5 replies to this topic

[kek12345]

Got 2x aMDEA absorption column's with structured packing removing CO2 receiving exactly the same feed gas.  Always have problems with one of the absorbers while the other one never has an issue. Occasionally the dP (based on dP instrument for each bed not individual PTs) across the packing of both the top and bottom bed plummets (reduces by 25-50%) on the troublesome absorber, with no change in gas or amine flow. We then go offspec and have to reduce gas rates by about 20%. Sometime later the dP will recover back to normal and the rates can be increased again. The only other symptom, that is repeatable, is that the temperature on the lean amine inlet and the gas outlet of the absorber inverts when these events occur. Normally the gas outlet temp is cooler than the the lean amine inlet temp (of course there could be  minor calibration issues). However when the issue occurs this inverts slightly (gas outlet becomes warmer than lean inlet). It seems to be completely random when these "dP" events occur however we have repeated it by taking off our carbon bed and filtration on the lean amine side for 7 days and we had issues until we brought back the carbon bed a few weeks later after finishing maintenance. 

 

The regeneration system is completely fine (regen temperature is constant) and there is no change in valve opening , levels suggesting there is significant foaming. The quality of the amine (activator, HSS , strength , lean loading, degradation etc) is the same in each unit and the amine is completely clear (like water) when sampled.  Use of antifoam (silicon based antifoam) is also the same along with the use of activated carbon and filters (5um filters U/S & D/S of carbon bed slipstream).  The troublesome column has been inspected and was literally spotless.

 

To me the only way the dP can change across the structured packing, at constant gas and liquid flow, is due to a change in density or viscosity of the gas / liquid inside the column. Impact on gas viscosity would be minimal so you would suggest the liquid phase. This would usually suggest the column is foaming or potentially flooding however you would expect the dP to rise in those scenarios hence the confusion. 

Edited by kek12345, 10 May 2024 - 02:59 AM.

[breizh]

Hi,

What are the differences, design speaking, between the 2 columns? 

If strictly the same, I would think about internal damages within the bed.

Why physical properties could affect one column, always the same? weird to me.

Any chances to accumulate dirt or braking material which could be responsible for the DP increase, same for distributors?

Hope you check the distributors during turn around (capacity, horizontality), this could affect the performance of the unit.

Hope you use structured packing from a reputable vendor, not looking like and less expensive. I've in mind issues with BX clone, not properly installed and not performing well (mass transfer).

My 2 cents.

Breizh 

[Pilesar]

The symptoms might be partially explained by poor liquid distribution. Is this a large diameter column? Ideally, if the column is opened I would check the levelness of the distributor and perform a distribution test for uniformity and capacity. Is the distributor the correct distance above the packed bed? Perhaps there is a problem with the packing installation leaving large gaps in the interior brick layers or walked-on crushed fins or missing wall wipers or hidden obstacles within the packed bed. So much can go wrong with structured packing installation! A thorough gamma scan of the column might help locate where the problem starts. You would probably need some hard evidence to justify proposing the solution of an expensive gutting and rebuilding of the internals.

  Amines are foaming systems and can be difficult to keep under control. Are you adding antifoam continually? Does a shot of antifoam solve the problem temporarily? Too much antifoam in the system can cause problems also. Carbon fines can increase foaming. Are you sure the filters are intact and not bypassing?

[kek12345]

The dP drops across the packing on the troublesome absorber are a few minutes before breakthrough occurs.  It is a large column (>5m). We have opened it before and checked everything we could however doing an insitu distribution test would be difficult giving the size / volume of water. It is also too thick to gamma scan.  

 

We add antifoam semi continuously across both units. Every X minutes we dose X amount of antifoam and that doesn't really change ever.   Antifoam doesn't help the problem when it occurs. 

 

Packing is from one of the most well known packing vendors in the world.  Filters are also from a well known / reputable filtration vendor and we do see slow rise in dP  and the amine is completely clear so its unlikely fines. 

 

The only design difference is that the troublesome absorber has a slightly lower capacity packing but higher efficiency in the top bed. Its the same packing just the next model up if that makes sense. Difference is about 12% higher on m2/m3 and 1% lower on voids.

 

We think mechanical issues causing bypass but its hard to explain what could cause this to come and go so to speak.

 

[breizh]

Hi, Sometimes during installation contractors damaged the packings, walking on them. Did you try to get contact with vendor?
My 2 cents
Breizh.

[Pilesar]

The dP drops across the packing on the troublesome absorber are a few minutes before breakthrough occurs.  It is a large column (>5m). 

 

The drop in differential pressure indicates to me that there is a path for vapor not obstructed by liquid. Large diameter columns are more sensitive to unequal liquid distribution. Your packing vendor has much experience and will offer advice. I am interested in how you eventually solve this.