Investigation of the depletion of ions through freeze desalination

Abstract

Producing potable water is an important but cost- and energy-intensive process. Small scale machines for insular solutions are not yet available. Whereas drinking water is regulated to a maximum concentration of 0.05wt% sodium chloride, sea water normally ranges from 3wt% NaCl to more than 4wt% NaCl. Freeze crystallization therefore can provide an energy- and cost-effective way to utilize small equipment as a good compromise between energy consumption and low maintenance effort. Because of this, different methods were investigated with respect to their desalination effect, ice growth and implementability. One method was a cooled plate in which dependencies of throughput and ice purity were tested as a function of operation conditions. Another procedure was heterogeneous heat transfer via droplets of non-miscible organic fluids. The last method was classical suspension crystallization were a vessel is cooled down and stirred to produce ice from a solution. Because no pure ice could be produced directly, centrifuging and pressing were investigated for ice purification post-treatment. To prove the whole concept, natural samples from the Atlantic Ocean were desalinated. The final result is that independent from the used freezing process all ice could be desalinated combining the ice production with adjacent mechanical drainage.