Abstract:
A gas turbine engine including a compressor section, a combustor section including a combustor, a turbine section, a gaseous fuel supply conduit with an upstream section and a downstream section, a fuel booster, and a heat exchanger is provided. The fuel booster is located in the gaseous fuel supply conduit. The fuel booster has a driving expander with a driving fluid inlet and a driving fluid outlet for discharging expanded air and a fuel compressor with a low pressure fuel inlet connected to the upstream section of the gaseous fuel supply conduit and a high pressure fuel outlet connected to the downstream section of the gaseous fuel supply conduit. The heat exchanger is located between the driving fluid on the one side and the gaseous fuel on the other side so that a heat transfer between the air and the gaseous fuel is possible.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is the US National Stage of International Application No. PCT/EP2008/053586, filed Mar. 27, 2008 and claims the benefit thereof. The International Application claims the benefits of European Patent Office application No. 07006445.6 EP filed Mar. 28, 2007, both of the applications are incorporated by reference herein in their entirety. 
     
    
     FIELD OF INVENTION 
       [0002]    The present invention relates to a gas turbine engine with a compressor section, a combustor section comprising at least one combustor and a turbine section. 
       BACKGROUND OF INVENTION 
       [0003]    The strive for higher simple cycle efficiency among gas turbine manufacturers has led to higher pressure ratios exceeding the supply pressures of gaseous fuels, e.g. natural gas. To overcome this insufficiency booster compressors for the gaseous fuel are used. Such separate compressors are driven by an electrical motor or by a high pressure fluid bled from the compressor or the turbine stage, as disclosed, e.g., in US 2004/0088987 A1 or U.S. Pat. No. 5,329,757. Similar systems are also known from gaseous fuel engines, as disclosed, e.g. in U.S. Pat. No. 5,899,070. If the compressor is used which is driven by air bled from the compressor or combustion gas bled from the turbine section, the air or gas, respectively, is expanded through a turbine connected to the fuel compressor. 
         [0004]    U.S. Pat. No. 5,329,757 further discloses a heat exchanger which is used to cool the compressed gaseous fuel after compression. Furthermore, a second heat exchanger may be present in the duct ducting pressurised gas for driving the turbine connected to the fuel compressor. This heat exchanger is used for heating pressurised driving gas if this is relatively cool, e.g. gas from the compressor section, in order to increase its energy per unit mass. The heat is taken from the exhaust gas of the gas turbine engine. 
         [0005]    A heat exchanger for heating fuel before injection into a combustor is disclosed in U.S. Pat. No. 6,817,187 B2. 
       SUMMARY OF INVENTION 
       [0006]    According to this state of the art it is an objective of the present invention to provide an improved gas turbine engine with a fuel booster located in a gaseous fuel supply conduit. 
         [0007]    This objective is solved by a gas turbine engine as claimed in the claims. The depending claims define further developments of the invention. 
         [0008]    An inventive gas turbine engine comprises a compressor section, a combustor section comprising at least one combustor, a turbine section and at least one gaseous fuel supply conduit with an upstream section and a downstream section, the downstream section being connected to the combustor for delivering gaseous fuel. A fuel booster is located in the gaseous fuel supply conduit which has a driving expander and a fuel compressor. The driving expander comprises a driving fluid inlet for receiving an unexpanded driving fluid and a driving fluid outlet for discharging expanded driving fluid. The fuel compressor comprises a low pressure fuel inlet connected to the upstream section of the gaseous fuel supply conduit and a high pressure fuel outlet connected to the downstream section of the gaseous fuel supply conduit. In the present invention a heat exchanger is present which is located between the unexpanded driving fluid or the expanded driving fluid on the one side and the low pressure gaseous fuel or the high pressure gaseous fuel on the other side in such a way that heat transfer between the driving fluid and the gaseous fuel is possible. 
         [0009]    While in the state of the art as described in U.S. Pat. No. 5,329,757, heat is taken away from the gaseous fuel after compression, heat can be transferred between the gaseous fuel and the driving fluid in the present invention. In particular, heat can be transferred from the driving fluid to the gaseous fuel. This offers the possibility to preheat the gaseous fuel and thus to increase the pressure of the gaseous fuel further as compared to a compression only by the fuel compressor. 
         [0010]    Transferring surplus heat from the driving fluid to the gaseous fuel also improves the relative efficiency of the gas turbine engine as the heat is brought back into the cycle and can produce work. 
         [0011]    There are four basic configurations how the heat exchanger may be located between the driving fluid and the gaseous fuel. 
         [0012]    In a first configuration, the heat exchanger is located between the unexpanded driving fluid, on the one hand, and the high pressure gaseous fuel, on the other hand. 
         [0013]    In a second configuration, the heat exchanger is located between the unexpanded driving fluid, on the one hand, and the low pressure gaseous fuel, on the other hand. 
         [0014]    In a third configuration, the heat exchanger is located between the expanded driving fluid, on the one hand, and the low pressure gaseous fuel, on the other hand. 
         [0015]    In a fourth configuration, the heat exchanger is located between the expanded driving fluid, on the one hand, and the high pressure gaseous fuel, on the other hand. 
         [0016]    Depending on the scheme which is used for heat transfer, it becomes possible to further raise the pressure in the fuel gas, to choose different sources of driving fluid, to adjust the mechanical loading on the fuel booster by the gaseous fuel (heating before compression decreases density) or optimising between compression work and efficiency (heating before compression increase the volume flow and hence the size of the components used). However, the auto ignition point for the compressed gaseous fuel should be also taken into consideration. 
         [0017]    The driving fluid inlet may, in the inventive gas turbine engine in particular be in flow connection with a compressed air outlet of the gas turbine engine&#39;s compressor so that compressed air can be used as unexpanded driving fluid. The expanded driving fluid would then be expanded air. In this case, the fuel booster could, e.g. be situated on a bleed chamber which is in flow connection with the compressor flow between the compressor inlet and the compressor outlet. In that case, the driving fluid inlet of the turbocharger would be open towards the interior of the bleed chamber. Alternatively, the bleed chamber could, e.g., be located on and be open to a burner plenum of the gas turbine engine. 
         [0018]    Driving the expander with compressed air taken from the compressor offers the possibility for the driving fluid outlet of the expander to be in flow connection with at least one cooling channel which is present in a combustor section and/or in a turbine section. The expanded air could then be used as a cooling fluid for cooling the combustor section and/or the turbine section. In addition, if at least one opening is present connecting the at least one cooling channel to a flow path for hot combustion gas in a combustor or in the turbine section, the expanded air may also be used as sealing air. Connecting the driving fluid outlet with at least one cooling channel which is present in a combustor section is, in particular, suitable for gas turbine engines with a high pressure turbine, a low pressure turbine, a primary combustor and a secondary combustor (or re-heat combustor) which is present between the high pressure turbine and the low pressure turbine and which comprises at least one cooling channel. An according gas turbine engine is, e.g., disclosed in U.S. Pat. No. 6,817,187 B2, to which it is referred to with respect to the configuration of such an engine. The driving fluid outlet can then be connected to the at least one cooling channel in the secondary combustor. 
         [0019]    The expanded air may also be used in an active clearance control system in which air is used for determining the diameter of the turbine casing outside the turbine rotor blades. The driving fluid outlet of the expander is then in flow connection with the active clearance control system. After active clearance control the air may be used further or released to the outside of the gas turbine engine. The active clearance control system may comprise an active clearance control configuration, whereby air is directed to at least one stator part of the turbine stator determining the diameter of the turbine casing outside the turbine rotor blades. The system could be thermal, i.e. the diameter of the turbine casing is varied by heating or cooling the at least one stator part by use of the expanded air, or mechanical, i.e. the diameter of the turbine casing is varied by mechanically acting on the at least one stator part, e.g. by a mechanical device operated or activated by the pressure of the expanded air or the air pressure of the expanded air itself if the pressure is high enough for mechanically acting on the stator part. 
         [0020]    Additionally, or alternatively, the expanded air outlet may be in flow connection with the compressor inlet which would, e.g. offer the possibility of using the expanded air as an anti-icing flow in the compressor intake. 
         [0021]    A further alternative would be that the driving fluid outlet is in flow connection with components of the gas turbine engine which can be controlled by the use of pressurised air. In this context it should be noted that although expanded, the driving fluid may still have a raised pressure compared to ambient pressure, in particular if compressor air bled from one of the last compressor stages or combustion gas bled from the turbine section is used as a driving medium. 
         [0022]    An alternative to using pressurised air or combustion gas as a driving medium is to use steam if a heat recovery steam generator is present with which the driving medium inlet would then be in flow connection. This embodiment can, in particular, advantageously be used in combined cycle engines which combine steam and gas turbine engines. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0023]    Further features, properties and advantages of the present invention will become clear from the following description of embodiments in conjunction with the accompanying drawings. 
           [0024]      FIG. 1  shows a gas turbine engine in a sectional view. 
           [0025]      FIG. 2  shows an example as to how to locate a fuel booster and a heat exchanger in the gas turbine engine shown in  FIG. 1 . 
           [0026]      FIG. 3  shows, in a highly schematic view, a first configuration of a fuel booster and a heat exchanger used for compressing gaseous fuel delivered to the burner of the gas turbine shown in  FIG. 1 . 
           [0027]      FIG. 4  shows a second configuration of the fuel booster and the heat exchanger. 
           [0028]      FIG. 5  shows a third configuration of the fuel booster and the heat exchanger. 
           [0029]      FIG. 6  shows a fourth configuration of the fuel booster and the heat exchanger. 
           [0030]      FIG. 7  shows a special design of the heat exchanger. 
       
    
    
     DETAILED DESCRIPTION OF INVENTION 
       [0031]      FIG. 1  shows an example of a gas turbine engine  100  in a sectional view. The gas turbine engine  100  comprises a compressor section  105 , a combustor section  106  and a turbine section  112  which are arranged adjacent to each other in the direction of a longitudinal axis  102 . It further comprises a rotor  103  which is rotatable about the rotational axis  102  and which extends longitudinally through the gas turbine engine  100 . 
         [0032]    In operation of the gas turbine engine  100  air  135 , which is taken in through an air inlet  104  of the compressor section  105 , is compressed by the compressor section and output to the burner section  106 . The burner section  106  comprises a burner plenum  101 , one or more combustion chambers  110  and at least one burner  107  fixed to each combustion chamber  110 . The combustion chambers  110  and sections of the burners  107  are located inside the burner plenum  101 . The compressed air from the compressor exit  108  is discharged into the burner plenum  101  from where it enters the burner  107  where it is mixed with a gaseous or liquid fuel. In the present embodiment a gaseous fuel and a liquid fuel, e.g. oil, can be used alternatively. The air/fuel mixture is then burned and the combustion gas  113  from the combustion is led through the combustion chamber  110  to the turbine section  112 . 
         [0033]    A number of blade carrying discs  120  are fixed to the rotor  103  in the turbine section  112  of the engine. In the present example, two discs  120  carrying turbine blades  121  are present. However, the number of blade carrying discs could be different, i.e. only one disc or more than two discs. In addition, guiding vanes  130 , which are fixed to a stator  143  of the gas turbine engine  100 , are disposed between the turbine blades  121 . Between the exit of the combustion chamber  110  and the leading turbine blades  121  inlet guiding vanes  140  are present. 
         [0034]    The combustion gas from the combustion chamber  110  enters the turbine section  112  and, while expanding and cooling when flowing through the turbine section  112 , transfers momentum to the turbine blades  121  which results in a rotation of the rotor  103 . The guiding vanes  130 ,  140  serve to optimise the impact of the combustion gas on the turbine blades  121 . 
         [0035]      FIG. 2  shows, in a highly schematic view, the location of a fuel booster  1  and a heat exchanger  3  in the gas turbine engine  100  shown in  FIG. 1 . The gas turbine engine  100  depicted in  FIG. 1  comprises a bleed chamber which is located in the compressor section  105 . Also visible in  FIG. 1  are a number of compressor guide vanes  114  and compressor blades  115  of the compressor. In the more detailed representation of  FIG. 2  an opening  116  is present in the wall  118  of the compressor casing so as to establish a flow connection from inside the compressor to the inside of the bleed chamber  5 . A bleed duct  7  emanates from the bleed chamber  5  for leading bleed air to the turbine section where it is used as cooling air. 
         [0036]    The fuel booster  1  shown in  FIG. 2  comprises an expander  9  with an air inlet  11  and an air outlet  13 . The air inlet  11  is open towards the bleed chamber so that bleed air can enter the expander  9 . The expander is implemented as a turbine which is driven by the bleed air thereby expanding and cooling the bleed air. The expanded and cooled bleed air is discharged through the air outlet  13  into an air duct  15 . The air duct  15  may be in flow connection with the turbine section or the combustor so that the cooled and expanded air can be used as cooling air or, depending on its remaining pressure, sealing air, e.g. for vanes in the turbine section or heat shield elements in the combustor, or in a clearance control configuration. 
         [0037]    The fuel booster further comprises a fuel compressor  17  with a gaseous fuel inlet  19  that is connected to an upstream section  23  of a gaseous fuel supply line and with a gaseous fuel outlet  21  which is connected to a downstream section  25  of the gaseous fuel supply line. A coiled fuel line section  27  is present between the gaseous fuel outlet  21  and the downstream section  25  of the gaseous fuel supply line such that it is completely located in the air duct  15  into which the expanded and cooled air is discharged by the air outlet  13 . Hence, the coiled fuel line section  27  acts as a heat exchanger  3  which allows heat to be exchanged between the expanded air and the gaseous fuel flowing through the coiled fuel line section  27 . 
         [0038]    Gaseous fuel which enters the fuel compressor  17  through the gaseous fuel inlet  19  is compressed by the fuel compressor  17  which is driven by the expander  9 . The compressed gaseous fuel, which is also heated due to the compression, then flows through the gaseous fuel outlet and the coiled fuel line section  27  into the downstream section  25  of the fuel supply line. From there it is delivered to the burner  107 . 
         [0039]    The expanded air which is discharged from the expander  9  through the air outlet  13  is, although cooled with respect to the compressed air in the bleed chamber, in many cases still warmer than the gaseous fuel after compression so that it can be used to preheat the gaseous fuel flowing through the coiled fuel line section  27 . By this measure, the pressure within the gaseous fuel and the cycle efficiency of the gas turbine can be further increased. However, one should take care that the temperature of the gaseous fuel after preheating is sufficiently below the auto ignition temperature of the compressed gaseous fuel in order to prevent ignition of the gaseous fuel within the fuel supply line or in the fuel nozzle of the burner. 
         [0040]    The temperature of the expanded air depends on the pressure ratio of the air before expanding to the air after expanding and the air temperature before expanding. Thus, the temperature of the expanded air can be adjusted by locating the opening  116  in a certain compressor stage, which determines the pressure and the temperature of the bleed air in the bleed chamber. The pressure ratio by which the gaseous fuel is compressed depends on the pressure ratio by which the air is expanded and by the gear ratio of a gear which may be present between the expander  9  and the fuel compressor  17 . 
         [0041]    Although a special configuration of the heat exchanger  3  with respect to the fuel booster  1  is shown in  FIG. 2 , there are other configuration possibilities. These possibilities are schematically shown in  FIGS. 3 to 6 . 
         [0042]      FIG. 3  shows a first configuration of the fuel booster  1  and the heat exchanger  3  in which the heat exchanger  3  is located between the air flowing into the expander  9  and the compressed gaseous fuel coming out of the fuel compressor  17 . As in  FIG. 2 , the heat exchanger  3  can be realised as a coiled fuel line  27  which is passed by the compressor air before it is taken in into the expander  9 . In the embodiment shown in  FIG. 2 , this configuration could be realised by providing a coiled fuel supply line  27  in the bleed chamber  5  which is connected to the compressed gaseous fuel outlet  21  and the downstream section  25  of the gaseous fuel line. 
         [0043]    Also shown in  FIGS. 3 to 6  are filters  29 ,  31  which are located upstream from the air inlet  11  of the expander  9  and the gaseous fuel inlet  19  of the fuel compressor  17  for protecting these components. 
         [0044]    A second configuration of the fuel booster  1  and the heat exchanger  3  is shown in  FIG. 4 . In this configuration, the heat exchanger  3  is located between the air taken into the expander  9  and the gaseous fuel taken into the fuel compressor  17 . Hence, in this configuration, the gaseous fuel is preheated before entering the fuel compressor  17  rather than after leaving the compressor. Preheating before entering the fuel compressor  17  would decrease the density of the gaseous fuel and thus increase the volume flow through the fuel compressor  17 . However, if the same mass flow, which is reciprocal to the volume flow, shall be achieved as with preheating after compression, the size of the fuel compressor  17  needs to be larger that in the case of preheating after compression. Therefore, if space for installing the fuel booster is limited, preheating after compression would be more desirable. If, on the other hand, the mass flow through the fuel compressor  17  shall be kept low, e.g. to reduce the loads acting on the components, a preheating before compression would be more desirable. 
         [0045]    The configuration shown in  FIG. 4  could be implemented in the embodiment shown in  FIG. 2  by locating the coiled fuel line section  27  in the bleed chamber  5  and connecting the coiled fuel line section  27  to the upstream section  23  of the fuel supply line, on the one hand, and the gaseous fuel inlet  19  of the compressor  17 , on the other hand. 
         [0046]    A third configuration of the fuel booster  1  and the heat exchanger  3  is shown in  FIG. 5 . In this configuration, the heat exchanger  3  is placed between the expanded air and the gaseous fuel before it enters the fuel compressor  17 . As in the configuration shown in  FIG. 4 , the gaseous fuel is preheated before compression. However, compared to the configuration in  FIG. 4 , the heat transfer through the gaseous fuel is reduced as the expanded air leaving the expander  9  is of lower temperature then the bleed air that enters the expander  9 . 
         [0047]    The configuration schematically shown in  FIG. 5  can be implemented in the embodiment shown in  FIG. 2  by locating the coiled gaseous fuel line section  27  within the air duct  15 , as it is shown in  FIG. 2 , but connecting the coiled fuel line section  27  to the upstream section  23  of the gaseous fuel line, on the one hand, and the gaseous fuel inlet  19 , on the other hand, rather than between the gaseous fuel outlet  21  and the downstream section  25  of the gaseous fuel line. 
         [0048]    A fourth configuration for the fuel booster  1  and the heat exchanger  27  is shown in  FIG. 6 . The configuration in this figure is implemented in the embodiment shown in  FIG. 2 , i.e. the heat exchanger  3  is located between the expanded air and the gaseous fuel before it is taken into the compressor. Hence, the gaseous fuel is preheated after compression, as in the configuration shown in  FIG. 3 . 
         [0049]    By suitably choosing the configuration of the fuel booster  1  and the heat exchanger  3  one can achieve an optimisation between compression work, which is done in the fuel compressor  17 , the efficiency of the compression and the load acting on the fuel compressor  17 . 
         [0050]    In all configurations the air may be used after passing through the expander  9  depending on the remaining pressure and temperature as seal air in bearings, e.g. in the turbine section, or for active clearance control (cooling) of turbine stators. It may also be used to cool certain components in the turbine or it may also simply be released in the exhaust channel downstream of the turbine. A further alternative is to lead the expanded air to the compressor intake where it can be used as an anti-icing flow. 
         [0051]    A configuration of the heat exchanger  3 , which is particularly advantageous if there is only limited space available for locating the heat exchanger  3 , is shown in  FIG. 7 . In this configuration, the fuel intake  33  into the fuel compressor  17  and the air intake  35  into the expander  9  are implemented as coils the windings of which are attached to each other for transferring heat. The coils may either be spirally wound or, as shown in  FIG. 7 , helically. The fuel compressor  17  and the expander  9  are located in the centre of the coils. While the spirally wound coils are desirable if the whole arrangement shall be rather flat, the helically wound coils are desirable if the radial extension of the arrangement shall be small. In both cases linear ducts  37 ,  39  are employed as the gaseous fuel outlet  21  of the fuel compressor  17  and air outlet  13  of the expander  9 .