JPS6280413A - Low nox combustion device for solid fuel - Google Patents

Abstract

PURPOSE:To enable a hot reducing flame to be formed near an injection port of a burner by a method wherein an L-shaped flame cap with its extremity end being opened is arranged at an extremity end of a fuel pipe, and at the same time an L- shaped bent part is arranged at an extremity end of a flow divider plate facing toward a furnace with a proper clearance being put between a fuel pipe within an extremity and passage of a fuel pipe, and a passage held by the fuel pipe and the flow divided plate is opened to a flame cap surface. CONSTITUTION:A flow divider plate 15 and a flame cap 100 are arranged around an oil injection nozzle 3 at the central part of a burner. The flow divider plate 15 arranged within a fine powder coal pipe 41 at the inner circumferential side of a flame cap 100 is a cylindrical form and its extremity end facing toward the furnace has an L-shaped bent part. A part 22 of the fine powder coal flow is flowed in an intermediate flow passage enclosed by the fine powder coal pipe 41 and the flow divided plate 15, guided by the bent part 15a at the extremity end of the downstream of the flow divider plate 15 and flowed as a fine powder coal flow 23, resulting in becoming a fine powder coal flow 24 flowing over the surface of the flame cap 100, merged with a secondary air swirl 25 by the flame cap 100, mixed with it and then a stable flame is generated on the flame cap.

Description

Detailed Description of the Invention (Industrial Application Field) The present invention relates to a combustion device for reducing nitrogen oxides (hereinafter referred to as NOx), and in particular to a combustion device for reducing nitrogen oxides (hereinafter referred to as NOx), and particularly for combustion of pulverized solid fuel such as pulverized coal and oil coke. The present invention relates to a combustion device that can sometimes achieve a significant reduction in NOx.

(Prior Art) Due to recent changes in the fuel situation, coal is increasingly being used as fuel in large boilers for commercial use, including large boilers for thermal power generation.

In this case, the coal is finely pulverized to improve the ease of combustion and the controllability of combustion. This pulverized coal combustion technology has been established for some time, and now enables highly efficient combustion comparable to that of heavy oil.

As with gas and heavy oil, various types of pulverized coal combustors have been developed and are in use. The most basic type of burner is a burner that has a pulverized coal supply pipe at its central axis and an annular air supply passage around its outer periphery.

In the burner, the coal is pulverized into fine powder by a mill, and then transported by air flow using conveying air that accounts for about 20 to 30% of the air required for combustion, and then introduced into the furnace through the fuel pipe nozzle. The remaining combustion air is injected from around the pulverized coal jet in a heavily or double annularly separated state, usually with some degree of swirl near the fuel nozzle.

The pulverized coal is flame-stabilized by the recirculation flow from the furnace near the burner throat toward the burner caused by this moderate swirling flow, and in some cases by a dish-shaped impeller added near the fuel pipe nozzle, resulting in steady combustion. maintained. If only pulverized coal is to be burned, this type of combustion device satisfactorily achieves the intended purpose.

However, as is well known, NOx, which is a by-product of fuel combustion, is often generated in high-load combustion burners (and because this is a cause of air pollution, burner improvements and combustion improvements throughout the furnace are being carried out. ing.

A particular problem in pulverized coal combustion is N caused by organic nitrogen (hereinafter referred to as Fueff N), which is contained in large amounts (usually 1 to 2 wt%) in pulverized coal.
0x (hereinafter referred to as Fueβ NOx), and occupies most of the NOx in the combustion exhaust gas.

Here, the reactions for producing NOx and NZ from FueβN are as shown in the following formulas (1) and (2), respectively, and both reactions are performed competitively.

Fue7! N+02. -=NOx (1)
Fue7! N0 NOx −=N2 (2
) Therefore, in order to prioritize the generation of N2 and maintain a certain degree of high-load combustion, securing a high-temperature reducing flame is an important point.

In general, the combustion method called two-stage combustion is an application of this combustion reaction, creating an air-deficient state in the burner zone of the furnace to form a high-temperature reducing flame, and then discharging the insufficient air into the downstream of the burner zone in the furnace. By injecting the fuel through the so-called after-air port, complete combustion is achieved, and combustion is improved throughout the furnace to reduce NOx emissions. Incidentally, currently, in the case of newly installed boilers that use common coal as fuel, the NOx emission concentration can be suppressed to about 200 ppm.

However, in the combustion of pulverized coal, it takes a considerable amount of combustion time to completely burn the reducing gas generated in the air-deficient burner zone and the remaining unburnt coal particles (char from which volatile matter has been removed) using afterair. This requires a large boiler furnace space. Therefore, although the above combustion method is in principle an extremely effective low NOx combustion method, it has certain limitations.

From this, instead of controlling the combustion of the entire boiler,
A so-called dual register type burner has been developed in which each burner is configured to perform low NOx combustion based on the above-mentioned principle.

FIG. 6 shows this dual register type burner. In the figure, the pulverized coal is injected into the furnace from a pulverized coal pipe 41 as a pulverized coal flow 10 together with its transportation air. This pulverized coal stream is injected into a furnace and combusted at a low air ratio to produce a reducing intermediate (gas) and reduce a portion of the NOx to N2 in the gas phase. On the other hand, the secondary air 2o that has passed through the secondary air register 61 and has been given a swirling force by the air vane 71 is directed to the outer periphery of the flame 105, and the tertiary air register 2o is directed to the outer periphery of the flame 105. Tertiary air 3o supplied via 62 is injected.

As a result, two-stage combustion is performed using the burner alone, and it has been demonstrated that NOx is reduced to about 400 ppm (reduction rate of 40%). This type of burner has low NO
In order to achieve the It is required that each of these air and flame (or gas) be mixed to effectively burn the unburned components.

However, in this type of burner, the secondary air 20 and the tertiary air 3o are usually separated from the fuel flow or each other by the pulverized coal pipe 41 and the secondary air pipe 43, but in reality, the secondary air 20 and the tertiary air 3o are Pulverized coal flow near the throat exit,
The secondary air jet and the tertiary air jet mix easily, and it is impossible to maintain sufficient separation of the high-temperature reducing flame in the early stages of combustion, making it extremely difficult to achieve further NOx reduction with this type of combustion device. It turned out to be difficult.

In view of the above points, the present inventors would like to invent and apply for a combustion device having the structure shown in FIG.
. In this device, first, the opening of the pulverized coal pipe 41 facing the furnace has an outward facing flame cap (hereinafter referred to as a flame cap) 100 whose diameter increases toward the opening end, and the flame 105 is It has started to form a stable shape. Next, as shown in the figure, the tips of the secondary air pipe 42 and the tertiary air pipe 43 on the outer periphery of the pulverized coal pipe 41 are funnel-shaped parts 101 and 102 whose diameter increases toward the open end, similar to the frame cap 100. The above-mentioned separation of fuel and air is effectively performed.

In the apparatus configured as shown in Fig. 7, a pulverized coal flow consisting of air and pulverized coal is injected into the furnace through a pulverized coal pipe 41 and burned. The impeller is not installed, and a small vortex part 103 is formed in the frame cap 100, and a small amount of pulverized coal is attracted to this from the outer peripheral surface of the pulverized coal flow jetting out from the pulverized coal pipe 41. There is also a sufficient supply of air from the outer periphery of the frame gear. Thus, a small and stable small flame is maintained here, ensuring reliable ignition of the pulverized coal stream injected into the furnace from the pulverized coal pipe 41. Therefore, the flame 105 ignites near the flame cap 100, as if the flame were close to the burner. Note that if the ignition is delayed, the flame 105 will be caused by the pulverized coal pipe 41
ignition occurs in the wake away from the nozzle, and flame formation shifts to the wake. In the one shown in FIG. 7, the flow rates of the secondary air 20 and tertiary air 30 are approximately 1:4, and the pressure of the tertiary air 30 is 120+nAq on the upstream side of the air register 62.
At the same time, by applying a strong turning force, the funnel-shaped portions 101.
102, the flame 105 is temporarily separated from the secondary and tertiary air.

By ejecting a relatively small amount of secondary air 20 with a swirling strength and direction different from that of the tertiary air, a stable vortex as shown at 106 in the figure is formed. This vortex 106
The small vortex 103 formed by the flame cap 100 suppresses the pulverized coal flow injected from the pulverized coal pipe 41 from spreading outward at the initial stage of charging into the furnace, and the flame 105 is strong at the initial stage. It becomes a high-temperature reducing flame. Due to radical substances such as NH2 and CN and reducing intermediate products such as CO in this high-temperature reducing flame,
Reduce NOx to N2. Further, on the downstream side of this high-temperature reducing flame, the injection energy of secondary air and tertiary air decreases and flows toward the burner axis, where unburned air is combusted.

(Problems to be Solved by the Invention) In the combustion apparatus shown in FIG. The remaining fixed carbon does not reach the point of combustion and cannot contribute to ignition near the flame cap.

The percentage of volatile matter in pulverized coal is determined by the fuel ratio (fuel ratio - fixed carbon/
Since the amount of coal with a high volatile content (volatile content) decreases, it becomes difficult to maintain a stable flame on the surface of the flame cap 100 and in the vortex section behind the flame cap 100 with coal having a high fuel ratio.

On the other hand, the pulverized coal that has been pulverized in the mill is conveyed to the pulverized coal pipe 41 using primary air, but at low load times when the boiler load is reduced, the safety of the mill and the coal feeding pipe from the mill to the burner and the safety of the coal feed pipe from the mill to the burner are To prevent backfire, the -deficit air volume cannot be lowered below a certain value despite the reduction in load. Therefore, under low load, the pulverized coal concentration of the mixed flow of pulverized coal and primary air flowing through the pulverized coal pipe 41 decreases.

As a result, the amount of pulverized coal supplied onto the surface of the flame camp 100 and into the vortex section 103 becomes insufficient, which impedes stable maintenance of the flame. Note that if the burner flame is ignited in the downstream region away from the burner nozzle, a flame detector that has a field of view near the burner nozzle will erroneously determine that the burner is misfiring.

An object of the present invention is to eliminate the drawbacks of the prior art described above, to form a high-temperature reducing flame near the burner nozzle, and to supply sufficient air in the downstream region of the flame even when the fuel ratio is high or the load is low. The purpose of the present invention is to provide a solid fuel low NOx combustion device that can perform the following steps.

(Means for Solving the Problems) The present invention has been made to solve the above problems, and in a combustion apparatus having a frame cap as shown in FIG. This is characterized by the provision of a device that actively guides a portion of the fluid to the frame cap surface and the vortex section 103. That is, in the present invention, a secondary air injection port is arranged substantially concentrically on the outside of a fuel pipe that injects a mixed fluid of solid fuel and primary air, and a tertiary air injection port is further arranged substantially concentrically on the outside of the fuel pipe. In this solid fuel device, an L-shaped frame cap that opens at the tip of the fuel tube is provided, and the tip of the secondary air tube that constitutes the outer peripheral surface of the secondary air injection port is shaped like a funnel whose diameter increases toward the open end. At the same time, a flow divider plate is provided in the fuel pipe tip passage at a distance from the fuel pipe, and an L is provided at the furnace side tip of the flow divider plate.
It is characterized by a letter-shaped bent part so that the passage sandwiched between the fuel pipe and the flow divider plate opens into the frame cap surface.

(Embodiment of the Invention) FIG. 1 is a cross-sectional view of the vicinity of a burner of a combustion apparatus showing an embodiment of the present invention, and FIG. 2 is a plan view of the burner in the B direction.

An oil spray nozzle 3 is provided at the center of the burner, and a flow divider plate 15 and a frame cap 100 are provided around it. The frame cap 100 has notches 100a divided into six parts to prevent deformation due to thermal expansion. The flow dividing plate 15 provided inside the pulverized coal pipe 41 on the inner peripheral side of the frame cap 100 has a cylindrical shape and has an L-shaped bent portion at the tip facing the furnace. Note that the flow dividing plate does not necessarily have to have a continuous cylindrical shape in the circumferential direction. The pulverized coal that has flowed into the gap between the flow divider plate 15 and the pulverized coal pipe 41 is guided by the L-shaped bend at the tip of the flow divider plate, and is supplied onto the surface of the frame cap 100 together with a portion of the primary air. It is supposed to be done. That is, the third
The figure is a detailed view of part A in Figure 1. Part 2 of the pulverized coal flow
The pulverized coal 2 flows through an intermediate flow path surrounded by the pulverized coal pipe 41 and the flow divider plate 15, is guided by the curved part 15a at the trailing end of the flow divider plate 15, and flows like the pulverized coal flow 23, and the pulverized coal flow 23 flows through the frame cap 100. The pulverized coal flow 24 flows over the surface and combines with the entrainment 25 of secondary air by the flame cap 100 to mix and create a stable flame on the flame cap. FIG. 4 shows the C parent diagram of FIG. 3. In FIG. 4, one or more slits 27 are provided to prevent thermal deformation of the frame cap 100.

In the apparatus configured as described above, the oil fuel 1 passes through the oil supply pipe 2 and is supplied in the form of mist to the furnace 16 from the spray nozzle 3. This oil fuel is used especially when the boiler is started, when the boiler is under low load, when the pulverized coal grinding mill is stopped, and is not used under normal operating conditions. From the bunker, the coal passes through a coal feeding and weighing machine and is turned into pulverized coal in a mill (not shown).
The pulverized coal is transported by air and supplied to the burner, and after being accelerated by the venturi 5, it flows through the pulverized coal pipe 41 and enters the fuel injection port 6.
is supplied into the furnace.

On the other hand, the combustion air is pressurized by a fan and then heated by an air heater to approx.
The temperature is raised to 00° C., guided through a duct, and supplied to the wind box 7 constituted by the boiler wall 50 and the wind box wall 8. A part of the combustion air is introduced from the secondary air intake 11 adjusted by the secondary slide damper 9, and is swirled by the secondary air register 71 provided in the passage between the secondary air pipe 43 and the pulverized coal pipe 41. After that, the furnace 1 is discharged from the secondary air injection port 12.
6. The remaining combustion air is turned into a swirling flow by the tertiary air register 62 and is supplied to the furnace 16 from the tertiary air injection port 13 . On the surface of the annular frame cap 100, a region where there is almost no velocity component in the axial direction is generated, and a small vortex portion is generated immediately after the frame cap. As described in the explanation of FIG. 7, the surface of the flame camp 100 serves as the ignition point and the flame is stabilized.

In the embodiment shown in FIG. 1 as well, the flow rate ratio of the secondary air and the tertiary air is set to about 1=3 to 1:4, and the air pressure of the tertiary air in front of the air register 62 is set to 120111 Aq or more, and the tertiary air It is effective to give a strong swirling flow to the air, and to make the swirling directions of the secondary air and tertiary air opposite to each other. By doing so, the flame camp 100 and the funnel-shaped enlarged portion at the tip of the sleeve 43 are combined to temporarily exchange the flame formed at the burner outlet [-1] with secondary air and tertiary air. A strong high-temperature reducing flame is formed at the burner outlet to reduce NOx to N2, and on the downstream side of this high-temperature reducing flame,
The injection energy of the secondary air and tertiary air also decreases and flows toward the burner axis, making it possible to burn unburned air.

As a modification of the present invention, as shown in FIG. 5, it is conceivable to provide a swirler 26 in a passage constituted by a pulverized coal pipe 41 and a flow divider plate 15. The degree of rotation of this swivel is
The angle can be changed by changing the angle of one or more variable blades. As mentioned above, this is to create optimal flame-holding combustion conditions by changing the amount of pulverized coal supplied to the flame cap surface when the volatile content ratio in the pulverized coal changes.

In addition, in the explanation so far, the case where pulverized coal is used as the fuel has been described, but the present invention is not limited to this, and can also be applied to solid pulverized fuel such as petroleum coke. It goes without saying.

(Effects of the Invention) In the combustion device according to the present invention, a part of the fuel can be reliably supplied onto the flame cap, so a stable flame can be formed from the burner injection port even with high fuel ratio coal with low volatile content. It is possible to measure flame stability even under low load. Therefore, a strong high-temperature reduction flame is formed near the burner nozzle, and as the combustion progresses,
In addition to reducing the generated NOx to N2, sufficient afterair is supplied in the downstream region of the flame, allowing complete combustion of unburned matter. Furthermore, since reliable fire formation at the burner nozzle can be ensured, erroneous judgments by the fire detector can be eliminated and stable combustion control can be performed.

[Brief explanation of drawings]

Fig. 1 is a sectional view of a solid fuel combustion device showing an embodiment of the present invention, Fig. 2 is a main view of B in Fig. 1, Fig. 3 is a detailed view of part A in Fig. Figure C and Figure 5 are views of the vicinity of the frame cap showing another embodiment of the present invention. FIGS. 6 and 7 are sectional views of conventional solid fuel combustion devices, respectively. 6...Fuel injection port, 12...Secondary air injection port, 13
... Tertiary air injection port, 15... Diversion plate, 15a...
・Bent portion of flow divider plate, 41...Pulverized coal pipe, 43...Secondary air pipe, 100...Frame cap, 102...
Enlarged tip of secondary air tube. Agent Patent Attorney Nicho Kawakita Figure 1 Figure 2 6, Fuel injection port 15a: Flow divider plate bent part 7
: Wind box 16 Secondary furnace 12/Secondary air injection port 41: Powder flame tube 13゛Tertiary air injection port 43: Secondary air pipe 14: Burner cone 100: Frame cap 15: Flow divider plate
102: Enlarged section of the tip of the secondary air pipe Fig. 3 Fig. 4 Fig. 5 Fig. 6 n Fig. 7

Claims (1)

[Claims] (1) Solid fuel in which a secondary air injection port is arranged approximately concentrically on the outside of a fuel pipe that injects a mixed fluid of solid fuel and primary air, and a tertiary air injection port is further arranged approximately concentrically on the outside of the fuel pipe. In the device, an L-shaped frame cap that opens at the tip is provided at the tip of the fuel tube, and the tip of the secondary air tube that constitutes the outer peripheral surface of the secondary air injection port is shaped like a funnel whose diameter increases toward the open end. At the same time, a flow divider plate is provided within the fuel pipe tip passage at a distance from the fuel pipe, and an L-shaped bent portion is provided at the furnace side end of the flow divider plate, so that the passage sandwiched between the fuel pipe and the flow divider plate is connected to the frame. A solid fuel low NO_x combustion device characterized by having an opening on a cap surface.