Case Study: Field Trial at an Olefin Cooling Tower
In 2010, B & V Group were contacted by a client in the Middle East who had long-running problems with their olefin cooling tower. High conductivity levels in the cooling tower had led to extensive corrosion, and major scale issues were exacerbating this.
B & V Group’s technicians examined the tower and came to the conclusion that a regime of three chemicals was required to remove scale, bring corrosion under control and also eliminate biofouling. The three products recommended were iChem 2232 (Corrosion / Scale Inhibitor), a Zinc/Phosphate/Phosphonate treatment dosed at 15-30 ppm; iChem 1032 (Scale Dispersant), a Phosphonate/ HM polymer treatment to control the Soluble/Total Ratio, dosed at 5-15 ppm; and Biosperse 1 (Bio Dispersant), a non-ionic surfactant at 1-5 ppm. The trial was run over the course of 45 days.
Olefin Cooling Tower Statistics
First priority was to bring corrosion within the cooling tower under control. The key to doing this was the polymer dispersant, which maintains the zinc and phosphate in a soluble form at higher pH’s than found in under normal circumstances. It therefore avoids zinc phosphate precipitation and disperses zinc throughout the system to form protective film on the surface. A pH of between 7.5 and 8.0 allows this program to provide excellent corrosion protection with very low levels of zinc (about 1 ppm) and about 5 ppm of O-PO4. As it is effective at high bulk water temperatures, and is not restricted by long holding times, the program used in this instance is particularly good for difficult‘to’treat systems. Despite the very challenging conditions (conductivity ranged between 3900 and 8600)’ iChem 2232 and iChem 1032 were designed to have the capacity to cope with these circumstances and still control corrosion through their Cathodic and Anodic inhibition mechanism.
Controlling High Calcium Hardness
High calcium and total hardness levels play very important roles in both corrosion and scale formation; high calcium hardness can interfere with low effective zinc / phosphate programs and aggravate pre-existing issues. Our program was furnished with a very chlorine-stable phosphonate and high effective dispersant polymer, specifically to combat this. Our polymer and phosphonate could stabilize phosphate and zinc in solution at an appropriate cycle of concentration, and although high levels of Ca/Total hardness were seen, no serious scaling and corrosion problems were observed throughout the trial.
Corrosion/Scale Inhibitor Dosage Trend
The following graph shows corrosion and scale inhibitor dosage throughout the trial.
The first 72 hours were treated as a pre-filming period at start up, thus the consumption rate was higher at about 60 ppm on average. The proposed continuous dosage rate was between 15-30 ppm - this is approximately half of the incumbent chemical consumption rate at another site we had trialled on this regime. Our chemical is a concentrated version and hence very effective at a low level. There were only a few fluctuations in dose rate during the trial due to a blow down cut off imposed by the production department without prior notice. This is why the concentration of chemical occasionally exceeded limit of 30 ppm. Sometimes it fell below 15 ppm due to an increased blow down rate without prior notice.
The Results / Conclusion
Overall, our iChem 2232 / iChem 1032 program coped very well with the fluctuations and upsets in the system it encountered during the 45-day trial. The corrosion rates of two coupons located in hot areas were 0.52 and 0.6 mpy respectively, in comparison with a standard rate of 2-6 mpy that was being recorded previously. The program was able to decrease consumption rate from previous levels of 50 ppm, to 25 ppm in the system. Our program is very resistant to high conductivity, hardness and excessive chlorination, and was able to protect the system in difficult circumstances. Due to the success of this trial, we believe that the treatment could tolerate even more adverse conditions, where it is met with poor quality raw water, water shortage, Blow down cut off, etc.
This trial demonstrates the tailor-made approach we take to resolving our customers’ on-site issues, a strategy which has delivered immense success and keeps our clients satisfied.