2. Distilling and Purification Plants

3. References Required Introduction to Naval Engineering (Ch 14). Recommended Principles of Naval Engineering (Ch 10 pg 221- 228).

4. Objectives A. Comprehend the theory of operation, principle components, basic layout, and safety considerations related to desalination plants. B. Comprehend the energy transformations occurring in desalination plants.

5. Fresh Water Uses STEAM PLANT!!! Electronics Cooling Hotel Services – Cooking/Drinking – Laundry – (Showers) Freshwater Washdown

6. Important Concepts Distillation: seawater freshwater – Evaporation – Condensation Feed (seawater @ 35,000 ppm Cl - ) – Distillate (<0.1 ppm Cl - ) – Brine (>35,000 ppm Cl - ) Salinity (salt concentration in H 2 0)

7. Distillation Process

8. Distilling Plant Types Flash-Type Vertical Basket Vapor-Compression Reverse-Osmosis

9. Flash Type Most combatants High capacity (12,000 –50,000 GPD) Distillate (<.065 ppm) 150# Auxiliary Steam Vacuum operation – More efficient – (-) soluble salts

10. Flash Type

12. Flash-Type Feed Path – Feed is heated via the distillate cooler, distillate condensers, air ejector condenser and feed heater. – Feed enters the first stage where a portion flashes to vapor( stage pressure is < Psat for Tfeed) – Feed that does not flash in the first stage passes via loop seal to the second stage (which is at a lower pressure than the first) – The brine is then pumped overboard Distillate Path – Vapor from each stage is condensed in the distillate condensers – Distillate is removed from the condensers and pumped through the distillate cooler to various freshwater tanks.

13. Vertical Basket Submarines Similar to Flash type Med. capacity (8,000 - 10,000 GPD) Low Pressure (Auxiliary) Steam

14. Vertical Basket

15. Feed Path – Feed is heated via the distillate cooler, distillate condensers, and air ejector condenser. – Feed enters the chamber where it receives heat from the steam basket (chamber pressure is < P sat for T feed ) and begins to boil. – The brine is then pumped overboard Heating Steam – Auxilliary steam enters the steam basket, where it transfers LHV to the feed. – Steam basket drains are collected and returned to the feed and condensate systems. Distillate Path – Vapor is condensed in the distillate condensers – Distillate is removed from the condenser and pumped through the distillate cooler to various freshwater tanks.

16. Vapor-Compression Ships without STEAM propulsion Diesels and submarines (as backup) Low capacity (4000 GPD) Compresses generated steam using electricity

17. Vapor-Compression

18. Low Pressure Evaporators Why do most evaporators operate at a vacuum? – Lower boiling point => less scale formation – Avoids the problem of negative solubility – Higher thermal efficiency Is there a limit to the low temp? – Temp must be high enough to kill bacteria and other living organisms

19. Reverse-Osmosis

20. Distillate is <50 ppm – good enough to drink – but not for engineering plant feedwater H 2 O migrates through semi-permeable membrane (salt is blocked) High pressure req’s (400 + psia) Multi-stage units preferred

21. RO Process Feed water is pumped at high pressure into the RO unit A semi-permeable membrane allows pure water to pass, but restricts the flow of impurities Brine is pumped overboard Purified water is sterilized and filtered before going to freshwater storage tanks.

22. Salinity Monitoring Salinity cells – Strategic placement throughout plant Freshwater side of: – Distillate coolers – Distillate Condenser – Feed Heater – Air Ejector Condenser Outlet of the evaporator – Continuous remote monitoring of fresh water – Auto flow shutoff using solenoid valves

24. Water Conservation Limited resource Standard “Navy shower” Water hours- used to conserve water when the ship’s ability to make water is limited – Within 4 miles of land – Water contaminated by oil, or other chemicals – Fukashima Daiichi – Material casualty – Tactical limitations

25. Take Aways List and describe the principles of operation of the four types of distillation systems used by the Navy Describe why evaporators operate at a vacuum. Draw a one-line diagram of a typical flash type and reverse osmosis evaporator Give examples of locations where it is advantageous to have a salinity cell Give examples of when water hours may be necessary

26. Questions?