Combined Technology of Water Softening, Desalination, and Deionization

Abstract

A low-waste combined technology for water softening, desalination, and deionization is proposed. The low-waste nature of the method is achieved through H-cationization of water using carboxylic polyacrylic ion exchange resin, followed by its deionization via reverse osmosis. If the requirements for desalinated water are high, such as when purified liquid is used for feeding supercritical pressure once-through boilers (SPB), it is additionally treated using ion exchange. The preconcentrate from reverse osmosis is processed through electrodialysis or electrolysis to yield acidic and alkaline solutions. These solutions are then used in conjunction with spent regeneration solutions from deep deionization ion exchange filters to regenerate the filter containing carboxylic polyacrylic ion exchange resin. The paper outlines the advantages of carboxylic cation exchange resins compared to sulfonated cation exchangers. A two-chamber H⁺,Na⁺-cation exchange filter operation circuit is proposed. Recirculation of the acidic portion of the spent regeneration solution from the BC storage reservoir through the H⁺Na⁺-cation exchange filter is planned to maximize the recovery of the cation exchange resin’s working capacity. The specifics of regenerating carboxylic cation exchange resin with acid solution in a fluidized bed mode are presented. The acidic solution storage tank should be constructed as a reservoir with a conical bottom and a cylindrical upper part. Such tank design enables its use as a gypsum particle crystallizer and settler. This circuit of separate water H⁺,Na⁺-cationization with a decarbonizer significantly expands technological capabilities. Intermediate water decarbonization decreases the alkalinity of the Na⁺-cation exchange filter effluent, thereby hindering the hydrolysis of the salt form of the cation exchanger. Water obtained through magnesium ionization is advisable to be directed into the softened water stream. To prevent an increase in liquid pressure drop across the filter and a sharp decrease in filtration rate, it is proposed to pass the alkaline regeneration solution from bottom to top.