We are experiencing frequent amine carry-over from our high pressure amine absorber. What are the possible causes and solutions?Jan-2022
Anibal Galan, KBC (A Yokogawa Company), email@example.com
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.