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A three-dimensional geometric model of the blast system of the 5500 m 3 blast furnace was established in this study. The velocity distribution of the blast system was calculated by OpenFOAM, and the velocity distribution at cross sections of the round pipe and the branch pipe was analysed. The main conclusions are as follows: (1) When the hot air enters the branch pipe, the air flow speed gradually increases and reaches its maximum value (approximately 266.7 m/s) at the tuyere outlet. (2) When the hot air enters the round pipe from the main pipe, there is momentum loss. When the hot air further reaches the opposite side of the junction between the round pipe and the main (Tuyere 1#), the speed of the hot air in the round pipe decreases to the minimum. (3) The maximum air flow average speed of the tuyere outlet is located at Tuyeres 20# and 21# at the junction of the main pipe and the round pipe, which can reach 264.5 m/s. The minimum air flow average velocity of the tuyere outlet is located at Tuyeres 19# and 22#, approximately 258.5 m/s.

The energy consumption of heating, ventilation, and air conditioning (HVAC) systems holds a significant position in building energy usage, accounting for about 65% of the total energy consumption. Moreover, with the advancement of building automation, the energy consumption of ventilation systems continues to grow. This study focuses on improving the performance of spherical tuyeres in HVAC systems. It primarily utilizes neural networks and multi-island genetic algorithms (MIGA) for multi-parameter optimization. By employing methods such as structural parameterization, accurate and fast computational fluid dynamics (CFD) simulations, a minimized sample space, and a rational optimization strategy, the time cycle of the optimization process is shortened. Additionally, a new comprehensive evaluation index is proposed in this research to describe the performance of spherical tuyeres, which can be used to more accurately assess spherical tuyeres with different structures. The results show that by establishing a neural network prediction model and combining it with the multi-island genetic algorithm, a novel spherical tuyere design was successfully achieved. The optimized novel spherical tuyeres achieved a 27.05% reduction in the spherical tuyeres effective index (STEI) compared to the traditional spherical tuyeres. Moreover, the resistance decreased by 15.68%, and the jet length increased by 7.57%. The experimental results demonstrate that our proposed optimization method exhibits high accuracy, good generalization capability, and excellent agreement at different Reynolds numbers.

This study established three-dimensional gas-phase flow combustion models for oxygen blast furnaces (OBF) and traditional blast furnaces (TBF) along with a water-cooled heat transfer stress model for the tuyere. The combustion processes of reducing gas and pulverized coal, and their effects on the tuyere's temperature and stress fields, were analyzed. Compared to TBF, results show that ambient temperature oxygen injection in an OBF significantly increases the average temperature of the raceway by 1005 K and creates symmetric high-temperature zones at the tuyere outlet. This injection generates substantial heat, promoting coal heating and decomposition, and increases oxygen concentration around coal particles, enhancing burnout rates by 32.45%, especially for medium-sized particles. Additionally, the low-temperature oxygen cools the tuyere interior surface. In contrast, the diffusion of oxygen to the outer layers and its reaction with the hot reducing gas heats the interior surface. The combined effects create a large temperature gradient, resulting in thermal stress of up to 341 MPa on the tuyere interior surface. This thermal stress increases the front stress by 80 MPa compared to TBF, which may reduce the lifespan of the tuyere because of the enhanced thermal stress and material fatigue.

Heat losses in the blast furnace may be decreased by incorporating a heat-insulating insert in the blast channel during assembly of the air tuyere. That decreases coke consumption. In order to avoid stress in the insert when pressure is applied to the tuyere, it is expedient to introduce the insert in the blast channel after most of the tuyere has been assembled. To evaluate this proposal, Ansys software is employed for mathematical modeling: the Fluent module for analysis of the gas dynamics, combustion, and heat transfer; and the Static Structural module for the stress in the insert. The geometry of the mass-produced insert is also modified, by decreasing its internal diameter at the input to the hot-blast channel and increasing the length from the flange to the smallest cross section. Static modeling shows that the insert life is increased and the heat losses with the cooling in the blast channel are decreased if the insert is introduced after most of the tuyere has been assembled. That further decreases coke consumption.

As an indispensable raw material in blast furnace ironmaking, coke plays an important role, which is also the key to low-carbon smelting and reducing ironmaking carbon emissions, so it is necessary to study its quality, degradation behavior, and microstructure evolution. In this work, the pore structure and micromorphology of the blast furnace incoming coke (IC) and tuyere coke (TC) were analyzed comprehensively by comparative research methods. The results showed that the microcrystalline structure of TC was more orderly than that of IC. In addition, the order degree of the coke microcrystalline structure increased first and then decreased in the radial direction and reached the highest value at the distance of 1–2 m from the tuyere. The porosity of radial TC increased obviously. The pore wall became thinner, and the pore size of the original micropores in TC expanded. Simultaneously, large numbers of micropores were also generated, and cracks appeared, resulting in the specific surface area and pore volume of TC becoming higher than that of IC. Moreover, the graphite structure inside TC increased, and the crystal structure became larger. In the radial direction, with an increase in temperature, the number of amorphous structures in coke decreased, the ordering increased, and the graphite structure continued to grow. However, along the direction of the furnace core, a decrease in temperature led to the stagnation of amorphous structure content and a decrease in graphitization degree.

In the presentation, previous archaeological achievements as well as analytical studies conducted on ironwork sites in Chungju are reviewed. In addition, the early iron production technology in the area can be characterized based on various evidences. Extensive ironworks were conducted at various sites concentrated especially in Chungju. Direct smelting was still the main technology until rather later on. Substantial amounts of tap slag and their analytical features support this idea. In addition, comprehensive studies as to the structure of furnaces and tuyeres used to do ironwork and their technical relationships also need to be discussed. Furthermore, smithing processes, which were mostly conducted at the smelting sites, were also described in detail so that the general ironworking process could be identified.

The COREX smelting-reduction route is a representative non-blast furnace technology, but its scale-up is hindered by insufficient gas and liquid permeability in the melter gasifier. To improve the gas and liquid permeability of the melter gasifier, coke is charged together with an iron-bearing material to partly replace lump coal to increase the burden voidage. The charged coke undergoes successive physical and chemical attacks that progressively weaken its strength, finally reducing the coke particle size and impairing overall burden permeability. Drilling “in situ” coke samples from the tuyere zone is an effective method to study coke behaviors inside a working melter gasifier. This work obtained tuyere coke samples by direct coke sample drilling during a melter gasifier blow-out and then systematically investigated the coke deterioration behaviors in the melter gasifier. The results show that the mean particle size decreased from an initial 50.3 mm to 31.6 mm at the tuyere, evidencing the severe fragmentation of coke. Basic oxides and alkali metals in the coke ash increased, indicating alkali recycling and enrichment occurred in the melter gasifier. Microcrystalline structure analysis of coke revealed a high degree of graphitization. Furthermore, coke degradation was further accelerated by both alkalis trapped in the coke pores and slag infiltration into the pores. This study clarifies the properties of the coke in the tuyere of the COREX melter gasifier and provides a theoretical basis for its operational optimization.

With combined metal blowing in an oxygen converter, the durability of the purge tuyeres when inert gases are supplied through the converter bottom is less than the durability of the converter lining because of the advanced wear of the tuyeres in relation to the bottom lining and the metallization of the capillaries/channels on the tuyeres with a slag–metal emulsion. To increase the performance of tuyeres, their placement in areas with the least wear of the lining and the avoidance of contact with the slag–metal emulsion are recommended.

Hydrogen can replace partially pulverized coal in the blast furnace injection as the clean and high-calorific energy, which can reduce energy consumption and carbon emission in molten iron production. In this study, a discrete phase model is used to describe the complex flow and thermochemical behavior associated with the co-injection of hydrogen and pulverized coal in the raceway. The effect of hydrogen injection rate on the raceway is studied from the aspects of gas velocity, temperature, concentration distribution and coal burnout rate. It can be concluded that with the hydrogen injection rate increases, the gas velocity slightly increases and the gas temperature decreases significantly at the deeper location of the coke bed. With the hydrogen injection rate increase every 10 m 3 ·t −1 , the theoretical combustion temperature decreases about 14 K and the amount of gas in the bosh increases about 46.91 m 3 . When the hydrogen injection rate increased to 50 m 3 ·t −1 , the coke ratio is reduced by 8.66%, and the concentration of CO and hydrogen along the axis of tuyere increases by 0.5% and 7.79%, respectively. However, when the hydrogen injection rate exceeds 30 m 3 ·t −1 , the pulverized coal burnout rate decreases. Graphical Abstract

Co-injection of natural gas (NG) with pulverized coal (PC) is carried out in blast furnace to increase the coal burnout; however, it has major challenges such as excess heat load on tuyere, lance overheating and competition between coal volatile matter and NG for available oxygen. A 3D computational fluid dynamics model of the blast pipe-tuyere-raceway region is developed to study the effects of: (1) NG and PC injection (PCI) through the co-axial lance and the subsequent oxygen enrichment on coal burnout and (2) relative positioning of NG and PCI lances in a double-lance design on coal burnout and localized temperature rise on PC lance. In the co-axial lance case, the use of NG as a cooling gas instead of oxygen decreases burnout from 54 to 43%. In double-lance design, positioning NG lance prior to PC lance results in relatively higher % burnout than the reverse configuration and does not lead to the overheating on PC lance.