Abstract:
Annular drying element ( 15 ) for mounting on a rotor axle in a drying plant for indirect heating or cooling of moist, comminuted, biological material such as fishmeal, offal from slaughterhouses, mash from breweries and similar materials of animal, vegetable or chemical origin. The drying element is configured with a number of through-going openings ( 25 ) extending from the one side of the element to the other. The drying element can be made of two identical, annular plate elements ( 16 ) with holes ( 25 ), in that tubular stays are welded between oppositely-lying holes. Through the openings ( 25 ), elongated elements can be inserted which increase the stirring in the product mass which is to be heat-treated.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention concerns an annular drying element. Such drying elements, which constitute a heat exchanger, are used in drying plants for indirect heating or cooling of moist, comminuted materials, e.g. biological materials such as fishmeal, comminuted offal from slaughterhouses, mash from breweries and similar materials of animal, vegetable or chemical origin. 
     The drying plant comprises a stationary housing and a rotatable rotor with a number of annular drying elements disposed at intervals. The rotor has means for supplying the medium for heating or cooling. For heating, steam is often used, and thus the rotor is also provided with means for the removal of a condensate thereof. 
     2. Description of the Prior Art 
     Plants of this type are known, e.g. from U.S. Pat. No. 3,923,097 (Atlas, DK) and U.S. Pat. No. 4,982,514 (Atlas, DK), and have been in use for many years. The plants have an opening in the one end for the supply of raw material, and an opening in the opposite end for the removal of the material after it has been treated. The transport through the plant is effected mainly as a consequence of the continuous filling with new raw material and the continuous removal of the treated material, but the transport can be increased or reduced by using vanes, lifting elements or the like, e.g. disposed directly on the drying elements. The transport through the plant is possible because the annular drying elements do not extend completely out to the stationary housing. Rotating driers with stirrers or transport vanes are known, e.g. from U.S. Pat. No. 3,800,865 (Stord Bartz, NO) or U.S. Pat. No. 3,777,810 (The Strong Scott Company, US). 
     In older constructions, cf. e.g. GB Patent No. 952,099 (A/S Myrens Verksted, NO), use has been made of a rotating drier with drying elements built up of tubes, e.g. annular or helical tube constructions, which can be configured so that the steam condensate is led towards a tapping-off point during the rotation. Furthermore, from U.S. Pat. No. 4,074,751 (Unice Machine Company, US) there are known rotating heat exchangers of tubes arranged for the heating or cooling of a fluid mass, e.g. sugar massecuites. 
     In the latter two constructions, the product to be heat treated or dried is fed forward in the plant by passing through the openings in the drying elements which arise between the tubes. This can have advantages with regard to the stirring and the transport of the product, but has great disadvantages with regard to the avoidance of the product settling on the drying element. Moreover, drying elements of this kind do not have as large a heating surface as the plate-formed drying elements mentioned earlier. 
     SUMMARY OF THE INVENTION 
     The invention also concerns a drying plant. If a drying plant with drying elements as explained above is to be used for the heat treatment, drying or cooling of a relatively fluid product, e.g. a very greasy or oily product, e.g. the boiling of oil- or fat-containing offal from slaughter-houses, the stirring in the product mass can cause increased processing time. Therefore, the need can arise for an increase in the stirring of the product mass. 
     By configuring the annular drying elements according to the invention, it is achieved that all of the known advantages with plate-formed drying elements are retained, and at the same time the possibility is provided of obtaining a changed product-flow through the plant. 
     There are many advantages from the point of view of production technique with drying elements of plate-formed elements, and as a rule a greater heat-exchange surface is achieved than with drying elements configured as tube constructions. 
     Moreover, the drying element of the kind disclosed in the application has advantages in that it can be produced by the welding together of parts which are configured in such a way that the welding can be automated in a simple manner by using automatic welding machines or welding robots, which reduces the production costs. 
     The openings in the annular plate elements are preferably configured by the insertion of a tube piece in each opening, preferably so that the longitudinal axes of the tube pieces are parallel with the axis of the drying element. Good possibilities are hereby achieved of simplifying the production of the drying elements. 
     However, the annular drying element according to the invention is preferably configured in such a way that it is built up of two substantially identical plate elements and, preferably has tube pieces inserted as stays between the plate elements at their oppositely-lying openings. There is hereby achieved a great degree of simplification in the production of the drying elements, and at the same time herewith a very strong and rigid construction is achieved which can tolerate a high pressure, which makes it possible to use steam at a high temperature as the heating medium. 
     The tubular stays are preferably configured with a circular cross-sectional profile. Among other things, this makes it possible to use tubes of standard manufacture which can be cut off in the desired lengths. 
     The tubular stays are preferably distributed over the surface of the drying element, so that there is minimal deflection or deformation of the drying element when pressurized steam is used as the heating medium. 
     The length of the tubular stays can be at least the thickness of the element. If the tube length corresponds to the thickness of the element, there is the possibility of being able to use scraping elements in the drying plant which scrape the drying elements clean, which e.g. can be relevant at that end where the product is most moist, or in that zone where the product is the most sticky. However, the tubular stays can also be of a length which is greater than the thickness of the element, and the free ends of the tubes can be configured so that they constitute a carrier or a stirring element for the product to be dried. 
     For certain constructions, it can be an advantage to configure the drying element by making use of tubular stays with different clearances on the same drying element. The possibility is hereby achieved of variations regarding where there may be larger openings and where there may be smaller openings on the drying element. 
     Finally, the drying element according to the invention can be configured in circles concentric with an outer edge of the drying element which offers important advantages from the point of view of production technique. 
     By configuring the plant a number of annular drying elements an increased stirring in the product mass can be achieved without this giving rise to other substantial disadvantages. An increased stirring will result in a quicker treatment of the product mass, e.g. possibility of quicker heat treatment, which increases the capacity of the plant. The mounted axial elements serve as stirrers and, depending on their configuration, also as lifting elements, so that the product mass can be stirred thoroughly if there is a need for it. 
     How many axial elements are mounted and which form they shall have will depend on the current conditions and the actual product, e.g. the degree to which it is desired to increase the stirring, and to what degree the transport of the product can possibly be desired to be reduced, in that the elements fill out some of the through-going openings in the rotor&#39;s drying elements. 
     Depending on how the stirring is desired to be carried out, the elements can be configured to extend over all of the drying elements. In brief, the number and the length of the axial elements are contributory factors in determining where in the drier an increased stirring is desired, and how great the increased stirring shall be. 
     It can be an advantage if the elements are configured as a tube with clearance. When using tubes as elements, e.g. tubes with circular cross-sectional profile, in many respects a suitably increased stirring is achieved without any considerable increase in the weight of the rotor. An advantage here is also that use can be made of standard tubes as elements. 
     It will be obvious to those familiar with the art that the axial elements can be configured from rods or tubes with almost any cross-sectional profile. However, it will be normal practice to take into account the shape of the through-going openings in the drying elements and to use elements which substantially fill out these openings, which is why tubular elements with circular cross-sectional profile constitute a preferred embodiment. 
     The elements in the drier can thus have different or varying cross-sectional profiles along their length, so that there are areas which provide suitable engagement with the drying elements, and areas which function as stirrers and/or lifting elements as required. 
     The elements are preferably secured to only one drying element, e.g. by welding, and preferably at the one end of the elements. Mechanical stresses due to differences in temperature etc. are hereby avoided, in that the axial elements can expand/contract in the longitudinal direction without this giving rise to mechanical influences on the rotor&#39;s drying elements, in that they can be displaced in the openings in the axial direction where they are not welded fast. 
     The possibility is achieved of increased energy supply via the axial elements in accordance with the invention. A plant with a given volume can thus be given a greater capacity, e.g. a greater heat treatment capacity, in that a greater amount of energy can be supplied. 
     A practical way in which thermal energy can be supplied to the axial tube elements is with a manifold. Use can be made of the same heat medium as that used for the annular drying elements, e.g. steam, but the supply of energy to the axial elements can also be configured separately, so that a lower or a higher temperature can be used herein if this is required. 
     Through a cover, preferably a cover in the one end of the drying plant housing, axial elements according to the invention can be mounted or removed as required. This has great practical and economical advantages, e.g. if a drying plant has to be changed to be able to process another product, or to process the product in a way which is different to that for which it was originally intended. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention will now be described in more detail with reference to the drawings, in that 
     FIG. 1 shows the principle in a known drying plant with annular drying elements on a rotor axle, 
     FIG. 2 shows a section through a known annular drying element, 
     FIG. 3 shows a first embodiment of a drying element according to the invention, 
     FIG. 4 shows a section in FIG. 3 seen in the direction IV—IV and shown on a larger scale, 
     FIG. 5 shows a section corresponding to FIG. 4, but in a second embodiment, 
     FIG. 6 shows a third embodiment of a drying element according to the invention, 
     FIG. 7 shows a section in FIG. 6 seen in the direction VII—VII and shown on a larger scale, 
     FIG. 8 shows a diagram of the flow and area relationship of different drying elements according to the invention, 
     FIG. 9 shows an axial section in a part of a rotor in a fourth embodiment of the invention, and 
     FIG. 10 shows an axial cross-section corresponding to FIG. 9 in a fifth embodiment of the invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIGS. 1 and 2 show the principle of the known technique, in that FIG. 1 shows a schematic longitudinal section in a drying plant comprising a stationary housing  2 , possibly with heat jacket, an opening  7  for the introduction of the material to be dried, and an opening  8  for the discharge of the material after it has been processed. The material introduced is dried by means of a heated, rotating rotor  3  with circular, plane drying elements  9  disposed at intervals. 
     When the plant is continuously filled with new raw material, which is to be heated and dried, possibly boiled or sterilised, it will move towards the discharge opening while giving off moisture which is removed from the housing in a known manner. 
     The rotor  3  has a supply pipe  4  for the heating medium, e.g. steam, which via a central pipe  11  is fed to the drying elements  12 . Return steam is led away via a discharge pipe  5 , and condensate via the discharge pipe  6 . 
     FIG. 2 shows part of the radial section of a drying element  9  and shows an example of how a known drying element can be arranged. The drying element consists of two annular plate elements welded together, in which there are formed channels  10  for the heating medium, e.g. steam. 
     The plant shown in FIGS. 1 and 2 explains the principle of a drying plant, and corresponds to that which is known from U.S. Pat. No. 4,982,514. 
     The present invention concerns a new configuration of the drying elements, which is explained in more detail with reference to FIGS.  3 - 7 . 
     In FIG. 3 is shown an embodiment according to the invention of a drying element  15  seen at right-angles to the surface, and in FIG. 4 is seen a radial section herein, for the sake of clarity shown on a larger scale. The drying element consists of two identical, plane, annular disks or plate elements  16  of steel plate. The annular disks or plate elements  16  are e.g. 2 m in diameter and have a number of holes  25 , e.g. 42 holes as shown. The two plate elements  16  are coupled together, in that they are joined together along the outer edge  18  by means of an annular steel band  19  and an annular weld  20 . At the inner edge, each of the plate elements  16  is provided with an annular foot-piece  17 . The plate elements have a thickness in the order of 6-10 mm. In all of the holes  25  there is inserted and welded a tube piece  26  for both plate elements, so that the tube pieces  26  constitute stays between the plate elements. In the example shown, the stays are 4′ tube pieces. 
     The tubular pieces  26  are welded solidly and in a pressure-tight manner to the two plate elements  16 , so that between these there is formed a chamber  22  for the heating medium, e.g. steam under pressure at 10 baro, said chamber having an annular opening  23  for the supply of steam and the removal of return steam and condensate in a commonly-known manner. The foot-pieces  17  which, as shown in the drawing, extend out on each side of the plate element, are arranged to be welded directly together with adjacent elements and hereby constitute a pipe element which surrounds the rotor axle in a drying plant as described earlier. 
     In the example in FIGS. 3 and 4, the axes  29  of the tubular stays  26  are parallel with the axis  30  of the drying element, and the tubular stays are of such a length that they correspond substantially to the thickness of the element. 
     In the example in FIG. 5, the tubular stays  27  are shown with a length which is greater than the thickness of the drying element  15  and thus extend out over the element&#39;s surface. Furthermore, it is possible for the tubular stays  27  to be cut off in a manner which is not parallel with the plane of the plate element  16 , but at an angle which is oblique hereto, or possibly with a completely different shape, so that the protruding tubular stays constitute vane elements, carriers or stirring elements which have influence on the stirring of the material which is dried in the plant. 
     Between the two sides of each drying element  15  there is now direct connection through the tubular stays  26 ,  27  via the openings  25  herein, hereby making it possible for the material to be transported axially through the drying element. 
     For production reasons, the axes  29  of the tubular stays are parallel with the axis  30  of the drying element, but naturally there is nothing to prevent the tubular stays being disposed so that the axes are not parallel. 
     In the example in FIGS.  3 - 5 , the tubular stays and herewith the openings  25  are disposed in two circles  28  which are concentric with the outer edge  18  of the drying element, and displaced from each other to provide a substantially even distribution of the tubular stays over the element, whereby it is achieved that the free plate area between the tubular stays does not become too great. This is of significance for how high a steam pressure can be applied to the element without any great deflections arising in the plate material between the tubular stays. 
     The drying element  15 ′ shown in the example in FIGS.  6 - 7  is of the same size, but use is made here of more, smaller tubular stays, i.e. 90 tubular stays distributed over three concentric circles  28 , in that the tubular stays are 3′ tubes. 
     According to the invention, it is thus possible, depending on the material to be treated in the drying plant, i.e. depending on the material&#39;s consistency, moistness, grain size etc., to optimally dimension the drying elements by the selection of the size and number of tubular stays, the configuration of the stays and their positioning, to provide a drying plant which has optimal energy efficiency, without detriment to the quality of the plant with regard to lifetime and operational reliability. 
     FIG. 8 is a diagram showing two curves A and B for different embodiments of the drying elements according to the invention. 
     The curve A shows variations in the heat surface area delta A in percentage (the ordinate at the right-hand side) on a drying element according to the invention in relation to a drying element with the same diameter but without tubular stays. 
     The curve B shows variations in the area of passage PF (Plug Flow) in percentage (the left-hand ordinate axis) in a drying element according to the invention in relation to a drying element with the same diameter but without openings. 
     The curves A and B are calculated for relevant numbers of tubular stays (AR) and stay diameters (RD), which are marked on the horizontal axis. 
     AR thus indicates the number of tubular stays used, and RD indicates the inside diameter of the tubular stays used. 
     The tubular stays are evenly distributed over the area of the drying element as shown in the earlier examples. 
     It will be seen that if a large number of small tubular stays are used, a large heat surface (delta A&gt;100%) is obtained, but with a low “plug flow”. The example discussed earlier and as shown in FIG. 3 is also directly marked in the diagram. In this example, the “plug flow” obtained is thus 16% with a Delta A of approx. 94%. For a quite modest reduction in the heat surface, it is thus possible to achieve a considerable flow through the drying elements. 
     The diagram thus shows how it is possible to a great extent to dimension a drying element according to the invention so that it has the desired characteristics, especially with regard to energy efficiency, production capacity etc. 
     In FIGS. 9 and 10 is seen an axial cross-section of a part of a rotor for a drying plant according to the invention. 
     The rotor&#39;s center axis  30  is shown, and above this is seen the rotor&#39;s central pipe  11  for the supply of steam for heating and for the removal of condensate, which is effected in a commonly-known manner and which therefore is not described in further detail. 
     A number of annular drying elements  15 ′ of the type discussed earlier in connection with FIGS.  3 - 7  is built up of plate elements  16  and, via their foot-pieces  17 , are annularly welded together around the central pipe  11 . The drying elements can be supplied with steam for heating via the tubular stubs  35 . 
     The central pipe  11  is shown closed at the one end with an axle journal closure  37  in a commonly-known manner, and sealed off from the end  32  of the housing  2 . The drying plant is otherwise built up in a commonly-known manner and will therefore not be described in more detail. 
     As explained earlier, each of the annular drying elements  15 ′ has a number of through-going openings  25  in the axial direction, which openings can be provided with tubular stays  26 . 
     In the drying plant according to the invention, all of the annular drying elements  15 ′ are welded together at the annular foot-pieces  17  in such a way that the through-going openings  25  lie axially in a line, so that oppositely-lying holes have the same center axis. It hereby becomes possible to mount axial, elongated elements  31  through the openings, e.g. in the form of hollow tubes as shown in FIGS. 9 and 10. The elements  31  have a length which at least extends over the space between two adjacent drying elements  15 ′, preferably over at least three adjacent elements. 
     The elements  31  can be tubular as shown, and can be divided into holding parts  31   a  for engagement with the drying elements  15 ′, and in lifting parts  31   b  which can be configured in any desired manner, so that they constitute a lifting element. The areas  31   b  can, for example, be polygonal or directly U-shaped, so that the product to be treated is lifted during the rotation. 
     The elements  31  are preferably secured to the first of the annular drying elements  15 ′ by welding  31   e . The elements  31  are preferably standard tubes with a diameter which substantially fills out the tubular stays  26 . 
     A cover  33  can be provided in the end  32  of the housing, e.g. secured with bolts  34 . When the cover is removed, drying elements  31  can be inserted in or removed from the rotor, in that by rotation of the rotor the openings in the drying elements  15 ′ can be brought into the opening which lies under the cover. The insertion of an element  31  is shown by way of a sketch. 
     In the example shown in FIG. 9, elongated elements  31  are placed in some of the outermost openings  25  and in some of the innermost openings, but not in the intermediate openings. The number of elongated elements and where they are placed will depend on the degree to which the stirring is desired to be increased. In the examples shown in FIGS. 9 and 10, four elements  31  displaced 90° are inserted in the outermost openings  25 , and four elements similarly displaced 90° are inserted in the innermost openings, i.e. eight elements in all. It will be obvious to those familiar with the art that the number of elements  31  and their positioning will depend on many different aspects, e.g. the type of product to be treated, how it is required to be treated and how the rotor is otherwise arranged and dimensioned etc. 
     FIG. 10 shows an embodiment of the invention where all of the elongated elements  31  are at the one end welded together with a manifold  39  by welds  31   d , said manifold comprising a distribution chamber  40  and a supply pipe  41  for steam. The opposite ends of the elements  31  are closed by caps  31   c . During the heating by the steam, condensate is formed which can be returned the same way as the steam is introduced, in that e.g. the whole of the drying plant can be inclined slightly towards the manifold  39 , e.g. at an angle of a few degrees, so that the condensate can return of its own accord to the manifold  39 . 
     The way shown in FIG. 10 of supplying heating or cooling medium to the elongated tube elements  31  is only an example of how this can be implemented.