METHOD AND APPARATUS FOR THE REMOVAL OF LIQUID FROM PARTICULATE MATERIAL

Abstract: Method and apparatus for the removal of liquid from particulate material by evaporation through the supply of heat, said heat being transferred substantially by superheated vapours or steam of the liquids existing in the particulate material, and where said method is executed in a substantially closed system. The particulate material is supplied continuously to a process chamber which is configured as an annular or partly annular chamber (1) which lies in a substantially horizontal manner, where the superheated vapours are introduced from below and up through openings (11) in a bottom (10) in the annular chamber, so that the particulate material is brought into movement by the superheated vapours, and such that a transport of the particulate material takes place through the annular chamber (1).

Description: 1 Method and Apparatus for the Removal of Liquid from Particulate Material The invention concerns a method for the removal of liquid from particulate material by evaporation through the supply of heat transferred mainly by superheated vapours or steam of the liquids existing in the particulate material, said method taking place in a substantially closed system. The invention also concerns an apparatus for the execution of such a method, said apparatus consisting of a substantially closed container which has means for the introduction of the particulate material from which liquid is to be removed, means for the removal of dried particulate material, means for the circulation of superheated vapours in the container, means for the supply of thermal energy to these vapours and means for the separation of dust particles from the vapours. The particulate material can contain particles which can be uniform in size as well as particles which in size can differ considerably from each other. The material can contain several different volatile and liquefied components which are desired to be removed, which is effected in an atmosphere of superheated vapours of the same volatile liquids. If the liquid which is to be removed is water, the process involved is a drying process where the drying takes place in a superheated water vapour. It will be understood, however, that where drying processes are referred to in the following, these could equally well involve similar processes where liquids other than water are removed from the particulate material. A method and an apparatus of the kind mentioned in the introduction are known, for example from EP Patent Application no. 82 850018.1 (publication no. EP 0.058.651 A1 ). With this known technique, the drying process is effected by the particles to be dried flowing through series-con- 2 nected vertical pipes or heat exchangers while suspended in the superheated water vapour. This method gives a uniform retention time which is relatively short, since in practice it is possible to build sufficiently high and sufficiently many vertical pipes and heat exchangers. For example, when the flow rate is 20 m/sec, a retention time of only a few minutes can be achieved with the use of 30 vertical processing zones, each of which is 40m high. This means that the particles must be of a very uniform particle size and have a very short drying time, which is why this method is suitable only for small, uniform particles, A method and an apparatus are also known from EP 0.153.704, which comprises a series of vertical, rather long processing zones, up through which superheated steam is supplied. Above the processing zones there is a common zone to which particles with reduced moisture content are transferred, in that from here the particles are conveyed further to the removal zone or removal zones. At the lower ends of the processing zones, at least some of the particles can be led through connection channels from one processing zone to the next. With this known technique, the configuration of the long, vertical processing zone means that a considerable part of the medium-sized particles receive a retention time which is too long. Consequently, they are dried to an undesirably high drystuff content which lowers the product quality, since where many products are concerned the re-absorption of water is hereby reduced. Moreover, the high construction involves relatively high building and installation costs. Finally, by the division of the processing zones there is a relatively great risk that wet, particulate material will block the first zones of the apparatus, partly by adhesion of the product and partly by steam condensing on the product, hereby making it so much heavier that it can no longer be held in movement by the flow of steam. 3 The object of the invention is to provide a method and an apparatus which avoids the above-mentioned disadvantages in connection with the use of several processing zones, and in that an optimum processing time is achieved for particles of all sizes in the particulate material. This is achieved with a method of the kind disclosed in the preamble, and which is executed in a manner such as that characterized in claim 1 , and with an apparatus of the kind described in the preamble which is configured in a manner such as that characterized in claim 4. In that use is made only of horizontal chambers, a suitably low configuration of the container is achieved for the execution of the method, and the apparatus is also of a suitably low construction height. With the steam flow and the configuration of the bottom in the annular chamber as disclosed, it is ensured that a circulating or rotating movement is achieved in the substantially vertical plane of the particulate material, so that all parts of the product are held in motion and such that a tight contact is achieved between the product and the superheated vapours. Expedient embodiments for the method according to the invention are disclosed in the related claims 2 and 3, and expedient embodiments of the apparatus according to the invention are disclosed in the related claims 5 - 10. The invention will now be described in more detail with reference to the drawing, where fig. 1 shows a vertical section of the bottom part for an apparatus according to the invention for the removal of liquids from par- ticulate material, taken along the line l-l in fig. 2, 4 fig. 2 shows a vertical section of the bottom part shown in fig. 1 , taken along the line ll-ll in fig. 1 , fig. 3 shows a vertical section of a conical transition piece for an apparatus according to the invention, fig. 4 shows a vertical section of the transition piece shown in fig. 3, taken along the long IV-IV in fig. 3, fig. 5 shows a vertical section of the upper part of an apparatus according to the invention, taken along the line V-V in fig. 6, fig. 6 shows a horizontal section of the part shown in fig. 5, taken along the line VI-VI in fig. 5, and fig. 7 shows a vertical section of a discharge opening with associated ejector, taken along the line VII-VII in fig. 6. The apparatus according to the invention consists substantially of three parts which are placed on top of one another, i.e. a bottom part 9 as shown in figs. 1 and 2, a conical transition piece as shown in figs. 3 and 4 and an upper part 20 which is shown in figs. 5 and 6. As will be seen in figs. 1 and 2, the bottom part 9 consists of a substantially cylindrical container which has an outer cylindrical surface 3 as outer wall. Inside the bottom part there is a low, annular or partly annular chamber 1 which is open at the top and which is limited at the sides partly by the outer cylindrical surface 3 and partly an inner cylindrical surface 2. At the bottom, the annular chamber 1 is limited by a double-curved bottom 10. This dou- ble-curved bottom can have an oval-shaped cross-section or be semicircular such as shown in fig. 1 , but can also have a cross-section which deviates from an oval or circular shape. The deepest part of the bottom 10 lies in the centremost half-part, and the sides curve upwards towards the inner and outer edges of the chamber, i.e. towards the inner cylindrical surface 2 and the outer cylindrical surface 3. For reasons of production, the 5 bottom can consist of single curves or plane plate pieces which are assembled so that they approximate the round form. Moreover, the double-curved bottom 10 is perforated in that it is provided with a series of openings 11 , these opening being described in more detail later. The bottom part 9 of the apparatus also has a supply pipe 5 for the particulate material which is to be dried, and a discharge pipe 6 for the material which has been dried. The inner cylindrical surface 2 forms a tubular middle chamber 4 which, as shown by the stippled lines, extends up through the remaining parts of the apparatus and which downwardly opens out in a chamber under the annular chamber 1. Finally, plates 13 are provided in the annular chamber, suspended as illustrated in figs. 1 and 2. These plates, the function of which will be described later, can extend from both the inner cylindrical surface 2 (such as shown) and from the outer cylindrical surface 3 (not shown in figs. 1 and 2), in that use can be made of one of these forms of positioning alone or a combination of both forms. The suspended plates 13 can be bent forwards or bent along a line 14 as shown. The function of the bottom part 9 of the apparatus will now be described in more detail. The particulate material to be dried is supplied continuously to the annular chamber 1 through the supply pipe 5 by means of commonly- known but not shown feeding means. At the same time, superheated steam is introduced from above as shown by the arrow 8 and down through the tubular middle chamber 4 to the space under the annular chamber 1 , from where the superheated steam flows up into the annular chamber 1 through the openings in the double-curved bottom 10. 6 The openings 11 in the bottom 10 consist of a combination of openings partly comprising simple holes through which the steam flows at right-angles to the bottom plate, and partly openings which give the steam an influx direction which forms an angle between 0° and 90° with the plate. This an- gle will preferably lie between 0° and 80°, and in practice the angle will as a rule be limited to an interval between 0° and 30°. Moreover, in terms of percentage, the perforated area in that part of the plate which is closest to the outer periphery is greater than in that part of the plate which is closest to the inner periphery. Together with the influx direction of the steam, this will result in a rotating movement of the particulate product in the substantially vertical plane, such as shown by the arrows 12 in fig. 1 , hereby ensuring the movement of particles of all sizes in the material flow. Moreover, the rotational movement of the particles will also support, e.g. a coating process or an introduction of liquid which is desired to be evaporated to- gether with the particles. The amount of angle on the angled openings 11 in the bottom 10 can be determined so that the angle depends on where the relevant opening 11 is placed, partly in the radial direction so that a suitable rotating movement is ensured, and partly in the peripheral direction to ensure a movement of the particles around inside the annular chamber 1 from the supply pipe 5 to the discharge pipe 6. The direction in which the superheated steam is blown in can thus be used to increase or reduce the transport forwards in the annular chamber. In addition, the suspended plates 13 can be used to control the transport. These plates will normally not be radial, but will be arranged to extend in such a direction that the transport forwards in the annular chamber 1 takes place in a suitably fast manner. Moreover, as mentioned earlier these plates can be bent forwards or bent along a line 14 as shown with the ob- 7 ject of ensuring the necessary transport speed of the particulate product. Finally, the plates 13 can as mentioned extend from the inner cylindrical surface 2 and/or the outer cylindrical surface 3, in that by a combination of these modes of suspension a kind of labyrinth effect is achieved between the plates. The energy necessary for evaporation of the liquids from the particles in the flow of material is derived partly from the supply of superheated steam, but a part of it can stem from the suspended plates 13 and the outer walls of the apparatus, which can be heat surfaces. These plates 13 can, for example, be configured of welded-together plates which form a cavity between them to which steam is led at a higher pressure than that which prevails in the annular chamber. When the particulate product is transported around inside the annular chamber 1 , it will finally reach a separator wall 7 which, in the immediate vicinity of the discharge pipe 6, will stop the forwards movement of the product flow in the annular chamber and lead the product out through the discharge pipe 6, from which by commonly-known means not shown the product can be transported further. As shown in fig. 2, the supply opening 5 is not placed in the very first part of the annular chamber 1 , but in such a manner that there is a certain distance between the separator wall 7 and the supply opening 5. It is hereby achieved that the moist, particulate material which is supplied is immediately mixed with partly dried material from the foremost part of the annular chamber, so that the risk of coatings and adherences with the moist material newly introduced is considerably reduced. 8 As is commonly used in connection with drying chambers of the fluid-bed type, over the fluid-bed itself, i.e. in this case the annular chamber 1 , there is a further chamber with a greater horizontal cross-sectional area. The transition to this area is a conical transition piece 15 which is configured such as shown in figs. 3 and 4, where with stippled lines it is also shown how the conical transition piece is connected with the remaining two parts of the apparatus. As will be seen, the outer cylindrical surface 3 extends from the bottom part 9 of the apparatus over into a conical outer wall 16 for the conical transition piece 15, and the inner cylindrical surface 2 continues up from the bottom part through the conical transition piece 15, so that the tubular middle chamber 4 is also to be found again here. The superheated steam which has flowed up through the annular chamber 1 , where it has imparted both heat and a rotating movement to the particulate material, will flow further up through the conical transition piece 15 between the inner cylindrical surface 2 and the conical outer wall 16, in that the steam will contain particles which are carried forward by the steam. The speed of the upwardly-flowing steam is so great that a considerable part of the particles will be conveyed up into this piece where these particles will be dried. The greater part of the particles driven by the steam will be separated in the conical transition piece 15, in that here they are separated by a method which has characteristics in common with laminar-sedimentation. In the conical transition piece 15, between the inner cylindrical surface 2 and the conical outer wall 16, a number of plates 17 are provided which radiate from the inner cylindrical surface 2 out towards the conical outer wall 16. These plates 17, of which only a few are shown in fig. 4, do not necessarily radiate in a radial manner from the inner cylindrical surface 2. The number of plates 17 which are provided in the conical transition piece 15 is such that the distance between the plates will preferably be between 200 mm and 500 mm. In order to achieve a distance which lies within these limits, pieces of such plates, e.g. half-plates, can be inserted furthest from the centre of the apparatus. The plates 17 are arranged so that they slope forward in the transport direction, and can possibly have one or more bend lines 18 as shown. The plates 17 do not reach out to the conical outer wall 16. However, there can be places, preferably at the top, where the plates have extensions 19 and reach out to and are supported by the conical outer wall 16. Moreover, the plates 17 can be provided with ribs (not shown) in order to stiffen the relatively large plates. When configured in a suitable manner, these ribs can also contribute towards controlling the flow of steam and the particulate material. Steam and the particles carried with it will pass up through the plates 17 where a deflection of the flow occurs due to the slope of the plates, and where the speed of the steam is reduced so that particles will fall down on the next underlying plate 17. The particles will slide downwards from the top of this plate to the slot between the plate and the conical outer wall 16, and from the conical outer wall down into the annular chamber 1 , from where the particles are again blown up between the plates 17 further forward in the transport direction. In that the steam passes between the plates 17, most of the particles are prevented from reaching out above the conical transition piece 15, and at the same time the particles are transported forward in the apparatus. Only particles of dust will be driven by the steam out over the conical transition piece 15. In the same way as the suspended plates 13, the plates 17 can be heated and like the outer wall 16 can thus serve as heating surfaces. A separator wall 7 is also provided in the conical transition piece 15, such as shown in fig. 4. This separator wall 7 prevents the particulate material 10 which has reached to the end of the annular chamber 1 , and is thus dried, from being once again blown up by the steam and over into the foremost part of the annular chamber. The conical transition piece 15 leads up to the uppermost part 20 of the apparatus, which is shown in figs. 5 and 6, and in which the final separation of dust takes place. As shown, the upper part 20 is cylindrical, in that the conical outer wall 16 from the conical transition piece 15 (indicated with the stippled lines in fig. 5) is extended upwards to form an outer wall which is closed at the top. On the inside, the cylindrical surface 2 and herewith the middle chamber 4 are extended for a distance upwards in the uppermost part. In the uppermost part 20, above the middle chamber 4 there is a cylindrical part 22 which over a section of its circumference at the top has an opening with vanes 21 , and which at the bottom is associated with the mid- die chamber 4 by an annular trough 23. The cylindrical part 22 constitutes a cyclone, in that the upwardly-flowing steam carrying particles of dust will flow into the part 22 between the vanes 21 , thus forming a cyclone field. Dust particles will collect on the wall of the cylindrical part 22, sink down along the wall and be rotated around inside the annular trough 23 until they pass through a discharge opening 24 (shown in fig. 6) in the annular trough 23. As is shown in more detail in fig. 7, the discharge opening 24 leads to an ejector 25 which sucks dust particles and a part-flow of steam into a vertical outlet cone 26. The ejector 25 is driven by steam from an external supply. The outlet cone 26 is preferably placed above the area where the dry product is removed from the apparatus, i.e. in the area above the discharge pipe 6. As shown in fig. 6, the vanes 21 providing inlet to the cylindrical part 22 are preferably placed above the last part of the annular chamber 1 , i.e. in that 11 part which is nearest to the area in which the discharge pipe 6 is placed. The result of this is that in the uppermost part 20, outside the cylindrical part 22, a rotating flow arises in the upwardly-rising steam. This rotating flow will pass through the plates 30, which are configured as parts of a cy- lindrical surface. By its passage through these plates 30, a part of the dust mass carried by the steam will slide down the plates in a boundary layer, so that the amount of dust which is carried forward to the vanes 21 and the cylindrical part 22 will be reduced. The rotational flow will be stopped by a separator wall 7 which is placed such as shown in fig. 6, after which the flow will be led in between the vanes 21 into the cylindrical part 22. The flow of steam which has reached into the cylindrical part 22 will pass in the form of a main steam flow down through the middle chamber 4 as shown by the arrow 27. However, in the drying of the particulate material, additional steam is added to the flow, which makes it necessary for a corresponding amount of excess steam to be led away. This takes place though an opening 28 in the top of the uppermost part 20 of the apparatus, such as shown by the arrow 29. This excess steam contains all of the energy which is used for the evaporation. By condensation of the excess steam, this energy can be regained and led back to the process, and the separation of liquid thus takes place with the least possible consumption of energy and without any pollution of the air. Moreover, by controlling the amount of steam led away, the pressure in the closed system can be controlled, in that it can be advantageous to work under a pressure of, e.g. 3 to 4 bar. When passing down through the middle chamber 4, the main steam flow will also pass a heat exchanger or superheater (not shown), whereby the superheating of the steam is increased so that it assumes new drying po- tential. In the bottom part 9 of the apparatus there is also a blower, e.g. a 12 centrifugal blower (not shown), which sends the superheated steam up through the annular chamber 1 again.

Claims: 13 CLAIMS 1. Method for the removal of liquid from particulate material by evaporation through the supply of heat transferred mainly by superheated vapours or steam of the liquids existing in the particulate material, said method taking place in a substantially closed system, characterized in that the particulate material is supplied continuously to a process chamber which is in the form of an annular or partly annular chamber (1) lying in a substantially horizontal manner, that the superheated steam is led from below up through openings (11) in a bottom (10) in the annular chamber, so that the particulate material is brought into movement by the superheated steam, and such that a transport of the particulate material occurs through the annular chamber (1). 2. Method according to claim ^ characterized in that the bottom (10) in the annular chamber (1) has a trough-shaped, double-bent or an approximately double-bent shape, through which the superheated steam is introduced in controlled directions, and in that a greater flow of superheated steam is fed into the annular chamber in the vicinity of the cham- ber's outer side than at the chamber's inner side. 3. Method according to claim 1 or 2, characterized in that a greater flow of superheated steam is fed into the annular chamber (1) in the vicinity of a supply opening (5) for particulate material than in parts of the annular chamber (1) which are in the vicinity of a discharge opening (6) for the particulate material. 4. Apparatus for the execution of the method according to claim 1, consisting of a substantially closed container which has means for the introduction of particulate material from which liquid is to be removed, means for the 14 removal of dried particulate material, means for the circulation in the container of superheated vapours, means for the supply of thermal energy to these vapours and means for the separation of dust particles from these vapours, c h a r a c t e r i z e d in that the container contains a process chamber which lies substantially horizontal and which is configured as an annular or partly annular chamber (1), said chamber having a bottom (10) through which steam can permeate, in that openings (11) are provided in the bottom (10), and in that the bottom has a relatively greater opening area close to the outer side of the annular chamber than close to the inner side of the chamber, and a relatively greater opening area in the vicinity of a supply opening (5) for the particulate material than in the vicinity of a discharge opening (6) for the particulate material, and that the openings (11 ) in the bottom (10) are shaped in such a manner that an influx of steam takes place partly at right-angles to the bottom and partly at angles to the bottom (10) of between 0° and 90°, and preferably between 0° and 80° and particularly between 0° and 30° in different directions, so that a rotating movement and possibly a movement in the annular chamber's peripheral direction is promoted in the particulate product. 5. Apparatus according to claim 4, c h a r a c t e r i z e d in that the bottom (10) of the annular chamber (1) is configured in such a manner that in vertical section it has a shape whereby it has a lowermost point which lies within the centremost half of the chamber's breadth between an inner and an outer edge of the annular chamber, in that the bottom (10) of the cham- ber can be semicircular in shape, oval in shape or an approximation of such shapes, possibly in angular form. 6. Apparatus according to claim 4 or 5, c h a r a c t e r i z e d in that plates (13) are suspended in the annular chamber (1), said plates (13) extending from the inner side (2) and/or from the outer side (3) of the annular cham- 15 ber (1), and being suspended in such a direction and with such a slope and/or bend that a suitable filling of the particulate material in the annular chamber is ensured. 7. Apparatus according to claim 6, characterized in that the plates (13) suspended in the annular chamber (1) are configured in such a manner that they serve as heating surfaces for the flow of steam and the particulate material, in that it is possible for the plates (13) to be configured with cavities to which steam can be supplied. 8. Apparatus according to one or more of the claims 4-7, characterized in that the apparatus comprises a container part in the form of a conical transition piece (15) which is disposed in the container above the annular chamber (1) and through which the superheated steam can flow, in which conical transition piece (15) there are plates (17) which radiate from an inner wall (2) and are bent or curved forwards in the direction in which the particulate material is transported, and in that over at least a part of the length of an outer edge out towards a conical outer wall (16) of the conical transition piece (15), said plates (17) lie at a distance from this conical outer wall (16). 9. Apparatus according to claim 8, characterized in that the plates (17) which radiate from the inner wall (2) of the conical transition piece (15) serve as heating surfaces for the flow of steam and the particulate material, in that it is possible for the plates (17) to be configured with cavities to which steam can be supplied. 10. Apparatus according to one or more of the claims 4-9, characterized in that the apparatus comprises a cylindrical part (22) upper- most in the container, said cylindrical part (22) constituting a cyclone in 16 which a separation of the dust from the superheated vapours takes place before these are led down to the means for the supply of thermal energy.

Inventors: JENSEN ARNE SLOTH, JENSEN, ARNE, SLOTH
Applicants: ASJ HOLDING APS, JENSEN ARNE SLOTH, JENSEN, ARNE, SLOTH
Application year: 1999
Main classification: B01D1
IPC codes: B01D1, F26B3, F26B17, F26B21