A single-stage evaporator processes 15,000 kg/s of an NaOH solution that is fed at 40C. The solution concentration is 10%. Saturated steam at 3.5 atm (138.2C and λ5513 kcal/kg) is available as hot utility. It exits as saturated liquid. The economy of the steam is 0.785. The vacuum at the evaporation chamber is 620 mmHg with respect to 1 atm.

The global heat transfer coefficient is 1600 kcal/m2 hC. Assuming no heat loss, compute:

(a) hot utility flowrate,

(b) evaporator surface area, and

(c) composition of the concentrated solution.