往复振动筛板塔对低界面张力体系萃取过程的强化

对低界面张力体系正丁醇-丁二酸-水在往复振动筛板塔中的萃取性能进行研究,体系中水为萃取剂,萃取正丁醇中的丁二酸。实验考察了两相流速、相比、传质方向和筛板振动速率对流体力学性能和传质性能的影响,并且与相同操作条件下固定筛板萃取塔的性能作对比。结果表明,筛板振动速率不高于3.5 cm/s的情况下体系没有发生乳化现象,相比增大到2.8时接近液泛点,实验稳定性较差。流速和相比增大能够获得更好的液滴分布和更大的体积传质系数,但增大的幅度要综合考虑设备的最大通量和两相在塔内的停留时间。分散相到连续相的传质方向传质相界面积大,更有利于提高传质效率。相同操作条件下,连续相中的轴向混合远大于分散相的轴向混合。与固定筛板塔的萃取性能相比,振动筛板改善液滴分布、增大处理能力和强化传质的作用都很明显。     

萃取塔数学模型及过程强化的若干研究进展

萃取塔因生产能力大、占地面积小、密闭性好等优点,在石油、化工、生物、医药和环境工程等多领域被广泛应用。本文从以下几个方面介绍了萃取塔近些年的研究进展：综述了传统萃取塔（脉冲萃取塔、转盘塔与Kühni塔等）的水力学、轴向扩散与传质模型的发展,分析比较了表面张力、传质方向、放大效应等因素对模型的影响;介绍了计算流体动力学（CFD）在萃取塔中单液滴、单相流模拟、液-液两相流模拟、外加能量模拟、与群体平衡模型（PBM）耦合模拟中的应用进展;介绍了国内外设计开发的新型萃取塔,包括改变传统塔的内构件和引入多种外场能量等方式来强化相间传质。研究表明,将先进实验研究方法、准确经验模型和可靠理论计算相结合,将会是萃取塔研究的重要手段和方向。     

板波纹规整填料塔中液相混合行为

引言填料塔中液相混合行为对传质有显著影响．关于散堆填料塔中液相轴向混合行为已有许多实验数据和一些模型发表,文献中对散堆填料塔径向混合行为也有一些研究．但对目前工业广泛使用的板波纹规整填料塔中的液相混合行为尚未见文献报道．为了解决板波纹填料塔中各种单元操作的合理设计,本文对此进行了研究．1实验本文用脉冲示踪法研究规整填料塔中液体的混合行为．实验在直径0.3m的填料塔中进行,塔体总高为7m,填料装填高度为1.4m．塔顶液体分布器为单层排管式分布器,共开有25个Φ3.5mm的喷淋孔．用水－空气系统及Mellapak250Y型填料…     

填料塔传质模型的研究——二维混合池随机模型

本文推导和提出了一个新的数学模型——二维混合池随机模型.它能用来模拟填料塔的液体流动和传质特性,以及计算塔中液、气两相浓度分布.该模型的主要特点是:(1)它通过调整混合池间轴向和径向的流动和混合,能很好地模拟填料塔复杂的液体流动状态;(2)模拟计算考虑了液体流动分布的随机性质.研究结果表明,填料塔塔径增大或填料层增高而产生的传质效率下降的原因主要是液体的非均匀流动、轴向混合的加剧和不完全的径向混合.     

轻重相交替进料筛板萃取塔中的传质性能研究

针对间歇操作萃取工艺生产能力低,而逆流连续操作萃取工艺返混严重等问题,研究提出了轻重相交替进料操作的萃取工艺,并对轻重相交替进料筛板萃取塔中的传质性能进行了研究。以煤油-苯甲酸-水为萃取体系,采用单个液滴的传质模型来计算萃取塔的分散相总传质系数,并研究了分散相流速、连续相流速、液滴上升速度以及塔板间距对分散相总传质系数的影响。实验得到分散相总传质系数Kod的数值在3.49?10?5~5.47?10?5 m?s?1,总分散相存留分数在1.63%~4.37%。结果表明轻重相交替进料筛板萃取塔的分散相总传质数高于Kühni搅拌萃取塔、脉冲萃取塔和振动挡板塔,并且流量变化对Kod的影响小,返混效应弱,总分散相存留分数小,不易液泛。     

超临界流体萃取塔的应用设计及理论研究

设计了超临界流体萃取塔系统，并对其流体力学特性和传质性能进行了研究，为工业设计提供了理论依据。在连续逆流操作的超临界填料萃取塔、筛板萃取塔和喷淋萃取塔中，应用超临界二氧化碳-异丙醇-水、超临界二氧化碳-乙醇-水两种实验体系对流体力学模型和传质模型进行了实验验证，计算结果与实验数据符合较好。     

往复振动板式萃取塔水力性能研究

以上－煤油为介质,在内径为０．０３１ｍ的往复振动板式萃取塔内研究了此塔的分散相持液量、轴向混合和液滴大小。研究表明分散相持液量与板振幅、频率、连续相流速和分散相流速有关;Ｓａｕｔｅｒ平均直径与板振幅、频率有关。应用脉冲响应法测试此塔的轴向混合,以无因次方程对轴向混合系数进行关联。     

脉冲筛板萃取塔CFD-PBM模型研究

脉冲筛板萃取塔是核工业等领域中最常用的萃取设备之一，为深入了解脉冲筛板萃取塔中两相流行为规律，使用CFD-PBM模型对脉冲筛板萃取塔中由有机相(30%TBP-正十二烷)、水相(HNO₃水溶液)组成的体系进行两相流过程模拟分析，模拟结果与实验数据吻合较好，分散相存留分数和Sauter平均液滴直径的相对偏差仅为8.28%和5.54%；随脉冲速度增加，Sauter平均液滴直径减小，液滴直径分布更均匀，分散相存留分数增加，特性速度减小；两相表观速度对液滴直径影响较小，分散相表观流速增加有利于提高分散相存留分数，而连续相表观流速影响不大；发生液泛时分散相液泛表观速度随连续相液泛表观速度增大而减小，随脉冲速度增加液泛通量先增后减，存在极值。     

转盘萃取塔中连续相轴向混合的研究

根据塔内流体运动规律,分别研究了转盘萃取塔单相流和两相逆流时连续相轴向混合的机理.采用光导纤维测定脉冲示踪的浓度响应,从而得到单相流轴向混合Peclet数和两相逆流时分散相对连续相轴向混合的影响(f_w-△~W)的数学表达式.这些表达式对轴向混合的计算,能从高转盘转速扩展到低转速,并能适用于较广的流速范围.为了分析连续相的轴向混合,对分散相滞留量及分散相液滴直径也作了初步研究,并得出了关联式.     

填料特性对鼓泡填料萃取塔性能影响

填料的结构与表面性能对鼓泡填料萃取塔性能有直接影响。利用空气 煤油 (苯甲酸 ) 水体系 ,测定了未装填料和分别装填板波填料、丝网填料、压延孔环填料的鼓泡萃取塔水力学性能和传质性能。实验表明 ,对未装填料和装有填料的萃取塔 ,气相搅拌都可以显著提高液液两相的接触与传质性能 ;液泛速度随表观气速的增大而下降 ;流道设计合理的规整填料传质性能明显高于散装填料 ;表面光滑的填料分散相滞存率低 ,因而液泛速度较高 ;填料的作用有利于降低轴向返混 ,明显提高萃取塔传质性能。     

充填式浮选柱二维返混特性的实验研究

以二维扩散模型为基础，采用点源脉冲示踪法对开式浮选柱和装有不同类型规整填料的充填式浮选柱内液相的轴向与径向返混进行了实验研究，得到了各种填料内轴向和径向彼克列准数与气相、液相表观雷诺数的关联式。通过比较发现，在所用填料中，装有250Y或350Y型填料的浮选柱不仅轴向返混最小，而且径向返混最大，最有利于提高回收率。另外，对起泡剂的影响进行了实验研究，发现起泡剂可以减小返混，但当起泡剂浓度大于一定值时反而会增大径向返混。     

Catalyst mixing in bubble column slurry reactors

The reported experimental data of Pandit and Joshi (1984) on axial and radial steady-state catalyst concentration in a semibatch bubble column slurry reactor is interpreted by the dispersion model. The elliptic partial differential equation with its associated boundary conditions is solved analytically for catalyst concentration by the method of separation of variables. The proposed model adequately fits the experimental data.     

Axial dispersion in a reciprocating plate column

Axial mixing in a reciprocating plate column with different amplitudes has been investigated for single-phase and two-phase (air-water) systems. Experiments were performed in water in a semi-batch scheme (no water flow) in a 1.26 m high and 101.6 mm internal diameter column. It was found that the axial dispersion coefficient is a strong function of reciprocation speed and amplitude. The presence of gas considerably affects the axial dispersion coefficient but its contribution appears to saturate at low gas flow rates and then, over a large range of gas flow rates, the axial dispersion coefficient was almost constant. Models are proposed based on experimental data to account for the effects of gas superficial velocity, amplitude and reciprocating frequency. The models predictions are compared with experimental data, obtained over a wide range of operating conditions, and the agreement between them was found to be good. A new class of nonlinear models, for which it is not necessary to have a constant dependency on each operating variable, was also used to correlate the axial dispersion coefficient. This new model allows to carry out sensitivity analysis on each operating variable.     

CFD and experimental studies of single phase axial dispersion coefficient in pulsed sieve plate column

This paper intends to study the single phase axial dispersion in pulsed sieve plate column using a combination of computational fluid dynamics (CFD) simulations and experimental measurements. Experiments and CFD simulations were conducted on 0.076 m diameter pilot scale column having standard geometry of 0.05 m plate spacing, 0.003 m hole diameter and 0.21 fractional free area. The effect of density of tracer solution and radial probe position on axial dispersion coefficient has been studied to ensure precision of the experimental measurement method. The effect of pulse velocity from 0.01 to 0.025 m/s and superficial velocity of water from 0.01 to 0.03 m/s has been studied. Simulations were carried out using commercial CFD software, FLUENT 6.2.16, with standard k–? model for turbulence. An unsteady state tracer injection technique was used for axial dispersion measurement. The range of velocity ratio (ψ = Re_o/Re_n) employed in this work was 1–4 which is very low. Therefore the effect of superficial velocity, V_c was found to be greater than pulse velocity. These results were critically compared with published data and it has been found that single phase axial dispersion coefficient is directly proportional to effective velocity (Af + 0.5 V_c). The presented CFD predictions and validation with experimental data will provide useful basis for further work on single phase axial dispersion with various geometrical parameters and understanding the two phase flow patterns in pulsed sieve plate column.     

HYDRODYNAMICS, MIXING AND MASS TRANSFER IN A LARGE DIAMETER JET BUBBLE COLUMN

Experimental measurements for the axial and radial variations in gas holdup, axial and radial dispersion coefficients, volumetric gas-liquid mass transfer coefficient and liquid phase circulation velocity in a cone of a large diameter (122 cm) jet bubble column are presented. Two diameters of the inlet nozzle, namely 10.16 cm and 15.24 cm, three superficial gas velocities (based on cylinder diameter), 3 cm/sec, 6 cm/sec and 8 cm/sec and two superficial liquid velocities, 0.3 cm/sec and 0.6 cm/sec, are examined. The experimental data are obtained for two different bed heights.

The experimental data showed significant axial and radial variations in the gas holdup. The volumetric average gas holdup was higher at higher gas velocity and larger nozzle diameter and somewhat higher at lower liquid velocity. The axial dispersion was high while the radial dispersion was low. The volumetric gas-liquid mass transfer coefficient was larger at higher gas velocity and larger nozzle diameter. The liquid recirculation begins only at the upper end of the cone. In general, experimental data indicate that a jet bubble column provides a high degree of mixing and transport rates.     

固定床内径向扩散研究

在直径为２６７ｍｍ的５Ａ分子筛固定床上，采用稳态有限源示踪技术，利用计算机数据采集系统，测定了不同流速下床层内部截面上示踪气体的浓度分布数据。并分别利用稳态有限源和稳态点源示踪条件下扩散模型的解析解，获得床层内的径向扩散系数值。结果表明，两种处理方法所获得的径向扩散系数值大致相等，且在实验条件范围内，当Ｒｅ数较小时，径向扩散系数值与分子扩散系数值相当，随着Ｒｅ数的增加，径向扩散系数值逐渐增大，最后几乎与流速成正比。文中还讨论了轴向扩散系数值对径向扩散系数计算结果的影响。     

INVISCID LIQUID CIRCULATION IN BUBBLE COLUMNS

For circulation in axi-symmetric (cylindrical) bubble columns, the recently developed mathematical model^25,26 has been used along with the criterion of minimum circulation strength to determine the height of each circulation cell in a tall column. This is then used to derive a theoretical expression, first of its kind, for gas hold-up inside a bubble column. The predictions of this equation as well as the equation derived here for axial liquid velocity at column axis have been compared with available data and the comparison is found to be excellent for both the variables. An explicit relation is derived for the average liquid circulation velocity. The model is also used to derive an expression for liquid axial dispersion coefficient which compares almost exactly with Deckwer et al.'s⁴ correlation.

For circulation in two-dimensional bubble columns a new mathematical model is developed. The predictions of bubble envelope shape and bubble envelope area compare well with published data. The predictions of number of circulation cells in the horizontal direction also compare well with published data.     

Mixing in bubble columns: a new approach for characterizing dispersion coefficients

Use of bubble columns as photobioreactors requires a quantitative knowledge of radial mixing in these columns. A complete model of liquid-phase dispersion was used to simultaneously characterize axial and radial mixing in a relatively large (0.06 m³, 2.3 m tall, 0.193 m in diameter) bubble column photobioreactor. Axial and radial dispersion coefficients and mixing times were determined in tap water and sea water for superficial aeration velocities of up to . The measured axial dispersion coefficients (D_z) were generally consistent with the predictions of the well established correlations, thus validating the complete dispersion model used in the analysis. The D_z values ranged from ∼150 to and were highly reproducible. There was evidence that the existing literature data on D_z in bubble columns are slightly underestimated, as consistent underestimation was found to be a characteristic of the widely used dispersion model that disregards radial dispersion. The value of the radial dispersion coefficient was typically about 1% of the D_z value under any given condition. Except at incipient aeration, the radial dispersion coefficient was not as sensitive to the magnitude of the aeration rate as was the axial dispersion coefficient. The mixing time data were generally consistent with the existing correlations.     

INVISCID LIQUID CIRCULATION IN BUBBLE COLUMNS

For circulation in axi-symmetric (cylindrical) bubble columns, the recently developed mathematical model^25,26 has been used along with the criterion of minimum circulation strength to determine the height of each circulation cell in a tall column. This is then used to derive a theoretical expression, first of its kind, for gas hold-up inside a bubble column. The predictions of this equation as well as the equation derived here for axial liquid velocity at column axis have been compared with available data and the comparison is found to be excellent for both the variables. An explicit relation is derived for the average liquid circulation velocity. The model is also used to derive an expression for liquid axial dispersion coefficient which compares almost exactly with Deckwer et al.'s⁴ correlation.

For circulation in two-dimensional bubble columns a new mathematical model is developed. The predictions of bubble envelope shape and bubble envelope area compare well with published data. The predictions of number of circulation cells in the horizontal direction also compare well with published data.     

Gas-bubble hold-up and axial dispersion coefficient of emulsion phases in fluidized beds

A model for liquid mixing in a gas-liquid bubble column is extended to predict gas-bubble hold-up and axial dispersion coefficient of emulsion phases in fluidized beds. Reasonable agreement is found between the proposed model which includes no adjustable parameter and the available experimental data and correlations.