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Role of Na2O and TiO2 on viscosity and structure of Sodium-Titanium-bearing slag
No full textThe viscosities of Na2O-TiO2-SiO2-CaO-MgO-Al2O3 slags were measured to enhance understanding of the effect of Na2O and TiO2 on the viscous behavior. An increase in the Na2O content lowered the viscosity but adding TiO2 increased the viscosity. The transformation of the structural units was investigated using in-situ temperature -dependent Raman spectra. TiO2 primarily existed in the slag system in the form of [TiO4]4-monomer, which acted as a network former. As Na2O increased, the chain structure (Q2, [Ti2O6]4-or [SiTiO6]4-) was broken by O2-ions to form tetrahedral monomer (Q0, [TiO4]4-or [SiO4]4-), which lowered the degree of polymerization. Adding TiO2, Q2 chain was formed by TiO2 and Q0 monomer to enhance the polymerization degree of the slag, resulting in the increase of the viscosity. Based on the Raman spectra and the hole theory, a quantitative rela-tionship, ln eta=3.7+0.88ln((Q2)/(Q0)2), between the structural units and viscosity of sodium-titanium-bearing slag was established
Insight into the mechanism of gasification fine slag enhanced flotation with selective dispersion flocculation
No full textCoal gasification fine slag (CGFS) produced in the coal chemical industry has caused severe environmental pollution and resource waste. To realize the utilization of CGFS, we have to efficiently separate unburned carbon (UC) in CGFS. In this work, based on the discovery of the covering between CGFS particles, the selective dispersion flocculation flotation method is proposed to improve the efficient separation of UC from CGFS. The mechanism of selective dispersion flocculation is revealed through adsorption mode, interaction force between particles, and the particle size distribution of floc under different reagent conditions. Results show that a hy-drophilic layer is formed on the surface of ash particles, which hinders the adsorption of PAM and ash particles due to the chemical adsorption of SHMP with ash particles. However, carbon particles are not affected by SHMP and can be directly adsorbed with PAM. This selective adsorption dominates the interaction force of adsorbed particles, and then controls the agglomeration of particles. After selective dispersion flocculation, the original carbon-ash selective agglomeration state is changed to the carbon-carbon selective agglomeration state. D90 of fine carbon particles changed from 110.21 mu m to 356.84 mu m. Compared with the traditional flotation process, the combustible recovery rate of foam products is increased by 10.4 % and loss on ignition (LOI) is increased by approximately 5 %. This work is conducive to fundamentally understanding the mechanism of selective dispersion flocculation. It is helpful to guide the separation of carbon and ash from gasification slag in industry
Trans-level multi-scale simulation of porous catalytic systems: Bridging reaction kinetics and reactor performance
No full textMulti-scale porous structures inside and/or between the catalyst pellets or particles are found in many chemical processes, where strong coupling of reaction and transport results in complex apparent reaction kinetics influ-ential to the reactor performance. Traditional continuum-based porous media models and simulation methods can hardly describe such structures and their scale effects faithfully. A trans-level multi-scale discrete compu-tational framework is hence proposed to address this complexity and implemented for an olefin catalytic cracking (OCC) process. The apparent reaction kinetics at the REV (representative elementary volume) scale is obtained by hard-sphere pseudo-particle modeling (HS-PPM), and coupled with computational fluid dynamics / discrete element method (CFD-DEM) for the reactor-level hydrodynamics via a one-dimensional (1D) finite difference scheme for particle-level diffusion. The mesoscales of the REVs and the flow networks between the particles are thus covered by the framework, which are previously described by simple average quantities in the continuum methods. The reactant conversion rate and target product selectivity obtained agree well with experimental results, while a continuum approach may give significantly different and unreasonable results. The multi-scale method is, therefore, demonstrated to be necessary and effective for bridging the intrinsic reaction kinetics with the performance of porous catalytic reactors
