Application of sulfur hexafluoride gas

  • SF6 gas has a history of 100 years. It is an artificial inert gas synthesized by two French chemists Moissan and Lebeau in 1900. Around 1940, the US military used it for the Manhattan Project.

    SF6 is a highly electronegative gas, and its molecules are easily adsorbed by free electrons to form large negative ions, weakening the collision ionization process in the gas. Therefore, its electrical insulation strength is very high, about 2.5 times that of air insulation strength in a uniform electric field. At t ≈ 2000K, SF6 gas exhibits a peak of thermal decomposition. Therefore, when the AC arc current exceeds zero, SF6 has a much stronger cooling effect on the arc channel than air, and its arc extinguishing ability is about 100 times that of air. Due to its excellent arc extinguishing and insulation properties, as well as good chemical stability, SF6 gas has been used as an arc extinguishing medium for high-voltage circuit breakers since the late 1950s. In ultra-high voltage and ultra-high voltage circuit breakers, SF6 has replaced oil as the arc extinguishing medium and has largely replaced compressed air.

  • SF6compressors
  • Since the mid-1960s, SF6 has been widely used as an insulation medium for high-voltage electrical equipment. SF6 gas insulated fully enclosed switchgear covers a much smaller area than conventional open high-voltage distribution devices, and its operation is not affected by external meteorological and environmental conditions. Therefore, it is not only widely used in ultra-high voltage and ultra-high voltage power systems, but also has begun to be used in distribution networks (SF6 gas insulated switchgear and ring network power supply units). The advantages of SF6 gas insulated pipeline transmission lines are low dielectric loss, large transmission capacity, and can be used in high drop situations. Therefore, they are commonly used in hydropower station outgoing lines to replace conventional oil filled cables. SF6 gas insulated transformers have the advantages of fire and explosion protection, making them particularly suitable for power supply in densely populated areas and high-rise buildings. SF6 gas insulated ultra-high voltage transformers have been successfully developed, and all gas insulated substations will be a direction for the development of substation technology.
  • Stable chemical properties. Slightly soluble in water, alcohol, and ether, soluble in potassium hydroxide. Does not react chemically with sodium hydroxide, liquid ammonia, and hydrochloric acid. It does not react with copper, silver, iron, and aluminum in a dry environment below 300 ℃. Below 500 ℃, it has no effect on quartz. React with metallic sodium at 250 ℃ and in liquid ammonia at -64 ℃. When mixed with hydrogen sulfide and heated, it decomposes. At 200 ℃, in the presence of specific metals such as steel and silicon steel, it can promote their slow decomposition.

    Because the density of sulfur hexafluoride is almost five times that of air, people who inhale sulfur hexafluoride will have longer wavelengths and lower frequencies when speaking, making their voice as powerful and domineering as a man. On the other hand, helium gas will have the opposite effect. After inhalation, the wavelength will become shorter, the frequency will become higher, and their voice will become as thin and weak as a woman.

  • Physical property data物性数据
      • Character: Colorless and odorless gas.

        Melting point (℃): -51

        Boiling point (℃): -64 (sublimation)

        Relative density (water=1): 1.67 (-100 ℃)

        Relative vapor density (air=1): 6.602

        Saturated vapor pressure (kPa): 2450 (25 ℃)

        Critical temperature (℃): 45.6

        Critical pressure (MPa): 3.76

        Octanol/water partition coefficient: 1.68

        Solubility: Slightly soluble in water, soluble in ethanol and ether

        Heat of vaporization (Kg/mol): 23.59 (sublimation heat)

        Melting heat (Kg/mol): 5.82

        Viscosity (mPa · s, gas): 0.01576

        Viscosity (mPa · s, liquid): 0.277

        Refractive index (gas): 1.000783

    • Sulfur hexafluoride (SF6) compressor -The advantages of the product lie in its compact and simple structure, oil-free, leak free, lightweight, and small size.
    • Similar to motors, long life lubrication and sealed roller bearings can greatly reduce friction in the crank mechanism. Therefore, there is no oil present in the entire compressor. Given sufficient focus, using small manufacturing tolerances and high-tech materials, such compressors are not only economical but also highly reliable in performance.

      When using process gas in the production process, smoke and leakage may occur during the production process. This has led to a trend towards using closed-loop systems with gas in production processes and process technologies.

      The cost saved by the equipment can be recovered from the equipment investment cost in the short term. For example:

      ★ Inert gases, such as xenon, argon or helium, sulfur hexafluoride (SF6);

      ★ SF6 (sulfur hexafluoride) gas in the power system;

      Leakage of natural gas in large-scale compression systems;

      ★ Inert gas processing to purify nitrogen gas;

      ★ Extracting carbon dioxide from supercritical CO2 process

      Leakage gases accumulated during processing, such as carbon monoxide (CO) and sulfur hexafluoride (SF6)

      The media that can be compressed by a sulfur hexafluoride compressor include: sulfur hexafluoride, helium, nitrogen, biogas, propylene, tail gas, well gas, coal gas, coalbed methane, chloroform, ethylene, LNG, butadiene, R22 refrigerant, ethane, butane, liquefied gas, etc.