WO2019193370A1

WO2019193370A1 - Gas burner

Info

Publication number: WO2019193370A1
Application number: PCT/GB2019/051021
Authority: WO
Inventors: Thomas Robert Llewelyn GOZNEY
Original assignee: Gozney Group Ltd
Current assignee: Gozney Group Ltd
Priority date: 2018-04-06
Filing date: 2019-04-08
Publication date: 2019-10-10
Anticipated expiration: 2020-10-06
Also published as: GB201805778D0

Abstract

A gas burner for an oven, comprises a mixing unit (20) including a gas inlet, which is connectable to a gas supply (15), an air inlet, and an outlet for the air-gas mixture. A burner head (12) is connected to the outlet of the mixing unit, the burner head being capable of burning the air-gas mixture, and a fan for drawing air through the air inlet of the mixing unit, while the the air-gas mixture is such a ratio that the flame produced at the burner head is luminous.

Description

GAS BURNER

The present specification relates to gas burner, particularly a gas burner for a masonry or pizza oven.

A traditional pizza oven is a masonry oven, built of brick or clay typically in a hemispherical dome over a flat floor. Wood is placed around the periphery of the floor where it meets the dome, and ignited, so that the flames of from the burning wood curve over the ceiling of the dome. The floor and dome absorbs the heat from the flames, and so that food placed on the floor of the oven is cooked from below by heat conducted and radiated from the floor, and from heat radiating downwards from the ceiling of the dome.

Modern gas-fired pizza ovens use an atmospheric gas burner where gas escapes from the burner orifice in into the oven; often a venturi tube may be used to entrain air from the oven into the gas stream to mix the air and the gas.

The flame from the burning wood is yellow, indicative of incomplete combustion, and also relatively long. A flame from a gas burner is typically well mixed with oxygen from the air, and so burns more completely with a hotter short blue flame. This flame does not extend over the ceiling of the dome of the oven, instead it heats the air in the oven to cook food placed in the oven. Food cooking in a gas-fired pizza oven therefore has a different and inferior taste.

A venturi of a gas burner can be adjusted to burn with a yellow flame to replicate the flame needed for a pizza oven but the burner is susceptible to small changes in air pressure or air flow. This can prove problematic when the restaurant with the oven is sited in certain locations where the airflow and pressure can change suddenly. For example, if the restaurant is in an open plan shopping mall and the front doors are constantly opening and closing. This can create negative air pressure around the gas burner that draws the flame back on itself or simply puts out the flame.

To combat this problem, such a gas must be carefully installed to ensure the air vent size and air circulation remain constant; in practice though, such ovens are still subject to poor performance.

The object of the present invention is to provide a gas-fired pizza oven or masonry-type oven that provides similar performance to a wood-fired oven. According to the present invention, there is provided a gas burner according to claim 1 and a method of operation according to claim 11.

In order that the present invention may be more fully understood a specific embodiment will now be described by way of example with reference to the accompanying schematic drawings, of which:

Figure 1 is an exploded perspective view of the gas burner;

Figure 2 is a longitudinal sectional view of the oven with the gas burner in use;

Figure 3 is a perspective view of a restrictor cap according to another embodiment of the invention;

Figure 4 is a longitudinal sectional view of the restrictor cap of figure 3;

Figure 5 is a perspective cross sectional view of the air flow in the restrictor cap and venturi according to the first embodiment of the invention; and

Figure 6 is a perspective cross sectional view of the air flow in the restrictor cap and venturi according to the second embodiment of the invention.

The mixing unit 20 includes a venturi 24 which is supplied with gas as shown by arrow g from a gas supply 15 via a valve assembly 28 as shown by arrows h and /^'. The venturi 24 is also supplied with air which is drawn through an air filter 26 shown by arrow a, through a restrictor cap 25 as shown by arrow b and into a venturi 24 as shown by arrow c by a fan module 18. The air and gas are thoroughly mixed in the venturi 24, and the mixture passes through the fan module 18 as shown by arrows d and e. The speed of the fan in the fan module 18, and the flow rate of the gas admitted through the gas valve assembly 28 are controlled by the burner controller 30, which allows the rate of air and the rate of gas that is supplied to the burner assembly 10 to be independently controlled.

This allows the burner controller 30 to control the characteristics of the flame, including the intensity and type of flame, and the height of the flame.

The burner assembly 10 includes a long strip burner head 12 which is fed by a gas-air mix supply tube 13 shown by arrow e, and is mounted in the pizza oven by a burner mounting plate 14. The gas-air mixture exits the fan module 18 through the gas-air mix supply tube 13 to the burner head 12. The gas-air mixture is ignited by an ignition electrode 16, the ignition electrode 16 is controlled by the burner controller 30, and combustion is monitored by a thermocouple in the ignition electrode 16 connected to the burner controller 30.

The fan module 18, burner controller 30 and valve assembly 28 are supplied with power from an electrical box 22 which is typically wired to mains power.

The fan module 18 draws in air from the environment at a accurately controlled rate; this ensures that the gas-air mix supplied to the burner assembly 10 produces a rolling luminous (i.e. luminous) flame, but is not affected by drafts or pressure changes around the oven's environment. The restrictor cap 25 serves to limit the air flow, and therefore provides a comparatively low air to gas ratio, and so ensure that the gas-air mixture burns at the burner head 12 with a luminous flame.

A luminous flame tends to be longer, and so will roll or curve up and along the roof of the oven, as shown in figure 2. Ideally, the gas-air mix, and the total amount of gas and air, is adjusted or chosen so that the flame height is at least 200 mm. This will depend on the particular dimensions and capacity of the gas burner, and to some degree on the type of gas used in the burner. For example, methane generally burns with a blue flame with an air-to gas ratio of 10:1, so the ratio for the burner is ideally lowered, for example to below 8:1.

Also, typically, a flame with less than 40% blue will have an adequate length to effectively function in the present invention; this will to an extent be dependent on routine experiment with the burner, and gas supply to be used. In particular, the restrictor element diameter may be chosen, or the venturi size varied, and/or a gas adjustment screw may be included to tune the ratio to give the desired flame characteristics.

The burner head 12 comprises of a stainless steel box section, with rectangular perforations in the top surface and a mesh layer 11 welded on top of this surface. As the mesh layer heats and promotes good ignition of the low-oxygen to gas mixture exiting the burner head 12 along the length of the burner head.

The restrictor cap allows the amount of air passing through the venturi to be reduced;

without this, too much air enters the system, creating a very efficient combusting flame; however, although the flame itself is efficient, it is not efficient for the oven; a high localised temperature is produced on the oven wall or roof, which means that food such as pizzas placed in the oven is heated indirectly by a distant, localised high temperature region. This does not cook the top of pizzas and similar foods correctly. It also means that the oven takes a long time to heat up - an efficient burner in a pizza oven is inefficient, and will produce more airborne contaminates.

Restricting the amount of air in the system with the restrictor cap reduces the efficiency and combustion of the flame, leading to the creation of a create a rolling flame that given even heat across the oven floor; the restrictor cap or adaptor regulates the air flow to the premix, and also allows the fitting of an air filter. He rolling flame heats a larger area of the roof or walls of the oven, leading to an even and distributed heat to radiate downwards from a larger area.

Using this burner provided increased efficiency as well as much greater control over the characteristics of the flame as both airflow and gas rate could be regulated. More importantly, the burner is not susceptible to external environmental factors.

Referring to figure 2, the flames exiting the burner assembly 10 are rolling luminous long flames. These follow the curve of the ceiling of the oven 34, so that the ceiling becomes hot. This heat radiates downwards as indicated by arrows r, to cook the food 35 from above.

A single aperture as shown in the embodiments illustrated in figures 1 and 2 however can lead to the air flow through the venturi 24 causing loud harmonics/resonance sound at certain fan/power levels.

Referring to figures 3 and 4, the restrictor cap 25, which in the embodiment of figure 2 has a single aperture for air to pass through, may instead comprise a cap having a cylindrical side wall 51 and a circular top 52 into which a plurality of apertures 53 are formed. The apertures 53 are formed close to of touching the periphery of the circular top 52.

Referring to figure 5, restrictor cap 25 with a single aperture 55 causes the whole airstream to pass down the central axis of the restrictor cap 25 and venturi into to then go on to be mixed with the gas. This however creates turbulent air flow close to the edge of inner surface of the venturi where the airstream is absent. This can lead to noise being caused and amplified by the resonance of the pre-mix system, burner and the oven itself.

Referring to figure 6, it has been found that increase the number of air in holes 53 in the top 52 of the cap achieves a more balanced flow, where separate airstreams 57 are moved to the sides of the restrictor cap adaptor 50, reducing the flow turbulence down the sides of the adaptor and the venturi; this reduces the noise created by the air flow, and prevents the resonant amplification by the pre-mix system, burner and oven.

The hole size, quantity and distance from the periphery of the circular top 52 can be adjusted to achieve the best balance between air in area and the resistance of increased overall circumference of the combined holes; the design can also be adjusted to suite different gas types, pressures and locations (such as the difference in air pressure between sea level locations and mountain locations at high altitude).

While a long burner head with an elongate mesh section is particularly suitable for this application, the mixing unit herein described can be used in conjunction with known burner heads to produce a reliable and constituent luminous flame.

Further, while a substantially hemispherical oven is particularly suitable for use with the mixing unit and the long luminous flame produced by it, the mixing unit can be fitted in ovens having a different shape where a reliable and consistent luminous flame is desired.

The fan module 18 is here situated upstream of the venturi 24; however, it could equally be situated downstream of the venturi 24. It will also be realised that alternative mixing devices to a venturi could be used to mix the air and the gas.

Many variations are possible without departing from the scope of the present invention as defined in the appended claims.

Claims

1. A gas burner for an oven, comprising a mixing unit including a gas inlet connectable to a gas supply, an air inlet, and an outlet for the air-gas mixture a burner head connected to the outlet of the mixing unit, the burner head being capable of burning the air-gas mixture a fan for drawing air through the air inlet of the mixing unit the air-gas mixture being of a ratio such that the flame produced at the burner head is luminous.

2. A gas burner for an oven according to claim 1, wherein a gas valve and a controller is included to regulate the amount of gas that enters the mixing unit.

3. A gas burner for an oven according to either previous claim, wherein the controller regulates the speed of the fan and therefore the amount of air that enters the mixing unit.

4. A gas burner for an oven according to any previous claim, wherein a restrictor element is included in the air inlet which restricts the flow of air into the air inlet.

5. A gas burner for an oven according to any previous claim, wherein the restrictor element includes a plurality of apertures arranged near to the edge of a circular cap.

6. A gas burner for an oven according to any previous claim, wherein an air filter is included between the mixing unit and the environment.

7. A gas burner for an oven according to any previous claim, wherein the ratio of air to gas is less than 10:1.

8. A gas burner for an oven according to any previous claim, wherein the burner head is elongate.

9. A gas burner for an oven according to claim 8, wherein the burner head includes an elongate mesh.

10. A masonry oven having a substantially domed-shape including a gas burner according to any previous claim, such that in use, the luminous flame produced by the burner head extends to the ceiling of the oven, so that the ceiling heats and radiates heat downwards into the oven.

11. A method of operating an oven, comprising providing a gas burner including a mixing unit including a gas inlet connectable to a gas supply, an air inlet, and an outlet for the air-gas mixture a burner head connected to the outlet of the mixing unit, the burner head being capable of burning the air-gas mixture a fan for drawing air through the air inlet of the mixing unit regulating the air-gas mixture being of a ratio such that the flame produced at the burner head is luminous.

12. A method of operating an oven according to claim 11 wherein the oven has a substantially domed-shape, and regulating the gas burner and air-gas mixture so that the luminous flame produced by the burner head extends to the ceiling of the oven, and the ceiling heats and radiates heat downwards into the oven.