JP2000140680A - Primary air flow rate controller for pulverized coal mill - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enable suitably regulating the minimum air flow rate of primary air according to pulverizing property of coal fed into a pulverized coal mill. SOLUTION: This controller is provided with: a fed coal quantity detector 17 attached to a coal feeder 11; a primary function generator 19 for outputting a flow rate command signal 20 according to a fed coal quantity signal 18 thereof; a second function generator 24 for outputting a correction signal 23 for increasing or decreasing the minimum air flow rate of primary air 7 according to a coal property signal 22 showing pulverizing property of coal 5; a signal generator 26 for outputting a zero signal 25; a signal monitor switch 28 for outputting a switching command signal 29 when the fed coal quantity is a prescribed set value or less; a selector 27 for selecting the correction signal 23 on inputting the switching command signal 29 and selecting the zero signal 25 on non-inputting; and an adder 21 for adding the selected signal thereof to the flow rate command signal 20 and outputting the sum to a flow rate regulating damper 16 of a primary air supply pipe 13.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a primary air flow control device for a pulverized coal mill.

[0002]

2. Description of the Related Art FIG. 3 shows an example of a conventional general pulverized coal mill. In this type of pulverized coal mill 1, in a pulverized coal mill 1, a coal 5 dropped from an upper chute 2 onto a rotary table 3 is used. The pulverized coal 5 ′ is pulverized by a roller 4 that is pressed against a plurality of locations in the circumferential direction of the rotary table 3 so as to roll following the rotation of the rotary table 3, and the pulverized pulverized coal 5 ′ is placed around the rotary table 3. The air is conveyed upward by primary air 7 blown out from a large number of ports 6 provided in an annular shape, and sent from the top to a burner of a coal-fired boiler (not shown) through a cyclone type coarse powder separator 8. is there.

Here, the supply of the coal 5 to the chute 2 is performed by feeding coal 5 extracted from a lower part of a coal bunker 9 into a top opening of the chute 2 by a horizontal circulation type belt conveyor 10. This is performed by the machine 11.

The supply of the primary air 7 to each of the ports 6 is performed by a primary air supply pipe 13 connected to an air chamber 12 formed immediately below each of the ports 6. Mixing ratio adjusting dampers 14 and 15 combine cold air supplied directly from a high pressure ventilator (not shown) with hot air superheated by heat exchange with the combustion gas of a coal-fired boiler.
Thus, the primary air 7 adjusted to the required temperature can be introduced into the air chamber 12 at an appropriate flow rate through the flow rate adjusting damper 16 by appropriately adjusting the ratio.

[0005] In such a pulverized coal mill 1,
A coal feed signal 18 from a coal feed detector 17 attached to the coal feeder 11 is converted into a flow command signal 20 by a function generator 19.
Is output to the flow rate adjusting damper 16 of the primary air supply pipe 13 so that the flow rate of the primary air 7 is appropriately adjusted according to the amount of coal supplied.

FIG. 4 shows a function set in the function generator 19. Basically, the flow rate of the primary air 7 increases as the amount of coal supplied increases. In order to prevent the pulverized material of the coal 5 from falling, the flow rate of the primary air 7 is maintained at a constant minimum air flow rate when the coal supply amount is equal to or less than a predetermined coal supply amount x.

[0007]

However, when the flow rate of the primary air 7 is uniformly set to the minimum air flow rate at a predetermined coal supply amount x or less, the pulverizability of the coal 5 is poor (the pulverized product of coal). The primary air 7 is determined based on the assumption that the coarse air is easily crushed and easily dropped into the port). Therefore, when the crushability of the coal 5 is relatively good, the coal 5 is crushed finely and the port 5 is finely crushed. Despite the situation where it is unlikely to drop to 6, the minimum air flow more than necessary is secured, and when the boiler load command is low (when the amount of coal supplied is low), pulverized coal 5 'has too much air. In a tendency (the ratio of the primary air flow rate to the coal supply amount is high) to the coal-fired boiler, the self-holding capacity of the combustion flame in the coal-fired boiler at a low load is weakened, and the coal supply amount is equal to or less than a predetermined coal supply amount x. Luck because the stable combustion area in There was a problem of restricting the application.

The present invention has been made in view of the above-mentioned circumstances, and is directed to a pulverized coal mill in which the minimum air flow rate of primary air can be appropriately adjusted according to the pulverizability of coal charged into the pulverized coal mill. It is intended to provide a primary air flow control device.

[0009]

SUMMARY OF THE INVENTION According to the present invention, there is provided a coal feed detector attached to a coal feeder, and a flow command signal serving as a base signal is calculated in accordance with the coal feed signal from the coal feed detector. A first function generator to output a second function generator to calculate and output a correction signal to increase or decrease the minimum air flow rate of the primary air according to the coal property signal indicating the pulverizability of the coal, and a zero signal A signal monitor switch for inputting a coal supply signal from the coal supply detector and outputting a switching command signal when the coal supply is equal to or less than a predetermined set value; A switch that selects a correction signal from the second function generator when a switching command signal is input from a switch, and selects and outputs a zero signal from the signal generator when the switching command signal is not input; Either the correction signal or the zero signal selected by the switch A pulverized coal mill primary air flow control device, comprising: an adder that adds to a flow command signal from the first function generator and outputs the resultant signal to a flow adjustment damper of the primary air supply pipe. Things.

Therefore, according to the present invention, while the coal feed signal from the coal feed detector attached to the coal feeder is input to the first function generator and the flow command signal serving as the base signal is output, When the coal supply amount is equal to or less than the predetermined set value, a switching command signal is output from the signal monitor switch to the switch, and the correction signal from the second function generator is selected by the switch,
The correction signal is added to the flow rate command signal by an adder and output to the flow rate adjustment damper of the primary air supply pipe, and the minimum air flow rate of the primary air is increased or decreased by the correction signal according to the pulverizability of the coal. As a result, pulverized coal is prevented from being conveyed to the pulverized coal supply destination at a low load (when the coal supply amount is low) due to the tendency of pulverized coal being excessive in air (the ratio of the primary air flow rate to the coal supply amount is high). Therefore, the self-holding capability of the combustion flame at the pulverized coal supply destination is enhanced.

When the amount of coal supplied exceeds a predetermined set value, the switching command signal from the signal monitor switch to the switching device is lost, and the switching device selects the zero signal from the signal generating device. The signal is added to the flow command signal from the first function generator by an adder, that is, the flow control signal of the primary air supply pipe is corrected without correcting the flow command signal from the first function generator. And the flow rate of the primary air is controlled in accordance with the amount of coal supplied in the same manner as in the prior art.

[0012]

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

FIGS. 1 and 2 show an example of an embodiment of the present invention, and the portions denoted by the same reference numerals as those in FIG. 3 represent the same components.

As shown in FIG. 1, in this embodiment, as in the conventional example shown in FIG. 3, a function corresponding to a coal feed signal 18 from a coal feed detector 17 attached to the coal feeder 11 is used. The flow rate command signal 20 is calculated and output by the generator 19 (hereinafter referred to as a first function generator), and the flow rate command signal 20 is used as a base signal to appropriately correct by the adder 21. After the addition, the output is output to the flow rate adjustment damper 16 of the primary air supply pipe 13.

That is, a second function generator 24 for calculating and outputting a correction signal 23 for increasing or decreasing the minimum air flow rate of the primary air 7 according to a coal property signal 22 indicating the pulverizability of the coal 5, and a zero signal 25 A signal generator 26 for outputting the correction signal 23 from the second function generator 24 and a zero signal 25 from the signal generator 26. The data is output to the adder 21.

Here, the coal property signal 22 input to the second function generator 24 is a hard globe index (Ha
rdgrove grindability index: a numerical value indicating the pulverizability of coal obtained under a specified condition using a hard glove tester, indicating a relative pulverizability in comparison with coal selected as pulverizability of 100, and The hard glove index is measured in advance for the operating coal, so that there is no problem in inputting it as the coal property signal 22 artificially.

A function as shown in FIG. 2 is set in the second function generator 24. This function is used in a region where the hard globe index determined from the coal property signal 22 is relatively small. The correction signal 23 is maintained at 0%, and in a region near the middle, the correction signal 23 gradually decreases from 0% to minus several percent as the hard globe index increases, and further decreases by a few percent in a relatively large region. The lower limit is maintained.

The switch 27 is provided with a signal monitor switch 28 when the coal supply is equal to or less than a predetermined set value x (see FIG. 4) according to the coal supply signal 18 from the coal supply detector 17. A switching command signal 29 output from the second function generator 24 is selected when the switching command signal 29 is input, and the switching command signal 29 is At the time of input, the zero signal 25 from the signal generator 26 is selected.

The coal feed signal 18 from the coal feed detector 17 attached to the coal feeder 11 is supplied to the first function generator 19.
Is output to output a flow command signal 20 serving as a base signal. When the amount of coal supplied is equal to or less than a predetermined set value, a switch command signal 29 from the signal monitor switch 28
7 and the second function generator 2
4 is selected, and the correction signal 23 is added to the flow command signal 20 by the adder 21 and is output to the flow control damper 16 of the primary air supply pipe 13 so that the lowest air of the primary air 7 is output. Since the flow rate is reduced according to the pulverizability of the coal 5 by the correction signal 23, the pulverized coal 5 ′ tends to be excessive in air at a low load (when the coal supply is low) (the primary air 7 with respect to the coal supply) Is prevented from being conveyed to the pulverized coal 5 'supply destination, and the self-holding capability of the combustion flame at the pulverized coal 5' supply destination is enhanced.

When the amount of supplied coal exceeds a predetermined set value, the switching command signal 29 from the signal monitor switch 28 to the switch 27 is lost, and the switch 27 outputs a zero signal 25 from the signal generator 26. Is selected, and the zero signal 25 is added to the flow command signal 20 from the first function generator 19 by the adder 21, that is, the flow command signal 20 from the first function generator 19 is corrected. This is output to the flow rate adjusting damper 16 of the primary air supply pipe 13 without being performed, and the flow rate control of the primary air 7 according to the coal supply amount is performed as in the conventional case.

Therefore, according to the above embodiment, the pulverized coal mill 1
Since the minimum air flow rate of the primary air 7 can be appropriately adjusted according to the pulverizability of the coal 5 charged into the pulverized coal, the pulverized coal 5 'tends to be in excess of air when the load is low and the coal-fired boiler (pulverized coal 5' Can be avoided beforehand, the self-holding capability of the combustion flame in the coal-fired boiler is strengthened, and the combustion stabilization region in the region below the predetermined coal supply x is expanded. Operational restrictions can be eliminated.

Incidentally, the primary air flow control device of the pulverized coal mill of the present invention is not limited to the above-mentioned embodiment, and the modified signal from the second function generator is described in the above embodiment. Although the case where the minimum air flow rate of the primary air is reduced is exemplified, it is assumed that the flow rate command signal from the first function generator assumes a medium case where the crushability of coal is not particularly bad or not good. For example, the correction signal from the second function generator may increase or decrease the minimum air flow rate of the primary air, and it is needless to say that various changes can be made without departing from the gist of the present invention. It is.

[0023]

According to the primary air flow control device of the pulverized coal mill of the present invention, the minimum air flow rate of the primary air can be appropriately adjusted according to the pulverizability of the coal charged into the pulverized coal mill. Since it is possible to prevent the pulverized coal from being conveyed to the pulverized coal supply destination due to excessive air at a low load, the self-holding capability of the combustion flame at the pulverized coal supply destination can be strengthened and specified. Therefore, it is possible to obtain an excellent effect that the combustion stabilization region in the region equal to or less than the coal supply amount can be expanded and restrictions on operation can be eliminated.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating an example of an embodiment of the present invention.

FIG. 2 is a graph showing a function set in a second function generator of FIG. 1;

FIG. 3 is a block diagram showing a conventional example.

FIG. 4 is a graph showing functions set in the function generator of FIG. 3;

[Explanation of symbols]

 Reference Signs List 1 pulverized coal mill 5 coal 5 'pulverized coal 7 primary air 11 coal feeder 13 primary air supply pipe 16 flow rate adjustment damper 17 coal feed quantity detector 18 coal feed quantity signal 19 first function generator 20 flow command signal 21 addition 22 Coal property signal 23 Correction signal 24 Second function generator 25 Zero signal 26 Signal generator 27 Switching device 28 Signal monitor switch 29 Switching command signal

Claims (1)

[Claims] A first function for calculating and outputting a flow rate command signal serving as a base signal in response to a coal supply signal from the coal supply detector and a coal supply detector attached to the coal feeder. A generator,
A second function generator that calculates and outputs a correction signal that increases or decreases the minimum air flow rate of primary air according to a coal property signal indicating the crushability of coal, a signal generator that outputs a zero signal, and the coal supply amount A signal monitor switch for inputting a coal feed signal from the detector and outputting a switch command signal when the coal feed is equal to or less than a predetermined set value; and a second switch for inputting a switch command signal from the signal monitor switch. A selector for selecting a correction signal from the function generator and selecting and outputting a zero signal from the signal generator when the switching command signal is not input; a correction signal and a zero signal selected by the switch. A primary air flow rate of the pulverized coal mill, comprising: an adder for adding any one of the above to the flow rate command signal from the first function generator and outputting it to the flow rate adjusting damper of the primary air supply pipe. Control device.