Gas and liquid contact apparatus – Contact devices – Wet baffle
Reexamination Certificate
1999-03-26
2001-09-25
Simmons, David A. (Department: 1724)
Gas and liquid contact apparatus
Contact devices
Wet baffle
C261S097000, C261S108000, C261S113000
Reexamination Certificate
active
06293528
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to gas-liquid contacting apparatus used primarily as fractionation trays for the separation of volatile chemical compounds in a fractional distillation column.
BACKGROUND OF THE INVENTION
Fractionation trays are widely used in the petrochemical and petroleum refining industries to promote the multistage vapor-liquid contacting performed in fractionation columns. The normal configuration of a fractionation column includes about 10 to 120 individual trays. Normally each tray is the same. The trays are mounted horizontally at uniform vertical distances referred to as the tray spacing of the column. This distance may vary within different parts of the column but is normally considered constant. Vapor generated at the bottom of the column rises through the tray which supports a quantity of liquid. The passage of the vapor through the liquid generates bubbles referred to as froth. The high surface area of the froth helps to quickly establish a compositional equilibrium between the vapor and liquid phases on the tray. The vapor loses less volatile material to the liquid and thus becomes slightly more volatile as it passes upward through each tray. The liquid separates from the froth and carries heavier components downward to the next lower tray. This froth formation and separation is performed on each tray. Trays therefore perform the two functions of contacting the rising vapor with liquid and then allowing the two phases to separate and flow in different directions. When the steps are performed a suitable number of times, the process can lead to highly effective separation of chemical compounds based upon their relative volatility.
RELATED ART
U.S. Pat. No. 3,410,540 illustrates a fractionation tray design comprising alternating decking sections and downcomers typical of a multiple downcomer tray. This tray design employs a rectangular cross-section downcomer. U.S. Pat. No. 5,382,390 illustrates modern developments in multiple downcomer tray design.
U.S. Pat. No. 2,767,967 illustrates a type of dual flow tray referred to in the art as a ripple tray. In this tray the rising vapor and descending liquid both pass through the same openings in the surface of the tray deck. The deck may have many topologies ranging from the sinosoidal curve of FIGS. 3 and 4 to the more planar shape of FIGS. 5 and 6 (see column 3, line 11). The variations in the elevation allow for less liquid depth on higher portions of tray which in turn allows for upward vapor passage, while liquid descends through the tray at points which allow for a greater liquid depth.
U.S. Pat. No. 5,407,605 illustrates fractional distillation column trays having a bed of packing material located below the trays and wetted by liquid exiting the downcomers.
U.S. Pat. No. 5,389,343 describes a fractionation column in which bundles of catalyst media used to promote chemical reactions are hung beneath fractionation trays to promote vapor phase reactions.
An article by G. X. Chen et al. appearing at page 382 of Volume 68 (June 1990) edition of
The Canadian Journal of Chemical Engineering
describes the performance of fractionation trays having layers of stainless steel knitted mesh packing placed on the top surface of the tray. This paper appears related to European Patent application No. 0381388 by the same authors.
A description of various types of packing materials for use in packed columns is provided in an article starting at page 40 of Chemical Engineering, Mar. 5, 1984.
U.S. Pat. No. 4,842,778 illustrates a fractional distillation column containing “random” (dumped) packing, structured packing and support grids.
BRIEF SUMMARY OF THE INVENTION
The subject invention is a high capacity fractionation tray which comprises a relatively thick layer of low surface area, highly vertical “grid” packing resting on the topmost surface of the tray deck or downcomer. The volume above the grid is preferably empty. This results in the tray having an unexpectedly increased vapor capacity. Additional packing material having a higher surface area may rest upon the grid packing to increase the efficiency of the overall tray system.
One embodiment of the invention may be characterized as a vapor-liquid contacting apparatus comprising a vertical enclosed column (
1
) having a circular cross section and an upper first end (
20
) and a lower second end (
21
); a plurality of evenly spaced-apart fractionation trays including a pair of vertically spaced apart fractionation trays (
2
) comprising a lower first and an upper second tray, with the trays being substantially planar and extending horizontally across substantially all of the cross-sectional area of the column (
1
), and with the trays (
2
) having perforations (
15
) evenly distributed across decking sections (
5
) of the tray (
2
), which decking sections are devoid of downcomers (
12
,
6
); and, a layer comprising low surface area structured grid packing (
3
) supported by the first tray (
2
) of said pair of fractionation trays, with the layer of structured grid packing (
3
) extending upward toward the second tray for a distance equal to from about one-tenth to about three-quarters of the vertical distance between the first and second trays. A sizable void volume may be present above the grid packing.
In some embodiments of the present invention a bed of structured or random (dumped) packing material is present on top of the low surface area grid structures, with the packing being wetted by liquid exiting the downcomers of the upper second tray. A further thin layer of the low surface area grid structure may rest upon the random packing.
REFERENCES:
patent: 1748595 (1930-02-01), Chillas et al.
patent: 2767967 (1956-10-01), Hutchinson
patent: 2832578 (1958-04-01), Gilmore
patent: 3410540 (1968-11-01), Bruckert
patent: 4105723 (1978-08-01), Mix
patent: 4304738 (1981-12-01), Nutter
patent: 4556522 (1985-12-01), Wilson
patent: 4627941 (1986-12-01), Bentham
patent: 4820456 (1989-04-01), Kiselev
patent: 4842778 (1989-06-01), Chen et al.
patent: 5244604 (1993-09-01), Miller et al.
patent: 5262094 (1993-11-01), Chuang
patent: 5382390 (1995-01-01), Resetarits et al.
patent: 5389343 (1995-02-01), Gentry
patent: 5407605 (1995-04-01), Resetarits et al.
patent: 0 381 388 (1990-08-01), None
Chen et al., “Performance of Combined Mesh Packing and Sieve Tray in Distillation,”The Canadian Journal of Chemical Engineering, vol. 68, Jun., 1990, pp. 382-386.
Chen, Gilbert K., “Packed column internals,”Chemical Engineering, Mar. 5, 1984, pp. 40-51.
Miller Robert J.
Monkelbaan Daniel R.
Resetarits Michael R.
Greene Jason M.
Simmons David A.
Spears, Jr. John F.
Tolomei John G.
UOP LLC
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