Design a Plant with Reserve or Surge Capacity

The suggested reserve capacity for quarry operations applies as well to open-pit mining operations employing power shovels for loading the ore. Usually the primary crusher is expected to produce the required daily tonnage in such plants in one or two shifts, so a time-reserve does exist which can be utilized to make up for delays. But this can only be accomplished by overtime operation of pit, transportation, and primary crusher-house, which under existing labor conditions is a costly expedient.

From the standpoint of economical operation, reserve capacity in the primary crusher is just as important here as it is in the commercial crushing plant Underground mining operations are, in many cases, provided with a substantial surge capacity between the mine and the primary crushing plant. Furthermore, in medium and large operations of this character, the primary crusher is almost invariably large enough (to meet the required output) so that the mined ore causes little or no trouble due to bridging or blocking. For such operations the reserve may safely be cut to a some what narrower margin than we have suggested for the preceding classes of operation. From 10 to 15 percent will usually be safe, if the crushing plant is designed for one-shift operation.

Underground mining operations without surge capacity ahead of the primary should be figured for at least 25 percent reserve.

The average gravel plant usually has some surge capacity between the pit and the primary crusher; in many instances, however, this surge is so small that it cannot be counted on to smooth out protracted delays in the pit. On the other hand, primary gravel crushers are not, as a rule, subjected to bridging and blocking, because provisions are easily made to keep oversize boulders out of the system. For gravel operations having little, or no, surge capacity ahead of the primary, a reserve crusher capacity of about 25 percent will usually suffice.