Study On Gas Short Cut Through the Dynamic Seal of Rotating Packed Bed

                                                         Study on gas short cut through the dynamic seal of rotating packed bed

Yumin Li, Xiaohua Li, Yunliang Yu, Zhichao Xu, Xuejun Liu, Jianbing Ji

Zhejiang Province key laboratory of biofuel, College of Chemical Engineering & Materials Science, Zhejiang University of Technology, 310032 Hangzhou, China 

     As process intensification technology, the rotating packed bed(RPB), which replaces gravity with centrifugal acceleration and named it “Higee”, can lead to dramatic reduction in equipment size due to an order of magnitude higher mass-transfer rate and gas-liquid throughput. The PRB includes one static casing and one rotor with high rotational speed in the casing. Fed through a distributor at the eye of the RPB, the liquid is through outwards by the centrifugal force as thin film or flying droplets. Fed into the casing, the gas flows inwards through the rotor by pressure difference from the outer periphery to the inner periphery of the rotor. And then, the gas enters the eye of the RPB, leaving the RPB through the gas outlet of the casing. To prevent the gas in the casing from taking a short cut into the gas outlet of the casing without passing through the rotor, a tight dynamic seal must exist between the eye of the rotor and the gas outlet of the casing. Usually, labyrinth dynamic seal, packing dynamic seal and centrifugal dynamic seal are employed in the RPB. However, these dynamic seals are not tight and a bit of gas may unavoidably take a short cut through the dynamic seal and enter the gas outlet of the casing, resulting in the reduction of theoretical plate number of RPB. So a model about the effect of gas short-cut on theoretical plate number of RPB is developed and given as:

           y_i′=y_i(1-Φ)+y_oΦ

where y_o is mole fraction of light component at the outer periphery of the rotor, y_i is mole fraction of light component at the inner periphery of the rotor without gas short-cut, y_i′ is mole fraction of light component at the inner periphery of the rotor with gas short-cut, Φ is the ratio of short-cut gas rate to the whole gas rate.

      With benzene and methylbenzene system at total reflux and y_o=0.3, if Φ=10% and 30%, theoretical plate number of RPB reduces by 28.9% and 51.2%, respectively. Therefore, the effect of gas short-cut on theoretical plate number of RPB is great, to which much attention is paid.

 Keyword: Distillation, dynamic seal, gas short cut and rotating packed bed

Correspondence to: Professor Jianbing Ji, Zhejiang Province key laboratory of biofuel, College of Chemical Engineering & Materials Science, Zhejiang University of Technology, Hangzhou, 310032, Zhejiang Province, China.

Tel.:+86 571 88320598  E-mail: jjb@zjut.edu.cn