Most water supplies contain certain amounts of dissolved minerals. Some of these minerals, like sodium, are very soluble and will remain in solution despite changes in water characteristics like temperature. Other “hard” minerals, calcium and magnesium, are not very soluble in water and have the propensity to precipitate out of solution as hard mineral scale when water characteristics change. Changes such as pressure or temperature allow hard minerals to fall out of solution in the form of hard tenacious mineral scale deposits often referred to as limescale. This is occurs most frequently in processes or equipment that heat water.
Mineral scale deposits in water-fed equipment cause many problems. In water heating equipment, scale builds up in layers on heat transfer surfaces, insulating water from efficient heat transfer resulting in higher energy costs. Scale build up also increases maintenance costs and decreases equipment life.
Traditional methods for controlling mineral scale deposits include water softening. Water softening equipment controls hard water scaling by removing scale-causing minerals from the water supply and replacing them with “soft” minerals like sodium that will not form scale deposits. The main drawbacks to water softening include space requirements, initial cost, electrical and drain requirements, and increasing environmental concerns.
The use of sequestering agents (polyphosphates) is another method of controlling mineral scale deposits. When added to the water supply, these agents bond with scale-causing minerals making them more soluble in water resulting in less mineral scale. This type of water treatment is widely used and effective in cold water applications such as ice machines, but standard polyphosphate treatment has shown little or no effectiveness in controlling mineral scale in high temperature applications (boilers, water heaters, coffee equipment, etc.)