Freeze Concentration of Liquid Waste Streams
Freeze concentration can provide an effective and economic alternative to other separation processes, such as the use of membranes or evaporation, and can produce a pure water stream from dilute, multi-component waste streams.
Solution-based crystallization is used to produce extremely pure crystals of ice in the waste stream, which leaves the impurities concentrated in the remaining liquid.
Separation of the pure ice crystals from the concentrated waste stream is then completed in a packed-bed wash column, and the pure ice crystals are melted back into pure water, which can either be discharged without additional treatment, or reused as process or cooling water, for example. GEA’s freeze concentration systems have been successfully applied for the treatment of waste water that contains a range of organic and inorganic compounds.
One commercial application of the process is the concentration of waste water streams prior to incineration. Concentrating the waste water increases the capacity of the downstream incinerator, increases the calorific value of the waste ‘fuel’, and reduces transportation and intermediate hold-up volumes, along with the related hazards and costs.
Seraya Chemical Singapore Ltd. (SCSL) and Shell Chemicals Moerdijk B.V. have both selected GEA freeze concentration technology as the pre-concentration step for their hazardous waste water, which is destined for incineration. Many of the components in the streams are harmful to standard bio treatment systems, so incineration was chosen as the preferred method.
Without pre-concentration, the low solute concentrations in the waste streams reduced the efficiency of the incinerator, and increased the processing costs. Freeze concentration effectively removed 75% of the water in the waste stream, at a much lower cost than direct incineration.