Select the proper size and number of cyclones for a rod mill$/$ball mill circuit $($shown below$)$

where new feed to the rod mill is $250$ metric tons per hour of solids. Overflow of the

cyclone is required to be $60\%$ minus $74-$ micron at a solid content of $40\%$ by weight.

Underflow of the cyclone is fed to the ball mill at a solid content of $80\%$ by weight. The

specific gravity of solid is $2\mathrm{.}9$ and estimated circulating load is $250\%.$ Assume that the

cyclone's operating pressure is $10.$