Combined cycle power generation system and method thereof

Abstract

The invention relates to a combined cycle power generation system and a method thereof. The combined cycle power generation system comprises a waste heat recovery system and a gas-steam combined cycle system which are connected with each other. The waste heat recovery system is configured to recover the high-temperature exhaust gas to generate first steam, part of the first steam is used for driving the extraction condensing type steam turbine to generate power, and part of the first steam is used for providing process steam according to process requirements. The gas-steam combined cycle system is configured as follows: the gas turbine directly generates power; and the high-temperature waste gas is recycled to generate second steam which is used for driving the straight condensing steam turbine to generate power. According to the combined cycle power generation system, waste heat resources can be fully utilized, the overall energy efficiency is improved, and fuel consumption and carbon emission are reduced.

Description

Technical Field

[0001] This application relates to the field of energy development and utilization, and in particular to a combined cycle power generation system and method thereof. Background Technology

[0002] This application relates to the field of marine energy development and utilization, particularly power generation and waste heat recovery technologies for floating liquefied natural gas (FLNG) plants. Specifically, it pertains to the application of combined cycle gas turbine (CCGT) power generation on offshore floating production, storage, and transportation platforms, encompassing gas turbine generators (GTG), heat recovery steam generators (HRSG), steam turbine generators (STG), dual-timescale control for heat and electricity, and energy recovery and comprehensive utilization.

[0003] Traditional FLNG typically uses GTG or dual-fuel internal combustion engine generators (DF Engine Generation) as the main power source. GTGs, employing a simple cycle, have limited efficiency, with a significant amount of waste heat from compressors and process fuels being directly emitted, resulting in low energy utilization. Dual-fuel engines are more efficient at low loads, but suffer from drawbacks such as high noise, strong vibration, and frequent maintenance. Furthermore, they have limited room for improvement in thermoelectric efficiency and relatively high emissions of particulate matter and nitrogen oxides.

[0004] Therefore, how to make full use of waste heat resources, improve overall energy efficiency, and reduce fuel consumption and carbon emissions has become an urgent issue that needs to be addressed. Summary of the Invention

[0005] Based on this, the embodiments of this application provide a combined cycle power generation system and method, which is conducive to making full use of waste heat resources, improving overall energy efficiency, and reducing fuel consumption and carbon emissions.

[0006] In some embodiments of this application, one aspect of the application provides a combined cycle power generation system, including: a waste heat recovery system and a gas-steam combined cycle system connected in series. The waste heat recovery system is configured to: recover high-temperature exhaust gas to generate first steam, a portion of which is used to drive an extraction condensing steam turbine to generate electricity, and a portion of which is used to provide process steam according to process requirements. The gas-steam combined cycle system is configured to: directly generate electricity using a gas turbine; and recover high-temperature waste gas to generate second steam, which is used to drive a pure condensing steam turbine to generate electricity.

[0007] In some embodiments of this application, the waste heat recovery system includes: a mixed refrigerant compressor-gas turbine module, a first waste heat recovery steam generation module, and a condensing steam turbine generator module.

[0008] The mixed refrigerant compressor-gas turbine module is configured such that the gas turbine drives the mixed refrigerant compressor to produce high-temperature exhaust gas.

[0009] The first waste heat recovery steam generation module is configured to: recover high-temperature exhaust gas to generate first steam; the first steam includes: high-pressure steam and low-pressure steam.

[0010] The extraction-condensing steam turbine generator module is configured to generate electricity in response to the expansion of high-pressure steam and to provide process steam in response to process requirements.

[0011] In some embodiments of this application, the first waste heat recovery steam generation module adopts a dual-pressure design, including a high-pressure evaporator and a low-pressure evaporator.

[0012] The high-pressure evaporator is configured to recover high-temperature exhaust gas and generate high-pressure steam.

[0013] The low-pressure evaporator is configured to recover high-temperature exhaust gas and generate low-pressure steam.

[0014] In some embodiments of this application, the extraction-condensing steam turbine generator module is provided with a steam extraction port. The steam extraction port is configured to extract a portion of the steam as process steam according to process requirements.

[0015] In some embodiments of this application, the waste heat recovery system further includes a power management system and a turbine regulation system, configured to coordinate and automatically balance electricity and process steam.

[0016] In some embodiments of this application, the gas-steam combined cycle system includes: a gas turbine power generation module, a second waste heat recovery steam generation module, and a pure condensing steam turbine generator module.

[0017] The gas turbine generator module is configured to burn fuel to drive the gas turbine generator module to generate electricity and produce high-temperature exhaust gas.

[0018] The second waste heat recovery steam generation module is configured to recover high-temperature waste gas and generate a second steam.

[0019] The condensing steam turbine generator module is configured to generate electricity in response to the expansion of a second steam.

[0020] In some embodiments of this application, when the first steam for process steam is insufficient, a second steam is provided as a supplement to provide process steam.

[0021] In some embodiments of this application, another aspect of this application also provides a combined cycle power generation method, which is executed using the combined cycle power generation system described in the foregoing embodiments. The combined cycle power generation method includes the following steps:

[0022] High-temperature exhaust gas is recovered to generate first steam. Part of the first steam is used to drive an extraction condensing steam turbine to generate electricity, and part of the first steam is used to provide process steam according to process requirements.

[0023] The gas turbine generates electricity directly; high-temperature exhaust gas is recovered to generate a second steam, which is used to drive a pure condensing steam turbine to generate electricity.

[0024] In some embodiments of this application, when the process demand for process steam increases, the extraction steam rate of the extraction condensing steam turbine is increased, and the power generation output is reduced accordingly.

[0025] When the process demand for process steam decreases, the amount of extracted steam is reduced, and the expansion work of the first steam in the extraction condensing steam turbine is increased to improve power generation output.

[0026] In some embodiments of this application, the power management system and the turbine regulation system are used to coordinate and automatically balance the power and process steam.

[0027] The embodiments of this application may have, or at least have, the following advantages:

[0028] This embodiment of the application changes the traditional simple cycle power generation mode, achieving an efficient and reliable supply of electricity and process steam through the coordinated operation of a waste heat recovery system and a gas-steam combined cycle system. First, the waste heat recovery system recovers waste heat from the gas turbine exhaust and supplies it to the extraction condensing steam turbine for power generation, providing process steam according to process requirements, thus achieving coordinated regulation of electricity and steam. Second, the gas-steam combined cycle system, as the main power generation unit, achieves optimal balance between steam and electricity through a gas turbine power generation module, a second waste heat recovery steam generation module, and a pure condensing steam turbine generator module. Thus, this embodiment of the application adopts central control and safety protection, combined with modular auxiliary facilities, to meet the high reliability, flexibility, and ease of maintenance requirements of offshore floating equipment operation, thereby fully utilizing waste heat resources, improving overall energy efficiency, reducing fuel consumption and carbon emissions, and significantly reducing fuel consumption and carbon dioxide emissions per unit of product, actively responding to the green and low-carbon development requirements of marine engineering.

[0029] Furthermore, this application innovatively adopts a combined mode of "extraction-condensing steam supply" and "pure condensing power generation". The extraction-condensing steam turbine can flexibly adjust the extraction steam volume and power generation according to process requirements to ensure a stable supply of process steam; the pure condensing steam turbine focuses on the efficient output of peak electricity. Under the unified scheduling of the central control system, the two achieve a dynamic optimal balance between the two major energy interfaces of electricity and steam, greatly enhancing the ability to cope with large load disturbances.

[0030] Furthermore, this application transforms the waste heat from gas turbine exhaust that was originally directly emitted into high-value electricity and process steam through system-level thermoelectric coupling and waste heat cascade utilization, achieving a qualitative change from "single power generation" to "combined heat and power", with overall energy efficiency significantly better than traditional solutions.

[0031] Therefore, the embodiments of this application adopt a system-level integrated and multi-stage regeneration approach for multi-source waste heat. Under the dual-pressure framework of high pressure and low pressure, a unified high-grade heat energy matching and distribution strategy is designed for both high-temperature exhaust gas and high-temperature waste gas to achieve global optimization for both extraction-condensation steam supply and condensation power generation. Compared with the simple thermodynamic cycle power generation system in the prior art where high-temperature exhaust gas is only recovered to the WHRU heat transfer oil system and high-temperature waste gas is not recovered, the embodiments of this application propose a system-level combined heat and power (CHP) optimization strategy. This strategy prioritizes process safety and operational stability, especially ensuring a reliable supply of process steam and meeting power demand and stability requirements, thereby further improving overall power generation efficiency, reducing fuel consumption, and reducing carbon emissions. Attached Figure Description

[0032] Figure 1 A schematic diagram of a combined cycle power generation system provided in an embodiment of this application;

[0033] Figure 2 This is a schematic flowchart of a combined cycle power generation method provided in an embodiment of this application.

[0034] Explanation of reference numerals in the attached diagram: 1. Waste heat recovery system; 11. Mixed refrigerant compressor-gas turbine module; 12. First waste heat recovery steam generation module; 13. Extraction-condensing steam turbine generator module;

[0035] 2. Gas-steam combined cycle system; 21. Gas turbine power generation module; 22. Second waste heat recovery steam generation module; 23. Pure condensing steam turbine generator module. Detailed Implementation

[0036] To facilitate understanding of this application, a more complete description will be provided below with reference to the accompanying drawings. Preferred embodiments of this application are shown in the drawings. However, this application can be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided to provide a thorough and complete understanding of the disclosure of this application.

[0037] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used herein in the specification of this application is for the purpose of describing particular embodiments only and is not intended to be limiting of the application. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0038] When using the terms “including,” “having,” and “comprising” as described herein, another component may be added unless explicitly qualifying terms such as “only,” “consisting of,” etc. are used. Unless otherwise stated, singular terms may include plural forms and should not be construed as having a quantity of one.

[0039] It should be understood that although the terms “first,” “second,” etc., may be used herein to describe various elements, these elements should not be limited by these terms. These terms are used only to distinguish one element from another. For example, without departing from the scope of this application, a first element may be referred to as a second element, and similarly, a second element may be referred to as a first element.

[0040] In this application, unless otherwise expressly specified and limited, the terms "connected" and "linked" should be interpreted broadly. For example, they can refer to a direct connection or an indirect connection through an intermediate medium, or they can refer to the internal connection of two elements or the interaction between two elements. Those skilled in the art can understand the specific meaning of the above terms in this application according to the specific circumstances.

[0041] It should be noted that the illustrations provided in this embodiment are only schematic representations of the basic concept of this application. Although the illustrations only show the components related to this application and are not drawn according to the actual number, shape and size of the components in the actual implementation, the form, quantity and proportion of each component in the actual implementation can be arbitrarily changed, and the layout of the components may also be more complex.

[0042] This application relates to the field of marine energy development and utilization, particularly power generation and waste heat recovery technologies for floating liquefied natural gas (FLNG) plants. Specifically, it pertains to the application of combined cycle gas turbine (CCGT) power generation on offshore floating production, storage, and transportation platforms, encompassing gas turbine generators (GTG), heat recovery steam generators (HRSG), steam turbine generators (STG), dual-timescale control for heat and electricity, and energy recovery and comprehensive utilization.

[0043] As a floating production facility integrating natural gas processing, liquefaction, storage, and export, FLNG needs to simultaneously meet the requirements of continuous process operation, power self-sufficiency, and stable power supply. FLNG generally operates in an islanded grid mode, and its power stability is highly dependent on the internal power generation system, with large load fluctuations (such as compressor start-up, process switching, LNG export, and propulsion).

[0044] Traditional FLNG systems typically use GTG (Gas Turbine Generator) or dual-fuel internal combustion engine generators (DF Engine Generation) as the main power source. GTGs with simple cycles have limited efficiency (30-38%), and a large amount of waste heat from compressors and process gas is directly emitted, resulting in low energy utilization. Dual-fuel engines are more efficient at low loads, but suffer from drawbacks such as high noise, strong vibration, and frequent maintenance. They also have limited potential for improving thermoelectric efficiency and relatively high emissions of particulate matter and nitrogen oxides. The mixed refrigerant cycle (MRC) compressor in the natural gas liquefaction process typically discharges at temperatures of 350–500°C, containing significant waste heat. Direct emission of this heat not only wastes energy but may also increase the cooling burden on the system. By adding a combined cycle system—either a waste heat recovery boiler (HRSG) + gas turbine generator (GTG) with a waste heat recovery boiler (HRSG) + steam turbine (STG)—to the MRC-driven gas turbine, energy utilization efficiency can be significantly improved. Combined cycle gas turbine (CCGT) power generation on land is widely used, achieving efficiencies of 50-63%, and offers significant advantages in fuel savings and emission reduction. However, its complex structure and stringent requirements for water / steam quality present certain technical challenges for direct application to offshore FLNG.

[0045] In recent years, major manufacturers have developed lightweight, modular gas turbines, waste heat boilers, and steam turbines to adapt to the single-lift and limited space requirements of floating platforms. The new generation of FLNG power systems not only considers electricity output but also integrates process heating, cold energy recovery, and carbon dioxide capture to achieve low-carbon operation and comprehensive energy management. Digital twins and AI-powered intelligent diagnostics are increasingly being applied to water and steam quality monitoring, load forecasting, and islanded grid stability control, improving the safety and intelligence of system operation. In summary, FLNG power generation technology is evolving from a single power source to combined cycle and integrated energy and intelligent systems. This technical solution is proposed against this backdrop, aiming to improve energy efficiency, reduce emissions, and meet the specific requirements of floating units for lightweighting, modularity, and intrinsic safety.

[0046] In currently known FLNG power systems, onshore combined cycle (CCGT) power plants consist of a gas turbine (GTG), a waste heat boiler (HRSG), and a steam turbine (STG). Advantages: high efficiency (50-63%), full utilization of waste heat, and low CO2 emission intensity. Floating Production Storage and Offloading (FPSO) CCGT technology, similar to onshore systems, consists of a GTG, HRSG, and STG, employing a modular design. It can be combined with dual-fuel gas turbine generator sets (diesel / natural gas) to adapt to fluctuations in gas supply. Advantages: higher thermal efficiency, reduced carbon emissions, and greater fuel flexibility. Most FLNGs use simple cycle gas turbine generators (GTG) for power generation, or partially use dual-fuel internal combustion engines (DF engines). Advantages: Waste Heat Recovery Units (WHRUs) recover hot water or hot oil used in the production process, recovering a certain degree of waste heat. Onshore combined cycle power plant (CCGT) technology is large in scale and weight, making it unsuitable for floating platforms; high water / steam quality requirements pose challenges to offshore freshwater production systems; conventional designs do not consider the vibration, tilting, module hoisting, and corrosion protection requirements of the marine environment. FPSO CCGT technology suffers from less stable coupling between dual-fuel units and waste heat boilers compared to onshore gas turbines, making it difficult to form an efficient and stable system under partial load or frequent start-stop operations. FPSOs often operate in isolation, experiencing significant grid frequency and voltage fluctuations, making it difficult to quickly respond to large load disturbances. FLNG GTG or DF Engine technologies have low single-cycle efficiency (30-38%), with a large amount of compressor / process gas waste heat not being fully utilized. Dual-fuel units have poor coupling with waste heat boilers, making it difficult to form an efficient and stable system; the grid operates in isolation, with poor frequency and voltage stability, unable to effectively cope with large load disturbances (such as compressor start-up, LNG export, and propulsion). Some FLNG trial waste heat utilization devices have limited functionality and do not form a complete and efficient cycle with the steam turbine. The thermal system is not fully optimized, resulting in limited energy utilization efficiency.

[0047] Therefore, how to make full use of waste heat resources, improve overall energy efficiency, and reduce fuel consumption and carbon emissions has become an urgent issue that needs to be addressed.

[0048] Based on this, the embodiments of this application provide a combined cycle power generation system and method, which is conducive to making full use of waste heat resources, improving overall energy efficiency, and reducing fuel consumption and carbon emissions.

[0049] In some embodiments, please refer to Figure 1This application provides a combined cycle power generation system, comprising: a waste heat recovery system 1 and a gas-steam combined cycle system 2 connected to each other. The waste heat recovery system 1 is configured to: recover high-temperature exhaust gas to generate first steam, a portion of which is used to drive an extraction-condensing steam turbine for power generation, and a portion of which is used to provide process steam according to process requirements. The gas-steam combined cycle system 2 is configured to: directly generate electricity using a gas turbine; and recover high-temperature waste gas to generate second steam, which is used to drive a pure condensing steam turbine for power generation.

[0050] In this embodiment, the traditional simple cycle power generation mode is changed. Through the coordinated operation of the waste heat recovery system 1 and the gas-steam combined cycle system 2, an efficient and reliable supply of electricity and process steam is achieved. First, the waste heat recovery system 1 recovers the exhaust waste heat from the gas turbine and supplies it to the extraction condensing steam turbine for power generation, providing process steam according to process requirements, thus achieving coordinated regulation of electricity and steam. Second, the gas-steam combined cycle system, as the main power generation unit, achieves optimal balance between steam and electricity through the gas turbine power generation module, the second waste heat recovery steam generation module, and the pure condensing steam turbine generator module. Thus, this embodiment adopts central control and safety protection, combined with modular auxiliary facilities, to meet the high reliability, flexibility, and ease of maintenance requirements of offshore floating equipment operation. This fully utilizes waste heat resources, improves overall energy efficiency, reduces fuel consumption and carbon emissions, and significantly reduces fuel consumption and carbon dioxide emissions per unit of product, actively responding to the green and low-carbon development requirements of marine engineering.

[0051] Furthermore, this application innovatively adopts a combined mode of "extraction-condensing steam supply" and "pure condensing power generation". The extraction-condensing steam turbine can flexibly adjust the extraction steam volume and power generation according to process requirements to ensure a stable supply of process steam; the pure condensing steam turbine focuses on the efficient output of peak electricity. Under the unified scheduling of the central control system, the two achieve a dynamic optimal balance between the two major energy interfaces of electricity and steam, greatly enhancing the ability to cope with large load disturbances.

[0052] Furthermore, this application transforms the waste heat from gas turbine exhaust that was originally directly emitted into high-value electricity and process steam through system-level thermoelectric coupling and waste heat cascade utilization, achieving a qualitative change from "single power generation" to "combined heat and power", with overall energy efficiency significantly better than traditional solutions.

[0053] Therefore, the embodiments of this application adopt a system-level integrated and multi-stage regeneration approach for multi-source waste heat. Under the dual-pressure framework of high pressure and low pressure, a unified high-grade heat energy matching and distribution strategy is designed for both high-temperature exhaust gas and high-temperature waste gas to achieve global optimization for both extraction-condensation steam supply and condensation power generation. Compared with the simple thermodynamic cycle power generation system in the prior art where high-temperature exhaust gas is only recovered to the WHRU heat transfer oil system and high-temperature waste gas is not recovered, the embodiments of this application propose a system-level combined heat and power (CHP) optimization strategy. This strategy prioritizes process safety and operational stability, especially ensuring a reliable supply of process steam and meeting power demand and stability requirements, thereby further improving overall power generation efficiency, reducing fuel consumption, and reducing carbon emissions.

[0054] In some embodiments, the waste heat recovery system 1 includes: a mixed refrigerant compressor-gas turbine module 11, a first waste heat recovery steam generation module 12, and a condensing steam turbine generator module 13.

[0055] The mixed refrigerant compressor-gas turbine module 11 is configured such that the gas turbine drives the mixed refrigerant compressor to generate high-temperature exhaust gas.

[0056] The first waste heat recovery steam generation module 12 is configured to: recover high-temperature exhaust gas to generate first steam; the first steam includes: high-pressure steam and low-pressure steam.

[0057] The extraction-condensing steam turbine generator module 13 is configured to generate electricity in response to the expansion of high-pressure steam and to provide process steam in response to process requirements.

[0058] In some embodiments, the first waste heat recovery steam generation module 12 adopts a dual-pressure design, including a high-pressure evaporator and a low-pressure evaporator.

[0059] The high-pressure evaporator is configured to recover high-temperature exhaust gas and generate high-pressure steam.

[0060] The low-pressure evaporator is configured to recover high-temperature exhaust gas and generate low-pressure steam.

[0061] In some embodiments, the extraction-condensing steam turbine generator module 13 is provided with a steam extraction port. The steam extraction port is configured to extract a portion of the steam as process steam according to process requirements.

[0062] In some embodiments, the waste heat recovery system 1 further includes a power management system and a turbine regulation system, configured to coordinate and automatically balance electricity and process steam.

[0063] In some embodiments, the gas-steam combined cycle system 2 includes: a gas turbine power generation module 21, a second waste heat recovery steam generation module 22, and a pure condensing steam turbine generator module 23.

[0064] The gas turbine generator module 21 is configured to burn fuel to drive the gas turbine generator module to generate electricity and produce high-temperature exhaust gas.

[0065] The second waste heat recovery steam generation module 22 is configured to: recover high-temperature waste gas and generate second steam.

[0066] The condensing steam turbine generator module 23 is configured to generate electricity in response to the expansion of the second steam.

[0067] In some embodiments, multiple natural gas / liquid fuel dual-fuel internal combustion engines can be combined to generate electricity, replacing the combined cycle power generation of a single gas turbine and waste heat boiler.

[0068] In some examples, a dual-fuel gas turbine generates electricity, while a hybrid chiller-gas turbine produces high-temperature exhaust gas, utilizing high-grade waste heat. For instance, this generates high-grade heat energy that can be used for steam in the FLNG process; it allows for flexible load adjustment, suitable for liquefaction processes with large load fluctuations; and it offers high system redundancy, enabling better load regulation.

[0069] In some examples, if the first steam source for process steam is insufficient, the second steam source is used as a supplement to provide process steam. That is, only when the entire FLNG unit is started up, if the first steam source is insufficient, the second steam source is used as a supplement to provide start-up steam for the process units. In this way, a stable process steam source can be provided in the initial stage of FLNG unit startup without relying on a separate auxiliary boiler.

[0070] In some examples, dual-fuel gas turbines generate electricity, and high- and low-grade waste heat is utilized in a cascade manner. For instance, high-temperature waste heat drives absorption chillers (i.e., providing cooling); low-temperature waste heat generates electricity through organic Rankine cycles (generating additional electricity), or is used for low-temperature heating (hot water and fresh water preparation in domestic areas); the electricity can drive mechanical chillers or pumps to achieve dynamic matching and optimized utilization of heating and cooling loads.

[0071] In some embodiments, the working principle of the waste heat recovery system 1 for recovering waste heat to the extraction condensing steam turbine is as follows:

[0072] First, heat source formation: The compressor of the mixed refrigeration unit on FLNG is directly driven by the gas turbine; after the gas turbine burns natural gas, it produces high-temperature and high-flow exhaust gas (usually >500℃), the main function of which is to drive the compressor, and the exhaust gas itself contains a large amount of high-grade waste heat.

[0073] Second, waste heat recovery: Please refer to the following section. Figure 1The four FLNG production lines have a total of four refrigeration compressors, and each refrigeration compressor is equipped with a waste heat boiler. The high-temperature exhaust gas passes through the high-pressure and low-pressure evaporators / superheaters, economizers and other heating surfaces in sequence to generate high-pressure steam and low-pressure steam. This steam is then transported to the extraction condensing steam turbine as its driving medium.

[0074] Third, energy conversion in extraction-condensing steam turbines: High-pressure steam enters the high-pressure stage of the extraction-condensing steam turbine, expands, and drives the generator, converting some of the energy into electricity. At certain stages of the high-pressure or low-pressure stages, some steam is extracted as needed; after desuperheating and pressure reduction, it is directly supplied to the FLNG process (such as reboilers, dehydrators, and heaters) to meet the high-pressure / low-pressure steam requirements for process heating; the steam pressure is kept stable by regulating the extraction steam flow rate through valves; the unextracted steam continues to expand in the low-pressure stage, finally entering the condenser to cool into condensate, and then is returned to the waste heat boiler for circulation.

[0075] Fourth, coordinated regulation of electricity and steam: When the demand for process steam increases, the amount of steam extracted increases, and the power output of the steam turbine decreases accordingly; when the demand for process steam decreases, more steam continues to expand and generate electricity, and the power output of the steam turbine increases; automatic balance is achieved through the power management system and the steam turbine regulation system to ensure that the FLNG can meet the needs of electricity and steam under different operating conditions (normal production, external transmission, positioning thrust, etc.).

[0076] Fifth, overall energy efficiency and advantages: It enables the waste of exhaust heat from the refrigeration compressor to be utilized in stages, with part of it being converted into electricity (power generation by extraction condensing steam turbine) and part of it being converted into directly usable process steam; it significantly improves system energy efficiency, reduces additional fuel consumption, and lowers carbon dioxide emissions; it is particularly suitable for the "dual demand for electricity and steam" of FLNG, and is more efficient and lower carbon dioxide than a simple GTG+WHRU.

[0077] In some embodiments, the working principle of the gas-steam combined cycle system 2 is as follows:

[0078] First, the gas turbine burns natural gas / light diesel to drive the generator and produce electricity, which is the primary power source of the combined cycle system. The high-temperature exhaust gas (usually >500℃) discharged from the gas turbine still contains a large amount of waste heat, which serves as the secondary heat source input for the combined cycle.

[0079] Second, there are 3 gas turbines, 2 in operation and 1 on standby, with a waste heat boiler installed after each gas turbine; the high-temperature exhaust gas passes through high-pressure and low-pressure heating surfaces (superheater, evaporator, economizer) in sequence to generate high-pressure / low-pressure steam; the waste heat boiler also has functions such as desuperheating and depressurization, continuous blowdown, and bypass flue gas venting to ensure steam quality and system safety.

[0080] Third, the high-pressure steam generated by the waste heat boiler enters the high-pressure stage of the pure condensing steam turbine, expands and does work to drive the generator to generate electricity; the steam expands and releases energy through the high and low pressure cylinders in sequence, maximizing the output of electrical power; after the expansion is completed, all the steam enters the condenser and is cooled to become condensate; the condensate is sent back to the waste heat boiler or the water supply system through the condensate pump and the water supply system to achieve closed-loop circulation.

[0081] Fourth, the pure condensing steam turbine is used only for power generation. All steam expands to the low-pressure stage and is discharged into the condenser, without participating in the process steam supply. When the power demand increases, the steam flow into the pure condensing steam turbine is increased by adjusting the steam valve opening and gas turbine load, thereby increasing the power generation capacity. When the power demand decreases, the steam valve is appropriately closed or the steam supply from the upstream waste heat boiler is reduced to decrease the power generation output and maintain the economical operation of the system. The system is jointly controlled by the power management system and the steam turbine regulation system to realize automatic grid connection of the generator set, load distribution and frequency / voltage stability, ensuring the continuity and safety of power supply under FLNG islanded grid conditions.

[0082] Fifth, overall energy efficiency and advantages: The combined heat and power system utilizes the gas turbine to generate electricity directly, while its high-temperature exhaust gas enters the waste heat boiler to drive the steam turbine for further power generation, increasing overall efficiency by approximately 15 percentage points compared to a simple cycle; low emissions, reducing exhaust heat loss through waste heat recovery, lowering the emission intensity of carbon dioxide and nitrogen oxides, meeting the emission reduction requirements for offshore installations; high adaptability, the pure condensing steam turbine focuses on power output, providing a stable base load power supply, particularly suitable for isolated grid operation and large load fluctuation scenarios like FLNG; redundancy and flexibility: The modular combination of multiple gas turbines and pure condensing steam turbines allows for flexible start-up and shutdown based on operating conditions (normal production, external transmission, targeted thrust, combined peak load), ensuring grid stability and power supply continuity.

[0083] In this embodiment, during the FLNG startup phase, when the entire FLNG vessel is started up, the liquefaction process, reboiler, dehydration unit, and utility systems all require a large amount of stable steam for purging, preheating, and driving. At this time, the gas turbine driven by the hybrid chiller compressor has not yet reached full load operation, and the waste heat is insufficient to meet the steam demand. The gas turbine in the combined cycle starts first, and the exhaust gas from the gas turbine enters the waste heat boiler to generate high-pressure / low-pressure steam, which is supplied to the steam turbine to drive power generation. At the same time, some steam is transported to the process system through the main pipeline. In this way, stable process steam can be provided in the early stage of FLNG startup without relying on a separate auxiliary boiler. Since the process steam comes directly from the main combined cycle system, it has redundancy and regulation capabilities, ensuring the continuity and stability of steam pressure and flow during the startup phase. Even under islanded grid operation conditions, the power management system can achieve dual power-steam protection by coordinating the output of the gas turbine, waste heat boiler, and pure condensing steam turbine generator.

[0084] In some embodiments, please refer to Figure 2 In another aspect, this application also provides a combined cycle power generation method, which is implemented using the combined cycle power generation system described in the foregoing embodiments. The combined cycle power generation method also possesses the technical effects of the combined cycle power generation system in the foregoing embodiments, and will not be repeated here. The combined cycle power generation method includes steps S100 to S200.

[0085] S100: High-temperature exhaust gas is recovered to generate first steam. Part of the first steam is used to drive the extraction condensing steam turbine to generate electricity, and part of the first steam is used to provide process steam according to process requirements.

[0086] S200: Gas turbine directly generates electricity; high-temperature exhaust gas is recovered to generate a second steam, which is used to drive a pure condensing steam turbine to generate electricity.

[0087] In some embodiments, when the process demand for process steam increases, the extraction steam rate of the extraction condensing steam turbine is increased, thereby reducing the power generation output accordingly.

[0088] When the process demand for process steam decreases, the amount of extracted steam is reduced, and the expansion work of the first steam in the extraction condensing steam turbine is increased to improve power generation output.

[0089] In some embodiments, power and process steam are coordinated and automatically balanced through a power management system and a turbine regulation system.

[0090] In the embodiments described above, unless otherwise expressly stated herein, there is no strict order restriction on the execution of the steps in the method. These steps may not necessarily be executed in the described order, but may be executed in other ways. Moreover, at least a portion of any step may include multiple sub-steps or multiple stages. These sub-steps or stages are not necessarily completed at the same time, but may be executed at different times. The execution order of these sub-steps or stages is not necessarily sequential, but may be executed alternately or in turn with other steps or at least a portion of the sub-steps or stages of other steps.

[0091] Please note that the above embodiments are for illustrative purposes only and do not imply any limitation on this application.

[0092] The various embodiments in this specification are described in a progressive manner, with each embodiment focusing on the differences from other embodiments. The same or similar parts between the various embodiments can be referred to each other.

[0093] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0094] The embodiments described above are merely illustrative of several implementation methods of this application, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this application, and these all fall within the protection scope of this application. Therefore, the protection scope of this patent application should be determined by the appended claims.

Claims

1. A combined cycle power generation system characterized by, Comprise: a waste heat recovery system and a gas-steam combined cycle system connected in series; the waste heat recovery system is configured to recover high-temperature exhaust gas to generate first steam, part of the first steam is used to drive an extraction condensing steam turbine to generate power, and part of the first steam is used to provide process steam according to process requirements; the gas-steam combined cycle system is configured to directly generate power by a gas turbine, and recover high-temperature exhaust gas to generate second steam, which is used to drive a pure condensing steam turbine to generate power.

2. The combined cycle power generation system of claim 1, wherein, The waste heat recovery system comprises a mixed refrigerant compressor-gas turbine module, a first waste heat recovery steam generation module, and an extraction condensing steam turbine generator module; the mixed refrigerant compressor-gas turbine module is configured to drive a mixed refrigerant compressor by a gas turbine to generate high-temperature exhaust gas; the first waste heat recovery steam generation module is configured to recover the high-temperature exhaust gas to generate the first steam; the first steam comprises high-pressure steam and low-pressure steam; the extraction condensing steam turbine generator module is configured to expand and do work to generate power in response to the high-pressure steam, and provide process steam according to process requirements.

3. The combined cycle power generation system of claim 2, wherein, The first waste heat recovery steam generation module adopts a double-pressure design and comprises a high-pressure evaporator and a low-pressure evaporator; the high-pressure evaporator is configured to recover the high-temperature exhaust gas to generate the high-pressure steam; the low-pressure evaporator is configured to recover the high-temperature exhaust gas to generate the low-pressure steam.

4. The combined cycle power generation system of claim 2, wherein, The extraction condensing steam turbine generator module is provided with a steam extraction port; the steam extraction port is configured to extract part of the steam as process steam according to process requirements.

5. The combined cycle power generation system of claim 2, wherein, The waste heat recovery system further comprises a power management system and a steam turbine regulation system, which are configured to cooperatively regulate and automatically balance power and process steam.

6. The combined cycle power generation system of claim 1, wherein, The gas-steam combined cycle system comprises a gas turbine power generation module, a second waste heat recovery steam generation module, and a pure condensing steam turbine generator module; the gas turbine power generation module is configured to burn fuel to drive the gas turbine generator module to generate power and generate high-temperature exhaust gas; the second waste heat recovery steam generation module is configured to recover the high-temperature exhaust gas to generate second steam; the pure condensing steam turbine generator module is configured to expand and do work to generate power in response to the second steam.

7. The combined cycle power generation system of claim 1, wherein, When the first steam for the process steam is insufficient, the second steam is provided as a supplement to the process steam.

8. A combined cycle power generation method characterized by, The method is performed by using the combined cycle power generation system as claimed in any one of claims 1-7; the method comprises: recovering high-temperature exhaust gas to generate first steam, part of the first steam is used to drive an extraction condensing steam turbine to generate power, and part of the first steam is used to provide process steam according to process requirements; directly generating power by a gas turbine, and recovering high-temperature exhaust gas to generate second steam, which is used to drive a pure condensing steam turbine to generate power.

9. The combined cycle power generation method according to claim 8, characterized in that, when the process requirements of the process steam increase, the steam extraction amount of the extraction condensing steam turbine is increased, and the power generation output is correspondingly reduced. When the process steam demand decreases, the extraction steam is reduced, the expansion work of the first steam in the extraction condensing steam turbine is increased, and the power generation output is increased.

10. The combined cycle power generation method of claim 8, wherein, The power management system and the steam turbine regulation system are used to cooperatively regulate and automatically balance the power and the process steam.

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