2.11. Vertical-Basket Distilling Vertical-basket units consist of an evaporator, a distiller condenser, a vapor feed heater, a distillate cooler, and air ejectors. Each unit is set up vertically in which the feed water is vaporized by low-pressure steam. The vapor generated by the boiling seawater passes through a cyclonic separator in which most of the entrained liquid particles are removed from the vapor by centrifugal force. After, the vapor passes through the second vapor separator, called the snail, where the remaining water droplets are separated from the vapor. The liquid particles from both of the separators drain downward and become part of the brine drains. This process is essentially repeated in which the vapor from the second effect shell is condensed and drained into a tank. 2.12. Advantages and Disadvantages of Vertical-Basket Distillation Vertical-basket distillation requires a significantly smaller system that operates on low pressure steam, and has a capacity of about 10,000 gallons per day. However, the system still requires the expenditure of fuel, still labor intensive to repair, and 10,000 gallons per day is not enough water to operate all systems on a large-scale system, such as a marine vessel.
23 2.13. Vapor-Compression Distillation Vapor-compression distilling units are commonly used as the primary means of producing fresh water on ships that don’t use steam propulsion systems. The three main components in vapor-compression systems are the evaporator, the compressor, and the heat exchanger. Vapor-compression works by first creating water vapor from the sea water. The generated vapor is then passed through a mist separator to remove any entrained water droplets that may contain salts. The vapor condenses on the outside of the tubes, is collected and is pumped into a three steam heat exchanger. The brine is also pumped into the heat exchanger which cools the distillate and brine while heating the incoming feed water. The use of the three-way heat exchanger helps to minimize energy consumption by the system. 2.14. Advantages and Disadvantages of Vapor-Compression DistillationA significant advantage of vapor-compression distillation is that the system does not require steam, so the expenditure of fuel is unnecessary. Not using fuel is a significant improvement, but the system has a very low capacity for producing water, only 4000 gallons per day. Thus the system is often used as an emergency back-up system.
24 Side by Side Analysis of Different Distillation Methods Type Of Distillation Maintenance Power Capacity Efficiency Reverse Osmosis 4 4 3 11 Flash Type Distillation 2 2 4 8 Vertical Basket Distillation 3 3 3 9 Vapor Compression Distillation 4 3 1 8 Figure 17: Comparison of Distillation In order to gauge to most viable solution to filter the water, the three most important aspects to our project were compared on a scale of 1-5 in order to select the best solution.
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- Fall '19