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The energy consumption of a mill is directly related to the movement of the grinding charge.
Naturally, gears and other components generate constant energy losses, but comminution of material is the major factor with respect to energy consumption.
Energy flows through the mill from the power plant, via the gears and lining to the grinding bodies.
This means that the lining must not only provide wear protection, but must also transfer energy and allow for optimal movement of the grinding charge.
In terms of energy consumption, the efficiency of the entire system can be determined by measuring the increase in temperature of the slurry. Overgrindiing can also be regarded as a source of energy, loss.
Rapid rises in energy costs have stimulated a number of projects for reducing the operations cost of dressing plants. The main effort in this connection must be devoted to the grinding system, as it is the major energy consumer.
Another very common problem is the need for additional capacity, which demands a greater energy input for the mill.
Solutions to these two problems can thus be described as follows:
- Energy consumption per ton of grinding mill output can be reduced, or tonnage can be increased while energy input remains unchanged.
- The energy input to the mill can be increased to obtain higher tonnage output despite higher energy consumption per ton of mill output.
The design of the mill lining has an effect on both solutions. Lining design must take account of several parameters, i.e.:
- Energy consumption
- Liner economy
- Liner life
- Grinding media economy
- Capacity
- Product size
If the factors are considered singly, the optimal lining design would be quite different for each one. For example, maximum liner economy would require a thick lining with high lifter bars, while maximum capacity would require a very thin lining. Maximum economy for grinding media would call for low lifter bars.
If the existing lining is of satisfactory design, it is difficult to reduce energy input per ton of mill output. The potential savings are often negated by reduced liner economy.
The entire energy input (less losses in mechanical components) to the mill is transferred to the charge, so that the appropriate energy input consumption can be determined by studying the movement of the charge.
Efficiency can the be determined on the basis of the relation between charge movement and required results. i.e. the question is whether the grinding media reduce a maximum of the material to the correct size or whether they generate excessive amounts of heat.
Theoretically, maximum energy input is needed if a maximum of grinding bodies are lifted as high as possible, to 12 o’clock, and are dropped as close to the vertical as possible, impacting at 6 o’clock.
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