Relationships between the physical forms of starch and performance of carbonatation clarification and press filtration at the refinery

Authors: COLE, MARSHA - Orise Fellow; Eggleston, Gillian; BORGES, EDUARDO - Fermentec; THOMPSON, JACK - Louisiana Sugar Refining; RATHKE, THOMAS - Imperial Sugar Co; NAIKI, JUNE - American Sugar Refining, Inc; DIAMOND, MARIA - American Sugar Refining, Inc

Submitted to: Meeting Proceedings
Publication Type: Proceedings
Publication Acceptance Date: 6/9/2017
Publication Date: 9/1/2017
Citation: Cole, M., Eggleston, G., Borges, E., Thompson, J., Rathke, T., Naiki, J., Diamond, M. 2017. Relationships between the physical forms of starch and performance of carbonatation clarification and press filtration at the refinery. In: Proceedings of the Sugar Industry Technologists Conference, May 7-11, 2017, Tainan, Taiwan. p. 1-12.

Interpretive Summary: Laboratory studies were undertaken to closely investigate how concentrations of insoluble, soluble, and swollen starch in raw sugars affected carbonatation refineries. Previous studies revealed that soluble starch preferentially interfered with the carbonatation clarification stage of sugar refining and produced small calcium carbonate crystals, but an explanation was not available until now. The formation of calcium carbonate crystals and decreased press filtration efficiency was attributable to strong soluble starch-calcium interactions; whereas increased milk of lime dosages and longer carbonatation reactions were because of insoluble starch-hydroxide interactions. Mixtures of soluble and insoluble starch exhibited features of both physical starch forms but soluble starch adversely and indirectly affect carbonatation clarification more. Results support the need for new refinery methods that accurately depict both soluble and insoluble starch’s behavior during carbonatation clarification and press filtration at the refinery.

Technical Abstract: Laboratory studies were conducted to underpin if and how the different physical forms of starch (insoluble or soluble) affected carbonatation clarification and press filtration, by using simulated melt liquors. Carbonatated liquors containing =250 ppm/Brix (USDA starch research method) of total starch and either insoluble or soluble physical starch forms (used separately or in a mixture at nearly equal amounts) were uniquely detrimental to the simulated carbonatation refining process and press filtration. High amounts of soluble starch accelerated carbonatation reactions by: (i) binding Ca2+ and removing it from solution, (ii) contributing to the production of CaCO3 fines (<5 µm), (iii) causing negligible mud yields, and (iv) producing inadequately clarified liquors. On the other hand, soluble starch was not involved in the viscosity of liquors or problems with press filtration. In comparison, insoluble starch prolonged carbonatation clarification reactions, but had better CaCO3 crystal sizes, mud yields, and impurity removal which influenced press filtration flow rates. Insoluble starch (precursor to swollen starch) also rapidly clogged filters and increased the viscosity of simulated melt liquors. Other studies using factory raw sugars confirmed that measuring filterability at the laboratory scale is complex and may not accurately reflect actual refinery performance without consideration of all impurities and carbonatation clarification reaction conditions since soluble starch, color, invert, dextran, and ash were indirectly involved. Results support the urgent need for new refinery methods that accurately measure both soluble and insoluble starch content in raw sugars and predict the filterability performance of raw sugars at the refinery with consideration of all impurities.