ENG298: Principles of Process Engineering Fresh Water is Produced - Engineering Assignment Help

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Task:

PROBLEM 1

 Fresh water is produced from seawater containing 3.5 wt% dissolved salts by using a doubleeffect evaporator (two evaporators in series). A flowchart of the process is shown below. Seawater enters the first effect at 296 K at a rate of 3500 kg/h and saturated steam at 3.80 bar absolute is fed into a tube bundle in the first effect. The steam condenses at 3.80 bar, and condensate is withdrawn at the saturation temperature corresponding to this pressure. The heat given up by the steam condensing in the tubes causes water to evaporate from the brine solution at a pressure of 0.70 bar, which is the pressure maintained in the effect. The exiting brine contains 5.7 wt% salt. The steam generated in the first effect is fed to a tube bundle in the second effect. The condensate from the bundle and the steam generated in the second effect at a pressure of 0.30 bar constitute the fresh water produced in the process. P= 0.7 bar P= 0.3 bar H2O(v) H2O(v) H2O(v) Saturated 3.8 bar H2O(l) Sat’d 3.8 bar Seawater, 296K 3.5 wt% salt 3500 kg/h Brine 5.7 wt% salt H2O(l) Sat’d 0.7 bar Fresh water product Brine Condenser ENG298 Principles of Process Engineering – Assignment April 7 th, 2021 Page 2 Assuming that the brine solutions in both effects have the physical properties of pure water and the effects operate adiabatically, solve the following:

i. Draw and label a flowchart of this process, giving the pressure and specific enthalpy of each stream.

ii. At what rate must steam be fed to the first effect?

iii. What is the production rate of fresh water and what is the salt concentration (weight percent) of the final brine solution?

iv. Why is it necessary that the pressure decreases from one effect to the next?

v. If a single-effect evaporator were used, operating at P = 0.30 bar, calculate the feed rate of saturated steam at P = 3.80 bar that would be required to achieve the same production rate of fresh water. What other information would you need to know to determine which process is more economical?

PROBLEM 2 (20 MARKS)

Freeze drying is a process by which substances are dehydrated at low temperatures in order to avoid degradation that may occur due to heating. The material that is to be dried is cooled to a temperature at which all of the water present turns to ice. The frozen substance is then placed in a vacuum chamber and may also be subjected to radiant or microwave heating; the ice in the food sublimates, and the vapor is carried off by the vacuum pump. A meat producer decides to freeze dry steaks in a heated chamber at 1 torr (1 mm Hg). The steaks, containing 75% water by mass, were placed into a chamber at -25°C at a rate of 100 kg/min. A total of 97% of the water that was in the steaks initially, leaves as a vapor at 63°C and the remainder leaves as a liquid with the steaks at 49°C. Use the heat capacity data given below and additional tabulated data for water to calculate the required heat input for this freeze drying process in kilowatts. (????????)???????????? = 2.17 ???? ????.°???? (????????)???????????? ???????????????? = 1.38 ???? ????.°????

NOTE

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