JP4605656B2 - Thermal power generation boiler and combustion air supply control method - Google Patents

Description

  The present invention relates to air flow control and reduction of exhaust gas in boilers for thermal power generation using fossil fuels such as coal and petroleum, and in particular, stabilizes and improves the efficiency of fossil fuel combustion in boiler furnaces. The present invention relates to a thermal power generation boiler and a combustion air supply control method suitable for the above.

  In a thermal power generation boiler using fossil fuels such as coal and oil, as shown in FIG. 2, it burns from an air duct 20 to an after-air port (hereinafter sometimes referred to as OFA) 18 which is a burner 17 and a two-stage combustion air port. Supply air is supplied. The combustion of the fuel in the boiler furnace 21 by the two-stage combustion method is a combustion method for reducing NOx and CO in the exhaust gas generated by the combustion of the fuel, and is necessary for the combustion of the fuel in the burner 17. An amount of air slightly smaller than the amount of air is supplied from the wind box damper 22 to the burner 17, and the shortage of air is supplied from the branch duct 19 as two-stage combustion air (hereinafter referred to as OFA damper). ) Is supplied from 23 to the after-air port 18, and this two-stage combustion air is both pushed into the ventilator (hereinafter also referred to as FDF) 24 and preheated in the air heater 26, and then to the boiler furnace 21. It is captured.

  That is, although both combustion air and two-stage combustion air are supplied from the air side outlet of the air heater 26, the air heater air side outlet pressure, which is the original pressure, is not controlled, so the air heater air side outlet pressure and the furnace The differential pressure with respect to the internal pressure was not stably controlled, which was one factor that deteriorated the accuracy of air flow control.

In the prior art, the moving blade of the FDF 24 controls the air flow rate to the furnace 21, the wind box damper 22 controls the air flow rate necessary for combustion in each burner 17, and the OFA damper 23 is the air required for two-stage combustion. The flow rate is controlled, and the air heater air side outlet pressure is corrected by the correction circuit to the wind box damper 22 when the pressure exceeds the control range, but the corresponding burner 17 is not ignited. The wind box damper 22 remains at the specified opening, and correction from the air heater air side outlet pressure may not be effective, and is not suitably controlled.
JP 11-14005 A

In the above-mentioned prior art, by adjusting the wind box damper opening to match the balance of theoretical plans of the combustion air and controls the combustion air flow, for the air heater air side outlet pressure, the There is also a circuit for correcting the opening degree of the windbox damper 22 in order to return to the control range when the control range is deviated. However, since the wind box damper 22 mainly controls the air flow rate for the burner 17, if the air heater air side outlet pressure is controlled by the wind box damper 22, the combustion of the burner 17 may become unstable. When the burner 17 is not ignited, the wind box damper 22 is operated at the specified opening. Therefore, the opening degree correction of the wind box damper 22 by the air heater air side outlet pressure is not effective.

Optimal Also, if the air heater air side outlet pressure is varied, the pressure of the corresponding air system is not optimal, the combustion air for igniting the torch which adjusts the air flow rate by a fixed type air damper not subject to automatic control also This makes the combustion of the ignition torch unstable.
An object of the present invention is to stabilize the flow rate of combustion air and improve the combustibility by keeping the air heater air side outlet pressure optimal at all times without adversely affecting the combustion in the boiler furnace.

The problems of the present invention are solved by the following means.
The invention according to claim 1 is a furnace (21) for burning fuel, a burner (17) for burning fuel at a theoretical air ratio or less provided on a wall surface of the furnace (21), and a rear of the burner (17). An after-air port (18) for injecting a short amount of combustion air in the burner (17) provided on the wall surface of the flow-side furnace (21) into the furnace (21), the burner (17) and the after-air port ( and 18) that to supply preheated combustion air air duct (20), the air and gas ducts (air heater for preheating the air which is provided to the 20) (26), which is preheated in the air heater (26) air A branch duct (19) with a duct opening / closing damper (23) for supplying a part of the air to the after-air port (18), and a predetermined ratio with respect to the air flow rate required for combustion of fuel in the furnace (21) in advance. Follow a predetermined program In thermal power boiler comprising a combustion control system (16) after air port air flow rate set value (A) is set,
The combustion control device (16) supplies (a) air heater air side outlet pressure measuring means (1) for measuring the pressure of air preheated by the air heater (26), and (b) supplying the burner (17). A fuel flow rate measuring means (2) for measuring the fuel flow rate, (c) an air heater air-side outlet pressure set value calculating means (3) calculated according to the fuel flow rate measured by the fuel flow rate measuring means (2), (D) Air heater air side outlet pressure measurement value (B) measured by the air heater air side outlet pressure measurement means (1) and air heater air side calculated by the air heater air side outlet pressure set value calculation means (3) Air heater air side outlet pressure set value deviation calculating means (4) for calculating a deviation (D) from the outlet pressure set value (C), and (e) an absolute value of the air heater air side outlet pressure deviation (D) is a predetermined value. (T2) When exceeding, a control signal for adjusting the air flow set value (A) for the after-airport by adjusting the opening of the duct opening / closing damper (23) so that the deviation (D) is equal to or less than the predetermined value (T2). It is a boiler for thermal power generation provided with the signal generation means (10) of (11).

According to a second aspect of the present invention, when the combustion control device (16) is started, the actual value (B) of the air heater air side outlet pressure is smaller than the air heater air side outlet pressure set value (C). 2. The thermal power generation boiler according to claim 1, wherein when the value is smaller than that of (), the duct opening / closing damper (23) is controlled not to be closed.

  The invention according to claim 3 includes a burner (17) for burning fuel at a theoretical air ratio or less provided on a wall surface of a furnace (21) for burning fuel, and a furnace (21) on the downstream side of the burner (17). Combustion preheated by an air heater (26) to an after air port (18) with a duct opening / closing damper (23) for injecting a short amount of combustion air in the burner (17) provided on the wall surface into the furnace (21) In the combustion air supply amount control method for controlling the supply amount of the combustion air when supplying the combustion air, the combustion air supply amount control method is predetermined at a predetermined ratio with respect to the air flow rate required for combustion of fuel in the thermal power generation boiler. The after-air port air flow set value (A) is set according to the program, and the absolute value of the deviation (D) between the measured value (B) of the air heater air side outlet pressure and the air heater air side outlet pressure set value (C) is predetermined. When exceeding (T2), the opening degree of the duct opening / closing damper (23) is adjusted so that the deviation (D) becomes equal to or less than the predetermined value (T2), and the after-airport air flow rate set value (A) is set. It is a combustion air supply amount control method characterized by performing correction control.

According to the fourth aspect of the present invention, the actual value (B) of the air heater air-side outlet pressure is smaller than the specified value (T1) which is smaller than the air heater air-side outlet pressure set value ( C ) when the thermal power generation boiler is started. 4. The combustion air supply control method according to claim 3, wherein when the value is smaller, the duct opening / closing damper (23) is controlled not to be closed.

(Function)
In general, in the two-stage combustion method, in order to reduce the NOx concentration in the furnace, less burner air is supplied to the burner (17) than theoretically required, and the remainder is a duct open / close damper (hereinafter referred to as OFA damper). Supply from (23).
In practice, the after-air port air flow rate setting value (A) is determined by the opening degree of the OFA damper (23) at a certain ratio with respect to the required air flow rate, and the ratio is set by a program in the function generator.

  Normally, the OFA damper (23) is controlled to match the air flow rate setting value (A) determined from the ratio, but according to the inventions of claims 1 and 3, for example, the air heater (AH) When the air-side outlet pressure becomes high, the correction signal (11) is added to the direction in which the OFA damper (23) is opened, that is, the programmed flow rate setting value (A) to obtain a new flow rate setting value (A ′). Conversely, if the air heater (AH) air-side outlet pressure is low, the correction signal (11) is subtracted from the flow rate setting value (A) set in the program to make a new flow rate setting value (A ′). .

  As described above, the corrected after-air port air flow rate setting value (A ′) obtained in the present invention is set to an invariable value (A) for each time set according to the time set by the program. This value is obtained by adding or subtracting a correction value corresponding to the change in the air-side outlet pressure.

  According to the first and third aspects of the present invention, the air heater air side outlet pressure is used as the combustion air pressure of the boiler using fossil fuel, and this pressure is optimized to increase the accuracy of the combustion air flow rate control. The combustibility in the boiler furnace can be improved, and the air flow rate can be optimized for the combustion air for the ignition torch, thereby providing stable combustion.

According to the invention of claim 2 and 4, wherein, in addition to the effects of the invention of claim 1 and 3 wherein, Oite when starting the boiler for thermal power generation, measured value of the air-side outlet pressure of the air heater (26) Is smaller than the specified value T1, the supply amount of the combustion air to the after-air port (18) is not controlled, so there is no possibility that the supply control of the combustion air cannot be disabled.

  FIG. 1 shows a correction signal for an air flow rate set value obtained by a program for completely burning unburned fuel supplied from the OFA damper 23 described in FIG. 11 shows a control circuit for outputting 11.

  Air that is less than the amount of air necessary for combustion of fuel in the burner 17 is supplied from the wind box damper 22 of the boiler furnace 21, and air that burns unburned fuel is supplied from the OFA damper 23 to the after-air port 18. This is as explained in FIG.

  The control circuit shown in FIG. 1 includes an air-side outlet pressure detector 1 of the air heater 26, a total fuel flow rate detector 2 that is the amount of fuel input to the boiler furnace 21, and a control device (calculation device) 16. When the OFA flow rate setting correction signal 11 is output from the control device (arithmetic unit) 16, it is transmitted to the flow rate control circuit of the OFA damper 23, and the OFA flow rate setting value (A) is used as a correction bias for the OFA flow rate setting value (A). Is added to or subtracted from.

  Here, the OFA flow rate setting value (A) is programmed in advance according to the combustion conditions in the furnace and is output by a general control circuit so as to change with the passage of time from the start of the boiler. Is not shown. The control circuit 16 of the present embodiment responds to the OFA flow rate setting value (A) in response to fluctuations in the air-side outlet pressure of the air heater 26 and the total fuel flow rate to the boiler furnace 21. Is a control circuit for increasing or decreasing the air flow rate.

The behavior of the control circuit and the control signal of the present invention will be described with reference to FIG.
Based on the signal from the total fuel flow rate detector 2, the function generator 3 calculates the air side outlet pressure set value (C) of the air heater 26 corresponding to the load condition of the boiler furnace 21 when the total fuel flow rate is detected. The subtractor 4 calculates a deviation from the air heater air side outlet pressure, which is the actual air side outlet pressure value (B), to obtain an air heater air side outlet pressure setting deviation (D).

When the absolute value of the pressure setting deviation (D) is equal to or less than the setting value T2 so that the OFA flow rate setting value (A) is not excessively corrected with respect to the air heater air side outlet pressure setting deviation (D), A dead zone for control is provided in the function generator 6 to obtain a corrected setting deviation 7 which is a corrected setting deviation.
Based on the correction setting deviation 7, the integrator 10 obtains an OFA flow rate setting correction signal 11 which is a correction bias for OFA flow rate setting in the following procedure.

  For example, the air heater air side outlet pressure setting deviation (D) is a positive value, that is, the actually measured value (B) of the air heater air side outlet pressure exceeds a specified value T1, and the deviation (D) is determined by the function generator 6. When it becomes larger than the predetermined value T2 that becomes the dead zone, the OFA flow rate setting correction signal 11 also becomes a positive value, and acts to increase the air amount from the OFA flow rate setting value (A), and as a result, the OFA damper 23 is opened. It operates, and the air side outlet pressure of the air heater 26 decreases. Therefore, it is avoided that the air heater air side outlet pressure continues to increase, and the air heater air side outlet pressure decreases.

  In addition, this control circuit corrects the OFA flow rate setting value (A) and operates the OFA damper 23 to control the air heater air side outlet pressure. Therefore, this control circuit is effective only when the OFA damper 23 can be automatically controlled. In other cases, the integrator 10 can perform integral calculation when the OFA damper 23 is automatically controllable so that the output of the OFA flow rate setting correction signal 11 is zero. In other cases, the integrator 8 can perform a constant time constant. Therefore, the integrator 10 returns the output of the OFA flow rate setting correction signal 11 to zero.

Further, when the air heater outlet pressure on the plant operation is continuously lower than the set value (C), such as in the boiler starting process, the OFA damper 23 is fully closed by this control circuit. In order to avoid this, when the actual measured value (B) of the air heater air-side outlet pressure, which is constantly measured by the low monitor 12, is smaller than the specified value T1, the switch 13 is set to the analog setting from the analog setting device 15 by the signal of the low monitor 12. The lower limit of the integrator 10 is set to zero so that the OFA flow rate setting correction signal 11 is not negative.
Further, when the air heater air-side outlet pressure measured by the low monitor 12 exceeds the specified value T1, it is not necessary to define the lower limit of the integrator 10, and therefore the analog setting device 15 is not necessarily required.

  The function generator 6 is not provided in the method described in the prior art or the invention described in Japanese Patent Application Laid-Open No. Sho 63-318404 and Japanese Patent Application Laid-Open No. 8-261410, so that the air heater air side outlet pressure setting deviation is not provided. When D is not zero, pressure control is always performed, and disturbance is given to the program control of the OFA damper 23.

  FIG. 3 shows how the air heater air-side outlet pressure (actual measurement value (B)) changes with time during the boiler start-up process and how the air heater air-side outlet pressure set value (C) changes with time (FIG. 3 (a)). ), The temporal change of the OFA flow rate setting value (A) set in advance so as to change with time according to the program (FIG. 3B), and the temporal change of the opening degree of the OFA damper 23 ( FIG. 3 (c)) is shown.

  When the air heater air-side outlet pressure (actual value (B)) is smaller than the specified value T1 during the boiler start-up process, the air heater air-side outlet pressure control is not performed by adjusting the opening degree of the OFA damper 23, and the lower limit of the integrator 10 is determined by the low monitor 12. Set the value to zero. A curve (A) in FIG. 3C shows a temporal change in the opening degree of the OFA damper 23 when there is no function of suppressing the air heater air side outlet pressure control when the air heater air side outlet pressure is smaller than the specified value T1. Thus, in the case of the curve (A), the air heater air-side outlet pressure set value (C) in which the air heater air-side outlet pressure (= measured value (B)) matches the load condition at the time of detecting the total fuel flow rate when the boiler is started. ), The OFA damper 23 is fully closed immediately, and the air heater air-side outlet pressure control cannot be performed.

  However, according to the present embodiment, the air heater air side outlet pressure (actual value (B)) exceeds the specified value T1 in the boiler starting process, and the absolute value of the air heater air side outlet pressure setting deviation (D) is a predetermined value (T2). Only when the value exceeds the value, the OFA damper 23 is corrected so that both the control of the air heater outlet pressure and the air flow rate control necessary for the two-stage combustion by the OFA damper 23 are achieved. For example, when the air heater air side outlet pressure set value (C) is increasing in accordance with a pre-programmed procedure from the start of the boiler, as shown in the hatched portion (b) of FIG. When the air heater air-side outlet pressure setting deviation (D = CB) exceeds the set value T2 because the actual pressure (B) has decreased for some reason, the deviation (D) is the setting of the air heater air-side outlet pressure. The output value of the correction signal 11 of the OFA flow set value (A) shown in FIG. 1 so as not to exceed the value T2 is lower than the OFA flow set value (A) set in advance by the program shown in FIG. As indicated by the dotted line (c), the set value (A ′) after the correction of the set value (A) is output. As a result, the OFA damper 23 is corrected in the closing direction ((d) in FIG. 3C).

  In a boiler equipped with a two-stage combustion air damper, when the set deviation (D) of the air heater air-side outlet pressure becomes large and deviates from the control range, a correction is applied to the windbox damper 22 supplied to the burner 17, Although there is a conventional technique including a control circuit for returning the air heater outlet pressure to the control range, the wind box damper 22 of this prior art mainly controls the combustion air flow rate of the burner 17, and the air heater 26. If the correction by the control of the air side outlet pressure is added, the combustion balance may be shifted.

  On the other hand, since the OFA damper 23 normally controls the flow rate of the air for two-stage combustion in this embodiment, the correction operation to the OFA damper 23 according to this embodiment may cause the balance of the two-stage combustion to shift. Since it is not involved in the main combustion unlike the box damper 22, the influence on the final combustion gas, that is, the increase in NOx concentration and CO concentration in the combustion gas is small and technically improved.

  Further, in the prior art, when the burner 17 is not ignited, the wind box damper 22 is fixed at a specified opening, and the damper opening correction becomes invalid, and the air heater air side outlet pressure cannot be controlled at all times. However, in this embodiment, since the OFA damper 23 is not fixed at the specified opening during the combustion operation (ignition operation of the burner 17), the above disadvantages in the prior art are eliminated.

The present invention has the availability of the coal and industrial Suitable equipment and methods to the air flow rate control of the thermal power boiler or the like that utilize fossil fuels such as oil.

It is a control circuit diagram concerning the Example of this invention. It is a block diagram which shows the example of the supply system of the fuel air to the burner and OFA of a boiler furnace. The graph (FIG. 3 (a)) which shows the relationship between the air heater air side outlet pressure and time change in the boiler starting process of the Example of this invention, and the graph which shows the relationship between OFA flow rate setting value A and time change (FIG. 3) FIG. 3B is a graph showing the relationship between the opening degree of the OFA damper and the temporal change (FIG. 3C).

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Air heater air side outlet pressure detector 2 Total fuel flow rate detector 3 Function generator 4 Subtractor 6 Function generator 7 Correction setting deviation 8 Switch 9 Analog setting device 10 Integrator 11 OFA flow rate setting correction signal 12 Low monitor 13 switching 14 Analog setter 15 Analog setter 16 Arithmetic unit 17 Burner 18 After air port 19 Branch duct 20 Air duct 21 Boiler furnace 22 Wind box damper 23 Two-stage combustion air damper (OFA damper)
24 Push-in ventilator (FDF) 26 Air heater
A After-air port air flow rate setting value (OFA flow rate setting value)
B Air heater air side outlet pressure measured value C Air heater air side outlet pressure set value D Air heater air side outlet pressure setting deviation T1 Specified value T2 Predetermined value

Claims (4)

A furnace (21) for burning fuel, a burner (17) for burning fuel at a theoretical air ratio or less provided on a wall surface of the furnace (21), and a furnace (21) on the downstream side of the burner (17) A combustion air preheated by the burner (17) and the after-air port (18), and an after-air port (18) for jetting a short amount of combustion air from the burner (17) provided on the wall surface into the furnace (21) the air duct that to supply air (20), said air duct air heater for preheating the air which is provided in (20) and (26), some after-air ports of the air preheated by the air heater (26) (18 ) And a branch duct (19) with a duct opening / closing damper (23), and an after-treatment according to a program determined in advance at a predetermined ratio with respect to the air flow rate required for combustion of fuel in the furnace (21). Airport In thermal power boiler with an air flow rate setpoint combustion control apparatus (A) is set (16),
The combustion control device (16)
(A) air heater air side outlet pressure measuring means (1) for measuring the pressure of air preheated by the air heater (26);
(B) fuel flow rate measuring means (2) for measuring the flow rate of fuel supplied to the burner (17);
(C) an air heater air side outlet pressure set value calculation means (3) calculated according to the fuel flow rate measured by the fuel flow rate measurement means (2);
(D) The air heater air side outlet pressure measured value (B) measured by the air heater air side outlet pressure measuring means (1) and the air heater air side outlet pressure calculated by the air heater air side outlet pressure set value calculating means (3). An air heater air side outlet pressure set value deviation calculating means (4) for calculating a deviation (D) from the pressure set value (C);
(E) When the absolute value of the air heater air side outlet pressure deviation (D) exceeds a predetermined value (T2), the duct opening / closing damper (23) is set so that the deviation (D) is equal to or less than the predetermined value (T2). And a signal generation means (10) for a control signal (11) for adjusting the after-air port air flow rate set value (A) by adjusting the opening degree of the thermal power generation boiler.   When the combustion control device (16) is started, the measured value (B) of the air heater air side outlet pressure is smaller than the specified value (T1) which is smaller than the air heater air side outlet pressure set value (C). If it is, the boiler for thermal power generation according to claim 1, wherein control is performed so as not to close the duct opening / closing damper (23). The burner (17) for burning fuel at a theoretical air ratio or less provided on the wall surface of the furnace (21) for burning fuel and the burner (17) provided on the wall surface of the furnace (21) on the downstream side of the burner (17) When the combustion air preheated by the air heater (26) is supplied to the after air port (18) with the duct opening / closing damper (23) for injecting the shortage of combustion air into the furnace (21). In the combustion air supply amount control method for controlling the supply amount of combustion air,
The after-air port air flow rate setting value (A) is set according to a predetermined program at a predetermined ratio with respect to the air flow rate required for fuel combustion in the boiler for thermal power generation,
When the absolute value of the deviation (D) between the measured value (B) of the air heater air side outlet pressure and the air heater air side outlet pressure set value (C) exceeds a predetermined value (T2), the deviation (D) is Combustion air supply amount control characterized in that control is performed to correct the after-airport air flow rate setting value (A) by adjusting the opening of the duct opening / closing damper (23) so as to be equal to or less than a predetermined value (T2). Method. When the thermal power generation boiler is started, the measured value (B) of the air heater air side outlet pressure is smaller than the specified value (T1), which is smaller than the air heater air side outlet pressure set value ( C ). 4. The combustion air supply control method according to claim 3, wherein control is performed so as not to close the duct opening / closing damper (23).

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