曳力模型对模拟鼓泡塔气含率的影响

引言 鼓泡塔由于其良好的传热、传质特性而被广泛用于化工、生物制药、冶金等领域.近年来,计算流体力学(CFD)越来越多地被应用于研究鼓泡塔内部复杂的流体力学状态.然而,如何合理地描述气液相间作用及湍流模型是CFD模拟能够准确复现鼓泡塔内复杂流动状态的关键和难点.     

板式塔应用于蒸发热水塔的研究

以多喷嘴对置式水煤浆气化技术中的蒸发热水塔为研究对象,将板式塔应用于热水室,一方面改善了热质传递效果,另一方面避免了蒸汽携带灰渣造成的堵塞。文中在实验室热模装置上获得了热质传递过程达平衡时塔内温度分布曲线,研究不同冷凝水量与蒸汽流量对温度分布的影响,采用筛孔板和固阀板进行了实验,所得结果与前期填料塔实验的分析比较表明,板式塔的处理能力和传热传质效果都好于填料塔。在实验条件下,板式塔内最佳液气比为6—8,填料塔为8左右,板式塔的最佳冷凝水进量小于填料塔,此外,鉴于蒸发热水塔中蒸汽携带灰渣容易造成堵塞,板式塔在工业中应用于蒸发热水塔是更为合适的。     

化工设计设备塔内件安装方法研究分析

国外LNG项目，塔内件为气象相、液液相提供传质、传热的接触场所；塔内件的主要形式有两大类：填料塔、板式塔。塔内件的作用是为了使气液在塔内更好的接触，以便于发挥填料塔的最大生产能力和最大效率。所以塔内件的安装好坏直接影响到整个填料塔的操作运行和调料性能的发挥。     

超声场与添加剂对鼓泡塔中传质性能的影响?

利用超声场鼓泡塔和双电导探针气泡特征参数测量仪实时测定了加入不同种类和不同浓度添加剂前后鼓泡塔内氨气气含率与传质系数变化规律。实验结果表明：无添加剂时,超声频率为20-50-100 kHz组合,功率100 W时,鼓泡塔内气含率比无超声作用时增加了37%~74%,传质系数增大了39%~61%;气含率和传质系数随加入正辛醇浓度的增大呈现逐渐增长的趋势,当正辛醇浓度超过1.0%(V)时,气含率和传质系数趋于稳定;超声频率为20-50-100 kHz组合,超声功率100 W,正辛醇浓度为1.0%时鼓泡塔内气含率比无添加剂加入时增加了20%,传质系数增大了16%,可见超声场与添加剂协同作用有利强化气液相间分布、提高传质效果。     

超声场与添加剂对鼓泡塔中传质性能的影响

利用超声场鼓泡塔和双电导探针气泡特征参数测量仪实时测定了加入不同种类和不同浓度添加剂前后鼓泡塔内氨气气含率与传质系数变化规律。实验结果表明:无添加剂时,超声频率为20-50-100 kHz组合,功率100 W时,鼓泡塔内气含率比无超声作用时增加了37%~74%,传质系数增大了39%~61%;气含率和传质系数随加入正辛醇浓度的增大呈现逐渐增长的趋势,当正辛醇浓度超过1.0%(V)时,气含率和传质系数趋于稳定;超声频率为20-50-100 kHz组合,超声功率100 W,正辛醇浓度为1.0%时鼓泡塔内气含率比无添加剂加入时增加了20%,传质系数增大了16%,可见超声场与添加剂协同作用有利强化气液相间分布、提高传质效果。     

连续泡沫分离塔回收水溶液中钼(Ⅵ)的研究

以十六烷基三甲基氯化铵为表面活性剂,在连续稳态操作条件下,研究了泡沫塔和填料泡沫塔回收水溶液中微量Mo(Ⅵ)的分离性能。结果表明:随鼓泡区高度的增加,泡沫塔的富集率逐渐增加,回收率逐渐减小;随填料层高度的增加,填料泡沫塔的回收率增加,富集率减小;随泡沫层高度的增加,两种塔的富集率均逐渐增加,回收率均逐渐减小。泡沫塔内的浓度分布基本一致,表明泡沫塔存在较大的液相返混,填料泡沫塔内浓度分布随填料层高度的增加而增大,表明填料泡沫塔的液相返混程度较泡沫塔小。填料的加入有效增大了气液传质面积,提高了气液传质速率。填料泡沫塔的回收率远高于泡沫塔,但富集比略有下降。在实验条件范围内,填料泡沫塔中Mo(Ⅵ)的回收率可达99.8%,富集率可达12.2。     

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。     

散射管气体鼓泡塔流场分布特性及优化

鼓泡塔因其较好的气-液传质性能具有高污染物脱除效率,被广泛应用于生物化工和烟气处理等领域。鼓泡塔散射管气体分布器的几何尺寸和结构是影响相间传质效率的关键因素,优化塔内流场对于提高鼓泡塔内气-液两相间的传质效率至关重要。采用Fluent软件对有内构件散射管横向进气口式的鼓泡塔进行模拟研究,基于双流体方法和群体平衡模型(PBM)模型对鼓泡塔三维建模,采用一阶迎风差分格式离散,使用Phase Coupled Simple算法进行压力速度耦合。研究了散射管所在圆环直径d分别为0. 375D、0. 5D、0. 625D、0. 75D时(D为鼓泡塔直径),散射管进气口的布置对整体和局部气含率、液速和气泡尺寸等的影响。研究结果表明,随着散射管分布环直径的增大,整体气含率先增大后减少,平均气泡直径先减小后增大;当散射管所在圆环直径d=0. 5D时,鼓泡塔整体气含率和液相循环速度最大,平均气泡直径最小,鼓泡塔流场综合性能最好。     

新型垂直筛板塔在中压变换饱和塔中的应用

饱和塔是变换系统的主要传质设备，它的作用是用回收了变换气中热量的热水将半水煤气提高温度、增加其饱和度，清洗有害的灰尘和杂质，最终达到回收热能而节约蒸汽的目的。显然，饱和塔的传质性能的好坏直接关系到变换系统的汽耗，并且这主要取决于塔内件装置的结构形式与传质传热性能的优劣。早期的饱和热水塔曾分别使用过空塔、旋流板塔、泡罩板塔、散装填料塔，但其传质效果较差。随着技术发展，塔内件发展也较快，规整填料的应用使饱和塔的节能降耗作用大为提高，尤其是近几年的新型垂直筛板塔在饱和热水塔中的技术改造取得了重要进展，使变换系统的能耗大幅下降。     

气液两相逆流状态下金属板波纹填料塔内液体流动分布

填料塔内液体流动分布状况直接关系到塔内气液两相的有效接触,影响塔的操作性能.由于液体分布不良,造成填料塔内局部区域的气液比与全塔宏观的气液比有显著差别,从而大大降低塔的总传质效率.因此,填料塔内的液体分布     

复合萃取剂提取林可霉素机理及填料萃取塔中试研究

以中试填料萃取塔为设备研究了复合萃取剂（正辛醇和煤油）萃取林可霉素的宏观特性及传质强化。使用斜率法确定萃合物的结构和反应平衡常数以指导改进设备和强化传质;为了提高林可霉素萃取效果,考察了溶液pH值、相比（W/O）、填料类型、分布盘的使用等因素对提取林可霉素效果的影响。结果表明：以正辛醇为萃取剂萃取林可霉素的过程中,反应平衡常数K为0.072;复合萃取剂中正辛醇最佳含量为0.8（体积分数）;萃取林可霉素的最佳pH值为10～11,最佳相比（W/O）为3;规整填料和散装填料萃取效果有限,分布盘可以大大加强传质,同时加装分布盘的填料萃取塔的单位体积处理量是混合澄清槽的12.8倍,萃取剂循环量大大减少。研究结果对复合萃取剂的萃取机理和填料萃取塔提取林可霉素的实际应用具有一定指导意义。     

水煤气水洗塔填料层高度计算模型的简化

针对气液两相在填料塔内同时传热传质的过程,提出了水洗冷却填料塔填料层高度的工程设计计算模型。研究过程基于C语言编程运算,从公式的选择、热力学数据的取值、步长的选择三方面将现有数学模型简化,提出适于工程设计的简化模型。与现有数学模型相比,简化模型的计算结果误差在±10%以内,计算量减少96%以上,符合工程设计的安全性要求。与传统的经验估算方法相比,简化模型提高了科学性和经济性。     

一个用于精馏塔模拟的新模型

A new computational mass transfer model is proposed for simulating the distillation process by solving the fluctuating mass flux for the closure of turbulent mass transfer equation in order to obtain the concentration profile and the separation efficiency of distillation column. The feather of the proposed model is to abandon the conventional way of introducing the turbulent mass transfer diffusivity (dispersion coefficient) to the turbulent mass transfer equation. To verify the validity of the proposed model, a commercial scale packed column and a sieve tray column were simulated and compared with published experimental data. The simulated results were satisfactorily confirmed in both concentration distribution and separation efficiency.     

Multiphase fluidization in large-scale slurry jet loop bubble columns for methanol and or dimethyl ether production

A solution methodology is proposed for the process development and process engineering of a continuously operated jet loop bubble column including integrated external or internal steam generation for, e.g., a high-efficiency large-scale medium pressure methanol and or dimethyl ether production, or other gas to liquid Fischer-Tropsch applications.A jet loop bubble column is defined in the present process development to study the combined integration of a jet-eductor draft tube system with an upper bubble column. The major advantages resulting from the integrated jet-eductor draft tube system in large-scale bubble columns are the guidance and good mixing efficiency of the multiphase flow up to the upper part of the bubble column. Reducing the bubble column operating liquid level at about 2.5-3.0 times of the column diameter above the upper end of the draft tube results in a classical jet-eductor draft tube reactor suitable for small and or medium-scale industrial applications.Methanol synthesis is usually executed catalytically in multistage packed beds at higher pressure, e.g. 26 MPa, and about 350-, resulting in a higher plant installation and operating cost. The successful scale-up of a slurry jet loop bubble column can achieve a higher catalytic selectivity at a lower pressure and temperature , and therefore reduce the overall plant investment and production cost [Toseland, 1999. Three phase flows under extreme conditions of pressure and temperature, Part II: industrial applications, Air products and Chemicals, Inc. Presented at the A.I.Ch.E. Annual Meeting, Dallas, TX; Fan, 1999. Three phase flows under extreme conditions of pressure and temperature, Part I: fundmental characteristics, Department of Chemical Engineering, The Ohio State University. Presented at the A.I.Ch.E. Annuxal Meeting, Dallas, TX]. In addition, the separate slurry production of dimethyl ether, or even coproduction with methanol, can be a more cost-effective process than the classical methanol dehydration process.The new Modified Slurry Process^© for large-scale methanol and or dimethyl ether production is presented including internal or external heat exchanger location for steam production.A process concept is developed of a Large Scale Slurry Jet Loop Bubble Column^© with external separator, auxiliary internal heat exchanger equipment and high-efficiency gas-liquid slurry jet-eductor mixing system including draft tubes and an upper bubble column. In addition, as comparison a simplified concept is discussed for a small-to-medium-scale slurry jet loop reactor including external steam production and bottom nozzle jet-eductor installation without the presence of an upper bubble column.The basic geometrical parameters of the proposed slurry jet loop bubble column and jet loop reactor are discussed. The influence of the selected geometrical parameters on the gas holdup, interfacial area and mixing is analyzed. Information about catalyst type and particle size distribution is also presented.The definition of optimal operating conditions related to the influence of the fluid dynamics and mixing on mass transfer efficiency and also information for the minimum required power input per unit volume for startup or stable reactor operation are discussed.A simplified estimation method is presented for the expected axial temperature difference across the overall length of the jet bubble column, and also the required heat transfer area of a new construction-type internal compact heat exchanger for efficient reactor cooling and operation.Scale-up is possible for large diameter jet loop bubble columns, typically up to 5 m diameter and 60 m height, including continuous three-phase slurry operation at higher power input and interfacial area, for more efficient synthesis gas absorption and reaction than in classical slurry bubble columns. Integration of suitable designed sieve trays can further guarantee an efficient operation of the lower jet loop draft tube system at higher column diameters and also achieve an efficient reactor operation in the upper bubble column section.     

垂直管内弹状气泡上升中壁面传递的实验研究

垂直管内弹状流壁面传递是诸多工业应用中需研究的重要问题之一。今用极限扩散电流技术,对弹状气泡上升时瞬时壁面剪应力和传质系数进行了测定,结果显示:当基于表观气速的Froude数FrG < 0.74时,壁面剪应力随弹状气泡和液塞的到来呈现方向相反的交替变化,壁面传质系数亦相应变化;而当FrG > 0.74时,剪应力方向一直向下,说明液膜向下流动,且弹状气泡和液塞的到来对壁面传质系数的影响很小。这说明下落液膜射流穿透了液塞段,控制了整个壁面传递过程。研究还对下落液膜区、尾迹区及液塞段的不同传递特征及机理进行了分析, 并结合气泡塔熔融结晶器中弹状气泡上升时的传热,对结晶操作条件的合理选择进行了讨论。     

Hydrodynamics and mass transfer in an upward venturi/bubble column combination

The hydrodynamics and mass transfer characteristics of a venturi/bubble column combination were studied at high liquid superficial velocities of up to 0.35 m/s. The gas hold-up was increased by 50% to 150% and the overall volumetric mass transfer coefficient was tripled when the venturi was used as “gas distributor” instead of a porous distributor. A correlation of the overall volumetric mass transfer coefficient (K_La) with the gas hold-up, valid for gas hold-ups as high as 0.3, was proposed for the cylindrical bubble column section. The energy consumption per mole of oxygen transferred was lower than with most distributors and the oxygen transfer rate per unit of reactor volume was higher than in a bubble column with a porous distributor. The venturi/bubble column combination is a compact and efficient system which does not have the operating problems of systems which require internals.     

A Study on Hydrodynamics and Heat Transfer in a Bubble Column Reactor with Yeast and Bacterial Cell Suspensions

Hydrodynamics and heat transfer experiments were carried out in a slurry bubble column with air‐water‐yeast cells and air‐water‐bacteria cells systems to investigate gas hold‐up, bubble characteristics and heat transfer coefficients with cell concentrations of 0.1% w/w and 0.4% w/w and superficial gas velocity up to 0.20 m/s. The gas hold‐ups and heat transfer coefficients were found to increase with increasing gas velocity and cell concentration. The heat transfer coefficients were higher at the centre of the column as compared to the near wall region. The development of empirical correlations to predict the heat transfer coefficient in two‐ and three‐phase systems was carried out with ±15% confidence interval at most.     

Mass transfer in bubble columns packed with motionless mixers

The cocurrent upward mode was employed to absorb pure oxygen into water in bubble columns packed with Koch (Sulzer) motionless mixers. The liquid-side volumetric mass transfer coefficient, K_La, in the packed bubble column was found to be always larger than that in the unpacked bubble column. In the range of liquid velocities from 6.7 cm/sec to 39.9 cm/sec, the value of K_La in the packed bubble column increased with the increasing liquid velocity while that in the unpacked bubble column was almost independent of the liquid velocity. The equation of the formK_La= mν_l^β? was successfully adopted to correlate the K_La data.     

Quality of mixing in a downflow bubble column based on information entropy theory

Quality of mixing in a modified downflow bubble column has been analyzed by using information entropy theory. Mass transfer efficiency based on quality of mixing has also been enunciated in this work. Empirical models have been developed for downflow system with the parameters which affect the quality of mixing and mass transfer efficiency. The developed correlation for quality of mixedness in the downflow bubble column was interpreted by the mass transfer phenomena. The present analysis on the quality of mixing in downward two-phase flow in bubble column may give insight into a further understanding and modeling of multiphase reactors in industrial applications.