Hydrogen utilization in a direct reduction shaft furnace is a promising technology for carbon neutrality. On the other hand, some kind of heat compensation appears to be necessary, because the temperature in the furnace decreases and the reduction degree stagnates due to hydrogen enrichment. Therefore, a tool which can quantitatively evaluate the efficiency of heat compensation from a kinetic viewpoint considering detailed heat and mass transfer is useful for operational design. Based on the above, a numerical simulation model based on DEM-CFD was developed for the direct reduction process, and the following findings were obtained. (1) A numerical analysis simulating a model plant confirmed that the calculation accuracy of the developed model is sufficiently high. The gas composition varies greatly depending on the degree of achievement of shift equilibrium. (2) A numerical analysis of a commercial plant revealed the distribution with low temperature and low reduction degree in the radial center of the furnace. Hydrogen enrichment lowers the temperature and expands the region with a low reduction degree. (3) As a technique for thermal compensation for hydrogen enrichment, it was found that increasing the inlet gas temperature increases the reduction degree exponentially. (4) DEM-CFD can be a useful approach, since operational design considering powder phenomena, as represented by reduction degradation and clustering, appears to be necessary.

One of the major hindrances in mitigating CO2 emission from the steel industries is the insufficient efficiency improvement of the ironmaking blast furnaces due to the mixed use of the coke fuels having different properties as the reducing agent. This study investigated the gas flow and the clogging in the coke packed bed by the fine coke particles as a cause of the operational instability of the blast furnace. We analyzed the changes in the permeability of the packed bed due to the mechanical destruction of the cokes, which resulted in the generation of fine particles. The changes in the shapes of cokes due to the mechanical stress were tracked via 3D scanning, and this measurement was applied to several cokes having different values of coke strength after reaction (CSR). Using the measured information about particle shape and its variation, the effects of coke degradation on the gas flow distribution in the coke bed were analyzed by the Eulerian-Lagrangian coupling technique. Despite the strong correlation between the amount of coke destruction and the CSR values, the packed beds containing the same amount of fine particles showed a relatively large difference in the pressure drop. Such difference was attributed by the difference in the bed structure that were caused by the rotation and the slippage among the cokes due to the presence of fines between the coke particles. The the slippage between the coke fuels promote the constriction of the voids, thereby increasing the pressure drop. Thus, this study proves that the formation of the bridging among the cokes can maintain the permeability of the packed coke structure, thereby increasing the possibility of performing low-coke operations.

Improving operation performance of blast furnaces is necessary to reduce CO2 emissions and pig iron costs. One of the important factors for the operation is keeping gas permeability well in the blast furnace. Coke fines affect gas permeability and the operation condition become worse, therefore clarification and prediction of the generation behavior of coke fines in blast furnaces are desired. In the present study, first of all, new evaluation method was developed to quantify coke abrasion behavior. And then, we proposed the prediction expression to estimate the amount of coke fines based on the results of abrasion experiments using new method. Finally, the distribution of coke fines in the blast furnace was numerically simulated by coupled 2D blast furnace model and Discrete Element Method (DEM) using proposed equation. The results are summarized as follows: 1) The influential factors of coke abrasion were mechanical conditions like shear distance or compressive stress, and coke quality like strength (Drum Index, DI) or porosity. The amount of coke fines increased by rising shear distance, compressive stress and porosity or decreasing DI. 2) According to numerical simulation using these models, coke fines generated around peripheral area in lower shaft, belly and bosh. In addition, the total amount of coke fines increased with the decrease of DI. These results are in accordance with the conventional knowledge. The distribution of coke fines in the blast furnace became predictable. This evaluation will lead optimum burden distribution and ideal coke quality to achieve highly efficient operation of blast furnaces.

In ironmaking blast furnaces, the particle size distribution and voids in the coke bed affects the upward flow of gas, and consequently, the efficiency of the combustion reaction. To clarify the influence of coke pulverization on the packing structure of the coke bed, the permeability of the bed was evaluated using detailed dynamics simulation and geometric data analysis. To obtain detailed 3D morphology of the coke, we derived digital geometric data using rotational strength tests. Using the Euler-Lagrange coupling approach with the multisphere discrete-element method, the effect of the volume fraction of fines and distribution in the coke bed on the gas flow was analyzed. The void shape in the 3D coke bed structure was quantified using geometric data and simulated gas flow distributions. Although a continuous void network was observed in the packed bed before pulverization, areas of highly restricted (or no) gas flow were observed after pulverization. The dominant effect of coke degradation on the packed bed structure was the disruption of the gas flow path because of fines clogging the pores and narrowing the gas flow path. The developed simulation method can comprehensively analyze the effects of coke degradation on the gas flow distribution in the coke bed and can be used to analyze and control the instability of industrial blast furnaces.

To achieve low RAR operation by coke mixed charging, it is important to control coke segregation behavior in mixed layer at blast furnace top. In this study, a numerical simulator based on screening layer model was developed to estimate the distribution of mixed coke ratio in mixed layer. The results are summarized as follows: (1) The parameters required for the screening layer model to estimate the segregation behavior of the burden materials were determined by PIV test and numerical fitting. (2) The screening layer model containing parameters obtained by experiments and fittings was taken into the blast furnace burden distribution simulator. The simulation results showed that the distribution of mixed coke ratio of the small coke in the ore can be accurately estimated under the charging conditions of the actual furnace. (3) The influence of the difference in tilting direction of the rotating chute on the distribution of mixed coke ratio was evaluated. In the reverse tilting, the radial distribution of the mixed coke ratio became more uniform as compared with the forward tilting charging. Therefore, it is considered that reverse tilting is more effective for carrying out coke mixed charging.

A 3D scanning technique was applied for understanding coke shapes obtained by a rotational strength test, and a numerical dynamic analysis based on the multi-sphere type discrete element method was carried out to clarify the influence of coke degradation on the packed structure. We constructed a trickle flow simulation of molten slag via the smoothed particle hydrodynamics model, and the liquid-gas permeability characteristics exhibited by the coke shapes in the lower part of the blast furnace are discussed accordingly. Coke diameter decreased due to collisions between particles, via the progress of surface- and volume-destruction, and that the particles subsequently became sphere-like in shape. Static holdup of molten slag showed a decreasing tendency with the coke degradation progress, as the void shape and holdup site be came spatially uniform as sphericity increased. In the case of packed bed formed by the initial low sphericity or large-sized cokes, the size of the air gap was maintained, although the flow path was non-uniform. Therefore, even if the large amount of holdup did not block the gaseous mam flow, in the case of lower coke strength, the sphericity increased due to the deformation progress, and void uniformity could be retained However, the existence of many narrow void regions remarkably decreased the gas permeability.

A fully-Lagrangian numerical model was applied for understanding packed bed structures containing non-spherical solids, such as coke, and the high-temperature melt trickle flow characteristics of such beds. Smoothed-particle hydrodynamics (SPH) simulations can track the motion of liquids without discriminating between continuous and dispersed phases, and the extended discrete element method (DEM) is employed as a highly accurate method for simulation of non-spherical solid-particle motion. Based on this model, we carried out large-scale trickle flow simulations using more than 10 million particles, investigated case studies of statistical processing, and evaluated the effects of packed bed formed from various non-spherical coke samples. We found that the pathway that the passing rivulet takes down depends on the structure of the void and the neck size between two voids. If the connecting neck is larger than the capillary length λ=σ/ρg, the slag will drain. The shape of pathway was related that the solids shape factor which is considered by the projected area in the direction of gravity. Even if cokes with similar size were obtained by sieving, low sphericity cokes block slag flow through channeling voids, i.e., as the projected area of the non-spherical solid shape increased, the liquid hold up showed a tendency to increase.

To achieve stable operation of coke oven batteries, a numerical model for estimating the clearance between the coke cake and the coke oven wall was developed. The influence of the temperature distribution in the combustion chamber on coke cake contraction was investigated by using the developed model. As a result, the following findings were obtained. 1) A temperature decrease on the coke side (CS) results in a larger clearance decrease at the end of the coke chamber compared with a temperature decrease on the machine side (MS). 2) The clearance decrease at the end of CS causes a higher pushing load of coke cake. Therefore, improvement of the CS flue gas temperature is particularly important for reducing the pushing force of the coke cake.

From the viewpoint of prevention of global warming, reduction of CO2 emissions has been an important issue for industry in recent year. In the steel industry, promotion of low RAR and low CR operation of blast furnaces is an important technical issue, as blast furnaces account for 70% of CO2 emissions from steel works. For low RAR operation, reducing lump coke consumption, which has a high production cost, is required. However, under this operating condition, the ore-to-coke ratio (O/C) increases, and this causes various problems, such as a delayed reduction reaction of the ore and an increase in the pressure drop in the blast furnace due to expansion of the cohesive zone. Coke mixed charging in the ore layer is known to be effective for high O/C operation. At Nippon Steel & Sumitomo Metal’s Hirohata Works, under-size coke (small coke) was initially applied to coke mixed charging for effective utilization of energy.1) Next, 28 kg/t-pig and 50 kg/t-pig small coke mixed charging was carried out at Nippon Steel & Sumitomo Metal’s Kimitsu and Oita Works,2,3) and improvement of gas permeability in the furnace bottom and reducibility were reported. Watakabe et al. studied the effect of coke mixing on the high temperature properties of the ore-coke mixed layer by an under-load-reduction test,4) finding that the gas permeability in the cohesive layer clearly increased. In addition to that effect, it has been suggested that coke Optimization of Coke Mixed Charging Based on Discrete Element Method

The strains generated in a reaction vessel of hydrogen storage alloys and the packing ratio distribution inside the vessel were measured in order to analyze the effects of packing on stress. More specifically strains generated on the vessel’s surface were measured when hydrogen is repeatedly absorbed and desorbed by the packed bed in the reaction vessel. The amount of deformation, local packing ratios and relative particle volumes in the vessel were also measured after repeated hydrogen absorption–desorption. As absorption–desorption was performed repeatedly, agglomeration regions where the value of the local packing ratio was around 0.6 were formed, and particularly strong stress was generated in these regions, causing deformation. More hydrogen packing causes agglomeration regions to form over a wider area. Since alloys are pulverized by repeated absorption–desorption, and concentrate in the lower parts of the vessel, agglomeration regions are also formed in the lower parts. Our experiments also revealed that the resulting agglomeration regions have a packing ratio of about 0.6.

A model for hydriding-dehydriding reactions was constructed by considering the hydrogen concentration dependency of diffusion coefficient, the particle size distribution, and the shape variation of MmNi(5)-based hydrogen-absorbing alloys was constructed. The effects of the diffusion coefficient and particle conditions on the rate of hydrogen absorption or desorption for MmNi(5)-based hydrogen-absorbing alloys were numerically investigated by the finite element method by comparing calculated results with the available experimental ones for pure hydrogen. When the experimentally determined diffusion coefficient was used and assumed to be constant regardless of concentration, the calculated results were in a good agreement with experimental ones. In the desorption processes, however, the results calculated with a diffusion coefficient that was dependent on hydrogen concentration showed better agreement with the experimental ones than those calculated with a constant diffusion coefficient. Thus, like that of LaNi5-based alloys, the diffusion coefficient of MmNi(5)-based alloys seems to depend on the hydrogen concentration. When particle size distribution was considered, the termination time of hydriding-dehydriding reaction was longer than when average particle size was used and it was shown that the larger particles determined the termination time. From these results, it is important to consider the particle size distributions to estimate the hydrogen diffusion coefficient in the hydrogen absorption-desorption measurements. When shape variations were considered, the reaction rate increased with an increase in the oblateness for the constant projected area. Furthermore, the reaction rate of cubic particles was larger than those of spherical and ellipsoidal particles. Thus, the diffusion coefficient calculated on the assumption of spherical particles is expected to be larger than the actual one.

The effects of long-term absorption-desorption testing with hydrogen containing water vapor and of reactivation on the hydrogen absorption-desorption properties of hydrogen-absorbing alloys were experimentally investigated. With absorption times, the hydrogen-absorbing alloys degraded in the first several cycles. In subsequent cycles, the degraded alloys recovered and degraded again due to the pulverization. On reactivation with pure hydrogen, the hydrogen absorbing-desorbing capacity and rate of hydrogen absorption-desorption recovered, but the hydrogen-absorbing capacity did not recover completely to that before degradation, due to the extrinsic degradation.