Liquid-liquid extraction column with variable weir cross section

Abstract

Liquid-liquid extraction column (1) comprising feed injection (2), washing (3) and backwash (4) points, two draw-off points (5, 6), trays (Pi) arranged along the column and defining 2 to 30 zones each comprising at least two trays, the n zones comprising: at least one extraction zone Zi comprising the zones from Z1 to Zx, x being greater than or equal to 1, and at least one backwash zone comprising the zones from Zx+1 to Zn, n being greater than x; in which the trays of the same zone have the same surface area of ​​the cross-sections (S) of the weirs (11, 12); in which when x > 1, said surface area in the zones Zi increases when i increases; and when x = 1, said surface area in the at least one backwash zone is less than said surface area in the zone Z1. Figure 4 to be published

Description

Title of the invention: Liquid-liquid extraction column with variable weir cross-section Technical field

[0001] The field of the invention relates to a column (extractor) for the liquid-liquid separation of hydrocarbon compounds, such as aromatic compounds (eg A6-A11) originating from extended hydrocarbon cuts (eg C6-C11 cut, such as originating from a catalytic cracking unit (FCC Fluid Catalytic Cracking according to English terminology). Prior art

[0002] A liquid-liquid extraction operation is a key building block of processes performing the separation of hydrocarbon cuts, such as the separation of a mixture of aromatics and non-aromatics. The operating principle is based on the differences in solubility of the compounds of a homogeneous liquid feed in a suitable solvent (e.g. aprotic and polar solvent, such as Sulfolane or DMSO). The addition of a partially miscible solvent to the feed causes the appearance of a second phase to which a portion of the compounds (e.g. aromatic compounds), the most soluble constituents, are preferentially transferred.

[0003] Typically, the liquid-liquid extraction technology uses a liquid-liquid separation column comprising a plurality of perforated trays and equipped with one or more overflows per tray depending on the targeted capacities (we speak of a 1 or 2-pass tray or multi-pass beyond 3 overflows).

[0004] The design rules for a conventional liquid-liquid extraction column consider a reference tray sized on the maximum flow rates of each phase and their physicochemical properties. This design is then implemented for the entire column by stacking a plurality of trays, the trays thus all being substantially identical.

[0005] The applicant has identified, however, that the operation of a liquid-liquid extraction column can generate great variability, depending in particular on - the flow rate of each of the phases along the column - this phenomenon is linked, on the one hand, to the transfer of matter from the solutes of the load to the solvent and, on the other hand, to the possibility of modulating the backwash flow rate according to the nature of the load and the specifications targeted; and - physicochemical properties and in particular the interfacial tension between the charge and the solvent linked to the progressive enrichment in compounds extracted from the charge towards the solvent.

[0006] The object of the present invention is to remedy the deficiencies mentioned above. Summary of the invention

[0007] In the context described above, a first object of the present description is to propose a liquid-liquid extraction column allowing: - to maintain a range between 5% and 20% of the average volume fraction of dispersed phase (i.e., solvent / heavy phase) in a compartment (i.e., area comprising a perforated tray and an adjacent inter-tray space); - non-entrainment of dispersed phase droplets in the spillways by the continuous phase (i.e., load / light phase) in order to limit axial mixing of the dispersed phase; - a coalesced layer height of the dispersed phase on each tray sufficient to prevent the passage of the continuous phase through the perforated tray (and force the exclusive passage of the continuous phase into the weirs); - a suitable continuous phase transverse velocity, which does not disturb the flow of the dispersed phase.

[0008] Surprisingly, the applicant has identified that particular characteristics of perforated trays, such as the cross-section (surface) of the weirs, make it possible to control the hydrodynamics along the entire length of the column by limiting axial mixing. This technical solution makes it possible to maintain satisfactory material transfer efficiency on each tray.

[0009] According to a first aspect, the aforementioned objects, as well as other advantages, are obtained by a liquid-liquid extraction column, comprising the following elements: - a first injection point of a first phase arranged at an intermediate position between the top and the bottom of the column; - a second injection point for a second phase and a third injection point for a backwash liquid, one (of the second and third injection points) being arranged at the top of the column and the other being arranged at the bottom of the column; - a first point for drawing off an extract and a second point for drawing off a raffinate, one (of the first and second drawing off points) being arranged at the bottom of the column and the other being arranged at the top of the column; - a plurality of trays arranged from the top of the column to the bottom of the column and defining n zones, each zone comprising at least two trays, n being between 2 and 30, preferably between 3 and 30; in which the n zones include: - at least one extraction zone Z comprised between a zone (e.g. column head) Z i comprising the second injection point of the second phase, and a feed zone Zx comprising the first injection point of the first phase, x being greater than or equal to 1 (preferably x is greater than 1); and - at least one backwash zone between a zone Zx+i and a zone (eg column bottom) Zn comprising the third injection point of the backwash liquid, n being greater than x; in which the trays of the same zone have substantially the same spillway cross-sectional area; and in which: - when x is greater than 1, the spillway cross-sectional area of ​​the zones Z increases as the value i increases; and - when x is equal to 1, the spillway cross-sectional area of ​​the at least one backwash zone is less than the spillway cross-sectional area of ​​zone Zh

[0010] According to one or more embodiments, n is between 3 and 30, and x is greater than 1.

[0011] According to one or more embodiments, the liquid-liquid extraction column, includes the following elements: - a first injection point of a first phase arranged at an intermediate position between the top and the bottom of the column; - a second injection point for a second phase located at the head of the column; - a third injection point for a backwash liquid placed at the bottom of the column; - a first point of withdrawal of an extract placed at the bottom of the column; - a second raffinate withdrawal point located at the head of the column; - a plurality of trays arranged from the top of the column to the bottom of the column and defining n zones, each zone comprising at least two trays, n being between 3 and 30; in which the n zones include: - a plurality of extraction zones Z comprised between a column head zone Z i comprising the second injection point of the second phase, and a feed zone Zx comprising the first injection point of the first phase, x being greater than 1; and - at least one backwash zone between a zone Zx+[ and a column bottom zone Zn comprising the third injection point of the backwash liquid, n being greater than x; in which the trays of the same zone have substantially the same spillway cross-sectional area; and in which the cross-sectional area of ​​the spillways of zones Zj increases as the value i increases.

[0012] According to one or more embodiments, in the extraction zones Zj or i varies from 1 to x (i.e., x greater than 1), the ratio between the surface area of ​​the cross-section of a spillway of a zone Z on the surface area of ​​the cross-section of a spillway of a zone Zi+i, is between 0.50 and 0.90.

[0013] According to one or more embodiments, in the extraction zones Zj or i varies from 1 to x (i.e., x greater than 1), the ratio between the surface area of ​​the cross-section of a spillway of a zone Z on the surface area of ​​the cross-section of a spillway of a zone Zi+i, is between 0.60 and 0.80.

[0014] According to one or more embodiments, in the extraction zones Zj or i varies from 1 to x (i.e., x greater than 1), the ratio between the surface area of ​​the cross-section of a spillway of a zone Z on the surface area of ​​the cross-section of a spillway of a zone Zi+i, is between 0.60 and 0.75.

[0015] According to one or more embodiments, when x is equal to 1, the ratio between the surface area of ​​the cross-sections of the spillways of the at least one backwash zone on the surface area of ​​the cross-sections of the spillways of zone Zb is between 0.50 and 0.95.

[0016] According to one or more embodiments, the at least one backwash zone is a plurality of zones, from a zone Zx+i to the zone (eg column bottom) Zn, and in which the surface area of ​​the cross-sections of the spillways increases, is constant, or decreases from the zone Zx+i to the zone Zn.

[0017] According to one or more embodiments, the at least one backwash zone is a plurality of zones subdivided into: - a plurality of zones Zj comprised between zone Zx+[ and a zone Zy, y being greater than x+1; and - a plurality of zones Zk between the zone Zy+i and the zone (eg column bottom) Zn, and - in zones Zj where j varies from x+1 to y, the surface area of ​​the cross-sections of the spillways increases, is constant, or decreases when the value j increases; and / or - in zones Zk where k varies from y+1 to n, the surface area of ​​the cross-sections of the spillways increases, is constant, or decreases when the value k increases.

[0018] According to one or more embodiments, in the zones Zj where j varies from x+1 to y, the ratio between the surface area of ​​the cross-section of a spillway of a zone Zj to the surface area of ​​the cross-section of a spillway of a zone Zj+i, is between 0.50 and 0.95.

[0019] According to one or more embodiments, in the zones Zj where j varies from x+1 to y, the ratio between the surface area of ​​the cross-section of a spillway of a zone Zj to the surface area of ​​the cross-section of a spillway of a zone Zj+b is between 1.05 and 2.0.

[0020] According to one or more embodiments, in the zones Zk where k varies from y+1 to n, the ratio between the surface area of ​​the cross-section of a spillway of a zone Zk to the surface area of ​​the cross-section of a spillway of a zone Zk+b is between 0.50 and 0.95.

[0021] According to one or more embodiments, in the zones Zk where k varies from y+1 to n, the ratio between the surface area of ​​the cross-section of a spillway of a zone Zk to the surface area of ​​the cross-section of a spillway of a zone Zk+b is between 1.05 and 2.0.

[0022] According to one or more embodiments, the number of zones Z is between 2 and 10 and / or the number of backwash zones is between 1 and 10.

[0023] According to one or more embodiments, the number of zones Zj is between 2 and 10 and / or the number of zones Zk is between 2 and 10.

[0024] According to one or more embodiments, the cross-sectional area of ​​a spillway of the backwash zone Zx+[ is less than, equal to or greater than the cross-sectional area of ​​a spillway of the extraction zone Zx.

[0025] According to one or more embodiments, the cross-sectional area of ​​a spillway of the backwash zone Zx+i is less than the cross-sectional area of ​​a spillway of the extraction zone Zx.

[0026] According to one or more embodiments, the cross-sectional area of ​​each spillway is between 1% and 25%, preferably between 2% and 10%, very preferably between 3% and 6% of the total cross-sectional area of ​​the extraction column.

[0027] Embodiments of the liquid-liquid extraction column according to the first aspect as well as other characteristics and advantages will appear on reading the description which follows, given solely for illustrative and non-limiting purposes, and with reference to the following drawings. List of figures

[0028] [Fig.l] schematically shows a sectional view of a liquid-liquid extraction column according to the present invention.

[0029] [Fig.2] schematically shows a sectional view of the flow of the dispersed phase and the continuous phase in a liquid-liquid extraction column according to the present invention.

[0030] [Fig. 3] schematically shows a sectional view of a liquid-liquid extraction column according to the present invention defined by a plurality of zones Z between the column head zone 1 and the feed zone Zx, a plurality of Zone Zj between the zone Zx+i and a zone Zy, and a plurality of zones Zk between the zone Zy+i and the column bottom zone Zn.

[0031] [Fig.4] is a graph showing the evolution of the axial weir velocity of the continuous phase along a liquid-liquid extraction column according to the present invention, in which the cross-section of the weirs is variable.

[0032] [Fig.5] is a graph showing the evolution of the axial weir velocity of the continuous phase along a reference liquid-liquid extraction column, in which the cross-section of the weirs is constant. Description of the embodiments

[0033] Embodiments of the invention will now be described in detail. In the following detailed description, numerous specific details are set forth in order to provide a more thorough understanding of the invention. However, it will be apparent to those skilled in the art that the invention may be practiced without these specific details. In other instances, well-known features have not been described in detail to avoid unnecessarily complicating the description.

[0034] In the present description, the term "comprise" is synonymous with (means the same as) "include" and "contain", and is inclusive or open and does not exclude other elements not recited. It is understood that the term "comprise" includes the exclusive and closed term "consist". Furthermore, in the present description, the term "substantially" corresponds to an approximation of ± 10%, preferably ± 5%, very preferably ± 2%, of a reference value such as a distance, a speed, a flow rate, a compound content, a temperature, a pressure, etc.

[0035] With reference to [Fig.l], a liquid-liquid extraction column 1 comprises the following elements: - a first injection point of a first phase 2 (or liquid to be separated), such as a feedstock (eg a mixture of aromatic and non-aromatic C6-C11 compounds), arranged at an intermediate position between the top and the bottom of column 1; - a second injection point for a second phase 3 (or separation liquid), such as a solvent (e.g. Sulfolane), placed at the top of column 1; - a third injection point for a backwash liquid 4, such as a recycle (eg a mixture comprising at least 50% by weight of light compounds, (i.e., C5-C8 compounds, preferably C5-C6), arranged at the bottom of column 1; - a first point of withdrawal of an extract 5 (in liquid phase), such as a solvent enriched in extracted compounds (eg aromatic compounds), placed at the bottom of column 1; and - a second point of withdrawal of a raffinate 6 (in liquid phase), such as a feed depleted in extracted compounds, placed at the top of column 1.

[0036] Furthermore, in order to increase the yield and purity, two distinct operating zones are defined opposite the injection point of the liquid to be separated 2: - an extraction sector 7, extending substantially from the first injection point of the first phase 2 to substantially the second injection point of the second phase 3, makes it possible in particular to extract compounds (e.g. aromatics) from the liquid to be separated 2 by contact with the separation liquid 3 in counter-current (so-called yield zone), and - a backwash sector 8 (or backwash according to the English terminology), adjacent to the extraction sector 7 and extending substantially up to the third injection point of the backwash liquid 4, makes it possible in particular to back-extract unwanted compounds (e.g. heavy non-aromatics) contained in the extract 5 by the backwash liquid 4 in order to guarantee a high level of purity.

[0037] Concretely, with reference to [Fig. 1], the separation liquid leaves column 1, carrying with it compounds of interest to be separated (e.g. aromatics) to form extract 5. The extract may also contain undesired compounds (e.g. light non-aromatics, such as C6-C7) which may be separated downstream (e.g. by distillation and / or stripping). Advantageously, extract 5 does not contain (or very few) undesired compounds that are difficult to separate (e.g. heavier non-aromatics, such as C8+), which are separated from the extract in the backwash sector 8. With reference to [Fig. 1], separation liquid 3 is heavier than liquid to be separated 2 and is injected at the top of column 1, while backwash liquid 4 is injected at the bottom of column 1.It is understood that the present invention also relates to liquid-liquid extraction columns, in which the separation liquid is lighter than the liquid to be separated 2, the injection point of the separation liquid 3 is at the bottom of column 1 and the injection point of the backwash liquid 4 is at the top of column 1.

[0038] With reference to [Fig.2], a two-pass liquid-liquid extraction column 1 comprises n perforated trays P, i being between 1 and n. Each perforated tray P; is arranged so that the dispersed phase (i.e., the separation liquid 3 heavier than the liquid to be separated 2) flows through the holes 9 of the perforated tray P, the droplets of the dispersed phase recoalescing on the following perforated tray Pi+i to form a liquid volume preventing the passage of the continuous phase (i.e., the liquid to be separated 2 lighter than the separation liquid 3) through the perforated tray Pi+i. The liquid to be separated 2 circulates counter-current to the separation liquid 3, i.e., from bottom to top through the central overflows 11 and peripheral overflows 12 of cross-section Sc and SP, respectively, and transversely in an inter-plate space 10 of height H. With reference to [Fig.2], the heavy phase is the phase dispersed and the light phase is the continuous phase. It is understood that a liquid-liquid extraction column 1 may comprise perforated trays adapted so that the dispersed phase is the light phase and the continuous phase is the heavy phase.

[0039] According to one or more embodiments, the perforated trays P; are trays with 1 pass (eg one type of spillway) or 2 passes (eg two types of spillways) or multi-pass.

[0040] The applicant has identified that the operation of a liquid-liquid extraction column can generate significant variations in flow rate and physicochemical properties of the phases circulating in the column, and that the use of different trays depending on their position in the column can lead to guaranteeing a homogeneous efficiency of the column unlike the prior art.

[0041] According to the invention, with reference to [Fig.3], a liquid-liquid extraction column 1 is further defined by: - at least one extraction zone Z;, and preferably a plurality of extraction zones Z;, defining the extraction sector 7, ie, the extraction zone or zones Zi are comprised between the column head zone Zi comprising the second injection point of the second phase 3, and the feed zone Zx comprising the first injection point of the first phase 2, x being greater than or equal to 1, preferably x being greater than 1; and - at least one backwash zone defining the backwash sector 8, i.e., the backwash zone(s) is or are comprised between the zone Zx+[ and the column bottom zone Zn comprising the third injection point of the backwash liquid 4, n being greater than x.

[0042] According to the invention, each extraction and backwash zone comprises at least two plates, each extraction and backwash zone defining the structural characteristics of the spillways present in said extraction and backwash zones. Thus, according to the invention, the plates P; of the same extraction or backwash zone have substantially the same surface area of ​​the cross-sections S of the spillways (central 11 and / or peripheral 12).

[0043] According to one or more embodiments, with reference to [Fig. 3], the at least one backwash zone is a plurality of zones, said plurality of zones starting from the zone Zx+i to the column bottom zone Zn.

[0044] According to one or more embodiments, with reference to [Fig. 3], the at least one backwash zone is a plurality of zones subdivided into: - a plurality of zones Zj comprised between zone Zx+1 and a zone Zy, y being greater than x+1; and - a plurality of zones Zk between zone Zy+1 and the column bottom zone Zn.

[0045] Advantageously, the number of zones Z, Zj and Zk can be defined with regard to the variability of flow rate and the physicochemical properties of the phase passing through said zones Z, Zj and Zk.

[0046] According to one or more embodiments, the total number n of zones is between 2 and 30, preferably between 3 and 30, very preferably between 4 and 24, such as between 4 and 18, in particular between 4 and 8.

[0047] In the present description, i, j, k, x, y and n are natural integers.

[0048] The number of extraction zones Z can be defined with respect to the phase which presents the most flow rate variability in the column. According to one or more embodiments, the number of zones Z (number of zones Zi to Zx) is between 1 and 10, preferably between 2 and 10, very preferably between 2 and 6, such as between 2 and 4.

[0049] The number of backwash zones can be defined with respect to the phase which has the most flow rate variability in the column. According to one or more embodiments, the number of backwash zones (number of zones Zx+[ to Zn) is between 1 and 10, preferably between 1 and 6, very preferably between 1 and 4. According to one or more embodiments, the number of backwash zones (number of zones Zx+[ to Zn) is greater than or equal to 2.

[0050] The number of zones Zj can be defined with respect to the phase which presents the most flow rate variability in the column. According to one or more embodiments, the number of zones Zj (number of zones Zx+[ to Zy) is between 2 and 10, preferably between 2 and 6, very preferably between 2 and 4.

[0051] The number of zones Zk can be defined with respect to the phase which presents the most flow rate variability in the column. According to one or more embodiments, the number of zones Zk (number of zones Zy+i to Zn) is between 2 and 10, preferably between 2 and 6, very preferably between 2 and 4.

[0052] According to one or more embodiments, the number of trays per zone Z, Zj and Zk can be determined by the number of actual stages required for the separation divided by the number of zones Z, Zj and Zk.

[0053] Control of the variation of flow rate of the continuous phase by optimized design of the cross section of the spillways

[0054] Advantageously, the liquid-liquid extraction column 1 according to the invention comprises central weirs 11 with variable cross-section and / or peripheral weirs 12 with variable cross-section so that the axial velocity (parallel to the central axis Z of the column) of the continuous phase remains substantially constant in the column. Indeed, due to the fluctuation of the flow rate of the continuous phase during passage through the column, the variation of the cross-sections S of the central and peripheral weirs (11 and 12) allows a more homogeneous distribution of the continuous phase in the weirs. By default, the weirs are sized for the highest continuous phase flow rate so as to minimize the entrainment of fine dispersed phase droplets in the upper compartment. As soon as flow fluctuations appear in the column, the velocity in the weirs can decrease significantly and generate continuous phase recirculations between the compartments through the weirs. It is desirable to limit this phenomenon so as not to generate axial mixing, which is unfavorable for the efficiency of the extraction column.

[0055] Specifically, in order to maintain a substantially constant velocity of the continuous phase in the overflows, the liquid-liquid extraction column 1 according to the invention is divided into: - x extraction zones Z, and - nx backwash zones.

[0056] According to one or more embodiments, the backwash zones are divided into:

[0057] - Y zones Zj arranged from zone Zx+[ adjacent to supply zone Zx, up to a zone Zy, and - N zones Zk including zones Zy+i to Zn.

[0058] According to the invention, when x is equal to 1, the surface area of ​​the cross-sections S of the spillways (central 11 and / or peripheral 12) of the at least one backwash zone (eg zone Z2) is less than the surface area of ​​the cross-sections S of the spillways (central 11 and / or peripheral 12) of the zone Zb. According to one or more embodiments, when x is equal to 1, the ratio between the surface area of ​​the cross-sections S of the spillways (central 11 and / or peripheral 12) of the at least one backwash zone (eg zone Z2) on the surface area of ​​the cross-sections S of the spillways (central 11 and / or peripheral 12) of the zone Zb is between 0.50 and 0.95, preferably between 0.60 and 0.90, very preferably between 0.65 and 0.85.

[0059] According to the invention, when x is greater than 1, in the extraction zones Z or i varies from 1 to x, ie, in the extraction sector 7, the surface area of ​​the cross-sections S of the spillways (central 11 and / or peripheral 12) increases when the value i increases. According to one or more embodiments, in the extraction zones Z or i varies from 1 to x, the ratio between the surface area of ​​the cross-section S of a spillway (central 11 or peripheral 12) of a zone Z; on the surface area of ​​the cross-section S of a spillway (central 11 or peripheral 12) of a zone Zi+b is between 0.50 and 0.90, preferably between 0.60 and 0.80, very preferably between 0.60 and 0.75.

[0060] According to one or more embodiments, the at least one backwash zone comprises a plurality of zones, i.e., from zone Zx+[ to column bottom zone Zn, and the surface area of ​​the cross-sections S of the spillways (central 11 and / or peripheral 12) increases from zone Zx+[ to column bottom zone Zn.

[0061] According to one or more embodiments, the at least one backwash zone comprises a plurality of zones, i.e., from zone Zx+i to column bottom zone Zn, and the surface area of ​​the cross-sections S of the spillways (central 11 and / or peripheral 12) is constant from zone Zx+i to column bottom zone Zn.

[0062] According to one or more embodiments, the at least one backwash zone comprises a plurality of zones, i.e., from zone Zx+[ to column bottom zone Zn, and the surface area of ​​the cross-sections S of the overflows (central 11 and / or peripheral 12) decreases from zone Zx+[ to column bottom zone Zn.

[0063] According to one or more embodiments, in the zones Zj where j varies from x+1 to y (in the backwash zone 8), the surface area of ​​the cross-sections S of the spillways (central 11 and / or peripheral 12) increases when the value j increases. According to one or more embodiments, in the zones Zj where j varies from x+1 to y, the ratio between the surface area of ​​the cross-section S of a spillway (central 11 and / or peripheral 12) of a zone Zj on the surface area of ​​the cross-section S of a spillway (central 11 and / or peripheral 12) of a zone Zj+i, is between 0.50 and 0.95, preferably between 0.60 and 0.95, very preferably between 0.65 and 0.95.

[0064] According to one or more embodiments, in the zones Zj where j varies from x+1 to y (in the backwash zone 8), the surface area of ​​the cross-sections S of the spillways (central 11 and / or peripheral 12) is constant.

[0065] According to one or more embodiments, in the zones Zj where j varies from x+1 to y (in the backwash zone 8), the surface area of ​​the cross-sections S of the spillways (central 11 and / or peripheral 12) decreases when the value j increases. According to one or more embodiments, in the zones Zj where j varies from x+1 to y, the ratio between the surface area of ​​the cross-section S of a spillway (central 11 and / or peripheral 12) of a zone Zj on the surface area of ​​the cross-section S of a spillway (central 11 and / or peripheral 12) of a zone Zj+i, is between 1.05 and 2.0, preferably between 1.05 and 1.7, very preferably between 1.05 and 1.55.

[0066] According to one or more embodiments, in the zones Zk where k varies from y+1 to n (in the backwash zone 8), the surface area of ​​the cross-sections S of the spillways (central 11 and / or peripheral 12) increases when the value k increases. According to one or more embodiments, in the zones Zk where k varies from y+1 to n, the ratio between the surface area of ​​the cross-section S of a spillway (central 11 and / or peripheral 12) of a zone Zk on the surface area of ​​the cross-section S of a spillway (central 11 and / or peripheral 12) of a zone Zk+[, is between 0.50 and 0.95, preferably between 0.60 and 0.95, very preferably between 0.65 and 0.95.

[0067] According to one or more embodiments, in the zones Zk where k varies from y+1 to n (in the backwash zone 8), the surface area of ​​the cross-sections S of the spillways (central 11 and / or peripheral 12) is constant.

[0068] According to one or more embodiments, in the zones Zk where k varies from y+1 to n (in the backwash zone 8), the surface area of ​​the cross-sections S of the spillways (central 11 and / or peripheral 12) decreases when the value k increases. According to one or more embodiments, in the zones Zk where k varies from y+1 to n, the ratio between the surface area of ​​the cross-section S of a spillway (central 11 and / or peripheral 12) of a zone Zk on the surface area of ​​the cross-section S of a spillway (central 11 and / or peripheral 12) of a zone Zk+[, is between 1.05 and 2.0, preferably between 1.05 and 1.7, very preferably between 1.05 and 1.55.

[0069] According to one or more embodiments, in the zones Zj where j varies from x+1 to y, the surface area of ​​the cross-sections S of the spillways (central 11 and / or peripheral 12) decreases when the value j increases; and in the zones Zk where k varies from y+1 to n, the surface area of ​​the cross-sections S of the spillways (central 11 and / or peripheral 12) increases when the value k increases.

[0070] According to one or more embodiments, in the zones Zj where j varies from x+1 to y, the surface area of ​​the cross-sections S of the spillways (central 11 and / or peripheral 12) increases when the value j increases; and in the zones Zk where k varies from y+1 to n, the surface area of ​​the cross-sections S of the spillways (central 11 and / or peripheral 12) decreases when the value k increases.

[0071] According to one or more embodiments, the surface area of ​​the cross-section S of a spillway (central 11 and / or peripheral 12) of the backwash zone Zx+[ is less than, equal to or greater than the surface area of ​​the cross-section S of a spillway (central 11 and / or peripheral 12) of the extraction zone Zx. According to one or more embodiments, the surface area of ​​the cross-section S of a spillway (central 11 and / or peripheral 12) of the backwash zone Zx+[ is less than the surface area of ​​the cross-section S of a spillway (central 11 and / or peripheral 12) of the extraction zone Zx. According to one or more embodiments, the ratio between the cross-sectional area of ​​a spillway of zone Zx+[ to the cross-sectional area of ​​a spillway of zone Zx, is between 0.50 and 0.95, preferably between 0.60 and 0.90, very preferably between 0.65 and 0.85.

[0072] According to one or more embodiments, the surface area of ​​the cross-section S of a spillway (central 11 and / or peripheral 12) is between 1% and 25%, preferably between 2% and 10%, very preferably between 3% and 6% of the total surface area of ​​the cross-section of the extraction column (1). Examples

[0073] Example 1: Liquid-liquid extraction column with variable weir cross-section

[0074] This example aims to describe the effect of adjusting the section surface transverse of the spillways on the homogeneity of the axial velocities of the continuous phase.

[0075] The column has a diameter of 2.9 m and comprises a succession of 108 perforated trays. The feed is injected into intermediate tray No. 47. The heavy solvent is injected at the top of the column into tray 1. The counter solvent is injected at the bottom of the column into tray 108.

[0076] Five zones are defined to adjust the surface of the spillways to the variations in flow rate of the continuous phase along the column: - the first zone Zl, is between plateau 1 to 6: the surface SI of the spillway is 0.12 m2, the rest of the geometry being unchanged; - the second Zone Z2, is included between plateau 7 to 27: the surface S2 of the spillway is 0.20 m2, with regard to the increase in flow of the continuous phase, the ratio S1 / S2 is 0.60; - the third Zone Z3, is included between plateau 28 to 40: the surface S3 of the spillway is 0.29 m2, with regard to the increase in flow of the continuous phase, the ratio S2 / S3 is 0.69; - the fourth Zone Z4, is included between plateau 41 to 47: the surface S4 of the spillway is 0.55 m2, with regard to the increase in flow of the continuous phase, the ratio S3 / S4 is 0.53; - the fifth Zone Z5, is included between plateau 48 to 74: the surface S5 of the spillway is 0.44 m2, with regard to the increase in flow of the continuous phase, the ratio S4 / S5 is 0.73; - the last Zone Z6, is included between plateau 75 to 108: the surface S6 of the spillway is 0.57 m2, with regard to the increase in flow of the continuous phase, the ratio S5 / S6 is 0.77.

[0077] In the extraction sector 7 between the head plate x = 1 and the feed plate x = 47, the surface area of ​​the spillways of zone Z1 is less than that of zone Z2, itself less than that of zone Z3, itself less than that of zone Z4.

[0078] In the backwash sector 8 between the plate x = 48 and the bottom plate x = 108, the surface area of ​​the spillways of zone Z5 is less than that of zone Z6.

[0079] [Fig.4] illustrates the technical effect of this adjustment: it ensures homogeneity of hydraulic operation along the column. In fact, the axial velocity in the spillways is, at any point in the column, close (80 - 100%) to the target velocity; this corresponds to the maximum velocity in the spillways to limit the entrainment of drops of the dispersed phase by the continuous phase.

[0080] Adjusting the surface area of ​​the spillways in these 6 zones thus guarantees constant performance regardless of the flow rate variations of the continuous phase and physicochemical properties of the mixture along the column.

[0081] Furthermore, this technical solution makes it possible to locally increase the perforated surface of the column, by making use of the additional surface, resulting from the readjustment of the overflows, in the active zone of the column. For example, the readjusted cross-sectional area is 0.12 m2 instead of 0.57 m2 without readjustment: the difference of 0.45 m2 can be used to advantage in the perforated area of ​​the column to increase the perforated area, allowing the dispersion of the aqueous phase.

[0082] Counterexample 2: Liquid-liquid extraction column with constant weir cross-section

[0083] The column has a diameter of 2.9 m and comprises a succession of 108 perforated trays. The feed is injected into intermediate tray No. 47. The heavy solvent is injected at the top of the column into tray 1. The counter solvent is injected at the bottom of the column into tray 108.

[0084] No adjustment is implemented: the surface area of ​​the spillways is constant (0.59 m2) and the characteristics of the trays are identical at all points.

[0085] [Fig.5] illustrates that, without adjustment of the weir surface, the axial velocity of the continuous phase in the weirs of the extraction zone is 20 to 50% of the target velocity for the design. These very low values ​​can lead to a malfunction of the column by formation of recirculation of the continuous phase between the plates and thus degrade the efficiency of the extraction zone.

[0086] Furthermore, in the backwash zone, the axial velocity of the continuous phase in the weirs is between 50 - 100% of the target velocity. For values ​​below 80%, a malfunction of the column may occur due to the formation of recirculation of the continuous phase between the plates and thus degrade the efficiency of the backwash zone.

Claims

Claims

1. Liquid-liquid extraction column (1) comprising the following elements: - a first injection point for a first phase (2) arranged at an intermediate position between the top and the bottom of the column (1); - a second injection point for a second phase (3) and a third injection point for a backwash liquid (4), one being arranged at the top of the column (1) and the other being arranged at the bottom of the column (1); - a first withdrawal point for an extract (5) and a second withdrawal point for a raffinate (6), one being arranged at the bottom of the column (1) and the other being arranged at the top of the column (1); - a plurality of trays (P;) arranged from the top of the column (1) to the bottom of the column (1) and defining n zones, each zone comprising at least two trays (Pi), n being between 2 and 30;in which the n zones comprise: - at least one extraction zone Zj comprised between a zone Zi comprising the second injection point of the second phase (3), and a feed zone Zx comprising the first injection point of the first phase (2), x being greater than or equal to 1; and - at least one backwash zone comprised between a zone Zx+i and a zone Zn comprising the third injection point of the backwash liquid (4), n being greater than x; in which the plates (Pi) of the same zone have the same cross-sectional area (S) of the spillway (11, 12); and in which - when x is greater than 1, the cross-sectional area (S) of the spillways (11, 12) of the zones Z increases when the value i increases;and - when x is equal to 1, the surface area of ​​the cross sections (S) of the spillways (11, 12) of the at least one backwash zone is less than the surface area of ​​the cross sections (S) of the spillways (11, 12) of the zone Zp;

2. The liquid-liquid extraction column (1) according to claim 1, wherein n is between 3 and 30, and x is greater than 1.

3. A liquid-liquid extraction column (1) according to claim 1 or claim 2, wherein in the extraction zones Z; or i varies from 1 to x, the ratio between the cross-sectional area (S) of a spillway (11, 12) of a zone Zj on the cross-sectional area (S) of a spillway (11, 12) of a zone Zi+b is between 0.50 and 0.

90.

4. Liquid-liquid extraction column (1) according to any one of the preceding claims, wherein, in the extraction zones Zj or i varies from 1 to x, the ratio between the cross-sectional area (S) of a weir (11, 12) of a zone Zj on the cross-sectional area (S) of a weir (11, 12) of a zone Zi+b is between 0.60 and 0.

80.

5. Liquid-liquid extraction column (1) according to any one of the preceding claims, wherein, in the extraction zones Zj or i varies from 1 to x, the ratio between the cross-sectional area (S) of a weir (11, 12) of a zone Zi on the cross-sectional area (S) of a weir (11, 12) of a zone Zi+b is between 0.60 and 0.

75.

6. A liquid-liquid extraction column (1) according to any preceding claim, wherein the at least one backwash zone is a plurality of zones, from zone Zx+[ to zone Zn, and wherein the cross-sectional area (S) of the weirs (11, 12) increases, is constant, or decreases from zone Zx+[ to zone Zn.

7. Liquid-liquid extraction column (1) according to any one of the preceding claims, wherein the at least one backwash zone is a plurality of zones subdivided into: - a plurality of zones Zj comprised between zone Zx+i and a zone Zy, y being greater than x+1; and - a plurality of zones Zk comprised between zone Zy+[ and zone Zn, and wherein: - in zones Zj where j varies from x+1 to y, the surface area of ​​the cross-sections S of the weirs (11, 12) increases, is constant, or decreases when the value j increases; and / or - in zones Zk where k varies from y+1 to n, the surface area of ​​the cross-sections S of the weirs (11, 12) increases, is constant, or decreases when the value k increases.

8. A liquid-liquid extraction column (1) according to claim 7, wherein, in zones Zj or j varies from x+1 to y, the ratio between the cross-sectional area (S) of a weir (11, 12) of a zone Zj and the cross-sectional area (S) of a weir (11, 12) of a zone Zj+i, is between 0.50 and 0.

95.

9. A liquid-liquid extraction column (1) according to claim 7, wherein, in zones Zj or j varies from x+1 to y, the ratio between the cross-sectional area (S) of a weir (11, 12) of a zone Zj to the cross-sectional area (S) of a weir (11, 12) of a zone Zj+i, is between 1.05 and 2.

0.

10. A liquid-liquid extraction column (1) according to any one of claims 7 to 9, wherein, in zones Zk or k varies from y+1 to n, the ratio between the cross-sectional area (S) of a weir (11, 12) of a zone Zk to the cross-sectional area (S) of a weir (11, 12) of a zone Zk+b is between 0.50 and 0.

95.

11. A liquid-liquid extraction column (1) according to any one of claims 7 to 9, wherein, in zones Zk or k varies from y+1 to n, the ratio between the cross-sectional area (S) of a weir (11, 12) of a zone Zk to the cross-sectional area (S) of a weir (11, 12) of a zone Zk+b is between 1.05 and 2.

0.

12. Liquid-liquid extraction column (1) according to any one of the preceding claims, wherein the number of zones Z; is between 2 and 10 and / or the number of backwash zones is between 1 and 10.

13. Liquid-liquid extraction column (1) according to any one of claims 7 to 12, wherein the number of zones Zj is between 2 and 10 and / or the number of zones Zk is between 2 and 10.

14. A liquid-liquid extraction column (1) according to any preceding claim, wherein the cross-sectional area (S) of a weir (11, 12) of the backwash zone Zx+i is less than, equal to or greater than the cross-sectional area (S) of a weir (11, 12) of the extraction zone Zx.

15. A liquid-liquid extraction column (1) according to any preceding claim, wherein the cross-sectional area (S) of each weir (11, 12) is between 1% and 25% of the total cross-sectional area of ​​the liquid-liquid extraction column (1).

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