AU2003201361A1 - Improved solid fuel stove - Google Patents

Description

AUSTRALIA

PATENTS ACT 1990 COMPLETE SPECIFICATION FOR A STANDARD PATENT (Original) APPLICATION NO:

LODGED:

COMPLETE SPECIFICATION LODGED:

ACCEPTED:

PUBLISHED:

RELATED ART: NAME OF APPLICANT: ACTUAL INVENTORS: ADDRESS FOR SERVICE: INVENTION TITLE: PAUL SINTES.

PAUL SINTES LORD COMPANY, Patent Trade Mark Attorneys, of 4 Douro Place, West Perth, Western Australia, 6005, AUSTRALIA.

IMPROVED SOLID FUEL STOVE DETAILS OF BASIC CONVENTION APPLICATION: NEW ZEALAND PATENT APPLICATION NO. 518159 FILED ON APRIL 4,2003 The following Statement is a full description of this invention including the best method of performing it known to me/us: TITLE: IMPROVED SOLID FUEL STOVE The present invention relates to a stove for burning solid fuel, typically wood or wood pellets or wood composites.

A majority of the solid fuel stoves currently on the market are not clean burning, i.e. the exhaust gases passing up the flue of the stove contain an undesirably high proportion of unburnt particles and incompletely burnt gases. This gives rise to air pollution problems when the stoves are used in areas which are not naturally windy and/or are prone to temperature inversion layers.

It is therefore an object of the present invention to provide a design for a solid fuel stove which overcomes, or at least substantially reduces, the above described problem.

A further object of the present invention is the provision of a solid fuel stove which burns fuel very efficiently, which is unaffected by the use of air evacuating appliances (e.g.

extractor fans, range hoods) in the same area as the stove, and which does not use heated room air for combustion.

The present invention provides a solid fuel stove of the type comprising an enclosed insulated firebox into which solid fuel may be inserted through a closable door, the firebox being connected to atmosphere by means of a flue through which exhaust gases can escape from the firebox; wherein the stove includes an air intake in the form of a jacket surrounding the flue, such that in use combustion air is drawn from the atmosphere and down the jacket into the firebox, being preheated by the heat of the exhaust gases in the flue.

Preferably, said jacket is in communication with primary, secondary and tertiary air ducts formed in the firebox; said primary air ducts being arranged to receive a major portion of the intake air and to supply said air to the lower part of the front of the firebox; said secondary air ducts being arranged to receive a first minor portion of the intake air and to supply said air to lower secondary air outlets at the lower part of the rear of the firebox; and said tertiary air duct being arranged to receive a second minor portion of the intake air and to supply said air at or adjacent the top of the firebox.

Preferably, said closable door is located on one side of the firebox and is provided with a transparent or translucent panel, and said primary air ducts are arranged to direct at least part of the primary air over the internal surface of said transparent or translucent panel.

Preferably, said secondary air ducts also supply air to upper secondary air outlets at the rear of the firebox at a position below said tertiary air duct but above the lower secondary air outlets.

By way of example only, a preferred embodiment of the present invention is described in detail with reference to the accompanying drawings in which:- Figure 1 is a horizontal section through a stove of the present invention; and Figure 2 is a vertical section through the stove of Figure 1.

Referring to the drawings, a stove 2 comprises an outer metal casing 3, lined with fire brick (not shown) in known manner. The casing 3 is roughly cuboid in shape. A door 4 with a central heat resistant glass panel (not shown) is hinged to the front of the casing and can be opened to allow fuel to be placed inside the firebox A circular cross-section flue 8 surrounded by a concentric circular cross-section jacket 9 are mounted on the top surface of the stove 2, adjacent the rear of the stove. The upper ends of both the flue 8 and the jacket 9 are open to the atmosphere. The flue 8 communicates with the firebox 5 through an exhaust duct 10 which opens into the firebox through a slot 11.

The lower end of the jacket 9 opens into a common air duct 12 at the top of the stove.

From the duct 12, combustion air entering the stove through the jacket 9 can pass into two primary air ducts 13 along each side of the stove, into two secondary air ducts 14 which extend one down each rear corner of the stove, and into a tertiary air tube which extends horizontally across the top of the firebox, about midway across the width of the firebox.

The secondary and tertiary air ducts 14,15, may be regulated or unregulated. The airflow through the primary air ducts 13 can be regulated by a pair of dampers (not shown) arranged one in each duct and controllable by a control lever at the front of the stove.

Primary combustion air is indicated by Arrow A and passes from the jacket 9 through the air ducts 13 along either side of the stove to the front of the stove where a first deflector plate 16 forms a front air duct across the front of the stove. The primary combustion air then is deflected by the first deflector plate 16 down the inside of the door 4; this helps to keep the transparent plate in the door clean. At the bottom of the door, the primary combustion air is deflected by a second deflector plate 161 to the lower part of the firebox 5, adjacent the fuel 17 stacked on the firebox floor 6.

Secondary combustion air is indicated by Arrow B and travels down the secondary air i0 ducts 14, entering the firebox 5, through an upper secondary air inlet formed by a series of apertures 14a in a secondary air tube 14b, and lower secondary air inlets 14c at the lower rear of the firebox. The air tube 14b extends horizontally between the secondary air ducts 14, in communication with the interior of the air ducts 14, across the rear wall of the firebox at a position about two-thirds of the height of the firebox from the firebox base. The apertures 14a may be slots or circular holes.

Tertiary combustion air travels through the tertiary air tube 15 and leaves the tube through the tube outlets (slots or holes) indicated by Arrows C in Figure 1. Thus, the tertiary combustion air enters the firebox 5 across the width of the firebox, near the top of the firebox.

The angle of the secondary and tertiary combustion air outlets can be varied so that the air can enter the firebox at any of a range of preset angles.

A fire brick baffle plate 18 is secured across the top of the firebox 5 above the tertiary air tube The above described stove operates as follows:- the door 4 is opened, and fuel 17 (e.g.

wood) is placed on the floor 6 and is set alight. The door 4 is then closed, and the dampers in the primary air ducts 13 are fully opened.

Combustion air flows down the jacket 9, and primary combustion air is directed to the fuel 17 by the deflector plate 16. Initially, the primary combustion air is at ambient temperature, but as combustion continues, exhaust gases leave the firebox through the slot 11 and flue 8, heating the flue 8. As further combustion air is drawn down the jacket 9, the air is preheated by contact with the hot flue once full combustion is established in the stove, the air temperature of the incoming combustion air is estimated at between 200-300 degrees centigrade.

The use of preheated combustion air greatly improves the efficiency of combustion:- if the fuel is wet, the hot combustion air can dry the surface sufficiently to allow effective combustion. More importantly, the hot combustion air gasifies the various volatiles in the surface layers of the fuel; these volatiles burn efficiently in the preheated air. The volatiles tend to be swept towards the back of the stove where they are mixed with secondary heated combustion air entering the firebox through the lower secondary air inlets 14c. The air from the secondary air inlets 14c creates turbulence in the gas flow io and ensures thorough mixing of the combustion air and volatiles. These gases are then moved towards the underside of the baffle plate 18 by further secondary combustion air admitted through the upper secondary air inlets 14a.

Any remaining unburnt volatiles rise towards the top of the firebox in the exhaust gases and are further mixed with heated tertiary combustion air entering the firebox through the tertiary air tube 15, causing combustion of any remaining unbumt volatiles.

After the tertiary combustion stage, part of the exhaust gases leave the firebox through slot 11 and flue 8 (Arrow and part (Arrow E) are swept downwards by the 'door wash' flow of primary combustion air (Arrow A) for further combustion in the embers in the firebox.

The use of four separate streams all of heated combustion air ensures very thorough combustion of all volatiles resins, creosotes, turpentines) and ensures that the fuel is burnt as thoroughly as possible. The volatile components are the first part of the fuel to bum and contain almost all of the components which cause pollution if not completely and correctly burnt. Thus, it is important to ensure that these components are fully burnt if the stove is to be clean burning. The volatiles will burn to form carbon dioxide if burnt completely and correctly.

Because the stove of the present invention draws all of its combustion air from outside the building being heated, operation of the stove does not create draughts inside the building nor is operation of the stove affected by air evacuating appliances within the building extractor fans or range hoods). Also, the stove can operate efficiently in rooms which are well sealed from drafts.

The above described stove may be fitted with heat dissipating fins secured to the exterior of the metal casing. Each fin comprises a strip of metal welded to the metal casing. Preferably the casing and each fin are made of steel and a strip of aluminium is inserted between each fin and the adjacent side of the casing. When the stove heats up during operation, the aluminium expands to a greater extent than the steel, and thus ensures a very close fit between the casing and the fin, to maximize heat conduction.

The fins may be exposed on the exterior of the stove or may be enclosed within a housing around the exterior of the stove. If the fins are enclosed within a housing, then a forced air draft may be circulated around the housing to improve heat transfer between the air and the fins.

The stove may be a free standing stove or may be fitted to an existing open fireplace.

The stove could be further modified by incorporating a Seebeck thermoelectric element array secured to, or located near, a surface of the stove. The array would be attached such that one side of the element would be heated and the other side would remain at room temperature; it is envisaged that this temperature difference would develop enough current to operate one or more small electric fans which could be used to circulate air around the heater as described above.

Alternatively, or in addition, the electricity generated from the Seebeck elements may be used to provide power to operate a microprocessor or microcomputer and sensors to sense the opacity or analyse the gas constitution of the flue gases, and to regulate the air flow through the primary, secondary or tertiary air ducts in accordance with the measurements taken by the sensors, so that the stove burns as cleanly and efficiently as possible.

Claims (17)

1. A solid fuel stove of the type including an enclosed insulated firebox into which solid fuel may be inserted through a closable door, the firebox being connected to atmosphere by means of a flue through which exhaust gases can escape from the firebox; wherein the stove includes an air intake in the form of a jacket surrounding the flue, such that in use combustion air is drawn from the atmosphere and down the jacket into the firebox, being preheated by the heat of the exhaust gases in the flue.

2. The stove as claimed in claim 1 wherein said jacket is in communication with primary, secondary and tertiary air ducts formed in the firebox; said primary air ducts being arranged to receive a major portion of the intake air and to supply said air to the lower part of the front of the firebox; said secondary air ducts being arranged to receive a first minor portion of the intake air and to supply said air to lower secondary air outlets at the lower part of the rear of the firebox; and said tertiary air duct being arranged to receive a second minor portion of the intake air and to supply said air at or adjacent the top of the firebox.

3. The stove as claimed in claim 2 wherein said closable door is located on one side of the firebox and is provided with a transparent or translucent panel, and said primary air ducts are arranged to direct at least part of the primary air over the internal surface of said transparent or translucent panel.

4. The stove as claimed in claim 2 or 3 wherein said secondary air ducts also supply air to upper secondary air outlets at the rear of the firebox at a position below said tertiary air duct but above the lower secondary air outlets.

The stove as claimed in any one of claims 2-4, wherein said primary air ducts include a pair of ducts arranged to extend one along each side of the top of the stove, between the jacket and the front of the stove.

6. The stove as claimed in claim 5 wherein each of said pair of ducts terminates at the front of the stove at a front duct with a deflector plate arranged so as to deflect at least part of said primary air down the front of the stove.

7. The stove as claimed in claim 4 or in claims 5 or 6 when dependent upon claim 4, wherein said secondary air ducts include a pair of ducts extending one down each rear comer of the stove, opening into said upper and lower secondary air outlets.

8. The stove as claimed in any one of claims 2-7, wherein said tertiary air duct provides air outlets across a major portion of the width of the firebox.

9. The stove as claimed in any one of claims 2-8 wherein the firebox includes an exhaust duct at the top of the firebox, adjacent the front of the firebox.

The stove as claimed in any one of claims 2-9 further including dampers arranged to regulate air flow through the primary air ducts.

11. The stove as claimed in any one of the preceding claims, wherein the firebox is provided with an exterior metal casing which is fitted with heat dissipating fins on at least part of the exterior thereof.

12. The stove as claimed in claim 11, wherein said heat dissipating fins are enclosed by a second casing, and a fan is arranged to provide a forced air circulation around said fins in use.

13. The stove as claimed in any one of the preceding claims, further including a Seebeck thermoelectric element array secured to, or adjacent, a surface of the stove.

14. The stove as claimed in claim 13 wherein said Seebeck element array is arranged to provide power for a microprocessor or microcomputer which is adapted to monitor and control the operation of the stove.

15. The stove as claimed in claim 13 or 14 wherein said Seebeck element array is arranged to provide power for an air circulation and/or an induced draft fan.

16. The stove as claimed in any one of claims 1-12 further including a microprocessor or microcomputer which is adapted to monitor and control the operation of the stove.

17. A solid fuel stove substantially as hereinbefore described with reference to and as shown in the accompanying drawings. Dated this 14th day of March 2003 PAUL SINTES By his Patent Attorneys LORD COMPANY Perth, Western Australia