Apparatus and method for electrically stabilized combustion

Abstract

An electrically stabilized burner is configured to support a combustion reaction such as a combustion reaction substantially at a selected fuel dilution and with a mixing rate selected to maximize the reaction rate without quenching the combustion reaction.

What is claimed is: 
     
         1 . An electrically stabilized burner, comprising:
 a fuel nozzle configured to providing a fuel jet flowing a fuel through a surrounding volume and entraining a first quantity of oxidant, air or flue gas, wherein the fuel and the first quantity of oxidant, air or flue gas are ignited to provide a combustion reaction;   a conductive flame holder configured for mounting proximate the fuel jet;   a mixer configured to mix the fuel and the first quantity of oxidant, air or flue gas above the conductive flame holder; and   wherein the mixer includes a plurality of field electrodes operatively coupled to the mixer controller and disposed such that the conductive flame holder is disposed between the plurality of field electrodes and a fuel nozzle;   wherein the mixer controller further includes a plurality of second power supplies each operatively coupled to one of each of the plurality of field electrodes;   wherein the mixer controller is configured to drive the plurality of field electrodes with a substantially constant bias voltage superimposed over a time-varying mixing voltage sequence; and   wherein the application of the bias voltage is selected to cause the plurality of field electrodes to operate as a charger.   
     
     
         2 . The electrically stabilized burner of  claim 1 , wherein the mixer controller is configured to drive the plurality of field electrodes in a manner selected to cause the plurality of field electrodes to mix the fuel and the first quantity of oxidant, air, or flue gas at a selected rate of mixing. 
     
     
         3 . The electrically stabilized burner of  claim 1 , wherein the mixer controller is configured to drive the plurality of field electrodes in a sequence selected to cause the plurality of field electrodes to form a stream-wise vortex in the combustion reaction to cause mixing of the fuel and the first quantity of oxidant, air, or flue gas. 
     
     
         4 . The electrically stabilized burner of  claim 1 , further comprising a third electrical insulator configured to be disposed peripherally to the combustion reaction or to the fuel and the first quantity of oxidant, air, or flue gas such that the conductive flame holder is disposed between the third electrical insulator and the fuel nozzle;
 wherein the plurality of field electrodes are at least partially carried by the third electrical insulator; and   wherein the third electrical insulator and the plurality of field electrodes form an integrated unit or a portion of an integrated unit.   
     
     
         5 . The electrically stabilized burner of  claim 1 , wherein the mixer includes a plurality of field electrodes operatively coupled to the mixer controller and disposed such that the conductive flame holder is disposed between the plurality of field electrodes and a fuel nozzle;
 wherein the mixer controller is configured to drive the plurality of field electrodes with a time-varying bias voltage superimposed over a time-varying mixing voltage sequence; and   wherein the application of the time-varying bias voltage is selected to cause the plurality of field electrodes to operate as charger.   
     
     
         6 . A method for operating an electrically stabilized burner, comprising the steps of:
 providing a fuel jet streaming a fuel;   supporting a conductive flame holder proximate to the fuel jet at a distance along the fuel jet corresponding to a selected fuel dilution;   mixing the fuel with the first quantity of oxidant, air, or flue gas above the conductive flame holder to provide a mixed fuel.   igniting the mixed fuel to provide a combustion reaction;   applying a voltage or charge to the combustion reaction; and   holding the combustion reaction with the conductive flame holder responsive to at least an intermittent voltage difference between the combustion reaction and the conductive flame holder.   
     
     
         7 . The method for operating an electrically stabilized burner of  claim 6 , wherein the selected fuel dilution corresponds to a fuel concentration at or above a lean flammability limit of the fuel. 
     
     
         8 . The method for operating an electrically stabilized burner of  claim 6 , further comprising the step of:
 mixing the fuel with the first quantity of oxidant, air, or flue gas at a mixing rate corresponding to a selected Damköhler number between about 1.1 to 1.7 at a location corresponding to the combustion reaction.   
     
     
         9 . The method for operating an electrically stabilized burner of  claim 6 , wherein the step of supporting a conductive flame holder proximate to a fuel jet at a distance along the fuel jet corresponding to a selected fuel dilution includes the step of supporting the conductive flame holder at a distance such that dilution in the fuel caused by fuel jet expansion between a nozzle and the conductive flame holder plus dilution in the fuel jet caused by the step of mixing the fuel with a first quantity of oxidant, air, or flue gas results in a selected fuel dilution near the lean flammability limit of the fuel. 
     
     
         10 . The method for operating an electrically stabilized burner of  claim 6 , wherein the step of mixing the fuel with a first quantity oxidant, air, and/or flue gas includes the step of injecting one or more fluid jets of the second quantity of any or the combination of fuel, oxidant, air, and/or flue gas into the combustion reaction in order to impart rotational inertia to the combustion reaction. 
     
     
         11 . The method for operating an electrically stabilized burner of  claim 6 , wherein the step of mixing the fuel with a first quantity of oxidant, air, or flue gas includes a step of applying a rotating electric field to the combustion reaction or to the mixed fuel above the conductive flame holder. 
     
     
         12 . The method for operating an electrically stabilized burner of  claim 11 , wherein the step of applying a rotating electric field includes a step of applying a sequential voltage waveform to a plurality of field electrodes. 
     
     
         13 . The method for operating an electrically stabilized burner of  claim 6 , wherein the steps of applying a voltage or charge to the combustion reaction and mixing the fuel with a first quantity of oxidant, air, or flue gas above the conductive flame holder is performed by sequentially applying a voltage waveform to at least an overlapping set of field electrodes. 
     
     
         14 . The method for operating an electrically stabilized burner of  claim 6 , wherein the step of mixing the fuel with a first quantity of oxidant, air, or flue gas above the conductive flame holder includes the step of applying an electric field to the combustion reaction or to the mixed fuel above the conductive flame holder. 
     
     
         15 . The method for operating an electrically stabilized burner of  claim 6 , wherein the step of mixing the fuel with a first quantity of oxidant, air, or flue gas includes the step of applying an electric field to the combustion reaction or to the mixed fuel with a charger. 
     
     
         16 . The method for operating an electrically stabilized burner of  claim 6 , wherein the step of mixing the fuel with a first quantity of oxidant, air, or flue gas above the conductive flame holder includes the step of mixing the fuel with the first quantity of oxidant, air, or flue gas above the conductive flame holder and below a location where the voltage or charge is applied to the combustion reaction. 
     
     
         17 . The method for operating an electrically stabilized burner of  claim 6 , wherein the step of mixing the fuel with a first quantity of oxidant, air, or flue gas above the conductive flame holder includes the step of mixing the fuel with the first quantity of oxidant, air, or flue gas above a location where the voltage or charge is applied to the combustion reaction. 
     
     
         18 . The method for operating an electrically stabilized burner of  claim 6 , wherein the step of mixing the fuel with a first quantity of oxidant, air, or flue gas above the conductive flame holder includes the step of mixing the fuel with the first quantity of oxidant, air, or flue gas at a location substantially coincident with a location where the voltage or charge is applied to the combustion reaction. 
     
     
         19 . The method for operating an electrically stabilized burner of  claim 6 , further comprising the step of:
 mixing the fuel with a first quantity of oxidant, air, or flue gas at a location below the conductive flame holder.   
     
     
         20 . The method for operating an electrically stabilized burner of  claim 6 , further comprising the steps of:
 selecting a fuel and an oxidant stoichiometry; and   adjusting the distance along the fuel jet at which the conductive flame holder is supported to correspond to the selected fuel and oxidant stoichiometry.   
     
     
         21 . The method for operating an electrically stabilized burner of  claim 6 , further comprising the step of:
 entraining at least an oxidant in the fuel jet.   
     
     
         22 . The method for operating an electrically stabilized burner of  claim 21 , wherein the step of entraining at least the oxidant in the fuel jet includes entraining a gas including the oxidant. 
     
     
         23 . The method for operating an electrically stabilized burner of  claim 21 , wherein the step of entraining at least the oxidant in the fuel jet includes entraining the oxidant and air or flue gas. 
     
     
         24 . The method for operating an electrically stabilized burner of  claim 21 , wherein entraining at least the oxidant in the fuel jet includes entraining a flue gas. 
     
     
         25 . The method for operating an electrically stabilized burner of  claim 6 , wherein the step of mixing the fuel with the first quantity of oxidant, air, or flue gas further includes the step of mixing the fuel with a flue gas. 
     
     
         26 . The method for operating an electrically stabilized burner of  claim 6 , wherein the step of holding the combustion reaction with the conductive flame holder includes the step of exciting at least an intermittent plasma state in the mixed fuel responsive to the at least an intermittent voltage difference between the combustion reaction and the conductive flame holder. 
     
     
         27 . The method for operating an electrically stabilized burner of  claim 26 , further comprising the step of:
 maintaining ignition of the mixed fuel with the plasma state.   
     
     
         28 . The method for operating an electrically stabilized burner of  claim 6 , further comprising the step of:
 holding the conductive flame holder at a voltage different than the voltage or charge applied to the combustion reaction.   
     
     
         29 . The method for operating an electrically stabilized burner of  claim 28 , wherein the step of applying a voltage or charge to the combustion reaction includes the step of applying a first time-varying voltage or charge to the combustion reaction and the step of applying a second time-varying voltage to the conductive flame holder, the second time-varying voltage being instantaneously opposite in sign from the time-varying voltage or charge applied to the combustion reaction. 
     
     
         30 . The method for operating an electrically stabilized burner of  claim 6 , further comprising the step of:
 holding the conductive flame holder substantially at a ground potential.   
     
     
         31 . The method for operating an electrically stabilized burner of  claim 15 , further comprising the step of:
 galvanically isolating the conductive flame holder from ground and from voltages other than the voltage applied to the ionizing electrode.