JP3765429B2 - Pulverized coal burner - Google Patents

Description

[0001]
[Technical field to which the invention belongs]
The present invention relates to a pulverized coal burner used in a pulverized coal combustion system used for boilers and the like.
[0002]
[Prior art]
The pulverized coal combustion system used for boilers and the like has a configuration in which coal is pulverized by a pulverized coal machine (mill) with a built-in classifier, and pulverized coal of a predetermined size or less is supplied to the burner section by air for classification. It has become. Such a pulverized coal combustion system will be described with reference to FIG.
[0003]
FIG. 17 is a system diagram of the pulverized coal combustion system. In this figure, 1 is a boiler furnace, 2 is a wind box, 3 is a pulverized coal burner, 4 is a gas recirculation charging duct, and 5 and 6 are heat exchangers. 7 is a gas recirculation fan that takes out the exhaust gas from the flow of the exhaust gas G and supplies it to the gas recirculation input duct 4, 8 is an FDF that supplies air to the wind box 2, and 9 is a primary air fan that supplies air for conveyance. Is a damper for adjusting the flow rate of each fluid. 11 is a coal bunker that stores coal, 12 is a mill that incorporates a classifier and crushes the coal in the coal bunker 11, 13 is a coal feeder that supplies coal from the coal bunker 11 to the mill 12, and 14 is a concentrator.
The primary air supplied by the primary air fan 9 conveys pulverized coal of a predetermined size or less pulverized by the mill 12 to the concentrator 14 as a solid-gas two-phase flow. The concentrator 14 converts the pulverized coal into a concentrated flow and a lean flow. The separated lean stream is supplied to the pulverized coal burner 3 through the pipe 15, and the concentrated stream is supplied through the pipe 16.
[0004]
In the pulverized coal combustion systems, low NO _X reduction by two-stage combustion method is used. The two-stage combustion method has an external expression and an internal expression. 2-stage combustion method of the external type, the reduction of the generation NO _X by keeping air ratio of the burner zone of a combustion furnace (1 stoichiometric equivalents at a rate of required air to fuel) to less than one fuel-rich conditions and achieving low NO _X reduction by a method to complete combustion by introducing air from the air insertion port which is disposed on the downstream of the burner zone for unburned fuel. The internal two-stage combustion method is a combustion method in a burner zone in which secondary and tertiary air is swirled and mixing with pulverized coal that is ignited and combusted only in primary air is delayed, and NR, NR2, etc. It is put into practical use in the pulverized coal low NO _X burner.
[0005]
In addition, in order to increase the solid concentration in the pulverized coal flow, a separation device that uses the difference in the inertia force between the solid and gas is installed inside the burner in order to increase the solid concentration in the pulverized coal flow. Alternatively, means for promoting ignition flame holding by installing a solid gas separator such as a cyclone or a vent pipe outside the burner has been put into practical use.
[0006]
[Problems to be solved by the invention]
The low NO _X reduction techniques according to an external type and an internal type combination in the two-stage combustion method, NO _X emissions in the boiler outlet, back and forth 100~150ppm [fuel ratio value (fixed carbon / volatile matter) is 2, coal It can be reduced to 1.5% or less of the reference coal with an N content of 5% or less in the ash. However, from the viewpoint of environmental measures, regulation of the NO _X emission amount included in the combustion exhaust gas is in one made stricter, so that it is required to the boiler outlet NO _X emission concentration is also less low value 100ppm .
[0007]
In the wide-area load operation by lowering the minimum load, the minimum load of the current burner is 30 to 40%, but in the next generation boiler, stable combustion at 25% or less is an important issue as the burner capacity increases. Yes. In addition to this, in Japan close dependence on imported coal to 100%, stable low NO _X reduction is not influenced by coal type, the probability of wide area load corresponding technology is the essential.
[0008]
As those aimed such NO _X emissions 100ppm or lower NO _X measures and wide area load corresponding internal holding in a stream of the concentrate stream of the burner supplied by separating pulverized coal to concentrate stream and lean stream Japanese Patent Application No. Hei 6-277733 proposes a method of strengthening the ignition flame holding by installing a flame unit.
[0009]
However, the problem with such a technique is that the internal flame holder is in the concentrated flow, so it is not useful for ignition flame holding on the lean flow side. As a countermeasure, it is conceivable to separate and supply the concentrated flow and the lean flow through the separation wall, and install an internal flame holder at the tip of the separation wall to ignite and hold both the concentrated flow and the lean flow. However, in that case, the entrainment of the wake flow of the internal flame stabilizer to the recirculation region occurs from both the concentrated flow and the lean flow, and in particular, if the flow from the lean flow increases, the flame holding effect is diminished. Problems arise.
[0010]
An object of the present invention is to solve the problems in the prior art, while maintaining ultra low NO _X reduction, it is possible to enhance the ignition flame holding, it is possible to cope with a consequently wide area load operation, the multi-coal types It is to provide a pulverized coal burner.
[0011]
[Means for Solving the Problems]
In order to achieve the above object, the present invention separates a solid-gas two-phase flow composed of solid fuel and a transport gas into a concentrated flow and a lean flow by a separation tube, and these are supplied side by side at the separation tube outlet. And, in the pulverized coal burner in which the internal flame stabilizer is installed at the outlet end of the separation pipe, the lean flow acceleration that makes the flow rate of the lean flow at the position of the internal flame stabilizer faster than the flow rate of the concentrated flow Means is provided.
[0012]
[Action]
Since the flow rate of the lean flow is larger than the flow rate of the concentrated flow, the concentrated flow containing a large amount of pulverized coal is entrained in the dilute flow and flows to the recirculation region downstream of the internal flame holder and is included in the entrained concentrated flow As the pulverized coal burns, the recirculation zone becomes hot and promotes the flame holding of unignited pulverized coal passing near the internal flame holder, thereby strengthening the ignition flame holding.
[0013]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the present invention will be described based on the illustrated embodiments.
FIG. 1 is a diagram showing a pulverized coal burner according to a first embodiment of the present invention, and FIG. 2 is a diagram showing a pulverized coal burner according to a second embodiment. In each figure, 20 is a concentrated flow lean flow separation tube (hereinafter simply referred to as a separation tube), which separates the lean flow C ₀ and the concentrated flow C ₁ . 200 tapered portion narrowed toward the center in the front end portion of the separation tube 20, 201 lean stream channel through which lean stream C _0, 202 denotes a concentrate stream flow path is concentrated stream C ₁ through. 21 is an outer flame holding ring, 22 is an internal flame holder installed at the outlet end of the separation tube 20, and 23 is a heavy oil nozzle for ignition. Reference numeral 24 denotes a venturi type resistor provided in the concentrated flow channel 202. Reference numerals 25 and 26 denote swirlers for swirling the secondary air A ₂ and the tertiary air A ₃ , respectively. In each figure, the right portion of the internal flame holder 23 is the inside of the boiler furnace 1.
[0014]
In each of these embodiments, since the tapered portion 200 narrowed toward the center is provided at the distal end portion of the separation tube 20, the outlet d ₁ of the lean flow channel 201 is narrowed, while the outlet d of the concentrated flow channel 202. ₂ is spread, thereby the flow rate of the lean stream C ₀ becomes larger than the flow rate of the concentrate stream C _1, the concentrate stream C ₁ at the outlet is involved in lean stream C _0, concentrate stream C ₁ contains much pulverized coal Flows into the recirculation region (the region on the right side of the internal flame holder 22 in the figure) in the wake of the internal flame holder 22, and the recirculation region becomes high due to the combustion of many pulverized coal contained in the entrained concentrated flow. Thus, the ignition flame holding to the unignited pulverized coal passing through the vicinity of the internal flame holder 22 is promoted, and the ignition flame holding is strengthened.
[0015]
The venturi-type resistor 24 is provided to prevent the gas flow distribution at the inlet from changing by reducing the cross-sectional area of the lean flow side outlet and preventing the flow into the lean flow side from decreasing. It is desirable to prevent the pulverized coal from burning by making the resistor a venturi type. However, this venturi type resistor 24 is not necessarily required, and a configuration in which the venturi type resistor 24 is removed is shown in FIG. 2, which is the second embodiment.
[0016]
The above entrainment operation will be described in more detail with reference to FIGS. The amount of the concentrated stream C ₁ flowing into the recirculation region depends on the magnitude of the momentum of both streams. The magnitude of the fluid momentum is given by the fluid density multiplied by the square of the flow velocity. Therefore, if the density of the lean flow C ₀ is ρ ₀ and the velocity is v ₀ , the momentum of the lean flow C ₀ is ρ ₀ · v ₀ ² , and the density of the concentrated flow C ₁ is ρ ₁ and the velocity is v _1. The momentum of the concentrated flow C ₁ is ρ ₁ · v ₁ ² . FIG. 3 is a graph showing the concentration of the concentrated flow C _{1 in} the recirculation region (the amount of entrainment of the concentrated flow C _{1 in} the recirculation region) relative to the ratio of the momentum of the lean flow C _{0 and} the momentum of the concentrated flow C ₁ . On the axis is the ratio of the momentum of the lean flow C _{0 to} the momentum of the concentrated flow C ₁ (ρ ₀ · v ₀ ² / ρ ₁ · v ₁ ² ), and on the vertical axis is the concentration of the concentrated flow C _{1 in} the recirculation region. There is. From FIG. 3, it can be seen that the greater the ratio of the momentum of the lean flow C _{0 and} the momentum of the concentrated flow C ₁ , the greater the amount of entrainment of the concentrated flow C _{1 in} the recirculation region.
[0017]
Here, an example of the flow rate determination method for the lean flow C ₀ and the concentrated flow C ₁ will be described with reference to FIGS. 4 and 3. FIG. 4 is a graph showing the average pulverized coal concentration with respect to the burner load. The horizontal axis represents the burner load, and the vertical axis represents the average pulverized coal concentration (the weight of pulverized coal in 1 kg of air, expressed as C / A). is there. Usually, the flow rate of the pulverized coal in the pulverized coal burner is 20 to 25 m / s, and if it is 15 m / s or less, there is a risk of flame blowing. Therefore, in the present embodiment, the flow rate of the lean flow C ₀ is limited to a range of 20 to 30 m / s, and the flow rate of the concentrated flow C ₁ is limited to a range of 15 to 25 m / s.
[0018]
From FIG. 4, C / A at a burner load of 50% is 0.33. In this case, with a burner with a concentration capacity of 1.3 times, the air is equally distributed, the C / A on the concentration side is 0.43 (0.33 × 1.3), and the C / A on the lean side is 0.3. 23. C / A = 1 corresponds to the equivalent ratio of combustion, and the temperature in the recirculation region of the internal flame holder 22 at that time is the highest, which is the optimum value for ignition flame holding. The pulverized coal contains about 30% of 20 μm or less when passing through 200 mesh at 80%, and particles of about 20 μm or less having a relatively small inertia force are caught in the recirculation region.
[0019]
Now, assuming that the volume concentration in the recirculation region of the concentrated stream C ₁ is C ₁₁ , in order to ensure C / A = 1 in the recirculation region,
0.3 [0.43 C ₁₁ +0.23 (1-C ₁₁ )] = 1
Must hold. From the above equation, C ₁₁ = 0.5.
In order to obtain this volume concentration, the ratio of the momentum of the lean flow C _{0 and} the momentum of the concentrated flow C ₁ may be selected to be 2.1, as indicated by the broken line in FIG. Since ρ ₀ / ρ ₁ is 0.23 / 0.43, v ₀ / v ₁ = 1.9.
For example, if the flow rate of the lean flow C ₀ is selected to be 30 m / s, the flow rate of the concentrated flow C ₁ is about 16 m / s.
In each of the above embodiments, in order to increase the flow rate of the dilute flow and decrease the flow rate of the concentrated flow, the tapered portion 200 that narrows toward the center side is formed at the distal end portion of the separation tube 20. In order to realize the above flow velocity, the shape of the tapered portion 200 may be formed so that (the outlet cross-sectional area of the concentration channel 202) / (the outlet cross-sectional area of the lean channel 201) = 1.9. .
[0020]
Thus, in each of the above embodiments, the flow rate of the lean flow is made faster than the flow rate of the concentrated flow, so that the concentrated flow can be engulfed into the recirculation region by the lean flow, and the pulverized coal is separated into the concentrated flow and the lean flow. while maintaining very low NO _X reduction of the pulverized coal burner supplies, it is possible to enhance the ignition flame holding, it is possible to cope with a consequently wide area load operation, multi-coal types.
[0021]
In the following, several embodiments are illustrated in which the flow rate of the lean stream C ₀ is increased and the flow rate of the concentrated stream C ₁ is decreased. In the following drawings, the same or equivalent parts as those shown in FIG.
[0022]
5 and 6 are views showing the pulverized coal burners of the third and fourth embodiments. In these drawings, 28 indicates an internal concentrator, and F indicates a center line passing through the heavy oil nozzle 23. In each of these embodiments, the pulverized coal is supplied as a solid-gas two-phase fluid (A + C), and is separated into a lean stream C ₀ and a concentrated stream C ₁ by a downstream separation pipe 20 via an internal concentrator 28. FIG. 5 shows one having a venturi type resistor 24, and FIG. 6 shows one without a venturi type resistor.
[0023]
7 and 8 are views showing the pulverized coal burners of the fifth and sixth embodiments. In each of these embodiments, the separation pipe 20 is not formed with a tapered portion, and instead, the cross-sectional area D ₂₀₁ of the lean flow channel ₂₀₁ is small and the cross-sectional area D ₂₀₂ of the concentrated flow channel ₂₀₂ is large. Yes. Due to such a difference in cross-sectional area, naturally, the flow rate of the lean flow C ₀ can be made larger than the flow rate of the concentrated flow C ₁ . FIG. 7 shows one without the venturi type resistor, and FIG. 8 shows one with the venturi type resistor 24.
[0024]
9 and 10 are views showing the pulverized coal burners of the seventh and eighth embodiments. In each of these embodiments, the pulverized coal is supplied as a solid-gas two-phase fluid (A + C) and swirled as indicated by arrow S by an appropriate means. By this swirling, the outer side (peripheral wall side) separates into a concentrated flow C ₁ and the inner side becomes a lean flow C _0, and enters the separation pipe 20. FIG. 9 shows the one with the venturi type resistor 24, and FIG. 10 shows the one without the venturi type resistor.
[0025]
11 and 12 are views showing the pulverized coal burner of the ninth and tenth embodiments. In these figures, 30 is a venturi. In each of these embodiments, the pulverized coal is supplied as a solid-gas two-phase fluid (A + C) and is concentrated by the venturi 30, and the lean stream C ₀ is separated to the outside and the concentrated stream C ₁ is separated to the center. FIG. 11 shows the one with the venturi type resistor 24, and FIG. 12 shows the one without the venturi type resistor.
[0026]
13 and 14 are views showing pulverized coal burners according to the eleventh and twelfth embodiments. In each of the embodiments shown in FIG. 1 and FIG. 2, the lean flow C ₀ is separated to the center and the concentrated flow C ₁ is separated to the outside. In the present embodiment, conversely, the lean flow C ₀ is separated. ₀ is separated to the outside and concentrated stream C ₁ is separated to the center. In this case, naturally, the tapered portion 200 is formed in a shape expanded outward, contrary to the tapered portion 200 shown in FIGS. 1 and 2. Even if separated in such a form, the operation and effect do not change. FIG. 13 shows the one with the venturi type resistor 24, and FIG. 14 shows the one without the venturi type resistor.
[0027]
FIG. 15 is a view showing a pulverized coal burner according to a thirteenth embodiment. In each of the above embodiments, the tapered portion 200 is formed at the distal end portion of the separation tube 20, but in the present embodiment, the tapered portion 200 is formed in a shape that is narrowed to the center side at a portion slightly away from the distal end portion. The lean stream C ₀ is separated to the center and the concentrated stream C ₁ is separated to the outside. FIG. 15 (a) shows a device without a venturi type resistor, and FIG. 15 (b) shows a device with a venturi type resistor 24.
[0028]
FIG. 16 is a view showing a pulverized coal burner according to a fourteenth embodiment. Similarly to the embodiment shown in FIG. 14, also in this embodiment, the tapered portion 200 is formed in a shape that expands outward in a portion slightly away from the tip portion. From the shape of the tapered portion 200, the lean flow C ₀ is separated to the outside, and the concentrated flow C ₁ is separated to the center side. FIG. 16 (a) shows a device without a venturi type resistor, and FIG. 16 (b) shows a device with a venturi type resistor 24. FIG.
[0029]
In the description of each of the above embodiments, the pulverized coal burner provided with the outer peripheral flame holding ring has been described. However, it is obvious that the present invention can also be applied to those not provided with the outer peripheral flame holding ring.
[0030]
【The invention's effect】
As described above, in the present invention, since the flow rate of the lean flow is made higher than the flow rate of the concentrated flow, the concentrated flow can be engulfed into the recirculation region by the lean flow, and the pulverized coal is separated into the concentrated flow and the lean flow. while maintaining very low NO _X reduction of the pulverized coal burner supplies, it is possible to enhance the ignition flame holding, it is possible to cope with a consequently wide area load operation, multi-coal types.
[Brief description of the drawings]
FIG. 1 is a view showing a pulverized coal burner according to a first embodiment of the present invention.
FIG. 2 is a view showing a pulverized coal burner according to a second embodiment of the present invention.
FIG. 3 is a diagram showing the concentration in the recirculation region of the concentrated flow relative to the ratio of the momentum of the lean flow to the momentum of the concentrated amount.
FIG. 4 is a graph showing average pulverized coal concentration with respect to burner load.
FIG. 5 is a view showing a pulverized coal burner according to a third embodiment of the present invention.
FIG. 6 is a view showing a pulverized coal burner according to a fourth embodiment of the present invention.
FIG. 7 is a view showing a pulverized coal burner according to a fifth embodiment of the present invention.
FIG. 8 is a view showing a pulverized coal burner according to a sixth embodiment of the present invention.
FIG. 9 is a view showing a pulverized coal burner according to a seventh embodiment of the present invention.
FIG. 10 is a view showing a pulverized coal burner according to an eighth embodiment of the present invention.
FIG. 11 is a view showing a pulverized coal burner according to a ninth embodiment of the present invention.
FIG. 12 is a view showing a pulverized coal burner according to a tenth embodiment of the present invention.
FIG. 13 is a view showing a pulverized coal burner according to an eleventh embodiment of the present invention.
FIG. 14 is a view showing a pulverized coal burner according to a twelfth embodiment of the present invention.
FIG. 15 is a view showing a pulverized coal burner according to a thirteenth embodiment of the present invention.
FIG. 16 is a view showing a pulverized coal burner according to a fourteenth embodiment of the present invention.
FIG. 17 is a system diagram of a pulverized coal combustion system.
[Explanation of symbols]
20 Separation tube 21 Outer flame holding ring 22 Internal flame holder 23 Heavy oil nozzle 24 Venturi type resistor 200 Tapered portion 201 Lean flow channel 202 Concentrated flow channel

Claims (4)

A solid-gas two-phase flow composed of solid fuel and transport gas is separated into a concentrated flow and a dilute flow by a separation pipe, which are supplied side by side at the separation pipe outlet, and are internally held at the outlet end of the separation pipe. In the pulverized coal burner in which a flame retardant is installed, the pulverized coal burner is provided with a lean flow speed increasing means for making the flow rate of the lean flow at the position of the internal flame holder higher than the flow rate of the concentrated flow. . 2. The pulverized coal burner according to claim 1, wherein the speed increasing means is means for narrowing a tip portion or a portion in the vicinity of the tip of the flow path of the lean flow in the separation pipe. 2. The pulverized coal burner according to claim 1, wherein the speed increasing means is means for making a cross-sectional area of the flow path of the lean flow in the separation pipe smaller than a cross-sectional area of the flow path of the concentrated flow. The pulverized coal burner according to any one of claims 1 to 3, wherein the speed increasing means includes a resistor provided on a flow path side of the concentrated flow.

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