Continuous Counter-current Process Research Articles

Dynamics of continuous countercurrent mass-transfer processes—II. Single-component systems with nonlinear equilibria

Based on the differential model presented in Part I, this paper discusses the effects of nonlinear equilibria on the propagation dynamics of continuous countercurrent mass-transfer processes by the aid of a numerical solution and two approximations. A nonlinear equilibrium tends to sharpen or spread concentration waves as in fixed-bed sorption; it also substantially affects the direction and velocity of wave propagation. More importantly, it plays a critical part in the propagation of a disturbance over a nonuniform steady-state profile. This dynamic phenomenon can be qualitatively predicted by the theory of interference for fixed-bed sorption with proper adjustments.

Dynamics of continuous countercurrent mass-transfer processes-I. Single-component linear systems

A differential (distributed-parameter) model has been established for the dynamics of continuous countercurrent mass-transfer processes in single-component linear systems. This model provides a more concise and more rigorous analytical solution than available previously; it also offers a better perception of the physical features involving propagation, reflection and superposition of concentration waves. Stressing the chromatographic nature of such processes, this model suggests a prospective approach for modeling multicomponent systems.

Separation of strontium from nuclear waste solutions by solvent extraction with crown ethers

The possibilities of strontium separation from medium activity waste (MAW) solutions have been investigated. MAW originates from the PUREX process and contains NaNO3 and HNO3 in a large excess. By solvent extraction with the crown ether dicyclohexano-18-crown-6 (DC-18-C-6) in 1,1,2,2-tetrachloroethane, separation is possible. The distribution ratio for Sr2+ depends on the concentration of HNO3, NaNO3 and Pb(NO3)2. The extraction system is employed in a continuous counter-current process. After use, the extraction agent can easily be regenerated by reextraction with pure water.

Numerical methods of solution for continuous countercurrent processes in the nonsteady state part I: Model equations and development of numerical methods and algorithms

AbstractSimple, efficient and noniterative algorithms are developed for the calculation of the dynamics of continuous countercurrent processes described by hyperbolic differential equations. The algorithms are derived using the method of characteristics and are particularly useful for either general quadratic or hyperbolic isotherms such as the Langmuir isotherm. The use of characteristic coordinates for the numerical solution avoids accumulating errors that would arise from computations based on a rectangular grid of real time and space coordinates.The proposed methods can provide an efficient framework for extension to transport processes with general nonlinear rate expressions. The algorithms and methods initially derived for simple models can be extended to more complex systems such as countercurrent flow with accumulating stationary phases and response to distributed disturbances.The application of the algorithm and methods to a number of countercurrent mass and heat transfer processes will be illustrated in Part II, where the accuracy and efficiency of the proposed methods will also be demonstrated by comparison to available analytic solutions. An example demonstrating the extension of the method to a system with complex coupled boundary conditions will also be discussed.

Effect of ionizing radiation on the mechanical and adsorption properties of granulated zeolites

1. The adsorption capacity of zeolites NaX and NaA relative to hydrogen in the case of high occupancies and high mechanical strength was found to be independent of the adsorbed dose up to 11,000 Mrd. 2. The increase in the capacity of irradiated zeolites relative to hydrogen at low equilibrium pressures is a consequence of stabilized electrons. In the air, this effect is due to O2− radical-anions. 3. The feasibility of using the zeolites studied in continuous countercurrent processes for tritium concentration was demonstrated.

Numerical methods of solution for continuous countercurrent processes in the nonsteady state part II: Application of numerical methods

AbstractThe numerical methods developed in Part I are applied to a number of important countercurrent processes. Examples involving simultaneous input disturbances, distributed disturbances, Langmuir isotherms, and nonlinear coupled boundary conditions are tested. These examples, if solved by previous methods, would have required interpolation or iterative procedures, but are solved efficiently and accurately by the explicit algorithms and coding sequence developed in Part I.The solutions for a linear system are in excellent agreement with the analytic solution. Numerical solutions obtained from explicit algorithms based on a nonlinear rate expression also shows very good agreement with the analytic solutions of Thomas (1944) for a fixed bed process. In both cases good accuracy is obtained with as few as sixteen increments.

Possibility for selective removal of calcium ions from black sea water using the continuous counter-current ion-exchange softening process with Wofatit KS-10

A possibility for selective removal of calcium ions from Black Sea water, by means of a continuous counter-current ion-exchange process, has been investigated. The application of this method is quite suitable for this purpose. It reduces some of the disadvantages of the fixed-bed ion-exchange method to a considerable degree. By means of a suitable choice of technological parameters of the continuous counter-current ion-exchange technique, it is possible to decrease the total hardness and calcium ion content in the water up to 65% and 80%, respectively. Under optimal conditions, Mg2+/Ca2+ = 10 in the softened water, and Mg+/Ca2+ = 4.1 in the non-treated water.

A New Continuous Solid-fluid Contacting Technique

A NOVEL technique for continuous countercurrent processes involving contact between participate solids and fluids has been developed here. This has been carried out on a small-scale apparatus using several different systems from which the essential features of the technique have been verified. The technique is directly applicable to operation on an industrial scale as well as in the laboratory, and has wide potential application in the processing industries.

Regeneration of Spent Limonite using Gasoline. II. Continuous Countercurrent Process

Regeneration of Spent Limonite using Gasoline. II. Continuous Countercurrent Process