JPH05237412A - Operation of grinding mill for coal firing boiler - Google Patents

Abstract

PURPOSE:To suppress the vibration of a grinding mill and to achieve stable operation of low load by preventing the slip of a grinding roller by increasing the coefficient of friction of coal particles by providing a means suppressing the drying of the surface of coal and operating said means when the vibration of the grinding mill is generated. CONSTITUTION:A vertical mill 1 for a coal firing boiler grinds and classifies coal to supply the ground coal to a boiler along with air from a coal feed pipe 19 through a burner. A coal supply system 100, an air supply system 200 and a control system 300 controlling an amount of coal, an amount of air and air temp. to regulate the supply amount of powdered coal to the burner and air temp. are provided to the vertical mill. In this case, the respective opening degrees of a cold air damper 81 and a hot air damper 82 are respectively controlled on the basis of the detection signal of the vibrometer 32 provided to the upper surface of a gear box 12 and the detection signal of the thermometer 36 provided to the outlet of the mill by the control system 300 through damper control drivers 42, 43. The primary air temp. at the inlet of the mill is changed to control the air temp. at the outlet of the mill.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a pulverizing mill for pulverizing, drying and classifying coal in a coal-fired boiler, and more particularly to a method of operating a pulverizing mill for a coal-fired boiler suitable for reducing vibration of the mill. ..

[0002]

2. Description of the Related Art A vertical roller mill is used, for example, in a pulverized coal producing apparatus for a coal-fired boiler that uses pulverized coal as a fuel. Coal-fired thermal power plants have also been required to operate an intermediate load to adjust the supply and demand of electric power. In addition, a wide variety of coal is commonly used in coal-fired power plants in Japan.

FIG. 2 shows a schematic system diagram of a coal-fired boiler.
Secondary air for burning coal is sent from the forced draft fan 50 to the boiler 70 via the air preheater 60. On the other hand, the primary air for carrying coal mixes hot air that has passed through the air preheater 60 from the forced draft fan 50 and cold air from the forced draft fan 80, and is usually adjusted to a temperature of around 250 ° C., It is sent to the vertical roller mill 1. The primary air temperature is adjusted by controlling the opening degree of the cold air damper 81 and the hot air damper 82, and the primary air amount is adjusted by controlling the opening degree of the primary air damper 83. The coal pulverized in the vertical roller mill 1 becomes pulverized coal and is sent to the boiler 70 through the burner with the primary air and burned.

Next, a conventional rigid mill system will be described with reference to FIG. A vertical roller mill system for a coal-fired boiler includes a coal supply system 100 for a vertical roller mill,
A vertical roller mill 1 for crushing coal, an air supply system 200 for the vertical roller mill, the amount of coal supplied to the vertical roller mill, the amount of air, and the air temperature are drive-controlled to supply the pulverized coal to the burner and the air. It is mainly composed of a control system 400 for adjusting the temperature.

The coal supply system 100 includes a coal bunker 2 and
It comprises a coal feeder 3 for supplying coal from the coal bunker 2 to the vertical roller mill 1.

The vertical roller mill 1 is provided with a crushing section consisting of a crushing table 4 and a crushing roller 5 in the lower part, and a classifier 22 for separating coarse powder in the upper part. Coal from the coal bunker 2 is supplied from the coal feeder 3 through the coal feeding pipe 7 located at the center of the vertical roller mill 1 onto the rotary table 4, and the coal amount is the belt conveyor 8 of the coal feeder 3. It is controlled by adjusting the rotation speed of the motor 9 by the motor 9.

On the other hand, air is introduced into the vertical roller mill 1 from the air duct 83a through the annular throat 11 at the bottom of the vertical roller mill 1, and the amount of air is adjusted by adjusting the opening of the primary air damper 83. Controlled. The air temperature at the mill outlet is always controlled to a constant temperature by adjusting the opening degree of the cold air damper and the hot air damper 82 to adjust the primary air temperature at the mill inlet.

In the figure, 33 is a rotation detector, 34 is a load cell, 36 is a thermometer, 37 is a calculator, 38 is a differential pressure detector, 41-43 are damper control drives, and 84.
Is an air flow meter.

The vertical roller mill 1 will be described with reference to FIG.
At the bottom of the vertical roller mill 1, there is a disk-shaped crushing table 4, and the crushing table 4 is connected to a gear box 12. The crushing table 4 is configured to rotate at several tens of rpm via a gear (not shown) in a gear box 12 that is rotationally driven by a motor 9.

On the outer periphery of the upper surface of the crushing table 4, an annular crushing ring 14 having a concave upper surface is fixed.
A plurality of crushing rollers 5 are in contact with the upper surface of the crushing ring 14 while being pressed by the pressure frame 15 on the upper side, and a rotational force is applied by the crushing ring 14 via the object to be crushed. The pressure applied to the pressure frame 15 is adjusted by the pressure cylinder 18 via the spring 16 and the spring frame 17. The crushing table 4, the crushing ring 14, and the crushing roller 5 constitute a crushing unit.

An object to be crushed such as coal is introduced between the crushing ring 14 and the crushing roller 5 and crushed to be crushed into powder. A coal feeding pipe 7 is provided above the center of the crushing unit, and the powder particles crushed around this are sorted according to their size,
A classifier 22 is provided for transferring particles having a predetermined particle size or less to the burner and returning particles having a particle size not reaching the predetermined particle size to the crushing section. Above the classifier 22, there is provided a coal feeding pipe 19 for transferring the finely divided particles to the burner of the boiler. The crushing unit and the classifier 22 are housed in the cylindrical housing 20, and the space between the inner wall of the housing 20 and the outer peripheral surface of the crushing unit and the outer peripheral surface of the classifier 22 is formed by crushing the pulverized powder particles by air. It forms the flow path to be transferred.

The hot air B for transfer is supplied from a throat ring 11 which is an annular flow path formed by the outer periphery of the crushing table 4 and the inner wall of the housing 20. In the figure, A is coal and C is a mixed fluid of pulverized coal and air.

Next, the operation will be described. Coal having a size of 40 mm or less, which normally contains about 8% of attached moisture through the coal feeding pipe 7, passes through the gap between the crushing ring 14 and the roller 5 due to the centrifugal force generated by the rotation of the crushing table 4. In the meantime, it is pulverized into pulverized coal and blown upward by the hot air B supplied through the throat ring 11.

Coarse particles of the coal particles blown upward are separated from the air stream and returned to the crushing table 4 again (primary classification). Further, the particles having a small particle diameter rise along the housing 20 along with the air and reach the classifier 22. In the classifier 22, the rotary blade 21 exerts a centrifugal force to separate coarse powder. On the other hand, the fine particles that receive only a small centrifugal force pass through between the rotary blades 21 and flow into the inside of the classifier 22, and are discharged to the outside of the system together with air without being separated (secondary classification). The coarse powder falls under its own weight and is crushed again.

The coal thus fed into the vertical roller mill circulates in the mill several times until it reaches a predetermined particle size,
Further, after being subjected to a drying action by the hot air B, it is taken out of the system as a product.

The amount of coal circulating in the mill, that is, the amount of coal passing through the crushing section composed of the crushing table 4, the crushing ring 14, the crushing roller 5, etc., varies depending on the particle size of the product, etc. It is less than 10 times, and about half of them are returned in the primary classification. Further, the outlet air temperature of the mill does not depend on the load factor of the mill and is always kept constant.

In a coal-fired boiler, about 6 vertical roller mills are usually installed, and the mill is also operated under a low load when the boiler is operated under a low load. When the load of the mill is low, the amount of coal that passes through the crushing unit may be less than twice the amount of product. In such a case, the crushing ring 14 and the crushing roller 5
The thickness of the charcoal layer formed between and becomes extremely thin compared to during high load operation, and at the same time, the particle size of the pulverized particles forming the charcoal layer also becomes finer. Generally, when the coal bed becomes thin and the particle size becomes fine, the crushing roller 5 becomes slippery on the coal bed.

Excessive vibration may occur due to the sliding of the roller 5. The slippage of the roller 5 is due to the coefficient of friction of the crushed particles and therefore depends on the coal species used. Therefore, depending on the type of coal, excessive vibration may occur at a mill load of 50%, and stable operation may occur at a mill load of 10%.

A method of reducing the crushing load (external load) as a method of suppressing excessive vibration under low load (Japanese Patent Laid-Open No. Sho 5)
7-87855), a method of lowering the rotation speed of the mill (JP-A-62-19253), and the like. However, these methods have a drawback in that the load and the variation range of the rotational speed must be large in order to solve the problem completely, which causes a large increase in the cost of the apparatus.

[0020]

When a coal-fired boiler is used as an intermediate-load operation thermal power for adjusting the supply and demand of electric power, the mill may cause excessive vibration when the load is low, depending on the type of coal used. The vibration of this mill has been an obstacle to cutting down the minimum load of the boiler as much as oil-fired power. For this reason, there is a drawback that it is not possible to meet the requirements for using various types of coal in a coal-fired boiler due to the fuel situation in Japan.

An object of the present invention is to eliminate the drawbacks of the prior art and to provide a rigid mill capable of effectively suppressing excessive vibration.

[0022]

Means for Solving the Problems The above object is to provide a coal surface drying suppressing means such as a temperature control means or a humidifying means for drying / conveying air, for example, when a load of vibration such as a boiler load or a vibration of a mill occurs. This is achieved by operating the coal surface drying suppressing means.

[0023]

By lowering the outlet air temperature of the mill when the load is low (for example, 30 to 50%), the drying of coal in the mill is suppressed, and the crushed particles passing through the crushing section are given a slight amount of moist air, so that the crushing ring It is possible to increase the friction coefficient of the coal layer, that is, the crushed particles formed between the crushing roller and the crushing roller, and prevent the crushing roller from slipping on the coal layer. By supplying water from a water supply facility provided in a coal bunker or a coal feeding pipe, the crushed particles can be slightly moistened, and similarly, the crushing roller can be prevented from slipping on the coal bed.

As described above, when the coal-fired boiler is used as an intermediate-load operation thermal power for adjusting power supply and demand, the minimum load of the boiler can be cut down as much as an oil-fired thermal power, and various types of coal can be used in the coal-fired boiler. Can meet the demands used in.

[0025]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 shows a schematic system diagram of a vertical roller mill system of a coal-fired thermal power plant for carrying out the present invention. The same parts as the conventional ones are designated by the same reference numerals.

The vertical roller mill system for a coal-fired boiler has a coal supply system 100 for the vertical roller mill 1 and a coal feeding pipe 19 for feeding pulverized coal together with air after crushing and classifying coal.
A vertical roller mill 1 to be supplied to the boiler via a burner (not shown), an air supply system 200 to the vertical roller mill 1, and a coal amount, an air amount, and an air temperature supplied to the vertical roller mill are drive-controlled. And a control system 300 for adjusting the pulverized coal supply amount to the burner and the air temperature.

The coal supply system 100 includes a coal bunker 2 and
It comprises a coal feeder 3 for supplying coal from the coal bunker 2 to the vertical roller mill 1. A water supply facility 31 is provided in the coal bunker 2.

The vertical roller mill 1 is provided with a crushing unit composed of a crushing table 4 and a crushing roller 5 at the lower part, and a classifier 22 at the upper part for separating coarse powder, and further the gear box 1
A vibrometer 32 is attached to the upper surface of 2. Coal from the coal bunker 2 is supplied from the coal feeder 3 through the coal feeding pipe 7 located at the center of the vertical roller mill 1 onto the rotary table 4, and the coal amount is the belt conveyor 8 of the coal feeder 3. It is controlled by adjusting the rotation speed of the motor 9 by the motor 9.

On the other hand, the air supply system 200 includes a cold air duct 81a, a hot air duct 82a, and a primary air duct 8
3a, a cold air damper 81, a hot air damper 82, a primary air damper 83, and an air flow meter 84.

The primary air is introduced into the vertical roller mill 1 through an annular throat ring 11 located below the vertical roller mill 1, and the amount of air is controlled by adjusting the opening of the primary air damper 83. The air temperature at the mill outlet is controlled by adjusting the openings of the cold air damper 81 and the hot air damper 82 and changing the mill inlet air temperature.

Further, the control system 300 takes in information on the amount of coal supplied by the coal feeder 3, the amount of air, the vibration level of the mill, and the air temperature at the mill outlet, and responds to the demand for load reduction of the boiler by means of a vertical roller mill. 1 can be controlled to stably achieve the low load operation of the vertical roller mill 1.

Now, the vertical roller mill system will be described in more detail. The coal feeder 3 includes a rotation detector 33 that detects the speed of the belt conveyor 8 and a load cell 34 that measures the weight of coal on the belt conveyor 8.
The coal from the coal bunker 2 can be supplied to the vertical roller mill 1. The vertical roller mill 1 usually has three crushing rollers 5 therein, and these crushing rollers 5 are rotatably supported by a fixed shaft (not shown). The gear reduces the rotational force of the drive motor 13 and transmits it to the rotary table 4.

A vibrometer 32 is attached to the upper surface of the gear box 12, and a thermometer 36 is attached to the outlet of the mill. The value of the vibrometer and the value of the thermometer are sent to the control system 300 as signals. ..

A primary air duct 83a is connected to the bottom of the vertical roller mill 1 and further upstream of this, an air preheater 6 is provided.
Hot air duct 82a and air preheater 60 connected from the 0 outlet
The cold air duct 81a continuous from the inlet joins.
A primary air damper 83, an air flow meter 84, and a damper control drive 41 that drives the primary air damper 83 are provided in the primary air duct 83a, and a hot air damper 82 and a hot air damper 82 are provided in the hot air duct. A damper control drive 42 for driving the cold air duct 8
An air supply unit including a cold air damper 81 and a damper control drive 43 that drives the cold air damper 81 is provided in the la 1a.

The cold air damper 8 is controlled by the damper control drives 42 and 43 in response to a signal from the control system 300.
1 and the hot air damper 82 are adjusted to change the primary air temperature at the mill inlet and control the air temperature at the mill outlet.

The coal bunker 2 has a water supply pipe 51 and a control valve 5
2 is provided, and the control valve 52 is opened or closed by a signal from the control system 300 to adjust the water content of the coal supplied into the mill.

By the way, the conventional coal-fired power plant is
It has become commonplace to operate at a low load of 50% or less due to the requirement for intermediate load operation. However, in a coal-fired thermal power plant of Japan that uses a wide variety of coal, the generation of excessive vibration at low load of the mill becomes a major obstacle to stable operation due to the type of coal, and it is not possible to meet the demand for intermediate load operation.

The occurrence of excessive vibration under a low load of the mill is caused by the crushing roller sliding on the coal layer formed on the crushing ring, and is often observed when the coal layer is thin and the particle size of the crushing part is small. And is related to the coefficient of friction of coal particles. Therefore, depending on the type of coal, even if the mill load is 10%, stable operation can be performed without generating vibration. Generally, the outlet air temperature of the mill is controlled at a constant temperature of 65 to 80 ° C. Now, when excessive vibration occurs, the amount of water adhering to the surface of the coal particles in the crushing section is increased by only lowering the mill outlet air temperature by only a few degrees Celsius, and the friction coefficient of the coal particles is increased to cause the crushing roller 5 to slide. Can be prevented. Generally, when the temperature is 60 ° C. or lower, particularly 55 ° C. or lower, the dew point of water becomes in the mill or in the coal feeding pipe, water condenses, and pulverized coal adheres to the wall surface or the pipe inner surface. It is desirable to maintain the temperature of.

Further, the cold air damper 81 and the hot air damper 8
If the vibration cannot be prevented by adjusting 2 to lower the mill outlet air temperature, the control system 300 opens the control valve 52 of the water supply equipment 31 provided in the coal bunker 1 by the signal of the occurrence of excessive vibration to supply water. By supplying water from the pipe 51 and adjusting the water content of the coal supplied into the mill, the amount of water adhering to the surface of the coal particles in the crushing section is increased, and the friction coefficient of the coal particles is increased to increase the crushing roller 5 Prevent slipping. Also in this case, it is desirable to normally keep the mill outlet air temperature at a temperature of 60 ° C. or higher.

[0041] Normally, to increase the moisture on the coal particle surface of the grinding unit at a high load of the mill from a high efficiency low NO plane of _X operation of the boiler, the coarse particle size of pulverized coal produced in the mill This is not preferable, but at a low load as in the present invention, the pulverizing ability of the mill is sufficient, so that the particle size of pulverized coal does not become coarse.

The method for detecting stable vibration and achieving stable operation of the mill under low load has been described above. However, the temperature of the air supplied to the mill during low load of 50% or less of the mill in the control system 300 in advance. It is also possible to prevent excessive vibration at a low load by incorporating a program for adjusting the temperature of the mill outlet and lowering the air temperature at the mill outlet by a certain constant temperature from that during high load operation. Furthermore, when the control system 300 has a low load of 50% or less of the mill, the air temperature at the outlet of the mill is lowered by a certain temperature from the high load operation, and the coal bunker 1
Even if a program that operates by supplying a fixed amount of water from the water supply facility provided inside is incorporated, excessive vibration at a low load can be similarly prevented.

In the above-described embodiment, the vibration generation load is determined by detecting the vibration of the mill or the load signal, but the vibration generation load may be detected by detecting the thickness of the coal bed, for example.

Although water was added to the coal in the above-mentioned embodiment, it may be moistened with the drying / conveying air of the mill.

[0045]

According to the present invention, when vibration of the crushing mill occurs or when the load of the mill is low, the outlet air temperature of the mill is lowered and water is supplied from the coal bunker to increase the friction coefficient of the coal particles in the crushing section. Since the crushing rollers can be prevented from slipping, a low load stable operation of the mill can be achieved for a wide variety of coals, and the minimum load of the coal-fired boiler can be greatly reduced.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram of a vertical roller mill system of a coal-fired boiler plant according to an embodiment of the present invention.

FIG. 2 is a schematic system diagram of a coal-fired boiler.

FIG. 3 is a schematic configuration diagram of a vertical roller mill system of a conventional coal-fired boiler plant.

FIG. 4 is a schematic view of a vertical roller mill.

[Explanation of symbols]

 1 Vertical roller mill 31 Water supply equipment 32 Vibration meter 36 Thermometer 70 Boiler 81 Cold air damper 82 Hot air damper

Front page continued (72) Inventor Tadashi Hasegawa 3-36 Takaracho, Kure-shi, Hiroshima Babkotuku Hitachi Co., Ltd. Kure Factory (72) Inventor Terumaki Tatema 3-36 Takaracho, Kure-shi, Hiroshima Babkotuku Hitachi Kure Factory (72) Inventor Yoshinori Taoka, No. 36, Takaracho, Kure City, Hiroshima Prefecture, Kaba Factory, Kure Factory (72) Hiroaki Kanemoto, No. 36, Takaramachi, Kure City, Hiroshima Prefecture

Claims (1)

[Claims] 1. A method for operating a pulverization mill for a coal-fired boiler, characterized in that means for suppressing coal surface drying is provided, and the means for suppressing coal surface drying is activated when a vibration is generated.