Thermal transport and chemical conversion in single reacting sorbent particles

The effects of particle size and carbon dioxide concentration on chemical conversion in engineered spherical particles undergoing calcium oxide looping are investigated. Particles are thermochemically cycled in a furnace under different carbon dioxide concentrations. Changes in composition due to chemical reactions are measured using thermogravimetric analysis. Gas composition at the furnace exit is evaluated with mass spectroscopy. A numerical model of thermal transport phenomena developed previously is adapted to match the physical system investigated in the present study. The model is used to elucidate effects of reacting medium characteristics on particle temperature and reaction extent. Experimental and numerical results show that (1) an increase in particle size results in a decrease in carbonation extent, and (2) the carbonation step consists of fast and slow reaction regimes. The reaction rates in the fast and slow carbonation regimes increase with increasing carbon dioxide concentration. The effect of carbon dioxide concentration and the distinction between the fast and slow regimes become more pronounced with increasing particle size.     

Desilication from illite by thermochemical activation

Illite occurs widely in bauxite ores and results in low alumina grade of the ores. Differential thermal analysis (DTA), thermal gravimetric analysis (TGA) and X-ray diffraction analysis (XRD) show the OH groups split off from the structural framework of illite between 500 ℃ and 700 ℃. With the increase in temperature up to about 1 100 ℃, the layer structure of illite breaks up and Si in the layers is transformed into the amorphous state. Meanwhile, mullite comes out at 1 100 ℃. Quartz occurring in illite keeps unchanged in structure in the range of 500 -1 200 ℃. A desilication process from illite by thermochemical activation followed by alkali leaching is therefore developed on the basis of the behavior that amorphous silica is alkali soluble. The investigation finds that the optimum parameters for desilication are activation temperature of 1 100 - 1 150 ℃, activation time of 90 - 120 min, leaching temperature of 95 - 110 ℃, leaching time of 90 - 120 min and concentration of caustic soda (Na2Ok) 120 - 150 g/L. An overall desilication about 45% is attained under these conditions. XRD analysis confirms that the active amorphous SiO2 has been dissolved in the alkali solution and removed from the samples, while quartz and mullite have not. The investigation also shows that the formation of mullite during activation and formation of sodium hydroalu minosilicates (Na96 Al96 Si96 O384 and 0.95Na2 O · Al2 O3 · 3.25SiO2 · 4.79 H2 O) during leaching lead to the relatively low desilication of illite.     

CH4-CaSO4和H2S-Fe2O3反应体系的热力学和动力学研究

The destruction of hydrocarbon in deep carbonate diagenetic environment is one of problems on the formation of oil and gas. Organic-inorganic reactions in the process of TSR(Thermochemical Sulfate Reduction) are the main reason to make disappearance of the hydrocarbons. The work in this field has often been the subject of much research work in recent years. In this paper, the thermodynamics of CH4-CaSO4 and H2S-Fe2O3 systems is discussed to investigate the possibility of reactions. It is found that these two reactions can proceed spontaneously.Increasing temperature is favorite for CH4-CaSO4 system but disfavorite for H2S-Fe2O3 system. Thermal simulation experiments were carried out using autoclave at high temperature and high pressure. The properties of the products were characterized by microcoulometry, FT-IR and XRD methods. On the basis of the experimental data, a reaction kinetic model is developed and kinetic parameters are determined.     

Activity measurement of gallium in the B2 phase of the CoGa–Sb system by the EMF method with zirconia-based solid electrolyte

Gallium activity in the B2 phase regions of both binary Co–Ga and ternary Co–Ga–Sb systems was measured by EMF method with stabilized zirconia solid electrolyte The temperature range was 1073–1273 K and Sb concentrations were 1, 2 and 3 mol fractions. Ga activity at 1173 and 1273 K increases sharply in Ga rich region and the addition of Sb to the CoGa phase increases Ga activity. Activity change corresponds to the lattice parameter change with Sb addition to the CoGa phase.     

Ab-initio calculation of enthalpies of formation of intermetallic compounds and enthalpies of mixing of solid solutions

A large number of ab-initio calculations of energies of formation of intermetallic compounds have been performed in the last 15 years. The currently used methods are listed. The paper presents a review of the aluminium based compounds which have been studied. Comparisons of calculated and experimental enthalpies of formation are provided for aluminim-3d and-4d transition metal alloys at equiatomic composition. The modelling of the enthalpies of mixing of solid solutions based on a given lattice is described.     

Isothermal section at 1673 K of the Mo–Ru–Si diagram and crystallographic structures of ternary phases

Efforts to improve the high temperature behavior of MoSi₂ in oxidizing environments led to the investigation of the Mo–Ru–Si phase diagram. The isothermal section at 1673 K was determined by X-ray diffraction, optical and scanning electron microscopies and EPMA. Five new silicides were identified and their crystallographic structure was characterized using conventional and synchrotron X-ray as well as neutron powder diffraction. Mo₁₅Ru₃₅Si₅₀, denoted α-phase, is of FeSi-type structure, space group P2₁3, a=4.7535 (5) Å, D_x=7.90 g. cm⁻³, Bragg R=7.13. Mo₆₀Ru₃₀Si₁₀ is the ordered extension of the Mo₇₀Ru₃₀ σ-phase with space group P4₂/mnm, a=9.45940(8) Å, c=4.94273(5) Å, D_x=6.14 g. cm⁻³, Bragg R=5.75.     

燃煤过程中重金属形态的热力平衡分析

对燃煤过程中痕量重金属的形态进行了热力学模型计算。通过对不同系统，包括多种痕量元素共存、汞/煤系统、汞/煤/氯系统、砷/煤/氯系统、硒/煤/氯系统、和汞/砷/硒//煤/氯的复杂系统的平衡计算，表明采用热力学平例分机可以为预测煤燃烧烟气中痕量重金属元素挥发或凝聚的倾向提供有价值的指导。     

Mechanisms of synthesis gas production via thermochemical cycles over La0·3Sr0·7Co0·7Fe0·3O3

La_0·3Sr_0·7Co_0·7Fe_0·3O₃ (LSCF3773) was chosen as an oxygen carrier material for synthesis gas production and synthesized using ethylene-diamine-tetra-acetic acid (EDTA) citrate-complexing method. LSCF exhibited a pure cubic structure where 110 and 100 plane diffractions were active for CO₂ splitting, while 111 was more favored by H₂O splitting. Overall oxygen storage capacity (OSC) of LSCF was 4072 μmol/g_cat. During the reduction process, regular cations (Co⁴⁺, Fe⁴⁺), polaron cations (Co³⁺, Fe³⁺) and localized cations (Co²⁺, Fe²⁺) were achieved when the LSCF was reduced at 500, 700 and 900 °C, respectively. The strength of the active sites depended on reduction temperatures. An increase in oxidation temperature enhanced H₂ production at temperature ranging from 500 °C to 700 °C while effected CO production at 900 °C. H₂O and CO₂ was competitively split during the oxidation step, especially at 700 °C. The activation energy of each reaction was ordered as; CO₂ splitting > H₂O splitting > CO₂ adsorption, supporting the above evidence where H₂ and CO production were found to increase when the operating temperature was increased.     

3D numerical investigation of ZnO/Zn hydrolysis for hydrogen production

The current research is focused on the hydrogen production through a two‐step ZnO/Zn thermochemical water splitting cycle. In the present paper, numerical modeling of the second step is conducted using Computational Fluid Dynamics (CFD)2, where steam reacts with zinc to produce hydrogen. The parametric study shows that the hydrogen yield is relatively insensitive to the steam/zinc molar ratio and inversely proportional to the argon/steam molar ratio. For large argon to steam molar ratios, hydrogen yield is relatively insensitive to the inlet temperature of zinc and steam, and increases marginally with an increase in the argon inlet temperature. Five different reactor configurations were evaluated comprehensively. Among all configurations, a cylindrical reactor with a tangential inlet for argon and zinc, and a radial inlet for steam (both in the bottom plane of the reactor) and a tangential outlet in the top plane of the reactor produced the highest hydrogen yield of 88%. Copyright © 2013 John Wiley & Sons, Ltd.     

Thermochemical investigation of Sm–Mg alloys

The paper focuses on the thermochemical behaviour of the binary Sm–Mg alloys. The enthalpies of formation of the Sm–Mg intermetallic compounds have been determined at 300 K by high temperature direct synthesis calorimetry. The following results in kJ/mole of atoms are reported: −18.5±2 (SmMg), −16.0±2 (SmMg₂), −12.0±2 (SmMg₃), −8.5±2 (SmMg₅) and −5.5±2 (Sm₅Mg₄₁). The results are compared with the earlier experimental value obtained by vapour pressure.