JPS594162B2 - extraction device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an extraction system in which particularly immiscible liquids with different densities are brought into contact and separated by sedimentation.

In particular, the present invention relates to liquid-liquid extraction and separation columns, and methods and apparatus for improving the operating efficiency of separation columns. In known liquid-liquid extraction techniques, the liquid to be treated is contacted with a substantially immiscible liquid solvent.

For example, liquid-selective solvents such as phenols can be added to hydrocarbon oils to extract aromatics, naphthenic and/or other components that are virtually dissolved in the solvent to form a liquid extraction phase. can be contacted. Parafine and (
or) other components such as other hydrocarbons remain undissolved and form a liquid ruffinate phase, which is soluble with some solvent. Contacting the liquid feedstock with a solvent and the resulting extraction is generally carried out in a countercurrent extraction column.

A countercurrent extraction column consists of an upright column with a plurality of horizontally extending trays spaced vertically. The spaces existing between the trays are interconnected to flow the light phase and the heavy phase through the column by earthflow pipes and downstream pipes, respectively. Conduits are provided at various locations in the column for introducing solvent and liquid feed into the column and for removing raffinate and extraction phases from the column. In operation, a relatively light liquid, such as a hydrocarbon oil feedstock, is introduced into the column near the bottom and flows by upstream pipes between the trays of the column from the lower space of the column to the upper space.

A relatively heavy liquid, such as a solvent, is introduced into the column near the top and flows by downstream pipes between the trays of the column from the upper space of the column to the lower space. Each tray is provided with an upstream tube and an overall tube for intimately dispersing one of the liquids in the other to aid mass transfer of undesirable and aromatic-rich components in the oil feedstock to the solvent phase. Means is provided coupled to the. In addition, a sedimentation zone is provided in the tray interior space,
The resulting dispersion is then allowed to settle to separate lighter and heavier liquids. Various tray arrangements have been provided for use with separation columns of the type described above.

In a particular form of tray arrangement used with phenol separation columns and known as an antablo weir tray, the space within the tray is separated into a dispersion zone and a settling zone by a nearly vertically extending seal box. In operation, the relatively light phase collects below the surface of the first tray;
It then spills into the associated seal box. Then,
The light phase flows through the V-notched weir seal box into the space above the seal box, where it is dispersed in the relatively heavier phenolic solvent extraction phase. The light dispersed oil phase coalesces and settles below the lower surface of the next upper adjacent tray;
The heavy phase settles on the surface of the first tray and the process is repeated again. Although the Antabro weir tray exhibited relatively good overall operating characteristics, oil throughput and (or)
Limits have been imposed on phenol treatment rates.

In some cases, this undesirable entrainment can be traced to instability of tray operation at relatively high throughputs due to the development of lift phenomena. The density of the fluid in the dispersion zone above the notched antablo weir seal box is relatively small due to the presence of dispersed droplets, and the oil level on one side of the seal box weir is reduced to compensate for this reduced density. Automatically enhanced. Although the seal box weir is designed to operate in response to this lift, the tray becomes unstable when the lift becomes relatively large due to excess oil in the dispersion zone. In this unstable condition, oil flows more and more rapidly from the seal box to the dispersion zone until it is depleted and the phenolic phase fills the seal box and stops oil flow. After a period of time, the oil phase will reform itself once more in the sealing box and the cycle will be repeated. These lubricating oil flow surges, several times the average oil volume, cause excessive mixing, incomplete phase separation, and the entrainment of oil into the solvent extraction phase. It is believed that a wide variety of factors contribute to the presence of excess oil in the mixing zone and the generation of lift greater than the equipment can tolerate.

These factors include low oil settling rate, high oil throughput,
low phenol-to-oil handling ratios, separation of dispersion and settling zones due to excessive seal box height, excessive entrainment in the tray (especially oil into the solvent phase), and poor coalescence in the seal box due to inadequate coalescence time under the tray. These include uncombined oil and unstable tray starting power where balance lift overruns result from temporarily high oil levels at the start of tray operation. In some liquid extraction systems, such as those where the interfacial tension is low, difficulties may be encountered due to poor separation rates, and therefore excessive mixing or mixing is necessary to avoid dispersion and prevent droplet settling and coalescence. Special tray designs are required to provide suitable conditions.

It has now been found in the present invention that the sensitivity of the antablo weir tray to small variations in operating conditions results in large part from the lack of light phase flow control in the dispersion zone when light phase level fluctuations occur. .

As the light phase level below the tray increases slightly,
For example, the flow area under a V-shaped weir increases rapidly, causing a relatively large decrease in flow impedance in response to a relatively small increase in flow rate. According to the general characteristics of the method of the invention, a liquid-liquid extraction comprising vertically spaced cross-flow trays and sealing box means for dividing the space within the tray into a dispersion zone and a settling zone. In the column, the light phase automatically changes the apertures and the effective cross-section of said apertures presented to the light phase substantially in accordance with variations in the level of the light phase below the tray, thereby meeting predetermined operating conditions. while the light phase flows to the tray distribution zone through a seal box containing means for maintaining a substantially constant flow rate of the light phase.

According to features of the apparatus of the invention, a plurality of vertically spaced cross-flow trays for liquid-liquid extraction between partially immiscible phases of lower density and higher density, comprising: In a countercurrent liquid-liquid contacting column comprising cross-flow trays including seal box means for dividing the space between the trays into a dispersion zone and a settling zone, the openings and the light phase below the trays are and means for automatically varying the effective cross-section of said apertures provided to the light phase substantially in accordance with level variations, thereby maintaining a substantially constant flow of the light phase. A liquid-liquid contact column is provided that includes a dispersion zone.

According to a further particular feature of the device of the invention, the sealing box comprises a plurality of substantially horizontally extending weirs with progressively increasing depths in the direction of light phase flow in a cascade arrangement.

This weir depends from a horizontal plate segment located below the dispersion zone. A plurality of apertures are formed in the plate at locations intermediate between weir locations, and the light phase flows vertically through the spaces and apertures between adjacent weirs and into the dispersion zone. With this tray arrangement, the weir arrangement automatically maintains the level or depth of the light liquid phase below the tray at a desired range of depths and as the light phase flow is increased or decreased, respectively. Automatically allowing the removal or introduction of additional weir from the light phase flow path provides adequate time for droplet settling and coalescence over a range of light phase flow rates. According to yet another feature of the invention, baffle means are provided and extend through the dispersion zone in a nearly horizontal direction to enhance actuation of the tray.

1 and 2, there is illustrated a column 10 constructed of cylindrical metal plate walls 11 and adapted for liquid-liquid contact of substantially immiscible materials.

The column includes a plurality of trays extending in a generally horizontal direction and vertically spaced within the column, three of which are designated by the reference numerals 12, 14 and 16. . The trays are fabricated from sheet metal and secured in place within the tower by conventional means such as welding. The tray consists of a cascade weir type seal box in which the interior space of the tray is separated into a dispersion zone and a settling zone. Tray 12 includes a seal box 18 having a surface with slanted segments 17 and horizontal segments 19, respectively. Seal box 18 separates the space above tray 12 into a settling zone 20 and a dispersion zone 22. The settling zone extends from the vertical plane 23 to the downstream pipe plane 60, discussed below. The dispersion zone extends from the vertical plane 23 to the vertical segment 25 of the downstream tube baffle plate 66, which will be described below. Similarly, tray 14 includes a seal box 24 that separates the intra-tray space into a settling zone 26 and a dispersion zone 28, and tray 16 includes a seal box 30 that separates the intra-tray space into a settling zone 32 and a dispersion zone 34. Although only trays 12, 14, and 16 are illustrated for convenience in describing the invention, it is understood that numerous additional trays of the type described may be disposed between trays 12 and 14. The column is continuously charged with a feedstock, such as a hydrocarbon oil, via an inlet pipe 40 passing through an aperture 41 in the column wall 11.

Feedstock flows from inlet tube 40 through conduit 42 which extends to an outlet orifice 46 located below the lower surface of tray 16. The column is also continuously supplied with a heavy phase liquid solvent, such as phenol, through an inlet pipe 48 passing through an aperture 49 formed in the upper portion of the column wall. Phenol flowing through the opening 49 is directed to the metal baffle plate 5.
0 to the seal box baffle plate and downstream pipe system described below. The solvent flows from dispersion zone 22 past seal box 18 to settling zone 20 during its flow through the column. The liquid extraction phase is removed from the column at an extract outlet opening 52 formed in the lower part of the wall 11. In addition, a relatively light or roughinate phase is removed from the column at outlet openings 54 located in the upper sector of the column wall 11. Each tray assembly includes a downstream tube and seal box means.

Downstream pipes 55, 57 and 59 of FIG. 1 extend from respective portions of respective adjacent sheet metal segments 60, 62 and 64 supported by and depending from tower wall 11 and trays 12, 14 and 16, respectively. It has been shown that The column downstream pipes provide a flow path for the relatively heavier liquid phase between the upper and lower portions of column 10 between each tray. For example, downstream pipe 55 provides a flow path from settling zone 20 in the space above tray 12 to the intra-tray space between trays 12 and 14. In order to suppress agitation of the light phase located in the seal box of each tray, the trays 12, 1
4 and 16 are provided with baffles 66, 68 and 70, respectively, at positions opposite to the inlet baffle 50, tower downstream pipe 55 and tower downstream pipe 57, respectively. To enable the introduction of a small amount of settled heavy phase into the seal box, baffle downstream tubes 72, 74 and 76 are provided which extend from baffles 66, 68 and 70, respectively, to the seal of the seal box. It stops above the pan segment. These latter downstream pipes constitute conduits for conveying some of the heavy phase to the seal box without stirring and without causing entrainment of the heavy phase as the light phase flows upstream through the apertures. do. 3 and 4, the typical seal box 24 of FIG. 1 is illustrated in more detail. Upper and lower adjacent trays 12
It is understood that seal boxes 18 and 24, respectively, and 16, as well as other seal boxes that may be included in the column, have similar construction. Seal box 2
4 limits undesirable recirculation of heavy phase from sedimentation zone 26 of tray 14 to dispersion zone 28 and allows flow of light phase from below the tray to dispersion zone 28. Additionally, the seal box provides a seal that prevents heavy phase located above the tray from flowing backward through the dispersion zone and thus bypassing the tray. As previously described, the seal box includes a weir or dam having an inclined surface 77 and a horizontal surface 79 and extending generally vertically from the average level of the tray. A seal pan 82 is provided and extends into segment 84 in a direction generally perpendicular to the volume occupied by dam 80. Segment 84 acts as a seal baffle so that light phase 86 rises above it and flows into the volume above seal pan 82. As is well known, the light phase rises and flows over the weir 84 due to its lower density compared to the solvent phase. In accordance with a feature of the invention, the seal box further includes a horizontally extending plate 88 from which a series of depending plates 90-104 are supported in the light phase flow path.

A plurality of apertures are formed in the plate 88;
8 into the heavier phase of the dispersion zone 28. The dispersed light phase rises and coalesces under the lower surface of the next upper adjacent tray or alternatively near the top of the column, from which point it is removed from the column. The rows of depending plates 90-104 (referred to herein as cascade weirs) are arranged in such a manner that the depth of the plates successively positioned in the light phase flow path increases slightly and gradually toward the end plates. Arranged in stages.

These cascade weirs, seal boxes, etc.
It extends in a chord from one side of the cylindrical tower to the other. As seen in FIGS. 1 and 4, the light phase flows from right to left under the lower surface of tray 14. This flows over the seal baffle 84 to the seal pox and into the cascade weirs 90, 92, 94, 96, 100, 102 and 10.
Overflowing at least some of the bottom of the 4. That is,
This is because the level of light phase below tray 14 tends to fluctuate. Thus, as the amount of light phase under tray 14 increases and tends to lower the interface 106 between light phase 86 and phenolic phase 107, the light phase in the seal box continues to form many cascade weirs. It automatically overflows underneath and flows through additional corresponding apertures in plate 88.

When the amount of light phase under tray 14 tends to decrease, the light phase in the seal box will flow under fewer cascading weirs and therefore will have fewer outflows for light phase flow through plate 88. An aperture is provided. Thus, a flow restriction means is provided for the light phase that automatically maintains a steady flow rate of the light phase that is substantially constant over time for a given operating condition, while at the same time allowing the oil feed rate to fluctuate up and down. An automatic means is provided for adjusting the number of apertures available to the light phase when An important feature of this cascaded weir arrangement is that this effective range variation is achieved completely automatically by hydraulic balancing and does not require any moving parts. Thus, the level of light phase below the tray is maintained within a relatively narrow range of levels, thereby providing droplet settling and coalescence times that are substantially independent of flow rate. In-tray and bottom entrainment for the arrangement described herein is lower than known antablo weir tray arrangements.

More specifically, in simulated operations, the trays described herein exhibited 4% oil entrainment at 100 barrels/day/Ft2 (0.09 i) of oil, compared to an improved conventional antablo. The tray is 70 barrels/day/Ft2 (0
．． In 2009 B), oil entrainment was 9%. Oil entrainment in the bottom phenol sample was relatively low for the invention described herein. This is because additional separation occurs below the bottom tray. Values of about 1% or less were observed for the invention described in Section X and the improved tray described above, which corresponded to the above conditions. This is about 1 for a conventional unstable underflow weir tray operating at about 40 barrels/day/ft2 (0.09 TI).
It can be compared to a value of 0%. For relatively long modified Herschel demulsification times, the entrainment values increased more rapidly for the conventional modified tray than for the invention described in Section X.
Although phenol entrainment into the oil phase was observed after settling under the tray and before redispersion into the upper tray, phenol entrainment was observed as a function of oil volume for the invention described herein and the improved conventional tray. It turns out that it increases linearly. However, 50 barrels/day/ft2 (0..o9m2
), the arrangement of the present invention has a flow rate of 1 of the improved conventional tray.
It showed about 6% entrainment compared to 5% entrainment. There are various advantages to using the tray arrangement described above.

A cascading weir forming part of the distributor or distributor provides horizontal stabilization. Thus, the horizontal baffle previously required for underflow trays is eliminated.
As a result, maximum coalescence time is provided. Also, no redispersion of the oil under the tray occurs and the lift effects that make the underflow tray unstable at relatively high oil levels are offset. This is because the flow rate of oil is restricted through the holes. This is achieved in combination with a desirable seal box that provides relatively good mixing and sedimentation characteristics along with separate mixing zones. The tray design has a number of additional beneficial features.

The light phase will overflow over the final weir 104 (FIG. 4) and through the apertures 105 formed therein if the apertures in plate 88 become overloaded due to excessively high flow rates. I can do it. The downstream tube provides an absolute seal against rising light phase droplets. The seal pan downstream tube eliminates a dead zone under the seal pan and allows effective use of coalescence promoting material under the bottom tray. The possibility of occluding the space under the weir with foreign objects is substantially reduced with said weir arrangement, and in that arrangement the pressure drop is substantially zero. A pressure drop is established across the apertured plate. The flow through the apertured plate 88 is essentially turbulent and the drainage efficiency is relatively insensitive to viscosity variations in the light phase. An important benefit of the tray arrangement described above is that it eliminates the instability encountered with conventional underflow weir trays while maintaining a relatively large effective dispersion or mixing band.

Approximately 91n below the tray surface between the mixing zone and settling zone
(22.9CTrL) The upwardly extending seal box stam allows placement of the aperture plate 88 at the tray level.
Thus, the bottom of the mixing zone in the above arrangement is essentially at tray level, thereby making use of a relatively large space above the tray for mixing while avoiding recirculation of heavy phase from the settling zone. enable. In particular, the height of the mixing zone, measured from plate 88, is always 101n (25.
4cTL). The accumulation of uncombined oil droplets in the column and their consequent entrainment in the phenolic phase is substantially reduced by the use of coalescing vessel 44 (FIG. 1) below tray 16. The rate of coalescence is increased by the added surface area and oil wettability properties provided by the coalescer 44VC. A coalescer positioned below tray 16 coalesces the oil droplets entrained in the phenolic phase from the upper tray. The emulsion build-up under this tray is substantially reduced and, as a result of the proper separation of the oil droplets in the phenolic phase leaving the column, the entrainment values are lower than 1% when observed under all conditions. The combiner includes, for example, a steel screen 106 attached to and supported by the oil feed inlet pipe 42 at a location below the outlet 46 on the underside of the tray 16. Relatively large columns, approximately 25 feet in diameter, typically have a relatively large internal tray space (which is
361n or 91.4 cm).

When the intra-tray space has this height, the mixing height that exists between adjacent trays is relatively large, a substantially large amount of mixing energy is present, and a large amount of mixing is formed as a result of this relatively large amount of mixing. The emulsion becomes relatively stable and does not settle. In addition, the mixing height is approximately 361
When n (91.4 CTrL), a relatively large amount of liquid from the settling zone is recycled to the mixing zone and this interferes with the settling process. According to another feature of the invention, a striker baffle plate 110 (FIG. 5) is provided, which is positioned in the dispersion zone above the aperture plate 88.

This deflecting plate consists of a plane segment 112 and a plate 11.
0 near the edge of the folded lip 114. In a typical arrangement, lip 114 extends approximately 61n (15.
2CTrL) Extends. Part of the emulsion is destroyed,
The settled oil then flows through the upstream pipe 116 to the underside of the tray above it. However, this tube is sized so that it does not pass all of the emulsion, and the remainder flows under the edge of lip 114 into the main settling zone. The use of this stator baffle specifically enhances emulsion settling, reduces recirculation from the settling zone to the mixing zone, and provides a significant extra surface area percentage for oil to settle out of the emulsion phase. The use of this single striker plate also effectively increases the effective area of the column by about 25-30% and significantly reduces intra-tray entrainment.
Table 1 shows a striker with no deflector and 241n
(61.0CTrL) and 361n (91.4cTrL
) with an internal tray space of 361n (91
．． 441) shows the improvement in performance reduction when using a single striker plate for the tray interior space.

241n (61.0cTn) without using a deflector
For the spatial increase from 361n (91.4C!IL),
This is accompanied by a noticeable increase in oil entrapment. However, as can be seen from this table, the performance of a tower with a 361n (91.4 cm) spacing can be improved by using the baffle plates described herein.
The performance can be made substantially close to that of the 1n (61.0α) space. Thus, an improved method and apparatus for liquid-liquid contacting and separation in a contacting column using cross-flow trays with seal boxes and cascading weirs has been disclosed.

The method and apparatus automatically vary the effective flow surface cross-sectional area imparted to the light phase, thereby maintaining the flow rate substantially constant over time and resulting in the light phase below the tray. This is particularly advantageous in that the depth of the trough is maintained within a relatively small acceptable range.

[Brief explanation of the drawing]

FIG. 1 is a flow diagram of a liquid-liquid contacting column constructed in accordance with features of the present invention. FIG. 2 is a view taken along line 2--2 of FIG. FIG. 3 is an enlarged perspective view of the seal box of FIG. 1, illustrating a weir arrangement constructed in accordance with features of the present invention. FIG. 4 is a side view of the seal pox of FIG. 3. Figure 5 shows
2 is an enlarged side view of the alternative tray arrangement of FIG. 1; FIG. The reference numbers representing the main parts are as follows. 10: tower, 12,1
4, 16: Tray 1, 20, 26, 32: Sedimentation zone, 22
, 28, 34: Dispersion zone, 18, 24, 30: Seal box, 40: Feed material inlet pipe, 44° combiner, 48:
Solvent inlet tube.

Claims (1)

Claims: 1. Providing and contacting first and second partially immiscible liquids having relatively high and low densities, respectively, thereby rendering the liquids relatively light. a vertical separation column for separating a raffinate phase and a relatively heavy extraction phase, comprising a plurality of vertically spaced trays, the raffinate phase being located between the trays and disposed below the lower surfaces of the trays; an apparatus for liquid-liquid contacting and separation comprising a vertical separation column having a space in which the extraction phase settles into a flowing layer over the upper surface of the tray; Downstream piping means are associated with each tray to provide a flow path for the liquid or extraction phase from a position above the tray to a position below the tray and for providing a flow path for said second liquid or roughinate phase from a position above the tray to a position below said tray. Seal box means are associated with each tray to provide a flow path from a location below the tray to a location above the tray, said seal box means being spaced horizontally from said column downstream pipe means. and is adapted to laterally separate the space above the tray into a dispersion zone and a sedimentation zone, and wherein the sealing box is configured to open the first tray from a position below the lowest surface of the first tray relative to the roughinate phase. comprising apertures having a cross-sectional area to provide a flow path to the space above one tray and to disperse and coalesce said roughinate phase into the layer below the lower surface of the next upper adjacent tray; for automatically varying the effective cross-sectional area of the apertures provided to the roughinate phase substantially in accordance with variations occurring in the level of the roughinate phase below, thereby maintaining a substantially constant flow rate of the roughinate phase; means comprising a surface having a plurality of apertures and an array of substantially vertically extending weirs depending from the surface and having depths increasing progressively in the flow direction of the roughinate phase; A substantially horizontal downstream pipe baffle plate is disposed on the opposite side of the outlet of the column downstream pipe means to suppress agitation of the roughinate phase in the seal box means; A substantially vertical baffle plate is provided to prevent climbing up the tube means and to provide a substantially absolute seal between the downstream tube means and the ruffinate phase below the surface of the next upper adjacent tray. Apparatus for liquid-liquid contact and separation, characterized in that it extends from a column downstream pipe baffle plate to a point near the lower portion of the column downstream pipe means. 2 providing and contacting first and second partially immiscible liquids having relatively high and low densities, respectively, thereby converting said liquids into a relatively light ruffinate phase and a relatively light ruffinate phase; a vertical separation column for separating a heavy extraction phase, comprising a plurality of vertically spaced trays, the ruffinate phase settling between the trays into a flowing layer below the lower surfaces of the trays; and a space in which the extraction phase settles into a flowing layer above the upper surface of the tray. Downstream piping means are attached to each tray to provide a flow path from a position above the tray to a position below said tray, and for said second liquid or ruffinate phase to be provided with a flow path from a position below said tray to a position below said tray. A seal box means is associated with each tray to provide a flow path to a location above the tray, said seal box means being horizontally spaced from said column downstream pipe means and said adapted to laterally separate a space into a dispersion zone and a sedimentation zone, and wherein the sealing box is adapted to laterally separate a space into a dispersion zone and a settling zone, and wherein the sealing box separates the space above the first tray from a position below the lowest surface of the first tray relative to the roughinate phase. including apertures having a cross-sectional area for providing a flow path to and dispersing and coalescing said roughinate phase into a layer below the lower surface of the next upper adjacent tray; means for automatically varying the effective cross-sectional area of the apertures provided to the roughinate phase substantially in accordance with variations occurring in level, thereby maintaining a substantially constant flow rate of the roughinate phase; means comprising a surface having a plurality of apertures and an array of substantially vertically extending weirs depending from the surface and having depths increasing progressively in the direction of flow of the roughinate phase; A substantially horizontal downstream pipe baffle plate is disposed opposite the outlet of said column downstream pipe means to suppress agitation of the roughinate phase and prevent said light liquid or raffinate phase from ascending said column downstream pipe means. and a substantially vertical baffle plate extends from the column downstream pipe baffle plate to the column to provide a substantially absolute seal between the column downstream pipe means and the ruffinate phase below the surface of the next upper adjacent tray. Above the seal box is a horizontally extending striker baffle extending to a point near the lower portion of the downstream pipe means and adapted for the passage of only a portion of the roughinate phase flowing from below through the seal box means. 1. A device for liquid-liquid contact and separation disposed in a tray interior space, the striker baffle plate comprising a flange segment.