Patent Application
20140186780
1. Field of the Invention
Embodiments described herein generally relates to control of jet velocity of a fuel gas or oxidizing gas. Specifically, embodiments described herein relate to maintaining proper jet velocity for gases delivered to a burner at non-standard temperatures.
2. Description of the Related Art
Many industrial operations employ furnaces within which fuel and oxidant are combusted, so that the heat of combustion can heat material that is in the furnace. Examples include furnaces that heat solid material to melt it, such as smelting furnaces, and furnaces that heat objects such as steel slabs to raise the material's temperature (short of melting it) to facilitate shaping or other treatment of the material or object. The required high temperature is generally obtained by combustion of a hydrocarbon fuel such as natural gas. The combustion produces gaseous combustion products, also known as flue gas. Even in metal heating equipment that achieves a relatively high efficiency of heat transfer from the combustion to the solid materials to be melted, the flue gases released generally reach temperatures in excess of 1300 degrees Celsius (° C.), and thus represent a considerable waste of energy that is generated in the high temperature operations, unless that heat energy can be at least partially recovered from the combustion products.
One mechanism to recover this lost energy is to preheat one or more of the combustion reactants (fuel or oxidant) using the flue gases. The combustion reactants can be heated to a critical temperature, thus increasing the heat delivered to the furnace during the combustion process. However, problems arise from the preheating of the combustion reactants. As the combustion reactants are heated, the gases expand leading to an increase in jet velocity. Jet velocity is the velocity with which the gases escape the burner. Increased jet velocity leads to shorter residence time before the combustion reaction which can reduce flame luminosity. A larger jet velocity can resolve this problem, but this solution is not applicable to both low temperature and high temperature combustion reactants.
Thus, there is a need in the art for automated control of jet velocity.
The invention described herein generally relates to systems and methods for controlling jet velocity. In one embodiment, a system for controlling jet velocity, can include a source of oxidizing gas; a source of fuel gas; at least one temperature-sensitive bimetallic valve in connection with one of the source of oxidizing gas or the source of fuel gas, the valve comprising a bimetallic strip, a blocking device and a flow control structure and configured to receive an oxidizing gas or a fuel gas, wherein the oxidizing gas or the fuel gas is at a first temperature; change the temperature of at least the bimetallic strip from a second temperature to the first temperature; change position of the bimetallic strip, as measured from the flow control structure, in response to the change in temperature from the second temperature to the first temperature; and change the velocity of the oxidizing gas or the fuel gas through the valve based on the position of the bimetallic strip; and a burner configured to receive an oxidizing gas or a fuel gas from the at least one temperature-sensitive bimetallic valve, wherein the oxidizing gas or the fuel gas is at the first temperature; combine and combust the fuel gas with the oxidizing gas to create a jet; and deliver the jet to a target material.
In another embodiment, a method for controlling of gas velocity can include flowing an oxidizing gas or a fuel gas into a temperature-sensitive bimetallic valve at a first temperature, the temperature-sensitive bimetallic valve comprising a bimetallic strip, a blocking device and a flow control structure; transferring heat from the oxidizing gas or the fuel gas to the bimetallic strip, wherein the bimetallic strip changes from a second temperature to the first temperature; changing the position of the bimetallic strip, as measured from the flow control structure, in response to the change in temperature from the second temperature to the first temperature; and delivering the oxidizing gas or the fuel gas from the temperature-sensitive bimetallic valve to a burner at a second velocity, wherein the second velocity of the oxidizing gas or fuel gas changes dependant on the position of the bimetallic strip.
So that the manner in which the above recited features of the present invention can be understood in detail, a more particular description of the invention, briefly summarized above, may be had by reference to embodiments, some of which are illustrated in the appended drawings.
It is to be noted, however, that the appended drawings illustrate only typical embodiments of this invention and are therefore not to be considered limiting of its scope, for the invention may admit to other equally effective embodiments.
To facilitate understanding, identical reference numerals have been used, where possible, to designate identical elements that are common to the figures. It is contemplated that elements disclosed in one embodiment may be beneficially utilized on other embodiments without specific recitation.
Methods and systems for controlling jet velocity are described herein. Significant energy is lost during the combustion process, specifically through heat that escapes to the atmosphere in flue gases. For example, in an oxy-fuel fired glass furnace, where all the fuel is combusted with pure oxygen, and for which the temperature of the flue gas at the furnace exhaust is of the order of 1350° C., typically 30% to 40% of the energy released by the combustion of the fuel is lost in the flue gas.
The methods and systems described herein propose heating the combustion reactants to recover a portion of the heat lost in the flue gases, which can then be redelivered to the furnace to reduce the reactant energy input required for the overall process. To maintain jet velocity in the heated combustion reactants, a temperature-sensitive bimetallic valve can be positioned between the gas source and the burner. The temperature-sensitive bimetallic valve can control the velocity of the combustion reactants to the burner, thus allowing for an optimal jet velocity and residence time for both preheated and cooled gases, based on the temperature of the gas delivered to the valve. The embodiments of the invention disclosed herein are more clearly described with reference to the figures below.
The temperature-sensitive bimetallic valves 110a and 110b can be used to control the jet velocity of the jet 102 produced by the burner 104. In this embodiment, a first temperature-sensitive bimetallic valve 110a is in fluid connection with the burner 104 through a first oxidizing gas pipe 112 and a second oxidizing gas pipe 114. A second temperature-sensitive bimetallic valve 110b is in fluid connection with the burner 104 through a first fuel gas pipe 116 and a second fuel gas pipe 118. The fuel gas and the oxidizing gas can be heated prior to flowing into the temperature-sensitive bimetallic valve 110a and 110b. The gases, either the fuel gas or the oxidizing gas, will equilibrate temperature with the temperature-sensitive bimetallic valves 110a and 110b, thus increasing the temperature of the valve from a second temperature to the first temperature in the presence of the heated gases. The increase in temperature causes the temperature-sensitive bimetallic valves 110a and 110b to change in port size upon over a gradient of temperatures. When the temperature-sensitive bimetallic valves 110a and 110b change in port size, the gas is delivered the velocity of either the fuel gas or the oxidizing gas is adjusted appropriate to the gas temperature.
The burner 104 can receive a fuel gas and an oxidizing gas as redirected through the temperature-sensitive bimetallic valves 110a and 110b. In this embodiment, the oxidizing gas is delivered through the temperature-sensitive bimetallic valve 110a to the first oxidizing gas pipe 112 and the fuel gas is delivered through the temperature-sensitive bimetallic valve 110b to the second fuel gas pipe 118. The temperature-sensitive bimetallic valves 110a and 110b have a first state and a second state. The temperature-sensitive bimetallic valve 110a is depicted in the first state based on receiving a cold oxidizing gas. The cold oxidizing gas does not have significant thermal energy to transfer to the temperature-sensitive bimetallic valve 110a, thus the temperature-sensitive bimetallic valve 110a remains in the first state. The first state of the temperature-sensitive bimetallic valve 110a prevents flow of the oxidizing gas through the second oxidizing gas pipe 114 while allowing flow through the first oxidizing gas pipe 112. The temperature-sensitive bimetallic valve 110b is depicted in the second state based on receiving a heated fuel gas. The heated fuel gas heats the temperature-sensitive bimetallic valve 110a as it flows in from the fuel gas line 108, thus the temperature-sensitive bimetallic valve 110a bends based on the bimetallic effect. The second state of the temperature-sensitive bimetallic valve 110b prevents flow of the oxidizing gas through the first fuel gas pipe 114 while allowing flow through the second fuel gas pipe 112.
Though shown here as permutations of a dual pipe embodiment, various designs may be employed to control velocity of gases delivered to the burner 104. In one embodiment, the oxidizing gas pipes 112 and 114 and the fuel gas pipes 116 and 118 may be a pipe-in-pipe design where a portion of the pipe is closed off for the standard temperature gas and the portion of the pipe is opened for heated gases. In general, the designs for both the valves and the pipes are only limited by the desire to maintain the same flame shape and size when flowing either heated or standard temperature gases at the same flow rate.
In one or more embodiments, the pipe used for the heated gases can be larger than the pipe used for the standard temperature gases. As the heated gases are delivered at a higher temperature, they are also at a higher pressure. The higher pressure can increase the velocity of the gas which reaches the burner, thus increasing the jet velocity. By effectively increasing the volume based on temperature, the jet velocity can be maintained between heated and standard temperature gases.
The fuel gas and the oxidizing gas can be any known fuel or oxidizer. In one embodiment, the fuel gas is natural gas and the oxidizing gas is oxygen. The fuel gas or the oxidizing gas may be heated. In order that the burners may use the heated oxidizing gas, such as preheated oxygen, with the fuel gas without serious safety problems, the difficulties in handling the preheated oxidizing gas should be considered. Therefore, the parts of the burners used in the apparatus and process of the invention in contact with the preheated oxidizing gas can be made of material compatible with preheated oxygen or other oxidant. These compatible materials can be refractory oxides such as silica, alumina, alumina-zirconia-silica, zirconia and the like. Alternatively, certain metallic alloys that do not combust in preheated oxygen use may be used. Coating metallic materials with ceramic materials on the surface exposed to the preheated oxidizing gas can also be employed for the construction of the burner. Components used in the temperature-sensitive bimetallic valves 110a and 110b or the burner 104 may be coated with Alconel.
A flue gas can be thermally connected with the fuel gas, the oxidizing gas or downstream contacts to either container which are prior to the burner 104. When using natural gas as the fuel gas and oxygen (O2) as the oxidizing gas, temperatures can be maintained below 450° C. and 550° C. respectively. As the flue gas can reach temperatures of 1350° C. or higher, the heat transfer from the flue gas can be delivered through a secondary device (not shown) to better maintain heat transfer to the fuel gas and the oxidizing gas.
There are various means by which the flow of the gases can be adjusted by the temperature-sensitive bimetallic valves 110a and 110b as the temperature changes. In one embodiment, the fuel gas or the oxidizing gas is flowed through a pipe wherein the outlet of the pipe expands as the tube heats up, based on blocking devices connected to bimetallic layers formed at the outlet. In another embodiment, the flow of the gases is redirected based on a pipe-in-pipe design, where a portion of the pipe is either blocked or open based on reaching a threshold temperature. This design would allow higher flow through the overall pipe when the threshold temperature is reached, thus allowing for a reduced jet velocity. In another embodiment, the flow of the gases is increased based on an “overlaying-leaf” design which increases in size as temperature increases. One skilled in the art will appreciate that numerous permutations of controlling velocity of a gas using a bimetallic strip as disclosed in the invention described herein.
Embodiments described herein relate to relevant portions of a typical burner useable with one or more embodiments of the invention. There can be other components that are not explicitly named which may be included or excluded based on the choice of design and other parameters. The components described herein may differ in shape, size or positioning from those used in practice. Further, the embodiments described herein are for exemplary purposes and should not be read as limiting of the scope of the invention described herein, unless explicitly limited herein.
The aperture 202 can be formed in the valve chamber 204 of the temperature-sensitive bimetallic valve 200. The valve chamber 204 can be fluidly sealed providing for the controlled velocity of the gases, which flow through the aperture 202. The valve chamber 204 can be composed of a material which is resistant to at least the expected levels of heat from and the chemistry of the gases delivered. In one embodiment, the valve 200 is composed of ceramics or metals coated with a ceramic. Though the valve chamber 204 is shown as a cylindrical structure, this is not intended to be limiting of possible embodiments of the invention. For example, the valve chamber 204 can be square, rectangular, cylindrical, circular, or combinations of those shapes.
The temperature-sensitive bimetallic valve 200 can include one or more bimetallic strips 206 in connection with the valve chamber 204, shown here as bimetallic strips 206a, 206b, 206c and 206d. The bimetallic strips 206a, 206b, 206c and 206d can be affixed at one end in connection with the valve chamber 204. The bimetallic strips 206a, 206b, 206c and 206d can be affixed by one or more connection devices, shown here as connection devices 207a, 207b and 207c. The connection devices 207a, 207b and 207c can include various connections to the valve chamber 204, such as a spot welding point, a rivet, a clamp or other devices as used in the art. The connection devices 207a, 207b and 207c can be thermally conductive.
The bimetallic strips 206a, 206b, 206c and 206d can be composed of two or more layers of a metal, which can be a pure metal or a metal alloy. These layers may be of any thickness and in any order, based on the desired movement from the bimetallic strips 206a, 206b, 206c and 206d. The layers may further be distinct from one another or may blend into one another. The first metal can expand during temperature changes at a rate which is higher than the second metal. The layers of metal can include a first metal which has a coefficient of thermal expansion which is at least 1.1 times greater than the second metal. In one embodiment, the first metal can be selected from the group consisting of iron, palladium, platinum or combinations thereof. In another embodiment, the second metal can be selected from the group consisting of copper, cobalt, nickel or combinations thereof.
Without intending to be bound by theory, the thermal expansion of a metal is generally believed to be a function of the amount of the metal present and the thermal expansion coefficient of the metal. When the first metal is placed in connection with a second metal and the metals have significantly different coefficients of expansion, the expansion of one metal will necessarily be greater than the expansion of another metal. This differential expansion creates tension against the slower expanding metal, thus creating a bend in the direction of the slower expanding metal.
The bimetallic strips 206a, 206b, 206c and 206d can be connected with one or more blocking devices 208, shown here as blocking devices 208a, 208b, 208c and 208d. The blocking devices 208a, 208b, 208c and 208d can form a partial barrier to flow through the end of the valve 200. The blocking devices can be composed of a material that is not sensitive to high temperatures or to the specific chemistries used in the valve. In one embodiment, the blocking devices 206a, 206b, 206c and 206d are resistant to oxidizing gases, such as oxygen. In another embodiment, the blocking devices 208a, 208b, 208c and 208d are resistant to oxidizing gases, such as oxygen. For example, the blocking devices 208a, 208b, 208c and 208d can be composed of an austenitic nickel-chromium-based alloy such as Inconel. Shown in
The bent bimetallic strips 206a, 206b, 206c and 206d cause the blocking devices 208a, 208b, 208c and 208d to separate from one another, thus exposing an port 203b. The port 203b is larger than port 203a, which allows the gas to flow at a constant velocity. By increasing the volume of the area, the velocity can be maintained between the cool gas and the more energetic preheated gas. With consideration of the temperatures, the automated process described above allows for safe transition between preheated and cold gas processes.
The number and shape of the bimetallic strips 216a, 216b, 216c and 216d and the blocking devices 218a, 218b, 218c and 218d are depicted here for exemplary purposes only. Further embodiments of this invention may include more of fewer bimetallic strips 216a, 216b, 216c and 216d and the blocking devices 218a, 218b, 218c and 218d as well as different shapes, based on the needs and desires of the user.
In one or more of the embodiments described above, the temperature may be directly delivered to the bimetallic strip 226 or indirectly. In one embodiment, the heat from the preheated gas is delivered through a conductive material to the mounting device 227. The mounting device 227 can then transfer heat to the bimetallic strip 226. The mounting device 227 can be formed of any material appropriate to the temperatures and chemistries of the gas flowed through the valve 200. The mounting device 227 may also be a conductive material, such as a metal. For example, the mounting device 227 may comprise copper or a copper alloy.
Though the embodiments above focus primarily on gradual effects of a bimetallic strip, one or more of the embodiments above can incorporate a design which requires a specific level of force to transition from one state to another. Stated another way, the bimetallic strip can be employed in a way that creates a transition temperature for redirecting gas flow. Further, one or more sources of force, such as springs, may be employed for more complex operations incorporating the bimetallic strip designs described above.
The method 300 begins at step 302 by flowing an oxidizing gas or a fuel gas into a temperature-sensitive bimetallic valve at a first temperature, the temperature-sensitive bimetallic valve comprising a bimetallic strip, a blocking device and a flow control structure. In one or more embodiment, the fuel gas can be heated by using a flue gas. As described above, thermal energy is wasted from the furnace in the form of heat in the flue gas. One mechanism to recover this lost heat, is to heat the oxidizing gas and/or the fuel gas prior to delivering to the burner. In one or more embodiments, either the oxidizing gas or the fuel gas is heated, while the other gas is maintained at standard temperature. After one or more of the gases are heated, the gases are then flowed to the temperature-sensitive bimetallic valve. In standard embodiments, the gas will enter at one velocity and exit at a predetermined velocity based on port size. The velocity of entry and the velocity of exit may be equal based on the size of the port and the initial flow velocity from the gas container. Preheated gases will enter the temperature-sensitive bimetallic valve at a faster velocity than comparatively colder gas, given other conditions such as flow rate remain constant between the preheated gas and cold gas.
At step 304, the oxidizing gas and the fuel gas can transfer heat with the bimetallic strip in the temperature-sensitive bimetallic valve. As the gases flow into the temperature-sensitive bimetallic valve, the components which are in thermal contact with the gas equilibrate based on the starting temperature of the gas and the starting temperature of the components of the temperature-sensitive bimetallic valve. The temperature-sensitive bimetallic valve is expected to start at a second temperature, which can be an ambient temperature, such as room temperature. However, this can be altered by preheating the valve to assure quick transition from one state to another. The oxidizing gas and the fuel gas will be delivered at a first temperature which is the temperature each was heated to in the previous step. When the fuel gas is natural gas, the first temperature should be less than or equal to about 450° C. When the oxidizing gas is oxygen (O2), the first temperature should be less than or equal to about 550° C. As the gases are delivered to the temperature-sensitive bimetallic valve, the components of the temperature-sensitive bimetallic valve including the bimetallic strip will change from the second temperature to the first temperature.
At step 306, the position of the bimetallic strip can change as measured form the flow control structure, in response to the change in temperature from the second temperature to the first temperature. As the bimetallic strip changes from the second temperature to the first temperature, the bimetallic strip can flex and bend in proportion to the change in temperature and the composition of the bimetallic strip. Based on the change in the bimetallic strip, the size of the port for the temperature-sensitive bimetallic valve can change. In further embodiments, the temperature change can be used to redirect the gas to a second port. The goal of either the size or the port change is maintain the velocity of the gas between the standard temperature gas and the heated gas as they exit the temperature-sensitive bimetallic valve. Using the bimetallic strip, the gas can be flowed into a second port or into a larger port to maintain the final velocity of the gas.
At step 308, the oxidizing gas or the fuel gas can be delivered from the temperature-sensitive bimetallic valve to the burner at a second velocity. In this embodiment, the temperature of the gas affects the position of the bimetallic strip in the temperature-sensitive bimetallic valve. By changing the bimetallic strip position in the temperature-sensitive bimetallic valve, the port size is increased by one or more of the above described means, which increases the volume and changes the velocity of the gas. The change in velocity of the gas creates a second velocity which is approximately equal between the standard temperature gas and the heated gas. In one or more embodiments, the temperature-sensitive bimetallic valve gradually shifts between two states, with the second state providing a larger port for the preheated gas to flow through after changing from the standard temperature gas to the preheated gas. It is important to note that, although the second velocity can be different from the first velocity, this is not required.
The transfer of heat to the bimetallic strip does not need to be a direct transfer. In one or more embodiments, an insulated heat pipe could sample and “transmit” heat from the area where process flow temperature is seen, to a bimetallic strip positioned proximate, but thermally isolated from, the gas, such that the bimetallic strip is not directly subject to the heat or chemistry of the gas. The bimetallic strip flexes based on the temperature change to either open a second port or decrease the effective size of the first port.
Embodiments described herein relate to automated control of the velocity of a gas based on temperature. Recovery of lost thermal energy is becoming more important as fuel costs rise. One important point of lost thermal energy in standard furnaces is through flue gas. One means to recapture this lost thermal energy is through heating of the combustion gases, one or more of the fuel gas or the oxidizing gas, prior to combustion. As gases heat up, they expand which changes the pressure and the subsequent velocity of the gas flow. This change can affect the proper mixture of the gases and subsequent burn in the furnace.
Embodiments described herein teach the method and apparatus for controlling jet velocity using a temperature-sensitive bimetallic valve. By redirecting the flow based on a temperature gradient, proper jet velocity at the burner can be maintained using high temperatures or standard temperature gases without the inherent dangers of manual manipulation of a valve.
While the foregoing is directed to embodiments of the present invention, other and further embodiments of the invention may be devised without departing from the basic scope thereof, and the scope thereof is determined by the claims that follow.
