Flash Calcination Research Articles

Impact of calcination technology on properties of calcined clays

Calcined kaolinitic clays are known to be very reactive pozzolans, and combined with limestone can enable significant clinker substitution in cementitious systems. Thermal activation of kaolinitic clays takes place when the hydroxyl groups are removed, leading to formation of an amorphous reactive structure. There are several technologies for clay activation, but the most used at industrial scale are flash and stationary calcination. The objective of this paper is to investigate the impact of the calcination regime on the properties of the calcined product. It presents the results of an experimental program carried out with a kaolinitic clay calcined at a flash calciner and at a laboratory furnace. Calcination brings about a drop in specific surface, and an increase of average diameter due to agglomeration, an effect more pronounced in stationary calcination. No major differences were found at the heat of hydration, CH consumption and phase assemblage for the fully dehydroxylated material. The flash calcined material had slightly better results mainly due to a finer PSD compared with the one stationary calcined. No major difference was found in water demand and compressive strength for both regimes. As expected, the main impact of the calcination regime is the agglomeration.

Flash calcination of magnesite in a one-throughput transport bed: reaction characterization and industrial justification

This study investigated flash calcination of magnesite powder in a one-throughput transport bed to clarify how the conversion and product activity as well as microstructure vary with reaction conditions including temperature, particle size, and numbers of re-calcination. Results showed that calcination of magnesite powder at 850–1000 °C is a quick reaction, allowing 99% of its containing MgCO3 to be decomposed in 1–2 s. Activity of product from the transport bed flash calcination (TBFC) is obviously higher than that from fixed bed calcination. Product activity depends on both decomposition rate and microstructure. During calcination, the surface structure of product changes from loose and porous to dense and smooth, even in a few seconds. A recently commissioned commercial TBFC plant indeed produced the light-burned magnesia according to the anticipation of this study, and it only requires a fuel consumption about 40 % lower than that of conventional reverberatory furnace.

Developing a High‐Performing Spinel LiMn2O4 Cathode Material with Unique Morphology, Fast Cycling and Scaled Manufacture

AbstractHigh power application of Li‐battery remains a challenge due to the lack of stable fast‐charging cathode materials. Lithium manganese oxide (LMO) cathode is very promising due to its high operating voltage and fast charging ability; however, the associated Mn‐dissolution is one of the main hindrances to its practical applicability. In this work, we demonstrate for the first time the use of a commercially scalable method through a proprietary Calix flash calcination (CFC) technology to develop high‐performance electrode materials where a novel CXL LMO material was manufactured and tested. CXL LMO|Li metal cell showed a reversible specific capacity of 110 mAh/g with 99 % retention after 100 cycles and showed excellent rate performance up to 20 C current rate (~20 mA/cm2 current density). CXL LMO|Graphite cell (areal capacity 1 mAh/cm2) was also reported with 86 % capacity retention over more than 500 cycles. Cross‐section morphology revealed a unique multi‐layered structure that was retained at the core of the novel LMO material. It obtained lesser Mn dissolution compared to commercial LMO. The scalable synthesis procedure through CFC technology, can be broadly applicable to produce unique electrode morphology as demonstrated here for the CXL LMO representing a promising pathway for electrode manufacturing for high‐power Li‐batteries.

Effect of swirling gas inlet design on particle motion and decomposition in magnesite flash calciner

In this work, a numerical simulation model of an industrial-scale magnesite flash calciner (MFC) was established based on computational fluid dynamics (CFD) method. The discrete phase model (DPM) was employed, and the results of kinetic analysis for magnesite decomposition were taken into consideration. Then, the influence of swirling gas inlet design on particle motion and decomposition in MFC was analyzed, thereby providing suggestions for production. The results indicate that incorporating a swirling design can attenuate the particle deposition at the feeding port and increase particle residence time in furnace. However, the conversion degree of magnesite is decreased. This phenomenon can be attributed to the particle accumulation near the wall, resulting in a localized lower gas temperature and subsequently leading to a gas-solid heat transfer degradation. By elevating the gas temperature and reducing its flow rate, the enhancement of magnesite decomposition and reduction in energy consumption are achieved. The gas-solid water equivalent ratio, determined by heat of reaction and sensible heat of flue gas, needs to be higher than 1.8 to maintain a mass fraction of MgO above 0.9.

Microstructure and mechanical properties of geopolymers utilizing excavated soils, metakaolin and slags

This paper presents a study on the potential of geopolymer (GP) as a substitute for ordinary Portland cement (OPC) in construction applications. OPC is widely used in construction due to its high strength and durability. However, manufacturing is extremely energy-intensive and produces large amounts of carbon dioxide (CO2) emissions. Also, In France, 130 million tons of excavated soils are generated each year [1] and classified as waste material without proper disposal methods. Therefore, the use of excavated clays coming from construction projects in GP formulations will have a positive impact on decreasing waste materials. Moreover, flash calcination used as heat thermal technique eliminate the organic matter and enhance the geopolymerization reaction with the alkaline reagent used in GP. On the other hand, GP are a type of alternative material made from industrial by-products such slags. This study used various methods to optimize GP mix design by evaluating the fresh and hardened properties. The results has shown that GP has a higher compressive strength than OPC in short term (between +5% and 76% at 1 day) and present a comparable strength in long term. The analysis of the microstructure throughout nuclear magnetic resonance (NMR), Fourier transform infrared (FTIR), X-ray diffraction (XRD) and Thermogravimetric analysis (TGA) has shown the GP designed has a stable reticulated polymeric structure. Mercury porosity has shown a finer nonometric porosity that corresponds to a compacted and fitted micelle structure. This study provides a solid contribution to the sustainability of the construction industry by developing a GP binder composed of flash-calcined excavated clay (FCC), metakaolin (MK), and slag (GBFS) that can achieve better results than OPC binder.

Reactivity of flash-calcined illitic clays

The paper discusses the reactivity of flash-calcined illitic clays for application as an alternative source of supplementary cementitious material. Structural and morphological changes induced by flash calcination improved the illitic clay reactivity despite the incomplete illite dehydroxylation and particle agglomeration. Performance indexes higher than 90%, lime consumption between 554 and 741mgCa(OH)2/g, and the electrical conductivity response ratified the pozzolanic activity. The unique properties achieved by flash-calcination, especially for particles with D90 35 µm submitted to 970 °C in the flash-calcining facility pre-heating, contribute to broadening the calcined clay spectrum for application as supplementary cementitious material, currently dominated by kaolinitic clay.

Flash-calcined sediments versus raw sediments: A comparative life cycle assessment of SCMs

The urgent need for reducing CO2 emissions and achieving sustainable development goals has prompted governments worldwide to adopt strategies such as Net-Zero targets for mitigating the environmental impact of various industries. Cement production, a major contributor to global emissions, has attracted significant attention due to its substantial carbon footprint. Simultaneously, the challenge of sediment disposal poses a pressing environmental concern. This study focuses on the environmental sustainability of cement and mortar production, particularly through the incorporation of dredged sediments as supplementary cementitious materials (SCMs). This research addresses a knowledge gap regarding the sustainability of flash calcined sediments (FCS) versus dried ground sediments (DGS) as SCMs. Using life cycle assessment (LCA), it examines their environmental performance, benefits, drawbacks, and the impact of sediment treatment. This approach sets it apart from prior research solely focused on the substitution effect of ordinary Portland cement (OPC). Substituting OPC with FCS/DGS sediments at 5–30% can reduce CO2 emissions by 6.44–15.51% with respect to the 52.5 MPa equivalent cement functional performance. FCS scenarios have shown a lower Global Warming Potential (GWP) than observed in cement with DGS except at a substitution rate of 15%. The study also highlighted the influence of cement functional performance, fuel type, and flash calcination techniques on the overall environmental performance. For mortar assembly, the findings revealed that utilizing FCS for 30% substitution of OPC has more environmental saving benefits than using DGS. Cement production, as well as the leaching behavior of trace elements, significantly affect the toxicity to ecosystems and human health categories. Future research should address the full burdens of sediments and develop appropriate allocation factors to accurately assess their environmental impact, especially if their classification shifts from waste to a valuable resource. This will ensure a comprehensive evaluation with respect to their effects on marine ecosystems and navigation improvement.

The Influence of External Sulfate Attack on the Durability of Reinforced Mortars in the Presence of Calcined River Sediments.

In France, the annual volume of dredged sediments is significantly increasing, which has become a real environmental problem. Nevertheless, these sediments can be used beneficially as supplementary cementing material. On the other hand, external sulfate attack is one of the most aggressive causes of deterioration that affects the durability of concrete structures. This study focused on the valorization of river-dredged sediments from Noyelles-Sous-Lens (Hauts-de-France) as a mineral addition in substitution of Portland cement, and it studied their impacts on the mechanical behavior and durability of reinforced mortars. X-ray diffraction (XRD) analysis indicated the presence of clay minerals in the raw sediment. In order to activate this clay fraction, flash calcination was applied at a temperature of 750 °C. In addition, four mixed mortars were formulated by mixing a Portland cement (CEM I 52.5 N) and the calcined sediments as a partial substitute for cement with proportions of 0%, 15%, 20%, and 30%, then stored in water tanks at room temperature (20 ± 2 °C) for 90 days in order to immerse them in a tank containing a 5% MgSO4 solution and to track the evolution of their corrosion potential as well as their mass variations every 20 days for a period of 360 days. The following additional tests were carried out on these mortars: tests of resistance to compression and flexion and to porosity by mercury intrusion. The results obtained from the majority of these tests showed that the mortar containing 15% calcined sediments is as effective and durable as the reference mortar itself. The main conclusion we can draw from these results is that the presence of these calcined sediments improves the overall behavior of the mortar.

Developing mortar using limestone flash-calcined dredged sediment/millstone-clay cement binder (LFC)

This study aims to develop a sustainable cement binder that resembles limestone calcined clay cement by examining the effects of flash calcination on the physical and mineralogical properties of materials, and their potential as pozzolanic material. The study will evaluate whether flash-calcined material, made from marine sediments or excavated clayey soils at 750 °C, can be a substitute for metakaolin (MK), commonly used to enhance cementitious formulations. The researchers aim to determine whether the flash-calcined material can achieve similar properties to MK when developing mortar made of limestone flash-calcined sediment/millstone-clay cement (LFC). The study shows that flash calcination improves pozzolanic reactivity by enhancing BET surface area and density without altering chemical characteristics. The Chapelle test confirms pozzolanic reactivity in the flash-calcined sediment (FCS) and flash-calcined millstone clay (FCMC), and physical, mechanical, and microstructural tests are conducted to analyze their impact on various formulations of mortar and paste samples. The results suggest that LFC with MK, FCS, and FCMC can achieve better strength than the reference mix C0. Microstructural tests demonstrate that mortar designed with FCS and FCMC have similar compositions to that with MK.

Flash-Calcined Sediments for Zinc Adsorption

Heavy metal contamination of the environment could pose health risks to humans. Until recently, several geochemical routes were considered to address the issue of metallic leachates from sources such as e-waste deposal sites or mining areas. Following the adsorption pathway, this study focused on investigating the ability of calcination products as a low-cost option for the remediation of zinc contaminated effluents. Sediments dredged in northern France were calcined by flash calcination method, before testing the calcination products (FCS750 hereafter) as adsorbent for zinc removal. The calcination process performed at 750 °C resulted in a denser material with a higher specific surface area and lower organic matter content, suited for aqueous remediation. Kinetic and equilibrium assessment underlined a rapid adsorption better described with the Pseudo Second Order model than the Pseudo First Order or Bangham equations. Adsorption models (Langmuir, Freundlich and Temkin) implemented to describe the interaction under two pH conditions (pH = 2; pH = 7) resulted in a maximum adsorption capacity (qmax) of 89.61 mg g−1 under the most favourable configuration. The pH conditions had poor influence on the adsorbing capacity value, which suggested a good buffering property of the calcined sediment and a potential applicability on effluents with different chemistries. A qmax comparison based on 42 studies indicated that FCS750 was more beneficial than most raw organic adsorbents but remained less effective than grafted and composite materials. Nevertheless, the low number of steps necessary for FCS750 processing, the easy access of its precursor (harboring wastes) and its low energy cost suggested good economic competitiveness and pleaded in favor of field experimentations.

Development of Flash-Calcined Sediment and Blast Furnace Slag Ternary Binders

Partial cement replacement by low-carbon-impact additions has the potential to reduce CO2 emissions. The aim of this study is the development of a ternary binder that includes ordinary Portland cement (OPC), ground granulated blast furnace slag (GGBS), and flash-calcined sediment (FCS). To upgrade dredged mineral material into FCS, a new heat treatment, i.e., flash calcination, was used. The used materials were physically, chemically, and mineralogically characterized. The mixture design method was used to optimize the design of the ternary blended binders. A model was developed and validated for the prediction of the 90-day compressive strength for mortars composed of OPC (C), GGBS (S), and FCS (F). Five mixes, reference RM (100% OPC), binary mix (50% OPC and 50% GGBS), and three ternary mixes with FCS rates of 10%, 15%, and 20% were characterized in fresh and hardened states. The results show that the incorporation of FCS reduced the workability of the mixes and increased their densities. Moreover, the initial setting time of the mix was delayed, and the heat of the hydration peak was decreased. The 90-day compressive strengths of the mix containing 10% FCS were higher than those of RM. In conclusion, the use of 10% FCS and 40% GGBS was an efficient substitute for 50% OPC.

Designing Efficient Flash-Calcined Sediment-Based Ecobinders.

To ensure the optimum navigation of boats and protection against flooding, waterways and ports are regularly dredged. The volume of dredged materials represents 56 million m3 in France and 300 million m3 in Europe. These materials show a high potential for a use as supplementary cementitious material (SCM). In this paper, sediments treated by the flash calcination method (STFC), which is based on a low-energy consumption process, are utilized as a mineral admixture in a cementitious matrix. The results of the physical, chemical, and mineralogical characterization prove that this heat treatment has an interesting impact on the final properties of the sediments. Mortars based on the flash-calcined product have comparable mechanical properties to control mortar. For a substitution rate below 10%, the performances are even equivalent to a metakaolin (MK80)-based mortar. Calorimetry testing demonstrated that calcined materials also improve hydration processes in the cement matrixes by generating additional heat release due to sediment pozzolanic activity. Across this study, it is shown that waste material including sediment can be transformed after optimized heat treatment into a valuable resource for the building and infrastructure sector.

The Pozzolanic Activity of Sediments Treated by the Flash Calcination Method

The Pozzolanic Activity of Sediments Treated by the Flash Calcination Method

Experimental Study of Blended Binders with Metakaolin

Three metakaolins are evaluated for use as supplementary cementitious materials in cement-based systems. The metakaolins vary in mineralogical composition and in fabrication (traditional and flash calcination), but are quite similar in their surface area (16–19 m2/g), but are quite similar in mineralogical composition. Performance of metakaolin mixtures will be compared to two control mixtures (standard concrete for foundation C40/50 and high performance concrete C60/75). In this study, the properties of fresh concrete and the mechanical and durability properties of hardened concrete will be examined. The rheological behaviour are aimed to determine the effect of metakaolin on mixture workability. Compressive, tensile and flexural strength and elastic modulus will be measured at various concrete ages. The influence of metakaolin on durability is assessed through rapid chloride migration and carbonation measurements. For high performance concrete mixtures, drying and autogenous shrinkage will be monitored and creep measurements are performed and compared.

The process for preparation of active aluminum hydroxyoxide via flash calcination of gibbsite in a new energy-efficient centrifugal drum-type reactor

A process for the preparation active aluminum hydroxyoxide using flash calcination (no longer than 3 s) of gibbsite in a new energy-effective centrifugal drum-type reactor TSEFLAR is considered. The influence of the process parameters on properties of the target product is determined. The temperature and residence time of the particles on the rotating drum surface is established to produce the active aluminum hydroxyoxide of the composition Al2O3·(3-z)H2O (where z = 2.5–2.8) with high chemical activity (solubility in the sodium hydroxide solution) and the specific surface area larger than 200 m2/g is characteristic of the product. Models of particle motion along the reactor surface and of their heat states are suggested to establish the process parameters determining the product properties, such as the residence time of the particles on the surface, particle temperature, and residual water content. The energy consumption for the gibbsite activation in the drum-type reactor is as low as one third of that of the currently used industrial technology based on thermal treatment of gibbsite in flowing flue gases.

Semi-Analytical Solution of a Nonlinear Heat Transfer Model for a Tubular Cocurrent Moving-Bed Reactor With a First-Order Chemical Reaction in the Solid Phase

Abstract The development of mathematical models plays a fundamental role in the design, optimization, and control of processes. Regarding heat transfer in moving bed reactors, the chemical reaction implies the inclusion of a nonhomogeneous and nonlinear term in model equations, making the analytical integration a very difficult task. Up to date, there is not an analytic and/or a semi-analytic solution to a heat transfer model of a moving bed reactor (MBR) with isothermal walls to the distributed parameters in the solid phase. Therefore, starting from analytical solutions of the associated homogeneous (linear) problems and through the spectral expansion of the nonhomogeneous vector, this work presents strategies for determining semi-analytical solutions of nonhomogeneous and nonlinear problems. An MBR with a first-order chemical reaction in the solid phase—kaolinite dehydroxylation in the kaolinite flash calcination process—is selected as the case study; however, the strategies can easily be applied to other nonlinear models. Results for conversion, and fluid and particle temperatures, are given for different parameter values. The solutions perform stable, fast, and accurate. When compared with a hybrid finite difference and finite analytic (FD&FA) numerical method, the solution showed a very good agreement.

Effect of phase type in the alumina precursor on the flash calcination synthesis

Economical alumina precursors, derived from bauxite or nepheline ores, were calcined through a very short time process. Results showed that phases of the precursor are a key parameter on the flash calcination process. The number of structural water molecules is the dominant phenomenon. A porous and fine structure of activated alumina was developed as the hydroxyl groups are explosively driven off and establish a hydrothermal condition. The presence of gibbsite phase with larger particle size and most structural water molecules has better product properties in comparison of other alumina precursors phase with small particle size because water vapor pressure achieves a critical value for splitting particles and developing nucleation desirable phases. The changes rate of properties reaches to its maximum value for gibbsite phase at lower calcination temperature. FESEM images showed the precursor phase forms different morphologies of products like, nanodimensional, a coral-like co-continuous or loose particles surrounded with macropores.

On the Effect of Flash Calcination Method on the Characteristics of Cobalt Catalysts for Ammonia Synthesis Process

AbstractThe influence of precursor calcination method on the properties of the cerium and barium promoted cobalt catalysts for ammonia synthesis was investigated. Three methods of cobalt‐cerium hydroxycarbonates mixture heat treatment were studied – flash, static and semi‐static calcination processes, differing in duration as well as heat and mass transfer conditions. Their effect on catalyst structural parameters, morphology, crystal structure and activity was determined. It was proven that compared to other heat treatment methods flash calcination of CoCe hydroxycarbonate precursor resulted with a catalyst of superior structural parameters and the highest activity in ammonia synthesis. However, the incomplete precursor transformation and insufficient active and promoter phases crystallization during this process were indicated. In order to improve surface activity and optimise properties of the catalyst it was stated that modification of flash calcination conditions is required.

Energy-saving strategy for a transport bed flash calcination process applied to magnesite

A transport bed flash calcination (TBFC) process applied to magnesite is systematically investigated through process simulation to optimize the energy-saving strategy. The high-temperature calciner flue gas is used to preheat the fed magnesite, while the sensible heat with the caustic calcined magnesia (CCM) product is cooled by air sent to the calciner. Pre-decomposition of magnesite during preheating is considered on basis of the kinetics measured using a micro fluidized bed reaction analyzer that allows the minimized effect of external diffusion on reaction. With staged fuel gas supply the TBFC process allows the equivalence ratios around 1.2 for combustion. The preferred arrangement of stages for magnesite preheating and CCM cooling are respectively 4 and 2, leading to the energy consumption of 4100 kJ/kg-CCM and the energy efficiency of 66.8%, which is almost doubly higher than the 33.9% of the conventional reverberatory furnaces (RF). The pre-decomposition occurs mainly in the 1st-stage preheater, and the maximal conversion is about 13%. Varying the stages of preheating appears more influential on the energy saving than varying the cooling stages, while residence time above 1 s in the preheaters has limited effect.

Optimizing the Properties of an Alumina Support of Hydrotreating Catalysts by Introducing Boron and Sulfur at the Stage of Obtaining Pseudoboehmite by Hydrothermal Treatment of the Product Produced by Flash Calcination of Gibbsite

The problem of optimizing the textural characteristics and chemical composition of the alumina support of a vacuum gasoil hydrotreating catalyst is considered. The catalyst is synthesized using the state-of-the-art environmentally friendly technology of flash calcination of gibbsite. Ways of increasing its specific surface area by introducing inorganic additives containing boron or sulfur at the stage of synthesizing boehmite with needle-shaped particles are developed. It is established that introducing such modifiers raises SBET by 50–100 m2/g, relative to the maximum values that can be attained by varying the standard parameters of hydrothermal treatment. It is shown that introducing boron at the stage of boehmite synthesis improves the catalytic activity of CoNiMoP catalyst in the hydrodesulfurization and hydrodenitrogenation of vacuum gasoil by two or more times, relative to a similar catalyst doped with boron from an impregnating solution.