JPH11211010A - Method for combustion in pulverized coal-fired boiler - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enable increase of concentration of carbon monoxide at a furnace exit because of cooling of gas in the vicinity of a boiler side wall to be restrained and decrease danger of corrosion of water tubes provided on furnace walls. SOLUTION: The combustion method comprises a plurality of pulverized coal-firing burners, pulverized coal nozzles 10 with which the pulverized coal- firing burners eject a mixture of pulverized coal and air (a pulverized coal flow), and air nozzles 11 for ejecting air. In this case, among a plurality of the pulverized coal-firing burners, in the ratio of air quantity to pulverized coal quantity, the pulverized coal-firing burner proximate to a wall end of a furnace side of a boiler has the greater air quantity than those in other burners.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for burning a pulverized coal boiler, and more particularly to a method for burning a pulverized coal combustion burner, wherein the pulverized coal combustion burner is a mixture of pulverized coal and air (pulverized coal flow). The present invention relates to a method for burning a pulverized coal boiler including a pulverized coal nozzle for ejecting air and an air nozzle for ejecting air.

[0002]

2. Description of the Related Art Conventionally, in a combustion burner, there is a problem in controlling nitrogen oxides (NOx) generated during combustion. In particular, coal has a higher nitrogen content than gaseous and liquid fuels. Therefore, reducing NOx generated during combustion of the pulverized coal combustion burner is more important than in the case of gaseous fuel or liquid fuel.

Most of the NOx generated during the combustion of pulverized coal is NOx (fuel NOx) generated by oxidizing nitrogen contained in coal. In order to reduce this NOx, various burner structures and combustion methods have been conventionally studied.

As one of the combustion methods, there is a method in which a region having a low oxygen concentration is formed in a flame, and a reduction reaction of NOx which becomes active when the oxygen concentration is low is used. For example, JP-A-1-305206, JP-A-3-211304, and JP-A-3-110308 disclose a method of forming a flame (reducing flame) in an atmosphere having a low oxygen concentration and completely burning coal. A method is disclosed, and further, a structure is disclosed in which a pulverized coal nozzle for air-flowing pulverized coal is provided, and an air nozzle for ejecting air is provided outside the nozzle.

According to these techniques, a region having a low oxygen concentration is formed inside a flame, and a reduction reaction of NOx proceeds in a reducing flame region to reduce the amount of NOx generated in the flame.

In Japanese Patent Application Laid-Open Nos. Hei 3-211304 and Hei 3-10308, a flame holding ring or an obstacle is provided at the tip of the pulverized coal nozzle to circulate downstream of the tip of the pulverized coal nozzle. It is shown to form a flow. Since the high-temperature gas stays in the circulation flow, the pulverized coal ignites and the stability of the flame can be improved.

[0007]

In this conventional combustion method, a region having a low oxygen concentration is formed in the flame in order to form a NOx reduction region. Carbon monoxide is generated in this low oxygen concentration region. The reaction of carbon monoxide does not proceed further in a low temperature region such as the furnace side wall, and is released from the furnace. Further, when a region having a high temperature and a low oxygen concentration is formed on the side wall, the water pipe provided on the furnace wall may be burned or corroded.

For this reason, conventionally, in order to suppress the concentration of carbon monoxide at the furnace outlet and protect the water pipe on the side wall, the air ratio indicating the ratio of pulverized coal supplied from the burner to the air cannot be reduced. Was. Further, in order to cause carbon monoxide to react, it was necessary to increase the input amount of post-stage air in the two-stage combustion method.

The present invention has been made in view of the above, and an object of the present invention is to suppress an increase in the concentration of carbon monoxide at the furnace outlet due to gas cooling near the side wall, and to install the apparatus on a furnace wall. It is an object of the present invention to provide a method for burning a pulverized coal boiler which can reduce the risk of corrosion of a water pipe.

[0010]

That is, the present invention comprises a plurality of pulverized coal combustion burners, and the pulverized coal combustion burner jets a mixture of pulverized coal and air (pulverized coal flow). And a combustion method for a pulverized coal boiler comprising an air nozzle for ejecting air, wherein the air amount of the pulverized coal combustion burner close to the furnace side wall end of the boiler among the plurality of pulverized coal combustion burners is determined. The ratio of the burner air amount to the pulverized coal amount is increased to achieve the intended purpose.

Further, the present invention comprises a plurality of pulverized coal combustion burners, wherein the pulverized coal combustion burner discharges air, and a pulverized coal nozzle for discharging a mixture of pulverized coal and air (pulverized coal flow). In the method for burning a pulverized coal boiler provided with an air nozzle, an air ratio indicating the ratio of the amount of pulverized coal supplied from the pulverized coal combustion burner to the amount of air (the amount of air actually supplied and the pulverized coal completely burned). The ratio of the burner near the end of the furnace side wall of the boiler is set to be 0.1 or more higher than the air ratio of the other burners.

[0012] In this case, the direction in which air is injected from the air nozzle of the pulverized coal combustion burner near the end of the side wall is defined as:
The angle formed with the center axis of the pulverized coal nozzle is in the range of 30 degrees to 50 degrees.

That is, according to the pulverized coal combustion method formed as described above, the burner near the furnace side wall end of the boiler is replaced with another burner by an air ratio indicating the ratio of the amount of pulverized coal supplied from the pulverized coal combustion burner to the amount of air. The oxygen ratio near the side wall was increased by increasing the air ratio of the burner near the end of the side wall by decreasing the air amount of the other burners by increasing the air amount of the burner near the end of the side wall. It is possible to suppress an increase in the concentration of carbon monoxide at the furnace outlet due to gas cooling,
Further, since the oxygen concentration near the side wall is increased, the danger of corrosion of the water pipe installed on the furnace wall can be reduced.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail with reference to the illustrated embodiments. FIG. 1 schematically shows the furnace of the pulverized coal combustion boiler. FIG. 2 shows a horizontal section thereof. In these figures, reference numeral 10 denotes a pulverized coal nozzle for conveying pulverized coal in a gas stream, and 11 denotes an air nozzle. Reference numeral 21 denotes a flame formed from the burner. The upstream side is connected to a pulverized coal transport pipe and an air pipe (not shown).

In the first embodiment of the present invention shown in FIGS. 1 and 2, the burner supplies a smaller amount of air than the amount of air required to completely burn the pulverized coal. And
An air supply port 17 for supplying insufficient air is provided from a place near the furnace outlet 14.

From the burner, an air amount of 1 or less is supplied at an air ratio (the ratio of the amount of air actually charged to the amount of air required to completely burn the pulverized coal). At this time, the amount of air supplied to burners near the adjacent side wall is increased, and the amount of air supplied to other burners is reduced. In the first embodiment shown in FIG. 2, the burner near the adjacent side wall has an air ratio of 0.9,
The air ratio of the other burners is set to 0.7.

At this time, the oxygen concentration near the side wall is higher than when the air ratio is uniform. Therefore, the concentration of carbon monoxide near the side wall decreases. Even when the gas is cooled on the side walls and the gas is released outside the furnace without the progress of the combustion reaction, the concentration of carbon monoxide can be kept low. Further, since the oxygen concentration is high near the water pipe installed on the furnace wall, corrosion of the material can be suppressed.

Although FIGS. 1 and 2 show a furnace of the opposed combustion type in which burners are attached to two longitudinal sections of the furnace facing each other, the burner is attached to one longitudinal section of the furnace. The same applies to the single-sided combustion system.

FIG. 3 is a schematic view of a furnace of a pulverized coal combustion boiler according to a second embodiment of the present invention. 3 shows a longitudinal section of the furnace passing through the central axis of the pulverized coal burner, and FIG. 4 shows a horizontal section.

In these figures, reference numeral 10 denotes a pulverized coal nozzle for conveying pulverized coal by air, 11 denotes an air nozzle, and the upstream side is connected to a pulverized coal transport pipe and an air pipe (not shown). Reference numerals 55, 56, and 57 indicate flames formed from the burners. Numerals 53 and 54 denote a pulverized coal flow and a flow of air ejected from an air nozzle, respectively.

In this embodiment, as in the case of the first embodiment, a smaller amount of air is supplied from the burner than the amount of air required to completely burn the pulverized coal. And the furnace exit 1
An air supply port 19 for supplying a shortage of air is provided from a position near 4. This two-stage combustion air flow is reduced to 20,
The two-stage combustion zone is shown at 58. 3 differs from the first embodiment shown in FIG. 1 in that the burner is attached to one section of the furnace and is of a single-sided combustion type.

In FIG. 3, a guide plate 51 is provided on a wall surface of the air nozzle 11 which is remote from the pulverized coal nozzle and close to the pulverized coal nozzle. This guide plate 51 allows the air nozzle 11
The air ejected from the nozzle is 30
Spouts outward at an angle of 50 degrees to 50 degrees. For this reason,
As the air flows away from the central axis of the pulverized coal nozzle, the flame spreads radially. Therefore, in the flame as in the present embodiment, the flow rate of the pulverized coal ejected from the burner is attenuated, and the residence time in the furnace becomes longer.

When air is ejected from the air nozzle at an angle of 30 to 50 degrees with respect to the center axis of the pulverized coal nozzle as in the present embodiment, the air ejection speed is determined by the mixture of pulverized coal and air (pulverized coal flow). It is desirable to make the ratio of 2: 1 to 3: 1 with respect to the jet flow velocity. The jet velocity of the mixture of pulverized coal and air is the velocity required for stable combustion of pulverized coal (13 m / s to 25 m
/ S), the jet velocity of air is about 30 m / s to 60 m / s. At this time, the air and pulverized coal flow ejected from the air nozzle flow apart near the burner due to their respective momentums, so that the flame width is widened. In addition, the flow rate of the pulverized coal rapidly attenuates after being blown out.

When the guide plate is provided in the air nozzle as in the present embodiment, the air ejected from the air nozzle provided with the guide plate is a straight flow having no swirl velocity component or a weak flow having a weak swirl component. A swirling flow is desirable. At this time, since the air and pulverized coal flow ejected from the air nozzle have a weak centrifugal force due to the swirling flow, the air from the burner has a throat diameter of 4 mm.
It becomes easier to mix downstream more than twice. Therefore, the combustion reaction proceeds, and the unburned portion in the ash decreases.

From the burner, an air amount of 1 or less is supplied at an air ratio (the ratio of the amount of air actually supplied to the amount of air necessary for completely burning the pulverized coal). At this time, the amount of air supplied to the burner near the end of the side wall is increased, and the amount of air supplied to other burners is reduced. In the embodiment shown in FIG. 2, the air ratio of the burner near the side wall end is set to 0.9, and the air ratio of the other burners is set to 0.7. At this time, the oxygen concentration near the side wall edge is higher than when the air ratio is uniform. Therefore, the concentration of carbon monoxide near the side wall decreases.

Therefore, the concentration of carbon monoxide can be kept low even when the gas is cooled on the side wall and the gas is released outside the furnace without the progress of the combustion reaction. Further, since the oxygen concentration is high near the water pipe installed on the furnace wall, corrosion of the material can be suppressed.

Further, as in the present embodiment, the mixing of pulverized coal and air is suppressed near the burner, and the mixing of pulverized coal and air is performed at the later stage of the flame (downstream of the burner throat diameter by four times or more from the burner). By promoting it, the reducing flame with less oxygen can be widely distributed in the flame. At this time, NOx generated by the combustion of the pulverized coal can be reduced.

FIG. 5 shows an example of the combustion characteristics of the pulverized coal burner used in this embodiment. The horizontal axis shows the air ratio, which is the ratio between the air and the fuel supplied from the burner. The vertical axis shows the NOx concentration at the furnace outlet at each air ratio. The characteristics of the conventional burner are indicated by white circles, and the characteristics of the burner used in the present embodiment are indicated by black circles.

In the conventional burner, the combustion reaction does not proceed because the mixing of air and pulverized coal is suppressed even in the later stage of the flame. Therefore, when mixed with the two-stage combustion air, NOx
Increased rapidly. So, if you lower the air ratio of the burner,
The NOx discharged from the furnace rises at a certain air ratio.

On the other hand, in the burner shown in the present embodiment, the combustion reaction is promoted by promoting the mixing of pulverized coal and air in the latter part of the flame (at least four times downstream from the burner throat diameter). NOx generated when mixed with the two-stage combustion air can be suppressed. In addition, since the reducing flame with less oxygen is widely distributed in the flame, most of the pulverized coal passes through the reducing region. For this reason, NOx generated in the front part of the flame by the NOx reduction reaction can be rendered harmless. Therefore, NOx at the same air ratio is reduced as compared with the conventional burner. Further, when the air ratio is reduced in the range up to the burner air ratio of 0.7, NOx monotonously decreases.

In FIG. 4, four burners are installed in a furnace,
An example is shown in which the air ratio of the burner on the side wall is 0.7, the others are 0.9, and the burner air ratio is 0.8 as a whole. In the case of a conventional burner, the burner air ratio is 0.
At 7, the NOx concentration is higher than at 0.8. For this reason,
The NOx concentration discharged from the furnace as a whole becomes higher as shown by point B in comparison with point A in FIG.

In the burner shown in this embodiment, when the burner air ratio is reduced in the range up to the burner air ratio 0.7, N
Ox decreases. Therefore, the N
The Ox concentration was A ′ in FIG.
The point is almost the same as indicated by the point C.

As described above, in a boiler using a burner in which the NOx concentration decreases monotonously when the burner air ratio is reduced, the NOx emission is increased by a combustion method in which the air amount of the burner near the side wall is increased and the air amount of the other burners is reduced. The amount is kept low, and the concentration of carbon monoxide generated near the side wall is reduced and the risk of corrosion of the side wall is reduced.

As described above, in such a pulverized coal combustion method, the air amount of the burner near the side wall is increased,
Since the air amount of the other burners is controlled to be reduced, the oxygen concentration near the side wall is increased, and the rise in the carbon monoxide concentration at the furnace outlet due to the cooling of the gas near the side wall is suppressed. Further, since the oxygen concentration near the side wall increases, the danger of corrosion of the water pipe installed on the furnace wall can be reduced.

[0035]

As described above, according to the present invention, it is possible to suppress an increase in the concentration of carbon monoxide at the furnace outlet due to gas cooling near the side wall, and to corrode water tubes installed on the furnace wall. Danger can be reduced.

[Brief description of the drawings]

FIG. 1 is a vertical sectional side view of a pulverized coal boiler according to an embodiment of the present invention.

FIG. 2 is a horizontal sectional view of the pulverized coal boiler of FIG.

FIG. 3 is an enlarged sectional view of a main part of a pulverized coal boiler according to another embodiment of the method of burning a pulverized coal boiler of the present invention.

FIG. 4 is a horizontal sectional view of the pulverized coal boiler of FIG.

FIG. 5 is a characteristic diagram of a pulverized coal burner.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 10 ... Pulverized coal nozzle, 11 ... Air nozzle, 12 ... Air inlet for two-stage combustion, 13 ... Furnace room, 14 ... Furnace outlet, 15
... air for combustion, 16 ... mixture of pulverized coal and air, 17 ... air supply port (air for two-stage combustion), 18 ... burner throat part, 21 ... flame, 20,22 ... flow of air for two-stage combustion,
51 ... guide plate.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Shunichi Tsumura 6-9 Takara-cho, Kure-shi, Hiroshima Pref. Inside the Kure Factory of Babcock Hitachi, Ltd. (72) Inventor Kenji Kiyama 6-9 Takara-cho, Kure-shi, Hiroshima Pref. Inside the Kure Factory (72) Inventor Tadashi Jimbo 6-9 Takaracho, Kure City, Hiroshima Pref. Inside Kure Factory, Babcock Hitachi Co., Ltd. (72) Inventor Koji Masashi 6-9 Takaracho, Kure City, Hiroshima Prefecture Bubcock Hitachi, Ltd. Kure Factory (72) Inventor Shigeki Morita 6-9 Takara-cho, Kure-shi, Hiroshima Pref. Inside the Babcock Hitachi Kure Plant (72) Inventor Shinichiro Nomura 3-36 Takara-cho, Kure-shi Hiroshima Pref. Miki Mori 3-36 Takaracho, Kure-shi, Hiroshima Babcock Hitachi Kure Research Laboratory

Claims (3)

[Claims] 1. A pulverized coal combustion burner comprising a plurality of pulverized coal combustion burners, wherein the pulverized coal combustion burner includes a pulverized coal nozzle for ejecting a mixture of pulverized coal and air (pulverized coal stream), and an air nozzle for ejecting air. In the method of burning a pulverized coal boiler, the air amount of the pulverized coal combustion burner near the furnace side wall end of the boiler among the plurality of pulverized coal combustion burners is determined by comparing the air amount and pulverized coal amount of the other burners. A combustion method for a pulverized coal boiler, characterized in that the ratio is increased relative to the ratio. 2. A pulverized coal combustion burner comprising a plurality of pulverized coal combustion burners, wherein the pulverized coal combustion burner includes a pulverized coal nozzle for ejecting a mixture of pulverized coal and air (pulverized coal stream), and an air nozzle for ejecting air. In the method of burning a pulverized coal boiler, the air ratio indicating the ratio of the amount of pulverized coal supplied from the pulverized coal combustion burner to the amount of air (the amount of air actually supplied and the amount required to completely burn the pulverized coal) The ratio of the burner closer to the furnace side wall end of the boiler to the air ratio of other burners is 0.
A method for burning a pulverized coal boiler, wherein the combustion temperature is increased by one or more. 3. The pulverized coal combustion burner near the side wall end has a direction in which air ejected from an air nozzle of the pulverized coal combustion burner has an angle of 30 ° to 50 ° with respect to a central axis of the pulverized coal nozzle. 2. The method for burning a pulverized coal boiler according to 2.