Hi Marget,
Sorry to hear you are having some difficulties. Seems par for the course.
We have had our QT system for 18 months and are still working our issues with them.
What is the size of you liquefaction system? How many cold heads? Just curious, \
not going to impact my answers below.
We have an 80 LPD system, 4 cold heads.
See below.
Feel free to reach out to me directly.
Best,
Mike
Michael Goger, Ph.D.
Senior Scientist, NMR Manager
New York Structural Biology Center
89 Convent Ave.
New York, NY 10027
Phone (212) 939-0660 ext. 203
Fax (212) 939-0863
gogerm_at_nysbc.org<mailto:gogerm_at_nysbc.org>
> From: main_at_ammrl.groups.io On Behalf Of Eastman, Margaret via groups.io
> Sent: Monday, October 21, 2024 10:26 AM
> To: main_at_ammrl.groups.io
> Subject: [AMMRL] Quantum Technology all-metal helium recovery system questions: transport dewar and transfers
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?
We transfer at ~ 3psi. When our system is liquefying the pressure in the dewar
and cold box is 7psi. We have a 350L mother dewar, with 250L transport dewars.
With mother dewar at 300-325L we just about get 250L in the transport dewar,
with ~ 10L left in the mother dewar.
To depressurize from 7 psi to 3psi through the QT control (pre-transfer) take a
little more than an 1.5 hours, and then the transfer takes another ~1.5 hours.
Yes a bit of time but not as much you describe, but still takes planning when
scheduling a magnet fill.
We typically start the pre-transfer and walk away, following the system remotely
through the Stidelinx monitoring, same for when we actually start the
transfer.
1. 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):
We have standard cryofab 250L transport dewars, with only the central neck.
The offset in your dewar seems odd to me, haven't seen it before.
In terms of boil off, do you keep the stinger from the transfer line in the
dewar after a fill. This could be acting as a heat sink with ambient temp
to increase boil off. We remove the stinger about 10-15min after the fill,
and our boil off rates are as expected.
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 overpressure 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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Received on Mon Oct 21 2024 - 08:20:30 MST