Fundamental Research On The Injection Of Biomass Char Into Blast Furnace

Due to the large energy consumption,the rapid development of steel industry has brought a lot of environmental pollutions.With the gradual implementation of carbon trading,it becomes urgent to develop new technologies to reduce the CO2 emissions for steel industry.Moreover,the key to reduce CO2 emissions lies in reducing the use of coal resource.As one of the most important environmental-friendly renewable energy sources,the rational utilization of biomass could be an effective way.Therefore,it is necessary to carry out systematic research on the injection of biochar into blast furnace(BF)and provide fundamental basis for BF injection of biochar.In this paper,the preparation of biochar,the co-combustion characteristics of biochar and coal,and the effect of injection of biochar into the BF were studied through series of experiments.Firstly,the pyrolysis behaviors of three kinds of biomasses were studied by thermogravimetry-mass spectrometer.It was found that the pyrolysis range of biomass was 200-600℃,and the pyrolysis was most severe in the range of 200-400℃.The tube furnace was used to prepare biochar with different pyrolysis conditions.It was found that the yield of biochar decreased with the increase of pyrolysis temperature and residence time.The reduction rate was the largest in the range of 300-400℃.The volatile matter decreased and the fixed carbon increased obviously.Meanwhile,based on the elemental composition,the carbon content increased greatly,but the hydrogen and oxygen contents exhibited an opposite trend.The contents of the biochar prepared at 600℃ were similar to those of coal.As the pyrolysis temperature and the residence time increased,the combustion and gasification reactivity of biochar gradually decreased,and the reaction behavior was closer to that of carbonaceous materials such as coal.It was also found that when the pyrolysis temperature was high,the residence time had little effect on the properties of the biochar.The results indicated that the optimal condition for the preparation of biochar were as follows:pyrolysis temperature 600℃ and residence time 60 min.Secondly,the physicochemical characteristics of the biochars were systematically studied by scanning electron microscopy(SEM),nitrogen adsorption,X-ray diffraction(XRD),Raman spectrometer and Fourier Transform Infrared(FTIR).The relationship between the physical pore structure,the crystalline composition and the functional groups of the biochar and the pyrolysis parameters were ascertained.The results showed that an increase in pyrolysis temperature led to the development of pore structure and specific surface area of the biochar.Besides,the aromaticity and ordered carbon structure of biochar also increased as the temperature increased.Therefore,biomass pyrolysis is a process in which a highly disordered structure gradually becomes an ordered structure and the crystalline structure order is gradually increased.Thirdly,the co-combustion characteristics and kinetic behaviors of the anthracite(YQ)and palm kernel shell char(PC)blends were investigated by thermogravimetric analysis.The combustion reactivity of YQ could be enhanced by mixing with PC.During the co-combustion process,two kinds of synergistic effects were distinguished:the existence of YQ restricts the ignition of PC,but the ignition and combustion of the solid carbon in the YQ can be obviously promoted by the PC.The RPM is more applicable than the VM for the co-combustion process.The proportion of PC should be less than 20%to reduce alkali load.Fourthly,the unburned carbon residues(UCR)of YQ,PC and YQ blend were prepared under laboratory conditions.The influence of UCR on the gasification reactivity of the coke was studied by thermogravimetric analyzer.A melt physical properties comprehensive tester was used to study the effect of UCR on the slag viscosity.It was found that the gasification reactivity of UCR was better than coke,which may protect the coke from gasification.And UCR could slightly promote the gasification reactivity of coke without further deterioration of coke.The results also indicated that the UCR could increase the viscosity of the slag.Moreover,the decrease of rotational speed and temperature,increase of UCR mass fraction could raise the slag viscosity.Due to the higher content of CaO and MgO in PC ash,the PC could reduce the influence of UCR on slag viscosity.Finally,the influence of the PC injection on the BF technical indexes was calculated by the mass and heat balance.The results indicated that the direct reduction degree and the fuel ratio were reduced,while the tuyere coke quantity and gas efficiency exhibited an opposite trend.In addition,the blast volume and the bosh gas volume were reduced,and the flame temperature was almost unchanged.As a result,the CO2 emission was significantly reduced.On the whole,PC injection can ensure the normal technical indexes,which indicated the feasibility of the PC injection into BF.