Gas turbine waste heat cascade energy storage and starting auxiliary system and control method thereof

Abstract

The invention relates to the technical field of gas turbine power generation, in particular to a gas turbine waste heat cascade energy storage and starting auxiliary system and a control method thereof. The system comprises a fused salt phase change energy storage module, a steam and fused salt heat exchange network module and an intelligent control system, the fused salt phase change energy storage module is arranged in a flue gas channel between a coal economizer and a superheater of the waste heat boiler, and the steam and fused salt heat exchange network module comprises three stages of heat exchangers; the main steam pipeline is connected with a cylinder assembly of a steam turbine and a pneumatic turning gear, the shaft seal steam supply subsystem is connected with the natural gas preheating module through a shaft seal steam pipeline, and the main steam pipeline is connected with the fused salt phase change energy storage module through a pipeline and connected with a steam loop in the superheater through a pipeline; the heat energy of the high-temperature molten salt and the steam are respectively received. The technical problems that flue gas waste heat energy is wasted, starting time is long, natural gas energy and electric energy are seriously wasted, and starting equipment purchase cost, installation cost and maintenance cost are high are solved.

Description

Technical Field

[0001] This application relates to the field of gas turbine power generation technology, and in particular to a gas turbine waste heat cascade energy storage and start-up auxiliary system and its control method. Background Technology

[0002] In a combined cycle gas and steam power plant, air is compressed in multiple stages by a compressor and then mixed with natural gas in the combustion chamber to produce high-temperature, high-pressure gas that drives the gas turbine impeller to rotate, thereby generating electricity. At this time, the flue gas discharged from the gas turbine still has a large amount of waste heat, with a temperature of about 600°C. This high-temperature flue gas from the gas turbine enters the waste heat boiler to heat the water in it, turning it into high-temperature, high-pressure steam. This high-temperature, high-pressure steam is then used to drive the steam turbine to rotate, thereby driving the generator to generate electricity, thus realizing the secondary utilization of the waste heat of the flue gas.

[0003] However, after the gas turbine is shut down normally, there is still 250~500℃ of flue gas waste heat in the waste heat boiler. Currently, this flue gas waste heat is generally discharged directly from the waste heat boiler outlet or partially recovered, but the waste heat recovery rate is less than 40%, resulting in waste of flue gas waste heat energy.

[0004] Furthermore, the startup of existing peak-shaving gas-fired combined cycle units relies entirely on independent start-up boiler systems, including electric turning gears and electric gas turbine frequency converters. These independent start-up boiler systems not only have high equipment purchase and installation costs, resulting in high initial investment, but also long startup times, requiring at least 60 minutes from ignition to cold start-up, making it difficult to respond to the grid's rapid peak-shaving demands. During startup, they consume large amounts of natural gas and electricity, leading to significant waste of these resources and high electricity costs. Additionally, the combustion of natural gas in the start-up boiler produces carbon dioxide, emitting approximately 400 kg per startup. With 50-60 startups per year, the cumulative emissions are substantial, resulting in poor environmental benefits. Moreover, these independent start-up boiler systems have high operation and maintenance costs, requiring at least 12 maintenance visits per year, with each maintenance costing at least 50,000 yuan, and the risk of equipment failure is high. Summary of the Invention

[0005] The purpose of this application is to provide a gas turbine waste heat cascade energy storage and start-up auxiliary system and its control method, in order to solve the existing technical problems such as waste of flue gas waste heat energy, long start-up time of start-up equipment, serious waste of natural gas and electric energy, and high purchase, installation and maintenance costs of start-up equipment.

[0006] In the first aspect, this application provides a gas turbine waste heat cascade energy storage and start-up auxiliary system, including: a molten salt phase change energy storage module, which is installed in the flue gas passage between the economizer and the superheater of the waste heat boiler, for recovering the waste heat of the flue gas after the gas turbine is shut down and storing it as molten salt thermal energy. A steam and molten salt heat exchange network module includes a three-stage heat exchanger consisting of a low-pressure heat exchanger, a medium-pressure heat exchanger, and a high-pressure heat exchanger. It is connected to the turbine cylinder assembly and pneumatic turning gear via a main steam pipeline, and to the shaft seal steam supply subsystem and natural gas preheating module via a shaft seal steam pipeline. The steam and molten salt heat exchange network module is also connected to the molten salt phase change energy storage module via pipeline and to the steam circuit within the superheater via pipeline, to receive the high-temperature molten salt thermal energy stored in the molten salt phase change energy storage module and the steam supplied by the steam circuit, respectively. The intelligent control system is connected to the molten salt phase change energy storage module, the steam and molten salt heat exchange network module, the waste heat boiler, and each connecting pipeline.

[0007] Furthermore, the gas turbine waste heat cascade energy storage and start-up auxiliary system also includes a three-way valve and three passages connected to its three interfaces, namely the first passage, the second passage and the third passage, and the intelligent control system is connected to the three-way valve for control. The first passage is fixedly connected to the steam circuit in the superheater, the second passage is switchably connected to the three-stage heat exchanger of the steam and molten salt heat exchange network module, and the third passage is switchably connected to the main steam pipeline. When heating is started, the intelligent control system controls the three-way valve to switch to the second passage, so that the first passage and the second passage are connected. During normal power generation, the intelligent control system controls the three-way valve to switch to the third passage, so that the first passage and the third passage are connected.

[0008] Furthermore, the steam circuit within the superheater includes a low-pressure steam circuit, a medium-pressure steam circuit, and a high-pressure steam circuit; the turbine cylinder assembly includes a low-pressure cylinder, a medium-pressure cylinder, and a high-pressure cylinder. When heat is started, the low-pressure steam circuit, the medium-pressure steam circuit, and the high-pressure steam circuit are respectively connected to the low-pressure heat exchanger, the medium-pressure heat exchanger, and the high-pressure heat exchanger of the steam and molten salt heat exchange network module to provide low-pressure steam, medium-pressure steam, and high-pressure steam. During normal power generation, the low-pressure steam circuit, the medium-pressure steam circuit, and the high-pressure steam circuit are respectively connected to the low-pressure cylinder, the medium-pressure cylinder, and the high-pressure cylinder of the steam turbine to provide low-pressure high-temperature steam, medium-pressure high-temperature steam, and high-pressure high-temperature steam, respectively.

[0009] Furthermore, the low-pressure high-temperature steam, medium-pressure high-temperature steam, and high-pressure high-temperature steam generated by the steam and molten salt heat exchange network module are respectively supplied to the low-pressure cylinder, medium-pressure cylinder, and high-pressure cylinder of the steam turbine through the main steam pipeline. The high-pressure high-temperature steam is also supplied to the pneumatic turning gear device through the main steam pipeline, and the medium-pressure high-temperature steam is also supplied to the shaft seal steam supply subsystem and the natural gas preheating module through the shaft seal steam pipeline. Furthermore, the shaft seal steam supply subsystem and the natural gas preheating module are started synchronously with the shaft seal steam pipeline.

[0010] Furthermore, the pneumatic turning gear includes a rotor driving device and a rotor high-speed drive device. The low-pressure heat exchanger provides low-pressure high-temperature steam to the low-pressure cylinder to drive the rotor driving device to slowly rotate the turbine rotor. The medium-pressure heat exchanger provides medium-pressure high-temperature steam to the medium-pressure cylinder to drive the gas turbine to ignite, and simultaneously provides it to the natural gas preheating module to raise the temperature of the natural gas. The high-pressure heat exchanger provides high-pressure high-temperature steam to the high-pressure cylinder and the rotor high-speed drive device to drive the gas turbine rotor ignition speed to the grid connection speed, thereby completing the rapid start-up of the gas turbine.

[0011] Furthermore, the molten salt phase change energy storage module includes a molten salt hot tank for storing high-temperature molten salt and a molten salt cold tank for storing low-temperature molten salt. The temperature of the high-temperature molten salt is at least 560°C, the temperature of the low-temperature molten salt is at least 290°C, and the temperature of the flue gas waste heat is between 250°C and 500°C. When the gas turbine is shut down, the low-temperature molten salt in the molten salt cold tank is directly heat-recovered by exchanging heat with the waste heat of the flue gas in the flue gas pipeline. After the temperature rises to 560°C and becomes high-temperature molten salt, it is pumped to the molten salt hot tank for storage. Furthermore, a molten salt pump is provided at the output end of the pipeline connecting the molten salt phase change energy storage module and the steam and molten salt heat exchange network module. The intelligent control system is also connected to the molten salt pump. When heat is required, the system controls the molten salt pump to start and pump the high-temperature molten salt heat energy stored in the molten salt phase change energy storage module into the three-stage heat exchanger.

[0012] Furthermore, the shaft seal steam supply subsystem includes a dedicated heater, a steam buffer tank, a desuperheating and pressure reducing device, and a temperature control system. The input end of the dedicated heater is connected to the shaft seal steam pipeline, and its output end is connected to the shaft seal pipeline of the gas turbine via the steam buffer tank and the desuperheating and pressure reducing device. The temperature control system monitors the steam temperature in real time through sensors; and / or The natural gas preheating module is configured as a shell-and-tube heat exchanger, with the shell side connected to the shaft seal steam pipeline and the tube side connected to the natural gas intake pipeline of the gas turbine. The shaft seal steam flow rate is adjusted by an intelligent control system to heat the natural gas to 50~80℃.

[0013] Furthermore, the steam turbine is also connected to a generator drive to drive the generator to produce electrical energy; and / or The exhaust pipe of the steam turbine is connected to the steam circuit of the superheater through the condenser and the feedwater pump, so that the exhaust steam discharged from the exhaust pipe of the steam turbine enters the condenser, condenses into water, and is then sent back to the steam circuit of the superheater by the feedwater pump for circulation.

[0014] Secondly, this application provides a control method for a gas turbine waste heat cascade energy storage and start-up auxiliary system, applied to any of the aforementioned gas turbine waste heat cascade energy storage and start-up auxiliary systems, wherein the control method includes: Off-peak energy storage phase: When the gas turbine receives a shutdown command, the intelligent control system switches to the shutdown heat storage state and controls the start of the molten salt pump. This allows the waste heat from the flue gas after the gas turbine shutdown to be heated by exchanging heat with the low-temperature molten salt in the molten salt phase change energy storage module, raising the temperature to high-temperature molten salt, and then storing it in the molten salt hot tank. When the flue gas temperature drops below 250℃ and remains below 250℃ for 30 seconds, the molten salt pump is shut down, the intelligent control system switches to standby mode, and the shutdown energy storage is completed. Start-up heating phase: When the gas turbine receives the start-up command, the intelligent control system switches to the start-up heat mode and controls the molten salt pump to start, so that the high-temperature molten salt in the molten salt phase change energy storage module is pumped into the three-stage heat exchanger of the steam and molten salt heat exchange network module. At the same time, the three-way valve is controlled to switch the connection between the steam circuit in the superheater of the waste heat boiler and the three-stage heat exchanger of the steam and molten salt heat exchange network module, so that the steam enters the three-stage heat exchanger of the steam and molten salt heat exchange network module. After the steam is heated by the high-temperature molten salt, it outputs low-pressure high-temperature steam, medium-pressure high-temperature steam and high-pressure high-temperature steam through its low-pressure heat exchanger, medium-pressure heat exchanger and high-pressure heat exchanger respectively. It is then delivered in stages through the main steam pipeline and shaft seal steam pipeline to the low-pressure cylinder, medium-pressure cylinder, high-pressure cylinder and pneumatic turning gear of the turbine, as well as the shaft seal steam supply subsystem and natural gas preheating module, so as to complete the rapid start-up of the gas turbine from low-speed turning gear to high-speed turning gear to turbine ignition and then to the gas turbine speed increase to grid connection speed. Once the gas turbine reaches its grid-connected speed, the intelligent control system switches to conventional power generation mode, the molten salt pump gradually shuts down, and the start-up heat utilization is completed.

[0015] Furthermore, the control method for the gas turbine waste heat cascade energy storage and start-up auxiliary system also includes: Conventional power generation phase: When the gas turbine is running at a stable grid-connected speed and the flue gas temperature is >500℃, the intelligent control system switches to the conventional power generation state, controls the three-way valve to switch the connection between the steam circuit in the superheater of the waste heat boiler and the main steam pipeline, directly supplying high-temperature steam to the turbine, the molten salt pump stops, and the molten salt phase change energy storage module enters the standby state. The high-temperature flue gas discharged from the gas turbine enters the waste heat boiler, and passes through its superheater and economizer in sequence. It first heats the water in the steam circuit to generate low-pressure high-temperature steam, medium-pressure high-temperature steam and high-pressure high-temperature steam, which are supplied to the low-pressure cylinder, medium-pressure cylinder and high-pressure cylinder of the steam turbine to drive the gas turbine to operate and at the same time drive the generator to generate electricity. The exhaust steam from the steam turbine enters the condenser and is condensed, and then sent back to the superheater of the waste heat boiler via the feedwater pump for steam circuit circulation. The shaft seal steam supply subsystem continues to operate, while the pneumatic turning gear device and natural gas preheating module stop working.

[0016] Compared with the prior art, the gas turbine waste heat cascade energy storage and start-up auxiliary system and its control method provided in this application, firstly, by setting a molten salt phase change energy storage module in the flue gas passage between the economizer and the superheater of the waste heat boiler, the waste heat of the flue gas after the gas turbine is shut down is recovered and stored as molten salt thermal energy, so as to realize the shutdown energy storage function, and at the same time realize the recovery and utilization of the waste heat energy of the flue gas after the gas turbine is shut down, effectively preventing resource waste, and can be used for subsequent start-up heating.

[0017] Second, a steam and molten salt heat exchange network module is set up and controlled by an intelligent control system. This steam and molten salt heat exchange network module includes a three-stage heat exchanger consisting of a low-pressure heat exchanger, a medium-pressure heat exchanger, and a high-pressure heat exchanger. The steam and molten salt heat exchange network module is connected to the molten salt phase change energy storage module through pipelines, and the high-temperature molten salt heat energy stored in the molten salt phase change energy storage module can be pumped into the three-stage heat exchanger of the steam and molten salt heat exchange network module through a molten salt pump. The steam and molten salt heat exchange network module is also connected to the steam circuit in the superheater through pipelines to receive steam provided by the steam circuit to the three-stage heat exchanger. After the steam is heated by the high-temperature molten salt, low-pressure high-temperature steam, medium-pressure high-temperature steam, and high-pressure high-temperature steam are generated. These are then supplied in stages to the cylinder assembly and pneumatic turning gear of the turbine through the main steam pipeline, and to the shaft seal steam supply subsystem and natural gas preheating module through the shaft seal steam pipeline, so as to realize the rapid start-up of the gas turbine.

[0018] This solves the problem that the waste heat boiler cannot generate high-temperature steam that meets the turbine's requirements due to the low exhaust gas temperature of the gas turbine at startup. The above-mentioned method in this application enables the recovery and storage of waste heat from the flue gas into high-temperature molten salt thermal energy through the molten salt phase change energy storage module when the gas turbine is shut down. This thermal energy is then used to provide heating steam to the steam and molten salt heat exchange network module during startup, forming high-temperature steam at different pressures that meet the turbine's startup requirements, thereby achieving rapid startup of the gas turbine.

[0019] Compared with existing starting equipment, it has a fast start-up speed and does not rely on electricity during the start-up process, which greatly saves electricity resources. It also does not consume a large amount of natural gas during the start-up process, which greatly saves natural gas resources and improves environmental benefits. Furthermore, it eliminates the need to purchase expensive starting equipment, which greatly reduces purchase, installation and operation and maintenance costs, and also improves the waste heat recovery rate. Attached Figure Description

[0020] To more clearly illustrate the technical solutions in the specific embodiments of this application or the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of this application. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0021] Figure 1 This is a schematic diagram of the structure of the gas turbine waste heat cascade energy storage and start-up auxiliary system provided in the embodiments of this application.

[0022] Figure label: 10-Molten salt phase change energy storage module; 11-Molten Salt Hot Pot; 12- Molten Salt Cold Tank; 20-Steam and molten salt heat exchanger network modules; 21-Low-pressure heat exchanger; 22-Medium pressure heat exchanger; 23-High-pressure heat exchanger; 241 - Main steam pipeline; 242 - Shaft seal steam pipeline; 31-Rotor drive device; 32-Rotor high-speed drive device; 40 - Intelligent Control System; 50- Waste heat boiler; 51-Economizer; 52-Superheater; 521 - Low-pressure steam circuit; 522 - Medium-pressure steam circuit; 523 - High-pressure steam circuit; 61 - Molten salt pump; 62-Three-way valve; 71-Shaft seal steam supply subsystem; 72-Natural gas preheating module; 81-Gas Turbine; 82-Steam turbine; 83-Generator; 84-Condenser; 85 - Water supply pump. Detailed Implementation

[0023] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. The components of the embodiments of this application described and shown in the accompanying drawings can generally be arranged and designed in various different configurations.

[0024] Therefore, the following detailed description of the embodiments of this application provided in the accompanying drawings is not intended to limit the scope of the claimed application, but merely to illustrate selected embodiments of the application. All other embodiments obtained by those skilled in the art based on the embodiments of this application without inventive effort are within the scope of protection of this application.

[0025] It should be noted that similar labels and letters in the following figures indicate similar items. Therefore, once an item is defined in one figure, it does not need to be further defined and explained in subsequent figures.

[0026] In the description of this application, it should be noted that the terms "center," "upper," "lower," "left," "right," "vertical," "horizontal," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, or the orientation or positional relationship commonly used when the product of this application is in use. They are only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation on this application. In addition, the terms "first," "second," and "third," etc., are only used to distinguish descriptions and should not be construed as indicating or implying relative importance.

[0027] Furthermore, terms such as "horizontal," "vertical," and "sag" do not imply that components must be absolutely horizontal or suspended, but rather that they can be slightly tilted. For example, "horizontal" simply means that its direction is more horizontal relative to "vertical," and does not mean that the structure must be completely horizontal, but can be slightly tilted.

[0028] In the description of this application, it should also be noted that, unless otherwise expressly specified and limited, the terms "set up," "install," "connect," and "link" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this application based on the specific circumstances.

[0029] The following detailed description of some embodiments of this application is provided in conjunction with the accompanying drawings. Unless otherwise specified, the following embodiments and features can be combined with each other.

[0030] like Figure 1 As shown, this application provides a gas turbine waste heat cascade energy storage and start-up auxiliary system, and a control method applied to the gas turbine waste heat cascade energy storage and start-up auxiliary system.

[0031] The gas turbine waste heat cascade energy storage and start-up auxiliary system includes a molten salt phase change energy storage module 10 installed in the flue gas passage between the economizer 51 and the superheater 52 of the waste heat boiler 50. It is used to recover the waste heat of the flue gas after the gas turbine 81 is shut down and store it as molten salt thermal energy during the shutdown energy storage stage, so as to realize the shutdown energy storage function, recover and utilize the waste heat energy of the flue gas after the gas turbine 81 is shut down, effectively prevent resource waste, and can be used for subsequent start-up heating.

[0032] Furthermore, the system of this application also includes a steam and molten salt heat exchange network module 20, which comprises a three-stage heat exchanger consisting of a low-pressure heat exchanger 21, a medium-pressure heat exchanger 22, and a high-pressure heat exchanger 23, with specific heat exchange areas of 50m² and 50m² respectively. 2 80 m 2 and 20m 2 The steam and molten salt heat exchange network module 20 is connected to the molten salt phase change energy storage module 10 via a pipeline. Specifically, a molten salt pump 61 can be installed on the pipeline so that when the heating phase starts, the high-temperature molten salt heat energy stored in the molten salt phase change energy storage module 10 can be pumped to the three-stage heat exchanger of the steam and molten salt heat exchange network module 20. The steam and molten salt heat exchange network module 20 is also connected to the steam circuit in the superheater 52 via a pipeline. Specifically, the steam circuit can include a low-pressure steam circuit 521, a medium-pressure steam circuit 522, and a high-pressure steam circuit 523 so that when the heating phase starts, the low-pressure steam, medium-pressure steam, and high-pressure steam provided by them can be received respectively.

[0033] Furthermore, the three-stage heat exchanger of the steam and molten salt heat exchange network module 20 is also connected to the cylinder assembly and pneumatic turning gear of the steam turbine 82 via the main steam pipeline 241, and to the shaft seal steam supply subsystem 71 of the shaft seal system and the natural gas preheating module 72 of the natural gas heating system via the shaft seal steam pipeline 242. Specifically, the low-pressure steam, medium-pressure steam and high-pressure steam received by the three-stage heat exchanger are heated by the high-temperature molten salt heat energy received by it to generate low-pressure high-temperature steam, medium-pressure high-temperature steam and high-pressure high-temperature steam, and are respectively supplied to the low-pressure cylinder, medium-pressure cylinder and high-pressure cylinder of the cylinder assembly of the steam turbine 82 via the main steam pipeline 241. The high-pressure high-temperature steam is also supplied to the pneumatic turning gear via the main steam pipeline 241, thereby realizing the rapid start-up of the gas turbine 81.

[0034] Simultaneously, the medium-pressure, high-temperature steam is also supplied to the shaft seal steam supply subsystem 71 and the natural gas preheating module 72 through the shaft seal steam pipeline 242. The shaft seal steam supply subsystem 71 and the natural gas preheating module 72 start synchronously with the shaft seal steam pipeline 242. Within 30 seconds, the shaft seal steam temperature can reach 280℃ and the pressure 0.25MPa, while the natural gas temperature can reach 60℃, solving the problem of slow steam production in traditional boiler start-up. Furthermore, preheating is completed within 30 seconds, preventing the precipitation of liquid hydrocarbons.

[0035] Furthermore, the system of this application also includes an intelligent control system 40, which is connected to the molten salt phase change energy storage module 10, the steam and molten salt heat exchange network module 20, the waste heat boiler 50, the molten salt pump 61 and each pipeline control, so as to control the switching of shutdown energy storage mode, start-up heat use mode or conventional power generation mode.

[0036] This solves the problem that the waste heat boiler 50 cannot generate high-temperature steam that meets the requirements of the steam turbine 82 because the exhaust gas temperature of the gas turbine 81 is low at the beginning of startup. The above-described embodiments of this application realize that when the gas turbine 81 is shut down, the waste heat of the flue gas is recovered and stored as high-temperature molten salt heat energy by the molten salt phase change energy storage module 10. When the gas turbine 81 is used for startup, the heat energy is used to provide heating steam to the steam and molten salt heat exchange network module 20, forming high-temperature steam at different pressures that meet the startup requirements of the steam turbine 82, thereby realizing the rapid startup of the gas turbine 81.

[0037] Compared to existing start-up equipment, the gas turbine waste heat cascade energy storage and start-up auxiliary system provided in this application has a faster start-up speed. The cold start-up time is reduced from the existing 60 minutes to only 45 minutes, and the preheating of shaft seal steam and natural gas can be completed in less than 30 seconds, meeting the grid's rapid peak-shaving requirements. Furthermore, the start-up process does not rely entirely on electricity, greatly saving electricity resources. It also does not consume large amounts of natural gas, significantly saving natural gas resources and improving environmental benefits. Moreover, it eliminates the need to purchase expensive start-up equipment, greatly reducing purchase, installation, and operation and maintenance costs. Specifically, the initial investment for a 200MW unit is reduced by 60%, from the existing 5 million yuan to 2 million yuan in this application, and the annual maintenance cost is reduced from the existing 600,000 yuan to 280,000 yuan in this application. Simultaneously, the waste heat recovery rate is high, exceeding 85%, achieving an additional 1.2 to 1.5 million kWh of power generation annually. Furthermore, by replacing the start-up boiler combustion, each start-up reduces the boiler's combustion capacity by 200 Nm³. 3 Natural gas consumption reduces CO2 emissions by approximately 502 tons per year, with no additional pollutant emissions, thus achieving emission reduction and environmental protection.

[0038] In a preferred embodiment, the intelligent control system 40 can use a fuzzy PID algorithm to adjust the flow rate of the molten salt pump 61. If the steam temperature is too low, the molten salt flow rate is increased; if the steam temperature is too high, the molten salt flow rate is decreased, ensuring that the steam temperature control accuracy reaches ±5℃.

[0039] like Figure 1 As shown, another preferred embodiment is that the gas turbine waste heat cascade energy storage and start-up auxiliary system may further include a three-way valve 62 and three passages connected to its three interfaces respectively, namely the first passage, the second passage and the third passage. The intelligent control system 40 is connected to the three-way valve 62 and can realize the steam connection switching line by controlling the three-way valve 62. Specifically, the three-way valve 62 may be a DN200 electrically adjustable three-way valve 62 with a response time of <100ms.

[0040] Specifically, the first passage of the three-way valve 62 can be fixedly connected to the steam circuit (including low-pressure steam circuit 521, medium-pressure steam circuit 522 and high-pressure steam circuit 523) in the superheater 52, its second passage can be switched to the three-stage heat exchangers (including low-pressure heat exchanger 21, medium-pressure heat exchanger 22 and high-pressure heat exchanger 23) of the steam and molten salt heat exchange network module 20, and its third passage can be connected to the main steam pipeline 241, so that it can be switched to the steam turbine 82 directly.

[0041] During the start-up heating phase, the intelligent control system 40 can control the three-way valve 62 to switch to the second passage, connecting the first passage with the second passage. This connects the low-pressure steam circuit 521, the medium-pressure steam circuit 522, and the high-pressure steam circuit 523 in the superheater 52 to the low-pressure heat exchanger 21, the medium-pressure heat exchanger 22, and the high-pressure heat exchanger 23 of the steam and molten salt heat exchange network module 20, respectively, to provide low-pressure steam, medium-pressure steam, and high-pressure steam.

[0042] During the normal power generation phase, the three-way valve 62 can be controlled to switch to the third passage, connecting the first passage with the third passage. This allows the low-pressure steam circuit 521, the medium-pressure steam circuit 522, and the high-pressure steam circuit 523 in the superheater 52 to be directly connected to the low-pressure cylinder, the medium-pressure cylinder, and the high-pressure cylinder of the turbine 82, respectively, to provide low-pressure high-temperature steam, medium-pressure high-temperature steam, and high-pressure high-temperature steam to drive the gas turbine 81 to operate.

[0043] Thus, by switching the connection of the three-way valve 62, the steam flow direction can be quickly and flexibly switched between the start-up heating state and the normal power generation state. The control method is simple, fast, and highly reliable.

[0044] In one specific embodiment, the aforementioned molten salt phase change energy storage module 10 may include a molten salt hot tank 11 for storing high-temperature molten salt at least 560°C and a molten salt cold tank 12 for storing low-temperature molten salt at least 290°C. When the gas turbine 81 is shut down, that is, during the shutdown energy storage phase, the low-temperature molten salt in the molten salt cold tank 12 directly exchanges heat with the waste heat of the flue gas in the flue gas pipeline (temperature between 250 and 500°C) for recovery. After the temperature rises to 560°C and becomes high-temperature molten salt, it is pumped into the molten salt hot tank 11 for storage, thus completing the conversion from waste heat of flue gas to molten salt thermal energy.

[0045] More specifically, the energy storage medium of the molten salt phase change energy storage module 10 can be a binary nitrate molten salt, including 60% sodium nitrate and 40% potassium nitrate, with an energy storage density of 380 kJ / kg and an operating temperature range of 290-565℃. Furthermore, the inner layers of the molten salt hot tank 11 and the molten salt cold tank 12 can be made of high-temperature resistant stainless steel, and the outer layer can be wrapped with ceramic fiber felt insulation material, achieving a heat loss rate of less than 2% / 24 hours, greatly reducing heat loss. More specifically, the dimensions of the molten salt hot tank 11 and the molten salt cold tank 12 can be at least 3m in diameter and at least 8m in height.

[0046] Regarding the aforementioned pneumatic turning gear device, a specific embodiment is that the pneumatic turning gear device may include a rotor pushing device 31 and a rotor high-speed drive device 32. More specifically, the rotor pushing device 31 may adopt a cylinder structure to drive the rotor, replacing the traditional electric turning gear, and the rotor high-speed drive device 32 may adopt a small impulse steam turbine, replacing the traditional gas turbine SFC device, thereby reducing plant power consumption and saving power resources.

[0047] Specifically, the low-pressure high-temperature steam provided by the low-pressure heat exchanger 21 of the aforementioned steam and molten salt heat exchange network module 20 is supplied to the low-pressure cylinder of the steam turbine 82 to drive the rotor drive device 31 to slowly rotate the steam turbine rotor, specifically at a slow rotation speed of 3~5 rpm. The medium-pressure high-temperature steam provided by the intermediate-pressure heat exchanger 22 is supplied to the intermediate-pressure cylinder of the steam turbine 82 to drive the gas turbine to ignite, reaching the ignition speed, specifically 670~700 rpm, and is simultaneously supplied to the natural gas preheating module 72 to raise the temperature of the natural gas to 50~80℃, which will be added when the gas turbine 81 speeds up to enhance combustion efficiency, working together to complete the start-up. The high-pressure high-temperature steam provided by the high-pressure heat exchanger 23 is supplied to the high-pressure cylinder and the high-speed rotor drive device 32 of the steam turbine 82 to drive the ignition speed of the gas turbine 81 rotor to increase to the grid connection speed, which can reach at least 3000 rpm, typically 15%~25% of the rated speed, to complete the rapid start-up of the gas turbine 81.

[0048] This enables the rotor to be uniformly heated and cooled during unit start-up and shutdown, facilitates component inspection during maintenance, and allows the gas turbine to accelerate from standstill to ignition speed and then to grid connection speed. It also participates in shutdown control without the need for electric equipment, reducing failure and maintenance costs, and is suitable for combined cycle power plants to improve energy utilization.

[0049] Furthermore, after the gas turbine 81 accelerates to the grid-connected speed, the steam output of the waste heat boiler 50 meets the demand, and the intelligent control system 40 can switch to the conventional power generation state. The shaft seal steam and natural gas preheating are switched to the waste heat boiler for energy supply. If the unit load is lower than 10% for 10 seconds, the intelligent control system 40 will automatically switch to the start-up heat use state to supplement the low load and supplement the steam supply through molten salt heat release.

[0050] In one optional embodiment, the aforementioned shaft seal steam supply subsystem 71 may specifically include a dedicated heater, a steam buffer tank, a desuperheating and pressure reducing device, and a temperature control system. The input end of the dedicated heater is connected to the shaft seal steam pipeline 242, and the output end of the dedicated heater is connected to the shaft seal pipeline of the gas turbine 81 via the steam buffer tank and the desuperheating and pressure reducing device. The temperature control system monitors the steam temperature in real time through a sensor and can output qualified shaft seal steam with a temperature of 250~300℃ and a pressure of 0.2~0.3MPa within 30 seconds.

[0051] Another specific embodiment is that the aforementioned natural gas preheating module 72 can be specifically configured as a shell and tube heat exchanger, the shell side of which can be connected to the shaft seal steam pipeline 242, and the tube side of which can be connected to the natural gas intake pipeline of the gas turbine 81. The shaft seal steam flow rate can be adjusted by the intelligent control system 40 to heat the natural gas temperature to 50~80°C, and preheating can be completed within 30 seconds to avoid the precipitation of liquid hydrocarbons.

[0052] like Figure 1 As shown, in one optional embodiment, the steam turbine 82 can also be driven to connect with the generator 83, and the steam turbine 82 is driven to rotate by steam, which drives the generator 83 to generate electrical energy.

[0053] Another optional embodiment is that the exhaust pipe of the steam turbine 82 can be connected to the steam circuit of the superheater 52 of the waste heat boiler 50 through the condenser 84 and the feedwater pump 85, so that the exhaust steam (i.e. low temperature and low pressure steam) discharged from the steam turbine 82 enters the condenser 84, condenses into water, and is then sent back to the steam circuit of the superheater 52 of the waste heat boiler 50 by the feedwater pump 85 to complete the steam recovery.

[0054] This application also provides a control method for a gas turbine waste heat cascade energy storage and start-up auxiliary system, applied to a gas turbine waste heat cascade energy storage and start-up auxiliary system. The control method includes: Off-peak energy storage phase: When the gas turbine 81 receives a shutdown command, the intelligent control system 40 switches to the shutdown heat storage state and controls the molten salt pump 61 to start (initial frequency 25Hz). This allows the waste heat of the flue gas after the gas turbine 81 shuts down (250-500℃) to exchange heat with the low-temperature molten salt in the molten salt phase change energy storage module 10, raising the temperature to high-temperature molten salt (at least 560℃) and storing it in the molten salt heat tank 11. The three-way valve 62 is in the neutral position, and the steam turbine 82 and generator 83 do not work (because the gas turbine 81 has shut down and there is no sufficient steam). Furthermore, when the flue gas temperature drops below 250℃ and remains below 250℃ for 30 seconds, the molten salt pump 61 is shut down, the intelligent control system 40 switches to standby mode, and the shutdown energy storage is completed, with a single heat storage capacity of up to 800MJ.

[0055] Start-up heating phase: When the gas turbine 81 receives the start-up command, the intelligent control system 40 switches to the start-up heat mode and controls the molten salt pump 61 (frequency 30Hz) to start. This allows the high-temperature molten salt in the molten salt heat tank 11 within the molten salt phase change energy storage module 10 to be pumped by the molten salt pump 61 into the three-stage heat exchangers (including low-pressure heat exchanger 21, medium-pressure heat exchanger 22, and high-pressure heat exchanger 23) of the steam and molten salt heat exchange network module 20. Simultaneously, the three-way valve 62 switches the connection between the steam circuit (including low-pressure steam circuit 521, medium-pressure steam circuit 522, and high-pressure steam circuit 523) in the superheater 52 of the waste heat boiler 50 and the three-stage heat exchangers of the steam and molten salt heat exchange network module 20, allowing steam to enter the three-stage heat exchangers within the steam and molten salt heat exchange network module 20. After the steam is heated by high-temperature molten salt, it outputs low-pressure high-temperature steam, medium-pressure high-temperature steam, and high-pressure high-temperature steam through its low-pressure heat exchanger 21, medium-pressure heat exchanger 22, and high-pressure heat exchanger 23, respectively. It is then transported in stages through the main steam pipeline 241 and the shaft seal steam pipeline 242 to the low-pressure cylinder, medium-pressure cylinder, and high-pressure cylinder of the turbine 82, as well as the pneumatic turning gear device, the shaft seal steam supply subsystem 71, and the natural gas preheating module 72. This allows for the rapid start-up of the gas turbine, from low-speed turning gear to high-speed turning gear to turbine ignition and then to the gas turbine speed increase to grid connection speed. Simultaneously, the shaft seal steam supply subsystem 71 and the natural gas preheating module 72 are started. Within 30 seconds, the shaft seal steam temperature reaches 280°C and the pressure reaches 0.25MPa, and the natural gas temperature reaches 60°C. Steam turbine 82 is driven to rotate by steam, which in turn drives generator 83 to generate electrical energy; The exhaust steam (i.e., low-temperature and low-pressure steam) discharged from the exhaust pipe of the steam turbine 82 enters the condenser 84, condenses into water, and is then sent back to the three-stage steam loop of the superheater 52 of the waste heat boiler 50 by the feedwater pump 85. Furthermore, once the gas turbine 81 accelerates to the grid-connected speed, the intelligent control system 40 switches to the conventional power generation state, the molten salt pump 61 gradually shuts down, and the start-up heat utilization is completed.

[0056] The flow rate of the molten salt pump 61 can be adjusted by the intelligent control system 40 using a fuzzy PID algorithm. If the steam temperature is too low, the molten salt flow rate will be increased; if the steam temperature is too high, the molten salt flow rate will be decreased, ensuring that the control accuracy of key parameters such as steam temperature reaches ±5℃.

[0057] Conventional power generation phase: When the gas turbine 81 is running at a stable grid-connected speed and the flue gas temperature is >500℃, the intelligent control system 40 switches to the conventional power generation state and controls the three-way valve 62 to switch the steam circuit (including low-pressure steam circuit 521, medium-pressure steam circuit 522 and high-pressure steam circuit 523) in the superheater 52 of the waste heat boiler 50 to be directly connected to the main steam pipeline 241, directly supplying low-pressure high-temperature steam, medium-pressure high-temperature steam and high-pressure high-temperature steam to the turbine 82, ensuring the normal operation of the gas turbine 81, the molten salt pump 61 stops, and the molten salt phase change energy storage module 10 enters the standby state; The gas turbine 81 discharges high-temperature flue gas into the waste heat boiler 50, which then passes through its superheater 52 and economizer 51 in sequence. The water in the steam circuit (including the low-pressure steam circuit 521, the medium-pressure steam circuit 522, and the high-pressure steam circuit 523) is heated to generate low-pressure high-temperature steam, medium-pressure high-temperature steam, and high-pressure high-temperature steam. These are then supplied to the low-pressure cylinder, medium-pressure cylinder, and high-pressure cylinder of the steam turbine 82, driving the gas turbine 81 to operate and simultaneously driving the generator 83 to generate electricity. The exhaust steam from the turbine 82 enters the condenser 84 and is condensed. Then, it is sent back to the superheater 52 of the waste heat boiler 50 via the feedwater pump 85 for circulation (including the low-pressure steam circuit 521, the medium-pressure steam circuit 522 and the high-pressure steam circuit 523). The shaft seal steam supply subsystem 71 continues to operate, while the pneumatic turning gear device and the natural gas preheating module 72 stop operating.

[0058] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of this application.

Claims

1. A waste heat cascade energy storage and start-up auxiliary system for gas turbines, characterized in that, include: The molten salt phase change energy storage module is installed in the flue gas passage between the economizer and the superheater of the waste heat boiler. It is used to recover the waste heat of the flue gas after the gas turbine is shut down and store it as molten salt thermal energy. A steam and molten salt heat exchange network module includes a three-stage heat exchanger consisting of a low-pressure heat exchanger, a medium-pressure heat exchanger, and a high-pressure heat exchanger. It is connected to the turbine cylinder assembly and pneumatic turning gear via a main steam pipeline, and to the shaft seal steam supply subsystem and natural gas preheating module via a shaft seal steam pipeline. The steam and molten salt heat exchange network module is also connected to the molten salt phase change energy storage module via pipeline and to the steam circuit within the superheater via pipeline, to receive the high-temperature molten salt thermal energy stored in the molten salt phase change energy storage module and the steam supplied by the steam circuit, respectively. The intelligent control system is connected to the molten salt phase change energy storage module, the steam and molten salt heat exchange network module, the waste heat boiler, and each connecting pipeline.

2. The gas turbine waste heat cascade energy storage and start-up auxiliary system according to claim 1, characterized in that, It also includes a three-way valve and three passages connected to its three interfaces, namely the first passage, the second passage and the third passage, and the intelligent control system is connected to the three-way valve for control. The first passage is fixedly connected to the steam circuit in the superheater, the second passage is switchably connected to the three-stage heat exchanger of the steam and molten salt heat exchange network module, and the third passage is switchably connected to the main steam pipeline. When heating is started, the intelligent control system controls the three-way valve to switch to the second passage, so that the first passage and the second passage are connected. During normal power generation, the intelligent control system controls the three-way valve to switch to the third passage, so that the first passage and the third passage are connected.

3. The gas turbine waste heat cascade energy storage and start-up auxiliary system according to claim 2, characterized in that, The steam circuit within the superheater includes a low-pressure steam circuit, a medium-pressure steam circuit, and a high-pressure steam circuit; the turbine cylinder assembly includes a low-pressure cylinder, a medium-pressure cylinder, and a high-pressure cylinder. When heat is started, the low-pressure steam circuit, the medium-pressure steam circuit, and the high-pressure steam circuit are respectively connected to the low-pressure heat exchanger, the medium-pressure heat exchanger, and the high-pressure heat exchanger of the steam and molten salt heat exchange network module to provide low-pressure steam, medium-pressure steam, and high-pressure steam. During normal power generation, the low-pressure steam circuit, the medium-pressure steam circuit, and the high-pressure steam circuit are respectively connected to the low-pressure cylinder, the medium-pressure cylinder, and the high-pressure cylinder of the steam turbine to provide low-pressure high-temperature steam, medium-pressure high-temperature steam, and high-pressure high-temperature steam, respectively.

4. The gas turbine waste heat cascade energy storage and start-up auxiliary system according to claim 3, characterized in that, The low-pressure high-temperature steam, medium-pressure high-temperature steam, and high-pressure high-temperature steam generated by the steam and molten salt heat exchange network module are supplied to the low-pressure cylinder, medium-pressure cylinder, and high-pressure cylinder of the steam turbine through the main steam pipeline, respectively. The high-pressure high-temperature steam is also supplied to the pneumatic turning gear device through the main steam pipeline, and the medium-pressure high-temperature steam is also supplied to the shaft seal steam supply subsystem and the natural gas preheating module through the shaft seal steam pipeline. Furthermore, the shaft seal steam supply subsystem and the natural gas preheating module are started synchronously with the shaft seal steam pipeline.

5. The gas turbine waste heat cascade energy storage and start-up auxiliary system according to claim 4, characterized in that, The pneumatic turning gear includes a rotor driving device and a rotor high-speed drive device. The low-pressure heat exchanger provides low-pressure high-temperature steam to the low-pressure cylinder to drive the rotor driving device to drive the turbine rotor to rotate slowly. The medium-pressure heat exchanger provides medium-pressure high-temperature steam to the medium-pressure cylinder to drive the gas turbine to ignite, and at the same time provides it to the natural gas preheating module to raise the temperature of the natural gas. The high-pressure heat exchanger provides high-pressure high-temperature steam to the high-pressure cylinder and the rotor high-speed drive device to drive the gas turbine rotor ignition speed to the grid connection speed, thereby completing the rapid start-up of the gas turbine.

6. The gas turbine waste heat cascade energy storage and start-up auxiliary system according to claim 1, characterized in that, The molten salt phase change energy storage module includes a molten salt hot tank for storing high-temperature molten salt and a molten salt cold tank for storing low-temperature molten salt. The temperature of the high-temperature molten salt is at least 560°C, the temperature of the low-temperature molten salt is at least 290°C, and the temperature of the flue gas waste heat is between 250°C and 500°C. When the gas turbine is shut down, the low-temperature molten salt in the molten salt cold tank is directly heat-recovered by exchanging heat with the waste heat of the flue gas in the flue gas pipeline. After the temperature rises to 560°C and becomes high-temperature molten salt, it is pumped to the molten salt hot tank for storage. Furthermore, a molten salt pump is provided at the output end of the pipeline connecting the molten salt phase change energy storage module and the steam and molten salt heat exchange network module. The intelligent control system is also connected to the molten salt pump. When heat is required, the system controls the molten salt pump to start and pump the high-temperature molten salt heat energy stored in the molten salt phase change energy storage module into the three-stage heat exchanger.

7. The gas turbine waste heat cascade energy storage and start-up auxiliary system according to claim 1, characterized in that, The shaft seal steam supply subsystem includes a dedicated heater, a steam buffer tank, a desuperheating and pressure reducing device, and a temperature control system. The input end of the dedicated heater is connected to the shaft seal steam pipeline, and its output end is connected to the shaft seal pipeline of the gas turbine via the steam buffer tank and the desuperheating and pressure reducing device. The temperature control system monitors the steam temperature in real time through sensors; and / or The natural gas preheating module is configured as a shell-and-tube heat exchanger, with the shell side connected to the shaft seal steam pipeline and the tube side connected to the natural gas intake pipeline of the gas turbine. The shaft seal steam flow rate is adjusted by an intelligent control system to heat the natural gas to 50~80℃.

8. The gas turbine waste heat cascade energy storage and start-up auxiliary system according to claim 1, characterized in that, The steam turbine is also connected to a generator drive to drive the generator to produce electrical energy; and / or The exhaust pipe of the steam turbine is connected to the steam circuit of the superheater through the condenser and the feedwater pump, so that the exhaust steam discharged from the exhaust pipe of the steam turbine enters the condenser, condenses into water, and is then sent back to the steam circuit of the superheater by the feedwater pump for circulation.

9. A control method for a gas turbine waste heat cascade energy storage and start-up auxiliary system, characterized in that, The control method, applied to the gas turbine waste heat cascade energy storage and start-up auxiliary system according to any one of claims 1 to 8, comprises: Off-peak energy storage phase: When the gas turbine receives a shutdown command, the intelligent control system switches to the shutdown heat storage state and controls the start of the molten salt pump. This allows the waste heat from the flue gas after the gas turbine shutdown to be heated by exchanging heat with the low-temperature molten salt in the molten salt phase change energy storage module, raising the temperature to high-temperature molten salt, and then storing it in the molten salt hot tank. When the flue gas temperature drops below 250℃ and remains below 250℃ for 30 seconds, the molten salt pump is shut down, the intelligent control system switches to standby mode, and the shutdown energy storage is completed. Start-up heating phase: When the gas turbine receives the start-up command, the intelligent control system switches to the start-up heat mode and controls the molten salt pump to start, so that the high-temperature molten salt in the molten salt phase change energy storage module is pumped into the three-stage heat exchanger of the steam and molten salt heat exchange network module. At the same time, the three-way valve is controlled to switch the connection between the steam circuit in the superheater of the waste heat boiler and the three-stage heat exchanger of the steam and molten salt heat exchange network module, so that the steam enters the three-stage heat exchanger of the steam and molten salt heat exchange network module. After the steam is heated by the high-temperature molten salt, it outputs low-pressure high-temperature steam, medium-pressure high-temperature steam and high-pressure high-temperature steam through its low-pressure heat exchanger, medium-pressure heat exchanger and high-pressure heat exchanger respectively. It is then delivered in stages through the main steam pipeline and shaft seal steam pipeline to the low-pressure cylinder, medium-pressure cylinder, high-pressure cylinder and pneumatic turning gear of the turbine, as well as the shaft seal steam supply subsystem and natural gas preheating module, so as to complete the rapid start-up of the gas turbine from low-speed turning gear to high-speed turning gear to turbine ignition and then to the gas turbine speed increase to grid connection speed. Once the gas turbine reaches its grid-connected speed, the intelligent control system switches to conventional power generation mode, the molten salt pump gradually shuts down, and the start-up heat utilization is completed.

10. The control method for the gas turbine waste heat cascade energy storage and start-up auxiliary system according to claim 9, characterized in that, Also includes: Conventional power generation phase: When the gas turbine is running at a stable grid-connected speed and the flue gas temperature is >500℃, the intelligent control system switches to the conventional power generation state, controls the three-way valve to switch the connection between the steam circuit in the superheater of the waste heat boiler and the main steam pipeline, directly supplying high-temperature steam to the turbine, the molten salt pump stops, and the molten salt phase change energy storage module enters the standby state. The high-temperature flue gas discharged from the gas turbine enters the waste heat boiler, and passes through its superheater and economizer in sequence. It first heats the water in the steam circuit to generate low-pressure high-temperature steam, medium-pressure high-temperature steam and high-pressure high-temperature steam, which are supplied to the low-pressure cylinder, medium-pressure cylinder and high-pressure cylinder of the steam turbine to drive the gas turbine to operate and at the same time drive the generator to generate electricity. The exhaust steam from the steam turbine enters the condenser and is condensed, and then sent back to the superheater of the waste heat boiler via the feedwater pump for steam circuit circulation. The shaft seal steam supply subsystem continues to operate, while the pneumatic turning gear device and natural gas preheating module stop working.

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