An evaporator-crystallizer system is being used to produce pure salt crystals from a liquid fresh feed (Stream 1) containing 87% water (W), 12% salt (S), and 1.0% highly soluble impurity (I). 1200 lb/hr of fresh feed is combined with recycled liquid (Stream 2) to form Stream 3 which is sent to the evaporator. Pure water leaves the evaporator as Stream 4, while the concentrated solution (Stream 5) is sent to a crystallization and filtration unit. The crystallizer produces pure salt crystals (Stream 6) and a saturated salt solution (Stream 7) with a composition of 52% water, 32% salt, and 16% impurity. 4.0% of Stream 7 is discarded as waste (Stream 8), while the remaining 96% is recycled (Stream 2).

a) Why is a recycle stream (Stream 2) included in this process?

b) What is the composition of Stream 8?

c) What is the mass flowrate of Stream 8?

d) How much salt crystal product is produced (Stream 6)?

e) What is the recycle to fresh feed ratio (Stream 2/Stream1)?

f) What are the mass flowrate and the component mass fractions of liquid leaving the evaporator (Stream 5)?

Bonus question - Why is a waste stream included in this process?

Recycle Stream 2 Fresh Feed Waste Stream 1 Stream 3 Evaporator Stream 5 Crystallizer Stream8 \& Filter Water Vapor Salt Crystals Stream 4 Stream 6