Boiler water wall adaptive to extreme peak shaving and control method thereof

Abstract

This invention relates to the field of boiler technology and discloses a boiler water-cooled wall adapted to extreme peak shaving and its control method. The boiler water-cooled wall includes a first branch and a second branch connected in parallel. The first branch includes a lower spiral section water-cooled wall and an upper vertical section water-cooled wall connected in series. The second branch includes a bypass heat exchanger. This invention solves the problems of increased feedwater pump selection costs, increased operating power consumption, and decreased unit economy caused by the significant increase in full-load water-cooled wall resistance in existing technologies.

Description

Technical Field

[0001] This invention relates to the field of boiler technology, specifically to a boiler water-cooled wall adapted to extreme peak shaving and its control method. Background Technology

[0002] A green and low-carbon new power system, primarily based on new energy sources, will become the main driver of electricity growth for a considerable period of time. Large-scale intermittent renewable energy sources, represented by wind and solar power, are accelerating the decarbonization of the energy structure. However, the grid connection of large-scale renewable energy generation requires sufficient flexibility resources in the power system to ensure the safe operation of the power grid.

[0003] As the "ballast" for ensuring energy supply, coal-fired power plants, with their excellent peak-shaving potential, are playing a crucial role in the power grid's basic regulation capacity in order to improve the absorption of renewable energy. With the vigorous promotion and development of new energy sources, the proportion of new energy connected to the grid will continue to increase in the future. The peak-shaving load of current coal-fired power plants may not be able to meet the requirements of future new power systems. To address the increased volatility and uncertainty brought about by the increased proportion of renewable energy generation, future coal-fired power plants will need to handle lower and more extreme peak-shaving loads.

[0004] Currently, the water-cooled walls of ultra-supercritical thermal power units that undertake deep peak shaving are basically all of the following structural types: lower spiral section water-cooled wall + middle transition section mixed + upper vertical section water-cooled wall; among them, ultra-supercritical refers to supercritical or ultra-supercritical.

[0005] In the spiral section of the water-cooled wall, where the heat load is higher, internally threaded tubes are used. Compared with bare tubes, the critical mass flow rate of the water-cooled wall is lower, which can further reduce the direct current load. At the same time, the internally threaded tubes increase heat exchange inside the tube, which can effectively reduce the wall temperature and provide a higher safety margin for the water-cooled wall.

[0006] According to research, the most advanced ultra-supercritical thermal power units can currently achieve a minimum load of approximately 20% to 25% for deep peak shaving. At this load, the boiler can operate in a dry state, with stable combustion and no overheating of the water-cooled walls without the need for auxiliary combustion. If the peak load is further reduced, the boiler will need to operate in a wet state, which will lead to increased coal consumption and prolonged wet operation will also affect the safety and stability of the unit.

[0007] When ultra-supercritical thermal power units are performing deep peak shaving, the boiler must maintain dry operation to ensure that the mass flow rate of the spiral section water-cooled wall is not lower than the minimum mass flow rate G0 (unit: kg / (sm)). 2If the water-cooled wall is designed based on the mass flow rate G0 of the spiral section water-cooled wall during dry operation of the boiler at a 10% peak load, the mass flow rate of the spiral section water-cooled wall will increase to about 10 times G0 at full load (about twice that of conventional projects). This will lead to a significant increase in the water-cooled wall resistance at full load (for example, in a 1000MW project, it will increase by about 2.7MPa compared to conventional projects), resulting in increased feedwater pump selection costs and operating power consumption, and a decrease in the unit's economic efficiency.

[0008] When the boiler is designed to operate at 10% of its maximum peak load in dry state (which must meet the minimum mass flow rate G0 requirement of the spiral section water-cooled wall), the resistance of the water-cooled wall at full load will increase significantly, leading to increased cost of feedwater pump selection and operating power consumption, and reduced unit economy. Summary of the Invention

[0009] To overcome the shortcomings of existing technologies, this invention provides a boiler water-cooled wall adapted to extreme peak shaving and its control method, which solves the problems of increased feedwater pump selection costs, increased operating power consumption, and decreased unit economy caused by the significant increase in the resistance of the water-cooled wall at full load in existing technologies.

[0010] The technical solution adopted by the present invention to solve the above problems is:

[0011] A boiler water-cooled wall adapted to extreme peak shaving includes a first branch and a second branch connected in parallel. The first branch includes a lower spiral section water-cooled wall and an upper vertical section water-cooled wall connected in series. The second branch includes a bypass heat exchanger.

[0012] As a preferred technical solution, it also includes an intermediate full mixing header located between the lower spiral section water-cooled wall and the upper vertical section water-cooled wall, and the intermediate full mixing header is connected to the lower spiral section water-cooled wall and the upper vertical section water-cooled wall respectively.

[0013] As a preferred technical solution, the system also includes an economizer outlet header, a centralized downcomer, a front wall water-cooled wall inlet header, a spiral section water-cooled wall outlet header, a vertical section water-cooled wall inlet header, a vertical section water-cooled wall outlet header, a water-cooled wall outlet mixing header, a rear wall water-cooled wall inlet header, a bypass heat exchanger inlet header, a bypass heat exchanger outlet header, and a steam-water separator. The economizer outlet header, centralized downcomer, front wall water-cooled wall inlet header, lower spiral section water-cooled wall, spiral section water-cooled wall outlet header, intermediate full mixing header, vertical section water-cooled wall inlet header, upper vertical section water-cooled wall, vertical section water-cooled wall outlet header, and water-cooled wall outlet mixing header are connected in sequence. The centralized downcomer, rear wall water-cooled wall inlet header, and lower spiral section water-cooled wall are also connected in sequence. Finally, the centralized downcomer, bypass heat exchanger inlet header, bypass heat exchanger, bypass heat exchanger outlet header, water-cooled wall outlet mixing header, and steam-water separator are connected in sequence.

[0014] As a preferred technical solution, the spiral section water-cooled wall outlet header, the vertical section water-cooled wall inlet header, and the vertical section water-cooled wall outlet header are all arranged on the front, back, left, and right walls, while the middle full-mixing header is arranged on the left and right side walls.

[0015] As a preferred technical solution, temperature measuring points and pressure measuring points are installed on the pipeline from the outlet header of the bypass heat exchanger to the mixing header of the water-cooled wall outlet.

[0016] As a preferred technical solution, the pipeline from the central downcomer to the inlet header of the bypass heat exchanger includes a main branch and a bypass. The main branch is equipped with a main regulating valve, a main gate valve, a check valve, and a flow measuring device, while the bypass is equipped with a bypass regulating valve and a bypass gate valve.

[0017] As a preferred technical solution, it also includes a primary superheater, with a bypass heat exchanger located at the furnace outlet, in front of the primary superheater along the flue gas flow direction.

[0018] The aforementioned control method for boiler water-cooled walls adapted to extreme peak loads involves closing the main gate valve and opening the bypass gate valve when the boiler is operating near the extreme peak load value. The minimum flow rate of the bypass heat exchanger is ensured by adjusting the bypass regulating valve. The determination condition for the extreme peak load value is set in advance.

[0019] As a preferred technical solution, when the boiler is operating above the extreme peak load, the bypass gate valve is closed and the main gate valve is opened. The main regulating valve is adjusted to ensure the safe operation of the water-cooled wall and prevent the water-cooled wall resistance from exceeding the set threshold.

[0020] As a preferred technical solution, when the superheat at the bypass heat exchanger outlet is ≤A℃, the flow rate of the water-cooled wall bypass is reduced by adjusting the bypass regulating valve; when the superheat at the bypass heat exchanger outlet is >A℃ and the bypass heat exchanger wall temperature is close to the alarm value, the flow rate of the water-cooled wall bypass is increased by adjusting the bypass regulating valve; above the extreme peak load, when the flow rate of the water-cooled wall bypass gradually increases to close to B%, if the wall temperature of the upper vertical section water-cooled wall is close to the alarm value, the flow rate of the water-cooled wall bypass is reduced by adjusting the main regulating valve; wherein, the values ​​of A and B are preset, and the judgment conditions for the water-cooled wall bypass flow rate approaching B%, the bypass heat exchanger wall temperature approaching the alarm value, and the upper vertical section water-cooled wall temperature approaching the alarm value are preset.

[0021] Compared with the prior art, the present invention has the following advantages:

[0022] This invention employs a bypass heat exchanger design on the water-cooled wall of a high-efficiency ultra-supercritical counter-firing tower boiler. This design can not only meet the safe operation of the boiler at approximately 10% extreme peak load, but also reduce the impact of increased resistance on the unit's economy at full load. Simultaneously, it takes into account both the safety of the boiler's hydrodynamics under extreme peak load and the economic efficiency of the unit's operation at full load. Attached Figure Description

[0023] Figure 1 This is a schematic diagram of the structure of a boiler water-cooled wall adapted to extreme peak shaving according to the present invention;

[0024] Figure 2 Figure 1 One of the magnified views of a section;

[0025] Figure 3 Figure 1 The second enlarged view of a section;

[0026] Figure 4 The working fluid flow diagram of a boiler water-cooled wall adapted to extreme peak shaving, as described in this invention;

[0027] Figure 5 for Figure 4 One of the magnified views of a section;

[0028] Figure 6 for Figure 4 The second enlarged view of a section;

[0029] Figure 7 for Figure 4 The third enlarged view of a section;

[0030] Figure 8 for Figure 4 Part 4 of the enlarged view;

[0031] Figure 9 for Figure 4 Fifth enlarged view of a section;

[0032] Figure 10 This is one of the schematic diagrams for bypass flow control of water-cooled walls;

[0033] Figure 11 This is the second schematic diagram of water-cooled wall bypass flow control.

[0034] The labels and their corresponding names in the attached diagram are as follows: 1-Lower spiral section water-cooled wall, 2-Upper vertical section water-cooled wall, 3-Bypass heat exchanger, 4-Intermediate full mixing header, 5-External furnace suspension tube, 6-First stage superheater, 7-Economizer outlet header, 8-Centralized downcomer, 9-Front wall water-cooled wall inlet header, 10-Rear wall water-cooled wall inlet header, 11-Bypass heat exchanger inlet header, 12-Spiral section water-cooled wall outlet header, 13-Vertical section water-cooled wall inlet header, 14-Vertical section water-cooled wall outlet header, 15-Water-cooled wall outlet mixing header, 16-Bypass heat exchanger outlet header, 17-Steam-water separator, 18-Main line gate valve, 19-Main line regulating valve, 20-Bypass gate valve, 21-Bypass regulating valve, 22-Check valve, 23-Flow measurement device, 24-Temperature measuring point, 25-Pressure measuring point. Detailed Implementation

[0035] The present invention will be further described in detail below with reference to the embodiments and accompanying drawings, but the embodiments of the present invention are not limited thereto.

[0036] Example 1

[0037] like Figures 1 to 11 As shown, in order to adapt to the more extreme peak load of about 10% for future thermal power units, the water-cooled wall of the high-efficiency ultra-supercritical counter-current combustion tower boiler of this invention adopts a design with a bypass heat exchanger to ensure that the boiler water-cooled wall can adapt to the extreme peak load of about 10%, and can also reduce the impact of increased resistance on the economic efficiency of the unit when at full load.

[0038] To address the above issues, this invention employs a bypass heat exchanger design on the water-cooled wall of a high-efficiency ultra-supercritical counter-current combustion tower boiler. This design not only ensures safe operation of the boiler at approximately 10% of its maximum peak load but also reduces the impact of increased resistance on the unit's economic efficiency at full load.

[0039] The boiler is arranged in a tower configuration and uses a front and rear wall opposed combustion method. The water-cooled wall heating surface mainly consists of a lower spiral section water-cooled wall 1, an upper vertical section water-cooled wall 2, and a bypass heat exchanger 3. The spiral section water-cooled wall uses internally threaded tubes. The lower spiral section water-cooled wall 1 and the upper vertical section water-cooled wall 2 are connected by an intermediate full mixing header 4.

[0040] The spiral section water-cooled wall outlet header 12, the vertical section water-cooled wall inlet header 13, and the vertical section water-cooled wall outlet header 14 all include four headers: front wall, rear wall, left side wall, and right side wall.

[0041] The front and rear wall headers of the vertical water-cooled wall inlet header 13 lead out the furnace external suspension pipe 5, which is used to suspend the furnace external headers of each level of the heating surface of the front and rear walls. The working fluid in the furnace external suspension pipe 5 is introduced into the front and rear wall headers of the vertical water-cooled wall outlet header 14 from bottom to top.

[0042] The bypass heat exchanger 3 is located at the furnace outlet, before the primary superheater 6. The bypass heat exchanger 3 adopts a serpentine tube screen with parallel and co-current arrangement, which can further smooth and homogenize the flue gas at the furnace outlet before it enters the primary superheater 6, ensuring uniform heat exchange on the subsequent heating surfaces and reducing deviations.

[0043] The working fluid of the water-cooled wall exits from the economizer outlet header 7, passes through the centralized downcomer 8, and part of it enters the front wall water-cooled wall inlet header 9 and the rear wall water-cooled wall inlet header 10 at the bottom of the furnace. It then flows sequentially through the lower spiral section water-cooled wall 1, the spiral section water-cooled wall outlet header 12, the intermediate full mixing header 4, the vertical section water-cooled wall inlet header 13, the upper vertical section water-cooled wall 2, and the vertical section water-cooled wall outlet header 14, finally converging into the water-cooled wall outlet mixing header 15. The other part enters the bypass heat exchanger inlet header 11, the bypass heat exchanger 3, and the bypass heat exchanger outlet header 16, finally converging into the water-cooled wall outlet mixing header 15. The water-cooled wall outlet mixing header 15 enters the steam-water separator 17 through a connecting pipe. The spiral section water-cooled wall outlet header 12, the vertical section water-cooled wall inlet header 13, and the vertical section water-cooled wall outlet header 14 are arranged on the front, back, left, and right walls, while the intermediate full mixing header 4 is arranged on the left and right side walls.

[0044] The pipeline from the central downcomer 8 to the inlet header 11 of the bypass heat exchanger is sequentially equipped with a main regulating valve 19, a main gate valve 18, a bypass regulating valve 21, a bypass gate valve 20, a check valve 22, and a flow measuring device 23. The pipeline from the outlet header 16 of the bypass heat exchanger to the mixing header 15 of the water-cooled wall outlet is equipped with a temperature measuring point 24 and a pressure measuring point 25 to monitor the superheat at the outlet of the bypass heat exchanger (the working fluid temperature minus the saturation temperature corresponding to the working fluid pressure) through temperature and pressure.

[0045] When the boiler is operating at or around the extreme peak load, close the main gate valve 18, open the bypass gate valve 20, and adjust the bypass regulating valve 21 to ensure the minimum flow of the bypass heat exchanger (to prevent the bypass heat exchanger from dry burning and overheating).

[0046] When the boiler is operating above the extreme peak load, close the bypass gate valve 20 and open the main gate valve 18. Adjust the main regulating valve 19 to ensure the safe operation of the water-cooled wall and avoid excessive water-cooled wall resistance.

[0047] The flow rate of the water-cooled wall bypass is adjusted by monitoring the superheat at the outlet of the bypass heat exchanger. When the superheat at the outlet of the bypass heat exchanger (superheat refers to the saturation temperature corresponding to the steam pressure minus the steam temperature) is ≤10℃, the flow rate of the water-cooled wall bypass is appropriately reduced. When the superheat at the outlet of the bypass heat exchanger is >10℃ and the wall temperature of the bypass heat exchanger is close to the alarm value, the flow rate of the water-cooled wall bypass needs to be increased. When the peak load is above the threshold, when the flow rate of the water-cooled wall bypass is close to 25%, special attention needs to be paid to the wall temperature of the water-cooled wall. If the wall temperature of the upper vertical section water-cooled wall 2 is close to the alarm value, the flow rate of the water-cooled wall bypass is reduced by adjusting the main regulating valve 19.

[0048] This invention employs a bypass heat exchanger design on the water-cooled wall of a high-efficiency ultra-supercritical counter-firing tower boiler. This design can not only meet the safe operation of the boiler at approximately 10% extreme peak load, but also reduce the impact of increased resistance on the unit's economy at full load. Simultaneously, it takes into account both the safety of the boiler's hydrodynamics under extreme peak load and the economic efficiency of the unit's operation at full load.

[0049] Example 2

[0050] like Figures 1 to 11 As shown, as a further optimization of Embodiment 1, this embodiment also includes the following technical features based on Embodiment 1:

[0051] 1. Under the condition that the boiler operates in a dry state at 10% extreme peak load, the mass flow rate of the spiral section water-cooled wall shall not be lower than the minimum mass flow rate G0 (unit: kg / (sm)). 2 The specifications, inclination angle, and pitch of the spiral water-cooled wall tubes are designed according to the requirements of the design.

[0052] 2. Compared to conventional water-cooled walls designed for a minimum mass flow velocity of G0 in the spiral section under 20%–25% peak load, the resistance of the water-cooled wall increases significantly at full load (approximately 2.7 MPa higher for a 1000MW project compared to conventional projects). This leads to increased feedwater pump selection costs and operating power consumption, resulting in decreased unit economics. Therefore, a portion of the water-cooled wall is bypassed (from the centralized downcomer through a bypass heat exchanger to the water-cooled wall outlet mixing header) to reduce the water-cooled wall resistance at full load and minimize the impact on unit economics during full load operation.

[0053] 3. Selection of water-cooled wall bypass flow rate: If the water-cooled wall bypass flow rate is too large, the water-cooled wall outlet temperature will be too high and the tube wall will overheat; if the water-cooled wall bypass flow rate is too small, the water-cooled wall resistance will not be reduced significantly, the unit's economy will be greatly affected, and the bypass heat exchanger outlet will also be prone to overheating.

[0054] Taking a 660MW ultra-supercritical project as an example, a preliminary analysis suggests that a bypass flow rate of 25% is reasonable. (See Table 1.)

[0055] Table 1. Variation of water-cooled wall outlet temperature and resistance under different bypass rates.

[0056]

[0057] When the water-cooled wall bypass flow rate is 25%, the water-cooled wall outlet temperature is still within the applicable range of conventional material 12Cr1MoVG. The strength requirements can be met by increasing the tube wall thickness, which also greatly reduces the water-cooled wall resistance and minimizes the impact on the unit's economy. If the water-cooled wall bypass flow rate is further increased to reduce resistance and improve the unit's economy, the water-cooled wall tube material needs to be upgraded.

[0058] In this invention, when the boiler is at 10% of its ultimate peak load, the minimum mass flow rate G0 (unit: kg / (sm)) of the spiral section water-cooled wall is required for dry operation. 2 The design and selection should be based on the following: at full load, the bypass flow rate of the water-cooled wall is adjusted to ensure that the water-cooled wall resistance does not exceed the limit, thus guaranteeing the economic operation of the unit. Based on currently available mature water-cooled wall materials, the bypass flow rate of the water-cooled wall can be selected at 25%.

[0059] In this invention, the bypass flow rate of the water-cooled wall is adjusted by monitoring the superheat at the outlet of the bypass heat exchanger.

[0060] As described above, the present invention can be implemented well.

[0061] All features disclosed in all embodiments of this specification, or steps in all methods or processes implied in the disclosure, may be combined and / or extended or replaced in any way, except for mutually exclusive features and / or steps.

[0062] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Based on the technical essence of the present invention, any simple modifications, equivalent substitutions, and improvements made to the above embodiments within the spirit and principles of the present invention shall still fall within the protection scope of the present invention.

Claims

1. A control method for a boiler water-cooled wall adapted to extreme peak shaving, characterized by: The boiler water-cooled wall includes: The first branch and the second branch are connected in parallel. The first branch includes the lower spiral section water-cooled wall (1) and the upper vertical section water-cooled wall (2) connected in series. The second branch includes the bypass heat exchanger (3). It also includes a central downcomer (8) and a bypass heat exchanger inlet header (11). The pipeline from the central downcomer (8) to the bypass heat exchanger inlet header (11) includes a main branch and a bypass. The main branch is equipped with a main regulating valve (19), a main gate valve (18), a check valve (22), and a flow measuring device (23). The bypass is equipped with a bypass regulating valve (21) and a bypass gate valve (20). The control method includes: When the superheat at the outlet of the bypass heat exchanger (3) is ≤ A℃, the flow rate of the water-cooled wall bypass is reduced by adjusting the bypass regulating valve (21); when the superheat at the outlet of the bypass heat exchanger (3) is > A℃ and the wall temperature of the bypass heat exchanger (3) is close to the alarm value, the flow rate of the water-cooled wall bypass is increased by adjusting the bypass regulating valve (21); above the extreme peak load, when the flow rate of the water-cooled wall bypass gradually increases to close to B%, if the wall temperature of the upper vertical section water-cooled wall (2) is close to the alarm value, the flow rate of the water-cooled wall bypass is reduced by adjusting the main regulating valve (19); where A and B values ​​are set in advance, and the judgment conditions of the flow rate of the water-cooled wall bypass being close to B%, the wall temperature of the bypass heat exchanger (3) being close to the alarm value, and the wall temperature of the upper vertical section water-cooled wall (2) being close to the alarm value are set in advance.

2. The control method of a boiler water wall adapted for extreme peak shaving according to claim 1, characterized by, It also includes an intermediate full mixing header (4) located between the lower spiral section water-cooled wall (1) and the upper vertical section water-cooled wall (2), and the intermediate full mixing header (4) is connected to the lower spiral section water-cooled wall (1) and the upper vertical section water-cooled wall (2) respectively.

3. The control method of a boiler water wall adapted for extreme peak shaving according to claim 2, characterized by, It also includes the economizer outlet header (7), the front wall water-cooled wall inlet header (9), the spiral section water-cooled wall outlet header (12), the vertical section water-cooled wall inlet header (13), the vertical section water-cooled wall outlet header (14), the water-cooled wall outlet mixing header (15), the rear wall water-cooled wall inlet header (10), the bypass heat exchanger outlet header (16), and the steam-water separator (17); the economizer outlet header (7), the centralized downcomer (8), the front wall water-cooled wall inlet header (9), the lower spiral section water-cooled wall (1), and the spiral section water-cooled wall outlet header (12). The intermediate full mixing header (4), the vertical section water-cooled wall inlet header (13), the upper vertical section water-cooled wall (2), the vertical section water-cooled wall outlet header (14), and the water-cooled wall outlet mixing header (15) are connected in sequence. The centralized downcomer (8), the rear wall water-cooled wall inlet header (10), and the lower spiral section water-cooled wall (1) are connected in sequence. The centralized downcomer (8), the bypass heat exchanger inlet header (11), the bypass heat exchanger (3), the bypass heat exchanger outlet header (16), the water-cooled wall outlet mixing header (15), and the steam-water separator (17) are connected in sequence.

4. The control method of a boiler water wall adapted for limit peaking according to claim 3, characterized by, The spiral section water-cooled wall outlet header (12), the vertical section water-cooled wall inlet header (13), and the vertical section water-cooled wall outlet header (14) are all arranged on the front, back, left, and right sides of the four walls, while the middle full-mix header (4) is arranged on the left and right sides of the two walls.

5. The control method of a boiler water wall adapted for extreme peak shaving according to claim 3, wherein, Temperature measuring point (24) and pressure measuring point (25) are installed on the pipeline from the outlet header (16) of the bypass heat exchanger to the mixing header (15) of the water-cooled wall outlet.

6. The control method of a boiler water wall adapted for extreme limit peaking according to any one of claims 1 to 5, characterized in that, It also includes a primary superheater (6), and a bypass heat exchanger (3) is located at the furnace outlet, in front of the primary superheater (6) along the flue gas flow direction.

7. The control method of a boiler water wall adapted for extreme peak shaving according to claim 6, characterized by, When the boiler is operating near the extreme peak load value, the main gate valve (18) is closed and the bypass gate valve (20) is opened. The minimum flow rate of the bypass heat exchanger is ensured by adjusting the bypass regulating valve (21). The judgment condition for the extreme peak load value is set in advance.

8. The control method of a boiler water wall adapted for extreme peak shaving according to claim 6, wherein, When the boiler is operating above the extreme peak load, close the bypass gate valve (20) and open the main gate valve (18). Adjust the main regulating valve (19) to ensure the safe operation of the water-cooled wall and prevent the water-cooled wall resistance from exceeding the set threshold.

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