| EP0084852A2 | 1983-08-03 | |||
| EP0168808A2 | 1986-01-22 | |||
| FR2516209A1 | 1983-05-13 | |||
| FR2583148A1 | 1986-12-12 | |||
| FR2583503A1 | 1986-12-19 | |||
| FR2592944A1 | 1987-07-17 |
| 1. | A furnace for biological fuels, comprising a fuel storage vessel (1) with a closable top, a fuelfeed lid (10) at the furnace top and an exhaustgas opening (5) at the bottom of the fuel storage vessel in order to create downwardly directed combustion, c h a r a c t e r i z e d in that the bottom (4) of the fuel storage vessel (1) slop towards the exhaustgas opening at an angle which is large then the angle of repose of the fuel material, in that sai exhaustgas opening (5) which also serves as the burner opening, is covered by a draftair supply means (3) which along a part (3a) of its outer periphery extends closely alongside the part of the sloping bottom (4) of the fuel storage vessel that is closest to the burner opening, and in that said draftair supply means (3) further comprises both downwardly directed draftair channels (24) which ope into the gap (2) formed between the draftair supply means and the fuel storage vessel bottom, and laterally directed upper draftair channels (19,23), an adjustable supply air fan being provided upstreams of the draftair supply means. |
| 2. | A biological fuel furnace as claimed in claim 1, c h a r a c t e r i z e d in that the draftair supply means has portions projecting over the outlet mounths of the draftair channels. |
| 3. | A biological fuel furnace as claimed in claim 2, c h a r a c t e r i z e d in that the draftair supply means (3) is a hollow body which removably placed in a poc (27) formed in the bottom part of the fuel storage vessel and which hollow body is made from a heatresistant materi preferably ceramics. |
| 4. | A biological fuel furnace as claimed in any one of the preceeding claims, c h a r a c t e r i z e d in that it is provided with a combustion chamber (7) position after the gas exhaust opening (5) at the bottom of the fuel storage vessel. 10 . |
| 5. | A biological fuel furnace as claimed in any one of the preceeding claims, c h a r a c t e r i z e d in that a valve (33) is provided in the upper part of the fu storage vessel in order to selectively interconnect this part of the fuel storage vessel with the exhaust channel system of the furnace. |
| 6. | A biological fuel furnace as claimed in any one of the preceeding claims, c h a r a c t e r i z e d in that the faces (3c,3d) of the draftair supply means (3) which are turned upwards slope downwards towards the bott (4) of the fuel storage vessel, preferably at an angle wh is larger than the angle of repose of the combustion mate. |
| 7. | A biological fuel furnace as claimed in any one of the preceeding claims, c h a r a c t e r i z e d in that the exhaust channel system of the furnace communicat with the refueling opening of the furnace which may be ex by means of the refueling lid (10), at least in the opene position of the latter, in order to receive gas flowing from the fuel storage vessel during refueling. |
| 8. | A biological fuel furnace as claimed in claim 7, c h a r a c t e r i z e d in that the fuelfeed lid has both an inner wall (14) which is sealed against the fuel storage vessel and an outer wall (12) which is sealed aga a portion of the furnace which is positioned outside the fuel storage vessel, for instance a heat exchange part, whereby communication is established with the exhaust cha system in the gap (25) formed between said two walls. |
| 9. | A biological fuel furnace as claimed in claim 8, c h a r a c t e r i z e d in that the gap ( 25) intermedi the interior and exterior sealing walls continuously comm nicates with the exhaust channel system, i.e. independent on whether the fuelfeed lid is open or closed. |
| 10. | A biological fuel furnace as claimed in any one of claims 79, c h a r a c t e r i z e d in that the tw sealing walls of the fuelfeed lid are movable relatively to one another against the action of a spring in order to provide an efficient sealing effect independently of any variations in the spacing between the interior and exteri sealing means with which the lid cooperates in the closed position. |
| 11. | A biological fuel furnace as claimed in any one of the preceeding claims, c h a r a c t e r i z e d in that its interior components, i.e. the fuel storage vessel and the combustion chamber part consist of moulded bodies of a ceramics material which are assembled into a unit. |
| 12. | A biological fuel furnace as claimed in any one of the preceeding claims, c h a r a c t e r i z e d in that the sloping planes (4) in the bottom part of the fuel storage vessel ( 1 ) are formed by removable ceramics slabs the facing bottom edges of which form the laterally limiti means of the burner opening (5) and thus determine the siz of the burner opening. |
| 13. | A biological fuel furnace as claimed in claim 2, 3 and 6, c h a r a c t e r i z e d in that the draftair supply means (3) is in the form of a horizontal paralellep body in which draftair supply openings (23,24) are formed at least in the faces (3b,3a) that are turned downwards. |
| 14. | A biological fuel furnace as claimed in claim 13, c h a r a c t e r i z e d in that the draftair inlet openings (19) which are provided at the upper part of the draftair supply means (3) are covered from above by eaves like projections (20). |
The present invention concerns a furnace for biologi fuels, i.e. a device for combustion of solid fuels.
More specifically, the invention concerns a furnace for biological fuels, comprising a fuel storage vessel wh is closable at its upper portion, a fuel-feed lid at the upper portion of the furnace, and an exhaust gas opening at the bottom of the fuel storage vessel in order to crea downwardly directed combustion.
A problem encounted in previously known constructions of the type outlined above is that when the heat extractio is low they emit fumes which are unacceptable from an environmental point of view. In addition, their combustive efficiency is low. This is due e.g. to the fact that it is not possible to control and mix the gas that develops and the air that is supplied for oxygenation purposes in the correct proportions. In addition, furnaces of this kin often are manufactured to operate at a high maximum effect approximatively 2-3 times the required thermal energy extr tion, with the result that they must be fired in batches, with resulting increase of work and efficiency losses.
The main purpose of the subject invention is to elimi these problems. This is achieved in a furnace in accordanc with the invention which is essentially characterized in that the bottom of the fuel storage vessel slopes towards the exhaust-gas opening at an angle which is larger than the angle of repose of the combustion material, in that said exhaust-gas opening which also serves as the burner opening is covered by a draft-air supply means which along a part of its outer periphery extends closely alongside the part of the sloping bottom of the fuel storage vessel that is closest to the burner opening, and in that said draft-air supply means further comprises both downwardly directed draft-air channels which open into the gap formed between the draft-air supply means and the fuel storage vessel bottom, and laterally directed upper draft-air channels, an adjustable supply air fan being provided
upstreams of the draft-air supply means.
One embodiment of the invention will be described in closer detail in the following with reference to the accompanying drawings, wherein Fig. 1 is a central sectional view along line I-I in
Fig. 2 through a furnace in accordance with the invention,
Fig. 2 is a corresponding central cross-sectional vie along line II-II in Fig. 1 through the lower furnace part, the outer furnace parts having been removed, Fig. 3 is a sectional view along line I-I in Fig. 2 and line III-III in Fig. 4 through the draft-air supply means,
Fig. 4 is a sectional view along line II-II in Fig. 1 and line IV-IV in Fig. 3 through the same draft-air supp means, and
Fig. 5 illustrates on an enlarged scale a vertical sectional view through the fuel-feed lid and adjoining par of the fuel supply opening of the furnace.
The furnace illustrated in the drawing comprises an interior part which is designated generally by numeral 6 and which is made from a heat-resistant material, such as ceramics, and an exterior part 11 enclosing the interior part and containing an exhaust channel system which, toge with the water jacket 13 surrounding the exhaust channel system forms a heat-exchange system for extraction of the energy from the furnace. Between the interior part 6 and the exterior part 11 is arranged a layer 17 of insulating material. In accordance with the embodiment illustrated, the interior part 6 comprises two moulded sections which are partitioned along plane II-II in Fig. 1. Preferably, these two halves are of symmetrical configuration, having an upper cavity portion 1 forming the fuel storage vessel, and a lower cavity part 7 forming the combustion chamber.
At its lower part the fuel storage vessel presents a sloping bottom which is covered by preferably removable bottom slabs 4, which likewise preferably consist of a ce or any other heat-resistant material. The inclination ang of the bottom slabs 4 preferably is equal to or larger th
the angle of repose of the fuel material and the opposite edges of the slabs are spaced mutually apart so that a ga is formed between them. The gap serves as an exhaust-gas opening 5 which in the subject case also serves as the bu opening. The ends of part 6 which are turned towards each other are covered by end wall slabs 26a and 26b which pref also are made of ceramics or some other heat-resistant material .
Centrally inside the bottom part of the fuel storage vessel the interior part 6 is formed with a pocket 27 into which is inserted a draft-air supply means, the latter lik wise being made from a heat-resistant material, preferably ceramics. In accordance with the embodiment illustrated in the drawings the draft-air supply means 3, which prefer is removable, has an essentially parallelepiped configurat and covers the burner opening 5 as well as the adjoining portions of the sloping bottom slabs or plane 4. The lower faces 3a of the draft-air supply means extend closely alon the bottom planes 4 whereby a comparatively small gap 2 is formed between the faces 3a and the planes. A number of draft-air bores 24 communicating the interior draft-air channel 28 of the draft-air supply means with the gap 2, open in the lower faces 3a. A number of additional draft-a bores 23 also open above the gap 2 and, at a yet higher level, open further draft-air bores 19. Consequently, all draft-air bores form air-intake openings. As is most clear apparent from Fig. 3 some portions of the draft-air supply means are positioned above all air intake openings so as to efficiently prevent any combustion material which may fall from the fuel storage vessel from obstructing the air intake openings.
In accordance with the shown embodiment the draft-air supply means has a parallelepiped configuration. This is a preferable configuration but obviously the invention is not restricted to this shape.
Because the faces 3a of the draft-air supply means as well as the faces 3b thereabove are turned downwards these faces as such form the portions covering the associa
openings. The upper air-intake openings 19 are covered by separate eaves-like projections 20. The faces 3c and 3d which are turned upwards are inclined at an angle which preferably could be larger than the angle of repose of the combustion material, thus preventing material from collect on top of the draft-air supply means.
In accordance with the embodiment shown, the faces 3a of the draft air supply means are essentially parallel with the sloping planes 4 but obviously it is within the scope of the invention to vary the spacing somewhat betwee the sloping planes and the draft-air supply means, should this be required in view of particular fuels or the heat extraction from the furnace. The combustion chamber 7 like wise communicates with the exhaust-gas channel system 8 via connection channels 29.
At its upper part the furnace is covered by a top slab 30 and at its base it is supported on a bottom slab 31. In Fig. 2 only a part of the jacket system of the furn is illustrated, more precisely the part surrounding the fuel supply opening 32 which may be closed by means of a fuel-feed lid 10. The fuel-feed opening 32 is surrounded by a flange 14 forming an inner sealing edge against the fuel-feed lid. The jacket system of the furnace also has an outer flange 12, forming an outer sealing edge against the lid. Between the interior portion of the furnace and the outer jacket system thereof there is a gap 25 in commu nication with the furnace exhaust-gas channel system.
The construction of the fuel-feed lid is clearly appa from Fig. 5, wherein the closed position of the lid is ill strated in continuous lines and its open position in dis¬ continuous lines. The fuel-feed lid consist of two tele- scopically movable portions 10a and 10b. These two lid portions are in the form of tube sections which are nested one in the other and which have one end wall each, 10c and 10d, respectively. A number of compression springs 21 are held between these end walls. The inner portion is provide with a lid plate 10e. By means of a packing 10f the lid
plate 1 Oe seals against the inner flange 14 and by means of a packing 1Og the end wall 1Od seals against the outer flange 12, as mentioned previously. Owing to the mutual movability of the two lids portions the latter provide an c efficient seal against their associated flange, also in case the spacing between the end edges of the flanges shou vary for some reason. To close the lid the inner flange 14 is moved first and the outer flange 12 thereafter to the closed positions. Also in the closed position of the 1 Q lid the space 15 surrounding the lid maintains communicati with the exhaust-gas canal system 25 of the furnace. The lid plane formed by the lid end wall 1 Od is designated by reference 18 on the drawings and the lid plane formed by the lid end wall 10e is designated by 16. 15 By numeral references 33 is designated a valve by means of which the upper part of the fuel storage vessel may communicate with the exhaust gas channel system of the furnace. This may be the case when the furnace operation is initiated. However, valve 33 preferably is maintained 0 i n closed position when the furnace is in operation.
In operation of the furnace, biological fuel present in the fuel storage vessel 1 is pyrolysed so as to form a gas which is formed downwards by its low atmospheric ove pressure through the burner opening 5 while being combuste 5 and at the same time pre-heated air is being supplied from the draft-air supply means 3. The fuel storage vessel 1, the combustion zone 9, the draft-air supply tube 3, the sloping planes 4 and the secondary combustion chamber 7 together with the ashes-collection cavity pertaining theret 0 . all preferably are made from a ceramics material as mention in the aforegoing. The exhaust gases preferably are transpo inside air gap 25 surrounding the ceramics part. The draft tube placed over the ' burner opening 5 is located in the hot combustion zone and consequently it will be heated to ι ~ a high temperature. The draft-air which is supplied by means of a preferably adjustable fan, not shown in the drawings, and which passes through the various openings 19, 23, 24 in the draft-air supply means 3 is pre-heated
6 before participating in the combustion process. The positi of the draft-air supply tube and its configuration includi air diffusing apertures provide an ejecting effect which in the case of varying heat-extraction ensures the correct 5 mixture of generated gas and supplied draft-air. Because of the inwardly directed openings in the draft tube 3 for the draft-air, turbulent combustion is created.
Part of the heat generated during the combustion fin it way upwards inside the fuel storage vessel, whereby th
-JO fuel is pyrolysed and gas is produced. Also when the heat extraction is low the heat inside the combustion zone 9 is sufficient to generate gases to an adequat degree. The com-bustion of gas travelling downwards essentially is th form of combustion of aldehyde. Aldehyde combustion oxidiz
15 hydrocarbons by way of aldehyde into CCA and H-.0. Aldehyd combustion generates the cleanest exhaust gases.
The portion of the fuel storage vessel that is posit above the combustion zone 9 forms an upwardly closed vess in the course of the process, provided that the valve 33
20 is closed, and consequently gas can only be emitted downw through the burner opening 5. In the course of the combus process the fuel storage simultaneously forms a gas bell, wherein generated gas accumulates at a slight overpressur •relatively to ' the surrounding atmosphere prior to its com
25 bustion and wherein the gas in the upper part of the fuel storage vessel will not be combustible on account of the poor oxygenation. When gas is generated from the fuel the volume of the gas increases and as a result a slight over pressure is formed in the fuel storage vessel. This press
30 combines with the pressure of the draft-air supply fan so as to pressurize the fuel storage vessel as required in order to force the gas downwards. Because the fuel storag vessel is pressurized it needs to be sealed. This require is met in that, as mentioned before, the fuel-feed lid is
3 formed with double lid walls, each one having a sealing function. Any gas that may pass the sealing of the inner lid is sucked out through the fume exhaust. Owing to this
arrangemnet, poisonous gases do not end up in the environ¬ ment. During refuel, when the fuel-feed lid is open, fumes are prevented from seeping out into the environment, becau these gases are evacuated by way of the free space 25 betw the inner and outer seals and are transferred further to the fume exhaust of the furnace.
When the process has progressed to the point where no more gas is generated, charcoal remains, if wood has been used as fuel. This charcoal is consumed continuously as draft-air is being supplied. The combustion of the char takes place in two steps, first 2C 2 + 02 = 2CO + heat, the
2 after 2C0 + 0 + heat. At this stage of the process, new fuel is supplied if the heating is to continue. The biolog fuel furnace preferably operates continuously, and the hea extraction could be varied in accordance with the rotation speed of the fan supplying air to the draft-air supply mea 3 from low extraction to high extraction, while maintainin purity of combustion and a high degree of efficiency. Owin to the angle of inclination 22 of the bottom part of the fuel storage vessel the fuel material is efficiently urged to collapse downwards. This material could be charcoal and ashes. The sloping bottom part also forms a burner opening the dimensions of which can easily be adjusted to the capa desired for the device. The sloping planes which are made from a heat resistant material, preferably a ceramics mate and which are replaceable, preferably are insulated from their support faces in order to retain the generated heat. This is of consideral importance to obtain good combustion results. The valve 33 provided in the fuel storage vessel 1 preferably is maintained in an open position during the starting-up stage, whereby the fumes will travel directly into the fume outlet. In this way the start-up is facilita During operation, this valve preferably is maintained in a closed position. The valve may also be opened while the device is being refueled, which contributes to preventing fumes from reaching the environment. Gas generated from the fuel storage vessel 1 is mixed with pre-heated air fro
the draft-air supply means 3 and is combusted downwards through the burner opening 5 into the secondary combustion chamber 7 underneath. This space also serves as an ashes collection chamber. After combustion, the hot gases flow from the secondary combustion chamber 7 to the heat exchan 8, wherein the thermal energy is utilized in the customary way in the water jacket 13, whereupon the exhaust gases proceed upwards.
The invention is not limited to the example described in the aforegoing and illustrated in the drawings but coul be varied as to its components and details within the scop of the appended claims without departing from the inventiv idea. For instance, the invention is not limited to the arrangement of e.g. the combustion chamber. Naturally, thi chamber could be made from other types of elements which could be assembled in any suitable way. Nor is the inventi limited to the particular design and mounting of the draft air supply means 3, the configuration and mounting of whic may be varied, although the embodiment shown has been foun to possess considerable advantages as concerns the service as well as the function of the furnace.