Study On The Melting Characteristics Of Coal And Biomass Ash And Corrosion Mechanism Of Refractory

Biomass has the disadvantages of being heavily influenced by seasons,high in volatile matter and high alkali metal content,which limits the scale of biomass gasification.The co-gasification of biomass and coal makes up for the shortcomings of biomass gasification,which can not only reduce the emission of pollutants,but also reduce the melting temperature of coal ash realizing the smooth slag discharge of the gasifier.The corrosion of refractory materials by slag is a key issue affecting the stable operation and smooth slag discharge of entrained-bed gasifier.The ash melting characteristics are significant to the design,operation temperature selection and slag discharge of the gasifier.In this paper,the ash fusion characteristics,mineral composition,corrosion mechanism of slag on refractory and the slag structure at high temperature were studied through the ash fusion experiment,high temperature corrosion experiment,FactSage thermodynamic simulation and molecular dynamics simulation.The contents are recounted as follows:1.The intelligent ash melting point tester was used to detect the melting temperature of the mixed ash of biomass(corn straw(CS)and wheat straw(WS))and Shenhua bituminous coal(WS)under weakly reducing atmosphere.The results indicated that a certain amount of CS and WS are both Certain fluxing effect,the fluxing effect of WS is the most obvious.The chemical composition of each ash sample was detected by X-ray fluorescence spectrometry(XRF),and the base to acid ratio of the ash was calculated,finding that the correlation between the flow temperature of the mixed ash and the was poor.X-ray diffractometer(XRD)and FactSage thermodynamic simulation software were used to calculate and analyze the mineral conversion in the ash melting process.It was found that when the CS addition amount reached 30wt%,K2O in the ash reacted with SiO2 and Al2O3 to produce a large amount of high melting lecucite resulting in the highest ash flow temperature(FT);when the amount of WS added is 30wt%,a large amount of low-temperature co-melting of diopside and anorthite in the ash minimizes the ash's FT.WS has the most obvious effect on reducing the melting temperature of ashes.2.The high temperature corrosion experiment was used to study the corrosion process of WS and SH mixed ash on alumina refractories.The corroded sample was cut,and the cross-section image was taken with an optical microscope.It was found that the penetration depth was the smallest when the amount of WS added was 10 wt%.SEM-EDS was used to detect the morphology and element changes of the infiltrated area.The penetration depth and aggregation of each element in the refractory were analyzed.The results showed that Mg had the strongest diffusion ability in the refractory.Qualitative analysis of the mineral composition of the cross section using Raman spectroscopy finding that anorthite and mullite appeared in the infiltration layer.FactSage was used to draw phase diagram,the results showed that Mg interacts with alumina in the infiltration layer to form spines,which can prevent the further penetration of ash and slag into the refractory.3.Molecular dynamics simulation had been used to calculate the structure of the model system at high temperature.The model was characterized through the radial distribution function,coordination number,mean square displacement,and oxygen bond type.The simulation results of slag indicated that with the increase of WS addition,the shoulder width of the Si-O and Al-O peaks in the ash system increases,and the bonding ability decreases;the average bond length of Mg-O decreases and bonding ability of Mg enhanced.In addition,the proportion of[SiO4]in ash decreases indicating the addition of WS promotes the depolymerization of Si tetrahedra;the diffusion coefficients of K and Mg increase meaning their diffusion capacity increases;The proportion of[SiO5]and[AlO4]decreases first and then increases with the increase of WS addition.When the amount of WS added is 30 wt%,the proportion reaches the lowest indicating that the polymerization degree of the system is the lowest and the ash has the best fluidity.A slag-alumina system was established to simulate the high-temperature corrosion process of refractory materials by slag.The results show that the diffusion coefficient of each particle in the slag-alumina system is increased compared with the slag system.The diffusion coefficient of Mg is the largest meanning the ability to penetrate alumina is the strongest.