GB2321417A - Vapour-liquid contact apparatus - Google Patents

Abstract

Apparatus has a vessel with horizontal trays 4 to support a vapour-liquid mixture. Each tray has a downcomer seal area 6, overflow weir 8 and bubble area 10. The bubble area has apertures to allow ascending vapour to flow into the vapour-liquid mixture on the tray. A downcomer passage 16 extends down from each weir to the seal area 6 of the tray below. The downcomer passage has a lower outlet end overlying and horizontally coextensive with the seal area 6 of the subsequent tray and also has a bottom wall which is horizontal and has apertures to regulate the effective head of fluid in the passage 16. The wall has arcuate and linear edges and the apertures occupy a greater area near the arcuate edge than near the linear edge. The seal area has no apertures in it's area which is vertically aligned with the apertures in the bottom wall of the downcomer and the seal area and upstream portion of the bubble area are elevated with respect to a major portion of the upper surface area of a tray. Also claimed, is apparatus with a corrugated sheet disposed vertically in a downcomer passage.

Description

VAPOUR-LIQUID CONTACT APtARARU5 The present application ls divided out of British Patent application number 97 00 602.7 which tf itself derived from International application PCT/US95/03431 filed on 17 March 1995 and claiming a priority date af 23 March 1994 from United States patent application 08/216,297.

The present invention relates to vapour-liquid contact apparatus, in which a vessel has a plurality of substantially horizontal trays.

Vapour-liquid contact apparatus are used in chemical processing in which liquid is introduced at the upper end of the vessel, whereafter it flow$ down from tray to tray via downcomers. The trays are apertured to provide bubble areas through which ascending vapours can rise to contact liquid and/or vapour-liquid mixtures which are supported on and flow across the respective trays.

There has been many proposals for improving contact apparatus of this type. For example US 4,504,426 shows gas-liquid contacting apparatus in which downcomers have apertured lower outlet walls. These downcomers 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 appsratus. ' ' A downcsmer with an apertured outlet wall positioned over an elevated downcomer seal area is shown in US 4,550,000. This also shows apertures in the elevated downcomer seal area and this is believed to be detrimental from the standpoint of tray pertormance.

US 4,956,127 shows a downcomer with an apertured outlet wall but in which the downcomer seal area is provided with gas introducing openings located directly beneath a downcomer outlet. A channel beam truss is also disclosed 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 trusssupported tray.

According to a first aspect of the present invention, there is provided a vapour-liquid contact apparatus, comprising a vessel, a plurality of suostantially horizontal trays for supporting a vapourliquid mixture, said trays being mounted in said vessel in vertically spaced relation, each of said trays having a downcomer seal area, an overflow weir and a bubble area which lies between the downcomer seal area and said overflow weir, said bubble area having apertures which permit ascending vapours to flow into the vapour-liquid mixture on the tray, a downcomer passage extending down from each weir for carrying liquid from a tray to the downcomer seal area of a subsequent tray therebelow, said downcomer passage having a lower outlet end which overlies and is horizontally coextensive with said downcomer seal area of the subsequent tray, each of sawd downcomer passages having a bottom wall which is substantially horizontal and is provided with apertures for regulating the effective head of fluid in the downcomer passage, said bottom wall of the downcomer having an arcuate edge and a linear edge, said apertures in the bottom wall of the downcomer occupying a greater area near the arcuate edge than near the linear edge, said downcomer seal area being substantially devoid of apertures in its area which is vertically aligned with said apertures in said bottom wall of the downcomer so as to prevent ascending vapours 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, said downcomer seal area and an upstream portion of said bubble area being elevated with respect to a major portion of the tray's upper surface area According to a second aspect of the present invention, there is provided a vapour-liquid contact apparatus, comprising, a vessel, , a plurality of substantially horizontal trays for supporting a vapourliquid mixture, said trays being mounted in said vessel in vertically spaced relation, a downcomer passage extending down from each tray, said downcomer passages each being arranged to receive a vapour-liquid mixture from one tray and to release liquid into a subsequent tray therebelow, a corrugated sheet positioned substantially vertically in said downcomer passage, said corrugated sheet having corrugations which form ridges and recesses, said corrugated sheets having at least one surface which is exposed to and openly faces the vapourliquid mixture in the downcomer passage to promote de entrainment of vapour from liquid in the mixture, said corrugations being inclined to position their ridges and recesses at an angle to the flow of liquid-vapour mixture in the downcomer passage so that said d ridges reduce local velocity of the mixture and said recesses provide channels for upwardly inclined flow of vapour which becomes de-entrained from the mixture.

In a preferred embodiment, the apparatus according to claim 2, wherein said corrugations are inclined at an angle of about 45 degrees.

Preferably, the corrugations are inclined at an angle of 20 degrees to 70 degrees from the horizontal.

In In a preferred embodiment the corrugations- include two separate corrugations which extend upwardly and outwardly on the sheet.

Figure 1 is a perspective view of one tray constructed according to the invention; Figure 2 is a planned view of a tray according to the invention, mounted in a vessel; Figure 3 is a diagrammatic sectional view of a tray in the vessel, as seen along line 3-3 in Figure 2.

Figure 4 is a view of the bottom wall of a downcomer in an apparatus constructed according to the invent ion; Figure 5 is a diagrammatic sectional view of three trays constructed according to the invention mounted in a vessel; Figure 6 shows a preferred configuration of a tray opening; Figure 7 shows a portion of a corrugated sheet of the type that is mounted in a downcomer according to one feature of the invention; Figure 8 shows a full corrugated sheet which is suited for mounting in a downcomer.

DESCRPTION OF OF A PREFERRED EMBODIMENT As shown in Figs. 2, 3, and 5, the complete apparatus includes a vessel 2 which contains a plurality of subtantially 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 X, and a bubble aria 10 which lies between the downcomer seal area 6 and the overflow weir 8. The downcomer seal area is elevated with respect to a mayor portion of the tray's upper surface area.

The bubble araa 10 has apertures represented schematically by plus signs ("+") 12 which perait ascending vapors to flow into the vapor-liquid mixture on the tray. A downcomer wail 14 is attached to and extends down rrcm each weir to provide a downcomer passage 16 which carries liquid from the downstream end of one tray to the downcomer seal ara 6 of the next lower tray. The lower outlet end of the downcomer passage 16 over lies and is substantially coextsnsive with the downcomer seal area 6 of the next lower try.

The downcomer seal area 6 is substantially devoid of any aperture This prevents ascending vapors from affecting the fluid flaw in the downcomer passage 16 above the downcomer seat 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 ara significantly affects performance because it permits the fluid to bypass two trays.

At the lower end af each downcomer passage 16, there is a bottom wall la 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 a and shape. For example, they may be square or round holes which each have an area no greater than about one square inch (6.45 square centimeters). Their total area can be from 10 to 50% of the horizontal area at the top of the downcomer 15. By changing the total area of the openings in the bottom 15 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 1 is greater near its arcuate edge 17 than near its linear edge 19. The bottom wall 18 18 has an unapertured segmental area 21 which is bounded in part by the edge 19. Near the edge 17, it has an arauat apertured area 23 which is perforated with circular hales 25.

The trays are spaced vertically from each other by a distance H. Each of the downcomer passages l has its bottom or outlet end la between a minimum elevation Emin which is at least H/24 higher than the weir of the subsequent tray and a maximum elevatian Ew,x which is a distance RJz above the downcomer seal area a: 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 araa 10 a 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 l. It has an upstream panel 30, two outboard panel5 32, and a central panel 34 which is removable to provide a manway during installation and maintenance af 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 35 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 lay to 408 of the bubble area of the tray.

Preferably, it is about 25 X 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 rlat, 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. Becous2 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 plato tnic.kriess than the downstream panels 32,34. Arcuate shits can be placed under the arcuate margin 44 in order t3 elevate the main portion 42 of the upstream panel 30. Chordal shims may be placed under the downstream mar portion of panel 30.

Each of the outboard panels 32 has an arcuate outboard edge 46 and a linear inboard edge 43 provided with an integral flange So 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 SO stiffen their respective panels, and they also support the upstream ends of the panels 32 on a transversely oriented truss So which may be of any mechanically suitable cross-section. PreRerabLy, the truss 56 has a channel shape with a vertical web 58 and two flanges GO 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 flaw 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 anway 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 3a.

The weir/downcsmer 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 tha invention is suited for sieve trays, valve trays, bubble cap trays, and trays with trapezoidal apertures such as those shown in U.S.

Patent 3,463,464 of August 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 Z maximum dimension transverse to the flow direction at its upstream end to a minimun 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 rspectjve 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 liens 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 af 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 tha 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 th adjacent deck define lateral outlet slots 76 which are arin8Qd t: direct vapor which passes up through the aperture in directions which are generally transverse to the flsw direction of liquid on the deck.

Each outlet slot has an area ae about 0.25 to o.3S square inches (1.6 to 2.3 square centimeters). Each of the outlet slots 76 has an upper edge no longer than about 0.85 inch (2.2 centimeters), a height which is no greater than 0.35 inch (0.9 centimeter), and a lower edge which is no longer than about 2.0 inches (5.1 centimeters).

Each aperture, in the plane of the tray deck, has a length no greater than 2.0 inches (S.1 centimeters) measured along its longitudinal axis, an upstream width no greater than about 1.0 inch (2.S centimeters), and a downstream width no greater than 0.75 inch (1.9 centimeters). Prefe-ably, the centers of the apertures are spaced apart no more than about 3.0 inches (7.6 centimeters) longitudinally of the flow direction, and no mare than about 2.0 inches (5.1 centimeters) transversely of the flow direction. The apertures ars 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. Tuber 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 discharge from the outlet at the bottsm 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 of a vertical plane. As shown in rig. 7, each of these sheets has corrugations which firm ridges 86 and recesses sa. 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 sleet or wall which contacts the ridges 86 to affect the flow oe 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 ar 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 sheaths are oriented so that their ridges 86 and recesses 88 are inclined. The sheet SO 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 at the sheet.

The sheets 80 and 22 can be formed of stainless steel having a thickness of .008 inch (0.2 mm), or carbon steel having a thickness of .12 inch (3.0 mm), or any other suitable material. The corrugations are inclined to the horizontal at an angle of about 4", although inclinations of 200 to 700 may be suitable. The corrugations can have a ridge-to-ridge distance 0 of about one inch (2.5 centimeters), and the total thickness of the corrugated sheers can be about cne-half inch (1.2 centimeters).

The corrugated sheets SO and 82 may be fabricated from perforated stock to permit limited pressure equalizaticn across them This is thought to enhance the deentrainment effect. creeerably, the perforations axe holes which have diameters of about 1/9 to 1/4 inch (0.3 to 0.6 centimeters), and the hole centers are spaced apart by distances of abcut twice their diameters, set at a triangular pitch Holes of 3/16 inch (0.5 centimeter) diameter at 3/8 inch (1.0 centSmeter) Spacing are well suited for this purpose.

The ridges 56 are not vertical, so they reduce the velocity or 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 at the sheets is not entirely understood, but the compressibility af vapor and the incompressibility of liquid may explain why the vapor rather than the liquid agglemerates 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 taR2 many other forms.

For example, the invention is applicable ta multi-pass trays as well as the cne-pass design disclosed herein; and, the integral flanges so can be provided on inboard as well as outboard panels at the tray. Accordingly, it is emphasized that the invention is not limited to the disclosed embodiment, and that it embraces modifications, variations, and imprsvements thereto which fall within the spirit or the following claims.

Claims (6)

Clalas

1. Vapour-liquid contact apparatus, comprising a a vessel, a plurality of substantially horizontal trays for supporting a vapour-liquid mixture, said trays being mounted in said vessel in vertically spaced relation, each of said trays having a downcomer seal area, an overflow weir and a bubble area which lies between the downcomer seal area and said overflow weir, said bubble area having apertures which permit ascending vapours to flow into the vapour-liquid mixture on the tray, a downcomer passage extending down from each weir for carrying liquid from a tray to the downcomer seal area of a subsequent tray therebelow, said downcomer passage having a lower outlet end which overlies and is horizontally coextensive with said downcomer seal area of the subsequent tray, each of said downcomer passages having a bottom wall which is substantially horizontal and is provided with. apertures for regulating the effective head of fluid in the downcomer passage, said bottom wall of the downcomer having an arcuate edge and a linear edge, said apertures in the bottom wall of the downcomer occupying a greater area near the arcuate edge than near the linear edge, said downcomer seal area being substantially devoid of apertures in its area which is vertically aligned with saii apertures in said bottom wall of the downcomer so as to prevent ascending vapours 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, said downcomer seal area and an upstream portion of said bubble area being elevated with respect to a major portion of the tray's upper surface area.

2. vapour-liquid contact apparatus, comprising, a vessel, a plurality of substantially horizontal trays for supporting a vapour-liquid mixture, said trays being mounted in said vessel in vertically spaced relation, a downcomer passage extending down from each tray, said downcomer passages each being arranged to receive a vapour-liquid mixture from one tray and to release liquid into 2 subsequent tray therebelow, a corrugated sheet positioned substantially vertically in said downcomer passage, said corrugated sheet having corrugations which form ridges and recesses, said corrugated sheets having at least one surface which is exposed to and openly faces the vapour-liquid mixture in the downcomer passage to promote de-entrainment of vapour from liquid in the mixture, - said corrugations being inclined to position their ridges and recesses at an angle to the flow of liquidvapour mixture in the downcomer passage so that said ridges reduce local velocity of the mixture and said recesses provide channels for upwardly inclined flow of vapour which becomes de-entrained from the mixture.

3. Apparatus according to claim 2, wherein said corrugations are inclined at an angle of about 45 degrees.

4. Apparatus according to claim 2, wherein said corrugations are inclined at an angle of 20 degrees to 70 degrees from the horizontal.

5. Apparatus according to claim 2, wherein said corrugations include two separate corrugations which extend upwardly and outwardly on the sheet.

6. Apparatus according to clan 2, wherein said corrugated sheets are perforated to permit some pressure equalisation across them.