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Sugarcane factory performance of cold, intermediate, and hot lime clarification processes

A comparative factory investigation of hot versus intermediate and cold lime clarification was undertaken to quantify performance. In cold liming, mixed cane juice (MJ) was incubated (8 min) and then limed in a lime tank (4 min), both at ~105F. For intermediate liming, 50% of the MJ was heated (180-200F) before incubation (8 min), then limed in a lime tank (4 min) at ~150F. Hot liming was configured very similar to intermediate liming except that incubation time was increased from 8 to 12 min, and that lime was added immediately after flash-heating (215F; 30 s). Overall, both hot and intermediate liming performed much better than cold liming, and hot liming offered some extra advantages over intermediate liming. Less sucrose was lost to inversion reactions across both hot (season avg. 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 from ~pH 6.0 to 6.3, in both hot and intermediate liming, markedly reduced sucrose inversion losses 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 lbs lime/ton cane compared to 1.28 for the previous grinding season when intermediate rather than hot liming was operated. Preheating 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 avg.) more turbidity removal (MJ to clarified juice [CJ]) occurred in both hot and intermediate liming compared to cold liming. Markedly less color formed and dextran removal was the best across hot liming. 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

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