Circuit Capacity of HPGR

The capacity of an HPGR circuit, as distinct from the unit capacity discussed above, is obviously a function of the circuit design. Of the above variables, the feed bottom size is particularly relevant in this regard, as a truncated feed necessarily implies the pres- ence of a screen or other classification device upstream of the HPGR.

It has been noted that capacity decreases with truncated feeds; however, the capac- ity of the circuit would increase if the amount of fines removed from the HPGR feed exceeded the reduction in HPGR unit capacity. Whether this occurs in practice remains the subject of some debate (and in any event is probably ore specific), but recent model- ing of pilot test data for two prospective applications indicates that this is the case, and this is supported by the limited evidence available in the literature.

However, an increase in circuit throughput achieved in this way may be offset by a decrease in product fineness and/or reduced microcracking such that, depending on the downstream processing route, a full-fines HPGR feed may be preferable to a truncated feed. For any given application, the more efficient flowsheet can be determined only by comprehensive tests and modeling, but where doubt exists, the circuit should, if possi- ble, be designed with the flexibility to operate with full fines or truncated feed to allow circuit performance to be optimised. This flexibility normally comprises the prescreening of the feed and a facility to recycle to HPGR feed a portion of either the HPGR product or, where the HPGR operates in closed circuit with a screen, the screen undersize.