TEG Contactor Issues
TEG contactors equipped with bubble cap trays may experience the following tower operating problems which result in poor gas dehydration performance:
- flooding
- foaming-based carryover
Flooding
Flooding is a tower problem where it becomes difficult to obtain a net downflow of TEG 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 (downflow flooding):
- In jet flooding, the high upward flow of gas entrains some of the TEG flowing across the trays and carries this TEG 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 dehydration 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 the openings on the bubble caps (thereby raising the differential pressureacross the tray). The gas velocity through the remaining unplugged bubble caps rises. In response, TEG 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 downflow 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 dehydration performance deteriorates sharply and the tower begins to rapidly retain liquid (i.e., the tower floods).
Foaming-based Carryover
The TEG foaming operating problem originates when TEG contaminant levels rise and increase the TEG’s tendency to foam:
- Dissolved contaminants such as hydrocarbon liquids, leaked TEG pump lube oil, and byproducts of TEG degradation result in TEG foaming inside the TEG contactor.
- Suspended particulate solids strengthen and stabilize the foam.
Tray fouling in combination with poor TEG solution quality can lead to foaming-based carryover, i.e., poor quality TEG entrained in the gas by jet flooding will form a stable foam in the TEG contactor.
The TEG contactor’s demister may be unable to break the TEG foam and coalesce the entrained TEG droplets resulting in TEG carryover out the top of the contactor. Foaming based carryover from the contactor is accompanied by high contactor differential pressure, loss of gas dehydration performance, increased risk of flooding, and the accumulation of TEG liquid in the contactor’s downstream sales gas filter/separator.
As a temporary relief against contactor foaming, the Control Room Operator can reduce gas flow to the contactors and notify the Area Operator to manually inject (via shot pot) a batch of antifoam chemical. Antifoam chemical can be injected into the TEG pump suction as the pumps discharge lean TEG to the TEG contactors.
Refer to TEG Regeneration for:
- the requirements of an effective TEG solution to ensure effective dehydration
- a further description of the nature of foaming
- a further description of the temporary use of antifoam chemical to suppress foaming
