Abstract:
A device and a method for using overcapacities in the power grid is provided. In case of an oversupply of energy, the energy is transferred to a thermal storage device directly via a heating element and in the discharge case of the thermal storage device the heat is removed from the thermal storage device and made available to a thermodynamic cycle whereby electrical energy is produced. The heat from the thermal storage device is used to preheat air in an air feed line to a combustion chamber, or fuel is pre-heated using heat from the thermal storage device.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is the US National Stage of International Application No. PCT/EP2009/052604, filed Mar. 5, 2009 and claims the benefit thereof. The International Application claims the benefits of European Patent Office application No. 08004589.1 EP filed Mar. 12, 2008. All of the applications are incorporated by reference herein in their entirety. 
     FIELD OF INVENTION 
     The invention relates to an apparatus and method for utilizing overcapacities in the power network. 
     BACKGROUND OF INVENTION 
     In the electrical network the power generated and consumption must always be in equilibrium. The extensive development of renewable energies means that sometimes there are significant overcapacities available. It is possible to manage the oversupply of controllable renewable energies in a number of ways; for example the fluctuating supply can be compensated for by increasing or reducing the capacity of conventional power plants, resulting renewable energy could not be fed into the network, in other words wind turbines could be deactivated, or the energy could be stored in an energy storage system, in other words in pumped storage power plants, compressed air storage power plants or batteries with high levels of system complexity and high costs in some instances. 
     EP 1 577 548 A1 and EP 1 577 549 A1 describe an apparatus and method for storing energy and generating power. A thermal storage unit is heated using electrical energy generated from renewable energies such wind or solar energy. The heat is used as required in the thermal storage unit to generate steam, which is fed directly to a thermodynamic process in a steam turbine, steam generation optionally being supplemented by conventional means. 
     U.S. Pat. No. 5,384,489 describes an apparatus in which electrical energy is generated by wind energy and used to operate a heating element to heat a fluid in a storage tank and an apparatus for extracting the stored energy from the tank again. The energy extracted from the storage tank is used for space heating/space cooling, general cooling and desalination but preferably for steam generation for generating electrical power. 
     SUMMARY OF INVENTION 
     The object of the invention is to propose a more efficient apparatus and method for utilizing overcapacities in the power network. 
     According to the invention this object is achieved by the features of the claims. 
     Further advantageous embodiments are set out in the subclaims. 
     One disadvantage of the apparatuses and methods of the prior art is that the quality and quantity of the steam generated in the thermal storage unit are not always adequate for operating a steam turbine, making conventional subsequent firing necessary. Apparatuses and methods of the prior art are also limited to one medium, namely steam, for power generation. 
     In contrast the inventive apparatus aims to utilize the overcapacities in the power network for a number of different heat consumers and therefore provides for a thermal storage unit and a heating element for storing energy from the power network in the thermal storage unit and a heat exchanger having a primary side and a secondary side, the primary side being coupled thermally to the thermal storage unit for extracting heat from the thermal storage unit and the secondary side being connected to a power plant system, the power plant system to which the heat exchanger is connected comprising a gas turbine. 
     The thermal storage unit is therefore not only used to generate steam which is fed directly to a steam turbine. 
     In one advantageous embodiment of the invention the heat exchanger is connected on the secondary side to an air supply line of a burner to preheat the air. 
     It is likewise advantageous if the heat exchanger is connected on the secondary side to a fuel supply line to preheat the fuel. 
     It is also expedient if the heat exchanger is connected on the secondary side to the flow of combustion gases for their intermediate superheating. 
     In a further advantageous embodiment of the invention however the heat exchanger can also be connected to a power plant system containing a steam turbine. 
     It is expedient then to connect the heat exchanger on the secondary side to the steam flow for intermediate superheating. 
     It is also expedient if the heat exchanger is connected on the secondary side to the water/steam circuit in the manner of a preheater. 
     It is also expedient if the heat exchanger is used for coal drying. 
     In one particularly advantageous combination of a gas and steam turbine, which comprises a waste heat steam generator for generating steam for the steam turbine by means of heat from the waste gases of the gas turbine, the feedwater preheater in the waste heat steam generator can be replaced or supplemented by a heat exchanger, which is connected on the primary side to the thermal storage unit. 
     In the inventive method, to utilize overcapacities in the power network when there are overcapacities of energy, such energy is fed directly into a thermal storage unit by way of a heating element and when said thermal storage unit is discharged, the heat is extracted from the thermal storage unit and made available to a thermodynamic cycle, for example an existing power plant process, the heat from the thermal storage unit being used to preheat air in an air supply line of a combustion chamber, in particular a gas turbine system, or fuel being preheated using heat from the thermal storage unit. 
     Both preheating operations reduce fuel consumption. Preheating therefore increases the overall efficiency of the gas turbine system for an almost identical output of the gas turbine. 
     A high energy yield can also be achieved by intermediate superheating of the waste gas flow in a turbine of a gas turbine. 
     In a further advantageous embodiment of the invention a steam flow in a steam turbine undergoes intermediate superheating using heat from the thermal storage unit. 
     However it can also be expedient at another point in the water/steam circuit to preheat the water using heat from the thermal storage unit, for example if the heat content of the thermal storage unit is not sufficient for intermediate superheating in the turbine. 
     Coal can also be dried using the heat from the thermal storage unit, so that there is no need to divert high-quality steam from the steam turbine process. 
     It is particularly advantageous, due to the minimal conversion losses, to use water as the heat-carrying medium on the secondary side of the heat exchanger, which is connected on the primary side to the thermal storage unit, and to feed the steam generated by the heat in the thermal storage unit directly into a steam turbine. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention is described in more detail below in an exemplary manner with reference to drawings, in which: 
         FIG. 1  shows a schematic diagram of the concept of storing electrical energy with a thermal storage unit and conversion back to electricity by means of a thermodynamic cycle, 
         FIG. 2  shows a schematic diagram of the inventive apparatus with heating element, thermal storage unit and heat exchanger, 
         FIG. 3  shows a gas turbine system with air preheating, fuel preheating and intermediate superheating, 
         FIG. 4  shows a steam turbine system, in which the steam generated by means of heat from the thermal storage unit is routed directly into the steam turbine, preheats the condensate and/or predries the fuel and 
         FIG. 5  shows a waste heat steam generator in a gas and steam system with direct steam and intermediate superheating. 
     
    
    
     Essentially identical elements are in principle designated with the same reference characters. 
     DETAILED DESCRIPTION OF INVENTION 
       FIG. 1  describes the inventive method for utilizing overcapacities in the power network. If at a time t 1  the power  1  generated exceeds consumption  3  in the network, the oversupply  2  of electrical energy is stored  4  directly in a thermal storage unit, for example a salt storage unit or concrete thermal storage unit, by way of a heating element. 
     When this energy storage system is discharged, for example when there is a greater demand for power in the power network, the heat is extracted from the thermal storage unit again and fed to a power plant system  5  by way of a heat exchanger, the primary side of which is coupled thermally to the thermal storage unit and the secondary side of which is connected to a power plant system, so that the power  6  generated at time t 2  covers demand  7  at time t 2 . 
       FIG. 2  shows the essential components of the inventive apparatus for utilizing overcapacities in the power network. Electrical energy from the power network  9  can be stored directly in the thermal storage unit  10  by way of a heating element  8 . The primary side of the heat exchanger  11  is coupled thermally to the thermal storage unit  10 . The secondary side of the heat exchanger  11  is connected to a power plant system  12 . 
     The power plant system  12  according to  FIG. 3  features a gas turbine  13  and comprises a compressor  14  for compressing the air which is then fed to a combustion chamber  15  and combusted with fuel. The hot combustion gases drive the turbine  16 , which is coupled by way of a shaft  17  to the compressor  14 . Heat from the thermal storage unit  10  can be used by way of heat exchangers  11  both to preheat  18  the compressed air and to preheat the fuel  19 . 
     The combustion chamber  15  is optionally deactivated completely and the turbine  16  is driven simply by the compressed air heated by way of a heat exchanger  11 . Intermediate superheating  20  expediently takes place in the region of the turbine  16 . 
     The power plant system according to  FIG. 4  features a steam power plant  21  and comprises a combustion chamber  15 , to which a fuel and an oxidation agent can be fed by way of a supply system. The heat released from the combustion chamber  15  during combustion of the fuel can be transferred to a steam generator  22 . In the exemplary embodiment this is indicated by a waste gas line  23  passing out of the combustion chamber  15  by way of a heat exchanger  24  disposed in the steam generator  22 . However any other type of suitable heat transfer from the combustion chamber  15  to the steam generator  22  is of course possible, for example by way of direct firing. 
     A steam turbine  26  is connected to the steam generator  22  by way of a water/steam circuit  25 , said steam turbine  26  being driven by way of a shaft  17  of a generator (not shown in detail). In the exemplary embodiment the steam turbine  26  is embodied in three stages and comprises a high-pressure part  27 , which is connected on the input side to the steam generator  22  by way of a steam line  28 . On the output side the high-pressure part  27  is connected to the downstream medium-pressure part  30  of the steam turbine  26  by way of a superheater line  29  passed by way of the steam generator  22 . The sub-turbines of the medium-pressure part  30  are in turn connected on the output side to the low-pressure parts  31  of the steam turbine  26 . 
     Instead of the steam turbine  26  thus embodied in three stages it is of course also possible to provide a two-stage or other type of suitably selected steam turbine. 
     The low-pressure part  31  of the steam turbine  26  is connected on the outflow side to a condenser  32 , in which the expanded steam flowing out of the steam turbine  26  is condensed. 
     The condenser  32  is in turn connected on the output side to a feedwater vessel  35 , in which the condensed water is temporarily stored, by way of a condensate line  33 , to which a condensate pump  34  is connected. This feedwater vessel  35  is connected on the feedwater side by way of a feedwater line  36 , to which a feedwater pump  37  is connected, to the steam generator  22 , so that the water can be fed back to the steam boiler and a closed water/steam circuit  25  results. 
     To improve efficiency, regenerative feedwater preheating generally takes place, in the course of which the feedwater is preheated using tapped steam  54  from the low-pressure part  31  of the steam turbine  26  for example, before it is fed back into the steam generator  22 . 
     In the inventive apparatus there is no need for such feedwater preheating, so the steam generally required for this purpose can be utilized to generate energy. Instead heat exchangers  11  are connected to the condensate line  33  and the feedwater line  36  on the secondary side, being connected to the thermal storage unit  10  on the primary side and being intended to insure the injection of the heat of the thermal storage unit  10  into the water/steam circuit  25  of the steam generator  22 . 
     The heat in the thermal storage unit  10  can also be used to generate steam, which is then fed directly into the steam turbine  26 . One possible feed-in point  48  is the steam line  28  leading to the high-pressure part  27  of the turbine  26 . The generated steam can however also be fed  49  into the superheater line  29 . Finally it is also possible to feed the steam into the steam lines between the medium-pressure part  30  and the low-pressure part  31  of the turbine  26 . 
     Steam-heated dryers are generally used to predry fuel, being heated to some degree using high-temperature steam from the water/steam circuit of the power plant process. To reduce the proportion of steam  51  required from the power plant process, it is also possible here to use heat from the thermal storage unit  10  to predry the fuel  52 . 
       FIG. 5  shows a schematic diagram of the steam circuit  38  of a gas and steam power plant having a waste heat steam generator  39  and its essential components—a feedwater preheater  40 , evaporator  41  and superheater  42 . The waste gases of a gas turbine (not shown) heat water and generate steam in successive steps in the waste heat steam generator  39 . 
     In the feedwater preheater  40  the residual heat of the gas turbine waste gas is used to preheat the feedwater before it reaches the steam boiler  43 , thereby reducing the energy requirement of the evaporator  41 . The steam passes by way of a collection line  44  in the top of the steam boiler  43  into the superheater  42 , where the temperature and pressure rise further. 
     The steam is routed to the high-pressure turbine  45 , the first of a multi-stage turbine process. 
     In the inventive apparatus the feedwater preheater  40  can either be supplemented by supplying heat  46  from the thermal storage unit  10  or even replaced. Alternatively or additionally however steam can also be generated directly using the heat from the thermal storage unit  10  and mixed in  47  with the steam generated in the waste heat steam generator.