Estimation of mass transfer coefficient in ozone absorption by linear least square fitting and Simplex search methods

For physical ozone absorption without reaction,two parametric estimation methods,i.e.the common linear least square fitting and non-linear Simplex search methods,were applied,respectively,to determine the ozone mass transfer coefficient during absorption and both methods give almost the same mass transfer coefficient.While for chemical absorption with ozone decomposition reaction,the common linear least square fitting method is not applicable for the evaluation of ozone mass transfer coefficient due to the difficulty of model linearization for describing ozone concentration dissolved in water.The nonlinear Simplex method obtains the mass transfer coefficient by minimizing the sum of the differences between the simulated and experimental ozone concentration during the whole absorption process,without the limitation of linear relationship between the dissolved ozone concentration and absorption time during the initial stage of absorption.Comparison of the ozone concentration profiles between the simulation and experimental data demonstrates that Simplex method may determine ozone mass transfer coefficient during absorption in an accurate and high efficiency way with wide applicability.

Prediction of mass transfer coefficients in an asymmetric rotating disk contactor using effective diffusivity

Mass transfer characteristics have been investigated in a 113 mm diameter asymmetric rotating disk contactor of the pilot plant scale for two different liquid–liquid systems. The effects of operating parameters including rotor speed and continuous and dispersed phase velocities on the volumetric overall mass transfer coefficients are investigated. The results show that the mass transfer performance is strongly dependent on agitation rate and interfacial tension, but only slightly dependent on phase flow rates. In this study, effective diffusivity is used instead of molecular diffusivity in the Grober equation for estimation of dispersed phase overall mass transfer coefficient.The enhancement factor is determined experimentally and there from an empirical expression is derived for prediction of the enhancement factor as a function of Reynolds number. The predicted results compared to the experimental data show that the proposed correlation can efficiently predict the overall mass transfer coefficients in asymmetric rotating disk contactors.

Mass Transfer Enhancement of Propane Absorption into Dodecane-Water Emulsions

A one-dimensional unsteady heterogeneous parallel mass transfer(ODUHPMT) model was developed for the absorption enhancement of volatile organic compounds(VOC) by the dispersed droplets.An analytical solution for enhancement factor was obtained based on surface renewal theory and the Laplace domain transformation. The absorption rate of propane into water at different stirring speeds with the added micro dodecane droplets was investigated experimentally in a thermostatic stirred tank.The mass transfer flux across the gas-liquid interface and the enhancement factor were measured.The results showed that the dodecane has an obvious enhancement effect on propane absorption into water,the maximum enhancement factor reached 11.The enhancement factor increased with increasing dodecane volume fraction and decreased with increasing stirring speed.The experiment data agreed well with the model predictions and showed high prediction accuracy of ODUHPMT model.

An Unsteady Heterogeneous Mass Transfer Model for Gas Absorption Enhanced by Dispersed Third Phase Droplets

A model for one-dimensional unsteady heterogeneous mass transfer was developed based on Danck-werts' surface renewal theory in order to describe the mass transfer enhancement of absorption process for a slightly soluble gas in a gas-liquid-liquid system.The model accounts for the mass transfer resistance within the dispersed phase and the effect of emulsion viscosity on mass transfer.An analytical solution for enhancement factor was obtained by Laplace domain transformation.The absorption rates of carbon dioxide in the dodecane-in-water and castor oil-in-water systems were measured in a thermostatic reactor,and the enhancement factors were calculated at different volume fractions of dispersed phase and stirrer speeds.The model predictions agree well with the experimental data.

The Enhancement of CO2 Chemical Absorption by K2CO3 Aqueous Solution in the Presence of Activated Carbon Particles

The enhancement of chemical absorption of CO2 by K2CO3/H2O absorbents in the presence of activated carbon （AC） particles was investigated. The results show that the gas absorption rates can be enhanced significantly in the presence of AC particles, and the maximum enhancement factor 3.7 was observed at low stirring intensities. The enhancement factor increased rapidly with the solid loading during the initial period of absorption and then be- came mild gradually to a maximum value. Both the liquid-solid contact area and the probability of solid particles residing at the gas-liquid interface decreased with the increase of the particle size, leading to a negative effect on the enhancement of mass transfer. The influence of the particles on gas absorption decreased with the reaction rate. The stirring speed changed the interfacial coverage and mass transfer rate on the liquid side and consequently affected the mass transfer between the gas and liquid phases; the enhancement factor decreased with the stirring intensity. A heterogeneous two-zone model was proposed for predicting the enhancement factor and the calculated results agreed well with the experimental data.

CFD simulation with enhancement factor of sulfur dioxide absorption in the spray scrubber

A model describing the absorption process of SO2 into limestone slurry with a spray scrubber is presented. Both the physical performance of the spray liquid in the scrubber and the involved chemical reactions are analyzed in the model. A con- tinuous concentration change of H+ was solved by iterative coupling using Matlab, and it was found that there was a remarkable influence on the concentration of the other elements in the process of SO2 absorption. The calculations show that the enhancement factor exponentially grows with an increasing value of pH and logarithmically decays with an increasing value of the driving force. To verify the accuracy of the model, experiments were also carried out, and the results suggest that the model, after combining the physical performance of the spray and the enhancement factor, can more precisely describe SO2 absorption in a spray scrubber. Furthermore, a commercial computational fluid dynamics (CFD) tool is used to perform several simulations which describe and clarify the effects of variables on SO2 absorption. The results of numerical simulation can provide a basis for further design and optimization of the scrubber.

Gas Absorption Enhancement of Carbon Dioxide into Ca(OH)_2 Slurries

Chemical absorption of CO2 into aqueous slurries of Ca(OH)2 was studied in a stirred thermostatic reactor. The influence of solid loading and stirring speed on absorption rate were investigated experimentally, and the results show that the enhancement factor increases with particle content due to the increase of reactive particles in the gas-liquid interfacial region. The absorption process was controlled by the diffusion of gas molecules in slurry. The influence of stirring intensity on enhancement factor is an integration of gas-liquid and liquid-solid mass transfer variation. A novel prediction model of enhancement factors was proposed with the partition of interface into two various zones, and the prediction values by the presented model are in agreement with the experimental data.

臭氧在水中的吸收和自分解

研究了臭氧在水中的吸收和自分解特性，探讨了ｐＨ值和气速对溶解臭氧平衡浓度的影响。实验测定了臭氧在鼓泡反应器中的传质系数。

磷石膏强化氨法CO_2捕集机理与模型

基于化学活性颗粒强化气液吸收机理,建立了磷石膏悬浮液强化氨法烟气CO2捕集模型。以液膜内量纲一传质距离λ*为特征参数,增强因子2E1/λqβλ/2**=+。用恒温反应器在不同搅拌转速及磷石膏颗粒固含量下实验测定CO2吸收增强因子对模型进行检验,结果表明:随颗粒固含量由5%增加到30%(质量分数),增强因子由1.69增加到2.10;而随搅拌转速从150 r·min-1增加到300 r·min-1,增强因子仅由1.75略增到1.80,表明磷石膏颗粒固含量及溶解速率是影响增强因子的控制性因素。实验结果与模型预测值吻合良好,偏差小于10%。

活性炭/水浆料中CO_2吸收过程的增强

针对分散相微粒增强难溶气体的吸收过程,提出了一个一维非稳态非均相传质的二区模型,并进行了理论求解。根据表面更新理论,得到了增强因子的数学表达式。利用恒温反应釜,对活性炭/水浆料中发生的CO2吸收过程进行了实验研究,测定了不同颗粒浓度及转速下的增强因子。实验结果与模型预测值吻合良好,表明本文模型具有很高的预测精度。

高压脉冲放电降解水溶液中4-氯酚过程的数学模型(Ⅱ)鼓泡过程中臭氧传质增强因子E与4-氯酚浓度的关系

臭氧从气相传质到废水溶液中并与其中的有机污染物发生氧化还原反应是一个含有化学反应增强的臭氧吸收过程. 在酸性废水中主要发生臭氧与4 -氯酚分子和 4- 氯酚盐离子的反应, 而臭氧在水溶液中分解形成的羟基自由基的氧化作用可以忽略. 提出了由于发生化学反应而形成的臭氧传质增强因子 E与废水中有机物浓度[PCP] 的定量关系的表达式.

分散液相强化微溶气体吸收的研究

在气升式搅拌反应器中,利用水对微溶气体CO2(常压和室温条件)的物理吸收过程,考察加入辛醇(有机分散相)对传质过程中体积传质系数和增强因子的影响。研究辛醇加入体积分数(1%—5%)、搅拌速率(200—700 r/min)、气体流速(350—700 L/min)变化对吸收效果的影响,用插值函数微商法确定体积传质系数。结果表明,向水体系中加入少量辛醇可以明显改善吸收效果,体积传质系数随辛醇加入体积分数的增加呈现先增加后减小的趋势,当辛醇加入的体积分数为4%左右时吸收效果最好。增强因子与CO2分配系数、扩散系数有关,与吸收效果呈线性关系,最大增强因子为2.76。

旋转填充床中SO_2与O_2同时吸收的扩散-反应模型

In this paper the rotating packed bed, a new type of absorber, which has high mass-transfer characteristic by means of centrifugal field instead of gravity field, is used to study on stimulated flue gas desulfurization. Based on experimental data,a model of mass-transfer and reaction of the sulfur dioxide chemical absorption in the rotating packed bed reactor is proposed according to the film-theory. It can be used to predict the performance of the total absorption rate and the enhancement factor of the sulfur dioxide and oxygen simultaneous absorption in the rotating packed bed reactor.The prediction of the model is consistent with the experimental result varying operating conditions, and the relative error between experimental result and predicted result is below 12%. Some interesting potential projects of simultaneous absorption of sulfur dioxide and oxygen in the rotating packed bed reactor are also discussed.

湿式石灰石烟气脱硫过程添加剂对传质的影响

以具有水平气液相界面的双搅拌釜为吸收设备,研究了湿式石灰石烟气脱硫过程中添加剂对传质的影响,得出了不同反应时间、不同pH值下的液相传质分系数、增强因子和总传质系数。硫酸钠、硫酸镁和腐殖酸钠均能有效地改善浆液的传质性能,与非强化过程相比,反应时间相同时,添加剂强化过程的传质系数大幅度提高;相同pH下,添加剂强化过程石灰石的利用率大幅度提高,其中以钠强化过程的提高幅度为最大。传质系数随浆液中石灰石含量的降低而降低。当浆液pH值较低而石灰石消耗殆尽时,脱硫剂将以亚硫酸钙为主。

气液界面传质过程Rayleigh对流模拟的格子Boltzmann方法

浓度梯度导致的Rayleigh对流是一种通常在传质过程中观察到的界面现象.为了模拟乙醇吸收CO2气液传质过程中界面传质引发的Rayleigh对流现象,提出了描述界面扰动的随机扰动模型,并建立了带有双分布模型的二维格子Boltzmann方法(LBM).模拟二维液相Rayleigh对流过程中,假设界面上CO2浓度为常数.通过模拟研究,确定了随机扰动模型的2个参数:局部扰动概率P和浓度扰动大小ρD.模拟结果表明,当0<ρD≤10-9,kg/m3、10-6≤P≤10-1时,平均液相传质系数存在一个稳定值:(1.09±0.02)×10-5,m/s.通过考察浓度分布结构,分析了Rayleigh对流的时空演化过程.根据模拟结果定义并计算了传质增强因子,其证明了Rayleigh对流能够有效地强化界面传质.

反应条件对MEA溶液提纯沼气传质性能的影响

对吸收剂浓度、进气流量及CO2体积分数、进液温度等反应条件对MEA溶液吸收沼气中CO2过程的八田数Ha、增强因子E及总体积传质系数KGae的影响进行了实验研究,并对吸收过程中反应对传质性能的影响及拟一级反应的条件进行了分析。结果表明:吸收过程中的八田数Ha、增强因子E及总体积传质系数KGae随吸收剂浓度增加而增大;随进气中CO2体积分数增加而减小;当进气流量增加时,Ha、E减小,KGae先增大后减小;Ha、E及KGae随吸收温度增加而增大,当吸收温度高于57.4℃时,KGae逐渐减小。在此条件下,仅当吸收剂浓度高于2.5 mol/L或者进气流量低于5.73 kmol/(m2·h)时,MEA与CO2的反应可用拟一级反应描述。研究结果可为沼气提纯工艺的优化及技术开发提供参考。

浆料反应器中吸附剂粒子对CO_2气体的吸收强化

研究了吸附剂粒子对气体吸收的增强作用。在一个带有搅拌的间歇反应釜中,分别测定了CO2在活性炭/水、S iO2/水浆液以及在活性炭/环己烷、S iO2/环己烷浆液中的吸收速率和增强因子。实验温度为298.15 K,初始压力为0.1 MPa,浆液中粒子的固含率为0—2 kg/m3,搅拌速度为1 s-1和4 s-1。结果表明,活性炭/水、S iO2/环己烷体系对CO2的吸收具有明显的增强作用,而S iO2/水、活性炭/环己烷体系则没有发现增强作用。因此,只有具有界面亲合能力且对溶质有吸附作用的颗粒才能对气体吸收产生显著的强化作用。将界面划为粒子覆盖和未覆盖区,提出了一个预测增强因子的一维双区模型,并进行了求解,模型预测值与实验结果吻合良好。

醇胺溶液吸收酸性气体的强化传质性能

选取二乙醇胺溶液作为化学吸收液吸收酸性气体CO2,通过建立气液两相强化吸收装置,考察吸收液温度、吸收液浓度、气相搅拌强化和液相搅拌强化等条件对气液两相间传质性能的影响。结果表明:在吸收液温度60℃,吸收液二乙醇胺溶液浓度1.2 mol/L,气相转速200 r/min,液相转速300 r/min时,传质系数为0.021kmol/(s·m2·MPa),具有较高的CO2吸收效率。

臭氧吸收及反应过程的传质系数与增强因子

从双膜理论、溶质渗透理论、膜-渗透理论和表面更新理论出发,研究分析了臭氧气体在液相中的物理吸收过程传质系数,臭氧与液相中的污染物化学反应过程的吸收系数。基于双膜模型理论,推导出在不同pH值区间内伴随着臭氧与污染物化学反应过程的增强因子表达式。

复合气液传质过程多元传质系数估算方法

以多元传质的扩散方程为基础，提出了化学反应、吸附对气液传质增强因子以及伴有化学反应、吸附的气液传质过程的多元传质系数的估算方法．用非平衡级模型及上述方法得到的传质系数模拟脂肪酸甲酯化反应精镏过程，与实验结果吻合．