Make-up Demineralizers

Operating power generation facilities incur steam cycle water evaporative losses and water discharge, which requires make-up water to be added to the steam cycle. These make-up demineralizers typically consist of one or more trains of three ion exchange resin vessels. First in sequence is a cation exchange vessel, followed by an anion exchange vessel. The final make-up polisher is a mixed bed of cation and anion exchange resins, which produces the highest quality water. The goal is to achieve low conductivity and low silica values in the make-up water. The make-up demineralizers are expected to produce high quality water and limit the impurity levels entering the cycle. High silica levels or high conductivity that indicates high impurity levels can contribute to scaling and metallurgical attack of the steam cycle components. Some systems operate without a mixed bed when the water quality is not as critical. Although strongly acidic cation and strongly basic anion exchange resins are often used, weak acidic cation and weak basic anion exchange resins are used under certain conditions.