Search Results (147)

The transition towards climate-neutral metallurgical production requires a broader transformation than the simple substitution of fossil-fuel combustion with electrical heating. While process electrification is a fundamental step towards reducing greenhouse gas emissions, achieving truly sustainable high-temperature processing also depends on the ability to maintain tightly controlled reaction environments, minimise thermal losses, and maximise the efficient use of process gases. These factors become increasingly important as the industry moves towards hydrogen-assisted processing routes and greater integration of renewable energy sources. By controlling heat transfer and gas composition, a stable processing environment can be maintained in which temperature, and gases’ partial pressure, can be accurately regulated throughout the treatment cycle. This study introduces the engineering concept of an airtight electrified indirect-fired rotary furnace, developed as a new process for efficient calcination, and also, hydrogen-based reduction processes. To assess the applicability of the proposed reactor concept, a bench-scale experimental campaign was carried out using two representative metallurgical processes: magnesite calcination and hydrogen-assisted reduction of lateritic ores. Throughout the testing campaign, the reactor maintained stable thermal conditions and a well-controlled process atmosphere, while the integrated monitoring system enabled continuous observation of temperature evolution and gas composition. The calcination trials achieved conversion efficiencies above 98%, whereas the hydrogen-reduction experiments successfully promoted the transformation of iron and nickel oxide phases into their metallic state. The results demonstrate that the integration of indirect electrical heating with airtight reactor operation provides a robust platform for hydrogen-assisted thermal processing. The proposed architecture improves atmosphere control and process efficiency while offering a scalable solution for the future implementation of electrified, low-carbon metallurgical technologies. Full article

Deep decarbonization of high-temperature industrial furnaces and kilns is essential for reducing greenhouse gas emissions in energy-intensive sectors. Hydrogen and hydrogen-enriched fuels are promising alternatives to conventional fossil fuels; however, their integration is not a straightforward fuel replacement. Owing to hydrogen’s high laminar burning velocity, wide flammability limits, low volumetric heating value, and water-vapor-rich combustion products, hydrogen substitution can substantially alter flame stability, heat transfer pathways, pollutant formation, and material service behavior. This review systematically summarizes the key technologies and application progress of hydrogen-based fuel substitution in high-temperature industrial systems. First, the thermophysical and kinetic differences between hydrogen and hydrocarbon fuels are analyzed. Subsequently, core enabling technologies are discussed, including flashback prevention, low-NOx combustion control, thermal-flow-field regulation, heat transfer optimization, and material compatibility under high-temperature, water-vapor-rich atmospheres. Application progress in representative scenarios—including metallurgy, heat treatment, petrochemical-fired heaters, waste treatment, rotary kilns, and cremation furnaces—is reviewed to identify scenario-specific constraints. The review indicates that successful hydrogen substitution requires a transition from isolated burner optimization toward system-level integration of combustion control, heat transfer management, emission mitigation, and material adaptation. Future research should prioritize integrated furnace design, long-term material service assessment, multi-fuel operating strategies, and data-driven control frameworks. Full article

The accumulation of non-recyclable construction, renovation, and demolition (CRD) wood waste necessitates sustainable management strategies, for which thermochemical valorization is a promising option. Slow pyrolysis is particularly suitable due to its high biochar yields and potential to partially replace fossil coal in energy, metallurgical, construction, and environmental applications. In this study, end-of-life CRD wood was converted into biochar using a pilot-scale vertical retort–kiln system at furnace set-point temperatures of 600 °C and 800 °C for 4 h. The biochar produced at 800 °C, which exhibited superior characteristics, was subsequently subjected to post-heat treatment at 600 °C for 30–90 min in the presence of nitrogen within a tightly sealed rotary retort-kiln assembly. Self-heating behavior was evaluated using adiabatic oven tests at 120–140 °C. Biochar properties were characterized by proximate and elemental analysis, TGA/DTG, R50, FTIR, and SEM–EDX. Increasing the pyrolysis temperature to 800 °C increased carbon content from 49.88% in the raw feedstock to 85.11% in biochar, while oxygen and hydrogen contents decreased to 5.91% and 1.52%, respectively. Van Krevelen ratios (H/C = 0.21; O/C = 0.05) indicated enhanced carbon stability, with the higher heating value reaching 30.81 MJ/kg. The thermostable fraction reached 75.18%, R50 recalcitrance index 0.57, fixed carbon 70.59%, volatile carbon 23.31%, pH 8.9, and surface area 188.33 m²/g. Post-heat treatment further enhanced aromaticity (H/C = 0.18; O/C = 0.02) of this higher pyrolysis temperature biochar, increasing its fixed carbon and stability, and reducing volatile content. Extending treatment time from 30 min to 90 min raised fixed carbon to 77–78% and thermostability to 84–85%, while volatile carbon decreased to 13–15%. Microporosity peaked at 350–380 m²/g by 75 min before declining due to pore widening. SEM and EDX analyses confirmed this structural evolution, increased carbon content, reduced oxygen, suppressed alkali metals, and enrichment of alkaline earth metals. Yield loss was highest at 90 min (20–21%), highlighting the need to balance treatment severity and biochar product yield. Both the 800 °C biochar and its post-heat-treated forms passed self-heating tests, confirming improved oxidative stability for energy and environmental applications. Full article

The valorization of industrial mining and organic wastes in construction materials constitutes a key strategy for reducing the environmental impact of the sector. In this context, the present study aims to evaluate the sustainability of innovative Artificial Lightweight Aggregates (ALAs) manufactured from mixtures of inorganic industrial wastes—such as granite and slate cutting sludge and aggregate washing sludge—together with organic wastes, like cork dust, coffee grounds, and olive pits. The methodology included a Life Cycle Assessment (LCA), considering different waste compositions and manufacturing conditions. The results show that the developed ALAs exhibit favorable environmental performance as their bulk density decreases, with an overall environmental impact lower than that of conventional lightweight aggregates made from expanded clay, achieving a reduction in the carbon footprint of up to 7%. Likewise, the comparative analysis reveals that the process stage with the greatest environmental impact is the heat energy required during the sintering stage in the rotary kiln, which in some cases accounts for more than 90% of the total impact. In summary, the results demonstrate the feasibility of obtaining ALAs manufactured solely from waste with a lower carbon footprint compared to traditional expanded clay aggregates. Furthermore, the study highlights that the process stages with the highest contributions to environmental impact are the transport of raw materials and the high-temperature sintering of the ALAs in the rotary kiln. Thus, their production from waste contributes to the valorization of by-products, fostering circular economy strategies and supporting decarbonization processes within the construction sector. Full article

Rotary kiln shell temperature monitoring is essential for metallic shell protection and refractory lining maintenance in high-temperature industrial processes, while smoke, dust, thermal diffusion and non-kiln heat sources make valid shell temperature extraction difficult. This study develops a multi-scale cascaded network with low-resolution space-to-depth downsampling (MSC-LSTD) for infrared kiln shell segmentation and temperature recognition. Global infrared thermal images and local laser temperature measurements are used to construct a calibrated rotary kiln infrared dataset, and predicted kiln shell masks are mapped to temperature matrices for valid shell temperature analysis. MSC-LSTD achieves 99.82% aAcc, 99.14% mAcc and 97.03% mIoU on the rotary kiln infrared dataset, showing robust segmentation performance under complex thermal interference. The proposed framework provides a practical image-based solution for kiln shell overheating warning and refractory lining degradation assessment. Full article

This study investigates the production of high-carbon ferrochrome (HCFeCr) using pre-reduced chromite pellets. Chromite ore from the Kempirsai deposit, semicoke as a reducing agent, and activated bentonite as a binder were used for pellet preparation. Pellets with a size of 12–14 mm were produced and subjected to reduction roasting at 1400 °C for 1–3 h. The results showed that increasing the roasting time promoted chromite reduction and increased the chromium metallization degree. After 3 h of roasting, the chromium metallization degree reached 43.93%. SEM analysis confirmed the formation of metallized chromium-containing phases and a porous structure favorable for subsequent smelting. Smelting experiments were carried out in a 0.1 MVA ore-thermal furnace using pre-reduced pellets. Stable furnace operation, satisfactory slag fluidity, and effective separation of metal and slag were observed. The obtained high-carbon ferrochrome contained 68.92 wt.% Cr, 1.54 wt.% Si, and 7.11 wt.% C. Chromium recovery into the alloy reached 92.17%, while the slag contained 2.14 wt.% Cr₂O₃. The specific electric energy consumption during experimental smelting was 4648.1 kWh/t of ferrochrome. Recalculation to industrial conditions showed an expected energy consumption of 3132.76 kWh/t, confirming the potential of pre-reduced chromite pellets for energy-efficient ferrochrome production. Full article

Ring formation in rotary kilns is a major operational problem in the ferronickel dry smelting process, in which nickel laterite ore undergoes drying, calcination, and partial reduction. Excessive ring accretion reduces thermal efficiency and disrupts stable kiln operation. In this study, the mechanism of ring formation was investigated through a combined approach integrating laboratory-scale experiments and long-term operational data obtained from a large-scale industrial rotary kiln. The effects of ore composition, particle size, and temperature on melting and sintering behavior were examined, and their correlations with operating variables such as fuel input and kiln rotational speed were analyzed. The results show that ring formation is governed by the selective melting and adhesion of low-melting constituents, particularly in ores with low basicity (MgO/SiO₂ < 0.55) and high Fe content (>14 wt.%). A high fraction of fine particles (<75 μm) further promotes adhesion due to their lower melting temperature and enhanced mechanical retention on the refractory surface. In industrial operation, localized overheating near the burner zone and low kiln rotational speeds (0.9–1.1 rpm) significantly accelerate ring growth. These findings provide a mechanistic understanding of ring formation and suggest that appropriate ore blending and optimized control of fuel input and kiln rotation are effective strategies for mitigating ring accretion in commercial ferronickel rotary kilns. Full article

Industrial kilns are widely used in energy-intensive industries. They consume large amounts of energy and emit significant pollutants. However, most of the existing studies focus on only one kiln type or incremental modifications. As a result, cross-type structure–performance relationships remain largely unexplored. Unlike previous reviews that concentrate on single kiln types or isolated structural improvements, this review puts forward a cross-type, structure-oriented evaluation framework. Five representative industrial kiln types are examined. The discussion covers how macroscopic configuration, key dimensional ratios, internal components, and combustion organization affect thermal efficiency, productivity, energy use, and emissions. To unify structural analysis and performance assessment, a conceptual three-level evaluation framework is introduced. It integrates structural factors, conventional performance indicators, and two scale-independent space-based indicators: unit volumetric productivity and unit volumetric flue gas emission. The framework allows for cross-type comparison on a common volumetric basis. It can also indicate whether performance limitations may be linked to scale, geometry, internal structure, or combustion arrangement. The comparison reveals that unit volumetric productivity varies by up to two orders of magnitude across kiln types. Rotary kilns show higher values, and tunnel kilns show lower ones. The results could provide a useful reference for the structural diagnosis, benchmarking, and performance-oriented optimization of industrial kilns. Full article

The lack of centralized waste management infrastructure in certain regions makes plastic waste an escalating environmental and economic problem. This research investigates how modular portable pyrolysis systems function as sustainable decentralized solutions. A standard shipping container houses a custom-designed pyrolysis unit which demonstrates flexibility and adaptability. The system contains a batch rotary kiln reactor with a processing capacity of 750 kg per batch which is fed with urban plastic waste, to produce pyrolytic oil, syngas and char. The produced pyrolytic oil exhibits an energy content comparable to that of conventional diesel fuel. Additionally, the integration of biomass briquettes and recycled pyrolytic gas can reduce to a big extent the external energy requirements, improving the system’s overall energy autonomy. Therefore, the system becomes economically reliable due to its low operational expenses and the short cycle of approximately 7-h operation. The unit’s mobility enables on-site treatment operations which reduces both transportation emissions and expenses. The analysis includes technical design elements together with performance metrics for different plastics. This conceptual study demonstrates the feasibility of containerized pyrolysis as a practical method to enhance plastic waste chemical recycling rates while presenting a scalable framework for industrial symbiosis and local waste-to-energy conversion. Full article

The depletion of global reserves of high-quality sulfide nickel deposits, coupled with the steady growth of nickel demand, has led to increased interest in the processing of oxidized (lateritic) nickel ores, including deposits with significant resource potential in the Republic of Kazakhstan. This paper provides an overview of global nickel ore reserves and their distribution, as well as the major nickel deposits in Kazakhstan, which are primarily located in the Aktobe, East Kazakhstan, Kostanay, and Pavlodar regions. Pyrometallurgical processing routes for lateritic nickel ores are also considered. Conventional production technologies, including the Rotary Kiln–Electric Furnace (RKEF), Krupp–Renn process, blast furnace smelting, Vaniukov process, and ISASMELT process, are reviewed, and their process flow diagrams are presented. These methods typically process lateritic nickel ores containing more than 1.2% Ni, whereas Kazakhstan ores are characterized by lower nickel grades, generally in the range of 0.75–1.1%. The advantages and limitations of conventional processing routes are analyzed, and the factors limiting the effective beneficiation of lateritic nickel ores using traditional methods are identified. The present study substantiates the feasibility of producing nickel-containing alloys from lateritic nickel ores using a metallothermic reduction approach. This method is based on the reduction of nickel and iron oxides using metallic reductants, which enables more selective extraction of target components and the formation of alloys with controlled composition. Metallothermic reduction is of particular interest for the processing of low-grade lateritic ores, as it allows the production of nickel-containing alloys without prior beneficiation, at lower energy consumption, and with reduced sensitivity to variations in the chemical and mineralogical composition of the raw materials. Therefore, this approach is considered a promising direction for the processing of lateritic nickel ores in Kazakhstan. Full article

Rotary kiln-based activated carbon production combines high-temperature operation with flammable/reducing gases, carbonaceous dust, and downstream off-gas treatment and acid/base washing, creating complex escalation pathways. This study prioritizes safety improvements by applying classical failure modes and effects analysis (FMEA) and a transparent Fuzzy-FMEA framework to 18 representative failure modes (six each for kiln/activation, acid/base handling, and atmosphere/control). Five experts evaluated Severity, Occurrence, and Detection on a 10-point scale. The fuzzy model used triangular membership functions (L/M/H), a monotonic 27-rule base, Mamdani max–min inference, and centroid defuzzification to compute a continuous fuzzy risk priority number (FRPN, 0–10). Classical FMEA identified dust explosion (RPN = 405), temperature control failure (RPN = 378), and off-gas leakage (RPN = 324) as the highest-ranked risks. Fuzzy-FMEA preserved the top-risk group while more strongly highlighting barrier-related risks, placing off-gas leakage, instrumentation/interlock failure, and electrostatic ignition control alongside dust explosion (FRPN 9.221–9.332). The rankings were strongly correlated (Spearman ρ = 0.871; Kendall τ = 0.752), yet mid-risk items were rearranged (mean |Δrank| = 2.06; max = 5), improving discrimination within tied RPN clusters. The five highest-priority scenarios were reconstructed into actionable engineering packages, including dust and ignition control, off-gas integrity linked to shutdown logic, interlock proof testing and bypass management, and independent protection layers for kiln temperature control. Full article

The accelerating transition to low carbon energy systems has intensified the demand for nickel and cobalt from low-grade (<1.5 wt.%) refractory lateritic ores. These low-grade laterites are however not amenable to conventional beneficiation due to their complex mineralogy, eclectic physicochemical properties, and fine Ni–Co dissemination. This review examines recent advances made in the extraction of nickel and cobalt from complex low-grade lateritic ores, emphasizing the interplay between ore mineralogy, chemistry, beneficiation, pretreatment, and processing route selection. Developments in selective ore comminution–classification have led to the generation of Ni-rich fine fractions (undersize) and Co-rich coarse fractions (oversize), enabling differentiated extraction strategies that improve resource utilization, frugal energy use, and process efficiency. Mechanical activation via stirred media milling, thermal calcination-induced structural disorder, and dehydroxylate goethite products, are shown to significantly enhance Ni–Co leaching kinetics under both atmospheric and heap leaching conditions. A critical comparison of pyrometallurgical (rotary-kiln electric furnace) and hydrometallurgical (HPAL, EPAL, heap, atmospheric, bioleaching) routes demonstrates that ore-specific optimization is essential to balance recovery, acid consumption, and greenhouse gas emissions. The novel resin in moist mix (RIMM) process, which integrates ambient leaching and in situ ion exchange selective recovery, is shown to offer potential for sustainable values extraction from sub-economic resources. Furthermore, the review highlights the key innovation challenges and concomitant opportunities for enhanced critical battery metal recovery from complex laterite ores. Full article

The accurate reconstruction of the internal temperature field in rotary kilns is critical for optimizing the clinker calcination process and ensuring energy efficiency. In this study, a rapid and high-fidelity surrogate modeling framework is proposed, utilizing snapshot ensembles generated by full-order Computational Fluid Dynamics (CFD) simulations to reconstruct the temperature field of the axial center section. The framework incorporates a symmetric Autoencoder (AE) coupled with a TabPFN network as its core components. Capitalizing on the kiln’s strong axial symmetry, this reduction–regression system efficiently maps the high-dimensional nonlinear thermodynamic topology of the central section into a compact low-dimensional latent manifold via AE, while utilizing TabPFN to establish a robust mapping between operating boundary conditions and these latent features. By leveraging the In-Context Learning (ICL) mechanism for prior-data fitting, TabPFN effectively overcomes the data scarcity inherent in high-cost CFD sampling. Predictive results demonstrate that the model achieves a coefficient of determination (R²) of 0.897 for latent feature regression, outperforming traditional algorithms by 6.53%. In terms of field reconstruction on the test set, the model yields an average temperature error of 15.31 K. Notably, 93.83% of the nodal errors are confined within a narrow range of 0–50 K, and the reconstructed distributions exhibit high consistency with the CFD benchmarks. Furthermore, compared to the hours required for full-scale simulations, the inference time is reduced to 0.45 s, representing a speedup of four orders of magnitude. Consequently, the predictive system demonstrates excellent accuracy and efficiency, serving as an effective substitute for traditional models to realize online monitoring and intelligent optimization. Full article

One thermodynamic parameter that is crucial to heat transport within the fluidized bed inside the rotary kiln, during clinker production, is the specific heat capacity. The particular parameter is often considered constant in the open literature, while, in reality, it strongly depends on the fluidized bed’s temperature and composition, considering that the temperature inside the kiln ranges from approx. 800 K up to 2000 K. For the current study, a mixing rule reported in the literature was applied in order to calculate the C_p of the fluidized bed, utilizing temperature and composition profiles available in the literature. An in-house code was developed for the comparison of the literature-reported C_ps and those resulting from the mixing rule. It was discovered that the C_p of the fluidized bed had a proportional increase with the increase in the temperature along the length of the kiln. The deviation between the two values (calculated and literature) is relatively small in some cases, whereas, in others, it is quite significant, ranging from 1.56% to 52.49%, thus making the adoption of the temperature-dependence of C_p necessary. Establishing a more accurate relation for the specific heat capacity leads to a better energy balance inside the kiln, which, along with other improvements, can lead to a decrease in the energy consumed and a significant reduction in greenhouse gas emissions. Full article

Refuse-derived fuel (RDF) presents a viable strategy to concurrently address the challenges of municipal solid waste management and the need for alternative energy. In this context, the present review systematically synthesizes recent advances in RDF preparation, combustion behavior, and efficient utilization technologies. The study examines the full chain of RDF production—including waste selection, mechanical/optical/magnetic sorting, granulation, briquetting, and chemical modification—highlighting how pretreatment technologies influence fuel homogeneity, calorific value, and emissions. The thermochemical conversion characteristics of RDF are systematically analyzed, covering the mechanism differences among slow pyrolysis, fast pyrolysis, flash pyrolysis, pyrolysis mechanisms, catalytic pyrolysis, fragmentation behavior, volatile release patterns, and kinetic modeling using Arrhenius and model-free isoconversional methods (e.g., FWO). Special attention is given to co-firing and high-efficiency combustion technologies, including ultra-supercritical boilers, circulating fluidized beds, and rotary kilns, where fuel quality, ash fusion behavior, slagging, bed agglomeration, and particulate emissions determine operational compatibility. Integrating recent findings, this review identifies the key technical bottlenecks—feedstock variability, chlorine/sulfur release, heavy-metal contaminants, ash-related issues, and the need for standardized RDF quality control. Emerging solutions such as AI-assisted sorting, catalytic upgrading, optimized co-firing strategies, and advanced thermal conversion systems (oxy-fuel, chemical looping, supercritical steam cycles) are discussed within the broader context of carbon reduction and circular economy transitions. Overall, RDF represents a scalable, flexible, and high-value waste-to-energy pathway, and the review provides insights into future research directions, system optimization, and policy frameworks required to support its industrial deployment. Full article