Abstract:
Two or more unipolar voltage generation systems may apply respective voltages to separate but complementary electrodes. The complementary electrodes may be disposed substantially congruently or analogously to one another to provide bipolar electrical effects on a combustion reaction.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    The present application claims priority benefit from U.S. Provisional Patent Application No. 61/745,540, entitled “ELECTRICAL COMBUSTION CONTROL SYSTEM INCLUDING A COMPLEMENTARY ELECTRODE PAIR”, filed Dec. 21, 2012; which, to the extent not inconsistent with the disclosure herein, is incorporated by reference. 
     
    
     BACKGROUND 
       [0002]    It has been found that the application of a high voltage to a combustion reaction can enhance the combustion reaction and/or drive the reaction, control or enhance heat derived therefrom, and/or cause flue gas derived therefrom to achieve a desirable parameter. In some embodiments, it may be desirable to drive an electrode assembly to a time-varying bipolar high voltage. 
         [0003]    Efficiently driving a single electrode to an arbitrary high voltage bipolar waveform may present challenges to system cost, size, reliability, power consumption, etc. What is needed is an approach that can apply variable voltage or bipolar voltage to a combustion reaction-coupled electrode assembly while minimizing negatives. 
       SUMMARY 
       [0004]    According to an embodiment, a system configured to apply time-varying electrical energy to a combustion reaction includes two electrodes including a first electrode and a second electrode operatively coupled to a combustion reaction in a combustion volume including or at least partly defined by a burner. A first unipolar voltage converter is operatively coupled to the first electrode and configured to output a first voltage for the first electrode. A second unipolar voltage converter is operatively coupled to the second electrode and configured to output a second voltage to the second electrode. A controller can be operatively coupled to the first and second unipolar voltage converters and configured to control when the first voltage is output by the first unipolar voltage converter for delivery to the first electrode and when the second voltage is output by the second unipolar voltage converter for delivery to the second electrode. 
         [0005]    According to an embodiment, an electrode assembly for applying electrical energy to a combustion reaction includes a complementary electrode pair configured to apply a time-varying electrical waveform to a combustion reaction. The complementary electrode pair includes a first electrode configured to receive a first polarity voltage during a first time and a second electrode, electrically isolated from the first electrode, and configured to receive a second polarity voltage during a second time. The first and second electrodes are configured to cooperate to apply respective first and second polarities of electrical energy to the combustion reaction during respective first and second times. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0006]      FIG. 1  is a diagram of a system configured to apply time-varying electrical energy to a combustion reaction, according to an embodiment. 
           [0007]      FIG. 2  is a diagram of a system configured to apply a time-varying bipolar electric field to a combustion reaction, according to an embodiment. 
           [0008]      FIG. 3  is a diagram of a system configured to apply a time-varying bipolar charge to a combustion reaction, according to an embodiment. 
       
    
    
     DETAILED DESCRIPTION 
       [0009]    In the following detailed description, reference is made to the accompanying drawings, which form a part hereof. In the drawings, similar symbols typically identify similar components, unless context dictates otherwise. Other embodiments may be used and/or other changes may be made without departing from the spirit or scope of the disclosure. 
         [0010]      FIG. 1  is a diagram of a system  100  configured to apply time-varying electrical energy to a combustion reaction  104 , according to an embodiment. The system  100  includes a complementary electrode pair  102 . The complementary electrode pair includes a first electrode  106   a  and a second electrode  106   b  operatively coupled to a combustion reaction  104  in a combustion volume  108  including or at least partly defined by a burner  110 . 
         [0011]    The system  100  includes a first unipolar voltage converter  112   a  operatively coupled to the first electrode  106   a  and configured to output a first voltage for the first electrode  106   a . A second unipolar voltage converter  112   b  is operatively coupled to the second electrode  106   b  and is configured to output a second voltage to the second electrode  106   b.    
         [0012]    An AC power source  116  can be operatively coupled to the first and second unipolar voltage converters  112   a ,  112   b . A positive unipolar voltage converter  112   a  increases the voltage output by the AC power source  112  during positive portions of the AC waveform. A negative unipolar voltage converter  112   b  increases negative voltage output by the AC power source  112  during negative portions of the AC waveform. The first and second unipolar voltage converters  112   a ,  112   b  can each include a voltage multiplier, for example. 
         [0013]    Optionally, a controller  114  is operatively coupled to the first and second unipolar voltage converters  112   a ,  112   b  and configured to control when the first voltage is output by the first unipolar voltage converter  112   a  for delivery to the first electrode  106   a  and when the second voltage is output by the second unipolar voltage converter  112   b  for delivery to the second electrode  106   b . For embodiments including the controller  114 , a DC power source can be substituted for an AC power source  116 . Moreover, the controller  114  can increase a switching frequency applied to the first and second unipolar voltage converters  112   a ,  112   b  to a rate higher than the periodicity of an AC power source  116 . The AC power source  116  (or optional DC power source) can optionally supply electrical power to operate the controller  114 . Additionally or alternatively, the AC power source  116  can be operatively coupled to control logic  118  of the controller  114 , for example to provide voltage signals for synchronization of the AC power source  116  with operation of the first and second unipolar voltage converters  112   a ,  112   b.    
         [0014]    The system  100  includes a burner  110 . According to embodiments, at least the combustion volume  108  and the burner  110  comprise portions of a furnace, boiler, or process heater. 
         [0015]    The first and second electrodes  106   a ,  106   b  of the complementary electrode pair  102  can be configured to apply electrical energy to the combustion reaction  104  from substantially congruent and/or analogous locations. Additionally and/or alternatively, the first and second electrodes  106   a ,  106   b  can be configured to respectively apply substantially antiparallel electric fields to the combustion reaction  104 . Additionally and/or alternatively, the first and second electrodes  106   a ,  106   b  can be configured to at least intermittently cooperate to form an arc discharge selected to ignite the combustion reaction  104 . 
         [0016]    According to an embodiment, the first voltage output by the first unipolar voltage converter  112   a  is a positive voltage. The first voltage can be a positive polarity voltage having a value of greater than 1000 volts. For example, the first voltage can be a positive polarity voltage having a value of greater than 10,000 volts. 
         [0017]    According to an embodiment, the first unipolar voltage converter  112   a  can include a voltage multiplier or a charge pump configured to output a positive voltage. The second unipolar voltage converter  112   b  can include a voltage multiplier or a charge pump configured to output a negative voltage. 
         [0018]    The second voltage can be a negative voltage having a value of greater than −1000 volts negative magnitude. For example, the second voltage can be a negative voltage having a value of greater than −10,000 volts magnitude. 
         [0019]    The system  100  can include at least one voltage source  116  that is selectively operatively coupled to the first and second unipolar voltage converters  112   a ,  112   b . The at least one voltage source  116  can include an alternating polarity (AC) voltage source. Additionally and/or alternatively, the at least one voltage source  116  can include at least one constant polarity (DC) voltage source. 
         [0020]    According to an embodiment, the controller  114  can be configured to control pump switching of a first polarity voltage from either an AC voltage source or at least one constant polarity (DC) voltage source to the first unipolar voltage converter  112   a , and can control pump switching of a second polarity voltage from either an AC voltage source or at least one constant polarity (DC) voltage source to the second unipolar voltage converter  112   b . The pump switching can be selected to cause stages of the first and second unipolar voltage sources  112   a ,  112   b  to increase the magnitudes of the first and second polarity voltages output by the one or more voltage sources  116  respectively to the first and second voltages output by the first and second unipolar voltage sources  112   a ,  112   b.    
         [0021]    The at least one voltage source can be set at different output levels for different embodiments. For example, according to one embodiment, the at least one voltage source  116  can be configured to output less than or equal to 1000 volts magnitude. According to another embodiment, the at least one voltage source  116  can be configured to output less than or equal to 230 volts magnitude. According to another embodiment, the at least one voltage source  116  can be configured to output less than or equal to 120 volts magnitude. According to another embodiment, the at least one voltage source  116  can be configured to output a safety extra-low voltage (SELV). For example, the at least one voltage source  116  can be configured to output less than or equal to 42.4 volts magnitude. According to another embodiment, the at least one voltage source  116  is configured to output less than or equal to 12 volts magnitude. According to another embodiment, the at least one voltage source  116  can be configured to output less than or equal to 5 volts magnitude. 
         [0022]    The controller  114  can include a control logic circuit  118  configured to determine when to operatively couple at least one voltage source  116  to the first unipolar voltage converter  112   a  and when to operatively couple the at least one voltage source  116  to the second unipolar voltage converter  112   b . According to an embodiment, the control logic circuit  118  can include or consist essentially of a timer. According to an embodiment, the control logic circuit  118  can include a microcontroller. 
         [0023]    The control logic circuit  118  can include a data interface  120  configured to communicate with a human interface and/or an external computer-based control system, for example. A computer control system can be operatively coupled to a data interface portion of the control logic circuit  118 . All or a portion of the computer control system can form a portion of the system  100 . 
         [0024]    According to an embodiment, the controller  114  can include at least one switching element  122   a ,  122   b  operatively coupled to the control logic circuit  118 . The control logic circuit  118  can be configured to control the at least one switching element  122   a ,  122   b  to make electrical continuity between the at least one voltage source  116  and the first unipolar voltage converter  112   a  and break electrical continuity between the at least one voltage source  116  and the second unipolar voltage converter  112   b  during a first time segment. The control logic  118  can be configured to subsequently control the at least one switching element  122   a ,  122   b  to break electrical continuity between the at least one voltage source  116  and the first unipolar voltage converter  112   a  and make electrical continuity between the at least one voltage source  116  and the second unipolar voltage converter  112   b  during a second time segment. By repeating the complementary make-break cycle of powering the first unipolar voltage converter and then the second unipolar voltage converter, the first and second unipolar voltage converters  112   a ,  112   b  can cause the complementary electrode pair  102  to apply a bipolar voltage waveform to the combustion reaction  104 . The first and second time segments together can form a bipolar electrical oscillation period applied to the first and second electrodes  106   a ,  106   b.    
         [0025]    In embodiments where one or more DC voltage sources  116  are selectively coupled to the first and second unipolar voltage converters  112   a ,  112   b , the controller  114  can apply pumping switching to cause the voltage converters  112   a ,  112   b  to raise the input voltage provided by the voltage sources to high voltages applied to the first and second electrodes  106   a ,  106   b . Such pump switching can typically occur at a relatively high frequency consistent with R-C time constants of the voltage converters  112   a ,  112   b.    
         [0026]    As used herein, pump switching refers to pumping a voltage converter  112   a ,  112   b  at a single polarity to cause the voltage converter  112   a  to multiply the input voltage. In contrast, cycle switching refers to switching the voltage converters  112   a ,  112   b  to change the polarity of voltage output by the electrode pair  102 . 
         [0027]    The cycle of making and breaking of continuity between the one or more voltage sources  116  and the voltage converters  112   a ,  112   b  typically occurs at a relatively low frequency consistent with the voltage converters  112   a ,  112   b  raising and holding their respective output voltage magnitudes for a substantial portion of each respective half cycle. For example, the first and second cycle switched time segments can be 5 times or more in duration than the pumping cycles. In another embodiment, the first and second time segments can be 10 times or more in duration than the pumping cycles. In another embodiment, the electrical oscillation period applied to the electrodes  106   a ,  106   b  can be about 100 times longer than the pumping period. 
         [0028]    The bipolar electrical oscillation (cycle switching) frequency applied to the first and second electrodes can be between 200 and 300 Hertz, for example. Other bipolar electrical oscillation frequencies can be used according to the needs of a given combustion system and/or designer preferences. 
         [0029]    According to an embodiment, the at least one switching element  122   a ,  122   b  can include a pair of relays and/or a double-throw relay. Additionally and/or alternatively, the at least one switching element  122   a ,  122   b  can include an electrically controlled single pole double throw (SPDT) switch. 
         [0030]    The at least one switching element  122   a ,  122   b  can include one or more semiconductor devices. For example, the at least one switching element  122   a ,  122   b  can include an insulated gate bipolar transistor (IGBT), a field-effect transistor (FET), a Darlington transistor and/or at least two sets of transistors in series. 
         [0031]    The system  100  includes an electrode assembly  102  for applying electrical energy to a combustion reaction  104 , according to an embodiment. The system includes a complementary electrode pair  102  configured to apply a time-varying electrical waveform to a combustion reaction  104 . The complementary electrode pair includes a first electrode  106   a  and a second electrode  106   b . The first electrode  106   a  is configured to receive a first polarity voltage during a first time interval. The second electrode  106   b  is electrically isolated from the first electrode  106   a  and is configured to receive a second polarity voltage during a second time interval. 
         [0032]    The first and second electrodes  106   a ,  106   b  are configured to cooperate to apply respective first and second polarities of electrical energy to the combustion reaction  104  during respective first and second times. 
         [0033]    Optionally, the first and second electrodes  106   a ,  106   b  can be driven to provide a combustion ignition spark by simultaneously driving the first electrode  106   a  to a high positive voltage and driving the second electrode  106   b  to a high negative voltage. Optionally, the system  100  includes a sensor (not shown) configured to sense a combustion condition in the combustion volume  108  and operatively coupled to the controller  114 . The controller can drive the first and second unipolar voltage converters  112   a ,  112   b  to apply opposite polarity high voltages respectively to the first and second electrodes  106   a ,  106   b  responsive to a sensed condition corresponding to flame  104  blow-out or responsive to a sensed condition indicative of unstable combustion. 
         [0034]      FIG. 2  is a diagram of a system  200  configured to apply a time-varying bipolar electric field to a combustion reaction, according to an embodiment. The system  200  includes first and second electrodes  106   a ,  106   b . The first and second electrodes  106   a ,  106   b  can be configured to apply the electrical energy to the combustion reaction  104  from substantially congruent locations. 
         [0035]    “Substantially congruent locations” is intended to mean locations resulting in electric fields caused by each electrode  106   a ,  106   b  of the complementary electrode pair  102  having a substantially equal and opposite effect on the combustion reaction  102 . For example, in the embodiment  200  of  FIG. 2 , each electrode  106   a ,  106   b  can be considered substantially congruent, because as a pair the electrodes  106   a ,  106   b  apply similar but opposite electric fields to the combustion reaction  104 . Electrodes  106   a ,  106   b  in substantially congruent locations occupy regions of space that are close together, at least relative to the scale of the combustion volume  108  and/or the combustion reaction  104 . Because opposite-sign voltages in close proximity can cause electrical arcing, closely-spaced complementary electrodes  106   a ,  106   b  can be placed sufficiently far apart to prevent arc discharge therebetween. A set of complementary electrodes  106   a ,  106   b  can be considered substantially congruent when they are placed close enough together to cause similar effect on the combustion reaction  104  (albeit with opposite polarity voltages) and far enough apart to substantially prevent electrical arc discharge between the electrodes  106   a ,  106   b . Additionally or alternatively, the first and second electrodes  106   a ,  106   b  can include features that are placed sufficiently close together to support a spark discharge when the controller  122  causes the first and second unipolar voltage converters  112   a ,  112   b  to simultaneously apply opposite polarity voltages to the first and second electrodes  106   a ,  106   b.    
         [0036]    The first and second electrodes  106   a ,  106   b  can be configured as field electrodes capable of applying antiparallel electric fields to the combustion reaction  104 . The first and second electrodes  106   a ,  106   b  can be toric, as shown in  FIG. 2 . 
         [0037]      FIG. 3  is a diagram of a system  300  configured to apply a time-varying bipolar charge to a combustion reaction, according to an embodiment. 
         [0038]    According to an embodiment, the first and second electrodes  106   a ,  106   b  can be configured to respectively eject oppositely charged ions for transmission to the combustion reaction  104 . The system  300  illustrates first and second electrodes  106   a ,  106   b  configured to apply the electrical energy to the combustion reaction from analogous locations. 
         [0039]    Analogous locations refers to locations from which each electrode  106   a ,  106   b  can produce the same effect on the combustion reaction, albeit with opposite polarity. For example, in the embodiment  300  of  FIG. 3 , two ion ejecting electrodes  106   a ,  106   b  are disposed near a combustion reaction  104 , configured to respectively apply positive and negative ions to the combustion reaction. If the polarities of the voltages applied to the electrodes  106   a  and  106   b  were reversed, each would still function substantially identically, albeit with opposite polarities. For example, in the embodiment  300 , an axis  302  can be defined by the burner  110  and the combustion reaction  104  (at least near the electrodes  106   a ,  106   b ). The analogous locations of the first and second electrodes  106   a ,  106   b  can be axisymmetric locations. 
         [0040]    According to an embodiment, the first and second electrodes  106   a ,  106   b  can be ion-ejecting electrodes. For example, the first and second electrodes  106   a ,  106   b  can be configured to apply a respective opposite polarity majority charge to the combustion reaction  104 . 
         [0041]    Referring to  FIGS. 2 and 3 , an electrode support apparatus  204 ,  204   a ,  204   b  can be configured to support the electrodes  106   a ,  106   b  forming the complementary electrode pair  102 . The electrode support apparatus  204 ,  204   a ,  204   b  can be configured to support at least the first and second electrodes  106   a ,  106   b  within a combustion volume  108 . For example, as indicated in  FIG. 2 , a combustor wall  202  can define at least a portion of the combustion volume  108 . The electrode support apparatus  204   a ,  204   b  support the electrodes  106   a ,  106   b  from the combustion volume wall  202 . The electrode support apparatus  204 ,  204   a ,  204   b  can include at least one insulator  206   a ,  206   b  configured to insulate voltages placed on the electrodes  106   a ,  106   b  from one another. The at least one insulator  206   a ,  206   b  can be further configured to insulate voltages placed on the electrodes  106   a ,  106   b  from ground. 
         [0042]    While various aspects and embodiments have been disclosed herein, other aspects and embodiments are contemplated. The various aspects and embodiments disclosed herein are for purposes of illustration and are not intended to be limiting, with the true scope and spirit being indicated by the following claims.