Protecting your system during the winter season with the right layup program will significantly reduce the amount of chip scale that will loosen up in the spring, prevent corrosion and iron-throw, and greatly extend the life of your equipment.
U.S. Water offers four products that can be used for cooling lay-up; Protect 649, CTL-440, TOWERCLEAN 819 and Tower Toads. Each chemical has a best fit, and each chemical must be applied a little differently. (See below to learn more about our lay-up products).
As with any passivation, the metal (or wooden) surfaces need to be clean. If they are not, they should be cleaned with a cleaner before the actual lay-up product is applied. The lay-up product will have some cleaning and slime penetrating ability but are not effective if the surfaces are too dirty, scaled or fouled. That determination is made by the Technical Service Representative during normal operation and during the shutdown.
U.S. Water's variety of tower cleaning products can be applied based on your plants unique needs. FERROCLEAN or PROCLEAN 351 are used for iron, PROCLEAN C284 or PROCLEAN 151 for organic/inorganic deposits, SOLVAL, SOLVIT or PROCLEAN 826 for heavy duty mineral scale, CWT-405 for biological slime and PROCLEAN 20 for carbon or oil contamination. During normal operation a biocide efficacy study should be done to determine the effectiveness of the chosen biocides. An efficient non-oxidizing biocide should be used during the lay-up.
Tower Shut Down and Lay-up Procedure
Preparation- Determine the operational biological condition of your system by doing a BioEfficacy Test (Dip Slide) and BioMass Test (ATP). Take a sample for Legionella testing if none has been done during the year. Gradually lower the conductivity in the circulating water to the low end of the operation range (or lower). Discontinue the use of your normal scale and corrosion inhibitor(s) and biocide(s). Acid addition may be continued to maintain a desired pH.
Determine System Shut Down Condition– Using visual or analytical deposit analysis determine the condition of your system and program success. If conditions warrant, clean the system prior to laying-up for removal of organic or inorganic deposits or biological slime. Manually remove any dirt and debris from the tower basin and other accessible areas. Wear appropriate protective gear.
Clean/Passivate the system with a Lay-up Product* while circulating for at least 24 hours.
Apply the Best Biocide as determined by your Bioefficacy test. If no test was done then use 300 to 500 ppm of BIOTROL 550 and circulate for three hours followed by 300 to 500 ppm of BIOTROL 509 while circulating for at least another hour. Verify kill by testing for both aerobes and anaerobes.
U.S. Water's Lay-up Products
1) PROTECT 649- This is a volatile corrosion inhibitor based on Vapor Phase Inhibitor (VPI) technologies. The product has azole as one of its ingredients as well as polymer. The normal feed rate is 4000 to 5000 ppm. At that rate the polymer will be 175 to 225 FAU on the DR-890. This product is volatile so that it protects parts of the system not contacted by the water. Best results will be achieved in systems which are sealed to prevent air circulation.
2) CTL 440- This product has an advantage where slime is an issue on system surfaces but you do not consider it severe enough to require a special cleaning with CWT-405. It has capability to passivate mild steel and yellow metal alloys. The normal feed rate is 3200 ppm. At that rate the PO4 level will be 70 ppm. The product uses DTEA technology to help remove slime. The passivating agents are phosphate, azole and HPA.
3) TOWERCLEAN 819– This product provides superior yellow metal and wood passivation. It is ideal for passivation of mild steel and yellow metals like copper. It can help “fix” the copper based wood preservative in modern cooling towers to help prevent the leaching of the preservative into the blowdown water. It contains an organic dispersant to help penetrate biofilm and slime. The normal feed rate is 1600 ppm. At that rate the orthophosphate level is 25 ppm, the polyphosphate level is 100 ppm and the azole level is at 85 ppm. The passivating agents are phosphate, polyphosphate and azole.
4) Tower Toads – This product is a powdered VPI chemistry in a dissolvable polyvinyl bag. Four “Toads” or bags are added per 1000 gallons of cooling system volume. The bags will dissolve in the water, and the VPI chemistry will circulate over the wetted metal. It will also volatilize and form a film on non-wetted surfaces. Tower Toads can also be added to a clean dry system without circulation. The polyvinyl bags need to be slit open, to allow the powder to vaporize. The bags should be added to various critical points throughout the cooling system. The same dosage applies (4 bags per 1000 gallons system volume). The best long term protection can be achieved through a combination of circulating a liquid cleaner / passivator and then adding Tower Toads for additional protection after the system is drained. In a tightly closed system, the protective VPI barrier will last up to 6 months. In an open system, the barrier will fade after a few months.