Use of a pilot scale heat exchanger-cooling tower system for the evaluation of mineral scale inhibitors

A pilot heat exchanger – cooling tower prototype was constructed and used for the evaluation of scale inhibitors in the inhibition of calcium carbonate (CaCO3) precipitation and deposition. The chemical additives that were used as inhibitors were 2phosphonobutane-1,2,4-tricarboxylic acid (PBTC, Dequest 7000), bis(hexamethylene triaminepenta (methylenephosphonic acid)) (BHPMP, Dequest 2090) and two carboxylatebased polymers of the carboxymethyl inulin family (Dequest PB 11615 and PB 11620). The carboxylate-based polymers are “green” additives since they are environmentallyfriendly, non toxic and biodegradable. Experiments were carried out in the absence of inhibitors (control) using local city water, and then in the presence of inhibitors. The inhibitors tested showed variable inhibitory activity in CaCO3 formation and deposition onto the heat exchanger. This conclusion was based on macroscopic observation (CaCO3 fouling) and on soluble Ca 2+ measurements. Finally, the role of temperature of the heat exchanger, the heating time and the water flow within the unit were very important factors for CaCO3 fouling on the heated surface, considering the CaCO3 inverse solubility features.