China's Refractories

Some refractory linings that protect metallic vessels from the hot temperature of the products they contain are made of masonries with or without mortar. The joints play an important role, reducing the stresses in the masonries during heating. Furthermore, the presence of these joints makes the behaviour of the masonry nonlinear and orthotropic. To perform a thermomechanical simulation using a finite element method of an industrial vessel that contains hundreds or thousands of bricks and joints, microscopic models are not suitable due to the high computational time and the management of the behaviour of the joints (opening/closing) which affects the convergence. To overcome these problems, it is proposed to replace the masonry by a homogeneous material that has a behaviour equivalent to the set of bricks and joints, using a periodic homogenization technique. Since the joints can be closed or open, the equivalent material will have a different behaviour according to the joint state. Furthermore, refractory materials have an elastic-viscoplastic behaviour at high temperatures. So, the equivalent material will have an orthotropic elastic-viscoplastic behaviour, requiring a nonlinear homogenisation technique. An overview of this approach developed at University of Orléans is presented with two industrial applications (blast-furnace and steel ladle).

In this study, biomass cokes from sunflower seed hull (SFSH) and wood pellets (WP) were added to a MgO-C batch (3 mass% C) to replace 1.1 mass% of graphite. After hardening and carbonizing the samples, the influence of the biomass cokes on the microstructure and thermal shock resistance was investigated. The replacement of flaky graphite by carbonized WP and SFSH reduced the bulk density and increased the apparent porosity after pressing and carbonization, but the degree was only marginal. This was confirmed by SEM investigations, where the biomass-coke containing samples exhibited a microstructure with a higher amount of pores between the fine MgO grains. The thermal shock resistance of the porous wood pellet coke containing MgO-C is at the same level as the reference sample but not superior to it.

Cement-free castables have attracted significant attention due to their superior thermal-mechanical properties and rapid dry-out in comparison to cement-bonded refractory castables. However, drying industrial-scale specimens can pose more challenges than lab-scale samples. In this study, the dry-out behavior and explosion resistance of microsilica-gel bonded no-cement castables (NCCs) were investigated on both lab- and industrial-scale specimens, employing various drying agents. First, the fast dry-out mechanism was assessed using thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), and scanning electron microscopy (SEM) on lab-scale small samples. Then, the drying behavior of industrial-scale large samples (300 mm×300 mm×300 mm cubes, approximately 80 kg) was studied using a unique macro-thermo-balance (macro-TGA). The results showed that EMSIL-DRY^® reduced the temperature level for maximum dewatering rate and effectively prevented explosions during heat-up, compared to other polymer fibres. The use of a specialty drying agent (EMSIL-DRY^®) significantly improved the explosion resistance, as demonstrated by the production of a perfect 400 kg block fired to 850 °C at a rate of 50 °C · h^-1. This research contributes to the understanding and application of cement-free castables in industrial settings.

The lamellar hydrates of CAC were designed with the introduction of nano CaCO₃ or Mg-Al hydrotalcite (M-A-H), and the effects on the green strength, pore structures, and high-temperature fracture behavior of alumina-spinel castables were investigated. The results show that nano CaCO₃ or M-A-H stimulates rapidly the hydration of CAC and the formation of lamellar C₄AcH₁₁ or coexistence of C₂AH₈ and C₄AcH₁₁ at 25 °C. The formation of lamellar hydrates can contribute to a more complicated pore structure, especially in the range of 400-2 000 nm. Meanwhile, the incorporation of well-distributed CaO or MgO sources from nano CaCO₃ or M-A-H also regulates the distribution of CA₆ and spinel (pre-formed and in-situ). Consequently, the optimized microstructure and complicated pore structure can induce the deflection and bridging of cracks, thus facilitating the consumption of fracture energy and enhancing the resistance to thermal stress damage.

Monolithic refractory castables comprising a hydraulic bond are still used in a vast majority of cases because of their flexibility and robustness, despite many developments for chemical as well as non-cement castable binders. The drying can however be a challenge, in particular for deflocculated dense castables of the low cement castable range. Many publications have been released on this topic for the last ten years, but they often focused on the drying mechanisms or on the addition of drying aids. This paper presents some experimental results on the effect of the composition on the drying properties, especially on the effect of silicon carbide, used for its high thermal conductivity, and on the matrix system. It also introduces two laboratory tests to study and iteratively improve the drying schedule of a given castable lining. The results show that the spalling resistance and the vapor pressure build-up are significantly influenced by the formulation. It is also shown that the castable properties after drying can be altered if the heating rate is very high.

The steel industry, known for its complexity and the need to reduce CO₂ emissions, is adopting advanced digitalization tools to move towards a more sustainable, integrated, and agile operating model. Digital twins with artificial intelligence-based optimization and scheduling models can improve decision-making in logistics, refractory maintenance, and energy efficiency. By incorporating advanced AI algorithms into this decision support system, the hot metal route scenarios can be evaluated, resulting in minimized hot metal temperature losses and increased scrap utilization. This paper integrated digital twins with reinforcement learning algorithms to investigate the logistics of torpedoes and hot metal ladles. It considered important input parameters such as the ladles and torpedoes' thermal state and location, refractory thickness, hot metal volume and temperature, and crane availability. By incorporating advanced AI algorithms into this decision support system, energy-efficient scenarios can be evaluated, increasing scrap utilization and resulting in a possible reduction of 15 °C in hot metal temperature losses.

Refractory materials, as the crucial foundational materials in high-temperature industrial processes such as metallurgy and construction, are inevitably subjected to corrosion and penetration from high-temperature media during their service. Traditionally, observing the in-situ degradation process of refractory materials in complex high-temperature environments has presented challenges. Post-corrosion analysis are commonly employed to assess the slag resistance of refractory materials and understand the corrosion mechanisms. However, these methods often lack information on the process under the conditions of thermal-chemical-mechanical coupling, leading to potential biases in the analysis results. In this work, we developed a non-contact high-temperature machine vision technology by the integrating Digital Image Correlation (DIC) with a high-temperature visualization system to explore the corrosion behavior of Al₂O₃-SiO₂ refractories against molten glass and Al₂O₃-MgO dry ramming refractories against molten slag at different temperatures. This technology enables real-time monitoring of the 2D or 3D overall strain and average strain curves of the refractory materials and provides continuous feedback on the progressive corrosion of the materials under the coupling conditions of thermal, chemical, and mechanical factors. Therefore, it is an innovative approach for evaluating the service behavior and performance of refractory materials, and is expected to promote the digitization and intelligence of the refractory industry, contributing to the optimization and upgrading of product performance.