A heating surface arrangement of a double-reheat boiler and a steam and flue gas treatment method

Abstract

The application provides a heating surface arrangement structure of a double-reheat boiler and a steam and flue gas treatment method; the heating surface arrangement structure of the double-reheat boiler comprises a furnace, a superheater, a primary reheater and a secondary reheater, the superheater comprises a low-temperature superheater and a high-temperature superheater, and the primary reheater comprises a primary reheating low-temperature reheater and a primary reheating high-temperature reheater; the application has the beneficial effect that: by arranging the primary reheating high-temperature reheater and the secondary reheating high-temperature reheater completely downstream of the high-temperature superheater, the problem that the high-temperature reheater of the traditional structure extends upstream of the high-temperature superheater is avoided, the heating surface arrangement is simplified, and the flue gas flow resistance is reduced.

Description

Technical Field

[0001] This invention relates to the field of secondary reheat boiler technology, and in particular to a heating surface arrangement structure and steam and flue gas treatment method for a secondary reheat boiler. Background Technology

[0002] Double reheat boilers, as an advanced coal-fired power generation technology, are being widely used due to their high efficiency and environmental friendliness. However, the difficulty and complexity of temperature control in double reheat boilers are far greater than in conventional single reheat boilers. To address the temperature control challenges of double reheat boilers, CN102889570B proposes a cross-parallel arrangement of reheaters, enabling simultaneous regulation of primary and secondary reheat steam temperatures. This solves the problem of achieving heat exchange temperature and pressure above 600℃ on the tertiary heating surface. The reheat steam temperature is primarily controlled by burner oscillation. To increase the sensitivity of burner oscillation in regulating reheat steam temperature, the cold sections of the primary and secondary high-temperature reheaters pass through the high-temperature superheater, and the flue gas flow is positioned before the high-temperature superheater, improving the radiative heat transfer characteristics of the high-temperature reheater. This technology has been successfully applied in the first batch of double reheat boilers in China, verifying the effectiveness of the parallel arrangement of reheater heating surfaces. However, since the capacity of the secondary reheat boilers is 600MW and above, the swing temperature regulation effect is limited. After the first batch of projects are put into operation, the load range that can reach the rated reheat steam temperature (65%THA and above) is relatively narrow, which is lower than that of general primary reheat units (50%THA and above).

[0003] To address these issues, researchers have proposed introducing flue gas recirculation for temperature control in double reheat boilers. By introducing cold flue gas into the furnace, the combustion temperature inside the furnace is reduced, thereby decreasing radiative heat transfer and increasing convective heat transfer to regulate the reheat steam temperature. Introducing a flue gas recirculation system can effectively improve the wide-load regulation capability of the double reheat unit's reheat steam temperature.

[0004] On the other hand, with the diversification of industrial production, the output of low-calorific-value coal gas (including blast furnace gas, converter gas, and semi-coke tail gas) is constantly increasing, becoming an important fuel resource. Previously, there was no experience with co-firing low-calorific-value coal gas in secondary reheat systems. Firing low-calorific-value coal gas in secondary reheat boilers with higher circulation efficiency can significantly improve the utilization efficiency of low-calorific-value coal gas. However, low-calorific-value coal gas generally has a lower combustion temperature, resulting in a larger volume of flue gas after combustion, weakened radiative heat transfer characteristics, and significantly enhanced convective heat transfer characteristics. In secondary reheat boilers using flue gas recirculation for temperature regulation or co-firing blast furnace coal, if the reheater hot surface cross-arrangement is still used, the reduced radiative heat transfer in the cold sections of the primary and secondary high-temperature reheaters when recirculating for temperature regulation or co-firing low-calorific-value coal gas at low loads will partially offset the temperature regulation effect of flue gas recirculation. Summary of the Invention

[0005] To overcome the aforementioned problems in the prior art, the present invention provides a heating surface arrangement structure and a steam and flue gas treatment method for a secondary reheat boiler.

[0006] This invention discloses a heating surface arrangement structure for a double reheat boiler, including a furnace, a superheater, a primary reheater, and a secondary reheater. The superheater includes a low-temperature superheater and a high-temperature superheater. The primary reheater includes a primary reheat low-temperature reheater and a primary reheat high-temperature reheater. The secondary reheater includes a secondary reheat low-temperature reheater and a secondary reheat high-temperature reheater. The primary reheat high-temperature reheater and the secondary reheat high-temperature reheater are arranged side by side downstream of the flue gas of the high-temperature superheater. An intermediate partition wall is provided downstream of the flue gas of the primary reheat high-temperature reheater and the secondary reheat high-temperature reheater, dividing the flue gas passage into a first flue and a second flue. The primary reheat low-temperature reheater is arranged in the first flue, and the secondary reheat low-temperature reheater is arranged in the second flue. The primary reheat high-temperature reheater and the secondary reheat high-temperature reheater are spatially located entirely downstream of the high-temperature superheater and do not have a radiant heating surface extending upstream of the high-temperature superheater.

[0007] Based on this, the boiler is a tower boiler, and the high-temperature superheater, the primary reheat high-temperature reheater and the secondary reheat high-temperature reheater are all arranged in the vertical flue. Economizers are arranged in both the first flue and the second flue.

[0008] Based on this, the low-temperature superheater is arranged upstream of the flue gas of the high-temperature superheater; the low-temperature superheater includes a low-temperature superheater suspension inlet pipe, a finned partition wall, a finless section at the bottom of the partition wall, a vertical section heating surface of the low-temperature superheater, and a low-temperature superheater screen tube section.

[0009] Based on this, the boiler is a π-type boiler, which also includes a horizontal flue and a tail flue. The high-temperature superheater, the primary reheat high-temperature reheater, and the secondary reheat high-temperature reheater are all arranged in the horizontal flue, and the intermediate partition wall is set in the tail flue. The primary reheat low-temperature reheater and the secondary reheat low-temperature reheater both include a vertical section and a horizontal section.

[0010] Based on this, the intermediate partition wall includes an upper finless segment and a lower fin segment; the first and second flues of the tail flue are respectively provided with flue gas baffles to regulate the flow rate of flue gas flowing through the two flues.

[0011] Another aspect of the present invention discloses a steam and flue gas treatment method for a double reheat boiler, applied to the heating surface arrangement structure of the double reheat boiler, comprising the following steps:

[0012] Main steam flow: The steam from the separator outlet flows sequentially through the low-temperature superheater and the high-temperature superheater;

[0013] First reheat process: The exhaust steam from the ultra-high pressure cylinder of the steam turbine flows sequentially through the first reheat low-temperature reheater and the first reheat high-temperature reheater, and after absorbing heat, it is sent to the high-pressure cylinder of the steam turbine.

[0014] Secondary reheat process: The exhaust steam from the high-pressure cylinder of the steam turbine flows sequentially through the low-temperature reheater and the high-temperature reheater of the secondary reheater, and after absorbing heat, it is sent to the intermediate-pressure cylinder of the steam turbine.

[0015] Flue gas flow path: The flue gas flows sequentially through the reheater, the parallel-arranged primary reheat high-temperature reheater and secondary reheat high-temperature reheater, and is then divided into two streams by the intermediate partition wall, which flow through the primary reheat low-temperature reheater and the secondary reheat low-temperature reheater respectively.

[0016] Based on this, the boiler is equipped with a flue gas recirculation system; when operating at low load, the proportion of recirculated flue gas is increased to reduce radiative heat absorption in the furnace and increase the amount of flue gas on the convective heating surface, thereby enhancing convective heat transfer.

[0017] Based on this, when the boiler is a tower boiler, flue gas side temperature regulation is adopted to regulate the primary reheat steam temperature and secondary reheat steam temperature in the same direction.

[0018] Based on this, when the boiler is a π-type boiler, the flue gas resistance of the flue gas ducts on both sides is changed by adjusting the flue gas baffles set in the tail flue, thereby balancing the heat absorption of primary reheat and secondary reheat.

[0019] Compared with the prior art, the beneficial effects of the present invention are:

[0020] (1) By arranging the primary reheat high-temperature reheater and the secondary reheat high-temperature reheater completely downstream of the high-temperature superheater, the problem of the high-temperature reheater extending into the high-temperature superheater in the traditional structure is avoided, the arrangement of the heating surface is simplified, and the flow resistance of flue gas is reduced.

[0021] (2) By separating the flue gas passages through intermediate partition walls, independent adjustment of the primary reheat and secondary reheat systems is achieved, improving the flexibility and adaptability of boiler operation; the flue gas flow design is reasonable, making full use of the waste heat of the flue gas and improving the boiler thermal efficiency. The configuration of the flue gas recirculation system further optimizes the heat exchange effect under low load conditions;

[0022] (3) Corresponding temperature control strategies are provided for different boiler types. Tower boilers use flue gas side temperature regulation, and π-type boilers use flue gas dampers for regulation. Both can achieve precise temperature control and have wide applicability and promotion value. Attached Figure Description

[0023] Figure 1 This is a schematic diagram of the heating surface arrangement structure in Embodiment 1 of the present invention;

[0024] Figure 2 This is a schematic diagram of the heating surface arrangement structure in Embodiment 2 of the present invention;

[0025] Figure 3 yes Figure 2 AA view;

[0026] In the diagram: 1. Suspended inlet tube of the low-temperature superheater; 2. Finned partition wall; 3. Lower section of the partition wall without fins; 4. Vertical heating surface of the low-temperature superheater; 5. Screen tube section of the low-temperature superheater; 201. Low-temperature superheater; 106. High-temperature superheater; 107. Single reheat low-temperature reheater; 108. Single reheat high-temperature reheater; 109. Double reheat low-temperature reheater; 1010. Double reheat high-temperature reheater; 11. Economizer; 12. Flue gas damper. Detailed Implementation

[0027] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only for explaining the present invention and are not intended to limit the present invention.

[0028] Example 1

[0029] refer to Figure 1 The boiler is a tower boiler, comprising a furnace, superheaters, a primary reheater, and a secondary reheater. The superheaters include a low-temperature superheater and a high-temperature superheater (106). The primary reheater includes a primary reheat low-temperature reheater (107) and a primary reheat high-temperature reheater (108). The secondary reheater includes a secondary reheat low-temperature reheater (109) and a secondary reheat high-temperature reheater (1010).

[0030] The furnace is located at the bottom of the boiler. The fuel is burned in the furnace to produce high-temperature flue gas. The vertical flue is located above the furnace and has a single-channel structure. The flue gas flows from bottom to top. In the vertical flue, from bottom to top, there are arranged the following: low-temperature superheater, high-temperature superheater 106, primary reheat high-temperature reheater 108, and secondary reheat high-temperature reheater 1010.

[0031] The primary reheat high-temperature reheater 108 and the secondary reheat high-temperature reheater 1010 are arranged side by side on the same horizontal plane and are downstream of the flue gas of the high-temperature superheater 106, and do not have a radiant heating surface extending into the upstream of the high-temperature superheater 106. The low-temperature superheater is arranged upstream of the flue gas of the high-temperature superheater 106. The low-temperature superheater includes a low-temperature superheater suspension inlet pipe 101, a finned partition wall 102, a non-finned section 103 at the bottom of the partition wall, a vertical section heating surface 104 of the low-temperature superheater, and a low-temperature superheater screen tube section 105. The low-temperature superheater suspension inlet pipe 101 is connected to the separator outlet. The finned partition wall 102 is connected to the furnace side wall to form a radiant heating surface. The non-finned section 103 at the bottom of the partition wall is connected to the vertical section heating surface 104 of the low-temperature superheater. The vertical section heating surface 104 of the low-temperature superheater is connected to the low-temperature superheater screen tube section 105. The outlet of the low-temperature superheater screen tube section 105 is connected to the inlet of the high-temperature superheater 106, forming a complete steam flow channel.

[0032] Downstream of the flue gas from the primary reheat high-temperature reheater 108 and the secondary reheat high-temperature reheater 1010, there is an intermediate partition wall. The intermediate partition wall is located in the flue gas duct at the tail of the boiler and divides the flue gas passage into a first flue and a second flue, ensuring that the two flue gas flows will not interfere with each other. The primary reheat low-temperature reheater 107 is arranged in the first flue and the secondary reheat low-temperature reheater 109 is arranged in the second flue. Economizers 1011 are arranged in both the first and second flues for further recovery of waste heat from the flue gas.

[0033] The flue gas flows from bottom to top through each stage of the heating surface. The main steam process is as follows: the saturated steam from the separator outlet enters the suspended inlet pipe 101 of the low-temperature superheater in sequence. Part of it enters the finned partition wall 102 and the unfinned section 103 at the bottom of the low partition wall, and is introduced into the screen tube section 105 of the low-temperature superheater. The other part enters the screen tube section 105 of the low-temperature superheater through the vertical section heating surface 104 of the low-temperature superheater. After the superheated steam merges in the low-temperature screen tube 105, it is introduced into the high-temperature superheater 106 for further heating into superheated steam, which is then sent to the high-pressure cylinder of the turbine to do work. The first reheat process is as follows: the wet steam discharged from the ultra-high pressure cylinder of the turbine flows through the low-temperature reheater 107 of the first reheater for preliminary heating, and then enters the high-temperature reheater 108 of the first reheater to complete the final heating. After absorbing heat in the boiler, it is sent to form high-temperature and high-pressure reheated steam, which is then sent into the high-pressure cylinder of the turbine to do work. Steam discharged from the high-pressure cylinder of the steam turbine first flows through the secondary reheat low-temperature reheater 109 for preliminary heating, and then flows into the secondary reheat high-temperature reheater 1010 for final heating. After absorbing heat in the boiler, it forms medium-temperature and medium-pressure reheated steam, which is then sent to the intermediate-pressure cylinder of the steam turbine to perform work. Flue gas flow: The high-temperature flue gas generated by combustion in the furnace flows sequentially through the low-temperature superheater, the high-temperature superheater 106, the parallel primary reheat high-temperature reheater 108 and the secondary reheat high-temperature reheater 1010, and is then divided into two streams by the intermediate partition wall, flowing through the primary reheat low-temperature reheater 107 and the secondary reheat low-temperature reheater 109 respectively, and finally flowing through the economizer 1011 before being discharged into the atmosphere.

[0034] The boiler is equipped with a flue gas recirculation system. During low-load operation, the proportion of recirculated flue gas is increased to reduce radiative heat absorption in the furnace and increase the amount of flue gas flowing through the convective heating surfaces, thereby enhancing convective heat transfer. The flue gas recirculation system includes a recirculation fan, flue gas extraction ducts, and a flue gas mixing device. During low-load operation, the recirculation fan extracts a portion of the low-temperature flue gas from the tail flue, mixes it with fresh air at the furnace inlet, and then sends it back into the furnace. This lowers the furnace combustion temperature, reduces radiative heat absorption, and simultaneously increases the flue gas flow rate and velocity on the convective heating surfaces, improving the convective heat transfer coefficient. This maintains stable boiler operation and efficient heat exchange under low-load conditions.

[0035] When the boiler is a tower boiler, flue gas-side temperature control methods are used to regulate the primary and secondary reheat steam temperatures in a consistent direction. In tower boilers, flue gas-side temperature control methods include adjusting the burner angle, changing the secondary air ratio, and adjusting the flue gas recirculation rate. These methods can simultaneously change the flue gas temperature and flow rate flowing through both the primary and secondary reheat high-temperature reheaters. Because both are arranged side-by-side in the same flue, the regulation effect is consistent, enabling simultaneous increases or decreases in primary and secondary reheat steam temperatures, thus simplifying the temperature control system.

[0036] Example 2

[0037] refer to Figure 2and Figure 3 The boiler is a π-type boiler, including a furnace, superheaters, a primary reheater, and a secondary reheater. The superheaters include a low-temperature superheater 201 and a high-temperature superheater 106. The primary reheaters include a primary reheat low-temperature reheater 107 and a primary reheat high-temperature reheater 108. The secondary reheaters include a secondary reheat low-temperature reheater 109 and a secondary reheat high-temperature reheater 1010. The difference from Embodiment 1 is that the boiler also includes a horizontal flue and a tail flue. The furnace is located at the front of the boiler, where fuel is burned to generate high-temperature flue gas. The horizontal flue is located above the furnace, and the flue gas flows out of the furnace and enters the horizontal flue. The tail flue is located behind the horizontal flue and is connected to it via a turning chamber. Within the horizontal flue, arranged sequentially from front to back are: the low-temperature superheater 201, the high-temperature superheater 106, the primary reheat high-temperature reheater 108, and the secondary reheat high-temperature reheater 1010. The primary reheat high-temperature reheater 108 and the secondary reheat high-temperature reheater 1010 are arranged side by side on the same horizontal plane and are located entirely downstream of the high-temperature superheater 106. The high-temperature superheater 106, the primary reheat high-temperature reheater 108, and the secondary reheat high-temperature reheater 1010 are all arranged in a horizontal flue, with intermediate partition walls located in the tail flue; the primary reheat low-temperature reheater 107 and the secondary reheat low-temperature reheater 109 both include vertical and horizontal sections.

[0038] After exiting the furnace, the flue gas first passes through a horizontal flue, then turns and enters the tail flue. Within the tail flue, it is divided into two streams by an intermediate partition wall, flowing through the primary reheat low-temperature reheater 107 and the secondary reheat low-temperature reheater 109, respectively. The vertical section of the primary reheat low-temperature reheater 107 is located above the first flue, and the horizontal section is located below it. The vertical section of the secondary reheat low-temperature reheater 109 is located above the second flue, and the horizontal section is located below it, forming a U-shaped flue gas flow path. The intermediate partition wall includes an upper finless section and a lower finned section. Flue gas baffles 12 are installed in both the first and second flues of the tail flue to regulate the flow rate of the flue gas passing through the two flues. The upper finless section of the partition wall uses a bare tube structure and is mainly used for flue gas separation; the lower finned section uses a finned tube structure and participates in heat exchange as part of the superheating system. The flue gas damper 12 is an adjustable damper. By changing the opening of the damper, the flue gas resistance on both sides of the flue can be adjusted, thereby controlling the ratio of flue gas flowing through the primary reheat low-temperature reheater and the secondary reheat low-temperature reheater, and realizing independent adjustment of the primary reheat steam temperature and the secondary reheat steam temperature.

[0039] Main steam flow: The saturated steam from the separator outlet first flows through the furnace top and the superheating system, the upper finless segment of the partition wall and the lower fin segment of the partition wall, and after absorbing some heat, it enters the low-temperature superheater 201 and the high-temperature superheater 106 in sequence. After completing the superheating process, it is sent to the high-pressure cylinder of the steam turbine to do work.

[0040] The reheat process is as follows: The wet steam discharged from the ultra-high pressure cylinder of the steam turbine first flows through the horizontal section of the primary reheat low-temperature reheater 107, then enters the vertical section of the primary reheat low-temperature reheater 107, and finally enters the primary reheat high-temperature reheater 108 to form high-temperature and high-pressure reheated steam, which is then sent back to the high-pressure cylinder of the steam turbine to continue to do work.

[0041] Secondary reheat process: The steam discharged from the high-pressure cylinder of the steam turbine first flows through the horizontal section of the secondary reheat low-temperature reheater 109, then enters the vertical section of the secondary reheat low-temperature reheater 109, and finally enters the secondary reheat high-temperature reheater 1010 to form medium-temperature and medium-pressure reheated steam, which is then sent to the intermediate-pressure cylinder of the steam turbine to do work.

[0042] Flue gas flow: The high-temperature flue gas generated by fuel combustion in the furnace area mixes with the recirculated flue gas and flows sequentially through the low-temperature superheater 201 and the high-temperature superheater 106. In the horizontal flue, it flows in parallel through the primary reheat high-temperature reheater 108 and the secondary reheat high-temperature reheater 1010. After entering the turning chamber, the flue gas is guided to flow through the vertical section of the primary reheat low-temperature reheater 107. Subsequently, the flue gas is divided into two parts: one part (accounting for about 45% of the total flue gas volume) flows through the horizontal section of the primary reheat low-temperature reheater 107 and the economizer 11 at the bottom of the primary reheat low-temperature reheater 107; the other part flows through the finless section at the top of the partition wall and sequentially through the vertical section of the secondary reheat low-temperature reheater 109, the horizontal section of the secondary reheat low-temperature reheater 109, and the economizer 11 located at the bottom of the secondary reheat low-temperature reheater 109. The flue gas on both sides is separated by the lower fin segment of the partition wall. Flue gas baffles 12 are arranged after the economizers 11 on both sides. By adjusting the opening of the flue gas baffles 12, the flow ratio of flue gas on both sides can be precisely controlled.

[0043] Temperature regulation method: In the π-type boiler, temperature regulation is achieved by adjusting the flue gas damper 12 in the tail flue. When the primary reheat steam temperature is too high and the secondary reheat steam temperature is too low, the opening of the flue gas damper 12 in the first flue is reduced from 80% to 60%, increasing the flue gas resistance in the first flue. This reduces the amount of flue gas flowing through the primary reheat low-temperature reheater 107 by 10%, while increasing the amount of flue gas flowing through the secondary reheat low-temperature reheater 109 by 10%. This reduces the heat absorption of the primary reheat low-temperature reheater 107, lowering the primary reheat steam temperature by 5°C; and increases the heat absorption of the secondary reheat low-temperature reheater 109, raising the secondary reheat steam temperature by 5°C, thus achieving a balance between the two. During low-load operation, the flue gas recirculation rate is increased, reducing the proportion of radiative heat absorption in the furnace and increasing the amount of flue gas on the convective heating surface, ensuring stable boiler operation under low-load conditions.

[0044] In the description of this invention, it should be understood that the terms "coaxial," "bottom," "one end," "top," "middle," "other end," "upper," "side," "top," "inner," "front," "center," "both ends," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limiting this invention.

[0045] In this invention, unless otherwise explicitly specified and limited, the terms "installation," "setting," "connection," "fixing," "screw-in," "pad," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal connection of two components or the interaction between two components. Unless otherwise explicitly limited, those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0046] The foregoing description illustrates and describes preferred embodiments of the present invention. As previously stated, it should be understood that the present invention is not limited to the forms disclosed herein and should not be construed as excluding other embodiments. It can be used in various other combinations, modifications, and environments, and can be altered within the scope of the inventive concept described herein through the foregoing teachings or techniques or knowledge in related fields. Any modifications and variations made by those skilled in the art that do not depart from the spirit and scope of the present invention should be within the protection scope of the appended claims.

Claims

1. A heating surface arrangement structure for a double reheat boiler, characterized in that: The system includes a furnace, a superheater, a primary reheater, and a secondary reheater. The superheater includes a low-temperature superheater and a high-temperature superheater. The primary reheater includes a primary reheat low-temperature reheater and a primary reheat high-temperature reheater. The secondary reheater includes a secondary reheat low-temperature reheater and a secondary reheat high-temperature reheater. The primary and secondary reheat high-temperature reheaters are arranged side-by-side downstream of the high-temperature superheater. A partition wall is provided downstream of the primary and secondary reheat high-temperature reheaters to divide the flue gas passage into a first flue and a second flue. The primary reheat low-temperature reheater is arranged in the first flue, and the secondary reheat low-temperature reheater is arranged in the second flue. The primary and secondary reheat high-temperature reheaters are spatially located entirely downstream of the high-temperature superheater and do not have a radiant heating surface extending upstream of the high-temperature superheater.

2. The heating surface arrangement structure of the double reheat boiler according to claim 1, characterized in that, The boiler is a tower boiler. The high-temperature superheater, the primary reheat high-temperature reheater, and the secondary reheat high-temperature reheater are all arranged in a vertical flue. Economizers are arranged in both the first and second flues.

3. The heating surface arrangement structure of the secondary reheat boiler according to claim 2, characterized in that, The low-temperature superheater is arranged upstream of the flue gas of the high-temperature superheater; the low-temperature superheater includes a low-temperature superheater suspension inlet pipe, a finned partition wall, a finless section at the bottom of the partition wall, a vertical section heating surface of the low-temperature superheater, and a low-temperature superheater screen tube section.

4. The heating surface arrangement structure of the double reheat boiler according to claim 1, characterized in that, The boiler is a π-type boiler, which also includes a horizontal flue and a tail flue. The high-temperature superheater, the primary reheat high-temperature reheater, and the secondary reheat high-temperature reheater are all arranged in the horizontal flue, and the intermediate partition wall is set in the tail flue. The primary reheat low-temperature reheater and the secondary reheat low-temperature reheater both include a vertical section and a horizontal section.

5. The heating surface arrangement structure of the secondary reheat boiler according to claim 4, characterized in that, The intermediate partition wall includes an upper finless segment and a lower fin segment; the first and second flues of the tail flue are respectively equipped with flue gas baffles to regulate the flow rate of flue gas passing through the two flues.

6. A method for treating steam and flue gas in a double reheat boiler, applied to the heating surface arrangement structure of the double reheat boiler as described in any one of claims 1 to 5, characterized in that, Includes the following steps: Main steam flow: The steam from the separator outlet flows sequentially through the low-temperature superheater and the high-temperature superheater; First reheat process: The exhaust steam from the ultra-high pressure cylinder of the steam turbine flows sequentially through the first reheat low-temperature reheater and the first reheat high-temperature reheater, and after absorbing heat, it is sent to the high-pressure cylinder of the steam turbine. Secondary reheat process: The exhaust steam from the high-pressure cylinder of the steam turbine flows sequentially through the low-temperature reheater and the high-temperature reheater of the secondary reheater, and after absorbing heat, it is sent to the intermediate-pressure cylinder of the steam turbine. Flue gas flow path: The flue gas flows sequentially through the reheater, the parallel-arranged primary reheat high-temperature reheater and secondary reheat high-temperature reheater, and is then divided into two streams by the intermediate partition wall, which flow through the primary reheat low-temperature reheater and the secondary reheat low-temperature reheater respectively.

7. The steam and flue gas treatment method for a double reheat boiler according to claim 6, characterized in that, The boiler is equipped with a flue gas recirculation system; when operating at low load, the proportion of recirculated flue gas is increased to reduce radiative heat absorption in the furnace and increase the amount of flue gas on the convective heating surface, thereby enhancing convective heat transfer.

8. The steam and flue gas treatment method for a double reheat boiler according to claim 7, characterized in that, When the boiler is a tower boiler, flue gas side temperature regulation is used to regulate the primary reheat steam temperature and the secondary reheat steam temperature in the same direction.

9. The steam and flue gas treatment method for a double reheat boiler according to claim 7, characterized in that, When the boiler is a π-type boiler, the flue gas resistance on both sides of the flue is changed by adjusting the flue gas baffle installed in the tail flue, thereby balancing the heat absorption of primary reheat and secondary reheat.

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