Patent Application
20070254252
1. Field of the Invention
The invention relates to apparatus providing for the combustion of hydrogen in air, and, more particularly to provisions within such apparatus for preventing the formation of an explosive mixture of hydrogen and air.
A conventional gas burner includes a mixing chamber in which the gas used as fuel is mixed with air and a distribution chamber in which the mixture is fed to a number of individual channels to form gas jets, with combustion occurring outside these individual channels. A valve for controlling the rate at which gas flows into the gas burner is located before the mixing chamber, often in a location remote from the gas jets. A problem with using this type of burner for hydrogen gas results from a potential for air to mix with the fuel within the distribution chamber, the mixing chamber, and associated tubing back to the point at which a shut-off valve is provided in the event of a failure in the gas supply pressure. The accumulation of a mixture of hydrogen and oxygen in such a large and extended enclosed space may result in an explosion, particularly when an attempt is made to restart the combustion process.
The patent literature includes a number of descriptions of apparatus configured particularly for hydrogen combustion. A number of patent documents describe hydrogen burning apparatus in which the hydrogen is mixed with air or oxygen before combustion is applied. In general, a catalyst is used so that combustion can occur at a relatively low temperature. For example, European Patent EP 1179709 B1 describes a hydrogen combustion heater operated by bringing a mixture of hydrogen gas and air into contact with a catalyst to achieve a catalytic oxidation of hydrogen gas. The ratio of air to hydrogen flowing into the mixing area is controlled to limit the combustion to a mild oxidation that avoids firing the hydrogen gas.
U.S. Pat. No. 6,019,172 describes a flameless process in which air and a fuel gas are heated in separate streams so that, when the streams are combined, the temperature of the mixture exceeds the autoignition temperature, with the temperature being less than that which would result in the oxidation upon mixing being limited by the rate of mixing.
U.S. Pat. No. 5,190,453 describes a staged combustor including a first combustion stage for burning a fuel rich mixture of a fuel, preferably hydrogen, and an oxidizer, preferably oxygen. A plurality of serially positioned secondary combustion stages, downstream of the first stage, are provided for receiving secondary flows of oxidizer to the increasing mass of combustion efflux. The gradual increase of oxidizer/fule ratios provides a resultant substantially stoichiometric combustion. A cooling system is provided for cooling these combustion stages.
International Patent Publication No. WO 2005/024301 A1 describes a burner in which hydrogen is mixed with air and burned in a burning chamber on a catalyzer at a low temperature in a flame-free manner.
U.S. Pat. No. 4,614,176 describes apparatus for heating air by burning hydrogen, with the combustion occurring in direct proximity to a metal hydride fuel storage means in order that the combustion heat effects the release of hydrogen from the metal hydride. The hydrogen mixes with air in a mixing and distributing area before flowing through catalytic combustion reactors. (See abstract, col. 2, lines 44-50).
U.S. Pat. App. Pub. No. 2001/0018915 A1 describes a catalytic heater burning a mixture of hydrogen and oxygen to heat water that is circulated to warm a diver's suit.
While the prior art describes apparatus for providing certain desirable features of hydrogen combustion, what is needed to gas burner preventing the accumulation of a substantial mixture of hydrogen and air or oxygen in the event of a failure of the combustion process or an interruption in an adequate flow of hydrogen through the gas burner.
In accordance with a first aspect of the invention, apparatus is provided including a pair of walls extending parallel to one another to form a distribution chamber, an input hole, a plurality of channels, and a shut-off valve. The distribution chamber extends between the walls, one of which includes the input hole. The channels extend outward within the walls from the distribution chamber and along a periphery of the distribution chamber. The shut-off valve, which is outwardly adjacent the input hole extending into the distribution chamber, allows a gas used as fuel to flow into the distribution chamber when the shut-off valve is open. The shut-off valve closes in response to a drop in the pressure at which the gas used as a fuel is supplied through the shut-off valve.
In one version of the invention, the shut-off valve is a check valve responding directly to a decrease in gas pressure. In another version of the invention, a thermal sensor is provided adjacent a combustion area formed by gas jets, with the shut-off valve being closed in response to a signal from the thermal sensor indicating that a temperature has fallen below a predetermined level due to a failure of the combustion process. Such a failure would naturally occur if the pressure at which the gas used for fuel were to drop below a level supporting combustion in the device. In yet another version of the invention, the shut-off valve is a check valve receiving the gas used as a fuel through a valve that is closed in response to detecting a combustion failure. In each case, the closing of the shut-off valve prevents a backward flow of air into the apparatus supplying the gas used as a fuel, which is preferably hydrogen, so potentially explosive conditions within this apparatus supplying the gas are avoided.
Potentially explosive conditions may also be avoided by mixing the gas used as a fuel with air only after it has passed through the channels leading from the distribution chamber to form gas jets, or the gas used as a fuel may be mixed with air within the distribution chamber. Preferably, the volume of the distribution chamber is minimized.
When hydrogen gas flows downward through the slots 28, gas jets are formed to extend downward from the slots 28, with the hydrogen gas mixing with ambient air immediately below the slots 28 to form a combustible mixture. Preferably, the gas burner 10 additionally includes an igniter 46 forming a spark within a gap 48 as a high voltage is applied for a short duration through an insulated wire 50 to ignite the mixture of hydrogen and air, starting the combustion process, which then continues as long as hydrogen is supplied under appropriate conditions through the inlet tube 22. In the example of
The hydrogen burner 90 is additionally provided with an igniter 108, producing a spark between a gap 110 when a high voltage pulse is applied to an electrical wire 112 and with a shut-off valve 114 that is electrically operated to remain open only when a temperature measured by a thermal sensor 116 remains above a predetermined minimum level, indicating that the combustion process has not failed.
Since the combustion process will fail when there is a sufficient loss in the pressure with which hydrogen is supplied, the valve 114 closes in the event of such a pressure loss, preventing a backward flow of air through the inlet tube 118 into the apparatus supplying hydrogen. Like the check valve 24 described above in reference to
The various features described as being included within the different versions and embodiments may be interchangeably used. For example, the formed and welded construction of the second embodiment of gas burner 90 may be used without the air supply chamber, with the mixing of air with hydrogen occurring only after pure hydrogen is supplied through the holes 94. A catalyst may be applied to surface of the burner to encourage the burning of hydrogen at low temperatures.
While the apparatus has been described as using hydrogen gas as a fuel, it is understood that the apparatus may effectively be used with other gaseous substances that may be used as a fuel. While the invention has been described and shown in its preferred versions and embodiments with some degree of particularity, it is understood that this description has been given only by way of example, and that many variations can be made without departing from the spirit and scope of the invention, as defined in the appended claims.
