JP4386279B2 - Burner operation - Google Patents

Description

This invention relates to a method of operating burners utilized in coal-fired boiler for burning in switching the pulverized solid fuel or with finely divided solid fuel and liquid fuel in order to co-firing a liquid fuel such as oil.

Since pulverized coal is a representative example of the pulverized solid fuel, the pulverized coal burner will be described below.
FIG. 7 shows a schematic cross-sectional configuration diagram of a conventional pulverized coal burner. A flame holder 2 that controls flame holding is attached to the tip of a pulverized coal nozzle 5 that guides a mixed fluid F of fuel and carrier air (primary air) to the furnace 1. A strong vortex flow (circulation flow region) 19 is formed on the downstream side of the flame stabilizer 2, and stable combustion is maintained. A secondary air flow path 3 and a tertiary air flow path 4 are installed on the outer peripheral portion of the pulverized coal nozzle 5 to separate and supply combustion air, thereby forming an excessive fuel reducing atmosphere in the center of the flame. The amount of NOx generated in can be kept low. The burner capable of reducing NOx combustion shown in FIG. 7 is described in, for example, Japanese Patent Application Laid-Open No. 2001-82706, which is the invention of the present applicant. 7 is provided with an oil burner 6 for fuel ignition, and a concentrator 13 is provided on the outer periphery of the oil burner 6.

  By the way, although pollution prevention regulations for environmental conservation are becoming stricter year by year, it is required to reduce the amount of NOx generated in the combustion gas as much as possible (hereinafter referred to as low NOx), particularly in the case of the pulverized coal boiler that burns the coal. Has been.

  In addition, compared with domestic coal-fired boilers, overseas-use coal-fired boilers have less restrictions on restricting the NOx concentration in the exhaust gas to a predetermined level or less, so fuel consumption is reduced to lower NOx. In many cases, a two-stage combustion apparatus capable of combustion is not provided.

  The two-stage combustion method is the air ratio in the burner zone of the furnace 1 (the flow rate of air to be injected into the furnace from the burner section) The air flow rate required to completely burn the pulverized coal (hereinafter, the theoretical air flow rate) The NOx generated by the combustion of the solid fuel is reduced by maintaining the fuel rich condition with a ratio of 1 or less) to 1 or less, and the NOx in the combustion gas is reduced. For the unburned fuel at this time, This is a system in which combustion air is introduced from the air inlet on the flow side and burned.

However, since it is indispensable to reduce NOx due to environmental regulations in recent years, a low-cost and low-NOx reduction method is desired, but it has been applied to domestic business boilers in the past. A method has been adopted in which NOx conversion technology is also applied to a coal-fired boiler for overseas use.
JP 2001-82706 A

  As described above, regulations on NOx concentration in exhaust gas tend to be strengthened overseas as well. However, conventional coal-fired boilers for overseas use have two-stage combustion equipment compared to domestic coal-fired boilers. It is often not provided. For this reason, it is necessary to install equipment that is compatible with low NOx in coal-fired boilers for overseas use, but existing boilers do not have a two-stage combustion port. Therefore, it is desired to develop a burner having a NOx reduction effect that can be handled with relatively low cost by simply replacing the burner in an existing coal-fired boiler combustion system.

  The coal-fired boiler is equipped with an oil burner not only for burning coal but also for burning oil such as heavy oil when starting the burner. Accordingly, a low soot and dust performance is required during heavy oil combustion while maintaining the NOx reduction combustion performance during coal combustion.

The problem of the present invention is that it has a low NOx reduction combustion effect at a low cost, and at the time of combustion of liquid fuel such as heavy oil while maintaining low NOx reduction combustion performance at the time of combustion of pulverized solid fuel such as pulverized coal, to provide a method for operating burners for low dust performance.

The above-mentioned problem of the present invention is solved by the following means.
The invention described in claim 1 is provided by being inserted into an opening portion of a water wall surrounding the furnace, in which the pulverized solid fuel and the liquid fuel are co-fired in the furnace, or the pulverized solid fuel and the liquid fuel are switched and the furnace is used. A burner operating method for burning, wherein as the burner, a mixed fluid nozzle in which a mixed fluid of the finely divided solid fuel and a carrier gas flows around the central axis of the burner, and the liquid fuel flows in the mixed fluid nozzle An oil burner, one or more combustion air passages through which combustion air flows on the outer periphery of the mixed fluid nozzle, a flame holding mechanism provided at the tip of the mixed fluid nozzle, and an outer periphery of the oil burner A core air flow path through which the core air flows, and a forward end side of the flame holding mechanism at the front end of the core air flow path, the direction of jetting the core air into the furnace is deflected radially outward with respect to the burner central axis Let me before Toward flow portion after the flame holding mechanism using a burner provided with a core air deflecting means for flowing the core air, when the oil burner starts, flowing core air flow rate of core air flow path at a maximum flow rate for the core air flow path, This is a burner operating method in which the core air flow rate is made to flow at the minimum set flow rate in the core air flow path when only the pulverized solid fuel is burned .

The invention according to claim 2 uses, as the burner, a burner provided with a core air flow rate adjusting means for adjusting the core air flow rate in the core air flow path. The core air flow rate is made to flow at the maximum set flow rate in the core air flow path, and when only the pulverized solid fuel is burned, the core air flow rate is made to flow at the minimum set flow rate in the core air flow path by the core air flow rate adjusting means. This is the operation method of the burner.

(Function)
According to the first aspect of the present invention, the combustion air can be supplied as needed by the core air deflecting means (deflection hub 11) to the outside of the burner in the radial direction with respect to the central axis of the burner. As a measure against black smoke when starting an oil burner, which was a drawback of the co-firing burner of finely divided solid fuel and liquid fuel, core air for oil combustion can be supplied to the center of the burner. Reduce NOx concentration.

Then , the core air can be effectively flowed toward the rear of the flame holding mechanism (flame holder 2) by the core air deflecting means (deflection hub 11), and the reduction combustion at the rear of the flame holding mechanism (flame holder 2). This can be reduced without destroying the area, expanding the oxidative combustion area, reducing the dust concentration during liquid fuel (oil) firing, and adjusting the flow rate of the core air in the exhaust gas. It is possible to reduce the NOx concentration.

When the oil burner is started, stable combustion can be maintained without generating black smoke when starting the oil burner by causing the core air flow rate in the core air flow path to flow at the maximum set flow rate in the core air flow path. Further, when only the fine powdered solid fuel is burned, the core air flow rate is made to flow at the minimum set flow rate so as to reduce the NOx concentration in the exhaust gas.

According to the invention of claim 2 , in addition to the action of the invention of claim 1, the core air flow rate adjusting means can easily adjust the combustion air flow rate in the core air flow path according to the combustion state of the fuel, Core air can be flowed at the time of oil combustion at the time of starting and stopping of the furnace such as when the boiler is started, and the core air flow rate at the time of normal fine powder solid fuel combustion can be made the minimum flow rate.

  According to the first aspect of the present invention, it is possible to prevent soot from adhering to the tip of the burner when starting the oil burner by adjusting the supply amount of the core air, and to reduce the NOx concentration in the combustion gas.

Further , it is possible to reduce the reduction combustion area behind the flame holding mechanism (flame holder 2) by supplying the core air without destroying it, and the NOx concentration in the exhaust gas is reduced by expanding the oxidation combustion area. And the flame holding mechanism can be prevented from being burned out.

And, when burning the oil burner, stable combustion can be maintained without generating black smoke, and when burning only fine powdered solid fuel, the core air flow rate is flowed at the minimum set flow rate to reduce the NOx concentration in the exhaust gas Can be achieved.

According to the invention described in claim 2 , in addition to the effect of the invention described in claim 1, the core air flow rate at the time of starting and stopping of the furnace and at the time of normal pulverized solid fuel combustion can be adjusted to an appropriate amount .

Embodiments of the burner used in the present invention will be described with reference to the drawings.
The burners of the following examples are those used in the low NOx pulverized coal burner shown in FIG.
FIG. 2 shows a schematic cross-sectional configuration diagram of the low NOx pulverized coal burner of the present embodiment. A flame holder 2 that controls flame holding is attached to the tip of a pulverized coal nozzle 5 that guides a mixed fluid of fuel and carrier air (primary air) to the furnace 1. The secondary air flow path 3 and the tertiary air flow path 4 are installed in the outer peripheral part of the pulverized coal nozzle 5, and the secondary air and the tertiary air are separated and supplied to the burner, and an excessive fuel reducing atmosphere is formed in the center of the flame. By forming it, it is possible to reduce the NOx concentration in the flame.
Although not shown, an after-air port is provided on the downstream side of the burner installation portion of the furnace 1, and oxygen is supplied to the flame that is reducing and burning to achieve complete combustion of the fuel.

  Further, a pulverized coal nozzle 5 through which a mixed fluid composed of pulverized coal and a conveying gas flows is provided at the center of the burner, and an oil burner 6 that is often used at the time of starting the burner is provided in the inner central shaft portion of the pulverized coal nozzle 5. A core air flow path 8 is provided on the outer periphery of the oil burner. Combustion air is supplied from the wind box 7 to the core air flow path 8. A damper 10 is provided at the inflow portion from the wind box 7 to the core air flow path 8 to adjust the flow rate of the core air.

FIG. 1 shows a partially enlarged view of the burner shown in FIG.
An oil burner 6 that is often used at the time of starting the burner and a core air flow path 8 are provided on the outer periphery of the oil burner 6 at the inner central shaft portion of the pulverized coal nozzle 5. The distal end portion of the core air passages 8 Ru Tei deflection hub 11 is provided. A concentrator 13 for reducing the mixed fluid flow path of the pulverized coal nozzle 5 is provided on the outer wall of the core air flow path 8.

  Further, a secondary air flow path 3 and a tertiary air flow path 4 to which combustion air is supplied from a wind box 7 are provided on the outer periphery of the pulverized coal nozzle 5, and an air swirler 14 is provided in the tertiary air flow path 4. It is done. Although not shown, an air swirler may be provided in the secondary air flow path 3. Further, a sliding damper 15 for adjusting the secondary air flow rate is provided at the inlet of the secondary air flow path 3.

  In addition, although air may be used as the gas for conveying pulverized coal, the combustion exhaust gas discharged from the furnace 1 is used in order to prevent the ignited pulverized coal from being ignited while being conveyed to the outlet of the pulverized coal nozzle 5. It may be used.

  In the burner shown in FIGS. 1 and 2 having the above-described configuration, the mixed fluid of the pulverized coal and the transfer gas flowing into the pulverized coal nozzle 5 has a flow of fuel particles (pulverized coal) having a larger inertia force than the fuel transfer gas. The flow direction is changed to the inner peripheral wall side of the pulverized coal nozzle 5 by the concentrator 13 and then flows along the inner peripheral wall side, and mixed with the secondary air entrained by the flame holder 2 at the outlet of the pulverized coal nozzle 5. A circulation flow with a relatively high pulverized coal concentration is formed. The pulverized coal having a relatively high concentration in the circulation flow is easily ignited, and the circulation flow is convenient for the flame holding of the ignited pulverized coal, and the combustion stability is also improved.

FIG. 3 shows the combustion state of the fuel in the furnace at the rear of the burner when the core air is not supplied, and FIG. 4 shows the combustion state of the fuel in the furnace when the core air is supplied.
As shown in FIG. 3, when oil combustion is performed without flowing the core air, an oxidation region 17 and reduction regions 18 and 19 as shown are formed in the burner wake. In particular, a large reduction region 19 is formed behind the flame holder 2, and this causes unburned soot and soot. Further, as described above, the reduction region 19 is also a circulation flow formation region and is a vast region. Therefore, the oil droplets ejected from the oil burner 6 are scattered, and the oil droplets are taken into the reduction region 19. Then, it adheres to the flame holder 2 and locally generates heat, which may lead to burning of the flame holder 2.

  On the other hand, FIG. 4 shows the combustion state in the burner wake portion when the core air is flowed. The flow direction of the core air into the furnace is effectively made to flow radially outward with respect to the burner central axis toward the rear side of the flame holder 2 by the deflection hub 11, so that the reduction region 19 is not destroyed. The oxide region 17 can be enlarged by reducing the size. As a result, the dust concentration can be reduced during the oil-only firing.

  As shown in FIGS. 5 and 6, the nozzle structure at the tip of the burner that effectively injects the core air has a plurality of concentric deflections around the central axis of the pulverized coal nozzle 5 at the tip of the core air flow path 8. A core air injection nozzle 21 is installed between the hubs 11.

  Since the cross-sectional area of the core air flow path 8 is disposed at the center of the burner, it is inevitable that the core air flow path 8 is smaller than the secondary air flow path cross-sectional area and the tertiary air cross-sectional area. In addition, since the core air changes the flow direction at the tip of the burner, there is a limit to the smaller channel cross-sectional area. Therefore, it is necessary to devise an opening ratio (nozzle area / main-axis direction channel cross section) as large as possible.

  FIG. 5 is a view of a nozzle having a slit structure as a deflection hub 11 that changes the flow of core air, as viewed from inside the furnace. The core air injection nozzle 21 has a comb-like shape in which the center portion of the burner is cut in the circumferential direction. With this structure, since the inner wall of the core air flow path 8 is not required, there is an advantage that the supply cross-sectional area of the core air can be increased.

  FIG. 6 is a view of the nozzle provided with the deflection hub 11 in which the circular core air injection nozzle 22 is arranged in the circumferential direction as viewed from inside the furnace. This is a structure in which a plurality of elliptical nozzles 22 are provided on the ring-shaped deflection hub 11, and the core air injection direction can be set more accurately than the core air injection nozzle 21 having the slit structure shown in FIG. Have However, the opening ratio of the core air injection nozzle 22 cannot be increased.

  In addition, the burner of the said Example can be utilized as a pluggable burner provided with the core air flow path instead of the burners, such as the conventional pulverized coal burner already installed in furnaces, such as a boiler.

The present invention can be used for a burner operation method used in a coal-fired boiler or the like for burning a pulverized solid fuel and a petroleum fuel together or by switching between a pulverized solid fuel and a petroleum fuel for combustion.

It is a sectional side view regarding the structure from the wind box of the burner of the Example of this invention to a furnace. It is sectional drawing including the core air introduction part of the burner of FIG. It is a figure explaining the combustion condition of the burner rear part in case the core air is not sent with the burner of FIG. It is a figure explaining the combustion condition of the burner rear part at the time of flowing core air with the burner of FIG. It is the figure which looked at the deflection | deviation hub part of the core air ejection part of FIG. 1 from the inside of a furnace. It is the figure which looked at the deflection | deviation hub part of the other Example of the core air ejection part of FIG. 1 from the inside of a furnace. It is a schematic sectional block diagram of the conventional pulverized coal burner.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Furnace 2 Flame stabilizer 3 Secondary air flow path 4 Tertiary air flow path 5 Pulverized coal nozzle 6 Oil burner 7 Wind box 8 Core air flow path 10 Damper 11 Deflection hub 13 Concentrator 14 Air swirler 15 Sliding damper 17 Oxidation region 18, 19 Reduction area 21, 22 Core air injection nozzle

Claims (2)

This is a burner operation method that is provided by being inserted into the opening of the water wall surrounding the furnace, and pulverized solid fuel and liquid fuel are co-fired in the furnace or switched between pulverized solid fuel and liquid fuel and burned in the furnace. And
As the burner, a mixed fluid nozzle in which a mixed fluid of the pulverized solid fuel and a carrier gas flows around the central axis of the burner, an oil burner in which the liquid fuel flows in the mixed fluid nozzle, and an outer periphery of the mixed fluid nozzle One or more combustion air flow paths through which combustion air flows, a flame holding mechanism provided at the tip of the mixed fluid nozzle, a core air flow path through which core air flows in the outer periphery of the oil burner, and the core air A posterior part of the flame holding mechanism by deflecting the ejection direction of the core air into the furnace radially outward with respect to the burner central axis at the front end of the flow path and on the upstream side of the flame holding mechanism Using a burner provided with a core air deflecting means for flowing the core air toward
When starting the oil burner, flow the core air flow rate in the core air flow path at the maximum set flow rate in the core air flow path, and when burning only fine powdered solid fuel, flow the core air flow rate at the minimum set flow rate in the core air flow path A burner operation method characterized by the above. As the burner, further using a burner provided with a core air flow rate adjusting means for adjusting the core air flow rate in the core air flow path ,
When starting the oil burner, the core air flow rate adjusting means causes the core air flow rate in the core air flow path to flow at the maximum set flow rate in the core air flow path, and when only the pulverized solid fuel is burned, the core air flow rate adjusting means causes the core air flow rate to be adjusted. 2. The burner operating method according to claim 1, wherein the flow is performed at a minimum set flow rate in the core air flow path .

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