Abstract:
A method for generating electricity by means of a thermal power plant and a liquid vaporization apparatus involves producing heat energy by means of the power plant and using the heat energy to vaporize water or to heat water vapor, expanding the water vapor formed in a first turbine and using the first turbine to drive an electricity generator in order to produce electricity, vaporizing liquefied gas coming from a cryogenic storage in order to produce pressurized gas, reheating the pressurized gas with a part of the water vapor intended for the first turbine of the power plant and expanding the pressurized fluid in a second turbine to produce electricity.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a §371 of International PCT Application PCT/FR2014/053391, filed Dec. 17, 2014, which claims the benefit of FR1363248, filed Dec. 20, 2013, both of which are herein incorporated by reference in their entireties. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The present invention relates to a method and apparatus for the generation of electricity using a thermal power plant. The invention may also relate to a method for the generation of electricity which also permits the storage of energy by the liquefaction of gas. The invention also relates to apparatus for the implementation of such methods. 
         [0003]    A first object of the invention is the generation of electricity with improved efficiency. 
         [0004]    A second object of the invention is the reduction of storage costs for energy generated by an electricity generation method using a power plant and incorporating an electrical energy storage facility using liquefied gas. 
       BACKGROUND OF THE INVENTION 
       [0005]    In a thermal power plant, hot gases generated by the combustion of fuel (coal, natural gas, oil, etc.) heat the water or water vapor to form water vapor which is to be fed to a steam turbine, which generates electricity. The same applies in a combined cycle where the combustion gases which expand in the gas turbine, and are still hot, are used to heat the water or water vapor to form water vapor which is to be fed a steam turbine, which generates electricity. 
         [0006]    It is surprising to observe that the generation of electricity is more efficient where a proportion of the heat generated by the power plant is used, not in the steam turbine of the power plant, but for the preheating of a gas which is to be fed to a turbine. 
         [0007]    According to the invention, primary (rather than residual) thermal energy is used, which is normally employed for the generation of electricity in the power plant, at the time, moreover, where electricity is to be supplied to the grid system. The superior efficiency of the vaporized air (or atmospheric gas) cycle, in comparison with the steam cycle of the steam turbine of the power plant, is exploited to deliver more energy to the grid system. 
         [0008]    During periods of low electricity consumption, it is sometimes necessary to store thermal energy generated by the power plant. Thermal energy storage facilities required for this purpose are voluminous, expensive and relatively difficult to implement. 
         [0009]    The present invention proposes the elimination or reduction in size of these storage facilities, and the replacement thereof, at least partially, by a system for the liquefaction of air or of atmospheric gas. 
         [0010]    US-A-2012151961 describes a method for the storage of liquefied air. During phases of low electricity demand, air is liquefied and stored. During phases of high electricity demand, liquid air is vaporized in a system which optimizes the recovery of cold, to generate a pressurized fluid which drives a turbine for the production of electricity. The energy obtained (and consequently the efficiency of storage) is all the more efficient if the fluid is heated using residual heat prior to expansion. 
         [0011]    The article “Cryogenic Solutions for Energy Storage and the Optimization of Energy Supply” in the Revue Generale du Froid, by Dubettier et al, describes the heating of vaporized air using residual heat, or by means of natural gas burners to increase the energy produced by the expansion of air. 
         [0012]    The solution described in the prior art is as follows:
       during phases of low demand:
           Electrical energy is used to produce liquid air   A proportion of the available thermal energy is stored for use at times of high demand, and will be used to heat up pressurized gas prior to expansion   
           and during phases of high demand:
           Liquefied gas is vaporized, with the recovery of cold, to produce a pressurized gas   The pressurized gas is heated using previously stored thermal energy   The gas is expanded to produce electricity   
               
 
       SUMMARY OF THE INVENTION 
       [0020]    Rather than storing thermal energy during phases of low demand, it is proposed that a proportion of the thermal energy produced by the power plant during phases of high demand should be tapped: this reduces electricity production by the thermal power plant, but permits a substantial increase in the electrical energy produced by the pressurized fluid, which has been heated by the thermal energy thus tapped. 
         [0021]    Although the energy efficiency performance is slightly impaired in this case, investment in a very large-scale and highly expensive thermal energy storage facility can be obviated. 
         [0022]    One object of the invention is the reduction of the cost of an electricity generating apparatus by eliminating the requirement for storage facilities. 
         [0023]    According to one object of the invention, a method is proposed for the generation of electricity by means of a thermal power plant and a liquid vaporization apparatus, wherein: 
         [0024]    a) thermal energy is produced by means of the thermal power plant, gases are produced, at least a proportion of the gases is used to vaporize water or to heat water vapor, the water vapor formed is expanded in a first turbine, and the first turbine is used to drive an electricity generator for the production of electricity 
         [0025]    b) liquefied gas sourced from a cryogenic storage facility is vaporized to produce a pressurized gas 
         [0026]    c) the pressurized gas is heated, and 
         [0027]    d) the pressurized fluid is expanded in a second turbine for the production of electricity 
         [0028]    e) to heat the pressurized fluid, a proportion of the thermal energy produced in step a) is used for the heating of the pressurized fluid, by employing a proportion of the gases from the thermal power plant or a proportion of the water vapor to be delivered to the first turbine of the thermal or nuclear power plant, or a proportion of the heat of the water vapor to be delivered to the first turbine of the thermal or nuclear power plant for the heating of the pressurized fluid,
       characterized in that gases are produced by the combustion of a fuel, a proportion of the heat of the gases is used to preheat the fluid to be delivered to the second turbine, and a further proportion of the heat of the gases is used to heat the water or water vapor delivered to the first turbine, where its expansion generates electricity.       
 
         [0030]    According to further optional aspects:
       a first proportion of the gases is used to heat the steam delivered to the first turbine for expansion, and a second proportion of the gases preheats the pressurized gas, whereby the flow of the second proportion of the gases is no more than 30% of the sum of the first and second proportions.   the gases firstly heat the pressurized gas, and are then used to heat the steam which is delivered to the first turbine, where it expands.   the first and second turbines in combination produce more electricity than would have been produced by the first turbine alone, using all the heat energy of the heated fluid or the gases respectively to heat the water or water vapor to be delivered to the first turbine.   the electricity generated by the first and/or second turbine is transmitted to the grid system.   the only gas which expands in the second turbine is the pressurized fluid.
 
According to another object of the invention, a method is proposed for the generation of electricity and the storage of energy, wherein:
   i) during a first period operation is as described above   ii) during a second period   a) thermal energy is produced by means of the thermal power plant and the thermal energy is used to generate electricity   b) electrical and/or mechanical energy generated by the power plant is used to liquefy the gas, and   c) the liquefied gas is stored in a storage facility.
 
According to further optional aspects:
   the second period corresponds to a period of lower electricity demand and/or a period in which the electricity tariff is lower than in the first period.   during the second period, the first turbine generates electricity, which is used to liquefy the gas.   during the first period, the gas is not liquefied.   during the first period, the stored liquid is not vaporized and/or the pressurized fluid is not expanded in the second turbine.       
 
         [0045]    According to a further object of the invention, an integrated electricity generating apparatus is provided, comprising a thermal power plant with a first turbine, which is a steam turbine, connected to means for the generation of electricity, an apparatus for the liquefaction of a gas and the vaporization of the liquefied gas with a second turbine, which is a turbine for the expansion of vaporized liquefied gas, connected to means for the generation of electricity, means for the transference of electrical or mechanical energy from the power plant to the liquefaction apparatus, and means for the preheating of the vaporized liquefied gas up-circuit of the expansion turbine, characterized in that it comprises means for the transmission 
         [0046]    i) of the gases or water vapor, originating from the thermal power plant, or 
         [0047]    ii) of the water vapor generated and/or heated by the nuclear reaction, and originating from the nuclear power plant, or 
         [0048]    iii) of a fluid heated by the nuclear reaction, originating from the nuclear power plant, to the means for the preheating of the vaporized liquefied gas. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0049]    These and other features, aspects, and advantages of the present invention will become better understood with regard to the following description, claims, and accompanying drawings. It is to be noted, however, that the drawings illustrate only several embodiments of the invention and are therefore not to be considered limiting of the invention&#39;s scope as it can admit to other equally effective embodiments. 
           [0050]      FIG. 1  represents a flow diagram in accordance with an embodiment of the present invention. 
           [0051]      FIG. 2  represents another embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0052]    The invention will be described in greater detail with reference to the figures, which illustrate a method according to the invention.  FIG. 1  shows a schematic and partial representation of a method according to the invention, and  FIG. 2  shows the details of one variant of a method according to the invention. 
         [0053]    In  FIG. 1 , for the implementation of a method for the generation of electricity, a power plant  3  is used, which may be a thermal power plant or a nuclear power plant, together with a liquid vaporization apparatus V. 
         [0054]    Thermal energy is produced by means of the thermal power plant  3  supplied with a fuel  1 , for example of coal or natural gas in the case of a thermal power plant. The latter produces gases, at least a proportion of which is used for the vaporization of water or the heating of water vapor. Accordingly, the thermal power plant produces water vapor  5 . 
         [0055]    A proportion  13  of the water vapor  5 , comprising at least 70% of the flow  5 , is expanded in a first turbine T 1 , whereby the expanded steam  19  is then generally condensed in a condenser C, then returned to the power plant  3 , and the first turbine is used to drive an electricity generator G 1  for the production of electricity. 
         [0056]    The remaining water vapor  9 , comprising no more than 30% of the flow rate  5 , is used to heat a vaporized cryogenic liquid  17 , which may be for example air or nitrogen. The vaporized liquid  17  is heated by the water vapor in the heat-exchanger E to a temperature which exceeds the ambient temperature, and delivered to the second turbine T 2 . The second turbine is used to drive an electricity generator G 2 . If the expansion of the vaporized liquid  17  proceeds in a number of steps, the vaporized liquid  17  may be heated in advance of each step. 
         [0057]    This represents the simplest form of embodiment of the invention. In this case, the air or nitrogen expanded in the second turbine T 2  may be discharged to the atmosphere. The water vapor  9  which has heated the gas  17  in the heat-exchanger E may be returned to the power plant  3 , where applicable after condensation in a condenser, which may be the same as that used down-circuit of the turbine T 1  (the condenser C), or discharged to the atmosphere. 
         [0058]    The quantity of electricity produced by the two generators G 1 , G 2  exceeds that which would be produced if all the steam  5  were delivered to the first turbine T 1 , and only generator G 1  were in service. 
         [0059]    It is possible to employ the method in a more integrated manner by employing mechanical or electrical energy  7  originating from the power plant  3  for the operation of an apparatus L for the liquefaction of an atmospheric gas, for example air or nitrogen. The liquefied gas is stored in a storage facility S, and the stored liquid is tapped for vaporization in the vaporizer V, in order to supply the gas to be expanded in the second turbine T 2 . 
         [0060]    The liquefied gas may be a gas other than an atmospheric gas, for example natural gas or carbon dioxide. 
         [0061]    Preferably, during a first period, the liquefaction apparatus L is not in service, and the stored liquid is vaporized, heated by the steam  9  and delivered to the second turbine T 2 . This period corresponds to a period of higher electricity demand and/or a period in which the electricity tariff is higher. Only a proportion  13  of the steam is delivered to the first turbine T 1 . The proportion  13  constitutes at least 70% of the flow rate  5 . 
         [0062]    During a second period, which is a period of lower electricity demand and/or a period in which the electricity tariff is lower than in the first period, the full amount of steam  5  is delivered to the first turbine T 1 , constituting the flow rate  13 , the liquefaction apparatus receives energy  7  for the liquefaction of gas and stores the liquefied gas. The vaporizer V and the turbine T 2  are not in service. No proportion of the steam is delivered to the heat-exchanger E. 
         [0063]    A further possibility would be the employment of a proportion of the gases to heat the gas  17  in the heat-exchanger E, and of the remainder of the gases to heat the water vapor or water, in order to generate steam for delivery to the first turbine T 1 . The proportion of the gases delivered to the heat-exchanger E will be limited to no more than 30% of the total flow rate, in order to permit the continuing operation of the turbine T 1 . 
         [0064]    Rather than dividing the water vapor  5  in two for the supply of the turbine T 1  and the heat-exchanger E, another possibility would be to feed the water vapor  5  into the heat-exchanger E first, prior to the expansion of the water vapor in the first turbine T 1 . 
         [0065]    The gases might firstly be fed to the heat-exchanger E for the heating of the gas  17 , then used to heat the water vapor to be delivered to the first turbine T 1 . 
         [0066]    The water vapor  9  for the heating of the heat-exchanger E may originate from an inter-stage in the first turbine T 1 . 
         [0067]    As illustrated in  FIG. 2 , a number of streams of water vapor at different temperatures may be used to heat the vaporized liquid  17  at different stages. 
         [0068]    In order to improve heat exchange efficiency, the turbine T 1  in  FIG. 1  is comprised of a high-pressure turbine T 1 ′, an intermediate-pressure turbine T 1 ″ and a low-pressure turbine T 1 ″. The water vapor  13  is expanded in these three turbines in series, and the steam is tapped at eight different pressure levels. Each of these streams of steam heats the vaporized liquid  17  in a heat-exchanger E 1 , E 2 , E 3 , E 4 , E 5 , E 6 , E 7 , E 8  to produce the heated stream delivered to the turbine T 2 . The heat-exchangers E 1 , E 2 , E 3 , E 4 , E 5 , E 6 , E 7 , E 8  fulfil the role of E in  FIG. 1 . Likewise, the turbine T 2  may be comprised of a number of expansion stages, with reheating prior to each expansion, in accordance with the principle described above. 
         [0069]    The streams of steam are combined again and delivered to the condenser C, where the steam  19  discharged from the final turbine T 1 ″ is condensed. As illustrated in  FIG. 1 , the steam condensed in the condenser C may be transmitted to the power plant  3 . 
         [0070]    While the invention has been described in conjunction with specific embodiments thereof, it is evident that many alternatives, modifications, and variations will be apparent to those skilled in the art in light of the foregoing description. Accordingly, it is intended to embrace all such alternatives, modifications, and variations as fall within the spirit and broad scope of the appended claims. The present invention may suitably comprise, consist or consist essentially of the elements disclosed and may be practiced in the absence of an element not disclosed. Furthermore, if there is language referring to order, such as first and second, it should be understood in an exemplary sense and not in a limiting sense. For example, it can be recognized by those skilled in the art that certain steps can be combined into a single step. The singular forms “a”, “an” and “the” include plural referents, unless the context clearly dictates otherwise. 
         [0071]    “Comprising” in a claim is an open transitional term which means the subsequently identified claim elements are a nonexclusive listing (i.e., anything else may be additionally included and remain within the scope of “comprising”). “Comprising” as used herein may be replaced by the more limited transitional terms “consisting essentially of” and “consisting of” unless otherwise indicated herein. 
         [0072]    “Providing” in a claim is defined to mean furnishing, supplying, making available, or preparing something. The step may be performed by any actor in the absence of express language in the claim to the contrary. 
         [0073]    Optional or optionally means that the subsequently described event or circumstances may or may not occur. The description includes instances where the event or circumstance occurs and instances where it does not occur. 
         [0074]    Ranges may be expressed herein as from about one particular value, and/or to about another particular value. When such a range is expressed, it is to be understood that another embodiment is from the one particular value and/or to the other particular value, along with all combinations within said range. 
         [0075]    All references identified herein are each hereby incorporated by reference into this application in their entireties, as well as for the specific information for which each is cited.