| Proper water treatment is critical to prevent corrosion, scaling, biological growth, and fouling in closed-loop cooling systems. Since CCCTs recirculate the same water (unlike open towers), maintenance focuses on long-term stability rather than constant bleed-off. 1. Key Water Quality Parameters for CCCTs Parameter Target Range Purpose pH Level 8.0 – 10.0 (alkaline) Prevents corrosion Conductivity < 5,000 µS/cm Controls dissolved solids Hardness (CaCO₃) < 200 ppm Prevents scaling Chlorides < 500 ppm (stainless steel: < 100 ppm) Avoids pitting corrosion Sulphates < 500 ppm Prevents sulphate attack Dissolved Oxygen < 50 ppb (with scavengers) Reduces oxidation Microbial Count < 10,000 CFU/mL Prevents biofouling 2. Water Treatment Chemicals for CCCTs A. Corrosion Inhibitors Molybdate-based (for steel/copper, non-toxic)Nitrite-based (for iron/steel, requires pH > 9)Silicate-based (for aluminum systems)Azoles (for copper protection) B. Scale Inhibitors Phosphonates (e.g., HEDP, ATMP) – Prevents CaCO₃ & CaSO₄ scalingPolyacrylates – Disperses suspended particlesPolyphosphates – Used in low-hardness water C. Biocides (Microbial Control) Oxidizing Biocides (e.g., chlorine, bromine, hydrogen peroxide) – Kills bacteria & algaeNon-Oxidizing Biocides (e.g., isothiazolin, DBNPA) – For biofilm controlBiofilm Dispersants (e.g., quaternary ammonium compounds) D. Oxygen Scavengers Sodium sulfite (common, but increases TDS)Hydrazine (high-efficiency, but toxic – used in power plants)Carbohydrazide (safer alternative to hydrazine) 3. Water Maintenance Procedures A. Initial System Fill & Flushing Pre-cleaning: Flush with alkaline detergent to remove mill scale & grease.Passivation: Apply nitrite or molybdate to form protective oxide layer.Inhibitor Charge: Add corrosion inhibitors at start-up. B. Routine Monitoring & Treatment Weekly Checks: pH & conductivity (adjust with inhibitors if needed).Visual inspection for leaks or discoloration. Monthly Tests: Corrosion coupons (measures metal loss).Microbial testing (ATP swabs or dip slides). Quarterly Maintenance: Dosing booster (replenish inhibitors/biocides).Filter cleaning/replacement (if installed). C. Annual/Shutdown Maintenance Full System Flush (remove sludge/debris). Coil Cleaning (high-pressure water or mild acid wash). Inhibitor Recharge (replace depleted chemicals). 4. Common Water-Related Issues & Solutions Problem Cause Solution Corrosion (rust) Low pH, high oxygen Increase pH, add oxygen scavenger Scale Build-up High hardness, high TDS Add scale inhibitor, soften makeup water Biofouling Bacteria/algae growth Shock-dose biocide, clean system Foaming High organics, surfactants Defoamers, filtration Copper Plating Galvanic corrosion Azole-based inhibitors 5. Makeup Water Requirements Softened water (if hardness > 200 ppm).Deionized (DI) or RO water (for ultra-high-purity systems).Chloride & sulfate control (critical for stainless steel systems). 6. Best Practices for CCCT Water Maintenance Automated Monitoring (real-time sensors for pH, conductivity, corrosion rate). Closed-Loop Testing (quarterly lab analysis for metals & microbes). Proper Chemical Dosing (avoid over/under-treatment). Leak Prevention (seal all connections to avoid oxygen ingress). |
