| As the national mainstay industry of our country,iron and steel industry has made great contribution to our country’s economy.In addition,with the increase of the production capacity of steel products,the consumption of fossil fuels gradually increases,and the emission of pollutants generated in the production process of steel products also gradually increases.As a green,renewable and clean fuel,biomass has low ash,sulfur and nitrogen content,as well as carbon neutral characteristics.Using biomass hydrochar in blast furnace injection process is one of the important and effective ways to save energy and reduce carbon emission in blast furnace ironmaking process.The transformation mechanism and directional preparation of biomass hydrochar are systematically studied through two ways of experimental research and theoretical research,which provides theoretical feasibility basis for blast furnace injection of biomass hydrochar,and has important significance for iron and steel enterprises to reduce fossil fuel consumption,develop new green fuel and reduce CO2 emissions.Firstly,the mechanism of microstructure transformation of biomass under hydrothermal carbonization(HTC)conditions was investigated.Corn straw,rice straw and poplar wood were selected as biomass materials.By preparing biomass hydrochar under different HTC conditions(temperature,holding time,liquid/solid ratio),the relationship between the physical and chemical characteristics of hydrochar and the preparation conditions was clarified.Then,the physicochemical structures of biomass samples and coal powder after HTC were analyzed by SEM,XRD,Raman and FTIR,so as to clarify the conversion mechanism of different agricultural and forestry wastes.Secondly,the microscopic transformation mechanism of biomass HTC process was investigated from the molecular perspective.The molecular model was constructed according to the content of lignin,cellulose and hemicellulose in poplar wood.Then,the molecular simulation calculation was carried out under the conditions of different HTC temperature,holding time and liquid-solid ratio.Finally,the simulation results of ReaxFF MD were analyzed and explained,so as to explain the carbonization path of biomass in the process of HTC,and the experimental results were verified and explained.Thirdly,the feasibility of using biomass hydrochar in blast furnace injection process is explored.Using agricultural and forestry wastes as biomass materials,different hydrochar samples were obtained by changing the HTC conditions.Blast furnace injection characteristics of hydrochar were characterized by ultimate analysis,proximate analysis,gas chromatography and thermogravimetric analysis.Based on the above research results,the influence of HTC conditions on the fuel performance of agricultural and forestry wastes was compared and analyzed.It makes theoretical contribution to obtain high-quality hydrochar,expand the application field of bio-wastes and improve the utilization rate of resources.Furthermore,the co-combustion and kinetic characteristics of biomass hydrochar and pulverized coal were investigated.The rice straw hydrochar and anthracite were selected as the raw materials in this part.The similarities and differences in the physical and chemical structure of biomass hydrochar and coal were analyzed by means of SEM,XRD,Raman and FTIR.Then,the combustion reaction processes of biomass hydrochar and pulverized coal were analyzed by thermogravimetric analysis.The effects of different mixing ratios of biomass hydrochar and pulverized coal on the combustion performance of the mixture were studied at different heating rates.Based on the above research results,the differences between hydrochar and anthracite in physicochemical structure and combustion performance are compared and analyzed,and the reaction mechanism of biomass hydrochar and anthracite mixture combustion reaction was clarified,which makes theoretical contribution to expanding the application of agricultural and forestry waste in the field of blast furnace iron making.Finally,the life cycle impact of biomass hydrochar on blast furnace production process after injection was studied.The evaluation content includes the traditional blast furnace ironmaking process(including sinter unit,coke unit,pulverized coal injection unit,pellet unit and blast furnace unit)and the new blast furnace ironmaking technology process(including sinter unit,coke unit,pulverized coal injection unit,pellet unit,blast furnace unit and biomass HTC unit).The life cycle impact assessment of traditional fossil fuel blast furnace ironmaking process and new blast furnace ironmaking technology using biomass resources as alternative fuel was carried out by Simapro software,so as to clarify the environmental feasibility of biomass resources replacing fossil fuels in blast furnace ironmaking process.Finally,the effect of biomass hydrochar on environmental benefit in the process of blast furnace ironmaking was determined. |
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