JP2011106754A - Circulating fluidized bed furnace and method for controlling the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a circulating fluidized bed furnace obtaining excellent denitration performance of exhaust gas in a wide range of furnace load, and also to provide a method for controlling the same. <P>SOLUTION: A boiler 1 includes: a furnace 3 for burning fuel; a cyclone 7 for separating circulation material from the exhaust gas generated in the furnace 3 and returning the material to the furnace 3; a furnace spray nozzle 21 for spraying a reducing agent into the furnace 3 and deoxidizing nitrogen oxide in the exhaust gas; a cyclone spray nozzle 22 for spraying the reducing agent into the cyclone 7 and deoxidizing the nitrogen oxide in the exhaust gas; and a spray control part 25 for controlling a ratio of a spray amount of the reducing agent in the furnace spray nozzle 21 and a spray amount of the reducing agent in the cyclone spray nozzle 22, based on a boiler operation load value. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a circulating fluidized bed furnace and a method for controlling the circulating fluidized bed furnace.

  Conventionally, a combustion furnace described in Patent Document 1 below is known as a technique in such a field. This combustion furnace includes a furnace that burns fuel and a cyclone that separates particulate matter from exhaust gas generated in the furnace. In this combustion furnace, a NOx reducing agent is introduced into a cyclone to perform a denitration process, thereby reducing NOx in the exhaust gas.

Japanese Examined Patent Publication No. 6-18610

  However, when this combustion furnace is operated at a low load, the temperature of the cyclone is lowered, and the reaction temperature between the NOx reducing agent and NOx in the exhaust gas is lowered. In this case, the NOx reduction performance of the NOx reducing agent is lowered, and there is a possibility that the desired NOx reduction rate during high-load operation cannot be achieved. Therefore, such a denitration process has been difficult to apply when the load on the combustion furnace is low.

  Accordingly, an object of the present invention is to provide a circulating fluidized bed furnace capable of obtaining a good exhaust gas denitration performance in a wide furnace load range and a control method thereof.

  The circulating fluidized bed furnace of the present invention includes a furnace for burning fuel, a cyclone for separating circulating material from exhaust gas generated in the furnace and returning it to the furnace, and reducing nitrogen oxides in the exhaust gas by spraying a reducing agent into the furnace. Furnace spraying means, cyclone spraying means for spraying a reducing agent into the cyclone and reducing nitrogen oxides in the exhaust gas, and furnace spraying means based on the furnace temperature in the furnace, the cyclone temperature in the cyclone, or the furnace load Spray control means for controlling the ratio between the amount of spraying of the reducing agent and the amount of spraying of the reducing agent in the cyclone spraying means.

  This circulating fluidized bed furnace includes a furnace spraying means for spraying a reducing agent on the furnace and a cyclone spraying means for spraying the reducing agent on the cyclone. Since a swirl flow of exhaust gas is generated in the cyclone, the reducing agent sprayed on the cyclone is stirred by the swirl flow and diffuses well in the exhaust gas. Furthermore, in the cyclone, the residence time of the exhaust gas in which the reducing agent is diffused is also long. Therefore, the reaction between the reducing agent and the nitrogen oxide is likely to occur, and the denitration performance of the exhaust gas is easily obtained. However, during low-load operation, the cyclone temperature is lowered, so that the reaction temperature between the reducing agent sprayed on the cyclone and the nitrogen oxide is lowered, and the denitration performance is lowered. On the other hand, since the temperature of the furnace is higher than that of the cyclone, the reaction temperature between the reducing agent and the nitrogen oxide is high. Therefore, in the furnace, although the diffusibility and residence time of the reducing agent do not reach that of the cyclone, the reduction in the denitration performance is relatively small even during low load operation. Based on this knowledge, in the circulating fluidized bed furnace of the present invention, the ratio of the amount of the reducing agent sprayed to the furnace and cyclone is controlled according to the furnace load. By spraying a reducing agent with a specific gravity placed on a simple cyclone, it is possible to obtain a denitration performance by good stirring. Even when the furnace load is reduced, good denitration performance due to the reaction temperature can be maintained by shifting the specific gravity to the denitration treatment by the furnace spraying means. As a result, good denitration performance of exhaust gas can be obtained in a wide furnace load range.

  The circulating fluidized bed furnace of the present invention includes a first supply line for supplying a reducing agent to the furnace spraying means, a second supply line for supplying the reducing agent to the cyclone spraying means, and a reducing agent supply line branched into the second supply line. A first valve provided on the first supply line and a second valve provided on the second supply line, and the spray control means includes the opening degree of the first valve and the second valve. It is good also as adjusting the opening degree of a valve. According to this configuration, the spray control means can easily adjust the ratio of the spray amount between the furnace spraying means and the cyclone spraying means by adjusting the opening degree of the first and second valves.

  Moreover, it is preferable that the cyclone spray means has a higher diffusibility of the sprayed reducing agent than the furnace spray means. In the furnace, the circulating material flows violently, and there is a downflow of the circulating material in the vicinity of the wall surface of the furnace. Accordingly, the furnace spraying means sprays the reducing agent from the vicinity of the wall surface of the furnace to the inside, with relatively low diffusivity, so that the reducing agent reaches the center of the furnace without being greatly affected by the downflow. Can be made. Further, in the cyclone, there is a swirling flow of exhaust gas that flows horizontally in the cyclone. Accordingly, the cyclone spraying means sprays the reducing agent in a relatively diffusive state from the vicinity of the cyclone wall surface to the inside, whereby the exhaust gas and the reducing agent are well stirred by the swirling flow of the exhaust gas.

  Further, the spray control means sets the ratio of the reducing agent spray amount in the furnace spray means to the reducing agent spray amount in the cyclone spray means to 0: 100 when the furnace load is a predetermined threshold value or more, and the furnace load is predetermined. If it is less than the threshold value, the ratio of the spray amount of the reducing agent in the furnace spraying means to the spray amount of the reducing agent in the cyclone spraying means may be set to 100: 0.

  The cyclone spraying means comprises a cyclone internal spraying means for spraying a reducing agent inside the cyclone, and a cyclone inlet spraying means for spraying a reducing agent at the inlet of the cyclone, and the spray control means is a furnace temperature of the furnace, Based on the cyclone temperature of the cyclone or the furnace load, the ratio between the spray amount of the reducing agent in the cyclone internal spraying means and the spray amount of the reducing agent in the cyclone inlet spraying means may be controlled. Since the exhaust gas temperature, diffusivity, and residence time are different between the inside of the cyclone and the cyclone inlet, further appropriate control can be performed by adjusting the spray amount according to the exhaust gas temperature, diffusibility, and residence time.

  The circulating fluidized bed furnace control method of the present invention is a circulating fluidized bed furnace control method comprising: a furnace that burns fuel; and a cyclone that separates the circulating material from exhaust gas generated in the furnace and returns it to the furnace. A furnace spraying step of spraying a reducing agent into the furnace to reduce nitrogen oxides in the exhaust gas, a cyclone spraying step of spraying a reducing agent into the cyclone to reduce nitrogen oxides in the exhaust gas, A spray control step for controlling the ratio of the reducing agent spray amount in the furnace spraying step and the reducing agent spray amount in the cyclone spraying step based on the furnace temperature, the cyclone temperature in the cyclone, or the furnace load. It is characterized by.

  This control method includes a furnace spraying step of spraying a reducing agent on the furnace and a cyclone spraying step of spraying the reducing agent on the cyclone. Since a swirl flow of exhaust gas is generated in the cyclone, the reducing agent sprayed on the cyclone is stirred by the swirl flow and diffuses well in the exhaust gas. Furthermore, in the cyclone, the residence time of the exhaust gas in which the reducing agent is diffused is also long. Therefore, the reaction between the reducing agent and the nitrogen oxide is likely to occur, and the denitration performance of the exhaust gas is easily obtained. However, during low-load operation, the cyclone temperature is lowered, so that the reaction temperature between the reducing agent sprayed on the cyclone and the nitrogen oxide is lowered, and the denitration performance is lowered. On the other hand, since the temperature of the furnace is higher than that of the cyclone, the reaction temperature between the reducing agent and the nitrogen oxide is high. Therefore, in the furnace, although the diffusibility and residence time of the reducing agent do not reach that of the cyclone, the reduction in the denitration performance is relatively small even during low load operation. Based on this knowledge, in the control method of the present invention, the ratio of the spray amount of the reducing agent to the furnace and the cyclone is controlled according to the furnace load. Therefore, when the furnace load is high, the cyclone has good diffusivity and residence time. By spraying the reducing agent with a specific gravity, it is possible to obtain denitration performance by good stirring. Even when the furnace load is reduced, good denitration performance due to the reaction temperature can be maintained by shifting the specific gravity to the denitration treatment by the furnace spraying means. As a result, good denitration performance of exhaust gas can be obtained in a wide furnace load range.

  According to the circulating fluidized bed furnace of the present invention, it is possible to provide a circulating fluidized bed furnace and a control method therefor that can obtain good exhaust gas denitration performance in a wide range of furnace loads.

It is a figure which shows the boiler which concerns on 1st Embodiment of the circulating fluidized bed furnace of this invention. It is a graph which shows the relationship between the operating load value of the boiler of FIG. 1, and the temperature of each part of a boiler. It is a flowchart which shows the process by the spray control part of the boiler of FIG. It is sectional drawing which shows the furnace spray nozzle and cyclone spray nozzle of the boiler of FIG. (A) is a top view of a furnace and a cyclone, (b) is the side view, and is a figure which shows the attachment range of the furnace spray nozzle and cyclone spray nozzle of FIG. It is a figure which shows the spray shape of a furnace spray nozzle and a cyclone spray nozzle. It is a figure which shows the boiler which concerns on 2nd Embodiment of the circulating fluidized bed furnace of this invention. It is a flowchart which shows the process by the spray control part of the boiler of FIG.

  Hereinafter, preferred embodiments of a circulating fluidized bed furnace according to the present invention will be described in detail with reference to the drawings.

(First embodiment)
FIG. 1 shows a boiler 1 which is an embodiment of a circulating fluidized bed 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, a cyclone classifier, or a cyclone separator, and functions as a solid-gas separator. 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. In order to recover the heat of the exhaust gas for power generation, the back path 11 is provided with a heat recovery unit 17. The heat recovery unit 17 has a boiler tube that crosses the flow path of the exhaust gas, and water, steam, and air flow in 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, steam and air in the tube, and the generated high-temperature steam is sent to the power generation turbine through the boiler tube. It is done.

  The exhaust gas discharged from the lower portion of the back path 11 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.

For the exhaust gas discharged from the chimney 15 of the boiler 1, it is necessary to suppress the concentration of nitrogen oxide (NOx), which is an air pollutant, to a regulated value or less in accordance with exhaust gas regulations such as laws and regulations. Therefore, in this boiler 1, in the region where the exhaust gas temperature is 700 to 1100 ° C., a reducing agent such as urea water or ammonia water is sprayed into the exhaust gas to react with NOx, and the N component of NOx is changed to nitrogen gas. Thus, exhaust gas treatment that reduces the NOx concentration in the exhaust gas is employed. An example of the reaction between ammonia and NOx at this time is as follows.
4NO + 4NH ₃ + O ₂ → 4N ₂ + 6H ₂ O ... Reaction formula (1)
At this time, ammonia itself is also partially decomposed as follows.
4NH ₃ + 3O ₂ → 2N ₂ + 6H ₂ O ... Reaction formula (2)
Ammonia that has not been consumed in the reaction with NOx according to the reaction formula (1) and has not been decomposed according to the reaction formula (2) flows out to the subsequent stage as leaked ammonia. As the reducing agent to be sprayed, urea water may be used instead of ammonia gas or ammonia water. In this case, ammonia is generated from urea according to the following reaction formula (3).
(NH ₃ ) ₂ CO → 2NH ₃ + CO ... Reaction formula (3)

  Specifically, the boiler 1 includes a furnace spray nozzle 21 that sprays a reducing agent into the furnace 3, and a cyclone spray nozzle 22 that sprays the reducing agent into the cyclone 7. By spraying the reducing agent into the furnace 3 from the furnace spray nozzle 21, NOx in the exhaust gas is reduced by the reducing agent and reduced (furnace spraying process). Further, by spraying a reducing agent from the cyclone spray nozzle 22 into the cyclone 7, NOx in the exhaust gas is reduced by the reducing agent and reduced (cyclone spraying step).

  Further, the boiler 1 includes a reducing agent supply line L20 that supplies the reducing agent by pumping or the like. The reducing agent supply line L20 is separated into two paths: a first supply line L21 that supplies the reducing agent to the furnace spray nozzle 21 and a second supply line L22 that supplies the reducing agent to the cyclone spray nozzle 22. An open / close valve V20 is provided on the reducing agent supply line L20, an open / close valve (first valve) V21 is provided on the first supply line L21, and an open / close valve (second valve) is provided on the second supply line L22. V22 is provided.

  Furthermore, the boiler 1 includes a spray control unit 25 that controls the spray amount in the furnace spray nozzle 21 and the cyclone spray nozzle 22 by adjusting the opening degree of the first valve V21 and the second valve V22. The spray control unit 25 is configured by, for example, a computer. Various data (referred to as “operation data”) relating to the operation of the boiler 1 are collected in the spray control unit 25. The operation data includes the boiler operation load value (furnace load), the furnace temperature (temperature in the furnace 3), the cyclone temperature (inside the cyclone 7), which is input by the user from the control information input unit 27 or controlled by a computer or the like. And the NOx concentration of the exhaust gas passing through the chimney 15 are at least included.

  In order to obtain the operation data, the boiler 1 includes a furnace temperature measuring unit 31 that measures the furnace temperature, a cyclone temperature measuring unit 33 that measures the cyclone temperature, and a concentration meter that detects the NOx concentration of the exhaust gas passing through the chimney 15. 35. As the furnace temperature measuring unit 31, for example, a thermometer installed near the outlet 3 b of the furnace 3 and measuring the furnace outlet temperature, or a thermometer installed below the furnace 3 and measuring the furnace lower temperature is used. Moreover, as the cyclone temperature measurement part 33, the thermometer which installs in the cyclone discharge port 7b and measures the cyclone exit temperature is used, for example.

  The boiler operation load value from the control information input unit 27 and the measured values of the furnace temperature measurement unit 31, the cyclone temperature measurement unit 33, and the concentration meter 35 are transmitted to the spray control unit 25 as electrical signals. The boiler operating load value can also be obtained from the amount of fuel input to the boiler 1 with respect to the rated conditions, the amount of steam generated from the boiler 1, or the feed water flow rate to the boiler 1.

  In the cyclone 7 provided with the cyclone spray nozzle 22, a swirling flow of exhaust gas is generated as described above. Therefore, the reducing agent sprayed from the cyclone spray nozzle 22 is stirred by the swirling flow in the cyclone 7 and diffused well in the exhaust gas. To do. Further, in the cyclone 7, the residence time of the exhaust gas in which the reducing agent is diffused is long. Accordingly, the reaction between the reducing agent and NOx is likely to occur, and the denitration performance of the exhaust gas is easily obtained.

  Here, FIG. 2 is a graph showing the relationship between the boiler operating load value, the furnace temperature T1, the cyclone temperature T2, and the cyclone inlet temperature T3 (the temperature of the cyclone inlet 7a). As shown in FIG. 2, the furnace temperature T <b> 1 and the cyclone temperature T <b> 2 substantially correspond to the boiler operation load value on a one-to-one basis. Therefore, during low-load operation of the boiler 1, the cyclone temperature is lowered, the reaction temperature between the reducing agent sprayed on the cyclone 7 and NOx is lowered, and the denitration performance is lowered. In order for the reaction shown in the above reaction formula (1) to occur satisfactorily, the exhaust gas temperature in the region where the reducing agent is sprayed needs to be 700 to 1100 ° C. When the boiler operation load value is low, The cyclone temperature may be less than 700 ° C. For example, according to FIG. 2, it can be seen that when the boiler operation load value is less than about 65%, the cyclone temperature becomes less than 700 ° C. In this case, since the reactivity between the reducing agent and NOx is low, the NOx removal rate is reduced, and ammonia flowing out to the subsequent stage without reacting with NOx is increased.

  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.

  On the other hand, since the temperature of the furnace 3 is higher than that of the cyclone 7, the reaction temperature between the reducing agent and NOx is high, and the above-described preferable exhaust gas temperature (700 to 1100 ° C.) is easily maintained. Therefore, although the diffusibility and residence time of the reducing agent do not reach that of the cyclone, the decrease in the denitration performance is relatively small even during low load operation.

  Based on such knowledge, the spray control unit 25 adjusts the opening degree of the first valve V21 and the second valve V22 based on the boiler operation load value, and thereby the spray amount of the furnace spray nozzle 21 and the cyclone spray nozzle. The ratio with the spray amount of 22 is controlled.

  Specifically, as shown in FIG. 3, the spray control unit 25 first acquires the boiler operation load value from the control information input unit 27 (S101), and the magnitude of the boiler operation load value and a predetermined threshold value is determined. Comparison is performed (S103). Here, the threshold value is 75%. And when the acquired boiler driving | running load value is 75% or more, the spray control part 25 opens the 2nd valve V22 (the opening degree is set to 100%), and closes the 1st valve V21 (the opening degree is set to 0%). ). In this case, the ratio of the reducing agent spray amount in the furnace spray nozzle 21 to the reducing agent spray amount in the cyclone spray nozzle 22 is 0: 100 (S105). On the other hand, when the boiler operation load value is less than 75%, the first valve V21 is opened (opening degree is 100%), and the second valve V22 is closed (opening degree is 0%). In this case, the ratio of the reducing agent spray amount in the furnace spray nozzle 21 to the reducing agent spray amount in the cyclone spray nozzle 22 is 100: 0 (S107). During the operation of the boiler 1, the spray control unit 25 repeats the processes of S101 to S107.

  In short, the spray control unit 25 switches the spray position of the reducing agent to the cyclone 7 when the boiler operation load value becomes 75% or more, and when the boiler operation load value becomes less than 75%, The spray position is switched to the furnace 3. With this control, the exhaust gas temperature at the spray position of the reducing agent can be set to a preferable temperature of 700 to 1100 ° C. even when the boiler operation load value is 75% or more and less.

  Moreover, by the said control, at the time of the high load driving | operation whose boiler operation load value is 75% or more, a reducing agent is sprayed in the cyclone 7 whose diffusibility and residence time of a reducing agent is favorable and reaction temperature is appropriate. Therefore, there are few reducing agents to be sprayed, and there are also few reducing agents (flowing ammonia etc.) which flow out to the latter stage. On the other hand, at the time of low load operation where the boiler operation load value is less than 75%, the reducing agent is sprayed into the higher-temperature furnace 3 instead of the cyclone 7 whose temperature has decreased. In the furnace 3, although the diffusibility / retention time of the reducing agent does not reach the cyclone 7, an appropriate reaction temperature is maintained and good denitration performance can be maintained. Therefore, also in this case, the reducing agent to be sprayed is small, and the reducing agent flowing out to the subsequent stage is also small.

  As a result, good exhaust gas denitration performance can be obtained in a wide range of boiler operating loads.

  Note that, as described above, the furnace temperature and the cyclone temperature substantially correspond to the boiler operation load value on a one-to-one basis, and therefore, the furnace temperature and the cyclone temperature may be used as the determination criteria for switching the spray position instead of the boiler operation load value. . Even with such a criterion, the same effect as the control using the boiler operation load value as the criterion as described above can be obtained.

  Specifically, when adjusting the first and second valves V21 and V22 based on the furnace temperature, the spray control unit 25 determines that the furnace temperature acquired from the furnace temperature measurement unit 31 has a predetermined threshold (for example, 750). In the case of (° C.) or higher, the second valve V22 is opened and the first valve V21 is closed. And when the furnace temperature acquired from the furnace temperature measurement part 31 is less than the said threshold value, the spray control part 25 opens the 1st valve V21 and closes the 2nd valve V22.

  Moreover, when adjusting 1st and 2nd valve | bulb V21, V22 based on cyclone temperature, as for the spray control part 25, the cyclone temperature acquired from the cyclone temperature measurement part 33 is more than predetermined threshold (for example, 750 degreeC). In this case, the second valve V22 is opened and the first valve V21 is closed. And the spray control part 25 opens the 1st valve V21 and the 2nd valve V22, when the cyclone temperature acquired from the cyclone temperature measurement part 33 is less than the said threshold value. In this configuration using the cyclone temperature as a criterion, the reduction of the reaction temperature of the reducing agent in the cyclone 7 is directly reflected and the reducing agent spraying position is switched to the furnace 3, so that the reducing agent spraying position can be accurately selected. Is preferable.

  Next, details of the furnace spray nozzle 21 and the cyclone spray nozzle 22 will be described.

  As shown in FIG. 4 (a), the furnace spray nozzle 21 is provided in the furnace water cooling wall 3Z that defines the furnace 3, and the leading end of the furnace water cooling wall 3Z penetrates the furnace water cooling wall 3Z. It is installed to reach. Similarly, the cyclone spray nozzle 22 is provided in the refractory wall 7Z of the cyclone 7, and the tip of the cyclone spray nozzle 22 passes through the refractory wall 7Z so that the reducing agent reaches the inside of the cyclone 7. Here, when a high concentration reducing agent is introduced into the high-temperature furnace 3 or the cyclone 7, the reducing agent may be deposited at the nozzle tip and the nozzle may be clogged. Therefore, from the furnace spray nozzle 21 and the cyclone spray nozzle 22, It is necessary to spray the diluted reducing agent.

  Therefore, the furnace spray nozzle 21 sprays diluted urea water or diluted ammonia water supplied from the first supply line L21 toward the center of the furnace 3 from the tip. 4B, undiluted urea water or ammonia water is supplied to the furnace spray nozzle 21 from the first supply line L21, and diluted water is supplied to the furnace spray nozzle 21 from another line L31. By supplying, diluted urea water or diluted ammonia water may be sprayed from the tip of the furnace spray nozzle 21. Moreover, as shown in FIG.4 (c), diluted urea water or diluted ammonia water is supplied to the furnace spray nozzle 21 from the 1st supply line L21, and spray air is supplied to the furnace spray nozzle 21 from another line L41. Thus, the diluted urea water or diluted ammonia water may be sprayed by two-fluid spraying.

  Similarly, as shown in FIG. 4A, the cyclone spray nozzle 22 sprays the diluted urea water or diluted ammonia water supplied from the second supply line L22 from the tip toward the center of the cyclone 7. . Note that the cyclone spray nozzle 22 can be modified into the configuration shown in FIGS. 4B and 4C in the same manner as the furnace spray nozzle 21.

  Further, the furnace spray nozzle 21 may be provided at any position in the nozzle attachment range 53 indicated by the hatched portion in FIGS. 5A and 5B in the furnace water cooling wall 3Z of the furnace 3. Further, the cyclone spray nozzle 22 may be provided at any position in the nozzle attachment range 57 indicated by the shaded portion in FIGS. 5A and 5B in the refractory wall 7Z of the cyclone 7. Moreover, the cyclone spray nozzle 22 may be provided in the refractory wall 7Z corresponding to the cyclone inlet 7a. The cyclone inlet 7a is an exhaust gas flow path that connects the furnace 3 and the inside of the cyclone 7, and the exhaust gas flowing from the furnace 3 toward the inside of the cyclone 7 is generated at the cyclone inlet 7a.

  Further, as shown in FIG. 6A, the circulating material is vigorously flowing in the furnace 3, and the downflow of particles of the circulating material exists in the vicinity of the wall surface of the furnace water cooling wall 3Z. Accordingly, the furnace spray nozzle 21 sprays the reducing agent in a spray shape with a narrow diffusion angle and a strong penetration force. For example, the furnace spray nozzle 21 sprays the reducing agent in a conical spray shape. In this way, by spraying the reducing agent from the furnace spray nozzle 21 with high directivity / straightness and low diffusivity, the reducing agent reaches the center of the furnace 3 without being greatly affected by the downflow. The exhaust gas and the reducing agent can be mixed well in the furnace 3. In order to increase the penetration force by narrowing the diffusion angle of the reducing agent spray, the configuration of the one-fluid spray that supplies the reducing agent diluted in advance from the supply line L21 (configuration in FIG. 4A) is preferable.

  On the other hand, in the cyclone 7, there is a swirling flow of exhaust gas that flows horizontally in the cyclone 7. Therefore, as shown in FIG. 6B, the cyclone spray nozzle 22 sprays the reducing agent in a spray shape having a higher diffusibility than the furnace spray nozzle 21. For example, the cyclone spray nozzle 22 sprays the reducing agent in a spray shape with an elliptical cross section that is vertically long (fan spray). The vertical diffusion angle β of the spray shape is made larger than the diffusion angle of the furnace spray nozzle 21. Thus, by spraying the reducing agent from the cyclone spray nozzle 22 in a relatively diffusive state, the exhaust gas and the reducing agent are well stirred by the swirling flow of the exhaust gas. The diffusion angle β of the cyclone spray nozzle 22 is adjusted to a size that does not adhere to the opening edge portion 7B of the refractory wall 7Z.

  Consider a case where a cyclone spray nozzle 22 is provided on the refractory wall 7Z of the inlet 7a of the cyclone 7. In this case, as shown in FIG.6 (c), since the exhaust gas flow path of the inlet 7a is narrow and the distance from the cyclone spray nozzle 22 to the refractory wall 7Z which faces is small, the fire resistance which the sprayed reducing agent faces is small. It is easy to adhere to the object wall 7Z. Therefore, when the cyclone spray nozzle 22 is provided at the inlet 7a, it is preferable to have a spray shape in which the spray droplet diameter becomes finer than when the cyclone spray nozzle 22 is provided at another position of the cyclone 7. . By making the spray droplet diameter fine, the possibility of the sprayed reducing agent adhering to the refractory wall 7Z facing each other can be reduced. As described above, in order to make the spray droplet diameter fine, a configuration in which the two-fluid spray is formed by introducing the spray air into the cyclone spray nozzle 22 through the line L41 different from the second supply line L22 (FIG. 4). The configuration (c) is preferable. In this case, the cyclone spray nozzle 22 sprays the reducing agent in a conical spray shape, for example.

  In addition to the above-described control, the spray control unit 25 further controls the opening degree of the valve V20 based on the NOx concentration of the exhaust gas obtained by the concentration meter 35. That is, the spray control unit 25 operates the spray amount of the furnace spray nozzle 21 or the spray amount of the cyclone spray nozzle 22 using the NOx concentration measurement value by the densitometer 35 as feedback, and controls the NOx concentration of the exhaust gas of the chimney 15 to the NOx restriction. Control is performed to stabilize at a desired value less than the value.

  For example, when the NOx concentration measurement value of the densitometer 35 increases, the spray control unit 25 increases the opening amount of the valve V20 to increase the spray amount of the furnace spray nozzle 21 or the spray amount of the cyclone spray nozzle 22. When the NOx concentration measurement value of the densitometer 35 decreases, the spray amount of the furnace spray nozzle 21 or the spray amount of the cyclone spray nozzle 22 is decreased. According to such control, even when the NOx removal rate fluctuates due to some disturbance, the NOx removal rate is adjusted by adjusting the NOx removal rate by the furnace spray nozzle 21 or the cyclone spray unit, and the NOx regulation value is set. Can be achieved.

  Note that the switching of the valves V20, V21, and V22 may be automatically performed by the spray control unit 25 including a computer as described above, or may be manually performed.

(Second Embodiment)
A CFB boiler 101 shown in FIG. 7 further includes a cyclone inlet spray nozzle 23 that sprays a reducing agent on the cyclone inlet 7a in addition to the configuration of the CFB boiler 1. And the reducing agent supply line L20 of the boiler 101 is branched into three of the first supply line L21 to the third supply line L23, and the third supply line L23 supplies the reducing agent to the cyclone inlet spray nozzle 23. . An open / close valve (third valve) V23 is provided on the third supply line L23. Since the cyclone inlet spray nozzle 23 is provided at the cyclone inlet 7a, it is preferable to have a spray shape in which the spray droplet diameter becomes fine as described above, and the spray air is introduced into the cyclone inlet spray nozzle 23. Therefore, a configuration in which the two-fluid spray is used (see the configuration in FIG. 4C) is preferable. Note that, in the boiler 101, the same or equivalent components as those of the above-described boiler 1 are denoted by the same reference numerals in the drawings, and redundant description is omitted.

  As shown in FIG. 2, the temperature T3 of the cyclone inlet 7a is higher than the cyclone temperature T2 and lower than the furnace temperature T1. When the boiler operating load value falls below about 40%, the temperature T3 of the cyclone inlet 7a becomes less than 700 ° C. In addition, since the flow of exhaust gas from the furnace 3 toward the inside of the cyclone 7 is generated at the cyclone inlet 7a, when the reducing agent is sprayed, it diffuses into the exhaust gas to some extent. Although the diffusibility of the reducing agent does not reach the cyclone 7, it is better than the furnace 3. Thus, since the cyclone inlet 7a has an intermediate property between the furnace 3 and the cyclone 7 as the reducing agent spraying position, the cyclone inlet 7a is additionally set as the reducing agent spraying position.

  That is, the spray control part 25 of the boiler 101 adjusts the opening degree of the 1st valve V21, the 2nd valve V22, and the 3rd valve V23 based on the boiler operation load value, and the spray amount of the furnace spray nozzle 21 The ratio of the spray amount of the cyclone spray nozzle (cyclone internal spray means) 22 and the spray amount of the cyclone inlet spray nozzle (cyclone inlet spray means) 23 is controlled.

  Specifically, as shown in FIG. 8, the spray control unit 125 first acquires the boiler operation load value from the control information input unit 27 (S201), and the boiler operation load value and two predetermined threshold values. Are compared (S203). Here, the first threshold is 50%, and the second threshold is 75%. And when the acquired boiler operation load value is 75% (2nd threshold value) or more, the spray control part 125 opens the 2nd valve V22 (it is set as 100% of opening degree), the 1st valve V21 and the 3rd valve V23 is closed (the opening degree is 0%). In this case, the ratio of the reducing agent spray amount in the furnace spray nozzle 21, the cyclone spray nozzle 22, and the cyclone inlet spray nozzle 23 is 0: 100: 0 (S205).

  When the boiler operation load value is 50% (first threshold) or more and less than 75% (second threshold), the spray control unit 125 opens the third valve V23 (with an opening degree of 100%), The first valve V21 and the second valve V22 are closed (the opening degree is 0%). In this case, the ratio of the reducing agent spray amount in the furnace spray nozzle 21, the cyclone spray nozzle 22, and the cyclone inlet spray nozzle 23 is 0: 0: 100 (S207). When the boiler operation load value is less than 50% (first threshold), the spray control unit 125 opens the first valve V21 (with an opening degree of 100%), and opens the third valve V23 and the second valve V22. Close (open 0%). In this case, the ratio of the reducing agent spray amount in the furnace spray nozzle 21, the cyclone spray nozzle 22, and the cyclone inlet spray nozzle 23 is 100: 0: 0 (S209). During the operation of the boiler 101, the spray control unit 125 repeats the processes of S201 to S109.

  In short, the spray control unit 125 switches the spray position of the reducing agent to the inside of the cyclone 7 when the boiler operation load value becomes 75% (second threshold) or more, and the boiler operation load value is 50% (first threshold). ) When it is more than 75% (second threshold), the reducing agent spraying position is switched to the cyclone inlet 7a, and when the boiler operating load value is less than 50% (first threshold), the reducing agent. Is switched to the furnace 3.

  According to this boiler 101, by adding the cyclone inlet 7a as described above as the spray position of the reducing agent and switching the spray position to three stages, the spray position of the reducing agent can be selected more appropriately, which is favorable. Denitration performance can be obtained.

  In the boiler 101 as well, the furnace temperature and the cyclone temperature may be used as the determination criteria for switching the spray position instead of the boiler operation load value.

  The present invention is not limited to the embodiment described above. For example, the reducing agent for the furnace spray nozzle 21 and the reducing agent for the cyclone spray nozzle 22 may be different from each other. In the embodiment, the present invention is not limited to application to a boiler, but can also be applied to denitration treatment of exhaust gas in other types of combustion furnaces. For example, the present invention is also applicable to a circulating fluidized bed incinerator that does not generate power by heat exchange of exhaust gas.

  DESCRIPTION OF SYMBOLS 1,101 ... CFB boiler (circulation fluidized bed furnace), 3 ... Furnace, 7 ... Cyclone, 21 ... Furnace spray nozzle (furnace spray means), 22 ... Cyclone spray nozzle (cyclone spray means, cyclone internal spray means), 23 ... Cyclone inlet spray nozzle (cyclone spraying means, cyclone inlet spraying means), 25 ... spray control unit (spray control means), L21 ... first supply line, L22 ... second supply line, V21 ... first valve, V22 ... second valve.

Claims (6)

A furnace that burns fuel;
A cyclone separating the circulating material from the exhaust gas generated in the furnace and returning it to the furnace;
A furnace spraying means for spraying a reducing agent into the furnace and reducing nitrogen oxides in the exhaust gas,
A cyclone spraying means for spraying a reducing agent into the cyclone and reducing nitrogen oxides in the exhaust gas;
Spray control means for controlling the ratio of the reducing agent spray amount in the furnace spraying means and the reducing agent spray amount in the cyclone spraying means based on the furnace temperature of the furnace, the cyclone temperature of the cyclone, or the furnace load; A circulating fluidized bed furnace comprising: A reducing agent supply line branched into a first supply line for supplying a reducing agent to the furnace spraying means and a second supply line for supplying a reducing agent to the cyclone spraying means;
A first valve provided on the first supply line;
A second valve provided on the second supply line,
The spray control means includes
The circulating fluidized bed furnace according to claim 1, wherein the opening degree of the first valve and the opening degree of the second valve are adjusted. The cyclone spray means is more preferable than the furnace spray means.
The circulating fluidized bed furnace according to claim 1 or 2, wherein the sprayed reducing agent has high diffusibility. The spray control means includes
When the furnace load is equal to or greater than a predetermined threshold, the ratio of the reducing agent spray amount in the furnace spraying means and the reducing agent spray amount in the cyclone spraying means is 0: 100,
The ratio of the reducing agent spray amount in the furnace spraying means to the reducing agent spray amount in the cyclone spraying means is set to 100: 0 when the furnace load is less than a predetermined threshold. The circulating fluidized bed furnace according to any one of?
The cyclone spraying means is
A cyclone internal spraying means for spraying the reducing agent into the cyclone;
A cyclone inlet spraying means for spraying the reducing agent on the inlet of the cyclone,
The spray control means includes
Based on the furnace temperature of the furnace, the cyclone temperature of the cyclone, or the furnace load, the ratio of the spray amount of the reducing agent in the cyclone internal spray means and the spray amount of the reducing agent in the cyclone inlet spray means is further controlled. The circulating fluidized bed furnace according to any one of claims 1 to 4, wherein the circulating fluidized bed furnace is provided. A furnace that burns fuel;
A cyclone separating a circulating material from exhaust gas generated in the furnace and returning it to the furnace, and a control method for a circulating fluidized bed furnace,
A furnace spraying step of spraying a reducing agent into the furnace and reducing nitrogen oxides in the exhaust gas;
A cyclone spraying step of spraying a reducing agent into the cyclone and reducing nitrogen oxides in the exhaust gas;
A spray control step of controlling a ratio of a reducing agent spray amount in the furnace spraying step and a reducing agent spray amount in the cyclone spraying step based on a furnace temperature of the furnace, a cyclone temperature of the cyclone, or a furnace load; A method for controlling a circulating fluidized bed furnace, comprising:

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