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Water Technologies & Solutions case study

GenGard* allows continued system protection, while optimizing polymer feed

challenge A Western Refinery, using a combination of clarified lake water and reverse osmosis (RO) reject water as cooling makeup water, was successfully maintaining both corrosion, and scale control with SUEZ’s Continuum* AEC program. The sixteen cooling towers at the site did not have provisions for acid or chemical feed. The Continuum AEC program along with bleach and sulfuric acid were fed to the makeup water header. Adjusting the blowdown rate to maintain the targeted 4 to 5 cycles of concentration controlled treatment residuals, water chemistry and pH. A makeup water free chlorine residual of 4 to 5 ppm was needed to develop 0.4 to 0.5 ppm free chlorine at the cooling tower. This necessitated the use of a halogen stable treatment.

The Continuum AEC program utilizes an alkyl epoxy carboxylate (AEC) for calcium carbonate control, a halogen resistant azole (HRA) for copper alloy corrosion protection, and a sulfonated copolymer (HPS-I) for calcium phosphate precipitation/deposition inhibition. Low levels of inorganic phosphate are used for steel corrosion protection.

The demands of the systems and the variability of the makeup water placed several stresses on the chemistry. First, acid under feeds and/or over cycling at the cooling towers significantly increased the propensity for calcium phosphate scaling of the cooling water, exacerbating scale control. Second, carryover of aluminum during clarifier upsets added to the potential for system fouling.

Soluble aluminum is problematic for inorganic phosphate programs because of the insolubility of aluminum phosphate. Aluminum contamination can lead to both aluminum phosphate scaling and a loss of calcium phosphate deposition control. As a result, the dispersant needs to be an excellent calcium phosphate inhibitor and particulate dispersant, as well as tolerant of soluble aluminium. Lastly, the high chlorine residuals encountered with the makeup water require the dispersant to be halogen stable.

All of these factors stressed the deposit control capabilities of the HPS-I polymer, requiring unusually high residuals to ensure system cleanliness.

solution The Continuum AEC program, containing the HPS-I polymer, was replaced with the GenGard cooling technology, containing a new stress tolerant polymer (STP). STP is an excellent calcium phosphate inhibitor that is not adversely affected by the presence of soluble iron or aluminum. STP provides superior deposition

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control during high pH excursions that can lead to calcium phosphate scaling of process equipment.

results Replacing Continuum AEC with GenGard ensured continued maximum system protection, without overfeeding of the polymer. Calcium phosphate scale control and precipitation inhibition in the cooling water remained unchanged. Aluminum deposition also remained in check.

System inspections after 12 months of operation have indicated excellent system results from the GenGard treatment program while optimizing polymer feed.

Stress Tolerant Polymer (STP) provides a unique safety net for both predictable and unpredictable circumstances.