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This review focuses on the usability of iron ore ultra-fines for hydrogen-based direct reduction. Such technology is driven by the need to lower CO2 emissions and energy consumption for the iron and steel industry. In addition, low operational and capital expenditures and a high oxide yield because of the direct use of ultra-fines can be highlighted. The classification of powders for a fluidized bed are reviewed. Fluid dynamics, such as minimum fluidization velocity, entrainment velocity and fluidized state diagrams are summarized and discussed regarding the processing of iron ore ultra-fines in a fluidized bed. The influence of the reduction process, especially the agglomeration phenomenon sticking, is evaluated. Thus, the sticking determining factors and the solutions to avoid sticking are reviewed and discussed. The essential theoretical considerations and process-relevant issues are provided for the usability of iron ore ultra-fines for hydrogen-based fluidized bed direct reduction.

Methanol-to-olefins (MTO), the most important catalytic process producing ethylene and propylene from non-oil feedstocks (coal, natural gas, biomass, CO 2 , etc.), is hindered by rapid catalyst deactivation due to coke deposition. Common practice to recover catalyst activity, i.e. removing coke via air combustion or steam gasification, unavoidably eliminates the active hydrocarbon pool species (HCPs) favoring light olefins formation. Density functional theory calculations and structured illumination microscopy reveal that naphthalenic cations, active HCPs enhancing ethylene production, are highly stable within SAPO-34 zeolites at high temperature. Here, we demonstrate a strategy of directly transforming coke to naphthalenic species in SAPO-34 zeolites via steam cracking. Fluidized bed reactor-regenerator pilot experiments show that an unexpectedly high light olefins selectivity of 85% is achieved in MTO reaction with 88% valuable CO and H 2 and negligible CO 2 as byproducts from regeneration under industrial-alike continuous operations. This strategy significantly boosts the economics and sustainability of MTO process. Methanol-to-olefins is hindered by rapid catalyst deactivation due to coke deposition. Here the authors demonstrate an approach of directly transforming coke to active intermediates to simultaneously recover catalyst activity and boost light olefins selectivity.

Based on the low-carbon transition needs of coal-fired boilers, this study conducted industrial trials of direct biomass co-firing on a 620 t/h high-temperature, high-pressure circulating fluidized bed (CFB) boiler, gradually increasing the co-firing ratio. It used compressed biomass pellets, achieving stable 20 wt% (weight percent) operation. By analyzing boiler parameters and post-shutdown samples, the comprehensive impact of biomass co-firing on the boiler system was assessed. The results indicate that biomass pellets were blended with coal at the last conveyor belt section before the furnace, successfully ensuring operational continuity during co-firing. Further, co-firing biomass up rates of to 20 wt% do not significantly impact the fuel combustion efficiency (gaseous and solid phases) or boiler thermal efficiency and also have positive effects in reducing the bottom ash and SOx and NOx emissions and lowering the risk of low-temperature corrosion. The biomass co-firing slightly increases the combustion share in the dense phase zone and raises the bed temperature. The strong ash adhesion characteristics of the biomass were observed, which were overcome by increasing the ash blowing frequency. Under 20 wt% co-firing, the annual CO2 emissions reductions can reach 130,000 tons. This study provides technical references and practical experience for the engineering application of direct biomass co-firing in industrial-scale CFB boilers.

Fluidized bed combustion of biomass requires maintaining stable properties of the inert bed material, which plays a key role in heat transfer, temperature stabilization and uniform fuel distribution in circulating fluidized bed (CFB) boilers. During long-term operation, quartz sand, i.e., the most commonly used inert material, undergoes physical and chemical degradation processes such as attrition, sintering and coating with alkali-rich ash, leading to changes in particle size distribution (PSD), deterioration of fluidization quality, temperature non-uniformities and an increased risk of bed agglomeration. This study analyzes quality management strategies for inert bed materials in biomass-fired CFB systems, with particular emphasis on the influence of PSD on boiler hydrodynamics and thermal behavior. Based on industrial operating data, sieve analyses and CFD simulations performed under representative operating conditions, a recommended mean particle diameter range of approximately 150–200 μm is identified as critical for maintaining stable circulation and uniform temperature fields. Numerical results demonstrate that deviations toward coarser bed materials significantly reduce solids circulation, promote segregation in the lower furnace region and lead to local temperature increases, thereby increasing agglomeration risk. The study further discusses practical approaches to bed material monitoring, regeneration and make-up management in relation to biomass type and ash characteristics. The results confirm that systematic control of inert bed material quality is an essential prerequisite for reliable, efficient and low-emission operation of biomass-fired CFB boilers.

The coupling of computational fluid dynamics (CFD) and discrete element method (DEM) has become an important method for studying dense fluidized beds. Since DEM can track the motion behavior of each particle individually and CFD can qualitatively and quantitatively describe the fluid evolution process, the discussion of fluidized beds using CFD–DEM method has been realized from small scale to laboratory scale and even extended to large engineering scale. This work presents a comprehensive review of the application of coupled CFD–DEM methods in fluidized beds and identifies the issues that need to be addressed. The detailed analysis is summarized mainly from the definition of particle flow system, DEM modeling theory (particle–fluid interaction and integration scheme of particle motion information, etc.), CFD modeling theory (discussion of turbulence model) and CFD–DEM coupled mapping methods (including Unresolved CFD–DEM and Resolved CFD–DEM). Existing studies have verified from multi-scales that the coupled CFD–DEM approach is reliable for predicting particle motion in fluidized beds. The findings are summarized and discussed, and future developments and challenges are highlighted. This work will provide theoretical guidance for subsequent researchers using the coupled CFD–DEM method.

The current study presents an integrated methodology for improving the performance of conventional fluidized bed reactors using swirling flow via a blade distributor and conical shape. The primary objective of this study is to investigate the combined effect of swirling flow and conical geometry on bed flow and heat transfer, which has not been sufficiently studied, especially through experimental techniques supported by machine learning modeling able to predict performance. A blade distributor was employed in the SCFBR, while the bed heat transfer coefficient and surface particle temperature were estimated and measured at different inlet velocities ranging from 0.993 to 2.5 m/s. The study results emphasized that the SCFBR clearly outperforms the CFBR based on lower bed pressure drop, more uniform particle distribution, and higher heat transfer coefficient. The heat transfer coefficient of the SCFBR increased by 40% compared to that of the CFBR, corresponding to a more homogenized distribution of particle surface temperature. The machine learning findings elucidate the superiority of the Extra Trees model in modeling the bed pressure drop and heat transfer coefficient, achieving with an R² of 0.973, an RMSE of 52.11, and a MAE of 35.11 for the heat transfer coefficient and an R² of 0.965, an RMSE of 8.76, and a MAE of 2.27 for the bed pressure drop. The good agreement between the experimental and ML results demonstrated the reliability of the proposed methodology. This study emphasizes the importance of integrating swirling flow with conical geometry, supported ML modeling, and represents a promising method for developing thermally efficient fluidized bed reactors with low energy consumption for advanced industrial applications.

Comprehensive control of greenhouse gas emissions and response to climate change are concerns of countries around the world to protect living homes. The steel industry is responsible for over 10% of global CO 2 emissions, with approximately 80% of these emissions coming from the ironmaking process. Great efforts have been made in both blast furnace (BF) and non-blast furnace ironmaking processes to reduce emissions. Fluidized bed technology has become a crucial method used to process iron ore powder in non-blast furnace ironmaking, such as smelting reduction and direct reduction. This paper introduces the working principle and several typical working states of fluidized bed (FB) technology to clarify the key to fluidized bed process operation. And different kinds of fluidized bed ironmaking processes in recent decades are compared, including FIOR, DIOS, Circored, Circofer, FINMET, HIsmelt, FINEX, etc. Finally, the possible problems and solutions in the future development of fluidized bed ironmaking are analyzed. Hope that this work can contribute to the advancement of basic theory and technology research in fluidized bed reduction, and provide support for hydrogen metallurgy in the steel industry. Graphical Abstract

The continuous generation of agricultural, industrial, and urban waste necessitates effective waste management strategies. One promising approach is incorporating these residues as fillers in polymer composites. This study investigated the influence of coal processing-derived fillers, specifically microspheres and fluidized-bed combustion fly ash, on the structure and properties of composite rigid polyurethane foam. Polyurethane foams were produced through manual mixing and casting, with composite foams containing a combination of 5% microspheres and 5–15% fly ash by weight. The analysis of the samples investigated their structural, thermal, and mechanical properties. The samples consistently displayed predominantly pentagonal, regularly shaped cells. Infrared spectroscopy revealed no observable chemical bonding between the matrix and filler materials. Mechanical analysis was performed to evaluate the materials’ characteristics, revealing significant variations in compressive strength and Young’s modulus values. The results indicate that the addition of fillers did not impact the cellular and chemical composition of the polyurethane matrix. Furthermore, the composite material specimens were subjected to accelerated aging in a laboratory dryer and outdoor exposure in order to assess their thermal stability. This analysis revealed notable alterations in both the cellular composition and mechanical properties of the composite foam materials.

This study investigates the effects of the co-combustion of coal and açai seed in circulating fluidized bed (CFB) boilers, highlighting the increase in thermal efficiency and relevance of a less-polluting source of energy. Using the computer software 1.5D CeSFaMB™® v4.3.0, simulations of the co-combustion process of coal and biomass were carried out in a CFB boiler, obtaining results such as the temperature profile, boiler efficiency and emissions. The work acquired data regarding the equipment in real operational conditions, consisting of the fundamental geometric and operational parameters used in the simulation campaign. The thermal and chemical properties of the fuels were analyzed by carrying out proximate, ultimate, heating value, particle size and specific mass analyses. The model validation was achieved by simulating the boiler in its real operating conditions and comparing the obtained results with the real data; the obtained error was below 10%. Simulations with different fractions of açai seed for energy replacement (10% and 30%) were carried out. As a result, an increase in the average temperature of the bed was observed, highlighting the region immediately above the dense bed. An increase in boiler efficiency was verified from 56% to 85% with 10% açai and to 83% with 30% açai seed. Decreases in SO2 and CO emissions with the insertion of açai were obtained, showing that co-combustion is more complete, while CO2 emissions were increased due to the higher quantity of fuel inserted into the equipment. The fossil CO2 emissions were reduced.

The supercritical circulating fluidized bed (CFB) boiler, which combines the advantages of CFB combustion with low cost emission control and supercritical steam cycle with high efficiency of coal energy, is believed to be the future of CFB combustion technology. It is also of greatest importance for low rank coal utilization in China. Different from the supercritical pulverized coal boiler that has been developed more than 50 years, the supercritical CFB boiler is still a new one which requires further investigation. Without any precedentor engineering reference, Chinese researchers have conducted fundamental research, development, design of the supercritical CFB boilers independently. The design theory and key technology for supercritical CFB boiler were proposed. Key components and novel structures were invented. The first 600 MWe supercritical CFB boiler and its auxiliaries were successfully developed and demonstrated in Baima Power Plant, Shenhua Group as well as the simulator, control technology, installation technology, commissioning technology, system integration and operation technology. Compared with the 460 MWe supercritical CFB in Poland, developed in the same period and the only other supercritical one of commercial running in the word beside Baima, the 600 MWe one in Baima has a better performance. Besides, supercritical CFB boilers of 350 MWe have been developed and widely commercialized in China. In this paper, the updated progress of 660 MWe ultra-supercritical CFB boilers under development is introduced.