| Biomass is basically self-renewing energy, through the photosynthesis of green plant, carbon dioxide plus water are converted into glucose and oxygen gas and the solar energy is converted into chemical energy. The quantity of carbon dioxide released from the burning of biomass is equal to the absorption of carbon dioxide in the process of plant growth, means biomass is CO2-neutralise.The utilization of biomass is very important for the country’s energy strategy and environmental protection. But there are large amounts of alkali metal and alkali earth metal in the biomass ash, which causes serious ash-related problems such as slagging, deposits, agglomeration and high temperature carrion. These problems are the main impediment to large-scale utilization of biomass. Therefore, based on the investigation of biomass ash fusion characteristic, the appropriate methods to predict biomass slagging tendency is built, and three kinds of additives is chosen burned with straw to investigate the influence on the straw ash fusion characteristic.Will straw, corn stover, wheat straw, peanut shells, branches, bark, six kinds of biomass were ashed in the muffle furnace, the ashing temperatures were600℃,700℃,800℃,900℃, afterwards the ash content’s change rule along with temperature was determined. Various biomass contained different ash content, the ash content of same biomass decreased gradually when the ashing temperature ascended, between600℃and800℃, its speed reduced quickly most, and after800℃, biomass ash content started to reduce slowly. Though the SEM, EDX analysis on the biomass ash in different temperature, it could be found that K and Si were the two highest levels of all elements, the biomass showed the slagging phenomenon when it burned at700℃, the alkali metal potassium and Cl of inorganic element content in the ash fell along with the rising of ashing temperature, and the changing tendency of the two elements was basically same, which explained Cl element that as the carrier of alkali metal potassium, promoting it volatilized in the form of KCl gas.In theory, as solid fuel, the combustion characteristics of biomass and coal were partly similar, the slagging tendency of biomass could be predicted by the slagging and fouling indices, but the alkali metal potassium, which played an important rule in biomass slagging characteristics, was easy to volatile in the form of KCl gas during combustion process. The error of ash composition measurement caused by alkali metal volatilization, made each biomass slagging tendency can not be determined by one single slagging and fouling index accurately. The determination of biomass ash melting characteristic temperature could illustrates biomass slagging tendency more intuitive, and when the initial deformation temperature of biomass is less than1100℃, the sintering intensity index could quantify biomass slagging tendency accurately.Based on experiments of biomass ash melting characteristic,(NH4)2SO4、(NH4)H2PO4and coal were selected as biomass additives, the amount of each additive was determined in accordance with the alkali metal (K+Na) content in the rice straw ash, then the simples were burned into ash in a muffle furnace.The influence of three kinds of additives on the straw ash slagging characteristic was investigated through the ash samples surface morphology, the ash fusion characteristics and sintering temperature intensity index, the results indicated that all of the three kinds of additives could improve straw ash slagging characteristic by increasing the initial deformation temperature and reducing the sintering intensity index. The effects of three kinds of additives was straw+(NH4)H2PO4> straw+coal> straw+(NH4)2SO4, phase analysis of bottom ash of straw+additives was done by XRD, the mechanism of additives inhibiting the straw ash slagging problem was analyzed. |
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