US2728995A

US2728995A - Drying granular material

Info

Publication number: US2728995A
Application number: US301452A
Authority: US
Inventors: Schaub Franz
Original assignee: Ruhrchemie AG
Current assignee: Ruhrchemie AG
Priority date: 1951-08-04
Filing date: 1952-07-29
Publication date: 1956-01-03
Anticipated expiration: 1973-01-03

Description

Jan. 3, 1956 F. SCHAUB DRYING GRANULAR MATERIAL s Sheet-Sheet 1 Filed July 29, 1952 PB M NH 0 ES m Jan. 3, 1956 F. SCHAUB DRYING GRANULAR MATERIAL 3 Sheets-Sheet 2 Filed July 29, 1952 Jan. 3, 1956 F. SCHAUB DRYING GRANULAR MATERIAL 5 Sheets-Sheet 3 Filed July 29, 1952 INVEWIDP Fm/z sum;

United States Patent DRYING GRANULAR MATERIAL Franz Schaub, Oberhausen-Holten, Germany, assignor to Rnhrchemie Aktiengesellschaft, Oberhausen-Holten, Germany, a corporation of Germany Application July 29, 1952, Serial No. 301,452

Claims priority, application Germany August 4, 1951 9 Claims. (Cl. 34-57) This invention relates to improvements in drying granular material. It more particularly relates to a method and apparatus for drying fine grained materials which are not free flowing in the moist state.

Considerable difiiculties have been encountered in the past in the drying of moist fine grained materials which will not flow freely at or above a certain moisture content. These difiiculties are also encountered if the free flowing characteristics of the granular materials is considerably reduced by a certain water content. The conventional trickle driers cannot be used for this type of material since the same will, especially in relatively high piles, conglomerate and adhere and will not travel down the trickling surfaces. In addition the conventional drying devices which in most cases operate with high gas velocities are not well suited for the treatment of moist materials which have a tendency to cake due to the fact that it is difficult to load the gas stream uniformly with these materials.

Moist materials which would cake together after the re moval of the moisture were generally dried on devices in which the moist mass was exposed to the drying gas stream on conveyor belts. Also multi-stage driers or plate driers operating with stirrers and stripping devices were also used for the treatment of this type of caking material. These devices, however, are very expensive, ditficult to operate and highly susceptible to troubles. In addition apparatuses of this type require a relatively large space.

One object of this invention is the drying of granular materials which are not altogether free flowing in the moist state and/ or which tend to cake together during the drying without the above mentioned difficulties. This and still further objects will become apparent from the following description read in conjunction with the drawing in which:

Fig. 1 shows a vertical cross-section of an embodiment of an apparatus in accordance with the invention;

Fig. 2 shows a vertical section of a different embodiment of a device in accordance with the invention with annular guide surfaces;

Fig. 3 shows a top elevation of the conical false bottom of the apparatus in Fig. 2; and

Fig. 4 shows a vertical section of another embodiment of an apparatus in accordance with the invention with conically sloped false bottoms.

In accordance with the invention, the granular material to be dried is maintained in a substantially continuously supplemented conical pile or heap. A gas stream, preferably a hot gas stream is directed against this conical pile and in preferably such a manner that it impinges upon the surface of the same. The gas stream must be directed at a sufiiciently high velocity so that as certain portions of the material are dried to a certain extent by the gas they will be continuously discharged and carried away by the drying gas stream itself. An additional drying, as for example, that which will effect com- 2,728,995 Patented Jan. 3, 1956 ice plete removal of the moisture, may occur in the gas stream as it transports the granular material.

In the drying process according to the invention, when the drying gas stream is directed so that it impinges on the surface of the conical pile, an extensively dehydrated layer continuously forms at the surface of the conical pile of the material. This dried layer of the material is disintegrated by the flow velocity of the drying gases into sufiiciently fine grained portions to be carried off by the energy of the flow of the gases discharged from the drying apparatus. Outside of the drying apparatus, the material may be separated in the conventional manner with the use of dust separators, cyclones, or the like. After having passed through the dust separator, the gaseous medium used for the drying, which in most cases is air, may be passed through a blower and a heating device and recycled to the apparatus.

The process according to the invention may be carried out with very simple devices having high capacities. Drying devices of this kind substantially consist of a suiliciently high sheet-metal container of round or polygonal cross section. This container may be of cylindrical shape or may be provided with a restriction thus forming a funnel-shaped section widening towards the top. In this way, a zone of a particularly high gas velocity results which facilitates the complete discharge of the dried materials.

The material to be dried enters the drying apparatus in the moist state from above through a funnel-shaped pipe. Hot air or other hot gases are blown in, preferably tangentially, at the bottom of the drying apparatus and withdrawn at the top of the container together with the dried and finely grained materials. The quantity of moist material which is divided into powder by the drying gases at the bottom of the container and discharged suspended in the gas stream, is made up by the corresponding quantity of undried material dropping through the feed hopper. Thus, a completely continuous operation results. The quantity of material to be charged per unit of time is automatically controlled by the velocity at which the material freed from. its moisture content is discharged. The dropping of the moist material through the feed hopper may be aided by appropriate tapping or shaking devices which are allowed to act at suitable points of the apparatus as, for example, at the side walls or at the top of the drying apparatus.

A spiral motion of the drying gas stream which causes the dry material divided into fine grains to be whirled up may be assisted by annular devices installed in the interior of the apparatus. In this way, the surface of the material exposed to the drying gas stream may be substantially enlarged.

The drying gas stream may also be blown tangentially onto the conical heap of the moist material simultaneously from several points. This results in a good loosening of the material and a rapid disintegration of primarily caked portions of the material which is partially freed from its moisture content. It is of particular advantage to provide the bottom of the drying apparatus, according to the invention, with a conical elevation over which the flow of material is allowed to spread in a thin layer.

Referring to the drawings in which several embodiments of the drying apparatus are illustrated 1 is a vertical vessel (Pig. 1) of round cross section having a bottom plate 2 and an upper covering plate 3. The covering plate 3 is provided with a centrally arranged inlet pipe 4 which does not extend to the bottom of the drying apparatus and is provided, at its upper end, with a feed hopper 5. The bottom 2 of the vessel is provided with a conical surface 6 upon which the material slides down the gas inlet, and at the top of the drying apparatus there is a likewise tangentially attached pipe connection 8 for the gas outlet. Instead of the

pipe connections

7 and 8 annular pipes may be used which are provided with nozzles connected to the vessel 1.

The moist material is passed to the hopper 5, drops through the pipe 4 into the interior of the vessel 1 and forms a conical pile or heap 9 which is continuously supplemented by the material in the pipe 4. The material in the form of the pile slides down over the conical surface 6. Hot gas as, for example, hot air, is tangentially blown in at a sufficiently high velocity through the pipe connection 7, and effects a loosening and efficient predrying of the moist material already at the bottom of the vessel. Due to the high gas velocity, a rapid interaction between the solid constituents and the gaseous medium occurs resulting in an intensive evaporation. The material which disintegrates into fine grains in the drying process is lifted by the gas stream rising in spiral paths, is further dried in the suspended state and discharged with the effiuent gases through the pipe connection 8 at the top of the vessel. The separation of the portions of material suspended in the gaseous medium offers no difliculties and may easily be carried out by means of dust separators as are used, for example, in the fluidized process.

A particularly intensive interaction between the moist material and the heated drying gas may be obtained by annular guide surfaces arranged in the interior of the drying vessel. A drying apparatus operating in this manner is shown by way of example in Figs. 2 and 3.

In this case, the drying apparatus consists of a housing which has the form, in its lower part 10, of a cylinder and, in its upper part 11, of a funnel with the narrowest portion at 12. The material to be treated is charged through a feed hopper 13. The hopper 13 passes into a feed pipe 14, the lower edge of which is at about the level of the most narrow point 12 of the shell of the apparatus.

In the lower cylindrical part of the drying apparatus there are arranged several superimposed plates 15 provided with central openings of sufficient width for the downward travelling material.

Hot air is blown into the apparatus through the pipe connection 16 at the bottom. The gaseous medium passes at first into the space formed by the conical surface 17. The hot gas flows through slots 13 arranged in the conical surface 17 in upward direction and acts, in the space 1?, upon the materials sliding down over the conical surface 17. Thereafter, the gases, laden with the dried portions of material, flow through the individual successive plates 15 in upward direction. The plates 15 are provided with sufficiently wide slots 20 for the gas passage, the position of which on the individual plates 15 is staggered with respect to each other as far as possible. if each plate 15 is provided with only one slot 26, the slots 20 are staggered each time by nearly 360 in order to cause the gas stream to make a full circalar movement between every two successive plates 15. In this way, an intensive interaction between the solid and gaseous constituents is obtained.

Due to the substantially restricted cross section, a particularly high gas velocity occurs at 12 (Fig. 2). This high gas velocity causes the dried materials to be completely caught in the gas stream and to be continuously carried olT by the same through the pipe 21.

The false bottoms disposed within the apparatus need not be positioned horizontally. In most cases, it is more advantageous to give also these false bottoms a conical slope. A drying apparatus constructed in this manner is shown on Fig. 4.

The construction of this drying apparatus substantially corresponds to the embodiments shown on Fig. 2. The

ryinggases supplied through the pipe connection 23 pass'througn a slot 24 located at'the edge of the bottom cone 25 and enter in interaction with the material sliding down, which has already extensively been predried in the preceding annular spaces. Thereupon the gas stream passes through similar slot openings into the successive superimposed annular conical surfaces 22 where it repeatedly again contacts the material. The gas openings on the individual false bottoms are arranged in such a manner as to compel the drying gases to execute a rapid circular motion thereby lifting and entraining the dried portions of material disintegrated into dust. The gas stream laden with dried material is drawn off at the top of the apparatus and conducted into a dust separator where the completely dried material is separated.

The devices required for carrying out the process according to the invention are very simple since no moving parts, stirrer blades or mechanical conveying devices are used. The materials which, in the moist state, have no or only limited free flowing properties are dried so far at the surface of one or several conical pourings forming in the superimposed stages of the apparatus, as to be disintegrated in layers into fine grains and to be discharged in the suspended state by the kinematic energy of the gas'stream. The dimensions of the drying apparatus with respect to basal surface, height, gas inlet, gas outlet, type and number of false bottoms are dependent on the properties of the material to be treated and on the gas velocity used.

The materials which may be dried in accordance with the invention may be any pulverant or granular materials which are capable of being piled and which have no or only limited free flowing properties in the moist state.

Various materials may be dried by means of the process according to the invention, such as ores, lime, sand, coal dust, salts, artificial resins, flour. The maximum grain size of the materials to be dried should not be in excess of 2 mm. The flow velocity of the drying gases is dependent upon the grain size of the material to be dried and must be increased so far that the dry material can be entrained and discharged by means of the air stream.

The temperature of the drying gases may vary within wide limits and is also dependent upon the temperature, the moisture and the flow velocity of the materials to be dried. With asmall throughput and a low moisture content, a satisfactory drying of the material may be obtained already with low gas temperatures.

I claim:

1. A device for the drying of pulverulent and granular materials capable of being piled, which comprises means defining a vertical, substantially enclosed vessel, gas inlet means positioned at the lower portion of said vessel, gas outlet means positioned at the upper portion of said vessel, a material feed pipe, extending through the top of said vessel and terminating at a sufficient height above the bottom of the vessel to allow a vertical, conical pile of granular material to be maintained therebetween, and a multiple number of superimposed annular plates, each plate defining a gas passage opening therethrough, the gas passage opening on each plate being defined in a position staggered with respect to the position of the gas passage opening defined on the next successive plate.

2. Device according to claim 1 in which said material feed pipe has a funnel shaped upper portion.

3. Device according to claim 1 in which the bottom of said vessel has an inwardly extending conical shape.

4. Device according to claim 3, in which said gas inlet means include openings defined through said conically shaped bottom.

5. Device according to claim 1 in which said vessel defines a portion of restricted cross section above the termination of said material feed pipe and in which the portion of said vessel above said restriction widens conically in an upward direction.

6. Device according to claim 5 in which the bottom of said vessel has an inwardly extending conical shape, and in which said gas inlet means include openings defined through said conically shaped bottom.

7. Device according to claim 1 in which said annular plates are conically shaped plates.

8. Device according to claim 7 in which said vessel is a cylindrical vessel.

9. Device according to claim 8, in which said gas inlet and gas outlet means are tangentially positioned with respect to said vessel.

References Cited in the file of this patent UNITED STATES PATENTS McGehee et a1 Nov. 30, 1937 Balassa May 18, 1948 FOREIGN PATENTS Great Britain July 19, 1937 Great Britain Dec. 9, 1941