Thermodynamic carbonatation modelling and potential energy savings

Carbonatation measurements as a rule register a drop in the temperature of the entering limed juice, attributable to the high water vapour content of the waste carbonatation gas. The resulting exhaust heat stream can amount to as much as 5 MJ/100 kg beet. With due regard to the liberated reaction heat in the carbonatation vessel, a model was developed which allows calculation of the enthalpy flows in accordance with various operating parameters. The results are compared with measurements taken in six sugar factories during the 1992 and 1993 campaigns. Relationships can be established between CO2 utilization, load level and juice temperature. Various proposals to reduce the exhaust heat stream are presented. A case study of the first carbonatation looks at heat recovery from the waste carbonatation gas and carbonatation under increased pressure. The example shows potential steam savings of about 0.2 kg/100 kg beet by pressure carbonatation and of 0.15 kg/100 kg beet by heat recovery. The authors make use of enthalpy balances and pinch analysis in studying the sugar factory as a system.