A system and method for auxiliary steam replenishment in thermal power plants under deep peak shaving

Abstract

This invention belongs to the field of thermal power generation technology and provides an auxiliary steam replenishment system and method for thermal power plants under deep peak shaving. The auxiliary steam replenishment system for thermal power plants under deep peak shaving includes a DCS control system and at least two generating units; each unit is equipped with an auxiliary steam header, the steam source of which comes from fourth-stage extraction steam from the turbine and low-temperature reheat steam. A connecting main pipe is provided between any two adjacent auxiliary steam headers; the DCS control system is used to interlock the generating units according to the unit's load rate and auxiliary steam parameters to achieve automatic control of the steam source switching of the auxiliary steam headers.

Description

Technical Field

[0001] This invention belongs to the field of thermal power generation technology, and particularly relates to an auxiliary steam replenishment system and method for thermal power plants under deep peak shaving. Background Technology

[0002] The statements in this section are merely background information related to the present invention and do not necessarily constitute prior art.

[0003] To ensure the grid connection of new energy sources, thermal power plants will increasingly participate in grid peak shaving, requiring more and more plants to have a 20% deep regulation capability. This presents challenges to various systems within thermal power plants. A thermal power plant typically consists of two or more generating units. Taking two units as an example, the auxiliary steam system is shared by both units, with a single auxiliary steam header throughout the plant. The parameters of this auxiliary steam header can meet the needs of all steam consumption points. The main steam source for this system comes from the fourth-stage extraction steam from the turbine and low-temperature reheat steam (cold section). During normal operation, the auxiliary steam is supplied by the fourth extraction steam from the same unit. When one unit participates in peak shaving, the pressure of the fourth extraction steam drops, and auxiliary steam can be supplied from the cold section of the same unit.

[0004] For power plants with start-up boilers, auxiliary steam can be provided during the start-up phase. However, when the unit frequently participates in deep peak shaving, the start-up boiler cannot provide steam in a timely manner. During deep peak shaving, the parameters of the cold section and the fourth extraction cannot meet production needs. When the power plant does not have a suitable auxiliary steam source, it cannot quickly respond to the grid's deep peak shaving requirements.

[0005] After deep peak shaving of the unit, a solution can be adopted to extract steam from the high-temperature reheat steam (hot section) through perforation, and then provide steam after desuperheating and pressure reduction by a desuperheater and pressure reducer. However, for older units already in operation, the hot section (usually made of P91 material) was factory-heat treated during the unit's construction. If this modification is carried out on an older unit, drilling and extracting steam from the frequently operating hot section on-site, drilling and welding can easily cause thermal stress concentration at the drilling points, posing certain safety risks. Summary of the Invention

[0006] To address the technical problems mentioned above, this invention provides an auxiliary steam replenishment system for thermal power plants under deep peak shaving conditions. This system enables the auxiliary steam system to operate normally under deep peak shaving conditions, thereby ensuring the operation of the entire plant and meeting the peak shaving requirements of the power grid.

[0007] To achieve the above objectives, the present invention adopts the following technical solution:

[0008] The first aspect of the present invention provides an auxiliary steam replenishment system for thermal power plants under deep peak shaving.

[0009] An auxiliary steam replenishment system for thermal power plants under deep peak shaving includes:

[0010] DCS control system and at least two generator sets;

[0011] Each unit is equipped with an auxiliary steam header, the steam source of which comes from the fourth stage extraction steam of the steam turbine and low temperature reheat steam. A connecting main pipe is provided between any two adjacent auxiliary steam headers.

[0012] The DCS control system is used to interlock the unit according to the unit's load rate and auxiliary steam parameters, so as to realize the automatic control of the auxiliary steam header's steam source switching.

[0013] In one implementation, the auxiliary steam header has an interface to all steam supply points in the plant.

[0014] In one implementation, the auxiliary steam header is provided with a first drainage point to drain water to a drainage expansion container or other locations.

[0015] As one implementation method, an additional steam supply line is added to the outlet pipeline of the high-temperature bypass valve and connected to the low-temperature reheat steam system.

[0016] In one implementation, the steam injection pipeline is equipped with a valve group, which is controlled by the DCS control system.

[0017] As one implementation, the steam injection pipeline is provided with a second drainage point to drain water to a drainage expansion container or other locations.

[0018] As one implementation method, during the process of interlocking the units according to the unit's load rate and auxiliary steam parameters in the DCS control system, when all units are operating normally or at reduced load, the auxiliary steam is supplied by the fourth-stage extraction steam from the unit's turbine.

[0019] As one implementation method, during the process of interlocking the units according to the unit's load rate and auxiliary steam parameters in the DCS control system, when any one of the units participates in peak shaving (non-deep peak shaving), the auxiliary steam is provided by the low-temperature reheat steam of the unit.

[0020] As one implementation method, during the process of the DCS control system interlocking the unit based on the unit's load rate and auxiliary steam parameters:

[0021] When one unit further participates in deep peak shaving, the auxiliary steam is supplied by the low-temperature reheat steam from any of the other (N-1) units.

[0022] When the two units further participate in deep peak shaving, the auxiliary steam is supplied by the low temperature reheat steam of any one of the other (N-2) units;

[0023] Similarly, when all N units need to participate in deep peak shaving, the valve group on the make-up steam pipeline is opened, and the main steam is used as the auxiliary steam source after being depressurized and de-cooled by the high-pressure bypass.

[0024] Where N≤4.

[0025] A second aspect of the present invention provides a method for operating an auxiliary steam replenishment system for a thermal power plant under deep peak shaving conditions, as described above.

[0026] A method for operating an auxiliary steam replenishment system for thermal power plants under deep peak shaving, as described above, includes:

[0027] When all units are operating normally or at reduced load, the auxiliary steam is supplied by the fourth-stage extraction steam from the turbine of this unit.

[0028] When any one of the units participates in peak shaving (non-deep peak shaving), the auxiliary steam is provided by the low-temperature reheat steam of the unit.

[0029] When one unit further participates in deep peak shaving, the auxiliary steam is supplied by the low-temperature reheat steam from any of the other (N-1) units.

[0030] When the two units further participate in deep peak shaving, the auxiliary steam is supplied by the low temperature reheat steam of any one of the other (N-2) units;

[0031] Similarly, when all N units need to participate in deep peak shaving, the valve group on the make-up steam pipeline is opened, and the main steam is used as the auxiliary steam source after being depressurized and de-cooled by the high-pressure bypass.

[0032] Where N≤4.

[0033] Compared with the prior art, the beneficial effects of the present invention are:

[0034] This invention adds a supplementary steam pipeline to the outlet pipeline of the high-temperature bypass valve, connecting it to the low-temperature reheat steam system. A valve group is installed on the supplementary steam pipeline, and these valve groups are controlled by the DCS control system. The DCS control system interlocks the units based on the unit's load rate and auxiliary steam parameters to achieve automatic control of the steam source switching of the auxiliary steam header. This solves the problem that the existing power plant auxiliary steam system cannot meet the parameter requirements when two or more units are engaged in deep peak shaving, providing timely and suitable auxiliary steam to meet the grid's demand for deep peak shaving from power plants. Furthermore, the system design of this invention is simple, and compared to the hot section extraction steam scheme, the system is safer and more reliable. The system operation of this invention is flexible; it can determine the auxiliary steam operation mode according to different loads based on the built-in control program.

[0035] Advantages of additional aspects of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. Attached Figure Description

[0036] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an improper limitation of the invention.

[0037] Figure 1 This is a schematic diagram of the auxiliary steam replenishment system for thermal power plants under deep peak shaving according to an embodiment of the present invention. Detailed Implementation

[0038] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0039] It should be noted that the following detailed description is illustrative and intended to provide further explanation of the invention. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0040] It should be noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the scope of exemplary embodiments according to the invention. As used herein, the singular form is intended to include the plural form as well, unless the context clearly indicates otherwise. Furthermore, it should be understood that when the terms "comprising" and / or "including" are used in this specification, they indicate the presence of features, steps, operations, devices, components, and / or combinations thereof.

[0041] To ensure the normal operation of the plant's auxiliary steam system under deep peak shaving conditions and meet the grid's deep peak shaving requirements, this invention provides an auxiliary steam replenishment system for thermal power plants under deep peak shaving conditions.

[0042] The following is combined Figure 1 The detailed implementation process of the present invention will be given in detail.

[0043] according to Figure 1 As can be seen, an auxiliary steam replenishment system for thermal power plants under deep peak shaving in this embodiment includes: a DCS control system and at least two generating units;

[0044] Each unit is equipped with an auxiliary steam header, the steam source of which comes from the fourth stage extraction steam of the steam turbine and low temperature reheat steam. A connecting main pipe is provided between any two adjacent auxiliary steam headers.

[0045] The DCS control system is used to interlock the unit according to the unit's load rate and auxiliary steam parameters, so as to realize the automatic control of the auxiliary steam header's steam source switching.

[0046] The following example uses two 660MW units in a power plant. The original auxiliary steam system configuration for each unit is as follows: Each unit is equipped with one auxiliary steam header, with the main steam source coming from the fourth-stage extraction steam and low-temperature reheat steam (cold section) of the turbine. A connecting main pipe is installed between the two auxiliary steam headers. During normal operation, the auxiliary steam is supplied by the fourth extraction steam of the unit. When one unit participates in peak shaving, the pressure of the fourth extraction steam drops, and the auxiliary steam can be supplied by the cold section of the unit.

[0047] The auxiliary header has an interface to all steam consumption points in the plant (multiple steam consumption points A, B, C, etc., only two are shown in the figure), and is equipped with a first drainage point to drain water to the drainage expansion container or other places.

[0048] In this embodiment, a pneumatic butterfly valve is also installed in the outlet pipeline of the high bypass valve of the original bypass system, and a make-up steam pipeline is added between the high bypass valve and the pneumatic butterfly valve to connect to the low temperature reheat steam system.

[0049] The steam injection pipeline is equipped with a second drainage point to drain water to a drainage expansion container or other locations.

[0050] The steam injection pipeline is equipped with a valve group, which is controlled by the DCS control system.

[0051] Specifically, the valve assembly consists of an electric gate valve, a start-up butterfly valve, and an electric gate valve.

[0052] In this embodiment, a supplementary steam pipeline is added to the outlet pipeline of the high-temperature bypass valve and connected to the low-temperature reheat steam system. A valve group is installed on the supplementary steam pipeline, and these valve groups are controlled by the DCS control system. The DCS control system interlocks the unit according to the unit's load rate and auxiliary steam parameters to realize automatic control of the steam source switching of the auxiliary steam header. This solves the problem that the current power plant auxiliary steam system cannot meet the parameter requirements when two or more units are deeply shaving, and provides suitable auxiliary steam in a timely manner to meet the power grid's demand for deep peak shaving of power plants.

[0053] In the specific implementation process, when the DCS control system is used to interlock the unit according to the unit's load rate and auxiliary steam parameters, when all units are operating normally or operating at reduced load (approximately 40% THA or more), the auxiliary steam is supplied by the fourth-stage extraction steam from the unit's turbine.

[0054] When any one of the units participates in peak shaving (approximately 25% THA to above 40% THA), the pressure of the fourth extraction unit drops, and the auxiliary steam is supplied by the low-temperature reheat steam of this unit.

[0055] When a unit further participates in deep peak shaving (below approximately 25% THA), auxiliary steam is supplied by low-temperature reheat steam from any of the other (N-1) units.

[0056] When both units further participate in deep peak shaving (below approximately 25% THA), auxiliary steam is supplied by the low-temperature reheat steam from any of the other (N-2) units.

[0057] Similarly, when all N generating units need to participate in deep peak shaving (below approximately 25% THA), the original auxiliary steam systems of all units in the power plant will not meet production demands. In this case, the N units participating in deep peak shaving can activate their newly added auxiliary steam supplementary gas systems and open the valve groups. The auxiliary steam is then primarily supplied by the main steam after being depressurized and de-cooled by a high-pressure bypass valve. Where N ≤ 4.

[0058] In some other embodiments, such as when the economic efficiency of the unit is not considered or all the auxiliary steam headers of the units are independent headers (i.e., not connected by an auxiliary steam connection main pipe), when any one of the units participates in deep peak shaving (below approximately 25% THA), the auxiliary steam replenishment system of the unit can be turned on to supplement auxiliary steam.

[0059] In one or more embodiments, the method of operating a thermal power plant auxiliary steam replenishment system under deep peak shaving as described above includes:

[0060] When all units are operating normally or at reduced load (approximately 40% THA or higher), auxiliary steam is supplied by the fourth-stage extraction steam from the turbine of this unit; where THA refers to the heat consumption acceptance condition.

[0061] When any one of the units participates in peak shaving (approximately 25% THA to above 40% THA), the auxiliary steam is provided by the low-temperature reheat steam of the unit.

[0062] When a unit further participates in deep peak shaving (below approximately 25% THA), auxiliary steam is supplied by low-temperature reheat steam from any of the other (N-1) units.

[0063] When both units further participate in deep peak shaving (below approximately 25% THA), auxiliary steam is supplied by the low-temperature reheat steam from any of the other (N-2) units.

[0064] Similarly, when all N units need to participate in deep peak shaving, the valve group on the make-up steam pipeline is opened, and the main steam is used as the auxiliary steam source after being depressurized and de-cooled by the high-pressure bypass.

[0065] Where N≤4.

[0066] The system of the present invention is simple in design and is safer and more reliable than the hot section extraction steam scheme. The system of the present invention is flexible in operation and can determine the operation mode of auxiliary steam according to different loads based on the built-in control program.

[0067] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A supplementary system for auxiliary steam of a thermal power plant under deep peak regulation, characterized in that, The utility model relates to a DCS control system and at least two units, each unit is equipped with an auxiliary steam header, the steam source of the auxiliary steam header comes from the fourth stage steam extraction of the steam turbine and the low-temperature reheat steam, and a communication header is arranged between any two adjacent auxiliary steam headers. The DCS control system is used to interlock the units according to the load rate and auxiliary steam parameters of the units to realize automatic control of the steam source switching of the auxiliary steam header. In the process that the DCS control system is used to interlock the units according to the load rate and auxiliary steam parameters of the units, when one unit further participates in deep peak regulation, the low-temperature reheat steam of any one of the other (N-1) units is used as the auxiliary steam; When two units further participate in deep peak regulation, the low-temperature reheat steam of any one of the other (N-2) units is used as the auxiliary steam; By analogy, when all the N units need to participate in deep peak regulation, the valve group on the supplementary steam pipeline is opened, and the main steam is used as the auxiliary steam source after being reduced in temperature and pressure by the high bypass. N≤4. The auxiliary steam header has an interface for removing the full-plant steam. The auxiliary steam header is provided with a first drain point to drain to a drain expansion vessel or other places. A supplementary steam pipeline is added to the high bypass valve outlet pipeline and connected to the low-temperature reheat steam system.

2. The auxiliary steam supplement system for a deep peak shaving down thermal power plant according to claim 1, wherein, The supplementary steam pipeline is provided with a valve group, and the valve group is controlled by the DCS control system.

3. The auxiliary steam supplement system for a deep peak shaving down thermal power plant of claim 1, wherein, The supplementary steam pipeline is provided with a second drain point to drain to a drain expansion vessel or other places.

4. The supplemental steam system for a deep load following fossil fuel power plant of claim 1, wherein, In the process that the DCS control system is used to interlock the units according to the load rate and auxiliary steam parameters of the units, when all the units are normally operated and are operated at a reduced load, the auxiliary steam is supplied by the fourth stage steam extraction of the steam turbine of the unit.

5. The supplemental steam system for a deep load following fossil fuel power plant of claim 4, wherein, In the process that the DCS control system is used to interlock the units according to the load rate and auxiliary steam parameters of the units, when any one of the units participates in peak regulation and is not deep peak regulation, the auxiliary steam is provided by the low-temperature reheat steam of the unit.

6. The supplemental steam system for a deep load following fossil fuel power plant of claim 4, wherein, When all the units are normally operated and are operated at a reduced load, the auxiliary steam is supplied by the fourth stage steam extraction of the steam turbine of the unit; 7. The supplemental steam system for a deep load following fossil fuel power plant of claim 1, wherein, When any one of the units participates in peak regulation, the auxiliary steam is provided by the low-temperature reheat steam of the unit; 8. The auxiliary steam supplement system for a deep peak shaving down thermal power plant according to claim 1 or 7, characterized in that, When one unit further participates in deep peak regulation, the low-temperature reheat steam of any one of the other (N-1) units is used as the auxiliary steam; 9. A method of operating a supplemental steam system for a deep peak shaving fossil fuel power plant as claimed in any one of claims 1-8, characterized in that, When two units further participate in deep peak regulation, the low-temperature reheat steam of any one of the other (N-2) units is used as the auxiliary steam; By analogy, when all the N units need to participate in deep peak regulation, the valve group on the supplementary steam pipeline is opened, and the main steam is used as the auxiliary steam source after being reduced in temperature and pressure by the high bypass. N≤4. ​ ​ ​ ​

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