Method for operating a crystallization vessel assembly and crystallization vessel assembly

Abstract

A method for operating a crystallization container assembly (100), the container assembly (100) comprising a crystallization container (110) and a rotator (130), the rotator comprising a rotator shaft, the rotator (130) comprising a plurality of rotator arms (140), the rotator arms (140) comprising an arm (141) attached to the rotator shaft and a scraper (150) attached to the arm (141). Crystals grow inside the container (110), and the rotator (130) rotates to scrape the crystals off. In order to improve the liquid flow in the crystallization container (110), the plurality of arms (141) of the rotator arms (140) are hollow arms (141), and each of the plurality of arms (141) comprises an inlet opening (341) relatively close to the shaft and an outlet opening (342) relatively far from the shaft.

Description

[0001] The present invention relates to a method for operating a crystallization container assembly, the container assembly comprising

[0002] - a crystallization container, the container comprising a top wall, a bottom wall and an upright wall extending from the bottom wall to the top wall, the top wall, the bottom wall and the upright wall defining an inner cavity,

[0003] - an upper structure, the upper structure being on top of the container, the upper structure comprising a bearing, the bearing comprising an upper race member, a lower race member and a roller body between the upper race member and the lower race member, the lower race member being attached to the upper structure,

[0004] - a rotator, the rotator comprising

[0005] - an upright rotatable shaft, said shaft comprising i) a top shaft section extending above the top wall, and ii) a bottom shaft section in said inner cavity, said top shaft section being provided with said upper race member allowing the rotator to rotate along a shaft axis of the upright rotatable shaft, which shaft axis coincides with the axis of rotation of the bearing;

[0006] as well as

[0007] - a plurality of rotator arms, the plurality of rotator arms comprising

[0008] - an arm, which is attached to the bottom shaft section by its proximal end, and

[0009] - a scraper attached at the distal end of the arm;

[0010] Therein, crystals grow inside the upright walls, and a rotor rotates to scrape the crystals off the upright walls.

[0011] The method according to the preamble is known in the art. Typically, the upright walls of the crystallization vessel are cooled. An example of a material to be crystallized is para-xylene, a compound used in the production of PET. After being discharged from the crystallization vessel, the crystals are separated from the mother liquor, which contains impurities.

[0012] In a crystallization vessel, it is important that the fresh liquid to be subjected to crystallization reaches the inner surface of the upright walls.

[0013] It is an object of the present invention to provide a method and a crystallization container for improving the flow of liquid in an inner cavity.

[0014] To this end, the method according to the preamble is characterized in that the plurality of arms of the rotator arm are hollow arms, each arm of the plurality of arms comprising an inlet opening relatively close to the axis and an outlet opening relatively far from the axis.

[0015] It has been found that rotating such an arm in a liquid undergoing crystallization causes the liquid to flow from the centerline of the lumen toward the upright walls. This allows the crystallization process to be performed faster (greater throughput) and / or a smaller crystallization vessel to be achieved for the same throughput (cost savings).

[0016] More specifically, cooling the vertical walls induces crystallization at the surface and a relatively cool solvent containing a reduced concentration (in moles / liter) of the compound being crystallized. By delivering liquid from the centerline to the walls, the concentration of the compound near the walls is increased, thereby allowing new crystals to grow at the walls and crystals scraped from the vertical walls to grow.

[0017] Typically, the crystallization process will be operated as a continuous process, where relatively warm fresh liquid undergoing crystallization is added at one end (typically the top) of the crystallization vessel, and relatively cool liquid (a suspension of crystals in mother liquor) is removed at the other end.

[0018] Typically, the inlet and outlet are separated by at least 40% of the length of the arm, preferably at least 75% of the length of the arm.

[0019] The surface area of ​​the inlet opening (or the total surface area where the arm has more than one inlet opening) is preferably at least 35% of the cross-sectional area of ​​the inner cavity of the arm (in a direction transverse to the longitudinal direction of the arm), and preferably at least 70%.

[0020] The surface area of ​​the outlet opening (or the total surface area where there is more than one outlet opening) is preferably at least 35% of the cross-sectional area of ​​the lumen of the arm (in a direction transverse to the longitudinal direction of the arm), and preferably at least 70%.

[0021] According to an advantageous embodiment, the arms have, in the longitudinal direction of the arms, a cross-sectional surface area of ​​the lumen having a width / height ratio of at least 1.25, preferably at least 1.5.

[0022] This allows the rotor arm to move relatively easily through the liquid, with the result that in steady state the arm moves faster than the liquid around the arm, while the liquid in the arm moves as fast as the arm. As a result, centrifugal force causes the liquid to be subjected to crystallization to be transported through the arm.

[0023] In fact, at the distal end of the arm, the liquid in the container is forced to move faster between the arm (equipped with a scraper) and the inner wall of the container, creating a reduced pressure zone that promotes the flow of liquid inside the arm out.

[0024] Relatively flat arms also allow for reduced (vertical) mixing, since it is desirable to establish a flow from the upright walls towards the axis of rotation and a flow in the arms from the axis of rotation to the upright walls.

[0025] According to an advantageous embodiment, the scraper comprises a scraper profile provided with a scraper blade, the scraper profile being attached to the distal ends of the at least two arms, said scraper profile having a conical cross section tapering in the forward direction of the rotating arm.

[0026] This allows the rotor arm to move relatively easily through the liquid, with the result that in steady state the arm moves faster than the liquid around the arm, while the liquid in the arm moves as fast as the arm. As a result, centrifugal force causes the liquid to be subjected to crystallization to be transported through the arm.

[0027] In fact, at the distal end of the arm, the liquid in the container is forced to move faster between the arm (equipped with a scraper) and the inner wall of the container, creating a reduced pressure zone that promotes the flow of liquid inside the arm out.

[0028] According to an advantageous embodiment, para-xylene dissolved in a solvent is introduced into the crystallization vessel assembly.

[0029] The crystallization of p-xylene is an important application of the process according to the invention. In this particular case, the solvent is typically formed from a mixture of isomers, i.e. o-xylene and m-xylene, which are also formed during the synthesis of p-xylene and (residual) solvents such as benzene and ethylbenzene.

[0030] Finally, the present invention relates to a crystallization container assembly, the container assembly comprising

[0031] - a crystallization container, the container comprising a top wall, a bottom wall and an upright wall extending from the bottom wall to the top wall, the top wall, the bottom wall and the upright wall defining an inner cavity,

[0032] - an upper structure, the upper structure being on top of the container, the upper structure comprising a bearing, the bearing comprising an upper race member, a lower race member and a roller body between the upper race member and the lower race member, the lower race member being attached to the upper structure,

[0033] - a rotator, the rotator comprising

[0034] - an upright rotatable shaft, said shaft comprising i) a top shaft section extending above the top wall, and ii) a bottom shaft section in said inner cavity, said top shaft section being provided with said upper race member allowing the rotator to rotate along a shaft axis of the upright rotatable shaft, which shaft axis coincides with the axis of rotation of the bearing;

[0035] as well as

[0036] - a plurality of rotator arms, the plurality of rotator arms comprising

[0037] - an arm, which is attached to the bottom shaft section by its proximal end, and

[0038] - a scraper attached at the distal end of the arm;

[0039] The plurality of arms of the rotator arm are hollow arms, and each of the plurality of arms comprises an inlet opening relatively close to the axis and an outlet opening relatively far from the axis.

[0040] In the method according to the invention, this allows the weight of the turner to be moved from the bearing to the base.

[0041] Typically, the inlet and outlet are separated by at least 40% of the length of the arm, preferably at least 75% of the length of the arm.

[0042] The surface area of ​​the inlet opening (or the total surface area where there is more than one inlet opening) is preferably at least 35% of the cross-sectional area of ​​the lumen of the arm (in a direction transverse to the longitudinal direction of the arm), and preferably at least 70%.

[0043] The surface area of ​​the outlet opening (or the total surface area where there is more than one outlet opening) is preferably at least 35% of the cross-sectional area of ​​the lumen of the arm (in a direction transverse to the longitudinal direction of the arm), and preferably at least 70%.

[0044] According to an advantageous embodiment, the arms have, in the longitudinal direction of the arms, a cross-sectional surface area of ​​the lumen having a width / height ratio of at least 1.25, preferably at least 1.5.

[0045] This allows the rotor arm to move relatively easily through the liquid, with the result that in steady state the arm moves faster than the liquid around the arm, while the liquid in the arm moves as fast as the arm. As a result, centrifugal force causes the liquid to be subjected to crystallization to be transported through the arm.

[0046] In fact, at the distal end of the arm, the liquid in the container is forced to move faster between the arm (equipped with a scraper) and the inner wall of the container, creating a reduced pressure zone that promotes the flow of liquid inside the arm out.

[0047] According to an advantageous embodiment, the scraper comprises a scraper profile provided with a scraper blade, the scraper profile being attached to the distal ends of the at least two arms, said scraper profile having a conical cross section tapering in the forward direction of the rotating arm.

[0048] This allows the rotor arm to move relatively easily through the liquid, with the result that in steady state the arm moves faster than the liquid around the arm, while the liquid in the arm moves as fast as the arm. As a result, centrifugal force causes the liquid to be subjected to crystallization to be transported through the arm.

[0049] In fact, at the distal end of the arm, the liquid in the container is forced to move faster between the arm (equipped with a scraper) and the inner wall of the container, creating a reduced pressure zone that promotes the flow of liquid inside the arm out.

[0050] According to an advantageous embodiment, a plurality of arms are distributed on the base shaft section in the longitudinal direction of the axis of rotation.

[0051] In use, this allows fresh liquid containing a relatively high concentration of the compound to be crystallized to be conveyed towards the upright walls over the height of the vessel.

[0052] The present invention will now be described with reference to the accompanying drawings, in which

[0053] Figure 1A and Figure 1B A side view and a cross-sectional view of the crystallizer are shown;

[0054] Figure 1C Shows Figure 1B Cross-sectional details of the superstructure of the crystallizer;

[0055] Figure 2A shows a perspective view of the rotator, Figure 2B is a cross-sectional detail view of a rotor within a crystallization vessel;

[0056] Figure 3A A cross-sectional top view showing a rotator shaft provided with a fixing device for a rotator arm; and

[0057] Figure 3B A cross-sectional top view of the distal end of a rotator arm provided with a scraper is shown.

[0058] Figure 1A and Figure 1B A side view and a cross-sectional view of a crystallizer vessel assembly 100 are shown, respectively, and the crystallizer vessel assembly includes a crystallization vessel 110, which includes a top wall 111, a bottom wall 112, and an upright wall 113 extending from the bottom wall 112 to the top wall 111. The top wall 111, the bottom wall 112, and the upright wall 113 define an inner cavity 114 for containing a fluid undergoing crystallization, such as paraxylene, which is a compound used to produce PET.

[0059] The crystallizer vessel assembly 100 includes a rotor 130. The rotor 130 includes a shaft having a top shaft section 131' extending above the top wall 111 and a bottom shaft section 131" extending in the interior cavity 114.

[0060] The bottom shaft section 131" is provided with a plurality of rotator arms 140. The rotator arms 140 include arms 141 provided with scrapers 150. In use, the upright wall 113 will be cooled, thereby causing the component to crystallize inside the upright wall 113. Here, the crystallized component is scraped off the upright wall 113 and new crystals can form.

[0061] On top of the container 110, a superstructure 170 (frame) is provided.

[0062] As in Figure 1C As can be seen in the cross-sectional view of the upper structure of FIG. 1 , the upper structure 170 is provided with a motor 160 for driving the rotator 130 via a gearbox 161 and a torque limiter 162 connected to the top end of the top shaft section 131 '. The torque limiter 162 is provided in case the rotator 130 gets stuck. A tapered roller bearing 175 is provided to allow the rotator 130 to be suspended from the upper structure 170. A seal 180 is also provided to form a barrier between the inner cavity 114 and the outside of the container 110.

[0063] The bearing 175 includes an upper race member 177 held by the top shaft section 131 ′, a lower race member 178 secured to the upper structure 170 , and a tapered roller body 179 .

[0064] Below the seal 180, the top shaft section 131' is provided with a frustoconical tapered element 190, and the top wall 111 is provided with a seat 195 having a complementary conical recess 196 for receiving the tapered element 190. When in contact, the contact area of ​​the surface defining the recess 196 and the bottom surface of the frustoconical tapered element 190 provides a seal.

[0065] Figure 2A A perspective view of the rotator 130 is shown, Figure 2B is a cross-sectional detail view of a rotor 130 within a crystallization vessel 110 having an upright wall 113 .

[0066] The rotator 130 comprises a bottom shaft section 131 ″ provided with rotator arms 140 , which comprise a scraper 150 . The scraper 150 comprises a scraper profile 152 provided with a scraper blade 151 .

[0067] exist Figure 2B In the figure, it can be seen that the scraper 150 extends parallel to the centerline of the rotor and against the inner surface of the upright wall 113. Scrapers are known in the art. The scraper blade 151 scrapes the crystal off the inner surface of the upright wall 113.

[0068] The arm 141 is connected by its proximal end to a fixture 250 which is connected to the bottom shaft section 131 ″.

[0069] Figure 3A A cross-sectional top view of a turret shaft provided with a fixing device 250 for the arm 141 of the turret arm 140 is shown. The detail view shows the inlet opening 341 of the hollow arm 141 , with arrows indicating the flow of liquid to be conveyed towards the upright wall 113.

[0070] Figure 3BA cross-sectional top view of the distal end of the rotator arm 140 is shown. The distal end of the arm 141 is provided with a scraper 150. The arm 141 is hollow and provides an outlet opening 342, with the arrows indicating the flow of liquid delivered from the hollow arm 141.

[0071] Another arrow indicates the direction of rotation of the rotator 130 .

Claims

1. A method for operating a crystallization vessel assembly (100), the crystallization vessel assembly comprising: a crystallization container (110), said container comprising a top wall (111), a bottom wall (112) and an upright wall (113) extending from said bottom wall to said top wall, said top wall, said bottom wall and said upright wall defining an inner cavity (114), - an upper structure (170) located on top of the container, the upper structure comprising a bearing (175) comprising an upper race member (177), a lower race member (178) and a roller body (179) between the upper race member and the lower race member, the lower race member being attached to the upper structure, - a rotator (130), said rotator comprising: - an upright rotatable shaft comprising i) a top shaft section (131') extending above the top wall, and ii) a bottom shaft section (131") in the inner cavity, the top shaft section being provided with the upper race member allowing the rotator to rotate along a shaft axis of the upright rotatable shaft, the shaft axis being coincident with the axis of rotation of the bearing; as well as - a plurality of rotator arms (140), the plurality of rotator arms comprising: - an arm (141) attached to the bottom shaft section by its proximal end, and - a scraper (150) attached at the distal end of the arm (141); The method comprises: causing crystals to grow on the inner surface of the upright wall (113), and causing the rotator (130) to rotate to scrape the crystals off the inner surface of the upright wall; Characterized in that the plurality of arms of the rotator arm are hollow arms (141), and each arm (141) of the plurality of arms includes an inlet opening (341) relatively close to the upright rotatable shaft and an outlet opening (342) relatively far from the upright rotatable shaft.

2. The method according to claim 1, wherein: The arm (141) has a cross-sectional surface area of ​​the lumen in the longitudinal direction of the arm, the cross-sectional surface area having a width / height ratio of at least 1.

25.

3. The method according to claim 2, wherein: The cross-sectional surface area has a width / height ratio of at least 1.

5.

4. The method according to any one of claims 1 to 3, wherein: The scraper (150) comprises a scraper profile (152) provided with a scraper blade (151), the scraper profile being attached to the distal ends of at least two arms (141), the scraper profile (152) having a tapered cross section that tapers gradually in the forward direction of the rotating arm.

5. The method according to any one of claims 1 to 3, wherein: Paraxylene dissolved in a solvent is introduced into the crystallization vessel assembly (100).

6. A crystallization container assembly (100), comprising: a crystallization container (110), said container comprising a top wall (111), a bottom wall (112) and an upright wall (113) extending from said bottom wall to said top wall, said top wall, said bottom wall and said upright wall defining an inner cavity (114), - an upper structure (170) located on top of the container, the upper structure comprising a bearing (175) comprising an upper race member (177), a lower race member (178) and a roller body (179) between the upper race member and the lower race member, the lower race member being attached to the upper structure, - a rotator (130), said rotator comprising: - an upright rotatable shaft, said upright rotatable shaft comprising i) a top shaft section (131') extending above said top wall, and ii) a bottom shaft section (131") in said inner cavity, said top shaft section being provided with said upper race member (177) allowing said rotator (130) to rotate along a shaft axis of said upright rotatable shaft, said shaft axis being coincident with the axis of rotation of said bearing (175); as well as - a plurality of rotator arms (140), the plurality of rotator arms comprising: - an arm (141 ) attached by its proximal end to the bottom shaft section (131 "), and - a scraper (150) attached at the distal end of the arm; Characterized in that the plurality of arms of the rotator arm are hollow arms (141), each of the plurality of arms comprising an inlet opening (341) relatively close to the upright rotatable shaft and an outlet opening (342) relatively far from the upright rotatable shaft.

7. The crystallization container assembly (100) according to claim 6, wherein: The arm (141) has a cross-sectional surface area of ​​the lumen in the longitudinal direction of the arm, the cross-sectional surface area having a width / height ratio of at least 1.

25.

8. The crystallization container assembly (100) according to claim 7, wherein: The cross-sectional surface area has a width / height ratio of at least 1.

5.

9. The crystallization container assembly (100) according to any one of claims 6 to 8, wherein: The scraper (150) comprises a scraper profile (152) provided with a scraper blade (151), the scraper profile being attached to the distal ends of at least two arms (141), the scraper profile having a tapered cross section that tapers in a forward direction of the rotating arm.

10. The crystallization vessel assembly (100) according to any one of claims 6 to 8, wherein: The plurality of rotator arms (140) are distributed on the bottom shaft section (131") in the longitudinal direction of the rotation axis.

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