Scale deposits can create numerous headaches for facilities, including higher energy and maintenance costs. While chemicals often are successfully used to control scale in cooling water, many facilities have begun looking for environmentally friendly, cost-effective alternatives.
One solution is a non-invasive physical water treatment system. Unlike traditional scale solutions, physical water treatment systems do not add anything to or remove anything from the water. Instead, they use magnetic fields to influence the crystalline structures of calcium and magnesium (the hard water minerals that cause scale) so that no scale is formed on the cooling surfaces. The treated water is safe to handle, send into the sewers and even drink, assuming that the water passing through the treatment site would otherwise be considered potable.
In cold water, calcium ions (Ca2+) and bicarbonate ions (HCO3) are surrounded by “sheaths” of electrically attracted water molecules, which insulate against the natural tendency of the oppositely charged ions to come together and form crystals. When water heats up or evaporates, it loses the ability to “insulate” these ions, and scale is formed on the cooling equipment.
In a physical water treatment system, a power box sends a signal through wires that wrap around the outside of the water pipe. The passage of electricity through these coils generates a series of penetrative magnetic fields that sweep through the water at pre-programmed frequencies, reducing the ability of the water molecules to prevent the calcium and bicarbonate ions from coming together. Although scale still forms, the crystals are microscopic and occur only at the treatment site. They are then carried downstream suspended in the water. When the water heats up or evaporates, the scale falls out of the water as a harmless precipitant instead of forming on the walls of the cooling equipment.
In addition to preventing scale from forming on the equipment, many physical water treatment systems also will remove existing scale from the cooling equipment. Scale formation is not a static process; the cooling water is constantly both depositing and dissolving scale. With harder water, more scale gets deposited than can be removed; hence, the scale growth on the equipment.
Because water treated by a physical water treatment device no longer deposits scale on the equipment, existing scale buildups can gradually be dissolved back into the water, thereby de-scaling the equipment without adding any chemicals or other additives to the water supply. While the process does not occur overnight, physical water treatment units have been known to remove existing scale at rates of around 0.125" per month or more.
Preventing ScaleIt is important to note that physical water treatment units cannot cure cooling water problems such as biological growths or corrosion of water/Freon/ammonia lines. But in facilities where scale is a major concern, a physical water treatment unit can be used as part of a plant's water treatment solution. Typically, these units are a one-time purchase that would replace either scale-inhibiting chemicals or water softeners. They rarely require user intervention other than occasionally clearing out scale sediment that precipitates from the water (not to be confused with the hard scale deposits typically found on cooling equipment). As a result, physical water treatment systems can reduce operating costs and labor over other methods of scale prevention and removal.
For facilities that are plagued with scale problems, a physical water treatment system can be a tool in the water treatment arsenal. PCE
Sidebar: A southwest Ontario refinery was experiencing scale problems with a four-bank tube-and-shell exchanger. The exchanger was undersized when designed and needed to be cleaned every 8 to 10 weeks to prevent complete equipment failure from scale buildup.
Cutting Costs with Physical Water Treatment
The company installed a physical water treatment system and began carefully tracking the performance of the heat exchanger. After four weeks, no loss of cooling had occurred. In the past, the exchanger would have lost almost all of its ability to cool after eight weeks of operation. With the physical water treatment system installed, the exchanger did not require de-scaling, and it lost only one degree of cooling over the next 21 months (90 weeks). The use of the physical water treatment system helped the refinery reduce its labor and maintenance costs and increase the efficiency of its operation, allowing the company to save approximately $60,000 over the 21-month period.