Boiler Water Treatment for Low and Medium Pressure Boilers

Each section of the steam cycle faces a different threat. Feedwater carries dissolved oxygen and hardness into the boiler. Inside the boiler, water is boiled off and dissolved solids concentrate. In the steam and condensate lines, carbon dioxide dissolves in condensate to form carbonic acid, which corrodes pipework. Treating only one point leaves the others exposed.

Dissolved oxygen in feedwater causes pitting of the boiler, the economizer and the feed lines, even in small amounts. Mechanical deaeration removes most of it, and a chemical oxygen scavenger removes what remains and protects during stand-by. Advanced Chemicals Industrial supplies two scavenger types: one based on DEHA and one based on sodium bisulfite.

The boiler water must stay alkaline enough to keep a protective magnetite layer on steel and to support the precipitation of hardness. Too low and the metal corrodes. Too high and the risk of caustic attack, foaming and carryover rises. A pH booster raises and holds the pH within the range the boiler design allows.

Even well softened feedwater leaves traces of hardness, iron and silica. An internal scale and corrosion inhibitor keeps these suspended, conditions the sludge so it can be removed by blowdown, and supports the protective film on metal. A thin layer of scale already acts as an insulator, which raises fuel use and overheats tube metal.

Carbonate and bicarbonate in the feedwater break down in the boiler and release carbon dioxide into the steam. When the steam condenses, the gas forms carbonic acid, which attacks condensate piping, traps and heat exchangers. A neutralizing amine travels with the steam and raises the pH of the condensate. Our range includes a neutralizing amine for steam and condensate systems. The choice of amine depends on the layout of the steam system, because different amines distribute differently along the line.

Boilers out of service corrode quickly if oxygen reaches wet metal. For short stand-by the boiler can be kept full with a higher scavenger residual, and for longer layup it is protected by dry or wet methods suited to the boiler. Plan the layup before the shutdown, and do not rely on routine operating treatment to cover it.

Blowdown removes dissolved solids and sludge from the boiler. Too little lets solids build up and risks carryover and deposits, too much wastes heat, water and chemicals. Automatic conductivity-controlled blowdown, with heat recovery where it is practical, keeps the balance more steadily than manual operation.

A softener or RO ahead of the boiler reduces hardness and dissolved solids, which lowers blowdown and chemical needs. Softener regeneration, breakthrough of hardness and the state of the deaerator all affect the program, so they are checked when a boiler problem appears.

Send your operating data and a recent water analysis to our technical team for a technical review. Product samples and technical data are available through the team.