WO2012012910A2

WO2012012910A2 - Fuel supply device for a furnace for power outputs down to less than 1 kw

Info

Publication number: WO2012012910A2
Application number: PCT/CH2011/000170
Authority: WO
Inventors: André Riemens
Original assignee: Vetsch, Gabriela; Basso, Salerno
Priority date: 2010-07-27
Filing date: 2011-07-21
Publication date: 2012-02-02
Also published as: CH703513B1; CH703513A2; WO2012012910A3

Abstract

The fuel supply device according to the invention is intended for granular fuel for a furnace for power outputs down to less than 1 kW. The fuel supply device comprises a conveyer screw (2) arranged in a pipe (8), wherein a circular, horizontal grate (1) having a central, round hole (6) and air supply openings (7) in the outer area of the grate (1) is arranged above the screw. The axis of the conveyer screw (2) runs upward into a steel bracket (19), which protrudes beyond the grate surface and the end (23) of which on an outer section (22) is directed downward toward the grate (1) and ends in the outer third of the radius of the grate (1) at a distance from the grate surface.

Description

Kiln feeder for a furnace for power down to less than 1kW

The burning of small portioned and therefore granular firewood, such as wood pellets, wood chips, small pieces of wood or dried corn proves to be energetically favorable and practical to use. It does not have large and unwieldy pieces of wood to be transported and stored and also no large logs to be fed to the fire. But dosing the firing power down to a low value is difficult. Namely, if a suitable furnace for such granular firing, for example, a wood pellet furnace, with only a small power of less than 1 kW as operated, there is so far no suitable combustor feed device to such a weak fire continuously and safely maintain. Namely, at such low powers, the difficulty is, first, to keep the fire burning safely, second, to continuously carry off the ashes, and, thirdly, to prevent the fire from feeding into the feed stream of the burning material.

There are already screw conveyors to wood pellet stoves, which feed the fire continuously or only when needed wood pellets. However, these augers are consistently designed for much higher fire performance and they do not succeed with them to drive the fire power to less than 1kW down by simply shrinking these augers in their geometry or reduces the rotational speed of the augers. conventional Augers are mostly skewed and work like an Archimedes screw. In addition, the known pellet screw conveyors are not suitable for a compact wood stove of small dimensions. Another observed problem is that with slow feed from the pellets from below into the fire, there is a risk that the fire will slowly migrate down into the auger. These problems are solved by a kiln firing device for granular kiln for power down to less than 1kW. This has a arranged in a pipe screw conveyor for the delivery of the granular material. It proves to be a special feature that the central screw axis tube of the screw conveyor, on the outer wall of which the screw thread is mounted and with which together the screw conveyor is rotatably mounted in the tube, fills at least a quarter of the pipe diameter. Furthermore, it is important that this auger tube tube ends up as a cone in a tip, above the screw a circular grid with central round hole and air supply openings in the outer area of the grate is arranged horizontally. This hole is smaller than the diameter of the screw conveyor and from its edge a conically widening wall extends as a sliding wall for the kiln to be conveyed downwards. This runs approximately or exactly parallel to the cone of the upper end of the screw axis. In such a device, it turns out that the ash is often clumped into a structure and then distributed irregularly on the grid. If the device is equipped with an ignition element for an automatic ignition of the burning material, it may create an ash accumulation in front of the ignition element, which impairs or prevents its function. It produces larger clumps of ash, which soon exhaust the volume in the ash catcher.

The object of this invention is to remedy these drawbacks and to provide a device which comminutes the ash structure continuously during operation and ensures a uniform distribution of the ash on the grid, so that an ash accumulation is prevented in front of a mounted ignition element that Finally, the ash falls evenly over the outer edge of the grate and the Ash quality generally becomes finer and firmer, resulting in less volume.

This object is achieved by a kiln feed device for granular kiln for a furnace for services down to less than 1kW, consisting of a arranged in a pipe screw conveyor, wherein above the screw a circular, horizontal grate with a central, round Hole and air supply openings in the outer region of the grate is arranged, and which is characterized in that the axis of the screw conveyor runs upwards in a steel bracket, which projects beyond the grate surface, and whose end is directed at an outer portion down against the grate and ends in the outer third of the radius of the grate at a distance to the grate surface.

With reference to the drawings, the supply device for the granular firing material is presented and described below and its function will be explained.

It shows:

Figure 1: seen the supply device with the arranged at the upper end grate in a longitudinal section;

Figure 2: A cross section through the screw conveyor, seen from above;

Figure 3: The entire screw conveyor seen from the side, in one

Longitudinal section shown;

Figure 4: The kiln feed device with the steel bracket

Ash processing;

Figure 5: The kiln feed device with the steel bow of Figure 4 shown in a longitudinal section. The slow Hochfördern of granular fuel, which usually consists of cylindrical wood pellets of about 6mm thickness and up to 50mm in length, but which are broken in the course of promotion to shorter particles, proves to be more difficult than you would expect. The following problems are observed with a conventional auger which simply opens up in the plane of a grate at the top: First, there is a great risk that the pellets in the auger will wedge and clump one another. It is then formed to a certain extent monolithic mass, which acts as a plug due to jamming and blocking the screw conveyor, even if it is driven with high torques. In a screw conveyor, it is important that the auger turns as well as possible sliding under the conveyed material and the conveyed must, without being substantially rotated in the conveyor tube, move upwards. With so-called pellets or similar granular firing succeeds over small distances quite well. If, however, the auger is 400 mm or longer, for a corresponding delivery height, wedging and agglomeration is observed due to the weight load of the kiln. This depends, among other things, on the rotational speed and geometry of the screw conveyor, on the size and type of wood of the granular pieces of firewood and, last but not least, on the humidity of the air. If you want to construct a stove with a low heat output, a very low supply of fuel must be achieved. If wood pellets of, for example, 6 mm in diameter and 10 to 25 mm in length are to be conveyed as slowly as possible over a conveying height of more than 400 mm, then the above-mentioned problems occur particularly frequently. It is therefore important to provide a kiln feed device for granular fuel with which these problems are reliably avoided.

Figure 1 shows such a conveyor for granular kiln for a furnace, which is designed for benefits of down to less than 1 KW. The kiln can consist of wood pellets, but also of wood chips, small pieces of wood or dried corn or other grains. The grate 1 of the furnace acts with the feed device together, and this is equipped with a screw conveyor 2. The screw conveyor 2 is arranged in the example shown perpendicular to the grate surface and the central screw axis tube 3, on the outer wall 4, the screw 5 is mounted and with which together the screw conveyor 2 is rotatably mounted in the conveyor tube 8, fills a considerable part of the conveyor tube 8, which the whole screw conveyor 2 encloses. The conveyor tube 8 with the screw conveyor 2 can also be arranged obliquely to the perpendicular. It is then achieved on the bottom of additional friction of the fuel with the delivery pipe 8, which is beneficial to the promotion. In the example shown, the pipe diameter of the worm axis pipe 3 measures one third of the screw diameter or the pipe diameter, and measures, for example, 60 mm. The diameter of the screw axis tube 3 should be at least a quarter of the screw conveyor diameter, because thus also a sufficient torque on the actual screw 2 and on the helical to the screw axis tube 3 wound smoothest possible conveying surface 5 are transmitted. On the conveying surface 5 of the screw 2 here is a single wood pellet 18 drawn to give an approximate size comparison. This screw axis tube 3 runs up as a cone 10 in a tip, wherein above the screw 2, the grate 1 is arranged horizontally with a central circular hole 6. It fits exactly on the upper end of the auger axle tube 8 and is placed on this.

The grate 1 is preferably circular as shown and interspersed with air supply openings 7 in the outer region. The circular hole 6 in the grate 1 measures approximately half of the delivery pipe diameter. From this circular hole 6 includes a downwardly projecting, funnel-shaped edge 9, which opens as a funnel down. The funnel wall is almost or exactly parallel to the cone 10 on the screw axis tube 3. In the example shown, the cone 10 includes the course direction of the funnel inner wall at an acute angle, the angle top is above. This angle may only be very small, otherwise a jamming of the fuel in the area between the cone 10 and the funnel inner wall is provoked. The the actual screw 2 or its winding conveying surface 5 terminates with an approximately perpendicular to the grate surface extension 11. The outer side of the extension with respect to the axis of rotation adjoins flush with the inner edge of the hole 6. This auger 2 as shown here rotates clockwise in operation as seen from above. Of course, it could also be designed to boost in a counterclockwise direction. The firing material to be conveyed remains approximately at the same point in relation to its rotational position in the conveying tube 8, and the conveying surface 5 of the screw 2 slides under the kiln, being lifted up in the conveying tube 8, until finally at the level of the hole 6 arrives. Important for a reliable conveyance of the kiln by the auger also proves that the inside of the tube 8 is equipped with a plurality of preferably axially extending plateaus or grooves 14, on which the auger turns past with a minimum distance, and between the plateaus or grooves a distance of the height of the plateaus or grooves to the inner wall of the tube 8 leaves open. For the same purpose, the inner wall of the tube 8 may also be provided with a rough surface.

However, the auger 2 rotates only very slowly, with a rotational speed of less than 1 rev / min. ^"1 Arrived at the top, the firing material is detected by the extension 11 and pushed clockwise from above, where the extension the edge of the As a result of this slow rotation of the extension 11, it is ensured that the parts of the burning material which have advanced due to the forces acting on them move radially outwards and finally onto the region 12 The area, a concentric ring, which immediately adjoins the hole 6 in the grate 1, is free of ventilation holes 7. Accordingly, the parts of the burning material burn there heavy and must first be pushed further radially outwards at the next passage of the extension 11, if of the same again parts of kiln a little bit on the Rostfläche be pushed. In this way, the kiln parts are moved every minute, dealing with handling of the extension 11, very slowly on the grid and finally on the fire zone, which by the region 13 is formed, which is equipped with air holes 7. The diameter of the whole grate 1 is about twice the diameter of the conveyor tube 8. So if this measures 60mm, then the grate 1 measures about 120mm in diameter. Due to the gentle and continuous supply of fresh fuel a nice, high and regular flame pattern on the grate 1 is achieved, and no flickering, technically effective flames.

In Figure 2 you can see the screw conveyor and the delivery pipe 8 shown in a cross section. Here you can see the grooves or the elevations 14 on the inside of the conveying tube 8, and a segment of the actual screw, 2 with its outer edge just past these elevations 14. 1. The kiln parts find at these ridges or grooves a backing, which helps avoid that they rotate with the screw conveyor 2. The rotation of the screw conveyor 2, which slides under the kiln, yes causes a force component which points radially outwards. Accordingly, the firing material is pressed against the inner wall of the conveying tube 8 and finds a hold on the elevations. If the outermost parts of the fuel are kept there, they keep the parts adjacent to the inside and these the more adjacent inside, etc., so that co-rotation of the Brenngutstücke is effectively avoided, regardless of whether the Brenngut of wood pellets, from wood chips, from small Pieces of wood or dried corn kernels or the like.

3 shows the screw conveyor 2 in its entire height. It measures between 200mm to 800mm in height and between 55mm and 85mm in diameter. The auger axle tube 3 measures one-quarter to a little over one-third of the diameter in diameter, and the pitch of the auger per revolution is about one-half auger diameter. Below the conveyor pipe 8 can be completely in a pile of kiln parts, or in a box 15, which can be fed from above or via, for example, an inclined surface 16 as a granulated material with kiln. The conveying tube 8 is open at the bottom on one side, and through this opening 17 in the conveying tube 8 trickle the kiln pieces, in the example shown cylindrical wood pellets, the screw 2 after. Figure 4 now shows this fuel feed with the crucial element for the solution of the above-mentioned problems in operation. For this purpose, namely a steel bracket 19, which extends from the upper end of the screw conveyor axis further up and thus first forms a screw axially extending portion 20, and then over an arc or here radially outwardly extending central portion 21 in a to axial section 20 parallel, outer section 22 leads. The lower end 23 of this outer portion 22 terminates just above the grate surface, ideally about 8mm above it. Depending on the size of the grate and the nature of the pellets, the distance may vary between 4mm to 12mm. Now, when the feed screw rotates, for example at a speed of less than 1 Umin ^"1, this outer bracket portion 22 moves with its lower end over the grate, and by the lying thereupon ash. Thus, the ash structure is furrowed, so to speak, and crumbles, so that a fine Homogeneous layer of ash remains on the grate, which is gradually pushed evenly around the outer edge of the grate by the material which has been added from the middle of the grate and falls downwards into the ash container, because the ashes are very fine due to their plowing As a result of the movement of the steel bracket 19, the tip 25 of the ignition element 24 remains constantly open and there is no danger of clogging or accumulation of ash the tip 25 of the ignition element 24 and thus no Beeinträchti his function.

FIG. 5 shows this fuel feed device with the steel strap 19 in a longitudinal section. In this illustration, it can be seen that the outer portion 22 of the bracket 19 is above the outer third of the radius of the grate 1 and its end over the grate surface, in detail about 8mm above the grate surface. The tip 25 of the ignition element 24 is close to the vorbedrehenden outer portion 22 of the bracket 19 and this area is therefore kept free of ash or cyclically. The kiln feed device for such wood stoves for powers of less than 1kW is equipped with an electric motor that drives the worm 2 via a reduction gear. Depending on the voltage-dependent control of the electric motor, the rotational speed of the screw conveyor 2 can be adjusted from 0.5 to 2 revolutions per minute and thus the supply amount of fuel per time and thus the heating power can be regulated. Overall, the steel strap offers the advantage that the ash is evenly distributed on the grate 1, the ash quality is finer and thus less volume is produced, and the ash falls evenly from the outer edge of the grate down on this fuel feed device. Furthermore, it is reliably avoided that an ash stowage can build up in front of the ignition element, and this ensures that the furnace can be operated for a long time without any maintenance.

Claims

claims

1. Brenngut-supplying means for granular fuel for a furnace for powers down to less than 1 kW, consisting of a in a pipe (8) arranged screw conveyor (2), wherein above the screw a circular, horizontal grate (1) with a central, round hole (6) and air supply openings (7) in the outer region of the grate (1) is arranged, characterized in that the axis of the screw conveyor (2) upwards in a steel bracket (19) terminates, which projects beyond the grate surface, and whose end (22) is directed downwardly against the grate (1) at an outer portion (21) and terminates in the outer third of the radius of the grate (1) at a distance from the surface of the grate.

2. Brenngut-supplying means for granular combustible material for an oven according to claim 1, characterized in that the steel bracket (19) has a screw conveyor for (2) axial portion (20), and a parallel, downwardly projecting outer portion (21) , which ends with 5mm to 12mm distance to the rust surface.

3. Brenngut-supplying means for granular combustible material for a furnace according to one of the preceding claims, characterized in that the circular grate (1) has an outer diameter of 150mm to 170mm and the steel bracket (19) to the screw conveyor (2) axial portion (20 ), and at a distance from the axial portion (20) by 55mm to 65mm spaced, parallel thereto, downwardly projecting portion (21), which ends at 6mm to 12mm distance to the grate surface.

4. Brenngut-supplying means for granular combustible material for a furnace according to one of the preceding claims, characterized in that an ignition element (23) above the grate (1) against the grate (1) out is inclined, with its front end (24) in front of the outer portion (21) of the steel bracket (19) ends.

5. Brenngut-supplying means for granular combustible material for a furnace according to one of the preceding claims, characterized in that the screw winding (5) of the screw conveyor (2) is guided to the height of the hole in the grate and thereafter in a vertical extension (1 ), softer the grate (1) surmounted above.

6. Brenngut-supplying means for granular combustible material for a furnace according to one of the preceding claims, characterized in that the hole (6) has half the diameter of the outer tube (8) of the screw conveyor (2) and the grate (1) outside a diameter of at least twice the diameter of the screw conveyor (2).

7. firing device for granular kiln for a furnace according to one of the preceding claims, characterized in that the screw conveyor (2) and its screw winding (5) are made of smooth steel, while the inside of the tube (8) with a plurality of axially extending Plateaus (14) or grooves is provided, on which the screw winding (5) rotates by a minimum distance, and between the plateaus (14) or grooves leaving a distance from the height of the plateaus or grooves to the inner wall of the tube (8).

8. Brenngut-supply means for granular combustible material for a furnace according to one of the preceding claims, characterized in that the inner wall of the tube (8) having a rough surface.

A kiln feed apparatus for granular kiln for an oven according to any one of the preceding claims, characterized in that the auger (2) measures between 500mm and 600mm in height, between 55mm and 65mm in diameter, while the The auger axle tube (3) measures one third of the diameter of the auger (2) in diameter and the pitch of the auger per round constitutes half a screw auger diameter.

Kiln-feeding device for granular kiln for a furnace according to one of the preceding claims, characterized in that the grate (1) is accurately placed on the upper end of the auger axle tube (3) can be placed.