JPH09159109A - Combustion method of pulverized coal, pulverized coal combustion device and pulverized coal combustion burner - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a combustion device which forms stable combustion flames only by the supply of pulverized coal or a pulverized coal combustion burner even under the condition which burns only nonflammable pulverized coal or under a low load condition. SOLUTION: An air nozzle 11, which feeds air in a swirling current, is laid out around the outer periphery of a fuel nozzle 10 which conveys pulverized coal by air. The fuel nozzle 10 forms a first recirculating current around the edge of the nozzle while the swirling current forms a second recirculating current on the outer periphery of a fuel jet, and forms a third recirculating current 22 in the peripheral direction of the second recirculating current 21 and the current 22, which is partially formed integrally with the first recirculating current 20. Since the third recirculating current 22 feeds a high temperature gas of the second recirculating current 21 to the fuel nozzle, it is possible to enhance the stability of flames of pulverized coal.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a pulverized coal combustion apparatus, a pulverized coal combustion burner, and a combustion method for pulverized coal, and in particular, an air nozzle is concentrically provided on the outer periphery of a fuel nozzle for carrying pulverized coal by air flow. The present invention relates to a pulverized coal combustion device and a pulverized coal combustion burner.

[0002]

2. Description of the Related Art Nitrogen oxides (N
It is required to reduce the amount of Ox) generated. Most of NOx generated during combustion of pulverized coal is NOx generated by oxidation of nitrogen contained in coal. This N
In order to reduce the amount of Ox generated, various modifications have been made to the structure of the combustion device and the burner and the combustion method.

As one method for reducing the amount of NOx produced, there is a so-called two-stage combustion method in a flame in which an oxidation region and a reduction region are formed in the burner. Nitrogen in coal produces hydrogen cyanide (HCN) and ammonia (NH) during thermal decomposition in the early stages of combustion.
It is decomposed into 3) and released into the gas phase. While these nitrogen compounds are oxidized to NOx, they have an effect of reducing NOx in a region where the oxygen concentration is low.

This two-stage combustion method in flame is based on NH3 and HC.
The NOx precursor of N effectively reduces NOx in a flame. That is, the burner has a structure in which a fuel nozzle for conveying pulverized coal in an air stream and an air nozzle for concentrically ejecting combustion air in a swirling flow are provided around the fuel nozzle. As a result, in the vicinity of the burner in the flame, excess fuel combustion with insufficient air is performed to expand the reducing flame region, and in the latter stage of the flame, combustion with a high oxygen concentration is performed to form an oxidizing flame region. A burner of this type
For example, JP-A-60-226609 and JP-A-61-226609
No. 22105, JP-A No. 61-280302, and the like.

Recently, in order to stably form a flame of pulverized coal supplied from a fuel nozzle, attempts have been made to change the supply state of pulverized coal and carrier air. The burner that adjusts the pulverized coal particle concentration by generating a swirling flow in the nozzle,
For example, JP-A-54-159741 and JP-A-Hei-3
-241208. A burner for arranging an object inside the fuel nozzle to adjust the particle concentration is disclosed in, for example, JP-A-3-110308 and JP-A-4-24404.
Japanese Patent Application Laid-Open No. 4-214102.

On the other hand, in order to stably form the flame of the pulverized coal, attempts have been made to form a recirculation region for forming the flame in the jet stream of the pulverized coal. This kind of burner
For example, JP-A 1-217109 and JP-A 2-11
No. 0202 publication. Further, as a burner that suppresses the mixing of the fuel jet and the combustion air jet by dividing the flow of the combustion air and supplying the gas in the combustion furnace to the jet, for example, JP-A-57-73305 can be cited. To be

[0007]

In order to improve the operability of a pulverized coal boiler, it is necessary to increase the number of types of coal that can stably form a flame only with pulverized coal without auxiliary combustion of oil (hereinafter, referred to as exclusive combustion). is there. In particular, if the burner structure is capable of burning the raw coal having a high calorific value, the number of coals that can be burned will dramatically increase. On the other hand, such a raw material coal is difficult to ignite because the content ratio of volatile components generated by thermal decomposition is 15 to 25%.

Further, if the fuel can be burnt exclusively to a condition where the fuel supply amount is small, the operation of starting and stopping the crusher is eliminated, the load of the boiler is likely to fluctuate, and the amount of oil mixed with pulverized coal under low load conditions is reduced. Will be able to.
However, from the viewpoint of preventing the particles from settling in the pipe, the minimum flow velocity of the carrier air for the particles is set. Therefore, under a low load condition, the concentration of fuel becomes lean, and it becomes difficult for the burner to form a stable flame.

Under such conditions of burning pulverized coal with a high fuel ratio or under low-load combustion conditions, it becomes difficult for the pulverized coal to burn, so that a reducing flame region is formed inside the flame where oxygen is deficient in combustion. Therefore, in this type of combustion apparatus, there is a dislike that the NOx concentration at the furnace outlet increases because NOx is not reduced in the reducing flame region.

The present invention has been made in view of the above, and an object thereof is to supply only the pulverized coal even under the condition that the flame-retardant pulverized coal is burned and the load is low. The object is to provide a pulverized coal combustion burner and a combustion device of this kind in which a stable combustion flame is formed. Further, another object of the present invention is to form a stable combustion flame even under the conditions of burning flame-retardant pulverized coal and under a low load, and to sufficiently reduce the NOx concentration at the furnace outlet. The present invention is to provide a combustion device and a pulverized coal burner device.

[0011]

That is, the present invention is directed to a fuel nozzle arranged upstream of a furnace for carrying pulverized coal in an air stream, and concentrically arranged around the outer periphery of the fuel nozzle to swirl the combustion air. In the combustion method of a pulverized coal combustion apparatus, which is configured to burn pulverized coal with swirling air, the pulverized coal combustion flame is swirl-held on the furnace side of the fuel nozzle rim, and The high temperature gas of the swirling flame is supplied in the direction of the fuel nozzle and the two circulating flows are integrally burned at a plurality of positions in the circumferential direction to achieve the intended purpose. Is.

Further, in a combustion method of a pulverized coal burner, which is concentrically provided with at least one air nozzle for supplying combustion air in a swirling flow to the outer periphery of a fuel nozzle for carrying pulverized coal by air flow, the fuel is supplied from the fuel nozzle. An ignition zone for igniting the pulverized coal is provided, and a reducing flame region in which the amount of oxygen supplied is smaller than the oxygen amount required for combustion of the pulverized coal is provided on the downstream side of this ignition zone, and the reducing flame is provided on the outer peripheral side. An oxidizing flame region in which the amount of oxygen supplied is larger than the amount of oxygen required for combustion of pulverized coal is provided, and a NOx reducing region for converting NOx to nitrogen is provided at the boundary between the oxidizing flame region and the reducing flame region, and At least one region in the circumferential direction of the ignition region is configured to burn adjacent to the oxidizing flame.

Further, there are provided a fuel nozzle arranged upstream of the furnace for carrying pulverized coal by air flow, and an air nozzle arranged concentrically around the outer periphery of the fuel nozzle for supplying combustion air in a swirling flow. In a pulverized coal combustion device, a first recirculation flow forming means for holding and forming the pulverized coal combustion flame on the furnace side of the fuel nozzle opening, and a swirling flow flame formed by the first recirculation flow forming means. Second recirculation flow forming means for supplying the high temperature gas in the direction of the fuel nozzle, and the circulation flow formed by the first recirculation flow forming means and the second recirculation flow forming means. The circulation flow formed in 1 is integrally formed at a plurality of positions in the circumferential direction.

Further, in a pulverized coal combustion burner provided concentrically with two air nozzles for supplying combustion air in a swirl flow to the outer periphery of a fuel nozzle for conveying pulverized coal in a stream, a high temperature formed by the swirl flow of the outer periphery. The recirculation flow is formed so as to be supplied to the fuel jet of the pulverized coal through the flow of the combustion air on the inner periphery that is divided and supplied.

That is, the pulverized coal combustion burner of the present invention is concentrically provided with at least one air nozzle for supplying combustion air to the outer periphery of the fuel nozzle for carrying pulverized coal by air flow.
At least one of the air nozzles is provided with a swirl flow generating means for generating swirl, and the fuel nozzle is provided with a means for forming a first recirculation flow in the vicinity of the pipe wall, and the swirling flow causes the first circulation flow to be generated. And a means for forming a third recirculation flow that is a part of the second recirculation flow and the first recirculation flow, in addition to forming a second recirculation flow on the downstream side of is there.

The first recirculation flow forms an area where the pulverized coal is ignited at the fuel nozzle rim, and the second recirculation flow forms an oxidation area where the pulverized coal is burned in the presence of oxygen. It is desirable that the recirculation region of 1) forms an oxidation region on the outer peripheral side of the ignition region. A reducing agent generation area for burning pulverized coal due to lack of oxygen is formed inside the oxidation area, and N generated in the reducing agent generation area is formed.
It is desirable to form a NOx reduction zone where H3, HCN and NOx generated in the oxidation zone react to convert into nitrogen.

One of the means for forming the third circulation flow can be achieved by forming a plurality of regions having a high pulverized coal concentration in the circumferential direction in a region near the rim of the fuel nozzle. By forming the flame more stably in the high fuel concentration region than in the other regions, the first recirculation flow can be extended in the flow direction and can be formed integrally with the second recirculation flow.

Another one of the means for forming the third circulating flow is to provide a solid wall surface between the outermost air nozzle for supplying the swirling flow and the fuel nozzle, and to use this solid wall surface around the fuel nozzle. It can be achieved by providing a plurality in the direction. The solid wall can form a low-pressure region on the downstream side of the solid wall, and the second recirculation flow formed by the swirling flow is expanded to the upstream side of the burner, and the first recirculation flow formed on the solid wall downstream. It can be integrated with the circulating flow.

The high fuel concentration region can be formed by bending a part of the rim of the fuel nozzle toward the central axis. Another means for forming a region having a high fuel concentration is characterized in that a swirl vane is provided inside the fuel nozzle, and a means for attenuating the swirl component is provided downstream of the swirl vane. The number of regions with high fuel concentration can be determined by the number of swirl vanes. It is desirable that the region of high fuel concentration formed by the swirl vanes be located on a plurality of collision plates provided at the edge of the fuel nozzle.

That is, such a method for forming a circulating flow in the pulverized coal combustion method is used in a pulverized coal burning boiler in which the burner has a low fuel concentration when the load is low and the volatile content is 15 to 25%. In order to form a stable flame only with coal even under the condition that a small amount of coal is burned, a first recirculation flow is provided in the vicinity of the fuel nozzle rim, and a second recirculation flow of combustion air is formed. It is important to form the second recirculation flow on the downstream side of the first recirculation flow and to make a part of the second recirculation flow into the third recirculation flow integrated with the first recirculation flow. Is.

It is important to provide a solid wall between the rim of the fuel nozzle and the inner peripheral end surface of the combustion air nozzle. The solid wall draws the second recirculation flow formed by the swirling flow of the combustion air to the edge of the fuel nozzle, so that the second circulation flow is the first recirculation flow formed at the edge of the fuel nozzle. And a third recycle stream is formed. Since the first recirculation flow returns a part of the flame to the fuel nozzle rim, the ignition region of the pulverized coal can be stabilized. The second recirculation flow mixes a part of the fuel jet with the jet of combustion air to form an oxidative flame region that burns pulverized coal under conditions of high oxygen concentration. The third recirculation flow draws the hot combustion gases generated in the oxidizing flame region back to the rim of the fuel nozzle.
This makes it easier for the pulverized coal to ignite, so that the ignition region is stably formed.

When a part of the combustion gas in the oxidizing flame region is supplied to the ignition region, the pulverized coal easily burns, so that the temperature of the flame in the ignition region rises. Therefore, the temperature of the reducing flame region included in the oxidizing flame region also rises, the thermal decomposition of pulverized coal is promoted, and the generation of NH3 and HCN which are NOx precursors is promoted. This precursor reacts with NOx in the mixed region formed at the boundary of the oxidative flame region, so that NOx is reduced to nitrogen. Thereby, low NOx combustion can be achieved.

The formation of three kinds of recirculation flows or the formation of a part of the oxidizing flame region on the outer circumference of the ignition region means that a plurality of regions having a concentration higher than a predetermined pulverized coal concentration are provided at the nozzle edge. It is promoted by providing a region having a concentration lower than a predetermined concentration of pulverized coal in the fuel nozzle while being provided.

Further, one of the methods for forming the concentration is to provide a diaphragm plate in which a part of the edge of the fuel nozzle is bent inward, or
Alternatively, by providing a nozzle structure that eliminates the swirling component after the nozzle swirling flow is generated, a concentration region higher than the predetermined pulverized coal concentration and a concentration region lower than the predetermined pulverized coal concentration are formed at the fuel nozzle rim. It is formed.

The diaphragm plate supplies the pulverized coal particles that collide with the diaphragm plate to the nozzle rim without the diaphragm plate, so that a concentration region higher than a predetermined pulverized coal concentration is formed. On the other hand, since the combustion air is supplied to the fuel nozzle along the outer peripheral surface of the diaphragm plate, a concentration region lower than a predetermined pulverized coal concentration is formed.

As to another method of forming the concentration, the swirl flow can be formed by a swirl flow generator provided inside the fuel nozzle. A structure having an axial flow type swirl vane is suitable for the swirl flow generator. When the swirl flow generator has a structure in which swirl vanes are arranged on the outermost periphery of the spindle,
The effect of the swirling flow can be enhanced.

The venturi provided on the upstream side of the swirl flow generator can further enhance the effect of the swirl flow generator. The venturi collects particles near the inner wall of the nozzle in the center of the flow path, so that the collected particles collide with the leading edge of the spindle of the swirl flow generator. As a result, the particles are guided to the swirl vanes, and the number of particles given the swirl component increases. At the same time, the outer diameter of the swirl vane can be made smaller than the inner diameter of the fuel nozzle, so that the pressure loss of the nozzle is reduced.

It is important that the swirl vanes of the swirl flow generator are plural. In the case of a fuel nozzle that supplies 5t to 10t of pulverized coal per unit time, it is desirable that the number of swirl blades is 6 to 10. A rectifier may be arranged downstream of the swirl flow generator to provide guide vanes that eliminate swirl flow components. The guide vane preferably has a structure in which thin plates are provided radially from the center of the nozzle.

The rectifier may have a structure in which the fuel nozzle is divided into an inner pipe and an outer pipe by having a cylinder. Further, the upstream end surface of the cylinder can be extended to the upstream side of the fuel nozzle to change the ratio of the area ratios of the inner pipe and the outer pipe. With such a structure of the rectifier, the velocities of the central portion (inner tube) of the fuel nozzle and its outer peripheral portion (outer tube) can be made substantially equal. If the speed ratios of the inner and outer tubes are equal, the mixing of fuel in the inner tube and the outer tube is suppressed.

The radial plate provided on the rectifier can improve the ignition performance of pulverized coal when combined with a flame stabilizer having a fuel collision plate at the edge of the fuel nozzle. Since the radial plate collects the pulverized coal supplied in the swirling flow, a region having a pulverized coal concentration higher than a predetermined concentration is formed along the radial plate. This high-concentration particle flow collides with the collision plate, reduces its velocity, and promotes turbulence, so that the pulverized coal is easily ignited. As a result, a stable flame can be formed at the rim of the fuel nozzle even under a low load condition where the fuel concentration is low and a condition where pulverized coal having a low volatile content is burned.

Since it is possible to select the number of swirl vanes that matches the concentration distribution of the pulverized coal, for example, only one pulverized powder which is apt to be present in a burner which produces a swirl flow by supplying pulverized coal in the tangential direction of the fuel nozzle is selected. There is no streaky flow in the high-concentration region. When pulverized coal flows in a line,
Since there is only one starting point for flame holding, the effect of increasing the concentration of pulverized coal is reduced.

Next, the solid wall on the outer periphery of the fuel nozzle will be described. On the outer peripheral side of the impingement plate of the flame stabilizer, a solid wall characterized by a space between the combustion air nozzle and the fuel nozzle is provided in the circumferential direction. It can be installed in a divided form. The solid wall extends a part of the second recirculation flow created by the swirling flow of combustion air to the burner side, and the third recirculation integrated with the first recirculation flow created by the flame stabilizer. Form a stream. The third recirculation flow can supply combustion gas of 1200 ° C. or higher generated by the oxidative flame to the rim of the fuel nozzle, so that the ignition performance of the pulverized coal is dramatically improved and the flame becomes stable.

On the other hand, since the pulverized coal supplied from the fuel nozzle in the portion without the solid wall is easily mixed with the combustion air, the ignited pulverized coal can continue to be burned, and the flame temperature is raised to 1500 ° C or more. Can be achieved. Due to this temperature, the pulverized coal reacts with water and carbon dioxide to generate hydrogen and carbon monoxide, thereby creating a strong reducing atmosphere even under the condition that oxygen is lost in the reducing flame region.
The reduction reaction of x can be promoted.

The solid wall may be circumferentially divided between the fuel nozzle and the combustion air nozzle. As a result, Japanese Patent Application Laid-Open No. 1-217109 and Japanese Patent Application Laid-Open No. 2-1
When a solid material is provided in the flow path of a fuel nozzle as shown in Japanese Patent No. 10202 to create a recirculation flow, the fuel dissipates in the radial direction of the burner and mixes with the combustion air. No large amount of NOx is generated.

Further, as disclosed in Japanese Patent Application Laid-Open No. 57-73305, the swirling flow of the combustion air is obstructed by dividing the flow of the combustion air and supplying the gas in the combustion furnace to the jet flow. Nothing. If the intensity of the swirl flow is attenuated, the second recirculation flow will not be formed well and the stability of the flame will be poor. Since the temperature of the pulverized coal flame supplied by the recirculation flow is higher than the temperature of the gas in the combustion furnace, flame stability is better when the recirculation flow and fuel are mixed.

[0036]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail with reference to the illustrated embodiments.

[0037]

First Embodiment Combustion Method FIG. 1 is a conceptual diagram showing the flow of pulverized coal jet and combustion air.
FIG. 2 is a conceptual diagram showing the structure of the flame produced by the flow shown in FIG. 1, and FIG. 3 is a diagram showing the fuel concentration distribution when the fuel nozzle is viewed from the furnace.

A fuel nozzle 10 for conveying pulverized coal in an air stream is arranged on the upstream side of the furnace, and an air nozzle for supplying combustion air concentrically with the fuel nozzle is provided on the outer periphery of the fuel nozzle 10. 11 is provided. The air nozzle 11 includes a swirl flow generator 12 on the upstream side of the nozzle.

The fuel nozzle 10 has a recirculation flow generating means for generating the first recirculation flow 20 at the rim of the nozzle. The swirling flow generator 12 supplies the combustion air 14 in a swirling flow to the downstream side of the first recirculation flow 20.
A second recycle stream 21 is formed. Further, in the combustion method of the present embodiment, a part of the first recirculation flow is enlarged so that the first recirculation flow 20 and the second recirculation flow 21 are integrally formed. It has a third recirculation flow generating means forming 22.

One of the methods for forming the third circulation flow is to provide a plurality of concentration regions having a concentration higher than a predetermined concentration at the nozzle edge, as shown in FIG. When pulverized coal having a high concentration is supplied, the pulverized coal is easily ignited, and at the same time, the flame is easily propagated in the burner radial direction. When a flame is formed, the viscosity of the gas increases with increasing temperature.
Since the mass transfer in the radial direction of the burner is suppressed, the size of the first recirculation flow is expanded to the furnace side and is formed integrally with the second recirculation flow.

On the other hand, in the concentration region lower than the predetermined pulverized coal concentration, since it is difficult to form a flame, the size of the first recirculation flow is larger than the predetermined pulverized coal concentration in the first concentration region. It becomes shorter than the circulation flow. As a result, a part of the combustion air 2
4 can be mixed with the fuel jet stream 25 in the wake of the first recycle stream. Thus, the contradictory requirements of adjusting the ratio of air in the combustion region of pulverized coal and forming a stable flame at the fuel nozzle rim can be achieved at the same time.

It is important to provide a plurality of concentration regions having a concentration higher than a predetermined concentration at the nozzle edge. As a result, a plurality of ignition points can be formed at the nozzle edge, so that the flame can spread from a plurality of points on the nozzle edge. The fuel in the concentration region leaner than the predetermined concentration can receive a sufficient amount of heat from the adjacent flame, so that the thermal decomposition is promoted and the flame is stabilized.

Further, it is necessary to supply the fuel jet in a state where there is no swirl velocity component. As a result, the radial dispersion of the fuel jet can be suppressed, so that the reducing flame region is formed in the flame and low NOx combustion can be achieved. A fuel jet having a swirling component cannot form a reducing flame region.

The first recirculation flow 20 ignites pulverized coal at the edge of the fuel nozzle 10 to form an ignition zone. The second recirculation flow 21 forms an oxidizing flame region by entraining a portion of the fuel jet flow 25 into the second recirculation flow 21.
The third recycle stream 22 is 1500 ° C generated in the oxidative flame region.
The above high-temperature gas can be supplied to the rim of the fuel nozzle to ignite the pulverized coal at 1200 ° C or higher. As a result, the flame temperature in the oxidizing flame region rises, so that the temperature in the reducing flame region formed inside the oxidizing flame region also rises.

In order to promote the solid-gas reaction of the pulverized coal gas, it is important to raise the flame temperature. In particular, it is carbon dioxide and water vapor that can react with the pulverized coal after the pulverized coal has completely consumed oxygen, and the reaction between both gases and the pulverized coal is activated at higher temperatures. Especially, the flame temperature is 1500
When the temperature becomes higher than ℃, the combustible components in the pulverized coal are easily released to the gas phase.

As a result, the air ratio on the gas phase side is reduced from 0.9 to 0.7, and a reducing flame region is formed. At the same time as the release of combustible components in the pulverized coal, the nitrogen content contained in the pulverized coal is simultaneously released into the gas phase, and HCN which is a precursor of NOx
Or NH3 is formed. Since the precursor of NOx converts NOx to nitrogen in the reducing flame region, NOx in the combustion exhaust gas is reduced.
The concentration decreases. Therefore, according to this embodiment, since the pulverized coal flame is stabilized and the reducing flame region is formed in the flame, low NOx combustion can be realized.

[0047]

Second Embodiment Burner Structure 1 Next, a structure of a burner for performing such a combustion method will be described with reference to FIGS. 4 to 6. The pulverized coal burner of the present embodiment is provided with a fuel nozzle 10 attached at the center, an air nozzle 11-1 for supplying combustion air 14-1 arranged concentrically with the fuel nozzle 10, and an air nozzle 11-. 1 and the air nozzle 11-2 which supplies the combustion air 14-2 attached to the outer periphery of 1.

The fuel nozzle 10 supplies a mixture 13 of primary air and pulverized coal. Two air nozzles 11-1 and 11-
Reference numeral 2 is a flow path for supplying the combustion air supplied to the wind box 37 to the furnace. The fuel nozzle 10 is a tubular flow path whose outer wall is the primary throat 31. In the case of this embodiment, an oil gun 30 for auxiliary combustion for preheating a water pipe attached to the inner wall of the furnace 39 is attached to the center of the fuel nozzle 10.

Further, the venturi 42 arranged upstream of the fuel nozzle has a role of controlling so that the pulverized coal sent from the pulverized coal supply device not shown in FIG. 4 becomes higher at the center of the fuel nozzle. It has become. Air nozzle 11-
1 has a secondary throat 32 with the primary throat 31 as an inner peripheral wall
Is an annular flow path having an outer peripheral wall. Air nozzle 11-
1 has a swirl flow generator 12-1 and a flow control valve 36 as it goes upstream from the furnace 39.

The swirling flow generator 12-1 includes the combustion air 14
-1 is supplied in a swirling flow. The swirl flow generator 12-1 is an axial flow swirl flow generator, and is composed of a plurality of fan-shaped blades arranged in the circumferential direction of the flow path and a support rod integrally attached to the blades. It The intensity of the swirl flow of the swirl flow generator 12-1 is adjusted by changing the angle of the blades by a driving device (not shown).

The flow rate control valve 36 controls the flow rate of the combustion air 14-1. The flow control valve 36 has a cylindrical shape,
The secondary throat 32 and the wind box 37 are attached to a position that covers an opening of an inflow hole that communicates with each other. Since the flow control valve 36 is moved in the central axis direction of the burner by an adjusting device not shown in FIG. 4, the area of the opening of the inflow hole is changed. By this operation, the combustion air 14-
The distribution ratio of 1 and 14-2 is adjusted.

The combustion air nozzle 11-2 is an annular passage having the secondary throat 31 as an inner peripheral wall and the tertiary throat 33 as an outer peripheral wall. Combustion air 14-2 in the wind box 37 passes through the swirl flow generator 12-2 and enters into the furnace 39.
Is supplied in the form of a swirl flow.

A part of the end face of the secondary throat 31 is bent toward the center of the fuel nozzle 10 by a plurality of shield plates 34. That is, the shielding plate 34 is the primary throat 31.
The oil gun 30 is narrowed and the primary throat 31 and the secondary throat 32 are widened.

Since the flow path of the fuel nozzle 10 is narrowed by the shield plates 34, pulverized coal particles having a higher inertia than air flow between the shield plates 34. On the other hand, air is supplied to the central portion of the fuel nozzle 10 because the air can be easily changed in direction. As a result, a concentration region higher than the predetermined pulverized coal concentration is formed at the nozzle edge between the shield plates 34.

On the other hand, a part of the combustion air 14-1 is supplied to the fuel nozzle along the shield plate 34. Since this combustion air is mixed with pulverized coal, a concentration region lower than a predetermined pulverized coal concentration is formed. When the flow path is expanded by the shielding plate 34, the combustion air 14 flowing near the shielding plate 34
-1 reaches the rim of the combustion nozzle 10 while decelerating its speed. The pulverized coal can create a flame at the rim of the fuel nozzle 10 because the slowed combustion air can form a low velocity turbulent first recirculation flow 20 by mixing with the fuel jet.

An air nozzle 11-1 is provided on the outer periphery of the fuel nozzle 10 in a concentration region higher than the above-mentioned predetermined pulverized coal concentration.
The solid wall 35 is attached so as to close the flow path of. The solid wall 35 forms the first recirculation flow 20 on the furnace side because the furnace side of the solid wall 35 is narrowed by the fuel jet flow 25 and the combustion air flow 23 and no fluid flows. . Pulverized coal with a concentration higher than the specified pulverized coal concentration is solid wall 3
As it is supplied to the first recycle stream 20 downstream of 5, the pulverized coal is ignited better than downstream of the shield 34. Therefore, the first recirculation flow 20 formed downstream of the solid wall 35 extends in the direction of the second recirculation flow 21 by the amount by which the flame temperature is increased, so that both are formed integrally. It becomes the third recirculation flow 22.

The third recirculation flow 22 supplies the combustion gas in the oxidizing flame region 19 to the fuel nozzle rim, so that the ignition region 16
The temperature becomes high, and flame-retardant pulverized coal with few volatile components can be ignited. FIG. 6 shows the relationship between the minimum load of the burner capable of burning coal exclusively and the fuel ratio when the pulverized coal burner of the second embodiment is used for combustion. Exclusive combustion of coal refers to a state in which a pulverized coal flame can be stably maintained without using a combustion improver such as oil. Further, the fuel ratio indicates the ratio of solid components and volatile components of coal obtained by industrial analysis, and the higher the fuel ratio, the more difficult the combustion becomes. In the case of the conventional example, the minimum load of a burner capable of burning coal exclusively is about 30% with coal having a fuel ratio of 1,
The minimum load of burner that can burn coal exclusively increases with the fuel ratio, and coal with a fuel ratio of 3 or more cannot form a stable flame without auxiliary combustion.

On the other hand, in the present embodiment, it can be seen that even if the fuel ratio is high, the coal can be burned exclusively, and the number of coal types that can be operated can be dramatically increased. For example, the types of coal that can be burned exclusively at a burner load of 50% can be expanded from conventional coal having a fuel ratio of 2.5 or less to coal having a fuel ratio of 4.5 or less.
Further, as far as 100% load operation is concerned, the pulverized coal burner of this embodiment can form a stable flame without auxiliary combustion even with coal having a fuel ratio of 7.

Next, the structure of another burner will be described.

[0060]

[Third Embodiment] Burner Structure 2 • Structure of Fuel Nozzle A burner according to a third embodiment will be described with reference to FIGS. 7 to 9. 7 is a sectional view of the pulverized coal burner of the third embodiment, FIG. 8 is a side view of the pulverized coal burner, and FIG. 9 is a distribution diagram showing the concentration of pulverized coal in the fuel nozzle of the pulverized coal burner. is there. The pulverized coal burner of the third embodiment is different from the fuel nozzle 10 shown in FIG. 7 only in the part of the separation wall provided between the air nozzles 14-1 and 14-2, and the burner structure other than this is the second structure. This is the same as the burner structure of the embodiment.

The fuel nozzle 10 of the third embodiment has a venturi 42, a swirler 56, a distributor 45, a rectifier 46 in its inside from the upstream, and a flame stabilizer 40 at the rim of the nozzle.

The swirler 56 has a structure in which a plurality of swirl vanes 44 are attached to the outermost peripheral surface of the spindle 43 in the circumferential direction. The spindle 43 is fixed inside the fuel nozzle 10 by an oil gun 30. The diameter of the inner peripheral wall of the fuel nozzle 10 is
The spindle 43 increases once toward the downstream side and then decreases again to become equal to the outer diameter of the oil gun 30. The swirl vane 44 is a thin plate having a kamaboko shape, and is attached to the outermost periphery of the spindle 43 at an angle so as to generate a swirl flow in the primary air. The length of both ends of the swirl vane 44, that is, the outermost circumference diameter of the swirler 56 is set to be smaller than the inner diameter of the venturi 42.

The distributor 45 is a cylindrical device, and divides the flow path of the fuel nozzle 10 into an annular flow path of an inner pipe 49 and an outer pipe 50. The inner pipe 49 is composed of the distributor 45 and the oil gun 30, and the outer pipe 50 is composed of the primary throat 31 and the distributor 45. The upstream diameter of the distributor 45 can be different than the downstream diameter.

The rectifier 46 is composed of a plurality of plates 59 and a cylinder 47. The plate 59 is attached radially from the center of the fuel nozzle 10. The number of plates 59 is the fuel nozzle 1
In the case of a fuel nozzle that supplies pulverized coal of 5t to 10t per unit time, the swirl vanes are 6 to 10 depending on the inner diameter of 0.
It is desirable to make one.

The flame stabilizer 40 includes a collision plate 48 and a baffle plate 6.
It consists of 0. The collision plate 48 is a plurality of plates attached to the end surface of the primary throat 31. The number of the collision plates 48 is preferably the same as the number of the plates 59 and is located downstream of the plates 5. The baffle plate 60 includes a member that increases the inner diameter of the air nozzle 14-1 and a plate member that directs the combustion air 14-1 toward the combustion air 14-2.

Action and Effect of Fuel Nozzle The Venturi 42 moves the pulverized coal particles in the inner peripheral direction of the fuel nozzle 10 at its contracting portion. As a result, it is possible to eliminate the drift of the fuel concentration caused by the curved pipe on the upstream side of the burner. Further, since the pulverized coal particles are collected on the inner peripheral portion of the fuel nozzle 10 by the contracted flow portion of the venturi 42, the number of particles colliding with the spindle 43 is increased. As a result, the swirl vane 44 is not located in the entire flow path, and the swirl vane 44
Even if there is a gap with the inner wall of the primary throat 31, most of the particles pass through the swirl vanes. When the particles are supplied in a swirling flow, due to the inertia of the particles, relatively large particles flow near the inner peripheral wall of the primary throat 31, and fine particles are dispersed in the entire flow passage of the fuel nozzle 10.

At the same time, the concentration of fuel becomes higher than the concentration at the outlet of the crusher as it approaches the inner peripheral wall of the primary throat 31.

Since the primary air can spread and flow in the entire flow path of the fuel nozzle 10, the amount of air passing through the swirl vanes 44 is smaller than the flow rate of the primary air. Since the flow rate of air supplied as a swirling flow can be reduced,
The pressure loss generated in the swirl vane 44 can be reduced.

Since the outer diameter of the swirler 56 is smaller than the inner diameter of the venturi 42, the swirler 56 can be taken out from the fuel nozzle 10 without removing the venturi 42. Thus, for example, even when the swirler needs to be replaced due to deterioration of the swirl vanes 56, the swirler can be replaced in a short time.

Since the distributor 45 can change the flow passage areas of the inner pipe 49 and the outer pipe 50 toward the downstream side, the velocity distribution downstream of the distributor 45 can have a predetermined shape. For example, as shown in FIG. 7, when the area of the inlet of the inner pipe 49 is larger than the area of the outlet, the flow velocity difference between the inner pipe 49 and the outer pipe 50 can be reduced.

In the vicinity of the inner peripheral wall of the primary throat 31, the swirling flow increases the flow velocity, but the distributor 4 described above is used.
By setting the number to 5, the flow passage area of the outer pipe 50 increases toward the downstream side, so that the flow velocity can be reduced. On the other hand, the inner pipe 49 increases the air flow velocity by reducing the flow passage area. Due to the synergistic effect of both
The velocity distribution at the outlet of the distributor can be smoothed.

Further, by changing the position of the upstream end surface of the distributor 45, the pulverized coal flowing near the inner wall of the primary throat 31 is supplied to the outer pipe 50, and the pulverized coal flowing inside the pulverized coal is supplied inside. Supply to tube 49. The pulverized coal supplied to the outer pipe 50 is a pulverized coal having a high concentration, and the inner pipe 49 supplies pulverized coal having a fine concentration and a small concentration.

When a plurality of swirl vanes 44 are provided, a density region having a density higher than a predetermined density is formed corresponding to the number of installed disks. FIG. 9 shows the fuel concentration distribution. The figure shows the fuel nozzle 1
Only the 1/4 part of 0 is shown and other parts are omitted.
In the figure, the fuel concentration is shown in descending order, from concentration A52 to concentration B55 in four stages. The concentration B53 indicates a region where the particles attracted to the inner peripheral wall of the primary throat 31 by the swirl vanes 44 are supplied. The concentration C54 is the fuel distributed by the distributor 45 to the outer pipe 50 and the inner pipe 49,
It becomes thinner than the concentration B54.

The density D55 is particles flowing along the outer surface of the spindle 43, and fine particles are supplied under the most dilute condition. The concentration A52 indicates the flow of the pulverized coal having the highest concentration. This allows the particles supplied by the swirling flow to be transferred to the plate 59.
It is the region of the concentration that was generated because it was received at. Particles with large inertia are taken into the boundary layer of the plate 59, whereas primary air spreads in the flow path partitioned by the plate 59, so the concentration of pulverized coal is further increased, and thus the concentration is higher than the concentration B53. Of.

It is best to arrange the plate 59 so as to overlap the collision plate 48 as shown in FIG. Concentration A52
Collides with the collision plate 48, decelerates, and is taken into the downstream side of the flame stabilizer 40. On the other hand, the flame of pulverized coal is generated by the collision plate 4
Start from 8. Due to the synergistic effect with high fuel concentration,
The ignition performance and flame holding performance of pulverized coal can be dramatically improved.

As a result, the first recirculation stream 20 can contain a large amount of pulverized coal particles, so that a stable flame is formed. As a result, the temperature of the oxidizing flame region formed by the second recirculation flow becomes 1500 ° C. or higher, and the temperature of the reducing flame region included in the oxidizing flame region also increases. This activates the reaction between carbon dioxide or water and the coal particles, so that the air ratio in the gas phase can be reduced.

Structure, action and effect of solid wall An annular separation wall 41 is provided between the air nozzles 11-1 and 11-2, and the air nozzle 11-1 has an annular flow path. Four solid walls 35 are arranged in the circumferential direction.

The separation wall 41 supplies the combustion air 14-2 in a swirling flow to stably form the second recirculation flow 21. Since the solid wall 35 hinders the supply of the combustion air 14-1 and lowers the pressure on the flow side thereafter, the second recirculation flow 21 is extended to the vicinity of the separation wall 41 and the third recirculation is performed. Stream 22 is formed. The third recirculation stream 22 supplies the combustion gas in the oxidizing flame region to the vicinity of the burner. This combustion gas is supplied to the flame stabilizer on the downstream side of the solid wall 35 from the direction of the flow 51 shown in FIG. 8, and ignites the pulverized coal jet.

Since this combustion gas was supplied from the oxidizing flame region, its temperature can be set to 1200 ° C. or higher. As a result, the ignition performance of the pulverized coal is improved, and the fact that the combustion air 14-2 is suppressed from being mixed in the vicinity of the burner makes it possible to form an oxidizing flame region of 1500 ° C. or higher. When such a high-temperature flame is formed, the reducing flame region is also increased at the same time, and it is possible to burn the coal particles with carbon dioxide or water even in the absence of oxygen. As a result, the air ratio of the gas phase in the reducing flame region becomes 0.7 to 0.9,
The reduction reaction of NOx proceeds, and low NOx combustion can be achieved.

As described above, with such a combustion burner, the NOx concentration can be reduced, and the load of the burner that can burn only with pulverized coal is widened to increase the amount of the auxiliary combustion material such as oil used. Can be reduced. Furthermore, since flame-retardant coal can be burned without using oil, it is possible to increase the types of coal used.

[0081]

As described above, according to the present invention, even under the condition that flame-retardant pulverized coal is burned,
Further, even under a low load condition, a combustion apparatus and a combustion method of this kind in which a stable combustion flame is formed only by supplying pulverized coal,
Further, a pulverized coal combustion burner can be obtained.

[Brief description of the drawings]

FIG. 1 is a conceptual diagram showing the flow of pulverized coal and combustion air according to the present invention.

FIG. 2 is a conceptual diagram showing the structure of a flame produced by the flow of FIG.

FIG. 3 is a distribution diagram showing a fuel concentration distribution when a fuel nozzle is viewed from a furnace.

FIG. 4 is a sectional view of a pulverized coal burner of a second embodiment.

5 is a side view of the pulverized coal burner of FIG. 4. FIG.

FIG. 6 is a characteristic diagram showing the performance of the pulverized coal burner of FIG.

FIG. 7 is a sectional view of a pulverized coal burner of a third embodiment.

FIG. 8 is a side view of the pulverized coal burner of FIG. 7.

9 is a distribution chart showing the concentration of pulverized coal in the fuel nozzle of the pulverized coal burner of FIG. 7.

[Explanation of symbols]

10 ... Fuel nozzle, 11 ... Air nozzle, 12 ... Swirl flow generator, 13 ... Mixture of primary air and pulverized coal, 14 ... Combustion air, 15 ... Unfired fuel, 16 ... Ignition area, 17 ... Reduction flame area , 18 ... NOx reduction area, 19 ... Oxidizing flame area, 20 ...
First recirculation flow, 21 ... Second recirculation flow, 22 ... Third recirculation flow, 23 ... Combustion air flow, 24 ... Combustion mixed with fuel in downstream of first recirculation flow Air flow, 25 ...
Flow of fuel jet, 26 ... Higher concentration region than predetermined concentration, 30 ... Oil gun, 31 ... Primary throat, 32 ... Secondary throat, 33 ... Tertiary throat, 34 ... Shielding plate, 35
... Solid wall, 36 ... Flow control valve, 37 ... Wind box, 38 ... Water tube, 39 ... Furnace, 40 ... Flame stabilizer, 41 ... Separation wall, 42 ... Venturi, 43 ... Spindle, 44 ... Swivel blade, 45 ... Distributor, 46 ... Rectifier, 47 ... Cylinder, 48 ...
Collision plate, 49 ... Inner tube, 5 ... Outer tube, 51 ... Flow, 52 ... Concentration A, 53 ... Concentration B, 54 ... Concentration C, 55 ... Concentration D, 5
6 ... swirler, 60 ... baffle plate.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Oka ▲ saki ▼ Western text 7-1, 1-1 Omika-cho, Hitachi City, Ibaraki Hitachi Ltd. Hitachi Research Laboratory (72) Inventor Hisayuki Orita Omika-cho, Hitachi City, Ibaraki Prefecture 7-1-1, Hitachi Ltd., Hitachi Research Laboratory (72) Inventor Ken Amano 7-1-1, Omika-cho, Hitachi, Hitachi, Ibaraki Prefecture Hitachi Ltd. Hitachi Research Laboratory (72) Inventor, Toshiyuki Tanaka Ibaraki Prefecture Hitachi City Omika-cho 7-1-1, Hitachi Ltd. Hitachi Research Laboratory (72) Inventor Kenji Kiyama 3-36 Takaracho, Kure City, Hiroshima Prefecture Babcock Hitachi Kure Research Laboratory

Claims (16)

[Claims] 1. A fuel nozzle arranged upstream of a furnace for carrying pulverized coal in an air stream, and an air nozzle arranged concentrically around the outer periphery of the fuel nozzle for supplying combustion air in a swirling flow, In a combustion method of a pulverized coal combustion apparatus adapted to burn pulverized coal with swirling air, the pulverized coal combustion flame is swirl-held on the furnace side of the fuel nozzle rim, and the high temperature gas of the swirling flow flame is A combustion method for a pulverized coal combustion apparatus, characterized in that the two circulating flows are integrally burned at a plurality of positions in the circumferential direction while being supplied in the direction of the fuel nozzle. 2. A combustion method for a pulverized coal burner concentrically provided with at least one air nozzle for supplying combustion air in a swirling flow to the outer periphery of a fuel nozzle for conveying pulverized coal in a stream, comprising: supplying from said fuel nozzle. An ignition zone for igniting pulverized coal is provided, and a reducing flame region in which the amount of oxygen supplied is smaller than the amount of oxygen required for combustion of pulverized coal is provided on the downstream side of this ignition zone, and on the outer peripheral side of this reducing flame. An oxidizing flame region in which the amount of oxygen supplied is larger than the amount of oxygen required for combustion of pulverized coal is provided, and NO is provided at the boundary between the oxidizing flame region and the reducing flame region.
A combustion method for a pulverized coal combustion apparatus, characterized in that a NOx reduction region for converting x into nitrogen is provided, and at least one region in the circumferential direction of the ignition region is burned adjacent to the oxidizing flame. 3. The pulverized coal having a concentration higher than a predetermined concentration is supplied to at least one region of the rim of the fuel nozzle, and the pulverized coal having a concentration lower than the predetermined concentration is supplied to other regions of the fuel nozzle. The method for combusting a pulverized coal combustion apparatus according to claim 1 or 2, further comprising: 4. A plurality of the air nozzles are concentrically provided on the outer circumference of the fuel nozzle, and a high temperature recirculation flow formed by a swirling flow on the outer circumference is divided and supplied to an inner circumference flow of combustion air The combustion method of a pulverized coal combustion apparatus according to claim 1, 2 or 3, wherein the fuel is supplied to the fuel jet of the pulverized coal via the space. 5. A fuel nozzle arranged upstream of the furnace for carrying pulverized coal by air flow, and an air nozzle arranged concentrically around the outer periphery of the fuel nozzle for supplying combustion air in a swirling flow. In a pulverized coal combustion device, a first recirculation flow forming means for holding and forming the pulverized coal combustion flame on the furnace side of the fuel nozzle mouth edge, and a swirling flow flame formed by the first recirculation flow forming means. Second recirculation flow forming means for supplying the high temperature gas in the direction of the fuel nozzle, and the circulation flow formed by the first recirculation flow forming means and the second recirculation flow forming means. A pulverized coal combustion apparatus characterized in that it is formed integrally with the circulation flow formed in 1. at a plurality of positions in the circumferential direction. 6. A plurality of the air nozzles are concentrically provided on the outer circumference of the fuel nozzle, and at least one solid wall is arranged in an annular flow path of the air nozzle located on the inner circumference side. Item 5. A pulverized coal combustion apparatus according to Item 5. 7. A pulverized coal combustion burner having concentrically provided two air nozzles for supplying combustion air to the outer periphery of a fuel nozzle for carrying pulverized coal by air flow, wherein the air nozzle on the inner peripheral side has an annular shape. At least 1 in the flow path
A pulverized coal combustion burner characterized by arranging two solid walls. 8. A pulverized coal combustion burner concentrically provided with two air nozzles for supplying combustion air to the outer periphery of a fuel nozzle for conveying pulverized coal in an air flow, in a pulverized coal combustion burner, wherein The pulverized coal combustion burner is characterized in that the recirculation flow is supplied to the fuel jet flow of the pulverized coal through the flow of the combustion air on the inner periphery divided and supplied. 9. The pulverized coal combustion burner according to claim 7, wherein a part or all of the outer peripheral wall of the fuel nozzle is inclined in the inner peripheral direction of the fuel nozzle. 10. The pulverized coal combustion burner according to claim 9, wherein a position where the outer peripheral wall of the fuel nozzle is inclined in the inner peripheral direction of the fuel nozzle is a position different from the position of the solid wall. 11. A pulverized coal combustion burner comprising, concentrically, two air nozzles for supplying combustion air in a swirling flow to the outer periphery of a fuel nozzle for conveying pulverized coal in an air stream, wherein the fuel nozzle is arranged in accordance with a fuel flow direction. A venturi having a small inner diameter of a fuel nozzle, a swirler for supplying a part of the pulverized coal in a swirl flow, a distributor for forming a concentric double pipe flow path, and a swirl flow for a straight flow A pulverized coal combustion burner, which is provided with a rectifier for converting. 12. The pulverized coal combustion burner according to claim 11, wherein the swirler includes swirl vanes on the outermost peripheral side of the spindle-shaped member. 13. The outermost diameter of the swirler is smaller than the innermost diameter of the venturi.
Pulverized coal combustion burner described. 14. The pulverized coal combustion burner according to claim 11, wherein a plurality of collision plates are provided on an end surface of the fuel nozzle. 15. The pulverized coal combustion burner according to claim 11, wherein the rectifier is composed of a plurality of partition plates arranged radially and a collision plate is provided on the downstream side of the partition plate. 16. The pulverized coal according to claim 14, wherein the swirler creates a plurality of pulverized coal high-concentration flows in the circumferential direction and collides the pulverized coal high-concentration flow with the collision plate. Combustion burner.