Stabilization of Basic Oxygen Furnace Slag by Hot-stage Carbonation Treatment.

Treatment and disposal of Basic Oxygen Furnace (BOF) slag, a residue of the steel production process characterized by high basicity and propensity for heavy metal leaching, is a costly burden on metallurgical plants; a sustainable valorization route is desired. The stabilization of BOF slag utilizing hot-stage carbonation treatment was investigated; this approach envisions carbonation during the hot-to-cold pathway followed by the material after the molten slag is poured and solidified. Three experimental methodologies were employed: (i) in-situ thermogravimetric analyzer (TGA) carbonation was used to assess carbonation reaction kinetics and thermodynamic equilibrium at high temperatures; (ii) pressurized basket reaction carbonation was used to assess the effects of pressurization, steam addition and slag particle size; and (iii) atmospheric furnace carbonation was used to assess the effect of carbonation on the mineralogy, basicity and heavy metal leaching properties of the slag. Free lime was found to be the primary mineral participating in direct carbonation of BOF slag. Initial carbonation kinetics were comparable at temperatures ranging from 500 to 800 oC, but higher temperatures aided in solid state diffusion of CO2 into the unreacted particle core, thus increasing overall CO2 uptake. The optimum carbonation temperature of both BOF slag and pure lime lies just below the transition temperature between carbonation stability and carbonate decomposition: 830-850 oC and 750-770 oC at 1 atm and 0.2 atm CO2 partial pressures, respectively. Pressurization and steam addition contribute marginally to CO2 uptake. CO2 uptake progressively decreases with increasing particle size, but basicity reduction is similar independent of particle size. The solubility of some heavy metals reduced after carbonation (barium, cobalt and nickel), but vanadium and chromium leaching increased

Modelling and simulations of a Monolith Reactor for three-phase hydrogenation reactions – Rules and recommendations for mass transfer analysis

A strategy for the scale-up of a monolith reactor dedicated to gas-liquid catalytic reactions is worked out; focus is made on the crucial step of gas-liquid mass transfer modelling via a steady-state numerical study based on a single channel and single unit cell representation, using a frame moving with the bubble and solving the liquid phase only. The relevance of this simplified approach is assessed through a specific case (given bubble shape, channel diameter and fluid flow rates), and hydrodynamics as well as mass transfer results are successfully compared to previously published numerical, semi-analytical and experimental works. Influence of unit cell length and of catalytic surface reaction rate is thoroughly investigated. Inferred overall mass transfer coefficients are found to increase with bubble frequency and resulting higher interfacial area in unit cell and intensified recirculation in slug. Film contribution to mass transfer is proved dominant in the case of short bubbles with reactive wall, and hardly varies with reaction rate. However, this contribution is strongly linked to bubble frequency, and a reliable evaluation of local mass transfer by correlations demands accurate knowledge on the precise dimensions of bubble, slug and film entities

Development of a reactor-heat exchanger of monolith type for three-phase hydrogenation reactions: proof of concept and modelling strategy

This study aimed at developing an innovative catalytic reactor inspired from monolith technology and equipped with in situ heat removal system. To illustrate the approach, the total hydrogenation of a bio-sourced olefin, alpha-pinene, was chosen as a model reaction. Preliminary thermal calculations proved the proposed reactor-heat exchanger configuration to be uniform in temperature, so that its behavior could be described through that of a single isothermal channel. The developed methodology then included the elaboration of the catalytic coating, the investigation of the reaction kinetics, the activity assessment of the catalytic capillary tube at pilot scale and the scale-up of the monolith reactor through multiscale and multiphysics modelling. First part of the work was dedicated to the catalytic tests, operated in a batch stirred autoclave reactor using both small coated platelets and powdered catalyst. Catalyst formulation and synthesis method were varied, leading to an efficient Pd/Al2O3 coating: it yielded a well adherent deposit of 5-10 µm thickness on aluminum alloy processed by selective laser melting and its initial activity exceeded that of a commercial egg-shell catalyst by more than one order of magnitude due to high metal dispersion (Pd nanoparticles of ca. 1 nm). The intrinsic kinetics of the reaction was investigated using the catalyst in powdered form: an overall activation energy of about 40 kJ/mol was obtained, and a Langmuir-Hinshelwood rate law with surface reaction as rate-determining step adequally described complex reaction orders with respect to alpha-pinene and hydrogen. This selected catalyst was then coated on a series of jacketed aluminium tubes of 2 mm internal diameter and 40 cm total height. Their activity was assessed on a continuous hydrogenation set-up operating in the Taylor flow regime at 10-20 bar and 100-160°C. The capillary reactor was modelled through a “Unit Cell” approach(gas bubble surrounded by a liquid film and separated by two liquid half-slugs) accounting for hydrodynamics, gas-liquid and liquid-solid mass transfer and complex reaction kinetics. Numerical simulation of Unit Cell hydrodynamics was first thoroughly questioned, by examining the merits of simplifying hypotheses regarding the bubble shape to be considered, as well as the equations and boundary conditions to be solved. It served as a support for the transient calculation of the reactant concentrations, that mimicked the progression of the Unit Cell along the reactor. In addition to the effects of operating parameters on pinene conversion, those of gas consumption along the reactor (hydrogen being here the limiting reactant), "initial" saturation conditions of the liquid and catalyst activity were analyzed thanks to the numerical model. It was also used to evaluate a more direct reactor sizing tool, based on plug flow behavior and overall exchange coefficients. The latter were calculated either from existing correlations or from the numerical simulations, by evaluating the separate contributions of different parts of the bubble surface (film and caps) to gas-liquid mass transfer and the concentration gradients near the reactor wall. Finally, the behavior of the entire monolith could be reproduced from this model by combining, in a mixing module at the reactor outlet, the liquid outflows of channels whose individual flow rates matched the fluid distribution measured on a cold mock-up of the reactor-heat exchanger

Passive Mineral Carbonation of Mg-rich Mine Wastes by Atmospheric CO2

Mg-rich process tailings and waste rocks from mining operations can react spontaneously with atmospheric CO2 to form stable carbonate minerals by exothermic reactions. Over the last decade, we have conducted a number of laboratory and field experiments and surveys on both mine waste rocks and different types of mine tailings from Ni-Cu, chrysotile, and diamond mines. The experiments and surveys cover a wide range of time (103 to 108 s) and mass (1-108 g) scales. Mine waste rich in brucite or chrysotile enhances the mineral carbonation reactions. Water saturation, but more importantly, watering frequency, are highly important to optimize carbonation. Adjusting the chemical composition of the interstitial water to favour Mg dissolution and to prevent passivation of the reaction surfaces is crucial to ensure the progress of the carbonation reactions. Preservation of the permeability structure is also critical to facilitate water and CO2 migration in the rock wastes and tailings. In field experiments, CO2 supply controled by diffusion in the mining waste is slower than the reaction rate which limits the capture of atmospheric CO2. Industrial implementation of passive mineral carbonation of mine waste by atmospheric CO2 can be optimized using the above parameters

Les réacteurs triphasiques à lit fixe à écoulement à co-courant vers le bas et vers le haut de gaz et de liquide : étude de l'influence de la pression sur l'hydrodynamique et le transfert de matière gaz-liquide

Not availableL’étude de l'hydrodynamique et du transfert de matière gaz-liquide des réacteurs catalytiques à lit fixe sous pression (0,2-8,1 MPa) en écoulement arrosé à co-courant descendant (RCLFA) ou noyé à co-courant ascendant (RCLNA) de gaz et de liquide, a été présentée. Quelques 3500 mesures expérimentales ont été obtenues sur une colonne de 1 m de haut et 0,023 m de diamètre, mettant en œuvre prés de 40 systèmes gaz-liquide-solide différents, afin d'étudier: i) la perte de pression monophasique de gaz ou de liquide; ii) les régimes d'écoulement dans les RCLFA; iii) la perte de pression biphasique dans les RCLFA et les RCLNA; iv) la saturation liquide dans les RCLFA et les RCLNA; v) l'aire interfaciale gaz-liquide dans les RCLFA; vi) le coefficient volumétrique de transfert de matière coté liquide dans les RCLFA. Deux critères d'extrapolation de l'influence de la pression sur l'hydrodynamique (perte de pression biphasique et saturation liquide), ainsi que quatre nouvelles corrélations (deux pour la perte de pression biphasique, une pour la saturation liquide et une pour l'aire interfaciale gaz-liquide) ont été développées. Une modification du diagramme d'écoulement de Charpentier et Favier a été proposée pour la prévision du déplacement de la transition entre les régimes ruisselant et pulsé en fonction de la pression dans les RCLF

Modeling and Simulations of NO_x and SO₂ Seawater Scrubbing in Packed-Bed Columns for Marine Applications

Seawater scrubbing of nitrogen oxides and sulfur oxide from marine emissions was simulated in packed-bed columns exposed to static inclination and heaving/oscillating motions. Fourth generation random packings (Raschig super-Rings) while providing much smaller pressure drop than traditional Pall-Rings ensure comparable absorption efficiency for the pollutants. Complete removal of SO2 was predicted over the tested pressure range with absorption efficiency indifferent to scrubber inclination or heaving/oscillating motions. In contrast, NOx and CO2 absorptions are negatively impacted for inclined seawater scrubbers. Removal efficiency is not lowered significantly owing to larger scrubber pressure and because diffusion of N2O4 into the liquid phase is associated with a rapid pseudo first-order reaction. The asymmetrical oscillating motion of the scrubber degrades the removal performance which exhibits wavy patterns close to the steady-state solution of the average inclination angle. NO and CO2 absorption performance waves are moving toward a steady-state solution of vertical scrubber when the asymmetry of the two inclined positions of the scrubber downgrades. Symmetric oscillation and heaving motion led to performance disturbance waves around a steady-state solution of the vertical scrubber which are determined by the parameters of angular/heaving motion

Pressure effects on the liquid saturation of a trickle-bed reactor.

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