CH707049A2

CH707049A2 - Method and device for treating wood pellets.

Info

Publication number: CH707049A2
Application number: CH14512013A
Authority: CH
Inventors: Stefan Wagner
Original assignee: Wagner Lizenzvermarktung Gmbh
Priority date: 2012-09-18
Filing date: 2013-08-26
Publication date: 2014-03-31
Also published as: AT513459A2; AT513459A3; DE102012108782B4; DE102012108782A1

Abstract

The invention relates to a method and a device for treating pellets (1), in particular wood pellets, wherein the pellets are introduced into a gas stream (2) in a windshaker in order to discharge fine particles (3). The invention provides for the gas stream (2) and / or the pellets (1) to be at least partially ionized by means of an ionization device (4).

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The invention relates to a method and a device for treating pellets, in particular wood pellets, according to the preamble of claims 1 and 2.

[0002] Wood pellets are used to an ever greater extent as dry fuel. Since wood pellets can primarily be produced from sawn products, it is an ecologically high-quality and carbon-neutral fuel. The wood pellets are usually produced near the raw material source, eg in sawmills or planers, where wood waste or sawed products are produced. The raw materials for the production of the wood pellets are first comminuted and then formed into pellets in a pelletizing plant. The pellets are usually rod-shaped and have diameters between 4 mm and 25 mm.

Due to their properties, which are essentially caused by the production process, wood pellets tend to form dust, which is essentially caused by material abrasion on the surface of the pellets. The abrasion of fine and fine particles from the surface of the pellets is caused above all by mechanical stress, in particular when transporting the pellets and when they are introduced into bearings. The abraded fine and fine particles are noticeable as dust particles in a pellet bed and are disadvantageous for the use of wood pellets as dry fuel. Too high fine and fine particles in a pellet deposit reduce the calorific value and impair the ignition behavior in the burner.

[0004] It is known from the prior art to remove fine particles from a pellet bed by screening processes. For this purpose, screen drums and sieve systems with trickling surfaces are used, for example. However, these screening processes are generally not sufficient to reduce the fine and fine particles in a pellet bed to an acceptable level.

WO 2011/057 608 A1 has already proposed a method for processing wood pellets by which the wood pellets are to be made more resistant to mechanical stress. In this process, the wood pellets are transported by means of a conveying device via a transport path, an elasticity-increasing additive which reduces the material stresses and at the same time lubricating and dust-binding additive is added to the wood pelts on the transport path through the conveying device. The dust-binding additive is an oil or a molten or liquid wax or fat which is intended to bind the fine particles in the pellet bed, which are formed in particular by abrasion from the surface of the pellets, to the pellets.

[0006] This method has proven disadvantageous because clogging can occur when the viscous or waxy additive is introduced. These can, in particular, when the additive is combustible, lead to vapors in the pellet heating system.

SUMMARY OF THE INVENTION The object of the invention is to provide a method and a device for the treatment of wood pellets with which the fine and fine particles can be removed as efficiently as possible in a pellet bed.

[0008] This object is achieved by a method with the features of claim 1 and with a device having the features of claim 2. Preferred exemplary embodiments of the method and the device are given in the dependent claims.

The invention proceeds from the realization that the screening processes which are conventionally used for removing fine particles and fine particles from wood pellet fillings frequently do not bring the desired result and are not sufficient for the fine and fine particles in a wood pellet bed Tolerable fractions. Surprisingly, it has now been found that the fine and fine particles in a wood pellet bed can not be removed to the desired degree by conventional screening methods because the fine and fine particles adhere to the surface of the pellets due to electrostatic attraction forces and are therefore not Can be separated from the pellets in the conventional screening process. The invention provides for the discharge of fine and fine particles from a pellet bed,

[0010] Due to the (at least partial) ionization of the gas stream and / or the pellets themselves by means of an ionization device, surface charges can be dissipated at the surface of the pellets. This results in the reduction or complete elimination of the electrostatic adhesion forces by which the fine and fine particles adhere to the surface of the pellets. By the reduction or elimination of these electrostatic adhesion forces the adhesion of the fine and fine particles on the surface of the pellets is solved and the fines and fine particles released thereby can be discharged from the pellet bed by means of the gas stream.

[0011] These and other advantages of the invention will be apparent from the exemplary embodiments described in more detail below with reference to the accompanying drawings. The drawings show:

1 is a sectional view of a device for treating pellets according to the invention in a first embodiment;

FIG. 2 shows a device according to the invention for the treatment of pellets in a two embodiment; FIG.

3: Schematic representations of various embodiments of a method according to the invention for the treatment of pellets.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows a first embodiment of a device for treating pellets with which fine and fine particles can be removed from a pellet bed. Fine and fine particles are understood here to mean all dust, fine and fracture fractions of pellet beds whose particles are smaller than 4 mm. This corresponds to DINplus for wood pellets, according to which pellets are considered to be both intact pellets and fragments having a diameter of more than 4 mm.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The device for treating pellets of FIG. 1 comprises a sieving device 9 as well as a windscreen 7 connected thereto. The sieving device 9 comprises a coarse screen 9a and a fine screen 9b as well as a pellet screen 12. Both the coarse screen 9a and The fine screen 9b comprises a trickle surface which is at an angle to the horizontal, the trickle surface of the fine screen 9b being arranged below the trickle surface of the coarse screen 9a so that the particles falling through the trickle surface of the coarse screen 9a can fall onto the trickle surface of the fine screen 9b. Through the pellet feed 12, which is connected to a pellet storage, for example a silo filled with pellets, a pellet bed to be cleaned of fine and very fine particles is fed to the apparatus. The (introduced into the pellet line 12 (and in FIG. 1) are first screened in the coarse screen 9a, in order to eject larger foreign bodies. The finer pellets trickle down through the coarse screen 9a onto the trickling surface of the fine screen 9b. Through the fine screen 9b, loose fine particles and finest particles as well as pellet fragments fall which are smaller than the mesh width of the fine sieve 9b. The fine fraction of the pellets is preferably between 0.08% and 1.2% after fine screening and is suitably about 0.1%. The pellets remaining on the pouring surface of the fine sieve 9b are conveyed onto a chute 13 by means of a conveying device. From there, the pellets enter the screen 7, which is connected to the screening device 9. The finer pellets trickle down through the coarse screen 9a onto the trickling surface of the fine screen 9b. Through the fine screen 9b, loose fine particles and finest particles as well as pellet fragments fall which are smaller than the mesh width of the fine sieve 9b. The fine fraction of the pellets is preferably between 0.08% and 1.2% after fine screening and is suitably about 0.1%. The pellets remaining on the pouring surface of the fine sieve 9b are conveyed onto a chute 13 by means of a conveying device. From there, the pellets enter the screen 7, which is connected to the screening device 9. The finer pellets trickle down through the coarse screen 9a onto the trickling surface of the fine screen 9b. Through the fine screen 9b, loose fine particles and finest particles as well as pellet fragments fall which are smaller than the mesh width of the fine sieve 9b. The fine fraction of the pellets is preferably between 0.08% and 1.2% after fine screening and is suitably about 0.1%. The pellets remaining on the pouring surface of the fine sieve 9b are conveyed onto a chute 13 by means of a conveying device. From there, the pellets enter the screen 7, which is connected to the screening device 9. The fine fraction of the pellets is preferably between 0.08% and 1.2% after fine screening and is suitably about 0.1%. The pellets remaining on the pouring surface of the fine sieve 9b are conveyed onto a chute 13 by means of a conveying device. From there, the pellets enter the screen 7, which is connected to the screening device 9. The fine fraction of the pellets is preferably between 0.08% and 1.2% after fine screening and is suitably about 0.1%. The pellets remaining on the pouring surface of the fine sieve 9b are conveyed onto a chute 13 by means of a conveying device. From there, the pellets enter the screen 7, which is connected to the screening device 9.

The windshaker 7 has a pellet feed opening 11, which can be closed by a pivotable flap 10, through which the pellets coming from the chute 13 enter the windshaker 7. [0014] The windshaker 7 also has a supply duct 8 for the supply of a gas stream 2. On its upper side, the windshield 7 comprises a discharge channel 14, which is subjected to vacuum, through which the gas stream is sucked off. The windshaker 7 is preferably designed as a climbing funnel with a rising pipe 5. The interior of the riser 5 forms a classifier channel 15. The cross-sectional area of the classifier channel 15 is expediently adjustable by means of a separating plate 16 which is arranged in the longitudinal direction of the riser 5 and is displaceable.

The gas stream 2 flowing from the supply channel 8 into the classifier channel 15, which is suitably an air stream, flows upwards in the classifier channel 15 because of the vacuum in the discharge channel 14. The pellets 1 coming from the screening device 9 flow as a pellet stream 6 through the pellet feed opening 11 as a transverse flow into the gas stream 2. In the embodiment shown in FIG. 1, the pellet flow 6 flows into the upwardly directed direction at an angle of approximately 45.degree Gas stream 2. The angle between the pellet stream 6 and the gas stream 2 can also be adjusted to other values in order to achieve as good an efficiency as possible in the sighting process in the windshield. The gas stream 2 passes through the pellet stream 6 and carries the lighter fine and finest fractions of the pellet stream 6 up into the sifter channel 15.

The invention is based on the knowledge that a substantial proportion of the fine and fine particles can not be removed to the desired degree by means of conventional air filters because a considerable proportion of the fine particles and finest particles (hereinafter referred to as fine fraction 3) ) Adheres to the surface of the pellets 1 due to electrostatic attraction. In order to remove the fine particles 3 adhering to the surface of the pellets 1, the invention provides an ionization of the gas stream 2 and / or of the pellets 1. In the exemplary embodiment of FIG. 1, an ionization device 4 is provided for this purpose in the region of the supply channel 8 for supplying the gas stream 2 in the windshield 7. The ionization device 4 is preferably an ionizing rod, which is expediently arranged in the bottom region of the supply channel 8, In order to ionize at least some of the gas molecules of the gas stream 2. The gas stream 2, which is at least partially ionized in this way, flows up into the classifier channel 15 and ensures electrostatic discharge of the surfaces of the pellets 1, which flow into the gas stream 2 as pellet stream 6. Due to the discharge of the surface of the pellets 1 by the ionized gas molecules of the gas stream 2, the electrostatic attraction forces which cause the adhesion of the fine particles 3 to the surface of the pellets 1 are reduced or eliminated completely. Which flow as pellet stream 6 into the gas stream 2. Due to the discharge of the surface of the pellets 1 by the ionized gas molecules of the gas stream 2, the electrostatic attraction forces which cause the adhesion of the fine particles 3 to the surface of the pellets 1 are reduced or eliminated completely. Which flow as pellet stream 6 into the gas stream 2. Due to the discharge of the surface of the pellets 1 by the ionized gas molecules of the gas stream 2, the electrostatic attraction forces which cause the adhesion of the fine particles 3 to the surface of the pellets 1 are reduced or eliminated completely.

Claims

As a result, the fine particles 3 adhering to the surface of the pellets 1 are detached from the pellets 1 and can be discharged with the gas stream 2 through the screening channel 15 and finally through the discharge channel 14. [0017] This mechanism is shown in FIG. 3a. The pellet stream 6 is shown schematically here, which flows from the sieve inlet direction 9 into the wind header 7 and consists of pellets 1, on the surface of which fine particles 3 adhere. The pellet stream 6 flows from obliquely upwards into the at least partly ionized gas stream 2, which flows upwards from the supply channel 8 in the sifter channel 15. The gas molecules of the gas stream 2 are at least partially ionized in the region of the supply channel 8 by the ionization device 4. The ionization of the gas stream 2 is indicated by "+ -" in FIG. 3a. The partially ionized gas stream 2 discharges the electrostatic charges on the surface of the pellets 1. As a result, the fine particles 3 adhering to the surface of the pellets 1 dissolve from the surface of the pellets 1 and are mixed with the (partially ionized) gas stream 2 in the Classifier channel 15 can be discharged upwards. The pellets 1 freed from the fine particles 3 fall down through the pellet discharge opening 17 from the wind sifter 7. The fine proportion of the pellet stream 6 treated in this way can be reduced to values of 0.08% to 0.1%. FIG. 2 shows a second embodiment of a device according to the invention for the treatment of pellets 1. The functional principle of this device corresponds to that of the device of FIG. 1. Corresponding parts are therefore provided with the devices shown in FIG. 1. The screen device 9 shown in FIG. 2 only in a side view corresponds in this case to the screen device 9 of FIG. 1. The pellet stream 6 coming from the screen device 9 flows through the pellet feed opening 11 which, as in the exemplary embodiment of FIG Pivoted flap 10, into the windshield 7. As in the exemplary embodiment shown in FIG. 1, the windshaker 7 is a rising funnel with a rising pipe 5 which forms a separating funnel channel 15, the cross-section of which can be adjusted by means of a displaceable separating plate 16, as in the exemplary embodiment of FIG. Connected to the ascending pipe 5 is a discharge channel 14, which is pressurized with a vacuum and which sucks the gas stream 2 flowing in the sifter channel 15 upwards. 2, the pellet stream 6 flows through the gas stream 2 in the countercurrent, ie, the pellet stream 6 flows downwardly in the classifier channel 15, while the gas stream 2 is sucked upwards. In the embodiment shown in FIG. As in the exemplary embodiment of FIG. 1, an ionization device 4 is arranged in the region of the supply channel 8, through which the gas stream 2 is guided into the classifier channel 15, which at least partially ionizes the gas molecules of the gas stream 2 . The at least partially ionized gas stream 2 flows through the pellet stream 6 and thereby discharges the surface of the electrically charged surface of the pellets 1. As a result, the fine particles 3 adhering to the surface of the pellets 1 due to electrostatic attraction are removed from the surface of the pellets 1 and can be discharged through the gas stream 2 flowing in the sifter channel 15. This countercurrent mechanism of the device of FIG. 2 is schematically illustrated in FIG. 3b. An alternative embodiment is schematically shown in FIG. 3c, in which the pellet stream 6 flows through the gas flow 2 as a transverse flow. The device according to the invention and the method according to the invention are particularly suitable for removing fine particles 3 from a pellet bed of wood pellets. However, the device according to the invention and the method according to the invention can also be used in a corresponding manner for the removal of fine particles and, in particular, dust particles from other types of pellets, such as feed pellets or the like. claims

The invention relates to a method for treating pellets (1), in particular wood pellets, wherein the pellets (1) are introduced into a gas stream (2) in order to discharge fine particles (3), characterized in that the gas stream (2) and / or the pellets (1) are at least partly ionized by means of an ionization device (4).
2. A device for the treatment of pellets (1), in particular wood pellets, comprising a wind former (7) in which the pellets (1) are introduced into a gas stream (2) in order to discharge fine particles (3) (4), with which the gas stream (2) and / or the pellets (1) are at least partially ionized.
3. Method or device according to claim 1, characterized in that the ionization device (4) is an ionizing rod.
4. The method or device according to claim 3, characterized in that at least a part of the gas molecules of the gas stream (2) is ionized by the ionizing rod.
5. Method or device according to claim 3, characterized in that superficial electrostatic charges are carried away on the pellets (1) by the introduction of the pellets (1) into the at least partially ionized gas stream (2).
6. The method or device according to claim 1, wherein the pellets are introduced into the gas stream in a windshaker.
7. The method as claimed in claim 1, wherein the pellets are introduced as a pellet stream into the gas stream flowing transversely or obliquely to the pellet stream.
8. The method according to claim 1, wherein the pellets are introduced as a pellet stream in a windshield in countercurrent flow to the gas stream flowing horizontally upwards.
9. The method or device according to claim 1, wherein the gas stream is a gas stream which contains ionizable gas molecules, in particular oxygen, nitrogen or air molecules.
10. The method according to claim 1, wherein the pellets are first sieved in a sieve by means of a screening device and then introduced into the gas stream in a windshaker.
11. The method or device as claimed in claim 10, characterized in that the windshield (7) has a supply channel (8) for supplying the gas stream (2), and the ionization device (4) is arranged in the supply channel (8).
12. The method or device according to claim 10, wherein the windscreen has a pellet feed opening, which can be closed by a pivotable flap, for supplying the pellet stream.
13. The method or device as claimed in claim 10, characterized in that the windshaker (7) is designed as a rising funnel with a standpipe (5), the standpipe (5) forming a sifter channel (15) whose cross-sectional area is adjustable ,