In the ion-exchange membrane caustic soda process, the primary brine fed to the electrolyzer must be preheated to around 80 ℃ to reduce electrolysis energy consumption. Saturated chlorine-salt solutions strongly corrode stainless steel at high temperatures, and conventional 316L plates have a service life of less than 6 months. This project uses SAMIT titanium plate heat exchangers to completely solve the corrosion problem.
1. Project Background
Customer
A large chlor-alkali enterprise in Shandong with a primary brine capacity of 800 kt/a, using imported ion-exchange membrane electrolyzers.
Operating Conditions
Saturated brine (NaCl 315 g/L) containing free chlorine 5 mg/L, pH 9.5, preheating temperature 50 → 80 ℃.
Original Pain Points
- 316L plates perforated by pitting corrosion within 6 months
- Frequent shutdowns for plate replacement, losing 1200 t of capacity per year
- Spare parts cost of 600,000 RMB/year
2. Technical Solution
SAMIT recommended using commercially pure titanium Gr.1 (TA1) plates. In saturated chlorine-salt + free-chlorine environments, titanium forms a dense TiO₂ passivation film on the surface, with a pitting resistance equivalent far higher than that of stainless steel.
| Material Comparison | 316L | Titanium Gr.1 |
|---|---|---|
| Pitting Resistance Equivalent (PREN) | 26 | Passivation film protection |
| Lifetime in saturated brine | 6 months | ≥ 15 years |
| Free-chlorine resistance | Prone to corrosion | Corrosion resistant |
| Plate unit price | 1.0× | 2.8× |
| 10-year total cost | 600,000 RMB + shutdown losses | One-time investment |
3. Process Flow
4. Implementation and Operation
- Equipment supply: 2 SAMIT BR0.4Ti plate heat exchangers, each 38 m², including 95 TA1 plates + EPDM gaskets
- Installation period: Completed tie-in during a 15-day shutdown overhaul
- 3-year opening inspection: The passivation film on the plate surfaces was intact with no pitting; the gaskets showed no aging; the units continued in service with no replacement required
Verification data: Under saturated chlorine-salt + free-chlorine conditions, the corrosion rate of titanium plates is < 0.001 mm/a; with a plate thickness of 0.6 mm, the theoretical lifetime is > 100 years. Taking gasket lifetime limits into account, the overall equipment design life is ≥ 15 years.
5. Operating Results
Capacity Recovery
Eliminated losses from shutdowns and plate replacements; caustic soda output increased by 1200 t/year, equivalent to additional revenue of 2.16 million RMB at 1800 RMB/t.
Maintenance Cost
Annual spare parts cost reduced from 600,000 RMB to 50,000 RMB, saving 550,000 RMB/year.
Electrolysis Energy Saving
Brine temperature raised from 50 → 80 ℃, electrolyzer power consumption dropped by 12 kWh/t caustic soda, saving 9.6 million kWh/year.
6. Lessons Learned
The corrosion problem in the chlor-alkali industry is a material selection problem, not an equipment selection problem. For the same plate heat exchanger, the service life of 316L versus titanium plates differs by more than 30 times. Investing 2.8 times more in titanium plates actually yields the lowest full life-cycle cost. The same logic applies to seawater desalination, marine engineering, vacuum salt production, and other chlorine-containing service conditions.