JP2583886B2 - Coal supply control method for boiler unit - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for controlling the amount of coal supplied to a boiler apparatus, and more particularly to a control method for preventing a drum water level from being lowered during a boiler load run.

[Conventional technology]

FIG. 9 shows a conventional coal supply control system in a boiler device. In the figure, 1 is a PI adjuster, 2 is an adder, 3 is a subtractor,
4 is a differential regulator, 5 is a function generator, 6 is a coal feeder speed regulator, and 7 is a primary air flow damper.

Conventionally, during the boiler load run-back, the load command is lowered at a constant rate to the run-back target load according to the load run-back command. However, in the case of a coal-fired boiler, the coal crusher (mill) has a minimum load, In the run back, the number of operating mills before the start of the run back is large, and if the mill is not stopped, the shared load per mill will be less than the minimum allowable value of the mill. It is necessary to stop one or two mills because the coal output cannot be reduced to the target.

As a specific method of stopping the mill, the mill cut, that is, the burner inlet stop valve at the mill outlet is closed to stop coal output to the furnace, while the coal feeder inlet gate is closed to stop coal supply to the coal feeder, In many cases, the coal feeder is warmed at the lowest speed in preparation for the next restart, and the mill is stopped. In order to prevent the temperature inside the furnace from dropping due to a rapid decrease in fuel, and to prevent other burners during operation from misfiring,
In addition, in order to prevent a drop in the water level of the drum caused by a decrease in subcooled boiling water in the water wall pipe, the mill cut is sequentially performed at least one to two seconds after the start of the run back. 20-25 of input amount
% Has the drawback of fluctuating with a single millcut and requires at least two millcuts, so that it is not very effective in preventing the water level of the drum from lowering.

[Problems to be solved by the invention]

The present invention has been made in view of the above points, and an object thereof is to avoid a sudden decrease in the amount of fuel input due to a mill cut during a load run of a coal-fired boiler, and to inject fuel into a flat ground like a heavy oil-fired boiler. By reducing the volume, disturbance to the drum water level is minimized and the drum water level is prevented from dropping.

[Means for solving the problem]

The above object is achieved by temporarily increasing the fuel supply amount and the primary air supply amount to other mills different from the mill to be milled during a load run.

[Action]

FIG. 3 shows the operation of the process and the controlled variable after the load run back.

After the load run starts, the boiler load command
mm and the mills A and B are subsequently cut. In Fig. 3, as can be seen from the coal output sharing of each mill, the remaining mills that were not cut were adjusted to correct the fuel input to the furnace, which was reduced too much by the A and B mill cuts. Increased, but not enough correction due to delay in mill response. After the improvement according to the present invention, in order to improve the response of the remaining mill immediately after the start of the lambuck, the primary air blowing rate is increased to discharge the pulverized coal held in the remaining mill, and at the same time, the speed of the coal feeder is temporarily reduced. Is to increase.

As a result, it is possible to correct a sudden decrease in fuel at the time of load back and to achieve a smooth and constant decrease in fuel.

(Example of the invention)

FIG. 1 shows a pulverized coal combustion system of a coal-fired boiler in the embodiment. In the figure, 11 is a coal crusher (mill), 12 is a coal feeder, 13 is a coal feeder inlet gate, 14 is pulverized coal, 15 is a burner inlet stop valve, 16 is a primary air preheater, and 17 is a hot air damper , 18 is a cold air damper, 19 is primary air, 20 is a forced draft fan, 21
Is a combustion gas, 22 is a boiler, 23 is a steam pipe, 24 is a combustion equipment management system, 25 is a boiler control system, 26 is a motor, 27
Is a water wall pipe and 28 is a burner.

The coal crusher (mill) 11 has two main systems, that is, the amount of coal supplied from the coal feeder 12 and the flow rate of the primary air 19. The coal supplied to the crushing section of the mill 11 is crushed. Is further dried and conveyed by the flow rate of the primary air 19,
It is coaled to 18.

In addition, the mill 11, the coal feeder 12, and its auxiliary equipment are controlled by a combustion equipment management system 24 and a boiler control system 25.

FIG. 2 shows a control circuit of the boiler control system in the embodiment. In the figure, 1 to 7 are 1 to 7 in FIG.
7 is the same as each means, 8 is a bias addition amount setting device (0 to 100%), 9 is a signal switching switch, 10 is a primary delay generator, 29 is a main steam pressure detector, and 30 is a main steam pressure detection. Value, 31 is a main steam pressure set value, and 32 is a main steam pressure deviation value.

The main steam pressure detection value 30 and the main steam pressure set value 31 from the main steam pressure detector 29 are calculated by the subtractor 3 to be calculated as a main steam pressure deviation value 32. The speed control of the mill 11 and the flow rate of the primary air 19 are performed based on the determined fuel input amount command and the deviation of the total fuel flow rate. The output signal of the switch 9 is switched to the input signal of the primary air flow damper 7 by the adder 2.
The output signal of the switching switch 9 is added by the adder 2 to the input signal of the coal feeder speed controller 6 through the primary delay generator 10.

When the switching switch 9 shown in FIG. 2 is switched to the bias supply setting unit 8 for about 15 seconds during load run, the primary air flow command (input signal of the primary air flow damper 7) flowing into the mill is changed to load run back. It increases temporarily after the start, discharges the pulverized coal held in the remaining mill, and surpasses the urgent need for the shortage of fuel input by the mill cut, while using the primary delay generator 10 for about 5 seconds. The input signal of the coal feeder speed controller, which is increased with a time delay, increases the coal feed while preventing excess feed to the remaining mill.

The shortage of fuel input due to the mill cut peaks at about 15 seconds after the start of the load runback, and the effect on the drum water level is considered to be a major disturbance due to fluctuations within this time. The switching switch 9 is returned to the normal operation side, that is, the bias addition amount is 0%.

By performing such control, it is possible to prevent the water level of the drum from lowering when the load of the boiler is run back.

 FIG. 4 shows another embodiment of the present invention.

This embodiment is an example in which the output signal of the switching switch 9 for switching the bias addition amount by the load back is added by the adder 2 to the common control signal of the coal feeder speed control and the primary air flow rate control.

In this embodiment, the time delay with respect to the coal feeder speed control is not taken into account, but the excess amount of coal supplied to the mill can be adjusted by the bias addition amount setting device 8 and the bias amount can be reduced as necessary. This is effective similarly to the previous embodiment, and has an advantage that the control circuit is particularly simplified.

FIG. 5 shows a pulverized coal transportation distribution system used in the boiler apparatus to which the present invention is applied. In the figure, 41 is a ventilator, 42 is an air preheater, 43 is a pulverized coal machine, 44 is a burner, 45
Is an additional air line, 46 is a flow control valve, 47 is a coal feed pipe, 48 is a ventilator for additional air, 49 is a heater, 50 is an orifice, and 51 is a valve.

The air pressurized by the ventilator 41 is heated by the air preheater 42, and the pulverized coal pulverized by the pulverized coal machine 43 is transported to the burner 44 via the coal pipe 47, but branches at the outlet of the ventilator 41. The air in the additional air line 45 is supplied to the coal pipe through the flow control valve 46.
It is injected into 47 and mixed with the pulverized coal in the coal feed pipe 47.

FIG. 6 shows the pressure loss curve of the coal feed pipes.
Have different pressure loss characteristics depending on the length and arrangement. Accordingly, air from the additional air line 45 is injected by the flow regulating valve 46 so as to balance the pressure loss difference shown in FIG. The branched additional air line 45 passes only clean air.

As a result, the pulverized coal transportation and distribution system can distribute the pulverized pulverized coal evenly and, for example, place the orifice 50 or valves 51 in the coal feed pipe 47 as shown in FIG.
It is possible to prevent the adjustment valve 46 from being worn out by pulverized coal as compared with the case where the control valve is provided.

FIG. 8 shows another pulverized coal transport system. This system takes in additional air as a separate system and has another ventilator 41 or heater 49. Therefore, the conditions of the additional air (flow rate, temperature, etc.) can be freely changed, and in combination with the control system, the amount of air passing through the pulverized coal machine can be increased or decreased while maintaining the pressure balance of the coal feed pipe. And the particle size of the pulverized coal can be adjusted.

〔The invention's effect〕

The present invention is as described above.If the control method of the present invention is used, a prompt back-up can be performed by a residual mill that does not perform a mill cut even when a mill cut is performed during a load run. It is possible to narrow down the fuel as flat as a heavy oil fired boiler at the time of load run, and it is possible to prevent the operation of the boiler in a dangerous state when the drum water level drops during the load run and the boiler is fired empty.

[Brief description of the drawings]

FIG. 1 is a diagram of a pulverized coal combustion system of an embodiment of the present invention, FIG. 2 is a diagram of a boiler control circuit of the embodiment, FIG. 3 is an explanatory diagram of the operation and effect of the present invention, and FIG. Boiler control circuit diagram, FIG. 5 is a system diagram of a pulverized coal transportation and distribution system in the embodiment, FIG. 6 is a diagram showing flow rate and pressure loss characteristics in a coal feed pipe, and FIG. 7 is a system of a conventional coal feed pipe system Fig. 8
The figure is an explanatory diagram of the additional air extraction unit of another pulverized coal transport system,
FIG. 9 is a conventional boiler control circuit diagram. 11 ... Coal crusher, 12 ... Coalizer, 14 ... Pulverized coal, 19 ...
... primary air, 22 ... boiler.

 ──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor Tetsuya Iwase 6-9 Takaracho, Kure City Inside the Kure Factory of Babkotsuk Hitachi, Ltd. (56) References JP-A-59-137701 (JP, A)

Claims (2)

(57) [Claims] A plurality of coal pulverizers are connected to one boiler, and a predetermined number of coal pulverizers are stopped based on a load runback command signal of the boiler, and the remaining coal pulverizers are connected. In addition to increasing the amount of primary air, the amount of coal supplied to the remaining coal crusher is increased for a predetermined time, and after the elapse of the predetermined time, the amount of coal is returned to the amount of primary air and the amount of coal supplied corresponding to the settling load after the load back. The method for controlling the amount of coal supplied to a boiler device. 2. A method for controlling the amount of coal supplied to a boiler apparatus according to claim 1, wherein after increasing the amount of primary air to the coal sanding machine, the amount of coal supplied is increased after a predetermined time. .