Freeze Concentratton by Layer Crystallization

ABSTRACT

Layer crystallization in laminar falling films has been studied for freeze concentration applications. A binary mixture of water and sucrose has been tested in order to compare with literature results from suspension crystallizers. The concentration of sucrose in ice, which is a measure for loss of solute. were from 0.4 to 26.5% for bulk concenwlions of sucrose of 5 to 40%. respectively. The time averaged ice growth rates varied from 3. l0-7 l0 3-10-6 m/s. The results are related to expressions for maximum ice growth rate developed from the gradient criteria. Also an expression for maximum ice growth rate from irreversible thermodvnamics is oresented. Althoueh the exwrimental results show that one–step layercrystallization has amuch lower separation effect than suspension crystallizers with washcolumns, multistep layer crystallization could provide an economical favourable freeze concentration process. A multistep process that combines freeze concentration and reverse osmosis is proposed. A case study shows that it is possibleto reduce the investment costs to less than half of existing processes, for dewatering capacity of 700kg per hour. The energy consumption is also reduced.

Keywords:

• freeze concenwtion
• layer crystallization
• falling film
• sucrose solution