The Mineral Transformations Of Coal And Bimass Conversion Under Pressurized O₂/N₂ And O₂/CO₂ Conditions

Solid fuel combustion is one of the main sources of particulate matter in the atmosphere.The mineral phase transformation behavior in the fuelwill directly affect the melting characteristics of the burnout ash,which will affects the safety of the equipment at the same time.Meanwhile,with the development of new technologies such as oxygen-enriched combustion pressure（POFC）,pressurized fluidized bed combustion（PFBC）,integrated gasification combined cycle（IGCC）,the mineral transformations of coal and bimass under pressurized conditions had greadually attracted the attention of scholars.The medium-high pressure reaction environment and the specificity of biomass belend may had different migration of various minerals during combustion comparing with conventional pulverized coal combustion process.In order to clarify in depth the mineral conversion behavior of biomaia belended with pulverized coal under pressure conditions,the influences of pressure and temperature on the mineral transformations of coal char and ash were investigated by a high temperature and high pressure tube furnace.The results showed that the main minerals in the char were not significantly affected by the pyrolysis pressure,but some individual mineral phases changed at elevated pressure.The effect of temperature on the mineral transformations of char was more significant than that of pressure.With increasing furnace temperature,some low temperature minerals can be decomposed,but the increase of pressure inhibited their decompositions due to the suppression of gas evolution.The different reaction atmospheres（O₂/N₂ and O₂/CO₂）had limited effect on the main minerals in the ashes,but O₂/CO₂ combustion retarded the decomposition of low temperature minerals and the formation of high temperature minerals.It was found that the pressure had little effect on the main minerals in the residual ashes,but it can affect the relative contents of mineral phases.And,temperature had more significant effect on the mineral transformations of ash than pressure.The low temperature minerals was promoted to be decomposed by increasing the furnace temperature,but their decompositions were inhibited due to the relatively low combustion temperature at 4 MPa.The influence of pressure（0.1-6 MPa）on the mineral phase of coal char and peanut husk char and the carbon crystal structure and the mineral conversion of blended ash were investigated by using the tube furnace at higher temperatureand pressure combined with the analysis of X-ray diffractometer（XRD）.The results indicated that the pressure had little effect on the main mineral phases of peanut husk char and coal char,but it could affect the relative contents of mineral phases.Meanwhile,the graphitization degree of peanut husk char and coal char increased with increasing pressure.The blending of peanut husk inhibited the formation of mullite and promoted the formation of anorthite.When blending ratio was relatively low,the pressure mainly affected the mineral behavior by affecting the way of coal powder ignition.When blending ratio was high,the pressure mainly affected the combustion of biomass and thus the transformation of minerals.The effect of temperature on the mineral conversion behavior of blended ash was more significant than that of pressure.