Chapter 4, Problem 4.41P

Seawater containing 3.50 wt% salt passes through a series of 10 evaporators. Roughly equal quantities of water are vaporized in each of the 10 units and then condensed and combined to obtain a product stream of fresh water. The brine leaving each evaporator but the tenth is fed to the next evaporator. The brine leaving the tenth evaporator contains 5.00 wt% salt.

1. Draw a flowchart of the process showing the first, fourth, and tenth evaporators. Label all the streams entering and leaving these three evaporators.
2. Write in order the set of equations you would solve to determine the fractional yield of fresh water from the process (kg H₂O recovered/kg H₂O in process teed) and the weight percent of salt in the solution leaving the fourth evaporator. Each equation you write should contain no more than one previously undetermined variable. In each equation, circle the variable for which you would solve. Do not do the calculations.
3. Solve the equations derived in Part (b) for the two specified quantities.

Exploratory Exercise—Research and Discover

The problem statement made no mention of the disposition of the 5 wt% effluent from the tenth evaporator. Suggest two possibilities for its disposition and describe any environmental concerns that might need to be considered.