In-furnace Phenomena Research Articles

Simultaneous Three-dimensional Analysis of Gas–Solid Flow in Blast Furnace by Combining Discrete Element Method and Computational Fluid Dynamics

Low reducing agent operation of the blast furnace is an essential method for mitigating CO2 emissions in ironmaking. Because the coke rate is reduced in low reducing agent operation, gas permeability tends to deteriorate. Recently, blast furnaces with inner volume larger than 5000 m3 have become usual not only in Japan, but also in other Asian nations. Under these conditions, detailed information on in-furnace phenomena is required to attain stable operation.In the present study, a combination model using the discrete element method and computational fluid dynamics (DEM-CFD) was introduced to understand the fully three-dimensional in-furnace phenomena in the whole blast furnace. Due to the limitations of computational resources, the number of DEM particles must be reduced when applying DEM to the whole blast furnace. On the other hand, small cells must be used in the continuum model in order to calculate the gas flow in detail. Thus, mutual conversion between the location of particles in DEM and the property of the cells in the continuum model is needed. In this study, a method of converting information on the locations of cluster-approximated particles treated in DEM to continuum cells was proposed. Furthermore, optimization in which cells could be obtained without conversion parameters was performed to avoid losing local information obtained by DEM calculations. Simulations of solid movement and gas flow were successfully carried out with this coupled DEM-CFD model. As a result, it became possible to understand the three-dimensional stress field among particles under gas flow, transient gas flow and pressure distribution caused by charging of the burden materials, as well as solid motion.

Three-dimensional modelling of in-furnace coal/coke combustion in a blast furnace

A three-dimensional mathematical model of the combustion of pulverized coal and coke is developed. The model is applied to the region of lance-blowpipe-tuyere-raceway-coke bed to simulate in-furnace phenomena of pulverized coal injection in an ironmaking blast furnace. The model integrates not only pulverized coal combustion model in the blowpipe-tuyere-raceway-coke bed but also coke combustion model in the coke bed. The model is validated against the measurements under different conditions. The comprehensive in-furnace phenomena are investigated in the raceway and coke bed, in terms of flow, temperature, gas composition, and coal burning characteristics. The underlying mechanisms for the in-furnace phenomena are also analysed. The simulation results indicate that it is important to include recirculation region in the raceway and the coke bed reactions for better understanding in-furnace phenomena. The model provides a cost-effective tool for understanding and optimizing the in-furnace flow-thermo-chemical characteristics of the PCI operation in full-scale blast furnaces.

Transient Behavior of Burden Descending and Influence of Cohesive Zone Shape on Solid Flow and Stress Distribution in Blast Furnace by Discrete Element Method

The present investigation intends to elucidate the transient behavior of burden descending, the influence of cohesive zone shape on the solid flow and the stress field through three-dimensional analysis by discrete element method (DEM) in blast furnace. Although many continuum models were developed to analyze the in-furnace phenomena such as solid flow, DEM enables to analyze the unsteady state solid flow, the stress distribution and slip of burden in the three dimensional state. In this study, it was clarified that the solid flow in blast furnace was composed of steady flow and transient flow which caused by burden charge and slip around raceway. Burden charge instantaneously causes high stress region and high velocity region to spread from upper part to lower part. High velocity region caused by slip around raceway spreads upwards and mitigates the stress field in the vicinity of raceway. The cohesive zone shape almost does not affect on the particle movement in the upper part of shaft and deadman shape. However, the distribution of high stress region and high slipping region is affected by the cohesive zone shape. Asymmetric high stress and slipping distribution are formed in the case of biased cohesive zone, and high cohesive zone enlarges the region of high stress. Weak slipping region in the upper part of shaft tends to be mitigated by the stress field in upper part. Belly receives the maximum stress from burden. The normal stress acting on the bottom is concentrated on the center of bottom by the buoyancy effect of pig iron in the hearth.

Numerical Simulation of the Moving Bed Furnace for Iron Scrap Melting

From the viewpoints of the limited deposit of natural resources and the protection of global environment, utilization of iron scrap is strongly requested. For estimating the effectiveness of the moving bed type scrap melting furnace, a two-dimensional mathematical model has been proposed, which considered transport phenomena of heat, mass and momentum together with melting and chemical reactions in the furnace for iron scrap melting. Numerical simulation was conducted to investigate in-furnace phenomena and effects of operating conditions on the process stability. According to the numerical results, the blast preheating was very effective for reducing coke consumption, because the coke rate can be reduced to 200 kg/t when it preheated to 673 K without oxygen enrichment. As the results, the process characteristics such as distributions of gas concentration, temperature and velocity have been obtained; they are useful to evaluate the performance of the iron scrap melting furnace and to improve the operations leading to less energy consumption and more iron scrap melting.

Numerical Analysis of Multi-Smelter for Melting Metal Waste

In view of the limited natural resources and the protection of the global environment, a process for treating the waste materials discharged from industrial production and human life is strongly requested to be developed. A multi smelter was proposed, which consists of coke packed bed in the lower part and free board where fine materials are fluidized during operation in the upper part. It can reduce significantly the volume, eliminate toxicity and recover some materials such as metals, because it has high temperature that can melt waste and reducing atmosphere. Many melting tests were done successfully from February 1999 using the multi-smelter constructed at Osaka Prefecture University. This reactor can treat the waste materials of 1 ton/day. In this operation test, industrial waste materials like used TV sets, air conditioners and refrigerators was melted without secondary emission of dangerous materials like dioxin. In this multi-smelter, the packed bed part seems to play an important role for melting metallic wastes effectively and for achieving a stable operation. On the basis of this foresight, a two-dimensional mathematical model has been proposed, which considered transport phenomena of heat, mass and momentum together with melting and chemical reactions in the high temperature packed bed for processing waste materials. Numerical simulation was conducted to investigate in-furnace phenomena and effects of operating conditions on the process stability. As the results, the process characteristics such as distributions of gas concentration, temperature and velocity have been obtained; they are useful to evaluate the performance of the multi-smelter and to improve the operations leading to less energy consumption and more waste materials treatment. The results showed the multi-smelter is a useful process for melting some kind of waste materials like used refrigerators, air-conditioners, the major part of which were originally made from iron and plastics.

96/03129 - Ammonia removal process upgrade to the Acme Steel Coke Plant

A three-dimensional mathematical model of the combustion of pulverized coal and coke is developed. The model is applied to the region of lance-blowpipe-tuyere-raceway-coke bed to simulate in-furnace phenomena of pulverized coal injection in an ironmaking blast furnace. The model integrates not only pulverized coal combustion model in the blowpipe-tuyere-raceway-coke bed but also coke combustion model in the coke bed. The model is validated against the measurements under different conditions. The comprehensive in-furnace phenomena are investigated in the raceway and coke bed, in terms of flow, temperature, gas composition, and coal burning characteristics. The underlying mechanisms for the in-furnace phenomena are also analysed. The simulation results indicate that it is important to include recirculation region in the raceway and the coke bed reactions for better understanding in-furnace phenomena. The model provides a cost-effective tool for understanding and optimizing the in-furnace flow-thermo-chemical characteristics of the PCI operation in full-scale blast furnaces.

High Rate Coal Injection of 218kg/t at Fukuyama No. 4 Blast Fukuyama.

At Fukuyama No. 4 Blast Furnace, a pulverized coal injection system with a capacity of 72 t/h was installed at the end of April 1994. In October, six months later, the highest coal injection was carried out. Eventually, a maximum injection rate of 230 kg/t and monthly average of 218 kg/t was successfully attained. The main features making the high rate injection of pulverized coal possible are the following: (1) high combustion efficiency with the newly designed eccentric double lance; (2) use of Hybrid Pelletized Sinter with superior reducibility and melting characteristics; and (3) optimum control of gas flow distribution to keep in-furnace permeability. Moreover, the in-furnace phenomena in the lower part were analyzed by the deadman probe, and it was confirmed that the good permeability in the deadman could be maintained by the improvement of injection lance and burden properties.

In-furnace phenomena in oxygen blast furnace

Results of the dissection of the quenched burden in a small experimental blast furnace are reported. The furnace was operated with a low-temperature oxygen blast, a coal injection rate of 300 kg/t iron and injection of preheating gas into the stack. Salient features were high productivity (iron output over 5 t/m{sup 3}d), absence of a cohesive zone, and low Si content of the iron. Scale-up to commercial size by simulation is discussed.