Hydrodynamic modeling on the external liquid–solid wetting efficiency in a trickling flow reactor

A three‐region model was proposed, which considers the bed cross section being composed of a stagnant liquid region, a liquid film region, and a rivulet flow region. To estimate the fractions of the three regions, the fraction of film flow was evaluated first, by transforming the complex trickling flow texture into pure liquid film flow. Through the measurements of liquid holdup and pressure drop for the film flow, a relationship between relative permeability and gas saturation was established, and from which the fraction of film flow region was obtained. It shows packing size is most important to the faction of rivulet flow. The external wetting efficiency of the packing was correlated as the sum of two‐third power of the liquid film fraction and the rivulet flow fraction, besides, a correlation based on Reynolds and Galileo numbers of the two phases in the form of was proposed. © 2012 American Institute of Chemical Engineers AIChE J, 59: 283–294, 2013     

De- and rehydration of Ca(OH)2 in a reactor with direct heat transfer for thermo-chemical heat storage. Part A: Experimental results

Heat storage technologies are used to improve energy efficiency of power plants and recovery of process heat. Storing thermal energy by reversible thermo-chemical reactions offers a promising option for high storage capacities especially at high temperatures. Due to its low material cost the use of the reversible reaction Ca(OH)₂ ? CaO + H₂O has been suggested. This paper reports on the thermal behavior of a reactor with direct heat transfer between the gaseous reactant and the solid material. Cycling stability is confirmed and the impact of the most significant parameters such as the maximum possible enthalpy difference of the heat transfer fluid between inlet and outlet, the heat transfer, the particle reaction rate and the mass transport is derived. In the test system the particle reaction rate could be identified as the main limiting parameter.     

De- and rehydration of Ca(OH)2 in a reactor with direct heat transfer for thermo-chemical heat storage. Part B: Validation of model

Heat storage technologies are used to improve energy efficiency of power plants and recovery of process heat. Storing thermal energy by reversible thermo-chemical reactions offers a promising option for high storage capacities especially at high temperatures. Due to its low material cost the use of the gas–solid reaction Ca(OH)₂ ? CaO + H₂O has been suggested. In Part A of this work the thermal behavior of a reactor with direct heat transfer was experimentally investigated. In this part a two-dimensional model is applied for the specified system. The experimental and simulated results during the exothermic hydration are discussed in order to confirm the validity of the model. The model is validated regarding heat transfer, integral reaction rate and maximum temperatures. In addition, an adaptation of the kinetic equation is proposed in order to take into account rate-limiting effects due to agglomeration in the powder bed.     

Modelling and simulation of a gas–solids dispersion flow in a high-flux circulating fluidized bed (HFCFB) riser

Radial solids velocity profiles were computed on seven axial levels in the riser of a high-flux circulating fluidized bed (HFCFB) using a two-phase 3-D computational fluid dynamics model. The computed solids velocities were compared with experimental data on a riser with an internal diameter of 76 mm and a height of 10 m, at a high solids flux of 300 kg m⁻² s⁻¹ and a superficial velocity of 8 m s⁻¹. Several hundreds of experimental and numerical studies on CFBs have been carried out at low fluxes of less than 200 kg m⁻² s⁻¹, whereas only a few limited useful studies have dealt with high solids flux. The k– two-phase turbulence model was used to describe the gas–solids flow in an HFCFB. The model predicts a core–annulus flow in the dilute and developed flow regions similar to that found experimentally, but in the region of highest solids concentration it is somewhat overpredicted at the level close to the inlet.     

Simulations of solid–liquid scalar transfer for a spherical particle in laminar and turbulent flow

Scalar transfer from a solid sphere to a surrounding liquid has been studied numerically. The simulation procedure involves full hydrodynamic resolution of the solid–liquid interaction and the flow (laminar and turbulent) of the carrier fluid by means of the lattice‐Boltzmann method. Scalar transport is solved with a finite volume method on coupled overlapping domains (COD): an outer domain discretized with a cubic grid and a shell around the solid sphere with a spherical grid with fine spacing in the radial direction. The shell is needed given the thin scalar boundary layer around the sphere that is the result of high Schmidt numbers (up to Sc = 1000). After assessing the COD approach for laminar benchmark cases, it is applied to a sphere moving through homogeneous isotropic turbulence with the sphere radius larger (by typically a factor of 10) than the Kolmogorov length scale so that it experiences an inhomogeneous hydrodynamic environment. This translates in pronounced scalar concentration variations and transfer rates over the sphere's surface. Overall scalar‐transfer coefficients are compared to those derived from classical Sherwood number correlations. © 2014 American Institute of Chemical Engineers AIChE J, 60: 1202–1215, 2014     

An unusual dichromium(II,II) compound bearing di-2-pyridyl ketone oximate ligands and prepared by the ligand-assisted reduction of a trichromium(III,III,III) complex in air

The reaction of the oxide-centred triangular, trichromium(III,III,III) complex [Cr₃O(O₂CCMe₃)₆(H₂O)₃](O₂CCMe₃) with di-2-pyridyl ketone oxime, (py)₂CNOH, in MeCN under aerobic and refluxing conditions yields the pivalate-free, dichromium(II,II) complex [Cr₂{(py)₂CNO}₄] · 2H₂O (1 · 2H₂O). The dinuclear complex can also be prepared by the reaction of [Cr(CO)₆] with (py)₂CNOH in refluxing MeCN/H₂O in air. The two high-spin Cr^II atoms are doubly bridged by two 2.1110 oximate ligands, while a chelating 1.0110 (py)₂CNO⁻ ion completes distorted trigonal bipyramidal coordination at each metal centre. The dimers are stabilized by intramolecular stacking interactions between the terminal (py)₂CNO⁻ ligands, and the structural effects of these interactions are discussed.     

Electrical resistance tomography (ERT) for flow and velocity profile measurement of a single phase liquid in a horizontal pipe

Electrical resistance tomography (ERT) is a novel, simple, and robust method of process imaging which uses non-invasive sensors located on the periphery of vessels to reconstruct a cross-sectional image of the vessel interior. This method of imaging when conducted on two adjacent planes on a pipe provides the ability to extract flow information. Previous studies have investigated this application on multi-phase flows in which the secondary phase provided the required pulse conductivity variation. In these studies the velocity profile and flow regime were identified using the common cross-correlation technique.     

Synthesis and characterization of new nitrogen‐ and oxygen‐rich cyclohexanone–formaldehyde resin for fast Cd(II) adsorption in aqueous solution

A new structure of cyclohexanone–formaldehyde resin (CFR) was synthesized via in situ condensation reaction of 2,4,6‐tris(p‐formylphenoxy)‐1,3,5‐triazine (TFPA) with CFR. TFPA was prepared by the reaction of cyanuric chloride and p‐hydroxybenzaldehyde and its structure was confirmed using spectroscopic methods and elemental analysis. The structural, thermal and morphological properties of the nitrogen‐ and oxygen‐rich CFR were studied using Fourier transform infrared spectroscopy, X‐ray diffraction, thermogravimetric analysis and field emission scanning electron microscopy. After characterization, the resin was used as an adsorbent for Cd(II) due to the high level of nitrogen and oxygen in its structure. The effects of various parameters such as pH, concentration and time on the adsorption process were studied. The maximum adsorption capacity of cadmium at pH 8 in 5 min was 83.61 mg L^?1. The adsorption isotherm was applied to the Langmuir, Freundlich, Temkin and Dubinin–Radushkevich models. Comparing the correlation coefficient (R²), the Langmuir model was fitted well. Pseudo‐first‐order, pseudo‐second‐order, Elivich and intra‐particle diffusion models of adsorption kinetics were explored. The pseudo‐second‐order model can better explain the adsorption kinetics that shows adsorption being dependent on the number of active sites of the adsorbent. © 2019 Society of Chemical Industry     

Evidence for a new type of vanadyl pairs in (VO)2P2O7: an ESR and magnetisation study

ESR and magnetisation experiments have identified a new type of antiferromagnetic pairing of vanadyl groups in the butane oxidation catalyst vanadylpyrophosphate. This pairing is an order of magnitude weaker than the coupling predominantly found in crystalline (VO)₂P₂O₇.