Zhiyun Ji

Effect of distribution of biomass fuel in granules on iron ore sintering and NOx emission

Abstract Pollutant emissions can be reduced by replacing coke breeze with biomass fuels in the sintering process. However, with increasing replacement ratio, yield and tumble index of the sinter decrease due to the increase in sintering vertical speed and the decrease in the combustion efficiency. The distribution of the fuel in the granules affects combustion, and the results of the research indicate that with the biomass fuels wrapped in the granules, the burning speed is reduced and the combustion efficiency improved because of the extended time of secondary combustion of CO. Biomass distribution inside the granules has been achieved by pregranulation. When biomass fuel replaced 40% coke breeze, the combustion efficiency increased from 86·92 to 87·90% by pregranulation and the yield and tumble index of the sinter was more competitive than using coke breeze alone. In addition, the emission of NOx is decreased by 30·71% with biomass distribution inside the granules.

Application of biomass fuel in iron ore sintering: influencing mechanism and emission reduction

Abstract The influence of biomass fuel replacing coke breeze on flame front and combustion efficiency were studied. The results show that when coke breeze is replaced, the flame front is accelerated since biomass has superior combustion characteristics. Combustion efficiency is decreased, however, as biomass is of excessively high reactivity, which can both lower the maximum temperature and reduce the time at high temperature of the sinter bed. The proportion of biomass fuel replacing coke breeze should, therefore, not exceed 40%, otherwise, the mineralisation of sinter material is insufficient and the yield and tumbler index of sinter significantly deteriorate. By increasing the size of biomass fuel, sinter indices are improved since the burning velocity of biomass fuel is optimised. When the proportion of biomass fuels is 40%, the emissions of SO2 and NO can be decreased by 40 and 28% respectively.

Influence of charcoal replacing coke on microstructure and reduction properties of iron ore sinter

This study was carried out to determine the influence of using charcoal as a supplementary fuel on the microstructure and reduction properties of sinter. The primary fuel was coke breeze with 0, 20, 30 and 40% replacement of weight input with charcoal to produce sinter. Experimental results indicate that when the replacement percentage of charcoal to coke breeze increased from 0 to 40%, the porosity and FeO content of sinter also rose. These changes result in an enhancement from 79.8 to 84.3% for the reducibility index due to the increased reducing surface area. In addition, the reduction degradation of sinter also improves since degradation during crystalline transformation is restricted. Therefore, replacing coke breeze with charcoal is able to improve the reducing properties of sinter, which is beneficial to small and large blast furnace operation.

Clean recycle and utilization of hazardous iron-bearing waste in iron ore sintering process

Applying recycled iron-bearing waste materials (RIM) into iron ore sintering process is the general disposal approach worldwide, while its use is still a thorny problem. Results showed that adding RIM increased contents of hazardous elements (K, Na, Pb, Zn, and Cl) in sinter product, and also enhanced emission concentration of PM2.5 in flue gas; increasing reaction temperature, and contents of CaO & coke breeze in raw mixtures improved hazardous elements removal. Based on these features, a novel method through granulating natural iron ores and RIM separately and distributing granulated RIM in bottom sintering layers was proposed for clean RIM cycle. When recycling 5% RIM, granulating RIM separately with higher contents of CaO and coke breeze removed hazardous elements effectively, the contents of which in sinter were reduced to comparable level of the case without RIM. Moreover, distributing RIM in bottom sintering layer reached intensive release of hazardous elements and PM2.5 during sintering, which reduced the flue gas volume needing purification by about 2/3. Through activated carbon purification, about 60% of PM2.5 comprised high contents of hazardous elements was removed. Novel technique eliminated the negative impact of RIM and has the prospect to reach clean recycle in sinter-making plants.

Participating patterns of trace elements in PM2.5 formation during iron ore sintering process

Patterns of trace elements participating in PM2.5 (aerosol dynamic diameter ≤2.5 μm) formation during iron ore sintering process were investigated. For elucidating this property, PM2.5 collected from before and after the flue-gas-temperature-rising point (stage-1 and stage-2) was examined. The results show that trace elements including Pb, K, Na, Cl and S presented an enriched tendency in PM2.5 from stage-2, while characterised lower contents in PM2.5 from stage-1. Owing to the tiny size of PM2.5, trace elements participated in the formation of Fe-rich and Fe–Al–Si-rich particles in heterogeneous manner. Moreover, S participated in the formation of CaSO4 particles from stage-1 and stage-2 in the form of homogeneous pattern, while Pb, K, Na and Cl participated homogeneously in the form of hybrid PbCl2–KCl, KCl and NaCl particles only from stage-2. The finding results clearly showed the relationship between the formation mechanisms of PM2.5 and the contribution of trace elements, which can serve as the guideline to control PM2.5 in sintering plants.

A laboratory-based investigation into the catalytic reduction of NOx in iron ore sintering with flue gas recirculation

The catalytic reduction behaviours between NOx and CO in sinter zone were studied as using flue gas recirculation (FGR). Minerals in sinter can act as catalysts during NOx reduction. The catalytic activity of minerals has the order of calcium ferrite > kirschsteinite > fayalite. The catalytic procedure includes two steps: iron-bearing minerals are reduced to lower valence oxides by CO, and then NO is reduced to N2 by lower valence oxides. Improving the generation amount of calcium ferrite, especially acicular-type silico-ferrite of calcium and aluminium (SFCA), contributes to significantly reinforcing the catalytic performance between NO and CO. As the basicity of sinter increases to 2.2, it enables to generate maximum amount of acicular-type SFCA which has larger specific surface areas, therefore facilitates decreasing NOx emission during FGR sintering.

Optimising method for improving granulation effectiveness of iron ore sintering mixture

Abstract The structure of granules has been investigated and a model of granulation determined. The results show that a granule consists of an adhesive layer and a nucleus. Particles with diameter under 0.5 mm act as adhesive fines, while the remainders act as nuclei. By studying the influencing factors of granulation, two significant particle characteristics assessing granulation performance were determined. One is the relative proportion of adhesive fines and nucleus particles, and the other is the specific surface area of adhesive fines. The method of optimising granulation of sinter mixtures is proposed as follows: the proportion of adhesive fines should be 40–50% and the specific surface area should exceed 1000 cm2 g−1, which contributes to achieving a better bed permeability, a faster sintering speed and higher productivity.

Influence of sulfur dioxide-related interactions on PM2.5 formation in iron ore sintering

ABSTRACT The formation of PM2.5 (aerosol particulate matter less than 2.5 µm in aerodynamic diameter) in association with SO2 emission during sintering process has been studied by dividing the whole sintering process into six typical sampling stages. A low-pressure cascade impactor was used to collect PM2.5 by automatically segregating particulates into six sizes. It was found that strong correlation existed between the emission properties of PM2.5 and SO2. Wet mixture layer (overwetted layer and raw mixture layer) had the function to simultaneously capture SO2 and PM2.5 during the early sintering stages, and released them back into flue gas mainly in the flue gas temperature-rising period. CaSO4 crystals constituted the main SO2-related PM2.5 during the disappearing process of overwetted layer, which was able to form perfect individual crystals or to form particles with complex chemical compositions. Besides the existence of individual CaSO4 crystals, mixed crystals of K2SO4-CaSO4 in PM2.5 were also found during the first half of the temperature-rising period of flue gas. The interaction between fine-grained Ca-based fluxes, potassium vapors, and SO2 was the potential source of SO2-related PM2.5. Implications: The emission property of PM2.5 and SO2 throughout the sintering process exhibited well similarity. This phenomenon tightened the relationship between the formation of PM2.5 and the emission of SO2. Through revealing the properties of SO2-related PM2.5 during sintering process, the potential interaction between fine-grained Ca-based fluxes, potassium vapors, and SO2 was found to be the source of SO2-related PM2.5. This information can serve as the guidance to develop efficient techniques to control the formation and emission of PM2.5 in practical sintering plants.

Preparing high-quality vanadium titano-magnetite pellets for large-scale blast furnaces as ironmaking burden

ABSTRACT The oxidation behaviour and the phase and microstructure evolution of VTM (vanadium titano-magnetite) pellets were studied during thermal processing in order to optimise the production method for producing high-quality pellets. The oxidation tests showed that titanium magnetite and ilmenite in VTM began to oxidise at 500°C and 700°C, respectively. When the temperature reached 875°C, VTM was mainly oxidised to Fe2O3, while Fe2TiO5 was the main oxidation product when the temperature reached 1050°C. The consolidation of the pellets was affected by the degree of oxidation and the oxidation products. Results indicated that the most suitable oxidation ratio was about 70%, and the preferred mineral phase was recrystallised Fe2O3, which was beneficial to improving pellet consolidation in roasting process. The most appropriate oxidation condition was 875°C for 12 min, which contributed to forming more Fe2O3 phase, and the compressive strength of roasted pellet reached 2939 N. The pellets could be used as a high quality ironmaking burden for large-scale blast furnaces.

High Temperature Mineralization Mechanism of Granules During Iron Ore Sintering Process

Mineralization during sintering is a process to make part of the raw material melt after serial complex chemical reactions at high temperature. However, high temperature mineralization behavior of the adhesion layer and nucleus particles in the granules during the sintering process has been studied. Research findings reveal that solid-phase reactions between iron ores and fluxes in adhesion layer occurred first, of which the product would induct the generation of the initial liquid phase. By the assimilation of the initial liquid phase, fluxes which served as nucleus particles in granules, such as limestone and dolomite, could dissolve in the liquid phase and extend its amount as increasing temperature, whereas iron ore nuclear particles remained as unfused ores for their insufficient mineralization. Therefore, the mineralization proceeding for sintering was achieved: the iron ores in fine fraction (−0.5 mm) reacted with all fractions of fluxes to form the melt zone, while the coarse iron ores (+0.5 mm) acted as unfused ores, which formed the final sinters together with the melt zone.