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dlkanolarnines for flvdrogen Surfide and Carbon Dioxide Removal 169

be 0.19 to 0.25 in. (Strigle, 1994). Larger orifices produce irregular, non-uniform droplets
that reduce mass transfer; while smaller orifices can lead to emulsion formation (DuPart
and Marchant, 1989).
The amine distributor is usually a ladder type consisting of a series of parallel tubes fed by
a central pipe. The dices in the parallel tubes are pointed down into the top packed bed and
are sized based on the amine velocity not exceeding 170 ftlmin. (Strigle, 1994; DuPart and
Marchant, 1989).
Although almost all LPG treaters have amine as the continuous phase with the interface
controller above the top bed, some have LPG as the continuous phase with the interface
below the bottom bed of packing. With the interface at the bottom, the amine is dispersed
above each bed. Strigle (1994) describes LPG contactor intemals for this interface control
arrangement.

M&zinrizing Enfrahrnenf. Adequate space must be provided below the LPG distributor to
prevent hydrocarbon entrainment in the rich amine leaving the LPG contactor. Honerkamp
(1975) recommends 10 minutes amine residence time as measured from the LE% distributor
to the bottom of the contactor. This residence time requirement should be coupled with a
minimum distance requirement where the distance is measured from the bottom of the LPG
distributor to the LPG contactor bottom tangent line. Tse and Santos (1993) report on an
LPG contactor where this distance was 10.5 feet. This distance is somewhat greater than nor-
mal. A conservative criterion for rich amine residence time at the bottom of the LPG contac-
tor is 10 minutes as measured from the bottom of the LPG distributor to the bottom tangent
line or eight ft, whichever is greater.
Amine entrainment in the LPG is minimized by providing adequate LPG residence time
above the normal LPG/amine interface level. Tse and Santos (1993) cite a case where the
LPG residence time, as measured from the interface to the top of the contactor, was 8 to 10
minutes. This is quite conservative. A more reasonable criterion is believed to be the =pater
of 8 feet cr 5 minutes LPG residence time as measured from the LPG/amine interface to the
LPG contactor top tangent line. This assumes that an external gra\ity settler or coalescer is
provided for the LPG product stream as shown in Figure 2-96.
The above criteria are based on maintaining the combined phase superficial velocity
below 15 d. If LPG entrainment in the rich amine is a problem, a shallow bed of small
packing or wire mesh to coalesce the LPG can be added below the LPG distributor. Similar-
ly, a shallow bed of packing or wire mesh can be added above the mineLPG interface to
reduce amine entrainment in the LPG.
LPG contactors using random packing have poor response to varying hydrocarbon flows
(Honerkamp, 1975). Widely varying flow rates can also aggravate amine carryover.
Changela and Root (1986) outline a technique where this problem was solved by recycling
some of the treated LPG back to the LPG booster pump to maintain constant LFG flow
through the treater. McClure and Morrow (1979B) also describe the use of recycle to main-
tain constant LFG flow.

Structured Packing

Sulzer and Koch have pioneered the use of structured packing for LPG treating with
amines. As of 1994, Sulzer had 5 operating units in Europe, and Koch had 11 operating units
in North America, 9 in gas plant service and 2 in refinery service (Rogers, 1994). For struc-
tured packing, the height of a theoretical stage is 6 to 8 ft, depending on the LE specific