Fuel gas-steam combined cycle system with bypass waste heat recovery function and control method of fuel gas-steam combined cycle system

Abstract

The invention discloses a gas-steam combined cycle system with bypass waste heat recovery and a control method thereof. The gas-steam combined cycle system comprises a gas turbine, a waste heat boiler, a steam turbine (comprising a high-pressure cylinder, an intermediate-pressure cylinder and a low-pressure cylinder) and a condenser, and is additionally provided with a bypass waste heat recovery device. The device is formed by sequentially connecting a low-pressure bypass cooler, a medium-pressure bypass cooler, an ejector, a gas-liquid separator, a gas compressor and a waste heat recovery heat exchanger, the heat absorption sides of the coolers are connected in parallel and then communicated with an inlet of the ejector, and a gas-phase working medium separated by the gas-liquid separator is pressurized by the gas compressor and then enters the waste heat recovery heat exchanger to release heat; the liquid-phase working medium returns to the cooler to form circulation, and the waste heat recovery heat exchanger and the energy accumulator are coupled to store heat. The bypass steam heat is efficiently recovered and stored in the energy accumulator in the start-stop stage of the unit, so that the gas consumption of the unit is remarkably reduced, and the comprehensive utilization efficiency of energy is improved.

Description

Technical Field

[0001] This invention relates to the field of gas-steam combined cycle technology, and particularly to a gas-steam combined cycle system with bypass waste heat recovery and its control method. Background Technology

[0002] Gas turbine combined cycle generator sets play a crucial role in grid peak shaving due to their advantages such as flexible operation, fast start-up speed, and high start-up success rate. In recent years, with the continuous expansion of renewable energy generation scale such as photovoltaic and wind power, the intermittency and volatility of their power output have posed challenges to the stable operation of the power grid. To balance the power fluctuations brought about by the integration of renewable energy and ensure the quality and security of power supply, higher operational requirements have been placed on gas turbine units undertaking peak shaving tasks, resulting in a significant increase in the frequency of unit start-ups and shutdowns, which may reach 2-3 times per day in some scenarios.

[0003] During unit startup and shutdown, to prevent low-temperature steam from entering the turbine and causing blade erosion, the system design requires steam to reach certain temperature and pressure parameters before it can enter the turbine through the main steam valve to perform work. During this transition phase, steam generated by the waste heat boiler cannot enter the turbine; instead, it is directly discharged into the condenser for condensation through the high, medium, and low-pressure bypass systems. This process results in a significant amount of heat from the high-grade steam capable of performing work being carried away by the circulating cooling water in the condenser and dissipated into the environment, causing direct energy waste. Especially under peak-shaving operation conditions with frequent start-ups and shutdowns, the cumulative heat loss from this bypass steam is considerable, leading to a decrease in overall unit thermal efficiency, an increase in power consumption, and impacting operational economy.

[0004] While combined cycle systems are widely operational in the present technology, their system configurations generally lack effective means of recovering heat from bypass steam when dealing with frequent start-up and shutdown conditions. Traditional bypass systems serve only as a safe passage for steam emissions and do not consider the reuse of their thermal energy. Therefore, how to effectively recover and utilize the heat contained in bypass steam during unit start-up and shutdown phases, reduce unit gas consumption, and improve overall energy efficiency has become an urgent technical problem to be solved in this field. Summary of the Invention

[0005] The purpose of this invention is to provide a gas-steam combined cycle system with bypass waste heat recovery and its control method. By adding a bypass waste heat recovery device consisting of a low-pressure bypass cooler, a medium-pressure bypass cooler, an ejector, a gas-liquid separator, a compressor, and a waste heat recovery heat exchanger, the high-quality heat in the bypass steam during the unit start-up and shutdown phases is effectively recovered and stored in an accumulator, thereby significantly reducing the unit's gas consumption and improving the overall energy utilization efficiency.

[0006] To solve the above-mentioned technical problems, a first aspect of the present invention provides a gas-steam combined cycle system with bypass waste heat recovery, comprising: a gas turbine, a waste heat boiler connected to the flue gas of the gas turbine, a steam turbine and a condenser driven by steam generated by the waste heat boiler, and a bypass waste heat recovery device. The steam turbine includes at least a high-pressure cylinder, an intermediate-pressure cylinder, and a low-pressure cylinder that receive steam through the main steam valve. The system is also provided with a bypass pipeline connected in parallel with the main steam valve, and the bypass pipeline is provided with a high-pressure bypass valve, an intermediate-pressure bypass valve, and a low-pressure bypass valve. The bypass waste heat recovery device includes: a low-pressure bypass cooler connected to the low-pressure bypass valve pipeline, a medium-pressure bypass cooler connected to the medium-pressure bypass valve pipeline, and an ejector, a gas-liquid separator, a compressor, and a waste heat recovery heat exchanger connected in sequence through pipelines. The heat absorption sides of the low-pressure bypass cooler and the medium-pressure bypass cooler are connected in parallel and are in fluid communication with the inlet of the ejector; The inlet of the gas-liquid separator is in fluid communication with the outlet of the ejector, the first outlet of the gas-liquid separator is in communication with the inlet of the compressor, and its second outlet is in fluid communication with the heat absorption side inlet of the low-pressure bypass cooler and the medium-pressure bypass cooler, thus forming a working fluid circulation. The heat release side of the waste heat recovery heat exchanger is coupled to an accumulator, and the recovered heat is stored in the accumulator.

[0007] Furthermore, the outlet of the high-pressure bypass valve is connected to the reheater in the waste heat boiler, so that the high-pressure bypass steam flows into the medium-pressure bypass pipeline via the reheater.

[0008] Furthermore, during the unit start-up and shutdown phases, the high-pressure bypass steam from the high-pressure bypass valve is cooled by the reheater in the waste heat boiler, and after cooling, it enters the main medium-pressure bypass steam flow controlled by the medium-pressure bypass valve.

[0009] Furthermore, the low-pressure bypass cooler and the medium-pressure bypass cooler are indirect heat exchangers, with steam from the corresponding bypass flowing on the heat-releasing side and the working fluid flowing on the heat-absorbing side. Heat exchange occurs through the indirect wall, reducing the temperature and pressure of the steam and heating the working fluid.

[0010] Furthermore, the ejector includes a high-pressure drive fluid inlet, a low-pressure ejector fluid inlet, and a mixed fluid outlet; The high-pressure drive fluid inlet is connected to the high-pressure working fluid output by the compressor; The low-pressure ejector fluid inlet is in fluid communication with the heat absorption side outlet of the low-pressure bypass cooler and the medium-pressure bypass cooler.

[0011] Furthermore, the gas-liquid separator separates the gas-liquid two-phase working fluid of the injector into a saturated gas phase working fluid and a saturated liquid phase working fluid or a subcooled liquid phase working fluid; The first outlet discharges the saturated gaseous working fluid to the compressor, and the second outlet discharges the saturated liquid working fluid or subcooled liquid working fluid to the heat absorption side inlet of the low-pressure bypass cooler and the medium-pressure bypass cooler.

[0012] Furthermore, the heat release side of the waste heat recovery heat exchanger is coupled to the accumulator through an intermediate heat medium loop; The intermediate heat medium transfers the heat energy from the heat release side of the waste heat recovery heat exchanger to the energy storage device.

[0013] Furthermore, the intermediate heat medium is heat-conducting oil or water.

[0014] Furthermore, the system is configured to have at least two operating modes: In normal power generation mode, the high-pressure bypass valve, medium-pressure bypass valve and low-pressure bypass valve are closed, and steam enters the steam turbine to do work through the high-pressure main steam valve, high-pressure main steam regulating valve, low-pressure main steam valve, low-pressure main steam regulating valve, medium-pressure main steam regulating valve and medium-pressure main steam valve. In the unit start-up and shutdown mode, the medium-pressure bypass valve and the low-pressure bypass valve are opened, and the high-pressure main steam valve, high-pressure main steam regulating valve, medium-pressure main steam valve, medium-pressure main steam valve, low-pressure main steam valve, and low-pressure main steam regulating valve are closed. Steam from the low-pressure bypass and the medium-pressure bypass flows through the low-pressure bypass cooler and the medium-pressure bypass cooler respectively for heat recovery before entering the condenser. Steam flowing through the high-pressure bypass flows through the reheater of the waste heat boiler into the medium-pressure bypass pipeline and is then guided to the condenser.

[0015] Accordingly, a second aspect of the present invention provides a control method for a gas-steam combined cycle system with bypass waste heat recovery, for controlling the aforementioned gas-steam combined cycle system with bypass waste heat recovery, the control method comprising the following steps: During the unit startup or shutdown phase, the high-pressure bypass valve, medium-pressure bypass valve, and low-pressure bypass valve are opened, and the main steam valve connected to the high-pressure cylinder, medium-pressure cylinder, and low-pressure cylinder is closed, allowing steam to flow through the bypass pipeline. The steam flowing through the high-pressure bypass valve is then channeled through the reheater of the waste heat boiler into the medium-pressure bypass pipeline and then guided to the condenser. Steam flowing through the low-pressure bypass valve enters the low-pressure bypass cooler, and the heat of the steam is recovered by the working fluid flowing on the heat absorption side of the low-pressure bypass cooler. Steam flowing through the medium-pressure bypass valve enters the medium-pressure bypass cooler, and the heat of the steam is recovered by the working fluid flowing on the heat absorption side of the medium-pressure bypass cooler. The working fluid absorbs heat in the low-pressure bypass cooler and the medium-pressure bypass cooler before entering the ejector, and then undergoes gas-liquid separation by the gas-liquid separator. The separated gaseous working fluid is pressurized by the compressor and enters the waste heat recovery heat exchanger to release heat to the accumulator. The separated liquid working fluid returns to the heat absorption side inlet of the low-pressure bypass cooler and the medium-pressure bypass cooler, forming a cycle.

[0016] The above-described technical solutions of the embodiments of the present invention have the following beneficial technical effects: 1. By adding an independent recovery loop consisting of a low-pressure bypass cooler, a medium-pressure bypass cooler, an ejector, a gas-liquid separator, a compressor, and a waste heat recovery heat exchanger, the steam heat that was originally wasted by bypassing the condenser during unit start-up and shutdown is effectively captured. After absorbing steam heat in the bypass cooler, the working fluid in this loop undergoes ejection, separation, and pressurization steps, and finally transfers high-quality heat energy to the accumulator for storage in the waste heat recovery heat exchanger, which can then be used by other equipment. This converts waste heat energy into usable energy, directly reducing the unit's fuel consumption and improving the operating economy and energy utilization efficiency of the entire combined cycle system. 2. The high-pressure bypass steam is cleverly guided to the existing reheater in the waste heat boiler for cooling, and then safely merged into the medium-pressure bypass pipeline. This avoids the need to set up a complex and expensive cooling and desuperheating device for the high-pressure bypass separately, simplifying the system structure. At the same time, by guiding the high, medium and low-pressure bypass steam to a shared waste heat recovery device and condenser, the integration and orderly processing of steam energy at different pressure levels is achieved. This not only ensures the safe operation of the unit under start-up and shutdown conditions and avoids the risk of water erosion of the turbine, but also improves the system integration and reliability. 3. By configuring two distinct operating modes—normal power generation and start-up / shutdown—and based on precise switching of valve status, the system can flexibly switch between "full-power generation" and "bypass heat recovery" states. This intelligent operating strategy enables the unit to easily cope with the increasingly frequent start-up and shutdown peak-shaving demands caused by the integration of a high proportion of renewable energy. While ensuring grid security, it ensures continuous energy recovery during each start-up and shutdown process, effectively solving the pain point of efficiency decline in traditional units during peak-shaving operation, and significantly enhancing the adaptability and competitiveness of combined cycle power plants under the new power system. Attached Figure Description

[0017] Figure 1 This is a schematic diagram of the principle of a gas-steam combined cycle system with bypass waste heat recovery provided in an embodiment of the present invention.

[0018] Figure label: 1. Low-pressure superheater; 2. Reheater; 3. Intermediate-pressure superheater; 4. High-pressure superheater; 5. Gas turbine; 6. Generator; 7. High-pressure cylinder; 8. Intermediate-pressure cylinder; 9. Low-pressure cylinder; 10. Condenser; 11. High-pressure main steam valve; 12. High-pressure main steam regulating valve; 13. Low-pressure main steam valve; 14. Low-pressure main steam regulating valve; 15. Intermediate-pressure main steam regulating valve; 16. Intermediate-pressure main steam valve; 17. Low-pressure bypass regulating valve; 18. Low-pressure bypass cooler; 19. Intermediate-pressure bypass cooler; 20. Intermediate-pressure bypass regulating valve; 21. Gas-liquid separator; 22. Ejector; 23. Waste heat recovery heat exchanger; 24. Compressor; 25. Accumulator; 26. Waste heat boiler; 27. High-pressure bypass regulating valve. Detailed Implementation

[0019] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to specific embodiments and the accompanying drawings. It should be understood that these descriptions are merely exemplary and not intended to limit the scope of the invention. Furthermore, descriptions of well-known structures and techniques are omitted in the following description to avoid unnecessarily obscuring the concept of the invention.

[0020] Please refer to Figure 1 The first aspect of the present invention provides a gas-steam combined cycle system with bypass waste heat recovery, comprising: a gas turbine 5, a waste heat boiler 26 connected to the flue gas of the gas turbine 5, a steam turbine and a condenser 10 driven by steam generated by the waste heat boiler 26, and a bypass waste heat recovery device.

[0021] A combined cycle gas turbine system uses a gas turbine as its core power unit. The high-temperature flue gas discharged from the gas turbine directly enters a waste heat boiler as its heat source. The waste heat boiler contains multiple stages of heating surfaces arranged sequentially along the flue gas flow direction, including a high-pressure superheater, an intermediate-pressure superheater, a reheater, and a low-pressure superheater, which are used to generate main steam and reheat steam at different pressure levels, respectively. The qualified steam generated by the waste heat boiler is transported to the turbine to perform work. The turbine typically adopts a multi-cylinder structure, including at least a high-pressure cylinder, an intermediate-pressure cylinder, and a low-pressure cylinder, each receiving steam through its own main steam valve. These cylinders are connected by steam pipelines and collectively drive one or more generators.

[0022] The steam turbine includes at least a high-pressure cylinder 7, an intermediate-pressure cylinder 8, and a low-pressure cylinder 9 that receive steam through the main steam valve. The system also has bypass pipelines connected in parallel with the main steam valves, equipped with a high-pressure bypass valve 27, an intermediate-pressure bypass valve 20, and a low-pressure bypass valve 17. To accommodate rapid start-up and shutdown and low-load operation, the system includes bypass pipelines connected in parallel with each main steam valve. These bypass pipelines are equipped with corresponding high-pressure, intermediate-pressure, and low-pressure bypass valves. During unit start-up, shutdown, or rapid load changes, when steam parameters do not meet the requirements for entering the turbine, these bypass valves open, guiding steam to the bypass system. This prevents substandard steam from entering the turbine and causing water erosion damage, while simultaneously maintaining normal boiler operation.

[0023] The bypass waste heat recovery device includes: a low-pressure bypass cooler 18 connected to the low-pressure bypass valve 17, a medium-pressure bypass cooler 19 connected to the medium-pressure bypass valve 20, and an ejector 22, a gas-liquid separator 21, a compressor 24, and a waste heat recovery heat exchanger 23 connected in sequence through pipelines.

[0024] An integrated dedicated bypass waste heat recovery system is incorporated. This system includes a low-pressure bypass cooler and a medium-pressure bypass cooler, respectively connected to the outlet pipelines of the low-pressure and medium-pressure bypass valves. Both coolers employ a partitioned heat exchange design, with steam from the corresponding bypass flowing on one side of the shell or tube side, and a dedicated recovery working fluid flowing on the other. As the steam flows through the cooler, it transfers its heat to the working fluid through the metal partition, achieving cooling and pressure reduction before being safely introduced into the condenser for condensation.

[0025] After the heat absorption sides of the low-pressure bypass cooler 18 and the medium-pressure bypass cooler 19 are connected in parallel, they are in fluid communication with the inlet of the ejector 22.

[0026] After absorbing heat, the gas-liquid two-phase working fluid flows out from the heat-absorbing side outlets of the two bypass coolers, merges in parallel, and is then transported to the low-pressure ejector fluid inlet of an ejector. This ejector also has a high-pressure drive fluid inlet and a mixing fluid outlet. Utilizing the high-pressure working fluid from within the system as a power source, the ejector generates a high-speed jet through its unique structure, entraining and mixing the low-pressure working fluid from the bypass coolers, thus achieving initial pressurization and kinetic energy transfer.

[0027] The inlet of the gas-liquid separator 21 is in fluid communication with the outlet of the ejector 22. The first outlet of the gas-liquid separator 21 is in fluid communication with the inlet of the compressor 24, and its second outlet is in fluid communication with the heat absorption side inlets of the low-pressure bypass cooler 18 and the medium-pressure bypass cooler 19, thus forming a working fluid circulation.

[0028] The mixed working fluid enters a gas-liquid separator from the ejector outlet. Inside the separator, the working fluid achieves effective separation of the gas and liquid phases through gravity, centrifugal force, or changes in flow direction. The separated saturated gas phase, due to its lower density, exits from the separator's first outlet and enters a compressor for further compression and pressurization. After being pressurized by the compressor, the working fluid's pressure and temperature increase significantly, becoming a high-temperature, high-pressure superheated or saturated gas.

[0029] The heat release side of the waste heat recovery heat exchanger 23 is coupled to an accumulator 25, storing the recovered heat in the accumulator 25. The high-temperature, high-pressure working fluid flows into the waste heat recovery heat exchanger. In the waste heat recovery heat exchanger, the working fluid acts as a heat source, transferring the sensible and latent heat it absorbs in the bypass cooler and carries after compression by the compressor to an intermediate heat medium on the other side through the heat exchange surface. This intermediate heat medium can be water, heat transfer oil, or other suitable fluids. After being heated, it flows into one or more accumulators to store the recovered heat energy as thermal energy. The accumulator, acting as a heat storage tank, can supply the stored heat to other heat-consuming equipment or processes as needed, such as plant heating, domestic hot water supply, or driving absorption chillers.

[0030] The working fluid that has completed the exothermic process is cooled and may partially condense in the waste heat recovery heat exchanger. It is then mixed with the saturated or subcooled liquid working fluid discharged from the second outlet of the gas-liquid separator. This mixed liquid working fluid, as a circulating working fluid, is transported back to the heat absorption side inlet of the low-pressure bypass cooler and the medium-pressure bypass cooler through pipelines, thus forming a complete and closed working fluid circulation loop, achieving continuous heat recovery and transfer.

[0031] By introducing an independent working fluid circulation recovery device coupled with the steam bypass system, the steam heat emitted by the unit under unstable operating conditions is effectively collected, transferred, and stored, and ultimately utilized. This scheme not only directly reduces heat loss to the environment, improves the overall utilization efficiency of the energy system, and reduces power consumption, but also realizes the spatial and temporal transfer of heat through the energy storage device, enhancing the flexibility and economy of system operation. It is particularly suitable for modern gas-steam combined cycle power plants that require frequent peak-shaving operation.

[0032] Furthermore, the outlet of the high-pressure bypass valve 27 is connected to the reheater 2 in the waste heat boiler 26, so that the high-pressure bypass steam flows into the medium-pressure bypass pipeline via the reheater 2.

[0033] In a preferred embodiment of the present invention, the outlet of the high-pressure bypass valve 27 is connected to the inlet of the reheater 2 located inside the waste heat boiler 26 via a pipeline. This connection constitutes a specific flow path for the high-pressure bypass steam. When the unit is in the start-up or shutdown phase, the high-pressure bypass valve 27 is opened, and the high-pressure main steam generated from the high-pressure superheater of the waste heat boiler does not enter the high-pressure cylinder of the turbine, but flows out through the valve and is then guided to the inlet of the reheater 2.

[0034] Reheater 2, a conventional heating surface in the waste heat boiler used to raise the exhaust temperature of the intermediate-pressure cylinder, is given an additional function in this design. The high-pressure bypass steam flowing into reheater 2 has a pressure and temperature much higher than the intermediate-pressure exhaust steam under the reheater's design operating conditions. As the high-pressure steam flows through the heat exchange tube bundle of the reheater, it exchanges heat with the cooled flue gas from the gas turbine flowing through the reheater's flue side. This is a crucial depressurization and decooling process: the high-pressure steam releases some sensible heat to the flue gas, thus lowering its temperature; simultaneously, due to the flow resistance as it flows through the reheater, the steam pressure naturally decreases. After being cooled by reheater 2, the original high-pressure steam parameters (such as temperature and pressure) are significantly reduced, transforming into steam with parameters matching those of the intermediate-pressure bypass.

[0035] Subsequently, this pre-treated steam exits from the outlet of reheater 2 and is piped into the main stream of the medium-pressure steam header or medium-pressure bypass system. Specifically, it mixes with the medium-pressure main steam from the medium-pressure superheater of the waste heat boiler, as well as steam from other medium-pressure sources that may be present during the start-up phase. The combined medium-pressure steam stream, with its parameters becoming more uniform, then flows together towards the medium-pressure bypass valve 20.

[0036] During unit start-up and shutdown, the medium-pressure bypass valve 20 is open. The merged medium-pressure steam passes through the valve 20 and enters the subsequent medium-pressure bypass cooler 19. In the bypass cooler 19, the steam transfers its heat to the working fluid in the recovery cycle, further cooling and condensing itself before finally flowing to the condenser 10. This design ensures that the high-pressure bypass steam is not directly discharged, but rather undergoes preliminary energy regulation and system integration via the boiler's own reheater before entering the unified waste heat recovery process. This structure cleverly utilizes the reheater heating surface in the existing waste heat boiler, providing a built-in, non-powered depressurization and cooling path for the high-pressure bypass steam, avoiding the need for a dedicated high-pressure bypass depressurization and pressure reduction device, simplifying the system structure, and reducing equipment investment. Simultaneously, by safely integrating the high-pressure bypass steam into the medium-pressure bypass pipeline, centralized management and recovery of bypass steam energy at different pressure levels are achieved, ensuring the coordination and safety of system operation during unit start-up, shutdown, and load changes.

[0037] Furthermore, during unit start-up and shutdown, the high-pressure bypass steam from high-pressure bypass valve 27 is cooled by reheater 2 within waste heat boiler 26, and after cooling, enters the main medium-pressure bypass steam stream controlled by medium-pressure bypass valve 20. During the transitional operating conditions of unit start-up or shutdown, when steam parameters do not meet the requirements for entering the turbine, high-pressure bypass valve 27 opens. At this time, the high-temperature, high-pressure main steam generated from the high-pressure superheater of waste heat boiler 26 does not enter the high-pressure cylinder 7 of the turbine, but flows out through high-pressure bypass valve 27 and enters the inlet pipe of reheater 2, which is directly connected to the valve outlet.

[0038] Reheater 2, originally used in the waste heat boiler for reheating the exhaust steam from the high-pressure cylinder of the steam turbine, now serves as the cooling unit for the high-pressure bypass steam. After entering the heat exchange tube bundle of reheater 2, the high-pressure bypass steam exchanges heat with the exhaust gas from the gas turbine flowing through the reheater flue. Since the exhaust gas from the gas turbine, at approximately 300-400°C, still flows through the reheater flue, while the high-pressure bypass steam temperature is typically higher (potentially above 400°C depending on the unit's condition), the steam releases sensible heat into the flue gas, achieving initial cooling. This heat exchange process reduces the high-pressure steam temperature by approximately 50-100°C, and simultaneously, due to the pressure drop generated by flowing through the reheater tube bundle, the steam pressure also decreases accordingly.

[0039] After cooling and depressurization, the steam exits from the outlet of reheater 2, with its temperature and pressure parameters approaching the level of the medium-pressure bypass pipeline steam. This steam is introduced into the medium-pressure steam header through a connecting pipe, where it mixes with the medium-pressure main steam from the medium-pressure superheater of the waste heat boiler. During unit start-up and shutdown, the medium-pressure main steam valve is closed, while the medium-pressure bypass valve 20 remains open. Therefore, the mainstream of the mixed medium-pressure steam flows entirely through the medium-pressure bypass valve 20 to the subsequent system. This mainstream of medium-pressure steam, containing components of the original high-pressure bypass steam, then enters the medium-pressure bypass cooler 19. In the indirect heat exchange medium-pressure bypass cooler 19, the steam undergoes deep heat exchange with the recovered working fluid, transferring its heat to the working fluid. After being further cooled to near saturation temperature, it is finally discharged into the condenser 10 for condensation.

[0040] Furthermore, the low-pressure bypass cooler 18 and the medium-pressure bypass cooler 19 are indirect heat exchangers, with steam from the corresponding bypass flowing on the heat-releasing side and working fluid flowing on the heat-absorbing side. Heat exchange occurs through the indirect wall, reducing the temperature and pressure of the steam and heating the working fluid.

[0041] In this system, both the low-pressure bypass cooler 18 and the medium-pressure bypass cooler 19 adopt a shell-and-tube heat exchanger structure, which can be implemented as either a shell-and-tube heat exchanger or a plate heat exchanger. The inlet of the low-pressure bypass cooler 18 is connected to the outlet of the low-pressure bypass valve 17 via a pipe, while the inlet of the medium-pressure bypass cooler 19 is connected to the outlet of the medium-pressure bypass valve 20 via a pipe. During unit start-up and shutdown, when these bypass valves are opened, steam from the corresponding pressure level enters the shell side of its respective cooler (taking a shell-and-tube type as an example), and undergoes non-contact heat exchange with the recovered working fluid in the tube side as it flows through the heat exchanger. During the flow, the steam continuously releases sensible and latent heat, and its temperature gradually decreases to near the saturation temperature at that pressure. At the same time, due to the flow resistance, its pressure also decreases accordingly. Finally, the cooled steam is discharged from the cooler outlet and guided to the condenser 10 for condensation. On the other side of the heat exchanger, the liquid recovery working fluid from the second outlet of the gas-liquid separator 21 enters the tube-side inlet of the low-pressure bypass cooler 18 and the medium-pressure bypass cooler 19 through parallel pipelines. As the working fluid flows through the tubes, it absorbs heat from the shell-side steam through the metal partition wall, causing its temperature to rise and partially vaporize, forming a gas-liquid two-phase mixture. The heat-absorbed working fluid flows out from the tube-side outlet of each cooler and is transported to the low-pressure ejector fluid inlet of the ejector 22 through a collecting pipeline. This heat exchange process effectively transfers the heat energy from the waste steam to the recovery working fluid, creating conditions for subsequent energy enhancement and storage.

[0042] By employing a partitioned heat exchanger as the core device for heat transfer, reliable isolation and efficient heat exchange between bypass steam at different pressure levels and the closed-loop working fluid are achieved. This arrangement ensures the purity and operational safety of both the steam and working fluid sides, while also enabling effective heat transfer through the thermal conductivity of the metal walls. Simultaneously, the parallel-connected cooler structure allows the system to simultaneously process bypass steam from different pressure levels and independently perform heat exchange based on the actual flow rate and parameters of each bypass. This improves the adaptability and operational stability of the entire waste heat recovery system, providing crucial technical support for energy recovery during start-up and shutdown of combined cycle units.

[0043] Furthermore, the ejector 22 includes a high-pressure driving fluid inlet, a low-pressure ejector fluid inlet, and a mixed fluid outlet; the high-pressure driving fluid inlet is connected to the high-pressure working fluid output by the compressor 24; the low-pressure ejector fluid inlet is connected to the heat absorption side outlet of the low-pressure bypass cooler 18 and the medium-pressure bypass cooler 19.

[0044] As a key component for conveying and pressurizing the working fluid in this waste heat recovery system, the ejector 22 adopts a structural design with a specific internal profile. Its shell is provided with three main interfaces: a high-pressure driving fluid inlet, a low-pressure ejector fluid inlet, and a mixed fluid outlet. The high-pressure driving fluid inlet is directly connected to the exhaust port of the compressor 24 through a pipeline to receive the high-pressure gaseous working fluid from the outlet of the compressor 24. The low-pressure ejector fluid inlet is connected to the heat absorption side working fluid outlets of the low-pressure bypass cooler 18 and the medium-pressure bypass cooler 19 through parallel connecting pipes to introduce the low-pressure gas-liquid two-phase working fluid formed after absorbing heat in them. During operation, the high-pressure working fluid from compressor 24 serves as the driving medium, entering the high-pressure driving fluid inlet of ejector 22. It flows through the internal Laval nozzle-shaped contraction-expansion channel, where its pressure energy is converted into kinetic energy, forming a high-speed, low-pressure jet. This high-speed jet creates a strong entrainment effect in the mixing chamber, generating sufficient vacuum at the low-pressure ejector fluid inlet, thereby continuously introducing the low-pressure working fluid from the bypass cooler into the mixing chamber. After sufficient momentum and mass exchange between the two working fluid flows of different energy levels in the mixing chamber, a medium-pressure mixed working fluid is formed. This mixed working fluid then flows through a diffuser section with gradually increasing cross-sectional area, where its kinetic energy is again converted into pressure energy, pressurizing the working fluid. Finally, it is discharged from the mixed fluid outlet and transported to the downstream gas-liquid separator 21. By utilizing the energy of the high-pressure working fluid to increase the pressure of the low-pressure working fluid, fluid transport and compression without external mechanical drive are achieved, effectively reducing the system's additional energy consumption.

[0045] Furthermore, the gas-liquid separator 21 separates the gas-liquid two-phase working fluid of the ejector 22 into a saturated gas phase working fluid and a saturated liquid phase working fluid or a subcooled liquid phase working fluid; the first outlet discharges the saturated gas phase working fluid to the compressor 24, and the second outlet discharges the saturated liquid phase working fluid or the subcooled liquid phase working fluid to the heat absorption side inlet of the low-pressure bypass cooler 18 and the medium-pressure bypass cooler 19.

[0046] The inlet of the gas-liquid separator 21 is directly connected to the mixed fluid outlet of the ejector 22 via a pipe, receiving the gas-liquid two-phase working fluid from the ejector. This separator employs centrifugal separation or gravity sedimentation principles and is internally equipped with baffles, swirling devices, or filling elements. When the gas-liquid two-phase working fluid enters the separator at a certain flow rate, its flow direction changes, the flow area increases, or it passes through a specially designed flow channel, significantly reducing the working fluid's velocity. During this process, the denser liquid working fluid settles to the bottom of the separator under gravity or centrifugal force, while the less dense gaseous working fluid accumulates at the top of the separator, thus achieving effective separation of the gas and liquid phases. The gaseous working fluid that has reached saturation after separation is discharged from the first outlet located at the top of the separator and transported through a pipeline to the inlet of the compressor 24 to provide a pure gaseous medium for the subsequent compression and pressurization process. The saturated liquid working fluid after separation or the subcooled liquid working fluid formed by further cooling is discharged from the second outlet located at the bottom of the separator and returned to the heat absorption side inlet of the low-pressure bypass cooler 18 and the medium-pressure bypass cooler 19 through parallel transport pipelines, respectively, to participate in the heat absorption process again as a circulating working fluid.

[0047] The application of this gas-liquid separation device ensures that the working fluid entering the compressor is in a pure gas phase state, effectively preventing liquid slugging and equipment damage that may be caused by liquid working fluid entering the compressor. At the same time, by accurately returning the separated liquid working fluid to each bypass cooler, the balance and stability of the working fluid circulation of the entire waste heat recovery system are maintained, providing an important guarantee for the long-term reliable operation of the system.

[0048] Furthermore, the heat release side of the waste heat recovery heat exchanger 23 is coupled to the accumulator 25 through an intermediate heat medium loop; the intermediate heat medium conducts the heat energy of the heat release side of the waste heat recovery heat exchanger 23 to the accumulator 25.

[0049] The heat release side of the waste heat recovery heat exchanger 23 is coupled to the accumulator 25 through a closed intermediate heat medium loop. The intermediate heat medium circulating in the loop acts as a heat transfer carrier, transporting the recovered heat from the heat exchanger to the accumulator. Specifically, the high-temperature and high-pressure gaseous working fluid from the compressor 24 outlet first enters the tube side of the waste heat recovery heat exchanger 23. The heat energy it has absorbed in the bypass cooler and compressed is released through the metal partition wall to the intermediate heat medium circulating in the shell side. After the heat release is completed, the working fluid temperature decreases and may partially condense, and then flows to the subsequent process. The heated intermediate heat medium (which may include, but is not limited to, heat transfer oil, water, or a mixture thereof) is driven by a circulating pump and flows through a connecting pipe into the heat exchange unit of the accumulator 25. In this unit, the intermediate heat medium exchanges heat with the heat storage material in the accumulator (such as water or ceramic material for sensible heat storage, or phase change material for latent heat storage, etc.), storing the heat it carries in the energy storage medium. After the intermediate heat medium releases heat, its temperature decreases, and it then returns to the shell-side inlet of the waste heat recovery heat exchanger 23 to be reheated, thus forming a complete closed loop of heat transfer and storage.

[0050] Furthermore, the system is configured to have at least two operating modes: In normal power generation mode, the high-pressure bypass valve 27, the medium-pressure bypass valve 20 and the low-pressure bypass valve 17 are closed, and steam enters the steam turbine to do work through the high-pressure main steam valve 11, the high-pressure main steam regulating valve 12, the low-pressure main steam valve 13, the low-pressure main steam regulating valve 14, the medium-pressure main steam regulating valve 15 and the medium-pressure main steam valve 16.

[0051] In normal power generation mode, the high-pressure bypass valve 27, the medium-pressure bypass valve 20, and the low-pressure bypass valve 17 are all closed. At this time, the main steam and reheat steam of each pressure level flow through the fully open high-pressure main steam valve 11 and high-pressure main steam regulating valve 12, medium-pressure main steam regulating valve 15 and medium-pressure main steam valve 16, and low-pressure main steam valve 13 and low-pressure main steam regulating valve 14, and enter the high-pressure cylinder 7, medium-pressure cylinder 8, and low-pressure cylinder 9 of the steam turbine in sequence to expand and do work, converting thermal energy into mechanical energy to drive the generator to generate electricity. At this time, the steam bypass system is in standby mode.

[0052] In the unit start-up and shutdown mode, the intermediate pressure bypass valve 20 and the low pressure bypass valve 17 are opened, and the high pressure main steam valve 11, the high pressure main steam regulating valve 12, the intermediate pressure main steam regulating valve 15, the intermediate pressure main steam valve 16, the low pressure main steam valve 13, and the low pressure main steam regulating valve 14 are closed. The steam from the low pressure bypass and the intermediate pressure bypass flows through the low pressure bypass cooler 18 and the intermediate pressure bypass cooler 19 respectively for heat recovery before entering the condenser 10. The steam flowing through the high pressure bypass is connected to the intermediate pressure bypass pipeline through the reheater 2 of the waste heat boiler 26 and then guided to the condenser 10.

[0053] When the unit enters the start-up or shutdown phase, the system switches to start-stop mode. At this time, the intermediate-pressure bypass valve 20 and the low-pressure bypass valve 17 are opened, while all main steam valves and control valves leading to the turbine, including the high-pressure main steam valve 11 and high-pressure main steam control valve 12, the intermediate-pressure main steam control valve 15 and intermediate-pressure main steam valve 16, and the low-pressure main steam valve 13 and low-pressure main steam control valve 14, are closed to isolate the turbine. In this configuration, the low-pressure superheated steam from the boiler is entirely introduced into the low-pressure bypass cooler 18 through the open low-pressure bypass valve 17, and the intermediate-pressure superheated steam is entirely introduced into the intermediate-pressure bypass cooler 19 through the open intermediate-pressure bypass valve 20. The two streams of steam exchange heat with the recovered working fluid in their respective coolers, transferring the heat they carry to the working fluid. The cooled steam is then finally discharged into the condenser 10. Meanwhile, the high-pressure superheated steam is led to the reheater 2 in the waste heat boiler 26 through the open high-pressure bypass valve 27. As it flows through the heating surface of the reheater, it is cooled down by the flue gas. Then it flows into the medium-pressure steam header and mixes with the steam from the medium-pressure superheater. Together, they enter the medium-pressure bypass cooler 19 through the open medium-pressure bypass valve 20 to participate in the heat recovery process, and finally are discharged to the condenser 10.

[0054] The operating condition-based mode switching mechanism ensures that the unit can maintain the best thermodynamic cycle efficiency during normal operation, while under unstable operating conditions such as start-up and shutdown, it can safely and effectively recover the originally abandoned bypass steam heat and realize the storage and subsequent utilization of thermal energy through energy storage devices, thereby significantly improving the comprehensive energy utilization level and economy of combined cycle power plants during peak-shaving operation.

[0055] Accordingly, a second aspect of the present invention provides a control method for a gas-steam combined cycle system with bypass waste heat recovery, wherein the control method includes the following steps: Step S1: During the unit startup or shutdown phase, open the high-pressure bypass valve 27, the medium-pressure bypass valve 20 and the low-pressure bypass valve 17, and close the main steam valve connected to the high-pressure cylinder 7, the medium-pressure cylinder 8 and the low-pressure cylinder 9, so that steam can flow through the bypass pipeline.

[0056] The control system issues commands to switch the high-pressure bypass valve 27, the medium-pressure bypass valve 20, and the low-pressure bypass valve 17 to the open state, while simultaneously switching the main steam valves connected to the high-pressure cylinder 7, the medium-pressure cylinder 8, and the low-pressure cylinder 9 to the closed state. This combination of valve state switching establishes a bypass flow path for steam, ensuring that all steam of various pressure levels generated from the waste heat boiler 26 flows through the bypass pipeline and no longer enters the turbine to perform work. This ensures the safety of the turbine when steam parameters do not meet requirements and creates the preconditions for subsequent heat recovery.

[0057] Step S21: The steam flowing through the high-pressure bypass valve 27 is connected to the medium-pressure bypass pipeline via the reheater 2 of the waste heat boiler 26 and then guided to the condenser 10.

[0058] High-temperature, high-pressure steam from the high-pressure superheater of the waste heat boiler enters the reheater 2 inside the waste heat boiler 26 via a connecting pipe after the high-pressure bypass valve 27 is opened. Inside the reheater, the high-pressure steam exchanges heat counter-currently with the medium-temperature flue gas flowing through the heating surface, reducing the steam temperature from over 500℃ to the range of 380-420℃, and the pressure correspondingly decreases to the medium-pressure bypass level. The steam, having completed parameter adjustment, exits from the reheater outlet and flows into the medium-pressure steam header through a tee fitting. After thorough mixing with the steam from the medium-pressure superheater, it forms a uniformly heated medium-pressure steam flow, which is finally guided to the condenser 10 via the medium-pressure bypass system to complete the condensation process.

[0059] Step S22: Steam flowing through low-pressure bypass valve 17 enters low-pressure bypass cooler 18, and the heat of the steam is recovered by the working fluid flowing on the heat absorption side of low-pressure bypass cooler 18.

[0060] Low-pressure saturated steam from the low-pressure superheater of the waste heat boiler enters the shell side of the low-pressure bypass cooler 18 through a pipe with a diameter of 200-300 mm when the low-pressure bypass valve 17 is open. As the steam flows through the cooler, it exchanges heat with the recovered working fluid flowing in the tube side, raising the working fluid temperature from 40-60℃ to 80-100℃. Simultaneously, the working fluid absorbs some of its latent heat of vaporization and evaporates, while the steam is cooled to its saturation temperature at the corresponding pressure and partially condenses. The mixture of condensate and uncondensed steam after heat exchange is discharged to the condenser 10 through the outlet pipe, achieving effective heat transfer.

[0061] Step S23: Steam flowing through medium-pressure bypass valve 20 enters medium-pressure bypass cooler 19, and the heat of the steam is recovered by the working fluid flowing on the heat absorption side of medium-pressure bypass cooler 19.

[0062] Step S23 involves two steam sources: one is medium-pressure steam directly from the medium-pressure superheater, and the other is the original high-pressure bypass steam after being processed by the reheater. These two steam streams mix in the medium-pressure header and then enter the medium-pressure bypass cooler 19 through the medium-pressure bypass valve 20. Inside the cooler, the steam transfers heat to the tube-side working fluid during its shell-side flow, raising the working fluid temperature from 50-70°C to 120-150°C, while the steam is cooled to its saturation temperature. The cooled steam-condensate mixture is then discharged into the condenser 10 through pipes, completing the entire heat exchange process.

[0063] Step S3: After absorbing heat in the low-pressure bypass cooler 18 and the medium-pressure bypass cooler 19, the working fluid enters the ejector 22, and then undergoes gas-liquid separation by the gas-liquid separator 21. The separated gaseous working fluid is pressurized by the compressor 24 and enters the waste heat recovery heat exchanger 23 to release heat to the accumulator 25. The separated liquid working fluid returns to the heat absorption side inlet of the low-pressure bypass cooler 18 and the medium-pressure bypass cooler 19, forming a cycle.

[0064] After the heat transfer on the steam side is completed, the working fluid that absorbs heat in the low-pressure bypass cooler 18 and the medium-pressure bypass cooler 19 forms a gas-liquid two-phase mixture, which enters the ejector 22 through the collecting pipeline. In the ejector 22, the working fluid undergoes an ejection and mixing process before entering the gas-liquid separator 21 for phase separation. The separated gas phase working fluid enters the compressor 24 for compression and pressurization to improve its energy grade, and is then transported to the waste heat recovery heat exchanger 23, where the high-grade heat energy it contains is released to the intermediate heat medium. Finally, the heat is stored in the accumulator 25. The separated liquid phase working fluid returns to the heat absorption side inlet of the low-pressure bypass cooler 18 and the medium-pressure bypass cooler 19 through the return pipeline to participate in the heat absorption process again, forming a continuous working fluid cycle.

[0065] The embodiments of the present invention aim to protect a gas-steam combined cycle system with bypass waste heat recovery and its control method, and have the following effects: 1. By adding an independent recovery loop consisting of a low-pressure bypass cooler, a medium-pressure bypass cooler, an ejector, a gas-liquid separator, a compressor, and a waste heat recovery heat exchanger, the steam heat that was originally wasted by bypassing the condenser during unit start-up and shutdown is effectively captured. After absorbing steam heat in the bypass cooler, the working fluid in this loop undergoes ejection, separation, and pressurization steps, and finally transfers high-quality heat energy to the accumulator for storage in the waste heat recovery heat exchanger, which can then be used by other equipment. This converts waste heat energy into usable energy, directly reducing the unit's fuel consumption and improving the operating economy and energy utilization efficiency of the entire combined cycle system. 2. The high-pressure bypass steam is cleverly guided to the existing reheater in the waste heat boiler for cooling, and then safely merged into the medium-pressure bypass pipeline. This avoids the need to set up a complex and expensive cooling and desuperheating device for the high-pressure bypass separately, simplifying the system structure. At the same time, by guiding the high, medium and low-pressure bypass steam to a shared waste heat recovery device and condenser, the integration and orderly processing of steam energy at different pressure levels is achieved. This not only ensures the safe operation of the unit under start-up and shutdown conditions and avoids the risk of water erosion of the turbine, but also improves the system integration and reliability. 3. By configuring two distinct operating modes—normal power generation and start-up / shutdown—and based on precise switching of valve status, the system can flexibly switch between "full-power generation" and "bypass heat recovery" states. This intelligent operating strategy enables the unit to easily cope with the increasingly frequent start-up and shutdown peak-shaving demands caused by the integration of a high proportion of renewable energy. While ensuring grid security, it ensures continuous energy recovery during each start-up and shutdown process, effectively solving the pain point of efficiency decline in traditional units during peak-shaving operation, and significantly enhancing the adaptability and competitiveness of combined cycle power plants under the new power system.

[0066] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the specific implementation of the present invention. Any modifications or equivalent substitutions that do not depart from the spirit and scope of the present invention should be covered within the scope of protection of the claims of the present invention.

Claims

1. A combined gas-steam cycle system with bypass waste heat recovery, characterized in that, include: Gas turbine (5), waste heat boiler (26) connected to the flue gas of the gas turbine (5), steam turbine and condenser (10) driven by steam generated by the waste heat boiler (26), and bypass waste heat recovery device; The steam turbine includes at least a high-pressure cylinder (7), a medium-pressure cylinder (8), and a low-pressure cylinder (9) that receive steam through the main steam valve. The system is also provided with a bypass pipeline connected in parallel with the main steam valve. The bypass pipeline is provided with a high-pressure bypass valve (27), a medium-pressure bypass valve (20), and a low-pressure bypass valve (17). The bypass waste heat recovery device includes: a low-pressure bypass cooler (18) connected to the low-pressure bypass valve (17) via pipeline, a medium-pressure bypass cooler (19) connected to the medium-pressure bypass valve (20) via pipeline, and an ejector (22), a gas-liquid separator (21), a compressor (24), and a waste heat recovery heat exchanger (23) connected in sequence via pipeline; The heat absorption sides of the low-pressure bypass cooler (18) and the medium-pressure bypass cooler (19) are connected in parallel and then fluidly communicated with the inlet of the ejector (22). The inlet of the gas-liquid separator (21) is in fluid communication with the outlet of the ejector (22), the first outlet of the gas-liquid separator (21) is in communication with the inlet of the compressor (24), and its second outlet is in fluid communication with the heat absorption side inlet of the low-pressure bypass cooler (18) and the medium-pressure bypass cooler (19), thus forming a working fluid circulation. The heat release side of the waste heat recovery heat exchanger (23) is coupled to an accumulator (25) to store the recovered heat in the accumulator (25).

2. The combined gas-steam cycle system with bypass waste heat recovery according to claim 1, characterized in that, The outlet of the high-pressure bypass valve (27) is connected to the reheater (2) in the waste heat boiler (26), so that the high-pressure bypass steam flows into the medium-pressure bypass pipeline through the reheater (2).

3. The combined gas-steam cycle system with bypass waste heat recovery according to claim 2, characterized in that, During the start-up and shutdown phase of the unit, the high-pressure bypass steam of the high-pressure bypass valve (27) is cooled by the reheater (2) in the waste heat boiler (26), and after cooling, it enters the medium-pressure bypass steam mainstream controlled by the medium-pressure bypass valve (20).

4. The combined gas-steam cycle system with bypass waste heat recovery according to claim 1, characterized in that, The low-pressure bypass cooler (18) and the medium-pressure bypass cooler (19) are partitioned heat exchangers. Steam from the corresponding bypass flows on the heat-releasing side, and the working fluid flows on the heat-absorbing side. Heat exchange is carried out through the partition to reduce the temperature and pressure of the steam and heat the working fluid.

5. The combined gas-steam cycle system with bypass waste heat recovery according to claim 1, characterized in that, The ejector (22) includes a high-pressure driving fluid inlet, a low-pressure ejector fluid inlet, and a mixed fluid outlet; The high-pressure driving fluid inlet is connected to the high-pressure working fluid output by the compressor (24); The low-pressure ejector fluid inlet is in fluid communication with the heat absorption side outlet of the low-pressure bypass cooler (18) and the medium-pressure bypass cooler (19).

6. The combined gas-steam cycle system with bypass waste heat recovery according to claim 1, characterized in that, The gas-liquid separator (21) separates the gas-liquid two-phase working fluid of the ejector (22) into a saturated gas phase working fluid and a saturated liquid phase working fluid or a subcooled liquid phase working fluid. The first outlet discharges the saturated gaseous working fluid to the compressor (24), and the second outlet discharges the saturated liquid working fluid or subcooled liquid working fluid to the heat absorption side inlet of the low-pressure bypass cooler (18) and the medium-pressure bypass cooler (19).

7. The combined gas-steam cycle system with bypass waste heat recovery according to claim 1, characterized in that, The heat release side of the waste heat recovery heat exchanger (23) is coupled to the accumulator (25) through an intermediate heat medium circuit; The intermediate heat medium conducts the heat energy from the heat release side of the waste heat recovery heat exchanger (23) to the energy storage device (25).

8. The combined gas-steam cycle system with bypass waste heat recovery according to claim 7, characterized in that, The intermediate heat medium is heat transfer oil or water.

9. The combined gas-steam cycle system with bypass waste heat recovery according to any one of claims 1-8, characterized in that, The system is configured to have at least two operating modes: In normal power generation mode, the high-pressure bypass valve (27), medium-pressure bypass valve (20) and low-pressure bypass valve (17) are closed, and steam enters the steam turbine to do work through the high-pressure main steam valve (11), high-pressure main steam regulating valve (12), low-pressure main steam valve (13), low-pressure main steam regulating valve (14), medium-pressure main steam regulating valve (15), and medium-pressure main steam valve (16). In the unit start-up and shutdown mode, the medium-pressure bypass valve (20) and the low-pressure bypass valve (17) are opened, and the high-pressure main steam valve (11), the high-pressure main steam regulating valve (12), the medium-pressure main steam valve (15), the medium-pressure main steam valve (16), the low-pressure main steam valve (13), and the low-pressure main steam regulating valve (14) are closed. The steam from the low-pressure bypass and the medium-pressure bypass flows through the low-pressure bypass cooler (18) and the medium-pressure bypass cooler (19) respectively for heat recovery before entering the condenser (10). The steam flowing through the high-pressure bypass merges into the medium-pressure bypass pipeline through the reheater (2) of the waste heat boiler (26) and is then guided to the condenser (10).

10. A control method for a gas-steam combined cycle system with bypass waste heat recovery, characterized in that, Controlling the gas-steam combined cycle system with bypass waste heat recovery as described in any one of claims 1-9, the control method includes the following steps: During the start-up or shutdown phase of the unit, the high-pressure bypass valve (27), the medium-pressure bypass valve (20) and the low-pressure bypass valve (17) are opened, and the main steam valve connected to the high-pressure cylinder (7), the medium-pressure cylinder (8) and the low-pressure cylinder (9) are closed, so that steam flows through the bypass pipeline; The steam flowing through the high-pressure bypass valve (27) is then channeled into the medium-pressure bypass pipeline via the reheater (2) of the waste heat boiler (26) and then guided to the condenser (10). Steam flowing through the low-pressure bypass valve (17) enters the low-pressure bypass cooler (18), and the heat of the steam is recovered by the working fluid flowing on the heat absorption side of the low-pressure bypass cooler (18). Steam flowing through the medium-pressure bypass valve (20) enters the medium-pressure bypass cooler (19), and the heat of the steam is recovered by the working fluid flowing on the heat absorption side of the medium-pressure bypass cooler (19). The working fluid absorbs heat in the low-pressure bypass cooler (18) and the medium-pressure bypass cooler (19) and then enters the ejector (22), where it is separated into gas and liquid by the gas-liquid separator (21). The separated gaseous working fluid is pressurized by the compressor (24) and enters the waste heat recovery heat exchanger (23) to release heat to the accumulator (25). The separated liquid working fluid returns to the heat absorption side inlet of the low-pressure bypass cooler (18) and the medium-pressure bypass cooler (19) to form a cycle.

Images