Combustion system

Abstract

Disclosed is a fireplace which includes a firebase, a primary combustion zone with a first air supply unit, a secondary combustion zone, and an exhaust flue. The fireplace place also includes a charcoal/reduction layer which forms between the primary combustion zone and the secondary combustion zone, the arrangement and construction being such that the gases and/or particulate matter produced from the pyrolysis and/or combustion of the biomass fuel in the primary combustion zone have to pass over, or through, the charcoal/reduction layer prior to entering the secondary combustion zone and/or the exhaust flue. The fireplace also includes a second air supply unit for introducing heated secondary air into, or adjacent to, the secondary combustion zone, the arrangement and construction being such that the secondary air passes through (or adjacent to the region of) the charcoal/reduction layer to thus heat the secondary air.

Claims

1. A combustion system, said combustion system comprising: a biomass burner that includes: i. a firebox, ii. a firebase at, or forming, a bottom of the firebox, iii. a primary combustion zone for pyrolyzing and combusting the biomass fuel, the pyrolyzing and combusting of the biomass fuel producing gases and particulate matter, iv. a first air supply having a first air pathway connected into the firebox to thereby supply primary air into the firebox, v. a secondary combustion zone for combusting the gases and the particulate matter produced from the pyrolysis and combustion of the biomass fuel, vi. an exhaust flue with an upper part that extends out of a top of the firebox and a lower portion that extends into the firebox to a location above a first portion of the firebase and adjacent a region of said secondary combustion zone, wherein the firebase includes a charcoal/reduction layer support region, the charcoal/reduction layer support region supporting a charcoal/reduction layer which forms below the primary combustion zone, in the region of the secondary combustion zone, and between the primary combustion zone and the secondary combustion zone, the secondary combustion zone being at least partially surrounded by the primary combustion zone, wherein an opening of the lower portion of the exhaust flue is located above the first portion of the firebase, the first portion of the firebase including a first part of the charcoal/reduction layer support region included in the region of said secondary combustion zone in which the charcoal/reduction layer is formed, wherein the gases and the particulate matter produced from the pyrolysis and combustion of the biomass fuel in the primary combustion zone pass over, or through, said charcoal/reduction layer and over said charcoal/reduction layer support region including the first portion of the firebase, prior to entering the secondary combustion zone and the opening of the exhaust flue; and a second air supply comprised of at least one aperture, each aperture having an inlet directly exposed to atmosphere, each aperture extending through the first portion of the firebase and having an outlet located below a lower surface of the charcoal/reduction layer in the region of the secondary combustion zone to thereby introduce a secondary air drawn from outside the firebox, through the at least one aperture, and discharged into the firebox at the first portion of the firebase below and through the charcoal/reduction layer in the region of the secondary combustion zone, wherein the secondary air, being discharged through the at least one aperture below a lower surface of the charcoal/reduction layer in the region of the secondary combustion zone, is heated by passing through the charcoal/reduction layer and the secondary combustion zone, as the secondary air is being introduced into the firebox, above 600? C. and maintained above 600? C. at a temperature sufficient to combust the combustible gases and the particulate matter in the secondary combustion zone.

2. The combustion system as claimed in claim 1, wherein said secondary combustion zone is wholly surrounded by said primary combustion zone.

3. The combustion system as claimed in claim 2, wherein said first air supply comprises an air damper.

4. The combustion system as claimed in claim 1, wherein said one or more apertures comprise plural apertures in the firebase below the secondary combustion zone.

5. The combustion system as claimed in claim 4, wherein said first air supply comprises an air damper.

6. The combustion system as claimed in claim 4, further comprising: a ceramic disc located above the plural apertures, the ceramic disc having a ring and a main body supported by the ring, the surrounding the plural apertures and supporting the main body spaced apart from the plural apertures, the ring and main body defining a space between an upper surface of the firebox located around the plural apertures and a lower surface of the main body, the main body having a central aperture and a cone portion extending into the central aperture, a top of the cone portion being located above a top surface of the main body, wherein the charcoal/reduction layer surrounds the ceramic disc, wherein the secondary air, after passing through the plural apertures, passes through the space along the lower surface of the ceramic disc and out through the central aperture of the main body along the cone portion into the secondary combustion zone, and wherein the firebase forms the bottom of the firebox.

7. The combustion system as claimed in claim 1, wherein said first air supply comprises an air damper.

8. The combustion system as claimed in claim 1, wherein the combustion system further includes insulation insulating the region of the secondary combustion zone and/or the charcoal/reduction layer.

9. The combustion system as claimed in claim 8, wherein said insulation includes one or more apertures, through which the secondary air may pass.

10. The combustion system as claimed in claim 8, wherein said insulation is in the form of a ceramic disc.

11. The combustion system as claimed in claim 1, wherein the firebase forms the bottom of the firebox, wherein said secondary combustion zone is wholly surrounded by said primary combustion zone, wherein said one or more apertures comprise plural apertures in the firebase below the secondary combustion zone, and further comprising: a ceramic disc located above the plural apertures, the ceramic disc having a ring and a main body supported by the ring, the surrounding the plural apertures and supporting the main body spaced apart from the plural apertures, the ring and main body defining a space between an upper surface of the firebox located around the plural apertures and a lower surface of the main body, the main body having a central aperture and a cone portion extending into the central aperture, a top of the cone portion being located above a top surface of the main body, wherein the charcoal/reduction layer surrounds the ceramic disc, and the secondary air, after passing through the plural apertures, passes through the space along the lower surface of the ceramic disc and out through the central aperture of the main body along the cone portion into the secondary combustion zone.

12. The combustion system as claimed in claim 1, wherein the firebase forms the bottom of the firebox, wherein said secondary combustion zone is wholly surrounded by said primary combustion zone, wherein said one or more apertures comprise plural apertures in the firebase below the secondary combustion zone, and further comprising: a ceramic disc located above the plural apertures, the ceramic disc having a ring and a main body supported by the ring, the surrounding the plural apertures and supporting the main body spaced apart from the plural apertures, the ring and main body defining a space between an upper surface of the firebox located around the plural apertures and a lower surface of the main body, the main body having a central aperture, wherein the charcoal/reduction layer surrounds the ceramic disc, and the secondary air, after passing through the plural apertures, passes through the space along the lower surface of the ceramic disc and out through the central aperture of the main body into the secondary combustion zone.

Description

DRAWINGS

(1) FIG. 1: is a cut-away, side view of one possible embodiment of the present invention,

(2) FIG. 2: is a perspective view of the embodiment illustrated in FIG. 1,

(3) FIG. 3: is a cut-away, side view of another possible embodiment of the present invention,

(4) FIG. 4: is a cut-away, side view of an embodiment of the present invention which has a rear exit flue,

(5) FIG. 5: is a cut-away side view of an embodiment of the present invention which includes a tapered firebase,

(6) FIG. 6: is a view of a control means, for use with the present invention.

(7) FIG. 7: is a table showing test result for an embodiment of the combustion system.

DESCRIPTION OF PREFERRED EMBODIMENTS

(8) Having regard to FIGS. 1 and 2 there is shown a combustion system generally indicated by arrow 1.

(9) The combustion system 1 includes a fireplace in the form of a wood burner 2.

(10) The wood burner 2 includes a metal firebox 8. The firebox 8 includes a firebase 3, which effectively forms the floor of the firebox 8 of the wood burner 2.

(11) The wood burner 2 also includes a primary combustion zone, generally indicated by arrow 4, for pyrolysing and/or combusting wood 6, and a secondary combustion zone, generally indicated by arrow 5, for combusting gases and/or particulate matter produced from the pyrolysis and/or combustion of the wood 6.

(12) The wood burner 2 includes a first air supply means 15 in the form of an adjustable air damper (not shown). The first air supply means 15 serves to provide a primary air supply into the firebox 8, and more particularly into the primary combustion zone 4.

(13) The wood burner 2 also includes an exhaust flue, generally indicated by arrow 7.

(14) The upper part 9 of the exhaust flue 7 extends out of the top 10 of the firebox 8 and ultimately extends up and out through the ceiling and roof of the dwelling in which the wood burner 2 is housed.

(15) The lower part 11 of the exhaust flue 7 extends into the firebox 8 to a position near to, or adjacent, the secondary combustion zone 5 (just above the firebase 3). This results in the downdraft or side draft of the combustion gases and/or particulate material. That is, the combustion gases and/or particulate material produced by the pyrolysis and/or the combustion of the wood 6 in the primary combustion zone have to work their way downwards in order to be able to enter the open end of the lower part 11 of the exhaust flue 7. This downdraft (or side draft) is primarily facilitated by the updraft created as heat travels up the flue 7 on the way to being exhausted through the roof or ceiling (that is, in the direction of arrow 21).

(16) The lower part 11 of the exhaust flue 7 may be retrofitted to existing wood burners 2. This is an important feature of the invention, as it allows for the combustion system to be fitted to the many wood burners that are currently being used. Furthermore, owners of wood burners may be encouraged to retro-fit the combustion system 1 to their wood burners given that the cost is minimal and the process simple. And because their modified wood burner will produce far fewer (or negligible) emissions, this clearly has positive environmental considerations. Moreover, if the only option to having a more efficient wood burner was to purchase a replacement wood burner, this cost may be prohibitive for many people.

(17) With respect to the embodiment illustrated, the lower part 11 of the exhaust flue 7 may be inserted into the firebox 8 and crimped onto the lower portion of the upper part 9 of the exhaust flue 7. Alternatively, the lower part 11 of the exhaust flue 7 may be slid into the bottom of the upper part 9 of the exhaust flue 7. Furthermore, the lower part 11 of the exhaust flue may be adjustable whereby the gap between the bottom of the lower flue 11 and the firebase 3 may be adjusted, as required or as desired.

(18) An advantage of such an arrangement is that the combustion system 1 may therefore effectively be retrofitted to existing wood burners 2, thus bringing them up to modern compliance standards. Furthermore, the task of retrofitting to existing wood burners 2, as described above, is a relatively simple, quick and inexpensive operation.

(19) Alternatively, the lower part 11 of the exhaust flue 7 may be incorporated into new wood burners 2.

(20) In the embodiments illustrated the combustion system 1, when in operation, results in a charcoal/reduction layer 12 forming below the primary combustion zone 4, and in the region between the primary combustion zone 4 and the secondary combustion zone 5. The arrangement and construction is such that the gases and/or particulate matter produced from the pyrolysis and/or combustion of the wood in the primary combustion zone 4 have to pass over or through the charcoal/reduction layer 12 prior to entering the secondary combustion zone 5 and/or the exhaust flue 11.

(21) The secondary combustion zone 5 is wholly surrounded by the primary combustion zone 4. The only part of the secondary combustion zone 5 which is not surrounded by the primary combustion zone 4 is where the secondary combustion zone 5 abuts the near side wall of the firebox 8.

(22) Because the secondary combustion zone 5 is surrounded by the primary combustion zone 4 (as well as being surrounded by the charcoal/reduction layer 12), the combustion system 1 is able to reach, and consistently maintain, hot temperatures within the wood burner 2, as well as being able to achieve maximum combustion efficiency (as will be evidenced later in this specification).

(23) That is, the fire-insulated secondary combustion zone 5 keeps temperatures high enough to combust even the compounds with the highest self-ignition temperatures and subsequently the combustion system 1 produces very low emissions. Particulate and carbon monoxide emissions for the combustion system 1 have in fact been measured and are lower than that published for natural gas (as will be evidenced later in this specification).

(24) The combustion system 1, when in operation, often results in an ash layer 13 forming on the firebase 3 below the primary combustion zone 4 and charcoal/reduction layer 12.

(25) The wood burner 2 also includes a drying zone 14 for drying the wood 6 and/or removing water from the wood 6 prior to the pyrolysis and/or combustion of the wood 6 in the primary combustion zone 4. The drying zone 14 is situated above (or within) the primary combustion zone 4. Provision for introducing wood 6 to the wood burner 2 is via a hinged door (not shown) at the front of the firebox 8.

(26) In the embodiment shown, the wood burner 2 also includes a second air supply means for introducing heated secondary air into the firebox 8 in the region of the fire-insulated secondary combustion zone 5, and adjacent to the charcoal/reduction layer 12, to thus heat the secondary air as it is being introduced into the firebox 8.

(27) The secondary air supply means includes a number of apertures 30 which are drilled into the firebase 3 in the region of where the secondary combustion zone 5 will form. Secondary air is drawn from outside of the firebox 8 and directed up through the apertures 30where the secondary air is heated by the secondary combustion zone 5 and by the adjacent charcoal/reduction layer 12.

(28) It is also envisaged that the apertures 30 could additionally or alternatively be formed in the firebase 3 in the region below the charcoal/reduction layer 12.

(29) Hence, the second air supply means can easily, cheaply and readily be retro-fitted to an existing wood burner as all that is required is the drilling of the apertures 30 in the firebase 3 (and, optionally, adding some ducting if required or desired).

(30) The combustion system 1 also includes insulation means for insulating the region of the secondary combustion zone 5 (and, to a lesser extent, the charcoal/reduction layer 12). The insulating means is in the form of a ceramic disc 18.

(31) One purpose of the ceramic disc 18 is to maximise temperatures within the region of the secondary combustion zone 5.

(32) Another (less important) purpose of the ceramic disc 18 is to introduce a small degree of air turbulence or mixing into the region of the secondary combustion zone 5 which serves to enhance the levels of combustion and/or increase the temperatures of combustion. That is, the presence of the ceramic disk 18 serves to create an air disturbance in the region of the secondary combustion zone 5, and the result may be compared to the act of blowing on a fire to increase its intensity.

(33) The ceramic disc 18 includes a ceramic cone-shaped portion 16 which sits above an aperture 17 in the ceramic disc 18. The cone-shaped portion 16 is supported above the aperture 17 by a metal mesh (metal mesh not shown).

(34) The ceramic disc 18 is surrounded by the charcoal/reduction layer 12. The charcoal/reduction layer 12 is one of the hottest places within the wood burner 2, with temperatures often reaching up to 1500? C. Furthermore, this very high temperature is usually maintained even when fresh wood 6 is placed in the wood burner 2.

(35) The ceramic disc 18 serves as a pre-heater of the secondary air, after the secondary air passes through into the firebox 8 via the apertures 30, but before it passes up through the aperture 17 and into the secondary combustion zone 5. This arrangement serves to heat the incoming secondary air to a point well above 600? C., which is the highest ignition point of wood gas. An advantage of this arrangement is that when new wood 6 is added to the combustion system 1, we are getting ignition instantaneously, whereas other prior art fireplaces take considerable time to reach this temperature (600? C.). And while prior art fireplaces are getting up to temperature, they are admitting polluting gases and particulate matter. Conversely, my combustion system 1 produces nil or negligible polluting gases and particulate matter, due to the consistently high temperature within the firebox 8, and especially within the region of the secondary combustion zone 5 and charcoal/reduction layer 12.

(36) The combustion system 1 and/or wood burner 2 may work, or be operated, as follows:

(37) Firstly, the firebox 8 of the wood burner 2 may be filled with wood 6, and perhaps initially filled with smaller pieces of wood such as kindling, sitting atop paper for ignition purposes.

(38) Once the fire within the firebox 8 has become well established, the wood 6 in the drying zone 14, situated above (or within) the primary combustion zone 4, will rapidly dry out, releasing water vapour in the process. This moisture vapour will in fact become a source of fuel when it is later split into hydrogen and carbon monoxide as it passes over the charcoal/reduction layer 12.

(39) Once the wood 6 has dried out and entered the primary combustion zone 4, it will firstly undergo pyrolysis and combustion to produce predominantly charcoal and tar.

(40) The pyrolysised wood 6 will then undergo further combustion to produce predominantly carbon dioxide and water vapour. If enough oxygen is present, the temperature of combustion may also be sufficient to partially consume the charcoal and tar produced from the pyrolysis of the wood 6, however most existing wood burners would not ordinarily be able to produce sufficient heat to be able to do this.

(41) An advantage of the combustion system 1, is that the combustion gases and particulate matter of pyrolysis are required to travel down and across to the mouth of the lower flue 11 in order to escape to the atmosphere, thus drawing them across the very hot charcoal/reduction layer 12which greatly enhances the further reduction of the combustion gases, particulate matter and products of pyrolysis to combustible gases. For example, carbon dioxide and water vapour are reduced to the more combustible gases of hydrogen and carbon monoxide. The natural draught created by, or adjacent, the lower part 11 of the exhaust flue 7 is adequate to facilitate this process, and one advantage of this process is that it provides for the side draught and/or down draft of the combustion gases and products.

(42) Furthermore, the resultant combustible gases such as hydrogen and carbon monoxide (as well as any other combustion gases and/or particulate materials and/or products of pyrolysis) then pass through the secondary combustion zone 5. The secondary combustion zone 5 includes the provision of secondary air supply means supplying super-heated secondary air which passes into the secondary combustion zone 5 via the aperture 17 in the ceramic disc 18. The secondary air is super heated (well above 600? C.) by virtue of being introduced through the very hot secondary combustion zone 5which is adjacent the very hot charcoal/reduction layer 12. Moreover, the secondary air is further heated, or intensified, by the presence of the insulating ceramic disc 18.

(43) This super-heated secondary air is important to maintaining consistently high temperatures within the firebox 8 and secondary combustion zone 5, to thus ensure that virtually all (if not all) of the combustion gases and/or particulate matter are fully and completely combusted whereby the combustion system 1 produces nil, or negligible, polluting gases and/or particulate matter.

(44) Furthermore, another important factor in being able to maintain consistently high temperatures within the secondary combustion zone 5 is because the secondary combustion zone is surrounded by, and/or encompassed within, the primary combustion zoneas previously described. That is, the combustion system 1 utilises fire to insulate or heat fire, and this has been found to be a very important feature of the combustion system 1.

(45) The combustion system 1 results in less pollutants being exhausted to the atmosphere generally, and also results in less build up of soot and creosote products on the inside of the exhaust flue 7. For example, testing has shown that these vastly reduced emissions only form very thin white or light grey deposits on the cowl at the top of the flue 7, whereas previously this whole area had been covered in substantive black deposits. It follows therefore that the flue 7 is much less prone to the build up of soot and creosote products, thus reducing maintenance and also reducing the likelihood of chimney fires. Moreover, the unnecessary build up of soot, creosotes or tars within the flue has the detrimental effect of cooling the flue (which this invention minimises or negates).

(46) In one embodiment, one way of further reducing the exhausting of particulate matter from the wood burner 2 would be by separating the primary combustion zone 4 and the secondary combustion zone 5, for example with a mesh screen (not shown).

(47) Some testing on the combustion system 1 was undertaken as part of the Wood Stove 20 Design Challenge in the USA in November 2013 and the results are shown in FIG. 7.

(48) Some details relating to the testing is as follows: 1. All the testing was undertaken by the US National Laboratory Brookhaven, owned by the US Government via the Department of Energy. 2. Each stove was tested twice with two different makes of portable gas analysers, the Testo 380 and Wohler SM500, and the probe inserted in an aperture in the flue about 500 mm above the stove. 3. The test result provided is from the Testo 380. 4. The test was conducted on the combustion system 1, when retro-fitted to a 30+ year old Treemont wood stove. 5. Each test was for 15 minutes, my test had to be abandoned at 8:05 minutes because the extreme temperature overheated the gas analyser. 6. My result of zero (uncorrected) carbon monoxide levels are the first instance ever of a wood burner being cleaner than oil or natural gas. 7. The Particulate Matter (PM) readings are also super low and on a comparative basis cleaner than oil or natural gas. 8. Both the PM and CO average emissions for this test are lower than the figure Wikipedia gives for Natural Gas. (Using an online converter for Natural Gas PM). 9. The readings spike at the start of the test because the testers open the flue to put the probe in. 10. The test results are shown in FIG. 7.

(49) FIGS. 3 to 6 illustrate different embodiments of the combustion system 1 (and/or additional features that may be utilised with the combustion system 1). For convenience only, the same reference numerals will be used in relation to the features of FIGS. 3 to 6, which are the same, or similar, to the features noted in FIGS. 1 and 2.

(50) Having regard to FIG. 3, there is shown a cut-away side perspective view of another possible embodiment of the present invention. FIG. 3 illustrates an alternative embodiment whereby the second air supply means includes an air channel 19 which penetrates the outside of the exhaust flue 7 and extends downwards into the region below the ceramic disc 18.

(51) This is achieved by creating an aperture 20 in the side of the exhaust flue 7 at a point above the firebox 8 of the wood burner 2. The air channel 19 may then be inserted through this aperture 20 and be extended downwards and into the ceramic disc 18, as shown. The secondary air travelling through this channel 19 is first heated by the exhausting flue gases within the lower exhaust flue 11. Furthermore, the secondary air is subsequently super heated by virtue of passing through and out of the ceramic disc 18, which sits within the very hot charcoal/reduction layer 12 (and secondary combustion zone 5)in substantially the same fashion as described in relation to the embodiments illustrated in FIGS. 1 and 2).

(52) FIG. 4 illustrates an embodiment whereby the combustion system 1 can be adapted for use with a wood burner 2 which has a rear exit flue 7.

(53) FIG. 5 illustrates an embodiment where the firebase 3 is tapered towards the secondary combustion zone 5 and/or the charcoal/reduction layer 12 and/or the ceramic disc 18. An advantage of such an embodiment is that the tapered firebase 3 helps to accumulate hot embers and/or charcoal towards, or over, the entrance to the secondary combustion zone 5 and/or around the ceramic disc 18.

(54) FIG. 6 illustrates a control means for controlling the transfer of the gases and/or the particulate matter produced from the pyrolysis and/or combustion of the biomass fuel. That is, the control means controls the transfer of the gases and/or the particulate matter from the primary combustion zone 4 to the secondary combustion zone 5.

(55) The control means is in the form of a metal sleeve 32 which is adapted to partially cut off the secondary combustion zone 5. The metal sleeve 32 serves to restrict the flow of the gases and/or the particulate matter from the primary combustion zone 4 to the secondary combustion zone 6. When the wood burner 2 is in the warm-up phase, then the sleeve 32 may be removed so that a free flow of air occurs between the primary combustion zone 4 and the secondary combustion zone 5. However, when the fireplace is hot, the fire will be more efficient if the transfer of the gases and/or the particulate matter from the primary combustion zone 4 to the secondary combustion zone 6 is restricted, that is by fitting the sleeve 32 around the lower portion of the flue 11.

VARIATIONS

(56) While the embodiments described above are currently preferred, it will be appreciated that a wide range of other variations might also be made within the general spirit and scope of the invention and/or as defined by the appended claims.