GAS DISPERSER FOR A SPRAY DRYER AND METHODS

Abstract

In the gas disperser (3), a flow conditioning device (5, 6) is located in the inlet duct section (32). The flow conditioning device comprises a hole plate (5) and a flow straightener (6) positioned in parallel with and at a distance (h) in the axial direction (axd) from the downstream side of the hole plate (5). The hole plate (5) has a predefined hole plate thickness (tp) in the axial direction (axd) and each flow straightener (6) has a predefined flow straightener length (Is) in the axial direction (axd), the flow straightener length (Is) being substantially larger than the hole plate thickness (tp).

Claims

1.-24. (canceled)

25. A spray drying apparatus comprising: at least one gas disperser for guiding gas into a drying chamber, said gas disperser comprising: an inlet duct section with an upstream end and a downstream end, and with an internal diameter defining a cross-sectional area, the inlet section defining an axial direction, a radial direction, and a tangential direction, and a flow conditioning device located in the inlet duct section and having a diameter substantially corresponding to an internal diameter of the inlet duct section, the flow conditioning device comprising: at least one hole plate having a plurality of holes distributed over substantially an entire cross-sectional area of the hole plate; and at least one flow straightener positioned substantially in parallel with and at a distance in the axial direction from the downstream side of the at least one hole plate, the flow straightener having a plurality of flow channels, each having a longitudinal extension in parallel with the axial direction, wherein the plurality of flow channels extend farther in the axial direction than a hole plate thickness by a factor of between 5 to 200.

26. The spray drying apparatus of claim 25, wherein a hole plate thickness is between 0.0005 to 0.05 of the internal diameter of the inlet duct section.

27. The spray drying apparatus of claim 25, wherein a flow channel length is between 0.005 to 1 of the internal diameter of the inlet duct section.

28. The spray drying apparatus of claim 25, wherein the plurality of holes are shaped as one or more of circular, oval, ovoid, rectangular, and polygonal.

29. The spray drying apparatus of claim 25, wherein the at least one hole plate is formed as a mesh formed by mesh threads defining the plurality of holes between them.

30. The spray drying apparatus of claim 25, wherein the at least one flow straightener comprises intersecting first and second sets of vanes forming a plurality of cross-sectionally rectangular flow channels.

31. The spray drying apparatus of claim 25, wherein the at least one flow straightener comprises at least one tangential vane and at least one set of radial vanes forming a plurality of arc-shaped flow channels.

32. The spray drying apparatus of claim 31, wherein the at least one flow straightener comprises a first, second, third and fourth tangential vane arranged concentrically.

33. The spray drying apparatus of claim 25, wherein the plurality of flow channels is between 25 to 150 per square meter of the inlet duct section.

34. The spray drying apparatus of claim 25, wherein a distance separating the at least one flow straightener from the downstream side of the at least one hole plate in the axial direction is below 100 times the hole plate thickness.

35. The spray drying apparatus of claim 25, wherein the at least one hole plate comprises two hole plates.

36. The spray drying apparatus of claim 35, wherein both hole plates are upstream from the at least one flow straightener.

37. The spray drying apparatus of claim 36, further comprising a third hole plate positioned on the downstream side of the at least one flow straightener.

38. The spray drying apparatus of claim 25, wherein the at least one flow straightener comprises two flow straighteners.

39. The spray drying apparatus of claim 38, wherein a first hole plate is disposed upstream of the first flow straightener and a second hole plate is disposed downstream of the first flow straightener and upstream of the second flow straightener.

40. A method of aligning a stream of gas in a spray drying apparatus, comprising: providing an inlet duct section with an upstream end and a downstream end, and with an internal diameter defining a cross-sectional area, the inlet section defining an axial direction, a radial direction, and a tangential direction; providing a flow conditioning device located in the inlet duct section and having a diameter substantially corresponding to an internal diameter of the inlet duct section, the flow conditioning device comprising: at least one hole plate having a plurality of holes distributed over substantially an entire cross-sectional area of the hole plate; and at least one flow straightener positioned substantially in parallel with and at a distance in the axial direction from the downstream side of the at least one hole plate, the flow straightener having a plurality of flow channels, each having a longitudinal extension in parallel with the axial direction, wherein the plurality of flow channels extend farther in the axial direction than a hole plate thickness by a factor of between 5 to 200; and directing a flow of gas in the axial direction through the flow conditioning device.

41. The method of claim 40, wherein a hole plate thickness is between 0.0005 to 0.05 of the internal diameter of the inlet duct section.

42. The method of claim 40, wherein wherein a flow channel length is between 0.005 to 1 of the internal diameter of the inlet duct section.

43. A flow conditioning device for a spray drying apparatus, comprising: at least one hole plate having a plurality of holes distributed over substantially an entire cross-sectional area of the hole plate; and at least one flow straightener positioned substantially in parallel with and at a distance in the axial direction from a downstream side of the at least one hole plate, the flow straightener having a plurality of flow channels, each having a longitudinal extension in parallel with the axial direction, wherein the plurality of flow channels extend farther in the axial direction than a hole plate thickness by a factor of between 5 to 200, and wherein the flow conditioning device is disposed in the inlet duct section and has a diameter substantially corresponding to an internal diameter of the inlet duct section.

44. A method of retro-fitting a spray drying apparatus, comprising installing the flow conditioning device of claim 43.

Description

BRIEF DESCRIPTION OF DRAWINGS

[0024] In the following description embodiments of the invention will be described with reference to the schematic drawings, in which

[0025] FIG. 1 is a schematic plan view of a spray drying apparatus incorporating a gas disperser;

[0026] FIGS. 2a to 2e show perspective views of various configurations of gas dispersers;

[0027] FIG. 3 is a partial perspective sectional view of a gas disperser in an embodiment of the invention;

[0028] FIG. 4 is a schematic side sectional view of the gas disperser of the embodiment of FIG. 3;

[0029] FIGS. 5a and 5b are perspective and break-out views on larger scales of a hole plate of one embodiment of the gas disperser;

[0030] FIGS. 6a and 6b are perspective and break-out views on larger scales of a hole plate of another embodiment of the gas disperser;

[0031] FIGS. 7a and 7b are perspective and break-out views on larger scales of a hole plate of a further embodiment of the gas disperser;

[0032] FIGS. 8a and 8b are plan and perspective views on larger scales of a flow straightener in a still further embodiment of the gas disperser;

[0033] FIGS. 9a and 9b are plan and perspective views on larger scales of a flow straightener in yet another embodiment of the gas disperser; and

[0034] FIGS. 10a to 10e are views corresponding to FIG. 4 of further embodiments of the gas disperser according to the invention.

DESCRIPTION OF EMBODIMENTS

[0035] Referring initially to FIG. 1, the general configuration of a spray drying apparatus is shown as one example of a device requiring a supply of air or gas to be guided to and introduced into the device. The fundamentals underlying the present invention are applicable to other devices than the spray dryer shown and described, including convective dryers, heaters, spray coolers, fluid beds, belt dryers, and upstream and downstream of heaters and filters etc.

[0036] The spray drying apparatus 1 comprises a drying chamber 2 in which a feed is atomized by atomizing means (not shown) including an atomizer wheel, atomizing nozzles or the like. A gas disperser generally designated 3 is shown, here mounted at the ceiling of the drying chamber. At the bottom of the drying chamber 2, an outlet 4 is provided for discharging a product. Auxiliary operational units may be present, including cyclones, filters and after-treatment units.

[0037] The gas disperser 3 may take many different configurations as indicated in FIGS. 2a to 2e. Common to all of them is that they are intended for guiding gas into a chamber 2 of a gas treatment apparatus, here the spray drying apparatus 1, from a gas supply, through a supply duct section 31 and further through an inlet duct section 32 in fluid communication with the interior of the drying chamber 2.

[0038] Referring initially to FIGS. 3 and 4, a more detailed description of the components of embodiments of the gas disperser 3 will be given.

[0039] The inlet duct section 32 has an upstream end 32a and a downstream end 32b. The upstream end 32a is located adjacent the supply duct section 31 and the downstream end 32b is located at the entry to the drying chamber 2 (not shown in FIG. 3). The inlet duct section 32 is provided as a substantially straight pipe of a circular cylindrical shape and defines an axial direction axd, corresponding to a longitudinal axis of the inlet duct section 32. Other configurations of the cross-sectional shape of the inlet duct section are conceivable as well, including square or rectangular. A radial direction rdd and a tangential direction tgd are defined relative to the axial direction axd and will also be referred to jointly as in-plane directions. The inlet duct section 32 has a total length denoted H and an internal diameter D defining a cross-sectional area which is here substantially circular.

[0040] A flow conditioning device is located in the inlet duct section 32, in the embodiment of FIGS. 3 and 4 in the form of one hole plate 5 and one flow straightener 6. The flow conditioner is provided for the purpose of changing one or more characteristics of the flow, e.g. increasing the uniformity in the flow direction, decreasing velocities perpendicular to flow direction or adding swirl. In the embodiments shown, the general flow direction coincides with the axial direction axd, and the undesired velocity components are the in-plane velocities, i.e. the velocity components of the flow in the radial and tangential directions, rdd and tgd. However, the invention is also applicable to technical applications in which it is desirable to induce a controlled swirl.

[0041] The hole plate 5 and the flow straightener 6 each has a diameter substantially corresponding to the internal diameter D of the inlet duct section 32 and defining a cross-sectional area substantially corresponding to the cross-sectional area of the inlet duct section 32. The flow straightener 6 is positioned substantially in parallel with and at a distance h in the axial direction axd from the downstream side of the at least one hole plate 5. The distance h according to the invention is chosen to encompass such mutual positions that the hole plate 5 and the flow straightener 6 are “at”, “near” “close” or “immediately adjacent” each other.

[0042] The hole plate 5 has a predefined hole plate thickness tp (cf. FIG. 5a) in the axial direction axd and each flow straightener 6 has a predefined flow straightener length Is (cf. FIG. 8b) in the axial direction axd. Whereas the hole plate 5 is a plane element of small thickness, the flow straightener has a substantial extension in the axial direction axd such that the flow straightener length Is is substantially larger than the hole plate thickness tp. By the terms “small thickness”, “substantial extension” and “substantially larger”, the skilled person will recognize that although such dimensions, or relative dimensions, may vary, they need to be chosen to fulfill the requirements to strength and ability to withstand the operational conditions in a gas disperser 3.

[0043] Expressed in relative dimensions, the distance h separating the flow straightener 6 from the downstream side of the hole plate 5 in the axial direction axd is for instance below 10 times the hole plate thickness tp, preferably below 5 times the hole plate thickness tp.

[0044] Correspondingly, the flow straightener length Is is preferably larger than the hole plate thickness tp by a factor in the range 5 to 200, for instance by a factor 10 to 150.

[0045] As a further element shown in FIG. 3, there is shown a central rod 33 extending in the axial direction axd. The central rod 33 does not form part of the present invention, but is a component provided for guiding for instance feed to the atomizing means or fine particles in the drying chamber 2.

[0046] Referring now also to FIGS. 5 to 6, the hole plate 5 in one embodiment is provided a plurality of holes 52 distributed over substantially the entire cross-sectional area of the hole plate 5.

[0047] The hole plate thickness tp may be chosen in accordance with other dimensions of the gas disperser, for instance in the range 0.0005 to 0.05 of the internal diameter D of the inlet duct section 32, preferably about 0.01 of the internal diameter D of the inlet duct section 32.

[0048] The hole plate 5 constitutes a component of the inventive flow conditioning device which has high flow resistance in the main flow direction, i.e. the axial direction agd, and low resistance in other directions, i.e. to in-plane velocities, rdd and tgd. It can therefore be used to increase uniformity of the flow in the axial direction. The main adjustable parameters of a hole plate are: hole size, hole shape, open area ratio and plate thickness. With a typical internal diameter D of 1 to 2 m, the hole plate thickness tp is thus about 10-20 mm.

[0049] Regarding the size and shape of the holes 52, it tends to apply that each hole 52 has a cross-sectional dimension in the same order of magnitude as the hole plate thickness tp, i.e. 10 to 20 mm. The open area ratio, i.e. the ratio between the total area of the holes 52 and the total area of the hole plate 5 will typically lie in the range 0.2 to 0.8, preferably about 0.5.

[0050] In principle, the shape of the holes 52 may be any suitable, for instance selected from the group comprising: circular, oval, ovoid, rectangular, polygonal.

[0051] The manufacturing of the hole plate 5 of the embodiments of FIGS. 5 and 6 is in the form of a perforated plate of plate material 51 in which the plurality of holes 52 have been provided.

[0052] Alternatively, the hole plate 5 is formed as a mesh formed by mesh threads 51a, 51b defining said plurality of holes 52 between them.

[0053] Referring now to FIGS. 8 and 9, embodiments of the gas disperser with particular focus on the flow straightener 6 will be described. The flow straightener 6 is provided with a plurality of flow channels 62, each having a longitudinal extension in parallel with the axial direction axd. In alternative embodiments, not shown, the flow straightener is formed as a spiral.

[0054] The flow straightener 6 is a component of the inventive flow conditioning device with high flow resistance in the directions perpendicular to the main flow direction, i.e. to in-plane velocities, and low resistance in the main flow direction, the axial direction axd. It can therefore be used to decrease velocities perpendicular to the main flow direction. The main adjustable parameters of a flow straightener are: length and cell size, i.e. cross-sectional dimensions of the flow channels. Flow straighteners generally have a significant extent in the main flow direction.

[0055] For instance, the flow straightener length Is is in the range 0.005 to 1 of the internal diameter D of the inlet duct section 32, preferably about 0. 1 of the internal diameter D of the inlet duct section 32. With an internal diameter D as mentioned in the above, the flow straightener length Is is about 100 to 200 mm.

[0056] As is apparent from the embodiments shown in FIGS. 8 and 9, the total cross-sectional area of the flow channels 62 constitutes the majority of the cross-sectional area of the flow straightener 6. Typical values of the ratio between the total area of the flow channels 62 and the area of the flow straightener 6 lies in the range 0.8 to 0.99.

[0057] Expressed in relative dimensions to the internal diameter D of the inlet duct section 32, the number of flow channels 62 is in the range 25 to 150 per square meter of the inlet duct section 32, preferably 50 to 100, most preferable 70 to 80.

[0058] In the embodiment of FIGS. 8a and 8b, which is very simple from a constructional point of view, the flow straightener 6 comprises intersecting first and second sets of vanes 61a, 61b. Here, the vanes 61a, 61b extend at right angles to each other, thus forming a plurality of cross-sectionally rectangular flow channels 62. As the vanes of the first and the second sets of vanes 61a, 61b are positioned equidistantly the flow channels 62 are substantially square in cross-section.

[0059] In the alternative embodiment shown in FIGS. 9a and 9b, the flow straightener 6 comprises one or more vanes extending in the tangential direction tgd. Here, four tangential vanes 611, 612, 613, 614 are provided. Intersecting the tangential vanes, a number of sets of radial vanes 615, 616, 617 are provided and together the sets form a plurality of arc-shaped flow channels 62.

[0060] The first, second, third and fourth tangential vane 611, 612, 613, 614 are here arranged concentrically, and a first, second, and third set of radial vanes 615, 616, 617 are distributed in the tangential direction tgd of the flow straightener 6. Also visible in FIG. 9a is central aperture 63 which in the embodiment shown is provided to accommodate central rod 33 shown in FIG. 3.

[0061] A combination of a hole plate and a flow straightener creates a new type of flow conditioning device. This device can be used to increase uniformity in the main flow direction as well as to decrease velocities perpendicular to the main flow direction.

[0062] As mentioned in the above, conditions for the combination to work most effectively include that the flow straightener should begin immediately downstream of the hole plate, typically the distance between the hole plate 5 and the flow straightener 6 should be less than 5 times the hole plate thickness tp. As will be apparent from the below exemplary configurations, it is also important to have a distance of unrestricted space upstream of the hole plate for it to work effectively. Typically, the distance upstream of hole plate 5 should be at least the same as the length of the flow straightener 6, or expressed in relative terms to the diameter D of the inlet section 32, at least 0.01 times the internal diameter D.

[0063] As mentioned in the present description, uniformity of a flow is a characteristic describing the level of variation a specific parameter in the flow e.g. velocity uniformity or temperature uniformity. A higher uniformity means that the variation in the flow is lower. The variation can be either spatial variation or temporal variation or both.

[0064] When considering spatial uniformity of the velocity in the main flow direction in an internal flow, a distinction between large scale uniformity and small scale uniformity can be made. Large scale uniformity considers the uniformity of the flow on a scale of the same order of magnitude as the length of the cross section of the internal flow e.g. the diameter in a pipe flow. An example of large scale uniformity is the difference in flow velocities between two halves of a circular pipe flow, or each quarter, or each ⅛ in a square pipe flow. Small scale uniformity instead considers the flow uniformity on a much smaller scale. An example of small scale uniformity is the non-uniformity caused by a hole plate as the flow splits into each of the holes in the hole plate.

[0065] Referring now to FIGS. 10a to 10e, a number of embodiments of the gas disperser 3 will be described.

[0066] FIG. 10a is a schematic, simplified expression of the flow conditioning device according to the invention, namely a set of one hole plate 5 and one flow straightener 6 positioned directly downstream of the hole plate 5.

[0067] In the embodiment of FIG. 10b, there is a first hole plate 5a positioned at a first distance h1 from the upstream side of the flow straightener 6, and a second hole plate 5b is positioned on the upstream side of the first hole plate 5a at a second distance h2 from the first hole plate 5a, seen in the axial direction axd, the second distance h2 being preferably larger than 0.01 of the internal diameter D of the inlet duct section 32 or larger than the length Is of the flow straightener 6.

[0068] In the embodiment of FIG. 10c, a third hole plate 5c is positioned on the downstream side of the flow straightener 6 at a third distance h3 from the downstream side of the flow straightener, seen in the axial direction axd, the third distance h3 being preferably larger than 0.01 of the internal diameter D of the inlet duct section 32 or larger than the length Is of the flow straightener 6.

[0069] A combination between the embodiments of FIGS. 10b and 10c is of course conceivable.

[0070] In the embodiment of FIG. 10d, a first flow straightener 6a is positioned directly downstream of the single hole plate 5 and a second flow straightener 6b is provided on the downstream side of the first flow straightener 6a at a fourth distance h4 from the downstream side of the first flow straightener 6a.

[0071] Finally, in the embodiment of FIG. 10e a second hole plate 5b is provided upstream of the second flow straightener 6b, at a fifth distance h5 from the downstream side of the first flow straightener 6a, and at a sixth distance h6 from the upstream side of the second flow straightener 6b, to form two sets of one upstream hole plate 5; 5a; 5b and one downstream flow straightener 6; 6a; 6b located at a distance h; h1; h6 from the respective hole plate, the fifth distance h5 being preferably larger than 0.01 of the internal diameter D of the inlet duct section 32 or larger than the length Is of the flow straightener 6.

[0072] In this way two sets of one upstream hole plate 5a, 5b and one downstream flow straightener 6a, 6b are provided. Each set has its own coefficient of performance, which may be the same or different dependent on the configuration of the individual set, and by combining two, three or more sets, the desired total flow conditioning effect may be attained.

[0073] The hole plate or plates 5 and the flow straightener(s) 6 may be provided as spare parts configured for retrofitting into an existing gas disperser.

[0074] Depending on whether the flow conditioning device of the invention is provided for retrofitting, as spare parts, or as an integral part of the gas disperser, the connection between the flow conditioning device and the inlet duct section may in principle be carried out in any suitable manner. As one possibility, each hole plate 5 and/or each flow straightener 6 are connected to the inlet duct section 32 of the gas disperser by releasable mechanical fastening means. Alternatively, each hole plate 5 and/or each flow straightener 6 are connected to the inlet duct section 32 of the gas disperser by permanent attachment such as welding. Regardless of how the parts are connected, all parts should be easily cleanable for instance by a Cleaning-in-Place (CIP) procedure.

[0075] During operation of the inventive gas disperser and spray drying apparatus, the stream of gas is thus aligned in its path from the supply to the drying chamber. Without wishing to be bound by theory, the following operational steps are run through:

[0076] The stream of gas containing velocity components in the axial direction axd, the radial direction rdd and the tangential direction tgd is allowed to enter the upstream end 32a of the inlet duct section 32.

[0077] First, the stream is subjected to flow resistance generally in parallel with the axial direction axd, from the at least one hole plate 5, whereby the axial velocity components are distributed over the cross-sectional area of the inlet duct section 32.

[0078] Second, the stream is subjected to flow resistance generally in the radial and tangential directions rdd, tgd from the at least one flow straightener 6, whereby the radial and tangential velocity components are reduced.

[0079] The invention is not limited to the embodiments shown and described in the above, but various modifications and combinations may be carried out.

LIST OF REFERENCE NUMERALS

[0080] 1 spray drying apparatus

[0081] 2 drying chamber

[0082] 3 gas disperser

[0083] 31 supply duct section

[0084] 32 inlet duct section

[0085] 32a upstream end

[0086] 32b downstream end

[0087] 33 central rod

[0088] 4 outlet

[0089] 5 hole plate

[0090] 5a first hole plate

[0091] 5b second hole plate

[0092] 5c third hole plate

[0093] 51 plate material

[0094] 51a thread of mesh

[0095] 51b thread of mesh

[0096] 52 holes

[0097] 6 flow straightener

[0098] 6a first flow straightener

[0099] 6b second flow straightener

[0100] 61a first set of vanes

[0101] 61b second set of vanes

[0102] 611 first tangential vane

[0103] 612 second tangential vane

[0104] 613 third tangential vane

[0105] 614 fourth tangential vane

[0106] 615 first set of radial vanes

[0107] 616 second set of radial vanes

[0108] 617 third set of radial vanes

[0109] 62 flow channels

[0110] 63 central aperture

[0111] axd axial direction

[0112] rdd radial direction

[0113] tgd tangential direction

[0114] h distance between hole plate(s)/flow straightener(s) in axial direction

[0115] H length of inlet duct section

[0116] D internal diameter of inlet duct section

[0117] tp thickness of hole plate

[0118] Is length of flow straightener in axial direction