The effect of coolant temperature and stirrer speed for concentration of sugarcane via progressive freeze concentration process

Abstract

Progressive freeze concentration system engaging an anti-supercooling holes crystalliser was used to concentrate sugarcane juice in order to increase its sugar content and achieve highly concentrated sugarcane juice without initial supercooling or ice lining process. The other function of this process is to retain the aromatic compound, quality and avoid operating pressure compared to using another separation process like evaporation and reverse osmosis. The process was conducted with a specific process condition including coolant temperature, stirrer speed, constant initial concentration and process time. The parameter of coolant temperature and stirrer speed was in the range of -6 to -14 °C and 150 to 350 rpm, meanwhile the constant process time was set at 180 min and constant initial concentration at 12 - 13 % Brix. The effects of coolant temperature at stirrer speed were evaluated and observed based on the value of effective partition constant, Kvalue, and concentration efficiency of the sugarcane juice. This system achieved its best performance at intermediate coolant temperature which is -8 °C and stirrer speed of 300 rpm, referring to the best K value and concentration efficiency with the values of 0.438 and 51.15 %. The heat transfer analysis was done by determination of overall heat transfer coefficient, where the highest overall heat transfer coefficient, Uo was found at coolant temperature of -8 °C and stirrer speed of 350 rpm, implying that the smallest thickness of ice was formed on the wall of the crystalliser at this condition, which favours the heat transfer in the process.