FI79753C - Process for drying powdered, granular, particulate or equivalent material - Google Patents

Description

79753 1 Method for drying powdered, granular, chipped or similar material Förfarande för torkning av pulverformigt, kornigt, spanformigt eller motsvarande material 5

The invention relates to a method for drying a powdery, granular, chipped or similar material, in which the material to be dried is mixed with a magnetic material at least during drying and that the drying material is dried in a mixture of said material to be dried by applying heat to said mixture and the mixture. the material and the dried material are separated on the basis of magnetism by one or more magnetic separators or the like, and wherein the dried material is passed on for use and the magnetic material is returned to the mixture of the material to be dried and the magnetic material.

The drying method according to the invention is suitable for use, for example, in the drying of various solid fuels, such as peat, wood chips or shavings and also cereals, various foodstuffs, fodder and powdered or granular products of the chemical industry.

Several different methods are known for drying solid fuels. FI patent 11,200 discloses a method in which the drying of an aqueous substance is carried out regeneratively by mixing hot particles heated in a heat source, e.g. flue gases, with the substance to be dried. The method requires that the heat carrier particles be heated as hot as possible in order to keep the material flow of the heat carrier particles reasonable. Therefore, the method is poorly suited for drying temperature-sensitive organic substances. This disadvantage can be eliminated by implementing the slurry with the fluidized bed technique. The fluidized bed technology is characterized by the uniform warmth of the mattress. One drying method is shown e.g. FI patent-35 in application 832049, in which the drying is carried out on the principle of a fluidized bed. In the method according to this publication, the drying is carried out in a special drying plant consisting of a tank through which 2 79753 l of pipes have been passed, through the pipes of which the flue gases coming from the boiler have been passed. The tank of the drying plant has a layer of sand arranged as a "mattress" on top of the grate, which is heated by flue gases passing through said pipes. The fuel to be dried is passed through said mattress material 5, whereby the moisture contained in the fuel evaporates as the fuel passes through the heated sand layer. The fuel is then passed to a cyclone where water vapor is separated from the fuel, and the fuel is then fed to a boiler for combustion.

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In the method described above, a considerable amount of sand used as mattress material remains in the dried fuel, which is recovered only after combustion. Therefore, this method is only suitable for use with boilers where there may be sand among the fuel 15. Thus, such a method cannot be used in cases where the dried material should be as clean as possible, i.e. when sand is not allowed in the dried material. The method according to FI publication 832049 described above can, of course, be supplemented with various cleaning devices, such as sieves or the like, but these do not in all cases achieve a sufficient degree of purity. In addition, the particle size of the sand used as the mattress material has to be kept quite large in previously known methods. However, when a large particle size is used, the heat transfer coefficient between the mattress material and the indirect heat exchanger remains quite poor.

With regard to the prior art, reference is further made to U.S. Patents 4,247,987, 4,254,558, 4,463,502, 4,349,967 and 4,488,958 and DE 556,385 and 3,225,647. U.S. Patents 4,247,987 and 4,254,558 disclose -30 ty solutions in which a magnetic field and magnetic material are used to stabilize the mattress by surrounding the fluidized bed with a magnetic field. In U.S. Patents 4,463,502 and 4,349,967, magnetic fields are used to control the flow of material by a solenoid valve. U.S. Patent 4,488,958, on the other hand, relates to magnetic separation in general. DE 35 556 385, on the other hand, generally discloses the principle of mixing, which, however, is not the mixing of the material to be dried with the magnetic material, and DE 3 225 647 relates to the general fluidized bed technique.

It is an object of the present invention to provide a method for drying a powdery, granular, chipped or similar material which does not have the above-described disadvantages of the prior art methods. To achieve this, the invention is characterized in that the drying of the material to be dried is carried out in a vessel or the like in such a way that the heat required for drying is indirectly passed through a heat exchanger to the mixture of material to be dried and magnetic material.

Advantages of the method according to the invention over previously known drying methods can be pointed out e.g. following. Separation of the material to be dried from the material in which the drying is performed is very advantageous because a magnetic material is used as the material. The material to be dried can then be separated from the other material by the so-called

15 of mattress material, e.g. using magnetic separators. As a result, the method according to the invention is very well suited for use in cases where foreign matter is not allowed among the dried material. Due to the above, since the dried material is well separated from the mattress material, the mattress material can be very finely divided in composition. This, in turn, results in a very good heat transfer coefficient between the mattress material and the indirect heat exchanger. Thanks to the good heat transfer, the equipment in which the drying is performed can be constructed to be small in size. As a result, the cost of installing the equipment is considerably lower than with equipment using previously known methods. Since a very fine material can be used as the magnetic material, said fine material improves the flowability of the material to be dried in different parts of the dryer. The magnetic material also helps to keep the surfaces of the dryer clean.

The invention will now be described in more detail with reference to the figures of the accompanying drawing. The devices according to the figures are shown only to illustrate the present invention, and the method according to the invention is not limited only to the embodiments shown in the figures.

4 79753 1 Figure 1 shows a schematic schematic diagram of a heated fluidized bed dryer which can be used to carry out the method according to the invention.

Figure 2 is a schematic cross-sectional view of a magnetic separator used in the method according to the invention.

Reference is first made to Figure 1, which schematically shows the principle of operation of a fluidized bed dryer 10 operating by the method according to the invention. In the system according to Figure 1, the main parts of the apparatus are a drying tank 11, in which the drying of the material to be dried is performed, a cyclone 20, in which a drying gas, e.g. superheated water vapor, is separated from the material to be dried, and a magnetic separator 30. The dryer tank 11 of the fluidized bed dryer can be, for example, an upright cylindrical vessel as shown in Fig. 1. At the lower end of the drying tank 11, near the bottom of the tank, a grate 12 with holes is mounted, on which a drying mattress of magnetic material A is formed as a mattress. As the magnetic mattress material A, a finely divided particulate or sandy material is used, e.g.

20 magnetites, although other magnetic materials are also suitable for use in the method of the invention.

Inside the drying tank 11, a heat exchanger 14 is installed, in which, for example, high-pressure water or steam is circulated, which heats the magnetic mattress material A and the material to be dried B. The dry tank 11 preferably has magnetic mattress material A to cover the heat exchanger 14 in the tank. wholly. A feed connection or the like 15 is formed in the lower part of the dryer tank 11, above the grate 12, from which the material B to be dried is fed under the mattress material 30, on top of the grate 12. The supply connection 15 can advantageously be provided, for example, with a screw-like feeding device with which the material B to be dried can be fed into the magnetic mattress material A. In the lower part of the dryer tanks 11, below the grate 12, a supply pipe 19 is formed, from which the drying gas C used for drying the material is fed into the dryer tank 11, the material to be dried B and the magnetic mattress material A.

li 5 79753 1 A first polystube 16 is formed in the upper part of the dryer tank 11, from which the drying gas C passing through the dryer tank 11 and with it a small amount of dried material B 'and magnetic mattress material A are removed from the dryer tank 11 to cyclone. a paddle pot 18 arranged in the dryer container 11 at such a height that a mixture of mattress material A and material to be dried B covers the mouth of said second outlet tube 18. The second outlet pipe 18 is provided, for example, with a screw conveyor or the like, with which the mixture of the magnetic mattress material A and the dried material B 'is removed from the dryer tank 11.

As already stated above, part of the dried material B *, together with a small amount of mattress material, passes with the drying gas C from the as-15 only tank 11 through the first outlet pipe 16 to the cyclone 20. The cyclone 20 separates solids from the drying gas. 21 to the magnetic separator 30. The drying gas C, in turn, is led out of the cyclone 20 via an outlet line 22 via a circulating duct 20 but 24, from which it is fed again from the supply pipe 19 into the dryer tank 11, for example by means of a fan 25.

Only one cyclone 20 is marked in Figure 1, but in practice it may be advantageous to arrange several from the cyclone 20 in succession, so that the imaging gas and solids can be better separated. It was further stated above that a mixture of magnetic mattress material A and dried material B 'is removed from the dryer tank 11 from the mattress via a second outlet pipe 18 by means of a screw conveyor and passed to a magnetic separator 30. In practice said second outlet pipe 30 18 can be connected to a solids outlet 21 after.

It was stated above that in the dryer according to Fig. 1, instead of the commonly used drying gas, air, superheated steam C can be used as the drying gas C. The superheated water vapor is obtained in the system during drying from the dried material B. The superheated water vapor is in many ways cheaper than air. First, if 6 79753 l of air is used as the drying gas for drying, the system becomes very flammable if the dried material is highly flammable. When superheated water vapor is used as the drying gas, the energy consumption of the drying process can be substantially reduced, e.g. by condensing the heat released for heating purposes. Furthermore, by constructing the dryer in several stages, in which a different pressure is applied in each stage, the water vapor released from the dryer operating at a higher pressure can be used to heat the dryer operating at a lower pressure. In addition, in a single-stage dryer, the released water vapor can be compressed to a higher pressure and used as the heater itself to heat the damper.

As already stated above, after drying, the mixture of magnetic mattress material A and dried material B 'is passed along the supply connection 31 to the magnetic separator 30, the structure and operation of the magnetic separator 30 are discussed in more detail in Fig. 2. The magnetic separator 30 separates the magnetic mattress material A and the dried material B 'apart. The magnetic separator 30 is provided with separate outlet connections 32 and 33 for the dried material B 'and the magnetic mattress material A. The mattress material A may be introduced into the dryer container 11 from the top of the container, as indicated by reference numeral 33, or the mattress material may be introduced into the material supply connection 15 of the material to be dried, as indicated by reference numeral 33A and shown in broken lines. Figure 1 schematically shows that there is only one magnetic separator 30 in the system. However, in order to improve the degree of separation, several successive magnetic separators can be connected to the system. In the preliminary separation tests, the dried material B 'leaving the fluidized bed dryer 10 had 25% of the mattress material A before the magnetic separator 30 and only 2% after the magnetic separator 30.

Figure 2 is a schematic cross-sectional view of a magnetic separator 30 used in the method of the invention. The magnetic separator 30 comprises a substantially cylindrical jacket 36 having a feed connection 31 for a mixture of magnetic material A and dried material B * and outlets 32 and 33 for dried material B '. and for magnetic material A. Inside the cylindrical shell 36 is

II

7 79753 1 is a metal cylinder 34 rotatably mounted substantially concentrically with said jacket 36 so that a certain amount of clearance is left between the outer surface of the metal cylinder 34 and the inner surface of the jacket 36. Inside the rotatable metal cylinder 34, a magnet 35 is arranged in the immediate vicinity of the inner surface of the metal cylinder, as shown in Fig. 2, which extends in the circumferential direction of the metal cylinder 34, as shown in Fig. 2, from the supply connection 34 over each outlet 32 and 33.

When a mixture of magnetic material A and dry material B 'is fed to the magnetic separator 30, the magnetic material A adheres to the surface of the metal cylinder 34 by the magnet 35 while the dried material B passes freely in the clearance between the metal cylinder 34 and the magnetic separator shell 36. The outlet connections 32 and 33 are arranged in the jacket 36 so that the outlet connection 32 of the dried material B 'is in the direction of rotation of the metal cylinder 34 before the outlet connection 33 of the magnetic material A. Thus, the dried material B * exits said outlet connection while the magnetic material A passes through the magnet 35 the effect of adhering to the metal cylinder 34 past the dried material outlet 32 and detaching from the metal cylinder 34 only after passing the area of action of the magnet 35 and then exiting the magnetic separator 30 through the magnetic material outlet 33.

The structure of the magnetic separator 30 may be different from that shown in Figure 2, as the embodiment according to the figure is only intended to illustrate the invention. By utilizing a magnetic material and a magnetic separator, for example, a considerable advantage is obtained over previously known fluidized bed dryers in that a much finer material can be used as the mattress material than before. In previously known methods and devices, the particle size has to be kept at about 1 mm, while in the method according to the invention, a mattress material with a particle size of, for example, 0.20-0.50 mm can be used. The thermal bridging coefficient between the mattress material and the indirect heat exchanger in the conveyor is then considerably better than in previous methods.

The invention has been described above with reference to the figures of the accompanying drawing. However, the method according to the invention is not intended to be limited solely to the embodiments shown in the figures. Thus, it is essential for the method according to the invention that the material B to be dried is mixed with the magnetic material A and that the drying of the material B to be dried is carried out in a mixture of materials A and B. Furthermore, based on magnetism, it is essential for the invention that, after drying, the materials are separated from each other and the magnetic material separated from the mixture is returned to the dryer used in the process.

In other respects, reference is made to the appended claims, within the scope of which it is intended to define the various details of the invention.

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Claims (7)

9 79753 A method for drying a powdery, granular, chipped or similar material, wherein the material to be dried (B) is mixed with the magnetic material (A) at least during drying, and the drying of the material to be dried (B) is performed by drying said material (B) and the magnetic material (A). ) by applying heat to a mixture of said materials (A) and (B) and wherein, after drying, the magnetic material (A) and the dried material 10 (B ') are separated on the basis of magnetism by one or more magnetic separators (30) or the like and wherein the dried material (Bf ) is passed on for use and the magnetic material (A) is returned to the mixture of drying material (B) and magnetic material (A), characterized in that the drying of the drying material (B) is carried out in a vessel or the like so that the heat required for drying is indirectly a mixture of material (B) and magnetic material (A) to be dried via a vacuum (14). 1 Claims Method according to Claim 1, characterized in that the drying is carried out on the fluidization principle in such a way that a mixture of the material to be dried (B) and the magnetic material (A) is fluidized with a drying gas (C). Method according to claim 2, characterized in that the drying gas (C) used for fluidizing said material mixture (A and B) is recycled in a closed cycle in the drying process. Method according to Claim 2 or 3, characterized in that superheated steam is used as the drying gas (C). Method according to one of the preceding claims, characterized in that the magnetic material (A) used for drying is a finely divided and particulate material. 35 10 79753 Method according to Claim 5, characterized in that the particle size of the magnetic material (A) is of the order of 0.20 to 0.50 mm. Method according to one of the preceding claims, characterized in that the magnetic material (A) is magnetite. 10 15 20 25 30 35 11 79753