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Overflow concentration setting control
Controlling the particle size of the graded overflow product in the grinding-grading closed circuit is mainly achieved by controlling the slurry concentration of the classifier. The overflow concentration not only affects the quality of the grinding product but also affects the process parameters of the flotation process. Therefore, the overflow concentration is an important operating parameter of 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 block diagram of the classifier overflow concentration control system with the concentration as the adjusted amount and the added water amount as the adjustment variable is shown in Figure 1b.
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 the pulp density and the slurry concentration, the concentration value (solid weight percentage) is converted. When the measured concentration value deviates from the concentration given value, the deviation is calculated by the regulator, and the output controls the opening degree of the water supply regulating valve to increase or decrease the water amount to maintain the slurry concentration value at a given value, and the change of the concentration is indicated by the recorder and recording. The slurry concentration detection can also be roughly the same as that of the gamma ray densitometer heavy float concentration meter.
The object characteristic of the overflow concentration is that the multi-step inertia link has a large hysteresis, and can generally be approximated by a pure lag first-order inertia link. Because the process response is slow and the time constant is large, the PID regulation law is basically used to 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. See Figure 4 for the multivariable integrated control system.
Figure 1 classifier overflow concentration control system
a. control block diagram; b. flow chart