JPS60228819A - Air flow rate controlling device of boiler - Google Patents

Abstract

PURPOSE:To prevent the percentage of excess air of a boiler from exceeding of the specified value and consequently stabilize the combustion in the boiler and at the same time prevent the nitrogen oxides in exhaust gas from increasing by a method wherein the signal detecting the oxygen content in the exhaust gas is compared with the set oxygen concentration value in exhaust gas at a subtracter. CONSTITUTION:An oxygen-in-exhaust-gas transmitter 6 detects the oxygen concentration in the exhaust gas passing through a flue 5 and outputs an oxygen-concentration-in- exhaust-gas signal 30 to a subtracter 7. The subtracter 7, in which the set oxygen concentration value 31 set in advance as for the desirable oxygen concentration in exhaust gas is inputted compares said signal 30 with the set oxygen concentration value 31 in order to input the difference between the signal 30 and concentration value 31 in the form of an oxygen-in-exhaust-gas deviation signal 32 to an integrating controller 8 and a function generator 9. When the oxygen concentration in exhaust gas decreases, the function generator 9 immediately outputs the correction signal to increase the air flow rate. On the contrary, when the oxygen concentration in exhaust gas increases, the function generator 9 outputs the correction signal to decrease the air flow rate so as to decrease the oxygen concentration in exhaust gas before the increase of nitrogen oxides become a problem.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention provides an air supply system for boiler combustion.
The present invention relates to an air flow rate control device for a boiler having an excess air correction function.

[Prior art] If the amount of air supplied for boiler combustion is larger than the required amount, nitrogen oxides contained in the boiler exhaust gas will increase, so the air supplied to the boiler must be controlled to maintain an appropriate flow rate. Must be.

An example of a conventional air flow control device for a boiler is explained with reference to FIG. This is what you enter. In addition to this signal, the exhaust gas 02 set value C is input to the subtracter, and the exhaust gas 02 set value C is input to the subtracter.
Reduce the signal from the transmitter a and the exhaust gas 021 fixed cell C,
The obtained deviation value is output to the integral controller d. The integral controller d has the function of matching and maintaining the signal of the exhaust gas 02 transmitter a and the exhaust gas 02 set value C, and outputs an excess air rate correction signal e proportional to the deviation value from the subtractor 1. Output. The air flow rate of the push-through machine that supplies combustion air to the boiler is controlled by the above-mentioned excess air ratio correction signal e.

In such conventional devices, since the response speed of the integral regulator d is slow, the adjustment operation of the air flow rate supplied to the boiler for combustion is slow, resulting in a decrease in the exhaust gas oxygen concentration, or a high exhaust gas oxygen concentration. In some cases, nitrogen oxides generated by combustion increased.

In addition, when starting and stopping the pulverized coal machine in a coal-fired boiler, the flow rate of pulverized coal fed into the boiler cannot be accurately measured, so the exhaust gas oxygen concentration may drop or become too high compared to other fuels, resulting in nitrogen The situation where the amount of oxides increased was remarkable.

[Problems to be Solved by the Invention] The present invention aims to prevent the excess air ratio of the boiler from becoming higher than a specified value, stabilize combustion within the boiler, and prevent an increase in nitrogen oxides in exhaust gas. That is.

[Means for Solving the Problems] In order to solve the above-mentioned problems, the present invention compares a signal that detects the amount of oxygen in exhaust gas with a set value for the amount of oxygen in exhaust gas using a subtractor, and converts the compared signal into a subtracter. an integral regulator for matching, a function generator that outputs a correction signal when the amount of oxygen in the exhaust gas decreases, an adder that adds the signal from the integral regulator and the signal from the function generator, and the adder a multiplier that multiplies a signal from the multiplier by an air flow rate command signal; a subtracter that compares the signal from the multiplier with a signal from the combustion air flow rate transmitter; This is an air flow rate control device for a boiler, which is equipped with a control drive that adjusts the flow rate of combustion air.

[Example] Hereinafter, one embodiment of the present invention will be described with reference to the drawings.

In FIG. 2, a forced draft fan 2 is provided in the combustion air supply passage 1 to supply combustion air to the boiler body 3. The air sent to the boiler body 3 burns the fuel supplied from the burner 4 within the boiler body 3, and the energy of the combustion gas is converted into steam energy. The exhaust gas passes through the flue 5 and is discharged into the atmosphere from a chimney (not shown).

An exhaust gas oxygen transmitter 6 is attached to the m-way 5 to detect the oxygen concentration in the exhaust gas passing through the flue 5 and output it to the subtractor 7 as an exhaust gas oxygen amount signal 30. An oxygen amount setting value 31 that is preset as a desirable oxygen concentration in exhaust gas is input to the subtracter 7, and the subtracter 7 compares the exhaust gas oxygen amount signal 30 and the oxygen type setting value 31, and calculates the difference. as the exhaust gas oxygen deviation signal 32, the integral regulator 8 and the function generator 9
Enter.

Although the integral regulator 8 has a slow response speed, it has a function of ensuring that the exhaust gas oxygen source signal 30 and the oxygen amount setting value 31 match and maintaining that state. The function generator 9 also has the function of outputting a correction signal 33 proportional to the exhaust gas deviation signal 32.

The feature of this function generator 9 is that, as shown in Fig. 3, when the amount of oxygen in the exhaust gas decreases, it immediately outputs a correction signal that increases the air flow rate, but when the amount of oxygen in the exhaust gas is large, it outputs a correction signal that increases the air flow rate up to a certain range. Instead of outputting a correction signal, the system outputs a correction signal that reduces the amount of oxygen in the exhaust gas by reducing the air flow rate before the increase in nitrogen oxides becomes a problem.

The output signal 34 from the integral regulator 8 and the correction signal 33 from the function generator 9 are added by an adder 10 to form an excess air ratio correction signal 35, which is input to a multiplier 11. Multiplier 1
An air flow rate command signal 36 corresponding to the fuel flow rate in the burner 4 is input to the multiplier 1.
1 multiplies the excess air ratio correction signal 35 and the air flow rate command signal 36, and outputs the subtractor 12 as a corrected air flow rate command signal 37.
Enter.

The air flow rate flowing through the combustion air supply passage 1 is detected by the combustion air flow rate transmitter 13 and inputted to the subtractor 12 as an air flow rate signal 38. Subtractor 12 compares corrected air flow rate command signal 31 and air flow rate signal 38 and inputs the difference therebetween as air flow deviation signal 39 to proportional-integral regulator 14 .

The proportional-integral regulator 14 inputs a control drive command signal 40 to the control drive 15 for adjusting the air flow rate based on the air flow rate deviation signal 39, and controls the forced air blower 2 so as to obtain the required combustion air flow interval. .

[Effect of the invention] The present invention can have the following effects.

(1) When the amount of oxygen in the exhaust gas decreases, the flow rate of combustion air can be increased proportionally to prevent the amount of oxygen in the exhaust gas from decreasing.

(i) Since a conventionally used integral regulator is also provided, the combustion air flow rate can be adjusted so as to maintain the exhaust gas oxygen amount at a specified value.

(g) When the amount of oxygen in the exhaust gas increases, the amount of nitrogen oxides generated in the boiler increases, but in order to prevent this, the flow rate of combustion air can be proportionally reduced to prevent the amount of nitrogen oxides from increasing. .

(f) Exhaust gas oxygen analyzers generally have a response delay, but
If only a normal proportional controller is used to deal with this response delay, an excessive correction signal may be output, but a function generator is used to set a limit for outputting an excessive air ratio correction signal. Therefore, it is possible to cope with the response delay of the exhaust gas oxygen analyzer, and by providing a dead zone between the regions where the exhaust gas oxygen reduction prevention operation and the nitrogen oxide increase prevention operation act, it is possible to avoid unnecessary correction operations.

[Brief explanation of the drawing]

FIG. 1 is a partial system diagram of a conventional device, FIG. 2 is a system diagram of an embodiment of the present invention, and FIG. 3 is a graph showing characteristics of a function generator. 1.12 is a subtractor, 8 is an integral regulator, 9 is a function generator,
10 is an adder, 11 is a multiplier, 13 is a combustion air flow rate transmitter, 15 is a control drive, 30 is an exhaust gas oxygen amount signal, 31 is an oxygen m setting value, and 3G is an air flow rate command signal.

Claims (1)

[Claims] 1) An integral controller that compares the signal that detects the amount of oxygen in the exhaust gas with the set value of the amount of oxygen in the exhaust gas using a subtractor, and makes the compared signals match, and outputs a correction signal when the amount of oxygen in the exhaust gas decreases. a function generator that adds the signal from the integral regulator and the signal from the function generator, a multiplier that multiplies the signal from the adder by the air flow command signal, and the multiplier. A subtractor that compares a signal from the combustion air flow rate transmitter with a signal from the combustion air flow rate transmitter, and a control drive that adjusts the combustion air flow rate in accordance with the signal from the subtractor. Boiler airflow control device.