EP0152317B1 - Boiler for wood with a preheating chamber for the fuel - Google Patents

Abstract

1. Combustion device of the closed furnace type, comprising a fuel reserve (16) located above a grate and a chamber (15) for preheating combustion air, the cavity of the said chamber being delimited by a hearth (17) surrounding the grate (12), by the said grate (12) and by a base wall (6), the said chamber being provided with an inlet (30) for ambient air, characterized : in that the said preheating chamber (15) is located below the said fuel reserve (16), by a tube (11) arranged below the said grate (12) and passing from top to bottom and through the centre of the said preheating chamber (15), the said preheating chamber chamber consequently having an approximately annular shape, and by a triple plurality of hot combustion air outlets, a first plurality of outlets being composed of passages (10) through the hearth (17), a second plurality of outlets being composed of ducts (13) opening out at the periphery of the hearth (17) at a certain height above it and a third plurality of outlets (31) being located in the vicinity of the downstream or lower end of the tube (11).

Description

The present invention is in the field of heating techniques and it relates more specifically to a combustion device of the closed hearth type comprising a reserve of fuel, such as wood, situated above a grate, said device being intended for provide hot water.

The high cost of fossil fuels such as coal and petroleum has, in the recent past, stimulated research aimed at burning wood for heating purposes. Thus, methods of heating by combustion of wood in logs are known, these methods generally consisting of burning wood in appropriate boilers using either reverse combustion, or semi-inverted or upward combustion. However, it seems that not all the problems inherent in the use of wood have been resolved; moisture and resinous resulting in excessive taring, and therefore incomplete combustion.

There is known from a patent FR-A-2,512,176 a combustion apparatus comprising two superimposed chambers separated by a partition provided with a grate; the upper chamber receives the fuel and has an air intake at its upper part, while the lower chamber is connected to the chimney and passed through by an air inlet duct opening into the terminal part of the lower chamber; an air intake takes place in the plane of the grid. Due to the need for air intake at the upper part of the fuel receiving chamber, it is expected that the pyrogenation will be little localized.

An object of the present invention is to burn the wood completely by generating a flame and the guiding idea of the Applicant was to obtain a concentration of heat so as to heat the combustion air on the one hand in order to dry and carbonize the wood on the other hand.

Another object of the invention is to avoid the drawbacks due to the great variations in humidity of the wood intended to be burned in the aforementioned manner while obtaining an improvement in the thermal efficiency of combustion and the guiding idea of the Applicant has been to obtain an area at high temperature and to take the energy necessary for drying the wood is to find in the "reserve" the means of condensing the water and the tars so that the latter decompose chemically on contact with the high temperature area to produce a gas.

Another object of the invention lies in the regular and controlled production of hot water by avoiding the problems of drawing chimneys linked to atmospheric and geographical conditions in order to obtain an "all" or "slowed down" operation, the latter possibly being continue for several days.

The main idea of the present invention, starting from the known principle of reverse draft fireplaces, consists in separating, by air flows of appropriate location, the firebox into a fuel and condensation water reserve zone. and tars, and in a pyrolysis zone.

According to the present invention, a combustion device of the closed hearth type comprising a fuel reserve situated above a grate, comprises, according to a first general characteristic of organization of its means, an annular chamber for preheating the air of combustion, the volume of said chamber being delimited by a nozzle, or truncated cone, disposed above the grate, by a hearth surrounding the grate and by a so-called bottom wall, said preheating chamber being provided with an inlet of ambient air and of a triple plurality of hot air outlets, a first plurality of outlets being constituted by passages through the hearth, also called injector or injection nozzle, a second plurality of outlets being constituted by conduits opening at the periphery of the hearth at a certain height above it and, optionally, a third plurality of outlets being located in the vicinity of the downstream or lower end of the nozzle, the latter plurality of outlets can be constituted by a circumferential lumen.

Still according to the present invention and according to more specific construction characteristics, the grid is limited in surface to a fraction of the surface of the sole constituting the bottom wall of the reserve, the sole comprising at least one of said preheated air passages. of said first plurality. It follows from this arrangement that carbonization or pyrolysis of the fuel takes place in an area of a certain height, this height being favorable for possible drying of the wood and for the gasification of the tars, from which ultimately combustion results. regular of any quality or species of wood.

According to another construction characteristic, the air passages of the first plurality are constituted by a plurality of nozzles substantially evenly distributed on the surface of the hearth, from which it follows that the carbonization of the fuel in the pyrolysis zone is transversely homogeneous . Preferably, the sole consists of a plate of refractory ceramic material supported by a steel sheet, and said nozzles are elements distinct from the sole in holes in which they are fitted. It follows from this arrangement that the nozzles can be brought to a sufficiently high temperature to prevent them from being blocked by tars during idling operation. Preferably these nozzles have a frustoconical interior shape open downwards, so as to prevent the ashes from being able to be retained inside.

According to another constructive arrangement relating to the invention, the combustion air supply ducts from the preheating chamber to the pyrolysis zone are distributed equally along the wall around the hearth and they open out to- below a peripheral inner rim inclined towards the center, this rim being called gutter and having the effect on the one hand of channeling towards the center of the hearth, the condensates formed along the wall above it, and of reducing towards the center of the zone the preheated air leaving the conduits .

The first result of this arrangement is that the gases formed in said pyrolysis zone above the hearth can be simultaneously ignited by the supply of incoming air and their flames directed downwards; secondly, it follows that the combustion thus effected results from a passage of the gases initially from bottom to top at the outlet of the nozzles, then from top to bottom from the outlet of the conduits; it results thirdly that above the pyrolysis zone, the fuel in reserve is sheltered from oxidizing gases, which prevents it from igniting; it results from it fourthly that the reserve can be as high as is wished without risk of ignition of the fuel which it contains.

According to another constructive arrangement, the lower end of the nozzle is shaped as a venturi by means of a toroidal part, preferably made of refractory material, resting on the bottom wall separating the preheating chamber from a combustion chamber situated at- below the nozzle; the end of the frustoconical part is separated from the torus by a small circumferential space connecting the preheating chamber and the interior of the nozzle to allow the passage of secondary combustion air.

According to another constructive arrangement, the hearth is entirely surrounded, with the exception of a part for introducing the fuel, with a water jacket, and a smoke duct surmounting at the rear said combustion chamber is itself - even jacketed with water; internal fins improve its exchanger performance. According to another constructive arrangement, the valve for entering ambient air into the preheating chamber is held in the closed position by a small magnet, thanks to which this valve can only be opened by the vacuum created by a fan placed in the conducts smoke. According to another other characteristic, the bars of the grate are removable and are perpendicular to the direction of introduction of the logs.

• la fig. 1 est une illustration en perspective d'une chaudière relevant de l'invention,
• la fig. 2 est une coupe de la même par un plan médian perpendiculaire à la face d'introduction,
• la fig. 3 est une vue de dessus en coupe par un plan suivant AA de la figure précédente,
• la fig. 4 est une vue de dessus de la pièce torique,
• la fig. 5 est une coupe d'une buse d'introduction d'air, et
  • les fig. 6 et 6a illustrent en coupe et en vue de côté un barreau de la grille.

The present invention will be better understood and details will be apparent from the description which will be given of a particular embodiment in relation to the figures of the appended plates, in which:

• fig. 1 is a perspective illustration of a boiler covered by the invention,
• fig. 2 is a section of the same by a median plane perpendicular to the introduction face,
• fig. 3 is a top view in section through a plane along AA of the previous figure,
• fig. 4 is a top view of the toric part,
• fig. 5 is a section through an air introduction nozzle, and
  • fig. 6 and 6a illustrate a section of the grid in section and in side view.

In fig. 1, a boiler of the invention has a generally parallelepiped shape on a facade from which we notice from top to bottom a loading door 25, a screen door 8 and an ashtray door 3. A water inlet 19 and an outlet of hot water 24 place the boiler in a heating circuit; a flue 23 allows the evacuation of the burnt gases to the outside.

In fig. 2 and / or 3, the boiler of the invention comprises an annular chamber 15 for preheating the combustion air; the volume of this chamber is defined by a cone-shaped nozzle 11 disposed below the grid 12, by a hearth 17 surrounding the grid and by a bottom wall 6; the preheating chamber is provided with an ambient air inlet 30 and with a triple plurality of hot air, namely a first plurality constituted by passages 10 also called injectors or injection nozzles, through the floor, a second plurality constituted by conduits 13 opening at the periphery of the hearth at a certain height above the latter and a third plurality of outlets constituted, in fact, by a circumferential lumen 31 comprised between the end of the nozzle and a toroidal part 5, called torus, supported by the bottom wall.

Note, more particularly in FIG. 3, that the injectors 10 are substantially evenly distributed on the floor of the reserve and that the grid 12 occupies only a central fraction of the surface of the floor. This sole of the reserve consists of a plate of refractory ceramic material supported by a steel sheet.

Returning to fig. 2 more particularly, it is noted that air ducts 13 disposed towards the middle of the sides of the hearth open out at a certain height above the latter and, more precisely below an inner peripheral rim 14 forming a gutter for canali- servers the center of the sole the condensates formed on the walls of the reserve 16; the upper end of the conduits 13 or of the rim 14 situates the delimitation between a pyrolysis zone situated between the hearth 17 and the rim 13 and a fuel reserve zone situated above the rim 13.

We also notice in fig. 2 that the outlet 33 of an exchanger 18 preceding the flue 23, is located at a level lower than that of the top of the reserve 16; this arrangement contributes to the regularity of idling. A fan 21 is arranged at the outlet of the exchanger, from the flue pipe 22. The exchanger 18 comprises a plurality of fins 20 spaced apart on one side and on the other of the exchanger.

Returning to the section in fig. 2, it can be seen that the air inlet 30 into the preheating chamber 15 is controlled by a valve 9 which can come into abutment against a small magnet 7, these last two elements being located behind the screened part 8.

It will also be noted in one and / or the other of the aforementioned figures that the fuel reserve, the pyrolysis zone and the exchanger are surrounded by a water jacket 26 itself coated on the outside with an insulation 27 , while the part of the boiler located below the bottom wall 6 of the preheating chamber, part called the combustion chamber 2, has a refractory lining 1.

In fig. 6 and 6a, a bar 35 of the grid 12 has a section partly rectangular and partly semi-cylindrical and it has at each of its ends an extension 36 allowing it to be positioned above the nozzle 11; the latter, as can be deduced from the comparative examination of figures, has a shape substantially in miter of chimney.

In fig. 5 a nozzle or injector 10 of the preceding figures has a frustoconical inner wall 37 open downwards; a flange 38 retains such a nozzle in a hole in the bottom 17.

In fig. 4, the torus 5 of FIG. 2 defines a central circular recess of substantially the same diameter as that of the end of the nozzle 11.

We will now explain the operation of such a boiler: after we have introduced into the enclosure 16, said reserve, wood logs perpendicular to the bars of the grid, the smoke extractor being in operation, the vacuum created by it will open the valve 9 retained when stopped in the closed position by the magnet 7; the air will penetrate through the injectors 10 which will cause an upward combustion allowing the gasification of a certain layer of wood; air will also penetrate through conduits 13 allowing the gases already produced to ignite and thus obtain reverse combustion, the flame being sucked through the grate 12, channeled in the cone 11, opening into the torus 5 ensuring the oxidation of said flame. This flame 4 develops in the combustion chamber 2 and is directed towards the finned exchanger 18 20. Then, these combustion gases enter the fan 21 and are evacuated in the flue pipe 23. During the operation of the boiler the gasification of wood on the floor of the reserve has the effect of producing a release of water vapors and tars which, due to their temperature rise in the upper part of the reserve and partially condense, the tar dripping on the walls of the reserve is gasified by "gutters" 14 which prevent it from accumulating if _' r the sole against the walls of the reserve that are at the temperature of the water contained in the boiler. This process according to the invention allows very rational use of wood, in particular avoiding all the drawbacks linked to atmospheric and geographical conditions on the one hand, and almost total control of the combustion of wood since a boiler conforms to the he invention allows the production of hot water for five days in summer without having to touch anything.

No system at present allows these advantages to be obtained: a boiler according to the invention can operate at idle for a long period (one week). Indeed, during idling, the valve 9 is closed and retained by a magnet thereby avoiding inadvertent opening created for example by excessive draft caused during high winds for example, the fan 21 is stopped. A slight stream of air penetrates through the injectors 10 and the conduits 13 which has the effect of maintaining a very slow combustion of the coal on the silk, this combustion not being able to accelerate because the gases produced rise in the upper part of the reserve which ensures a counter draft and thereby self-regulation. Even without removing calories, the water temperature does not rise and never reaches the boiling point as occurs in boilers of the prior art.

Claims (11)

1. Combustion device of the closed furnace type, comprising a fuel reserve (16) located above a grate and a chamber (15) for preheating combustion air, the cavity of the said chamber being delimited by a hearth (17) surrounding the grate (12), by the said grate (12) and by a base wall (6), the said chamber being provided with an inlet (30) for ambient air, characterized:

in that the said preheating chamber (15) is located below the said fuel reserve (16),

by a tube (11) arranged below the said grate (12) and passing from top to bottom and through the centre of the said preheating chamber (15), the said preheating chamber consequently having an approximately annular shape, and

by a triple plurality of hot combustion air outlets, a first plurality of outlets being composed of passages (10) through the hearth (17), a second plurality of outlets being composed of ducts (13) opening out at the periphery of the hearth (17) at a certain height above it and a third plurality of outlets (31) being located in the vicinity of the downstream or lower end of the tube (11).

2. Device according to Claim 1, characterized: in that the surface of the said grate (12) is limited to a fraction of the surface of the hearth (17) of which the base wall of the said reserve (16) is composed, the said hearth having at least one inlet (10) for air to pass into the said reserve (16).

3. Device according to Claim 2, characterized: in that the said air inlet (10) is composed of the said passages (10) in the shape of nozzles which are distributed substantially equidistantly over the surface of the said hearth (17).

4. Device according to Claim 3, characterized: in that the said hearth (17) is composed of a plate of refractory ceramic material supported by a steel sheet, and

in that the said nozzles (10) are elements separate from the hearth (17) and are fitted into holes in the latter.

5. Device according to Claim 4, characterized: in that the said nozzles (10) have a frustoconical shape internally which is open towards the bottom.

6. Device according to Claim 2, characterized: by ducts (13) for conveying combustion air which are arranged at the periphery of the hearth (17).

7. Device according to Claim 2, characterized: by an internal peripheral shoulder (14) inclined towards the centre, the said shoulder forming a gutter for removing condensate from the wall, the said shoulder being at the edge of the carbonization zone.

8. Device according to Claim 2, characterized: by a piece (11) of conical shape, called a tube, located below the grate, the said piece being intended to channel and focus the flame in the direction of a combustion chamber (2) located in the lower part of the device.

9. Device according to Claim 1, characterized: in that the air inlet (30) of the said preheating chamber (15) has a valve (9) which is capable of opening under the effect of a partial vacuum in the said chamber, the said valve being held in a normally closed position by means of a magnet (7), the force of which corresponds to a specific value of the partial vacuum.

10. Device according to Claim 1, characterized: in that it has an exchanger (18) provided with fins (20) internally, the outlet (39) of the exchanger being located at a lower level than the top of the reserve (16).

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