Research On Structural Optimization Design And Performance Of Cross-flow Rotating Packed Bed

High gravity rotating packed bed?RPB?is one of the novel process intensification equipment in chemical engineering.So far,massive research in-depth on the RPB from two aspects of mass transfer and hydrodynamic performance has been studied.The mass transfer performance research system tends to mature.From the research results,it can be found that the axial thickness and radial length of the packing,the structure of liquid distributor and the liquid distribution in the packing would have an impact on the mass transfer efficiency of RPB.Meanwhile,the uneven liquid distribution in the packing has been confirmed,but quantitative analysis method is still lacked.Accounting for these issues,in this paper,the suitable axial thickness and radial length of metal wire mesh packing and the number of spray holes in the central tubular liquid distributor were investigated,respectively.Furthermore,a method to measure liquid distribution in RPB was proposed in order to provide theoretical guidance and data support for mass transfer research.As the packing structure changes,the packing volume would change accordingly,and the adjustment in the axial thickness and radial length of the packing mainly affect the gas residence time and the liquid residence time,respectively.In order to eliminate the influence of packing volume,the effective mass transfer specific surface area a_e was measured by NaOH-CO₂.And the liquid volume mass transfer coefficients k_la_e and gas volume mass transfer coefficients k_ya_e were measured with NH₃-H₂O at different radial lengths and axial thicknesses,separately.Meanwhile,the influence of the number of nozzles in liquid distributor on specific surface area a_e and liquid volume transfer coefficient k_la_e in RPB was investigated by NaOH-CO₂.On the basis of optimum structure of filler and liquid distributor,the structure-activity relationship between liquid distribution and mass transfer performance was explored using self-made liquid distribution detection device with NaOH-CO₂.The results showed that:When the axial thickness of packing changes,the operation parameters were high gravity factor?,the liquid volume L and the gas volume G.The results showed that a_e and k_ya_e increased with the increase of?,L and G.The mass transfer effect of cross-flow RPB with smaller axial thickness of packing is better than that of larger axial thickness,which indicated that"end effect zone"exists when gas enters the packing from the bottom of the shell.The end effect zone contributes most to the overall mass transfer effect of cross-flow RPB.When the radial length of packing changes,the operation parameters were rotational speed N,the liquid volume L and the gas volume G.The results showed that a_e and k_la_e increase with the increase of N,G and L,but the change rule is unobvious with packing radial length increasing.While it can be found by experimental analysis that there exits inner-end effect zones and outer-end effect zones in the packing layer.The nozzle holes of the central tubular liquid distributor are symmetrically distributed along both sides of the central axis.The number of nozzle holes is 4,6,8 and 10,respectively.In this part,a_e and k_la_e were determined with NaOH-CO₂ system,and the operating variables were?,L and G.The results showed that a_e and k_la_e increase with the increase of?and increase first and then decrease with the increase of L and G.Besides,a_e and k_la_e become largest when the number of spray holes is 6 under different?and L,but decrease obviously with G increasing despite becoming largest when that is 8.Therefore,the optimum number of spray holes in this paper is 6.In this section,the effect of N,G and L on the uniformity of liquid distribution,M_f,in RPB was investigated by applying pressure sensor to RPB and taking the mass distribution of liquid as the standard.The smaller the M_f is,the more uniform the liquid distribution would be.The results showed that M_f decreases with the increase of N,decreases first and then increases with L increasing,and the influence of G on M_f is not significant.Because of the existence of inner and outer effect zones of packing,M_f decreases first and then increases with the growth of packing radial length.But the value of M_f mainly distributes between 0 and 0.008,which indicated that the liquid distribution tends to be uniform under the action of high-speed rotating packing.The results of this paper established a new method for the detection of liquid distribution in RPB,provided a reference on the design and optimization of cross-flow RPB,and had a certain guiding significance for the industrialization of RPB.