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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

Answers


  • Nagarathinam S Murthy, McKinsey & Company, Chennai, nssvdvr@gmail.com

    Best is to keep circulating amine clean... Follow these... 99% problem will be solved. Good luck

    Sl. No    Attributes         UOM            Industry         AFPM
    1            Oxalate              ppm             500                 250
               Sulphate            ppm             500                 500
    3            Formate             ppm             1000               500
               Acetate              ppm             1000               1000
    5            Chloride             ppm             1000               250
    6            Thiosulphate      ppm             10,000           10,000
    7            Thiocyanate       ppm             10,000           10,000
         
                  Total HSS          ppm            10,000 max    5000**max
    1            pH                      -                   -                     10.5min
               Acid Loading     mole ratio     -                     0.45 max
    3            TSS (0.45 mic)   ppm             -                     50 max
    4            RFB (MDEA)      % wt            -                     35 min
    5            Foam Test          secs            -                     < 7

     

    Feb-2022

  • Berthold Otzisk, Kurita Europe, berthold.otzisk@kurita-water.com

    If amine losses are regularly found in the absorber, the reasons are usually foaming and emulsification, equipment design, housekeeping practice, and hydrocarbon solubility. Unwanted formation of soaps from reaction between organic acids and hydrocarbons, suspended solids, inadequate amine filtration, heat stable salt build-up or other contaminants cause foaming. In most cases, foaming in the absorber can be prevented or at least very significantly reduced by using a suitable antifoam agent. Not every antifoam is suitable and, if used incorrectly, can itself lead to foaming and emulsion formation. Therefore, the selection must be made very carefully and the antifoam must not be overdosed. A temporary treatment (batch treatment) is usually more suitable. Kurita FC-6702 has proved very successful in amine plants.

    Please check if the absorber is equipped with enough stages for the required removal of acidic gases. Loss of contact trays or plugged packings could result in poor distribution with lack of contact between amine and gas. The feed gas inlet separator could also result in unwanted foaming due to a demister failure. The lean amine temperature to the absorber should be about 6-8°C warmer than the feed gas temperature to avoid condensation of hydrocarbons with emulsification.

     

    Jan-2022

  • Marcello Ferrara, ITW Technologies, mferrara@itwtechnologies.com

    This is a very common problem in amine absorbers. The causes of the carry-over can be various and often linked together: fouling, plugged trays, foaming, antifoam performance, off-spec inlet gas, corrosion and erosion of metal components, low filtration efficiency.

    Generally, all these causes are related to amine degradation and therefore to a high HSS content and connected problems.

    Sometimes even at low HSS concentrations the problems of fouling, foaming, and corrosion may not be sustainable.

    Given that all reclaiming techniques have no impact on the existing fouling and on HSS control methods such as neutralisation and solution purging/amine make-up have almost no effect on HSS formation/build- up, ITW technologies can give a holistic solution to the problem.

    The holistic ITW approach implies the use of different proprietary technologies, according to the following path:
    1) ITW Online Cleaning for cleaning the entire unit. This implies circulation of a proprietary chemical, which will dissolve the existing fouling. The cleaning will take 24 hours on a feed-out/feed-in basis.

    The unit will resume production under clean conditions. This will be particularly beneficial for foaming control, in that the existing fouling has a major contribution to foam, namely: a) by creating delta P inside the absorber and thereby reducing the capacity; b) by creating a restriction inside the internals and thereby locally increasing gas velocity; c) by stabilising the foam because some fouling will be suspended in the amine.

    2) HSS reduction on the circulating amine. Another proprietary chemical will be added (on a shot basis) to reduce the existing HSS in the amine.

    3) HSS formation prevention. After the previous steps, the unit will be clean and the circulating amine will have reduced HSS.

    At this point, another proprietary chemical will be added on a continuous basis to prevent HSS formation. This will allow sustainable operations and reduce operating costs.

     

    Jan-2022

  • Anibal Galan, KBC (A Yokogawa Company), anibal.galan@kbc.global

    Amine carry-over in the absorber is typically a consequence of foaming in the amine system, which causes poor gas-liquid contact in the amine absorber and abnormal tray flooding levels, leading to amine particulates and droplets being carried over in the up-flowing gas. Foaming can be prevented by minimising hydrocarbon content in the amine system, which is basically achieved by controlling the lean amine temperature entering the absorber at 5 to 10ºC above inlet gas temperature to avoid condensation of hydrocarbons. It is also recommended to filter between 10 to 20% of the circulating amine solution through a carbon filter to control hydrocarbon content in the system and keep FeS particulates controlled (use particulate filters) since FeS stabilises amine solution foaming. Other measures, such as intermittent use of anti-foaming agents and slightly reducing the flash drum operating pressure, can temporarily help with foaming caused by hydrocarbons. However, long-term solutions are always required to sustain smooth operating conditions in the system.

    In addition, amine carry-over can be caused by faulty mist eliminators or top trays, high gas/amine flow rate ratio, although these are not the most common causes and will normally be considered once foaming has been ruled out. If equipment malfunction is suspected as the main cause of amine carry-over, it is advised to inspect and repair mist eliminators (contactor and knock-out drum) and/or top trays during maintenance shutdown of the unit. Regarding gas/amine flow rate ratio, design conditions against actual operating conditions should be compared since amine carry-over can be explained by either high gas flow rate or low amine circulation flow rate. Usually, only amine circulation rate can be controlled, however any adjustment should also take into consideration its impact on other process variables such as H2S load in lean and rich amine, treated gas specifications and regenerator operating conditions, to mention some.

    Hence, a holistic study of the unit operation is recommended if gas/amine flow rate ratio is suspected as the main cause of amine carry-over.

     

    Jan-2022

  • 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



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