French Creek is prominently featured in the latest CTI Journal with their paper, “Optimizing Treatment Cost Performance” by Robert J. Ferguson.
Download the latest Journal for free at CTI.org or directly at: http://tinyurl.com/CTI-Summer2011
ABSTRACT
The control and prediction of scale formation in cooling water systems is increasingly of economic significance, and is of special interest as chemists push the envelope of operation and control through water reuse, the utilization of less than desirable waters for makeup (including high TDS sources, high silica waters, and those with high levels of barium and strontium), and through concentrating the recirculating water to the mechanical limits of an open recirculating cooling system. Thermodynamic indices have been used traditionally to predict scale in these and other industrial water systems where mineral scale formation can be a costly problem. Dosage models for minimizing treatment dosages are derived from these thermodynamic indices. An understanding of the basis for the driving forces used for developing scale inhibitor dosage optimization models is essential for understanding their use in the dosage requirement kinetic models and in developing as universal a model as possible. Dosage models can only be as accurate and reproducible as the thermodynamic driving force indices used to develop them. Thermodynamics and kinetics answer several critical questions concerning projected water related problems and their solution:
WILL SCALE FORM? Thermodynamics only based indices tell only one part of the scale formation and control story. Indices such as ion association model free ion saturation ratios (degree of supersaturation) 1,2,3,4,5 and less rigorous methods such as the simple indices (Langelier Saturation Index 6, Ryznar Stability Index7, Practical Scaling Index 8, and other indices based upon total analytical values) indicate whether or not scale is likely to form. And the seasoned professional can interpret them to reach a usually reliable prediction of whether or not scale will form, how bad a problem it will cause, and whether or not inhibitors can control it.
HOW MUCH WILL DEPOSIT? Other thermodynamic derived indicators, such as free ion momentary excess9 describe the instantaneous precipitation (or dissolution) required to bring a water to equilibrium. They are frequently used to estimate the quantity of scale that might form, as are their less rigorous counterparts such as the CCPP (calcium carbonate precipitation potential) 10 used in municipal water treatment.
WHEN WILL IT HAPPEN? WILL IT HAPPEN IN MY LIFETIME? Kinetic models add the element of time. Thermodynamic models tell you what will happen if a water is allowed to rest unperturbed for an infinite period of time. Kinetic models portray what will happen within the time constraints of your particular system, be it a twenty four (24) hour half life cooling tower, a six (6) second residence time utility once through condenser cooling system, or a three (3) week turnover fire water system in a nuclear power plant. Kinetic models add the parameters of induction time and growth rate. When inhibitors are added to the equation, their impact on induction time is critical to practical dosage calculation. Continue on Page 42 ยป