Evaluation of new ion exchange resins for hardness removal from boiler feedwater

Abstract

Ion exchange is widely used for the removal of selected ions from water streams. Within oil & gas, one application is boiler feedwater treatment to remove hardness, i.e. calcium and magnesium. Weak acid cation (WAC) resins are typically used and advances in material science, polymer chemistry and manufacturing methods have resulted in new resins being introduced to the market. These new resins can lower operating costs through higher capacity, reduced chemical consumption during regeneration or improved physical properties. In this research, the performance of a WAC resin used for boiler feedwater treatment in oil & gas operations (resin A) was compared with two new commercial resins (resins B & C). The results indicated that resin B had the highest operational capacity in comparison to A & C. During regeneration, resin B was the most efficient with 0.43 meq of calcium and magnesium removed from the feed per meq of HCl consumed during regeneration, slightly higher than resins A & C at 0.38 and 0.30 meq/meq respectively. All three resins demonstrated preferential affinity for calcium over magnesium. As breakthrough approached, previously adsorbed magnesium ions were released back to the water resulting in a spike in effluent magnesium that was ≈3× higher than in the feed stream. In full-scale systems, breakthrough can be determined by measuring only the effluent magnesium concentration which can be more sensitive parameter than total hardness and/or calcium.