Hamchang constructs seawater desalination plants in many different countries suffering water shortage. The company successfully constructed such plants with the uses of commercialized techniques : Reverse Osmosis (RO), Multiple Effect Distillation (MED) and Multi Stage flash(MSF).
As the name suggests, pressure is applied to seawater through semi-permeable membrane in order to separate substances like water and salt and thereby produce fresh water. Its relatively easy operation and low energy consumption make it ideal for all capacities – small, medium and large plants.
The first commercial operation of RO dates back to the 1970s. Compared to MSF and MED, RO is a relatively recent technology. RO uses semi-permeable membrane to separate water from the solute in the seawater. In RO, most of the energy is needed to pressurize the feed water.
The seawater desalination by RO system consists of pretreatment system, high pressure pump and RO membrane. The auxiliary units include water intake and effluent systems and power reception and transmission systems.
MED (Multi-Effect Distillation) is similar to MSF, but only makes use of devices called Effect instead of “Stage” from MSF. The MED method has the advantage of reducing energy consumption if applied with dump heat, and is mostly used for medium-capacity desalination plants.
Its principle is to spray seawater on the outside of metal tubes to condense the vapor flowing inside. The seawater outside the tube boils to generate steam which flows into the tubes to condense in the next cycle. The process is then repeated. Since the outside of the tubes is maintained in a vacuum, the seawater boils even when it is sprayed at a low temperature. The big difference from MSF is that it is relatively smaller in size as it is operated at low temperatures (60 ~ 70 ℃) but is more efficient and consumes less electricity per unit production.
With the MSF (Multi-Stage Flash) method, sea water flows through a multi-level heat exchange system, is heated with steam from the power generating plant until evaporation, and is then condensed on the outside of pipes through which cold seawater flows.
The MSF method generates fresh water from seawater using flashing which is a phenomenon of instantaneously discharging water vapor. MSF is a facility designed to use energy more effectively by continuously generating flashing of seawater at low steam pressure from each stage without the addition of heat source.