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Amine Regenrator Column Differential Pressure

amine regenrator column dp

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#1 betty

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Posted 13 April 2014 - 07:25 AM

Dears,

 

The Amine Regenrator Column in Amine Regenerator Unit has very normal operation . The one issue that the Differnatil Pressure Indicator indicates wrongly (-0.005 bar) , the normal pressure is (0.13-0.16 bar)  .

 

There was Turnaround for the plant, (since one year), the Lean Amine was changed from DIPA to MDEA.

 

The Differential Pressure Indicator indicates normal pressure (0.13-0.16 bar) after tunround but since last Novmber it was reading wrongly (-0.005 bar).

 

Find attched Drawing for Amine Regenrator Column, hopefully to get good feedback to find out reason of wrong DP indication.

Attached Files



#2 TS1979

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Posted 13 April 2014 - 08:18 PM

The pressure transmitters need to be calibrated. One pressure sensor may be plugged.



#3 betty

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Posted 14 April 2014 - 01:19 AM

This calibration was done for sure, but it could not slove the problem.



#4 breizh

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Posted 14 April 2014 - 02:39 AM

Betty ,

It seems that the DP transmitter is not working , ask your E&I Engineer or Technician to take a look at it . It could be the line ,the sensor , the wiring or the DCS/PLC I/O analog card , the value should not be negative .

 

Breizh


Edited by breizh, 14 April 2014 - 02:40 AM.


#5 K J

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Posted 16 April 2014 - 07:28 AM

Betty you are not only the person who is facing this problem, in our ammonia plant we are also facing same problem and we have checked transmeter calibration and all that but still pdi indication remains negetive. noticeble thing is that this is remote seal type DP transmeter and during night time PDI indication becomes more negetive.


Edited by K J, 16 April 2014 - 07:29 AM.


#6 Art Montemayor

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Posted 16 April 2014 - 01:25 PM

Betty:

 

I may be wrong, but what has frequently been a major problem with dP meter readings in the past has been resolved by simply piping (or “tubing”) up the connections to the meter in a manner such that any condensable vapor cannot get trapped in the sensing tubing.

 

Let’s face it: you have a 100% chance of forming liquid condensed water solution in the tubing if you have installed your dP cell BELOW the sensing points.  And, unfortunately, that’s where your instrument technicians like to have the instrument placed for easy access and readings.  The best manner to install a dP cell in your specific case is ABOVE the sensing points (which means that you require a ladder and platform on top of the stripper and which may not be your situation) and employ a dP cell that has BOTH the input pressure nozzles located at the BOTTOM of the cell case (never at the top).  This allows you to make the pressure tubing connections such that any condensate forming in the tubing always drains down and away from the cell’s diaphagm.

 

You will note that if your vapor pressure sensing tubing (located on top of tray 17) is going down and to the dP cell, it will collect water condensate (this vapor is essentially pure acid gas + water vapor).  This pressure point that the cell is sensing should be LESS than the other pressure (the one below tray 17).  Using common sense tells us that if there is liquid in the tubing from the top of tray 17, the pressure sensed by the cell will be MORE than the pressure sensed below tray 17 – just the opposite of what one would expect and (guess what?) a NEGATIVE reading.

 

Please refer to the attached Rev1 of your stripper sketch.  I am speculating because you haven’t given us the detailed, important layout of the instrument tubing and cell, but I may be correct.  I’ll let you be the judge.

 

I don’t know how accurate your sketch is, but I have a lot of trouble accepting what you show.  Who designed and built your unit?  You show a once-through piping arrangement going to the kettle reboiler when it is totally not required – nor needed.  A kettle reboiler – by nature – is inherently once-through.  I wonder why you show it that way.

Attached File  Amine Regen DP Rev1.xlsx   145.28KB   63 downloads



#7 breizh

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Posted 16 April 2014 - 08:29 PM

Betty ,

Consider this technology with sealed diaphragms , it may help you to eliminate the risk associated with condensation explained by Art .

 

Hope this helps you and others

 

Breizh


Edited by breizh, 16 April 2014 - 09:40 PM.


#8 betty

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Posted 07 May 2014 - 09:20 AM

Dears,

 

Your points are clear so far, but all solutions have been done by our instrumentation team and still the reading is error.

 

 

Would do you like to give me your input for the below observation:

 

One of our Absorbers (HP amine absorber) has the same problem of PDI error reading. In fact this column is not performing well (the H2S inlet is around 4000 ppm but the outlet H2S is 400+ ppm against the target design 50 ppm Max). The absorption efficiency is boor. Waitng till startup to obsereve this column's PDI reading.

 

 

That’s why during the shutdown, this column was opened and the trays (5 trays) were fall down and  some of them were bended.

 

 

The outcome is:

 

Is the Amine Regenerator might have the same issue inside the column? Which might lead to Wrong PDI reading.



#9 Padmakar Katre

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Posted 09 May 2014 - 01:43 AM

Hello,

1. Can u share the column general arrangement drawing; if not please check the PT point location (elevation and orientation). Since your absolute pressure values are correct, elevation/orientation should not be an issue but let us know.

2. As Art has rightly pointed out, please tell us DP transmitter location (physically where is it mounted w.r.t. both PT points/tubing)



#10 mehdi

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Posted 09 May 2014 - 11:10 PM

hi petty

please read pressure of top and bottom of tower by one gage and calculate of real Dp, if Dp is positive ( i'm sure that is positive)

you can use of tow PT transmitter in Top and Bottom and show Dp

 

amiri



#11 betty

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Posted 11 May 2014 - 12:16 AM

Dear mehdi,

Your point is valid, this action is long term solution and will take time, but definitely it will be the last soultion.

 

Dear Padmakar,

 

 

Soon I'll bring back the points for your Q.






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