FR2671166A1 - Boiler specially designed for burning wood scraps - Google Patents

Abstract

a) Boiler specially designed for burning wood scraps. b) Boiler characterised in that the burner (3) comprises: - an outer casing (11) - a second casing (12), of e.g. polygonal section, designed to receive the wood scraps and defining in its interior a burn chamber (13) subdivided into an upstream chamber (20) for drying, gasifying and pyrolysing the wood scraps (2), and a downstream chamber (21) for burning the carbonised residues, - this second casing (12) being located inside the outer casing (11), and - members (22) for distributing the oxygen-containing air between the upstream chamber (20) and the downstream chamber (21).

Description

"Boiler room specially designed for the combustion of wood chips".

 The present invention relates to a boiler room specially designed for the combustion of wood chips.

 Logging and processing companies generate large volumes of related products (edging files) and waste (sawdust, bark, etc.) which have so far been little or little valued.

 However, the scarcity and increasing price of traditional fossil energy sources (coal, oil, natural gas, etc.) encourage scientists to seek new alternative energies such as, for example, nuclear or solar energy. . In doing so, however, it is necessary to take into account a number of imperatives, the most important of which are linked to pollution.

 However, it has been realized that, due to the aforementioned increase in the price of oil, the use of wood chips as an energy source could become competitive for certain applications. This observation opens up prospects all the more interesting since wood has the advantage of promoting job creation (4 to 5 times more than oil or gas for the same amount of energy produced and delivered) and preserving the environment since, unlike fossil fuels, it does not release gaseous pollutants such as sulfur dioxide or nitrogen oxides.

 Given the above considerations, manufacturers have already proposed several types of boilers specially designed for the combustion of wood chips: these prove to be economically viable only for powers exceeding around 500 kW, and the fuel savings achieved are insufficient to allow their transposition to more modest equipment, taking into account the "overinvestment" necessary at the start.

The object of the present invention is to remedy this drawback by proposing a boiler specially designed for the combustion of shredded wood and other crushed wood waste, the cost of which is not prohibitive for low-power installations (small groups: groups schools, retirement homes, set of pavilions
HLM, swimming pools, ...).

 This boiler room conventionally comprises automatic feed elements for the shredded wood, a burner associated with a boiler and cooperating with primary and secondary air blowing fans acting as oxidizer, as well as a programmable controller allowing to control all the mechanical and thermal functions of the boiler room. This is essentially distinguished by the particular configuration of the burner, which enables remarkable energy efficiency to be obtained.

 According to the invention, the boiler room burner is for this purpose constituted by a first enclosure or essentially cylindrical horizontal outer enclosure; a second enclosure, in particular of polygonal section, intended to receive the shredded wood and delimiting at its internal part a burning chamber subdivided into an upstream chamber for drying, gasification and pyrolysis of the shredded wood, and a downstream chamber for combustion of the residues carbonaceous, as well as by primary air distribution members between the upstream chamber and the downstream chamber.

 According to the invention, the second enclosure is arranged coaxially inside the exterior enclosure and cooperates with the latter to define, on the one hand, a lower peripheral chamber associated with a first fan for channeling the primary air and introduce it into the shredded wood so as to allow it to burn in thin and stable layers, and, on the other hand, an upper peripheral chamber associated with a second fan to channel the secondary air and introduce it into the boiler. so as to allow the formation and development of the flame at this level.

 In this presentation, the terms upstream and downstream relate to the direction of circulation of the primary air or of the secondary air.

 It is important to stress the importance of the uniform distribution of the primary air over the entire burning chamber, and therefore between the upstream chamber and the downstream chamber: it is indeed essential that the upstream chamber receives a quantity of sufficient oxidizer to allow drying, pyrolysis and uniform gasification of the wood.

 In accordance with the invention, a conventional boiler can be associated with the burner, in particular a water-blade boiler surmounted by a smoke tube exchanger making it possible to reject the fumes after passing through a cyclone dust collector at a temperature of the order of 200 "C; the pressure losses can be compensated by a smoke extractor putting the boiler in slight depression, which eliminates the risks of rising fire and smoke in the fuel supply tube.

 According to another characteristic of the invention, the internal hexagonal enclosure is formed by the association of two superimposed refractory stainless steel buckets, namely an upper bucket forming a vault, provided with cooling fins, and a lower bucket forming grid pierced with a multitude of perforations so as to allow the introduction of primary air into the shredded wood to be burned.

 The fixing of fins on the external face of the vault, essentially perpendicular to the latter, has proved essential to avoid overheating of the burn chamber.

 The number and dimensions of the holes must be chosen so as to avoid any risk of falling wood in the lower peripheral chamber, but, at the same time, to guarantee a sufficient ventilation surface: it is also essential that the burning of the wood does not not in a fluidized bed, but in thin, stable layers.

 Another essential imperative in accordance with the invention consists in avoiding any clogging of the lower peripheral chamber by ashes which can collect thereon following the combustion of the wood. It is therefore essential to provide for bodies for evacuating the ashes.

 To this end, and according to another characteristic of the invention, the peripheral chambers are closed at their downstream part by a crown comprising a central orifice of configuration corresponding to that of the interior enclosure, as well as, on the one hand, at its upper part of the secondary air passage holes, and, on the other hand, at its lower part at least one ash discharge hole under the action of the primary air flow.

 It is important to ensure that the speed of the primary air is not too high to prevent any flight of wood particles in the boiler.

 The configuration, (in particular the number and dimensions) of the secondary air passage holes, is also essential: it is indeed imperative to obtain a flame developing properly in the boiler; for this purpose, it is necessary that the secondary air is divided into small air streams sufficiently powerful to be able to mix with the pyrolysis gas.

 However, avoid creating disturbances in the boiler that could be harmful to the development of the flame. For this purpose, it is possible to also provide a certain number of perforations at the level of the downstream end of the vault, so as to bring down part of the secondary air, on the downstream part of the burning chamber.

 According to a preferred characteristic of the invention, the primary air distribution members between the upstream chamber and the downstream chamber are constituted by a baffle partially blocking the passage of the primary air flow in the separation zone between the two chambers and cooperating with members for closing the perforations of the grid in this zone.

 Experience has shown that the baffle should be placed about two-thirds the length of the burn chamber; its presence makes it possible to prevent the major part of the primary air flow going towards the downstream part of the burning chamber, by "washing" the carbonaceous residues being at this level, which would have the consequence of entraining harmful take-offs of carbonaceous particles.

 Experience has also shown that it is essential to close off the perforations in the grid located at the level of the baffle so as not to create an excessive and therefore unbalanced circulation of primary air in the orifices located at this point. level.

 Another essential aspect of the invention is linked to the particular configuration of the automatic feeding devices for the wood chips in the burning chamber.

 In the boilers of the prior art, the wood was in fact most often supplied by means of a worm screw system causing the risk of blockages or jams, and above all causing the risk of fire as a result of rising the flame, due to the absence of a physical rupture between the burn chamber and the feed members.

The automatic shredded wood feed members of the boiler room according to the invention make it possible to remedy these drawbacks; they are characterized in that they include - a storage tank at the bottom of which moves,
in a back and forth movement, an organ of
main scraping likely to push the wood
shredded in a chute located below the
reservoir, - a supply channel placed in the extension of the
chute and at the bottom of which also moves a
auxiliary scraping device according to a movement of
back and forth essentially perpendicular to the
movement of the main scraping device for
push the shredded wood into the room of a
injector piston, - a conical tube allowing communication between the
injector piston chamber and the
burning, and - a hydraulic unit for controlling the
movements of the main scraping members and
auxiliary as well as the injector piston.

 The automatic feeding devices for the shredded wood are thus constituted by three "pusher" members mounted "in cascade" perpendicularly to one another, which allow a metered and smooth distribution of the wood in the burning chamber. This configuration has two major advantages linked, on the one hand, to its great compactness which limits the footprint of the boiler room, and, on the other hand, to its high reliability linked to the fact that it is not used with only one driving energy, hydraulic energy, to animate slow movements, in cascade, controlled by the hydraulic central unit / programmable controller.

 According to another characteristic of the invention, the main and auxiliary scraper members are respectively constituted by a series of scraper bars mounted in parallel and cooperating with at least one hydraulic cylinder, the scraper bars, with an asymmetric delta-shaped section, comprising a sloping front face directed towards the trough / chamber of the injector piston, and a more inclined rear face.

 In accordance with this configuration, during their reciprocating movement, the scraper bars first push the shredded wood towards the chute or the chamber of the injector piston, before penetrating, on the return, into the mass of wood, thus avoiding any risk of vaulting and jamming, regardless of the grain size of the wood.

 To further improve the characteristics of the distribution of shredded wood, it is advantageous to provide, according to another characteristic of the invention, fixed scraper bars mounted parallel to the movable scraper bars and cooperating therewith to prevent the shredded wood to move back into the storage tank or into the intake channel.

 Furthermore, and according to another characteristic of the invention, there are provided safety members making it possible to automatically shut off the chamber of the injector piston in the event of a power failure so as to exclude any risk of the fire rising. These organs can in particular be constituted by a nitrogen ball accumulator.

 The boiler room according to the invention can of course also include other safety devices, conventional, in order to avoid possible malfunctions or limit the consequences.

 It is possible, for example, to equip the hydraulic unit with safety devices making it possible to reverse the operation of the jacks, in particular in the presence of a foreign body, or to stop the injector piston in the event of extinction of the hearth.

 One can also provide a thermostatic valve, connected to the city water network and located above the intake channel, capable of opening under the effect of a rise in temperature to flood the fuel.

 According to another characteristic of the invention, the programmable automaton comprises members making it possible to control the hydraulic jacks associated with the main and auxiliary scraping members as well as the injector piston, and therefore to adjust the flow of shredded wood introduced into the chamber of burning, as well as organs making it possible to vary the flow rates of combustion air blown by the first and by the second fan as a function of the characteristics of the wood chips, in particular its moisture content, and the oxygen content of the gas escaping from the boiler.

The characteristics of the boiler room which is the subject of the invention will be described in more detail with reference to the accompanying drawings in which
FIG. 1 is a general view of the boiler room,
FIG. 2 is a front view of the burner,
FIG. 3 is a schematic cross section of this same burner,
FIG. 4 is a perspective view showing the interior enclosure,
FIG. 5 represents the primary air distribution members,
- Figure 6 is a front view of the crown.

 - Figure 7 is a schematic section of the installation showing more precisely the feed members.

 - Figure 8 is a sectional view along the axis 8-8 of Figure 7.

 According to FIG. 1, the boiler room is schematically constituted by a storage tank 1 for shredded wood 2 associated with supply members A which will be described in more detail in the remainder of this description, as well as by a burner 3 and a programmable logic controller B.

 The burner 3 is associated with a boiler 4 and cooperates with fans 5 and 6 respectively intended to supply the burner with primary combustion air and with secondary combustion air.

 The boiler 4 is a boiler with a water slide surmounted by a smoke tube exchanger 7 making it possible to reject the fumes in a chimney 8 after passing through a dedusting cyclone 9.

 According to Figures 2, 3 and 4, the burner 3 communicates with a conical tube 10 through which the wood chip is introduced in a manner which will be described in more detail later in this presentation and is schematically constituted by an outer enclosure 11 longitudinal and arranged horizontally, essentially cylindrical, and of an internal enclosure 12 of hexagonal section which is mounted inside the external enclosure 11, coaxially with the latter, and is shown in more detail in FIG. 4. This second enclosure 12 which is intended to receive the shredded wood and delimits at its internal part a burning chamber 13 is actually constituted by two buckets 14, 15 made of superimposed refractory stainless steel. The upper bucket 15 which constitutes the vault of the burning chamber 13 is provided with cooling fins 16; the lower bucket 14 is itself pierced with a multitude of perforations 17 so as to constitute a grid.

 According to Figures 2 and 3, the enclosures 11 and 12 define therebetween, on the one hand, a lower peripheral chamber 18 associated with the first fan 5 and channeling the primary air according to the arrows a to introduce it into the wood shredded by the perforations 17 so as to allow it to burn, and, on the other hand, an upper peripheral chamber 19 associated with the second fan 6 to channel the secondary air according to the arrows b and introduce it into the boiler 4 so as to allow the formation and development at this level of the flame not shown.

 According to FIG. 3, the burning chamber 13 is subdivided into an upstream chamber 20 which represents approximately 2/3 of its length and inside which the gasification and pyrolysis of the shredded wood are carried out, and a downstream chamber 20 for combustion of carbonaceous residues. It is essential that the primary air, introduced into the mass of firewood according to arrows a, is distributed evenly between these two chambers; distribution members 22 are provided for this purpose in the lower peripheral chamber 18 at the level of the separation zone between the two chambers 20 and 21.

 According to FIG. 5, these distribution members 22 consist of a baffle comprising two branches 23, 23 ′ which laterally blocks the passage of the primary air flow a and by a cap 24 making it possible to close the perforations 17 located in the separation zone between the two chambers 20 and 21. Not shown, a similar result could be obtained by not providing a perforation 17 in this zone.

 The presence of the shutter members 22 makes it possible to guarantee that the perforations 17 located in the chamber 20 are suitably supplied with air without the risk that the latter collects for the most part at the level of the downstream part of the burning chamber.

 Furthermore, and as shown in FIG. 6, the peripheral chambers 18 and 19 are closed, at their downstream part, by a crown 44 which has not been shown in FIG. 3 for the sake of clarity, and which comprises a hexagonal central orifice 24 whose configuration corresponds to that of the inner enclosure 12.

 A hole 25 allows the lower peripheral chamber 18 and the internal part of the boiler 4 to be placed in communication so as to guarantee the evacuation according to arrow a '(FIG. 3) of the ashes fallen into this chamber, and therefore prevent any risk of clogging thereof.

 Holes 26 for the passage of secondary air (arrow b) are also provided in the upper part of the crown 44. The configuration and the number of these holes are chosen so as to optimize the characteristics of the flame at the level of the internal part of the boiler 4.

 According to FIGS. 1 and 7, the feed members A make it possible to transfer the shredded wood from the storage tank 1 to the conical tube 10 for introduction into the burning chamber 13 and into the boiler 4.

 According to FIGS. 1, 7 and 8, these members schematically comprise, in addition to the storage tank 1, a chute 27 located below, perpendicular to the latter, and extending by a supply channel 28 opening perpendicularly into the working chamber 29 of an injector piston 30. The chamber 29, semi-cylindrical, communicates with the conical tube 10.

 According to Figures 7 and 8, a main scraping member 31 moves back and forth along the bottom 33 of the storage tank 1 (arrow c) under the action of a main cylinder 32 to push the shredded wood in chute 27.

 This main scraper member 31 is constituted by a series of scraper bars 34 mounted parallel to a certain distance from each other so as to define a scale. According to FIG. 8, the section of the scraper bars 34 has the shape of an asymmetrical delta comprising a sloping front face 35 directed towards the chute 27 and a more inclined rear face 36; this configuration allows the bars, on the way out, to push the shredded wood towards the chute 27, and, on the way back, to penetrate into the mass of the wood so as to avoid the formation of vaults and jams whatever the particle size of the wood. The movable bars 34 cooperate with fixed bars 37 of similar section fixed on the bottom 33 of the storage tank 1 to prevent the wood from moving back, and therefore contribute to a homogeneous "emptying" of the storage tank 1.

 According to Figures 7 and 8, the chute 27 and the supply channel 28 have a rectangular section, and in particular a flat bottom 38 along which moves, according to a back and forth movement (arrow d), a auxiliary scraping member 39, the movement of which, controlled by a set of two auxiliary cylinders 40, 40 ′, makes it possible to convey the chipped wood into the working chamber 29 of the injector piston 30. The auxiliary scraping member 39 has a configuration similar to that of the main scraper member 31, and therefore consists of a series of scraper bars 41 with an asymmetric delta-shaped section.

 According to FIG. 7, the wood pushed by the auxiliary scraping member 39 reaches the working chamber 29 of the piston 30 which is driven back and forth along the arrow e by an injection cylinder 42 to allow supply the burn chamber 13 of the burner 3.

 The movements of the various jacks 32, 40, 40 'and 42 are controlled from a hydraulic unit 43 shown in FIG. 1.

 The various aforementioned movements are controlled automatically and "in cascade" by the programmable automaton B according to the following well-defined sequence: the injector piston 30 first moves backwards to open the working chamber 29, then the organs auxiliary scraper 39 move back and forth to inject an adjustable predetermined dose of wood into the chamber 29, before the injector piston 30 moves forward. At a predetermined time interval, the automaton B also controls a return trip from the main scraping member 31.

 Many safety devices not shown also make it possible to avoid possible malfunctions or limit the consequences.

Claims (10)

CLAIMS between the upstream chamber (20) and the downstream chamber (21). of the flame at this level, as well as - primary air distribution members (22) so as to allow formation and secondary development and introduce it into the boiler (4) of second fan (6) to channel the 'air upper peripheral chamber (19) associated with a thin and stable layers, and, on the other hand, a shredded (2) so as to allow its burning in the primary air and introduce it into the wood associated with a first fan (5) to channel part, a lower peripheral chamber (18) (11) and cooperating with it to define, coaxially inside the outer enclosure combustion of carbonaceous residues, - this second enclosure ( 12) being disposed shredded (2), and a downstream chamber (21) for drying, gasification and pyrolysis of the firewood (13) subdivided into an upstream chamber (20) of (2) and delimiting at its internal part a chamber polygonal, intended to receive chipped wood essentially cylindrical horizontal unit, - a second enclosure (12), in particular of cross section  1 ") Boiler room specially designed for the combustion of wood chips and comprising organs (A) for automatic supply of wood chips (2), a burner (3) associated with a boiler (4) and cooperating with fans (5, 6) for blowing primary air and secondary air, as well as a programmable automaton (B) for controlling all of the mechanical and thermal functions of the boiler room, boiler room characterized in that the burner (3) comprises - a first enclosure (11) or external enclosure  2 ") Boiler room according to claim 1, characterized in that the hexagonal inner enclosure (12) is formed by the association of two superimposed stainless steel buckets (14, 15), namely an upper bucket (15) forming an arch provided with cooling fins (16) and a lower trough (14) forming a grid pierced with a multitude of perforations (17) so as to allow the introduction of primary air into the shredded wood (2) to be burned.  3 ") Boiler room according to any one of claims 1 and 2, characterized in that the burner (3) comprises members (44, 25) for evacuating in the boiler (4) the ashes fallen into the lower peripheral chamber ( 18).  4 ") Boiler room according to any one of claims 1 to 3, characterized in that the peripheral chambers (18, 19) are closed at their downstream part by a crown (44) comprising a central orifice (24) of configuration corresponding to that of the inner enclosure (12) as well as, on the one hand, at its upper part of the holes (26) for the passage of the secondary air, and, on the other hand, at its lower part at least one hole ( 25) ash removal under the action of the primary air flow.  5 ") Boiler room according to any one of claims 1 to 4, characterized in that the organs (22) for distributing the primary air between the upstream chamber (20) and the downstream chamber (21) consist of a baffle (23, 23 ') laterally blocking the passage of the primary air flow in the separation zone between the two chambers (20, 21), and cooperating with shutter members (24) of the perforations (17) of the grid (14) in this area.  injector piston (30).  main - (31) and auxiliary (39) as well as  control the movements of the scraping members  burn chamber (13), and - a hydraulic unit (43) making it possible to  the chamber (29) of the injector piston (30) and the  injector (30), - a conical tube (10) allowing communication  in the working chamber (29) of a piston  main (31) for pushing the chipped wood (2)  perpendicular to the movement of the scraper member  a back and forth movement basically  also an auxiliary scraping member (39) according to  the chute (27) at the bottom (38) of which moves  (27) located below the tank (1), - a supply channel (28) placed in the extension of  push the shredded wood (2) into a chute  main scraping member (31) capable of  moves, in a back-and-forth motion, a  6) Boiler room according to any one of claims 1 to 5, characterized in that the members (A) automatic feeding of the shredded wood (2) comprise - a storage tank (1) at the bottom (33) of which is  7 ") Boiler room according to claim 6, characterized in that the main (31) and auxiliary (39) scraping members are respectively constituted by a series of scraper bars (34, 41) mounted in parallel and cooperating with at least one jack hydraulic (32, 40, 40 '), the scraper bars, of asymmetric delta-shaped section, comprising a sloping front face (35) directed towards the trough (27) / the chamber (29) of the injector piston (30) , and a rear face (36) more inclined.  8) Boiler room according to claim 7, characterized in that the movable scraper bars (34, 41) cooperate with fixed scraper bars (37) mounted parallel to them to prevent the shredded wood (2) from moving back into the storage tank (1) or in the supply channel (28).  9 ") Boiler room according to any one of claims 6 to 9, characterized in that it comprises safety members making it possible to automatically close the chamber (29) of the injector piston (10) in the event of a power failure of so as to exclude any risk of fire rising.  10) Boiler room according to any one of claims 7 to 9, characterized in that the programmable controller (B) comprises members for controlling the hydraulic cylinders (32, 40, 40 ', 42) associated with the main scraper members (31) and auxiliary (39), as well as the injector piston (30), and therefore to adjust the flow of shredded wood (2) introduced into the burning chamber (10), as well as members making it possible to vary the oxidizing air flows blown by the first and by the second fan (5, 6) as a function of the characteristics of the wood chip (2) and in particular of its moisture content.