JPH0783407A - Method and apparatus for controlling nox of coal fired boiler - Google Patents

Abstract

PURPOSE:To prevent an increase in NOx of a burner due to excess air by reducing a supply amount of the air to the burner connected to a pulverized coal mill to be started and stopped. CONSTITUTION:A flow rate of secondary air 7 to be supplied based on a boiler load command to a plurality of burners 2 connected to pulverized coal mills 3 to be started and stopped is reduced by throttling for a predetermined time when the mills 3a-3f so connected as to supply pulverized coal at each of groups 2a-2f of predetermined number to the burners 2 provided in a furnace of a coal fired boiler, thereby alleviating an excess air state of the burner 2 connected to the mills 3 to be started and stopped.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to NOx of a coal-fired boiler.
The present invention relates to a control method and device.

[0002]

2. Description of the Related Art FIGS. 3 and 4 show an example of a coal-fired boiler, in which 1 is a coal-fired boiler furnace, 2 is a front-rear wall of the furnace 1, and a plurality of them are arranged in parallel in the left-right direction and vertically in multiple stages. The attached burner 3 for burning pulverized coal is a pulverized coal mill which pulverizes coal and conveys the pulverized pulverized coal by the primary air 10 and supplies it as fuel 4 to the burner 2. Is a secondary air supply pipe for supplying the burner 2 to the burner 2 via a preheater 8, and 9 is a separate damper provided in the secondary air supply pipe 5 for adjusting the flow rate of the secondary air 7 supplied to the burner 2. .

An OAP (over air port) 28 is provided above the burner 2 of the furnace 1, and an air pipe 29 branched from the secondary air supply pipe 5 is provided in the OAP 28. The secondary air 7 is connected and a part of the secondary air 7 is supplied to the upper part of the furnace to reduce NOx by the two-stage combustion.

The burner 2 has six stages in each stage provided on the front and rear walls of the furnace 1, forming groups 2a to 2f, and each group is connected to its own pulverized coal mill 3a to 3f.

Further, the secondary air supply pipe 5 is provided with two systems for dividing the burner 2 of the furnace 1 into left and right parts and supplying the secondary air separately to the left and right parts. One separate damper 9a to 9f and 9a 'to 9f' is provided for every left and right three in 2a to 2f.

The separate dampers 9a to 9f and 9a '
As shown in FIG. 5, 9 f ′ to 9 f ′ are controlled by a separate damper control device 15 that adjusts the opening according to a basic opening command 13 obtained from a boiler load command 11 via a function generator 12. There is. In the figure, 14 is a manual / automatic switching device.

Conventionally, in the coal-fired boiler, each of the separate dampers 9a to 9f, 9a 'is controlled by the basic opening command 13 obtained from the boiler load command 11 by the function generator 12.
The opening of 9f 'is automatically set.

[0008]

However, conventionally, as described above, the separate dampers 9a to 9f and 9a 'to 9f' are used.
Since the opening degree of the boiler is set according to the boiler load command 11, the boiler outlet NO when starting and stopping the boiler
There was a problem that x increased significantly.

That is, the pulverized coal mill 3 uses the boiler load command 11
Although it is operated by a mill load command (not shown) based on the above, when the boiler is started and stopped, the mill load command is low, so the amount of pulverized coal pulverized by the pulverized coal mill 3 is small, Since the minimum primary air flow rate is required to supply the burner 2, the burner 2 that starts and stops tends to be in an air excess (air rich) state, and the burner 2 that starts and stops has a boiler. Since the secondary air 7 is supplied from the separate damper 9 opened by the basic opening command 13 corresponding to the load command 11, there is a problem that the air becomes further in excess and NOx increases.

The present invention has been made in view of the above circumstances, and it is an object of the present invention to reduce the amount of air supplied to the burner at the time of starting and stopping to prevent an increase in NOx due to excess air.

[0011]

The present invention is directed to a pulverized coal mill connected to a burner 2 provided in a furnace 1 of a coal-fired boiler so as to supply pulverized coal to a required number of groups 2a to 2f. When starting / stopping 3a to 3f,
Pulverized coal that is started and stopped by reducing the flow rate of the secondary air 7 that is supplied to the burner 2 connected to the pulverized coal mill 3 that is stopped based on the boiler load command 11 for a predetermined time. A NOx control method for a coal-fired boiler, which is characterized by alleviating an excess air state of a burner 2 connected to a mill 3, and a required number of groups 2a for the burners 2 provided in the furnace 1 of the coal-fired boiler.
Pulverized coal mills 3a to 3f for supplying pulverized coal every ~ 2f, and separate dampers 9a to 9f, 9 to secondary air supply pipes 5 for supplying secondary air 7 to each of the burners 2.
a ′ to 9f ′ are provided, and the separate damper 9 is provided.
Each of a to 9f and 9a 'to 9f' is a boiler load command 1
Basic opening command 1 from the function generator 12 inputting 1
A NOx control device for a coal-fired boiler in which the opening degree is adjusted by 3, and a function for outputting a mill start-up narrowing signal 17 in which a narrowing amount and a narrowing time at the time of mill startup are set based on a mill load command 16 Generator 18
And a function generator 20 that outputs a mill stop narrowing signal 19 in which a narrowing amount and a narrowing time when the mill is stopped based on the mill load, and a mill start / stop signal 21 are input to narrow down the mill when starting the mill. The signal 17 is selected, and the milling stop narrowing signal 19 is selected when the mill is stopped.
Switch 22 and the mill start / stop signal 21 are input to select the signal from the first switch 22 at the start / stop of the mill, and the 0% signal generator is generated at a normal time other than the start / stop of the mill. The second switch 24 for selecting the normal side of 23, the change rate limiter 25 for giving a change rate to the signal selected by the second switch 24, and the signal from the change rate limiter 25 The present invention relates to a NOx control device for a coal-fired boiler, which is provided with an adder 26 that adds the boiler load command 11 to the basic opening command 13 from the function generator 12.

[0012]

[Function] When the pulverized coal mill is started and stopped, if the flow rate of the secondary air supplied to the burner connected to the pulverized coal mill that is started and stopped is reduced by narrowing down the separate damper for a predetermined time, The excess air state of the burner connected to the pulverized coal mill that starts and stops is mitigated, and the increase in NOx due to the burner connected to the pulverized coal mill that starts and stops is suppressed.

[0013]

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

FIG. 1 shows an embodiment of the present invention applied to the pulverized coal burning boiler shown in FIGS. 3 and 4, and the separate damper control device 15 shown in FIG. 5 has the following structure. I have to.

That is, as shown in FIG. 1, the mill load command 16
A function generator 18 which outputs a mill narrowing-down signal 17 by setting a narrowing-down amount and a narrowing-down time at the time of starting the mill based on
A function generator 20 that outputs a mill narrowing-down signal 19 by setting a narrowing-down amount and a narrowing-down time when the mill is stopped based on the mill load command 16 and a mill start / stop signal 21 are input to input a milling-down narrowing signal when the mill is started. 17 (a side) is selected, and when the mill is stopped, the milling stop time narrowing signal 19 (b side)
First switch 22 for selecting the mill and mill start / stop signal 2
Input 1 to start and stop the mill.
The second switch 24 that selects the signal (a side) from 2 and selects the normal side (b side) of the 0% signal generator 23 during normal times other than mill start / stop, and the second switch A rate-of-change limiter 25 that gives a rate of change to the signal selected by the unit 24, and an adder 26 that adds the signal from the rate-of-change limiter 25 to the basic opening command 13 from the function generator 12. A damper opening correction circuit 27 is provided.

The damper opening correction circuit 27 includes groups 2a to 2a of the burner 2 connected to the pulverized coal mills 3a to 3f.
Separate dampers 9a, 9a ', 9b, 9b', 9c, 9 provided on the secondary air supply pipe 5 communicating with 2f.
c ', 9d, 9d', 9e, 9e ', 9f, 9f' are provided. That is, the separate dampers 9a and 9a 'for supplying the secondary air 7 to the group 2a of the burners 2 connected to the pulverized coal mill 3a are controlled together by the damper opening correction circuit 27.

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

Of the pulverized coal mills 3 shown in FIGS. 3 and 4, for example, the case of activating the pulverized coal mill 3a will be described.
The pulverized coal mill 3a is activated by the mill activation signal 21 and started to operate at a low load by the mill load command 16, and the fuel 4 having a low concentration of pulverized coal is supplied to the group 2a of the burner 2.

At this time, the first switch 22 inputting the mill start signal 21 of FIG. 1 is switched to the function generator 18 side (a side), and the mill shown in FIG. The mill start-up narrowing-down signal 17 from the function generator 18 in which the narrowing-down amount α and the narrowing-down time T based on the load command 16 are set is selected.

At this time, the mill start signal 21 is also input to the second switch 24, so that the second switch 24 outputs the mill start narrowing signal 17 (a side) from the first switch 22. ) Is selected.

Therefore, the change rate limiter 25 determines the change rate of the mill start-up narrowing-down signal 17 selected by the second switch 24, as shown in FIG.
Via the boiler load command 11 to the basic opening command 13 obtained by the function generator 12. Therefore, the separate damper 9 supplying the secondary air 7 of the burner 2 connected to the pulverized coal mill 3 to be started is controlled to the opening degree shown in FIG. 2, so that the load of the pulverized coal mill 3 is small. At the time of starting the mill, by narrowing the supply of the secondary air 7 to the burner 2 connected to the pulverized coal mill 3, it is possible to prevent the burner 2 from becoming an excess air state and to reduce NOx. it can.

In the above, the secondary air 7 of which the flow to the burner 2 is suppressed by the narrowing down of the separate damper 9 is sent to the OPA 28 and other burning burners 2.

When the start-up is completed, the mill start-up signal 21 disappears so that the second switching unit 24 causes the 0% signal generator 2 to operate.
It is switched to select the 3 side (b side), so that the separate damper 9 is controlled by the basic opening command 13 based on the boiler load command 11.

In the above description, when the mill is started up, when the mill is stopped, the first switch 22 is switched by the mill stop signal 21 so as to select the stop narrowing signal 19 side (b side). Works exactly the same as at startup.

The NOx control method and device for a coal-fired boiler of the present invention is not limited to the above-described embodiment, and the narrowing-down amount α and the narrowing-down time T of the narrowing-down signals 17 and 19 can be set arbitrarily. Needless to say, various changes can be made without departing from the scope of the present invention.

[0026]

As described above, according to the NOx control method and apparatus for a coal-fired boiler of the present invention, the supply of secondary air to the burner connected to the pulverized coal mill that is started or stopped is narrowed down. The burner is prevented from becoming an excess air state by reducing the
It is possible to obtain an excellent effect of reducing NOx.

[Brief description of drawings]

FIG. 1 is a block diagram of a separate damper control device showing an embodiment of the present invention.

FIG. 2 is a diagram showing an example of a startup narrowing-down signal.

FIG. 3 is a side view showing an example of a pulverized coal burning boiler to which the present invention is applied.

FIG. 4 is a view taken along the line IV-IV in FIG.

FIG. 5 is a block diagram of a conventional separate damper control device.

[Explanation of symbols]

 1 furnace 2 burner 2a-2f group 3 pulverized coal mill 3a-3f pulverized coal mill 5 secondary air supply pipe 7 secondary air 9 separate damper 9a-9f separate damper 9a'-9f 'separate damper 11 boiler load command 12 function generation Device 13 Basic opening command 16 Mill load command 17 Start-up narrowing signal 18 Function generator 19 Stop-down narrowing signal 20 Function generator 21 Mill start / stop signal 22 First switch 23 0% signal generator 24 Second Switching device 25 Change rate limiter 26 Adder α Narrowing amount T Narrowing time

Claims (2)

[Claims] 1. A pulverized coal mill 3a to 3f connected so as to supply pulverized coal to a required number of groups 2a to 2f to a plurality of burners 2 provided in a furnace 1 of a coal-fired boiler is started and stopped. At this time, the flow rate of the secondary air 7 which is to be supplied to the burner 2 connected to the pulverized coal mill 3 to be started / stopped based on the boiler load command 11 is narrowed down for a predetermined time to reduce the start / stop. A NOx control method for a coal-fired boiler, which is characterized by mitigating an excess air state of a burner 2 connected to a pulverized coal mill 3 for stopping. 2. A pulverized coal mill 3a to 3f for supplying pulverized coal for each required number of groups 2a to 2f is connected to a plurality of burners 2 provided in a furnace 1 of a coal-fired boiler, and each of the burners 2 is connected. The secondary air supply pipe 5 for supplying the secondary air 7 is provided with separate dampers 9a to 9f and 9a 'to 9f', and the separate dampers 9a to 9f, 9 are provided.
NO in a coal-fired boiler in which the opening of each of a ′ to 9f ′ is adjusted by the basic opening command 13 from the function generator 12 inputting the boiler load command 11.
x control device, which is a function generator 18 for outputting a milling start-up narrowing signal 17 in which a narrowing-down amount and a narrowing-down time at mill startup are set based on a mill load command 16, and a narrowing-down when a mill is stopped based on a mill load Function generator 2 which outputs a narrowing signal 19 when the mill is stopped and which sets the amount and the narrowing time
0 and the mill start / stop signal 21 are input to select the mill start-up narrowing-down signal 17 at the mill start-up, and select the mill stop-time narrowing-down signal 19 at the mill stop.
And the mill start / stop signal 21 is input to select the signal from the first switching device 22 at the time of mill start / stop, and the normal side of the 0% signal generator 23 at the normal time other than the mill start / stop. A second switching device 24 for selecting a change rate, and a change rate limiting device 25 for giving a change rate to the signal selected by the second switching device 24,
The signal from the change rate limiter 25 is used as the boiler load command 1
Basic opening command 1 from the function generator 12 inputting 1
An NOx control device for a coal-fired boiler, which is provided with an adder 26 for adding to 3.