AU2006201189B2 - A method of reducing CO and NOx emissions in a Heating appliance and a respective appliance - Google Patents

Description

AUSTRALIA

Patents Act 1990 WORGAS BRUCIATORI SRL COMPLETE SPECIFICATION STANDARD PATENT Invention Title: A method of reducing CO and NOx emissions in a Heating appliance and a respective appliance The following statement is a full description of this invention including the best method of performing it known to us:- SA method of reducina CO and NOx emissions in heatina aooliance and Sresoective aooliance.

N The invention concerns a method of reducing CO and NOx emissions in a heating appliance, and a respective appliance.

Particularly, the invention may be used in heating appliances which are not 00 provided with a flue, that is, for instance stoves and fireplaces fed with a caseous fuel, which discharge the combustion products in the room where they C- are installed.

IN These appliances are commonly used to heat rooms which are not provided with 0 a flue to convey to the outside the combustion products.

Since the combustion products are discharged in the room where the appliance is installed, there are very restrictive safety rules concerning the allowable content of toxic substances, such as carbon oxide CO and nitrogen oxides, in said combustion products.

The formation of CO in the combustion products depends on a plurality of factors: non-complete combustion of the fuel, which may be caused by an insufficient quantity of air in the air-fuel mixture supplied to the appliance; coolinc of flame during combustion, which may be caused by a contact of the flame with cold surfaces, that is with surfaces having a temperature less than the temoerature of the flame, or by a flow of cold air, the so-called secondary air, from the room onto the surface of the flame; excess of air in the air-fuel mixture supplied to the appliance, which causes a combustion with a too low temperature of the flame, resulting in a non-complete combustion of the fuel.

With regard to the formation of NO 2 it has been found that said formation does not take place directly at the inside of the flame during combustion, but subsequently in a region directly surrounding the flame wherein NO generated during combustion is oxidised.

Therefore, the formation of NO 2 depends both on the presence of NO in the combustion products and on the presence of oxidisers, such as 02 and OH radicals, such as, for instance, H02 radical, in said region directly surrounding the flame. The quantity of H02 radical depends on the temperature of the flame and decreases as the temperature increases.

2 The quantity of N02 in the combustion products may be reduced to very low values by using a bladed flame burner, such as disclosed in EP-B-0373157 Z and EP-A-0537244, both in the name of the applicant. This burner makes cl possible to obtain very low contents of N02 in the combustion products.

However, the use of the above mentioned burner does not allow to reduce CO emissions to very low values.

00 If a conventional burner with a "Bunsen" flame is used, it is possible to obtain a Slow content of CO in the combustion products, but the content of NO 2 continues (to be high.

In addition, from EP-A-0512801 a combustion method for a radiant burner and c a respective burner being fed with a hyperstoichiometric mixture of gas fuels and air are known, wherein the formation of CO and N02 in the combustion products is eliminated or, at least, reduced to very low levels by having the combustion brought about on the surface of the diffuser of the burner, or on in close proximity of said surface, thus limiting the contact of the combustion products with the ambient air, the so-called secondary air.

The above mentioned method, however, is not able to reduce the formation of CO to acceptable levels in bladed flame burners as described in the above mentioned EP-B-037315 7 and EP-A-0537244 and the formation of N02 in "Bunsen" flame burners, because the flames of both said burners has a substantiIal height and the combustion does not take place on the surface of the burner or in close proximity of said surface.

In addition, the above method can not be used in a fireplace which is provided with a large front aperture through which the ambient air is free to enter the combustion chamber.

It is also known from EP-A-766046, which is considered the closest prior art, a flueless heating appliance comprising a combustion chamber having an opening in at least one side thereof to provide e view of at least a substantial portion of the combustion chamber, a flammable fluid fuel supply to said combustion chamber to provide, upon combustion, a substantial portion of yellow flame, an artificial log assembly provided in said combustion chamber and at least one reflective surface provided on at least one side of said primary combustion chamber to provide a reflected view of said substantially yellow flame and artificial log assembly. The heating appliance further comprises air circulating means to provide and/or direct a stream of air across at least a portion of said opening into said combustion chamber.

The primary object of the heating appliance disclosed in EP-A-766046 is to provide a trealistic visual appearance of a wood fireplace. This object is obtained by generating Sflames having a substantially yellow appearance in the combustion chamber and by N providing the combustion chamber with mirrors which provide a larger visual appearance of the fire. It is known that yellow flames produce combustion products containing a substantial amount of CO and NOx, which can not be exhausted in the 00 environment where the appliance is placed. For this reason, the heating appliance disclosed in EP-A-766046 is provided with a catalytic converter forming a secondary CI combustion chamber in which the combustion products are further combusted to reduce the content of CO and NO, to acceptable levels. In addition, the air circulating means provided in the heating appliance serve to present or at least reduce spillage of the combustion products from the combustion chamber towards the environment in which the heating appliance is placed. The need for a catalytic converter and air circulating means makes the heating appliance disclosed in EP-A-766046 very costly and not completely reliable due to possible faults of the catalytic converter or air circulating means.

According to a first aspect of the present invention there is provided a method of combustion of a gaseous fuel in a heating appliance provided with at least one burner, comprising mixing said gaseous fuel with a pre-established quantity of air, supplying said mixture to the body of said at least one burner, which is provided with a diffuser on which openings are made through which said mixture passes, causing the combustion of said mixture in order to generate at least one flame, characterised in that it further comprises irradiating heat towards said at least one flame and a region directly surrounding said flame.

According to a second aspect of the present invention there is provided a method of combustion of a gaseous fuel in a heating appliance provided with at least one burner, comprising mixing said gaseous fuel with a pre-established quantity of air to obtain an air-fuel mixture, supplying said mixture to the body of said at least one burner, which is provided with a diffuser on which openings are made through which said mixture passes, causing the combustion of said mixture in order to generate flames, limiting the inflow of air from the outside of said appliance into a region directly surrounding said flames, said limiting being obtained by means of gaseous barrier means, characterised in that said gaseous barrier means is obtained by means of natural circulation of gaseous means.

According to a third aspect of the present invention there is provided a heating appliance provided with at least one burner fed with a mixture of gaseous fuel and air, m:\specifications\500000\504000\504266divmaw.doc said at least one burner being provided with a diffuser having openings through which t said mixture passes and with means to cause the combustion of said mixture and the Sformation of at least one flame, characterised in that it further comprises heat irradiating means which are capable of irradiating heat towards said at least one flame and a region directly surrounding said flame.

According to a fourth aspect of the present invention there is provided a heating OC appliance provided with at least one burner fed with a mixture of gaseous fuel and air, said at least one burner being provided with a diffuser having openings through which C said mixture passes and with means to cause the combustion of said mixture and the formation of flames, said heating appliance comprising barrier means capable of limiting the inflow of air from the outside into said heating appliance in a region directly surrounding said flames, said barrier means comprising gaseous barrier means, characterised in that said gaseous barrier means is obtained by means of natural circulation of gaseous means. Irradiating heat on the flame and in the region directly surrounding the flame makes it possible to keep in said region a temperature high enough to substantially reduce the formation, and the presence, of CO and NO 2 in the combustion products.

In addition the provision of gaseous barrier means to limit the inflow of air from the outside into the heating appliance minimizes losses of heat from the combustion chamber, preventing the temperature in the region of the flames from decreasing below the value required for minimising the formation of CO and NO,.

In another aspect the invention provides a method of combustion of a gaseous fuel in a heating appliance provided with at least one burner, comprising mixing said gaseous fuel with a pre-established quantity of air to obtain an air-fuel mixture, supplying said mixture to the body of said at least one burner, which is provided with a diffuser on which openings are made through which said mixture passes, causing the combustion of said mixture in order to generate flames, characterized in that for reducing CO and

NO

2 emissions it further comprises limiting the inflow of air from the outside of said appliance into a region surrounding said flames, said limiting being obtained by physical barrier means arranged in the vicinity of said region.

In another aspect the invention provides a method of combustion of a gaseous fuel in a heating appliance provided with at least one burner, comprising mixing said gaseous fuel with a pre-established quantity of air to obtain an air-fuel mixture, supplying said mixture to the body of said at least one burner, which is provided with a diffuser on which openings are made through which said mixture passes, causing the combustion of said mixture in order to generate flames, characterized in that for reducing CO and m:\specifications\500000\504000\504266divmaw.doc (NI NO 2 emissions it further comprises limiting the inflow of air from the outside of said tappliance into a region surrounding said flames, said limiting being obtained by Sgaseous barrier means arranged in the vicinity of said region; said gaseous barrier means is obtained by means of natural circulation of gaseous means.

In another aspect the invention provides a heating appliance provided with at least one burner fed with a mixture of gaseous fuel and air, said at least one burner being 00 provided with a diffuser having openings through which said mixture passes and with means to cause the combustion of said mixture and the formation of flames, 0 N characterized in that for reducing CO and NO 2 emissions it further comprises physical barrier means so shaped and arranged as to limit the inflow of air from the outside of said appliance into a region surrounding said flames.

In a further aspect the present invention provides a heating appliance provided with at least one burner fed with a mixture of gaseous fuel and air, said at least one burner being provided with a diffuser having openings through which said mixture passes and with means to cause the combustion of said mixture and the formation of flames, characterized in that for reducing CO and NO 2 emissions it further comprises gaseous barrier generating means arranged to generate a gaseous barrier to limit the inflow of air from the outside of said appliance into a region surrounding said flames, said gaseous barrier generating means being arranged in the vicinity of said region, said gaseous barrier being obtained by natural circulation of gaseous means.

Further features and advantages of the present invention will be explained in the following description, made only by way of non-limiting example, and in the enclosed drawings wherein: Figure 1 is a cross section of a heating appliance featured as a stove without m:\specifications\500000\504000\504266divmaw.doc O flue; Figure 2 is a partly sectioned front view of the heating appliance of Figure 1; Figure 3 is a section as in Figure 1, concerning variation of the heating Sappliance of Figure 1; Figure 4 is a transverse section of a heating appliance featured as a fireplace without flue; 0 Figures 5 and 6 are transverse sections as in figure 3, concerning variations of the heating appliance of Figure 4.

C With reference to Figure 1, 1 denotes a heating appliance featured as a stove, provided with an outer casing 2 inside which a combustion chamber 3 is O defined, which is bounded sideways, on the front and on the back by said outer Scasina 2.

A front portion 4 of said casing 2 is movable in order to have access to said combustion chamber 3, said portion 4 being provided with a glass 5, so that said combustion chamber 3 is visible from the outside.

The combustion chamber 3 is provided with an upper opening 6 in its upper portion, defined by two wall portions 7 and 8 converging upward, said upper opening communicating with a conduit 8a discharging outside the combustion O products. The conduit 8a is provided, at a first end facing toward the back side of the appliance 1, with a first opening 9 allowing air to enter into the conduit from Sthe outside and, at a second end facing toward the front side of the appliance 1, with a second opening 10 leading, for instance, to a position above said front c- section 4 of the casing 2 and is provided with a grid 11. The air entering said first opening 9 from the outside is mixed to the combustion products coming from the \combustion chamber 3 in order to cool them, so that emission of too hot fumes o00 through the grid 11.

The combustion chamber 3 is further provided with a lower opening 12 defined N by two lower wall portions 13 and 14 converging upward. A burner 15, for Sinstance a burner as disclosed in EP-B-0373157 and EP-A-0537244 is arranged CI below said lower wall portions 13 and 14, so that the body of the burner 15 is forced against said wall portions. Two seal means 16 and 17 are interposed between the burner 15 and said wall portions 13 and 14, so that the inflow of air from the outside through said lower opening 12 into the combustion chamber 3 is prevented.

The mixture of fuel gas and air supplied to the burner 15, passes through openings 18 made in the burner diffuser 19 and penetrates, through said lower opening 12. into said combustion chamber 3, in which the combustion of said mixture takes place, generating a plurality of flames 20. for instance bladed flames, as disclosed in EP-B-0373157 and EP-A-0537244. above said openings 18. The appliance 1 is further provided with a pilot burner 21, designed to ignite the combustion of the mixture supplied to the burner The walls of the casing 2 defining the combustion chamber 3, with the exception of the front wall 4 provided with glass 5, are provided on the whole of the respective surface, or only on a portion of it, with a lining 47 made of a material capable of accumulate and irradiate heat, for instance a ceramic material. Said lining may be also extended to the upper wall portions 7 and 8 and to the lower wall portions 13 and 14.

During operation of the appliance 1, said lining 47 accumulates heat and irradiates it into the combustion chamber 3, particularly toward the flames 20 and the region directly surrounding the flames, thus allowing the temperature of said region to be maintained so high as to prevent, or at least reduce to very low levels, the formation of CO and NO 2 in the combustion products.

Particularly, when a burner 15, as disclosed in EP-B-0373157 and EP-A- 0537244 is used, that is a burner with a very low formation of NO 2 the

O

O accumulation of heat in the lining 47 and its subsequent irradiation, allows, in Nparticular, the formation of NO 2 to be prevented, or reduced to very low levels.

It is to be noticed, that, when the lining 47 is limited only to some regions of the inner surface of the walls of the combustion chamber, said regions are chosen in Cl such a way as the heat accumulated in the lining 47 is irradiated mainly toward the flames 20 and the region directly surrounding the flames.

1 In Figure 3 a variation of the appliance is illustrated, wherein the lower wall oo00 portions 13 and 14 are not in contact with the burner 15, thus defining two 0passages 43 and 44 through which air from the outside, the so-called secondary Nair, enter the combustion chamber 3.

With reference now to Figures 4 to 6, they illustrate heating appliances 22 N featured as fireplaces without flue. that is heating appliances fed by a burner for gas fuels which simulate a conventional fireplace.

Heat irradiating means 45 and 46 are arranged on respective supports 48 and 49 above the diffuser 19 of the burner 15. substantially for the whole length of that portion of diffuser provided with the apertures 18. said irradiating means, when the appliance 1 operates. irradiate heat toward the flames 42 and in the region directly surrounding the flames.

Said heat irradiating means 45 and 46 may comprise heat accumulating means made of a material capable of accumulating heat and irradiate it, for instance a ceramic material. Alternatively, said irradiating means may comprise heat reflecting means, such as, for instance, parabolic mirrors. In addition, said irradiating means 45 and 46 may comprise heat generating means, for instance electric resistance heat generating means.

The use of said irradiating means 45 and 46 is particularly advisable when burners with "Bunsen" flames are used, which need secondary air for a proper operation and when the burner 15 is fed with liquid gas fuel, because it is more likely the formation of NO 2 in the combustion products when said kind of fuel is used.

In figures 4, 5 and 6 heating appliances without flue according to the invention, featured as fireplaces, are shown.

Said appliances comprise a casing 23 inside which a combustion chamber 24 is defined, which is provided with a front opening 25 communicating with the outside and with an upper opening 26 through which the combustion products are discharged. Inside the combustion chamber 24 one or more elements 28, made of a material resistant to high temperatures, for instance made of ceramic ceramic material and simulating bits of wood, are arranged on respective supports 27 provided with apertures, for instance grid supports.

SIn a first embodiment of the appliance 22. snown inFigure 4, a burner 29 is ,i arranged below the support 27, said burner having a body divided into two sections 30 and 31 fed independently. A first section 30 is capable of generating first violet coloured flames 32, for instance bladed flames as disclosed in EP-Boo0 0373157 and EP-A-0537244, which get in touch with said elements 28 increasing their temperature up to red heat, in order to simulate embers of a conventional fireplace.

ND The second section 31 of the burner 29 is capable to generate second yellow "Bunsen" flames, which simulate the flames generated by the combustion of a piece of firewood in a conventional fireplace.

The second section 31 of the burner 29 is arranged in such a way as the second flames 33 are located between the first flames 32 and the front opening 25 of the appliance 22. Owing to this arrangement, the second flames 33 and/or a natural circulation of the column of hot combusted gases produced by said flames constitute a barrier preventing air entering the combustion chamber 24 from the outside, which allows a so high temperature to be maintained in the combustion chamber and. particularly, in the region directly surrounding the flames 32 and 33, as to reduce the formation of CO and NO 2 in the combustion products of the first flames 32.

The reduction of formation of CO and NO 2 in the combustion products may be optimised if the first section 30 of the burner 29 is made like a bladed flame burner, as disclosed in EP-B-0373157 and EP-A-0537244. A further reduction of the formation of NO 2 may be obtained if the thermal power produced by said first section 30 is not less than the thermal power produced by said second section, preferably substantially higher. For instance, the thermal power produced by said second section may be between 20% to 30% of the total thermal power of the burner 29.

Figure 5 shows a second embodiment of the appliance 22, wherein three burners are arranged below the support 27: a first central burner 34, for instance a burner like that disclosed in EP-B-0373157 and EP-A-0537244, capable of generating first violet flames 32, e second front burner 35, capable of generating second yellow "Bunsen" flames 33 and a third rear burner 36 capable of generating third yellow "Bunsen" flames 37, which simulate the flames generated by the combustion of pieces of firewood in a conventional fireplace. Said third 0 fireplace. Said third burner 36 is arranged in such a way as said third flames 37 are more remote from said front opening 25 than said second flames 32 are and C may be seen. for instance, behind said elements 28, when one look at the combustion chamber through the front opening 25, which improves the visual Ssimulation of the combustion of pieces of firewood in a conventional fireplace.

Even in said second embodiment of the appliance 22, the second flames 33 Sgenerated by the second burner 35 and/or a natural circulation of the respective 00 column of hot combusted gases constitute a barrier against the penetration of air 0into the combustion chamber 24 from the outside.

IDEven in said second embodiment, in order to optimise the reduction of the Sformation of NO 2 in the combustion products, it is advisable that the thermal C~ power generated by the first burner 34 is not less, or preferably substantially higher. than the thermal power generated by the second burner 35 and third burners 36 together.

Figure 6 shows a third embodiment of the appliance 22 according to the invention, which is provided with a single burner 38 having a body divided into three section fed separately: a first central section 39 capable of generating said first flames 32. for instance bladed flames such as disclosed in EP-B-0373157 and EP-A-0537244, a second front section 40 capable of generating said second flames 33 and a third rear section 41 capable of generating said third flames 37.

Even in said third embodiment of the appliance 22, it is advisable that the thermal power generated by said first central section 39 is not less, preferably substantially higher, than the thermal power generated by said second front section 40 and said third section 41 together.

All the embodiments of the appliance 22 shown in Figures 4, 5 and 6 may have the walls of the combustion chamber 24 provided with a lining 47 made of a material capable of accumulating heat.

The exemplary embodiments of the invention shown concern heating appliances without flue, but the invention may be equally used in heating appliances provided with flue.

(NI Throughout this specification the word "comprise", or variations such as "comprises" or Ct "comprising", will be understood to imply the inclusion of a stated element, integer or step, or group of elements, integers or steps, but not the exclusion of any other element, N, integer or step, or group of elements, integers or steps.

Any discussion of documents, acts, materials, devices, articles or the like which has been included in the present specification is solely for the purpose of providing a 00 context for the present invention. It is not to be taken as an admission that any or all of these matters form part of the prior art base or were common general knowledge in the

O

Ni field relevant to the present invention as it existed before the priority date of each claim of this application.

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Claims (37)

1. A method of combustion of a gaseous fuel in a heating appliance provided with ,I at least one burner, comprising mixing said gaseous fuel with a pre-established quantity of air to obtain an air-fuel mixture, supplying said mixture to the body of said at least one burner, which is provided with a diffuser on which openings are made through 0_ which said mixture passes, causing the combustion of said mixture in order to generate flames, characterized in that for reducing CO and NO 2 emissions it further comprises i limiting the inflow of air from the outside of said appliance into a region surrounding INO 010 said flames, said limiting being obtained by physical barrier means arranged in the vicinity of said region.

2. A method according to claim 1 and further comprising providing heat irradiating means for irradiating heat towards said flames and said region surrounding said flames.

3. A method according to claim 1 or 2, wherein said physical barrier means comprises said heat irradiating means.

4. A method according to claim 2, or 3, wherein said heat irradiating means comprises heat accumulating means.

A method according to claim 2, or 3, wherein said heat irradiating means comprises heat reflecting means.

6. A method according to claim 2, or 3, wherein said heat irradiating means comprises heat generating means.

7. A method of combustion of a gaseous fuel in a heating appliance provided with at least one burner, comprising mixing said gaseous fuel with a pre-established quantity of air to obtain an air-fuel mixture, supplying said mixture to the body of said at least one burner, which is provided with a diffuser on which openings are made through which said mixture passes, causing the combustion of said mixture in order to generate flames, characterized in that for reducing CO and NO 2 emissions it further comprises limiting the inflow of air from the outside of said appliance into a region surrounding said flames, said limiting being obtained by gaseous barrier means arranged in the m:\specifications\500000\504000\5O4266divmaw.doc C'N vicinity of said region; said gaseous barrier means is obtained by means of natural tcirculation of gaseous means.

8. A method according to claim 7, wherein said gaseous barrier means comprises flames generated by the combustion of said mixture and/or the combusted gas generated by said flames. 00oO

9. A method according to claim 7 or 8, wherein said gaseous barrier means are 0 C arranged between an opening of a combustion chamber of said appliance 010 communicating with the outside and the combustion chamber.

A heating appliance provided with at least one burner fed with a mixture of gaseous fuel and air, said at least one burner being provided with a diffuser having openings through which said mixture passes and with means to cause the combustion of said mixture and the formation of flames, characterized in that for reducing CO and NO 2 emissions it further comprises physical barrier means so shaped and arranged as to limit the inflow of air from the outside of said appliance into a region surrounding said flames.

11. A heating appliance according to claim 10 and further comprising heat irradiating means for irradiating heat towards said flames and said region surrounding said flames.

12. A heating appliance according to claim 11, wherein said heat irradiating means are arranged close to the surface of said diffuser substantially through that portion of diffuser provided with said openings.

13. A heating appliance according to claim 11, or 12, wherein said physical barrier means comprises said heat irradiating means.

14. A heating appliance according to one of claims 11 to 13, wherein said heat irradiating means comprises heat accumulating means.

A heating appliance according to one of claims 11 to 13, wherein said heat irradiating means comprises heat reflecting means. m:\specifications\500000\504000\54266divmaw.doc

16. A heating appliance according to one of claims 11 to 13, wherein said heat Sirradiating means comprises heat generating means.

17. A heating appliance according to one of claims 10 to 16, wherein said physical barrier means comprises upward converging lower wall portions of a combustion 00 chamber defined at the inside of a casing of the heating appliance, said at least one burner being arranged below said lower wall portions, sealing means being arranged Ci between said lower wall portions and said at least one burner, said lower wall portions defining at least one passage for said mixture of gas fuel and air.

18. A heating appliance according to claim 17, wherein said at least one burner is arranged so as to exert a pressure against said sealing means.

19. A heating appliance provided with at least one burner fed with a mixture of gaseous fuel and air, said at least one burner being provided with a diffuser having openings through which said mixture passes and with means to cause the combustion of said mixture and the formation of flames, characterized in that for reducing CO and NO 2 emissions it further comprises gaseous barrier generating means arranged to generate a gaseous barrier to limit the inflow of air from the outside of said appliance into a region surrounding said flames, said gaseous barrier generating means being arranged in the vicinity of said region, said gaseous barrier being obtained by natural circulation of gaseous means.

20. A heating appliance according to claim 19, wherein said gaseous barrier generating means comprises flames generated by the combustion of said mixture and/or the respective combusted gas generated by said flames.

21. A heating appliance according claim 19, or 20, wherein said gaseous barrier generating means are arranged between an opening of a combustion chamber defined at the inside of a casing of the heating appliance and the combustion chamber itself, said opening communicating with the outside of the heating appliance.

22. A heating appliance according to claim 20, or 21, wherein said at least one burner comprises a body divided into two sections fed independently: a first section capable of generating first flames and a second section capable of generating second m:\specifications\500000\504000\5O4266divmaw.doc flames, said second flames and the combusted gas generated by said second flames tconstituting said gaseous barrier means. N

23. A heating appliance according to claim 22, wherein said first section is capable of generating bladed flames. 0

24. A heating appliance according to claim 22, or 23, wherein said second section is arranged in such a way as the second flames are interposed between said first flames O N and said opening.

25. A heating appliance according to one of claims 22 to 24, wherein said first section generates a thermal power at least equal to the thermal power generated by said second section.

26. A heating appliance according to claim 20, or 21, wherein said at least one burner comprises a first burner generating first flames and a second burner generating second flames, said second flames and the combusted gases generated by said second flames constituting said gaseous barrier means.

27. A heating appliance according to claim 26, wherein said first burner is capable of generating bladed flames.

28. A heating appliance according to claim 26, or 27, wherein said second burner is arranged in such a way as said second flames are interposed between said first flames and said opening.

29. A heating appliance according to one of claims 26 to 28, further comprising a third burner generating third flames.

30. A heating appliance according to claim 29, wherein said third burner is arranged in such a way as said third flames are more remote from said opening than said second flames are.

31. A heating appliance according to claim 29 or 30, wherein said first burner generates a thermal power at least equal to the thermal power generated by said second burner and said third burner together. m:\specifications\500000\504000\5O4266divmaw.doc ed

32. A heating appliance according to claim 20, or 21, wherein said at least one Sburner comprises a body divided into three sections fed independently: a central section N capable of generating first flames, a second front section capable of generating second flames and a rear section capable of generating third flames, said second flames and the combusted gases generated by said second flames constituting said gas barrier means. 00

33. A heating appliance according to claim 32, wherein said central section is

34. A heating appliance according to claim 32, or 33, wherein said front section is arranged in such a way as said second flames are interposed between said first flames and said opening.

35. A heating appliance according to one of claims 32 to 34, wherein said central section generates a thermal power at least equal to the thermal power generated by said front section and said rear section together.

36. A method according to any one of claims 1 to 9 substantially as hereinbefore described.

37. An appliance according to any one of claims 10 to 35 substantially as hereinbefore described. Dated this twenty-first day of March 2006 Worgas Bruciatori SRL Patent Attorneys for the Applicant: F B RICE CO m:\specifications\500000\504000\504266divmaw.doc