JP2012181003A - Boiler device and high temperature air combustion system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a boiler device and a high temperature air combustion system for high temperature air combustion capable of shortening a time the high temperature air combustion becomes possible in the boiler and the operation from starting the boiler to reaching the high temperature air combustion can be smoothly carried out.SOLUTION: The boiler device has a boiler 1, a pulverized coal nozzle 4 arranged in the furnace wall of the boiler and discharging pulverized coal, air nozzles 5 arranged adjacent to the pulverized coal nozzle discharging the secondary air, a heat exchanger 2 raising the temperature of the secondary air fed to the air nozzles 5 by the heat exchanging with the exhausted gas of the boiler, and a duct burner 21 raising the temperature of the secondary air by carrying out combustion in the supplying channel 18 of the secondary air, the high temperature air combustion is carried out with the secondary air discharged from the air nozzles 5 and the pulverized coal discharged from the pulverized coal nozzle 4.

Description

  The present invention relates to a boiler apparatus and a high-temperature air combustion system that perform high-temperature air combustion.

  There is a high-temperature air combustion type boiler apparatus (hereinafter referred to as a high-temperature air combustion boiler apparatus) in which high-temperature combustion air is supplied by an air nozzle separated from fuel and the fuel is injected into a furnace in a high-temperature state and burned. In the high-temperature air-fired boiler device, the furnace can be heated to a high temperature, so that the furnace can be downsized, and combustion can be performed in a reducing atmosphere with a low oxygen concentration, thereby suppressing the generation of nitrogen oxides. There is an advantage that can be.

  On the other hand, it is desired that the high-temperature air combustion boiler apparatus smoothly performs the operation from the boiler start to the high-temperature air combustion.

  In addition, as a boiler apparatus which carries out high temperature air combustion, there exists what is shown by patent document 1, and patent document 1 extracts a part of combustion exhaust gas from a furnace, and finely pulverizes combustion air with the extracted combustion exhaust gas. A boiler device that generates high-temperature combustion air by heating to a temperature equal to or higher than the ignition temperature of charcoal is disclosed.

JP 2005-265300 A

  In view of such circumstances, the present invention shortens the time until the boiler can realize high-temperature air combustion, and can perform a high-temperature air combustion boiler apparatus and a high-temperature combustion apparatus that can smoothly perform operations from boiler startup to high-temperature air combustion. An air combustion system is provided.

  The present invention includes a boiler, a pulverized coal nozzle that is provided on a furnace wall of the boiler and ejects pulverized coal, an air nozzle that is provided adjacent to the pulverized coal nozzle and ejects secondary air, and exhaust gas of the boiler A heat exchanger that raises the temperature of the secondary air supplied to the air nozzle by heat exchange with the duct, and a duct burner that burns in the supply path of the secondary air and raises the temperature of the secondary air. The present invention relates to a boiler device that performs high-temperature air combustion using secondary air ejected from the air nozzle and pulverized coal ejected from the pulverized coal nozzle.

  The present invention further includes a temperature detector for detecting the temperature of the secondary air supplied to the air nozzle, and a control device for controlling the combustion amount of the duct burner based on the detection result of the temperature detector. It concerns a boiler device.

  Further, the present invention provides a boiler, a burner provided on the furnace wall of the boiler, which performs high-temperature air combustion with pulverized coal and high-temperature secondary air, and the secondary air for combustion by heat exchange with the exhaust gas of the boiler. A heat exchanger that raises the temperature, a duct burner that burns in the supply path of the secondary air and raises the temperature of the secondary air, an exhaust circulation system that extracts a part of the exhaust gas and mixes it with the secondary air, A first temperature detector for detecting the temperature of the secondary air supplied to the burner; and a controller for controlling the combustion of the duct burner and for controlling the amount of exhaust gas to be mixed. The high-temperature air combustion system controls the amount of combustion of the duct burner and the amount of exhaust gas mixed into the secondary air so that the temperature of the secondary air detected by the temperature detector 1 becomes a predetermined value. .

  Furthermore, the present invention further comprises a second temperature detector for detecting the temperature of the exhaust gas and a third temperature detector for detecting the temperature of the secondary air heated by the heat exchanger, Is related to a high-temperature air combustion system for controlling the amount of combustion of the duct burner and the amount of exhaust gas mixed into the secondary air based on the detection results of the second temperature detector and the third temperature detector.

  According to the present invention, a boiler, a pulverized coal nozzle that is provided on a furnace wall of the boiler and ejects pulverized coal, an air nozzle that is provided adjacent to the pulverized coal nozzle and ejects secondary air, and the boiler A heat exchanger that raises the temperature of the secondary air that is fed to the air nozzle by heat exchange with the exhaust gas, and a duct burner that burns in the supply path of the secondary air and raises the temperature of the secondary air Since the high-temperature air combustion is performed by the secondary air ejected from the air nozzle and the pulverized coal ejected from the pulverized coal nozzle, the temperature of the exhaust gas is low, and the temperature of the secondary air is sufficiently increased by the heat exchanger. Even if this is not possible, high-temperature air combustion can be realized, the time until high-temperature air combustion can be realized can be shortened, and the operation from the start of the boiler to high-temperature air combustion can be performed smoothly. That.

  According to the present invention, a boiler, a burner provided on the furnace wall of the boiler, which performs high-temperature air combustion with pulverized coal and high-temperature secondary air, and a secondary for combustion by heat exchange with the exhaust gas of the boiler A heat exchanger that raises the temperature of the air, a duct burner that burns in the supply path of the secondary air and raises the temperature of the secondary air, and an exhaust circulation system that extracts a part of the exhaust gas and mixes it with the secondary air A first temperature detector for detecting the temperature of the secondary air supplied to the burner, and a controller for controlling the combustion of the duct burner and controlling the amount of exhaust gas to be mixed. Since the combustion amount of the duct burner and the amount of exhaust gas mixed into the secondary air are controlled so that the temperature of the secondary air detected by the first temperature detector becomes a predetermined value, the temperature of the exhaust gas is low. , The heat exchanger and exhaust gas Even if the temperature of the secondary air cannot be sufficiently increased by mixing, it is possible to realize high-temperature air combustion, and to shorten the time until high-temperature air combustion can be realized. It exhibits an excellent effect that the operation leading to high-temperature air combustion can be performed smoothly.

It is a schematic block diagram which shows the boiler apparatus which concerns on the Example of this invention. It is a schematic sectional drawing which shows an example of the pulverized coal burner and combustion air nozzle which are used for this boiler apparatus. It is a flowchart explaining the stepwise control of the high temperature air combustion in this boiler apparatus.

  Embodiments of the present invention will be described below with reference to the drawings.

  First, referring to FIG. 1, an outline of the boiler apparatus according to this embodiment will be described.

  In FIG. 1, 1 is a furnace, 2 is a heat exchanger using the residual heat of the exhaust gas as a heat source, 3 is a pulverized coal mill, 4 is a required number of pulverized coal burners provided on the furnace wall, and 5 is provided on the furnace wall A combustion air nozzle, 6 is a primary air blower that sends out primary air, 7 is a secondary air blower that sends out secondary air, 8 is an exhaust gas blower that discharges exhaust gas, and 9 is a control device. The pulverized coal burner 4 and the combustion air nozzle 5 are arranged in a plurality of stages (three stages are illustrated in the figure) vertically. The furnace wall of the furnace 1 is provided with a heat transfer tube (not shown) for absorbing radiant heat from the inside of the furnace, and a super heater (not shown) for heating the generated steam above the furnace 1. Steam generator) is provided.

  The pulverized coal burner 4 and the combustion air nozzle 5 are arranged adjacent to each other vertically, and the pulverized coal burner 4 and the combustion air nozzle 5 are alternately arranged at a predetermined pitch in the horizontal direction. That is, the pulverized coal burner 4 and the combustion air nozzle 5 are disposed so as to be adjacent to each other in the horizontal direction and the vertical direction.

  Note that the rows of the pulverized coal burners 4 and the combustion air nozzles 5 that are alternately arranged in the horizontal direction may be two rows in the top and bottom, or one row or three or more rows in the top and bottom.

  A primary air blower duct 11 is connected to the pulverized coal mill 3 via the heat exchanger 2, and the primary air blower 6 is provided at the upstream end of the primary air blower duct 11. The primary air blowing duct 11 guides the primary air heated to a predetermined temperature, for example, 200 ° C. by the heat exchanger 2 to the pulverized coal mill 3. The pulverized coal mill 3 pulverizes massive coal into pulverized coal, uses primary air as a carrier medium, and individually feeds the pulverized coal mixed flow to the pulverized coal burner 4 through the pulverized coal supply pipe 12. Each pulverized coal supply pipe 12 is provided with a cut damper 13, and the pulverized coal supply pipe 12 can be individually cut off and opened by the cut damper 13, and is independent of the pulverized coal burner 4. Thus, the supply of pulverized coal can be stopped.

  The upstream end of the primary air bypass duct 14 and the upstream end of the auxiliary combustion air duct 15 are connected to the upstream side of the heat exchanger 2 of the primary air blowing duct 11. The downstream end of the primary air bypass duct 14 is connected to the downstream side of the heat exchanger 2 of the primary air blowing duct 11 and mixes the low temperature primary air before heating with the heated primary air. It can be done. The primary air bypass duct 14 is provided with a flow rate adjusting valve 16, which adjusts the amount of low temperature primary air mixed by the flow rate adjusting valve 16 and adjusts the temperature of the primary air supplied to the pulverized coal mill 3. Is done.

  The downstream end of the auxiliary combustion air duct 15 is connected to an auxiliary combustion burner (described later) of the pulverized coal burner 4, and low-temperature air before heating is supplied to the auxiliary combustion burner as auxiliary combustion air. The auxiliary combustion air duct 15 is provided with an auxiliary combustion air flow rate adjustment damper 17 for adjusting the flow rate of low-temperature air supplied to the auxiliary combustion burner by the auxiliary combustion air flow rate adjustment damper 17, or The supply of cold air is cut off.

  The secondary air blowing duct 18 which is a supply path for secondary air has an upstream end connected to the secondary air blower 7 via the heat exchanger 2 and a downstream end connected to each combustion air nozzle 5. . The secondary air sent from the secondary air blower 7 is heated by the heat exchanger 2 through the secondary air blower duct 18 as combustion air, and further through the secondary air blower duct 18 to the combustion air. It is fed to the nozzle 5.

  A third temperature detector 19, a duct burner 21, a first temperature detector 22, and a combustion air flow rate adjustment damper 23 are provided on the downstream side of the heat exchanger 2 of the secondary air blowing duct 18 from the upstream side. .

  The third temperature detector 19 has a function of detecting the temperature of the secondary air heated by the heat exchanger 2 and sending the detection result to the control device 9. The duct burner 21 sprays and ignites fuel such as oil in the secondary air blower duct 18 to perform combustion, and mixes high-temperature combustion gas generated by combustion with secondary air. The temperature of the secondary air that is higher than that heated by the heat exchanger 2 can be obtained.

  The first temperature detector 22 is provided on the downstream side from a junction of an exhaust gas conduit 25 and a secondary air blowing duct 18 to be described later, and the temperature of the secondary air supplied to the combustion air nozzle 5 And a detection result is sent to the control device 9. The combustion air flow rate adjustment damper 23 collectively stops the supply of high-temperature combustion secondary air to the plurality of combustion air nozzles 5 and further adjusts the flow rate.

  An upstream end of the exhaust gas conduit 25 is connected to the flue 24 of the furnace 1, and the downstream end of the exhaust gas conduit 25 is connected to the duct burner 21 of the secondary air blowing duct 18 and the first temperature detector 22. Connected between. The exhaust gas conduit 25 is provided with a second temperature detector 26 and an exhaust gas flow rate regulator 27 from the upstream side, and the exhaust gas conduit 25 and the exhaust gas flow rate regulator 27 constitute an exhaust gas circulation system. The exhaust gas conduit 25 extracts the high temperature exhaust gas before being heat exchanged by the heat exchanger 2 from the flue 24, and the exhaust gas is supplied to the high temperature secondary air heated by the heat exchanger 2 and the duct burner 21. It can be mixed. By mixing the high-temperature exhaust gas with the secondary air, it is possible to obtain secondary air having a temperature higher than that heated by the heat exchanger 2.

  The second temperature detector 26 is provided in the immediate vicinity of the exhaust gas inlet of the exhaust gas conduit 25 and has a function of detecting the temperature of the exhaust gas flowing through the exhaust gas conduit 25 and sending the detection result to the control device 9. ing. The exhaust gas flow regulator 27 has a flow rate adjusting function and an opening / closing function, and is opened when high-temperature air combustion described later is performed, and the high-temperature exhaust gas is mixed with the secondary air, and the secondary air becomes a high temperature. Is supplied to the combustion air nozzle 5 as combustion air for high-temperature air combustion.

  Here, the secondary air temperature before the exhaust gas is mixed, that is, the secondary air temperature heated by the heat exchanger 2 is 250 ° C. to 300 ° C., and the temperature of the exhaust gas extracted from the furnace is 800 ° C. The secondary air temperature for high temperature air combustion after mixing is 550 ° C to 1350 ° C. In view of the stability of high-temperature air combustion, thermal efficiency, etc., it is preferable to set the temperature to 600 ° C. to 850 ° C., for example, about 800 ° C.

  The pulverized coal burner 4 has an auxiliary combustion burner (described later). The auxiliary combustion burner uses oil or gas as fuel, and is capable of self-combustion at a low temperature (for example, room temperature). The auxiliary combustion burner is connected to the auxiliary combustion air duct 15 and a fuel supply pipe 28, and the auxiliary combustion burner is connected to a fuel supply source (not shown) via the fuel supply pipe 28. The fuel supply pipe 28 is provided with a flow rate adjusting valve 29, the fuel supply amount is adjusted by the flow rate adjusting valve 29, and the fuel supply is stopped.

  The control device 9 includes a main control for comprehensively controlling the temperature signals detected by the third temperature detector 19, the first temperature detector 22, the second temperature detector 26, and the boiler device body. A combustion control command for requesting a combustion state corresponding to the boiler load state is input from the apparatus, and based on the temperature signal and the combustion control command, the pulverized coal mill 3, the cut damper 13, the flow rate adjustment valve 16, and the auxiliary combustion. The air flow rate adjusting damper 17, the combustion air flow rate adjusting damper 23, the exhaust gas flow rate adjusting device 27, the flow rate adjusting valve 29 are driven and opened / closed at required timings, and the combustion amount of the duct burner 21 is controlled. The combustion state of the pulverized coal burner 4 and the ejection of high-temperature air from the combustion air nozzle 5 are controlled.

  An oxygen concentration detector (not shown) is provided on the downstream side of the first temperature detector 22 of the secondary air blower duct 18, and the oxygen concentration detector is supplied to the combustion air nozzle 5 2. The oxygen concentration of the secondary air is detected, and the detection result is sent to the control device 9. Based on the signal from the oxygen concentration detector, the control device 9 determines a predetermined oxygen concentration, for example, the combustion amount of the duct burner 21 and the combined flow rate of the exhaust gas combined with the secondary air so that the oxygen concentration does not fall below 14%. That is, the opening degree of the exhaust gas flow regulator 27 is controlled.

  FIG. 2 shows an example of the pulverized coal burner 4 and the combustion air nozzle 5 used in this embodiment. The outline of the pulverized coal burner 4 and the combustion air nozzle 5 will be described below with reference to FIG.

  A wind box 34 is attached to the anti-furnace side of the furnace wall 31 of the furnace 1, and a cylindrical or substantially cylindrical burner support 33 is attached to the inside of the wind box 34. A pulverized coal burner 4 is provided concentrically with the burner support portion 33 so as to penetrate the inside of the wind box 34, and a base end portion of the pulverized coal burner 4 is supported by the wind box 34, and the pulverized coal A midway part of the burner 4 is supported by the burner support part 33, and a tip is opened in the furnace 1.

  The pulverized coal burner 4 has a nozzle body 36, and the nozzle body 36 is an inner cylinder nozzle 37 provided concentrically with the nozzle body 36, and an auxiliary combustion burner disposed on the center line of the inner cylinder nozzle 37. An oil burner 38 is provided. A front end of the inner cylinder nozzle 37 is opened in the furnace 1, and a fuel conduction space in which a side end of the furnace 1 is opened in a hollow cylindrical space between the nozzle body 36 and the inner cylinder nozzle 37. 39 is formed.

  The pulverized coal supply pipe 12 communicates with the base of the nozzle body 36 (the end on the counter-fired furnace side), and the pulverized coal mixed flow 41 flows into the fuel conduction space 39 via the pulverized coal supply pipe 12. The fuel flows in the fuel conduction space 39 toward the tip, and is ejected from the tip.

  Further, the auxiliary combustion air duct 15 communicates with the base portion (end portion on the side of the counter-fired furnace) of the inner cylinder nozzle 37, and the low temperature primary air is supplied to the auxiliary combustion air via the auxiliary combustion air duct 15. 42 flows into the inner cylinder nozzle 37, flows along the oil burner 38, and is ejected from the tip.

  The secondary air blowing duct 18 communicates with the wind box 34, and the secondary air flows as combustion air 43 through the secondary air blowing duct 18.

  The combustion air nozzle 5 is provided in parallel with the pulverized coal burner 4, and the distal end opens into the furnace 1 and the proximal end opens into the wind box 34. The combustion air nozzle 5 is supported by the wind box 34 via a combustion air nozzle support portion 35. A flow rate adjustment damper 44 is provided at the base end of each combustion air nozzle 5, and the flow rate adjustment damper 44 is rotatably supported via a drive shaft 45. The drive shaft 45 projects from the window box 34 and is connected to an actuator 46 such as an air cylinder provided outside the window box 34, and the flow rate adjusting damper 44 is rotated by the actuator 46. The actuator 46 is controlled by the control device 9 and cuts off and adjusts the flow rate of each combustion air nozzle 5 with respect to the combustion air 43 (hereinafter referred to as high-temperature air 43 ′) flowing into the combustion air nozzle 5. It is supposed to be done.

  Although not shown, the actuator 46 is similarly provided for the flow rate adjusting damper 44 below the paper surface, and is driven by the actuator 46 via the drive shaft 45. Further, the flow rate adjusting damper 44 may control the actuator 46 by the control device 9, or may be manually opened and closed for each flow rate adjusting damper 44 via a lever or the like.

  The combustion in the above-mentioned pulverized coal burner 4 and the combustion air nozzle 5 will be briefly described. Oil is supplied to the oil burner 38 as fuel, and the auxiliary combustion air 42 is supplied from the auxiliary combustion duct 15 into the inner cylinder nozzle 37. In addition, the oil is sprayed toward the tip of the inner cylinder nozzle 37 and ignited, whereby auxiliary combustion is performed. The auxiliary combustion is continued until the temperature in the furnace rises to a predetermined temperature at which high-temperature air combustion is possible (a first preset temperature set in advance). Further, based on the detection results of the first temperature detector 22 and the third temperature detector 19, the control device 9 controls the combustion of the duct burner 21. With the combustion air 43 at a temperature sufficient to cause pulverized coal to burn with high temperature air, for example, 800 ° C., the high temperature air 43 ′ is supplied from the secondary air blowing duct 18 to the wind box 34, Further, the high-temperature air 43 ′ whose flow rate is adjusted by the flow rate adjusting damper 44 is ejected from the combustion air nozzle 5 into the furnace.

  While the inside of the furnace reaches a predetermined temperature at which high temperature air combustion is possible, the high temperature air 43 ′ is ejected from the combustion air nozzle 5, and a pulverized coal mixed stream 41 is supplied from the pulverized coal supply pipe 12. The pulverized coal mixed stream 41 flows in the fuel conduction space 39 and is contracted in the process of passing through the fuel conduction space 39, and is ejected from the tip of the nozzle body 36.

  When the pulverized coal ejected from the pulverized coal burner 4 is in a state where self-sustained combustion (high-temperature air combustion) is possible, auxiliary combustion by the oil burner 38 is stopped. The pulverized coal mixed stream 41 and the high-temperature air 43 ′ are jetted in parallel and gradually mixed in the furnace to shift to high-temperature air combustion that gradually burns in a low oxygen atmosphere.

  The pulverized coal mixed stream 41 is gradually mixed with the high-temperature air 43 ′, so that slow combustion is performed under low oxygen and high temperatures, and the combustion state of the pulverized coal is gentle combustion with no peak of the combustion temperature. . Further, combustion occurs in an environment having a low oxygen concentration, and generation of nitrogen oxides (NOx) can be suppressed.

  Next, high temperature air combustion in the boiler apparatus according to the present embodiment will be described with reference to the flowchart of FIG.

  When the boiler is started and the furnace temperature is low, the control device 9 opens the flow rate adjusting valve 29 to start the supply of oil and adjust the supply amount. Further, the auxiliary combustion air flow rate adjustment damper 17 is opened, low temperature primary air is supplied to the pulverized coal burner 4, and auxiliary combustion is performed by the oil burner 38 provided in the pulverized coal burner 4 ( (STEP: 01).

  In the state where auxiliary combustion is performed by the oil burner 38, the exhaust gas flow rate regulator 27 is closed and the cut damper 13 is also closed.

  When the temperature in the furnace rises due to combustion by the oil burner 38 and the temperature detected by the second temperature detector 26 reaches a preset first set temperature, for example, 500 ° C. (STEP: 02), The combustion air flow rate adjusting damper 23 is opened by the control device 9 and oil is supplied to the duct burner 21, and combustion of the duct burner 21 is started (STEP 03).

  The first temperature detector is set such that the combustion of the duct burner 21 causes the secondary air in the secondary air blowing duct 18 to have a predetermined temperature set in advance, for example, 800 ° C. suitable for high-temperature air combustion. The combustion of the duct burner 21 is controlled based on the detection result 22, and the heated high-temperature air 43 ′ is supplied to the wind box 34. Further, the pulverized coal mill 3 is started, the cut damper 13 is opened, pulverized coal is supplied to the pulverized coal burner 4, and a pulverized coal mixed stream 41 is ejected from the tip of the pulverized coal burner 4.

  As the pulverized coal is supplied to the pulverized coal burner 4, the flow rate adjusting valve 29 is closed, and combustion by the oil burner 38 is stopped (STEP: 04). Further, the flow rate adjusting damper 44 is opened, and the ejection of the high temperature air 43 ′ from the combustion air nozzle 5 is started.

  The pulverized coal mixed stream 41 ejected from the pulverized coal burner 4 is mixed and contacted with the high-temperature air 43 ′ ejected from the adjacent combustion air nozzle 5 in the furnace, and the pulverized coal mixed stream 41 and the duct burner are mixed. The primary high-temperature air combustion is started by the high-temperature air 43 ′ heated only by 21 (STEP: 05).

  The temperature of the exhaust gas detected by the second temperature detector 26 is the temperature after heat exchange by the super heater, and is therefore lower than the actual furnace temperature. Therefore, the temperature in the furnace 1 is determined based on the temperature of the exhaust gas detected by the second temperature detector 26 by associating the relationship between the furnace temperature and the exhaust gas temperature lowered by heat exchange in advance. can do. The first set temperature is appropriately set according to the capacity of the boiler, the operating state, etc., and is not limited to 500 ° C.

  Further, when the temperature in the furnace rises and the temperature detected by the second temperature detector 26 exceeds a preset second preset temperature, for example, 800 ° C. (STEP: 06), the exhaust gas flow regulator 27 Is opened at a predetermined opening, exhaust gas is extracted from the flue 24, and the exhaust gas is mixed with the combustion air 43 flowing through the secondary air blowing duct 18 through the exhaust gas conduit 25 (STEP: 07). The second set temperature is also set as appropriate depending on the boiler capacity, operating conditions, etc., and is not limited to 800 ° C.

  Even after the temperature detected by the second temperature detector 26 reaches the second set temperature, only the exhaust gas from the flue 24 is a temperature suitable for high-temperature air combustion in which the combustion air 43 is preset, For example, since it cannot be raised to 800 ° C., the combustion of the duct burner 21 is continued, and the high-temperature air 43 ′ heated by the combustion by the duct burner 21 and mixing with the exhaust gas is supplied, and the secondary high-temperature air combustion (STEP: 08).

  Based on the detection result of the second temperature detector 26, the control device 9 controls the exhaust gas flow regulator 27 so that the temperature of the combustion air 43 detected by the first temperature detector 22 becomes 800 ° C. The amount of exhaust gas to be extracted is controlled, and the combustion of the duct burner 21 is controlled. As the temperature of the exhaust gas rises and the amount of exhaust gas mixed into the combustion air 43 increases, the amount of combustion in the duct burner 21 gradually decreases.

  Further, the temperature detected by the second temperature detector 26 is a preset third set temperature, that is, a temperature at which the combustion air 43 can be raised to 800 ° C. only by mixing with the exhaust gas, for example, extraction. When the exhaust gas temperature to be reached reaches 1000 ° C. (STEP: 09), the combustion of the duct burner 21 is stopped (STEP: 10).

  After the combustion of the duct burner 21 is stopped, the opening amount of the exhaust gas flow regulator 27 is controlled to adjust the amount of exhaust gas mixed, and the combustion air 43 is maintained at 800 ° C. The process proceeds to tertiary high-temperature air combustion using the high-temperature air 43 'heated only by mixing and the pulverized coal mixed stream 41 (STEP: 11).

  As described above, in this embodiment, the duct burner 21 is provided in the secondary air blowing duct 18 that is a supply path of secondary air, and combustion air 43 is produced even if the temperature of the exhaust gas is low due to combustion of the duct burner 21. Can be heated to a temperature suitable for high-temperature air combustion, so that high-temperature air combustion is possible when the exhaust gas reaches the first set temperature without waiting for the temperature to rise to the third set temperature. When the temperature of the exhaust gas reaches the second set temperature, mixing of the exhaust gas into the secondary air is started. When the temperature of the exhaust gas reaches the third set temperature, the high-temperature air is generated even if the duct burner 21 is not burned. Combustion can be realized. Accordingly, it is possible to shorten the time during which high-temperature air combustion can be realized, and it is possible to smoothly perform the operation from boiler startup to high-temperature air combustion.

  In this embodiment, the first to third set temperatures are set in advance, and the control is performed step by step by comparing the first to third set temperatures with the detection value of the second temperature detector 26. However, based on the detection results of the second temperature detector 26 and the third temperature detector 19 without setting the third set temperature, the control device 9 is only heated by the heat exchanger 2 and mixed with the exhaust gas. Thus, it may be determined whether the temperature of the combustion air 43 can be raised to 800 ° C., and the stop of the duct burner 21 and the opening degree control of the exhaust gas flow rate regulator 27 may be performed.

  In this embodiment, the auxiliary combustion is stopped after the first set temperature is reached, but the auxiliary combustion is continued until the third set temperature is reached, and the time until the third high-temperature air combustion is shortened. May be.

  In this embodiment, three temperature detectors, the first temperature detector 22, the second temperature detector 26, and the third temperature detector 19, are provided, but only the first temperature detector 22 is provided. It is good. In this case, it is determined that the temperature of the combustion air 43 detected by the first temperature detector 22 exceeds 800 ° C. in a state where the temperature of the exhaust gas is increased and the exhaust gas is mixed with the combustion air 43. Then, the temperature of the combustion air 43 is lowered by decreasing the amount of combustion of the duct burner 21 first. If it is determined that the temperature exceeds 800 ° C. even after extinguishing the duct burner 21, the opening of the exhaust gas flow rate regulator 27 is adjusted, and the temperature of the combustion air 43 is lowered, thereby reducing the combustion air 43. The temperature can be kept at 800 ° C. If the temperature of the combustion air 43 does not reach the set temperature even when the exhaust gas flow rate regulator 27 is maximized, the exhaust gas flow rate regulator 27 is throttled to ignite the duct burner 21 again. As a result, the temperature of the combustion air 43 is raised to 800 ° C.

  In addition, when using pulverized coal with little volatile matter or pulverized coal that cannot be self-sustained combustion, auxiliary combustion by the oil burner 38 may be used in combination.

DESCRIPTION OF SYMBOLS 1 Furnace 2 Heat exchanger 4 Pulverized coal burner 9 Control apparatus 18 Secondary air ventilation duct 19 3rd temperature detector 21 Duct burner 22 1st temperature detector 25 Exhaust gas conduit 26 2nd temperature detector 27 Exhaust gas flow rate regulator 41 Pulverized coal Mixed flow 43 Combustion air

Claims (4)

  Heat exchange between the boiler, the pulverized coal nozzle provided on the furnace wall of the boiler and ejecting pulverized coal, the air nozzle provided adjacent to the pulverized coal nozzle and ejecting secondary air, and the exhaust gas of the boiler A heat exchanger that raises the temperature of the secondary air supplied to the air nozzle and a duct burner that burns in the supply path of the secondary air and raises the temperature of the secondary air. A boiler apparatus characterized by causing high-temperature air combustion using secondary air ejected from a pulverized coal and pulverized coal ejected from the pulverized coal nozzle.   The boiler according to claim 1, further comprising: a temperature detector that detects a temperature of secondary air supplied to the air nozzle; and a control device that controls a combustion amount of the duct burner based on a detection result of the temperature detector. apparatus.   Heat that increases the temperature of secondary air for combustion by heat exchange between a boiler, a burner that is provided on the furnace wall of the boiler and performs high-temperature air combustion with pulverized coal and high-temperature secondary air, and the exhaust gas of the boiler An exchanger, a duct burner that burns in the supply path of the secondary air and raises the temperature of the secondary air, an exhaust circulation system that extracts a part of the exhaust gas and mixes it with the secondary air, and is supplied to the burner A first temperature detector that detects the temperature of the secondary air; and a control device that controls the combustion of the duct burner and the amount of exhaust gas to be mixed. The control device includes the first temperature detector. The high-temperature air combustion system is characterized in that the amount of combustion of the duct burner and the amount of exhaust gas mixed into the secondary air are controlled so that the temperature of the secondary air detected by the above becomes a predetermined value.   A second temperature detector for detecting the temperature of the exhaust gas; and a third temperature detector for detecting the temperature of the secondary air heated by the heat exchanger. The high-temperature air combustion system according to claim 3, wherein the combustion amount of the duct burner and the amount of exhaust gas mixed into the secondary air are controlled based on the detection results of the detector and the third temperature detector.

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