sf6 gas processing & recovery

8/22/2019 Sf6 Gas Processing & Recovery

1/42

SF6 GAS PROCESSING & RECOVERYSudhanshu GuptaQualitrol Company LLC


2/42

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)


3/42

1) SF6 OVERVIEW


4/42

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


5/42

SF6 Non-electrical Applications

Magnesium Casting

Aluminum Degassing

Leak Detection

Particle Accelerators (Universities)

Window Pane Insulation

Nike-Air Shoes


6/42

-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


7/42

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).


8/42

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.)


9/42

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.


10/42

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


11/42

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


12/42

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


13/42

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


14/42

Gas Categories

New

Non Arced

Normally Arced

Heavily Arced

Gas In

cylinders

Used Gas

Degreeofcontamin

ation

Decomposition Products of SF6Low

High


15/42

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.


16/42

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


17/42

Pure SF6 prior to electrical arc


18/42

Dissociated SF6 immediately after arc


19/42

Natural recombination


20/42

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.)


21/42

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


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.


22/42

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


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.


23/42

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.


24/42

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


25/42

Chemical Behavior in the presence of water vapor


26/42



27/42


H F

SF

F

O


28/42

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


29/42

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)


30/42

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


31/42

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)


32/42

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


33/42

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


34/42

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


35/42

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.


36/42

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.


37/42

2. SF6 PRODUCTS


38/42

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


39/42

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


40/42

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


41/42

I t ti t ff


42/42

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)

sf6 gas processing & recovery

Documents