Abstract:
A method for producing hot gas for operating a turbomachine fired with at least one combustion chamber includes premixing a fuel with a plurality of operating gases by introducing fuel into the plurality of operating gases in a mixing chamber disposed upstream of the combustion chamber using a burner arrangement, wherein the fuel includes at least one of a combustible gas and a H 2 -rich fuel; and introducing the premixed fuel into the combustion chamber.

Description:
CROSS REFERENCE TO PRIOR APPLICATIONS 
       [0001]    This application is a divisional of U.S. patent application Ser. No. 12/876,508, filed Sep. 7, 2010, which is a continuation of International Patent Application No. PCT/EP2009/051764, filed Feb. 16, 2009, which claims priority to Swiss Patent Application No. CH 00350/08, filed Mar. 7, 2008. The entire disclosure of both applications is incorporated by reference herein. 
     
    
     FIELD 
       [0002]    The present invention relates to the field of combustion technology. It refers to a method for combusting H 2 -rich fuels. It also refers to a burner arrangement for implementing the method and for its use. 
       BACKGROUND 
       [0003]    From WO-A1-2006/069861, a premix burner with subsequent mixing section or mixer tube (a so-called AEV burner) has been known, in which in the premix burner, which is formed according to EP-A1-704 657, a first fuel can be centrally injected and between the air inlet slots or passages which are formed by the shells in the swirler (shown clearly especially in EP-A1 321 809) at least one second fuel can be introduced into the air which flows into the inner space there. In the subsequent mixer tube, provision is made for a further device for injecting a third fuel. All printed publications which are referred to here or later, and their further developments, form an integrating element of this application. 
         [0004]    For combusting H 2 -rich fuels, as created for example in the form of syngas during coal gasification, it has already been proposed to inject at least some of the H 2 -rich fuel via the mixer tube of such a premix burner. Also, such a premix burner has already been tested with natural gas in lean premix operation, during which under high pressure H 2 -rich fuels with H 2 -to-N 2  ratios of 70/30 and 60/40 have been injected in an axially staged manner in the premix burner and in the mixer tube. 
         [0005]    During these tests, it has been shown that if a changeover is made from natural gas entirely to the H 2 -rich fuel, the flame migrates upstream into the mixer tube. Although the burner was able to be operated in this way without damage and with sufficiently low NOx emission, numerous disadvantages arose, however, specifically:
       The pressure losses in the premix burner are increased by the factor of 3. This is undesirable in the case of gas turbines with regard to an associated gas turbine cycle.   The available mixing length, i.e. the distance between the location of the injection of the fuel and the flame front, is reduced, which leads to increased NOx-emission.   High-frequency pulsations gain in importance. In this context, it may be mentioned that the thermoacoustic vibrations represent a hazard for each type of combustion application. They lead to high-amplitude pressure vibrations, to limitation of the operating range, and they can increase pollutant emissions. This applies especially to combustion systems with low acoustic damping, as is the case for example in annular combustion chambers with reverberant walls. In order to ensure a high performance conversion over a wide operating range with regard to pulsations and pollutant emissions, provisions against these pulsations must be made.       
 
       SUMMARY OF THE INVENTION 
       [0009]    In an aspect of the invention, a method for combusting H 2 -rich fuels is provided which reliably prevents migrating of the flame back into the burner and also pulsations, even during a changeover from natural gas to H 2 -rich fuels. 
         [0010]    In an embodiment of the invention, in addition to the H 2 -rich fuel, a small amount of natural gas is introduced into the burner arrangement during premix operation and combusted together with the H 2 -rich fuel. 
         [0011]    One development of the method according to the invention is characterized in that first of all an air/fuel mixture is created from the air and the natural gas, and in that the H 2 -rich fuel is then injected into the air/fuel mixture. In particular, a burner arrangement, which comprises a premix burner and a mixer tube which is connected to it, is used for this purpose, wherein the fuel/air mixture is created in the premix burner. The H 2 -rich fuel can be injected into the mixer tube and/or into the swirler. A swirler can be advantageously used as the head stage of the premix burner, as is described for example in EP-A1-321 809. 
         [0012]    Another development of the method according to the invention is characterized in that first of all the natural gas and the H 2 -rich fuel are intermixed, and in that the resulting fuel mixture is mixed and combusted with air in the burner arrangement. As a result of this, the system of fuel feed and fuel distribution can especially be simplified. Also in this case, a burner arrangement can preferably be used which comprises a premix burner and a mixer tube which is connected to it, wherein in the premix burner the air/fuel mixture is created from the air and the fuel mixture. 
         [0013]    A burner arrangement can also be used, however, as is disclosed for example in WO-A1-2007/113074, in which within the scope of a sequential combustion a fuel lance projects into a hot gas flow, and wherein the fuel mixture is injected via the fuel lance, if necessary with additional air, into the hot gas flow. The fuel lances which are shown in this printed publication (FIGS. 2-6) are designed for use in the low-pressure combustion chamber (Pos. 14). Also, this last-named printed publication forms an integrating element of this application. The operation of such a low-pressure combustion chamber with the use of a fuel lance which is described above in a sequentially fired gas turbine, results for example from EP 620 362 A1, which printed publication also represents an integrating element of this description. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0014]    The invention shall subsequently be explained in more detail based on exemplary embodiments in conjunction with the drawing. All elements which are not necessary for the direct understanding of the invention have been omitted. Like elements are provided with the same designations in the various figures. The flow direction of the media is indicated by arrows. 
           [0015]    In the drawings: 
           [0016]      FIG. 1  shows a simplified schematized view of a burner arrangement of the AEV type, in which according to one exemplary embodiment of the method according to the invention the additional natural gas and the H 2 -rich fuel are injected one after the other in the flow direction, wherein the H 2 -rich fuel can also be selectively injected into the swirler; 
           [0017]      FIG. 2  shows a view which is comparable to  FIG. 1  of a burner arrangement of the AEV type, in which according to another exemplary embodiment of the method according to the invention the additional natural gas and the H 2 -rich fuel are first of all mixed and the resulting mixture is then injected; 
           [0018]      FIG. 3  shows a simplified schematized view of a burner arrangement with a fuel lance, which is provided for sequential combustion, in which according to another exemplary embodiment of the method according to the invention the additional natural gas and the H 2 -rich fuel are first of all mixed and the resulting mixture is then injected into a hot gas flow; and 
           [0019]      FIG. 4  shows use of the fuel lance according to  FIG. 3  in a combustion chamber of a gas turbine with sequential combustion. 
       
    
    
     DETAILED DESCRIPTION 
       [0020]    Reproduced in  FIG. 1 , in a simplified schematized view, is a burner arrangement with a head stage, which is formed as a swirler, and an adjoining mixer tube, in which according to one exemplary embodiment of the method according to the invention the additional natural gas and the H 2 -rich fuel are injected one after the other in the flow direction. The burner arrangement  10  comprises a swirler  11 , which at times can also be used as a stand-alone premix burner, wherein this is formed in a known manner per se in the shape of a cone, as is described for example in EP-A1-321 809. In this case, it is important that the swirl intensity in the swirler is selected via its geometry so that the bursting of the vortex, or vortices, does not take place in the mixer tube but further downstream at the combustion chamber inlet, wherein the length of the mixer tube  13  is to be dimensioned so that a satisfactory mixture quality is established for all fuels which are in use. If such a swirler is taken as a basis, then the swirl intensity results from the design of the corresponding cone angle, of the air inlet slots or passages, and their number. Combustion air flows into the interior of the premix burner  11  through said air inlet slots or passages, wherein in the region of these air inlet slots or passages provision is made for means for injecting a fuel in such a way that an air/fuel mixture  12  is formed in the inner space which is formed by the partial cone shells. The air/fuel mixture  12  is given a swirl around the axis  15  of the burner arrangement  10  and enters a mixer tube  13  downstream, where the complete mixing-through of air and fuel takes place. The mixer tube  13  opens into a combustion chamber  14  in which a flame front is formed, with which the air/fuel mixture is combusted. On the mixer tube  13 , provision is made for an injection device  16  of preferably annular design, through which fuel can be additionally injected into the mixer tube  13  and incorporated into the combustion. When required, transfer passages, which are not shown in more detail in this figure, are provided in a transition region between swirler  11  and mixer tube  13  and undertake the transfer of air or air/fuel flow, which is formed in the swirler  11 , into the mixer tube  13 . Such a configuration results from EP-A1-704 657, wherein its disclosure content forms an integrating element of this application. Furthermore, the swirler can be designed so that this comprises at least two hollow partial shells which are nested one inside the other in the flow direction, making up a body, the cross section of which in the flow direction, in contrast to the swirler  11  above, does not extend conically but cylindrically or virtually cylindrically, wherein in the inner space, preferably on the symmetry axis of the body, an inner body is provided, the cross section of which in the flow direction reduces conically or virtually conically. Such a configuration has been known for example from EP-A1-777 081, wherein this printed publication also forms an integrating element of this application. 
         [0021]    According to the exemplary embodiment which is shown in  FIG. 1 , a small quantity of natural gas F 1  is injected into the premix burner  11  during premix operation and mixed with air. The natural gas F 1  is fed via a first fuel feed line  17  and can be adjusted to the required mass flow for example by means of a valve  19 . The main part of the output of the burner arrangement  10  is contested, however, by an H 2 -rich fuel F 2  which is directed to the injection device  16  via a second fuel feed line  18  and injected there into the air/fuel mixture  12  from the swirler  11  acting upstream. A portion of this H 2 -rich fuel  18 ′ can also be selectively injected into the swirler  11 , as results from  FIG. 1 , wherein its portion typically constitutes up to 30%. This type of burner operation has the following advantages:
       The pressure loss coefficient Zeta is reduced from 2.8 to 1.5, which corresponds to a sharp reduction of the pressure loss in the burner.   The high-frequency pulsations (of 2 to 4 kHz) are practically eliminated.   NOx-emissions are minimized, this based on the fact that the flame is maintained by a maximized premixed air/fuel mixture.   The fuel feed lines  17  in the region of the swirler  11  are constantly purged for the natural gas so that changing over to natural gas operation is possible within an extremely short time.   If the flame front actually migrates upstream into the burner, it is anchored relatively far downstream in the mixer tube and burns in a stable and reliable manner. If in a multi-burner arrangement, as is customary in gas turbines, a flashback occurs in a burner, this leads more easily to a stable state in the burner and not to an operation-relevant negative development in which the flame front migrates still further upstream until destruction of the burner commences, as is immanently the case in normal burners. If this state occurs, then the reason to be looked for is that the burner in question is blocked and the throughflow of air is reduced. This then also means that an individual burner can be temporarily shut down and reignited. The operation of the other burners in the gas turbine is consequently not affected.   The reason that the flame front in this case cannot flash back to the premixed burner  11  which is used according to the invention, and destruction cannot correspondingly occur, is to be seen as that of the very same flame front assuming a fixed local anchoring inside the mixer tube  13  in such a way that it also cannot creep upstream either, the air flow hardly being impaired in the process.       
 
         [0028]    Whereas in the exemplary embodiment of  FIG. 1  the natural gas F 1  and the H 2 -rich fuel F 2  are injected separately and in axial staging in the burner arrangement  10 , it is also conceivable to premix the two fuels before injection according to  FIG. 2 . For this purpose, the two fuel feed lines  17  and  18  for the fuels F 1  and F 2  are brought together and the resulting fuel mixture is then injected on the one hand into the swirler  11  and on the other hand into the injection device  16  on the mixer tube  13 . 
         [0029]    Stabilizing the flame position and limiting NOx-emissions which is associated therewith, and avoiding pulsations by means of a small addition of natural gas, can also be applied in a gas turbine with sequential combustion, specifically in the second or subsequent combustion stage. In  FIG. 3 , a fuel lance  20  is reproduced, as is disclosed in WO-A1-2007/113074 which is referred to in the introduction, wherein this printed publication also forms an integrating element of this application. The fuel lance  20  projects into the hot gas flow  26  from a previous combustion stage which can comprise for example the burner arrangement which is shown in  FIG. 1 . In the fuel lance  20 , an outer tube  21  and an inner tube  22  are arranged one inside the other. The outer tube has injection orifices  23 . Air  25  is fed into the gap between inner tube  22  and outer tube  21 , while through the inner tube  22  a mixture consisting of the H 2 -rich fuel F 2  and the small portion of natural gas F 1  is introduced. The air/fuel mixture which is formed discharges into the hot gas flow  26  and ignites there, forming a flame. 
         [0030]      FIG. 4  shows in schematic view a low-pressure combustion chamber  27  in a gas turbine which is operated by means of sequential combustion. Such a gas turbine results for example from an article by Joos, F. et al., “Field Experience of the Sequential Combustion System for the ABB GT24/GT26 Gas Turbine Family”, IGTI/ASME 98-GT-220, 1998 Stockholm, wherein  FIG. 1  shows the construction of such a gas turbine. Furthermore, reference is made to a publication in ABB Review February 1997 (pages 4-14), especially to FIG. 15 (page 13), in which the main components of such a gas turbine are also shown. The low-pressure combustion chamber is referred to here as a “SEV combustor”. The operation of this low-pressure combustion chamber  27  is designed for self-ignition, i.e. the hot gas flow  26  which flows into the combustion chamber  27  has a very high operating temperature in such a way that combustion of the fuels F 1  or F 1 +F 2  or F 2 , which are injected via at least one fuel lance  20 , is carried out by means of self-ignition. With this type of combustion, it is important that the flame front in the combustion chamber  14  which is arranged downstream remains stable as regards location. Also, for achieving this aim, provision is made in this self-ignition combustion chamber  27 , preferably arranged on the inner or outer wall in the circumferential direction, for a row of elements  28 , so-called vortex generators, which are positioned in the axial direction preferably upstream of the fuel lance  20  which basically comprises a vertical outer tube  21  and a horizontal outer tube  21 ′. The purpose of these elements  28  is to generate vortices which induce a backflow zone. The design of these vortex generators  28  and also the arrangement in the combustion chamber  27  results from DE-44 46 611 A1, wherein this printed publication also forms an integrating element of this description. With regard to the different injection possibilities  29  of the fuels F 1  or F 1 +F 2  of F 2  into the combustion chamber  27 , reference is made essentially to WO 2007/113074 A1. A further possibility is apparent in  FIG. 4  itself, in which the symbolized fuel jets  29  flow from one or more injection orifices which are arranged on the circumference of the axial outer tube  21 ′ of the fuel lance  20  and inject the fuel, or fuels, into the flowing  26  of the combustion chamber  27  at a specific injection angle α. This injection angle a preferably varies between 20° and 120° in relation to the surface of the horizontal outer tube section  21 ′ of the fuel lance  20 , wherein injection angles of less than 20° and more than 120° are also possible, however. A further injection of the fuels F 1  or F 1 +F 2  or F 2  is provided downstream of the fuel lance  20  via the injection device  16  which also has one or more injection orifices, wherein the direction of the fuel jets  30  can assume a broad spectrum, as results from  FIG. 4 , the injection preferably having an angle α′ of between 20° and 120° in relation to the surface of the inner wall of the combustion chamber  27 , wherein injection angles of less than 20° and more than 120° are also possible. The type of operation of this combustion chamber  27  concerning the fuels which are introduced there and with regard to the injection angle of the fuel jets or of the fuel orifices  29 ,  30 , depends upon factors which are related to the sequential combustion. Naturally, the introduction of the fuels according to  FIG. 4  can also be provided in the same or similar manner in the case of the previously described combustion chambers according to  FIGS. 1 and 2 . An additional introduction of a quantity of air, as results from  FIG. 3 , is likewise possible and also provided, when required, also during operation of the combustion chamber  27  from  FIG. 4 . 
         [0031]    The subject according to the invention can be used with particular advantage in a gas turbine with at least one combustion chamber stage, wherein the hot gas which is produced is expanded in the gas turbine, performing work. 
       LIST OF DESIGNATIONS 
       [0000]    
       
           10  Burner arrangement 
           11  Swirler 
           12  Air/fuel mixture 
           13  Mixer tube 
           14  Combustion chamber 
           15  Axis 
           16  Injection device 
           17 ,  18  Fuel feed line 
           19  Valve 
           20  Fuel lance 
           21  Vertical outer tube of the fuel lance 
           21 ′ Horizontal outer tube of the fuel lance 
           22  Inner tube 
           23  Injection orifice 
           24  Fuel 
           25  Air 
           26  Hot gas flow 
           27  Low-pressure combustion chamber operated by means of self-ignition 
           28  Vortex generators 
           29  Fuel injection 
           30  Fuel injection 
         F 1  Fuel (natural gas) 
         F 2  Fuel (H 2 -rich, for example syngas) 
         α Injection angle 
         α′ Injection angle