Faster Kinetics

Condensate polishing applications utilize mixed beds, which operate at high flow rates in high purity condensate to remove dissolved and particulate solids. In these instances, the ability of the resin to remove extremely low levels of ionic impurities depends, in part, on the kinetics or the rate of reaction of the ion exchange process. The reaction rate is improved by the smaller average bead diameters of the UPS resins as well as the greater surface area per unit volume. By selecting resins with high bead size uniformity, the larger kinetically slower beads are eliminated, and the rate of reaction of the entire process is enhanced.

Better Separation

Mixed beds must be separated to be regenerated, either in-situ or in an external regeneration vessel. Complete separation of the anion and cation components of a mixed bed is necessary to reduce cross-contamination which will increase the amount of ionic leakage during the subsequent operating cycle. UPS resins for mixed bed applications, in which the anion average bead size is 100 microns smaller than the diameter of the cation beads, are designed to have terminal settling velocities (dependent on the bead size and density) that result in little or no cross-contamination after the backwash cycle.

Better Color Differentiation

Verifying resin separation after the backwash cycle is enhanced because of the distinct color difference between the anion (cream) and cation (black) resin components. The color of the anion resin may darken with time as organics accumulate on the surface and within the resin matrix. This can be avoided or minimized by the proper operation of the pretreatment system and the implementation of a brine cleaning before the resin becomes irreversibly fouled.

Higher Physical Integrity

The resins in a mixed bed must survive the physical stress of high flow rate compaction, separation, transfer, and regeneration. If the beads crack and break into smaller fragments, the fines produced can fill the void fraction between the larger beads thus contributing to an increase in pressure drop. In addition, fines that escape the bed during backwash can plug downstream filters. UPS resins designed for mixed beds resist the tendency to fragment under these conditions and have, in fact, a higher crush strength or friability rating than many comparable conventional resins.

Reduced TOC Leachables

All cation resins oxidize over time and release some sulfonate leachables that contribute to the TOC level of the water. Low molecular weight leachables are usually picked up by the anion resin, but high molecular weight leachables can pass through the polisher to contaminate downstream processes or equipment. UPS cation resins for mixed beds are very stable against oxidative degradation and, consequently, release very low levels of both low and high molecular weight leachables.