Question

Fresh orange juice containing 10 % solids and the balance water is fed to an evaporator to produce final product of concentrated orange juice containing 40% solids. A fraction of the fresh juice bypassed the evaporator to insure fresh taste. The juice that enters the evaporator at 10% is concentrated and leaves the evaporator at 60% solids, and the evaporator product stream is then mixed with the bypassed fresh juice to achieve the desired final concentration of 40 % solids. All percentages are in mass%. Draw and label a flowchart of this process and based on 100 lb/hr of the final 40% mass product. calculate the following flow rates in Lb/hr:

a. Fresh overall feed rate to the process

b. Flow rate of pure water leaving the evaporator and the bypass flow rate

Answer 1

Final product contains =100 lb/hr and contains 40% solids. So solids in final product =100*40/100 =40 lb/hr

Fresh organce juice contains 10% solids. Let F= feed flow rate

Overall material balance gives F*0.1= 40 , F =40/0.1= 400 lb/hr

Let B= Flow rate of bye-pass stream , then *(400-B)= Feed entering the evaporator

Solids in feed entering the evaporator = (400-B)*0.1

Let M= Produict from evaporator

Writing solids mass balance across the mixing point of evaporated feed and bye-passed feed

M*0.6 +B*0.1= 40

M +B*0.167= 66.7 (1)

Writing water mass balance across the mixing point of evaporated feed and bye-passed feed

M*0.4 +B*0.9= 60

M+B*2.25= 150 (2)

Eq.2- Eq.1 , B*(2.25-0.167)= 83.3

B =32 lb/hr and Feed entering the evaporator = 400-32= 368 lb/hr

Water leaving the evaporator = 368*0.4 = 147.2 lb/hr