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Erosion and Corrosion of Gas-solid Two-phase Flow in Pipes

Author: ZhangYi
Tutor: ZhouZuoMin
School: Central South University
Course: Power Engineering
Keywords: medium and low temperature flue gas gas-solid two-phase flow low-temperature corrosion flow erosion numerical simulation
CLC: TG172
Type: Master's thesis
Year: 2011
Downloads: 188
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Abstract

In the process of utilizing medium and low temperature flue gas waste heat in nonferrous metallurgy, the low-temperature electrochemical corrosion of the pipe line and the two phase flow erosion happen frequently. This process has complex mechanism and strong coupling effect. Hence, it has important theoretical significance and practical application value for further study on these problem. This thesis focuses on the issue of low-temperature corrosion and flow erosion. It aims at recovering low temperature flue gas waste heat in nonferrous metallurgy effectively.As for flow erosion, the thesis adopted computation fluid dynamics to make numerical simulation study, establishes the gas-solid two-phase flow mathematical model which suits for the calculation working conditions. Wearing capacity, shear stress and its distributing situation along the pipeline were simulated. Furthermore, a comparative analysis of the simulation results was made under different hydromechanics factor such as gas phase velocity, solid phase flow, two phase velocity, particle diameter and solid content. As for corrosion, the polarization curves, corrosion potential and current of 45#carbon steel, A6NO1S-T5aluminum and stainless steel 310 were discussed. In addition, the experiment results with different concentration of H2SO4 and experimental temperature were analyzed.The main conclusions of this thesis are as follows:1) As the gas flow velocity increases, the wearing capacity and shear stress increases, but the area of concentrative erosion reduces. The material’s maximum wearing capacity increases suddenly and shear stress also increases in a degree when the solid flow velocity increases to 25～30 m/s. The wearing capacity of material and shear stress increases when two-phase velocity increases, what more, the area of concentrative erosion reduces and its position moves forward.2) In certain area, the augmentation of particle diameter makes the decreasing of wearing capacity, and area of concentrative erosion reduces and its position remains unchanged, the shear stress almost remains unchanged too. Increasing of solid content makes the increase of wearing capacity and the enlargement of area of concentrative erosion. What’s more, its position moves backward while the shear stress almost remains unchanged.3) The corrosion rate of aluminum is relatively smaller under low or moderate concentrations of acid and relatively higher temperature. While the corrosion rate of stainless steel is extremely small in solution of high concentration.4) Generally, the influence of the increase of concentration of H2SO4 upon corrosion rate tends from promotion to inhibition. When the solution concentration is low, the increase of concentration promotes precipitation of H2 in cathode reaction and accelerates the process of electrochemical corrosion, and then the corrosion rate becomes larger. With the increasing of solution concentration, the oxidability of H2SO4 strengthens, which leads to oxidization of material’s surface. The membrane inhibits corrosion.5) The rising of temperature plays a positive role in corrosion rate. The rising temperature strengthens ion activity, accelerates diffusion velocity and promotes hydrogen evolution reaction in cathode.

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