JPH08285231A - Low nox pulverized coal burner and pulverized coal combustion device - Google Patents

Abstract

PURPOSE: To prevent the adhesion of combustion ash to a furnace wall across a wide range by a method wherein a part of air stream in an air feeding flow passage is branched to provide an air inducing member for forming wall surface jet stream flowing against a furnace wall around a burner, in a combustion device burning solid fuel such as coal or the like by carrying it to the burner by air. CONSTITUTION: In a pulverized coal burning boiler, pulverized coal is carried to a burner by air stream. The burner is a tertiary air flow branching type low NOx pulverized coal burner and a primary air flow passage 14 of mixed flow 12 of primary air and pulverized coal is provided at the outer periphery of a starting burner 11 at the center of the burner. A secondary air flow passage 15 and a tertiary air flow passage 16 are provided sequentially around the outer periphery of a bulkhead provided around the outer periphery of the primary air flow passage 14. In this case, tertiary air separators 22a, 22b are provided at the end of the furnace side of the bulkhead for the secondary and tertiary air passages 15, 16 to branch air by a separator 22b and produce wall surface jet stream 19b. The separator 22b is formed by bending toward the outer peripheral side of the burner and is provided with a twisted structure so as to swirl the tertiary air 19.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a low NOx pulverized coal burner and a pulverized coal combustion apparatus equipped with the burner, and particularly to a low NOx pulverized coal burner.
The present invention relates to a combustion apparatus suitable for stably performing low NOx combustion in a pulverized coal burner that requires combustion.

[0002]

2. Description of the Related Art As a pulverized coal combustion system used in a conventional boiler or the like, a pulverized coal machine (hereinafter referred to as a mill) having a built-in classifier pulverizes coal and conveys fine powder of a predetermined size or smaller by classification. A combustion system that directly supplies the burner with air for commercial use has been put into practical use. A two-stage combustion method is typical as a NOx reduction technology in this pulverized coal combustion system.

The two-stage combustion method has an external type and an internal type,
Of these, the external method is to maintain the air ratio (the ratio of necessary air to fuel, where the air ratio is 1 is the stoichiometric equivalent) in the burner zone in the furnace in a fuel-rich condition of 1 or less. Generated NOx is reduced to reduce NOx and
The unburned fuel generated in the burner zone under the above-mentioned combustion conditions is completely burned by injecting sufficient combustion air from the air injection hole installed in the downstream of the burner zone in the furnace. .

On the other hand, the internal type is intended to reduce NOx and completely burn unburned fuel in the burner zone, and the pulverized coal is used in a fuel-rich condition where the air ratio of only primary air is 1 or less. By igniting and burning, the NOx is reduced, and the secondary air and the tertiary air, which are the combustion air, are swirled to delay the mixing of the secondary air and the tertiary air into the combustion region generated in the burner zone. The unburned fuel is completely burned by prolonging the residence time of the pulverized coal in the burner zone, which has been put into practical use.

[0005]

Due to the NOx reduction technology using the above-mentioned external and internal two-stage combustion methods, the fuel ratio (fixed carbon / volatile matter) is 2, and the nitrogen content in coal is 1.
With the standard coal of 5%, the NOx emission concentration at the boiler outlet can be reduced to around 100 to 150 ppm, and the unburned content in ash can be reduced to 5% or less.

However, due to the recent stricter regulation of the NOx emission amount contained in the fuel exhaust gas, the NOx emission concentration at the boiler outlet is required to be a low value of 100 ppm or less. On the other hand, in Japan, where the dependence on coal imports is close to 100%, it is essential to establish stable low NOx combustion technology regardless of coal type.

Low NOx emissions with NOx emissions of 100 ppm or less
As a countermeasure, in the internal two-stage combustion method, a flame stabilizer is installed in the primary air flow path that conveys pulverized coal to strengthen the ignition and flame protection of pulverized coal, and in the boiler combustion system, a mill is used. A method has been proposed in which pulverized coal is classified into fine-grained powder and coarse-grained powder on the way from the container to the burner, and further the fine-grained powder is conveyed by a mixed gas of air and exhaust gas.

In such a low NOx fine powder burner and combustion apparatus, the combustion ash produced by the combustion of pulverized coal adheres to the furnace wall around the burner and is exposed to high temperature to melt the combustion ash. The generated slag adheres to the furnace wall and grows into a lump, which causes a problem. That is, since the surface of the furnace wall is covered with the slag that is the heat insulating material, heat transfer in the furnace heat transfer tube that constitutes the furnace wall is reduced, which causes a decrease in boiler efficiency.

FIG. 8 and FIG. 9 show sectional structural views of a conventional pulverized coal burner. Each shows a half-section portion with respect to the central axis of the burner.

FIG. 8 shows a partition wall having a primary air flow passage 14 through which a mixed flow 12 of primary air and pulverized coal flows, and a venturi 13 and a flame stabilizer 26 provided on the outer periphery of a starting burner 11 using oil as a fuel. 30 shows a burner cross section in which the secondary air flow passage 15 and the tertiary air flow passage 16 are further provided on the outer periphery thereof.

FIG. 9 shows a partition wall 30 on the outer periphery of the primary air passage 14.
8 is the same as that of FIG. 8 up to the configuration of FIG. 8 and shows a burner cross section in which a secondary air flow path 15 and a tertiary air flow path 16 having a bypass are provided on the outer periphery thereof.

In the burner shown in FIG. 8, the pulverized coal becomes a mixed flow 12 of primary air and pulverized coal, which is accelerated by a venturi 13 provided in a primary air flow passage 14 on the outer periphery of the starter burner 11 to be burned by the burner. Injected into the flame stabilizer 2
Ignition is held by 6 and the air register 17
Are completely combusted by the secondary air 18 and the tertiary air 19 which are combustion air replenished from the secondary air flow path 15 and the tertiary air flow path 16 provided with.

At this time, in combustion of pulverized coal, the air ratio is 1
In order to increase the combustion time in the following fuel-rich state, the secondary air 18 and the tertiary air 19 are supplied as a swirling flow by the respective air registers 17, and the secondary air flow path 15 and the tertiary air are supplied. The end of the partition wall 22 with the flow path 16 inside the furnace is bent toward the tertiary air flow path 16 on the outer periphery.

The burner shown in FIG. 9 is different from the burner shown in FIG. 8 in that an air flow rate adjusting damper 27 is provided in place of the air register 17 of the secondary air passage 15, and a swirling flow is formed at the outlet portion. And the provision of the secondary air swirl vane 29 of
The secondary air passage 15 is provided with a detour path that makes a U-turn on the side of the primary air passage 14.

As shown in FIGS. 8 and 9, pulverized coal is ignited and burned under a fuel-rich condition in which only the primary air has an air ratio of 1 or less to reduce NOx, and secondary air 1 as combustion air is used.
8. NOx produced by swirling the tertiary air 19 to delay mixing of the secondary air 18 and the tertiary air 19 in the combustion region generated in the burner zone, and prolong the residence time of the pulverized coal in the burner zone. Is sufficiently reduced, and at the same time, low NOx combustion and complete combustion of unburned fuel are performed.

FIG. 10 shows the gas flow at the burner outlet in the furnace and the state of slag adhesion to the furnace wall surface. The pulverized coal is conveyed by the mixed flow 12 of the pulverized coal and the primary air and is ejected into the furnace. On the other hand, the secondary air 18 that is combustion air
Flows outside the partition wall 30 (see FIG. 8) with the primary air flow path 14, and the tertiary air 19 flows outside the partition wall 22 with the secondary air flow path 15 and is jetted into the furnace. While the primary air is a straight flow, the secondary air 18 and the tertiary air 19 are often swirled as described above.

At the end of the partition wall 30 of the primary air flow path inside the furnace, a flame stabilizer 26 having an L-shaped cross-section and having a divergent shape is installed. Ignition flame holding is promoted due to the formation of (not shown). That is, the flow velocity inside the circulation flow is the mixed flow 12 or the secondary air 18
The slower than the average flow velocity of, the flame is stably formed, which is advantageous for combustion. In addition, the secondary air 1
8 or a vortex flow due to the difference in flow velocity is formed at the boundary of the region (circulation region) where the primary air and the circulation flow in the mixed flow 12 are formed, and pulverized coal and air are easily taken into this region. As a result, even in the case of pulverized coal, which is a solid fuel that is more difficult to burn than other gas fuels or oil fuels, the stability of ignition and flame holding can be improved by providing the flame stabilizer 26 having an L-shaped cross-section and a flared shape. We are trying to improve.

A problem with a pulverized coal burner having a cross-sectional shape as shown in FIGS. 8 and 9 is the sticking of slag on the furnace wall 23 around the burner. FIG. 10 shows the state of gas flow around the burner in the furnace as well as the state of sticking of the slag 31. That is, since the atmosphere temperature in the furnace is high and the fuel concentration is highest around the burner, the concentration of the combustion ash that causes the slag 31 is high, and the combustion ash is easily heated above its melting point. Further, since the area around the burner is a region where the gas flow convects, the particles of the combustion ash generated by the combustion of pulverized coal are easily taken in, and the ratio of the particles of the combustion ash that collides with the furnace wall 23 becomes high. 31 The reason for sticking is mentioned.

During combustion, the surface of the furnace wall 23 around the burner becomes high in temperature due to radiation from the flame and contact with combustion gas. Therefore, if the combustion ash generated by combustion adheres to the furnace wall 23 around the burner, the temperature will rise. In many cases, the slag 31 is melted and fixed, and further grows in a lump.

In recent years, domestic commercial boilers burn a large amount of imported coal from overseas, and the types thereof are increasing year by year. These include flame-retardant coal and coal having a low melting temperature of ash, and in a pulverized coal burner, measures for preventing slag sticking when these coals are burned are indispensable.

The object of the present invention is to prevent the combustion ash generated by combustion in the furnace from adhering to the furnace wall over a wide range of the furnace wall, and especially the combustion ash adhering to the periphery of the burner is fixed as slag by melting. The object is to provide a low NOx pulverized coal burner or a pulverized coal combustion device that prevents growth and has a low NOx emission concentration.

[0022]

The above objects of the present invention can be achieved by the following constitutions. That is, a solid fuel such as coal is conveyed to a burner using a compressive fluid such as air,
In a combustion device that supplies combustion air to the burner in multiple stages, air that divides a part of the air flowing into the air input passage located at the outermost periphery of the burner to form a wall surface jet that flows toward the furnace wall around the burner. A low NOx pulverized coal burner in which an induction member is provided in the flow path, or. A pulverized coal combustion apparatus equipped with the low NOx pulverized coal burner.

The air guide member of the low NOx pulverized coal burner of the present invention is the outlet end of the air flow passage inside the furnace of the flow passage wall surface which divides the air flow passage located at the outermost periphery of the burner and the air flow passage inside thereof. It is possible to use a separator formed by dividing a part into a plurality of parts in the circumferential direction and bending at least a part thereof. Further, the separator may be configured to include a configuration in which the separator is twisted so as to have a predetermined angle with respect to the air flow direction.

Further, the air guide member of the present invention is a plurality of air swirl blades provided inside the air passage located at the outermost periphery of the burner and in the circumferential direction near the outlet of the air passage inside the furnace. You may comprise. A configuration in which the direction of the air swirl vanes is arranged at a predetermined angle with respect to the air flow direction, and the swirl strength of a part of the air flow is changed from the swirl strength of the main flow of the air flow path in which the air swirl vanes are arranged. can do.

[0025]

[Operation] NOx is generated when slag adheres to the furnace wall of the burner
Will increase. It is due to the following two reasons. (1) An increase in thermal NOx due to an increase in gas temperature is predicted. However, this increase is 10-20ppm
It is a degree and a little. (2) The slag flows out when the burner is stopped, and blocks a part of the tertiary air passage of the burner. In this case, the burner's damage is large. Because the burner secures the reduction area by swirling the tertiary air, a partial blockage of the tertiary air flow path has the same result as the swirling strength of the tertiary air is lost, and it is about 50 to 100 ppm. There is an increase in the amount of NOx.

How to prevent the combustion ash generated by the combustion in the furnace from adhering to a wide area of the furnace wall, and in particular, preventing the combustion ash adhering to the periphery of the burner from sticking and growing as slag due to melting. On the other hand, in the burner of the present invention, as a member for diverting a part of the air in the air flow passage located in the outermost peripheral portion of the burner, for example, an air diverting blade is attached to reduce the pulverized coal low N
A wall jet of air is formed on the surface of the furnace wall around the burner without changing the state of the main flow of combustion gas for performing Ox combustion, so that particles of combustion ash collide directly with the furnace wall and adhere to them. Can be prevented.

Further, since the jet stream formed on the surface of the furnace wall is obtained by diverting the combustion air, the oxygen partial pressure near the surface of the furnace wall around the burner increases, so that the melting temperature of the combustion ash is increased. Increases by about 150 ° C,
In addition to the effect of preventing the combustion ash from adhering due to the air sealing effect, it is possible to prevent the slag from sticking over a wide range of the furnace wall, especially around the burner. Thus, according to the present invention, the amount of NOx produced can be significantly reduced.

[0028]

An embodiment of the present invention will be described with reference to the drawings. FIG. 7 shows a system diagram of a pulverized coal burning boiler to which the pulverized coal burner of the embodiment of the present invention is applied. Coal, which is a fuel, is temporarily stored in a coal bunker 1 and then crushed by a mill 2 to be processed into pulverized coal. On the other hand, the primary air that conveys this pulverized coal to the burner of the wind box 3 is PAF (Primary Air Fan) 5
After being pressurized by the heat exchanger, heat is exchanged with the high temperature boiler combustion exhaust gas by the heat exchanger 6 provided around the boiler,
After being heated to 00 ° C., it is sent to the mill 2. The pressurized and heated air evaporates the moisture adhering to the coal inside the mill 2 and then is sent to the burner in the wind box 3 together with the pulverized coal. Also, combustion air such as secondary air and tertiary air is FD
It is pressurized by an F (Forced Draft Fan) 7 and supplied to the wind box 3 in which a burner is arranged via a heat exchanger 6. In addition, a part of the boiler combustion exhaust gas is GRF (Gas Recirculat
It is supplied to the bottom of the boiler furnace 10 by an ion fan) 9 for the purpose of utilizing waste heat.

FIG. 1 shows a tertiary air distribution type low N according to this embodiment.
It shows a cross-sectional view of an Ox pulverized coal burner, showing a half cross-section with respect to the central axis of the burner. A starter burner 11 that uses oil as fuel is installed in the central portion of the burner, and a primary air flow passage 14 through which a mixed flow 12 of primary air and pulverized coal flows is provided on the outer periphery thereof, and a venturi 13 is provided on the outer periphery thereof.
A partition 30 having a flame stabilizer 26 is provided. Further, on the outer periphery thereof, a secondary air flow path 15 and a tertiary air flow path 16 are provided in this order with a ring-shaped flow path.

An air register 17 is provided in each of the secondary air flow path 15 and the tertiary air flow path 16, and the secondary air 18 and the tertiary air 19 which are combustion air are swirled by the respective air registers 17. And is ejected into the furnace. The swirl strength applied to the secondary air 18 and the tertiary air 19 has a swirl number of 0.6 to 1.
It is effective to set it to about 2 (swirl number: axial flux of angular momentum / axial momentum / nozzle radius) and adjust the jet so that it does not form a wall jet.

On the other hand, the secondary air passage 15 and the tertiary air passage 1
At the inner end of the furnace of the partition wall 22 of No. 6, the tertiary air separator 2
2a and 22b are provided, of which the separator 22b splits a part of the tertiary air 19 and jets it into the furnace as a wall surface jet 19b.

FIG. 2 shows a perspective view of a tertiary air splitting type pulverized coal burner portion of an embodiment of the present invention. On the surface of the furnace wall 23 (see FIG. 1) around the burner, a part of the tertiary air 19 is diverted to flow as a wall surface jet 19b. A separator 22b is provided on the outer peripheral side of the plurality of pieces so that the wall surface jet 19b is generated from the burner toward the wall surface evenly in the circumferential direction of the burner.

When the tertiary air separator 22b is bent toward the outer peripheral side of the burner, it is desirable to have a twisted structure so that the split tertiary air can be swirled. In this embodiment, the tertiary air separator 22 is twisted only in the separator 22b, and is not twisted in the other part, the separator 22a. A plurality of the tertiary air separators 22b are provided not at the entire cross section of the tertiary air flow path 16 but at an equal ratio in the circumferential direction. The separators 22a and 22b are formed by cutting the ends of the partition wall 22 or provided separately by connecting the separators 22a and 22b to the ends of the partition wall 22.
In the latter case, the separators 22a and 22b may have a flared shape. Further, the twist of the separator 22b can be made not in the root of the separator but in the middle thereof.

Due to the plurality of twisted tertiary air separators 22b, the primary swirl flow 1 of the tertiary air 19 is generated by the tertiary air separator 22a in a part of the tertiary air 19.
A swirling force equal to or higher than the swirling strength of 9a is applied to form a wall surface jet 19b, which is an air flow covering the furnace wall surface, around the burner. Therefore, due to the strong swirling effect obtained by the tertiary air separator 22b, a part of the tertiary air 19 is partially generated in FIG.
As shown in FIG. 5, the wall surface jet 19b is formed, and the wall surface jet 19b forms an air curtain on the surface of the furnace wall 23, so that particles of combustion ash can be prevented from colliding with and adhering to the furnace wall 23. Further, since the main swirl flow 19a of the tertiary air 19 forms an air flow similar to that of conventional combustion air, it is possible to perform low NOx combustion with good ignition and flame holding.

FIG. 4 shows, as another embodiment, an example in which the separator 22b is simply twisted to the outer circumference without being twisted. Although this structure is not as strong as the burner shown in FIG. 2, an air flow is formed on the furnace wall, so that slag can be prevented from sticking to the furnace wall.

Another embodiment shown in FIG. 5 is an example in which the present invention is applied to the burner shown in FIG. 9 as a conventional example, and the secondary air passage 15 is made to make a U-turn to the primary air passage 14 side. It is an example of application to a burner provided with a detour. In FIG. 5, members having the same functions as those in FIG. 1 are given the same numbers. The example shown in FIG. 5 is a mixed flow 12 of primary air and pulverized coal,
The tertiary air separator 25 is attached to a burner which delays the mixing with the tertiary air 19 which occupies most of the combustion air by widening the width of the partition wall 22.

In the burner shown in FIG. 5, the partition wall 22 for the secondary air 18 and the tertiary air 19 is composed of a duct, and since the partition wall 22 cannot be easily bent like a plate, the tertiary air 19 is removed. As a means to make a strong turn partially,
The structure is such that the separator 25, which is a turning device having a vane structure, is attached. FIG. 6 shows a detailed view of mounting the separator 25 having the vane structure. The separator 25 is provided on the inner wall surface of the furnace wall 23 (see FIG. 5) of the burner throat, and the mounting angle θ with respect to the plane perpendicular to the burner axis is appropriately adjusted so that part of the tertiary air 19 becomes the wall surface jet 19b. To do. By attaching the separator 25 to the tertiary air flow path 16 (see FIG. 5), when the air is blown in the axial direction of the burner, the tertiary air 19 is partly swirled, and the swirling effect causes the swirling effect. Around the burner, a wall surface jet 19b, which is an airflow covering the wall surface of the furnace, is formed.

In the embodiment shown in FIG. 5, as in the burner shown in FIG. 1, the separator 25 is not attached to the entire cross section of the tertiary air passage 16, but the separator 25 is attached to a part of the tertiary air passage 16. Since the main swirl flow 19a of the burner tertiary air 19 forms an air flow similar to that of conventional combustion air, low NOx with good ignition and flame protection.
Burning can take place.

[0039]

According to the low NOx pulverized coal burner or the low NOx pulverized coal burner according to the present invention, the combustion ash generated by combustion in the furnace, which has been a problem in the conventional pulverized coal burner, is generated. It is possible to prevent the ash from adhering to the wall of the furnace over a wide range of the furnace wall, in particular, to prevent the combustion ash attached to the periphery of the burner from being fixed as a slag due to melting and growing, and to achieve low NOx combustion. In addition, the reduction of NOx has an effect of reducing the amount of ammonia consumption in the denitration device on the downstream side.

[Brief description of drawings]

FIG. 1 is a tertiary air shunt type low NOx according to an embodiment of the present invention.
It is a sectional view of a pulverized coal burner.

FIG. 2 is a partial perspective view of the tertiary air split type low NOx pulverized coal burner of FIG.

FIG. 3 is an explanatory diagram of a slag removal state around the tertiary air split type low NOx pulverized coal burner of FIG. 1.

FIG. 4 is a partial perspective view of a burner showing an example in which the tertiary air separator of FIG. 2 is simply twisted to the outer circumference without being twisted.

FIG. 5 is a tertiary air split type low NOx according to an embodiment of the present invention.
It is a sectional view of a pulverized coal burner.

FIG. 6 is a perspective view illustrating how to install the tertiary air separator in FIG.

FIG. 7 is a system diagram of a pulverized coal combustion device according to an embodiment of the present invention.

FIG. 8 is a cross-sectional view of a prior art low NOx pulverized coal burner.

FIG. 9 is a cross-sectional view of a prior art low NOx pulverized coal burner.

FIG. 10 is an explanatory diagram of a gas flow and a slag fixing state around a burner according to a conventional technique.

[Explanation of symbols]

11 ... Start-up burner, 12 ... Mixed flow of primary air and pulverized coal, 13 ... Venturi, 14 ... Primary air flow path, 15 ...
Secondary air flow passage, 16 ... Tertiary air flow passage, 17 ... Air register, 18 ... Secondary air, 19 ... Tertiary air, 19a ... Main swirling flow of tertiary air, 19b ... Wall jet, 22 ... Secondary air and tertiary Partition walls of air, 22a, 22b, 25 ... Tertiary air separator, 23 ... Furnace wall

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Noriyuki Oyatsu 3 36 Takaracho, Kure City, Hiroshima Prefecture Babcock Hitachi Ltd. Kure Research Institute (72) Inventor Shigeki Morita 6 9 Takaracho, Kure City Hiroshima Prefecture Babcock Hitachi Ltd. Kure Factory

Claims (6)

[Claims] 1. A combustor in which a solid fuel such as coal is transported to a burner by using a compressive fluid such as air and combustion air is supplied to the burner in multiple stages. An air injection flow located at the outermost periphery of the burner. A low NOx pulverized coal burner, characterized in that an air guide member for dividing a part of the air flowing in the passage to form a wall surface jet flowing toward the furnace wall around the burner is provided in the flow passage. 2. The air guide member comprises a plurality of air passage outlet ends on the inside of the furnace on the wall surface of the flow passage that divides the air passage located at the outermost periphery of the burner and the air passage inside the burner in the circumferential direction. 2. The low NOx according to claim 1, which is composed of a separator having a shape in which at least a part of the separator is bent.
Pulverized coal burner. 3. The low NOx pulverized coal burner according to claim 2, wherein the separator includes a separator twisted so as to have a predetermined angle with respect to a flow direction of air. 4. The air guide member is an air swirl vane, which is provided inside the air passage located at the outermost periphery of the burner and is provided in the circumferential direction in the vicinity of the air passage outlet inside the furnace. A low NOx pulverized coal burner according to claim 1. 5. The swirl strength of a part of the air flow is determined by arranging the direction of the air swirl vane at a predetermined angle with respect to the air flow direction, and the swirl strength of the main flow of the air flow path in which the air swirl vane is arranged is 5. The low NOx pulverized coal burner according to claim 4, wherein 6. A pulverized coal combustion apparatus comprising the low NOx pulverized coal burner according to any one of claims 1 to 5.