Evaporator performance monitoring at Farleigh mill

During recent seasons, the crushing rate at Farleigh Mill has been regularly limited by evaporator capacity. In 1998 and 1999 seasons, evaporator performance was investigated by analysing variations in the values of juice and steam temperatures within the evaporator set. Problems identified were (a) differences between parallel effets, (b) inefficient condensate removal, (c) excessively high steam temperatures into No.1 effet, (d) adverse effects of level changes on juice temperature, (e) the potential for juice shortcircuiting in No.1 effet, and (f) poor performance of No.5 effet. A baffle installed underneath No. 1 effet calandria produced 1.5 °C increase in juice temperature out of this vesseL This increase in temperature is estimated to have produced a 5 t/h increase in evaporator rate. Analysis of temperature data was also used to improve understanding of processes within the evaporator set, and to assess evaporator cleaning effectiveness. Effective cleaning of No.5 effet tended to produce lower juice and steam temperatures out of the first four effects and higher liquor temperatures out of the final effet. The effectiveness of chemicals such as sulphamic acid in No.1 effet and EDTA in No.5 effet was clearly demonstrated, as was the ineffectiveness of some cleans using caustic alone.