JPS63279018A - Feed coal amount control method for boiler device - Google Patents

Abstract

PURPOSE:To minimize the occurrence of turbulence on a water level in a drum and to prevent lowering of a water level in a drum, by a method wherein, during load run back, the amount of fuel and the amount of primary air fed to other mill different from a mill being mill-cut are temporarily increased. CONSTITUTION:During load run back, a change-over switch 9 is changed over to the bias feed amount setter 8 side for approximate 15sec. A primary air flow rate command flowing to a mill is temporarily increased after the starting of load run back, and pulverized coal held in a remaining mill is discharged. Insufficiency of fuel charge, due to mill cut, is tided over, and meanwhile and the amount of feed coal is increased by means of an input signal from a coal feeder speed regulator to increase with a delay of approximate 5min caused by a primary delay generator 10 as a surplus coal fed to a remaining mill is prevented from occurring. After 15sec. the change-over switch 9 is returned to the normal running side, i.e. 0% bias addition amount. This control enables prevention of lowering of a water level in a drum during load run back of a boiler.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to a method for controlling the amount of coal fed into a boiler device.

In particular, the present invention relates to a control method that prevents the drum water level from decreasing when the boiler load is lowered.

[Conventional technology]

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

Conventionally, during boiler load runback, the load command is lowered to the runback target load at a constant rate by the load runback command, but in the case of coal-fired boiler 2, there is a minimum load on the coal sander (mill). , In a run bank from a high load, the number of mills operating before the start of runback is large (because if the mill is not stopped, the shared load per machine will be less than the minimum allowable value of the mill, and the mill slow Because the coal output of the mill cannot be reduced to the target within the required runback time due to the delay in response, it is necessary to stop one or two mills.

The specific method for stopping the mill is to cut the mill, that is, close the burner inlet stop valve at the mill outlet to stop the coal from going to the furnace, and close the coal feeder inlet gate to stop the supply of coal to the coal feeder. In many cases, the coal feeder is warmed up at the lowest speed in preparation for the next restart, and the mill is stopped. This is to prevent the temperature inside the furnace from dropping due to a sudden decrease in fuel, causing other burners in operation to misfire, and also to prevent the drum water level from dropping due to a decrease in air bubbles in the subcooled boiling water in the ice wall tube. Therefore, mill cuts are performed sequentially with a delay of at least 1 to 2 seconds after the start of runback.
5-chi has the disadvantage that it fluctuates depending on one mill-cut, and the number of mill-cuts required is at least two, so it was not very effective in preventing the drum water level from dropping.

[Problem that the invention seeks to solve]

The present invention has been made in view of the above points, and its purpose is to: avoid a sudden decrease in the amount of fuel input due to mill cut during load runback of a coal-fired boiler; By reducing the amount of fuel input, disturbances to the drum water level can be minimized and a drop in the drum water level can be prevented.

[Means for solving problems]

The above object is achieved by temporarily increasing the fuel supply amount and secondary air supply amount to other mills other than the mill being cut during load runback.

[For production]

FIG. 3 shows the process and control variable operation after load runback.

After the load runback starts, the boiler load command becomes 100%.
Narrows down with /-, and mills A and B are successively cut. In Figure 3, as you can see from the coal production share of each mill, the mill that remained uncut is A.

In an attempt to compensate for the excessive reduction in fuel input to the furnace due to the B mill cut, the amount of coal output is increased, but due to the delay in the response of the mill, the amount of coal output is not sufficient. After the improvement according to the present invention, in order to improve the response of the remaining mill immediately after the start of runback, the amount of primary air blowing is increased to discharge the pulverized coal held in the remaining mill, and at the same time, the coal feeder speed is temporarily reduced. It is intended to increase the

This makes it possible to correct the rapid fuel decrease during load runback and achieve a smooth and constant fuel decrease.

[Embodiments of the invention]

FIG. 1 shows a pulverized coal combustion system of a coal-fired boiler in an example. In the figure, 11 is a coal powder sander (mill), 12 is a coal feeder, 13 is a coal feeder entrance 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 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 tube, and 28 is a burner.

The coal powder sander (mill) 11 has two main systems: the amount of coal fed from the coal feeder 12 and the flow rate of primary air 19. The coal fed to the crushing section of the mill 11 is crushed. It is further dried and conveyed by the flow rate of primary air 19, and then passed through the mill 11.
The coal is discharged from the coal to the burner 18.

Also, Mill 11. The coal feeder 12 and its attached devices are connected to a combustion equipment management system 24 and a boiler control system 25.
controlled by

FIG. 2 shows a control circuit of a boiler control system in an embodiment. During the period, 1 to 7 are the same as 1 to 7 in Fig. 5 described above.
8 is a bias addition amount setter (0
9 is a signal changeover switch, 10 is a primary delay generator, 29 is a main steam pressure detector, 30 is a detected main steam pressure value, 31 is a main steam pressure set value, and 32 is a main steam pressure deviation value. .

The main steam pressure detected value 30 from the main steam pressure detector 29 and the main steam pressure set value 31 are calculated by the subtractor 3 to be calculated as the main steam pressure deviation value 32, and based on this main steam pressure deviation value 32 and the load command. The speed of the mill 11 and the flow rate of the primary air 19 are controlled based on the deviation between the determined fuel input amount command and the total fuel flow rate. When a runback start command is issued, the selector switch 9 changes the bias addition amount for about 15 seconds. The output signal of the changeover switch 9 is added to the input signal of the primary air damper 7 by the adder 2, while the output signal of the changeover switch 9 is added to the input signal of the primary air damper 7 through the primary lag generator 10. The adder 2 adds the signal to the aircraft speed controller 60 input signal.

During load runback, the changeover switch 9 shown in Fig. 82 is switched to the bias supply amount setting device 8 for about 15 seconds, so that the primary air flow rate command (input signal of the negative air flow rate damper 7) flowing into the mill is changed to the load The time increases temporarily after the start of the runback, and while the pulverized coal held in the remaining mill is discharged to overcome the emergency of insufficient fuel input due to mill cut, the time delay is approximately 5 seconds due to the primary delay generator 10. Increase the amount of coal fed without preventing excessive coal feeding to the remaining mill by increasing the input signal of the coal feeder speed regulator.

The shortage of fuel input due to the mill cut peaks approximately 15 seconds after the start of load 2 back-up, and the influence on the drum water level is considered to be mainly due to fluctuations within this time, so the fuel input amount peaks after 15 seconds. returns the selector switch 9 to the normal operation side, that is, the bias addition amount is 0.

By performing such control, it becomes possible to prevent the drum water level from dropping during load runback of the boiler.

Another embodiment of the invention is shown in FIG.

This embodiment is an example in which the adder 2 adds the output signal Bi of the changeover switch 9 which switches the bias addition amount according to the load runback to the common control signal for coal feeder speed control and primary air flow rate control.

In this embodiment, the time delay with respect to the coal feeder speed control is not taken into consideration, but in case of excessive coal feeding to the mill, it is possible to adjust the amount using the bias addition amount setter 8 and reduce the bias amount Bi as necessary. This embodiment is as effective as the previous embodiment, and particularly has the advantage of simplifying the control circuit.

FIG. 5 shows a pulverized coal transport and distribution system used in a boiler apparatus to which the present invention is applied.

In the figure, 41 is a ventilator, 42 is an air preheater, 43 is a pulverizer, 44 is a burner, 45 is an additional air line, 46 is a flow rate adjustment valve, 47 is a coal feed pipe, 48 is an additional air ventilator, 49
50 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 pulverizer 43 is conveyed to the burner 44 via the coal feed pipe 41', but is branched at the outlet of the ventilator 41. The additional air of 2 in. 45 is injected into the coal feed pipe 47 through the flow rate regulating valve 46 and mixed with the pulverized coal in the coal feed pipe 47.

Figure 6 shows the pressure loss curve of the coal conveyance pipes, and each coal conveyance pipe 47
The pressure drop characteristics differ depending on the length and arrangement of each. Therefore, air is injected from the additional air line 45 by the flow rate regulating valve 46 so as to balance the pressure loss difference t shown in FIG. Only clean air passes through the branched additional air line 45.

As a result, the pulverized coal conveying and distribution system can evenly distribute the pulverized pulverized coal and, for example,
Compared to the arrangement in which an orifice 50 or valves 51Y are installed in a coal feed pipe 47 with a diameter of 5 as shown in the figure, abrasion of the regulating valve 46 due to pulverized coal can be prevented.

FIG. 8 shows another pulverized coal conveying system.

This system incorporates additional air as a separate system and has a separate fan 41 or heater 49. Therefore, the conditions of the additional air (flow rate, temperature, etc.) can be changed freely, and in combination with the control system, the air passing through the pulverizer can be controlled while maintaining the pressure balance in the coal feed pipe.
The pulverized coal particle size can be adjusted by increasing or decreasing l.

〔Effect of the invention〕

The present invention is as described above, and if the control method of the present invention is used, prompt backup is possible with the remaining mill that does not perform mill cut even if mill cut v is performed during load runback.
During load runback, it is possible to squeeze the fuel as flat as a heavy oil-fired boiler, and it is possible to prevent the boiler from operating in dangerous conditions such as when the drum water level drops during load runback and the boiler runs dry.

[Brief explanation of drawings]

Figure 1 is a pulverized coal combustion system diagram of an embodiment of the present invention, Figure 2 is a boiler control circuit diagram of the same embodiment, Figures W and 3 are explanatory diagrams of the effects of the present invention, and Figure 4 is another embodiment. Figure 5 is a system diagram of the pulverized coal conveyance distribution system in the example, Figure 6 is a diagram showing the flow rate and pressure loss characteristics in the coal conveyance pipe, and Figure 7 is a diagram of the conventional coal conveyance pipe system. A system diagram, FIG. 8 is an explanatory diagram of an additional air extraction section of another pulverized coal conveyance system, and FIG. 9 is a conventional boiler control circuit diagram. 11... Coal powder and sand machine, 12... Coal feeding machine, 14... Pulverized coal, 19... - next air, 22... ·boiler. Fig. 1 Fig. 2 Fig. 3 Fig. 1 Loading bar

Claims (2)

[Claims] (1) Multiple coal crushers are connected to one boiler device, and the operation of a predetermined number of coal crushers is stopped based on the load runback command signal of the boiler device, and the operation of the remaining coal crushers is It is characterized by increasing the amount of primary air and increasing the amount of coal fed to the remaining coal crusher for a predetermined time, and after the predetermined time has passed, returning to the primary air amount and coal feed amount corresponding to the settled load after load runback. A method for controlling the amount of coal fed into a boiler system. (2) The method for controlling the amount of coal fed into a boiler apparatus according to claim 1, wherein the amount of coal fed is increased after a predetermined time delay after increasing the amount of primary air to the coal powder sander.