JPH07190335A - Nox reducing method for coal-fired boiler - Google Patents

Abstract

PURPOSE:To largely reduce NOX of a coal-fired boiler by supplying ultrafine powder having enhanced powder fineness as compared with fine powder coal to be supplied to a burner of other stage to an uppermost stage burner of burner units of multiple stages in a furnace. CONSTITUTION:Fine powder coal mills 8a, 8b and 8c, 8d for supplying fine powder coals 5 finely pulverized from coal and having mean particle size of about 40-60mum are connected to lower stage burners 4a, 4b and intermediate stage burners 4c, 4d of a burner unit 4 provided in a furnace l of a coal-fired boiler. Ultrafine powder coal mills 18, 19 for finely pulverizing coal and supplying ultrafine powder coal 17 having a mean particle size of about 5-10mum are respectively connected to uppermost stage burners 4e, 4f. In this case, the mills 18, 19 have a rotary table 20 and a final pulverizing roller 21 for finely pulverizing coal under a large pressure, and a rotary classifier 22 for enhancing classifying performance. Thus, an ultrahigh temperature reducing atmosphere is formed in the furnace to reduce NOX generated at a lower side from the atmosphere.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to NOx of a coal-fired boiler.
It relates to a reduction method.

[0002]

2. Description of the Related Art FIG. 2 shows an example of a coal-fired boiler. A plurality of coal-fired boilers are provided on a front wall 2 and a rear wall 3 of a furnace 1 of the coal-fired boiler in a left-right direction (a direction perpendicular to the plane of FIG. 2). There is provided a burner device 4 including lower burners 4a and 4b, middle burners 4c and 4d, and uppermost burners 4e and 4f, in which groups arranged in parallel are vertically arranged in multiple stages (three stages in FIG. 2).

Further, each of the burners 4a to 4f of the respective stages provided on the front and rear walls 2 and 3 is charged with coal and pulverized, and the pulverized pulverized coal 5 is pulverized into a pulverized coal pipe 7 by primary air 6. Pulverized coal mills 8a, 8b, 8c, 8d, 8e, 8f, which are conveyed through and are supplied as fuel to the burners 4a-4f at each stage, are connected.

Further, the secondary air 10 from the fan 9 is supplied to each of the burners 4a to 4f at the respective stages.
1 and is also supplied through the burners 4a to 4
A part of the secondary air 10 supplied to f is branched and supplied to the OAP 12 (over air port) provided above the burner device 4.

A conventional method for reducing NOx in a coal-fired boiler is to supply a part of the secondary air 10 to the OAP 12 to reduce the amount of the secondary air 10 to be supplied to the burner device 4, thereby reducing the amount of air. To form a high-temperature reducing atmosphere 13 in the furnace 1, and reduce NOx generated by the combustion of the pulverized coal 5 by an intermediate reducing substance such as NH, CN, or CO generated in the high-temperature reducing atmosphere 13 NOx at the 1st outlet is being reduced.

[0006] The normal vertical pulverized coal mills 8a to 8f provided in the conventional coal-fired boiler are equipped with a rotary table 14
A crushing roller 15 for pressing the rotary table 14 to crush coal, a rotary table 14 and a crushing roller 1
And a classifier 16 for classifying the pulverized coal 5 crushed by the action of No. 5 and rising by the primary air 6 into an average particle size of about 40 to 60 μm.
The pulverized coal 5 that has passed through 6 is supplied to the burners 4a to 4f for combustion.

The pulverized coal 5 can be improved in combustibility as the pulverized coal 5 is made finer by increasing the fineness. However, when the pulverized coal 5 is made to have a higher fineness, the pulverized coal mills 8a to 8f have a strong structure. In terms of economic efficiency, pulverized coal
As described above, the limit is about pulverization to about 40 to 60 μm.

[0008]

However, the above-mentioned conventional N
In the method of reducing Ox, the high-temperature reducing atmosphere 13 is formed in the furnace 1 by the combustion of the burners 4a to 4f of each stage, but as described above, the conventional pulverized coal mill conventionally used. In 8a to 8f, the average particle size of the pulverized coal 5 to be crushed is about 40 to 60μ, and when the secondary air supplied to the burners 4a to 4f is reduced by the above-described multi-stage combustion to strengthen the air-deficient state, NOx falls. However, there is a problem that unburned content increases.

The present invention has been made in view of such circumstances, and an object thereof is to significantly reduce NOx of a coal-fired boiler.

[0010]

Means for Solving the Problems The present invention provides an ultra-fine coal having a fineness higher than that of the pulverized coal supplied to the burners of other stages in the uppermost burner of a burner device provided in multiple stages in the furnace of a coal-fired boiler. By supplying, an ultra-high temperature reducing atmosphere is formed in the furnace, and NOx generated below the ultra-high temperature reducing atmosphere
A method for reducing NOx in a coal-fired boiler, which is characterized by suppressing the generation of NOx by reducing NOx, and the average particle size of the ultrafine coal supplied to the uppermost stage burner is about 5 to 10μ, The average particle size of the pulverized coal supplied to the burner is about 4
NO of coal-fired boiler characterized by 0-60μ
x reduction method.

[0011]

[Operation] Ultra fine coal (average particle size of about 5 to 10μ) with higher fineness than the pulverized coal (average particle size of about 40 to 60μ) supplied to the other stage burner in the uppermost burner of the coal-fired boiler
When it is supplied and burned, it becomes possible to form an ultra-high temperature reducing atmosphere in the furnace by allowing good combustion even if the amount of fuel with respect to secondary air is increased due to the improvement of combustibility due to the ultrafine coal. Therefore, the NOx generated under the ultra-high temperature reducing atmosphere in the furnace is well reduced in the ultra-high temperature reducing atmosphere.

Further, since ultra-fine coal is supplied to the uppermost burner of the coal-fired boiler to form an ultra-high temperature reducing atmosphere, regardless of the point extinction of the burner of the other stage due to fluctuations in the boiler load, it is always possible. Since a high NOx reduction effect can be exhibited, the intended purpose can be achieved with the minimum equipment and the minimum operating cost for producing ultrafine coal.

[0013]

Embodiments of the present invention will be described below with reference to the drawings.

As shown in FIG. 1, the lower burners 4a and 4b and the intermediate burners 4c and 4d of the burner unit 4 provided in the furnace 1 of the coal-fired boiler have an average particle size of about 40 obtained by crushing coal.
The usual pulverized coal mills 8a, 8b and 8c, 8d similar to the conventional ones that supply pulverized coal 5 of up to 60μ are connected, and the top burners 4e, 4f crush coal to obtain an average particle size of about 5-10μ ultra-fine coal 17 (about one tenth of the conventional particle size)
The ultra-fine coal mills 18 and 19 which are designed to be supplied are connected.

The pulverized coal mills 18 and 19 include a rotary table 20 and a crushing roller 21 capable of crushing coal with a large reduction force, and a rotary classifier 2 capable of enhancing classification performance.
It has a configuration including 2 and. Reference numeral 23 in the drawing denotes an ultrahigh temperature reducing atmosphere formed at the uppermost burners 4e, 4f in the furnace 1 by burning the ultrafine coal 17 from the uppermost burners 4e, 4f.

Next, the operation of the above embodiment will be described.

Top burners 4e and 4f of the coal-fired boiler
In addition, ultrafine coal 17 (average particle size of about 5 to 10 μm) having a fineness higher than that of pulverized coal (average particle size of about 40 to 60 μm) supplied to the other stage burners 4a, 4b and 4c, 4d is supplied. When burned in this manner, the ultrafine coal 17 can be made to have good combustibility, and can be burned well even if the supply ratio (air-fuel ratio) of the ultrafine coal 17 to the secondary air 10 is increased. Therefore, the combustion temperature of the flame can be remarkably increased to form the ultra-high temperature reducing atmosphere 23 in the furnace 1.

Therefore, the lower and middle burners 4a, 4a,
In the reducing atmosphere 13 by the combustion in 4b, 4c, and 4d, NH, CN, C are generated by the ultra-high temperature reducing atmosphere 23.
The amount of intermediate reducing substances such as O generated increases. Fuel N based on the nitrogen content contained in coal by this intermediate reducing substance
Not only can Ox be greatly reduced, but also thermal NOx based on the nitrogen content contained in the air can be reduced, and a significant NOx reduction effect can be exhibited.

The uppermost burner 4e of the coal-fired boiler,
Since the ultra-fine coal 17 is supplied to 4f to form the ultra-high temperature reducing atmosphere 23, even if the burners 4a, 4b and 4c, 4d of the other stages are extinguished due to fluctuations in the boiler load, the lower side Since the NOx generated in the above can be effectively reduced by the intermediate reducing substance generated in the above-mentioned ultra-high temperature reducing atmosphere 23 at the top, it is always good with the minimum equipment and the minimum operating cost for producing ultra-fine coal. The NOx reduction effect can be exhibited.

[0020]

According to the NOx reduction method of the coal-fired boiler of the present invention, the fineness of coal is higher than that of the pulverized coal (average particle size of about 40 to 60 μm) supplied to the burner of the other stage in the uppermost burner of the coal-fired boiler. By supplying ultra-fine pulverized coal (average particle size of about 5 to 10 μm) having a high temperature, an ultra-high temperature reducing atmosphere can be formed in the furnace, and therefore, an ultra-high-temperature reducing atmosphere is generated below. NOx can be satisfactorily reduced in the ultra-high temperature reducing atmosphere to significantly reduce NOx.

Further, since ultra-fine coal is supplied to the uppermost burner of the coal-fired boiler to form an ultra-high temperature reducing atmosphere, even if the fire extinguishing of the burner of the other stage occurs due to fluctuations in the boiler load, Since NOx generated on the lower side can be reduced by the intermediate reducing substance, a high NOx reduction effect can be achieved with the minimum equipment and minimum operating cost for producing ultrafine coal.

[Brief description of drawings]

1 is a schematic side view showing an example of an apparatus for carrying out the method of the present invention.

FIG. 2 is a schematic side view showing an example of a conventional coal-fired boiler.

[Explanation of symbols]

 1 furnace 4 burner device 4a, 4b lower burner 4c, 4d middle burner 4e, 4f uppermost burner 5 pulverized coal 17 ultrafine coal 23 ultra high temperature reducing atmosphere

Claims (2)

[Claims] 1. An ultrafine coal having a fineness higher than that of the pulverized coal supplied to the burners of other stages is supplied to the uppermost burner of a burner device provided in multiple stages in a furnace of a coal-fired boiler,
NOx is generated by forming an ultra-high temperature reducing atmosphere in the furnace and reducing NOx generated below the ultra-high temperature reducing atmosphere.
NO of coal-fired boiler characterized by suppressing the generation of
x reduction method. 2. The ultrafine coal supplied to the uppermost burner has an average particle size of about 5 to 10 μ, and the pulverized coal supplied to another stage of the burner has an average particle size of about 40 to 60 μ. A method for reducing NOx in the described coal-fired boiler.