We are using R-51 Ring granulator for secndary crushing of ROM raw coal from 100mm to -13 mm size.
Secondary crushing circuit is closed loop type.
Over size generation is 30 to 40%. It is too high.
Gap between Crusher ring to cage bar is 50mm to 35 mm & gap between cage bar is 50 mm.
Crusher is design for 390tph.There are two such crushers are in the circuit both running.
We are using M16 ,TRF make Primary Vibrex Screen , 25degree decline.nominal stroke 1/2" at 625 rpm one for each crusher. Deck opening is 1/2" square mesh. There are 5 nos. of 7"x16" TRF make M11 Vibrex Screen each of capacity 150tph, deck opening is 1/2"square mesh.declination 18degree, nominal stroke 3/8"at 800 rpm.
Moisture content is 4to6%.We are running secondary Crushing circuit at 350 to 450 tph now.

Pl. advice me:
1. How over size generation (which is at present 30to40%) can be minimised?
2. How we can increase secondary circuit tph from 450 to 600?
3. What improvement should be done to increase crushing efficiency?