Low-NOx burner with metal fibers

Abstract

 The present invention discloses a burner including a shell, a number of fuel-air mixing elements, and a metal fiber cover. The burner is received in the shell for mixing introduced air and fuel gas to generate a fuel-air mixture. The metal fiber cover is received in the shell and positioned above the number of fuel-air mixing elements for burning the fuel-air mixture thereon. By employing a number of fuel-air mixing elements, the fuel gas and air can be completely mixed to a predetermined stoichiometric proportion before reaching the metal fiber cover, thereby achieving a full combustion on metal fibers and reducing the generation of nitrogen oxides accordingly.

Description

FIELD OF THE INVENTION

[0001] The present invention relates to burners utilizing metal fibers to decrease generation of nitrogen oxides.

BACKGROUND OF THE INVENTION

[0002] Gas water heating appliances, such as gas water heaters and gas boilers, generally have burners, heat exchangers, and combustion chambers formed by the burners and the heat exchangers. The exhaust gases produced by the burners usually contain toxic compounds, like carbon monoxide (CO) and nitrogen oxides (NOx). Nowadays, people pay more attention to domestic gas appliances in the emissions of harmful gases, and a lot of measures have been adopted to reduce emissions of CO, however, no enough attention has been paid for the NOx emissions.

[0003] A lot of studies show that, nitrogen oxides is more toxic than carbon monoxide, and long-term emissions of NOx may cause acid rain and photochemical smog. According to Chinese national NOx emission standards for domestic gas appliances, the highest level, namely the fifth level provides the upper limit of nitrogen oxides concentration is 70 mg/kWh. Various measures for decreasing the generation of NOx in burners of combustion apparatus have been developed and utilized, for example, burners applying rich-lean combustion technique, burners utilizing flame cooling elements, and burners employing metal fibers, etc..

[0004] Metal fiber burner refers to the burner is equipped with metal fibers as a burning surface. These metal fibers can be made into a porous plate with three-dimensional network structure by way of sintering, or can be made into soft permeable fabrics by way of weaving. Because metal fibers have the characteristic of uniform permeability, the burner employing metal fibers can achieve a steady and evenly distributed combustion on surface of the metal fibers, so as to avoid the existence of regional hyperthermia, thereby inhibiting the generation of nitrogen oxides.

[0005] European patents EP 0 157 432 B1 and EP 0 628 146 B1 each discloses a similar metal fiber burner. The burner is provided with a combustible fuel-air mixture in a preset stoichiometric proportion, and then the fuel-air mixture is burnt on the surface of metal fibers. However, mixing fuel gas and air to the predetermined stoichiometric proportion can not always be guaranteed, therefore, it is desired to regulate and control to ensure fuel gas and air are completely mixed before reaching the metal fibers for a full combustion, thereby effectively reducing the generation of nitrogen oxides.

SUMMARY OF THE INVENTION

[0006] It is an object of present invention to provide a burner capable of completely mixing fuel gas and air to a predetermined air-to-fuel ratio, thereby achieving a full combustion on metal fibers and reducing the generation of nitrogen oxides accordingly; also, provide a gas water heating appliance employing the burner.

[0007] According to one aspect of the present invention there is provided a burner including a shell, a number of fuel-air mixing elements, and a metal fiber cover. The burner is received in the shell for mixing introduced air and fuel gas to generate a fuel-air mixture. The metal fiber cover is received in the shell and positioned above the number of fuel-air mixing elements for burning the fuel-air mixture thereon.

[0008] Preferably, the number of fuel-air mixing elements are disposed side by side in a lateral direction.

[0009] Preferably, each of the number of fuel-air mixing elements is shaped in a blade and includes an inlet portion, a mixing chamber, and an outlet portion.

[0010] Preferably, the mixing chamber includes a venturi portion.

[0011] Preferably, the outlet portion includes a number of slits arranged longitudinally.

[0012] In a further embodiment, the burner includes a distribution element disposed between the metal fiber cover and the number of fuel-air mixing elements, wherein the distribution element includes a lot of holes evenly arranged therein for distributing the fuel-gas mixture to the metal fiber cover.

[0013] Preferably, the metal fiber cover includes a metal fiber plate, wherein the metal fiber plate is made of a number of metallic fibers by means of sintering or weaving, and each metal fiber at least contains ferrum, chromium, and aluminium.

[0014] Preferably, the number of fuel-air mixing elements each has a same air-to-fuel ratio for the fuel-air mixture mixed therein.

[0015] Preferably, the air-to-fuel ratio is within an interval of 1.3∼ 1.45.

[0016] By employing a number of fuel-air mixing elements, the fuel gas and air can be completely mixed to a predetermined stoichiometric proportion before reaching the metal fiber cover, thereby achieving a full combustion on metal fibers and reducing the generation of nitrogen oxides accordingly.

[0017] The foregoing has outlined rather broadly the features and technical advantages of the present invention in order that the detailed description of the invention that follows may be better understood. Additional features and advantages of the invention will be described hereinafter which form the subject of the claims of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

[0018] For a more complete understanding of the present invention, and the advantages thereof, reference is now made to the following descriptions taken in conjunction with the accompanying drawings, in which:

Fig. 1 is a perspective view showing a burner in accordance with an embodiment of the present invention;

Fig. 2 is an exploded view showing the burner of Fig. 1;

Fig. 3 is a sectional view showing the burner of Fig. 1;

Fig. 4 is a perspective view showing a metal fiber cover of the burner of Fig. 1;

Fig. 5 is a planar view showing a distribution element of the burner of Fig. 1;

Fig. 6 is a planar view showing a gas heating appliance employing the burner of Fig. 1 in accordance with an embodiment of the present invention, wherein the front plate has been removed to show internal components of the appliance.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0019] Reference will now be made to the drawing figures to describe the preferred embodiments of the present invention in detail. However, the embodiments can not be used to restrict the present invention. Changes such as structure, method and function obviously made to those of ordinary skill in the art are also protected by the present invention.

[0020] Gas water heaters and gas boilers could be fired with combustible gas, such as natural gas, city gas, liquefied petroleum gas, methane, etc., thereby supplying hot water and/or heating living space for domestic sanitary usage and heating purpose. The embodiments to be described below take a gas water heater as an example, however, the present invention is not limited to this, and it can also be applied on gas boilers

[0021] First referring to Fig. 6, a gas water heater 1 in accordance with one embodiment of present invention, includes a housing, and a a burner 1, a heat exchanger 71, an air supply fan 72, and a flue hood 73 accommodated in the housing, and an inlet tube, an outlet tube, and a gas supply pipe extending out of the housing.

[0022] The housing may be composed of a number of plates, such as a front plate, a back plate, a top plate, a bottom plate, and a pair of side plates. The heat exchanger 71 is generally placed above the burner 1. The heat exchanger may include multiple heat absorbing fins and a heat absorbing pipe passing through the multiple heat absorbing fins. The heat absorbing pipe is connected with an upstream water supply channel and a downstream hot water delivering channel. Fuel gas and air mixture is burnt in a combustion chamber defined by a shell of the burner and a casing of the heat exchanger after the two components being connected, and combustion exhaust gas of the burner pass through the fins of the heat exchanger with the generated heat interchanging with water passing through the heat absorbing pipe, then heated hot water is fed to the downstream hot water delivering channel and further passes through the outlet tube for domestic sanitary usage, like drinking, showering, or bathing.

[0023] The air supply Fan 72 is provided at a lower portion of the housing, which is operated to supply outside air to the burner 1 as combustion air, also, force the flue gas to be discharged outdoors. The flue hood 73 is placed upon the heat exchanger 71 for collecting flue gas containing carbon monoxide and nitrogen oxides, and then the flue gas is discharged to the outdoors through discharging ducts (not shown).

[0024] Referring to Figs. 1, 2 and 3, a burner 1 in accordance with one embodiment of present invention, includes a shell 10, and a metal fiber cover 20, a number of fuel-air mixing elements 30, and a distribution element 40 all received in the shell 10. The shell 10 is made of metallic materials, and it takes the form of a square-shaped frame. The shell 10 includes a front panel 11, a rear panel 12, and a pair of side panels 13 connected with the front and the rear panels 11, 12. The front, the rear and the side panels 11, 12, 13 can be assembled by traditional connection ways, for example, by engagement of bolts and nuts. An ignition electrode 15 is disposed in the front panel 11, as shown in Fig. 3, the ignition electrode 15 extends above the metal fiber cover 20 to ignite fuel-air mixture for forming combustion on upper surface of the metal fiber cover 20.

[0025] The fuel-air mixing elements 30 are arranged in the shell 10 side by side in a lateral direction. Each fuel-air mixing element 30 is shaped in a blade, includes an inlet portion 31, a mixing chamber 32, and an outlet portion 33. The inlet portion 31 receives fuel gas supplied from a fuel injection device (not shown) and air brought together with the fuel gas at the inlet. Then the fuel gas and air mix in the mixing chamber 32. The mixing chamber 32 includes a venturi portion 321 (as shown in Fig. 3) adjacent to the inlet portion 31. The venture portion 321 sucks the fuel gas and air at the inlet portion 31 by the venturi effect. The venture portion 321 typically has a constricted section which causes a reduction of fluid pressure thus results in an increasement of fluid velocity. As venturi effect is well known in the art, a detailed explanation is omitted for purpose of simplicity.

[0026] In this embodiment, the outlet portion 33 of each fuel-air mixing element 30 includes a number of slits arranged longitudinally at top of the fuel-air mixing element. In this way, the fuel-air mixture mixed in the mixing chamber 32 can be discharged from the fuel-air mixing element 30 evenly. The air-to-fuel ratio for the fuel-air mixture exiting from each fuel-air mixing element 30 is the same, and such ratio can be within the interval of 1.3∼1.45, preferably within the interval of 1.35∼1.4.

[0027] Referring to Fig. 4, the metal fiber cover 20 is placed above the fuel-air mixing elements 30. The metal fiber cover 20 can be removablely mounted in the shell, for example, the shell 10 can be provided with racks extending from inner surface of the panels, and the metal fiber cover can be placed on the racks. The metal fiber cover 20 includes a frame 21 engaged with the shell 10 and a metal fiber plate 22 disposed in and connected with the frame 21. It is well known to person skilled in the art that, the metal fiber plate can be made of metal fibers which at least contain ferrum, chromium, and aluminium. European patent EP 0 157 432 B1 gives examples of the composition of the metal fiber, which is incorporated herein by reference.

[0028] The metal fibers can be made into a porous plate with three-dimensional network structure by way of sintering, or can be made into soft permeable fabrics by way of weaving. Since these two structures both have the characteristic of uniform permeability, the burner employing metal fibers can achieve a steady and evenly distributed combustion on surface of the metal fibers, so as to avoid existence of regional hyperthermia, thereby inhibiting the generation of nitrogen oxides.

[0029] As shown in Fig. 5, the distribution element 40 is placed between the metal fiber cover 20 and the number of fuel-air mixing elements 30. The distribution element 40 can take form of a plate, and it may be assembled in the shell 10 by placing it on the racks. The distribution element 40 includes a number of holes 41 evenly defined therein for uniformly distributing the fuel-gas mixture to the metal fiber cover 20, thereby achieving a steady and evenly distributed combustion on upper surface of the metal fiber plate 22.

[0030] The combustion experiments show that, when fuel gas and air are mixed at an air-to-fuel ratio around 1.3, the NOx concentration detected within the exhaust gas is 60 mg/kWh; when fuel gas and air are mixed at an air-to-fuel ratio around 1.35, the NOx concentration detected within the exhaust gas is around 44.5 mg/kWh; and when fuel gas and air are mixed at an air-to-fuel ratio around 1.45, the NOx concentration detected within the exhaust gas is 26 mg/kWh. It is obvious that, the generation of NOx of the burner in accordance with present invention is below the limit of 70 mg/kWh which is the highest level of the national standards for NOx emission of domestic gas appliances.

[0031] By employing a number of fuel-air mixing elements, the fuel gas and air can be completely mixed to a predetermined stoichiometric proportion before reaching the metal fiber cover, thereby achieving a full combustion on metal fibers and reducing the generation of nitrogen oxides accordingly.

[0032] It is to be understood, however, that even though numerous, characteristics and advantages of the present invention have been set forth in the foregoing description, together with details of the structure and function of the invention, the disclosed is illustrative only, and changes may be made in detail, especially in matters of number, shape, size, and arrangement of parts within the principles of the invention to the full extent indicated by the broadest general meaning of the terms in which the appended claims are expressed.

Claims

1. A burner (1) comprising:

a shell (10);

a plurality of fuel-air mixing elements (30) received in the shell for mixing introduced air and fuel gas to generate a fuel-air mixture; and

a metal fiber cover (20) received in the shell and positioned above said plurality of fuel-air mixing elements for burning the fuel-air mixture thereon.

2. A burner according to claim 1, wherein said plurality of fuel-air mixing elements are disposed side by side in a lateral direction.

3. A burner according to claims 1 or 2, wherein each of said plurality of fuel-air mixing elements is shaped in a blade and comprises an inlet portion (31), a mixing chamber (32), and an outlet portion (33).

4. A burner according to claim 3, wherein said mixing chamber (32) comprises a venturi portion (321).

5. A burner according to claim 3, wherein said outlet portion comprises a plurality of slits arranged longitudinally at top of the fuel-air mixing element.

6. A burner according to claim 1, further comprising a distribution element (40) disposed between the metal fiber cover and the plurality of fuel-air mixing elements, wherein said distribution element comprises a plurality of holes (41) evenly arranged therein for distributing the fuel-gas mixture to the metal fiber cover.

7. A burner according to claim 1, wherein said metal fiber cover comprises a metal fiber plate (22); wherein said metal fiber plate is made of a plurality of metallic fibers by means of sintering or weaving, and each metal fiber at least contains ferrum, chromium, and aluminium.

8. A burner according to claim 1, wherein said plurality of fuel-air mixing elements each has a same air-to-fuel ratio for the fuel-air mixture mixed therein.

9. A burner according to claim 8, wherein said air-to-fuel ratio is within an interval of 1.3 ∼ 1.45.

10. A gas water heating appliance (100) comprising:

a burner (1) according to any of the preceding claims; and

a heat exchanger (71) for absorbing heat generated by said burner and transferring the heat to water passing therethrough.

Drawing