改良型CO2湿壁塔内气液两相流动规律及传质特性

基于Fluent软件，采用层流模型、VOF模型及非稳态类型，模拟基准湿壁塔和改良型湿壁塔的气液两相流场，分析稳定液膜边界气液两相流场对传质过程的影响。结果表明，随液相入口流量的增大，在稳定液膜边界气相涡旋运动逐渐增强，气液两相混合程度加强，利于改良型湿壁塔的气液两相传质。在一定气相入口流量范围内，随气相入口流量的增大，液膜界面涡旋运动增强，气液两相混合程度加强，利于改良型湿壁塔的气液两相传质；气相入口流量不宜过大，否则导致液相不能沿湿壁柱向下流动形成稳定的液膜，不利于传质。改良型湿壁塔的变径结构和气体挡板均利于气液两相混合，利于传质。改良型湿壁塔的传质过程在液膜边界发生，随液相入口流量的增大液膜厚度增加，液膜表面积增大，有效传质面积增大，利于气液两相传质。通过对比基准湿壁塔和改良型湿壁塔的气液两相流场，改良型湿壁塔内气液两相混合程度加强，更利于传质。     

湿壁塔氨法烟气脱硫模型

近年来氨法脱硫以其低投入,脱硫率高以及有价值的副产物越来越受到重视。今以并流式湿壁塔脱硫实验装置为例,以氨水作为吸收液,在20℃和常压下研究了氨法烟气脱硫的气液传质与化学反应过程,并且在伴有快速的化学反应吸收的双膜理论的基础上,建立了数学模型。利用该模型对并流式湿壁塔氨法脱硫过程进行了模拟,分析了吸收液pH值、液气比、吸收液浓度、烟气流速以及初始SO2浓度对脱硫效率的影响,并与实验结果进行了对比。结果表明:在进气浓度为2500 mg·m·3时,最佳的工艺条件为液气比为2.2~2.8 L·m·3,吸收液pH值为5.8~6.5,烟气流速为1.5~2.5 m·s-1;该模型的计算值与实验数据基本吻合,为氨法烟气脱硫的工业化应用提供了理论参考。     

湿壁塔中钴氨络合物烟气脱硝的传质系数

为了研究钴氨络合物烟气脱硝的传质系数,搭建了湿壁塔反应装置。通过改变进入湿壁塔内模拟烟气的NO和SO_2浓度、钴氨络合物的浓度、反应温度等,对钴氨络合物吸收NO的传质系数进行了实验研究。实验结果表明,当烟气中NO浓度和钴氨络合物浓度增加时,NO传质系数增大;当SO_2浓度增大时,NO传质系数减小。并且发现,钴氨络合物吸收NO的最佳反应温度为55℃。可为开发钴氨络合物同时脱硫脱硝技术提供参考。     

湍球塔气液相界面结构及传质面积

湍球塔因其防堵塞、强湍动、传质面积大等特点,可作为烟气氨法脱碳后用磷石膏浆料净化尾气微量氨的气液传质设备。本文基于湍球塔液滴团聚分散理论研究了液滴和液膜形成的气液相界面结构,并得到气液传质面积的数学模型。在磷石膏浆料吸收氨法脱碳尾气微量氨的湍球塔实验装置中,在气体Re_g157~475、液气比1~6范围内进行实验研究,从实验数据回归得到的气液传质面积与理论计算值吻合。结果表明,湍球塔气液传质面积以团聚分散的液滴为主,湍球表面积占比不足25%。     

应用多孔转盘的转盘塔进行液膜分离的初步研究

采用带多孔转盘的转盘塔作为液膜分离的连续操作装置,进行了流体力学和传质特性的初步研究.实验表明:开有小孔的转盘塔板具有良好的液液分散性能和传质性能,适用于液膜分离的连续操作.     

中空纤维更新液膜在己内酰胺精制中的应用

研究了中空纤维更新液膜技术用于己内酰胺精制时的传质性能,考察了两相流速、萃取剂用量对传质的影响,并与大块液膜技术以及萃取塔技术进行了对比。在实验范围内,中空纤维更新液膜过程总传质系数随两相流速的增大而增大,且壳程流速对传质的影响较大。中空纤维更新液膜过程传质通量可达大块液膜的1．5倍,总体积传质系数可达工业萃取塔的2．3倍,萃取剂用量相比于大块液膜、工业萃取塔大幅度降低,具有很大的应用潜力。     

气液氯化反应填料塔的设计模型

将短湿壁管中的液膜面积和气体所通过的有效通道体积分别视作填料塔内有效传质面积和空隙体积,从短湿壁管测得的氯气与丙酮反应的气相传质关联式导出全新的且较为可靠的气液氯化反应填料塔的设计模型。其计算值与实际运行结果的最大相对误差仅为3.56%。     

氨法烟气脱硫SO_2吸收传质系数研究

喷淋塔氨法脱硫技术被广泛应用于净化烟气的SO_2,传质系数是喷淋吸收塔重要的设计和运行参数,但目前文献中有关氨法脱硫传质系数的报道很少,还有待进一步研究。在喷淋塔中对氨法脱硫SO_2吸收传质过程进行了实验研究,结合对液滴和塔壁液膜运动的计算,得到不同实验条件下SO_2的吸收传质速率,并建立了氨法脱硫SO_2吸收传质系数表达式。该传质系数包含浆液pH、烟气流速ug和液气比L/G等主要参数,能够反映不同pH、ug和L/G条件下SO_2在单位气液接触面积上的传质速率。对比验证结果表明,该传质系数计算得到的SO_2吸收传质速率与实验值之间的相对误差小于±12%,二者能够较好地吻合。建立的传质系数表达式能够为喷淋塔氨法脱硫的优化设计和运行提供理论参考。     

改进的Ⅱ型促进迁移液膜传质渐进前沿模型

提出了改进的Ⅱ型促进迁移液膜传质渐进前沿模型,该模型不仅考虑了滴内外扩散阻力、外界面反应,还同时引进了乳液渗透溶胀和液膜破损效应。用间歇式液膜提取苯丙氨酸进行了定量验证。模型计算值和实验值吻合良好。     

螺旋型旋转吸收器

<正>传统的吸收设备一般为塔型。传质的效果除与气液接触面的大小、气液流动状况、气液本身的物理性质等因素有关外,还与重力加速度g密切相关。Van Krevelen等推导出的关系式中,传质系数是k_L∞g~(1/3),Vivian通过对湿壁塔中气体吸收过程的研究,Norman等利用溶质渗透理论,都导出k_L∞g~(1/6)。但g是一个不可改变的有限值,若用人为可改变的旋转速度ω取代,则是一条强化传质过程的途径。作者从1983年研究旋转吸收器,屡经改进,制造了现用的实验螺旋型旋转吸收器。用该装置的实验结果表明,当ω增大时,k_L和α随之增大,液泛速度相应提高,操作范围增大,传质效果增强。     

An estimation of the film-penetration model parameters

It it shown in this paper that the process of evaporation of liquids into a turbulent gas flow in a wetted-wall column can be represented by the film-penetration model. The numerical values of the two parameters S and L of this model, estimated from mass transfer data, appear to be well defined functions of flow conditions. The surface renewal mechanism used in the considered mass transfer model was shown to be consistent with the momentum transfer concept.The results may be used to predict mass transfer processes with chemical reactions in similar flow systems, by applying the theoretical developments using the film-penetration theory [7–10].The same procedure may be used to estimate the film-penetration parameters in other flow systems, such as the flow of liquid films in a wetted-wall column, or other complicated system such as stirred tanks, bubble columns, packed columns etc.     

2,4-Xylidine Degradation with Ozonation: Mass Transfer and Reaction Kinetics

The kinetics of the degradation of 2,4-xylidine by ozonation as well as the ozone mass transfer in a wetted-wall column were investigated. A laboratory-scale ozone contactor was designed, and a steady-state wetted wall reactor model was developed. The model was based on countercurrent-connected and perfectly mixed mass transfer stages. It was possible to describe the evolution of the pollutant and ozone concentrations along the reactor length coordinate in various conditions. The model was used for the evaluation of the ozone mass transfer coefficient, reaction rate kinetics, and stoichiometric coefficient from experimental data. The ozone mass transfer coefficient for the wetted-wall column was estimated from the experiments in the absence of chemical reactions. When the estimated parameters were applied, the ozonation model of the wetted-wall column showed good agreement between the fitted and experimental data.     

Simultaneous heat and mass transfer for multicomponent distillation in a wetted-wall column

A simultaneous heat and mass transfer model was applied to multicomponent distillation in a wetted-wall column. Experiments were carried out, using the benzene-toluene-ethylbenzene ternary system, in a wetted-wall column of 2.2 cm i.d. and 100 cm long equipped with special probes designed for simultaneous liquid sampling and temperature measurements. The experimental results show that the bulk liquid phase was saturated, indicating no resistance to mass transfer in the liquid film. Confirmation of the liquid phase saturation was made through a comparison of the experimentally measured liquid temperature with the calculated bubble point temperature. The average deviation between the measured and calculated temperatures was found to be 0.26°C.Individual mass transfer rates were evaluated locally by measuring compositions and temperatures as functions of column height and were compared to theoretical predictions using the exact film model solution of the Maxwell-Stefan multicomponent equations developed by Krishna and Standart. The comparison shows good agreement with average deviations of 15.76% for benzene, 23.09% for toluene and 23.23% for ethylbenzene.     

Simultaneous heat and mass transfer in turbulent gas streams in wetted-wall columns

The effect of the gas and liquid flow rates on the gas-phase mass and heat transfer rates in turbulent gas streams in wetted-wall columns with cocurrent and countercurrent gas-liquid flow was studied. The experiments were carried out on the adiabatic vaporization of water into a turbulent air stream under both conditions of rippling and no rippling on the surface of the falling liquid film. The experimental results showed that the effect of the gas and liquid flow rates on the mass and heat transfer rates are in good agreement with the theoretical predictions and that the effect of the rippling on the mass and heat transfer rates can be neglected.     

Surfactant effects on gas absorption in a coke-oven gas treatment process

The effect of organic impurities in industrial stripped coal water (SCW) on the absorption of CO₂ was measured experimentally. Removal of these impurities via activated carbon showed a marked improvement in interphase mass transfer of a vertical wetted-wall column absorber. However, this benefit was not found in a stirred-cell absorber, in which a different flow pattern from that in wetted-wall column absorber is expected. An ad hoc systematic study on the effects of three deliberately added surfactants on gas absorption by pure water in three different absorbers with different flow patterns was thereafter conducted. The experimental results reveal that absorption deterioration also prevails only in a vertical, wetted-wall column absorber and the reduction in liquid phase mass transfer by the addition of surfactant can be satisfactorily correlated with surface pressure of solutions. This indicates that the effect of the industrial impurities in SCW on gas absorption may successfully be simulated under the same flow pattern by a surfactant solution with the same surface pressure. A possible modification of the existing coke-oven gas (COG) treatment process for the benefit of absorption enhancement was finally proposed.     

GAS ABSORPTION INTO WAVY AND TURBULENT FALLING LIQUID FILMS IN A WETTED-WALL COLUMN

Experiments are conducted for gas absorption in a long wetted-wall column. Liquid-side mass transfer coefficients are measured for absorption of CO₂ and O₂ into falling water films on the outside of a stainless steel pipe 2.72 cm OD and 183 cm absorption length. The liquid film Reynolds number ranges from 129 to 10500 which encompasses the wavy-laminar, wavy-transition and turbulent flow regimes. The experimental data are correlated by a dimensionless equation of the form kt = (k_tD) (v²/g) ^1/3 = a-Re^p-Sc^1/2. The correlation is well supported by a viscosity-damped turbulence model at the gas-liquid interface which tends to confirm that viscosity is probably the major mechanism causing eddy damping and not surface tension as proposed by Levich and Davies. The form of the above correlation also represents previous experimental work at different temperatures and for different gases quite well.     

相际传质(三)填料塔相际面积的测定和传质模型的研究

本文分别用含有AsO_2~-和ClO~-不同催化剂的Na_2CO_3-NaHCO_3缓冲溶液,在填料塔中吸收CO_2气体,进行化学法测定相际面积的研究.用Danckwerts表面更新模型和表面膜更新修正模型分别将传质数据进行处理和比较.结果表明:两种模型得到的比相际面积a十分接近,更新频率S相差较大.用AsO_2~-和ClO~-两种不同催化剂测得a的平均差值为±(9.2—15.5)%,修正模型考虑了气液两相开始接触时传质和反应的瞬息过程,提出了k_1θ>2作为化学法测定相际面积的条件,明确了应选择物系的k_1值范围,由此判别ClO~-催化物系测得的a和S值较为准确.文中还通过Na_2SO_4水溶液的物理吸收与上述化学吸收的数据相关联进行了讨论,说明修正模型的S用于分析膜式填料塔中气液吸收的操作特性较为合理.     

倒锥型真空填料精馏塔的性能

在倒锥型塔中,采用两种小型散装高效填料和三种回流比,在5～50 mmHg的塔压范围内,就塔压、空塔汽速、回流比、填料类型和塔的结构等诸要素对真空填料精馏塔的传质性能和流体力学性能的影响进行了研究,并与文献报导的直塔和四段塔进行了比较。实验结果表明,锥型塔在传质和流体力学性能两方面,都较为优越。作者还推导了一个能较好地描述锥型塔传质特性的数学模型。     

第二液相的加入对气液传质系数的影响

以搅拌罐中的水吸收CO2为研究体系,分别采用异戊醇、苯和正己烷为第2液相,通过实验考察了第2液相的加入对气液传质的影响.实验结果表明:第2液相的加入对气液体积传质系数KLa有很大的影响,且不同的第2液相的影响程度也不同.在一定的操作条件下,KLa均随搅拌速度和第2液相体积分数的增加呈先增大后减小的趋势,随表观气速(在一...     

Modelling reactive absorption of CO2 in packed columns for post-combustion carbon capture applications

A rate-based process model for the reactive absorption of carbon dioxide (CO₂) from a gas mixture into an aqueous monoethanolamine (MEA) solution in a packed column is developed. The model is based on the fast second-order kinetics for the CO₂-MEA reactions and takes into account the mass transfer resistances. The heat effects associated with the absorption and chemical reaction are included through energy balances in the gas and liquid phases. Appropriate correlations for the key thermodynamic and transport properties and for the gas-liquid mass transfer are incorporated into the model to ensure reliable predictions. The model predictions are validated by simulating a series of experiments conducted in pilot and industrial scale absorption columns with random and structured packings reported in the literature. Comparisons between the simulation results and the experimental data reveal good quality predictions of the gas phase CO₂ and MEA concentrations and the liquid temperature along the column height. The sensitivity studies reveal that the correlations for the gas- and liquid-film mass transfer coefficients given by Onda et al. (1968) provide better predictions than the penetration theory of Higbie (1935) and the correlation of Bravo et al. (1985).