JPH0626677B2 - Vertical roll mill operation control method - Google Patents

Description

TECHNICAL FIELD The present invention relates to an operation control method for a vertical roller mill used in the ceramic industry such as the cement industry or the steel industry.

[Prior Art] FIG. 2 is a schematic system diagram of a typical conventional vertical roller mill. An object to be ground (hereinafter referred to as a new feed) 1 supplied to a roller mill is thrown into a central portion of a grinding table 4 which is rotated around a vertical axis by a drive motor 3 through a material supply pipe 2 to be ground and ground by a centrifugal force. It is blown on the table 4 in the radial direction, and is crushed by being caught between the crushing table 4 and a plurality of crushing rollers 5 arranged on the circumference of the crushing table 4. The pulverized pulverized product is blown into the mill from below the outer periphery of the pulverizing table 4 by a gas flow 6
The particles are subjected to a classification action by and are divided into coarse particles and relatively fine particles. The coarse particles fall downward against the gas flow 6 and are carried upward as a stone discharge 7 by a belt conveyor or a bucket elevator to be combined with the new feed 1 and again as an object to be crushed, at the center of the crushing table 4 Be thrown into. On the other hand, the relatively fine particles are carried together with the gas flow 6 to the air separator 8 which is located on the crushing table 4 and rotates around the vertical axis, and undergoes the second classification action there.
The fine particles that have passed through the air separator 8 are sucked by the suction fan 27 and collected as the product 10 by the downstream bag filter 9. The particles that cannot pass through the air separator 8 and are separated fall into the lower part of the mill and are guided again onto the grinding table 4 so as to be ground.

In such a vertical roller mill, conventionally, a control method has been adopted in which the new feed amount is automatically adjusted so that the differential pressure at the mill entrance and exit (hereinafter referred to as mill differential pressure) becomes a predetermined value (mill. Differential pressure constant value control method). Further, in order to maintain the particle size (average diameter or specific surface area) of the product at a certain level, the particle size of the sample of the product is measured at certain time intervals, and the air separator 8 is adjusted according to the deviation from the target. The operator manually changes the set value of the rotational speed or the flow rate of the gas flow flowing in the mill (hereinafter referred to as the mill airflow).

[Problems to be Solved by the Invention] Normally, the differential pressure of a mill increases as the amount of raw material staying in the vertical roller mill and the amount of discharged stone increase, and decreases when the amount decreases. In the control method of the vertical roller mill described above, when the pulverizability of the new feed changes, for example, when it becomes difficult to pulverize, the following response is given. Since the particles become coarser as a whole, the amount of accumulated raw materials in the mill floating in the vertical roller mill or existing on the crushing table and the amount of discharged stones increase, and as a result, the differential pressure of the mill increases, which is predetermined. The new feed amount will decrease automatically if it deviates from the set value. The particle size of the pulverized product, which has increased due to the decrease in the new feed amount, becomes finer again, and the raw material retention amount in the mill also returns to the previous state. When the pulverizability of the new feed is improved, the reverse operation is performed.

The control method in the conventional control method certainly agrees with the stabilization direction of the mill. However, the mill differential pressure constant value control in which the pulverized state in the mill is represented by only the mill differential pressure and is controlled by one operation variable of the new feed amount has the following problems.

(1) The mill differential pressure as a controlled variable has poor responsiveness to the new feed amount, which is an operation variable, and even if the pulverization state in the mill changes, the change does not affect the amount of discharged stones or the amount of retention in the mill. Since the mill differential pressure is transmitted through the change, the mill differential pressure constant value control becomes a delayed control with a very dead time.

(2) The mill differential pressure is less preferable as a controlled variable from the viewpoint of sensitivity, because the fluctuation of the differential pressure due to the magnitude of disturbance is small.

(3) As described above, the mill differential pressure is a controlled variable that is the only representative of the pulverization state of the entire vertical roller mill, which has poor responsiveness and sensitivity. Therefore, the stability is required and the mill differential pressure is set small. Then, the new feed amount falls into over-action, which tends to cause a change in the operating condition.

(4) The standard of the mill operation is the particle size of the product, and constant mill differential pressure control does not always keep the product particle size constant.
Vibration and layer thickness generated from the mill are far superior as variables representative of product grain size. Also, the influence of the new feed amount on the product particle size is small, and even if the mill differential pressure is kept constant by the operation of the new feed amount, the product particle size is not always controlled within a certain standard range. . In fact, in the actual vertical roller mill, although the mill differential pressure control is performed, the particle size of the sampled and analyzed product varies. Therefore, in order to prevent the product grain size from deviating from a predetermined control value, the operator often manually adjusts the set values of the air separator rotation speed and the mill air flow rate. In addition, this change of the set value of the mill air flow directly affects the mill differential pressure and becomes a disturbance factor.Therefore, in order to prevent the product grain size from deviating from a certain reference range, remove the mill differential pressure constant value control It is necessary to switch the feed amount to manual or automatic constant value control.

(5) It is impossible to always maintain the operating state at the optimum control level that minimizes the power consumption of the mill by the constant value control of the mill differential pressure. The controlled variable mill differential pressure has a slow response, and since it is controlled by one manipulated variable, it is inevitable that there is an overshoot as seen in the above-mentioned overaction, and the operation is at a point deviated from the optimum operating point.

[Means for Solving Problems] It was stated above that all the problems of the conventional control method are caused by the fact that the mill differential pressure is not suitable as a controlled variable. Therefore, these problems can be solved by using, as the controlled variable, a variable having excellent responsiveness and controllability and which is representative of the product grain size. As a result of the investigation on the actual vertical roller mill, the vibration which is one of the controlled variables is
It has been found that the crushed state of the material crushed by the crushing roller and the crushing table represents the crushed state, and the other one, the layer thickness, represents the new feed amount. Therefore, from the relationship between these three variables, the new feed amount, the mill air flow, and the compression force of the crushing roller, which have a strong relationship with the two controlled variables of the vibration and the layer thickness, the values of the vibration and the layer thickness are changed every moment. The operation amount of the operation variable is calculated, and the operation amount is changed to stabilize the roller mill operation.

[Operation] Appropriate operation values of the new feed amount, mill air amount, and crushing roller compression force are automatically integrated based on the vibration and layer thickness information that is corrected moment by moment. By using the operation value for operation, the fluctuation of the mill can be quickly suppressed.

[Example] Application of the control method of the present invention to cement clinker grinding 1
An embodiment is shown in FIG. 1 and the details will be described below.

The cement clinker as the new feed 1 is thrown into the center of the crushing table 4 which is rotated around the vertical axis by the driving motor 3 through the crushed object supply pipe 2, and is blown in the radial direction on the crushing table 4 by the centrifugal force. It is bitten between the crushing table 4 and the crushing roller 5 and crushed.
The pulverized pulverized material is subjected to classification by the gas flow 6 blown into the mill from below the outer peripheral portion of the pulverization table 4, and is divided into coarse particles and relatively fine particles. The coarse particles fall downward against the gas flow 6, are carried upward as a stone discharge 7 by a belt conveyor or a bucket elevator, and are combined with the new feed 1 to be thrown into the center of the pulverizing table 4 again as an object to be pulverized. To be done. On the other hand, the relatively fine particles are carried together with the gas flow 6 to the air separator 8 which is located on the crushing table 4 and rotates around the vertical axis, and undergoes the second classification action there. The fine particles that have passed through the air separator 8 are sucked by a suction fan 27 and collected as a product 10 by a bag filter 9 located downstream. The particles which cannot pass through the air separator 8 and are separated fall to the lower part of the mill and are introduced again onto the crushing table 4 so as to be crushed.

In order to carry out the present invention in such a vertical roller mill grinding system, first, a vibrometer 11 is provided on the mill body, and a layer thickness meter 13 is provided on the arm 12 of the milling roller and the mill body.
However, the new feed supply device 14 has a weighing device 15,
The crushing roller tension pressure adjusting unit 16 includes a tension pressure gauge 17
However, the air volume measuring device 1 is installed in the bag filter outlet duct 18.
9. A damper opening adjustment device 20 is installed. The signal detected by the vibrometer 11 is filtered by the filter 21.
Unnecessary frequency components are removed and sent to the controller 26. Similarly, the signal from the layer thickness gauge 13, the signal from the metering device 15, the signal from the tension pressure gauge 17, and the signal from the mill air flow measuring device 19 are also respectively filtered.
It is sent to the controller 26 through 2, 23, 24 and 25. Based on these five signals, the operation amounts of the new feed amount, the crushing roller tension pressure, and the mill air amount are calculated in the controller 26 by a predetermined calculation formula, and the new feed supply device 14 and the tension are controlled according to the calculated values. The pressure adjusting unit 16 and the damper opening adjusting device 20 for adjusting the mill air flow rate are automatically controlled.

In such a vertical roller mill crushing system, when the new feed amount of the crushed object, which is an operation variable, is increased, the layer thickness of the crushed object is increased and the mill vibration is reduced. When the amount of mill air flow, which is another operation variable, is increased, the layer thickness of the object to be crushed is reduced, and the mill vibration is reduced. When the roller tension pressure, which is another operation variable, is increased, the layer thickness of the object to be crushed is reduced, and the mill vibration is increased.

The reason for this will be described in detail. When the new feed amount is increased, the layer thickness of the material to be ground on the grinding table 4 is increased, and the grinding roller 5 pressing down the material to be ground is lifted and tends to rise. However, since the crushed object layer between the crushing roller 5 and the crushing table 4 becomes thick, the crushed object serves as a cushion, and the vibration of the mill decreases and decreases.

When the amount of new feed is decreased, the layer thickness and mill vibration move in the opposite direction.

When the flow rate through the mill is increased, among the raw material powders passing through the air separator 8, the raw material powders collected by the air separator 8 (particles separated without being able to pass through the air separator 8) lose to the wind speed. The amount of the raw material powder flowing to the mill discharge port without going to the lower crushing table 4 and falling on the crushing table 4 of the mill is reduced. Therefore, the amount of powder on the crushed object on the crushing table 4 is reduced,
By reducing the layer thickness of the crushed powder and further reducing the fine powder between the crushing table 4 and the crushing roller 5, the slip of the crushing roller 5 is reduced, the crushing of the crushed material is improved, and the mill vibration is reduced. Reduce. It should be noted that if a large amount of powder is present on the crushing table 4, slipping easily occurs in the crushed object layer thickness.

When the mill air volume is reduced, the exact opposite phenomenon occurs.

When the roller tension pressure is increased, the material to be ground on the grinding table 4 is pressed down by the grinding roller 5 and the layer thickness is reduced.
Since the raw material is more strongly consolidated, the object to be crushed on the crushing table 4 is easily crushed into fine powder, and the powder on the crushing table 4 increases. For this reason, slip occurs in the crushed material layer, the crushed material becomes unstable, and the mill vibration increases.

The opposite phenomenon occurs when the roller tension pressure is reduced.

As described above, the movements of the layer thickness which is a controlled variable and the signal of the mill vibration depend on what is manipulated among the new feed amount, the mill air flow, and the roller tension pressure which are the operating variables. Each move differently depending on the relationship.

In consideration of such influence among the five variables, the multivariable control system is operated as follows.

That is, if the mill vibration as the controlled variable becomes large,
Depending on the degree, the new feed amount of the crushed material to the mill, which is an operation variable, is increased, the roller tension pressure, which is an operation variable, is decreased, and the mill air flow, which is an operation variable, is increased. Reduces mill vibration and restores the original stable state.

Also, when the layer thickness of the crushed object as the controlled variable becomes large, the new feed amount of the crushed object to the mill of the manipulated variable is decreased and the roller tension pressure of the operated variable is increased according to the degree. By increasing the mill variable of the operation variable, the layer thickness of the crushed object as the controlled variable is decreased, and the original stable state is restored.

When the mill vibration as the controlled variable or the layer thickness of the material to be crushed becomes the size of the state opposite to the above, each of the three operation variables becomes the size of the state opposite to the above. Thus, it goes without saying that a reverse operation such as returning to a stable state is performed.

[Effects of the Invention] As described above, the present invention can solve the problems of the conventional control method for the vertical roller mill, and has the following effects.

(1) Since the two variables of the vibration generated from the mill and the layer thickness of the crushed material sandwiched between the crushing table and the crushing roller are the controlled variables, the crushed state in the mill and the amount of crushed material are controlled. It can detect accurately and quickly, and can take appropriate measures against recoil.

(2) Since the three variables of the new feed amount, the crushing roller tension pressure, and the mill air volume are used as the operating variables, the fluctuation due to the disturbance detected by the vibration or the layer thickness can be quickly controlled.

(3) Since the operation width of each operation variable is small because it is controlled by three operation variables, no overaction occurs and no extra disturbance is given to the mill. Further, it is possible to always operate in the vicinity of the optimum operating point without largely deviating from the optimum operating state.

(4) Due to the reasons (1) and (2) above, the mill operating conditions are very stable, and fluctuations in the product grain size can be suppressed to an extremely small level.

(5) Because of the reason (3) above, the mill can be efficiently operated, and energy can be saved.

[Brief description of drawings]

FIG. 1 is a schematic system diagram showing one embodiment of the present invention, and FIG. 2 is a schematic system diagram of a typical conventional vertical roller mill. 1 ... New feed, 2 ... Grinding material supply pipe, 3 ... Drive motor, 4 ... Grinding table, 5 ... Grinding roller, 6 ... Gas flow, 7 ... Stone discharge, 8 ... Air separator , 9 ... Bag filter, 10 ... Product, 11 ... Vibrometer, 12 ... Arm, 13 ... Layer thickness gauge, 14 ... New feed supply device, 15 ... Measuring device, 16 ... Grinding roller tension Pressure adjusting unit, 17 ... tension pressure gauge, 18 ... bag filter outlet duct, 19 ... air volume measuring device, 20 ... damper opening adjusting device, 21-25 ... filter, 26 ... controller, 27 ... Suction fan.

Claims (1)

[Claims] 1. A crushed object is crushed between a horizontally rotating crushing table and a crushing roller which is rotated while being pressed against the upper surface of the crushing table, and the crushed crushed object is coarse powdered by an air separator above the crushing table. In a vertical roller mill that classifies into fine powder and returns coarse powder to the crushing table and crushes again
The vibration generated from the vertical roller mill and the layer thickness of the crushed object sandwiched between the crushing table and the crushing roller are 2
The variable is a controlled variable, and the amount of the crushed material newly supplied to the vertical roller mill, the tension pressure for pressing the crushing roller against the crushing table, and the gas flow rate introduced into the vertical roller mill from below the crushing table. When the above-mentioned 5 variables are incorporated into a multivariable control system and the above-mentioned vibrations as controlled variables become large,
The supply amount of the material to be crushed to the mill as an operation variable, the tension pressure, and the gas flow rate introduced into the mill are set to be large, small, and large, respectively. When the layer thickness becomes large, the supply amount of the pulverized material to the mill as an operation variable, the tension pressure, and the gas flow rate introduced into the mill are small, respectively.
Considering the influence between the controlled variable and the manipulated variable in order to return the controlled variable to the original size and to return to the original stable state by setting the large and large, An operation control method for a vertical roller mill, characterized in that the operation is comprehensively controlled by using 5 variables, 2 controlled variables and 3 operation variables.