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• We are experiencing frequent amine carry-over from our high pressure amine absorber. What are the possible causes and solutions?

  Jan-2022

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Answers

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• Celso Pajaro, Sulzer Chemtech, celso.pajaro@sulzer.com

  An absorber will always have liquid carry-over due to the vapour liquid interaction within the column internals. For well operated amine units, the typical amine loss oscillates between 2-4 lb of amine/MMSCF of treated gas. If the amine losses in your unit are higher than the referenced value, check the following:
  -    Mist eliminator: the absorber should have a mist eliminator in the top of the column itself or a downstream K.O. drum equipped with a mist eliminator. The lack of a mist eliminator or an improperly designed or damaged mist eliminator will allow some of the amine carry-over to leave with the gas.
      <    Amine carry-over from trayed columns can vary from negligible up to 0.2% of the gas flow rate without reaching flooding.
      <    Dual filament mesh type mist eliminators maximise amine droplet capture, reducing amine losses. The use of variable mesh densities can improve the mist eliminator fouling resistance while maximising capacity and efficiency.
      <    Mist eliminators can be subject to mechanical damage due to a sudden depressurisation of the absorber (typically a pressure control valve is located downstream of the absorber/knockout drum). The mist eliminator should be designed for potential uplift conditions to ensure that the eliminator remains in place during operation.
      <    Proper installation of the mist eliminator is essential to avoid gas bypass carrying amine droplets.
  -    Column internals reaching maximum capacity: entrainment from internals will increase as a function of gas flow rate. As the maximum capacity of the internals is reached, the rate of entrainment increases exponentially. A hydraulic evaluation of the column internals will indicate if they are close to their maximum capacity.
  -    Foaming: the presence of foam will lead to amine carry-over; this is a typical problem for amine units. Amine solution foaming tendency can be tracked by performing shake tests and measuring the time for the foam to break. Daily shake tests will provide trends on amine solution foaming tendency which can help operators to adjust amine filtration (mechanical and activated carbon) flow rate. There are several indications of foam generation: strong oscillations in the absorber bottom liquid level, an increase or fluctuation in column pressure drop without a change in gas flow rate, or large liquid level changes in the downstream knockout drum. In these cases, adding antifoam can reduce carry-over and column pressure drop

  The most common causes of foaming are the presence of liquid hydrocarbons, solids, and surfactants.
      <    Liquid hydrocarbons can be introduced into the absorber either by condensation or entrainment. To avoid hydrocarbon condensation, the lean amine going to the absorber needs to be hotter. To reduce hydrocarbon entrainment, a knockout drum equipped with a high efficiency mist eliminator should be located upstream (sometimes coalescers are added to remove submicron hydrocarbon droplets). Also, an activated carbon filter in the lean amine stream will remove heavy hydrocarbons.
      <    Solids stabilise foam by making it difficult for bubbles to break. Filtering the amine solution should reduce foaming stabilised by solids. Poor amine hygiene can lead to corrosion. Corrosion products (solids) then lead to more corrosion and more foaming. Amine should be checked regularly and should remain clear and not dark.
      <    Surfactants can get into the amine solution with untreated gas, make-up water, or the excessive use of antifoam. Activated carbon treatment should keep the surfactant concentration low. The use of oxygen free demineralised water for make-up will reduce/eliminate any surfactants in the make-up water.

   

  Jan-2022