FIELD OF THE INVENTION AND PRIOR ART

The present invention relates to a fire grate according to the preamble of claim 1 and a burner according to the preamble of claim 14.

Burners for burning of solid fuels, such as pellets, grain and other fuels consisting of essentially solid fuel bodies, normally comprises a so-called fire grate forming a bottom and side wall sections in the combustion chamber where the fuel is combusted under the formation of flue gases and ash. Fuel bodies are placed in this fire grate by being fed into the combustion cham¬ ber by means of some sort of feeding device. Conventional pel- let burners usually comprise a fire grate of metal sheet provided with holes for supply of primary air to a seat of fire and a bed of embers on the fire grate. Under the influence of the primary air, a so-called primary combustion takes place. The flue gases and some of the combustion residues from the primary combustion are then usually subjected to a so-called secondary combustion under the influence of secondary air supplied in the upper part of the combustion chamber, for instance via a so-called gas throat. During the combustion of the fuel bodies in the combustion chamber, combustion residues in the form of soot and ash are formed. Some of these combustion residues will be carried along with the flue gases out of the combustion

chamber, but some of the combustion residues are accumulated on the fire grate.

It has recently become more and more common to use grain as fuel. When burning grain, such as for instance oats, an active stirring of the seat of fire is required in order to obtain an effi¬ cient combustion of the grain. In order to make possible burning of grain in a conventional pellet burner, this is therefore usually supplemented by a mechanical stirrer which achieves the re- quired stirring of the seat of fire. A problem in this connection is that the stirrer is exposed to very hard wear due to the very high combustion temperature (up to about 1200 ⁰ C) required when burning grain, the stirrer therefore has to be replaced at regular intervals. Another problem associated with burning of grain is that considerably larger amounts of ash are formed when burning grain than when burning other comparable bio fuels, such as wood pellets. The ash will often melt in the combustion chamber, sinter and form slag. There is inter alia a risk that this formation of slag will cause clogging of the outlet holes for primary air arranged in the fire grate.

OBJECT OF THE INVENTION

The object of the present invention is to create, in a simple man- ner, good possibilities for an efficient combustion of solid fuel bodies in a burner.

SUMMARY OF THE INVENTION

According to the invention, said object is achieved by means of a fire grate having the features defined in claim 1. The fire grate according to the present invention is characterized in that its in¬ side comprises two or more spaces, each of which being formed by a hollow arranged in said inside and each of which having at least one outlet hole for combustion-supporting gas, for instance in the form of air, arranged in the associated hollow. With the

inventive solution, the combustion space closest to the fire grate is in a simple manner divided into separate smaller spaces, each of which being associated with a separate supply of combustion-supporting gas, for instance in the form of so-called primary air, via outlet holes in the inside of the fire grate. Hereby, a good contact between fuel and combustion-supporting gas is obtained in the respective space, at the same time as an efficient stirring of the fuel in the respective space is made possible by the separate supply of gas to the respective space. With a fire grate according to the present invention, it will be possible to process the seat of fire on the fire grate in smaller areas and thereby "disrupt" the seat of fire so as to obtain a good burning process.

By a suitable choice of the number of separate spaces, i.e. the number of individual hollows, in the inside of the fire grate and suitable location of said outlet holes and direction of the outlets of the gas ducts connected to the outlet holes, it will in a simple manner be possible to achieve a stirring of the fuel bodies and bed of embers resting on the fire grate that is sufficiently ef¬ ficient in order to fulfil the degree of stirring required for an efficient combustion of grain, such as for instance oats. By means of the inventive fire grate, it will consequently be possi¬ ble to achieve a desired degree of stirring without requiring any mechanical stirrers. By creating, in this manner, a continuous active movement in the bed of embers, the bed of embers is pre¬ vented from being burned in a coherent mass, which will reduce the risk of coherent ash and sintering.

According to a preferred embodiment of the invention, the respective space has at least one outlet hole for combustion- supporting gas arranged in or close to the deepest part of the associated hollow. Hereby, it is secured that said gas in an effi¬ cient manner can be made to affect the fuel bodies and combus- tion residues present in one of said spaces, so that a good combustion is made possible at the same time as ash can be

prevented from accumulating in the bottom of the respective space.

According to a further preferred embodiment of the invention, at least one, preferably the main part or all, of said spaces has at least one outlet hole for combustion-supporting gas arranged in the associated hollow, which outlet hole is connected to a gas duct having its outlet directed towards the downstream end of the fire grate. Said gas, which normally consists of primary air, will hereby assist in directing the combustion and the formed combustion residues, such as ash, towards the downstream end of the fire grate and consequently towards the outlet opening of the combustion chamber.

According to another preferred embodiment of the invention, at least the inside of the fire grate, preferably the entire fire grate, is made of ceramic material or stone material. These materials have a high resistance to heat and have high heat storage capability. By using this type of material in the fire grate instead of metal material, improved possibilities to maintain the comparatively high combustion temperature required when burning grain are created.

According to another preferred embodiment of the invention, the respective outlet hole is connected to a gas duct extending through the fire grate and being integrated therein, the respec¬ tive gas duct suitably being formed by a through hole in the fire grate. Hereby, the combustion conditions in a combustion cham¬ ber can easily be adapted by the design of the fire grate located in the combustion chamber, since the fire grate according to this embodiment also defines the gas ducts connected to the outlet holes and consequently the directions of the outlets of the gas ducts. By a suitable choice of the number of separate spaces in the inside of the fire grate and suitable location of the outlet holes and direction of the outlets of the gas ducts connected to the outlet holes, it will in a simple manner be possible to achieve

the desired combustion conditions in a combustion chamber provided with this fire grate. These combustion conditions may easily be changed when necessary, for instance when a change of fuel type is to take place, by replacing a fire grate in a combustion chamber with a fire grate having another detail con¬ struction.

Further preferred embodiments of the inventive fire grate will ap¬ pear from the dependent claims and the subsequent description.

The invention also relates to a burner according to claim 14.

BRIEF DESCRIPTION OF THE DRAWINGS

With reference to the enclosed drawings, a more specific description of embodiment examples of the invention will follow hereinbelow. It is shown in:

Fig 1 a schematic, cut lateral view of a burner according to a first embodiment,

Fig 2 an exploded view of a fire grate according to a first em¬ bodiment,

Fig 3 a partly cut lateral view of the bottom plate of the fire grate according to Fig 2,

Fig 4 a partly cut perspective view of a section of a burner according to a second embodiment.

Fig 5 a cross-sectional view of a fire grate according to a second embodiment,

Fig 6 a cross-sectional view of a fire grate according to a third embodiment.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

An embodiment of a burner 1 according to the present invention is schematically illustrated in Fig 1. This burner is designed for burning of solid fuel bodies, for instance in the form of wood pel¬ lets, grain, wood chips, peat briquettes, etc. The burner 1 com¬ prises a combustion container 2, a so-called combustion cup, which includes a combustion chamber 3 where the combustion of fuel bodies is intended to take place. The combustion con- tainer is in the illustrated embodiment mounted inside an exte¬ rior casing 4 of the burner. The combustion container 2 has a first opening 5 for allowing fuel bodies to be fed into the combustion chamber 3 and a second opening 6, via which flue gases and combustion residues are intended to flow out of the combustion chamber. In the illustrated embodiment, the first opening 5 is arranged at a first end of the combustion container 2 and the second opening 6 at the opposite second end of the combustion container. The exterior casing 4 of the burner has an opening which co-insides with said second opening 6 of the combustion container. A feeding conduit 7 for fuel bodies leads to the combustion chamber 3 via said first opening 5. In the illustrated embodiment, the feeding conduit 7 is designed as a tip chute so as to let fuel bodies be fed into the combustion chamber 3 by the gravitation. The inventive burner 1 could how- ever be provided with another type of feeding member, such as a feed screw or the similar, for feeding fuel bodies into the combustion chamber. The wall 2a of the combustion container facing the feeding conduit 7 is suitably lined on its inside with a plate 30 of ceramic material or stone material and also the other walls of the combustion container 2 are suitably lined on the in¬ side with elements of ceramic material or stone material. The walls 2a, 2b of the combustion container are suitably made of metal sheet.

The burner 1 further comprises a device 8 for feeding combus¬ tion-supporting gas, for instance in the form of air, to the

combustion chamber 3. In the illustrated embodiment, this de¬ vice 8 is constituted by a fan arranged to blow air into the combustion chamber so as to thereby support the combustion of fuel bodies in the combustion chamber. In this case, the air is led in the space between the exterior casing 4 of the burner and the combustion container 2 and thereafter into the combustion container via not shown inlets therein. The air is led into the combustion chamber 3 partly as primary air, illustrated by the arrows P1 , at the lower part of the combustion chamber, and partly as secondary air, illustrated by the arrows P2, at the up¬ per part of the combustion chamber. According to the present invention, the lower part of the combustion chamber is formed by a fire grate 9 of a type that will be described in closer detail below with reference to Figs 2 and 3. The upper part of the combustion chamber is formed by a gas throat 32 of a type that will be described in closer detail below with reference to Fig 4.

The burner 1 may also comprise further components of conven¬ tional character besides those here described, such as for in- stance a lighter and different types of supervision members and control members. The inventive burner 1 is intended to form part of a conventional heating boiler for supplying heat to a heating system for heating indoor air in a building, such as for instance in a residential property in the form of a detached house or a multi-family house. The burner 1 is with advantage designed to replace the oil burner in a conventional domestic boiler in order to make possible utilization of another fuel than oil.

In this description and the subsequent claims, the expression "fire grate" refers to the element which is intended to form the bottom and side wall sections connected to the bottom in a combustion chamber and which is intended to accommodate solid fuel bodies during the burning thereof in said combustion chamber.

In this description and the subsequent claims, the expression "gas throat" refers to the element which is intended to form the upper part in a combustion chamber and which assists in conveying the formed flue gases in the desired direction.

A fire grate 9 according to an embodiment of the present inven¬ tion is illustrated in Fig 2. According to this embodiment, the fire grate is divided into several separate elements, which here con¬ sist of a bottom plate 9a, two side elements 9b, 9c, which are connected to the bottom plate and extend along the bottom plate 9a on a respective side thereof, a central front element 9d con¬ nected to one end 40 of the bottom plate, and two lateral front elements 9e, 9f, which are connected to the end 41 , 42 of a respective side element 9b, 9c. The front elements 9d-f form a stopping member intended to retain not yet fully combusted fuel bodies in the fire grate 9.

Said elements 9a-f are shown separated from each other in Fig 2, but they are intended to abut tightly to each other so as to form a fire grate when they are arranged in a combustion cham¬ ber. By the division of the fire grate 9 into separate detachable elements, the mounting of the fire grate in a combustion con¬ tainer of an existing burner is facilitated at the same time as it will be possible to remove individual elements of the fire grate afterwards for cleaning, repair or replacement. Owing to the fact that the different elements of the fire grate are detachable, it will also be possible to replace an element of a certain configuration against an element of another configuration so as to thereby adapt the combustion conditions in dependence on the type of fuel bodies presently intended to be utilized as fuel in the burner. It is of course also possible to design the entire fire grate in one single piece, if so considered suitable.

The inventive fire grate 9 comprises an inside 10 with a support- ing surface 1 1 intended for receiving fuel bodies. The inside 10 of the fire grate comprises two or more spaces 12, each of

which being formed by a hollow 13 arranged in said inside 10 and each of which having at least one outlet hole 14 for combus¬ tion-supporting gas arranged in the associated hollow. At least a part of the surface of the respective hollow 13 constitutes a sec- tion of said supporting surface 1 1 , and the respective hollow 13 consequently has such a size that the fuel bodies to be burned are at least partially receivable therein. Said outlet holes 14 are intended to make possible supply of combustion-supporting gas to fuel bodies received in the fire grate. The fire grate 9 has a downstream end 43a, through which flue gases and combustion residues formed during the combustion of fuel bodies resting on the fire grate are intended to be carried off from the fire grate.

In the embodiment illustrated in Fig 2, the inside 10 of the fire grate is formed by the upper surface 10a of the bottom plate 9a and of the inner surfaces 10b, 10c of the side elements 9b, 9c. All these surfaces 10a-c are here provided with spaces 12 and outlet holes 14 of the above-indicated type.

Preferably, at least the inside 10 of the fire grate and suitably the entire fire grate 9 is made of ceramic material or stone mate¬ rial.

In the embodiment illustrated in Fig 2, the bottom plate 9a of the fire grate is provided with ten spaces 12 of said type and each space is in this case provided with one or two outlet holes 14 for combustion-supporting gas. Five spaces 12 are here arranged after each other in a first row 16a in the longitudinal direction of the bottom plate and five additional spaces 12 are arranged after each other in a second row 16b in the longitudinal direction of the bottom plate, the second row 16b of spaces extending in parallel with the first row 16a of spaces. The spaces 12 in the respective row are mutually separated by transversal ridges 15 arranged in the inside 10 of the fire grate and the spaces in the first row 16a are separated from the adjacent spaces in the

second row 16b by longitudinal ridges 17 arranged in the inside 10 of the fire grate.

The inventive fire grate may of course be provided with more as well as fewer spaces 12 of the type in question than shown in Fig 2, and these spaces may also have other shapes and be mutually configured in other ways than shown in this figure.

In the embodiment illustrated in Fig 2, longitudinal upwards open channels 44 are arranged at the upstream end of the bot¬ tom plate 9a and the side elements 9b, 9c in order to contribute, at the upstream end 43b of the fire grate, to air currents favour¬ able to the combustion.

In each space 12, at least one outlet hole 14 ought to be ar¬ ranged in or near to the deepest part of the associated hollow 13 so that the combustion-supporting gas flowing into a hollow via said outlet hole 14 can be made to affect as large a part as possible of fuel bodies and combustion residues present in the hollow. At least one, preferably the main part or all, of said out¬ let holes 14 is suitably connected to a gas duct 18 (see Fig 3) having its outlet 18a directed towards the downstream end 43a of the fire grate. At least one, preferably each, outlet hole 14 is connected to a gas duct 18 which extends through the fire grate 9 and is integrated therein and which suitably is formed by a through hole in the fire grate, as illustrated in Fig 3.

In the embodiment illustrated in Fig 2, longitudinal feed chan¬ nels 45 are arranged on the outwardly facing side of the side elements 9b, 9c of the fire grate in order to lead combustion- supporting gas up to the gas ducts 18 in the side elements 9b, 9c.

In the illustrated embodiments, each one of said spaces 12 ar- ranged in a row comprises a pair of walls forming part of the associated hollow 13 and comprising:

- a first wall 20a facing the downstream end 43a of the fire grate, and

- a second wall 20b arranged at an angle to the first wall 20a and being connected to the lower part of the first wall 20a via a connecting line 21 extending essentially in the cross-direction of the fire grate.

The first wall 20a is suitable shorter than the second wall 20b in the respective pair of walls, as illustrated in Figs 2 and 3.

In the illustrated embodiments, the second wall 20b in the respective pair of walls faces away from the downstream end of the fire grate, i.e. faces the upstream end 43b of the fire grate, and said first and second wall 20a, 20b together extend across the entire distance between the ends of the associated space 12 as seen in the longitudinal direction of the fire grate, i.e. the en¬ tire distance between two adjacently arranged cross-directed ridges 15. As seen in a longitudinal section through the fire grate 9, the respective hollow 13 has in the illustrated embodi¬ ments a V-like shape, as clearly appears from Fig 3, and the in- side of the fire grate has a stepped-like shape. In the embodi¬ ment illustrated in Figs 2 and 3, the first wall 20a in the respec¬ tive pair of walls has at least one outlet hole 14 for combustion- supporting gas, which outlet hole 14 is connected to a gas duct 18 having its outlet 18a directed towards the downstream end 43a of the fire grate.

According to a preferred embodiment of the inventive burner 1 , also the gas throat 32 comprises on its inside two or more spaces 33, each of which being formed by a hollow arranged in the inside of the gas throat and each of which having at least one outlet hole 34 for combustion-supporting gas, for instance in the form of secondary air, arranged in the associated hollow, as illustrated in Fig 4. Hereby, the entire inside surface of the combustion chamber, with the exception of the gable facing the feeding conduit, will have an irregular surface structure.

At least the inside of the gas throat 32, preferably the entire gas throat, is made of ceramic material or stone material. As in the fire grate 9 described above, at least one, preferably the main part or all, of said outlet holes 34 is suitably connected to a gas duct 35 having its outlet directed towards the outlet opening 6 of the combustion chamber. At least one, preferably each, outlet hole 34 is connected to a gas duct 35 which extends through the gas throat 32 and is integrated therein and which suitably is formed by a through hole in the gas throat, as illustrated in Fig 4. Combustion-supporting gas, for instance in the form of secon¬ dary air, is led to the respective gas duct 35 via feed channels 38 (schematically indicated in Fig 4) arranged in the gas throat 32 for instance in the form of longitudinal channels on the out¬ side of the gas throat. In the embodiment illustrated in Fig 4, said gas throat 32 is designed as a part of a cylinder, but it may of course also have another design depending on the shape of the combustion container. The gas throat 32 is suitably a sepa¬ rate detachable part of the burner.

The transverse ridges 15 in the bottom plate 9a are suitably ar¬ ranged in line with the transverse ridges 15 in the side elements 9b, 9c when the fire grate is mounted in the combustion con¬ tainer, as illustrated in Fig 4, so as to form spaces 12, each of which extending uninterruptedly from the bottom plate 9a and up along one of the side elements 9b, 9c. In the same manner, the ridges 15 in the side elements 9b, 9c are suitably arranged in line with the transverse ridges 15 in the gas throat 32 when the fire grate 9 and the gas throat 32 are mounted in the combustion container, as illustrated in Fig 4.

In the embodiment illustrated in Fig 4, the fire grate 9 and the gas throat 32 are enclosed in a metal casing 50 constituting an external casing of the combustion container 2 of the burner.

In the embodiment illustrated in Fig 1 , a block 31 , suitably of ce¬ ramic material or stone material, is located in front of the fire

grate 9. The block rests on the bottom of the combustion container and protrudes somewhat above the fire grate in order to retain not yet fully combusted fuel bodies in the combustion chamber 3. In order to facilitate removal of the fire grate 9, this block 31 is suitably a separate detachable part of the burner. A corresponding block 31 is also illustrated in Fig 4 in a position separated from the fire grate 9.

If so considered suitable, an air layer or heat-insulating material may be arranged in the interface between the metal casing 50 and the fire grate 9 and/or between the metal casing 50 and the gas throat 32 in order to limit the thermal dissipation via the metal casing 50.

Two different embodiments of a fire grate 9 and a gas throat 32 arranged in a combustion container 2 with another cross-sec¬ tional shape than the combustion container according to Fig 4 are illustrated in Figs 5 and 6. The combustion container 2 illus¬ trated in Fig 5 has a circular cross-sectional shape and the fire grate 9 has in this case an arched shape and is designed in one single piece. The combustion container 2 illustrated in Fig 6 has a rectangular cross-sectional shape and the fire grate 9 consists in this case of three separate elements, namely a bottom plate 9a and two side elements 9b, 9c.

A combustion container of a burner of the type here in question may of course be provided with a fire grate and a gas throat of the type described above already during the manufacturing of the combustion container, but the combustion container of an existing burner may alternatively be supplemented with such a fire grate and gas throat afterwards, for instance in order to adapt an existing pellet burner for burning of grain.

The inventive burner is particularly suitable to be used for burning of grain, but may of course also be used for burning of other types of fuel consisting of solid fuel bodies.

The invention is of course not in any way limited to the preferred embodiments described above. On the contrary, several possibilities to modifications thereof should be apparent to a person skilled in the art without departing from the basic idea of the invention as defined in the appended claims.