ANATOMY OF A MULTIFUNCTIONAL PRODUCT

Multifunctional cooling water products address scale and corrosion control and include blends of inhibitors in “one drum”. Less than optimum ratios of inhibitors can result in product overfeed, increased costs, and in some cases, inhibitor induced fouling. This paper describes the use of computer modeling to optimize ratios of scale and corrosion inhibitors for different waters. INHIBITOR MODELS Computerized modeling and optimization of cooling water inhibitors has been common practice since the late 1970’s. (1,2,3) Models have been used for screening molecules as potential scale inhibitors,(4) for online real time control,(5) as a formulating aid, for troubleshooting failures and as sales tools. Models have been developed for most cooling water scale inhibitors and corrosion inhibitors and refined through in field usage. Typical models are as follows: Scale Inhibitors The development of scale inhibitor models has been covered thoroughly in the literature. (2,5,6,7) Models typically predict the inhibitor dosage required to “delay ” precipitation or growth until after the water has passed through the system. Typical parameters for the models are: a) Driving Force: Ion association saturation ratios are typically used driving force for seed crystal formation and growth including calcite saturation index (CSI) for calcium carbonate, gypsum and anhydrite saturation indices for calcium sulfate, tricalcium phosphate and hydroxylapatite saturation indices for calcium phosphate scale inhibition, silica saturation and magnesium silicate saturation level for silica control. b) Temperature: Temperature affects the rate of reactions and has been found to directly influence dosages, all other factors being equal. c) Time: Higher dosages are required to delay scale formation or growth. The longer the time during which an inhibitor must prevent scale, the higher the dosage