Optimization Design Method for Preventing Sticking of Steam Turbine High Pressure Control Valve Disc Combined with CFD Simulation Calculation

Abstract

The present invention discloses an optimization design method for preventing the valve disc of a high-pressure regulating valve of a steam turbine from jamming in combination with CFD simulation calculation, which includes the following steps: 1) Establish a three-dimensional geometric model of the high-pressure regulating valve of the steam turbine including the valve cavity, valve disc, valve disc sleeve, pre-opening valve and positioning strip, and perform grid discretization on the flow field region and structural body region of the three-dimensional geometric model; 2) Take the actual working parameters of the valve as boundary conditions and conduct thermal-fluid-solid coupling CFD simulation analysis; 3) Through CFD simulation calculation, determine the relationship among the lifting force magnitude, valve disc vibration, positioning strip position, clearance size and the throat diameter of the pre-opening valve; 4) Through CFD gas-solid two-phase flow simulation analysis, determine the probability of oxidation scale jamming and the specific structural relationship of the key clearance and positioning strip, and judge whether the current positioning strip is reasonable. This method can solve the problem of valve disc jamming caused by oxidation scale particles and ensure the safe operation of the unit.

Description

Technical Field

[0001] The present invention belongs to the technical field of mechanical engineering. It relates to an optimization design method for preventing jamming of the valve disc of a high-pressure regulating valve of a steam turbine combined with CFD simulation calculation. Background Art

[0002] In modern conventional thermal power plants, nuclear power plants, and geothermal power plants that use fossil fuels, steam turbines are used to drive generators to generate electric energy. Therefore, the combination of a steam turbine and a generator is called a steam turbine generator set. The main function of the high-pressure regulating valve of a steam turbine is to regulate the power of the steam turbine generator set and quickly cut off the steam source when the unit operates abnormally, ensuring the safe operation of the steam turbine and the generator. Approximately 80% of the electric energy in the world is generated by steam turbine generator sets. Therefore, improving the reliability of the high-pressure regulating valve is of great significance for stable power supply.

[0003] For a high-pressure regulating valve, the valve disc is a moving part and can move freely within the valve disc sleeve fixedly connected to the valve housing. The clearance between the mating surfaces of the valve disc and the valve disc sleeve is very small. Its main purpose is to have good restraint and guiding effects on the movement of the valve disc under the condition of ensuring the free movement of the valve disc, reduce the vibration under the disturbance of high-speed steam flow when the valve opens, and make the valve disc accurately fit with the seat sealing surface when the valve closes, ensuring the tightness of the valve closure. It should be noted that since the high-pressure regulating valves of large steam turbines all have pre-opening valves, the pre-opening valves can reduce the valve opening lifting force, and the pre-opening valves remain in the open state after the high-pressure regulating valves open. Therefore, the steam leakage amount between the valve disc and the valve disc sleeve does not affect the economy of the steam turbine, but has an important impact on the magnitude of the valve lifting force and the reliability of the valve disc movement. Generally speaking, under the condition that the throat diameter and lift of the pre-opening valve remain unchanged, increasing the clearance between the valve disc and the valve disc sleeve will lead to an increase in the pressure difference before and after the pre-opening valve, a decrease in the unloading degree of the pre-opening valve, and an increase in the valve lifting force. In addition, after the clearance between the valve disc and the valve disc sleeve increases, the guiding property of the valve disc movement weakens, but the increase in the pressure difference before and after the pre-opening valve caused will improve the stability of the valve disc. Therefore, the impact on the reliability of the valve disc movement is very complex and has always been a difficult problem in the industry. There has long been a lack of specific design and optimization methods.

[0004] Due to the extremely harsh working environment of the valve disc and the valve disc sleeve of the high-pressure regulating valve, an oxide film is likely to form on their surfaces. After falling off under the action of steam force, mechanical friction, vibration, and thermal stress, oxide scale particles are generated. In addition, oxide scale in the upstream steam pipeline will also be carried by the steam into the clearance between the mating surfaces of the valve disc and the valve disc sleeve. The clearance between the mating surfaces of the conventionally designed valve disc and the valve disc sleeve is very small, and the oxide scale particles are extremely likely to cause jamming of the valve disc, such as Figure 2 described, causing the steam turbine to overspeed and seriously affecting the safe operation of the steam turbine. With the intensification of unit deep regulation, the occurrence of jamming accidents of high-pressure regulating valves of ultra (super) critical units is becoming more and more frequent. Summary of the Invention

[0005] The object of the present invention is to overcome the disadvantages of the above-mentioned prior art, and provides an optimization design method for preventing jamming of the valve disc of a high-pressure regulating valve of a steam turbine combined with CFD simulation calculation. This method can solve the problem of valve disc jamming caused by oxide scale particles and ensure the safe operation of the unit.

[0006] To achieve the above object, the optimization design method for preventing jamming of the valve disc of a high-pressure regulating valve of a steam turbine combined with CFD simulation calculation described in the present invention includes the following steps:

[0007] 1) Establish a three-dimensional geometric model of the high-pressure regulating valve of the steam turbine including the valve cavity, valve disc, valve disc sleeve, pre-opening valve and positioning strip, and perform mesh discretization on the flow field region and the structural body region of the three-dimensional geometric model;

[0008] 2) Take the actual working parameters of the valve as the boundary conditions and perform thermal-fluid-structure interaction CFD simulation analysis;

[0009] 3) Through CFD simulation calculation, determine the relationship between the lifting force magnitude, valve disc vibration, positioning strip position, clearance size and the throat diameter of the pre-opening valve;

[0010] 4) Through CFD gas-solid two-phase flow simulation analysis, determine the probability of oxide scale jamming and the specific structural relationship between the key clearance and the positioning strip, and judge whether the current positioning strip is reasonable. When the current positioning strip is unreasonable, go to step 2). When the current positioning strip is reasonable, complete the optimization design for preventing jamming of the valve disc of the high-pressure regulating valve of the steam turbine combined with CFD simulation calculation.

[0011] The specific operation of step 1) is as follows:

[0012] 11) According to the structural form of the valve model, construct a three-dimensional geometric model of the high-pressure regulating valve of the steam turbine including the valve cavity, valve disc, valve disc sleeve, pre-opening valve and positioning strip. The three-dimensional geometric model includes a flow field region and a structural region;

[0013] 12) Discretize the mesh of the flow field region in ICEM. Divide the internal mesh of the valve into the valve cavity, valve seat, annular gap and unloading chamber. Among them, structured meshes are used for the valve cavity, valve seat and annular gap, and unstructured meshes are used for the unloading chamber. The boundary layer mesh of the flow field region is encrypted;

[0014] 13) Add a positioning strip to the fluid region and encrypt the boundary layer mesh of the positioning strip;

[0015] 14) Discretize the mesh of the structural region in ICEM. Divide the structural region into the pre-opening part and the valve sleeve part. Among them, structured meshes are used for both the pre-opening part and the valve sleeve part.

[0016] The specific operation of step 2) is as follows:

[0017] 21) The inlet boundary and outlet boundary of the fluid region are respectively set at 5 times the pipe diameter at the valve inlet and valve outlet. The total inlet pressure condition is set at the inlet, and the outlet static pressure is set as the outlet boundary condition at the outlet. The wall surface adopts an adiabatic no-slip boundary condition;

[0018] 22) Set the initial calculation field of the fluid domain, calculate the pressure ratio before and after the valve. When the pressure ratio before and after the valve is greater than the choking pressure ratio, select the inlet velocity as the initial velocity field. When the pressure ratio before and after the valve is less than the choking pressure ratio, select the high-pressure ratio condition as the initial velocity field;

[0019] 23) Select the Realizable k-ε model as the turbulence model for the fluid domain calculation;

[0020] 24) On the structural side, different thermal boundary conditions are given according to the temperature distributions of the pre-opening part and the valve disc part.

[0021] The specific operation of step 3) is as follows:

[0022] 31) Calculate the downward loading force of the valve by extracting the vertically downward acting forces on the surfaces of the unloading chamber, valve disc and valve stem.

[0023] 32) Obtain the maximum amplitude of the valve disc vibration by deriving the displacement at the valve disc, and derive the dimensions at the key clearances under the hot condition;

[0024] 33) Derive the lifting force magnitudes, valve disc vibrations, positioning bar positions, clearance sizes and pre-opening valve throat diameters under different structures, and establish the relationships among the lifting force magnitudes, valve disc vibrations, positioning bar positions, clearance sizes and pre-opening valve throat diameters.

[0025] The specific operation of step 4) is as follows:

[0026] 41) Add scale particles at the valve inlet, conduct a CFD gas-solid two-phase flow simulation analysis, and calculate the probability of scale jamming at the key clearances under different key clearance and positioning bar arrangement modes;

[0027] 42) When the probability calculated in step 41) is less than or equal to the preset value, it indicates that the current positioning bar setting is reasonable. Otherwise, go to step 2).

[0028] The cross-sectional shape of the positioning bar is composed of several splicings of rectangle, semi-circular arc, inverted rounded trapezoid, rectangle and semi-circular arc.

[0029] The present invention has the following beneficial effects:

[0030] When the optimized design method for preventing the high-pressure regulating valve disc of a steam turbine from jamming in combination with CFD simulation calculation is specifically operated in the present invention, through CFD simulation calculation, the relationships among the lifting force magnitude, valve disc vibration, position of the positioning strip, clearance size, and throat diameter of the pre-opening valve are determined. Through CFD gas-solid two-phase flow simulation analysis, the probability of oxidation and pitting jamming and the specific structural relationships of the key clearances and positioning strips are determined, and the rationality of the current positioning strip is judged, so as to comprehensively optimize the mating structure between the valve disc and the valve disc sleeve, the sizes of various clearances, and the throat diameter of the pre-opening valve. Under the condition of not exceeding the allowable lifting force of the valve and ensuring the reliability of valve disc movement, the clearance between the valve disc and the valve disc sleeve is increased as much as possible, effectively reducing the valve disc jamming problem caused by oxidation scale and improving the operation safety of the steam turbine. Brief Description of the Drawings

[0031] Figure 1 Schematic flow chart of the present invention;

[0032] Figure 2 Schematic diagram of the valve structure and the position of oxidation and pitting jamming;

[0033] Figure 3a Schematic diagram of the valve mesh division in the fluid domain;

[0034] Figure 3b Side view of the valve in the fluid domain after meshing;

[0035] Figure 3c Structural diagram of the middle part of the valve in the fluid domain;

[0036] Figure 3d Structural diagram of the valve in the fluid domain;

[0037] Figure 4 Schematic structural diagram of the mating cross-section of the valve disc and the valve disc sleeve of the present invention;

[0038] Figure 5 Schematic diagram of a cross-sectional shape of the positioning strip;

[0039] Figure 6 Schematic diagram of another cross-sectional shape of the positioning strip;

[0040] Figure 7 Schematic diagram of another cross-sectional shape of the positioning strip;

[0041] Figure 8 Schematic diagram of another cross-sectional shape of the positioning strip;

[0042] Figure 9 Schematic diagram of the shape of the positioning strip along the movement direction of the valve disc. Detailed Description of the Invention

[0043] To enable those skilled in the art to better understand the solution of the present invention, the technical solution in the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, not all of the embodiments, and are not intended to limit the scope of the present invention. In addition, in the following description, the description of well-known structures and technologies is omitted to avoid unnecessarily confusing the concepts disclosed in the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the scope of protection of the present invention.

[0044] The schematic structural diagrams according to the disclosed embodiments of the present invention are shown in the accompanying drawings. These figures are not drawn to scale, and for the purpose of clear expression, some details are enlarged and some details may be omitted. The shapes of various regions and layers shown in the figures and their relative sizes and positional relationships are only exemplary, and may actually deviate due to manufacturing tolerances or technical limitations. Those skilled in the art can additionally design regions / layers with different shapes, sizes, and relative positions according to actual needs.

[0045] The optimization design method for preventing jamming of the high-pressure regulating valve disc of a steam turbine in combination with CFD simulation calculation according to the present invention includes the following steps:

[0046] 1) Establish a three-dimensional geometric model of the high-pressure regulating valve of a steam turbine including a valve cavity, a valve disc, a valve disc sleeve, a pre-opening valve, and a positioning strip, and perform grid discretization on the flow field region and the structural body region of the three-dimensional geometric model respectively;

[0047] The specific operation of step 1) is as follows:

[0048] 11) According to the structural form of the valve model, establish a three-dimensional geometric model of the high-pressure regulating valve of a steam turbine including a valve cavity, a valve disc, a valve disc sleeve, a pre-opening valve, and a positioning strip. The three-dimensional geometric model includes a flow field region and a structural region;

[0049] 12) Perform grid discretization on the flow field region in ICEM, divide the internal grid of the valve into a valve cavity, a valve seat, an annular gap, and a relief chamber. Among them, structured grids are used for the valve cavity, the valve seat, and the annular gap, and unstructured grids are used for the relief chamber. The boundary layer grid of the flow field region is encrypted and optimized;

[0050] 13) Add a positioning strip in the fluid region and perform encryption processing on the boundary layer grid of the positioning strip;

[0051] 14) Perform grid discretization on the structural region in ICEM, divide the structural region into a pre-opening part and a valve sleeve part. Among them, structured grids are used for both the pre-opening part and the valve sleeve part.

[0052] 2) Taking the actual working parameters of the valve as the boundary conditions, conduct a thermal-fluid-solid coupling CFD simulation analysis;

[0053] The specific operation of step 2) is as follows:

[0054] 21) The inlet boundary and outlet boundary of the fluid region are respectively set at 5 times the pipe diameter at the valve inlet and valve outlet. The total inlet pressure condition is set at the inlet, and the outlet static pressure is set as the outlet boundary condition at the outlet. The wall surface adopts an adiabatic no-slip boundary condition;

[0055] 22) Set the initial calculation field of the fluid domain and calculate the pressure ratio before and after the valve. When the pressure ratio before and after the valve is greater than the choking pressure ratio, select the approximate inlet velocity as the initial velocity field. When the pressure ratio before and after the valve is less than the choking pressure ratio, select the adjacent large pressure ratio condition as the initial velocity field;

[0056] 23) Select the Realizable k-ε model as the turbulence model for fluid domain calculation. When using the couple method in Fluent, the CourantNumber should be less than 5. Preferably, the CourantNumber is 3, and the relaxation factors of the momentum and pressure equations do not exceed 0.5. Preferably, the relaxation factor is 0.2, and the relaxation factors of the other variables remain unchanged. When a convergence trend appears after 100 - 200 steps of calculation, on the premise of ensuring convergence, increase the time step to accelerate the calculation convergence speed;

[0057] 24) On the structure side, according to the temperature distributions of the pre-opening part and the valve disc part, different thermal boundary conditions are given respectively. Among them, the outer surface temperatures of the pre-opening part and the valve disc part are taken as 600 °C, and the outer surface temperature of the valve housing is taken as 200 °C.

[0058] 3) Through CFD simulation calculations, determine the relationships among the lifting force magnitude, valve disc vibration, position of the positioning strip, clearance size, and throat diameter of the pre-opening valve;

[0059] The specific operation of step 3) is as follows:

[0060] 31) Calculate the downward loading force of the valve by extracting the vertically downward acting forces on the surfaces of the unloading chamber, valve disc, and valve stem.

[0061] 32) Obtain the maximum amplitude of valve disc vibration by exporting the displacement at the valve disc, and export the dimensions at the key clearances under the hot state;

[0062] 33) Export the lifting force magnitude, valve disc vibration, position of the positioning strip, clearance size, and throat diameter of the pre-opening valve under different structures, and establish the relationships among the lifting force magnitude, valve disc vibration, position of the positioning strip, clearance size, and throat diameter of the pre-opening valve.

[0063] 4) Through CFD gas-solid two-phase flow simulation analysis, determine the probability of oxide scale jamming, the specific structural relationship between the key clearance and the positioning strip, judge whether the current positioning strip is reasonable, and determine whether the current structure is reasonable.

[0064] The specific operation of step 4) is as follows:

[0065] 41) In the proposed structure containing the positioning strip, add oxide scale particles at the valve inlet, conduct CFD gas-solid two-phase flow simulation analysis, and calculate the probability of oxide scale jamming at the key clearance under different key clearances and positioning strip arrangement methods;

[0066] 42) When the probability calculated in step 41) is less than or equal to the preset value, it indicates that the current positioning strip setting is reasonable; otherwise, go to step 2).

[0067] The anti-solid particle jamming structure is specifically: on the outer wall of the valve disc or the inner wall of the valve disc sleeve at the mating surface of the valve disc and the valve disc sleeve, several positioning strips are provided, and the clearance thereof is smaller than the existing clearance between the valve disc and the valve disc sleeve (referred to as the small clearance area), and the clearance between the valve disc and the valve disc sleeve at the non-positioning strip position (referred to as the large clearance area) is much larger than the clearance between the valve disc and the valve disc sleeve at the positioning strip position. Among them, the clearance of the small clearance area is about 50%-90% of the current clearance between the valve disc and the valve disc sleeve; the clearance of the large clearance area is about more than 150% of the current clearance between the valve disc and the valve disc sleeve, which is larger than the common oxide scale thickness.

[0068] The length direction of the positioning strip corresponds to the movement direction of the valve disc, and the positioning strip can be intermittent or not fill the full stroke of the valve disc. The number of positioning strips is not less than 3 and is evenly distributed in the circumferential direction.

[0069] The cross-sectional shape of the positioning strip is formed by splicing several of rectangle, semi-circular arc, inverted rounded trapezoid, rectangle and semi-circular arc.

[0070] The comprehensive optimization is: using three-dimensional thermal-fluid-solid coupling simulation analysis to optimize the positioning strip structure, the clearance size between the valve disc and the valve disc sleeve at the non-positioning strip position, the clearance size between the valve disc and the valve disc sleeve at the positioning strip position, and the throat diameter of the pre-opening valve, and as much as possible increase the clearance between the valve disc and the valve disc sleeve at the non-positioning strip position under the condition of not exceeding the allowable lifting force of the valve, and reduce the retention of solid particles at the non-positioning strip position.

[0071] The innovation of the present invention lies in: the comprehensive optimization design method of the valve disc-valve disc sleeve structure, clearance size and pre-opening valve throat diameter aiming at reducing valve disc jamming; any equivalent implementation or change that does not deviate from the above ideas and methods belongs to the scope of the claims of the present invention patent.

[0072] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit them. Although the present invention has been described in detail with reference to the above embodiments, those of ordinary skill in the art should understand that: modifications or equivalent substitutions can still be made to the specific embodiments of the present invention, and any modification or equivalent substitution that does not depart from the spirit and scope of the present invention shall be covered by the protection scope of the claims of the present invention.

Claims

1. An optimization design method for preventing jamming of the steam turbine high-pressure control valve disc combined with CFD simulation calculation, characterized in that, The steps include: 1) Establish a three-dimensional geometric model of the high-pressure regulating valve of a steam turbine including a valve chamber, a valve disc, a valve disc sleeve, a pre-opening valve and a positioning strip, and discretize the mesh of the flow field region and the structural region of the three-dimensional geometric model; 2) Perform a thermal-fluid-structure coupling CFD simulation analysis with the actual working parameters of the valve as boundary conditions; 3) Through CFD simulation calculations, determine the relationship between the lifting force magnitude, valve disc vibration, positioning strip position, clearance size and the throat diameter of the pre-opening valve; 4) Through CFD gas-solid two-phase flow simulation analysis, determine the probability of oxidation pitting and the specific structural relationship between the key clearances and the positioning strip, and judge whether the current positioning strip is reasonable. When the current positioning strip is unreasonable, go to step 2). When the current positioning strip is reasonable, complete the anti-sticking optimization design of the valve disc of the high-pressure regulating valve of the steam turbine combined with CFD simulation calculations.

2. The anti-sticking optimization design method for the high-pressure control valve disc of a steam turbine combined with CFD simulation calculation according to claim 1, characterized in that The specific operation of step 1) is as follows: 11) According to the structural form of the valve model, construct a three-dimensional geometric model of the high-pressure regulating valve of a steam turbine including a valve chamber, a valve disc, a valve disc sleeve, a pre-opening valve and a positioning strip. The three-dimensional geometric model includes a flow field region and a structural region; 12) Discretize the mesh of the flow field region in ICEM. Divide the internal mesh of the valve into a valve chamber, a valve seat, an annular gap and a relief chamber. Among them, structured meshes are used for the valve chamber, valve seat and annular gap, and unstructured meshes are used for the relief chamber. The boundary layer mesh of the flow field region is encrypted; 13) Add a positioning strip to the fluid region and encrypt the boundary layer mesh of the positioning strip; 14) Discretize the mesh of the structural region in ICEM and divide the structural region into a pre-opening part and a valve sleeve part.

3. The anti-sticking optimization design method for the steam turbine high-pressure regulating valve disc combined with CFD simulation calculation according to claim 2, characterized in that In step 14), both the pre-opening part and the valve sleeve part adopt structured meshes.

4. The anti-jamming optimization design method of the high-pressure control valve disc of a steam turbine combined with CFD simulation calculation according to claim 1, characterized in that, The specific operation of step 2) is as follows: 21) Set the inlet boundary and outlet boundary of the fluid region at 5 times the pipe diameter at the valve inlet and valve outlet respectively. Set the inlet total pressure condition at the inlet, and set the outlet static pressure as the outlet boundary condition at the outlet. The wall surface adopts an adiabatic no-slip boundary condition; 22) Set the initial calculation field of the fluid domain and calculate the pressure ratio before and after the valve. When the pressure ratio before and after the valve is greater than the choking pressure ratio, select the inlet velocity as the initial velocity field. When the pressure ratio before and after the valve is less than the choking pressure ratio, select the high-pressure ratio condition as the initial velocity field; 23) Determine the turbulence model for the fluid domain calculation; 24) On the structural side, give different thermal boundary conditions according to the temperature distributions of the pre-opening part and the valve disc part.

5. The optimized design method for preventing jamming of the high-pressure control valve disc of a steam turbine combined with CFD simulation calculation according to claim 4, characterized in that, In step 23), select the Realizable k-ε model as the turbulence model for the fluid domain calculation.

6. The anti-sticking optimization design method of the high-pressure control valve disc of a steam turbine combined with CFD simulation calculation according to claim 1, characterized in that The specific operation of step 3) is as follows: 31) Calculate the downward loading force of the valve by extracting the vertically downward acting forces on the surfaces of the relief chamber, valve disc and valve stem; 32) Obtain the maximum amplitude of the valve disc vibration by exporting the displacement at the valve disc, and export the dimensions at the key clearances under the hot condition; 33) Export the lifting force magnitude, valve disc vibration, positioning strip position, clearance size and the throat diameter of the pre-opening valve under different structures, and establish the relationship between the lifting force magnitude, valve disc vibration, positioning strip position, clearance size and the throat diameter of the pre-opening valve.

7. The anti-sticking optimization design method for the high-pressure regulating valve disc of a steam turbine combined with CFD simulation calculation according to claim 1, characterized in that, The specific operation of step 4) is as follows: 41) Add oxide scale particles at the valve inlet for CFD simulation analysis of gas-solid two-phase flow, and calculate the probability of oxide scale jamming at the critical gap under different critical gaps and positioning bar arrangements; 42) If the probability calculated in step 41) is less than or equal to the preset value, it indicates that the current positioning bar setting is reasonable; otherwise, go to step 2).

8. The optimized design method for preventing jamming of the high-pressure control valve disc of a steam turbine combined with CFD simulation calculation according to claim 1, characterized in that, The cross-sectional shape of the positioning bar is composed of several splicings of rectangle, semi-circular arc, inverted rounded trapezoid, rectangle and semi-circular arc.

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