SO enhanced desorption from basic aluminum sulfate desulphurization-regeneration solution by falling-film evaporation.

To find the optimal structure of the converging-diverging tube and develop a high-efficiency falling-film evaporator, the heat and mass transfer performances of falling-film evaporation with converging-diverging tubes of different dimensions were studied. The optimal converging-diverging tube was used in falling-film evaporation desorption of the basic aluminum sulfate desulphurization-regeneration solution, and different influential factors on the desorption effect were analyzed. It was found that converging-diverging tubes with large falling-film flow rate performed well in the heat and mass transfer of falling-film evaporation, and their rib height largely affected the heat and mass transfer performances. At the same rib height and rib pitch, the longer the converging segment of the converging-diverging tube was, the better the heat transfer performance was. The evaporation heat transfer coefficient and evaporation mass transfer rate in the optimal converging-diverging tube were 1.6 and 1.38 times larger than the smooth tube, respectively. The optimal converging-diverging tube was used in falling-film evaporation desorption of basic aluminum sulfate desulphurization-regeneration solution, at a perimeter flow rate of 0.114-0.222 kg m s, the desorption efficiency inside the tube was up to 94.2%, which was 10.3-10.5% higher than that of the smooth tube. At the inlet sulfur concentration of 0.02-0.1 kmol m, the desorption efficiency was up to 94.1%, which was 12.0-16.3% larger than that of the smooth tube. At the heating temperature of 371.15-386.15 K, the desorption efficiency was up to 93.4%, which was 6.7-11.5% larger than that of the smooth tube. Smaller falling-film flow rate, higher sulfur concentration, or higher heating temperature was more constructive to SO desorption. Correlations were obtained to predict the mass transfer coefficient and SO desorption efficiency. This study develops a new type of falling-film evaporator for SO desorption from basic aluminum sulfate desulphurization-regeneration solution and provides a basis for process design and industrial application.