Question

2 tonnes of galena is to be reduced to fine powder by passing through a crusher and a grinder in succession, drawing powder from the same drive. Screen analysis of feed, product from crusher and product from grinder indicated surface areas of 5, 115 and 1000 m²/kg respectively. If the power required by the drive to run the crusher driver assembly is 20 KW and efficiency of crusher is 20%, find the efficiency of grinder. Rittinger's number for galena is 100 m²/kj

Answer 1

20kW = ∆A (115/5)

x kW = ∆A (1000/115)

x = $\dfrac{1000}{115}×20×\dfrac{5}{115}$

x = 7.56kW

7.56W = 20%

$\therefore$ 100% = 37.8kW

2 tonnes = 2000kg

$2000kg ×\dfrac{1000}{115}m²/kg= 17391m²$

Rate of grinder reduction = ${37.8×}{100} =3780m²/s$

$\%E =\dfrac{3780}{17391} ×100\%= 21.74\%$