Abstract:
A computerized system for accurate, independent verification of natural gas fuel flow in order to control H 2 O injection flows. The H 2 O is injected into a combustion system to control emissions. The system comprises:  
     receiving gas turbine control parameters from a gas turbine control system;  
     receiving control parameters from a megawatt transducer;  
     calculating values based upon readings from said control system and said megawatt transducer;  
     comparing said values to a megawatt reference curve;  
     detecting an abnormal reading;  
     starting a timing sequence during which said reading is monitored;  
     transferring NO x  and H 2 O water injection control to a megawatt module at completion of said timing sequence;  
     alerting operator said transfer;  
     allowing for return of control to said gas turbine control system once said abnormal reading is corrected.

Description:
FIELD OF THE INVENTION  
         [0001]    The present invention relates to a method for providing an independent verification of gas fuel flow which may be used to control water injection flows, which are used to control emissions from a natural gas power plant.  
         BACKGROUND OF THE INVENTION  
         [0002]    As the demand for electricity skyrockets in the United States and the world, government and private industry must uncover and maximize power sources. One of these sources is natural gas.  
           [0003]    Origins of methane (CH 4 ) include conversion of organic material by microorganisms (biogenesis), thermal decomposition of buried organic matter (thermogenesis), and deep crustal processes (abiogenesis). Buoyant methane migrates upward through rock pores and fractures and either accumulates under impermeable layers or eventually reaches the surface and dissipates into the atmosphere. Biogenic methane results from the decomposition of organic matter by methanogens, which are methane-producing micro-organisms and which pervade the near surface of the Earth&#39;s crust in regions devoid of oxygen, where temperatures do not exceed 97 degrees Celsius (207 degrees Farenheit). Methanogens also live inside the intestines of most animals (people included) and in the cud of ruminants such as cows and sheep, where they aid in the digestion of vegetable matter.  
           [0004]    Because the methane generated in the subsurface is less dense than the rocks in which it is produced, it diffuses slowly upward through tiny, interconnected pore spaces and fractures, and it can eventually reach the Earth&#39;s surface and dissipate into the atmosphere. In places, however, the diffusion of methane is impeded by impermeable rock layers and gas can become trapped in structures. If enough gas accumulates under these impermeable layers, the structures can be drilled and gas can be extracted for use as an energy source.  
           [0005]    For natural gas, the cycle begins at gas wells, where gas is extracted from the ground. After processing, the gas is compressed and distributed through pipelines. To generate electricity, fuels such as oil, coal, natural gas, nuclear, hydroelectric and others must be extracted, processed, transported and converted.  
           [0006]    Natural gas can be used to generate electricity in many different ways. Natural gas power plants generating more than a couple of hundred megawatts (1 megawatt=1 MW=1 million watts) use the same technology as coal fired power plants. Natural gas is burned to produce heat, which boils water, creating steam which passes through a turbine to generate electricity. Slightly smaller natural gas power plants can use gas turbines to produce electricity. Gas turbines are similar to jet engines and can convert up to half the energy of the natural gas fuel into electricity.  
           [0007]    These power plants produce emissions that can be harmful to the environment, and are subject to regulatory control by local, state and national governments. In the case of natural gas fired electricity plants, these emission include Nitrous Oxides (NO x ) and Carbon Monoxide (CO).  
           [0008]    One current approach to controlling and monitoring these emissions utilizes a control algorithm and control system, which uses a signal generated from fuel flow transmitters associated with a metering tube orifice. These transmitters are set up in a split-range function; such that the first transmitter measures low gas flows and the second transmitter measures high gas flows, in order to provide accurate flow readings across the full range of gas flow. The transmitters are used to provide readings to a control system, which in turn controls the injection of steam or water into the combustors to meet emissions and operating requirements. The amount of water required is a function of the fuel flow, the fuel type, the ambient humidity and NO x  emissions levels required by the relevant regulations. Transmitters of this type tend to drift and require biannual calibration, at a minimum, to stay within acceptable tolerances.  
           [0009]    When the transmitters are miscalibrated, or gas condensate collects in a leg of the fuel flow transmitter, an out-of-compliance event can exist and yet not be detected by the current monitoring system, or a false alarm may be generated.  
           [0010]    The present invention is particularly suitable for use with the General Electric SPEEDTRONIC™ Mark IV, Mark V, and Mark VI Gas Turbine Control Systems. The SPEEDTRONIC™ Control Systems are computer systems that utilize microprocessors to execute programs to control the operation of the gas turbine using the transmitter data, sensor inputs and instructions from human operators.  
           [0011]    While the above device is a fair representation of the current prior art, there remains room for improvement as defined by the currently-claimed invention.  
         SUMMARY OF THE INVENTION  
         [0012]    It is an object of the present invention to provide a highly accurate system for measuring natural gas fuel flow.  
           [0013]    It is a further object of the present invention to generate an algorithm which can be used to detect and control out-of-compliance events.  
           [0014]    It is a further object of the present invention to monitor gas fuel flow transmitters and provide notification when gas fuel flow transmitters are out of calibration.  
           [0015]    It is a further object of the present invention to utilize an existing megawatt transducer signal to produce a conditioned signal, in the form of a curve, which is compatible with fuel flow scaling.  
           [0016]    It is a further object of the present invention to allow for H 2 O injection based on a megawatt reference curve for NO x  control when required.  
           [0017]    These as well as other objects are accomplished by a computerized system for accurate, independent verification of natural gas fuel flow in order to control H 2 O injection flows as said H 2 O is injected into a combustion system primarily to control NO x  and CO emissions. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0018]    [0018]FIG. 1 illustrates a gas turbine constructed in a well known manner and an associated control system in accordance with the invention.  
         [0019]    [0019]FIG. 2 illustrates part of the control algorithm of the invention.  
         [0020]    [0020]FIG. 3 illustrates part of the control algorithm of the invention.  
         [0021]    [0021]FIG. 4 illustrates part of the control algorithm of the invention.  
         [0022]    [0022]FIG. 5 illustrates part of the control algorithm of the invention. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0023]    In accordance with this invention it has been found that a reliable process source, particularly the megawatt transducer, can be utilized for detecting and controlling out-of-compliance events as they relate to gas flow when being used for control of NO x  and CO emissions through a water injection-based system. Various other advantages and features will become apparent from the following detailed description, together with reference to the figures.  
         [0024]    The description and figures will utilize a mnemonic nomenclature typical as set forth in Gas Turbine Standard TM-30 and reproduced for clarity in the following Table:  
                           TABLE                       Letter   Gas Turbine Origin   Physical Parameter   Type                   A   Air   Current, Amperes           B   Bearing   Vibration       C   Compressor   Clearance       D   Driven Load   Differential Pressure       E   Electrical       F   Fuel   Frequency       G   Governor   Stress       H       Hertz       I   Intercooler   Impact Press       J       K   Combustion       Constant       L   Lube   Force       M   Extractions   Miscellaneous       N   Inlet Air Nozzle   Speed       0       P   Start Turn Device   Static Pressure       Q   (Buffers)   Volume or weight               flow       R   Regenerator       Reference, Control       S   Station on Steam   Stroke/Position       T   Turbine   Temperature       U   Auxiliary   Utilization       V   Voltage       W   Water/Steam   Watts       X   Exhaust   Ratio       Y       Z   (Local Signals)                  
 
         [0025]    By way of illustration, signal “DW” would represent a driven load, in differential pressure, of water or steam, in watts. Similarly, signal “KDWC”, would represent a signal related to combustion, driven load differential pressure, water/steam watts and compressor clearance. Other control parameters referred to herein are defined accordingly.  
         [0026]    The present invention is specific to a MW reference curve which is based on a megawatt signal (DW) being multiplied by a gain (WQDWG) which is then representative of Total Fuel Flow (FQT). Currently, all water injection flows are derived from fuel flows. The ability to shape the megawatt signal to a fuel flow relationship is an important aspect of the present invention.  
         [0027]    The gains are derived by data gathering during the gas turbines&#39;s normal operating conditions and with the unit in NO x  compliance using the fuel flow (FQT) as the controlling signal for water injection control. The data is manipulated in accordance with the present invention and the result is a set of gain values that characterize the megawatt signal such that it can be used in place of the fuel flow signal.  
         [0028]    The megawatt signal is developed from electrical taps off of the generator output lines and feed back into a megawatt transducer, which converts this voltage into a control signal (DW) that is sent to the control system software.  
         [0029]    For the purposes of the present invention the General Electric SPEEDTRONIC™ Gas Turbine Control System is used for describing the invention. It would be apparent to one of ordinary skill in the art that the control parameters could be used from any gas turbine control system and that the present invention would be usable therewith.  
         [0030]    [0030]FIG. 1 illustrates a gas turbine constructed in a well known manner and an associated control system in accordance with the invention. A gas turbine  23  is drivingly connected to a compressor  21 . A fuel controller  17  introduces fuel into the combustor  19 , which is then introduced into the turbine  23  along with the products of the compressor  21 . The turbine  23  drives a generator  25  which produces electrical power.  
         [0031]    The control system  15  of the preferred embodiment is a General Electric SPEEDTRONIC™ Gas Turbine Control System. However, it should be appreciated by those skilled in the art that the present invention may be used with a variety of control systems as well as differing versions of any one manufacturer&#39;s control system. This system is designed to fulfill all requirements of operating a gas turbine electric power generating system. The control system performs many functions, such as: fuel, air and emissions control; sequencing of turbine fuel and auxiliary for start-up, cool down and shutdown; monitoring of all turbine, control and auxiliary functions; protection against unsafe and unlawful operating conditions; and providing feedback to human users.  
         [0032]    The General Electric SPEEDTRONIC™ system uses signals generated from sensors located in the combustor  19 , compressor  21  and turbine  23  as input variables for its algorithms. Specifically, for emissions control, the SPEEDTRONIC™ system uses a signal generated from only one source: fuel flow transmitters that are associated with a metering tube orifice. These transmitters are set up in a split-range function, such that the first transmitter measures low gas flows and the second transmitter measures high gas flows, in order to provide accurate flow readings across the full range of gas flow. This reliance on a single source can result in errors which can cause the control system  15  to indicate that it is in compliance with applicable government regulations, even though it is not.  
         [0033]    As there exists only one source of data which is sent to the control system  15  for fuel flow evaluation, an actual fuel flow error can possibly be created due to the single transmitter function and its effect directly relates to the NO x  Emissions Monitoring as reported to the state.  
         [0034]    Several problems can exist with the transmitter, independently, that will cause emissions to be incorrectly reported. An error in the calibration of the transmitter or an offset to a properly calibrated transmitter, such as gas fuel condensate in one leg of the transmitter, can report a lower fuel flow. This in turn, due to how the GE algorithm is designed, will not cause or show out of compliance alarms by the emissions monitoring system unless a continuous emissions monitoring system is in use.  
         [0035]    The megawatt module  13  is a modification to the SPEEDTRONIC™ system to allow for water injection based on a megawatt reference curve for NO x  control when required. The addition of a second and independent data source, other than the gas fuel flow transmitter function, can be used as a backup reference for mitigating any single source data problems. Since the megawatt transmitter is an extremely accurate data source, requiring in most cases no recalibration year after year of unit operation, it is an excellent comparison for the gas fuel flow transmitter.  
         [0036]    The megawatt module  13  is designed to allow the units to operate as in the past in compliance to NO x  emissions as permitted for each specific site and does not change or modify the existing GE algorithm. By now monitoring the variances, between the existing gas fuel flow and newly installed megawatt reference signal, the control system  15  is capable of detecting and transferring NO x  water injection control from the existing GE algorithm to the megawatt algorithm.  
         [0037]    This megawatt module  13  utilizes the existing megawatts transducer signal in the SPEEDTRONIC™ system to produce a conditioned signal that is compatible with fuel flow scaling, in pounds per second (#/sec). The megawatt module  13  also adds: two operator alarms and the ability of automatically switching between megawatt and fuel flow curves; the ability to start and stop the unit while functioning on the megawatt control curve; and the ability to perform maintenance on the NO x  fuel flow system while the unit is in-service with the megawatt function in control and manual curve compensation through the use of one control constant that affects both Fuel and megawatt curves.  
         [0038]    With reference now to FIG. 2, part of the control algorithm of the invention is illustrated wherein control constants are used at different times of the slope of the megawatt reference curve. The signal DW  101 ,  105 ,  109 ,  113  is compared to control constants KDWC1  103 , KDWC2  107 , KDWC3  111 , KDWC4  115 . The comparison code  117 ,  119 ,  121 ,  123  outputs Boolean values LDWC1  125 , LDWC2  127 , LDWC3  129 , LDWC4  131 . The value LDWC1  125  is then used to determine which of the two constants, WQDWG — 1  133  or WQDWG — 2  135  proceeds to the next comparison and is designated WQDWGA  143 . The value LDWC3  129  is then used to determine which of the two constants WQDQG — 3  137  or WQDQG — 4  139  proceeds to the next comparison and is designated WQDWGB  145 . The value LDWC2  127  is used to determine which of the resultant constants, WQDWGA  143  or WQDWGB  145  proceeds to the next comparison and is designated WQDWGC  147 . The value LDWC4  131  is used to determine whether WQDWGC  147  or control constant WQDWG — 5  141  proceeds from the control block and is designated WQDWG  151 . This is the gain to be used based on a range in a megawatt scale.  
         [0039]    With reference now to FIG. 3, another part of the control algorithm of the invention is illustrated. Constant controls WQKR1  201  and WQKR2  205  are fed into a median select operator  221  along with a compressor temperature inlet value  203 . The resultant median value is designated CTIM2  225  and is scaled  229  with a constant WQKR8  207  to result in the value CTIM0  230 . CTIM0  230  is then multiplied with a gain constant WQK1_T  209  to result in a positive value CTDW  237 .  
         [0040]    Additionally, constant controls WQKR5  211  and WQKR6  215  are fed into a median select operator  223  along with a relative humidity value  213 . The resultant median value is designated CTHUM2  227  and is scaled  231  with a constant WQKR7  217  to result in the value CMHUM0  230 . CTIM0  230  is then multiplied  235  with a gain constant WQK1_H  219  to result in a value CMHDW  239 . CMHDW  239  is then subtracted  241  from CTDW  237  to result in temperature reference CTH_REF  243 .  
         [0041]    With reference now to FIG. 4, another part of the control algorithm of the invention is illustrated whereby alarms may be activated. A measurement WQ_DW  301  based on water flow in megawatts is offset  317  with a value FQG  303  to result in a value WQ_DIF  319 . This value is compared  325  with constant value WQDW_DIF  311  if the enable value L84TG  321  is active high, which occurs when the system is operating on total gas as opposed to a mixture of gas and fuel such as diesel. The resulting Boolean value LWQD  327  is sent to an “AND” comparison with a value derived as follows. The value DW  305  comes in through a megawatt transducer and is compared to KDW_EN  307  if the enable value L84TG  309  is active high, which occurs when the system is operating on total gas as opposed to a mixture of gas and fuel such as diesel. The resulting Boolean value is compared in the “AND” comparison  329  and the resultant value is entered into a TMV  331  along with a duration constant K30A196  313 . If the signal  330  goes into the TMV  331  for longer than the duration constant  313 , then the alarm values L30A196 and L30A197  333  are sent on to further areas of the system.  
         [0042]    With reference now to FIG. 5, another part of the control algorithm of the invention is illustrated. The signal DW  401  is based on actual megawatts and is multiplied  431  with the gain to be used based on a range in the megawatt scale, WQDWG  403  and results in the water flow based on megawatts, WQ_DW  433 . WQ_DW  433  is multiplied  455  with CTH_REF  467  to result in CTHR  465 .  
         [0043]    WQ_DW  433  is further offset by the value WQKB  435 , which is either constant WQK0_B  413  or constant WQK1_B  415  depending on control value L83WK1  405  which comes from the original GE algorithm and is based on high flow versus low flow. The result of the offset is WQDWB  457  is then multiplied by the value WQKK  437  which is either constant WQK0_K  417  or constant WQK1_K  419  depending on control value L83WK1  407  which comes from the original GE algorithm and is based on high flow versus low flow. This result is WQDWK  459  which is then offset by value WQKN  439  which is either constant WQK0_N  421  or constant WQK1_N  423  depending on control value L83WK1  409  which comes from the original GE algorithm and is based on high flow versus low flow. The resultant offset WQDWN  461  is offset  463  with value CTHR  465  and fed into a median select operation  471 . Also fed into the median select operation  471  is value WQKN  439  and value WQKM  441 , which is either constant WQK0_M  425  or constant WQK1_M  427  depending on control value L83WK1  411  which comes from the original GE algorithm and is based on high flow versus low flow.  
         [0044]    The output from the median select  471  is WQDR1  473  is offset with constant value WQKPL3  429  and the result WQDPL  445  is a protective limit fed into a comparison  447  with WQJ  485 , which is the actual flow based on flow meters in the fuel injection line. This comparison is enabled  467  by the result of an “AND” comparison between GE controls L60WQPLE  477  and L84TG  479 . The result L60WQPL  475  may be used in the control algorithm at a further time.  
         [0045]    The control constant WQKR3  461  is offset with WQDR1  473  to result in a master value WQDR2  529 . This master value or a constant equaling zero WQDW_Z  527  is then output as the water ratio input WQRI  531  which defines how much H2O is injected into the system. The decision between WQDW_Z  527  and WQDR2  529  is made based upon the following derivation which results in control value L3DWQR  525  which is used to promote value WQDW_Z  527  or WQDR2  529 .  
         [0046]    Total fuel flow is represented as FQT  499  and the water flow equivalent in MW is WQ_DW  501 , and alarm condition L30A196  333  is used to promote either FQT  499  or WQ_DW  501  to value DWFQ  515 . DWFQ  515  is compared to the resultant of constants WQK0_E  506  or WQK1_E  507  based upon a value L83WK1  509  from the GE subsystem. The resulting value is offset  513  with constant WQKR4  511  and compared with DWFQ  515 , with the resultant  521  placed in an “AND” comparison with a master permissive from the GE algorithm L4WN  491 , a GE water protection value L83WQEN  493 , the alarm signal L30A196  333  and the total gas Boolean L84TG  497  to result in L3DWQR  525 , which is the control to determine the final output WQRI  531 .  
         [0047]    The use of GE variable WQRI  531  is crucial to the invention, as WQRI  531  is not used in the GE algorithm and is constant at zero. This enables the megawatt algorithm to match existing GE control constants, so that if the manufacturer changes the value of the GE constants, no recoding of the invention algorithm is necessary. Also, as many jurisdictions mandate the use of GE-compatible algorithms, this use of a previously unused GE variable (WQRI  531 ) allows the use of the invention without compromising GE compatibility.  
         [0048]    It would be apparent to one of ordinary skill in the art that any data transmission herein can be recorded by a digital storage medium as known in the art.  
         [0049]    It is thus seen that this invention provides a highly accurate means of detecting and controlling variations in the water injection process, traditionally based on process fuel flow, that is used in controlling the gas turbine&#39;s water injection for meeting Federal and State regulatory limits on NO x  and CO emissions per the issued site license in such a manner that out-of-compliance fines are highly unlikely to be incurred.  
         [0050]    As the above description is exemplary in nature many variations will become apparent to those with skill in the art. Such variations however may be embodied within the spirit and scope of this invention as defined by the following appended claims.