A method for arranging a heating surface of a boiler with variable transverse pitch

Abstract

The application discloses a variable transverse pitch boiler heating surface arrangement method and relates to the technical field of boiler heating surface arrangement. The low-temperature reheater and / or low-temperature superheater are arranged in the range with the flue gas temperature of 850 DEG C to 450 DEG C. In the same level heating surface, according to the flue gas temperature distribution of the position of the heating surface, the variable transverse pitch is adopted along the flue gas flow direction. In the high flue gas temperature section with the flue gas temperature higher than the preset temperature threshold value, the transverse pitch between the two adjacent heating surfaces is the first transverse pitch. In the low flue gas temperature section with the flue gas temperature lower than or equal to the preset temperature threshold value, the transverse pitch between the two adjacent heating surfaces is the second transverse pitch. The first transverse pitch is greater than the second transverse pitch, and the first transverse pitch meets the anti-contamination bridging requirement. The application effectively prevents the contamination bridging phenomenon by adopting the variable transverse pitch design in the same level heating surface, and meanwhile, the heat exchange efficiency and the space utilization rate are ensured.

Description

Technical Field

[0001] This invention relates to the field of boiler heating surface arrangement technology, specifically to a method for arranging boiler heating surfaces with variable transverse pitch, which is particularly suitable for boiler heating surface design that burns fuels with a strong tendency to fouling and slagging, such as high-alkali coal. Background Technology

[0002] my country is the world's largest producer and consumer of coal, with abundant and diverse coal resources. Among them, the Zhundong Coalfield boasts proven reserves of 213.6 billion tons and predicted reserves of 390 billion tons, making it my country's largest and most extensive open-pit coalfield. Its vast reserves and low mining costs make its large-scale, efficient, and clean utilization of coal extremely valuable and strategically significant. However, Zhundong coal is characterized by its high sodium and potassium content. Sodium oxide content is typically greater than 2.0%, and potassium oxide content is typically greater than 1.0%, with some coal types even exceeding 3.0% sodium oxide. During combustion, alkali metal compounds (mainly NaCl and KCl) in the coal volatilize into the flue gas phase at high temperatures (usually above 800℃). As the flue gas temperature decreases, these gaseous alkali metal compounds condense on the surfaces of convective heating surfaces (such as high-temperature superheaters, high-temperature reheaters, low-temperature reheaters, and low-temperature superheaters), forming a highly adhesive initial fouling layer.

[0003] The formation mechanism of fouling is quite complex, mainly including the following stages: First, gaseous alkali metal compounds condense on the surface of the heated tube walls, forming an extremely thin initial deposit layer with strong adhesion. Second, fly ash particles in the flue gas adhere to the initial deposit layer, forming a thicker deposit layer. Third, the deposit layer sinters under the action of high-temperature flue gas, forming a dense and hard slag. Fourth, deposits on adjacent tube banks continue to grow and adhere to each other, eventually forming a bridging phenomenon that blocks the flue gas passage. Studies have shown that when the flue gas temperature is above 700-750℃, the condensation and deposition rate of alkali metal compounds accelerates significantly, and the tendency for fouling and slag formation is most severe. When the thickness of the fouling and slag reaches a certain level, it will seriously affect the normal heat transfer capacity of the convective heated surfaces, leading to a decrease in boiler thermal efficiency and an increase in flue gas temperature. More seriously, dirt and slag on adjacent pipe banks can easily stick together at high temperatures, forming a bridging phenomenon. This can lead to blockage of flue gas passages, increased ventilation resistance, and in severe cases, even force the boiler to shut down for slag removal, seriously affecting the safe and stable operation of the boiler and the availability of the unit.

[0004] When burning coals with a strong tendency to fouling and slagging, such as Xinjiang high-alkali coal, to prevent bridging of the heating surfaces due to fouling and slagging, a transverse pitch of at least 200 mm is typically required within the flue gas temperature range of 700-750℃ (the specific temperature threshold needs to be determined based on the coal's fouling and slagging characteristics). A larger transverse pitch increases the spacing between adjacent tube banks, providing sufficient space for the growth of fouling and slagging materials and preventing deposits on adjacent tube banks from adhering to each other and forming bridging. However, in conventional boiler designs, low-temperature reheaters or low-temperature superheaters, or two types of low-temperature heating surfaces sharing a heat exchange area, are usually arranged within the flue gas temperature range of 800℃ to 450℃. To improve heat exchange efficiency and save space, these low-temperature heating surfaces are often arranged in a close-packed configuration with a transverse pitch of only 100mm to 150mm. Close-packed arrangements increase the heating area per unit space, improve heat exchange efficiency, reduce the overall boiler size, and lower equipment investment costs.

[0005] For the portion of the heating surface where the flue gas temperature is above 700℃, the existing close-packed structure cannot meet the requirements for preventing fouling and slagging, posing a serious risk of bridging. Increasing the transverse pitch of the entire heating surface to over 200mm can prevent fouling and bridging, but it will significantly increase the boiler size, reduce heat exchange efficiency, and increase equipment and operating costs. Existing technologies typically employ the following solutions: First, the heating surface is arranged in stages, using a large pitch in high flue gas temperature areas and a small pitch in low flue gas temperature areas, but this increases system complexity, piping layout difficulty, and cost; second, a large overall pitch arrangement is used, but this significantly increases boiler size and cost; third, a conventional close-packed arrangement is used, but this limits boiler load or requires frequent soot blowing during operation, affecting boiler operating efficiency and availability; fourth, additives (such as fly ash recirculation, limestone injection, etc.) are used to alleviate fouling problems, but this requires additional systems and equipment, increasing operating costs and maintenance workload, with limited effectiveness.

[0006] Therefore, there is a prominent contradiction between the anti-fouling and slagging performance and the heat exchange economy in the existing technology. There is an urgent need for a heat transfer surface arrangement method that can take into account both the anti-fouling and slagging performance and the heat exchange economy without significantly increasing the overall size of the boiler or the number of heat transfer surface stages. Summary of the Invention

[0007] To address the shortcomings of the existing technologies, this invention provides a variable transverse pitch arrangement scheme for the same-stage heating surface, which aims to meet the anti-fouling and slagging requirements when burning specific coal types, while taking into account heat exchange efficiency and space utilization. It achieves a good balance between anti-fouling and slagging performance and heat exchange economy without significantly increasing the overall size of the boiler.

[0008] To address the aforementioned technical problems, this invention provides a method for arranging boiler heating surfaces with variable transverse pitch. The boiler heating surfaces include one or both of a low-temperature reheater and a low-temperature superheater, wherein the low-temperature reheater and / or the low-temperature superheater are arranged within a flue gas temperature range of 850°C to 450°C. Within the same stage of heating surfaces, a variable transverse pitch is adopted along the flue gas flow direction based on the flue gas temperature distribution at the location of the heating surfaces: in high flue gas temperature sections where the flue gas temperature is higher than a preset temperature threshold, the transverse pitch between two adjacent heating surfaces is the first transverse pitch; in low flue gas temperature sections where the flue gas temperature is lower than or equal to the preset temperature threshold, the transverse pitch between two adjacent heating surfaces is the second transverse pitch; the first transverse pitch is greater than the second transverse pitch, and the first transverse pitch meets the requirements for preventing fouling and bridging.

[0009] The transverse pitch should be rationally allocated based on the flue gas temperature distribution at different locations on the heating surface. In high flue gas temperature zones (typically above 700-750℃), alkali metal compounds are prone to volatilization and condensation on the heating surface, leading to severe fouling and slagging. Using a larger first transverse pitch (typically greater than 200mm) can effectively increase the spacing between adjacent tube banks, providing sufficient space for the growth of fouling and slagging, and preventing deposits on adjacent tube banks from bridging each other. In low flue gas temperature zones (typically below 700-750℃), the tendency for fouling and slagging is significantly reduced. Using a smaller second transverse pitch (typically 100-150mm) can ensure sufficient heat exchange area, improve heat exchange efficiency, and avoid a significant increase in boiler size.

[0010] Preferably, the preset temperature threshold ranges from 700℃ to 750℃, with the specific value determined based on the coal's fouling and slagging characteristics. For coal types with a particularly severe tendency to foul and slag (such as Zhundong coal with a sodium oxide content greater than 3.0%), a higher preset temperature threshold (e.g., 750℃) can be used; for coal types with a relatively mild tendency to foul and slag, a lower preset temperature threshold (e.g., 700℃) can be used. Determining the preset temperature threshold requires comprehensive consideration of various factors, including coal characteristics, boiler operating parameters, and the location of the heating surfaces.

[0011] Preferably, the first lateral pitch ranges from 200mm to 300mm, and the second lateral pitch ranges from 100mm to 150mm. The specific value of the first lateral pitch needs to be determined based on factors such as the coal's fouling and slagging characteristics, the space required for the heating surface arrangement, and boiler size limitations. For coal types with a particularly severe tendency to foul and slag, a larger value (e.g., 250-300mm) can be used; for coal types with a relatively mild tendency to foul and slag, a smaller value (e.g., 200-250mm) can be used. The specific value of the second lateral pitch needs to be determined based on factors such as heat exchange requirements, space limitations, and tube specifications.

[0012] Preferably, the second lateral pitch is 40% to 60% of the first lateral pitch. More preferably, the second lateral pitch is 50% of the first lateral pitch. Using a 50% ratio ensures that the number of heat exchange surface plates in the low-temperature flue gas section is twice that in the high-temperature flue gas section, guaranteeing both the heat exchange area and facilitating the arrangement and connection of the heat exchange surface tubes. For example, when the first lateral pitch is 250mm, the second lateral pitch is 125mm; when the first lateral pitch is 200mm, the second lateral pitch is 100mm.

[0013] Preferably, a transition section is provided between the high-temperature flue gas section and the low-temperature flue gas section. This transition section facilitates a smooth transition of the transverse pitch from the first transverse pitch to the second transverse pitch. The transition section avoids the flow resistance and uneven heat transfer problems caused by abrupt changes in transverse pitch, ensuring stable flue gas flow and uniform heat transfer. The transition section's function is not only to achieve a smooth pitch transition but, more importantly, to ensure the stability of flue gas flow and the uniformity of heat transfer. If the high-temperature and low-temperature flue gas sections are directly connected, abrupt pitch changes can lead to uneven flue gas velocity distribution, generating eddies and dead zones at the abrupt pitch change points, exacerbating local fouling and wear. The transition section, through the bending structure of the heated surface tubes, allows the pitch to change gradually, avoiding these problems. The length of the transition section is typically 10% to 20% of the total length of the heated surface; the specific length needs to be determined based on factors such as the pitch change range, the space available for the heated surface arrangement, and the tube bending radius. If the transition section is too short, the pitch change will be too drastic, and the transition effect will not be fully utilized; if the transition section is too long, the difficulty and cost of arranging the heated surface will increase. The length of the transition section needs to be determined reasonably while ensuring the transition effect.

[0014] Preferably, in the transition section, the heating surface tubes achieve a gradual change in lateral pitch through a bending structure. The bending radius of the bending structure is determined based on the pitch change range and the length of the transition section. The bending structure can employ uniform bending or segmented bending to ensure a smooth change in tube spacing. The bending radius of the bending structure is typically 1.5 to 3 times the outer diameter of the tube, with the specific value determined based on factors such as tube specifications, pitch change range, and manufacturing process.

[0015] Preferably, the boiler is a π-type layout boiler, including a screen-type superheater, a high-temperature superheater, a high-temperature reheater, a low-temperature reheater, a low-temperature superheater, and an economizer. The low-temperature reheater and the low-temperature superheater are respectively arranged in two parallel flues. The π-type layout boiler is a typical arrangement for large power plant boilers, with advantages such as compact structure, flexible layout, and easy maintenance. In the π-type layout boiler, flue gas enters the tail shaft from the furnace outlet through a horizontal flue. In the tail shaft, it is divided into two parallel flues by a partition wall, where the low-temperature reheater and the low-temperature superheater are arranged respectively. The reheat steam temperature is regulated by flue gas dampers.

[0016] Preferably, the boiler is a tower-type boiler, where flue gas flows sequentially from bottom to top through each stage of heating surfaces, and the low-temperature superheater is arranged after the high-temperature superheater and the high-temperature reheater. Tower-type boilers are another common arrangement for large power plant boilers, offering advantages such as stable flue gas flow, uniform heating surface distribution, and ease of soot blowing. In tower-type boilers, all heating surfaces are suspended in the upper part of the furnace, and the flue gas flows from bottom to top, avoiding ash accumulation and wear on the heating surfaces.

[0017] Preferably, the boiler uses high-alkali coal as fuel, which contains more than 2.0% sodium oxide and more than 1.0% potassium oxide. During combustion, this high-alkali coal easily forms fouling and slagging deposits on the heating surface. A typical example of high-alkali coal is Xinjiang Zhundong coal, which has a high alkali metal content and a severe tendency to fouling and slagging. The variable transverse pitch arrangement method of this invention is particularly suitable for boilers burning this type of coal and can effectively solve the problem of fouling and bridging.

[0018] Preferably, the high-temperature flue gas section is located on the inlet side of the heating surface, and the low-temperature flue gas section is located on the outlet side of the heating surface. The flue gas flows sequentially through the high-temperature flue gas section, the transition section, and the low-temperature flue gas section along the flow direction of the heating surface tubes. This arrangement conforms to the natural law of gradually decreasing flue gas temperature. A large pitch is used in the high-temperature flue gas section to prevent fouling and bridging, while a small pitch is used in the low-temperature flue gas section to ensure heat exchange efficiency, achieving a good balance between anti-fouling and slagging performance and heat exchange economy.

[0019] Preferably, the length ratio of the high-temperature flue gas section to the low-temperature flue gas section is determined based on the flue gas temperature distribution curve, and the length of the high-temperature flue gas section accounts for 30% to 50% of the total length of the heating surface. The specific length of the high-temperature flue gas section needs to be determined based on factors such as the inlet flue gas temperature of the heating surface, the preset temperature threshold, and heat exchange requirements. For heating surfaces with high inlet flue gas temperatures (e.g., above 850℃), the length of the high-temperature flue gas section can be a larger value (e.g., 40% to 50%); for heating surfaces with relatively low inlet flue gas temperatures (e.g., around 750℃), the length of the high-temperature flue gas section can be a smaller value (e.g., 30% to 40%).

[0020] Preferably, the heating surface adopts a serpentine tube structure, with each heating surface consisting of multiple parallel tubes connected by headers. The serpentine tube structure is a typical structural form for boiler heating surfaces, offering advantages such as compact structure, high heat exchange efficiency, and ease of arrangement. Each heating surface typically consists of 10 to 20 parallel tubes, connected by inlet and outlet headers to ensure uniform distribution and collection of the working fluid.

[0021] Preferably, the variable transverse pitch arrangement method is applicable to 660MW and 1000MW ultra-supercritical boilers or 300MW and 600MW subcritical boilers. The variable transverse pitch arrangement method of the present invention has wide applicability and can be applied to boilers of different capacities and parameters, especially large ultra-supercritical boilers.

[0022] Compared with the prior art, the present invention has the following effects:

[0023] (1) This invention employs a variable transverse pitch design within the same stage of the heating surface. In the high flue gas temperature section where the flue gas temperature exceeds a preset temperature threshold, a large pitch of more than 200 mm is used, effectively increasing the spacing between adjacent tube banks. This provides sufficient space for the growth of fouling and slag, preventing deposits on adjacent tube banks from bridging each other. Based on actual operating experience, after adopting the variable transverse pitch arrangement method of this invention, the phenomenon of fouling and bridging on the heating surface is significantly reduced, the continuous operation cycle of the boiler is significantly extended, the soot blowing frequency is reduced, and the reliability and availability of boiler operation are significantly improved.

[0024] (2) In the low-temperature section where the flue gas temperature is below or equal to a preset temperature threshold, this invention employs a smaller pitch design (typically 40%–60% of the pitch in the high-temperature section), ensuring sufficient heat exchange area and improving heat exchange efficiency. Compared to the overall large pitch arrangement, this invention uses a smaller pitch in the low-temperature section, which can increase the heat exchange area by 30%–50%, significantly improving the heat exchange effect, reducing the flue gas temperature, and increasing the boiler thermal efficiency. According to actual test data, after adopting the variable transverse pitch arrangement method of this invention, the boiler flue gas temperature can be reduced by 5℃–10℃, and the boiler thermal efficiency can be increased by 0.3%–0.6%.

[0025] (3) Through reasonable pitch design and layout optimization, this invention achieves a good balance between anti-fouling and slagging performance and heat exchange economy without significantly increasing the overall size of the boiler. Compared with the scheme of using a graded arrangement of heating surfaces, this invention avoids additional headers, pipes, supports and hangers, etc., simplifies the system structure, and reduces equipment costs and installation expenses. Compared with the scheme of using an overall large pitch arrangement, this invention reduces the space for heating surface arrangement by 20% to 30% while ensuring anti-fouling performance, reduces the overall size of the boiler, and saves boiler room construction and operation costs.

[0026] (4) The variable transverse pitch design of this invention is not limited to specific coal types or fuels, but is applicable to all boiler operating conditions where there are differences in the risk of fouling and slagging in different areas of the heating surface. Burning highly fouling and slagging coal (such as Xinjiang high-alkali coal) is only one of the typical application scenarios of this arrangement scheme. For boilers burning other coal types with a tendency to fouling and slagging (such as Shenhua coal, Pingzhuang coal, etc.), or boilers that blend high-alkali coal, the variable transverse pitch arrangement method of this invention is also applicable. In addition, this invention is applicable to both π-type boilers and tower-type boilers, and has strong versatility and adaptability.

[0027] (5) The variable transverse pitch arrangement method of the present invention can be flexibly adjusted according to changes in coal quality and operating parameters. For coal types with a particularly severe tendency to fouling and slagging, the preset temperature threshold can be appropriately increased to extend the length of the high flue gas temperature section; for coal types with a relatively mild tendency to fouling and slagging, the preset temperature threshold can be appropriately decreased to reduce the length of the high flue gas temperature section. In addition, by adjusting the ratio of the first transverse pitch to the second transverse pitch, the heat exchange performance and anti-fouling performance of the heating surface can be optimized to achieve the best balance between economy and reliability. This flexible adjustment capability enables the present invention to adapt to different coal quality characteristics and operating conditions, and has strong practicality and adaptability. Attached Figure Description

[0028] Figure 1 This is a schematic diagram of the heating surface arrangement in Example 1;

[0029] Figure 2 This is a schematic diagram of the heating surface arrangement in Example 2;

[0030] Figure 3 This is a schematic diagram of the transition section of the heated surface with varying transverse pitch.

[0031] Figure label:

[0032] Figure 1 In the middle section: 1-1, Screen-type superheater; 1-2, High-temperature superheater; 1-3, High-temperature reheater; 1-4, Vertical section of low-temperature reheater; 1-5, Vertical section of low-temperature superheater; 1-6, High-temperature section of low-temperature reheater; 1-7, High-temperature section of low-temperature superheater; 1-8, Transition section of low-temperature reheater; 1-9, Transition section of low-temperature superheater; 1-10, Low-temperature section of low-temperature reheater; 1-11, Low-temperature section of low-temperature superheater; 1-12, Finless upper section of partition wall; 1-13, Finned lower section of partition wall; 1-14, Economizer; 1-15, Flue gas damper;

[0033] Figure 2 In the middle section: 2-1, secondary superheater; 2-2, tertiary superheater; 2-3, secondary reheater; 2-4, high-temperature section of primary superheater; 2-5, transition section of primary superheater; 2-6, low-temperature section of primary superheater; 2-7, primary reheater; 2-8, economizer;

[0034] Figure 3 In the middle: A, pipe number one; B, pipe number two. Detailed Implementation

[0035] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. It should be noted that the embodiments of the present invention are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. All other embodiments obtained by those skilled in the art without inventive effort are within the scope of protection of the present invention.

[0036] Example 1

[0037] like Figure 1 As shown, this embodiment provides a method for arranging the variable transverse pitch heating surface of a π-type 660MW ultra-supercritical boiler. The boiler burns high-alkali coal from Zhundong, Xinjiang, with a sodium oxide content of 2.5% and a potassium oxide content of 1.2%, exhibiting a severe tendency for fouling and slagging. The boiler adopts a π-type arrangement, including a furnace, horizontal flue, and a tail shaft. The tail shaft is divided into two parallel flues by a partition wall, housing a low-temperature reheater and a low-temperature superheater, respectively.

[0038] like Figure 1 As shown, the arrangement of the heated surfaces in this embodiment is as follows:

[0039] The high-temperature flue gas from fuel combustion in the furnace burner area flows sequentially through the screen-type superheater 1-1, high-temperature superheater 1-2, and high-temperature reheater 1-3. After entering the turning chamber, it flows through the vertical section 1-4 of the low-temperature reheater. Then, the flue gas is divided into two parts: one part flows through the high-temperature section 1-6, the transition section 1-8, the low-temperature section 1-10, and the economizer 1-14 of the low-temperature reheater; the other part flows through the upper finless segment 1-12 of the partition wall, sequentially through the vertical section 1-5, the high-temperature section 1-7, the transition section 1-9, and the low-temperature section 1-11, and the economizer 1-14 of the low-temperature superheater. The flue gas on both sides is separated by the lower fin segment 1-13 of the partition wall. Flue gas baffles 1-15 are arranged after the economizers on both sides to adjust the resistance of the flue gas on both sides, thereby regulating the reheat steam temperature.

[0040] like Figure 3 As shown, the variable lateral pitch design in this implementation is as follows:

[0041] The low-temperature reheater and low-temperature superheater are arranged within the range of 850℃ to 450℃. The inlet flue gas temperature of the low-temperature reheater is 850℃ and the outlet flue gas temperature is 550℃; the inlet flue gas temperature of the low-temperature superheater is 820℃ and the outlet flue gas temperature is 520℃. Based on the flue gas temperature distribution, a variable transverse pitch design is adopted within the same stage of heating surface.

[0042] For the high flue gas temperature zones of the low-temperature reheater and low-temperature superheater, specifically the vertical sections 1-4 of the low-temperature reheater, 1-5 of the low-temperature superheater, 1-6 of the low-temperature reheater, and 1-7 of the low-temperature superheater (flue gas temperature above 700℃), the transverse pitch S1 between adjacent heating surfaces is 250mm. This pitch is larger than the conventional design pitch of 150mm, effectively increasing the spacing between adjacent tube banks and providing sufficient space for the growth of contaminants and slag, preventing deposits on adjacent tube banks from adhering to each other and forming bridging. The high flue gas temperature zone accounts for approximately 40% of the total length of the heating surface, with the high flue gas temperature zone of the low-temperature reheater being 8m long and the high flue gas temperature zone of the low-temperature superheater being 7m long.

[0043] After passing through the low-temperature reheater transition section 1-8 and the low-temperature superheater transition section 1-9, a smooth transition is achieved from the lateral pitch S1=250mm to S2=125mm. The transition section is 2m long, accounting for approximately 10% of the total length of the heated surface. Figure 3 As shown, in the transition section, pipe A and pipe B gradually change their lateral pitch through a bend structure. Specifically, at the end of the high flue gas temperature section, the lateral pitch of pipe A and pipe B is S1 = 250 mm; in the transition section, the distance between the two pipes gradually decreases through the bend structure, and the bending radius of the bend structure is twice the outer diameter of the pipe (i.e., 76 mm, the outer diameter of the pipe is 38 mm); at the beginning of the low flue gas temperature section, the lateral pitch of pipe A and pipe B becomes S2 = 125 mm.

[0044] For the low-temperature reheater and the low-temperature superheater's low-temperature flue gas temperature zone (flue gas temperature below or equal to 700℃), specifically the low-temperature reheater section 1-10 and the low-temperature superheater section 1-11, the transverse pitch between two adjacent heating surfaces is S2 = 125 mm. This pitch is 50% of the transverse pitch S1 of the high-temperature section, ensuring that the number of heating surface plates in the low-temperature section is twice that of the high-temperature section. This guarantees the heat exchange area while facilitating the arrangement and connection of the heating surface tubes. The length of the low-temperature section accounts for approximately 50% of the total length of the heating surface, with the low-temperature reheater section being 10 m long and the low-temperature superheater section being 9 m long.

[0045] The working process of this embodiment:

[0046] During boiler operation, the high-temperature flue gas (approximately 1200℃) generated by combustion in the furnace burner area flows sequentially through the screen-type superheater 1-1, high-temperature superheater 1-2, and high-temperature reheater 1-3, gradually decreasing in temperature to around 850℃. The flue gas then enters the turning chamber, flowing through the vertical sections 1-4 and 1-5 of the low-temperature reheater and low-temperature superheater, respectively. At this point, the flue gas temperature remains above 700℃, placing it in the high-temperature zone. Due to the use of a large 250mm pitch, the spacing between adjacent tube banks is substantial. Even if contaminants and slag form on the tube surfaces, there is sufficient space to accommodate these deposits, preventing bridging and adhesion between adjacent tube banks.

[0047] The flue gas continues to flow, entering the high-temperature sections 1-6 of the low-temperature reheater and 1-7 of the low-temperature superheater, where the flue gas temperature gradually decreases from 800℃ to 700℃. During this process, the flue gas temperature remains high, and the tendency for fouling and slagging is still severe. However, due to the adoption of a large pitch design, fouling and bridging are effectively prevented.

[0048] After the flue gas temperature drops to 700℃, it enters the low-temperature reheater transition section 1-8 and the low-temperature superheater transition section 1-9. In the transition sections, the heat-receiving tubes gradually change their lateral pitch through a bending structure, decreasing from 250mm to 125mm. The design of the transition sections avoids the flow resistance and uneven heat transfer problems caused by abrupt changes in lateral pitch, ensuring the smoothness of flue gas flow and the uniformity of heat transfer effect.

[0049] After passing through the transition section, the flue gas enters the low-temperature reheater section 1-10 and the low-temperature superheater section 1-11. At this point, the flue gas temperature is below 700℃, significantly reducing the tendency for fouling and slagging. Due to the use of a small 125mm pitch, the number of heating surface plates is doubled, significantly increasing the heat exchange area and ensuring high heat exchange efficiency. The flue gas undergoes thorough heat exchange with the working fluid inside the heating surface tubes, gradually reducing the flue gas temperature to approximately 450℃ before entering the economizer section 1-14 for further heat exchange.

[0050] This embodiment uses a variable pitch design, employing a large pitch of 250mm in the high flue gas temperature range where the flue gas temperature is above 700℃. This effectively prevents bridging of contaminants and slag, extending the continuous operation cycle of the boiler from the original 3 months to more than 6 months, reducing the soot blowing frequency by 50%, and significantly improving the boiler's operational reliability and availability.

[0051] Example 2

[0052] like Figure 2As shown, this embodiment provides a method for arranging the variable transverse pitch heating surfaces of a tower-type 1000MW ultra-supercritical boiler. The boiler burns a blend of high-alkali coal from Zhundong, Xinjiang, and Shenhua coal. The blend contains 2.2% sodium oxide and 1.0% potassium oxide, exhibiting a significant tendency for fouling and slagging. The boiler employs a tower-type arrangement, with all heating surfaces suspended in the upper part of the furnace, and the flue gas flowing from bottom to top.

[0053] like Figure 2 As shown, the arrangement of the heated surfaces in this embodiment is as follows:

[0054] The high-temperature flue gas from fuel combustion in the furnace burner area flows sequentially through the secondary superheater 2-1, the tertiary superheater 2-2, the secondary reheater 2-3, the high-temperature section 2-4 of the primary superheater 2-4, the transition section 2-5 of the primary superheater 2-5, the low-temperature section 2-6 of the primary superheater 2-6, the primary reheater 2-7, and the economizer 2-8. The primary superheater (i.e., the low-temperature superheater) is located within the 850℃ to 600℃ range, with an inlet flue gas temperature of 850℃ and an outlet flue gas temperature of 600℃.

[0055] like Figure 3 As shown, this embodiment features a variable lateral pitch design:

[0056] Based on the flue gas temperature distribution, a variable transverse pitch design is adopted within the same stage of heating surface. The preset temperature threshold is 750℃, meaning that the section with a flue gas temperature above 750℃ is the high flue gas temperature section, and the section with a flue gas temperature below or equal to 750℃ is the low flue gas temperature section.

[0057] For the high-temperature section 2-4 of the primary superheater (flue gas temperature above 750℃), the transverse pitch S1 between two adjacent heating surfaces is 250mm. This pitch is larger than the conventional design pitch of 150mm, effectively preventing fouling and bridging. The high-temperature section accounts for approximately 35% of the total length of the heating surface, with a length of 7m.

[0058] After the transition section 2-5 of the primary superheater, a smooth transition is achieved from the lateral pitch S1=250mm to S2=125mm. The length of the transition section is 1.5m, accounting for approximately 7.5% of the total length of the heated surface. Figure 3 As shown, in the transition section, pipe A and pipe B gradually change their lateral pitch through a bend structure. The bending radius of the bend structure is 2.5 times the outer diameter of the pipe (i.e., 95 mm, while the outer diameter of the pipe is 38 mm).

[0059] For the low-temperature section 2-6 of the primary superheater (flue gas temperature below or equal to 750℃), the transverse pitch between two adjacent heat exchange surfaces is S2 = 125mm. This pitch is 50% of the transverse pitch S1 of the high flue gas temperature section, ensuring that the number of heat exchange surface plates in the low flue gas temperature section is twice that of the high flue gas temperature section, thus guaranteeing the heat exchange area. The length of the low flue gas temperature section accounts for approximately 57.5% of the total length of the heat exchange surface, with a length of 11.5m.

[0060] The working process of this embodiment:

[0061] During boiler operation, the high-temperature flue gas (approximately 1300℃) generated by combustion in the furnace burner area flows sequentially through the primary superheater 2-1, the tertiary superheater 2-2, and the secondary reheater 2-3, gradually decreasing in temperature to around 850℃. The flue gas then enters the high-temperature section 2-4 of the primary superheater, where the temperature exceeds 750℃, placing it in the high-temperature zone. Due to the use of a large 250mm pitch, the spacing between adjacent tube banks is substantial, effectively preventing bridging of contaminants and slag.

[0062] After the flue gas temperature drops to 750℃, it enters the transition section 2-5 of the first-stage superheater. In the transition section, the lateral pitch of the heat-receiving tubes gradually changes from 250mm to 125mm through a bending structure. The design of the transition section ensures the smoothness of the flue gas flow and the uniformity of the heat exchange effect.

[0063] After passing through the transition section, the flue gas enters the low-temperature section 2-6 of the first-stage superheater, where the flue gas temperature is below 750℃, significantly reducing the tendency for fouling and slagging. Due to the use of a small 125mm pitch, the number of heating surface plates is doubled, significantly increasing the heat exchange area and ensuring high heat exchange efficiency. The flue gas undergoes thorough heat exchange with the working fluid inside the heating surface tubes, gradually reducing the flue gas temperature to around 600℃ before entering the first-stage reheater 2-7 and economizer 2-8 for further heat exchange.

[0064] This embodiment uses a variable pitch design, employing a large pitch of 250mm in the high flue gas temperature range (above 750℃), which effectively prevents bridging of contaminants and slag. The continuous operation cycle of the boiler is extended from the original 4 months to more than 7 months, the soot blowing frequency is reduced by 40%, and the reliability and availability of boiler operation are significantly improved.

[0065] Example 3

[0066] This embodiment is basically the same as Embodiment 1, except that: the preset temperature threshold is 730℃, and the division between the high-temperature and low-temperature flue gas sections is determined based on the 730℃ flue gas temperature threshold. Furthermore, the lateral pitch S2 of the low-temperature flue gas section is 40% of the lateral pitch S1 of the high-temperature flue gas section. Specifically, the lateral pitch S1 of the high-temperature flue gas section is 250mm, and the lateral pitch S2 of the low-temperature flue gas section is 100mm. This design is suitable for coal types with a particularly severe tendency to fouling and slagging (such as Zhundong coal with a sodium oxide content greater than 3.0%), using a larger pitch in the high-temperature flue gas section to further reduce the risk of fouling and bridging.

[0067] In this embodiment, the lateral pitch S2 of the low-temperature flue gas section is 100mm, which is 40% of the lateral pitch S1 of the high-temperature flue gas section. This results in 2.5 times the number of heat exchange surface plates in the low-temperature flue gas section compared to the high-temperature section, further increasing the heat exchange area and ensuring heat exchange efficiency. A total of 40 heat exchange surface plates are arranged in the high-temperature flue gas section, and a total of 100 heat exchange surface plates are arranged in the low-temperature flue gas section.

[0068] In this embodiment, during boiler operation, the high-temperature flue gas section (temperature above 730℃) utilizes a large pitch of 250mm to effectively prevent bridging by fouling and slag. After the flue gas temperature drops to 730℃, it enters a transition section where the transverse pitch gradually decreases from 250mm to 100mm. Following the transition section, the flue gas enters the low-temperature flue gas section. Due to the use of a smaller pitch of 100mm, the number of heating surfaces increases by 1.5 times, further increasing the heat exchange area and ensuring high heat exchange efficiency.

[0069] Example 4

[0070] This embodiment is basically the same as Embodiment 1, except that the transverse pitch S2 in the low flue gas temperature section is 60% of the transverse pitch S1 in the high flue gas temperature section. Specifically, the transverse pitch S1 in the high flue gas temperature section is 250 mm, and the transverse pitch S2 in the low flue gas temperature section is 150 mm. This design is suitable for coal types with a relatively low tendency to fouling and slagging (such as a blend of Zhundong coal with a sodium oxide content of 1.5% to 2.0% and low-alkali coal), which, while ensuring anti-fouling performance, further improves heat exchange efficiency, reduces the number of heating surfaces, and lowers manufacturing costs.

[0071] In this embodiment, the lateral pitch S2 of the low-temperature flue gas section is 150mm, which is 60% of the lateral pitch S1 of the high-temperature flue gas section. This results in the number of heat exchange surface plates in the low-temperature flue gas section being 1.67 times that in the high-temperature flue gas section, ensuring the heat exchange area while reducing the number of heat exchange surface plates and lowering manufacturing costs. A total of 40 heat exchange surface plates are arranged in the high-temperature flue gas section, and a total of 67 heat exchange surface plates are arranged in the low-temperature flue gas section.

[0072] In this embodiment, during boiler operation, the high-temperature section with flue gas temperatures exceeding 700℃ utilizes a large pitch of 250mm to effectively prevent bridging by fouling and slag deposits. After the flue gas temperature drops to 700℃, it enters a transition section where the transverse pitch gradually decreases from 250mm to 150mm. Following the transition section, the flue gas enters the low-temperature section. Due to the 150mm pitch, the number of heating surfaces is moderate, ensuring heat exchange efficiency while reducing manufacturing costs.

[0073] Example 5

[0074] This embodiment provides a method for arranging the variable transverse pitch heating surfaces of a 300MW subcritical boiler. The boiler burns Pingzhuang coal with a sodium oxide content of 1.8% and a potassium oxide content of 0.9%, exhibiting a moderate tendency for fouling and slagging. The boiler adopts a π-type arrangement, similar in structure to Embodiment 1, but with different heating surface specifications and pitch parameters.

[0075] In this embodiment, the preset temperature threshold is 700℃. Sections with smoke temperatures above 700℃ are considered high-temperature sections, and sections with smoke temperatures below or equal to 700℃ are considered low-temperature sections. The lateral pitch S1 of the high-temperature section is 200mm, and the lateral pitch S2 of the low-temperature section is 120mm. The lateral pitch S2 of the low-temperature section is 60% of the lateral pitch S1 of the high-temperature section.

[0076] In this embodiment, during boiler operation, the high-temperature flue gas section (temperature above 700℃) uses a 200mm pitch, effectively preventing bridging of fouling and slag. After the flue gas temperature drops to 700℃, it enters the transition section, where the transverse pitch gradually decreases from 200mm to 120mm. After the transition section, the flue gas enters the low-temperature flue gas section. Due to the 120mm pitch, the number of heating surfaces is moderate, ensuring heat exchange efficiency while saving layout space.

[0077] Example 6

[0078] This embodiment provides a method for arranging the transverse pitch heating surface of a 600MW supercritical boiler. The boiler is a blend of 30% high-alkali coal from Zhundong, Xinjiang, and 70% Shenhua coal. The blend contains 1.5% sodium oxide and 0.7% potassium oxide, resulting in a relatively low tendency for fouling and slagging. The boiler adopts a tower-type arrangement, similar in structure to Embodiment 2, but with different heating surface specifications and pitch parameters.

[0079] In this embodiment, the preset temperature threshold is 720℃. Sections with smoke temperatures above 720℃ are considered high-temperature sections, and sections with smoke temperatures below or equal to 720℃ are considered low-temperature sections. The lateral pitch S1 of the high-temperature section is 220mm, and the lateral pitch S2 of the low-temperature section is 110mm. The lateral pitch S2 of the low-temperature section is 50% of the lateral pitch S1 of the high-temperature section.

[0080] In this embodiment, during boiler operation, the high-temperature flue gas section (temperature above 720℃) uses a 220mm pitch to effectively prevent bridging by fouling and slag. After the flue gas temperature drops to 720℃, it enters the transition section, where the transverse pitch gradually decreases from 220mm to 110mm. After the transition section, the flue gas enters the low-temperature flue gas section. Due to the 110mm pitch, the number of heating surfaces doubles, significantly increasing the heat exchange area and ensuring high heat exchange efficiency.

[0081] The above embodiments are merely preferred embodiments of the present invention, and the scope of protection of the present invention is not limited to the above embodiments. Any modifications, equivalent substitutions, and improvements made based on the technical essence of the present invention should be included within the scope of protection of the present invention. Those skilled in the art can reasonably adjust and optimize parameters such as the specific value of the transverse pitch, the preset temperature threshold, the transition section length, and the heating surface specifications according to the technical solution of the present invention, combined with specific application scenarios and design requirements. These adjustments and optimizations should be considered equivalent substitutions of the present invention and fall within the scope of protection of the present invention.

Claims

1. A method for arranging the heating surfaces of a variable transverse pitch boiler, characterized in that, The boiler heating surface includes one or both of a low-temperature reheater and a low-temperature superheater, wherein the low-temperature reheater and / or the low-temperature superheater are arranged within a flue gas temperature range of 850°C to 450°C; within the same stage of heating surface, a varying transverse pitch is adopted along the flue gas flow direction according to the flue gas temperature distribution at the location of the heating surface: in the high flue gas temperature section where the flue gas temperature is higher than a preset temperature threshold, the transverse pitch between two adjacent heating surfaces is the first transverse pitch; in the low flue gas temperature section where the flue gas temperature is lower than or equal to the preset temperature threshold, the transverse pitch between two adjacent heating surfaces is the second transverse pitch; the first transverse pitch is greater than the second transverse pitch, and the first transverse pitch meets the requirements for preventing fouling and bridging.

2. The method for arranging the heating surface of a variable transverse pitch boiler according to claim 1, characterized in that, The preset temperature threshold ranges from 700℃ to 750℃, and the specific value is determined based on the coal's fouling and slagging characteristics.

3. The method for arranging the heating surface of a variable transverse pitch boiler according to claim 1, characterized in that, The first lateral pitch ranges from 200mm to 300mm, and the second lateral pitch ranges from 100mm to 150mm.

4. The method for arranging the heating surface of a variable transverse pitch boiler according to claim 1, characterized in that, The second lateral pitch is 40% to 60% of the first lateral pitch.

5. The method for arranging the heating surface of a variable transverse pitch boiler according to claim 4, characterized in that, The second lateral pitch is 50% of the first lateral pitch.

6. The method for arranging the heating surface of a variable transverse pitch boiler according to claim 1, characterized in that, A transition section is provided between the high smoke temperature section and the low smoke temperature section. The transition section is used to achieve a smooth transition of the lateral pitch from the first lateral pitch to the second lateral pitch.

7. The method for arranging the heating surface of a variable transverse pitch boiler according to claim 6, characterized in that, In the transition section, the heating surface tubes gradually change their transverse pitch through a bend structure, and the bending radius of the bend structure is determined according to the pitch change range and the length of the transition section.

8. The method for arranging the heating surface of a variable transverse pitch boiler according to claim 1, characterized in that, The boiler is a π-type boiler, including a screen-type superheater, a high-temperature superheater, a high-temperature reheater, a low-temperature reheater, a low-temperature superheater, and an economizer. The low-temperature reheater and the low-temperature superheater are respectively arranged in two parallel flues.

9. The method for arranging the heating surface of a variable transverse pitch boiler according to claim 1, characterized in that, The boiler is a tower-type boiler, with flue gas flowing from bottom to top through each stage of heating surfaces. The low-temperature superheater is arranged after the high-temperature superheater and the high-temperature reheater.

10. The method for arranging the heating surface of a variable transverse pitch boiler according to claim 1, characterized in that, The high flue gas temperature section is arranged on the inlet side of the heating surface, and the low flue gas temperature section is arranged on the outlet side of the heating surface. The flue gas flows sequentially through the high flue gas temperature section, the transition section and the low flue gas temperature section along the flow direction of the heating surface tube.

11. The method for arranging the heating surface of a variable transverse pitch boiler according to claim 1, characterized in that, The length ratio of the high-temperature flue gas section to the low-temperature flue gas section is determined according to the flue gas temperature distribution curve, and the length of the high-temperature flue gas section accounts for 30% to 50% of the total length of the heated surface.

12. The method for arranging the heating surface of a variable transverse pitch boiler according to claim 1, characterized in that, The heating surface adopts a serpentine tube structure, and each heating surface consists of multiple parallel tubes connected by a header.

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