Control of silicon in high carbon ferrochromium produced in submerged arc furnace through redistribution of quartzite in the charge bed

Abstract

High carbon ferrochromium produced in a submerged arc furnace may contain as much as 4%Si. A high level of silicon in this alloy is not desired. In addition to bringing down the value of the alloy, a high level of silicon increases the specific energy consumption during production of the alloy. Controlling the proportion of silica and coke in the charge can help in bringing down the level of silicon in the hot metal. This strategy is adopted by some ferrochromium manufacturers. However, these practices lead to difficulties in tapping, and to reduced recovery of chromium. A thermochemical analysis of the process showed that silicon in the hot metal was at equilibrium with the slag only at high temperatures, which usually prevailed in regions close to the electrodes. Based on this analysis, a strategy was devised to control silicon in the hot metal by appropriate redistribution of quartzite at the top of the charge bed. Trials were carried out at an industrial plant to control the silicon level using this strategy. Results showed that the silicon level in the hot metal was drastically reduced on redistribution of quartzite. This method can result in a reduction of specific energy and specific coke consumption.     

空时编码中的BLAST分析

分层空时编码技术是近几年来通信领域新兴的研究方向,它主要用于解决高速无线通信下行传输问题。主要从分层空时编码的技术原理、设计准则及一种典型的译码算法入手,全面地分析了BLAST的特点,并通过仿真对几种典型的译码算法的性能进行了对比。最后对目前的研究动态做了简要的介绍。     

相关性对BLAST系统信道容量性能的影响

贝尔实验室分层空-时(Bell Labs Layered Space-Time,BLAST)通信系统相比其他的通信系统具有更高的频谱效率,能有效地提高系统信道容量.利用指数相关矩阵和均匀相关矩阵模型,分析比较了相关信道下BLAST系统的信道容量,并利用Matlab进行仿真.仿真结果表明:利用指数相关矩阵模型,BLAST...     

Concept of dynamic foaming index and its application to control of slag foaming in electric arc furnace steelmaking

Abstract

To sustain a foam in steelmaking processes, two basic requirements should be fulfilled, i.e. appropriate physical properties of the slag such as high viscosity, low density, and low superficial tension, and the generation of sufficient reaction gas. To date, foaming indexes have been focused on the physical properties of refining slags. In the present paper a dynamic foaming index (DFI) that involves both above requirements is proposed, using a kinetic model of the electric arc furnace process to calculate the generation rate of reaction gas, mainly CO. When the arc distortion, as affected by electrode submergence in the foam, is compared with the DFI, calculated via the kinetic model, it is observed that both parameters follow very similar trends. This finding indicates the feasibility of knowing the foaming conditions of a heat in advance, or of using the kinetic model online to control the foaming phenomena. Furthermore, experimental results relating to dynamic behaviour of the slag chemistry are well simulated using the kinetic model. To take into account the effect of size distribution of carbon particles injected into the slag to reduce FeO, a Monte Carlo simulation has been integrated into the process simulator, allowing a more realistic prediction of the current steelmaking process.     

Slab cracking after continuous casting of API 5L X-70 grade steel for pipeline sour gas application

Abstract

An API 5L X-70 grade steel for large diameter pipeline application with sour gas resistance was developed. The resulting Fe–C–Mn–Nb slabs were controlled rolled and accelerated cooled. In most of the slabs, mechanical properties equivalent to the above grade were broadly achieved. However, despite achieving excellent mechanical properties, during the test period, several slabs exhibited cracks in the cooling yard, causing their rejection. To elucidate the nature of the crack, several specimens were analysed by employing optical, scanning electron, and transmission electron microscopy. Microstructural characterisation together with microanalysis and thermal analysis carried out on as cast specimens showed the presence of rodlike and/or dendritelike precipitates of the Fe₂ Nb type associated with the cracks. The elimination of the cracks was achieved by increasing the niobium content in the Nb ferroalloy to ensure its dissolution in the liquid bath after its addition during the alloying stage.     

Mixed burden softening and melting phenomena in blast furnace operation Part 3 – Mechanism of burden interaction and melt exudation phenomenon

Abstract

This research was focused on expanding the current understanding of the mechanism of softening and melting of ferrous materials including liquid exudation and high temperature material interaction. The bulk softening and melting experiments were interrupted at temperatures of interest and samples were examined for morphological changes. The results of these experiments were complimented with viscosity, surface energy and deformation rate calculations which were helpful in understanding the melt exudation phenomenon. The microstructure of the materials showed a transition from heterogeneous to homogenous state with increasing temperatures. The melt dripping was predominantly observed in olivine fluxed pellets. The exuded slag was primarily composed of an alkali rich phase which was found least viscous of the slags present in this system. The viscosity of the liquid and the structure of metallic shell jointly control the flow of liquid from the ferrous materials. Addition of magnesia in lieu of lime was found to provide beneficial impact, in particular on the rate of liquid evolution at high temperature. Based on the metallographic examination of the samples a mechanism of burden interaction is proposed.     

Model based scheduling of a continuous annealing furnace

Abstract

The operational complexities and process constraints of an industrial continuous annealing operation invariably lead to empirically designed process cycles as well as manual scheduling practices. This methodology often results in suboptimal and inefficient operations. An integrated approach is presented here for maximising the productivity of a continuous furnace, where bundles of steel rods are annealed. For this purpose, a scheduling algorithm is proposed, which is coupled with a process model. The phenomenological process model is based on heat transfer and annealing kinetics. The scheduling algorithm is formulated to analyse the continuous annealing furnace under different operating conditions. The advantage of coupling the scheduling algorithm to the process model in enhancing productivity has been illustrated. Furthermore, it is shown that optimising the bundle diameter at a constant hearth speed is favourable for frequent dispatches of the product, whereas for less frequent dispatches, it is more efficient to vary the hearth speed.     

Testing of cement bonded briquettes under laboratory and blast furnace conditions Part 1 – Effect of processing parameters

Abstract

Cement bonded agglomerates made of iron rich byproducts from the iron and steel industry have been used as burden material for blast furnaces for over a decade. In spite of that, their use is restricted to less than 5% of the total burden material, because at higher percentages the blast furnace starts behaving erratically. It is suspected that this is due to the disintegration of the agglomerates under high temperature and reducing conditions. In order to improve the quality of the cement bonded briquettes, the effects of various parameters on their behaviour have been studied. The briquettes have been tested in the laboratory under isothermal test conditions and under simulated blast furnace conditions. The briquettes have also been tested in a pilot blast furnace. This paper describes the effect of different parameters on the performance of briquettes tested under the three conditions.     

无线通信中的空时编码技术

空时编码技术是抗信道衰落和提高系统容量的一种最新编码方法，这里简介了三种典型空时码：分层空时码、空时格型码和空时分组码，比较了它们的优缺点，并分析了下一代通信中空时编码的发展方向。     

Identification of Mitochondrial DNA (NUMTs) in the Nuclear Genome of Daphnia magna

This is the first study in which the Daphnia magna (D. magna) nuclear genome (nDNA) obtained from the GenBank database was analyzed for pseudogene sequences of mitochondrial origin. To date, there is no information about pseudogenes localized in D. magna genome. This study aimed to identify NUMTs, their length, homology, and location for potential use in evolutionary studies and to check whether their occurrence causes co-amplification during mitochondrial genome (mtDNA) analyses. Bioinformatic analysis showed 1909 fragments of the mtDNA of D. magna, of which 1630 were located in ten linkage groups (LG) of the nDNA. The best-matched NUMTs covering >90% of the gene sequence have been identified for two mt-tRNA genes, and they may be functional nuclear RNA molecules. Isolating the total DNA in mtDNA studies, co-amplification of nDNA fragments is unlikely in the case of amplification of the whole tRNA genes as well as fragments of other genes. It was observed that TRNA-MET fragments had the highest level of sequence homology, thus they could be evolutionarily the youngest. The lowest homology was found in the D-loop-derived pseudogene. It may probably be the oldest NUMT incorporated into the nDNA; however, further analysis is necessary.