Study On Surface Modification Of Process Equipment And Adhesion Behavior Of Fouling

Corrosion and fouling on the heat transfer surface of process equipment are the main problems that affect the safety and efficiency of the system.Under the influence of the thermophysical parameters of the circulating working medium,the nucleation,agglomeration,deposition and migration of corrosion products and crystallization fouling will occur in the circulating system.However,when the corrosion products and crystallization fouling formed on the heat exchange surfaces with different corrosion degrees,the deposition and peeling of corrosion products and crystallization fouling were different.And the crystal structure of corrosion products and crystallization fouling,the density of fouling layer and the concentration of solution ions in the heat transfer medium are distinguishing microscopically.In this paper,the first principle and molecular dynamics method were used to study the correlation theory of corrosion and fouling.Based on the combination of crystallization fouling with iron-based and corrosion interface,the adhesion mechanism of crystallization fouling was microscopically analyzed.The adsorption behavior of different crystal forms of calcium carbonate?calcite,aragonite and vaterite?on the surface of?-Fe₂O₃?0 0 1?was investigated.Besides,the density of state,mean square displacement curve,relative concentration distribution,radial distribution function and binding energy were further researched.Furthermore,the mechanism of the different crystal forms of calcium carbonate crystallization fouling on the corrosion interface and the deposition rule of crystallization fouling under the different temperatures were studied.Compared with the results of molecular dynamics simulation,the morphology and phase structure of crystallization fouling before and after corrosion were discussed with flow corrosion fouling experiment rig,scanning electron microscope,energy dispersive spectrometer and X-ray diffractometer.The phase structure of the fouling can be affected by different corrosion and surface energy of the sample,and the corrosion resistance of the sample is closely related to the formation of the fouling.The Ni-W-P electroless plating technology and laser cladding technology can reduce the adhesion energy between the substance and the adsorbate to a certain extent,and they have certain inhibition effect on the adhesion and deposition of crystallized fouling and corrosive fouling.The surface morphology and microstructure of Ni-W-P anti-fouling coating were studied.The thermal conductivity of ternary Ni-W-P anti-fouling coating with different tungsten content was measured and analyzed by heat flow method.The anti-fouling and heat transfer characteristics of Ni-W-P coating before and after fouling were calculated by flow fouling deposition experiment and fouling thermal resistance method.Additionally,the adsorption behavior of various lattice types of calcium carbonate fouling on the surface with different corrosion degree were compared.The results proved that the oxidation products were always accompanied by calcite-phase calcium carbonate fouling.Due to the difference of surface free energy,the binding energy of calcium ion and carbonate ion was also different,which leads to the formation of more aragonite-phase calcium carbonate on the Ni-W-P ternary coating,and the formation of more calcite-phase calcium carbonate on the surface of bare substrate or Ni-W-P coating with high tungsten content.The thermal conductivity of ternary Ni-W-P coating decreases with the increase of tungsten content.Meanwhile,with the increase of heat source temperature and the extension of time,the heat transfer efficiency of Ni-W-P surface after fouling is superior than that of the bare substrate after fouling.The ternary Ni-W-P coating with different tungsten content was further prepared to conduct the supercritical water experiment.Crystallization characteristics and evolution of the oxide film of Ni-W-P coating before and after oxidation in supercritical water were compared.The evolution mechanism of ternary Ni-W-P coating with different tungsten content after supercritical oxidation was characterized with fractal method.The oxidation characteristics of the coating under supercritical condition was revealed and the optimal plating parameters was obtained.Consequently,with the increase of tungsten content,the fractal dimension of the coating decreases,and the supercritical water oxidation resistance and the stability of the coating became worse.The fractal characterization of not heavily oxidized coatings is of a linear change after supercritical water oxidation.Therefore,the Ni-W-P coating with a certain ratio still has good oxidation resistance of supercritical water at high temperature and high pressure.The coating surface has good compactness and can effectively inhibit the deposition of corrosion fouling under supercritical condition.The iron-based?Fe-Cr-Ni?and nickel-based?Ni-Cr-Mo-Nb?coatings were prepared with laser cladding method to improve the oxidation resistance of the materials under supercritical conditions.After that,the crystallization characteristics and the evolution process of the laser cladding layer before and after supercritical oxidation were analyzed.Meantime,the applicability of two laser cladding coatings in supercritical water was verified.The results demonstrated that the diffusion of transition elements in the coating could be influenced by the high temperature and high pressure,while the influence on diffusion behavior of the matrix element was relatively limited.The element close to the fusion line still maintain good characteristics.During the process of supercritical water oxidation,crystals in different regions were connected,resulting in the transformation from equiaxed crystals to columnar crystals.The effect of supercritical water and oxygen on the phase structure of laser cladding coating was restricted,and the deposition of corrosion fouling on the two laser cladding coatings was effectively inhibited.Iron-based and nickel-based coatings have good compactness and can be effectively used in supercritical water oxidation.Comparatively,the oxidation resistance of supercritical water of nickel-based laser cladding layer is better than that of iron-based laser cladding layer.This work plays a significant role in the formation of corrosion products on the heat transfer surface and the adhesion mechanism of crystallization fouling,and provide basic theoretical support for the protection of pipeline components under supercritical conditions.The dissertation has 92 figures,15 tables and 235 references.