Grinding automation technology (1)

The main task of the automatic control of the grinding process is to make the grinding and grading production process work under stable or optimal conditions, fully exert and improve the grinding and grading efficiency, so that the useful minerals and gangues can achieve sufficient monomer dissociation to ensure overflow. Product quality in order to achieve higher economic benefits.
In the closed-circuit grinding process consisting of a grinding machine and a spiral classifier, the process from feeding to grading products has a large lag time. Grinding machine lining wear changes the effective volume and effective power of the mill. The wear of the steel ball is out of balance with the amount of steel ball and the diameter of the steel ball. The wear of the spiral classifier spiral will change the characteristics of the controlled object and control. The requirements of the system, that is, the controlled object has time-varying characteristics. This controlled object also has nonlinear characteristics, such as a nonlinear relationship in which the grinding efficiency and the filling rate have the maximum value. The grinding process is restricted by various parameters. Some parameters are uncontrollable and unmeasurable. For example, the hardness of the ore does not have an effective process detection method. The grinding machine and the cyclone closed circuit process have similar conditions. Therefore, the corresponding control strategy should be designed for this object feature. The examples presented here focus on the control strategy. The selection of the automatic control device should meet the design requirements of the control system and the development of the control device itself and the possibility of its selection.
Grinding control system according to the actual requirements of the beneficiation plant, the control system is also different, which can be controlled mainly by the amount and the control amount is divided into the basic parameters of a single control loop, such as to control the amount of ore, to the water (grinding Concentration) control and overflow concentration or particle size control, etc. In view of the interaction between the loops, it is possible to form a grinding on the basis of these loops. Cheng multi-parameter integrated control system, two-stage grinding adjustment control and adaptive optimization control.
First, the grinding machine to control the amount of mine

The traditional method of controlling the ore supply of the ball mill is to use a single parameter fixed value to mine control, as shown in Figure 1 for the ball mill fixed value feed control system block diagram. It consists of a belt scale (photoelectric conversion device), a regulator, a recorder, a funnel automatic switching device, a thyristor governor, and a belt feeder for three DC motor drives. Its principle block diagram is shown in Figure 2.

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The operator sets the ore amount (ton/hour) in the regulator. When the ore change deviates from the given value, the deviation signal is generated. After the proportional integration and differential operation of the regulator, the output automatically changes the thyristor governor. The DC mA signal causes the output voltage of the thyristor to change, and adjusts the speed of the belt feeder to adjust the speed of the belt feeder to make the ore return to or near (within the tolerance) Set value to achieve the purpose of the mine. The control loop stabilizes the ore supply of the grinding machine, generally improving the processing capacity of the grinding machine by 3 to 5% to ensure the quality of the grinding product.
The grinding machine can use the electronic belt scale for the mine quantity detection, or it can be modified by the original mechanical belt scale. For example, the speed of the belt scale counter is converted into a milliamp signal by photoelectric conversion, or the differential transformer is used to correspond to the belt scale. The displacement signal of the ore is converted into a voltage signal.
The control system has three belt feeders, and only one of them is used for mining. When a mine ore bin is not mined, the belt scale (photoelectric conversion device) outputs a zero signal, and the logic and time of the automatic switching device are used to discriminate the ore feeder without the ore funnel, and the ore feeder with the ore funnel is started. And switch the output signal of the regulator to the corresponding thyristor governor. Realize automatic switching of the mining machine to ensure continuous supply of ore to the grinding machine. When the mine bins are not mine or the funnel is blocked, the belt scale output is a no-mineral signal, and the system automatically stops the feeder and sends an alarm signal.
The object characteristics of the ore amount are approximately pure first-order inertia, and the process response is slow. Usually, the PID adjustment algorithm can meet the control requirements. The PID parameters of the regulator can be set by empirical methods. However, the position of the three feeders is different, so that the pure lag time of the object is different. A set of PID parameters of the regulator must meet the requirements of different pure lags to obtain the best transition process. To this end, the magnification factor of the object is changed. For example, if the mine discharge port of the corresponding mining machine is changed, the mine discharge port with a large pure lag time is adjusted smaller, and the amplification factor of the object is correspondingly reduced.
This control system is implemented with a unit combination meter and can also be controlled by a computer.
Second, grinding concentration feedforward control
In the closed grinding of the grinding machine-screw classifier, automatic continuous detection of the grinding concentration of the grinding machine is not easy to achieve. Feedforward control is usually used to meet the grinding concentration required by the process. The block diagram of the control system is shown in Figure 3. The system uses the microprocessor to perform regression analysis, establishes the mathematical model of feedforward control, calculates the given value of the ball mill water addition at each moment, and it measures the water flow signal with the electromagnetic flowmeter. In comparison, the deviation is calculated by the regulator, and the valve opening is automatically adjusted to achieve the required water addition amount for the given value. The feedback loop automatically eliminates the disturbance caused by the water pressure fluctuation in the water supply pipe during the control process.

The main interference factors of the system are the quantity of Q ( _o /ton) of the ore feeding (dry mine), the mineral quantity of Q' _O as the water content, and the amount of returning sand (thousands of mine) of the classifier (ton/hour). Raw ore water a (%), returning sand liquid to solid ratio β, the adjustment parameter is the ball mill water addition amount Fw (m ³ / hour), the adjusted parameter is the slurry slurry solid ratio R in the ball mill.
The ore signal is taken from the electronic belt scale. The YBG-3 active power transmitter is used to measure the power of the spiral classifier motor, which represents the screw shaft power as the return sanding signal. The motor power and the amount of sand return are regression analysis based on the measured data. After conversion and calculation, the functional relationship between the amount of sand return (Y) and the motor power (x) is:
Y=a+bx (1)
The amount of sand returned was determined by three-point sampling method and determined by analysis of variance. b=2.13, a=-52.87 for a mine, the functional relationship is Y=-52.87+2.13x (2)
The method of directly weighing the amount of sand returned is used to determine the relationship between the amount of sand return and the motor power as Y=-102.39+2.05x (3)
The sand return amount data calculated by the above two cases can represent the actual amount of sand return, and the error is less than 4%.
The amount of water added to the ball mill should be proportionally added according to the total amount of ore fed to the ball mill, and the water content in the ore and return sand should be deducted. According to the material balance equation, the mathematical model of feedforward control for grinding concentration is derived as follows:
F _w =[R(1-a)-]Q' _O +[R-β][bx+a] (4)
When the system does not have a moisture analyzer, a and β take an estimate.
Industrial continuous operation according to this model shows that the grinding concentration can still be maintained near the given value when the raw ore treatment step increment is 30%.
The characteristics of the water supply object generally respond faster and have noise. The proportional and integral adjustment rules can be used to overcome the interference of water pressure fluctuation. [next]
Third, the overflow concentration fixed value control in the grinding-grading closed circuit, control the granularity of the graded overflow product, mainly by controlling the slurry concentration of the classifier. The overflow concentration not only affects the quality of the grinding products, but also affects the process parameters of the flotation process. Therefore, the overflow concentration is an important operating parameter for the grinding process.
There are various control methods for the overflow concentration of the classifier, such as concentration setting control, fixed value and proportional control according to the amount of ore. However, concentration setting control is often used. The concentration control system is composed of the concentration adjustment and the addition of water as the adjustment. The block diagram is shown in Figure 4(a) and the flow chart is shown in Figure 4(b).

The control system uses the slurry static pressure method and detects the density change of the slurry through a differential pressure transmitter. According to the relationship between pulp density and pulp concentration, it is converted into divergence value (solid weight percentage). When the measured concentration value deviates from the concentration given value, the deviation is calculated by the regulator, and its output controls the opening of the feedwater regulating valve, that is, increases. Or reduce the amount of water to maintain the slurry concentration value at a given value, the change in concentration is indicated and recorded by the recorder. The slurry concentration test can also use a gamma ray densitometer, a heavy float concentration meter, etc., and the control system is substantially the same.
The object characteristic of the overflow concentration is a multi-order inertia link with a large hysteresis, which can generally be approximated by a pure lag first-order inertia link. Due to the slow process response and large time constant, the PID regulation rule is usually used to basically meet the production requirements. Some systems also use partial change of the overflow concentration according to the change of the ore supply quantity, that is, use the ore amount to modify some given values ​​in the concentration setting control system. [next]
Fourth, grinding multivariable integrated control system
The grinding circuit is not a univariate object characteristic, but a multivariable control problem, and the object characteristics of the grinding circuit have nonlinear, time-varying, and large hysteresis characteristics. For example, the relationship between the grinding efficiency of the grinding machine and the load, the relationship between the ore supply of the mill and the grinding concentration, and the overflow concentration of the classifier. Therefore, the multi-parameter integrated control system of grinding should consider the main parameters in the grinding process and their mutual influences. In addition, the requirements of the flotation process on the quality of grinding products should be considered. Thus, the traditional constant ore or simple fixed value control system is difficult to meet these requirements, and a multivariable control system must be used. The JS-872 type grinding unit control system is an example of a multi-parameter integrated control system. Figure 5 is a diagram of a JS-872 type grinding control system, and Figure 6 is a schematic block diagram of the system.

In the design of the multi-variable control system of grinding, the original single-parameter control loop is considered. According to the principle of the main control quantity and the controlled quantity, the total quantity of the ore-grinding machine and the water supply of the grinding machine are given. The slurry concentration of the grinding machine, the water supply of the classifier, the overflow concentration of the classifier, and the three pairs of parameters constitute three basic circuits, and the parameters affecting each other are introduced into the three circuits to meet the requirements of the process. [next]
The grinding machine feed control loop (algorithm 1, 2) is a cascade control system with the amount of ore and mill load as the controlled amount, which overcomes the interference effects such as the ore supply and ore properties. The load of the mill is not only affected by the amount of ore, but also the change of the ore property. When the hardness and particle size of the ore change, the amount of sand returned by the classifier changes, resulting in a change in the loading. The amount of media (such as steel balls) and the amount of water are also factors that often affect the loading. Therefore, the load is controlled as the main loop in the control system. According to the requirements of the flotation process, the ore supply needs to be basically stable. Therefore, the ore amount is controlled as the secondary ring. According to the fixed value control principle, the set value is changed only by the main ring when the ore property changes greatly. To this end, the main parameters (loading) use a nonlinear controller algorithm, and this loop can also complete the fixed value control of the ore. Grinding equipment is constantly worn during operation, and the characteristics of the controlled object are also changed (time-varying object characteristics). The set value of the nonlinear controller should be changed by the operator according to experience, or the self-organizing fuzzy controller should be pressed by the monitoring level computer. The principle automatically changes the set value.
The mill feed water control loop (Algorithm 3, 4) is a ratio or ratio-valued control system with the feed water quantity and the feed quantity as input parameters. When the ore supply is equal to zero, the amount of water required to flush the sand from the classifier cannot be zero, so the ratio-fixed value control is more suitable for the actual situation. Since the return sand and the ore water change are not detected, the set parameters controlled by the ratio value are determined according to the actual situation and experience. Of course, the water supply quantity setting control can also be realized by the algorithm 4, and the three control modes can be selected by the operator at any time according to the process requirements.
The purpose of the classifier overflow concentration control is to control the overflow particle size. The concentration control usually adopts the fixed value control system, but considering the influence of the ore-mining quantity change on the overflow volume flow rate and the particle size, the algorithm 5 is introduced in the loop to introduce the correction of the concentration change value to the concentration setting value, which constitutes “(value) ) Overflow concentration control of ± (proportion of minerals). In actual production, due to the influence of slurry volume flow on the grading and flotation process, the slurry flow detection value is introduced into the circuit, and the overflow concentration value is modified by Algorithm 6, and the overflow concentration is not constant, and most of them are Fixed, small parts are variable, forming a two-variable composite control. The circuit can also use the flow rate instead of the concentration controlled parameter to form an overflow flow control system with similar concentration control modes, and also obtain better control effects, and at the same time ensure the stability of the flotation liquid level. The above various control methods are selected according to the actual production requirements.
The JS-872 control system is based on the DDZ-III type instrument. The above control algorithm is implemented by a programmable regulator, which can also be realized by an industrial control computer. The programmable regulator has rich functions and flexible configuration. It can be configured according to the specific process requirements. In the application, only some data can be replaced or different buttons can be used to realize the conversion of the above various control states. In addition, the system also has fault self-diagnosis and display alarm function, which is convenient for maintenance and use.
In addition to the instrumentation and actuators, the main instrument is installed in the control cabinet of the control room, and the operator operates and manages it in the control room.
There is a variety of control strategies for a multi-parameter control of grinding and closing, and a simpler algorithm can be realized by appropriate connection and configuration between the above three circuits. The complex algorithm is operated by the host computer or the monitoring level, and the set values ​​of the above three loops are changed with the optimal parameters to perform the grinding optimization control. The above control system is structurally distributed. With the industrial control machine, it can also be composed of a centralized control system to achieve multi-parameter control. In the control strategy, optimization control can be implemented in various ways according to the actual production situation and experience. For example, a section of an iron ore concentrator milling - hierarchical control system, including a ball mill load, grinding concentration, the concentration of three overflow the reference control loop. The ball mill load Q and the ore amount F constitute a cascade adjustment to achieve load fixed value control; the grinding concentration D ₁ achieves open loop control according to the ratio of the ore supply amount and the return sand amount, maintaining a given grinding concentration; the overflow concentration D ₂ adopts closed-loop fixed value control to stabilize the overflow particle size. Z. According to the long-term operation experience of the ore dressing plant, different ore values ​​of the ore and different grinding parameters of the mine are applied, and better grinding indexes can be obtained.
A+D ₂ +Z (5)
According to the actual measured value of the concentrate grade produced in the previous hour, the operator can determine the type of ore and the control parameters of the grinding process by empirically determining the overflow concentration D ₂ value, where Q, D ₁ and D _{2 are} three. The set values ​​of the loops are manually placed into the loop to achieve precise control of the grinding. From grade analysis to setpoint change can also be done automatically by the computer.

Anti-Scald Electric Kettle

Anti-Scald Electric Kettle