GB2188142A

GB2188142A - Combustion device for solid fuel

Info

Publication number: GB2188142A
Application number: GB08704145A
Authority: GB
Inventors: Daihachiro Murase
Original assignee: Individual
Current assignee: Individual
Priority date: 1986-02-21
Filing date: 1987-02-23
Publication date: 1987-09-23
Anticipated expiration: 2007-02-23
Also published as: CN1011063B; AU595005B2; KR870008147A; GB2188142B; KR950011330B1; GB8704145D0; CN1046971A; AU6915687A; CN87100753A

Abstract

A combustion device for solid fuel comprises a base stand 1 with an opening therein, an imperforate board 5' locatable to close the opening, a combustion chamber 3 standing on the stand 1 with the board 5' constituting the bottom of the chamber 3, and means for moving the board 5' to and away from the opening for removal of ash. <IMAGE>

Description

SPECIFICATION Combustion means for solid fuel and related equipment The present invention relates to a combustion means for solid fuel which can be used for a heating system in the house, or in a greenhouse orfora boiler. It is suitable for solid fuel such as coal, coke, charcoal, coal-dust briquettes, etc. More particularly, the present invention relates to a combustion means forsolidfuelwhich includes a holding board for holding the solid fuel during combustion and an ignition means for igniting the solid fuel.

Fan heaters and stoves, burning paraffin, have disadvantages such as the amounts of paraffin to be supplied,the instability in price, the danger of fire, or the risk in storage and handling of paraffin.

Solid fuel (such as coal-dust briquettes, charcoal) ischeaperandsaferto handle, and combustion apparatuses using such fuels are employed for factories, greenhouses, heating systems in cold districts, etc. Atype of conventional combustion deviceforexample, as shown in Japanese Utility Model Publication No.23003/1965, shows a grid having air slits at a lower position of a combustion chamber, with solid fuels piled on the grid and burning while ashes drop out through the grid so as to make ventilation smooth.

Solid fuel having a low ash content of 10% or less is cheap and of high calorie content. When such solid fuel is used air contamination is minimised and only a little ash remains in the combustion device during burning.

There have also been proposed combustion devices using solid fuels such as charcoal, lignite, coal pitch coke, petroleum coke, carsina coke, etc.

(Japanese Patent Publication (unexamined) Nos.

89905/1884, and 100302/1984). These combustion devices comprise a plane imperforate holding board which holds a solid fuel having low ash content, and a combustion chamber covering the holding board atthe lower end of which chamber spaces or holes for introducing air is provided. The spaces for introducing air accelerate the burning ofthe fuels.

In the combustion devices described above, there are used start-up igniting materials such as paper.

firewood, and molded rods made of compressed paper orfibers, which are dipped in oil and fats; or igniting means producing an arc with use of a ceramic heater, carbon rod or metal rod; or a gas burner provided at the lower surface of the holding board so astojetflamesupwards.

Solids fuels such as coal, coal-dust briquettes, etc are required to provide combustion for a long period oftime, a warmth-retention property and a long lasting fire. Sincethese solid fuels have an ash content of 10% or more, they remain as ashes in their original shapes on the holding board even after completion of burning soasto retainwarmthfora long time. Accordingly, the amount of ashes remaining aftercompletion of burning becomes large, which requires troublesome labour such as removal of ashes from air holes of roasters and disposal of the ashes. Further, and also in the combustion devices as shown in the above literature, ashes orunburntfuel are produced on and must be removed from the holding board.

Further, as igniting means, ceramic-based heaters are expensive, and the electrodes and leads soon deteriorate because ofthe high temperatures.

Igniting materials as mentioned above, e.g. paper orfirewood, or oil-dipped moulded materials, must be lighted with a match, etc which is troublesome.

The use of gases is dangerous.

The present invention sets outto provide a combustion means for solid fuel in which the fuel is burnt efficiently. It also envisages a holding board for a solid fuel combustion means, from which ashes and fuel residues can be easily removed. Further envisages an ignition means of durable construction by which ignition of the solid fuel can be easily effected.

The invention consists in a combustion device for solid fuel, comprising: a base stand with an opening therein; an imperforate heat resistant holding board normally located to close said opening; a combustion chamber standing on the base stand with the holding board constituting the bottom thereof; an inlet means art a lower edge of said chamber above the base plate, and/or in a surrounding wall of said chamber, whereby combustion air may enter as exhaust gases leave the combustion chamber; an exhaust pipe for the exhaust gases; generally tubular gas-flow heat-exchange ducting putting the combustion chamber and exhaust pipe into communication; and means capable of moving the holding board into or out ofthe opening for removal of ash or other residue.

Typically, the holding board is mounted to be pivotabletowards orawayfrom the opening in accorance with the movement of a motor-actuable connecting mechanism pivoted at one end to said board.

More detailed features of such a mechanism are described below.

In another majorfeature ofthe invention, again described in more detail below, a wiper arm is pivoted for horizontal wiping movement overthe base ofthe combustion chamber.

It is also envisaged in accordance with the invention, again as described in more detail below, to provide that the holding board is supported upon a support plate beneath the base stand, the support plate being connected at one end to the base frame and a manually operable operating rod being pivotableto hold or relasethesupport plate in or from the vicinity of the base plate and hence move the holding board between a closed position in the opening and an open position beneath the opening.

The combustion device mayfurther comprise electrical ignition means at, or constituting, a lower portion ofthecombustion chamber, including an electrical heating element located in a surface groove or grooves thereof, and protected by a heat-insulating fire-resistant material from the action ofthe combustion chamber, said groove or grooves being in communication with the atmosphere by at least one hole or like opening on a rearface ofthe ignition means.

The holding board mechanisms, wiper mechanism and ignition device also constitute aspects ofthe present invention.

In the combustion device of the present invention, even solid fuels having high ash content such as charcoal, coal-dust briquettes, etc can be burnt efficiently. The remaining ashes can easily be removed by opening the holding board and rotating the wiper. Further, solid fuels having low ash content such as cokes, etc (which are apt to crack during burning and become fines which fall down unburnt between bars of a grid) can efficiently be burnt by accumulating them on the imperforate holding board.

Accordingly,cokeswhich areusuallymoulded into a fixed size so as nottofall through a grid, can be used without any molding process without loss or incomplete combustion. In addition, since the solid fuels can be almost completely burntata high temperature, there is a cleaner throughflow into the heat-exchange ducts and exhaust. Thus, the combustion device ofthe present invention can be used for a steam raising boiler, and for a heating system for greenhouses or roomswhich circulates warm air by fans but still use inexpensive solid fuels.

The ignition means ofthe presentinvention,which is used also as a fire grate, comprises a resistance elemente.g.commerciallyavailablenichromewire without using fine ceramics which are expensive and difficult to work. The resistance element is covered with a heat-insulating material and fixed in a groove or grooves in the base plate, whereby the heat-generating substance is not exposed to oxygen in the air, and can be prevented from burning or deterioration at hightemperatures. Ventilation of the grooves in which the heating element is embedded can be effected by provision of air holes.An air-cooling function can be achieved so asto improve protection ofthe electrical heating element Further, since the surface-protecting portion may be made of material such that melting and remaining ashes of solid fuels are not adherent, any residue of the solid fuel can easily be removed.

The invention will be further described with reference to the accompanying drawings in which: Figure lisa partially exploded perspective view o' a combustion device for solid fuel according to the present invention; Figure 2 is a non-exploded vertical sectional view ofthe combustion device of Figure 1; Figure 3 is a plan view of the under surface of th e base stand ofthe combustion device of Figure 1; Figure 4 is an enlarged front view showing me;ans for rotating the holding board downwards; Figure5is a cross-section of Figure 4, taken along line X-X, Figure 6 is a perspective view of another embodiment of combustion device ofthe present invention;; Figure 7 is a partially cut-away plan view ofti' je base stand showing another embodiment, wherein the holding board is slid out ofthe base stand; Figure 8 is a plan view showing the undersurface of the holding board of Figure 7; Figure 9 is an enlarged perspectiveviewofan ignition means used in the combustion device ofthe present invention; Figure 10 is a cross-section of the essential part of the ignition means of Figure 9; Figures 7 1 (at to (f) are perspective views showing other embodiments of ignition means, with Figures (b) and (c) being in partial cross section; Figure 12 is a cross section showing the ignition means in operation; and Figures 13 (aJ to (e) show ignition means used in conventional combustion devices for solid fuels Figures 13(a), (c), (d) and (e) being cross sections and Figure 13(b) being a plan of Figure 13(c).

in Figure 1,thecombustion apparatusAcomprises a combustion portion B, a heat-exchange portion 4 and an air-exhaust pipe 7. It is mounted on a base stand 1 in such a manner that the combustion apparatus can optionally be taken off. The combustion portion B is connected with a numberof heat-exchange members 4b each in the shape of a flat box. Each member 4b is connected with a heat-exchange box 4a. The box 4a is connected with the air-exhaust pipe 7 and is provided in an appropriate position with an opening for tasking out any unburnt substance residuel.

The combustion portion B comprises a solid fuel holding portion 2, a combustion chamber3 and a holding board 5, located on the base stand 1. Atthe four corners ofthe base stand 1 are provided supporting legs 1b, and between the upper surface of the base stand 1 and the solid fuel-holding portion 2 is provided by means of legs 2b a space 2a of fixed dimensionfortaking in air. The dimension ofthe space 2a can be selected sothatthe amount ofair taken in is proportional to the amount of airto be exhausted from the exhaust pipe 7. It can be easily established that the dimension of the space 2a has a great influence on the combustion of the solid fuel.

By appropriately balancing the amount of airtaken in and taken out, solid fuels can be completely burnt without accumulating in thickness, and without any forced draft of air. When the dimension of the space 2a is too large, a large quantity of cold air is introduced into the combustion chamber and the exchange is greaterthan the heat-generating rate for solid fuelds. The temperature in the combustion chamber is lowered and eventually the fire goes out.

When the dimension of the space is too small, however, the extent of combustion becomes insufficient and again the fire goes out. Accordingly, the dimension of the space should be selected by prior experiments.

An an alternative, a conventional opening 2a' for taking in air may be provided on the peripheral wall ofthe combustion chamber, the amount of air being controlled by a controlling lid. Or, as shown in Figure 12there may be provided on the peripheral wall of the combustion chamber a number of opening 2a" for introducing air at the outer circumference, on which openings are provided rings movable up and down.

The solid-fuel-holding portion 2 and the combustion chamber3 are connected to each other, and may be constructed either integrally or separately but inconnected units. In the combustion chamber is provided a heat-exchange portion 3'.

Within the inner periphery of upper opening 3b of the combustion chamber3 is fixed a horizontal lid 8, with balancing weight8a. However, the inletforfuel is not limited to the opening 3b, and any air inlet on the peripheral wall ofthe combustion chamber may also be used as a fuel inlet.

Branches 4b for heat-exchange are connected to a side wall of chamber 3. An edge frame 1 caroundthe base stand 1 prevents burning fuels falling from air inlet 2a on to the floor. The fuel-holding portion 2 includes an internal heat retaining layer2.

This layer 2' is produced by fabricating a heat-insulating material structure, e.g. such as heat-resistant ceramic or heat-retaining brick, etc on the inside of the fuel-holding portion. Alternatively, the heat-retaining material is previously molded into fixed thickness and shape and is located on the inside of the fuel-holding portion. The solid fuels are thus held within the inner surface ofthe heat-retaining layer 22' and above the holding board 5 provided on the base stand 1. The spacewithinthe het-retaining layer 2' typically has trapezoid section, as shown.

Holding board is formed byfilling a heat resistant metal frame 6 with a heat-insulating material 5' having the same properties and effects as the heat-retaining layer2'. The surface ofthe heat-insulating material may be reinforced by sintered, oxidized or carbonized substances to improvethe heat resistance and durabilityofthe holding board. The holding board need not be a plan square (as shown in Figure 1) but may be polygonal or circular in periphery and conical or pyramidal in shape. The fuel-holding portion 2 and the combustion chamber3 have a horizontal cross-section corresponding to the shape of the holding board.

The holding board 5 is fixed to the base stand 1 on one side by a supporting means 9 in such a manner that the holding board can be pivoted downward. On the other side it is supported horizontally in such a mannerthat it can be put into or removed from a setting hole 1 a ofthe base stand 1 by an operating means 14.

The supporting means 9 comprises a supporting arm 9a pivoted to a lug 9c beneath the base stand 1 by a horizontal shaft 9b. The undersurface ofthe holding board is fixed to the upper surface ofthe supporting arm 9a. The operating means 14 comprises an inclined supporting rod 10 fixed to the lower surface ofthe metal frame 6, and is connected to a motor M1 through a horizontal connecting rod 11, and arm 11 ', a pinion 12 and a worm 13.

Numerals 1 1a and 11 b indicate pivots and 12a is a pinion shaft.

When motor M1 is driven the pinion 12 engaging with the worm 13 is rotated, together with the arm 11', through 180to and the holding board 5 rotates to hang down as shown by the chain-dotted chain line.

Subsequently, when the pinion is rotated in the opposite direction, the holding board is returned from the hanging condition to the horizontal condition and locates in the setting hole 1 a.

Motor1 is controlled byvariouslimitswitches.

and remote-control switches (not shown in the drawings) confirming the position ofthe holding board.

In Figures 1 and 2, pivoted wiper 15 for sweeping the upper surface of the holding board 5can move to and fro over a fixed angle.

Pivoting shaft 1 5b (Figure 3) for base portion 15' of the wiper 15 projects out from the under surface of the base stand 1. Projecting arm 1 5a is connected to the shaft 1 sub so as to keep fixed angle relative to the wiper 15. The projecting arm 1 5a is contacted by an operating arm 17 fixed on a shaft of a pinion 16.

Rotation of the shaft causes arm 17 to pivot arm 15 over a predetermined range, against restoring spring 19. Elastomeric (e.g. rubber) stop member 20, provided at a fixed position on the base stand or on the motor frame, regulates the overall range of the operating arm 17.Thustheoperatingarmrotatesin the direction as shown by the arrow and pushes the projecting arm 1 5a against spring 19 so thatthe wiper 15 moves through its desired angular extent.

At the end of this movement, since the operating arm 17 becomes disconnected from the projecting arm 1 5a, the wiper 15 is swiftly restored to the starting place bythe spring 19.

The motor M2 is immediately stopped and the operating arm 17 is gradually stopped by the braking action at 20. Of course, any convenient stop mechanism may be provided for motor M2.

In a preferred embodiment, movement ofthe wiper (M2) and opening and closing ofthe holding board (M1) are both operable with the use of an electric battery and a 12(v) motor.

Thus, when burning stops, or is stopped, operation of motor M1 causes ashes on the heat-insulating material 5' to fall into an ash receiver orextinguisher 30. When the holding board is restored to its original position,the wiper 15 is operated to clean off adherent ash on the surface of the holding board.

The wiper can also be driven using an electromagnetto sway a projecting arm e.g. in the fashion of a solenoid.

In another embodiment shown in Figure 5, the holding board is divided in the centre, and each holding barod portion 5,5 rotates downward to dump any unburnt solid fuel or ash. The construction of each portion ofthe holding board is shown in Figure 4. Two hanging rods 21,21 are pivoted atthe base stand 1 by pivots 21a, 21a, and the holding portions 5,5 are supported in hollowed portions 21 b, 21 b provided on the side edges of the lower end of the hanging rods 21, 21 by means of shafts 22, 22 on the inner ends ofthe holding portion boards. The outer ends ofthe holding board are each connected to the base stand 1 by hinge pins 22a, 22a. Between opposed lugs 21 c, 21 c projecting from the insides of the upper ends ofthe hanging rods 21,21 there is located a spring 23 which biasses each hollowed portions 21 to the relevant supporting shaft 22.

Thus, if lugs 21 c, 21 care pressed towards one another (direction a) against the spring bias they move the hanging rods 21,21 outward. On movement in direction (b) suspension is disconnected and the holding board portions fall to hang as shown bythechain-dotted lines.

Shape-memory alloys may be also used as materials for supporting and operating the board portions.

Figure 6 is a perspective view showing other embodiment of the combustion device of the present invention. The heat-exchange portion 4 and the holding board 5 differ from that earlier embodiment.

In Figure 6the heat-exchange portion comprises a base portion 4a surrounding the fuel-holding portion 2 on the base stand 1, U-shaped in plan and of square tube section, togetherwith curved, branched portions 4b and 4b each connected to the base portion 4a at the lower end and to the combustion chamber 3 at the upper end. Exhaust pipe 7 is located in an appropriate position.

Doors are provided in the base portion 4a at both front sides, and ash, etc may be removed in a receiving frame placed inside. In the drawing, 3' is a further heat-exchange extension, 3' is an air-inlet hole and 4c is a catch ring.

The holding board may be ofvarious shapes (such as polygon,square, etc) and is not necessarily a circie as shown in Figure 7. The outer circumference ofthe holding board 5 is held with a holding frame 24. The holding board is located into a setting opening 1 a of the base stand 1 to be supported on both side edges 27,27' of a supporting board 27 provided on the undersurface ofthe base stand 1 by means of two metal guide rails 25 of curved shape.

One end ofthe supporting board 27 is fixed to the base stand by a hinge (not shown) and the other end lies on the undersurface ofthe basestand with an inner end of a operating rod 28 pivoted at 29 and set in an arc-shaped groove on its undersurface.

By rotating of the operating rod 28, the end ofthe supporting board 27 may be disconnected. The holding board 5 comes out of its setting hole and slides outtothe end ofthe supporting board 27 on the guide rails 25,25. Ashes produced during combustion can be removed on receiving plate 30.

In the above embodiment, the combustion device is not provided with an ignition means and ignition must be effected by using kindling wood, etc or by directly igniting the solid fuel.

Another aspect ofthe present invention however to provide an ignition means which can also be used as a fire grate.

Figure 9 is a perspective view of such an ignition means 31a. On aflatsurface of a circular base plate 32 there is engraved a spiral groove 33 into which heating element 34 comprising for example nichrome wire, etc is set. Protective layer 35 covering outer and inner surfaces ofthe heating element substance 34, to protect from contact with air, comprises heat-resistant materials (castable alumina cement, heat-insulating and fire-resistant clay etc). The protective layer 35 may indeed cover the whole surface ofthe base plate. Ventilation hole 36 is provided for each groove 33 at an appropriate position.

Figure 11 (a) shows another embodiment in which a protective layer 35' comprising sintered carbonized products or oxidized products, or a mixture of such is formed on a surface of an ignition means 31 b, panda downwardlyopen groove 36' isformed beneath each groove 33 in an undersurace of a cast base board 32. The ventilation hole 36 (Figure 10) and the line groove 36 (Figure 11 a) prevent cracks by absorbing heat.

The base board 32 may comprise a heat-insulating material as conventionally used in such electrical equipment such as diatomaceous earth, clay, alumina cement, etc. Numeral 37 is a lead wire.

Figure 11 (b) shows an ignition means 31 cwhich projects from the base of a combustion chamber and hasa hollowtriangularsection. On its outer periphery is provided a helical groove in which a resistance wire 34 and a protective layer 35 is located, together with ventilation holes 36. The ignition means 31 c is an improvement ofthe ceramic ignition means shown in Figure 13(c) described below.

The ignition means comprises heat-resistant castable material which has heat resistance upto a combustion temperature of 1500 C and a surface-protecting layer 35' made of sintered oxidized material in fine powder as described with reference to Figure 11(a) above.

As shown in Figure 12, the solid fuel 38 located between the ignition means (31 a, 31 to 31 g) is heated by electrical resistance heating, volatilizes, and starts to burn. When the temperature reaches a predetermined value, or the fuel is seen to be alight, the electricity is switched off. As the solid fuels continue to burn they reach high temperatures and radiate heat. The solid fuel, especially fuel of low ash content, cracks and gives a fine scattered material.

However, since a stream of air reaches to the inside of the combustion chamber from the air inlet the fine materials do notfall outorburstoutfromthe air-absorbing space 2a but stay in the combustion chamber at high temperatures and combustfully.

When the ignition means 31 d is used (Figure 12) it can actually constitute the fuel-holding portion 2.

Ignition means 31e (Figure 1 1d) is of " roaster" type and issuitableforfuels having low ash content. In Figure 11 (e) a heating element31 (f) is rod shaped. it may be assembled, with others, such as at 31 g (Figure 11 (f) by arranging a plural of rod-like shapes in a row.

The ignition means of the various types above mentioned may be protected by a metal frame for maintaining mechanical strength over a long period.

Further, the ignition means can be used not only for high calorie solid fuels having low ash content but also forsolid fuels having a high ash content by provision of means for easily removal of ashes, for example, means for tilting downward or siding out the base board 32, out of the setting hole of the base stand 1.

Combustion of solid fuel is effected as follows: a fixed amount of solid fuel is charged from the fuel charging lid 8 onto the holding board 5 and accumulated thereon. The resistance element or other ignition material is heated to heat the solid fuel, which gradually becomes hot from the base upwards. Eventually, volatile components are produced from the fuels by heat decomposition. This volatile component burns in the air in the combustion chamber and causes the atmospheric temperature in the combustion chamberto rise.

Oxygen isthen drawn in via the space 2a.

The combustion ofthe solid fuel spreads throughout the whole accumulation, which goes red-hot.This high temperature combustion causes the solid fuelsto crack. Although small pieces ofthe fuel scatter about they are retained by the holding board which has a plane imperforate nature. Thus, they are retained in the combustion chamber until complete combustion is achieved by air absorption, the radiant heat and high temperature atmosphere.

The gas generated by combustion is exhausted through pipe 7, and outside air in a compensatory amount is introduced into the combustion chamber through the space 2a.

As combustion proceeds, the combustion chamber3 and the heat exchange portion 4 getvery hot. Hot air flows from the combustion chamber into the branches of heat-exchange portion 4b and the base portion 4a, whereby natural convection can be smoothly effected. The fine powdered ash and any unburntfuel fall into the portion 4a, and accumulate therein. This can be removed from outlets on the front end of the base portion 4a. Thus, soot and dust is not discharged through the exhaust pipe. The provision of a filter in the pipe 7 can further improve the removal of harmful soot and dust.

With continuing combustion, since unburnt substances and ashes accumulate on the holding board (though usually only small amounts) they are cleaned by driving motors M1, M2 (or manually) so that the holding board hangs down, at one end orat the centre (or the operating rod 28 projects out of the front end ofthe base stand, and the holding board is slid outward by disconnection and inclination ofthe supporting board). When the combustion stops or is stopped, the remaining fuels can be dropped offthe holding board into an extinguisher.

In Figures 13(a)to (e),there are shown some conventional combustion devices. Figure 13(a) shows one embodiment using oil dipped igniting material. For igniting solid fuels, the igniting material 31 is lit and burntto produce heat and flames. In Figure 13(b) a ceramic heater32a is shown. 32b is an electrode, and 37 is a lead wire.

Figure 13(c) is a cross-sectional view of Figure 13(b).

Figure 13(d) shows another example using a ceramic heater33a. Figure 13(e) shows one embodiment using a gas burner 34.

Claims

1. Acombustion deviceforsolidfuel, comprising: a base stand with an opening therein, an imperforate heat resistant holding board normally located to close said opening; a combustion chamber standing on the base stand with the holding board constituting the bottom thereof; an inlet means art a lower edge of said chamber above the base plate, and/or in a surrounding wall of said chamber, whereby combustion air may enter as exhaust gases leave the combustion chamber; an exhaust pipe for the exhaust gases; generally tubular gas-flow heat-exchange ducting putting the combustion chamber and exhaust pipe into communication; and means capable of moving the holding board into or out ofthe opening for removal of ash or other residue.

2. Acombustion device as claimed in claim 1 wherein the holding board is mounted to be pivotable towards or away from the openi ng in accordance with the movement of a motor-actuable connecting mechanism pivoted at one end to said board.

3. Acombinationdeviceasclaimedinclaim2 wherein a motor-driven worm gear rotates through a predetermined angle a meshing pinion attached to said connecting mechanism so asto move the board between a closed position within the opening to an open position hanging from its pivot beneath the opening.

4. Acombustion device as claimed in claim 1,2 or 3 wherein a wiper arm is pivoted for horizontal wiping movement over the base of the combustion chamber.

5. Acombustion device as claimed inclaim4in which the wiper arm shares its pivot with an operating arm located at a fixed angle to the wiper arm beneath the base stand, whereby movement of the operating arm moves the wiper arm through its horizontal wiping movement.

6. A combustion device as claimed in claim 5 wherein a motor driven worm is located to rotate a meshing pinion carrying an actuating arm to move the said operating arm and then release it; and wherein the wiper arm is spring-biassed to return to its original position on such release of the operating arm.

7. Acombination device as claimed in anyone preceding claim in which the holding board is supported upon a support plate beneath the base stand, the upper plate being connected at one end ot the base frame and a manually operable operating rod being pivotable to hold or release the support plate in or from the vicinity of the base plate and hence move the holding board between a closed position in the opening and the open position beneath the opening.

8. Acombustion device as claimed in claim 7 in which the said holding board is capable of sliding in relation to the support plate.

9. Acombustion device as claimed in anyone preceding claim further comprising electrical ignition means at, or constituting, a lower portion of the combustion chamber, including an electricl heating element located in a surface groove or grooves thereof, and protected by a heat-insulating fire-resistant material from the action of the combustion chamber, said groove or grooves being in communication with the atmosphere by at least one hole or like opening on a rearface ofthe ignition means.

10. Acombustion device as claimed in claim 1 and substantially as herein described with reference to the accompanying drawings.

11. For a combustion device, the mechanism for opening and closing the holding board into and out of its opening as setforth in claims 2 or3 or7 or8.

12. For a combustion device, the wiper mechanism ofthe holding board as set forth in claims 4,5 or 6.

13. Foracombustion device,theelectrical ignition means as setforth in claim 9.