COLUMN FOR HEAT AND/OR MASS EXCHANGE BETWEEN TWO FLUIDS COMPRISING A COLLECTION TRAY AND FLUID SEPARATION MEANS

Abstract

The present invention relates to a column for exchanging material and, if appropriate, heat between a gas and a liquid. The column comprises at least one collector tray 1 and a liquid distribution system 5, 6 arranged between two packed beds 7, and gas and liquid separation means 8. The present invention proposes arranging gas and liquid separation means 8 between the collector tray 4 and the liquid distribution means 5, 6.

Claims

1. A column for exchanging material and/or heat between a gas and a liquid comprising at least two packed beds (7), a collector tray (1) arranged between two packed beds (7), and distribution means for distributing said liquid collected by said collector tray from an upper packed bed (7) to a lower packed bed (7), said distribution means being situated below said collector tray (1), characterized in that the column further comprises means (8, 9, 10, 11) for separating said liquid entrained by the gas, said separation means (8, 9, 10, 11) being arranged between said collector tray and said distribution means.

2. The column as claimed in claim 1, in which said means (8, 9, 10, 11) for separating said liquid entrained by the gas comprise at least one impact element, on which said liquid impacts then descends in said column by gravity.

3. The column as claimed in claim 2, in which said impact element is an inclined plate (8).

4. The column as claimed in claim 3, in which said plate (8) is substantially in the shape of an inverted L.

5. The column as claimed in claim 2, in which said impact element comprises at least one chicane.

6. The column as claimed in claim 5, in which said chicane is formed by at least one chevron (9).

7. The column as claimed in claim 2, in which said impact element is formed by a lattice or mat of fibers (10).

8. The column as claimed in claim 2, in which said impact element is formed by a packing.

9. The column as claimed in claimed 2, in which said impact element is substantially in the shape of a ram's horn (11).

10. The column as claimed in claim 1, in which said means (8, 9, 10, 11) for separating said liquid entrained by the gas further comprise at least one cannula for draining said liquid.

11. The column as claimed in claim 1, in which said means (8, 9, 10, 11) for separating said gas and said liquid are arranged in proximity to said distribution means.

12. The column as claimed in claim 1, in which said distribution means comprise at least one vertical supply conduit (5) linked to said collector tray and at least one substantially horizontal pipe (6) linked to said supply conduit, said substantially horizontal pipe (6) comprising at least one orifice and/or one nozzle for the distribution of said liquid.

13. The column as claimed in claim 12, in which said means (8, 9, 10, 11) for separating said liquid entrained by the gas are arranged around said vertical supply conduit (5).

14. The column as claimed in claim 1, in which said means (8, 9, 10, 11) for separating said liquid entrained by the gas occupy substantially from 75 to 98% of the cross section of the column available for the passage of the vapor.

15. The column as claimed in claim 1, in which said collector tray (1) comprises at least one riser (2) for the passage of said gas.

16. A method for gas treatment, acid gas capture, distillation, dehydration or air separation method, comprising processing a gas and a liquid to exchange a material and/or heat between the gas and liquid in a column according to claim 1.

Description

BRIEF DESCRIPTION OF THE FIGURES

[0046] Other features and advantages of the device according to the invention will become apparent on reading the following description of nonlimiting exemplary embodiments, with reference to the figures attached and described hereinbelow.

[0047] FIG. 1, already described, illustrates a diagram of a gas/liquid contactor containing packing, operating in counter-current, and implementing several packed beds with intermediate redistribution of the liquid flow, according to the prior art.

[0048] FIG. 2, already described, illustrates a collector tray with risers according to the prior art.

[0049] FIG. 3, already described, illustrates a collector tray equipped with a distribution system according to the prior art.

[0050] FIG. 4, already described, illustrates the phenomenon of liquid entrainment by the vapor for a collector tray equipped with a distribution system according to the prior art.

[0051] FIG. 5 illustrates a portion of a column according to a first embodiment of the invention.

[0052] FIG. 6 illustrates a portion of a column according to a second embodiment of the invention.

[0053] FIG. 7 illustrates a portion of a column according to a third embodiment of the invention.

[0054] FIG. 8 illustrates a separation means according to an embodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION

[0055] The present invention relates to a column for exchanging material and possibly heat between a gas and a liquid. According to the invention, the exchange column comprises at least two packed beds. The term packed bed is used to denote a packing section which is distributed over a certain height of the column. The packing can be random packing or structured packing. The packing corresponds to a contactor, and makes it possible to bring the liquid and the gas into contact, in order to enable the exchanges of heat and/or of material between the fluids.

[0056] According to the invention, the exchange column comprises at least one liquid redistribution system comprising a collector tray and a liquid distributor. Each liquid redistribution system is arranged between two packed beds, in a zone called inter-bed zone. The collector tray collects the liquid on its upper surface, and allows the passage of the gas through the tray. The passage of the gas through the tray can be notably performed by means of risers, equipped or not equipped with caps. Indeed, upon the passage of a liquid through a packing, the latter tends to build up in certain preferential passage zones, generating radial concentration gradients (over the section of the column) for the gas and liquid phases, thus degrading the efficiency of contact of the liquid and gaseous fluids and the overall efficiency of the column. When a tall contact height is required, it becomes preferable to use a plurality of packed beds and a plurality of liquid collection and redistribution devices. In this case, it is advantageous to redistribute as uniformly as possible the flow of liquid over the surface of the lower packing. It becomes generally preferable to use liquid collectors/redistributors between two packing sections, beyond a packing height of eight meters (height recommended by the FRI). This recommended maximum height can be modified (generally reduced) depending on the operating conditions (floating offshore, packing type, fluid properties, operational conditions, etc.).

[0057] According to the invention, the exchange column comprises liquid distribution means. The liquid distribution means are situated below the collector tray in the inter-bed zone, and are linked to the collector tray for the passage of the liquid. The liquid distribution means make it possible to distribute the liquid from the collector tray over a lower packed bed. Thus, the liquid flows by gravity from an upper packed bed, through the collector tray and distribution means to be distributed over a lower packed bed. The distribution means can be of any known type, notably that illustrated in FIG. 3 (tubular distributor with orifice). Alternatively, the distribution means can be spray (with nozzles) or trough distribution means. The liquid distribution means allow for a good liquid distribution over the lower packed bed, including in floating offshore conditions (at sea), for which the column can be inclined relative to the vertical.

[0058] The column according to the invention further comprises gas and liquid separation means. The gas and liquid separation means are arranged between the collector tray and the liquid distribution means. The gas and liquid separation means make it possible to separate the liquid droplets from the gas which entrains them upward. Thus, the liquid droplet entrainment by the gas is reduced, the backmixing phenomenon is limited and the efficiency of the column is maintained. The arrangement of the separation means between the collector tray and the distribution means makes it possible for the gas passing through the distributor tray (entering and leaving) to be dry, that is to say without liquid droplets entrained by the gas. Dry gas should be understood to be a gas entraining less than 10 ml of liquid droplets per Sm.sup.3 of gas, preferably entraining less than 1 ml and more preferably entraining less than 0.1 ml.

[0059] Preferably, the gas and liquid separation means can be situated in proximity to the distribution means, that is to say just above the distribution means, and away from the collector tray: the gas and liquid separation means are then closer to the distribution means than the collector tray. Thus, the droplet entrainment zone is limited to a low height, and the rest of the inter-bed zone can continue the action of de-entrainment by the force of gravity. The separated liquid is sent back into direct proximity to the lower packed bed, and the re-entrainment phenomenon is lessened. Thus, the droplets are advantageously reinjected into the lower packed bed by gravity.

[0060] According to an embodiment of the invention (that can be combined with the different variants described hereinbelow), the distribution means comprise at least one vertical supply conduit linked to the collector tray, and at least one, preferably a plurality of, substantially horizontal pipe(s) linked to the supply conduit. Each horizontal pipe is equipped with at least one orifice and/or one nozzle for the distribution of the liquid.

[0061] Advantageously, for this embodiment, the gas and liquid separation means can be arranged around the vertical conduit. Furthermore, preferably, the gas and liquid separation means are arranged in proximity to the horizontal pipes of the distribution means. Preferentially, these separation means are situated in the lower half of the fluid distribution zone, and more preferentially in the lower quarter of the distribution zone.

[0062] According to an embodiment of the invention (that can be combined with any one of the embodiments described), the gas and liquid separation means occupy between 15 and 98%, and preferably substantially more than 75%, of the cross section of the column available for the passage of the vapor phase. Thus, the separation of the droplets and of the gas is performed over virtually the entire section of the column, which allows for an efficient separation, which makes it possible to minimize the entrainment of the droplets to the collector tray, and a fortiori to the upper packed bed.

[0063] According to an embodiment of the invention (that can be combined with the embodiments described above), the gas and liquid separation means comprise at least one (preferably a plurality of) impact element(s), on which the liquid droplets impact and build up then descend in the column by gravity. The principle used for this embodiment is the separation by impact of the liquid droplets on a surface (for example metal), a lattice or any other obstacle placed over the passage of the gas flow. This is then called separation by impaction. The impaction principle consists in accumulating the liquid droplets on the surface, then in grouping them together by coalescence, until the force of gravity becomes greater than the entrainment force of the gas. The obstacle (impact element) can have different profiles. The gas flow is directed toward the obstacle, on which the liquid droplets impact to form large drops, and, subsequently, form a liquid film by coalescence. The force of gravity can then compensate the combined effect of the gas entrainment and of the surface tension. The liquid film is then drained from the obstacle (the impact element) to the lower packed bed.

[0064] Advantageously, the impact elements can be metal, or produced in any type of material resistant to the operating conditions of the column. Furthermore, the impact elements can be fixed directly to the column or to the liquid distribution means.

[0065] This embodiment can be combined with distribution means comprising a vertical conduit and horizontal pipes, for example according to the design of FIG. 3. Alternatively (and for all the variant embodiments described hereinbelow), this embodiment can be adapted to distribution means of any type, notably trough or spray means.

[0066] According to a first variant of this embodiment, the impact element can be formed by an inclined plate. The inclined plate can be a corrugated plate, so as to favor the coalescence of liquid drops in order to form a liquid film in the corrugations. Furthermore the plate can, in cross section, be substantially in the shape of an inverted L, that is to say with the head downward (that is to say substantially the shape of a gamma F). This shape favors the impaction of the liquid droplets, and therefore the separation of the gas and of the liquid.

[0067] FIG. 5 illustrates, in a nonlimiting manner, an exemplary embodiment of this first variant. A collector tray 1 is placed in the inter-bed zone between two packed beds 7. As represented, the collector tray 1 comprises a number of risers equipped with caps for the passage of the gas. The distribution means comprise a vertical conduit 5 and a set of horizontal pipes 6 equipped with orifices and/or nozzles. FIG. 5 illustrates only two packed beds and one collector tray, but the column can comprise several packed beds, one such collector tray (with the distribution means and the separation means) being inserted in each inter-bed zone. The gas and liquid separation means comprise a plurality of inclined plates 8 substantially in the shape of an inverted L: the lower part of the L becomes its upper part, and its height is inclined relative to a vertical axis. The inclined plates 8 are arranged just above the horizontal pipes 6 of the distribution means. As represented, the inclined plates 8 are oriented toward the center of the column, so as to allow a uniform distribution of the gas flow. By virtue of the shape and of the arrangement of the inclined plates 8, only the gas GA flows between the inclined plates 8, which makes it possible to limit the entrainment of the droplets, thus favoring the efficiency of the column.

[0068] According to a second variant of this embodiment, the impact element can form chicanes which modify the trajectory and the kinematics of the gas in order to preferentially spray the droplets onto the walls. According to a design of this variant, the chicanes can be produced by impact elements substantially in the shape of a chevron (or inverted V), or any other shape that modifies the trajectory of the gas by sets of chicanes. The gas and liquid separation means can comprise several rows of chevrons, preferably between 1 and 5 rows. The chevrons of one row can be offset relative to the adjacent rows, so as to increase the number of chicanes, which favors the separation of the gas and of the liquid.

[0069] FIG. 6 illustrates, in a nonlimiting manner, an exemplary embodiment of this second variant. A collector tray 1 is placed in the inter-bed zone between two packed beds 7. As represented, the collector tray 1 comprises a number of risers equipped with caps for the passage of the gas. The distribution means comprise a vertical conduit 5 and a set of horizontal pipes 6 equipped with orifices and/or nozzles. FIG. 6 illustrates only two packed beds and one collector tray, but the column can comprise several packed beds, one such collector tray (with the distribution means and the separation means) being inserted in each inter-bed zone. The gas and liquid separation means comprise, by way of example and in a nonlimiting manner, three rows of chevrons 9. For this configuration, the arrangement of the chevrons 9 of the central row is offset relative to the arrangement of the chevrons 9 of the first and third rows. The rows of chevrons 9 are arranged just above the horizontal pipes 6 of the distribution means. By virtue of the shape (inverted V) and of the arrangement of the chevrons 9, only the gas GA passes through this arrangement of chevrons 9, whereas the liquid LI is redirected toward the lower packed bed 7, which makes it possible to limit the entrainment of the liquid droplets, thus favoring the efficiency of the column.

[0070] According to a third variant of this embodiment, the impact element can be formed by a lattice, the lattice being able to be compacted in a volume also called mat. The lattice and/or the mat can be formed by a mesh, notably of metal. The liquid droplets then impact on the lattice, to be separated from the gas.

[0071] FIG. 7 illustrates, in a nonlimiting manner, an exemplary embodiment of this third variant. A collector tray 1 is placed in the inter-bed zone between two packed beds 7. As represented, the collector tray 1 comprises a number of risers equipped with caps for the passage of the gas. The distribution means comprise a vertical conduit 5 and a set of horizontal pipes 6 equipped with orifices and/or nozzles. FIG. 7 illustrates only two packed beds and one collector tray, but the column can comprise several packed beds, one such collector tray (with the distribution means and the separation means) being inserted in each inter-bed zone. The gas and liquid separation means comprise a mat of fibers 10. The lattice (or mat of fibers) 10 is placed just above the horizontal pipes 6 of the distribution means. By virtue of the shape and of the arrangement of the lattice 10, only the gas GA passes through this lattice 10, whereas the liquid LI is redirected toward the lower packed bed 7, which makes it possible to limit the entrainment of the liquid droplets, thus favoring the efficiency of the column.

[0072] According to a fourth variant of this embodiment, the impact element can be formed by a volume of packing. The packing can be a random packing or a structured packing. Preferably, the packing type used as gas and liquid separation means can be identical to the type of packing used in the packed beds of the column. The liquid droplets then impact on the packing to be separated from the gas.

[0073] An exemplary design of this fourth variant can consist in taking the configuration of FIG. 7 and replacing the lattice 10 with a packing.

[0074] According to a fifth variant of this embodiment, the impact element can be substantially in the shape of a ram's horn (called vapor horn). This type of impact element makes it possible to both limit the liquid entrainment and to reorganize the vapor flow.

[0075] FIG. 8 illustrates an exemplary, nonlimiting embodiment of an impact element 11 substantially in the shape of a ram's horn.

[0076] Advantageously, and for all the variant embodiments described previously, the gas and liquid separation means can comprise cannulas to facilitate the draining of the liquid droplets to the lower packed bed, without contact with the gas flow.

[0077] Different types of separation means (for example several impact elements) can be combined to optimize the separation of the gas and of the liquid.

[0078] The column according to the invention is advantageously an amine-based washing column but it is suitable for all types of solvents used in absorption.

[0079] The column according to the invention is suitable for the counter-current flows.

[0080] The column according to the invention can be used in gas treatment, CO.sub.2 capture, liquid product distillation, dehydration, air separation or heat exchange methods. The column according to the invention can be used for floating offshore or on-land applications.

[0081] Furthermore, the invention can more particularly relate to floating barges or offshore platforms, for example of FPSO (floating production, storage and offloading) type, or of the FLNG (floating liquefied natural gas) type. On the floating barges, distillation columns and/or dehydration columns using this device can also be installed.