We have a triple effect evaporator which has steam supply of 5kg/hr, the setup is a forward pass setup, the feed enters the 1st setup at 10kg/hr of 50% concentration and leaves the final effect at 75% concentration. What is the economy of this setup?

Correct Answer: 66%
Applying mass balance, Total feed F = E + P3, where E = E1+E2+E3, P3 = XFF/XP = 0.5×10/0.75 = 6.67kg/hr. Hence, we have E = 10 – 6.67 = 3.33kg/hr. Economy of an evaporator is defined as, E = Capacity/Consumption = (E1+E2+E3)/S = 3.33/5 = 0.66 = 66%.