Electrical conductivity of 50% glycol with inhibitors
Electrical conductivity of 50% glycol with inhibitors
(OP)
Does anyone have any information on electrical conductivity of 50% propylene glycol with inhibitors? I have a system that is using heated glycol to heat make-up air. The glycol is heated in a shell and tube heat exchanger, and I need to detect any glycol leaks into the condensate by measuring conductivity.
Alternatively, is there something I can add (without deleterious effect) to increase the conductivity?
Alternatively, is there something I can add (without deleterious effect) to increase the conductivity?





RE: Electrical conductivity of 50% glycol with inhibitors
RE: Electrical conductivity of 50% glycol with inhibitors
Heat exchanger tubes are .035" wall
I've never had to monitor glycol leakage as you propose
RE: Electrical conductivity of 50% glycol with inhibitors
See the following link: http://www.axiomind.com/home.htm
Under products see RIA10-1-SAA.
Another method would be to draw a line on the tank indicating the level when the system is topped up.
RE: Electrical conductivity of 50% glycol with inhibitors
The equipment referenced above is OK for small stuff, but large chilled water systems are often measured by specific gravity - the same method typically used to check the antifreeze in your car. However, this is not a reliable indicator of leaks, and it requires periodic sampling - not something that can be used in a control loop.
A second method in favor these days - one much more accurate - is measurement with a refractometer. Handheld refractometers are economical at only $200-$300 each. For process applications, an online digital model is preferred. Those can cost a thousand dollars or more. However, they can continuously monitor mixtures under a wide variety of conditions.
Misco has a bunch of them -
http://www.misco.com/index.php
AFAB Industries is another -
http://www.refractometer.com/
RE: Electrical conductivity of 50% glycol with inhibitors
RE: Electrical conductivity of 50% glycol with inhibitors
RE: Electrical conductivity of 50% glycol with inhibitors
Frankly, I don't see any need for continual monitoring of glycol concentracion! Maintenance people can do regular checks with gravity tester (the same as for cars) and if you heve leaks, mixture will leak, so concentration will not change.
If lack of water in system can endanger your primary process, I propose you use of flow switch, that is sufficiant.
As I understand, your make-up air is outside air entrance to HVAC system. In that case you can save money and just set an alarm on your pre-heater controller, normally that can give you warning on malfunctioning of pre-heating system (would it be leak or something else).
If you really need additional warning, then use flow switch!
RE: Electrical conductivity of 50% glycol with inhibitors
RE: Electrical conductivity of 50% glycol with inhibitors
RE: Electrical conductivity of 50% glycol with inhibitors
I still don't beleive that you can handle this problem with measuring conductivity.
Secondary exchanger for purpose of separation is allways the best, but also the most expensive solution.
I had problem similar to yours in food industry, where we had to prevent any possible leak in plate heat exchanger. Temporary solution was to maintain higer pressure on clean side (it was water-water exchanger so it was not a big problem) so if some leak occurs, it would run in non-critical direction.
But you have steam-water system and problem is that pressure drops on steam side when you shutdown the boiler. There are some design possibilities, to install check valve downstream the boiler, automatic on-off valve upstream the steam trap, which closes when boiler shuts down, and you additionaly need one safety valve between these two. That way you can achive contolled minimum pressure on steam side when boiler is off. This is not so simple, but maybe it is cheaper then additional heat exshanger (for which you will also need additional piping, control valve trim and so on).
In my mentioned situation we decided on permanent solution - to replace plate exchanger with monster-big shell and tube exchanger, beacuse they are much, much more resistant to any leaks! But you already have shell & tube?! It shouldn't leak so easily - when it leaks it means it is significantly damaged - has apparent crack on plate-tube weld or on tube itself (while with plate exchanger slightly imbalanced gasket tightening can cause big leak).
Interesting?!
RE: Electrical conductivity of 50% glycol with inhibitors
DOW quotes refractive indexes for all of its glycol treatments, not conductivity. Conductivity is a reasonable solution to measure turbidity, not glycol concentration.
RE: Electrical conductivity of 50% glycol with inhibitors
RE: Electrical conductivity of 50% glycol with inhibitors
My concern is that you will not be able to reliably measure increasing concentrations to detect a leak, or reliably enough to prevent damage to your boiler - but maybe so.
The best that I could find several days ago was the graph below. This one is for Ethylene Glycol, not propylene. I found it at:
http:/
http:/
The second one is for "Diethylene Glycol", but I don't even know what that is. In any event, these are not with inhibitors. What you can deduce from the graph is similar to everything I've read about glycol. You may get a small spike in conductivity as glycol concentration is initiated, then it rapidly declines to very little. That would seem to be a contradictory mechanism to test for a leak.
RE: Electrical conductivity of 50% glycol with inhibitors
Properties for Dowfrost (Propylene Glycol)
Electrical conductivity for 50% at 25 deg C = 2,060 micromhos/cm
and 249 micromhos/cm for 50% at 0 deg C. Looks like the inhibitors increase the conductivity substantially. I'll have to check detection equipment sensitivity.
RE: Electrical conductivity of 50% glycol with inhibitors
Also, I thought we were talking about leaks of a Glycol aqueous solution into non-glycol water. So, the conductivity values will have to adjusted for the volume of the 50% glycol leak (small) divided by the volume of water solvent in the shell (very large). Seems like you would need conductivity values for glycol at 1%, 0.1%, or less, instead.
Unless I'm missing something, this may be too difficult.
RE: Electrical conductivity of 50% glycol with inhibitors
The other way might be to trace the Glycol with a Nalco product, TRASAR, and have a Trasar unit monitoring the condensate stream.