Counterflow regeneration

Increasing the number of ion-exchange sites by the use of counter-current (counterflow) regeneration... 

FIG. 16-42 Ion -exchanger regeneration, (a) Conventional. Acid is passed downflow through the cation-exchange resin bed. (b) Counterflow. Regenerant solution is introduced upflow with the resin bed held in place by a dry layer of resin. 

In order to sustain the benefits from fixed bed counterflow regeneration it is imperative that the resin bed remains consolidated and undisturbed at all times during loading and reverse flow regeneration. Some ways this is achieved are discussed later in Chapter 10, but it follows that conventional backwashing of a counterflow designed column is undesirable since the inevitable bed disturbance causes exhausted resin to mix with the lightly loaded resin zone at... 

Figure 7.6 The effect of backwashing upon a counterflow regenerated column profile...

As discussed in Chapter 7 (Column Breakthrough and Leakage ) counterflow regeneration designs not only provide for better operational efficiencies compared with coflow systems but leakage residuals are virtually eliminated such that the column effluent quality only begins to deteriorate as the resin begins to truly exhaust. 

TABLE 17.9 General Functional Relationships and Basic Definitions of Dimensionless Groups for e-NTU and A-fl Methods for Counterflow Regenerators... 

A closed-form solution for a balanced and symmetric counterflow regenerator [C = 1, (hA) = 1] has been obtained by Baclic [31], valid for all values of C, as follows. 

Extensive numerical results have been obtained by Lambertson as reported in Ref. 20 for a counterflow regenerator and Theoclitus and Eckrich [33] for a parallelflow regenerator for a wide range of NTU , C, and C, . Their results for C = 1 are presented in Figs. 17.32 and 17.33. Note that longitudinal heat conduction in the wall is neglected in these results since infinite thermal resistance is specified for the matrix in the flow direction. 

Razelos, as reported in Refs. 15 and 29, proposed the following approximate procedure to calculate the counterflow regenerator effectiveness e for unbalanced and unsymmetric regenerators for C r > 1,0.25 < (hA) < 4, and the complete range of C and NTUe. For the known values of NTU , C, and C), calculate appropriate values of NTUe and C r for an equivalent balanced regenerator (C = 1), designated with a subscript m, as follows ... 

B. S. Baclic, The Application of the Galerkin Method to the Solution of the Symmetric and Balanced Counterflow Regenerator Problem, ASMEJ. Heat Transfer, Vol. 107, pp. 214-221,1985. 

Unfortunately, complexity of the equations requires a numerical solution. Hausen s solution for a counterflow regenerator with equal cooling and heating periods is shown in Fig. 5.25. 

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