Minimization of Seasonal Sucrose Losses Across Robert's- Type Evaporators in Raw Sugar Manufacture by pH Optimization

Abstract

Factory staff must consider all costs to make sound economic decisions on how to improve the performance of evaporators, which includes knowing optimum pH levels to minimize sucrose losses. A factory study was conducted to determine the effects of target final evaporator syrup (FES) pH values across the season on sucrose losses. The factory operated Robert's type calandria evaporators, with two (2787 and 2322 m2) preevaporators in parallel and three sets of triple-body evaporators (1148 m2 each) in parallel; Rt values were 11.4 and 9.5 min in the two preevaporators, respectively, and increased from 10.0 to 21.8 min across the triple bodies. Gas chromatography was used to determine sucrose losses as Delta%glucose/%sucrose ratios on a degrees Brix basis. Most sucrose losses to acid hydrolysis occurred in the preevaporators. Increasing the target pH of the FES or clarified juice (CJ) systematically reduced losses of sucrose; however, scaling effects overrode pH effects in later bodies. Seasonal effects on evaporator sucrose losses were dramatic. In the early season when cane quality was lowest, higher amounts of impurities catalyzed further hydrolysis of sucrose. In the late season, resilient scale built-up across the season contributed to higher hydrolysis. An optimum target FES pH of approximately 6.3-6.5 measured at room temperature (equivalent to a CJ pH of approximately 7.1-7.3) is recommended, with a higher target FES pH in the early season or when processing immature cane, to reduce excessive losses. Across the evaporation station, the juice/syrup pH decreased up to the 2nd body with a consistent increase in the 3rd body due to evaporation of volatile acids into the condensate. Equations to assess the economic implications of evaporator sucrose losses are described. A target FES pH of 5.9 caused a season average sucrose loss of 0.55% equivalent to 1.52 lbs sucrose lost/ton of cane and a minimum USD 390,400 loss in profits. In contrast, a target FES pH of 6.5 reduced this sucrose loss to 0.36% and 1.01 lbs sucrose lost/ton of cane and saved the factory a minimum of USD 131,100.