cigre guide for sf6gas mixtures...h% % corporate research center epa.ppt 1 / 25.08.2000 handling and...

Corporate Research CenterEPA.ppt 1 / 25.08.2000

Handling and Recycling of SF6 Mixtures EPA 2000

CIGRE GUIDE FOR SF6 GAS MIXTURES:APPLICATION AND HANDLING IN ELECTRICAL POWER EQUIPMENT

Lutz Niemeyer

ABB Corporate Research Ltd.Baden-Dättwil / Switzerland



WHAT IS THE PROBLEM?

• SF6 is a strong greenhouse gas

• There is no functionally equivalent substitute

• “Second best” gas: air--> Larger design --> higher cost --> More materials--> More environmental impact

As we cannot substitute SF6 in T&D equipment we must minimize its emission



MINIMIZATION OF SF6 LIFECYCLE EMISSION

• Reduce leakage in-service - Repair or retrofit leaking (old) equipment- Early leak detection

• Implement responsible handling/recycling

• Minimize SF6 per function- Compact design (cost driven)- Synergetic dilution of SF6 by N2



CIGREINTERNATIONAL CONFERENCE ON LARGE POWER NETWORKS

Working Group 23 - 02, Task Force 01: SF6

Mission:

PROMOTE RESPONSIBLE SF6 HANDLING IN THEELECTRIC INDUSTRY



ACTIVITIES OF CIGRE SF6 TASK FORCE

• Assessing the environmental features of SF6

• Proposing standards

• Preparing SF6 handling documents

• Distributing SF6-related information



CIGRE SF6 INTERNET SITE

www.cigre-sc23.org/sf6/

• SF6-related CIGRE documents• Other SF6-related documents• (Links to SF6 service providers)



SF6 IN THE ELECTRIC INDUSTRY, STATUS 2000:

• Handling processes, criteria, standards, and equipment have been developed

• On-site handling equipment is commercially available

• Services for further treatment off-site are available

• Responsible care practice is progressively implemented



SUCCESS OF SF6 RECYCLING EFFORTS?

Max Planck Institute for Chemistry:*

“…annual emissions of SF6 have declined by 27% from 1995 to 1998.”

“…a major part of the reduction must come from magnesium industry and electrical applications.”

* M. Maiss and C.A.M. Brenninkmeijer, “A reversed trend in emissions of SF6 into the atmosphere?” (Proc. 2nd Int. Symp. on Non-CO2 Greenhouse Gases, Noordwijkerhout,Sept. 1999)



WHY SF6 MIXTURES IN T&D?

(1) Enabling equipment operation at low ambient (arctic) temperatures

(2) Saving SF6 in large insulation systems (cost and environmental impact)



ARCTIC ENVIRONMENT

• Avoiding SF6 liquefaction • Reducing SF6 pressure • Compensation by adding non-liquefying gas

N2 High insulation synergyLow switching performance

CF4 High switching performanceLow insulation synergy



LIQUEFACTION TEMPERATURE OF SF6 IN MIXTURES



SWITCHING SYNERGY OF SF6 MIXTURES

0

0.2

0.4

0.6

0.8

1

1.2

0 20 40 60 80 100

Imix

/I SF6

% SF6

CF4

N2



SAVING SF6 IN INSULATION SYSTEMS

Basic effect: Strong insulation synergy in “diluted” SF6-N2 mixtures (~10% SF6)

Typical applications:Gas-insulated lines (GIL)Large GIS

Several GIL projects ongoing



INSULATION SYNERGY OF SF6 MIXTURES

0

0 .1

0 . 2

0 . 3

0 . 4

0 . 5

0 . 6

0 . 7

0 . 8

0 . 9

1

0 0 .1 0 .2 0 . 3 0 .4 0 .5 0 .6 0 . 7 0 .8 0 .9 1ν

f (ν)

S F 6 -C F 4

S F 6 -N 2



ENVIRONMENTAL ASSESSMENT

Relevant figure:• The total environmental impact• Of a functional system• With specified power handling performance

SF6 is only one contributor to environmental impact

Critical figure: SF6 lifecycle emission



COMPARATIVE LIFECYCLE ASSERTION

Procedure: ISO 14040Based on

• Detailed design

• Defined functional unit (bay, supply system)

• Defined power handling performance



SF6 HANDLING IS ESTABLISHED PRACTICE

WHAT’S DIFFERENT FOR SF6 MIXTURES?

• Criteria• On-site handling equipment• Further treatment off-site



HANDLING CRITERIA FOR SF6 MIXTURES

(1) Criteria for reuse: as for pure SF6new: mixturecomposition

(2) Transport criteria: as for pure SF6

(3) Environmental criteria: as for pure SF6

(4) Safety: as for pure SF6



MIXTURE PREPARATION

• Supplier - premixed gas

• Reused mixed gas

• Dynamic mixing at filling

• “One after the other” filling



REUSE OF SF6 MIXTURES ON-SITE

• Mixtures can normally be reused on-sitewithout separation

• Conventional SF6 reclaimers cannot handle mixtures but can be upgraded for this function

• Mixtures must be stored without SF6liquefaction



MAXIMAL STORAGE PRESSURE OF SF6 MIXTURES

0

5

10

15

20

0 50 100

SF6 concentration ν [%]

Max

imal

sto

rage

pre

ssur

e p

com

p [M

Pa]

-20 oC

0 oC

+20 oC



SF6 RECLAIMER UPGRADING FOR MIXTURES

filter

mixer

SF6 reclaimer

compositioncontrol

SF6

N2/CF4

%SF6 meter

storageextension

for gaseousstorage

reuse

recovery



FURTHER TREATMENT OF SF6 MIXTURES OFF-SITE

(1) Purification of contaminated mixtures

(2) SF6 separation

(3) Final disposal of SF6 and CF4



SF6 SEPARATION BY LIQUEFACTION20 bar 50 bar 200 bar 400 bar 200 bar

80%SF6

100%50%

12%

SF6100%20o C

SF6/X50/50%20o C

SF6/X10/90%20o C

SF6/X10/90%20o C

SF6/X10/90%-50o C



FINAL DISPOSAL OF SF6 AND CF4

Thermal dissociationSF6 --> S and FH2O --> H and O (combustion)

Reaction:S + O --> SOxF + H --> HF

Flue gas treatmentSOx + CaO --> CaSO4 (gypsum)HF + CaO --> CaF2 (fluorspar)



CONCLUSIONSUSE OF SF6 MIXTURES

• SF6 mixtures enable equipment operation at low (arctic) ambient temperatures

• Diluted SF6 nitrogen mixtures promise cost and environmental advantages

• Environmental advantages have to be assessed by comparative LCA (ISO 14040)



CONCLUSIONS

MIXTURE REUSE ON-SITE

• SF6 mixtures can be reused on-site without separation

• Conventional SF6 reclaimers can be upgraded for mixture reuse on-site



CONCLUSIONS

CLOSING THE ECO-CYCLE

• Non-reusable SF6 mixtures can be further treated off-site:

- Purification - SF6-separation

• Closing the eco-cycle: SF6 can be destroyed through re-transformation into natural substances

cigre guide for sf6gas mixtures...h% % corporate research center epa.ppt 1 / 25.08.2000 handling and...

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