Search Results (112)

This paper builds a one-dimensional transient numerical model of mixed fuel of woody and non-woody biomass to simulate the multistage conversion process of biomass in a moving grate-fired bed, including drying, pyrolysis, gasification, and char combustion. Based on time and space discretization, the model comprehensively considers the conservation of mass, momentum, and energy. It also introduces reaction kinetics and freeboard radiation coupling effects to more accurately describe the bed temperature distribution and reaction process. The analysis focuses on the effects of different non-woody biomass mixing ratios and moisture content. This provides references for optimization of the design of future furnaces and operating parameters and mixed fuel composition. The simulation results show that, for pure woody biomass, the surface temperature reaches approximately 200 °C in the first zone, followed by char reactions with peak temperatures up to 592 °C. The whole conversion process takes about 62% of the grate length. Increasing the pepper mixing ratio leads to lower bed temperatures due to the higher moisture content. The maximum bed temperature in the first zone decreases from 592 °C for pure wood to 551 °C at 30 wt.% pepper, with delayed pyrolysis and a thinner char reaction zone. When the pepper mixing ratio is below 20 wt.%, the combustion process maintains a stable temperature gradient and a continuous reaction front, compared to the mixing ratio of 30% pepper case. This confirms the feasibility of non-woody biomass application to combustion technology. Although a higher pepper mixing ratio leads to a slight temperature decrease, the reaction remains stable along the grate, indicating reliable combustion performance. Full article

The most important segment of the electric arc furnace (EAF) steelmaking process is the stirring and decarburization of the molten bath during the oxidation stage, with the bath temperature typically ranging from 1550 to 1600 °C. The coherent jet is a key factor influencing the stirring and decarburization of the molten bath. The factors affecting the impact capability of coherent jets have been widely studied, including the nozzle flow parameters and arrangement methods. However, there are few studies on the combustion chamber structure of the coherent jet oxygen lance. In order to study the effect of the combustion chamber structure on the characteristics of the coherent jet, a method combining numerical simulation and combustion experiments is used to study the flow fields of the coherent jet for a combustion chamber under different length and inclination angle conditions. The results show that the flow field characteristics of the coherent jet are influenced by the length and inclination angle of the combustion chamber. Compared with the coherent jet oxygen lance without a combustion chamber, the potential core length of the main oxygen jet under the short-distance horizontal combustion chamber condition is longer, but the potential core length of the main oxygen jet with the excessively long horizontal combustion chamber is shorter. The influence of the inclination angle on the potential core length of the main oxygen jet is complex. The influence mode is different depending on the length of the combustion chamber. Finally, it is found that the combined horizontal and inclined combustion chamber can achieve the best effect on prolonging the potential core length of the main oxygen jet. Full article

This study investigated the effects of waste steel fiber and high-volume blast furnace slag (BFS) substitution on the mechanical and physical properties of three-dimensional printable concrete (3DPC) to improve its environmental performance. BFS was substituted for cement at 0%, 25%, 50%, and 75% by volume. Waste steel fibers were added to the mixtures at three lengths (5, 10, and 15 mm) and two volumetric ratios (0.5% and 1.0%). Twenty-eight mixtures were optimized based on extrudability, buildability, and shape stability criteria. Parameters such as compressive and flexural strength, surface moisture content, and drying shrinkage were evaluated. The results showed that using up to 0.5% waste steel fibers increased compressive strength by up to 23%, but decreased it to a level of 1%. Fiber reinforcement improved the flexural strength of all blends by up to 53% at both ages, regardless of fiber ratio or length. Increasing the BFS substitution rate generally increased surface moisture however, this value decreased in mixtures containing 75% BFS and silica fume. Furthermore, using steel fibers and in-creasing fiber length significantly improved the drying shrinkage performance of the mixtures. Full article

This study designed a novel coherent tuyere device capable of adjusting the core length of the jet flow. Physical experiments were first conducted to investigate how the number of secondary nozzles in the coherent tuyere affects the gas–solid two-phase flow behavior within the raceway during the blasting process. Subsequently, the Computational Fluid Dynamics (CFD) method was employed to examine the influence of structural parameters on jet morphology in coherent tuyere. Finally, computational fluid dynamics and discrete phase method (CFD-DPM) was adopted, and the velocity, temperature, and composition distribution patterns within the raceway were analyzed following the injection of hydrogen-rich gas through the coherent tuyere. The results of the physics experiment indicate that increasing the number of secondary nozzles in the coherent tuyere can significantly enlarge the raceway size and broaden the particle kinematic zone, thereby enhancing particle fluidization at the periphery of the raceway. CFD numerical simulation results indicate that increasing the number of secondary nozzles of the tuyere can effectively extend the length of the velocity jet core region. Compared with conventional tuyeres, a six-nozzle coherent tuyere can increase the core length of the blast velocity by about 40%. When the diameter of the secondary nozzles in the coherent tuyere is doubled, the core length of the blast velocity increases by 10%. The results of the CFD-DPM coupled simulation show that unburned carbon particles flow and combust along the periphery of the raceway with the hot air, leading to the formation of a high-temperature region in this area. After the injection of hydrogen-rich gas through the coherent tuyere, the temperature in the raceway decreased significantly. A high-concentration region of H₂ appeared at the periphery of the raceway, while the high-concentration CO region increased in concentration and gradually extended toward the upper part of the raceway. This research achievement is of significant importance for optimizing blast furnace blast kinetic energy and hydrogen-rich gas injection. Full article

This study explores the mechanical behavior of concrete reinforced with recycled carbon fiber (RCF) and incorporating modified basic oxygen furnace slag (MBOF) as a sustainable aggregate. The RCF was recovered from waste carbon fiber-reinforced polymer (CFRP) bicycle rims via microwave-assisted pyrolysis (MAP), while MBOF was produced by water-based treatment of hot BOF slag. The experimental program included compressive, splitting tensile, and flexural strength tests, as well as impact resistance and stress-reversal Split Hopkinson Pressure Bar (SRSHPB) tests. The effects of RCF length (6 mm and 12 mm) on the mechanical performance of MBOF-based concrete were systematically examined. The results demonstrated that incorporating MBOF as aggregate, combined with the addition of RCF, significantly enhanced both static strength and dynamic impact resistance. Compared with fiber-free MBOF concrete, the incorporation of 6 mm and 12 mm RCF increased compressive strength by 3.03% and 13.77%, flexural strength by 14.50% and 19.74%, and splitting tensile strength by 2.60% and 25.84%, respectively. Similarly, the impact number increased by approximately 6.81 and 12.67 times for the 6 mm and 12 mm RCF specimens, respectively, relative to the fiber-free specimen. Furthermore, the SRSHPB test results indicated that MBOF concrete reinforced with 12 mm RCF exhibited greater dynamic compressive strength than that reinforced with 6 mm RCF. Overall, MBOF concrete incorporating 12 mm RCF demonstrated superior performance to its 6 mm counterpart across all evaluated strength parameters. These findings highlight the potential of utilizing metallurgical and composite waste to develop high-performance, sustainable concrete materials. Full article

This study investigates the fact that reinforcing geopolymers with natural fibers provides a practical way to improve their strength and durability. Offering environmental benefits compared to Portland cement, their mechanical performance still presents challenges. The particularity of this study lies in the pretreatment of natural fibers to limit their degradation within the alkaline geopolymer matrix. It also explores the effect of their length and content on matrix geopolymer. XRD (X-ray diffraction) analysis confirmed the crystalline structure of the geopolymer gels, unaffected by fiber inclusion. SEM (Scanning Electron Microscopy) observations showed a decrease or even disappearance of mineralization in treated sisal and palm fibers within the matrix, along with some partial detachment of the fibers. Optimal compressive strength was achieved using metakaolin and GGBS (Ground Granulated Blast-furnace slag). Incorporating 4% short palm fibers enhanced flexural strength, while long sisal fibers led to a 30% increase in flexural strength compared to short fibers, representing a 10.7% overall improvement. However, current geopolymer systems still face challenges such as low flexural strength and brittleness, which this study overcomes by incorporating processed natural fibers as sustainable reinforcements with optimal content. Full article

In this study, the effects of waste steel fiber and high volume blast furnace slag (BFS) substitution on rheological properties, thixotropic behavior and carbon emission were investigated in order to increase the sustainability of three-dimensional (3D) printable concrete (3DPC). Cement was replaced with BFS at 0%, 25%, 50% and 75% by volume, while waste steel fibers were added to the mixtures at three different lengths (5, 10, 15 mm) and volumetric ratios (0.5% and 1.0%). A total of 39 mixtures were optimized with respect to extrudability, buildability and shape stability criteria, and their rheological and thixotropic properties were characterized by a modified rheometer procedure. Results showed that 50% BFS substitution reduced dynamic yield stress and viscosity by 69% and 52%, respectively, and eliminated the need for a water-reducing admixture. 75% BFS substitution improved structural build-up (A_thix) but required 6% silica fume. The fiber effect interacted with length and BFS content, with short fibers increasing rheological resistance, while the effect of long fibers decreased in mixtures with high BFS. The carbon emission assessment revealed that 75% BFS substitution provided an outstanding CO₂ reduction of up to 71% compared to the control mix. These findings prove that high-volume BFS and waste fibers are an effective strategy to optimize rheological performance and environmental impact for sustainable 3D concrete printing. Full article

This study investigates the adhesion of polypropylene (PP), steel and basalt fibres to geopolymer matrices of varying composition. Geopolymers formed via alkali activation of fly ash (FA) and ground granulated blast-furnace slag (GGBFS) offer significant environmental advantages over Portland cement by reducing CO₂ emissions and energy consumption. The addition of water treatment sludge (WTS) was also investigated as a partial or complete replacement for FA. Pull-out tests showed that replacing FA with WTS significantly reduces the mechanical properties of the matrix and at the same time the adhesion to the fibres tested. The addition of 20% WTS reduced the compressive strength by more than 50% and full replacement to less than 5% of the reference value. Steel fibres showed the highest adhesion (9.3 MPa), while PP fibres had the lowest, with adhesion values three times lower than steel. Increased GGBFS content improved fibre adhesion, while the addition of WTS weakened it. Calculated critical fibre lengths ranged from 50 to 70 mm in WTS-free matrices but increased significantly in WTS-containing matrices due to reduced matrix strength. The compatibility of the fibres with the geopolymer matrix was also confirmed via SEM microstructural observations, where a homogeneous transition zone was observed in the case of steel fibres, while numerous discontinuities at the interface were observed in the case of other fibres, the surface of which is made of organic polymers. These results highlight the potential of fibre-reinforced geopolymer composites for sustainable construction. Full article

This study focuses on the detailed investigation of the eutectic Aluminium Silicon (Al-12.6 wt% Si) alloy, which was solidified without and with a 10 mT induction rotating magnetic field (RMF). The experiments were conducted as part of the MICAST Hungary project, as the mirror experiments were solidified in the Solidification and Quenching Furnace (SQF) at the International Space Station (ISS). The mirror samples were solidified using solidification parameters similar to the ISS experiments. This study examined the meso-structure of the samples and the eutectic microstructure in both stirred (RMF-applied) and non-stirred (RMF-free) samples. Special attention was given to the influence of magnetic stirring on key microstructural features, such as the eutectic lamellae distance, the length of the lamellae, and the spatial orientation of the lamellae were investigated. Measuring and analysing these parameters gives us an overall picture of the microstructure of the eutectics. The 10 mT low-intensity RMF used in the experiment has a demonstrable effect on the formation of the eutectic structure; short aluminium dendrites concentrate at both edges of the stirred sample, and their proportion decreases as the sample approaches its end. In contrast, in the non-stirred sample, long, elongated Al dendrites solidify parallel to the direction of heat removal, and their proportion and size continuously increase as the sample progresses. Furthermore, a possible relationship was found between the decrease in the eutectic lamella length and the lamellae’s average distance. Full article

In this study, we investigated how to design a tube furnace for the oxygen annealing of a REBa₂Cu₃O_7−x (REBCO, where RE = rare earth) superconducting joint. We confirmed the annealing temperature threshold of REBCO tape I_c degradation, which was 175C. A heat exchange model that included REBCO tape and a tube furnace was established by using this temperature as the boundary condition. At the same time, the temperature distribution of the REBCO tape in a commercial tube furnace was measured for the calibration of the heat exchange model. The feasibility and accuracy of the model were confirmed by comparing the real measurements and the simulation results. We then optimized the furnace design based on the model according to two criteria: a 20 mm length of REBCO tape should be kept at high temperatures for the oxygen annealing of REBCO joints and the length of tape at temperatures over the I_c degradation temperature should be as short as possible. The results of this furnace design investigation could help fabricate shorter REBCO superconducting joints, making the magnet more compact and decreasing the length of the Cu stabilizer layer to be removed. Full article

Compared to traditional temperature measurement methods, ultrasonic temperature measurement technology based on the principle of resonance offers advantages such as shorter section lengths, higher signal amplitude, and reduced signal attenuation. First, the type of sensor-sensitive element was determined, with a resonant design chosen to improve measurement performance; using magnetostrictive and resonant temperature measurement principles, the length, diameter, and resonator dimensions of the waveguide rod were designed, and a molybdenum–rhenium alloy (Mo-5%Re) material suitable for high-temperature environments was selected; COMSOL finite element simulation was used to simulate the propagation characteristics of acoustic signals in the waveguide rod, observing the distribution of sound pressure and energy attenuation, verifying the applicability of the model in high-temperature testing environments. Second, a resonant temperature sensor consistent with the simulation parameters was prepared using a molybdenum–rhenium alloy waveguide rod, and an ultrasonic resonant temperature-sensing system suitable for high-temperature environments up to 1800 °C was constructed using the molybdenum–rhenium alloy waveguide rod. The experiment used a tungsten–rhenium calibration furnace to perform static calibration of the sensor. The temperature range was set from room temperature to 1800 °C, with the temperature increased by 100 °C at a time, and it was maintained at each temperature point for 5 to 10 min to ensure thermal stability. This was conducted to verify the performance of the sensor and obtain the functional relationship between temperature and resonance frequency. Experimental results show that during the heating process, the average resonance frequency of the sensor decreased from 341.8 kHz to 310.37 kHz, with an average sensitivity of 17.66 Hz/°C. During the cooling process, the frequency increased from 309 kHz to 341.8 kHz, with an average sensitivity of 18.43 Hz/°C. After cooling to room temperature, the sensor’s resonant frequency returned to its initial value of 341.8 kHz, demonstrating excellent repeatability and thermal stability. This provides a reliable technical foundation for its application in actual high-temperature environments. Full article

Hot metal is produced in a blast furnace. Subsequently, the hot metal is loaded from the blast furnace into a torpedo car and transported to the ladle, where the desulfurization process of the hot metal is realized. After desulfurization, the hot metal is poured from the ladle into the oxygen converter. The temperature of the hot metal has an impact on the steelmaking process realized in the oxygen converter. The complex model presented in the article calculates the temperature drop of the hot metal in the torpedo car and the ladle. Predicting the hot metal temperature behavior allows for determining the length of time the hot metal transport requires and thus initiating steelmaking at its required hot metal temperature. This model, based on heat transfer by conduction, convection, radiation, heat accumulation, and chemical reactions, also allows for the monitoring of the hot metal temperature drop in the torpedo car and the ladle, the analysis of the influence of the linings in terms of heat accumulation, the investigation of the desulfurization process in the ladle, and the optimization torpedo and ladle selection in terms of the accumulated heat in the lining for their entry into the hot metal transport process. An absolute and relative error calculation was used to verify the proposed model. Full article

Radiant tubes are essential in industrial furnaces, with thermal efficiency often improved by extending the tube length which reduces durability and complicates production. Integrating finned-tube heat exchangers enhances durability without lengthening tubes but increases NO_x emissions. Using staged combustion with four nozzle designs, the emission of NO_x is reduced as smaller nozzle diameters lower flame temperatures and suppress NO_x production. U-shaped tubes without heat exchangers require higher flame temperatures and NO_x emissions 20 times more than double P-type tubes. Full article

Due to their low environmental impact, various mineral or cellulose-based natural fibres have recently attracted attention in the construction industry. Hence, the current study focused on basalt fibres and explored the changes in the physical, mechanical, and micro-structural properties of geopolymer concrete reinforced with such fibres. The current study used self-compacting geopolymer concrete, an eco-friendly concrete composed of fly ash, ground granulated blast furnace slag, and an alkali activator, in addition to the regular components of normal concrete. The self-compacting geopolymer concrete compacts under its own weight, so extra compaction is not required. The present study investigated the effect of the fibre content and length. Two different fibre lengths were considered: 12 mm and 30 mm. Three different percentages (1%, 2%, and 3% of the weight of the total mix) of the basalt fibres were considered to determine the optimum fibre content. The mix design was carried out for all the mixes with different fibre contents and fibre lengths, and the workability properties in the slump flow, T-500, and J-ring tests are presented. The effects of the fibre length and content were evaluated in terms of compressive strength (28 and 56 days) and split tensile strength. The results indicated that a higher fibre content effectively increased the compressive strength of 12 mm long fibres. In contrast, a lower fibre content was ideal for the 30 mm long fibres. In addition, the short fibres were more effective in enhancing the geopolymer concrete’s tensile strength than the long fibres. Furthermore, a detailed microscopic analysis was carried out, which revealed that fibre clustering, voids, etc., changed the strength of the selected fibre-reinforced self-compacting geopolymer concrete. Moreover, the analytical method’s predicted tensile strength agreed with the experimental results. Full article

This study presents a theoretical analysis of the solar flux distribution within the receiver of the high-flux solar furnace at IER-UNAM. The furnace comprises an array of 409 first-surface spherical facets, each hexagonal in shape with a side length of 20 cm, and all mounted on a spherical framework. Each facet is carefully adjusted to focus sunlight onto a single focal point. Initially, the distribution of solar radiation is evaluated based on measurements obtained in Temixco, Morelos, Mexico (18°50′21″ N, 99°14′7.5″ W). Using these data, an analytical model is proposed to describe the solar radiation distribution using a Gaussian approximation. An additional analytical model is then developed to estimate the concentration distribution and its geometric shape at the furnace’s focal point, considering the solar width’s root mean square (RMS) value along with the optical errors associated with the heliostat and the reflective facets. Ultimately, by applying the concept of the effective solar source, an analysis of the solar flux distribution within the furnace receiver is conducted. This results in an analytical equation that characterizes the two-dimensional and three-dimensional distribution of the concentrated solar flux. Calculations reveal that the system captures approximately 30 kW of power, with peak concentrations reaching around 10,000 suns. Full article