An optimization method for connection mode and spatial arrangement of a power plant flue gas system

Abstract

The application discloses an optimization method for the connection mode and spatial arrangement of a power plant flue gas system, and the power plant flue gas system is one of the most important systems of a power plant, mainly including a primary air duct, a secondary air duct, a flue and a powder feeding pipeline. The application finds out the components with relatively large resistance, unreasonable connection mode and spatial arrangement mode by respectively simulating and calculating each part of the air duct, analyzing and optimizing the primary air duct, the secondary air duct, the flue and the powder feeding pipeline of the existing power plant flue gas system, and putting forward a spatial arrangement mode with relatively small resistance, so that the optimization operation purpose is achieved. After the improvement is completed, the design level of the boiler flue gas, air and coal powder pipeline of the power plant and the actual operation efficiency of the fan are improved, and the optimization operation and energy saving and emission reduction of the power plant have very important significance.

Description

Technical Field

[0001] This invention relates to an optimization technique for a power plant flue gas system, specifically an optimization method for the connection method and spatial layout of the power plant flue gas system. Background Technology

[0002] The flue gas system is one of the most critical systems in a power plant, and its stable operation significantly impacts the plant's economic efficiency and overall stability. Current economic studies of power plants fail to recognize the importance of flue gas duct design and resistance calculation. The existing research methods for power plant flue gas and pulverized coal pipelines primarily involve: firstly, using outdated standards and calculation methods for design and calculation; and secondly, focusing on fan selection, fan margin selection, and leakage mitigation in the flue gas ducts. A common approach is to use experimental methods, taking the power plant boiler flue gas system as the research object, conducting energy consumption analysis on induced draft fans to identify the causes of low fan efficiency and implement targeted modifications. Additionally, experimental studies and analyses are conducted on forced draft fans, induced draft fans, flue gas dust collectors, and pulverizing systems to propose modification methods for reducing energy consumption and improving efficiency. However, these studies neglect the potential for improper fan selection due to calculation errors in flue gas duct resistance, and also overlook the optimization and modification of components with high resistance in the flue gas and pulverized coal pipelines. Summary of the Invention

[0003] In order to solve the problems existing in the prior art, the purpose of this invention is to provide an optimization method for the connection method and spatial layout of the flue gas system in power plants. This method improves the efficiency of the flue gas system by improving the connection method and spatial layout of the flue gas system in power plants, which is of great significance to the overall economic efficiency of the plant.

[0004] To achieve the above objectives, the technical method employed in this invention is as follows:

[0005] An optimization method for the connection method and spatial layout of power plant flue gas systems is proposed. The optimization of the flue gas duct of the primary air system in power plants includes four methods: Method A involves transforming square tubes into circular tubes and optimizing the space by replacing the three consecutive bends in the original method with two bends and a section of inclined tube; Method B, where space permits, reduces the number of bends by rearranging the fan positions and decreasing the turning angle of the bend before the air preheater inlet, thereby reducing resistance; Method C, based on Method B, changes the conical diffuser to a tower-shaped diffuser, thus changing the bend at the air preheater inlet from a diffuser bend to a regular bend; Method D, without changing the area, changes the rectangular tube in Method B to a circular tube.

[0006] The optimization of the flue gas duct of the primary hot air system in the power plant includes: Option A is to reduce the use of one elbow by replacing the original "Z" shaped elbow with a 45° elbow; Option B is to replace all the rectangular pipes in this section with round pipes based on Option A.

[0007] The optimization of the air preheater outlet to the furnace front hot primary air main pipe in the power plant flue gas system includes: first, reducing the distance between the second elbow and the contraction pipe, and simultaneously reducing its turning radius; second, reducing the distance between the space elbows so that L / b = 2 to 4, where L is the length of the transition section connecting the two elbows and b is the pipe cross-sectional diameter; finally, using the space obtained from the optimization, the right-angle elbows and sharp turns are all transformed into gentle turns and the distance between them is adjusted.

[0008] Optimization of the flue gas duct of the power plant's flue gas system and secondary hot air system includes: modifying the converging right-angle bends into converging chamfered bends or gentle bends, and optimizing the spacing between the bend and the next bend to make L / b = 3.5, thereby reducing the resistance of this section; the resistance at the groove is equivalent to the sudden contraction and expansion of the cross-section of the pipe, so a chamfer or rounded corner is added at the sudden expansion or contraction to allow the streamline to transition slowly;

[0009] The optimization of the flue gas duct from the air preheater outlet to the dust collector inlet includes the following aspects: each flue has only two bends, and the turning angle of each bend is the same, which is 30°. At the same time, the flue length is shortened, and the total length is reduced to 2 / 3 of the original length.

[0010] The modification and optimization of the dust collector outlet to the induced draft fan inlet of the power plant's flue gas system includes the following aspects: First, the original pipeline was merged and the vertical bend was changed to a bend followed by merging, thus avoiding fluid collision; second, the rectangular pipes in the original pipeline were replaced with circular pipes; finally, the spatial bends formed by continuous bends were spatially optimized, and the angle between the two flue gas duct merging sections was changed from the original relative arrangement to 60°, and the angle between the flue gas duct inlet section and the merging section was changed from the original 90° to 135°.

[0011] The present invention has the following advantages:

[0012] This invention provides an optimization method for the connection method and spatial layout of a power plant's flue gas system. This method improves the connection method and spatial layout of the power plant's flue gas system and determines the degree of optimization by comparing and analyzing numerical simulation data of the pipes before and after the modification. The results show that the modification of the power plant's flue gas system mentioned in this invention reduces the economic cost of the power plant, saves resources, and has extremely high economic and environmental benefits, providing an effective guarantee for the safe and efficient production of the power plant. Attached Figure Description

[0013] Figure 1This invention relates to an optimized method for the connection method and spatial layout of a power plant flue gas system, specifically for the cold primary air duct of the flue gas system.

[0014] Figure 2a and Figure 2b The present invention relates to optimization schemes A and B for the cold primary air duct of a flue gas system, which is an optimization method for the connection method and spatial layout of a power plant flue gas system.

[0015] Figure 3a and Figure 3b The present invention relates to optimization schemes C and D for the cold primary air duct of a flue gas system, which is an optimization method for the connection method and spatial layout of a power plant flue gas system.

[0016] Figure 4 This invention relates to an optimization method for the connection method and spatial layout of a power plant flue gas system, specifically for the hot primary air duct of the flue gas system.

[0017] Figure 5a , Figure 5b and Figure 5c The present invention relates to the original scheme, modification scheme A, and modification scheme B of the hot primary air duct of the flue gas system, which is an optimization method for the connection method and spatial layout of the flue gas system in power plants.

[0018] Figure 6 The present invention relates to an optimization method for the connection method and spatial arrangement of a power plant flue gas system, specifically the air preheater outlet to the inlet of the primary hot air header in front of the furnace.

[0019] Figure 7 This invention relates to an optimization method for the connection method and spatial arrangement of a power plant flue gas system, specifically the connection from the air preheater outlet to the inlet of the preheater hot secondary air manifold.

[0020] Figure 8a and Figure 8b This invention relates to an optimization method for the connection method and spatial layout of a power plant flue gas system. The flue gas system includes a three-dimensional view of the dust collector inlet and the modified dust collector inlet flue.

[0021] Figure 9a and Figure 9b This invention provides a vector diagram of the velocity of the flue gas duct at the inlet of the dust collector and the modified inlet of the dust collector, representing an optimization method for the connection method and spatial layout of a power plant flue gas system.

[0022] Figure 10a and Figure 10b This invention relates to the original and optimized design of the duct from the dust collector outlet to the induced draft fan inlet of a power plant flue gas system, which is an optimization method for the connection method and spatial layout of the flue gas system. Detailed Implementation

[0023] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments.

[0024] In the subsystems of thermal power plants, the boiler flue gas and pulverized coal system plays a crucial role in the transportation and distribution of boiler flue gas and pulverized coal. Most modern power plant fans are high-efficiency fans, with peak efficiencies exceeding 85%, but actual operating efficiency is often significantly lower. Due to space constraints and limitations in pipeline manufacturing, the ductwork layout of power plant flue gas and pulverized coal systems is often quite compact, with rectangular ducts commonly used. This mismatch between fans and the flue gas and pulverized coal system stems from unreasonable boiler flue gas and pulverized coal duct design and inappropriate fan selection. This leads to phenomena such as stalling, surge, and even runaway of some fans during operation. Inappropriate fan selection is caused by imperfect fan selection design methods and inaccurate calculations of flue gas and air volume and system resistance during power plant design. Therefore, improving the spatial layout of power plant flue gas and pulverized coal ducts and modifying duct designs can significantly improve the design level of power plant flue gas and pulverized coal ducts and the actual operating efficiency of fans, which is of great significance for optimized power plant operation and energy conservation and emission reduction.

[0025] Based on the operational characteristics of a power plant's flue gas system, the following optimization methods for the power plant's flue gas system are proposed to address the shortcomings of low efficiency and high losses in the flue gas system.

[0026] Figure 1 This section of the duct is part of a primary cooling air system in a power plant. It contains a diffuser-connected elbow and a spatial elbow, with the latter part of the spatial elbow being a diffuser elbow. The diffuser-connected elbow exhibits significant resistance, and its direct connection to the elbow further increases resistance and leads to uneven airflow. Furthermore, the distance between the two elbows in the subsequent spatial elbow is not within the optimal range of L / b = 2–4. Therefore, the design of this section of the duct is flawed and requires appropriate modification.

[0027] There are four main ways to improve the flue gas duct of the primary air cooling system in this power plant, including: Option A, such as... Figure 2a As shown, Scheme B involves transforming the square tube into a round tube and optimizing the space by replacing the three consecutive bends in the original scheme with two bends and a section of inclined tube; Scheme B is as follows. Figure 2b As shown, under space-constrained conditions, by rearranging the fan positions, two bends are reduced in this section, and the turning angle of the bend before the air preheater inlet is decreased, thereby reducing resistance; Scheme C is as follows. Figure 3a As shown, Scheme B involves changing the conical diffuser tube to a tower-shaped diffuser tube, thus changing the bend at the air preheater inlet from a diffuser bend to a regular bend; Scheme D is as follows. Figure 3b As shown, Scheme B is changed from a rectangular tube to a circular tube while keeping the area unchanged.

[0028] Comparing the original and optimized schemes, it was found that although Scheme A reduced the number of bends, the total resistance value did not decrease. The advantage of this scheme is that it reduces the length of the flue, thus saving steel consumption and manufacturing costs. The reason why the resistance not only did not decrease but actually increased is that the connection method between the bend and the diffuser before the air preheater inlet in this scheme changes from the original non-plane to the same plane, thus increasing the resistance. Schemes B and C can both effectively reduce resistance; Schemes B and C can reduce resistance by about 50 Pa. However, Scheme B consumes significantly less steel than Scheme C, thus greatly reducing costs. Therefore, Scheme B also provides a new approach for optimizing the tower-shaped diffuser. Compared to Schemes B and C, Scheme D has even lower resistance, reducing it by about 70 Pa, and also consumes less steel. Therefore, using a circular pipe instead of a rectangular pipe in the cold primary air duct can not only reduce resistance and achieve economical operation goals but also reduce manufacturing costs.

[0029] For example Figure 4 and Figure 5a The hot primary air duct shown presents two optimization schemes, such as... Figure 5b Modification scheme A shown reduces the use of one elbow by replacing the original "Z" shaped elbow with a 45° elbow, as follows: Figure 5c Scheme B, as shown, replaces the entire rectangular tube section with a circular tube, based on Scheme A. Numerical simulations show that the original scheme exhibits significant low-velocity flow zones on the concave surfaces of the two bends of the "Z"-shaped elbow and near the inner wall of the "Z"-shaped elbow outlet, where vortices are easily formed. The modified scheme, however, does not exhibit these significant vortex zones. Furthermore, when the entire section is constructed using circular tubes, the drag of Scheme B is only about one-third that of the original scheme, demonstrating a significant drag reduction effect.

[0030] Figure 6 The diagram shows a three-dimensional view of the air preheater outlet to the inlet of the primary hot air main pipe in the power plant. It can be observed that the original air duct has unreasonable component design, irregularly shaped connections, and spatial arrangement, resulting in significant flow losses and potential blockages, leading to high resistance in actual test results. The reasons for the resistance loss in this section of the air duct can be attributed to the following points:

[0031] 1) The original flue has right-angle turns and sharp turns. As can be seen from the velocity vector diagram, the speed at the right-angle turns and the outer corner of the sharp turns is significantly lower than the speed values ​​at other parts. Furthermore, according to the streamline diagram and velocity vector diagram, there are obvious vortices at the outer corners of the right-angle turns and sharp turns.

[0032] 2) There are continuously arranged bends. The channel has two spatial bends and one Z-shaped bend. As can be seen from the previous simulation, there is an optimal distance between the spatial bends, which is generally between 2 and 4. However, the distance arrangement of the spatial bends in the original scheme is unreasonable.

[0033] 3) The second turning radius from the air preheater outlet is relatively large, but as can be seen from the drag coefficient curve of the gentle turn, the drag coefficient changes very little after R / b is greater than 2. Therefore, the turning radius can be appropriately reduced to provide space for the next turn and the distance between them.

[0034] 4) In the air preheater outlet section, there is a continuous arrangement of contraction followed by a bend. As can be seen from the irregularly shaped connections, the resistance value of the bend following the contraction pipe increases with the increase of the distance between them. Therefore, firstly, the distance between the contraction pipe and the bend can be appropriately reduced. This reduces the connection resistance between the contraction pipe and the bend, and also provides space for subsequent right-angle bend modifications. Secondly, the length of the contraction pipe can be increased, which reduces both the contraction pipe resistance and the distance between the contraction pipe and the bend, thereby reducing the overall resistance.

[0035] Based on the above analysis, the following modification plan can be derived: First, appropriately reduce the distance between the second elbow and the contraction pipe, and at the same time, appropriately reduce its turning radius; second, reduce the distance between the spatial elbows so that L / b = 2-4; finally, make full use of the space obtained through optimization to modify both the right-angle elbows and sharp turns into gentle turns and adjust the distance between them.

[0036] Figure 7 For the air preheater outlet to the inlet of the boiler front hot secondary air header in the power plant's flue gas system, based on the duct space structure before and after optimization, numerical simulation was used to obtain the velocity vector, streamlines, and related data from the air preheater outlet to the boiler front hot secondary air header inlet. The conclusion is that significant vortices exist at the upper and lower corners of the tee and at the groove in the duct before the header inlet. The vortices at the tee are mainly due to right-angle turns in the flow, which can be viewed separately as a contracting right-angle bend, followed by another bend, forming a spatial bend. Therefore, the main method to reduce resistance at this point is to modify the contracting right-angle bend into a contracting chamfer or a gentle turn, and to rationally arrange the distance from the next bend to reduce resistance in this section. The resistance at the groove is equivalent to a sudden contraction and expansion of the cross-section of a pipe; therefore, a chamfer or fillet can be added at the sudden expansion or contraction to allow for a gradual transition of the streamlines.

[0037] Figure 8a and Figure 8bThis image shows a 3D view of the dust collector inlet and the modified dust collector inlet flue in the power plant's flue gas system. The original flue had three bends in each channel, but the spacing of these bends was unreasonable, resulting in high overall resistance. Furthermore, the third bend in the shortest channel had a negligible turning angle, leading to significant differences in resistance among the three channels and uneven flow distribution, which was detrimental to the dust collector's operation. The modified flue has only two bends in each channel, with a 30° difference in turning angle between each bend. This reduces the flue's resistance and ensures a more uniform flow distribution at the dust collector inlet. Additionally, the optimized flue is less than two-thirds the length of the original channel, saving steel and reducing investment costs.

[0038] Figure 9a and Figure 9b The vector diagrams of the flue gas velocity at the inlet of the power plant's dust collector and the inlet of the modified dust collector show that the flow states in each channel of the optimized flue are similar, resulting in more uniform resistance and flow distribution. The flow turns are also relatively gentle, thus minimizing the scouring effect on the pipes.

[0039] Figure 10a and Figure 10b This paper presents the original and optimized ductwork design from the dust collector outlet to the induced draft fan inlet. The main modifications to the original design are as follows: First, the vertical bends in the original design were changed from merging to a bend-then-merge configuration, thus avoiding fluid collisions; second, the rectangular pipes in the original design were replaced with circular pipes; and finally, the spatial bends formed by continuous turns were optimized. Calculations show that the modified flue significantly reduces resistance, decreasing by 139.8 Pa and 160.1 Pa respectively. This is highly beneficial for the economical operation of the dust collector. Simultaneously, the optimized flow is smoother and more uniform, reducing wear on the flue.

Claims

1. An optimization method for the connection method and spatial layout of a power plant flue gas system, characterized in that: There are four optimization methods for the flue gas duct of the primary air cooling system in power plants. Option A involves converting square tubes into round tubes and optimizing the space by replacing the three consecutive bends in the original scheme with two bends and a section of inclined tube. Option B, where space allows, reduces the number of bends by rearranging the fan positions and decreasing the turning angle of the bend before the air preheater inlet, thereby reducing resistance. Option C, based on Option B, changes the conical diffuser to a tower-shaped diffuser, thus changing the bend at the air preheater inlet from a diffuser bend to a regular bend. Option D, without changing the area, converts the rectangular tube in Option B into a round tube. The optimization of the flue gas duct of the primary hot air system in the power plant includes: Option A is to reduce the use of one elbow by replacing the original "Z" shaped elbow with a 45° elbow; Option B is to replace all the rectangular pipes in this section with round pipes based on Option A. The optimization of the air preheater outlet to the furnace front hot primary air main pipe in the power plant flue gas system includes: first, reducing the distance between the second elbow and the contraction pipe, and simultaneously reducing its turning radius; second, reducing the distance between the space elbows so that L / b = 2 to 4, where L is the length of the transition section connecting the two elbows and b is the pipe cross-sectional diameter; finally, using the space obtained from the optimization, the right-angle elbows and sharp turns are all transformed into gentle turns and the distance between them is adjusted. Optimization of the flue gas duct of the power plant's flue gas system and secondary hot air system includes: modifying the converging right-angle bends into converging chamfered bends or gentle bends, and optimizing the spacing between the bend and the next bend to make L / b = 3.5, thereby reducing the resistance of this section; the resistance at the groove is equivalent to the sudden contraction and expansion of the cross-section of the pipe, so a chamfer or rounded corner is added at the sudden expansion or contraction to allow the streamline to transition slowly; The optimization of the flue gas duct from the air preheater outlet to the dust collector inlet includes the following aspects: each flue has only two bends, and the turning angle of each bend is the same, which is 30°. At the same time, the flue length is shortened, and the total length is reduced to 2 / 3 of the original length. The modification and optimization of the dust collector outlet to the induced draft fan inlet of the power plant's flue gas system includes the following aspects: First, the original pipelines were merged, and then the vertical bends were changed to bend first and then merge, thus avoiding fluid collisions. Second, the rectangular pipes in the original pipelines were changed to circular pipes. Finally, the spatial bends formed by continuous bends were spatially optimized and modified, and the angle between the two flue merging sections was changed from the original relative arrangement to 60°, and the angle between the flue inlet section and the merging section was changed from the original 90° to 135°.

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