JPH04284857A - Roller mill and its operation - Google Patents

Abstract

PURPOSE:To prevent a roller mill from damage of the system and devices thereof or the noise by an extraneous vibration. CONSTITUTION:A roller mill comprises a grinding table 9 rotated by a motor 21 via a speed reducer 22 on a horizontal plane in a lower part of a mill housing 10, a grinding ring 8 whose section is in a U form planted on this table and a grinding roller provided on the grinding ring 8 to rotate with a grinding load, wherein a material is ground between the grinding ring and the grinding roller. In this roller mill, there are controlled a system 36 detecting changes of torque as is fed into the grinding table and at least one factor selected from among the number of rotation of a classifier 3, the angle of grinding blades and the load of grinding roller which are all decided according to the so detected value, thereby preventing the generation of an extraneous vibration without adversely affecting the grinding performance 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 roller mill for pulverizing coal, cement clinker, or raw materials for chemical products, and more particularly to a roller mill capable of suppressing the occurrence of abnormal vibrations and a method of operating the same.

0002

[Prior Art] In coal-fired boilers, low-pollution combustion (low NOx, reduced unburned matter) and rapid load fluctuation operations are implemented.
As a result, pulverizers (mills) are required to be able to operate more flexibly, such as by widening the range of fluctuations in the amount of coal fed.

One type of pulverizer for finely pulverizing lumps such as coal, raw materials for cement, raw materials for new materials, etc. is a vertical type equipped with a pulverizing table that rotates at a low speed and a plurality of pulverizing rollers that rotate on the table. roller mill, which has recently become one of the representative models. A general roller mill will be explained using FIG. 1. This figure is a cross-sectional view of the mill vertically divided along a plane passing through the center axis of the mill. This type of crusher has a crushing table 9 that rotates at low speed in a horizontal plane within a cylindrical casing 10 (referred to as a mill housing).
A plurality of crushing rollers 7 are provided which rotate on their own axis while being pressed onto the crushing table 9 (this pressing force is hereinafter referred to as a crushing load). The crushing table 9 is fixedly driven by a motor 21 via a speed reducer 22 to a vertical shaft 11 that rotates at a low speed. Further, the rotation shaft 6 of the crushing roller 7 is supported by a roller bracket 5 provided on the top of the crushing roller 7. The roller bracket 5 is supported by upper and lower pressurizing frames 26 and 27, which are provided at the upper part and have a spring 33 between them, via a pin 4 called a roller pivot. The crushing load, which is the main factor governing the crushing performance, is determined by the crushing roller 7,
It is applied as the resultant force of the weight of the structural members such as the upper and lower pressurizing frames 26 and 27 and the downward load caused by the tension rod 12 equipped with the hydraulic device 31 for pressurizing the upper pressurizing frame 27 and the foundation mat 15. It will be done.

[0004] The object to be crushed 30 supplied to the center of the crushing table 9 from the supply pipe 29 moves to the outer circumference on the crushing table 9 in a spiral trajectory due to the centrifugal force caused by the rotation of the crushing table 9. The pulverizing ring 8 inserted into the outer peripheral side of the pulverizing table 9 is caught between the surface of the pulverizing race 28, which is a grooved ring on the upper surface of the pulverizing roller 7, and the pulverizing roller 7, and is pulverized. A duct supplies hot air 2 to the base of the mill housing 10.
3 is guided, and this hot air 23 is blown up from an air throat 24 in the gap between the outer circumference of the grinding table 9 and the inner circumference of the mill casing 12. The powder and granules after pulverization rise within the mill housing 10 due to the flow of the hot air 23, and fall from the coarse particles due to gravity. The powder is classified by the classifier 3, and the powder particles having a predetermined particle size or less are sent to the outside of the mill via the product fine powder discharge pipe 1.

In such roller mills, abnormal vibrations occur depending on operating conditions such as the type of coal and the amount of coal fed, causing problems such as damage to structural members and vibration propagation to the surrounding area. FIG. 8 shows the relationship between the coal feeding amount (mill load) and the nondimensional vibration level at representative points of the reducer. Vibrations in a roller mill tend to occur in a low load range when the coal layer in the crushing section is thin. There is also another necessary condition for vibration to occur. In other words, it is necessary to have a high particle size (small particle size). This is caused by increasing the rotation speed of the rotary classifier. With such a low coal layer thickness and high particle size, slippage occurs between the crushing roller 7 and the crushing table 9, which causes abnormal vibrations.

As a countermeasure against such vibrations, the inventors have so far proposed inventions mainly from the perspective of improving the structure of the crushing section, but as a simpler and more practical method, we have proposed a method that monitors the occurrence of vibrations. Adjust operating conditions while
We have been studying methods to control vibration.

[0007]

[Problems to be Solved by the Invention] The above conventional technology does not give sufficient consideration to vibration prevention, and there are problems with the structural reliability of the mill body or the environment around the mill in terms of vibration and noise. . An object of the present invention is to propose a roller mill and a method of operating the same that avoid vibrations without reducing grinding efficiency.

[0008]

[Means for Solving the Problems] In order to achieve the above object, the first invention of the present application provides a grinding table that is powered by a motor through a speed reducer and rotates in a horizontal plane below the inside of a mill housing; A crushing ring attached to the outer circumference of the table and having a groove-shaped crushing race on the top surface, a plurality of crushing rollers that rotate on the crushing race while receiving a vertically downward crushing load, and a rotation axis of the crushing rollers are held. In a roller mill equipped with a roller bracket, a motor,
A roller mill comprising: a device that detects fluctuations in the rotational torque of one or more of a reducer and a grinding table; and a vibration control device that suppresses vibrations of the roller mill based on the detection results of the device. Regarding.

[0009] The second invention rotates the grinding table in a horizontal plane in the lower part of the mill housing by transmitting power by the motor through the reducer, and the grooved ring surface of the grinding race provided on the upper surface of the outer periphery of the grinding table rotates. A plurality of grinding rollers are rotated at the top while applying a load to grind the material to be ground, and the material to be ground that has been ground in the mill is classified by a classifier to separate granules of desired particle size. In the operating method of the roller mill, fluctuations in the rotating torque of the crushing table, the meter that rotates it, or the reducer are detected, and based on this, the rotation speed of the classifier, the angle of the classifier blades,
The present invention relates to a method of operating a roller mill characterized by controlling any of the loads on the crushing rollers.

[0010] The third invention rotates the grinding table in a horizontal plane in the lower part of the mill housing by transmitting power by the motor through the reducer, and the grooved ring surface of the grinding race provided on the upper surface of the outer periphery of the grinding table rotates. A plurality of grinding rollers are rotated at the top while applying a load to grind the material to be ground, and the material to be ground that has been ground in the mill is classified by a classifier to separate granules of desired particle size. In the operating method of a roller mill, the operating conditions of the classifier and/or the load of the grinding roller are controlled by detecting fluctuations in the rotational torque for rotating the grinding table, and the vibration status of the roller mill is detected to control the vibration to a predetermined level. The present invention relates to a method for operating a roller mill, which is characterized by restoring the operating conditions of a classifier and/or the load of a crushing roller to normal operating conditions when a situation occurs.

[0011]

[Operation] The DC (average) component of torque always increases abnormally before mill vibration occurs. Therefore, by monitoring this component, the roller mill and its operating method according to the present invention can predict the occurrence of vibration and immediately change the operating conditions to outside the vibration generation range, thereby avoiding vibration of the mill.

0012

Embodiment The overall configuration of a specific embodiment of the present invention will be explained with reference to FIG.

First, two monitor signals, a motor torque signal and a reduction gear acceleration signal, are used. The torque signal is used by converting the strain due to shaft torsion obtained from the strain gauge 36 attached to the motor output shaft 20 into torque. The easiest way to extract signals from the rotating shaft is to use an FM telemeter. Furthermore, an accelerometer 37 is attached to the reducer casing. These two signals are extended to the central control room and taken into the mill vibration control system, which consists of an amplifier and an arithmetic/processing unit. This device processes this monitor signal, and if it predicts the occurrence of vibration based on the results, it instructs the subsequent mill control device to change the operating conditions to avoid the occurrence of vibration. The calculation/processing of the monitor signal, the determination method, and the specific method of changing the operating conditions will be described later.

In addition to the strain gauge method described above, it is also possible to monitor the torque of the motor shaft 20 by using a current flowing through the motor (commonly referred to as a mill current). The data processing method is exactly the same for both.

When explaining the data processing of this embodiment, FIG.
, a method for processing randomly fluctuating signals will be explained using FIG. FIG. 3 is applied to torque fluctuation processing, and considers a case where a high frequency component is mixed in a slowly rising trend. By applying a bypass filter to such a signal M(t) and removing high frequency components, trend components can be extracted.

Only [Example 1] can be extracted. This trend component (external 1
) is called the DC component or average component.

FIG. 4 shows the details of waveform processing applied to the acceleration waveform of the speed reducer. The strength of the fluctuation of the randomly fluctuating waveform x(t) is the effective value (rms value) shown by the following formula:

[Outside 2] Represented by

[Equation 1] Here, T is the duration of data to be captured at one time, and is a value on the order of several tens of seconds. By gradually shifting the time for performing this capture operation as shown in the upper diagram of FIG. 4, a curve of effective values (outer 2) as shown in the lower diagram of FIG. 4 can be obtained.

FIG. 5 shows the data of the torque DC component (outer 1) and the effective value of the reduction gear acceleration (outer 2) before and after the occurrence of mill vibration, obtained by performing such processing. It should be noted that all of the data shown in FIG. 5 and below are made dimensionless using values under standard operating conditions. The reduction gear acceleration effective value (outer 2) is made dimensionless using the value at the time of vibration occurrence. From this figure, it can be seen that the DC component of torque (outer 1) increases about 2 minutes before the mill vibrations occur. Note that this phenomenon suggests that the rolling state of the crushing roller deteriorates for some reason and the rolling resistance increases before the vibration occurs. From FIG. 5, it can be seen that by monitoring the DC component of torque, the occurrence of vibration can be predicted about two minutes in advance.

The next task is to find a specific method for changing the operating conditions to avoid vibration during these two minutes. FIGS. 6 and 7 show experimental data showing the relationship between mill operating conditions and vibration levels in order to study this point. In FIG. 6, the vibration is reduced by lowering the rotational speed of the rotary classifier while vibration is occurring. FIG. 7 shows a case in which vibration is also reduced by reducing the crushing load. The crushing load can be easily controlled by operating the hydraulic device 31 attached to the tension rod 12. Note that the responsiveness of the vibration level to changes in operating conditions is better in the rotating classifier rotational speed, and the vibration level decreases with a time delay on the order of several seconds. The reason for this is that the vibration is reduced by lowering the rotational speed of the rotary classifier (opening the vanes in the case of a vane classification system), but from past experience, mill vibration is caused by the "low coal layer thickness" and "low coal layer thickness" in the crushing section. It is known that vibrations occur when the two conditions of "high particle size" are satisfied, and it is thought that the above-mentioned driving operation acts in the direction of coarsening the particle size, thereby reducing vibrations.

FIG. 2 shows the flow of a vibration control method devised based on the above-described knowledge regarding the behavior of the DC component of torque and the relationship between operating conditions and vibration levels. First, the torque data Mi(t) is input into the computer, and its DC component (
External 1) Calculate i. By comparing this with the previously processed value (outside 1) i-1, an increment Δ(outside 1)i as the difference between the two is calculated. If the value of △ (outside 1) i is larger than a certain standard value, it is determined that there is a high possibility of vibration occurring, and the generation of vibration is avoided by reducing the rotation speed of the rotary classifier, reducing the crushing load, etc. Change the operating conditions for this purpose. If this condition continues for too long, it will cause a decline in grinding performance, so monitor the effective value (outside 2) k of vibration data xk (t) for 2 to 3 minutes and check if the level is below a certain standard value. If the condition is maintained, the operating conditions are restored.

By repeating the above operations, it is possible to prevent vibrations from occurring without impairing the grinding performance of the mill.

[0021]

[Effects of the Invention] To summarize the effects of the present invention, first, abnormal vibrations can be prevented from occurring without impairing the grinding performance of the mill. As a result, reliability regarding the structural strength of the roller mill is improved. The level of vibration propagation to the surrounding area is reduced, improving the environment regarding vibration and noise. Additionally, it becomes possible to lower the minimum load of the roller mill, making it possible to operate the mill flexibly in response to fluctuations in the boiler load.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing a roller mill equipped with a vibration control device according to the present invention.

FIG. 2 is a control procedure diagram for vibration control in the roller mill according to the present invention.

[Figure 3]

FIG. 4 is a diagram showing a data processing method for the torque of the mill and the acceleration waveform of the reducer for the mill, respectively.

FIG. 5 is a diagram showing the relationship between the DC component of torque and vibration generation.

[Figure 6]

FIG. 7 is a diagram showing the relationship between the rotation speed of a rotary classifier and the vibration level due to mill load.

FIG. 8 is a diagram showing the state of vibration that occurs in the low load range of the mill.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1... Product fine powder discharge pipe, 3... Rotating classifier, 5... Roller bracket, 7... Grinding roller, 8... Grinding ring, 9... Grinding table, 10... Mill housing, 12... Tension rod, 21... Motor, 22... Reduction Machine, 26...Lower pressure frame, 27...Upper pressure frame, 28...Crushing race, 2
9... Supply pipe, 30... Material to be crushed, 31... Hydraulic system, 32...
Crushing load, 36...strain gauge, 37...accelerometer.

Claims (3)

[Claims] 1. A grinding table that is powered by a motor through a speed reducer and rotates in a horizontal plane below the mill housing, and a grinding ring that is attached to the outer circumferential side of the grinding table and has a grooved grinding race on its upper surface. In a roller mill equipped with a plurality of crushing rollers that rotate on a crushing race while receiving a vertically downward crushing load, and a roller bracket that holds the rotating shaft of the crushing rollers, the motor, reducer, and crushing table are A roller mill characterized in that it is provided with a device that detects fluctuations in rotational torque of any one or more of the devices, and a vibration control device that suppresses vibrations of the roller mill based on the detection results of the device. 2. A motor transmits power through a speed reducer to rotate a grinding table in a horizontal plane at the lower part of the mill housing, and a plurality of grinding wheels are formed on the grooved ring surface of a grinding race provided on the upper surface of the outer periphery of the grinding table. Operation of a roller mill in which the material to be crushed is crushed by rotating the crushing rollers while applying a load, and the material to be crushed that has been crushed in the mill is classified by a classifier to separate powder and granules of desired particle size. In this method, fluctuations in the rotating torque of the crushing table, the motor that rotates it, or the reducer are detected, and based on this, the rotation speed of the classifier, the angle of the blades of the classifier, and the load on the crushing roller are adjusted. A method of operating a roller mill characterized by controlling the following: 3. A motor transmits power through a speed reducer to rotate a grinding table in a horizontal plane below the inside of the mill housing, and a plurality of grinding rings are formed on the grooved ring surface of a grinding race provided on the upper surface of the outer circumference of the grinding table. Operation of a roller mill in which the material to be crushed is crushed by rotating the crushing rollers while applying a load, and the material to be crushed that has been crushed in the mill is classified by a classifier to separate powder and granules of desired particle size. In the method, the operating conditions of the classifier and/or the load of the crushing roller are controlled by detecting fluctuations in the rotational torque for rotating the crushing table, and the vibration condition of the roller mill is detected and a predetermined vibration condition is achieved. time, classifier operating conditions and/or
Alternatively, a method of operating a roller mill characterized by restoring the load of the crushing roller to the state during normal operation.