Abstract:
A power generation system including: at least one elevated steam turbine receiving input steam at an elevated pressure and exhausting steam as low pressure steam; a low pressure steam turbine receiving low pressure steam exhausted from the elevated steam turbine, and a drive shaft for the low pressure steam turbine connected to a clutch which is reasonably coupled to a power generator, wherein the clutch has a first position in which power from the low pressure steam turbine is applied to the power generator and a second position in which power from the low pressure steam turbine is not applied to the generator.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    The present invention relates to power generation systems including multiple steam turbines and, particularly, to coupling steam turbines to such systems. 
         [0002]    Large power generator systems often employ two or more steam turbines to drive generators to produce power. The steam turbines are conventionally coupled together to drive power generators. For example, multiple steam turbines may be connected by a common shaft that drives a generator. A cross compound turbine arrangement has two or more generators each driving one or more steam turbines. A power generation system having cross-compound turbines typically has a generator for the high pressure and intermediate steam turbine, and a separate generator for the low pressure steam turbines. 
         [0003]    The power demand loads applied to power generator systems often vary during the course of a day, weeks, and months. It is desirable for power generation systems to adapt to the variations in the power generation demands. Specifically, there is a need for power generator systems to engage and disengage its steam turbines depending on the power demand. 
       BRIEF DESCRIPTION OF THE INVENTION 
       [0004]    A system of valves and a clutch has been developed to disengage and engage one or more steam turbine sections from a power generation system. For example, the system may include a planetary clutch between a low pressure steam turbine and other steam turbines, and associated valves to open and turn off the steam flow to the low pressure steam turbine depending on whether the clutch engages or disengages the low pressure steam turbine. The low pressure steam turbine may be disengaged while the demand for power from the generator is low and may be engaged when the demand for power is high. 
         [0005]    A power generation system including: at least one elevated steam turbine receiving input steam at an elevated pressure and exhausting steam as low pressure steam; a low pressure steam turbine receiving low pressure steam exhausted from the elevated steam turbine, and a drive shaft for the low pressure steam turbine connected to a clutch which is reasonably coupled to a power generator, wherein the clutch has a first position in which power from the low pressure steam turbine is applied to the power generator and a second position in which power from the low pressure steam turbine is not applied to the generator. 
         [0006]    The at least one elevated steam turbine may include a high pressure steam turbine receiving high pressure steam and an intermediate steam turbine receiving steam exhausted from the high pressure steam turbine, wherein steam exhausted from the intermediate steam turbine is applied as the low pressure steam for the low pressure steam turbine. The power generation system may further include a first low pressure steam valve in a conduit for low pressure steam flowing to the low pressure steam turbine and a second low pressure steam valve in a conduit for low pressure steam flowing to a steam process extraction device, wherein the first low pressure steam valve is open while the second low pressure steam valve is closed, and the first low pressure steam valve is closed while the second low pressure steam valve is open. 
         [0007]    A power generation system has been developed comprising: a high pressure steam turbine receiving high pressure steam and exhausting steam at an intermediate pressure; an intermediate steam turbine receiving steam exhausted from the high pressure steam turbine and exhausting low pressure steam; a low pressure steam turbine receiving low pressure steam exhausted from the intermediate steam turbine, and a drive shaft for the low pressure steam turbine connected to a clutch and the clutch is releasably coupled to a power generator, wherein the clutch has a first position in which power from the low pressure steam turbine is applied to the power generator and a second position in which power from the low pressure steam turbine is not applied to the generator. 
         [0008]    A method has been developed for power generation using a generator, an elevated pressure steam turbine, a low pressure steam turbine and a clutch coupled to a drive shaft of the low pressure steam turbine, the method comprising: applying low pressure steam to the low pressure steam turbine; driving the generator by the low pressure steam turbine while the clutch is closed, and opening the clutch to disengage the low pressure steam turbine from the generator. 
         [0009]    The method may further comprise closing a first valve to terminate the application of low pressure steam to the low pressure steam turbine and opening a second valve to direct low pressure steam to a process extraction device, wherein the first valve is closed and the second valve is open while the clutch is open. In the method, the low pressure steam turbine may be a first low pressure steam turbine and the method further comprises: applying low pressure steam to the second low pressure steam turbine during the application of low pressure steam to the first low pressure steam turbine; driving the generator by the second low pressure steam turbine in addition to the driving of the generator by the first low pressure steam turbine, and continuing to drive the generator by the second low pressure steam turbine, while the clutch is open. Further, the opening of the clutch may disengage a drive shaft for the first low pressure steam turbine from a drive shaft for the second low pressure steam turbine. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]      FIG. 1  is a schematic diagram of a power generation system including steam turbines having a clutch coupling. 
           [0011]      FIG. 2  is a schematic diagram of another power generation system similar to the power generation system shown in  FIG. 1 , except the other system has a single pair of low pressure steam turbines. 
           [0012]      FIG. 3  is a schematic diagram of a cross-compound power generation system having a first drive shaft(s) with a high pressure steam turbine and an intermediate pressure steam turbine that collectively drive a first generator, and a second drive shaft(s) with low pressure steam turbines that drive a second generator, wherein at least one of the low pressure steam turbines is coupled by a clutch to the second drive shaft(s). 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0013]      FIG. 1  is a schematic diagram of a power generation system  10  including an electrical power generator  12  providing electricity to a load  13 , such as an electrical power utility or grid. The generator is rotationally driven by a series of steam turbines including a high pressure steam turbine (HP)  14 , an intermediate pressure steam turbine (IP)  16 , a first pair of low pressure steam turbines (LPA)  18  and a second pair of low pressure steam turbines (LPB)  20 . The generator and steam turbines are connected along a common drive shaft assembly  22 , which may be two or more coaxial drive shafts coupled together. 
         [0014]    High pressure steam, e.g., 2,500 pounds-per-square-inch (psi) at a temperature of 1,050 degrees Fahrenheit (566 degrees Celsius) from a boiler  13  is provided to the inlet of the high pressure steam turbine. The reaction blades (buckets) and steam passages in the high pressure steam turbine tend to be small as compared to the reaction blades and steam passages in the intermediate steam turbine. The reaction blades and steam passages in the low pressure steam turbines tend to be larger than those in the intermediate steam turbine. Steam exhausted from the high pressure turbine passes through a reheater  15 , e.g., to be reheated to 1,050 degrees Fahrenheit and flows to the intermediate pressure steam turbine. Low pressure steam, e.g., below 700 psi and preferably at or below 200 psi and 700 degrees Fahrenheit (370 degrees Celsius), is provided from the intermediate pressure steam turbine  16  through a low pressure steam conduit  30  to the low pressure steam turbines  18 ,  20 . 
         [0015]    A planetary clutch  24  couples the drive shafts of the pair of low pressure turbines (LPA, LPB)  18 ,  20 . The planetary clutch allows the second pair of low pressure turbines (LPB) to be disengaged from the first pair of low pressure turbines (LBA)  18  and the other steam turbines and generator  12  in the power generation system  10 . 
         [0016]    A first low pressure steam valve  32  and an isolation low pressure steam valve  34  in the conduit  30  may be opened to allow steam to flow to the second pair of low pressure steam turbines  20  and closed to shut off steam to the second pair of low pressure steam turbines. The isolation valve  34  may have an open position and a closed, and no intermediate positions. The first low pressure steam valve may have open and closed positions, and intermediate positions to regulate the flow of low pressure steam through the conduit  30  and to the low pressure steam turbine. These low pressure steam valves  32 ,  34  may be closed in conjunction with opening the clutch  24  to disengage the drive shaft of the second pair of low pressure steam turbines from the drive shafts of the other steam turbines. The second pair of low pressure steam turbines  18  may be disengaged while the load  13  is relatively low and power from the second pair of steam turbines is not needed. 
         [0017]      FIG. 2  shows a power generation system  40  similar to the power generation system  10 , except with respect to the low pressure steam turbines  42 . System  40  has a single pair of low pressure steam turbines  42  having a drive shaft  44  coupled to a planetary clutch  46  that engages the drive shaft  22  of the intermediate pressure steam turbine  16 . A first valve  48  governs the flow of steam to the pair of low pressure steam turbines  42 . A second valve  50  directs steam to an external process  52 , while the first valve is closed. 
         [0018]    In operation, the first valve is open and the second valve is closed when the clutch is closed to couple the drive shaft  44  of the low pressure steam turbines  42  to drive the generator  12  in cooperation with the high pressure steam turbine  14  and the intermediate pressure steam turbine  16 . When the load demand on the generator  12  is low, the low pressure steam turbines  42  are disengaged by opening the clutch, closing the first valve  48  to shut off the flow of low pressure steam to the low pressure steam turbines and opening the second valve  50  to direct the low pressure steam to a process extraction device  52 , such as steam recirculation conduits extending through a boiler providing steam for the high pressure steam turbine or an other steam heated or driven device nearby the low pressure steam turbine. 
         [0019]      FIG. 3  is a schematic diagram of a cross-compound power generation system  60  having a first drive shaft(s)  62  with a high pressure steam turbine  14  and an intermediate pressure steam turbine that collectively drive a first generator  64 . The low pressure steam turbines include a first pair of low pressure steam turbines  66  and a second pair of low pressure steam turbines  68  are connected to a common drive shaft(s)  70  that drive a second generator  72 . A planetary clutch  74  allows the first pair of low pressure steam turbines  66  to be disengaged from the second pair of low pressure steam turbines and the generator. The first pair of low pressure steam turbines may be disengaged when there is a low load demand on the second generator  72 . 
         [0020]    In conjunction with the operation of the clutch  74 , valves are operated to control the flow of low pressure steam from the intermediate pressure steam turbine  16  to the low pressure steam turbines  66 ,  68  and to a process extraction device  52 . First and second steam valves  76 ,  78  turn on and turn off low pressure steam to each, respectively, of the first and second pairs of low pressure steam turbines. Both steam valves  76 ,  78  are open to allow steam to flow to both pairs of low pressure steam turbines  66 ,  68 , while the clutch is closed so that the common drive shaft(s)  70  are coupled together and both pairs of low pressure steam turbines  66 ,  68  drive the second generator  72 . To disengage the first pair of low pressure steam turbines, the clutch  74  is opened and the first steam valve  76  is closed to shut off low pressure steam to the first pair of low pressure steam turbines  66 . When the first steam valve  76  is closed, the second steam valve  78  remains open and the third steam valve  80  is opened to direct low pressure steam to the process extraction device. 
         [0021]    The clutch and low pressure steam valves disclosed herein may be arranged to disengage low pressure steam turbines during certain operational conditions, such as when the load demand on the generator(s) is well below the capacity of the steam turbines that drive the generator(s). When the load is below capacity, the clutch and low pressure steam valves may be operated to disengage at least one low pressure steam turbine from the power generation system. The efficiency of the system is increased by allowing the remaining low pressure steam turbine(s), if any, to operate at a higher power output and hence higher capacity than if all of the low pressure steam turbines were engaged and operating at below capacity and hence lower efficiency. The disengaged steam turbine can be idled so that it is ready to be reengaged to the power system when needed, such as when the load demand increases. 
         [0022]    While the invention has been described in connection with what is presently considered to be the most practical and preferred embodiment, it is to be understood that the invention is not to be limited to the disclosed embodiment, but on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims.