Predicting and preventing absorber fouling The identification and reduction of fouling contaminants in lean amine solutions are crucial for optimising operational efficiency
Benjamin Spooner and Steven Ayres SGS Amine Experts
A frequent problem in Indian refineries is amine absorber fouling. To clean the absorber, the amine and gas supplies must be temporarily stopped. This is very costly. Usually, there is not enough time to thoroughly clean the tower. To determine the origin of fouling, samples of the lean and rich amine are required. Correct laboratory methods must be used to analyse the solids in the samples and define the composition. The internals and hydraulics of the vessel play a significant role in whether the tower will foul. Even with considerable amine contamination, the right operation and the right internals can enable the system continue to perform satisfactorily. It is important to know the vapour (also called jet) and liquid (also called downcomer) flooding levels in the tower. This involves understanding the gas and amine flow rates, their respective compositions, and the operating conditions within the tower so that a simulation can be developed. Interpreting an increasing differential pressure across an absorber Absorber fouling is mainly suspected by an increase in differential pressure across the tower. This is a representation of the resistance the gas phase encounters as it flows through the vessel. High differential pressure across an amine absorber can be due to fouling, but it could also be from flooding or foaming events. It is important to know the difference. Fouling Fouling of an absorber occurs when solids deposit on the tray deck or within the packing, restricting the flow of gas. More restriction means
more differential pressure across the column. As internals become plugged, the gas must find alternative pathways, which reduces the total contact area of the trays or packing. If this area is affected enough, the absorption will decline, leaving more H2S or CO2 in the treated gas, as well as a greater potential for amine carryover. The main difference between fouling and other types of differential-pressure increase symptoms is that fouling is a constant, even after antifoam is added or the amine circulation rate is changed. Fouling in an absorber can be from three possible sources: “ High differential pressure across an amine absorber can be due to fouling, but it could also be from flooding or foaming events. It is important to know the difference ” Contaminants entering with the feed gas. Contaminants being carried with the amine. Contaminants that form within the amine absorber. All three areas must be investigated to determine the cause of the fouling and how to mitigate it. Predicting fouling Absorber fouling is the result of solids or sludge depositing in the internals of the tower to the point where either the gas flow is constricted or the amine is backed up, causing flooding. Fouling is usually not a sudden phenomenon but occurs gradually. The differential pressure increases, there is greater difficulty in meeting
Refining India
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