EP1454094B1

EP1454094B1 - A grate for heaters for burning solid fuel bodies and a heater having such a grate

Info

Publication number: EP1454094B1
Application number: EP02775676A
Authority: EP
Inventors: Tomas Andersson
Original assignee: Sahlins Pellets Power AB
Current assignee: Sahlins Pellets Power AB
Priority date: 2001-11-22
Filing date: 2002-11-05
Publication date: 2007-06-27
Anticipated expiration: 2022-11-05
Also published as: SE520631C2; SE0103885L; ATE365894T1; DE60220943D1; SE0103885D0; DE60220943T2; EP1454094A1; AU2002341528A1; WO2003044429A1; PL371294A1

Abstract

The invention relates to a grate for small heaters for burning solid fuel bodies 37 having a limited size 6-10 mm. The grate comprises a plurality of interspaced elements 25 that are rotatable in order to, during burning of the fuel bodies 37 on the same, set the fuel bodies in motion in a direction from a feeding end towards an opposite end of the grate while tumbling the same as the burning progresses and as ashes or other residual deposits automatically fall down into a subjacent ash space 9 via interspaces 38 between adjacent elements. Said interspaces are of a substantially uniform narrow width that is within the range of 2-4 mm, and the individual grate elements 25 being of a maximum cross-section dimension or diameter that is within the range of 10-18 mm.

Description

In a first aspect, this invention relates to a grate for heaters for burning solid fuel bodies of the type that comprises a plurality of interspaced elements, at least some of which are rotatable in order to, during burning of fuel bodies on the same, set the fuel bodies in motion while tumbling the same as the burning gradually progresses and as ashes or other residual deposits automatically fall down into a subjacent ash space via interspaces between adjacent elements, a plurality of grate elements being drivable in one and the same direction of rotation in order to convey the fuel bodies in a direction from one end of the grate towards the opposite end thereof.

Prior Art

In heaters for burning solid fuels, such as pellets, a grate that forms a bottom in the burning chamber where the fuel is burnt and gasified is usually included. In the burning chamber, some type of feeder device mouths on a level above the grate, e.g. a worm conveyer, which continuously or intermittently feeds out the fuel bodies so that these fall down on the grate. Below the grate, there is a space in which ashes or other residual deposits are allowed to fall down and accumulate. Prior art grates for small heaters have generally been composed of solid and rigid constructions, which on one hand are able to retain the fuel bodies during the time required for burning and on the other hand allow supply of primary air from below. Perforated sheet metal plates, for instance, have been employed for this purpose. The purpose of these holes is to let through primary air to the fuel, the ashes subsequently being allowed to fall down over an edge of the sheet metal.
A disadvantage of the previously known, fixed grates for small heaters is that the distribution of the fuel bodies and burning of these on the grate takes place in an uncontrolled and uneven way. Furthermore, it happens that the temperature in the heart or core of the fire becomes so high that residual deposits sinter and stick onto the grate. Such factors may easily cause that the mode of burning becomes unclean and uneconomical and that sooting smoke emissions arise.
In larger installations for burning solid fuel bodies, it is previously known to use grates having rotatable grate elements in the shape of rolls. Thus, in EP 044 652 A2 a grate designed for large furnaces is described, which grate includes a plurality of rotatable, cylindrical rolls, which are intended to receive the fuel from above and crush or disintegrate residual deposits in the form of, among other things, ashes with the intention to facilitate the passage thereof to an ash space situated below the grate via the interspaces between the rolls. Said rolls are all formed with external, cog-like projections and are arranged to interact in pairs, more precisely in such a way that the two rolls in each pair rotate in opposite directions powdered, granular or cluster-like components in the interspace between the rolls. This grate is, however, associated with the disadvantage that the down-falling, fresh fuel bodies remain in the drop area without being conveyed surface-wise on top if the grate. The consequence of this may easily be that parts of unburnt fuel bodies still rich in energy may be disintegrated and fall down into the ash space situated below the grate.
Also GB 251,849 A discloses a mechanical grate for heaters for burning solid fuel bodies. Said known grate comprises a plurality of interspaced elements (P), at least some of which are rotatable in order to, during burning of fuel bodies on the same, set the fuel bodies in motion while tumbling the same as the burning progresses and as ashes or other residual deposits automatically fall down onto a subjacent ash space via interspaces between adjacent elements. A plurality of grate elements (P) being drivable in one and the same direction of rotation in order to convey the fuel bodies in a direction from one end of the grate towards the opposite end, whereby the grate elements are mutually parallel and the interspaces between the same are of a substantially uniform width. This known grate is also associated with the disadvantage that bigger parts of unburned fuel bodies may fall down into the ash space situated below the grate, or may be outfeed unburnt.
Furthermore, by US 5 452 670 an installation is known to destruct car tyres by means of burning or gasification. This installation includes a grate-like set of rotatable rolls by means of which tyres that are fed in at one end of a surrounding housing may during burning be conveyed surface-wise on the top side of the rolls to an opposite exit end, at which residual deposits may fall down onto a conveyer via the interspaces between the rolls. All rolls, with the exception of the one roll situated nearest to the exit end, are rotatable in one and the same direction of rotation, whereas said last roll in the set of rolls is rotatable in a direction of rotation being opposite to the others. This known installation is by no means suited for use in small heaters of the kind to which the invention relates. Thus, the rolls have a diameter that is approximately equal to the diameter of the tyres. This means that the wedge-shapedly or V-shapedly tapering flutes between adjacent rolls become utmost deep. For this reason, not only the tyres, but above all smaller fuel bodies, may easily get caught in the interspaces between the rolls without being conveyed further in the direction towards the exit ends. What is more, the installation is intended for destruction and not for burning with the objective of extracting heat from high-energy solid fuel bodies.

Objects and Features of the Invention

The present invention aims at obviating the above-mentioned shortcomings of previously known grates and at providing an improved grate. Thus, a primary object of the invention is to provide a grate that is suitable for use in small heaters and that not only facilitates the passage of the ashes down into a subjacent ash space, but also guarantees an even distribution and burning of solid fuel bodies of limited size. In particular, the grate should be suited for burning biomaterial pellets of the type that is fed out on the grate at one end thereof through a fuel feeder tube.
According to the invention, at least the primary object is attained by means of the features defined in the characterizing clause of claim 1. Preferred embodiments of the invention are furthermore defined in the dependent claim 2.
In a second aspect, the invention also relates to a heater as such. The features of the heater according to the invention are defined in the dependent claim 3.

Brief Description of the Appended Drawings

In the drawings:

Fig. 1 is a vertical section through a heater made in accordance with the invention in which a grate according to the invention is included,
Fig. 2 is a vertical section A-A in a 90° angle to the section in fig. 1,
Fig. 3 is a horizontal section B-B in fig. 1,
Fig. 4 is an enlarged detailed cut showing the grate in cross-section, and
Fig. 5 is a partly cut planar view from above of the grate only together with an appurtenant driving source.

Detailed Description of Preferred Embodiments of the Invention

The heater shown in the drawings comprises an outer wall 1 and a roof in the form of a removable lid 2. A water jacket, in its entirety designated 3, is arranged in the interior of the heater, which water jacket is composed of two concentric, cylindrical sheet-metal plates that define a rotationally symmetrical space 4 in which water may be present. The water jacket 3 is intersected by a plurality of individual tubes 5A, 5B through which flue gases may pass. More specifically, the flue gases pass in the direction upward through the tubes 5A (the ones to the left in fig. 3) and in the direction downward through the tubes 5B (the ones to the right in fig. 3). Cooled water may be led into the water jacket via a conduit 6, while heated water is fed out through a conduit 7.
In the lower part of the heater, a burning chamber 8 and under this an ash space 9 are arranged. The burning chamber 8 is confined by a vertical tube construction 10, as well as a grate in its entirety designated 11, which constitutes a bottom in the burning chamber 8. Said grate will be described in detail below with reference to figs. 4 and 5.
The tube construction 10 includes an external tube 12 and an internal tube 13, in the upper part of which a plurality of small holes 14 are recessed for supply of secondary air to the burning chamber, more precisely through the gap 15 that is formed between the tubes 12, 13. On top of the tube construction 10, a fireproof tube 16 is arranged, e.g., a ceramic tube. Primary air to the burning chamber is in a suitable way led in from the ash space 9 via the grate 11, as is outlined by the arrow C in fig. 1.
The requisite fuel is fed into the grate through a tube 17 having an internal feed worm 18. This feeder tube 17 intersects the tube construction 10 and mouths at one end of the grate 11 (to the left in fig. 2). Diametrically opposite the feeder tube 17, an inspection tube 19 is arranged that is accessible via a door 20. The tube construction 10 together with the ceramic tube 16 are carried by a horizontal carrier 21, which at the bottom side thereof also carries the grate 11. The carrier 21 may advantageously consist of a plate or sheet metal plate that separates the ash space 9 from a space 22 where the flue gases turn upward. Said space 22 is accessible via a side door 23. An analogous side door 24 enables access to the ash space 9.
Now reference is made to figs. 4 and 5, which in detail illustrate the nature of the grate according to the invention.
The grate 11 is composed of a plurality of interspaced elements 25 that are rotatable. In the embodiment shown, said grate elements are exemplified in the form of cylindrical rolls that are mounted in a common frame 26. The frame 26 may advantageously be quadrangular and composed of a pair of parallel side pieces 27, 28 and a pair of end pieces 29, 30, the first-mentioned one of which is situated in the proximity of the feeder tube 17. More precisely, the frame 26 is placed in such a way that the mouth of the feeder tube 17 is located somewhat inside the end piece 29 of the frame, as shown in fig. 4. In the example shown, it is assumed that all of the grate elements or rolls 25 are rotatable, the same being drivable by means of a common driving source 31, e.g., an electric motor, by a transmission in its entirety designated 32. The rolls 25 are at one end thereof connected to bars or shanks 33 that are more slender than the rolls and carry cogwheels 34 at the free ends thereof. Chains or notched belts 35 are included in the transmission, which transfer power to the cogwheels from an output shaft 36 of the driving source. In the example shown, every second shank 33 is longer than the other shanks, the cogwheels 34 being arranged in two rows displaced laterally in relation to each other.
The function of the grate according to the invention is best seen in fig. 4. When the fuel bodies 37, e.g., in the form of cylindrical pellets (e.g. of a diameter within the range of 6-10 mm), are fed out of the tube 17, the same fall down a short distance onto the rolls 25 being nearest to the end piece 29 of the frame, i.e. at an in-feeding end of the grate. In this area, the burning of the bodies is started, more precisely by means of the primary air that is brought in from below through the grate. As the rolls 25 are rotating, the fuel bodies will successively be conveyed in a direction towards the opposite end of the grate, i.e. in the direction of the furthest end piece 30 of the frame. During this transport in the direction from the left to the right in figs. 4 and 5, the bodies are burnt while forming ashes, which gradually fall down into the interspaces 38 between adjacent rolls 25. Such an evacuation of ashes down between the rolls is to a great extent facilitated by the rotation of the rolls in so far that the rolls are kept in motion and disintegrate possible residual deposits of a granular character. In other words, the rotation of the rolls guarantees that the process of burning results in only fine, powdered particles that without difficulty can fall down through the interspaces 38. During the transport thereof from the feeding end towards the opposite end of the grate, the initially solid bodies are tumbled by being continually helter-skeltered between the different rolls. In this way, the fuel bodies are distributed evenly along the grate while guaranteeing an even and clean process of burning.
The choice of dimensions of the rolls 25 and the interspaces there-between, respectively, is important. In order to, on one hand, obviate the risk of unburnt bodies, or such parts of the same that still have an energy content, unintentionally falling down via the interspaces 38, these interspaces should have a maximum width of approx. 4 mm. On the other hand, the interspaces should not be narrower than approx. 2 mm in order to guarantee an unimpeded passage of the fine ashes. In practice a width of the interspaces of approx. 3 mm is preferred. In turn, the diameter of the rolls should be within the range of 10-18 mm and preferably amount to 11 to 12 mm. In this way, it is guaranteed that the upwardly directed, substantially V-shaped flutes that are formed between adjacent rolls do not become so deep that they render the horizontal feed of the fuel along the top side of the grate difficult.
In this connection, it should be pointed out that the rolls 25 of the grate advantageously may be conformal and mutually parallel, as is shown in the drawings. All interspaces or gaps 38 between the rolls may advantageously - though not necessarily - be equally wide. Furthermore, it may be mentioned that the grate advantageously is horizontally oriented, although it is also feasible to arrange the same at a certain limited inclination, e.g. in the direction obliquely upwards/backwards towards the end piece 30 of the frame.
The described grate may also be modified in other respects. For instance, the grate elements do not necessarily need to consist of rolls of a cylindrical shape. Thus, the grate elements may be of a polygonal, e.g. hexagonal shape, or of a cross-section shape being not circular in another way. Furthermore, on the envelope surfaces or outsides of the elements, it is feasible to apply particular projections or combs, e.g. helicoidal combs with the purpose of improving the disintegration of granular residual deposits. In particular, it is feasible to form the elements nearest to the furthest end piece 30 of the frame with such projections, whereas the elements nearer the feeding end may have a smooth surface. In this connection, it should be pointed out that it is not necessary that all rolls or elements in the grate are rotatable. Thus, grates in which every second grate element is rotatable and every second fixed have been tried successfully. Neither do the grate elements need to be conformal. For instance, rotatable elements may be of a cylindrical shape, whereas interjacent, fixed elements may consist of flat iron or rods.
Within the scope of the invention, it is also feasible to reverse the direction of rotation of one or more grate elements in relation to the direction of rotation of other rotatable grate elements. For instance, it is possible to let all grate elements counted from the fuel in-feeding end of the grate rotate in a first direction of rotation (clockwise in fig. 4) with the exception of the last grate element (nearest to the end piece 30 of the frame), which is brought to rotate in the opposite direction. In this way, the grinding effect in the interspace or gap between the two adjacent grate elements that are situated furthest away from the fuel in-feeding end is enhanced.
Finally, it should be pointed out that the grate according to the invention is useful in other types of heaters than precisely the type being exemplified in figs. 1-3.

Claims

Grate for heaters for burning solid fuel bodies, comprising a plurality of interspaced elements (25), at least some of which are rotatable in order to, during burning of fuel bodies on the same, set the fuel bodies in motion while tumbling the same as the burning progresses and as ashes or other residual deposits automatically fall down into a subjacent ash space (9) via interspaces (38) between adjacent elements, a plurality of said grate elements (25) being drivable in one and the same direction of rotation in order to convey the fuel bodies in a direction from one end of the grate towards the opposite end thereof, characterized in that the grate elements 825) are mutually parallel and the interspaces (38) between the same are of a substantially uniform narrow width that is within the range of 2-4mm, that the individual grate elements (25) are of maximum cross-section dimension that is within the range of 10-18mm, and that a number of grate elements situated nearest to an in-feeding end of the grate consist of cylindrical rolls (25) having a smooth surface, whereas one or more grate elements situated nearest to the opposite end of the grate are formed with external projections having the purpose of disintegrating granular residual deposits.
Grate according to claim 1, characterized in that a grate element situated furthest from the in-feeding end and formed with grinding projections is arranged to rotate in the opposite direction of rotation in relation to the adjacent grate element.
Heater for burning solid fuels in the form of small fuel bodies, comprising a burning chamber (8), which is delimited by an internal tube (13) situated in a tube construction (10) and extending upwards from a bottom in the form of a grate (11), according to any one of claims 1-2, which construction also includes an external tube (12), which is separated from the internal tube (13) by a gap (15) through which secondary air may be supplied to the burning chamber (8) trough a plurality of small holes (14) in the internal tube, and primary air may be supplied to the burning chamber via the grate (11) from an ash space (9) positioned under the same and that a horizontal feeder tube (17) intersects said tube construction (10) and mouths at an end of the grate in order to, from the side, feed in the fuel bodies onto the grate.