• Technology

    Introduction

    There are more than 21,000 desalination plants in operation around the globe. The largest ones are in the United Arab Emirates, Saudi Arabia, and Israel.
    Desalination is currently expensive, so it is usually only economically practical for high-valued uses such as for household and agricultural use in highly populated areas such as Singapore or California. The most extensive use is in the Persian Gulf.

    Desalination

    Desalination is an artificial process by which seawater is converted to freshwater.

    The most common desalination processes are distillation and reverse osmosis. There are several methods for both processes with each having advantages and disadvantages. These methods are either thermal based or membrane based.

    Thermal-based Desalination

    • Solar distillation
    • Natural evaporation
    • Vacuum distillation
    • Multi-stage flash distillation
    • Vapor-compression distillation
    • Wave-powered desalination
    • Membrane distillation

    Membrane-based Desalination

    • Reverse Osmosis
    • Forward osmosis
    • Freeze–thaw
    • Electrodialysis
    • Microbial desalination

    Experimental techniques

    • Waste heat
    • Low-temperature thermal
    • Thermoionic process
    • Evaporation and condensation for crops
    • Ion concentration polarization (ICP)
    • Adsorption-based
    • Hydrogel based desalination
    • Small-scale solar
    • Passarell
    • Geothermal
    • Nanotechnology
    • Biomimesis
    • Electrochemical
    • Electrokinetic shocks
    • Temperature swing solvent extraction
    • Wave energy

    Evaporators

    • Combined supply
    • Vacuum evaporators
    • Compound evaporators
    • Evaporator pumps
    • Flash distillers
    • Vapour-compression distillers

    Multi-stage flash distillation

    Multi-stage flash distillation flashes a portion of the seawater into steam in multiple stages of heat exchangers. Energy consumption is high due to the amount of heat required and also the cooling for condensation of the steam. Much of this energy can be recycled under the right conditions. If this process is combined with other processes that have waste heat and require cooling, then the energy costs are negated.

    Low-temperature thermal desalination does not require as much heat to flash the water because it uses a vacuum to lower the pressure enough to flash the water at ambient temperature. This can allow for a temperature difference of around 8°C between heating water and cooling water. The cooling water can come from deeper ocean water, as it is colder than the surface water.

    Reverse Osmosis

    This method is common for large scale plants as it requires much less energy than flash evaporation. This method uses membranes that allow water to pass through, but not the minerals, as long as the water is pumped at the correct pressure. This method requires clean, filtered water, which makes this process have an added cost for the high amount of consumable and maintenance. I question the decision to choose this method because the people involved stand to make a large recurring revenue stream to supply these consumables as well as provide service contracts for maintenance. The competing method would not provide this revenue stream.

    Conclusion

    We believe that the flash evaporation method is the better choice and will begin the design for the prototype.