5. Materials balance in continuous centrifuging of milk
If 35,000 kg of whole milk containing 4% fat is to be separated in a 6 h period into skim milk with 0.45% fat and cream with 45% fat, what are the flow rates of the two output streams from a continuous centrifuge which accomplishes this separation?
Basis 1 hour's flow of whole milk
Mass in
Total mass = 35,000 = 5833 kg.
6
Fat = 5833 x 0.04 = 233 kg.
And so water plus solids-not-fat = 5600 kg.
Mass out
Let the mass of cream be x kg then its total fat content is 0.45x. The mass of skim milk is (5833 - x) and its total fat content is 0.0045(5833 - x).
Material balance on fat:
Fat in = Fat out
5833 x 0.04 = 0.0045(5833 - x) + 0.45x.
and so x = 465 kg.
So that the flow of cream is 465 kg h-1 and skim milk (5833 - 465) = 5368 kg h-1