Re: [foxboro] Compensated Level Indication
- From: "Steinbrecher, Nick" <E.Steinbrecher@xxxxxxxxxxxx>
- To: <foxboro@xxxxxxxxxxxxx>
- Date: Wed, 1 Sep 2010 10:02:30 -0400
I have to agree with Mr. Riccardi. Unless you have bubbles to deal with
in a propane tank like you do in a steam drum, the two legs of a dP
instrument ( one in the top and one in the bottom) should work, both for
level and mass since you have a density data as related to temperature.
>Nick Steinbrecher
>
-----Original Message-----
From: foxboro-bounce@xxxxxxxxxxxxx [mailto:foxboro-bounce@xxxxxxxxxxxxx]
On Behalf Of Putman, Robert
Sent: Wednesday, September 01, 2010 7:59 AM
To: foxboro@xxxxxxxxxxxxx
Subject: Re: [foxboro] Compensated Level Indication
I agree with Corey's comments that this issue should be very similar to
power boiler drum level control. As I recall, boiler drums typically
have a choice between single element and three element control. There
should be significant information on the web on how this is done.
Foxboro also should be a resource. At one time they had an excellent
group in Foxboro, MA that worked on boiler controls.
Taking an educated guess - As temperature goes down density increases
which should drive level down. However, at the same time the vessel
should contract which should make the level increase. Not sure what the
net result of this is but it could be tested.
Also, remember that levels are integrating processes with a different
set of tuning rules than flows, temperatures, or pressures.
Best of luck,
Bob
-----Original Message-----
From: foxboro-bounce@xxxxxxxxxxxxx [mailto:foxboro-bounce@xxxxxxxxxxxxx]
On Behalf Of Corey R Clingo
Sent: Tuesday, August 31, 2010 11:28 PM
To: foxboro@xxxxxxxxxxxxx
Subject: Re: [foxboro] Compensated Level Indication
Got too occupied to respond today, but I did this once upon a time on a
steam drum on a fired boiler. If I recall correctly, we used steam
tables
to determine the vapor and liquid densities based on temperature and
pressure and used those with the dP leg liquid heights to calculate
actual
level based on P, T, and dP (not even sure we used T, as it had less
effect for the conditions we saw than the pressure). It probably had
the
most effect under normal operating conditions when boiler demand
changed,
and the level fluctuated due to "shrink and swell" effects. If you need
details I can dust the Brand H cobwebs off of my brain and get the
particulars.
For propane, I wouldn't think you would need to go to such great
lengths,
unless the density changes are great over your operating range (I don't
have the physical properties of propane handy, though). If not, just do
the density calculations ahead of time for "typical" operating
conditions
and calibrate the transmitter accordingly.
Corey Clingo
BASF
P.S I'm an electrical guy by training, so take my chemistry with a mole
or
two of NaCl.
"Joseph M. Riccardi" <Joe@xxxxxxxxxxxxx>
Sent by: foxboro-bounce@xxxxxxxxxxxxx
08/31/2010 07:32 PM
Please respond to
foxboro@xxxxxxxxxxxxx
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Re: [foxboro] Compensated Level Indication
Troy,
I have been waiting for all of the measurement experts to chime in
before
possibly embarrassing myself but it seems they are few and far between.
Another dying breed? I am certainly no expert but I'll throw my 2 cents
on
the table to start the bidding process.
In a closed tank pressurized system, the only pressure compensation
required
on the level measurement is from the pressure in the vapor space above
the
liquid; no? Isn't the low pressure side of the dP level transmitter
connected to the top of the tank; this is called the reference leg?
This
reference leg can be dry or wet depending on the application and/or
installation. Changes to the vapor pressure are automatically
compensated
for in the same way as the effect of barometric pressure changes are
canceled out in open tanks (low pressure side of the dP level
transmitter
is
open to atmosphere).
Temperature changes affect the Specific Gravity but I think this is a
straight forward calculation that must be included.
Any help so far or should I fold them...
Joseph M. Riccardi
DCS Services - Industrial Process Control
North-Central Office (OH, PA, MI, IN, WV Area)
South-East Office (FL, GA, AL, SC, NC Area)
"To give real service you must add something that cannot be bought or
measured with money; and that is sincerity and integrity." - Donald A.
Adams
-----Original Message-----
From: foxboro-bounce@xxxxxxxxxxxxx [mailto:foxboro-bounce@xxxxxxxxxxxxx]
On
Behalf Of Brazell, Troy L
Sent: Tuesday, August 31, 2010 12:12 PM
To: foxboro@xxxxxxxxxxxxx
Subject: [foxboro] Compensated Level Indication
All knowing list,
I have had a request thrown at me that I have never had before.
This plant is asking for pressure and temperature compensated level
indication on a propane refrigerant surge tank.
I have the dP level, head pressure and vapor temperature. Has anyone
done
this?
Thanks
Troy
**************************
Troy Brazell
DCP Midstream
ISA CCST
Sr. Process Control Analyst
Office 405-605-3877
Cell 405-301-2994
tlbrazell@xxxxxxxxxxxxxxxx
**************************
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Systems (formerly The Foxboro Company). Use the info you obtain here at
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