SO₂ enhanced desorption from basic aluminum sulfate desulphurization-regeneration solution by falling-film...

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^-1 s^-1, 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^-3, 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 SO₂ desorption. Correlations were obtained to predict the mass transfer coefficient and SO₂ desorption efficiency. This study develops a new type of falling-film evaporator for SO₂ desorption from basic aluminum sulfate desulphurization-regeneration solution and provides a basis for process design and industrial application.