Does RO Make Sense for Cooling Tower Makeup? James McDonald, Chem-Aqua, Inc.
While introduced as a water-saving alternative to once-through applications, cooling towers still use large volumes of water. As communities strive to conserve our natural resources, cooling towers are an obvious target for saving water in industrial, commercial, and institutional settings. How much water they use is based on many variables, but it could easily be 20% to 30% of a facility’s total water usage.
and start to form scale and deposits within the water system, which can reduce heat transfer, increase corrosion, block flow, and negatively impact the system. It is typically the saturation limits of these nonvolatile components that limit how concentrated the water can be allowed to get as the cooling tower continues to evaporate water. The cycles of concentration refers to how many times the cooling tower water is concentrated compared to the makeup water entering the system to maintain the system water level. A common range is 4 to 6 in many areas. The cycles of concentration is controlled by wasting a portion of the concentrated water by blowdown (i.e., bleed).
Cooling towers achieve their temperature-reducing effect through sensible (direct contact) and evaporative cooling. On average, evaporative cooling is the primary driving factor. As water evaporates, it leaves the nonvolatile components in the water (e.g., calcium, magnesium, bicarbonate, chlorides) behind. Eventually, these components will reach their saturation limits
Equation 1 and Figure 1 show the overall mass balance around a cooling tower. Most of the makeup water requirements to a
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the Analyst Technology Supplement 2019
