control)
Next, sensor self-diagnosis control as a feature of the present invention will be described with reference to FIG. Referring to FIG. 9, in processing step S <b> 1 (hereinafter, processing step SN is simply referred to as SN), it is determined whether or not the current control stage is reduction combustion. If the determination here is NO, the process returns to S1. If YES is determined in S <b> 1, the process proceeds to S <b> 2 and the electromagnetic valve 42 is opened. Then, assuming that the concentration ratio is controlled to 1.44 in FIG. 10, the gas on the primary side of the catalyst 4 containing about 2500 ppm and about 1700 ppm of CO and O ₂ , respectively, passes through the guide tube 41 and the detection. It is introduced into the box 35. As a result, the CO sensor 32 detects a high concentration of CO as compared with the time of combustion at the time of reduction (the CO concentration on the secondary side of the catalyst 4 and O ₂ is approximately 20 ppm, substantially zero, respectively). become.

Here, if the CO sensor 32 is normal, CO contained in the diagnostic gas introduced by the guide tube 41 is combusted by O ₂ contained in the diagnostic gas in the CO sensor 32. As a result, the value detected by the CO sensor 32 greatly exceeds the set value. However, when it is in an abnormal state due to deterioration or the like, it becomes less than the set value. As a result, YES is determined in S3, and the process proceeds to S5 to perform sensor abnormality control. In S5, the combustion is continued at the rated time combustion by the rated air ratio. As a result, since the burner 1 burns at a high air ratio, the amount of CO contained in the gas from the burner 1 is reduced to a level of, for example, several tens of ppm or less. When the process of S5 is not performed, a situation where a large amount of CO leaks to the secondary side of the catalyst 4 due to deterioration of the catalyst 4 and the leakage cannot be detected due to abnormality of the CO sensor 32 is avoided. Can do. And since combustion can be continued without stopping a boiler, it will not suffer from the economic loss by stopping a boiler. In S5, since the alarm for sensor abnormality is notified by the alarm device 44, the abnormality can be eliminated by performing inspection by the manager of the boiler owner or a maintenance company.

  If NO is determined in S3, the process proceeds to S4, the electromagnetic valve 42 is closed, the introduction of the diagnostic gas is stopped, and the combustion at the time of reduction is continued.

As described above, according to the combustion control of the first embodiment, the controller 8 determines whether or not it is the stage of combustion at the time of reduction, and when it is determined that combustion at the time of reduction, performs the self-diagnosis of the CO sensor 32, If it is determined that the sensor is abnormal, the air ratio of the burner 1 is adjusted to a rated air ratio that is higher than the reduced air ratio and combustion is continued.
As a result, the CO sensor 32 can be replaced when the boiler is stopped and maintenance management is possible based on the notification without stopping the combustion of the burner 1. In this way, by using the high concentration carbon monoxide generated by the combustion at the time of reduction as the diagnostic gas, the sensor can be self-diagnosed without injecting a diagnostic gas different from the exhaust gas.

  Further, according to the first embodiment, when the combustion amount is changed, inconvenience due to unstable combustion can be avoided by the rated time control, and at the time of steady combustion, the air ratio of the burner 1 is set by the reduction time control. A low air ratio close to 1.0 is controlled, and the concentration ratio change width of the gas on the primary side of the catalyst 4 is controlled to be small, so that the formula (3) can be satisfied stably. 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 by almost zero. If the set air ratio m0 is less than 1.0, the nitrogen oxide concentration on the secondary side can be made substantially zero, and the carbon monoxide concentration can be reduced to a predetermined value or less in the practical range.

  Further, according to the first embodiment, the air ratio adjusting means 28 controls the air ratio to 1.0, so that the concentration ratio of oxygen, nitrogen oxide and carbon monoxide on the primary side of the catalyst 4 is increased. The specific reference concentration ratio K0X can be controlled (the adjustment is 0), and the exhaust NOx concentration and the exhaust CO concentration can be reduced to substantially zero. Therefore, compared with the NOx reduction technology by water / steam addition and the NOx reduction technology by introduction of a denitration agent, low NOx and low CO can be realized with a simple configuration using the air ratio adjusting means and the catalyst.

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

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

  Another embodiment 2 of the present invention will be described with reference to FIG. In the second embodiment, the air ratio sensor 7 for detecting the oxygen concentration is provided not on the secondary side of the catalyst 4 but on the primary side. The air ratio sensor 7 is only an air ratio sensor that detects only the oxygen concentration, and the rest is the same as that of the first embodiment, and a description thereof will be omitted.

In the second embodiment, the air ratio sensor 7 detects the primary side oxygen concentration of the catalyst 4 so that the reference set air ratio m0 is 1 (the secondary side oxygen concentration of the catalyst 4 is zero). Thus, the air ratio is indirectly controlled. Based on various experimental results, when the oxygen concentration O ₂ on the primary side of the catalyst 4 is controlled to a value of 0% <O ₂ ≦ 1.00%, the above equation (3) is satisfied and the secondary of the catalyst 4 It has been found that the oxygen concentration on the side can be made substantially zero, that is, the air ratio can be made nearly 1.0.

In the third embodiment, as shown in FIG. 12, the set air ratio is set such that the NOx concentration in the secondary characteristic substantially exceeds zero and becomes lower than the NOx concentration in the primary characteristic. . This value is the secondary side N of the secondary characteristic where the set air ratio substantially exceeds 1.0.
This is the air ratio of the Ox leakage region R1. The adjustment of the density ratio K in Example 3 is the adjustment 2.

This is a case where the center of the control range (target air ratio) in the third embodiment, for example, an air ratio of 1.005 (O ₂ concentration: about 1000 ppm) is used. This will be described with reference to FIG. 8. 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.

  Next, a fourth embodiment of the present invention will be described with reference to FIG. In the fourth embodiment, the air ratio control means 28 adjusts the damper 31 as a flow rate adjusting means for adjusting the opening degree (flow passage sectional area) of the air supply passage 27 and the opening position of the damper 31. The first embodiment is different from the first embodiment in that a damper position adjusting device 45 for controlling the operation of the damper position adjusting device 45 is included. That is, in the fourth embodiment, the air ratio is adjusted, that is, the ratio of the combustion air amount is adjusted by adjusting the opening degree of the damper 31. Since other configurations are the same as those of the first embodiment, the description thereof is omitted.

  A fifth embodiment of the present invention will be described with reference to FIG. The fifth embodiment is a steam boiler that does not include the catalyst 4, unlike the first embodiment. The boiler of the fifth embodiment is configured not to perform the combustion at the time of reduction of the first embodiment but to perform only the combustion at the rated time. At the time of rated combustion, the controller 8 controls the combustion by feedback control so that the rated air ratio is obtained based on the signal of the air ratio sensor 7.

  A CO sensor 32 is provided to detect a large amount of CO generated when the burner 1 burns at an abnormal air ratio, and the CO sensor is used when the burner 1 burns at the rated air ratio. Diagnostic gas contact means 33 for bringing the gas sensor 32 into contact with the diagnostic gas, and determination means for determining that the CO sensor is abnormal when the output of the CO sensor is equal to or less than a set value when contacting the diagnostic gas (control procedure of the controller 8) As a part of.). A guide pipe 41 is connected to the gas fuel supply pipe 24 so that the diagnostic gas uses a part of the combustible gas supplied through the gas fuel supply pipe 24. In the fifth embodiment, the same components as those of the first embodiment are denoted by the same reference numerals, and the description thereof is omitted. Further, the configuration of the gas detector 34 is the same as that shown in FIG.

  In the fifth embodiment, the controller 8 operates the diagnostic gas contact means 33 during rated combustion to open the electromagnetic valve 42 to contact the combustible gas as the diagnostic gas with the CO sensor 32. As in the first embodiment, the CO sensor 32 is self-diagnosed in the same manner as in the first embodiment. When the output of the CO sensor 32 is equal to or lower than a set value, it is determined that the sensor is abnormal, and the notification device 44 notifies the abnormality. It is composed.

  A sixth embodiment of the present invention will be described with reference to FIG. In Example 6, the catalyst 4 that oxidizes carbon monoxide contained in the gas with oxygen and reduces the nitrogen oxide with carbon monoxide, and the concentration of carbon monoxide in the gas on the secondary side of the catalyst are detected. A harmful substance reduction system comprising a CO sensor 7, wherein a diagnostic gas contact means 33 for bringing the CO sensor 7 into contact with a diagnostic gas, and an output of the CO sensor 32 when the diagnostic gas is in contact with a set value or less. And determining means for determining that the CO sensor 32 is abnormal (configured as part of the control procedure of the controller 8).

The harmful substance reduction system of the first embodiment is provided with a gas turbine 51 as an exhaust gas generation source in which the composition and temperature of the exhaust gas fluctuate, and provided downstream of the gas turbine 51, and the exhaust gas oxygen, nitrogen oxides and A gas property adjusting means 52 for adjusting the composition and temperature of carbon monoxide to a predetermined concentration ratio and a predetermined temperature, respectively, and a first reaction and nitrogen oxide provided downstream of the gas property adjusting means 52 for oxidizing carbon monoxide The catalyst 4 for reducing the carbon monoxide and nitrogen oxide concentrations by the second reaction of reducing the catalyst with carbon monoxide and the exhaust gas boiler 53 provided downstream of the catalyst 4 are provided as main parts. The components of the sixth embodiment will be described below.

  In the gas turbine 51, the composition and temperature of the oxygen, nitrogen oxide, and carbon monoxide of the gas to be discharged vary depending on the load.

  The gas property adjusting means 52 includes a first detection means 54 for detecting the composition and temperature of the exhaust gas discharged from the gas turbine 51, and concentrations of carbon monoxide, nitrogen oxides and oxygen of the exhaust gas on the primary side of the catalyst 4. A burner 55 that adjusts the ratio and temperature, a second detection means 56 that detects the composition and temperature of the exhaust gas whose concentration and temperature are adjusted by the burner 55, the first detection means 54, and the second detection means 56 A controller that controls the combustion of the burner 55 based on the detected value by the control so that the concentration ratio satisfies the equation (3) and the temperature of the exhaust gas becomes a predetermined temperature at which the catalyst 4 is activated. 8 and so on.

  More specifically, the concentration ratio of carbon monoxide, nitrogen oxide and oxygen contained in the exhaust gas before flowing in the catalyst 4 is adjusted so as to satisfy the formula (3), and the temperature of the exhaust gas is set to a predetermined value. It is comprised so that it may adjust to temperature (150 degreeC-500 degreeC which is the activation temperature of the catalyst 4 of this Example 6).

  The first detection means 54 and the second detection means 56 are respectively an oxygen concentration sensor and a carbon monoxide sensor for adjusting the gas composition, and a flow rate sensor and a gas temperature sensor for adjusting the gas temperature (both not shown). ).

The burner 55 is a premixed burner having a function of adjusting the concentration ratio and temperature of carbon monoxide and oxygen of the exhaust gas. The adjustment of carbon monoxide and oxygen by the burner 55 is configured such that the carbon monoxide concentration is increased by incomplete combustion of the burner 55 and the O ₂ concentration is increased by high O 2 combustion. Further, the temperature of the gas is adjusted by changing the combustion amount of the burner 55.

  The burner 55 is provided with a fuel valve 57 as a gas fuel supply amount adjusting means and a blower 58 capable of controlling the rotation speed as a combustion air supply amount adjusting means. The concentration ratio and the temperature are adjusted by controlling the rotational speed of the blower 58. Reference numerals 59 and 60 denote a first flow path and a second flow path.

  The control by the controller 8 is realized by a gas property adjustment program and a sensor self-diagnosis program stored in advance. The adjustment program includes a difference signal between the first detection value of the first detection unit 54 and a set value of the concentration ratio (for example, carbon monoxide concentration: 4000 ppm, oxygen concentration: 2000 ppm) and the first detection unit 54. The first control signal is sent to the fuel valve 57 and the blower 58 based on the difference signal between the second detection means 56 and the concentration ratio, based on the difference signal between the second detection means 56 and the concentration ratio. The second control signal is sent to the fuel valve 57 and the blower 58 based on the difference signal and the difference signal between the second detection value and the set value of the temperature to perform fine control. That is, this control mainly controls the combustion of the burner 55 based on the detection value of the first detection means 54 that is upstream of the burner 55, and the second detection means 56 that is downstream of the burner 55. The main control is corrected based on the detected value.

  The sensor self-diagnosis program activates the diagnostic gas contact means 33 during rated combustion, opens the electromagnetic valve 42, contacts the combustible gas as diagnostic gas with the CO sensor 32, and performs an abnormality in the CO sensor 32. As in Example 1, the self-diagnosis of the CO sensor 32 is performed, and when the output of the CO sensor 32 is equal to or less than a set value, it is determined that the sensor is abnormal, and the notification device 44 notifies the user.

  One end of the guide pipe 41 of the diagnostic gas contact means 33 is connected to a gas fuel supply pipe 61 on the downstream side of the fuel valve 57, but a gas fuel supply pipe (illustrated) on the upstream side of the fuel valve 57. (Omitted). Since the structure of the gas detector 34 is the same as that of the first embodiment, the description thereof is omitted.

  The present invention is not limited to the first to sixth embodiments. For example, in the first embodiment, when the controller 8 determines an abnormality, the burner 1 is combusted at an air ratio having a higher air ratio than the NOx reduction combustion and a sensor abnormality is notified. However, when the controller 8 determines abnormality, the combustion of the burner 1 can be stopped and the sensor abnormality can be notified. This can be realized by performing the process of S5 in FIG. 9 to stop the combustion of the burner 1 and to give an alarm.

  The air ratio-NOx / CO characteristics shown in FIGS. 5 and 12 have different curves and concentration values depending on the structure of the burner 1 and the can 3 of the combustion apparatus, and therefore different characteristics can be used. . In the first and second embodiments, the set air ratio is set to 1.0 or more. However, the air ratio can be set to a value lower than 1.0 within a range in which the combustibility is not impaired and hydrocarbons are not generated.

  In addition, the inverter 30 is controlled by a single controller (controller for boiler control) 8, but another controller (not shown) for the inverter 30 is provided separately from the controller 8. The controller 8, the air ratio 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 explanatory drawing of the principal part expanded cross section of FIG. It is a figure which shows the air ratio -NOx * CO characteristic of the present Example 1. FIG. 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 air ratio sensor of the present Example 1. FIG. It is a figure explaining the combustion control by the air ratio control of the first embodiment. It is a flowchart explaining the sensor self-diagnosis control of the first embodiment. It is a figure explaining the NOx and CO reduction characteristic of the present Example 1. It is explanatory drawing of the longitudinal cross-section of the steam boiler of the present Example 2. It is a figure explaining the NOx and CO reduction characteristic of the present Example 3. It is explanatory drawing of the longitudinal cross-section of the steam boiler of the present Example 4. It is explanatory drawing of the longitudinal cross-section of the steam boiler of the present Example 5. It is a schematic block diagram of the harmful substance reduction system of the present Example 6. It is a figure explaining the NOx * CO primary characteristic and secondary characteristic by this invention

DESCRIPTION OF SYMBOLS 1 Burner 4 Catalyst 7 Air ratio sensor 8 Controller 25 Fuel adjustment valve 28 Air ratio adjustment means 29 Motor 30 Inverter 32 CO sensor 33 Diagnostic gas contact means 44 Alarm

Claims (7)

An oxidation catalyst for oxidizing carbon monoxide contained in a gas from a gas generation source with oxygen and reducing nitrogen oxide with carbon monoxide;
A harmful substance reduction system comprising a carbon monoxide concentration sensor for detecting a carbon monoxide concentration in a gas on the secondary side of the oxidation catalyst,
Diagnostic gas contact means for bringing the carbon monoxide concentration sensor into contact with the diagnostic gas;
A harmful substance reduction system comprising: a determination unit that determines that the carbon monoxide concentration sensor is abnormal when the output of the carbon monoxide concentration sensor is equal to or less than a set value when in contact with the diagnostic gas. A combustion apparatus comprising a carbon monoxide concentration sensor for detecting a carbon monoxide concentration in a gas generated by a burner,
Diagnostic gas contact means for bringing the carbon monoxide concentration sensor into contact with the diagnostic gas;
A combustion apparatus comprising: a determination unit that determines that the carbon monoxide concentration sensor is abnormal when the output of the carbon monoxide concentration sensor is equal to or less than a set value when in contact with the diagnostic gas. A burner that burns a hydrocarbon-containing fuel to produce a gas containing oxygen, nitrogen oxides, and carbon monoxide;
An air ratio adjusting means for adjusting the air ratio of the burner;
An oxidation catalyst for oxidizing carbon monoxide contained in the gas with oxygen and reducing nitrogen oxide with carbon monoxide;
An air ratio sensor for detecting an air ratio of the burner;
A carbon monoxide concentration sensor for detecting a carbon monoxide concentration in a gas on the secondary side of the oxidation catalyst,
The burner has a characteristic that when the air ratio is a set air ratio, the concentration ratio of oxygen, nitrogen oxide and carbon monoxide in the gas on the primary side of the oxidation catalyst is a predetermined concentration ratio,
In the oxidation catalyst, when the concentration ratio is the predetermined concentration ratio, the nitrogen oxide concentration on the secondary side of the oxidation catalyst is substantially zero or less than a predetermined value, and the carbon monoxide concentration is substantially zero or a predetermined value. It has the following characteristics:
Diagnostic gas contact means for contacting the carbon monoxide concentration sensor and diagnostic gas during NOx reduction combustion in which the burner burns at the set air ratio;
A combustion apparatus comprising: a determination unit that determines that the carbon monoxide concentration sensor is abnormal when the output of the carbon monoxide concentration sensor is equal to or less than a set value when in contact with the diagnostic gas.   4. The combustion apparatus according to claim 3, wherein when the determination means determines abnormality, the burner is burned at an air ratio having an air ratio higher than that of the NOx reduction combustion and a sensor abnormality is reported.   The combustion apparatus according to claim 3, wherein when the determination means determines abnormality, the combustion of the burner is stopped and a sensor abnormality is notified. The diagnostic gas is a part of the gas on the secondary side of the oxidation catalyst.
The combustion apparatus according to claim 4.   The combustion apparatus according to claim 6, wherein the carbon monoxide concentration sensor is a catalytic combustion type CO sensor.

Images