Abstract:
A method to facilitate improving electrostatic precipitator performance is provided. The method includes providing an electrostatic precipitator including an inlet, a collector chamber and an outlet, where the collector chamber includes a plurality of discharge electrodes and a plurality of collector electrodes. The method also includes defining a respective discharge electrode V-I performance for each of the plurality of discharge electrodes, identifying a particle removal characteristic for each respective discharge electrode based on the respective discharge electrode V-I performance for each of the plurality of discharge electrodes and positioning each of the plurality of discharge electrodes in the electrostatic precipitator according to the particle removal characteristic for each respective discharge electrode.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    This invention relates generally to electrostatic precipitators, and more particularly, to methods of improving electrostatic precipitator performance. 
         [0002]    Known electrostatic precipitators remove particles from gas and are generally used in industrial applications. At least some known methods of determining electrostatic precipitator performance are based on current density (A/m 2 ). Generally the current density may be determined by measuring the electrons bridging a gap between emitting electrodes and sets of collecting electrodes. Electrode operating voltage may be variable because of the buildup of dust or contaminant particles on the collecting plates or the emitting electrodes. 
         [0003]    Known emitting electrodes have an associated electric field, are positioned at least at the precipitator input and output, and may be designed to generate the most possible current for any given situation. The electric fields of properly functioning discharge electrodes located at the precipitator inlet may capture significantly more contaminant particles than electric fields of properly functioning discharge electrodes located at the precipitator outlet. As such, electric fields at the inlet may need to overcome a space charge caused by a huge number of particles collected between the emitting and collecting electrodes. Generally, electric fields at the outlet may be subjected to significantly fewer particles, so electrons migrate much easier. Because it is easier to have high current densities in an electric field at the precipitator output than in an electric field at the precipitator input, it may be difficult to impart power to an electric field at the input and it may be easier to impart excessive power to an electric field at the output. 
         [0004]    Electrostatic precipitators may not fully use their power supplies. For example, mismatched impedance may prevent the power supply from reaching secondary design limits. This may result in operating voltages of about 10-20% lower than rated voltage, while the input power may be at its operating limit. The opposite may also occur. Should the sparking rate remain the same, minimally increasing or decreasing the system impedance may increase the total wattage input to the electric field, which may improve overall precipitator performance. 
         [0005]    Known discharge electrodes are generally not designed to match the impedance of their associated electric fields. Rather, they are generally designed to facilitate maximizing the power in their associated electric fields. Measuring and optimizing watts may provide the best impedance matching. 
       BRIEF DESCRIPTION OF THE INVENTION 
       [0006]    In one aspect, a method to facilitate improving electrostatic precipitator performance is provided. The method includes providing an electrostatic precipitator including an inlet, a collector chamber and an outlet, where the collector chamber includes a plurality of discharge electrodes and a plurality of collector electrodes. The method also includes defining a respective discharge electrode V-I performance for each of the plurality of discharge electrodes, identifying a particle removal characteristic for each respective discharge electrode based on the respective discharge electrode V-I performance for each of the plurality of discharge electrodes and positioning each of the plurality of discharge electrodes in the electrostatic precipitator according to the particle removal characteristic for each respective discharge electrode. 
         [0007]    In another aspect, a system for improving electrostatic precipitator performance is provided. The system includes an electrostatic precipitator including an inlet, an outlet and a collector chamber extending between the inlet and the outlet. The collector chamber includes a plurality of discharge electrodes and a plurality of collector electrodes and a respective discharge electrode V-I performance, related to a respective discharge electrode geometry associated for each of the plurality of discharge electrodes. Each of the discharge electrode V-I performances is used to identify a particle removal characteristic for each respective discharge electrode and each of the plurality of discharge electrodes is positioned in the electrostatic precipitator based on the particle removal characteristic for each respective discharge electrode. 
         [0008]    In yet another aspect, an apparatus to facilitate matching impedance of discharge electrodes in electrostatic precipitators is provided. The apparatus includes an electrostatic precipitator including an inlet, a collector chamber and an outlet, the collector chamber includes a plurality of discharge electrodes and a plurality of collector electrodes, wherein a relationship between a secondary voltage and a secondary current is determined by at least one discharge electrode geometry. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0009]      FIG. 1  is a perspective view of a known exemplary electrostatic precipitator; 
           [0010]      FIG. 2  is a top cross-sectional view of the known exemplary electrical precipitator shown in  FIG. 1 ; 
           [0011]      FIG. 3  is a perspective view of an exemplary dual blade discharge electrode; 
           [0012]      FIG. 4  is a perspective view of an exemplary quad blade discharge electrode; 
           [0013]      FIG. 5  is a perspective view of an exemplary opposed pin discharge electrode; 
           [0014]      FIG. 6  is a perspective view of an exemplary V-pin discharge electrode; and 
           [0015]      FIG. 7  is a graph of exemplary discharge electrode performance curves. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0016]      FIG. 1  is a perspective view of an exemplary electrostatic precipitator  10 .  FIG. 2  is a top cross-sectional view of electrostatic precipitator  10 . In the exemplary embodiment, precipitator  10  includes a body  12  that has an entry channel  14 , an exit channel  16  and a collector chamber  18  positioned between entry channel  14  and exit channel  16 . Collector chamber  18  includes an inner top surface  20  and a plurality of rigid discharge electrodes  22  that each extend from surface  20 . Collector chamber  18  also includes a plurality of collector electrodes  24  that are suspended from inner surface  20 . Electrodes  24  are positioned within a flow path  26  that extends from entry channel  14  through collector chamber  18  and to exit channel  16 . 
         [0017]    In the exemplary embodiment, Collector electrodes  24  are square plates that are positioned substantially parallel to, and uniformly spaced from, each other such that a gap  28  is defined between adjacent electrodes  24 . Each of the plurality of discharge electrodes  22  extends from surface  20  into gap  28  between adjacent collector electrodes  24 . Furthermore, collector chamber  18  includes a bottom surface  30  that includes a plurality of sloughing channels  32  that are positioned above a hopper (not shown). Each sloughing channel  32  includes at least two sides  34  that slope towards an exit passage  36 . It should be appreciated that although collector electrodes  24  are described as square plates, collector electrodes  24  may be any collector electrode, that enables electrostatic precipitator  10  to function as described herein, such as, but not limited to, plain wire, barbed wire, spiral wire, twisted round wire, twisted square wire, thin metal sheets cut with points and a tube with various styles of pins, barbs, projections or edges. 
         [0018]    During operation, fluid containing suspended particles  38  is channeled through entry channel  14  into collector chamber  18 . The fluid channeled along flow path  26  between collector electrodes  24 . Rigid discharge electrodes  22  are charged with a high current, creating a corona of electrons and an associated electric field which ionizes suspended particles  38  causing particles  38  to migrate towards collector electrodes  24 . Generally, discharge electrodes  22  have a negative potential and collector electrodes  24  have a positive potential. As such, rigid discharge electrodes  22  charge suspended particles  38  and collector electrodes  24  collect suspended particles  38 . It should be appreciated that the term “fluid” as used herein includes any material or medium that flows, including but not limited to, gas, air and liquids. 
         [0019]    Because a plurality of discharge electrodes  22  extend into collector chamber  18 , collector chamber  18  is divided into a plurality of electric fields that are each defined by a corresponding discharge electrode  22 . Moreover, it should be appreciated that the impedance of each electric field is a function of the amount of dust in the electric field. 
         [0020]    It should be understood that precipitator performance is optimized when power is maximized. More specifically, matching the impedance of each rigid discharge electrode  22  with the impedance of its associated electric field facilitates maximizing the total power, in watts, input to its associated electric field. It should be appreciated that matching the impedance of each rigid discharge electrode  22  with the impedance of its associated electric field is accomplished by altering the geometry of each rigid discharge electrode  22 . Altering the geometry of each rigid discharge electrode  22  also modifies the relationship between a secondary voltage and a secondary current. For example, the geometry of each rigid discharge electrode  22  may be altered by adjusting a pin length, pin spacing, tube diameter and pin angle. 
         [0021]    A voltage is applied to each discharge electrode  22 , and when a pre-determined voltage is applied a corona begins to develop and a secondary current begins to develop between discharge electrode  22  and collector electrode  24 . Corona onset voltage is defined as the point at which measurable secondary current is first observed. After the corona onset voltage is reached, for each increase in the applied voltage there is an increase in the secondary current. It should be understood that applied voltages exceeding the corona onset voltage are considered secondary voltages. Moreover, it should be understood that for a given rigid electrode geometry and fluid conditions, the applied secondary voltage drives the level of secondary current realized. In addition, discharge electrodes each have a V-I performance curve determined by plotting applied secondary voltage versus measured secondary current. In electrodes, the current is dependent and increases exponentially with the voltage, and maximizing the secondary voltage may optimize precipitator performance. 
         [0022]      FIG. 3  is a perspective view of an exemplary dual blade discharge electrode  40 . More specifically, dual blade discharge electrode  40  includes a central discharge electrode body  42  having an outer surface  44  and two blades  46  extending radially outward therefrom. In the exemplary embodiment, electrode body  42  is cylindrically-shaped and has a substantially circular cross-section. Blades  46  are positioned about outer surface  44 , extend generally radially outward from surface  44 , and are diametrically opposed to each other. It should be appreciated that although the exemplary embodiment is described as including an electrode body  42  having a substantially circular cross-section, in other embodiments, electrode body  42  may have any cross-sectional shape that enables discharge electrode  40  to function as described herein. 
         [0023]      FIG. 4  is a perspective view of an exemplary quad blade discharge electrode  48 . More specifically, dual blade discharge electrode  48  includes a central discharge electrode body  50  having an outer surface  52  and four blades  54  extending radially outward therefrom. In the exemplary embodiment, electrode body  50  is cylindrically-shaped and has a substantially circular cross-section. Blades  54  are positioned about the periphery of outer surface  52 , are separated by an angle θ of approximately ninety degrees and extend generally radially outward from outer surface  52 . It should be appreciated that although the exemplary embodiment is described as including an electrode body  50  having a substantially circular cross-section, in other embodiments, electrode body  50  may have any cross-sectional shape that enables discharge electrode  48  to function as described herein. Moreover, it should be appreciated that angle θ between blades  54  may be any angle θ, not necessarily equal, that enables discharge electrode  48  to function as described herein. 
         [0024]      FIG. 5  is a perspective view of an exemplary opposed pin discharge electrode  56 . More specifically, opposed pin discharge electrode  56  includes a central discharge electrode body  58  having an outer surface  60  and two pins  62  extending radially outward therefrom. Electrode body  58  is cylindrically-shaped and has a substantially circular cross-section. Pins  62  have a length L of approximately 1½ inches, are positioned at an angle α of approximately one hundred eighty degrees from each other about the periphery of outer surface  60  and extend radially outward from outer surface  60 . It should be appreciated that although the exemplary embodiment is described as including an electrode body  58  having a substantially circular cross-section, in other embodiments, electrode body  58  may have any cross-sectional shape that enables discharge electrode  56  to function as described herein. Moreover, it should be appreciated that angle α between pins  62  may be any angle α that enables discharge electrode  56  to function as described herein. Furthermore, it should be appreciated that although the exemplary embodiment describes pins  62  as having a length of approximately 1/1-2 inches, in other embodiments, pins  62  may have any length L that enables discharge electrode  56  to function as described herein. 
         [0025]      FIG. 6  is a perspective view of an exemplary V-pin discharge electrode  64 . More specifically, V-pin discharge electrode  64  includes a central discharge electrode body  66  having an outer surface  68  and four pins  70  extending radially outward therefrom. Electrode body  66  is cylindrically-shaped and has a substantially circular cross-section. Pins  70  have a length L 1 , are positioned in pairs about the periphery of outer surface  68 , and extend radially outward from outer surface  68 . Each pair of pins  70  includes two pins  70  separated at an acute angle β about outer surface  68  such that each pair of pins  70  defines a generally V-shaped configuration. Moreover, each pin  70  included in each pair of pins, is diametrically opposed to another pin included in another pair of pins. It should be appreciated that although the exemplary embodiment is described as including an electrode body  66  having a substantially circular cross-section, in other embodiments, electrode body  66  may have any cross-sectional shape that enables discharge electrode  64  to function as described herein. Moreover, it should be appreciated that angle β between pins  70  may be any acute angle β that enables discharge electrode  64  to function as described herein. Furthermore, it should be appreciated that length L 1  of pins  70  may be any length that enables discharge electrode  64  to function as described herein. 
         [0026]      FIG. 7  is a graph showing exemplary curves of secondary voltage plotted against secondary current for a plurality of rigid discharge electrode  22  embodiments. These curves are known as V-I performance curves. More specifically, V-I curves are shown for dual blade discharge electrode  40 , quad blade discharge electrode  48 , opposed pin discharge electrodes  56  and V-pin discharge electrode  64 . The V-I performance curve of dual blade discharge electrode  40  shows that providing dual blades in this configuration results in relatively low secondary current at an applied secondary voltage. The V-I performance graph for quad blade discharge electrode  48  shows that providing quad blades in this configuration results in relatively high secondary currents at an applied secondary voltage, versus dual blade discharge electrode  40 . 
         [0027]    The V-I performance graph of dual pin discharge electrode  56  shows that providing dual pins  62  in this configuration, and having a length L of 1-½ inches, facilitates providing secondary voltages and secondary currents intermediate those provided by dual blade electrode  40  and quad blade electrode  48 . Modifying the length L of pins  62  alters the V-I performance of dual pin electrode  56 . For example, by increasing the length L to two inches, dual pin electrode  56  provides marginally less secondary current at the same secondary voltage versus using L of 1-½ inches. By increasing length L to three inches, dual pin electrode  56  provides smaller corresponding secondary current than both 1-½ and 2 inch pins  62  at the same secondary voltage. 
         [0028]    The V-I performance graph of V-pin discharge electrode  64  provides discharge electrode performance similar to quad blade electrode  48 . However, starting at about a secondary voltage of about 45 kV V-pin electrode  64  provides increased secondary current for the same secondary voltage versus quad blade electrode  48 . 
         [0029]    It should be appreciated that each of the discharge electrode exemplary embodiments  40 ,  48 ,  56  and  64  described herein is based on empirical data reflecting process parameters, such as, but not limited to, precipitator configuration, particle resistivity and operating volume, as well as the V-I curve of an electric field and a transformer/rectifier&#39;s rating. 
         [0030]    For low dust loading composed of primarily fine particles, discharge electrode  22  should be designed to maintain relatively high voltage to maintain adequate electric field strength without reaching a secondary current limit of the power supply. Thus, of the discharge electrode embodiments described herein, dual blade discharge electrode  40  is the most effective for removing fine particles from the fluid. 
         [0031]    For heavy dust loading composed primarily of coarse particles, discharge electrodes  22  should be designed to produce high secondary current at an applied secondary voltage. This maximizes charging of the dust with the available electric field. Thus, of the discharge electrode embodiments described herein, quad blade discharge electrode  48  operates at a high secondary current with a minimal secondary voltage to provide the best charging, and is the most effective at removing coarse particles from the fluid. 
         [0032]    V-I performance characteristics of discharge electrodes  22  may be used to determine their most effective location within precipitator  10 . For example, the first electric field of precipitator inlets collects about eighty percent of the particles contained in the dust, and these particles are generally coarse. Consequently, positioning quad blade discharge electrodes  48  proximate precipitator inlet  14  facilitates optimizing coarse particle removal from the fluid. As another example, electric fields located downstream from the first electric fields encounter less dust than the first electric field and the dust generally contains finer particles. Consequently, positioning dual blade discharge electrodes  40  proximate precipitator outlet  16  facilitates optimizing fine particle removal from the fluid. The fluid in chamber  18  flowing from inlet  14  towards outlet  16  contains progressively fewer coarse particles and progressively more fine particles, on a percentage basis. Consequently, opposed pin discharge electrodes  56  designed to have pin lengths L corresponding to both coarse and fine particle removal, should be positioned proximate a center of chamber  18 . Thus, electrostatic precipitators  10  may be designed to contain discharge electrodes  22  that are specifically positioned within precipitator  10  for facilitating optimal particle removal in a particular region of electrostatic precipitators  10 . 
         [0033]    Rigid discharge electrodes  22  operating at a high secondary current for a given secondary voltage should be positioned proximate precipitator areas containing heavy loading of coarse particles. Discharge electrodes  22  operating with high secondary current while maintaining adequate secondary voltage should be positioned proximate precipitator areas containing lower dust loading of fine particles. Discharge electrodes  22  with intermediate secondary voltage and intermediate secondary current should be positioned proximate precipitator areas containing a mix of coarse and fine particles. Thus, the electric fields of discharge electrodes  22  positioned proximate inlet  14  operate at the highest secondary voltage, and the electric fields of discharge electrodes  22  positioned downstream of the inlet operate at progressively lower secondary voltages and progressively higher secondary currents. 
         [0034]    In each embodiment the above-described rigid discharge electrodes facilitate operating transformer/rectifiers closer to their maximum ratings. More specifically, in each embodiment, by modifying rigid discharge electrode geometry the relationship between the secondary voltage and the secondary current is modified such that V-I curves are designed to facilitate matching the impedance of the discharge electrode with its associated electric field, thus, optimizing the power input into the electric field. As a result, operating voltage is facilitated to be maximized, operating performance is facilitated to be improved and the cost of rebuilding electrostatic precipitators is facilitated to be reduced. Accordingly, electrostatic precipitator performance and component useful life are each facilitated to be enhanced in a cost effective and reliable manner. 
         [0035]    Exemplary embodiments of rigid discharge electrodes are described above in detail. The rigid discharge electrodes are not limited to use with the specific precipitator embodiment described herein, but rather, the rigid discharge electrodes can be utilized independently and separately from other rigid discharge electrode components described herein. Moreover, the invention is not limited to the embodiments of the rigid discharge electrodes described above in detail. Rather, other variations of rigid discharge electrode embodiments may be utilized within the spirit and scope of the claims. 
         [0036]    While the invention has been described in terms of various specific embodiments, those skilled in the art will recognize that the invention can be practiced with modification within the spirit and scope of the claims.