JPS5816123A - Combustion control system for coal burning boiler - Google Patents

Abstract

PURPOSE:To provide a stable combustion by a method wherein a secondary air instruction system is provided with a characteristic compensation function which is suited for a dynamic characteristic of a variation of a volume of a pulverized coal at the inlet of the burner, and a variation of volume of air is adapted for a variation of volume of coal at the burner. CONSTITUTION:A dynamic characteristic compensation unit 19 for delay-controlling a volume of air detected by the secondary air flow rate sensor 16 and the millmaster instruction M collated in the subtractor unit 17 are provided. This compensation unit 19 delays a subtraction performed by the subtracter unit 17 be delaying the millmaster instruction M, controls the secondary air damper opening degree instruction 35 and delays the opening and closing of the secondary air damper 12. This characteristic of delay is set such that the volume of secondary air 100 is set at the same delay characteristic as that of the volume of the pulverized coal 200 at the inlet of the burner. Thereby, the pulverized coal is burnt efficiently to enable a prevention of a transient incomplete combustion or an increased volume of NOx.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a combustion control method for a coal-fired boiler, and particularly to a coal-fired boiler that can compensate for a delay in the dynamic characteristics of a pulverizer (mill) and adjust the amount of combustion air optimally. This relates to a boiler combustion control method.

A general coal-fired couplant will be explained using FIGS. 1 and 2. Figure 1 is a schematic diagram of the plant;
The figure is a diagram showing a specific example of the fuel (coal) supply system in FIG. 1. In Figure 1, the coal stored in the bunker 8 is transported to the coal feeder 7.
The coal is sent to the pulverizer 6 by the conveyor inside the pulverizer 6.
It is crushed by. The pulverized coal that has been ground into defined particles is conveyed to the burner 9 by compressed air (secondary air) from the high-pressure ventilation fan 5 and the second ventilation fan 11, and is burned in the boiler 1. On the other hand, air (secondary air) necessary for the burner 9 is supplied from the strong pressure fan 5 to the fan box 10. The pulverized coal fuel supply system (mill equipment) is installed in n sets (generally 4 to 6 pieces) per boiler can.

Combustion in the boiler is determined by the supply of pulverized coal by the coal feeder 7 and the total amount of secondary air and secondary air. The supply of this pulverized coal is controlled by the coal feeder rotation speed of the conveyor in the coal feeder 7, as shown in detail in FIG. It is controlled by 12.

FIG. 3 is a diagram illustrating a conventional fuel and air control system for the fuel supply system shown in FIG. 2.

In the figure, a total burnt wood count command 31, which is an instruction from another device, is compared with a total coal sight 32 detected by a detector 14 of the rotation speed of the belt conveyor of the coal feeder 7 in a subtractor 17, and the difference is processed by the proportional integrator 18 to become a mill master command M, and 11 sets of mill equipment are controlled in parallel by this command M.

This mill master command M becomes a coal feeder speed command 33 that instructs each mill equipment to drive the belt conveyor of the corresponding coal feeder 7. Air amount detected by detector 16 and subtractor 1
7 and the deviation thereof is processed by the proportional integrator 18 to generate a damper opening command 34 that instructs opening and closing of the medical air damper 13 and the secondary air damper 12.
and 35, and the respective operating ends are operated in parallel. Therefore, in the -medical Qi damper and secondary air damper control loops, the sum of -Medical Qi damper and -Medical Qi ■ and secondary air amount is fed back, respectively, so that the combustion air is maintained at an appropriate value. It is composed of

By the way, in the mill equipment configured as described above, since a coal pulverization process is involved, a lag time occurs in the amount of pulverized coal in the burner population. This is shown in Figure 4 (a) and (
This will be explained using 1)). FIGS. 4(a) and (1)) are diagrams showing the relationship between the secondary air amount 100 and the burner artificial pulverized coal amount 200 in response to the rise and fall of the mill mask command M.

In the figure, when the mill master command M is increased or decreased in a stepwise manner, the amount of secondary combustion air is 100 and the amount of pulverized coal is 2.
00, an imbalance will occur.

The reason for this is that when the conveyor rotation speed of the coal feeder 7 is increased or decreased, the coal that flows into the mill 6 is pulverized into specified particles 1, and then the process of being circulated within the mill and re-pulverized must be repeated. This is because there is an accumulation of coal in the mill, and it takes time for the transitional increase or decrease in the amount, which causes a delay in the increase or decrease in the amount of pulverized coal in the burner.

Let us consider the effects when such a phenomenon (transient excess or deficiency of combustion air) occurs. Air transient combustion is NOX
On the other hand, combustion with insufficient air causes incomplete combustion to generate black smoke and the like. In recent boilers, burner air/
As it has become more common to reduce the fuel t1 ratio for combustion,
It has become more important than ever to suppress the phenomenon of excess or deficiency of air volume as described above.

The purpose of the present invention is to eliminate the problems caused by the above-mentioned prior art, and to add a characteristic compensation function adapted to the dynamic characteristics of the change in the amount of pulverized coal in the burner to the secondary air command system. To provide a combustion control system for a coal boiler that can maintain a proper air-fuel ratio when the amount of coal in a mill increases or decreases by matching the change in air amount with a change in the amount of air, thereby achieving stable combustion.

An embodiment of the present invention will be described in detail below with reference to the drawings.

FIG. 5 is a diagram illustrating a fuel and air control scheme according to the present invention. In the figure, the same reference numerals as those shown in FIG. 3 indicate the same parts. The difference from the prior art is that a dynamic characteristic compensator 19 is provided for delay-controlling the mill master command M, which is matched with the air amount detected by the secondary air flow amount detector 16 in the subtracter 17. This compensator 19 delays the subtraction process by the subtractor 17 by delaying the mill master command M, controls the secondary air damper opening command 35, and delays the opening and closing of the secondary air damper 12. This delay characteristic is set to be the same as the delay characteristic when the amount of secondary air is 100 and the amount of pulverized coal in the burner is 200.

This characteristic will be explained using FIGS. 6(a) and (b).

When the input signal of the compensator 19, that is, the mill master command M, is changed stepwise, the secondary air command signal 100 increases or decreases with a characteristic that follows the amount of pulverized coal 200, which increases or decreases with a delay. . For this reason, pulverized coal burns efficiently.

As described above, according to the present invention, air that follows the amount of pulverized coal is supplied even during the transient stage when the power plant load increases or decreases, for example, when the amount of coal increases or decreases.
It is possible to prevent an increase in OX.

[Brief explanation of the drawing]

Figure 1 is a schematic system diagram of a coal-fired couplant, Figure 2 d,
FIG. 2 is a diagram showing the fuel supply system of FIG. 1; FIG. 3 is a diagram illustrating the fuel and air supply system according to the prior art;
FIG. 4 is a diagram showing the mill operation characteristics of the 31st sill. FIG. 5 is a diagram for explaining the mode and air supply system according to an embodiment of the present invention, and FIG. 6 is a diagram showing the mill characteristics in the conventional system shown in FIG. 1... Boiler, 2... Turbine, 3... Generator,
4... Water supply pump, Death... Strong pressure ventilation fan, 6... Pulverized coal machine (mill), 7... Coal feeder, 8... Bunker, 9...
...Burner, 1.0...Full box, 11...-Secondary ventilation fan, 12...Secondary air damper, 13...-Medical air damper, 14...Rotation speed detector, 15 ...-Missing air flow rate detector, ]6... Secondary air flow rate detector, 17...
Subtractor, 18...Proportionality, Integrator, 19...Gravity characteristic compensator, 31...Total fuel/1■ command, 32...Second port 30 1 Kayaoguchi (cA-) 1 Inner-mouth rod Otokyo (b) -11

Claims (1)

[Claims] 1. In a combustion control system for a coal-fired boiler comprising a pulverizer that supplies pulverized coal to a burner in accordance with a mill master command, and an air supply means that supplies combustion air for pulverized coal to the burner in accordance with the mill master command, the air supply The means are
A combustion control system for a coal-fired boiler, characterized in that combustion air is supplied to a burner with a delay characteristic that matches the delay characteristic of the pulverizer according to a mill master directive.