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 loading amount, the relationship between the ore supply amount 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. Such a traditional constant ore or simple fixed value control system is difficult to meet these requirements must use a multivariable control system. The JS-872 grinding unit control system is an example of a multi-parameter integrated control system. Figure 1 is a JS-872 type grinding control system. Figure 2 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 amount of the ore-milling machine is the water quantity of the grinding machine-grinding. The slurry concentration of the 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.
The grinding machine feeding control loop is a cascade control system with the amount of ore and grinding machine loaded as the controlled quantity, which overcomes the interference effects such as changes in the ore properties of the ore. The load of the mill is not only affected by the ore content but also the change of ore properties. 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 content needs to be basically stable, so the ore amount is controlled as the secondary ring. According to the fixed value control principle, the set value is changed by the main ring only when the ore property changes greatly. For this purpose, the main parameter (loading amount) adopts the nonlinear controller algorithm, and this circuit can also complete the fixed value control of the ore. During the operation of the grinding equipment , the characteristics of the controlled object are also changed (the time-varying object characteristics). The set value of the nonlinear controller should be changed by the operator according to the experience or automatically by the monitoring level computer according to the self-organizing fuzzy controller principle. Change the set value.
Figure 1 JS-872 grinding multivariable control system diagram
The mill feed water control loop is a control system with a ratio of ratio of feed water amount and feed amount to 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 change are not detected, the set value of the ratio-fixed value control is determined according to the actual situation and experience. Of course, the water supply quantity setting control can also be realized by the algorithm 1. The three control modes can be selected by the operator at any time according to the process requirements.
Figure 2 Schematic block diagram of JS-872 control system
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 considers the influence of the ore-mining quantity change on the overflow volume flow rate and the particle size. In the loop, the correction of the concentration change to the concentration setting value is introduced by the algorithm 5, which constitutes “(fixed value)± (concentration of the amount of ore) "overflow concentration control". In actual production, due to the influence of slurry volume flow on classification and flotation process, the slurry flow detection value is introduced in the circuit and the overflow concentration is modified by algorithm 6. The overflow concentration is not constant and most of them are fixed and small. Part of the change is the two-variable composite control. The circuit can also adopt 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 effect and 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 uses a programmable regulator to implement the above control algorithm based on the DDZ-III type instrument. It can also be realized by an industrial control computer. The programmable regulator has rich functions and flexible configuration. According to the specific process requirements, the application can be converted by changing some data or pressing different buttons. In addition, the system also has fault self-diagnosis and display alarm function for easy maintenance.
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. Refer to Table 1 for the parameter setting values ​​of each regulation loop of the system.
Table 1 parameter setting values ​​of each regulation loop of the system
project | δ% | T 1 min | T d ,min | |||
Raw ore feeding circuit | Secondary ring | Main ring | Secondary ring | Main ring | Secondary ring | Main ring |
100 | 200 | 0.3 | 1.5 | 0.1 | 0.1 | |
Grinding water supply circuit (fixed value) | 50 | 0.05 | ||||
Overflow concentration loop (fixed value) | 50 | 1.5 | 0.4 | |||
Note: δ. proportionality; T 1 integral time constant; T d . differential time constant.
There is a variety of control strategies for a multi-parameter control of grinding and closing closed circuit. In the simpler case, the 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 to change the set values ​​of the above three loops with its optimal parameters, and the grinding optimization control is performed. The above control system is structurally distributed. It can also be integrated into the centralized control system using industrial control machines 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 milling period iron ore processing plant - hierarchical load control system comprising a ball mill, 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 according to the ratio of the ore supply and the amount of return sand to achieve open loop control to maintain a given grinding concentration; overflow concentration D 2 Closed-loop setting control is used 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 of the mine, different values ​​of the grinding parameters can be used to obtain better grinding index. The actual data is shown in Table 2, where the relative wearability A value is
A=D 2 +Z
Table 2 best operating parameter values
Raw ore properties | Relative wearability A value | Overflow particle size Z% | Overflow concentration D 2 % | Grinding load (meter reading) QmA | Grinding concentration D 1 % | Feeding amount Ft/h | |
Hard mine | Difficult to choose Good choice | 78 82 | 50 49 | 28 33 | 15.2 14.4 | 85 83 | 93 96 |
Medium hard mine | Difficult to choose Good choice | 89 89 89 89 89 | 50 46 44.5 43 40 | 39 43 44.5 46 49 | 13.6 13.6 13.6 13.6 12.8 | 83 83 83 83 81 | 98 108 114 118 125 |
Soft mine | >91 | 50 | 43 | 12 | 81 | 104 | |
The operator determines the overflow concentration D 2 value based on the measured value of the concentrate grade produced in the previous hour, and knows the type of ore processed and the control parameters of the grinding process. Among them, Q, D 1 and D 2 are used as three circuits. The set value is manually placed into the loop to achieve fine grinding control. From grade analysis to setpoint change can also be done automatically by the computer.
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