Combustion system

Abstract

This invention relates to a combustion system. The combustion system includes a fireplace which has a fire base, a primary combustion zone for pyrolysising and/or combusting a biomass fuel, and a secondary combustion zone for combusting gases and/or particulate matter produced from the pyrolysis and/or combustion of the biomass fuel. The combustion system also includes an exhaust flue, the exhaust flue extending to a position near to, or adjacent, the secondary combustion zone and/or the fire base. The invention may be particularly suitable for use in relation to wood burners, either by retrofitting to existing wood burners or by incorporating into new wood burners.

Claims

1. A combustion system, said combustion system including: a) a biomass burner, said biomass burner including: i) a firebox, ii) a fire base at, or forming, the bottom of the firebox, iii) a primary combustion zone for pyrolyzing or combusting a biomass fuel, the primary combustion zone being located within an interior of the firebox, iv) a first air supply arranged to supply air to the primary combustion zone, v) a secondary combustion zone for combusting gases or particulate matter produced from the pyrolysis or combustion of the biomass fuel, the secondary combustion zone being located adjacent the fire base, b) an exhaust flue, a lower portion of the exhaust flue extending within the interior of the firebox to an upper portion of the firebox and out of the firebox, the lower portion of the exhaust flue having a lowermost perimeter that defines an inlet of the exhaust flue, the lowermost perimeter being located at a position adjacent to said fire base and above said secondary combustion zone, wherein exhausting flue gases travel within the lower portion of the exhaust flue and along an inner surface of the exhaust flue, and c) a secondary flue which wholly surrounds the lower portion of the exhaust flue, the secondary flue having a lower perimeter wholly surrounding the lowermost perimeter of the lower portion of the exhaust flue and defining therebetween an air channel that extends downward to and exits to an upper part of said secondary combustion zone, the air channel providing an air gap between an outer surface of the lower portion of the exhaust flue and an inner surface of the secondary flue, the air gap defining a second air supply providing a downwardly directed air path from the upper portion of the firebox to source air from within the upper portion of the firebox and channel the air sourced from within the upper portion of the firebox downwardly through the air gap to exit to the upper part of the secondary combustion zone, wherein, the exhausting flue gases traveling within the lower portion of the exhaust flue and along an entire circumference of the interior side of the exhaust flue heat the air of the second air supply travelling downwardly through the air gap along the exterior side of the exhaust flue.

2. The combustion system, as claimed in claim 1, wherein said combustion system further includes, or results in, a charcoal/reduction layer forming below the primary combustion zone, or between the primary combustion zone and the secondary combustion zone, the combustion system configured such that gases or particulate matter produced from the pyrolysis or combustion of the biomass fuel in the primary combustion zone have to pass over or through said charcoal/reduction layer prior to entering the secondary combustion zone or the lower portion of the exhaust flue.

3. The combustion system, as claimed in claim 2, wherein said combustion system includes a drying zone for drying the biomass fuel or removing water from the biomass fuel prior to the pyrolysis or combustion of the fuel.

4. The combustion system, as claimed in claim 2, wherein the combustion system further includes insulation insulating the region of the secondary combustion zone.

5. The combustion system, as claimed in claim 1, wherein said combustion system includes a drying zone for drying the biomass fuel or removing water from the biomass fuel prior to the pyrolysis or combustion of the fuel.

6. The combustion system, as claimed in claim 5, wherein the combustion system further includes insulation insulating the region of the secondary combustion zone.

7. The combustion system, as claimed in claim 1, wherein the combustion system further includes insulation insulating the region of the secondary combustion zone.

8. The combustion system, as claimed in claim 7, wherein said insulation is arranged to introduce a degree of air turbulence or mixing into the region of the secondary combustion zone.

9. The combustion system, as claimed in claim 7, wherein said insulation comprises a ceramic disc.

10. The combustion system, as claimed in claim 1, wherein said combustion system is configured to be retro-fitted to an existing wood burner.

11. The combustion system, as claimed in claim 1, wherein the air gap is 25 mm between the outer surface of the exhaust flue and the inner surface of the secondary flue.

Description

DRAWINGS

(1) FIG. 1: is a perspective front view of a wood burner which incorporates one possible embodiment of the present invention,

(2) FIG. 2: is a cut-away side view of the embodiment illustrated in FIG. 1,

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

(4) FIG. 4: is a perspective front view of yet another possible embodiment of the present invention, and

(5) FIG. 5: is a cut-away side view of the embodiment illustrated in FIG. 4.

DESCRIPTION OF PREFERRED EMBODIMENTS

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

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

(8) The wood burner 2 includes a metal firebox 8 and an adjustable air intake control (not shown). The firebox 8 includes a fire base 3, which effectively forms the floor of the firebox 8 of the wood burner 2.

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

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

(11) 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.

(12) 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 (or fire base 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 have to work their way downwards from the inside of the firebox 8 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 hot air (or gases) ultimately travel up the flue 7 on their way to being exhausted through a roof or ceiling (that is, in the direction of arrow 21).

(13) The lower part 11 of the exhaust flue 7 may be retrofitted to existing wood burners 2.

(14) For example, 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.

(15) 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.

(16) Furthermore, the task of retrofitting to existing wood burners 2, as described above, is a relatively simple, quick and inexpensive operation.

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

(18) The combustion system 1, when in operation, results in a charcoal/reduction layer 12 forming below the primary combustion zone 4, and 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 the charcoal/reduction layer 12 prior to entering the secondary combustion zone 5 and/or the exhaust flue 11.

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

(20) 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. 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.

(21) 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 an air supply to the interior of the firebox 8, and more particularly to the primary combustion zone 4.

(22) The wood burner 2 also includes a second air supply means for introducing super heated air into the region of the secondary combustion zone 5.

(23) The second air supply means is provided for by a secondary flue 16 which wholly surrounds the lower part 11 of the exhaust flue 7. This is facilitated by placing the piece of larger secondary flue 16 (175 mm in diameter) around the lower exhaust flue 11 (150 mm in diameter), leaving an air gap 17 of approximately 25 mm therebetween. The air gap 17 serves to take air from the top of the firebox 8 and channel it down through the air gap 17 to the secondary combustion zone 5 at the base of the lower part 11 of the exhaust flue 7. The air travelling through this air gap 17 is super heated by the exhausting flue gases within the lower exhaust flue 11 on one side, and the primary combustion zone 4 on the other side.

(24) Furthermore, the primary combustion zone 4 derives benefit by a much increased flame path as the flames are drawn down the air gap 17 from the top of the firebox 8, thus maintaining a high temperature and increasing the time available to fully burn in.

(25) The combustion system 1 includes insulation means for insulating the region of the secondary combustion zone 5. The insulating means is in the form of a ceramic disc 18.

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

(27) Another purpose of the ceramic disc 18 is to introduce a 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.

(28) It may also be appreciated that the secondary combustion zone 5 is surrounded by, and therefore also insulated by, the primary combustion zone 4, thus resulting in the maintenance of very high combustion temperatures in the region of the secondary combustion zone 5.

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

(30) 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.

(31) 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.

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

(33) The pyrolysised wood 6 will then undergo 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.

(34) An advantage of the combustion system 1, is that the combustion gases and products of pyrolysis are required to travel down and across to the mouth of the lower flue 11 in order to escape to atmosphere, thus drawing them across the charcoal/reduction layer 12 which 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.

(35) 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 an air supply of super heated air which passes down the air gap 17 and into the secondary combustion zone 5 (as described previously).

(36) Tests have shown that sustained temperatures in the region of the secondary combustion zone 5 vary between approximately 1050 C.-1400 C.compared to approximately 600 C.-800 C. for a conventional wood burner.

(37) A sustained temperature in the region of the secondary combustion zone 5 of approximately 1000 C. or above is usually sufficient to combust both hydrogen and carbon monoxide, thus ensuring that none of these otherwise undesirable gases are exhausted to the atmosphere. My invention therefore clearly reaches these temperatures, and this compares favourably with the prior art appliances referred to previously, which do not appear to reach these kind of temperatures.

(38) Furthermore, tests have shown that the very high temperatures achieved within the secondary combustion zone 5 serve to combust virtually all other gases and/or air pollutants (or smoke) produced by the wood burner 2.

(39) This 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).

(40) 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).

(41) Alternatively, there could be provided a tapered hearth (not shown) between the primary and secondary combustions zones 4,5which would serve to concentrate the charcoal/reduction layer 12 at the point where the volatile gases and/or particulate material pass from the primary combustion zone 4 to the secondary combustion zone 5.

(42) One of the reasons for the popularity of air-controlled wood burners is that the rate of combustion can be controlled through control of the air intake, or oxygen. However, starving the fire of air results usually results in incomplete combustion and increased pollution. The combustion system 1 uses oxygen, liberated from steam, to help the combustion process, thereby making it less polluting to restrict the air flow into the wood burner 2.

(43) Having regard to FIG. 3, there is shown a cut-away side perspective view of another possible embodiment of the present invention. For convenience, the same numbers are used in FIG. 3 that correspond to the same (or similar) features which are also present in the embodiment described in FIGS. 1 and 2.

(44) 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 secondary combustion zone 5.

(45) This is achieved by creating an aperture 20 in the side of the exhaust flue 7 at a point just above the firebox 8 of the wood burner 2. The air channel 19 may then be inserted through this aperture 20 and extended downwards into, or adjacent, the secondary combustion zone 5 at the bottom of the lower flue 11. The air travelling through this channel 19 is super heated by the exhausting flue gases within the lower exhaust flue 11- and the channel 19 therefore serves essentially the same purpose as the secondary flue 16 illustrated in FIG. 2.

(46) Having regard to FIGS. 4 and 5, there is shown another possible embodiment of the present invention. Again, and for convenience only, the same numbers are used in FIGS. 4 and 5 that correspond to the same (or similar) features of the invention which are also present in the embodiments described in FIGS. 1, 2 and 3.

(47) Having regard to FIG. 4, there is shown a front perspective view of a wood burner 2. The lower portion 11 of the exhaust flue 7 is centrally located within the firebox 8, and the fire base 3 is in the form of a grate, the grate being generally indicated by arrow 22. Below the grate 22 is an ash pit 24.

(48) The grate 22 is comprised of a number of open-ended hollow tubes 23 which extend from the sides 25 of the ash pit 24 to the region of the secondary combustion zone 5 (formed just below the periphery of the lower portion 11 of the exhaust flue 7).

(49) There are holes 26 formed in the sides 25 of the ash pit 24, and these holes 26 may be drilled or pre-formed in the sides 25. Air is able to flow from the ash pit 24, through the holes 26, and along the hollow tubes 23 to the region of the secondary combustion zone 5. This air flow is indicated by the arrows shown in FIG. 5.

(50) This air flow serves as the second air supply means for introducing super heated air into the region of the secondary combustion zone 5. That is, the air travelling up and along the hollow tubes 23 is super heated by virtue of the heat provided by the charcoal reduction layer 12, which is above the hollow tubes 23. Hence, the secondary combustion zone 5 is heated by both the primary combustion zone 4, the charcoal reduction layer 12 and the super heated air emanating from the ends of the hollow tubes 23.

(51) This differs from the embodiment illustrated in FIGS. 1 and 2 in that the super heated air in FIGS. 1 and 2 is provided through the gap 17 between the secondary flue 16 and the lower portion 11 of the exhaust flue 7. The embodiment illustrated in FIGS. 4 and 5 does away with the secondary flue 16 and instead utilises the air flow through the hollow tubes 23, as indicated in FIG. 5, to produce essentially the same result.

(52) The wood burner of FIGS. 4 and 5 also includes a baffle 27. The baffle 27 is designed to lengthen the flame path and slow the velocity of the gases and/or particulate matter, whereby there is more time for any gases to be combusted and/or whereby any particulate matter may drop back down to be properly combusted.

VARIATIONS

(53) 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.