Abstract:
A method and system for controlling an exhaust gas recirculation (EGR) system is provided. The EGR system recirculates a portion of an exhaust through an inlet portion of the turbomachine. The EGR system reduces the level of harmful constituents within the exhaust before the recirculation occurs.

Description:
BACKGROUND OF THE INVENTION 
     This application is related to commonly-assigned U.S. patent application Ser. No. 11/928,038, filed Oct. 30, 2007 and U.S. patent application Ser. No. 11/953,524, filed Dec. 10, 2007. 
     The present invention relates to an exhaust gas recirculation system, and more particularly to a method and system for controlling the quantity of exhaust reentering a turbomachine after processing by a recirculation system. 
     There is a growing concern over the long-term effects of Nitrogen Oxides (hereinafter NOx) and Carbon Dioxide (hereinafter “CO 2 ”) and Sulfur Oxides (SOx) emissions on the environment. The allowable levels of emissions that may be emitted by a turbomachine, such as a gas turbine, are heavily regulated. Operators of turbomachines desire methods of reducing the levels of NOx, CO 2 , and SOx emitted. 
     Significant amounts of condensable vapors exist in the exhaust gas stream. These vapors usually contain a variety of constituents such as water, acids, aldehydes, hydrocarbons, sulfur oxides, and chlorine compounds. Left untreated, these constituents will accelerate corrosion and fouling of the internal components if allowed to enter the gas turbine. 
     Exhaust gas recirculation (EGR) generally involves recirculating a portion of the emitted exhaust through an inlet portion of the turbomachine. The exhaust is then mixed with the incoming airflow prior to combustion. The EGR process facilitates the removal and sequestration of concentrated CO 2 , and may also reduce the NOx and SOx emission levels. 
     There are a few concerns with the currently known EGR systems. The quantity and rate of the recirculated exhaust impacts the turbomachine operability. combustor stability, emissions, compressor stability, and component life. 
     For the foregoing reasons, there is a need for a method and system for controlling the composition of the inlet fluid exiting the EGR system. The method and system should control the quantity and rate of exhaust reentering the turbomachine. The method and system should use the composition of the inlet fluid as a control parameter. 
     BRIEF DESCRIPTION OF THE INVENTION 
     In accordance with an embodiment of the present invention, a method of controlling an exhaust stream, wherein the exhaust stream is generated by a turbomachine; the method comprising: providing at least one exhaust gas recirculation (EGR) system comprising: at least one EGR flow conditioning device, a constituent reduction system, at least one flow control device; wherein the at least one EGR flow conditioning device increases the flowrate of the exhaust stream and comprises a source of air; wherein the source of air comprises a fan, wherein the EGR system reduces constituents within the exhaust stream from a first concentration to a second concentration and recirculates the exhaust stream to an inlet section of the turbomachine; receiving a target EGR fraction comprising the portion of the exhaust stream within an inlet fluid, wherein the inlet fluid enters the inlet section of the turbomachine; determining a target level of at least one constituent from the target EGR fraction; determining a current level of the at least one constituent; determining whether the current level of the at least one constituent is within a constituent range; and adjusting a recirculation rate of the exhaust stream if the at least one constituent is outside of the constituent range. 
     In accordance with an alternate embodiment of the present invention, a method of controlling an exhaust stream, wherein the exhaust stream is generated by a turbomachine; the method comprising: providing at least one exhaust gas recirculation (EGR) system comprising: at least one EGR flow conditioning device, a constituent reduction system, at least one flow control device; wherein the at least one EGR flow conditioning device comprises a fan; wherein the EGR system reduces constituents within the exhaust stream from a first concentration to a second concentration and recirculates the exhaust stream to an inlet section of the turbomachine; wherein the constituent reduction system removes up to about 99 percent of SOx constituents within the exhaust stream; receiving a target EGR fraction comprising the portion of the exhaust stream within an inlet fluid, wherein the inlet fluid enters the inlet section of the turbomachine; determining a target level of at least one constituent from the target EGR fraction comprising receiving data on the at least one constituent from at least one constituent feedback device; determining a current level of the at least one constituent; determining whether the current level of the at least one constituent is within a constituent range; and adjusting a EGR rate of the exhaust stream if the at least one constituent is outside of the constituent range; wherein the step of adjusting the EGR rate comprises providing at least one notification when the EGR rate of the exhaust stream requires adjustment; wherein the at least one constituent comprises at least one of: SOx, NOx, CO 2 , water, chloride ions, acids, aldehydes, hydrocarbons, or combinations thereof. 
     In accordance with another alternate embodiment of the present invention, a system for controlling an exhaust stream, wherein the exhaust stream is generated by a turbomachine; the system comprising: at least one exhaust gas recirculation (EGR) system comprising: at least one EGR flow conditioning device, a constituent reduction system, at least one flow control device; wherein the EGR system reduces constituents within the exhaust stream from a first concentration to a second concentration and recirculates the exhaust stream to an inlet section of the turbomachine; means for receiving a target EGR fraction; means for determining a target level of at least one constituent from the target EGR fraction; means for determining a current level of the at least one constituent; means for determining whether the current level of the at least one constituent is within a constituent range; means for adjusting a EGR rate of the exhaust stream if the at least one constituent is outside of the constituent range; and means for providing at least one notification when the EGR rate of the exhaust stream requires adjustment. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic illustrating the environment in which an embodiment of the present invention operates. 
         FIG. 2  is a flowchart illustrating an example of a method of controlling the composition of an inlet fluid in accordance with an embodiment of the present invention. 
         FIG. 3  is a block diagram of an exemplary system for adjusting an EGR rate in accordance with an embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The following detailed description of preferred embodiments refers to the accompanying drawings, which illustrate specific embodiments of the invention. Other embodiments having different structures and operations do not depart from the scope of the present invention. 
     Certain terminology is used herein for the convenience of the reader only and is not to be taken as a limitation on the scope of the invention. For example, words such as “upper,” “lower,” “left,” “right,” “front”, “rear” “top”, “bottom”, “horizontal,” “vertical,” “upstream,” “downstream,” “fore”, “aft”, and the like; merely describe the configuration shown in the Figures. Indeed, the element or elements of an embodiment of the present invention may be oriented in any direction and the terminology, therefore, should be understood as encompassing such variations unless specified otherwise. 
     The present invention has the technical effect of controlling the composition of an inlet fluid exiting an EGR system and entering the inlet portion of a turbomachine. 
     An EGR rate may be considered the rate and quantity of exhaust stream that enters the inlet section of the turbomachine. The composition of the inlet fluid includes, but is not limiting of, the exhaust stream, the inlet air, and at least one of the aforementioned constituents, and combinations thereof. 
     The present invention may be applied to the variety of turbomachines that produce a gaseous fluid, such as, but not limiting of, a heavy duty gas turbine; an aero-derivative gas turbine; or the like (hereinafter referred to as “gas turbine”). An embodiment of the present invention may be applied to either a single gas turbine or a plurality of gas turbines. An embodiment of the present invention may be applied to a gas turbine operating in a simple cycle or a combined cycle configuration. 
     Referring now to the Figures, where the various numbers represent like elements throughout the several views,  FIG. 1  is a schematic illustrating the environment in which an embodiment of the present invention operates.  FIG. 1  illustrates a site  100 , such as but not limiting of a powerplant site, having a turbomachine  105 , an EGR system  107 , a heat recovery steam generator (HRSG)  155 , and an exhaust stack  165 . Alternatively, the present invention may be integrated with a site  100  not having the HRSG  155 . 
     The EGR system  107  comprises multiple elements. The configuration and sequence of these elements may be dictated by the composition of the exhaust stream  170  and the type of cooling fluid used by the components of the EGR system  107 . Furthermore, alternate embodiments of the EGR system  107  may include additional or fewer components than the components described below. Therefore, various arrangements, and/or configurations, which differ from  FIG. 1 , may be integrated with an embodiment of the present invention. 
     As illustrated in  FIG. 1 , the EGR system  107  comprises: a mixing station  115 , an inlet modulation device  120 , a bypass modulation device  125 , a bypass stack  130 , at least one EGR flow conditioning device  135 , a downstream temperature conditioning device  140 , a constituent reduction system  145 , a upstream temperature conditioning device  150 , at least one exhaust modulation device  160 , and constituent feedback devices  175 , 177 . 
     Generally, the process used by the EGR system  107  may include: cooling of the exhaust stream  170 ; reduction and removal of the aforementioned constituents within the exhaust stream  170 ; and then mixing the exhaust stream  170  with the inlet air, forming an inlet fluid; which flows from the inlet section  110  through to the exhaust stack  165 . The EGR system  107  may reduce the temperature of the exhaust stream  170  to a saturation temperature where the aforementioned constituents may condense and then be removed. Alternatively, the EGR system  107  may also reduce the temperature of, and use a scrubbing process (or the like) on, the exhaust stream  170  to remove the aforementioned constituents. 
     While EGR system  107  operates, constituent feedback devices  175 , 177  may determine the level of at least one constituent within the inlet fluid. As illustrated in  FIG. 1 , a constituent feedback device  175  may be located adjacent the exhaust stack  165  and another constituent feedback device  177  may be located adjacent the inlet section  110  of the turbomachine  105 . In an alternate embodiment of the present invention at least one constituent feedback device  175 , 177  may be located adjacent at least one extraction port located on the turbomachine. Generally, the placement of the constituent feedback devices  175 , 177  allows for determining the concentration of at least one constituent within the inlet fluid. 
     As will be appreciated, the present invention may be embodied as a method, system, or computer program product. Accordingly, the present invention may take the form of an entirely hardware embodiment, an entirely software embodiment (including firmware, resident software, micro-code, etc.) or an embodiment combining software and hardware aspects all generally referred to herein as a “circuit”, “module,” or “system”. Furthermore, the present invention may take the form of a computer program product on a computer-usable storage medium having computer-usable program code embodied in the medium. 
     Any suitable computer readable medium may be utilized. The computer-usable or computer-readable medium may be, for example but not limited to, an electronic, magnetic, optical, electromagnetic, infrared, or semiconductor system, apparatus, device, or propagation medium. More specific examples (a non exhaustive list) of the computer-readable medium would include the following: an electrical connection having one or more wires, a portable computer diskette, a hard disk, a random access memory (RAM), a read-only memory (ROM), an erasable programmable read-only memory (EPROM or Flash memory), an optical fiber, a portable compact disc read-only memory (CD-ROM), an optical storage device, a transmission media such as those supporting the Internet or an intranet, or a magnetic storage device. Note that the computer-usable or computer-readable medium could even be paper or another suitable medium upon which the program is printed, as the program can be electronically captured, via, for instance, optical scanning of the paper or other medium, then compiled, interpreted, or otherwise processed in a suitable manner, if necessary, and then stored in a computer memory. In the context of this document, a computer-usable or computer-readable medium may be any medium that can contain, store, communicate, propagate, or transport the program for use by or in connection with the instruction execution system, apparatus, or device. 
     Computer program code for carrying out operations of the present invention may be written in an object oriented programming language such as Java7, Smalltalk or C++, or the like. However, the computer program code for carrying out operations of the present invention may also be written in conventional procedural programming languages, such as the “C” programming language, or a similar language. The program code may execute entirely on the user&#39;s computer, partly on the user&#39;s computer, as a stand-alone software package, partly on the user&#39;s computer and partly on a remote computer or entirely on the remote computer. In the latter scenario, the remote computer may be connected to the user&#39;s computer through a local area network (LAN) or a wide area network (WAN), or the connection may be made to an external computer (for example, through the Internet using an Internet Service Provider). 
     The present invention is described below with reference to flowchart illustrations and/or block diagrams of methods, apparatuses (systems) and computer program products according to embodiments of the invention. It will be understood that each block of the flowchart illustrations and/or block diagrams, and combinations of blocks in the flowchart illustrations and/or block diagrams, can be implemented by computer program instructions. These computer program instructions may be provided to a processor of a public purpose computer, special purpose computer, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, create means for implementing the functions/acts specified in the flowchart and/or block diagram block or blocks. 
     These computer program instructions may also be stored in a computer-readable memory that can direct a computer or other programmable data processing apparatus to function in a particular manner, such that the instructions stored in the computer-readable memory produce an article of manufacture including instruction means which implement the function/act specified in the flowchart and/or block diagram block or blocks. The computer program instructions may also be loaded onto a computer or other programmable data processing apparatus to cause a series of operational steps to be performed on the computer or other programmable apparatus to produce a computer implemented process such that the instructions which execute on the computer or other programmable apparatus provide steps for implementing the functions/acts specified in the flowchart and/or block diagram block. 
     The present invention may include a control system, or the like, that has the technical effect of controlling the composition of an inlet fluid exiting an EGR system and entering the inlet portion of a turbomachine. The present invention may be configured to automatically or continuously monitor the inlet fluid of the turbomachine  105  to determine the quantity of the exhaust stream  170  that should enter the inlet section  110 . Alternatively, the control system may be configured to require a user action to the initiate operation. An embodiment of the control system of the present invention may function as a stand-alone system. Alternatively, the control system may be integrated as a module, or the like, within a broader system, such as a turbine control or a plant control system. For example, but not limiting of, the control system of the present invention may be integrated with the control system operating the EGR system  107 . 
     Referring now to  FIG. 2 , which is a flowchart illustrating an example of a method  200  of controlling the composition of an inlet fluid in accordance with an embodiment of the present invention. In an embodiment of the present invention the EGR system  107  may be integrated with a graphical user interface (GUI), or the like. The GUI may allow the operator to navigate through the method  200  described below. The GUI may also provide at least one notification of the status of the EGR system  107 . 
     In step  210 , of the method  200 , the EGR system  107  may be processing an exhaust stream  170 , as described. Depending on either the type and/or operation of the turbomachine  105 , the generated exhaust may have a flowrate of about 10,000 Lb/hr to about 50,000,000 Lb/hr and a temperature of about 100 Degrees Fahrenheit to about 1,100 Degrees Fahrenheit. 
     In step  220 , the method  200  may receive a target EGR fraction. The EGR fraction may be considered the amount, such as, but not limiting of, a percentage of the exhaust stream  170  within the inlet fluid. EGR fraction may be determined by dividing the mass flowrate of the exhaust stream  170  by the mass flowrate of the inlet air. In an embodiment of the present invention, the method  200  may automatically receive the EGR fraction from the control system operating the EGR system  107 . In an alternate of the present invention, a user may enter the EGR fraction. 
     In step  230 , the method  200  may determine the target level of at least one constituent. The method  200  may utilize a species conservation engine, or the like, to determine the target level. The species conservation engine may incorporate a plurality of turbomachine operating data along with the target EGR fraction to calculate the target level. The plurality of turbomachine operating data may include: at least one fuel composition; the compressor airflow of the turbomachine  105 ; and the fuel flow of the turbomachine  105 . The at least one fuel composition may include, but are not limited to: the composition of the fuel entering a combustion system of the turbomachine  105 ; and the composition of the fuel used in an auxiliary firing system integrated with the turbomachine  105 , wherein the auxiliary firing system may include an auxiliary boiler, or combinations thereof. 
     The species conservation engine may incorporate a physical equation, or the like, to calculate the target level of at least one constituent. As discussed, the at least one constituent includes at least one of: SOx, NOx, CO 2 , water, chloride ions, acids, aldehydes, hydrocarbons, or combinations thereof. 
     The species conservation engine may incorporate a physical equation, or the like, to calculate the target level of at least one constituent. For example, but not limiting of, the species conservation engine may calculate a target exhaust CO 2  mole fraction as a function of: a target EGR mass fraction, fuel flow, fuel composition, and turbomachine  105  inlet flow. The target exhaust CO 2  mole fraction value may be compared to a CO 2  mole fraction measured by the constituent feedback device  175 . The comparison process may yield an error signal, which the method  200  may use for feedback control of the EGR flow rate. 
     Additionally, the combustion reaction for the turbomachine  105  that burns a hydrocarbon fuel in standard air may be described by Equation 1, using molar coefficients, as illustrated below:
 
C α H γ +(a+e)(O2+3.76N2)=&gt;bCO2+cH2o+eO2+(a+e)(3.76)N2  [Equation 1]
 
Here, “fuel composition” is defined by the carbon and hydrogen subscripts, α and γ. The excess oxygen molar coefficient, e, may be calculated as a function of EGR mass fraction (X EGR ), compressor inlet mass flow (W C ) and fuel mass flow (W F ) as illustrated by Equation 2.
 
                   e   =         1   4.76     ⁢         W   C     ⁡     (     1   -     X   EGR       )         W   F       ⁢       MW   fuel       MW   air         -     (     α   +     γ   ⁢     /     ⁢   4       )               Equation   ⁢           ⁢   2               
The target exhaust CO 2  mole fraction (y CO2     —     target ), on a dry basis, may be calculated from the reaction in Equation 1 according to Equation 3.
 
     
       
         
           
             
               
                 
                   
                     y 
                     
                       CO 
                       
                         2 
                         ⁢ 
                         _target 
                       
                     
                   
                   = 
                   
                     α 
                     
                       α 
                       + 
                       e 
                       + 
                       
                         
                           ( 
                           
                             α 
                             + 
                             
                               γ 
                               ⁢ 
                               
                                 / 
                               
                               ⁢ 
                               4 
                             
                             + 
                             e 
                           
                           ) 
                         
                         ⁢ 
                         
                           ( 
                           3.76 
                           ) 
                         
                       
                     
                   
                 
               
               
                 
                   Equation 
                   ⁢ 
                   
                       
                   
                   ⁢ 
                   3 
                 
               
             
           
         
       
     
     Equations 1 through 3 may be adapted to perform similar species conservation calculations for constituents other than CO 2  or for a turbomachine  105  operating with different working fluids or fuel types. As discussed, the constituent includes at least one of: SOx, NOx, CO 2 , water, chloride ions, acids, aldehydes, hydrocarbons, or combinations thereof. 
     In step  240 , the method  200  may determine the current level of at least one constituent. As discussed, the EGR system  107  may include constituent feedback devices  175 , 177 . The constituent feedback devices  175 , 177  may include sensors, transmitters, and similar devices that may provide data on the current level of the at least one constituent. The positions of the constituent feedback devices  175 , 177  may provide feedback on the composition of the inlet fluid. The constituent feedback devices  175 , 177  are generally located upstream and downstream of the combustion system of the turbomachine  105 , increasing the accuracy of the feedback. The constituent feedback devices  175 , 177  may be integrated with the control system used to operate the method  200 . The data provided by the constituent feedback devices  175 , 177  may be used to directly or indirectly determine the current level of at least one constituent. 
     In step  250 , the method  200  may determine whether the current level of the at least one constituent is within a constituent range. Here, the method  200  compares the target level determined in step  230 , and the current level determined in step  240 , of the at least one constituent. In an embodiment of the present invention an operator may determine the range. In an alternate embodiment of the present invention the range may be automatically determined. For example, but not limiting of, if the target level is 1 and the current level is from about 0.95 to about 1.05, then the method  200  may determine that the current level of the at least one constituent is within range. 
     Additionally, for example, but not limiting of, the turbomachine  105  may be operated with a target EGR mass fraction of 30%, a fuel/compressor inlet flow ratio near 0.019 and a fuel composition of 97% methane (CH 4 ), 2% ethane (C2H6) and 1% propane (C3H8) which yields a target exhaust CO 2  mole fraction (dry) of 0.051. The method  200  may adjust the EGR flow rate to maintain the measured exhaust CO 2  mole fraction (dry) within +/−0.001 of the target, over a range of measured CO 2  mole fractions from 0.005 to 0.25. 
     If the level of at least one constituent is outside of the range then the method  200  may proceed to step  260 ; otherwise the method  200  may revert to step  210  where the steps  210 - 250  may repeat until the at least one constituent is outside of the range. 
     In step  260 , the method  200  may adjust an EGR rate. As discussed, the EGR rate may be considered the rate and quantity of exhaust stream  170  entering the mixing station  115  where the inlet fluid is created. 
     An embodiment of the present invention may utilize the components of the EGR system  107  to adjust the EGR rate. For example, but not limiting of, the method  200  may incorporate at least one of the following functions: adjusting a speed of an EGR flow conditioning device  135 , such as but not limiting of a source of air; wherein the source of air comprises a fan, a blower, or combinations thereof; adjusting a pitch of at least one EGR fan blade; modulating at least one flow control device. The flow control device may include at least one of: an inlet damper, a bypass damper, an exhaust damper, or combinations thereof. 
     In an embodiment of the present invention, the GUI may provide a notification to the user if the EGR rate should be adjusted. 
       FIG. 3  is a block diagram of an exemplary system  300  for adjusting an EGR rate in accordance with an embodiment of the present invention. The elements of the method  200  may be embodied in and performed by the system  300 . The system  300  may include one or more user or client communication devices  302  or similar systems or devices (two are illustrated in  FIG. 3 ). Each communication device  302  may be for example, but not limited to, a computer system, a personal digital assistant, a cellular phone, or similar device capable of sending and receiving an electronic message. 
     The communication device  302  may include a system memory  304  or local file system. The system memory  304  may include for example, but is not limited to, a read only memory (ROM) and a random access memory (RAM). The ROM may include a basic input/output system (BIOS). The BIOS may contain basic routines that help to transfer information between elements or components of the communication device  302 . The system memory  304  may contain an operating system  306  to control overall operation of the communication device  302 . The system memory  304  may also include a browser  308  or web browser. The system memory  304  may also include data structures  310  or computer-executable code for adjusting an EGR rate that may be similar or include elements of the method  200  in  FIG. 2 . 
     The system memory  304  may further include a template cache memory  312 , which may be used in conjunction with the method  200  in  FIG. 2  for adjusting an EGR rate. 
     The communication device  302  may also include a processor or processing unit  314  to control operations of the other components of the communication device  302 . The operating system  306 , browser  308 , and data structures  310  may be operable on the processing unit  314 . The processing unit  314  may be coupled to the memory system  304  and other components of the communication device  302  by a system bus  316 . 
     The communication device  302  may also include multiple input devices (I/O), output devices or combination input/output devices  318 . Each input/output device  318  may be coupled to the system bus  316  by an input/output interface (not shown in  FIG. 3 ). The input and output devices or combination I/O devices  318  permit a user to operate and interface with the communication device  302  and to control operation of the browser  308  and data structures  310  to access, operate and control the software to adjust an EGR rate. The I/O devices  318  may include a keyboard and computer pointing device or the like to perform the operations discussed herein. 
     The I/O devices  318  may also include for example, but are not limited to, disk drives, optical, mechanical, magnetic, or infrared input/output devices, modems or the like. The I/O devices  318  may be used to access a storage medium  320 . The medium  320  may contain, store, communicate, or transport computer-readable or computer-executable instructions or other information for use by or in connection with a system, such as the communication devices  302 . 
     The communication device  302  may also include or be connected to other devices, such as a display or monitor  322 . The monitor  322  may permit the user to interface with the communication device  302 . 
     The communication device  302  may also include a hard drive  324 . The hard drive  324  may be coupled to the system bus  316  by a hard drive interface (not shown in  FIG. 3 ). The hard drive  324  may also form part of the local file system or system memory  304 . Programs, software, and data may be transferred and exchanged between the system memory  304  and the hard drive  324  for operation of the communication device  302 . 
     The communication device  302  may communicate with a at least one unit controller  326  and may access other servers or other communication devices similar to communication device  302  via a network  328 . The system bus  316  may be coupled to the network  328  by a network interface  330 . The network interface  330  may be a modem, Ethernet card, router, gateway, or the like for coupling to the network  328 . The coupling may be a wired or wireless connection. The network  328  may be the Internet, private network, an intranet, or the like. 
     The at least one unit controller  326  may also include a system memory  332  that may include a file system, ROM, RAM, and the like. The system memory  332  may include an operating system  334  similar to operating system  306  in communication devices  302 . The system memory  332  may also include data structures  336  for adjusting an EGR rate. The data structures  336  may include operations similar to those described with respect to the method  200  for adjusting an EGR rate. The server system memory  332  may also include other files  338 , applications, modules, and the like. 
     The at least one unit controller  326  may also include a processor  342  or a processing unit to control operation of other devices in the at least one unit controller  326 . The at least one unit controller  326  may also include I/O device  344 . The I/O devices  344  may be similar to I/O devices  318  of communication devices  302 . The at least one unit controller  326  may further include other devices  346 , such as a monitor or the like to provide an interface along with the I/O devices  344  to the at least one unit controller  326 . The at least one unit controller  326  may also include a hard disk drive  348 . A system bus  350  may connect the different components of the at least one unit controller  326 . A network interface  352  may couple the at least one unit controller  326  to the network  328  via the system bus  350 . 
     The flowcharts and step diagrams in the figures illustrate the architecture, functionality, and operation of possible implementations of systems, methods, and computer program products according to various embodiments of the present invention. In this regard, each step in the flowchart or step diagrams may represent a module, segment, or portion of code, which comprises one or more executable instructions for implementing the specified logical functions. It should also be noted that, in some alternative implementations, the functions noted in the step may occur out of the order noted in the figures. For example, two steps shown in succession may, in fact, be executed substantially concurrently, or the steps may sometimes be executed in the reverse order, depending upon the functionality involved. It will also be noted that each step of the step diagrams and/or flowchart illustration, and combinations of steps in the step diagrams and/or flowchart illustration, can be implemented by special purpose hardware-based systems which perform the specified functions or acts, or combinations of special purpose hardware and computer instructions. 
     The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. As used herein, the singular forms “a”, “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises” and/or “comprising,” when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. 
     Although specific embodiments have been illustrated and described herein, it should be appreciated that any arrangement, which is calculated to achieve the same purpose, may be substituted for the specific embodiments shown and that the invention has other applications in other environments. This application is intended to cover any adaptations or variations of the present invention. The following claims are in no way intended to limit the scope of the invention to the specific embodiments described herein.