Abstract
In the operating process of the coal-fired generation during flexible peaking regulation, the primary and secondary water droplets in the steam flowing through the last two stages of the low-pressure cylinder could influence the efficiency and safety of the steam turbine definitely. However, systematic analysis of the movement characteristics of water droplets under low-load conditions is scarcely in the existing research, especially the ultra-low load conditions below 30%. Toward this end, the more novel algebraic slip model and particle transport model mentioned in this paper are used to simulate the primary and secondary water droplets. Taking a 600 MW unit as a research object, the droplets motion characteristics of the last two stages were simulated within four load conditions, including 100, 50, 40, and 30% THA. The results show that the diameter of the primary water droplets is smaller, ranging from 0 to 1 µm, during the flexible peak regulation process of the steam turbine. The deposition is mainly located at the entire moving blades and the trailing edge of the last two stator blades. With the load decreasing, the deposition effect decreases sustainably. And the larger diameters of secondary water droplets range from 10 to 300 µm. The erosion of secondary water droplets in the last stage is more serious than that of the second last stage for different load conditions, and the erosion of the second last stage could be negligible. The pressure face and suction face at 30% blade height of the last stage blade have been eroded most seriously. The lower the load, the worse erosion from the secondary water droplets, which poses a potential threat to the fracture of the last stage blades of the steam turbine. This study provides a certain reference value for the optimal design of steam turbine blades under flexible peak regulation.
Highlights
Under the condition of deep peak shaving of thermal power unit, the steam intake of the steam turbine is significantly reduced, and the low-pressure cylinder is in a small flow condition, and water erosion will occur in the last two stages of the low-pressure cylinder (Li et al, 2020; He et al, 2021; Wang et al, 2021)
During the operation process of the steam turbine, the primary water droplets that condenses by expansion are mixed with pure steam and moves together when the steam passes through the last two stages of the low-pressure cylinder. (Gribin et al, 2017)
A part of it will adhere to the surface of the blade of the steam turbine, and when the water droplets deposited on the surface of the blade accumulate to a certain amount, the water droplets will adhere to the blade by water film
Summary
Under the condition of deep peak shaving of thermal power unit, the steam intake of the steam turbine is significantly reduced, and the low-pressure cylinder is in a small flow condition, and water erosion will occur in the last two stages of the low-pressure cylinder (Li et al, 2020; He et al, 2021; Wang et al, 2021). Due to the movement characteristics of the secondary water droplets, it will impact the turbine blades and erode the blade surface, and the last stage blades of the steam turbine will appear water erosion (Ahmad, 2018; Ahmad et al, 2018; Bohn et al, 2021). The research on the movement characteristics of water droplets in the low-pressure cylinder of steam turbines is limited to a single rated load. Droplet transport model to simulate and analyze the water droplet movement characteristics in the last two stages of the steam turbine under different load conditions. In order to better simulate the motion characteristics of water droplets in the low-pressure cylinder of a steam turbine, a physical model is established with the last two stage blades of a low-pressure cylinder of a 600 MW steam turbine as the research object. Where mp is the particle quality, u is the velocity, ρ is the density, μ is the fluid kinematic viscosity coefficient, CD is the drag coefficient, Fb is the buoyancy due to gravity, ω is the rotational angular velocity, R is the calibrate the direction vector of the rotation axis, FU is the user-defined other forces, f, p represents vapor phase and liquid respectively, t0 is the start time, t1 is the end time
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