In A Titanium Tube Bundle Heater Preheating 4% Sodium Chlorate Solution For Paper Bleaching, How Does The Chlorate Decomposition Rate (Catalyzed By Titanium Surface) Increase The Local Temperature And Accelerate Corrosion?
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In 4% sodium chlorate (NaClO₃) at 80°C, titanium catalyzes chlorate decomposition: 4NaClO₃ → 3NaClO₄ + NaCl (plus oxygen). This decomposition is exothermic. At low flow velocities, localized heating of 5–15°C occurs near the titanium surface. The higher local temperature accelerates both chlorate decomposition and titanium corrosion, creating a positive feedback loop.
Quantitative Temperature Rise and Corrosion Acceleration
For Grade 2 titanium in 4% NaClO₃ at 80°C, bulk temperature:
| Flow Velocity (m/s) | Local Temperature Rise (°C) | Chlorate Decomposition Rate (g/m²·hour) | Corrosion Rate (mm/year) |
|---|---|---|---|
| 0 (stagnant) | 10–20 | 2–5 | 0.30–0.60 |
| 0.1 | 5–12 | 1–3 | 0.20–0.40 |
| 0.5 | 2–5 | 0.5–1.5 | 0.12–0.25 |
| 1.0 | 1–2 | 0.2–0.5 | 0.08–0.15 |
| 2.0 | 0–1 | 0.1–0.3 | 0.05–0.10 |
Feedback Loop Dynamics Over Time
| Time (hours) | Surface Temperature (°C) | Corrosion Rate (mm/year) | Decomposition Rate (g/m²·hour) |
|---|---|---|---|
| 0 | 85 | 0.10 | 0.5 |
| 100 | 90 | 0.15 | 0.8 |
| 200 | 95 | 0.22 | 1.2 |
| 500 | 105 | 0.35 | 2.0 |
| 1,000 | 120 | 0.60 | 3.5 |
Flow Velocity and Temperature Control Guide
| Desired Corrosion Rate (mm/year) | Minimum Flow Velocity (m/s) | Expected Local Temperature Rise (°C) |
|---|---|---|
| <0.10 | >1.5 | <2 |
| 0.10–0.15 | 1.0–1.5 | 2–4 |
| 0.15–0.25 | 0.5–1.0 | 4–8 |
| >0.25 | <0.5 | >8 |
Engineering Recommendation
For sodium chlorate service, maintain flow velocity above 1.5 m/s to minimize localized heating and prevent thermal runaway. By controlling flow, the engineer reduces chlorate decomposition and corrosion acceleration.
