Know Your Make-Up Water
A great deal of attention is paid to watching cooling water and boiler water chemistries. Conductivity, calcium hardness, total hardness, alkalinity, scale inhibitors (such as phosphonates and polymers), corrosion inhibitors (such as phosphate, zinc, and molybdate in cooling water and sulfite in boiler water), and pH are among the parameters regularly tested. Adjustments to chemical feeds and the system blowdown rate are then made to keep scale, corrosion, and fouling at a minimum in the systems.
But many people need to pay more attention to make-up water quality. Doing so will help improve control of your treatment program. Whether your make-up water is city water, surface water, well water, mine water, or from any other source, variations in its chemistries can occur—daily, or more slowly over time. These changes can cause poor treatment results (scale, fouling, and/or corrosion), as well as increased costs associated with maintenance, water, chemicals, and energy.
With cooling water, knowing about variations in make-up water quality allows you to better manage your program by anticipating changes in the cycles of concentration due to conductivity and hardness fluctuations. Since most blowdown rates are automatically controlled on conductivity, make-up water changes that increase the incoming conductivity level (and corresponding dissolved solids) will cause a decrease in cycles of concentration. This results in expensive water and treatment chemicals going down the drain. Managing cycles of concentration and the blowdown rate is especially critical when you’re on an allorganic cooling water program because these generally already have lower cycles of concentration, higher blowdown rates, and higher treatment costs.
Of course, the reverse is true if the make-up water chemistry decreases in conductivity. Lower levels of dissolved solids can lead to higher cycles of concentration and lower blowdown rates. From a water/treatment cost basis, this is usually a good thing, but you do have to watch the Holding Time Index (HTI) to make sure you don’t overextend your treatment chemicals. Otherwise, this could lead to the product(s) breaking down with the consequences being higher maintenance costs and reduced energy efficiencies.
For boiler waters, changes in make-up water characteristics mainly affect water-conditioning and pretreatment equipment such as clarifiers, softeners, dealkalizers, ROs, and demineralizers. Chemistry fluctuations alter product water quality and can increase the amount of regenerants needed to maintain the units. If you’re working with softened water and have a relatively high make-up water demand, then make-up water quality fluctuations can also adversely impact boiler water cycles of concentration as well as fuel and treatment costs.
Be proactive. Test source water weekly if it’s reasonably stable (not fluctuating more than 10% over a year’s time for any critical parameter), and record your results. Test more frequently in areas where water quality fluctuations regularly affect your treatment programs’ control. You should at least be looking at these critical parameters: conductivity or TDS, total and calcium hardness, alkalinity, pH, chlorine, and chloride levels. Where there are specific known concerns, you may also need to monitor phosphate, silica, iron, manganese, or bacteria concentrations. Taylor can help you determine which of our products are best suited for the waters you are testing. We offer individual tests like the K-1716 for iron; combination kits like the K-1645 for boiler and cooling systems; and the portable TTi™ 3000 Colorimeter, which will test over two dozen analytes important to industrial water treaters (purchase reagent packs separately). You can also build a customized combination kit by purchasing a carrying case, reagents, and testing apparatus separately, or we can design one for you—including proprietary test formulations and private labeling—if purchase quantities make this option feasible. Are you someone who would gain better control of your water treatment programs if you monitored your systems’ make-up water proactively?