Submitted to: Journal of Agriculture and Food Chemistry
Publication Type: Peer reviewed journal
Publication Acceptance Date: 6/27/2005
Publication Date: 7/7/2005
Citation: Eggleston, G., Monge, A. 2005. Minimization of seasonal sucrose losses across robert's type evaporators in raw sugar manufacture by ph optimizationl. Journal of Agriculture and Food Chemistry. 53(16):5332-6339. Interpretive Summary: Currently, sugarcane factory staff do not take into account losses of sucrose across evaporators for the improvement of evaporator performance. A large factory study was undertaken to measure the effect of varying the factory target pH of syrups on sucrose losses, in order to provide optimum juice and syrup pH levels to U.S. sugarcane factories so that losses can be minimized. Increasing the factory target pH of the syrup systematically reduced losses of sucrose; however, scaling formation in evaporators overrode pH effects in later evaporators. Seasonal effects on evaporator sucrose losses were dramatic. An optimum target FES pH of ~6.3-6.5 measured at room temperature is recommended, with a higher target FES pH in early season or when processing immature cane, to reduce excessive losses. The economic cost of sucrose losses are also described.
Technical Abstract: A factory study was conducted to determine the effects of target final evaporator syrup (FES) pHs across the season on sucrose losses. The factory operated Robert's-type calandria evaporators, with two (2,755 and 2,297 m2, respectively) pre-evaporators in parallel, and three series of triple-body evaporators (1,148 m2 each) in parallel; Rts were 11.4 and 9.5 min in the two pre-evaporators, respectively, and increased from 10.0 to 21.8 min across the triple-bodies. GC was used to determine sucrose losses as '%gluc/%sucrose ratios on a oBrix basis. Most sucrose losses to acid inversion occurred in the pre-evaporators. Increasing the factory 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 early season when cane quality was lowest, higher amounts of impurities catalyzed further inversion of sucrose. In late season, resilient scale built-up across the season contributed to higher inversion. An optimum target FES pH of ~6.3-6.5 measured at room temperature (equivalent to a CJ pH of ~7.1-7.3) is recommended, with a higher target FES pH in early season or when processing immature cane, to reduce excessive losses. Across the evaporation station, 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 min. US$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 min. $131,089.