A stream of aqueous hydrochloric acid, 57.3 wt% HCl, is mixed with pure water to produce a stream of 16.5% acid. Perform a DFA.
Degree of freedom = Number of unknowms – Number of equations
Number of unknowns
1) acid flowrate
2) % water in acid feed
3) flow rate of water
4) Flow rate of product
5) mass % of water in product
Number of equations:
1) sum of mass % = 100 in feed
2) sum of mass % = 100 in product
3) mass balance of HCl
4) Total mass balance (mass feed + mass water = mass product)
Note: mass balance of water is a redundant equation.
.: COF = 5 – 4 = 1