JP3477885B2 - Primary air draft controller for coal-fired boiler - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a primary air draft control device for a coal-fired boiler. 2. Description of the Related Art Generally, as shown in FIG. 3, in a coal-fired boiler, combustion air (secondary air) pressurized by a forced air ventilator (FDF) 1 is heated by an air preheater 2. rear,
While being supplied to a plurality of burners 5 arranged in a furnace 4 of the boiler 3, a part of the combustion air was branched and led to a primary ventilator (PAF) 6, and the pressure was increased by the primary ventilator 6. After the primary air is heated by the air preheater 2, the primary air is introduced into a plurality of (in the example of FIG. 3, three units A, B, and C) mills 7,
The pulverized coal as a fuel pulverized in each of the mills 7 is conveyed to each of the burners 5 so as to be burned in the furnace 4. A boiler 3 is located downstream of the forced draft fan 1.
Flow meter 8 for measuring the total amount of air supplied to the furnace 4
A primary air draft detector 9 for detecting the pressure (draft) of primary air heated by the air preheater 2 and supplied to each mill 7 is provided downstream of the primary ventilator 6. A temperature control damper 10 is provided for adjusting the flow rates of the primary air heated by the air preheater 2 and the primary air bypassing the air preheater 2 to adjust the temperature of the primary air supplied to each mill 7. On the downstream side, a shutoff damper 11 that shuts off the supply of primary air to each mill 7.
And a flow rate adjusting damper 12 for adjusting the flow rate of the primary air supplied to each mill 7, and each mill 7 has a mill differential pressure (= mill inlet draft−mill outlet). A mill differential pressure detector 13 for detecting a draft is provided. A flow meter provided on the downstream side of the forced draft fan 1 so that the total amount of air supplied to the furnace 4 of the boiler 3 is equal to the amount of fuel supplied in response to the boiler load command. 8 is controlled by appropriately adjusting the opening degree of the inlet vane 1a of the push-in ventilator 1 based on the measurement value of 8. [0005] The pressure (draft) of the primary air heated by the air preheater 2 and supplied to each mill 7 is detected by a primary air draft detector 9 and as shown in FIG.
The difference between the pressure of the primary air detected by the primary air draft detector 9 and the set value is determined in the subtractor 14, and a pressure deviation signal 15 is output to the proportional-integral controller 16. The pressure deviation signal 15 output from the subtracter 14 is proportionally integrated, an opening correction command 17 for controlling the air flow is output to the primary ventilator 6, and the opening of the inlet vane 6a of the primary ventilator 6 is adjusted. Then, the air volume is controlled, whereby the pressure of the primary air is maintained at a set value. Further, the mill differential pressure of each of the mills 7 is detected by a mill differential pressure detector 13, and when the mill differential pressure in a certain mill 7 is extremely low, the mill 7 is urgently stopped. It is like that. In the above-described example, a case where a centrifugal fan is used as the push-in ventilator 1 and the primary ventilator 6 is shown, but a case where an axial fan is used as the push-in ventilator 1 and the primary ventilator 6. Has inlet vanes 1a, 6a
Instead, the opening of the rotor blade is adjusted. In this case, a flow meter 8 is installed on the inlet side of the forced draft fan 1. However, as described above, the pressure of the primary air heated by the air preheater 2 and supplied to each of the mills 7 is detected by the primary air draft detector 9 and is subtracted by the subtractor. At 14, the difference between the pressure of the primary air detected by the primary air draft detector 9 and the set value is determined, and a pressure deviation signal 15 is output to the proportional-integral controller 16;
The proportional-integral controller 16 performs a proportional-integral process on the pressure deviation signal 15 output from the subtractor 14 to output an opening correction command 17 for controlling the air volume to the primary ventilator 6. If the air volume is controlled by adjusting the opening of the vane 6a to maintain the pressure of the primary air at a set value, it is a mere proportional integral (PI) control. Drive only the remaining mill 7
Is stopped, that is, only the shut-off damper 11 leading to one operating mill 7 is fully opened, and the shut-off damper 11 leading to the remaining mill 7 stopped is fully closed. In order to increase the number of operating mills 7 with the increase in the boiler load command, when the mill 7 is started with the shut-off damper 11 leading to the stopped mill 7 being fully opened, the primary air is supplied to the mill 7. Is partially sucked in, the pressure of the primary air temporarily drops, but the draft control of the primary air cannot completely follow this, and the desired amount of pulverized coal is no longer discharged from the already operating mill 7, Boiler 3
Has the disadvantage of adversely affecting combustion and steam temperature and pressure. Conversely, from a state in which a plurality of mills 7 are operating, that is, a state in which the cut-off damper 11 leading to the plurality of operating mills 7 is fully opened, a decrease in the boiler load command causes In order to reduce the number of operating mills 7, among the operating mills 7, when the shut-off damper 11 leading to a desired mill 7 is fully closed to stop the mill 7, the mill 7 is stopped.
The supply of primary air to the mill is interrupted, and the pressure of the primary air temporarily increases, but the draft control of the primary air cannot follow this, and the amount of pulverized coal discharged from the mill 7 already in operation is reduced. It also had an adverse effect on boiler combustion and steam temperature and pressure. The present invention has been made in view of the above circumstances, and provides a primary air draft control device for a coal-fired boiler capable of suppressing primary air draft fluctuations caused by starting and stopping a plurality of mills and stabilizing combustion. What you want to do. According to the present invention, a primary ventilator 6 is provided.
A primary air draft control device for a coal-fired boiler that conveys pulverized coal pulverized by a plurality of mills 7 to a plurality of burners 5 disposed in a furnace 4 of the boiler 3 by primary air pumped from A primary air draft detector 9 for detecting the pressure of the primary air pressure-fed from the primary ventilator 6; a difference between the primary air pressure detected by the primary air draft detector 9 and a set value; Subtractor 1 that outputs 15
4, a proportional-integral controller 16 for performing proportional-integral processing on the pressure deviation signal 15 output from the subtractor 14 and outputting an opening correction command 17 for controlling the airflow of the primary ventilator 6, and a mill for each mill 7 A mill differential pressure detector 13 for detecting a differential pressure and a mill differential pressure detected by the mill differential pressure detector 13 when the shut-off dampers 11 provided on the inlet side of each mill 7 for shutting off the primary air are fully closed. Is output while the cut-off damper 1
1 When not fully closed, a switching relay 1 that outputs the mill differential pressure detected by the mill differential pressure detector 13 as a signal 18 as it is.
9 and a signal 18 output from each switching relay 19, and a first adder 21 that outputs a mill differential pressure sum signal 20
A function generator 23 for outputting a basic opening command 22 for controlling the air flow rate of the primary ventilator 6 based on the mill differential pressure sum signal 20 output from the first adder 21; The sum of the output opening correction command 17 output and the basic opening command 22 output from the function generator 23 is obtained,
A second adder 25 for outputting a basic opening correction command 24 for controlling the air volume to the primary ventilator 6 is provided. Accordingly, the pressure (draft) of the primary air supplied from the primary ventilator 6 to each of the mills 7 is detected by the primary air draft detector 9 and input to the subtractor 14 where the primary air draft is detected. The difference between the pressure of the primary air detected by the primary air draft detector 9 and the set value is determined, and a pressure deviation signal 15 is output to the proportional-integral controller 16. The pressure deviation signal 15 output from the adder 14 is subjected to proportional integration processing, and the second adder 2
5, an opening correction command 17 for controlling the air volume of the primary ventilator 6 is output, while the mill differential pressure in each of the mills 7 is detected by the mill differential pressure detector 13 and input to the switching relay 19, and during operation. , The mill differential pressure of the mill 7 in which the cut-off damper 11 is not fully closed is output as a signal 18 from the switching relay 19 to the first adder 21 and the mill 7 that is stopped
That is, the mill differential pressure of the mill 7 in which the cut-off damper 11 is fully closed is output to the first adder 21 as 0, and the first adder 21 sums the signals 18 output from the respective switching relays 19. Is calculated, and a mill differential pressure sum signal 20 is output to a function generator 23. The function generator 23 controls the air volume of the primary ventilator 6 based on the mill differential pressure sum signal 20 output from the first adder 21. Is output to the second adder 25, and the second adder 25
The opening correction command 1 output from the proportional-integral controller 16
7 and the basic opening command 22 output from the function generator 23 are obtained, a basic opening correction command 24 for controlling the air flow is output to the primary ventilator 6, and the basic opening correction command 2 is output.
4, the air volume of the primary ventilator 6 is controlled. As a result, for example, only one of the mills 7 is operated and the remaining mills 7 are stopped, that is, only the cut-off damper 11 leading to the operated one of the mills 7 is fully opened. From the state in which the cut-off damper 11 leading to the remaining mill 7 that is stopped is fully closed, and in order to increase the number of operating mills 7 as the boiler load command increases, the path to the stopped mill 7 is used. When the mill 7 is started with the shutoff damper 11 fully opened, a part of the primary air is sucked into the mill 7 and the pressure of the primary air tends to temporarily decrease. By detecting with the signal 20, the air volume of the primary ventilator 6 is increased in advance, the pressure of the primary air is maintained at a set value, and a desired amount of pulverized coal continues to be discharged from the already operating mill 7. And boiler 3 combustion and steam Every time, is prevented from adversely affect the pressure. Conversely, from a state in which a plurality of mills 7 are operating, that is, a state in which the cut-off damper 11 leading to the plurality of operating mills 7 is fully opened, a decrease in the boiler load command causes In order to reduce the number of operating mills 7, among the operating mills 7, when the shut-off damper 11 leading to a desired mill 7 is fully closed to stop the mill 7, the mill 7 is stopped.
The supply of primary air to the air is cut off, and the pressure of the primary air tries to rise temporarily,
By detecting at 0, the air volume of the primary ventilator 6 is reduced in advance, the pressure of the primary air is maintained at a set value, and the amount of pulverized coal discharged from the mill 7 already operating is also increased. Without
A bad influence on the boiler combustion and steam temperature and pressure is avoided. Embodiments of the present invention will be described below with reference to the drawings. FIGS. 1 and 2 show one embodiment of the present invention. In the drawings, the portions denoted by the same reference numerals as those in FIGS. 3 and 4 represent the same components, and the control system shown in FIG. Basically, when the shut-off damper 11 for shutting off the primary air provided on the inlet side of each mill 7 is fully closed (that is, when the operation of the mill 7 is stopped), the mill differential pressure detected by the mill differential pressure detector 13 is detected. Is output while the cut-off damper 11 is not fully closed (that is, during operation of the mill 7), the mill differential pressure detected by the mill differential pressure detector 13 is output as it is as a signal 18. Switching relay 19 and signal 1 output from each switching relay 19
8 and outputs a mill differential pressure sum signal 20. A first adder 21 outputs the mill differential pressure sum signal 20, and a basic air flow control of the primary ventilator 6 based on the mill differential pressure sum signal 20 output from the first adder 21. The sum of a function generator 23 that outputs an opening command 22, an opening correction command 17 output from a proportional-plus-integral controller 16, and a basic opening command 22 output from the function generator 23 is obtained. Basic opening correction command 24 for air flow control to ventilator 6
And a second adder 25 that outputs the same. A function as shown in FIG. 2 is input to the function generator 23 based on data collected at the time of the test operation. This indicates that the basic opening command 22 of the inlet vane 6a of the primary ventilator 6 is increased or decreased in proportion. Next, the operation of the above embodiment will be described. The pressure (draft) of the primary air heated by the air preheater 2 and supplied to each of the mills 7 is detected by a primary air draft detector 9 and input to a subtractor 14 where the primary air is drafted. The difference between the pressure of the primary air detected by the air draft detector 9 and the set value is determined, and a pressure deviation signal 15 is output to the proportional-integral controller 16, where the subtractor 14 outputs The output pressure deviation signal 15 is proportionally integrated, and an opening correction command 17 for controlling the air volume of the primary ventilator 6 is output to the second adder 25. On the other hand, the mill differential pressure in each mill 7 is detected by the mill differential pressure detector 13 and input to the switching relay 19, and the mill differential of the operating mill 7, ie, the mill 7 in which the shut-off damper 11 is not fully closed, is obtained. The pressure is output from the switching relay 19 to the first adder 21 as a signal 18, and the mill differential pressure of the stopped mill 7, that is, the mill 7 in which the cut-off damper 11 is fully closed, is set to 0 and the first adder is set. 21. In the first adder 21, the sum of the signals 18 output from the respective switching relays 19 is obtained, and a mill differential pressure sum signal 20 is output to a function generator 23. Based on the mill differential pressure sum signal 20 output from the first adder 21, a basic opening degree command 22 for controlling the air volume of the primary ventilator 6 is output to the second adder 25,
In the second adder 25, the opening correction command 17 output from the proportional integration controller 16 and the function generator 23
Is obtained with the basic opening degree command 22 output from the controller, a basic opening degree correction instruction 24 for air flow control is output to the primary ventilator 6, and based on the basic opening degree correction instruction 24, the primary ventilation 6
The opening degree of the inlet vane 6a is adjusted, and the air volume is controlled. As a result, for example, only one of the mills 7 is operated and the remaining mills 7 are stopped, that is, only the cut-off damper 11 leading to one of the operated mills 7 is fully opened, and the operation is performed. From the state in which the cut-off damper 11 leading to the remaining mill 7 that is stopped is fully closed, and in order to increase the number of operating mills 7 as the boiler load command increases, the path to the stopped mill 7 is used. When the mill 7 is started with the shut-off damper 11 fully open, a part of the primary air is sucked into the mill 7 and the pressure of the primary air tends to temporarily decrease. By detecting the signal 20, the opening degree of the inlet vane 6 a of the primary ventilator 6 is preliminarily increased, the pressure of the primary air is maintained at a set value, and a desired amount of fine powder is supplied from the mill 7 already in operation. Coal continues to be removed, boiler Combustion and steam temperature, is avoided adversely affect the pressure. Conversely, from a state in which a plurality of mills 7 are operating, that is, a state in which the shut-off damper 11 leading to the plurality of operating mills 7 is fully opened, with a decrease in the boiler load command, In order to reduce the number of operating mills 7, among the operating mills 7, when the shut-off damper 11 leading to a desired mill 7 is fully closed to stop the mill 7, the mill 7 is stopped.
The supply of primary air to the air is cut off, and the pressure of the primary air tries to rise temporarily,
By detecting at 0, the opening degree of the inlet vane 6a of the primary ventilator 6 is reduced in advance, the pressure of the primary air is maintained at a set value, and the pulverized coal discharged from the mill 7 already in operation. Does not increase, thereby avoiding adverse effects on boiler combustion and steam temperature and pressure. In this way, it is possible to suppress the draft fluctuation of the primary air due to the start and stop of the plurality of mills 7 and to stabilize the combustion. The primary air draft control device of the coal-fired boiler of the present invention is not limited to the above-described embodiment, but may be applied to a case where an axial fan instead of a centrifugal fan is used as the primary ventilator 6. It goes without saying that various changes can be made without departing from the gist of the present invention, such as adjusting the opening of the moving blade instead of the inlet vane 6a. As described above, according to the primary air draft control device for a coal-fired boiler of the present invention, it is possible to suppress the primary air draft fluctuation caused by starting and stopping of a plurality of mills, and An excellent effect of stabilizing can be achieved.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram of one embodiment of a primary air draft control device for a coal-fired boiler according to the present invention. FIG. 2 is a diagram showing functions set in the function generator shown in FIG. FIG. 3 is an overall schematic configuration diagram of a general coal-fired boiler. FIG. 4 is a block diagram of a conventional primary air draft control device for a coal-fired boiler. [Description of Signs] 3 Boiler 4 Furnace 5 Burner 6 Primary ventilator 7 Mill 9 Primary air draft detector 11 Cut-off damper 13 Mill differential pressure detector 14 Subtractor 15 Pressure deviation signal 16 Proportional integral controller 17 Opening correction command 18 Signal 19 Switching relay 20 Mill differential pressure sum signal 21 First adder 22 Basic opening command 23 Function generator 24 Basic opening correction command 25 Second adder

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Claims (1)

(57) [Claims 1] Pulverized coal pulverized by a plurality of mills (7) by primary air fed from a primary ventilator (6) is converted into a furnace (4) of a boiler (3). A primary air draft control device for a coal-fired boiler conveyed to a plurality of burners (5) disposed in a primary air draft detector for detecting a pressure of primary air pressure-fed from a primary ventilator (6). (9) a subtractor (14) for obtaining a difference between a pressure of the primary air detected by the primary air draft detector (9) and a set value, and outputting a pressure deviation signal (15); Pressure deviation signal (15) output from (14)
Proportional-integral controller (16) that outputs an opening correction command (17) for controlling the air flow rate of the primary ventilator (6)
And a mill differential pressure detector (1) for detecting a mill differential pressure of each mill (7).
3) and a shut-off damper (11) provided on the inlet side of each mill (7) for shutting off the primary air when the mill differential pressure detector (1) is fully closed.
A signal (18) for setting the mill differential pressure detected in 3) to 0 is output, while the mill differential pressure detected by the mill differential pressure detector (13) is used as it is when the shut-off damper (11) is not fully closed. A first adder (21) for obtaining a sum of a switching relay (19) output as a signal (18) and a signal (18) output from each switching relay (19) and outputting a mill differential pressure sum signal (20) ), And a function generator (22) for outputting a basic opening command (22) for controlling the air volume of the primary ventilator (6) based on the mill differential pressure sum signal (20) output from the first adder (21). 23), the sum of an opening correction command (17) output from the proportional-integral controller (16) and a basic opening command (22) output from the function generator (23) is obtained. Ventilator (6)
A primary air draft control device for a coal-fired boiler, comprising: a second adder (25) for outputting a basic opening correction command (24) for air flow control.