Abstract:
A process for producing electrical power including the steps of: a) combusting a stoichiometric amount of a reactant in air in the presence of atomized water to obtain a gaseous mixture having a terminal temperature less than a maximum operating temperature of a gas turbine, b) feeding the gaseous mixture to the gas turbine to generate electrical power wherein a gas turbine exhaust exits the gas turbine, c) feeding the gas turbine exhaust stream into a boiler to generate superheated steam and a boiler exhaust stream, d) feeding the superheated steam to a steam turbine to generate electrical power, e) feeding the boiler exhaust stream to a heat exchanger condensing water, and f) circulating at least a portion of the condensed water to the combustion step a).

Description:
RELATED APPLICATION  
       [0001]     This application claims priority of U.S. Provisional Patent Application Ser. No. 60/564,818 filed Apr. 23, 2004, which is incorporated herein by reference. 
     
    
     BACKGROUND OF THE INVENTION  
       [0002]     1. Field of the Invention  
         [0003]     The invention relates to a process for producing electrical power, and more particularly, to a process for producing electrical power by combusting a stoichiometric amount of a reactant in the presence of atomized water.  
         [0004]     2. Description of the Related Art  
         [0005]     Modern power plants typically use a gas turbine to produce electrical power from a combusted fuel mixture. Typically the gas turbine includes a compressor section for pressurizing air which is mixed with a fuel and burned in one or more combustors.  
         [0006]     Typical combustors do not combust the fuel mixture and air in a stoichiometric ratio, as such combustion of an air fuel mixture results in very high temperatures within the combustor. The high temperatures can damage the turbine section of a gas turbine, as well as lead to increased amounts of nitrogen oxides produced by the combustion process.  
         [0007]     Attempts at limiting the temperature produced in a combustor include reacting air fuel mixtures in ratios considerably less than stoichiometric using excess amounts of air to cool the combustion gas to temperatures suitable for use in the turbine section. However, by introducing an excess amount of air into the combustion process, a large amount of energy or work is required by a compressor to compress the additional air, resulting in an over all loss of efficiency of producing electrical power.  
         [0008]     There is, therefore, a need in the art for a process for producing electrical power that combusts an air fuel mixture in an approximate stoichiometric ratio and limits the temperature of the combustion gases for use in a gas turbine, resulting in an overall increase in capacity of an electrical power plant.  
       SUMMARY OF THE INVENTION  
       [0009]     Accordingly, it is an object of the present invention to provide a process for producing electrical power by combusting a stoichiometric amount of a reactant and air; thereby, increasing an overall efficiency of a power plant.  
         [0010]     These and other objects of the present invention are accomplished by a process for producing electrical power including the steps of: a) combusting a stoichiometric amount of a reactant and air in the presence of atomized water to obtain a gaseous mixture having a terminal temperature less than a maximum operating temperature of a gas turbine, b) feeding the gaseous mixture to the gas turbine to generate electrical power wherein a gas turbine exhaust stream exits the gas turbine, c) feeding the gas turbine exhaust stream into a boiler to generate superheated steam and a boiler exhaust stream, d) feeding the superheated steam to a steam turbine to generate electrical power, e) feeding the boiler exhaust stream to a heat exchanger condensing water, and f) circulating at least a portion of the condensed water to the combustion step a). 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0011]      FIG. 1  is a schematic diagram of a first embodiment of the process using methane as a reactant for producing electrical power of the present invention;  
         [0012]      FIG. 2  is a schematic diagram of a second embodiment of the process using propane as a reactant for producing electrical power of the present invention;  
         [0013]      FIG. 3  is a schematic diagram of a third embodiment of the process using hydrogen as a reactant for producing electrical power of the present invention;  
         [0014]      FIG. 4  is a schematic diagram of an alternative first embodiment of the process using methane as a reactant for producing electrical power of the present invention.  
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0015]     Referring to  FIG. 1 , there is shown a schematic representation of a process  5  for producing electrical power of a first embodiment having methane as a reactant. In a first combustion step  10  of the process  5  for producing electrical power of the present invention, a stoichiometric amount of methane and compressed air is combusted in the presence of atomized water to obtain a gaseous mixture having a terminal temperature less than a maximum operating temperature of a gas turbine. Modern day gas turbines typically have an upper operating range of from 1150 to 1510 degrees Celsius dependant upon the materials used to form the gas turbine. The stoichiometric combustion of methane includes the reaction of one mole of methane with two moles of oxygen and eight moles of nitrogen yielding one mole of carbon dioxide, two moles of water and eight moles of nitrogen with a flame temperature of about 1918 degrees Celsius, well above the range of gas turbines outlined above. To regulate this temperature to an acceptable range, the combustion step includes providing atomized water to the combustion mixture resulting in a flame temperature less than the maximum operating temperature of the gas turbine.  
         [0016]     In a preferred aspect of the present invention, the atomized water has an initial droplet size in the range of from 30 microns to 200 microns; thereby, preventing damage to blades of a gas turbine by droplets having a large size. The atomized water regulates the temperature of the gaseous mixture by absorbing heat when it is vaporized from a liquid to a gaseous state. To assure that the liquid droplets of water are flash-evaporated, the droplets preferably contact a hot metallic surface. For example, metal screens or similar structures may be utilized to increase the surface or contact area for the liquid droplets; thereby regulating the temperature of the combustion stream.  
         [0017]     The combustion step of the process of the present invention preferably comprises two (or more) separate combustion steps  15 ,  20 . A first step  15  includes combusting a portion of the reactant (total reactant-x) with the total stoichiometric amount of air, in the presence of an amount of atomized water (y) to produce a first combustion stream  25  which has a temperature that exceeds an auto-ignition temperature of the reactant. The second combustion step  20  comprises combusting the remaining portion of the reactant (x) with the first combustion stream  25 , again in the presence of atomized water (total water-y) to obtain a gaseous mixture  30  that has a terminal temperature less than the maximum operating temperature of the gas turbine outlined above.  
         [0018]     Again referring to  FIG. 1 , there is shown a schematic representation of a 140 megawatt power plant utilizing methane as the reactant. A typical present day 140 megawatt power plant burns 13.89 pounds per second of methane with 790 pounds per second of compressed air to regulate the temperature of the combustion mixture. This amount of air greatly exceeds a stoichiometric amount, as used by the present invention. The first embodiment, disclosed in  FIG. 1 , burns 13.89 pounds per second of methane in a stoichiometric ratio with 251.7 pounds per second of air.  
         [0019]     As described above, the combustion step includes two separate stages or combustion steps  15 ,  20 . In a first combustion step  15 , 2.48 pounds per second of methane (total methane-x where 13.89&gt;x&gt;0) is combusted with 251.7 pounds per second of air in the presence of 8.2 pounds per second of atomized water (y where 88.4&gt;y&gt;0) yielding a first combustion stream  25  having a temperature of 709 degrees Celsius. The first combustion stream  25  having a temperature of 709 degrees Celsius is above the auto-ignition temperature of methane (705 degrees Celsius), thereby yielding a continuous self-sustaining combustion. The first combustion stream  25  is then combusted with 11.41 pounds per second methane (x) and 80.2 pounds per second atomized water (total water-y) yielding a gaseous mixture  30  having a terminal temperature of 1130 degrees Celsius at a pressure of 180 PSI. The gaseous mixture  30  is then fed to a gas turbine  35  where the gaseous mixture  30  is dropped to a pressure of 14.7 PSI including a temperature drop to 594 degrees Celsius; thereby, generating 127.6 megawatts of electric power. The gas turbine exhaust stream  40  exits at a temperature of 594 degrees Celsius and is fed to a boiler  55  to generate superheated steam  45  and a boiler exhaust stream  50 . The superheated steam  45  has a temperature of approximately 530 degrees Celsius, and a pressure of approximately 1250 PSI. The superheated steam  45  is fed to a steam turbine  60  to generate 28.45 megawatts of electrical power. The steam  45  is then condensed at  70  and recycled to the boiler  55 . The boiler exhaust stream  50  is fed to a heat exchanger  65  for condensing water. As can be seen from  FIG. 1 , a first portion  75  of the condensed water equaling 88.4 pounds per second is recycled to the combustion step  10  with the remaining portion of water  80  sent to a storage container  85  for use in other applications. The top stream  90  of the heat exchanger  65  emits to the atmosphere 6.984 pound moles of nitrogen per second, 0.86 pound moles carbon dioxide per second and 0.781 pound moles of water per second.  
         [0020]     The overall amount of atomized water necessary for maintaining the gaseous mixture  30  of the combustion step in the range of 1130 degrees Celsius is computed by calculating the overall heat of combustion produced for a given flow rate of reactant and calculating the amount of water necessary to absorb sufficient heat by vaporization to maintain the temperature in the range of 1130 degrees Celsius. The amount of water used in the first combustion step  15  is calculated by determining an amount of water necessary to produce a first combustion stream  25  having a temperature above the auto ignition temperature of the reactant.  
         [0021]     Referring to  FIG. 4 , there is shown an alternative embodiment of the first embodiment for producing electrical power having methane as the reactant. In the depicted alternative embodiment, the methane is added in a step-wise manner with five separate combustion steps  16 ,  17 ,  18 ,  19 ,  21 , as opposed to the two combustion steps  15 ,  20  of the first embodiment. While 5 combustion steps are described in the alternative embodiment of  FIG. 4 , it should be realized that other numbers of step-wise combustion steps may be used by the present invention.  
         [0022]     The rate of combustion of CH 4  is 2-3 orders of magnitude greater than the rate of evaporation of water droplets added to control the flame temperature. As a consequence, the flame temperature at the instant of ignition approaches 1900 degrees Celsius and results in the generation of an excessive concentration of NO. To limit the flame temperature to 1300 degrees Celsius a stepwise addition of CH 4  may be utilized.  
         [0023]     For a 5-step addition of CH 4 , as shown in  FIG. 4  and detailed in Table 1 appended at the end of the specification, the first combustion step  16  includes combusting 2.5 pounds per second CH 4  and 256.7 pounds per second air. The addition of 6.2 pounds per second liquid water reduces the top temperature of 1300 degrees Celsius to 710 degrees Celsius. The second combustion step  17  includes combusting the product stream of the first combustion step with 2.5 pounds per second CH 4 , and 31.0 pounds per second of liquid water to reduce the peak temperature to 709 degrees Celsius. The third combustion step  18  includes combusting the product stream of the second combustion step with 2.5 pounds per second CH 4 , and 29.4 pounds per second of liquid water to reduce the peak temperature to 721 degrees Celsius. The fourth combustion step  19  includes combusting the product stream of the third combustion step with 1.5 pounds per second CH 4  and no liquid water to produce a peak temperature of 870 degrees Celsius. The fifth combustion step  21  includes combusting 4.9 pounds per second CH 4  and no liquid water to produce a fifth product stream having a peak temperature of 1300 degrees Celsius.  
         [0024]     The fifth product stream corresponds to the gaseous mixture  30  of the first embodiment. At this point, the process of the first and alternative embodiments is the same. The fifth product stream, which is the same as the gaseous mixture  30  is fed to a gas turbine  35  to generate 133.3 megawatts of electric power. Table 2, appended at the end of the specification, details the flow rates, temperatures, and pressures of the alternative embodiment corresponding to the various components of the process shown in  FIG. 1 . The gas turbine exhaust stream  40  from the gas turbine is fed to a boiler  55  to generate superheated steam  45  and a boiler exhaust stream  50 . The superheated steam  45  is fed to a steam turbine  60  to generate 31.0 megawatts of electrical power. From the combined cycles, a total of 161.39 megawatts of power are generated, a gain of 15 percent over a conventional 140 megawatt plant.  
         [0025]     Additionally, 38.1 pounds per second CO 2  is produced by both a conventional plant and the alternative embodiment. However, 13 percent more CO 2  is generated per megawatt by the conventional power plant. As shown in  FIG. 4 , the terminal concentration of O 2  in the fifth combustion is very small, 0.5 pounds per second. This results in a very small concentration of NO released to the atmosphere.  
         [0026]     Referring to  FIG. 2 , there is shown a second embodiment  305  of the process for producing electrical power of the present invention. The second embodiment  305  utilizes propane as a reactant. As with the first embodiment, the propane is combusted in a first step  310  with air in a stoichiometric amount in the presence of atomized water to obtain a gaseous mixture having a terminal temperature less than the maximum operating temperature of the gas turbine. As can be seen in  FIG. 2 , the combustion step  310  preferably comprises two steps  315 ,  320 . In the first step  315 , 2.61 pounds per second of propane is combusted with 245.6 pounds per second air in the presence of 8.2 pounds per second atomized water, yielding a first combustion stream  325  having a temperature of 708 degrees Celsius. In a second combustion step  320 , 12.42 pounds per second of propane is combined with the first combustion stream  325  and 82.9 pounds per second of atomized water yielding a gaseous mixture  330  having a temperature of approximately 1123 degree Celsius at 180 PSI. The gaseous mixture  330  is fed to a gas turbine  335  and is subjected to a pressure drop to 14.7 PSI with a temperature of the turbine exhaust  340  of approximately 633 degrees Celsius. The gas turbine generates 124.3 megawatts of power. The 633 degree Celsius turbine exhaust stream  340  is fed to a boiler  355  for generating superheated steam  345  at a temperature of 530 degrees Celsius and a pressure of 1250 PSI. The superheated steam  345  is then fed to a steam turbine  360  generating 30.4 megawatts of power. The boiler exhaust stream  350  is fed to a heat exchanger  365  for condensing water. As with the first embodiment, a first portion  375  of the condensed water equaling 91.1 pounds per second is recycled to the combustion step  310  with the remaining portion  380  of 10.54 pounds per second of water being sent to a storage container  385 . The top stream  390  of the heat exchanger  365  comprises 6.91 pound moles of nitrogen per second, 1.014 pound moles of carbon dioxide per second and 0.779 pound moles of water per second that is released into the atmosphere. As with the previously described first embodiment, the second embodiment results in an increased capacity due to the significantly smaller amount of compressed air utilized as compared to common present day power plants. A further advantage of the process includes a nitrogen oxide emission of less that two parts per million by volume.  
         [0027]     Referring to  FIG. 3 , there is shown a third embodiment  405  of the present invention in which hydrogen is utilized as the reactant. As with the previously described embodiments, the combustion step  410  includes two steps  415 ,  420 . In the first step  415  one pound per second of hydrogen is combusted with 206.9 pounds per second of air in the presence of 21.85 pounds per second of atomized water, yielding a first combustion stream  425  having a temperature of 571 degrees Celsius. In the second combustion step  420 , 4.79 pounds per second of hydrogen is combined with the first combustion stream  425  and combusted in the presence of 73.0 pounds per second of atomized water, yielding a gaseous mixture  430  having a terminal temperature of 1121 degrees Celsius. The gaseous mixture  430  is fed to a gas turbine  435  and is subjected to a pressure drop to 14.7 PSI; thereby generating 121.1 megawatts of power. The gas turbine exhaust stream  440  at 628 degrees Celsius is fed to a boiler  455  generating superheated steam  445  at a temperature of 530 degrees Celsius and 1250 PSI. The superheated steam  445  is fed to a steam turbine  460 ; thereby generating 29.07 megawatts of power. The boiler exhaust stream  450  is fed to a heat exchanger  465  for condensing water. The water condensed includes a first portion  475  equaling 94.85 pounds per second which is recycled to the combustion step  410  and a second portion  480  equaling 41.42 pounds per second which is sent to a storage container  485 . The top stream  490  of the heat exchanger  465  emits 160.7 pounds per second of nitrogen gas and 10.28 pounds per second of water vapor to the atmosphere. As with the previously described embodiments, the third embodiment  405  limits the amount of compressed air utilized and thereby the amount of energy used for the compression, resulting in an increased capacity for producing electrical power. No CO 2  is generated.  
         [0028]     Comparing the cost of generating electrical power, one notes that the fuel cost is the same for any plant at any particular site. However, the capital costs are markedly lower for the stoichiometric plant utilizing the process of the present invention. The size and flow capacity of compressors and turbines is significantly reduced with a corresponding reduction in the amount of power needed to operate the compressors. For example, if the cost of a 500 megawatt gas turbine for a conventional power plant is $100,000,000, then the cost of the gas turbine for a 500 megawatt stoichiometric power plant is in the range of only $33,000,000. As a result, significant cost savings are achieved by the process of the present invention.  
         [0029]     The invention has been described in an illustrative manner, and it is to be understood that the terminology that has been used is intended to be in a nature of words of description rather than limitation.  
         [0030]     Many modifications and variations of the present invention are possible in light of the above teachings. It is therefore, to be understood that within the scope of the appended claims, the invention may be practiced other that as specifically described.  
                                                                                                                                                                 TABLE 1                                           COMPAIR           MXSTRM1           MIXSTRM2           INPUTAIR   REACTOR1   1CH4   1H2O   REACTOR2   2CH4   2H2O   REACTOR3           AIRCOMP   AIRCOMP   REACTOR1   REACTOR1   REACTOR1   REACTOR2   REACTOR2   REACTOR2           VAPOR   VAPOR   VAPOR   LIQUID   VAPOR   VAPOR   LIQUID   VAPOR                        Vapor Frac   1.00   1.00   1.00   0.00   1.00   1.00   0.00   1.00       Liquid Frac   0.00   0.00   0.00   1.00   0.00   0.00   1.00   0.00       Solid Frac   0.00   0.00   0.00   0.00   0.00   0.00   0.00   0.00       Mass Flow lb/sec       NITRO-01 (N 2 )   195.8   195.8   0.0   0.0   195.8   0.0   0.0   195.8       CARBO-01 (CO 2 )   0.0   0.0   0.0   0.0   6.8   0.0   0.0   13.6       WATER   0.0   0.0   0.0   6.2   11.7   0.0   31.0   48.3       METHA-01 (CH 4 )   0.0   0.0   2.5   0.0   0.0   2.5   0.0   0.0       OXYGE-01 (O 2 )   55.9   55.9   0.0   0.0   46.0   0.0   0.0   36.1       PROPA-01 (C 3 H 8 )   0.0   0.0   0.0   0.0   0.0   0.0   0.0   0.0       Total Flow   251.7   251.7   2.5   6.2   260.3   2.5   31.0   293.8       (lb/sec)       Temperature C.   15   371   30   30   710   30   30   709       Pressure atm   0.98   13.93   13.93   13.93   13.93   13.93   13.93   13.93       Pressure (psi)   14.4   204.8   204.8   204.8   204.8   204.8   204.8   204.8                                MIXSTRM3       MIXSTRM4                   3CH4   3H2O   REACTOR4   4CH4   REACTOR5   5CH4   MIXSTRM5           REACTOR3   REACTOR3   REACTOR3   REACTOR4   REACTOR4   REACTOR5   REACTOR5           VAPOR   LIQUID   VAPOR   VAPOR   VAPOR   VAPOR   VAPOR                            Vapor Frac   1.00   0.00   1.00   1.00   1.00   1.00   1.00           Liquid Frac   0.00   1.00   0.00   0.00   0.00   0.00   0.00           Solid Frac   0.00   0.00   0.00   0.00   0.00   0.00   0.00           Mass Flow lb/sec           NITRO-01 (N 2 )   0.0   0.0   195.8   0.0   195.8   0.0   195.8           CARBO-01 (CO 2 )   0.0   0.0   20.4   0.0   24.6   0.0   38.1           WATER   0.0   29.4   83.3   0.0   86.7   0.0   97.7           METHA-01 (CH 4 )   2.5   0.0   0.0   1.5   0.0   4.9   0.0           OXYGE-01 (O 2 )   0.0   0.0   26.2   0.0   20.2   0.0   0.5           PROPA-01 (C 3 H 8 )   0.0   0.0   0.0   0.0   0.0   0.0   0.0           Total Flow   2.5   29.4   325.7   1.5   327.2   4.9   332.1           (lb/sec)           Temperature C.   30   30   721   30   870   30   1300           Pressure atm   13.93   13.93   13.93   13.93   13.93   13.93   13.93           Pressure (psi)   204.8   204.8   204.8   204.8   204.8   204.8   204.8                      
 
         [0031]    
       
         
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
             
           
               
                   
                 TABLE 2 
               
               
                   
                   
               
               
                   
                   
               
               
                   
                 (30) 
                 (40) 
                 (50) 
                 (45) 
                   
                   
               
               
                   
                 PRODUCT 
                 PRODUCT2 
                 PRODUCT3 
                 HOTSTEAM 
                 (80) 
                 (90) 
               
               
                   
                 TURBINE 
                 BOILER 
                 COOLER 
                 TURBINE2 
                 CONDH2O 
                 VENTGAS 
               
               
                   
                 REACTOR 
                 TURBINE 
                 BOILER 
                 BOILER 
                 COOLER 
                 COOLER 
               
               
                   
                 VAPOR 
                 VAPOR 
                 VAPOR 
                 VAPOR 
                 LIQUID 
                 VAPOR 
               
               
                   
                   
               
             
             
               
                   
               
             
          
           
               
                 Vapor Frac 
                 1.00 
                 1.00 
                 1.00 
                 1.00 
                 0.00 
                 1.00 
               
               
                 Liquid Frac 
                 0.00 
                 0.00 
                 0.00 
                 0.00 
                 1.00 
                 0.00 
               
               
                 Solid Frac 
                 0.00 
                 0.00 
                 0.00 
                 0.00 
                 0.00 
                 0.00 
               
               
                 Mass Flow lb/sec. 
               
               
                 NITRO-01 (N 2 ) 
                 195.8 
                 195.8 
                 195.8 
                 0.0 
                 0.1 
                 195.7 
               
               
                 CARBO-01 (CO 2 ) 
                 38.1 
                 38.1 
                 38.1 
                 0.0 
                 0.2 
                 37.9 
               
               
                 WATER 
                 97.7 
                 97.7 
                 97.7 
                 94.7 
                 83.7 
                 14.1 
               
               
                 METHA-01 (CH 4 ) 
                 0.0 
                 0.0 
                 0.0 
                 0.0 
                 0.0 
                 0.0 
               
               
                 OXYGE-01 (O 2 ) 
                 0.5 
                 0.5 
                 0.5 
                 0.0 
                 0.0 
                 0.5 
               
               
                 PROPA-01 (C 3 H 8 ) 
                 0.0 
                 0.0 
                 0.0 
                 0.0 
                 0.0 
                 0.0 
               
               
                 Total Flow 
                 332.1 
                 332.1 
                 332.1 
                 94.7 
                 84.0 
                 248.2 
               
               
                 (lb/sec) 
               
               
                 Temperature C. 
                 1300 
                 747 
                 132 
                 370 
                 44 
                 44 
               
               
                 Pressure atm 
                 13.93 
                 1.01 
                 0.99 
                 86.06 
                 0.99 
                 0.99 
               
               
                 Pressure (psi) 
                 204.8 
                 14.8 
                 14.6 
                 1265.0 
                 14.6 
                 14.6