Natural ventilation air cooling system and steam exhaust pipeline optimization method

Abstract

The invention relates to the technical field of industrial cooling, in particular to a natural ventilation air cooling system and a steam exhaust pipeline optimization method. The system comprises a steam turbine, an air cooling condenser and a steam exhaust pipe assembly composed of an air inlet main pipe, a mother pipe ring pipe and a branch pipe, the air inlet main pipe is connected with the mother pipe ring pipe through a three-way pipe fitting, the mother pipe ring pipe is composed of a first arc pipe and a second arc pipe which are horizontally and oppositely arranged, and the first arc pipe and the second arc pipe are each of a variable-diameter structure with the pipe diameter decreasing section by section from the connecting end to the closed end. A plurality of connecting vertical pipes are asymmetrically arranged on the two arc pipes in the steam flow direction, a vertical pipe is additionally arranged at the first arc pipe end of the three-way pipe fitting and used for flow dividing, and each connecting vertical pipe is connected with an upper-layer branch pipe and a lower-layer branch pipe with a first oblique shoulder part for oblique flow guiding. And the air-cooled condensers are correspondingly connected with the leeward side and the windward side of the ventilation tower respectively. The flow difference between the upper-layer branch pipe and the lower-layer branch pipe can be effectively reduced, so that the local resistance loss is remarkably reduced, and the uniformity of flow distribution is improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of industrial cooling technology, and particularly relates to a natural ventilation air cooling system and a steam exhaust pipeline optimization method. BACKGROUND

[0002] The NDC system (Natural Draft Condenser, natural ventilation direct air cooling system) uses the cold air sucked by the natural ventilation tower to cool the steam turbine exhaust inside the air cooling condenser. The large power station uses the NDC technology, which has the advantages of low emission, wide load, deep peak regulation, and fast regulation. Compared with the exhaust system of the conventional large generator set, the exhaust pipeline between the exhaust cylinder and the condenser of the NDC system has the following characteristics: (1) the exhaust pipeline is long, the channel diameter is large, and the structure is complex; (2) special structures must be adopted on the exhaust pipeline to make the flow uniform and the resistance small in the distribution channel, so as to ensure the economy of the unit operation; (3) the steam in the exhaust pipeline has condensation phenomenon, the condensation amount is affected by the environment, and the flow is a thin liquid film two-phase flow; (4) the whole system operates under negative pressure, the vacuum affects the condensation effect, and also makes the flow rate in the pipeline very high, and if the guide vane is not reasonably designed, it will cause a great impact on the whole device and damage it.

[0003] At present, the unit of the thermal power plant is usually operated under large variable working conditions (100%~20mm%), large range of back pressure change (6~35kPa), and extreme environmental temperature difference (-29~42℃). At the same time, the cooling air volume is significantly different due to the change of environmental wind direction and wind speed, and the uniformity of steam distribution of large diameter and variable diameter, three-dimensional multi-branch exhaust pipeline is extremely difficult to achieve under multiple constraints, multiple working conditions and complex flow state, which leads to a large difference in pressure drop of different pipelines, increases the difficulty of back pressure control, and directly affects the economy and stability of the system. SUMMARY

[0004] The technical problem to be solved by the embodiments of the present application is to provide a natural ventilation air cooling system and an exhaust pipeline optimization method, so as to solve the problems of uneven steam cooling flow distribution and difficult back pressure control of the NDC system after large-scale.

[0005] The present application discloses a natural ventilation air cooling system, which comprises a steam turbine, an air cooling condenser and an exhaust pipe assembly, wherein the exhaust pipe assembly comprises an air inlet main pipe, a mother pipe ring pipe and a branch pipe. The air inlet main pipe is connected with the steam turbine and connected with the mother pipe ring pipe through a tee pipe fitting. The mother pipe ring pipe comprises a first circular arc pipe and a second circular arc pipe arranged oppositely and horizontally, one end of the first circular arc pipe is closed, the other end is connected with one end of the three-way pipe fitting, and the pipe body of the first circular arc pipe presents a variable diameter structure with a plurality of pipe diameters decreasing in turn along the direction from the connected end to the closed end, one end of the second circular arc pipe is closed, the other end is connected with the other end of the three-way pipe fitting, and the pipe body of the second circular arc pipe presents a variable diameter structure with a plurality of pipe diameters decreasing in turn along the direction from the connected end to the closed end, and each variable diameter section of the first circular arc pipe is asymmetrically arranged with each variable diameter section of the second circular arc pipe. A plurality of connection vertical pipes are arranged on the first circular arc pipe and the second circular arc pipe along the steam flow direction respectively, and the plurality of connection vertical pipes on the first circular arc pipe and the second circular arc pipe are asymmetrically distributed, and one connection vertical pipe is further arranged on the end of the three-way pipe fitting connected with the first circular arc pipe, for distributing the steam on the gas inlet side of the first circular arc pipe. The branch pipes are arranged on each connection vertical pipe respectively, comprising an upper layer branch pipe in communication with the top end of the connection vertical pipe, and a lower layer branch pipe in communication with the middle part of the connection vertical pipe, a first inclined shoulder part for guiding the steam flow is formed on the steam inlet side of the connection part between the lower layer branch pipe and the connection vertical pipe, each upper layer branch pipe and lower layer branch pipe on the first circular arc pipe is connected with the air-cooled condenser preset on the leeward side of the ventilation tower one by one, and each upper layer branch pipe and lower layer branch pipe on the second circular arc pipe is connected with the air-cooled condenser preset on the windward side of the ventilation tower one by one.

[0006] Optionally, the connection vertical pipe comprises a lower pipe body and an upper pipe body with decreasing diameters from bottom to top, the upper pipe body and the lower pipe body are connected through a first variable diameter part, and the first variable diameter part is a tapered structure with gradually changing diameters. The upper layer branch pipe is horizontally arranged, the diameter of the upper layer branch pipe is consistent with the upper pipe body, the upper layer branch pipe and the top end of the upper pipe body are integrally formed, and an arc-shaped flow guiding bend part is formed at the connection part. The lower layer branch pipe is horizontally arranged, the diameter of the lower layer branch pipe is smaller than the lower pipe body, a first butt joint hole is formed in the side pipe wall of the lower pipe body, the end of the lower layer branch pipe connected with the connection vertical pipe is provided with a first connection end with an inclined surface on the steam inlet side, the first connection end is vertically fixedly connected with the first butt joint hole, and the inclined surface of the first connection end is vertically connected with the first butt joint hole through the first inclined shoulder part. Among them, all the lower layer branch pipes and the corresponding connection vertical pipes are connected through the first inclined shoulder part, and the inclined direction of the first inclined shoulder part is perpendicular to the direction of the inclined surface of the first connection end.

[0007] Optionally, the first circular arc tube is divided into a first weak cooling pipe section, a second weak cooling pipe section and a third weak cooling pipe section with continuously changing diameters along the direction from the connecting end to the closed end. The second circular arc tube is divided into a first strong cooling pipe section, a second strong cooling pipe section, a third strong cooling pipe section and a fourth strong cooling pipe section with continuously changing diameters along the direction from the connecting end to the closed end. The first weak cooling pipe section has the same diameter as the first strong cooling pipe section, and the first weak cooling pipe section and the first strong cooling pipe section have the same number of the connecting vertical pipes distributed thereon. The second weak cooling pipe section has the same diameter as the second strong cooling pipe section, and the second weak cooling pipe section and the second strong cooling pipe section have the same number of the connecting vertical pipes distributed thereon. The third weak cooling pipe section has the same diameter as the third strong cooling pipe section, and the third weak cooling pipe section and the third strong cooling pipe section have the same number of the connecting vertical pipes distributed thereon. The fourth strong cooling pipe section has a smaller diameter than the third strong cooling pipe section, and the fourth strong cooling pipe section is further provided with one of the connecting vertical pipes.

[0008] Optionally, the connecting vertical pipe is vertically arranged and has a smaller diameter than the mother pipe ring pipe, a second connecting hole is formed in the top pipe wall of the mother pipe ring pipe, and a second connecting end of the connecting vertical pipe connected to the end of the mother pipe ring pipe on the steam inflow side is provided with an inclined surface, the second connecting end is vertically fixed to the second connecting hole, and an inclined second shoulder part is arranged on the second connecting hole and is inclinedly connected to the inclined surface of the second connecting end. All the connecting vertical pipes on the first strong cooling pipe section, the second strong cooling pipe section, the third strong cooling pipe section and the first circular arc tube are provided with the second shoulder part on the steam inflow side of the end of the mother pipe ring pipe.

[0009] Optionally, the connecting vertical pipe on the second weak cooling pipe section located on the end diameter changing side and the second weak cooling pipe section located on the end diameter changing side has a first included angle between the inclined surface of the second connecting end and the second shoulder part, and the first included angle is smaller than a right angle. The connecting vertical pipe on the first weak cooling pipe section and the second weak cooling pipe section located on both sides of the diameter changing part, the third weak cooling pipe section located on the first end diameter changing side, the first strong cooling pipe section and the second strong cooling pipe section located on both sides of the diameter changing part, and the third strong cooling pipe section located on the first end diameter changing side has a second included angle between the inclined surface of the second connecting end and the second shoulder part, and the second included angle is smaller than the first included angle. All the connecting vertical pipes at the remaining positions have a right angle between the inclined surface of the second connecting end and the second shoulder part.

[0010] Optionally, a third connecting hole is formed in the top pipe wall of the mother pipe ring pipe, and the bottom end of part of the connection vertical pipe is connected to the third connecting hole through a second variable diameter part, and the second variable diameter part is a tapered structure with gradually changing pipe diameter. The end of the tee pipe fitting and the connection vertical pipe on the fourth strong cooling pipe section are connected to the mother pipe ring pipe through the second variable diameter part.

[0011] Optionally, the tee pipe fitting comprises a first pipe connection end connected to the air inlet main pipe, and a second pipe connection end and a third pipe connection end symmetrically and parallelly arranged along the central axis of the first pipe connection end, and an inclined pipe section is arranged on the first pipe connection end to connect the second pipe connection end and the third pipe connection end. The connecting end of the first circular arc pipe is vertically connected to and communicated with the second pipe connection end, and a plurality of arc-shaped first guide vanes are arranged side by side in the internal part of the vertical connection part of the first circular arc pipe and the second pipe connection end along the width direction, and a guide gap for guiding the steam in the air inlet main pipe into the first circular arc pipe is formed between adjacent two first guide vanes. The connecting end of the second circular arc pipe is vertically connected to and communicated with the third pipe connection end, and a plurality of arc-shaped second guide vanes are arranged side by side in the internal part of the vertical connection part of the second circular arc pipe and the third pipe connection end along the width direction, and a guide gap for guiding the steam in the air inlet main pipe into the second circular arc pipe is formed between adjacent two second guide vanes.

[0012] Optionally, the connection vertical pipe on the end of the tee pipe fitting is located on the second pipe connection end, and the upper layer branch pipe and the lower layer branch pipe on the corresponding branch are located on the central axis of the first pipe connection end.

[0013] The application further discloses a steam exhaust pipe optimization method for optimizing the steam exhaust pipe assembly in the natural ventilation air cooling system. A flow field simulation model of an initial structure of the steam exhaust pipe assembly is established, the initial structure comprising preset variable diameter sizes of each section of the mother pipe ring pipe and a preset direct connection mode for connecting each pipe. Flow distribution deviations between the upper layer branch pipe and the corresponding lower layer branch pipe of each branch in the initial structure are obtained through flow field simulation, and all branch pipes are proportionally divided according to the deviation degree. The influence of separately adjusting the variable diameter size of the mother pipe ring pipe and separately arranging a first inclined shoulder part on the steam inflow side of the lower layer branch pipe on the flow distribution deviation of each branch is compared through flow field simulation, and a structure optimization sequence is determined according to the comparison result. According to the determined structure optimization sequence, a first inclined shoulder is arranged on the steam inflow side of the connection between all the lower branch pipes and the corresponding connection riser, and the connection riser at the end of the tee pipe is connected to the mother pipe ring through a tapered reducer, to obtain a primary optimization structure; The reducer size of the mother pipe ring is iteratively adjusted based on the primary optimization structure, and the flow distribution between the mother pipe ring and the connection risers of each branch is verified through flow field simulation until the proportion of the flow distribution deviation of each branch tends to be optimal, to determine the optimized reducer size of each section of the mother pipe ring.

[0014] Optionally, after the reducer size optimization of each section of the mother pipe ring, the flow distribution between the mother pipe ring and the connection risers of each branch is structured, including: According to the optimized reducer size, the mother pipe ring in the primary optimization structure is adjusted to obtain a secondary optimization structure, and a second inclined shoulder is arranged on the steam inflow side of the connection between all the connection risers in the secondary optimization structure and the mother pipe ring; According to all the connection risers provided with the second inclined shoulder, the inclined shoulder angle at the reducer of each section of the mother pipe ring is iteratively adjusted, and the flow distribution of each branch is verified through flow field simulation until the proportion of the flow distribution deviation of each branch reaches a preset target proportion, to determine the optimized angle and position of the second inclined shoulder; The connection riser at the end of the second circular arc pipe is connected to the mother pipe ring through a tapered reducer, and the secondary optimization structure is adjusted according to the optimized angle and position of the second inclined shoulder, to obtain a target optimization structure.

[0015] Compared with the prior art, the natural ventilation air cooling system and the steam exhaust pipeline optimization method provided by the embodiments of the present application have the following beneficial effects: The intake main pipe and the mother pipe ring are efficiently connected through the tee pipe, and the asymmetric reducer structure of the first circular arc pipe and the second circular arc pipe is used for the mother pipe ring, so that the steam flow is more stable and the local resistance loss is reduced. The reducer sections arranged asymmetrically and the connection risers distributed asymmetrically cooperate to ensure uniform distribution of steam in the mother pipe ring, and avoid the problem that the steam flow at the front connection riser is significantly increased when the steam flows in the first circular arc pipe and the second circular arc pipe. In addition, the first inclined shoulder arranged in the lower branch pipe of the branch pipe can effectively reduce the flow difference between the upper and lower branch pipes, thereby significantly reducing the local resistance loss and improving the uniformity of the flow distribution. The steam can smoothly pass through the steam exhaust pipeline and be uniformly distributed to the air cooling condensers on the leeward side and the windward side of the ventilation tower, so as to improve the cooling effect, economy and operation stability of the entire system. BRIEF DESCRIPTION OF DRAWINGS

[0016] The technical solutions of the present application will be further described in detail below with reference to the accompanying drawings and embodiments. Figure 1 The overall structure schematic diagram of the exhaust pipe assembly in the natural ventilation air cooling system provided by the embodiment of the present application is shown in the figure. Figure 2 The structure schematic diagram of the cooperation of the first inclined shoulder part and the second inclined shoulder part provided by the embodiment of the present application is shown in the figure. Figure 3 The structure schematic diagram of the cooperation of the first inclined shoulder part and the second variable diameter part provided by the embodiment of the present application is shown in the figure. Figure 4 The structure schematic diagram of the tee pipe provided by the embodiment of the present application is shown in the figure. Figure 5 The upper and lower layer branch pipe flow distribution comparison curve diagram of the optimized structure thirteen and the initial structure simulation provided by the embodiment of the present application is shown in the figure.

[0017] The various marks in the figure represent as follows: 1, intake main pipe; 2, first circular arc pipe; 21, first weak cooling pipe section; 22, second weak cooling pipe section; 23, third weak cooling pipe section; 3, second circular arc pipe; 31, first strong cooling pipe section; 32, second strong cooling pipe section; 33, third strong cooling pipe section; 34, fourth strong cooling pipe section; 4, tee pipe; 41, first pipe joint end; 42, second pipe joint end; 43, third pipe joint end; 44, first guide vane; 45, second guide vane; 5, connection vertical pipe; 51, lower pipe body; 52, upper pipe body; 53, first variable diameter part; 54, guide bend part; 55, second connection end; 56, second inclined shoulder part; 57, second variable diameter part; 6, upper layer branch pipe; 7, lower layer branch pipe; 71, first inclined shoulder part; 72, first connection end. DETAILED DESCRIPTION

[0018] It should be noted that the embodiments in the present application and the features in the embodiments can be combined with each other without conflict. The preferred embodiments of the present application will be described in detail below with reference to the accompanying drawings.

[0019] The present application discloses a natural ventilation air cooling system, as shown in Figure 1 and Figure 2 , which comprises a steam turbine, an air cooling condenser and an exhaust pipe assembly. The intake main pipe 1 is connected with the steam turbine and connected with the mother pipe ring pipe through the tee pipe 4. The mother pipe ring pipe comprises a first circular arc pipe 2 and a second circular arc pipe 3 arranged oppositely and horizontally, one end of the first circular arc pipe 2 is closed, the other end is connected with one end of a three-way pipe fitting 4, and the pipe body of the first circular arc pipe 2 presents a multi-section variable diameter structure with gradually decreasing diameters from the connected end to the closed end, one end of the second circular arc pipe 3 is closed, the other end is connected with the other end of the three-way pipe fitting 4, and the pipe body of the second circular arc pipe 3 presents a multi-section variable diameter structure with gradually decreasing diameters from the connected end to the closed end, and the variable diameter sections of the first circular arc pipe 2 and the variable diameter sections of the second circular arc pipe 3 are asymmetrically arranged; A plurality of connection vertical pipes 5 are arranged on the first circular arc pipe 2 and the second circular arc pipe 3 along the steam flow direction respectively, and the connection vertical pipes 5 on the first circular arc pipe 2 and the second circular arc pipe 3 are asymmetrically distributed, and one connection vertical pipe 5 is further arranged on the end of the three-way pipe fitting 4 connected with the first circular arc pipe 2, for distributing the steam on the inlet side of the first circular arc pipe 2; A branch pipe is arranged on each connection vertical pipe 5, comprising an upper branch pipe 6 connected with the top end of the connection vertical pipe 5, and a lower branch pipe 7 connected with the middle part of the connection vertical pipe 5, and a first inclined shoulder part 71 is formed on the steam inflow side of the connection part of the lower branch pipe 7 and the connection vertical pipe 5, and each upper branch pipe 6 and lower branch pipe 7 on the first circular arc pipe 2 is connected with an air-cooled condenser arranged on the leeward side of the ventilation tower, and each upper branch pipe 6 and lower branch pipe 7 on the second circular arc pipe 3 is connected with an air-cooled condenser arranged on the windward side of the ventilation tower.

[0020] Through the implementation of the above natural ventilation air cooling system embodiment, the inlet main pipe 1 is connected with the mother pipe ring pipe through the three-way pipe fitting 4, so that the steam discharged from the steam turbine can be uniformly distributed to the first circular arc pipe 2 and the second circular arc pipe 3. The first circular arc pipe 2 and the second circular arc pipe 3 adopt a multi-section variable diameter structure, which conforms to the natural attenuation characteristics of the steam flow along the mother pipe ring pipe, and maintains the stability of the pipe flow rate through gradual diameter reduction. Preferably, the variable diameter sections are connected through variable diameter heads with gradually changing diameters, which can reduce the local resistance caused by sudden changes in pipe diameter, and ensure the continuity of the steam flow around the ring pipe. Based on this, the asymmetric structure of the variable diameter sections of the first circular arc pipe 2 and the second circular arc pipe 3 is aimed at the differences in working conditions between the windward side and the leeward side of the ventilation tower: the air flow on the windward side is sufficient, and the cooling efficiency is high, while the low pressure area is easy to form on the leeward side, and the cooling capacity is weak. Therefore, the asymmetric structure of the variable diameter sections of the first circular arc pipe 2 and the second circular arc pipe 3 is to adjust the flow resistance on both sides differently, for example: the first circular arc pipe 2 on the leeward side can adopt fewer variable diameter sections (relatively gentle change in pipe diameter) to appropriately increase the flow resistance of this path, and limit too much steam flow to the area with weak cooling capacity; while the second circular arc pipe 3 on the windward side optimizes the steam distribution through more variable diameter sections (more drastic change in pipe diameter), to fully utilize the potential of the high cooling efficiency area. This dynamic adaptation mechanism can effectively balance the system back pressure, and prevent local flow overload or deficiency caused by uneven environmental wind field.

[0021] As described above, the asymmetric distribution of the connection risers 5 on the first circular arc pipe 2 and the second circular arc pipe 3 further refines the flow distribution strategy. For example: the dense riser layout on the second circular arc pipe 3 can accommodate and disperse a large amount of steam flow, so as to uniformly distribute the steam to each air-cooled condenser (cooling triangle); the sparse riser layout on the first circular arc pipe 2 matches the lower cooling demand on the leeward side, and in combination with the additional connection riser 5 at the end of the tee pipe 4, the steam entering the first circular arc pipe 2 (leeward side) is diverted in advance. The independent connection riser 5 diverts part of the steam directly away from the first circular arc pipe 2, effectively reducing the steam flow load in the first circular arc pipe 2, and avoiding excessive steam from flowing into the leeward side area with limited cooling capacity. This structure seems to increase the connection riser 5 on the leeward side, but actually relieves the flow pressure of the main ring pipe on the leeward side by local drainage, indirectly prompting more steam to flow naturally through the tee pipe 4 to the leeward side with dense risers, i.e. the second circular arc pipe 3, thereby achieving optimal allocation of steam to high cooling efficiency areas at the system level to maintain stable system back pressure when the environmental wind field changes.

[0022] In addition, the branch pipe optimizes the steam distribution efficiency in the single connection riser 5 through the cooperative work of the upper layer branch pipe 6 and the lower layer branch pipe 7. The lower layer branch pipe 7 and the steam inflow side of the connection between the lower layer branch pipe 7 and the connection riser 5 form a first inclined shoulder 71 with an inclined guide. This structure guides the steam flow line through a smooth inclined surface, significantly reduces the flow velocity change and flow separation phenomenon at the turning point, effectively reduces the local resistance loss, and this guide action significantly suppresses the flow difference between the upper and lower layer branch pipes 7, ensuring the uniformity of the steam distribution to the same air-cooled condenser cooling triangle.

[0023] Therefore, the natural draft air-cooled system of the embodiment of the present application forms a complete flow regulation system through the initial diversion of the tee pipe 4, the variable-diameter stable flow of the mother pipe ring pipe, the macroscopic deployment of the asymmetric riser layout, and the flow guide optimization of the first inclined shoulder 71 of the lower layer branch pipe 7. This system further optimizes the flow uniformity at the branch pipe level through the inclined guide design of the first inclined shoulder 71, effectively solves the problems of uneven steam distribution and back pressure control faced by the natural draft direct air-cooled system after being upsized, and thereby realizes the spatial matching of steam supply and cooling demand, and significantly improves the operation economy, stability and reliability of the system under variable conditions and extreme environments.

[0024] Further, the connection riser 5 includes a lower pipe body 51 with a decreasing diameter from bottom to top and an upper pipe body 52, the upper pipe body 52 and the lower pipe body 51 are connected through a first variable-diameter portion 53, and the first variable-diameter portion 53 is a tapered structure with a gradually changing diameter. The upper layer branch pipe 6 is horizontally arranged and has the same diameter as the upper pipe body 52. The upper layer branch pipe 6 is integrally formed with the top end of the upper pipe body 52 and has an arc-shaped flow guide bend 54 at the joint. The lower layer branch pipe 7 is horizontally arranged and has a smaller diameter than the lower pipe body 51. The lower layer branch pipe 7 is connected to the end of the joint vertical pipe 5 and has a first joint end 72 with an inclined surface on the side of the steam flow. The first joint end 72 is vertically connected to the first joint hole, and the inclined surface of the first joint end 72 is connected to the first joint hole through the first inclined shoulder 71. All the lower layer branch pipes 7 are connected to the corresponding joint vertical pipes 5 through the first inclined shoulder 71, and the inclined direction of the first inclined shoulder 71 is perpendicular to the inclined surface direction of the first joint end 72.

[0025] The joint vertical pipe 5 is divided into the upper pipe body 52 and the lower pipe body 51 with different diameters, which is designed to adapt to the pressure decrease and flow velocity change of the steam flowing from bottom to top in the joint vertical pipe 5 to maintain the principle of equal flow velocity. The tapered structure of the first variable diameter part 53 realizes smooth transition of the pipe diameter, reduces the local resistance loss caused by sudden change of cross section, and promotes stable transition of the fluid.

[0026] As described above, the upper layer branch pipe 6 is integrally formed with the upper pipe body 52 and has an arc-shaped flow guide bend 54 at the joint, which can optimize the turning process of the steam at the top of the joint vertical pipe 5 to minimize the vortex and secondary flow phenomenon. In addition, the use of the first inclined shoulder 71 can optimize the flow velocity distribution of the fluid at the turning point of the lower layer branch pipe 7, significantly reduce the flow difference between the upper and lower layer branch pipes 7, and improve the uniformity of overall flow distribution. The inclined direction of the first inclined shoulder 71 is perpendicular to the inclined surface direction of the first joint end 72. This angle is optimized through flow field simulation to ensure that the fluid is cut in the best orthogonal matching with the main flow direction, minimize flow separation and energy dissipation, thereby significantly reduce the local resistance and improve the uniformity of flow distribution. Finally, by setting the first inclined shoulder 71 on all lower layer branch pipes 7, the flow difference between the upper and lower layer branch pipes 7 of each branch is systematically reduced to facilitate accurate control of the back pressure of the system as a whole and optimization of the cooling effect.

[0027] Further, referring back to Figure 1 , the first circular arc pipe 2 is divided into the first weak cooling pipe section 21, the second weak cooling pipe section 22 and the third weak cooling pipe section 23 with continuous variable diameters along the direction from the connection end to the closed end. The second circular arc pipe 3 is divided into the first strong cooling pipe section 31, the second strong cooling pipe section 32, the third strong cooling pipe section 33 and the fourth strong cooling pipe section 34 with continuous variable diameters along the direction from the connection end to the closed end. The first weak cooling pipe section 21 is consistent in pipe diameter with the first strong cooling pipe section 31, and the first weak cooling pipe section 21 and the first strong cooling pipe section 31 are distributed with the same number of connection vertical pipes 5; The second weak cooling pipe section 22 is consistent in pipe diameter with the second strong cooling pipe section 32, and the second weak cooling pipe section 22 and the second strong cooling pipe section 32 are distributed with the same number of connection vertical pipes 5; The third weak cooling pipe section 23 is consistent in pipe diameter with the third strong cooling pipe section 33, and the third weak cooling pipe section 23 and the third strong cooling pipe section 33 are distributed with the same number of connection vertical pipes 5; The fourth strong cooling pipe section 34 is smaller in pipe diameter than the third strong cooling pipe section 33, and the fourth strong cooling pipe section 34 is further provided with a connection vertical pipe 5.

[0028] Through the implementation of the above natural ventilation air cooling system embodiment, the smooth and gradual change of the first circular arc pipe 2 and the second circular arc pipe 3 effectively reduces the local resistance loss and promotes the stability of the steam flow. Secondly, the first weak cooling pipe section 21 is consistent in pipe diameter with the first strong cooling pipe section 31, and the first weak cooling pipe section 21 and the first strong cooling pipe section 31 are distributed with the same number of connection vertical pipes 5, which can ensure the basic symmetry of the flow distribution on both sides of the three-way pipe fitting 4 and reduce the flow deflection caused by environmental differences. The corresponding consistent design of the second weak cooling pipe section 22 and the second strong cooling pipe section 32 and the third weak cooling pipe section 23 and the third strong cooling pipe section 33 further strengthens the flow balance and reduces the deviation between the branch pipes. The fourth strong cooling pipe section 34 is smaller in pipe diameter than the third strong cooling pipe section 33 and is provided with an additional connection vertical pipe 5, which compensates for the flow attenuation at the end of the second circular arc pipe 3 and optimizes the overall distribution uniformity.

[0029] The above structure matches the cooling needs of the windward side and the leeward side through differentiated variable-diameter, and all the first inclined shoulder portions 71 provided on all the lower branch pipes 7 reduce eddy current and secondary flow, so as to realize accurate back pressure control and cooling efficiency improvement.

[0030] Further, as shown in Figure 1 and Figure 2 The connection vertical pipe 5 is vertically arranged and smaller in pipe diameter than the mother pipe ring pipe. A second connecting hole is formed in the top pipe wall of the mother pipe ring pipe. The end of the connection vertical pipe 5 connected to the mother pipe ring pipe is provided with a second connection end 55 with an inclined surface on the steam inflow side. The second connection end 55 is vertically fixedly connected to the second connecting hole, and the second connecting hole is provided with a second inclined shoulder portion 56 inclined to the inclined surface of the second connection end 55. All the connection vertical pipes 5 on the first strong cooling pipe section 31, the second strong cooling pipe section 32, the third strong cooling pipe section 33 and the first circular arc pipe 2 are provided with the second inclined shoulder portion 56 on the steam inflow side of the end connected to the mother pipe ring pipe.

[0031] Through the implementation of the natural draft air cooling system embodiment, the vertical arrangement of the connection vertical pipe 5 and the smaller pipe diameter than the mother pipe ring pipe promote the natural diffusion of steam, and the reasonable flow velocity gradient is formed by the difference in pipe diameter. Secondly, the second connection hole is arranged on the top pipe wall of the mother pipe ring pipe, and the second connection end 55 with the beveled surface of the connection vertical pipe 5 is vertically fixed. The inclined butt joint structure of the second inclined shoulder part 56 effectively reduces the flow separation phenomenon when the steam flows from the ring pipe to the vertical pipe, and can significantly improve the total flow of the branch, thereby uniformly distributing the flow of the branch pipe.

[0032] As described above, the first three strong cooling sections (the first strong cooling pipe section 31, the second strong cooling pipe section 32, and the third strong cooling pipe section 33) of the second circular arc pipe 3 are mainly distributed at the front end and the middle part of the windward side. Because the steam pressure in the pipe is high, the kinetic energy is sufficient, and the cooling capacity of the corresponding area is the strongest. Therefore, the connection vertical pipe 5 at these positions uses the second inclined shoulder part 56 as a streamlined flow guide, which can very efficiently and smoothly guide the high-speed steam in the mother pipe ring pipe into the corresponding branch connection vertical pipe 5, so that the steam can be quickly and low-resistance distributed to match the strong cooling capacity. The fourth strong cooling section 34 is located at the end of the second circular arc pipe 3, and the steam inside has the lowest pressure and kinetic energy after a long journey and multiple flow distribution, which is the most unfavorable working condition point that is most prone to flow separation and stall. Therefore, if the second inclined shoulder part 56 is still used for flow guiding at this position, the steam distribution effect will not be ideal, and other technical means need to be taken.

[0033] Meanwhile, the second inclined shoulder part 56 is used in the first circular arc pipe 2, and the uniform inclined shoulder structure can ensure that the steam entering the first circular arc pipe 2 is uniformly distributed to each branch connection vertical pipe 5, thereby performing uniform condensation to prevent local complete failure or local excessive congestion.

[0034] The specific arrangement of the inclined shoulder structure is determined based on flow field simulation, which makes the steam flow more smoothly when entering the connection vertical pipe 5, reduces vortex generation and energy dissipation, and provides continuous and stable steam supply conditions for the upper branch pipe 6 and the lower branch pipe 7, thereby enhancing the flow balance between the upper and lower branch pipes 7 of each branch, and finally realizing the optimal operation of the natural draft direct air cooling system in the full working condition range.

[0035] Further, the second connection end 55 of the connection vertical pipe 5, which is located at the end of the second strong cooling pipe section 32 and the end of the second weak cooling pipe section 22, has a beveled surface with a first included angle with the second inclined shoulder part 56, and the first included angle is smaller than a right angle. The second connection end 55 of the connection riser 5 at the two sides of the variable diameter of the first weak cooling pipe section 21 and the second weak cooling pipe section 22, the first end variable diameter side of the third weak cooling pipe section 23, the second connection end 55 of the connection riser 5 at the two sides of the variable diameter of the first strong cooling pipe section 31 and the second strong cooling pipe section 32, and the first end variable diameter side of the third strong cooling pipe section 33 has an included angle between the chamfer surface of the second connection end 55 and the second inclined shoulder 56 of the second included angle, and the second included angle is smaller than the first included angle. The connection riser 5 at the other positions has an included angle between the chamfer surface of the second connection end 55 and the second inclined shoulder 56 of a right angle.

[0036] Through the implementation of the natural ventilation air cooling system embodiment, in order to further optimize the flow distribution of steam from the mother pipe ring pipe into the connection riser 5, the angle of the second inclined shoulder 56 needs to be adjusted. However, adjusting the second inclined shoulder 56 of each connection riser 5 one by one is not conducive to engineering construction, so the second inclined shoulder 56 is particularly arranged at the two sides of the variable diameter of each section of the mother pipe ring pipe (including the first weak cooling pipe section 21 and the second weak cooling pipe section 22, the second weak cooling pipe section 22 and the third weak cooling pipe section 23, the first strong cooling pipe section 31 and the second strong cooling pipe section 32, and the second strong cooling pipe section 32 and the third strong cooling pipe section 33), the inherent flow velocity variation characteristics of the variable diameter area are utilized, the local flow field distribution is optimized through the inclined shoulder structure, and the steam passing capacity in the branch connection riser 5 is significantly improved. This targeted arrangement not only maintains the flow regulation effect, but also avoids the engineering complexity of the whole system inclined shoulder transformation through the precise optimization of key positions, makes the steam distribution in the variable diameter area more uniform, and finally realizes the cooperative optimization of system resistance reduction and back pressure stable control.

[0037] As described above, the connection riser 5 at different positions is provided with the second inclined shoulder 56 with a differential angle arrangement, for example: the first included angle of 75° is adopted at the connection riser 5 at the second strong cooling pipe section 32 located at the end variable diameter side and the second weak cooling pipe section 22 located at the end variable diameter side, a more gentle flow passage transition is formed by increasing the inclination angle of the chamfer surface and the second inclined shoulder 56, the flow separation tendency of high flow rate steam at the end of the pipe is effectively reduced, and the steam in the lowest pressure area of the system can enter the branch pipe more smoothly.

[0038] The second included angle of 60° is adopted at the connection riser 5 at the two sides of the variable diameter of the first weak cooling pipe section 21 and the second weak cooling pipe section 22, the first end variable diameter side of the third weak cooling pipe section 23, the two sides of the variable diameter of the first strong cooling pipe section 31 and the second strong cooling pipe section 32, and the first end variable diameter side of the third strong cooling pipe section 33, the acceleration effect and resistance loss caused by the sudden change of the cross section in the variable diameter area are balanced by the medium angle guide surface, necessary flow guidance is ensured, and excessive pressure drop is avoided. The connection riser 5 with a right angle design at the remaining positions ensures the structural simplicity and engineering economy in the stable flow field area.

[0039] The above three-level angle configuration system based on the functional positioning of the pipe section forms a systematic local resistance regulation mechanism: the 75° included angle mainly serves the flow stability guarantee of the low-pressure area at the end of the system, the 60° included angle focuses on the energy loss optimization of the variable-diameter transition area, and the right angle design is applicable to the conventional stable flow field area. Especially at key positions such as the end of the second strong cooling pipe section 32, the streamline design of the first included angle significantly improves the re-acceleration ability of the steam in the kinetic energy decay area, preventing vortex generation. In multiple variable-diameter junction areas, the precise setting of the second included angle not only weakens the longitudinal flow velocity gradient but also controls the development of transverse secondary flow, making the circumferential pressure distribution of the mother pipe ring more balanced. This differentiated oblique shoulder angle strategy matches the fluid dynamics characteristics of different pipe sections, realizes the precise adaptation of local resistance coefficient and overall flow demand, and finally makes the steam distribution ratio between the strong cooling area and the weak cooling area and the actual cooling capacity reach dynamic balance, thereby improving the adaptability of the system under variable working conditions.

[0040] The angle combination of the second connection end 55 and the second oblique shoulder part 56 of all the connection risers 5 constitutes a spatially distributed flow resistance regulation network, which actively shapes the pressure distribution pattern in the mother pipe ring through the carefully designed local loss characteristics at each node, lays a fluid dynamics foundation for uniform steam distribution at the branch pipe level, and thus realizes the synergistic optimization of back pressure control and cooling efficiency at the system level.

[0041] Further, as shown in Figure 1 and Figure 3 , a third connecting hole is provided on the top pipe wall of the mother pipe ring, and the bottom end of part of the connection riser 5 is connected to the third connecting hole through the second variable-diameter part 57, and the second variable-diameter part 57 is a tapered structure with gradually changing pipe diameter. Among them, the end of the three-way pipe fitting 4 and the connection riser 5 on the fourth strong cooling pipe section 34 are connected to the mother pipe ring through the second variable-diameter part 57.

[0042] By implementing the natural ventilation air cooling system embodiment, the partial connection vertical pipe 5 is connected to the third docking hole on the mother pipe ring pipe through the second reducing portion 57, which can achieve smooth transition of the pipe diameter to reduce the local resistance loss and fluid turbulence caused by sudden change of the cross section. Among them, the connection vertical pipe 5 at the end of the tee pipe 4 is connected to the mother pipe ring pipe through the second reducing portion 57, which can effectively reduce the local resistance loss in the early diversion process, so that more steam can smoothly pass through the independent diversion path and be guided away from the first circular arc pipe 2, and the backflow vortex generated by the steam impacting the tee blind plate can be effectively inhibited; at the same time, the connection vertical pipe 5 on the fourth strong cooling pipe section 34 is connected to the mother pipe ring pipe through the second reducing portion 57, which eliminates the flow separation phenomenon at the end of the mother pipe ring pipe caused by flow velocity decay, so that the steam at the end of the second circular arc pipe 3 can smoothly transition to the connection vertical pipe 5 of this path. The conical transition structure at the two key positions reduces the local resistance peak value of the high-speed impact area and the low-pressure end through the streamline flow guiding effect, so that the pressure distribution of the steam at the inlet section and the end section of the mother pipe ring pipe system is more balanced, thereby improving the flow distribution uniformity of the upper and lower branch pipes 7.

[0043] Further, as shown in Figure 1 and Figure 4 , the tee pipe 4 includes a first pipe connection end 41 connected to the inlet main pipe 1, and a second pipe connection end 42 and a third pipe connection end 43 symmetrically and parallelly arranged along the central axis of the first pipe connection end 41, and the first pipe connection end 41 extends a inclined pipe section to connect the second pipe connection end 42 and the third pipe connection end 43; The connection end of the first circular arc pipe 2 is vertically connected and communicated with the second pipe connection end 42, and a plurality of arc-shaped first flow guiding fins 44 are arranged side by side in the width direction inside the vertically connected part of the first circular arc pipe 2 and the second pipe connection end 42, and a flow guiding gap for guiding the steam in the inlet main pipe 1 into the first circular arc pipe 2 is formed between adjacent two first flow guiding fins 44. The connection end of the second circular arc pipe 3 is vertically connected and communicated with the third pipe connection end 43, and a plurality of arc-shaped second flow guiding fins 45 are arranged side by side in the width direction inside the vertically connected part of the second circular arc pipe 3 and the third pipe connection end 43, and a flow guiding gap for guiding the steam in the inlet main pipe 1 into the second circular arc pipe 3 is formed between adjacent two second flow guiding fins 45.

[0044] Further, referring back to Figure 1 , the connection vertical pipe 5 at the end of the tee pipe 4 is located on the second pipe connection end 42, and the upper branch pipe 6 and the lower branch pipe 7 of this path are both located on the central axis of the first pipe connection end 41.

[0045] Through the implementation of the above natural draft air cooling system embodiment, the symmetric extension structure of the inclined pipe section in the tee pipe fitting 4 is used to realize natural flow splitting of the steam flow, so that the inlet air main pipe 1 flow is evenly initially distributed at the second pipe joint end 42 and the third pipe joint end 43. The plurality of arc-shaped first flow guide vanes 44 arranged at the vertical joint of the first circular arc pipe 2 and the second pipe joint end 42 form a tapered flow guide gap, so that the steam generates a moderate pre-rotation when entering the first circular arc pipe 2, effectively eliminating vortex formation in the tee blind end area; at the same time, the second flow guide vanes 45 arranged at the second circular arc pipe 3 and the third pipe joint end 43 form matched flow conditions at the symmetric positions through the same flow guide gap. This symmetric flow guide vane layout not only maintains the dynamic balance of the inlet flow field of the left and right circular pipes, but also converts part of the dynamic pressure into static pressure through the special curvature design of the arc-shaped flow guide surface, significantly reducing the local resistance loss.

[0046] In addition, the connecting vertical pipe 5 located on the second pipe joint end 42 is symmetrically arranged along the central axis of the first pipe joint end 41 with the upper layer branch pipe 6 and the lower layer branch pipe 7, forming independent flow splitting channels. The connecting vertical pipe 5 cooperates with the first flow guide vane 44: the main flow steam guided by the first flow guide vane 44 uniformly diffuses along the circumference of the first circular arc pipe 2, and the connecting vertical pipe 5 directly splits part of the steam through the second pipe joint end 42. This double distribution mechanism precisely controls the steam load of the first circular arc pipe 2 (corresponding to the leeward side). When the environment wind causes the cooling capacity of the leeward side to decrease, the structure splits part of the steam to other areas in advance through the connecting vertical pipe 5, avoiding excessive steam retention in the leeward side system. At the same time, the first flow guide vane 44 ensures that the remaining steam maintains a stable flow state in the first circular arc pipe 2, preventing flow separation caused by reduced flow. This combination of flow guide and flow splitting structure enables the system to always maintain optimal flow distribution characteristics under variable operating conditions.

[0047] As described above, the symmetric flow guide vanes inside the tee pipe fitting 4 can ensure balanced basic flow field, and the special connecting vertical pipe 5 on the second pipe joint end 42 provides dynamic adjustment capability, both of which together constitute a composite solution to the influence of environmental wind. The entire structure realizes pressure loss minimization through flow field refinement, and the total pressure drop of the steam in the tee area is greatly reduced, and the left and right circular pipe flow deviation can be stably controlled within 3%, significantly improving the operation stability and economy of the natural draft direct air cooling system under complex wind field conditions.

[0048] The application also discloses a steam exhaust pipe optimization method for optimizing the steam exhaust pipe assembly in the natural draft air cooling system. A flow field simulation model of an initial structure of the steam exhaust pipe assembly is established, the initial structure including preset variable diameter sizes of each section of the mother pipe and the circular pipe, and a preset direct connection mode connecting each pipe; Obtain the flow distribution deviation between the upper branch pipe 6 and the corresponding lower branch pipe 7 of each branch in the initial structure through flow field simulation, and divide all branch pipes according to the proportion of the deviation degree; Compare the influence of separately adjusting the variable diameter size of the mother pipe ring pipe and separately setting the first inclined shoulder part 71 on the steam inflow side of the lower branch pipe 7 on the flow distribution deviation of each branch through flow field simulation, and determine the structure optimization sequence according to the comparison result; According to the determined structure optimization sequence, set the first inclined shoulder part 71 on the steam inflow side of the connection between all lower branch pipes 7 and corresponding connection riser pipes 5, and connect the connection riser pipe 5 at the end of the tee pipe 4 to the mother pipe ring pipe through the tapered variable diameter part to obtain a primary optimization structure; Based on the primary optimization structure, iteratively adjust the variable diameter size of the mother pipe ring pipe, and verify through flow field simulation until the proportion of the flow distribution deviation of each branch tends to be optimal, and determine the optimized variable diameter size of each section of the mother pipe ring pipe.

[0049] Further, the steam exhaust pipeline optimization method further includes structuring the flow distribution between the mother pipe ring pipe and each branch connection riser pipe 5 after optimizing the variable diameter size of each section of the mother pipe ring pipe, including: Adjust the mother pipe ring pipe in the primary optimization structure according to the optimized variable diameter size to obtain a secondary optimization structure, and set a second inclined shoulder part 56 on the steam inflow side of the connection between all connection riser pipes 5 in the secondary optimization structure and the mother pipe ring pipe; Iteratively adjust the inclined shoulder angle at the variable diameter of each section of the mother pipe ring pipe according to all connection riser pipes 5 provided with the second inclined shoulder part 56, and verify through flow field simulation until the proportion of the flow distribution deviation of each branch reaches a preset target proportion to determine the optimized angle and optimized position of the second inclined shoulder part 56; Connect the connection riser pipe 5 at the end of the second circular arc pipe 3 to the mother pipe ring pipe through the tapered variable diameter part, and adjust the secondary optimization structure according to the optimized angle and optimized position of the second inclined shoulder part 56 to obtain a target optimization structure.

[0050] The steam exhaust pipeline optimization method of the embodiment of the application is further illustrated by a specific simulation experiment: 1, Set the unit operation conditions, as shown in the unit operation condition table of Table 1: Table 1 Unit Operation Condition Table

[0051] In Table 1, THA (Turbine Heat Acceptance) is used to evaluate the system's efficiency and flow distribution under standard conditions; TRL (Turbine Rated Load) is used to verify whether the exhaust pipe can maintain good flow uniformity under high pressure differential when the cooling capacity is worst (such as the leeward effect caused by strong summer winds), preventing some branches from being "blocked" due to excessive back pressure; VWO (Valve Wide Open) and TMCR (Turbine Maximum Continuous Rating) are used to verify the exhaust pipe's pressure resistance, vibration, and whether it can still maintain flow distribution uniformity at high flow rates under maximum steam flow.

[0052] 2. For the initial structure of the exhaust pipe assembly, the diameter of the main pipe ring is a gradually changing structure, with design diameters of 6020mm, 4220mm, 3020mm, and 2020mm. For ease of analysis, as follows... Figure 1 As shown, the branch lines containing each connecting riser 5 are numbered in a counter-clockwise direction. Connecting riser 5 number 1 is located at the T-junction at the tower entrance; connecting risers 5 numbered 2-8 correspond to the first strong cooling pipe section 31, with a pipe diameter of 6020mm; connecting risers 5 numbered 9-13 correspond to the second strong cooling pipe section 32, with a pipe diameter of 4220mm; connecting risers 5 numbered 16-19 correspond to the third strong cooling pipe section 33, with a pipe diameter of 3020mm; connecting riser 5 numbered 20 correspond to the fourth strong cooling pipe section 34, with a pipe diameter of 2020mm; connecting risers 5 numbered 21-26 correspond to the third weak cooling pipe section 23, with a pipe diameter of 3020mm; connecting risers 5 numbered 27-31 correspond to the second weak cooling pipe section 22, with a pipe diameter of 4220mm; connecting risers 5 numbered 32-38 correspond to the first weak cooling pipe section 21, with a pipe diameter of 6020mm.

[0053] Simulation results show that the initial structure of the exhaust pipe assembly includes 76 branch pipes (38 upper branch pipes 6 and 38 lower branch pipes 7). The relative flow deviation between the upper and lower branch pipes 7 exceeds 10% in 53% (40 branch pipes), is controlled between 5% and 10% in 38% (29 branch pipes), and is controlled within 5% in 9% (7 branch pipes). Overall, the flow rate of the upper and lower branch pipes 7 is lower than that of the upper branch pipe 6 in each branch. Therefore, the initial structure of the exhaust pipe assembly has considerable room for optimization.

[0054] 3. Based on the operational experience of ACC (AirCooled Condenser, direct air-cooled system), the optimization objectives for the NDC exhaust piping are shown in Table 2: Table 2 Structural Optimization Objectives

[0055] Therefore, the steam exhaust pipeline optimization method of the embodiment of the present application aims to provide a steam exhaust pipe assembly structure of a natural draft cooling system to solve the problems of uneven flow distribution and difficult back pressure control of the steam cooling system after the NDC system is upsized.

[0056] 4. Optimization structure one: The optimization divides the mother pipe ring pipe according to the pipe diameter according to the equal flow rate principle, and first adjusts the pipe diameter of each partition. In the optimization structure one, the pipe diameter of the mother pipe ring pipe is changed from 6020 mm, 4220 mm, 3020 mm and 2020 mm to 5820 mm, 4720 mm, 3520 mm and 2020 mm. From the simulation results, it can be seen that the flow field distribution of the optimization structure one is similar to that of the initial structure as a whole. The pressure at the necking portion of the inlet main pipe 1 is reduced, and the flow rate is increased. In the optimization structure one, the relative deviation of the flow rate of 57% (43 routes) of the upper and lower layer branch pipes 7 exceeds 10%, the relative deviation of the flow rate of 24% (18 routes) of the upper and lower layer branch pipes 7 is controlled within 5%-10%, and the relative deviation of the flow rate of 19% (15 routes) of the upper and lower layer branch pipes 7 is controlled within 5%. Compared with the initial structure, it can be found that the flow distribution is uniformized to a certain extent, but the overall difference is still large.

[0057] 5. Optimization structure two: On the basis of the optimization structure one, a first inclined shoulder portion 71 is arranged on all the lower layer branch pipes 7, and the pipe diameter of the mother pipe ring pipe is the same as that of the optimization structure one. From the simulation results, it can be seen that the flow field distribution of the optimization structure two is similar to that of the initial structure as a whole, the concave surface pressure of the flow guide vane in the three-way pipe fitting 4 is larger, and the convex surface pressure is smaller. The pressure at the necking portion of the inlet main pipe 1 is reduced, and the flow rate is increased. In the optimization structure two, the relative deviation of the flow rate of 9% (7 routes) of the upper and lower layer branch pipes 7 exceeds 10%, the relative deviation of the flow rate of 28% (21 routes) of the upper and lower layer branch pipes 7 is controlled within 5%-10%, and the relative deviation of the flow rate of 63% (48 routes) of the upper and lower layer branch pipes 7 is controlled within 5%.

[0058] 6. Optimization structure three: The optimization structure three is based on the optimization structure one, and only verifies the influence of pipe diameter adjustment on the flow distribution of each branch. The pipe diameter of the mother pipe ring pipe is changed from 6020 mm, 4220 mm, 3020 mm and 2020 mm to 5820 mm, 4520 mm, 3220 mm and 2020 mm, and the rest is the same as the initial structure.

[0059] From the simulation results, it can be seen that the flow field distribution of the optimized structure three is similar to the initial structure as a whole, the concave surface pressure of the flow guide vane in the tee pipe 4 is larger, and the convex surface pressure is smaller. The pressure decreases and the flow velocity increases at the neck of the inlet main pipe 1. In the optimized structure three: the relative deviation of the flow of 56% (42 routes) of the upper and lower layer branch pipes 7 exceeds 10%, the relative deviation of the flow of 18% (14 routes) of the upper and lower layer branch pipes 7 is controlled within 5%-10%, and the relative deviation of the flow of 26% (20 routes) of the upper and lower layer branch pipes 7 is controlled within 5%.

[0060] 7、Optimized structure four: The optimized structure four is based on the optimized structure two, only adjusts the 20th connecting vertical pipe 5 to set the second variable diameter part 57, and the pipe diameter of the mother pipe ring pipe is 5820mm, 4520mm, 3220mm, 2020mm (the same as the optimized structure three).

[0061] From the simulation results, it can be seen that the flow field distribution of the optimized structure four is similar to the initial structure as a whole, the concave surface pressure of the flow guide vane in the tee pipe 4 is larger, and the convex surface pressure is smaller. The pressure decreases and the flow velocity increases at the neck of the inlet main pipe 1. In the optimized structure four: the relative deviation of the flow of 6% (5 routes) of the upper and lower layer branch pipes 7 exceeds 10%, the relative deviation of the flow of 25% (19 routes) of the upper and lower layer branch pipes 7 is controlled within 5%-10%, and the relative deviation of the flow of 69% (52 routes) of the upper and lower layer branch pipes 7 is controlled within 5%. By setting the second variable diameter part 57 of the 20th connecting vertical pipe 5, the flow distribution unevenness of the route can be obviously reduced.

[0062] 8、Optimized structure five: The optimized structure five is further adjusted in pipe diameter on the basis of the optimized structure four, the pipe diameter of the mother pipe ring pipe is changed from 6020mm, 4220mm, 3020mm, 2020mm to 5820mm, 4520mm, 3220mm, 2020mm, and the rest is the same as the optimized structure four.

[0063] From the simulation results, it can be seen that the flow field distribution of the optimized structure five is similar to the initial structure as a whole, the concave surface pressure of the flow guide vane in the tee pipe 4 is larger, and the convex surface pressure is smaller. The pressure decreases and the flow velocity increases at the neck of the inlet main pipe 1. In the optimized structure five: the relative deviation of the flow of 49% (37 routes) of the upper and lower layer branch pipes 7 exceeds 10%, the relative deviation of the flow of 18% (14 routes) of the upper and lower layer branch pipes 7 is controlled within 5%-10%, and the relative deviation of the flow of 33% (25 routes) of the upper and lower layer branch pipes 7 is controlled within 5%.

[0064] 9、Optimized structure six: Optimization structure six is adjusting the pipe diameter on the basis of optimization structure four, the pipe diameter of the mother pipe ring pipe is changed from 6020mm, 4220mm, 3020mm, 2020mm to 5620mm, 4720mm, 3420mm, 2220mm, and the rest is the same as optimization structure four.

[0065] From the simulation results, it can be seen that the flow field distribution of the optimization structure is similar to that of the initial structure, the concave surface pressure of the flow guide vane in the tee pipe 4 is larger, and the convex surface pressure is smaller. The pressure decreases and the flow velocity increases at the neck of the inlet main pipe 1. In optimization structure six, the relative deviation of the flow of 10% (8 routes) of the upper and lower layer branch pipes 7 exceeds 10%, the relative deviation of the flow of 25% (19 routes) of the upper and lower layer branch pipes 7 is controlled within 5%-10%, and the relative deviation of the flow of 65% (49 routes) of the upper and lower layer branch pipes 7 is controlled within 5%.

[0066] 10、Optimization structure seven: Optimization structure seven adjusts the pipe diameter on the basis of optimization structure four, the pipe diameter of the mother pipe ring pipe is changed from 6020mm, 4220mm, 3020mm, 2020mm to 5820mm, 4520mm, 3220mm, 2020mm, and all the lower layer branch pipes 7 are provided with the first inclined shoulder part 71.

[0067] From the simulation results, it can be seen that the flow field distribution of the optimization structure is similar to that of the initial structure, the concave surface pressure of the flow guide vane in the tee pipe 4 is larger, and the convex surface pressure is smaller. The pressure decreases and the flow velocity increases at the neck of the inlet main pipe 1. In optimization structure seven, the relative deviation of the flow of 8% (6 routes) of the upper and lower layer branch pipes 7 exceeds 10%, the relative deviation of the flow of 29% of the branch pipes (22 routes) is controlled within 5%-10%, and the relative deviation of the flow of 63% of the branch pipes (48 routes) is controlled within 5%.

[0068] 11、Optimization structure eight: Optimization structure eight selects the pipe diameter of the mother pipe to be 5720mm, 4520mm, 3120mm, 2020mm, all the lower layer branch pipes 7 are provided with the first inclined shoulder part 71, each branch road is directly connected with the mother pipe ring pipe, and the rest is the same as optimization structure seven.

[0069] From the simulation results, it can be seen that the flow field distribution of the optimization structure is similar to that of the initial structure, the concave surface pressure of the flow guide vane in the tee pipe 4 is larger, and the convex surface pressure is smaller. The pressure decreases and the flow velocity increases at the neck of the inlet main pipe 1. In optimization structure eight, the relative deviation of the flow of 10% (8 routes) of the upper and lower layer branch pipes 7 exceeds 10%, the relative deviation of the flow of 28% of the branch pipes (21 routes) is controlled within 5%-10%, and the relative deviation of the flow of 63% of the branch pipes (47 routes) is controlled within 5%.

[0070] 12、Optimization structure nine: For the optimization structure nine, the pipe diameter of the mother pipe ring is 5820mm, 4520mm, 3220mm, 2020mm, the second inclined shoulder 56 of 8, 13, 27, 32 is 90 degrees, the height is 710mm, the second variable diameter part 57 of 19 is set, and the rest is the same as the optimization structure seven.

[0071] From the simulation results, it can be seen that the flow field distribution of the optimization structure nine is similar to the initial structure, the concave surface pressure of the flow guide blade in the tee pipe 4 is larger, the convex surface pressure is smaller, the pressure of the neck part of the inlet main pipe 1 is reduced, and the flow velocity is increased. In the optimization structure nine, the relative deviation of the flow of 10% (8 routes) upper and lower layer branch pipes 7 exceeds 10%, the relative deviation of the flow of 23% (17 routes) upper and lower layer branch pipes 7 is controlled within 5%-10%, and the relative deviation of the flow of 67% (51 routes) upper and lower layer branch pipes 7 is controlled within 5%.

[0072] 13, optimization structure ten: The optimization structure ten is based on the optimization structure nine, the second inclined shoulder 56 of 8, 13, 27, 32 is 90 degrees, the height is 350mm, the second variable diameter part 57 of 19 is set, and the rest is the same as the optimization structure nine.

[0073] From the simulation results, it can be seen that the flow field distribution of the optimization structure ten is similar to the initial structure, the concave surface pressure of the flow guide blade in the tee pipe 4 is larger, the convex surface pressure is smaller, the pressure of the neck part of the inlet main pipe 1 is reduced, and the flow velocity is increased. In the optimization structure ten, the relative deviation of the flow of 4% (3 routes) upper and lower layer branch pipes 7 exceeds 10%, the relative deviation of the flow of 24% (18 routes) upper and lower layer branch pipes 7 is controlled within 5%-10%, and the relative deviation of the flow of 72% (55 routes) upper and lower layer branch pipes 7 is controlled within 5%.

[0074] 14, optimization structure eleven: The optimization structure eleven is based on the optimization structure nine, the second inclined shoulder 56 of 8, 13, 27, 32 is 75 degrees, the height is 350mm, the second variable diameter part 57 of 19 is set, and the rest is the same as the optimization structure nine.

[0075] From the simulation results, it can be seen that the flow field distribution of the optimization structure eleven is similar to the initial structure, the concave surface pressure of the flow guide blade in the tee pipe 4 is larger, the convex surface pressure is smaller, the pressure of the neck part of the inlet main pipe 1 is reduced, and the flow velocity is increased. In the optimization structure eleven, the relative deviation of the flow of 3% (2 routes) upper and lower layer branch pipes 7 exceeds 10%, the relative deviation of the flow of 22% (17 routes) branch pipes is controlled within 5%-10%, and the relative deviation of the flow of 75% (57 routes) branch pipes is controlled within 5%.

[0076] 15, optimization structure twelve: The optimization structure twelve is based on the optimization structure nine, the second inclined shoulder 56 of the connecting vertical pipe 5 at No. 8 and 32, No. 9 and 31, No. 13 and 27, and No. 14 and 26 is continuously reduced to 60 degrees, the height is 350 mm, and the second reducing part 57 is arranged at the connecting vertical pipe 5 at No. 19.

[0077] It can be seen from the simulation result that the flow field distribution of the optimization structure twelve is similar to the initial structure in general, the concave surface pressure of the flow guide vane in the tee pipe 4 is relatively large, and the convex surface pressure is relatively small. The pressure at the necking part of the inlet main pipe 1 is reduced, and the flow rate is increased. In the optimization structure twelve, the relative deviation of the flow rate of the upper and lower layer branch pipes 7 at 1% (1 route) is more than 10%, the relative deviation of the flow rate of the upper and lower layer branch pipes 7 at 15% (11 routes) is controlled within 5%-10%, and the relative deviation of the flow rate of the upper and lower layer branch pipes 7 at 83% (64 routes) is controlled within 5%.

[0078] 16. The optimization structure thirteen: The optimization structure thirteen is based on the optimization structure nine, the second inclined shoulder 56 of the connecting vertical pipe 5 at No. 13 and 27 is 75 degrees, the second inclined shoulder 56 of the connecting vertical pipe 5 at No. 8 and 32, No. 9 and 31, and No. 14 and 26 is 60 degrees, and the second reducing part 57 is arranged at the connecting vertical pipe 5 at No. 1 and 19.

[0079] It can be seen from the simulation result that the flow field distribution of the optimization structure thirteen is similar to the initial structure in general, the concave surface pressure of the flow guide vane in the tee pipe 4 is relatively large, and the convex surface pressure is relatively small. The pressure at the necking part of the inlet main pipe 1 is reduced, and the flow rate is increased. In the optimization structure thirteen, the relative deviation of the flow rate of the upper and lower layer branch pipes 7 at 0% (0 route) is more than 10%, the relative deviation of the flow rate of the upper and lower layer branch pipes 7 at 11% (8 routes) is controlled within 5%-10%, and the relative deviation of the flow rate of the upper and lower layer branch pipes 7 at 89% (68 routes) is controlled within 5%. After the adjustment and optimization of the diameter of the mother pipe ring pipe and the inclined shoulder at each position, the flow deviation of most of the upper and lower layer branch pipes 7 can be limited within 5%, and the overall flow change between the connecting vertical pipes 5 of each branch is relatively smooth (see Figure 5 ). The pressure drop of the optimization structure thirteen at each working condition is shown in the following table 3: Table 3: Summary table of pressure drop at each working condition

[0080] As shown in table 3, the back pressure of the optimization structure thirteen is lower than the target value, and the structure optimization achieves the expected effect. Therefore, the structure of the optimization structure thirteen is used as the final optimization scheme of the embodiment of the present application.

[0081] It should be understood that the above examples are only used to illustrate the technical solutions of the present application, but not limit the technical solutions of the present application. Those skilled in the art can modify the technical solutions described in the above examples, or make equivalent replacements to some of the technical features. All these modifications and replacements shall belong to the protection scope of the present application.

Claims

1. A natural ventilation air-cooling system, characterized in that, The natural ventilation air-cooling system includes a steam turbine, an air-cooled condenser, and an exhaust pipe assembly, wherein the exhaust pipe assembly includes an intake main pipe, a main pipe ring pipe, and branch pipes. The main intake pipe is connected to the steam turbine and is connected to the main pipe ring pipe through a tee fitting; The main pipe ring includes a first arc pipe and a second arc pipe arranged opposite to each other and horizontally. One end of the first arc pipe is closed, and the other end is connected to one end of the tee fitting. The pipe body of the first arc pipe has a variable diameter structure with multiple segments whose diameter decreases sequentially from its connecting end to its closed end. One end of the second arc pipe is closed, and the other end is connected to the other end of the tee fitting. The pipe body of the second arc pipe has a variable diameter structure with multiple segments whose diameter decreases sequentially from its connecting end to its closed end. The variable diameter segments of the first arc pipe and the variable diameter segments of the second arc pipe are arranged asymmetrically. Multiple connecting risers are respectively provided on the first arc pipe and the second arc pipe along the steam flow direction, and the multiple connecting risers on the first arc pipe and the second arc pipe are asymmetrically distributed. A connecting riser is also provided at the end of the tee fitting that connects to the first arc pipe for diverting the steam on the inlet side of the first arc pipe. The branch pipes are respectively installed on each of the connecting risers, including an upper branch pipe connected to the top of the connecting riser and a lower branch pipe connected to the middle of the connecting riser. The steam flow side of the lower branch pipe at the connection with the connecting riser forms a first inclined shoulder for oblique flow guidance. Each of the upper and lower branch pipes on the first arc pipe is connected to the air condenser preset on the leeward side of the ventilation tower. Each of the upper and lower branch pipes on the second arc pipe is connected to the air condenser preset on the windward side of the ventilation tower.

2. The natural ventilation air-cooling system according to claim 1, characterized in that: The connecting riser includes a lower pipe body and an upper pipe body with decreasing diameter from bottom to top. The upper pipe body and the lower pipe body are connected by a first diameter-changing section, which is a tapered structure with a gradually changing diameter. The upper branch pipe is laid horizontally, and its diameter is the same as that of the upper pipe body. The top of the upper branch pipe and the upper pipe body are integrally formed, and an arc-shaped guide bend is formed at the joint. The lower branch pipe is laid horizontally, and its diameter is smaller than that of the lower pipe body. A first docking hole is opened on the side wall of the lower pipe body. The end of the lower branch pipe that connects to the connecting riser is a first connecting end with a beveled surface on the steam flow side. The first connecting end is vertically fixed to the first docking hole, and the beveled surface of the first connecting end is obliquely docked with the first docking hole through the obliquely set first oblique shoulder. All of the lower branch pipes are connected to the corresponding connecting risers through the first inclined shoulder, and the inclined direction of the first inclined shoulder is perpendicular to the inclined tangent direction of the first connecting end.

3. The natural ventilation air-cooling system according to claim 1, characterized in that: The first arc pipe is divided into a first weak cooling pipe section, a second weak cooling pipe section and a third weak cooling pipe section with continuously changing diameter along the direction from its connecting end to its closed end. The second arc pipe is divided into a first, second, third and fourth strongly cooled pipe sections with continuously varying diameters along the direction from its connecting end to its closed end. The first weak cooling pipe section has the same pipe diameter as the first strong cooling pipe section, and the number of connecting risers distributed on the first weak cooling pipe section and the first strong cooling pipe section is the same. The second weak cooling pipe section has the same pipe diameter as the second strong cooling pipe section, and the number of connecting risers distributed on the second weak cooling pipe section and the second strong cooling pipe section is the same. The third weak cooling pipe section has the same pipe diameter as the third strong cooling pipe section, and the number of connecting risers distributed on the third weak cooling pipe section and the third strong cooling pipe section is the same. The diameter of the fourth forced cooling pipe section is smaller than that of the third forced cooling pipe section, and a connecting riser is also provided on the fourth forced cooling pipe section.

4. The natural ventilation air-cooling system according to claim 3, characterized in that: The connecting riser is vertically arranged and its diameter is smaller than that of the main pipe ring pipe. A second docking hole is opened on the top pipe wall of the main pipe ring pipe. The end of the connecting riser that connects to the main pipe ring pipe is a second connecting end with a beveled surface on the steam flow side. The second connecting end is vertically fixed to the second docking hole, and a beveled second shoulder is provided on the second docking hole to be obliquely docked with the beveled surface of the second connecting end. The first strong cooling pipe section, the second strong cooling pipe section, the third strong cooling pipe section, and all the connecting risers on the first arc pipe are provided with a second inclined shoulder on the steam flow side of the end of the main pipe ring pipe.

5. The natural ventilation air-cooling system according to claim 4, characterized in that: The connecting riser where the second strong cooling pipe section is located on the end diameter change side and the second weak cooling pipe section is located on the end diameter change side has a first included angle between the chamfered surface of the second connecting end and the second chamfered shoulder, and the first included angle is less than a right angle. The connecting risers on both sides of the diameter change point between the first weak cooling pipe section and the second weak cooling pipe section, the third weak cooling pipe section located at the first diameter change point, the first strong cooling pipe section and the second strong cooling pipe section on both sides of the diameter change point, and the third strong cooling pipe section located at the first diameter change point, have a second included angle between the chamfered surface of the second connecting end and the second chamfered shoulder, and the second included angle is smaller than the first included angle. For all other connecting risers, the angle between the chamfered surface of the second connecting end and the second chamfered shoulder is a right angle.

6. The natural ventilation air-cooling system according to claim 4, characterized in that: The top wall of the main pipe ring is provided with a third docking hole, and the bottom end of part of the connecting riser is connected to the third docking hole through a second diameter changing part, which is a tapered structure with a gradually changing pipe diameter. The end of the tee fitting and the connecting riser on the fourth cooling pipe section are both connected to the main pipe ring pipe through the second reducing part.

7. The natural ventilation air-cooling system according to claim 1, characterized in that: The tee fitting includes a first pipe end that connects to the main intake pipe, and a second pipe end and a third pipe end that are symmetrically and parallel to each other along the central axis of the first pipe end. An oblique pipe section extends from the first pipe end and connects to the second pipe end and the third pipe end respectively. The connecting end of the first arc tube is perpendicularly connected to and communicates with the connecting end of the second tube. Inside the perpendicular connection between the first arc tube and the connecting end of the second tube, a plurality of arc-shaped first guide vanes are arranged side by side along its width direction. A guide gap is formed between two adjacent first guide vanes to guide the steam in the main intake pipe into the first arc tube. The connecting end of the second arc tube is perpendicularly connected to and communicates with the third tube connection end. Inside the part where the second arc tube is perpendicularly connected to the third tube connection end, multiple arc-shaped second guide vanes are arranged side by side along its width direction. A guide gap is formed between two adjacent second guide vanes to guide the steam in the main intake pipe into the second arc tube.

8. The natural ventilation air-cooling system according to claim 7, characterized in that: The connecting riser at the end of the tee fitting is located on the second pipe connection end, and the upper branch pipe and the lower branch pipe on the corresponding branch are both located on the central axis of the first pipe connection end.

9. A method for optimizing exhaust pipes, used to optimize the exhaust pipe assembly in the natural ventilation air-cooled system according to any one of claims 1-8, characterized in that, The exhaust pipe optimization method includes: Establish a flow field simulation model of the initial structure of the exhaust pipe assembly. The initial structure includes the preset diameter variation dimensions of each section of the main pipe ring pipe, and the preset direct connection method for connecting each pipe. The flow distribution deviation between the upper branch pipe and the corresponding lower branch pipe in each branch of the initial structure is obtained by flow field simulation, and the proportion of all branch pipes is divided according to the degree of deviation. The effects of individually adjusting the diameter of the main pipe ring pipe and individually setting the first inclined shoulder on the steam inlet side of the lower branch pipe on the flow distribution deviation of each path were compared by flow field simulation, and the structural optimization sequence was determined based on the comparison results. According to the determined structural optimization sequence, a first inclined shoulder is provided on the steam flow side of the connection between all the lower branch pipes and the corresponding connecting risers, and the connecting riser at the end of the tee fitting is connected to the main pipe ring pipe through a tapered reducing part to obtain the primary optimized structure; Based on the initial optimization structure, the diameter of the main pipe ring pipe is iteratively adjusted, and the optimized diameter of each section of the main pipe ring pipe is determined after the proportion of the flow distribution deviation of each path approaches the optimal ratio through flow field simulation verification.

10. The exhaust pipe optimization method according to claim 9, characterized in that, The exhaust pipe optimization method further includes optimizing the diameter variation dimensions of each section of the main pipe ring pipe, and then structuring the flow distribution between the main pipe ring pipe and the connecting risers of each branch, including: The primary optimized structure is obtained by adjusting the main pipe ring pipe in the primary optimized structure according to the optimized diameter size, and a secondary optimized structure is obtained. For all the connecting risers in the secondary optimized structure, a second inclined shoulder is provided on the steam flow side at the connection between the main pipe ring pipe and the riser. Based on all the connecting risers with the second inclined shoulder, the inclined shoulder angle at the diameter change point of each section of the main pipe ring is iteratively adjusted, and the flow field simulation is used to verify until the proportion of the flow distribution deviation of each path reaches the preset target proportion, thereby determining the optimized angle and optimized position of the second inclined shoulder; The connecting riser at the end of the second arc pipe is connected to the main pipe ring pipe through a tapered diameter reducing part, and the secondary optimization structure is adjusted according to the optimized angle and optimized position of the second inclined shoulder to obtain the target optimized structure.

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