Contactor Troubleshooting

Amine contactors equipped with bubble cap valve trays may experience the following tower operating problems which result in poor gas sweetening performance:

Flooding

Flooding is a tower problem where it becomes difficult to obtain a net down-flow of amine liquid through the tower. Flooding may be caused by an excessive gas flow rate up through the contactor (jet flooding) or an excessive liquid flow rate fed to the contactor (down-flow flooding):

• In jet flooding, the high upward flow of gas entrains some of the amine flowing across the trays and carries this amine mist upward and out the contactor. At the same time, the differential pressure across each tower tray rises as the high gas flow passes through the restrictive tray valve openings. To match the high differential pressure, the liquid level in each downcomer rises in an attempt to increase the head pressure and force liquid onto the tray below. If the liquid level in a downcomer rises to the tray above, the head pressure provided by the liquid in the downcomer cannot increase further; liquid can no longer flow through the downcomers and across the trays. With the trays being unable to function properly, gas sweetening performance deteriorates sharply and the tower begins to rapidly retain liquid (i.e., the tower floods).
• Jet flooding may also result if the flow rate of rising vapor is normal but tray fouling has plugged shut some tray bubble cap valves (thereby raising the differential pressure across the tray). The gas velocity through the remaining open tray valves rises. In response, Amine liquid is entrained by the rising fast flow of gas (and the downcomer liquid levels rise). With the trays unable to function properly, the tower is at imminent risk of flooding.
• In down-flow flooding, the high downward flow of liquid exceeds the downcomers’ capacity to drain liquid from tray to tray. The liquid level in a downcomer rises to the tray above, resulting in high differential pressure across the trays. With tray-to-tray drainage lost, gas sweetening performance deteriorates sharply and the tower begins to rapidly retain liquid (i.e., the tower floods).

Foaming-based Carryover

The amine foaming operating problem originates when amine contaminant levels rise and increase the amine s tendency to foam:

• Dissolved contaminants such as hydrocarbon liquids and acidic byproducts of amine degradation result in amine foaming inside the Amine contactor.
• Suspended solids such as iron sulphide strengthen and stabilize the foam.

Tray fouling in combination with poor amine solution quality can lead to foaming-based carryover, i.e., poor quality amine entrained in the gas by jet flooding will form a stable foam in the amine contactor.

The amine contactor’s demister may be unable to break the amine foam and coalesce the entrained amine droplets resulting in amine carryover out the top of the contactor. Foaming based carryover from the contactor is accompanied by high contactor differential pressure, loss of gas sweetening performance, increased risk of flooding, and the accumulation of amine liquid in the contactor’s downstream water wash tower.

As a temporary relief against contactor foaming, the CRO can reduce sour gas flow to the contactors. The process area operator can trigger the injection of antifoaming chemicals. Antifoaming chemical can be injected into the lean amine supply piping to the amine contactors. Refer to Amine Solution Conditioning for:

• the requirements of an effective amine solution to ensure quality sweetening of sour gas
• a further description of the nature of amine foaming
• a further description of the temporary use of antifoam chemical to suppress foaming