Inherent potential of steelmaking to contribute to decarbonisation targets via industrial carbon capture and storage

Accounting for ~8% of annual global CO2 emissions, the iron and steel industry is expected to undertake the largest contribution to industrial decarbonisation. Despite the launch of several national and regional programmes for low-carbon steelmaking, the techno-economically feasible options are still lacking. Here, based on the carbon capture and storage (CCS) strategy, we propose a new decarbonisation concept which exploits the inherent potential of the iron and steel industry through calcium-looping lime production. We find that this concept allows steel mills to reach the 2050 decarbonisation target by 2030. Moreover, only this concept is revealed to exhibit a CO2 avoidance cost (12.5–15.8 €2010/t) lower than the projected CO2 trading price in 2020, whilst the other considered options are not expected to be economically feasible until 2030. We conclude that the proposed concept is the best available option for decarbonisation of this industrial sector in the mid- to long-term

Investigation on viscosity and non-isothermal crystallization behavior of P-bearing steelmaking slags with varying TiO2 content

The viscous flow and crystallization behavior of CaO-SiO2-MgO-Al2O3-FetO-P2O5-TiO2 steelmaking slags have been investigated over a wide range of temperatures under Ar (High purity, >99.999 pct) atmosphere, and the relationship between viscosity and structure was determined. The results indicated that the viscosity of the slags slightly decreased with increasing TiO2 content. The constructed nonisothermal continuous cooling transformation (CCT) diagrams revealed that the addition of TiO2 lowered the crystallization temperature. This can mainly be ascribed to that addition of TiO2 promotes the formation of [TiO6]-octahedra units and, consequently, the formation of MgFe2O4-Mg2TiO4 solid solution. Moreover, the decreasing viscosity has a significant effect on enhancing the diffusion of ion units, such as Ca2+ and [TiO4]-tetrahedra, from bulk melts to the crystal–melt interface. The crystallization of CaTiO3 and CaSiTiO5 was consequently accelerated, which can improve the phosphorus content in P-enriched phase (n2CaO·SiO2-3CaO·P2O5). Finally, the nonisothermal crystallization kinetics was characterized and the activation energy for the primary crystal growth was derived such that the activation energy increases from −265.93 to −185.41 KJ·mol−1 with the addition of TiO2 content, suggesting that TiO2 lowered the tendency for the slags to crystallize

Synthesis and Characterization of MgA1ON-BN refractories

In order to meet the need of metallurgical industry in the world, a new MgAlON-BN composite which can be used for example in special refractory nozzles, tubes and break rings for the continuous casting of steel was studied in the present thesis. The aim was to understand the mechanism of synthesis and their physicochemical properties during the application. Thus, the thermodynamic properties, synthesis process, mechanical properties, thermal shock behaviour, thermal diffusivity/conductivity as well as corrosion resistance to molten iron containing oxygen and molten slag of MgAlON and MgAlON-BN composites have been investigated. The Gibbs energy of formation of MgAlON was estimated using the method proposed by Kaufman. The phase stability diagram of Mg-Al-O-N-B was investigated, and consequently the synthesis parameters were determined. MgAlON and MgAlON-BN composites were fabricated by hot-pressing method. The composites obtained this way were characterized by XRD, SEM, TEM and HREM analyses. A Matrix-flushing method was employed in the quantitative XRD analysis for the multi-component samples to understand the mechanism of synthesis. The relationship between mechanical properties and microstructure of the composites was investigated. The experimental results indicated that BN addition has significant influence on the mechanical properties of the composites. These can be explained by the fact that BN has low Young’s modulus, density and non-reactive nature as well as considerable anisotropy of many properties such as thermal expansion, thermal diffusivity/conductivity. Thus, the addition of BN in MgAlON is likely to lead to the presence of microcracks caused by the mismatch of thermal expansion coefficient. The microcracks result in the enhancement of the strength at elevated temperature and thermal shock durability of the composites. Effective thermal conductivities were evaluated from the present experimental results of thermal diffusivities, heat capacity and density. A model suitable for present composites has been derived based on Luo’s model. The predicted lines calculated by the model were in good agreement with experimental results. The reactions between the composites and molten iron as well as the slag were investigated by ‘‘finger’’ experiments and sessile drop experiments. Both experimental results indicated that the BN addition has positive influence on the corrosion resistance. These are attributed to the excellent corrosion resistance of BN to molten iron and slag, such as the higher contact angle between BN substrate and liquid iron and molten slag compared with that obtained for pure MgAlON.QC 2010092

Utilization of high-temperature slags from metallurgy based on crystallization behaviors

Here, following the principle of modifying crystallization behaviors, including avoidance and optimization, we review recent research on the utilization of hot slags. Because of the high-temperature property (1450-1650A degrees C), the utilization of hot slags are much different from that of other wastes. We approach this issue from two main directions, namely, material recycling and heat utilization. From the respect of material recycling, the utilization of slags mainly follows total utilization and partial utilization, whereas the heat recovery from slags follows two main paths, namely, physical granulation and chemical reaction. The effective disposal of hot slags greatly depends on clarifying the crystallization behaviors, and thus, we discuss some optical techniques and their applicable scientific insights. For the purpose of crystallization avoidance, characterizing the glass-forming ability of slags is of great significance, whereas for crystallization modification, the selection of chemical additives and control of crystallization conditions comprise the central routes

General roles of sludge ash, CaO and Al2O3 on the sludge pyrolysis toward clean utilizations

Herein we identified the characteristics of sludge pyrolysis theoretically and experimentally, where the general roles of sludge ash, CaO and AlO were analyzed. Both valuable products and polluting materials were considered. Regarding the latter one, we for the first time proposed the principles of competitive effect and linkage effect in the silicate category, and accordingly, we put forward a general clue for trace element fixations. For syngas, the total yield composed of CO, H and CH increased while the char yield decreased in the presence of ash and CaO; for polluting gases, the presence of CaO had a pronounced mitigation effect. Then the distributions of trace elements were identified by analyzing their network roles. For the network modifiers such as Ba and Zn, CaO weakened their fixation due to the competitive effect while AlO and ash had a positive effect due to the linkage effect. For the network formers such as As and the elements with large atomic radius such as Co, CaO improved their fixation due to the linkage effect whilst AlO and ash had an negative effect. Accordingly, we acquire significant ideas for clean and effective utilization of sludge, as well as coal and other solid wastes

Distributional and compositional insight into the polluting materials during sludge combustion: roles of ash

Here we systemically elucidated the compositions and distributions of polluting materials during sludge combustion using both experimental and theoretical methods where the roles of ash were clarified in a category within aluminosilicate system. With regard to the polluting gases, an increasing temperature increased the SO release in replace of SO and sulfates while continuously enhanced the formation of NO and NO. Comparatively, an increasing input oxygen amount had limited effect on S-bearing gases whilst continuously increased the NO release. Additionally, the ash had a sulfur fixation effect through inducing the transformation from oxides to sulfates. The trace elements were overall categorized into four types based on their volatilities and the distributions and mineral phases of them were then clarified in detail. It was proved that with increasing temperature, they were increasingly distributed in gaseous state with ash providing a fixation effect. Moreover, 5 kinds of decomposition reactions related to polluting materials, namely sulfates, oxides, arsenates, silicates and hydroxides, were deeply analyzed from a respect of Gibbs energy where their stabilities and roles of ash were identified. Furthermore, the sludge combustion was experimentally clarified using a TG-MS system and here we defined a new parameter, namely peak index, to characterize the releases of polluting gases. This not only deepened the understanding of sludge combustion experimentally but also partially validated the theoretical analysis in quantity. Most importantly, the present study contributed to establishing a foundation for controlling and mitigating the environmental impacts of polluting materials toward efficient and clean sludge combustions