TABLE OF CONTENTS This section covers the basics of how ion exchange systems are sized, the requirements for ancillary systems, and the selection of materials of construction. These vary depending on the type of equipment and the equipment suppliers preferences. Therefore, the subject is presented as a brief introduction rather than as a design manual.
Most ion exchange systems are limited by flow rate for physical reasons such as pressure loss or the physical characteristics of the resin rather than by any particular chemical requirements. With respect to linear flow rates, if the linear flow rate exceeds about 20 gpm/ft 2, the pressure exerted on the resin bed, together with other stresses such as osmotic and thermal, is sufficiently large to begin to break some of the resin beads. The strength of the individual beads is actually much higher, but when pressure loss across the bed routinely reaches about 50 psi, excessive bead breakage can be expected. In general, the maximum allowable pressure loss across the cation beds should always be less than 20 psi and across the anion beds less than 20 psi. It is common practice to allow for a 5- to 10-psi increase in pressure drop across the resin bed over time. Therefore, the design value for the maximum flow rate across a resin bed is usually in the neighborhood of 15 gpm/ft 2.
On the low end, the minimum flow rate is that which the liquid distributors can accommodate. Typically this...
