Abstract:
Heat flow from a steam seal header could be used in a stage, such as a low pressure stage, of a steam turbine. However, the dump steam temperature from the steam seal header can be too high requiring removal of excess heat, typically through attemperation, before the dump steam is provided to the low pressure stage. Attemperation poses reliability and life issues and lowers efficiency. To address such short comings, one or more heat pumps are used to transfer heat from the dump steam to the fluid entering a boiler. This allows the dump steam temperature to be within acceptable limits, and at the same time, increase the temperature of the fluid so that the steam cycle performance is enhanced. Preferably, solid-state heat pumps are used as they are reliable, silent and can be precisely controlled.

Description:
[0001]    One or more aspects of the present invention relate to method, apparatus and system for thermodynamic cycle optimization for a steam turbine cycle. In particular, one or more aspects relate to improving thermodynamic cycle performance in steam turbines utilizing excess heat that is normally wasted in conventional steam turbines. 
       BACKGROUND OF THE INVENTION 
       [0002]    Currently, excess heat flow from a steam seal header is dumped to a condenser as illustrated in  FIG. 1 . This steam can be at a very high temperature—up to 900° F. depending on the throttle and reheat temperature of the unit. This excess heat could be used to produce power by admitting into downstream low pressure stages. However, due to the high, perhaps even excessive mismatch between the dump steam and the low pressure reentry stage temperature, there are many unfavorable mechanical implications. 
         [0003]    Hence, before admitting the dump steam into the low pressure stage, the temperature of the dump steam needs to be brought down within acceptable limits. Conventionally, this is achieved through attemperation, mixing with low grade steam, and so on. But such conventional methods can be wasteful in that the heat of the dump steam lost through attemperation is not used for useful work. This reduces the steam turbine cycle efficiency. Also the heat transfer is limited by the sink temperature of the heat exchanger (in the case of feed water heater line). The dump steam cannot be cooled below the feed water heat temperature conventionally without using attemperation. 
         [0004]    It would be desirable to utilize the excess heat, and thereby enhance the efficiency of the steam turbine cycle. 
       BRIEF SUMMARY OF THE INVENTION 
       [0005]    An aspect of the present invention relates to a steam turbine that comprises a high pressure turbine stage, a low pressure turbine stage, a steam seal header, a boiler, and a heat pump. The high pressure turbine is fluidly connected to a high pressure steam source to receive a high pressure entry steam from the high pressure steam source. The high pressure turbine stage is structured to convert energy of the high pressure entry steam into mechanical energy and output a high pressure exhaust steam. The low pressure turbine stage is fluidly connected to a low pressure steam source to receive a low pressure entry steam from the low pressure steam source. The low pressure turbine stage is structured to convert energy of the low pressure entry steam into mechanical energy and output a low pressure exhaust steam. The steam seal header is fluidly connected to an output of the high pressure turbine stage and fluidly connected to an input of the low pressure turbine stage. The steam seal header is structured to receive at least a portion of the high pressure exhaust steam from the high pressure turbine stage and output a dump steam to the low pressure turbine stage such that the dump steam comprises the portion of the high pressure exhaust stream. The boiler is fluidly connected to a work fluid source to receive work fluid from the work fluid source. The boiler is structured to generate primary steam by applying heat to the work fluid. The heat pump is fluidly located in between the steam seal header and the low pressure turbine stage, and is also fluidly located in between the work fluid source and the boiler. The heat pump is structured to transfer heat from the dump steam to at least a portion of the work fluid. 
         [0006]    The invention will now be described in greater detail in connection with the drawings identified below. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0007]    These and other features of the present invention will be better understood through the following detailed description of example embodiments in conjunction with the accompanying drawings, in which: 
           [0008]      FIG. 1  illustrates flow of excess heat in a conventional steam turbine system; 
           [0009]      FIG. 2  illustrates an example flow of excess heat in which the excess heat is used in a useful manner; 
           [0010]      FIG. 3  illustrates another example flow of excess heat in which the excess heat is used in a useful manner; 
           [0011]      FIG. 4  illustrates an architecture of a steam turbine system according to an embodiment of the present invention; 
           [0012]      FIG. 5  illustrates an architecture of a steam turbine system according to another embodiment of the present invention; 
           [0013]      FIG. 6  illustrates an architecture of a steam turbine system according to yet another embodiment of the present invention; and 
           [0014]      FIG. 7  illustrates an example configuration of steam turbine stages according to an embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0015]    Novel method, system, and apparatus for thermodynamic cycle optimization for a steam turbine cycle are described. In one aspect, the described method, system, and apparatus utilize heat pumps to transfer the excess heat from a dump steam in a useful manner. For example, the heat from the dump steam can be transferred to an exiting feed water heater flow and/or to leak-off flows from pressure packing and valve stems. In this way, the mismatch between the dump steam and the reentry steam temperature at a header of a steam turbine stage can be brought within acceptable limits. 
         [0016]    Typically, the pressure difference between a seal steam header (SSH) and a low pressure (LP) turbine stage is the main factor in driving the flow. Thus, in many instances, the dump steam will be provided to the header of the low pressure turbine stage. The dump steam may be provided to the header of any turbine stage where there is an availability of suitably high pressure steam and provisions on the shell at the required sections in the steam turbine. 
         [0017]      FIG. 2  illustrates an example flow of excess heat in which the excess heat can be used in a useful manner according to an aspect of the present invention. As seen in this figure, the steam seal header  240  can be fluidly connected to an output of a high pressure (HP) turbine stage. Fluid connection can be achieved in a variety of ways including pipes, valves, and other conduits. Through this fluid connection, the steam seal header  240  can receive exhaust steam, or at least a portion thereof, from a high pressure turbine stage seal packing. The steam seal header  240  can output some, none or all of this high pressure exhaust steam as dump steam, and output any remaining portion to the low pressure turbine stage seal packing. Whenever there is at least some high pressure exhaust steam output as the dump steam, it can be said that the dump steam comprises a portion of the high pressure exhaust steam. 
         [0018]    If there is another source of dump steam such as an intermediate pressure (IP) turbine stage, the steam seal header  240  can be fluidly connected to an output of the intermediate pressure turbine stage to receive intermediate pressure exhaust steam, or at least a portion thereof, from the intermediate pressure turbine stage seal packing. In this instance, the dump steam can comprise a portion of the high pressure exhaust steam and/or a portion of the intermediate pressure exhaust steam. 
         [0019]    Note that the terms low pressure and high pressure should be interpreted in a relative sense and not in an absolute sense. For example, low pressure turbine stage is not limited to the lowest pressure turbine stage. The phrase “low pressure turbine stage” simply indicates that relative to a high pressure turbine stage or an intermediate pressure turbine stage, the low pressure turbine stage works with lower pressure steam. In one aspect, the pressure of the steam entering the low pressure turbine stage (low pressure entry steam) is lower than the pressure of the steam entering the high pressure turbine stage (high pressure entry steam) or the pressure of the steam entering the intermediate pressure turbine stage (intermediate pressure entry steam). Similarly, high pressure turbine stage does not necessarily refer to a highest pressure turbine. 
         [0020]    Unlike the conventional system illustrated in  FIG. 1 , the steam seal header  240  can be fluidly connected to an input of the low pressure turbine stage  230  such that the steam seal header  240  can provide the dump steam to the low pressure turbine stage  230  instead of to the condenser. Recall the temperature of the dump steam from the steam seal header  240  can be very high—much too high for the low pressure turbine stage  230 . To address this short coming of the conventional steam turbine system, in one aspect, a heat pump  250  can be fluidly located in between the dump steam output of the steam seal header  240  and the header input of the low pressure stage turbine  230 . The heat pump  250  can extract heat from the dump steam such that the temperature of the dump steam entering the low pressure turbine stage  230  is within acceptable temperature limits of the low pressure turbine stage  230 . 
         [0021]    One way to extract the heat from the dump steam is to transfer the heat to work fluid flowing to a boiler. In the  FIG. 2  example, the work fluid, in the form of feed water, flows from a work fluid source through a feed water heater (FWH)  270  to the boiler. The FWH  270 , which can be fluidly located in between work fluid source and the boiler, can preheat the work fluid to output the preheated work fluid. 
         [0022]    Note that while some of the preheated work fluid can bypass the heat pump  250 , at least some can also flow through the heat pump  250 . That is, in addition to being fluidly located in between the steam seal header  240  and the low pressure turbine stage  230 , the heat pump  250  can be fluidly located in between the FWH  270  and the boiler such that at least a portion of the preheated work fluid flows through the heat pump  250 . The heat pump  250  can transfer the heat from the dump steam to the portion of the work fluid flowing through it to reduce the temperature of the dump steam entering the low pressure stage  230 . Preferably, the temperature of the dump steam is sufficiently reduced to be within acceptable temperature limits. 
         [0023]    By using the heat pump  250  to transfer heat from the dump steam to the work fluid, additional work can be extracted from the dump steam. Also, greater thermodynamic efficiency can be gained by further heating the work fluid entering the boiler  480 . 
         [0024]    In an aspect, the heat pump  250  can include one or several heat transfer devices  255 . The arrows on the heat transfer devices  255  indicate the direction of heat transfer. Preferably, the heat transfer devices  255  are solid state heat transfer devices. Examples of solid state heat transfer devices include thermoelectric devices, thermionic devices, and thermoelectric-thermionic combination devices. The heat transfer devices  255  can be used as heat pumps via the peltier effect. 
         [0025]    While not illustrated, it is fully contemplated that one or more flow control mechanisms can be put in place, such as controllable valves, fluid pumps, etc. so as to control flow rates of any of the dump steam flow, the work fluid flow within the heat pump  250 , and the work fluid flow that bypasses the heat pump  250 . It is also contemplated that the electrical power applied to the solid state heat transfer devices  255  can be controlled. In this way, rate of heat transfer from the dump steam to the work fluid can be controlled as well. 
         [0026]    In  FIG. 2 , the direction of heat transfer in the heat pump  250  is shown to be from the dump steam to the work fluid. In most circumstances, this will be the direction. But it should be noted that the heat pump  250  itself is not so limited. The direction of the heat transfer can also be controlled through controlling the direction of the current of the electrical power applied to the solid state heat transfer devices  255 . Thus, while it is unlikely, the heat pump  250  can be controlled to transfer heat from the work fluid to the dump steam if that becomes necessary. 
         [0027]    Also in  FIG. 2 , the steam seal header  240  is shown to receive inputs from two sources of the dump steam—the high pressure turbine stage and the intermediate pressure turbine stage. This is merely an example and should not be taken to be limiting. The number of sources for the dump steam can be one or any number greater than one. Also, only output one dump steam flow illustrated from the steam seal header  240 . Again, this should not be taken to be limiting. The steam seal header  240  can output multiple dump steam flows flowing to different downstream turbine stages. Further, the feed water heater  270  is not strictly necessary. That is, the heat pump  250  can transfer heat from the dump steam to the work fluid that has not been preheated. 
         [0028]      FIG. 3  illustrates an example flow of excess heat in which the excess heat can be used in a useful manner according to another aspect of the present invention.  FIG. 3  is similar to  FIG. 2  in many respects. For example, the steam seal header  240  can be fluidly connected one or both output of the high and intermediate pressure turbine stages. The heat pump  250  can be fluidly located in between the steam seal header  240  and the low pressure turbine stage  230 . 
         [0029]    But instead of the FWH  270 , a leak-off collector  360  is shown. The leak-off collector  360  can collect leak-off steam flows from end packings, from valve stems of one or more turbine stages, or from both. The leak-off collector  360  can output leak-off flow to the FWH  270  (not shown in  FIG. 3 ). Thus, the leak-off flow can be considered as work fluid and the leak-off collector  360  can be viewed as an example of a work fluid source. 
         [0030]    As seen in  FIG. 3 , the heat pump  250  can be fluidly located in between leak-off collector  360  and FWH. More generally, the heat pump  250  can be fluidly located in between a work fluid source and the boiler. The heat pump  250  can transfer the heat from the dump steam to the portion of the leak-off flow flowing though the heat pump  250 . Again, it is preferable that the temperature of the dump steam is sufficiently reduced to be within acceptable temperature limits of the low pressure turbine stage  230 . 
         [0031]      FIG. 4  illustrates an architecture of a steam turbine system  400  according to an embodiment of the present invention. The system  400  can include multiple turbine stages. In  FIG. 4 , the multiple stages comprise a high pressure turbine stage  410 , an intermediate pressure turbine stage  420 , and a low pressure turbine stage  430 . This is an example and should not be taken to be limiting. The described aspects can be applicable to a steam turbine system with as few as two stages or more than three. 
         [0032]    For explanation, the reader&#39;s attention is directed to  FIG. 7  which illustrates an example configuration of steam turbine stages. The configuration  700  can include multiple turbine stages. In each stage, the turbine of that stage can receive an entry steam from a steam source (fluidic connection to the steam source not shown), converts the energy of the entry steam into mechanical energy, and output an exhaust steam. For example, the high pressure turbine stage  410  can receive a high pressure entry steam from a high pressure steam source, convert the energy of the high pressure entry steam into mechanical energy and output a high pressure exhaust steam. Similarly, the intermediate and low pressure turbine stages  420 ,  430  can receive intermediate and low pressure entry steams from their respective sources, convert the energy of the intermediate and low pressure entry steams, and output intermediate and low pressure exhaust steams. 
         [0033]    In one aspect, the stages are differentiated by the pressure of the entry steams. That is, the pressure of the high pressure entry steam is higher than that of the intermediate pressure entry steam, which is higher than that of the low pressure entry steam. Recall that “high pressure”, “intermediate pressure” and “low pressure” should be interpreted in a relative sense.  FIG. 7  shows this more clearly. As seen, there can be even a higher pressure turbine stage than the high pressure turbine stage  410 . Similarly, there can be even a lower pressure turbine stage than the low pressure turbine stage  430 . But among the high, intermediate, and low pressure turbine stages  410 ,  420 ,  430 , there can be a relative ordering of the entry pressures. 
         [0034]    Further, the high, intermediate, and low pressure turbine stages  410 ,  420 ,  430  need not be consecutive. That is, there can be intervening stages between the high and intermediate pressure stages  410 ,  420  or between the intermediate and low pressure stages  420 ,  430 . Yet further, the number of stages at a particular pressure is not limited to one. For example,  FIG. 7  illustrates three low pressure turbine stages  430 . While not shown in this figure, the dump steam can be provided to any one of these stages. 
         [0035]    Referring back to  FIG. 4 , the system  400  can include a generator  490  which converts the mechanical energy of the turbine stages into electricity. The system  400  can also include a steam seal header  440 , a heat pump  450 , a condenser  460 , a FWH  470 , and a boiler  480 . The condenser  460  can be fluidly connected to an output of the low pressure turbine stage  430  and condense the low pressure exhaust steam. The condensed steam can be provided as work fluid to the boiler  480 , which can generate primary steam by applying heat to the work fluid. Thus, the condenser  460  can be considered as being work fluid source. The specifics of the steam seal header  440 , the heat pump  450 , and the FWH  470  have been described above with respect to  FIGS. 2 and 3 , and therefore will not be repeated. 
         [0036]    As seen in  FIG. 4 , the steam seal header  440  can be fluidly connected to an output of the high pressure turbine stage  410  and to an input of the low pressure turbine stage  430 . The steam seal header  440  can receive at least a portion of the high pressure exhaust steam and output the dump steam to the low pressure turbine stage  430 . The dump steam thus can comprise a portion of the high pressure exhaust stream. 
         [0037]    As indicated above, the aspects described in this disclosure can be applied to a steam turbine system two stages. Thus, the intermediate pressure turbine stage  420  is not strictly necessary. However, when the system  400  does include the intermediate pressure turbine stage  420 , the steam seal header  440  can also be fluidly connected to an output of the intermediate pressure turbine stage  420  to receive at least a portion of the intermediate pressure exhaust steam such that the dump steam also comprises a portion of the intermediate pressure exhaust stream. 
         [0038]    The heat pump  450  can be fluidly located in between the steam seal header  440  and the low pressure turbine stage  430  and in between the work fluid source, e.g. the condenser  460 , and the boiler  480 . In this instance, the heat pump  450  can transfer heat from the dump steam to at least a portion of the work fluid. 
         [0039]    The system  400  can also include a FWH  470 , which can be fluidly located in between the work fluid source and the boiler  480 , and the heat pump  450  can be fluidly located in between the FWH  470  and the boiler  480 . In this instance, the heat pump  450  can transfer heat from the dump steam to at least a portion of the preheated work fluid. 
         [0040]    Note that in  FIG. 4 , the high pressure entry steam is the primary steam from the boiler  480 , the intermediate entry steam is the high pressure exhaust steam from the high pressure turbine stage  410 , and the low pressure entry steam is the intermediate pressure exhaust steam from the intermediate pressure turbine stage  420 . In other words, the high pressure, intermediate pressure, and low pressure steam sources can respectively be the boiler  480 , the high pressure turbine stage  410 , and the intermediate pressure turbine stage  420 . Again, this is a specific example and should not be taken to be limiting. 
         [0041]      FIG. 5  illustrates an architecture of a steam turbine system according to another embodiment of the present invention. The system  500  illustrated in  FIG. 5  is similar in many respects to the system  400  illustrated in  FIG. 4 . Therefore, only those details that are particular to this embodiment will be described. 
         [0042]    In this embodiment, the leak-off collector  560  can be a work fluid source. Thus, the heat pump  450  can be fluidly located in between the work fluid source, e.g., the leak-off collector  560 , and the boiler  480 , and can transfer heat from the dump steam to the work fluid. The dump steam can comprise a portion of the high pressure exhaust steam from the high pressure turbine stage  410 . When the system  500  also includes the intermediate pressure turbine stage, the dump steam can include a portion of the intermediate pressure exhaust steam as well. Like  FIG. 4 , the system  500  can include the FWH  470 . But in this instance, the heat pump  450  can be fluidly located in between the leak-off collector  560  and the FWH  470 . 
         [0043]    Of course, the embodiments may be combined as illustrated in  FIG. 6 . In this figure, the system  600  includes two heat pumps—first and second heat pumps  450 - 1 ,  450 - 2 . The first heat pump  450 - 1  is similar to the heat pump  450  of system  400  in  FIG. 4 , and the second heat pump  450 - 2  is similar to the heat pump  450  of system  500  in  FIG. 5 . The details of the individual components of system  600  will be omitted since they have been described previously. 
         [0044]    The disclosed aspects are applicable to turbine systems other than the specific examples described thus far. The number of steam seal headers and heat pumps are not limited. Also, excess heat from any exhaust flow that would not be utilized in the conventional system can be converted for useful purposes in light of the disclosed aspects. 
         [0045]    There are numerous advantages associated with the disclosed aspects. Among them are:
       SSH flow which, instead of dumping into the condenser, can be used for power extraction;   Admission of the SSH flow can be accomplished to reduce the temperature mismatch of the low pressure turbine stage without attemperation, and thus save on costs and reduce unfavorable effects on the system performance;   Effective control of the temperature of the steam entering the low pressure turbine stage through regulating the electrical power to the solid state heat transfer devices;   Flexibility to meet specific requirements afforded due to modular construction of the heat transfer devices, and   Easy integration with existing control systems.       
 
         [0051]    This written description uses examples to disclose the invention, including the best mode, and also to enable any person skilled in the art to practice the invention, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the invention is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they have structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal language of the claims.