Primary steam system adapting to working medium-to-direct current operation in ultra-low load water cooling wall of boiler
By adding a large-screen superheater and additional desuperheating water pipelines to the primary steam system, the safety and economic issues of water-cooled walls in ultra-supercritical thermal power units during deep peak shaving were solved, achieving safe operation of water-cooled walls under ultra-low loads and stable resistance under high loads.
Patent Information
- Application Number
- CN202511686426.1
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-11-18
- Publication Date
- 2026-02-27
AI Technical Summary
During deep peak shaving of ultra-supercritical thermal power units, the wet operation of the working fluid inside the boiler water-cooled wall leads to heat loss and control difficulties, affecting the safety and stability of the unit. In addition, conventional designs increase the resistance of the water-cooled wall under low load, affecting economic efficiency.
A large-screen superheater and additional desuperheating water pipeline are added to the primary steam system, increasing the capacity of the desuperheating water pipeline by more than 10%, and a desuperheating water pipeline is added between the low-temperature superheater and the large-screen superheater to ensure the safe operation of the water-cooled wall under ultra-low load, while keeping the water-cooled wall resistance from increasing under high load.
It achieves safe operation of the water-cooled wall under ultra-low load, avoids wall temperature overheating, maintains the unit's economy and the stability of water-cooled wall resistance under high load, and ensures the safe and stable operation of the unit.
Smart Images
Figure CN121576575A_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of boiler technology, and specifically relates to a primary steam system adapted to the direct current operation of the working fluid inside the water-cooled wall of a boiler under ultra-low load. Background Technology
[0002] Currently, the most advanced ultra-supercritical thermal power units can achieve a minimum load of approximately 20% for deep peak shaving. At this load, the working fluid inside the boiler water-cooled walls can switch to direct-flow dry operation, ensuring that film boiling does not occur and that the water-cooled walls operate safely and stably. If the peak load is further reduced, the working fluid inside the boiler water-cooled walls needs to operate in a wet state to avoid overheating and tube rupture. However, wet operation of the working fluid inside the water-cooled walls leads to heat and working fluid loss in the boiler, and frequent switching between dry and wet states makes unit control difficult, affecting the unit's safety and stability.
[0003] For conventional ultra-supercritical thermal power units operating at the lowest load during deep peak shaving, the key factor affecting the safe operation of the boiler water-cooled wall is the mass flow velocity at its lower section. Assuming operation at 20% load switching to DC mode, the critical mass flow velocity for safe operation of the spiral section water-cooled wall is G (unit: kg / (sm)). 2 If a lower load is required, such as 15% dry-state operation, the mass flow rate of the spiral section water-cooled wall under this condition needs to be maintained at least at the level of G. The boiler can achieve this by reducing the working fluid flow area of the water-cooled wall. However, at full load, the mass flow rate of the spiral section water-cooled wall will increase to about 6.7 times G (about 1.3 times that of conventional projects). This will result in a significant increase in the water-cooled wall resistance at full load (for example, in a 1000MW project, it will increase by about 1.24MPa compared to conventional projects), leading to increased feedwater pump selection costs and operating power consumption, and a decrease in the unit's economic efficiency.
[0004] Conventional primary steam systems, such as Figure 2 As shown: The heating surface of the water-cooled wall of the ultra-supercritical boiler is mainly composed of the lower spiral section water-cooled wall 1 and the upper vertical section water-cooled wall 2, wherein the spiral section water-cooled wall adopts an internally threaded tube; the lower spiral section water-cooled wall 1 and the upper vertical section water-cooled wall 2 are connected by a full mixing header 3.
[0005] Superheated system steam-water flow: The feedwater provided by the feedwater pump 11 is divided into two flows after heat exchange in the economizer 10. The main flow medium is introduced into the water-cooled wall and flows sequentially through the lower spiral section water-cooled wall 1, the full mixing header 3, the upper vertical section water-cooled wall 2, the water-cooled wall outlet mixing header 4, and the separator 5. The steam after steam-water separation passes sequentially through the roof, the wall 6, the low-temperature superheater 7, the rear screen superheater 8, and the high-temperature superheater 9 to absorb heat before entering the steam turbine to do work. The other part of the medium at the outlet of the economizer 10 is sprayed as desuperheating water into the inlet b path of the rear screen superheater 8 and the inlet a path of the high-temperature superheater 9. The flow rates of the desuperheating water in path a and path b are measured by the first desuperheating water flow measuring device 12 and the second desuperheating water flow measuring device 13, respectively.
[0006] In conventional boilers, the desuperheating water pipeline capacity of route A and route B is typically designed at 3% each. However, for boilers designed to reduce the flow area of the pipe sections in the high heat load area of the water-cooled wall to meet the mass flow velocity G of the spiral section water-cooled wall during dry operation at 15% load, the design capacity of the desuperheating water pipeline is increased. The design capacity of desuperheating water pipelines of route A and route B can be increased to more than 10% each. During high load operation, the flow rate of the medium entering the water-cooled wall is such that, while ensuring that the water-cooled wall resistance remains basically unchanged compared to conventional boilers, the excess medium is bypassed to the next high-temperature stage heating surface in the form of desuperheating water. The temperature rise of the low-temperature superheater 7 and the rear screen superheater 8 increases by approximately 15% or more.
[0007] The increased temperature rise of the rear superheater 8 can easily lead to excessive deviations in the working fluid temperature during boiler operation, resulting in excessive wall temperature. Summary of the Invention
[0008] In order to solve the above-mentioned problems in the existing technology, the purpose of the present invention is to provide a primary steam system that adapts to the switching of the working fluid in the water-cooled wall of the boiler to DC operation at ultra-low load, so as to ensure that the thermal power unit switches to DC operation at even lower load, ensure the safe operation of the water-cooled wall at this load, and at the same time not increase the resistance of the water-cooled wall at full load, and not affect the economic efficiency of the unit.
[0009] The technical solution adopted in this invention is as follows: A primary steam system adapted to the direct current operation of the working fluid inside the water-cooled wall of a boiler under ultra-low load includes a feedwater pipeline. The other end of the feedwater pipeline is connected to a boiler water-cooled wall pipeline and a desuperheating water pipeline. The other end of the boiler water-cooled wall pipeline is connected in sequence to a ceiling wall unit, a low-temperature superheater, a large screen superheater, a rear screen superheater, and a high-temperature superheater. The other end of the desuperheating water pipeline is divided into three branches and connected to the inlet of the large screen superheater, the inlet of the rear screen superheater, and the inlet of the high-temperature superheater, respectively.
[0010] In conventional boilers, the capacity of the two desuperheating water pipes is usually designed at 3% each. However, for boilers designed to reduce the flow area of the pipe sections in the high heat load area of the water-cooled wall to meet the requirements of 15% load dry operation (which must meet the mass flow rate G of the spiral section water-cooled wall), the design capacity of the desuperheating water pipes is increased. The design capacity of the two desuperheating water pipes can be increased to more than 10% each. When operating at high load, the flow rate of the medium entering the water-cooled wall is such that, while ensuring that the water-cooled wall resistance remains basically unchanged compared with conventional boilers, the excess medium is bypassed to the next high-temperature stage heating surface in the form of desuperheating water. The temperature rise of the low-temperature superheater and the rear screen superheater increases by about 15% or more.
[0011] Increased temperature rise in the rear superheater can easily lead to excessive working fluid temperature deviation and overheating of the boiler walls. This invention adds a large-screen superheater between the low-temperature superheater and the rear superheater, and simultaneously adds a desuperheating water pipeline between the low-temperature superheater and the large-screen superheater. This reduces the temperature rise of each stage of the heating surface, and the added desuperheating water further ensures the safety of the heating surface. The primary steam desuperheating water is taken from the economizer outlet and returns to the primary steam system. Although the capacity is increased from the conventional 4%–6% to over 10%, it does not affect the economic efficiency of the thermal system.
[0012] As a preferred embodiment of the present invention, a water supply pump and an economizer are connected to the water supply pipeline, with the economizer located on the outlet side of the water supply pump.
[0013] As a preferred embodiment of the present invention, the boiler water-cooled wall pipeline includes a spiral water-cooled wall located in the lower section of the boiler and a vertical water-cooled wall located in the upper section of the boiler, with an intermediate mixing manifold connecting the spiral water-cooled wall and the vertical water-cooled wall.
[0014] As a preferred embodiment of the present invention, the top of the vertical water-cooled wall is further connected to a water-cooled wall outlet mixing header.
[0015] As a preferred embodiment of the present invention, the outlet end of the water-cooled wall outlet mixing header is connected to a steam-water separator via a pipeline, and the gas phase outlet of the steam-water separator is connected to the inlet of the ceiling wall unit via a pipeline.
[0016] As a preferred embodiment of the present invention, the section of the desuperheating water pipeline connected to the inlet of the high-temperature superheater is the first desuperheating water pipeline, the section of the desuperheating water pipeline connected to the inlet of the rear screen superheater is the second desuperheating water pipeline, and the section of the desuperheating water pipeline connected to the inlet of the large screen superheater is the third desuperheating water pipeline.
[0017] In a preferred embodiment of the present invention, a first desuperheating water flow rate measuring device is connected to the first desuperheating water pipeline, a second desuperheating water flow rate measuring device is connected to the second desuperheating water pipeline, and a third desuperheating water flow rate measuring device is connected to the third desuperheating water pipeline. The flow rate of the first desuperheating water pipeline is measured by the first desuperheating water flow rate measuring device, the flow rate of the second desuperheating water pipeline is measured by the second desuperheating water flow rate measuring device, and the flow rate of the third desuperheating water pipeline is measured by the third desuperheating water flow rate measuring device.
[0018] As a preferred embodiment of the present invention, the design capacity of the first desuperheating water pipeline and the second desuperheating water pipeline is increased to more than 10%.
[0019] As a preferred embodiment of the present invention, the ceiling-wall unit includes a ceiling and a wall.
[0020] As a preferred embodiment of the present invention, the water supply pipeline is connected to the bottom of the boiler water-cooled wall pipeline.
[0021] The beneficial effects of this invention are as follows: This invention adds a large-screen superheater between the low-temperature superheater and the rear-screen superheater, and simultaneously adds a desuperheating water pipeline between the low-temperature superheater and the large-screen superheater to reduce the temperature rise of each stage of the heating surface. The additional desuperheating water further ensures the safety of the heating surface. The primary steam desuperheating water is taken from the economizer outlet and returns to the primary steam system. Although the capacity is increased from the conventional 4%–6% to over 10%, it does not affect the economic efficiency of the thermal system. Attached Figure Description
[0022] Figure 1 This is a schematic diagram of the structure of the present invention; Figure 2 This is a schematic diagram of a conventional primary steam system.
[0023] In the diagram: 1- Spiral water-cooled wall; 2- Vertical water-cooled wall; 3- Intermediate mixing header; 4- Water-cooled wall outlet mixing header; 5- Steam-water separator; 6- Roof wall unit; 7- Low-temperature superheater; 8- Rear screen superheater; 9- High-temperature superheater; 10- Economizer; 11- Feed water pump; 12- First desuperheating water flow measurement device; 13- Second desuperheating water flow measurement device; 14- Third desuperheating water flow measurement device; 15- Large screen superheater; 16- First desuperheating water pipeline; 17- Second desuperheating water pipeline; 18- Third desuperheating water pipeline. Detailed Implementation
[0024] 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.
[0025] 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. It should be noted that, unless otherwise specified, the embodiments and features described in the embodiments of the invention can be combined with each other.
[0026] In boiler design, there is a contradiction between the safe operation of the water-cooled wall in a dry-state, once-through configuration under ultra-low load and the increased steam-water resistance and decreased unit economy caused by the increased mass flow rate under high load. To address these issues, a new design method is proposed for the steam-water system of an ultra-supercritical boiler. First, the flow area of the tube section in the high-heat-load region of the lower water-cooled wall is reduced to ensure that the working fluid velocity within the water-cooled wall reaches the critical velocity for safe once-through operation under ultra-low load. Second, by increasing the design capacity of the superheating system's desuperheating water and making targeted adjustments to the heating surfaces, the desuperheating water spray volume is increased during high-load operation, reducing the flow rate of the medium flowing into the water-cooled wall and maintaining the steam-water resistance of the water-cooled wall essentially unchanged compared to conventional designs. This approach ensures both safe once-through operation of the boiler's water-cooled wall under ultra-low load and prevents an increase in steam-water resistance under high load, thus maintaining the unit's economic efficiency during high-load operation.
[0027] like Figure 1 As shown, the primary steam system adapted to the direct-flow operation of the working fluid inside the boiler's ultra-low load water-cooled wall in this embodiment includes a feedwater pipeline. The other end of the feedwater pipeline is connected to both the boiler water-cooled wall pipeline and the desuperheating water pipeline. The other end of the boiler water-cooled wall pipeline is sequentially connected to a ceiling-mounted wall unit 6, a low-temperature superheater 7, a large-screen superheater 15, a rear-screen superheater 8, and a high-temperature superheater 9. The other end of the desuperheating water pipeline is divided into three branches, connected to the inlet of the large-screen superheater 15, the inlet of the rear-screen superheater 8, and the inlet of the high-temperature superheater 9, respectively. The ceiling-mounted wall unit 6 includes a ceiling and a wall; the feedwater pipeline is connected to the bottom of the boiler water-cooled wall pipeline.
[0028] In conventional boilers, the capacity of the two desuperheating water pipes is usually designed at 3% each. However, for boilers that reduce the flow area of the pipe sections in the high heat load area of the water-cooled wall to meet the requirements of 15% load dry operation (which must meet the mass flow rate G of the spiral section water-cooled wall), the design capacity of the desuperheating water pipes is increased. The design capacity of the two desuperheating water pipes can be increased to more than 10% each. When operating at high load, the flow rate of the medium entering the water-cooled wall is such that, while ensuring that the water-cooled wall resistance remains basically unchanged compared with conventional boilers, the excess medium is bypassed to the next high-temperature stage heating surface in the form of desuperheating water. The temperature rise of the low-temperature superheater 7 and the rear screen superheater 8 increases by about 15% or more.
[0029] The increased temperature rise of the rear superheater 8 can easily lead to excessive working fluid temperature deviation and overheating of the boiler walls. This invention adds a large superheater 15 between the low-temperature superheater 7 and the rear superheater 8, and simultaneously adds a desuperheating water pipeline between the low-temperature superheater 7 and the large superheater 15 to reduce the temperature rise of each stage of the heating surface. The additional desuperheating water further ensures the safety of the heating surface. The primary steam desuperheating water is taken from the economizer 10 outlet and returns to the primary steam system. Although the capacity is increased from the conventional 4%–6% to over 10%, it does not affect the economic efficiency of the thermal system.
[0030] Specifically, the water supply pipeline is connected to a water supply pump 11 and an economizer 10, with the economizer 10 located at the outlet side of the water supply pump 11. The boiler water-cooled wall pipeline includes a spiral water-cooled wall 1 located in the lower section of the boiler and a vertical water-cooled wall 2 located in the upper section of the boiler, with an intermediate mixing header 3 connecting the spiral water-cooled wall 1 and the vertical water-cooled wall 2. A water-cooled wall outlet mixing header 4 is also connected to the top of the vertical water-cooled wall 2. The outlet end of the water-cooled wall outlet mixing header 4 is connected to a steam-water separator 5 via a pipeline, and the gas phase outlet of the steam-water separator 5 is connected to the inlet of the ceiling wall unit 6 via a pipeline.
[0031] Specifically, the section of the desuperheating water pipeline connected to the inlet of the high-temperature superheater 9 is the first desuperheating water pipeline 16, the section connected to the inlet of the rear screen superheater 8 is the second desuperheating water pipeline 17, and the section connected to the inlet of the large screen superheater 15 is the third desuperheating water pipeline 18. The design capacity of the first desuperheating water pipeline 16 and the second desuperheating water pipeline 17 is increased by more than 10%.
[0032] A first desuperheating water flow rate measuring device 12 is connected to the first desuperheating water pipeline 16, a second desuperheating water flow rate measuring device 13 is connected to the second desuperheating water pipeline 17, and a third desuperheating water flow rate measuring device 14 is connected to the third desuperheating water pipeline 18. The flow rate of the first desuperheating water pipeline 16 is measured by the first desuperheating water flow rate measuring device 12, the flow rate of the second desuperheating water pipeline 17 is measured by the second desuperheating water flow rate measuring device 13, and the flow rate of the third desuperheating water pipeline 18 is measured by the third desuperheating water flow rate measuring device 14.
[0033] This invention, while ensuring dry-state operation at 15% deep-load (meeting the mass flow rate G requirement of the spiral section water-cooled wall), aims to reduce the mass flow rate of the water-cooled wall at high loads and maintain a relatively constant steam-water resistance at full load. It increases the design capacity of the superheating system's desuperheating water, increases the desuperheating water spray volume during high-load operation, and reduces the flow rate of the medium flowing into the water-cooled wall. The steam-water resistance of the water-cooled wall remains essentially unchanged compared to conventional designs. This approach ensures both the economic efficiency of full-load unit operation and the safe operation of the boiler at 15% deep-load peak loads.
[0034] When the present invention operates under high load, the amount of desuperheating water sprayed increases, the temperature rise of the rear superheater 8 increases, and the wall temperature is prone to overheating. To address this, an additional heating surface can be added to reduce the enthalpy increase of each heating surface. At the same time, an additional desuperheating water can be added to further ensure the safety of the heating surface.
[0035] In this invention, the primary steam desuperheating water is taken from the economizer 10 outlet and returned to the primary steam system. Although the capacity is increased from the conventional 4-6% to more than 10%, it does not affect the economy of the thermal system.
[0036] This invention is not limited to the above-described optional embodiments. Anyone can derive other various forms of products under the guidance of this invention. However, regardless of any changes made in their shape or structure, any technical solution that falls within the scope of the claims of this invention shall be protected by this invention.
Claims
1. A primary steam system adapted to convert a water wall in a boiler from subcritical to supercritical operation at low loads, characterized in that: The feedwater pipeline is connected with a feedwater pump (11) and an economizer (10) on the pipeline, and the economizer (10) is located on the outlet side of the feedwater pump (11).
2. The primary steam system of claim 1, wherein the system is adapted to switch from the water wall to the once-through operation when the boiler is operating at a load below the predetermined load. The boiler water wall pipeline includes a spiral water wall (1) located at the lower section of the boiler and a vertical water wall (2) located at the upper section of the boiler, and the spiral water wall (1) and the vertical water wall (2) are connected with an intermediate mixing header (3).
3. The primary steam system of claim 1, wherein the primary steam system is adapted to switch from a once-through operation to a direct flow operation when the boiler is operating at an ultra-low load. The top of the vertical water wall (2) is further connected with a water wall outlet mixing header (4).
4. The once-through steam system adapted for the boiler to operate under ultra-low load with the working medium in the water wall being converted into a direct current according to claim 3, characterized in that: The outlet end of the water wall outlet mixing header (4) is connected with a steam-water separator (5) through a pipeline, and the gas phase outlet of the steam-water separator (5) is connected with the inlet of the ceiling wall covering unit (6) through a pipeline.
5. The once-through steam system adapted for the boiler to operate at ultra-low load with water-cooled walls and the working medium converted to direct current according to claim 4, characterized in that: The section of the desuperheating water pipeline connected with the inlet of the high-temperature superheater (9) is a first desuperheating water pipeline (16), the section of the desuperheating water pipeline connected with the inlet of the rear screen superheater (8) is a second desuperheating water pipeline (17), and the section of the desuperheating water pipeline connected with the inlet of the large screen superheater (15) is a third desuperheating water pipeline (18).
6. The primary steam system of claim 1, wherein the primary steam system is adapted to switch from a once-through operation to a direct flow operation when the boiler is operating at an ultra-low load. The first desuperheating water pipeline (16) is connected with a first desuperheating water flow measuring device (12), the second desuperheating water pipeline (17) is connected with a second desuperheating water flow measuring device (13), and the third desuperheating water pipeline (18) is connected with a third desuperheating water flow measuring device (14).
7. The once-through steam system adapted for the boiler to operate at ultra-low load with water-cooled walls and with the working medium converted to direct current according to claim 6, characterized in that: The design capacity of the first desuperheating water pipeline (16) and the second desuperheating water pipeline (17) is increased by more than 10%.
8. The once-through steam system adapted for the boiler ultra-low load water wall inner working medium to direct current operation according to claim 6, characterized in that: The ceiling wall covering unit (6) includes a ceiling and a wall covering.
9. The primary steam system of claim 1, wherein the primary steam system is adapted to switch from a once-through operation to a direct flow operation when the boiler is operating at an ultra-low load. The feedwater pipeline is connected to the bottom of the boiler water wall pipeline.
10. A once-through steam system adapted for the transition from water wall to direct flow operation of a boiler at ultra-low load according to any one of claims 1 to 9, characterized in that: