Study On Saccharate Calcium Preparation From Secondary Juice Of Sugar Mill

Hundreds of clarifying agents have been tried in the clarification of juice since sugar clarification technology development. However, only lime, phosphate acid, sulfurous acid, carbonic acid and magnesia can be adapted to the clarification of industrialization. Lime is the clarifying agent which is the mostly used, and it is also indispensable whether in the production of raw sugar or plantation white sugar. In our country, juice is exclusively limed with milk of lime in clarification, resulting consequently in some deficience, such as the pipeline of lime is easy to be plugged and the control of liming pH is not accurate. It has been comment that although liming with saccharate instead of milk of lime, such as in Australia, is able to eliminate some impacts of liming with milk of lime, there is still something inadequate, the clarification of saccharate, for instance, is hard to implement due to the high concentration of syrup. In addition, the repeated circling of sugar juice increases sucrose conversion.In this paper, saccharate calcium was prepared by clarifying the secondary juice, which was used to clarify the primary juice as one of the clarifying agents. The lime was firstly slaked with clarified secondary juice to prepare the lime milk of secondary juice, which was used to clarify the secondary juice at high alkalinity to make the targeted saccharate calcium. Under sufficient investigation of the properties of lime dissolving in secondary juice, the influence of process parameters were investigated and optimum conditions were concluded. With the confirmed process and conditions, the optimum conditions for reducing the filter mud pol and the properties of solid-liquid separation based on centrifugal-concentration-and-filtration for clarification of secondary juice were investigated. The main contents and results are as follows:1. The relationships of CaO addition, pH value and the molar ratio of sucrose to calcium in the secondary juice under different temperature were studied. The variations of purity and color of the secondary-juice saccharate calcium and lime milk with time were studied, showing that the purities and color values of the two materials could remain stable in a certain time under the temperature of30～50℃. Based on the experimental data, the relationships of CaO addition, pH value and the molar ratio of sucrose to calcium in the secondary juice at50℃were regressed as the following: pH=8.79C0.211(0.67<C<3.33) pH=14.25e-0.0417Rs/c (13.81<Rs/c<5.88)(0.67<C<3.33) 2. In the study of alkali clarification of secondary juice, the influence of phosphate dossage, reaction pH value and reaction temperature on turbidity and color of saccharate solution were investigated through single factor experiments. Based on single factor experiments, the Responsive Surface Method (RSM) experiment was performed. The optimal conditions were found to be phosphate dossage28mL/L, reaction pH value11.44and reaction temperature41.9℃. With correlation coefficient of the regression equation being0.9676, the RSM shows good correlation and reliability. The clarifying effect of new technology and traditional sulfitation method were compared under the same experimental condition, the result showed that new method could improve the quality of clarified juice, especially turbidity and color, the reductions of turbidity and color could achieved40%and38%respectively. The purity and calcium content were also improved, the average of purity was increased by2AP and the calcium content decreased by0.104%°Bx.3. The influences of lime milk grinding time, pH value and stirring speed of reaction on filter mud pol when clarifying the secondary juice by addition of secondary lime milk were studied through orthogonal test, showing that the reaction pH was the most significant factor. Without addition of wash water, the average pol of the filter mud could be as low as11.59%under the conditions of pH value11.4, grinding time60s and stirring speed300r/min, which was at the same level as the addition of milk of lime. The incomplete dissolve of tri-calcium saccharate did not show influence on the filter mud pol.4. The thickening rate of centrifugal sedimentation and the properties of filtration were experimental investigated. The result showed that the thickening rate of mud juice increased with the increase of the centrifugal rotational speed, which tended to be stable when the speed was up to2000r/min. The the average of thickening rate of the mud juice was16.09when the rotational speed was above2000r/min. The vacuum filtration showed that the filtration of secondary alkali juice could be operated easily while the temperature was above80℃. The optimal operating conditions for pressure filtration were at0.1～0.15MPa and100℃.