Behavior of direct reduced iron and hot briquetted iron in the upper blast furnace shaft: Part II. A model of oxidation

The high-temperature properties of the ferrous burden in the cohesive zone of the blast furnace (BF) are a function of its history in the upper shaft. It is considered that charging direct reduced iron (DRI) and hot briquetted iron (HBI) into the BF increases its efficiency and productivity. However, oxidation of DRI and HBI can occur in the low-temperature zone in the BF, which may affect their softening and melting properties. This work was designed to estimate the oxidation degree of DRI/HBI in the upper BF shaft. In this article, a model of oxidation was developed, which predicted that DRI and HBI can be oxidized up to 10 and 2 pct, respectively. The model was then put forth to a laboratory-simulated test and industrial simulated blast furnace (SBF) test for its verification. The results of SBF tests indicated that the oxidation of DRI/HBI occurs in a temperature range of 700 °C to 950 °C with the gas compositions used for the tests. The morphology of iron in DRI is expected to exhibit Fe-FeO-Fe layers in varying thickness at the beginning of the cohesive zone. The oxidation in HBI briquettes is primarily limited to its external surface. These results indicate that the impact of oxidation of DRI/HBI on the cohesive zone will not be significant.     

Kinetics and mechanism of corrosion of laboratory hot briquetted iron

While considerable work has been reported in the literature on the corrosion behavior and products of direct reduced iron and sponge iron, very little has been published on hot briquetted iron (HBI). The present article reports the kinetics and mechanism of HBI corrosion. As corrosion is an electrochemical process, measurements using electrochemical techniques have been made and these are compared to data gained by measuring mass changes in the briquettes over time. Similar trends were seen in data from both techniques, and the corrosion extent predicted by electrochemical measurements in saline solution was very close to the mass gain result obtained. Kinetic analysis of the data from mass gain over time trials was conducted. The activation energy for corrosion at temperatures between 25 °C and 80 °C has been calculated. The values of activation energy obtained indicate that corrosion was predominantly controlled by diffusion of oxygen in the liquid state. The internal structure of the briquettes was observed by microscopy both before and after corrosion in distilled water.     

Thermal and chemical analysis of massive use of hot briquetted iron inside basic oxygen furnace

The integrated steelmaking cycle based on the blast furnace-basic oxygen furnace (BOF) route plays an important role in the production of plain and ultra-low carbon steel, especially for deep drawing operations.BOF steelmaking is based on the conversion of cast iron in steel by impinging oxygen on the metal bath at supersonic speed.In order to avoid the addition of detrimental chemical elements owing to the introduction of uncontrolled scrap and in order to decrease environmental impact caused by the intensive use of coke for the production of cast iron, HBI (hot briquetted iron) can be used as a source of metal and a fraction of cast iron.Forty industrial experim ental tests were perform ed to evaluate the viability of the use of HBI in BOF.The experimental campaign was supported by a ther-mal prediction model and realized through the estimation of the oxidation enthalpy.Furthermore, the process was thermodynamically analyzed based on oxygen potentials using the off-gas composition and the bath temperature evolution during the conversion as reference data.     

Utilization of direct reduced iron in an electric arc furnace

Abstract

A discussion of the essential characteristics of the materials needed for processing through a counter-current direct reduction furnace and usage in an electric arc furnace constitutes the rust part of this article. Some of the physical and chemical properties are reviewed and correlated with the performance of the Sidbec-Dosco reduction plant.

The impact of utilization of direct reduced iron on the Electric Arc furnace steelmaking practice is then evaluated, in terms of energy, consumption, productivity, electrode and refractories consumptions. Finally the characteristic of the steels produced for wire and flat rolled products using direct reduced iron is reviewed.

Résumé

La première partie de ce travail discute des caractéristiques essentielles des boulettes nécessaires à la réduction directe par un gaz à contrecourant, pour changement dans un four électrique. Certaines propriétés physiques et chimiques sont revues et permettent une corrélation avec les performances de l'usine de réduction de Sidbec-Dosco.

On évalue l'impact que peut avoir l'utilisation de fer directement réduit au four électrique à arc dans la pratique de l'acierage, ceci du point de vue de la consommation d' énergie, de la productivité et de la consommation d' électrodes et de réfractaires. On discute finalement des caractéristiques de l'acier produit pour fils et produits laminés à plat en utilisant le fer réduit directement.     

邯钢4号高炉炉身上部及炉喉喷补造衬实践

邯钢4号高炉对炉身上部及炉喉部位进行了遥控喷补造衬，喷补后高炉煤气流分布趋于合理，消除了突然悬料和频繁崩料，炉况稳定、顺行，生产技术指标明显改善。     

Simplified simulation of the transient behavior of temperatures in the upper shaft of the blast furnace

A one-dimensional dynamic model of the upper part of the blast furnace shaft is applied to study the evolution of gas and burden temperatures, mainly in order to shed light on the transient phenomena after charging dumps of burden. The effects of irregularities in the burden descent and charging are also studied briefly. The simulations demonstrate that the temperatures of the burden layers in the lower part of the simulated region assume a quasi-steady state, indicating that the changes in the top gas temperature experienced immediately after a dump of burden arise primarily because of heat transfer between the gas and the dump. These results support the idea that such temporary changes can be interpreted in terms of distribution of the dumps on the burden surface.     

高炉富氧对炉身上部的影响

通过分析高炉热流比的技术特征,从理论和国内外的实践方面对富氧高炉的生产状态变化进行了探讨.重点集中在高富氧情况下炉身上部煤气加热炉料的能力不足的问题.热流比(ωs/ωg)升高的明显特征是炉顶温度的急剧下降,热滞区不复存在引起炉况失常,低燃料比高炉更要当心,大高炉的实绩进一步证明了这一点.     

Carbonising mechanism and carbon distribution behaviour during direct reduction in shaft furnace

Abstract

The process of sponge iron production in a shaft furnace has been simulated in the laboratory. On the basis of the results obtained, the carbonising mechanism and carbon distribution in the charge are discussed. Below 724°C the carbon potential in the gas phase in the shaft furnace is far higher than that in the charge. Therefore, the charge is always in the process of carbonisation via the reaction 2CO = CO₂ + C. The carbon content of the sponge iron increases rapidly in the lower zone of the shaft furnace above 724°C. The main reason for this is the deposition of coal tar in the gas. The influence of the hydrogen in the gas on the carbon content of the sponge iron is negligible.     

ZSD热风炉在安钢300m^3高炉上的应用

安钢１号高炉（３００ｍ＾３）内燃式热风炉进行技术改造时，采用了ＺＳＤ热风炉。该热风炉具有结构简单、气体分布均匀、蓄热能力大等特点。安钢１号高炉１年来的生产实践表明，该热风炉工作状况正常，１９９４年２月份风温月平均达到了１０９３℃。     

Sticking behaviour and mechanism of iron ore pellets in COREX pre-reduction shaft furnace

COREX is a clean process releasing lower pollution and consuming fewer cokes than the blast furnace process. However, serious sticking phenomenon often occurs in COREX shaft furnace, causing many problems to the normal operation. In this study, the loading reduction experiments of iron ore pellets were carried out under the simulating COREX reducing conditions. The influence of temperature and H₂ content in the syngas on the sticking behaviour of the pellets was observed by scanning electron microscope, energy-dispersive spectrometer and X-ray diffraction. The results indicated that the sticking index increased from 6.7 to 90.43%, when the temperature increased from 750 to 950°C. The main composition of sticking material was metallic iron, and the sticking behaviour depended upon the amount and morphology of precipitated iron on the pellets’ surface. The sticking mechanism was the interpenetrating diffusion mechanism of iron atoms between the adjacent pellets.     

气基竖炉生产直接还原铁工艺的技术经济分析

介绍了焦炉煤气竖炉直接还原铁工艺,在分析气基竖炉生产直接还原铁技术的市场前景基础上,从成本、盈亏平衡、敏感性等方面对焦炉煤气竖炉直接还原铁工艺进行了技术经济分析,提出了降低生产成本的建议,即:廉价的原料气、能源介质,搞好综合利用,回收有用资源,选择合适的规模等。     

Effect of direct reduced iron on alumina activity in electric arc furnace slags

Abstract

Test trials were conducted in a 70 t ultrahigh power (UHP) electric arc furnace. The proportion of direct reduced iron (DRI) in the charge varied between 40 and 95%. Slag samples were taken at various time intervals and analysed. The analyses were used for estimating the activity of alumina in the slag. The activity was correlated with the basicity, temperature and DRI proportion in the charge. The results of correlation show that the activity is mainly dependent on the basicity of the slag. It is inversely proportional to the basicity and increases as the temperature rises. The activity increases by 3·8×10- 4 for every 10% increase in DRI proportion in the charge.     

The reduction of iron oxides by volatiles in a rotary hearth furnace process: Part I. The role and kinetics of volatile reduction

With iron ore reduction processes using coal-ore pellets or mixtures, it is possible that volatiles can contribute to reduction. By simulating the constituents of the individual reducing species in the volatiles, the rates for H₂ and CO were investigated in the temperature and reduction range of interest; hydrogen is the major reductant and was studied in detail. The kinetics of the reduction by H₂ has been found to be a complex mechanism with, initially, nucleation and growth controlling the rate. There is a catalytic effect by the existing iron nuclei, followed by a mixed control of chemical kinetics and pore diffusion. This results in a topochemical reduction of these iron oxide particles. Up to 1173 K, reduction by H₂ is considerably faster than by carbon in the pellet/mixture or by CO. It was also found that H₂S, which is involved with the volatiles, does not affect the rate at the reduction range of interest.     

Mechanical behavior and damage kinetics in nodular cast iron: Part I. Damage mechanisms

Numerous authors consider that in nodular cast iron, the interface between the graphitic nodule and the α-matrix is so weak that nucleation appears suddenly at the beginning of plastic strain. Nevertheless, the present experimental study indicates that the nucleation of voids is a continuous process as a function of the imposed mechanical parameters (Σ _m , ɛ _peq ). This result is explained in terms of interaction effects between closely spaced particles. A critical parameter for interaction is determined. Growth kinetics are also investigated and comparison with the Gurson-Tvergaard law allows identification of the q1 and q2 parameters of the potential. A critical void volume fraction f ^c is finally defined and is shown to depend on the stress triaxiality level. At last, the role of the various microstructural heterogeneity levels on the damage kinetics is emphasized. Then, it is clearly demonstrated that all these heterogeneity levels must be considered to estimate a critical interfacial stress.     

邢钢5号高炉热风系统设计及运行实践

对邢钢5号高炉热风炉工艺设计进行了总结,并对热风炉系统各部位的特点进行了分析。邢钢5号高炉运行实践表明,中型高炉采用球式热风炉在只烧高炉煤气情况下可以获得高风温。