Abstract:
Apparatus for electric power generation. A system includes a boiler for heating a fluid, the boiler directing a first portion of the heated fluid to a turbine for the generation of electric power and a second portion of the heated fluid to a thermoelectric (TE) generator, and a condenser connected to the turbine that condenses hot fluid emitted from the turbine and feeds the condensed fluid to the TE generator, the TE generator generating electric power from a difference in temperature of the second portion of the heated fluid and the condensed fluid from the turbine.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    The invention generally relates to the generation of energy, and more specifically to electric power generation. 
         [0002]    In general, electricity is produced at an electric power plant. Some fuel source, such as coal, oil, natural gas, or nuclear energy produces heat. The heat is used to boil water to create steam. The steam under high pressure is used to spin a turbine. The spinning turbine interacts with a system of magnets to produce electricity. The electricity is transmitted as moving electrons through a series of wires to homes and business. 
         [0003]    A by-product of electrical power generation is heat. The efficiency of any system that generates heat as a by-product can be greatly improved by recovering or reducing the energy lost as heat. 
       SUMMARY OF THE INVENTION 
       [0004]    The following presents a simplified summary of the innovation in order to provide a basic understanding of some aspects of the invention. This summary is not an extensive overview of the invention. It is intended to neither identify key or critical elements of the invention nor delineate the scope of the invention. Its sole purpose is to present some concepts of the invention in a simplified form as a prelude to the more detailed description that is presented later. 
         [0005]    The present invention provides methods and apparatus for electric power generation. 
         [0006]    In general, in one aspect, the invention features a system including a boiler for heating a fluid, the boiler directing a first portion of the heated fluid to a turbine for the generation of electric power and a second portion of the heated fluid to a thermoelectric (TE) generator, and a condenser connected to the turbine that condenses hot fluid emitted from the turbine and feeds the condensed fluid to the TE generator, the TE generator generating electric power from a difference in temperature of the second portion of the heated fluid and the condensed fluid from the turbine. 
         [0007]    In another aspect, the invention features a system including a feed water pump, a line linking the feed water pump to a boiler, the boiler heating cold fluid from the feed water pump to produce hot fluid, a line linking the boiler to a turbine and a feed water reheater, the line providing a first portion of the hot fluid from the boiler to the turbine and a second portion of the hot fluid from the boiler to the feed water reheater, and a first thermoelectric (TE) unit for receiving hot fluid from the feed water reheater and condensate from the condenser, the first TE unit generating electric power from a difference between a temperature of the hot fluid from the feed water reheater and the temperature of the condensate from the condenser. 
         [0008]    In still another aspect, the invention features a method including, in a system including a boiler linked to a turbine, enabling a thermoelectric (TE) generator to receive a boiler generated hot fluid from the boiler and a turbine and condenser generated cold fluid from the turbine and a condenser and generate electric power from a difference between a temperature of the boiler generated hot fluid and a temperature of the turbine generated cold fluid. 
         [0009]    In still another aspect, the invention features a method including, in a power generation system, extracting high temperature fluid from a heat exchanger, extracting cold feed water before it is reheated and pumped into the heat exchanger, generating electrical power from a difference in a temperature of the extracted high temperature fluid and a temperature of the extracted cold feed water in a thermoelectric (TE) generator, capturing any thermal energy discharged by the TE generator, and sending the thermal energy back to the heat exchanger. 
         [0010]    Other features and advantages of the invention are apparent from the following description, and from the claims. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0011]    The invention will be more fully understood by reference to the detailed description, in conjunction with the following figures, wherein: 
           [0012]      FIG. 1  is a block diagram of an exemplary power generation system. 
           [0013]      FIG. 2  is a block diagram of an exemplary power generation system. 
           [0014]      FIG. 3  is a block diagram of one embodiment of the present invention. 
           [0015]      FIG. 4  is an exemplary chart illustrating thermoelectric module cost and power output as a function of steam flow. 
           [0016]      FIG. 5  is an exemplary chart illustrating an estimate of a performance improvement achievable using one embodiment of the present invention. 
           [0017]      FIG. 6  is a block diagram of another embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0018]    The subject innovation is now described with reference to the drawings, wherein like reference numerals are used to refer to like elements throughout. In the following description, for purposes of explanation, numerous specific details are set forth in order to provide a thorough understanding of the present invention. It may be evident, however, that the present invention may be practiced without these specific details. In other instances, well-known structures and devices are shown in block diagram form in order to facilitate describing the present invention. 
         [0019]    As used herein, the term “or” is intended to mean an inclusive “or” rather than an exclusive “or.” That is, unless specified otherwise, or clear from context, “X employs A or B” is intended to mean any of the natural inclusive permutations. That is, if X employs A; X employs B; or X employs both A and B, then “X employs A or B” is satisfied under any of the foregoing instances. Moreover, articles “a” and “an” as used in the subject specification and annexed drawings should generally be construed to mean “one or more” unless specified otherwise or clear from context to be directed to a singular form. 
         [0020]    In general, thermodynamic cycles can be divided into two general categories, i.e., power cycles, which produce a net power output, and refrigeration and heat pump cycles, which consume a net power input. Furthermore, thermodynamic power cycles can be categorized as gas cycles and vapor cycles. In gas cycles, a working fluid remains in a gas phase throughout an entire cycle. In vapor cycles, a working fluid exits as vapor phase during one part of a cycle and as liquid phase during another part of the cycle. 
         [0021]    Steam power plants run vapor power cycles with water as the working fluid. The vapor power cycle is often referred to as a “Rankine cycle.” 
         [0022]    As shown in  FIG. 1 , an exemplary vapor power plant  10 , which can generate electrical power by using fuels such as coal, oil or natural gas, includes a subsystem  12 , subsystem  14 , subsystem  16 , and subsystem  18 . Subsystem  12  involves energy conversion from heat to work and subsystem  14  involves an energy source required to vaporize the fluid, e.g., water. Subsystem  16  is an electric generator  20  and subsystem  18  is a cooling water system  22 . The thermodynamic cycle in  FIG. 1  is called the Rankine cycle. 
         [0023]    As shown in  FIG. 2 , subsystems  12  and  14  include a boiler  30 , a turbine  32 , a condenser  34  and a pump  36 . Fuel, burned in the boiler  30 , heats water to generate steam (i.e., subsystem  14  of  FIG. 1 ). This steam is used to run the turbine  32  that powers the generator  20  (subsystem  16  of  FIG. 1 ). Electrical energy is generated when the generator windings rotate in a magnetic field (subsystem  16  of  FIG. 1 ). After the steam leaves the turbine  32 , it is cooled to its liquid state in the condenser  34  by transferring heat to the cooling water system  22  (subsystem  18  of  FIG. 1 ). The liquid is pressurized by a pump  36  prior to going back to the boiler  30 . 
         [0024]    The four components  30 ,  32 ,  34  and  36  associated with the Rankine cycle are steady-flow devices and can be analyzed as steady-flow process. The kinetic and potential energy changes of water are small relative to the heat and work terms, and thus neglected. 
         [0025]    The pump  36  pressurizes the liquid water from the condenser  34  prior to going back to the boiler  30 . Assuming no heat transfer with the surroundings, the energy balance in the pump  36  is: 
         [0000]    
       
      
       w 
       pump,in 
       =h 
       2 
       −h 
       1  
      
     
         [0026]    Liquid water enters the boiler  30  and is heated to a superheated state in the boiler  30 . The energy balance in the boiler  30  is: 
         [0000]    
       
      
       q 
       in 
       =h 
       3 
       −h 
       2  
      
     
         [0027]    Steam from the boiler  30 , which has an elevated temperature and pressure, expands through the turbine  32  to produce work and then is discharged to the condenser  34  with relatively low pressure. Neglecting heat transfer with the surroundings, the energy balance in the turbine  32  is: 
         [0000]    
       
      
       w 
       turbine,out 
       =h 
       3 
       −h 
       4  
      
     
         [0028]    Steam from the turbine  32  is condensed to liquid water in the condenser  34 . The energy balance in the condenser  34  is: 
         [0000]    
       
      
       q 
       out 
       =h 
       4 
       −h 
       1  
      
     
         [0029]    For the entire cycle, the energy balance can be obtained by summarizing the four energy equations above, which yield: 
         [0000]      ( q   in -q out )−( w   turbine,out   −w   pump,in )=0
 
         [0030]    The thermal efficiency of the Rankine cycle is determined from: 
         [0000]      η th   =w   net,out   /q   in =1 −q   out   /q   in  
 
         [0031]    where the net work output from the cycle is: 
         [0000]    
       
      
       w 
       net,out 
       =w 
       turbine,out 
       −w 
       pump,in  
      
     
         [0032]    The net work output may be drastically improved with the addition of a thermoelectric (TE) generator. In general, a TE generator is a semiconductor-based electronic component that converts heat (temperature differences) into electrical energy using a phenomenon called the “Seebeck Effect.” ATE generator generally includes two or more elements of n- and p-type doped semiconductor material that are connected electrically in series and thermally in parallel. These thermoelectric elements and their electrical interconnects typically are mounted between two ceramic substrates. The substrates hold the overall structure together mechanically and electrically insulate the individual elements from one another and from external mounting surfaces. Examples of thermoelectric materials that may be used include, but are not limited to, bismuth telluride, lead telluride, and silicon-germanium. 
         [0033]    As shown in  FIG. 3 , a first exemplary electric power generation system  100  includes a boiler  102 . Fluid within the boiler  102  is heated, and steam exits through an output line  104  to a turbine  106  and as a hot fluid through an output line  108  to a thermoelectric (TE) generator  110 , sometimes referred to as a TE unit. The TE generator  110  may include one or more thermoelectric generators or other thermoelectric modules and thus when referred to herein, the TE generator  110  need not consist solely of a single TE generator or module. Example hot fluids include hot water, steam, superheated steam, and so forth. Although  FIG. 3  shows a single output line exiting the boiler which splits into a turbine input line  104  linked to the turbine  106  and a TE generator input line  108  linked to the TE generator, alternatively the lines  104  and  108  may be implemented as lines that exit the boiler  102  separately. Steam entering the turbine  106  causes elements within the turbine  106  to rotate. 
         [0034]    Extractor  112  extracts steam from the turbine  106 , which is fed into an open heater  116 , enabling steam from the extractor  112  to mix with and heat feed water with the intent of increasing an overall system efficiency. Although one extractor  112  is shown in  FIG. 3  for purposes of example, the system  100  may include any number of extractors, such as one, three, or more extractors. Fluid heated by the open heater  116  is outputted to a pump  122 , which feeds the heated feed water back into the boiler  102 . 
         [0035]    Steam and some condensate exiting the turbine  106  also enters a condenser  118 , where it is condensed at a constant pressure and temperature to become a liquid. A condenser output line  120  provides condensed fluid to the TE generator  110 . 
         [0036]    A temperature difference in the TE generator  110  created by hot fluid from the boiler  102  through output line  108  and condensate from the condenser  118  flowing through condenser output line  120  results in the generation of electric power through the Seebeck Effect. 
         [0037]    An exhaust of hot fluid from a hot side of the TE generator  110  through output line  123  to open heater  116  and exhaust of condensate on a cold side of the TE generator  110  through output line  124  to the open heater  116  captures heat not converted directly to electricity in the TE generator  110 , thus enabling the heat to be recycled and reutilized. 
         [0038]    Other implementations may include, for example, any one or more of flow control and pressure control valves, closed heaters, deaerators, flash tanks, heat exchangers, desuperheaters, pumps, flow restrictors, reheaters, and so forth. 
         [0039]    The thermal efficiency of a thermoelectric module in a TE unit can be defined as the percentage of heat entering the thermoelectric module that is actually converted directly to electricity. Therefore a thermal efficiency of 6% means that 6% of the heat flux at the hot surface of the thermoelectric module is converted directly to electricity. The balance of 94% is transferred to the cold medium. The Thermal efficiency of a BiTe thermoelectric generator is generally low, less than 6%, because heat rejected by the generator to the cold medium is considered to be irreversibly lost. Embodiments of the present invention place the thermoelectric generator  110  in a Rankine Cycle such that heat rejected by the thermoelectric generator  110  is not lost but returned to the boiler  102  and where the role of the boiler  102  is to replace the energy converted to electric power in both the TE generator  110  and the turbine generator  106  and replace any thermal energy lost to the environment. The resulting thermal efficiency of the subsystem within the Rankine Cycle of the TE generator  110  coupled with that proportion of the boiler  102  that replaces heat converted to electricity in the TE generator  110  is effectively near 100%. Embodiments of the present invention, therefore, provide a significant positive impact on overall system efficiency, fuel consumption, stack emissions, and waste heat. 
         [0040]    Implementations of using hot fluid to feed the TE generator  110  can be adapted for use in all types of power plants, including gas turbine power plants, fossil fired steam power plants (e.g., coal, natural gas, and oil), nuclear power plants (e.g., boiling water reactor (BWR) and pressurized water reactor (PWR)), combined cycle power plants, co-generation power plants, integrated gasification combined cycle (IGCC) power plants, and so forth. 
         [0041]    Extraction of hot fluid used to feed the TE generator  110  can originate from any one or more or multiple locations within the overall system  100 . For example, in power plants with a furnace/boiler arrangement (e.g., fossil fired steam power plants), hot fluid may be obtained from a reheater, steam exhausted from the high pressure turbine prior to entering the reheater, main steam (superheated) flowing to a HP Turbine, steam leaving a steam drum before entering the superheater, steam from the steam drum, steam leaving the reheater before entering the IP turbine, steam leaving a reheater before entering the LP turbine, hot feed water before entering the boiler, hot water leaving the economizer, hot water from the steam drum, and so forth. 
         [0042]    In power plants with a heat recovery steam generator (or boiler), hot fluid may be obtained from a reheater, feed water entering a low pressure economizer, feed water leaving the low pressure economizer, steam leaving a low pressure evaporator, steam vented to atmosphere, feed water entering a high pressure economizer, feed water leaving the high pressure economizer, steam leaving a high pressure evaporator, steam leaving a superheater, steam leaving a desuperheater, and so forth. 
         [0043]    In nuclear power plants (e.g., boiling water reactors and pressurized water reactors), hot fluid can be obtained from main steam out of a boiling water reactor before entering a high pressure turbine, main steam out of a steam generator before entering a high pressure turbine on a pressurized water reactor, and so forth. 
         [0044]    Equipment used between a point of extraction and the TE generator  110  to regulate temperature, flow, pressure or steam quality can include a flash tank, a heat exchanger, a desuperheater, a flow control valve, a pressure regulating valve, a pump, one or more flow restrictors, one or more reheaters, and so forth. 
         [0045]    As shown in  FIG. 4 , a chart  400  illustrates the relationship between a cost of the thermoelectric modules in a TE generator and steam flow to a TE unit for a 46 MW plant, assuming thermoelectric modules are purchased at $2.00 per watt. Also shown is the electric power produced by the TE unit as a function of steam flow. For a 46 MW power plant with total steam flow to the turbine at 350,000 lbm per hour, at 90,000 lbm per hour of steam flow to the TE unit, the turbine produces almost 780 KW and the thermoelectric modules of the TE unit cost $2,000/KW. 
         [0046]    As shown in  FIG. 5 , a chart  500  illustrates the benefits to a TE unit integrated into a power plant where power produced by the TE unit is offset by an equivalent reduction in turbine generator output and total plant output remains unchanged. 
         [0047]    At 90,000 lbm per hour of steam flow to the TE unit, the TE unit produces 780 KW or approximately 1.7% of a total plant output. Thus, benefits to the plant include total fuel savings of 1.3%, a reduction in waste heat flowing from a condenser to a cooling tower of 2%, and an overall plant efficiency gain of almost 0.5%. 
         [0048]    What is also illustrated in  FIG. 4  and  FIG. 5  is a point of diminishing return for both steam flow to the TE unit as well as for the size of the TE unit for a given plant. This limitation is related to the fixed rate of condensate flow from the condenser and the resulting decline in a mean temperature difference between hot and cold fluids in the TE unit and resulting lower conversion efficiency of a thermoelectric module in a TE unit as steam flow (hot side) to the TE unit is increased without a corresponding increase in condensate flow. 
         [0049]    As shown in  FIG. 6 , a second exemplary electric power generation system  600 , where solid flow lines indicate hot fluid and dashed flow lines indicate cold fluid, includes a feed water pump  602  connected to a cold fluid line  604  that includes a line  606  to a feed water reheater  618  and a bypass  607 . As used herein, the term “reheater” may refer to any kind of heat exchanger. The bypass  607  enables flow of feed water to a boiler  608  and flow control valve  611 . The line  606  enables flow of feed water to the feed water reheater  618  and flow control valve  610 . A boiler  608  heats cold fluid to generate hot fluid, such as, for example, hot water, saturated steam, or superheated steam. A main hot fluid line  612  exiting the boiler  608  includes a bypass  614 . The main hot fluid line  612  enables steam to flow into a turbine  616  and the bypass  614  to the feed water reheater  618 . A dry vapor (e.g., steam) expands through the turbine  616 , generating power. This decreases the temperature and pressure of the vapor, and some condensation may occur. 
         [0050]    Hot fluid flows from the boiler  608  through output lines  612  and  614  or  615  to the feed water reheater  618 . Hot fluid from the feed water reheater  618  then flows through output line  628  to a hot side of a TE unit  630 . Hot fluid exhausted by the hot side of TE unit  630  flows to a hot side of TE unit  634  through output line  632 . Hot fluid exhausted by the hot side of TE unit  634   632  flows to an open heater  624  through output line  639 . 
         [0051]    Hot fluid exhausted by the turbine  616  enters a condenser  623 , where it is condensed at a constant pressure and temperature to become a saturated liquid. The pressure and temperature of the condenser  623  are fixed by a temperature of cooling coils within the condenser  623  as the fluid is undergoing a phase-change. 
         [0052]    Condensate from the condenser  623  is pumped by a condensate pump  640  to a cold side of TE unit  630  through output line  641 . Condensate exhausted from the cold side of TE unit  630  flows through output line  636  to a cold side of TE unit  634 . Condensate exhausted from the cold side of TE unit  634  flows to a closed heater  626  through output line  637 . Alternatively, the cold fluid may flow from unit  634  to unit  630 , even while the hot fluid flows from unit  630  to unit  634 . 
         [0053]    TE Unit  630  uses a temperature difference between the high temperature fluid entering though line  628  and exhausting though output line  632  and the relatively colder fluid entering though line  641  and exhausting through line  636  to produce electric energy through the Seebeck Effect. 
         [0054]    TE unit  634  uses the temperature difference between the high temperature fluid entering though line  632  and exhausting though output line  639  and the relatively colder fluid entering though line  636  and exhausting through line  637  to produce electric energy through the Seebeck Effect. 
         [0055]    Condensate flowing though the cold side of TE unit  630  and TE unit  634  is heated by a thermal energy flowing from the hot side fluid and not converted to electric energy through the Seebeck Effect. 
         [0056]    Condensate entering the closed heater  626  is further heated by steam extracted  622  from the turbine  616 . Condensate then flows to the open heater  624  through output line  638  where it mixes with hot fluids exhausted from TE unit  634  and is further heated by steam extractor  620  from the turbine  616 . Line  642  enables the flow of hot fluid extracted  622  from the turbine  616  to heat condensate in the closed heater  626  to flow to the open heater  624 . 
         [0057]    Feed water collected in the open heater  624  is pumped to the boiler  608  and feed water reheater  618  by the feed water pump  602 . 
         [0058]    Multiple steam extractors  620 ,  622  extract hot fluid from the turbine  616  and enable the extracted hot fluid to enter the open heater  624  and the closed heater  626 , respectively. 
         [0059]    Design of the systems described herein increases power plant efficiency, electric power output, fuel efficiency, reduces waste heat produced and gas emissions in relation to a conventional power plant. This is achieved using the thermal energy of hot fluid produced by the boiler on the hot side and condensate and/or makeup feed fluid on the cold side and recapturing (e.g., in open or closed heaters) any thermal energy not converted to electric energy in the TE generator. 
         [0060]    The foregoing description does not represent an exhaustive list of all possible implementations consistent with this disclosure or of all possible variations of the implementations described. A number of implementations have been described. Nevertheless, it will be understood that various modifications may be made without departing from the spirit and scope of the systems, devices, methods and techniques described here. For example, various forms of the flows shown above may be used, with steps re-ordered, added, or removed. Accordingly, other implementations are within the scope of the following claims.