基于CFD的搅拌萃取塔结构优化与流场分析

为降低搅拌萃取塔内轴向返混并增大通量，在搅拌筛板萃取塔基础上改进内部结构，设计了返混相对较轻的搅拌萃取塔。通过停留时间分布模拟，结合返混模型和流场分析，研究了通道面积、环隙位置、开孔方式和澄清段高度等因素对流体流动特性的影响。结果表明，级间转动挡板可以有效抑制塔内轴向返混，且挡板直径越大，塔内通道面积越窄，抑制返混效果越好；固定环开孔和级间挡板开孔均会带来一定程度的返混，尤以搅拌桨下方的级间挡板开孔影响最为严重；设立澄清段可以降低塔内返混，且澄清段高度越高返混越小，实际应用时考虑到设备成本，澄清段高度与塔径之比以0.7左右为宜。     

湿法磷酸净化中往复式振动筛板塔的应用研究

研究在往复式振动筛板萃取塔中用有机溶剂萃取湿法磷酸的性能,考察振动筛板萃取塔结构参数和操作条件对磷酸萃取率的影响。结果表明:筛板开孔率53%,筛板间距7cm,振动频率150r/min时,萃取率可达84%;结合洗涤和反萃可以得到合格的工业级磷酸。     

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。     

往复筛板式萃取塔液泛的研究

本文对萃取段高度为97.3cm,直径为35.5mm的往复筛板式萃取塔进行实验研究,采用两种物系:煤油—水和煤油—甘油水溶液,通过实验观察认为往复筛板式萃取塔操作可以分成三种流动状态(或称三个区域),即混合澄青区,过渡区和乳化区,正常操作应控制在乳化区。本实验对物系物性,筛板开孔率,往复筛板的振幅,搅动强度以及两相流率比对液泛的影响进行了研究。     

搅拌筛板萃取塔液泛特性研究

为明确萃取塔对不同体系、不同操作条件下的性能,在内径为50 mm的三级搅拌筛板萃取塔中,针对7个不同物性特点的体系进行了液泛特性研究,液泛点采用观察法判断。实验结果表明,穿流式筛板的过孔阻力和过度搅拌是液泛产生的两个原因;萃取塔的两相总空塔流速与搅拌转速关系曲线将塔的操作区域分为搅拌不足液泛区、正常操作区、搅拌过度液泛区和流速过高液泛区等区域;增大分散相流速比增大连续相流速更容易造成液泛。通过比较不同界面张力、两相密度差、连续相黏度体系的液泛特性可知,该萃取塔适合中、低界面张力体系在低流速下操作。     

带转动挡板的搅拌萃取塔连续相停留时间分布研究

为获取带转动挡板的搅拌萃取塔内部流体流动状况，采用脉冲示踪法对塔内连续相停留时间分布(RTD)进行研究，并结合轴向返混模型得到了连续相的返混系数。结果表明，随着连续相体积流量、总流量或连续相与分散相体积流量比值的增大，连续相RTD曲线收窄、峰值明显增大、连续相停留时间和返混系数均减小；改变分散相体积流量，连续相RTD以及返混系数基本不变。此外，改变搅拌转速对连续相RTD影响较小。将返混系数与操作条件和物性参数进行关联，关联式最大偏差为19.8%、平均偏差为7.7%，表明关联式可用于带转动挡板的搅拌萃取塔的连续相轴向返混程度的评估。     

一种有利于母液和萃取液分离的新型萃取设备的开发和研制

本文研制了一种有利于母液和萃取液分离的新型萃取设备,它可以与传统的填料萃取塔或筛板萃取塔对接,具备传统的填料萃取塔或筛板萃取塔的优点,设计了新型的母液和萃取液分离段,强化了母液相中萃取液的回收也强化了萃取液相中母液的回收,与传统结构的萃取塔相比,本文研制的新型萃取设备具有以下优点：（1）轻、重组分按照最大负荷设计,满足最大负荷以下的各种负荷生产状况,生产负荷调节范围宽;（2）在萃取液和母液分离段返混程度最低,分离效果好,液体的宏观流动方向与轻重液的分离方向垂直;（3）操作控制简单,生产负荷变化时,无需人工调节。     

机械搅拌萃取塔中影响传质效果的几个因素

对桨叶旋转式和筛板振动式2种机械搅拌萃取塔进行了传质方面的研究，通过测试大量的实验数据及计算绘制的图表，较系统地考察分析了旋转(振动)频率、筛板振幅、两相界面、停留时间即取样时间等因素对传质效果的影响，并确定出了最适宜的操作条件。     

机械搅拌萃取塔中影响传质效果的几个因素

对浆叶旋转式和筛板振动式两种机械搅拌萃取塔进行了传质方面的研究。通过测试大量的实验数据。及计算绘制的图表，校系统地考察分析了旋转（振动）频率，筛板振幅，两相界面，停留时间即取样时间等因素对传质效果的影响，并确定出了最适宜的操作条件。     

多层筛板并流鼓泡塔中液体轴向混合的研究

本文检验了级内完全混合-级间有返混的模型对于多层筛板鼓泡塔中液体轴合混合的适用性。在空气-水系统中,用示踪剂研究了级间返混系数与设备参数、操作参数间的关系,对返混机理进行了考察,得到了返混系数与主要设备参数、操作参数间的关系式。实验中发现,气体分布板附近四层的返混系数受到气体分布板即端效应的影响。因此只有第四层以上的返混系数才逐层相等。     

Reaction extraction of furfural from pentose solutions in a modified Scheibel column

Furfural, which is one of the most promising platform chemicals derived from biomass, has the potential for the production of biofuels and biochemicals. However, the current industrial furfural production process relies on relatively old and inefficient technology, which has some problems such as low production yields, environmental pollutions, and lack of biomass comprehensive utilization. The main contribution of this paper is the use of a modified Scheibel column to improve the furfural recovery. Integration of pentose dehydration to furfural and the solvent phase extraction of furfural occurred simultaneously in this column. Compared with the prevailing batch biphasic reactor, the use of this modified column intensified the extraction efficiency as well as the furfural recovery. Process parameters including organic feed flow rate, reaction temperature, and stirring speed were evaluated and turned out to be significant. In order to achieve the optimal operating conditions, the CCD design was used to optimize the process parameters, and the maximum furfural yield of 80.5% was obtained.     

An Improved Correlation of the Mean Drop Size in a Modified Scheibel Extraction Column

The drop size is of fundamental importance in the design of liquid‐liquid extraction columns, the drop size was measured as a function of the geometry, operating conditions, and physical properties of a liquid‐liquid system with no mass transfer in a five‐stage modified Scheibel extraction column. An improved correlation of the mean drop size in the Scheibel extraction column is presented. The correlation was divided into three sections in terms of the Reynolds number. It could be applied in a wide range and could be further used for the study of mass transfer performance of the modified Scheibel extraction column.     

Direct extraction of Mo(VI) from sulfate solution by synergistic extractants in the rotation column

Direct extraction of molybdenum from sulfate solution with synergistic extractants (mixture of D₂EHPA and TBP) was studied in the rotation column. The influence of extractant concentration and initial pH of aqueous phase was studied in the bench scale experiments. The outcomes demonstrated that the synergistic solvent extraction enhances the constancy of the extracted complexes for transfer into the organic phase. In the continuous experiments, the effect of different operating parameters such as speed of agitation, inlet solvent flow rate and inlet aqueous flow rate on the holdup, mean drop size, drop size distribution, slip and characteristic velocities and extraction percentage were examined. Modified correlations were proposed for prediction of hydrodynamic parameters with consideration of reaction extraction condition in the rotation column. Furthermore, these correlations were compared with the experimental data. According to the results, the direct extraction of Mo (VI) from aqueous solution and sulfuric media with extraction efficiency of 90.4% was obtained at higher rotor speed (240 r·min^-1 rpm) in this column.     

正交设计优选湿法磷酸萃取搅拌桨

为改进湿法磷酸净化中桨式搅拌器,在水/磷酸/TBP+煤油体系中,采用正交实验设计探讨了4种搅拌器的萃取效果和功率消耗。结果表明,影响磷酸萃取率的因素由主到次为:搅拌器类型、反应时间、搅拌转速、相比、桨槽比;影响单位体积功率消耗的因素由主到次为:搅拌器类型、桨槽比、搅拌转速、相比、反应时间。通过综合平衡法获得的优化方案为:大三角搅拌桨,桨槽比1∶3,搅拌转速300 r/min,相比为4∶1,反应时间为8 min。在此条件下,磷酸萃取率为41.21%,单位体积功耗为0.26 kW/m3。     

Holdup measurements in a Scheibel column by means of an ultrasonic technique

An ultrasonic technique developed by Bonnet and Tavlarides for dispersed phase holdup determination in liquid–liquid contactors has been applied in a 0·10 m diameter Scheibel extraction column. The column consists of three alternate mixing and packing sections of 0·03 and 0·055 m in height, respectively. The packings were built with polypropylene mesh with 96% voidage. The liquid–liquid systems were toluene (dispersed)/water (continuous) and MIBK (dispersed)/water (continuous); the Rushton-type impellers were operated at 400, 500 and 600 rpm, and with four dispersed and continuous phase flow rates. In one of the mixing chambers two different holdup measuring devices were installed: two ultrasonic transducers and one controlled dispersion sampler. The values of dispersed phase holdup obtained by both methods were compared using statistical methods. It was found that at low agitation and for high interfacial tension, conditions for which the dispersion is not completely uniform, the difference was significant, whereas at high agitation and low interfacial tension the values obtained through both methods were statistically equal. This work demonstrates the applicability of the ultrasonic technique for holdup measurements to Scheibel columns, in which the only technique used so far was sampling. This ultrasonic technique allows us to solve the axial monitoring and control problems of these columns.     

煤化工废水萃取脱酚流程模拟

为提高煤化工高浓度含酚废水萃取脱酚的处理效果,减轻废水排放环境污染,采用Aspen Plus流程模拟软件对煤化工废水萃取脱酚流程进行了优化设计。模拟采用真实煤化工废水的组成设置物流数据,废水进料流量为100 t/h,温度为40℃,压力为0.1 MPa,并利用UNIQUAC和NRTL活度系数模型,分别对萃取脱酚塔、溶剂回收塔、溶剂汽提塔进行了参数调整。模拟结果表明,当萃取脱酚塔萃取级数n=6,萃取相比R=1∶4时;溶剂回收塔的理论塔板数N=10,进料位置为第5块塔板时;溶剂汽提塔的理论塔板数N=5,进料位置为第1块塔板时,废水总酚浓度从18 600 mg/L降至400mg/L以下,单元酚浓度从14 000 mg/L降低至50 mg/L以下,萃取剂回收利用率达到99%以上。     

应用液滴停留时间模型优化萃取塔设计

很多因素影响着萃取塔的工作效率,其中最为重要的为塔内液滴的空间分布和停留时间。文中基于欧拉-拉格朗日二相流模型,利用CFD技术,模拟了塔内的液滴空间分布和停留时间,提出了萃取塔优化设计和操作的原则。结果显示:在满足萃取塔优化设计原则的基础上,通过优化萃取塔设计和操作参数如塔单元高度、叶片转速等,可以有效提高萃取塔的效率。提出的优化方法简单易行,适合实际设计工作。     

Pilot-scale two-phase extraction of canola

An extraction process was developed in our laboratory for rapeseed (canola) with 10% (w/w) ammonia in methanol, containing 5% (vol/vol) water, and hexane to simultaneously produce an improved meal and a high-quality oil. To remove the hazards associated with the use of ammonia, a two-phase solvent extraction, with 0.08% (w/w) sodium hydroxide replacing the ammonia, was tested on a semipilot scale with a Szego mill and a Karr reciprocating-plate extraction column. Flooding curves and appropriate agitation parameters were examined for this system. Then, the effects of polar solvent-to-seed ratio, slurry-to-hexane flow ratio, plate amplitude and plate agitation frequency on extraction efficiency were investigated. The process is technically viable for industrial application. A meal that contained 0.9% residual oil, 44.4% protein and 2.79 mmol/kg glucosinolates (moisture and oil-free basis) and a miscella with 19.5% oil were obtained.     

Measurement of concentration profiles in a liquid-liquid extraction column

A novel experimental technique for withdrawing uncontaminated samples of each phase from a highly agitated two liquid phase system (primary dispersion) is presented. The technique has been applied in the study of the continuous and dispersed phase axial mixing characteristic of a mechanically agitated liquid Scheibel extraction column operating under different conditions treating the chemical system acetone-toluene-water. The column mixing compartments were separated by a mixed stainless steel-polypropylene knitted mesh packed bed which was completely ‘wetted’ by the organic dispersed phase. Several concentration profiles are presented and the non-ideal flow parameters as well as the mass transfer coefficients for the column and system under study are reported.     

Mathematical modeling and steady-state analysis of a scheibel extraction column

The steady-state behavior of a nine-stage Scheibel extraction column was modeled and simulated using a back flow stagewise model. Steady-state experiments were conducted, using the system water-acetone-toluene, for three phase ratios and three agitator speeds. The mathematical model was validated with the experimental concentration profiles by a single parameter fitting technique with an unconstrained optimization algorithm. Steady-stage analysis of the experiments was performed for a further control study. The calculated steady-state gain matrices were used for interaction analysis using different steady-state analysis methods, e.g. Bristol numbers, Condition numbers, Morari Indexes of Integral Controllability, and Niederlinski Indexes. The results indicate that both agitator speed and phase ratio have a substantial influence on the control structure. Dynamic analysis should therefore be performed to verify the optimum control method for this process.