EP3146284A1

EP3146284A1 - Gas distributer for a convective dryer having improved radial gas velocity control

Info

Publication number: EP3146284A1
Application number: EP15727584.3A
Authority: EP
Inventors: Henrik SCHØNFELDT; Christian HOLM FRIDBERG
Original assignee: SPX Flow Technology Danmark AS
Current assignee: SPX Flow Technology Danmark AS
Priority date: 2014-05-21
Filing date: 2015-05-21
Publication date: 2017-03-29
Also published as: CN106413831A; WO2015177324A1

Abstract

The invention relates to a gas distributer for, and a method of, controlling the velocity profile of a drying gas in a convective dryer, particularly the radial velocity profile, by creating an advantageous velocity profile prior to introducing the drying gas into the convective dryer chamber. The velocity profile may have different requirements depending on the convective process, chamber dimensions and atomizing means, but common gas distributer targets may be defined, such as a radial gas rotationally symmetrical velocity distribution and axial alignment. The invention further concerns a convective dryer comprising the gas distributer of the present invention, the use of said method to produce a powdery substance in a convective dryer according to the present invention.

Description

Title of the Invention

Gas Distributer for a Convective Dryer Having Improved Radial Gas Velocity Control

Field of Invention

The present invention relates to the field of gas distributers or gas dispersers mounted on spray dryers, spray coolers, spray absorbers and similar equipment, collectively called convective dryers, wherein the gas or air dispersed or distributed may be e.g. atmospheric air or a specialty gas or mixture of specialty gasses and wherein the equipment collectively called convective dryers are useful in many diverse technical fields wherein it is desired to produce a powdery material from an atomized liquid containing one or more substances to be dried and retrieved as a powdery, agglomerated, coated, or granulated material.

Background of the Invention

A convective dryer is an apparatus that produces dry powdery substances from an atomized liquid. In the process atomized droplets are dried or solidified within a processing chamber by convective heat and often mass transfer with a fluid. This process takes place in a confined space. The processing chamber is usually called a drying chamber. In case of a spray dryer, the liquid feed is atomized using an atomization device such as a rotary atomizer, a pressure nozzle or a multi-fluid nozzle, and mixed with a drying gas typically in the temperature range of -50-800 °C. The dry powdery substance can be e.g. a powder, an agglomerated powdery substance, a coated powdery substance or a granulated substance; which are all examples of products the skilled person knows may result from drying an atomizing liquid capable of forming such a powdery substance.

In order to avoid product build-up, or deposits, on the walls of the drying chamber, and hence to maintain capacity, controlled inlet conditions for the gas are required. The drying gas itself may be any gaseous phase fluid, but is often air, nitrogen, or steam. Often a dedicated component called a gas or an air distributer is used as a component for directing the gas appropriately into the drying chamber, taking into account the selected means of atomization, by ensuring a proper gas velocity profile suitable for the convective dryer.

By the term "gas distributer" or "air distributer" as used herein is meant any disperser or distributer supplied with a drying gas to be used in a convective dryer. A skilled person will know that the term "gas" may be taken to cover any single component gas, such as e.g. molecular nitrogen or argon, as well as any mixture of gases such as is found in e.g. air or steam. The present invention is hence not limited by any particular choice of the drying gas intended for distribution by the gas distributer. The skilled person will further know that air or steam is often used as the drying gas when the liquid to be atomized is an aqueous solution, while an inert gas is often used when the liquid to be atomized is a non-aqueous solution. Consequently, the term "drying gas" covers any drying gas, which may be used in a convective dryer. The gas distributer can be of any type known to the skilled person but may e.g. be in the shape of a bend duct type, a plenum type or a scroll type with each type potentially having area contractions and expansions. The gas distributer may encapsulate or include the atomizing means, in particular an atomizer, or be decoupled from the atomizing means.

As the gas velocity into the chamber is higher than the average chamber gas velocity, a drying gas jet is formed extending from a gas distributer exit surface and into the chamber. The drying gas jet has a center core that protrudes a certain distance into the chamber while continuously mixing with the surroundings, eventually becoming fully mixed with the surrounding gas.

The velocity field of the drying gas jet can be described in terms of its axial, tangential and radial gas velocity components. The axial gas velocity component is aligned with the center axis of the gas distributer; the tangential gas velocity component defines the rotational velocity component of the gas with respect to the center axis of the gas distributer while the radial velocity component defines a direction of gas movement perpendicular to the axial and tangential velocity components. The axial gas velocity component carries the gas into the chamber, the tangential velocity aids in breaking up the inlet jet, while the radial component controls direction stability.

The flow pattern in the disclosed invention can be described by applying the continuity, Navier-Stokes and energy equations as in eq. 1.3a, 1.9a and 1.11 from Fundamental mechanics of fluids by I.G. Currie 2nd edition from McGraw-Hill mechanical engineering series. The energy equation may be disregarded for isothermal flows which often is the case for well isolated ducts or ducts with small area-to-flow ratio such as the invention. Once in the spray chamber, the flow cannot be described accurately without the energy equation.

As such no single preferred value for the tangential velocity is given in the art; rather this velocity is dependent on e.g. atomizing means and chamber geometry. The tangential velocity may be influenced by the presence of guide vanes such that when these guide vanes are properly installed, a rotation of the drying gas flow is obtained. In the art it is known to use guide vanes which may be straight or curved or a combination hereof.

The radial velocity component as described above is the object of the present invention. The present inventors have now realized that for high capacity, low deposit convective drying it is preferable that the drying gas jet should be aligned best possible with the axis of the gas distributer with the radial gas velocity components being conferred a substantial degree of rotational symmetry around the central axis of the gas distributer and/or a controlled radial velocity. This ensures that as much as possible of the dryer volume is utilized, keeping the wet product away from the walls with reduced risk of deposits on the walls. As the jet by nature is unstable it is not possible to remove all instabilities, but using the teachings of the present invention, an improved jet is produced being additionally controlled along the main jet axis compared to jets prepared by conventional gas distributers . In the art (FR 1.289.817) it is known to use perforated plates in gas distributers in order to smooth the gas flow by using the pressure drop across the plate, thereby obtaining a more uniform distribution of the gas. Such perforated plates, which generally are much thinner than the average diameter of the holes in the perforated plates, influence primarily the axial velocity components and in minor degree the tangential and the radial components of the velocity field of the jet.

However, the use of such perforated plates has been shown to cause difficulties with respect to keeping the drying chamber clean. Especially, when the convection dryer is to be used in the food or pharmaceutical industry the sanitary aspects of the production design are very important. It is an objective of the present invention to improve the prior art such that this recognized problem displayed by prior art perforated plates in gas distributers is minimized or eliminated.

Also well known in the art (WO 2007/071238, WO 2011/047676) is utilizing one or more guide vanes assembled within the gas distributer to regulate the flow path and velocity of its constituent velocity components, particularly the tangential velocity components, before contacting the drying gas with the atomized liquid.

However, none of these assemblies of guide vanes have achieved the benefits of the present invention in conferring a substantial degree of rotational symmetry for the radial gas velocity component and/or a controlled radial velocity around the central axis of the gas distributer to the radial gas velocity components of the present invention. The benefits of the present invention are explained below in further detail. Summary of the Invention

The present invention relates to a convective dryer and a gas distributer for, and a method of, controlling the velocity profile of a drying gas in a convective dryer, particularly the radial velocity profile of the drying gas, by creating an advantageous velocity profile of the drying gas prior to introducing the drying gas into the convective dryer chamber. The invention is further described in the claims.

The velocity profile may have different requirements depending on the convective process, chamber dimensions and atomizing means, but common gas distributer targets may be defined, such as an advantageous velocity distribution and flow alignment. In particular it is the aim of the present invention to confer a controlled rotational symmetry and/or a controlled radial velocity on the radial gas velocity field by controlling the radial gas velocity component of the gas velocity field.

When following the directions of the present invention, the radial gas velocity component will retain a non-zero velocity, the size of which will be dependent on the distance to the central axis of the gas distributer, which can be significant and comparable to the initial radial gas velocity in size. Nevertheless, upon passage of the gas distributers and flow aligners of the present invention the radial gas velocity will become substantially rotationally symmetrical around the central axis of the gas distributer or flow aligner and/or will have a controlled radial gas velocity component.

The invention further concerns a convective dryer comprising the gas distributer of the present invention, and the use of said convective dryer and said gas distributer in a method to produce a powdery substance in a convective dryer according to the present invention. The inventors have become aware of the importance of reducing uncontrolled or random radial gas velocity components in order to achieve improvement of the mixing profile; while at the same time utilizing as much of the dryer volume as possible and simultaneously keeping any wet product away from the dryer walls. Thereby the risk of undesired materials deposits on the walls of the convective dryer is reduced. Hence, the invention comprises a gas distributer for a convective dryer configured to produce a drying gas jet in a drying chamber of a convective dryer, said drying gas jet having a radial gas velocity component which is substantially rotationally symmetrical around a common center axis and/or has a controlled radial velocity respective to said center axis; which common center axis will be further defined below. Further, the present invention also relates to a method of controlling the gas velocity profile in a convective dryer using a gas distributer capable of achieving the above goal. In the context of the present invention, it is the aim to obtain a substantially rotationally symmetrical radial gas velocity component of the drying gas jet. However, practically it is easier to consider the degree of asymmetry as the measure of success of the invention, wherein it can be considered that the requirement of a substantially rotational symmetrical radial gas velocity component is equally well defined by requiring a low or zero rotationally a-symmetrical radial gas velocity component of the drying gas jet.

In the context of the present invention, the term a low or zero rotationally asymmetrical radial gas velocity component is to be understood to mean that the average resulting rotationally asymmetrical radial gas velocity component of a drying gas jet at the entrance to the exit surface of a gas distributer and before entry into a drying chamber compared to the average initial rotationally asymmetrical radial gas velocity component at constant gas mass-flow in the drying chamber is smaller by at least a factor of 4, at least a factor of 8, preferably by at least a factor of 16 and more preferably by at least a factor of 32. Due to the inherent difficulty in measuring radial gas velocities in drying gas jets, it is sufficient for considering the target of the present invention achieved if the target is confirmed to the skilled person within reasonable accuracy using computational continuum simulation tools, e.g. by simulating the velocity profile of a gas in a convective dryer of the present invention or in a convective dryer comprising a gas distributer according to the present invention using the CD-Adapco Star-ccm+ software (2013-build) .

The present inventors have discovered that the above goals advantageously can be achieved by the provision of a flow aligner adaptable to be installed into the flow path of a drying gas within an gas distributer for a convective dryer, said flow aligner having a plurality of flow channels, said plurality of flow channels so organized as to form a mesh or mesh-like structure and so dimensioned that a low or zero rotationally asymmetrical radial gas velocity component of the drying gas upon exit from the gas distributer is obtained

Brief Description of the Drawings Figure 1 shows a convective dryer with a gas distributer and a flow aligner according to the invention. Figure la shows a sideways view of the convective dryer whereas Figure lb shows a top view of the convective dryer along an axis centered on the gas distributer.

Figure 2 shows a diagrammatic representation of three different mesh or mesh-like structures for use in a flow aligner according to the invention. Figure 3 shows a diagrammatic representation of a flow aligner having a circular-like mesh or mesh-like structure adapted to align a gas jet with the central axis of a convective dryer and to reduce the radial gas velocity to a low or zero value.

Figure 4 shows a diagrammatic representation of a flow aligner comprising a plurality of evenly spaced conically shaped guide vanes. Figure 5 shows a diagrammatic representation of a flow aligner comprising a plurality of increasingly spaced conically shaped guide vanes. Figure 6 shows a diagrammatic representation of a flow aligner comprising a plurality of decreasingly spaced conically shaped guide vanes. Figure 7 shows a diagrammatic representation of a flow aligner comprising a plurality of increasingly spaced conically shaped guide vanes having varying gas exit levels . Figure 8 shows a diagrammatic representation of a flow aligner comprising a plurality of trumpet opening shaped guide vanes .

Detailed Description of the Invention and of Preferred Embodiments

As described above, the provision of a drying gas jet for a convective dryer having improved rotationally symmetrical radial gas velocity control and/or controlled radial velocity at the exit surface of an associated gas distributer is central to the present invention. As previously mentioned this is tantamount to reducing the rotationally asymmetrical radial gas velocity component in the velocity field of said drying gas.

The present inventors have realized that an improvement to jet stability can be achieved in a simple manner by inserting a flow aligner according to the present invention into the flow path of the drying gas, wherein said gas distributer comprises said flow aligner.

Hence a further object of the present invention is to provide a flow aligner for a gas distributer resulting in a low or zero rotationally asymmetrical radial drying gas velocity component upon exit from said gas distributer and into said drying chamber as a drying gas jet.

Accordingly, the present invention relates to a convective dryer (100) configured for producing a powdery substance from an atomized liquid, said convective dryer (100) comprising at least one gas distributer (110) configured to generate a drying gas jet (120), said jet protruding from an exit surface (111) of said gas distributer (110) into a drying chamber (101) of said convective dryer (100), said drying gas jet (120) having a center axis (121) aligned with an axis of said gas distributer (110); said drying gas jet (120) characterizable by a gas velocity field; said gas velocity field having an axial gas velocity component with said axial gas velocity component carrying said drying gas into said drying chamber (101), a tangential gas velocity component and a radial gas velocity component, said radial gas velocity component comprising a rotationally asymmetrical radial gas velocity component; and wherein said drying gas jet (120) has a low or zero rotationally asymmetrical radial gas velocity component . In Figure 1 an exemplary, but non-limiting, convective dryer (100) according to the invention is described. The convective dryer (100) comprises a drying chamber (101), a gas distributer (110), atomizing means (112) and a flow aligner (130) . In the figure, a drying gas exits a flow conduit (141) and enters the gas distributer (110) at a point along the flow path (140) of the drying gas. In the gas distributer (110) the drying gas is directed into the drying chamber (101) and further, the drying gas is passed through a flow aligner (130) of the present invention. The drying gas forms a gas jet (120) in the drying chamber (101) upon exiting the gas distributer (110) and flow aligner (130) at an exit surface (111), wherein gas distributer (110), flow aligner (130) and the gas jet (120) are now aligned to create a common center axis (121) . In the shown embodiment the atomizing means (112) are also aligned along the common center axis (121) just described. In an embodiment of the above convective dryer (100), said gas distributer (110) is configured to reduce or minimize the rotationally asymmetrical radial velocity components in said drying gas jet (120) velocity field. In a preferred embodiment of said convective dryer (100), said gas distributer (110) comprises a flow aligner (130,410,510,610,710,810), said flow aligner

(130,410,510,610,710,810) mounted into a flow path (140) of said drying gas either inside said gas distributer (110), said flow aligner (130,410,510,610,710,810) configured to reduce said rotationally asymmetrical radial gas velocity components of said velocity field to a low or zero rotationally asymmetrical radial gas velocity . Further, the present invention describes in one embodiment, a gas distributer (110) for directing a drying gas jet (120) into a drying chamber (101) of a convective dryer (100), said convective dryer (100) configured for producing a powdery substance from an atomized liquid, said gas distributer (110) configured to generate a drying gas jet (120) protruding from an exit surface (111) of the gas distributer (110) into said drying chamber (101), said drying gas jet (120) having a center axis (121) aligned with an axis of said gas distributer (110) essentially perpendicular to said gas distributer exit surface (111); said drying gas jet characterizable by a gas velocity field; said gas velocity field having an axial gas velocity component, a tangential gas velocity component and a radial gas velocity component, said radial gas velocity component comprising a rotationally asymmetrical radial gas velocity component, with said axial gas velocity component carrying said drying gas into said drying chamber (101); wherein said gas distributer (110) is configured to reduce or minimize rotationally asymmetrical radial gas velocity components in said gas velocity field to a low or zero rotationally asymmetrical radial gas velocity.

The gas distributer (110) may be in the shape of a bend duct type gas distributer, a plenum type, or a scroll type, and may have area contractions and expansions. The gas distributer may encapsulate or include the atomizing means or can be decoupled from the atomizing means.

In a preferred embodiment according to the present invention the gas distributer (110) comprises a flow aligner (130,410,510,610,710,810) inserted into the flow path (140) of said drying gas internally in said gas distributer (110), said flow aligner defining a plurality of flow channels (211,221,231,241) for reducing or minimizing a rotationally asymmetrical radial gas velocity component in the flow field of the drying gas jet (120), said plurality of flow channels (211,221,231,241) organized to form a mesh or mesh-like structure (210,220,230,240) and so dimensioned that a low or zero rotationally asymmetrical radial gas velocity component of said drying gas upon exit from said gas distributer (110) is obtained after passing said drying gas through said plurality of flow channels (211, 221, 231, 241) . In the context of the present invention a mesh or a mesh^¬ like structure (210,220,230,240) is to be understood as a 3-dimensional structure or construction, which influences the gas flow velocity field of a drying gas passing through the mesh or mesh-like structure by reducing or minimizing the rotationally asymmetrical radial gas velocity components to a low value or zero during passage .

A mesh or mesh-like structure (210,220,230,240) of the present invention may be tubular in construction, such that the drying gas passes through a plurality of tubes during its passage of the mesh or mesh-like structure. It can also be constructed from a plurality of guide vanes having an extension along the direction of said center axis (121), at least a subset of the guide vanes forming an inclination angle to said center axis (121) . The mesh or mesh-like structure (210,220,230,240) may also be constructed from a plurality of sets of guide vanes, each set of guide vanes having an extension along the direction of said center axis and each set of guide vanes being differently radially oriented with respect to the center axis within the mesh or mesh-like structure.

To best observe said mesh or mesh-like structure (210,220,230,240), said flow aligner

(130,410,510,610,710,810) can be observed along said center axis (121) . Said mesh or mesh-like structure (210,220,230,240) will now be observable as the projection area visible on a projection plane spanned by the tangential and the radial gas velocity components of said gas velocity field. A characteristic length scale (δ) can now be defined, herein called the radial distance (δ) , which is the maximum distance between two walls of a mesh observed by projection as described above, when measured from said center axis (121) along a straight line connecting said center axis (121) to an outer rim (215,225,235,245) of said flow aligner

(130,410,510,610,710,810). It shall be understood that the actual mesh or mesh-like structure is angled with respect to the center axis (121) .

Figure 2 shows a diagrammatic representation of three different mesh or mesh-like structures (210,220,230,240) for use in a flow aligner (130,410,510,610,710,810) according to the invention. Figure 2a shows the projection area of a flow aligner having a square-like mesh or mesh-like structure (210) . Figure 2b shows the projection area of a flow aligner having a circular-like mesh or mesh-like structure (220) . Figure 2c shows the projection area of a flow aligner having a honeycomb-like mesh or mesh-like structure (230) and Figure 2d shows the projection area of a flow aligner having a honeycomb-like mesh or mesh-like structure (240) without fines in the middle. The value δ is a characteristic length of the flow aligner as explained above. The flow channels (211,221,231,241) created by the mesh or mesh-like structures have been indicated on the figures in an exemplary manner. Further it has been indicated in the figures the location of exemplary guide vanes (212,213,222,223,232,233) or tubes (242) in a non- limiting manner as described below. While the embodiment comprising a mesh or mesh-like structure is preferred, it is possible to dispense with control of the tangential gas velocity and still obtain a significant portion of the benefits of the present invention through control of the radial gas velocity in itself .

Figure 3 shows a diagrammatic representation of a flow aligner having a circular-like mesh (320) or circular- like mesh-like (310) structure adapted to align a gas jet

(120) with the central axis (121) of a convective dryer (100) and to reduce the radial gas velocity to a low or zero value. The value a is a characteristic length of the flow channels which is defined by the length the flow channel (211,221,231,241) measured along the center axis

(121) . Although the flow aligners of figure 3 are not comprised by the present invention; the construction examples shown in the figure are exemplary for the flow aligners of the invention and the skilled person will easily deduct from these figures in combination with the below descriptions how to assemble flow aligners of other mesh types.

To assemble the flow aligners (310,320) of Figure 3 a plurality of tangential guide vanes (223) in the form of rings or cylinders are assembled concentrically around the center axis (121) of the flow aligner and combined with a plurality of radial guide vanes (222), these radial guide vanes serving like spokes in a wheel. In the flow aligner (310) of Figure 3b, the radial (222) and tangential (223) guide vanes are separated along the center axis of the flow aligner (310) into a first layer (340) and a second layer (330); whereas in the flow aligner (320) of Figure 3c the radial (222) and tangential (223) guide vanes are connected into a single first layer (350) thereby forming tubes. The resulting flow channels (221) are indicated with reference to the two-dimensional projection of the constructed flow aligners of figure 3a.

Figures 4A and 4B show a diagrammatic representation of a flow aligner (410) according to the present invention, said flow aligner (410) comprising a plurality of evenly spaced conically shaped guide vanes (423) , said plurality of evenly spaced conically shaped guide vanes (423) arranged to form a circular-like mesh or mesh-like structure and adapted to reduce or minimize a rotationally asymmetrical radial gas velocity component in the gas velocity field of a drying gas jet (120) to a low value or zero, said circular-like mesh or mesh-like structure conforming to the requirements of the above definitions of mesh or mesh-like structures. The flow aligner (410) having a circular-like mesh or mesh-like structure adapted to reduce or minimize a rotationally asymmetrical radial gas velocity component in the gas velocity field of a drying gas jet (120) to a low value or zero of the embodiment shown in the figures is constructed in parallel to the flow aligner (310) shown in figure 3b. It has a first layer (440) and a second layer (430) which separates radial (422) and tangential (423) guide vanes along the center axis (121) of the flow aligner (410) . However, the tangential guide vanes (423) are now no longer ring or cylinder shaped, rather they form cut-off cones which have been spaced apart by said characteristic distance δ, to form a second layer of conically shaped tangential guide vanes (423) arranged concentrically around said center axis (121). Depending on the inclination angle (Θ) which said conically shaped tangential guide vanes (423) form to said center axis (121), a smaller or larger rotationally symmetrical radial gas velocity is controllably conferred to said drying gas jet (120), while simultaneously suppressing the rotationally asymmetrical radial gas velocity components in the gas velocity field of said drying gas jet (120) to a low value or zero. The inclination angle (Θ) is locally defined as positive (as shown in Figure 4) if, when defining a radial distance, Rl, for the inlet as well as a radial distance for the outlet, R2, of the second layer Rl < R2. The inclination angle (Θ) is defined as positive by average (as shown in Figure 4) if, when defining an average radial distance, Rl, for the inlet as well as average radial for the outlet, R2, of the second layer Rl < R2. In both cases, if the ratio is 1, the inclination angle (Θ) is zero which corresponds to the situation of Figure 3.

The present invention relates to flow aligners wherein (Θ) is larger than 0° but smaller than 90°. Preferably 0°< Θ < 45° and more preferably 5° < Θ < 35° but the skilled person will know to select useful, but different, values of Θ within the broader interval of between 0° and 90° based on the information contained herein where different purposes require such selections. In general, Θ shall at least be larger than 0°, larger than 2°, larger than 5° or larger than 10°, but smaller than 90°, preferably smaller than 75°, preferably smaller than 60°, preferably smaller than 50°, and most preferably smaller than 45°. The flow aligner (410) having a circular-like mesh or mesh-like structure adapted to reduce or minimize a rotationally asymmetrical radial gas velocity component in the gas velocity field of a drying gas jet (120) to a low value or zero may also be constructed as a combination of the embodiment shown in Figure 3c with a first layer (350) of combined radial (222) and tangential (223) guide vanes and a second layer (430) constructed as described above. Likewise, it is possible to construct the flow aligner (410) having a circular-like mesh or mesh-like structure adapted to reduce or minimize a rotationally asymmetrical radial gas velocity component in the gas velocity field of a drying gas jet (120) to a low value or zero in parallel to the flow aligner (240) of figure 2D by allowing each throughgoing opening or flow channel (241) of the embodiment in figure 2D to form said inclination angle (Θ) with said center axis (121) . The guide vanes shown in Figures 4A and 4B have been defined as conically shaped. A substantially true cone- shape is the preferred geometry for the guide vanes of the present invention as this particular geometry provides optimal symmetry around the center axis (121) of the flow aligner when the guide vanes are concentrically assembled .

However, the skilled person will know from the disclosure herein, that also other geometries of such guide vanes (such as oligo-angular or poly-angular) will, when arranged concentrically around the center axis (121) in a flow aligner as exemplified in Figure 4A or 4B and at an inclination angle (θ) , impart some of the benefits of the present invention to the flow properties of drying gas passing such a flow aligner before entering into said drying chamber (101) of said convective dryer (100) . Preferentially, the guide vanes of the present invention which shall be considered oligo-angular shall have at least 3 corners; while guide vanes of the present invention which shall be considered poly-angular shall have at least 6 corners, preferably at least 12 corners, more preferably at least 20 corners. Obviously, as the number of angles of the guide vanes increase, these will more and more approach a true cone structure,

In a further development according to the present invention, the strict requirement of δ being constant is relaxed in favor of a radially dependent δ. This will lead to a variance in both δ and Θ as these parameters are geometrically linked. This further development is described in more detail below in exemplary embodiments.

The consequence of relaxing the requirement of δ being constant is that the rotational symmetrical radial gas velocity component of the drying gas jet (120) will no longer be uniform in size with the distance from central axis (121), rather the size of the rotational symmetrical radial gas velocity component will have a dependency of the distance to the central axis (121) . However, due to the presence of the guide vanes of the invention, the same target of a low or zero asymmetrical radial gas velocity component of the drying gas jet (120) will be achieved .

Figure 5 shows a diagrammatic representation of a flow aligner (510) comprising a plurality of increasingly spaced conically shaped guide vanes (530) . In the figure is indicated values δο and δι. The values θ, δο and δι are related by the following equation:

(1) δ₁ = δ₀+ δ(θ), a » δ₁ wherein Θ and a are as previously defined. Due to the manner the value δ was defined above, δο and δι will always be smaller or equal to the value δ with the largest value of δο or δι being equal to δ. Due to the manner in which the guide vanes are constructed, δ will not be constant over a guide vane. In figure 5 e.g., δι increases exponentially with constant exponent between every two guide vanes. Rather, each guide vane will have a constant inclination angle (Θ) albeit different from its neighbors. It is sufficient to define the value δι as according to equation (1) either at the drying gases' entry surface to, or exit surface from, the flow aligner comprising the conically shaped guide- vanes of the invention, in order to define a representative value of δι and hence of δ.

Figure 6 shows a diagrammatic representation of a flow aligner (610) comprising a plurality of decreasingly spaced conically shaped guide vanes (630) . In figure 6, δι decreases exponentially with constant exponent between every two guide vanes making δ₀ equal to δ.

Figure 7 shows a diagrammatic representation of a flow aligner (710) comprising a plurality of increasingly spaced conically shaped guide vanes having varying gas exit levels . The inventors have found, that for some purposes it is advantageous to allow the above defined exit surface from the flow aligners (410,510,610,710) of the invention to deviate from being perpendicular to the center axis (121) . In figure 7, the exit surface follows a hyperbole, but e.g. linear, exponential, logarithmic, or circular exit surfaces could be equally relevant depending on the purpose of use of the convective dryer (100) comprising the gas distributer (110) and flow aligner (410,510,610,710) of the invention.

Figure 8 shows a diagrammatic representation of a flow aligner (810) comprising a plurality of trumpet opening shaped tangential guide vanes (830) . The radial guide vanes are not shown to ease the reader's understanding.

In the embodiment detailed in Figure 8, the tangential guide vanes (830) are constructed with a first section (831) and a second section (832) . The first section is aligned parallel with the center axis (121) and serves to achieve the target of a low or zero asymmetrical radial gas velocity component of the drying gas jet (120) upon exit of the drying gas jet from the gas distributer. The second section (831) is angled with respect to the center axis as defined above. In the drawing, Θ is 45°, but this of course may be varied as detailed in the present document .

In the construction shown the radial guide vanes must be located either as a first layer or constructed as a combined layer with the second layer in order to obtain the benefits of the present invention. In the embodiment of the drawing, the first section (831) is substantially more elongated in the direction of the center axis (121) than the second section (832), but this is not necessary as flow alignment will take place in both sections. Accordingly, the second section (832) may be as long or longer as the first section (831) . However, the advantage of the embodiment detailed in Figure 8 is that a more compact flow aligner (810) can be constructed, where an angular direction is not imposed on the flow until close to the exit surface from the flow aligner (810) of the invention.

In the figures, the radial guide vanes arranged in the first layer (440,540,640,740) of the flow aligners (410,510,610,710) appear to larger than the radial guide vanes of the second layer (430,530,630,730), which however shall not be considered limiting on the present invention. The first layer comprising the tangential guide vanes (440,540,640,740) of the invention may be larger, smaller, or of the same size as the second layer (430,530,630,730,830) comprising the radial guide vanes of the invention. Also the order of the first and second layers may be reversed or the layers may be built into each other as elsewhere detailed.

In some embodiments it will be advantageous to construct the flow aligners (130,410,510,610,710,810) of the present invention with one or more throughgoing passages, these one or more throughgoing passages traversing said mesh or mesh-like structure (210,220,230,240) comprised in said flow aligners (130,410,510,610,710,810) in the direction of said drying gas flow (140) . These one or more throughgoing passages may have a diameter or cross section which is larger than the characteristic radial length (δ) associated with the mesh or mesh-like structure (210,220,230,240) comprised in the flow aligners (130,410,510,610,710,810) also comprising said one or more throughgoing passages. This is e.g. shown in the flow aligner (130) comprising the atomizer (112) of Figure 1.

When constructing such one or more throughgoing passages in a flow aligner (130,410,510,610,710,810) of the present invention it is advantageous that said passages are circular, and describable by a single diameter, but this is not limiting on the invention. Other geometrical shapes of said one or more throughgoing passages are equally useful and available to the skilled person as a matter of experience.

The advantage of this embodiment is to allow space for instalment of further equipment, such as but not limited to, atomizers and/or additional air nozzles of interest in the art of convective drying, when this further equipment is of a size which is too large to fit within a single mesh of said mesh or mesh-like structure in said flow aligner. By ascertaining that the combined surface area of the one or more throughgoing passages installed into said flow aligner is sufficiently smaller than the surface area of the mesh or mesh-like structure of the present invention the benefits otherwise obtained from using the present invention are not lost. Further, it is advantageous to install such one or more throughgoing passages closer to the center axis (121) than to the aforementioned rim (215,225,235,245) of said mesh or mesh-like structure (210,220,230,240) in said flow aligner (130,410,510,610,710,810) . In parallel to the construction of the circular-like flow aligner of figure 3 (310,320) another mesh or mesh-like structure, either constructed from a plurality of tubes (242) or from a plurality of guide vanes (232,233), could be a honeycomb structure (230,240) . The honeycomb structure (230,240) could be preassembled as a tubular structure or assembled as a layered structured from at least two layers each presenting a plurality guide wanes (232,233) in the form of zigzag walls (232,233) and wherein the two layers are oriented at an angle to each other such that an essentially honeycomb-like structure is created when the projection area of the assembled flow aligner (130,310,320) onto the plane defined by the tangential and the radial gas velocity components is observed. In the actual construction the plurality of tubes (242) or guide vanes (232, 233) will have one or more inclination angles (Θ) to the center axis (121) as detailed above. In order to assemble a flow aligner

(130, , 410, 510, 610, 710, 810) according to the present invention, numerous options are available to the skilled person such as but not limited to e.g. welding, soldering, extrusion, molding, insertion of pre-fitted parts into each other, water cutting, laser cutting, drilled, casted, glued, 3D printed. Also the skilled person will know to select appropriate materials for the manufacture of the flow aligner according to the specific needs of the gas distributer. Such materials could be, but not limited to, e.g. stainless steel, sheet metal, aluminum, or plastics.

Also possible are gas distributers (110) wherein a plurality of tubular and/or a plurality of guide vanes structure elements of any shape are bundled together into smaller insert substructures which are subsequently assembled to form a larger flow aligner (410,510,610,710,810) according to the present invention and fitting the dimensions of the gas distributer (110) wherein the larger flow aligner (410,510,610,710,810) is intended to be installed.

The present inventors have discovered that it is advantageous for achieving an appropriate radial velocity control that the said flow channels (211,221,231,241) have an axial length (a) and a radial distance (δ) , such that said flow channels can be characterized by an axial length (a) to radial distance (δ) ratio (DR) of 2<DR, preferably 3 < DR, more preferably 4 < DR, more preferably 3 < DR < 100, more preferably 3 < DR < 50, more preferably 3 < DR <20, most preferably 4 < DR≤ 20.

In an embodiment of the flow aligner (130,410,510,610,710,810) according to the present invention, the plurality of flow channels

(211,221,231,241) forming said mesh or mesh-like structure (210,220,230,240) is a plurality of tubes or a plurality of guide vanes or a combination thereof. The plurality of tubes or plurality of guide vanes or combination thereof can either be connected or organized in layers, preferably at least two layers, more preferably two layers. When said flow aligner (130,410,510,610,710,810) comprises more than two layers, e.g. a first layer (340) and a second layer (330); a sequence of layers can be envisaged such as e.g. a first first layer (340), a first second layer (330), a second first layer (340), a second second layer (330) and so forth. Further structural variations can easily be envisaged by the skilled person.

In another embodiment said plurality of guide vanes (212,213,222,223,232,233,423) are oriented radially and tangentially with respect to said velocity field thereby forming a set of radial guide vanes and tangential guide vanes. In an embodiment said tangential guide vanes may be formed as a set of rings or cylinders (223) and/or straight guide vanes (222) . In yet another embodiment multiple sets of straight guide vanes (212,213) are assembled into a cross pattern having an angle with respect to the axial gas velocity component axis. The plurality of flow channels (211,221,231,241) of the present invention may in one embodiment form a rounded or a polygonal structure or a combination thereof in particularly the plurality of flow channels (211,221,231,241) may form a honeycomb structure ( 231, 241) . In particular a combination of separate guide vanes (232,233) may be oriented radially and tangentially to form an axially stretched honeycomb (231) .

In a further embodiment of the present invention, the plurality of tubes or guide vanes

(212,213,222,223,232,233,242,423) may be manufactured from a metal or from a plastic and can be extruded, point wise or fully welded, or loosely assembled to form an assembled flow aligner (130,310,320) within said gas distributer (110) .

To exemplify the present invention a honeycomb structured flow aligner (230) was simulated using the CD-Adapco Star-ccm+ software (2013-build) . The approximate pressure loss across the honeycomb structure was Δρ = lOmmWG, the equivalent diameter ≤ 20mm and the axial length (a) to radial distance (δ) ratio, DR ≥ 3. The honeycomb construction guides both the tangential and the radial velocity components independently with the purpose of reducing the radial gas velocity components while allowing a given amount of tangential gas velocity to be maintained for improved mixing. When DR is larger than 2, preferably larger than 3, most preferably larger than 4, the benefits of the present invention are achieved.

Some exemplary dimensions for use in commercial spray towers have a between 40 mm to 300 mm and δ between 10 mm to 50 mm in combinations suitable for yielding an appropriate DR-value.

In an exemplary calculation using a = 150 mm and δ = 24 mm, i.e. a DR-value of 6.25, using the flow aligner of Figure 4, the flow alignment dependence on geometry was calculated based on an average total velocity at inlet of 20 m/s. Without flow alignment, i.e. no guide rings, the average radial angle given the above conditions equal - 9.9° and average radial velocity is 3.0 m/s. For Θ = 0° (embodiment of Figure 3, 5 guide rings) , the average radial angle is -0.1° and average radial velocity is - 0.04 m/s (with 1 or 3 guide rings the average radial velocities are 2.2 and 1.6 m/s respectively) . For Θ = 10°, the average radial angle is 6.2° and average radial velocity is 2.6 m/s. For Θ = 25°, the average radial angle is 10.3° and average radial velocity is 5.0 m/s, and for the trumpet-like flow aligner of Figure 8 (Θ = 45°), the average radial angle is 19.3° and average radial velocity is 8.9 m/s. The flow alignment to geometry is seen in the examples by increasing geometry angles resulting in an increasing radial component as shown in the flow angle. The radial angle for the example with no guide rings is seen to be high and inward pointing (and gas flow is therefore directed towards the center rather than away from the center) and determined by upstream conditions, whereas gas flow alignment ensures a close to zero flow angle or a controlled outward direction decoupled from inlet conditions with enforced radial velocity. The use of guide rings has a significant effect on the average radial velocity at entrance to the dryer.

Without any guide rings the radial velocity component will for the present example be 3.0 m/s whereas for 3 rings inserted in the duct between the dryer and the inlet the radial velocity has been calculated to be 1.6 m/s. The reduction will depend on the number of rings, the length, diameter and spacing of the rings as well as the position of the rings. As such, the mere presence of a single (or a few) tangential guide vanes in the flow aligners of the invention are not sufficient to achieve the goals of the present invention, even if an effect on the radial velocity can be observed.

The present invention further relates to a convective dryer (100) comprising a gas distributer (110) as previously described; preferably the gas distributer (110) comprises a flow aligner (130,410,510,610,710,810) as previously described.

In one preferred embodiment, the gas distributer (110) comprises a flow aligner (130,410,510,610,710,810). In a most preferred embodiment said flow aligner (130,410,510,610,710,810) has an axial length (a) and comprises a plurality of tubes or guide vanes (212, 213, 222, 223, 232, 233, 242, 423) , said plurality of tubes or guide vanes organized to form a mesh or mesh- like structure (210,220,230,240) having a plurality of openings (211,221,231,241), said tubes or guide vanes being so dimensioned that a low or zero rotationally asymmetrical radial gas velocity of said drying gas upon exit from said gas distributer (110) is obtained after passing said drying gas through said plurality of tubes or guide vanes.

The present invention also relates to a method for controlling the gas velocity field of a drying gas jet (120) protruding from a gas distributer (110) into a drying chamber (101) of a convective dryer (100), said gas velocity field comprising an axial gas velocity component, a tangential gas velocity component and a radial gas velocity component, said radial gas velocity component comprising a rotationally asymmetrical radial gas velocity component, said method comprising reducing or minimizing said rotationally asymmetrical radial gas velocity component such that the rotationally asymmetrical radial gas velocity of said drying gas jet (120) is low or zero.

The present invention in particular also relates to a method for controlling the gas velocity field of a drying gas jet (120) protruding into a drying chamber (101) of a convective dryer (100) from an exit surface (111) of a gas distributer (110), said gas distributer (110) comprising a flow aligner (130,410,510,610,710,810), said flow aligner comprising flow channels (211,221,231,241), said flow aligner defining an axial length (a) and a radial distance (δ) , wherein said flow channels are characterized by an axial length (a) to radial distance (δ) ratio (DR) of 2 < DR , preferably 3≤DR, more preferably 4 < DR, more preferably 3 < DR < 100 , more preferably 3 < DR < 50 , more preferably 3 < DR < 20 , most preferably 4 < DR≤ 20 .

Finally, the present invention relates to the use of a method for controlling the gas velocity field of a drying gas jet (120) protruding from a gas distributer (110) into a drying chamber (101) of a convective dryer (100) as described above for producing a powdery substance, such as e.g. a powder, an agglomerated powdery substance, a coated powdery substance or a granulated substance from an atomizing liquid capable of forming a such powdery substance in a convective dryer (100) and a powdery substance produced from an atomizing liquid containing a material capable of forming a powdery substance in a convective dryer (100) using a method as described above.

Although the teaching of this application has been described in detail for purpose of illustration, it is understood that such detail is solely for that purpose, and variations can be made therein by those skilled in the art without departing from the scope of the teaching of this application. The term "comprising" as used in the claims does not exclude other elements or steps. The term "a" or "an" as used in the claims does not exclude a plurality .

Claims

A gas distributer (110) for directing a drying gas jet (120) into a drying chamber (101) of a convective dryer (100), said convective dryer (100) configured for producing a powdery substance from an atomized liquid, said gas distributer (110) configured to generate a drying gas jet (120) protruding from an exit surface (111) of said gas distributer (110) into said drying chamber (101), said drying gas jet (120) having a center axis (121) aligned with an axis of said gas distributer (110) essentially perpendicular to said gas distributer exit surface (111); said drying gas jet (120) characterizable by a gas velocity field, said gas velocity field having an axial gas velocity component with said axial gas velocity component carrying said drying gas into said drying chamber (101), a tangential gas velocity component and a radial gas velocity component, said radial gas velocity component comprising a rotationally asymmetrical radial gas velocity component which is substantially rotationally asymmetrical around said common center axis (121); wherein said gas distributer (110) is configured to reduce or minimize said rotationally asymmetrical radial gas velocity component of said drying gas jet (120) to low or zero rotationally asymmetrical radial gas velocity .

A gas distributer (110) for directing a drying gas jet (120) into a drying chamber (101) of a convective dryer (100), said convective dryer (100) configured for producing a powdery substance from an atomized liquid, said gas distributer (110) configured to generate a drying gas jet (120) protruding from an exit surface (111) of said gas distributer (110) into said drying chamber (101), said drying gas jet (120) having a center axis (121) aligned with an axis of said gas distributer (110) essentially perpendicular to said gas distributer exit surface (111); said drying gas jet (120) characterizable by a gas velocity field, said gas velocity field having an axial gas velocity component with said axial gas velocity component carrying said drying gas into said drying chamber

(101), a tangential gas velocity component and a radial gas velocity component, said radial gas velocity component comprising a rotationally asymmetrical radial gas velocity component which is substantially rotationally asymmetrical around said common center axis (121); wherein said gas distributer (110) comprises a flow aligner

(130,410,510,610,710,810), said flow aligner

(130,410,510,610,710,810) defining a plurality of flow channels (211,221,231,241), said flow aligner

(130,410,510,610,710,810) being configured to reduce or minimize said rotationally asymmetrical radial gas velocity component of said drying gas jet (120) to low or zero rotationally asymmetrical radial gas velocity .

3. A gas distributer (110) according to claim 2, wherein said plurality of flow channels (211,221,231,241) in said flow aligner

(130,410,510,610,710,810) is organized to form a mesh or mesh-like structure (210,220,230,240), said mesh or mesh-like structure (210,220,230,240) being so dimensioned that a low or zero rotationally asymmetrical radial velocity of said drying gas in said drying gas jet (120) upon exit from said gas distributer (110) through said exit surface (111) is obtained after passing said drying gas through said plurality of flow channels (211,221,231,241).

4. A gas distributer according to claim 3 wherein said mesh or mesh-like structure is characterized by a characteristic length (δ) ; and said plurality of flow channels by a characteristic length (a) and a characteristic inclination angle (Θ) .

5. A gas distributer (110) according to claims 2 to 4, wherein said plurality of flow channels (211,221,231,241) in said flow aligner (130,310,320,410) is a plurality of tubes (242) or a plurality of guide vanes (212,213,222,223,232,233, 422,423) or a combination thereof.

6. A gas distributer (110) according to claim 5, wherein said plurality of tubes (242) or plurality of guide vanes (212,213,222,223,232,233,422,423) or combination thereof in said flow aligner

(130,410,510,610,710,810) are organized in layers

(430,440,530,540,630,640,730,740,830), said plurality of tubes (242) or plurality of guide vanes

(212,213,222,223,232,233,422,423) or combination thereof in said flow aligner (130,410,510,610, 710,810) comprising at least one layer

(430,440,530,540,630,640,730,740,830), but prefer^¬ ably at least two layers (430,440,530,540,630,640, 730, 740, 830) . A gas distributer (110) according to claims 5 or 6 wherein said plurality of guide vanes

(212,213,222,223,232,233,422,423) in said flow aligner (130,410,510,610,710,810) are oriented radially and tangentially with respect to said velocity field to form a set of radial guide vanes

(222,422) and tangential (223,433) guide vanes.

A gas distributer (110) according to claim 7 wherein said radial guide vanes (212,213,222,232,233,422) in said flow aligner (130,410,510,610,710,810) are angled for imparting the drying gas flow a tangential direction.

A gas distributer (110) according to claim 7 or 8 wherein said tangential guide vanes (423) in said flow aligner (410,510,610,710) are formed as a set of cut-off cones; thereby forming a layer (430,530,630,730) of conically shaped tangential guide vanes arranged concentrically around said center axis (121), each tangential guide vane (423) spaced apart by a characteristic distance δ, and having a positive inclination angle Θ to said center axis (121) .

A gas distributer (110) according to claims 7 to 10 wherein said tangential guide vanes (423) in said flow aligner (410,510,610,710) are arranged to form a second layer (430,530,630,730); said second layer (430,530,630,730) being a second layer of conically shaped tangential guide vanes arranged concentrically around said center axis (121), each tangential guide vane (423) spaced apart by a characteristic distance δ, and having a positive inclination angle Θ to said center axis (121) .

11. A gas distributer (110) according to any of the claims 7 to 10 wherein said flow aligner (410) comprises a plurality of evenly spaced conically shaped tangential guide vanes (430) .

12. A gas distributer (110) according to any of the claims 7 to 10 wherein said flow aligner (510) comprises a plurality of increasingly spaced conically shaped tangential guide vanes (530).

13. A gas distributer (110) according to any of the claims 7 to 10 wherein said flow aligner (610) comprises a plurality of decreasingly spaced conically shaped tangential guide vanes (630).

14. A gas distributer (110) according to any of the claims 7 to 13 wherein said plurality of conically shaped guide vanes (430,530,630,730) of said flow aligner (410,510,610,710) are arranged to permit said drying gas to exit said flow aligner (410,510,610,710) at an exit surface which is not perpendicular to said center axis (121) .

15. A gas distributer (110) according to any of the claims 7 to 14 wherein said conically shaped guide vanes (430,530,630,730) are oligo-angular or poly- angular or true cut-off cones or a combination thereof .

16. A gas distributer (110) according to claims 2 to 15 wherein said plurality of flow channels in said flow aligner (130,410,510,610,710) form a rounded (220) or a polygonal structure (210,230,240) or a combination thereof.

17. A gas distributer (110) according to claims 2 to 16 wherein said plurality of flow channels in said flow aligner (130,410,510,610,710) form a honeycomb structure (230,240).

18. A gas distributer (110) according to claim 17 wherein a combination of separate guide vanes

(232,233) in said flow aligner (130,410,510,610,710) are oriented radially and tangentially to form an axially stretched honeycomb (230). 19. A gas distributer (110) according to any of the claims 2 to 8 wherein said tangential guide vanes (830) of said flow aligner (810) are substantially trumpet opening shaped, having a first section (831) and a second section (832), said first section aligned in parallel with said center axis (121) with said second section (831) angled with respect to said center axis (121) by an angle Θ.

20. A gas distributer (110) according to claims 2 to 19 wherein the plurality of tubes or guide vanes in said flow aligner (130,410,510,610,710,810) is manufactured from a metal or from a plastic or a combination thereof. 21. A gas distributer (110) according to claims 2 to 20 wherein the plurality of tubes or guide vanes in said flow aligner (130,410,510,610,710,810) is drilled, cast, extruded, point wise or fully welded, or loosely assembled to form an assembled flow aligner (130,410,510,610,710,810) within said gas distributer (110).

22. A gas distributer (110) according to any of the claims 1 to 21, comprising a flow aligner (130,410,510,610,710,810), said flow aligner (130,410,510,610,710,810) comprising a plurality of flow channels (211,221,231,241), wherein said flow aligner (130,410,510,610,710,810) defines an axial length (a) and a radial distance (δ) and said plurality of flow channels (211,221,231,241) are characterized by an axial length (a) to radial distance (δ) ratio (DR) of 2<DR, preferably 3≤DR.

23. A gas distributer (110) according to any of the claims 1 to 22, comprising a flow aligner (130,410,510,610,710,810), said flow aligner (130,410,510,610,710,810) comprising one or more throughgoing passages, said one or more throughgoing passages traversing said mesh or mesh-like structure (210,220,230,240) comprised in said flow aligner (130,410,510,610,710,810) in the direction of said drying gas flow (140), said one or more throughgoing passages having a diameter larger than the characteristic radial distance (δ) associated with said mesh or mesh-like structure (210,220,230,240) comprised in said flow aligner (130,410,510,610,710,810) also comprising said one or more throughgoing passages.

24. A gas distributer (100) according to any of the claims 1 to 23 wherein said flow aligner (130,410,510,610,710,810) is located at or near said exit surface (111).

25. A gas distributer (110) according to any one of the claims 1 to 24 comprising at least one atomizer.

26. A convective dryer (100) comprising a gas distributer (110) according to any one of claims 1 to 25.

27. A method for controlling the gas velocity field of a drying gas jet (120) protruding from a gas distributer (110) into a drying chamber (101) of a convective dryer (100), said gas velocity field comprising an axial gas velocity component, a tangential gas velocity component and a radial gas velocity component, said radial gas velocity component comprising a rotationally asymmetrical radial gas velocity component, said method comprising reducing or minimizing said rotationally asymmetrical radial gas velocity component such that the rotationally asymmetrical radial gas velocity of said drying gas jet (120) is low or zero.

28. The method of claim 27 wherein said gas distributer (110) is a gas distributer according to any of the claims 1 to 26.

29. The method of any of the claims 27 or 28 wherein said gas distributer comprises a flow aligner (130,410,510,610,710,810) .