US3060589A - Drying granular materials - Google Patents

Description

S. WALLIN DRYING GRANULAR MATERIALS Oct. 30, 1962 2 Sheets-Sheet 1 Filed March 25, 1959 INVENTOR. JWW BY Oct. 30, 1962 s. WALLIN DRYING GRANULAR MATERIALS 2 Sheets-Sheet 2 Filed March 25, 1959 INVENTOR.

United States Patent Ofi 3,060,589 Patented Oct. 30, 1962 ice 3,060,589 DRYING GRANULAR MATERIALS Sven Wallin, Jonkoping, Sweden, assignor to Aktiebolaget Svenska Flaktfabriken, Stockholm, Sweden Filed Mar. 23, 1959, Ser. No. 801,049 Claims priority, application Sweden Mar. 25, 1958 3 Claims. (Cl. 34-13) The present invention relates to a method and an apparatus for drying or other treatment of loose materials in form of grains, lumps or fibers. The invention has particular utility in apparatus wherein a gaseous treating medium is caused to pass through the material while it is conveyed as a continuous bed in zig-zag passage ways over a number of superimposed perforated surfaces which are provided with guiding side walls.

In drying or other treatment of such loose materials in prior art apparatus, in order to obtain an effective treatment it has been necessary to supply the treating medium in such a quantity and at such a pressure that the material is given a whirling motion, thereby wasting considerable power. Also relatively large spaces have been required in the treatment apparatussince the material by reason of said whirling motion frequently is raised well above the normal level of the material bed.

The present invention relates to an improved method and apparatus by which the disadvantages of the prior art can be eliminated. In practicing the method according to the invention, the height of the material bed is regulated in relation to the quantity and pressure of the supplied treating medium so that the fiow velocity of the medium through the material is sutficient to overcome the inner frictional resistance of the material and make it possible for the material to move only by the action of the treating medium through said passageways by causing the material to flow as a continuous bed without any mixing and to be conveyed along and between the passageways in the form of a coherent belt or layer wherein the relative position of the material particles with respect to one another remains substantially unchanged. If pulverous or granular material is caused to fall in a natural position on a horizontal plane, that material will form of its own accord a natural angle of repose. However, when drying medium is passed through the material with insuflicient velocity to cause fluidization, but sufficient velocity to eliminate most of the internal friction, the granular material assumes what we refer to hereafter as a modified angle of repose which is less than the natural angle of repose of the material. In accordance with the invention, when the modified angle of repose is between 0.5 and by reason of the control of the air moving upwardly therethrough, interruption of the discharge of the material from the apparatus arrests the flow of the material throughout the apparatus by reason of its being a coherent bed.

An apparatus for carrying out the method according to the invention consists of a number of super-imposed units, which are identical except that alternate ones are the mirror image of the intermediate ones. Each unit is formed as a rectangular box equipped with inlet and outlet openings in the opposite end walls for the material to be treated and is provided with a horizontal, perforated, intermediate bottom functioning as a conveying plane for the material. A ventilator connected to the space below the intermediate bottom for supplying the treating medium and a discharge opening for'the medium is provided above the intermediate bottom at a predetermined distance relative to the height of the bed. Said apparatus is characterized by a stationary feeding table arranged at the inlet end of each passage way and which declines steeply towards the perforated intermediate bottom, an adjustable shutter being mounted above said table in order to regulate the intended height of the material bed.

The invention will now be described more in detail with reference to the accompanying drawings, showing as an example one embodiment of an apparatus made in accordance with the invention and in which:

FIG. 1 is a vertical, longitudinal cross section of the apparatus.

FIGS. 2 and 3 illustrate cross sections through the apparatus, taken on the lines 22 and 33 respectively of FIG. 1.

Referring to the drawing, the apparatus comprises a number of superimposed units 1, 2, 3, 4, and 5 which are identical, except that the alternate units 1, 3, and 5 are mirror images of the intermediate units 2 and 4. Each unit is generally rectangular in form and is provided with inlet and outlet openings 6 and 7 respectively for the material to be treated in the opposite end walls. In the illustrated apparatus, the unit 1 functions as a pro-heating zone, the units 2, 3 and 4 as drying zones and the unit 5 as a cooling unit for the material. Each unit has a substantially horizontal, perforated, intermediate bottom 9 functioning as a conveying surface for the material. A space 19 below said intermediate bottom functions as a distributing box for the supplied treating medium. These distributing boxes are connected to means 11 for supply ply of the treating medium. Cleaning openings 16 and 17 are provided in the boxes 10 to remove foreign material which may enter the boxes. The openings are closed by flaps which are opened either intermittently or continuously to discharge the foreign material. The openings are dimensioned so that when the openings are open, they do not interrupt the movement of the material on the conveying surface. As illustrated each unit may be provided with separate ventilators or one single ventilator can be used, which by means of distributing ducts is connected to said spaces 10 (not shown). The outlet openings 12 discharge the treating medium after the passage of said medium through the material bed, and, in the illustrated embodiment, are formed by bevelling all the distributing boxes at the bottom along the longitudinal side walls thereof whereby the arrangement of the outlet openings will not increase the height of the complete apparatus, which otherwise would be the case if these outlet openings were arranged in the side walls of the units. These outlet openings 12 terminate into a common chamber 21 provided with an inclined filter 22 for the separation of chaff and other impurities carried by the treating medium. Partitions 23 and 24 form a separate space 25 in the chamber 21, into which space the outlet from the unit '5-functioning as the cooling zon*eterrninates. The space 25 leads into the fan 11 of the unit 4 by means of a duct 33. A free passage way 27 is provided below the filter 22 for a part of the treating medium and for the discharge of separated impurities. The above mentioned chamber 21 is connected through a heating element 18 and a transition 19 to the means 11 for the circulation of the treating medium through the units 1, 2 and 3. In the present instance, each fan 11 is driven by an electric motor 20. The fan 11 for the cooling unit 5 receives air from the atmosphere directly without passing through a heater.

By this arrangement it is possible to recirculate the treating medium in the drying units (as indicated by the arrow A in FIG. 3). In order to exhaust the water evaporated in the apparatus a part of the medium must continuously be discharged which takes place partly through the outlet 32 (see FIG. 1) in the pre-heating unit and partly through the outlet '26 (see FIG. 2) from the chamber 21. A corresponding quantity of compensating air is supplied to the drying units partly from the cooling unit through the chamber 25 (as indicated by the arrow B in FIG. 1) and partly from the atomsphere through the .19 openings 28 arranged in each drying unit (as indicated by the arrow C in FIG. 3). By an adjustment of the free area of the openings 28 it is possible both to vary as required the proportion between recirculated air and compensating air and to decide to which unit or units outdoor air is to be supplied.

The treating time for the material is regulated only by regulating the quantity of discharged material. For this regulation a discharge pocket 29 is connected to the discharge opening 7 of the last unit 5, said p cket extending across the whole width of the unit. Regulating means is mounted in said discharge pocket, and in the present instance is in the form of a rotatable winged wheel 30 with a length corresponding to the width of said pocket. The winged wheel rotates counterclockwise and thereby lifts the material and discharges the same through a discharge slot 31. The quantity of the material flowing through each unit is regulated by the clearance between the slanting table 13 and the cooperating adjustable shutter 14.

Without departing from the invention the construction of the discharge means can be varied and in the same way the heating of the medium can be carried out by means of a direct supply of heated air to the ditferent drying units instead of utilizing the illustrated heating elements 18.

Thus, the present invention provides a method and apparatus for drying and similar treatment of granular material wherein the material is moved over perforated bottom plates. The height of the material bed is regulated relative to the quantity and pressure of the treating medium supplied to the under surface of the perforated bottom plates so that the medium substantially overcomes the internal friction resistance of the material without mixing the same. Thus, the material is caused to pass through the dryer in the form of a continuous coherent layer. The material is caused to pass in five separate runs, the first of which is a preheating run and the last of which is a cooling run, the intermediate runs being drying runs. Where the material flows downwardly through the apparatus, the treating medium is caused to pass generally upwardly through the apparatus with partial recirculation in each drying run. In each unit, the medium flows under the preforated bottom plate in the same direction as the material flows over the bottom plate. The upward flow of the treating medium operates to produce in the material, a modified angle of repose in the order of to preferably about 5", so that the material flows through the apparatus as a coherent belt, at a velocity in each run determined by the velocity of discharge at the outlet end of the last passageway.

What I claim is:

1. In the treatment of loose, granular or pulverous materials by means of a gaseous medium in a plurality of superimposed passageways equipped with guiding side walls and wherein the fioor of each passageway is a fixed substantially horizontal perforated plane and the successive passageways are connected by vertical passages at alternate ends of said perforated planes, the method of moving the material through the successive passageways which consists in feeding the material onto said perforated planes and distributing the material across the width of said passageways to form a bed, passing gaseous treating medium upward through each perforated plane and the material bed thereon, controlling the height of the material bed in each passageway in correlation to the quantity and pressure of the treating medium supplied thereto to such a value that the flow velocity of the medium overcomes the internal friction of the material bed to the extent of imparting to said material a modified angle of repose in the order of 0.5 to 10 whereby said material is conveyed along said passageways and passages in the form of a coherent belt in which the relative positions of the material particles with respect to one another are substantially unchanged during movement through said passageways and passages and regulating the velocity of conveyance of the material in each and every passageway and thereby the treatment of the material by adjusting the velocity of discharge of the material at the outlet end of the last passageway.

2. A method according to claim 1 including the step of providing separate treating medium supply means for each of said passageways operable to effect fiow of said treating medium below each perforated plane prior to passing through said plane in a direction concurrent with that of the moving bed of the material.

3. A method according to claim 2 wherein the treatment of the material comprises pre-heating, drying and cooling in successive passageways respectively, characterized in that the treating medium supplied to each of the different passageways is treated separately and is conditioned according to the aforesaid treatment of the material in said passageway.

References Cited in the file of this patent UNITED STATES PATENTS 115,833 Eaton June 13, 1871 2,270,903 Rudbach Jan. 27, 1942 2,582,688 Ford Jan. 15, 1952 FOREIGN PATENTS 500,734 Great Britain Feb. 15, 1939

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