PROCESS PRINCESS
mass balance with bypass and recycle
Example
Raw sugarcane juice has a concentration of 70% solids and 30% water (by weight). In order to make this mixture easier to work with, it is diluted with recycled filtrate from filtering the raw sugarcane juice. The blended product has a composition of 50 wt% solids, with the rest being water.The filtered solids are discarded and the final product, the filtrate has a composition by weight of 95% water and 5% solids. Taking 100kg of final product as basis of calculation, calculate the weight of fresh feed, weight of solids discarded and the weight of product recycled
As always, we start by drawing a flowchart
.png)
Then we do the D.O.F analysis for all parts
Overall System
2 unknowns (m, m)
2 balance eq.
Mixing Point
2 unknowns (m, m)
2 balance eq.
0 D.O.F
0 D.O.F
Filter
2 unknowns (m, m)
2 balance eq.
0 D.O.F
Now we can solve the equations
Overall Water Balance
Overall mass balance
Mass balance at mixing point
Solid balance at mixing point
0.3m₁ = 0.95(100)
m₁ = 316.67
m₁ = m₃ + 100kg
m₃ = 216.67
m₂ = m₁ + m₅
0.5m₂ = 0.7m₁ + 0.05m₅
Solve simultaneously
m₂ = 457.4
m₅ = 140.74
Splitting point
2 unknowns (m, m)
1 balance eq.
1 D.O.F
the compositions are all the same, so only one independent eq. can be written
n₄ = n₅ + 100
0.95n₄ = 0.95n₅ = 0.95(100)
if first eq inserted,
0.95n₄ = 0.95(n₄ - 100) + 95
0.95n₄ = 0.95n₄
Exercise
An example of bypass process is in coronary bypass surgery, where bloodflow is directed around a blocked artery in the heart.
-
Draw a flowchart of the flow of blood in a normal heart and in a heart that has undergone coronary bypass surgery (can refer to diagrams of coronary bypass from internet)
-
Give another example of recycle or bypass process