High-capacity vapor/liquid contacting device

Details High-capacity vapor/liquid contacting device High-capacity vapor/liquid contacting device

1999-12-15

2001-09-11

Simmons, David A. (Department: 1724)

Gas separation: processes

Liquid contacting

And recycle or reuse of contact liquid for further contact

C095S199000, C095S267000, C261S075000, C261S113000, C261S114100, C261S114500

Reexamination Certificate

active

06287367

ABSTRACT:

FIELD OF THE INVENTION
This invention is directed to a series of vapor/liquid contacting trays and a separation process which employs this series of trays. Contacting trays such as the one of this invention are useful in distillation and related mass transfer or heat transfer applications where liquid flows down and gas or vapor flows up through a vessel.
BACKGROUND OF THE INVENTION
Liquid entrainment is a problem frequently encountered in distillation tray technology. Gas-liquid contacting employing plate and tray columns and potential problems involved are discussed in Section 18 of The Chemical Engineers' Handbook, Fifth Edition, by Robert H. Perry and Cecil H. Chilton. Tray designs with baffles and dispersers of various types are illustrated and discussed.
Copending application Ser. No. 08/833,490 (which is commonly owned with the instant invention)is directed to a means of de-entraining liquid. In Ser. No. 08/833,490, a plurality of de-entrainment devices (such as vane packs) on the trays are specified to accomplish the vapor/liquid de-entrainment.
A series of conventional sieve trays is illustrated in FIG.
1
. Liquid that is entrained upwards from the tray can be thrown up against the perforated area of the tray above, and get carried up to the next tray. This backmixing of liquid up the column, contrary to the desired downward liquid flow, can greatly decrease the separation efficiency of the column and can cause flooding (hydraulic overloading) of the column.
U.S. Pat. No. 4,356,132 (Belyakov et al) discloses a mass-transfer apparatus which comprises a vertical cylindrical housing, contact trays accomodated inside the housing and made up of perforated and non-perforated sectors, the neighboring trays being arranged so that the perforated sectors of one tray overlie the non-perforated sectors of another tray and vice-versa. The overflow passageways of the contact trays are positioned on the non-perforated sectors. Overflow deflectors are arranged on the contact trays, and baffles are adapted to extend downwardly from each contact tray from the borderline between the perforated and non-perforated sectors and inclined toward the perforated sector. Belyakov differs from the instant invention in that it does not teach the use of multiple baffles vertically located between the perforated area and the impermeable roof, in order to decrease entrainment of liquid. The instant invention imparts co-current flow of both gas and liquid with substantially all the liquid being purposely entrained upward into the vanes (or baffles) where the liquid is deflected downward, at an angle, into a disengaging area opposite the perforated area where the liquid and gas efficiently separate. Belyakov's device specifically does not act in this way as illustrated by Belyakov's Figure's
3
and
6
(see solid and dashed flow lines). Our invention has a rather large sloping open disengaging area extending well below the plane of and opposite the perforated area for enhanced separation of liquid from vapor. Belyakov has no such area extending below the plane of the perforated area.
SUMMARY
In the instant invention, the phase separation can take place in an essentially empty disengagement area by the forces of gravity and liquid downward inertia, without the aid of special de-entrainment devices. Although they are not necessary, mesh pads, vanes, plates, louvers or other means to assist phase separation or other means of assisting phase separation may be placed within the disengagement area.
FIG. 2
illustrates the instant invention. There is an impermeable “roof” directly above the bubbling area (or perforated area) of one tray, so liquid cannot be thrown directly up against the perforated area of the tray above. There is at least one outlet weir (or baffle, or alternately, vane) or other surface projecting up at some angle from the level of the perforated area at or near the exit end of the perforated area, to help direct the froth at least partially upwards initially.
Complete entrainment of the liquid is not necessary in the functioning of this invention. Some liquid can simply spill over the outlet weir. It is preferred, however, to initially impart some upward momentum to the bulk of the liquid. There is at least one baffle that then helps direct the liquid at least partially downward, such that the liquid is moving generally downward, rather than upward, as it enters the disengaging zone where the vapor flows upward to the next tray. One or more curved turning vanes may also be used to direct the liquid momentum downward.
Many FCC units are limited by the downstream gas plant. The trays of the instant invention can help debottleneck gas plants, other high pressure towers, and amine towers with high liquid loads. The capacity benefits of this invention are probably highest at conditions of high liquid flux (greater than about 20 gpm/ft2 of tower area).


REFERENCES:
patent: 2116933 (1938-05-01), Ragatz
patent: 2610046 (1952-09-01), Collins
patent: 2772748 (1956-12-01), Manning, Jr.
patent: 4226678 (1980-10-01), Kende et al.
patent: 4356132 (1982-10-01), Belyakov et al.
patent: 5756055 (1998-05-01), Kelly et al.
patent: 6076813 (2000-06-01), Yeoman et al.
patent: 6095504 (2000-08-01), Heldwein et al.
patent: WO 99 26718A (1999-06-01), None

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