LPG amine absorber is design for 15t/h sour LPG from crude unit and delayed coker unit and we are running it at 20t/h. Amine flow rate is 24t/h for absorption. Column operating conditions is 13.8kg/cm2 and 36degC. Delta T between lean amine and LPG is maintain between 5-8degC.
We are facing problem of continuous Hydrocarbon carry over in Rich Amine from absorber. What can be the possible reason?
Answers
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16/11/2020
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Nagarathinam S Murthy, Ashphil Consultancy, Chennai, nssvdvr@gmail.com
Not sure whether the problem is being faced even today. A couple of additional points might help.
1. The back pressure is too low. Normally one has to operate a LPG amine absorber at 7 bar plus the bubble point pressure of LPG in the absorber. Assuming LPG vapour at 36 deg C is around 8 bar, the minimum back pressure needs to be 15 bar.
2. The viscosity of amine will be higher (best level is less than 3 cp at flowing temperature). Ideally, check the amine viscosity and adjust the operating envelope. Accordingly, change back pressure too.
3. Look at the type of filming amine used in the CDU which can influence carry-over in the amine absorber owing to a drop in interfacial tension.
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12/05/2016
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Frank Rukovena Jr, Rukovena Consulting: FRI-Retired, Rukovenaengr@gmail.com
Given the increased vapor rate you are operating at above the design rate, and I assume the amine rate was increase accordingly, it is very likely the tower is flooding or at minimum very near the flood point which is causing the liquid entrainment. Is the tower trayed or packed? it does not make much difference as both devices are normally not design with 10-20% excess capacity above the designed operating point. This also applies to the liquid distributors in a packed tower. If you have some historic operating data on pressure drop at the design rate it would be useful to compare the two. You could as get the tower gamma scanned to check for flood. If you can get intermediate pressure drop measurements, you may be able to locate the pinch point that way. Sometime a flood DC can be locate with a thermal scan. Hope this helps. Frank
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12/05/2016
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NS Murthy, Suez, murthy.ns.ext@suez.com
Apart from the answers / suggestions given by our fellow refiners. pl look into the quality of amine specially with regard to HSAS content in the lean amine and filterable solids present in amine. Contact your nearest GE representative to take a holistic approach and if needed dope MAXAmine additive to prevent foaming and amine carry overs.
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11/05/2016
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Celso Pajaro, Sulzer Chemtech, celso.pajaro@sulzer.com
What is the column diameter?, where is the amine-hydrocarbon interface being controlled top or bottom of the column?
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11/05/2016
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Morgan Rodwell, Fluor Canada Limited, morgan.rodwell@fluor.com
LPG Liquid distribution into continuous amine phase depends on making sure atomization does NOT occur. You want droplet sizes to be of moderate size (>10 mm). Smaller droplets will entrain in the rich amine.
The local velocity for LPG entering the column (via the holes in the distributor) should be less than 1.25 ft/s (0.38 m/s). Velocities above this will tend to make very small droplets due to the shear stresses at the edges of the holes/nozzles.
Additionally, you should check the disengagement (Stokes Law) of propane droplets from the amine in the bottom of the column. Typically, a residence time of 10 minutes below the LPG distributor is recommended to reduce entrainment in the rich amine. Comparably, the superficial amine velocity should be <0.5 ft/min (0.15 m/min).
Assuming the unit was designed according to this criteria, operating at 33% over the design capacity may be the reason for the entrainment as design velocities are exceeded.
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