JPH08320103A - Method for controlling primary air temperature of coal-fired boiler and apparatus used for the method - Google Patents

Abstract

(57) [Summary] [Purpose] Even if high-moisture coal is supplied to the mill, it is possible to prevent the operating efficiency of the boiler from decreasing. A combustion exhaust gas duct 5 connected to a boiler body 3 and sequentially connected to a denitration device 6 and an air preheater 7,
A mill 12, a primary air duct 11 for supplying the primary air b heated by the air preheater 7 to the mill 12, and a pulverized coal pipe 13 for supplying pulverized coal to the boiler body 3 by the primary air b.
And a secondary air duct 15 for supplying the secondary air c heated by the air preheater 7 to the boiler body 3, one end of the secondary air duct 15 at the exit side of the combustion exhaust gas duct 5 of the air preheater 7, and the other end of the air preheat The gas recirculation duct 17 connected to the outlet side of the secondary air duct 15 of the air conditioner 7, and an opening / closing valve 17a and a circulation fan 17b arranged in the gas recirculation duct 17 of the air preheater outlet side are provided.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a primary air temperature control method for a coal fired boiler and an apparatus used for the method.

[0002]

2. Description of the Related Art FIG. 4 shows an example of a conventional coal-fired boiler. The coal-fired boiler includes a furnace 1 and a furnace 1.
The boiler main body 3 is composed of a rear heat transfer portion 2 provided in the rear portion, and the furnace 1 is provided with a combustion burner 4.

A combustion exhaust gas duct 5 is connected to a lower portion of the rear heat transfer section 2 described above, and the combustion exhaust gas duct 5 is connected.
A denitration device 6, an air preheater 7, and an electrostatic precipitator 8 are sequentially connected to the downstream side of the exhaust gas, and the downstream end of the combustion exhaust gas duct 5 is connected to a chimney 9.

Further, a coal economizer bypass duct 10 having a bypass damper 10a in the middle is disposed upstream of the economizer 2a in the rear heat transfer section 2 to bypass the economizer 2a. The downstream end of the economizer bypass duct 10 is connected to the combustion exhaust gas duct 5 on the inlet side of the denitration device 6.

The air preheater 7 is supplied with the primary air b from the primary air fan 11a and exchanges heat with the combustion exhaust gas a from the combustion exhaust gas duct 5 to heat the heated primary air b into the coal 18 A primary air duct 11 adapted to supply to the pulverizing mill 12 is connected.

In the mill 12, the pulverized coal pulverized by the mill 12 is blown by the primary air b into the boiler body 3
The pulverized coal pipe 13 supplied to the combustion burner 4 is connected.

Further, there is provided a temperature control duct 14 having one end connected to the inlet side of the air preheater 7 in the primary air duct 11 and the other end connected to the inlet side of the mill 12 in the primary air duct 11, and the temperature control duct 14 is provided. A flow rate adjusting damper 14a is arranged in the adjusting duct 14, and a flow rate adjusting damper 11b is arranged between the outlet side of the air preheater 7 in the primary air duct 11 and a connecting portion of the temperature adjusting duct 14 to adjust the flow rate. By adjusting the openings of the dampers 11b and 14a, the ratio between the primary air b heated through the air preheater 7 and the cold primary air b bypassed is changed, and the mill 1
The temperature of the primary air b supplied to No. 2 can be adjusted.

Further, the air preheater 7 is supplied with the secondary air c from the secondary air fan 15a and exchanges heat with the combustion exhaust gas a from the combustion exhaust gas duct 5, thereby heating the secondary air. A secondary air duct 15 for supplying c to the combustion burner 4 of the furnace 1 is connected.

Further, a rear heat transfer section having one end connected to the outlet side of the rear heat transfer section 2 of the combustion exhaust gas duct 5 and the other end connected between the boiler body 3 and the air preheater 7 in the secondary air duct 15. An outlet side gas recirculation duct 16 is arranged, and the rear heat transfer section outlet side gas recirculation duct 16 is provided with a flow rate adjusting damper 1
6a is arranged, and a circulation fan 16b is arranged.

In the coal-fired boiler having the above structure, the high temperature combustion exhaust gas a generated by the combustion in the furnace 1 is
The NOx (nitrogen oxide) contained in the combustion exhaust gas a is processed by the NOx removal device 6 by flowing into the combustion exhaust gas duct 5 from the rear heat transfer part 2.

The flue gas a discharged from the denitration device 6 is introduced into an air preheater 7 to be described later as a primary air b and a secondary air c.
The combustion exhaust gas a whose temperature has been lowered by heat exchange is introduced into the electric dust collector 8 to collect dust in the combustion exhaust gas a, and then released from the chimney 9 to the outside air. .

On the other hand, the primary air b sent to the air preheater 7 through the primary air duct 11 by the primary air fan 11a is the above-mentioned combustion exhaust gas a in the air preheater 7.
It is heated by exchanging heat with, and flows through the primary air duct 11 and is supplied to the crushing mill 12 for coal 18.

In the mill 12 described above, the mill 12
The coal 18 supplied to the above is pulverized while being dried by the high temperature primary air b to generate pulverized coal, and the pulverized coal is burned by the primary air b through the pulverized coal pipe 13 to the combustion burner 4
Is being supplied to.

The secondary air c sent to the air preheater 7 by the secondary air fan 15a through the secondary air duct 15 is heated in the air preheater 7 by exchanging heat with the combustion exhaust gas a. Then, it flows through the secondary air duct 15 and is supplied to the combustion burner 4 and the like of the furnace 1.

Further, in order to prevent an increase in the amount of NOx (nitrogen oxide) generated due to a higher combustion temperature in the furnace 1, a part of the combustion exhaust gas a flowing through the combustion exhaust gas duct 5 is discharged from the rear heat transfer section outlet. O _{2 of the} secondary air c sent to the secondary air duct 15 by the side gas recirculation duct 16 and mixed with the combustion exhaust gas a to the secondary air c before being supplied to the combustion burner 4 and supplied to the combustion burner 4. The concentration is reduced to suppress the generation of NOx during combustion.

Further, in the denitration device 6, unless the temperature of the combustion exhaust gas a at the inlet of the denitration device 6 is maintained at 300 ° C. or higher, even if ammonia as a reducing agent is injected at the inlet of the denitration device 6, unreacted. Ammonia reacts with the sulfur content (SO ₃ ) in the combustion exhaust gas a to produce ammonium sulfate, and this ammonium sulfate deteriorates the catalyst of the denitration device 6, so that the temperature of the combustion exhaust gas a at the inlet side of the denitration device 6 decreases. Is to increase the opening degree of the bypass damper 10a of the economizer bypass duct 10 to increase the high temperature combustion exhaust gas a flowing in the economizer bypass duct 10, and to increase the temperature of the combustion exhaust gas a on the inlet side of the denitration device 6. Is being raised.

As described above, in the mill 12 for crushing coal, pulverized coal is produced while the coal 18 is being dried by the primary air b in the step of crushing the coal 18, so the heat of the primary air b is taken away during this step. As a result, the temperature of the primary air b on the outlet side of the mill 12 is significantly lower than that of the primary air b on the inlet side of the mill 12.

At this time, if the temperature of the primary air b on the outlet side of the mill 12 is lowered, the combustion efficiency of the furnace 1 is drastically reduced and the operating efficiency of the boiler is deteriorated. The outlet temperature is maintained at, for example, 80 ° C.

Thus, the air preheater 7 for heating the primary air b is designed on the basis of the case where the moisture content of the coal 18 is about 10% at the time of design, and the coal supplied to the mill 12 is designed. When the water content rate of 18 fluctuates, the flow rate adjustment damper 1b of the primary air duct 11 and the flow rate adjustment damper 1 of the temperature adjustment duct 14 are adjusted to the water content rate.
The temperature of the primary air b supplied to the mill 12 is adjusted by adjusting the opening degree of 4a to maintain the temperature of the primary air b at the outlet of the mill 12 at about 80 ° C.

[0020]

However, the water content of the coal 18 supplied to the above-mentioned mill 12 is usually about 5 to 20%, but depending on the coal 18, the water content exceeds about 20%. When such high-moisture coal is supplied to the mill 12, a large amount of heat of the primary air b is removed during the drying operation of the coal 18, and the temperature of the primary air b sent to the mill 12 is adjusted. However, the temperature of the primary air b on the outlet side of the mill 12 becomes 80 ° C. or lower, and as a result,
There is a problem that the combustion efficiency in the furnace 1 is reduced and the operation efficiency of the boiler is reduced.

Therefore, in order to prevent the temperature of the primary air b on the outlet side of the mill 12 from falling below about 80 ° C., the flow rate of the combustion exhaust gas a supplied to the air preheater 7 is increased to increase the air preheater 7. It suffices to raise the temperature of the primary air b on the inlet side of the mill 12 by improving the heat exchange efficiency of the above. In the conventional coal-fired boiler, the amount of combustion exhaust gas supplied to the air preheater 7 is changed. I couldn't adjust it.

In view of the above-mentioned circumstances, the present invention provides a method for controlling the primary air temperature of a coal-fired boiler, which can prevent the operating efficiency of the boiler from decreasing even when high-moisture coal is supplied to the mill, and an apparatus used for the method. The purpose is to provide.

[0023]

The first means of the present invention is to:
The combustion exhaust gas a discharged from the boiler main body 3 is introduced into the air preheater 7, and the primary air b heated by the air preheater 7 is guided to the mill 12 to supply pulverized coal to the boiler main body 3 and the air A method for controlling a primary air temperature of a coal-fired boiler, which supplies secondary air c heated by a preheater 7 to the boiler body 3, wherein when high-moisture coal 18 is supplied to the mill 12, air A part of the combustion exhaust gas a on the outlet side of the preheater 7 is mixed with the secondary air c on the outlet side of the air preheater 7 to increase the flow rate of the secondary air c and introduced from the boiler body 3 to the air preheater 7. The primary air temperature control method for a coal-fired boiler is to increase the temperature of the primary air b supplied from the air preheater 7 to the mill 12 by increasing the flow rate of the combustion exhaust gas a.

The second means of the present invention is a combustion exhaust gas duct 5 connected to the boiler body 3 and sequentially connected to the denitration device 6 and the air preheater 7, a mill 12 for crushing coal 18, and the air. A primary air duct 11 for supplying the primary air b heated by the preheater 7 to the mill 12; a pulverized coal pipe 13 for supplying the pulverized coal pulverized by the mill 12 to the boiler body 3 by the primary air b; A primary air temperature control device for a coal-fired boiler, comprising: a secondary air duct 15 for supplying the secondary air c heated by the air preheater 7 to the boiler body 3;
The other end of the combustion exhaust gas duct 5 at the outlet side of the air preheater 7
Gas recirculation ducts 17 respectively connected to the outlet side of the secondary air duct 15 and the gas recirculation duct 1 of the air preheater outlet side
7 is a primary air temperature control device for a coal-fired boiler equipped with an opening / closing valve 17a and a circulation fan 17b arranged in FIG.

[0025]

In the first and second means of the present invention, a part of the combustion exhaust gas a at the outlet side of the air preheater 7 is mixed with the secondary air c heated by the air preheater 7, so that the boiler is used. The flow rate of the secondary air c supplied to the main body 3 increases, and as a result, the flow rate of the combustion exhaust gas a flowing from the boiler main body 3 into the combustion exhaust gas duct 5 increases.

When the flow rate of the combustion exhaust gas a increases, the flow rate of the combustion exhaust gas a flowing into the air preheater 7 also increases.
The heat exchange efficiency in the air preheater 7 is improved, and the temperature of the primary air b can be significantly increased.

Therefore, even if the high-moisture coal is supplied to the mill 12 for crushing coal and the coal 18 is dried by the primary air b in the mill 12, the temperature of the primary air b on the outlet side of the mill 12 is kept. It is possible to prevent the combustion efficiency of the boiler main body 3 from decreasing as a result, because the temperature does not drop below a predetermined temperature.
The operation efficiency of the boiler can be kept high.

[0028]

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

FIG. 1 shows an embodiment of a primary air temperature control device for a coal-fired boiler according to the present invention. Since the structure is substantially the same as that of the coal-fired boiler shown in FIG. 4, only the characteristic parts will be described.

In FIG. 1, air preheating, one end of which is connected to the combustion exhaust gas duct 5 on the outlet side of the air preheater 7 and the other end of which is connected to the secondary air duct 15 between the boiler body 3 and the air preheater 7. An outlet side gas recirculation duct 17 is provided, and an opening / closing valve 1 is provided in the air preheater outlet side gas recirculation duct 17.
7a is arranged and a circulation fan 17b is arranged.

Next, the operation of this embodiment will be described.

When high-moisture coal 18 (having a water content of more than 20%) is supplied to the mill 12 for crushing coal,
Open / close valve 1 of the gas recirculation duct 17 on the outlet side of the air preheater
7a is opened and the circulation fan 17b is driven to drive the air preheater 7
A part of the combustion exhaust gas a on the outlet side is mixed with the secondary air c in the secondary air duct 15 heated by the air preheater 7.

As a result, the flow rate of the secondary air c supplied to the furnace 1 is significantly increased, and accordingly, the flow rate of the combustion exhaust gas a flowing from the rear heat transfer section 2 into the combustion exhaust gas duct 5 is increased. The flow rate of the combustion exhaust gas a flowing into the air preheater 7 increases.

As a result, the heat exchange efficiency in the air preheater 7 can be increased, and the temperature of the primary air b introduced into the air preheater 7 can be greatly increased.

For example, in a conventional coal-fired boiler,
As shown in FIG. 3, combustion exhaust gas a on the inlet side of the air preheater 7
When the temperature T1 of the air preheater 7 is about 370 ° C., the combustion exhaust gas a on the outlet side of the air preheater 7 which has finished the heat exchange in the air preheater 7
Temperature T2 is about 124.degree.

The temperature T3 of the primary air b on the inlet side of the air preheater 7 is about 50 ° C., and the temperature T4 of the primary air b on the outlet side of the air preheater 7 after being heated by the air preheater 7 is It is about 320 ° C.

The heat absorption amount Q of the primary air b at this time is obtained by the equation (1).

[Equation 1] Q≈ (T4-T3) · C · Wg (1) C: Specific heat (0.24 kcal / kg) Wg: Combustion exhaust gas amount Therefore, Q≈ (320-50) × 0.24 × Wg≈ 6
It becomes 4.8 Wg.

On the other hand, in the primary air temperature control device of the coal-fired boiler shown in this embodiment, the air preheater 7 similar to the conventional one is used.
Secondary air c heated by the air preheater 7 and discharged from a part of the combustion exhaust gas a on the outlet side of the air preheater 7.
2 and increasing the flow rate of the combustion exhaust gas a flowing out of the rear heat transfer section 2 to increase the flow rate of the combustion exhaust gas a flowing into the air preheater 7 by about 1.1 times, as shown in FIG. The temperature T1 of the combustion exhaust gas a on the inlet side of the air preheater 7 is about 370.
When the temperature is ℃, the temperature T2 of the combustion exhaust gas a at the outlet side of the air preheater 7 after the heat exchange in the air preheater 7 is about 130.
℃.

The temperature T3 of the primary air b on the inlet side of the air preheater 7 is about 50 ° C., and the temperature T4 of the primary air b on the outlet side of the air preheater 7 after heat exchange in the air preheater 7 is performed. Is about 340 ° C.

The heat absorption amount Q of the primary air b at this time is obtained by the equation (2).

[Equation 2] Q≈ (T4-T3) · C · Wg (2) C: Specific heat (0.24 kcal / kg) Wg: Combustion exhaust gas amount Therefore, Q≈ (340-50) × 0.24 × Wg≈ 6
It becomes 9.6 Wg.

As a result, conventionally, it is necessary to lower the temperature of the combustion exhaust gas a at the outlet side of the air preheater 7 to about 124 ° C. by heat exchange in the air preheater 7, but in this embodiment, the flow rate of the combustion exhaust gas a is reduced. By increasing 1.1 times, the temperature of the combustion exhaust gas a on the outlet side of the air preheater 7 is reduced to about 13
The temperature can be suppressed to 0 ° C., and the heat absorption amount Q of the primary air b is increased by about 7% to 8% as compared with the conventional case.

Therefore, in the mill 12, the high-moisture coal 18
Even if the drying operation (with a water content of more than about 20%) is performed, the temperature of the primary air b is significantly increased by the air preheater 7, so that the temperature of the primary air b on the outlet side of the mill 12 is increased. Can be prevented from falling below 80 ° C, and as a result,
Since the temperature of the secondary air c supplied into the furnace 1 does not decrease, as a result, it is possible to prevent the combustion efficiency in the furnace 1 from decreasing, and it is possible to obtain an excellent effect that the operation efficiency of the boiler can be kept high. .

It should be noted that the present invention is not limited to the embodiments, and various changes can be made without departing from the scope of the present invention.

[0044]

According to the inventions of claims 1 and 2, even if the high-moisture coal 18 is supplied to the crushing mill 12 for coal 18, the temperature of the primary air b in the air preheater 7 is significantly increased. Therefore, it is possible to prevent the temperature of the primary air b on the outlet side of the mill 12 from decreasing to a predetermined temperature or lower, and as a result, to prevent the combustion efficiency of the boiler body 3 from decreasing.
An excellent effect that the operation efficiency of the boiler can be kept high can be obtained.

[Brief description of drawings]

FIG. 1 is a schematic diagram showing an embodiment of a primary air temperature control device for a coal-fired boiler of the present invention.

FIG. 2 is a schematic diagram showing a temperature balance between combustion exhaust gas and primary air in the air preheater according to the present invention.

FIG. 3 is a schematic diagram showing a temperature balance between combustion exhaust gas and primary air in a conventional air preheater.

FIG. 4 is a schematic diagram showing an example of a conventional coal-fired boiler.

[Explanation of symbols]

 3 Boiler main body 5 Combustion exhaust gas duct 6 Denitration device 7 Air preheater 11 Primary air duct 12 Mill 13 Pulverized coal tube 15 Secondary air duct 17 Air preheater outlet side gas recirculation duct 17a Open / close valve 17b Circulation fan 18 Coal a Combustion exhaust gas b Primary air c Secondary air

Claims (2)

[Claims] 1. A combustion exhaust gas (a) discharged from a boiler body (3) is introduced into an air preheater (7), and primary air (b) heated by the air preheater (7) is milled (12). ) To supply the pulverized coal to the boiler body (3) and to supply the secondary air (c) heated by the air preheater (7) to the boiler body (3). A primary air temperature control method, wherein when a high-moisture coal (18) is supplied to the mill (12), a part of the combustion exhaust gas (a) on the outlet side of the air preheater (7) is partly supplied to the air preheater. (7) Combustion exhaust gas (a) that is mixed with the secondary air (c) on the outlet side to increase the flow rate of the secondary air (c) and is introduced from the boiler body (3) into the air preheater (7) Of the primary air (b) supplied to the mill (12) from the air preheater (7) by increasing the flow rate of A method for controlling the primary air temperature of a coal-fired boiler, which is characterized by increasing the temperature. 2. A combustion exhaust gas duct (5) connected to a boiler body (3) and sequentially connected to a denitration device (6) and an air preheater (7), and a mill (12) for pulverizing coal (18). ), The primary air duct (11) for supplying the primary air (b) heated by the air preheater (7) to the mill (12), and the pulverized coal pulverized by the mill (12) as the primary air ( Pulverized coal pipe (13) for supplying to the boiler body (3) by b), and secondary air duct for supplying the secondary air (c) heated by the air preheater (7) to the boiler body (3). (15) A primary air temperature control device for a coal-fired boiler, comprising: (1) one end of the combustion exhaust gas duct (5) of the air preheater (7) and the other end of the air preheater (7). Gas recirculation connected to the outlet side of the secondary air duct (15) Primary air temperature of a coal-fired boiler comprising a duct (17), an opening / closing valve (17a) and a circulation fan (17b) arranged in the gas recirculation duct (17) on the outlet side of the air preheater. Control device.