EP2664847A1

EP2664847A1 - Boiler device

Info

Publication number: EP2664847A1
Application number: EP12734688.0A
Authority: EP
Inventors: Akihito Orii; Hirofumi Okazaki
Original assignee: Babcock Hitachi KK
Current assignee: Mitsubishi Power Ltd
Priority date: 2011-01-12
Filing date: 2012-01-12
Publication date: 2013-11-20
Anticipated expiration: 2032-01-12
Also published as: EP2664847B1; JP2012145267A; PL2664847T3; EP2664847A4; WO2012096319A1; JP5530373B2; TW201248089A

Abstract

Areliable and cost-effective boiler equipped with a sound air supply nozzle which enables the following is provided: even when there is a gap between the nozzle provided in a through hole communicating with the interior of a furnace and the through hole, a strong swirl flow along the inner surface of the furnace wall can be formed; and burnout due to radiant heat can be suppressed. The air supply nozzle has the through hole in the furnace wall comprised of a water pipe, the nozzle supplying air is inserted into the through hole, and there is the gap between the nozzle and the through hole. The air supply nozzle is so configured that the position of the tip of the nozzle is located at a distance of 0.8 times the nozzle inside diameter or more away from the furnace wall inner surface and a tangential velocity component is given to gas jetting out of the nozzle.

Description

Technical Field

The present invention relates to boilers and in particular to a boiler having an air supply nozzle which supplies air into a furnace.

Background Art

A pulverized coal burning boiler in which coal is pulverized and suspended and burned in a furnace is configured as disclosed in, for example, Patent Document 1. The boiler furnace is provided at the lower part thereof with a pulverized coal burner and an after-air nozzle is provided downstream of the burner (upper part of the boiler). Pulverized coal fuel and combustion air are supplied from the burner and only air is supplied from the after-air nozzle.
Combustion at the burner portion is carried out as described below. Air in such a quantity or less that an excess air ratio required for the complete combustion of pulverized coal fuel is obtained is supplied from the burner. Thus the pulverized coal is burned in the shortage of air to create a reducing atmosphere and the production of NOx is thereby suppressed. In the reducing atmosphere, unburned components are left because of the shortage of oxygen and CO (carbon monoxide) is produced. To completely burn the unburned components and CO produced in the reducing atmosphere, the following measure is taken: combustion air in a quantity slightly larger than the air quantity equivalent to the insufficient excess air ratio is supplied into the furnace from the after-air nozzle positioned downstream of the burner. As a result, combustion exhaust gas with reduced unburned components and CO is discharged from the furnace.

Citation List

Patent Document

Patent Document 1: Japanese Unexamined Patent Application Publication No. Hei 9(1997)-310807
Patent Document 2: Japanese Unexamined Patent Application Publication No. Hei 4(1992)-52414
Patent Document 3: Japanese Unexamined Patent Application Publication No. 2009-174751

Summary of Invention

Technical Problem

It is important for combustion equipment such as pulverized coal burning boilers and oil burning boilers to completely burn fuel. For this reason, to implement complete combustion by supplying air from an after-air nozzle positioned downstream of a burner as in, for example, the above-mentioned pulverized coal burning boiler, it is desirable to take the following measure: air is evenly distributed in the furnace to facilitate mixing with unburned components. In this case, in addition to supplying air to the center of the furnace, it is necessary to supply air to the proximity of a furnace wall to reduce the unburned components in fuel in the proximity of thefurnacewall. One of means for supplying air to the proximity of a furnace wall is a method of swirling air in a nozzle and supplying it into the furnace as a swirl flow. For example, Patent Document 2 discloses a swirl structure in which air is given a straight flow and a swirl flow to facilitate mixing by adjusting the flow mode of an after-air jet. To supply air to the proximity of a furnace wall with the above structure, the following method is taken: the ratio of swirl flow is increased and air is diffused by centrifugal force after the air is blown out of the nozzle. When an especially strong swirl flow is produced, a wall surface flow can be formed along a furnace wall surface by the Coanda effect under which air flows along a wall surface even after it is blown out of a nozzle.
The furnace wall which is a partition wall comprising the furnace of the boiler is thermally expanded with rise in in-furnace temperature. Generally, a furnace has its upper part supported and is suspended. For this reason, its furnace wall is moved downward by thermal expansion. When a furnace is supported at its lower part, its furnace wall is moved upward by thermal expansion. For this reason, in general, an air supply nozzle such as an after-air nozzle is not brought into tight contact with a through hole communicating with the interior of the furnace and is provided with a gap. As the result of the provision of the gap, a through hole in the furnace wall moved by thermal expansion is not brought into contact or does not interfere with the air supply nozzle fixed in the foundation of the equipment.
The interior of the furnace is controlled under negative pressure to prevent combustion gas from flowing out of the furnace. Air flows as a leak flow from this gap into the furnace. Since the leak flow goes straight into the furnace, it works in the direction in which a swirl flow is hindered and this makes it difficult to form a strong wall surface flow along the wall. Even when a structure (seal member) is provided between the air supply nozzle and the furnace wall for the prevention of the inflow of air, the following problem arises: in a stepped portion produced between the air supply nozzle and the furnace wall, a flow path is abruptly expanded; therefore, a flow is separated from the wall surface and a circulating flow is produced to prevent air jetting out of the nozzle from flowing along the wall surface. This makes it difficult to form a flow along the furnace wall surface and air is not sufficiently supplied to the proximity of the furnace wall and unburned components can be left.
Patent Document 3 discloses a nozzle which jets out air along a waterwall. However, a component member is protruded into the furnace and the nozzle member can be burned by radiant heat from a burner flame and this can prevent a required air jet from being formed.
An object of the invention is to provide an air supply nozzle with improved soundness and a boiler with improved reliability and cost efficiency. In the air supply nozzle, the following can be implemented even when there is a gap between the nozzle provided in a through hole in a furnace wall communicating with the interior of a furnace and the through hole: it is possible to form a strong swirl flow and a wall surface flow on a furnace inner wall surface and burnout of the nozzle due to radiant heat is suppressed.

Solution to Problem

The invention is a boiler including: a burner burning fuel supplied into a furnace; a furnace wall comprising a furnace in which a water pipe is installed and a through hole is formed; and an air supply nozzle having a nozzle inserted into the through hole and supplying air into the furnace and a swirling member giving a tangential velocity component to air supplied into the nozzle and having a gap between the nozzle and the through hole. The boiler is characterized in that the position of the tip of the air supply nozzle in the through hole is located at a distance of 0.8 times the nozzle inside diameter or more from the furnace wall inner surface.
A boiler including an air supply nozzle is characterized in that it has an expanded structure in which the cross-sectional area of the tip portion of the nozzle is increased toward the downstream side.
A boiler including an air supply nozzle is characterized in that the nozzle is provided therein with a cylindrical expanded member whose cross-sectional area is increased toward the downstream side.
A boiler including an air supply nozzle is characterized in that the tip of the nozzle is provided with a projected and depressed member.
A boiler including an air supply nozzle is characterized in that a through hole has an expanded structure on the furnace inner surface side.
A boiler including an air supply nozzle is characterized in that a structure for preventing the inflow of air is provided in an area where the outside of a furnace wall and the nozzle are in contact with each other.
A boiler including an air supply nozzle is characterized in that an adjusting member is provided for adjusting the tangential velocity component of fluid.
A boiler including an air supply nozzle is characterized in that the air supply nozzle is provided on the downstream side of the burner.
A boiler including an air supply nozzle is characterized in that: a nozzle for supplying a shortage of combustion air in a burner into a furnace is provided in at least two or more stages on the downstream side of the burner; and the air supply nozzle is provided as part of the nozzles.
A boiler including an air supply nozzle is characterized in that the air supply nozzle is provided at the height at which a burner is placed.

Advantageous Effects of Invention

According to the invention, the tip of a nozzle is installed at a distance of 0.8D or more from a furnace wall inner surface. Therefore, a flow jetted out of the nozzle is gradually expanded in the radial direction and goes along the inner wall of a through hole on the upstream side of the outlet of a through hole. It is further expanded at the outlet of the through hole and goes along the furnace wall inner surface over the surface of a water pipe.
For this reason, even though there is a gap between the nozzle provided in the through hole communicating with the interior of the furnace and the through hole, a wall surface flow along the wall can be formed.
When an air supply nozzle of the invention is installed downstream of a burner, a sufficient quantity of oxygen can be supplied to the proximity of a wall and unburned components and CO existing in the proximity of the wall are reduced in quantity. When it is installed at the height at which a burner is placed, oxygen can be supplied along the surface of a furnace wall to suppress corrosion. Further, since the nozzle is not protruded into the furnace, burnout of the nozzle due to radiant heat can be suppressed and a reliable and cost-effective boiler can be provided.

Brief Description of Drawings

[FIG. 1] FIG. 1 is a front view of an air supply nozzle in a first embodiment of the invention.
[FIG. 2] FIG. 2 is a schematic diagram showing a section taken along line A-A of FIG. 1.
[FIG. 3] FIG. 3 is a graph indicating the state of a jet changed depending on L and the presence or absence of a gap 24.
[FIG. 4] FIG. 4 is a schematic diagram illustrating a jet obtained when a wall surface flow is formed in FIG. 3 (H region).
[FIG. 5] FIG. 5 is a schematic diagram illustrating a jet when a wall surface flow is not formed in FIG. 3 (F region) .
[FIG. 6] FIG. 6 is a schematic diagram illustrating an air supply nozzle in a second embodiment of the invention.
[FIG. 7] FIG. 7 is a schematic diagram illustrating an air supply nozzle in a third embodiment of the invention.
[FIG. 8] FIG.8 is a schematic diagram illustrating an air supply nozzle in a fourth embodiment of the invention.
[FIG. 9] FIG. 9 is a schematic diagram illustrating an air supply nozzle in a fifth embodiment of the invention.
[FIG. 10] FIG.10 is a schematic diagram illustrating an air supply nozzle in a sixth embodiment of the invention.
[FIG. 11] FIG.11 is a schematic diagram illustrating a boiler in a seventh embodiment of the invention.
[FIG. 12] This is a schematic diagram illustrating a boiler in the eighth embodiment of the invention.
[FIG. 13] FIG. 13 is a fragmentary view of the boiler in FIG. 12 taken in the direction of arrow B-B. Description of Embodiments

Hereafter, a description will be given to boilers in embodiments of the invention with reference to the drawings.

(First Embodiment)

FIG. 1 is a front view of an air supply nozzle 4 in an embodiment of the invention and FIG. 2 is a schematic diagram showing a section taken along line A-A of FIG. 1. A water pipe 11 is provided on the surface of a furnace wall 1 and the water pipe 11 is also deformed in accordance with the shape of a through hole 30 and placed so as not to interfere with the circular through hole 30. The furnace wall 1 is elongated downward by thermal expansion due to heat in the furnace; therefore, a gap 24 is provided between the outside diameter of a nozzle 20 installed in the through hole 30 and the inside diameter of the through hole 30. In the nozzle 20, a circular swirl vane 25 is installed as an air swirling member. A duct 16 is so configured that it can supply air 15 from the through hole 30 into the furnace through the nozzle 20.
The air 15 goes through the duct 16 and flows in from an inflow port 22 provided in the nozzle 20. It is turned into a swirl flow having the velocity of flow of a tangential velocity component by the swirl vane 25 and flows out from the tip of the nozzle 20 and flows from the through hole 30 into the furnace. The air flow rate is adjusted by the opening of a damper 21. The furnace wall 1 and the duct 16 are brought into tight contact with each other so that the full quantity of air 15 flows into the furnace; however, there is a gap 26 between the duct 16 and the furnace wall 1.
The interior of the furnace is constantly controlled under negative pressure during operation so as to prevent combustion gas from getting out of the furnace. Consequently, there is a leak flow 23 formed by air flowing in from the gap 26 and jetting out from the gap 24 into the furnace. Since this leak flow 23 is a straight flow going into the furnace, it hinders a wall surface flow along the wall formed by a strong swirl flow jetting out of the nozzle 20. Even when seal is implemented by a seal member 27 which prevents the inflow of air to suppress the leak flow 23, the following problem is caused because of the presence of the gap 24: a circulating flow 31 is produced at the tip of the nozzle 20 and prevents a swirl flow jetting out of the nozzle 20 from going along the wall surface.
FIG. 3 indicates the influence of the presence or absence of the gap 24 on a jet. The horizontal axis indicates the value obtained by dividing the distance L from the tip of the nozzle 20 illustrated in FIG. 2 to the inner surface of the furnace wall 1 by the inside diameter D of the nozzle 20 (L/D).
The vertical axis indicates the presence or absence of the gap 24. O in the drawing indicates that a wall surface flow formed by a jet jetting out of the through hole 30 along the wall is formed and X indicates that a wall surface flow is not formed. The hatched area H in the drawing indicates a region where a wall surface flow is formed and F indicates a non-wall surface flow region. Even in region F in the drawing, a wall surface flow may be temporarily formed in some cases; however, when disturbance due to pressure fluctuation in the furnace or the like is given, the wall surface flow cannot be stably maintained. Under the conditions of region H, a wall surface flow can be formed without the influence of these disturbances. From FIG. 3, the following is understood: to form a wall surface flow in the presence of the gap 24, a distance of approximately 0.8 times the inside diameter D of the nozzle 20 or more is required as the distance L from the tip of the nozzle 20 to the inner surface of the furnace wall 1.
FIG. 4 is a schematic diagram of a jet obtained when a wall surface flow equivalent to region H in FIG. 3 is formed. The position of the tip of the nozzle 20 is located sufficiently, or 0.8D or more, away from the inner surface of the furnace wall 1. For this reason, a swirl flow jetting out of the nozzle is gradually expanded in the radial direction. It suppresses the leak flow 23 and the circulating flow 31 and is further expanded at the outlet of the through hole 30, turned into a wall surface flow going along the inner surface of the furnace wall 1 over the surface of a water pipe 11.
FIG. 5 is a schematic diagram of a jet obtained in the case of a non-wall surface flow equivalent to region F in FIG. 3. Since the tip of the nozzle 20 is positioned close to the inner surface of the furnace wall 1, a swirl flow jetting out of the nozzle 20 goes out into the furnace before it is expanded in the radial direction. The leak flow 23 straightly goes into the furnace and the circulating flow 31 also prevents a wall surface flow frombeing formed; therefore, a stable wall surface flow is difficult to be formed.
According to a first embodiment, the following can be implemented even when there is the gap 24 between the through hole 30 communicating with the furnace and the nozzle 20: a stable wall surface flow can be formed without the influence of disturbance due to fluctuation in in-furnace pressure or the like. This is done by locating the position of the tip of the nozzle 20 at a distance of 0.8 times the inside diameter D of the nozzle 20 or more from the inner surface of the furnace wall 1.

(Second Embodiment)

FIG. 6 is a schematic diagram of a nozzle in a second embodiment of the invention. In addition to the condition of the position of the tip of the nozzle in the first embodiment, this nozzle has an expanded structure in which the tip of the nozzle 20 is increased in cross-sectional area toward the downstream side. According to the second embodiment, an expanded portion 32 provided in the nozzle 20 faces in the radial direction. This brings the following advantages: the production of a circulating flow 31 is suppressed; a swirl flow jetting out of the nozzle 20 is readily expanded in the radial direction; and a more stable wall surface flow can be formed.

(Third Embodiment)

FIG. 7 is a schematic diagram of a nozzle in a third embodiment of the invention. This nozzle is provided at the tip thereof inside the nozzle 20 with a cylindrical expanded member 33 whose cross-sectional area is increased toward the downstream side. Also with respect to the third embodiment, the expanded member 33 faces in the radial direction and the following advantages are brought: a swirl flow is readily expanded in the radial direction and the production of a circulating flow 31 is suppressed; and thus a more stable wall surface flow can be formed. Since the expanded member 33 is positioned in the nozzle, an advantage of the reduced influence of radiant heat is brought.

(Fourth Embodiment)

FIG. 8 is a schematic diagram of a nozzle in a fourth embodiment of the invention. This nozzle is provided at the tip thereof inside the nozzle 20 with a projected and depressed member 34 in which tooth-like or strip-like members are arranged in the circumferential direction. A flow jetting out of the nozzle is disturbed by the member 34 and is readily diffused in the circumferential direction. For this reason, a flow jetting out of the nozzle is readily expanded and the production of a circulating flow 31 is suppressed; consequently, the flow jetting out of the nozzle 20 becomes a stable wall surface flow.

(Fifth Embodiment)

FIG. 9 is a schematic diagram of a nozzle in a fifth embodiment of the invention. This nozzle has an expanded structure in which an expanded portion 28 expanded toward the outlet is formed at the outlet portion of the through hole 30 in the furnace wall 1.
According to the fifth embodiment, a swirl flow jetting out of the nozzle 20 is readily expanded in the radial direction at the outlet of the through hole 30 and the production of a circulating flow 31 is suppressed. This brings an advantage that a more stable wall surface flow can be formed.

(Sixth Embodiment)

FIG. 10 is a schematic diagram of a nozzle in a sixth embodiment of the invention. A guide vane 29 in which the radial angle of blades arranged in the circumferential direction can be inclined and adjusted is provided in place of the swirl vane 25 illustrated in FIG. 9. The air flow rate is adjusted by a damper 36. Also according to the sixth embodiment, a strong swirl flow making a wall surface flow can be formed similarly to the embodiment in FIG. 9. In addition, the tangential velocity component (swirl intensity) can be adjusted by adjusting the angle of the guide vane 29 by an adjust handle 35 as an adjusting member. This brings an advantage that the shape of a jet can be widely controlled.

(Seventh Embodiment)

FIG. 11 is a schematic diagram of a boiler to which a nozzle structure in a seventh embodiment of the invention is applied. A burner 2 is provided at the lower part of the boiler. Gas 5 containing unburned components ascends from the burner portion. After-air (air) 7 is supplied from an after-air nozzle 3 provided at the upper part of the boiler and the unburned components are completely burned and the gas is discharged as exhaust gas 9 from the furnace. An air supply nozzle 4 of the invention is provided below the after-air nozzle 3. Air (oxygen) is supplied as a wall surface flow 8 to the proximity of the wall where air cannot be supplied by the after-air nozzle 3. Air can be thereby evenly mixed in the furnace and unburned components and CO in the proximity of the wall can be reduced in quantity. Consequently, the rate of combustion of fuel in the furnace is improved and a cost-effective boiler can be provided.

(Eighth Embodiment)

FIG. 12 is a schematic diagram of a boiler to which an air supply nozzle structure in an eighth embodiment of the invention is applied. In the eighth embodiment, the air supply nozzle 4 is provided in the proximity of a burner 2 at the lower part of the boiler. In the proximity of the burner, the oxygen concentration is low and a furnace wall is prone to corrode. FIG. 13 is a fragmentary view taken in the direction of arrow B-B of FIG. 12. The following can be implemented by installing the air supply nozzle 4 of the invention at the height at which the burner is installed: air (oxygen) is caused to flow over the surface of a water pipe by a wall surface flow along the furnace wall like the jets 8 illustrated in FIG. 13; therefore, the surface of the water pipe can be brought into an oxidizing atmosphere and corrosion can be suppressed. Since members comprising the nozzle are not protruded into the furnace, burnout due to radiant heat does not occur and high reliability is achieved. In FIG. 12, burners 2 are provided only on one side. Even when burners 2 are provided on both sides as in FIG. 11, the same effect is obtained. In FIG. 12 illustrating this embodiment, the air supply nozzles 4 are provided in three faces other than the burner 2 installation face; however, they can also be provided in the burner 2 installation face. In FIG. 12 illustrating this embodiment, the air supply nozzles 4 are provided at the height at which the lowermost burner 2 is installed. However, they may be provided at any height at which a burner 2 positioned below the after-air nozzles 3 (upstream side) is installed.
According to the invention, a flow along a wall can be formed even when there is a gap between a nozzle provided in a through hole communicating with the interior of a furnace and the through hole. When it is applied to an after-air nozzle positioned downstream of a burner, oxygen can be supplied to the proximity of a wall and unburned components and CO existing in the proximity of the wall are reduced in quantity. When it is applied to the proximity of a burner, oxygen can be supplied along the surface of a water pipe and corrosion of the furnace wall can be suppressed. In addition, since structural materials comprising the nozzle are not protruded into the furnace, burnout of the nozzle members due to radiant heat can be suppressed and a reliable and cost-effective boiler can be provided.

Reference Signs List

1 --- Furnace wall
3 --- After-air nozzle
4 --- Air supply nozzle
8 --- Air jet
9 --- Combustion exhaust gas
11 --- Water pipe
15 --- Air flow
20 --- Nozzle
23 --- Leak flow
24, 26 --- Gap
25 --- Swirl vane
7 --- Seal member
28, 32 --- Expanded portion
29 --- Guide vane
30 --- Through hole
31 --- Circulating flow
33 --- Cylindrical expanded member
34 --- Projected and depressed member
35 --- Adjust handle
D --- Nozzle inside diameter
L --- Distance between nozzle tip and furnace wall inner surface

Claims

A boiler equipped with a burner burning fuel supplied into a furnace, a furnace wall comprising the furnace in which a water pipe is installed and a through hole is formed, and an air supply nozzle including a nozzle inserted into the through hole and supplying air into the furnace and having a gap between the nozzle and the through hole, and a swirling member giving a tangential velocity component to air supplied into the nozzle,
the boiler equipped with the air supply nozzle being characterized in that the position of the tip of the air supply nozzle in the through hole of the nozzle is located at a distance of 0.8 times the nozzle inside diameter or more away from the furnace wall inner surface.
The boiler equipped with the air supply nozzle according to Claim 1, characterized in that the air supply nozzle has an expanded structure in which the tip of the nozzle is increased in cross-sectional area toward the downstream side.
The boiler equipped with the air supply nozzle according to Claim 1, characterized in that the nozzle is provided therein with a cylindrical expanded member whose cross-sectional area is increased toward the downstream side.
The boiler equipped with the air supply nozzle according to Claim 1, characterized in that the nozzle is provided at the tip thereof with a projected and depressed member.
The boiler equipped with the air supply nozzle according to any of Claims 1 to 4, characterized in that the through hole has an expanded structure on the furnace inner surface side.
The boiler equipped with the air supply nozzle according to any of Claims 1 to 5, characterized in that a structure preventing the passage of air is provided in a place where the outside of the furnace wall and the nozzle are in contact with each other.
The boiler equipped with the air supply nozzle according to any of Claims 1 to 6, characterized in that an adjusting member adjusting the tangential velocity component of fluid is provided.
The boiler equipped with the air supply nozzle according to any of Claims 1 to 7, characterized in that the air supply nozzle is provided on the downstream side of the burner.
The boiler equipped with the air supply nozzle according to Claim 8, characterized in that a nozzle supplying a shortage of combustion air in the burner into the furnace is provided in at least two or more stages on the downstream side of the burner and the air supply nozzle is provided as part of the nozzles.
The boiler equipped with the air supply nozzle according to any of Claims 1 to 9, characterized in that the air supply nozzle is provided at the height at which the burner is placed.