Patent Publication Number: US-2016222947-A1

Title: Power plants with an integrally geared steam compressor

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a national stage application under 35 U.S.C. § 371(c) of prior filed, co-pending PCT application Ser. No. PCT/EP2014/071796, filed on Oct. 10, 2014, which claims priority to Italian patent application serial number FI2013A000238, titled “POWER PLANTS WITH AN INTEGRALLY GEARED STEAM COMPRESSOR”, filed Oct. 14, 2013. The above-listed applications are herein incorporated by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     Embodiments of the subject matter disclosed herein generally relate to power plants and systems. Some embodiments relate to concentrated solar thermal power plants and systems for their operation. Other embodiments relate to plants for converting thermal energy into useful mechanical or electric energy. 
     Conventional solar thermal power technologies generally include collectors that focus the energy from the sun so that the high pressure and temperature needed for efficient power generation may be obtained. Different kinds of collectors are known in the art. They usually are combined to form a so-called solar field, wherein a plurality of collectors concentrate the solar energy in a heat collecting circuit, wherein a heat transfer fluid or heat transfer medium circulates, said medium transferring the collected thermal energy into a thermodynamic cycle. 
     For example, the collected solar thermal energy can be used in a Rankine cycle to generate mechanical power, which can optionally be converted into electrical power by an electric generator. 
     The efficiency of the thermodynamic cycle depends upon the available solar thermal energy and in particular upon the pressure and temperature conditions, which can be achieved in the thermodynamic cycle. 
     The power, which can be collected by the solar field, is strongly dependent upon the weather conditions as well as from the position of the sun during the day. In some embodiments of the prior art heat collecting and storing means are used for storing excess thermal energy available during the central part of the day, which can be used to improve the overall efficiency of the thermodynamic cycle during periods where less solar energy is available. This notwithstanding, the solar thermal power plants must be turned off for several hours a day due to insufficient solar power availability or lack of solar power, e.g. at night and during sunrise and sunset. 
       FIG. 1  illustrates a concentrated solar thermal power plant  1  of the current art. Solar energy is collected by a solar field schematically shown at  3 . The solar field  3  can be comprised of a plurality of solar concentrators  5 , for example in the form of parabolic troughs, focusing the solar energy on pipes  5 A arranged in the focus of the troughs and made of heat conducting material, wherein a heat transfer medium flows. The pipes  5 A collecting the thermal energy from individual rows of troughs  5  merge in a duct  7 . The heat transfer medium flowing in the duct  7  delivers thermal energy to a system, where thermal power is converted into mechanical power, e.g. via a thermodynamic cycle, such as a Rankine cycle by means of a steam turbine. 
     A plurality of heat exchangers  9 ,  11 ,  13 ,  15 , arranged in sequence are used to transfer thermal energy from the heat transfer medium to a working fluid of a thermodynamic cycle. The heat exchanger  9  is a super-heater, where a working fluid circulating in a closed circuit  17  is superheated. The heat exchanger  11  is a steam generator, where the working fluid is transformed from a liquid phase to a saturated vapor phase. If the working fluid is water, the vapor is water vapor, i.e. steam. The heat exchanger  13  forms part of a solar pre-heater, wherein the working fluid is pre-heated in the liquid phase before being transformed into steam or vapor. 
     The heat exchanger  15  forms part of a solar re-heater, which is used to re-heat the steam or vapor circulating in the closed circuit  17  between a first expansion step and a second expansion step performed into sequentially arranged high-pressure steam or vapor turbine  19  and low-pressure steam or vapor turbine  21 . The heat transfer medium entering the re-heater is at the same temperature as the heat transfer medium entering the super-heater  9  and connection between the duct  7  and the re-heater  13  is through a bypass line  7 A. 
     A return duct  23  returns the heat transfer medium or heat transfer fluid from the heat exchangers towards the solar field. An expansion vessel  24  is provided upstream of the return duct  23 . 
     A bypass line  25  is provided, through which part or the entire heat transfer medium flow can be diverted when the thermal energy collected by the solar field  3  is higher than the thermal energy required by the circuit  17  and/or when the thermodynamic cycle is shut down for whatever reason. Heat contained in the heat transfer medium flowing through the bypass line  25  can be transferred in a heat exchanger  27  to a heat storing medium, e.g. a salt, collected in a hot-salt storage tank  29 . When the thermal energy collected by the solar field  3  is insufficient to run the thermodynamic cycle in circuit  17 , supplemental heat can be provided by the hot salt stored in storage tank  29 , by pumping the hot salt from the storage tank  29  to a cold-salt storage tank  31  via the heat exchanger  27 , where thermal energy is transferred by indirect heat exchange from the heat-storage salt to the heat transfer medium circulating in by-pass line  25 . 
     The working fluid circulating in the circuit  17  usually performs a so called Rankine cycle and is usually water. In some embodiments the Rankine cycle can be an Organic Rankine Cycle, using an organic fluid, e.g. cyclopentane. 
     The working fluid delivered by the super-heater  9  is in a superheated gaseous state and is firstly expanded in the high-pressure turbine  19  and subsequently further expanded in the low-pressure turbine  21 . Between the first expansion and the second expansion the working fluid can be re-heated by circulating the working fluid in a circuit  33 , including the solar re-heater  15 . The two turbines  21  and  19  can be used to drive an electric generator  22 , which can in turn deliver electric power to an electric distribution grid schematically shown at G. 
     Spent and optionally partly condensed steam or vapor from the low-pressure turbine  21  is condensed in a condenser  35  and possibly pre-heated in a low-pressure pre-heater  37  by means of heat exchange with a side flow of the partially expanded vapor or steam, which bleeds from an intermediate stage of the low-pressure turbine  21 , for example. A circulating pump  39  pumps the working fluid to a de-aerator  41 . A feed water pump  40  pumps the working fluid from the de-aerator  41  through the solar pre-heater  13 , the steam generator  11  and the super-heater  9 . 
       FIG. 2  shows a typical steam turbine arrangement with a high-pressure steam turbine  19  and a low-pressure steam turbine  21  connected to one another through a gearbox  20 . Reference number  15  designates again a re-heater. If the solar field does not provide sufficient energy to run the thermodynamic cycle at the minimum load conditions, the thermodynamic cycle must be shut down. 
     There is a need for improving the efficiency of concentrated solar power plants of the current art, especially when the available solar energy is below a minimum threshold and insufficient to superheat the steam. 
     SUMMARY OF THE INVENTION 
     According to some embodiments, a power producing system is provided, comprising at least one integrally geared compressor arrangement, comprised of a bull gear and a compressor shaft with a pinion meshing with said bull gear. A vapor source is fluidly connectable with an inlet of the integrally geared compressor arrangement, to provide vapor to the integrally geared compressor arrangement. A vapor turbine arrangement is configured for receiving a stream of compressed and superheated vapor from the integrally geared compressor arrangement. The vapor turbine arrangement converts at least part of the energy contained in the vapor into useful energy, in form of mechanical energy. In some embodiments an electric generator driven by the vapor turbine arrangement can further convert at least part of the mechanical power produced by the vapor turbine arrangement into electric power. In some embodiments the electric generator can be co-axial with the bull gear of the integrally geared compressor arrangement and driven thereby. In other embodiments, the electric generator can be coaxial with the vapor turbine arrangement and driven thereby. 
     A main driver or prime mover can be provided for rotating the bull gear of the integrally geared compressor arrangement. In some embodiments the prime mover can be an electric motor. 
     In some embodiments the prime mover driving the bull gear can be co-axial with the bull gear. For instance, an electric motor can be provided with a driving shaft connectable with a shaft of the bull gear, e.g. through a clutch. 
     In other embodiments, the prime mover can be a vapor turbine, e.g. the above mentioned vapor turbine arrangement. For instance, the vapor turbine arrangement can be drivingly connected with the bull gear, such that mechanical power produced by the vapor turbine arrangement drives into rotation the bull gear of said integrally geared compressor arrangement. 
     The vapor turbine arrangement can comprise one or more turbines or turbine stages. In some embodiments the vapor turbine arrangement can comprise a high-pressure vapor turbine and a low-pressure vapor turbine. Vapor re-heating can be provided between the high-pressure vapor turbine and the low-pressure vapor turbine. 
     The vapor turbine arrangement can be mechanically disconnected from the integrally geared compressor arrangement, in the sense that no drive connection therebetween is provided. In other embodiments, the vapor turbine arrangement can comprise at least one vapor turbine or at least one vapor turbine stage, which is comprised of a turbine shaft drivingly connected with the integrally geared compressor arrangement. For instance, the turbine shaft can be drivingly connected with the bull gear of the integrally geared compressor arrangement. In some embodiments, the turbine shaft is comprised of a pinion mounted thereon, which meshes with the bull gear of the integrally geared compressor arrangement. The rotary speed of the turbine shaft can be different from the rotary speed of the bull gear. In other embodiments, the vapor turbine arrangement comprises a turbine shaft coaxial with the bull gear and drivingly connected therewith, e.g. through a clutch for selectively connecting the vapor turbine to the bull gear or disconnecting the vapor turbine from the bull gear. In some embodiments a gear box can also be provided between the turbine shaft and the bull gear, so that also in this case the rotary speed of the vapor turbine can be different from the rotary speed of the bull gear. 
     The vapor turbine arrangement can for instance include a main turbine drivingly connected to an electric generator and an auxiliary turbine drivingly connected to the bull gear of the integrally geared compressor. In some embodiments, the vapor source can be selectively connected with the integrally geared compressor arrangement, or with the main turbine, alternatively, for instance depending upon the vapor conditions. 
     A system as described herein can be used for the production of mechanical and/or electric power from solar energy collected e.g. through a solar collector configured and arranged for transferring solar heat to a liquid for producing vapor. In this case the vapor source is powered by solar energy, e.g. collected by a solar field of a concentrated solar power plant. 
     According to other embodiments, different heat sources can be used for producing vapor. Any source of waste heat in an industrial plant, for instance, can be usefully exploited for providing vapor. In some embodiments the vapor source is a vapor generator powered by heat from exhaust combustion gases of an internal combustion engine, such as a reciprocating engine, e.g. a diesel engine, or else a gas turbine. 
     According to a further aspect, the present disclosure concerns a concentrated solar power plant comprising a solar field for collecting solar energy, a vapor turbine system comprising a vapor turbine arrangement receiving superheated vapor generated by heating a working fluid circulating in the vapor turbine system and a thermal transfer system configured for transferring solar thermal energy from said solar field to said vapor turbine system. The system can further comprise an integrally geared compressor arrangement, configured for superheating the vapor when the solar thermal energy from the solar field is insufficient to generate sufficient superheated vapor. 
     The integrally geared compressor arrangement can be driven by an electric motor and/or by the vapor turbine arrangement, arranged for receiving compressed vapor from said integrally geared compressor arrangement. For instance, a main turbine arrangement can be provided for driving an electric generator and an auxiliary vapor turbine can be provided, which is arranged for receiving compressed vapor from the integrally geared compressor arrangement. 
     Generally, vapor of any fluid can be used, e.g. an organic fluid. In some embodiments the fluid is water and the vapor is steam. 
     The vapor turbine system can comprise a Rankine cycle system. 
     In some embodiments, the solar plant can comprise a heat transfer medium circuit receiving thermal energy from the solar field and a separate working fluid circuit, wherein a working fluid is circulated and caused to undergo a cyclic thermodynamic transformation, e.g. according to a Rankine cycle. A heat exchanger arrangement can be provided, configured and arranged for transferring thermal energy from a heat transfer medium, circulating in the heat transfer medium circuit, to the working fluid. In other embodiments, heat is collected in the solar field directly by the working fluid, which is processed through the vapor turbine. 
     The heat exchanger arrangement can comprise one or more heat exchangers, such as a vapor generator and a super-heater. 
     The working fluid circuit can comprise a secondary circuit configured and arranged for selectively diverting the working fluid from the heat exchanger arrangement through the integrally geared compressor arrangement and therefrom to said vapor turbine arrangement, for instance if the solar field does not provide sufficient solar energy for superheating the vapor. 
     According to yet a further embodiment, the disclosure concerns a method for producing useful power from heat, comprising the steps of: circulating a working fluid in a closed circuit; heating said working fluid to generate compressed vapor; superheating said vapor by means of an integrally geared compressor arrangement; expanding said superheated vapor in a vapor turbine arrangement and producing useful power therewith. 
     According to a further aspect, the present disclosure concerns a method of operating a concentrated solar power plant, comprising the steps of: collecting solar thermal energy with a solar field; generating superheated vapor by heating a working fluid with said solar thermal energy; expanding said superheated vapor in a vapor turbine arrangement and generating mechanical power therewith; supplementing said solar thermal energy with supplemental energy delivered by an integrally geared compressor arrangement for superheating vapor delivered to said vapor turbine arrangement, when said solar thermal energy is insufficient to generate sufficient superheated vapor. 
     According to some embodiments, the method disclosed herein further comprises the following steps: 
     circulating a heat transfer medium in a first circuit for transferring solar thermal energy from said solar field to a second circuit; 
     circulating a working fluid in said second circuit, said working fluid performing a thermodynamic cycle to convert at least part of said solar thermal energy into mechanical energy in said vapor turbine arrangement; 
     processing said working fluid in said integrally geared compressor arrangement for supplementing energy to said working fluid, when the solar thermal energy is insufficient to generate sufficient superheated vapor. 
     Here below reference will specifically be made to a system using water and steam, i.e. water vapor. However, the present disclosure more generally refers to a system where any suitable working fluid can be used. For example, the system and method of the present disclosure can be based on an organic Rankine cycle using an organic working fluid. Suitable working fluids can be pentane, cyclopentane or other hydrocarbons having suitable properties. 
     Features and embodiments are disclosed here below and are further set forth in the appended claims, which form an integral part of the present description. The above brief description sets forth features of the various embodiments of the present invention in order that the detailed description that follows may be better understood and in order that the present contributions to the art may be better appreciated. There are, of course, other features of the invention that will be described hereinafter and which will be set forth in the appended claims. In this respect, before explaining several embodiments of the invention in details, it is understood that the various embodiments of the invention are not limited in their application to the details of the construction and to the arrangements of the components set forth in the following description or illustrated in the drawings. The invention is capable of other embodiments and of being practiced and carried out in various ways. Also, it is to be understood that the phraseology and terminology employed herein are for the purpose of description and should not be regarded as limiting. 
     As such, those skilled in the art will appreciate that the conception, upon which the disclosure is based, may readily be utilized as a basis for designing other structures, methods, and/or systems for carrying out the several purposes of the present invention. It is important, therefore, that the claims be regarded as including such equivalent constructions insofar as they do not depart from the spirit and scope of the present invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       A more complete appreciation of the disclosed embodiments of the invention and many of the attendant advantages thereof will be readily obtained as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings, wherein: 
         FIG. 1  illustrates a concentrated solar power plant according to the current art; 
         FIG. 2  illustrates a typical reheat steam turbine arrangement for a concentrated solar power plant with a high-pressure steam turbine working with superheated steam; 
         FIG. 3  illustrates a first embodiment of a concentrated solar power plant according to the present disclosure; 
         FIGS. 3A and 3B  illustrate two possible embodiments of solar concentrator arrangements for a concentrated solar power plant according to the present disclosure; 
         FIG. 4  illustrates the pressure-enthalpy diagram for a concentrated solar power plant using a modified Rankine cycle according to the present disclosure; 
         FIG. 5  illustrates a temperature-entropy diagram for the modified Rankine cycle according to the present disclosure in a simplified arrangement; 
         FIG. 6  illustrates a diagram similar to the diagram of  FIG. 5 , showing a reheated cycle; 
         FIG. 7  illustrates a further embodiment of a concentrated solar power plant according to the present disclosure; 
         FIG. 8  illustrates yet a further embodiment of a concentrated solar power plant according to the present disclosure; 
         FIG. 9  illustrates a further embodiment of a power plant according to the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     The following detailed description of the exemplary embodiments refers to the accompanying drawings. The same reference numbers in different drawings identify the same or similar elements. Additionally, the drawings are not necessarily drawn to scale. Also, the following detailed description does not limit the invention. Instead, the scope of the invention is defined by the appended claims. 
     Reference throughout the specification to “one embodiment” or “an embodiment” or “some embodiments” means that the particular feature, structure or characteristic described in connection with an embodiment is included in at least one embodiment of the subject matter disclosed. Thus, the appearance of the phrase “in one embodiment” or “in an embodiment” or “in some embodiments” in various places throughout the specification is not necessarily referring to the same embodiment(s). Further, the particular features, structures or characteristics may be combined in any suitable manner in one or more embodiments. 
     In the following detailed description of some embodiments, the plant uses a thermodynamic cycle based on the Rankine cycle using water and steam as a working fluid. In other embodiments, as noted above, however, a different working fluid can be used. The operative method will be substantially the same, except that instead of steam, vapor of such different working fluid will be generated and processed. 
     Referring to  FIG. 3 , the main components of a concentrated solar power plant  101  according to the present disclosure will be described. The concentrated solar power plant  101  comprises a solar field  103 . The solar field  103  comprises a plurality of solar concentrators  105 . In the schematic diagram of  FIG. 3  a solar field  103  comprising a plurality of trough concentrators  105  is schematically represented. The concentrators focus the solar energy on a plurality of pipes  107 , which are located in the focus of the parabolic troughs  105 .  FIG. 3A  illustrates by way of example one such solar concentrator  105 , which includes a parabolic mirror  105 A, in the focus point whereof the pipe  107  is arranged. A heat transfer fluid flowing in the pipe  107  is thus heated by means of the solar energy, which is collected by the trough  105 A. 
     In a manner known to those skilled in the art, the solar field  103  usually comprises a large number of solar concentrators  105  arranged in rows, each row being provided with one pipe  107  for collecting the thermal energy in the heat transfer medium flowing in the pipes  107 . The troughs  105 A are controlled to track the sun during the day so as to collect the maximum radiant energy. 
     In other embodiments the solar field  103  can be designed differently.  FIG. 3B  illustrates by way of example a solar field  103  comprising a plurality of planar mirrors  106 , which are arranged so as to focus the solar energy in an area  108  on top of a tower  110 . In the area  108  a heat exchanger is provided, through which the heat transfer medium circulates, in order to be heated by the solar energy focused by the mirrors  106 . The mirrors  106  are motor-controlled to track the sun in order to maximize the solar energy concentrated on the area  108 . 
     In some embodiments, as shown in  FIG. 3 , heat collected by the heat transfer medium circulating through the solar field  103  is transferred to as separate circuit, where a second fluid circulates and performs a thermodynamic cycle. The solar heat is thus transferred from a primary circuit, where the heat transfer fluid circulates without undergoing any thermodynamic transformation, to a secondary circuit, where a different fluid undergoes thermodynamic transformations to convert the heat energy into useful mechanical and/or electrical energy. The possibility is not excluded of using one and the same closed circuit where a single fluid circulates, collects heat from the solar field, is transformed into pressurized vapor, expands in an expander or turbine, condenses in a condenser and is pumped in the liquid phase back to the solar field. 
     In  FIG. 3 , the pipes  107  are collected in a delivery duct  109 , which delivers the heated heat transfer medium from the solar field  103  through a heat exchanger arrangement. In some embodiments the heat exchanger arrangement comprises a series of heat exchangers, which will be referred to as a solar super-heater  111 , a steam (i.e. water vapor) generator or evaporator  113  and a solar pre-heater  115 . In other embodiments, not shown, two or more of the above mentioned heat exchangers can be combined to a single heat exchange arrangement or unit. 
     According to some embodiments, a solar re-heater  117  is further provided, through which a fraction of the heat transfer medium, flowing in a bypass line  104  is delivered. The heat transfer medium flowing in line  104  bypasses the solar super-heater  111 , the steam generator  113  and the solar pre-heater  115 . In other embodiments, no re-heater is provided. 
     In the serially arranged heat exchangers  111 - 115  the heat transfer medium transfers thermal energy at progressively lower temperatures to a working fluid circulating in a closed circuit  141 , which will be described later on, wherein the working fluid performs a thermodynamic cycle, for example a Rankine cycle, to convert thermal energy or heat into mechanical energy and eventually into electric energy. 
     After passing through the heat exchangers, the cooled heat transfer medium is collected in an expansion vessel  119  and pumped by a pump  123  along a return duct  121  back into the solar field  103  again. 
     In some embodiments, an intermediate thermal energy storage arrangement  125  can be provided, for storing excess thermal energy available from the solar field  103 . 
     In some embodiments the thermal energy storage arrangement  125  can include a bypass line  127  receiving hot heat transfer medium from delivery duct  109  and delivering it through a heat exchanger  129 , wherein thermal energy is transferred to a heat storage medium, which flows from a low-temperature tank  133  to a high-temperature tank  131 . Thermal energy stored in the high-temperature tank  131  is returned back to the hot transfer medium by means of the heat exchanger  129 , when required, e.g. when less solar energy is collected by the solar field  103 . 
     The heat transfer medium, therefore, circulates in a closed loop or circuit comprising the solar field  103 , the hot side of the heat exchanger arrangement including the solar super-heater  111 , the steam generator  113 , the solar pre-heater  115 , the solar re-heater  117 , the delivery duct  109  and the return duct  121 . 
     The thermal energy collected by the solar field  103  is transferred by the heat transfer medium through the heat exchangers  111 - 117  to a second closed circuit  141 , wherein the working fluid circulating therein performs a thermodynamic cycle and converts the thermal energy into mechanical power. 
     The closed circuit  141  includes the cold side of the solar super-heater  111 , the steam generator  113 , the solar pre-heater  115  and the solar re-heater  117 . 
     Superheated steam delivered by the solar super-heater  111  flows through a duct  143  towards a steam turbine arrangement  145 . 
     In some embodiments the steam turbine arrangement  145  comprises a first, high-pressure steam turbine  147  and a second, low-pressure steam turbine  149 , arranged in sequence and including respectively a high-pressure rotor and a low-pressure rotor. The high-pressure rotor of the high-pressure steam turbine  147  and the low-pressure rotor of the low-pressure steam turbine  149  can be mounted on a common turbine shaft  151 . 
     The turbine shaft  151  can be linked to an electric generator  153 , which converts mechanical power available on the turbine shaft  151  into electric power, which can be delivered to an electric distribution grid G. 
     In some embodiments, the low-pressure turbine  149  and the high-pressure steam turbine  147  can rotate at different rotary speeds, as illustrated by way of example in  FIG. 2 . In this case a gearbox or another speed manipulation device is usually arranged between the high-pressure rotor shaft and the low-pressure rotor shaft. The shaft line formed by the two rotors and the gearbox arranged there between is then connected at one end to the electric generator  153 . 
     In some embodiments the steam is partly expanded in the high-pressure steam turbine  147  and subsequently delivered to the solar re-heater  117  through a duct  155 . In the solar re-heater  117  the partly expanded steam is reheated and the reheated steam is delivered through a duct  157  to the inlet of the low-pressure steam turbine  149 . 
     Spent steam exiting the steam turbine arrangement  145  is condensed in a condenser  159  and finally delivered through a de-aerator  161  and to the solar pre-heater  115 . 
     In some embodiments a low-pressure pre-heater  160  can be arranged along the flow path of the condensed working fluid between the condenser  159  and the de-aerator  161 . In the low-pressure pre-heater  160  the low-pressure condensed working fluid is pre-heated exchanging heat against a side-stream of steam bleeding from an intermediate stage of the low-pressure steam turbine  149 . 
     A pump  163  boosts the pressure of the water or condensed working fluid collected in the de-aerator  161  to the required upper pressure and delivers the pressurized working fluid in the liquid phase through the solar pre-heater  115 . From the solar pre-heater  115  the heated working fluid, still in the liquid phase, is delivered through the steam generator  113  where it is vaporized and converted into saturated steam. The saturated steam is finally superheated in the solar super-heater  111 . 
     The steam turbine system including the steam turbine arrangement  145 , along with the piping and heat exchangers, de-aerator  161  and condenser  159  through which the working fluid flows in order to perform the thermodynamic cycle, further comprises a secondary circuit  171 . The working fluid can be diverted in the secondary circuit  171 , in order to be superheated by means of an integrally geared steam compressor  179 , when the thermal energy available from the solar field  103  is insufficient to achieve proper superheated conditions of the working fluid at the outlet of the solar super-heater  111 . 
     In some embodiments the secondary circuit  171  comprises a diverting line  173 , which is in fluid communication with the duct  143  leading from the solar super-heater  111  to the steam turbine arrangement  145 . The diverting line  173  can be in fluid communication also with a water/steam separator  175 . The steam outlet of the water/steam separator  175  can be connected to the inlet of the integrally geared steam compressor  179 . 
     Saturated steam or partly superheated steam from the water/steam separator  175  is delivered to the suction side of the integrally geared steam compressor  179 . The integrally geared steam compressor  179  compresses the saturated steam to a pressure, which is sufficiently high to ensure that at the outlet of the integrally geared steam compressor  179  the steam is in a superheated condition suitable for expansion in the steam turbine arrangement  145 . The delivery side of the integrally geared steam compressor  179  can be put in fluid communication through a line  181 A with the inlet of the low-pressure steam turbine  149  or through a line  181 B with the inlet of the high-pressure steam turbine  147 . Valves  189 A,  189 B can be arranged on the lines  181 A and  181 B for selective connection of the integrally geared steam compressor  179  with either one or the other of the two steam turbines  147 ,  149 . In other embodiments, only the line  181 A and the valve  189 A can be provided. 
     In some embodiments the integrally geared steam compressor  179  comprises a bull gear or central gear  179 A which can be driven into rotation by an electric motor  196 . The electric motor  196  can be powered by the electric distribution grid G, as schematically shown in  FIG. 3 , or directly by the electric generator  153 . 
     In some embodiments the integrally geared steam compressor  179  can comprise a plurality of stages. In the schematic representation of  FIG. 3  only a first stage  179 D and a second stage  179 E are shown, but it shall be understood that larger number of stages can be provided. 
     The rotors of the two stages  179 D,  179 E can be keyed on a common shaft  179 C, which is driven into rotation by the motor  196  via the bull gear  179 A and a pinion  179 B keyed on the shaft  179 C. 
     In other embodiments, not shown, the integrally geared steam compressor  179  can comprise separate shafts for separate compressor stages. Each shaft can be provided with its own pinion meshing with the bull gear  179 A, so that each compressor stage can rotate at a different speed. 
     In yet further embodiments, the integrally geared steam compressor  179  can comprise more than one shaft, driven by the bull gear  179 A. Two rotors of two compressor stages can be mounted on one, some or all the shafts. 
     One, some or all the compressor stages can be provided with variable inlet guide vanes, for optimal fluid flow control, adapting the operation of the integrally geared steam compressor  179  to the operating conditions, e.g. the steam flow rate available. 
     As will be described in greater detail here below, the secondary circuit  171  can be selectively connected to the main steam circuit, or isolated therefrom, depending upon the operative conditions of the solar field  103 . 
     Along the duct  143  a first valve  183  can be arranged, which is alternatively opened or closed depending upon the mode of operation of the thermodynamic cycle. A second valve  185  can be provided along the diverting line  173 , a third valve  187  can be arranged between the outlet of the water/steam separator  175  and the suction side of the integrally geared steam compressor  179 . Further valves  189 A and  189 B can be arranged along the lines  181 A and  181 B, as mentioned above, between the delivery side of the integrally geared steam compressor  179  and the inlet of the low-pressure steam turbine  149  and of the high-pressure steam turbine  147 , respectively. 
     A bypass  191  can be provided between the duct  155  and the discharge side of the low-pressure steam turbine  149 . A valve  193  can be provided on the bypass line  191 . As will be described in greater detail later on, under certain operating conditions the high-pressure turbine  147  is bypassed and only the low-pressure steam turbine  149  is operative. In this case the interior of the high-pressure steam turbine  147  must be placed under vacuum conditions. This is obtained by opening valve  193  and connecting the inoperative high-pressure turbine  147  with the condenser  159  through bypass line  191 . 
     The concentrated solar power plant  101  described so far with reference to  FIG. 3  operates as follows. 
     Under normal operating conditions, when sufficient solar energy is collected by the solar field  103 , the concentrated solar power plant of  FIG. 3  operates substantially in the same way as a plant of the current art ( FIG. 1 ). The thermal energy is extracted from the solar field  103  by the heat transfer medium flowing in the ducts  109 ,  104 ,  121  and transferred to the working fluid circulating in the steam turbine system of the second closed circuit  141 . The working fluid circulating in the steam turbine system performs a Rankine cycle converting thermal power received from the solar field  103  into mechanical power available on the turbine shaft  151 . 
     The secondary circuit  171  is closed. The valves  185 ,  187 ,  189 A and  189 B are closed, while the valve  183  is opened. The superheated steam flows along duct  143  into the high-pressure steam turbine  147 . The partly expanded steam is re-heated in the re-heater  117  and finally expanded in the low-pressure steam turbine  149 . The spent steam is condensed in condenser  159  and delivered to the solar pre-heater  115 , where the water is heated and subsequently transformed into steam in the steam generator  113  and again superheated in the solar super-heater  111 . 
     If the thermal power available from the solar field  103  is insufficient to generate a suitable flow of superheated working fluid at the outlet of the solar super-heater  111 , the steam turbine system is switched to a modified operating mode, wherein the working fluid is superheated using the integrally geared steam compressor  179 . The valve  183  is closed, while the valves  185 ,  187  and at least one of the valves  189 A  189 B is opened. 
     Working fluid in a saturated steam condition or in an insufficiently super-heated condition is delivered through the diverting line  173  in the water/steam separator  175 . Water is drained from the bottom of the water/steam separator  175  and flows back to the solar pre-heater  115 , while saturated steam is delivered through valve  187  and a delivery duct  187 A into the integrally geared steam compressor  179 . The integrally geared steam compressor  179  introduces energy in the steam by increasing the pressure thereof in a substantially adiabatic compression process. The steam delivered by the steam compressor  179  is therefore in a superheated condition and at a pressure, which is higher than the outlet pressure at the solar super-heater  111 . Usually, the compressor delivery pressure is lower than the pressure of the superheated steam delivered by the solar super-heater  111  when the concentrated solar power plant  111  is operating in design conditions, i.e. when the steam is superheated using the solar energy. 
     The super-heated and partially pressurized steam is delivered through valve  189 A to the low-pressure steam turbine  149 , by-passing the high-pressure steam turbine  147 . If the pressure of the pressurized steam delivered by the integrally geared steam compressor  179  is sufficiently high, the pressurized steam can be delivered to the high-pressure steam turbine  147  through valve  189 B. 
     By flowing through the low-pressure steam turbine  149  (or alternatively through both the high-pressure steam turbine  147  and the low-pressure steam turbine  149 ) the steam is expanded and the energy contained therein is at least partly converted into mechanical energy available on the turbine shaft  151 . Spent steam exiting the low-pressure steam turbine  149  is condensed in the condenser  159  and undergoes the usual further transformations until it is again delivered, in the liquid phase, through the solar pre-heater  115 , the steam generator  113  and the solar super-heater  111 . 
     Under these modified operating conditions the re-heater circuit can be inoperative. Depending upon the steam pressure at the delivery side of the integrally geared steam compressor  179 , also the high-pressure steam turbine  147  can be inoperative. The valve  183  is closed. 
       FIG. 4  illustrates a pressure/enthalpy diagram, showing three different operating conditions of the concentrated solar power plant of  FIG. 3 . 
     Under normal design conditions the thermodynamic cycle performed by the working fluid in the circuit  141  is represented by points A, B, C, D and E. In an exemplary embodiment the low pressure in the cycle can be around 0.05 bar, said pressure being achieved by the condenser system  159  and the condensate is pumped into the de-aerator by the condensate pump through low-pressure heater(s)  160 . The feed pump  163  boosts the fluid pressure from the pressure in the de-aerator  161  to the high cycle pressure of e.g. around 100 bar and the fluid is heated up to point B before starting the water/steam phase change ending at C, said point being on the saturation line. The saturated steam is then superheated reaching point D, which represents the working fluid condition at the output of the solar super-heater  111 . Superheated steam is expanded in the steam turbine arrangement  145  from point D to point E. In the schematic diagram of  FIG. 4  steam re-heating is omitted. 
     Under minimum load conditions the Ranking cycle is defined by curve AFGH. An upper working fluid pressure of e.g. around 17.6 bar with superheat, suitable for operation of the high-pressure steam turbine is achieved from saturated steam pressure of about 8 bar. Said upper pressure value is substantially lower than the pressure in design conditions. Sufficient solar energy is available for superheating the steam from point G to point H and the superheated steam is then expanded in the steam turbine arrangement  145 . Also in this case re-heating is not represented in the diagram. 
     If even less solar energy is available, the concentrated solar power plant will not be able to perform a standard Rankine cycle. The plant is therefore switched to the modified operation mode, where supplemental energy is delivered to the working fluid by the integrally geared steam compressor  179 . The thermodynamic cycle performed by the working fluid is in this case represented by the curve AIJHE. The cycle is operated at an upper pressure, which can be lower than the minimum operating pressure of the normal cycle, e.g. an upper pressure of around 8 bar. 
     Between point I and point J of the curve the water is heated and transformed into saturated steam at point J using the solar energy available from the solar field  103 . Point J represents the condition of the saturated steam at the outlet of the solar super-heater  111 . Under these conditions the super-heater  111  actually operates as a steam generator exchanger, since the steam delivered by the super-heater is in saturated or approximately saturated conditions. AES is the energy provided by the solar field  103 . The saturated steam is then delivered through the integrally geared steam compressor  179 , and is brought in the condition represented by point H at a higher pressure of, for example, around  17 . 6  bar in a superheated condition. AEC represents the energy supplied by the integrally geared steam compressor  179 . The subsequent steam expansion from point H to point E provides mechanical energy. AET is the useful mechanical energy produced by the low-pressure steam turbine  149 . 
       FIG. 5  illustrates the same thermodynamic cycle on a temperature-entropy diagram. Also in this case the reheating step is not shown. 
     In both diagrams of  FIGS. 4 and 5  the thermodynamic cycle has been represented in a simplified embodiment, where no re-heating is provided. The same considerations apply in case of a re-heated cycle.  FIG. 6  illustrates the same curves as  FIG. 5  in a situation where the normal operating conditions provide for re-heating of the steam after expansion in the high-pressure steam turbine  147 . In this case in normal operating conditions, i.e. when the solar field  103  delivers sufficient solar power to superheat the steam in the Rankine cycle, steam is superheated up to point D, expanded in the high-pressure steam turbine  147  to point D 1  and then re-heated in the re-heater  117  to reach point D 2 . From there the re-heated steam is expanded in the low-pressure steam turbine  149  to the low cycle pressure and condensed (point A). Curve A, I, J, H, E illustrates the thermodynamic cycle in the modified operating condition, where superheating (curve JH) is performed by the integrally geared steam compressor  179 . 
     The pressure and temperature values reported in  FIGS. 4, 5 and 6  are to be considered as exemplary and not limiting. 
     In the exemplary embodiment of  FIG. 3 , the integrally geared steam compressor  179  is used only to superheat the saturated steam when the solar energy is insufficient to run the turbine arrangement with a standard Rankine cycle. In other embodiments the steam compressor  179  can be used also for additional functions. In some embodiments, not shown, the integrally geared steam compressor can be used to boost the pressure of superheated steam, which is then stored in a superheated steam storage tank for subsequent use during transient phases, e.g. when the solar energy collected by the solar field  103  diminishes. 
       FIG. 7  illustrates a further embodiment of a concentrated solar plant embodying the subject matter disclosed herein. The same elements, components and part already shown in  FIG. 3  and described above are labeled with the same reference numbers and will not be described again. 
     In the embodiment shown in  FIG. 7  the integrally geared steam compressor  179  comprises a gearbox  200  comprised of a bull gear  201  and one or more pinions mounted on peripherally arranged shafts. 
     In some embodiments, a first pinion  203  meshing with the bull gear  201  is mounted on a first shaft  205 , driving into rotation one or more stages of the integrally geared steam compressor  179 . In some exemplary embodiments, a low-pressure compressor stage  207  and a high-pressure compressor stage  209  are arranged on opposite sides of the shaft  205  and driven thereby. As in the previously described embodiment, each compressor stage comprises an impeller arranged in an overhung arrangement on the respective shaft. Variable inlet guide vanes can be provided for one, some or all the stages of the compressor. 
     The two compressor stages  207  and  209  are connected in sequence, so that steam entering the first compressor stage  207  is compressed thereby and delivered to the suction side of the second compressor stage  209 . 
     In other embodiments, not shown, more than two compressor stages can be provided, e.g. driven by several shafts and relevant pinions meshing with the bull gear  201 , such that each shaft supports one or two overhung impellers. 
     A further pinion  111  can mesh with the bull gear  201  and is mounted on a shaft  213 . The shaft  213  is an output shaft of an auxiliary steam turbine  215 . Power generated by the auxiliary steam turbine  215  drives into rotation the bull gear  201  through the pinion  211  and thereby the compressor stages  207  and  209  through the pinion  203  and shaft  205 , as well as any other additional shaft and relevant compressor stage(s), not shown, the compressor might be comprised of 
     The steam outlet of the water-steam separator  275  can be connected through duct  287 A and valve  287  selectively to the low-pressure compressor stage  207  or to the auxiliary steam turbine  215 . Valves  217  and  219  are provided for selectively connecting the duct  287 A to the auxiliary steam turbine  215  and/or to the low-pressure compressor stage  207  respectively. 
     The delivery side of the high-pressure compressor stage  209  can be fluidly connected selectively with the auxiliary steam turbine  215 , with the low-pressure steam turbine  149  or with the high-pressure turbine  147  of the steam turbine arrangement  145 . For that purpose a pressurized steam delivery duct  221  can be connected through a valve  223  with the inlet of the auxiliary steam turbine  215  or with an intermediate stage thereof. The delivery duct  221  is further connected to lines  181 A and  181 B by a valve  189 A and  189 B respectively, to deliver compressed steam to the low-pressure steam turbine  149  or to the high-pressure steam turbine  147 , respectively. 
     The plant shown in  FIG. 7  operates substantially in the same manner as the plant of  FIG. 3  when sufficient energy is available from the solar field  103  to generate superheated steam, which is delivered through line  143  to the steam turbine arrangement  145 , the bypass valve  185  being closed. 
     When the steam generated by the heat exchanger arrangement  111 - 115  is saturated or only partly superheated, due to insufficient solar radiation, for example, the valve  193  is closed and the valve  185  provided on line  173  is opened so that partly superheated or saturated steam is delivered to the water/steam separator  175  as already disclosed in connection with  FIG. 3 . Water is drained from the bottom of the water/steam separator  175  and recirculated in the liquid branch of the closed circuit  141 , while saturated steam or wet steam is delivered through line  187 A and valve  187  towards the integrally geared steam compressor  179  and to the auxiliary steam turbine  215 . 
     Depending upon the operating conditions, at least in some transient phases saturated steam from the water/steam separator  175  can be delivered to the auxiliary steam turbine  215  only, maintaining valve  219  closed. The steam is thus used to generate mechanical power through the auxiliary steam turbine  215  and to rotate the bull gear  201  of the integrally geared steam compressor  179 . 
     If sufficient power is available on the auxiliary turbine shaft  213 , saturated steam can be delivered to the suction side of the low-pressure compressor stage  207  by opening the valve  219 . Power generated by the auxiliary steam turbine  215  is thus used to drive the compressor stages  207 ,  209  of the integrally geared steam compressor  179 , thus increasing the pressure of the steam. Superheated steam is thus delivered at the delivery side of the high-pressure compressor stage  209 . 
     Once the integrally geared steam compressor  179  has been started and sufficiently superheated steam is generated thereby, the valve  217  can be closed and the valve  223  can be opened so that superheated steam delivered by the integrally geared steam compressor  179  is expanded in the auxiliary steam turbine  215  to generate mechanical power, which maintains the integrally geared steam compressor  179  in operation. 
     Part of the superheated compressed steam delivered by the integrally geared steam compressor  179  can be delivered through line  181 A and valve  189 A to the low-pressure steam turbine  149  of the steam turbine arrangement  145 . Under certain operating conditions, if sufficiently high pressure is achieved at the delivery side of the integrally geared steam compressor  179 , the superheated steam can be delivered through line  181 B and valve  189 B to the high-pressure steam turbine  147  of the steam turbine arrangement  145 , at the first or at an intermediate stage thereof, if needed. The superheated steam will then expand in the high-pressure steam turbine  147  and subsequently in the low-pressure steam turbine  149 . 
     In the embodiment of  FIG. 7 , therefore, supplemental power for superheating the steam to be expanded in the steam turbine arrangement  145  is generated by the same steam delivered by the water/steam separator  175  using the auxiliary steam turbine  215 , rather than by an auxiliary electrical motor. In substance, the saturated steam flow delivered by the water/steam separator  175  is split: part of the steam flow is used to generate additional mechanical power to drive the integrally geared steam compressor  179 , and part of the compressed and superheated steam is expanded in the steam turbine arrangement  145 , to produce useful power which is converted by electric generator  153  into electric power and finally delivered to the electric power distribution grid G. 
     Spent steam from the auxiliary steam turbine  215  is collected along a line  225  in the condenser  159 . Spent steam from the steam turbine arrangement  145  is also collected in the condenser  159  as described above. 
     The curves representing the modified Rankine cycle performed by plant of  FIG. 7  on the pressure-vs.-enthalpy and temperature-vs.-entropy diagrams are substantially the same as shown in  FIGS. 4 through 6  described above. 
       FIG. 8  illustrates a further embodiment of a concentrated solar thermal power plant using an integrally geared steam compressor for superheating the steam when insufficient solar energy is available from the solar field. The same reference numbers as used in  FIGS. 3 and 7  indicate the same or equivalent parts, components or elements, which will not be described again. 
     In the exemplary embodiment of  FIG. 8  the integrally geared steam compressor  179  is provided with a bull gear  179 A driving into rotation four compressor stages. A first pinion  179 B keyed on a shaft  179 C meshes with the bull gear  179 A and drives into rotation two compressor stages  179 D and  179 E. A further pinion  179 F keyed on a further shaft  179 G meshes with the bull gear  179 A and drives into rotation two further compressor stages  179 H and  179 J. The number of stages can clearly be different and the four stages depicted in  FIG. 8  are by way of example only. One, some or all the compressor stages can be provided with variable inlet guide vanes as mentioned above. 
     Saturated or partly superheated steam delivered by the water/steam separator  175  is sequentially processed by the compressor stages  179 D,  179 E,  179 H,  179 J and delivered to the steam turbine arrangement  145 . In some embodiments the steam can be delivered to the high-pressure steam turbine  147  and expand sequentially in the high-pressure steam turbine  147  and in the low-pressure steam turbine  149 . A valve arrangement can be provided for bypassing the high-pressure steam turbine  147  and delivering the steam directly to the low-pressure steam turbine  149 , depending upon the steam conditions. In other embodiments a connection of the integrally geared steam compressor  179  to the low-pressure steam turbine  149  only can be provided. 
     The turbine shaft  151  can be selectively connected to the integrally geared steam compressor  179  or disconnected therefrom, for instance by means of a clutch  184 . 
     The operation of the system illustrated in  FIG. 8  when sufficient solar energy is available, is the same as described above with respect to  FIG. 3 . If insufficient solar energy is available for superheating the steam, saturated or insufficiently (partly) superheated steam or wet steam is delivered through the integrally geared steam compressor  179 , as already described above. The integrally geared steam compressor  179  is driven in rotation in this case by mechanical power provided by the steam turbine arrangement  145 . Thus, part of the power converted by the steam turbine arrangement  145  from the steam into mechanical power is used to drive the integrally geared steam compressor  179  and any excess power available on the turbine shaft  151  can be converted into electric power by the electric generator  153  and delivered to the electric power distribution grid G. 
       FIG. 9  illustrates a further embodiment of an arrangement according to the present disclosure. In this embodiment an integrally geared steam compressor  300  is used as a source of supplemental energy for superheating steam from a low temperature steam generator using for example heat waste from another plant, such as a gas turbine or the like. 
     Reference number  301  schematically illustrates a source of heat used to generate saturated or partially superheated steam, which is delivered through a steam line  303  to the integrally geared steam compressor  300 . In some embodiments a water/steam separator  305  can be provided for separating water from the steam flow delivered through line  303 . Water drained from the bottom of the water/steam separator  305  is recirculated from example at the inlet of the heat exchanger  301  through a return line  307 . Steam from the water/steam separator  305  can be delivered through a line  309  to the integrally geared steam compressor  300 . 
     The integrally geared steam compressor  300  can be comprised of a gear box  311  including a bull gear  313  mounted for rotation around an axis  313 A. A compressor shaft  315  whereon a pinion  317  is mounted is driven into rotation by the bull gear  313 . The pinion  317  meshes with the bull gear  313 . In some embodiments a low-pressure compressor stage  319  and a high-pressure compressor stage  321  can be mounted on the shaft  315 . One or more additional shafts driving one or more additional compressor stages can be provided. 
     Variable inlet guide vanes can be provided for one, some or all the compressor stages. 
     As in the previous embodiments, since the impellers of the compressor stage(s) are arranged in an overhung manner on the relevant shaft, variable inlet guide vanes can be easily provided at the inlet of each stage, thus allowing fine adjustment and tuning of the operating conditions of each stage, individually. 
     According to some embodiments, a further shaft  323  provided with a further pinion  325  is drivingly connected to the bull gear  313 . The pinion  325  meshes with the bull gear  313 . A high-pressure steam turbine  327  and a low-pressure steam turbine  329  can be drivingly connected to the shaft  323 , so that power generated by the steam turbines  327 ,  329  can be used to rotate the bull gear  313 . The two steam turbines  327 ,  329  can be arranged at opposite ends of the shaft  323 . In other embodiments, only a single turbine can be provided at one end of the relevant shaft  323 . 
     An electric generator  331  can be drivingly connected with the integrally geared steam compressor  300 , so that mechanical power generated by the steam turbine(s)  327 ,  329  can be at least partly used to drive the electric generator and be converted into electric power. According to some embodiments, the electric generator  331  can be connected with the central shaft  313 A of the bull gear  313 . In other embodiments the electric generator  331  can be driven by a shaft provided with a pinion meshing with the bull gear  313 . 
     The suction side of the low-pressure compressor stage  319  is connected to line  309  for receiving wet or saturated steam from the water/steam separator  305 . Steam compressed by the low-pressure compressor stage  319  is delivered from the delivery side of said low-pressure compressor stage  319  to the suction side of the high-pressure compressor stage  321 . Compressed steam is then delivered from the delivery side of the high-pressure compressor stage  321  through line  335  to the inlet of the high-pressure turbine  327 , the outlet whereof is connected with the inlet of the low-pressure steam turbine  329 . 
     In the embodiment shown in  FIG. 9 , the integrally geared steam compressor  300  comprises only two compressor stages  319 ,  321 , driven by a common shaft  315 , so that the impellers of the two compressor stages  319 ,  321  rotate at the same speed. In other embodiments, the two compressor stages  319 ,  321  can be driven at different speeds using separate shafts, each one being provided with a corresponding pinion meshing with the bull gear  313 . The two pinions can have different diameters so that the two compressor stages can be rotated at different speeds. 
     In yet further embodiments, not shown, the integrally geared steam compressor  300  can be provided with more than two stages, driven by one, two or more separate shafts, each drivingly connected with the bull gear  313  with respective pinion meshing therewith, so that each compressor stage or each pair of compressor stages driven by a common shaft can rotate at different speeds. The rotary speeds of the various compressor stages can be optimized based on the compression ratio of the various stages. 
     In some embodiments, the delivery side of the integrally geared steam compressor  300  can be selectively connected to the turbine arrangement  327 ,  329  or to a superheated steam tank  337 . The superheated steam tank  337  can be in turn connected through a line  339  to the inlet of the steam turbine arrangement  327 ,  329  and more specifically, for example (as shown in the embodiment shown in  FIG. 9 ) with the inlet of the high-pressure steam turbine  327 . A valve arrangement comprising for example valves  341 ,  343 ,  345  can be provided for controlling and adjusting the steam flow through lines  335  and  339 . 
     The outlet of the low-pressure steam turbine  329  is connected through a line  347  with a condenser  349 . Spent steam is condensed in the condenser  349  and pumped by a pump  351  to the heat exchanger  301 . 
     The plant of  FIG. 9  operates as follows. The heat source  301  generates a flow of saturated or partly superheated steam, which is delivered through line  303  in the water/steam separator  305 . Steam from the water/steam separator  305  is delivered through line  309  to the low-pressure compressor stage  319 . The low-pressure compressor stage  319  and the high-pressure compressor stage  321  are driven into rotation by the steam turbine arrangement  327 ,  329  and the mechanical power generated by the steam turbine arrangement is partly used to increase the energy content of the steam from line  309 . After being processed through the compressor stages  319 ,  321 , the steam coming from line  309  is superheated and is delivered through line  335  and valve  345  to the high-pressure steam turbine  327 . 
     The steam is partly expanded in the high-pressure steam turbine  327  and subsequently delivered to the low-pressure steam turbine  329 , where it further expands until the condenser pressure is achieved at the outlet of the low-pressure steam turbine  329 . 
     In some embodiments, as mentioned above, only one steam turbine can be provided, for expanding the compressed superheated steam. 
     The power generated by the steam turbine arrangement  327 ,  329  is used, as mentioned above, to drive the integrally geared steam compressor  300  including the low-pressure compressor stage  319  and the high-pressure compressor stage  321 . Excess power available on the shaft  323  is used to drive the electric generator  331  and is converted in electric power, which can be delivered to an electric power distribution grid G. 
     While the disclosed embodiments of the subject matter described herein have been shown in the drawings and fully described above with particularity and detail in connection with several exemplary embodiments, it will be apparent to those of ordinary skill in the art that many modifications, changes, and omissions are possible without materially departing from the novel teachings, the principles and concepts set forth herein, and advantages of the subject matter recited in the appended claims. Hence, the proper scope of the disclosed innovations should be determined only by the broadest interpretation of the appended claims so as to encompass all such modifications, changes, and omissions. In addition, the order or sequence of any process or method steps may be varied or re-sequenced according to alternative embodiments.