JP4628922B2 - After airport - Google Patents

Description

  The present invention relates to an after-airport for a boiler combustion apparatus suitable for minimizing the generation level of nitrogen oxides (NOx) and carbon monoxide (CO) at a boiler outlet.

  The burner used in the boiler combustion apparatus is generally of a two-stage combustion type for the purpose of reducing the NOx concentration in the boiler exhaust gas. In the two-stage combustion type burner, the combustion air is divided into two stages and supplied to the burner section, the fuel is reduced and burned at an air ratio of 1 or less (usually 0.75 to 0.95), and the downstream side after-sales In this configuration, a shortage of air is introduced at the airport to completely burn it.

  The two-stage combustion type burner burns fuel at a low air ratio from the burner portion to the after-airport portion, resulting in a reduction effect for both thermal NOx and fuel NOx. Therefore, it is possible to reduce the NOx concentration of the combustion gas regardless of the fuel type such as gas, oil and pulverized coal.

  As a method for reducing the NOx concentration of the combustion gas, there is a method in which after-air ports are provided in multiple stages and the after-air is dividedly supplied. FIG. 10 shows a typical two-stage after-airport configuration in a counter-combustion burner used in a pulverized coal-fired boiler furnace.

  Two burners 32a and 32b are installed in the furnace 31 on the furnace wall surface facing the furnace 31. For the purpose of reducing NOx of the combustion gas by effectively utilizing the space of the furnace 31, two upper and lower after-airports are provided above the upper burner 32b. 33a and 33b are installed facing each other.

  Combustion air preheated from the FDF 36 via the air heater 37 is distributed to the burner portion and the after-airport portion by the wind box 39 while being adjusted in flow rate by the damper 38, and is then introduced into the furnace 31. In the two-stage combustion zone from the burner section to the after-air ports 33a and 33b, the operation is performed at a theoretical air ratio or less, so that unburned gas remains in the furnace 31. The unburned gas is mixed with the after air downstream from the after air port (upward of the furnace) to complete the combustion. The flue gas exiting the furnace 31 is discharged from the chimney 42 via the denitration device 41 and the air heater 37.

  Since the conventional two-stage combustion technique shown in FIG. 10 has the same shape of the after-air ports 33a and 33b installed in multiple stages, if the air amount of the upstream-side air port 33a is increased at the same two-stage combustion ratio, the downstream-side air port 33b. As the amount of air is reduced and the downstream after-air does not have sufficient penetrating force, the effect of supplying the after-air in multiple stages cannot be exhibited, and the NOx concentration in the combustion gas increases, or the CO concentration In addition, there is a problem that the unburned content increases.

  Regardless of changes in combustion conditions such as the burner air ratio by solving the above problems, by properly maintaining mixing in the furnace near the after-airport, NOx, CO and soot and dust in the combustion gas at the boiler outlet ( The present applicant has filed a patent application regarding the invention of a boiler combustion apparatus having an after-airport that suppresses the generation level of unburned components to a minimum (Patent Document 1).

The invention of Patent Document 1 will be described with reference to the after-airport cross-sectional view of FIG.
The airport 4 includes a primary sleeve 22 to which the first divided air 21 is supplied and a secondary sleeve 24 to which the second divided air 23 is supplied to the outer periphery of the primary sleeve 22 so that the combustion air can be supplied in two. A dual-type after-airport structure is provided.

  The primary sleeve 22 of the airport 4 is provided with a slide damper 26 that adjusts the amount of air supplied from the opening 22a. The secondary sleeve 24 is also provided with a slide damper 27 that opens and closes the opening 24a. The slide dampers 26 and 27 are driven by driving devices 28 and 29, respectively. The secondary sleeve 24 is provided with a swirler 30 for applying a swirling force and a penetrating force to the combustion air. The swirler 30 is controlled by the driver 31 to optimize the swirl force and penetration force of the combustion air, thereby minimizing the passage of unburned gas in the furnace 31 near the after-airport section. It becomes.

  In the burner using the after-air port shown in FIG. 11, the penetration force of the after-air is equal to the base condition even if the after-air increases when the upstream after-air amount is increased due to the burner combustion conditions. Furthermore, in order to widen the air flow path area of the after-airport, good mixing is performed even in the center of the furnace, and NOx does not rise.

In addition, when the upstream after-air amount is lowered from the base condition, the operation of ensuring the penetration force by narrowing the air flow path area of the after-air port prevents the unburned gas from passing through in the center of the furnace. Since it can be prevented and good mixing is performed, the amount of CO generated and dust (unburned matter) do not increase.
Japanese Patent Laid-Open No. 11-304109

  Even in the invention described in Patent Document 1, the swirling air jet from the after-air port cannot sufficiently reduce the unburned gas near the furnace wall, and it is almost the same as the burner although it is an after-air port (AAP). Therefore, it was necessary to improve the manufacturing cost.

  A feature of the AAP provided in the upper stage of the burner of the coal-fired boiler furnace is that it effectively mixes the unburned gas in the vicinity of the AAP, that is, in the vicinity of the boiler furnace wall. Although it is well known that mixing can be performed by increasing the flow rate of AAP and entraining many gases, the problem of increase in NOx concentration in the combustion gas due to increase in flow rate and power increase therefor occurs. Therefore, it is necessary to increase the mixing effect of unburned gas and fuel air at a low flow rate.

  FIG. 6 shows a comparison of the mixing effect of fuel air and ambient gas due to the difference in nozzle structure. FIG. 6A shows a flow velocity distribution of air in the reduced flow type nozzle, and FIG. 6B shows a comparative example with a straight pipe nozzle. In the reduced flow type nozzle shown in FIG. 6A, it can be seen that the flow velocity distribution at the outlet portion is flat and the turbulent flow is not sufficiently developed. On the other hand, in the straight pipe type nozzle shown in FIG. 6B, the pipe is long, and the flow velocity distribution of air becomes a normal distribution due to the influence of the pipe wall. In the entrainment of ambient gas, the reduced flow type nozzle having a flat flow velocity distribution shown in FIG. 6A is excellent.

  An object of the present invention is to provide an after-airport capable of enhancing the mixing effect of unburned gas and fuel air at a low flow rate at the airport outlet portion.

The above-described problems of the present invention are solved by the following configuration.
The invention according to claim 1 is an after-air port for introducing into the furnace the air for complete combustion of the fuel in the reduced combustion state, which is disposed downstream of the burner for reducing and burning the fuel provided in the furnace together with the primary air. A cylindrical primary air nozzle through which the primary air for mainstream combustion provided in the center flows, a secondary air nozzle through which the secondary air for combustion provided in the outer periphery of the primary air nozzle flows, and a cylindrical primary It is an after air port provided with the plate-shaped edge member which shrinks | reduces the primary air flow path provided in the direction orthogonal or substantially orthogonal to the gas flow at the opening end part by the side of the furnace of an air nozzle.

The invention according to claim 2 is the after-airport according to claim 1, wherein an inclined portion is provided at the tip of the plate-like edge member.
The invention according to claim 3 is characterized in that the plate-like edge member is provided with an opening at a location corresponding to the opening end of the secondary air nozzle on the furnace side. It is.

In the present invention, the basic characteristics of the reduced flow type nozzle are reflected in the AAP structure, and the flow passage of the primary air nozzle is determined by the edge member provided at the opening end of the primary air nozzle on the furnace side. A structure that obtains a flat gas flow velocity distribution by narrowing down rapidly.
In addition, since the flow velocity distribution is likely to be near the flow path wall of the primary air nozzle, an inclined part is provided at the tip of the edge member to eliminate the boundary layer thickness, and the edge tip is attenuated to the flow velocity around the gas jet. I tried not to be.

FIG. 7 compares the effect of reducing the CO concentration in the gas at the furnace outlet between the AAP according to the present invention and the conventional AAP. The flow rate change width of each AAP is constant and is 35 m / s to 45 m / s.
According to FIG. 7, the kinetic energy u in the XZ-axis direction of the three-dimensional XYZ axis in the vicinity of the jet at the furnace outlet is greater in the AAP according to the present invention than in the conventional AAP, although in the same flow velocity range. ² (the square of the flow velocity) is large, indicating that the CO concentration in the gas at the furnace outlet is effectively reduced accordingly.

Now, the turbulence around the jet flow is large at the AAP furnace outlet, and the surrounding combustion gas is likely to be accompanied, but the ash contained in the combustion gas also accompanies, so the ash adhesion potential at the AAP furnace outlet is reduced. is necessary.
This mechanism and preventive measures will be described with reference to the furnace wall structure at the AAP furnace outlet in FIGS. Since the primary air (2) is a free jet without swirling in the air flow, the combustion gas in the furnace is entrained in the edge member (16), and ash adheres to the furnace wall (1a) of the furnace as shown in FIG. To do. This is because a negative pressure is generated in the wake portion of the edge member (16), and a circulation region is formed. The ash is adhering in a small amount behind the edge member (16) in the initial state, but is expected to gradually grow along the gas jet.

  It is necessary to reduce the amount of ash adhering to the furnace wall (1a) on the rear side of the edge member (16) by increasing the static pressure behind the edge member (16). However, if a large amount of air is supplied to this region, the high flow velocity by the edge member (16) is destroyed, so it is desirable to eject a small amount along the furnace wall (1a) after the edge member (16). For this reason, a method is used in which the secondary air (6) is swirled in a small amount and supplied. Alternatively, swirling is not necessary in the method of supplying air along the furnace wall that spreads out toward the end. And as a supply method of secondary air (6), as shown in FIG. 8, the opening part (16a) for injection of secondary air (6) is provided in the board which comprises an edge member (16), and a furnace is provided. A method of spraying from the opening (16a) is adopted as one aspect of the present invention.

  According to the present invention, it goes without saying that a flow of air reaching the center of the furnace and an air flow that accelerates mixing in the vicinity of the furnace wall are formed, but a strong entrained flow of ambient gas is generated in the vicinity of the primary air nozzle. However, there is a concern that this entrained flow entrains ash and adheres and melts in the vicinity of the primary air nozzle. However, since the negative pressure in the vicinity of the wall can be removed by the effective input of the secondary air, it is possible to operate with high reliability to obtain a generated exhaust gas having a low NOx concentration and a low CO concentration.

  According to the first aspect of the present invention, the combustion air not only mixes well with unburned gas in the vicinity of the furnace center and the furnace wall, but also can supply a combustion air jet near the furnace wall, so that negative pressure is removed. As a result, it is possible to obtain a highly reliable product combustion gas having a low NOx concentration and a low CO concentration.

According to the second aspect of the invention, in addition to the effect of the first aspect of the invention, the flow velocity distribution near the flow path wall of the primary air nozzle is prevented from being attenuated by the flow velocity around the gas jet at the tip of the edge member. Made difficult to form.
According to the invention described in claim 3, in addition to the effects of the invention described in claim 1 or 2, secondary air flows from the opening of the edge member, and the static pressure behind the edge is increased to increase the rear pressure of the edge. The amount of ash adhering to the side furnace wall can be reduced.

Embodiments of the present invention will be described with reference to the drawings.
FIG. 1 shows a cross-sectional view of the AAP structure of this embodiment. The AAP structure of the present embodiment has a double structure, and a primary air nozzle 5 for supplying primary air 2 to the center of the wind box 3 provided at a position facing the opening of the furnace wall 1a of the furnace 1; A secondary air nozzle 7 for supplying secondary air 6 around the primary air nozzle 5 is provided. The primary air nozzle 5 is configured to blow out air in the wind box 3 supplied from an opening 9 a provided in a box-shaped case 9 toward the furnace 1 as primary air 2. The opening degree of the opening 9 a provided in the box-shaped case 9 is adjusted by operating a gate adjustment lever 12 provided with a primary air flow rate adjusting slide gate 10 outside the wind box 3. Further, a swirler 13 is disposed in the secondary air nozzle 7, and the combustion air from the wind box 3 is supplied into the furnace 1 while being swirled by the swirler 13. The swirler 13 is configured such that the swivel angle of the secondary air 6 can be adjusted by operating a driver 14 provided outside the wind box 3.

  An edge plate 16 is provided between the outer wall portion of the furnace wall 1 a and the secondary air nozzle 7 along the outer wall plane of the furnace wall 1 a and extends in a direction crossing the primary air nozzle 5. Further, an opening 16 a is provided at a portion of the edge plate 16 that contacts the outlet of the secondary air nozzle 7.

  Therefore, the primary air 2 is separated from the secondary air 6 in the box-shaped case 9, and the flow rate thereof is adjusted to an appropriate amount by the operation of the primary air flow rate adjusting slide gate 12, and then flows into the primary air nozzle 5. While the flow passage cross-sectional area is gradually reduced at the nozzle wall of the secondary air nozzle 7, the flow velocity is increased and the flow is ejected into the furnace 1. Since the primary air 2 is blocked by the edge plate 16 immediately before jetting in the furnace, the flow velocity is further increased and jetted into the furnace. Therefore, the primary air 2 jetted into the furnace 1 can penetrate to the center of the furnace. Have

  Further, the secondary air 6 in the secondary air nozzle 7 is swirled by the swirler 13 and is jetted into the furnace 1 from the opening 16a of the edge plate 16 along the inclined surface of the furnace wall 1a in the furnace 1. Then, it diffuses and mixes in the vicinity of the furnace wall 1a at a low flow rate to burn the lean unburned gas in the vicinity of the furnace wall 1a.

  FIG. 2 shows a sectional view of an AAP structure of another embodiment. 2 is different from the embodiment of FIG. 1 in that the secondary air nozzle 7 is not provided with the swirler 13 and the secondary air nozzle 7 is provided with a secondary air flow rate adjusting slide gate 19. In other words, the secondary air flow rate adjusting slide gate adjusting lever 20 provided outside the wind box 3 can be used to adjust the amount of secondary air supplied to the secondary air nozzle 7. Since other configurations are the same as those of the embodiment shown in FIG. 1, the same reference numerals as those in FIG.

  The AAP structure shown in FIG. 2 is different from the embodiment shown in FIG. 1 in that the secondary air 6 ejected from the secondary air nozzle 7 into the furnace 1 is not swirled. The AAP structure is almost the same. According to the present embodiment, compared to the case where the secondary air 6 is swirled, the air is less likely to circulate in the radial direction. There is no problem.

  3 and 4 are front views of the AAP structure of FIGS. 1 and 2 as viewed from the furnace 1, respectively. In the case of the AAP structure that swirls the secondary air 6, the opening 16a of the edge plate 16 has a slit structure as shown in FIG. 3, and in the case of the AAP structure that does not swirl the secondary air 6, FIG. The edge plate 16 has a multi-nozzle 16a ′. In either case, the purpose is to adjust the negative pressure generated by the edge plate 16 and to prevent ash adhering to the furnace wall 1a.

  FIG. 5 shows a cross-sectional view of the AAP structure of another embodiment, whereas the edge portion of this embodiment has a structure in which the edge portion shown in FIG. The only difference is that it is parallel to the gas flow, and the rest of the configuration is the same. In the AAP structure shown in FIG. 5, since the tip of the edge plate 16 is parallel to the gas flow, the inner side of the edge plate 16 is less likely to be burnt and deformed compared to the AAP structure shown in FIG. There is an effect.

  Since the AAP structure of the present invention is inexpensive and can provide a combustion system with a high NOx effect of combustion exhaust gas, it is highly applicable to low NOx combustion apparatuses such as boilers.

It is sectional drawing of the AAP structure of one Example of this invention. It is sectional drawing of the AAP structure of one Example of this invention. It is a front view to the AAP structure of FIG. It is a front view to the AAP structure of FIG. It is sectional drawing of the AAP structure of one Example of this invention. It is a figure explaining the gas flow velocity distribution in the nozzle exit part by the difference in AAP structure. It is a figure which compares and shows the reduction performance of CO density | concentration in the furnace exit gas in the conventional AAP structure and the AAP structure which becomes this invention. It is a figure explaining the ash adhesion prevention principle by the secondary air of AAP structure. It is a figure explaining the ash adhesion situation in the furnace exit vicinity of an AAP structure. It is a block diagram of the boiler combustion apparatus of a prior art. It is sectional drawing of the AAP structure of a prior art.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Furnace 1a Furnace wall 2 Primary air 3 Wind box 4 Airport 5 Primary air nozzle 6 Secondary air 7 Secondary air nozzle 9 Box-shaped case 9a Opening part 10 Primary air flow control slide gate 12 Gate adjustment lever 13 Swivel 14 Driver 16 Edge plate 16a Opening 19 Secondary air flow rate adjusting slide gate 20 Gate adjusting lever 21 First divided air 22 Primary sleeve 22a Opening 23 Second divided air 24 Secondary sleeve 24a Opening 26, 27 Slide damper 28, 29 Drive device 30 Swivel 31 Driver 31 Furnace 32a Lower burner
32b Upper burner 33a Upstream after-air port 33b Downstream after-air port 36 FDF
37 Air heater 38 Damper 41 Denitration equipment 42 Chimney

Claims (3)

In an after-air port for introducing air into the furnace for complete combustion of the fuel in the reduced combustion state, which is disposed downstream of a burner for reducing and burning fuel provided in the furnace together with primary air,
A cylindrical primary air nozzle through which primary air for mainstream combustion provided in the center flows;
A secondary air nozzle through which secondary air for combustion is provided on the outer periphery of the primary air nozzle;
A plate-like edge member for reducing the primary air flow path provided at the opening end of the cylindrical primary air nozzle on the furnace side in a direction orthogonal or substantially orthogonal to the gas flow;
An after-airport characterized by comprising.   The after-airport according to claim 1, wherein an inclined portion is provided at a tip portion of the plate-like edge member.   The after-air port according to claim 1 or 2, wherein the plate-like edge member is provided with an opening at a location corresponding to the opening end of the secondary air nozzle on the furnace side.

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