JP2006052917A - Pulverized coal burner and boiler - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a pulverized coal burner capable of reducing abrasion of a pulverized coal mixed air flow passage wall and a pulverized coal nozzle, by further realizing ignition stability and low NOx. <P>SOLUTION: This pulverized coal burner 19 has a pulverized coal mixed air passage 35 for introducing a pulverized coal mixed air of pulverized coal and carrier air, a core 49 arranged in a substantially central part in a cross section of the pulverized coal mixed air passage 35, forming a through-part 55 penetrating in the flowing direction of the pulverized coal mixed air in its central part and forming an accelerating part 57 gradually reducing toward the downstream side in an interval with a pulverized coal supply pipe 37 on the upstream side of its outer peripheral part, and a secondary air passage 39 arranged on the outer peripheral side of the pulverized coal mixed air passage 35 and introducing secondary air heated by an air preheater 33; and is characterized in that the core 49 has an air input nozzle 53 arranged in the through-part 55 and blowing the secondary air taken in from the secondary air passage 39 in the through-part 55. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a pulverized coal burner suitable for use in a pulverized coal burning boiler that generates steam for power generation or industrial use, and a boiler using the pulverized coal burner.

These pulverized coal burners are required to have stable ignition and low NOx. As what solves this, there exists a thing shown by patent document 1, for example.
This is provided with a core for adjusting the pulverized coal concentration in the pulverized coal mixture passage through which the pulverized coal mixture composed of pulverized coal and carrier air passes. An air-fuel mixture passage is opened at the center of the core, and the outer shape of the core is small on the upstream side and large toward the downstream side, and is formed so as not to change substantially after the middle.
When the pulverized coal mixture passes between the core and the inner wall of the pulverized coal mixture passage, the pulverized coal mixture is drifted to the inner wall side of the pulverized coal mixture passage. As a result, the pulverized coal is concentrated on the inner wall side of the pulverized coal mixture passage by the inertial force, so that after passing through the core, the pulverized coal mixture has a high pulverized coal concentration on the outer peripheral side and a low pulverized coal concentration on the inner side. In this state, the pulverized coal mixture is blown into the furnace from the pulverized coal nozzle.
In this way, the pulverized coal mixture blown into the furnace is always ignited because the pulverized coal concentration on the outer peripheral side becomes high, so the generation of volatile matter in the pulverized coal is increased by receiving radiant heat from the furnace. This makes it easy to form a pulverized coal flame with excellent ignition stability.
In addition, since the pulverized coal concentration varies between the front side and the inner side, so-called light and dark combustion occurs, so that the generation of NOx can be reduced.

Japanese Patent Laid-Open No. 10-332110 (paragraphs [0028] to [0048] and FIGS. 1 to 2)

By the way, although further ignition stability and NOx reduction have been demanded in recent years, the one described in Patent Document 1 has a problem that it cannot functionally meet the requirements functionally.
In addition, when passing through the outer periphery of the core and being blown into the pulverized coal nozzle, the pulverized coal mixture has a high pulverized coal concentration and a high flow rate, so the wall of the pulverized coal mixture passage and the pulverized coal nozzle are heavily worn. There was a problem.

  In view of the above problems, the present invention uses a pulverized coal burner that can realize further ignition stability and NOx reduction and can reduce wear of a pulverized coal mixture channel wall and a pulverized coal nozzle. The purpose is to provide a boiler.

In order to solve the above problems, the present invention employs the following means.
That is, the pulverized coal burner according to the present invention is provided in the pulverized coal mixture passage for guiding the pulverized coal mixture of the pulverized coal and the carrier air, and at the substantially central portion in the cross section of the pulverized coal mixture passage, An accelerating portion in which a through portion penetrating in the flow direction of the pulverized coal mixture is formed in the portion, and an interval between the outer wall and the wall surface of the pulverized coal mixture passage gradually decreases toward the downstream side. In a pulverized coal burner having a core formed with a combustion air passage that is provided on an outer peripheral side of the pulverized coal mixture passage and guides combustion air heated by an air preheater, Is provided with an air input member that is provided in the penetrating portion and blows combustion air taken in from the combustion air passage into the penetrating portion.

  Thus, since the core is provided with the air input member that is provided in the through portion and blows the combustion air taken in from the combustion air passage into the through portion, the high temperature combustion air is contained in the core by the air input member. The pulverized coal mixture that is blown into the penetrating part of the child and passes through the penetrating part is heated. Since the high temperature atmosphere of the heated pulverized coal mixture passing through the penetration part is propagated to the pulverized coal mixture passing through the outer periphery of the core, the pulverized coal mixture injected from the pulverized coal burner into the furnace is hot. It becomes. Therefore, when high-concentration pulverized coal exists on the outer peripheral side and high-temperature pulverized coal mixture is injected into the furnace, volatile matter generation in the pulverized coal is further increased, so that ignition stability is further improved. Can do.

Further, since the combustion air is blown into the pulverized coal mixture that passes through the penetrating portion, the pulverized coal concentration of the pulverized coal mixture that flows through the substantially central portion in the cross section of the pulverized coal mixture passage further decreases. Thereby, the pulverized coal mixture injected from the pulverized coal burner into the furnace expands the difference in the pulverized coal concentration between the outer peripheral portion and the central portion, so that the generation of NOx can be reduced.
Furthermore, since the pulverized coal mixture becomes high temperature on the downstream side of the outlet portion of the core, the density of the pulverized coal mixture, that is, the mass flow rate decreases. When the mass flow rate of the pulverized coal mixture decreases, the flow area of the pulverized coal mixture decreases because the cross-sectional area of the pulverized coal mixture flow path is constant. For this reason, wear of the pulverized coal mixture channel wall and the pulverized coal nozzle can be reduced.
As the combustion air, it is preferable to take in secondary air because it is easy to process in close proximity, but in some cases, tertiary air may be taken in.

  The pulverized coal burner according to the present invention is characterized in that a backflow prevention structure is provided in the combustion air intake portion of the air input member.

  Thus, the combustion air intake part of the air input member is provided with a backflow prevention structure, so that, for example, even when the pressure in the furnace increases, the pulverized coal mixture flows back to the combustion air passage. Can be prevented. For this reason, since pulverized coal does not accumulate in a combustion air passage, pulverized coal ignition and backfire in a combustion air passage can be prevented. Thereby, stable fuel supply can be performed even at the time of partial load in which the air flow rate is reduced.

  Furthermore, in the pulverized coal burner according to the present invention, the air input member blows out the combustion air in a direction orthogonal to the flow of the pulverized coal mixture passing through the through portion.

  In this way, the air input member blows out combustion air in a direction orthogonal to the flow of the pulverized coal mixture passing through the penetration portion, so that the fuel air is quickly mixed with the pulverized coal mixture, The temperature of the mixture can be raised.

  A boiler according to the present invention includes the pulverized coal burner according to any one of claims 1 to 3.

  Since a pulverized coal burner with improved ignition stability and reduced NOx generation is employed, the boiler can be improved in operational stability and reduced in NOx.

In the pulverized coal burner according to the present invention, the core is provided with an air input member that is provided in the penetrating portion and blows combustion air taken in from the combustion air passage into the penetrating portion, so that ignition stability and low NOx are provided. Can be further improved. Further, the wear of the pulverized coal mixture channel wall and the pulverized coal nozzle can be reduced.
In the boiler according to the present invention, the operational stability is improved and NOx is reduced.

An embodiment according to the present invention will be described below with reference to FIGS.
FIG. 1 is a block diagram showing an overall schematic configuration of a boiler 1 according to the present embodiment.
The boiler 1 includes a furnace 3 installed in a vertical direction, a combustion device 7 installed in a lower part of the furnace wall 5 of the furnace 3, a flue 9 connected to an outlet of the furnace 3, and an upper part of the furnace 3. A superheater 11, a reheater 13 and a economizer 15 provided over the flue 9, and a steam drum 17 provided at the upper part of the furnace 3 are provided.

A large number of water pipes (not shown) extend in the vertical direction inside the furnace wall 5. Each water pipe is connected to the steam drum 17 at upper and lower ends.
The combustion device 7 includes a plurality of pulverized coal burners 19 (see FIG. 2) attached to the furnace wall 5, pulverized coal supply means 21 for supplying pulverized coal to the pulverized coal burner 19, and combustion for the pulverized coal burner 19. And air supply means 23 for supplying secondary air as air.

The pulverized coal supply means 21 includes a pulverized coal machine 25 for pulverizing coal supplied via a coal feeder and a meter (not shown) to a size suitable for combustion (for example, several μm to several hundred μm), and pulverized coal. The pulverized coal produced by the machine 25 is provided with a coal supply pipe 27 that carries the air current to the pulverized coal burner 19 as pulverized coal mixture by pressurized carrier air supplied from an air source (not shown).
The carrier air is set so that the outlet temperature of the pulverized coal machine 25 is about 80 ° C. from the safety aspect of the pulverized coal machine 25.

The air supply means 23 includes a not-shown push ventilator that pressurizes and supplies air, a wind box 29 provided on the outer wall of the furnace 3, and an air pipe 31 that connects the push ventilator and the wind box 29. It has been.
The secondary air passing through the air pipe 31 is heat-exchanged with, for example, about 360 ° C. combustion exhaust gas passing through the flue 9 by the rotary regenerative heat exchanger 33 and heated to 300 to 350 ° C. Supplied.

The pulverized coal burner 19 will be described with reference to FIGS. 2 is a longitudinal sectional view showing the furnace 3 side portion of the pulverized coal burner 19, FIG. 3 is an XX sectional view of FIG. 2, and FIG. 4 is a YY sectional view of FIG.
The pulverized coal burner 19 includes a pulverized coal supply pipe 37 that forms a pulverized coal mixture passage 35, and a secondary air supply pipe 41 that is provided outside the pulverized coal supply pipe 37 so as to cover it with a space therebetween. The pulverized coal nozzle 43 attached to the tip of the pulverized coal supply pipe 37, the secondary air nozzle 45 provided to cover the outer side of the pulverized coal nozzle 43 with a space therebetween, and the pulverized coal nozzle 43 A flame holding plate 47 attached to the tip and a core 49 provided at a substantially central portion in the cross section of the pulverized coal mixture passage 35 are provided.

The secondary air supply pipe 41 has a substantially rectangular cross section and is provided so as to extend in the thickness direction of the furnace wall 5. The secondary air supply pipe 41 is fixed to a hole formed through the furnace wall 5.
The pulverized coal supply pipe 37 has a substantially rectangular cross-sectional shape, and is attached to the furnace wall 5 so as to extend in the thickness direction of the furnace wall 5.
A space between the pulverized coal supply pipe 37 and the secondary air supply pipe 41 communicates with the wind box 29 to form a secondary air passage 39.
The pulverized coal mixture passage 35 is configured to communicate with the coal supply pipe 27.

The pulverized coal nozzle 43 and the secondary air nozzle 45 have a substantially quadrangular pyramid shape with a smaller area toward the tip.
The flame holding plate 47 has a substantially quadrangular pyramid shape that expands toward the tip.
In the present embodiment, the pulverized coal supply pipe 37, the secondary air supply pipe 41, the pulverized coal nozzle 43, the secondary air nozzle 45, and the flame holding plate 47 have a substantially rectangular cross-sectional shape. This may be, for example, a substantially circular shape, a substantially elliptical shape, or an arbitrary polygonal shape.

The core 49 includes a core body 51 and an air injection nozzle (air input member) 53.
The core body 51 has a hollow, substantially quadrangular prism shape, and is arranged so that the hollow portion penetrates in the flow direction 50 of the pulverized coal mixture. This hollow portion constitutes the through portion 55. On the upstream side in the flow direction 50 of the core body 51, the thickness gradually decreases toward the upstream side in the flow direction 50, that is, the core body 51 and the pulverized coal supply pipe 37 from the upstream end of the core body 51 toward the downstream side. An acceleration portion 57 is formed in which the distance between and gradually decreases.
The core body 51 is attached to the pulverized coal supply pipe 37 by a support member 52 (see FIG. 4).

The air injection nozzle 53 has a substantially rectangular parallelepiped shape, and is provided at a substantially central portion in the vertical direction 60 of the penetrating portion 55 with the longitudinal direction extending in the width direction 70. The upstream end portion in the flow direction 50 of the air injection nozzle 53 gradually decreases in thickness toward the upstream side, and the downstream end portion gradually decreases in thickness toward the downstream side. Therefore, the cross-sectional shape along the vertical direction has a long and narrow hexagonal shape (see FIG. 2). Thereby, the pulverized coal mixture flowing through the penetrating portion 55 can flow smoothly downstream.
An air introduction part 59 that is a space into which secondary air is introduced is formed inside the air injection nozzle 53. Three nozzles 61 extending in the vertical direction to the surface of the air injection nozzle 53 are provided in the width direction 70 at the downstream portion in the flow direction 50 of the air introduction portion. In addition, what is necessary is just to set the number of the nozzles 61 suitably as needed.

On both sides with respect to the width direction 70 of the air injection nozzle 53, tubular air intake members 63 each having a bowl shape are attached. The short side of each air intake member 63 is located in the secondary air passage 39 and is arranged such that the opening at the end faces the upstream side in the flow direction 50.
The air injection nozzle 53 is fixed by the air intake member 63 being fixedly attached to the core body 51 and the pulverized coal supply pipe 37.
The communication part between the air intake member 63 and the air introduction part 59 is provided with a backflow prevention structure 65 in which curved plates are alternately attached to form a zigzag flow path. The plate constituting the backflow prevention structure 65 is configured to be longer when it is located on the air introduction part 59 side.

The operation of the boiler 1 according to this embodiment described above will be described.
The pulverized coal generated by the pulverized coal machine 25 is mixed with the pressurized carrier air to form a pulverized coal mixture, and is sent to the pulverized coal mixture passage 35 of the pulverized coal burner 19 through the coal supply pipe 27. It is done. On the other hand, the secondary air pressurized and supplied by a not-shown forced air fan is supplied with heat from the combustion exhaust gas by the rotary regenerative heat exchanger 33, heated to 300 to 350 ° C. and passed through the air pipe 31. It is supplied to the wind box 29. The secondary air is sent from the wind box 29 to the secondary air passage 39 of the pulverized coal burner 19.
A pulverized coal mixture and secondary air are supplied from the pulverized coal burner 19 into the furnace 3, and when ignited, a flame is generated in the furnace.

  When a flame is generated in the lower part of the furnace 3 in this way, the combustion gas flows from the bottom to the top in the furnace 3 and is discharged to the flue 9. At this time, water supplied from a water supply pump (not shown) is preheated by the economizer 15 and then supplied to the steam drum 17. The water supplied from the steam drum 17 to each water pipe (not shown) of the furnace wall 5 is heated to flow into the steam drum 17 while flowing through the water pipe from the bottom to the saturated steam. Further, the saturated steam of the steam drum 17 is introduced into the superheater 11 and is heated by the combustion gas. The superheated steam generated by the superheater 11 is supplied to a predetermined plant (for example, a turbine or the like).

In addition, the steam taken out in the middle of the expansion process in the turbine is introduced into the reheater 5 and reheated and returned to the turbine.
The combustion exhaust gas that has passed through the economizer 15 is supplied with heat to the secondary air that passes through the air pipe 31 in the rotary regenerative heat exchanger 33, and is subjected to processing such as desulfurization, denitration, and dust removal, and then from the chimney. Released into the atmosphere.

Next, the operation of the pulverized coal burner 19 will be described.
The pulverized coal mixture supplied in the pulverized coal supply pipe 37 is split by the core into the pulverized coal mixture A passing through the outer periphery of the core body 51 and the pulverized coal mixture B passing through the through portion 55. .
Since the flow channel area of the pulverized coal mixture A is gradually narrowed by the accelerating unit 57, the pulverized coal mixture A is brought closer to the pulverized coal supply pipe 37 side, that is, the outer peripheral side of the pulverized coal mixture passage 35, and the flow velocity is increased to increase the core 49. Pass through. Since the flow path of the pulverized coal mixture A that has passed through the core 49 is enlarged, the flow velocity is reduced. Thereby, air with a small inertia force returns to the center direction of the pulverized coal mixture passage 35, but the pulverized coal advances along the pulverized coal supply pipe 37 side because the inertia force is large. Therefore, a portion having a high pulverized coal concentration is formed on the outer peripheral side of the pulverized coal mixture passage 35.

On the other hand, the pulverized coal mixture B flows along the surface of the air injection nozzle 53. In the meantime, the high-temperature (300 to 350 ° C.) secondary air taken in from the air taking-in member 63 is discharged from the nozzle 61 through the air introducing portion 59, so that the pulverized coal mixture B is mixed with this secondary air. The mixture is heated up.
At the same time, since the secondary air is mixed with the pulverized coal mixture B, the pulverized coal concentration of the pulverized coal mixture B is diluted.
As described above, when the pulverized coal mixture B passes through the through portion 55, the temperature is increased and the pulverized coal mixture C is diluted with the pulverized coal concentration.

At this time, since the secondary air from the nozzle 61 is blown in the vertical direction 60 perpendicular to the flow direction 50 of the pulverized coal mixture B passing through the upper and lower sides of the core body 51, the secondary air is finely divided. It is quickly mixed with the coal mixture B, and the temperature of the pulverized coal mixture B can be raised in a short time.
The direction in which the secondary air is ejected from the nozzle 61 is not limited to the vertical direction, and may be an oblique direction or a horizontal direction toward the downstream side. In this case, the mixing speed of the secondary air and the pulverized coal mixture B is slightly slowed down, but the possibility that the pulverized coal mixture B will flow back to the air introduction unit 59 due to, for example, pressure fluctuation in the furnace 3 is further increased. Will be reduced.

Since the connection part between the air introduction part 59 and the air intake member 63 is provided with a backflow prevention structure 65, for example, even when the pressure in the furnace increases, the pulverized coal mixture flows back into the combustion air passage. Can be prevented. For this reason, since pulverized coal does not accumulate in a combustion air passage, pulverized coal ignition and backfire in a combustion air passage can be prevented. Thereby, stable fuel supply can be performed even at the time of partial load in which the air flow rate is reduced.
In this embodiment, the zigzag passage is formed by two curved plates as the backflow prevention structure 65, but the backflow prevention structure is not limited to this, and may be a backflow prevention valve. Other structures may be used as appropriate.

The high temperature of the pulverized coal mixture C is also propagated to the pulverized coal mixture A, and the pulverized coal mixture sent to the pulverized coal nozzle 43 becomes a high temperature as a whole, and the pulverized coal is easily volatilized. In this state, the pulverized coal mixture is supplied from the pulverized coal nozzle 43 into the furnace 3.
Thus, when a high concentration of pulverized coal is present on the outer peripheral side and a high-temperature pulverized coal mixture is injected into the furnace 3, volatile matter is generated in the pulverized coal by receiving radiant heat from the furnace 3. Since it becomes more, it becomes easier to ignite. Therefore, ignition stability can be further improved and a stable pulverized coal flame can be formed.

  Further, the pulverized coal mixture C that has passed through the through portion 55 that flows through the substantially central portion in the cross section of the pulverized coal mixture passage 35 is diluted with secondary air, and the pulverized coal concentration is further reduced. In the pulverized coal mixture injected from the nozzle 43 into the furnace 3, the difference in the pulverized coal concentration between the outer peripheral portion and the central portion is further enlarged. Therefore, since a greater difference in pulverized coal concentration can be produced between the surface side and the inner side, the effect of so-called concentration combustion is increased, and the generation of NOx can be further reduced.

  Furthermore, since the pulverized coal mixture becomes high temperature downstream from the outlet portion of the core 49, the density of the pulverized coal mixture, that is, the mass flow rate decreases. When the mass flow rate of the pulverized coal mixture decreases, the flow area of the pulverized coal mixture decreases because the sectional area of the pulverized coal mixture channel 35 is constant. For this reason, since the flow rate of pulverized coal also falls, the wear of the pulverized coal mixture passage 37 wall and the pulverized coal nozzle 43 can be reduced.

1 is a block diagram showing an overall schematic configuration of a boiler according to an embodiment of the present invention. It is a longitudinal cross-sectional view which shows the front-end | tip part of the pulverized coal burner concerning one Embodiment of this invention. It is XX sectional drawing of FIG. It is YY sectional drawing of FIG.

Explanation of symbols

1 Boiler 33 Air Preheater 35 Pulverized Coal Mixture Passage 39 Secondary Air Passage 49 Core 53 Air Input Nozzle 55 Through Portion 57 Acceleration Portion

Claims (4)

A pulverized coal mixture passage for guiding a pulverized coal mixture of pulverized coal and carrier air;
The pulverized coal mixture passage is provided at a substantially central portion in the cross section of the pulverized coal mixture passage, and a through portion is formed in the center of the pulverized coal mixture passage in the flow direction. A core formed with an accelerating portion in which the space between the wall surface of the air passage gradually decreases toward the downstream side;
A combustion air passage which is provided on the outer peripheral side of the pulverized coal mixture passage and guides combustion air heated by an air preheater;
In a pulverized coal burner having
The pulverized coal burner is characterized in that the core is provided with an air input member that is provided in the through portion and blows combustion air taken in from the combustion air passage into the through portion. The liquid fuel burner according to claim 1, wherein a backflow prevention structure is provided in a combustion air intake portion of the air input member. 3. The pulverized coal burner according to claim 1, wherein the air input member blows out the combustion air in a direction orthogonal to a flow of the pulverized coal mixture passing through the through portion. . A boiler comprising the pulverized coal burner according to any one of claims 1 to 3.

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