Combined-cycle thermal power generation system using feedwater heaters

Abstract

To provide a combined thermal power generation system capable of increasing efficiency of a bottoming cycle by arranging a feed water heater in a combined thermal power plant to which super critical and ultra super critical main steam pressure is applied, and applying a regenerative cycle.SOLUTION: A combined thermal power generation system using a feed water heater includes: a gas turbine for generating electric energy by mixing air and fuel and burning the mixture; an exhaust heat recovery boiler for discharging steam generated by exchanging heat with gas turbine exhaust gas discharged from the gas turbine and water; a steam turbine supplied with the steam discharged from the exhaust heat recovery boiler for generating electricity; a steam condenser for condensing the steam discharged from the steam turbine; and a low pressure feed water heater for increasing thermal efficiency by sending condensed water generated by recovering extraction steam generated from the steam turbine and exchanging heat to the steam condenser.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present invention relates to a combined cycle power generation system, and more particularly to a combined cycle power generation system using a feedwater heater.

Background Art

[0002] Generally, combined cycle power generation is a system that generates electricity by combining a gas turbine generator and a steam turbine generator. Combined cycle power generation primarily utilizes the combustion heat of fuel in a gas turbine and then re-uses it in a heat recovery boiler, thereby enhancing the energy utilization efficiency.

[0003] A conventional combined cycle power generation system injects air with a compressor, injects fuel into a combustion device to burn the fuel. The high-temperature combustion exhaust gas generated by the combustion of the fuel rotates the gas turbine, and electricity is primarily generated by a first generator. Thereafter, in order to utilize the heat remaining in the exhausted gas, the exhausted gas is injected into a heat recovery steam generator (HRSG), and water is heated in a boiler heat exchanger of the heat recovery steam generator to produce high-temperature and high-pressure steam. The high-temperature and high-pressure steam rotates a steam turbine, and electricity is secondarily generated by a second generator. At this time, the steam after rotating the steam turbine is cooled and condensed by a condenser, and the condensed water is supplied again to the heat recovery steam generator by a condensate pump.

[0004] However, in a conventional combined cycle power generation system, although the utilization efficiency of combustion heat can be increased, in the process of condensing steam into water, a large amount of heat loss occurs due to the warm drainage waste heat generated in the condenser and the waste heat (residual heat) of the exhaust gas generated in the heat recovery steam generator. If such waste heat and residual heat are not recovered, there are problems that the efficiency of the entire power plant decreases and a large amount of cooling water is consumed for cooling.

Summary of the Invention

Problems to be Solved by the Invention

[0005] The technical problem that this invention aims to solve is to provide a combined cycle thermal power generation system that can increase the efficiency of the bottoming cycle and reduce the equipment costs of the power plant by the amount of the increased efficiency, by arranging a feedwater heater in a combined cycle thermal power plant to which supercritical and ultra-supercritical main steam pressures are applied and applying a regenerative cycle.

[0006] The technical problems that this invention aims to solve are not limited to those mentioned above, and other technical problems not mentioned will be clearly understood by a person with ordinary skill in the art to which this invention pertains from the following description. [Means for solving the problem]

[0007] To achieve the aforementioned technical objectives, one embodiment of the present invention provides a combined thermal power generation system using a feedwater heater, comprising: a gas turbine that generates electrical energy by burning a mixture of air and fuel; a heat recovery steam generator (HRSG) that discharges steam and water generated by heat exchange with the gas turbine exhaust gas discharged from the gas turbine; a steam turbine that generates electricity by being supplied with steam discharged from the heat recovery steam generator; a condenser that condenses the steam discharged from the steam turbine; and a low-pressure feedwater heater that increases thermal efficiency by sending condensed water generated by recovering and heat-exchanging the extracted steam generated from the steam turbine to the condenser.

[0008] In embodiments of the present invention, the combined cycle power generation system may be used in a combined cycle power plant to which a supercritical or ultra-supercritical main steam pressure is applied.

[0009] In embodiments of the present invention, the steam turbine comprises a high-pressure turbine driven using steam having a first pressure range, an intermediate-pressure turbine driven using steam having a second pressure range, and a low-pressure turbine driven using steam having a third pressure range, and the condenser may be connected to the low-pressure turbine and supplied with steam discharged from the low-pressure turbine.

[0010] In an embodiment of the present invention, the combined thermal power generation system may further include an intermediate-pressure feedwater heater that extracts steam discharged from the steam turbine and transmits condensed water, generated by heat exchange between the extracted steam and water supplied from the condenser, to the low-pressure feedwater heater.

[0011] In an embodiment of the present invention, the combined thermal power generation system further comprises an intermediate-pressure feedwater pump that supplies water supplied from the condenser to the intermediate-pressure feedwater heater, and the intermediate-pressure feedwater heater may comprise a second intermediate-pressure feedwater heater that exchanges heat using steam discharged from the high-pressure turbine and water supplied from the intermediate-pressure feedwater pump, and a first intermediate-pressure feedwater heater that exchanges heat using steam discharged from the intermediate-pressure turbine and water supplied from the intermediate-pressure feedwater pump.

[0012] In embodiments of the present invention, the condensed water discharged by heat exchange in the first intermediate-pressure feedwater heater and the second intermediate-pressure feedwater heater may be recovered on the low-pressure feedwater heater side.

[0013] In embodiments of the present invention, the condensed water discharged from the condenser may be branched and sent to the condensate preheater side of the intermediate-pressure feedwater heater and the waste heat recovery boiler.

[0014] In an embodiment of the present invention, the waste heat recovery boiler may include: a high-pressure superheater that discharges steam in a first pressure range, generated by heat exchange of gas turbine exhaust gas discharged from the gas turbine, to the steam turbine; a high-pressure once-through evaporator that converts supplied water into steam through heat exchange and sends the converted steam to the high-pressure superheater; an intermediate-pressure evaporator connected to the intermediate-pressure feedwater heater, which receives water from the intermediate-pressure feedwater heater, and generates steam in a second pressure range through heat exchange; a reheater connected to the steam turbine, which discharges steam to the steam turbine; a low-pressure superheater that discharges steam in a third pressure range, generated by heat exchange of the exhaust gas of the gas turbine, to the steam turbine; a condensate preheater that heats the water condensed in the condenser; and a low-pressure evaporator that converts water supplied from the condensate preheater into steam through heat exchange and sends the converted steam to the low-pressure superheater.

[0015] In embodiments of the present invention, the condensate preheater may be connected to the low-pressure feedwater heater and driven to heat by being supplied with water.

[0016] In embodiments of the present invention, a plurality of low-pressure feedwater heaters may be provided. [Effects of the Invention]

[0017] According to embodiments of the present invention, by installing a feedwater heater in a combined cycle thermal power plant where supercritical or ultra-supercritical main steam pressure is applied and applying a regenerative cycle, the efficiency of the bottoming cycle can be increased, and the equipment costs of the power plant can be reduced by the amount of the increased efficiency.

[0018] The effects of the present invention are not limited to those described above, but should be understood to include all effects that can be inferred from the detailed description of the present invention or the configuration of the invention as described in the claims. [Brief explanation of the drawing]

[0019] [Figure 1] This is a circuit diagram shown to explain the operating method of a conventional combined-cycle thermal power plant. [Figure 2] It is a circuit diagram schematically showing the configuration of a combined heat and power generation system using a feedwater heater according to an embodiment of the present invention. [Figure 3] It is a circuit diagram schematically showing the configuration of a combined heat and power generation system using a feedwater heater according to another embodiment of the present invention.

Embodiments for Carrying Out the Invention

[0020] Hereinafter, the present invention will be described with reference to the attached drawings. However, the present invention can be realized in various different forms, and thus is not limited to the embodiments described herein. And, in order to clearly explain the present invention in the drawings, parts not related to the explanation are omitted, and the same reference numerals are given to the same or similar components throughout the specification.

[0021] Throughout the specification, when a certain part is said to be "connected (connected, contacted, coupled)" to another part, this includes not only the case where it is "directly connected", but also the case where it is "indirectly connected" with other elements interposed therebetween. Throughout the specification, when a certain part is said to "comprise (include)" a certain component, this means that, unless otherwise specified, it does not exclude other components, and may further comprise other components.

[0022] The terms used in this application are merely used to describe specific embodiments and are not intended to limit the present invention. Singular expressions include plural expressions unless the context clearly indicates otherwise. In this specification, terms such as "comprising" or "having" are intended to specify the presence of the features, numbers, steps, operations, components, parts, or combinations thereof described in the specification, and do not preclude the presence or addition of one or more other features, numbers, steps, operations, components, parts, or combinations thereof.

[0023] Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.

[0024] FIG. 1 is a circuit diagram shown for explaining the operation mode of a conventional combined cycle power plant.

[0025] Referring to FIG. 1, to explain the operation mode of a conventional cogeneration plant, first, air and natural gas (fuel) in the atmosphere flow into the gas turbine, and the inflowing air and fuel burn in the gas turbine to drive the generator to generate electricity.

[0026] The exhaust gas generated by the combustion of the inflowing air and fuel in the gas turbine is discharged, and the exhaust gas thus discharged flows into a heat recovery steam generator (HRSG).

[0027] The exhaust gas is supplied to each heat exchanger while passing through a plurality of heat exchangers provided in the heat recovery steam generator. The heat recovery steam generator uses the heat absorbed by each heat exchanger to raise the temperature of water, generate steam, and raise the temperature of the steam. The steam with increased temperature and pressure drives the steam turbine to generate steam. After the steam turbine is driven, the steam is supplied to the condenser for regeneration because the energy for driving the steam turbine is insufficient and is condensed. The condensate in the condenser is sent back to the heat recovery steam generator (HRSG) again and used for steam generation.

[0028] As described above, in the conventional combined cycle power system, the utilization efficiency of combustion heat can be increased. However, in the process of cooling steam with water, a large amount of heat loss occurs due to the warm waste heat generated in the condenser and the waste heat of the exhaust gas generated in the heat recovery steam generator. If such waste heat and waste heat are not recovered, there is a problem that the efficiency of the entire power plant decreases and a large amount of cooling water is consumed for cooling.

[0029] The present invention relates to a combined cycle power system, and more particularly, to a combined cycle power system using a feed water heater for solving the above-described problems of the prior art.

[0030] Figure 2 is a schematic circuit diagram showing the configuration of a combined thermal power generation system using a feedwater heater according to one embodiment of the present invention.

[0031] The combined cycle power generation system according to an embodiment of the present invention is a system used in a combined cycle power plant that applies a supercritical 220 bar main steam pressure or an ultra-supercritical 240 bar main steam pressure. The combined cycle power generation system according to the present invention can increase the efficiency of the bottoming cycle by applying a regenerative cycle using a feedwater heater, and the cost of the power plant equipment can be reduced by the amount of the increased efficiency.

[0032] Specifically, as the main steam pressure for application to ultra-supercritical combined cycle power plants increases, the thickness of the heat exchanger tubes on the high-pressure (HP) side of the HRSG increases, and in recent years, raw material costs have been soaring. Due to these rising raw material costs, it has become difficult in many places to construct highly efficient supercritical or ultra-supercritical combined cycle power plants. To solve this problem, the present invention applies a feedwater heater, thereby increasing the efficiency of the bottoming cycle through a regenerative cycle, and having the advantage of reducing equipment costs by the amount of the increased efficiency. Here, the bottoming cycle is a typical Rankine cycle consisting of a boiler and a steam turbine.

[0033] Referring to Figure 2, when air and fuel are mixed and supplied to the gas turbine 100, electrical energy is produced and gas turbine exhaust gas is discharged.

[0034] The gas turbine 100 compresses air from the atmosphere, mixes it with fuel using a combustor, and generates combustion gases through a combustion process. The combustion gases thus generated expand while driving the blades of the gas turbine 100, and at this time, thermal energy is converted into rotational energy, and the rotational energy is converted into electrical energy, thereby generating electricity.

[0035] The discharged gas turbine exhaust gas flows into the waste heat recovery boiler 300, which exchanges heat with the incoming gas turbine exhaust gas to produce steam and raise the temperature of the steam. The steam generated in this process is used to generate electricity, and the water generated in this process may be used to raise the temperature of the steam.

[0036] The waste heat recovery boiler 300 uses the high-temperature exhaust gas flowing in from the gas turbine 100 to raise the temperature of the water (condensate), create steam, and then superheats (increases the temperature of) the steam to supply it to the steam turbine 500.

[0037] As shown in Figure 2, the waste heat recovery boiler 300 according to an embodiment of the present invention may be configured to include a plurality of superheaters, evaporators, and economizers.

[0038] The waste heat recovery boiler 300 according to this embodiment may include a second reheater 310, a second high-pressure superheater 320, a first reheater 330, a first high-pressure superheater 340, a high-pressure once-through evaporator 350, an intermediate-pressure superheater 360, a second high-pressure economizer 370, an intermediate-pressure evaporator 380, an intermediate-pressure drum 390, a first valve 400, a low-pressure superheater 410, a first high-pressure economizer 420, a low-pressure evaporator 430, a low-pressure drum 440, a high-pressure feedwater pump 450, a second valve 460, and a condensate preheater 470.

[0039] The second high-pressure superheater 320 sends high-temperature steam in the first pressure range, generated by heat exchange using gas turbine exhaust gas discharged from the gas turbine 100, to the steam turbine 500 via the main steam piping 210. The first high-pressure superheater 340 raises the temperature of the steam generated from the high-pressure once-through evaporator 350, and then the heated steam is supplied to the high-pressure turbine 510 via the second high-pressure superheater 320 and the main steam piping 210.

[0040] The high-pressure once-through evaporator 350 converts water supplied from the second high-pressure economizer 370 into steam through heat exchange, and this converted steam is sent to the high-pressure superheater 340.

[0041] The first high-pressure coal cutter 420 heats the water supplied from the low-pressure drum 440 and sends it to the second high-pressure coal cutter 370.

[0042] The steam generated in the intermediate-pressure evaporator 380 passes through the intermediate-pressure superheater 360, where its temperature is first increased. This steam, with its temperature first increased, then flows through the first reheater 330 to the second reheater 310, where its temperature is secondarily increased, before being supplied to the intermediate-pressure turbine 530 via the high-temperature reheat steam piping 220.

[0043] The intermediate-pressure evaporator 380 is connected to the intermediate-pressure feedwater heater 900, and generates steam in the second pressure range by heat exchange with water supplied from the intermediate-pressure feedwater heater 900. At this time, the generated steam is sent to the intermediate-pressure superheater 360 via the intermediate-pressure drum 390.

[0044] The low-pressure evaporator 430 converts water supplied from the condensate preheater 470 into steam in the third pressure range, which is then sent to the low-pressure superheater 410 via the low-pressure drum 440. The heated steam is then supplied to the low-pressure turbine 550 via the low-pressure steam piping 240.

[0045] The water supplied via the low-pressure drum 440 is then sent to the first high-pressure coal cutter 420 via the high-pressure water supply pump 450.

[0046] The condensate preheater 470 receives and heats the water condensed in the condenser 700. For example, the condensate preheater 470 according to an embodiment of the present invention can heat the water (condensed water) condensed in the condenser 700 at 20°C to 30°C to 150°C. The condensate preheater of the present invention has substantially the same configuration as a low-pressure coal cutter.

[0047] In this case, the condensate preheater 470 is connected to the low-pressure feedwater heater 800 and can be heated by being supplied with water.

[0048] The high-pressure feedwater pump 450 can supply water whose temperature has risen in the condensate preheater 470 to the high-pressure once-through evaporator 350 of the waste heat recovery boiler 300.

[0049] The steam turbine 500 can generate electricity by being supplied with steam discharged from the heat recovery boiler 300. In the steam turbine 500, high-temperature, high-pressure steam generated in steam generators such as nuclear reactors, boilers, and heat recovery steam generators (HRSGs) drives the blades inside the turbine, causing an expansion process. Thermal energy is converted into rotational energy, and rotational energy is converted into electrical energy to generate electricity.

[0050] The steam turbine 500 according to an embodiment of the present invention may be configured to include a high-pressure turbine 510 driven using steam having a first pressure range, an intermediate-pressure turbine 530 driven using steam having a second pressure range, and a low-pressure turbine 550 driven using steam having a third pressure range.

[0051] More specifically, the generator 600 may be connected to the steam turbine 500 in order to generate electricity using the rotational energy.

[0052] The condenser 700 condenses the steam discharged from the steam turbine 500, and by creating a vacuum due to the density difference during the condensation process, it increases the output and efficiency of the steam turbine 500.

[0053] In the present invention, the condenser 700 is connected to the low-pressure turbine 550, as shown in Figure 2, and can be supplied with low-pressure steam discharged from the low-pressure turbine 550.

[0054] The low-pressure feedwater heater 800 is connected to the low-pressure turbine 550 and the condenser 700. This allows for the recovery of extraction steam generated from the steam turbine 500, heat exchange, and the resulting condensate to be sent to the condenser 700, thereby increasing thermal efficiency.

[0055] In conventional condensers, 50% of the total energy was lost as waste heat. However, in the low-pressure feedwater heater according to the present invention, a portion of the energy can be recovered and used, thereby significantly reducing the proportion of heat wasted from the condenser to the outside of the power plant.

[0056] The condensate pump 710 plays the role of supplying the water condensed in the condenser 700 to the waste heat recovery boiler 300.

[0057] The intermediate-pressure feedwater heater 900 is supplied with steam extracted from the steam turbine 500, and by exchanging heat between the extracted steam and water supplied from the condenser 700, the condensed water generated in the intermediate-pressure feedwater heater 900 can be recovered into the low-pressure feedwater heater 800. In this embodiment, the intermediate-pressure feedwater heater 900 can extract steam from both the high-pressure turbine 510 and the intermediate-pressure turbine 530.

[0058] The intermediate-pressure feedwater heater 900 may be located on the piping leading from the condensate system to the intermediate-pressure evaporator 380, as shown in Figure 2.

[0059] The medium-pressure feedwater pump 950 can supply water from the condenser 700 to the medium-pressure feedwater heater 900.

[0060] An intermediate-pressure feedwater heater 900 according to an embodiment of the present invention may be configured to include a second intermediate-pressure feedwater heater 910 and a first intermediate-pressure feedwater heater 930.

[0061] The second intermediate-pressure feedwater heater 910 extracts high-pressure steam from the high-pressure turbine 510 and performs heat exchange using water supplied from the intermediate-pressure feedwater pump 950.

[0062] The first intermediate-pressure feedwater heater 930 extracts intermediate-pressure steam from the intermediate-pressure turbine 530 and performs heat exchange using water supplied from the intermediate-pressure feedwater pump 950.

[0063] The condensed water discharged from the condenser 700 is branched and sent to the medium-pressure feedwater heaters 910 and 930, and to the condensate preheater 470 of the waste heat recovery boiler 300.

[0064] Figure 3 is a schematic circuit diagram showing the configuration of a combined thermal power generation system using a feedwater heater according to another embodiment of the present invention. In this embodiment, the combined thermal power generation system may be configured such that the low-pressure feedwater heater 800 includes a second low-pressure feedwater heater 810 and a first low-pressure feedwater heater 830.

[0065] The second low-pressure feedwater heater 810 and the first low-pressure feedwater heater 830 are each connected to the low-pressure turbine 550, and can recover extracted gas generated from the low-pressure turbine 550 and exchange heat with it.

[0066] As described above, the combined-cycle thermal power generation system of the present invention is composed of a combination of two gas turbines, two waste heat recovery boilers, and one steam turbine (a 2:2:1 combination), and when the low-pressure feedwater heater 800, the first intermediate-pressure feedwater heater 930, and the second intermediate-pressure feedwater heater 910 are arranged on the combined-cycle thermal power generation system, the following advantages are obtained.

[0067] Firstly, it is economical because it reduces the heat exchange area of ​​existing condensate preheaters.

[0068] Secondly, by providing the feedwater heater, it becomes unnecessary to use a separate medium-pressure economizer (IP Economizer) that was previously included in conventional waste heat recovery boilers, thereby reducing the cost of the HRSG.

[0069] Thirdly, while the heat exchangers of a heat recovery steam generator (HRSG) are installed on top of each HRSG, the feedwater heater of the present invention can be installed at 100% capacity in each building where the steam turbine is installed, thereby reducing installation costs.

[0070] Fourthly, the combined thermal power generation system of the present invention can form a regenerative cycle by arranging a feedwater heater, so that condensed water (condensate) is reduced compared to conventional power generation systems, and consequently the heat exchange area of ​​the condenser and the amount of piping can be reduced.

[0071] Fifth, it is possible to prevent corrosion of the condensate preheater due to the rise in the exhaust gas outlet temperature of the heat recovery steam generator (HRSG), and to omit the bypass pump and recirculation pump of the heat recovery steam generator that were installed in conventional combined cycle power plants.

[0072] Sixth, according to the present invention, in the case of medium-pressure feedwater, the water is immediately sent to the medium-pressure heat exchanger of the waste heat recovery boiler, which has the advantage of reducing the amount of water in the low-pressure drum.

[0073] The above description of the present invention is illustrative, and a person with ordinary skill in the art to which the invention pertains will understand that it can be easily modified into other specific forms without altering the technical idea or essential features of the invention. Therefore, the embodiments described above should be understood to be illustrative in all respects and not limiting. For example, each component described as a single type may be implemented in a distributed manner, and similarly, components described as distributed may be implemented in a combined form to the extent that a person with ordinary skill can understand.

[0074] The scope of the present invention is defined by the claims described below, and all modified or altered forms derived from the meaning and scope of the claims and the concept of equivalents thereof are included within the scope of the present invention. [Explanation of Symbols]

[0075] 100 Gas Turbine 300 Waste heat recovery boiler 450 High-pressure water supply pump 470 Condensate preheater 500 Steam Turbine 600 generator 700 Condenser 800 Low-pressure feedwater heater 900 Medium-pressure feedwater heater 950 Medium-pressure water supply pump

Claims

1. A combined cycle power plant system used in a combined cycle power plant to which a supercritical or ultra-supercritical main steam pressure is applied, and which uses a feedwater heater, A gas turbine generates electrical energy by mixing and burning air and fuel, A heat recovery boiler (HRSG) discharges steam and water generated by heat exchange with the gas turbine exhaust gas discharged from the aforementioned gas turbine, A steam turbine that generates electricity by being supplied with steam discharged from the aforementioned heat recovery boiler, A condenser for condensing the steam discharged from the steam turbine, The system includes a low-pressure feedwater heater that increases thermal efficiency by recovering extraction steam generated from the steam turbine and exchanging heat with it to produce condensate, which is then supplied to the condenser. The ratio of the gas turbine, the heat recovery boiler, and the steam turbine is 2:2:

1. The aforementioned steam turbine is A high-pressure turbine driven using steam having a first pressure range, An intermediate-pressure turbine driven using steam having a second pressure range, A low-pressure turbine driven by steam having a third pressure range is provided, The condenser is connected to the low-pressure turbine and supplied with steam discharged from the low-pressure turbine. The system further comprises an intermediate-pressure feedwater heater that extracts steam discharged from the steam turbine and transmits condensed water, generated by heat exchange between the extracted steam and water supplied from the condenser, to the low-pressure feedwater heater. The system further comprises a medium-pressure feedwater pump that supplies water supplied from the condenser to the medium-pressure feedwater heater, The aforementioned medium-pressure feedwater heater is A second intermediate-pressure feedwater heater that exchanges heat using steam discharged from the high-pressure turbine and water supplied from the intermediate-pressure feedwater pump, The system includes a first intermediate-pressure feedwater heater that performs heat exchange using steam discharged from the intermediate-pressure turbine and water supplied from the intermediate-pressure feedwater pump, The condensed water discharged through heat exchange in the first and second intermediate-pressure feedwater heaters is recovered on the low-pressure feedwater heater side. The aforementioned waste heat recovery boiler is A high-pressure superheater that discharges steam in a first pressure range, generated by heat exchange with gas turbine exhaust gas discharged from the gas turbine, to the steam turbine, A high-pressure once-through evaporator that converts supplied water into steam through heat exchange and sends the converted steam to the high-pressure superheater, A medium-pressure evaporator is connected to the aforementioned medium-pressure feedwater heater and receives water from the medium-pressure feedwater heater to exchange heat and generate steam in a second pressure range, A reheater connected to the steam turbine and which discharges steam to the steam turbine, A low-pressure superheater that discharges steam in a third pressure range, generated by heat exchange with the exhaust gas of the gas turbine, to the steam turbine. A condensate preheater for heating the condensed water in the condenser, The system includes a low-pressure evaporator that heat-exchanges water supplied from the condensate preheater to convert it into steam, and sends the converted steam to the low-pressure superheater, Furthermore, the high-pressure feedwater pump sends water whose temperature has risen in the condensate preheater to the high-pressure once-through evaporator of the heat recovery boiler. In the high-pressure once-through evaporator, the water sent from the high-pressure economizer is converted into steam through heat exchange. The converted steam is then sent to the first high-pressure superheater where its temperature is raised, and the heated steam is then supplied to the high-pressure turbine via the main steam piping through the second high-pressure superheater. A combined thermal power generation system characterized by the following features.

2. The condensed water discharged from the condenser is branched and sent to the condensate preheater side of the intermediate-pressure feedwater heater and the waste heat recovery boiler. The combined thermal power generation system according to claim 1.

3. The condensate preheater is, It is connected to the aforementioned low-pressure feedwater heater and is driven to heat when water is supplied to it. The combined thermal power generation system according to claim 2.

4. Multiple low-pressure feedwater heaters are provided. The combined thermal power generation system according to claim 1.

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