As with the pebble crusher close side setting the pebble crusher feed rate can be used to vary the pebble crusher specific energy. To quantify the effect of the pebble crusher feed rate on this specific energy the pebble crusher throughput rate was varied whilst maintaining a constant close side setting. Figure 2 illustrates the results obtained for various feed rates at a crusher close side setting of 11 mm. A positive linear correlation is evident between the pebble crusher feedrate and the pebble crusher specific energy, with the pebble crusher specific energy increasing with an increase in feed rate. This result highlights the benefit of "choke feeding" the pebble crushers. This causes greater inter-particle breakage and a resultant finer product.
The product of the pebble crusher specific energy and the feed rate is equivalent to the net power drawn for each crusher (kW). The installed motor power provides a limitation on the maximum crusher specific energy that can be achieved. At Telfer, the pebble crushers are generally operated at a power draw targeting approximately 85 per cent of the total installed motor power. Due to the erratic nature of Telfer"s crusher power draw, operation at average target levels higher than this can result in overloading of the pebble crusher motor. The maximum net power (205 kW) has been calculated using 85 per cent of the installed power minus the noload power. This is shown by the curved dashed line in Figure 2. Once this maximum crusher net power draw has been reached, it is not possible to increase this specific energy further by increasing the feed rate without overloading the pebble crusher motor. Achieving a finer product once the maximum net power draw has been reached requires a shift upwards and along the maximum net power draw curve, ie a lower feed rate and narrower close side setting to increase the pebble crusher specific energy whilst not exceeding the maximum net power draw.
There are occasions at Telfer when, if two crushers were to be operated in parallel at their maximum capacity, the maximum carrying capacity of the pebble conveying systems (720 t/h)would be exceeded. If this is the case, the current practice when operating two crushers is to "choke feed", or maximise the power draw to one crusher, whilst "trickle feeding" the other. The result of this practice, as is shown in Table 1, suggests there is a benefit to be gained by operating in this manner, rather than evenly feeding both crushers at less than maximum power draw.
In practice for normal feed properties, if the close side setting is correctly set and the pebble crusher hydraulic clamping system is in a good condition and correctly adjusted, there should be very little need for either of the pebble crushers to be "trickle fed" to any great extent. Maximum available net power, or close to, should be able to be achieved on each crusher at combined throughput rates which do not exceed the conveyor capacity.
For more details, you can contact us online or send email to sales@kefidinc.com now.
