Lost my liquid compensation column in measurement liquid level by diferenctial pressure

[mendocarter]

Hi¡ My name is Alejandro and y work in a power plant. I have a pre-heater off low pressure whose internal pressure is vacum (near 0,3 bara). I have tree instruments of diferential presure for measure the level. I put water in the reference column (superior tap), but part off this column disappear. I think that this water is evaporated, because de pressure in the heater is lower than seteam pressurre at the temperature of the column, so I have two possibles solutions:

1.- Look for some method to refrigerate water column like one pipe of refregeration water near the tubing.

2.- Use glycerin like compensation fluid and change the range off instrument. The problem is that if the glycerine also is evaporated it could mix with water in the water steam cycle and it cluld be dangerous

I would like your opinions about this solutions an others than you know work properly for this problem.

Excuse by my English.

 

[IRstuff]

How much water do you think you lost? How does that compare to the nonliquid volume of the column.


TTFN
faq731-376

 

[mendocarter]

It´s depend, in some ocasions I lost 10% y others 25%...etc off the columns, in the tree levels that I have I lost difeerent percentaje off column, but in all cases it is an importatn error in the mesaurement and I don´t know what is the solution, but I think that in other plants have the same problem.

Thank you very much.

 

[hacksaw]

use of water/condensate is rarely used. Anti-freeze solution or some other fluid compatable with your process can also be used. good luck

 

[IRstuff]

Complete saturatation of water vapor results in only about 30gram/m^3 of water, which should be considerably less than your 25%. I would look elsewhere.

TTFN
faq731-376

 

[roydm]

Check your steam tables, the water has most likely boiled off at the low pressure.

A couple of ideas
Add a constant makup of water

Try running the leg dry.
I have had goos sucess by running the dry leg up to a point several feet above the top tapping point then down to connect. This way any water that does condense in the line runs back to the vessel.
You could also add a drip leg to catch any that does happen to accumulate.

 

[roydm]

Like This

http://files.engineering.com/getfil...9312-4139-8fde-6ddad612f59a&file=1883_001.jpg

 

[mendocarter]

Good Idea, but do you think that nothing condensate in the leg dry?. Is possible that I need isolated and electrical heater for the tubing in order to have a temperature higher than saturation temperature at the tank pressure. What do you think about that?

To put air purge is imposibble in this case.

Thank you very much.

 

[roydm]

I have used this on several occasions such as crystalizer, condensate tank.

There may be sone condensation in the dry leg but not much, I think the air remains in there.

Any condensation should run down into the drip leg below the transmitter.

I think the problem with your existing setup is the wet leg is above the vaporization temperature at vacuum, you could also try something like an un-insulated condensate pot, perhaps even cool it down with water so it's below the boiling point.

Can you top up the wet leg with a steady water purge?


I'm sure you will come up with a solution, we will be interested to find out what it is.

Roy

 

[mendocarter]

Than you Roydm. The instrumentation boss of my plant have decided changing all level transmiter in dis tanks by diferential pressure transmiter with difragme and capilar tube, I think that It is worse because we have a small measerument range and this instrument don´t have presición in de diafragme zone but I don´t decide so It´the live, I probe your ideas next time.