Development of a new crystallisation chamber for a progressive freeze concentration system

Abstract

Concentration enhancement of solutions is often a process neccessary in many industrial processes, including in liquid food concentrations and wastewater treatment. At present, there are three available methods to carry out such a task, namely evaporation, reverse osmosis and freeze concentration. in evaporation, the water vapour from the heating process is removed and a more concentrated liquid left behind. It is the simplest and commonest method but it uses a large amount of energy to supply for the heat of vaporisation of water which is 1000Btu/lb (Hunter and Hayslet, 2002). It is also not suitable to be engaged if the solution to be concentrated contains volatile organic compounds (VOCs), which would easily turn into dangerous and hazardous vapour when heated. Another increasingly favoured process for solution concentration enhancement is reverse osmosis (RO), which separates the solute and the liquid phase through a water selective membrane. RO uses the least amount of energy because it involves no phase changes and can produce water of very high purity, but clogging of the membrane can easily occur in most cases and replacement of the membrane will definetely involve a high cost. Its efficiency is also sometimes limited by the compatibility of the membrane with the chemical component of the solution, apart from the expensive cost in attaining the osmotic pressure required for the process