Steam turbine system for improving wide-load cycle efficiency based on regenerative small machine and operation method of steam turbine system

Abstract

The invention discloses a steam turbine system for improving wide-load cycle efficiency based on a regenerative small machine and an operation method thereof. The steam turbine system comprises a pressurization module, and the pressurization module comprises the regenerative small machine, a pressurization cylinder and a water supply secondary heater; the pressure cylinder and the high-pressure cylinder are coaxially arranged; the main steam pipeline comprises a pressure cylinder branch and a high-pressure cylinder branch; a first steam exhaust port and a second steam exhaust port of the pressure cylinder are connected with a high-pressure cylinder branch and a water supply secondary heater through a first steam exhaust pipeline and a second steam exhaust pipeline respectively; a first steam exhaust valve and a second steam exhaust valve are respectively arranged on the first steam exhaust pipeline and the second steam exhaust pipeline; a high-pressure cylinder steam inlet valve is arranged on the high-pressure cylinder branch between the pressure cylinder branch and the first steam exhaust pipeline; a steam inlet of the regenerative small machine is connected with a first steam exhaust pipeline and a high-pressure cylinder steam extraction opening through a first steam inlet branch and a second steam inlet branch which are connected with the steam inlet main pipe in parallel. A first steam inlet valve and a second steam inlet valve are respectively arranged on the first steam inlet branch and the second steam inlet branch; and the steam inlet end of the first steam inlet branch is connected to the first steam exhaust pipeline between the steam exhaust port of the pressure cylinder and the first steam exhaust valve.

Description

Technical Field

[0001] This invention belongs to the field of steam turbine power generation technology, specifically a steam turbine system and its operation method based on a regenerative small turbine to improve wide-load cycle efficiency. Background Technology

[0002] Against the backdrop of building a new power system, steam turbine units, as the core equipment of thermal power generation, face new challenges in their operating characteristics. With the increasing proportion of new energy power generation, steam turbine units need to operate frequently within a wide load range, which places higher demands on the variable operating condition performance of steam turbines.

[0003] With its role as a regulating power source, steam turbine units participate more frequently in low-load peak-shaving operations, leading to a gradual decrease in annual utilization hours and making low-load economic efficiency increasingly important. Conventional steam turbines are primarily optimized for rated operating conditions during design; however, under rated conditions, conventional steam turbines experience significant reductions in main steam pressure and feedwater temperature during low-load operation, resulting in a substantial decrease in cycle efficiency and a marked decline in economic efficiency, making it impossible to simultaneously meet the requirements of efficient regulation. Summary of the Invention

[0004] The purpose of this invention is to address the shortcomings of existing technologies by providing a steam turbine system and its operation method based on a regenerative turbine to improve the cycle efficiency under wide loads, thereby effectively increasing the main steam pressure and feedwater temperature at partial loads and achieving high-efficiency regulation over wide loads.

[0005] The technical objective of this invention is achieved through the following technical solution: A steam turbine system for improving wide-load cycle efficiency based on a regenerative turbine includes a boiler, a high-pressure cylinder, an intermediate-pressure cylinder, a low-pressure cylinder, and a booster module. The booster module includes a regenerative turbine, a booster cylinder, and a feedwater secondary heater. The booster cylinder is coaxially arranged with the high-pressure cylinder and connected to the main generator. The boiler is connected in parallel to the steam inlets of the high-pressure cylinder and the booster cylinder via a main steam pipeline. The main steam pipeline includes a booster cylinder branch and a high-pressure cylinder branch for connecting the steam inlets of the booster cylinder and the high-pressure cylinder, respectively. The first and second exhaust ports of the booster cylinder are connected to the high-pressure cylinder branch via the first and second exhaust pipelines, respectively. The system includes a secondary heater for feedwater; a first exhaust valve and a second exhaust valve are respectively installed on the first exhaust pipe and the second exhaust pipe; a high-pressure cylinder inlet valve is installed on the high-pressure cylinder branch between the booster cylinder branch and the first exhaust pipe; the steam inlet of the regenerative turbine is connected to the first exhaust pipe and the high-pressure cylinder extraction port respectively through a first steam inlet branch and a second steam inlet branch connected in parallel with the main steam inlet pipe; a first steam inlet valve and a second steam inlet valve are respectively installed on the first steam inlet branch and the second steam inlet branch; the steam inlet end of the first steam inlet branch is connected to the first exhaust pipe between the exhaust port of the booster cylinder and the first exhaust valve.

[0006] Preferably, the regenerative turbine and the high-pressure cylinder are arranged on separate shafts, the regenerative turbine and the water pump are arranged on the same shaft, and a small generator is connected to the regenerative turbine.

[0007] Preferably, the exhaust steam of the regenerative turbine is connected to a high-pressure heater, a deaerator, and a first low-pressure heater group via pipelines.

[0008] Preferably, the exhaust port of the high-pressure cylinder is connected to the boiler via a reheat steam cold section pipeline; the boiler is connected to the intermediate-pressure cylinder via a reheat steam hot section pipeline, and the intermediate-pressure cylinder is connected to the low-pressure cylinder via a connecting pipe.

[0009] Preferably, the exhaust port of the low-pressure cylinder is connected to the second low-pressure heater group of the regenerative system via a pipeline.

[0010] Preferably, the booster cylinder is designed to operate at the same speed as the main engine or at a higher speed; when the booster cylinder is designed to operate at a higher speed, it is also equipped with a gearbox that matches the speed of the main engine.

[0011] Based on the above-described method for improving the efficiency of a steam turbine system with a regenerative small turbine to enhance wide-load cycle efficiency, the method is as follows: When the unit is under high load, the high-pressure cylinder inlet valve is fully open and the first exhaust valve is fully closed; the booster cylinder operates in parallel with the high-pressure cylinder; the first inlet valve is fully open and the second inlet valve is fully closed, and the exhaust steam from the booster cylinder supplies steam to the regenerative turbine; the second exhaust valve is fully closed, the feedwater secondary heater is not in operation, and the high-pressure heater, deaerator, first low-pressure heater group and second low-pressure heater group are in normal operation. When the unit is under low load, the high-pressure cylinder inlet valve is fully closed and the first exhaust valve is fully open, with the booster cylinder and high-pressure cylinder operating in series; the first inlet valve is fully closed and the second inlet valve is fully open, with steam extracted from the high-pressure cylinder to supply steam for the regenerative turbine; the second exhaust valve is fully open, introducing a portion of the exhaust steam from the booster cylinder into the feedwater secondary heater for heating, thus putting the feedwater secondary heater into operation; the high-pressure heater, deaerator, first low-pressure heater group, and second low-pressure heater group are all in normal operation.

[0012] Preferably, during the unit load reduction process, the main steam pressure, the exhaust pressure of the booster cylinder and the high-pressure cylinder, and the feedwater temperature decrease; the unit heat consumption gradually increases; after the load decreases to the predetermined load switching point, the high-pressure cylinder inlet valve is gradually closed and the first exhaust valve is gradually opened to switch the booster cylinder and the high-pressure cylinder to series operation; the first inlet valve is gradually closed and the second inlet valve is gradually opened to switch the steam source of the regenerative turbine to steam extraction from the high-pressure cylinder; the second exhaust valve is gradually opened to put the feedwater secondary heater into operation.

[0013] Preferably, during the unit load increase process, after the load increases to the predetermined load switching point, the high-pressure cylinder inlet valve is gradually opened and the first exhaust valve is gradually closed to switch the booster cylinder and the high-pressure cylinder to parallel operation; the first inlet valve is gradually opened and the second inlet valve is gradually closed to switch the steam source of the regenerative turbine to the steam supply from the exhaust of the booster cylinder; the second exhaust valve is gradually closed to shut down the feedwater secondary heater.

[0014] Compared with the prior art, the beneficial effects of the present invention are: 1. The system of the present invention adds a booster module, which mainly includes a regenerative turbine, a booster cylinder, and a feedwater secondary heater. Under low load, the booster cylinder operates in series with the high-pressure cylinder to supply steam to the high-pressure cylinder, while simultaneously activating the feedwater secondary heater, which can effectively increase the main steam pressure and feedwater temperature at part load, thereby improving the economy of part load and achieving efficient regulation. Under high load, the booster cylinder operates in parallel with the high-pressure cylinder to supply exhaust steam to the regenerative turbine, enabling the booster cylinder to operate normally under wide load, avoiding energy loss caused by the booster cylinder being in hot standby at high load. Attached Figure Description

[0015] Figure 1 This is a schematic diagram of the system structure of the present invention; Figure reference numerals: 1—boiler; 11—main steam header; 12—booster cylinder branch; 13—high pressure cylinder branch; 131—high pressure cylinder inlet valve; 14—reheat steam hot section pipeline; 15—reheat steam cold section pipeline; 2—High-pressure cylinder; 3—Medium-pressure cylinder; 4—Low-pressure cylinder; 41—Second low-pressure heater group; 5—Main generator; 6—Booster cylinder; 61—First exhaust steam pipeline; 611—First exhaust steam valve; 62—Second exhaust steam pipeline; 621—Second exhaust steam valve; 63—Feedwater secondary heater; 7—Regenerative turbine; 71—Steam inlet header; 72—First steam inlet branch; 721—First steam inlet valve; 73—Second steam inlet branch; 731—Second steam inlet valve; 74—High-pressure heater; 75—Deaerator; 76—First low-pressure heater group; 8—Water pump; 9—Small generator. Detailed Implementation

[0016] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. The components of the embodiments of the present invention described and shown in the accompanying drawings can generally be arranged and designed in various different configurations.

[0017] Therefore, the following detailed description of the embodiments of the invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of the invention without inventive effort are within the scope of protection of the invention.

[0018] It should be noted that similar reference numerals 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. Furthermore, the terms "first," "second," etc., are used only to distinguish descriptions and should not be construed as indicating or implying relative importance.

[0019] like Figure 1As shown, a steam turbine system for improving wide-load cycle efficiency based on a regenerative turbine includes a boiler 1, a high-pressure cylinder 2, an intermediate-pressure cylinder 3, a low-pressure cylinder 4, and a booster module. The booster module includes a regenerative turbine 7, a booster cylinder 6, and a feedwater secondary heater 63. The booster cylinder 6 is coaxially arranged with the high-pressure cylinder 2 and connected to the main generator 5. The boiler 1 is connected in parallel to the steam inlets of the high-pressure cylinder 2 and the booster cylinder 6 via a main steam pipeline. The main steam pipeline includes a booster cylinder branch 12 and a high-pressure cylinder branch 13 for connecting the steam inlets of the booster cylinder 6 and the high-pressure cylinder 2. The first and second exhaust ports of the booster cylinder 6 are connected to the high-pressure cylinder branch 13 and the feedwater secondary heater 63 via a first exhaust pipeline 61 and a second exhaust pipeline 62, respectively. 3; The first exhaust pipe 61 and the second exhaust pipe 62 are respectively equipped with a first exhaust valve 611 and a second exhaust valve 621; the high pressure cylinder branch 13 between the booster cylinder branch 12 and the first exhaust pipe 61 is equipped with a high pressure cylinder inlet valve 131; the steam inlet of the regenerative small machine 7 is connected to the first exhaust pipe 61 and the high pressure cylinder 2 extraction port through the first steam inlet branch 72 and the second steam inlet branch 73 connected in parallel with the steam inlet main pipe 71; the first steam inlet branch 72 and the second steam inlet branch 73 are respectively equipped with a first steam inlet valve 721 and a second steam inlet valve 731; the steam inlet end of the first steam inlet branch 72 is connected to the first exhaust pipe 61 between the exhaust port of the booster cylinder 6 and the first exhaust valve 611. In practical implementation, a booster module is added, mainly including a regenerative turbine 7, a booster cylinder 6, and a feedwater secondary heater 63. Under low load, the booster cylinder 6 operates in series with the high-pressure cylinder 2, supplying steam to the high-pressure cylinder 2, and simultaneously activating the feedwater secondary heater 63. This effectively increases the main steam pressure and feedwater temperature at part load, thereby improving part load economy and achieving efficient regulation. Under high load, the booster cylinder 6 operates in parallel with the high-pressure cylinder 2, supplying exhaust steam to the regenerative turbine 7, enabling the booster cylinder 6 to operate normally under wide loads and avoiding energy loss caused by hot standby of the booster cylinder 6 under high loads. By adopting this technical measure, through the dual-mode switching of the booster cylinder 6 at high and low loads (parallel power generation at high loads, series boosting at low loads) and the dual steam source design of the regenerative turbine 7, the booster cylinder 6 is utilized efficiently at full load, simultaneously increasing the main steam pressure and feedwater temperature at wide loads, significantly improving the unit's low-load economy.

[0020] like Figure 1 As shown, the high-pressure cylinder 2, intermediate-pressure cylinder 3, low-pressure cylinder 4, and main generator 5 are coaxially arranged, and the booster cylinder 6 of the booster module is also coaxially arranged with the high-pressure cylinder 2. The boiler 1 is connected in parallel to the steam inlets of the high-pressure cylinder 2 and the booster cylinder 6 via a main steam pipeline. The main steam pipeline includes a main steam header 11 and booster cylinder branch 12 and high-pressure cylinder branch 13 for connecting the steam inlets of the booster cylinder 6 and the high-pressure cylinder 2. One end of the main steam header 11 is connected to the boiler 1, and the other end is connected in parallel to the booster cylinder branch 12 and the high-pressure cylinder branch 13.

[0021] like Figure 1As shown, the exhaust port of the high-pressure cylinder 2 is connected to the boiler 1 via a reheat steam cold section pipeline 15; the boiler 1 is connected to the intermediate-pressure cylinder 3 via a reheat steam hot section pipeline 14, and the intermediate-pressure cylinder 3 is connected to the low-pressure cylinder 4 via a connecting pipe. The exhaust port of the low-pressure cylinder 4 is connected to the second low-pressure heater group 41 of the regenerative system via a pipeline. The regenerative system generally includes a high-pressure heater 74, a deaerator 75, and a first low-pressure heater group 76, etc.

[0022] In this embodiment, the booster cylinder 6 includes a first exhaust port and a second exhaust port, which are connected to the high-pressure cylinder branch 13 and the feedwater secondary heater 63 via a first exhaust pipe 61 and a second exhaust pipe 62, respectively. A first exhaust valve 611 and a second exhaust valve 621 are respectively installed on the first exhaust pipe 61 and the second exhaust pipe 62. A high-pressure cylinder inlet valve 131 is installed on the high-pressure cylinder branch 13 between the booster cylinder branch 12 and the first exhaust pipe 61. During actual operation, under high load, the first exhaust valve 611 is closed, and the high-pressure cylinder inlet valve 131 is opened, allowing the booster cylinder 6 and high-pressure cylinder 2 to generate electricity in parallel. Under low load, the first exhaust valve 611 is opened, and the high-pressure cylinder inlet valve 131 is closed, allowing the booster cylinder 6 to exhaust steam in series into the high-pressure cylinder branch 13 to increase the main steam pressure; simultaneously, the second exhaust valve 621 is opened, and the exhaust steam enters the feedwater secondary heater 63 to compensate for temperature losses.

[0023] like Figure 1 As shown, the regenerative turbine 7 and the high-pressure cylinder 2 are arranged on separate shafts, while the regenerative turbine 7 and the feedwater pump 8 are arranged coaxially and connected to the small generator 9. By arranging the regenerative turbine 7 and the high-pressure cylinder 2 on separate shafts, the turbine speed can be independently optimized to accurately match the power requirements of the feedwater pump 8. At the same time, the small generator 9 recovers excess steam energy, significantly improving the efficiency and energy utilization of the water supply system under full load conditions.

[0024] like Figure 1 As shown, the steam inlet of the regenerative turbine 7 is connected to the first exhaust pipe 61 and the extraction port of the high-pressure cylinder 2 via a first steam inlet branch 72 and a second steam inlet branch 73 connected in parallel with the main steam inlet pipe 71. A first steam inlet valve 721 and a second steam inlet valve 731 are respectively installed on the first steam inlet branch 72 and the second steam inlet branch 73. The steam inlet end of the first steam inlet branch 72 is connected to the first exhaust pipe 61 between the exhaust port of the booster cylinder 6 and the first exhaust valve 611. In a specific implementation, the steam inlet pipe includes the main steam inlet pipe 71 and the first steam inlet branch 72 and the second steam inlet branch 73 for connecting the first exhaust pipe 61 and the extraction port of the high-pressure cylinder 2. One end of the main steam inlet pipe 71 is connected to the steam inlet of the regenerative turbine 7, and the other end is connected in parallel to the first steam inlet branch 72 and the second steam inlet branch 73.

[0025] like Figure 1As shown, the exhaust steam from the regenerative turbine 7 is connected to the high-pressure heater 74, the deaerator 75, and the first low-pressure heater group 76 via pipelines. The exhaust steam from the regenerative turbine 7 is directly supplied to the high / low-pressure heaters and the deaerator 75, replacing the conventional steam extraction from the steam turbine, realizing the cascade utilization of high-quality steam, significantly improving the energy efficiency of the regenerative system and reducing the unit's heat consumption.

[0026] In practical use, the booster cylinder 6 is designed for either the same speed as the main unit or a higher speed. When the booster cylinder 6 is designed for a higher speed, it is also equipped with a gearbox that matches the speed of the main unit. By leveraging the speed flexibility of the booster cylinder 6 (simplified structure at the same speed / improved efficiency at high speed), it can be matched with the space and efficiency requirements of different units. Combined with the gearbox, it achieves full-load power coupling, maximizing the working efficiency of the booster cylinder 6 while ensuring system reliability.

[0027] The specific operation method of a steam turbine system based on a regenerative small turbine to improve the efficiency of wide-load cycle is as follows: When the unit is under high load, the high-pressure cylinder inlet valve 131 is fully open and the first exhaust valve 611 is fully closed; the booster cylinder 6 and the high-pressure cylinder 2 operate in parallel; the first inlet valve 721 is fully open and the second inlet valve 731 is fully closed, and the exhaust steam from the booster cylinder 6 supplies steam to the regenerative turbine 7; the second exhaust valve 621 is fully closed, and the feedwater secondary heater 63 is not in operation; the high-pressure heater 74, the deaerator 75, the first low-pressure heater group 76, and the second low-pressure heater group 41 are in normal operation; When the unit is under low load, the high-pressure cylinder inlet valve 131 is fully closed and the first exhaust valve 611 is fully open, with the booster cylinder 6 and the high-pressure cylinder 2 operating in series; the first inlet valve 721 is fully closed and the second inlet valve 731 is fully open, with the high-pressure cylinder 2 extracting steam to supply the regenerative turbine 7; the second exhaust valve 621 is fully open, introducing a portion of the exhaust steam from the booster cylinder 6 into the feedwater secondary heater 63 for heating, thus putting the feedwater secondary heater 63 into operation; the high-pressure heater 74, deaerator 75, first low-pressure heater group 76, and second low-pressure heater group 41 are all in normal operation.

[0028] Through valve linkage and coordinated control under high and low load conditions (parallel / series switching of 6 booster cylinders, automatic conversion of steam source for small turbine, and precise switching of secondary heaters), dynamic optimization of main steam pressure and feedwater temperature is achieved across the entire load range, significantly improving thermal efficiency over a wide load range and eliminating equipment idle losses.

[0029] In actual operation, it also includes the process of reducing unit load and the process of increasing unit load.

[0030] During the load reduction process, the main steam pressure, the exhaust pressure of the booster cylinder 6 and the high-pressure cylinder 2, and the feedwater temperature decrease; the unit's heat consumption gradually increases; after the load decreases to the predetermined load switching point, the high-pressure cylinder inlet valve 131 is gradually closed and the first exhaust valve 611 is gradually opened, switching the booster cylinder 6 and the high-pressure cylinder 2 to series operation; the first inlet valve 721 is gradually closed and the second inlet valve 731 is gradually opened, switching the steam source of the regenerative turbine 7 to steam extraction from the high-pressure cylinder 2; the second exhaust valve 621 is gradually opened, and the feedwater secondary heater 63 is put into operation.

[0031] During the load increase process, after the load rises to the predetermined load switching point, the high-pressure cylinder inlet valve 131 is gradually opened and the first exhaust valve 611 is gradually closed to switch the booster cylinder 6 and the high-pressure cylinder 2 to parallel operation; the first inlet valve 721 is gradually opened and the second inlet valve 731 is gradually closed to switch the steam source of the regenerative turbine 7 to be supplied by the exhaust steam of the booster cylinder 6; the second exhaust valve 621 is gradually closed to shut down the feedwater secondary heater 63.

[0032] The technical solutions provided by the embodiments of the present invention have been described in detail above. Specific examples have been used to illustrate the principles and implementation methods of the embodiments of the present invention. The descriptions of the embodiments above are only for helping to understand the principles of the embodiments of the present invention. At the same time, for those skilled in the art, there will be changes in the specific implementation methods and application scope based on the embodiments of the present invention. Therefore, the content of this specification should not be construed as a limitation of the present invention.

Claims

1. A steam turbine system for improving the efficiency of a wide load cycle based on a regenerative small machine, characterized by, The application relates to a supercharged steam turbine unit and a running method thereof.

2. The regenerative small machine-based steam turbine system for improving wide load cycle efficiency according to claim 1, characterized by, The supercharged steam turbine unit comprises a boiler, a high-pressure cylinder, a medium-pressure cylinder, a low-pressure cylinder and a supercharging module, wherein the supercharging module comprises a regenerative small machine, a supercharging cylinder and a feedwater secondary heater; the supercharging cylinder is coaxially arranged with the high-pressure cylinder and is connected with a main generator; the boiler is connected with the steam inlets of the high-pressure cylinder and the supercharging cylinder through a main steam pipeline in parallel, the main steam pipeline comprises a supercharging cylinder branch and a high-pressure cylinder branch for connecting the steam inlets of the supercharging cylinder and the high-pressure cylinder; the first and second steam outlets of the supercharging cylinder are connected with the high-pressure cylinder branch and the feedwater secondary heater through first and second steam discharge pipelines respectively; first and second steam discharge valves are arranged on the first and second steam discharge pipelines respectively; a high-pressure cylinder steam inlet valve is arranged on the high-pressure cylinder branch between the supercharging cylinder branch and the first steam discharge pipeline; the steam inlets of the regenerative small machine are connected with the first steam discharge pipeline and the high-pressure cylinder steam outlet through first and second steam inlet branches connected with a steam inlet main pipeline in parallel respectively; first and second steam inlet valves are arranged on the first and second steam inlet branches respectively; the steam inlet end of the first steam inlet branch is connected on the first steam discharge pipeline between the steam outlet of the supercharging cylinder and the first steam valve.

3. The regenerative small machine based turbine system for improving wide load cycle efficiency as claimed in claim 1 wherein, The regenerative small machine is arranged coaxially with the high-pressure cylinder, and the regenerative small machine is coaxially arranged with a feedwater pump and is connected with a small generator.

4. The regenerative small machine based turbine system for improving wide load cycle efficiency as claimed in claim 1 wherein, The steam discharged from the regenerative small machine is connected with a high-pressure heater, a deaerator and a first low-pressure heater group through pipelines respectively.

5. The regenerative small machine based turbine system for improving wide load cycle efficiency as claimed in claim 4 wherein, The steam outlet of the high-pressure cylinder is connected with the boiler through a reheated steam cold section pipeline; the boiler is connected with the medium-pressure cylinder through a reheated steam hot section pipeline; and the medium-pressure cylinder is connected with the low-pressure cylinder through a communication pipeline.

6. The regenerative small machine based turbine system for improving wide load cycle efficiency as claimed in claim 4 wherein, The steam outlet of the low-pressure cylinder is connected with a second low-pressure heater group of a regenerative system through a pipeline.

7. The method of operating a regenerative small machine-based steam turbine system to boost the efficiency of a wide load cycle according to any one of claims 1-6, wherein, The supercharging cylinder is designed with the same rotating speed as a large machine or with high rotating speed; when the supercharging cylinder is designed with high rotating speed, a gearbox matched with the rotating speed of the large machine is arranged. The running method is as follows: When the unit is under high load, the high-pressure cylinder steam inlet valve is fully opened, the first steam discharge valve is fully closed, the supercharging cylinder and the high-pressure cylinder are operated in parallel, the first steam inlet valve is fully opened, the second steam inlet valve is fully closed, the steam discharged from the supercharging cylinder is used for the regenerative small machine, the second steam discharge valve is fully closed, the feedwater secondary heater is not put into operation, the high-pressure heater, the deaerator, the first low-pressure heater group and the second low-pressure heater group are normally put into operation; when the unit is under low load, the high-pressure cylinder steam inlet valve is fully closed, the first steam discharge valve is fully opened, the supercharging cylinder and the high-pressure cylinder are operated in series, the first steam inlet valve is fully closed, the second steam inlet valve is fully opened, the steam extracted from the high-pressure cylinder is used for the regenerative small machine, the second steam discharge valve is fully opened, part of the steam discharged from the supercharging cylinder is introduced into the feedwater secondary heater to realize the operation of the feedwater secondary heater, and the high-pressure heater, the deaerator, the first low-pressure heater group and the second low-pressure heater group are normally put into operation.

8. The method of operating a regenerative small machine-based steam turbine system to boost wide load cycle efficiency of claim 7, wherein, During the process of load reduction, the main steam pressure, the exhaust pressure of the platen cylinder and the high pressure cylinder, and the feed water temperature are reduced, and the heat consumption is gradually increased. When the load is reduced to the predetermined switching load point, the high pressure cylinder inlet valve is gradually closed, the first exhaust valve is gradually opened, the platen cylinder and the high pressure cylinder are switched to series operation, the first inlet valve is gradually closed, the second inlet valve is gradually opened, the back-heat small machine steam source is switched to the high pressure cylinder extraction steam, and the second exhaust valve is gradually opened to put the feed water secondary heater into operation.

9. The method of operating a regenerative small machine-based steam turbine system to boost wide load cycle efficiency of claim 7, wherein, During the process of load increase, when the load is increased to the predetermined switching load point, the high pressure cylinder inlet valve is gradually opened, the first exhaust valve is gradually closed, the platen cylinder and the high pressure cylinder are switched to parallel operation, the first inlet valve is gradually opened, the second inlet valve is gradually closed, the back-heat small machine steam source is switched to the platen cylinder exhaust steam, and the second exhaust valve is gradually closed to stop the feed water secondary heater.

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