Applied Fundamental Research Of Injecting Agricultural And Forestry Residues Into Blast Furnace

A large amount of fossil fuels are consumed in blast furnace process, furthermore, quantitiesof greenhouse gases such as carbon dioxide are emitted. Lightening the environmental impacthas become a serious issue for sustainable development of blast furnace in the21st century.From the perspective of various modes of energy use, agricultural and forestry residues injectionin a blast furnace can reduce the consumption of fossil fuels. Moreover, the large-scaleprocessing of wastes would be achieved because of huge consumption. In this paper, severaltheory and techniques concerning agricultural and forestry waste injection in a blast furnace wereprimary studied by experiments, theoretical analyses and calculation model.Compared with the pulverized coal, straw has characteristics of high volatile, high oxygencontent and low emissions of SO2and NOx. The heat value of straw is about two thirds ofanthracite. It was found from SEM that there is no change in structure after fine broken of straw.The thermal decomposition behavior of straw and anthracite under air condition was investigatedby means of TG in order to distinguish the combustion property of straw and anthracite.Compared with pulverized coal, straw powder has lower ignition temperature, lower rapidignition temperature, shorter burning time and higher burning rate, which is beneficial to BFinjection. Mixing of straw powders promotes an improvement in burning behavior of anthracite,and could increase the utilization rate of coal.The melting characteristic of the straw ash was determined by histogram method, and thekey elements in the straw ash was analysed by EDS. The results show that straw ash fusiontemperature is low and it’s not suitable for injection alone. This may be because the alkali metal(Na, K) oxides and salts can react with SiO2in the ash to form low temperature melt. The ashfusion temperature of mixture of straw and anthracite coal is between the two substances. So theslagging problem caused by low biomass ash fusion temperature can be avoided by reasonablecollocation of the coal type, biomass type and mixing ratio.Effects of carbonization temperature on charcoal yield and composition were studied byslow pyrolysis in vacuum muffle furnace. The results show the yield decreases with the increaseof temperature, and the contents of fixed carbon and ash increase, the content of volatile matterdecreases. The unit mass charcoal’s calorific value increases with the increase of carbonizationtemperature, and the maximum total calorific value is achieved at350℃.The comparison of energy consumption and environmental impact was made when coal wassubstituted partially by straw or charcoal injecting into blast furnace. The energy consumption ofstraw injection is higher, and the coal consumption has doubled or more, and the oil consumptionincreases almost four times. In comparison with coal, discharge amount of pollutants is larger,and it is about seven times especially in the process of grinding straw. The discharge amount ofpollutants (CO2, CO and blast furnace slag) is about the same in the process of injection.Charcoal injection needs more raw materials and the energy consumption in carbonizationprocess is high. Based on pollution discharge fee and market price of international CO2emission indicator, environmental cost is reduced by2.23yuan producing a ton of hot metal. For a blastfurnace of2500m3inner volume, the total environmental cost reduced by5.5million yuan and11.32million yuan per year for straw injection and charcoal injection, repectively.