Abstract:
A power plant ( 10 ) having a primary water-steam cycle ( 11 ) that generates a primary electrical load via a generator ( 101 ) and a recovery cycle ( 12 ) that generates a secondary electrical load via a generator ( 102 ). The overlap between the cycles ( 11, 12 ) occurs in the condensing section ( 40 ). An evaporator ( 45 ) transfers heat from the exhaust line ( 41 ) of the primary cycle  11 ) to the conveying line ( 44 ) of the recovery cycle ( 12 ).

Description:
RELATED APPLICATION 
       [0001]    This application claims priority under 35 U.S.C. §119(e) to U.S. Provisional Patent Application No. 61/238,357 filed on Aug. 31, 2009. The entire disclosure of this application is hereby incorporated by reference. To the extent that inconsistencies may occur between the present application and the incorporated application, the present application governs interpretation to the extent necessary to avoid indefiniteness and/or clarity issues. 
     
    
     BACKGROUND 
       [0002]    A power plant converts fuel (e.g., coal, oil, nuclear, etc.) into electrical kilowatts via a closed steam cycle. In a typical cycle, feedwater is superheated into high pressure steam, and then routed to the high pressure (HP) turbine. The steam exiting the HP turbine can be reheated and then passed (as superheated steam) through the intermediate pressure (IP) turbine. From the IP turbine the steam passes to the low pressure (LP) turbine whereat it becomes saturated steam. The steam exits LP turbine into a condenser whereat it is condensed into liquid, pumped through cascading heaters, and returned to the boiler to repeat the cycle. Conventional wisdom suggests that the lower the outlet pressure of the LP turbine, the more efficient the conversion and the better the heat rate. 
       SUMMARY 
       [0003]    A power plant is provided wherein the condensing section is constructed to convert heat into usable electricity via a secondary generator. This results in optimum power plant operation going completely against the traditional approach of constantly striving to reduce LP-turbine-exhaust pressure in the interest of efficiency. The water-steam cycle is purposely operated to provide a high LP-outlet pressure (e.g., at or above 5 psia and more preferably above 15 psia) to capitalize on the heat expelled during condensation. Instead of this heat being lost to a lake or a cooling tower, it serves as the heat source for separate heatpump system. 
     
    
     
       DRAWINGS 
         [0004]      FIG. 1  is a schematic diagram of a power plant. 
           [0005]      FIG. 2  is a schematic diagram of the condensing section of the power plant. 
       
    
    
     DESCRIPTION 
       [0006]    Referring now to the drawings, and initially to  FIG. 1 , a power plant  10  is schematically shown. The power plant  10  incorporates a water-steam cycle  11  used to generate a primary amount of electricity. The plant  10  also incorporates a refrigerant recovery cycle  12  used to generate electricity from the heat normally expelled during condensation. 
         [0007]    In the primary cycle  11 , feedwater is superheated in a boiler  21 . The superheated high pressure steam flows to the HP turbine  31  and the HP-turbine-exhaust steam is reheated in boiler  22  (which may be part of the same furnace structure as the superheater boiler  21 ). The reheated steam passes to the inlet of the IP turbine  32 . The exhaust steam from the IP turbine  32  (usually still superheated steam) then enters the LP turbine  33  whereat it becomes wet steam. The wet steam leaving the LP turbine flows to the condensing section  40  (via line  41 ) whereat it is condensed into liquid water. 
         [0008]    The condensate flows to the suction side of the hotwell pump  51  (via line  42 ) whereat it is pumped through heaters  61 - 64 . The heaters  61 - 64  have crossflows supplied by extracted steam from descending stages of the LP turbine  33 . The crossflow drains of the heaters  61 - 64  cascade to the upstream heater, with the first heater  61  draining into the condensate section  40  (via line  43 ). 
         [0009]    The condensate exiting the heater  64  is delivered to the dearator  71  and thereafter to the suction side of the boiler-feed-water pump  81 . The pump  81  pushes the feedwater through the heaters  91 - 92  and back to the boiler  21 . The heater  91  has a crossflow supply extracted from the IP turbine  32  and a crossflow drain to the dearator  71 . The heater  92  has a crossflow supply extracted from the HP turbine  31  and a crossflow drain to the heater  91 . 
         [0010]    When the exiting feedwater from the last heater  92  is returned to the superheater boiler  21 , the cycle is repeated. 
         [0011]    Referring now to  FIG. 2 , the condensing section  40  is shown in more detail. The condensing section  40  incorporates part of the primary water-steam cycle  11  (e.g., lines  41 - 43  pass through this section). The condensing section  40  also encompasses the refrigerant recovery cycle  12 , which absorbs heat expelled by line  41  as wet steam from the LP turbine exhaust is condensed into liquid. 
         [0012]    The recovery cycle  12  includes a refrigerant line  44  carrying a fluid that can be evaporated within the expected temperature range of the wet steam exiting the LP turbine  33 . In most instances, this will be greater than 160° F., greater than 180° F., greater than 200° F. and/or greater than 220° F. As is explained in more detail below, the primary cycle  10  is purposely operated so as to have a higher LP exhaust pressure and thus (because the steam is wet at this stage) a higher temperature. 
         [0013]    The recovery cycle  12  further comprises an evaporator  45  that places the recovery line  44  in heat-transfer relationship with exhaust line  41  from the LP turbine  33 . A turbine  46  is situated downstream of the evaporator  45 , a compressor  47  is situated downstream of the turbine  46 , and a condenser  48  is situated downstream of the evaporator and an expander  49  is downstream of the condenser  48  (and upstream of the evaporator  45 ). 
         [0014]    The turbine string  31 - 33  of the primary cycle  11  is operably coupled to a generator  101  which produces the primary electrical output of the power plant  10  (e.g., more than 10 MW, more than 500 MW, more than 1000 MW, more than 1100 MW, more than 1300 MW, etc.) The turbine  46  of the recovery cycle  12  is operably coupled to a generator  102 . While the electricity generation of the generator  102  may be significantly less than that of generator  101  (e.g., less than 10%, less than 5% and/or less than 2% of that generated by generator  101 ), this electricity is produced from heat conventionally lost in the condensation section. 
         [0015]    The advantages of incorporating the recovery cycle  12  into a power plant are perhaps best explained by establishing a baseline back to conventional operation for comparison. In a traditional power-plant cycle, optimum performance is believed to occur at a condenser pressure of about 2.5 psia, which corresponds to a saturation temperature of about 100° F. and an enthalpy of about 1100 Btu/lb. Assume for the purposes of comparison that the power plant (when conventionally operated) has a respectable heat rate of 10,000 Btu/Kw and 1300 MW are when 1000 psig superheated steam is supplied to the HP turbine  31  at a rate of 14 MMlb/hr. (This corresponds to a 13,000 MMBtu/hr being provided to the turbine string  31 - 33 .) 
         [0016]    If the heat of vaporization is approximated at 1000 Btu/hr, about 14,000 mM Btu/hr must be rejected in the condensation section for the LP exhaust steam to liquefy (i.e., 14 MM lb/hr/1000 Btu/hr). Assuming that the recovery cycle  12  is presumed to have coefficient of performance of 3 (which is not overly generous), about 4700 MM Btu/hr can be recovered and turned into about 470 MW of additional power by the generator  102 . 
         [0017]    With the power plant  10 , optimum power plant operation may occur when parameters are adjusted to provide relatively high LP-outlet pressure (e.g., at or above 10 psia, 12 psia, 14 psia, 16 psia, 18 psia, 19 psia, etc.) to capitalize on the heat expelled during condensation. This is significantly greater than the LP-outlet pressures traditionally strived for in power-plant operation, specifically below 10 psia, below 5 psia, and/or about 2.5 psia (≈5″ mercury). 
         [0018]    Such a purposely higher LP outlet enthalpy will most likely result a reduction of MW production by the primary cycle  10 . For example, with an LP exhaust of 19 psia (about 1100 Btu/hr enthalpy) versus 2.5 psia (about 1150 Btu/hr enthalpy), about 700 mM Btu/hr (i.e., 50 Btu/lb*14 MMlb/hr) will not be converted by the primary cycle  10  into megawatts. Assuming a heat rate of 10,000 Btu/Kw, this translates into a loss 70 MW loss. 
         [0019]    The MW loss suffered by the primary cycle  10  will usually be more than offset by that gained by the recovery cycle  12 . For example, with a 70 MW loss by the primary cycle  10  and 470 MW gain by the recovery cycle  12 , the net additional power is about 400 MW. This means that 1700 MW can now be produced for the same heat input, which reflects a heat rate of less than 7700 Btu/Kw (i.e., 13,000 MMBtu/hr/1700 MW). This corresponds to 23% improvement in heat rate, in an industry where 5% improvements are considered economically significant. Moreover, the condensing section  70  of the present invention substantially removes seasonal fluctuations (due to changing ambient temperatures) from the efficiency equation. 
         [0020]    Although the power plant  10  and/or the condensing section  70  have been shown and described with respect to a certain embodiment or embodiments, it is obvious that equivalent alterations and modifications will occur to others skilled in the art upon the reading and understanding of this specification and the annexed drawings. In regard to the various functions performed by the above described elements (e.g., components, assemblies, systems, devices, compositions, etc.), the terms (including a reference to a “means”) used to describe such elements are intended to correspond, unless otherwise indicated, to any element which performs the specified function of the described element (i.e., that is functionally equivalent), even though not structurally equivalent to the disclosed structure which performs the function. In addition, while a particular feature of the invention may have been described above with respect to only one or more of several illustrated embodiments, such feature may be combined with one or more other features of the other embodiments, as may be desired and advantageous for any given or particular application.