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ISIJ International Vol. 54 (2014), No. 11

ISIJ International
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ONLINE ISSN: 1347-5460
PRINT ISSN: 0915-1559
Publisher: The Iron and Steel Institute of Japan

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ISIJ International Vol. 54 (2014), No. 11

Preface to the Special Issue on “Recent Progress of Cokemaking Technologies for Low-quality and Unused Carbon Resources”

Hideyuki Aoki

pp. 2425-2425

DOI:

10.2355/isijinternational.54.2425

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Preface to the Special Issue on “Recent Progress of Cokemaking Technologies for Low-quality and Unused Carbon Resources”

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Relationship between Chemical Structure of Caking Additives Produced from Low Rank Coals and Coke Strength

Naoto Sakimoto, Toshimasa Takanohashi, Yasuyuki Harada, Hidekazu Fujimoto

pp. 2426-2431

DOI:

10.2355/isijinternational.54.2426

Abstract

Coke strength can be enhanced by adding HyperCoals (HPC). HPC can be produced from different rank of coals including low rank coals. The aim of this study is to investigate and evaluate the usability of HPC from low rank coals as caking additive. 1H-NMR, solid state 13C-NMR, and elemental analysis were carried out to investigate the molecular structure of HPC prepared from low rank coals. The results showed that the number of aromatic rings in unit structure increased from 1-2 in original coals to 2-3 in HPCs extracted at 633 K. Effect of extraction temperature was also investigated and it was found that ratio of 3 aromatic rings increased in HPC extracted at 673 K, in comparison to HPC extracted at 633 K. The strength of cokes produced by adding HPC was directly a function of number of aromatic rings in the HPC and increased with increasing number of rings.

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Relationship between Chemical Structure of Caking Additives Produced from Low Rank Coals and Coke Strength

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Co-pyrolysis Behavior of Low-grade Coal and Binder Using High Temperature Solvent Fractionation

Ryuichi Ashida, Sho Nagaya, Kouichi Miura, Yukihiro Kubota, Yuko Nishibata, Atsushi Kotani

pp. 2432-2438

DOI:

10.2355/isijinternational.54.2432

Abstract

The authors have proposed a high temperature solvent fractionation method that can separate coals into several fractions having different molecular weight without destroying coal structure. In this study the method was applied to characterization of low-grade coals and binder during their co-pyrolysis to clarify chemical interaction between them. When a sub-bituminous coal or a slightly-caking coal was co-pyrolyzed with asphalt pitch (ASP), it was found that smaller-molecular weight compounds less than 800 in molecular weight which were abundant in ASP could be added by appearance as can be expected from the calculation assuming no interaction between the coals and ASP. The added smaller-molecular weight compounds contributed to the reduction of viscosity of the pyrolyzing coal. The possibility was also suggested that part of smaller-molecular weight compounds in ASP were converted to heavier compounds whereas some smaller-molecular weight compounds were formed from coals to compensate the loss of such compounds derived from ASP. It was also shown that oxygen existent in the heaviest fraction of the low-grade coals was removed to form H2O and CO2 by chemical interaction with ASP. This interaction was found to contribute to the reduction of shrinkage of low-grade coals during carbonization.

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Co-pyrolysis Behavior of Low-grade Coal and Binder Using High Temperature Solvent Fractionation

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Sulfur and Nitrogen Distributions during Coal Carbonization and the Influences of These Elements on Coal Fluidity and Coke Strength

Naoto Tsubouchi, Yuuki Mochizuki, Yohei Ono, Kazuya Uebo, Toshimasa Takanohashi, Naoto Sakimoto

pp. 2439-2445

DOI:

10.2355/isijinternational.54.2439

Abstract

The present study focuses on examining the fate of coal-S and coal-N during carbonization in detail and making clear the effects of these elements on coal fluidity and coke strength. When eight kinds of caking coals with 80–88 mass%-daf C are carbonized in high-purity He at 3°C/min up to 1000°C with a quartz-made fixed bed reactor, 50–75% of coal-S remains as FeS and organic-S in the coke, and the rest is released as tar-S and H2S. Most of coal-N is also retained in the coke, and the remainder is converted to tar-N, HCN, NH3 and N2. The eight coals give Gieseler maximum fluidity values between 435 and 480°C, and the value tends to be larger at a smaller sulfur content in coal or in the carbonaceous material recovered after carbonization at 450°C. It also seems that the value increases with increasing nitrogen content in coal or total amount of either HCN or NH3 formed up to 450°C. Furthermore, the addition of S-containing compounds to an Australian bituminous coal lowers coal fluidity and coke strength considerably, whereas indole gives the reverse effect on them. On the basis of these results, it is suggested that coal-S or some coal-N has a negative or positive effect on the two properties, respectively.

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Sulfur and Nitrogen Distributions during Coal Carbonization and the Influences of These Elements on Coal Fluidity and Coke Strength

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Coking Technology Using Heavy Oil Residue and Hyper Coal

Yasushi Sekine, Fumitaka Sumomozawa, Takahiro Shishido

pp. 2446-2453

DOI:

10.2355/isijinternational.54.2446

Abstract

Oil sand bitumen and hypercoal are examined as a caking additives to the mixture of strongly coking coal and non-slightly coking coal. Samples were coked, then their strength, crystallinity of the carbon structure, and an anisotropic microstructure were measured. Oil sand bitumen addition enhanced strength, but 15% addition caused a strength decline because of the formation of large pores and cracks. Hypercoal addition increased strength with increased its content. Correlation was observed between increased strength and the crystallinity of a carbon structure or the anisotropic microstructure. Results suggest that mutual melting occurred between a coal blend and a caking additive. Then the caking additive took a carbon structure with high crystallinity by coking, achieved a function as a binder material that connects coal-particle interfaces, and ultimately enhanced strength.

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Coking Technology Using Heavy Oil Residue and Hyper Coal

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Effect of Woody Biomass Addition on Coke Properties

Yasuaki Ueki, Yoko Nunome, Ryo Yoshiie, Ichiro Naruse, Yuko Nishibata, Sadayoshi Aizawa

pp. 2454-2460

DOI:

10.2355/isijinternational.54.2454

Abstract

The price of caking coal, which is used in the production of metallurgical coke, has risen in recent years. Also of concern is the amount of CO2 emitted from steel industries, comprising approximately 15% of total CO2 emissions in Japan. Therefore, CO2 emissions from the ironmaking process should be reduced to avoid global warming. In this work, fundamental research is conducted on the effect of adding woody biomass to the properties of coke, with the aim of possibly using woody biomass, which is carbon neutral, as a raw material in coke-making. Experimental results showed that the connectivity between coal particles in the coke sample during carbonization and coke strength drastically decrease by adding woody biomass to caking coal. However, the coke properties of the coke sample with added woody biomass could be improved by removing the partly volatile matter of woody biomass before mixing with caking coal, and as a result, the possibility of using woody biomass as a raw material for coke-making with prior carbonization at temperatures of more than 500°C was found.

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Effect of Woody Biomass Addition on Coke Properties

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Preparation of Coke from Hydrothermally Treated Biomass in Sequence of Hot Briquetting and Carbonization

Shinji Kudo, Aska Mori, Ryosuke Soejima, Fusa Murayama, Karnowo, Seiji Nomura, Yusuke Dohi, Koyo Norinaga, Jun-ichiro Hayashi

pp. 2461-2469

DOI:

10.2355/isijinternational.54.2461

Abstract

A sequence of briquetting of biomass solids (bamboo, larch and mallee) at temperature and mechanical pressure of 130–200°C and 114 MPa, respectively, and carbonization at 900°C produces coke with tensile strength (TS) of 5–19 MPa. Introduction of heat treatment in hot-compressed water (i.e., hydrothermal treatment; HT) of the biomass prior to the briquetting increases TS up to 44, 57 and 42 MPa for the bamboo, larch and mallee, respectively. TS of coke is correlated well and positively with the coke/briquette bulk density ratio, and HT increases the ratio if operated under appropriate conditions. The efficacy of HT is attributed primarily to increase in the coke yield on a basis of the briquette mass. HT hydrolytically removes highly volatile cellulosic material (i.e., cellulose and hemicellulose), transforms it into solid that contributes to coke as effectively as lignin, and thereby increases the mass yield of coke by a factor of 1.4 to 2.1. HT also enhances the plasticizability of the biomass during the briquetting by degradation of the lignin to reasonable extent, and then promotes particles’ coalescence/fusion and densification of the briquettes. Applying mechanical pressure over a range of 12–114 MPa to the briquetting of a solid from HT of the bamboo at 240°C successfully results in production of coke with TS of 41–44 MPa.

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Preparation of Coke from Hydrothermally Treated Biomass in Sequence of Hot Briquetting and Carbonization

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Physical and Chemical Characteristics of Coal-binder Interface and Carbon Microstructure near Interface

Atul Sharma, Naoto Sakimoto, Daisuke Anraku, Kazuya Uebo

pp. 2470-2476

DOI:

10.2355/isijinternational.54.2470

Abstract

In this study, investigations were made to understand the mechanism of increase in coke strength on binder addition by analyzing physical and chemical characteristics of coal-binder interface. Three binders, oil derived Asphalt pitch (ASP), coal derived HyperCoal (HPC) and Coal tar pitch (CTP) were used to understand the effect of binder. A new method to observe the coal-binder interface boundary at microscopic level by Scanning Electron Microscope (SEM) was developed. When base coal was a non-caking coal, coal-binder interface boundary was clearly observed by SEM for the first time. From observed images, it was found that ASP and HPC bound differently on the coal surface. When base coal is a caking coal, the interface could not be distinguished but sulfur mapping confirmed the presence of interface. Preliminary Laser Raman analysis suggests there may be some interactive effect of coal and binder on each other’s carbon structure development. Contribution of fraction of coal surface coated with binder towards coke strength is considered.

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Physical and Chemical Characteristics of Coal-binder Interface and Carbon Microstructure near Interface

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Observation of the Coal Thermoplastic Layer Using μ-focus X-ray CT and Sole-heated Oven

Hideyuki Hayashizaki, Yukihiro Kubota, Takashi Arima, Kazuya Uebo, Seiji Nomura

pp. 2477-2483

DOI:

10.2355/isijinternational.54.2477

Abstract

The pore structure of coke is one of the factors governing coke strength. As a step toward technology development to control the coke pore structure, we observed the behavior of coal thermoplastic layers in which coke pores are formed using our newly developed technique with sole-heated oven and μ-focus X-ray CT.
Coal packed bed was heated in the sole-heated oven, and then cooled rapidly after the sample temperature reached 350°C at the top and 550°C at the bottom. Next, many cross-section images of the coal and coke layers were observed nondestructively and continuously by the μ-focus X-ray CT. As a result, the following knowledge was obtained.
The thermoplastic layer of coal goes through the following four processes: 1) initial process of pore formation, 2) initial softening process whereby the growth of pores, expansion of coal, filling of voids between coal particles, and decrease in porosity occur, 3) intermediate softening process whereby the porosity becomes maximum, and 4) final softening process (resolidification process) whereby the pore size and porosity decrease.
With a given type of coal, firstly pores are formed inside the particles over 1 mm in diameter, while the pore formation inside the particles less than 1 mm occurs at approximately 10°C temperature higher than the temperature at which pore formation inside large particles.

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Observation of the Coal Thermoplastic Layer Using μ-focus X-ray CT and Sole-heated Oven

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A Novel Measurement Method for Coal Thermoplasticity: Permeation Distance

Yusuke Dohi, Kiyoshi Fukada, Tetsuya Yamamoto, Takashi Matsui, Hiroyuki Sumi, Izumi Shimoyama

pp. 2484-2492

DOI:

10.2355/isijinternational.54.2484

Abstract

A novel measurement method for coal thermoplasticity was developed, where permeation distance of thermally plastic coal into glass beads layer placed on the coal sample was measured. The characteristic of this method is simulating the condition in a coke oven, especially void structure around the plastic layer by using glass beads and coking pressure by applying a load. In a standard condition, the coal sample is heated to 550°C, and coal sample softens and permeates into the glass beads layer, then the permeation distance is measured after cooling the sample. The maximum permeation distance measured is roughly correlated with Gieseler fluidity, however large deviation is observed especially for high fluidity coals. Moreover, the deterioration of coke strength is observed in case that long permeation distance coal is used in a coal blend for cokemaking. This new measurement method clearly shows the difference in coking property of high fluidity coal as well as solving the problems in Gieseler plastometer method for evaluating high fluidity coals. By employing the permeation distance method, contribution to the production of high strength coke and effective usage of caking coal will be expected.

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A Novel Measurement Method for Coal Thermoplasticity: Permeation Distance

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A Simplified Bubble Nucleation, Growth and Coalescence Model for Coke Production Process

Kentaro Taki, Hideyuki Hayashizaki, Kiyoshi Fukada

pp. 2493-2502

DOI:

10.2355/isijinternational.54.2493

Abstract

Coke production process, which involves gas generation, cross-linking, gas foaming as well as solidification phenomena, is extremely complex and is difficult to model them without simplification. In this study, a simple phenomenological model was developed based on a gas foaming simulation model of polymer foaming, which enabled us to simulate the number density of bubbles and their distributed size. The model was extended to account their kinetics of bubble nucleation, growth and coalescence in non-isothermal chemical reactions of gas generation and cross-linking. The bubbles size and morphology obtained from the numerical simulation of two different coals agreed with the pictures of the experiment qualitatively. Five different coals were investigated to understand the relationship between the kinetic and final morphology of coke.

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A Simplified Bubble Nucleation, Growth and Coalescence Model for Coke Production Process

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Evaluation of Coal Thermoplastic and Dilatation Behavior with Coke Pore Structure Analysis

Yusuke Hayashi, Sadayoshi Aizawa, Kazuya Uebo, Seiji Nomura, Takashi Arima

pp. 2503-2511

DOI:

10.2355/isijinternational.54.2503

Abstract

The strength of coke largely depends on the thermoplastic and dilatation behavior of its coal constituents. Therefore, understanding the behaviors that ensure high-strength coke is important. In this study, the combination of blended coal was varied and (in a separate experiment) asphalt pitch (ASP) was added to the blended coal. The resulting changes in coke pore structure were investigated by image analysis of a cross-section of coke. The main findings are summarized below.
(1) When the thermoplastic temperature of low- and high-rank coal was very different, the proportion of low-circularity pores increased in the textures of both the grades of coal. It was concluded that when the particles of high-rank coal did not dilate, those of the low-rank coal freely expanded. Meanwhile, the dilatation of high-rank coal decreased the extent of dilatation in the neighboring low-rank coal. Consequently, high-rank coal not adjacent to low-rank coal achieved free expansion, and its texture became characterized by increased low-circularity pore areas.
(2) The addition of ASP to blended coal decreased the number of low-circularity pores in the texture of high-rank coal. ASP appears to lower the softening temperature of high-rank coal, enabling it to fill the voids between coal particles before the low-rank coal solidifies.
The abovementioned investigation of coke pore structure assists our understanding of the thermoplastic and dilatation behavior of coal.

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Evaluation of Coal Thermoplastic and Dilatation Behavior with Coke Pore Structure Analysis

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Image Recognition Method for Defect on Coke with Low-quality Coal

Yasuhiro Saito, Tetsuya Kanai, Daisuke Igawa, Yukinori Miyamoto, Shohei Matsuo, Yohsuke Matsushita, Hideyuki Aoki, Seiji Nomura, Hideyuki Hayashizaki, Shigeto Miyashita

pp. 2512-2518

DOI:

10.2355/isijinternational.54.2512

Abstract

The image recognition method was proposed to quantify non-adhesion grain boundaries which were considered as a factor of coke strength besides pores, and the correlation between coke strength and the amount of defects evaluated by the method was investigated in comparison with the one by the marking method. Coke with low-quality coal was fractured by a diametral-compression test, and the fracture cross-sections were observed by a scanning electron microscopy (SEM) and a 3D laser scanning microscope (LSM). The marking method and image recognition method were applied to SEM and LSM images, respectively. As a result, the fracture strength measured by the diametral-compression test was linearly decreased with an increase in blending ratio of low-quality coal. In the marking method, most non-adhesion grain boundaries were not detected up to 50% in the blending ratio, and the boundaries increased sharply from 50 to 100% in the blending ratio. On the other hand, in the recognition method, the defects which were composed of both pores and non-adhesion grain boundaries, increased linearly with the blending ratio, and the amount of defects corresponded to coke strength. Therefore, the image recognition method is expected as the quantification technique of defects decreasing coke strength.

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Image Recognition Method for Defect on Coke with Low-quality Coal

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Effect of Random Pore Shape, Arrangement and Non-adhesion Grain Boundaries on Coke Strength

Yasuhiro Saito, Shohei Matsuo, Tetsuya Kanai, Ayuko Toishi, Ataru Uchida, Yoshiaki Yamazaki, Yohsuke Matsushita, Hideyuki Aoki, Seiji Nomura, Hideyuki Hayashizaki, Shigeto Miyashita

pp. 2519-2526

DOI:

10.2355/isijinternational.54.2519

Abstract

In this study, the rigid bodies-spring model (RBSM) was used to numerically investigate how the fracture behavior of coke is affected by pore structure and non-adhesion grain boundaries. To study the effects of pore structure, randomly shaped pores were generated and randomly positioned in a coke matrix. The random shapes of pores were controlled by pore roundness and their random sizes were controlled by equivalent circle diameters. Non-adhesion grain boundaries were also randomly located in the coke matrix. First, results for a coke model with realistic pore structures showed that large distorted pores decrease coke strength. Second, fracture behavior was analyzed for a coke model composed of a coke matrix, pores, and non-adhesion grain boundaries. Coke strength decreased as the number of non-adhesion grain boundaries increased; these numerical results agreed with previous experimental data. Further, coke strength decreased even in the presence of only a relatively small number of non-adhesion grain boundaries. This is because, when non-adhesion grain boundaries occur in stress-concentrated regions, those boundaries become origins for fracture. This indicates that the presence of non-adhesion grain boundaries is one factor that decreases the strength of coke when it has been blended with low-quality coal.

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Effect of Random Pore Shape, Arrangement and Non-adhesion Grain Boundaries on Coke Strength

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Development of the Coke Model with the Non-adhesion Grain Boundary and Its Fracture Analysis

Shohei Matsuo, Daisuke Igawa, Tetsuya Kanai, Ayuko Toishi, Yasuhiro Saito, Yohsuke Matsushita, Hideyuki Aoki, Seiji Nomura, Hideyuki Hayashizaki, Shigeto Miyashita

pp. 2527-2532

DOI:

10.2355/isijinternational.54.2527

Abstract

The strength of the coke with the low-quality coals is related to the non-adhesion grain boundaries. Therefore, the effect of the boundaries on the coke fracture was numerically investigated. A coke model reproducing the actual boundaries was developed by the random arrangement of the coal particle polygons and expansion of the polygons based on experimental results. Then, the fracture behavior and strength of the coke model were analyzed using the Rigid Bodies-Spring Model (RBSM) method. The boundaries were generated around the low-quality coals in the model and the predicted amount of the boundaries corresponded with the experimental results. Therefore, the present coke model reproduced the generation of the actual boundaries. Furthermore, the size and complexity of the boundaries increased with an increase in the low-quality coals. In the model, springs at the gap or edge of the boundaries were fractured. The boundaries themselves were found to concentrate stress, and the arrangement and shape of the boundaries were supposed to affect the coke fracture. Moreover, the concentrated boundaries were thought to decrease the coke strength. Stress-strain curves showed that the coke with the larger blending ratio of the low-quality coal fractured with the weaker strength because of the increment in the size and complexity of the boundaries. The calculated fracture strength showed the same pattern as the experimental one in the higher blending ratio of the low-quality coals. Above all, the present method can predict the coke strength with the non-adhesion grain boundaries on the basis of the blending ratio of the low-quality coal.

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Development of the Coke Model with the Non-adhesion Grain Boundary and Its Fracture Analysis

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Reaction Behavior of Ca-loaded Highly Reactive Coke

Seiji Nomura

pp. 2533-2540

DOI:

10.2355/isijinternational.54.2533

Abstract

Usage of highly reactive coke in order to decrease the thermal reserve zone temperature in a blast furnace is considered promising to increase the reaction efficiency in the blast furnace and to decrease the reducing agent rate. In order to develop a new method to produce highly reactive coke by adding a Ca catalyst other than Ca-rich coal, in this paper, firstly the effects of Ca compounds pre-addition to coal on coke qualities were investigated. It was shown that carbonizing the mixture of coal and Ca compounds (CaO, CaCO3) greatly increased coke reactivity and that it was possible to produce Ca-loaded highly reactive coke with high coke strength by adding 3% of Ca compounds under such conditions as high strength coke was produced. Furthermore, the reaction behavior of Ca-loaded highly reactive coke when mixed with conventional coke in the presence of an alkali was investigated. It was shown that when a mixture of Ca-loaded highly reactive coke and conventional coke was heated in a reaction gas, Ca-loaded coke selectively and preferentially reacted. It was also confirmed that Ca acted as catalyst in the existence of K. This shows that the reactivity of Ca-loaded coke is higher than that of conventional coke in an actual blast furnace whereby coke reactivity is promoted by condensed alkali vapor.

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Reaction Behavior of Ca-loaded Highly Reactive Coke

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Appropriate Technology Parameters of Iron Ore Sintering Process with Flue Gas Recirculation

Xiaohui Fan, Zhiyuan Yu, Min Gan, Xuling Chen, Tao Jiang, Hongli Wen

pp. 2541-2550

DOI:

10.2355/isijinternational.54.2541

Abstract

Flue gas recirculation (FGR) is being introduced into the sintering process with the aim of reducing the emissions of pollutants. The influences of FRG ratio and circulating flue gas properties such as components, contents and temperature on sintering process are researched. The results show that a cleaning production with good sinter indexes can be obtained in the case of FGR ratio of 30–40%. As the circulating flue gas passes through the sintering bed, the combustion speed of fuel is reduced with O2 content decreasing; CO in circulating flue gas can be reused due to its post-combustion in the sinter zone; the combustion speed and efficiency of fuel are reduced if CO2 content is too high; the velocity of gas-solid heat transfer is increased while the condensation at over-wet zone is intensified with the increase of H2O(g) content; and the thermal state of sintering bed is improved if the temperature of circulating flue gas is not too high. The sinter indices can be maintained in case of FGR with 15 vol%O2, 6 vol%CO2, less than 8 vol%H2O(g) and 150–250°C of inlet gas.

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Appropriate Technology Parameters of Iron Ore Sintering Process with Flue Gas Recirculation

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Interaction between Steel and Distinct Gunning Materials in the Tundish

Pengcheng Yan, Marie-Aline Van Ende, Enno Zinngrebe, Sieger van der Laan, Bart Blanpain, Muxing Guo

pp. 2551-2558

DOI:

10.2355/isijinternational.54.2551

Abstract

Gunning materials are used as a dispensable protective layer to extend the tundish life. Their use however, affects the steel cleanliness by introducing steel reoxidation and exogenous inclusions. In the present work, the interaction between molten steel and three types of refractory, i.e. MgO, Al2O3, and MgO + 2MgO∙SiO2 based gunning materials (GM) have been investigated. Compared to MgO and MgO + 2MgO∙SiO2 GM, the Al2O3 GM exhibited better infiltration resistance to molten steel. The two phase MgO + 2MgO∙SiO2 GM was found to be less prone to steel infiltration than single-phase MgO GM. The compositional evolution of steel influenced by gunning material was experimentally measured and also predicted with thermodynamic equilibrium calculations. The steel cleanliness in terms of inclusion size, number density, area fraction and morphology was measured and evaluated. Although large Al2O3/AlTiOX inclusions were formed through the erosion of Al2O3 GM, the use of Al2O3 GM resulted in an improved steel cleanliness due to its lower content of reducible compounds compared to that of MgO and MgO + 2MgO∙SiO2 GM.

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Interaction between Steel and Distinct Gunning Materials in the Tundish

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Decarburization of Molten Fe–C Droplet: Numerical Simulation and Experimental Validation

Hyun-Jin Cho, Sung-Hoon Jung, Sang-Joon Kim, Hae-Geon Lee, Youn-Bae Kang

pp. 2559-2568

DOI:

10.2355/isijinternational.54.2559

Abstract

Decarburization of Fe–C droplet was investigated by fluid dynamics numerical simulation based on physical properties under gas phase mass transfer controlled regime. Fluid flow and species concentration fields around the droplet implementing a reaction of carbon with oxidant gas at the interface were calculated by a commercial CFD package which solves a set of transport equations. Overall decarburization rate of the molten Fe–C droplet was obtained by the simulation, and it was additionally validated by the present authors’ own experiment using gas-liquid drop reaction in a levitation melting equipment. It was observed by the simulation that decarburization rate on the surface of a droplet was not homogeneous due to inhomogeneous gas distribution around the droplet. A new concept of local mass transfer coefficient ratio was proposed in the present study as a ratio of effective local mass transfer coefficient at a specific site over average mass transfer coefficient, as a function of θ (angle between direction of gas flow and direction to reaction site on the droplet surface from the droplet center) and dimensionless numbers regarding fluid flow:

Furthermore, effect of distance between two droplets was investigated by the present numerical model for decarburization of multiple droplets. The local mass transfer coefficient was found to have a significant impact on decarburization rate of a droplet when the other droplet locates very close. Relation between decarburization rate of two droplets and distance between them were analyzed.

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Decarburization of Molten Fe–C Droplet: Numerical Simulation and Experimental Validation

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Kinetic Analysis of Compositional Changes in Inclusions during Ladle Refining

Akifumi Harada, Nobuhiro Maruoka, Hiroyuki Shibata, Masafumi Zeze, Norifumi Asahara, Fuxiang Huang, Shin-ya Kitamura

pp. 2569-2577

DOI:

10.2355/isijinternational.54.2569

Abstract

It is well known that the composition of inclusions is determined by alloying elements and by reaction with slag. For example, MgO·Al2O3 spinel-type inclusions form, even though Mg is not added, due to the supply of Mg through the reaction between slag and metal. To clarify the mechanism of compositional changes in inclusions, the authors have developed a kinetic model to simulate the reactions during the ladle refining process. In this study, experiments were conducted using an induction furnace, and the compositional changes in molten steel, slag, and inclusions were investigated. The inclusions were analyzed by P-SEM, which incorporates an automatic analysis system. By the application of the developed simulation model to these experiments, the validity of the model was evaluated. The inclusion composition gradually changed from Al2O3 to MgO·Al2O3 after the addition of Al, and the inclusions originating from slag were also observed at all times. The compositional change of the deoxidation product by the model calculation corresponded well to the observed variation in the composition of inclusions, and the calculated composition of inclusions originating from slag also agreed with the experimental results. The rate of compositional change increased with increasing Ar gas flow rate, and this tendency was captured well by the model. Therefore, the validity of the developed model is considered to be confirmed.

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Kinetic Analysis of Compositional Changes in Inclusions during Ladle Refining

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Assessment of Turbulence Models for Prediction of Intermixed Amount with Free Surface Variation Using Coupled Level-Set Volume of Fluid Method

Md Irfanul Haque Siddiqui, Pradeep Kumar Jha

pp. 2578-2587

DOI:

10.2355/isijinternational.54.2578

Abstract

In continuous casting tundish steelmaking, old ladle is replaced by new one to ensure continuous supply of steel from tundish to mold. Bath height changes in case of ladle change-over. To bring the bath height level to normal height, the flow rate of liquid steel from the new ladle is increased. This has a direct bearing on the fluid flow pattern and resultant intermixed amount formed. In the present work, assessment of Reynolds-averaged Navier-stokes (RANS) equations based standard k-ε, Renormalization group (RNG) k-ε, Realizable k-ε standard k-ω, and Shear-stress transport (SST) k-ω turbulence models have been carried out for prediction of free surface level of steel in tundish during ladle change-over and the intermixed amount formed. Coupled Level-Set Volume of Fluid (CLSVOF) method was used for free surface tracking in the three dimensional, multi-phase numerical model. Physical investigations were carried on water model setup of reduced scale tundish. Inflow rate of steel into the tundish from second ladle was varied due to which free-surface height of water varied and grade mixing in tundish was analyzed. Results obtained through physical investigations were compared with that of numerical investigations. The predictions revealed that RNG k-ε model have good approximation of F-curves as well as the interface between the two phases. Predictions made by all models except SST k-ω model have shown a satisfactory approximation with the experimental values. Free-surface interface profiles predicted by variants of k-ε models were seen to closely match with experimental data.

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Assessment of Turbulence Models for Prediction of Intermixed Amount with Free Surface Variation Using Coupled Level-Set Volume of Fluid Method

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A Fast Heuristic Algorithm for Ladle Scheduling Based on Vehicle Routing Problem with Time Windows Model

Zheng Wei, Tan Zhu, Tianzhang He, Shixin Liu

pp. 2588-2597

DOI:

10.2355/isijinternational.54.2588

Abstract

In the process of steelmaking and continuous casting production, an optimized ladle schedule will greatly reduce energy consumption and improve production. The ladle scheduling problem can be modeled as vehicle routing problem with time windows (VRPTW) and extra constraints. The main extra constraint is that components of the ladle, at the right time, have to be repaired no later than serving certain number of heats. The objective of ladle scheduling problem is minimizing the number of serving ladles and reducing the waiting time between serving two adjacent heats. According to the serving process of ladles, a mathematical model is established to solve this specific problem. In this paper, a three-step heuristic algorithm with time complexity of O(n2) is proposed, which is based on characteristics of the model and some preliminary experiments. The algorithm has been tested by several practical instances from a steel plant in China. Comparing with the schedules used in actual production, the computational results show that our algorithm optimizes the ladle schedules and solves the problem in less than 1 second, which proves the algorithm’s efficiency.

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A Fast Heuristic Algorithm for Ladle Scheduling Based on Vehicle Routing Problem with Time Windows Model

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Surface Defect Detection Method Using Saliency Linear Scanning Morphology for Silicon Steel Strip under Oil Pollution Interference

Ke-Chen Song, Shao-Peng Hu, Yun-Hui Yan, Jun Li

pp. 2598-2607

DOI:

10.2355/isijinternational.54.2598

Abstract

Surface defect detection of silicon steel strip is an important section for non-destructive testing system in iron and steel industry. To detect the interesting defect objects for silicon steel strip under oil pollution interference, a new detection method based on saliency linear scanning morphology is proposed. In the proposed method, visual saliency extraction is employed to suppress the clutter background. Meanwhile, a saliency map is obtained for the purpose of highlighting the potential objects. Then, the linear scanning operation is proposed to obtain the region of oil pollution. Finally, the morphology edge processing is proposed to remove the edge of oil pollution interference and the edge of reflective pseudo-defect. Experimental results demonstrate that the proposed method presents the good performance for detecting surface defects including wipe-crack-defect, scratch-defect and small-defect.

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Surface Defect Detection Method Using Saliency Linear Scanning Morphology for Silicon Steel Strip under Oil Pollution Interference

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Flatness Intelligent Control Based on T-S Cloud Inference Neural Network

Xiuling Zhang, Liang Zhao, Jiayin Zang, Hongmin Fan, Long Cheng

pp. 2608-2617

DOI:

10.2355/isijinternational.54.2608

Abstract

The accuracy of traditional flatness control methods are limited and it is difficult to establish a precise mathematical model of the rolling mill. In addition, the flatness control system is complex and multivariate. General model approaches can not satisfy the high precision demand of rolling process. In this paper, T-S cloud inference neural network and its stability are proposed. It is constructed by cloud model and T-S fuzzy neural network. The stability of T-S cloud inference neural network is analyzed by Lyapunov method in details. Based on the new network, flatness recognition model and flatness predictive model are established. And they are applied for 900HC reversible cold rolling mill. The flatness control system is designed and a simple controller is developed. Initial parameters of the controller are firstly determined through offline training based on measured data, and then they are optimized online automatically. Genetic Algorithm (GA) is used as the optimizing method which is compared with particle swarm optimization (PSO). The simulation results demonstrate that the flatness control system is effective and has a better precision and robustness.

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Flatness Intelligent Control Based on T-S Cloud Inference Neural Network

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Development of Pig Iron and Molten Slag Level Measurement Technique for Blast Furnace

Tomohiko Ito, Junichi Yotsuji, Akio Nagamune

pp. 2618-2622

DOI:

10.2355/isijinternational.54.2618

Abstract

Measurement of the pig iron and slag level in the blast furnace is essential to operate the furnace stably because an increase of these liquids level can cause fluctuations of the pressure in the furnace or the temperature of the furnace which are related to the furnace condition and may finally result in reduced productivity or serious trouble.
The conventional method is the EMF (electromotive force) measurement correlated with the liquid level. It can be thought that a voltage generated electrochemically (as in a battery) by the reduction reaction of iron oxides. However some reports said that EMF sometimes loses correlation with the liquid level because of thermal influence.
In this paper a new method is proposed using a quite small electrical resistance measurement of the hearth of a blast furnace which contains pig iron and molten slag. Accordingly the four point contact method was adopted and a pseudo random signal as a current pattern was fed to improve the S/N ratio.
Measurements were done at plural positions along the circumference of the blast furnace. However when the current signal is independently fed at each position, spike noises are generated. These noises are originated in the induced voltage which is generated at neighbor positions when the polarity of the current changes. But finally this noise problem can be solved by feeding synchronized current and measuring the signal on the noiseless timing.
The measurement results indicated that the level in the hearth is not necessary identical at all positions.

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Development of Pig Iron and Molten Slag Level Measurement Technique for Blast Furnace

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Development of an Operation Guidance System to Reduce Pushing Load of Coke Ovens Based on Probabilistic Optimization

Yoshinari Hashimoto, Kazuro Tsuda, Seitaro Akiyama, Michio Honma

pp. 2623-2626

DOI:

10.2355/isijinternational.54.2623

Abstract

In recent years, the increase in the pushing load of coke ovens caused by aging has become a problem in steel works. In order to reduce this problem, an operation guidance system by a statistical approach was developed. The prediction model was developed based on an individual oven database, to deal with the variations in the characteristics of the ovens. The pushing process which involves complicated motion of coke grains can be regarded as a probabilistic phenomenon. Therefore, a guidance system using probabilistic optimization was constructed. The system was evaluated in actual operation, and the effect of reducing high pushing load ratio to 1/3 has been confirmed.

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Development of an Operation Guidance System to Reduce Pushing Load of Coke Ovens Based on Probabilistic Optimization

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A Microstructure Evolution Model for Intercritical Annealing of a Low-carbon Dual-phase Steel

Mykola Kulakov, Warren J. Poole, Matthias Militzer

pp. 2627-2636

DOI:

10.2355/isijinternational.54.2627

Abstract

A model was developed to describe the microstructure evolution during intercritical annealing of a low-carbon steel suitable for industrial production of DP600 grade dual-phase steel on a hot-dip galvanizing line. The microstructure evolution model consists of individual submodels for ferrite recrystallization, austenite formation and decomposition constructed using the Johnson-Mehl-Avrami-Kolmogorov approach and the additivity principle. The submodels for recrystallization and austenite formation are adopted from a previous study. The present paper provides a detailed analysis of the model development for the decomposition of intercritical austenite. The overall microstructure evolution model is validated using simulated industrial thermal paths for intercritical annealing. Model validation is expedited by in-situ measurements of the recrystallization completion temperature using laser ultrasonics and the intercritical austenite formation and decomposition using dilatometry.

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A Microstructure Evolution Model for Intercritical Annealing of a Low-carbon Dual-phase Steel

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Repulsive Nature for Hydrogen Incorporation to Fe3C up to 14 GPa

Hidenori Terasaki, Yuki Shibazaki, Keisuke Nishida, Ryuji Tateyama, Suguru Takahashi, Miho Ishii, Yuta Shimoyama, Eiji Ohtani, Ken-ichi Funakoshi, Yuji Higo

pp. 2637-2642

DOI:

10.2355/isijinternational.54.2637

Abstract

We have performed in situ X-ray diffraction measurements under high pressure and high temperature to study hydrogen solubility in Fe3C carbide. Hydrogen solubility can be estimated from a volume expansion associated with hydrogen incorporation into metal. The lattice volumes and phase relations of Fe3C–H system and Fe3C were measured up to 14 GPa and 1973 K. The lattice volumes of Fe3C measured in this study are well fitted using the 3rd order Birch–Murnaghan equation of state with the reported elastic parameters of Fe3C. Obtained lattice volumes of Fe3C–H are quite consistent with those of Fe3C. No difference between the melting temperatures of Fe3C–H and Fe3C was observed. These results demonstrate that hydrogen incorporation into Fe3C does not occur and hydrogen is unlikely to coexist with carbon in iron-alloy up to 14 GPa.

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Repulsive Nature for Hydrogen Incorporation to Fe3C up to 14 GPa

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Anomalous Segregation Kinetics of Phosphorus and Carbon Governed by Carbide Reactions in 2.25Cr-1.5W Heat-resistant Steel

Hyun Je Sung, Nam Hoe Heo, Yoon-Uk Heo, Sung-Joon Kim

pp. 2643-2648

DOI:

10.2355/isijinternational.54.2643

Abstract

In a 2.25Cr-1.5W heat-resistant steel containing V and Nb, the formation sequence of carbides are detailed. Such carbide reactions determine directly the anomalous segregation kinetics of phosphorus and carbon at the grain boundary/carbide interface. The anomalous segregation kinetics of phosphorus consists of two maximum segregation peaks and one minimum peak corresponding to the high segregation concentration of carbon. The roles of the carbide reactions on the anomalous segregation kinetics of the solutes are fully understood from the viewpoint of the dissolution of unstable carbides into the matrix for forming the stable carbides, the active segregation of the dissolved carbon into the newly formed carbide interface for the growth and the resultant repulsive segregation between carbon and phosphorus.

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Anomalous Segregation Kinetics of Phosphorus and Carbon Governed by Carbide Reactions in 2.25Cr-1.5W Heat-resistant Steel

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Microstructure of Martensite in Fe–C–Cr and its Implications for Modelling of Carbide Precipitation during Tempering

Ziyong Hou, Peter Hedström, Yunbo Xu, Wu Di, Joakim Odqvist

pp. 2649-2656

DOI:

10.2355/isijinternational.54.2649

Abstract

The microstructure of as-quenched martensite in four Fe–C–Cr alloys (0.15C-1Cr, 0.15C-4Cr, 1C-1Cr, 1C-4Cr, mass%) has been investigated. Moreover, the microstructures served as input for setting up modeling of carbide precipitation during tempering of martensite. The modelling was conducted using the Langer-Schwartz approach and the software TC-PRISMA, which retrieves thermodynamic data from the Thermo-Calc databank. It was found that the martensite in the low carbon steels is predominantly lath martensite with units arranged parallel to each other. On the other hand, the plate martensite dominates the microstructure in the high carbon steels. The ratio of high-angle to low-angle grain boundaries was found to increase with increasing Cr in the low carbon steels, which indicates that Cr has a similar effect as C on the lath martensite microstructure, however, the micro-hardness remained unaffected by the addition of Cr. Finally, the precipitation modeling clearly demonstrates the importance of proper definition of the initial microstructure for predictive modelling. Parameters such as dislocation density and frequency of high-angle grain boundaries have a drastic effect on e.g. the mean size of carbides.

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Microstructure of Martensite in Fe–C–Cr and its Implications for Modelling of Carbide Precipitation during Tempering

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Material Flow of Iron in Global Supply Chain

Kenichi Nakajima, Keisuke Nansai, Kazuyo Matsubae, Tetsuya Nagasaka

pp. 2657-2662

DOI:

10.2355/isijinternational.54.2657

Abstract

Recently, sustainable management of resources has become an increasingly recognized issue. Accordingly, interest in understanding the relationship between natural resources consumption and the global product supply chain has also been increasing. Material flow analysis (MFA) is a useful tool for understanding resource consumption and material cycles in national economies. However, detailed MFA studies of the materials embedded in foreign trade flows are rare.
This study identified global trade flow of iron embedded in bilateral trade between 231 countries by multiplying the trade volume of the commodities in the BACI (Base pour l’Analyse du Commerce International) database and the iron content of each commodity. We focused on the cases of Japan, China, and United States, and estimated the mass of iron embedded in imports and export. The identified total flows of iron embedded in international trade were 1.15 × 109 t-Fe with 35.2% of the flows concentrated in three countries, Japan, China and United States, which are major crude steel production countries.

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Material Flow of Iron in Global Supply Chain

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