Vapor-liquid contact apparatus

Vapor-liquid contact apparatus includes a plurality of substantially horizontal trays which are vertically spaced in a vessel. Liquid and vapor-liquid mixtures flow horizontally across the trays, over weirs, and vertically through downcomers to subsequent trays. Each tray has a bubble area with apertures which permit ascending vapors to flow into the vapor-liquid mixture supported on the tray. Each downcomer has an apertured bottom wall which is horizontally coextensive with an unapertured downcomer seal area on the tray therebelow. The downcomer seal area and a portion of the apertured bubble area are elevated with respect to a major portion of the tray's upper surface area. The tray has two outboard panels with integral flanges at their edges, and the upstream ends of these integral flanges are supported on a stationary truss in the vessel. To promote deentrainment of vapor from the mixture in the downcomer, a perforated sheet with inclined corrugations is positioned substantially vertically in the downcomer.

BACKGROUND OF THE INVENTION 
This invention relates to liquid contact apparatus used in chemical 
processing, and particularly to such apparatus in which a vessel contains 
a plurality of substantially horizontal trays which support a vapor-liquid 
mixture. In apparatus of this type, liquid is introduced at the upper end 
of the vessel and it flows down from tray-to-tray, via downcomers. The 
trays are apertured to provide bubble areas through which ascending vapors 
can rise to contact liquid and/or vapor-liquid mixtures which are 
supported on and flowing across the respective trays. 
There have been many proposals for improving contact apparatus of this 
type. However, significant features of the apparatus disclosed in this 
specification are believed to represent new approaches to the design and 
construction of such apparatus. 
Chuang et al. U.S. Pat. No. 4,504,426 shows gas-liquid contacting apparatus 
in which downcomers have apertured lower outlet walls. These downcomers, 
however, discharge directly over apertured areas of the deck therebelow. 
Such an arrangement can result in undesirable jetting of liquid down from 
the downcomer apertures through the apertures in the deck therebelow, thus 
bypassing two subsequent trays and reducing the performance of the 
apparatus. 
A downcomer with an apertured outlet wall positioned over an elevated 
downcomer seal area is shown in Bentham U.S. Pat. No. 4,550,000. Bentham 
also has apertures in the elevated downcomer seal area, and this is 
believed to be detrimental from the standpoint of tray performance. 
In U.S. Pat. No. 4,956,127 issued to Binkley et al., FIG. 8 shows a 
downcomer with an apertured outlet wall, but the downcomer seal area is 
provided with gas introducing openings located directly beneath a 
downcomer outlet. Binkley et al. also disclose a channel beam truss which 
directly supports an elevated upstream panel provided with the downcomer 
seal area. However, the channel truss is positioned where it inherently 
obstructs the horizontal flow of gas immediately beneath the 
truss-supported tray. 
SUMMARY OF THE INVENTION 
This invention relates to improvements in vapor-liquid contact apparatus of 
the type comprising a vessel, a plurality of substantially horizontal 
trays mounted in the vessel in vertically spaced relation to support a 
vapor-liquid mixture, and downcomer passages extending down from the 
trays. In a known manner, the downcomer passages are arranged to receive a 
vapor-liquid mixture from one tray and to release liquid onto a subsequent 
tray therebelow. 
one aspect of the invention pertains to such apparatus in which each of 
said trays having a downcomer seal area, an overflow weir, and a bubble 
area which lies between the downcomer seal area and the overflow weir. The 
bubble area has apertures which permit ascending vapors to flow into the 
vapor-liquid mixture on the tray. The downcomer passage has a lower outlet 
end which overlies and is horizontally coextensive with a downcomer seal 
area of the subsequent tray. The novel combination of features in such an 
apparatus are as follows: 
(a) each of the downcomer passages has a bottom wall which is substantially 
horizontal and is provided with apertures for regulating the effective 
head of fluid in the downcomer passage, 
(b) the downcomer seal area is substantially devoid of apertures so as to 
prevent ascending vapors from affecting the flow in a preceding downcomer 
passage of a tray thereabove and to prevent fluid in the preceding 
downcomer passage from weeping through the downcomer seal area; and 
(c) the downcomer seal area and an upstream portion of said bubble area are 
elevated with respect to a major portion of the tray's upper surface area. 
Preferably, the trays are spaced vertically from each other by a distance 
H, and each of said downcomer passages has its lower outlet end between a 
minimum elevation which is at least H/24 higher than the weir of the 
subsequent tray and a maximum elevation which is a distance H/3 above the 
downcomer seal area of the subsequent tray. This elevation of the outlet 
prevents excessive horizontal velocity of fluid where it flows from the 
downcomer seal area to the bubble area of the tray. The downcomer seal 
area and the upstream portion of said bubble area are on an upstream 
panel, and the upstream portion of the bubble area is from 10% to 40% of 
the bubble area of the tray. The main portion of the upstream panel is 
elevated with respect to said arcuate margin portion on the upstream 
panel. Additionally or alternatively, the apparatus can include a shim 
which lies beneath the arcuate margin portion to elevate the upstream 
panel. 
The bottom wall of the downcomer has an arcuate edge and a linear edge, and 
the area occupied by the apertures in the bottom wall of the downcomer is 
greater near the arcuate edge than near the linear edge. 
In another respect, the invention involves a construction in which each 
tray is formed of a plurality of panels including two downstream panels 
which are laterally spaced apart and have downstream portions of the 
bubble area formed in them. These downstream panels each have a horizontal 
deck portion with an edge which has an integral flange extending 
downwardly therefrom. Each integral flange has a lower end provided with a 
horizontal web. The apparatus has a stationary truss which supports the 
upstream ends of said integral flanges. The stationary truss is spaced 
below the horizontal deck portions to provide an open area which permits 
vapors to flow between the truss and the deck portions. 
Preferably, the truss has a web and flanges which extend from the web in a 
substantially horizontally direction which is upstream with respect to the 
tray therebelow so as to capture and laterally disperses part of the 
liquid froth or spray which is moving in a downstream direction on the 
tray therebelow. There is a third downstream panel which has a side margin 
which overlies and is supported by at least one of the downstream panels. 
The third downstream panel having a main portion which includes part of 
said bubble area, and the third downstream panel has its side margin 
elevated with respect to its main portion. 
According to a further feature of the invention, a corrugated sheet is 
positioned vertically in a downcomer passage. The corrugated sheet has 
corrugations which form ridge and recesses, and the corrugated sheet has 
at least one surface which is exposed to and openly faces the vapor-liquid 
mixture in the downcomer passage to promote deentrainment of vapor from 
liquid in the mixture. The corrugations are inclined to position their 
ridges and recesses at an angle to the flow of liquid-vapor mixture in the 
downcomer passage so that the ridges reduce the local velocity of the 
mixture and the recesses provide channels for upward inclined flow of 
vapor which becomes deentrained from the mixture. 
Preferably, the corrugations are inclined at an angle of about 45.degree.. 
However, this angle may range from 20.degree. to 70.degree. from the 
horizontal. The corrugations are arranged in two sets of corrugations 
which extend upwardly and outwardly on the sheet. The corrugated sheets 
can be perforated to permit some pressure equalization across them.

DESCRIPTION OF A PREFERRED EMBODIMENT 
As shown in FIGS. 2, 3, and 5, the complete apparatus includes a vessel 2 
which contains a plurality of substantially horizontal trays 4 for 
supporting a vapor-liquid mixture. Liquid is introduced at the upper end 
of the vessel and it flows down from tray-to-tray where it is contacted by 
ascending vapors which are introduced at the lower end of the vessel. 
The trays are vertically spaced from each other. Each tray has a downcomer 
seal area 6, an overflow weir 8, and a bubble area 10 which lies between 
the downcomer seal area 6 and the overflow weir 8. The downcomer seal area 
is elevated with respect to a major portion of the tray's upper surface 
area. 
The bubble area 10 has apertures represented schematically by plus signs 
("+") 12 which permit ascending vapors to flow into the vapor-liquid 
mixture on the tray. A downcomer wall 14 is attached to and extends down 
from each weir to provide a downcomer passage 16 which carries liquid from 
the downstream end of one tray to the downcomer seal area 6 of the next 
lower tray. The lower outlet end of the downcomer passage 16 overlies and 
is substantially coextensive with the downcomer seal area 6 of the next 
lower tray. 
The downcomer seal area 6 is substantially devoid of any apertures. This 
prevents ascending vapors from affecting the fluid flow in the downcomer 
passage 16 above the downcomer seal area, and it also prevents fluid in 
the downcomer passage from weeping through the downcomer seal area 6. The 
latter characteristic is particularly important because any weepage 
through the downcomer seal area significantly affects performance because 
it permits the fluid to bypass two trays. 
At the lower end of each downcomer passage 16, there is a bottom wall 18 
which is substantially horizontal and is provided with apertures 25 for 
regulating the effective head of fluid in the downcomer passage 16. These 
apertures may have any suitable size and shape. For example, they may be 
square or round holes which each have an area no greater than about one 
square inch. Their total area can be from 10 to 50% of the horizontal area 
at the top of the downcomer 16. By changing the total area of the openings 
in the bottom 18 of the downcomer, it is possible to adjust the head in 
the downcomer to ensure total vapor disengagement from the liquid flowing 
to the next lower tray, thus affecting the overall performance of the 
apparatus. 
As shown in FIG. 4, the area occupied by the openings in the bottom wall 18 
of the downcomer 16 is greater near its arcuate edge 17 than near its 
linear edge 19. The bottom wall 18 has an unapertured segmental area 21 
which is bounded in part by the edge 19. Near the edge 17, it has an 
arcuate apertured area 23 which is perforated with circular holes 25. 
The trays are spaced vertically from each other by a distance M. Each of 
the downcomer passages 16 has its bottom or outlet end 18 between a 
minimum elevation E.sub.mm which is at least M/24 higher than the weir of 
the subsequent tray and a maximum elevation E.sub.max which is a distance 
H/3 above the downcomer seal area of the subsequent tray. This is a higher 
downcomer outlet elevation than is customary in the industry, and it is 
beneficial because it results in a slower flow of liquid from the 
downcomer seal area 6 to the bubble area 10 of the tray. By avoiding 
excessive horizontal fluid velocities in this area, the aeration of the 
liquid is promoted in the upstream portions of the bubble area. 
Details of a typical tray 4 are shown in FIG. 1. It has an upstream panel 
30, two outboard panels 32, and a central panel 34 which is removable to 
provide a manway during installation and maintenance of the apparatus. The 
vessel 2 has an internal support ring which supports the circumferential 
margins of the tray 4. The upstream panel 30 includes an unapertured 
upstream area 38 which constitutes the downcomer seal area, and an 
apertured area 40 which is the upstream portion of the tray's bubble area 
10. The bubble area in panel 30 is from 10% to 40% of the bubble area of 
the tray. Preferably, it is about 25% of the tray's total bubble area. The 
upstream panel 30 of the tray 4 has a flat main horizontal deck portion 42 
and an arcuate margin portion 44. The main horizontal deck portion 42 is 
flat, and it is about one tray thickness higher than the margin portion 
44. The downstream margin portion of the panel 30 overlies the upstream 
margins of the downstream panels 32 and 34. Because the upstream panel 30 
is supported on the downstream panels 32,34 and on the arcuate margin 
portion 44 which rests on the support ring in the vessel, the main portion 
42 of the upstream panel 30 is higher by about one plate thickness than 
the downstream panels 32,34. Arcuate shims can be placed under the arcuate 
margin 44 in order to elevate the main portion 42 of the upstream panel 
30. Chordal shims may be placed under the downstream margin portion of 
panel 30. 
Each of the outboard panels 32 has an arcuate outboard edge 46 and a linear 
inboard edge 48 provided with an integral flange 50 which extends 
downwardly. A horizontal web 52 extends laterally in an outboard direction 
from the lower end of each of the flanges 50. The flanges 50 stiffen their 
respective panels, and they also support the upstream ends of the panels 
32 on a transversely oriented truss 56 which may be of any mechanically 
suitable cross-section. Preferably, the truss 56 has a channel shape with 
a vertical web 58 and two flanges 60 which extend horizontally from the 
web in a downstream direction which is upstream with respect to fluid flow 
on the tray therebelow. Due to this orientation, the truss 56 captures and 
laterally disperses part of the liquid froth or spray which is moving in a 
downstream direction on the tray therebelow. Above the truss 56, between 
the flanges 50, there are open areas 62 through which vapor can flow as it 
travels toward the bubble portion 40 of the upstream panel of the tray 
thereabove. The path of this flow is represented by the arrow 64 in FIG. 
1. The ends of the truss are clamped rigidly to the support ring in the 
vessel. Except for their flange portions, the outboard panels 32 are 
substantially flat, and their upstream margin portions are overlapped by 
the downstream margin portion of the upstream panel 30. 
The central or manway panel 34 has side margin portions 36 which overlie 
the inboard margin portions of the panels 32. The main surface area of the 
central panel is one plate thickness lower than the margin portions 36 so 
it lies in substantially the same horizontal plane as the outboard panels 
32. An upstream margin portion of the central panel 34 lies beneath and is 
bolted to the downstream margin portion of the upstream panel 30. 
The weir/downcomer assembly is fastened to and supports the downstream ends 
of the panels 32,34 and to the vessel 2 to provide a fluid tight seal. 
Since the upstream panel 30 is slightly higher than the central and 
outboard panels 32,34, the liquid head on the upstream panel is less. This 
reduces the head potential so the initial vapor bubbling will occur here. 
This also deters weepage down through the apertures in the upstream panel 
in this area where the liquid has not yet become significantly aerated. 
It is believed that the invention is suited for sieve trays, valve trays, 
bubble cap trays, and trays with trapezoidal apertures such as those shown 
in U.S. Pat. No. 3,463,464 of Aug. 26, 1969. 
A recent improvement to trays of the latter type is shown in FIG. 6. It has 
a longitudinal axis which is parallel to the flow direction indicated by 
arrow 69, and it is tapered in the plane of the deck from a maximum 
dimension transverse to the flow direction at its upstream end to a 
minimum dimension transverse to the flow direction at its downstream end. 
A deflector overlies the aperture, and it includes an upstream portion 70, 
a central portion 72, and a downstream portion 74. Each deflector is 
integral with the deck and is, in vertical projection, substantially 
geometrically identical to its respective aperture. The upstream portion 
70 of the deflector extends at an obtuse angle above the deck at an 
upstream end of the associated aperture, and it lies across the entire 
maximum transverse extent of the aperture so that the entirety of the 
aperture is shielded from liquid which is moving in the flow direction 
toward the aperture. The downstream portion 74 of the deflector extends at 
an obtuse angle above the deck at the downstream end of its aperture, and 
it lies across the entire transverse extent of the downstream end of the 
aperture to prevent vapors from impelling liquid in a downstream 
direction. The central portion 72 of the deflector is supported on the 
deck by the upstream and downstream deflector portions 70, 74. The 
deflector and the adjacent deck define lateral outlet slots 76 which are 
oriented to direct vapor which passes up through the aperture in 
directions which are generally transverse to the flow direction of liquid 
on the deck. Each outlet slot has an area of about 0.25 to 0.35 square 
inches. Each of the outlet slots 76 has an upper edge no longer than about 
0.85 inch, a height which is no greater than 0.35 inch, and a lower edge 
which is no longer than about 2.0 inches. Each aperture, in the plane of 
the tray deck, has a length no greater than 2.0 inches measured along its 
longitudinal axis, an upstream width no greater than about 1.0 inch, and a 
downstream width no greater than 0.75 inch. Preferably, the centers of the 
apertures are spaced apart no more than about 3.0 inches longitudinally of 
the flow direction, and no more than about 2.0 inches transversely of the 
flow direction. The apertures are arranged in longitudinal rows, and the 
apertures in adjacent longitudinal rows are staggered so that an aperture 
in one row has a longitudinal position which is midway between the 
longitudinal positions of two apertures in an adjacent row. 
The two phase mixture of vapor and liquid is in a turbulent state when it 
enters the upper end of a downcomer 16. There is some circular motion as 
indicated by the arrow 78 in FIG. 5. During the residence time of the 
mixture in the downcomer 16, the vapor is deentrained from the liquid. The 
deentrained vapors rise, and the liquid is discharged from the outlet at 
the bottom end of the downcomer. 
Deentrainment in the downcomer is promoted by mounting corrugated sheets 80 
and/or 82 in the downcomer substantially vertically, i.e. within 
15.degree. of a vertical plane. As shown in FIG. 7, each of these sheets 
has corrugations which form ridges 86 and recesses 88. Each sheet has at 
least one exposed surface which openly faces the vapor-liquid mixture in 
the downcomer passage 16. The term "openly faces" means that there is no 
adjacent sheet or wall which contacts the ridges 86 to affect the flow of 
the two phase mixture in the region of the exposed surface of the 
corrugated sheet. 
The sheets 80 and 82 each have one exposed surface. Additionally or 
alternatively, a corrugated sheet may be suspended vertically between and 
spaced from the sheets 80 and 82, and it would have two exposed surfaces. 
The corrugations in the sheets are oriented so that their ridges 86 and 
recesses 88 are inclined. The sheet 80 shown in FIG. 8 is laterally 
symmetrical. It has two mirror image sets of corrugations 90 and 92 which 
each occupy one half of the sheet. The corrugations extend upwardly toward 
opposite outboard or lateral edges 94 and 96 of the sheet, so that the 
deentrained vapors will be released from the channel outlets at the upper 
edge 98 and outboard edges 94 and 96 of the sheet. 
The sheets 80 and 82 can be formed of stainless steel having a thickness of 
0.008 inch, or carbon steel having a thickness of 0.12 inch, or any other 
suitable material. The corrugations are inclined to the horizontal at an 
angle of about 45.degree., although inclinations of 20.degree. to 
70.degree. may be suitable. The corrugations can have a ridge-to-ridge 
distance D of about one inch, and the total thickness ! of the corrugated 
sheets can be about one-half inch. 
The corrugated sheets 80 and 82 may be fabricated from perforated stock to 
permit limited pressure equalization across them. This is thought to 
enhance the deentrainment effect. Preferably, the perforations are holes 
which have diameters of about 1/8 to 1/4 inch, and the hole centers are 
spaced apart by distances of about twice their diameters, set at a 
triangular pitch. Holes of 3/16 inch diameter at 3/8 inch spacing are well 
suited for this purpose. 
The ridges 86 are not vertical, so they reduce the velocity of the two 
phase mixture. The recesses 88 are not horizontal, so they provide the 
channels 100 which agglomerate and shield the vapor bubbles from local 
velocities so that they can rise up in the downcomer. The vapor 
deentrainment phenomenon within the boundaries near the exposed surfaces 
of the sheets is not entirely understood, but the compressibility of vapor 
and the incompressibility of liquid may explain why the vapor rather than 
the liquid agglomerates and flows in the channels of the corrugated sheet. 
Although only one embodiment of the invention has been shown, persons 
skilled in the art will realize that the invention may take many other 
forms. For example, the invention is applicable to multi-pass trays as 
well as the one-pass design disclosed herein; and, the integral flanges 50 
can be provided on inboard as well as outboard panels of the tray. 
Accordingly, it is emphasized that the invention is not limited to the 
disclosed embodiment, and that it embraces modifications, variations, and 
improvements thereto which fall within the spirit of the following claims.