A method for determining the degree of water erosion of the last stage of a low-pressure cylinder of a steam turbine under different loads

Abstract

A method for determining the degree of water erosion at the last stage of the low-pressure cylinder of a steam turbine under different loads belongs to the technical field of steam turbine power generation. The present invention aims to solve the problem that the existing water erosion determination methods are relatively one-sided and not applicable to low-load and ultra-low-load operating conditions. It includes: modeling the entire cylinder blades of the low-pressure cylinder of the steam turbine and solving the flow field; obtaining the water erosion coefficient of the steam turbine under different loads; and analyzing the water erosion of the steam turbine under different loads according to the water erosion coefficient. The present invention is used to determine the water erosion at the last stage of the low-pressure cylinder of a steam turbine under low load or even ultra-low load.

Description

Technical Field

[0001] The present invention relates to a method for determining the degree of water erosion at the last stage of a low-pressure cylinder of a steam turbine, belonging to the technical field of steam turbine power generation. Background Art

[0002] In the wet steam stage of a steam turbine, small water droplets gradually form in the steam, which are called primary water droplets. Most of the generated primary water droplets flow smoothly through the cascade with the steam, and a small part deposits on the last-stage blades of the low-pressure cylinder of the steam turbine due to the effects of diffusion deposition and inertial deposition. After a huge number of primary water droplets deposit, they adhere to the trailing edge of the stationary blades at the last stage of the low-pressure cylinder of the steam turbine in the form of a liquid film. Under the action of the steam flow force, they are torn into water droplets with larger diameters, and these water droplets are called secondary water droplets. The formed secondary water droplets impact the last-stage moving blades of the steam turbine with a certain initial velocity, resulting in the water erosion phenomenon of the steam turbine. The water erosion phenomenon of the last-stage blades of the low-pressure cylinder of the steam turbine has existed for a long time. It not only deteriorates the aerodynamic performance of the blades, reduces the stage efficiency, but also threatens the safe operation of the steam turbine. Therefore, it is particularly necessary to determine the water erosion of the last-stage blades of the steam turbine.

[0003] The research on steam turbine water erosion mainly focuses on two approaches: experiments and simulations. In experimental research, the erosion of steam turbine blade materials is carried out through a water droplet injection experimental device. The maximum water erosion depth, water erosion characteristics, and erosion performance of different materials are analyzed respectively. Then, the effects of factors such as droplet impact velocity, impact angle, and material damage degree on water erosion are discussed, and it is concluded that the water erosion mass loss has an exponential relationship with the impact velocity. The prior art has also conducted research from the material aspect, attempting to obtain the water erosion resistance of materials. It is found that factors such as the hardness, rebound rate, strain capacity, and toughness of materials have a significant impact on the ability of materials to withstand droplet erosion. Moreover, the roughness and irregularity of the material surface are also the main factors affecting the water erosion performance of materials, and these factors accelerate the water erosion damage, thus affecting the maximum water erosion rate. In numerical simulation, it is to analyze the liquid-solid impact mechanism and use the numerical method of finite elements to discuss the water erosion problem of materials. For parameters such as the size, shape, and impact angle of water droplets, the water erosion characteristics of materials are studied, and then the water erosion of steam turbine blades is analyzed. There are water erosion determination methods in the prior art to determine the water erosion of steam turbines, and thus the steam turbine blades can be effectively protected. Currently, there are mainly seven water erosion determination methods proposed by Gloger, Swiss EW Company, Engelke, Japanese Sanlian Company, German EWU Company, and American Westinghouse Company.

[0004] However, due to the lack of comprehensive consideration of factors, the existing water erosion determination methods are only applicable to the determination of steam turbine water erosion under medium and high load operating conditions, and are not applicable to low load or even ultra-low load. Summary of the Invention

[0005] The object of the present invention is to solve the problem that the existing water erosion determination method is relatively one-sided and not applicable to low-load and ultra-low-load operating conditions, and to provide a method for determining the water erosion degree of the last stage of a steam turbine low-pressure cylinder under different loads.

[0006] A method for determining the water erosion degree of the last stage of a steam turbine low-pressure cylinder under different loads according to the present invention includes:

[0007] S1. Model the entire cylinder blades of the steam turbine low-pressure cylinder and solve the flow field;

[0008] S2. According to the results obtained in S1, obtain the water erosion coefficient of the steam turbine under different loads;

[0009] The method for obtaining the water erosion coefficient E is as follows:

[0010]

[0011] Where: G v represents the relative volume flow rate at the outlet of the last-stage stationary blade, y1 represents the humidity at the outlet of the last-stage stationary blade, p1 represents the pressure at the outlet of the last-stage stationary blade, v1 represents the velocity at the outlet of the last-stage stationary blade, D represents the outer diameter of the last-stage impeller, n represents the steam turbine speed, L c represents the chord length along the streamline of the last-stage moving blade, A1 represents the axial clearance between the last-stage stationary and moving blades, and λ represents the throat ratio;

[0012] S3. Analyze the water erosion of the steam turbine under different loads according to the water erosion coefficient obtained in S2.

[0013] Preferably, the specific method for modeling the entire cylinder blades of the steam turbine low-pressure cylinder and solving the flow field in S1 includes:

[0014] S1-1. Establish a model of the entire cylinder blades of the steam turbine low-pressure cylinder according to the structure of the entire cylinder blades of the steam turbine low-pressure cylinder;

[0015] S1-2. Perform mesh division on the model of the entire cylinder blades of the steam turbine low-pressure cylinder, and import the divided mesh into the fluid analysis simulation module;

[0016] S1-3. According to the thermal characteristics specification of the entire cylinder blades of the steam turbine low-pressure cylinder, set the inlet boundary conditions, outlet boundary conditions, and convergence conditions for the mesh imported in S1-2;

[0017] S1-4. The fluid analysis simulation module calculates according to the inlet boundary conditions and outlet boundary conditions;

[0018] S1-5. The fluid analysis simulation module determines whether the calculation result reaches the convergence conditions. Otherwise, return to execute S1-4. If yes, output the result file;

[0019] S1-6. Use fluid post-processing software to process the result file to obtain the humidity at the outlet of the last-stage stationary blade, the pressure at the outlet of the last-stage stationary blade, the velocity at the outlet of the last-stage stationary blade, and the relative volume flow rate at the outlet of the last-stage stationary blade;

[0020] S1-7. According to the structure and thermodynamic characteristic specification of the whole-cylinder blades of the steam turbine low-pressure cylinder, obtain the steam turbine speed, the axial clearance between the last-stage moving and stationary blades, the outer diameter of the last-stage impeller, the chord length of the last-stage moving blade along the streamline, and the throat ratio.

[0021] Preferably, the fluid analysis and simulation module described in S1-2 is implemented by ANSYS-CFX.

[0022] Preferably, the inlet boundary conditions described in S1-3 include temperature and pressure inlets; the outlet boundary condition described in S1-3 is a pressure outlet; the convergence condition described in S1-3 is a convergence residual of 10 -5 .

[0023] Preferably, the fluid post-processing software described in S1-6 is implemented by CFD-POST.

[0024] Preferably, the specific method for analyzing the steam turbine water erosion under different loads according to the water erosion coefficient in S3 includes:

[0025] Import the water erosion coefficient into the function plotting software. The function plotting software exports the water erosion coefficient curve graph of the steam turbine under different loads, and analyzes the water erosion degree of the steam turbine according to the water erosion coefficient curve graph to obtain the size and location of the steam turbine water erosion under different loads.

[0026] Preferably, the function plotting software described in S3 is implemented by the software Origin.

[0027] Preferably, when the water erosion coefficient E > 0.0001, the steam turbine has a water erosion risk. Advantages of the present invention: The present invention proposes a method for determining the water erosion degree of the last stage of the steam turbine low-pressure cylinder under different loads. According to the flow field solution results, the water erosion coefficient of the steam turbine under different loads is obtained, and then the size and location of the water erosion of the last stage of the steam turbine under different loads are obtained. The water erosion degree determination method proposed by the present invention can well determine the water erosion degree of the last stage of the steam turbine under different loads, provide guarantee for the safety of the last-stage blades of the steam turbine low-pressure cylinder, and ensure the safe and stable operation of the steam turbine unit and the entire power plant. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 is the principle block diagram of a method for determining the water erosion degree of the last stage of a steam turbine low-pressure cylinder according to the present invention;

[0029] Figure 2 is a schematic diagram of a single-flow channel model of the whole-cylinder blades of a 300MW steam turbine low-pressure cylinder proposed in Embodiment 2;

[0030] Figure 3 is a schematic diagram after meshing Figure 2 ;

[0031] Figure 4 is the erosion coefficient of the integral blades of the low-pressure cylinder of a 300MW steam turbine under 100% THA condition proposed in Embodiment 2;

[0032] Figure 5 is the erosion coefficient of the integral blades of the low-pressure cylinder of a 300MW steam turbine under 50% THA condition proposed in Embodiment 2;

[0033] Figure 6 is the erosion coefficient of the integral blades of the low-pressure cylinder of a 300MW steam turbine under 20% THA condition proposed in Embodiment 2. Specific embodiments

[0034] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described 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, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0035] It should be noted that, without conflict, the embodiments in the present invention and the features in the embodiments may be combined with each other.

[0036] Next, the present invention will be further described in conjunction with the accompanying drawings and specific embodiments, but it is not a limitation of the present invention.

[0037] Embodiment 1:

[0038] Next, in conjunction with Figure 1 this embodiment will be described. The method for determining the erosion degree of the last stage of the low-pressure cylinder of a steam turbine under different loads in this embodiment includes:

[0039] S1. Model the integral blades of the low-pressure cylinder of the steam turbine and solve the flow field;

[0040] S2. According to the results obtained in S1, obtain the erosion coefficients of the steam turbine under different loads;

[0041] The method for obtaining the erosion coefficient E is:

[0042]

[0043] Where: G vrepresents the relative volumetric flow rate at the outlet of the last-stage stator blade, y1 represents the humidity at the outlet of the last-stage stator blade, p1 represents the pressure at the outlet of the last-stage stator blade, v1 represents the velocity at the outlet of the last-stage stator blade, D represents the outer diameter of the last-stage impeller, n represents the steam turbine speed, L c represents the chord length along the streamline of the last-stage rotor blade, A1 represents the axial clearance between the last-stage stator and rotor blades, λ represents the throat ratio;

[0044] S3. Analyze the water erosion of the steam turbine under different loads according to the water erosion coefficient obtained in S2.

[0045] Furthermore, the specific method of modeling the integral blades of the low-pressure cylinder of the steam turbine and solving the flow field described in S1 includes:

[0046] S1-1. Establish a model of the integral blades of the low-pressure cylinder of the steam turbine according to the structure of the integral blades of the low-pressure cylinder of the steam turbine;

[0047] S1-2. Mesh the model of the integral blades of the low-pressure cylinder of the steam turbine, and import the meshed grid into the fluid analysis simulation module;

[0048] S1-3. Set the inlet boundary conditions, outlet boundary conditions and convergence conditions for the grid imported in S1-2 according to the thermal characteristics specification of the integral blades of the low-pressure cylinder of the steam turbine;

[0049] S1-4. The fluid analysis simulation module calculates according to the inlet boundary conditions and outlet boundary conditions;

[0050] S1-5. The fluid analysis simulation module determines whether the calculation result reaches the convergence conditions. Otherwise, return to execute S1-4. If yes, output the result file;

[0051] S1-6. Use fluid post-processing software to process the result file to obtain the humidity at the outlet of the last-stage stator blade, the pressure at the outlet of the last-stage stator blade, the velocity at the outlet of the last-stage stator blade, and the relative volumetric flow rate at the outlet of the last-stage stator blade;

[0052] S1-7. Obtain the steam turbine speed, the axial clearance between the last-stage stator and rotor blades, the outer diameter of the last-stage impeller, the chord length along the streamline of the last-stage rotor blade, and the throat ratio according to the structure and thermal characteristics specification of the integral blades of the low-pressure cylinder of the steam turbine.

[0053] Furthermore, the fluid analysis simulation module described in S1-2 is implemented by ANSYS-CFX.

[0054] Furthermore, the inlet boundary conditions described in S1-3 include temperature and pressure inlets; the outlet boundary condition described in S1-3 is a pressure outlet; the convergence condition described in S1-3 is a convergence residual of 10 -5 。

[0055] Furthermore, the fluid post-processing software described in S1-6 is implemented using CFD-POST.

[0056] Furthermore, the specific method for analyzing the water erosion of a steam turbine under different loads according to the water erosion coefficient described in S3 includes:

[0057] Import the water erosion coefficient into a function plotting software, and the function plotting software exports the water erosion coefficient curve graph of the steam turbine under different loads. Analyze the degree of water erosion of the steam turbine according to the water erosion coefficient curve graph to obtain the size and location of the water erosion of the steam turbine under different loads.

[0058] Furthermore, the function plotting software described in S3 is implemented using the software Origin.

[0059] Furthermore, when the water erosion coefficient E > 0.0001, the steam turbine is at risk of water erosion.

[0060] Embodiment 2:

[0061] The following combines Figures 2 - 6 to illustrate this embodiment. The method for determining the degree of water erosion at the last stage of the low-pressure cylinder of a steam turbine under different loads described in this embodiment includes:

[0062] S1. Model the entire cylinder blades of the low-pressure cylinder of the steam turbine and solve the flow field;

[0063] S2. According to the results obtained in S1, obtain the water erosion coefficient of the steam turbine under different loads;

[0064] The method for obtaining the water erosion coefficient E is:

[0065]

[0066] Where: G v represents the relative volumetric flow rate at the outlet of the last-stage stationary blade, y1 represents the humidity at the outlet of the last-stage stationary blade, p1 represents the pressure at the outlet of the last-stage stationary blade, v1 represents the velocity at the outlet of the last-stage stationary blade, D represents the outer diameter of the last-stage impeller, n represents the rotational speed of the steam turbine, L c represents the chord length along the streamline of the last-stage moving blade, A1 represents the axial clearance between the last-stage stationary and moving blades, and λ represents the throat ratio;

[0067] S3. According to the water erosion coefficient obtained in S2, analyze the water erosion of the steam turbine under different loads.

[0068] Further, taking a 300MW steam turbine as an example, the method for determining the degree of water erosion at the last stage of its low-pressure cylinder is described:

[0069] Model the entire cylinder blades of the low-pressure cylinder of the steam turbine, as Figure 2 shown, and then perform mesh division on it, as Figure 3 shown.

[0070] According to the steam turbine blade design drawings and the thermal characteristics specification, the rotational speed of the steam turbine n = 3000 r / min, the axial clearance A1 between the last-stage moving and stationary blades = 0.00384 m, and the chord length L of the last-stage moving blade along the streamline c = 0.3691, the throat ratio λ = 0.2198, and the outer diameter D of the last-stage impeller = 3.786.

[0071] According to the simulation results, at 100%, 50%, and 20% THA operating conditions, the humidity y1, pressure p1, velocity v1, and relative volume flow rate G at the outlet of the last-stage stationary blade along the blade height direction v . After importing the above data into the water erosion coefficient E for calculation, the water erosion coefficients E under these three operating conditions are obtained, as Figures 4 - 6 shown. When the water erosion coefficient E exceeds 0.0001, water erosion occurs at the last stage of the low-pressure cylinder of the steam turbine. It can be seen from the water erosion coefficient curve that water erosion occurs when the steam turbine operates under three loads. And as the load decreases from 100% THA to 50% THA, the degree of water erosion gradually deepens. And the severely water-eroded area is concentrated at 40% of the blade height. When the load is at 20% THA, the unit reaches the blowing condition, the temperature rises, and the water erosion coefficient decreases.

[0072] Although the present invention has been described herein with reference to specific embodiments, it should be understood that these embodiments are merely examples of the principles and applications of the present invention. Therefore, it should be understood that many modifications can be made to the exemplary embodiments, and other arrangements can be designed, as long as they do not depart from the spirit and scope of the present invention as defined by the appended claims. It should be understood that different dependent claims and the features described herein can be combined in a manner different from that described in the original claims. It should also be understood that the features described in connection with a single embodiment can be used in other described embodiments.

Claims

1. A method for determining the degree of water erosion at the last stage of the low-pressure cylinder of a steam turbine under different loads, characterized in that, It includes: S1. Model the integral blades of the low-pressure cylinder of the steam turbine and solve the flow field; S2. According to the results obtained in S1, obtain the erosion coefficient of the steam turbine under different loads; The method for obtaining the erosion coefficient E is as follows: Where: G v represents the relative volume flow rate at the outlet of the last-stage static blades, y1 represents the humidity at the outlet of the last-stage static blades, p1 represents the pressure at the outlet of the last-stage static blades, v1 represents the velocity at the outlet of the last-stage static blades, D represents the outer diameter of the last-stage impeller, n represents the rotational speed of the steam turbine, L c represents the chord length along the streamline of the last-stage moving blades, A1 represents the axial clearance between the last-stage static and moving blades, and λ represents the throat ratio; S3. According to the erosion coefficient obtained in S2, analyze the erosion of the steam turbine under different loads.

2. A method for determining the water erosion degree of the last stage of a steam turbine low-pressure cylinder under different loads, characterized in that, The specific method of S1 for modeling the integral blades of the low-pressure cylinder of the steam turbine and solving the flow field includes: S1-1. Establish a model of the integral blades of the low-pressure cylinder of the steam turbine according to the structure of the integral blades of the low-pressure cylinder of the steam turbine; S1-2. Perform mesh division on the model of the integral blades of the low-pressure cylinder of the steam turbine, and import the divided mesh into the fluid analysis simulation module; S1-3. According to the thermal characteristics specification of the integral blades of the low-pressure cylinder of the steam turbine, set the inlet boundary condition, outlet boundary condition and convergence condition for the mesh imported in S1-2; S1-4. The fluid analysis simulation module performs calculations according to the inlet boundary condition and outlet boundary condition; S1-5. The fluid analysis simulation module determines whether the calculation result reaches the convergence condition. Otherwise, return to execute S1-4. If yes, output the result file; S1-6. Use fluid post-processing software to process the result file to obtain the humidity at the outlet of the last-stage stationary blade, the pressure at the outlet of the last-stage stationary blade, the velocity at the outlet of the last-stage stationary blade, and the relative volume flow rate at the outlet of the last-stage stationary blade; S1-7. According to the structure and thermal characteristics specification of the integral blades of the low-pressure cylinder of the steam turbine, obtain the steam turbine speed, the axial clearance between the last-stage moving and stationary blades, the outer diameter of the last-stage impeller, the chord length of the last-stage moving blade along the streamline, and the throat ratio.

3. A method for determining the degree of water erosion of the last stage of a steam turbine low-pressure cylinder under different loads, characterized in that, The fluid analysis simulation module described in S1-2 is implemented by ANSYS-CFX.

4. A method for determining the degree of water erosion at the last stage of a low-pressure cylinder of a steam turbine under different loads, characterized in that, The inlet boundary conditions described in S1-3 include temperature and pressure inlets; the outlet boundary condition described in S1-3 is a pressure outlet; the convergence condition described in S1-3 is a convergence residual of 10 -5 .

5. A method for determining the water erosion degree of the last stage of a steam turbine low-pressure cylinder under different loads, characterized in that, The fluid post-processing software described in S1-6 is implemented by CFD-POST.

6. A method for determining the water erosion degree of the last stage of a steam turbine low-pressure cylinder under different loads, characterized in that, The specific method of S3 for analyzing the erosion of the steam turbine under different loads according to the erosion coefficient includes: Import the erosion coefficient into the function plotting software. The function plotting software exports the erosion coefficient curve graph of the steam turbine under different loads. Analyze the erosion degree of the steam turbine according to the erosion coefficient curve graph to obtain the size and location of the erosion of the steam turbine under different loads.

7. A method for determining the water erosion degree of the last stage of a steam turbine low-pressure cylinder under different loads, characterized in that, The function plotting software described in S3 is implemented by the software Origin.

8. A method for determining the water erosion degree of the last stage of a steam turbine low-pressure cylinder under different loads, characterized in that, When the erosion coefficient E > 0.0001, the steam turbine has an erosion risk.

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