JP5442411B2 - Exhaust gas treatment apparatus, combustion furnace, and exhaust gas treatment method - Google Patents

Description

  The present invention relates to an exhaust gas treatment device, a combustion furnace, and an exhaust gas treatment method.

  Conventionally, a denitration reactor described in Patent Document 1 below is known as a technique in such a field. In an incineration facility using this denitration reactor, waste is combusted in an incinerator, and exhaust gas generated by the combustion is introduced into the denitration reactor through a cooler, an alkali spray tower, and a bag filter. The denitration reactor is filled with a denitration catalyst, and the concentration of nitrogen oxide (NOx) in the exhaust gas is reduced by the action of the denitration catalyst. Such a denitration catalyst has its denitration performance deteriorated with the operation time, and therefore it has been proposed to determine the degree of deterioration of this denitration performance and use it for predicting the life of the denitration catalyst.

Japanese Patent Laid-Open No. 10-109018

  As described above, in the exhaust gas treatment using the denitration catalyst, the performance of the denitration catalyst may be deteriorated, but it is necessary to always achieve a desired NOx removal rate in order to comply with exhaust gas regulations such as laws and regulations. Therefore, in the incineration facility of Patent Document 1, the denitration reactor is filled with a large amount of denitration catalyst so that a desired NOx removal rate can be achieved even if the performance of the denitration catalyst is somewhat deteriorated. It was necessary to keep. Since this type of denitration catalyst is expensive, an increase in the amount of denitration catalyst in a margin hinders facility cost reduction. Accordingly, it has been desired to reduce the amount of the denitration catalyst prepared for the denitration of exhaust gas.

  An object of the present invention is to provide an exhaust gas treatment apparatus, a combustion furnace, and an exhaust gas treatment method capable of reducing the amount of a denitration catalyst prepared for the denitration treatment of exhaust gas.

The exhaust gas treatment apparatus of the present invention is an exhaust gas treatment apparatus for treating exhaust gas generated in a furnace of a combustion furnace, and sprays a reducing agent for non-catalytic denitration in exhaust gas to reduce nitrogen oxides in the exhaust gas. A denitration means, a catalytic denitration means for reducing a nitrogen oxide in the exhaust gas by spraying a reducing agent for catalytic denitration in the exhaust gas after the treatment by the non-catalytic denitration means, and contacting the exhaust gas with the denitration catalyst, and a denitration catalyst The reaction rate constant detecting means for detecting the reaction rate constant of the catalyst as the performance deterioration degree of the denitration catalyst, and the ratio of the spray amount of the reducing agent for non-catalytic denitration and the spray amount of the reducing agent for catalytic denitration is Spray control means for controlling based on the reaction rate constant detected by the reaction rate constant detection means, and the spray control means is for catalytic denitration as the reaction rate constant decreases with the aging of the denitration catalyst. Spray amount of reducing agent Characterized by increasing the ratio of the spraying amount of the reducing agent for the non-catalytic denitration against.

Further, the combustion furnace of the present invention includes a furnace for burning fuel, an exhaust gas passage for conveying and discharging exhaust gas generated in the furnace, and a nitrogen oxide in the exhaust gas by spraying a reducing agent for non-catalytic denitration in the exhaust gas. Non-catalytic denitration means for reducing NOx and nitrogen oxidation in exhaust gas by spraying a reducing agent for catalytic denitration into exhaust gas after treatment by non-catalytic denitration means and contacting exhaust gas with denitration catalyst Catalyst denitration means for reducing waste, and reaction rate constant detection means for detecting the reaction rate constant of the denitration catalyst as the performance deterioration degree of the denitration catalyst, the spray amount of the reducing agent for non-catalytic denitration, and the catalyst denitration And a spray control means for controlling the ratio of the reducing agent spray amount based on the reaction rate constant detected by the reaction rate constant detection means , the spray control means having a reaction rate constant of the denitration catalyst. Smaller with age Etc., characterized by increasing the ratio of the spraying amount of the reducing agent for the non-catalytic denitration for spraying amount of the reducing agent for organic catalyst denitration.

  In this exhaust gas treatment apparatus and combustion furnace, nitrogen oxides in exhaust gas are treated by non-catalytic denitration means and catalytic denitration means. Since the spray control means can control the ratio of the spray amount of the reducing agent for non-catalytic denitration and the spray amount of the reducing agent for catalytic denitration, nitrogen oxide removal in the non-catalytic denitration means The ratio between the rate and the nitrogen oxide removal rate in the catalytic denitration means can be controlled. For example, when performance degradation of the denitration catalyst occurs, the nitrogen oxide removal rate in the catalytic denitration means decreases. In this case, the spray control means performs nitrogen oxidation in the non-catalytic denitration means by controlling the ratio of the spray amount. The ratio of the object removal rate can be increased. Therefore, even if performance degradation of the denitration catalyst occurs, it is possible to suppress a decrease in the nitrogen oxide removal rate of the exhaust gas treatment apparatus as a whole by compensating for the nitrogen oxide removal rate for non-catalytic denitration. Therefore, the margin of the denitration catalyst prepared in advance in the catalyst denitration means can be reduced, and the amount of the denitration catalyst can be reduced.

  Specifically, the reaction rate constant detection means includes the amount of exhaust gas generated in the furnace, the spray amount of the reducing agent for catalytic denitration, and the reducing agent for catalytic denitration in the exhaust gas after contact with the denitration catalyst. The reaction rate constant may be calculated based on the concentration of NO and the concentration of nitrogen oxides in the exhaust gas after contact with the denitration catalyst. The reaction rate constant can be calculated relatively easily based on such a measured value that is relatively easy to acquire.

Specifically, the spray control means is configured to increase the ratio of the spray amount of the reducing agent for non-catalytic denitration to the spray amount of the reducing agent for catalytic denitration as the reaction rate constant decreases. If the reaction rate constant decreases, it is considered that the performance of the denitration catalyst is greatly deteriorated. In this case, by increasing the ratio of the spray amount in the non-catalytic denitration means, it is possible to compensate for the nitrogen oxide removal rate for the performance deterioration of the denitration catalyst, and to suppress the decrease in the nitrogen oxide removal rate of the entire apparatus.

  Further, the spray control means further determines the spray amount of the reducing agent for non-catalytic denitration or the spray amount of the reducing agent for catalytic denitration based on the concentration of nitrogen oxides in the exhaust gas after contact with the denitration catalyst. It is good also as controlling.

  According to this configuration, even when the nitrogen oxide removal rate fluctuates due to disturbance, the nitrogen oxide removal rate of the non-catalytic denitration means or the catalyst denitration means can be adjusted, and the nitrogen oxide removal as a whole apparatus can be adjusted. The rate can be stabilized.

The exhaust gas treatment method of the present invention is an exhaust gas treatment method for treating exhaust gas generated in a furnace of a combustion furnace, and sprays a reducing agent for non-catalytic denitration into the exhaust gas to reduce nitrogen oxides in the exhaust gas. A non-catalytic denitration step, a catalytic denitration step of reducing the nitrogen oxides in the exhaust gas by spraying a reducing agent for catalytic denitration in the exhaust gas after the treatment by the non-catalytic denitration step and bringing the exhaust gas into contact with the denitration catalyst; A reaction rate constant detection step for detecting the reaction rate constant of the denitration catalyst as the performance deterioration degree of the denitration catalyst, and the spray amount of the reducing agent for non-catalytic denitration and the spray amount of the reducing agent for catalytic denitration A spray control step for controlling the ratio based on the reaction rate constant detected in the reaction rate constant detection step . In the spray control step, the catalyst rate increases as the reaction rate constant decreases with the aging of the denitration catalyst. Prolapse Characterized by increasing the ratio of the spraying amount of the reducing agent for the non-catalytic denitration for spraying amount of reducing agent use.

  In this exhaust gas treatment method, treatment of nitrogen oxides in exhaust gas is performed by a non-catalytic denitration step and a catalytic denitration step. The spray control process can control the ratio between the spray amount of the reducing agent for non-catalytic denitration and the spray amount of the reducing agent for catalytic denitration, so that nitrogen oxide removal in the non-catalytic denitration step is possible. The ratio between the rate and the nitrogen oxide removal rate in the catalytic denitration step can be controlled. For example, when the performance of the denitration catalyst deteriorates, the nitrogen oxide removal rate in the catalytic denitration process decreases. In this case, the spray control process performs nitrogen oxidation in the non-catalytic denitration process by controlling the ratio of the spray amount. The ratio of the object removal rate can be increased. Therefore, even if performance degradation of the denitration catalyst occurs, it is possible to suppress a decrease in the nitrogen oxide removal rate of the exhaust gas treatment apparatus as a whole by compensating for the nitrogen oxide removal rate for non-catalytic denitration. Therefore, the margin of the denitration catalyst prepared in advance in the catalytic denitration step can be reduced, and the amount of the denitration catalyst can be reduced.

  According to the present invention, it is possible to provide an exhaust gas treatment apparatus, a combustion furnace, and an exhaust gas treatment method capable of reducing the amount of a denitration catalyst prepared for the denitration treatment of exhaust gas.

It is a figure which shows one Embodiment of the circulating fluidized bed boiler in which the waste gas processing apparatus of this invention is used. (A) is a top view which shows the soot removal apparatus in the circulating fluidized bed boiler of FIG. 1, (b) is the side view. It is a flowchart which shows the process by a boiler control part.

  Hereinafter, preferred embodiments of an exhaust gas treatment apparatus, a combustion furnace, and an exhaust gas treatment method according to the present invention will be described in detail with reference to the drawings.

  FIG. 1 shows a boiler 1 which is an embodiment of a combustion furnace of the present invention. The boiler 1 is of a type called a circulating fluidized bed boiler or a CFB (Circulating Fluidized Bed) boiler. In the boiler 1, not only fossil fuels such as coal, but also a wide range of fuels such as biomass, plastics, tires, sludge, RFP, and RDF can be used.

  The boiler 1 includes a fluidized bed furnace 3 for burning fuel. A fuel inlet for supplying fuel is provided on the side surface of the furnace 3, and a gas outlet 3 b for discharging exhaust gas generated by combustion is provided at the upper portion of the furnace 3. A cyclone 7 is connected to the gas outlet 3b. The cyclone 7 is also called a separator or a cyclone separator, and functions as a solid-gas separation device. An inlet 7 a of the cyclone 7 is connected to the gas outlet 3 b, and an outlet 7 b of the cyclone 7 is connected to a downstream gas processing system via a back path 11. A return line 9 called a downcomer extends downward from the bottom outlet of the cyclone 7, and the lower end of the return line 9 is connected to the lower side surface of the furnace 3.

  In the furnace 3, the combustion / flowing air introduced from the lower air supply line causes the solid matter including the fuel introduced from the inlet to flow, and the fuel burns while flowing in the furnace 3. . Exhaust gas generated in the furnace 3 is introduced into the cyclone 7 with accompanying solid particles. The cyclone 7 generates a swirling flow of exhaust gas inside and separates solid particles and gas by a centrifugal separation action. The cyclone 7 returns the separated solid particles (circulated material) to the furnace 3 through the return line 9 and sends the exhaust gas from which the solid particles have been removed to the back path 11 from the discharge port 7b. The solid particles circulate in the furnace 3, the cyclone 7 and the return line 9.

  The back path 11 is a duct that conveys exhaust gas, and includes an upstream portion 11a, a midstream portion 11b, and a downstream portion 11c. The back path upstream portion 11a extends substantially horizontally from the discharge port 7b, the back path midstream portion 11b has a U shape, and the back path downstream portion 11c extends substantially vertically. And in order to collect | recover the heat | fever of waste gas for electric power generation, the heat recovery part 21a is provided in the back path upstream part 11a, the heat recovery part 21b is provided in the back path middle stream part 11b, and the back path downstream part 11c Is provided with a heat recovery part 21c. Each of the heat recovery units 21a, 21b, and 21c has a boiler tube that traverses the exhaust gas flow path, and water or water vapor passes through the boiler tube. When the high-temperature exhaust gas sent from the cyclone 7 comes into contact with the boiler tube, the heat of the exhaust gas is recovered into water or steam in the tube, and the generated high-temperature steam is sent to the turbine for power generation through the boiler tube.

  In addition, since the back path midstream portion 11b is U-shaped, the exhaust gas to be transported flows through a complicated path. Therefore, in the back path midstream portion 11b, the solid particles accompanying the exhaust gas easily fall away from the exhaust gas. . Then, the solid particles separated from the exhaust gas are accumulated at the bottom of the back path midstream portion 11b. In order to discharge the accumulated solid particles, an openable / closable particle discharge port 23 is provided at the bottom of the back path midstream portion 11b. And the particle discharge path 25 which connects the particle discharge port 23 and the lower part of the back path downstream part 11c is provided. When the particle discharge port 23 is opened, the solid particles accumulated at the bottom of the back path midstream portion 11 b are sent to the bottom of the back path downstream portion 11 c through the particle discharge path 25. The solid particles accumulated at the bottom of the back path downstream portion 11 c are periodically discharged out of the back path 11. In this way, with the configuration in which the back path midstream portion 11b is U-shaped, solid particles that have not been separated by the cyclone 7 can be removed by the backpass midstream portion 11b. Since the CFB boiler 1 tends to generate a lot of solid particles, such solid particle discharge means is particularly useful.

  The exhaust gas discharged from the lower portion of the back path downstream portion 11c is introduced into the exhaust gas purification device 13 through the line L13. The exhaust gas purification device 13 removes fine particles such as fly ash still accompanying the exhaust gas and desulfurizes the exhaust gas. The exhaust gas after being cleaned by the exhaust gas purification device 13 is discharged from the chimney 15 through the line L15.

  Next, the exhaust gas treatment in the boiler 1 will be described.

  Regarding the exhaust gas discharged from the chimney 15 of the boiler 1, it is necessary to keep the concentration of nitrogen oxide (NOx), which is an air pollutant, below the NOx regulation value in accordance with exhaust gas regulations such as laws and regulations. As one method for reducing NOx in exhaust gas, there is a catalytic denitration method in which a reducing agent such as ammonia is sprayed into the exhaust gas and this exhaust gas is brought into contact with a denitration catalyst to remove NOx by reaction. In this case, the denitration catalyst is installed in an exhaust gas temperature range of 200 to 400 ° C. Further, as another method for reducing NOx in exhaust gas, a non-catalytic denitration method in which a reducing agent such as ammonia is sprayed into the exhaust gas in an exhaust gas temperature range of 700 to 1100 ° C., and NOx is reacted and removed without a denitration catalyst. There is. NOx in exhaust gas can be reduced by changing the N component of NOx to nitrogen gas by either the catalytic denitration method or the non-catalytic denitration method.

  The catalytic denitration method can efficiently perform denitration treatment at a low NH3 / NOx molar ratio, and can reduce NOx to a very low concentration. On the other hand, in the catalytic denitration method, the initial investment cost for the catalyst is high, and it is also necessary to periodically replace the catalyst in response to aging degradation. In contrast, the non-catalytic denitration method is superior in that it is not necessary to provide expensive equipment such as a catalyst, but the denitration efficiency is poor compared to the catalytic denitration method, and it is necessary to spray the reducing agent excessively. In addition, the non-catalytic denitration method cannot reduce NOx to a lower concentration than the catalytic denitration method.

  The exhaust gas treatment device 30 of the boiler 1 includes both a catalytic denitration unit that performs a catalytic denitration method using ammonia as a reducing agent, and a non-catalytic denitration unit that performs a noncatalytic denitration method using ammonia as a reducing agent. The catalytic denitration means is provided downstream of the noncatalytic denitration means, and the exhaust gas is denitrated by the noncatalytic denitration means and then further denitrated by the catalytic denitration means. As described above, the exhaust gas treatment is performed by the non-catalytic denitration means and the catalytic denitration means provided in series, and the NOx concentration in the exhaust gas is set to the NOx regulation value or less.

  Specifically, the exhaust gas treatment device 30 includes an ammonia spray unit 31 provided in the cyclone 7 as non-catalytic denitration means. Ammonia spray unit 31 is supplied with ammonia from ammonia supply device 41 through ammonia supply line L31. And the ammonia spray part 31 sprays ammonia gas from the spray nozzle in the cyclone 7 which is the area | region of exhaust gas temperature 700-1100 degreeC. Thus, by mixing ammonia with the exhaust gas in the cyclone 7, NOx in the exhaust gas reacts with ammonia, and the NOx concentration in the exhaust gas decreases (non-catalytic denitration step). In this case, the greater the amount of ammonia sprayed in the ammonia spraying part 31, the more the NOx in the exhaust gas can be reduced to a lower concentration. In addition, since the swirling flow of the exhaust gas exists in the cyclone 7, the sprayed ammonia is efficiently mixed with the exhaust gas.

  Further, the exhaust gas treatment device 30 includes an ammonia spraying part 33 and a denitration catalyst 35 as a catalyst denitration means. The ammonia spray part 33 is provided on the downstream side of the heat recovery part 21b in the back path midstream part 11b. The denitration catalyst 35 is installed on the upstream side of the heat recovery section 21c in the back path downstream section 11c. Ammonia spray unit 33 is supplied with ammonia from ammonia supply device 41 through ammonia supply line L33. And the ammonia spraying part 33 sprays ammonia gas in the back path midstream part 11b from the spray nozzle.

  The denitration catalyst 35 is a catalyst for the reaction between ammonia and NOx. For example, a catalyst in which vanadium is supported on ceramic is used. Three denitration catalysts 35 are installed in the exhaust gas temperature range of 200 to 400 ° C. in the back path downstream portion 11c, and the exhaust gas in the back path downstream portion 11c sequentially passes through the three mesh-shaped denitration catalysts 35. Flows downward. After the ammonia is mixed with the exhaust gas by the ammonia spraying section 33, the exhaust gas comes into contact with the downstream denitration catalyst 35, whereby NOx reacts with ammonia by the catalytic action of the denitration catalyst 35, and the NOx concentration in the exhaust gas decreases. (Catalytic denitration process). In this case, if the performance deterioration degree of the NOx removal catalyst 35 is the same, the NOx in the exhaust gas can be reduced to a lower concentration as the ammonia spray amount in the ammonia spray section 33 is larger. As the aging deterioration of the denitration catalyst 35 progresses, the NOx removal rate decreases even with the same ammonia spray amount.

  The exhaust gas that passes through the denitration catalyst 35 includes soot that could not be removed by the cyclone 7, soot accumulates on the upper surface of each denitration catalyst 35, and smooth passage of the exhaust gas is impeded. There is. Therefore, as shown in FIG. 2, a soot wiping device 37 for removing the soot accumulated on the upper surface of the denitration catalyst 35 is provided above each denitration catalyst 35. The soot wiping device 37 includes a trunk pipe 37a inserted through the outer wall of the back path downstream portion 11c and a branch pipe 37b communicated with the trunk pipe 37a. The branch pipe 37b is orthogonal to the trunk pipe 37a and extends with a length corresponding to the width of the rectangular denitration catalyst 35. The trunk pipe 37a and the branch pipe 37b form a connected water vapor channel, and the water vapor introduced from the base end side of the main pipe 37a is circulated through the water vapor channel.

  A plurality of ejection holes 37c arranged along the extending direction of the branch pipe 37b are formed on the lower surface of the branch pipe 37b, and steam is sprayed from the ejection holes 37c toward the upper surface of the denitration catalyst 35. It is done. Further, the soot wiping device 37 moves back and forth in the extending direction of the trunk pipe 37 a, so that steam is sprayed over the entire upper surface of the denitration catalyst 35. The soot accumulated on the upper surface of the denitration catalyst 35 is released from the denitration catalyst 35 and passes through the denitration catalyst 35 and flows downward. By periodically driving the soot wiping device 37, the soot accumulated on the upper surface of the denitration catalyst 35 is removed, and the exhaust gas can be smoothly passed through the denitration catalyst 35. Since the CFB boiler 1 tends to generate a large amount of solid particles, such a sooting means is particularly useful.

As shown in FIG. 1, the exhaust gas treatment device 30 further includes a flow rate control device 43 that controls the flow rate ratio of ammonia in the supply lines L31 and L33. In addition, the flow rate of ammonia in the supply lines L31 and L33 corresponds to the spray amount of the ammonia spray units 31 and 33, respectively. The flow rate control device 43 includes a flow meter and a valve, and operates under the control of the boiler control unit 45. The boiler control unit 45 is configured by, for example, a computer. For example, the boiler control unit 45 also has a function of performing overall control of the entire boiler 1 based on information such as operating conditions input by the user from the control information input unit 47. The boiler control unit 45 collects various data related to the operation of the boiler 1 (referred to as “operation data”). The operation data includes the boiler operation load value input from the control information input unit 47, the O ₂ concentration in the exhaust gas, the NOx concentration in the exhaust gas downstream of the denitration catalyst 35, and the exhaust gas downstream of the denitration catalyst 35. At least the NH ₃ concentration and the spray amount in the ammonia spray sections 31 and 33 are included.

In order to collect such operation data, the exhaust gas treatment device 30 includes a concentration meter 51 provided on the line L13, a concentration meter 53 provided on the line L15, and a flow meter provided on the supply line L33. 55 and a flow meter 57 provided on the downstream side of the ammonia supply device 41. The concentration meter 51 continuously measures the NH ₃ concentration and the oxygen concentration of the exhaust gas in the line L13, and transmits the measured value to the boiler control unit 45 as an electrical signal. The concentration meter 53 continuously measures the NOx concentration of the exhaust gas in the line L13 and transmits the measured value to the boiler control unit 45 as an electric signal. The flow meter 55 continuously measures the flow rate of ammonia in the supply line L33 (that is, the amount of ammonia sprayed in the ammonia spray unit 33), and transmits the measured value to the boiler control unit 45 as an electrical signal. The flow meter 57 continuously measures the flow rate of ammonia supplied from the ammonia supply device 41 and transmits the measured value to the boiler control unit 45 as an electrical signal.

  Next, control of the spray amount of the ammonia spray units 31 and 33 by the boiler control unit 45 will be described.

  As described above, the boiler 1 uses not only fossil fuels such as coal but also a wide range of fuels such as biomass, plastics, tires, sludge, RFP, and RDF. Since these fuels contain catalyst poisoning substances such as sodium, potassium, phosphorus, and heavy metals (lead, zinc, etc.), the performance of the denitration catalyst 35 is deteriorated faster than that of a fossil fuel-fired boiler. Therefore, the boiler control unit 45 calculates a reaction rate constant K of the denitration catalyst 35 as an index of the degree of deterioration of the denitration catalyst 35 based on operation data and the like.

Specifically, the reaction rate constant K is represented by the following formula (1).
K = −AV · ln (1-Eff./α) (1)
Where AV is the area velocity,
Area velocity AV (Nm / h) = treatment exhaust gas amount (Nm ³ / h) / catalyst geometric surface area (m ² )
Also, Eff. Is denitration efficiency,
Denitration efficiency Eff. = (Catalyst inlet NOx concentration (ppm) −Catalyst outlet NOx concentration (ppm)) / Catalyst inlet NOx concentration (ppm)
The catalyst inlet NOx concentration (ppm) is
The catalyst inlet NOx concentration (ppm) = the catalyst outlet NOx concentration (ppm) + the catalyst inlet NH ₃ concentration (ppm) −the catalyst outlet NH ₃ concentration (ppm).
Α is a molar ratio,
Molar ratio α = (catalyst inlet NH ₃ concentration (ppm)) / (catalyst inlet NOx concentration (ppm)).

The amount of treated exhaust gas used for calculating the area speed AV is the exhaust gas flow rate generated in the furnace 3 and passing through the back path 11, and is uniquely determined from the boiler operation load value (%) input by the user from the control information input unit 47. It is determined. The catalyst geometric surface area is a fixed value depending on the denitration catalyst 35 used. The catalyst outlet NOx concentration is the NOx concentration in the exhaust gas after the exhaust gas has passed through the denitration catalyst 35, and is measured by the concentration meter 53. The catalyst outlet NH 3 concentration is the NH ₃ concentration in the exhaust gas after the exhaust gas has passed through the denitration catalyst 35, and is measured by the concentration meter 51. The catalyst inlet NH ₃ concentration, a NH ₃ concentration in the exhaust gas before the exhaust gas passes through the denitration catalyst 35, the spray amount of ammonia measured by the flow meter 55 is calculated by dividing the treated flue gas of the aforementioned The The catalyst inlet NOx concentration is the NOx concentration in the exhaust gas before the exhaust gas passes through the denitration catalyst 35. As described above, the catalyst inlet NOx concentration (ppm) = the catalyst outlet NOx concentration (ppm) + the catalyst inlet NH ₃ concentration. (ppm) —expressed as catalyst outlet NH ₃ concentration (ppm).

  From the above, the boiler control unit 45 can calculate the reaction rate constant K by the above equation (1) based on the operation data and the like. That is, the boiler control unit 45 functions as a reaction rate constant detecting unit that detects the reaction rate constant K as the performance deterioration degree of the denitration catalyst 35. And the boiler control part 45 operates the flow rate ratio control apparatus 43 based on the calculated reaction rate constant K, and the optimal spray amount in the ammonia spray part 31 and the ammonia spray part 33, and the ratio of the spray amount Realize. Here, the ratio of the spray amount is controlled based on a preset correspondence curve. The larger the reaction rate constant K, the larger the ratio of the spray amount of the ammonia spray unit 33, and the smaller the reaction rate constant K, the more the ammonia spray. Control is performed so that the ratio of the spray amount of the unit 31 is increased (spray control step). Note that the corresponding curve is created in advance by a trial run or the like.

Specifically, as shown in FIG. 3, the boiler control unit 45 acquires a boiler operation load value from the control information input unit 47 (S101). Furthermore, the boiler control unit 45 acquires the catalyst outlet NH ₃ concentration and the catalyst outlet NOx concentration from the concentration meters 51 and 53, and acquires the spray amount in the ammonia spray unit 33 from the flow meter 55 (S103). And the boiler control part 45 calculates reaction rate constant K using Numerical formula (1) based on these acquired operation data (S105). Next, the boiler control unit 45 calculates the optimum spray amount in the ammonia spray unit 31 and the ammonia spray unit 33 based on the reaction rate constant K (S107). Here, as the reaction rate constant K decreases, the spray amount of the ammonia spray portion 33 decreases and the spray amount of the ammonia spray portion 31 increases. And the boiler control part 45 operates the flow ratio control apparatus 43 in order to implement | achieve the optimal spraying quantity calculated by S107 (S109). During the operation of the boiler 1, the boiler control unit 45 repeats the processes of S101 to S109.

  According to such control, since the reaction rate constant K is large while the performance deterioration degree of the denitration catalyst 35 is small, the ratio of the spray amount of the ammonia spray part 33 is large. Therefore, NOx removal of the exhaust gas is performed with a specific gravity on the catalytic denitration method which is more efficient than the non-catalytic denitration method. In general, since a sufficient amount of denitration catalyst 35 is prepared in anticipation of performance deterioration, immediately after the denitration catalyst 35 is installed (immediately after replacement), the catalyst capacity of the denitration catalyst 35 is excessive with respect to the NOx regulation value. There will be. Therefore, while the performance deterioration degree of the denitration catalyst 35 is small, for example, without using the noncatalytic denitration method or minimizing the use of the noncatalytic denitration method, the NOx regulation value is almost only with the catalytic denitration method. Can be achieved.

  Further, when the reaction rate constant K of the denitration catalyst 35 falls below a predetermined value, the performance of the denitration catalyst 35 is greatly deteriorated, and NOx reduction cannot be sufficiently performed only by the catalytic denitration method. In such a case, if excess ammonia is sprayed by the ammonia spray section 33, the amount of ammonia that passes through the denitration catalyst 35 and flows out increases, and ammonia is wasted. Also, the ammonia that has flowed out causes problems such as an increase in deposits on the subsequent equipment. For example, when there is a large amount of effluent ammonia, there is a problem that a strong ammonia odor remains in the exhaust gas or fly ash, or the ammonium sulfate produced by the reaction of the effluent ammonia with sulfurous acid gas is condensed in the exhaust gas purification device 13. Problems such as clogging the filter cloth of the bug filter may occur.

  Therefore, as the reaction rate constant K decreases with the aging deterioration of the denitration catalyst 35, the spray amount of the ammonia spray portion 33 is decreased and the spray amount of the ammonia spray portion 31 is increased. As a result, when the NOx removal rate by the catalytic denitration method decreases due to the deterioration of the denitration catalyst 35 over time, the NOx removal rate by the non-catalytic denitration method is increased and compensated by increasing the spray amount of the ammonia spray part 31. A decrease in the NOx removal rate of the entire processing apparatus 30 can be suppressed. Further, by reducing the spray amount of the ammonia spray unit 33, waste of ammonia in the ammonia spray unit 33 can be reduced. Moreover, in the ammonia spraying part 33, excessive ammonia spraying exceeding the performance of the denitration catalyst 35 can be suppressed, and the ammonia flowing out to the subsequent stage can be reduced, so that the above-mentioned problems caused by the flowing out ammonia can be suppressed. Note that the NOx reduction performance of the non-catalytic denitration method in the ammonia spray section 31 is confirmed in advance by a trial operation or the like.

  As described above, according to the exhaust gas treatment device 30 of the boiler 1, when the performance degradation of the denitration catalyst 35 is small, the NOx reduction treatment is performed with a specific gravity placed on the catalytic denitration method that can efficiently use ammonia. Thus, the amount of ammonia to be sprayed can be reduced, and the operation cost can be reduced. In addition, even when the performance of the NOx removal catalyst 35 has progressed, the NOx reduction treatment is performed while shifting the specific gravity to the catalystless NOx removal method, so that the NOx regulation value can be achieved by compensating for the reduced performance of the catalyst removal NOx removal method. The operation of the boiler 1 can be continued.

  Further, since the reaction rate constant K that can be calculated from the operation data is used as an indicator of the performance deterioration degree of the denitration catalyst 35, the performance deterioration degree of the denitration catalyst 35 can be continuously detected during operation of the boiler 1. Therefore, for example, it is not necessary to carry out a sampling survey of the denitration catalyst 35, and the specific gravity of the catalytic denitration method and the non-catalytic fluorination method with good response at an optimum ratio according to the performance of the denitration catalyst 35 at each time point during operation. Can be optimally controlled.

  As a result of such an operation, in the denitration catalyst 35, it is possible to reduce the margin for installing a large amount in anticipation of performance deterioration, and it is possible to reduce the amount of the denitration catalyst 35 installed in the boiler 1, Equipment costs can be reduced. Moreover, the replacement period of the denitration catalyst 35 can be lengthened, and the continuous operation time of the boiler 1 can be lengthened.

  In addition to the above-described control, the boiler control unit 45 performs spray amount control for controlling the spray amount of the ammonia spray unit 31 or the spray amount of the ammonia spray unit 33 based on the NOx concentration of the exhaust gas in the line L15. The NOx concentration of the exhaust gas in the line L15 is measured by the densitometer 53. That is, the boiler control unit 45 operates the spray amount of the ammonia spray unit 31 or the spray amount of the ammonia spray unit 33 using the NOx concentration measurement value by the densitometer 53 as feedback, and controls the NOx concentration of the exhaust gas in the line L15 to NOx regulation. Control is performed to stabilize at a desired value less than the value.

  For example, when the NOx concentration measurement value of the densitometer 53 increases, the boiler control unit 45 increases the spray amount of the ammonia spray unit 31 or the spray amount of the ammonia spray unit 33, and the NOx concentration measurement value of the densitometer 53. Is reduced, the spray amount of the ammonia spray section 31 or the spray amount of the ammonia spray section 33 is decreased. According to such control, even when the NOx removal rate fluctuates due to some disturbance, the NOx removal rate of the entire apparatus 30 can be stabilized by adjusting the NOx removal rate of the non-catalytic denitration method or the catalytic denitration method. Thus, the NOx regulation value can be achieved. In this case, the boiler control unit 45 may operate either the spray amount of the ammonia spray unit 31 or the spray amount of the ammonia spray unit 33, or may operate both. Here, even if the spray amount of the ammonia spray part 33 is increased due to the deterioration of the denitration catalyst 35, it is considered that the improvement of the NOx removal rate is small. Therefore, it is particularly preferable to manipulate the spray amount of the ammonia spray section 31 here.

  The present invention is not limited to the embodiment described above. For example, the reducing agent sprayed from the spray units 31 and 33 is not limited to ammonia, and urea water may be used. Moreover, it is good also considering the reducing agent of the spraying part 31 and the reducing agent of the spraying part 33 as mutually different reducing agents. In the embodiment, the spray unit 31 is provided in the cyclone 7. However, the spray unit 31 may be provided in the furnace 3 to spray the reducing agent in the furnace 3. In short, what is necessary is just to provide the spray part 31 in the area | region of exhaust gas temperature 700-1100 degreeC. Similarly, the spray unit 33 and the denitration catalyst 35 may be installed at any position in the exhaust gas flow path as long as an area with an exhaust gas temperature of 200 to 400 ° C. is selected. For example, the spray unit 33 and the denitration catalyst 35 may be installed at the subsequent stage of the exhaust gas purification device 13.

  In the embodiment, the reaction rate constant K is calculated from the operation data. However, the reaction rate constant K and the performance deterioration degree of the denitration catalyst 35 are directly obtained by analyzing the catalyst activity by sampling the denitration catalyst 35. May be. Further, the present invention is not limited to application to a circulating fluidized bed boiler, but can also be applied to denitration treatment of exhaust gas in other types of combustion furnaces. For example, the present invention can be applied to an incinerator that does not generate power by heat exchange of exhaust gas.

  DESCRIPTION OF SYMBOLS 1 ... Circulating fluidized bed boiler (combustion furnace), 3 ... Furnace, 11 ... Back path (exhaust gas flow path), 30 ... Exhaust gas processing apparatus, 31 ... Ammonia spray part (non-catalytic denitration means), 33 ... Ammonia spray part (existence) Catalyst denitration means), 35... Denitration catalyst (catalyst denitration means), 45... Boiler control section (reaction rate constant detection means, spray control means).

Claims (5)

An exhaust gas treatment device for treating exhaust gas generated in a furnace of a combustion furnace,
Non-catalytic denitration means for spraying a reducing agent for non-catalytic denitration in the exhaust gas to reduce nitrogen oxides in the exhaust gas,
Catalytic denitration means for reducing a nitrogen oxide in the exhaust gas by spraying a reducing agent for catalytic denitration in the exhaust gas after the treatment by the non-catalytic denitration means and bringing the exhaust gas into contact with a denitration catalyst;
Reaction rate constant detecting means for detecting the reaction rate constant of the denitration catalyst as the performance deterioration degree of the denitration catalyst, the spray amount of the reducing agent for non-catalytic denitration, and the spray of the reducing agent for catalytic denitration And a spray control means for controlling the ratio of the amount based on the reaction rate constant detected by the reaction rate constant detection means ,
The spray control means increases the ratio of the spray amount of the reducing agent for non-catalytic denitration to the spray amount of the reducing agent for catalytic denitration as the reaction rate constant decreases with the aging of the denitration catalyst. An exhaust gas treatment apparatus characterized by: The reaction rate constant detecting means includes
The amount of the exhaust gas generated in the furnace;
A spray amount of the reducing agent for catalytic denitration,
The concentration of the reducing agent for catalytic denitration in the exhaust gas after contact with the denitration catalyst;
The concentration of nitrogen oxides in the exhaust gas after contact with the denitration catalyst;
The exhaust gas processing apparatus according to claim 1, wherein the reaction rate constant is calculated based on The spray control means further includes
Based on the concentration of nitrogen oxides in the exhaust gas after contact with the denitration catalyst,
The exhaust gas treatment apparatus according to claim 1 or 2 , wherein the spray amount of the reducing agent for non-catalytic denitration or the spray amount of the reducing agent for catalytic denitration is controlled. A furnace that burns fuel;
An exhaust gas passage for conveying and discharging exhaust gas generated in the furnace;
Non-catalytic denitration means for spraying a reducing agent for non-catalytic denitration in the exhaust gas to reduce nitrogen oxides in the exhaust gas,
A reducing agent for catalytic denitration is sprayed into the exhaust gas after being treated by the non-catalytic denitration means provided in the exhaust gas flow path, and the exhaust gas is brought into contact with the denitration catalyst to reduce nitrogen oxides in the exhaust gas. Catalytic denitration means,
Reaction rate constant detecting means for detecting the reaction rate constant of the denitration catalyst as the performance deterioration degree of the denitration catalyst, the spray amount of the reducing agent for non-catalytic denitration, and the spray of the reducing agent for catalytic denitration And a spray control means for controlling the ratio of the amount based on the reaction rate constant detected by the reaction rate constant detection means ,
The spray control means increases the ratio of the spray amount of the reducing agent for non-catalytic denitration to the spray amount of the reducing agent for catalytic denitration as the reaction rate constant decreases with the aging of the denitration catalyst. A combustion furnace characterized by. An exhaust gas treatment method for treating exhaust gas generated in a furnace of a combustion furnace,
A non-catalytic denitration step of spraying a reducing agent for non-catalytic denitration in the exhaust gas to reduce nitrogen oxides in the exhaust gas;
A catalytic denitration step of reducing a nitrogen oxide in the exhaust gas by spraying a reducing agent for catalytic denitration in the exhaust gas after the treatment by the non-catalytic denitration step and bringing the exhaust gas into contact with the denitration catalyst;
A reaction rate constant detecting step for detecting a reaction rate constant of the denitration catalyst as a performance deterioration degree of the denitration catalyst, and a spray amount of the reducing agent for the non-catalytic denitration and a spray of the reducing agent for the catalytic denitration A spray control step of controlling the ratio of the amount based on the reaction rate constant detected in the reaction rate constant detection step ,
In the spray control step, the ratio of the spray amount of the reducing agent for non-catalytic denitration to the spray amount of the reducing agent for catalytic denitration is increased as the reaction rate constant decreases with the aging of the denitration catalyst. An exhaust gas treatment method comprising:

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