Patent Application
20160258619
This invention relates to gas fueled heating devices.
Gas fueled infrared heating devices ignite propane or natural gas to heat an object such as a glass or ceramic tile. The heated object emits infrared radiation. Thermal radiation is generated when heat from the movement of charged particles within atoms is converted to electromagnetic radiation in the infrared heat frequency range. Heat is uniformly distributed across the surface of the heated object. Examples of applications for infrared heating include cooking applications and industrial drying applications.
Infrared radiation uses electromagnetic waves rather than heated air for cooking or drying. Heat may be more uniformly distributed than when heating air by burning gas, and with regard to cooking, there is less drying of the food.
Gas fueled infrared heating devices are subject to limitations of other gas fueled heating devices, since a fuel-air mixture is burned to provide heat for the plate or other infrared radiation emitting device. There is a need for a device that will improve the efficiency of gas fueled infrared heating devices, while retarding auto ignition from back flow of the flame.
The present invention is a gas burner having a mixture plenum that receives a gas air mixture. A port plenum is positioned above the mixture plenum. The port plenum comprises a plurality of ports. The ports discharge the gas air mixture for combustion that occurs externally to the port plenum and adjacent to the ports.
A quenching plate is positioned between the mixture plenum and the port plenum to separate the mixture plenum from the port plenum. The quenching plate comprises a plurality of apertures. The gas air mixture flows through the plurality of apertures and from the mixture plenum to the port plenum. The plenum, quenching plate and apertures retard back flow and auto ignition, and the quenching plate will quench a flame in the event of back flow.
The present invention according to a preferred embodiment is a gas burner 2 comprising a first plenum, or mixture plenum 4, for introduction of a gas air mixture to the burner, and a second plenum, or port plenum 6, having a plurality of ports formed therein that discharge the gas air mixture for combustion at an exterior of the port plenum.
The mixture plenum 4 and the port plenum 6 are preferably completely separated from each other by a quenching plate 8. The quenching plate has a plurality of apertures 12 therein. The apertures may be formed, for example, by perforations in the quenching plate, and/or a screen, such as a woven screen. The quenching plate is constructed to be capable allowing sufficient flow of air gas mixture from the mixture plenum to the port plenum, while also quenching any flame that undesirably enters the port plenum due to back flow. As shown in
The port plenum 6 comprising the plurality of ports 14 is preferred to be located within the combustion zone. The mixture plenum 4, which is positioned below the port plenum, may be located partially or entirely outside of the combustion zone. This separation between the port plenum and mixture plenum may be accomplished by a partition, which may be a flange or similar construct, and is referred to herein as a quenching plate 8. The quenching plate is positioned between the mixture plenum and the port plenum.
The use of the multiple plenums allows the burner to be mounted to the bottom of the combustion chamber 16 or other similar enclosure that contains combustion.
In one embodiment, the mixture plenum is positioned generally below the combustion zone and below the port plenum. In another embodiment the mixture plenum is generally positioned beside the combustion zone of the heating device and beside the port plenum. The combustion zone of the heating device may be the area between the infrared energy emitter 26 and the gas burner 2, and including the port plenum 6.
The volume of the mixture plenum 4 provides an area for the gas and air to substantially uniformly mix to the desired ratio. The volume of the mixture plenum is preferred to be larger than the volume of the upper, port plenum. In a preferred embodiment, the port plenum 6 has a volume that is 15% to 35% of the volume of the mixture plenum, and more preferably 16% to 25% of the volume of the mixture plenum. In one embodiment, the port plenum has a depth of about % inch, while the mixture plenum has a depth of about 3 inches, when the length and width of each plenum is generally the same. The port plenum operates within the higher temperature of the combustion zone, with the burner structure preventing auto-ignition.
In some applications, the port plenum may be exposed to temperatures as high as 1650° F. The use of multiple plenums separated by a quenching plate 8 comprising apertures allows the mixture plenum to be exposed to lower temperatures than the port plenum, with the quenching plate retarding auto-ignition from flame retrogression or backflow. The temperature in the mixture plenum may be 500°-800° F. lower than the port plenum. The lower temperature of the mixture plenum also reduces the likelihood of auto-ignition from flame 20 retrogression or backflow.
In a preferred embodiment, the gas air mixture is transmitted at substantially uniform pressure and volume from the lower, mixture plenum 4 to the upper port plenum 6 along the length of the quenching plate. In many applications of combustion and heat transfer, it is necessary that the burner be substantially elongated long relative to its cross sectional area. The result is that as combustible mixture flows from a venturi 18 into the burner, the gas pressure drops along the length of the burner as the gas-air exits through ports along the length of the burner. The gas-air pressure and volume is therefore lower in many cases as the distance from the venture increases. The result is inconsistent heating along the length of the burner.
This present invention overcomes this problem in a preferred embodiment by varying the flow area through the apertures 12 of the quenching plate 8. The size of the apertures, or the density of the apertures, or both, may be varied to increase or decrease the flow of combustible mixture to the upper plenum. Pressure and volume of the gas-air mixture may be measured at the quenching plate on the port plenum side to construct a plate that has substantially equal flow volume along the length of the plate.
In a preferred embodiment of the invention, the mixture plenum 4 and the port plenum 6 are constructed as separate units.
The area of the individual ports 14, as well as the collective area of the ports, may be increased as compared to ports of conventional burners. An increase in the port area allows more primary air to be introduced through a venturi 18 or other air injector than with previously known gas heating devices. It is neither a good nor safe practice to allow the flame to retrogress back to the orifice when the burner is turned off. If the port size is too large, and the velocity of the fuel air mixture is decreased below the flame velocity, retrogression of the flame into the ports will occur. For this reason, the diameter of the ports of a conventional burner must be small enough to quench the flame when the velocity of the mixture is below the flame velocity.
In the present invention, the diameter of the ports 14 may be formed to have a larger area than other gas fueled burners. When the burner is turned off, if the flame retrogresses through the ports into the upper plenum, the flame is quenched by the quenching plate between the plenums, and the flame cannot retrogress to the fuel source.
The use of larger ports allows increased thermal efficiency and increased heating of the infrared energy emitter 26. More air for combustion is provided by primary air through the ports. Less secondary air is required through the secondary air ports 22. Therefore, less heat from the burner is applied to air moving through the heating device 28, and more heat from the burner is available to heat the infrared energy emitter. The ports 14 in some embodiments may range from 0.045 inches to 0.15 inches in diameter.
The above discussion is based upon a gas fueled heating device having naturally aspirated primary air and a means to supply secondary air. However, this burner may also operate with the same benefits using a premixed air and gas composition, as is frequently the case in industrial applications.
The flame quenching plate allows a flow of gas from the mixture plenum to the port plenum, but does not allow a flame to pass through the quenching plate. Apertures in the quenching plate may be formed by perforating a sheet of metal that forms the plate, or by positioning spaced apart screens, including wire mesh screens, in the quenching plate. The apertures are small enough to stop the passage of the flame, while permitting sufficient flow of the gas through the quenching plate. This method of quenching a flame provides for a change in the molecular carriers.
In this embodiment, flame quenching occurs between the two plenums that are separated by the quenching plate. Therefore, there is unlimited flow area available. When the port diameter of a burner is used to prevent retrogression of the flame, the restrictions imposed can create other problems. The ability to inject primary air is dependent on the pressure in the burner tube or the burner plenum. Decreasing the flow area of the ports increases the pressure, which decreases the volume of primary air that is injected. The present invention does not depend on quenching the flame at the ports. Therefore, more latitude is available in selecting the diameter of the ports.
The burner as described herein provides flexibility in heating devices where the temperature of the combustion zone is in excess of the auto ignition. This temperature varies with the type of gas, but the temperature in the mixture plenum may be 500° F. to 600° F. less, and up to 800° F. less, than the temperature in the port plenum under some conditions. The burner of the present invention can operate in an environment up to about 1650° F., which is above the auto ignition temperature for natural gas and propane gas.
Other preferred applications of the present invention include the situation in which a burner greater than about 2 ft. in length is required and the fuel air entrance to the burner is required to be at one end of the burner. Also, the burner may be used in the food cooking applications, such as gas grills and commercial griddles. The burner may be used in the heating of water and other liquids.
A preferred use of the invention is with industrial ovens used for various processes such as paint baking. The invention provides an ideal burner for use in large infrared energy ovens, such as the “Radiant Wall Oven”, Best, U.S. Pat. No. 5,594,999.
Applicant claims the benefit of U.S. Provisional Application Ser. No. 62/127,300 filed Mar. 3, 2015.
| Number | Date | Country | |
|---|---|---|---|
| 62127300 | Mar 2015 | US |
