CLAIMS
1. An apparatus for continuous drying of particulate materials comprising a perforated board with covered perforations (13) for the passage of the drying medium (8) on which the dried material (3) is placed cha racterized in th at the board is made up by a bottom (12) of a drying chute (2) having a rake chain conveyor (4) for advancing the dried material (3) from the input portion (15) of the drying chute (2) to the output portion (16) of the drying chute and the perforations (13) are situated on the lower part of the bottom (12) covered by covering lamellae (14) extending at least to the rims of the perforations (13) directed towards the input portion (15) forming an aperture for passages of the drying medium (8) and on the input portion (15) of the drying chute (2) there is a feed hopper (1) with a formatting device (10) to adjust the thickness of the layer of the dried material (3) in the drying chute (2).
2. The apparatus according to claim 1 characterized in that a sweeping device (11) is located in the output portion (16) of the drying chute (2) to remove the dried material (3).
3. The apparatus according to claim 1 cha racterized i n that the formatting device (10) is made up by a rake chain conveyor with pins or with a revolving cylinder with pins or flights.
4. The apparatus according to claim 2 cha racte rized i n th at the sweeping device (11) is made up by a rake chain conveyor with pins or with a revolving cylinder with pins or flights.
5. The apparatus according to at least one of the claims 1 to 4 characterized in that the perforations (13) are made in the central part of the bottom (12) between the input portion (15) and the output portion (16) of the drying chute (2) and they are undercovered by an air chamber (7) fixed to the lower portion of the bottom (12) into which at least one input of the drying medium (8) from the ventilator (9) is introduced from a side portion.
6. The apparatus according to at least one of the claims 1 to 5 characterized i n that the covering lamella (14) has an inclined portion (17) and a straight portion (18) connected to the inclined portion (17) and is parallel to the bottom (12) in the direction of the input portion (15) of the drying chute (2) extending over the rim of the perforation (13).
7. The apparatus according to at least one of the claims 1 to 5 cha racterized in that the perforations (13) are carried out as piercings of the bottom (12) transversal to the direction of advancement of the dried material (3) and they are stamped into a concave shape on the lower part of the perforated bottom (12). |
Apparatus for continuous drying of particulate materials
Field of the invention
The invention relates to drying particulate materials, particularly to an apparatus designed for continuous drying of such materials. The apparatus is appropriate especially for moist materials with a little free-flowing consistency having tendency to vault such as wood chips, sawdust, bark, agricultural products, municipal waste determined for energetic purposes etc.
Background and summary of the invention
At present drum dryers are most frequently used for drying of the aforementioned materials, consisting of a rotatable drum the dried material is induced into as well as the hot air heated mainly by a gas burner. The disadvantage of these dryers consists in their energetic demand for the drying takes place under high temperatures and also in higher investment and construction intensity as the dryer with the heating device with the communicating conveyor, pollution abatement facility and dust arrester form a relatively large unit. The high temperature of drying often causes the dried materiel to inflame.
Further, belt dryers are known where the dried material is deposited on a movable belt. This solution is technically complicated and cost demanding, having a lower operation reliability.
Further, dryers are known where the dried material is deposited on a perforated board under which hot air is propelled and the material on the board is moved and spread by means of a travelling slide with revolving flights. Such dryer is described for example in the patent document FR 2035 693, where the lower part of the dryer is divided into two drying portions- with a warmer air and a colder air.
The perforations in the board are from above covered with grids or cylindrical covers to impede the clogging up during the movement of the dried material in both senses,
which is disclosed in the patent document DE 43 14 645. A similar dryer for drying forage is described in the patent CZ 251 076.
The German utility model DE 203 16 982 discloses a dryer with an inclined perforated drying board. The hot air is ducted through the perforated drying floor, having a feed screw sweeping the dried material to the outlet opening in the upper part of the drying board.
The disadvantage of the aforementioned dryers consists in the fact that they are designed for drying granulated or free-flowing materials that do not tend to form vaults and that are easily pushed, poured and interstratified. These types of dryers are not appropriate for drying larger volumes of moist particulate biomass having a tendency to form vaults, such as e.g. wood chips, for their drying capacity in relation to the energy input and costs is low.
It is the task of this present invention to create a dryer eliminating the disadvantages of the aforementioned disclosed drying apparatuses.
This task is resolved and the disadvantages are eliminated by the creation of an apparatus for continuous drying of particulate materials according to this invention. The apparatus is based on the principle of moving the dried material on a perforated board blown through by a drying medium placed below.
The merits of this present invention consist in the fact that the board is made up by a bottom of a drying chute having a rake chain conveyor for advancing the dried material from the input portion of the drying chute to the output portion of the drying chute. The rake chain conveyor carries the dried material in a continuous layer in the whole length of the drying chute avoiding the material to spill; the drying medium passes through the whole layer of the material in an upward direction and it exits from the upper layer of the material in the air. The perforations are situated on the lower part of the bottom covered by covering lamellae extending at least to the rims of the perforations directed towards the input portion, eventually they can even overlap the rims, forming an aperture for passage of the drying medium, impeding the
dried material to fall through under the bottom of the drying chute. On the input portion of the drying chute there is a feed hopper with a formatting device to adjust the thickness of the layer of the dried material in the drying chute. The formatting device regulates the supply of dried material from the hopper into the drying chute. It returns the redundant material back to the hopper ensuring thus an even thickness of the layer of the dried material throughout the whole length of the drying chute.
In some kinds of dried material, e.g. wood chips, it is advantageous to regulate even the removal of the dried material from the output portion of the drying chute where a sweeping device is located to remove the dried material. By means of synchronizing the driving mechanism of the main rake chain conveyor and of the sweeping device an effective and continuous operation of the drying apparatus is ensured.
As for the particular construction it is advantageous that the formatting device be made up by a rake chain conveyor with pins or with a revolving cylinder with pins or flights.
Also the sweeping device can advantageously be made up by a rake chain conveyor with pins or with a revolving cylinder with pins or flights.
For an optimal course of the drying and the passage of the drying medium it is advantageous that the perforations be made in the central part of the bottom between the input portion and the output portion of the drying chute and beneath them is an air chamber fixed to the lower part of the bottom into which at least one input of the drying medium from the ventilator is introduced from a side portion. The air chamber and the distribution pipes of the drying medium and the ventilator are designed for the drying medium under a necessary positive pressure to pass through the whole layer of the dried material and to overcome its hydraulic resistance.
As for one construction embodiment of the covering lamellae for the perforations of the bottom it is advantageous that the covering lamellae have an inclined portion and a straight portion connected to the inclined portion and the straight portion be parallel to the bottom in the direction of the input portion of the drying chute. The flow of the
drying medium in an aperture arising in the above described manner is strong enough and conveniently oriented as to impede penetration of the dried material into the air chamber.
In another construction and technologic embodiment, the perforations are carried out as piercings of the bottom transversal to the direction of advancement of the dried material. These piercings are followed by offsets projected in a concave manner to the lower side of the perforated bottom and form thus the covering lamellae the front rim of which corresponds with the rim of the perforations. The dried material fails to fall through this type of aperture, although productionwise this design is very simple.
The advantages of the apparatus for continuous drying of particulate material consist in the fact that it allows for drying of materials that are not free-flowing and tend to create vaults, for the dried material moves in the drying chute in a constant layer that does not mix during drying.
The apparatus is appropriate for using a low temperature drying medium with temperature range from 4O 0 C to 14O 0 C, which allows for secondary use of waste heat from condensing turbines, cooling of compressors, engines, waste gases of engines etc. As the operating temperatures are low the operation of the apparatus is safe and there is no danger of inflammation of the dried material. The temperature of the exiting drying medium and vapours arising from the drying of the material are very close to the ambient temperature so that the specific heat consumption is lower by 30% to 40% compared to the known drum or belt dryers. The investment costs for the apparatus are very low and also its building parameters are small compared to the known dryers, for the dried material is carried as a whole at a very low speed. Due to the very low output speed of the drying medium from the surface of the dried material, the dust is not carried which excludes the need for a dust exhausting device. This is one of the great advantages of the apparatus according to this invention. Due to the low operation speed the operation of the apparatus is very silent compared to common dryers. The principal driving unit of the rake chain conveyor needs a very small electric input compared to common dryers (e.g. in a dryers with an output 1t/hour the input is 0,25 kW compared to 12 kW in a drum dryer
with the same output). The large layer of the dried material moving as a compact unit and the low operation speed enables the drying of the material to a very low final moisture of 4% and the apparatus is therefore appropriate for drying biomass for energetic purposes where a lower moisture means a higher valorization of the fuel.
Compared with the known dryers the construction of the apparatus according to the invention is simpler, more reliable, less demanding for maintenance and requiring significantly lower investment and operational costs.
Brief description of the drawings
The invention will be presented in more detail in the drawings where figure 1 is a vertical longitudinal sectional view of the apparatus, figure 2 is a cross section through the A-A plane and figure 3 is a view of the lower part of the perforated bottom with the concave covering lamellae.
Examples of preferred embodiments
It should be understood that the hereinafter described and shown specific examples of embodiments of the invention are represented as examples only, not as a limitation of the invention. Those skilled in the art will find or will be able to find by routine experimenting a greater or smaller number of equivalents of the present invention, described here in a specific embodiment. Also these equivalents shall be included in the claims for protection.
In the embodiment shown in fig. 1 and 2 the apparatus is made up by the drying chute 2 having a perforated bottom 12 and full side walls 21 The chute 2 is a weldment of a steel sheet metal and carrier beams. The input portion 15 of the chute 2 makes up a feed hopper 1 into which the dried material 3 from the feeding conveyor Ij) falls, e.g. wood chips. The movement of the dried material 3 in the drying chute 2 towards the output portion 16 is secured by the rake chain conveyor 4 made up by rakes 4^ fastened to the link chain 5 driven by chain wheels on the drive shaft 6. The drive of the drive shaft 6 can be made as an electric motor with a
gearbox or can be made by discontinuous rotation by means of a latch mechanism latch-locking ratchet propelled by a hydraulic cylinder. This solution is simple, reliable and has a small consumption of electric energy.
The dried material 3 moves through the drying chute 2 as . a compact whole being blown through by the drying medium 8, most frequently hot air, driven by a ventilator 9 from a source not shown here via the respective distribution pipes through the side into the air chamber 7, made as a sheet metal weldment and fixed to the lower part of the bottom 12 of the chute 2 so that it overlaps the perforations 13 through which the drying medium 8 flows into the dried material 3, from which, together with the steam it exits through the free surface of the material 3 to the ambient atmosphere. The positive pressure in the air chamber 7 must surpass the hydraulic resistance of the material 3. To impede the clogging up of the perforations 13 by the dried material 3 moving on the bottom 12, are these covered by covering lamellae 14 made from sheet metal provided with an inclined portion 17 and a straight portion 18 which runs parallel to the lower part of the bottom 12. The covering lamella , 14 overlaps the rim of the perforation 13 and forms an aperture for the drying medium 8 to penetrate from the air chamber 7 into the dried material 3. The apertures are oriented in such way that the output of the stream is in the direction of the movement of the material 3, impeding the material 3 to fall through and to clog up the perforations 13 (this embodiment is shown in fig. 1 and 2).
Another embodiment of the perforated bottom 12 with perforations 13 secured against clogging up by the dried material 3 is shown in fig. 3. The perforation 13 is made as a transversal piercing of the bottom 12. By stamping the pierced portion of the bottom Xλ downwards a covering lamella 14 occurs, e.g. in the shape of a part of a cone surface that does not overlap the rim of the perforation 13, nevertheless it surprisingly also impedes the dried material 3 to fall through during drying.
On the output portion 16 the dried material 3 falls from the drying chute 2 on an offtake conveyor 20. For the output of the material 3 to be smooth the output is provided with a sweeping device H, carried out in the form of a rake chain conveyor the rakes
of which are provided with pins 22 to plough out the dried material 3 from the chute 2 smoothly.
On the output portion 15 of the drying chute 2 in the feed hopper 1 there is situated a formatting device IjO the task of which is to adjust the maximum thickness of the layer of the dried material 3 before it enters the drying chute 2 for the layer to be constant and correspond to the type of dried material 3 and the required parameters of drying. The formatting device IQ is also made up by a small rake chain conveyor with rakes provided with pins 22. In the embodiment of the formatting device JhO and sweeping device H with rakes the drying of the material 3 is appropriate in layers from 0,3 to 1 ,5 m but for smaller thicknesses of layers another embodiment can be applied, e.g. revolving cylinders with pins or flights.
The width and length of the apparatus is chosen according to the required output of the apparatus, according to the dried material 3. The thickness of the layer, the amount of the dried material and the temperature of the drying medium is monitored by means of a control unit not shown here.
Industrial applicability
The apparatus according to the invention can be used for continuous drying of particulate materials the particle size of which extend from 3 to 100 mm. The dried material may not be sticky but it need not be free-flowing material and can form vaults. In preference the apparatus is applicable for drying agricultural products, wood waste, wood chips, municipal waste determined for energetic purposes etc.
Overview of references
1 feed hopper
2 drying chute
3 dried material
4 rake chain conveyor
5 link chain
6 drive shaft
7 air chamber
8 drying medium
9 ventilator
10 formatting device
11 sweeping device
12 bottom
13 perforation
14 covering lamella
15 input portion
16 output portion
17 inclined portion
18 straight portion
19 feeding conveyor
20 off-take conveyor
21 side wall
22 pins