Abstract:
In a method for monitoring the supply system ( 10 ) of a gas turbine having a multiburner system, said supply system ( 10 ) comprising at least one distribution system ( 15, 24 ), via which a pressurized medium required for operating the multiburner system is distributed to a plurality of individual burners ( 12, . . . , 14 ) opening into a combustion chamber, reliable detection and analysis of faults is achieved in that, while the gas turbine is operating, the pressure loss in the at least one distribution system ( 15, 24 ) is measured continuously, in that the measured pressure loss is compared with a desired value characteristic of the respective operating state of the gas turbine, and in that a communication is issued when the measured pressure loss deviates from the associated desired value by a predetermined value.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to the field of gas turbines. It refers to a method for monitoring the supply system of a gas turbine having a multiburner system, said supply system comprising at least one distribution system, via which a pressurized medium required for operating the multiburner system is distributed to a plurality of individual burners opening into a combustion chamber. 
     The invention refers, furthermore, to an apparatus for carrying out the method, comprising a plurality of burners which open into a combustion chamber and which are supplied via a fuel distribution system with a pressurized liquid fuel. 
     2. Discussion of Background 
     In modern gas turbines which are equipped with low-emission multiburner systems, the fuel is conveyed to the burners or fuel lances via a complex fuel distribution system. The same applies to water which is distributed to the burners via a corresponding water distribution system for the purpose of reducing the NOx emission. A series of switching valves, nonreturn valves and filters, which allow the fuel (water) to be distributed properly to the burners, is installed in the fuel and water lines. 
     While the plant is being assembled or operated, malfunctions of the fuel or water system may occur. For example, individual nonreturn valves may fail or switching valves may be wrongly activated. Moreover, in many cases, it has been shown, in practice, that impurities in the fuel system lead to the clogging of individual filters or fuel nozzles. In other cases, the regulating valves and fuel nozzles are subject to erosion phenomena due to small solid particles entrained in the fuel. 
     All the abovementioned irregularities in fuel distribution (or water distribution) lead to an uneven load on the burners and, consequently, to increased thermal load on individual hot gas parts. They thus shorten the lifetime of the gas turbine. It is therefore desirable to have the possibility of detecting malfunctions in the supply systems, in particular in fuel or water distribution, reliably at an early stage and thereby enable the operator of the gas turbine to conduct a clear analysis of the state of his plant. 
     SUMMARY OF THE INVENTION 
     Accordingly, one object of the invention is to provide a novel method, by means of which the supply system of a gas turbine can be monitored in a simple and reliable way and, if deviations occur, relevant countermeasures can be taken early, and to specify an apparatus for carrying out the method. 
     In a method of the type mentioned initially, the object is achieved in that, while the gas turbine is operating, the pressure loss in the at least one distribution system is measured continuously, in that the measured pressure loss is compared with a desired value characteristic of the respective operating state of the gas turbine, and in that a communication is issued when the measured pressure loss deviates from the associated desired value by a predetermined value. The supply systems of the gas turbine, in particular the fuel systems and fuel nozzles, may be operated in the form of a line-up of appliances having a fixed throughflow. The result of this is that, for any desired load state, there is, for example, a clearly defined fuel pressure loss or necessary fuel pressure. If, then, irregularities occur in the fuel distribution system, the fuel pressures actually measured deviate from the theoretic curve. The method according to the invention makes use of this fact. 
     A first preferred embodiment of the method according to the invention is distinguished in that, in order to measure the pressure loss in the at least one distribution system, the pressure at the inlet of the distribution system and in the combustion chamber is measured and the pressure difference is formed from the two pressure values, in that the medium to be distributed is fed to the at least one distribution system via a pump and a regulating valve located downstream of the pump, and in that, in order to determine the pressure in the distribution system, the pressure at the outlet of the regulating valve is measured. By selecting the measurement locations, the pressure drop (pressure loss) over the entire distribution system is measured in a simple way, without the constantly changing position of the regulating valve being able to have a noticeable falsifying effect. 
     In order to obtain in a simple manner a reference curve of desired values which has evidential force, said reference curve making it possible to detect all the changes in the plant during subsequent operation, is desirable if, according to a second preferred embodiment of the method according to the invention, in order to provide the desired values of the pressure loss of the at least one distribution system, the pressure loss in this distribution system is measured and stored for various possible operating states when the gas turbine is first commissioned. 
     The apparatus according to the invention for carrying out the method comprises a plurality of burners which open into a combustion chamber and which are supplied via a fuel distribution system with a pressurized liquid fuel. Said apparatus is defined in that a pressure transducer is arranged in each case both on the fuel distribution system and on the combustion chamber, and in that the pressure transducers are connected to a common monitoring unit. 
     A preferred embodiment of the apparatus according to the invention is defined in that the burners are combined in burner groups, in that each burner group is assigned its own fuel distribution system or water distribution system, and in that a pressure transducer is arranged for monitoring in each fuel distribution system or water distribution system and is connected to the monitoring unit. 
     Further embodiments emerge from the dependent claims. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     A more complete appreciation of the invention and many of the attendant advantages thereof will be readily obtained as the same becomes better understood by reference to the following detailed description, when considered in connection with the accompanying drawings, wherein: 
     FIG. 1 shows a simplified plant diagram of a preferred exemplary embodiment of a gas turbine supply system with monitoring according to the invention; and 
     FIG. 2 shows a graph, as an example of the method according to the invention, of a desired value curve (A) and a limit value curve (B) for the pressure loss (P) in the fuel distribution system of a gas turbine as a function of the gas turbine output (GTL) 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring now to the drawings, wherein like reference numerals designate identical or corresponding parts throughout the several views, in FIG. 1 a preferred exemplary embodiment of a gas turbine supply system with monitoring according to the invention is reproduced in a simplified plant diagram. The supply system  10  supplies a plurality of burners or fuel lances  12 ,  13  and  14  which are combined to form a burner group  11 . Further burners or burner groups are normally present, but are omitted in FIG. 1 for the sake of clarity. The supply system  10  comprises a fuel distribution system  15  and a water distribution system  24 . The two distribution systems  15  and  24  are provided for the burner group  11 . The other burner groups (not shown) are supplied by identical distribution systems (not shown). 
     Fuel (conventionally oil) is fed under pressure to the fuel distribution system  15  via a fuel pump  16 , a downstream quick-acting stop valve  17  and a regulating valve  18 . The fuel is distributed to the individual burners  12 , . . . ,  14  by the fuel distribution system  15 , a first section valve  123 ,  133 ,  143  being arranged on each burner  12 , . . . ,  14 , said section valve making it possible to control the fuel feed for each burner individually. In addition, a ventilating valve  21  and a bleed valve  22  are provided on the fuel distribution system  15  for maintenance purposes. Between the quick-acting stop valve  17  and the regulating valve  18  competent for the fuel distribution system  15 , further lines  23  lead off to parallel fuel distribution systems and burner groups. All the fuel distribution systems are connected to a relief valve  19 . In addition, the burners  12 , . . . ,  14  may be supplied with fuel gas via a fuel gas feedline  40 . 
     Water (or steam) is fed under pressure to the water distribution system  24  in a similar way to the fuel distribution system  15  via a water pump  25 , a downstream quick-acting stop valve  26  and a regulating valve  27 . The water is distributed to the individual burners  12 , . . . ,  14  by the water distribution system  24 , a second section valve  121 ,  131 ,  141  being arranged on each burner  12 , . . . ,  14 , said section valve making it possible to control the feed of water to each burner individually. A nonreturn valve  122 ,  132 ,  142  is provided transversely in each case between the pairs of section valves  121 ,  123  and  131 ,  133  and  141 ,  143 . Between the quick-acting stop valve  26  and the regulating valve  27  competent for the water distribution system  24 , further lines  30  lead off to parallel water distribution systems and burner groups. All the water distribution systems together are likewise protected by means of a common relief valve  28 . 
     Both the fuel in the fuel distribution system  15  and the water in the water distribution system  24  experience a pressure loss due to the flow resistance in the system, said pressure loss being characteristic of the respective state of the system. In this case, the pressure loss is the pressure difference between the pressure at the inlet of the respective distribution system and at the outlet of the burners  12 , . . . ,  14  or in the combustion chamber (not shown), into which the burners open and which receives compressed combustion air from the compressor part of the gas turbine. According to the invention, then, the pressure loss is measured and monitored. In this case, deviations from a reference value (desired value) or a reference value curve (desired value curve A or desired value Al in FIG. 2) are detected and are utilized for the early analysis of faults in the supply system or for the early preparation of inspection and servicing work. 
     In order to measure the pressure loss, a pressure transducer  20  and  29  is arranged in each case at the inlet of each distribution system  15  and  24 , behind the respective regulating valve  18  and  27 , respectively, said pressure transducer measuring the inlet pressure in the distribution system continuously (for example, periodically) and transmitting the measured values (via the lines represented by broken lines) to a central monitoring unit ( 32 ). A further pressure transducer  31 , which is arranged on the combustion chamber, at the same time measures the pressure in the combustion chamber and likewise transmits the measured values to the monitoring unit  32 . In the monitoring unit  32 , then, the differences from the pressure values measured by the pressure transducers  20  and  31  or  29  and  31  are formed in each case in differentiators  33  and  34  and are in each case transmitted to following comparators  35  and  36 . There, the pressure differences, which correspond to the pressure losses in the distribution systems  15  and  24 , are compared with desired values which are filed in a memory (not shown) and which are retrieved from there. The results of the comparison are transmitted to an evaluation unit  37 . If a deviation of the measured pressure differences from the corresponding desired values which is greater than the predetermined limit value (limit value curve B or limit value B 1  in FIG. 2) is detected in the comparators  35 ,  36 , this is indicated by the evaluation unit  37  on an indicator  38 . At the same time, the evaluation unit  37  transmits a corresponding control signal (warning or alarm signal) via a signal line  39  to a central control (not illustrated) of the gas turbine plant. Differentiation and result comparison may, of course, also be carried out in an appropriately programmed microcomputer. The pressure transducers  20 ,  29  and  31 , in addition to performing the monitoring function, are also, of course, available for normal regulating tasks. For this purpose, their measured values are transmitted directly to the central control, although this is not dealt with in any more detail. 
     In order to provide the desired values or desired value curve, the following procedure is adopted: during commissioning, the combustion chamber operation concept is installed in such a way that the plant guarantees are met. In this case, the actual pressure drops or pressure losses in the fuel distribution systems or water distribution systems are measured and documented as a function of the output of the gas turbine and of the operating concept. This results, for the fuel pressure loss P (in bar), in, for example, the desired value curve A, shown in FIG. 2, as a function of the gas turbine output GTL (in MW). The desired value curve A shows, in the initial region (below 50 MW), discontinuities which are caused by changeovers and which are identified by blocked areas C, D. The monitoring method according to the application is interrupted in the blocked areas. In the other areas, the desired value curve A, which defines the desired state of fuel distribution, serves as a reference curve for the subsequent permanent measurements. Comparable desired value curves may also be derived and used in a similar way for the water distribution systems. 
     During commercial operation, the fuel pressure drops are measured via the selected system and are compared with the values expected in the relevant output range. If the gas turbine works, for example, just in the output range around 130 MW (broken line in FIG.  2 ), the measured value for the pressure drop is compared with the desired value A 1  there on the desired value curve A. The desired value curve A, then, has an associated limit value curve B (FIG. 2) fixed for it, said limit value curve indicating how great the deviation of the actual value from the desired value may be, without an alarm being triggered or a corresponding communication being issued. For the output range around 130 MW, the associated limit value is designated, in FIG. 2, by B 1 . If, then, the pressure loss measured in the fuel distribution system exceeds the limit value B 1  in the direction of the arrow, the presence of a fault is inferred from this in the monitoring unit  32 . The way in which the deviation has come about, in particular the time profile of the deviation, allows a detailed analysis of the causes. If, for example, an abrupt change in the throughflow characteristic occurs, a malfunction of one of the valves of the group affected is probable. By contrast, if the characteristics vary continuously, this suggests a drifting of the valve drives or a clogging of filters and nozzles or the erosion of these as explanation of the cause. 
     The state of the fuel system of the gas turbine or of the supply system as a whole can thus be monitored permanently by using, according to the invention, the protective concept based on the monitoring of the throughflow characteristics of the distribution systems. Inspection and servicing work can be planned early and total failures of individual burner systems are reliably avoided. 
     The following particular advantages of the invention may be mentioned: 
     reduction in the load on hot gas parts 
     increase in the lifetime of the components 
     increase in plant availability 
     optimization of inspection and servicing intervals. 
     Obviously, numerous modifications and variations of the present invention are possible in the light of the above teachings. It is therefore to be understood that, within the scope of the appended claims, the invention may be practiced otherwise than is specifically described herein.