Effect of titanium on the sticking of pellets based on hydrogen metallurgy shaft furnace:Behavior analysis and mechanism evolution

Direct reduction based on hydrogen metallurgical gas-based shaft furnace is a promising technology for the efficient and low-carbon smelting of vanadium-titanium magnetite.However,in this process,the sticking of pellets occurs due to the aggregation of metal-lic iron between the contact surfaces of adjacent pellets and has a serious negative effect on the continuous operation.This paper presents a detailed experimental study of the effect of TiO2 on the sticking behavior of pellets during direct reduction under different conditions.Results showed that the sticking index(SI)decreased linearly with the increasing TiO2 addition.This phenomenon can be attributed to the increase in unreduced FeTiO3 during reduction,leading to a decrease in the number and strength of metallic iron interconnections at the sticking interface.When the TiO2 addition amount was raised from 0 to 15wt%at 1100°C,the SI also increased from 0.71%to 59.91%.The connection of the slag phase could be attributed to the sticking at a low reduction temperature,corresponding to the low sticking strength.Moreover,the interconnection of metallic iron became the dominant factor,and the SI increased sharply with the increase in re-duction temperature.TiO2 had a greater effect on SI at a high reduction temperature than at a low reduction temperature.

Development and progress on hydrogen metallurgy

Hydrogen metallurgy is a technology that applies hydrogen instead of carbon as a reduction agent to reduce CO2 emission,and the use of hydrogen is beneficial to promoting the sustainable development of the steel industry.Hydrogen metallurgy has numerous applications,such as H2reduction ironmaking in Japan,ULCORED and hydrogen-based steelmaking in Europe;hydrogen flash ironmaking technology in the US;HYBRIT in the Nordics;Midrex H2TM by Midrex Technologies,Inc.(United States);H2FUTURE by Voestalpine(Austria);and SALCOS by Salzgitter AG(Germany).Hydrogen-rich blast furnaces(BFs)with COG injection are common in China.Running BFs have been industrially tested by AnSteel,XuSteel,and BenSteel.In a currently under construction pilot plant of a coal gasification–gas-based shaft furnace with an annual output of 10000 t direct reduction iron(DRI),a reducing gas composed of 57 vol%H2 and 38 vol%CO is prepared via the Ende method.The life cycle of the coal gasification–gas-based shaft furnace–electric furnace short process(30 wt%DRI+70 wt%scrap)is assessed with 1 t of molten steel as a functional unit.This plant has a total energy consumption per ton of steel of 263.67 kg standard coal and a CO2 emission per ton of steel of 829.89 kg,which are superior to those of a traditional BF converter process.Considering domestic materials and fuels,hydrogen production and storage,and hydrogen reduction characteristics,we believe that a hydrogen-rich shaft furnace will be suitable in China.Hydrogen production and storage with an economic and large-scale industrialization will promote the further development of a full hydrogen shaft furnace.

Physicochemical principles of hydrogen metallurgy in blast furnace

Based on the stoichiometric method and the free energy minimization method,an ideal model for the reduction of iron oxides by carbon and hydrogen under blast furnace conditions was established,and the reduction efficiency and theoretical energy consumption of the all-carbon blast furnace and the hydrogen-rich blast furnace were compared.The results show that after the reduction reaction is completed at the bottom of the blast furnace,the gas produced by reduction at 1600℃still has a certain excessive reduction capacity,which is due to the hydrogen brought in by the hydrogen-rich blast as well as the excess carbon monoxide generated by the reaction of the coke and the oxygen brought in by the blast.During the process of the gas with excessive reduction capacity rising from the bottom of the blast furnace and gas reduction process,the excessive reduction capacity of the gas gradually decreases with the increase in the dydrogen content in the blast.In the all-carbon blast furnace,the excess gas reduction capacity is the strongest,and the total energy consumption per ton of iron reduction is the lowest.This shows that,for the current operation mode of the blast furnace,adding hydrogen in the blast furnace cannot reduce the consumption of carbon required for reduction per ton of iron,but rather increases the consumption of carbon.

Prospects for green steelmaking technology with low carbon emissions in China

The steel industry is a major source of CO_(2) emissions,and thus,the mitigation of carbon emissions is the most pressing challenge in this sector.In this paper,international environmental governance in the steel industry is reviewed,and the current state of development of low-carbon technologies is discussed.Additionally,low-carbon pathways for the steel industry at the current time are proposed,emphasizing prevention and treatment strategies.Furthermore,the prospects of low-carbon technologies are explored from the perspective of transitioning the energy structure to a“carbon-electricity-hydrogen”relationship.Overall,steel enterprises should adopt hydrogen-rich metallurgical technologies that are compatible with current needs and process flows in the short term,based on the carbon substitution with hydrogen(prevention)and the CCU(CO_(2) capture and utilization)concepts(treatment).Additionally,the capture and utilization of CO_(2) for steelmaking,which can assist in achieving short-term emission reduction targets but is not a long-term solution,is discussed.In conclusion,in the long term,the carbon metallurgical process should be gradually supplanted by a hydrogen-electric synergistic approach,thus transforming the energy structure of existing steelmaking processes and attaining near-zero carbon emission steelmaking technology.

Direct reduction swelling behavior of pellets in hydrogen-based shaft furnaces under typical atmospheres

Hydrogen-based shaft furnace process is gaining more and more attention due to its low carbon emission, and the reduction behavior of iron bearing burdens significantly affects its operation. In this work, the effects of reduction degree, temperature, and atmosphere on the swelling behavior of pellet has been studied thoroughly under typical hydrogen metallurgy conditions. The results show that the pellets swelled rapidly in the early reduction stage, then reached a maximum reduction swelling index (RSI) at approximately 40%reduction degree. The crystalline transformation of the iron oxides during the reduction process was the main reason of pellets swelling. The RSI increased significantly with increasing temperature in the range of 850-1050℃, the maximum RSI increased from 6.66%to 25.0%in the gas composition of 100%H_(2). With the temperature increased, the pellets suffered more thermal stress resulting in an increase of the volume. The maximum RSI decreased from 19.78%to 17.35%with the volume proportion of H_(2) in the atmosphere increased from 55%to 100%at the temperature of 950℃.The metallic iron tended to precipitate in a lamellar structure rather than whiskers. Consequently, the inside of the pellets became regular, so the RSI decreased. Overall, controlling a reasonable temperature and increasing the H_(2) proportion is an effective way to decrease the RSI of pellets.

Isothermal kinetic analysis on reduction of solid/liquid wustite by hydrogen

Isothermal thermogravimetric analysis was used to study the reduction process of solid/liquid wustite by hydrogen.Results show that wustite in both states can be reduced entirely at all temperatures.The thermal and kinetic conditions for the hydrogen reduction of molten phases are better than those when the reactants and products are in the solid state,with a higher reaction rate.The hydrogen reduction of different wustite phases fits the Mampel Power model(power exponent n=1/2)well,and this model is independent of the phase state.The average apparent activation energies of the reduction process calculated by the iso-conversional method are 5.85 kJ·mol^(−1) and 104.74 kJ·mol^(−1),when both reactants and products are in the solid state and the molten state,respectively.These values generally agree with those calculated by the model fitting method.

Multi-process production occurs in the iron and steel industry,supporting‘dual carbon'target:An in-depth study of CO_(2)emissions from different processes

Reducing CO_(2)emissions of the iron and steel industry,a typical heavy CO_(2)-emitting sector is the only way that must be passed to achieve the‘dual-carbon’goal,especially in China.In previous studies,however,it is still unknown what is the difference between blast furnace basic oxygen furnace(BF-BOF),scrap-electric furnace(scrap-EF)and hydrogen metallurgy process.The quantitative research on the key factors affecting CO_(2)emissions is insufficient There is also a lack of research on the prediction of CO_(2)emissions by adjusting industria structure.Based on material flow analysis,this study establishes carbon flow diagrams o three processes,and then analyze the key factors affecting CO_(2)emissions.CO_(2)emissions of the iron and steel industry in the future is predicted by adjusting industrial structure The results show that:(1)The CO_(2)emissions of BF-BOF,scrap-EF and hydrogen metallurgy process in a site are 1417.26,542.93 and 1166.52 kg,respectively.(2)By increasing pellet ratio in blast furnace,scrap ratio in electric furnace,etc.,can effectively reduce CO_(2)emissions(3)Reducing the crude steel output is the most effective CO_(2)reduction measure.There is still 5.15×10^(8)-6.17×10^(8) tons of CO_(2)that needs to be reduced by additional measures.