Scale Inhibitors

Scale inhibitors for cooling towers are chemicals used to prevent the formation of scale on the surfaces of heat exchangers, pipes, and other equipment due to the deposition of minerals (usually calcium carbonate, calcium sulfate, silica, etc.) found in the circulating water. Without inhibitors, scale can cause a decrease in heat transfer efficiency, an increase in energy consumption, and even equipment damage.

Types of Scale Inhibitors

1. Polyphosphates

   • Inhibits crystallization of calcium and magnesium.

   • Suitable for preventing light scale.

2. Organophosphonates (e.g. HEDP, ATMP, PBTC)

   • More stable to high temperatures and a wider range of pH.

   • Widely used in modern cooling towers.

3. Polymer dispersants (e.g. acrylic acid, maleic acid copolymer)

   • Works by dispersing particles to prevent them from settling.

   • Effective against mixed scale and suspended solids.

4. Blended formulations (blended inhibitors)

   • Combines phosphonates and polymers to increase efficiency.

   • Often used in systems with high mineral loads.

Mode of action

• Threshold inhibition: inhibits crystal growth even at low doses.

• Crystal distortion: changes the shape of the crystal so that it cannot grow normally.

• Dispersion: keeps particles floating in the water so they don't stick together.

Inhibitor Selection

• Make-up water quality (hardness, alkalinity, silica, TDS).

• Cooling tower operating temperature.

• System pH.

• Environmental regulations (some inhibitors such as phosphates are restricted).

Usually cooling tower chemical suppliers (e.g. Nalco, Kurita, Solenis, Veolia, etc.) will recommend specific formulations based on local water conditions.