US20090087801A1 - System and Method for Superadiabatic Counterflow Reactor - Google Patents

System and Method for Superadiabatic Counterflow Reactor Download PDF

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US20090087801A1
US20090087801A1 US12/282,020 US28202007A US2009087801A1 US 20090087801 A1 US20090087801 A1 US 20090087801A1 US 28202007 A US28202007 A US 28202007A US 2009087801 A1 US2009087801 A1 US 2009087801A1
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channel
mixture
channels
fuel
burner
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Ingmar M. Schoegl
Janet L. Ellzey
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University of Texas System
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    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F23—COMBUSTION APPARATUS; COMBUSTION PROCESSES
    • F23C—METHODS OR APPARATUS FOR COMBUSTION USING FLUID FUEL OR SOLID FUEL SUSPENDED IN  A CARRIER GAS OR AIR 
    • F23C99/00—Subject-matter not provided for in other groups of this subclass
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F23—COMBUSTION APPARATUS; COMBUSTION PROCESSES
    • F23C—METHODS OR APPARATUS FOR COMBUSTION USING FLUID FUEL OR SOLID FUEL SUSPENDED IN  A CARRIER GAS OR AIR 
    • F23C3/00—Combustion apparatus characterised by the shape of the combustion chamber
    • F23C3/002—Combustion apparatus characterised by the shape of the combustion chamber the chamber having an elongated tubular form, e.g. for a radiant tube
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F23—COMBUSTION APPARATUS; COMBUSTION PROCESSES
    • F23C—METHODS OR APPARATUS FOR COMBUSTION USING FLUID FUEL OR SOLID FUEL SUSPENDED IN  A CARRIER GAS OR AIR 
    • F23C2900/00—Special features of, or arrangements for combustion apparatus using fluid fuels or solid fuels suspended in air; Combustion processes therefor
    • F23C2900/03002—Combustion apparatus adapted for incorporating a fuel reforming device

Definitions

  • the present disclosure relates in general to combustion processes, and more particularly to a system and method for superadiabatic counterflow reactors.
  • Recirculation of heat concentrates the energy such that local temperatures can exceed the adiabatic flame temperature by a significant amount. Such temperature may be called superadiabatic combustion.
  • Superadiabatic combustion may significantly broaden conventional flammability limits. Without such recirculation, operation outside of the conventional flammability limits (e.g., ultra-lean or ultra-rich mixtures) often fails because the energy content of the reactants is not sufficient to sustain a free flame.
  • various systems and methods may provide superadiabatic combustion in a counterflow reactor.
  • fuel/oxidizer mixtures may be reacted in channels in a counterflow arrangement so that heat from one channel preheats the gas in the neighboring channel.
  • a system for reacting fuel and oxidizer mixtures may be provided.
  • the system may include a first channel configured to communicate gas in a first direction, a second channel configured to communicate gas in a second direction substantially opposite the first direction, a first heat source positioned such that gas flowing through the first channel preheats gas in the second channel, and a second heat source positioned such that gas flowing through the second channel preheats gas in the first channel.
  • a method for reacting a fuel and oxidizer mixture may be provided.
  • the method may include communicating gas to a first channel in a first direction, simultaneously communicating gas to a second channel in a second direction substantially opposite the first direction, heating the gas in the first channel with a first heat source positioned such that gas flowing through the first channel preheats gas in the second channel and heating the gas in the second channel with a second heat source positioned such that the gas flowing through the second channel preheats gas in the first channel.
  • a system for reacting a fuel and oxidizer mixture may be provided.
  • the system may include a means for communicating first gas in a first direction, a means for communicating a second gas in a second direction substantially opposite the first direction, a means for heating the first gas positioned such that the first gas preheats the second gas, and a means for heating the second gas positioned such that the second gas preheats the first gas.
  • FIG. 1 illustrates a block diagram of a reaction system for a mixture of fuel and oxidizer in accordance with teachings of the present disclosure
  • FIG. 2A illustrates an example porous burner for combustion of a mixture of fuel and oxidizer in accordance with teachings of the present disclosure
  • FIG. 2B illustrates an example co-flow burner for combustion of a mixture of fuel and oxidizer in accordance with teachings of the present disclosure
  • FIG. 2C illustrates an example counter-flow burner for combustion of a mixture of fuel and oxidizer in accordance with teachings of the present disclosure
  • FIG. 3A illustrates an example system for use in the combustion of a mixture of fuel and oxidizer in accordance with teachings of the present disclosure
  • FIG. 3B illustrates an example system for use in the combustion of a mixture of fuel and oxidizer in accordance with teachings of the present disclosure
  • FIG. 4 illustrates a flowchart of a method for use in for combustion of a mixture of fuel and oxidizer in accordance with teachings of the present disclosure.
  • FIGS. 1 through 4 Preferred embodiments and their advantages are best understood by reference to FIGS. 1 through 4 , wherein like numbers are used to indicate like and corresponding parts.
  • combustion is described as a series of reactions between a fuel and an oxidant producing energy (e.g., heat and/or light).
  • energy e.g., heat and/or light
  • a typical example of combustion is a fire.
  • a mixture of a liquid fuel with an oxidant normally will not result in combustion unless the temperature of the mixture exceeds its flash point. From the other point of view, the flash point may be described as the minimum temperature at which enough of the fuel will evaporate to form a combustible mixture.
  • a combustion process preferably results in the conversion of a large portion of the chemical energy of the fuel into thermal energy (e.g., heat).
  • FIG. 1 illustrates a block diagram of a reaction system for a mixture of fuel and oxidizer in accordance with teachings of the present disclosure.
  • reactor 4 may receive input from heat source 1 , fuel 2 , and oxidizer 3 . As a result of the reaction, reactor 4 may produce exhaust 5 .
  • Reactor 4 may include any system or apparatus configured to accept heat source 1 , fuel 2 , and oxidizer 3 and combine them in an appropriate manner.
  • Reactor 4 may include any system or apparatus configured to communicate exhaust 5 away from reactor 4 .
  • reactor 4 may include burners, fluid channels, a combustion chamber, or other features and/or components.
  • Heat source 1 may include any source of thermal energy configured to communicate thermal energy to reactor 4 or any components therein.
  • heat source 1 may include flame.
  • heat source 1 may include an electric spark, and/or any other appropriate source of thermal energy operable to raise the temperature of fuel 2 and oxidizer 3 to the flash point (and/or above the flash point) of fuel 2 .
  • Fuel 2 may include any material that is capable of releasing energy when its chemical or physical structure is altered through combustion.
  • fuel 2 may include hydrocarbons (e.g., gasoline, diesel, petroleum, natural gas, and/or combinations or mixtures including hydrocarbons).
  • Oxidizer 3 may include any oxidizing agent (e.g., oxidant and/or oxidizer).
  • oxidizer 3 may include room air or ambient air.
  • oxidizer 3 may include a more specific combination or mixture configured to provide an oxidizing agent to a combustion process (e.g., ozone, sulfoxides, nitrous oxide, and/or any other oxidizing agent).
  • Exhaust 5 may include any material resulting from use of the reaction system depicted in FIG. 1 .
  • exhaust 5 may include water vapor and carbon dioxide.
  • exhaust 5 may include any combustion product, byproduct, excess oxidizer 3 and/or incompletely oxidized fuel 2 .
  • Complete combustion although not achieved in typical practice, refers to the conceptual complete oxidation of fuel 2 . That is, fuel 2 may be completely converted to its constituent products and its entire reserve of chemical energy may be converted into thermal energy. Any deviation from complete combustion may result in an increase in byproducts and incompletely oxidized fuel 2 . A suboptimal mixture of fuel 2 and oxidizer 3 may result in deviation from complete combustion. In extreme cases, a mixture of fuel 2 and oxidizer 3 in some proportions may not result in combustion at all. Operation outside of the conventional flammability limits (e.g., ultra-lean (too little fuel 2 ) or ultra-rich (too much fuel 2 ) mixtures) often fails because the energy content of fuel 2 and oxidizer 3 is not sufficient to sustain a free flame.
  • ultra-lean too little fuel 2
  • ultra-rich too much fuel 2
  • fuel reforming One process of stripping hydrogen from a fuel-rich hydrocarbon/air mixture is referred to as fuel reforming.
  • Some methods for accomplishing fuel reforming include the use of catalysts to enhance the reaction rates. Catalysts, however, are subject to poisoning by sulfur compounds occurring in many fuels (e.g., catalyst ageing). In addition to problems with catalyst ageing, catalytic surfaces add substantially to the cost of the reactor.
  • Another approach may include use of a porous reactor including a porous matrix without a catalytic surface. In such a porous reactor, gas phase reactions dominate the chemistry and, therefore, surface poisoning is not an issue.
  • a conventional inert reactor may consist of a single tube of porous media.
  • Some fuel reforming techniques without catalysts include the propagation of rich combustion waves (filtration waves) in the direction of the exit of the porous channel. Such propagation may inhibit continuous operation of the combustor.
  • One technique to overcome such an inhibition may include cyclical reversal of the fuel flow direction. This technique may successfully hold the combustion zone inside the reactor but, however, significantly complicates the reactor design.
  • Another technique includes establishment of a stationary combustion front at the interface between an upstream small pore section and a downstream large pore section. Although the latter technique may address the propagation problem previously discussed, reactors embodying this technique have been observed to limit the peak temperatures in the reaction zone close to the adiabatic flame temperature previously discussed.
  • Fuel cell systems are considered likely to be appropriate for transportation purposes and small-scale power generation devices. Conversion efficiencies of fuel cells are not limited by the Carnot cycle and thus promise higher energy efficiencies than conventional combustion engines.
  • Current fuel cells technologies are highly specific to a small variety of fuel types, with hydrogen representing the most common energy source. Inside a fuel cell, hydrogen and atmospheric oxygen react to form water in an electrochemical process and thus generate electricity without potentially polluting emissions. While substances containing hydrogen are extremely abundant, hydrogen itself is not naturally available in molecular form and thus has to be extracted from water, ammonia, fossil hydrocarbon fuels or renewable energy sources (e.g. ethanol and biodiesel).
  • TD and SR are endothermic processes and require external energy sources
  • pox is exothermic and thus a self-sustaining process.
  • ATR uses the reactions of SR and can be performed nearly thermoneutral in a single reactor design (e.g., Christensen and Primdahl, 1994), or a counterflow reactor design (e.g., Frauhammer et al., 1999).
  • Most current reforming technologies use catalysts to promote the conversion of hydrocarbons to syngas.
  • FIGS. 2A , 2 B and 2 C illustrate some embodiments of burners that may be used to react fuel and oxidizer mixtures in accordance with teachings of the present disclosure.
  • a mixture of fuel and oxidizer may flow through a channel or channels in the direction shown by arrows.
  • a reactor including burners in accord with the depictions in FIGS. 2A , 2 B, and 2 C may include additional features or components (not expressly shown) to deliver and/or premix fuel and oxidizer, to provide a heat source to the mixture of fluid and oxidizer, or perform any other functions appropriate to facilitate combustion of the mixture.
  • FIG. 2A depicts a conventional porous burner 10 in section which may be used in an inert reactor to avoid problems associated with catalysts, as described above.
  • Burner 10 may be generally configured to facilitate combustion of fuel 2 and oxidizer 3 .
  • burner 10 may include outer wall 12 for containing inlet mixture 16 of fuel 2 and oxidizer 3 , and porous matrix 14 for maintaining the mixture of fuel 2 and oxidizer 3 in a largely gaseous phase.
  • Burner 10 may be configured to accept inlet mixture 16 and reject exhaust 18 .
  • burner 10 may include multiple outer walls 12 and porous matrices 14 arranged in series and/or in parallel.
  • Outer wall 12 may include any device or feature of burner 10 configured to contain mixture 16 of fuel 2 and oxidizer 3 and/or channel mixture 16 from one end of burner 10 to the other.
  • outer wall 12 may define a fluid channel configured to channel mixture 16 from one end of burner 10 to the other.
  • outer wall 12 may define a round tube, a square tube, an array of fluid channels and/or any combination of the above.
  • Outer wall 12 may have any surface features appropriate for channeling mixture 16 , including a smooth wall and/or selected textures.
  • Outer wall 12 may be formed of any material appropriate for channeling mixture 16 .
  • outer wall 12 may be formed of an inert material (e.g., formed of some material unaffected by the desired combustion process).
  • Porous matrix 14 may include any device or feature of burner 10 configured to provide reduced flow apertures for mixture 16 .
  • porous matrix 14 may be configured to result in atomization of mixture 16 .
  • the conversion of liquid fuel into a spray or mist e.g., by atomization
  • may increase the efficiency of a combustion process e.g., by reducing the flash point, by better mixing fuel 2 and oxidizer 3 and/or other physical or chemical effects).
  • Inlet mixture 16 may include any mixture of fuel 2 and oxidizer 3 configured to react or combust as desired in reactor 4 as previously discussed in relation to FIG. 1 .
  • inlet mixture 16 may include hydrocarbons contained in fuel 2 and oxygen contained in room air or oxidizer 3 .
  • Exhaust 18 may include any combustion product, byproduct, excess oxidizer 3 and/or incompletely oxidized fuel 2 .
  • Porous burners such as that depicted in FIG. 2A , are characterized by a stationary reaction zone inside porous matrix 14 .
  • the portion of porous matrix 14 upstream of the reaction zone may be heated by radiation between its surfaces as well as conduction from the hot region downstream of the reaction zone.
  • incoming mixture 16 may be preheated by both convection and radiation from porous matrix 14 as mixture 16 travels through the interstitial spaces of porous matrix 14 . Such preheating may result in local heat recirculation and increased firing rates.
  • FIG. 2B depicts in cross-section an example co-flow burner 20 for combustion of a mixture of fuel and oxidizer in accordance with teachings of the present disclosure.
  • Co-flow burner 20 may be generally configured to facilitate combustion of fuel 2 and oxidizer 3 .
  • co-flow burner 20 may include inner wall 21 for separating two or more gas flows, outer walls 22 , and fluid channels 24 for containing inlet mixture 26 of fuel 2 and oxidizer 3 .
  • Co-flow burner 20 may be configured to accept inlet mixture 26 and reject exhaust 28 .
  • co-flow burner 20 may include multiple outer walls 22 and fluid channels 24 arranged in series and/or in parallel.
  • Inner wall 21 may include any device or feature of co-flow burner 20 configured to separate two or more gas flows.
  • inner wall 21 may be configured to separate inlet mixture 26 into two or more streams.
  • inner wall 21 may be configured to separate inlet mixture 26 into substantially equal streams (e.g., equal volume flow rate, mass flow rate, and/or equal volume) or may be configured to separate inlet mixture 26 without regard to the amount of inlet mixture 26 in each stream.
  • inner wall 21 may define part of a round tube, a square tube, an array of fluid channels and/or any combination of the above.
  • Inner wall 21 may have any surface features appropriate for channeling mixture 26 , including a smooth wall and/or selected textures.
  • Inner wall 21 may be formed of any material appropriate for channeling mixture 26 .
  • inner wall 21 may be formed of an inert material (e.g., formed of some material unaffected by the desired combustion process).
  • inner wall 21 may be configured to serve as the separator for more than two fluid streams.
  • Outer wall 22 may include any device or feature of co-flow burner 20 configured to contain mixture 26 of fuel 2 and oxidizer 3 and/or channel mixture 26 from one end of co-flow burner 20 to the other.
  • outer wall 22 may, in part, define fluid channel 24 configured to channel mixture 26 from one end of co-flow burner 20 to the other.
  • outer wall 22 may define a round tube, a square tube, an array of fluid channels and/or any combination of the above.
  • Outer wall 22 may have any surface features appropriate for channeling mixture 26 , including a smooth wall and/or selected textures.
  • Outer wall 22 may be formed of any material appropriate for channeling mixture 26 .
  • outer wall 22 may be formed of an inert material (e.g., formed of some material unaffected by the desired combustion process).
  • Fluid channels 24 may include any device or feature of co-flow burner 20 configured to channel inlet mixture 26 through co-flow burner 20 from one end to the other. In some embodiments, such as that shown in FIG. 2B , fluid channels 24 may be formed between inner walls 21 and outer walls 22 . Although pictured as a straight path in FIG. 2B , fluid channels 24 may include any path, whether straight or tortuous. In some embodiments, fluid channels 24 may include varying cross-sectional shapes and/or areas.
  • Inlet mixture 26 may include any mixture of fuel 2 and oxidizer 3 configured to react or combust as desired in reactor 4 as previously discussed in relation to FIG. 1 .
  • inlet mixture 26 may include hydrocarbons contained in fuel 2 and oxygen contained in room air or oxidizer 3 .
  • Exhaust 28 may include any combustion product, byproduct, excess oxidizer 3 and/or incompletely oxidized fuel 2 .
  • FIG. 2C depicts an example counter-flow burner 30 for combustion of a mixture of fuel and oxidizer in cross-section in accordance with teachings of the present disclosure.
  • Counter-flow burner 30 may be generally configured to facilitate combustion of fuel 2 and oxidizer 3 .
  • counter-flow burner 30 may include inner wall 31 for separating two or more gas flows, outer walls 32 , and fluid channels 34 for containing inlet mixture 36 of fuel 2 and oxidizer 3 .
  • Counter-flow burner 30 may be configured to accept inlet mixture 36 and reject exhaust 38 .
  • counter-flow burner 30 may include multiple outer walls 32 and fluid channels 34 arranged in series and/or in parallel.
  • Inner wall 31 may include any device or feature of counter-flow burner 30 configured to separate two or more gas flows and communicate the two or more flows in substantially opposing directions.
  • inner wall 31 may define part of a round tube, a square tube, an array of fluid channels and/or any combination of the above.
  • Inner wall 31 may have any surface features appropriate for channeling mixture 36 , including a smooth wall and/or selected textures.
  • Inner wall 31 may be formed of any material appropriate for channeling mixture 36 .
  • inner wall 31 may be formed of an inert material (e.g., formed of some material unaffected by the desired combustion process).
  • inner wall 31 may be configured to serve as the separator for more than two fluid streams.
  • Outer wall 32 may include any device or feature of counter-flow burner 30 configured to contain mixture 36 of fuel 2 and oxidizer 3 and/or channel mixture 36 from one end of co-flow burner 30 to the other.
  • outer wall 32 may, in part, define fluid channels 34 configured to channel mixture 36 from one end of counter-flow burner 30 to the other.
  • outer wall 32 may define one or more round tubes, square tubes, an array of fluid channels and/or any combination of the above.
  • Outer wall 32 may have any surface features appropriate for channeling mixture 36 , including a smooth wall and/or selected textures.
  • Outer wall 32 may be formed of any material appropriate for channeling mixture 36 .
  • outer wall 32 may be formed of an inert material (e.g., formed of some material unaffected by the desired combustion process).
  • Fluid channels 34 may include any device or feature of counter-flow burner 30 configured to channel inlet mixture 36 through counter-flow burner 30 from one end to the other. In some embodiments, such as that shown in FIG. 2C , fluid channels 34 may be configured to communicate inlet mixture 36 in at least two streams. In such embodiments, the at least two streams of inlet mixture 36 may be disposed to flow in substantially opposite directions. When two streams are so disposed, they may be described as counter-flow. Fluid channels 34 may be formed between inner walls 31 and outer walls 32 . Although pictured as a straight path in FIG. 2C , fluid channels 34 may include any path, whether straight or tortuous. In some embodiments, fluid channels 34 may include varying cross-sectional shapes and/or areas.
  • Inlet mixture 36 may include any mixture of fuel 2 and oxidizer 3 configured to react or combust as desired in reactor 4 as previously discussed in relation to FIG. 1 .
  • inlet mixture 36 may include hydrocarbons contained in fuel 2 and oxygen contained in room air or oxidizer 3 .
  • Exhaust 38 may include any combustion product, byproduct, excess oxidizer 3 and/or incompletely oxidized fuel 2 .
  • FIGS. 3A and 3B depict cross-sectional views of some embodiments of burner configurations that may be used to react fuel and oxidizer mixtures in accordance with teachings of the present disclosure.
  • a mixture of fuel and oxidizer may flow through a channel or channels in the direction shown by arrows.
  • a reactor including burners in accord with the depictions in FIGS. 3A and 3B may include additional features or components (not expressly shown) to deliver and/or premix fuel and oxidizer, to provide a heat source to the mixture of fluid and oxidizer, or perform any other functions appropriate to facilitate combustion of the mixture.
  • a process of fuel reforming may include recirculation of heat generated during the combustion process. Recirculation of heat concentrates the energy such that local temperatures can exceed the adiabatic flame temperature by a significant amount. Such temperature may be called superadiabatic combustion. Superadiabatic combustion may significantly broaden conventional flammability limits (e.g., allow combustion when the mixture of fuel 2 and oxidizer 3 includes too much or too little fuel 2 for conventional combustion).
  • Internal and/or external heat recirculation may be used to raise the temperature level of the reaction to a level that is sufficient for a self sustained reaction. If the mixture of fuel 2 and oxidizer 3 includes too little fuel 2 (i.e., ultra-lean), superadiabatic combustors may be used as a thermal oxidizer, where high temperatures facilitate the combustion of mixtures with sparse amounts of fuel 2 . If the mixture of fuel 2 and oxidizer 3 includes too much fuel 2 (i.e., ultra-rich), the high temperatures inside reactor 4 promote the conversion of a rich hydrocarbon fuel/air mixture into H 2 , CO, CO 2 , H 2 O and other hydrocarbon species.
  • fuel 2 and oxidizer 3 includes too little fuel 2 (i.e., ultra-lean)
  • superadiabatic combustors may be used as a thermal oxidizer, where high temperatures facilitate the combustion of mixtures with sparse amounts of fuel 2 . If the mixture of fuel 2 and oxidizer 3 includes too much fuel 2 (i.e., ultra-
  • VOCs volatile organic compounds
  • FIG. 3A illustrates in cross-section an example system for use in the combustion of a mixture of fuel and oxidizer in accordance with teachings of the present disclosure including co-flow burner 20 .
  • Co-flow burner 20 may be generally configured to facilitate combustion of fuel 2 and oxidizer 3 .
  • co-flow burner 20 may include inner wall 21 for separating two or more gas flows, outer walls 22 , and fluid channels 24 for containing inlet mixture 26 of fuel 2 and oxidizer 3 .
  • Co-flow burner 20 may be configured to accept inlet mixture 26 and reject exhaust 28 .
  • co-flow burner 20 may include multiple outer walls 22 and fluid channels 24 arranged in series and/or in parallel.
  • Inner wall 21 may include any device or feature of co-flow burner 20 configured to separate two or more gas flows.
  • inner wall 21 may be configured to separate inlet mixture 26 into two or more streams.
  • inner wall 21 may be configured to separate inlet mixture 26 into substantially equal streams (e.g., equal volume flow rate, mass flow rate, and/or equal volume) or may be configured to separate inlet mixture 26 without regard to the amount of inlet mixture 26 in each stream.
  • inner wall 21 may define part of a round tube, a square tube, an array of fluid channels and/or any combination of the above.
  • Inner wall 21 may have any surface features appropriate for channeling mixture 26 , including a smooth wall and/or selected textures.
  • Inner wall 21 may be formed of any material appropriate for channeling mixture 26 .
  • inner wall 21 may be formed of an inert material (e.g., formed of some material unaffected by the desired combustion process).
  • inner wall 21 may be configured to serve as the separator for more than two fluid streams. Persons having ordinary skill in the art will appreciate that the specific features and characteristics of inner wall 21 (e.g., thermal conductivity and thickness) may serve to facilitate or restrict heat conduction between adjoining fluid channels 24 .
  • Outer wall 22 may include any device or feature of co-flow burner 20 configured to contain mixture 26 of fuel 2 and oxidizer 3 and/or channel mixture 26 from one end of co-flow burner 20 to the other.
  • outer wall 22 may, in part, define fluid channel 24 configured to channel mixture 26 from one end of co-flow burner 20 to the other.
  • outer wall 22 may define a round tube, a square tube, an array of fluid channels and/or any combination of the above.
  • Outer wall 22 may have any surface features appropriate for channeling mixture 26 , including a smooth wall and/or selected textures.
  • Outer wall 22 may be formed of any material appropriate for channeling mixture 26 .
  • outer wall 22 may be formed of an inert material (e.g., formed of some material unaffected by the desired combustion process).
  • Fluid channels 24 may include any device or feature of co-flow burner 20 configured to channel inlet mixture 26 through co-flow burner 20 from one end to the other. In some embodiments, such as that shown in FIG. 3A , fluid channels 24 may be formed between inner walls 21 and outer walls 22 . Although pictured as a straight path in FIG. 3A , fluid channels 24 may include any path, whether straight or tortuous. In some embodiments, fluid channels 24 may include varying cross-sectional shapes and/or areas.
  • Inlet mixture 26 may include any mixture of fuel 2 and oxidizer 3 configured to react or combust as desired in reactor 4 as previously discussed in relation to FIG. 1 .
  • inlet mixture 26 may include hydrocarbons contained in fuel 2 and oxygen contained in room air or oxidizer 3 .
  • Exhaust 28 may include any combustion product, byproduct, excess oxidizer 3 and/or incompletely oxidized fuel 2 .
  • combustion of inlet mixture 26 occurs at combustion zone 42 in each fluid channel 24 .
  • Combustion zone 42 for each fluid channel 24 may be defined as the location along the length of fluid channel 24 within which combustion of inlet mixture 26 begins and is completed. The location of combustion zone 42 may further serve to define upstream portion 46 (before inlet mixture 26 has reached combustion zone 42 ) and downstream portion 48 (as exhaust 28 leaves combustion zone 42 and travels out of burner 20 ).
  • combustion zone 42 in each fluid channel 24 may depend on a variety of conditions (e.g., the configuration of fluid channel 24 , the mass or volume flow rate of inlet mixture 26 , the fuel/oxidizer ratio in inlet mixture 26 , the inlet temperature of inlet mixture 26 , the amount of heat energy added to inlet mixture 26 , and/or any other relevant data).
  • combustion zone 42 in each fluid channel 24 may be aligned along the length of fluid channel 24 so as to be located at substantially the same position along the length of fluid channel 24 .
  • downstream portion 48 of each fluid channel 24 may be at a significantly higher temperature than upstream portion 46 .
  • heat transfer effects may conduct heat from downstream portion 48 to upstream portion 46 through inner wall 21 .
  • These potential heat transfer effects are represented by arrows 40 in FIG. 3A .
  • heat from downstream portion 48 may serve to preheat upstream portion 46 . This preheating may serve to allow the superadiabatic combustion discussed herein.
  • FIG. 3B depicts in cross-section an example counter-flow burner 30 for combustion of a mixture of fuel and oxidizer in accordance with teachings of the present disclosure.
  • Counter-flow burner 30 may be generally configured to facilitate combustion of fuel 2 and oxidizer 3 .
  • counter-flow burner 30 may include inner wall 31 for separating two or more gas flows, outer walls 32 , and fluid channels 34 for containing inlet mixture 36 of fuel 2 and oxidizer 3 .
  • Counter-flow burner 30 may be configured to accept inlet mixture 36 and reject exhaust 38 .
  • counter-flow burner 30 may include multiple outer walls 32 and fluid channels 34 arranged in series and/or in parallel.
  • Inner wall 31 may include any device or feature of counter-flow burner 30 configured to separate two or more gas flows and communicate the two or more flows in substantially opposing directions.
  • inner wall 31 may define part of a round tube, a square tube, an array of fluid channels and/or any combination of the above.
  • Inner wall 31 may have any surface features appropriate for channeling mixture 36 , including a smooth wall and/or selected textures.
  • Inner wall 31 may be formed of any material appropriate for channeling mixture 36 .
  • inner wall 31 may be formed of an inert material (e.g., formed of some material unaffected by the desired combustion process).
  • inner wall 31 may be configured to serve as the separator for more than two fluid streams. Persons having ordinary skill in the art will appreciate that the specific features and characteristics of inner wall 31 (e.g., thermal conductivity and thickness) may serve to facilitate or restrict heat conduction between adjoining fluid channels 34 a and 34 b.
  • Outer wall 32 may include any device or feature of counter-flow burner 30 configured to contain mixture 36 of fuel 2 and oxidizer 3 and/or channel mixture 36 from one end of co-flow burner 30 to the other.
  • outer wall 32 may, in part, define fluid channels 34 configured to channel mixture 36 from one end of counter-flow burner 30 to the other.
  • outer wall 32 may define one or more round tubes, square tubes, an array of fluid channels and/or any combination of the above.
  • Outer wall 32 may have any surface features appropriate for channeling mixture 36 , including a smooth wall and/or selected textures.
  • Outer wall 32 may be formed of any material appropriate for channeling mixture 36 .
  • outer wall 32 may be formed of an inert material (e.g., formed of some material unaffected by the desired combustion process).
  • Fluid channels 34 may include any device or feature of counter-flow burner 30 configured to channel inlet mixture 36 through counter-flow burner 30 from one end to the other. In some embodiments, such as that shown in FIG. 3B , fluid channels 34 may be configured to communicate inlet mixture 36 in at least two streams. In such embodiments, the at least two streams of inlet mixture 36 may be disposed to flow in substantially opposite directions. When two streams are so disposed, they may be described as counter-flow. Fluid channels 34 may be formed between inner walls 31 and outer walls 32 . Although pictured as a straight path in FIG. 3B , fluid channels 34 may include any path, whether straight or tortuous. In some embodiments, fluid channels 34 may include varying cross-sectional shapes and/or areas.
  • Inlet mixture 36 may include any mixture of fuel 2 and oxidizer 3 configured to react or combust as desired in reactor 4 as previously discussed in relation to FIG. 1 .
  • inlet mixture 36 may include hydrocarbons contained in fuel 2 and oxygen contained in room air or oxidizer 3 .
  • Exhaust 38 may include any combustion product, byproduct, excess oxidizer 3 and/or incompletely oxidized fuel 2 .
  • combustion of inlet mixture 36 occurs at combustion zone 42 in each fluid channel 34 .
  • Combustion zone 42 for each fluid channel 34 may be defined as the location along the length of fluid channel 34 within which combustion of inlet mixture 36 begins and is completed. The location of combustion zone 42 may further serve to define upstream portion 46 (before inlet mixture 36 has reached combustion zone 42 ) and downstream portion 48 (as exhaust 38 leaves combustion zone 42 and travels out of burner 30 ).
  • combustion zone 42 in each fluid channel 34 may depend on a variety of conditions (e.g., the configuration of fluid channel 34 , the mass or volume flow rate of inlet mixture 36 , the fuel/oxidizer ratio in inlet mixture 36 , the inlet temperature of inlet mixture 36 , the amount of heat energy added to inlet mixture 36 , and/or any other relevant data).
  • combustion zone 42 in each fluid channel 34 may be aligned along the length of fluid channel 34 so as to be located at some distance from one another along the length of fluid channels 34 .
  • downstream portion 48 of each fluid channel 34 when operated in accord with teachings of the present disclosure, may be at a significantly higher temperature than upstream portion 46 .
  • heat transfer effects may conduct heat from downstream portion 48 to upstream portion 46 through inner wall 31 .
  • this effect may include conduction from downstream portion 46 of fluid channel 34 to upstream portion 46 of fluid channel 34 .
  • first arrows 40 These potential heat transfer effects are represented by first arrows 40 .
  • operation of a counter-flow reactor in accordance with the present teachings may also provide that heat from downstream portion 48 of first fluid channel 34 a may conduct through inner wall 31 to upstream portion of second fluid channel 34 b .
  • second arrows 44 As shown in FIG. 3B , the effect of heat transfer at first arrows 40 and second arrows 44 may serve to allow the superadiabatic combustion discussed herein.
  • FIGS. 3A and 3B are only representative of the embodiments that may be useful in practicing the teachings of the present disclosure and persons having ordinary skill in the art may use the teachings of the present disclosure to design and/or operate reactors without some or all of the features disclosed herein.
  • Application of the teachings of the present disclosure provides that otherwise inflammable mixtures may be preheated to sufficiently high temperature levels that promote self-sustaining chemical reaction fronts without the need for a moving combustion zone.
  • FIG. 4 illustrates a flowchart of a method for use in for combustion of a mixture of fuel and oxidizer in a reactor 4 in accordance with teachings of the present disclosure.
  • method 100 may include steps to be completed simultaneously, or ongoing steps that may be performed in any sequence as long as the relevant durations overlap.
  • a user may communicate a first gas in a first channel.
  • the first gas may include any appropriate combination of fuel 2 and oxidizer 3 .
  • a user may communicate a second gas in a second channel.
  • the second gas may include any appropriate combination of fuel 2 and oxidizer 3 .
  • a user may heat the gas in the first channel and preheat the second gas.
  • the process of heating the gas in the first channel may include heating the gas above its flash point to facilitate combustion.
  • a user may heat the gas in the second channel and preheat the first gas.
  • the process of heating the gas in the second channel may include heating the gas above its flash point to facilitate combustion.
  • the working principle of superadiabatic combustion relies on convective heating of an otherwise inflammable fuel/air mixture to temperature levels at which self-sustained chemical reaction zones become feasible.
  • the overall system can be understood as filtration waves in opposing flow channels that interact over a dividing wall. Additionally, the porous matrix may enhance the heat transfer between the channels.
  • the combustion zones 42 in the individual fluid channels act as heat sources. As the gas in fluid channel 34 a passes from the inlet to combustion zone 42 it is preheated by the combustion products in adjoining fluid channel 34 b . Once reacted, exhaust 38 in fluid channel 34 a passes through a high temperature zone that is defined by the locations of combustion zones 42 in fluid channels 34 a and 34 b .
  • filtration waves are initiated at the fluid channel inlets.
  • This section considers fluid channels that include porous media therein. Initially, exhaust 38 heats the porous media downstream of combustion zone 42 , and the propagation of each front will be similar to a normal filtration wave. As the filtration waves travel downstream, the high temperature zones approach each other, and the two filtration waves start to interact. Once the tails of the high temperature zones have moved past combustion zones 42 , heat is transferred from exhaust 38 to unreacted inlet mixture 36 . Due to the heat transfer across inner wall 31 , the direction of wave propagation is reversed and the reaction zones move towards the channel inlets. The regions between channel inlet and respective combustion zone 42 form a balanced counterflow heat exchanger. Steady state conditions are reached whenever the temperature profile is fully established and the preheating increases the local flame speed to a level that balances the incoming flow.
  • the fully established temperature profile shows a plateau-like temperature distribution between the reaction zones, which is beneficial for fuel reforming applications.
  • Kinetic simulations reveal that conversion of methane to hydrogen occurs in a two-stage process of partial oxidation followed by steam reforming.
  • the reaction In the partial oxidation zone, the reaction is exothermic and methane is converted to hydrogen.
  • the reaction In the steam reforming zone, the reaction is endothermic. Hydrogen is produced through the reaction CH 4 +H 2 O ⁇ 3H 2 +CO in which water produced in the exothermic reaction reacts with unburned methane.
  • Heat source 1 is located in channel 34 a and heat source 2 is located in channel 34 b .
  • inlet mixture 36 passes towards the heat source in channel 34 a , its temperature increases.
  • heat is transferred to the inner wall 31 and subsequently to inlet mixture 36 in channel 34 b .
  • Inlet mixture 36 in channel 34 b is flowing in the opposite direction and undergoes the same processes.
  • Equations (1) through (3) denote gas and wall, respectively.
  • the parameters in the equation describe channel height d g , wall thickness d w , conductivities for gas k g and solid wall k w , densities for gas ⁇ g and wall ⁇ w , specific heat for gas c g and solid c w , as well as flow velocity ⁇ , heat addition Q, convective heat transfer coefficients to wall and environment, h w and h ⁇ as well as molecular gas diffusivity D g .
  • the axial coordinate of the channel x is resealed to the interval [ ⁇ 1,1]. Furthermore, the time t is non-dimensionalized by half of the residence time of the gas in the channels, the temperature T is normalized by the adiabatic heat addition and the concentration y is scaled to the initial concentration of the limiting species. Thus, the scaled variables become:
  • Equations (10) through (14) form a system of 5 nonlinear 2nd-order equations, which require 10 boundary conditions.
  • the equations can be solved for the half-length of the channels.
  • the boundary conditions are:
  • T f is the (maximum) flame temperature at the flame front and x f is the location of the flame front.
  • the validity of the approximation is limited to small deviations from the adiabatic case, ⁇ >>1 and (T f ⁇ T b )/T b ⁇ 1.
  • the overall problem can be split into two coupled problems that have to be solved iteratively:
  • Heat exchanger with point heat sources (macroscopic problem): Preheating and/or superadiabaticity is determined as a function of flow velocity and location/strength of the source. The strength of the source is treated as a parameter, and temperature and concentration distributions can be solved independently.
  • Flame sheet (microscopic problem): The strength of the source is determined as a function of initial temperature and flow velocity.
  • the gas temperatures decouple from the species concentrations and the equations characterizing the temperature inside the heat exchanger can be solved independently.
  • One example of typical solutions of the problem includes: the incoming stream is heated up by the hot gas in the adjacent channel until it reaches the location of the heat source, where the gradient flattens and a zone of high temperatures is maintained until the gas passes the location of the heat source in the opposing channel. The remaining stretch to the channel exit is used as a counter-flow heat exchanger to heat up the gas in the opposing channel.
  • the internal high temperature zone shows that the counter-flow heat exchanger concept is capable of concentrating energy in the central part of the channels.
  • the non-dimensional temperature ⁇ is an indicator of the enhancement or superadiabaticity of the maximum temperature. As noted above, for a single channel porous media reactor, superadiabatic temperatures are attainable only for the co-flowing case, i.e. the reaction wave is propagating downstream. In the counterflow design, temperatures above the adiabatic temperature rise are possible for stationary fronts as indicated by the fact that ⁇ is greater than 1 for many different combinations of parameters.
  • the superadiabaticity ⁇ is directly proportional to the strength of the heat source H/V Furthermore, an optimum Pe is observed for all locations of the heat source. For low Pe, external heat losses become dominant and decrease the local peak temperature. At high Pe, the gas flows out of the reactor before it is heated by the heat source.

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US12/282,020 2006-03-08 2007-03-08 System and Method for Superadiabatic Counterflow Reactor Abandoned US20090087801A1 (en)

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US10557391B1 (en) 2017-05-18 2020-02-11 Advanced Cooling Technologies, Inc. Incineration system and process

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