JPH09250709A - Burner for solid fuel and combustion device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To remarkably reduce an amount of NOX generated by a single burner by a method wherein ignition in the vicinity of a burner outlet and especially at the central part of a burner is accelerated, consumption of oxygen is expedited, and a reduction region produced by a single burner is enlarged. SOLUTION: An inner cylinder 10 is inserted in a pulverized coal feed pipe and an external flame stabilizing ring 35 is arranged at the peripheral part of the outlet tip of the inner cylinder 10. Further, an internal flame stabilizer 34 to accelerate ignition is attached to the outlet of a flow passage in the inner cylinder and the planes, crossing in the direction of a fuel flow at right angles, of the flame stabilizer 34 and the flame stabilizing ring 35 are attached from a position where the planes are on the same surface to a position where the planes are deviated from each other. Fine grain powder out of pulverized coal previously divided into fine grain powder and coarse grain powder is fed to the inner side of the inserted inner cylinder 10, and the coarse grain powder is fed into the outer cylinder.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a combustion device,
In particular, the present invention relates to a solid fuel burner and a combustion device capable of significantly reducing the production of nitrogen oxides (NOx) and stably burning coal having a wide range of properties in a wide load range with low NOx.

[0002]

2. Description of the Related Art In recent years, the problem of air pollution has become more and more serious, and it is necessary to reduce the amount of NOx generated as much as possible in a coal-fired boiler. A NOx reduction method that has already been established as a combustion system is in-furnace denitration. According to this method, as shown in FIG. 6, the NOx reduction region is formed by maintaining the air ratio (the amount of air supplied from the burner unit 51 / theoretical air amount) in the burner unit 51 of the combustion furnace 50 at a fuel rich condition of 1 or less. By doing so, the generated NOx is reduced and the exhausted NOx amount is reduced. At this time, unburned fuel is completely combusted in a complete combustion region formed by introducing air from an AAP (after air port) 52 installed in the upper stage of the burner section 51.

The above-mentioned in-furnace denitration method is a low NOx technology established as a system, but a technology of forming a NOx reduction region by a burner alone to reduce NOx is also established. FIG. 7 shows the concept of low NOx combustion.

As shown in FIG. 7, an internal flame stabilizer is provided at the outlet of the primary flow passage formed by the mixed flow of pulverized coal and primary air of the burner, and the outlet of the pipe forming the primary flow passage is provided. A flame holding ring is provided to bypass the mixed flow, the secondary air flow and the tertiary air flow to form a main combustion region and a reduction region, a swirling flow of secondary air and tertiary air, etc. in the combustion furnace. In this way, combustion is performed in the combustion area of char including the combustion area of volatile matter and the combustion of a part of volatile matter, and further in the complete combustion area,
Complete combustion is performed by the two-stage combustion air from the AAP 52 (FIG. 6).

A cross-sectional view of a low NOx burner represented by the prior art is shown in FIG. With conventional low NOx burners,
By attaching the external flame holding ring 63 around the outlet of the supply pipe 62 through which the mixed flow 61 of pulverized coal and primary air flows,
Improve the ignition of pulverized coal. Further, an annular flow path is provided around the supply pipe 62 in the order of a flow path 65 for the secondary air 64 and a flow path 68 for the tertiary air 67. The swirling of the air flow in the secondary air flow path 65 and the tertiary air flow path 68 is performed by a register damper 70 provided in each of the flow paths 65 and 68 and having a function as a swirler.
71 respectively. Therefore, the secondary air 64 and the tertiary air 67 are swirled by the register dampers (swirlers) 70 and 71 and sent to the combustion furnace 72.

A secondary air swirl vane 74 for enhancing swirl force is provided at the outlet of the secondary air passage 65 in the combustion furnace. In addition, a startup burner 75 that uses heavy oil as fuel is installed in the central portion of the burner.

Swirlers 70, 71 for secondary air and tertiary air
By swirling with the swirling vane 74 or the swirling vane 74, the mixing of the pulverized coal that is ignited and burned with the mixed flow 61 of the primary air is delayed, and the NOx reduction region formed by the burner alone is expanded. With these technologies, the emission NOx amount is 130 ppm
(Fuel ratio = fixed carbon / volatile content is 2, nitrogen content in coal is 1.5)
%, And the final combustion content in ash is 5% or less).

However, the NOx regulation value tends to become stricter year by year, and the emission NOx regulation value required in the future is 100 p.
pm or less.

[0009]

DISCLOSURE OF THE INVENTION The conventional low NOx described above
The technology is not sufficient to reach the NOx regulation value of 100 ppm or less. An object of the present invention is to significantly reduce the amount of NOx produced by the burner alone. Another object of the present invention is to promote ignition in the vicinity of the burner outlet, particularly in the center of the burner, accelerate oxygen consumption, and expand the reduction region made by the burner alone.

[0010]

The above object of the present invention can be achieved by the following constitution. That is, a solid-gas two-phase flow passage through which a solid-gas two-phase flow composed of a solid fuel and a gas for carrying the fuel flows is provided as a double pipe composed of an inner cylinder and an outer cylinder which are divided into two parts. In the burner for solid fuel, which has at least one air flow path through which combustion air flows and has a flame stabilizer having a plane orthogonal to the flow at the burner outlet, the flame stabilizer is solid-gas two-phase The flame stabilizer and the outside of the flow passage outlet in the inner cylinder are respectively provided at the flow passage outlet in the inner cylinder of the flow passage and the flow passage outlet in the outer cylinder of the solid-gas two-phase flow passage. It is a burner for solid fuels installed in positions where planes provided in a direction orthogonal to a fuel flow direction of a flame stabilizer at a flow path outlet in a cylinder are displaced from positions on the same plane.

The solid fuel burner of the present invention is configured to supply the fine powder of the solid fuel previously divided into the fine powder and the coarse powder to the solid-gas two-phase flow passage in the inner cylinder. Alternatively, the plane provided in the direction orthogonal to the fuel flow direction of the flame stabilizer provided inside the solid-gas two-phase flow passage inside the inner cylinder is the solid-gas two-phase flow inside the outer cylinder. Being installed on the upstream side of the plane provided in the direction orthogonal to the fuel flow direction of the flame stabilizer provided in the passage improves the ignition flame holding in the center of the burner and accelerates oxygen consumption, It is convenient for expanding the reduction region.

Further, a mixed fluid of air and exhaust gas may be used as the fine powder carrying gas flowing in the solid-gas two-phase flow passage in the inner cylinder. In that case, the oxygen partial pressure in the air is 5 as the fine powder carrying gas flowing in the solid-gas two-phase flow channel in the inner cylinder.
Using a mixed fluid mixed with exhaust gas of less than volume%,
It is desirable that the oxygen partial pressure of the air for conveying fine particles after mixing with the exhaust gas does not fall below 16% by volume.

The present invention also includes a combustion device provided with the solid fuel burner. As described above, the solid fuel burner according to the present invention is provided with the internal flame stabilizer which is offset from the same plane as the external flame holding ring in the peripheral portion of the outlet tip of the inner cylinder inserted into the pulverized coal supply pipe, NOx is greatly reduced by improving the ignition and flame maintenance in the central part of the burner, accelerating the consumption of oxygen, and expanding the reduction region. Further, since the ignition and flame holding property is very excellent, it is suitable for coal having a wide load range and a wide range of properties, and is also suitable for combustion of high fuel ratio coal and coarse coal which are usually difficult to combust.

[0014]

Embodiments of the present invention will be described below. FIG. 5 is an example of a boiler combustion system diagram when the burner of the present invention is used. The coal stored in the bunker 2 is supplied from the coal feeder 3 to the mill 4 according to the load of the combustion device in the furnace 1. The pulverized coal crushed by the mill 4 is
A pulverized coal conveying air pressurized by a PAF (Primary Air Fan) 5 and passed through a heat exchanger 6 to classify the pulverized coal 8
It is transported to and divided into coarse powder and fine powder. The coarse powder is supplied to the burner unit 11 through the coarse powder supply pipe 9 as it is, but the fine powder is once collected by the bag filter 12 and then stored in the bin 13 and fed by the feeder 15 to the fine powder entraining device 16 And then mixed with the exhaust gas from the exhaust gas mixing damper 17 and fed with the carrier air to the fine powder supply pipe 10.
And is supplied to the burner unit 11.

In addition, FDF (Force Draft)
The combustion air is pressurized from the fan 19 and the burner 11
And is divided into secondary air and tertiary air by the burner unit 11 and supplied respectively.

In FIG. 5, the coal is crushed by using one mill 4 to separate fine powder and coarse powder, and then the fine powder is mixed with the exhaust gas and supplied to the burner section 11 by the conveying air. Although an example was shown, an auxiliary mill (not shown) was newly installed, and fine powder and coarse powder were crushed separately by multiple mills,
After the fine powder is collected in the bottle 13, it may be supplied to the burner unit 11 by air for transportation. Also in this case, the fine powder carrier gas is discharged by the exhaust gas mixing damper 17 into the GRF (Gas R gas).
The mixture with the exhaust gas taken out by the EC 20 is used.

Next, the operation of the burner of the present invention in these combustion systems will be described in detail. FIG. 1 is a sectional view of a burner which is an embodiment of the present invention. A starter burner 21 using heavy oil as fuel is installed in the central portion of the burner, and a fine powder supply pipe 10 for conveying a mixed flow (lean flow) 22a composed of fine coal powder, air and exhaust gas around the burner 21.
Is installed. Around the pipe 10, a coarse-grain powder supply pipe 9 through which a mixed flow (concentrated flow) 22b of coarse-grain powder coal and air passes is provided. Around the coarse-grained powder supply pipe 9, a flow path 26 for the secondary air 25 and a flow path 29 for the tertiary air 28 have an annular flow path in this order. The swirling of the air flow in the secondary air flow path 26 and the tertiary air flow path 29 is determined by the respective flow paths 26, 29.
Register damper 3 with a function as a swivel installed in
0 and 31 respectively. Therefore, the secondary air 25 and the tertiary air 28 are swirled by the register dampers 30 and 31 and fed into the wall surface 32 of the boiler furnace 1.

Further, a flame stabilizer 34 (bluff body type flame stabilizer) is installed at the tip of the fine grain powder supply pipe 10 between the mixed streams 22a and 22b, and the outer wall of the outlet of the coarse grain powder supply pipe 9 inside the furnace. Has an external flame holding ring 35.

The feature of this burner is that the mixed streams 22a, 22
Internal flame stabilizer 34 having a plane plate in a direction perpendicular to b
This enhances the cooling effect of the flame stabilizer 34 itself, and at the same time increases the entrainment and turbulence of the pulverized coal flow, enhances the ignition / flame holding property, and lowers the NOx of the combustion gas.

The greatest feature of this embodiment is that the internal flame stabilizer 3 is used.
4 is the installation position. The reason why the installation position of the internal flame stabilizer 34 is important will be described below. That is, the burner alone is NO
In order to reduce x, it is very important to promote the consumption of oxygen in the center of the burner and increase the reduction region. In a general low NOx burner, since a large flame is generated by the external flame holding ring 35 at the outlet end of the coarse-grained powder supply pipe 9,
Propagation of the flame to the center of the burner governs combustion. At this time, the flame spread to the center of the burner becomes faster as the grain size of coal becomes smaller.

However, the feature of this embodiment is that the fine powder supply pipe 10 is provided.
When installing the internal flame stabilizer 34 at the tip of the outlet, the internal flame stabilizer 3
Since the installation position of No. 4 is shifted so as not to be installed on the same plane as the plane orthogonal to the fuel flow formed by the outer flame holding ring 35, the inner flame stabilizer 34 is not attached
Compared to when installed on the same plane as the plane formed by
The velocity of the coal particles passing near the flame created by the internal flame stabilizer 34 can be slowed. This greatly improves the ignition promotion property, flame propagation property, and stability near the burner outlet. In particular, the inner flame stabilizer 34 is connected to the outer flame stabilizer ring 35.
This effect is remarkable when installed on the upstream side of the same plane as the plane orthogonal to the fuel flow formed by.

However, the installation of the internal flame stabilizer 34 accelerates ignition, and the flame formed near the internal flame stabilizer 34 may burn the external flame stabilizer ring 35. Therefore, it is necessary to set conditions for the installation location in order to prevent the external flame holding ring 35 from burning.

In this case, when the inner flame stabilizer 34 is displaced forward from the same plane as the plane orthogonal to the fuel flow formed by the outer flame stabilizing ring 35, the distance is L (see FIG. 2).
Then, as the installation location of the internal flame stabilizer 34, a location where the distance L satisfies the following condition is desirable.

The internal flame stabilizer 34 is shown in FIG.
5 shows the installation positional relationship of No. 5. Vertical distance r from burner central axis 37 to internal flame stabilizer 34, vertical distance ro from burner central axis 37 to external flame stabilizer ring 35, flow velocity v of mixed flow 22a, internal flame stabilizer 34 to burner center Axis 37
A velocity v ′ at which the flame propagates in the direction perpendicular to the outer flame holding ring 35, and a time t required for the flame to propagate vertically from the inner flame stabilizer 34 to the outer flame holding ring 35,
The following relational expression holds during the time t ′ required for the flame to propagate in the axial direction of the burner shaft 37 from the internal flame stabilizer 34 to the burner outlet.

T = (r-ro) / v 't' = L / v. Therefore, when determining the distance L for preventing the external flame holding ring 35 from burning, it is desirable to satisfy the following relationship. (R-ro) / v '> L / v FIG. 3 shows another embodiment of the present invention in which the internal flame stabilizer 34 is flush with the plane orthogonal to the fuel flow formed by the external flame stabilizing ring 35. It is sectional drawing of the burner installed in the more downstream side.

Further, in the burner according to the present invention, since the fine powder is supplied to the inside of the fine powder supply pipe 10 from the fine coal which has been divided into the fine powder and the coarse powder in advance, the propagation of the flame to the central portion of the burner is promoted. It At this time, if the exhaust gas having an oxygen partial pressure of 5 vol% or less is mixed into the air for conveying fine particles, the absolute value of the oxygen concentration in the central portion of the burner decreases, and the oxygen consumption time can be further shortened. However, at this time, in consideration of the stability of the flame during combustion, it is preferable that the oxygen concentration in the transport air after mixing the exhaust gas does not fall below 16%.

FIG. 4 shows the N by the separate supply type burner of the present invention.
The Ox reduction effect is shown. According to this, the NOx reduction effect of the burner according to the present invention is about 2 as compared with the conventional low NOx burner.
5%.

Further, the air for conveying fine particles has an oxygen concentration of 5 v.
When exhaust gas of less than ol% is mixed, volatile matter containing a large amount of HCN and NH ₃ which are reducing substances of NOx is generated.
There is a further NOx reduction effect.

As described above, in the present invention, the plane perpendicular to the fuel flow of the internal flame stabilizer 34 is not flush with the plane perpendicular to the fuel flow of the external flame holding ring at the outlet end of the fine powder feed pipe. In particular, the ignitability of the conventional low NOx burner and the flame can be improved by installing it in the position on the upstream side of the external flame holding ring and by conveying the fine powder to the inside of the fine powder supply pipe with the transport air mixed with the exhaust gas. By greatly promoting the propagating property and forming a stable and large reduction region, it is possible to significantly reduce the amount of NOx produced.

The effect on low NOx has been mainly described above, but the burner according to the present invention is excellent in ignition flame holding property.
It is also suitable for coal with a wide load range and a wide range of properties, and can sufficiently handle combustion of high fuel ratio coal and coarse coal, which are usually difficult to burn.

[0031]

The effects of the present invention are shown below. (1) Ultra-low NOx to create a stable large reduction region
Can be achieved. (2) Since it has excellent ignition and flame protection, it is also suitable for the combustion of coal with a wide load range and wide range of properties, and it can sufficiently handle high fuel ratio coal and coarse coal that are difficult to burn. (3) The burner can obtain an excellent denitration effect by itself, it is not necessary to provide a plurality of burners as a low NOx combustion system, and the compactness of the device and improvement of operability are possible.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of a burner of a pulverized coal combustion apparatus in which an internal flame stabilizer is installed on the front side of the same plane as an external flame holding ring in one embodiment of the present invention.

FIG. 2 is a diagram illustrating the positional relationship between an internal flame stabilizer and an external flame stabilizer ring of a burner according to an embodiment of the present invention.

FIG. 3 is a cross-sectional view of a burner of a pulverized coal combustion apparatus in which an internal flame stabilizer according to an embodiment of the present invention is installed on the wake side from the same plane as the external flame holding ring.

FIG. 4 is an N diagram of a pulverized coal combustion apparatus according to an embodiment of the present invention
It is a figure explaining the Ox reduction effect.

FIG. 5 is a boiler combustion system diagram when the fine powder is conveyed by the conveying air mixed with exhaust gas.

FIG. 6 is a diagram showing the concept of low NOx combustion in a furnace.

FIG. 7 is a diagram illustrating a concept of a combustion region of low NOx combustion.

FIG. 8 is a cross-sectional view of an NR burner that is typical of conventional low NOx burners.

[Explanation of symbols] 1 furnace 2 bunker 3 coal feeder 4 mill 5 PAF 6 heat exchanger 8 classifier 9 coarse powder supply pipe 10 fine powder supply pipe 11 burner part 12 bag filter 13 bin 15 feeder 16 fine powder entrainer 17 exhaust gas Mixed damper 21 Startup burner 22a Mixed flow (diluted flow) 22b Mixed flow (concentrated flow) 25 Secondary air 26 Secondary air flow path 28 Tertiary air 29 Tertiary air flow path 30, 31 Register damper 32 Fire wall surface 34 Internal flame holding Instrument 35 Flame retaining ring 37 Burner central axis

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Noriyuki Oyatsu 3 36 Takaracho, Kure City, Hiroshima Prefecture Babcock Hitachi Co., Ltd. Kure Research Institute (72) Nobuyasu Makai 3 36 Takaracho, Kure City, Hiroshima Prefecture Babcock Hitachi Ltd. Kure Research Institute (72) Inventor Shunichi Tsumura 6-9 Takaracho, Kure City, Hiroshima Prefecture Babcock Hitachi Kure Factory (72) Inventor Keinobu Kobayashi 4026 Kujicho, Hitachi City, Ibaraki Hitachi Research Laboratory, Hitachi Co., Ltd.

Claims (7)

[Claims] 1. A solid-gas two-phase flow channel through which a solid-gas two-phase flow composed of a solid fuel and a carrier gas for the fuel flows is provided as a double pipe composed of an inner cylinder and an outer cylinder divided into two parts. Having at least one air flow path through which combustion air flows in the outer periphery of the double pipe,
In a burner for solid fuel in which a flame stabilizer having a plane orthogonal to the flow is installed at the burner outlet, the flame stabilizer is used as a solid gas two-phase flow The flow path outlet in the outer cylinder of the passage and the flame stabilizer at the flow path outlet in the inner cylinder and the fuel flow direction of the flame stabilizer at the flow path outlet in the outer cylinder are orthogonal to each other. A burner for a solid fuel, characterized in that planes provided in a direction are installed at positions displaced from each other on the same plane. 2. The fine powder of the solid fuel divided into fine powder and coarse powder in advance is supplied to the solid-gas two-phase flow passage in the inner cylinder. Burner for solid fuel. 3. A solid-gas two-phase flow passage in the outer cylinder is provided with a plane provided in a direction orthogonal to the fuel flow direction of the flame stabilizer provided inside the solid-gas two-phase flow passage in the inner cylinder. The burner for solid fuel according to claim 1 or 2, wherein the burner for solid fuel is installed on a front flow side of a plane provided in a direction orthogonal to a fuel flow direction of the provided flame stabilizer. 4. The solid according to claim 1, wherein a mixed fluid of air and exhaust gas is used as a fine particle powder-carrying gas flowing in the solid-gas two-phase flow passage in the inner cylinder. Burner for fuel. 5. A mixed fluid in which an exhaust gas having an oxygen partial pressure of 5% by volume or less is mixed in air is used as a gas for conveying fine particles in the solid-gas two-phase flow passage in the inner cylinder. The solid fuel burner according to claim 4. 6. The burner for solid fuel according to claim 4 or 5, wherein the oxygen partial pressure of the air for conveying the fine powder after mixing the exhaust gas is set to 16% by volume or less. 7. A combustion apparatus provided with the burner for solid fuel according to claim 1. Description: