A DRYER AND A METHOD FOR DRYING A LIQUID FEED INTO A POWDER

Abstract

A dryer for drying a liquid feed into a powder comprises a drying chamber defined by a chamber wall including a bottom wall portion; a feed inlet for receiving the liquid feed and dispersing particulate feed into the drying chamber; at least one air inlet for entering drying air into the drying chamber; and at least one drying chamber outlet for dried powder and/or spend drying air from the drying chamber. The feed inlet comprises a decanter centrifuge with an axis of rotation; a first axial end; a second axial end; and a solid phase outlet at the first axial end.

Claims

1.-16. (canceled)

17. A dryer for drying a liquid feed into a powder, comprising: a drying chamber defined by a chamber wall including a bottom wall portion; a feed inlet for receiving the liquid feed and dispersing particulate feed into the drying chamber; at least one air inlet for entering drying air into the drying chamber; and at least one drying chamber outlet for dried powder and/or spent drying air from the drying chamber, wherein the feed inlet comprises a decanter centrifuge having: an axis of rotation; a first axial end; a second axial end; and a solid phase outlet at the first axial end; wherein the axis of rotation of the decanter centrifuge is vertical; and wherein the first axial end of the decanter centrifuge is positioned below the second axial end of the decanter centrifuge.

18. The dryer of claim 17, wherein the drying chamber has a common drying chamber outlet for dried powder and spent drying air, and a product conduit is connected to the common drying chamber outlet for pneumatic conveyance of the dried powder through the product conduit.

19. The dryer of claim 18, wherein the product conduit is connected to a separator for separating the dried powder and the spent drying air.

20. The dryer of claim 17, wherein the air inlet is configured to provide a swirl of drying air inside the drying chamber.

21. The dryer of claim 17, wherein the bottom wall portion of the drying chamber is conical.

22. The dryer of claim 17, wherein the decanter centrifuge comprises a rotatable bowl with a cylindrical part and a conical part, the rotatable bowl having: a central axis of rotation; a conveyor screw in the bowl that conveys material towards the conical part; a liquid feed inlet for letting a liquid feed into the bowl; a solid phase or heavy phase outlet at the narrow end of the conical part; and a liquid phase or light phase outlet at the opposite end of the bowl.

23. The dryer of claim 17, wherein the decanter centrifuge is suspended at an upper end of the drying chamber for the solid phase outlet to extend inside the drying chamber.

24. A dryer for drying a liquid feed into a powder, comprising: a drying chamber defined by a chamber wall including a bottom wall portion; a feed inlet for receiving the liquid feed and dispersing particulate feed into the drying chamber; at least one air inlet for entering drying air into the drying chamber; and at least one drying chamber outlet for dried powder and/or spent drying air from the drying chamber, wherein the feed inlet comprises a decanter centrifuge having: an axis of rotation; a first axial end; a second axial end; and a solid phase outlet at the first axial end, wherein the drying chamber has a common drying chamber outlet for dried powder and spent drying air, and wherein a product conduit is connected to the common drying chamber outlet for pneumatic conveyance of the dried powder through the product conduit; wherein the air inlet is configured to provide a swirl of drying air inside the drying chamber; and wherein the drying chamber generally has a disk shape with a circumferential wall, a part of which constitutes the bottom wall portion, and wherein the drying chamber has a tangential drying chamber outlet and, optionally, a tangential air inlet for entering at least part of the drying air.

25. The dryer of claim 24, wherein the product conduit is connected to a separator for separating the dried powder and the spent drying air.

26. The dryer of claim 24, wherein the decanter centrifuge comprises a rotatable bowl with a cylindrical part and a conical part said bowl having a central axis of rotation; a conveyor screw in the bowl that conveys material towards the conical part; a liquid feed inlet for letting a liquid feed into the bowl; a solid phase or heavy phase outlet at the narrow end of the conical part; and a liquid phase or light phase outlet at the opposite end of the bowl.

27. The dryer of claim 24, wherein the axis of rotation of the decanter centrifuge is horizontal.

28. The dryer of claim 24, wherein the solid phase outlet of the decanter centrifuge is positioned centrally in the drying chamber.

29. A dryer for drying a liquid feed into a powder, comprising: a feed inlet for receiving the liquid feed and dispersing particulate feed into a drying chamber, wherein the feed inlet comprises a decanter centrifuge having: an axis of rotation; a first axial end; a second axial end; and a solid phase outlet at the first axial end.

30. The dryer of claim 29, wherein the first axial end is positioned below the second axial end.

31. The dryer of claim 29, wherein the drying chamber has a common drying chamber outlet for dried powder and spent drying air.

32. The dryer of claim 31, wherein a product conduit is connected to the common drying chamber outlet for pneumatic conveyance of the dried powder through the product conduit.

33. The dryer of claim 29, wherein the drying chamber generally has a disk shape with a circumferential wall and wherein the drying chamber has a tangential drying chamber outlet and a tangential air inlet for entering at least part of a drying air.

34. A method of drying a liquid feed into a powder using a dryer according to claim 29, comprising: separating a liquid feed into a solid phase and a liquid phase in the decanter centrifuge; dispersing the solid phase directly into the drying chamber from the solid phase outlet of the decanter centrifuge; letting drying air into the drying chamber to mix with the dispersed solid phase thereby drying the dispersed solid phase; and removing the dried solid phase from the drying chamber.

35. The method of claim 34, wherein the step of removing the dried solid phase from the drying chamber includes pneumatically conveying the dried solid phase by means of the drying air.

36. The method of claim 35, wherein the removed dried solid phase is conveyed to a separator for separation of the dried solid phase from the pneumatically conveying drying air.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0025] The invention will in the following be explained in further detail by way of non-limiting examples having reference to the accompanying schematic drawings, in which

[0026] FIG. 1 shows a prior art ring dryer;

[0027] FIG. 2 shows a first embodiment of a dryer according to the invention comprising a decanter centrifuge with a horizontal axis of rotation;

[0028] FIG. 3 shows a variant of the dryer shown in FIG. 2;

[0029] FIG. 4 shows a second embodiment of a dryer according to the invention comprising a decanter centrifuge with a vertical axis; and

[0030] FIG. 5 shows a third embodiment of a dryer according to the invention comprising a decanter centrifuge with a vertical axis.

[0031] In the following different embodiments of a dryer according to the invention are described with reference to the drawings and similar features in the different embodiments are designated by similar reference numerals.

DETAILED DESCRIPTION

[0032] FIGS. 2 and 3 show, in two variants, a dryer 1 comprising a drying chamber 3 defined by a chamber wall 5, which includes a bottom wall portion 7; a liquid feed inlet in the form of a decanter centrifuge 9 for receiving a liquid feed 11 and dispersing dewatered, particulate feed 13 into the drying chamber 3; an air inlet 15 for entering drying air into the drying chamber; and a drying chamber outlet 17 for outletting in common dried powder and spend drying air from the drying chamber 3. The decanter centrifuge 9 has a horizontal axis of rotation 19 and for the sake of explanation it has a first axial end 21 and a second axial end 23. A solid phase outlet dispersing in operation the particulate feed 13 is at the first axial end 21.

[0033] A product conduit 25 is connected to the common drying chamber outlet 17 for pneumatic conveyance of the dried powder through the product conduit 25 to a separator, which in the present embodiment is a cyclone 27. The dried powder may comprise dried as well as semi-dried particles and drying of the particles may continue as long as the particles are suspended by the drying air, i.e. the drying of the particles may continue outside the drying chamber. Thus the drying process may continue in the product conduit 25 and in the cyclone 27 until the powder is eventually separated from the stream of drying air suspending and conveying the powder through the product conduit 25 and into the cyclone 27.

[0034] An air heater 29 is provided for heating the drying air up-stream of the air inlet 15.

[0035] Centrally at the second axial end 23 the decanter centrifuge 9 comprises an inlet for the liquid feed 11, and the decanter centrifuge 9 has a liquid phase outlet 30 at the second axial end 23.

[0036] The drying chamber 3 is generally disk-shaped and co-axial with the decanter centrifuge 9 and the drying chamber 3 has a circular, circumferential wall 31, a part of which constitutes the bottom wall portion 7. The drying chamber 3 and the decanter centrifuge 9 being co-axial entails that the solid phase outlet of the decanter centrifuge 9 is positioned centrally in the drying chamber 3. The air inlet 15 is connected tangential to the circumferential wall 31 to introduce drying air into the drying chamber in an angular direction relative to the axis of the drying chamber, and the drying chamber outlet 17 is correspondingly connected to the circumferential wall 31 to exit the dried powder and spend drying air from the drying chamber 3 in the same angular direction relative to the axis. Hereby is provided for the formation of a swirl of the air inside the drying chamber 3 which effectively promotes the drying of the particulate feed 13. Further, the configuration of the air inlet 15 and the drying chamber outlet 17 facilitates pneumatic transport of the lot of dried powder out of the drying chamber 3.

[0037] The air inlet 15 and the drying chamber outlet 17 may be positioned axially askew, i.e. at slightly different axial positions thereby further promoting the swirl of air inside the drying chamber 3. Moreover, by positioning the air inlet 15 and the drying chamber outlet 17 axially askew the particles or powder suspended in the air inside the drying chamber may be forced to spirally circulate an extra 360° around the axis of rotation before leaving the drying chamber 3.

[0038] The cyclone 27 receives in operation spend drying air and dried powder from the drying chamber outlet 17. The cyclone 27 separates in a manner known per se the spend drying air 33 and the dried powder 35. The spend drying air 33 may in part be recirculated to the air heater 29 and the air inlet 15 as indicated by broken line 37, when the spend drying air 33 is far from saturated by vapour of the liquid of the liquid feed. By recirculating part of the spend drying air, which is still relatively hot compared to the air of the surroundings, energy for heating the drying air in the air heater 29 before entering through the air inlet 15 may be saved.

[0039] As indicated by comparison of FIG. 2 and FIG. 3 the air inlet 15 and the drying chamber outlet 17 may be positioned at different angular positions relative to the axis 19.

[0040] FIGS. 4 and 5 show two different embodiments of a dryer 1′ according to the present invention in which a decanter centrifuge 9′ is arranged for the axis of rotation 19′ to be vertical. In both embodiments of FIGS. 4 and 5 a drying chamber 3′ is generally formed like it is known per se from spray dryers, cf. the above mentioned WO9104776A1, and thus the drying chamber 3′ of both embodiments comprise an upper cylindrical part 41 and a lower conical part 43 the latter providing a bottom wall portion 7′ of the drying chamber 3′. At the top of the drying chamber 3′ an air inlet 15′ is comprising an air disperser 45, which in an embodiment is provided for even distribution of the drying air around the common axis 19′ of the decanter centrifuge 9′ and the drying chamber 3′ and for providing a swirl of the in-flowing drying air and thus of the drying air inside the drying chamber 3′. In the embodiments shown an air heater 29′ is provided up-stream of the air disperser 45. A common drying chamber outlet 17′ is provided at the lower end of the conical part 43 and a product conduit 25′ connects the drying chamber outlet 17′ with a separator in the form of a cyclone 27′. In operation the cyclone 27′ separates dried powder 35′ and spend drying air 33, and provisions can be made for recycling a part of the spend drying air to the air heater 29′ as indicated by a broken line 37′, like in the embodiment shown in FIGS. 2 and 3.

[0041] In the embodiment shown in FIG. 4 the decanter centrifuge 9′ is suspended at the upper end of the drying chamber 3′ with the solid phase outlet provided at a first axial end 21′ of the decanter centrifuge 9′ extending into the drying chamber 3′ for the decanter centrifuge 9′ to disperse, from the solid phase outlet, particulate feed 13′ into the drying chamber 3′, a second axial end 23′ comprising a liquid phase outlet 30′ of the decanter centrifuge 9′ being positioned above the first axial end 21′. Centrally at the second axial end 23′ the decanter centrifuge 9′ comprises an inlet for liquid feed 11′.

[0042] In the embodiment shown in FIG. 5 the decanter centrifuge 9′ is provided inside the drying chamber 3′ and has its first axial end 21′ with the solid phase outlet positioned above the second axial end 23′ with the inlet for liquid feed 11′ and the liquid phase outlet 30′. In this embodiment a partition 47 may be provided to provide a hollow chamber inside the drying chamber 3′ for accommodating the main part of the decanter centrifuge 9′ to avoid that it is heated by hot air in the drying chamber 3′.

[0043] For all of the above embodiments of the dryer 1, 1′ the following continuous process may be conducted using the dryer 1, 1′.

[0044] A liquid feed 11, 11′ is entered into the decanter centrifuge 9, 9′ whereby a solid phase of the liquid feed is separated from a liquid phase of the liquid feed, said liquid phase leaving the decanter centrifuge 9, 9′ through the liquid phase outlet 30, 30′. The solid phase is dispersed from the solid phase outlet of the decanter centrifuge 9, 9′ and since the bowl of the decanter centrifuge 9, 9′ including the solid phase outlet, as well known to the skilled person, is spinning fast around the axis 19, 19′ the solid phase is ejected as a particulate feed 13, 13′ comprising small particles of solid phase.

[0045] The particulate feed 13, 13′ is thus dispersed into the drying chamber 3, 3′ and into a swirl of hot air in the drying chamber 3, 3′, said hot air being introduced through the air inlet 15, 15′ after being heated to a predetermined temperature in the air heater 29, 29′. By the encounter with the hot air in the drying chamber 3, 3′ the particulate feed 13, 13′ is dried into dried powder, which by pneumatic transport is carried through the drying chamber outlet 17, 17′ by the now spend drying air, through the product conduit 25, 25′ and into the cyclone 27, 27′ where the dried powder 35, 35′ is separated from the spend drying air 33, 33′ to be let out through respective outlets as indicated in the figures and as recognised by the skilled person.

[0046] The dried powder 35, 35′ may be collected as product of the process.

[0047] Thus the apparatus, or dryer, and the method, or process, described above may be utilised for providing a powder product of most different materials by adjusting process parameters, such as temperature, etc. in accordance with the nature and character of the liquid feed and its solid and liquid phases. Using a decanter centrifuge as feed inlet for a drying process energy for evaporation of a large part of the liquid phase of the liquid feed may be saved. Moreover, using a decanter centrifuge as feed inlet for a drying process thus letting the solid phase outlet of the decanter centrifuge directly into the drying chamber a very gentle treatment of solid particles may be obtained that may give improved product quality compared to traditional drying processes.

[0048] Though the invention has herein ben described with reference to specific embodiments it should be understood that the scope of the invention is not limited to said embodiments.