EP1788307B1

EP1788307B1 - Device for introducing and distributing fuel in a burner, particularly for a pellet-fired boiler or stove

Info

Publication number: EP1788307B1
Application number: EP06123782A
Authority: EP
Inventors: Mario Acquaro
Original assignee: FAMAR ITL (Innovation Technology Lab) Srl
Current assignee: FAMAR ITL (Innovation Technology Lab) Srl
Priority date: 2005-11-18
Filing date: 2006-11-09
Publication date: 2011-03-30
Anticipated expiration: 2026-11-09
Also published as: ITTV20050180A1; ATE503968T1; EP1788307A1; DE602006020970D1

Abstract

A device (1) for introducing and distributing fuel in a burner, particularly for a pellet stove or boiler, which comprises at least one screw feeder (2), the delivery of which is connected to the burner; means (23) for the conveyance and uniform distribution of the pellets in the burner are associated with the delivery of the at least one screw feeder (2).

Description

The present invention relates to a device for introducing and distributing fuel in a burner, particularly for a pellet-fired boiler or stove.
Boilers and stoves are currently in use which use as fuel small elements obtained by compressing sawdust or wood chips, also known as pellets.
These stoves and burners usually comprise a hopper, in which the pellets are stored and periodically introduced automatically in a burner, where they are burned; below the burner there is a removable tray for collecting the ash produced by combustion.
The pellets are removed from the hopper and introduced in the burner typically by means of a screw feeder, which is actuated by an electric motor and whose delivery leads into the combustion chamber.
The pellets thus exit from the screw feeder and fall into the burner, where they burn.
The main drawback of these known types of device is that the pellets always fall approximately in a same point of the burner and cover the ignited pellets that are present therein; accordingly, a concentration of unburned or imperfectly burned pellets forms in a limited region of the burner below the delivery of the screw feeder and can choke the combustion, reducing its efficiency considerably and even stopping it.
This effect occurs in particular with flow-rates of pellets introduced in the burner above 3-4 kg per hour.
In order to limit this drawback, pellet boilers and stoves are known in the burner of which there is a spatula which automatically moves the pellets that have fallen into the burner alternately into two preset positions, respectively to the right and to the left of the delivery of the screw feeder.
However, this known type of solution has a drawback: since two combustion focuses form within the burner, one to the right and one to the left of the delivery of the screw feeder, the flame, and therefore the distribution of the temperature within the burner, is not uniform.
Further, the spatula conveys the fresh pellets that fall into the burner so that they alternately cover the ignited pellets that are present respectively to the right and to the left of the delivery of the screw feeder; accordingly, two piles of unburned pellets form at the two combustion focuses and can choke the combustion and even stop it.
Moreover, the movement of the spatula can cause unburned pellets to fall into the ash collection tray, consequently wasting said pellets.
US-5 243 963 discloses a furnace for solid fuels, as defined in the preamble of claim 1.
WO 01/29481 discloses a stove and a feeding device for a burner.
US 5 070 798 discloses pellet burner appliances and burners therefor.
The aim of the present invention is to solve the above mentioned problems, eliminating the drawbacks of the cited background art, by providing a device which allows to introduce automatically the fuel in a burner, particularly of a pellet boiler or stove, so as to maintain high combustion efficiency.
Within this aim, an object of the invention is to provide a device that allows to feed the fuel to the burner without the risk of interrupting combustion.
Another object of the invention is to allow to obtain a flame which is as uniform as possible, so as to make the temperature in the burner uniform by making the combustion uniform.
Another object of the invention is to minimize the waste of pellets.
Another object is to provide a device which is structurally simple and has low manufacturing costs.
This aim and these and other objects, which will become better apparent hereinafter, are achieved by a device for introducing and distributing fuel in a burner, particularly for a pellet stove or boiler, as defined in claim 1.
Further characteristics and advantages of the invention will become better apparent from the following detailed description of a particular but not exclusive embodiment thereof, illustrated by way of non-limiting example in the accompanying drawings, wherein:

Figure 1 is a front perspective view of a device according to the invention;
Figure 2 is a rear perspective view of the device of Figure 1;
Figure 3 is a side view of the device of Figure 1;
Figure 4 is a front view of the device of Figure 1;
Figure 5 is a sectional view, taken along the line V-V of Figure 4;
Figure 6 is a sectional view, taken along the line VI-VI of Figure 4;
Figure 7 is a sectional view, taken along the line VII-VII of Figure 6.

In the exemplary embodiments that follow, individual characteristics, given in relation to specific examples, may actually be interchanged with other different characteristics that exist in other exemplary embodiments.
With reference to the figures, the reference numeral 1 designates a device for introducing and distributing fuel in a burner, particularly for a pellet stove or boiler, not shown in the accompanying figures.
The device 1 comprises at least one screw feeder 2, constituted by a substantially cylindrical tubular element 3, which is contained partially within a box-like body 5 which has a transverse cross-section shaped approximately like an inverted letter Ω and affects longitudinally the entre tubular element 3.
The box-like body 5 forms a bottom 6, which is substantially flat and approximately parallel to the longitudinal axis of the tubular element 3 and is advantageously approximately rectangular in plan view; two arms, respectively designated by the reference numerals 7a and 7b, protrude approximately at right angles from the longitudinal perimetric edges of said bottom and partially enclose laterally the tubular element 3; two wings, respectively designated by the reference numerals 8a and 8b, protrude from the free ends of the arms 7a and 7b approximately at right angles, on the opposite side with respect to the tubular element 3.
A first opening 10 is provided proximate to the rear end 9 of the tubular element 3, on the lateral surface thereof, opposite the bottom 6 of the box-like body 5, advantageously has an approximately rectangular plan shape and is suitable to introduce into the screw feeder 2 the pellets contained in an overlying hopper, not shown in the accompanying figures.
Two second openings, generally designated by the reference numeral 12, are provided proximate to the front end 11 of the tubular element 3, on its lateral surface and on the facing bottom 6 of the box-like body 5; said second openings are substantially mutually identical, face each other, and advantageously have an approximately circular plan shape; a tube 13 protrudes from the perimetric edge of the second opening provided in the tubular element 3 approximately at right angles and toward the outside of said element, so as to pass through the facing second opening provided in the bottom 6; the tube 13 constitutes the delivery of the screw feeder 2 and is advantageously shaped, in a cross-section taken along a plane which is perpendicular to the bottom 6 and passes through the longitudinal central plane thereof, approximately like a right trapezoid, in which the parallel sides are perpendicular to the bottom 6 and the oblique side is directed away from the rear end 9 of the tubular element 3.
Advantageously, two first tabs, respectively designated by the reference numerals 14a and 14b, protrude from the longitudinal ends of the bottom 6 of the box-like body 5, proximate to the front end 11 of the tubular element 3 and laterally with respect to the tube 13, and lie approximately on the same plane as the bottom 6 and advantageously have an approximately rectangular plan shape.
Advantageously, a second tab 50, which advantageously has an approximately rectangular plan shape, protrudes from the bottom 6 of the box-like body 5, approximately at right angles and to the rear of the tube 13, and a third advantageously substantially circular opening, not shown in the accompanying figures, is provided approximately centrally in said second tab.
The tubular element 3 and the box-like body 5 are closed, respectively at the rear and front ends of the tubular element 3, by a first flange 15 and by a second flange 16, between which the shaft 17 of a worm screw 18 is supported rotatably; said worm screw is suitable to convey the pellets from the rear end 9 to the front end 11 of the tubular element 3, so as to make them exit by gravity from the tube 13 which constitutes the delivery of the screw feeder 2.
Advantageously, a first end 19 of the shaft 17 is supported rotatably in an appropriately provided through hole, not shown in the accompanying figures, which is provided approximately centrally with respect to the first flange 15, while the second end 20 of the shaft 17 is advantageously supported rotatably in an appropriately provided seat, which is approximately cylindrical and is formed by an annular protrusion 21, which protrudes approximately centrally from the second flange 16 toward the inside of the tubular element 3.
Advantageously, the first end 19 of the shaft 17 protrudes longitudinally outside the tubular element 3 and engages suitable motion-generation means, constituted for example by a gearmotor 22.
Means for the conveyance and uniform distribution of the pellets into the burner are associated with the delivery of the screw feeder 2 and comprise advantageously a first chute 23, which protrudes approximately at right angles from the bottom 6 of the box-like body 5 at the first tabs 14a and 14b to the rear of the tube 13.
The first chute 23 is advantageously constituted by a first plate 24, which is preferably approximately flat and substantially perpendicular to the bottom 6 and is connected to said bottom and to the first tabs 14a and 14b at a first transverse end, to the rear of the tube 13; advantageously, the first plate 24 is rigidly associated with the second tab 50, for example by bolting.
A fourth opening, not shown in the accompanying figures and advantageously but not necessarily circular, is provided in the first plate 24, in the region thereof which faces the tube 13 and at the third opening provided in the second tab 50.
Two first shoulders, designated respectively by the reference numerals 25a and 25b, protrude from the longitudinal ends of the first plate 24 approximately at right angles thereof and in the opposite direction with respect to the rear end 9 of the tubular element 3 and enclose laterally the tube 13.
The first chute 23 is further connected to the tubular element 3 by means of an appropriately provided strut 26, which is fixed with one of its ends to the bottom 6 of the box-like body 5 and with its other end to the first plate 24.
Such means for conveying and uniformly distributing the pellets further comprise a second chute 27, which is associated rotatably, by means of its upper end, with the first chute 23 in the region thereof that is contiguous to the tube 13.
Advantageously, the second chute 27 is constituted by a second plate 28, which is preferably approximately flat and substantially parallel to the first plate 24 and advantageously has an approximately isosceles-trapezoid plan shape, in which the longer parallel side 29 is arranged between the tube 13 and the first plate 24.
Two second shoulders, designated respectively by the reference numerals 30a and 30b, protrude from the longitudinal ends of the second plate 28, approximately at right angles and in the opposite direction with respect to the first plate 24; during use, the second shoulders are arranged laterally with respect to the tube 13 and inside the first shoulders 25a, 25b of the first chute 23.
Advantageously, the second plate 28 of the second chute 27 is keyed, proximate to its longer parallel side 29, to a secondary shaft 31, which is arranged so that its longitudinal axis is approximately perpendicular to the first plate 24 and rotatably associated with the fourth opening provided therein and with the third opening of the second tab 50 by way of suitable rotary support means of a known type, such as for example a first cylindrical guide 32, which is fixed to the second tab 50 on the opposite side with respect to the tube 13; the second chute 27 can thus be turned with respect to the first chute 23 about the longitudinal axis of the secondary shaft 31, by way of suitable motion-transmission means which are connected to the motion-generation means.
The motion-generation means comprise a first pulley 33, which is advantageously provided with teeth and is keyed to the portion of the first end 19 of the shaft 17 that protrudes from the tubular element 3 and is connected, by means of a belt 34, which is advantageously a toothed belt, to a second pulley 35, which is keyed to an underlying shaft 36, which is approximately parallel to the shaft 17 and is advantageously axially offset with respect to said shaft relative to a plane which is perpendicular to the first plate 24 of the first chute 23 and passes through the central longitudinal axis of said plate.
The shaft 36 is supported rotatably by a second cylindrical guide 37, which is in turn supported by an appropriately provided bracket 38 connected to the box-like body 5.
A cam 39 is keyed to the end of the shaft 36 that is directed toward the first chute 23, and one end of a linkage 40 is pivoted to the cam; such linkage 40 is pivoted, at the other end, to a crank 41, which is keyed to the secondary shaft 31.
Operation is therefore as follows: with reference to the accompanying figures, the device 1 is associated for example with a pellet boiler or stove by arranging the rear end 9 of the tubular element 3 at the bottom of the pellet hopper, so that said pellets can enter the first opening 10 by gravity.
The front end 11 of the tubular element 3 is instead arranged within the burner, not shown in the accompanying figures, of the boiler or stove, directing the first chute 23 toward the underlying combustion chamber of said burner.
Advantageously, the device 1 is arranged so that the shaft 17 is inclined at approximately 45° with respect to the horizontal plane.
By turning the worm screw 18 by means of the gearmotor 22, the pellets are moved within the tubular element 3 and thus arrive at the second opening 12, from which they exit by gravity through the tube 13.
The rotation of the shaft 17 entails the rotation of the first pulley 33, which is keyed to it; the first pulley 33, by means of the toothed belt 34, turns the second pulley 35 and the shaft 36 to which said pulley is keyed.
Accordingly, the cam 39, the linkage 40 and the crank 41 are also turned, producing the oscillation of the secondary shaft 31 with respect to its longitudinal axis.
The second chute 27, which is keyed to the secondary shaft 31, thus oscillates periodically with respect to the first chute 23; the pellets that exit from the tube 13 enter the second chute 27, traveling along it by gravity, and thus reach the first chute 23, from which they fall into the combustion chamber of the burner.
The oscillation of the second chute 27 prevents the pellets from falling in a single region of the burner and distributes them approximately uniformly therein.
It has thus been found that the invention has achieved the intended aim and objects, a device having been devised for introducing fuel in a burner, particularly for a pellet stove or boiler, which allows to obtain a uniform distribution of the pellets in the burner, so as to achieve high efficiency in combustion.
Further, the possibility to distribute the pellets uniformly reduces the risk that an excessive accumulation of said pellets in a confined region of the burner might interrupt combustion.
By way of the uniform distribution of the pellets, it is further possible to achieve a more uniform flame, so as to render the temperature of the burner uniform.
Further, the production costs of the device according to the invention remain low, since it is provided only by means of components which are easy to manufacture and/or assemble.
The invention is of course susceptible of numerous modifications and variations, all of which are within the scope of the appended claims.
Of course, the materials used, as well as the dimensions that constitute the individual components of the invention, may be more pertinent according to the specific requirements.
Where technical features mentioned in any claim are followed by reference signs, those reference signs have been included for the sole purpose of increasing the intelligibility of the claims and accordingly, such reference signs do not have any limiting effect on the interpretation of each element identified by way of example by such reference signs.

Claims

A device for introducing and distributing fuel in a burner, particularly for a pellet stove or boiler, comprising at least one screw feeder (18) the delivery of which is connected to said burner, and wherein means for the conveyance and uniform distribution of said fuel in said burner are associated with said delivery of said at least one screw feeder, and wherein a tube (13) constitutes said delivery of said screw feeder, characterized in that said means for the conveyance and uniform distribution of said fuel in said burner comprise a second chute (27) that is associated rotatably, by means of its upper end, with a first chute (23) in a region thereof which is contiguous to said tube.
The device according to claim 1, characterized in that said at least one screw feeder is constituted by a substantially cylindrical tubular element, which is contained partially in a box-like body which has a transverse cross-section shaped approximately like an inverted letter Ω and affects longitudinally all of said tubular element, said box-like body forming a bottom, which is substantially flat and approximately parallel to the longitudinal axis of said tubular element and has, in plan view, an approximately rectangular shape, two arms protruding approximately at right angles from the longitudinal perimetric edges thereof, said arms partially enclosing laterally said tubular element, a first opening suitable for the introduction of said pellets in said screw feeder being provided at the opposite end with respect to said bottom of said box-like body proximate to the rear end of said tubular element, on its lateral surface.
The device according to claims 1 and 2, characterized in that two second openings are provided proximate to the front end of said tubular element, on its lateral surface and on said facing bottom of said box-like body, said openings being substantially mutually identical and facing each other, a tube which constitutes said delivery of said screw feeder protruding from the perimetric edge of said second opening provided in said tubular element approximately at right angles and toward the outside of said tubular element so as to pass through said facing second opening provided in said bottom.
The device according to claims 1 and 3, characterized in that said tube is shaped, in a cross-section taken along a plane which is perpendicular to said bottom and passes through its longitudinal central plane, approximately like a right trapezoid, in which the parallel sides are perpendicular to said bottom and the oblique side is directed away from said rear end of said tubular element.
The device according to claim 2, characterized in that two first tabs protrude from the longitudinal ends of said bottom of said box-like body, proximate to said front end of said tubular element and laterally to said tube, and lie approximately on the same plane as said bottom.
The device according to claim 5, characterized in that a second tab protrudes from said bottom of said box-like body, approximately at right angles and to the rear of said tube, and has an approximately rectangular plan shape, a third opening being provided approximately centrally thereto.
The device according to claim 2, characterized in that said tubular element and said box-like body are closed, respectively at the rear and front ends of said tubular element, by a first flange and a second flange, between which a shaft of a worm screw is supported rotatably, said worm screw being suitable to convey said pellets from said rear end to said front end of said tubular element, so as to make them exit by gravity from said tube which constitutes said delivery of said screw feeder.
The device according to claims 1 and 7, characterized in that a first end of said shaft is supported rotatably in a hole formed approximately centrally with respect to said first flange, a second end of said shaft being supported rotatably in an appropriately provided seat, which is approximately cylindrical and is formed by an annular protrusion which protrudes approximately centrally from said second flange toward the inside of said tubular element.
The device according to claims 1 and 8, characterized in that said first end of said shaft protrudes longitudinally outside said tubular element and engages motion-generation means, constituted preferably by a gearmotor.
The device according to one or more of the preceding claims, characterized in that said means for uniform distribution and conveyance of said pellets within said burner comprise a first chute, which protrudes approximately at right angles from said bottom of said box-like body at said first tabs and to the rear of said tube.
The device according to claims 1 and 10, characterized in that said first chute is constituted by a first plate which is approximately flat and substantially perpendicular to said bottom and is connected to said bottom and to said first tabs, at a first transverse end thereof, to the rear of said tube.
The device according to claims 1 and 13, characterized in that said first plate is rigidly associated with said second tab.
The device according to claims 1 and 12, characterized in that a fourth opening is provided in said first plate in the region thereof which faces said tube and at said third opening provided in said second tab.
The device according to claims 1 and 13, characterized in that two first shoulders which enclose laterally said tube protrude from the longitudinal ends of said first plate approximately at right angles thereto and in the opposite direction with respect to said rear end of said tubular element.
The device according to claims 1 and 14, characterized in that said first chute is connected to said first tubular element by means of an appropriately provided strut, which is fixed by means of one of its ends to said bottom of said box-like body and by means of its other end to said first plate.
The device according to claim 10, characterized in that said rotatable chute is constituted by a second plate, which is approximately flat and substantially parallel to said first plate and advantageously has an approximately isosceles-trapezoid plan shape, in which the longer parallel side is arranged between said tube and said first plate.
The device according to claim 16, characterized in that two second shoulders protrude from the longitudinal ends of said second plate, approximately at right angles and at the opposite end with respect to said first plate, and are arranged laterally, during use, with respect to said tube and within said first shoulders of said first chute.
The device according to claim 17, characterized in that said second plate of said second chute is keyed, proximate to the longer parallel side thereof, to a secondary shaft, which is arranged so that its longitudinal axis is approximately perpendicular to said first plate and is rotatably, associated with said fourth opening provided in said first plate and with said third opening of said second tab by way of suitable rotary support means.
The device according to claims 18, characterized in that said rotary support means are constituted by a first cylindrical guide, which is fixed to said second tab on the opposite side with respect to said tube, said second chute being able to rotate with respect to said first chute about the longitudinal, axis of said secondary shaft by way of the action of suitable motion-transmission means connected to said motion-generation means.
The device according to claim 19, characterized in that said motion-transmission means comprise a first pulley, which is keyed to the portion of said first end of said shaft which protrudes from said tubular element and is connected, by means of a belt, to a second pulley which is keyed to an underling shaft, which is approximately parallel to said shaft and is axially offset with respect to it relative to a plane which is perpendicular to said first plate of said first chute and passes through the longitudinal central axis thereof.
The device according to claim 20, characterized in that said shaft is supported rotatably by a second cylindrical guide, which in turn is supported by an appropriately provided bracket connected to said box-like body, a cam being keyed to the end of said shaft that is directed toward said first chute, one end of a linkage being pivoted to said carn, said linkage being pivoted, at its other end, to a crank which is keyed to said secondary shaft.