JPS5888536A - Device for combustion control of boiler - Google Patents

Abstract

PURPOSE:To prevent the generation of an insufficient condition of air upon increasing the load of the boiler by a method wherein an air volume delay correction signal, outputted through a first delay circuit and a limiter, is added to or reduced from a fuel control signal to provide a fuel set signal. CONSTITUTION:A difference between the main steam pressure signal 5 of the boiler 1 and the main steam pressure set signal 6, set by a main steam pressure setting knob 10, is operated by adding and reducing unit 7. The difference is operated by a proportional operator 11 and an integral operator 12 and is added by an adder 13 to produce the standard fuel control signal 21. Subsequently, the primary delay circuit 17 and the limiter 19 output a signal having a delay equivalent to the delay of the changing air volume upon receiving the fuel control signal 21 while the signal is outputted from the adding and reducing unit 11 as the fuel set signal 14. The limiter in this circuit is constituted so as to pass the signal of plus side and the fuel set signal 14 is outputted by adding the delay correction signal 29 of the air volume only upon increasing of the load of the boiler.

Description

[Detailed description of the invention] The present invention relates to a combustion control device for a boiler.

A conventional combustion control device for a small boiler controls fuel and air supplied to a boiler 1 via a fuel control valve 2 and an air damper 3, as shown in FIG. The fuel control valve 2 and the air damper 3 are each connected to a control motor 4 via a link system. This control motor 4 is connected to the main steam pressure signal 5 detected in the boiler 1.
It is connected to an adder/subtractor 7 and a proportional-integral calculator 8, which add and subtract the value to the main steam pressure setting signal 6. Air is pushed in/9
Press-fitted by In this way, boiler combustion control is based on the main steam pressure signal 5, controlling the fuel control valve 2 by the control motor and link system via the proportional integral control device (PI calculator 8), and controlling the fuel amount. The amount of air is controlled by the air damper 3, and nitrogen oxide NO.
The aim is to reduce x and improve fuel efficiency. The control block is shown in FIG.

The main steam pressure signal is connected to an adder/subtractor 7 together with a main steam pressure setting signal 6 from a main steam pressure setting knob 10, and its output is connected to a proportional calculator 11. The output of the proportional calculator 11 is input directly to the adder 13 and also via the integral calculator 12. The output of the adder 13 is input to the control motor, and the output is the fuel setting signal 1.
4 is linked on one side to the fuel control valve 2 and on the other hand to the air damper 3 via a function generator 15 which sets the air quantity relative to the fuel quantity.

As described above, conventional combustion control devices are operated using a mechanical link system, and the amount of air relative to the amount of fuel is controlled with a margin. Recently, electronic control methods have been devised to reduce the ratio of excess air to fuel, reduce NOx, and improve efficiency.

In this case, in transient conditions where the load increases.

Detects a drop in main steam pressure due to an increase in load.

The fuel is increased and the air damper is opened to increase the amount of air. However, there is a delay in filling up the volume of the duct system, resulting in insufficient air volume (see Figure 3).
. If there is insufficient air cover during fuel combustion, combustion will be incomplete and soot will be generated, which will adversely affect the boiler.

The present invention has been made in view of the above-mentioned circumstances, and is applied in a transient state where the boiler load increases. According to the present invention, the purpose is to prevent incomplete combustion due to a delay in air amount change, and the fuel setting signal is passed through an air amount change delay circuit and a limiter circuit that takes into account the air amount delay only when the load increases. It is characterized by the fact that

A preferred embodiment of the present invention illustrated in FIG. 4 will be described in detail below. Components in FIG. 4 that are equivalent to those in FIGS. 1 and 2 are designated by the same reference numerals.

In FIG. 4, the fuel amount control device 16 includes an adder/subtractor 7 for adding and subtracting the main steam pressure signal 5 and the main steam pressure setting signal 6 from the main steam pressure setting knob 10, a proportional calculator 11, an integral calculator 12, and In addition to the adder 13, the first-order delay circuit 1
7. Output of this first-order delay circuit 17 and fuel control signal 2
1, a limiter 19, and an adder/subtractor 20 that receives a delay correction signal 29 and a fuel control signal 21, which are the outputs of the limiter 19.

The output of this fuel quantity control device 16 is supplied to the fuel control valve 2 as a fuel setting signal 14. In the first-order delay circuit 17, T is a time constant and S is a Laplace operator.

A fuel control signal 21, which is the output of the adder 13 of the fuel amount control device 16, is supplied to the air amount control device 22 via the air amount setting function generator 15.

The air amount control device 22 receives an air amount setting signal 23 from the function generator 15 and an air amount signal 2 fed back from the air valve 3.
4, a proportional calculator 26, an integral calculator 27, and an adder 28.

To explain the operation, the main steam pressure signal 5 of boiler 1
The deviation between the main steam pressure setting signal 6 and the main steam pressure setting signal 6 set by the main steam pressure setting dial 10 is calculated by the adder/subtractor 7. The deviation is calculated by a proportional calculator 11 and an integral calculator 12,
It is added by an adder 13 to form a basic fuel control signal 21. Next, the first-order delay circuit 17 and limiter 19
In response to this basic fuel control signal 21, a signal with a delay equivalent to the interruption of the changing air amount becomes a fuel setting signal 1.
4 from the adder/subtractor 11. Further, the limiter of this circuit is designed to pass only the positive side signal, and only when the load increases, the fuel setting signal 14 is outputted with the addition of the air amount delay correction signal 29. When the load decreases,
Since the air amount delay correction signal 29 is limited by the limiter, the fuel setting signal 14 follows the load change (tj) and is output as equivalent to the fuel control signal 21.Fuel setting signal 1
4g is transmitted to the fuel control valve 2, the opening degree is controlled and the fuel amount 30 is determined.

Further, as for the fuel control signal 21 which is the output of the adder 13, the generator 15 outputs an air setting/setting signal 2-3 optimal for combustion during the air amount setting period. The deviation of this signal from the air amount signal 24 of the air damper 3 is calculated by an adder/subtractor 25, proportional and integral calculations are performed by a proportional calculator 20 and an integral calculator 27, and then added by an adder 28. This determines the opening degree of the air valve 3, and the amount of air 31 is determined.

According to the present invention, the fuel control signal 21 is transmitted to the first-order delay circuit 17.
By adding and subtracting the air amount delay correction signal 29 outputted via the limiter 19 to the fuel setting signal 14, the first-order delay circuit 17 takes into account a delay equivalent to the air amount change delay, With the limiter 19, it is possible to take into account the delay only when the load increases, and when the load decreases, the delay is not added to the action of the limiter 19, so it is possible to respond quickly to the increase in the main steam pressure of the boiler. As a result, an air shortage condition does not occur when the load increases, and soot generation is prevented.

[Brief explanation of the drawing]

Figure 1 is a diagram showing the configuration of a conventional boiler combustion control device.
2 is a block diagram of the control device shown in FIG. 1, FIG. 3 is a diagram showing characteristics of a conventional combustion control device, and FIG. 4 is a block diagram of a combustion control device for boiler 2 according to the present invention. 1. Boiler, 2. Fuel control valve, 3. Air tamper,
4. Control motor, 5. Main steam pressure signal, 6
...Main steam pressure setting signal, 7.. Adder/subtractor, 8.. Proportional integral calculator, 9.. Force fan, 10.. Main steam pressure setting knob, 11.. Proportional calculator, 12.. Integral calculator. , 13...Adder, 14...Fuel setting signal, 15...Function generator. 16...Fuel amount control device, 17...1st order delay circuit. 18: Adder/subtractor, 19: Limiter, 20: Adder/subtractor, 21: Fuel control signal, 22: Air amount control device,
23... Air amount setting signal, 24... Air amount signal, 25...
・Adder/subtractor, 26: Proportional calculator, 27: Integral calculator, 28: Adder, 29: Delay correction signal, 30: Fuel amount, 31: Air amount.

Claims (1)

[Claims] In a combustion control device for a boiler that controls a fuel control valve via a proportional-integral control device based on a main steam pressure signal from the boiler, a primary A delay circuit and a limiter circuit are provided, and a fuel setting signal supplied to the fuel control valve is outputted by a fuel control signal from the proportional-integral control device and the fuel control signal via the primary delay circuit and limiter circuit. A combustion control device for a boiler, characterized in that the combustion control device obtains the air amount delay correction signal by addition and subtraction with the air amount delay correction signal.