Abstract:
A power plant including a turbine unit having a turbine, a generator connected to the turbine for power transmission, and a cooling device for cooling the generator is provided. The cooling device is provided to release waste heat from the generator to a device of the power plant. Waste heat may be used in the power plant process, thus attaining increased efficiency.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is the US National Stage of International Application No. PCT/EP2009/065374, filed Nov. 18, 2009 and claims the benefit thereof. The International Application claims the benefits of European Patent Office application No. 08021764.9 EP filed Dec. 15, 2008. All of the applications are incorporated by reference herein in their entirety. 
     
    
     FIELD OF INVENTION 
       [0002]    The invention relates to a power plant comprising a turbine unit having a turbine, a generator connected to the turbine for power transmission and a cooling device for cooling the generator. 
       BACKGROUND OF INVENTION 
       [0003]    Various power plant systems are known in which primary energy is converted by means of a generator into electrical energy. In these power plants the heat of a heat generator is generally used to drive a thermal power machine which is connected mechanically to the generator. Both in the conversion of thermal energy into mechanical energy in the primary energy generator, for example a turbine, and also of the mechanical energy into electrical energy in the generator the respective available energy is not completely utilized. Residual energy—usually in the form of heat—is released into the environment. 
         [0004]    In a generator this heat is usually taken away by a cooling medium, e.g. in a closed circuit, in order to prevent overheating of the generator. Since this heat is present at a low temperature level, usually below 100° C., this heat is released unused into the environment and is thus lost to the power plant process. 
       SUMMARY OF INVENTION 
       [0005]    An object of the invention is to specify a power plant with a higher level of efficiency. 
         [0006]    This object is achieved by a power plant of the type stated above, in which the cooling device is provided in accordance with the invention to release waste heat from the generator to a device of the power plant. The feeding back of waste heat into the power plant process means that it is not removed from the power plant process and is thus not a loss. The efficiency of the power plant can be increased in this way by the proportion of heat fed back into the working process. The turbine can be a gas turbine or a steam turbine. 
         [0007]    Through the use of the generator waste heat in a power plant with a steam turbine for example either the maximum temperature of the steam of the turbine unit embodied as a steam turbine can be increased or the mass flow through the steam turbine can be increased. For a gas and steam turbine block with a total power of 400 to 500 MW the following picture typically emerges: the heat losses created by the generator range between 3 and 5 MW, of which around 2 to 4 MW can be fed back as a power increase into the gas and steam process or into a steam process. With a feed water mass flow of around 80 kg per second and 3 MW fed back generator power loss a temperature increase of around 10° C. is produced in the feed water. With an overall output of 400 to 500 MW this corresponds to a power increase of around 0.5%. With pure steam power processes this allows the quantity of steam which is used for preheating the feed water and which is thus no longer available for generating energy to be reduced. 
         [0008]    In an advantageous form of embodiment of the invention the turbine unit includes a fuel preheater which is thermally connected to the cooling device. The output of waste heat from the generator to the fuel preheater enables the quantity of primary energy which would otherwise have to be supplied to the fuel preheater to be reduced accordingly. The driving force for the feedback is the temperature difference, since the heat can only be transferred to a medium that has a lower temperature than the waste heat of the generator. This usually applies to the fuel of a fossil-fuel power plant, which is at about ambient temperature. Gaseous or fluid fuels in particular can be preheated in a technically simple manner via a heat circuit. Such fuels are especially used in gas turbines. The preheating of the fuel reduces the necessary quantity of fuel for achieving the upper process temperature in the thermodynamic circulation process, whereby its efficiency is increased. 
         [0009]    Advantageously the fuel preheater has a heat exchanger which is thermally connected to a cooling water circuit of the cooling device. For safety reasons fuels may only be combined with a non-oxidizing medium in a heat exchanger in order to avoid combustible mixtures in the event of leakages. The waste heat of the generator is predominantly taken away from the generator via a water circuit. Fuels can be preheated by a heat exchanger in the water circuit without an oxidizing medium coming into contact with the fuel in the event of a leak. If hydrogen is used example for direct cooling of the generator, the outer water circuit can be replaced by the fuel preheater. 
         [0010]    It is also proposed that a fuel feed to the turbine is advantageously routed through the generator for heating of the fuel. The fuel can assume the function of the cooling medium in the generator so that a separate circuit for removing heat from the generator, for example a water circuit, can be dispensed with. 
         [0011]    In a further advantageous embodiment of the invention the turbine unit includes an air feed which is thermally connected to the cooling device. The entry temperature of fresh air which enters into a compressor of a gas turbine is that of the environment. It can thus accept waste heat from the generator. This enables the thermal efficiency of the power plant to be increased. 
         [0012]    In the part load range in a combined cycle gas and steam power plant the overall efficiency is increased for fixed power if the compressor entry temperature is increased. If in this power range the generator waste heat is used for this purpose, a corresponding increase in the thermodynamic efficiency of the power plant is achieved. The feeding of the waste heat to the fresh air can be undertaken by a heat exchanger in the air feed or by the air feed being routed through the generator. 
         [0013]    Advantageously the power plant includes a control means for controlling a heat feed from the generator to a power plant device. The device can be the air feed of the turbine unit for example. In particular the control means is provided for controlling the heat feed as a function of a danger of icing of the air supply. With ambient temperatures close to freezing point and high air humidity air can be heated up before entering the compressor in order to avoid ice formation which can result in damage to components. For this purpose compressed and thereby heated air is fed back to the compressor unit, which adversely affects the efficiency of the compressor. If the waste heat of the generator is used instead, the compressor efficiency remains unaffected and a higher level of efficiency can be advantageously achieved. The control of the control medium can comprise a closed loop process. The probability of icing up can be referred to as danger of icing. 
         [0014]    In a further advantageous form of embodiment of the invention the cooling device has an open cooling circuit and a cooling air feed to an air feed of the turbine unit. In this way the air used for cooling the generator in the open air circuit can be used directly as combustion air for the turbine unit. 
         [0015]    It is also proposed that the turbine unit has an air preheater which in a cooler stage is connected thermally to the cooling device and in a warmer stage to a further heat source of the power plant, for example to a flue gas heat exchanger. In steam power plants the combustion air is typically heated up by an air preheater before entry into the flame chamber of the steam generator. The air preheater is usually supplied with heat from flue gas. However the flue gas may only be cooled down to above dew point since otherwise condensation of water with sulfur compounds results. This would result in greater corrosion. Since the heat from generator and flue gas is present at different temperature levels it can expediently be used sequentially for preheating the combustion air. First of all the combustion air can be preheated by using waste heat of the generator or warm waste air of the generator and in a second step the combustion air can be heated up by heat from the flue gas, in a further heat exchanger for example. 
         [0016]    Advantageously the turbine unit includes a feed water heater, with the cooling device being thermally connected to the feed water heater. In this way waste heat of the generator can be used to preheat the feed water of a steam process or of a gas and steam process. The hot cooling medium in the generator cooling circuit typically reaches the temperature of around 80° C. The preheating is undertaken expediently immediately beyond the feed water pump, where the steam circuit usually reaches the lowest temperature level. 
         [0017]    In principle feed water preheating can be achieved in two ways: In direct incorporation the feed water flows directly through the heat exchanger on the generator. In indirect incorporation a further heat exchanger is used on the feed water side and a separate circuit transfers the heat from the generator to the feed water. For indirect incorporation the cooling device advantageously includes a cooling water circuit which is a part of the feed water circuit of the turbine unit. 
         [0018]    Large power plant systems usually have an extensive complex of buildings which, in addition to the machine halls and the control rooms, also includes office buildings for the administration. In the respective buildings, depending on type and use and taking into consideration the appropriate health and safety at work regulations, appropriate air-conditioning systems must be provided. To this end heating is required in winter while in summer both in the office buildings and also in the machine halls cooling of the ambient air is sensible. 
         [0019]    If the cooling device is connected thermally to a building heating system of the power plant, generator heat occurring in the cooling circuit can be made available for heating the buildings. 
         [0020]    In a further variant the generator waste heat can be used for operating an absorption cooler for buildings air-conditioning. This enables generator waste heat to also be included in the cooling. The overall energy balance of the power plant is increased by relieving the load on the in-house demand network. The load on the feedback cooling circuit of the generator can be relieved in order to contribute in this way to an additional reduction of the power plant&#39;s own demands—through the increased net power plant output. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0021]    The invention will be explained in greater detail with reference to exemplary embodiments which are shown in the drawings: 
           [0022]    The figures show: 
           [0023]      FIG. 1  a schematic diagram of power plant with a turbine unit and a generator, the waste heat of which is used for preheating a fuel, 
           [0024]      FIG. 2  a schematic diagram similar to  FIG. 1 , with the fuel being routed through the generator as a cooling medium, 
           [0025]      FIG. 3  a schematic diagram of a power plant in which generator waste heat is transferred into an air compressor inflow, 
           [0026]      FIG. 4  a schematic diagram of a power plant in which the feed water of a steam turbine is routed through a generator for heating, 
           [0027]      FIG. 5  a feed water circuit for a steam turbine which is thermally connected via a heat exchanger to a coolant circuit of the generator, 
           [0028]      FIG. 6  the feed water circuit in which feed water is routed as a cooling medium via an intermediate cooling circuit of the generator, 
           [0029]      FIG. 7  a schematic diagram of the generator, the waste heat of which is supplied to an air supply before an air preheater for a steam generator, and 
           [0030]      FIG. 8  a diagram similar to  FIG. 7 , with an airflow being supplied to an air preheater as a coolant flow through the generator. 
       
    
    
     DETAILED DESCRIPTION OF INVENTION 
       [0031]      FIG. 1  shows a schematic diagram of a layout of a power plant  2  with a turbine unit  4  which is connected via a shaft  6  to a generator  24  of a generator unit  8 . The turbine unit  4  comprises a turbine  10  which is embodied as a gas turbine and operates an air compressor  12  via the shaft  6  in an air supply  14  to a combustion chamber  16  of the turbine unit  4 . In the combustion chamber  16  fuel from a fuel line  18  is mixed into the compressed air and burned. The hot exhaust gases are supplied to the turbine  10  for its operation. In addition the turbine unit  4  comprises a fuel preheater  20  in the fuel line  18  for preheating the gaseous fuel. 
         [0032]    During the operation of the power plant  2  the turbine  10  drives the air compressor  12  via the shaft  6  and drives the generator  24  via a coupling  22 . During this operation the generator  24  generates heat which is removed from the generator  24  via a cooling circuit  26 . The cooling circuit  26  and a heat exchanger  28  are a component of a cooling device  30  of the generator unit  8  for cooling the generator  24 . The cooling medium of the cooling circuit  26 , for example water, transfers heat in the heat exchanger  28  which it has taken from the generator  24  to a heating circuit  32  through which the heat in its turn is transferred in the fuel preheater  22  the fuel in the fuel line  18 . Through this generator waste heat is used for the purposes of fuel preheating. This causes the necessary quantity of fuel for reaching the upper process temperature in the turbine unit  4  to be reduced and the thermodynamic efficiency of the power plant  2  is increased. 
         [0033]    Instead of the transmission of the waste heat from the generator  24  to the fuel in the fuel line  18  by the fuel preheater  20 , the waste heat from the generator  24  can be used as depicted in the exemplary embodiment shown in  FIG. 1  for heating of buildings. A heat exchanger which transfers the waste heat in the heat circuit to a buildings heating circuit would be used for this purpose instead of the fuel preheater  20 . Also conceivable would be the routing of the heating circuit  32  directly through a building and through corresponding heating elements for heating the building for example. 
         [0034]      FIG. 2  shows a schematic diagram of the power plant  2  with an alternate cooling device  36 . The descriptions below are essentially restricted to the differences from the respective preceding exemplary embodiments, to which the reader is referred for features and functions which remain the same. Components which essentially remain the same are basically labeled with the same reference characters and features not mentioned are transferred into the following exemplary embodiments without being described once again. 
         [0035]    By contrast with  FIG. 1 , the fuel line  18  is designed with a branch which is routed through the generator  24 . The quantity of fuel to be routed through the generator  24  or a fuel preheater  40  can be adjusted by a valve  38  through a control means  34 . By contrast with the preceding exemplary embodiment the fuel preheater  40  is not thermally supplied with waste heat from the generator  24  but from another heat source. Through the combination of heat transfer to the fuel by the fuel preheater  40  and the cooling device  36  the fuel in the fuel line  18  can also be heated up to a desired temperature independently of the heat occurring in the generator  24 . 
         [0036]    Of course an additional arrangement of the fuel preheater  40  in the fuel line  18  from  FIG. 1  is also possible and advantageous. For example it can be arranged in the fuel flow after the fuel preheater  20  as an additional heat source for heating the fuel. 
         [0037]    In the exemplary embodiment shown in  FIG. 3  waste heat is transferred from the generator  24  via the cooling circuit  26  and the heat exchanger  28  of the cooling device  30  via a heat exchanger  42  to combustion air in the air feed  14 . Since the overall efficiency of the combined gas and steam power plant can be increased with a fixed output especially in the part load range if the compressor inlet temperature of the combustion air is increased, the combustion air preheating is sensible for increasing the efficiency of the power plant  2 . If the generator waste heat is used to this purpose in this power range in particular, a corresponding increase in the thermodynamic efficiency is achieved. 
         [0038]    A further advantage of the heating of compressor induction air lies in being able to counteract a danger or air filter, compressor diffuser and the first stages of the compressor icing up. Compressor induction air is expediently heated up by this so called anti-icing if it has a temperature around freezing point, i.e. typically between +5° C. and −5° C., and when an air humidity of over 80% exists. The corresponding heating of the compressor induction air is controlled by the control means  34  and by means not shown in the diagram for taking heat from the cooling device  30 . 
         [0039]    The schematic diagram in  FIG. 4  shows a power plant  44  with a turbine unit  46  comprising a steam turbine  48 . The steam turbine  46  is supplied with fresh steam which drives the steam turbine  48  via a feed water circuit  50 . Expanded steam is condensed in a condenser  52  and routed by a feed water pump  54  to the generator unit  8  in order to take heat from the cooling device  30  of the generator unit  8  with it for preheating the feed water. In a vessel  56  the feed water preheated with the generator waste heat is brought up to its upper temperature and pressure level and is subsequently routed as fresh steam to the steam turbine  48 . 
         [0040]    To make additional cooling of the generator unit  8  possible the cooling device  30  includes a secondary cooling circuit  58  with a secondary cooler  60  and a cooling water pump  62 . With the aid of the control means  34  and valve  64  additional heat can be extracted by the secondary cooling circuit  58  from the generator  24 , even if no feed water heating is necessary at that moment and the feed water circuit is stationary because the valves  66  are closed. 
         [0041]    The generator  24  is manufactured with a water-called stator and cooling channels made of stainless steel, typically V2A, so that the feed water is routed directly through the stator and can be used for cooling the stator windings. 
         [0042]    Compared to pure steam power processes the quantity of steam which is normally used for preheating the feed water and is thus no longer available for energy generation can be reduced. 
         [0043]    In the exemplary embodiments shown in  FIGS. 5 and 6  feed water of the feed water circuit  50  is likewise heated with generator waste heat. In the layout shown in  FIG. 5  the feed water is heated up directly in a heat exchanger  72  on the generator  24 . By contrast, in the exemplary embodiment shown in  FIG. 6 , an indirect incorporation is realized, in which a further heat exchanger  74  is used on the feed water side and the waste heat from the generator  24  is transferred to the feed water on a separate circuit  76 . 
         [0044]      FIGS. 7 and 8  show sections from a power plant layout similar to  FIGS. 1 and 2 , in which the generator waste heat is used by means of a heating circuit  32  ( FIG. 7 ) or directly for heating fresh air for fossil firing of the power plant  2  ( FIG. 8 ). To this end a heat exchanger  42  is arranged in the air feed  14  to a steam generator or vessel of the power plant  2  for example for heating the ambient air with generator waste heat. For additional heating of the combustion air a further heat exchanger  68  is available which is supplied with flue gas heat. In the exemplary embodiment from  FIG. 8  the combustion air is routed directly via an air compressor  70  as the cooling medium through the generator  24  and thus directly extracts waste heat from the generator  24 . 
         [0045]    Since the temperature level of the generator  24  and thus of the heating circuit  32  is lower than the temperature level of the flue gas and thus of the heat exchanger  68 , the waste heat from the generator unit  8  is used for first preheating of the combustion air. The subsequent second preheating to a higher temperature level occurs in the heat exchanger  68 .