Research On Corrosion Characteristics Of Alloy Fiber Filter Material For High Temperature Dust Removal

In order to vigorously promote energy conservation and emission reduction and adhere to green development,high-temperature flue gas filtration and dust removal technology,as an important part and key technology of advanced production technology,is widely used in many fields.However,the current common high temperature resistant filter materials cannot meet the requirements of high temperature dust removal.Among them,the glass fiber filter material has poor temperature resistance and folding resistance;the ceramic porous filter material has poor thermal vibration resistance,short service life and high cost.Therefore,it is of great significance for environmental protection,energy conservation and sustainable development to develop and research new and high-performance alloy fiber filter materials with the research goal of high-temperature flue gas filtration and dust removal.In this paper,starting from the research of corrosion mechanism and prediction of corrosion life,the corrosion behavior and corrosion mechanism of three kinds of alloy fiber filter materials（316L,904L,Hastelloy C-276）in SO₂,SO₃,HCl and HF atmospheres were studied by laboratory corrosion simulation,and the service life of 316L alloy fiber filter materials was predicted by thermal analysis kinetics.Sulfur oxides have weak corrosive effects on the alloy fiber filter material.In addition to the dehumidifying SO₃ atmosphere,there are protective corrosion layers on the surface of the alloy fiber filter material in other atmospheres.In the SO₂ atmosphere,the overall corrosion degree of the three alloy fiber filter materials is relatively low.HC alloy fiber is highly sensitive to O₂,and the corrosion resistance of HC filter media after partial oxidation is the best among the three.The change of SO₂ concentration has a weak effect on the corrosion reaction.The addition of H₂O significantly inhibits the corrosion reaction,and water vapor and its derivatives in high temperature gas can keep SO₂ in molecular state.The corroded316L filter material has local pitting pits which occur at the surface of non-metallic inclusions Mn S.The reason is that the potential difference between the inclusions and the metal matrix accelerates the migration of metal ions.In SO₃ atmosphere,the corrosion resistance of HC filter material is still excellent.In dry SO₃ atmosphere,the fitting indexs of corrosion weight gain rate of three kinds of alloy fiber filter media are greater than 2.The corrosion products contain some metal sulfate besides oxide,both playing a role in retarding the reaction.In a wet SO₃ atmosphere,part of SO₃ will react with H₂O to generate H₂SO₄ molecules,which accelerates the corrosion reaction.The corrosion rate in a wet SO₃ atmosphere is negatively correlated with temperature changes.Through the characterization of the 316L filter material after corrosion in dry/wet SO₃ atmosphere,it is found that at a temperature lower than the acid dew point,sulfuric acid vapor will condense on the surface of the fiber filaments,resulting in the formation of a large number of pitting holes,accelerating the penetration of corrosive gas,and causing cracks and peeling.Compared with the sulfur oxide in flue gas,the two kinds of hydrogen halide have stronger corrosion effect on the alloy fiber filter.After corrosion,the mechanical properties of the 316L alloy fiber filter material declined seriously,and it completely failed under the HF+O₂ atmosphere.For HCl atmosphere,the chlorine resistance of three kinds of alloy fiber filter materials increases with the increase of Mo content in the alloy.Mo element can inhibit the growth of the grains in the alloy,which is beneficial to the corrosion resistance of the alloy.The concentration of HCl plays a key role in the corrosion resistance of alloy.The combination of HCl+O₂ with a certain concentration is disastrous for 316L alloy fiber filter material.The corrosive ability of HCl in an oxidizing atmosphere is stronger than that of a pure HCl atmosphere because of the autocatalysis of Cl₂.In HF atmosphere,Cr,which is excellent in high temperature oxidation resistance,does not improve the corrosion resistance of the filter material.The reason is that the main products Fe F₂ and Cr F₂ formed by the corrosion of Fe and Cr are non-compact structures without blocking effect on the entry of corrosive gas.According to the microscopic morphology of the filter material after corrosion,the corrosive effect of HF is mainly carried out in the form of pore growth.In the initial stage of the corrosion reaction,under the combined action of HF and O₂,the surface of the filter material forms loose structure including metal oxide and fluoride.Then the corrosion gas penetrates into the inner along the gap of surface product,and corrosion reaction occurs at the interface between alloy matrix and external corrosion layer where metal fluoride and H₂O gas are generated.During the process of diffusion of H₂O gas to the outside,metal fluoride is oxidized to metal oxide and HF is released at the same time,forming HF cycle,which eventually causes mechanical damage on the surface of alloy fiber material.In order to predict the service life of 316L filter,the corrosion reaction under simulated flue gas atmosphere was analyzed by thermal analysis dynamics,and the three factors of corrosion reaction were obtained;Then,the dynamic three factors were substituted into the heterogeneous dynamic equation,and the prediction model of 316L alloy fiber filter material life was established.At the same time,two 316L filter were suspended in the flue of the actual project,and the actual working conditions of 270 days and 542 days were corroded respectively.The corrosion products were characterized by the results that the filter material corroded for 542 days had been completely invalid,which was in line with the calculation results of the service life prediction model established in this paper.