Many conventional SF₆ recovery systems rely solely on membrane separation technology to separate SF₆ from nitrogen or air.
While membrane systems can recover part of the SF₆, their separation efficiency decreases when processing gas mixtures with varying compositions. They also require membrane elements that gradually wear over time and must be replaced periodically.
To overcome these limitations, KSTONE® developed a dual purification technology that combines cryogenic purification with membrane separation.
The core of the KSTONE system is its independently developed cryogenic purification process.
After gas recovery, the mixed gas is cooled to approximately −70°C.
At this temperature:
- SF₆ solidifies.
- Nitrogen, air and other non-condensable gases remain gaseous.
- The gases are naturally separated according to their different physical properties.
Unlike membrane-only systems, this is a physical phase-change separation process, providing much higher separation efficiency.
After warming, the recovered SF₆ reaches a purity of 99.99% or higher.
- Handles any SF₆ concentration from 0–100%
- High-purity recovered SF₆ (≥99.99%)
- Very low SF₆ loss
- Stable separation regardless of gas pressure, temperature or flow rate
After cryogenic purification, only a very small amount of residual SF₆ remains in the exhaust gas.
KSTONE then uses a membrane module to recover this remaining SF₆ before discharge.
The membrane is not the primary purification method.
Instead, it serves as a polishing stage that further reduces emissions.
This allows the system to achieve:
- Tail gas SF₆ concentration ≤100 ppm
- Compliance with environmental emission requirements
- Maximum SF₆ recovery
By assigning different tasks to different technologies, KSTONE® achieves better overall performance.
| Cryogenic Purification | Membrane Separation |
|---|---|
| Main purification process | Tail gas polishing |
| Produces ≥99.99% SF₆ purity | Recovers trace SF₆ from exhaust |
| Handles all gas compositions | Reduces emissions below 100 ppm |
| Very low SF₆ loss | Improves environmental performance |
Recovery systems based solely on membrane separation may face several practical limitations:
- Membrane elements are consumable components that require periodic replacement.
- Long-term maintenance costs are relatively high.
- Higher SF₆ losses may occur during separation.
- Recovery efficiency can vary depending on the composition of the incoming gas.
KSTONE combines cryogenic purification and membrane separation to deliver both high-purity SF₆ recovery and environmentally compliant emissions.
Key benefits include:
- Cryogenic purification at −70°C
- SF₆ solidification separation technology
- SF₆ purity ≥99.99%
- Suitable for 0–100% SF₆ gas mixtures
- One-touch automatic operation
- No strict requirements for inlet gas pressure, flow rate or temperature
- Tail gas emissions ≤100 ppm
- Mature industrial components for easy maintenance
- Lower operating cost than membrane-only purification systems