DP Level Transmitters in De-Ethanizer Re-Boilers

If you prefer to stick with DP level measurement you could get reliable readings by using remote seals. Or the application may lend itself to GWR?

Ace

Thanks for the response ACE...

I have to work with the DP transmitter as of now since the remote seal/GWR order would take 11 weeks delivery time....

This is a concern.....

Regards,

Shan

Shanivas,

What is the temperature and pressure in that process?

I could be recommend you make a test using two pressure transmitter (gage) in order to get two pressure and substract these two signal (bottom minus top) for know the liquid level inside the drum. It is not a reliable method but as you don´t have anything more can be a partial solution.

Of course this is possible if you have the transmitters in your facilities, workshop.

Rosemount is replacing its capillary system with solutions as this.

http://www2.emersonprocess.com/en-US/brands/rosemount/Pressure/DP-Level-Products/3051S-ERS/Pages/index.aspx

Best regards

JP

Hi SAV,

That seems like a good idea.

A fresh eye could definitely give new dimension...

And SAV, Since this is a Re-boiler, the temperature is varied from 50 to 130 deg Celcius and pressure is nearly 20 bar. And another important concern is the ambient temperature...(-45 to + 45) now it is -8.

I have to look for new pressure transmitters and cable to control room.

Totally four Installations, so I would require 8 Pressure transmitters, Obviously I dont have them.... Would give a try for atleast two.

Looking ahead for similar responses which could help my situation.

Regards,

Shan.

If possible you can use a small rotameter and purge the low pressure leg with Nitrogen.You want the minimum flow possible. If done correctly the low pressure leg will be full of Nitrogen with very little to no effect on the reading.

I must have been working on my reply without seeing the details of 20 bar pressure.

This makes my idea very difficult as finding flowraters that can handle more then 200 psig is difficult but not impossible.

> 1) Installation of the Condensation Drain POT - Volume of condensate formed during the operation is high and has to be drained frequently.  . The purpose of a condensate pot is to  - provide a fill point to  fill an empty leg at start-up/commissioning - provide a resevoir to ensure that the leg remains filled with condensate during operation.  The description, "has to be drained frequently" and the 100mm syphon/pigtail loop at the exit of the condensate pot makes it appear that you are attempting to use a condensate pot to prevent condensate from filling the leg.  Is that the case?   If not, a)  What is the "condensate draining" is referred to? b)  what is the purpose of the syphon loop/pigtail?

Mount the DP above the tank,with the Low port facing down.This will prevent condensate from accumulating in low side port.

I dint understand your suggestion. Could you plz explain it with a sketch.....

Regards,

Shan

With a pressurised vessel use the high side of your DP cell to the top tapping. Use your condensate pot, placed at the upper level, to keep the impulse line full. Do not raise the impulse line above the pot as in your drawing. This leg is now used as the reference for upper level. The low side of the cell is connected to the lower tapping point to read the level.

Your transmitter should be calibrated in the negitive region ( -(height of mesurement) mmH₂O to 0mm h₂O) ie: 4mA =-level 20mA= 0.

This set up seems counterintuitive but it is the only way to get a level with one cell on a pressurised vessel.

Steam-trace the low- and high-pressure process lines. Keeps vapor in both legs (as long as it's hot enough to boil at pressure) without introducing inert gas to the process. Or follow Iris's instructions.

Note the view of the liquid level (color green) in the condensate pots, even though the diagram is a DP steam flow, not liquid level DP. The concept remains the same, even if dated.

Shan,

Posts #8, and #11 are not good solutions. (posters please don't take this as a personal insult)

#3 will work but level reading accuracy will be reduced proportional to pessure range, for instruments calibrated at the same tolerance.

#10 is the best solution presented here so far, given the constraints that were mentioned after the OP. It would also be possible to leave the DP transmitter direct acting if you can elevate the zero enough.

I can go with #10, assuming the process temperature always > ambient. After reviewing OP's first post, it appears that this is what was originally intended, but a few critical details were missed. Proving, once again, that the devil really is in the details. And OP won't need to purchase anything, saving time and $.

Why do you rule out 8 & 11? I know they have both been used successfully in the proper setting.

I will be glad to explain my reasoning.

The problem with #8 is that by having some liquid and some gas in the hi side sensing line, the liquid level in the sensing line itself would fluctuate more due to process pressure changes than from process level changes. The DP measured by the instrument would not necessarily be proportional to the process level.

Mounting the transmitter above the re-boiler could work if one were to keep gas bled from the hi sensing line - which would then become the low pressure sensing line due to siphon- and appropriately elevate or suppress the zero and potentially reverse the action. But none of that was mentioned.

The problem with #11 (where to begin?) Even if one were willing to expend the great amount of energy it would take to continually boil out the hi side sensing line at up to 20 bar with steam trace, and somehow not cook the transmitter, process liquid would repeatedly flow in and boil out which would create pressure fluctuations like a Mr. Coffee on steroids.

I actually have a problem with #10 as well, because it is not the ONLY way as stated, but now I am just getting too darn nit-picky.

I hope that helps, Ace