Reaction (overall):
Na₂SO₃ + ½ O₂ → Na₂SO₄

Catalyst accelerates the reaction at lower temperatures and shorter residence times (e.g., in deaerator outlets and feedwater lines)

• Deaerator outlet O₂: ≤ 7–10 ppb (if DA present)
• Sulfite residual in boiler water:
• Normal operation: 20–40 mg/L as Na₂SO₃
• High risk / wet lay-up: 60–100 mg/L as Na₂SO₃
• pH (feedwater/boiler): follow your internal treatment program (commonly FW pH 8.5–9.2; boiler water pH 10.5–11.5 depending on pressure).

• Preferably deaerator storage section or feedwater line upstream of economizer to ensure complete O₂ removal before the boiler.

Example Dose Calculation

Feedwater DO = 0.10 mg/L (100 ppb) at 20 m³/h.
Stoichiometric Na₂SO₃ = 0.10 × 7.88 = 0.788 mg/L.
With 1.3× safety factor → ~1.0 mg/L Na₂SO₃.
At 20 m³/h → 20 g/h Na₂SO₃ (as pure).
Using 38% liquid: 20 / 0.38 ≈ 52.6 g/h (~40 mL/h) (SG 1.32 ⇒ ~30 mL/h by mass; verify on site).
Fine-tune to maintain target sulfite residual in boiler.