On boundary conditions to the film model of mass transfer in chemical absorption

The problem of appropriate boundary conditions for mass transfer within the liquid film in chemical absorption ih reconsidered. It has been shown that the most general solution to the problem of mass transfer in the liquid film can be obtained if a fixed bulk composition is taken as a film-bulk boundary condition to the differential balance equations of the film. This method leads to solutions which can be incorporated into absorber balance equations of any type. As an illustrative example, the simultaneous absorption of two gases which react together in a semi-batch absorber is discussed. A new, approximate but very simple and accurate solution to this problem is proposed.     

Simultaneous absorption of two gases reacting between themselves in a liquid—I exact solutions

Simultaneous absorption and irreversible second order chemical reaction of two gases in an inert liquid have been considered. The nonlinear differential equations describing the absorption process have been solved analytically for particular cases by the use of the Weierstrass elliptic function and Airy functions. It is impossible to obtain a general analytical solution and therefore the accurate numerical solution for the diffusion-reaction process based on the film theory has been developed. The approximate formula for the enhancement factor E_A, in the range of large values of the dimensionless parameter M is given.     

Simultaneous absorption of two gases reacting between themselves in a liquid—II: Approximate solutions

An attempt has been made to analyse the hitherto existing approximate solutions of nonlinear differential equations representing a mass balance of two gases which react between themselves in an inert liquid. New approximate analytical solutions of the problem have been obtained and compared with the numerical and the existing approximate solutions in order to show the best approximations and the most convenient mathematical formulas for calculating the concentration profiles and the enhancement factors.     

Gas absorption with exothermic bimolecular reaction in a thin liquid film: Fast reactions

A problem of gas absorption with a fast nonisothermal bimolecular reaction in a thin liquid film has been analysed. Approximate analytical solutions for the interfacial temperature rise and enhancement factor have been derived incorporating the influence of depletion of liquid reactant concentration at the interface. The effects of heat generation, heat dissipation and reaction rate parameters on enhancement factor and interfacial temperature rise have been discussed. For a certain range of parameters, multiple steady state solutions of enhancement factor and interfacial temperature rise are observed. Another interesting observation is that as the value of a dimensionless parameter ? increases, the enhancement factor approaches its instantaneous asymptote which is the same as that for the isothermal case in an instantaneous regime. The analysis presented here is simple and avoids complex numerical computations and it is likely to be useful in design applications.     

Simultaneous absorption of two gases which react between themselves in a liquid medium: An approximate solution

An approximate solution for the simultaneous absorption and reaction of two gases in a liquid has been presented based on the film theory, assuming a nonlinear (exponential) profile for the concentration of each of the gaseous species in the film. The solution obtained has been compared with the numerical solution of Roper, Hatch and Pigford and found to be in good agreement, thus proving the validity of the approximations.     

CFD modeling of turbulent reacting flow in a semi-batch stirred-tank reactor

For the mixing-sensitive reactions,both chemical kinetics and mixing conditions of the reactants determine the distributions of products.The direct quadrature method of moments combining with the interaction by exchange with the mean micro-mixing model (DQMOM-IEM) has been validated for the chemical reacting flows in microreactors.Quite encouraging simulation results offer great promise,but the applicability of this method is needed to be explored furthermore,such as in stirred reactors.In this work,the two-environment DQMOM-IEM model was created with C language and used to customize Fluent through the user-defined functions.The mixing effects on the course of parallel competing chemical reactions carried out in a semi-batch single-phase stirred reactor were predicted.The simulation results show that the rising feed velocity enlarges the volume of reaction zone and maximize the yield of the by-product,which also indicates that the feed stream is more difficultly dispersed into the main stream and the zone surrounding feedpipe exit with high turbulent kinetic dissipation rate cannot be efficiently used.     

浆料反应器中吸附剂粒子对CO2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。     

Behaviour of an elementary oxidation reaction in a semi-batch reactor

The dynamics of a non-isothermal bi-molecular gas-phase reaction in a semi-batch reactor is investigated. It is assumed that one of the reactants flows into a reactor containing the second. A reduced model is obtained by making a ‘pool-chemical’ approximation on the concentration of the reactant initially in the reactor. The region in parameter space in which oscillations are observable in the full transient model is estimated by determining the Hopf bifurcation locus in the reduced system. The contribution of the current work is its comparative study of the behaviour of the full system to that of the pool-chemical model. Although the reaction scheme is symmetric with respect to the reactants the regions of oscillatory behaviour are not identical because the reactants have different heat capacities.     

Kinetics of absorption of sulfur dioxide in dimethylaniline solution

Absorption of sulfur dioxide accompanied by reversible reaction in dimethylaniline has been studied using a short falling-film apparatus. Solutions of the amine in kerosene were used for this purpose. The effects of gas and liquid concentrations, contact time and temperature on the rate of absorption were investigated. Reaction equilibrium constant values were obtained at different temperatures from separate measurement of solubility of sulfur dioxide gas in kerosene as well as in dimethylaniline solutions. The heat of reaction was also calculated from these data. The absorption data could be satisfactorily interpreted by using the penetration theory of mass transfer with simultaneous pseudofirst order chemical reaction. The rate equations for the forward and reverse reactions were established.     

Film and penetration theories for a first-order reaction in exothermic gas absorption

Film and penetration models for simultaneous heat and mass transfer are developed for the absorption of gas with a first-order chemical reaction in the liquid phase with temperature-dependent solubility and reaction rate coefficient. These two models represent two extreme conditions of interfacial temperature rise and gas solubility and they are compared with some previous models (Allan and Mann, 1979; Asai et al., 1985). The approximate analytical expressions of the penetration model of Asai et al. (1985) are in good agreement with the numerical results of this work. The results reveal that under many practical circumstances the gas-liquid interfacial temperature may be several degrees Kelvin higher than the bulk liquid temperature. The degree of deviation of the enhancement factor from its isothermal value at the bulk liquid temperature depends on the degree of difference of a certain dimensionless activation energy group from zero, which confirms the previous finding of Asai et al. (1985).     

旋流吸收器气液吸收传质过程研究

根据旋流吸收器中分散液相不同的运动形态建立了伴有化学反应的气液吸收传质模型,且该模型的表达形式与Danckwerts的表面更新理论一致。从模型上看,液侧传质系数kL正比于扩散系数DA和表面更新率S的平方根,这一正比关系还得到了实验结果的部分验证。根据实验结果可以看出,与其他吸收器相比,作为一种结构简单的静态设备,旋流吸收器同样可以提供一个强化传热、传质的流体力学环境。     

Preparation of nanoparticles with a semi-batch gas-liquid membrane contactor

Nanosized calcium carbonate particles were prepared with a semi-batch gas-liquid membrane contactor. A mathematical model of the semi-batch operated contactor was given, and the effects of Ca(OH)₂ concentration, CO₂ partial pressure and additives on the absorption rate were estimated theoretically. The predicted data were consistent with the experimental results. The Ca(OH)₂ concentration and CO₂ pressure have no apparent effects on the particles. In the presence of PVP and PEG, the particles are well-dispersed and the size is effectively reduced. After reaction, the membranes were washed with dilute hydrochloric acid and the membranes can be reused for at least 9 times without apparent performance deterioration.     

正十二烷-水乳液吸收丙烷的传质增强作用(英文)

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 dif-ferent 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 enhance-ment 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.     

A general enhancement factor model of the physical absorption of gases in multiphase systems

A general mass transfer enhancement factor model (GEFM) has been developed based on the enhancement mechanism proposed in this paper taking both shuttle effect and hydrodynamic effect into account to calculate the overall enhancement factor due to the presence of dispersed particles. GEFM can describe the phenomena of the enhancement factor increasing with partition coefficient (m), surface covering fraction (α) and dispersed phase volume fraction (φ) increase, leveling off at higher φ, changing of enhancement factor (E) at different conditions. Moreover, GEFM can give the enhancement factor not only of multiphase system relative to the pure liquid phase (even at quite high φ), but also in the same system under different conditions (e.g. stirrer speed, viscosity). The enhancement factors predicted from GEFM are consistent with the experimental observations well.     

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。     

Effect of surface resistance arising due to surfactant on gas absorption accompanied by a chemical reaction in a foam-bed-reactor

On the basis of an idealized foam bed, a model to predict conversion in a foam-bed-reactor containing surfactant has been developed. The model takes into account the effect of surface resistance, arising due to the presence of a surface active agent, on gas absorption accompanied by a chemical reaction in a foam matrix. To verify the theory, experiments have been carried out in a semi-batch foam-bed-reactor for the absorption of air-carbon dioxide mixture in a foam of sodium hydroxide solution containing finite; concentrations of different surfactants. The surface resistance offered by the molecules of surfactant at the gas-liquid interface reduces the mass transfer rates significantly. The proposed model predicts fairly well the experimentally found depletion values of sodium hydroxide.     

非灰系统当量灰吸收系数的反演

提出了一种由气体温度场反向分析计算气体当量灰吸收系数的方法.采用段法（区域法）求解正问题,反演中采用求目标函数极小值的共轭梯度法.以直通式实验炉的测量数据为求解条件,用该计算得到了炉内气体介质当量灰吸收系数的分布.数值模拟结果表明,段法与共轭梯度法结合可以较好地反演非灰系统的当量灰吸收系数.与指数宽带段法模型结果的比较表明,反演得到的当量灰吸收系数具有与指数宽带模型相当的精度,但计算量小于宽带模型的1/10.