Grinding automation technology (2)

Five and two stages of grinding load and product size control

The two-stage grinding process of the rod mill-gravel mill-hydrocyclone is shown in Figure 7. The first section is the open rod mill and the second section is the gravel mill and the 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.
Main measurement parameters of the grinding circuit: P ₁ - gravel mill power, F ₂ - rod mill feed, F ₃ - rod mill water supply, F ₄ - sand pump tank water supply, L ₅ - sand pump pool Level, D ₆ - cyclone feed concentration, F ₇ - cyclone feed slurry volume flow, Z ₈ - cyclone overflow product size. The controllable parameters are the amount of rod grinding 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. [next]
(I) 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 mill is too long and is affected by many factors. By changing the amount of gravel added, the load of the gravel mill can be changed more quickly, and the load control or extreme value control of the gravel mill can be realized, and the entire grinding system can be stabilized under the condition that the concentration of the cyclone is constant. It also has a great influence on the grinding efficiency of the gravel mill.
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 load-power curve of the operating point. The gravel mill load control system is shown in Figure 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 feed belt and adds gravel to the gravel mill. When the motor power reaches a maximum (100%), the power relay disconnects the gravel to the motor of the ore belt and stops the gravel addition. Repeatedly, the grinder crane load setting control is realized.

(2) Rod mill fixed value mine control Three belt scales are installed on the rod mill feeding belt to measure the ore amount F ₂ . When the mine detection value deviates from the set value, the fixed value controller is passed. (2) Change the rotation speed of the ore belt motor so that the ore supply remains unchanged. Its control principle is shown in Figure 9(I), usually with PID or PI control. [next]
(III) Control of grinding concentration of rod mill In the open grinding of rod mill, the water supply F _{3 of the} grinding machine is measured by electromagnetic flowmeter to realize the fixed water supply control through the fixed value controller (3). 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 ensuring the rod mill The grinding concentration is unchanged. The control principle diagram is shown in Figure 9 (II).

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(IV) Cyclone overflow particle size setting control Both the rod mill and the gravel mill discharges into the pump pool and enter the hydrocyclone by the sand pump. The control loop consists of a three-stage controller cascade. The slurry size Z _{8 of the} product is detected by the PSM-200 particle size analyzer. The water pump F _{4 is} detected by the electromagnetic flowmeter, and the slurry concentration of the sand pump outlet is detected by the gamma ray concentration meter. D ₆ . 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, which is compared with the measured value D _{6 of the} concentration meter, and the deviation value is subjected to the concentration. After the controller 6 calculates, the output value is used as the feed water setting value of the next-stage control loop; it is compared with the actual sand pump pool water supply amount F ₄ , and the deviation is calculated by the feed water constant value controller 4 to adjust the sand pump pool water supply. The opening of the valve changes the ore concentration of the cyclone to ensure that the particle size of the overflow product is stable within a given range. The control schematic diagram is shown in Figure 9 (III).
(V) Sand pump pool liquid level control The level of the sand pump pool liquid level has a great impact on the sand pump work, and will also cause the slurry to overflow from the pump pool or air into 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 are installed on the outlet line of the sand pump. 7. The set value of the ratio 5 is the ratio of the flow rate to the liquid level (about 4.0). When the liquid level rises When 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 calculated by the controller PI7, the output control increment is adjusted, the hydraulic coupling joint hydraulic pressure is adjusted, the sand pump rotation speed is increased, and the slurry flow rate is made. (The amount of feed to the cyclone) is increased to maintain the relative height of the level of the sand pump pool and vice versa. The control schematic is shown in Figure 9 (IV).
(VI) Automatic adjustment of the rod mill set value control The above grinding process is the setting and ratio control under the condition of the ore property and the grinding medium. 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 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 gravel mill according to the following formula:
P ₉ =K ₁ +K ₂ F ₁ (1+D ₆ )K ₃ D ₆ (6)
Where F ₇ ———puld flow, m ³ /h;
D ₆ ———Pulp concentration, g/cm ³ .
K ₁ (10.0), K ₂ (0.1), K ₃ (1.0) — coefficient.
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 P ₉ is also small. The deviation value between P ₉ and the set value of the fixed value controller (9) is positive. After the controller (9), the output set value of the output is increased, and the value is increased. The amount of processing 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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