Investigation of freeze crystallization and ice pressing in a semi-batch process for the development of a novel single-step desalination plant

Potable water production is an essential but energy intensive process and usually requires many chemicals. Furthermore, small-scale plants are not yet available because of the problems associated with downscaling the thermal evaporation or reverse osmosis processes. Freeze crystallization is an alternative, especially for the self-sufficiency of potable water in remote areas. The use of a crystallizer and a separate press in combination with a perforated pressing mold has shown that the desalination of saltwater can be achieved by pressing the ice only; no additional washing step is necessary. A pressing force of 37.4 kN (100 bar) and a holding time of 180 s were found to be sufficient. Therefore, these parameters were used to design a single-step plant, which also showed good results in the case of ion expulsion. Nonetheless, the variation in the test parameters showed their influence on crystal growth and crystal purity and demonstrated the need to find the optimal design parameters for future continuously operating systems.