Sf6 Gas Processing & Recovery
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Transcript of Sf6 Gas Processing & Recovery
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SF6 GAS PROCESSING & RECOVERYSudhanshu GuptaQualitrol Company LLC
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SF6 History
Sulfur Hexafluoride (SF6) discovered in 1900 by Henri
Moissan
In 1937 it was discovered that SF6 possessed a much
higher dielectric strength than air
Major supplier Allied Signal (Silver Bottle) beganprocessing SF6 gas in 1948
Other major North American supplier is Air Products
(Blue Bottle)
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1) SF6 OVERVIEW
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SF6 Characteristics
Sulfur Hexafluoride has a unique combination ofphysical and electrical properties:
- Colorless, odorless, and non-flammable gas
- Chemical Inertness
- Thermal Stability- Non-toxicity (in its un-altered state)
- Excellent Heat Transfer, and cooling properties.
- Non-flammability
- High dielectric (Insulation)breakdown strength
- Non-corrosive (in its un-altered state)- Ability to regenerate
- SF6 is one of the heaviest known gases
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SF6 Non-electrical Applications
Magnesium Casting
Aluminum Degassing
Leak Detection
Particle Accelerators (Universities)
Window Pane Insulation
Nike-Air Shoes
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-Circuit Breakers Typically ~172kV-500kV
-Circuit Switches Typically ~7-35kV
- SF6 Bus Duct ~172-800kV
-Puffer Breakers Typically ~72kV-800kV
-GIS (Gas Insulated Substation) Typically ~72kV-800kV
Voltage levels of typical SF6 equipment
SF6 Electrical Applications
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SF6 Characteristics
Not withstanding the excellent properties associated for use inhigh voltage switchgear, SF6 does have disadvantages
SF6 does breakdown under certain conditions, the products of
which can be:
A)Hazardous to human health.
B)Detrimental to longevity of Switchgear
Sulphur Hexafluoride is considered to be a fully fluorinated
compound (FFC).
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Origins of contamination in SF6(when used in High Voltage apparatus applications)
1.Gas Handling. (Air and moisture contamination)
2.Leakage. (Air and moisture contamination)
3.Desorption from Surfaces, bulk materials and
adsorbers.(Air and moisture contamination)
4.Mechanical generation of dust particles. 5. Decomposition by electrical discharges (FragmentedSF
6
molecules created.)
6.Secondary reactions of electrical dischargedecomposition products. (FragmentedSF
6molecules
created.)
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Contamination of SF6(when used in High Voltage apparatus applications)
Contam inat ion by decompos i tion products is
no rmal ly very low andour main attent ion shou ld
normal ly be focus sed on removing Humid i ty.
Typical ly the chemical ly act ive, corro sive and toxic pro ducts WF6, SF4, SOF4, SO2F2, SO2, HF
remain below th e 100ppmv level
The other main focu s is on the reclamat ion of SF6 to
m inim ise or el im inate release into th e atmosphere.
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Acceptable Moisture Levels
Transmission lines & bus duct can accept higher moisture levels
Main concern is condensation of dew
Switchgear requires lower levels due to potential for arcing.
Due to moisture the main concern is formation of HF.
Hydrofluoric Acid (HF) is a highly corrosive substance that attacks glassand porcelain
More stringent requirements needed for GIS
Manufacturers limits vary between 50 ppm and 1000ppm
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Decomposition Products of SF6(when used in High Voltage apparatus applications)
Reactive decomposition by-products are created when SF6is exposed to:
spark discharges,
partial discharges,
switching arcs, failure arcing
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Decomposition Products of SF6
At very high temperatures, or in the presence of an electricarc, SF6 can be slowly decomposed
Decomposition byproducts include lower fluorides of sulfur,which are hydrolysable, yielding SO2 and HF.
Moisture will react with SF6 decomposition products in thepresence of an electrical discharge to form a variety ofcompounds.
Decomposition by-products can take the form of gas orpowders
Other types of contaminants can include moisture and air(from handling or leakage), dust and particles (mechanical
generation)
Detailed chemical analysis in section 3
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SF6 Byproducts
SOF4 Thionyl tetrafluoride
SOF2 Thionyl fluoride
SO2 Sulfur Dioxide
HF Hydrogen Fluoride
Many more complex compounds are formed in variousconcentrations
Good maintenance practices will include periodic SF6 gasanalysis
Detailed chemical analysis in section 3
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Gas Categories
New
Non Arced
Normally Arced
Heavily Arced
Gas In
cylinders
Used Gas
Degreeofcontamin
ation
Decomposition Products of SF6Low
High
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SF6 Greenhouse Gas??
Sulphur Hexafluoride is considered to be a fully fluorinated compound(FFC).
Since FFC's have atmospheric lifetimes of up to 50,000 years, these
potent greenhouse gases could contribute significantly and, essentially,
permanently to global warming if emissions continue to grow.
For example, lets compare the global warming potential of CO2 and SF6.
CO2 has a global warming potential of 1, whereas SF6 has a global
warming potential of 24,900!!
The electric power industry uses roughly 80% of SF6 products
worldwide.
SF6 is an expensive asset.
It can be collected, purified and reused.
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Chemical behavior under the
influence of electrical discharges
High energy electrical discharges cause
decomposition of SF6, dissociating into its atomic
constituents
SF6 S + 6 F
The reaction is immediately reversible and theproducts recombine
SF6 S + 6 F
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Pure SF6 prior to electrical arc
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Dissociated SF6 immediately after arc
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Natural recombination
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Origins of contamination in SF6(when used in High Voltage apparatus applications)
1.Gas Handling. (Air and moisture contamination)
2.Leakage. (Air and moisture contamination)
3.Desorption from Surfaces, bulk materials and
adsorbers.(Air and moisture contamination)
4.Mechanical generation of dust particles. 5. Decomposition by electrical discharges (FragmentedSF
6
molecules created.)
6.Secondary reactions of electrical dischargedecomposition products. (FragmentedSF
6molecules
created.)
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Reactive decomposition by-products are created when
SF6 is exposed topartial discharges:Partial discharges decompose SF6 into Fragments of SF4 and F which further react with O2 and H2O
to form compounds:
SF5+OH SOF
4+HF
SF5+O SOF4 +F
SF4+O SOF2 +2F
SF3+O+OH SO2F2 +HF
HF Hydrogen Fluoride
SO2 Sulphur DioxideSOF4 Sulphur Tetrafluoride Oxide (Thionyl tetrafluoride)
SOF2 Thionyl Fluoride (SF4 is readily Hydrolised to SOF2)
SO2F2 Sulphural Fluoride
Higher molecular compounds are also formed(However in practically insignificant Quantities)
S2F10 Disulphur Decafluoride
S2OF10 Pentafluorsulphur Oxide
S2O2F10 bis Pentafluor-sulphur peroxide
S203F6
By products found in Breakers and disconnectors. Lesserquantities found in disconnectors they tend to operate rarely.
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Similar reactive decomposition by-products are created
when SF6 is exposed to spark discharges:Spark discharges decompose SF6 into Fragments of SF4 and F which further react with O2 and H2O
to form compounds:
SF5+OH SOF
4+HF
SF5+O SOF4 +F
SF4+O SOF2 +2F
SF3+O+OH SO2F2 +HF
HF Hydrogen Fluoride
SO2 Sulphur DioxideSOF4 Sulphur Tetrafluoride Oxide (Thionyl tetrafluoride)
SOF2 Thionyl Fluoride (SF4 is readily Hydrolised to SOF2)
SO2F2 Sulphural Fluoride
Higher molecular compounds are also formed(However in practically insignificant Quantities)
S2F10 Disulphur Decafluoride
S2OF10 Pentafluorsulphur Oxide
S2O2F10 bis Pentafluor-sulphur peroxide
S203F6
By products found in Breakers and disconnectors. Lesserquantities found in disconnectors they tend to operate rarely.
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Powder decomposition by-products created when SF6 is exposed to Switching arcs:Some secondary reactions can take place with vaporized electrode metal, container walls, and other
construction material. High current flow in these arcs leads to erosion of contact and insulation
materials by the hot arc.
CU + SF6 CUF2 +SF4
W + 3SF6 WF6 +3SF4
CF2 + SF6 CF4 +SF4
Al +3F AlF33SOF2 +AlO3 2AlF3 + 3SO2
Other Powder By-products:
WO3 (TungstenTrioxide/ Tungsten(VI) oxide / Tungstic anhydride )WO2F2 (Tungsten dioxide difluoride)
WOF4 (Tungsten oxide tetrafluoride)
CUF2 Copper(II) fluoride
WF6 Tungsten hexafluoride
AlF3 (Aluminium trifluoride) Additional powder by products found in Breakers due
to switching arcs occuring in load break switches
and power circuit breakers.
Erosion of arcing contacts normally made
from Copper/Tungsten.
Due to eroded PFTE(A CF2 Polymer)
Erosion of arcing contacts normally made
from Aluminium.
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Chemical behavior in the presence of water vapor.
Attention should be focussed on Humidity removal filtration to
remove major ppmv contaminants.
SF6 decomposition products combine with
water to form secondary products
SF6 + H2O 2 HF + SOF2 + 2 F
Hydrofluoric Acid (HF) is a highly corrosive
substance that attacks glass and porcelain
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Chemical Behavior in the presence of water vapor
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Chemical Behavior in the presence of water vapor
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Chemical Behavior in the presence of water vapor
H F
SF
F
O
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The following two slides show us levels of
contamination, what is critical and what really
has no effects on SF6 performance.
C t i t M i O i i D t i ti M i I it l l P ti l I it
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Contaminant Main Origin Deteriorating
effect on
Maximum
Tolerable
impurity levels in
equipment
Impurity levels
for reclaimed SF6to be reused
Practical Impurity
detection level
Air
CF4
Handling
Switching arcs
Switching
Gas insulation
3% vol 2% vol < 1% vol
Humidity Desorption from
surfaces and
polymers
Surface
insulation by
liquid
condensation
200ppmv at 2Mpa1)
120ppmv
compressed to
liquification
< 25 ppmv
800ppmv at 500
kPa 1)320ppmv at 500
kPa 1)< 25 ppmv
4000 ppmv at 100
kPa 1)1600 ppmv at 100
kPa 1)< 25 ppmv
SOF4 SF4 WF6
HF SO2 SOF2 SO2F2
Arcing Partial
discharges
Secondary Reactions
Surface
insulation
Surface
insulation
100ppmv
100ppmv 50 ppmv
total 7)
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Prepared forU.S. Environmental Protection AgencyOffice of Air and RadiationGlobal Programs Division1200 Pennsylvania Avenue, NWWashington, DC 20460
Prepared by :ICF Consulting 9300 Lee Highway Fairfax, VA 22031
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Moisture in Gas Insulated Switchgear
Sources of moisture in sealed GIE
Surface adsorption (Major cause)
Bulk absorption (Second Major cause)
Leaks through cracks (Small affects but will accumulate)
Permeation through seals (Small affects but will accumulate)
Aluminum porosity (Small affects but will accumulate)
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Adsorbed and Absorbed Moisture
Adsorbed moisture sticks to surfaces of aluminum conductors, enclosures,
and epoxy spacers
Absorbed moisture is water in molecular form that permeates into the
organic solid such as the filled epoxy spacers
Due to initial exposure prior to assembly
Large mass of spacers hold large amount of moisture
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Application of Desiccants
Desiccants can help to remove moisture from SF6 filled equipment.
Desiccants should not be re-used due to absorption of arc by-products
Recharging (heating) of the desiccant could release these harmful
byproducts
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SF6 Acceptable Moisture Levels
in HV equipment
Transmission lines & bus duct can accept higher moisture levels
Main concern is condensation of dew
Switchgear requires lower levels due to potential for arcing.
Main concern is formation of HF.
Hydrofluoric Acid (HF) is a highly corrosive substance that attacks glass and
porcelain
More stringent requirements needed for GIS
Manufacturers limits vary between 50 ppm and 1000ppm
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SF6 Gas Processing - Mixed gas
Very low temperatures stress a circuit breaker in a complex manner. Mixed-gas
circuit breakers were developed for use at temperatures as low as -50oC. These
breakers utilize a gas mixture of SF6 and CF4 or SF6and N2 to prevent
condensation of the SF6 gas. At low ambient temperatures, below -30oC or -40oC
(depending on filling pressure), there is a risk of SF6condensation, which cancause some reduction of breaking capacity. Mixed gas filling with SF6and N2deteriorates the thermal and dielectric breaking capacity. The deteriorated
dielectric characteristics can be compensated for with a slightly higher operating
pressure.
COLD-WEATHER APPLICATION OF
GAS MIXTURE (SF6/N2, SF6/CF4) CIRCUIT BREAKERS
Typical in Canada, Russia, Nordic Countries.
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SF6 Gas Processing
The SF6 recovery units are designed to minimise the
disadvantages of SF6 by means of the following:-
1)Greenhouse gas reduction through transfer of the
SF6 from its current housing to onboard or external
storage cylinders the gas does not need to be vented
into the atmosphere.
2) By-product removal by use of suitably designed
filters and scrubbers it is possible to remove hazardous
contaminants from the SF6 gas.
3) Cost reduction by efficiently recycling the gas
through the recovery unit it is possible to reuse theexisting SF6 gas minimising the requirement of
purchasing new gas.
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2. SF6 PRODUCTS
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Typical specification
Water removal down to 10 PPM or less
Particulate removal to less than 0.1
Equipment vacuum to below 1 Torr
Recovery to better than 99.8%
SF6 Gas Recovery & Purification Products
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Typical Features
Oil-less or oil-free compressors
Onboard or external storage of liquefied SF6Mobile, static or hand-cart
Wide range of accessories
Comprehensive test equipment option
SF6 Gas Recovery & Purification Products
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SF6 Gas Recovery ProductsAccessories and test equipment
Systems can be supplied with hoses, power cables, inline
hygrometer and weighing scales. Gauging can be digital or
analogue.
Operating voltage can be 220V (50/60 Hz), 380V (50 Hz), 415V (50 Hz), 460V (60 Hz) or575V (60 Hz)
Optional accessories include:
Contamination detection
Leak detectors
Electronic moisture measurementExternal scrubbing systems for heavily contaminated gas
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I t ti t ff
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Interesting stuff
For Sf6 we purify to virtually new parameters.
A desiccant dryer complete with Molecular Sieve and Redragon Proprietary Media to remove moisture and lowerfluorides of sulphur from arced SF6 gas.
Stainless steel filter housing c/w filter cartridge good for 0.1 micron filtration at 98% efficiency. This filter is used
at the dryer discharge side to remove any dust or particulate matter.
Inlet Stainless Steel Filter housing complete with filter cartridge good for 0.1 micron filtration at 98% efficiency.
This filter is used at the suction side of the vacuum compressor to prevent any contamination from getting into the
pumping side of the system.
Suitably designed filters and scrubbers remove and lower fluorides of sulphur from arced SF6 gas.
Water removal down to 10ppm or less
Particulate removal down to less than 0.1 Micron
Vacuum to below 1 Torr
Recovery better than 99.8%
International standards - Purify Gas by filtering
50 ppmv-maximum tolerable impurity level for reuse
which translates into a reading of 12 ppmv if the sum concentration of SO2and SOF2is measured(IEC 60480 and CIGRE TFB3.01.01/2004)
(China National standard(GB12022-89)