Combined cycle unit power generation system and method

Abstract

The present invention relates to the field of power generation technology and discloses a combined cycle unit power generation system, including a gas turbine, a waste heat boiler, a steam turbine, a direct current boiler and a first heat exchanger. The gas turbine is suitable for driving a generator to generate electricity, the waste heat boiler is connected to the gas turbine, the waste heat boiler is provided with a first circulation pipeline, the steam turbine is connected to the waste heat boiler, and the direct current boiler is provided with a first pipeline and a second pipeline. The first pipeline is connected to the waste heat boiler, the first circulation pipeline connects the first heat exchanger and the waste heat boiler, and the second pipeline connects the first heat exchanger and the direct current boiler. By arranging a direct current boiler, the present invention can transport the generated high-temperature flue gas from the first pipeline to the waste heat boiler, exchange heat with the working medium water in the waste heat boiler, thereby increasing the temperature of the flue gas in the waste heat boiler, accelerating the heating of the working medium water into high-temperature and high-pressure steam, and can quickly generate sufficient steam to drive the generator operation, thereby improving the flexibility of the combined cycle power generation unit during peak regulation.

Description

Technical Field

[0001] The present invention relates to the technical field of power generation, and in particular to a combined cycle unit power generation system and method. Background Art

[0002] A combined cycle power plant (CCPP) is a gas-steam power plant that first pressurizes natural gas or other combustible gas through a compressor, mixes it with air that is forced into a combustion chamber, and burns it to generate high-temperature, high-pressure gas. The gas then expands and produces work in a gas turbine, driving the gas turbine to drive the compressor and external load to rotate at high speed. The exhaust gas from the gas turbine is then directed to a waste heat boiler to generate high-temperature, high-pressure steam that drives a steam turbine, which in turn drives a generator to generate electricity.

[0003] In the existing technology, since the flue gas generated by the gas turbine has low heat content and poor heat transfer efficiency, it takes a long time to input a large amount of flue gas to heat the working water in the waste heat boiler into high-temperature, high-pressure steam. When supplying power to the grid for peak load regulation, it is impossible to generate sufficient steam to drive the generator in time, resulting in poor flexibility of the combined cycle power generation unit during peak load regulation. Summary of the Invention

[0004] In view of this, the present invention provides a combined cycle unit power generation system and method to solve the problem of poor flexibility of combined cycle power generation units during peak load regulation in the prior art.

[0005] In a first aspect, the present invention provides a combined cycle unit power generation system, comprising:

[0006] a gas turbine adapted to drive a generator to generate electricity;

[0007] a waste heat boiler connected to the gas turbine and adapted to recover heat from the flue gas of the gas turbine, the waste heat boiler being provided with a first circulation pipeline;

[0008] a steam turbine connected to the waste heat boiler and adapted to drive a generator to generate electricity;

[0009] A once-through boiler, adapted to generate high-temperature flue gas, the once-through boiler being provided with a first pipeline and a second pipeline, the first pipeline being connected to the waste heat boiler;

[0010] The first heat exchanger, the first circulation pipeline connects the first heat exchanger and the waste heat boiler, the second pipeline connects the first heat exchanger and the once-through boiler, and the medium in the first circulation pipeline and the high-temperature flue gas in the second pipeline exchange heat in the first heat exchanger.

[0011] Beneficial effects: By setting up a direct-flow boiler, the generated high-temperature flue gas can be transported from the first pipeline to the waste heat boiler, and heat is exchanged with the working water in the waste heat boiler, thereby increasing the temperature of the flue gas in the waste heat boiler and accelerating the heating of the working water into high-temperature, high-pressure steam. At the same time, the flue gas in the second pipeline can heat the working water after heat exchange in the waste heat boiler again to increase the temperature of the working water. When supplying peak power to the power grid, it can quickly generate sufficient steam to drive the generator, thereby improving the flexibility of the combined cycle generator set during peak load regulation.

[0012] In an optional embodiment, the method further includes:

[0013] a separator, disposed on the second pipeline, connected to the first heat exchanger, and adapted to separate the flue gas and water in the high-temperature flue gas after heat exchange;

[0014] The expander is connected to the separator and is suitable for driving the generator to generate electricity.

[0015] Beneficial effect: By setting up a separator, the gas and water in the flue gas after heat exchange in the first heat exchanger can be separated, and the separated gas can be used to drive the expander to do work, thereby driving the generator to generate electricity, thereby improving the efficiency of power generation.

[0016] In an optional embodiment, the method further includes:

[0017] The tail gas treatment device is connected to the separator and the waste heat boiler and is suitable for absorbing carbon dioxide in the flue gas.

[0018] Beneficial effects: By setting up the tail gas treatment device, the carbon dioxide in the flue gas of the waste heat boiler and the water separated in the separator can be absorbed, thereby reducing carbon emissions and improving environmental protection effects.

[0019] In an optional embodiment, the exhaust gas treatment device includes:

[0020] an electrolyzer connected to the separator and suitable for electrolyzing brine;

[0021] An absorber is connected to the electrolyzer and the waste heat boiler.

[0022] Beneficial effects: By setting up an electrolyzer, the water separated in the separator can be electrolyzed to produce sodium hydroxide, and the carbon dioxide in the waste heat boiler flue gas reacts with sodium hydroxide in the absorber to produce sodium carbonate, thereby reducing carbon emissions. The generated sodium carbonate can be used as fertilizer or chemical raw material.

[0023] In an optional embodiment, the method further includes:

[0024] The second heat exchanger is connected to the direct-flow boiler, the first heat exchanger, the separator and the electrolyzer. The high-temperature flue gas and the water separated by the separator are heat-exchanged in the second heat exchanger.

[0025] Beneficial effect: By providing the second heat exchanger, the water separated in the separator can be heated to increase the temperature of the electrolyzed water in the electrolyzer, thereby facilitating the electrolysis reaction.

[0026] In an optional embodiment, the exhaust gas treatment device further includes:

[0027] A purifier is arranged between the waste heat boiler and the absorber.

[0028] Beneficial effects: By setting up a purifier, impurities in the flue gas can be absorbed, thereby reducing the content of impurities in the flue gas emissions and improving the purity of the sodium carbonate generated in the absorber.

[0029] In an optional embodiment, the method further includes:

[0030] an intake manifold, disposed on the gas turbine;

[0031] a third pipeline, provided between the once-through boiler and the waste heat boiler, adapted to input steam into the once-through boiler;

[0032] The third heat exchanger is connected to the intake manifold and the third pipeline, and is suitable for exchanging heat between the high-temperature gas in the gas turbine and the steam in the third pipeline.

[0033] Beneficial effects: By setting up an intake manifold, part of the high-temperature, high-pressure gas in the gas turbine can be extracted as the intake air of the gas turbine, thereby increasing the intake pressure and moderately reducing the air flow, which is beneficial to the combustion of low-calorific value fuels. By setting up a third heat exchanger, the low-temperature steam in the third pipeline can be heat exchanged, thereby increasing the temperature of the steam entering the direct-flow boiler.

[0034] In an optional embodiment, the method further includes:

[0035] a fuel pipeline connected to the gas turbine;

[0036] The fourth heat exchanger is connected to the first circulation pipeline and the fuel pipeline.

[0037] Beneficial effect: By providing the fourth heat exchanger, the fuel entering the gas turbine can be heat exchanged with the working water in the first circulation pipeline to increase the temperature of the fuel.

[0038] In a second aspect, the present invention further provides a combined cycle unit power generation method, using the above-mentioned combined cycle unit power generation system, the power generation method includes:

[0039] Start gas turbines and once-through boilers;

[0040] The flue gas from the gas turbine is fed into the waste heat boiler for heat exchange to produce low-pressure steam, which is then fed into the once-through boiler for combustion.

[0041] The flue gas in the once-through boiler is input into the first heat exchanger for heat exchange with the medium-pressure steam in the first circulation pipeline;

[0042] The medium-pressure steam after heat exchange is returned to the waste heat boiler for further heat exchange;

[0043] The high-pressure steam after reheating is input into the steam turbine to generate electricity.

[0044] In an optional embodiment, the flue gas from the gas turbine is fed into a waste heat boiler for heat exchange to produce low-pressure steam, and the low-pressure steam is then fed into a once-through boiler for combustion, which includes:

[0045] The flue gas in the second pipeline after heat exchange with the first heat exchanger is input into the separator, the flue gas separated in the separator enters the expander to generate electricity, and the separated water enters the exhaust gas treatment device;

[0046] The flue gas from the once-through boiler is input into the first heat exchanger for heat exchange with the medium-pressure steam in the first circulation pipeline, including:

[0047] The medium-pressure steam in the first circulation pipeline exchanges heat with the first heat exchanger, and the medium-pressure steam after the heat exchanger exchanges heat with the fuel pipeline in the fourth heat exchanger. The fuel after heat exchange enters the gas turbine through the fuel pipeline.

[0048] Because the combined cycle unit power generation method adopts a combined cycle unit power generation system and has the same effect as the combined cycle unit power generation system, it will not be described in detail here. BRIEF DESCRIPTION OF THE DRAWINGS

[0049] In order to more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the specific embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0050] Figure 1 Schematic diagram of a combined cycle power generation system according to an embodiment of the present invention;

[0051] Figure 2 The present invention is a flowchart of a combined cycle unit power generation method according to an embodiment of the present invention.

[0052] Description of reference numerals:

[0053] 1. Gas turbine; 101. Intake manifold;

[0054] 2. Waste heat boiler; 201. First circulation pipeline; 202. Third pipeline; 203. First steam drum; 204. Second steam drum;

[0055] 3. Steam turbine;

[0056] 4. Once-through boiler; 401. First pipeline; 402. Second pipeline;

[0057] 5. First heat exchanger;

[0058] 6. Separator;

[0059] 7. Expander;

[0060] 8. Tail gas treatment device; 801. Electrolyzer; 802. Absorber; 803. Purifier;

[0061] 9. Second heat exchanger;

[0062] 10. The third heat exchanger;

[0063] 11. Fuel pipeline;

[0064] 12. The fourth heat exchanger. DETAILED DESCRIPTION

[0065] To make the purpose, technical solutions, and advantages of the embodiments of the present invention more clear, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without making creative efforts shall fall within the scope of protection of the present invention.

[0066] In the related art, when the gas turbine 1 uses blast furnace or coke oven synthesis gas with a low carbon content as fuel, due to the low calorific value of the synthesis gas, the temperature of the flue gas generated by combustion is low. Directly incorporating it into the waste heat boiler 2 will result in insufficient heat of the flue gas, thereby making the amount of steam generated insufficient to drive the operation of the steam turbine 3, resulting in low power generation efficiency.

[0067] The following combination Figures 1 to 2 , describing embodiments of the present invention.

[0068] According to an embodiment of the present invention, on the one hand, a combined cycle unit power generation system is provided, such as Figure 1As shown, it includes a gas turbine 1, a waste heat boiler 2, a steam turbine 3, a direct current boiler 4 and a first heat exchanger 5. The gas turbine 1 is suitable for driving a generator to generate electricity. The waste heat boiler 2 is connected to the gas turbine 1 and is suitable for recovering heat in the flue gas of the gas turbine 1. The waste heat boiler 2 is provided with a first circulation pipeline 201. The steam turbine 3 is connected to the waste heat boiler 2 and is suitable for driving a generator to generate electricity. The direct current boiler 4 is suitable for generating high-temperature flue gas. The direct current boiler 4 is provided with a first pipeline 401 and a second pipeline 402. The first pipeline 401 is connected to the waste heat boiler 2. The first circulation pipeline 201 connects the first heat exchanger 5 and the waste heat boiler 2. The second pipeline 402 connects the first heat exchanger 5 and the direct current boiler 4. The medium in the first circulation pipeline 201 and the high-temperature flue gas in the second pipeline 402 exchange heat in the first heat exchanger 5.

[0069] Specifically, in this embodiment, the gas turbine 1 can use natural gas, blast furnace gas with low carbon content, and coke oven synthesis gas as fuel. The gas turbine 1 is provided with a compressor for compressing and pressurizing the air. The flue gas generated after the combustion of the fuel and the compressed air is input into the waste heat boiler 2. The waste heat boiler 2 is provided with a heat exchanger. The heat exchanger contains working water. The heat exchanger can heat the working water into working steam by exchanging heat with the flue gas. The working steam is output to the steam turbine 3 to drive the steam turbine 3, thereby driving the generator to operate and generate electricity.

[0070] In this embodiment, the direct current boiler 4 can adopt a boiler in which the feed water passes through each heating surface once to become steam, and its circulation ratio is equal to 1.0. The low-pressure water vapor generated in the waste heat boiler 2 is input into the direct current boiler 4 to participate in combustion to suppress the generation of nitrogen oxide pollutants. The fuel, low-pressure water vapor and air are burned to produce a mixture of subcritical steam and combustion exhaust gas.

[0071] Specifically, the temperature of the low-pressure hot water or steam added to the direct-current boiler 4 is not lower than 300°C. By configuring the direct-current boiler 4 to directly burn a mixture of natural gas, water and air, high-temperature, high-pressure superheated steam can be generated.

[0072] By setting up a direct-flow boiler 4, the generated high-temperature flue gas can be transported from the first pipeline 401 to the waste heat boiler 2, and heat exchange is performed on the working water in the waste heat boiler 2, thereby increasing the flue gas flow in the waste heat boiler 2, increasing the temperature of the flue gas in the waste heat boiler 2, and accelerating the heating of the working water into high-temperature, high-pressure steam. At the same time, the flue gas in the second pipeline 402 can heat and heat the working water after heat exchange in the waste heat boiler 2 again to increase the temperature of the working water. When supplying peak power to the power grid, sufficient steam can be quickly generated to drive the generator, thereby improving the flexibility of the combined cycle power generation unit during peak power regulation.

[0073] In one embodiment, a separator 6 and an expander 7 are further included. The separator 6 is arranged on the second pipeline 402 and is connected to the first heat exchanger 5. It is suitable for separating the flue gas and water in the high-temperature flue gas after heat exchange. The expander 7 is connected to the separator 6 and is suitable for driving the generator to generate electricity.

[0074] By providing the separator 6, the gas and water in the flue gas after heat exchange in the first heat exchanger 5 can be separated, and the separated gas can be used to drive the expander 7 to do work, thereby driving the generator to generate electricity, thereby improving the efficiency of power generation.

[0075] In some other embodiments, the flue gas used to drive the expander 7 can be input into the waste heat boiler 2 again.

[0076] Preferably, if the flue gas flow rate of the once-through boiler 4 is the same as the flue gas flow rate of the gas turbine 1 , the flue gas flow rate in the waste heat boiler 2 can be as high as 200% of the flue gas flow rate of the gas turbine 1 .

[0077] In one embodiment, the system further comprises a tail gas treatment device 8 connected to the separator 6 and the waste heat boiler 2, which is suitable for absorbing carbon dioxide in the flue gas.

[0078] By providing the tail gas treatment device 8, the carbon dioxide in the flue gas of the waste heat boiler 2 and the water separated in the separator 6 can be absorbed, thereby reducing carbon emissions and improving environmental protection effects.

[0079] In one embodiment, the tail gas treatment device 8 includes an electrolyzer 801 and an absorber 802 . The electrolyzer 801 is connected to the separator 6 and is suitable for electrolyzing brine. The absorber 802 is connected to the electrolyzer 801 and the waste heat boiler 2 .

[0080] By setting up the electrolyzer 801, the water separated in the separator 6 can be electrolyzed to produce sodium hydroxide, and the carbon dioxide in the flue gas of the waste heat boiler 2 reacts with the sodium hydroxide in the absorber 802 to produce sodium carbonate, thereby reducing carbon emissions. The generated sodium carbonate can be used as fertilizer or chemical raw material.

[0081] In one embodiment, a second heat exchanger 9 connected to the direct-flow boiler 4 , the first heat exchanger 5 , the separator 6 and the electrolyzer 801 is further included, and the high-temperature flue gas and the water separated by the separator 6 are heat-exchanged in the second heat exchanger 9 .

[0082] By providing a second heat exchanger 9, the water separated in the separator 6 can be heated to increase the temperature of the electrolyzed water in the electrolyzer 801, thereby facilitating the electrolysis reaction to generate sodium hydroxide, a regenerable absorbent for carbon dioxide. When the temperature of the electrolysis reactants increases, the amount of sodium hydroxide generated increases, and the carbon dioxide capture efficiency also increases.

[0083] Preferably, the temperature of the water separated from the separator 6 after heat exchange with the flue gas of the direct current boiler 4 in the second heat exchanger 9 is not lower than 400°C. Since there is no parameter requirement for the pressure of the generated hot water or steam, the second heat exchanger 9 can adopt an ordinary shell and tube heat exchanger to allow the water containing impurities to fully exchange heat therein.

[0084] In one embodiment, the tail gas treatment device 8 further includes a purifier 803 disposed between the waste heat boiler 2 and the absorber 802. The purifier 803 can absorb impurities in the flue gas, thereby reducing the content of impurities in the flue gas emissions and improving the purity of the sodium carbonate generated in the absorber 802.

[0085] In one embodiment, it also includes an intake manifold 101, a third pipeline 202 and a third heat exchanger 10. The intake manifold 101 is arranged on the gas turbine 1, and the third pipeline 202 is arranged between the direct-flow boiler 4 and the waste heat boiler 2, and is suitable for inputting steam into the direct-flow boiler 4. The third heat exchanger 10 is connected to the intake manifold 101 and the third pipeline 202, and is suitable for exchanging heat between the high-temperature gas in the gas turbine 1 and the steam in the third pipeline 202.

[0086] By providing an intake manifold 101, part of the high-temperature, high-pressure gas in the gas turbine 1 can be extracted as the intake air of the gas turbine 1, thereby increasing the intake pressure and moderately reducing the air flow, which is beneficial to the combustion of low-calorific value fuels. By providing a third heat exchanger 10, the low-temperature steam in the third pipeline 202 can be heat exchanged, thereby increasing the temperature of the steam entering the direct-flow boiler 4.

[0087] When low calorific value synthesis gas is added to the gas turbine 1 as fuel, the required amount of air is reduced. Therefore, a portion of the high-pressure air in the compressor is cooled through the fourth heat exchanger 12 and returned to the compressor intake, thereby increasing the pressure ratio of the compressor.

[0088] Specifically, in this embodiment, the temperature of the air returning to the compressor inlet of the gas turbine 1 after the compressor inlet air is heated is not less than 200°C.

[0089] In one embodiment, a fuel pipeline 11 and a fourth heat exchanger 12 are further included. The fuel pipeline 11 is connected to the gas turbine 1, and the fourth heat exchanger 12 is connected to the first circulation pipeline 201 and the fuel pipeline 11. By providing the fourth heat exchanger 12, the fuel entering the gas turbine 1 can be heat exchanged with the working water in the first circulation pipeline 201 to increase the temperature of the fuel.

[0090] Specifically, in this embodiment, the fuel in the fuel pipeline 11 is liquefied natural gas. After heat exchange, the temperature of the natural gas rises to about 15°C, and the temperature of the medium-pressure hot water or steam output from the fourth heat exchanger 12 is not lower than 60°C, which meets the parameter requirements for the medium-pressure steam of the waste heat boiler 2 to enter the reheat system of the waste heat boiler 2.

[0091] In this embodiment, the waste heat boiler 2 is further provided with a first steam drum 203 and a second steam drum 204 , wherein the first steam drum 203 is provided on the first circulation pipeline 201 , and the second steam drum 204 is provided on the third pipeline 202 .

[0092] The heat of the flue gas of the direct-flow boiler 4 is used to heat the hot water in the fourth heat exchanger 12. This part of the feed water is heated and then returned to the first steam drum 203, thereby rationally recovering the water that was originally condensed due to the low temperature, enhancing the self-consistency of the steam system, and avoiding the problem of insufficient temperature of the medium-pressure steam in the combined cycle waste heat boiler 2 of the gas turbine 1, which leads to a reduction in the thermal energy of the reheated steam.

[0093] According to an embodiment of the present invention, on the other hand, a combined cycle unit power generation method is provided, which uses the above-mentioned combined cycle unit power generation system, such as Figure 2 As shown, the power generation method includes:

[0094] Start the gas turbine 1 and the once-through boiler 4;

[0095] Specifically, when the combined cycle unit is running, if the power generation load needs to be increased, the once-through boiler 4 is started and operated simultaneously with the combined cycle unit, and the fuel amount of the once-through boiler 4 is increased to increase the load of the combined cycle unit.

[0096] By coupling the once-through boiler 4 with the combined cycle unit consisting of the gas turbine 1 , the waste heat boiler 2 , and the steam turbine 3 , rapid load increase / decrease and small-scale peak regulation can be achieved.

[0097] The flue gas from the gas turbine 1 is fed into the waste heat boiler 2 for heat exchange to produce low-pressure steam, which is then fed into the once-through boiler 4 for combustion;

[0098] The flue gas in the once-through boiler 4 is input into the first heat exchanger 5 for heat exchange with the medium-pressure steam in the first circulation pipeline 201;

[0099] The medium-pressure steam after heat exchange is returned to the waste heat boiler 2 for further heat exchange;

[0100] Specifically, the waste heat boiler 2 outputs low-pressure steam and enters the direct current boiler 4 to participate in the combustion of the low calorific value synthesis gas. Part of the flue gas in the direct current boiler 4 enters the waste heat boiler 2, and the flue gas volume increases accordingly. Therefore, the power generation of the combined cycle unit increases, meeting the output power requirements of the unit's load increase. The flue gas generated by the combustion passes through the first heat exchanger 5 to heat the medium-pressure feed water in the first circulation pipeline 201, thereby increasing the temperature of the medium-pressure steam in the waste heat boiler 2.

[0101] The high-pressure steam after the reheating is input into the steam turbine 3 to operate and generate electricity.

[0102] In one embodiment, the flue gas from the gas turbine 1 is fed into the waste heat boiler 2 for heat exchange to produce low-pressure steam, and the low-pressure steam is then fed into the once-through boiler 4 for combustion, which includes:

[0103] The flue gas in the second pipeline 402 after heat exchange with the first heat exchanger 5 is input into the separator 6. The flue gas separated in the separator 6 enters the expander 7 for power generation, and the separated water enters the exhaust gas treatment device 8.

[0104] Specifically, the separated hot water is reheated through the second heat exchanger 9, and the generated steam is used to produce the carbon dioxide absorbent sodium hydroxide; when the combined cycle unit is not in operation, the direct current boiler 4 can be started separately, and the flue gas and reheated steam directly enter the expander 7 to generate electricity, which can meet the needs of small-scale peak-shaving power generation.

[0105] Inputting the flue gas from the once-through boiler 4 into the first heat exchanger 5 for heat exchange with the medium-pressure steam in the first circulation pipeline 201 includes:

[0106] The medium-pressure steam in the first circulation pipeline 201 exchanges heat with the first heat exchanger 5 , and the medium-pressure steam after the heat exchanger exchanges heat with the fuel pipeline 11 in the fourth heat exchanger 12 . The fuel after heat exchange enters the gas turbine 1 through the fuel pipeline 11 .

[0107] Specifically, when the combined cycle unit needs to add some low calorific value synthesis gas as fuel for the gas turbine 1, some high-temperature and high-pressure air is extracted from the gas turbine 1 and heat-exchanged with the low-pressure feed water output by the waste heat boiler 2 in the first circulation pipeline 201 to form high-temperature feed water or steam, which is sent to the direct-flow boiler 4 to participate in combustion; and the cooled high-pressure air returns to the inlet of the gas turbine 1, increasing the intake pressure and temperature to be suitable for the combustion of the low calorific value synthesis gas.

[0108] Although the embodiments of the present invention have been described with reference to the accompanying drawings, those skilled in the art may make various modifications and variations without departing from the spirit and scope of the present invention. Such modifications and variations are all within the scope defined by the appended claims.

Claims

1. A combined cycle unit power generation system, characterized in that: include: a gas turbine (1) adapted to drive a generator to generate electricity; A waste heat boiler (2) is connected to the gas turbine (1) and is suitable for recovering heat from the flue gas of the gas turbine (1). The waste heat boiler (2) is provided with a first circulation pipeline (201); a steam turbine (3), connected to the waste heat boiler (2), and adapted to drive a generator to generate electricity; A once-through boiler (4) is suitable for generating high-temperature flue gas, wherein the once-through boiler (4) is provided with a first pipeline (401) and a second pipeline (402), wherein the first pipeline (401) is connected to the waste heat boiler (2); A first heat exchanger (5), wherein the first circulation pipeline (201) is connected to the first heat exchanger (5) and the waste heat boiler (2), and the second pipeline (402) is connected to the first heat exchanger (5) and the once-through boiler (4), and the medium in the first circulation pipeline (201) and the high-temperature flue gas in the second pipeline (402) are heat-exchanged in the first heat exchanger (5); An intake manifold (101) is provided on the gas turbine (1); A third pipeline (202) is provided between the once-through boiler (4) and the waste heat boiler (2), and is suitable for inputting steam into the once-through boiler (4); The third heat exchanger (10) is connected to the intake manifold (101) and the third pipeline (202), and is suitable for exchanging heat between the high-temperature gas in the gas turbine (1) and the steam in the third pipeline (202).

2. The combined cycle power generation system according to claim 1, characterized in that: Also includes: a separator (6), arranged on the second pipeline (402), connected to the first heat exchanger (5), and suitable for separating flue gas and water in the high-temperature flue gas after heat exchange; The expander (7) is connected to the separator (6) and is suitable for driving a generator to generate electricity.

3. The combined cycle power generation system according to claim 2, characterized in that: Also includes: The tail gas treatment device (8) is connected to the separator (6) and the waste heat boiler (2) and is suitable for absorbing carbon dioxide in the flue gas.

4. The combined cycle power generation system according to claim 3, characterized in that: The tail gas treatment device (8) comprises: an electrolyzer (801), connected to the separator (6), suitable for electrolyzing brine; The absorber (802) is connected to the electrolyzer (801) and the waste heat boiler (2).

5. The combined cycle power generation system according to claim 4, characterized in that: Also includes: The second heat exchanger (9) is connected to the direct-flow boiler (4), the first heat exchanger (5), the separator (6) and the electrolyzer (801), and the high-temperature flue gas and the water separated by the separator (6) are heat-exchanged in the second heat exchanger (9).

6. The combined cycle power generation system according to claim 5, characterized in that: The tail gas treatment device (8) further comprises: The purifier (803) is arranged between the waste heat boiler (2) and the absorber (802).

7. The combined cycle power generation system according to any one of claims 1 to 6, characterized in that: Also includes: A fuel pipeline (11) connected to the gas turbine (1); The fourth heat exchanger (12) is connected to the first circulation pipeline (201) and the fuel pipeline (11).

8. A combined cycle unit power generation method, characterized in that: The combined cycle unit power generation system according to any one of claims 1 to 7 is used, and the power generation method includes: Starting the gas turbine (1) and the once-through boiler (4); The flue gas from the gas turbine (1) is fed into the waste heat boiler (2) for heat exchange to produce low-pressure steam, and the low-pressure steam is then fed into the once-through boiler (4) for combustion; The flue gas in the once-through boiler (4) is input into the first heat exchanger (5) for heat exchange with the medium-pressure steam in the first circulation pipeline (201); The medium-pressure steam after heat exchange is returned to the waste heat boiler (2) for further heat exchange; The high-pressure steam after the reheating is input into the steam turbine (3) to operate and generate electricity.

9. The combined cycle unit power generation method according to claim 8, characterized in that: The flue gas from the gas turbine (1) is fed into the waste heat boiler (2) for heat exchange to produce low-pressure steam, and the low-pressure steam is then fed into the once-through boiler (4) to participate in combustion, including: The flue gas in the second pipeline (402) after heat exchange with the first heat exchanger (5) is input into the separator (6), the flue gas separated in the separator (6) enters the expander (7) to generate electricity, and the separated water enters the tail gas treatment device (8); Inputting the flue gas from the once-through boiler (4) into the first heat exchanger (5) for heat exchange with the medium-pressure steam in the first circulation pipeline (201) includes: The medium-pressure steam in the first circulation pipeline (201) exchanges heat with the first heat exchanger (5), and the medium-pressure steam after the heat exchanger exchanges heat with the fuel pipeline (11) in the fourth heat exchanger (12). The fuel after heat exchange enters the gas turbine (1) through the fuel pipeline (11).

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