METHOD AND APPARATUS FOR DRYING WET PARTICULATE MATERIAL

Abstract

 The invention relates to a method and a system for drying wet particulate material.
The method comprises the step of supplying wet particulate material to a dryer and transporting the wet particulate material along a flow path in the dryer along which flow path, the material is dried. The method further comprises the step of extracting part of the semi-dried material from the flow path, at a position distanced from an inlet and circulating the extracted material to the first part of the apparatus, the first part comprising the inlet and where the extracted material is mixed with the supplied wet material.

Description

TECHNICAL FIELD

[0001] The present invention relates to a method and an apparatus for drying wet particulate material.

BACKGROUND OF THE INVENTION

[0002] It is known to dry moist bulk particulate material by contacting the particulate material, such as residue from ethanol production or sugar beet pulp etc., with superheated steam, where liquid contained within the material is evaporated and the material is dried.

[0003] An early disclosure of the above-mentioned steam drying technologies includes EP 0 058 651 A1, which relates to a method of preparing cattle feed from various agricultural products, such as sugar beet pulp, citrus fruit pulp and peel and various fermentation products.

[0004] Another disclosure is EP 0 153 704 A2, which teaches a process of removing liquid from a particulate solid material in which the material is passed through a row of interconnected cells and superheated steam is introduced into said cells at their lower ends so as to impart a whirling movement during which dried panicles to be dried are lifted out of the cells and into a common transfer zone and into a discharge cell with no steam supply.

[0005] The prior art document WO 92/01200 discloses an apparatus for drying a moist particulate material having a non-uniform particle size with superheated steam. The apparatus comprises a cylindrical vessel comprising a number of parallel, substantially vertical drying chambers located in ring form. The preferred embodiment includes fifteen drying chambers connected in series, and a discharge chamber located between the first and the last drying chamber.

[0006] At the first drying chamber after the inlet, the particulate material will have a high liquid content, whereas the particulate material at the last drying chamber will have a low liquid content. The drying chambers are adapted to induce a movement of the flow of superheated steam in order to improve the contact between the steam and the particulate material and to cause the particulate material to pass all cells just in time to be dried. In particular, the moist particles tend to be heavier than the dry particles and thus require a larger flow and steam velocity.

[0007] It has been noted by the applicant that the introduced moist particulate material, and in particular the large and heavy particles, tend to accumulate in the apparatus or even clog the flow path inside the apparatus such that the drying process is compromised.

[0008] It is thus an object of the present invention to provide an improved technology for avoiding clogging of the flow path inside the apparatus.

[0009] The above object and advantages, together with numerous other objects and advantages, which will be evident from the description of the present invention, are according to a first aspect of the present invention obtained by:

A method for drying wet particulate material, such as residue from ethanol production or sugar beet pulp, where the wet particulate material is dried in an apparatus having a vessel,

the vessel being a pressure vessel capable of maintaining superheated steam at a pressure larger than the ambient pressure surrounding the vessel,

the vessel having a flow path for transporting the wet particulate material under pressure, through the vessel, the particulate material being dried along the flow path by applied heat,

the vessel comprising an inlet arranged in a first part of the vessel, for receiving the wet particulate materials and an outlet arranged in a second part of the vessel, for ejecting the dried particulate materials from the vessel, the flow path being arranged between the inlet and the outlet,

the method comprising the following steps:

• supplying wet particulate material via the inlet into the first part, the particulate material having an initial wt% of dry material,
• transporting the wet particulate material along the flow path towards the outlet,
• extracting part of the particulate material from the flow path, at an extraction position distanced from the inlet, said extracted material being semi-dried and less wet compared so the supplied wet particulate material, and circulating the extracted material to the first part,
• mixing the circulated extracted material with supplied wet particulate material within the first part, such that the wt% of dry material of the mixed particulate material is larger compared to the initial wt% of dry material.

[0010] The vessel is typically made of metal capable of withstanding temperatures of superheated steam exceeding 100°C and pressures exceeding the ambient atmospheric pressure, and defines a closed system. Typical pressures range from ambient atmospheric pressures to a pressure of up to 4 bar.

[0011] The vessel preferably comprises a source of heat, such as a source of superheated steam, which is supplied to the vessel and contacts the particulate material transported along the flow path. Hereby, liquid contained within the material is evaporated and the material is dried.

[0012] As an alternative to a dryer using superheated steam, a drum dryer, disc dryer, paddle dryer, etc. may be used.

[0013] The particulate material arriving at the first part, i.e. at the inlet, may be very wet and contains a large portion of liquid, and thus tends to be heavy and clogging up the chamber. In relation to the process of manufacturing ethanol from corn biomass, the residue material from the production is a wet sticky mass containing a high percentage of water, hereby making it difficult to establish the flow of material through the vessel. This leads to reduced flow through the flow path and less distribution of particulate material, which results in accumulation of moist/wet material in some parts of vessel, especially at the inlet in the first part of the vessel.

[0014] In order to decrease the water content of the material introduced into the first part of the vessel effectively and almost instantly, as the wet material enters the first part via the inlet, tests have shown that a recirculation of dried or semi-dried material extracted upstream of the flow path into the first part, where it is mixed with the wet material, immediately reduces the overall water content of the mixed material.

[0015] It is hereby achieved that very wet and sticky material unsuitable for a given standard drying process being mixed with dried or semi-dried material at the inlet, is rendered suitable for the given drying process such that the apparatus does not clog.

[0016] According to a further embodiment of the first aspect of the invention, the applied heat is superheated steam.

[0017] Especially when using a drying process in which the heating is superheated steam, the semi-dried and hereby heated recirculated material effectively absorbs moisture from the supplied material, whereby the average wt% of dry material in the first part of the vessel rapidly increases.

[0018] According to a further embodiment of the first aspect of the invention, at least 90% of said superheated steam are generated from vaporized fluid from said supplied material.

[0019] Arranging the apparatus, such that at least 90% and preferable approximately close to 100% of the superheated steam is generated from vaporized fluid deriving from the supplied material, provides an energy efficient drying apparatus without the need for an external steam source, such as a boiler.

[0020] According to a further embodiment of the first aspect of the invention, the method comprises the mixed material comprising at least 1/4 of extracted material and 3/4 of supplied wet particulate material, preferably at least 1/2 of extracted material and 1/2 of supplied wet particulate material, such as at least 2/3 of extracted material and 1/3 of supplied wet particulate material.

[0021] Providing the mixed material with the above defined amounts of extracted and supplied material ensures a sufficient increase of the average wt% of dry material of the mixed recirculated and supplied material, such that a clogging of the apparatus is avoided while at the same time ensuring a satisfying overall flow of material through the apparatus.

[0022] According to a further embodiment of the first aspect of the invention, the extracted material is semi-dried and has a wt% of dry material being 50-92%, preferably 50-85%.

[0023] The extracted material preferably comprises a higher water content than the dried material ejected via the outlet. Tests have shown that a wt% of dry material corresponding to the extracted material being between 50-92% has the technical effect that the extracted material, once recirculated into the first part, has a faster water absorption compared to the ejected material. In this way, once the extracted material is recirculated into the first part, the transfer of water from the received wet material via the inlet is increased, such that the wt% of dry material of the injected material quickly increases. The absorption rate of a fully dried material is slower compared to a semi-dried material.

[0024] According to a further embodiment of the first aspect of the invention, the extracted material is semi-dried and has a wt% of dry material corresponding to between 55-100% compared to the wt% of dry material at said outlet (24).

[0025] An advantage of recirculating the semi-dried material is that fully dried material tends to change color due to the applied heat, and recirculating fully dried material influences the color of mixed material in the first part. Hereby, the risk of color change of the conveyed material is minimized. Providing the extracted material being semi-dried and having a wt% of dry material corresponding to between 55-100% compared to the wt% of dry material at said outlet (24) ensures minimal risk of color change from the recirculated material combined with optimal heat transfer between the recirculated material and the wet applied material.

[0026] According to a further embodiment of the first aspect of the invention, the mixed material has at least 30 wt% (MDS) of dry material as a function of:

without influence from the applied heat in said first part,
where:

E is extracted material kg/h,

EDS is wt% of dry material in the extracted material,

S is supplied material kg/h,

SDS is wt% of dry material in the supplied material,

M is mixed material Kg/h.

[0027] A mixing of the material in the first part in steady state, where the mixed material has a wt% of dry material being at least 30% wt, such as at least 50% of dry material according to the above function, without influence from the applied heat in said first part, ensures a lower threshold value of the wt% of dry material in the first part. It is however to be understood that the value MDS is the lowest possible value. In a situation where heat is into the first part for drying the mixed material, the MDS will immediately increase further. In a preferred embodiment the mixed material has a wt% of dry material not higher than 80%, which ensures sufficient dry material in the first part without extracting a too high amount of material from the flow path.

[0028] According to a further embodiment of the first aspect of the invention, the extracted material is circulated under pressure, the pressure being larger than the ambient pressure surrounding the vessel.

[0029] The extracted material is recirculated with the closed system under the same pressure as the conveyed material. Hereby, compared to a recirculated material injected from outside the vessel, such as material under ambient pressure, a minimum requirement of energy is ensured, as the recirculated material requires energy for being heated.

[0030] According to a further embodiment of the first aspect of the invention, the pressure within the vessel is approximate 0,2-4 barg, preferably 2-4 barg.

[0031] A pressure inside the vessel being approximate 0,2-4 barg, preferably 2-4 barg, proves the most optimal conditions for mixing and heat transfer between the extracted material and the new injected material.

[0032] According to a further embodiment of the first aspect of the invention, the vessel comprises a number of partitioning walls extending vertically within the vessel and defining, in the vessel, an inlet chamber in the first part, an outlet chamber in the second part and a number of intermediate chambers located between the inlet chamber and the outlet chamber, hereby arranging the flow path between said inlet and outlet chamber, the inlet chamber comprising the inlet for receiving the wet particulate material, the outlet chamber comprising the outlet for ejecting the dried particulate material, the inlet chamber and the intermediate chambers each comprising a steam permeable bottom, wherein at least one of the intermediate chambers comprises extraction means for extracting the part of said particulate material from the flow path, the vessel further comprising circulating means for circulating the extracted material into said inlet chamber.

[0033] The vessel typically comprises a lower cylindrical part and an upper cylindrical part which form part of the outer enclosure of the vessel and an intermediate conical part between the lower and upper cylinder.

[0034] A supplier of steam may be a boiler, or an outlet of steam in another system utilizing pressurized steam, for example an outlet of a turbine.

[0035] The vessel comprises a first fluid path inside the inner cylindrical part and a second fluid path between the outer enclosure of the vessel and the inner cylindrical part defining the recirculation of the superheated steam. The flow of superheated steam is established by an impeller which is located in the lower cylindrical part below the steam permeable bottom and/or between the inner cylindrical part and the steam permeable bottom of the lower cylindrical part in order to establish a high pressure below the steam permeable bottom, which in turn establishes a fluid bed and the recirculating flow of superheated steam. The inner cylindrical part includes a heat exchanger which maintains the recirculating steam in a superheated state to avoid any condensation from occurring within the vessel.

[0036] The drying is taking place by superheated steam contacting the moist particulate material and transferring some of its heat to the moist particles. The liquid content of the moist particulate material will vaporize, and the vapor becomes part of the circulating steam. The heat energy required for the vaporization and thereby removed from the superheated steam is replenished at the heat exchanger in order to avoid condensation of the superheated steam into liquid within the vessel. Any surplus steam may be released from the dryer through the top part of the vessel e.g., through a valve. The vessel also includes means for inducing a circumferential flow component in order to cause the particulate material to move slowly in a circumferential direction from the inlet to the outlet.

[0037] The partitioning walls serve to delimit the lower cylindrical part into several chambers. The first chamber is the inlet chamber, which may be connected to a closed off screw conveyor or the like for injecting the moist particulate material into the inlet chamber. The outlet chamber may also comprise a closed off screw conveyor or the like for discharging the dry particulate material to the outside of the vessel.

[0038] The intermediate chambers are located between the inlet chamber and the outlet chamber. The partitioning walls may include openings for allowing particulate material to be transported from the inlet chamber to the outlet chamber via the intermediate chambers. The inlet chamber and the intermediate chambers receive superheated steam from a steam permeable bottom and thus constitute drying chambers.

[0039] Within the drying chambers a fluid bed and a flow are established, which maintain most of the particulate material in the lower cylindrical part and increase the contact between the superheated steam and the particulate material.

[0040] The outlet chamber preferably does not have a steam permeable bottom to allow the particulate material to settle before being discharged. The number of chambers influences the standard deviation of the distribution retention time. Increasing the number of chambers reduces the standard deviation of the retention time of the particulate material.

[0041] The particulate material arriving at the first drying chamber, i.e. the inlet chamber, is extremely sticky, wet and contains a large portion of liquid, and the material thus tends to be heavy, and sticky material clogs up the chamber. In relation to the process of manufacturing ethanol from corn biomass, the residue material is a wet sticky mass containing a high percentage of water, hereby making it difficult to establish the flow of material through the vessel. This leads to reduced, or even no lift in the fluid bed, less whirling motion of the flow, and less distribution of the particulate material, which results in accumulation of moist/wet particulate material in some parts of the inlet chamber, especially in the first part of the vessel at the inlet. The particulate material arriving at the last drying chamber before the outlet chamber in which the now dried particulate material is ejected, is substantially dry.

[0042] In order to avoid a clogging of the apparatus, and especially avoid a clogging of the apparatus in the first cell, being the inlet chamber, a recirculation of dried or semi-dried material extracted upstream of the flow path into the first part where it is mixed with the wet material, immediately reduces the overall water content of the mixed material. It is hereby achieved that extremely wet and sticky material unsuitable for a given standard drying process is mixed with dried or semi-dried material at the inlet and hereby arranged suitable for the given drying process.

[0043] According to a further embodiment of the first aspect of the invention, the vessel in connection with the inlet chamber comprises injection means for injecting the extracted material into the inlet chamber.

[0044] In order to ensure that the extracted material is mixed with the injected material fast and efficiently, whereby the optimal heat transfer between the extracted material and the injected material is ensured, the inlet chamber, in connection with the bottom thereof, comprises injection means, such as a propeller or similar, which injects the extracted and recirculated material into the inlet chamber. The injection means may be connected with the source of superheated steam in the same way as the steam permeable bottom, and thus semi-dried material being extracted and transported to the injection means, the injection means preferable being arranged in an opening in the steam permeable bottom, will be blown up into the inlet chamber where it immediately mixes with the supplied wet material.

[0045] According to a further embodiment of the first aspect of the invention, the extracted part of the particulate material is transported at a level below the steam permeable bottom.

[0046] In order to ensure minimal interference with the transported particulate material along the flow path, the extracted material is transported from the extraction point to the first part at a level below the flow path, hereby at a level below the permeable bottom and the generated fluid bed.

[0047] According to a further embodiment of the first aspect of the invention, the extracted material is introduced into the first chamber through the inlet.

[0048] As an alternative to recirculating the extracted material directly into the inlet chamber, the extracted material may be supplied to a feeding mechanism arranged in connection with the inlet. The feeding mechanism may include a screw conveyor which conveys the received moist/wet particulate material from a valve, such as a drum valve, to the inlet and into the inlet chamber. Such embodiment provides a solution where the recirculated material is premixed with the moist/wet material in the screw conveyor before entering the inlet chamber, and a solution which does not interfere with the fluid bed in the inlet chamber.

[0049] According to a further embodiment of the first aspect of the invention, the extracted material is extracted upstream in relation to the outlet and downstream in relation to the inlet.

[0050] The above-described embodiment provides a solution for extracting dried material and introducing the dried material back into the first part of the vessel in a mixture of extracted dried material and supplied wet material, with least constructional changes to the vessel. The dried material is extracted upstream of the outlet, and thus outside of the vessel, but still within the same pressure zone, and may be recirculated downstream in relation to the inlet. The means for extracting and recirculating the dried material may thus easily be retrofitted into an existing dryer.

[0051] According to a second aspect of the present invention, the above objects and advantages are obtained by:

An apparatus comprising a vessel for drying wet particulate material under a pressure being larger than the ambient pressure surrounding the vessel, the vessel being a pressure vessel capable of maintaining superheated steam at a pressure larger than the ambient pressure surrounding the vessel,

the vessel having a flow path for transporting the wet particulate material under pressure, through the vessel, such that the particulate material is dried along the flow path,

the vessel comprising an inlet in a first part for receiving the wet particulate materials and an outlet in a second part, for ejecting the dried particulate materials from the vessel, the flow path being arranged between the inlet and the outlet,

the apparatus comprising extraction means for extracting part of the particulate material from the flow path, at a position distanced from the inlet, and circulating the extracted material to the first part.

[0052] A recirculation of dried or semi-dried material extracted up-stream of the flow path in relation to the inlet and into the first part, where it is mixed with the wet material, immediately reduces the overall water content of the mixed material compared to the received material.

[0053] It is hereby achieved that very wet and sticky material unsuitable for a given standard drying process, is mixed with dried or semi-dried material at the inlet, such that the mixture is arranged suitable for the given drying process, whereby clogging of the apparatus, and especially the inlet chamber, is avoided.

[0054] According to a further embodiment of the second aspect of the invention, the vessel comprises a number of partitioning walls extending vertically within the vessel and defining, in the vessel, an inlet chamber in the first part, an outlet chamber in the second part and a number of intermediate chambers located between the inlet chamber and the outlet chamber, hereby arranging the flow path between the inlet and outlet chamber, the inlet chamber comprising the inlet for receiving the wet particulate material, the outlet chamber comprising the outlet for ejecting the dried particulate material, the inlet chamber and the intermediate chambers each comprising a steam permeable bottom, wherein at least one of the intermediate chambers comprises the means for extracting the part of the particulate material from the flow path, the vessel further comprising means for circulating the extracted material into the inlet chamber.

[0055] The above-described apparatus provides the possibility of extracting the dried or semi-dried material from any given intermediate cell and recirculating the extracted material into the inlet chamber.

[0056] According to a further embodiment of the second aspect of the invention, the vessel in connection with the inlet chamber comprises injection means for injecting the extracted material into the inlet chamber.

[0057] In order to ensure that the extracted material is mixed with the injected material fast and efficiently, whereby the optimal heat transfer between the extracted material and the injected material is ensured, the inlet chamber, in connection with the bottom thereof, comprises injection means, such as a propeller or similar, which injects the extracted and recirculated material into the inlet chamber. The injection means may be connected with the source of superheated steam in the same way as the steam permeable bottom, and thus semi-dried material being extracted and transported to the injection means, the injection means preferable being arranged in an opening in the steam permeable bottom, will be blown up into the inlet chamber where it immediately mixes with the supplied wet material.

Fig. 1 shows a side sectional view of an apparatus for drying bulk particulate material.

Fig. 2 shows a cross sectional view of part of a drying apparatus.

Fig. 3 shows a perspective partial exploded view of a drying apparatus.

Fig. 3A shows a partial enhanced view of fig. 3.

Fig. 4 shows a cross sectional view of part of a drying apparatus.

Fig. 5 shows a perspective partial exploded view of a drying apparatus.

Fig. 6 shows a cross sectional view of part of a drying apparatus.

Fig. 6A shows a perspective partial view of a drying apparatus.

[0058] The present invention will now be described more fully hereinafter with reference to the accompanying drawings, in which exemplary embodiments of the invention are shown. The invention may, however, be embodied in different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. Like reference numerals refer to like elements throughout. Like elements will thus not be described in detail with respect to the description of each figure.

[0059] Fig. 1 shows a side sectional view of an apparatus 10 for drying bulk particulate material. The apparatus 10 comprises a vessel 12 having a lower cylindrical part 14, an intermediate conical part 16 and an upper cylindrical part 18.

[0060] The vessel 12 further comprises an inner cylindrical part 20 extending within the vessel 12 between the upper cylindrical part 18 and the lower cylindrical part 14. The inner cylindrical part 20 includes a heat exchanger (not shown) and defines a fluid path from the upper cylindrical part 18 to said lower cylindrical part 14, within the inner cylindrical part 20, and a fluid path from the lower cylindrical part 14 to the upper cylindrical part 18 outside the inner cylindrical part, as shown by the arrows.

[0061] The vessel 12 further comprises an inlet 22, which may comprise a screw conveyor for introducing moist/wet particulate material into the lower cylindrical part 14 of the vessel 12, as shown by the arrow 22', and an outlet 24, which may also comprise a screw conveyor for ejecting dry particulate material from the lower cylindrical part 14 of the vessel 12, as shown by the arrow 24'. The inlet 22 is located above and circumferentially displaced relative to the outlet 24. A motor 26 is located below the vessel 12 for driving an impeller 28, located in the lower cylindrical part 14 below the inner cylindrical part 20. The impeller 28 generates a flow of superheated steam going through a steam permeable bottom 30 located above the impeller 28. The steam permeable bottom 30, comprises a plurality of perforations for directing the superheated steam in a substantially vertical direction and/or a plurality of louvers (not shown) for directing the superheated steam towards the lower cylindrical inner wall.

[0062] A number of partitioning walls 32 are extending radially in the lower cylindrical part 14 dividing the space into a number of chambers 34, 36, 38. The chamber located at the inlet 22 is designated inlet chamber 36, and the chamber located at the outlet 24 is designated outlet chamber 38. Typically, the inlet chamber 36 and the outlet chamber 38 are located adjacent each other, however, the particulate material should not be able to move directly from the inlet chamber 36 to the outlet chamber 38 without passing the intermediate chambers 34. The moist/wet particulate material is received in the inlet chamber 36 on a fluid bed established by the flow of superheated steam above the steam permeable bottom 30. The outlet chamber 38 preferably has a non-permeable bottom, which allows the dried particulate material to be ejected via the outlet 24 as shown by the arrow 24'.

[0063] The upper cylindrical part 18 of the vessel 12 comprises guide blades 40 for generating a cyclone field in the upper cylindrical part 18. The guide blades 40 will establish a whirling movement of the flow of superheated steam and force any particles outwardly which have been lifted from the lower cylindrical part 14 through the intermediate conical part 16 into the upper cylindrical part 18. The superheated steam will be introduced into the inner cylindrical part 20 and be reheated by the heat exchanger assembly before returning to the impeller 28.

[0064] The apparatus 10 comprises valves 64 at the inlet 22 and outlet 24 for suppling and retracting the moist/wet material and the dried material to and from the pressurised vessel. The valves are preferably drum valves, which are known in the art.

[0065] Fig. 2 shows a cross sectional view of part of a drying apparatus 10, and fig. 3 shows a perspective partial exploded view of a drying apparatus 10.

[0066] The figures show a lower cylindrical part 14, corresponding to the one shown in fig. 1. The lower cylindrical part 14 comprises a number of partition walls 32 dividing the lower cylindrical part 14 into a number of intermediate chambers, 34, and inlet chamber 36 and an outlet chamber 38. It should be noted that though the embodiments shown in the figures comprise a specific number of intermediate chambers 34, that number may vary. The apparatus 10 may thus comprises a higher or lower number of intermediate cells than what is shown in the figures.

[0067] The apparatus comprises extraction means 46, in the form of an opening, allowing for part of the transported material to be extracted from the flow path between the inlet chamber 36 and the outlet chamber 38, and circulated into the inlet chamber 36.

[0068] The extracted material is transported from intermediate chambers 34 to the inlet chamber 36, at a level below the steam permeable bottom 30 (shown in fig 1) via extraction piping 52-58. The extraction piping 52-58 comprises an extraction main pipe 52' and a number of extraction pipe branches 54-58.

[0069] It must be noted that even though the figure (and figures 3-5) show three pipe branches 54-58, the apparatus in a preferred embodiment comprises only one of the pipe branches 54-58 connected to one specific intermediate chamber 34. The embodiment shown is thus an alternative embodiment comprising three pipe branches 54-58, where the extracted material can be extracted from either one of the three intermediate chambers 34 individually associated with the pipe branches 54-58.

[0070] The extraction piping 52-58 comprises circulating means 48 shown as screw conveyer(s) for conveying the extracted material from the intermediate chamber(s) 34 to the inlet chamber 36. Each screw conveyer may be regulated such that the amount of extracted material is regulated, depending on the need. A more moist/wet material received in the inlet chamber 36 may require a larger amount of recirculated semi-dried material in order to lower the average water content of the mixed material inside the inlet chamber.

[0071] The apparatus 10 further comprises injection means 50 for injecting the extracted and circulated semi-dried material from one or more of the intermediate chambers 34 into the first chamber 36, where the circulated material is mixed with the received moist/wet material. In order to ensure a fast and proper mixing of the recirculated semi-dried material and the received moist/wet material, the injection means injects the recirculated material into the bottom part of if inlet chamber 36.

[0072] The steam permeable bottom 30 of the inlet chamber 36 comprises an opening 50' in connection with the injection means 50, such that the recirculated material can be injected into the inlet chamber 36 via the opening.

[0073] The injection means 50 may thus be arranged as a propeller, which throws the recirculated semi-dried material into the inlet chamber, where it hereby rapidly mixes with the already present received moist/wet material. Such rapid mixing ensures that the average water content of the mixed material is reduced to below the water content of the received moist/wet material. Hereby, the risk of clogging the first chamber is minimised.

[0074] Fig. 3A shows a partial enhanced view of the circulation means 48 arranged as a screw conveyor and the injection means 50 arranged as a propeller, as disclosed above.

[0075] Fig. 4 shows a cross sectional view of part of a drying apparatus 10, and fig. 5 shows a perspective partial exploded view of a drying apparatus 10.

[0076] The figures show an alternative compared to the embodiment shown in figs. 2-3A. The construction is basically the same, but the arrangement of the extraction piping and injection means is different.

[0077] In the shown embodiment, the extraction piping 52 is connected to a further extraction piping 60 connected to the feeding mechanism arranged in connection with the inlet. The feeding mechanism includes a screw conveyor (shown in fig. 4), which conveys the received moist/wet particulate material from a valve 64, such as a drum valve, to the inlet 22 into the inlet chamber 36. Such embodiment provides a solution where the recirculated material is premixed with the moist/wet material in the screw conveyor before entering the inlet chamber 36.

[0078] Fig. 6 shows a cross sectional view of part of a drying apparatus 10 and fig. 6A shows a perspective partial view of a drying apparatus 10.

[0079] The figures show a second alternative of the previously described apparatus.

[0080] In the shown embodiment, the previously described extraction means 46, circulation means and extraction piping 52-60 are omitted, instead the apparatus comprises an alternative extraction piping 62 comprising circulation means (not shown), such as a screw conveyor, for conveying the extracted material. The alternative extraction piping 62 extends from an outlet piping connected to a valve 64, being an outlet valve, to the above-mentioned feeding mechanism arranged between the inlet 22 and a valve 64, being an inlet valve. This embodiment provides a solution which can easily be incorporated into an existing drying apparatus 10.

[0081] In the following is given a list of reference signs that are used in the detailed description of the invention and the drawings referred to in the detailed description of the invention.

10

Drying apparatus

12

Vessel

14

Lower cylindrical part

16

Intermediate conical part

18

Upper cylindrical part

20

Inner cylindrical part

22, 22'

Inlet

24, 24'

Outlet

26

Motor

28

Impeller

30

Steam permeable bottom

32

Partition walls

34

Intermediate chambers

36

Inlet chamber

38

Outlet chamber

40

Guide blades

42

First part

44

Second part

46

Extraction means

48

Circulating means

50

Injection means

50'

Injection opening

52-62

Extraction piping

64

Valve

Claims

1. A method for drying wet particulate material, such as residue from ethanol production or sugar beet pulp, where said wet particulate material is dried in an apparatus (10) having a vessel (12),

said vessel (12) being a pressure vessel capable of maintaining superheated steam at a pressure larger than the ambient pressure surrounding said vessel,

said vessel (12) having a flow path for transporting said wet particulate material under pressure, through said vessel (12), said particulate material being dried along said flow path by applied heat,

said vessel (12) comprising an inlet (22) arranged in a first part (42) of said vessel (12), for receiving said wet particulate materials and an outlet (24) arranged in a second part (44) of said vessel (12), for ejecting said dried particulate materials from said vessel (12), said flow path being arranged between said inlet (22) and said outlet (24),

said method comprising the following steps:

- supplying wet particulate material via said inlet (22) into said first part (42), said particulate material having an initial wt% of dry material,

- transporting said wet particulate material along said flow path towards said outlet (24),

- extracting part of said particulate material from said flow path, at an extraction position distanced from said inlet (22), said extracted material being semi-dried and less wet compared so said supplied wet particulate material, and circulating said extracted material to said first part (42),

- mixing said circulated extracted material with supplied wet particulate material within said first part (42), such that said wt% of dry material of said mixed particulate material is larger compared to said initial wt% of dry material.

2. A method according to claim 1, said applied heat being superheated steam.

3. A method according to claim 2, wherein at least 90% of said superheated steam are generated from vaporized fluid from said supplied material.

4. A method according to any of the previous claims, wherein said mixed material comprises at least 1/4 of extracted material and 3/4 of supplied wet particulate material, preferably at least 1/2 of extracted material and 1/2 of supplied wet particulate material, such as at least 2/3 of extracted material and 1/3 of supplied wet particulate material.

5. A method according to any of the previous claims, wherein said extracted material is semi-dried and has a wt% of dry material being 50-92%, preferably 50-85%.

6. A method according to any of the previous claims, wherein said extracted material is semi-dried and has a wt% of dry material corresponding to between 55-100% compared to the wt% of dry material at said outlet (24).

7. A method according to any of the previous claims, wherein said mixed material has at least 30 wt% (MDS) of dry material as a function of

without influence from the applied heat in said first part,
where:

E is extracted material kg/h,

EDS is wt% of dry material in the extracted material,

S is supplied material kg/h,

SDS is wt% of dry material in the supplied material,

M is mixed material Kg/h.

8. A method according to any of the previous claims, said extracted material being circulated under pressure, said pressure being larger than the ambient pressure surrounding said vessel (12).

9. A method according to claim 8, wherein said pressure within said vessel (12) is approximate 0,2-4 barg, preferably 2-4 barg.

10. A method according to any of the previous claims, wherein said vessel (12) comprises a number of partitioning walls (32) extending vertically within said vessel (12) and defining, in said vessel (12), an inlet chamber (36) in said first part (42), an outlet chamber (38) in said second part (44) and a number of intermediate chambers (34) located between said inlet chamber (36) and said outlet chamber (38), hereby arranging said flow path between said inlet and outlet chamber (36,38), said inlet chamber (36) comprising said inlet (22) for receiving said wet particulate material, said outlet chamber (38) comprising said outlet (24) for ejecting said dried particulate material, said inlet chamber (36) and said intermediate chambers (34) each comprising a steam permeable bottom (30), wherein at least one of said intermediate chambers (34) comprises extraction means (46) for extracting said part of said particulate material from said flow path, said vessel (12) further comprising circulating means (48) for circulating said extracted material into said inlet chamber (36).

11. A method according to claim 10, wherein said vessel (12) in connection with said inlet chamber (36) comprises injection means (50) for injecting said extracted material into said inlet chamber (36).

12. A method according to claim 10, wherein said extracted part of said particulate material is transported at a level below said steam permeable bottom (30).

13. A method according to any of the previous claims, wherein said extracted material is introduced into said first chamber (36) through said inlet (22).

14. A method according to any of the previous claims, wherein said extracted material is extracted upstream in relation to said outlet (24) and downstream in relation to said inlet (22).

15. An apparatus (10) comprising a vessel (12) for drying wet particulate material under a pressure being larger than the ambient pressure surrounding said vessel (12), said vessel (12) being a pressure vessel capable of maintaining superheated steam at a pressure larger than the ambient pressure surrounding said vessel (12),

said vessel (12) having a flow path for transporting said wet particulate material under pressure, through said vessel (12), such that said particulate material is dried along said flow path,

said vessel (12) comprising an inlet (22) in a first part (42) for receiving said wet particulate materials and an outlet (24) in a second part (44) for ejecting said dried particulate materials from said vessel (12), said flow path being arranged between said inlet (22) and said outlet (24),

said apparatus (10) comprising extraction means (46) for extracting part of said particulate material from said flow path, at a position distanced from said inlet (22) and circulating said extracted material to said first part (42).

16. An apparatus (10) according to claim 15, said vessel (12) comprising a number of partitioning walls (32) extending vertically within said vessel (12) and defining, in said vessel (12), an inlet chamber (36) in said first part (42), an outlet chamber (38) in said second part (44) and a number of intermediate chambers (34) located between said inlet chamber (36) and said outlet chamber (38), hereby arranging said flow path between said inlet and outlet chamber (36,38), said inlet chamber (36) comprising said inlet (22) for receiving said wet particulate material, said outlet chamber (38) comprising said outlet (24) for ejecting said dried particulate material, said inlet chamber (36) and said intermediate chambers (34) each comprising a steam permeable bottom (30), wherein at least one of said intermediate chambers (34) comprises said extraction means (46) for extracting said part of said particulate material from said flow path, said vessel (12) further comprising circulation means (48) for circulating said extracted material into said inlet chamber (36).

17. An apparatus (10) according to claim 16, wherein said vessel (12) in connection with said inlet chamber (36) comprises injection means (50) for injecting said extracted material into said inlet chamber (36).

Drawing