Solvent extraction based on mixer-settler is the major industrial method of rare earth （RE） separation. In the mixer-settler extraction process, due to the insufficient settling time in normal circumstances, backmix...Solvent extraction based on mixer-settler is the major industrial method of rare earth （RE） separation. In the mixer-settler extraction process, due to the insufficient settling time in normal circumstances, backmixing of the aqueous phase could have signifi- cant impact on the process of RE extraction separation. Therefore on the basis of the extraction equilibrium and mass balance of the mixer-settler extraction process, here we developed a mathematic expression of the aqueous phase backmixing in a two-component separation process, and obtained a quantitative analysis of the backmixing effect on the purification process by the approximations according to certain hypotheses. Two extraction systems of La/Ce and Pr/Nd separation were chosen as the examples to analyze the backmixing effect, and the results showed that the aqueous backmixing had greater influence in the scrubbing segment than in the ex- traction segment, especially in the system with a high separation factor such as La/Ce separation. Therefore it was suggested that the aqueous backmixing effect should be well attended in the design and application of RE extraction separation.展开更多
Five different internals were designed,and their effects on phase holdup and backmixing were investigated in a gas–liquid concurrent upflow reactor where the spherical alumina packing particles of three diameters(3.0...Five different internals were designed,and their effects on phase holdup and backmixing were investigated in a gas–liquid concurrent upflow reactor where the spherical alumina packing particles of three diameters(3.0,4.5 and6.0 mm)were slightly expanded under the conditions of varied superficial gas velocities(6.77×10^(-2)-3.61×10^(-1) m·s^(-1))and superficial liquid velocities(9.47×10^(-4)-2.17×10^(-3) m·s^(-1)).The experimental results show that the gas holdup increases with the superficial gas velocity and particle size,opposite to the variational trend of liquid holdup.When an internal component is installed amid the upflow reactor,a higher gas holdup,a less liquid holdup and a larger Peclet number characterizing the weaker backmixing are obtained compared to those in the bed without internals under the same operating conditions.Additionally,the minimal backmixing is observed in the reactor equipped with the internals with a novel multi-step design.Finally,empirical correlations were proposed for estimating gas holdup,liquid holdup and Peclet number with the relative deviations within 11%,12%and 25%,respectively.展开更多
1 INTRODUCTIONDowncomers,employed in tray columns,are widely used nowadays in industrialseparation processes.They function as channels for the liquid phase to fall fluentlyfrom one tray onto its neighbouring places fo...1 INTRODUCTIONDowncomers,employed in tray columns,are widely used nowadays in industrialseparation processes.They function as channels for the liquid phase to fall fluentlyfrom one tray onto its neighbouring places for the held-up bubble to separate fromthe liquid phase.It is well known that liquid flow patterns and mixing characteristicsin downcomers are closely related to the initial liquid distribution on the tray,andhence to tray efficiency.For a long period of time,little attention has been paid展开更多
An experimental study of the extent of axial backmixing in both gas and liquid phases was conducted in a 150 mm ID column packed with Mellapak 250Y corrugated structured packing. The column was operated at pressures r...An experimental study of the extent of axial backmixing in both gas and liquid phases was conducted in a 150 mm ID column packed with Mellapak 250Y corrugated structured packing. The column was operated at pressures ranging from 0.3 MPa to 2.0MPa with nitrogen and water flowing countercurrently through the packing. The amount of axial backmixing was experimentally evaluated by the pulse response techniques using hydrogen in gas phase and an aqueous solution of NaCl in liquid phase as inert tracers. The response of the tracer was monitored by means of thermal conductivity in the gas phase and electrical conductance in the liquid phase. The experimentally determined residence time distribution (RTD) curves were interpreted in terms of the diffusion-type modei. The results indicated that the axial backmixing in the gas increased notably with gas flowrate and slightly with operating pressure and liquid flowrate. The liquid-phase axial backmixing was an increasing function of both gas and liquid flowrates and insensitive to pressure. Various correlations were developed for reproducing the experimental mixing data. The agreement between experimental and correlated data appeared to be acceptable and within ±20% of difference.展开更多
Performance of Mellapak 250Y and 350Y corrugated structured packing in distillation applications at pressures ranging from 0.3 to 2.0MPa is analysed by using HTU-NTU method. These data are obtained in a distillation c...Performance of Mellapak 250Y and 350Y corrugated structured packing in distillation applications at pressures ranging from 0.3 to 2.0MPa is analysed by using HTU-NTU method. These data are obtained in a distillation column with 0.15 m diameter op-erated with n-butane/n-pentane system at total reflux. In considering the axial backmixing effects, the height of an overall gas phase transfer unit, HTUOG , is divided into two parts. One part represents the height of an overall gas phase transfer unit, without backmixing, designated as*OGHTU, and the other part, designated as the height of a backmixing unit (HBUO), accounts for the backmixing effects. The HTUOG is evaluated from the measured concentration profile of n-butane in liquid phase. The HBUO obtained experimentally is correlated in terms of the properties of the materials being separated and the equivalent diameter of the structured packing. Our result shows that HBUO varies from 0.12 to 0.34 m as pressure increases from 1.0 to 1.9 MPa. It indicates that the overall efficiency of the structured packing decreases gradually at high pressure, as a result of the vapor backmixing.展开更多
基金supported by National High Technology Research and Development Program of China("863Plan",2010AA03A405)Major Project of Chinese National Programs for Fundamental Research and Development("973Program",2012CBA01200)
文摘Solvent extraction based on mixer-settler is the major industrial method of rare earth （RE） separation. In the mixer-settler extraction process, due to the insufficient settling time in normal circumstances, backmixing of the aqueous phase could have signifi- cant impact on the process of RE extraction separation. Therefore on the basis of the extraction equilibrium and mass balance of the mixer-settler extraction process, here we developed a mathematic expression of the aqueous phase backmixing in a two-component separation process, and obtained a quantitative analysis of the backmixing effect on the purification process by the approximations according to certain hypotheses. Two extraction systems of La/Ce and Pr/Nd separation were chosen as the examples to analyze the backmixing effect, and the results showed that the aqueous backmixing had greater influence in the scrubbing segment than in the ex- traction segment, especially in the system with a high separation factor such as La/Ce separation. Therefore it was suggested that the aqueous backmixing effect should be well attended in the design and application of RE extraction separation.
基金Supported by the National Key Research and Development Program(2016YFB0301701)the National Natural Science Foundation of China(21776283,21427814)+1 种基金Key Research Program of Frontier Sciences of CAS(QYZDJ-SSW-JSC030)the Instrument Developing Project of Chinese Academy of Sciences(YZ201641)and Petro China.
文摘Five different internals were designed,and their effects on phase holdup and backmixing were investigated in a gas–liquid concurrent upflow reactor where the spherical alumina packing particles of three diameters(3.0,4.5 and6.0 mm)were slightly expanded under the conditions of varied superficial gas velocities(6.77×10^(-2)-3.61×10^(-1) m·s^(-1))and superficial liquid velocities(9.47×10^(-4)-2.17×10^(-3) m·s^(-1)).The experimental results show that the gas holdup increases with the superficial gas velocity and particle size,opposite to the variational trend of liquid holdup.When an internal component is installed amid the upflow reactor,a higher gas holdup,a less liquid holdup and a larger Peclet number characterizing the weaker backmixing are obtained compared to those in the bed without internals under the same operating conditions.Additionally,the minimal backmixing is observed in the reactor equipped with the internals with a novel multi-step design.Finally,empirical correlations were proposed for estimating gas holdup,liquid holdup and Peclet number with the relative deviations within 11%,12%and 25%,respectively.
文摘1 INTRODUCTIONDowncomers,employed in tray columns,are widely used nowadays in industrialseparation processes.They function as channels for the liquid phase to fall fluentlyfrom one tray onto its neighbouring places for the held-up bubble to separate fromthe liquid phase.It is well known that liquid flow patterns and mixing characteristicsin downcomers are closely related to the initial liquid distribution on the tray,andhence to tray efficiency.For a long period of time,little attention has been paid
基金National Natural Science Foundation of China(No. 20136010)
文摘An experimental study of the extent of axial backmixing in both gas and liquid phases was conducted in a 150 mm ID column packed with Mellapak 250Y corrugated structured packing. The column was operated at pressures ranging from 0.3 MPa to 2.0MPa with nitrogen and water flowing countercurrently through the packing. The amount of axial backmixing was experimentally evaluated by the pulse response techniques using hydrogen in gas phase and an aqueous solution of NaCl in liquid phase as inert tracers. The response of the tracer was monitored by means of thermal conductivity in the gas phase and electrical conductance in the liquid phase. The experimentally determined residence time distribution (RTD) curves were interpreted in terms of the diffusion-type modei. The results indicated that the axial backmixing in the gas increased notably with gas flowrate and slightly with operating pressure and liquid flowrate. The liquid-phase axial backmixing was an increasing function of both gas and liquid flowrates and insensitive to pressure. Various correlations were developed for reproducing the experimental mixing data. The agreement between experimental and correlated data appeared to be acceptable and within ±20% of difference.
基金Supported by the National Natural Science Foundation of China (No. 20136010).
文摘Performance of Mellapak 250Y and 350Y corrugated structured packing in distillation applications at pressures ranging from 0.3 to 2.0MPa is analysed by using HTU-NTU method. These data are obtained in a distillation column with 0.15 m diameter op-erated with n-butane/n-pentane system at total reflux. In considering the axial backmixing effects, the height of an overall gas phase transfer unit, HTUOG , is divided into two parts. One part represents the height of an overall gas phase transfer unit, without backmixing, designated as*OGHTU, and the other part, designated as the height of a backmixing unit (HBUO), accounts for the backmixing effects. The HTUOG is evaluated from the measured concentration profile of n-butane in liquid phase. The HBUO obtained experimentally is correlated in terms of the properties of the materials being separated and the equivalent diameter of the structured packing. Our result shows that HBUO varies from 0.12 to 0.34 m as pressure increases from 1.0 to 1.9 MPa. It indicates that the overall efficiency of the structured packing decreases gradually at high pressure, as a result of the vapor backmixing.
