GB2043224A

GB2043224A - Method and apparatus for drying granular material

Info

Publication number: GB2043224A
Application number: GB8004584A
Authority: GB
Original assignee: Kloeckner Humboldt Deutz AG
Current assignee: Kloeckner Humboldt Deutz AG
Priority date: 1979-02-26
Filing date: 1980-02-12
Publication date: 1980-10-01
Also published as: ES488782A1; DK79880A; FR2449860A1; DE2907481A1

Abstract

A method and apparatus for drying granular but lumpy material 3 comprises a drying process divided into three parts, which drying takes place in a preliminary drying device, a pulverising and drying device, and a subsequent drying device 6. The preliminary device and the pulverising device may comprise respectively radial arms on a horizontal, rotatable shaft, and a wheel on the same or a different, offset, shaft, and both devices may be in a common casing 1. Hot gas 5 is delivered to the casing 1, and acts, with the arms of the first device, to transport the material through the casing to a flow drier 6. Coarse material may be recycled via 8. <IMAGE>

Description

SPECIFICATION A method and apparatus for drying fine-grain materials The invention relates to a method of drying moist, granular but lumpy material such as filter cake obtained when filtering raw cement slurry. The invention also relates to a device suitable for carrying out this method of drying.

In order to dry moist fine-grain materials, it is known and common to use a flow drier. If however the material to be dried which is ready to be processed is notfiowable or if it has agglomerated and will not yield its internal cohesion even during the drying process, special measures have to be taken in order to be able to use the flow drier despite this. The main measures at present are mixing the moist material with material which has already been dried with helically arranged paddles for example, drying the material in circulation with the aid of a separator in the flow pipe and crushing the agglomerated grains (see Krisher/Kroll, Trocknungstechnik, 2nd Volume, 1959, published by Springer-Verlag, Berlin/Gottingen/Heidelbergl.

However there are fine-grain materials of this type which are not broken up into very fine granulate by mixing them with material which has already been dried, as mentioned earlier, as successfully as was desired, because conditions were encountered during the mixing process which led to the formation of lumps. In addition, because of its plasticity, this lumpy feed material cannot even be broken down by means of impact pulverising with the aid of an appropriate impeller. In such a case, the flow drier can only be used to a certain extent, if exceptionally high flow speeds in the flow pipe are used, these high flow speeds being necessary for conveying the very coarse proportions of the material pneumatically.Energy consumption in the drying process rises sharply because of this, thus resulting in methods and devices which are not very economical and in some cases are not viable at all.

The present invention seeks to provide a method of drying these difficult materials in the manner described: filter cake obtained when filtering raw cement slurry being one of such difficult materials.

The invention also seeks to provide apparatus suitable.

According to a first aspect of the invention, there is provided a method of drying moist, granular but lumpy material, wherein the drying process is subdivided into preliminary drying, pulverising and drying and subsequent drying.

Thus the feed material is dried preliminarily and broken down subsequently, if necessary, and is then subjected to residual drying. Moist raw cement powder may also be dried in this way, the raw cement powder containing a moisture content of approximately 15 to 20% after the raw cement slurry has been filtered by means of filter presses for example. In the first instance, this agglomeration of the grains may be broken up by the method of drying in accordance with the invention and pulverises to such an extent that intensive drying of the moist and agglomerated fine-grain materials may take place and that then almost dry fine-grain to dust-fine feed material is available for possible subsequent thermal treatment.

Initial or preliminary drying may be accomplished by means of centrifugal drying. This type of drying carries out the necessary pulverising of the feed material which has become caked together because of its moisture content, and this pulverising takes place, for example, with the movement pulten which is brought about by a high-speed (helicat) paddle arrangement.

The pulverising and drying may be carried out with the aid of impact drying so that, after preliminary drying, the pulverising and break-up of the feed material which has become caked is effectively promoted and the material is made finer.

Subsequent drying or redrying may take place in a flow dryer preferably in circulation, so that the coarser components of the material which have been separated during flow drying are brought back into the preliminary drying stage or the pulverising and drying stage and may be repulverised.

According to a second aspect of the invention, there is provided apparatus for drying moist granular but lumpy material wherein the apparatus comprises a device for preliminary drying, a device for pulverising and drying, and a device for subsequent drying.

Preferably the devices for preliminary drying and those for pulverising and drying are housed in a casing common to both, the casing being connected to a flow drier. A very compact drying device may thus be achieved which also has advantages in terms of the method used besides having the design advantage that the moist and lumpy material may immediately be fed in to the active region of the hot gas flow of the drying device and then drop downwards into the casing through the flow of hot gas. It is then broken up and hurled around again and again in the flow of hot gas inside the casing until the predried material passes the pulverising and drying region inside the casing and may be supplied from the casing directly to the flow drying device.

The device for predrying may be constructed as a centrifugal drier, preferably in the form of an impel ler shaft the lumpyfeed material being largely broken up in the first part of the drier casing and being hurled around again and again in the flow of hot gas inside the casing. The material may be transported by the impeller shaft if it has inclined impeller arms like a (helical) paddle arrangement.

The impeller of the pulveriser and drier may be arranged and mounted separately and be connected to a separate drive so that during pre-drying or pulverising and drying process may be controlled separately in each case in accordance with the properties of the feed material. The impeller of the pulverising and drying device may be seated on the shaft of the centrifugal drier thus providing simple and uncomplicated design for the drying device which is particularly suitable for a feed material which may be broken up and dried relatively easily.

The flow drier used for re-drying may be constructed as a circulation drier so that the fairly coarse grains of material separated out in the flow drier may be passed back into the impact region of the pulverising impeller and repulverised there.

The invention will now be described in greater detail, by way of an example, with reference to the drawings, in which; Figure 1 shows the drying device comprising a joint casing for pre-drying and pulverising and drying and a flow drier connected thereto which is designed for re-drying; Figure 2 is a longitudinal section of the preliminary dryer and pulveriser and dryer taken along the line II - II of figure 3; Figure 3 is a longitudinal section of the preliminary dryer and pulveriser and dryer taken on the line Ill Ill of figure 2; Figure 4 is a section taken on the line IV - IV of figure 2; Figure 5is a section taken on the line V - V of figure 2.

Figure 6 is a view similar to figure 2 of a modified embodiment, taken on the line VI - VI of figure 7, and Figure 7 is a section taken on the line VII - VII of figure 6.

In Figure 1 a drying device is shown in perspective view. A casing 1 in which are arranged both an impeller shaft and an impeller wheel for pre-drying and drying and grinding, pulverising respectively has a feed valve 2 for the material to be dried and an inlet opening 4forthe hot drying gases SAt the outlet end, the casing supports a flow drier 6 with a separating device 7 and a return line 8 for the coarse grains, with a separating cyclone 9 and an extraction valve 10 for dried fine-grain material 11 and finally a waste gas blower 12.

In Figures 2 to 5 the drying casing for drying moist fine-grain materials is shown in various sections. An impeller shaft 14 is inserted into a trough-shaped casing 13 and is mounted in the bearings 15 outside the casing and is equipped with a V-belt pulley 16, for example, for the drive.

While at one end of the casing there is an inlet opening 17 for the hot drying gas and a feed valve 18 for the material to be dried, the other end of the casing is provided with a broadened portion 19 which accommodates an impeller wheel 20. This impeller wheel 20 is also mounted in the bearings 21 outside the casing and is equipped in turn with a V-belt pulley 22, for example, for the drive.

In the top of the same casing end, an outlet opening 23 for gas and material for connection to the flow drier located in the vertical projection between the impeller shaft and the impeller wheel. The flow drier itself is not shown here for clarity but can be seen in Figure 1.

A valve 24 for re-entry of the coarse material obtained from the separator during (circulation) is provided in the broadened portion 19 of the casing.

In orderto screen off the impeller shaft from material which might hit against it, an angle guide is located in the region of the impeller wheel 20. However other impact surfaces (not shown) may be arranged in this region in order to assist the pulverising action of the impeller wheel 20 if necessary.

Another especially suitable shaping of the drying device in accordance with the invention is shown in section in Figures 6 and 7. An impeller shaft 26 is arranged in turn in a trough-shaped casing 27 which is provided at one end with an inlet opening 28 for the hot drying gases and with a feed valve 29 for the material to be dried while the other casing end has the broadened portion 31 for accommodating the impeller wheel 30, atthe top of which broadened portion 31 above the upward moving side of the impeller wheel the outlet opening 32 is located for gas and material. The flow drier is connected here and is shown in Figure 1.

Above the downward moving side of the impeller wheel 30 is located a valve 33 for re-entry of coarse material which has been separated out in the flow drier 6 during circulation drying. The impeller wheel 30 is seated on the impeller shaft 26 in this type of embodiment of the drying device and the shaft is in turn mounted, outside the casing 27, in bearings 34 and is equipped with a V-belt pulley 35 for a drive belt which is connected to a drive (not shown).

The method using the drying device will now be described with reference to Figures 1, 6 and 7. The moist fine-grain material 3, which is to be dried, is fed with the aid of the feed valve 2, 29 at that point in the casing 1,27 at which the drying gases 5 are introduced via the gas inlet 4, 28. The lumps of material thus immediately fall through the flow of hot gas in a downward direction and are broken up by the impeller shaft 26 and are hurled about again and again in the flow of gas within the casing while the material which has been pre-dried is transported towards the impeller wheel 30 at the outlet opening 32, by the flow of gas and/or by impeller shaft arms which are inclined like (helical) paddles.The portion of the material which is already sufficiently fine for pneumatic transportation is extracted directly from the casing by the drying gas in the region of the impeller wheel 30, while the portions of material which are too coarse for this fall into the impact region of the impeller wheel 30 and are pulverised thereby until they have achieved a fineness which is sufficient for pneumatic extraction into the flow drier 6. Fairly coarse grains which have been separated, in the flow drier, by the separating device 7 during circulation drying are brought back into the impact region of the impeller 30 via the coarse grain return line 8 and the coarse material valve 33 for repulverising. The dried fine-grain feed material is separated from the drying gases in the separating cyclone 9 and is supplied for further use, for example to a cyclone heat exchanger for dry raw cement powder, via the extraction valve 10. The drying gases released from the fine-grain material in the separating cyclone 9 are finally drawn off from the drying device with the aid of the waste gas fan 12.

Claims

1. A method of drying moist, granular but lumpy material, wherein the drying process is subdivided into preliminary drying, pulverising and drying and subsequent drying.

2. A method according to Claim 1, wherein the preliminary drying is carried out by means of centrifugal drying.

3. A method according to Claim 1 or 2, wherein the pulverising and drying are carried out by means of impact drying.

4. A method according to claim 1, 2, or 3, wherein that subsequent drying takes place in circulation in the form flow drying.

5. Apparatus for drying moist granular but lumpy material wherein the apparatus comprises a device for preliminary drying, a device for pulverising and drying and a device for subsequent drying.

6. Apparatus according to Claim 5, wherein the devices for preliminary drying and the devices for pulverising and drying are housed in a casing common to both which is in connection with a flow dryer for subsequent drying.

7. Apparatus according to Claim 6, wherein the device for preliminary drying is constructed as a centrifugal drier.

8. Apparatus according to claim 7, wherein the centrifugal device comprises an impeller shaft.

9. Apparatus according to any one of claims 5 to 8, wherein the pulverising and drying device has an impeller wheel retained in special bearings and connected to a separate drive.

10. A device according to Claim 9, wherein at least one angle guide is arranged in the region of the impeller wheel to screen off the impeller.

11. A device according to Claim 8 or any claim appendent directly or indirectly thereto, wherein approximately in the vertical projection between the impeller shaft and the impeller wheel, the upper face of the casing has an outlet opening for gas and material to which the flow drier is subsequently connected.

12. A device according to Claim 8 or any claim appendent directly or indirectly thereto, wherein the impeller wheel of the pulverising and drying device is arranged on the shaft of the centrifugal drier.

13. A device according to Claim 12, wherein the outlet opening for gas and material which is connected to the flow drier is arranged above the upward moving side of the impeller wheel in the casing.

14. A device according to any one of Claims 6 to 13, wherein the flow drier used for drying is constructed as a circulation drier.

15. A device according to Claim 14, wherein the circulation flow drier has a separator device which is connected to the casing via a coarse grain return line and a coarse grain valve.

16. A device according to Claim 15, wherein the coarse grain valve is arranged in the casing above the downward moving side of the impeller wheel.

17. A method of drying fine grain material substantially as described herein with reference to the drawings.

18. Apparatus for drying fine grain material substantially as described herein with reference to the drawings.