JP2007232328A - Air port for dual-stage combustion, its operation method, and boiler - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an air port for dual-stage combustion suitable for reducing NOx and an unburnt portion. <P>SOLUTION: The air port for dual-stage combustion for supplying additional air for complete combustion into a combustion space through which inflammable combustion gas of a boiler furnace flows, is structured to comprise at least two nozzles in the port to eject an air jet inward. The two nozzles ejecting the air jet inward are arranged facing with a space on both sides of a port center axis. The jets ejected from the two nozzles arranged facing collide in the combustion space. Mixing of fuel supplied from the burner and inflammable gas formed by combustion of air is thereby accelerated to reduce NOx and the unburnt portion. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a two-stage combustion air port for supplying additional air to a combustible combustion gas formed by combustion of fuel and air supplied from a burner, an operation method thereof, and a boiler. The present invention is particularly suitable for a combustion apparatus that burns by supplying coal and air from a burner.

  Combustion apparatuses are required to reduce nitrogen oxide (NOx) concentration and unburned carbon such as carbon monoxide (CO). In order to meet these demands, a two-stage combustion method is employed in which fuel and air are supplied from a burner, burned in a state of air shortage, and then added again to complete combustion. In a two-stage combustion boiler, it is required to reduce the unburned amount by promoting the mixing of after-air introduced from a two-stage combustion air port (hereinafter referred to as an after-air port). As an improvement measure, a method has been proposed in which a plurality of after-air ports are installed in multiple stages and the after-air is introduced in multiple stages (see, for example, Patent Document 1).

Japanese Patent No. 3021195

  In order to reduce NOx and CO, it is one effective method to install after airports in multiple stages. However, this method has problems that it is difficult to determine the multi-stage air amount distribution and that the operation range is narrow. Furthermore, there is a problem that the cost becomes high.

  An object of the present invention is to provide an after-air port which can reduce NOx or CO without being installed in multiple stages. Moreover, it is providing the operation method of an after airport, and the boiler provided with the after airport.

  The present invention resides in an after-air port characterized in that at least two nozzles that allow an air jet to be ejected inward into the port face each other across the center axis of the port and are spaced from each other. .

  The present invention also provides a burner for ejecting fuel and air, and a two-stage combustion air port for supplying additional air to a combustible combustion gas formed by combustion of fuel and air supplied from the burner. And at least two nozzles that are arranged so that the jet of air is jetted inwardly at the two-stage combustion air port, facing each other across the center axis of the port and spaced apart from each other The boiler is characterized by

  In addition, the present invention is provided with an after-air port having the above-described structure so that the nozzle is arranged in the direction in which the combustible combustion gas flows, and when the NOx concentration of the combustion gas is high, the port center axis is opposed. The after-airport operating method is characterized in that the air flow rate of the nozzle arranged on the upstream side in the flow direction of the combustion gas among the nozzles is increased.

  In addition, the present invention is provided with an after-air port having the above-described structure so that the nozzle is arranged in the direction in which the combustible combustion gas flows, and when the CO concentration of the combustion gas is high, it is opposed across the port center axis. The after-airport operating method is characterized in that the air flow rate of the nozzle arranged on the downstream side in the flow direction of the combustion gas among the nozzles is increased.

  According to the present invention, air jets are jetted inward from the nozzles arranged on both sides of the center axis of the after-airport and collide in the combustion space, thereby promoting mixing with the primary combustion gas. Therefore, NOx and unburned content are reduced.

  In the after-air port of the present invention, air is further ejected in the direction of the port center axis between a plurality of nozzles arranged to face each other across the port center axis and ejecting an air jet inward. Additional nozzles can be provided. By using this additional nozzle, it is possible to adjust the flow rate and flow velocity of the air jetted inward.

  In a normal case, it is sufficient that one nozzle is provided on each side of the port center axis to eject the air jet inward.

  It is desirable that the plurality of nozzles provided in the after air port be arranged in the flow direction of the combustion gas formed by the combustion of the fuel and air supplied from the burner. Although it is possible to arrange a plurality of nozzles in the direction perpendicular to the flow direction of the combustion gas, the arrangement of the nozzles in the flow direction of the combustion gas is more effective in reducing unburned fuel and NOx. Great effect.

  In the after-air port, it is preferable that the outlet of the nozzle ejected into the furnace is a single hole, and the hole of the outlet can be square, round, or the like, but is preferably square, especially rectangular. Furthermore, it is desirable to install a damper for adjusting the air flow rate upstream of the nozzle that jets the air jet inward. The present invention is suitable for a combustion apparatus that uses coal as a fuel for a burner.

  Examples of the present invention will be described below with reference to the drawings, but the present invention is not limited to the following examples.

  FIG. 1 is a longitudinal sectional view showing an example of an embodiment of an after airport according to the present invention, FIG. 2 is a front view, and FIG. 3 is a transverse sectional view. As shown in FIG. 1, air is supplied from a wind box 20. The air is separated into an upper nozzle 18 and a lower nozzle 19 to form an upper jet 12 and a lower jet 13. The two jets collide to form a jet 14 after joining, and are supplied to the combustion space 16. By causing the two jets to collide, mixing of the jet and the combustion gas 15 can be promoted.

  In order to make the jets collide, the upper nozzle 18 and the lower nozzle 19 are configured such that the jets are jetted toward the center axis of the port. That is, the jet is configured to be ejected inward. The optimum value of the air ejection angle of the upper nozzle 18 and the lower nozzle 19 varies depending on the combustion state, but is preferably in the range of 10 ° to 45 °. In the present embodiment, the primary nozzle 1 is further disposed between the upper nozzle 18 and the lower nozzle 19 to eject an air jet in the direction of the port center axis.

  As shown in FIG. 1, the upper nozzle 18 and the lower nozzle 19 are desirably arranged in the flow direction of the combustion gas 15. Although not shown in FIG. 1, they can be arranged side by side in a direction perpendicular to the flow direction of the combustion gas 15.

  In the case of a boiler, a wind box 20 is installed on the furnace wall 3, and an after-air port is attached to the wind box outer wall 17. The furnace wall 3 is formed of a water pipe 4, and if the tip of the nozzle outer wall 2 of the after air port is formed of a water pipe, the nozzle tip can be cooled.

  It is desirable that the flow rates of the upper jet 12 and the lower jet 13 can be adjusted individually. For this purpose, as shown in FIG. 1, it is preferable to install air conditioning dampers 7 and 8 upstream of the upper nozzle 18 and air conditioning dampers 9 and 10 upstream of the lower nozzle.

  When the jet 14 after joining is directed horizontally, that is, when the jet 14 is jetted in a direction perpendicular to the flow direction of the combustion gas 15, all of the air adjustment dampers 7, 8, 9, 10 are used. Opening will slow down the flow rate. If the flow rate is constant, closing the air conditioning dampers 8 and 9 on the inside increases the flow velocity at the inlet, and the speed of the upper jet 12 and the lower jet 13 can be increased. When the pressure in the wind box 20 is the same, the flow rate decreases when the air adjustment damper is closed. When all of the air adjustment dampers 7, 8, 9, 10 are closed, the flow rate is minimized. In order to further reduce the flow velocity, the primary air damper 5 is fully opened and the flow rate of the primary air 6 flowing through the primary nozzle 1 is increased.

  Next, the case where the jet 14 is directed upward will be described with reference to FIG. In addition, what is necessary is just to perform operation opposite to the case where it is directed upwards when directing the jet flow 14 below. If the flow rates of the upper jet 12 and the lower jet 13 are controlled, the ejection direction can be controlled. In the after-air port having the structure shown in FIG. 4, the flow rate of the upper jet 12 can be reduced by closing the air adjustment dampers 7 and 8 of the upper nozzle 18. In this case, since the flow rate of the lower jet 13 is increased, the jet 14 after joining is directed upward. As a result, since the mixing of the combustion gas 15 and the air in the jet 14 is delayed, the NOx concentration decreases. Although there is a possibility that the unburned portion becomes higher due to the slow mixing, the flow velocity of the lower jet is increased, so that the downstream mixing can be promoted and the unburned portion can be reduced. When the jet flow 14 is directed upward and the flow velocity is desired to be further reduced, the primary air damper 5 is opened to increase the flow rate of air from the primary nozzle 1. Under this condition, the flow rate of the lower jet 13 is reduced, and the flow velocity of the jet 14 after joining is reduced.

  In FIG. 5, the example which applied the after airport of this invention to the boiler furnace was shown. The boiler furnace 105 is formed of a water pipe, and generally has a substantially square cross section. A burner wind box 104 is installed on each of the front wall and the rear wall of the furnace 105, and a plurality of burners 114 are installed in multiple stages in the wind box. In this embodiment, burners are installed in three stages. Air and fuel are supplied to the burner 114. These burn and form a flow of combustible gas 101. The combustible gas 101 and the jet 14 from the after-air port 50 are mixed and completely burned to become a combustion gas 106. The air flow rates of the burner 114 and the after-air port 50 can be adjusted by the air adjustment damper 109 and the air adjustment damper 110. The air flowing through the air supply line 108 is supplied to the burner wind box 104 through the air adjustment damper 109 and the burner air supply line 111. Air flowing through the air supply line 108 is supplied to the wind box 20 through the air adjustment damper 110 and the air supply line 112. In adjusting the combustion of the boiler, first, the air adjustment damper 109 is adjusted by the control device 115 so that the combustion state of the burner is optimal, and the amount of air in the burner is adjusted. Next, the air adjustment damper 110 and the air adjustment dampers 7, 8, 9, and 10 are adjusted so that the combustion state in the after-air is optimized.

  Next, an after-airport damper open / close control method will be described. First, the case where the NOx concentration is high will be described. In FIG. 5, the gas sensor 116 is installed downstream of the furnace. When the NOx concentration measured by the gas sensor 116 is high, an operation for decreasing the flow rate of the after-air port is performed. That is, the air adjustment dampers 7, 8, 9, 10 and the primary air damper 5 are opened. Another method is to open the air conditioning dampers 7 and 8 to increase the air flow rate of the upper nozzle 18 so that the jet 14 is ejected in the upstream direction of the furnace.

  Next, a case where the CO concentration is high will be described. When the CO concentration measured by the gas sensor 116 is high, the primary air damper 5 is closed to increase the overall flow rate. Alternatively, the air adjustment dampers 7 and 8 of the upper nozzle 18 or the air adjustment dampers 9 and 10 of the lower nozzle 19 may be closed to increase the flow velocity. The CO concentration decreases as the air flow rate of the upper nozzle 18 is increased. This method is also effective when there are many unburned components other than CO.

  Next, a case where the temperature of the after-air port is high will be described. A temperature sensor 30 is installed in the after air port as shown in FIG. If the temperature rises, the after-airport failure tends to occur. When the temperature is high, the air flow rate of the after-air port is increased. However, if the air flow rate of the after-air port is changed, the burner combustion may not be maintained in an optimum state. In such a case, it is better to increase the primary air flow rate of the after-air port. Alternatively, it is effective to close the air adjustment damper 7 on the upper side of the upper nozzle 18 and the air adjustment damper 10 on the lower side of the lower nozzle 19 to increase the air flow velocity on the inside.

  FIG. 8 shows the result of predicting the combustion state in the boiler furnace by three-dimensional numerical analysis of combustion, flow, and heat transfer. The fuel is pulverized coal. The burner air ratio is 0.8, and the overall furnace air ratio is 1.15. CO and NOx in FIG. 8 are average values at the furnace outlet. Condition A is when the nozzle of the after airport is circular and the nozzle is not divided into a plurality of nozzles. Condition B is an embodiment of the present invention, and is a case where the nozzle outlet hole is rectangular as shown in FIG. 1 and is divided into an upper nozzle 18 and a lower nozzle 19. In the case of the present invention, it was found that the CO concentration can be greatly reduced compared with the same NOx concentration.

  As described above, the case where the after-hole of the outlet has a square shape, in particular, a rectangular shape has been described. However, it is also possible to replace it with a round-shaped after-air port of the outlet.

  FIG. 6 shows another embodiment of the after-airport according to the present invention. In the embodiment shown in FIG. 1, the primary air flows in the center, but the primary air is not supplied in this embodiment. When primary air is flowed and the overall air flow rate is not adjusted, the structure is simplified if the shape is as shown in FIG. In FIG. 6, the upper nozzle 18 and the lower nozzle 19 are both formed by the nozzle outer wall 2 and the nozzle inner wall 11. The nozzle outer wall 2 and the nozzle inner wall 11 are fixed by a support plate 23. If it is necessary to fix the center portion of the after air port between the upper nozzle 18 and the lower nozzle 19, the plate 22 may fix the space between the nozzle inner wall 11 on the upper nozzle side and the nozzle inner wall 11 on the lower nozzle side. Since the nozzle inner wall 11 is heated by radiant heat, it is preferable that the hole 22 is provided and cooled.

  FIG. 7 shows still another embodiment of the after-air port. In this embodiment, in addition to the embodiment of FIG. 1, an automatic opening / closing function of the damper is added. The upper and lower nozzle moving rods 28 are connected to the air adjustment dampers 7, 8, 9 and 10. A motor box 26 is installed at the tip of the rod, and the damper can be operated by the motor. The primary air damper 5 can also be moved using the primary air moving rod 29 and the primary air motor box 27. These motor boxes are operated by a control signal of the control device 115 shown in FIG.

It is a longitudinal cross-sectional view of the after airport by one Example of this invention. It is a front view of the after airport shown in FIG. It is a cross-sectional view of the after airport shown in FIG. It is explanatory drawing at the time of changing the air flow state of the after-airport shown in FIG. 1 is a system configuration diagram of a boiler according to an embodiment of the present invention. It is sectional drawing which shows the structure of the after airport by another Example of this invention. It is sectional drawing which shows the structure of the after airport by other Example of this invention. It is a figure which shows the difference in performance by the difference in the structure of an after airport.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Primary nozzle, 2 ... Nozzle outer wall, 3 ... Furnace wall, 4 ... Water pipe, 5 ... Primary air damper, 6 ... Primary air, 7 ... Air adjustment damper, 8 ... Air adjustment damper, 9 ... Air adjustment damper, 10 ... Air adjusting damper, 11 ... Nozzle inner wall, 12 ... Upper jet, 13 ... Lower jet, 14 ... Jet, 15 ... Combustion gas, 16 ... Combustion space, 17 ... Windbox outer wall, 18 ... Upper nozzle, 19 ... Lower nozzle, 20 DESCRIPTION OF SYMBOLS ... Window box, 30 ... Temperature sensor, 104 ... Burner window box, 105 ... Furnace, 106 ... Combustion gas, 109 ... Air adjustment damper, 110 ... Air adjustment damper, 114 ... Burner, 115 ... Control device, 116 ... Gas sensor .

Claims (14)

  In a two-stage combustion air port that supplies additional air to the combustion space in the furnace through which the combustion gas formed by the combustion of fuel and air supplied from the burner flows, an air jet injects inward into the port A two-stage combustion air port, characterized in that at least two nozzles arranged so as to face each other across the center axis of the port and are spaced from each other.   2. The two-stage combustion air port according to claim 1, wherein at least two of the nozzles are installed in a flow direction of the combustion gas.   The two-stage combustion air port according to claim 1, wherein the outlets of at least two of the nozzles are one hole.   4. The two-stage combustion air port according to claim 3, wherein the hole has a rectangular cross-sectional shape.   2. The two-stage combustion air port according to claim 1, wherein a damper for adjusting an air flow rate is provided upstream of the nozzle.   2. The two-stage combustion apparatus according to claim 1, further comprising a nozzle for injecting air in the direction of the port center axis between at least two nozzles arranged opposite to each other with the port center axis interposed therebetween. Air port.   In Claim 1, the fuel supplied from the said burner is coal, and supplies additional air with respect to the combustible combustion gas formed by burning coal in the state where air is insufficient. Air port for two-stage combustion characterized by   In a boiler comprising a burner for ejecting fuel and air, and a two-stage combustion air port for supplying additional air to a combustible combustion gas formed by combustion of fuel and air supplied from the burner A boiler characterized in that at least two nozzles through which a jet of air is jetted inward are disposed facing and spaced apart from the center axis of the port in the two-stage combustion air port.   9. The boiler according to claim 8, wherein at least two of the nozzles provided in the two-stage combustion air port are all disposed in the flow direction of the combustion gas.   9. The nozzle according to claim 8, further comprising a nozzle for injecting air in the direction of the port center axis between at least two nozzles facing each other with the port center axis of the two-stage combustion air port interposed therebetween. Boiler.   9. The boiler according to claim 8, wherein coal is supplied as fuel from the burner.   9. The boiler according to claim 8, wherein a damper for adjusting an air flow rate is provided upstream of the nozzle of the two-stage combustion air port.   A method of supplying additional air from a two-stage combustion air port to a combustion space in a furnace in which a combustible combustion gas formed by combustion of fuel and air supplied from a burner flows, the two-stage combustion The two-stage combustion has an air port having a structure in which at least two nozzles in which a jet of air is jetted inward into the port face each other across the port center axis and are spaced apart from each other. An air port is installed so that the nozzle is arranged in the direction in which the combustion gas flows, and when the NOx concentration of the combustion gas is high, among the nozzles facing each other across the port center axis, the combustion gas flow direction upstream A method for operating a two-stage combustion air port, wherein the air flow rate of a nozzle located on the side is increased.   A method of supplying additional air from a two-stage combustion air port to a combustion space in a furnace through which combustible combustion gas formed by combustion of fuel and air supplied from a burner flows, the two-stage combustion The two-stage combustion has an air port having a structure in which at least two nozzles in which a jet of air is jetted inward into the port face each other across the port center axis and are spaced apart from each other. An air port is installed so that the nozzle is arranged in the direction in which the combustion gas flows, and when the CO concentration of the combustion gas is high, the combustion gas in the flow direction downstream of the nozzles opposed across the center axis of the port A method for operating a two-stage combustion air port, wherein the air flow rate of a nozzle located on the side is increased.

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