Fluidized bed dryers and methods for drying wet materials in fluidized bed dryers.

Abstract

The invention relates to a fluidized bed dryer (1) for drying wet material by drying air, the fluidized bed dryer (1) comprising two or more drying zones (2) arranged in series in a vertical direction between the drying air supply connector (11) and the discharge (12) inside the fluidized bed dryer (1), the consecutive drying zones (2) separated by a partition (3) by a hole (4) to create flow connections between consecutive drying zones (2), and an additional drying air supply connector (13) connected to each drying zone (2), the additional drying air supply connector (13) arranged to supply additional drying air to the drying zone (2). The invention also relates to a method for drying wet material in a fluidized bed dryer (1).

Description

[0001]A^ FLUIDIZED^ BED^ DRYER^ AND^ A^ METHOD^ FOR^ DRYING^ WET^ MATERIAL^ IN^ A^ FLUIDIZED^BED^DRYER FIELD OF THE INVENTION The present invention relates to a fluidized bed dryer, and moreparticularly to a fluidized bed dryer as defined in the preamble of the independent claim 1. The present invention also relates to a method for drying wet material in a fluidized bed dryer, and more particularly to a method as defined in the preamble of the independent claim 11. BACKGROUND OF THE INVENTION Different types of fluidized bed dryers are known in the art. Typical fluidized bed dryers comprise a drying chamber in which the material is floated so that it dries and then the dried material is removed from the drying chamber. In most cases, fluidized bed dryers are designed for specific material and specific needs, in which case the type of material that can be dried in a fluidized bed dryeris very limited. The material to be dried may require a long drying time or a lot ofspace to dry, which determines the characteristics required of a fluidized bed dryer. In this case, the large size of the fluidized bed dryer or its orientation vertically or horizontally can cause problems in the location. BRIEF DESCRIPTION OF THE INVENTION An object of the present invention is to provide a fluidized bed dryerand a method for drying wet material in a fluidized bed dryer which at least alleviates the problems of the prior art. The objects of the invention are achieved by a fluidized bed dryer and amethod for drying wet material in a fluidized bed dryer which are characterized bywhat is stated in the independent claims. The preferred embodiments of the invention are disclosed in the dependent claims. The invention is based on the idea of drying wet material, which can vary depending on the process, more effectively and for a shorter time than in a conventional fluidized bed dryer. The material can comprise fibre based material, biobased fibres, mineral material, sludge, biomass, or any other material that can be dried in a fluidized bed dryer. A fluidized bed dryer according to the invention for drying wet materialwith drying air comprises in the lower part of the fluidized bed dryer a wet material supply connection provided at a side wall of the fluidized bed dryer through whichwet material is fed to the fluidized bed dryer, and a drying air supply connectionthrough which drying air is fed to the fluidized bed dryer. The fluidized bed dryeralso comprises in the upper part of the fluidized bed dryer a discharge outletthrough which a mixture of dried material and drying air is discharged from thefluidized bed dryer. The drying air supply connection and the discharge outletdetermine a flow direction in the fluidized bed dryer from the drying air supplyconnection to the discharge outlet. The fluidized bed dryer further comprises twoor more drying zones arranged successively in vertical direction between the drying air supply connection and the discharge outlet inside the fluidized bed dryer, the successive drying zones are separated from each other by a wall with anopening to form a flow connection between successive drying zones, and anadditional drying air supply connection in connection with each drying zone, the additional drying air supply connection is arranged to feed additional drying air to the drying zone. In other words, the fluidized bed dryer according to the invention is avertical fluidized bed dryer having a top end and a bottom end such that thefluidized bed dryer extends between the top end and the bottom end. The fluidizedbed dryer receives the wet material to the lower part of the fluidized bed dryerthrough a connection provided at a side wall of the fluidized bed dryer. The drying air supply connection through which drying air is supplied to the fluidized beddryer is also provided to the lower part of the fluidized bed dryer. The drying airsupply connection may be provided to the side wall or to the bottom end of thefluidized bed dryer or to an inclined wall extending from the side wall to the bottomend if there is such. For the sake of clarity, the bottom end of the fluidized bed dryeris the end of the fluidized bed dryer that is opposite the top end of the verticallyextending fluidized bed dryer, which is the other end of the fluidized bed dryer,while the upper part of the fluidized bed dryer is a larger entity than just the topend, i.e., the end of the fluidized bed dryer, comprising at its maximum the part ofthe fluidized bed dryer extending from the middle of the fluidized bed dryerupwards. Similarly, the lower part of the fluidized bed dryer is at its maximum thepart of the fluidized bed dryer extending from the middle of the fluidized bed dryerdownwards. The wet material is arranged to float inside the fluidized bed dryer bymeans of the drying air supplied from the lower part of the fluidized bed dryer. Thewet material is floated in the fluidized bed dryer with the help of drying air supplied to the fluidized bed dryer and mechanical agitation if needed. The discharge of drying air from the fluidized bed dryer is through the discharge outlet arranged at the upper part of the fluidized bed dryer, and in a preferable embodiment of the fluidized bed dryer through the discharge outletarranged at the top end of it. Together with the drying air the dried material isremoved through the discharge outlet from the fluidized bed dryer. The drying air which is supplied to the fluidized bed dryer from the lower part of the fluidized beddryer is warm and dry, so that it will dry the wet material, whereas the drying airdischarged from the upper part of the fluidized bed dryer is moist, because it has bound moisture from the wet material after the material has dried. The flow direction of the drying air in the fluidized bed dryer is from the bottom end to the top end. The drying air supply connection and the discharge outlet determine a flow direction in the fluidized bed dryer from the drying airsupply connection to the discharge outlet. This means that the operating directionof the fluidized bed dryer is from the bottom end to the top end of the fluidized bed dryer. The fluidized bed dryer comprises two or more drying zones, which means that there is at least two drying zones. The drying zones are separated from each other by a wall and arranged vertically on top of each other. This means that, for example, in the case of only two drying zones, the fluidized bed dryer comprises two drying zones, which are separated from each other by the wall and which together form the drying zones of the fluidized bed dryer. The fluidized bed dryer may also comprise a floatation chamber in the lower part of the fluidized bed dryer into which the wet material and the drying air is supplied and in which the wet material starts to float. This floatation chamber may be a separate chamber which means that it is separated from the lowest drying zone with a wall or it may be part of the lowest drying zone. The same also applies to more than two drying zones. In order the drying air and the material to flow from the lower part of the fluidized bed dryer to the upper part of the fluidized bed dryer the wall between the successive drying zones comprises an opening through which the drying air and the material flows from the previous drying zone to the successive drying zone, i.e., from a lower drying zone to a successive upper drying zone. For each drying zone, the fluidized bed dryer has an additional dryingair supply connection, which supplies dry and warm additional drying air to thedrying zone. Dry and warm additional drying air promotes the drying of wetmaterial because the main drying air supplied through the drying air connection at the lower part of the fluidized bed dryer loses its energy, i.e., heat, in the fluidized bed dryer. According to the invention the opening in the wall separating successivedrying zones is provided with a flow tube forming a flow channel through which the mixture of material and drying air is arranged to flow from one drying zone to another successive drying zone. In other words, a flow tube is arranged in connection with the wall separating the successive drying zones such that the flow channel extending through the flow tube is in flow connection with the opening. Thereby the opening is provided with the flow tube extending toward the drying zone. The flow tube is connected to the wall. According to the invention the flow tube is arranged to extend from theopening to the previous drying zone in the flow direction. This means that the flowtube is arranged to extend from the opening to downstream side of the opening.This also means that in a drying zone the opening is provided in the bottom wall of the drying zone, the bottom wall being the wall that separates the drying zone from the previous successive drying zone, and which has the opening from where the mixture of material and drying air come from the previous drying zone, and in the same drying zone the flow tube is arranged to extend from the top wall of thedrying zone towards the drying zone, which the top wall is the wall that separatesthe drying zone from the next successive drying zone. An exception for this is the first drying zone in which the drying air and the material are supplied through separate connections and there is no bottom wall because there is no previous successive drying zone. According to the invention the flow tube is adjustable in its length toregulate a flow of the mixture of material and drying air through the flow tube fromone drying zone to another; or alternatively the flow tube is adjustable in itsdiameter to regulate a flow of the mixture of material and drying air through theflow tube from one drying zone to another; or alternatively the flow tube isadjustable in its length and in its diameter, to regulate a flow of the mixture ofmaterial and drying air through the flow tube from one drying zone to another. According to the invention the wall separating the successive drying zones comprises a truncated cone which opens upwards in the flow direction directing at least part of the mixture of material and drying air towards the side wall of the fluidized bed dryer. In other words, the wall separating the successive drying zones comprises a truncated cone which can be only part of the wall or the wall can be completely in the form of a truncated cone. A truncated cone comprises twocircular bases and a side face which means that when the truncated cone forms thewall separating the successive drying zones, the side face forms the wall separatingthe successive drying zones and the opening of the wall is the smaller one of thecircular bases. According to the invention the additional drying air supply connection is arranged in the side wall of the fluidized bed dryer to supply additional air tangentially to the drying zone. This means that the additional drying air supply connection is arrangedsuch that the additional drying air flow enters the drying zone tangentially. Theadditional drying air connection is arranged at the side wall of the fluidized bed dryer such that the connection is tangentially arranged relative to the drying zone and the additional drying air entering the drying zone will flow along the inner surface of the fluidized bed dryer, i.e., along the side wall of the drying zone and provides a vortex flow in the drying zone. According to the invention the additional drying air supply connection is arranged at an upper part of the drying zone. In other words, the additional drying air supply connection is arranged above the middle of the drying zone. This means that when the drying zone isdivided in half horizontally so that both sides are the same size, the additionaldrying air supply connection is arranged on the side wall in the upper half of the drying zone. The additional drying air supply connection is preferably arranged sothat it is vertically on the same level as the flow tube meaning that the additionaldrying air supply connection supplies air to flow along the inner surface of the side wall facing toward the flow tube, to flow to the space between the inner surface of the side wall and the flow tube. According to the invention each additional drying air supply connectionis adapted to regulate the amount of the additional drying air supplied to the dryingzone. This means that the additional drying air supply connection isadjustable, for example, with control dampers so that the additional air flowsupplied through the additional drying air supply connection can be adjusted. The additional drying air supply connection can be adjusted online.According to the invention each drying zone further comprises a flowbaffle, which is arranged in the drying zone at a vertical distance from the opening leading to the next drying zone in the flow direction. In other words, the drying zone comprises a flow baffle which directs the flow of the mixture of material and drying air coming from the previous successive drying zone towards the side wall of the fluidized bed drier and prevents the flow from entering straight to the flow tube which leads to the next successive drying zone. This increases the time spent in the drying zone for the material to be dried. The flow baffle is preferably larger than the size of an inlet of the flow tube. The flow tube comprises an inlet and an outlet and the flow channel extending between the inlet and the outlet. The inlet is arranged at the drying zone and the outlet is in connection with the opening at the wall. The flow baffle can be arranged in the drying zone at a vertical distance for example 10-50 cm from theinlet of the flow tube.According to the invention the flow baffle is a plate baffle extending inthe drying zone transverse to the vertical direction. Alternatively, the flow baffle isa conical baffle having an apex toward the opening leading to the next drying zonein the flow direction. Alternatively, the flow baffle is a hemispherical baffle havingan apex away from the opening leading to the next drying zone in the flow direction. In other words, the flow baffle has a shape that directs the mixture of material and drying air flowing from the previous drying zone to the current drying zone such that it does not straight forwardly flow to the next subsequent drying zone but together with the additional drying air coming from the additional drying air connection flows in the drying zone so that the material is dried along with thedrying air. The shape of the flow baffle arranged to the drying zone may vary basedon the material and / or its degree of wetness. Amethod for drying wet material in a fluidized bed dryer according tothe invention comprises steps of a) supplying wet material and drying air into thefluidized bed dryer through separate connections in a lower part of the fluidizedbed dryer and drying the wet material with the drying air, b) drying the wetmaterial further by supplying additional drying air into a drying zone arranged in the lower part of the fluidized bed dryer above the connections supplying wetmaterial and drying air, to increase dry and warm additional drying air to thedrying zone and to create a mixture of material and drying air, c) directing themixture of material and drying air into a subsequent drying zone in a vertical direction of the fluidized bed dryer through an opening provided at a wallseparating successive drying zones in the fluidized bed dryer, and d) dischargingmixture of dried material and drying air from the fluidized bed dryer through a discharge outlet provided at an upper part of the fluidized bed dryer. In other words, in the method, warm and dry drying air is fed into thelower part of the fluidized bed dryer in such a way that the wet material fed into the lower part of the fluidized bed dryer begins to float with the help of the dryingair and dries due to the warm and dry drying air. When the material dries, moistureis transferred to the drying air and the drying air loses heat. Because of this, thereis a drying zone into which additional drying air is supplied to further dry the wetmaterial. The additional drying air is warm and dry and it mixes with the drying aircoming from the lower part which has already lost heat in the drying process, sowith the help of the additional drying air, the material can be further dried in the drying zone. Eventually the mixture of material and drying air is directed to the next successive drying zone in vertical direction of the fluidized bed dryer. The successive drying zones have a flow connection through an opening in a wall separating the successive drying zones from each other. The drying process is continued in this successive drying zone similarly as in the previous drying zone and finally the dried material and the drying air, which is now moist, is discharged through the discharge outlet out from the fluidized bed dryer. According to the invention the method further comprises a step ofsupplying additional drying air into the subsequent drying zone. In other words, the additional drying air is supplied to each successive drying zone to increase warm and dry drying air so that the material is more effectively dried in the drying zone before moving to the next successive drying zone or eventually out from the fluidized bed dryer. According to the invention the step c) further comprises directing themixture of material and drying air to a flow tube having a flow channel whichextends from the opening to the present drying zone and directing the mixturethrough the flow channel to the subsequent drying zone.In other words, in the method the mixture of material and drying air is directed through a flow tube to the next successive drying zone. The length and / ordiameter of the flow tube can be changed, which allows the flow rate of the mixturefrom one drying zone to another to be changed depending for example of thematerial that is dried.According to the invention the method further comprises a step ofcontrolling the mixture of material and drying air in the drying zone by preventing its flow directly to the opening leading to the successive drying zone with a flow baffle placed in the drying zone, which is arranged at a vertical distance from theopening leading to the next drying zone in the flow direction.According to the invention the method further comprises supplyingadditional drying air by introducing it to enter tangentially into the drying zone forcreating a vortex flow for the mixture of wet material and drying air in the dryingzone. By directing the addition drying air tangentially to the drying area, themixture of material and drying air rotates in the drying area, which promotes drying of the material. In other words, the tangential additional drying air brings rotational movement to the floating material in the drying zone. An advantage of the invention is that the wet material is moreeffectively dried in the fluidized bed dryer according to the invention, where thetime spent in the fluidized bed dryer is reduced, because each drying zone dries the material faster with the help of an effective supply of new warm and dry additionalair and the movement of the material enhances the drying.BRIEF DESCRIPTION OF THE DRAWINGS The invention is described in detail by means of specific embodimentswith reference to the enclosed drawings, in whichFigure 1 shows a fluidized bed dryer according to the invention; Figure 2 shows another fluidized bed dryer according to the invention; Figure 3 shows another fluidized bed dryer according to the invention; and Figure 4 shows another fluidized bed dryer according to the inventionas part of a process. DETAILED DESCRIPTION OF THE INVENTION Figure 1 shows a fluidized bed dryer 1 according to the invention inwhich the fluidized bed dryer 1 comprises a top end 20 and a bottom end 30 such that the fluidized bed dryer 1 extends between the top end 20 and the bottom end30. The fluidized bed dryer 1 also comprises a side wall 14 that surrounds a dryingchamber inside the fluidized bed dryer 1. According to the invention the fluidizedbed dryer 1 comprises two or more successive drying zones 2. The drying zones 2 form the drying chamber, therefore the drying chamber has no reference number because the drying zones 2 form the drying chamber. The embodiment of the fluidized bed dryer 1 according to the invention shown in figure 1 comprises twosuccessive drying zones 2 that are arranged vertically on top of each other. Thedrying air is supplied to the fluidized bed dryer 1 from the lower part of the fluidized bed dryer 1 and in this embodiment of the invention through a drying air supply connection 11 arranged at the side wall 14 of the fluidized bed dryer 1. The drying air is supplied to the lower part of the fluidized bed dryer 1 and preferably near the bottom end 30 of the fluidized bed dryer 1 such that when the wet materialis supplied through the wet material supply connection 10 provided at a side wall14of the fluidized bed dryer 1 at the lower part of the fluidized bed dryer 1, the drying air gets the wet material to float in the fluidized bed dryer 1. Thereby the drying air is preferably supplied to the fluidized bed dryer 1 from below the supply of the wet material. The lowest drying zone 2 may be separated but not necessarily from that part of the fluidized bed dryer 1 into which the wet material and the drying air is supplied, which then forms a floatation chamber which is the lowest part of the fluidized bed dryer and where the floatation of the wet material begins.For the sake of clarity, the floatation chamber is not presented in these figuresbecause the invention is about the drying zones. The drying air supplied through the drying air supply connection 11 and the wet material supplied through the wet material supply connection 10 form a mixture of material and drying air. The mixture of material and drying air move in the first drying zone 2 which is the at the lower part of the fluidized bed dryer 1 whereupon the warm and dry drying air supplied through the drying air supplyconnection 11 dries the wet material and at the same time loses its heat. Additionaldrying air that is warm and dry is supplied to the upper part of the same drying zone 2 through an additional drying air supply connection 13. The additionaldrying air is supplied in such a way that it enters the drying zone 2 as a tangentialadditional air flow and mixes with the mixture of material and drying air comingfrom the lower part of the drying zone 2. The tangential additional air flow causesthe mixture to swirl in the drying zone 2 and the material in the mixture is furtherdried with new warm and dry additional air. The drying zone 2 is provided with aflow baffle 5 which prevents the mixture of material and drying air to escape straight from the drying zone 2 to the next successive drying zone 2, but instead maintains the mixture longer in the current drying zone 2 by directing the mixture toward the side wall 14. In the example shown in figure 1 the flow baffle 5 in the lower drying zone 2 is a plate baffle whereas in the upper drying zone 2 the flow baffle 5 is a conical baffle. However, these are exemplary figures and in a normal situation the flow baffles 2 are typically in each drying zone 2 the same. Finally, the mixture of material and drying air flows from the currentdrying zone 2 to the next successive drying zone 2 through an opening 4 arrangedat a wall 3 separating the successive drying zones 2. In the example shown in figure 1 the wall 3 is provided with a flow tube 6 forming a flow channel 7 inside the flow tube 6. The flow channel 7 and the opening 4 are in a flow communication together such that the mixture flowing through the flow channel 7 flows also through theopening 4 to the next successive drying zone 2. The flow tube 6 is connected to thewall 3 such that the opening 4 and the flow channel 7 are preferably concentric. The flow tube 6 may be connected to the wall 3 such that the flow tube 6 is provided within the opening 4 and connected to the circumference of the opening 4. Alternatively, the flow tube 6 may be connected to the wall 3 on the side facing toward the lower drying zone 2. The flow tube 6 extends from the wall 3 in the direction of the lower drying zone 2. The mixture of material and drying air floats in the next successive drying zone 2 similarly as in the previous drying zone 2 and additional drying air is also provided similarly to the drying zone 2. The additional drying air connection 13 is preferably arranged in the side wall 14 of the fluidized bed dryer 2 at such a height of the fluidized bed dryer 1 that the additional air coming through theconnection 13 is fed above the vertical half of each drying zone 2 and preferably tothe area where the flow tube 6 extends. So, in other words, the additional dryingair is preferably supplied between the side wall 14 and the flow tube 6. The supply of the additional drying air may be controlled online or otherwise for example with control dampers 40 which can regulate the amount of additional drying air supplied to the drying zone 2. The mixture of dry material and drying air is finally discharge througha discharge outlet 12 at the top end 20 of the fluidized bed dryer 1. The exampleshown in figure 1 comprises only two drying zones 2, but the invention is not limited to only two drying zones 2, there may be two or more drying zones 2 depending on the process which the fluidized bed dryer 1 is used. Figure 2 shows another fluidized bed dryer 1 according to the invention, in which the features of the fluidized bed dryer 1 are the same as in theembodiment shown in figure 1 and therefore not repeated here again. However,there are two features that are different from the embodiment shown in figure 1.The first difference is that the drying air supply connection 11 supplying the main drying air to the fluidized bed dryer 1 is arranged at the bottom end 30 of the fluidized bed dryer 1. Another difference is the flow baffle 5, which in the example shown in figure 2 is a plate baffle in the lower drying zone 2 whereas in the upper drying zone 2 the flow baffle 5 is a hemispherical baffle having an apex facing away from the opening leading to the next drying zone in the flow direction. However, these are exemplary figures and in a normal situation the flow baffles 2 are typically in each drying zone 2 the same. Figure 3 shows another fluidized bed dryer 1 according to the inventionwhich comprises three drying zones 2 vertically arranged on top of each other. Thedrying air supply connection 11 is provided at the bottom end 30 of the fluidized bed dryer 1 and the wet material supply connection 10 is provided at the side wall 14 of the fluidized bed dryer 1 in the lower part of the fluidized bed dryer 1. The additional drying air supply connections 13 are arranged similarly as in the examples shown in previous figures. The wall 3 separating the drying zones 2 from each other is in the form of a truncated cone which opens upwards in the flow direction of the mixture of material and drying air. The opening 4 is provided with the flow tube 6 extending downwards from the truncated cone-shaped wall 3towards the previous drying zone 2. The truncated cone-shaped wall 3 directs atleast part of the mixture of material and drying air flowing along the flow channel7 of the flow tube 6 towards the side wall 14 of the fluidized bed dryer 1. In otherwords, the mixture of material and drying air is first moving in the lower part of the drying zone 2 and the flow baffle 5 directs the mixture towards side wall 14 where the additional drying air mixes to the mixture and the material is further dried. Therefrom the mixture flows to the flow tube 6 and through the flow channel 7 and the opening 4 to the next successive drying zone 2. The truncated cone- shaped wall 3 directs the flow of mixture toward the side wall 14 and the drying of the material continues and the additional drying air mixes to the mixture. In the last drying zone 2 in the upper part of the fluidized bed dryer 1 the mixture is discharged out from the fluidized bed dryer through the discharge connection 12 at the top end 20 of the fluidized bed dryer 1. Figure 4 shows another fluidized bed dryer 1 according to the inventionas part of a process. The embodiment of the fluidized bed dryer 1 shown in figure4 comprises in the lower part of the fluidized bed dryer 1 a wet material supplyconnection 10 provided at a side wall 14 of the fluidized bed dryer 1 through whichwet material is fed to the fluidized bed dryer 1, and a drying air supply connection11 through which drying air is fed to the fluidized bed dryer 1. In this embodiment of the invention the drying air supply connection 11 is arranged at the bottom end 30 of the fluidized bed dryer 1. The fluidized bed dryer 1 comprises in the upper part of the fluidized bed dryer 1 and specifically at the top end 20 of the fluidizedbed dryer 1 a discharge outlet 12 through which a mixture of dried material anddrying air is discharged from the fluidized bed dryer 1. The drying air supply connection 11 and the discharge outlet 12 determine a flow direction in the fluidized bed dryer 1 from the drying air supply connection 11 to the dischargeoutlet 12, this means that the flow direction is from down to up. The fluidized beddryer 1 comprises in the embodiment of figure 4 two drying zones 2 arrangedsuccessively in vertical direction between the drying air supply connection 11 and the discharge outlet 12 inside the fluidized bed dryer 1. The successive dryingzones 2 are separated from each other by a wall 3 with an opening 4 to form a flowconnection between successive drying zones 2. The fluidized bed dryer 1 furthercomprises an additional drying air supply connection 13 in connection with each drying zone 2, the additional drying air supply connection 13 is arranged to feed additional drying air to the drying zone 2. The mixture of material and drying air moves through the fluidized bed dryer 1 from one drying zone 2 to another and when the material is dry, the mixture is finally discharged through the discharge outlet 12 to the next process phases. The invention has been described above with reference to the examples shown in the figures. However, the invention is in no way restricted to the aboveexamples but may vary within the scope of the claims.

Claims

CLAIMS 1. A fluidized bed dryer (1) for drying wet material with drying air, thefluidized bed dryer (1) comprises in the lower part of the fluidized bed dryer (1) awet material supply connection (10) provided at a side wall (14) of the fluidizedbed dryer (1) through which wet material is fed to the fluidized bed dryer (1), anda drying air supply connection (11) through which drying air is fed to the fluidizedbed dryer (1), and the fluidized bed dryer (1) comprises in the upper part of the fluidized bed dryer (1) a discharge outlet (12) through which a mixture of dried material and drying air is discharged from the fluidized bed dryer (1), the drying air supply connection (11) and the discharge outlet (12) determine a flow direction in the fluidized bed dryer (1) from the drying air supplyconnection (11) to the discharge outlet (12), c h a r a c t e r i z e d in that thefluidized bed dryer (1) further comprises: two or more drying zones (2) arranged successively in vertical directionbetween the drying air supply connection (11) and the discharge outlet (12) insidethe fluidized bed dryer (1), the successive drying zones (2) are separated from eachother by a wall (3) with an opening (4) to form a flow connection betweensuccessive drying zones (2), andan additional drying air supply connection (13) in connection with each drying zone (2), the additional drying air supply connection (13) is arranged tofeed additional drying air to the drying zone (2).

2. A fluidized bed dryer (1) according to claim 1, c h a r a c t e r i z e din that the opening (4) in the wall (3) separating successive drying zones (2) isprovided with a flow tube (6) forming a flow channel (7) through which themixture of material and drying air is arranged to flow from one drying zone (2) toanother successive drying zone (2).

3. A fluidized bed dryer (1) according to claim 2, c h a r a c t e r i z e din that the flow tube (6) is arranged to extend from the opening (4) to the previousdrying zone (2) in the flow direction.

4. A fluidized bed dryer (1) according to claim 2 or 3,c h a r a c t e r i z e d in thatthe flow tube (6) is adjustable in its length; orthe flow tube (6) is adjustable in its diameter; or the flow tube (6) is adjustable in its length and in its diameter, to regulate a flow of the mixture of material and drying air through theflow tube (6) from one drying zone (2) to another.

5. A fluidized bed dryer (1) according to any preceding claim,c h a r a c t e r i z e d in that the wall (3) separating the successive drying zones(2) comprises a truncated cone which opens upwards in the flow directiondirecting at least part of the mixture of material and drying air towards the sidewall (14) of the fluidized bed dryer (1).

6. A fluidized bed dryer (1) according to any preceding claim,c h a r a c t e r i z e d in that the additional drying air supply connection (13) isarranged in the side wall (14) of the fluidized bed dryer (1) to supply additional airtangentially to the drying zone (2).

7. A fluidized bed dryer (1) according to claim 6, c h a r a c t e r i z e din that the additional drying air supply connection (13) is arranged at an upper partof the drying zone (2).

8. A fluidized bed dryer (1) according to any preceding claim,c h a r a c t e r i z e d in that each additional drying air supply connection (13) isadapted to regulate the amount of the additional drying air supplied to the dryingzone (2).

9. A fluidized bed dryer (1) according to any preceding claim,c h a r a c t e r i z e d in that each drying zone (2) further comprises a flow baffle(5), which is arranged in the drying zone (2) at a vertical distance from the opening (4) leading to the next drying zone (2) in the flow direction.

10. A fluidized bed dryer (1) according to claim 9,c h a r a c t e r i z e d in that the flow baffle (5) isa plate baffle extending in the drying zone (2) transverse to the vertical direction; or aconical baffle having an apex toward the opening (4) leading to thenext drying zone (2) in the flow direction; ora hemispherical baffle having an apex away from the opening (4)leading to the next drying zone (2) in the flow direction.

11. A method for drying wet material in a fluidized bed dryer (1),c h a r a c t e r i z e d in that the method comprises steps of:a) supplying wet material and drying air into the fluidized bed dryer (1)through separate connections (10, 11) in a lower part of the fluidized bed dryer (1)and drying the wet material with the drying air, b) drying the wet material further by supplying additional drying air into a drying zone (2) arranged in the lower part of the fluidized bed dryer (1) above the connections (10, 11) supplying wet material and drying air, to increasedry and warm additional drying air to the drying zone (2) and to create a mixtureof material and drying air, c) directing the mixture of material and drying air into a subsequentdrying zone (2) in a vertical direction of the fluidized bed dryer (1) through an opening (4) provided at a wall (4) separating successive drying zones (2) in the fluidized bed dryer (1), and d) discharging mixture of dried material and drying air from thefluidized bed dryer (1) through a discharge outlet (12) provided at an upper partof the fluidized bed dryer (1).

12. Method according to claim 11, c h a r a c t e r i z e d in that themethod further comprises a step of: supplying additional drying air into the subsequent drying zone (2).

13. Method according to claim 11 or 12, c h a r a c t e r i z e d in thatthe step c) further comprises directing the mixture of material and drying air to a flow tube (6) havinga flow channel (7) which extends from the opening (4) to the present drying zone(2) and directing the mixture through the flow channel (7) to the subsequentdrying zone (2).

14. Method according to any of claims 11 - 13, c h a r a c t e r i z e d inthat the method further comprises a step of:controlling the mixture of material and drying air in the drying zone (2)by preventing its flow directly to the opening (4) leading to the successive dryingzone (2) with a flow baffle (5) placed in the drying zone (2), which is arranged at avertical distance from the opening (4) leading to the next drying zone (2) in theflow direction.

15. Method according to claim 11-14, c h a r a c t e r i z e d in that themethod further comprisessupplying additional drying air by introducing it to enter tangentiallyinto the drying zone (2) for creating a vortex flow for the mixture of wet materialand drying air in the drying zone (2).

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