Abraham Tamir

Modeling and experimental studies of SO2 absorption in coaxial cylinders with impinging streams: Part I

Abstract A new `wet-type’ desulfurization absorber comprising coaxial cylinders with impinging streams has been developed, modeled and tested with Ca(OH) 2 as sorbent. The spray nozzle used was of external complete mixing type where mixing between the flue gas and the sorbent took place only after the exit from the nozzle. The absorber operated satisfactorily, absorption efficiency of SO 2 varied in the range of 93–97%, and predictions of the model were within ±15% making it a potential tool to design a large-scale absorber.

Explaining characteristic azeotropic behaviour

Abstract An explanation of the formation of minimum-boiling, maximum-boiling and saddle-type azeotropes is given (with illustrative examples) in terms of the molecular interactions in the solutions and in the pure liquids. “Interaction weakening” and “interaction strengthening” effects are defined which tend to be associated with the formation of minimum-boiling and maximum-boiling azeotropes respectively. As defined these effects correspond respectively to positive and to negative values of the interchange energy in regular solution theory, though the concept is considered to be of more general application than is this simple model. When more than two components are present it is possible for both effects to occur leading to the possibility of saddle-type azeotropy. By considering the nature of the intermolecular fones it is possible to predict the kind of azeotope which will be formed, if an azeotrope is formed at all. Although present knowledge of intermolecular fones is far from complete, enough is known to enable this prediction to be made in many cases. The more exacting question of whether or not an azeotope will be formed cannot yet be answered with the same certainty partly because of the lack of a completely satisfactory model of the liquid state.

Correlation of the boiling points of mixtures

Abstract A modified Swietoslawski equation has been developed to correlate the boiling points of mixtures. Vapor—liquid equilibrium data have been determined at 760 mm for the binary systems normal butanol-tertiary butanol and normal butanol-secondary butanol. Both systems present slight negative deviations from ideal solution behavior. The boiling points of the two binaries and of several other non-ideal systems were satisfactorily correlated by means of the above equation. Prediction of ternary boiling points from binary data and simplifications in the correlation which are useful for practical applications are also discussed.

APPLICATIONS OF IMPINGING-STREAMS IN CHEMICAL ENGINEERING PROCESSES—REVIEW

Various aspects of the method of impinging-streams, which proved to be one of the most efficient methods for performing the gas-solid operations in Chemical Engineering, are discussed. The aim of the review is to bring the method of impinging-streams and its possibilities to the attention of the Chemical Engineering community, to stimulate further research in the field and to encourage the technological applications of this method. KEYWORDS: Impinging streams, Impinging jets, Impingement zone, Opposed jets

Thermodynamics of acetone—chloroform mixtures

Abstract Apelblat, A., Tamir, A. and Wagner, M., 1980. Thermodynamics of acetone—chloroform mixtures. Fluid Phase Equilibria , 4: 229–255. The excess thermodynamic functions G E , H E , S E , C p E and V E and the vapour—liquid equilibria at constant temperature, at constant pressure and azeotropic behaviour are satisfactorily described for the acetone + chloroform system using the ideal association model of the type A + B + AB + AB 2 . Existing data in the literature for the system were supplemented by determination of vapour pressures at 25.0° and 35.17°C, excess volumes of mixing at 35°C and excess heat capacities at 30°C.

Characterization of a two-phase impinging jet absorber—II. Absorption with chemical reaction of CO2 in NaOH solutions

Absorption of CO2 into NaOH solutions was performed in a two-impinging-jet absorber under conditions of second-order chemical reaction. The enhancement factor, interfacial area and mass transfer coefficient were determined. The values of the specific area a varied between 0.9 and 20.5 cm−1 and those of the mass transfer coefficient kL between 0.029 and 0.066 cm/s corresponding to values of kLa ranging between 0.025 and 1.22s−1, as already reported in the first part of this paper. These values are among the highest encountered for conventional absorbers. The characteristic two-maxima behavior of absorption rate vs internozzle distance repeated itself in this case too.

Monte Carlo simulation of gas−solids suspension flows in impinging streams reactors

Abstract Impinging streams reactors have been employed in various fields of chemical engineering, as a means of enhancing the rates of convective transfer processes. The analysis of the hydrodynamics of gas-solids suspension flows in these reactors requires that collisions between particles be taken into account. The stochastic model for gas-solids suspension flows, based on the Boltzmann transport equation, is presented. The system of nonlinear integro-differential transport equations is solved using the Monte Carlo method. A qualitative agreement is obtained between the predicted and experimental results for the particle concentration distribution in an impinging streams reactor. The particle concentrations in the impingement zone of two particle-laden jets are strongly reduced by the effects of inter-particle collisions. The analysis of laminar pipe flows in the absence of gravity and lift forces (Saffman force etc.) reveals a collision-induced migration of particles towards the pipe wall and, to a lesser extent, towards the core. In turbulent vertical pipe flow, particles migrate towards the pipe core and the laminar sublayer. Collison-induced effects become more pronounced in mixture flows with particles of different sizes and densities.

An evaluation of thermodynamic analyses of the vapor—liquid equilibria in the ternary system acetone—chloroform—methanol and its binaries

Abstract The vapor—liquid equilibria for the ternary system acetone—chloroform—methanol and its binaries was determined at 25°C by a modified isoteniscope technique. These data and also those available, were used to develop recommendations for general procedures to be used in treating any ternary system. Calculations of azeotropic behaviour were made and the change in vapor pressure with temperature — along the azeotropic line — as well as the latent heat of vaporization of the azeotropic mixtures was established. Various equations were explored (relating P and Y directly with X, the Wilson equation and an equation based on the separation factor) for correlating the data and predicting azeotropes.

Vapour-liquid equilibria in associating solutions

Abstract Isobaric vapour—liquid equilibria data were measured for the binary mixtures of acetic acid—propionic acid and formic acid—propionic acid at 760 mm Hg. The data were tested against a new thermodynamic model which extends the one proposed by Marek in that it is suitable for the case of binary mixtures containing two associating species and takes into account hetero-dimerization in the vapour phase. The proposed model converts into that of Christian for the particular case of an ideal liquid solution. The model fits well the system acetic acid—propionic acid with regard to the thermodynamic consistency of the overall activity coefficients, but does not fit the second mixture so well, probably because higher degrees of polymerization have to be included in it.

Effect of diffusivity on gas-side mass transfer coefficient

Abstract Experiments conducted in a stirred cell on evaporation of pure liquids into various carrier gases yield that the gas-side mass transfer coefficient, k g is proportional to the binary diffusivity, D , raised to the power 0.684 (2-3).