Apparatus for producing a powdery substance and method for using the same

Abstract

The present invention relates to an apparatus for producing powdery substances, comprising a device (5) for dropletization of the liquid phase, a gas addition point (15) above the device (5) for dropletization, at least one gas withdrawal point (19) on the periphery of the apparatus (1), a solids withdrawal point (12), and a tower shell (13) located between the device (5) for dropletization and the gas withdrawal point (19), with a region (11) above the solids withdrawal point (12) that at least partially has a hydraulic diameter that gradually decreases towards the solids withdrawal point (12), the region (11) having a maximum hydraulic diameter that is greater than the average hydraulic diameter of the tower shell (13), The tower shell (13) projects into the region (11) at least partially having a decreasing hydraulic diameter, thereby forming an annular channel (23) between the part of the tower shell (13) projecting into the region (11) at least partially having a decreasing hydraulic diameter and an upper part (27) of the region at least partially having a decreasing hydraulic diameter, at least one gas withdrawal point (19) is disposed in the annular channel (23), and the part of the tower shell (13) projecting into the region (11) at least partially having a decreasing hydraulic diameter and forming the inner wall of the annular channel (23) is at least partially made of a gas-permeable material (29). The present invention further relates to a method of using the apparatus (1) for producing powdered poly(meth)acrylate.

Description

Technical Field

[0001] The present invention relates to an apparatus for producing a powdery substance, the apparatus comprising a device for dropletization of a liquid phase, a gas addition point above the device for dropletization, at least one gas extraction point at the periphery of the apparatus, a solid extraction point, and a tower shell between the device for dropletization and the gas extraction point, having, above the solid extraction point, a region at least partially having a hydraulic diameter that gradually decreases towards the solid extraction point and having a maximum hydraulic diameter greater than the average hydraulic diameter of the tower shell, the tower shell protruding into the region at least partially having a gradually decreasing hydraulic diameter, whereby an annular flow path is formed between the part of the tower shell protruding into the region at least partially having a gradually decreasing hydraulic diameter and the upper part of the region at least partially having a gradually decreasing hydraulic diameter, and at least one gas extraction point is disposed in the annular flow path. The present invention further relates to a method of using such an apparatus.

Background Art

[0002] One use of such an apparatus is, for example, in the production of poly(meth)acrylates used, in particular, as water-absorbing polymers for the production of, for example, diapers, tampons, sanitary napkins, and other hygiene articles, or as water retention agents for market-oriented vegetable cultivation.

[0003] Various methods are known for the production of water-absorbent polymers. For example, additives used in the production of monomers and poly(meth)acrylates can be added to a kneading mixer, in which the monomers react to yield a polymer. A rotating shaft with kneading bars in the kneading mixer pulverizes the formed polymer into lumps. The polymer taken out of the kneading mixer is dried and pulverized and sent for further processing. In an alternative variant, the monomers are introduced in the form of a monomer solution, which may further contain other additives, into a reactor for droplet polymerization. When introducing the monomer solution into the reactor, the solution decomposes into droplets. The mechanism of droplet formation may be turbulent or laminar jet breakup, or other droplet formation. The mechanism of droplet formation depends on the entry conditions and the physical properties of the monomer solution. The droplets fall downward in the reactor, and in the process, the monomers react to yield a polymer. There is a fluidized bed in the lower region of the reactor, into which the polymer particles formed from the droplets by the reaction fall. Then, further reactions occur in the fluidized bed. Corresponding methods are described, for example, in International Publication No. WO 2006 / 079631, International Publication No. WO 2008 / 086976, International Publication No. WO 2007 / 031441, International Publication No. WO 2008 / 040715, International Publication No. WO 2010 / 003855, International Publication No. WO 2011 / 026876, and International Publication No. WO 2017 / 085093.

[0004] In the reactor for the above-mentioned droplet polymerization, gas is added at two locations. The first gas stream is introduced above the device for droplet formation, and the second gas stream is introduced from below through the fluidized bed. These gas streams have flow directions opposite to each other. The gas is withdrawn from the reactor through an annular flow path formed by the outer tower shell protruding into a region with a gradually decreasing hydraulic diameter. In this case, the total gas volume supplied to the reactor must be guided to be removed. This leads to a high gas velocity in the region of the annular flow path, and the gas velocity can be high enough for the polymer material to be mixed into the gas passing through the annular flow path. This first leads to a decrease in yield or an increased load on off-gas dust removal, and second, as a result of the monomer solution that has not fully reacted yet, there is a risk that the mixed particles will adhere to the walls of the annular flow path and the downstream gas guiding line, thus leading to undesirable deposits.

[0005] To avoid the mixing of droplets or particles, WO 2017 / 085093 proposes designing the annular flow path such that the ratio of the horizontal area of the annular flow path to the horizontal area surrounded by the outer tower shell is within the range of 0.3 to 5.

[0006] The fact that the gas flow is narrowed and the gas flowing downstream in the reactor has to be turned 180° by the gas flow flowing upward through the fluidized bed due to the outer tower shell protruding into a region having at least partially a gradually decreasing hydraulic diameter is a disadvantage of the reactor for droplet polymerization. As a result, turbulent flow and in some cases the mixing of small particles, or vortices in which particles are trapped may occur. Furthermore, as a result of the outer tower shell being elongated and protruding into a region having at least partially a gradually decreasing hydraulic diameter, additional weight is generated, which hinders the handling of the outer tower shell, and according to the description of WO 2017 / 085093, additional supports may be required in the annular flow path for static stabilization. However, such supports in the annular flow path are disadvantageous because they form constrictions, which lead to high velocities at the entrance of the annular flow path and thus may lead to more particle mixing into the flow path.

Prior Art Documents

Patent Documents

[0007]

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

Patent Document 5

Patent Document 6

Patent Document 7

Summary of the Invention

Problems to be Solved by the Invention

[0008] Therefore, an object of the present invention is to provide an apparatus for producing a powdery substance that has no disadvantages of the apparatuses known in the art.

Means for Solving the Problems

[0009] This object is achieved by an apparatus for producing a powdery substance, the apparatus comprising a device for atomizing a liquid phase, a gas addition point above the device for atomizing, at least one gas extraction point at the periphery of the apparatus, a solid extraction point, and a tower outer shell between the device for atomizing and the gas extraction point, having, above the solid extraction point, a region at least partially having a hydraulic diameter that gradually decreases towards the solid extraction point and having a maximum hydraulic diameter larger than the average hydraulic diameter of the tower outer shell, the tower outer shell protruding into the region at least partially having a gradually decreasing hydraulic diameter, whereby an annular flow path is formed between the part of the tower outer shell protruding into the region at least partially having a gradually decreasing hydraulic diameter and the upper part of the region at least partially having a gradually decreasing hydraulic diameter, at least one gas extraction point being arranged in the annular flow path and protruding into the region at least partially having a gradually decreasing hydraulic diameter, and the part of the tower outer shell forming the inner wall of the annular flow path being made of at least partially a gas-permeable material.

[0010] Since the part of the tower outer shell that protrudes into the region at least partially having a gradually decreasing hydraulic diameter and forms the inner wall of the annular flow path is made of at least partially a gas-permeable material, in particular, a part of the gas flowing downward in the tower outer shell can flow directly into the annular flow path through the part made of the gas-permeable material, without having to flow around the tower outer shell protruding into the region at least partially having a gradually decreasing hydraulic diameter. The part made of the gas-permeable material has a larger area through which the gas can flow, and thus can reduce the velocity of the gas entering the annular flow path. As a result, there is an additional effect that the entrapment of particles is reduced and the entry of particles into the annular flow path is reduced. The reduced gas velocity also has the additional advantage of reducing the formation of vortices, resulting in a further reduction in the entry of particles into the annular flow path.

[0011] In addition, since a part of the tower outer shell is made of a gas-permeable material, material can be saved, thus reducing the weight of the tower outer shell and making it possible to omit the support struts extending into the annular flow path.

[0012] Hydraulic diameter d h is defined as follows: d h = 4·A / C where A is the area and C is the circumference. Using this hydraulic diameter, the configuration of the device becomes independent of the shape of the cross-sectional area. This area may be, for example, circular, rectangular, of any polygonal shape, oval or elliptical. However, a circular cross-sectional area is preferred. In the context of the present invention, the average hydraulic diameter is understood to mean the arithmetic mean.

[0013] The powdery substance produced by the device preferably has a Sauter mean particle diameter in the range of 1 μm to 10 mm, more preferably in the range of 10 μm to 1 mm, particularly in the range of 50 μm to 500 μm.

[0014] The gas-permeable material is preferably selected such that droplets or particles dispersed in the gas stream cannot pass through the gas-permeable material. Thus, the gas-permeable material preferably has a mesh size that depends on the average value and width of the particle size distribution. The larger the particles produced in the device and the narrower the particle size distribution, the larger the mesh size can be. Preferably, the gas-permeable material has a mesh size in the range of 0.5 μm to 5 mm. More preferably, the gas-permeable material has a mesh size in the range of 2 μm to 1 mm, particularly in the range of 10 μm to 500 μm. Therefore, the mesh size of the gas-permeable material is selected such that at least 50% by weight of the powdery substance, more preferably at least 75% by weight of the powdery substance, particularly at least 90% by weight of the powdery substance, with respect to the particle size distribution of the powdery substance produced in the device, is retained by the gas-permeable material.

[0015] Suitable gas permeable materials are, for example, metal braids, fabrics, nets, lattice materials, mesh materials, perforated plates, or non-woven fabrics or felts. The gas permeable material is preferably made of a temperature- and chemical-resistant metal, ceramic, natural fiber, synthetic fiber, or mineral fiber, or a combination of these materials. Examples of such materials are stainless steel, chromium steel, bronze, brass, copper, natural fibers such as wool, cotton, linen, bamboo, or cellulose, carbon fibers, glass fibers, mineral fibers, or polymers such as polyamides, polyesters, polypropylenes, polyether ether ketones, polyphenylene sulfides, and fluoropolymers. When the gas permeable material is a fabric, net, mesh material, or non-woven fabric or felt, the fibers of the above materials are usually used. Particularly preferably, the gas permeable material is made of a woven stainless steel braid, lattices or grids. When the gas permeable material is a perforated plate, the holes forming the perforations of the perforated plate may all have the same size or different sizes. Further, the holes may be uniformly distributed or randomly distributed in the perforated plate. When the perforated plate is used as the gas permeable material, it is particularly preferable that the hole size of the perforated plate corresponds to the above mesh size.

[0016] The portion of the outer shell of the tower that forms the inner wall of the annular flow path is made of at least a partially gas-permeable material, at least within the region where the gas extraction point is disposed. By making the portion of the outer shell of the tower that forms the inner wall of the annular flow path at least partially from a gas-permeable material within the region where the gas extraction point is disposed, gas can flow directly through the gas-permeable material to the gas extraction point. When a compressor is used to extract gas from the apparatus into the gas extraction line, a more uniform gas flow can be achieved within the annular flow path by forming the portion of the outer shell within the region where the gas extraction point is disposed from a gas-permeable material. This is because, typically, at the gas extraction point, the pressure is lower than in the region of the annular flow path where the gas extraction point is not located due to the suction of the compressor, and due to the lower pressure, the gas velocity within the region where the gas extraction point is located is higher. By making the outer shell from a gas-permeable material within the region where the gas extraction point is located, the flow cross-sectional area increases and thus the velocity is reduced.

[0017] When the portion of the outer shell of the tower that forms the inner wall of the annular flow path is made partially of a gas-permeable material, the portion made of the gas-permeable material and the solid material of the outer shell may have any pattern. For example, it is possible to have alternating sections made of the solid material of the outer shell and sections made of the gas-permeable material, or to have an opening of any shape, closed by the gas-permeable material, in the solid material. When the solid material of the outer shell and the gas-permeable material form alternating sections, the sections may be present horizontally (perpendicular to the axis of the outer shell), vertically (parallel to the axis of the outer shell), or inclined at any angle with respect to the axis of the outer shell. When the solid material of the outer shell has an opening closed by the gas-permeable material, the openings may be uniformly distributed, randomly distributed, and may all have the same size or different sizes.

[0018] When the outer shell of the tower that forms the inner wall of the annular flow path and protrudes into a region having at least partially a hydraulically diameter that decreases successively includes a section extending in the horizontal direction, it is particularly preferable that the outer shell of the tower that forms the inner wall of the annular flow path has an upper portion made of the material of the outer shell and a lower portion made of a gas-permeable material. In this embodiment, the lower portion is entirely made of a gas-permeable material.

[0019] When the outer shell is made of a gas-permeable material only within the region where the gas extraction point is located, it is also possible that the region of the inner wall of the annular flow path made of the gas-permeable material has an upper portion made of the material of the outer shell and a lower portion made of a gas-permeable material.

[0020] When the inner wall of the annular flow path has an upper portion made of the material of the outer shell and a lower portion made of a gas-permeable material, the ratio of the height of the upper portion to the height of the lower portion is preferably in the range of 0 to 3. More preferably, the ratio of the height of the upper portion to the height of the lower portion is in the range of 0.5 to 2, particularly in the range of 0.75 to 1.25. The area made of the gas-permeable material is preferably such that the ratio of the area made of the gas-permeable material to the gas volumetric flow is in the range of 0.1 to 1000 m 2 / (m 3 / s), more preferably in the range of 0.5 to 100 m 2 / (m 3 / s), particularly in the range of 0.5 to 10 m 2 / (m 3 / s).

[0021] In this context, the "upper portion" and the "lower portion" refer to the positions within the outer shell of the tower. The "upper portion" is closer to the device for atomization than the "lower portion". Further, the heights of the upper portion and the lower portion are given with reference to the direction parallel to the axis of the outer shell of the tower.

[0022] Furthermore, it is also possible that the portion of the outer shell of the tower that forms the inner wall of the annular flow path is entirely made of a gas-permeable material.

[0023] However, it is particularly preferable that a portion of the outer shell of the tower that protrudes into a region having at least partially a gradually decreasing hydraulic diameter and forms the inner wall of the annular flow path has an upper portion made of the material of the outer shell of the tower and a lower portion made of a gas-permeable material. In this embodiment, the lower portion is entirely made of a gas-permeable material. Being entirely made of a gas-permeable material also includes configurations having, for example, a support structure for connecting sections of the gas-permeable material or stabilizing the gas-permeable material to maintain its form. Such a support structure may cover up to 5% of the area of the region made of the gas-permeable material.

[0024] When only a part of the inner wall of the annular flow path is made of a gas-permeable material, the area made of the gas-permeable material and the pressure loss characteristics of the gas-permeable material are preferably selected such that at least 10%, more preferably at least 20%, particularly at least 30% of the total gas flow flows through the gas-permeable material.

[0025] Regardless of whether it is made entirely of a gas-permeable material or only partially of a gas-permeable material, the part of the tower outer shell that protrudes into the region having a gradually decreasing hydraulic diameter at least partially and forms the inner wall of the annular flow path is oriented parallel to the axis of the tower outer shell and thus may have a constant cross-sectional area, or may have a gradually increasing or decreasing cross-sectional area, especially in combination with a hydraulically uniformly increasing or decreasing diameter. When the part of the tower outer shell that protrudes into the region having a gradually decreasing hydraulic diameter at least partially and forms the inner wall of the annular flow path has a circular cross-sectional area and a gradually increasing or decreasing hydraulic diameter, it is particularly preferred that this part of the tower outer shell has a frustum of a cone shape. Particularly preferably, the part of the tower outer shell that forms the inner wall of the annular flow path has a gradually increasing or decreasing hydraulic diameter together with an angle with respect to the axis of the tower outer shell in the range of -45 to +30°, more preferably in the range of -30 to +20°, especially in the range of -25 to +10°. In this context, a positive angle means that the hydraulic diameter, and thus the cross-sectional area, increases in the direction towards the lower end of the tower outer shell, and correspondingly, a negative angle means that the hydraulic diameter, and thus the cross-sectional area, decreases in the direction towards the lower end of the tower outer shell.

[0026] An advantage of the gradually increasing hydraulic diameter of the part of the tower outer shell that forms the inner wall of the annular flow path is that particles generated within the device do not fall onto this part and thus cannot form deposits thereon. However, due to the gas flow and the lower gas velocity when flowing into the annular flow path, it is preferred that the part of the tower outer shell that forms the inner wall of the annular flow path has a gradually decreasing hydraulic diameter.

[0027] When the part of the tower wall forming the inner wall of the annular flow path is made entirely of a gas-permeable material, or when the lower part of the part of the tower wall forming the inner wall of the annular flow path is made entirely of a gas-permeable material, it is preferable that the gas-permeable material forms compartments connected to each other. Particularly preferably, the compartments have a height corresponding to the distance from the lower end to the upper end of the part of the tower outer shell made of the gas-permeable material. In order to connect the gas-permeable material and, in particular, to direct the part of the tower outer shell made of the gas-permeable material in the desired direction, it is particularly preferable that a fixing element is connected to the tower outer shell and the compartments of the gas-permeable material are fixed to the fixing element. For this purpose, the fixing element is preferably in the form of a rod and is either connected to the tower outer shell, for example, by welding, screwing, bolting, or is integrally formed with the tower outer shell, for example, by cutting out that part from the material of the tower outer shell at the location where the compartment is to be fixed. The fixing of the fixing element and / or the compartments of the gas-permeable material to the tower outer shell is also possible, for example, by welding, screwing, soldering, gluing, clamping, pressing, spot welding, riveting, nailing, bolting, or hanging using loops. Particularly preferably, for reasons of maintenance and to enable the replacement of the compartments of the gas-permeable material, the compartments of the gas-permeable material are fixed to the fixing element by screwing.

[0028] To avoid deposits on the fixing element, it is particularly preferable that the fixing element is arranged on the outside, that is, it faces into the annular flow path and does not face into the space surrounded by the tower outer shell.

[0029] The gas-permeable material can be supported by a support structure or can hang freely like a curtain. When a support structure is used, its design depends on the gas-permeable material, the size of the device, and the gas velocity. It is particularly preferable to provide a support structure when intense movement of the gas-permeable material is expected. When the gas-permeable material is fixed within a compartment of the tower outer shell, the fixing element used for fixing the compartment of the gas-permeable material can also serve the role of the support structure.

[0030] In addition to at least partially forming the lower part of the outer casing of the tower that also forms the inner wall of the annular flow path, it is additionally possible for the inlet to the annular flow path to be at least partially closed by a gas-permeable material. For this purpose, the gas-permeable material is connected to the lower edge of the outer casing of the tower that protrudes into a region having at least partially a gradually decreasing diameter and a region having at least partially a gradually decreasing hydraulic diameter. By at least partially closing the annular flow path with a gas-permeable material, it is possible to avoid particles generated within the device being drawn out with the gas flow at the gas extraction point. In addition to only partially closing the inlet to the annular flow path, it is also possible for the inlet to the annular flow path to be completely closed by a gas-permeable material. However, in order to avoid clogging of the gas-permeable material and thus an increase in pressure loss and blockage of the inlet to the annular flow path, it is preferred to only partially close the inlet to the annular flow path.

[0031] The outer wall of the annular flow path formed by the upper part of the region having at least partially a gradually decreasing hydraulic diameter may have a gradually increasing hydraulic diameter in the direction of the upper end of that region. However, preferably, at least the upper part of the region having at least partially a gradually decreasing hydraulic diameter that forms the outer wall of the annular flow path has a constant hydraulic diameter. The upper end of the annular flow path is closed by a cover that connects the upper end of the region having at least partially a gradually decreasing hydraulic diameter and the outside of the outer casing of the tower. Therefore, the cover is oriented perpendicular to the axis of the outer casing of the tower and may form a flat cover or any suitable form. The cover may be designed, for example, to terminate the annular flow path with a curved section, preferably in the form of a parabola, ellipse, or quarter circle. When the cover that terminates the annular flow path in the upward direction has a curved section, the latter is adjusted such that the curvature is concave within the annular flow path.

[0032] When the upper end of a region having at least partially a gradually decreasing hydraulic diameter has a constant hydraulic diameter and a gas-permeable material is connected to the region having at least partially a gradually decreasing hydraulic diameter, the gas-permeable material is preferably connected to the region having at least partially a gradually decreasing hydraulic diameter at the transition from the constant hydraulic diameter to the gradually decreasing hydraulic diameter.

[0033] At least one gas extraction point may be arranged at the upper end of the region having at least partially a gradually decreasing hydraulic diameter and forming the outer wall of the annular flow path, or on the cover of the annular flow path. Regardless of whether it is arranged on the outer wall or on the cover of the annular flow path, the gas extraction point is arranged such that the lower edge of the gas extraction point is higher than the lower edge of the outer casing of the tower forming the inner wall of the annular flow path. Particularly when the cover is in the shape of a frustum of a cone, it is preferable to arrange the gas extraction point on the cover of the annular flow path. In order to avoid an excessive flow velocity in the annular channel at the lower edge of the wall of the outer casing protruding into the region having at least partially a gradually decreasing hydraulic diameter, the flow cross-sectional area between the lower edge of the permeable part of the outer casing and the outer wall of the annular flow path is preferably larger than 80%, more preferably larger than 90%, particularly preferably equal to or larger than 100% of the flow cross-sectional area in the annular flow path. The flow cross-sectional area in the annular flow path is defined as the area of the portion obtained by horizontally cutting the annular flow path at the lower edge of the permeable part of the outer casing forming the inner wall of the annular flow path. The flow cross-sectional area between the lower edge of the permeable part of the outer casing and the outer wall of the annular flow path is defined as the surface area of the cone connecting the edge and the outer wall of the annular flow path, and the cone angle is such that the cone surface is perpendicular to the outer wall.

[0034] To keep the cross-sectional area of the gas extraction points, and thus the gas flow through one gas extraction point, at a manageable size, and to ensure a symmetric arrangement of the gas extraction points for a flawless flow profile within the device, it is preferred that at least two gas extraction points are provided, and these gas extraction points are evenly arranged over the periphery of the annular flow path. The number of gas extraction points is calculated from the gas volume flowing through the device and the cross-sectional area of the gas extraction points. It is particularly preferred that at least three gas extraction points, especially at least four gas extraction points, are provided. "Evenly arranged over the periphery of the annular flow path" means that the distance between the centers of two adjacent gas extraction points is the same in each case for all gas extraction points.

[0035] To enable the reuse of the gas, it is preferred that the gas flows through a circuit. To provide a circuit, the gas flow path connects the gas extraction points and the gas addition points. And the gas flow can be assisted by providing a gas conveyance device within the gas flow path.

[0036] Since it cannot be ruled out that particles of the substance produced within the device are withdrawn together with the gas flow, it is possible to provide a solid separation device within the gas flow path. Suitable solid separation devices are, for example, filters or centrifuges, such as cyclones. To enable the inspection or cleaning of the solid separation device without interrupting the operation of the device for producing a powdery substance, it is possible to provide, for example, a redundant system where two solid separation devices are provided in parallel in each case, the gas flow always takes place through one solid separation device, and the other can be switched off for cleaning. This is particularly recommended when using filters.

[0037] In addition to solid separators such as filters and centrifuges, it is also possible to additionally or alternatively provide further devices for gas workup, such as gas scrubbers or condensers. Such devices for gas workup are particularly preferred when the gas is reused and flows through a circuit in the gas flow path from the gas extraction point to the gas addition point. In this case, the device for gas workup is preferably arranged within the gas flow path. If it is intended to supply the device with a gas containing water or a solvent, it is also possible to introduce the solvent or water into the gas within the device for gas workup. The amount of water or solvent in the gas is preferably kept below the saturation point so that the water or solvent in the gas is in the gaseous state.

[0038] An apparatus for producing a powdery substance generally comprises a top part having a device for atomizing a liquid starting material, an intermediate region through which the liquid starting material falls and is converted into solid particles, and a bottom region where the solid particles fall and a solid extraction point is arranged. The solid extraction point is thus at the lower end of a region having at least partially a gradually decreasing hydraulic diameter.

[0039] In order to prevent the liquid starting material emerging from the device for atomization from impinging on the walls of the apparatus and at the same time to advantageously configure the apparatus in terms of both statics and material costs, it is preferred to form the top part of the apparatus in the shape of a truncated cone and to arrange the device for atomization within the truncated conical top part of the apparatus.

[0040] The truncated conical configuration of the top part of the apparatus makes it possible to save material compared to a cylindrical configuration. Furthermore, the truncated conical top part improves the structural stability of the apparatus. A further advantage is that the gas introduced from the top part of the apparatus has to be supplied through a relatively small cross-section and then, due to the truncated conical configuration, comes into better contact with the droplets generated within the device for atomization and there is no gas bypass near the wall of the truncated conical top part.

[0041] To keep the height of the device as low as possible, it is further advantageous if the device for atomizing the liquid starting material is arranged as high as possible within the frustum-conically configured top head. This means that the device for atomizing the liquid starting material is arranged within the frustum-conically configured top head at a height where the diameter of the frustum-conically configured top head is approximately the same as the diameter of the device for atomizing.

[0042] To prevent the liquid starting material emerging from the device for atomizing within the region of the outermost holes from impinging on the wall of the frustum-conically configured top head, it is particularly preferred that the hydraulic diameter of the frustum-conically configured top head at the height at which the device for atomizing is arranged is 2% to 30%, more preferably 4% to 25%, and more particularly 5% to 20% larger than the hydraulic diameter of the area enclosed by the shortest line connecting the outermost holes. The somewhat larger hydraulic diameter of the top head additionally ensures that the droplets do not hit and adhere to the wall of the device even below the top head of the device at an early stage.

[0043] Above the device for atomizing the liquid starting material there is a gas addition point, and thus gas and droplets flow simultaneously through the device from top to bottom.

[0044] Preferably, the device for producing the powdery substance comprises a fluidized bed arranged at the bottom of a region having at least partially a gradually decreasing hydraulic diameter. In this fluidized bed, the powdery substance accumulates and may preferably continue to dry or react without agglomeration of individual particles. To fluidize the powdery substance in the fluidized bed, a fluidizing gas is supplied to the fluidized bed at the bottom. This fluidizing gas also enters the device and is withdrawn from the device at a gas extraction point. From the fluidized bed, the powdery substance can be withdrawn at a solid withdrawal point.

[0045] Since the fluidized bed is in the lower region of the device, the effect of this is that the gas flows in the opposite direction from bottom to top in the lower region of the device. Since the gas is introduced into the device from both above and below, the gas needs to be withdrawn between the device for atomizing the liquid starting material and the fluidized bed. Therefore, the gas extraction point is arranged at the transition part from the device outer shell to the region having a hydraulic diameter that gradually decreases in the direction of the fluidized bed.

[0046] In the region having a gradually decreasing hydraulic diameter, the hydraulic diameter decreases in the direction of the fluidized bed from the gas extraction point downward. The decrease in the hydraulic diameter is preferably linear, whereby the region having a gradually decreasing hydraulic diameter takes the form of an inverted truncated cone.

[0047] The outer shell of the tower extending between the top having the device for atomization and the gas extraction point preferably has a constant hydraulic diameter. More preferably, the outer shell of the tower is cylindrical. Alternatively, it is also possible to configure the outer shell of the tower such that its hydraulic diameter increases from top to bottom. However, in that case, it is preferable that the hydraulic diameter at the lower end of the outer shell of the tower is 10% or less, preferably 5% or less, particularly 2% or less, larger than the hydraulic diameter at the transition part from the device top to the outer shell of the tower. However, more preferably, the outer shell of the tower is implemented with a constant hydraulic diameter, and the outer shell of the tower is more preferably cylindrical.

[0048] The height of the annular flow path is preferably configured such that the ratio of the distance between the outer wall of the outer shell of the tower and the wall of the region having a gradually decreasing hydraulic diameter at the inlet to the annular flow path to the height of the annular flow path between the inlet to the annular flow path and the lower edge of the gas extraction point is in the range of 0.05 to 50. Preferably, the ratio of the distance between the outer wall of the outer shell of the tower and the wall of the region having a gradually decreasing hydraulic diameter at the inlet to the annular flow path to the height of the annular flow path between the inlet to the annular flow path and the lower edge of the gas extraction point is in the range of 0.2 to 25, particularly in the range of 0.3 to 10.

[0049] The appropriate ratio of the distance between the outer wall of the tower housing and the wall of the region with a gradually decreasing hydraulic diameter at the inlet to the annular flow path, and the height of the annular flow path between the inlet to the annular flow path and the lower edge of the gas extraction point, is such that a significant increase in velocity resulting from the standard cross-sectional narrowing in the region of the gas extraction point, generally at least a three-fold increase in velocity, is prevented from leading to an increase in particle entrainment from the device, by realizing a sufficiently large volume of the annular flow path in the form of a quiescent sedimentation zone.

[0050] The inlet to the annular flow path is understood in the context of the present invention to mean the area formed at right angles to the axis of the device between the lower end of the tower housing and the wall of the region with a gradually decreasing hydraulic diameter.

[0051] The present device can be used in any process for producing particulate materials from liquids, such as spray drying, or chemical reactions that form solid powders from liquid reactants. Processes in which a device for producing particulate materials can be used are, for example, processes for producing particulate or granular solids such as polymer particles, superabsorbents, catalysts, vitamins, enzymes, surfactants, dyes, pharmaceuticals, basic chemicals, or zeolites. Particularly preferably, the device is used in a process for producing powdered poly(meth)acrylate used, for example, as a superabsorbent. When the device is used to produce powdered poly(meth)acrylate, the liquid starting material is a liquid monomer solution, and the atomized monomer solution is converted to a polymer while falling through the intermediate region of the device. In this case, the device further comprises a fluidized bed through which the generated particles fall and the reaction is completed. Furthermore, in the fluidized bed, the generated particles are dried and residual monomers are removed from the particles.

[0052] Embodiments of the present invention are shown in the figures and will be described in more detail in the following description.

Brief Description of the Drawings

[0053]

Figure 1

Figure 2

Figure 3

Figure 4a

Figure 4b

Figure 4c

Figure 5a

Figure 5b

Figure 5c

Embodiments for Carrying Out the Invention

[0054] FIG. 1 shows a longitudinal cross section passing through an apparatus for manufacturing a powdery substance in a first embodiment.

[0055] An apparatus 1 for manufacturing a powdery substance includes a top portion 3 that houses a device 5 for atomization, an intermediate region 7 where a liquid starting material 9 is converted into solid particles, and a lower region 11 that has at least partially a gradually decreasing hydraulic diameter and is provided with a solid withdrawal point 12 at the bottom.

[0056] To produce a powdery substance, a liquid starting material 9 is supplied to a device 5 for droplet formation. For this purpose, the device 5 for droplet formation can be any device known to the person skilled in the art, by means of which droplets are formed. In particular, for the production of poly(meth)acrylate, it is preferred that the device 5 for droplet formation comprises a plurality of channels, each channel being connected to a monomer supply that provides a monomer solution that serves as the liquid starting material in the production of poly(meth)acrylate. In this case, in order to generate droplets, each channel is provided with a hole on its bottom side, through which the liquid starting material 9 drops into the device in the form of small droplets. Therefore, the size of the droplets depends on the size of the holes as well as the viscosity of the liquid starting material, the flow rate at the holes, and the surface tension. Through a first addition point 15 of a gas above the device 5 for droplet formation, a gas, for example nitrogen or air, is introduced into the device 1. This gas flow assists the liquid starting material 9 emerging from the device 5 for droplet formation to break down into individual droplets. In addition, the way in which the gas addition point 15 is designed promotes the absence of contact between individual droplets and their coalescence into larger droplets.

[0057] The intermediate region 5 of the device 1 is formed by the tower outer shell 13, which preferably has a cylindrical shape with a constant hydraulic diameter. To make the tower outer shell 13 as short as possible and further avoid the droplets of the liquid starting material 9 hitting the tower outer shell 13, the top 3 is preferably conical as shown here. In this case, the device 5 for atomization is above the cylindrical part of the tower outer shell 13 that forms the intermediate region 7 within the conical top 3. However, alternatively, it is also possible to form the top 3 of the device 1 into a cylinder with the same diameter as the intermediate region 7. However, the conical configuration of the top 3 is preferred. The position of the device 5 for atomization is selected such that there is still a sufficiently large distance between the outermost hole through which the liquid starting material is supplied and the wall of the device to prevent the droplets from hitting the wall. For this purpose, the distance should preferably be in the range of at least 50 - 1500 mm, more preferably 100 - 1250 mm, and particularly 200 - 750 mm. It will be understood that a larger distance from the wall of the device is also possible. However, this has the disadvantage that a larger distance is associated with poor utilization of the cross-section of the device.

[0058] The lower region 11 may end with a fluidized bed 17, into which the particles formed from the liquid starting material during the fall drop. The fluidized bed 17 is particularly preferred when the device 1 is used for producing poly(meth)acrylate. In this case, in the fluidized bed, further reactions proceed to yield the desired substances. Preferably, the outermost hole through which the liquid starting material is atomized is arranged such that the droplets falling vertically downward fall into the fluidized bed 17. This can be achieved, for example, by the hydraulic diameter of the fluidized bed 17 being at least as large as the hydraulic diameter of the area surrounded by the line connecting the outermost holes of the device 5 for atomization, the cross-sectional area of the fluidized bed and the area formed by the line connecting the outermost holes having the same shape, and the centers of these two areas being in the same position in the vertical projection of one onto the other.

[0059] In addition, in order to avoid droplets hitting the wall of the device 1 even in the intermediate region 7, the hydraulic diameter at the height of the midpoint between the droplet-forming device 5 and the gas extraction point 19 is at least 10% larger than the hydraulic diameter of the fluidized bed 17.

[0060] The device 1 may have any desired cross-sectional shape. However, the cross-section of the device 1 is preferably circular. In that case, the hydraulic diameter corresponds to the diameter of the device 1.

[0061] Above the solid extraction point 12 and, if present, above the fluidized bed 17, the diameter of the device 1 increases in the embodiment shown here such that the device 1 flares conically upwards from the bottom in the lower region 11. This has the advantage that particles hitting the wall formed within the device 1 can slide smoothly down along the wall to the solid extraction point 12. To avoid solidification, it is additionally possible to provide tappers (not shown here) outside the conical part of the device 1, along with vibrating the wall of the device 1, so that the adhering particles fall off and slide smoothly into the fluidized bed 17 or, if present, to the solid extraction point 12.

[0062] For the gas supply for the operation of the fluidized bed 17, a gas distributor 21 present below the fluidized bed 17 blows gas into the fluidized bed 17.

[0063] Since gas is introduced into the apparatus 1 from both above and below, it is necessary to extract gas from the apparatus 1 at an appropriate position. For this purpose, at least one gas extraction point 19 is arranged at the transition from an intermediate region 7 having a constant cross-section to a lower region 11 having at least partially a gradually decreasing diameter. In this case, the wall of the cylindrical intermediate region 7 projects into the lower region 11 which has at least partially a gradually decreasing hydraulic diameter, and the diameter at this position of the lower region 11 which has at least partially a gradually decreasing hydraulic diameter is larger than the diameter of the intermediate region 7. In this way, an annular flow path 23 surrounding the wall of the intermediate region 7 is formed, and gas can flow into and be extracted from the annular flow path 23 through at least one gas extraction point 19 connected to the annular flow path 23.

[0064] In order to form the annular flow path 23, it is particularly preferred that the lower region 11 comprises a part 25 which widens conically and a part 27 having a constant hydraulic diameter, and the part 27 has a constant hydraulic diameter and thereby forms the outer wall of the annular flow path 23.

[0065] The particles formed within the apparatus 1 are extracted through at least one solid extraction point 12.

[0066] According to the present invention, the part of the tower outer shell 13 protruding into the lower region 11 is made at least partially of a gas-permeable material 29. By making at least a part of the tower outer shell 13 protruding into the lower region 11 of the gas-permeable material 29, only a part of the gas flows into the annular flow path through its inlet between the tower outer shell and the wall of the lower part 11, and the other part of the gas flows through the gas-permeable material 29, so that the velocity of the gas flowing into the annular flow path 23 can be reduced. This is shown by arrow 31. Since the gas velocity at the inlet to the annular flow path is reduced, particle entrainment can be reduced.

[0067] Figure 2 shows a longitudinal cross-section through an apparatus for producing a powdery substance in a second embodiment.

[0068] In the embodiment shown in FIG. 2, the orientation of the gas permeable material 29 is different from that in FIG. 1. In the embodiment shown in FIG. 1, the gas permeable material 29 is oriented parallel to the axis of the tower outer shell 13, which means that the tower outer shell is stretched straight without bending or buckling. In contrast, in the embodiment shown in FIG. 2, the gas permeable material 29 has an angle α with respect to the central axis of the tower outer shell 13.

[0069] When the gas permeable material 29 is oriented as shown in FIG. 2, it is possible for the inlet to the annular flow path 23 to open as shown here, or for the inlet to the annular flow path 23 to be at least partially closed by the gas permeable material 29. When the inlet to the annular flow path 23 is at least partially closed by the gas permeable material 29, the gas permeable material 29 is connected to the wall of the lower region 11 that forms the outer wall of the annular flow path 23.

[0070] A longitudinal cross-section through the apparatus for producing the powdery substance in the third embodiment is shown in FIG. 3.

[0071] The embodiment of FIG. 3 is different from the embodiment of FIG. 2 in the orientation of the gas permeable material 29. Instead of having an angle α such that the hydraulic diameter of the tower outer shell increases towards the lower edge of the tower outer shell as shown in FIG. 2, according to the embodiment of FIG. 3, the angle α is such that the hydraulic diameter of the tower outer shell decreases towards the lower edge of the tower outer shell, whereby the cross-sectional area of the inlet to the annular flow path 23 is larger compared to the orientation as shown in FIG. 1 or FIG. 2, and thus the velocity of the gas flowing around the lower edge of the tower outer shell and entering the annular flow path is further reduced.

[0072] Examples of the design of the lower part of the tower outer shell 13 protruding into the lower region 11 to form the annular flow path 23 are shown in FIGS. 4a - 4c.

[0073] In FIG. 4a, the entire portion of the tower outer shell 13 protruding into the lower region 11 having at least partially a gradually decreasing hydraulic diameter is made entirely of the gas permeable material 29. In this case, therefore, the entire inner wall of the annular flow path 23 is made of the gas permeable material 29.

[0074] According to FIG. 4b, the portion of the outer tower shell 13 protruding into the lower region 11 has an upper portion 31 made of the material of the outer tower shell 13 and a lower portion 33 made of a gas-permeable material 29.

[0075] In the embodiment shown in FIG. 4c, only a part of the wall portion of the outer tower shell 13 forming the inner wall of the annular flow path 23 is made of the gas-permeable material 29. In this case, it is particularly preferable that the portion of the outer tower shell 13 protruding into the lower region 11 and forming the inner wall of the annular flow path 23 is made of the gas-permeable material 29 in the region where the gas extraction point 19 is arranged. However, it is also possible to partially make the portion of the outer tower shell 13 forming the inner wall of the annular flow path 23 from the gas-permeable material 29 in any other pattern.

[0076] When only a part of the wall of the outer tower shell 13 forming the inner wall of the annular flow path 23 is made of the gas-permeable material 29, it is also possible to form an opening 35 in the outer tower shell 13 and close it with the gas-permeable material. The opening 35 may have any shape, for example, circular as shown in FIG. 5a or rectangular as shown in FIG. 5b. The openings may be uniformly or randomly dispersed. Further, all the openings may have the same size or different sizes. FIG. 5a shows an example of a random dispersion of openings having different sizes, and FIG. 5b shows a uniform dispersion of openings all having the same size. In addition to the embodiment shown here where the randomly dispersed openings have different sizes, it is also possible to randomly disperse openings all having the same size. Further, it is also possible to have a uniform dispersion of openings having different sizes. Such a pattern is illustrated in FIG. 5c for circular openings. Further, regardless of whether the openings 35 are randomly dispersed or uniformly dispersed, in addition to the shapes of the openings shown in FIGS. 5a to 5c, the openings may have any other form.

Claims

1. An apparatus for producing a powdery substance, comprising: a device (5) for atomizing a liquid phase; a gas addition point (15) above the device (5) for atomizing; at least one gas extraction point (19) at the periphery of the apparatus (1); a solid extraction point (12); a tower outer shell (13) between the device (5) for atomizing and the gas extraction point (19); characterized in that: above the solid extraction point (12), there is a region (11) having at least partially a hydraulic diameter that gradually decreases towards the solid extraction point (12), and having a maximum hydraulic diameter larger than the average hydraulic diameter of the tower outer shell (13); the tower outer shell (13) protrudes into the region (11) having at least partially a gradually decreasing hydraulic diameter, whereby an annular flow path (23) is formed between the part of the tower outer shell (13) protruding into the region (11) having at least partially a gradually decreasing hydraulic diameter and the upper part (27) of the region having at least partially a gradually decreasing hydraulic diameter; the at least one gas extraction point (19) is disposed in the annular flow path (23) and protrudes into the region (11) having at least partially a gradually decreasing hydraulic diameter; the part of the tower outer shell (13) forming the inner wall of the annular flow path (23) is made of at least partially a gas-permeable material (29).

2. The apparatus according to claim 1, wherein the gas-permeable material (29) is a metal braid, a fabric, a net, a lattice material, or a mesh material.

3. The apparatus according to claim 1 or 2, wherein the gas-permeable material (29) has a mesh size in the range of 0.5 μm to 5 mm.

4. The apparatus according to any one of claims 1 to 3, wherein the part of the tower outer shell (13) protruding into the region (11) having at least partially a gradually decreasing hydraulic diameter and forming the inner wall of the annular flow path (23) is made of the gas-permeable material (29) in the region where the gas extraction point (19) is disposed.

5. projecting into said region (11) having at least partially a decreasing hydraulic diameter, a portion of said outer tower shell (13) forming said inner wall of said annular flow path (23) having an upper portion (31) made of the material of said outer tower shell (13) and a lower portion (33) made of said gas-permeable material (29), the device according to any one of claims 1 to 3.

6. The device according to claim 5, wherein a ratio of a height of said upper portion (31) to a height of said lower portion (33) is greater than 0 and up to 3.

7. The device according to any one of claims 1 to 3, wherein a portion of said outer tower shell (13) forming said inner wall of said annular flow path (23) is made entirely of said gas-permeable material (29).

8. By connecting said gas-permeable material (29) to an end of said outer tower shell (13) projecting into said region having at least partially a decreasing hydraulic diameter and to said region (11) having at least partially a decreasing diameter, an inlet to said annular flow path (23) is at least partially closed by said gas-permeable material (29), the device according to any one of claims 1 to 7.

9. The device according to any one of claims 1 to 8, wherein said gas-permeable material (29) consists of a plurality of compartments bonded together.

10. The device according to any one of claims 1 to 9, wherein said gas-permeable material (29) is made of at least one of stainless steel, chrome steel, bronze, brass, copper, natural fiber, carbon fiber, glass fiber, mineral fiber, or polymer.

11. The device according to any one of claims 1 to 10, wherein said region (11) having at least partially a decreasing hydraulic diameter has a constant hydraulic diameter at an upper end (27) of said region (11) forming an outer wall of said annular flow path (23).

12. The device according to any one of claims 1 to 11, wherein a gas flow path connects said gas extraction point and said gas addition point.

13. The device according to claim 12, wherein said gas flow path comprises a gas conveyance device.

14. A method of using the device according to any one of claims 1 to 13 for producing powdered poly(meth)acrylate.

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