How SF₆ Recovery, Separation and Purification Works: A Complete Process

SF₆ is widely used as an insulating and arc-extinguishing medium in GIS, GIL, circuit breakers, and other high-voltage electrical equipment. When electrical equipment is decommissioned, maintained, or retrofitted, the gas inside the chamber may need to be recovered before the equipment is opened.

For conventional SF₆ recovery, the objective is usually to collect and reuse the gas. However, when SF₆ is mixed with other gases such as nitrogen (N₂), a more advanced process is required to separate the SF₆ from the non-SF₆ components and recover as much reusable SF₆ as possible.

KSTONE has developed an integrated SF₆ recovery, separation, and purification system based on ultra-low-temperature solidification combined with residual SF₆ adsorption and recovery.

The process is designed to recover high-purity SF₆ while reducing SF₆ emissions and allowing the remaining N₂-rich gas to be discharged after treatment.

1. Mixed Gas Recovery from GIS, GIL and Other Gas Chambers

The process starts with an SF₆-containing mixed gas recovered from equipment such as:

• Gas Insulated Switchgear (GIS)
• Gas Insulated Lines (GIL)
• SF₆ circuit breakers
• Gas-insulated electrical equipment
• Other SF₆-containing gas chambers

Depending on the application, the recovered gas may contain SF₆ together with nitrogen or other gases.

The mixed gas is introduced into the KSTONE gas handling system and transferred to the compression and separation stage.

2. Compression and Ultra-Low-Temperature Solidification

The recovered mixed gas first passes through the compressor unit.

After compression, the gas enters the ultra-low-temperature separation stage.

Under controlled ultra-low-temperature conditions, SF₆ is solidified and separated from gases that remain in the gaseous state under the same operating conditions.

This creates two streams:

Solidified SF₆

and

Non-solidified gas containing residual SF₆

The solidification stage therefore provides the primary separation mechanism for recovering SF₆ from the mixed gas.

3. Collection of Recovered SF₆

The solidified SF₆ is collected in an integrated 120 L cryogenic stainless-steel collection tank.

After the separation process, the recovered SF₆ can be transferred from the collection system using an SF₆ liquid transfer pump.

The recovered gas can then be transferred into SF₆ cylinders for storage, transportation, or subsequent reuse, subject to the required gas-quality verification.

This allows the recovered SF₆ to return to the operating cycle rather than being treated as waste.

4. What Happens to the Non-Solidified Gas?

Not all of the gas entering the low-temperature separation stage becomes solidified SF₆.

The remaining gas is mainly an N₂-rich gas containing residual SF₆.

It is important that this gas is not simply discharged directly. Even a relatively small amount of SF₆ represents recoverable gas and should be treated before release.

The non-solidified gas is therefore transferred by the gas exhaust/transfer pump to the residual SF₆ adsorption and recovery module.

5. Residual SF₆ Adsorption and Recovery

The adsorption module captures the residual SF₆ from the N₂-rich gas.

After adsorption treatment, the SF₆ concentration in the remaining gas is reduced to below 0.05% (500 ppm), and can be further reduced to as low as 10 ppm under suitable operating conditions.

The treated N₂-rich gas can then be discharged in accordance with the applicable environmental and operational requirements.

More importantly, the SF₆ captured by the adsorption module is not simply discarded.

It is recovered and returned to the separation process.

6. A Closed-Loop SF₆ Recovery Process

This return process is one of the key features of the KSTONE system.

The SF₆ recovered during the primary low-temperature solidification stage is collected for reuse, while residual SF₆ remaining in the non-solidified gas is captured by the adsorption module and returned to the separation stage.

The process can therefore be represented as:

SF₆-containing mixed gas

→ Compression

→ Ultra-low-temperature solidification

→ SF₆ collection

→ Liquid transfer

→ Cylinder filling and reuse

At the same time:

Non-solidified N₂-rich gas

→ Residual SF₆ adsorption

→ SF₆ recovery

→ Return to the separation process

→ Further SF₆ recovery

This circulation continues until the recoverable SF₆ has been separated and recovered to the required level.

7. Why Combine Low-Temperature Separation with Adsorption?

A single separation step cannot necessarily recover all of the SF₆ from a mixed gas stream.

The ultra-low-temperature stage is responsible for the primary separation and collection of SF₆, while the adsorption stage deals with the residual SF₆ remaining in the non-solidified gas.

The two stages therefore perform different but complementary functions:

This combination helps improve overall SF₆ recovery while minimizing unnecessary SF₆ release.

8. From SF₆ Recovery to SF₆ Reuse

The objective of an advanced SF₆ gas handling system is not simply to remove gas from electrical equipment.

The larger objective is to recover valuable SF₆, separate it from unwanted gases, treat it to the required quality, and return it to practical use.

For utilities, GIS manufacturers, maintenance contractors, and SF₆ gas service providers, this approach can provide several benefits:

• Reduced SF₆ loss during equipment maintenance
• Recovery of SF₆ from mixed-gas applications
• Improved utilization of recovered SF₆
• Reduced environmental release of SF₆
• Closed-loop recovery of residual SF₆
• More efficient management of recovered gas

The actual achievable gas purity and recovery performance depend on the original gas composition, operating conditions, equipment configuration, and required gas-quality specifications.

9. KSTONE SF₆ Recovery, Separation and Purification Technology

KSTONE develops SF₆ gas handling equipment for recovery, separation, purification, filling, and related gas-management applications.

Our recovery and separation systems combine ultra-low-temperature processing with SF₆ adsorption and recovery, providing a process for recovering SF₆ from mixed gases and returning captured SF₆ to the separation cycle.

For applications requiring a more advanced separation solution, KSTONE also develops membrane-assisted separation combined with ultra-low-temperature purification technology.

This technology is particularly relevant when SF₆ needs to be separated from other gases and recovered at high purity.

Typical Applications

KSTONE SF₆ recovery and separation systems can be considered for:

• GIS and GIL maintenance
• SF₆ circuit breaker servicing
• SF₆/N₂ mixed-gas recovery
• Gas-insulated electrical equipment
• SF₆ gas recycling projects
• Electrical equipment manufacturers
• SF₆ gas service and maintenance companies
• Industrial gas recovery applications

Conclusion

SF₆ recovery from mixed gases is more than a simple pumping operation.

A complete recovery process needs to address both the main SF₆ stream and the residual SF₆ remaining in the non-solidified gas.

KSTONE’s process uses ultra-low-temperature solidification to recover SF₆, a cryogenic collection system to collect the recovered gas, and an adsorption-based recovery stage to capture residual SF₆ from the N₂-rich gas.

By returning the captured SF₆ to the separation process, the system creates a recovery loop designed to maximize SF₆ recovery and minimize unnecessary emissions.

For projects involving SF₆/N₂ mixed gas separation, SF₆ recovery, gas purification, or SF₆ recycling, KSTONE can develop the gas handling configuration according to the gas composition, gas volume, required recovery rate, and target gas quality.