Boiler Water Treatment

Overview

Engineering reference data for Boiler Water Treatment in water systems.

Key Formulas

Hydrostatic Pressure

$P = \rho g h$

Pressure due to water column.

Flow Rate

$Q = A v$

Area × velocity.

Variables

References

• Original Source

Scavenger Chemicals for Oxygen Removal

Oxygen in make-up water is a primary cause of corrosion in carbon steel steam systems. Scavenger chemicals are used to remove dissolved oxygen through chemical reactions. Common options include:

• Sodium Sulfite: Effective in systems operating below 1000 psi. It decomposes at high temperatures and can increase dissolved solids and conductivity. Above 1000 psi, it may break down into corrosive gases like hydrogen sulfide.
• Hydrazine: Reacts with oxygen to form water and nitrogen gas. It is efficient for high-pressure systems but is toxic and prohibited in food processing applications by the FDA.
• Sodium Erythorbate: A non-toxic alternative suitable for food processing systems. It can replace sodium sulfite and hydrazine as an oxygen scavenger.

For optimal performance, scavenger chemicals should be added to the storage tank before the feed tank to allow sufficient reaction time. Adding directly to the make-up water feed line is less effective due to short contact time.

Deaeration Towers

Deaeration towers are used to physically remove oxygen and other gases from make-up water. Water is fed through the tower into the feed tank, where elevated temperatures reduce the solubility of gases. This forces oxygen out of the water, and it is vented from the system. Deaeration complements chemical scavenging and is essential for maintaining water quality.

Supercritical Units and Condensate Polishing

In supercritical power plants, condensate polishing is critical for controlling contaminants that cause corrosion and deposition. Modern units often operate under oxidizing treatment, maintaining a positive potential with dissolved oxygen (>50 ppb). This reduces the corrosion rate of carbon steel and forms less soluble oxides compared to fully deaerated conditions. Deaerator vents may be closed, or oxygen feeders may be added to maintain the desired oxygen levels without using scavengers.