JPS59125324A - Combustion control method of coal fired stoker boiler - Google Patents

Abstract

PURPOSE:To prevent the feed of coal lumps from exceeding a requirement quantity for achieving a safe operation, by monitoring the feeding condition of coal lumps and by retaining the feeding quantity of coal lumps and the flow rate of combustion air close to a critical level that an abnormality appears while an abnormal coal feeding condition is present. CONSTITUTION:An ammeter 50 measuring the electric current of the driving mechanism 3 of coal feeder has its output inputted to a coal feeding condition monitoring/verification device 51. The verification device 51 receives to compare input signals of ammeter 50 and driving mechanism 3. When the electric current lowers to a level that it (as the output signal of ammeter 50) no longer corresponds to an input signal, the verification device 51 judges that an abnormality is present to switch an adjuster 12 from an automatic to a manual mode for switching a relay 53 to an analog memory side 52, and retaining the analog memory 52 in a hold mode. Thus, the input signal of driving mechanism 3 of coal feeder is held close to a level that an abnormality appears. In this manner, it has become possible to prevent a great deal of coal lumps from being fed on a grate 7 for thereby maintaining a consistent combustion state.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a combustion control method for a coal-fired stoker boiler.

First, a conventional combustion control method for a coal-fired stoker boiler will be explained with reference to FIG. Coal lumps to be burned are supplied to a hopper 1. The supplied coal lumps reach a coal feeder 2 provided at the bottom of the hopper 1. The coal feeder 2 is driven and operated by a coal feeder drive device 3 and supplies coal lumps to the spreader 4 .

A spreader 4 having spreading blades rotating at high speed is installed at the lower part of the furnace 17 and spreads coal almost uniformly onto a grate 7 which is moved by a grate (firebed) drive device 6 and a drive machine 5. Combustion air is fed into this grate 7 from a wind box 8 located below it. Combustion air is supplied by a ventilator 16, and its flow rate is regulated by a damper 15.

An actively burning coal seam is formed on the grate 7, and the coal seam is moved by the grate 7 from the rear of the furnace (on the side of the grate drive device 6) to the front of the furnace and is disposed of in the ash bit 18.

The high-temperature exhaust gas generated by combustion on the grate 7 gives heat to the foiler 9, where the heat is exchanged and steam is generated, which then reaches the outside of the furnace through a duct 19.

Steam generated in the boiler 9 is supplied to the load-side plant through a steam pipe 10. In this case, the steam flow rate (hereinafter referred to as steam flow rate) sent to the load-side plant (required by the load-side plant) is not constant but constantly changing. For this reason, it is necessary to change the supply amount of coal blocks (coal feed amount) and combustion air supply amount in response to changes in the steam flow rate required by the load-side plant, but it is difficult to do this manually. Since this is very difficult, the following control method is adopted. That is, the steam pressure supplied to the load side (hereinafter referred to as main steam pressure) is detected by the pressure gauge 11 attached to the steam piping 10, and the signal is sent to the controller 12. A correction signal is output to the coal feeder drive device 3 and the ratio calculator 13 so that the value (set value) is achieved. The ratio calculator 13 outputs a value that guarantees the air flow rate necessary for combustion to the drive device 14 that drives the damper 15.

For example, when the steam flow rate tends to decrease, the main steam pressure tends to increase. This pressure increase is detected by the pressure gauge 11 and inputted to the controller 12. In this controller 12, the detection signal and the setting value are compared.

In this case, since the detection signal is larger than the set value, the controller 12 reduces the output signal to correct this. This output signal is input to the coal feeder drive device 3 and the ratio calculator 13 (given to the damper drive device 14 via the ratio calculator 13). Therefore, the rotation of the coal feeder 2 decreases, the amount of coal fed decreases, and the opening degree of the damper also decreases, resulting in a decrease in the combustion air flow rate. Therefore, the combustion is suppressed and the steam generated in the boiler 9 is reduced, and the increase in main steam pressure is suppressed and settles to near the set value.

Conversely, when the steam flow rate tends to increase, the amount of coal feed and the flow rate of nitrogen for combustion increase due to the same effect, combustion is promoted, and the main steam pressure settles around the set value, making it possible to achieve stable operation.

As described above, by the conventional method, stable operation with little variation in main steam pressure can be achieved even when the steam flow rate fluctuates, and even when the steam flow rate is constant. However, when the properties of the supplied coal lumps are good, stable operation as described above can be achieved, but when the grain size and moisture content of the coal lumps are not uniform (if the coal properties are not good, for example, coal is piled up in the open) In cases where the moisture content fluctuates significantly due to changes in the weather during storage, or when the particle size is small, etc.), the main steam pressure fluctuates significantly, impairing various controllability of the load-side plant. The load-side plant is forced to manually intervene, which not only requires labor, but also may force the plant to stop. Furthermore, when a turbine (power generation device) is connected as a load-side plant, there is a risk of damaging the turbine in the worst case.

As mentioned above, the main reason why the steam pressure fluctuates significantly is that even if the rotation speed of the coal feeder 2 is changed (even if the input signal of the coal feeder drive device 3 is changed), the amount of coal fed will change accordingly. By not changing. The cause of this is that the coal properties are not good, so coal adheres to the hopper 1, coal feeder 2, etc.
Due to partial blockage within the coal feeder 2.
This is because the amount of coal feed that is commensurate with the number of rotations is not given.

In addition, when such a partial blockage phenomenon occurs, whether it is left untreated and the partial blockage phenomenon disappears naturally, or if a person notices it and takes action, the phenomenon will not disappear. Due to this generation, the amount of coal fed decreases, so the main steam pressure drops rapidly, and the output of the controller 12 suddenly increases (the number of revolutions of the coal feeder 2 may approach the maximum). If the partial group closure phenomenon disappears in this state, a very large amount of limestone will be supplied, which will cause a disturbance to the combustion control system, and the main steam pressure will fluctuate significantly, impairing stable operation.

In addition, the coal seam on the grate becomes thicker, resulting in insufficient draft and lower combustion efficiency, resulting in the generation of black smoke and clinker.

The present invention has been made in view of the above-mentioned circumstances, and is a combustion control for a coal-fired stoker boiler that eliminates the conventional drawbacks and prevents the output of the controller 12 from increasing during the period when an abnormality occurs. This method provides a control system for a coal-fired stoker boiler that obtains steam by scattering coal lumps on a moving grate and burning them, by manipulating the supply amount of coal lumps and the flow rate of combustion air. A control system that maintains the pressure of steam supplied from the coal-fired stoker boiler to the load side at a predetermined value monitors the supply state of coal lumps, and during a period when an abnormality in the supply state occurs, This is characterized by maintaining the supply amount of combustion air and the flow rate of combustion air near the values before the occurrence of the abnormal condition.

According to the present invention, even if the properties of the coal lumps are poor and the supply status of the coal lumps becomes abnormal, a larger amount of coal lumps than necessary will not be supplied, and fluctuations in the main steam pressure will be less than before. The effect is that stable operation can be achieved without generating black smoke.

A preferred embodiment of the present invention illustrated in FIG. 2 will be described in detail below.

In FIG. 2, elements that are the same as those in FIG. 1 are designated by the same reference numerals (numerals 1 to 19). Reference numbers 50-54
is a new element added to implement the present invention. Reference numeral 50 is an ammeter that measures the current of the coal feeder drive device 3 (motor). The output of this ammeter 50 is sent to a supply state monitoring and determining device 51 (hereinafter referred to as a determining device). The judgment device 51 sends the output to the relay 53 as its drive signal, to the analog memory 52 as its mode (tracking mode/hold mode) switching signal, and to the controller 12 as its mode (automatic/manual) switching signal. do. Further, the determination device 51 outputs an alarm signal to the alarm device 54 so as to notify the operator when the supply state is abnormal.

The determination device 51 receives the input signal of the ammeter 50 and the coal feeder drive device 3, compares them, and determines that the current has decreased and the current (output signal of the ammeter 50) commensurate with the input signal is not obtained. Sometimes, it is determined that the supply status is abnormal, the controller 12 is switched from automatic to manual, and the relay 53 is switched to the analog memory 52.
At the same time, the analog memory 32 is placed in hold mode. Before the analog memory 52 receives a signal indicating that there is an abnormality in the supply state, it is in the tracking mode and follows the output of the controller 12. Therefore, the input signal of the coal feeder drive device 3 is fixed near the value before the supply state abnormality. In addition, since the main steam pressure will drop when an abnormality occurs in the supply state, in order to recover it quickly, the fixed value should be set somewhat higher than the value before the abnormality (for example, 1.1
In other words, when the analog memory 52 tracks the output of the controller 12, the output may be multiplied by 1.1.

Further, the determining device 51 determines that the supply state has become normal due to the recovery of the output of the ammeter 50 once the phenomenon of partial blockage of the coal block has disappeared, and switches the relay 53 to the output side of the controller 12, thereby setting the controller 12 to automatic mode. At the same time, the analog memory 52 is set to tracking mode. As a result, the input signal of the coal feeder drive device 3 is changed by the output signal of the controller 12 with the initial value given and fixed by the analog memory 52, and the combustion control system is changed to the value before the abnormality occurs. Return to control method.

In this way, according to the method of the present invention, the steam flow rate is stabilized,
If an abnormality occurs in the supply state in a stable operating state in which the combustion control system is operating well, the determination device 51 determines that there is an abnormality, and the input signal of the coal feeder drive device 3 is changed during the abnormality period. Since the coal feeder 2 is fixed in rotation speed (the rotational speed of the coal feeder 2 is fixed), there is no need to feed a large amount of coal lumps onto the grate 7 as in the past, and even when the coal lump properties are poor, the main steam This is a coal-fired stoker boiler that maintains stable combustion conditions without significant pressure fluctuations.

Therefore, various controllability of the load-side blunt is facilitated, the labor of the person operating the coal-fired boiler and the load-side plant is reduced, and plant stoppage and damage to the plant can be prevented.

Although the present invention has been described above with reference to embodiments, the present invention is of course not limited to these embodiments.
Modifications to the design of the formations may be made without departing from the spirit of the invention.

[Brief explanation of the drawing]

FIG. 1 is a diagram illustrating a conventional combustion control method for a coal-fired stoker boiler, and FIG. 2 is a diagram illustrating a combustion control method for a coal-fired stoker boiler according to the present invention. 1. Hopper, 2. Coal feeder, 3. Coal feeder drive device,
4. Spreader, 5. Drive machine, 6. Grate drive device, 7. Grate, 8. Wind box, 9. Boiler, 10.
・Steam piping, 11.・Pressure gauge, 12.・Controller, 13.
・Ratio calculator, 14...Drive device, 15...Tanba, 1
6. Ventilator, 17. Furnace, 18. Ash bit, 19
... Duct, 50 ... Ammeter, 51 ... Judgment device, 52
...Analog memory, 53..Relay, 54..Alarm.

Claims (1)

[Claims] Among the control systems for coal-fired stoker boilers that obtain steam by scattering and burning coal lumps on a moving grate,
In a control system that maintains the pressure of steam supplied from the coal-fired stoker boiler to the load side at a predetermined value by manipulating the supply amount of coal lumps and the flow rate of combustion air, monitoring the supply state of coal lumps, Combustion control for a coal-fired stoker boiler, characterized in that during a period when the abnormality in the supply state occurs, the supply amount of coal lumps and the flow rate of combustion air are maintained near the values before the occurrence of the abnormal state. Method.