The two-stage grinding process of the rod mill--gravel mill-hydrocyclone is shown in Figure 5-3-7. The first section is an open rod mill, and the second section is a gravel mill and a hydrocyclone closed circuit. The ore supply, ore size and hardness of the rod mill and the ore concentration of the rod mill have a great influence on the ore size of the mill. The final product particle size is primarily controlled by the slurry concentration and flow rate of the cyclone feed. The load of the gravel mill has a unimodal characteristic relationship with the transmission power of the gravel mill.
The main measurement parameters of the grinding circuit: P1 ---- gravel mill power, "F2--rod mill feed, F3--rod mill water supply, F4--sand pump pool water supply, L5 -- Sand pump tank liquid level, D6---cluster feed concentration, F7---cycler feed ore slurry volume flow, Z8--cyclone overflow product particle size. Controllable parameters have rod grinding feed amount And the amount of water supplied, the amount of gravel added and the amount of water supplied by the sand pump pool.
The main control objective of the two-stage grinding system is to separate the useful minerals in the ore from the maximum amount of ore and the size of the stabilized product without excessive pulverization. In order to achieve this control goal, the system controls the load of the gravel mill, the ore control of the rod mill, the control of the water supply, the slurry level control of the sand pump pool, the concentration of the cyclone feed and the size of the overflow product. Control, as well as automatic adjustment of the grinding load and product size control of the ore setting.
First, the gravel mill load control
The gravel mill is in the second stage of closed-circuit grinding. The ore is the underflow (return sand) and gravel of the cyclone. The underflow is constrained by the first stage of grinding, and the adjustment of the first stage of grinding to change the ore supply of the gravel is too long and is subject to many factors. The effect of changing the amount of gravel added can change the load of the gravel mill more quickly, realize the fixed value control or extreme value control of the gravel mill, and stabilize the entire grinding system under the condition that the concentration of the cyclone is constant. And the gravel mill grinding efficiency also has a greater impact.
There is a single peak characteristic relationship between the gravel mill load (load) and its actual motor power value. As the load gradually increases, the power increases as it reaches a maximum value and then begins to fall. Grinding efficiency is highest at the maximum power consumption, so the system is required to have an extreme value control function, or to control the rising section to the left of the maximum value of the curve to be close to the maximum value. The control system is required to make a logical judgment on the left or right side of the maximum value of the load-power-curve. The gravel mill load control system is shown in Figure 5-3-8. The latter is often used in actual use. When the power of the gravel mill motor is less than a certain set value (90%), if the operating point is to the left of the maximum value, the power relay turns on the gravel to the ore belt and adds gravel to the gravel mill. When the motor power reaches the maximum value [100] When the power relay disconnects the gravel to the motor of the ore belt and stops the gravel addition. This is repeated, and the load control of the gravel mill is controlled.
Second, the rod mill fixed value mine control
Install three belt scales on the ore belt of the rod mill to measure the ore amount F2. When the value of the mine detection deviates from the set value, the speed of the belt motor is changed by the constant value controller [2]. The ore amount remains unchanged. Its control principle is shown in Figure 5-3-9(1), usually controlled by PID or PI.
Third, rod mill grinding concentration control
In the open grinding of the rod mill, the electromagnetic water flow meter F3 is used to measure the water supply amount of the grinding machine through the fixed value controller [3] to realize the fixed value water supply control. The set value of the controller [3] is calculated according to the actual ore supply amount of the rod mill, and the ratio (10) is manually set, thus realizing proportional water supply control according to the ore supply amount, and the rod mill is ensured. The grinding concentration is unchanged. The control principle diagram is shown in Figure 5-3-9 [ II].
Figure 5-3-9 Bar Mill - Cyclone Control System Block Diagram
Fourth, cyclone overflow particle size fixed value control
Both the rod mill and the gravel mill discharge into the pump pool, and the sand pump enters the hydrocyclone to classify. The control loop consists of a three-stage controller cascade. The POM--200 particle size analyzer is used to detect the slurry size Z' of the product. The electromagnetic pump is used to detect the water supply volume F4 of the sand pump pool, and the γ-ray concentration meter is used to detect the slurry concentration D6 of the sand pump outlet. . The size of the overflow slurry of the cyclone is closely related to the concentration of the slurry entering the cyclone. Under other conditions, changing the amount of water added to the slurry sand pump pool can change the concentration of the slurry.
The detected value of the particle size analyzer is compared with the manual set value, and the deviation is calculated by the particle size controller (8) as the concentration given value of the next-level controller 6; compared with the measured value D6 of the concentration meter, the deviation value is controlled by the concentration After the operation of the device 6, the output value is used as the feed water setting value of the next-stage control ring; it is compared with the actual sand pump pool water supply amount F4, and the deviation is calculated by the feed water constant value controller 4 to adjust the sand pump pool water supply valve. The opening degree, thereby changing the ore concentration of the cyclone, ensures that the overflow product particle size is stable within a given range. The control schematic diagram is shown in Figure 5-3 -9 [III].
Five, sand pump pool level control
The level of the sand pool has a great influence on the work of the sand pump, and it will cause the slurry to overflow from the pump pool or the air to enter the sand pump. The running speed of the sand pump directly affects the ore supply of the cyclone and the classification effect of the cyclone. The liquid level control of the sand pump pool not only facilitates the grinding operation, but also creates favorable conditions for the flotation operation.
A level gauge 5 is installed in the sand pump tank, and a concentration meter 6 and an electromagnetic flow meter 7 are installed on the outlet line of the sand pump. The set value of ratio 5 is the ratio of flow rate to liquid level (about 4.0). When the liquid level rises, the ratio 5 is calculated as the given value of the slurry flow rate, and compared with the measured value of the flow rate, the deviation is passed through the controller P17. Calculation, output control increment, adjust the hydraulic coupling hydraulic pressure, increase the speed of the sand pump, increase the slurry flow (the amount of the cyclone feed) to maintain the relative height of the sand pump pool level, and vice versa. The control schematic is shown in Figure 5-3 -9 [IV].
Sixth, automatic adjustment rod mill feeding set value control
The above grinding process is the setting and ratio control performed under the condition that the ore properties and the grinding media are constant. In fact, due to the hardness or particle size of the ore, or due to the reduction of the grinding medium, the qualified particle size of the cyclone overflow will be reduced, and even the grinding machine will be overloaded; otherwise, the ore size will be reduced and the ore hardness will be reduced. In the case of softening, the processing capacity of the mill cannot be fully utilized. To this end, the change of the ore content of the ore is used to compensate for the influence of changes in the hardness and grain size of the ore, and the control of the set value of the ore is introduced on the basis of the fixed value control. The control principle is shown in Figure 5-3-9.
According to the flow rate and concentration of the slurry supplied to the ore by the cyclone, the system calculates the intermediate parameter P9 of the total load of the reaction rod mill and the gravel mill by the following formula.
When the ore is easy to grind, the content of -200 mesh particle size in the overflow slurry of the cyclone increases, and the particle size control loop reduces the water addition amount of the sand pump pool to ensure the particle size constant, the pulp concentration is correspondingly increased, and the cyclic load is reduced. At this time, the calculated value of P9 is also small. The deviation value between the set value of P9 and the fixed value controller (9) is positive. After the controller (9) calculates, the set value of the output of the output increases, which increases the processing capacity of the rod mill. Conversely, when the ore becomes hard or the ore size becomes coarse, the control system automatically reduces the amount of ore fed to the rod mill in order to ensure the granularity of the grinding product without overloading and overflowing the circuit.
Adjusting the set value of the ore control is more stable than the set value of the cyclone overflow of the mine control, but the ore supply has some fluctuations, and it has higher processing capacity under the condition of ensuring the product granularity.
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