Patent Application
20140186781
1. Field of the Invention
Embodiments described herein generally relate 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 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 control of jet velocity during burner operations based on temperature.
The embodiments of the invention described herein generally relate 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 magnetic valve in connection with one of the source of oxidizing gas or the source of fuel gas, the valve comprising a curie material, a magnet, 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 curie material from a second temperature to the first temperature; change position of the curie material, as measured from the flow control structure or the magnet, 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 curie material; and a burner configured to receive an oxidizing gas or a fuel gas from the at least one temperature-sensitive magnetic 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 magnetic valve at a first temperature, the temperature-sensitive magnetic valve comprising a magnet, a curie material, a blocking device and a flow control structure; transferring heat from the oxidizing gas or the fuel gas to the curie material, wherein the curie material changes from a second temperature to the first temperature; changing the position of the curie material, as measured from the flow control structure or the magnet, 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 magnetic 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 curie material.
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, apparatus and systems for controlling gas flow 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, apparatus 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 site of combustion to reduce the reactant energy input required for the overall process. To maintain gas flow in the heated combustion reactants, a temperature-sensitive magnetic valve can be positioned between the gas source and the jet. The temperature-sensitive magnetic valve can control flow of the combustion reactants to the jet, thus allowing for an optimal gas flow rate for both heated and cooled gases, based on the temperature delivered to the valve. The embodiments of the invention disclosed herein are more clearly described with reference to the figures below.
The temperature-sensitive magnetic 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 magnetic 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 magnetic 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 magnetic valve 110a and 110b. The gases, either the fuel gas or the oxidizing gas, will equilibrate temperature with the temperature-sensitive magnetic 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 magnetic valves 110a and 110b to shift from a first state to a second state base on reaching a threshold or curie temperature. When the temperature-sensitive magnetic valves 110a and 110b shifts from the first state to the second state, 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 magnetic valves 110a and 110b. In this embodiment, the oxidizing gas is delivered through the temperature-sensitive magnetic valve 110a to the first oxidizing gas pipe 112 and the fuel gas is delivered through the temperature-sensitive magnetic valve 110b to the second fuel gas pipe 118. The temperature-sensitive magnetic valves 110a and 110b have a first state and a second state. The temperature-sensitive magnetic valve 110a is depicted in the first state based on receiving a standard temperature oxidizing gas. The standard temperature oxidizing gas does not have significant thermal energy to transfer to the temperature-sensitive magnetic valve 110a, thus the temperature-sensitive magnetic valve 110a remains in the first state. The first state of the temperature-sensitive magnetic 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 magnetic valve 110b is depicted in the second state based on receiving a heated fuel gas. The heated fuel gas heats the temperature-sensitive magnetic valve 110a as it flows in from the fuel gas line 108, thus the temperature-sensitive magnetic valve 110a switches to a second state when the magnet releases the curie material. The second state of the temperature-sensitive magnetic 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 magnetic 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 magnetic 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 magnetic 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 there are numerous permutations of controlling velocity of a gas using a magnetic device as disclosed in the embodiments 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 203 of the temperature-sensitive magnetic valve 200. The valve chamber 203 can be fluidly sealed providing for the controlled flow of the gases, which flow through the aperture 202 from the gas container. The valve chamber 203 should 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 203 is shown as a square structure, this is not intended to be limiting of the possible embodiments. For example, the valve chamber 203 can be square, rectangular, cylindrical, circular, or combinations of those shapes.
The temperature-sensitive magnetic valve 200 can have a flow control structure 204. The flow control structure 204 can be fluidly connected to the aperture 202 to control flow of gas through the temperature-sensitive magnetic valve 200. The flow control structure 204 can include one or more walls which prevent flow in one or more directions, such as through ports 205a and 205b. The walls of the flow control structure 204 can be of any shape based on the shape of the valve chamber 203. The flow control structure 204 can be composed of various materials dependant on the needs of the user, the flow design and the gas being used. In one embodiment, the flow control structure 204 is composed of the same material as the valve chamber 203.
The temperature-sensitive magnetic valve 200 can further comprise a curie material 208. The curie material 208 is a ferromagnetic material which becomes paramagnetic at a specific temperature, known as the curie temperature. The curie temperature of a substance is dependent upon the composition of the substance. In one or more embodiments, the curie material 208 is primarily nickel, which has a curie temperature of 358° C. In one embodiment, the curie material 208 is a nickel alloy which contains more than 95% nickel, such as nickel alloy 200. The curie material 208 can be of any composition which has a curie temperature in the desired range. In embodiments of the present invention which use oxygen or natural gas, the desired curie temperature for the curie material 208 can be between 300° C. and 400° C. Further embodiments may include other temperatures, even temperatures below room temperature, for which a low curie temperature is desirable.
The temperature-sensitive magnetic valve 200 can further comprise a blocking device 206. The blocking device 206 can be in contact with an opening in the flow control structure 204, such as ports 205a and 205b, to prevent flow through the opening. The blocking device 206 can be of the same composition as the flow control structure 204 or valve chamber 203. The blocking device 206 may be made of the same material as the curie material 208 or a different material which is suitable for contact with the temperatures of the gases and the chemistry of the gases, which are flowed therein.
The temperature-sensitive magnetic valve 200 can further include a magnet 210. The magnet 210 can be positioned in proximity of the curie material 208. The magnet 210 can be of a standard composition for a high temperature magnet, such an AlNiCo magnet. Though shown here as internal to the flow control structure 204, the magnet 210 can be positioned either internal, external or as part of the flow control structure 204. Further, the magnet 210 can be an electromagnet or a permanent magnet. In embodiments described here, the magnet 210 is shown as a permanent magnet.
In operation, as shown in
The heated embodiment is shown in
Designs herein generally rely on one or more sources of force to actuate between the first state and the second state. When the curie material 208 reaches the curie temperature, the magnet 210, which acts as the first source of force, no longer holds it in place. The second source of force, in the absence of the first source of force, moves the curie material 208 and the blocking device 206 to a second state. Examples of the second source of force can include springs, gravity, pressure (such as dynamic or differential static pressures) or even additional magnets (such as magnets acting on a different section, a different material e.g. carbon steel, or with a different strength).
As gas flows through the temperature-sensitive magnetic valve 200, the curie material equilibrates to the temperature of the gas, as shown in
Without intending to be bound by theory, most simple designs utilize actuation that moves a single component only a few millimeters due to the limited range of the magnetic field. As such, several magnets can be “cascaded” to increase the range of movement. Advantageously, it is believed to be possible to move the actuator a much greater distance using cascaded magnets. A curie material can only travel a certain distance relative to a fixed magnet. Thus by using more than one magnet with at least one intermediate magnet which is not stationary, the overall travel distance can be increased. Further, the valve could be gradually closed using a multiple magnet design. If oriented properly or composed of curie materials with separate curie temperatures, the individual curie materials used for actuation would reach the threshold temperature at different rates. This is believed to create a time delay between when the preheated gas is delivered and when the curie material actually heats up sufficiently. The time delay can be based on convective heat transfer which itself depends on material properties and flow dynamics/geometry (which can be altered between components to achieve different delays). One skilled in the art will understand that there are various permutations of the cascading design which can be employed without diverging from the invention described herein. Possible designs include any design which maintains the same flame shape and flame size using both standard temperature gases and heated gases for the jet produced by the burner.
In
The heated state, or second state, is shown in
The curie material 234a and the blocking device 234b can be composed of the same material or separate materials. As only the curie material 234a needs to be composed of a temperature-sensitive substance, the composition of the blocking device 234b beyond pivot 237 can be different from the curie material 234a before pivot 237, as measured from the magnet 236. For example, the composition of blocking device 234b beyond an imaginary line 239 can be a material which is more or less dense than the composition of curie material 234a. The imaginary line 239 need not be positioned at the pivot 237 and the separation between the curie material 234a and the blocking device 234b can be at any point along the combination.
In the embodiments described above, rotating pieces are generally avoided for simplicity and to cut down on excess friction. However, one or more embodiments can employ rotating components or be adapted to use rotating components, as shown in the exemplary embodiment of
When a preheated gas flows into the valve chamber, the curie material 240 can begin to heat up, described with reference to
When a preheated gas flows into the valve chamber 250, shown in
As stated with reference to other embodiments, curie materials 254a and 254b may be of the same composition as one another, the same composition as the blocking device 256 or of different compositions based on the needs of the user. The imaginary lines 255a and 255b are positioned for exemplary purposes and the imaginary lines 255a and 255b between the curie materials 254a and 254b and the blocking device 256 may be more or fewer than two, may be in different positions than shown or may not exist, in one or more embodiments.
When a preheated gas flows into the valve chamber 260 described with reference to
The protective cover 265 is positioned to allow the magnetic field of the magnet 264 to be delivered to the curie material 266, while protecting the magnet 264 from the gas delivered to the valve chamber 261. The protective cover 265 can be formed of a ferromagnetic material which does not degrade in the operative environment, such as nickel or Inconel. Further, the protective cover may be a magnet itself, such as an AlNiCo magnet. The protective cover can allow stronger magnets which are not optimal for the conditions of the tube, for example magnets which are sensitive to temperatures or gases, to be used in the temperature-sensitive magnetic valve 200.
Insulation may also be used to isolate the magnet 264, in one or more embodiments described above, from the high temperatures or certain chemistries. For example, a very thin vacuum insulated housing may protect the magnet 264 from excess heat. Passive or active convective/conductive cooling may be utilized to keep the magnet cool, relying on other cooler process flows in the vicinity of the magnet 264. Of note, most magnets of useful size only have a field that will attract objects within a few millimeters. Thus, the amount and type of insulation used should take account of the limited range for these magnets. The insulation used to isolate the magnet 264 can be less than 10 mm.
Most designs are depicted with one magnet for simplicity purposes only. Other designs may include one or more magnets, in one or more positioning and orientations based on the needs of the user and the design of the valve, without diverging from the scope of the invention described herein. In one embodiment, additional magnets 264 could be employed for increasing the overall field strength, such as magnets oriented to create a field in the same direction, whether in series or in parallel. In another embodiment, additional magnets can be employed to achieve a more complex motion of the actuated pieces, such as magnets aligned perpendicularly to allow for a two-step series of motion below the curie temperature. In another embodiment, additional magnets can be “staged” in such a way that they actuate at slightly different times due to different heating rates. In another embodiment, additional magnets and additional curie materials can be staged so as to increase the distance travelled.
The method 300 begins at step 302 by flowing an oxidizing gas or a fuel gas into a temperature-sensitive magnetic valve at a first temperature and a first velocity, the temperature-sensitive magnetic valve comprising a magnetic 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 magnetic valve. In standard embodiments, the gas will enter at one velocity and exit at a predetermined velocity based on a change in port size between the first state and the second state. 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 magnetic 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 magnetic strip in the temperature-sensitive magnetic valve. As the gases flow into the temperature-sensitive magnetic 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 magnetic valve. The temperature-sensitive magnetic 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 magnetic valve, the components of the temperature-sensitive magnetic valve including the curie material will change from the second temperature to the first temperature.
At step 306, the position of the curie material can change as measured from the flow control structure or the magnet, in response to the change in temperature from the second temperature to the first temperature. As the curie material changes from the second temperature to the first temperature, the curie material can lose magnetic properties and no longer be attracted to the magnet. At this point a second force, such as a spring or gravity can overcome the magnetic attraction between the magnet and the curie material thus shifting the temperature sensitive magnetic valve from a first state to a second state. Based on the change in the curie material, the size of the port or the port itself for delivery of the gas through the temperature-sensitive magnetic valve to the burner can change. The goal of either the size change 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 magnetic valve. Using the magnetic 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 magnetic valve to the burner at a second velocity. In this embodiment, the temperature of the gas affects the position of the curie material in the temperature-sensitive magnetic valve. By changing the curie material position in the temperature-sensitive magnetic valve, the port is changed or 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 magnetic valve shifts based on the curie temperature between a first state and a second state, 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 curie material 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 the curie material positioned proximate, but thermally isolated from, the gas, such that the curie material is not directly subject to the heat or chemistry of the gas. The curie material loses magnetic attraction based on the temperature change. A mechanical connection can then transmit the action of the curie material back to the blocking device and the flow control structure to redirect the process flow.
Embodiments described herein relate to automated control of the jet velocity of a gas based on temperature. Recovery of lost thermal energy is becoming more important as fuel costs rise. One important source 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 to the burner. This change can affect the flame size and shape as delivered through the burner to the furnace.
Embodiments described herein teach methods and systems for controlling jet velocity using a temperature-sensitive magnetic valve. By redirecting the flow based on a threshold temperature, flame size and shape can be maintained using high temperature gases and 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.
