Sulphur hexafloride.

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Pommie

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SF6 has been in the news lately as being the most potent greenhouse gas. I worked for a company in the early 80s that made a SF6 circuit breaker. However the news reports are of it being used in wind turbines. How is it used in a wind turbine? Do they operate at many killovolts such that they need very good insulation?

Mike.
 
Yes, the megawatt class wind turbines need insulated/enclosed switchgear for emergency disconnects and so on. No different from the switchgear you made so many years ago. The smallest SF6 switches go fo about $80k today.
 
Surely it wouldn't be that expensive to recycle it like they do with refrigerants.

Mike.
 
Pommie said:
Surely it wouldn't be that expensive to recycle it like they do with refrigerants.
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You're rather assuming that refridgerants are recycled

Last I heard they were just piling them up wondering what to do with them.

You also need to consider that most fridges failing now don't even contain CFC's anyway.
 
According to the Wikipedia article, SF6 is also used as an inert filler in double glazing.
That seems a far worse application in an environmental sense, as no one will recycle old windows to remove gas (if it's not leaked out over time), they would just be broken up and the glass itself either be recycled or end in landfills.

I thought double glazing was filled with argon, on similar?


On a slightly different subject of a surprising use of a gas (to me, at least) - one of the engineering companies we used to maintain machine tools for had a lot of involvement in the power generation industry.

One thing they made was a replacement housing for an existing generator, which I remember had to undergo a massive amount of pressure and leak testing - as apparently the generator system it was going in to was hydrogen cooled!

I think they said it was to do with viscosity, hydrogen giving the best flow and heat transfer rates...

This is the thing, as it was being transported out.



Example stator frame and rotor at the same place, for some generators (probably not the above one), just as they are in the same batch of photos..



 
Pommie said:
Surely it wouldn't be that expensive to recycle it like they do with refrigerants.

Mike.
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$80k Is the price for the whole switch, not just the gas. Not many companies that can build a completely sealed box with a seal around a mechanical with arm that will not lose pressure for the 15-year warranty period (ideally 30+ year lifetime).
 
While SF6 may be a potent greenhouse gas, at a quick guess there is not exactly much of it in use when compared with CO2, so a few cubic metres of the stuff leaking out now and then is not the "end of the world".

Pun intended.

JimB
 
It is kind of sad when companies try to extend the life of switchgear by setting up a scheduled refilling program them instead of replacing them as they continue to leak.

 
gophert said:
It is kind of sad when companies try to extend the life of switchgear by setting up a scheduled refilling program them instead of replacing them as they continue to leak.
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Hmmm...
Let me think about that...

So how should I proceed when the air pressure in the tyres on my car is a bit lower that the optimal pressure shown in the handbook?
Should I have new wheels and tyres fitted at (say) £300 per "corner", or should I just get out my little pump and raise the pressure to the nominal value?

Going back to the switchgear, the ideal maintenance scenario would be to replace the faulty seals prior to re-filling the SF6.

JimB
 
Refrigerant:
I maintain a chiller plant, the suppliers say they keep old R22 and the likes removed from old machines before being scrapped, so they do have a stockpile, however they are allowed to re-use it in other customers non-new equipment, or they were.
To me that kinda mutes the point, as if you kept using it eventually it would all leak out to atmosphere anyway, as old equipment tends to do that.
I believe a guideline has been passed forcing people to get someone in as soon as a leak is spotted, thats only good though if said leak hasnt vented the 'ole lot before its been drained.
 
JimB said:
While SF6 may be a potent greenhouse gas, at a quick guess there is not exactly much of it in use when compared with CO2, so a few cubic metres of the stuff leaking out now and then is not the "end of the world".

Pun intended.

JimB
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SF6 is a very dense gas unlike CO2. it doesn't seem like it would diffuse much into the upper atmosphere. maybe it eventually does. my main beef with the "greenhouse gas" theory is that if CO2 reflects thermal energy, then it reflects as much of incoming thermal energy as it does outgoing thermal energy. the atmosphere isn't a one-way mirror (and even a one-way mirror reflects as much incoming light as outgoing light).
 

Been my theory for a long time.
 
Which means the manufacturing site has to be taken down, the mains feeding the manufacturing site has to be taken down, switch disassembled, reassembled, pressure tested and then reinstalled and energize. $80k for a new one is much cheaper.
 
I use the stuff in RF resonators (cans on the top and bottom) for accelerator Linacs. We don't need to recycle the small amounts of the gas used in industry.

 
When you see lot's of stainless steel and shiny bits, you just KNOW it's expensive!

A few years ago now, I happened to notice my daughter was on-line on Facebook (when she was doing her Phd), so I Messengered her as it was a Thursday morning. So I enquired why she was on Facebook, and she told me she was at the Neutron Source near Oxford (one of only three in the world I believe) running some experiments - and basically you stick your sample in the multi-million pound machine, press 'Start' and then wait - so she was in the waiting phase.

So while she was on she turned her webcam on, and walked out of the office with it - the place was absolutely amazing, it looked like a set out of James Bond - now that was an expensive place .

Incidentally, that's how get a funded Phd place - you go and run experiments for the company paying you, and as you're a student it's 'free' - otherwise they have to pay £12,000 a day!. So for a few fun days running interesting experiments she got paid a decent wage for the 3.25 years of her Phd.
 
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Nigel Goodwin said:
When you see lot's of stainless steel and shiny bits, you just KNOW it's expensive!
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The alternative to that expensive machine is another expensive machine that also uses SF6 in a massive pressure vessel. The TANDETRON. The last time I worked on one (3MeV double ion charge) was about 20 years ago. The principle is still used in semiconductor production fabs but with the addition of magnesium cloud charge exchange (negative ion source) for some normally positive generated ION species.

https://www.iitk.ac.in/ibc/Tandem_Accl.pdf
https://www.bo.imm.cnr.it/users/lulli/didattica/Resources/Lulli_2014.pdf
 
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SF6 is an old friend going back maybe close to 30 years. We did quite a bit of work with the MK 50 torpedo system. The torpedo was powered by a steam turbine system. You take a small tank of sulfur hexafluoride gas, which is sprayed over a block of solid lithium, and it's showtime. When I moved to Navy Nuclear away from ordinance I think it was Gould or Westinghouse who bought out our interest and development, that was a long time ago. I remember one boiler test that went very, very wrong. After the fire the remains of the boiler system looked like a large version of a Thanksgiving turkey skeleton which was picked clean. Those years were my short experience with SF6.

Ron
 

Sweet. Don't do this at home!
 
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