FURTHER INSIGHTS ON THE FACTORY PERFORMANCE OF COLD, INTERMEDIATE, AND HOT LIME CLARIFICATION SYSTEMS

摘要

Since 1996, Cora Texas factory in Louisiana has been operating intermediate lime clarification and was, therefore, one of the few U.S. factories that did not operate cold lime clarification. In an attempt to further improve clarification performance, the factory made the decision to convert to hot lime clarification during the 2000 grinding season. A comparative investigation of hot versus intermediate and cold lime clarification was undertaken to quantify performance. In cold liming, mixed juice (MJ) was incubated (8min) and then limed in a lime tank (4min), both at ～105℉. For intermediate liming, 50% of the MJ was heated (180-200℉) before incubation (8min), then limed in a lime tank (4min) at～150℉. Hot liming was configured very similar to intermediate liming except that incubation time was increased from 8 to 12 mins, and that lime was added immediately after flash-heating (215℉; 30sec). Hourly samples across each of the three processes were collected over a six hour sampling period, on three consecutive days respectively, and these were repeated three times across the 2000 grinding season. For most clarification parameters investigated, both hot and intermediate liming performed much better than cold liming, and hot liming generally offered some extra advantages over intermediate liming. Less sucrose was lost to inversion reactions across both hot (season av. 0.79%) and intermediate (0.97%) lime processes than across cold liming (1.48%). By operating hot liming, the reduction in sucrose losses alone saved the factory approximately US$283,000 over cold liming. Increasing the factory target pH of the final evaporator syrup (FES) from ～pH 6.0 to 6.3, in sampling period 3 in both hot and intermediate liming, caused a very marked reduction in sucrose inversion losses, particularly across the clarifiers and evaporators. Dramatically less lime had to be added in hot liming compared to either cold or intermediate liming, with the factory consuming, on season average, only 1.01 Ibs lime/ton cane compared to 1.28 for the 1999 grinding season when intermediate rather than hot liming was operated. Pre-heating 50% of the MJ in both intermediate and hot liming consistently removed color, dextran, and starch, but silicate levels were not significantly changed. Although, the fastest settling occurred in intermediate liming, ～ 2.1% (season av.) more turbidity removal (MJ to clarified juice [CJ]) occurred hi both hot and intermediate liming compared to cold liming, with better CJ turbidity control. Subsequent FES and raw sugar turbidity values were better in hot liming. Markedly less color (～2.5%) formed on hot liming because of reduced retention time of liming, compared to ～17% color formation in cold and intermediate lime clarification. Dextran removal was best across hot liming and, as expected, dextran formed in the cold lime tanks. Using hot liming across the season, the factory observed 12-15% more heating capacity in the limed juice heat exchangers and a 90% reduction in the quantity of chemicals needed to clean the heat exchangers.