JP2000102740A - Coal pulverizer device for coal boiler - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress the slip phenomenon of a mill roller by deciding an open timing signal of a water feed quantity control valve and a purge air flow rate control valve corresponding to a coal feed quantity directive signal and deciding a water flow rate set value and a purge air flow rate set value corresponding to the coal feed quantity directive signal. SOLUTION: A water feed line for feeding water to a mill pulverizing part is provided and a water flow valve 41 is mounted in the water feed line. And a purge air line is provided in parallel to the water feed line and a purge air flow control valve 41' is mounted. In a purge air control device, the purge air flow rate set value and the purge air flow control open timing are decided based on the mill coal feed quantity directive signal. Similarly in a water feed control device, the water flow rate set value and the water flow control valve open timing are decided based on the mill coal feed quantity directive signal. As a result, the slip phenomenon is suppressed by scattering the fine powder by the air purge to the mill pulverizing part or decreasing the degree of the dryness of the pulverized coal by feeding water.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a pulverized coal mill, and more particularly to a pulverized coal mill (hereinafter referred to as a "mill"). The present invention relates to a combined air flow control device.

[0002]

2. Description of the Related Art Mill vibration prevention in a conventional pulverized coal machine has been performed by an operator adjusting a set value of a mill outlet temperature without supplying water or purging air to a mill pulverizing section. The reason for this is that the dryness of the pulverized coal in the mill is lowered by lowering the set value of the mill outlet temperature, the frictional relationship between the fine powder on the mill crushing ring and the mill roller is increased, and the slip of the mill roller is reduced. The purpose is to reduce the occurrence of mill vibration due to the phenomenon.

[0003] A mill outlet temperature control method in a conventional pulverized coal machine will be described below with reference to FIG. The mill outlet temperature control includes a hot air damper (see hot air damper 32 in FIG. 4) so as to maintain the mill outlet temperature at a specified value in order to transport combustion air and pulverized coal pulverized by the mill to the combustion equipment.
The cold air damper (see the cold air damper 37 in FIG. 4) is controlled. The mill outlet temperature setting can be arbitrarily set by the mill outlet temperature setting device 1, but at least the signal selector 3 sets the mill outlet temperature. The temperature is set higher than the minimum temperature set by the signal generator 4 so that the temperature does not become lower than the required mill outlet temperature.

[0004] The mill outlet temperature set value produced in this manner is a setting based on static characteristics, and in fact, the mill outlet temperature fluctuates due to an increase or decrease in the amount of coal supplied at the time of a load change, and the output of the mill is reduced. In order to affect the characteristics, to keep the mill outlet temperature constant even during load changes and when extinguishing the coal burner,
Bias 6 during load change and Bias 5 when extinguishing coal burner
Is added to the mill outlet temperature setting by the adder 13, and control is performed through the change rate limiter 7 so that the mill outlet temperature does not suddenly fluctuate.

[0005] In addition, at the start of the mill, there is a phenomenon that the mill outlet temperature temporarily drops due to the initial coal supply to the mill.
Also at the time of starting the mill, the mill starting bias 9 of the temperature setting is added by the adder 8 to make the final setting of the mill outlet temperature.

A deviation between the final setting and the actual temperature detected by the mill outlet temperature detector 10 is created by a subtracter 11, and the controller 12 controls the mill hot air damper 32 and the cold air damper 37 by the controller 12 to eliminate the deviation. are doing. The mill hot air damper 32 and the cold air damper 37 operate in reverse (see the characteristics shown in (2) of FIG. 3). That is, when the detected mill outlet temperature is higher than the set value, the cold air damper 37 operates to increase the opening, and the hot air damper performs the opening decreasing operation to adjust the mill outlet temperature.

[0007] In the current control method, the primary air amount for pulverized coal transport is reduced as the coal supply amount is reduced. However, unless the flow rate of the primary air is higher than a certain level, the combustion gas in the furnace may flow back from the coal burner to the mill through the coal pipe and ignite in the mill (backfire phenomenon). In order to prevent this flashback, it is necessary to secure the primary air amount to a specified value or more. When the mill outlet temperature is constant in a state where the coal supply amount is small, the temperature of the pulverized coal in the mill pulverizing section increases. This is because the mill outlet temperature detector is installed at the mill outlet, and because there is a distance between the mill pulverizing unit and the mill outlet temperature detector, even when the mill outlet temperature is constant and the coal supply is large, The temperature of the pulverizing section decreases, and the temperature of the pulverizing section increases when the amount of coal supplied is small.

Along with this, there is a phenomenon that a dry phenomenon of the pulverized coal in the pulverizing section (between the mill roller and the pulverizing section ring) causes a slip phenomenon of the mill roller, restricts the operation of the mill, and makes it impossible to stably supply the pulverized coal to the combustion equipment. . Further, even if the setting device 1 of the mill outlet temperature is adjusted, it takes time to lower the temperature of the mill crushing section due to the heat retained in the mill main body, so that it has not been a decisive factor in suppressing the mill vibration.

[0009] Such a point has not been considered in the conventional apparatus.

[0010]

In the above prior art, the temperature of the mill outlet is controlled to a constant value, the amount of hot air and the amount of cold air are adjusted without considering the properties of the coal, and the pulverized coal in the mill is adjusted. Attention was not always paid to keeping the degree of drying constant. As described above, when the amount of coal supplied is small, the temperature of the pulverized coal in the mill increases as described above, and the pulverized coal on the crushing unit ring becomes dry. There is a problem that the vibration is lowered and a large vibration is generated due to the slip phenomenon of the mill roller.

At this time, if the number of revolutions of the rotary classifier is increased to improve the classification performance, the pulverized coal in the mill is further atomized, so that the frictional resistance between the pulverized coal on the crushing unit ring and the mill roller decreases. The problem is that the mill easily vibrates due to the slip phenomenon of the mill roller, so that the mill's crushing ability and the classification performance of the pulverized coal cannot be sufficiently exhibited, so that a stable supply of pulverized coal and a stable combustion state cannot be maintained. There was a point.

An object of the present invention is to determine whether to perform water injection or air purging to a mill pulverizing section depending on the properties of coal, to adjust a water supply or purge air flow rate based on a coal feed command signal of the mill and the properties of coal, By adjusting the timing of water injection or the start of purge air, the degree of dryness of the pulverized coal on the mill crushing unit ring is kept constant, so that the friction coefficient between the fine powder on the mill crushing unit ring and the mill roller is increased, and the mill roller slips. It is to perform stable operation of a mill by suppressing the phenomenon.

[0013]

In order to solve the above problems, the present invention mainly employs the following configuration.

In the pulverizer for coal pulverization, there is provided a water injection system path for injecting water into a pulverizing section, and a purge air system path for purging air to the pulverizing section in parallel with the water injection system path.
A water injection flow rate control valve is disposed in the water injection system path, and a purge air flow rate control valve is disposed in the purge air system path, and in response to a coal supply command signal representing the coal supply to the pulverized coal machine, Determine the opening timing signal of the water injection flow control valve and the purge air flow control valve, and determine the water injection flow set value and the purge air flow set value according to the coal supply amount command signal, to a predetermined coal supply amount. In response, one of the water injection flow rate control valve and the purge air flow rate control valve is opened by the opening timing signal, and based on the water injection flow rate set value or the purge air flow rate set value, A pulverized coal machine device which adjusts a water injection flow rate or a purge air flow rate to suppress vibration of the pulverized coal machine due to a slip phenomenon of a mill roller in the pulverizing section.

Further, in the pulverized coal machine, the operation of either the water injection flow control valve or the purge air flow control valve is automatically selected according to the coal properties related to the pulverizability of the coal.

[0016]

FIG. 4 is a system diagram of a pulverized coal combustion facility according to an embodiment of the present invention. In the pulverized coal combustion system, coal as a fuel is supplied from a coal bunker 21 to a coal feeder 22, further supplied to a pulverized coal machine 23 (hereinafter referred to as a mill), and the coal is pulverized by a mill roller 24. The pulverized coal is blown up to the upper part of the mill by the primary air 31 supplied from the primary air duct 25, and the pulverized coal having a large particle size falls by its own weight, is circulated in the mill, and is again pulverized by the rollers.

On the other hand, the pulverized coal having a small particle size reaches the rotary classifier 26, where the particle size is further classified by the rotary classifier. It is supplied to a coal burner 28. Here, the rotation classifier 26 is controlled at a rotation speed corresponding to the mill coal supply command in order to adjust the fine particle size.

The pulverized coal whose particle size has been classified by the rotary classifier 26 is prevented from adhering to the coal pipe 27 when passing through the coal pipe 27 by the primary air supplied from the primary air duct 25. Also, since the air is supplied to the combustion equipment as combustion air, it is necessary to keep the mill outlet temperature at a constant temperature. The mill outlet temperature is controlled to a specified temperature by adjusting the degree of opening of the mill hot air damper 32 and the cold air damper 37.

Further, as a configuration showing the features of the embodiment of the present invention, a water injection system for injecting water into a mill pulverizing section is provided, and a water injection flow rate control valve 41 and a water injection flow meter 42 are installed in the water injection system. A purge air system is provided in parallel, and a purge air flow control valve 41 'and a purge air flow meter 42' are installed.

FIG. 1 shows a purge air control device for a combined use device of a purge air control device and a water injection control device of a mill pulverizing section according to an embodiment of the present invention. The signals of the mill coal feed command 46, the mill outlet temperature 29, and the coal coal type 48 are input, and the purge air prediction circuit 49 'calculates the purge air flow rate set value 50' and the purge air flow rate based on these signals. The control valve opening timing signal 53 'is determined and used as an output signal.

Here, a purge air prediction circuit 49 'is provided.
5 will be described with reference to FIG. 5. The planned purge air amount corresponding to the size of the coal supply command is calculated (input / output relationship having a curve shown in FIG. 5A), and the planned purge air amount is calculated. Correction factor f _T based on mill exit temperature
Determining (FIG relationship shown in (2) of 5) and the correction coefficient due to moisture content coal type f _W (the relationship shown in (2) in FIG. 5) and the purge air flow rate set value 50 by multiplying the '. That is, if the coal supply command is large, the purge air amount is small, and if the mill outlet temperature is higher than the planned temperature, the purge air amount is corrected to be large. The correction is made to be small.

In the purge air prediction circuit 49 ', a valve opening timing signal corresponding to the coal supply command is set, and a correction coefficient f _OT based on the mill outlet temperature and a water-containing coal type are set for the set valve opening timing. _Is multiplied by a correction coefficient f _OW to set a final valve opening timing signal. That is,
When the coal supply command becomes equal to or less than a preset value, the valve opening timing is output. At this time, if the mill outlet temperature is higher than the planned temperature, a correction to increase the set value is performed, and if the coal type has a high moisture content, a correction to decrease the set value is performed. In addition, since the amount of coal in the mill crushing section is small at the beginning and at the start of the mill, the mill vibration due to the slip phenomenon of the mill crushing section is likely to occur. Is set to be provided.

The opening of the purge air flow control valve 41 'is adjusted by the subtractor 43 and the controller 44 so that the purge air flow set value 50' calculated by the purge air prediction circuit 49 'is obtained. The purge air flow 42 'is used as a feedback signal. The automatic-manual switch is shown as 45. Further, an open timing signal 53 'of the purge air flow control valve 41' is created, and the switch 51 is switched.

When the purge air to the mill pulverizing section becomes necessary, the 0% signal from the signal generator 52 is switched from the state in which the purge air flow control valve 41 'is fully closed through the switch 51 to the time of opening. The switch 51 is switched by the signal 53 ′ to switch to the signal from the controller 44. As a result, the amount of purge air in the mill crushing section is set to be suitable for the mill, and the fine powder on the ring of the crushing section is scattered so as not to cause the mill vibration due to the slip phenomenon of the mill crushing section (the fine powder causing the slip phenomenon). Blowing off)
In addition, the particle size of the fine powder having an influence on the flammability can be ensured by increasing the rotation speed of the rotary classifier, so that a stable pulverized coal supply and stable combustion can be achieved.

Next, the water injection control device is shown in FIG. A signal of a mill coal supply command 46, a mill outlet temperature 29, and a coal coal type 48 is input, and a water injection predicting circuit 49 calculates based on these signals to obtain a water injection flow rate set value 50 and a water injection flow control valve opening timing signal. 53 is determined and used as an output signal.

The operation of the water injection predicting circuit 49 is the same as that of FIG. 5 showing the operation of the purge air prediction circuit 49 'except that the purge air flow rate is replaced by the water injection flow rate. In other words, the planned water injection amount corresponding to the size of the coal supply command is calculated (input / output relation having a curve shown in FIG. 5A), and the planned water injection amount is corrected by the mill outlet temperature. The coefficient f _T (FIG. 5
(2) and the correction coefficient f according to the type of coal containing water.
_W (the relationship shown in (2) of FIG. 5) is multiplied to determine the water injection flow rate set value. That is, if the coal supply amount command is large, the water injection amount is small, and if the mill outlet temperature is higher than the planned temperature, the water injection amount is corrected to be large and the coal type having a large amount of water (coal properties differ depending on the coal type) If so, a correction is made to reduce the amount of injected water.

The water injection prediction circuit 49 sets a valve opening timing signal corresponding to the coal supply command, and corrects the set valve opening timing by a correction coefficient f based on the mill outlet temperature.
_The final valve opening timing signal is set by multiplying _OT by the correction coefficient f _OW based on the type of coal containing water. That is, when the coal supply command becomes equal to or less than a preset value, the valve opening timing is output. At this time, if the mill outlet temperature is higher than the planned temperature, a correction is made to increase the set value, and if the mill has a high moisture content, a correction is made to lower the set value. In addition, when the mill is initially started and stopped, the amount of coal in the mill pulverizing unit is small, so that the mill vibration due to the slip phenomenon of the mill pulverizing unit is likely to occur. It is set as follows.

The opening of the water injection flow control valve 41 is adjusted by the subtractor 43 and the controller 44 so that the water injection flow set value 50 calculated by the water injection prediction circuit 49 is obtained. The water injection flow rate 42 is used as a feedback signal. The automatic-manual switch is shown as 45. Further, an opening timing signal 53 of the water injection flow control valve 41 is created, and the switch 51 is switched.

When it is necessary to inject water into the mill pulverizing section, the 0% signal from the signal generator 52 is switched from the state in which the water injection flow control valve 41 is fully closed through the switch 51 to the state of the open timing signal 53. The switch 51 is switched to the signal from the controller 44. As a result, the water injection amount in the mill crushing section is set to be suitable for the mill, and the dryness of the pulverized coal in the crushing section is reduced so as not to cause mill vibration due to the slip phenomenon of the mill crushing section, and the flammability is affected. The fine particle size is secured by increasing the number of revolutions of the rotary classifier, so that stable pulverized coal supply and stable combustion can be achieved.

The manner in which the switch 54 for switching between the input from the signal generator 55 and the input from the controller 44 according to the properties of the coal type in FIGS. 1 and 2 will be described below. In the combined use of the purge air control and the water injection control, the selection of which control device is used is automatically selected according to the properties of the coal type. Coal properties and coal with a large hard group index have good grindability.
Since the coal having a small hard group index has poor pulverizability, a purge air control device is selected. Switching is performed by operating the switch 54 according to the properties of the coal type.

That is, coal having a small hard group index and poor pulverizability uses the purge air of FIG. 1, so that 0% from the signal generator 55 of FIG. 2 is put in, and the water injection valve 41 is fully closed. In addition, since coal having a high hard group index and good crushability uses a water injection system, 0% from the signal generator 55 in FIG. 1 is put in, and the purge air valve 41 'is fully closed.

As described above, according to the embodiment of the present invention, the fine powder on the ring of the mill crushing section is scattered by blowing air to the mill crushing section (blowing out the fine powder causing a slip phenomenon). Alternatively, the degree of dryness of the pulverized coal in the mill can be reduced by injecting water (in a state with a large amount of water), and the frictional resistance between the fine powder on the crushing unit ring in the mill and the mill roller can be kept large. Therefore, the mill vibration due to the slip phenomenon of the mill roller can be suppressed, and the stable operation of the mill can be achieved.

The decision as to whether to use purge air or water injection into the mill pulverizing section is made according to the type of coal coal. In the case of purge air, it is determined according to the coal feed command signal, the type of coal and the temperature at the mill outlet. , Setting the purge air flow rate and adjusting the purge air start timing. In addition, in the case of water injection, by setting the water injection flow rate and adjusting the water injection start timing, the slip phenomenon of the mill crushing section can be avoided, so that the upper limit of the rotation speed of the rotary classifier can be increased. For this reason, it becomes possible to secure the pulverized coal particle size in the same manner as in the past, and stable combustion can be performed.

[0034]

According to the present invention, it is determined whether to supply the purge air or the water injection to the mill pulverizing section. In the case of the purge air control, the setting of the purge air flow rate and the opening timing of the purge air amount control valve are performed. In the case of water injection control, it is possible to optimize the setting of the water injection flow rate and the timing of opening the water injection amount control valve to lower the dryness of the fine powder. In addition, the mill vibration due to the slip phenomenon of the mill roller in the pulverizing section can be suppressed, and at the same time, the pulverized coal can be stably supplied to the combustion equipment, and stable combustion can be realized.

[Brief description of the drawings]

FIG. 1 is a system diagram of a purge air control system for a mill pulverizing unit according to an embodiment of the present invention.

FIG. 2 is a diagram of a water injection control system for a mill pulverizing unit according to the embodiment of the present invention.

FIG. 3 is a diagram of a mill outlet temperature control system in a conventional example.

FIG. 4 is an overall system diagram of a pulverized coal combustion device according to an embodiment of the present invention.

FIG. 5 is a diagram for explaining the operation of a purge air prediction circuit.

[Explanation of symbols]

 24 Mill Roller 26 Rotary Classifier 28 Coal Burner 29 Mill Outlet Temperature Detector 32 Hot Air Damper 37 Cold Air Damper 41 Water Injection Flow Control Valve 41 'Purge Air Flow Control Valve 42 Water Injection Flow Meter 42' Purge Air Flow Meter 43 Subtractor 44 Proportional Integral controller 45 Automatic manual switch 46 Coal feed amount command signal 47 Function generator 48 Coal coal type signal 49 Water injection prediction circuit 49 'Purge air prediction circuit 50 Water injection flow rate set value 50' Purge air prediction circuit 51 Switch 52 Signal generation 53 Injection flow control valve opening timing signal 53 'Purge air flow control valve opening timing signal 54 Switching unit 55 Signal generator

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 4D063 EE03 EE12 GA08 GC12 GC19 GC29 GC32 GD04 GD11 GD15 GD22 4D067 FF04 FF11 FF14 FF16 GA04 GB02

Claims (3)

[Claims] 1. A water injection system path for injecting water into a pulverizing section of a pulverized coal machine for coal pulverization, and a purge air system path for purging air to the pulverizing section in parallel with the water injection system path is provided. A water injection flow control valve, and a purge air flow control valve disposed in the purge air system path, and the water injection flow control valve according to a coal feed command signal indicating the coal feed to the pulverized coal machine. And an open timing signal of the purge air flow control valve is determined, and a water injection flow rate set value and a purge air flow rate set value are determined in accordance with the coal supply amount command signal. Opening one of the water injection flow control valve and the purge air flow control valve by an open timing signal, and injecting the water flow or purging to the pulverizing section based on the water injection flow set value or the purge air flow set value. Adjusting the air flow rate, coal pulverizer and wherein the achieved suppression of coal pulverizer vibration due slip phenomenon of Mirurora of the crushing unit. 2. The pulverized coal machine according to claim 1, wherein an operation selection of one of the water injection flow rate control valve and the purge air flow rate control valve is automatically selected based on a coal property relating to coal pulverizability. A pulverized coal machine device. 3. The pulverized coal machine according to claim 1, wherein an open timing signal of the water injection flow control valve or the purge air flow control valve is provided in accordance with a coal coal type and a mill outlet temperature, respectively. The pulverized coal machine device, wherein the correction is performed and the water injection flow rate set value or the purge air flow rate set value is corrected.