SF6 Gas Recovery Unit, Refrigeration-Liquefaction 6-in-1 Integrated GIS Gas Recovery and Purification Equipment

Sulfur hexafluoride (SF6) gas is widely used in GIS switchgear, SF6 circuit breakers, current and voltage transformers and other high-voltage electrical equipment for its excellent insulation properties and arc quenching capability. However, SF6 gas is expensive and decomposes into toxic byproducts under arcing and corona discharge. During equipment maintenance, SF6 gas must be professionally recovered and purified to avoid direct emission causing greenhouse effect and environmental pollution, while enabling recycling of the costly gas.

Traditional SF6 recovery methods suffer from single-function equipment, complex piping connections, high residual pressure and insufficient gas purification. Our introduces the device SF6 gas recovery and purification unit employing advanced refrigeration liquefaction principle with environmentally-friendly R404 refrigerant, integrating six functions: recovery storage, filling, vacuum pumping, cylinder filling and purification drying. Equipped with Shenyang Shengu SF6 compressor (12m³/h) and BSV90 two-stage vacuum pump (90m³/h), 200L carbon steel tank storing 200kg liquid SF6, final recovery pressure as low as 53KPa, purified moisture ≤60PPM and oil content ≤10PPM. With built-in automatic phase sequence protection, electromagnetic anti-oil-backflow valve and regenerable dryer, hand-push mobile design with air cooling — delivering an efficient, reliable and convenient integrated SF6 gas handling solution for GIS maintenance, circuit breaker overhaul and transformer service.

The unit adopts industry-standard refrigeration liquefaction recovery principle, utilizing the physical property of SF6 gas liquefying under pressure and reduced temperature for efficient recovery. The SF6 compressor draws and compresses gas from electrical equipment to high pressure, while an independent refrigeration system with R404 eco-friendly refrigerant cools the hot high-pressure SF6 gas through the evaporator to condensation temperature, converting it to liquid state for storage.

R404 refrigerant features low evaporation temperature, high refrigeration efficiency and zero ozone depletion, paired with a fully-hermetic piston refrigeration compressor and air-cooled condenser ensuring rapid SF6 condensation. Compared with direct gaseous compression storage, liquefied storage dramatically increases storage density — the 200L tank holds 200kg of liquid SF6, accommodating complete recovery of medium-to-large GIS compartments. Final recovery pressure reaches as low as 53KPa absolute, greatly improving recovery rate, reducing residual losses and lowering maintenance costs.

The unit integrates six core functions, comprehensively covering the entire SF6 electrical equipment maintenance gas handling workflow: Recovery Storage draws and liquefies gas from equipment into the built-in tank; Filling charges stored SF6 back into electrical equipment; Vacuum Pumping evacuates equipment and piping to remove moisture and air; Cylinder Filling transfers recovered gas directly into transport cylinders; Purification Drying removes oil, moisture and solid impurities; Self-circulation Purification repeatedly cleans stored gas for higher purity.

All functions switch via centrally-located ball valves and control box, with clear flow diagrams on the panel and straightforward valve operation logic. Compared with traditional solutions requiring multiple separate devices, the integrated design dramatically reduces field piping work and connection leak risks. The entire system is factory-sealed and pre-tested; only two rubber hoses need connection on site, greatly improving maintenance efficiency.

The unit features two high-efficiency oil separators installed in series at the SF6 compressor outlet, effectively removing compressor lubricant through centrifugal separation and filter adsorption dual action. Paired with 0.02μm precision filters, solid particulate contaminants are removed. The dryer filter uses molecular sieve adsorbent for deep dehydration and hydrolyzable fluoride removal, with acidity controlled below 0.1PPM.

After one pass of recovery purification, SF6 gas moisture drops below 60PPM by weight, oil content below 10PPM, hydrolyzable fluorides ≤0.2PPM, non-toxic biological test results, and gas purity ≥99.9% — fully meeting DL/T 662 standard requirements for recycled SF6 gas quality. The dryer features built-in heating regeneration; saturated molecular sieve is activated via vacuum heating without frequent desiccant replacement, significantly reducing maintenance costs while maintaining long-term stable purification performance.

The unit features a comprehensive safety protection system safeguarding both equipment and personnel. A high-pressure controller at the SF6 compressor discharge automatically stops the compressor above 2.0MPa and restarts when pressure drops, preventing overpressure operation. The storage vessel is equipped with a safety valve that automatically relieves excess pressure and reseats when normal.

The electrical system includes phase failure and phase sequence protection relay with automatic phase reversal correction, eliminating compressor reverse rotation damage from miswired site power. An electromagnetic vacuum charging valve at the pump inlet interlocks with the vacuum pump, automatically sealing the vacuum side and admitting air to the pump chamber when stopped — completely preventing pump oil backflow contamination. All ball valves use built-in butterfly seal elements with self-compensation for leak-free operation after thousands of cycles. Temperature protection ensures reliable starting down to -20°C ambient. Multiple protection layers guarantee safe and stable operation under all conditions.

Hand-push mobile construction with premium casters enables easy movement while protecting floor finishes, ideal for relocating between switchyard bays and GIS rooms. Compact, well-laid-out structure with attractive industrial orange-red paint finish (Class I adhesion) resists wear and corrosion. Control box, operating valves and monitoring gauges all arranged on one side panel with clear flow labeling for intuitive operation.

Fully air-cooled design requires no external water supply, expanding application range. Operating temperature range -10°C to 40°C, total power ≤15kW, three-phase five-wire 380V supply meeting standard industrial power requirements. System noise controlled within 75dB(A) for improved working environment. Annual leakage rate ≤1% of nominal storage capacity, ensuring reliable long-term sealing. Balancing functionality, mobility and durability, it is the ideal mobile SF6 gas handling equipment for power maintenance field work.

1. Step 1: Pre-Start Preparation and Piping Connection

   Before use, position the unit at the work site ensuring at least 0.5 meter clearance between condenser intake and walls for proper ventilation. Check SF6 compressor and vacuum pump oil levels; oil should remain between 1/4 and 3/4 on the sight glass, top up with specified lubricant if low. Inspect refrigeration lines for damage, loose fittings and verify fan operation.

   Connect rubber hoses per the task, keeping hoses as short as possible to minimize losses. Recovery: equipment gas compartment → hose → recovery inlet. Filling: filling outlet → hose → equipment compartment. Cylinder filling requires two hoses connected to equipment and cylinder respectively. Verify seal integrity after connections. Connect three-phase five-wire 380V power; built-in phase protector automatically corrects reversal. On first use or after atmospheric exposure, evacuate the unit itself before proceeding.

2. Step 2: System Vacuum Pumping

   Before recovery or filling, connecting lines and equipment compartments must be evacuated to remove air and moisture and prevent SF6 contamination. Confirm the system is at zero gauge pressure or below before starting the vacuum pump. Unit self-evacuation: start vacuum pump and open valves V1, V2, V3, V5, monitor vacuum reading by holding the resistance vacuum gauge switch; close valves then stop pump when ultimate vacuum is reached.

   Equipment-side line evacuation: start vacuum pump with V1 and V6 open, evacuate recovery lines then close V6 first before V1 and pump. Cylinder-side evacuation follows the same procedure. Monitor vacuum progress during pumping; if vacuum fails to drop, inspect joints for leaks. Never start SF6 compressor while under vacuum hold. After evacuation, maintain slight positive SF6 pressure in the system to prevent air ingress.

3. Step 3: SF6 Gas Recovery and Storage

   Based on ambient temperature and gas volume, start the refrigeration compressor 30 to 60 minutes in advance for pre-cooling and keep it running throughout recovery. Confirm initial recovery pressure within 0~1.0MPa. Open V6, partially open V2, start SF6 compressor then open V3 — gas compresses, condenses and liquefies into the storage tank.

   During recovery, closely monitor discharge pressure gauge M2, maintaining below 2.0MPa; adjust V2 opening if pressure rises too fast. Observe liquid level through the sight glass; never exceed 2/3 of the view to prevent overfilling. When final pressure of 53KPa or target value is reached, close V3, SF6 compressor, V2, V6 in sequence, then stop refrigeration compressor. Confirm tank pressure and level are normal and document readings.

4. Step 4: SF6 Gas Filling and Cylinder Filling

   For filling operations, first evacuate the equipment side. When tank pressure is high, directly open V4 to fill by differential pressure, monitoring M6 until rated working pressure. When tank pressure drops too low for direct filling, use external gas source through V7 and V6, or start SF6 compressor for pressurized filling. On shutdown, run compressor to pull residual line gas back into storage until suction reaches zero gauge, then stop compressor and close valves.

   For cylinder filling, first evacuate cylinder and lines. Open V4 and cylinder valve, gravity fill by pressure difference. Once pressures equalize, switch to pressurized mode: close V4, open V5, V2, start SF6 compressor and V8 to continue filling under pressure. Note that the storage tank must contain sufficient liquid SF6 before cylinder filling; monitor liquid level throughout. Stop at rated cylinder weight by closing cylinder valve and corresponding valves.

5. Step 5: Purification Self-Circulation and Shutdown Storage

   When recovered gas has high moisture content or after extended use, run self-circulation purification to improve gas quality. Start refrigeration compressor, open V5, V2, start SF6 compressor then V3 — gas circulates through oil separators and dryer, progressively removing oil and moisture. Adjust V2 if discharge pressure runs too high to maintain normal circulation. Run for appropriate duration based on contamination level then stop.

   Saturated desiccant can be thermally regenerated by heating under vacuum without disassembly. After all operations, close all valves and disconnect power. Coil and stow hoses and power cable, inspect unit for damage. Maintain slight positive SF6 pressure in tank and lines to prevent air and moisture ingress. Periodically calibrate pressure and vacuum gauges, schedule compressor and pump oil changes per maintenance schedule, and keep service records to ensure reliable performance for the next use.

Some SF6 recovery units using direct compression or with insufficient condensation only achieve final pressures of 0.1MPa or higher, leaving substantial residual gas unrecovered. This not only wastes expensive gas increasing operating costs, but released gas also contributes to greenhouse effect. For large-volume GIS compartments, gas loss from high residual pressure is significant, accumulating considerable economic loss over time.

This unit employs refrigeration liquefaction with high-performance SF6 compressor, achieving final recovery pressure as low as 53KPa absolute — far superior to basic recovery equipment. R404 refrigerant provides sufficiently low evaporation temperature ensuring continuous condensation at the compressor low-pressure side, progressively drawing down equipment-side pressure. 12m³/h compressor displacement combined with large-capacity condensation system recovers 1m³ compartment from 0.8MPa to 53KPa in just 2.5 hours. Dramatically improves per-tank recovery rate, reduces residual loss, lowers maintenance gas costs and meets environmental emission reduction requirements.

SF6 compressor lubricating oil carries over into the gas stream during compression; inadequate oil separation leaves high oil content in recovered gas. Meanwhile, air and moisture ingress during maintenance elevates gas humidity. Oily, wet SF6 recharged into equipment contaminates the interior — moisture decomposes into corrosive substances under arcing, and oil deposits on insulation surfaces reduce dielectric strength, severely compromising equipment safety and service life.

Two-stage oil separators in series at compressor outlet remove oil via centrifugal and filtration dual action, achieving ≤10PPM oil content after purification. Molecular sieve dryer deeply adsorbs moisture to ≤60PPM, hydrolyzable fluorides ≤0.2PPM, acidity ≤0.1PPM. 0.02μm precision filters remove solid particulates, resulting in ≥99.9% SF6 purity fully meeting recharge quality standards per DL/T 662. The dryer supports thermal regeneration — saturated molecular sieve reactivates via vacuum heating without replacement — maintaining long-term purification performance and ensuring consistent recovered gas quality.

When the vacuum pump stops after evacuation, pump oil flows backward into vacuum lines and the SF6 system under pressure differential, causing oil contamination. At minimum this requires re-purification exceeding oil limits; worst case it contaminates entire SF6 compartments requiring full gas replacement, seriously impacting maintenance quality and schedule. Traditional units require operators to manually sequence valve closing and pump shutdown — momentary inattention causes backflow incidents.

An electromagnetic vacuum charging valve installed at the pump inlet is wired on the same circuit as the vacuum pump for synchronized operation. The instant the pump stops, the valve automatically seals the vacuum system side while admitting atmosphere to the pump chamber, fundamentally preventing oil backflow into the SF6 system. No manual valve timing coordination required — fully automatic protection eliminates human-error oil contamination, effectively preserving gas system cleanliness.

Temporary power wiring at substation maintenance sites is often inconsistent with reversed three-phase sequences common. Both SF6 compressor and vacuum pump use three-phase motors; reversed phase sequence causes backward rotation, at minimum drastically reducing pumping efficiency and at worst damaging compressor valve plates and moving components, causing equipment failure and project delays. Conventional equipment requires manual phase identification and wire swapping — cumbersome with electric shock hazards.

The electrical system incorporates phase failure and phase sequence protection relay with automatic phase correction. Upon power connection the unit automatically detects phase order and switches to correct sequence if reversed — no manual line swapping needed, compressor always rotates correctly. Phase failure protection automatically cuts power on missing phase. Indicator lights within 15 seconds of power-on confirm normal phase sequence and standby status. Completely resolves on-site phase sequence confusion, reduces wiring skill requirements and improves operational safety and equipment reliability.

Traditional SF6 maintenance requires separate vacuum pump, recovery compressor, storage tank, dryer filter and more — assembling multiple independent units on site with complex piping connections and frequent reconfiguration. Not only is setup time-consuming, but each additional joint adds a potential leak point with poor sealing causing gas escape. Scattered equipment also complicates relocation between bays, reducing multi-compartment maintenance throughput.

This 6-in-1 integrated design incorporates recovery, filling, vacuum, purification, storage and cylinder filling into one hand-cart unit with all internal piping factory-sealed and commissioned. Field operation requires only two rubber hose connections; function modes switch via panel ball valves with simple intuitive operation. Dramatically fewer connection points effectively reduces leak risk. Wheeled mobility facilitates transfer between GIS bays for continuous multi-compartment servicing. The overall solution simplifies field preparation, reduces operator workload and improves overall maintenance efficiency.

1. Substation GIS Switchgear Maintenance Gas Recovery

   GIS switchgear accounts for the largest SF6 gas volume in power systems; all compartments require full gas recovery during periodic maintenance and fault handling. This unit accommodates all voltage class GIS equipment, 53KPa final pressure ensures maximum gas extraction, and 200kg liquid tank capacity handles standard bay compartment full recovery. Refrigeration liquefaction efficient recovery combined with purification enables direct recharging without off-site processing. Wheeled design facilitates movement between GIS room bays — the core gas handling equipment for substation GIS maintenance.

2. High-Voltage SF6 Circuit Breaker Installation and Overhaul Gas Handling

   SF6 circuit breakers require chamber evacuation, gas filling and recovery during commissioning and major overhaul disassembly. The 90m³/h high-speed vacuum pump rapidly evacuates interrupter chambers, 10Pa ultimate vacuum ensuring thorough moisture removal. Fast filling rate charges 1m³ chamber to 0.8MPa in under an hour. Recovery function captures all gas before teardown and recharges after reassembly — saving gas cost while avoiding emission pollution. Essential equipment for switchgear manufacturers and service companies performing circuit breaker overhauls.

3. CT/VT SF6 Gas Maintenance and Handling

   SF6-insulated current and voltage transformers are numerous and widely distributed, requiring gas recovery and recharging for periodic testing and fault resolution. The unit's mobility enables transformer-by-transformer processing across substations. Fast recovery for small-volume chambers with purification ensuring reusable gas quality. Compared with large recovery trucks, this unit's moderate size is better suited to distributed, smaller-volume transformer maintenance — flexible and cost-effective, effectively elevating professional transformer servicing standards.

4. SF6 Gas Cylinder Filling and Transport Storage

   Recovered SF6 sometimes requires transport to other locations or specialized processing facilities, necessitating transfer into certified cylinders. This unit features cylinder filling capability, directly transferring gas recovered from equipment or liquid SF6 from storage into standard cylinders. Initial gravity fill by pressure differential, then compressor-pressurized filling after equalization for improved throughput. 200kg tank capacity fills multiple cylinders in one session for batch transport requirements. Integrated purification ensures filled gas meets quality standards — ideal for gas utilities and testing organizations performing SF6 cylinder filling services.

5. Power Testing Service Company Mobile Inspection Services

   Third-party power testing and maintenance companies serving multiple clients need versatile, portable and reliable recovery equipment. This unit's six-in-one functionality covers all SF6 gas handling scenarios — one machine addresses every maintenance situation. Wheeled air-cooled design requires no additional facilities, easily trucked to job sites and ready to work on arrival. Complete safety protection and purification systems deliver professional standardized operations. The ideal choice for power service contractors' equipment inventory, enhancing service capability and professional image.

The device SF6 gas recovery unit, built on refrigeration liquefaction technology with integrated recovery storage, filling, vacuum pumping, cylinder filling and purification drying — combined with two-stage oil separation, molecular sieve purification, automatic phase protection and electromagnetic anti-backflow — effectively solves industry pain points of high residual pressure, poor purification, complex piping and cumbersome operation in traditional SF6 gas recovery. 53KPa low final pressure recovery, 99.9% high-purity purification and portable deployment deliver an efficient, eco-friendly and economical integrated gas handling solution for SF6 electrical equipment maintenance in the power industry.

Our focuses on SF6 gas handling equipment R&D and manufacturing, continuously optimizing product performance based on frontline power maintenance requirements. The device recovery unit further expands the SF6 O&M equipment product line, widely applicable to grid companies, power generators, switchgear manufacturers, power testing contractors and industrial users. It helps improve SF6 gas recovery utilization, reduce greenhouse gas emissions and provides reliable technical equipment support for green operation and safe production in the power industry.

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