WO2015121331A1

WO2015121331A1 - Solid-fuel combustion chamber

Info

Publication number: WO2015121331A1
Application number: PCT/EP2015/052919
Authority: WO
Inventors: Gérard Pitance
Original assignee: Stuv S.A.
Priority date: 2014-02-13
Filing date: 2015-02-12
Publication date: 2015-08-20
Also published as: EP3108180A1; CA2972650A1; BE1023167B1; EP3108180B1; CA2972650C

Abstract

The present invention relates to a solid-fuel combustion chamber comprising a staged burner with a lower stage in which, during use, primary combustion of the solid fuel takes place and with an upper stage in which, during use, secondary combustion of the gases (12) derived from the primary combustion takes place, said burner comprising in the upper stage: a first hollow body (4) intended to accommodate, within its interior volume, the gases (12) derived from the primary combustion, said first hollow body (4) comprising a conical part, and a secondary-air duct (8) arranged around said first hollow body (4) and opening at the upper end thereof, said duct (8) being delimited, on the one hand, by the first hollow body (4) and, on the other hand, by a wall of a shape that substantially complements that of the first hollow body (4) so as to ensure parallel injection of the secondary air along the first hollow body (4).

Description

SOLID FUEL FIREPLACE

Object of the invention

The present invention relates to a solid fuel fireplace having a stepped burner.

Technological background and state of the art

[0002] The combustion of solid fuels has the specific feature that it decomposes in two stages. A first phase takes place at the level of the fuel bed which, when heated to high temperature, decomposes into combustible gas, on the one hand, and solid carbon, on the other hand. This same solid carbon is consumed in the presence of oxygen which makes it possible to maintain the fuel bed at a high temperature and to maintain the pyrolysis phenomenon. Once released, the pyrolysis gases can also be burned. To do this, it is necessary that they are brought into the presence of oxygen, mixed with it and brought to a high temperature for a period of time sufficient for the combustion to be complete.

To optimize combustion and minimize emissions of gaseous pollutants, it is necessary to stagger the air distribution to control the amount of contact with the fuel in these different phases.

Thus, EP 0 401 205 B1 discloses a boiler with a primary combustion chamber, a secondary combustion chamber and respective primary air and secondary air transmission devices. In this document, the secondary air supply device has the configuration of a double-walled cone frustum, the inner envelope being pierced with holes allowing the distribution of secondary air inside the truncated cone crossed by the gases of the primary combustion chamber. This system has the disadvantage that it has been optimized to obtain good combustion at the expense of the aesthetics of the flame. Indeed, the many secondary air supply holes inside the truncated cone will give rise to small unsightly flames in the secondary combustion chamber. However, in certain applications such as fireplaces having a window for viewing the flame, it is not only important to optimize the combustion but also to ensure the aesthetics of the flame. When choosing a fireplace, the consumer will be particularly sensitive to the color (ideally yellow-orange), the size (the largest possible relative to the combustion chamber) and the vigor (ideally calm and dancing) of it.

JP S55 155110 A discloses an oxidation device mounted on a combustion chamber to remove carbon monoxide. In this device, secondary air is introduced into a passage around a conical body in which the combustion gases circulate. Due to the upward movement of the combustion gases and the secondary air, the latter are mixed above the conical body before coming into contact with a catalyst layer.

[0006] US Pat. No. 4,945,837 A discloses a pellet feed system for a furnace. This system has a fin to direct the fuel to the combustion plate in the upper position and includes ventilation tubes to prevent ignition and combustion of fuel stored in bins. The fin prevents the fuel particles from falling back into the auger and being ground into smaller particles.

Goals of the invention

The present invention aims to achieve a home whose layout of the various components of the burner provides an optimized combustion while ensuring the aesthetic qualities of the flame.

Short description of the fairs

Figure 1 shows a sectional view of the burner within the fireplace according to the invention. Figures 2 and 3 show a top view of the burner trays. In Figure 2, the openings in the plate for the introduction of primary air are in the form of circular orifices while in Figure 3, they are in the form of grooves.

Figure 4 shows a sectional zoom on the arrangement of the first hollow body and the second hollow body hosting the pyrolysis gases from the primary combustion. The flows of primary air, secondary air and pyrolysis gases are schematically represented by arrows. In this variant, the upper end of the first hollow body is smooth and the latter has no disc. Figure 5 shows the same arrangement with the upper end of the first hollow body having a sinusoidal cut.

Figure 6 shows at two different angles the first hollow body provided with a sinusoidal cut at its upper end. Figures 7 and 8 also show at two different angles the first hollow body with a crenellated cut and a sawtooth cut respectively.

Figure 9 is a sectional zoom on the arrangement of the first hollow body and the second hollow body welcoming the pyrolysis gases from the primary combustion. In this variant, compared to Figure 4, the upper end of the first hollow body is sinusoidal and a disk is positioned inside the first hollow body.

FIG. 10 illustrates, using a simulation, the tangential injection of secondary air into the duct formed by the wall of the first hollow body on the one hand, and by the wall of the second hollow body on the other hand; on the one hand, as well as the effect of mixing by recirculation of the pyrolysis gases above the disk disposed inside the first hollow body.

Figure 11 shows a top view of the guide fins disposed in the secondary air duct. Figure 12 shows the same fins in a sectional view.

Figure 13 shows a top view of the guide vanes disposed within the first hollow body around the disc. Figure 14 shows the same fins in a sectional view with in this variant also fins inside the secondary air duct. Figure 15 shows a sectional view of the burner within the fireplace according to one embodiment of the invention with a variant of the ignition system.

Figure 16 shows a top view of the burner tray with a deashing system in the closed position. Figure 17 shows the same view with the deashing system in the open position. In Figure 18, the ash removal mechanism according to the invention is shown with a cross sectional view of the burner in the fireplace.

[0018] Legend

(I) burner tray

(2) Feed screw

(3) Spark plug or ignition system

(4) First hollow body

(5) Opening in the burner tray

(6) Primary air supply

(7) Second hollow body

(8) Secondary air supply duct

(9) Disruptive element, also called obstacle

(10) Guide fin

(II) Ashtray

(12) Pyrolysis gas

(13) Heating element

(14) Sheath

(15) Orifice

(16) Conduit

(17) Volume supplied with outside air

(18) Bottom Burner Tray

(19) Top grid of burner tray

(20) Upper vertical actuating rod

(21) Horizontal actuating rod, secured to the vertical rod

(22) Openwork part in grids for deashing Main characteristic elements of the invention

The terms "lower", "upper", "above" and "below" which will be considered relatively with respect to the upward movement of air or combustion gases will subsequently be used. The expression "of substantially complementary shape" will also be used to designate walls that are parallel or almost parallel to one another as shown, for example, in FIG. 4 in the overlap area where the first hollow body is attached inside the second hollow body.

The present invention relates to a solid fuel combustion chamber comprising a stepped burner with a lower stage where takes place, in use, a primary combustion of the solid fuel and with an upper stage where takes place, in use, a secondary combustion gases from the primary combustion, said burner comprising at the upper stage:

a first hollow body intended to receive in its interior volume the gases resulting from the primary combustion, said first hollow body having a conical portion or being entirely of conical shape, and

a secondary air supply duct disposed around said first hollow body and opening at its upper end, said duct being delimited, on the one hand, by the first hollow body and, on the other hand, by a substantially shaped wall; complementary to that of the first hollow body to ensure a parallel injection of the secondary air along the first hollow body.

According to particular embodiments of the invention, the focus comprises at least one or a suitable combination of the following characteristics:

the upper end of the first hollow body which opens the secondary air supply duct has a cut in the form of a succession of projections and recesses;

the first hollow body is surmounted by a second hollow body;

the first hollow body is partially attached to the inside of the second hollow body in a so-called overlap area, the second hollow body acting as a wall delimiting the air supply duct in the covering zone;

in the overlap zone, the first hollow body and the second hollow body are respectively of convergent shape in the direction of movement of the gases; in the overlap zone, the first hollow body and the second hollow body are respectively of divergent shape in the direction of movement of the gases; the second hollow body is of divergent shape at the outlet of the upper stage in order to widen and slow down the flow of the pyrolysis gases;

- The upper end of the first hollow body comprises a conical or divergent conical portion or a cylindrical portion overlying the lower conical portion;

the upper end of the first hollow body which opens the secondary air supply duct has a sawtooth cut, a sinusoidal cut or a crenellated cutout;

the first hollow body and / or the second hollow body comprise in their internal volume a disturbing element ensuring a recirculation of the gases above said disturbing element;

it comprises oblique guide vanes disposed in the secondary air supply duct and / or in the interior volume of the first hollow body in order to respectively induce a circular movement to the secondary air and to the pyrolysis gas; the guide vanes are positioned around the disturbing element; the guide vanes are arranged at an angle of between 15 and 45 °;

the lower stage of the burner comprises a plate and a worm allowing the supply of solid fuel on said plate;

the plate has openings allowing the introduction of primary air; the tray is configured so that the ashes generated by the primary combustion fall overflowing the tray;

the plate comprises two superimposed grids each having perforated portions of complementary shape, a first grid in the upper position being rotatably mounted relative to a second grid in the lower position, said hearth comprising an actuating mechanism ensuring the rotation of the grid upper to allow the setting in vis-à-vis the perforated parts of each grid and thus the evacuation of ashes; the actuating mechanism comprises a vertical rod secured to the first grid and a horizontal rod movably mounted and secured to the vertical rod, the displacement of the horizontal rod causing the rotation of the first grid; it comprises an ignition system, said system comprising a metal furnace provided with an orifice, a heating element inserted into said metal furnace, an interior volume at the furnace connected to the orifice and intended to be supplied with outside air which is, in use, heated by the heating element before being injected into the lower stage of the burner. Detailed description of the invention

The present invention relates to a stove-type fireplace or solid fuel insert such as pellets, coal, biofuels, etc..

The fireplace according to the invention comprises a stepped burner, that is to say a burner with a two-stage combustion.

The burner shown in Figure 1 comprises da ns its lower part a plate 1 on which is fed the fuel through a feed screw 2. Above the burner plate 1 is positioned a candle d ignition 3 which, during the ignition phase, blows hot air at very high temperature on the fuel and leads to the ignition of the latter. The very high temperature present in the volume between the burner plate 1 and the first hollow body 4 will lead to the decomposition of the fuel pyrolysis gas and solid carbon (pyrolysis phenomenon).

The burner plate 1 is provided with openings 5 in the form of circular holes or grooves, allowing the introduction of primary air 6 which feeds the combustion of solid carbon from the pyrolysis (see FIG. 3, 4 and 5).

Once produced, pyrolysis gases 12 enter the first hollow body 4 and a second hollow body 7 (see Figures 4 and 5). The first hollow body 4 has a conical portion or is conically shaped and the second hollow body 7 has one or more conical portions. As illustrated in FIGS. 4 and 5, the first hollow body 4 comprises a portion of convergent conical shape in the direction of displacement of the pyrolysis gases and the second hollow body 7 comprises two conical parts successively convergent and divergent in the direction of movement of the gases leading to a depression at the limit of the convergent and divergent zones by venturi effect. The secondary air is injected parallel along the first hollow body 4 in an oblique conduit 8 opening on the upper end of the first hollow body 4 (see Figures 1, 4 and 5). In this configuration, the secondary air is preheated by contact with the hot walls of the first hollow body.

Preferably, the upper part of the first hollow body 4 is attached to the inside of the second hollow body 7 so that the conduit 8 is formed, on the one hand, by the outer wall of the first hollow body 4 and, on the other hand, by the inner wall of the second hollow body 7. In order to ensure the parallel injection of the secondary air, which will also be called tangential injection, the second hollow body comprises in its lower part a portion of substantially complementary shape to that of the first hollow body. Thus, the first convergent hollow body is attached to the interior of the converging lower portion of the second hollow body.

As shown in Figures 4 and 5, the inner wall of the second hollow body 7 comprises the aforementioned convergent and divergent portions joined by a substantially cylindrical zone. This succession of convergent, cylindrical and divergent portions may be composed of a combination of conical volumes or be of toric form. As mentioned above, the convergent portion delimits the duct 8 to ensure a tangential injection of secondary air. As for the divergent portion, it leads to an enlargement and a slowing of the flow at the outlet of the burner. This makes it possible to increase the time of presence of the gases in a hot zone in order to ensure their complete combustion and to obtain a wide and calm flame which optimizes their aesthetic character. According to a variant of the invention (not shown), the second hollow body may be entirely of divergent shape in the direction of movement of the gases. In this case, the first hollow body is also divergent in the direction of movement of the gas to ensure the tangential injection.

According to the invention and as already explained, the first hollow body 4 comprises a conical portion which defines the air supply duct and allows its tangential injection. The upper end of this first hollow body 4 may have a particular cutting that optimizes the mixing between the secondary air and the pyrolysis gases. The cut is in the form of a succession of hollows and ridges. For example, the upper end of the first hollow body 4 may have a sinusoidal shape shown in FIGS. 5, 6 and 9. In a variant, it may be in the form of saw teeth or crenellations (see FIGS. 8 and 7 respectively). . The upper end is either of convergent shape in the continuity of the conical portion as shown in Figure 9 or may have as shown in Figures 6 to 8 a diverging cylindrical or conical portion (not shown). In other words, the first hollow body has a conical portion surmounted at its upper end of a conical or divergent conical portion or a cylindrical portion. According to the invention, the three types of cutting apply regardless of the shape of the upper end (conical or cylindrical).

Optionally, a disturbing element 9 visible among others in Figures 1 and 9 may be mounted within the first hollow body 4. It may be in the form of disk, ring, star, etc.. and its function is to promote the recirculation of the pyrolysis gases above the disturbing element as simulated in FIG. 10 (the disruptive element in disk form being schematized by a white space). It can be mounted inside the first hollow body as illustrated in the figures but also inside the second hollow body with the same function of promoting the mixing of the gases.

Still for the sake of optimization of the mixture, oblique guide vanes with an angle of between 15 ° and 45 ° may be arranged at the level of the secondary air channel 8 as shown inter alia in FIGS. and 12 and / or between the disturbing element 9 and the inner wall of the first hollow body 4 as shown inter alia in FIGS. 13 and 14. They may be added in order to induce a circular movement to the flow and thus to promote the mixing gases and expand the flame at the burner outlet.

Regarding the ignition system, it may according to one embodiment of the invention be composed of a heating element 13 inserted into a metal sleeve 14 closed by a wall at its upper end and by the heating element at its end. lower (see Figure 15). An orifice 15 formed in the lower part of the sheath and a conduit 16 connected to the upper part of the sleeve allow a flow of air from the volume 17 supplied with outside air. In contact with the heating element 13, the air is heated and is injected at the level of the burner plate 1. The fact of taking the air in the volume 17 and not in the room makes it possible to optimize the tightness of the apparatus.

Finally, it will be specified that the ashes generated by the combustion fall from the burner tray 1 overflow and that the device may include a mechanism for facilitating the evacuation of the ashes from the burner tray 1 to the ashtray 11.

According to an alternative shown in Figures 16 to 18, the burner tray 1 comprises two grids 18,19 superimposed each provided with openings 5 for the primary air inlet and perforated portions 22 of complementary shape. The grid in the lower position 18 is stationary while the grid in the upper position 19 is rotatably mounted around the center of the burner plate. Under the effect of an actuating mechanism described below, the perforated portions 22 of the upper grid are brought vis-à-vis the perforated portions 22 of the lower grid to ensure the evacuation of ash. The upper grid 19 is actuated by means of the vertical rod 20 which is integral with the horizontal rod 21, the front-to-rear actuation of the horizontal rod ensuring the rotation of the upper grid with respect to the lower grid. It will be specified that the present invention also covers the variant where the actuation is provided by a motor.

Advantages of the invention

The absence of lateral orifices in the first hollow body and the control of the flow conditions at the outlet of the burner through the diverging zone of the second hollow body to obtain a large calm and dancing flame of orange color .

The injection in a direction parallel to the wall of the first hollow body ensures a progressive contact between the gases from the primary combustion with the secondary air and therefore a progressive combustion of the pyrolysis gases. This makes it possible to obtain a long flame as well as a relatively calm flow downstream of the secondary air injector. On the other hand, the parallel injection induces a driving effect of the primary flow, i.e. pyrolysis gases, by the secondary flow, which allows to model the flame according to the orientation of the secondary injection.

The particular cut of the first hollow body allows, on the one hand, to create turbulence at the places of contact between the gases from the primary combustion with secondary air. This promotes mixing at the reaction zone and provides complete combustion. It allows, on the other hand, to obtain a passage section of the gases from the primary combustion leading to a quiet flow while guiding the gas to allow the modeling of the flame.

Thanks to the optimization of the reaction conditions between the pyrolysis gas and oxygen, the combustion efficiency is improved and the emission of polluting gases is reduced.

There is no disturbance of the flame and slag generation induced by the fall of the granules as observed in supply systems using a spout from the top.

The aesthetics of the burner is optimized thanks to its shape and the absence of visible mechanical elements in the combustion chamber.

Claims

A solid fuel burning furnace comprising a stepped burner with a lower stage where, in use, a primary combustion of the solid fuel takes place and with an upper stage where, in use, a secondary combustion of the gases (12) produced by the primary combustion, said burner comprising in the upper stage:

a first hollow body (4) for accommodating in its interior volume the gases (12) resulting from the primary combustion, said first hollow body (4) having a conical portion, and

a duct (8) for supplying secondary air arranged around said first hollow body (4) and opening at its upper end, said duct (8) being delimited, on the one hand, by the first hollow body (4) and, on the other hand, by a wall of a shape substantially complementary to that of the first hollow body (4) so as to ensure parallel injection of the secondary air along the first hollow body (4),

characterized in that the upper end of the first hollow body (4) which opens the conduit (8) for supplying secondary air has a cut in the form of a succession of projections and recesses.

2. The fireplace according to claim 1, comprising a second hollow body

(7), the first hollow body (4) being surmounted by said second hollow body (7).

The fireplace according to claim 2, wherein the first hollow body

(4) is partially attached to the interior of the second hollow body (7) in a so-called overlap area, the second hollow body (7) acting as a wall delimiting the duct

(8) supplying air into the overlap area.

4. Fireplace according to claim 3, wherein, in the area of overlap, the first hollow body (4) and the second hollow body (7) are respectively of convergent shape in the direction of movement of the gas (12).

5. Fireplace according to claim 3, wherein, in the area of overlap, the first hollow body (4) and the second hollow body (7) are respectively of divergent shape in the direction of movement of the gas (12).

6. Fireplace according to any one of claims 2 to 5, wherein the second hollow body (7) is of divergent shape at the outlet of the upper stage in order to widen and slow the flow of the pyrolysis gases (12). .

7. A fireplace according to any one of the preceding claims, wherein the upper end of the first hollow body (4) comprises a conical or divergent conical portion or a cylindrical portion.

8. Fireplace according to any one of the preceding claims, wherein the upper end of the first hollow body (4) which opens the duct (8) for supplying secondary air has a sinusoidal cut, a cut in teeth saw or cut in the form of crenellations.

9. Fireplace according to any one of the preceding claims, wherein the first hollow body (4) and / or the second hollow body (7) comprise in their internal volume a disturbing element (9) ensuring a recirculation of gases (12). above said disturbing element (9).

10. Fireplace according to any one of the preceding claims, comprising oblique guide vanes (10) arranged in the duct (8) for supplying secondary air and / or in the interior volume of the first hollow body (4) to to respectively induce a circular motion to the secondary air and the gas (12).

11. Fireplace according to claim 10, wherein the guide vanes (10) are positioned around the disturbing element (9).

12. Fireplace according to claim 10 or 11, wherein the guide vanes (10) are arranged at an angle between 15 and 45 °.

13. Fireplace according to any one of the preceding claims, wherein the lower stage of the burner comprises a plate (1) and an endless screw (2) for feeding solid fuel on said plate (1).

14. Fireplace according to claim 13, wherein the plate (1) has openings (5) for the introduction of primary air (6).

15. Fireplace according to claim 13 or 14, wherein the plate (1) is configured so that the ashes generated by the primary combustion fall overflowing the plate (1).

16. Fireplace according to claim 13 or 14, wherein the plate (1) comprises two grids (18,19) superimposed each having perforated portions (22) of complementary shape, a first grid in upper position (19) being mounted movably in rotation with respect to a second gate in the lower position (18), said hearth comprising an actuating mechanism (20,21) ensuring the rotation of the upper gate (19) to allow the facing of the parts perforated (22) of each grid (18,19) and thus the evacuation of ashes.

17. The hearth of claim 16, wherein the actuating mechanism comprises a vertical rod (20) integral with the first grid (19) and a horizontal rod (21) movably mounted and secured to the vertical rod (20), the moving the horizontal rod (21) causing the first grid (19) to rotate.

Fireplace according to any one of the preceding claims, comprising an ignition system, said system comprising a metal sleeve (14) provided with an orifice (15), a heating element (13) inserted into said metal sleeve (14). ), a fireplace interior volume (17) connected to the orifice (15) and for supplying outside air which is, in use, heated by the heating element (13) before being injected into the lower stage of the burner.