A novel membrane-free electrochemical separation-filtering crystallization coupling process for treating circulating cooling water

Abstract

The traditional electrochemical descaling process exhibits drawbacks, including low OH^- utilization efficiency, constrained cathode deposition area, and protracted homogeneous precipitation time. Consequently, this study introduces a novel membrane-free electrochemical separation-filtering crystallization (MFES-FC) coupling process to treat circulating cooling water (CCW). In the membrane-free electrochemical separation (MFES) system, OH^- is rapidly extracted by pump suction from the porous cathode boundary layer solution, preventing neutralization with H⁺, thereby enhancing the removal of Ca²⁺ and Mg²⁺. Experimental results indicate that the pH of the pump suction water can swiftly increase from 8.13 to 11.42 within 10 min. Owing to the high supersaturation of the pump suction water, this study couples the MFES with a filtration crystallization (FC) system that employs activated carbon as the medium. This approach captures scale particles to enhance water quality and expedites the homogeneous precipitation of hardness ions, shortening the treatment time while further augmenting the removal rate. After the MFES-FC treatment, the single-pass removal rates for total hardness, Ca²⁺ hardness, Mg²⁺ hardness, and alkalinity in the effluent reached 92 %, 97 %, 64 %, and 67 %, respectively, with turbidity of 3 NTU, current efficiency of 86.6 %, and energy consumption of 7.19 kWh·kg^-1 CaCO₃. This coupling process facilitates an effective removal of hardness and alkalinity at a comparatively low cost, offering a new reference and inspiration for advancements in electrochemical descaling technology.

Keywords: Electrochemical descaling; Filtration crystallization; H(+)and OH(−)separation; Membrane-free.