Study On The Performance And Ideal Start-up Model Of A Modified Scheibel Extraction Tower

Scheibel extraction tower is one of the available countercurrent agitated contactors. The main disadvantage of the Scheibel extraction tower is the severe backmixing. In order to reduce the backmixing effect and provide efficient phase separation, a modified Scheibel tower was designed. Two sieve plates were installed at the two ends of the packed section and it can reduce the backmixing greatly.The performance of the modified Scheibel extraction tower (diameter 50 mm, stage height 75 mm) was studied in this paper using propanol-heptane-water system. The factors of opening ratio of the sieve plates, ratio of the height of packed section and the height of agitation section, agitation speed and overall flow rate were studied. The optimized structural parameters and operating conditions were determined that the opening ratio of the sieve plate, the ratio of the height of the packed section and the height of the agitation section, the agitation speed and the overall feed flow rate are 10%, 0.5:1, 100 rpm and 6.0 mL/min, respectively. The extraction efficiency of the traditional Scheibel extraction tower and the modified Scheibel extraction tower were studied with the optimized structural parameters and operating conditions. The results demonstrated that the extraction efficiency of the modified Scheibel extraction tower was much better than that of the traditional one. Then, this paper conducted a study on the extraction rate of the modified one stage, three stages, and five stages Scheibel extraction tower, and the results demonstrated that the extraction rate increased with the increase of stages. The extraction rate was more than 99% when the stages of the modified Scheibel extraction tower were more than five stages, and it can satisfy for the normal industrial needs.As the start-up of the extraction process is very important, an ideal start-up model of the modified Scheibel extraction tower was developed under reasonable model assumptions. The analytical solution for the single stage and the numerical solution for the n-stage Scheibel extraction tower were obtained from solving the model equations. For one stage extraction tower, the calculated results of the model agreed with the experimental one, but the latter was better than the former, because the mass transfer in the packed section made the extraction efficiency in the one stage extraction tower higher than one ideal extraction stage. While for three stages extraction tower, the extraction efficiency was much lower than the model. The main reason was that the backmixing could not be ignored in the ideal model.