Ao Huang

Mathematical Modeling on Erosion Characteristics of Refining Ladle Lining with Application of Purging Plug

According to parameters of the refining ladle with argon bottom blowing, the mathematical model describing the erosion behavior of ladle lining materials was established, the flow process of molten steel and thermal transmission of ladle lining were coupled, and the erosion of ladle lining in the condition of blowing argon at the bottom was researched. It has been found that either single or double blowing is applied, the larger erosion rates are mainly distributed in the slag line and the area of ladle lining near purging plugs, and the erosion is accelerated with the gas flow rate increasing, so the areas with higher erosion rates of the lining should be enhanced to avoid early partial damage. The erosion rate of ladle lining with double blowing is larger and the distribution of erosion is obviously different as the gas flow rate is increasing; serious erosion areas are in the slag line region and the higher erosion areas are concentrated on the slag lining and extended toroidally. And, as the distance between the purging plug and the lining of ladle is shortened, the partial erosion is easy to deteriorate and the refractories in the area with higher erosion rate need specialized selection and design. Meanwhile, the purging plug should be located away from the lining wall under the condition of good blowing effect in order to avoid increasing of the partial erosion and shortening of the lining service life.

Finite Element Analysis on Temperature-Stress of Permeable Refractory Ceramic under Working Process in Ladle

According to the practical physical dimension and processing parameters of ladle with bottom gas blowing in a factory, a geometrical model was established and mesh structure was completed, Eulerian multiphase model and porous media model were adopted for the two-phase flow in ladle, which was coupled, the effect of temperature field and thermal stress in course of working process of permeable- gas refractory ceramic was studied by finite element approach. The correlations between processing, structure, and high-temperature mechanical properties were discussed, and the material and structure of permeable-gas ceramic were designed to optimum. The results show that: The steady gas flow rate can avoid wearing of permeable-gas refractory ceramic from cataclysm of temperature-stress; After the material and structure of permeable-gas refractory ceramic are optimized, the effect on ceramic wearing of temperature-stress in condition of oxygen washing is weakened. It is an important guiding for prepara- tion of permeable-gas refractory ceramic with long life, which will make for highly active refining ladle.

Potash Erosion Resistance of Chromium-Containing Materials

Compared with the traditional entrained flow gasifier, coal catalytic gasifier has the advantages of low reaction temperature, high production efficiency and low energy consumption, but it also has higher requirements for potash erosion resistance. Chromium-containing material is commonly used as lining material for gasification furnaces. In this paper, potash erosion resistance of chromium-containing raw materials and products were respectively researched by using powder tabletting sintering and potassium vapor erosion method. The potash erosion resistance are characterized by XRD and SEM. The study show that:(1)There are obvious potassium salt deposition on the surface of chromium-containing raw materials and products after potash erosion experiment. Potash reacts with chrome-corundum and magnesium-chrome spinel to form K2CrO4,and reacts with chromium oxide to form K2Cr2O7 at 750°C. (2)Potassium vapor enters into chromium-containing products through pores and leads to crack formation and volume change, which destroy the structure and reduce high temperature volume stability of material.

Oxidation Resistance and Mechanical Enhancement of Ferro-Silicon Nitride on Silica Sol Bonded SiC Castable

Silica sol bonded SiC castable have obvious advantages of slag resistance and thermal stress damage resistance. However, they are not widely used due to their weak oxidation resistance at high temperature. Ferro-silicon nitride is added to improve the oxidation resistance of SiC castable. The efficiency of SiC castable in the presence of different contents of ferro-silicon nitride was evaluated through sintered properties, isothermal oxidation behaviors and microstructural analysis. The results show that sample with 5wt% ferro-silicon nitride possessed good mechanical behavior after heat treatment due to its acceleration for the formation of SiC whiskers. At 1500 °C, Isothermal oxdation curve indicated that the oxidation progress performed two-stage model controlled by chemical reaction at the earlier period and diffusion at the later period. Sample with 5wt% ferro-silicon nitride present faster oxidation rate (kc) at the earlier stage versus the contrast sample (0.025 mg·cm-2·min-1 vs 0.087 mg·cm-2·min-1), and slower oxidation rate (kd) at the later stage (0.145 mg·cm-2·min-1 vs 0.137 mg·cm-2·min-1). After 470 min isothermal oxidation test, the weigh gain of sample with 0 wt% ferro-silicon nitride exceeded the sample with 5wt% ferro-silicon nitride.

Effects of Atmospheric Conditions on Slag Corrosion Resistance of Lightweight Al2O3-MgO Castables

By adopting dynamic induction furnace corrosion test, the corrosion mechanism of lightweight Al2O3-MgO castable with different environmental oxygen partial pressure was investigated through macro- and micro-analysis, XRD and thermodynamic simulation. The atmospheric condition was set to P(O2) = 0.21 atm or P(Ar) = 1.0 atm. The attained results showed that a reduced slag corrosion but intensified slag penetration happened at low environmental oxygen partial pressure condition. With P(O2) = 0.21atm, Mn and Fe in slag were present in the form of divalent and/or trivalent cations and were incorporated into spinel to form MnFe2O4 solutions and MgAl2O4 solutions during corrosion process. Since Fe, Mn ions are largely consumed, liquid with high viscosity formed and the continuing infiltration was suppressed. Under P(Ar) =1.0 atm, corrosion on castable aggregates was significantly weakened, and the reaction products under this condition are mainly MgAl2O4 and CA6.

The Interfacial Behavior of Alumina-Magnesia Castables and Molten Slag under an Alternating Magnetic Field

Electromagnetic metallurgical technology has become an important method for the smelting of high purity steel with the development of metallurgical technology. The electromagnetic fields existing extensively in the steelmaking process can not only affect the smelting efficiency and the cleanness of steel, but also the interfacial behavior between the refractory and the molten slag. Focusing on alumina-magnesia castables, an important lining material in ladles, the interfacial behavior between the castable and different ladle slags with or without an AMF is studied in this paper. The results showed that the slag corrosion and especially the slag penetration of the alumina-magnesia castable are more severe under an AMF. Moreover, an AMF accelerates the migration of Fe, Mn and their oxides from the molten slag to the castable. Meanwhile, some low melting point phases such as diopside and anorthite form in the corrosion layer of the castable, which was deduced to accelerate the slag corrosion and penetration of the alumina-magnesia castable.

Effects of Matrix Densification Based on Particle Packing on Lightweight Al2O3-MgO Castables

The property of refractory matrix was dominated by both the maineral composition and particle packing behaviors. In this study, the theoretical packing density of refractory castables was calculated to design the particle size distribution (PSD) of its matrix. Four lightweight Al2O3-MgO castables with different matrix PSD (represented by q-value) were prepared and examined. Results show that a suitable q-value was needed to ensure acceptable properties including sintering characteristics, strength and slag resistance, which deteriorated distinctly at high q ( > 0.31). For the sample with q = 0.28, the matrix showed dense and uniform mirostructure, and the properties of castable reached a favorable compromise among sintering characteristics (apparent porosity = 14.8%, bulk density = 3.02g∙cm-3, permanent linear change < 0.6%), strength (cold modulus of rapture = 12.4MPa, cold crashing strength=155.5MPa), and resistance against both slag corrosion (Ic = 22.4%) and penetration (Ip = 11.5%). The sample with q = 0.25 showed the highest strength and resistance against slag corrosion, but its slag penetration resistance was lower due to the existence of cracks between aggregates and matrix.

The Influence of Thermal Radiation on Effective Thermal Conductivity in Porous Material

Effective thermal conductivity is an important parameter of porous materials for measurement of heat insulation performance. Two-dimensional geometrical models based on micrographs of real material were constructed in this paper and the finite element approach was applied for thermal analysis, the effective thermal conductivity was calculated. The influence of radiation heat transfer, temperature, and porosity on thermal conductivity were analyzed. The results show that conduction heat transfer plays an important role in total heat transfer and the influence of radiation heat transfer was small at low temperature. Because of the increase in radiation heat transfer, the temperature gradient decreased obviously at high temperature and the heat flux lines passed through the pores and became relatively smooth; thus the radiation heat transfer plays an important role in total heat transfer at high temperature and the influence of radiation heat transfer cannot be ignored. Thermal conductivity for a high porosity value will be greater than thermal conductivity for a low porosity value at high temperature. This paper provides guidance for predicting thermal conductivity and reducing the heat transfer efficiency of porous materials at high temperature.

Corrosion Mechanism of Foamed Slag on the Lightweight Corundum-Spinel Castable

Development of lightweight linings for metallurgical furnaces is an important research direction in the development of refractory materials. In the steelmaking process, slag foaming is a common phenomenon, and it usually plays a positive role. However, because of the reactions between refractories and slag, the corrosion of wear lining refractories is not only related to the safety and stable operation of high-temperature furnaces but also affects steel quality. Foamed slag is likely to affect refractory corrosion, especially lightweight refractories containing lightweight porous aggregates. In this study, the slag corrosion experiments of lightweight corundum-spinel castable were performed in contact with the ordinary and foamed slag respectively and the foamed slag caused more serious corrosion to the lightweight corundum-spinel castable. Based on the corroded microstructure and Marangoni effect, slag corrosion mechanism was analyzed systematically, and could provide the basis for foamed slag resistance.

Study on a Lime-Fluorite Slag Melting Agent for Ladle Slag Buildup

The Al2O3-MgO-Cr2O3 brick, which is used for wear lining in the ladle slag line, was selected, and the static crucible method was applied to perform a slag sticking test with the refining slag and then investigate the effect of the lime-fluorite slag melting agent with different recipes. The slag corrosion and penetration rate of samples were measured, and the microscopic structure was analyzed through a scanning electron microscope (SEM), the possible slag melting effect and the proportion of active lime and fluorite were discussed. The results show that, with an increase of CaF2 in the slag melting agent, the corrosion and penetration rate rise as well, and a corrosion ring in the sample was observed while the content of CaF2 reached the certain value. The high melting point phases including MA, CA2, CA6, C3T2 and the low melting point phases including C2AS, CAS2, CA were distributed discontinuously. Suitable slag melting agents could reduce the viscosity of the slag, form the discontinuous high melting phases and corrosion ring, so as to achieve the purpose of slag melting for ladle lining.