Abstract:
A burner arrangement for a combustion system for combusting liquid fuels including a burner hub, at least one air supply channel and at least one fuel supply channel for each fuel type is provided. The at least one fuel supply channel is embodied at least partially in the burner hub, with a flow divider arranged in at least one fuel supply channel, which is distanced from the wall of the fuel supply channel so that an interspace associated with the flow path of the fuel flowing through the fuel supply channel is formed between the wall of the fuel supply channel and the flow divider. A method for operating such a burner arrangement is also provided.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims priority of European Patent Office application No. 09162827.1 EP filed Jun. 16, 2009, which is incorporated by reference herein in its entirety. 
       FIELD OF INVENTION 
       [0002]    The invention relates to a burner arrangement for a combustion system for combusting liquid fuels and method for operating such a burner arrangement with the features cited in the preambles of the respective independent claims. 
       BACKGROUND OF INVENTION 
       [0003]    With respect to universal efforts to reduce the pollutant emissions of combustion systems, particularly in gas turbines, burners were developed over the last few years which have particularly minimal nitrogen oxide (NOx) emissions. Considerable importance is attached here to such burners not only being operable with one fuel, but instead as far as possible with various fuels, for instance oil, domestic gas and/or coal gas or in combination, in order to increase the supply reliability and flexibility of the operation. Such burners are described for instance in EP 0 276 696 B1. 
         [0004]    One problem with the design of burners for all possible different operating conditions and operating materials consists in the volume of the individual operating materials needed during operation being different in each instance so that it becomes difficult for all operating materials to use the same supply system and the same injection openings. It is therefore known in the prior art to use different supply systems for liquid and gaseous mediums. 
         [0005]    A further problem nevertheless also arises if gaseous fuels are then optionally also to be used with completely different specific fuel values, for instance natural gas and coal gas. The different relative volume ratios when using these two fuels and the different chemical processes during their combustion require a modification or extension of the known systems. 
         [0006]    It is known for inert substances, in particular water or water vapor, to be injected in order to reduce the pollutant emissions in certain operating states, as a result of which the combustion temperature is reduced and the Nox pollutant emissions are consequently lowered. WO 89/08803 A1 also discloses that with the use of heavy oils as fuel, for example, admixtures should also be mixed with the injected substances in order to prevent damage to components of a subsequent gas turbine. 
         [0007]    EP 0 276 696 B1 discloses a hybrid burner for premixing operation with gas and/or oil, like is used in particular for gas turbine systems. The burner consists of a central pilot burner system, which can be operated with gas and/or oil as a so-called diffusion burner or a separate premix burner. Provision is also made for the possibility of feeding inert substances. The pilot burner system is surrounded by a main burner system, which has an air supply annular channel system with a helical blading located therein having a plurality of blades for the premixing operation with gas. Inlet nozzles for oil are also present in the region of the helical blading in the main burner system, thereby enabling the main air flow to be premixed with oil. 
         [0008]    DE 42 12 810 B4 and EP 0 580 683 B1 emanating therefrom describe the prior art closest to the present invention. It is assumed here that when combusting combustion gas with a low fuel value, no special measures are needed to reduce the pollutant emission, since when combusting such gases, no excessively high flame temperatures occur and the formation of Nox therefore remains practically insignificant. It is therefore sufficient to create a further simple supply system, with attention having to be paid to ensuring that this system does not disadvantageously influence the other systems and does not reduce the operational reliability during operation of the other systems. It is therefore important for the further annular channel to open for the other fuels on the inflow side above the outlet nozzles. In this way, no ignitable mixture can reach the further annular channel if the burner is supplied with a different type of fuel through the outlet nozzles. 
         [0009]    One challenge with these burners emerges as a result of the mechanical stresses in the walls of the metallic housing, the so-called hub, which occur due to an uneven thermal distribution, in which hub the supply annular channels of the gas and oil energy carriers, are arranged relatively close to one another. An annular gas compartment supplies the main burner in respect of the flow direction of the inflowing air on the input side upstream of the so-called helical blades, which convey a mixed helix to the air flow with the combustion gas or through the helical blades. An oil supply is also available as the gas supply, which is generally arranged in the vicinity of the burner outlet. It includes an annular oil compartment, and an oil supply channel leading to the annular compartment, which is arranged in the hub wall located between the annular gas compartment and the pilot burner. 
         [0010]    As gas has a lower density than oil, it requires a larger cross-section, as a result of which the dimensioning of the gas supply is considerably larger than the oil supply. The part of the burner hub with the gas supply therefore has a larger external surface facing the air channel than the oil supply. The air supply takes place with precompressed air, which has passed through a compressor, as a result of which this supplied air has a temperature, as a result of the compression, which already reaches above 400° C. The region of the burner hub with the gas supply is consequently rapidly heated to a temperature in the region of above 400° C. and remains at this operating temperature. The oil supply channel leading to the annular oil compartment is by contrast distanced far from the hot air supply channel so that the oil in the oil supply channel barely experiences any heating and thus only has a temperature of approximately 50° C. 
         [0011]    As, on the one hand, the burner hub experiences a strong heating in the region of the annular gas compartment and, on the other hand, the adjacent oil supply channel is considerably cooler, the wall between the annular gas compartment and the oil supply channel is subjected to a large temperature gradient both during continual operation and also when flushing out the burner hub. If the hub, i.e. the oil channel, is flushed with water, the gas channels remain hot and the oil channel cools down significantly. The channels are very close to one another as a result of the limited space in the hub and high temperature/thermal gradients result. As a result of the temperature gradient, thermal stresses result, which significantly shorten the service life of such burner hubs. 
       SUMMARY OF INVENTION 
       [0012]    The object of the present invention is thus to reduce the described thermally specific stresses in the burner hub during operation and when flushing the hub of the burner arrangement. 
         [0013]    This object is achieved by a burner arrangement as claimed in the claims and/or a method for operating such a burner arrangement as claimed in the claims. The dependent claims contain advantageous embodiments of the invention. 
         [0014]    An inventive burner arrangement for a combustion system for combusting liquid fuels includes a burner hub, at least one air supply channel and at least one fuel supply channel for each type of fuel. The at least one fuel supply channel is embodied at least partially in the burner hub, so that the material of the burner hub forms a wall of the fuel supply channel. In accordance with the invention, a flow divider is provided in at least one fuel supply channel, said flow divider being distanced from the wall of the fuel supply channel so that an interspace associated with the flow path of the fuel flowing through the fuel supply channel is formed between the wall of the fuel supply channel and the flow divider. 
         [0015]    In the inventive burner arrangement, the interspace forms a region associated with the flow path, in which an adjustable continual fuel flow flows. This fuel flow prevents deposits from forming in the interspace and thus prevents a blockage of the nozzles through which the fuel escapes. Furthermore, the flow in this region decouples the hot structure from the cold structure and thus represents a heat shield. As a result of the reduced thermal transfer, the thermally specific stresses reduce compared with the burner arrangements without a flow divider. 
         [0016]    In the inventive burner arrangement, the flow divider consists of a flow-through means, in particular a pipe with a flow-through opening, and a disk with a corresponding flow-through opening. A central bore in the center of the flow divider is preferably provided as a flow-through opening. The majority of the fuel flows through this central bore. 
         [0017]    When viewed in the flow direction, the disk is also provided at the first end on the flow-through means. 
         [0018]    In a preferred embodiment, the disk has a larger diameter than the diameter of the flow-through means. The disk can be clamped here in the wall of the fuel supply channel. Positioning means, e.g. a positioning projection, can however also be provided on the wall of the fuel supply channel. 
         [0019]    The flow divider in the disk preferably has at least one bore. The disk also has several bores, which are essentially distributed equally over the periphery. These bores route a small part of the preferably cold fuel flow into the interspace, with the hot carrier structure thus being thermally decoupled from the inflowing cold fuel. The heat transfer in this region is thus reduced. 
         [0020]    According to a further aspect of the present invention, said object is achieved by a method for operating such a burner arrangement, with, during operation, fuel being routed through the fuel supply channel, with the majority of the fuel flowing through the flow-through opening of the flow divider and a small part of the fuel flowing through the interspace of the flow divider, thereby largely preventing deposits in the interspace. 
         [0021]    A small part of the flow is thus routed through the interspace and thus prevents the formation of deposits in the interspace, in other words, above all on the wall of the carrier structure of the combustion chamber hub. A blockage of the nozzles is thus prevented. 
         [0022]    Through the minimal flow, a function as a heat protection shield is provided, since the hot carrier structure is thermally decoupled from the inflowing cold fuel, in particular from cold oil. The main flow for supplying the nozzles flows through the flow-through opening of the flow divider, with this flow-through opening preferably being provided as a large, central bore in the center of the flow divider. High temperatures and stress gradients therefore no longer form. A significant increase in the service life is the desired result. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0023]    Further features, properties and advantages of the invention result from the following description of an exemplary embodiment with reference to the appending figures, in which; 
           [0024]      FIG. 1  shows a burner arrangement known from EP 0 580 683 B1, 
           [0025]      FIG. 2  shows a partial cross-sectional view through a known burner arrangement, 
           [0026]      FIG. 3  shows a basic diagram of an inventive helical blade with two integrated gas stages which can be controlled independently of one another, 
           [0027]      FIG. 4  shows a basic diagram of a burner chamber hub with two integrated gas stages, which can be controlled independently of one another and an oil channel, 
           [0028]      FIG. 5  shows a burner chamber hub  18  with an inventive flow divider  40 , 
           [0029]      FIG. 6  shows an inventive flow divider  40 . 
       
    
    
     DETAILED DESCRIPTION OF INVENTION 
       [0030]      FIG. 1  shows a burner arrangement  20  as claimed in the prior art, which, if necessary in conjunction with several similar arrangements, can be used in the combustion chamber of a gas turbine system for instance. 
         [0031]    It consists of an inner part, the pilot burner system and an outer part, the main burner system, which is disposed concentrically thereto. Both systems are suited to operation with gaseous and/or liquid fuels in any combination. The pilot burner system consists of a central oil supply  1  (medium G) and an inner gas supply channel  2  (medium F) arranged concentrically around the latter. This is in turn surrounded by an inner air supply channel  3  (medium E) which is arranged concentrically around the axis of the burner. 
         [0032]    A suitable ignition system can be arranged in or on this channel, for which many embodiment possibilities are known and the representation thereof was therefore omitted here. The central oil supply  1  has an oil nozzle  5  at its end and the inner air supply channel  3  has a helical blading  6  in its end region. A pilot burner system  1 ,  2 ,  3 ,  5 ,  6  can be operated in a manner known per se, i.e. predominantly as a diffusion burner. Its task is to keep the main burner stable during combustion, since this is mostly operated with a lean mixture which tends towards instabilities. 
         [0033]    The main burner system has an outer air supply annular channel system  4  which is arranged concentrically with respect to the pilot burner system and runs obliquely thereto. This air supply annular channel system  4  is also provided with a helical blading  7 . The helical blading  7  consists of hollow blades with outlet nozzles  11  in the flow cross-section of the air supply annular channel system  4  (medium A). These are fed from a supply line  8  and an annular channel  9  through openings  10  for the medium B. The burner also has a supply line  12  for a medium C, preferably oil, which opens into an annular channel  13 , which has outlet nozzles  14  for the medium C in the region or below the helical blading  7 . 
         [0034]    A spray jet  15  of the medium C is also shown. In accordance with the invention, the burner also has a further coal gas supply channel  16  for medium D. This opens into the outer air supply annular channel system  4 , just above the helical blading  7  with the outlet nozzles  11 , and on its internal side, so that in principle both together form a diffusion burner. 
         [0035]      FIG. 2  shows an enlarged partial cross-sectional view through a known burner hub  18  as claimed in the prior art. The burner arrangement is circular, so that the annular channel  9  and  13  can also be represented as circular. 
         [0036]    The region of the main burner in  FIG. 1  can also be realized similarly. The helical blades  9  only have a supply channel with the outlet nozzles  11 , which are preferably provided to inject a gaseous medium B. An outlet nozzle  14  for injecting preferably liquid medium V is provided therebelow in the flow direction. A plurality of outlet nozzles  14  is arranged along the circular annular channel  13 , so that the injection of the medium C can take place equally in the similarly circular combustion chamber. 
         [0037]    Contrary to  FIG. 1 , this representation nevertheless only has one gas supply line and one oil supply line. 
         [0038]      FIG. 3  shows a basic diagram of a helical blade  7  with two integrated gas stages B and D which can be controlled independently of one another. 
         [0039]    The helical blade  7  has two supply channels  11  and  21  which are independent of one another. The one supply channel with the outlet nozzles  11  can be used to inject the medium D for instance and the second supply channel  21  can be used to inject the medium B by way of the outlet nozzles  24 . Both mediums to be injected through the supply channels of the helical blade  7  are preferably gaseous, e.g. the one natural gas and the other coal gas. An inert substance such as water vapor for instance can similarly be injected by way of these outlet nozzles  11  and/or  21  as required. 
         [0040]      FIG. 4  shows a fuel hub  18  with the supply channel  16 , the annular channels  9  and  13  and openings  10 , which lead the fuel into the blade  7 . 
         [0041]    If the supply channel  12 , subsequently referred to as oil channel  12 , is flushed with water, different temperature distributions result. The two gas supplies remain hot and the oil channel  12  cools down significantly. The adjusting high thermal gradients between the flushed oil channel and the heated gas passages reduce the service life of the fuel hub  18 . 
         [0042]      FIG. 5  shows an inventive fuel hub  18  with a flow divider  40 . The flow divider  40  ( FIG. 6 ) consists of a pipe  45  with a flow-through opening  55  (subsequently referred to as pipe opening  55 ). A disk  42  is attached to the first end of the pipe  45  when viewed in the flow direction. The disk  42  likewise has a pipe opening  55 , which corresponds to the pipe opening  55 . The diameter of the disk  42  is larger than the diameter of the pipe  45 . As a result, an interspace  38  font&#39;s in the flow direction between the wall  21  and the pipe  45 , so that the flow divider almost adopts the form of a double pipe, namely the pipe  45  and the wall  21 , which is likewise embodied here in the manner of a pipe. The disk  42  can essentially be attached e.g. clamped to the wall  21  in a faun-fit manner. The embodiment of a positioning projection  35  is also possible, on which the disk  42  rests. Bores  50  are attached in the disk  42 . These bores  50  are preferably evenly distributed over the periphery. As a result of the bores in the flow divider  40  attached above the disk  42 , a fluid flow is divided. An adjustable small part of the flow is routed through these smaller bores  50  into the interspace  38 . This fluid flow thus prevents the formation of deposits in the interspace  38  and a blockage of the nozzles  14 . The minimal flow also functions as a heat protection pipe. In addition, the reduced flow in this region decouples the hot structure from the code and thus represents a heat shield. The hot carrier structure is thus thermally decoupled from the inflowing fuel, preferably cold oil. The main flow for supplying the nozzles  14  also flows through the pipe opening  55 . This is preferably realized as a central bore in the center of the flow divider  40 . As a result of the flow divider  42  and a minimal flow of the fuel in the interspace  38 , the thermal transfer a in the interspace is essentially less than the thermal transfer α previous  without the flow divider at the same point; therefore α&lt;&lt;α previous . The main flow for supplying the nozzle  14  nevertheless also flows through the central bore, in other words through the pipe opening  55 . The thermal transfer α essentially remains unchanged here, i.e. α≈α previous . 
         [0043]    As result of the minimal flow in the interspace  38 , the flow divider  40  therefore functions as a heat protection shield and the hot carrier structure is thus decoupled from the inflowing cold oil. High temperature and tensile gradients therefore no longer form. The service life of the combustion chamber hub  19  is thus significantly increased. 
         [0044]    The inventive flow divider  40  thus divides the fluid flow namely into a minimal flow, which flows through the interspace  38  and a quantitative main flow, which flows through the pipe opening  55 . The flow divider  40  thus prevents deposits and a blockage of nozzles when using liquid fuels. The reduced flow also decouples the hot structure from the cold and thus represents a heat shield. Furthermore, high thermal gradients and thermal stresses resulting therefrom are prevented by way of a minimal cross-section. With the use of the flow divider  40 , the component  18  can thus fulfill the high demands in terms of service life. The flow divider  40  is simple to manufacture and easy to adapt in existing fuel chamber hubs  18 .