Gerhard Klein

Ion-exchange pretreatment for scale prevention in desalting systems

Abstract Ion exchange pretreatment can protect dependably against scaling from calcium sulfate and alkaline deposits in desalting equipment, and against acid corrosion. When a feedwater is “softened” by ion exchange to replace most of its calcium by sodium, use of the sodium-rich reject brine from desalination to regenerate the exchanger makes the treatment chemically self-sufficient. An inexpensive vessel construction using salt-resistant reinforced concrete appears suitable for large-scale use. For moderate concentration factors (up to around 5 for seawater feed), and moderately low sulfate/chloride ratios, regeneration can be carried out in fixed-bed mode, preferably counterflow (upflow). At higher sulfate levels, precipitation occurs, and regeneration must be done in fluidized- (expanded-) bed mode to keep calcium sulfate from collecting in the bed. When weak-acid cation exchange with acidified exchanger is used to eliminate bicarbonate, feedwater acidity excursions are avoided, and the total-dissolved solids level is reduced rather than increased.

Calcium removal from sea water by fixed-bed ion exchange

Abstract Calcium removal from sea water prior to evaporation permits increased temperature and concentration during evaporation. The results of laboratory studies on calcium removal by fixed-bed ion exchange are reported. Synthetic regenerants were employed, simulating in composition and total amount the waste brine from the evaporator. In actual practice, use of this brine eliminates the need to purchase regenerant chemicals. Commercial polystyrene sulfonate resins were used at room temperature, employing downflow for the softening step, and upflow for regeneration, without rinse. In multicyclic operation, the effects of particle size, bed depth, flow rate, and regenerant concentration on the degree of calcium removal have been studied. Relations for predicting resin volume and cycle time under given operating conditions are presented as an aid in calculations leading to economic optimization of the process.

Calculation of ideal or empirically modified mass-action equilibria in heterovalent, multicomponent ion exchange

Abstract For chemical-engineering design purposes, it is useful, where possible, approximately to characterize the equilibrium between an ion-exchange material and any two exchangeable ion species involved by a constant selectivity coefficient. This can be done with the ideal or empirically modified mass-action law, but the application of even this simplified model to systems involving more than two exchangeable ion species, some of which differ in their valences, can lead to extremely cumbersome calculations. To overcome this difficulty, a successive-approximation algorithm is presented here, and specifically applied in the form of a program for a small electronic calculator. Within the limitations of the model, the program can compute the exchanger-phase composition of up to 10 ion species from the counterionic composition of the fluid phase, and vice versa. In addition to the given composition, a set of indepedent selectivity-coefficient and valence values is accepted as input. Instead of the valences, empirical, noninteger powers may be used where this improves the fit to experimental data. A method for bringing the data into a form suitable for direct solution is given, and the calculation procedure is illustrated with examples. Even in cases for which closed-form algebraic solutions can be developed, the present method, as implemented with the relatively slow, handheld electronic calculator, is fast enough to warrant its preferment, often even for the simplest binary ion-exchange calculations.

A method of using irrigation drainage water for power plant cooling

Abstract The accumulation of large quantities of saline water collected from irrigated fields by underground tile drainage systems presents environmental problems in the South-Western U.S. and Mexico. A major project conducted in this Laboratory indicates technical and economic feasibility for using such wastewaters for power plant cooling. A novel process sequence is employed comprising (a) ion-exchange resin softening whereby nearly all the calcium is removed, followed by (b) using this softened water as feed to the power plant cooling tower, concentrating it by a factor of 5 to 15; this cooling tower blowdown is subsequently (c) further concentrated by vertical tube foam evaporation (VTFE) to provide a 20-fold concentrate of the initially softened wastewater which is then adequate to (d) serve as the sole regenerant for the ion-exchange resin used in the initial softening step. Step (d) is carried out in an upflow fluidized bed mode which ensures favorable reaction kinetics by the formation and removal of calcium sulphate precipitate from the resin bed. A new pilot plant facility of 2,000 gpd capacity is described including a softening and regeneration facility, a cooling tower operating under realistic process conditions and a complete VTFE facility; test data are presented indicating technical feasibility. Long term field tests with this facility are planned in the San Joaquin Valley to determine the viability of this approach for the beneficial use and simultaneous disposal of irrigation drainage. This project is sponsored by several major U.S. power utilities, the Electric Power Research Institute and the California Department of Water Resources.

Fixed-Bed Ion Exchange with Formation or Dissolution of Precipitate

The nature, utility, and limitations of fixed-bed ion-exchange systems that involve precipitates are discussed, together with possible applications of the relevant theory in other fields. Local-equilibrium theory is reviewed briefly and extended to exchange accompanied by precipitation or dissolution. The differences between the behavior of beds containing stationary and moving precipitates are discussed qualitatively and with respect to their effect on the continuity relations.

Zeolite a for selective calcium removal from brackish water

Abstract Plans are being transformed into practice to facilitate the disposal of very large volumes of high-salinity, high-sulfate agricultural drainage water in California by subjecting it to reverse-osmosis treatment, resulting in a concentrated and a fresh-water stream. Calcium removal to prevent calcium sulfate scaling at the membranes is required as a pretreatment, and is intended to be accomplished with a standard cation-exchange resin. The present study utilizes published three-component equilibrium data for zeolite A to show that, with local-equilibrium performance, a zeolite bed would remove only little magnesium, the removal of which is not required, and thus make additional capacity available for calcium. The results of column experiments at various flow rates have confirmed this finding and permitted a preliminary economic comparison of calcium removal by zeolite with that by a standard ion-exchange resin. Although the resin exhibits a favorable three-to-one margin over zeolite cost, this margin is narrow enough to leave open the possibility of sufficiently improving the economic attractiveness of the zeolite by suitable modifications in its preparation (affecting, for example, particle configuration and binder material), and acceptance of a lower and less expensive grade, to the point of competitiveness, or beyond.

A mathematical model of the cyclic operation of desalination-feedwater softening by ion-exchange with Fluidized-bed regeneration

Abstract The goal of this work was to optimize the steady cyclic operation of an ion-exchange pretreatment of an agricultural wastewater that is fed to a desalination plant. The ion-exchange resin is exhausted to remove calcium in a fixed bed. Brine from the desalination plant regenerates the ion exchanger in a fluidized bed to prevent plugging by calcium sulfate. After the calcium sulfate precipitates, the regenerant can be reused. To predict how the plant should be operated, a mathematical model was needed. The model qualitatively agrees with experimental results. Conclusions about operating such a plant are drawn.

Theodore Vermeulen’s Contributions To Process Design For Sorption Operations

A summary is given of Theodore Vermeulen’s scientific contributions in the field of process design for sorption operations.

The solution of multicomponent distillation columns

Abstract The equations of A. J. V. U nderwood for solution of distillation columns are arranged to give a solution in the form of a sum of difference products. For many distillation problems the present solution is much less tedious than the straightforward solution of U nderwoods equations or the determinantal solution proposed by A lder and H anson [1]. The solution is illustrated by an example employing a five-component system.