Robert,
>
> Try recovery. We do it at the whole UF at least 100 systems. NSF
> gave a grant to us for the whole campus. Small systems are available
> and NSF loves it. Once it is gone it is gone forever and accelerates
> to the Earth's escape velocity. Helium will Always be the luxury
> cryogen for many beautiful reasons irregardless of HT supercons
> advances ... most important being safety. Yes it is expensive ...
> treat it like gold and platinum.
Situation is not as easy as you describe it here. Of course we have
to think about a recovery solution, but we should not neglect the
disadvantages.
You gave the benefits, so please let me add some ideas
concerning the disadvantages.
In the case of your huge
installation with some large consumers maybe recovery is economic.
But usually you have to take into account
- the very high costs of installation,
- the personal to keep the whole system running
- the needed rooms
- the energy demands
- the water demands
- the maintenance costs
Usually we tend to neglect especially the costs of installation (in your case the
costs are hidden due to the grant) and as a
consequence we are doing a naïve reasoning.
Beside all of the recovery costs you have to take into account at least
two further aspects.
Within the recovery system you have to live with statistical variations
of the pressure. This is deadly for high resolution NMR if you don't
own an absolute pressure regulation (5k $ for each machine). Otherwise
you have to live with incrased T1 noise depending on the individual
magnet. Furthermore you increase the risk to quench the magnet.
At the one side you have to increase the pressure within the magnet
to connect it to a recovery system. This will increase the helium
temperature and the drift rate. If your system is installed anywhere
within the mountains this doesn't matter, but nearby the ocean
I would at least carefully look for the change of the drift rates.
The most critical time is refillng. There is a low amount of helium
in the magnet and you have to lower the pressure for the filling
procedure. This will cause an immediate boiling of the liquid helium
and provides a chance for warmer helium gas to reach the joints.
Of course you can lower the pressure very carefully, but are you really
sure to think about this every time?
Concerning the non renewable resource helium you are right
in part. Of course helium made from natural gas is not renewable.
But it doesn't move to the empty space immediately. There is a
steady state helium concentration within the atmosphere since
millions of years within the 5 ppm range. It is expensive but not
impossible to produce helium from air. In a last instance we have
to compare the costs of a recovery solution with the costs of helium
made from air.
As you maybe know, MRI magnets become active cooled since years
using pulse tube coolers. Because of the vibrations this method is
less suited for high resolution NMR magnets, but maybe this situation
will change. In principle the cooling unit for the Bruker cryoprobes
would be a good machine for the magnet colling.
In general, I believe recovery is reasonable if there is a large
facility like yours nearby and if you can keep the pressure variations
in the helium line away from you magnets. This is especially true for
the pumped magnets, where the vacuum pump ensure an ideal
pressure decoupling.
Finally I would append a few links concerning the helium situation:
Oveviews concerning the helium situation made from the Bureau of Land Management
http://minerals.usgs.gov/minerals/pubs/commodity/helium/
Scheme of the helium production
http://www.praxair.com/praxair.nsf/AllContent/999EEE6BD4DEAF258525656900606F61
?OpenDocument&Menu=&ThemeId=339999&View=LeftNavMenu&Expand=
New helium plant in algeria (german)
http://www.linde-process-
engineering.com/en/p0002a/p0002a.jsp?produktion=true&oid=4262
Selling of the federal helium reserve
http://books.nap.edu/books/0309070384/html/14.html#pagetop
helium made from hot springs in india
http://www.veccal.ernet.in/~vecpage/hrp.htm
magnets without liquid cryogens
http://www.cryomagnetics.com/cryogen-free.htm
>
> Helium and it's close cousins are a strategic materials that gives the
> owners of large quantites huge world-wide leverage. You are feeling
> the effects of our decades of waste now. If we don't stop we won't
> have enough for the cool planes, trains, cars, tranformers, and etc
> the designs of which are in the minds of many of you now. These
> designs can make us all richer wiser and healthier.
>
Regards
Rainer
(TU Munich)
BTW: We recover our helium from the pumped magnets, because our
neighbour is the Walter-Meissner-institute of deep temperature physics -)
And please excuse my bad english
Received on Mon Jan 13 2003 - 10:59:47 MST