AMMRL Folks,
Thanks so much for your multitude of interesting and varied responses to my
question last week about cryogen costs for small labs. There was so many
responses, I have decided to summarize them below, if for no other reason
than archival value. Names and institutions have been removed.
Responses varied from "Your prices are cheap" to "You're paying too much".
The most common response was to use smaller Liq N2 dewars to cut down on
evaporation losses.
A few extra pieces of information I left out of my first email:
- we do the He fill every 4 weeks as that is the timeframe for the magnet to
require 30 L - its about 40% at that time. We could wait another 2-3 weeks,
but would then have to order a 60L tank, and not be able to use it all. The
magnet is ~ 15 years old, was installed last year, and is using about as
much He as in its previous location. I hadn't thought of it previously, but
I could check to see if a 60L He tank is cheaper per L than a 30 - maybe
we'd break even, and have to do 50% less fills.
- None of the suppliers of Liq N2 I've talked to will supply N2 in anything
other than low-pressure 230L dewars. I haven't inquired about having our own
tank filled from a micro-bulk truck - this will be an option I'll
investigate when we get slightly more liquidity than we do now.
- Because we pay for the cryogen from Smithsonian funds, we're more of a US
govt organization than an academic one. (For instance, we're about a mile
away from the main Harvard campus, so wheeling tanks over from Harvard Chem
really isn't an option, unfortunately.) I think being a US govt purchase
means we get slightly better rates; but our beauracracy means its very hard
to change suppliers during our Fiscal Year.
With all that in mind, I've discovered that our He vendor will ship us 230L
tanks of N2 for $43, with no delivery or rental charges! I'd never
investigated this previously, assuming the vendor that everyone else uses
for N2 here must have been the cheapest. Our first order is coming from them
today - we'll see how it goes. Following on from all the advice, I'll look
further afield for a vendor who may ship 160 L dewars, or who will fill a
tank from a micro-bulk truck. I may get the opportunity to switch over to
them come October 1 and FY2006!
I've put my original question below, then the responses.
Many Thanks once again,
Ross Mair
-----
Here at the CFA, we have one, lone 200-WB magnet. We put in maybe 30 L of
LiqN2 every week, and 30L of LiqHe every month.
I have no problem with our He supplier. We get a 30L tank on two days
notice, and are charged a flat rate of around $110 (~$3.50 per liter). We
use the entire tank when it arrives, and its taken away again soon after.
There are no delivery charges, Hazfees, extra charges, monthly fees,
surcharges, or anything else.
LiqN2, on the other hand, comes in 230L tanks, which nominally cost $55.
Because we only have one magnet to fill, the tank sits around and we lose a
lot due to evaporation - so we only get 2 fills out of each tank. I doubt we
can do much about that. So we order two tanks a month. However, the combined
add delivery fees, and other misc charges mean we end up spending 1.5 - 2
times as much per month on Liq N2 as we do on He.
I'm about to investigate alternative Liq N2 suppliers, but I was wondering
if any of you, from small institutions with only 1 or 2 magnets, no on-site
Liq N2 "tap", etc, have any comments which may indicate I'm expecting the
unreasonable.
Many Thanks,
Ross
-----
Hi Ross, long time no see, but it doesn't sound like such an unreasonable
deal. We pay $49 for a slightly smaller tank of nitrogen and a monthly
demurrage charge of $49 for any tank we hold on the last business day of a
month.
-----
In our institution, we have one 400 MHz magnet that we refill with 50
Liters LN2 every 10 days. We get our LN2 in a stainless liquid gas
container of about 100 Liters, maybe twice a month. We also get charged a
rental fee per cylinder per month. So it looks like we are pretty much on
the same boat.
What I then do is to transfer the liquid to a 50 L dewar on wheels. This
is pressurized on its own to about 5 psi (takes a day or so), then we
wheel it into the lab an fill the magnet from the 50L dewar. I believe
the LN2 kept in the 50 L dewar evaporates much less. Mainly the reason we
do this is that we don't have the facility to wheel in the big stainless
container into the lab, and this liquid container doesn't have the
pressure controls appropriate for the magnet, so we don't fill from that.
If you cannot get LN2 in smaller tanks, you might want to invest in
30 or 50 L dewars to transfer the LN2 into and maybe keep it liquid a bit
longer. And the self-pressurizing draw tube as well. The drawback is
having to refill and install the draw tube, which require manual labor.
-----
In my case I have two 500 (one ultrashield and one not shielded) and one
300 (not shielded).
About the LN2 what we did two years ago was that we installed a 1,500
gallons tank from which we supply LN2 to all the labs (physics,
chemistry and biology); for the magnets, I fill two 120 L dewars each
week to fill the magnets and supply others that use small dewars (< or 25 L).
Before, the price of the LN2 for me was $1.15/liter in 230 liters dewar.
Others were paying more (some of the close to $2.50/liter). Now the
price is $0.75/gallon and the rent of the 1,500 gallons tank is $300 per
month.
The price for the LHe is $4.50/liter. Before I had two 300 and one 500,
now two 500 (shield/unshield) and one 300. Before (two 300, one 500) I
could use one 100L dewar to fill the 3 magnets every 1 1/2 to 2 months.
Now (two 500, one 300) I'm not sure yet because the ultrashield was
installed recently (past february); I'm not 100% sure but I think that
100 L will not be enough.
Other academics labs in universities in Puerto Rico that has only one
magnet (200, 300, 400 or 500) do it similar to the way that you do. But
our problem here is that we have only two suppliers for LHe. One of the
supplier has 100, 250 or 500 L dewars for LHe. The other has 250 and 500
L dewars. Therefore the people that fill only one magnet 100 liters is
too much.
-----
It sounds to me like you are paying way to much for liquid nitrogen. I
found that a very effective way to get good pricing was to find out who is
the main supplier of cyrogens to Harvard (CO2, N2, He) (it is most likely a
site wide contract) and entice a competitor with the opportunity to get a
foothold at such a large site.
-----
Filling up the LHe once a month sounds high to me. When was the last time
you had your magnet serviced? It sounds like you may have a bad vacuum due
to bad seals or some other leak.
We have a 500 narrow bore and I fill up LHe about every 4-5months and then
I'm only down by 30-40L. For LN2 I do fill every week between 30-40L. Our
LN2 comes in a 180L dewar and that'll last me two weeks (mind you, I'm in
Texas, where it can get pretty hot....keeping it out of the sun helps). It
sounds like they may not be filling up your dewar completely, either that
or the pressure relief valve has a really low setting 20-50 psi and the
dewar is constantly venting. On our 180L dewar, the valve is set at
350psi. This helps to cut down on the venting, but it does require you to
blow down the dewar to whatever pressure you use when filling (typically,
I find ~50 psi works fine for me). You lose some N2 when blowing down, but
overall it seems less than if the dewar was venting constantly.
The prices sound reasonable, especially the LHe. Unfortunately, our LHe
supplier is not nearby. It takes a week for delivery and typically costs
us 5-10x as much as your prices.
-----
At XXXXXXXXXXXXX we get 230L tank of LN2 for $52.80 and no other
charges. EVen though it is Massachusetts I am sure our supplier,
Merriam-Graves is not available to you in Boston Area but I would have
thought city would be cheaper. Your helium
rate is the same as ours from Praxair.
-----
We have a small magnet (300) which takes 30 L once a week in a different
building so we order a 230 L for it alone. However, it lasts for a month -
four fills every time. No way you should only be getting two fills per tank.
-----
Can't help you with the Liquid Nitrogen costs, but was wondering who your
supplier was for liquid Helium. The rate you are being charged for
liquid helium is extremely good. And I have been told our rate is somewhat
high, only because we only have one magnet and only use 30L at a time.
-----
I think the price you are getting is very reasonable. I don't think
you will find any better terms. However, you may want to look into
buying your own liq. N2 tank and having it filled on site, if such an
arrangement is available at your place. If it looks good, you may be
able to buy 100L or 160 L tank. It may pay off in a few years. You
have to do the math and decide if it is good for you.
-----
I also have a single NMR spectrometer in my lab. Your LHe cost per 30 L
dewar is about half of what I am charged by Airgas (the only supplier
who will deliver 30L to me). Fortunately, my Oxford compact 300 MHz
magnet only takes 30 L every three months.
For LN2, my supplier fills up a roll-around 260 L dewar at my lab from
their microbulk LN2 truck. There are several advantages to this system.
It uses a higher quality dewar that is supposed to have less boiloff
loss. Also, you only pay for the LN2 that it takes to top off your
dewar-most dewars are still 20% full when they are returned. We are on
a two week delivery schedule and rarely run out. We also use LN2 for
cooling vacuum traps in our synthesis lab. The boiloff is used as a
low-pressure N2 gas source for the laboratory (it's cheaper than using
high pressure cylinders). You can save money by getting a yearly lease
on the dewar instead of paying monthly charges. In my opinion, you are
getting a good deal at $55 per dewar. I hope this helps.
-----
At ~$0.24/liter, you are getting a pretty good price. However, most
dewars should only have about 1 - 5 % loss/day, so even with evaporation
you should be able to get by with 1 dewar.
I would see about obtaining a small storage dewar and having the
company fill it. Also, see about getting a smaller dewar delivered.
-----
our chem dept here, which fills a 300 MHz R2D2 magnet, bought their own
liquid nitrogen dewar. They calculated that the $1600 dewar would pay for
itself in dewar rental in 2 years. An added benefit is that many rental
dewars have gone soft, meaning they lose nitrogen faster than they
should. Also, they rigged a second back-pressure regulator so they can
store it at 200 psi (the liquid nitrogen is warmer, so it boils off slower)
and bleed it down to 20 psi for fills.
Even if you don't buy your own dewar, putting your specific needs out to
bid among suppliers should get you a much better deal. They may have
better options - like a smaller dewar; or letting you take 30 L off of a
nitrogen dewar which you only keep for a day.
How far is it to wheel a dewar over from your chemistry or physics
department?
-----
WOW! Your rates are CHEAP.
We're a minor user (a single 300 MHz instrument in the middle of
Nebraska). We pay $0.84 / L for Nitrogen (180L tanks last 2 - 3
fills). Helium is about $300 / 60 L with a two week notice/delivery
time. We don't pay shipping, demurrage, or any other fees.
To make it worse, we're only 3 to 4 hours north (by car) from the site
where they "make" the helium.
-----
Your situation sounds familiar. I manage two magnets (400 and 500 MHz,
actively shielded Oxfords) which get weekly nitrogen fills and helium fills
(~70 L total) every 3 months. We, too, order 230 L dewars of nitrogen at
$55 per dewar, plus a $1 per day rental fee. I can typically get 2-week's
use from one dewar, estimated at about 70 L per week as total liquid
nitrogen used. If you check the boil-off specification for your dewar, you
can calculate (estimate) the expected losses; perhaps you would be better
off to order a smaller dewar.
-----
Your costs look about right. I think we pay about $4/L for He and used to
pay $50/230L plus demurage (high rent). You can investigate purchasing your
own dewar to avoid rental (maybe $1500 for a used one).
-----
To begin with, you should be able to get liquid N2 in smaller
containers. Even if the $/l is higher you will probably come out ahead, as
you won't lose as much by evaporation. Mine comes in approx. 100l dewars,
even though we have 4 magnets. The dewars are also a much more manageable
size -- we've had 200l dewars for the initial fill on new systems, and
have found them a real pain when trying to manoeuvre in tight spaces.
Also, your cost per litre seems excessive to me. We pay close to twice per
litre what you do for liquid helium, but our nitrogen cost is about half of
yours. Victoria is situated on an island, and all our cryogens come by
truck and ferry from the mainland (about 1 1/2 hour ferry trip), so the
trucking costs will be significantly more than yours ought to be. You
might want to shop around for a better price.
-----
Your basic nitrogen cost sounds cheap, but you clearly lose a lot.
Ours is delivered in 160 liter tanks at a thirty something cents per
liter and a small delivery charge. I get two and a bit fills out of a
tank unless it has a very poor vacuum. We use Airgas and the
department users a huge amount. There is a truck delivery every day,
I would guess that one of their delivery trucks just services UCI.
So could you save by using the same supplier as other people? Get
smaller tanks that you can use more efficiently? Airgas offer 200
liter on wheels as well as the 160s that I normally use.
-----
My gut feeling is that helium and nitrogen should cost about the same.
There are enough LN2 vendors out there that you should be able to find a better
supplier than your present one. You also might try to piggyback on Harvard
Chemistry, but that's obviously up to them.
-----
Sounds like your nitrogen dewars are not insulated well. I get 2 fills on my
240 liter low pressure nitrogen (2 weeks), but this is to fill a 400 and a
600 MHz NMR. You may want to consider the smaller 160 liter dewar, buy 2 of
them and have one on hand in use and the other being filled by the vendor. No
demurage (rental) charges that way.
--
Ross Mair email: rmair_at_cfa.harvard.edu
Staff Scientist CFA Phone: (617) 495 7218
Harvard-Smithsonian Center for Astrophysics CFA Fax: (617) 496 7690
60 Garden St, MS 59, MIT Phone:
Cambridge, MA 02138 MIT Lab Phone: (617) 452 3002
USA MIT Fax: (617) 253 0760
Received on Mon Apr 04 2005 - 18:57:03 MST