Date: Mon, 21 Oct 2024 14:25:41 +0000
AMMRL:
We have a Quantum Technology all-metal (bagless) helium recovery system and
started running it earlier this year. Although we are technically out of the
start-up phase and have experienced a good bit of the learning curve, there
are still questions and concerns. To anyone else who has such a system that
I have not bothered already:
1. Our mother dewar size is 250 L. I wonder if we are the only ones with
this size mother dewar, or do other systems have that size? I’m particularly
wondering if some of our troubles with transfers are due to this mother dewar
size, since the standard size is 150 L. For transfers to the transport dewar,
to get down to 2 PSI or less pressure in the mother dewar takes about 5-7 hours.
We have so far most often used a target of 1.8 PSI, and this has taken
5.5 – 6.5 hours. Is this what you see also, or not? I’m curious about whether
this relates to mother dewar size, so either way, what is the mother dewar size
in your system? If your wait time for a transfer was long, but you found a way
to reduce it, how did you do that?
2. Our transport dewar has two necks on top (meaning those pieces that
extend up above the top surface of the dewar, where connections are made). One
central neck is about 3.5” diameter and a second off-center neck is larger
than that. Measurements vary but putting a round number on it we get about
7 L/day loss from this transport dewar, compared to a specification of
about 2 L/day. The high boil-off brings a lot of troubles, such as more helium
must be transferred to keep the dewar cold, maybe for just one week, while that
amount would keep it cold much longer with lower boil-off, making for extra
transfer work. I suspect it also has a detrimental effect on filling the
transport dewar efficiently. I’d like to hear from all of you who have this
type of dewar, to know what sort of boil-off you get and see if this design
sometimes works or in general does not meet the spec. Necks are not so well
insulated as the main part of the dewar and the usual approach seems to be to
have only one and make it as small in diameter as practical. If you have a
single-necked dewar, do you have a liquid level gauge? I’m including a picture
of the dewar top (our liquid level gauge is on the bottom right in the picture):
[A large round silver container with a metal valve and pipes Description a=
utomatically generated with medium confidence]
1. Continuing about transfers, we are still struggling to get them to go
well, and quickly. If anyone has tips on setting the parameters, or how to
adjust them during a transfer to fill at a good pace, or other procedural
choices, we would appreciate advice. Not only do the transfers take too long,
one hour or more, but far too much helium boils off during a transfer. QT
suggested it may take 50 L of boil-off to fill a warm dewar, but our last
transfer, which increased the volume in the (cold) transport dewar from 21L
to 138 L and took 75 minutes, boiled off about 63 L.
So, I’m asking a lot, but maybe I can offer one little bit of info that
might (?) have value to someone: We started out with a recovery inlet pressure
of about 0.27 – 0.30 PSI, which meant that we would often have a pressure
inconveniently close to the standard start pressure for the recovery compressor
(0.30 PSI). (Our system has a pump for moving helium into the liquefier during
regular daily boil-off, and the recovery compressor that can handle magnet fill
flash boil-off.) We also had too much venting due to over pressure during
transfers, and too strong a cold blast coming out of the magnet inlet ports at
the end of fills. We have a pressure control valve in the recovery compressor,
for us PCV302, and the first advice was to back its adjustment out to lower the
pressure, but we backed it out all the way and still had high pressure. Recently
QT offered a new solution: a new spring for the valve that is much softer. It was
one of the most rewarding moments in my recent life when I popped that new spring
in and found that with it, we have ~0.20- 0.23 PSI inlet pressure, often right at
the expected book value of 0.22 PSI! Ahhh- I think my blood pressure went down too.
But now it is going up again over transfers and the transport dewar.
Margaret
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