Studies on the Evaporation and Combustion of Calcium-base Sulfite Spent Liquor (XIV). Over-all Heat-transfer Coefficients and Boiling Point Rises in the Evaporation of Decalcified Sulfite Spent Liquor and Kraft Black Liquor in a Long-tube Vertical Evapora

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Small-scale pilot-plant experiments were conducted on the evaporation of decalcified sulfite spent liquor (I) in a long-tube vertical evaporator. The evaporator used had only one heating tube 2.54cm in ID and 3.5m in length (heating surface 0.28m2). The feed concentration was varied from 10 to 50% (by wt.). In all cases, the feed rate was 34±2l/h, the boiling point was 95±1.0°C., and the temperature drop was 10.0±1°C. Also, for purposes of comparison, kraft black liquor (II) was evaporated under similar conditions in the same evaporator. The over-all heat-transfer coefficients U (kcal/m2h°C) in the evaporation of I from given initial concentrations were as follows : (The initial and final concentrations in weight per cent are given in order in parentheses.) 2, 800 (10, 20%), 2, 600 (20, 30%), 2, 400 (27, 40%), 2, 100 (36, 50%), and 1, 700 (45, 60%). The boiling point rises were 2.7, 4.0 and 5.0°C., respectively, at concentrations of 40, 50 and 55%. The values of U in the evaporation of II under similar conditions were nearly equal to the corresponding values found in the experiments with I. The boiling point rises were 4.0, 6.4 and 8.0°C respectively, at concentration of 4.0, 50 and 55%.
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