Patent Publication Number: US-2016245506-A1

Title: Gradual oxidation and multiple flow paths

Description:
RELATED APPLICATION 
     This application is a divisional of U.S. patent application Ser. No. 13/417,132, filed Mar. 9, 2012, which is hereby incorporated by reference in its entirety herein. 
    
    
     BACKGROUND 
     In some industrial processes such as power generation, steam generation, and thermally driven chemical processing, heat can be provided directly or indirectly by the combustion of high-energy-content (HEC) fuels, such as propane or natural gas. 
     Emissions from landfills and other sources of gas containing volatile organic compounds (VOCs) are considered pollutants. These waste streams often contain too little fuel to sustain combustion on their own. Some methods of disposing of VOC-containing waste streams use thermal oxidizers of the following types: (1) Fired- or supplemental-fired thermal oxidizers, (2) Catalytic thermal oxidizers, (3) Oxidizers with heat recovery, and (4) Regenerative thermal oxidizers (RTOs). 
     Fired- or supplemental-fired thermal oxidizers can include a burner, a residence chamber, a mixing chamber, and an exhaust stack.  FIG. 1-1A  illustrates a configuration wherein an air-fuel mixture  6  is provided to the burner  2  to create a continuous flame and the waste stream  7  is introduced into the flame and continues to oxide as the hot gases pass through the mixing chamber  3  and residence chamber  4 . If the waste stream  7  is within flammability limits, it may be directly combusted in the burner  2  in place of the air-fuel mixture  6 . The mixing chamber  3  is required if the waste stream and burner are separately supplied. The residence chamber  4  provides enough time to complete the oxidative chemical reactions. The exhaust stack  5  conveys the products of oxidation to the atmosphere. 
     Catalytic oxidizers, as shown in  FIG. 1-1B , avoid the creation of thermal NOx by keeping the oxidation reaction temperature low. A waste stream  7  containing VOCs is provided into a catalytic reaction chamber  8  having a large internal surface area coated with a catalyst. Catalytic materials include noble metals such as platinum, palladium, and iridium as well as, for certain VOCs, copper oxide, vanadium, and cobalt. The concentration of VOCs in the waste stream  7  must be low enough that the reaction temperatures will not exceed the catalyst maximum use temperature. The waste stream  7  typically has to be heated to a specific temperature range appropriate for the catalytic reactivity. 
     The use of a recuperator  9 , as shown in  FIG. 1-1C , can reduce the operating costs of fired thermal oxidizers and catalytic oxidizers. The exhaust from the reaction chamber  1 , which may be by way of example either of the systems of  FIG. 1-1A or 1-1B , is supplied to a high-temperature recuperator  9  to heat either the VOC-laden waste stream  7 , as shown in  FIG. 1-1C , or the separate combustion air-fuel mixture if supplied separately, as shown in  FIG. 1-1A . Use of a recuperator  9  can reduce or eliminate the need for supplemental fuel to heat the reactants to their oxidation temperature. 
     Lastly, RTOs can be used to oxidize VOCs. In an RTO, heat is stored on an intermediate heat sink material, usually a ceramic solid, for recovery during an alternate cycle. The cycle uses heat from a previously heated flow to preheat the VOC-laden waste stream to a higher temperature. If the temperature is sufficiently high, oxidation will take place due to autoignition, as discussed in greater detail later in the present disclosure. If the temperature is not high enough, supplemental firing from another fuel and air source may be required. The higher-temperature exhaust is then conveyed through a colder heat sink to capture the energy. 
     There are different approaches to achieve the cycling of the heat exchange material.  FIGS. 1-1D  illustrates a system using two regenerative oxidizers. In the depicted configuration, the waste stream  7  is introduced into hot regenerative oxidizer #1. The waste stream is heated as it passes through regenerative oxidizer #1, thereby incrementally cooling the heat sink material with the oxidizer #1 starting at the inlet. After the waste stream  7  autoignites, the hot exhaust gas exits from the oxidizer #1 and is provided to the inlet of oxidizer #2, thereby “regenerating” the stored thermal energy in the heat sink material in oxidizer #2. The oxidized waste stream cools as it passes through oxidizer #2. When oxidizer #2 is sufficiently heated, the system is reconfigured such that the flow from the waste stream  7  is provided to the inlet of oxidizer #2 and the exhaust from oxidizer #2 is provided to the inlet of oxidizer #1 to regenerate oxidizer #1. The process cycles between the two configurations so that the oxidizer that was previously cooled while heating the waste stream  7  is heated, and visa-versa. Some RTO designs make use of rotating hardware to variably change the flow streams between cycles or to move the regenerative oxidizers between cycles. Another approach is to use a single regenerative oxidizer but to reverse the flow direction for each cycle. One end of the oxidizer will be preheating while the other end is capturing heat after the oxidative reaction. The reversing of flow direction is necessary because the end of the oxidizer proximal to the inlet cools to the point where it can no longer heat the incoming waste stream  7  to a temperature that will initiate the reaction. 
     SUMMARY 
     In some circumstances, it is advantageous to dispose of low-energy-content (LEC) fuel, such as the methane that evolves from some landfills, while minimizing undesirable components such as carbon monoxide (CO) and NOx in the exhaust. In other circumstances, it is desirable to provide heat from a HEC fuel, such as propane, to drive an industrial process or generate power without creating these same undesirable components. To accomplish these operations, an air-fuel mixture formed from one or both of LEC and HEC fuels must reach a temperature that is high enough to convert the VOCs and hydrocarbons in the fuel to carbon dioxide (CO2) and water (H2O) while keeping the maximum temperature of the air-fuel mixture below the temperature at which thermal NOx will form. Any conventional open-flame combustion process is a candidate to be replaced by a process that reduces the formation of NOx compounds through a reduced-temperature oxidation process. 
     There also is a desire to utilize the energy that is otherwise wasted when an LEC fuel is simply being disposed of by being oxidized to convert the VOCs to CO2 and H2O. One of the drawbacks of existing power-generation systems driven by gas turbines is that a HEC fuel is burned to provide the heat that drives the turbine. It would be advantageous to provide this heat using the essentially “free” LEC fuel and avoid or decrease the expense of purchasing fuel. 
     The processes described above in  FIGS. 1-1A through 1-1D  have various drawbacks. With respect to the thermal oxidizer of  FIG. 1-1A , for example, if supplemental fuel is required to provide the air-fuel mixture  6 , the cost of the fuel is additive to the cost of the process. In addition, the reaction temperatures in the burner  2  are high enough to form thermal NOx, discussed in greater detail later in the present disclosure. 
     Catalysts can have challenges associated with their use. Noble-metal catalysts are rare and expensive. The process requires that the waste stream be heated to a specific range using any of a variety of means, including heat recovery as described below, but often is additive to the cost of the process. Catalysts can be rendered chemically inactive due to processes like sintering, fouling, or volatilization. Waste fuels, such as landfill gas, often contain contaminants that can significantly shorten the life of the catalyst. To control the reaction temperatures to avoid volatilization, the fuel composition and process variables are maintained within predefined limits, adding cost to monitor and adjust these variables. 
     Recuperators have several disadvantages. The recuperator is an additional investment cost for a thermal oxidation system. Recuperators also add pressure drop to the system, increasing the power requirement for the flow conveyance apparatus, i.e. fans, that move the waste stream  7  and air-fuel mixtures  6  through the system. If the recuperator contains small passages, they can be subject to fouling and corrosion from various exhaust gas constituents. If the temperature of the exhaust gas from the reaction chamber is above the maximum service temperature for the materials of a recuperator, additional process equipment is required to cool to exhaust prior to introducing the exhaust into the recuperator. 
     Regenerative oxidizers have the drawbacks that the reconfiguration of the flow path between cycles requires significant complexity in either high-temperature valving and piping or in physically moving the hot regenerative oxidizers. The reconfiguration also interrupts the process, requiring some system for accumulating the waste stream  7  during the reconfiguration operation. 
     The gradual oxidation (GO) process disclosed herein avoids the drawbacks associated with conventional systems for processing waste streams containing VOCs. The GO process, once through the start-up process, operates on LEC fuel and does not require additional HEC fuel to sustain the oxidation process. The GO process does not require the use of an expensive catalyst, thereby reducing the required investment and avoiding the operational hazard of poisoning the catalyst. The disclosed GO process transfers the heat produced by the oxidation of the waste stream into the incoming flow, thereby avoiding the problem of incrementally cooling the media as seen in regenerative oxidizers and eliminating the need for expensive and potentially unreliable valves as well as the need for an accumulator to handle the incoming waste stream while the regenerative system is reconfigured between cycles. 
     There also are circumstances wherein it is desirable to use a HEC fuel while minimizing the formation of undesirable NOx compounds and CO as well as reducing unburned hydrocarbons in the exhaust. One of the drawbacks of existing power-generation systems driven by gas turbines using a HEC fuel is that the combustion process occurs at a temperature at which NOx may form and that there may be some level of remaining hydrocarbons as the mixture falls below the lower flammability limit during the combustion process. 
     The disclosed systems use a GO process that occurs within an oxidizer (also referred to herein as a gradual oxidizer, a GO chamber, and a GO reaction chamber) in place of a conventional combustion chamber to generate the heat that drives the system. In certain configurations, the oxidizer contains a material, such as a ceramic, that is structured to be porous to a gas flow and retains its structure at temperatures above 1200° F. 
     In certain embodiments, a system for oxidizing fuel described herein includes an oxidizer having a reaction chamber with an inlet and an outlet, the reaction chamber configured to receive a gas comprising an oxidizable fuel through the inlet, the oxidizer configured to maintain gradual oxidation of the fuel within the reaction chamber, and means for drawing heat from the reaction chamber, such that when an adiabatic reaction temperature within the reaction chamber approaches a flameout temperature, heat is drawn out of the reaction chamber to reduce an actual temperature within the reaction chamber to a temperature that does not exceed the flameout temperature. 
     In certain embodiments, the means for drawing heat from the reaction chamber comprises a heat exchanger. In certain embodiments, the means for drawing heat from the reaction chamber comprises a fluid. In certain embodiments, the means for drawing heat from the reaction chamber comprises a means for generating steam. In certain embodiments, the means for drawing heat is configured to draw heat from the reaction chamber when the actual temperature within the reaction chamber increases to the flameout temperature. In certain embodiments, the system also includes a means for raising a temperature of the gas, at the inlet of the reaction chamber to above the autoignition temperature of the fuel. In certain embodiments, the means comprises a heat exchanger within the oxidizer. In certain embodiments the reaction chamber is configured to maintain gradual oxidation of the oxidizable fuel without a catalyst. In certain embodiments, the means is configured to draw heat out of the reaction chamber when the temperature within the reaction chamber exceeds 2300° F. In certain embodiments, the system also includes a turbine that receives gas from the reaction chamber outlet and expands the gas. In certain embodiments, the system also includes a compressor that receives and compresses gas, comprising a fuel mixture, prior to introduction of the fuel mixture into the reaction chamber. In certain embodiments, the oxidizable fuel comprises at least one of hydrogen, methane, ethane, ethylene, natural gas, propane, propylene, propadiene, n-butane, iso-butane, butylene-1, butadiene, iso-pentane, n-pentane, acetylene, hexane, and carbon monoxide. 
     In certain embodiments, a system for oxidizing fuel described herein includes an oxidizer having a reaction chamber with an inlet and an outlet, the reaction chamber configured to receive a gas comprising an oxidizable fuel through the inlet, the oxidizer configured to maintain a gradual oxidation process within the reaction chamber, and a heat exchanger configured to draw heat from the reaction chamber when an adiabatic reaction temperature within the reaction chamber approaches a flameout temperature, such that an actual temperature within the reaction chamber is reduced to a level that does not exceed the flameout temperature. 
     In certain embodiments, the heat exchanger is configured to draw heat from the reaction chamber when the actual temperature of the reaction chamber increases to the flameout temperature. In certain embodiments, the system also includes a turbine that receives gas from the reaction chamber and expands the gas. In certain embodiments, the system also includes a compressor that receives and compresses gas, comprising a fuel mixture, prior to introduction of the fuel mixture into the reaction chamber. In certain embodiments, the heat exchanger is configured to raise a temperature of the gas, at the inlet of the reaction chamber, to above the autoignition temperature of the fuel. In certain embodiments, the heat exchanger comprises a fluid introduced into the reaction chamber. In certain embodiments, the heat exchanger is configured to evacuate the fluid from the reaction chamber. In certain embodiments, the heat exchanger comprises a means for generating steam. In certain embodiments, the reaction chamber is configured to maintain gradual oxidation of the oxidizable fuel without a catalyst. In certain embodiments, the heat exchanger is configured to draw heat out of the reaction chamber when the temperature within the reaction chamber exceeds 2300° F. In certain embodiments, the oxidizable fuel comprises at least one of hydrogen, methane, ethane, ethylene, natural gas, propane, propylene, propadiene, n-butane, iso-butane, butylene-1, butadiene, iso-pentane, n-pentane, acetylene, hexane, and carbon monoxide. 
     In certain embodiments, a method for oxidizing fuel described herein includes the steps of receiving a gas comprising an oxidizable fuel into an oxidizer having a reaction chamber with an inlet and an outlet, the reaction chamber configured to maintain a gradual oxidation process of the fuel within the reaction chamber; and drawing heat from the reaction chamber when an adiabatic reaction temperature within the reaction chamber approaches a flameout temperature, such that an actual temperature within the reaction chamber does not exceed the flameout temperature. 
     In certain embodiments, the method includes the step of expanding gas from the reaction chamber in a turbine. In certain embodiments, the method also includes the step of compressing the fuel with a compressor prior to introduction of the fuel mixture into the reaction chamber. In certain embodiments, the method includes the step of drawing heat from the reaction chamber comprises introducing a fluid into the reaction chamber. In certain embodiments, the method includes the step of evacuating the fluid from the reaction chamber. In certain embodiments, the fluid is evacuated from the reaction chamber in the form of steam. In certain embodiments, the reaction chamber maintains gradual oxidation of the oxidizable fuel without a catalyst. In certain embodiments, heat is drawn out of the reaction chamber when the temperature within the reaction chamber exceeds 2300° F. In certain embodiments, oxidizable fuel comprises at least one of hydrogen, methane, ethane, ethylene, natural gas, propane, propylene, propadiene, n-butane, iso-butane, butylene-1, butadiene, iso-pentane, n-pentane, acetylene, hexane, and carbon monoxide. 
     In certain embodiments, a method for oxidizing fuel described herein includes the steps of receiving a gas comprising an oxidizable fuel into an oxidizer having a reaction chamber with an inlet and an outlet, the reaction chamber configured to maintain a temperature within the reaction chamber to gradually oxidize the fuel within the reaction chamber; and reducing the temperature within the reaction chamber, such that an actual temperature within the reaction chamber remains below a flameout temperature. 
     In certain embodiments, reducing the temperature comprises drawing heat from the reaction chamber. In certain embodiments, the method includes the step of expanding gas from the reaction chamber in a turbine. In certain embodiments, the method includes the step of compressing the fuel with a compressor prior to introduction of the fuel mixture into the reaction chamber. In certain embodiments, reducing the temperature comprises introducing a fluid into the reaction chamber. In certain embodiments, the method includes the step of evacuating the fluid from the reaction chamber. In certain embodiments, the fluid is evacuated from the reaction chamber in the form of steam. In certain embodiments, the reaction chamber maintains gradual oxidation of the oxidizable fuel without a catalyst. In certain embodiments, the temperature is reduced such that the temperature within the reaction chamber does not exceed 2300° F. In certain embodiments, the oxidizable fuel comprises at least one of hydrogen, methane, ethane, ethylene, natural gas, propane, propylene, propadiene, n-butane, iso-butane, butylene-1, butadiene, iso-pentane, n-pentane, acetylene, hexane, and carbon monoxide. 
     In certain embodiments, a method for oxidizing a fuel described herein includes the steps of determining a temperature within a reaction chamber of an oxidizer, the reaction chamber having an inlet and an outlet and being configured to maintain gradual oxidation of an oxidizable fuel; and outputting a signal to reduce the temperature within the reaction chamber when the temperature within the reaction chamber approaches a flameout temperature, such that the temperature remains beneath the flameout temperature. 
     In certain embodiments, the signal comprises instructions to draw heat from the reaction chamber by introducing a liquid into the reaction chamber. In certain embodiments, the signal comprises instructions to evacuate the fluid from the reaction chamber. In certain embodiments, the instructions to evacuate the fluid from the reaction chamber comprise instructions to evacuate the fluid in the form of steam. In certain embodiments, the signal to draw heat from the reaction chamber is output when the temperature within the reaction chamber exceeds 2300° F. In certain embodiments, the signal to draw heat from the reaction chamber is output when the temperature exceeds a flameout temperature of at least one of hydrogen, methane, ethane, ethylene, natural gas, propane, propylene, propadiene, n-butane, iso-butane, butylene-1, butadiene, iso-pentane, n-pentane, acetylene, hexane, and carbon monoxide. 
     In certain embodiments, a method for oxidizing a fuel described herein includes the steps of determining a temperature within a reaction chamber of an oxidizer, the reaction chamber having an inlet and an outlet and being configured to maintain gradual oxidation of an oxidizable fuel; and outputting a signal to a heat exchanger to draw heat from the reaction chamber when the temperature within the reaction chamber approaches a flameout temperature. 
     In certain embodiments, the signal comprises instruction to remove heat from the reaction chamber. In certain embodiments, the signal comprises instruction to reduce the temperature by introducing a fluid into the reaction chamber. In certain embodiments, the signal comprises instruction to evacuate the fluid from the reaction chamber. In certain embodiments, the instruction to evacuate the fluid from the reaction chamber comprises evacuating the fluid in the form of steam. In certain embodiments, the method also includes the step of repeatedly calculating, based on data of the oxidizable fuel, an adiabatic reaction temperature within the reaction chamber. In certain embodiments, the signal to reduce the temperature within the reaction chamber is output when the temperature within the reaction chamber exceeds 2300° F. In certain embodiments, the signal to draw heat from the reaction chamber is output when the temperature approaches a flameout temperature of at least one of hydrogen, methane, ethane, ethylene, natural gas, propane, propylene, propadiene, n-butane, iso-butane, butylene-1, butadiene, iso-pentane, n-pentane, acetylene, hexane, and carbon monoxide. In certain embodiments, the signal to draw heat from the reaction chamber is output when the temperature increases to the flameout temperature. 
     In certain embodiments, a method for oxidizing a fuel described herein includes the steps of determining a temperature within a reaction chamber of an oxidizer, the reaction chamber having an inlet and an outlet and being configured to maintain gradual oxidation of an oxidizable fuel; and determining, with a sensor, when the temperature within the reaction chamber approaches a flameout temperature of the fuel within the reaction chamber. 
     In certain embodiments, the method includes the step of outputting a signal to reduce the temperature within the reaction chamber when a calculated adiabatic reaction temperature within the reaction chamber exceeds the flameout temperature. In certain embodiments, the calculated adiabatic reaction temperature is based on the oxidizable fuel and an oxidant within the reaction chamber. In certain embodiments, the signal comprises instruction to remove heat from the reaction chamber. In certain embodiments, the signal comprises instruction to reduce the temperature by introducing a liquid into the reaction chamber. In certain embodiments, the signal to reduce the temperature within the reaction chamber is output when the temperature within the reaction chamber exceeds 2300° F. In certain embodiments, the signal to draw heat from the reaction chamber is output when the temperature exceeds a flameout temperature of at least one of hydrogen, methane, ethane, ethylene, natural gas, propane, propylene, propadiene, n-butane, iso-butane, butylene-1, butadiene, iso-pentane, n-pentane, acetylene, hexane, and carbon monoxide. 
     In certain embodiments, a system for oxidizing fuel described herein includes an oxidizer having a reaction chamber with an inlet and an outlet, the reaction chamber configured to receive a gas comprising an oxidizable fuel through the inlet, the oxidizer configured to maintain an oxidation process without a catalyst; a detection module that detects when at least one of a reaction temperature within the reaction chamber approaches a flameout temperature of the fuel within the reaction chamber and a reaction chamber inlet temperature approaches an autoignition threshold; and a correction module that outputs instructions, based on the detection module, to change at least one of removal of heat from the reaction chamber, and the inlet temperature of the reaction chamber; wherein the correction module is configured to at least one of maintain an actual temperature within the reaction temperature to below the flameout temperature and maintain the inlet temperature above the autoignition threshold of the fuel. 
     In certain embodiments, the correction module outputs instructions to remove heat from the reaction chamber by a heat exchanger. In certain embodiments, the correction module outputs instructions to remove heat from the reaction chamber by a fluid. In certain embodiments, the correction module outputs instructions to raise the inlet temperature. In certain embodiments, a heat exchanger positioned within the reaction chamber. In certain embodiments, the reaction chamber is configured to maintain oxidation of the oxidizable fuel beneath the flameout temperature. In certain embodiments, the correction module outputs instructions to remove heat from the reaction chamber when the temperature within the reaction chamber exceeds 2300° F. In certain embodiments, a turbine that receives gas from the reaction chamber and expands the gas. In certain embodiments, the system also includes a compressor that receives and compresses gas, comprising a fuel mixture, prior to introduction of the fuel mixture into the reaction chamber. In certain embodiments, the oxidizable fuel comprises at least one of hydrogen, methane, ethane, ethylene, natural gas, propane, propylene, propadiene, n-butane, iso-butane, butylene-1, butadiene, iso-pentane, n-pentane, acetylene, hexane, and carbon monoxide. 
     In certain embodiments, a system for oxidizing fuel described herein includes an oxidizer having a reaction chamber with an inlet and an outlet, the reaction chamber configured to receive a gas comprising an oxidizable fuel through the inlet, the oxidizer configured to maintain an oxidation process without a catalyst; a detection module that detects when at least one of a reaction temperature within the reaction chamber approaches a flameout temperature of the fuel within the reaction chamber and a reaction chamber inlet temperature approaches an autoignition threshold; and a correction module that outputs instructions, based on the detection module, to at least one of maintain an actual temperature within the reaction temperature to below the flameout temperature or maintain the inlet temperature above the autoignition threshold of the fuel. 
     In certain embodiments, the correction module outputs instructions to a heat exchanger to remove heat from the reaction chamber. In certain embodiments, the correction module outputs instructions to remove heat from the reaction chamber by a fluid. In certain embodiments, the correction module outputs instructions to raise the inlet temperature. In certain embodiments, the system also includes a heat exchanger positioned within the reaction chamber. In certain embodiments, the reaction chamber is configured to maintain oxidation of the oxidizable fuel beneath the flameout temperature. In certain embodiments, the correction module outputs instructions to remove heat from the reaction chamber when the temperature within the reaction chamber exceeds 2300° F. 
     In certain embodiments, a system for oxidizing fuel described herein includes an oxidizer having a reaction chamber with an inlet and an outlet, the reaction chamber configured to receive a gas comprising an oxidizable fuel through the inlet, the oxidizer configured to maintain an oxidation process without a catalyst; and a processor that detects when at least one of a reaction temperature within the reaction chamber approaches a flameout temperature of the fuel within the reaction chamber and a reaction chamber inlet temperature drops approaches an autoignition threshold. 
     In certain embodiments, a correction module that, based on the processor, reduces an actual temperature within the reaction chamber to remain beneath the flameout temperature of the fuel by removing heat from the reaction chamber. In certain embodiments, a correction module that, based on the processor, raises the inlet temperature above the autoignition threshold of the fuel by increasing a residence time of the oxidizable fuel within the reaction chamber. 
     In certain embodiments, a method for oxidizing fuel described herein includes the steps of receiving a gas comprising an oxidizable fuel into an oxidizer having a reaction chamber with an inlet and an outlet, the reaction chamber configured to maintain an oxidation process of the gas; and changing at least one of removal of heat from the reaction chamber and an inlet temperature of the reaction chamber when at least one of an actual temperature within the reaction chamber approaches or increases to a flameout temperature of the fuel and the reaction chamber inlet temperature approaches or drops below an autoignition threshold of the fuel. 
     In certain embodiments, the actual temperature of the reaction chamber is maintained below the flameout temperature. In certain embodiments, the inlet temperature of the reaction chamber is increased to a level that will support oxidation of the fuel without a catalyst. In certain embodiments, the inlet temperature is increased to above the autoignition threshold. In certain embodiments, a temperature of the gas is increased by a heat exchanger located within the reaction chamber. In certain embodiments, the method also includes the step of expanding gas from the reaction chamber outlet in a turbine or a piston engine. In certain embodiments, the method also includes the step of compressing the fuel with a compressor prior to introduction of the fuel mixture into the reaction chamber. In certain embodiments, removal of heat from the reaction chamber comprises introducing a liquid into the reaction chamber. In certain embodiments, the method also includes the step of evacuating the liquid from the reaction chamber. In certain embodiments, the liquid is evacuated from the reaction chamber in the form of steam. In certain embodiments, the reaction chamber maintains gradual oxidation of the oxidizable fuel without a catalyst. In certain embodiments, heat is removed from the reaction chamber when the temperature within the reaction chamber exceeds 2300° F. In certain embodiments, the oxidizable fuel comprises at least one of hydrogen, methane, ethane, ethylene, natural gas, propane, propylene, propadiene, n-butane, iso-butane, butylene-1, butadiene, iso-pentane, n-pentane, acetylene, hexane, and carbon monoxide. 
     In certain embodiments, a method for oxidizing fuel described herein includes the steps of receiving a gas comprising an oxidizable fuel into an oxidizer having a reaction chamber with an inlet and an outlet, the reaction chamber configured to maintain a gradual oxidation process; and increasing at least one of removal of heat from the reaction chamber when an adiabatic reaction temperature within the reaction chamber approaches a flameout temperature of the fuel; and an inlet temperature of the reaction chamber when the reaction chamber inlet temperature drops below an autoignition threshold of the fuel. 
     In certain embodiments, an actual temperature of the reaction chamber is maintained below the flameout temperature. In certain embodiments, the inlet temperature of the reaction chamber rises to a level that will support oxidation of the fuel without a catalyst. In certain embodiments, the inlet temperature rises above the autoignition temperature. In certain embodiments, a gas temperature is increased by a heat exchanger located outside the reaction chamber, and the gas is passed through the heat exchanger prior to being introduced into the reaction chamber. 
     In certain embodiments, a method for oxidizing fuel described herein includes the steps of receiving a gas comprising an oxidizable fuel into an oxidizer having a reaction chamber with an inlet and an outlet, the reaction chamber configured to maintain a gradual oxidation process without a catalyst; and increasing at least one of removal of heat from the reaction chamber when a reaction temperature within the reaction chamber approaches a flameout temperature of the fuel, such that an actual temperature of the reaction chamber is maintained below the flameout temperature; and an inlet temperature of the reaction chamber when the reaction chamber inlet temperature drops below an autoignition threshold of the fuel, such that the inlet temperature of the reaction chamber is maintained above a level that will support oxidation of the fuel without a catalyst. In certain embodiments, the inlet temperature is maintained above the autoignition temperature. 
     In certain embodiments, a system for oxidizing fuel described herein includes an oxidizer having a reaction chamber with an inlet and an outlet, the reaction chamber configured to receive a gas comprising an oxidizable fuel through the inlet and to maintain an oxidation process within the reaction chamber; a detection module that detects when a reaction chamber inlet temperature of the gas approaches or drops below an autoignition threshold of the gas entering the first reaction chamber; and a correction module that outputs instructions, based on the detection module, to change the inlet temperature of the gas to maintain the inlet temperature above autoignition threshold, such that the gas within the reaction chamber oxidizes without a catalyst. 
     In certain embodiments, the correction module outputs instructions to a heat exchanger to raise the inlet temperature. In certain embodiments, the heat exchanger is positioned within the reaction chamber. In certain embodiments, the reaction chamber is configured to maintain oxidation of the gas beneath a flameout temperature of the fuel within the reaction chamber. In certain embodiments, the system also includes a turbine or a piston engine that receives gas from the reaction chamber and expands the gas. In certain embodiments, the system also includes a compressor that receives and compresses gas, comprising a fuel mixture, prior to introduction of the fuel mixture into the reaction chamber. In certain embodiments, the oxidizable fuel comprises at least one of hydrogen, methane, ethane, ethylene, natural gas, propane, propylene, propadiene, n-butane, iso-butane, butylene-1, butadiene, iso-pentane, n-pentane, acetylene, hexane, and carbon monoxide. 
     In certain embodiments, a system for oxidizing fuel described herein includes an oxidizer having a reaction chamber with an inlet and an outlet, the reaction chamber configured to receive a gas comprising an oxidizable fuel through the inlet and to maintain an oxidation process within the reaction chamber, a detection module that detects when a reaction chamber inlet temperature of the gas drops toward an autoignition threshold of the fuel; and a correction module that, based on the detection module, maintains the inlet temperature above the autoignition threshold. 
     In certain embodiments, the correction module outputs instructions to a heat exchanger to maintain the inlet temperature. In certain embodiments, the heat exchanger is positioned within the reaction chamber. In certain embodiments, the reaction chamber is configured to maintain an actual temperature within the reaction chamber beneath a flameout temperature of the fuel. In certain embodiments, the system also includes a turbine or a piston engine that receives gas from the reaction chamber and expands the gas. In certain embodiments, the system also includes a compressor that receives and compresses gas, comprising a fuel mixture, prior to introduction of the gas into the reaction chamber. In certain embodiments, the oxidizable fuel comprises at least one of hydrogen, methane, ethane, ethylene, natural gas, propane, propylene, propadiene, n-butane, iso-butane, butylene-1, butadiene, iso-pentane, n-pentane, acetylene, hexane, and carbon monoxide. 
     In certain embodiments, a system for oxidizing fuel described herein includes an oxidizer having a reaction chamber with an inlet and an outlet, the reaction chamber configured to receive a gas comprising an oxidizable fuel through the inlet and to maintain an oxidation process; and a heat exchanger that maintains a reaction chamber inlet temperature above an autoignition threshold of the fuel, such that the fuel oxidizes within the reaction chamber above the autoignition threshold and beneath a flameout temperature of the fuel. 
     In certain embodiments, a detection module that detects when the reaction chamber inlet temperature approaches the autoignition threshold. In certain embodiments, the heat exchanger is positioned within the reaction chamber. In certain embodiments, the system also includes a turbine or a piston engine that receives gas from the reaction chamber and expands the gas. In certain embodiments, the system also includes a compressor that receives and compresses gas, comprising a fuel mixture, prior to introduction of the fuel mixture into the reaction chamber. In certain embodiments, the oxidizable fuel comprises at least one of hydrogen, methane, ethane, ethylene, natural gas, propane, propylene, propadiene, n-butane, iso-butane, butylene-1, butadiene, iso-pentane, n-pentane, acetylene, hexane, and carbon monoxide. 
     In certain embodiments, a method for oxidizing fuel described herein includes the steps of determining, in a reaction chamber, with an inlet and an outlet, that is configured to maintain an oxidation process of an oxidizable fuel, at least one of an actual reaction temperature of the fuel in the reaction chamber, and an inlet temperature of the reaction chamber, determining, with a sensor, when at least one of the actual reaction temperature approaches or exceeds a flameout temperature of the fuel, and the inlet temperature approaches or drops below an autoignition threshold of the fuel; and determining at least one of a reduction of the actual reaction temperature within the reaction chamber to remain below the flameout temperature, and an increase in the inlet temperature to maintain the inlet temperature above the autoignition threshold. 
     In certain embodiments, the reduction of the actual reaction temperature comprises removal of heat from the reaction chamber. In certain embodiments, removal of heat from the reaction chamber comprises introducing a fluid into the reaction chamber. In certain embodiments, removal of heat further comprises evacuating the fluid from the reaction chamber. In certain embodiments, the reaction chamber is configured to evacuate the fluid in the form of steam. In certain embodiments, the increase in the inlet temperature comprises directing the fuel through a heat exchanger. In certain embodiments, the heat exchanger is positioned within the reaction chamber. In certain embodiments, the flameout temperature is about 2300° F. In certain embodiments, the oxidizable fuel comprises at least one of hydrogen, methane, ethane, ethylene, natural gas, propane, propylene, propadiene, n-butane, iso-butane, butylene-1, butadiene, iso-pentane, n-pentane, acetylene, hexane, and carbon monoxide. 
     In certain embodiments, a method for oxidizing fuel described herein includes the steps of determining, in a reaction chamber, with an inlet and an outlet, that is configured to maintain an oxidation process of an oxidizable fuel, at least one of an actual reaction temperature of the fuel in the reaction chamber, and an inlet temperature of the gas at the inlet; determining when at least one of the actual reaction temperature approaches or exceeds a flameout temperature of the fuel and a reaction chamber inlet temperature approaches or drops below an autoignition threshold of the fuel; and outputting instructions to at least one of reduce the actual temperature or reduce increase of the actual temperature within the reaction chamber to be maintained below the flameout temperature, and increase the inlet temperature to be above the autoignition threshold of the fuel. 
     In certain embodiments, the outputting comprises instructions to remove heat from the reaction chamber. In certain embodiments, the method also includes the step of removing heat from the reaction chamber by introducing a fluid into the reaction chamber. In certain embodiments, removing heat further comprises evacuating the fluid from the reaction chamber. In certain embodiments, the fluid is evacuated from the reaction chamber in the form of steam. In certain embodiments, the outputting comprises increasing the inlet temperature by directing the fuel through a heat exchanger. In certain embodiments, the heat exchanger is positioned within the reaction chamber. In certain embodiments, the flameout temperature is about 2300° F. In certain embodiments, the oxidizable fuel comprises at least one of hydrogen, methane, ethane, ethylene, natural gas, propane, propylene, propadiene, n-butane, iso-butane, butylene-1, butadiene, iso-pentane, n-pentane, acetylene, hexane, and carbon monoxide. 
     In certain embodiments, a method for oxidizing fuel described herein includes the steps of receiving a gas comprising an oxidizable fuel into an oxidizer having a reaction chamber with an inlet and an outlet, the reaction chamber configured to maintain an oxidation process; and when a reaction chamber inlet temperature of the gas approaches or drops below an autoignition threshold of the fuel, introducing additional heat to the gas such that the inlet temperature is maintained above the autoignition threshold, and the reaction chamber maintains oxidation of the fuel within the reaction chamber without a catalyst. 
     In certain embodiments, the additional heat is introduced by a heat exchanger. In certain embodiments, the heat exchanger is positioned within the reaction chamber. In certain embodiments, the reaction chamber maintains oxidation of the oxidizable fuel beneath a flameout temperature of the fuel. In certain embodiments, the method also includes the step of a turbine or a piston engine that receives gas from the reaction chamber and expands the gas. In certain embodiments, a compressor that receives and compresses gas, comprising a fuel mixture, prior to introduction of the fuel mixture into the reaction chamber. In certain embodiments, the oxidizable fuel comprises at least one of hydrogen, methane, ethane, ethylene, natural gas, propane, propylene, propadiene, n-butane, iso-butane, butylene-1, butadiene, iso-pentane, n-pentane, acetylene, hexane, and carbon monoxide. 
     In certain embodiments, a method for oxidizing fuel described herein includes the steps of receiving a gas comprising an oxidizable fuel into an oxidizer having a first reaction chamber with an inlet and an outlet, the first reaction chamber being configured to maintain an oxidation process of the fuel; and when a reaction chamber inlet temperature of the gas approaches or drops below an autoignition threshold of the fuel, increasing the inlet temperature to a level above the autoignition threshold. 
     In certain embodiments, the reaction chamber maintains gradual oxidation of the fuel within the reaction chamber without a catalyst. In certain embodiments, the inlet temperature is increased by a heat exchanger. In certain embodiments, the heat exchanger is positioned within the reaction chamber. In certain embodiments, the reaction chamber is configured to maintain oxidation of the fuel beneath a flameout temperature of the fuel. In certain embodiments, the method also includes the step of a turbine or a piston engine that receives gas from the reaction chamber and expands the gas. In certain embodiments, the method also includes the step of a compressor that receives and compresses gas, comprising a fuel mixture, prior to introduction of the fuel mixture into the reaction chamber. In certain embodiments, the oxidizable fuel comprises at least one of hydrogen, methane, ethane, ethylene, natural gas, propane, propylene, propadiene, n-butane, iso-butane, butylene-1, butadiene, iso-pentane, n-pentane, acetylene, hexane, and carbon monoxide. 
     In certain embodiments, a method for oxidizing fuel described herein includes the steps of in a reaction chamber, with an inlet and an outlet, that is configured to maintain an oxidation process, determining when an inlet temperature of a gas, comprising an oxidizable fuel, at the inlet approaches or drops below an autoignition threshold of the fuel; and outputting a signal to increase the inlet temperature of the gas, such that the inlet temperature remains above the autoignition threshold. 
     In certain embodiments, the signal comprises instructions to heat the gas with a heat exchanger. In certain embodiments, the heat exchanger is positioned within the reaction chamber. In certain embodiments, the reaction chamber is configured to maintain oxidation of the fuel beneath a flameout temperature of the fuel. In certain embodiments, the reaction chamber is configured to maintain oxidation of the fuel below about 2300° F. In certain embodiments, the method also includes the step of a turbine or a piston engine that receives gas from the reaction chamber and expands the gas. In certain embodiments, the method also includes the step of a compressor that receives and compresses gas, comprising a fuel mixture, prior to introduction of the fuel mixture into the reaction chamber. In certain embodiments, the oxidizable fuel comprises at least one of hydrogen, methane, ethane, ethylene, natural gas, propane, propylene, propadiene, n-butane, iso-butane, butylene-1, butadiene, iso-pentane, n-pentane, acetylene, hexane, and carbon monoxide. 
     In certain embodiments, a method described herein for oxidizing fuel in a system that receives a gas, comprising an oxidizable fuel, into an oxidizer having a reaction chamber with an inlet and an outlet, the reaction chamber being configured to maintain a gradual oxidation of the fuel without a catalyst, the method comprising detecting when a reaction chamber inlet temperature of the gas approaches or drops below an autoignition threshold of the gas, and outputting instructions to increase the inlet temperature such that the gas inlet temperature is maintained above the autoignition temperature, while a temperature within the reaction chamber remains below a flameout temperature. 
     In certain embodiments, the instructions increase heat transfer to the gas by a heat exchanger. In certain embodiments, the heat exchanger is positioned within the reaction chamber. In certain embodiments, the reaction chamber is configured to maintain oxidation of the fuel beneath a flameout temperature of the fuel. In certain embodiments, the reaction chamber is configured to maintain oxidation of the fuel beneath about 2300° F. In certain embodiments, the method also includes the step of a turbine or a piston engine that receives gas from the reaction chamber and expands the gas. In certain embodiments, the method also includes the step of a compressor that receives and compresses gas, comprising a fuel mixture, prior to introduction of the gas into the reaction chamber. 
     In certain embodiments, a method for oxidizing fuel described herein includes the step of in a reaction chamber, having an inlet and an outlet, that is configured to maintain an oxidation process, determining, with a sensor, when an inlet temperature of a gas, comprising an oxidizable fuel, at the inlet approaches an autoignition threshold of the gas; wherein an actual temperature within the reaction chamber is maintained at a level below the flameout temperature and above the autoignition threshold, such that gradual oxidation of the fuel is maintained within the reaction chamber. 
     In certain embodiments, a signal increase the inlet temperature of the gas to remain above the autoignition threshold. In certain embodiments, the signal comprises instructions to increase heat transfer to the gas by a heat exchanger. In certain embodiments, the heat exchanger is positioned within the reaction chamber. 
     In certain embodiments, a system for oxidizing fuel described herein includes an oxidizer having a reaction chamber with an inlet and an outlet, the reaction chamber configured to receive a gas comprising an oxidizable fuel through the inlet, and to maintain an oxidation process of the gas; and heat exchange media disposed within the reaction chamber, the media configured to maintain an internal temperature of the reaction chamber below a flameout temperature and to maintain a reaction chamber inlet temperature of the fuel to be greater than an autoignition temperature of the fuel; wherein the media is configured to circulate outside the reaction chamber and thereby draw heat from the reaction chamber to maintain the internal temperature below the flameout temperature. 
     In certain embodiments, circulation of the media is configured to heat gas at the inlet and to maintain the inlet temperature of the fuel above the autoignition temperature. In certain embodiments, circulation of the media is configured to draw heat from the gas within the reaction chamber to maintain the internal temperature of the gas beneath a flameout temperature of the gas. In certain embodiments, the media comprises a plurality of steel structures that is circulated through the reaction chamber. In certain embodiments, the media comprises a fluid that is circulated through the reaction chamber. In certain embodiments, a speed that the media circulates is based on at least one of the internal temperature and the inlet temperature. In certain embodiments, heat is drawn from the media when the media circulates outside the reaction chamber. 
     In certain embodiments, a system for oxidizing fuel described herein includes an oxidizer having a reaction chamber with an inlet and an outlet, the reaction chamber configured to receive a gas comprising an oxidizable fuel through the inlet, the oxidizer configured to maintain an oxidation process of the gas within the reaction chamber; and a recirculation pathway that directs at least a portion of product gas, after oxidation within the reaction chamber, toward the inlet of the reaction chamber and introduces the product gas into the reaction chamber at the inlet; wherein introduction of the product gas increases an inlet temperature of the gas to be above the autoignition temperature of the gas. 
     In certain embodiments, recirculation of the product gas decreases an oxygen content level within the reaction chamber. In certain embodiments, an amount of product gas that is recirculated is based on the inlet temperature. In certain embodiments, an amount of product gas that is recirculated is based on an internal temperature of the reaction chamber. 
     In certain embodiments, a system for oxidizing fuel described herein includes an oxidizer having a reaction chamber with an inlet and an outlet, the reaction chamber configured to receive a gas comprising an oxidizable fuel through the inlet, the oxidizer configured to maintain an oxidation process of the gas within the reaction chamber; and heat exchange media disposed within the reaction chamber, the media configured to maintain an internal temperature of the reaction chamber below a flameout temperature and to maintain a reaction chamber inlet temperature of the fuel to be greater than an autoignition temperature of the fuel. 
     In certain embodiments, the heat exchange media comprises a fluid. In certain embodiments, the fluid is circulated, and circulation of the media is configured to heat gas at the inlet and to maintain the inlet temperature of the gas above the autoignition temperature of the gas. In certain embodiments, the heat exchange media comprises sand. In certain embodiments, the heat exchange media comprises a plurality of uniformly stacked structures. In certain embodiments, the heat exchange media comprises a plurality of stacked disk, each having a plurality of apertures through which the gas is permitted to flow. In certain embodiments, heat exchange media is configured to conduct heat within the reaction chamber toward the inlet, whereby gas being received through the inlet is heated to above the autoignition temperature. 
     In certain embodiments, a split cycle reciprocating engine described herein includes an intake that receives an air-fuel mixture, the mixture comprising a mixture of air and a gas fuel; a compression chamber, coupled to the reciprocating engine that compresses the mixture in a reciprocating piston chamber; an oxidation chamber that is configured to receive the mixture from the compression chamber via a first inlet and to maintain oxidation of the mixture at an internal temperature beneath a flameout temperature of the mixture and sufficient to oxidize the mixture without a catalyst; and an expansion chamber, that receives oxidation product gas from the oxidation chamber and expands the product gas within the expansion chamber via a reciprocating piston. 
     In certain embodiments, the oxidation chamber is configured to maintain an inlet temperature of the mixture above an autoignition temperature of the mixture. In certain embodiments, the system also includes a heat exchanger that is configured to draw heat from the product gas and heat the mixture prior to introducing the mixture into the oxidation chamber. In certain embodiments, the heat exchanger comprises a tube-in-tube heat exchanger. In certain embodiments, the system also includes a heat exchange media disposed within the oxidation chamber. In certain embodiments, the media is configured to maintain the internal temperature of the oxidation chamber below a flameout temperature by conducting heat toward the inlet of the oxidation chamber, and wherein media at the inlet of the oxidation chamber is cooled by the mixture being introduced into the oxidation chamber. In certain embodiments, the fuel comprises at least one of hydrogen, methane, ethane, ethylene, natural gas, propane, propylene, propadiene, n-butane, iso-butane, butylene-1, butadiene, iso-pentane, n-pentane, acetylene, hexane, and carbon monoxide. 
     In certain embodiments, a split cycle reciprocating engine described herein includes a reciprocation cycle comprising at least one compression chamber having therein a reciprocating piston and at least one expansion chamber having therein a reciprocating piston; and a heating cycle comprising an intake that receives a gas air-fuel mixture comprising a mixture of air and a gas fuel, the intake being configured to direct the mixture to the compression chamber; a reaction chamber, configured to receive the mixture from the compression chamber and to maintain oxidation of the mixture at an internal reaction chamber temperature sufficient to oxidize the mixture without a catalyst; wherein the expansion chamber is configured to receive oxidation product gas from the reaction chamber and to expand the product gas within the expansion chamber via the reciprocating piston. 
     In certain embodiments, the reaction chamber comprises an inlet, and the reaction chamber is configured to maintain an inlet temperature of the mixture at the inlet above an autoignition temperature of the mixture. In certain embodiments, the system also includes a heat exchanger that is configured to draw heat from product gases of the reaction chamber and heat the mixture prior to introducing the mixture into the reaction chamber. In certain embodiments, the heat exchanger comprises a tube-in-tube heat exchanger. In certain embodiments, the product gases are directed back into the reaction chamber and combined with the air-fuel mixture introduced into the reaction chamber. In certain embodiments, the system also includes a heat exchange media disposed within the reaction chamber. In certain embodiments, the media is configured to maintain the internal temperature of the reaction chamber below a flameout temperature of the mixture by conducting heat toward an inlet of the reaction chamber, and wherein media at the inlet of the oxidation chamber is cooled by the mixture being introduced into the oxidation chamber. In certain embodiments, the fuel comprises at least one of hydrogen, methane, ethane, ethylene, natural gas, propane, propylene, propadiene, n-butane, iso-butane, butylene-1, butadiene, iso-pentane, n-pentane, acetylene, hexane, and carbon monoxide. 
     In certain embodiments, a method for oxidizing fuel described herein includes the steps of receiving a gas air-fuel mixture through an intake, the mixture comprising a mixture of air and a gas fuel; compressing the mixture with a compression chamber, the compression chamber being coupled to a reciprocating engine and compressing the mixture in a reciprocating piston chamber; oxidizing the mixture in a reaction chamber that is configured to receive the mixture from the compression chamber via an inlet and to maintain oxidation of the fuel at an internal temperature of the reaction chamber without a catalyst; and expanding heated product gas from the reaction chamber in a reciprocating piston chamber coupled to the reciprocating piston chamber, thereby driving the reciprocating engine. 
     In certain embodiments, the internal temperature of the reaction chamber is maintained beneath a flameout temperature of the fuel. In certain embodiments, the steps also include removing heat from the reaction chamber when a temperature in the reaction chamber approaches or raises above the flameout temperature. In certain embodiments, a temperature of the mixture at the inlet is maintained above an autoignition temperature of the mixture. In certain embodiments, the steps also include heating the mixture by a heat exchanger prior to oxidizing the mixture in the reaction chamber. In certain embodiments, the heat exchanger is located within the reaction chamber. In certain embodiments, an inlet temperature of the mixture at the inlet of the reaction chamber is beneath an autoignition temperature of the mixture. In certain embodiments, the mixture is heated within the heat exchanger to a temperature above the autoignition temperature. 
     In certain embodiments, a method for oxidizing fuel described herein includes the steps of compressing an air-fuel mixture, comprising a mixture of air and a gas fuel, in a reciprocating piston compression chamber coupled to a reciprocating engine; oxidizing the mixture in a reaction chamber, configured to receive the mixture from the compression chamber via an inlet, above an autoignition temperature of the fuel and beneath a flameout temperature of the fuel; and expanding product gas from the reaction chamber in a reciprocating piston chamber coupled to the reciprocating engine, thereby driving the reciprocating engine. 
     In certain embodiments, an internal temperature of the reaction chamber is maintained beneath a flameout temperature of the mixture. In certain embodiments, the method also includes the step of removing heat from the reaction chamber when an adiabatic temperature in the reaction chamber approaches or raises above the flameout temperature. In certain embodiments, a temperature of the mixture at the inlet is maintained above an autoignition temperature of the mixture. In certain embodiments, the method also includes the step of heating the mixture by a heat exchanger prior to oxidizing the fuel in the reaction chamber. In certain embodiments, the heat exchanger is located within the reaction chamber. In certain embodiments, an inlet temperature of the mixture at the inlet of the reaction chamber is beneath an autoignition temperature of the mixture. In certain embodiments, the mixture is heated within the heat exchanger to a temperature above the autoignition temperature. 
     In certain embodiments, a method for oxidizing fuel described herein includes the steps of directing an air-fuel mixture, comprising a mixture of air and a gas fuel, to be compressed in a reciprocating compression piston coupled to a reciprocating engine; directing the mixture from the compression piston to a reaction chamber, configured to gradually oxidize the mixture within the reaction chamber above an autoignition temperature of the mixture and beneath a flameout temperature of the mixture; and directing product gas from the reaction chamber to be expanded in a reciprocating expansion piston coupled to the reciprocating engine, thereby driving the reciprocating engine. 
     In certain embodiments, the method also includes the step of determining, with a sensor, when a temperature in the reaction chamber approaches or exceeds the flameout temperature. In certain embodiments, the method also includes the step of directing removal of heat from the reaction chamber when the temperature in the reaction chamber approaches the flameout temperature, such that the temperature in the reaction chamber is maintained below the flameout temperature. In certain embodiments, the method also includes the step of maintaining an internal temperature within the reaction chamber below about 2300° F. 
     In certain embodiments, a method for oxidizing fuel described herein includes the steps of determining an oxygen content level within the reaction chamber having an inlet and an outlet and configured to gradually oxidize a fuel, in a gas mixture, without a catalyst; outputting instructions to introduce flue gas, received from the outlet of the reaction chamber and containing product gases from oxidation of the fuel within the reaction chamber, into the reaction chamber based on the determined oxygen content level. 
     In certain embodiments, introducing the flue gas comprises mixing the flue gas with the gas mixture. In certain embodiments, the method also includes the step of determining if an internal temperature within the reaction chamber approaches a flameout temperature of the fuel. In certain embodiments, the method also includes the step of outputting instructions to reduce the internal temperature within the reaction chamber when an adiabatic temperature within the reaction chamber approaches the flameout temperature of the fuel. In certain embodiments, the instructions comprise removing heat from the reaction chamber. In certain embodiments, outputting instructions is configured to change a flameout temperature of the fuel within the reaction chamber. In certain embodiments, the method also includes the step of determining an inlet temperature of the gas mixture at the reaction chamber inlet. In certain embodiments, the method also includes the step of increasing a temperature of the gas mixture at the inlet when the inlet temperature approaches an autoignition temperature of the fuel, such that the inlet temperature is maintained above the autoignition temperature. In certain embodiments, increasing the temperature comprises mixing the flue gas with the gas mixture at or near the reaction chamber inlet. 
     In certain embodiments, a method for oxidizing fuel described herein includes the steps of determining at least one of an oxygen content level within the reaction chamber having an inlet and an outlet and configured to gradually oxidize a fuel, in a gas mixture, without a catalyst and an inlet temperature of the gas mixture at the reaction chamber inlet; based on at least one of the determined oxygen content level and the inlet temperature, introducing flue gas, received from the outlet of the reaction chamber and containing heated product gases from oxidation of the fuel within the reaction chamber, into the reaction chamber when at least one of the determined oxygen content level is approaching or beyond a predetermined threshold and the inlet temperature is approaching or below an autoignition temperature of the fuel. 
     In certain embodiments, introducing the flue gas comprises mixing the flue gas with the gas mixture. In certain embodiments, the method also includes the step of determining if an internal temperature within the reaction chamber approaches a flameout temperature of the fuel. In certain embodiments, the method also includes the step of reducing the internal temperature within the reaction chamber when an adiabatic temperature within the reaction chamber approaches the flameout temperature of the fuel. In certain embodiments, reducing the internal temperature comprises removing heat from the reaction chamber. In certain embodiments, the method also includes the step of comprising increasing the flameout temperature within the reaction chamber by reducing the oxygen content within the reaction chamber. 
     In certain embodiments, a method for oxidizing fuel described herein includes the steps of determining, with a processor, an oxygen content level within the reaction chamber having an inlet and an outlet and configured to gradually oxidize a fuel, in a gas mixture, without a catalyst; and based on the determined oxygen content level, introducing flue gas, received from the outlet of the reaction chamber and containing heated product gases from oxidation of the fuel within the reaction chamber, into the reaction chamber. 
     In certain embodiments, introducing the flue gas comprises mixing the flue gas with the gas mixture. In certain embodiments, the flue gas is mixed with the gas mixture at or near the reaction chamber inlet. In certain embodiments, the method also includes the step of determining if an internal temperature within the reaction chamber approaches or exceeds a flameout temperature of the fuel. In certain embodiments, the method also includes the step of reducing the internal temperature within the reaction chamber when an adiabatic temperature within the reaction chamber approaches or exceeds the flameout temperature of the fuel. In certain embodiments, reducing the internal temperature comprises removing heat from the reaction chamber. In certain embodiments, the method also includes the step of changing the flameout temperature within the reaction chamber by changing the oxygen content within the reaction chamber. 
     In certain embodiments, a method for oxidizing fuel described herein includes the steps of in a first reaction chamber, with an inlet and an outlet, that is configured to maintain a gradual oxidation process without a catalyst, determining when an inlet temperature of a gas mixture, comprising an oxidizable fuel, at the reaction chamber inlet approaches or drops below an autoignition temperature of the fuel; and when the inlet temperature is determined to approach or drop below the autoignition temperature of the fuel, increasing the inlet temperature of the gas mixture by introducing flue gas, comprising at least partially oxidized product gas from the reaction chamber, into the gas mixture at or near the inlet. 
     In certain embodiments, a method for oxidizing fuel described herein includes the steps of gradually oxidizing a first fuel, in a first gas mixture, in a first reaction chamber that is configured to maintain gradual oxidation of the first fuel within the first reaction chamber without a catalyst; introducing flue gas, comprising heated product gas from oxidation of the first fuel in the first reaction chamber, into a second reaction chamber; introducing a second fuel into the second reaction chamber; and oxidizing the second fuel in the second reaction chamber in a gradual oxidation process without a catalyst; wherein a first internal temperature within the first reaction chamber is maintained beneath a flameout temperature of the first fuel. 
     In certain embodiments, the method includes the step of maintaining a second internal temperature within the second reaction chamber beneath a flameout temperature of the second fuel. In certain embodiments, the method also includes the step of reducing the second internal temperature within the second reaction chamber when an adiabatic temperature within the second reaction chamber approaches or exceeds the flameout temperature of the second fuel within the second reaction chamber. In certain embodiments, reducing the second internal temperature comprises removing heat from the second reaction chamber. In certain embodiments, the flameout temperature of the second fuel is higher than the flameout temperature of the first fuel. In certain embodiments, the method also includes the step of reducing the first internal temperature within the first reaction chamber when an adiabatic temperature within the first reaction chamber approaches or exceeds the flameout temperature of the first fuel within the first reaction chamber. In certain embodiments, reducing the first internal temperature comprises removing heat from the first reaction chamber. In certain embodiments, the method also includes the step of determining a first inlet temperature of the gas mixture at the first reaction chamber inlet. In certain embodiments, the method also includes the step of increasing the first inlet temperature when the first inlet temperature approaches or drops below an autoignition temperature of the first fuel within the first reaction chamber, such that the first inlet temperature is maintained above the autoignition temperature. In certain embodiments, the method also includes the step of determining a second inlet temperature at a second reaction chamber inlet. In certain embodiments, the method also includes the step of increasing the second inlet temperature when the second inlet temperature approaches or drops below an autoignition temperature of the second fuel within the second reaction chamber, such that the second inlet temperature is maintained above the autoignition temperature. In certain embodiments, the method also includes the step of increasing the second inlet temperature comprises introducing the flue gas to mix with the second fuel at or near the second reaction chamber inlet. 
     In certain embodiments, a method for oxidizing fuel described herein includes the steps of gradually oxidizing a first fuel, in a first gas mixture, in a first reaction chamber that is configured to maintain gradual oxidation of the first fuel within the first reaction chamber without a catalyst; introducing flue gas, comprising heated product gas from oxidation of the first fuel in the first reaction chamber, into a second reaction chamber configured to maintain gradual oxidation without a catalyst; determining, with a processor, an oxygen content level within the second reaction chamber, introducing a second fuel into the second reaction chamber; and oxidizing the second fuel in the second reaction chamber in a gradual oxidation process without a catalyst. 
     In certain embodiments, an amount and distribution within the second chamber of the introduction of flue gas into the second chamber is based on the determined oxygen content level. In certain embodiments, a first internal temperature within the first reaction chamber is maintained beneath a flameout temperature of the first fuel. In certain embodiments, the method also includes the step of maintaining a second internal temperature within the second reaction chamber beneath a flameout temperature of the second fuel. In certain embodiments, the method also includes the step of reducing the second internal temperature within the second reaction chamber when an adiabatic temperature within the second reaction chamber approaches or exceeds the flameout temperature of the second fuel within the second reaction chamber. In certain embodiments, reducing the second internal temperature comprises removing heat from the second reaction chamber. In certain embodiments, the method also includes the step of reducing the first internal temperature within the first reaction chamber when an adiabatic temperature within the first reaction chamber approaches or exceeds the flameout temperature of the first fuel within the first reaction chamber. In certain embodiments, reducing the first internal temperature comprises removing heat from the first reaction chamber. In certain embodiments, the method also includes the step of determining a first inlet temperature of the gas mixture at the first reaction chamber inlet. In certain embodiments, the method also includes the step of increasing the first inlet temperature when the first inlet temperature approaches or drops below an autoignition temperature of the first fuel within the first reaction chamber, such that the first inlet temperature is maintained above the autoignition temperature. In certain embodiments, the method also includes the step of determining a second inlet temperature at a second reaction chamber inlet. In certain embodiments, the method also includes the step of increasing the second inlet temperature when the second inlet temperature approaches or drops below an autoignition temperature of the second fuel within the second reaction chamber, such that the second inlet temperature is maintained above the autoignition temperature. In certain embodiments, increasing the second inlet temperature comprises introducing the flue gas to mix with the second fuel at or near the second reaction chamber inlet. 
     In certain embodiments, a system for oxidizing fuel described herein includes a first reaction chamber with a first inlet and a first outlet, the first reaction chamber configured to receive a first gas comprising a first oxidizable fuel, the first reaction chamber configured to maintain a gradual oxidation process of the first fuel; and a second reaction chamber with a second inlet and a second outlet, the second reaction chamber configured to receive a second gas comprising a second oxidizable fuel, the second reaction chamber configured to maintain a gradual oxidation process of the second fuel; wherein the first and second reaction chambers are configured to maintain an internal temperature in the respective reaction chambers below a flameout temperature of the respective fuel; wherein the second reaction chamber is configured to receive flue gas comprising heated product gas from oxidation of the first fuel in the first reaction chamber, into a second reaction chamber through the second inlet. 
     In certain embodiments, the system includes a heat exchange media disposed within at least one of the reaction chambers, the media configured to maintain an internal temperature of the reaction chamber below an adiabatic flameout temperature. In certain embodiments, at least one of the first and second reaction chambers is configured to reduce the respective internal temperature when an adiabatic temperature within the respective reaction chamber approaches or exceeds the flameout temperature of the respective fuel. In certain embodiments, at least one of first and second reaction chambers is configured to reduce the respective internal temperature by removing heat from the respective reaction chamber by a heat exchanger. In certain embodiments, the heat exchanger comprises a fluid introduced into the respective reaction chamber. In certain embodiments, the heat exchanger is configured to evacuate the fluid from the respective reaction chamber. In certain embodiments, the heat exchanger comprises a means for generating steam. 
     In certain embodiments, the heat exchanger is configured to draw heat out of the respective reaction chamber when the temperature within the respective reaction chamber exceeds 2300° F. In certain embodiments, the first reaction chamber is configured to increase a temperature of the first gas at the first inlet when a first inlet temperature, at the first inlet, approaches or drops below an autoignition temperature of the first fuel. In certain embodiments, the second reaction chamber is configured to increase a temperature of the second gas at the second inlet when a second inlet temperature, at the second inlet, approaches or drops below an autoignition temperature of the second fuel. 
     In certain embodiments, the second reaction chamber is configured to mix the flue gas with the second gas when a second inlet temperature of the second gas at the second inlet approaches or drops below an autoignition temperature of the second fuel. In certain embodiments, distribution of the flue gas within the second reaction chamber is based on at least one of a second inlet temperature of the second gas at the second inlet and the internal temperature of the second reaction chamber. In certain embodiments, the system also includes a turbine or a piston engine that receives gas from at least one of the reaction chambers. In certain embodiments, the turbine receives gas from the second reaction chamber. In certain embodiments, a compressor that receives and compresses gas, comprising a fuel mixture, prior to introduction of the fuel mixture into at least one of the reaction chambers. In certain embodiments, the compressor is configured to compress the second gas prior to introducing the second gas into the second reaction chamber. 
     In certain embodiments, a system for oxidizing fuel described herein includes an oxidizer having a reaction chamber configured to receive and oxidize a gas mixture comprising an oxidizable fuel in a gradual oxidation process within the reaction chamber; an inlet configured to introduce fluid into the reaction chamber during the oxidation process, the fluid being at an inlet temperature lower than an internal temperature of the reaction chamber, such that the fluid is heated as it is introduced into the reaction chamber; and an outlet configured to extract the heated fluid from the reaction chamber; wherein the reaction chamber is configured to maintain the internal temperature above an autoignition temperature of the fuel and below a flameout temperature of the fuel. 
     In certain embodiments, the inlet is configured to introduce a liquid into the reaction chamber. In certain embodiments, the liquid is introduced into the reaction chamber by passing through one or more coils within the reaction chamber. In certain embodiments, the coils are not in fluid communication with the reaction chamber. In certain embodiments, the liquid is introduced into the reaction chamber by injecting the liquid into the reaction chamber, such that the liquid mixes with the gas mixture within the reaction chamber. In certain embodiments, the inlet is configured to introduce the fluid into the reaction chamber as a gas. In certain embodiments, the gas is introduced into the reaction chamber by passing through one or more coils within the reaction chamber. In certain embodiments, the coils do not permit mixing of the gas and the gas mixture within the reaction chamber. In certain embodiments, the gas is introduced into the reaction chamber by injecting the gas into the reaction chamber, such that the gas mixes with the gas mixture within the reaction chamber. In certain embodiments, the outlet is configured to extract the heated fluid from the reaction chamber as a gas. In certain embodiments, the outlet is configured to redirect the gas into the reaction chamber, such that the gas mixes with the gas mixture within the reaction chamber. In certain embodiments, an adiabatic reaction temperature within the reaction chamber approaches a flameout temperature, the fluid is introduced into the reaction chamber. In certain embodiments, the inlet temperature is below an autoignition temperature of the fuel. In certain embodiments, the oxidizable fuel comprises at least one of hydrogen, methane, ethane, ethylene, natural gas, propane, propylene, propadiene, n-butane, iso-butane, butylene-1, butadiene, iso-pentane, n-pentane, acetylene, hexane, and carbon monoxide. 
     In certain embodiments, a method for oxidizing fuel described herein includes the steps of directing a gas mixture, comprising an oxidizable fuel, to an oxidizer having a reaction chamber configured to receive and oxidize the fuel in a gradual oxidation process within the reaction chamber, the reaction chamber being configured to maintain an internal temperature above an autoignition temperature of the fuel and below a flameout temperature of the fuel; and introducing fluid into the reaction chamber during the oxidation process, the fluid being at an inlet temperature lower than the internal temperature of the reaction chamber, such that the fluid is heated as it is introduced into the reaction chamber; and extracting the heated fluid from the reaction chamber. 
     In certain embodiments, the fluid is introduced into the reaction chamber as a liquid. In certain embodiments, the liquid is introduced into the reaction chamber by passing through one or more coils within the reaction chamber. In certain embodiments, the liquid is injected into the reaction chamber, such that the liquid mixes with the gas mixture within the reaction chamber. In certain embodiments, the fluid is introduced into the reaction chamber as a gas. In certain embodiments, the gas is introduced into the reaction chamber by passing the gas through one or more coils within the reaction chamber. In certain embodiments, the gas is injecting the gas into the reaction chamber, such that the gas mixes with the gas mixture within the reaction chamber. In certain embodiments, the heated fluid is extracted from the reaction chamber as a heated gas. In certain embodiments, the method also includes the step of redirecting the heated gas into the reaction chamber, such that the heated gas mixes with the gas mixture within the reaction chamber. In certain embodiments, the oxidizable fuel comprises at least one of hydrogen, methane, ethane, ethylene, natural gas, propane, propylene, propadiene, n-butane, iso-butane, butylene-1, butadiene, iso-pentane, n-pentane, acetylene, hexane, and carbon monoxide. 
     In certain embodiments, an oxidizer for oxidizing fuel described herein includes a reaction chamber having one or more inlets that are configured to direct at least one gas of fuels, oxidants, or diluents, into the reaction chamber and one or more outlets that are configured to direct reaction products from the reaction chamber, and a heater that is configured to maintain a temperature of one or more of the at least one gas, at or before the one or more inlets, to above an autoignition temperature of a resulting mixture within the reaction chamber that comprises the at least one gas of fuels, oxidants, or diluents, and wherein the reaction chamber is configured to oxidize the mixture and maintain an adiabatic temperature and a maximum reaction temperature in the reaction chamber below a flameout temperature of the mixture. 
     In certain embodiments, the reaction chamber comprises a single inlet. In certain embodiments, the oxidizer is configured to change a flow rate that the mixture is introduced into the reaction chamber through the inlet. In certain embodiments, the heater comprises a heat exchanger that transfers heat from the reaction products to the mixture at or before the one or more inlets. In certain embodiments, the heater is configured to mix at least one of oxidants or diluents with fuel at or before the one or more inlets. In certain embodiments, the oxidizer is configured to use heat from the reaction products to generate steam. In certain embodiments, the oxidizer is configured to use heat from the reaction products to drive a generator for power generation. In certain embodiments, the oxidizer is configured to drive a generator by a turbine or a piston engine that is configured to expand the reaction products from the reaction chamber. In certain embodiments, the oxidizer is configured to use heat from the reaction products to heat material that is not passed through the oxidizer. In certain embodiments, the oxidizer is configured to change a flow rate that one or more of the at least one gas of fuels, oxidants, or diluents is introduced into the reaction chamber through the one or more inlets. In certain embodiments, the oxidizer is configured to change a flow rate that the reaction products are directed from the reaction chamber through the outlets. In certain embodiments, the oxidizer also includes a regulator that is configured to change at least one of a flow of the mixture or a pressure of the mixture at or near the inlet. 
     In certain embodiments, an oxidizer for oxidizing fuel described herein includes a reaction chamber having an inlet that is configured to direct at least one gas of fuels, oxidants, or diluents, into the reaction chamber and an outlet that is configured to direct reaction products from the reaction chamber, and means for maintaining a temperature of the incoming gas, at or before the inlet, to above an autoignition temperature of a resulting mixture within the reaction chamber that comprises the at least one gas of fuels, oxidants, or diluents, wherein the reaction chamber is configured to oxidize the mixture and maintain an adiabatic temperature and a maximum reaction temperature in the reaction chamber below a flameout temperature of the mixture. 
     In certain embodiments, the reaction chamber comprises a plurality of inlets. In certain embodiments, the reaction chamber comprises a plurality of outlets. In certain embodiments, the means for raising a temperature comprises a heat exchanger that transfers heat from the reaction products to the mixture at or before the inlet. In certain embodiments, the means for raising a temperature is configured to mix diluents with fuel at or before the inlet. In certain embodiments, the oxidizer is configured to use heat from the reaction products to generate steam. In certain embodiments, the oxidizer is configured to use heat from the reaction products to drive a generator for power generation. In certain embodiments, the oxidizer is configured to drive a generator by a turbine or a piston engine that is configured to expand the reaction products from the reaction chamber. In certain embodiments, the oxidizer is configured to use heat from the reaction products to heat material that is not passed through the oxidizer. In certain embodiments, the oxidizer is configured to change a flow rate that the mixture is introduced into the reaction chamber through the inlet. In certain embodiments, the oxidizer is configured to change a flow rate that the reaction products are directed from the reaction chamber through the outlet. In certain embodiments, the oxidizer also includes a regulator that is configured to change at least one of a flow of the mixture or a pressure of the mixture at or near the inlet. In certain embodiments, the oxidizer is configured to change a flow rate that one or more of the at least one gas of fuel, oxidants, or diluents is introduced into the reaction chamber through one or more inlets. 
     In certain embodiments an oxidizer for oxidizing fuel described herein include a reaction chamber having one or more inlets that are configured to direct at least one gas of fuels, oxidants, or diluents, into the reaction chamber and one or more outlets that are configured to direct reaction products from the reaction chamber; and a heater that is configured to maintain a temperature of one or more of the at least one gas, at or before the one or more inlets, to above an autoignition temperature of a resulting mixture within the reaction chamber that comprises the at least one gas of fuel, oxidants, or diluents, wherein the reaction chamber is configured to oxidize the mixture and maintain an adiabatic temperature within the reaction chamber above a flameout temperature of the mixture and a maximum reaction temperature within the reaction chamber below the flameout temperature of the mixture. 
     In certain embodiments, the oxidizer comprises a heat extractor that is configured to remove heat from the reaction chamber. In certain embodiments, the heat extractor is configured to remove heat from the reaction chamber by generating steam. In certain embodiments, the reaction chamber comprises a single inlet. In certain embodiments, the oxidizer is configured to change a flow rate that the mixture is introduced into the reaction chamber through the single inlet. In certain embodiments, the heater comprises a heat exchanger that transfers heat from the reaction products to the mixture at or before the one or more inlets. In certain embodiments, the heater is configured to mix diluents with fuel at or before the one or more inlets. In certain embodiments, the oxidizer is configured to use heat from the reaction products to generate steam. In certain embodiments, the oxidizer is configured to use heat from the reaction products to drive a generator for power generation. In certain embodiments, the oxidizer is configured to drive a generator by a turbine or a piston engine that is configured to expand the reaction products from the reaction chamber. In certain embodiments, the oxidizer is configured to use heat from the reaction products to heat material that is not passed through the oxidizer. In certain embodiments, the oxidizer is configured to change a flow rate that the reaction products are directed from the reaction chamber through the outlets. In certain embodiments, the oxidizer is configured to change a flow rate that one or more of the at least one gas of fuel, oxidants, or diluents is introduced into the reaction chamber through the one or more inlets. In certain embodiments, the oxidizer also includes a regulator that is configured to change at least one of a flow of the mixture or a pressure of the mixture at or near the inlet. 
     In certain embodiments, an oxidizer for oxidizing fuel described herein includes a reaction chamber having an inlet that is configured to direct at least one gas of fuel, oxidants, or diluents, into the reaction chamber and an outlet that is configured to direct reaction products from the reaction chamber, means for maintaining a temperature of the mixture, at or before the plurality of inlets, to above an autoignition temperature of the mixture, and means for maintaining a temperature of the incoming gas, at or before the inlet, to above an autoignition temperature of a resulting mixture within the reaction chamber that comprises the at least one gas of fuels, oxidants, or diluents, wherein the reaction chamber is configured to oxidize the mixture and maintain an adiabatic temperature within the reaction chamber above a flameout temperature of the mixture and a maximum reaction temperature within the reaction chamber below the flameout temperature of the mixture. 
     In certain embodiments, the reaction chamber comprises a plurality of inlets. In certain embodiments, the reaction chamber comprises a plurality of outlets. In certain embodiments, the means for raising a temperature comprises a heat exchanger that transfers heat from the reaction products to the mixture at or before the inlet. In certain embodiments, the means for raising a temperature is configured to mix diluents with fuel at or before the inlet. In certain embodiments, the oxidizer is configured to use heat from the reaction products to generate steam. In certain embodiments, the oxidizer is configured to use heat from the reaction products to drive a generator for power generation. In certain embodiments, the oxidizer is configured to drive a generator by a turbine or a piston engine that is configured to expand the reaction products from the reaction chamber. In certain embodiments, the oxidizer is configured to use heat from the reaction products to heat material that is not passed through the oxidizer. In certain embodiments, the oxidizer is configured to change a flow rate that the mixture is introduced into the reaction chamber through the inlet. In certain embodiments, the oxidizer is configured to change a flow rate that the reaction products are directed from the reaction chamber through the outlet. In certain embodiments, the oxidizer also includes a regulator that is configured to change at least one of a flow of the mixture or a pressure of the mixture at or near the inlet. 
     In certain embodiments, an oxidizer for oxidizing fuel described herein includes a reaction chamber having one or more inlets that are configured to direct at least one gas of fuels, oxidants, or diluents, into the reaction chamber and one or more outlets that are configured to direct reaction products from the reaction chamber; and a heater that is configured to maintain a temperature of one or more of the at least one gas, at or before the one or more inlets, to below an autoignition temperature of a resulting mixture within the reaction chamber that comprises the at least one gas of fuel, oxidants, or diluents, wherein and the reaction chamber is configured to oxidize the mixture and maintain an adiabatic temperature within the reaction chamber below a flameout temperature of the mixture and a maximum reaction temperature within the reaction chamber below the flameout temperature of the mixture. 
     In certain embodiments, the reaction chamber comprises a single inlet. In certain embodiments, the oxidizer is configured to change a flow rate that the mixture is introduced into the reaction chamber through the one or more inlets. In certain embodiments, the oxidizer is configured to change a flow rate that one or more of the at least one gas of fuel, oxidants, or diluents is introduced into the reaction chamber through the one or more inlets. In certain embodiments, the oxidizer also includes a heat exchanger that transfers heat from the reaction products to the mixture at or before the one or more inlets. In certain embodiments, the heater is configured to mix diluents with fuel at or before the one or more inlets. In certain embodiments, the oxidizer is configured to use heat from the reaction products to generate steam. In certain embodiments, the oxidizer is configured to use heat from the reaction products to drive a generator for power generation. In certain embodiments, the oxidizer is configured to drive a generator by a turbine or a piston engine that is configured to expand the reaction products from the reaction chamber. In certain embodiments, the oxidizer is configured to use heat from the reaction products to heat material that is not passed through the oxidizer. In certain embodiments, the oxidizer is configured to change a flow rate that the reaction products are directed from the reaction chamber through the outlets. In certain embodiments, the oxidizer also includes a regulator that is configured to change at least one of a flow of the mixture or a pressure of the mixture at or near the inlet. 
     In certain embodiments, an oxidizer for oxidizing fuel described herein includes a reaction chamber having an inlet that is configured to direct at least one gas of fuel, oxidants, or diluents, into the reaction chamber and an outlet that is configured to direct reaction products from the reaction chamber, and means for maintaining a temperature of the incoming gas, at or before the inlet, to below an autoignition temperature of a resulting mixture within the reaction chamber that comprises the at least one gas of fuel, oxidants, or diluents, wherein the reaction chamber is configured to oxidize the mixture and maintain an adiabatic temperature within the reaction chamber below a flameout temperature of the mixture and a maximum reaction temperature within the reaction chamber below the flameout temperature of the mixture. 
     In certain embodiments, the reaction chamber comprises a plurality of inlets. In certain embodiments, the reaction chamber comprises a plurality of outlets. In certain embodiments, the means for maintaining a temperature comprises a heat exchanger that transfers heat from the reaction products to the mixture at or before the inlet. In certain embodiments, the means for maintaining a temperature is configured to mix diluents with fuel at or before the inlet. In certain embodiments, the oxidizer is configured to use heat from the reaction products to generate steam. In certain embodiments, the oxidizer is configured to use heat from the reaction products to drive a generator for power generation. In certain embodiments, the oxidizer is configured to drive a generator by a turbine or a piston engine that is configured to expand the reaction products from the reaction chamber. In certain embodiments, the oxidizer is configured to use heat from the reaction products to heat material that is not passed through the oxidizer. In certain embodiments, the oxidizer is configured to change a flow rate that the mixture is introduced into the reaction chamber through the inlet. In certain embodiments, the oxidizer is configured to change a flow rate that the reaction products are directed from the reaction chamber through the outlet. In certain embodiments, the oxidizer includes a regulator that is configured to change at least one of a flow of the mixture or a pressure of the mixture at or near the inlet. 
     In certain embodiments, an oxidizer for oxidizing fuel described herein includes a reaction chamber having one or more inlets that are configured to direct at least one gas of fuel, oxidants, or diluents, into the reaction chamber and one or more outlets that are configured to direct reaction products from the reaction chamber, and a heater that is configured to maintain a temperature of one or more of the at least one gas, at or before the one or more inlets, to below an autoignition temperature of a resulting mixture within the reaction chamber that comprises the at least one gas of fuel, oxidants, or diluents, wherein the reaction chamber is configured to oxidize the mixture and maintain an adiabatic temperature within the reaction chamber above a flameout temperature of the mixture and a maximum reaction temperature within the reaction chamber below the flameout temperature of the mixture. 
     In certain embodiments, a heat extractor that is configured to remove heat from the reaction chamber. In certain embodiments, the heat extractor is configured to remove heat from the reaction chamber by generating steam. In certain embodiments, the oxidizer also includes a heat conveyor within the reaction chamber that is configured to distribute heat within the reaction chamber. In certain embodiments, the heat conveyor comprises a porous media within the reaction chamber. In certain embodiments, the heat conveyor comprises a fluid media within the reaction chamber. In certain embodiments, the heat conveyor comprises a media that is circulated through the reaction chamber. In certain embodiments, the reaction chamber comprises a single inlet. In certain embodiments, the oxidizer also includes a heat exchanger that transfers heat from the reaction products to the mixture at or before the one or more inlets. In certain embodiments, the heater is configured to mix diluents with fuel at or before the one or more inlets. In certain embodiments, the oxidizer is configured to use heat from the reaction products to drive a generator for power generation. In certain embodiments, the oxidizer is configured to drive a generator by a turbine or a piston engine that is configured to expand the reaction products from the reaction chamber. In certain embodiments, the oxidizer is configured to use heat from the reaction products to heat material that is not passed through the oxidizer. In certain embodiments, the oxidizer is configured to change a flow rate that one or more of the at least one gas of fuel, oxidants, or diluents is introduced into the reaction chamber through the one or more inlets. In certain embodiments, the oxidizer is configured to change a flow rate that the reaction products are directed from the reaction chamber through the outlets. In certain embodiments, the oxidizer also includes a regulator that is configured to change at least one of a flow of the mixture or a pressure of the mixture at or near the inlet. 
     In certain embodiments, an oxidizer for oxidizing fuel described herein includes a reaction chamber having an inlet that is configured to direct at least one gas of fuel, oxidants, or diluents, into the reaction chamber and an outlet that is configured to direct reaction products from the reaction chamber, and a heater for maintaining a temperature of the incoming gas, at or before the inlet, to below an autoignition temperature of a resulting mixture within the reaction chamber that comprises the at least one gas of fuel, oxidants, or diluents, wherein the reaction chamber is configured to oxidize the mixture and maintain an adiabatic temperature within the reaction chamber above a flameout temperature of the mixture and a maximum reaction temperature within the reaction chamber below the flameout temperature of the mixture. 
     In certain embodiments, the oxidizer includes means for removing heat from the reaction chamber. In certain embodiments, the means for removing heat is configured to remove heat from the reaction chamber by generating steam. In certain embodiments, the oxidizer also includes means for distributing heat within the reaction chamber. In certain embodiments, the means for distributing heat comprises a porous media within the reaction chamber. In certain embodiments, the means for distributing heat comprises a fluid media within the reaction chamber. In certain embodiments, the means for distributing heat comprises a media that is circulated through the reaction chamber. In certain embodiments, the reaction chamber comprises a plurality of inlets. In certain embodiments, the reaction chamber comprises a plurality of outlets. In certain embodiments, the heater comprises a heat exchanger that transfers heat from the reaction products to the mixture at or before the inlet. In certain embodiments, the heater is configured to mix diluents with fuel at or before the inlet. 
     In certain embodiments, the oxidizer is configured to use heat from the reaction products to drive a generator for power generation. In certain embodiments, the oxidizer is configured to drive a generator by a turbine or a piston engine that is configured to expand the reaction products from the reaction chamber. In certain embodiments, the oxidizer is configured to use heat from the reaction products to heat material that is not passed through the oxidizer. In certain embodiments, the oxidizer is configured to change a flow rate that one or more of the at least one gas of fuel, oxidants, or diluents is introduced into the reaction chamber through the inlet. In certain embodiments, the oxidizer is configured to change a flow rate that the reaction products are directed from the reaction chamber through the outlet. In certain embodiments, the oxidizer also includes a regulator that is configured to change at least one of a flow of the mixture or a pressure of the mixture at or near the inlet. 
     In certain embodiments, a system for oxidizing fuel described herein includes a first reaction chamber having a first inlet and a first outlet, the first reaction chamber being configured to receive a first gas, comprising an oxidizable fuel, through the first inlet, the first reaction chamber configured to maintain gradual oxidation of the first gas and to communicate flue gas through the first outlet; and a second reaction chamber, separate from the first reaction chamber, having a second inlet and a second outlet, the second reaction chamber being configured to receive a second gas, comprising an oxidizable fuel, and the flue gas through the second inlet, the second reaction chamber configured to maintain gradual oxidation of the second gas; wherein the flue gas is communicated from the first outlet to the second inlet until an internal temperature within the second reaction chamber is above an autoignition temperature of the second gas. 
     In certain embodiments, the flue gas is not communicated from the first outlet to the second inlet after the internal temperature is above the autoignition temperature. In certain embodiments, at least one of the first or second reaction chambers is configured to reduce a respective internal temperature when the internal temperature within the respective reaction chamber approaches or exceeds a flameout temperature of the respective fuel. In certain embodiments, at least one of first or second reaction chambers is configured to reduce the respective internal temperature by removing heat from the respective reaction chamber. In certain embodiments, at least one of first or second reaction chambers is configured to remove heat by a heat exchanger. In certain embodiments, the heat exchanger comprises a fluid introduced into the respective reaction chamber. In certain embodiments, the heat exchanger is configured to evacuate the fluid from the respective reaction chamber. In certain embodiments, the heat exchanger comprises a means for generating steam. In certain embodiments, the heat exchanger is configured to draw heat out of the respective reaction chamber when the temperature within the respective reaction chamber exceeds 2300° F. In certain embodiments, the second reaction chamber is configured to mix the flue gas with the second gas when a temperature of the second gas at the second inlet approaches or drops below the autoignition temperature of the second fuel. In certain embodiments, the system also includes a turbine or a piston engine that receives gas from at least one of the reaction chambers. In certain embodiments, the turbine receives and expands gas from the second reaction chamber. In certain embodiments, the system also includes a compressor that receives and compresses gas prior to introduction of the gas into at least one of the reaction chambers. In certain embodiments, the compressor is configured to compress the second gas prior to introducing the second gas into the second reaction chamber. 
     In certain embodiments, a system for oxidizing fuel described herein includes a first reaction chamber having an outlet, the first reaction chamber being configured to maintain gradual oxidation of a first gas, comprising an oxidizable fuel, and to communicate reaction products through the first outlet; and a second reaction chamber, separate from the first reaction chamber, having an inlet that is configured to receive a second gas, comprising an oxidizable fuel, and the reaction products, the second reaction chamber being configured to maintain gradual oxidation of the second gas and to receive the reaction products from the first reaction chamber through the inlet while an internal temperature within the second reaction chamber is below an autoignition temperature of the second gas. 
     In certain embodiments, the reaction products are not communicated to the second reaction chamber from the first reaction chamber after the internal temperature is above the autoignition temperature. In certain embodiments, at least one of the first or second reaction chambers is configured to reduce a respective internal temperature when the internal temperature within the respective reaction chamber approaches or exceeds a flameout temperature of the respective fuel. In certain embodiments, at least one of first or second reaction chambers is configured to reduce the respective internal temperature by removing heat from the respective reaction chamber. In certain embodiments, the second reaction chamber is configured to mix the reaction products with the second gas when a temperature of the second gas at the inlet approaches or drops below the autoignition temperature of the second fuel. In certain embodiments, the system also includes a turbine or a piston engine that receives gas from at least one of the reaction chambers. In certain embodiments, the turbine receives and expands gas from the second reaction chamber. In certain embodiments, the system also includes a compressor that receives and compresses gas prior to introduction of the gas into at least one of the reaction chambers. In certain embodiments, the compressor is configured to compress the second gas prior to introducing the second gas into the second reaction chamber. 
     In certain embodiments, a system for oxidizing fuel described herein includes an oxidizer having a reaction chamber with an inlet and an outlet, the reaction chamber configured to receive a gas comprising an oxidizable fuel through the inlet and to maintain an oxidation process; a detection module that detects when a reaction chamber temperature of the gas approaches or drops below an autoignition threshold of the gas within the reaction chamber, such that the reaction chamber will not oxidize the fuel; and a correction module that outputs instructions, based on the detection module, to change at least one of a residence time of the gas within the reaction chamber and an autoignition delay time within the reaction chamber sufficient for the gas to autoignite and oxidize while within the reaction chamber. 
     In certain embodiments, the correction module is configured to change the residence time of the gas within the reaction chamber by altering flow of the gas through the reaction chamber. In certain embodiments, the correction module is configured to increase the residence time of the gas within the reaction chamber by decreasing flow of the gas through the reaction chamber. In certain embodiments, the correction module is configured to increase the residence time of the gas within the reaction chamber by recirculating flow of the gas from the outlet to the inlet of the reaction chamber. In certain embodiments, the correction module is configured to change the autoignition delay time within the reaction chamber by changing a gas temperature within the reaction chamber. In certain embodiments, the correction module is configured to decrease the autoignition delay time within the reaction chamber by increasing a gas temperature within the reaction chamber with a heater. In certain embodiments, the correction module is configured to decrease the autoignition delay time within the reaction chamber by circulating product gas from the outlet to the inlet. In certain embodiments, the reaction chamber is configured to maintain oxidation of the oxidizable fuel beneath the flameout temperature without a catalyst. In certain embodiments, the system also includes a turbine or a piston engine that receives gas from the reaction chamber and expands the gas. In certain embodiments, the system also includes a compressor that receives and compresses gas, comprising a fuel mixture, prior to introduction of the fuel mixture into the reaction chamber. In certain embodiments, the oxidizable fuel comprises at least one of hydrogen, methane, ethane, ethylene, natural gas, propane, propylene, propadiene, n-butane, iso-butane, butylene-1, butadiene, iso-pentane, n-pentane, acetylene, hexane, and carbon monoxide. 
     In certain embodiments, a system for oxidizing fuel described herein includes an oxidizer having a reaction chamber with an inlet and an outlet, the reaction chamber configured to receive a gas comprising an oxidizable fuel through the inlet and to maintain an oxidation process, a detection module that detects when a reaction chamber temperature of the gas approaches or drops below an autoignition threshold of the gas within the reaction chamber, such that the reaction chamber will not oxidize the fuel, and a correction module that is configured to determine, with a processor and based on the detection module, a change to at least one of a residence time of the gas within the reaction chamber and an autoignition delay time within the reaction chamber sufficient for the gas to autoignite and oxidize while within the reaction chamber, wherein the oxidizer is configured to, based on the change to at least one of the residence time and the autoignition delay time, oxidize the gas while the gas is within the reaction chamber. 
     In certain embodiments, the correction module is configured to change the residence time of the gas within the reaction chamber by altering flow of the gas through the reaction chamber. In certain embodiments, the correction module is configured to increase the residence time of the gas within the reaction chamber by decreasing flow of the gas through the reaction chamber. In certain embodiments, the correction module is configured to increase the residence time of the gas within the reaction chamber by recirculating flow of the gas from the outlet to the inlet of the reaction chamber. In certain embodiments, the correction module is configured to change the autoignition delay time within the reaction chamber by changing a gas temperature within the reaction chamber. In certain embodiments, the correction module is configured to decrease the autoignition delay time within the reaction chamber by increasing a gas temperature within the reaction chamber with a heater. In certain embodiments, the correction module is configured to decrease the autoignition delay time within the reaction chamber by circulating product gas from the outlet to the inlet. In certain embodiments, the reaction chamber is configured to maintain oxidation of the oxidizable fuel beneath the flameout temperature without a catalyst. 
     In certain embodiments, a system for oxidizing fuel described herein include an oxidizer having a reaction chamber with an inlet and an outlet, the reaction chamber configured to receive a gas comprising an oxidizable fuel through the inlet and to maintain an oxidation process, and a module that outputs instructions, based on detection of a reaction chamber temperature, to increase at least one of a residence time of the gas within the reaction chamber and a reaction temperature within the reaction chamber, such that the fuel oxidizes while in the reaction chamber. 
     In certain embodiments, the module is configured to change the residence time of the gas within the reaction chamber by altering flow of the gas through the reaction chamber. In certain embodiments, the module is configured to increase the residence time of the gas within the reaction chamber by decreasing flow of the gas through the reaction chamber. In certain embodiments, the module is configured to increase the residence time of the gas within the reaction chamber by recirculating flow of the gas from the outlet to the inlet of the reaction chamber. In certain embodiments, the module is configured to decrease the autoignition delay time within the reaction chamber by increasing a gas temperature within the reaction chamber with a heater. In certain embodiments, the correction module is configured to decrease the autoignition delay time within the reaction chamber by circulating product gas from the outlet to the inlet. 
     In certain embodiments, a method for oxidizing fuel described herein includes the steps of in an oxidation system that receives a gas comprising an oxidizable fuel into a reaction chamber having an inlet and an outlet and being configured to maintain an oxidation process, detecting when a reaction chamber temperature of the gas approaches or drops below a level such that the reaction chamber alone will not support oxidation of the fuel, and changing, based on the detection module, at least one of a residence time of the gas within the reaction chamber and an autoignition delay time within the reaction chamber sufficient for the gas to autoignite and oxidize while within the reaction chamber. 
     In certain embodiments, the residence time of the gas is changed within the reaction chamber by altering flow of the gas through the reaction chamber. In certain embodiments, the residence time of the gas is changed within the reaction chamber by decreasing flow of the gas through the reaction chamber. In certain embodiments, the residence time of the gas is changed within the reaction chamber by recirculating flow of the gas from the outlet to the inlet of the reaction chamber. In certain embodiments, the autoignition delay time within the reaction chamber is changed by changing a gas temperature within the reaction chamber. In certain embodiments, the autoignition delay time is decreased within the reaction chamber by increasing a gas temperature within the reaction chamber with a heater. In certain embodiments, the autoignition delay time is decreased by circulating product gas from the outlet to the inlet. In certain embodiments, the reaction chamber maintains oxidation of the oxidizable fuel beneath the flameout temperature without a catalyst. In certain embodiments, the method also includes the step of expanding product gas from the reaction chamber in a turbine or a piston engine. In certain embodiments, the method also includes the step of compressing the gas prior to introducing the gas into the reaction chamber. In certain embodiments, the oxidizable fuel comprises at least one of hydrogen, methane, ethane, ethylene, natural gas, propane, propylene, propadiene, n-butane, iso-butane, butylene-1, butadiene, iso-pentane, n-pentane, acetylene, hexane, and carbon monoxide. 
     In certain embodiments, a method for oxidizing fuel described herein includes the steps of in an oxidation system that receives a gas comprising an oxidizable fuel into a reaction chamber having an inlet and an outlet and being configured to maintain an oxidation process, detecting when a reaction chamber temperature of the gas approaches or drops below a level such that the reaction chamber alone will not support gradual oxidation of the fuel, and changing, based on the detection module, an autoignition delay time within the reaction chamber sufficient for the gas to autoignite and oxidize while within the reaction chamber. 
     In certain embodiments, changing the autoignition delay time comprises introducing additional heat into the reaction chamber, thereby increasing an internal reaction chamber temperature to a level that will maintain oxidation of the fuel. In certain embodiments, the method also includes the step of changing the residence time of the gas within the reaction chamber by altering flow of the gas through the reaction chamber. In certain embodiments, the method also includes the step of changing the residence time of the gas within the reaction chamber by decreasing flow of the gas through the reaction chamber. In certain embodiments, the method also includes the step of changing the residence time of the gas within the reaction chamber by recirculating flow of the gas from the outlet to the inlet of the reaction chamber. In certain embodiments, the reaction chamber maintains oxidation of the oxidizable fuel beneath the flameout temperature without a catalyst. In certain embodiments, the method also includes the step of expanding product gas from the reaction chamber in a turbine or a piston engine. In certain embodiments, the oxidizable fuel comprises at least one of hydrogen, methane, ethane, ethylene, natural gas, propane, propylene, propadiene, n-butane, iso-butane, butylene-1, butadiene, iso-pentane, n-pentane, acetylene, hexane, and carbon monoxide. 
     In certain embodiments, a method for oxidizing fuel described herein includes the step of maintaining oxidation of an oxidizable fuel by introducing a heat source into the reaction chamber, thereby increasing an internal reaction chamber temperature to a level that will maintain oxidation of the fuel when a reaction chamber temperature of the gas approaches or drops below a temperature level such that the reaction chamber alone will not support oxidation of the fuel. 
     In certain embodiments, increasing the internal temperature decreases autoignition delay time. In certain embodiments, the method also includes the step of changing the residence time of the gas within the reaction chamber by altering flow of the gas through the reaction chamber. In certain embodiments, the method also includes the step of changing the residence time of the gas within the reaction chamber by decreasing flow of the gas through the reaction chamber. In certain embodiments, the method also includes the step of changing the residence time of the gas within the reaction chamber by recirculating flow of the gas from the outlet to the inlet of the reaction chamber. In certain embodiments, the reaction chamber maintains oxidation of the oxidizable fuel beneath the flameout temperature without a catalyst. In certain embodiments, the method also includes the step of expanding product gas from the reaction chamber in a turbine or a piston engine. In certain embodiments, the oxidizable fuel comprises at least one of hydrogen, methane, ethane, ethylene, natural gas, propane, propylene, propadiene, n-butane, iso-butane, butylene-1, butadiene, iso-pentane, n-pentane, acetylene, hexane, and carbon monoxide. 
     In certain embodiments, a method of oxidizing a fuel described herein includes the steps of mixing a gas having a low-energy-content (LEC) fuel with one or more of the group of a gas comprising a high-energy-content (HEC) fuel, a gas comprising an oxidant, and a gas comprising a diluent to form a gas mixture, wherein all of the gases are at temperatures below the autoignition temperature of any of the gases being mixed; increasing the temperature of the gas mixture to at the least an autoignition temperature of the gas mixture and allowing the gas mixture to autoignite; and maintaining the temperature of the gas mixture below a flameout temperature while the autoignited gas mixture oxidizes. 
     In certain embodiments, the gas mixture is raised to at least the autoignition temperature by a heat exchanger. In certain embodiments, the heat exchanger is positioned within a reaction chamber that maintains oxidation of the gas mixture without a catalyst. In certain embodiments, the gas mixture is raised to at least the autoignition temperature within a reaction chamber that maintains oxidation of the gas mixture without a catalyst. In certain embodiments, the reaction chamber maintains oxidation of the mixture beneath a flameout temperature of the gas mixture. In certain embodiments, the method also includes the step of expanding gas with a turbine or a piston engine that receives the gas from the reaction chamber. In certain embodiments, the gas mixture comprises at least one of hydrogen, methane, ethane, ethylene, natural gas, propane, propylene, propadiene, n-butane, iso-butane, butylene-1, butadiene, iso-pentane, n-pentane, acetylene, hexane, and carbon monoxide. 
     In certain embodiments, a method of oxidation described herein includes the steps of heating a gas comprising an oxidant to at the least an auto-ignition temperature of a first gas mixture comprising a gas with an oxidant mixed with determined ranges of a low-energy-content (LEC) fuel and a high-energy-content (HEC) fuel; injecting, after the heating, a second gas mixture of the LEC fuel gas and the HEC fuel, wherein the ratio of the LEC and HEC gas and the rate of injection are selected to produce substantially the same first gas mixture ratios when injected into the heated gas containing an oxidant; mixing the injected second gas with the heated gas containing an oxidant at a rate to produce a substantially homogeneous first gas mixture in a time less than the ignition delay time for the second gas mixture and allowing the first gas mixture to auto-ignite; and maintaining the temperature of the first gas mixture below a flameout temperature while the auto-ignited first gas mixture oxidizes. 
     In certain embodiments, the first gas mixture is raised to at least the autoignition temperature by a heat exchanger. In certain embodiments, the heat exchanger is positioned within a reaction chamber that maintains oxidation of the first gas mixture without a catalyst. In certain embodiments, the first gas mixture is raised to at least the autoignition temperature within a reaction chamber that maintains oxidation of the gas mixture without a catalyst. In certain embodiments, the reaction chamber maintains oxidation of the second gas mixture beneath a flameout temperature of the gas mixture. In certain embodiments, the method also includes the step of expanding gas with a turbine or a piston engine that receives the gas from the reaction chamber. In certain embodiments, the first gas mixture comprises at least one of hydrogen, methane, ethane, ethylene, natural gas, propane, propylene, propadiene, n-butane, iso-butane, butylene-1, butadiene, iso-pentane, n-pentane, acetylene, hexane, and carbon monoxide. In certain embodiments. 
     In certain embodiments, a method of oxidization described herein includes the steps of receiving into a reaction chamber, via a chamber inlet, the inlet configured to accept a gas having a mixture of a low-energy-content (LEC) fuel and at least one of the group of a high-energy-content (HEC) fuel, an oxidant-comprising (OC) gas, and a diluent-containing (DC) gas, the gas mixture being at a temperature below an auto-ignition temperature of the gas mixture; maintaining an internal temperature of the reaction chamber below a flameout temperature by heat exchange media disposed within the reaction chamber, maintaining a reaction chamber inlet temperature of the fuel to be greater than an autoignition temperature of the fuel by transferring heat through the heat exchange media, and directing gas entering the inlet through a first path through media that is hotter than an auto-ignition temperature of the gas mixture until the gas mixture reaches a temperature above the auto-ignition temperature of the gas mixture; and directing the gas through a second path through the media to a chamber outlet, the second path being generally opposite to the first flow path. 
     In certain embodiments, the reaction chamber maintains oxidation of the gas mixture without a catalyst. In certain embodiments, the reaction chamber maintains oxidation of the mixture beneath a flameout temperature of the gas mixture by circulating the heat exchange media outside the reaction chamber. In certain embodiments, the method also includes the step of expanding gas with a turbine or a piston engine that receives the gas from the reaction chamber outlet. In certain embodiments, the gas mixture comprises at least one of hydrogen, methane, ethane, ethylene, natural gas, propane, propylene, propadiene, n-butane, iso-butane, butylene-1, butadiene, iso-pentane, n-pentane, acetylene, hexane, and carbon monoxide. 
     In certain embodiments, an oxidizer described herein includes a reaction chamber having an inlet and an outlet, the inlet configured to accept a gas having a mixture of a low-energy-content (LEC) fuel and at least one of the group of a high-energy-content (HEC) fuel, an oxidant-comprising (OC) gas, and a diluent-containing (DC) gas, the gas mixture being at a temperature below an auto-ignition temperature of the gas mixture; a heat exchange media disposed within the reaction chamber, the media configured to maintain an internal temperature of the reaction chamber below a flameout temperature and to maintain a reaction chamber inlet temperature of the fuel to be greater than an autoignition temperature of the fuel; and at least one flow path through the chamber from the inlet to the outlet, the flow path configured to direct the gas entering the inlet through a first path through media that is hotter than an auto-ignition temperature of the gas mixture until the gas mixture reaches a temperature above the auto-ignition temperature of the gas mixture, whereupon the flow path is further configured to direct the oxidizing gas mixture through a second path through the media to the outlet, the second path being generally opposite to the first flow path. 
     In certain embodiments, the reaction chamber is configured to maintain oxidation of the gas mixture along at least one of the first and second flow paths without a catalyst. In certain embodiments, the reaction chamber is configured to maintain oxidation of the mixture beneath the flameout temperature of the gas mixture by circulating heat exchange media outside the reaction chamber. In certain embodiments, the system also includes at least one of a turbine or a piston engine that is configured to receive gas from the reaction chamber outlet and expand the gas. In certain embodiments, the gas mixture comprises at least one of hydrogen, methane, ethane, ethylene, natural gas, propane, propylene, propadiene, n-butane, iso-butane, butylene-1, butadiene, iso-pentane, n-pentane, acetylene, hexane, and carbon monoxide. 
     In certain embodiments, an oxidizer described herein includes a reaction chamber having an inlet and an outlet, the inlet configured to accept a gas having a mixture of a low-energy-content (LEC) fuel and at least one of the group of a high-energy-content (HEC) fuel, an oxidant-comprising (OC) gas, and a diluent-containing (DC) gas, the gas mixture being at a temperature below an auto-ignition temperature of the gas mixture; and a heat controller that is configured to increase a temperature of the gas mixture to at the least an autoignition temperature of the gas mixture, thereby permitting the gas mixture to autoignite and to maintain the temperature of the gas mixture below a flameout temperature while the autoignited gas mixture oxidizes. 
     In certain embodiments, the heat controller comprises a heat exchanger that is configured to raise the temperature of the mixture to at least the autoignition temperature. In certain embodiments, the heat exchanger is positioned within the reaction chamber. In certain embodiments, the heat exchanger is configured to heat the mixture to above the autoignition temperature after the mixture is within the reaction chamber. In certain embodiments, the reaction chamber is configured to maintain oxidation of the mixture beneath a flameout temperature of the gas mixture without a catalyst. In certain embodiments, the system also includes at least one of a turbine or a piston engine that receives gas from the reaction chamber and expands the gas. In certain embodiments, the gas mixture comprises at least one of hydrogen, methane, ethane, ethylene, natural gas, propane, propylene, propadiene, n-butane, iso-butane, butylene-1, butadiene, iso-pentane, n-pentane, acetylene, hexane, and carbon monoxide. 
     In certain embodiments, an oxidizer described herein includes a reaction chamber having an inlet and an outlet, the inlet configured to accept a gas having a mixture of a low-energy-content (LEC) fuel and at least one of the group of a high-energy-content (HEC) fuel, an oxidant-comprising (OC) gas, and a diluent-containing (DC) gas, the gas mixture being at a temperature below an auto-ignition temperature of the gas mixture; a heat controller that is configured to heat the gas to at the least an auto-ignition temperature of a first gas mixture, comprising a gas with an oxidant mixed with determined ranges of a low-energy-content (LEC) fuel and a high-energy-content (HEC) fuel; an injector that is configured to inject, after the first gas is heated to at the least an auto-ignition temperature of a first gas mixture, a second gas mixture of the LEC fuel gas and the HEC fuel, wherein the injector injects a ratio of the LEC and HEC gas and at a rate of injection that is selected to produce substantially the same ratio of LEC and HEC gas as the first gas mixture when the gas is injected into the reaction chamber, wherein the reaction chamber is configured to mix the injected second gas with the heated gas containing an oxidant at a rate to produce a substantially homogeneous first gas mixture in a time less than the ignition delay time for the second gas mixture and allowing the first gas mixture to auto-ignite and to maintain the temperature of the first gas mixture below a flameout temperature while the auto-ignited first gas mixture oxidizes. 
     In certain embodiments, the heat controller comprises a heat exchanger that is configured to raise the temperature of the mixture to at least the autoignition temperature. In certain embodiments, the heat exchanger is positioned within the reaction chamber. In certain embodiments, the reaction chamber is configured to maintain oxidation of the first gas mixture within the reaction chamber without a catalyst. In certain embodiments, the reaction chamber is configured to maintain oxidation of the second gas mixture beneath a flameout temperature of the gas mixture without a catalyst. In certain embodiments, the system also includes at least one of a turbine or a piston engine that is configured to receive gas from the reaction chamber and to expand the gas. In certain embodiments, the first gas mixture comprises at least one of hydrogen, methane, ethane, ethylene, natural gas, propane, propylene, propadiene, n-butane, iso-butane, butylene-1, butadiene, iso-pentane, n-pentane, acetylene, hexane, and carbon monoxide. 
     The details of one or more embodiments of these concepts are set forth in the accompanying drawings and the description below. Other features, objects, and advantages of these concepts will be apparent from the description and drawings, and from the claims. As described herein various embodiments referenced above or described below may be used together and in conjunction with other embodiments described or suggested herein. The separate discussion of different embodiments should not be construed, unless otherwise clearly described, as meaning that the embodiments are distinct or cannot be combined, as embodiments described in one portion, figure, section, or paragraph can be combined with other embodiments described elsewhere. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings, which are included to provide further understanding and are incorporated in and constitute a part of this specification, illustrate disclosed embodiments and together with the description serve to explain the principles of the disclosed embodiments. 
         FIG. 1-1A  is a schematic representation of a conventional fired or supplemental-fired oxidizer system for disposing of a waste stream containing VOCs. 
         FIG. 1-1B  is a schematic representation of a conventional catalytic oxidizer system. 
         FIG. 1-1C  is a schematic representation of a conventional oxidizer system that includes a recuperator. 
         FIG. 1-1D  is a schematic representation of a conventional regenerative oxidizer system. 
         FIG. 1-2A  is a diagram of the ignition energy of an air-methane mixture. 
         FIG. 1-2B  is a diagram of the reaction temperatures of various combustion and oxidation processes. 
         FIG. 1-3  is a diagram of the gradual oxidation of a pre-mixed air-fuel mixture according to certain aspects of the present disclosure. 
         FIG. 1-4A  is a diagram of the gradual oxidation of a fuel mixture when injected into pre-heated air according to certain aspects of the present disclosure. 
         FIG. 1-4B  is a diagram of the gradual oxidation process used to heat an external fluid according to certain aspects of the present disclosure. 
         FIG. 1-4C  is a diagram of a multi-stage gradual oxidation process according to certain aspects of the present disclosure. 
         FIG. 1-5  is a flow chart of an exemplary gradual oxidation process of a pre-mixed air-fuel mixture according to certain aspects of the present disclosure. 
         FIG. 1-6  is a flow chart of an exemplary gradual oxidation process of a fuel mixture that is injected into pre-heated air according to certain aspects of the present disclosure. 
         FIG. 1-7  is a schematic diagram of an exemplary pre-mix oxidation system according to certain aspects of the present disclosure. 
         FIG. 1-8  is a schematic diagram of an exemplary injection gradual oxidation system according to certain aspects of the present disclosure. 
         FIG. 1-9  is a schematic representation of an exemplary turbine-driven power-generation system according to certain aspects of the present disclosure. 
         FIG. 1-10  is a schematic representation of another turbine-driven power-generation system according to certain aspects of the present disclosure. 
         FIG. 1-11  is a cutaway view of an exemplary GO reaction chamber with direct fuel or air-fuel mixture according to certain aspects of the present disclosure. 
         FIG. 1-12  schematically depicts the flow through a gradual oxidation system having a sparger according to certain aspects of the present disclosure. 
         FIG. 1-13  is a schematic representation of a multi-stage GO reaction chamber according to certain aspects of the present disclosure. 
         FIG. 1-14  is a schematic representation of a fluidized bed GO reaction chamber according to certain aspects of the present disclosure. 
         FIG. 1-15A  is a schematic representation of a recirculating bed GO reaction chamber according to certain aspects of the present disclosure. 
         FIG. 1-15B  is a schematic representation of another recirculating bed GO reaction chamber according to certain aspects of the present disclosure. 
         FIG. 1-16  is a schematic representation of a GO reaction chamber with flue gas recirculation according to certain aspects of the present disclosure. 
         FIGS. 1-17A and 1-17B  depict a GO reaction chamber with structured reaction elements according to certain aspects of the present disclosure. 
         FIG. 2-1  is a schematic representation of an oxidizer coupled to a heat exchanger to provide process heating to an industrial process according to certain aspects of the present disclosure. 
         FIG. 2-2  is a schematic representation of an oxidizer coupled to a heating chamber to heat a process material according to certain aspects of the present disclosure. 
         FIG. 2-3  is a schematic representation of an oxidizer comprising an internal heat exchanger through which a process gas passes according to certain aspects of the present disclosure. 
         FIG. 2-4  is a schematic representation of another embodiment of an oxidizer comprising a plurality of internal heat exchangers through which a process gas passes according to certain aspects of the present disclosure. 
         FIG. 2-5  is a schematic representation of an oxidizer comprising a plurality of gradual oxidation zones with adjoining reaction zones wherein batches of a process material are heated according to certain aspects of the present disclosure. 
         FIG. 2-6  is a schematic representation of an oxidizer comprising a plurality of gradual oxidation zones with adjoining reaction zones wherein continuous flows of a process material are heated according to certain aspects of the present disclosure. 
         FIGS. 2-7A and 2-7B  are a perspective view and a cross-section view of an example design detail of an oxidizer element according to certain aspects of the present disclosure. 
         FIG. 2-8  is a plot of the temperatures with the oxidizer of  FIGS. 2-7A and 2-7B  according to certain aspects of the present disclosure. 
         FIG. 2-9  is a perspective view of an oxidizer assembly using the oxidizer element of  FIGS. 2-7A and 2-7B  according to certain aspects of the present disclosure. 
         FIG. 3-1  is a schematic of an exemplary Schnepel cycle power generation system according to certain aspects of the present disclosure. 
         FIG. 3-2  is a conceptual depiction of the power generation system of  FIG. 3-1  according to certain aspects of the present disclosure. 
         FIGS. 3-3 to 3-10  are schematic representation of additional embodiments of Schnepel cycle power generation systems according to certain aspects of the present disclosure. 
         FIG. 4-1  is a three-stage gradual oxidizer fluid heater system according to certain aspects of the present disclosure. 
         FIG. 4-2  is another embodiment of a three-stage gradual oxidizer fluid heater system according to certain aspects of the present disclosure. 
         FIG. 4-3  is another embodiment of a single-stage recuperative fluid heating system according to certain aspects of the present disclosure. 
         FIG. 4-4  is another embodiment of a two-stage water-tube type of steam generation system according to certain aspects of the present disclosure. 
         FIG. 4-5  is another embodiment of a two-stage fire-tube type of fluid heating system according to certain aspects of the present disclosure. 
         FIG. 4-6  schematically depicts the flow through a gradual oxidation system, which generates steam, having a sparger according to certain aspects of the present disclosure. 
         FIG. 5-1  is a schematic diagram of an exemplary gradual oxidation system incorporating steam generation and additional fuel injection according to certain aspects of the present disclosure. 
         FIG. 5-2  is a schematic diagram of an exemplary gradual oxidation system incorporating steam generation and cogeneration according to certain aspects of the present disclosure. 
         FIG. 5-3  is a schematic diagram of an exemplary gradual oxidation system incorporating dual compressors with intercooling according to certain aspects of the present disclosure. 
         FIG. 5-4  is a schematic diagram of an exemplary gradual oxidation system incorporating a starter gradual oxidizer according to certain aspects of the present disclosure. 
         FIG. 5-5  is a schematic diagram of an exemplary gradual oxidation system incorporating multiple points of water injection according to certain aspects of the present disclosure. 
         FIG. 5-6  is a diagram of the typical gas content of the exhaust of various systems. 
     
    
    
     DETAILED DESCRIPTION 
     The following description discloses embodiments of a system for oxidation of a gas that comprises an oxidizable fuel. In certain embodiments, the system includes an oxidizer that can operate to gradually oxidize fuel while maintaining a temperature within the oxidizer below a flameout temperature, so that formation of undesirable pollutants, e.g., nitrogen oxide (NOx) and carbon monoxide (CO), is significantly limited. The fuel desirably enters the oxidizer at or near an autoignition temperature of the fuel. The system is particularly adapted for utilization of a fuel with low energy content, such as a methane content below 5%, in a sustainable gradual oxidation process to drive a turbine that further drives a power generator as well as driving a compressor in the system. 
     In the following detailed description, numerous specific details are set forth to provide an understanding of the present disclosure. It will be apparent, however, to one ordinarily skilled in the art that embodiments of the present disclosure may be practiced without some of the specific details. In other instances, well-known structures and techniques have not been shown in detail so as not to obscure the disclosure. 
     Certain embodiments of methods and systems disclosed herein are presented in terms of a turbine system that drives a power generator using a low-energy-content fluid, such as a methane-containing gas, as a primary fuel and a higher-energy-content fluid, such as natural gas or commercial propane, as an auxiliary fuel. Nothing in this disclosure should be interpreted, unless specifically stated as such, to limit the application of any method or system disclosed herein to a particular primary or auxiliary fuel or a turbine system of this particular configuration. Other configurations of turbine-compressor systems are known to those of skill in the art can be used, and the components and principles disclosed herein can be applied to these other systems. 
     Certain embodiments of methods and systems disclosed herein are presented in terms of an oxidizer coupled to a reciprocating-piston system that drives a power generator. Nothing in this disclosure should be interpreted, unless specifically stated as such, to limit the application of any method or system disclosed herein with respect to a turbine system, such as the use of an auxiliary fuel during a portion of the operation, from application to a reciprocating-piston system or a combination of reciprocating-piston and turbine systems. 
     Certain embodiments of methods and systems disclosed herein are presented in terms of integrated process equipment that utilizes a GO process separately or integrally with material processing functions. Nothing in this disclosure should be interpreted, unless specifically stated as such, to limit the application of any method or system disclosed herein with respect to a turbine system or reciprocating-piston system, such as the use of an auxiliary fuel during a portion of the operation, from application to integrated process equipment or a combination of one or more of the reciprocating-piston systems, turbine systems, and integrated process equipment. 
     Within this document, the term “NOx” refers to a group of oxides of nitrogen that includes nitric oxide and nitrogen dioxide (NO and NO2). There are at least three commonly acknowledged processes that form NOx. “Thermal NOx” is formed when oxygen and nitrogen present in the combustion air dissociate in the high temperature area of the combustion zone and subsequently react to form oxides of nitrogen. “Prompt NOx” is formed in the proximity of the flame front as fuel fragments attack molecular nitrogen to form products such as HCN and N, which are then oxidized to form NOx. “Fuel NOx” is formed by fuel compounds containing nitrogen, e.g., amines and cyano species, when fuels containing nitrogen are burned. Diatomic nitrogen (N2) is not considered a fuel-bound nitrogen that will generate fuel NOx. 
     Within this document, the term “flammable” refers to a characteristic of a material wherein the material will combine with oxygen in an exothermic self-sustaining or self-propagating reaction when the material and oxygen are present within a defined range of relative amounts. It may require an initiating event, such as a spark or flame, to initiate the exothermic reaction. 
     Within this document, the terms “lower flammability limit” (LFL), sometimes called the “lower explosive limit.” and “upper flammability limit” (UFL), sometimes called the “rich flammability limit” or “upper explosion limit.” refer to the volumetric fuel concentration where a flame can exist. Concentrations below the LFL or above the UFL will not cause a flame reaction to sustain or propagate. 
     Within this document, the term “low-energy-content fuel” (LEC fuel) refers to a gas that comprises a flammable gas as a secondary component and an inert gas as a primary component. A non-limiting example of an LEC fuel is the methane-containing gas that is emitted from a landfill or other waste disposal site. For example, LEC methane gas typically contains less than about 30% methane, but may contain as low as 1-5% methane. 
     Within this document, the term “high-energy-content fuel” (HEC fuel) refers to a gas that comprises a flammable gas as a primary component. HEC fuel may contain secondary components that are naturally mixed with the primary component, inert, or cannot be economically removed. A non-limiting example of a HEC fuel is “commercial propane.” the composition of which varies locally, but generally contains &gt;85% propane (C3H8) and allows up to 10% propylene, up to 10% ethane (C2H8), up to 2.5% butane (C4H10) and heavier hydrocarbons, and may include ˜0.01% of an odorant, usually ethyl mercaptan. A second non-limiting example of a HEC fuel is “natural gas,” wherein a typical unrefined composition may contain as little as 70% methane and a combined 20% or more of ethane, propane, and butane as well as smaller amounts of carbon dioxide (CO2), oxygen (O2), nitrogen (N2), and hydrogen sulfide (H2S). A third non-limiting example is a landfill gas comprising more than about 50% methane with the balance C02, N2, and a little O2. 
     Within this document, the term “oxidant” refers to a gas that comprises sufficient oxygen to support combustion or oxidation of a flammable fuel. A nonlimiting example of an oxidant is ambient air. 
     Within this document, the term “diluent” refers to a generally inert gas. Nonlimiting examples of a diluent are commercial CO2, N2, and H2O. Diluents can be present in the oxidation products or the fuel reactants. 
     Within this document, the term “generally inert” is used to refer to a material or mixture that does not contain enough flammable material or oxygen to support combustion or oxidation when mixed with either oxygen or fuel when supplied with an ignition source. 
     Within this document, the term “combustible concentration” refers to the amount of flammable material present in a mixture, wherein the concentration is usually expressed in terms of a ratio of the flammable material in a mixture to the total gas. 
     Within this document, the term “gradual oxidation” refers to a process where a material combines with oxygen in an exothermic reaction while the material remains below a determined temperature during the entire process. A non-limiting example of such a determined temperature is 2300° F., wherein oxidation processes that stay below this temperature will not form generally significant amounts of NOx with respect to air pollution regulations and standards. 
     Within this document, the term “air-fuel mixture” refers to a mixture of a combustible fuel and an oxidant, and preferably to a gaseous mixture comprising air. An air-fuel mixture is considered to be generally homogeneous unless stated otherwise. In certain circumstances, an LEC or HEC fuel is mixed with ambient air to form an air-fuel mixture. In certain circumstances, an LEC fuel may contain sufficient oxygen and fuel to be considered an air-fuel mixture without the further addition of air or fuel. 
     Within this document, the term “autoignition” refers to the spontaneous initiation of an oxidation or combustion process in a mixture comprising flammable material and an oxidant. The autoignition temperature is the minimum temperature at which an oxidation or combustion process will occur in the absence of an ignition source and may depend on the pressure and/or the oxygen and fuel concentrations of the mixture. 
     Within this document, the term “autoignition delay time” refers to the amount of time a for a mixture, at a temperature above the autoignition temperature, to oxidize and release the majority of its exothermic energy. By way of illustration, methane has an autoignition temperature of about 1000° F. If a mixture of methane and air is raised to 1000° F., then it will eventually react to produce H2O and CO2. However, if this same mixture is brought up to a higher temperature, for example 1200° F., then the ignition delay time might be 2 seconds. If the mixture is brought up to 1400° F., then the delay might be 100 milliseconds. Autoignition delay time is generally exponentially faster with higher temperatures, and is a function of fuel and oxygen concentrations. Autoignition delay times can be calculated with chemical kinetic software programs using complex kinetic mechanisms that can include hundreds of reactions and tens of molecular and radial species. 
     Within this document, the term “premixed” refers to mixing of air and flammable material, such as an LEC or HEC fuel, to form a generally homogeneous air-fuel mixture prior to introducing the mixture into a chamber in which oxidation or combustion will take place. 
     Within this document, the terms “short residence time” is defined relative to combustion apparatus such as conventional combustion engines, gas turbine combustors, reciprocating engines, burners for boilers, etc. In these conventional combustors, the combustion process is completed within a time period that is typically well below 1 second, usually below 100 milliseconds, and can be below 10 milliseconds. A process having a residence time closer to 1 second, or exceeding 1 second, is termed as having a “long residence time.” 
     Within this document, the term “volatile organic compound” (VOC) refers to organic compounds that will enter a gas phase when at a temperature in the range of 40-120° F. and may combine with oxygen in an exothermic reaction. Examples of VOCs include, but are not limited to, acetone, acrolein, acrylonitrile, allyl alcohol, allyl chloride, benzene, butene-1, chlorobenzene, 1-2 dichloroethane, ethane, ethanol, ethyl acrylate, ethylene, ethyl formate, ethyl mercaptan, methane, methyl chloride, methyl ethyl ketone, propane, propylene, toluene, triethylamine, vinyl acetate, and vinyl chloride. 
     Within this document, the term “maximum reaction temperature” refers to the maximum temperature of the chemical oxidation reaction, which includes heat transfer or work losses or additions. For example, if heat is removed simultaneously while the reaction occurs, the maximum reaction temperature will be less that the adiabatic reaction temperature. Similarly, the maximum reaction temperature can be higher than the adiabatic reaction temperature if heat is added. 
     Within this document, “flame strain rate” or “flame stretch” refers to coupling of the turbulent straining of the flame front, either by stretching or curvature, that removes heat from the flame front. High rates of flame stretch can be created with strong shear layers, and if the strain rate is high enough, can extinguish a flame. 
     Within this document, the term “adiabatic reaction temperature” refers to the temperature that results from a complete chemical oxidation reaction that occurs without any work, heat transfer, or changes in kinetic or potential energy. This is sometimes referred to as a constant-volume adiabatic reaction temperature. 
     Within this document, the term “flameout temperature” refers to the temperature of a substantially uniformly mixed air-fuel mixture below which a flame will not propagate through the mixture. In some instances, by way of example and as shown herein, the flameout temperature may be equivalent to the LFL at any particular temperature of the air-fuel mixture. 
     Gradual Oxidation 
       FIG. 1-2A  is a diagram of the ignition energy for an air-methane mixture. A mixture of methane and air is flammable in the range of approximately 5-15%, by volume, of methane. A stoichiometric mixture of methane and air. i.e., a mixture having precisely enough oxygen to combine with the methane, is approximately 9.5%, by volume.  FIG. 1-2A  shows that a stoichiometric air-methane mixture  55  requires the least ignition energy and that increased energy is needed at lower and higher methane concentrations to ignite the mixture. 
       FIG. 1-2B  is a diagram of the reaction temperatures of various combustion and oxidation processes, as depicted by system  60 . In Zone  1 , the combustion must be propagated by an energy source. With a flowing source of mixture, as typical in combustion devices, the energy source to stabilize combustion must be relatively constant with respect to time. This energy source is typically created by creating a hot local pocket of hot combustion products in a recirculation zone. These zones are created behind bluff bodies or other geometric features (V-gutters, corner recirculation zones). A second method is to swirl a portion of the mixture sufficiently such that “vortex breakdown” occurs, and a recirculation zone is formed inside or behind the swirling mixture. These types of flame stabilization techniques are well-known in the combustion art. The hot recirculation zone serves as a continuous ignition source to keep the premixed fuel and air mixture in Zone  1  constantly burning. 
     In Zone  2  of  FIG. 1-2B , a flame, even when initiated by a spark or other ignition source, will not propagate through an air-fuel mixture. The uniform air-fuel mixture is too lean to burn. One method to react a premixed air-fuel mixture in this zone is to lower the activation energy of the reaction with a catalyst. Another method is to provide a locally richer mixture within the combustion chamber. This locality would have a combustible concentration, and therefore reaction temperatures consistent with Zone  1 . This richer mixture burns and keeps a flame within the combustion chamber, however, propagating the reaction into the lean regions within the combustion chamber will not occur by flame propagation and will have to be performed using gas mixing techniques. 
     Zone  1  and Zone  2  are separated by a line indicating the flameout temperature over a range of temperatures. One cannot maintain a flame with a premixed fuel concentration that results in an adiabatic reaction temperature below this line. To expand on this, if one starts with a premixed flame in Zone  1  and slowly reduces the fuel concentration, the flame temperature, which in this case is the maximum reaction temperature shown as the Y-axis of  FIG. 1-2 , will decrease. When the temperature approaches the flameout temperature line, the flame will be extinguished. 
     A homogeneous air-fuel mixture in Zone  3  of  FIG. 1-2B  will autoignite and react relatively quickly. The challenge of this “flameless combustion” quadrant is to uniformly mix the fuel and air and bring the mixture to the desired temperature before the air-fuel mixture ignites. For example, if one mixes the fuel and air at a temperature below the autoignition limit, as designated by point “ 62 ” in Zone  1 , then any unplanned spark will ignite the mixture while still in Zone  1 . In addition, once the air-fuel mixture is fully mixed at point “ 62 ”, the air-fuel mixture is heated to point “ 64 ” by, for example, a heat exchanger or other heating method. 
     Practitioners of flameless combustion avoid the challenge of mixing at low temperatures without combustion by mixing the fuel with hot air in Zone  3 . To prevent ignition from occurring prior to reaching a uniform mixture, the autoignition is delayed by the use of one of two techniques. One technique is to inject the fuel into a mixture of air and recirculated flue gas. The flue gas has, relative to air, excess CO2 and H2O and a reduced amount of O2. The reduced O2 concentration will delay autoignition, thereby permitting the mixture of the fuel with the air-flue gas mixture to reach a generally homogeneous composition. 
     A second technique is to induce “flame strain rate” or “flame stretch” to delay autoignition. Strained flames are flames that occur in highly turbulent flows with strong shear layers. They create a turbulent-chemistry interaction which delays reactions and, in extreme cases, can extinguish flames. To implement flame stretch, the fuel is injected into a turbulent air flow, e.g. the air is emitted from a nozzle at a high velocity and the fuel is injected into the stream of emitted air. The air-fuel mixture reaches a generally homogeneous composition before the flow of the air-fuel mixture becomes non-turbulent, and flame stretch causes the delay of autoignition during this mixing period. It is possible to combine the two techniques and inject the fuel into a jet of an oxidant that comprises a mixture of air and recirculated flue gas, thereby delaying the autoignition of the oxidant-fuel mixture by both a reduction in the O2 concentration and flame stretch, thereby achieving a distributed reaction throughout the chamber. 
     One aspect of the flame structure in Zone  1  is that the oxidation reaction takes place in a relatively narrow reaction zone, called the flame front. In this locality, heat from the post-combustion zone and chemical radicals from the flame are diffusing, both molecularly and turbulently, into the unreacted gases. In Zone  2 , reaction occurs locally near the catalyst, and is termed heterogeneous combustion. Only Zones  3  and  4  are capable of a volumetrically-distributed reaction due to the autoignition initiating the reaction, as opposed to thermal feedback from an existing flame. 
     Zone  4  is the region wherein the fuel concentration is too low to sustain a flame, i.e. below the flameout temperature line, and hot enough to autoignite. Gradual oxidation is suitable for the oxidation of fuels in this zone. In contrast to Zones  1 - 2 , reactions in Zone  4  may occur relatively uniformly within the entire reactor/combustor volume with no well-defined ‘reaction flame front.’ 
       FIG. 1-3  is a schematic diagram of an exemplary gradual oxidation process according to certain aspects of the present disclosure.  FIG. 1-3  shows the various regions, numbered  72 ,  74 ,  75 ,  76   a ,  76   b , and  78 , of flame reaction behavior for a homogenous air-fuel mixture at a constant pressure. The ordinate is the temperature of the air-fuel mixture and the abscissa is the concentration of fuel in the air-fuel mixture. The LFL becomes lower, i.e., a leaner combustible concentration, as the temperature of the air-fuel mixture increases. The UFL becomes higher, i.e. a richer combustible concentration, as the temperature increases. It can be seen that a wider range of combustible concentrations becomes flammable as the temperature increases. 
     Zone  72  is a region where a mixture will not autoignite, but a flame will propagate through the air-fuel mixture after the introduction of a sufficient energy source. The usual form of energy introduction is a spark from a spark plug or igniter, although other devices such as glow plugs or ionized plasmas could be used. 
     Zone  74  lies below the LFL and below the autoignition temperature. In this region, a flame, even if initiated by a spark, will not propagate through the mixture. 
     Zone  76  is broken into two zones  76   a  and  76   b  to account for the time to complete the reaction. If a spark occurs within Zones  76   a  or  76   b , a flame will be initiated and will propagate through the air-fuel mixture. Air-fuel mixtures in Zones  76   a  or  76   b  may also autoignite because the energy contained by the air-fuel mixture at these temperatures exceeds the activation energy of the air-fuel mixture, as previously discussed with respect to  FIG. 1-2B . The minimum temperature at which a mixture will autoignite, given enough time, is known as the autoignition temperature (AIT). Zone  76  is bounded by the AIT and the UFL and LFL, and any mixture having a combustible concentration and a temperature within Zone  76   b  or  76   a  will autoignite. Combustion of air-fuel mixtures in Zone  76   a  will autoignite and react in a timeframe shorter than a short residence time. Air-fuel mixtures at combustible concentrations and temperatures in Zone  76   b  will also autoignite and react, but will react in a timeframe consistent with a long residence time. 
     In Zone  78 , a spark or other energy source will not initiate a flame nor will a flame propagate through the air-fuel mixture. It is possible to oxidize the fuel through autoignition by allowing enough time for the oxidation reactions to complete. The time for these reactions in Zone  78  is consistent with a long residence time. 
     Zone  75  is irrelevant to most combustion devices. A flame cannot propagate through an air-fuel in Zone  75  as the combustible composition is too rich. If an oxidation process were to be initiated in the portion of Zone  75  that is above the autoignition temperature, there is not enough air to complete the oxidation of the fuel and the oxidation process will self-extinguish, resulting in unburned fuel being exhausted from the combustion device. 
     In certain aspects, a process starting at point  80  heats an air-fuel mixture to a temperature above an autoignition temperature of the air-fuel mixture, indicated by point  82 . A reaction chamber, such as reaction chamber  500  of  FIG. 1-11 , is configured to oxidize the air-fuel mixture and maintain an adiabatic temperature and a maximum reaction temperature in the reaction chamber below the flameout temperature of the air-fuel mixture, as indicated by the dashed line connecting points  82  and  84  remaining below the LFL. 
       FIG. 1-4A  is a diagram of the gradual oxidation of a fuel mixture when injected into pre-heated air according to certain aspects of the present disclosure. In this process, ambient air at point “ 92 ” in Zone  74  is heated by various means (heat exchange, compression) to point “94” in Zone  78 . Fuel, which may be LEC fuel, diluted HEC fuel, or a mixture of HEC and LEC fuels, is then added to the hot air, thereby moving the air-fuel mixture from point “94” to point “96” that would be within the Zone  76   a  of  FIG. 1-3  wherein the air-fuel mixture would autoignite and, since point “96” is within Zone  76   a  of  FIG. 1-3 , the combustion reaction would occur rapidly, consistent with a short residence time. As the combustion process progresses, the temperature of the air-fuel would rise while the concentration of combustible gas drops and the process would follow the arrow from point “96” to point “98.” As point “98” is above the thermal NOx formation temperature, this process would produce a greater quantity of NOx than a process that remains below the thermal NOx formation temperature. 
     However, if a diluent, such as recirculated flue gas, is added to the air, the oxygen content of the resulting air-diluent mixture is reduced. The use of hot recirculated flue gas can also aid in heating the air from point “92” to point “94.” The addition of the diluent to the air, as well as the use of flame stretch mixing technique in mixing fuel into the air-diluent mixture, moves the upper and lower flammability limits to new lines annotated as “UFL (air+diluent+stretch)” and “LFL (air+diluent+stretch)” as shown in  FIG. 1-4A . 
     With the addition of a diluent and use of a flame stretch mixing technique, point “ 96 ” is no longer in Zone  76   a  but is in Zone  76   b , where the reaction process would be delayed, longer than in Zone  76   a . The diluents within the mixture reduce the temperature rise so that the process follows the arrow from point “ 96 ” to point “ 99 ” and remains under the thermal NOx formation temperature. Thus, use of a diluent can reduce the amount of NOx produced by the combustion/oxidation process. 
     In certain aspects, a process starting at point  92  heats air to a temperature, indicated by point  82 , above an autoignition temperature of a target air-fuel mixture. Fuel is then injected into the hot air, bringing the sair-fuel mixture to point  97 . A reaction chamber, such as reaction chamber  500  of  FIG. 1-11 , is configured to oxidize the air-fuel mixture and maintain an adiabatic temperature within the reaction chamber above a flameout temperature of the mixture and a maximum reaction temperature within the reaction chamber below the flameout temperature of the mixture, as indicated by the dashed line connecting points  97  and  98  quickly transitioning to below the LFL. 
       FIG. 1-4B  is a diagram  120  of the gradual oxidation process used to heat an external fluid according to certain aspects of the present disclosure. Ambient air at point  92  is heated to point  94 , wherein fuel is injected into the pre-heated air taking the air-fuel mixture to point  96 . As the air-fuel mixture is above the auto ignition temperature, gradual oxidation will begin while, at the same time, the air-fuel mixture is transferring heat to an external fluid, for example through a steam coil  5220  of  FIG. 5-3 , such that the temperature of the air-fuel mixture drops as the fuel concentration also declines to point  122 . The air-fuel mixture then moves away from the external fluid and continues to gradually oxidize without losing heat to an external fluid such that the temperature of the air-fuel mixture rises as the fuel concentration continues to decline, thereby moving to point  124  where the fuel has been completely consumed. 
       FIG. 1-4C  is a diagram  130  of a multi-stage gradual oxidation process according to certain aspects of the present disclosure. An ambient-temperature air-fuel mixture at point  132  is heated to point  134  that is above the autoignition temperature such that gradual oxidation is initiated and the air-fuel mixture progresses to point  136  whereupon the fuel is completely consumed. The hot air-diluent mixture is passed through a heat exchanger and heat removed, thereby moving the air-diluent mixture to point  138 . Additional fuel is injected into the air-diluent mixture, thereby moving the mixture to point  140 . The gradual oxidation process is initiated, as the mixture is still above the autoignition temperature, and the process moves along the line to point  142  whereupon the fuel is again completely consumed. In can been seen that the hot air-diluent mixture can be again circulated through a heat exchanger as before and the loop of points  142 - 138 - 140  repeated several times until all of the oxygen in the mixture is consumed, all the while keeping the peak reaction temperatures below the thermal NOx formation temperature. 
       FIGS. 1-5 and 1-6  are flow chart of exemplary gradual oxidation processes according to certain aspects of the present disclosure.  FIG. 1-5  discloses a pre-mix process  100  wherein an oxidant, a diluent, and LEC and HEC fuels are mixed and then heated to an autoignition temperature, thereby initiating a gradual oxidation of the fuels. A particular embodiment of the process of  FIG. 1-5  may include only some of the disclosed steps or may have such steps in an order different from depicted in  FIG. 1-5 . As an example, the most complete process starts at step  102  wherein an LEC fuel, for example a landfill gas, is provided in step  102 . 
     An oxidant, for example air, is added to the LEC fuel in step  104 . In some aspects, the amount of oxidant added depends on the concentration of combustible gas in the LEC fuel so as to achieve a target concentration of combustible gas in the resulting oxidant-LEC fuel mixture. In some aspects, the amount of oxidant added depends on the concentration of oxygen in the LEC fuel so as to achieve a minimum concentration of oxygen in the resulting oxidant-LEC fuel mixture. In some aspects, the concentration of combustible gas and/or oxygen in the LEC fuel is at least periodically measured and the amount of oxidant being added in step  104  adjusted in response to this measurement. 
     An HEC fuel could optionally be added in step  106 . In some aspects, the amount of HEC fuel added depends on the concentration of combustible gas in the oxidant-LEC fuel mixture so as to achieve a target concentration of combustible gas in the resulting oxidant-LEC-HEC fuel mixture. In some aspects, the concentration of combustible gas in the oxidant-LEC fuel mixture is at least periodically measured and the amount of HEC fuel being added in step  106  adjusted in response to this measurement. 
     Step  108  adds a diluent, such as recirculated flue gas, to the oxidant-fuel mixture. In certain aspects, the amount of diluent is adjusted to achieve a target concentration of combustible gas in the resulting oxidant-fuel-diluent mixture. In certain aspects, the recirculated flue gas also adds heat to the oxidant-fuel mixture, thereby reducing the amount of heat that will be added later in step  112 . In some aspects, the concentration of combustible gas in the oxidant-fuel mixture is at least periodically measured and the amount of diluent being added in step  108  adjusted in response to this measurement. The oxidant, LEC and HEC fuels, and diluent are mixed in step  110  into a generally homogeneous mixture. In certain aspects, mixing takes place incrementally after one or more of steps  104 ,  106 , and  108 . The homogenous oxidant-fuel-diluent mixture is heated in step  112  until the temperature of the mixture reaches at least the autoignition temperature of the mixture. The oxidant-fuel-diluent mixture autoignites in step  114  and gradually oxidizes in step  116  until the fuel and oxygen in the mixture no longer react and process  100  is thus completed. 
       FIG. 1-6  discloses a fuel-injection process  150  wherein an oxidant and a diluent are mixed and then heated to an autoignition temperature, whereupon a mixture of LEC and HEC fuels is injected into the oxidant-diluent mixture and mixed. A particular embodiment of the process of  FIG. 1-6  may include only some of the disclosed steps or may have such steps in an order different from depicted in  FIG. 1-6 . As an example, the most complete process starts at step  104   a  wherein an oxidant is provided. A diluent is added to the oxidant in step  108  and mixed in step  110   a  and heated in step  112  to at least an autoignition temperature of a target oxidant-diluent-fuel mixture. In some aspects, the amount of diluent added depends on the concentration of oxygen in the oxidant so as to achieve a target concentration of oxygen in the resulting oxidant-diluent mixture. In certain aspects, when the diluent is recirculated flue gas, the recirculated flue gas also adds heat to the oxidant, thereby reducing the amount of heat that will be added later in step  112 . 
     In a parallel process, an LEC fuel is proved in step  102  and a HEC fuel is added in step  106  and mixed in step  110   b . In some aspects, the amount of HEC fuel added depends on the concentration of combustible gas in the LEC fuel so as to achieve a target concentration of combustible gas in the resulting LEC-HEC fuel mixture. In some aspects, the concentration of combustible gas in the LEC fuel is at least periodically measured and the amount of HEC fuel being added in step  106  adjusted in response to this measurement. 
     The LEC-HEC fuel mixture is injected into the hot oxidant-diluent mixture in step  152  and mixed in step  110   c . In certain aspects, the mixing of step  110   c  comprises providing the oxidant-diluent mixture into an oxidation chamber through a turbulence-inducing jet and the fuel mixture is injected into the turbulent oxidant-diluent mixture flow. The oxidant-diluent mixture and fuel mixture mix rapidly in the turbulent flow in step  110 C and then autoignite in step  114  and gradually oxidize in step  116  until the fuel and oxygen in the mixture no longer react and the process  150  is thus completed. 
       FIG. 1-7  is a schematic diagram of an exemplary pre-mix oxidation system  200  according to certain aspects of the present disclosure. LEC fuel is obtained, in this example, from a landfill  202  through a gas-collection piping system  204  and provided as an LEC fuel flow  206   a . In certain aspects, for example if the methane content of the LEC fuel flow  206   a  is less than a determined percentage, an HEC fuel  210  is added in a mixer  208   a , producing an LEC-HEC fuel mixture  206   b . In certain aspects, for example if the oxygen content of the LEC-HEC fuel mixture  206   b  is less than a determined percentage, an oxidant  212 , for example air, is added in a mixer  208   b , producing an oxidant-fuel mixture  206   c . In certain aspects, for example if the oxygen content of the oxidant-fuel mixture  206   c  is greater than a determined percentage, a diluent  214 , for example recirculated flue gas, is added in a mixer  208   c , producing an oxidant-diluent-fuel mixture  206   d . In certain aspects, a mixer  220  is provided to further mix the oxidant-diluent-fuel mixture  206   d , thereby producing a homogenized oxidant-diluent-fuel mixture  206   e . In certain aspects, a compressor or blower  222  is provided to pressurize and heat the homogenized oxidant-diluent-fuel mixture  206   e , thereby producing a pressurized homogenized oxidant-diluent-fuel mixture  206   f  that is introduced into the oxidizer  224 . After the gradual oxidation process is completed, the exhaust  226  exits the oxidizer  224 . In certain aspects, a portion of the exhaust  226  is tapped off to provide the diluent  214 . The remaining exhaust  226  is provided to other systems or vented to atmosphere. 
       FIG. 1-8  is a schematic diagram of an exemplary injection oxidation system  300  according to certain aspects of the present disclosure. Many elements of system  300  are common to the system  200  previously discussed and their description is not repeated with respect to  FIG. 1-8 . In system  300 , the oxidant  212  is compressed and heated separately with a compressor or blower  222   a  and the resulting pressurized oxidant  304  is provided to the oxidizer  224 . In certain aspects, a diluent (not shown in  FIG. 1-8 ) is added to the oxidant  212  prior to the compressor  222   a . Separately, the LEC-HEC fuel mixture  206   b  is compressed and heated with a separate compressor or blower  222   b  to produce a pressurized fuel mixture  302  that is injected into the compressed oxidant-diluent mixture  304  within the oxidizer  224 . Methods of injecting the fuel mixture  302  into the oxidant-diluent mixture  304  within the oxidizer are discussed with respect to later figures. 
       FIG. 1-9  is a schematic representation of an exemplary turbine-driven power-generation system according to certain aspects of the present disclosure. Many elements of system  400  are common to previously discussed systems and their description is not repeated with respect to  FIG. 1-9 . In system  400 , the oxidant-diluent-fuel mixture  206   d  is provided at the inlet of a compressor  410  that is coupled to shaft  412  that is also coupled to a turbine  414  and to power generator  416 . The pressurized oxidant-diluent-fuel mixture  206   f  from the compressor  410  is passed through a heat exchanger  418  wherein the mixture  206   f  absorbs heat from the exhaust  420 . The heated mixture  206   g  is provided to the oxidizer  224 . The exhaust  226  is provided to the turbine  414  that extracts a portion of the energy from the hot compressed exhaust  226 , thereby driving the compressor  410  and generator  416  through shaft  412 . In certain aspects, a portion of the exhaust from the turbine is tapped off to provide the diluent  214  and the remaining exhaust  420  passes through the previously mentioned heat exchanger  418  and then through a second heat exchanger  422 , wherein the exhaust gas is further cooled by a flow of water  430  before being exhausted to the environment. The heated water  430 , after passing though heat exchanger  422 , may be used for beneficial uses such as hot water supply, building heating, or other applications. 
       FIG. 1-10  is a schematic representation of another turbine-driven power-generation system according to certain aspects of the present disclosure. Many elements of system  450  are common to previously discussed systems and their description is not repeated with respect to  FIG. 1-10 . The system  450  includes a warmer combustor  454  and a turbine combustor  456  before and after, respectively, the oxidizer  224 . An HEC fuel  452  is selectively provided to each of the warmer combustor  454  and a turbine combustor  456 . The method of using these combustors  454 ,  456  to initiate operation of the oxidizer-driven turbine is described in the previously referenced U.S. patent application Ser. No. 13/289,996. 
       FIG. 1-11  is a cutaway view of an exemplary GO reaction chamber  500  according to certain aspects of the present disclosure. The GO reaction chamber  500  has a vessel  510  that, in certain aspects, is configured to withstand a pressurized internal gas. A tower  514  is positioned, in this example, along a center axis of the vessel  510 , and configured to accept at an external end a flow of an oxidant-diluent-fuel mixture  530  through inlet  515 . A plurality of distribution pipes  516  are coupled to the tower  514  such that the oxidant-diluent-fuel mixture  530  passes from the tower into the distribution pipes  516 . Each of the distribution pipes  516  comprise a plurality of injection holes (not visible in  FIG. 1-11 ) that allow the mixture  530  to pass from the interior of the distribution pipes  516  into the interior of the vessel  510 . The interior of the vessel is at least partially filled with a porous media  512 . This media  512  absorbs heat from the GO process and then releases this heat to unreacted mixture  530 , thereby raising the temperature of the unreacted mixture  530  above the autoignition temperature. Porous media  512  also functions to mix products of oxidation from prior stages with unreacted oxidant-diluent-fuel mixtures injected through pipes  516 . 
     In certain aspects, the GO reaction chamber  500  comprises one or more secondary inlets  518  through which an oxidant, a fuel, or a mixture thereof can be injected directly into the interior of the vessel  510 . In certain aspects, the GO reaction chamber  500  comprises one or more heaters  522  that may be used to heat the porous media  512 . In certain aspects, the GO reaction chamber  500  comprises one or more sensors  524  that are configured to measure one or more of a temperature, an oxygen content, or a fuel content of the gases at one or more points within the vessel  510 . 
     In certain aspects, the GO reaction chamber  500  comprises a sensor  524  that comprises a temperature sensing element and outputs a signal that is representative of a temperature within the reaction chamber  500 . In certain aspects, the GO reaction chamber  500  comprises a sensor  525  that comprises a temperature sensing element and outputs a signal that is representative of the temperature of the oxidant-diluent-fuel mixture  530 . In certain embodiments, the temperature signals from sensors  524  and  525  are accepted by a controller  529  that outputs a signal  532  to reduce the temperature within the reaction chamber  500  when the temperature within the reaction chamber  500  approaches a flameout temperature, such that the temperature remains beneath the flameout temperature. In certain embodiments, adjustment of the temperature within the reaction chamber  500  is accomplished by adjusting one or more of the flow of the oxidant-diluent-fuel mixture  530 , the composition of the oxidant-diluent-fuel mixture  530 , the temperature of the oxidant-diluent-fuel mixture  530 , the flow of the auxiliary air-fuel mixture  540 , the composition of the auxiliary air-fuel mixture  540 , the temperature of the auxiliary air-fuel mixture  540 , the flow of exhaust gas through outlet  520 , a flow of a coolant through an internal heat exchanger such as shown in  FIG. 2-3  (not shown in  FIG. 1-11 ), or a flow of a non-combustible fluid introduced into the reaction chamber  500  through an injection subsystem (not shown in  FIG. 1-11 ). In certain aspects, the signal  532  is provided to a control module  531  configured to control at least one of a flow rate, a composition, and a temperature of the oxidant-diluent-fuel mixture  530 . 
     In certain aspects, the detection module  527  is configured to detect when at least one of a reaction temperature within the reaction chamber  500 , for example the temperature at sensor  524 , approaches or exceeds a flameout temperature of the oxidant-diluent-fuel mixture within the reaction chamber  500  and a reaction chamber inlet temperature, i.e. the temperature of the oxidant-diluent-fuel mixture  530  at sensor  525 , approaches or drops below an autoignition threshold. 
     In certain aspects, the controller  529  comprises a correction module  528  that outputs instructions, based on the detection module  527 , to change at least one of removal of heat from the reaction chamber and the temperature of the oxidant-diluent-fuel mixture  530  at the inlet of the tower  514  within the reaction chamber  500 . In certain aspects, the correction module  528  is configured to maintain an actual temperature within the reaction temperature, for example at sensor  524 , to a temperature below the flameout temperature and/or maintain the inlet temperature above the autoignition threshold of the fuel. In certain aspects, the controller  529  is configured to maintain the temperature of the oxidant-diluent-fuel mixture  530  at the inlet to tower  514  above the autoignition threshold, such that the gas within the reaction chamber  500  oxidizes without a catalyst. In certain aspects, the controller  529  is configured to determine at least one of a reduction of the temperature within the reaction chamber to remain below the flameout temperature, and an increase in the temperature of the oxidant-diluent-fuel mixture  530  at the inlet to tower  514  to maintain the temperature of the oxidant-diluent-fuel mixture  530  above the autoignition threshold. 
     In certain aspects, the controller  529  is configured such that when the temperature of the oxidant-diluent-fuel mixture  530  at the inlet to tower  514  approaches or drops below an autoignition threshold of the oxidant-diluent-fuel mixture  530 , the controller  529  outputs a signal  532  to cause additional heat to be added to the oxidant-diluent-fuel mixture  530  such that the temperature of the oxidant-diluent-fuel mixture  530  at the inlet to tower  514  is maintained above the autoignition threshold, and the reaction chamber  500  maintains oxidation of the fuel within the reaction chamber  500  without a catalyst. In certain embodiments, the correction module  528  outputs instructions, based on the detection module  527 , to change either a residence time of the gas within the reaction chamber, for example by reducing the flow of the oxidant-diluent-fuel mixture  530 , and/or changing the autoignition delay time, for example by adjusting the composition of the oxidant-diluent-fuel mixture  530  or increasing the temperature within the reaction chamber  500  with the heater  522 , within the reaction chamber sufficient for the oxidant-diluent-fuel mixture  530  to autoignite and oxidize while within the reaction chamber  500 . 
     In certain aspects, the detection module  527  is configured to detect when a reaction chamber inlet temperature of the gas approaches or drops below a level such that the reaction chamber alone will not support oxidation of the fuel, and the correction module  528  is configured to change, based on the detection module  527 , the residence time of the gas within the reaction chamber and/or the autoignition delay time within the reaction chamber sufficient for the gas to autoignite and oxidize while within the reaction chamber  500 . 
     In some embodiments, the temperature of the fuel or gas mixture within the reaction chamber may be above the lower flammability limit or the flameout temperature. In these instances, for example, mixing a HEC fuel gas into the reaction chamber, there may be a period of time that the mixture passes through a flammability area, which is below the upper flammability limit and above the lower flammability limit. While a residence time within this area may not be, in some instances, desirable, the residence time of the mixture within the area can be reduced by either changing the temperature of the mixture or changing the flow of the mixture. In some instances, heat may be drawn out of the reaction chamber to reduce the temperature of the mixture to be below the lower flammability limit, or flameout temperature, such that the residence time of the mixture within the flammability area is less than the autoignition delay time. In some instances, the flow rate of the mixture through the reaction chamber can be increased to reduce the residence time of the mixture within the reaction chamber, this reduced residence time of the mixture within the reaction chamber can equate to a reduced residence time of the mixture being exposed to temperatures within the reaction chamber that are within the flammability area and may be acceptable if the residence time is less than the autoignition delay time. In some instances, heat may be added to the mixture such that the reaction temporarily moves into a flammability area for a brief period of time relative to the autoignition delay time. 
     In some instances, at least one of the temperature or the flow of the mixture through the reaction chamber can be controlled such that the residence time of the fuel within the flammability area is less than 5% of the autoignition delay time. In some instances, the residence time of the fuel within the flammability area can be between about 5% and about 10% of the autoignition delay time. In some instances, the residence time of the fuel within the flammability area can be between about 10% and about 20% of the autoignition delay time. In some instances, the residence time of the fuel within the flammability area can be between about 15% and about 25% of the autoignition delay time. In some instances, the residence time of the fuel within the flammability area can be between about 25% and about 50% of the autoignition delay time. In some instances, the residence time of the fuel within the flammability area can be between about 30% and about 75% of the autoignition delay time. 
     In certain aspects, the control module  531  is configured to raise the temperature of the oxidant-diluent-fuel mixture  530  at or before the inlet  515  to or above an autoignition temperature of the oxidant-diluent-fuel mixture  530 . In certain embodiments, the reaction chamber  500  is configured to oxidize the oxidant-diluent-fuel mixture  530  and maintain an adiabatic temperature above the autoignition temperature of the oxidant-diluent-fuel mixture  530  and a maximum actual temperature of the reaction chamber  500  below a flameout temperature of the oxidant-diluent-fuel mixture  530 . 
     In certain aspects, the oxidizer  500  is configured to create the oxidant-diluent-fuel mixture  530  by mixing, in a system not shown in  FIG. 1-11 , a gas having a LEC fuel with one or more of the group of a gas comprising a HEC fuel, a gas comprising an oxidant, and a gas comprising a diluent while all of the gases are at temperatures below the autoignition temperature of any of the gases being mixed. The oxidizer  500  is also configured to increase the temperature of the oxidant-diluent-fuel mixture  530  to at the least an autoignition temperature of the oxidant-diluent-fuel mixture  530  and allowing the oxidant-diluent-fuel mixture  530  to autoignite, and then maintaining the temperature of the oxidant-diluent-fuel mixture  530  below a flameout temperature while the autoignited the oxidant-diluent-fuel mixture  530  oxidizes. 
     In certain aspects, the porous media  512  within the oxidizer  500  is configured to maintain an internal temperature of the reaction chamber below a flameout temperature and to maintain a reaction chamber inlet temperature of the fuel to be greater than an autoignition temperature of the fuel. In certain aspects, at least one flow path from the inlet to the outlet of the oxidizer  500  is configured to direct the oxidant-diluent-fuel mixture  530  through a portion of the porous media  512  that is hotter than the autoignition temperature of the oxidant-diluent-fuel mixture  530  until the oxidant-diluent-fuel mixture  530  reaches a temperature above the autoignition temperature of the oxidant-diluent-fuel mixture  530 , whereupon the flow path is further configured to direct the oxidizing oxidant-diluent-fuel mixture  530  to the outlet along a path being generally opposite to the first flow path, for example using internal baffles such as the tubes  1055 / 1060  shown in  FIG. 2-7B . 
     In some embodiments, the controller  529  can direct other parts of the oxidation system. For example, other controls that the controller  529  may direct are described in copending U.S. patent application Ser. No. 13/289,989, filed Nov. 4, 2011, and Ser. No. 13/289,996, filed Nov. 4, 2011, both of which are incorporated by reference herein in their entirety to the extent the teachings within the applications are not inconsistent with the teachings of this description. 
       FIG. 1-12  schematically depicts the flow through a gradual oxidation system  4500  having a sparger according to certain aspects of the present disclosure. The processes and elements of  FIG. 1-12  are described in relation to the oxidizer  500  of  FIG. 1-11 . The following processes occur as air  4502  and fuel  4220  flow through the oxidizer: 
     1. Fuel/air mixer  4510  creates an initial lean air-fuel mixture from one or both of air  4502  and fuel  4220 . 
     2. Heater  4512  heats the air-fuel mixture up to temperatures proximate to the autoignition temperature. The heat may also be added through compression of the mixture as well as heat exchange. In some embodiments, heat may be added by introducing a heated gas (e.g., flue gas). 
     3. A first stage gradual oxidizer that may include a heater  522  ( FIG. 1-11 ) or heater  4516  ( FIG. 1-12 ), for example a pilot burner, to initiate the gradual oxidation  4518 . In certain aspects, this heater is an electric heater of various types known to those of skill in the art. The output of this is hot gas comprising un-consumed O2 and oxidation products CO2 and H2O. Since the portion of fuel and air flowing into this first oxidizer  4518  is small, less heat is required to heat the mixture above the autoignition temperature to initiate the oxidative reaction. In certain aspects, heat is added to the first stage by preheating a porous media with a starter-combustor upstream. The preheated media then heats the fuel/air mixture in  4516  to start the oxidation. Since only a small portion of flow goes through the heated media in heater  4516 , thermal condition and radiation of energy opposite the flow direction is able to maintain the media temperature high enough to continue to heat the flow. This stage anchors the reaction. 
     4. A divide-mix-oxidize stage  4530 , for example as occurs in an arm  516  of sparger  514  of  FIG. 1-11 , wherein a portion of the air-fuel mixture is split off, mixed with the hot gas from the prior process, and gradually oxidized, shown as processes  4514 ,  4520 , and  4518 . Since the prior oxidized gases from oxidizer  4518  are hot, typically above 1400° F. but below 2300° F. they serve to heat the unreacted fuel and air from divider  4514  in mixer  4520 , and initiate the oxidation of this next stage of oxidation 
     5. A repetition of stage  4530  oxidizes all of the fuel from LEC source  4220  so that no fuel remains after the final oxidizer  4518 . The staged-approach to starting the oxidation process in the anchoring first stage, and the oxidizing portions of the gas thereafter, is the gradual oxidation process. 
       FIG. 1-13  is a schematic representation of a multi-stage GO reaction chamber  600  according to certain aspects of the present disclosure. In this example, the chamber  600  comprises four reaction chambers  602   a .  602   b ,  602   c , and  602   d  that are serially coupled together. In this example, a flow of an air-fuel mixture  604 , for example an LEC fuel, is provided into each of the four reaction chambers  602   a ,  602   b ,  602   c , and  602   d . In certain aspects, the amount of the air-fuel mixture  604  provided into each reaction chamber  602   a ,  602   b ,  602   c , and  602   d  is different. In certain aspects, one or more different air-fuel mixtures (not shown in  FIG. 1-12 ) are provided to the downstream reaction chambers  602   b .  602   c , and  602   d . In certain aspects, an oxidant (not shown in  FIG. 1-13 ) is separately provided to one or more of the downstream reaction chambers  602   b .  602   c , and  602   d . In certain aspects, an HEC fuel (not shown in  FIG. 1-13 ) is separately provided to one or more of the reaction chambers  602   a ,  602   b .  602   c , and  602   d.    
       FIG. 1-14  is a schematic representation of a fluidized bed GO reaction chamber  700  according to certain aspects of the present disclosure. In this example, the reaction chamber  700  comprises a vessel  710  at least partially filled with a media  720  that, when a gas is introduced at the bottom of the media  720 , becomes fluidized. The air-fuel-diluent mixture  604  gradually oxidizes as the mixture  604  passes through the fluidized media  720  and is removed at the top as exhaust  226 . The fluidized media circulates within vessel  710 , transferring heat from the exhaust products of oxidation to the inlet reactants. Fluidized particles  720  near the exhaust end of vessel  710  (proximal to exhaust  226 ) are heated by hot products of oxidation. The fluidized media then is conveyed, either purposely or incidentally, to the inlet end of the oxidation vessel  710 . The heated fluidized media then impart their heat to the incoming, cooler, unreacted air-fuel-diluent mixture  604  to heat the flow, as is taught for the GO process. Fluidized media  720  therefore serves to transfer the heat from the products of oxidation to the air-fuel-diluent reactants. There are many ways to implement fluidized beds to move heat around closed chemically reacting systems, especially when combined with the staged-injection of the GO process, and implementing fluidized beds is one example of how heating is accomplished (see, e.g.,  FIG. 1-12, 4512, 4516 ). 
       FIG. 1-15A  is a schematic representation of a recirculating bed GO reaction chamber  800  according to certain aspects of the present disclosure. In this example, the reaction chamber  800  comprises a vessel  810  that is at least partially filled with a media  820 . A portion  810   a  of the media  820  is at least periodically removed at the bottom of the vessel  810  and transported through a transfer system  820  to the top of vessel  810 , whereupon the portion  810   a  is returned to the interior of vessel  810 . At the same time, a flow of an air-fuel mixture  604  is introduced at the bottom of the vessel  810  and passes upward through the media  820 . The mixture  604  gradually oxidizes as it passes through the media  820  and is removed at the top as exhaust  226 . As the media  820  that is within the vessel  810  is moving downward as portions  810   a  are removed at the bottom, the hottest media  820 , i.e. the media  820  that is on top of the media  820  that is within the vessel  810 , moves toward the inlet thereby counteracting the tendency of the incoming air-fuel mixture  604  to locally cool the media  820 . The cold media portions  810   a  removed from the bottom are delivered to the top where the portions  810   a  are heated by the hot oxidized gas. 
       FIG. 1-15B  is a schematic representation of another recirculating bed GO reaction chamber  801  according to certain aspects of the present disclosure. In this embodiment, the recirculating portions  810   b  are drawn from a hot portion of the bed  820 , for example a midpoint in the depth of the bed  820 , and circulated through pipe  822  wherein heat  824  is extracted from the recirculating portions  810   b . The cooled portions  810   b  are provided back to the chamber  801 , for example at the top so as to fall onto the top of the bed  820 . This extraction of heat from the recirculating portions  810   b  draws heat from the reaction chamber  801 . In certain aspects, the flow rate of portions  810   b  is controlled to maintain an internal temperature of the reaction chamber  801  below a flameout temperature. 
       FIG. 1-16  is a schematic representation of a GO reaction chamber  850  with flue gas recirculation according to certain aspects of the present disclosure. The vessel  810  and media  820  are similar to those of the GO oxidizer  800  of  FIG. 1-15 . In the example of  FIG. 1-16 , however, a portion  852  of the exhaust gas  226 , also referred to herein as flue gas, is recirculated and provided at the bottom of the vessel  810  so as to heat the incoming air-fuel mixture  604  and anchor the GO process within the vessel  810 , as well as provide an additional diluent to the incoming air-fuel mix  604 . 
     In certain aspects, the GO reaction chamber  850  comprises an oxygen sensor, such as sensor  524  of  FIG. 1-11 , that is configured to determine an oxygen content level within the reaction chamber  850  and provide a signal representative of the oxygen content level. In certain aspects, a controller (not shown in  FIG. 1-16 ) accepts the oxygen content level signal and outputs instructions to introduce flue gas  852 , received from the outlet of the reaction chamber and containing product gases from oxidation of the fuel within the reaction chamber, into the reaction chamber  850  based on the oxygen content level. 
     In certain embodiments, an oxidizer can includes a reaction chamber inlet configured to accept a gas having a mixture of a low-energy-content (LEC) fuel and at least one of the group of a high-energy-content (HEC) fuel, an oxidant-comprising (OC) gas, and a diluent-containing (DC) gas. The gas mixture can be regulated to be at a temperature below an auto-ignition temperature of the gas mixture. The oxidizer can also include a heat exchange media disposed within the reaction chamber. The media may be configured to maintain an internal temperature of the reaction chamber below a flameout temperature and to maintain a reaction chamber inlet temperature of the fuel to be greater than an autoignition temperature of the fuel. The reaction chamber can provide at least one flow path through the chamber from the inlet to the outlet. The flow path may be configured to direct the gas entering the inlet through a first path through media that is hotter than an auto-ignition temperature of the gas mixture until the gas mixture reaches a temperature above the auto-ignition temperature of the gas mixture, whereupon the flow path is further configured to direct the oxidizing gas mixture through a second path through the media to the outlet, the second path being generally opposite to the first flow path. Examples of this are illustrated in  FIGS. 2-7A through 2-9 . 
     In certain embodiments, a method of oxidization described herein includes the steps of receiving into a reaction chamber, via a chamber inlet, the inlet configured to accept a gas having a mixture of a low-energy-content (LEC) fuel and at least one of the group of a high-energy-content (HEC) fuel, an oxidant-comprising (OC) gas, and a diluent-containing (DC) gas, the gas mixture being at a temperature below an auto-ignition temperature of the gas mixture; maintaining an internal temperature of the reaction chamber below a flameout temperature by heat exchange media disposed within the reaction chamber, maintaining a reaction chamber inlet temperature of the fuel to be greater than an autoignition temperature of the fuel by transferring heat through the heat exchange media, and directing gas entering the inlet through a first path through media that is hotter than an auto-ignition temperature of the gas mixture until the gas mixture reaches a temperature above the auto-ignition temperature of the gas mixture; and directing the gas through a second path through the media to a chamber outlet, the second path being generally opposite to the first flow path. 
     In certain embodiments, the reaction chamber is configured to maintain oxidation of the gas mixture along at least one of the first and second flow paths without a catalyst. In certain embodiments, the reaction chamber is configured to maintain oxidation of the mixture beneath the flameout temperature of the gas mixture by circulating heat exchange media outside the reaction chamber. In certain embodiments, the system also includes at least one of a turbine or a piston engine that is configured to receive gas from the reaction chamber outlet and expand the gas. In certain embodiments, the gas mixture comprises at least one of hydrogen, methane, ethane, ethylene, natural gas, propane, propylene, propadiene, n-butane, iso-butane, butylene-1, butadiene, iso-pentane, n-pentane, acetylene, hexane, and carbon monoxide. 
     In certain embodiments, the oxidizer described can include a reaction chamber inlet that is configured to accept a gas having a mixture of a low-energy-content (LEC) fuel and at least one of the group of a high-energy-content (HEC) fuel, an oxidant-comprising (OC) gas, and a diluent-containing (DC) gas. The gas mixture can be regulated to be at a temperature below an auto-ignition temperature of the gas mixture. The oxidizer can also have a heat controller that is configured to increase a temperature of the gas mixture to at the least an autoignition temperature of the gas mixture, thereby permitting the gas mixture to autoignite and to maintain the temperature of the gas mixture below a flameout temperature while the autoignited gas mixture oxidizes. 
     In some methods of oxidizing a fuel described herein includes the steps of mixing a gas having a low-energy-content (LEC) fuel with one or more of the group of a gas comprising a high-energy-content (HEC) fuel, a gas comprising an oxidant, and a gas comprising a diluent to form a gas mixture, wherein all of the gases are at temperatures below the autoignition temperature of any of the gases being mixed; increasing the temperature of the gas mixture to at the least an autoignition temperature of the gas mixture and allowing the gas mixture to autoignite; and maintaining the temperature of the gas mixture below a flameout temperature while the autoignited gas mixture oxidizes. 
     In certain embodiments, the oxidizer can include an inlet configured to accept a gas having a mixture of a low-energy-content (LEC) fuel and at least one of the group of a high-energy-content (HEC) fuel, an oxidant-comprising (OC) gas, and a diluent-containing (DC) gas. The gas mixture can be regulated to be at a temperature below an auto-ignition temperature of the gas mixture. A controller (e.g., a heat controller) can be configured to heat the gas to at the least an auto-ignition temperature of a first gas mixture, comprising a gas with an oxidant mixed with determined ranges of a low-energy-content (LEC) fuel and a high-energy-content (HEC) fuel. An inlet (e.g., an injector) can also be configured to inject, after the first gas is heated to at the least an auto-ignition temperature of a first gas mixture, a second gas mixture of the LEC fuel gas and the HEC fuel. The inlet or injector can injects a ratio of the LEC and HEC gas and at a rate of injection that is selected to produce substantially the same ratio of LEC and HEC gas as the first gas mixture when the gas is injected into the reaction chamber. The reaction chamber can be configured to mix the injected second gas with the heated gas containing an oxidant at a rate to produce a substantially homogeneous first gas mixture in a time less than the ignition delay time for the second gas mixture and allowing the first gas mixture to auto-ignite and to maintain the temperature of the first gas mixture below a flameout temperature while the auto-ignited first gas mixture oxidizes. 
     In certain embodiments, a method of oxidation described herein includes the steps of heating a gas comprising an oxidant to at the least an auto-ignition temperature of a first gas mixture comprising a gas with an oxidant mixed with determined ranges of a low-energy-content (LEC) fuel and a high-energy-content (HEC) fuel; injecting, after the heating, a second gas mixture of the LEC fuel gas and the HEC fuel, wherein the ratio of the LEC and HEC gas and the rate of injection are selected to produce substantially the same first gas mixture ratios when injected into the heated gas containing an oxidant; mixing the injected second gas with the heated gas containing an oxidant at a rate to produce a substantially homogeneous first gas mixture in a time less than the ignition delay time for the second gas mixture and allowing the first gas mixture to auto-ignite; and maintaining the temperature of the first gas mixture below a flameout temperature while the auto-ignited first gas mixture oxidizes. 
       FIGS. 1-17A and 17B  depict a GO reaction chamber  860  with structured reaction elements  864  according to certain aspects of the present disclosure.  FIG. 1-17A  is a schematic representation of a vessel  862  that contains, in this example, a stack of structured reaction elements  864 . 
       FIG. 1-17B  shows an exemplary structured reaction element  864  that is formed as a disk  866  with a plurality of holes  868  through the thickness of the disk  866 . In certain embodiments, the edges of the disk  866  are raised so as to provide a gap between stacked elements  864  thereby allowing lateral flow of the air-fuel mixture between holes as the air-fuel mixture passes through a stack of the reaction elements  864 . When stacked in the vessel  862 , the elements  864  may be randomly rotated about a center point so that the holes  868  of adjacent elements  864  do not line up, thereby providing a more serpentine path through a stack of elements  864 . 
     As another example of the structured media inside vessel  862  ( FIG. 1-17A ), extruded metal or ceramic such as cordierite will serve to conduct heat from downstream of the flow, near exit  226 , to upstream of the flow. This will serve to heat the inlet air-fuel mixture  604  above the autoignition temperature and initiate the oxidation reactions. 
     Gradual Oxidizer as Heat Source 
       FIG. 2-1  is a schematic representation of an oxidizer  224  coupled to a heat exchanger  1010  to provide process heating to an industrial process according to certain aspects of the present disclosure. In  FIG. 2-1 , the gradual oxidation reactant gases  604  are admitted into the oxidizer  224  and undergo gradual oxidation and leave as product gases  1015  that pass through a heat exchanger  1010  wherein heat is rejected and the product gases are exhausted to the atmosphere as exhaust  1030  at a reduced temperature. Entering the other passage of the heat exchanger  1010  is a cool fluid  1020 , for example air, water, or an industrial fluid, which is beneficially heated and exits as hot fluid  1025  that flows to its point of use (not shown in  FIG. 2-1 ). Heat exchanger  1010  can be configured as co-flow, counterflow, cross-flow, or any of the other heat exchanger options described and illustrated herein or other that may be known in the art. The gradual oxidation reaction products  1015 , which are comprised of pollutant-free hot gases, are directed to a heat exchanger that beneficially heats a stream of air to warm a living space for personal comfort, or a volume of water for domestic usage, or any industrial material requiring heating. 
       FIG. 2-2  is a schematic representation of an oxidizer  224  coupled to a heating chamber  1050  to heat a process material  1055  according to certain aspects of the present disclosure. The air-fuel mixture  604  is admitted into the oxidizer  224  where it undergoes gradual oxidation and leaves as product gas  1015 , after which it proceeds into the heating chamber  1050  where a material  1055  is beneficially heated by the hot gases, after which the gases exit the heating chamber as exhaust  1030  and are exhausted to atmosphere. The material  1055  may be processed by one or more of thawing, melting, evaporating, subliming, drying, baking, curing, sintering, or calcining using the beneficial heat. In a similar embodiment (not shown in  FIG. 2-2 ), where ventilation is sufficient to prevent harmful levels of oxygen depletion, the hot gradual oxidation reaction products are directed into an occupied space for comfort heating. In another similar embodiment (not shown in  FIG. 2-2 ), the hot products are directed to an absorption chiller to provide the motive energy for an absorption-refrigeration cycle. 
       FIG. 2-3  is a schematic representation of an oxidizer  224  comprising an internal heat exchanger  1060  through which a fluid passes according to certain aspects of the present disclosure. The heat exchanger  1060  is disposed internally to the oxidizer  224  reaction chamber. The air-fuel mixture  604  is admitted into the oxidizer  224  and undergoes gradual oxidation. Cool fluid  1020  enters the heat exchanger  1060  and a portion of the thermal energy generated by the gradual oxidation process is transferred to the fluid through the heat exchanger  1060 . The cooled product gasses exit as exhaust  1030 . The hot fluid  1025  exits the heat exchanger  1060  and is directed to its point of use (not shown in  FIG. 2-3 ). An example embodiment of the oxidizer  224  comprises a vessel lined internally with tubes where air is conveyed through the tubes. 
     In certain embodiments, heat is drawn from the reaction chamber of the oxidizer  224  using one of the cool fluid  1020  being a liquid that at least partially vaporizes in the heat exchanger  1060 , the cool fluid  1020  being a gas, or the cool fluid  1020  being a liquid that increases in temperature without vaporizing. In certain embodiments, the amount of heat being drawn from the reaction chamber of oxidizer  224  is adjusted by one or more of controlling the flow rate of the cool fluid  1020 , controlling the flow rate of the hot fluid  1025 , or controlling the temperature of at least one of the cool fluid  1020  and the hot fluid  1025 . In certain aspects, the cool fluid  1020  is at a temperature that is less than an internal temperature within the oxidizer  224 , wherein the reaction chamber is configured to maintain the internal temperature above an autoignition temperature of the fuel within the air-fuel mixture  604  and below a flameout temperature of the fuel within the air-fuel mixture  604 . 
       FIG. 2-4  is a schematic representation of another embodiment of an oxidizer  224 , comprising a plurality of internal heat exchangers  1060  according to certain aspects of the present disclosure. Similar to  FIG. 2-3 , an air-fuel mixture  604  is admitted into an oxidizer  224  where gradual oxidation occurs and a portion of the thermal energy is transferred to a cool fluid  1020  through the heat exchangers  1070 , which are disposed internally to the gradual oxidizer  224 . In certain embodiments, the heat exchangers  1060  comprise a plurality of the heat removal surfaces (not shown in  FIG. 2-4 ) that are positioned internally proximate to the outer circumference of the oxidizer vessel to absorb much of the beneficial heat that might otherwise be lost to the environment through imperfect wall insulation. 
       FIG. 2-5  is a schematic representation of an oxidizer  224  comprising a plurality of gradual oxidation zones  1075 A- 1075 C with adjoining reaction zones  1080 A- 1080 C wherein batches of a process material are heated according to certain aspects of the present disclosure. 
     An air-fuel mixture  604  is admitted into an oxidizer  224  in three separate reactant streams  1090 A.  1090 B, and  1090 C that are respectively directed to gradual oxidation zones  1075 A- 1075 C where gradual oxidation and the release of exothermic energy from the gases occur. Granular, industrial materials (not visible in  FIG. 2-5 ) are disposed within the reaction zones  1080 A- 1080 C where they are fluidized by the reactant gases and are beneficially heated in a batch manner. A fraction of the heat removal surface is positioned in such a manner that it absorbs sufficient beneficial heat from the gradual oxidation process to reduce local temperatures below the point where damage to internal components may occur. The product gases from the gradual oxidation process are recombined into a single exhaust stream  1030  that exits to atmosphere or other end use. In a similar embodiment (not shown in  FIG. 2-5 ), additional heat removal surfaces are provided so as to permit the gradual oxidation process to be operated at greater energy-release-density (and thereby, smaller overall reactor volume) without overheating and damaging internal components. 
       FIG. 2-6  is a schematic representation of an oxidizer  224  comprising a plurality of gradual oxidation zones  1075 A- 1075 C with adjoining reaction zones  1120 A- 1120 C wherein continuous flows of a process material  1105  are heated according to certain aspects of the present disclosure. As in  FIG. 2-5 , an air-fuel mixture  604  is admitted into an oxidizer  224  in three separate reactant streams  1090 A.  1090 B, and  1090 C that are respectively directed to gradual oxidation zones  1075 A- 1075 C where gradual oxidation and the release of exothermic energy from the gases occurs, followed by recombination of the product gas streams into a single exhaust  1030  that exits to atmosphere. Cold, unreacted, granular, industrial materials  1105 A- 1105 C are admitted into reaction zones  1120 A- 1120 C where the materials are fluidized by the gradual oxidation reactant gases and are heated in a continuous manner to a beneficially-altered condition  1110 A- 1110 C that is removed from the oxidizer  224 . 
     On the downstream side of the each reaction zone  1120 A- 1120 C are weirs  1085 A- 1085 C that retain a portion of the beneficially heated granular materials and permit the balance  1110 A- 1110 C to exit the oxidizer  224  whereupon the altered materials are collected for later use (not shown in  FIG. 2-6 ). Each of the multiple stages of a gradual oxidation process are independently carried out in the presence of a circulating fluidized bed of granular process material, which concurrently exchanges heat with the reacting gradual oxidation gases while the material  1105 A- 1105 C itself undergoes a drying, curing, sintering, calcining, or other thermally-induced alteration due to the heat from the gradual oxidation gases. The circulating fluidized bed process that beneficially alters the granular material can be performed in a batch or continuous manner in each gradual oxidation stage. In a continuous process, the addition rate of cold, unreacted granular material  1105 A- 1105 C should be sufficiently small to ensure the gradual oxidation process is not quenched and extinguished. In certain embodiments, the mass rate of cold unreacted granular material  1105 A- 1105 C being continuously added to the reaction zones  1120 A- 1120 C is 1-20% of the mass flow rate of gradual oxidation gases entering the reaction zones  1120 A- 1120 C. 
       FIGS. 2-7A and 2-7B  are a perspective view and cross-section view of an example design detail of an oxidizer element  1150  according to certain aspects of the present disclosure. Two concentric pipes  1055  and  1060  are used to form a process flow path wherein the incoming air-fuel mixture  604  enters the inner pipe  1060  at point A flows through the smaller pipe  1060 , and then exits the inner pipe  1060  at point B and counter-flows between the inner pipe  1060  and the outer pipe  1055  while continuing to gradually oxidize and then exits the oxidizer element  1150  at point C as fully oxidized product gas. As the air-fuel mixture  604  flows through the inner pipe  1060 , the mixture is heated through walls of pipe  1060  by the hot product gas counter-flowing past the outside of the pipe  1060 . 
       FIG. 2-8  is a plot of the temperatures within the oxidizer of  FIGS. 2-7A and 2-7B  according to certain aspects of the present disclosure. Incoming air-fuel mix at point A is at temperature T 1 . The mixture is heated during the initial part of the flow through inner pipe  1060  by heat transfer from the hot gas counter-flowing between the inner pipe  1060  and the outer pipe  1055  to the temperature T 2  when the gradual oxidation reaction is initiated. Exothermal release of chemical energy in the gradual oxidation process raises the temperature to T 3  when the majority of the reaction has already occurred. Gas then enters the middle section between the two concentric pipes  1055  and  1060  and flows back counter to the initial flow. The gas temperature may continue to increase slightly, due to continued gradual oxidation, or decrease as heat is lost to the outer pipe  1055 . The gas then keeps moving and exchanges thermal energy with the incoming (colder) air-fuel mix  604  through the walls of the inner pipe  1060 , thereby cooling the product gas to T 4 . 
       FIG. 2-9  is a cross-sectional view of an assembly using the oxidizer element of  FIGS. 2-7A and 2-7B  according to certain aspects of the present disclosure. The assembly  1200  comprises multiple elements  1150  disposed in a housing  1205  that, in this example, is a cylindrical vessel. In certain embodiments, the vessel  1205  is a shape other than round. In certain embodiments, the vessel  1205  is pressurized. Two solid cross-sectional plates  1210  and  1220  are positioned across the interior of vessel  1205 . The inner pipes  1160  penetrate the plate  1210  and the outer pipes  1055  are attached to plate  1220 . Separate passages  1225  are provided through the plate  1220 . An air-fuel mixture  604  flowing through the vessels  1205  passes into each of the inner pipes  1060 , through the pipes  1060  and  1055  as previously discussed with respect to  FIGS. 2-7A and 2-7B , and then past the outside of outer pipes  1055  and through the passages  1225 . As the air-fuel mixture  604  is converted into a product gas, the mixture travels three times through the same length of the vessel  1205 : (1) through the inner pipes  1060 , (2) between the inner and outer pipes  1060  and  1055 , and (3) through the volume between outside of the outer pipes  1055  and the vessel  1205 . This provides additional heat exchange and promotes higher efficiency and a smaller volume of the oxidizer assembly  1200 . 
     Schnepel Cycle for Reciprocating Engine 
       FIG. 3-1  is a schematic of an exemplary Schnepel cycle power generation system  3000  according to certain aspects of the present disclosure. An air-fuel mixture  3005 , comprising a mixture of an LEC fuel. HEC fuel, oxidant, and diluent as described with reference to the air-fuel mixture  206   e  of  FIG. 1-7 , is provided to a compressor cylinder  3010  having a piston  3030   a  that is coupled through a connecting rod  3032  to a crankshaft  3034  that is generally similar to the crankshafts found in conventional internal-combustion engines having reciprocating cylinders. In certain aspects, the compressor cylinder  3010  is a part of a drive assembly  3036  as indicated by the dashed line box  3036  that, as an assembly, is generally similar to portions of conventional internal-combustion engines having reciprocating cylinders. As the piston  3030   a  descends within the compressor cylinder  3010 , the air-fuel mixture  3005  is drawn into the internal space  3015  through a controllable intake valve (not shown in  FIG. 3-1 ). When the piston  3030   a  is near the bottom of its stroke, the intake valve closes. As the piston  3030   a  ascends, the internal volume  3015  is reduced, thereby compressing the air-fuel mixture  3005 . When the piston  3030   a  reaches a designated point, an outlet valve (not shown in  FIG. 3-1 ) opens and connects the internal space  3015  to line  3040 , thereby allowing the compressed air-fuel mixture  3005  to flow into line  3040 . In this example, the compresses air-fuel mixture  3005  passes through a recuperator  3045  and then through line  3050  into a heat exchanger  3055 , then into line  3060  and into the oxidizer  224 . 
     As previously described, the air-fuel mixture  3005  is gradually oxidized within the oxidizer  224  and exists as a hot combustion product gas in line  3065 . This hot gas is routed to the second side of the heat exchanger  3055 , wherein the hot gas transfers a portion of its thermal energy to the incoming air-fuel mixture  3050 . The product gas now flows through line  3070  into the internal space  3025  of an expander cylinder  3020 . 
     In operation, an inlet valve (not shown in  FIG. 3-1 ) opens when the piston  3030   b  is at or just past top-dead-center such that the hot pressurized product gas can flow into the internal space  3025 . As the crankshaft  3034  rotates and the piston  3030   b  descends within the expander cylinder  3020 , the hot pressurized product gas continues to flow into the internal space  3025 , thereby maintaining a constant pressure within the internal space  3025  for the entire stroke. 
     In certain aspects of the operation, the inlet valve closes prior to piston  3030   b  reaching the bottom of its travel. As the piston travels from this intermediary point to bottom-dead-center, the gas pressure reduces and cools due to the expanding volumetric cavity. 
     The compressor cylinder  3010  and expander cylinder  3020  are coupled to a common crankshaft  3034  and offset from each other by about 180 degrees of rotation of the crankshaft  3034 , i.e. the piston  3030   b  is at the top of its stroke when the piston  3030   a  is at the bottom of its stroke. As the air-fuel mixture  3005  in the interior space  3015  of the compressor cylinder  3010  is initially, in this example, at atmospheric pressure while the pressure in the interior space  3025  is at or near the maximum pressure that will be reached at the end of the compression stroke in the compressor cylinder  3010 , there is a force imbalance for most of the 180 degrees of rotation while the piston  3030   b  is descending and the piston  3030   a  is ascending. It is this force imbalance that drives the rotation of the crankshaft  3034 . This force also drives the rotation of generator  416 , thereby creating power. In certain aspects, the generator  416  generates electricity. In certain aspects, the generator  416  generates pressurized fluid or produces mechanical work. As the piston  3030   a  of the compressor cylinder  3010  reaches the top of its stroke, there is a short period where the pressure in interior space  3015  is approximately equal to the pressure in interior space  3025 . While there is no net driving force during this period, the inertia of the rotating crankshaft, which may include a flywheel (not shown in  FIG. 3-1 ) to provide increased rotational inertia, will carry the crankshaft past the top-dead-center after which the compressor cylinder  3010  is drawing in new air-fuel mixture  3005  and the expander cylinder is exhausting the gas from the interior space  3025  through line  3080  and through the recuperator  3045  after which the gas is exhausted as exhaust  3085 . 
     In certain aspects, the drive assembly  3036  is referred to as a split cycle reciprocating engine having an intake that receives the air-fuel mixture  3005 , the compressor cylinder  3010  is referred to as a compression chamber coupled to a reciprocating engine, and the internal space  3015  is referred to as a reciprocating piston chamber. In certain aspects, the oxidizer  224  is referred to as an oxidation chamber that is configured to receive the mixture from the compression chamber via a first inlet and to maintain oxidation of the mixture at an internal temperature beneath a flameout temperature of the mixture and sufficient to oxidize the mixture without a catalyst. In certain aspects, the expander cylinder  3020  is referred to as an expansion chamber that receives heated oxidation product gas from the oxidation chamber and expands the product gas within the expansion chamber, thereby driving the reciprocating engine. 
       FIG. 3-2  is a conceptual depiction of the power generation system  3000  of  FIG. 3-1  according to certain aspects of the present disclosure. The engine assembly  3036  is centrally mounted with the oxidizer  224  attached at one end through the recuperator  3045  and heat exchanger  3055 . In this example, LEC fuel, such as from a remote landfill  202  (not shown in  FIG. 3-2 ), is provided through line  3007  and the air-fuel mixture  3005  is created in the indicated box. 
       FIG. 3-3  is a schematic representation of another embodiment of a Schnepel cycle power generation system  3100  according to certain aspects of the present disclosure. Many elements of system  3100  are common to system  3000  and their description is not repeated with respect to  FIG. 3-3 . The system  3100  includes a turbine  3110  coupled to a compressor  3105 . The compressor  3105  functions in series with the reciprocating piston compressor  3010  such that the compression ratio of the piston compressor  3010  is reduced compared to system  3000  with the compressor  3105  providing sufficient compression to bring the output from the piston compressor  3010  up to the system pressure. In certain aspects, the system pressure of system  3100  is higher than the system pressure of system  3000  thereby improving the efficiency. The output of the compressor  3105  passes through the heat exchanger  3055  and into the oxidizer  224 . The output of the oxidizer  224  passes through the turbine  3110  before passing through the heat exchanger  3055  and then into the piston expander  3020 , after which the pressurized gas is exhausted to the environment. The absolute pressures and temperatures of the fluid at various numbered points, shown in  FIG. 3-3 , in the system  3100  are provided by way of illustration in the table below the drawing of  FIG. 3-3 . 
       FIG. 3-4  is a schematic representation of another embodiment of a Schnepel cycle power generation system  3150  according to certain aspects of the present disclosure. Many elements of system  3150  are common to system  3100  and their description is not repeated with respect to  FIG. 3-4 . In this example, the air-fuel mixture  3005  is pressurized by the compressor  3105  and then provided to the piston compressor  3010 , which is the reverse of the configuration of system  3100 . The pressures and temperatures of the fluid at various numbered points, shown in  FIG. 3-4 , in the system  3500  are provided in the table below the drawing of  FIG. 3-4 . 
       FIG. 3-5  is a schematic representation of another embodiment of a Schnepel cycle power generation system  3200  according to certain aspects of the present disclosure. Many elements of system  3200  are common to previously presented systems and their description is not repeated with respect to  FIG. 3-5 . In this embodiment, the output from the oxidizer  224  is routed to the piston expander  3020  and then through the heat exchanger  3055  to the turbine  3110 , after which the gas is exhausted. 
       FIG. 3-6  is a schematic representation of another embodiment of a Schnepel cycle power generation system  3250  according to certain aspects of the present disclosure. Many elements of system  3250  are common to previously presented systems and their description is not repeated with respect to  FIG. 3-6 . In this embodiment, the air-fuel mixture  3005  is compressed in the turbine-driven compressor  3105  and then further compressed in the piston compressor  3010 . The exhaust from the oxidizer  224  passes through the heat exchanger  3055  then through the piston expander  3020  before passing through the turbine  3110  and being exhausted. 
       FIG. 3-7  is a schematic representation of another embodiment of a Schnepel cycle power generation system  3300  according to certain aspects of the present disclosure. Many elements of system  3300  are common to previously presented systems and their description is not repeated with respect to  FIG. 3-7 . This embodiment is similar to system  3250  except that the output from the oxidizer  224  is provided to the piston expander  3020  and then passes to the heat exchanger  3055 . 
       FIG. 3-8  is a schematic representation of another embodiment of a Schnepel cycle power generation system  3350  according to certain aspects of the present disclosure. Many elements of system  3350  are common to previously presented systems and their description is not repeated with respect to  FIG. 3-8 . This embodiment is similar to system  3250  except that the output from the oxidizer  224  is provided to the heat exchanger  3055  and then passes through the turbine  3110  before reaching the piston expander  3020 , after which the gas is exhausted. 
       FIG. 3-9  is a schematic representation of another embodiment of a Schnepel cycle power generation system  3400  according to certain aspects of the present disclosure. Many elements of system  3400  are common to previously presented systems and their description is not repeated with respect to  FIG. 3-9 . This embodiment is similar to system  3200  except that the output from the oxidizer  224  is provided to the heat exchanger  3055  and then passes through the turbine  3110  before reaching the piston expander  3020 , after which the gas is exhausted. 
       FIG. 3-10  is a schematic representation of another embodiment of a Schnepel cycle power generation system  3450  according to certain aspects of the present disclosure. Many elements of system  3450  are common to previously presented systems and their description is not repeated with respect to  FIG. 3-10 . This embodiment is similar to system  3200  except that the output from the oxidizer  224  is provided to the heat exchanger  3055  and then passes through the piston expander  3020  before reaching the turbine  3110 , after which the gas is exhausted. 
     Process Equipment Using Gradual Oxidation 
       FIG. 4-1  is a schematic of a three-stage gradual oxidizer fluid heater system  4000  according to certain aspects of the present disclosure. A pre-mixed air-fuel mixture  4005  is provided to a series of three oxidizers  4010   a .  4010   b , and  4010   c . In certain aspects, the three oxidizers  4010   a .  4010   b , and  4010   c  are different in size and configuration. In certain aspects, the three oxidizers  4010   a .  4010   b , and  4010   c  are substantially identical. The air-fuel mixture  4005  enters the first oxidizer  4010   a  where the fuel is consumed by a portion of the oxygen in the air and hot combustion products  4035   a  are produced. Products  4035   a  contain oxygen, as the proportion of fuel to oxidizer was lean, i.e. excess air. The hot combustion products  4035   a  are directed through a first fluid heat exchanger  4020   a  wherein heat is transferred from the hot combustion products  4035   a  to the heat transfer fluid, in this example water  430 , which exits as a hotter fluid, in this example steam  4040 . In certain aspects, a heat transfer fluid, such as an oil or a gas, is provided in place of the water  430  and the output is hot heat transfer fluid. 
     In certain aspects, the first oxidizer  4010   a  is referred to as a first reaction chamber that is configured to maintain gradual oxidation of the first fuel. i.e. the fuel component of the air-fuel mixture  4005 , within the first reaction chamber without a catalyst while maintaining a first internal temperature within the first reaction chamber beneath a flameout temperature of the first fuel. 
     The product gases  4035   a  then pass into a second oxidizer  4010   b  and mixed with LEC fuel  4007 . In certain aspects, the LEC fuel  4007  is mixed with one of an oxidant, a diluent or flue gas, and a HEC fuel (none of which are shown in  FIG. 4-1 ) before being provided to oxidizer  4010   b . The fuel of the resultant mixture is consumed by a portion of the oxygen in the mixture and hot combustion products  4035   b  are produced. The hot combustion products  4035   b  are directed into a second fluid heater  4020   b  wherein heat is transferred from the hot combustion products  4035   b  to a separate flow of water  430  that exits as steam  4040  that is mixed with the steam  4040  from the first heat exchanger  4020   a.    
     In certain aspects, the second oxidizer  4010   b  is referred to as a second reaction chamber that is configured to maintain gradual oxidation of the second fuel, i.e. the remaining fuel in the hot combustion products  4035   a  and the newly introduced LEC fuel  4007 , in a gradual oxidation process without a catalyst. In certain aspects, the second oxidizer  4010   b  comprises an oxygen sensor (not shown in  FIG. 4-1 ) that is coupled to a processor that is part of a controller (not shown in  FIG. 4-1 ), wherein the processor is configured to determine an oxygen content level. 
     The product gases  4035   b , or flue gas, then pass into a third oxidizer  4010   c  and mixed with additional LEC fuel  4007 . In certain aspects, the LEC fuel  4007  to be provided to oxidizer  4010   c  is mixed with one of an oxidant, a diluent or flue gas, and a HEC fuel (not shown in  FIG. 4-1 ) before being provided to oxidizer  4010   c . In certain aspects, the air-fuel mixture provided to oxidizer  4010   c  is different from the air-fuel mixture provided to oxidizer  4010   b . The fuel in the resultant mixture in oxidizer  4010   c  is consumed by a portion of the oxygen in the mixture and hot combustion products  4035   c  are produced. These hot combustion products  4035   c  are directed into a third fluid heat exchanger  4020   c  wherein heat is transferred from the hot combustion products  4035   c  to a separate flow of water  430  that exits as steam  4040  that is mixed with the steam  4040  from the first and second heat exchangers  4020   a  and  4020   b.    
     The multiple stages of gradual oxidation, heat transfer to a fluid to reduce the gas temperature, and introduction of new fuel ( FIG. 4-1 ) can be used to limit the gas temperatures to below the thermal NOx temperature threshold, while reducing the amount of oxygen exhausting from the hot combustion products  4035   c . High efficiency, as measured by the amount of energy transferred from the fuel  4005  and  4007  to the steam  4040 , provides that oxygen content leaving system  4000  via hot combustion products  4035   c  be as low as possible, typically 3-5% by volume. It also provides that the exiting hot combustion products  4035   c  be as cool as possible. If one were to attempt to oxidize the fuel in one step, then the fuel-to-air ratio would be close to the stoichiometric value, which would yield high temperatures. For example, the adiabatic reaction temperature of methane at a stoichiometric apportionment is 3484° F. well above the threshold of 2300° F. for the formation of thermal NOx. The staged process of  FIG. 4-1  cools the various gas flows  4035   a ,  4035   b ,  4035   c  from the three oxidizers  4010   a ,  4010   b , and  4010   c  so that more fuel can be introduced and oxidized, and the majority of oxygen can be removed from the system in the form of H2O and CO2, without creating high temperatures and thermal NOx. 
     Other configurations of fluid flow from the input source, in this example water  430 , to the output, in this example steam  4040 , will be apparent to those of skill in the art. The system  4000  may have fewer or greater numbers of oxidizers and heat exchangers. One or more heat exchanges  4020   a .  4020   b , etc. can be linked in series to increase the temperature of the output fluid. The air-fuel mixture provided to each oxidizer  4010   a ,  4010   b , etc. can be different and adjustable in response to measurements of oxygen in the combustion products flow  4035   a ,  4035   b , etc. 
     A gradual oxidizer fluid heater arrangement  4000  facilitates the efficient oxidation of fuel and air in three stages and the capture of thermal energy by a fluid. The first stage comprises a first gradual oxidizer which enables the gradual oxidation of a fuel and produces a hot, low-emission product gas stream that is directed into a first fluid heater where a first fluid stream is beneficially heated. In order to reduce or eliminate the likelihood of flashback and explosion of the fuel-air mixture  4005  entering the first-stage oxidizer  4010   a , the concentration of fuel in the air-fuel mixture  4005  is limited to about 20-90% of the lower flammability limit concentration of the fuel. In certain aspects, it is desirable to limit the fuel content to 25-50%. In certain aspects, there may be applicable fire safety standards that limit the allowable fuel concentration of the air-fuel mixture  4005 . 
     After oxidation of the fuel in the first oxidizer  4010   a , the product gases  4035   a  contain about 11-19% oxygen, plus carbon dioxide and water vapor, at a temperature of approximately 1500-2300° F. In certain aspects, the oxidation process is controlled such that temperature of the product gases  4035   a  is 1600-2000° F. After transferring a portion of its heat to the heat transfer fluid in the heat exchanger  4020   a , the product gas  4035   a  is at a temperature of 700-1300° F. and more preferably 900-1200° F. At such a reduced temperature, a fuel stream  4007  can be blended into the product gas  4035   a  without undergoing immediate reaction, which may occur at temperatures at or above 1400° F. The temperature of the mixed product gas  4035   a  and fuel  4007  is nonetheless high enough to initiate oxidation reactions after an ignition delay of 0.01 to 5 seconds. In certain aspects, the ignition delay is 0.1-0.5 seconds. 
     After the ignition delay has transpired, the mixture will have entered the second oxidizer  4010   b  that is the preferred location for efficient oxidation of the fuel to occur. The second oxidizer  4010   b  generates a hot product gas stream  4035   b  with 2-16% oxygen at a temperature preferably between 1600-2000° F. that is directed into a second fluid heater  4020   b , where a portion of its thermal energy is transferred to the heat transfer fluid. The temperature of product gas  4035   b  is then reduced to 900-1200° F. and a second stream of LEC fuel  4007  is blended in product gas  4035   b  without a premature reaction. The mixture of fuel  4007  and product gas  4035   b  enters a third oxidizer  4010   c , wherein the oxidation process repeats, producing an exhaust gas  4035   c  with 1.5-14% oxygen. In certain aspects, between two and eight stages of gradual oxidation followed by fluid heating can be combined, with the ultimate goal of producing a final product gas stream with 1.5-5% oxygen and a temperature of approximately 150-700° F. In certain aspects, the temperature of the final product gas stream is approximately 250-400° F. The heated fluid streams can be combined together, as shown in  FIG. 4-1 , or left apart. 
       FIG. 4-2  is a schematic of another embodiment of a three-stage gradual oxidizer fluid heater system  4100  according to certain aspects of the present disclosure. An air-fuel mixture  4005  enters a first oxidizer  4110   a  where the fuel is consumed by a portion of the oxygen in the air-fuel mixture  4005  producing heat which passes through a first steam coil  4120   a  and boils a stream of liquid water  4130   a  to make saturated steam  4105 . The cooled product gases  4035   a  exit the first oxidizer  4110   a  and are mixed with additional LEC or HEC fuel and diluents  4007  whereupon the mixture enters a second gradual oxidizer  4110   b . Similar to the reaction in the first oxidizer  4110   a , the fuel in the fuel-product gas mixture is consumed by a portion of the oxygen in the mixture producing heat which passes through a second steam coil  4120   b  and boils a second stream of liquid water  4030  to make saturated steam  4105 . The cooled gases  4035   b  exit the second oxidizer  4110   b  and are mixed with additional fuel  4007  whereupon the mixture enters a third oxidizer  4110   c  wherein the process repeats, heating the liquid water  4130  in the third steam coil  4120   c  to make saturated steam  4105 . 
     It will be apparent to one of skill in the art that the fluid heater system  4100  may be used with a variety of heat transfer fluids. For example, an oil may be used to absorb heat from within one or more of the oxidizers  4110 A,  4110   b , etc. Separate flows of different types of heat exchange fluids may be individually provided to one or more of the oxidizers  4110   a ,  4110   b , etc. and provided for separate use by external systems (not shown in  FIG. 4-2 ). In certain aspects, one or more of the heat exchange coils  4120 A,  4120 B, etc. may be linked in series. 
     The partially-cooled product gases  4035   c  are directed into an economizer  4140  wherein the available heat in the product gas  4035   c  raises the temperature of a subcooled liquid water stream  4150  to a temperature slightly less than the water&#39;s saturation temperature. The cooled product gases  4035   d  are exhausted to the atmosphere. 
     While similar to the more generic fluid heater of  FIG. 4-1 , one distinguishing feature of system  4100  is the installation of a fluid heating element, i.e. a steam coil, into the same unit as the gradual oxidizer. The preferred temperature ranges and oxygen levels at the exit of each stage are the same as in the prior embodiment. A final heat recovery unit. i.e. economizer  4140 , is added to the tail end of the product gas stream to extract as much heat as possible from the gases before they exhausted to atmosphere. The steam coils  4120   a ,  4120   b ,  4120   c  may be embedded in the porous ceramic bed of the oxidizers  4110   a ,  4110   b ,  4110   c  or suspended above the top of the bed. In certain aspects, additional bed height or a porous, partial radiation shield may be added between the gradual oxidation zone and the steam generation zone to help ensure the gases aren&#39;t quenched by the relatively cold surfaces of the steam coils  4120   a ,  4120   b ,  4120   c  before the gradual oxidation reactions are complete. 
       FIG. 4-3  is a schematic representation of a single-stage recuperative steam generation system  4200  according to certain aspects of the present disclosure. Air  4210  is directed into the cold side of a recuperator  3045  where it receives heat and exits as a preheated air stream that is combined with a reduced-oxygen, recirculated product gas stream  4225  to which is added an LEC fuel  4220 . In certain aspects, the LEC fuel  4220  comprises a HEC fuel. In certain aspects, LEC or HEC fuel can be mixed with the air  4210  prior to entering the recuperator  3045 . 
     The air-fuel-diluent mixture enters an oxidizer  224  where the fuel is consumed by a portion of the oxygen and produced heat. 
     A liquid water stream  4230  is heated in the economizer  3055  to create a hot water stream that is directed to the steam coil  4240 . A portion of the heat from the oxidation process is transferred through the steam coil  4240  into the hot water, thereby creating steam  4242  for beneficial use. The partially-cooled product gases exit the oxidizer  224  and are divided into two streams. A portion of the product gases is directed through a recirculation blower  4245  where the product gases exit at a slightly higher pressure and are combined with the air-fuel stream as described above. The remaining portion of the product gases passes through the economizer  3055  where more heat is removed, thereby heating the incoming water  4230 , and the cooled product gases then pass through the hot side of the recuperator  3045  where additional heat is removed, thereby heating the incoming air  4210 , before the fully-cooled product gases exit to atmosphere. 
     System  4200  inhibits flashback and explosion of the pre-mixed air-fuel mixture by maintaining the oxygen concentration of the mixture entering the oxidizer  224  at less than 12%, and preferably less than 9%, through the recirculation of the product gases  4225 . The recirculation provides for oxidizer inlet temperatures in the range of 700-1300° F. and preferably 900-1200° F. Through recirculation, this embodiment also generates a total hot gas flow rate through the oxidizer equal to 1.5-4.0 times, preferably 2.0-3.0 times, the exhaust flow. The greater hot gas flow rate permits the installation of more heat transfer surface area within the oxidizer  224  and the production of greater amounts of steam. The specific heat (cp) of the gas stream performing the heat transfer to the steam coils is also greater than the specific heat of oxidation products that have less C02, less H2O, and more 02. Greater specific heat leads to greater potential for heat transfer, with a fixed temperature difference between the cold and hot streams. 
     System  4200  incorporates an economizer  3055  that recovers heat from the product gas stream by raising the temperature of the water  4230  to just below its boiling point. System  4200  also incorporates a recuperator  3045  that recovers additional heat by preheating the combustion air before it enters the oxidizer  224 . This recuperator  3045  reduces or eliminates the amount of auxiliary heating that is added to initiate the gradual oxidation process within the oxidizer  224  and also reduces the loss of heat in the exhaust. 
       FIG. 4-4  is a schematic representation of a two-stage water-tube type of steam generation system  4300  according to certain aspects of the present disclosure. An air-fuel mixture  4005  is provided at a bottom inlet of an oxidizer  4321 . The air-fuel mixture  4005  flows through the sparger tree  4322  and enters the porous media  512  where gradual oxidation occurs and all the fuel is consumed by a portion of the oxygen. A portion  4315  of the hot product flue gas exits the bed  512  and passes through steam coils  4325  where heat is removed from the gas, while a smaller portion  4314  of the hot gas passes through a core zone where no steam coils are located and no heat is removed. The first steam coils  4325  are arranged around the circumference of the enclosure, so that product gases  4314  flowing upward in the vicinity of the center axis of the enclosure will remain at a high temperature and serve as an ignition source for the 2nd stage gradual oxidation occurring just in the upper section. 
     Additional LEC fuel or HEC fuel with diluents  4220  is injected into the middle zone of the oxidizer  4321  and mixes with the product gases  4315  to form an oxidant-diluent-fuel mixture  4316  that enters an inverted sparger cone  4324  through a plurality of horizontal spokes that penetrate through the walls of the cone  4324 . These spokes have a plurality of injection holes to distribute mixture  4316  in a nearly uniform manner. The hot gas portion  4314  enters the inverted sparger cone  4324  through an opening at the bottom and serves to initiate gradual oxidation of the mixture streams  4316  thereby consuming the additional fuel and generating a reduced-oxygen, hot product stream  4317 . 
     The product stream  4317  is directed through steam coils  4326  where heat is removed from the product stream  4317  that then exits the oxidizer  4321  as cooled product gases  4318 . Water  4353  at near-saturated conditions is admitted into each of the steam coils  4325  and  4326  and exits as saturated steam streams  4354 . A two-stage, water-tube-style, gradual oxidizer steam generator  4300  is arranged in a single enclosure, and equipped with a means for reducing gas pressure drop in the second stage. A vertical enclosure incorporates a first gradual oxidizer for oxidizing fuel and creating a hot product gas stream, followed by a first set of steam coils (water tubes) to remove heat from the product stream. 
     The quantity of water or steam directed to the final coils  4326  may be greater than the prior stages to remove as much heat as possible from the gas flow  4317  before it exits to the atmosphere as exhaust  4318 . While it is desirable to maintain product gas temperature above 900° F. as it exits primary or intermediate stages ( 4316 ), dropping below 900° F. is not a concern in the very last stage of a multistage system because there is no subsequent gradual oxidizer that requires temperatures above 900° F. The steam generation surface area and or any economizer surface area can be as large as desired to achieve the objective of heat removal in the final stage. 
       FIG. 4-5  is a schematic representation of a two-stage fire-tube type of steam generation system  4400  according to certain aspects of the present disclosure. An air-fuel mixture  4005  enters the bottom zone of a sparger tree  4422 . The air-fuel mixture  4005  flows through the sparger tree  4422  and enters the bed of porous ceramic  512  where gradual oxidation occurs and all the fuel is consumed by a portion of the oxygen. The hot product gas  4419  exits the porous media  512  and enters fire tubes  4425  where heat is removed from the gas by the surrounding water  4451 . 
     Additional LEC or HEC fuel  4220  and optionally diluents (not shown) are mixed with the cooled product stream  4419  to form an oxidant-diluent-fuel mixture, which is admitted into the second sparger  4426  and the second bed of porous media  512  wherein the additional fuel is consumed and a reduced-oxygen, hot product stream  4415  is generated and directed through fire tubes  4429  where heat is removed by the surrounding water  4451 . The cooled product gases  4415  collect in a plenum  4430  and exit the oxidizer as a cooled exhaust stream  4417 . The two gradual oxidation zones have insulated walls  4424 ,  4428  to prevent excessive cooling of the reactant gases which leads to undesired quenching of the gradual oxidation reactions. Water  4451  at subcooled or near-saturated conditions is admitted into the gradual oxidizer enclosure  4401  and exits as saturated steam  4452 . In certain aspects, additional heating surfaces are added for superheating the steam  4452  to a temperature substantially higher than its boiling point. In certain aspects, the water  4451  is pressurized leading to higher saturated steam temperatures. 
     By reducing the oxygen in the final exhaust gas stream to 1.5-5.0% while reducing the exit gas temperature to 250-400° F., the overall cycle efficiency is estimated to be 85-90%, which represents an improvement over conventional steam generators that operate at 80-86% cycle efficiency. Increased cycle efficiency corresponds to reduced fuel usage for the same useful heat output. 
     By maintaining gradual oxidation temperatures below about 2300° F., and preferably below 2000° F. the formation of thermal NOx is reduced. Conventional burners have flames with maximum reaction temperatures exceeding 2300° F. and generate substantially more NOx than a gradual oxidation process. 
     In certain aspects, electric heating elements (not shown in  FIG. 4-5 ) are located at the inlet of one or both of the oxidizer stages to help initiate oxidation of the air-fuel mixture  4005  or oxidant-diluent-fuel mixture at that location. 
     In certain aspects, porous ceramic media  512  is reduced in amount or not present and the reaction temperature is allowed to go higher in the open volume. Furthermore, if the porous media is removed, a greater fraction of the total flow can be distributed to the final sparger  4426 . 
     In certain aspects, the internal pressure is maintained low enough so fuel can be added at each stage using only line pressure. i.e. without a gas pressure booster. 
     In certain aspects, an economizer or recuperator (not shown in  FIG. 4-4 or 4-5 ) is added to condense the moisture of combustion from the product gases, or alternatively to leave the water in the vapor phase. 
     In certain aspects, a fluidized bed (not shown in  FIG. 4-4 or 4-5 ) similar to the system shown in  FIG. 1-13  replaces the porous media  512  to facilitate heat feedback and ignition in the oxidizer  4321 ,  4401  as well as enhance heat transfer to the steam coils. Other options include flue-gas recirculation and structured media, similar to the systems shown in  FIGS. 1-15 and 1-16A / 16 B. 
       FIG. 4-6  schematically depicts the flow through a gradual oxidation system  4600  having a sparger according to certain aspects of the present disclosure. The processes and elements of  FIG. 4-6  are described in relation to the system  4500  of  FIG. 1-12 , wherein steps  1 - 6  are accomplished, which is shown as receiving the output from point A of system  4500 . In certain aspects, air  4602  and fuel  4220  are mixed, for example using a mixer similar to mixer  4510  of system  4500 , and provided in place of point A in  FIG. 4-6 . The gas mixture entering from point A undergo the following process steps: 
     7. The hot gas leaving the lower section is split into portions  4315  and  4314 , wherein portion  4315  is passed through a heat exchanger, such as the coils  4325  of  FIG. 4-4 , and a portion of the heat extracted from the hot gas, thereby cooling the gas to temperatures proximate to the autoignition temperature. This stage uses the heat extracted to generate steam or vaporize another liquid. 
     8. In this example, fuel  4220  is injected into both streams  4314  and  4315 . The  4314  portion is hot enough to initiate gradual oxidation in the portions that are mixed in each stage  4630 . 
     Hybrid Cycles and Gradual Oxidation 
       FIG. 5-1  is a schematic diagram of an exemplary gradual oxidation system  5100  incorporating steam generation and additional fuel injection according to certain aspects of the present disclosure. A compressor  410  is coupled to a shaft that is further coupled to a turbine  414  and a power generator  416 , as previously shown in  FIG. 1-9 . An air-fuel mixture  5102  is provided to a compressor  410  that provides a pressurized air-fuel mixture  206   f  to a heat exchanger  418  that heats this mixture  206   f  with heat from the turbine exhaust  420 . The hot, pressurized mixture  206   g  is conveyed into the oxidizer  224 . In certain aspects, an additional air-fuel mixture  5104 , is injected into the oxidizer. In certain aspects, the air-fuel mixture  5104  comprises only LEC or HEC fuel. The air-fuel mixtures  206   g  and  5104  are gradually oxidized in the oxidizer  224  and the hot flue gas  226  is exhausted to the turbine  414 . In passing through the turbine, energy is extracted from the hot flue gas  226  and the cooled, expanded turbine exhaust  420  is passed back to the heat exchanger  418 . After passing through the heat exchanger  418 , the flue gas  420  may still comprise free oxygen. Additional air-fuel mixture  5112  is injected into the flue gas  420  within a duct burner  5110  to reheat the flue gas to produce a hot flue gas  5111 , which then passes through a heat exchanger  422  wherein heat is transferred from the hot flue gas  5111  to water  430  thereby producing steam  5108  which is provided to an end use (not shown in  FIG. 5-1 ). The cooled flue gas is now exhausted as exhaust stream  5106  to the environment. In certain aspects, the air-fuel mixture  5102  comprises only air and fuel is provided from air-fuel mixture  5104 . 
       FIG. 5-2  is a schematic diagram of an exemplary gradual oxidation system  5200  incorporating steam generation and cogeneration according to certain aspects of the present disclosure. Many elements of system  5200  are common to the system  5100  previously discussed and their description is not repeated with respect to  FIG. 5-2 . In system  5200 , steam-generating coils  5220  are embedded in the oxidizer  224 . Extraction of heat from the oxidation process within the oxidizer  224  reduces the maximum reaction temperature, thereby reducing NOx formation, while generating steam  5204 . The air-fuel mixture  5104  is then injected into the cooled gas within the oxidizer  224  that is “downstream” of the coils  5220 , thereby allowing additional combustion so as to reduce the oxygen level in the exhaust  226  going into the turbine  414 . This injection of additional fuel and the further combustion that reduces the oxygen within the exhaust  226  increases the mass flow through the turbine  414 , increases the specific heat of exhaust gas  226 , and decreases the ratio of specific heats, thereby increasing the power output of the turbine  414 . System  5200  eliminates the duct burner  5110  while still producing steam from the coils  5220 . As the coils  5220  operate at the peak temperature of the system  5200 , the steam  5204  will be at a higher temperature or pressure than the steam  5108  produced in system  5100 . 
     In certain aspects, steam  5230  is injected into the working fluid within oxidizer  224 . Injection of steam in the gradual oxidation process within oxidizer  224  could help reduce emissions while burning near-stoichiometric air-fuel ratios. In certain aspects, injection of steam  5230  allows pre-mixed air-fuel mixtures  206   g  to be closer to a stoichiometric ratio without exceeding the flammable range of the air-fuel mixture  206   g  due to the inert water vapor present. In certain aspects, the steam is injected in a manner to create a swirling flow pattern within the oxidizer  224 , further aiding in the gradual oxidation process. In certain aspects, the steam  5230  is introduced through axial pipes (not shown in  FIG. 5-2 ) having radial holes and positioned around the perimeter of the oxidizer  224 . In certain aspects, steam  5204  from the coils  5220  is returned as steam  5230  and, if the steam  5204  is at a pressure equal to or greater than the pressure within oxidizer  224 , there is less parasitic energy loss because the steam  5230  is already pressurized. 
       FIG. 5-3  is a schematic diagram of an exemplary gradual oxidation system  5300  incorporating dual compressors  410 ,  5308  with intercooling according to certain aspects of the present disclosure. Many elements of system  5300  are common to the systems  5100  and  5200  previously discussed and their description is not repeated with respect to  FIG. 5-3 . The use of intercooler  5304  allows a higher total compression across compressors  410  and  5308 , thereby improving the efficiency of the system  5300 . Intercooler  5304  cools stream  5302  which is further compressed by  5308 . A lower temperature into compressor  5308  reduces the amount of thermodynamic work, i.e., power, used to compress the gas. The intercooler permits the flow at  5310  to be at a lower temperature than would exist without intercooler  5304 . This permits more thermal energy to be recovered in recuperator  418 . The amount of recovered energy in recuperator  418  is proportional to the temperature difference between the turbine exhaust  420  and the recuperator inlet temperature  5310 . 
       FIG. 5-4  is a schematic diagram of an exemplary gradual oxidation system incorporating a starter gradual oxidizer according to certain aspects of the present disclosure. Many elements of system  5400  are common to the systems  5100 ,  5200 , and  5300  previously discussed and their description is not repeated with respect to  FIG. 5-4 . The air-fuel mixture  5102  is provided as a flow of warmed, compressed air-fuel mixture  5408  to an inlet of oxidizer  224 . Use of a starter oxidizer  5420  allows the main oxidizer  224  to be brought up to operating temperature, i.e. above the autoignition temperature of the warmed, compressed air-fuel mixture  5408 , with a reduced amount of NOx formation compared to using a conventional combustor burning a HEC fuel in an open flame (for example,  FIG. 1-10 ). The starter oxidizer  5420  is provided with a supply of an air-fuel mixture  5428  and, in certain embodiments, pressurized with a blower  5422 . The hot combustion product gases, i.e. flue gas, is provided from an outlet of the starter oxidizer  5420  to an inlet on the oxidizer  224 . In certain embodiments, the flue gas from the starter oxidizer  5420  enters the oxidizer  224  through the same inlet as the warmed, compressed air-fuel mixture  5408 . A valve  5426  is provided to shut off this start-up subsystem when the main oxidizer  224  reaches operational temperature and the compressor/turbine  410 / 414  subsystem is started. In system  5400 , filters  5402  and  5424  are provided to remove particulates and other undesired components from the respective air-fuel mixtures  5102  and  5428 . 
     The advantages of using a starter gradual oxidizer of  FIG. 5-4  include reduction of emissions of criteria pollutants, for example NOx, during start-up of the system. It also allows the use of the native LEC gas at the site, rather than retaining a separate HEC supply of fuel for start-up combustion systems. 
       FIG. 5-5  is a schematic diagram of an exemplary gradual oxidation system  5500  incorporating multiple points  5504 ,  5510 ,  5516 , and  5522  of water  430  injection according to certain aspects of the present disclosure. Many elements of system  5500  are common to the systems  5100 - 5400  previously discussed and their description is not repeated with respect to  FIG. 5-1  through  FIG. 5-4 . Processes subsequent to each injection point  5504 ,  5510 ,  5516 , and  5522  will vaporize some amount of water in the process input to a gas while cooling the process output gas flow due to the latent heat of evaporation of the injected water. Water injection may be strategically performed at individual locations only, or in combination with other water injection locations. 
     Water injection at location  5504  can be used to cool the inlet flow stream temperature of compressor  410 . Lower inlet temperatures increase the density of the fluid entering the gas turbine cycle, increasing the power output. Cooler compressor inlet temperatures also reduce the amount of work (power) used to compress gas  5508 , leaving more shaft power  412  available to drive generator  416 . 
     Water injection at locations  5510 ,  5516 , and into heat exchanger  418  increase the power output of the turbine cycle. Compression of liquid water, as typically performed by a pump, can be more efficient than compressing a gaseous mixture in compressor  410 . Turbine  414  will generate more work due to the higher amount of mass flow of flue gas. These cycles are sometimes referred to as “humid air cycles” in the art. System  5500  can therefore leverage the beneficial effects of water injection in a cycle, while not producing thermal NOx due to the gradual oxidizer process. 
     Injection and evaporation of water in recuperator  418  can present more than just the thermodynamic cycle performance advantages listed in the prior paragraph. Recuperator  418  is naturally being heated by the exhaust flow  5526 . Evaporation of water can increase the effective heat transfer coefficient of the flow between  5512  and  5514 , thereby enabling a smaller physical heat exchanger. 
     Other embodiments and methods of injecting water can also be used in accordance with the description provided herein. For example, other systems and methods of injecting water into the oxidation system are described in U.S. application Ser. No. 13/048,796, filed Mar. 15, 2011, the entirety of which is incorporated by reference herein to the extent the teachings of that application are not inconsistent with the present description. 
       FIG. 5-6  is a diagram  5600  of the gas content of the exhaust of various systems. It can be seen that conventional gas turbines generally operate with greater than approximately 9%, by mass, residual free oxygen in the exhaust stream. By using the gradual oxidation techniques in the oxidizer of  FIG. 5-2  and  FIG. 5-3  while generating simultaneous steam, the oxygen content exiting the oxidizers and gas turbine cycles will be lower, preferably in the 1.5-5% range.  FIG. 5-6  shows this to be well below the range for conventional gas turbines. Hence, the simultaneous generation of pollutant-free flue gas and steam in a gradual oxidizer/steam generator, for example system  5200  of  FIG. 5-2 , is novel in the art. And as discussed previously in this document, lower oxygen and higher levels of CO2 and H2O are beneficial to the Brayton gas turbine cycle. 
     Control of the gradual oxidation system can be performed in a number of ways. In certain aspects, a method of ensuring complete oxidation changes the residence time of the fuel and air mixture within the oxidizer vessel. In certain aspects, a gas turbine supplies the gradual oxidizer and the turbine is configured to vary its rotational speed using, for example, variable speed generators and power electronics or inverters, as are known to those of skill in the art. In certain aspects, a fan feeds a fuel and air mixture to an oxidizer, for example as shown in  FIG. 2-1 , and the fan is powered by a variable speed drive, with the fan speed reduced to increase residence time inside the oxidizer. 
     In some embodiments, the oxidation systems described herein can be used for oxidizing fuel in a flexible, efficient, and clean manner. The oxidation reactions described herein provides methods for the oxidation of waste materials and the prevention or minimization of air pollution thereby. For example, methods and systems of how the oxidation reactions can be used are provided in U.S. patent application Ser. No. 13/115,910, filed May 25, 2011, and Ser. No. 13/115,902, filed May 25, 2011, both of which are incorporated herein by reference in their entirety to the extent their teachings are not inconsistent with the descriptions provided herein. 
     The previous description is provided to enable a person of ordinary skill in the art to practice the various aspects described herein. While the foregoing has described what are considered to be the best mode and/or other examples, it is understood that various modifications to these aspects will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other aspects. Additionally, although various embodiments are described in different sections, paragraphs, and with respect to different figures, unless otherwise expressed, various embodiments may be combined with other described embodiments. Thus, the claims are not intended to be limited to the aspects shown herein, but is to be accorded the full scope consistent with the language claims, wherein reference to an element in the singular is not intended to mean “one and only one” unless specifically so stated, but rather “one or more.” Unless specifically stated otherwise, the terms “a set” and “some” refer to one or more. Headings and subheadings, if any, are used for convenience only and do not limit the disclosure. 
     It is understood that the specific order or hierarchy of steps in the processes disclosed is an illustration of exemplary approaches. Based upon design preferences, it is understood that the specific order or hierarchy of steps in the processes may be rearranged. Some of the steps may be performed simultaneously. The accompanying method claims present elements of the various steps in a sample order, and are not meant to be limited to the specific order or hierarchy presented. 
     Terms such as “top,” “bottom,” “front,” “rear” and the like as used in this disclosure should be understood as referring to an arbitrary frame of reference, rather than to the ordinary gravitational frame of reference. Thus, a top surface, a bottom surface, a front surface, and a rear surface may extend upwardly, downwardly, diagonally, or horizontally in a gravitational frame of reference. 
     A phrase such as an “aspect” does not imply that such aspect is essential to the subject technology or that such aspect applies to all configurations of the subject technology. A disclosure relating to an aspect may apply to all configurations, or one or more configurations. A phrase such as an aspect may refer to one or more aspects and vice versa. A phrase such as an “embodiment” does not imply that such embodiment is essential to the subject technology or that such embodiment applies to all configurations of the subject technology. A disclosure relating to an embodiment may apply to all embodiments, or one or more embodiments. A phrase such an embodiment may refer to one or more embodiments and vice versa. 
     The word “exemplary” is used herein to mean “serving as an example or illustration.” Any aspect or design described herein as “exemplary” is not necessarily to be construed as preferred or advantageous over other aspects or designs. 
     As used herein, listings that recite “at least one of A. B, and C” or “at least one of A. B, or C” are intended to mean only A, only B, only C, or any combination of A, B, and C, including all of A, B, and C. 
     All structural and functional equivalents to the elements of the various aspects described throughout this disclosure that are known or later come to be known to those of ordinary skill in the art are expressly incorporated herein by reference and are intended to be encompassed by the claims. Moreover, nothing disclosed herein is intended to be dedicated to the public regardless of whether such disclosure is explicitly recited in the claims. No claim element is to be construed under the provisions of 35 U.S.C. §112, sixth paragraph, unless the element is expressly recited using the phrase “means for” or, in the case of a method claim, the element is recited using the phrase “step for.” Furthermore, to the extent that the term “include,” “have,” or the like is used in the description or the claims, such term is intended to be inclusive in a manner similar to the term “comprise” as “comprise” is interpreted when employed as a transitional word in a claim.