Diffusion Of Gaseous Products Research Articles

Reduction Behavior and Mechanism of Iron Ore in Molten Iron in the Process of Converter Steelmaking

AbstractXRD and SEM methods were applied to the reduction behavior and mechanism of iron ore in molten iron at temperatures of 1400 °C, 1450 °C, and 1500 °C. The results showed that iron ore could be reduced by carbon in molten iron. When the reduction of iron oxide occurred at the reaction interface, carbon in the molten iron was affected by the concentration gradient. This promoted reduction and the reduction effect improved with increase in reaction temperature. After the carbon in the molten iron almost disappeared, the surfaces of the iron ore and molten iron exhibited oxidizing atmospheres causing different degrees of oxidation of the reduced metal iron and molten iron at 1500 °C. Through analysis of the reduction mechanism of iron ore, it was known that the maximum reaction activation energy during gas phase diffusion was 1612.1 kJ/mol, which restricts the iron ore reduction reaction. At low temperatures, the diffusion of gaseous products in solid-liquid is difficult. Increasing the temperature and stirring accelerate the reduction reaction while increasing gas diffusion.

Dynamic simulation of coupled transmission processes and reaction mechanisms in porous calcined limestone

The particle reaction model and dynamic reaction characteristics of limestone over a wide particle size range from 0.15 to 10 mm were studied by thermogravimetric analysis and nitrogen adsorption‐desorption techniques. A clear boundary between the sintered porous product layer and the undecomposed part was found by field emission scanning electron microscopy (FESEM) analysis. A dynamic coupling model considering the effects of varied pore structure and transport resistances was established based on the appropriate particle reaction model, which allowed us to predict the decomposition ratio and reaction regimes in a broad range of particle sizes. The dynamic characteristics of pore size distribution and reaction mechanisms were discussed. Over the defined particle size range and calcination temperature range, the diffusion of gaseous product through porous product layer will become the rate determining factor as the ratio of (r0‐rc)/r0 corresponding to 25 % Damköhler number above 0.35.

Detailed modeling study of low-velocity combustion of crude oil at different moisture content

ABSTRACTThe authors developed a kinetic model of crude oil combustion in different moisture contents and operating conditions by considering the reaction rates and fuel properties. To model the diffusion of gaseous products under high-temperature conditions, the authors used a binary diffusion equation that depends on the physical properties of fuel used and the reaction temperature. Results showed that the combustion of crude oil at higher moisture is not more favorable because of a considerable increase in greenhouse gas emissions, although an optimum condition for output temperature is obvious. It also found that the char conversion is higher for the high residence times. Model validated against the experimental data available in the literature, which showed fully good agreement.

Influence of Cuprous Oxide on Enhancing the Flame Retardancy and Smoke Suppression of Epoxy Resins Containing Microencapsulated Ammonium Polyphosphate

In this work, Cu2O exhibited better synergistic effect with microencapsulated ammonium polyphosphate (MAPP) than other metal oxides, such as CuO, ZnO, SnO, Fe2O3, Ni2O3, and Co2O3, on improving the flame retardancy of epoxy resins (EP). Moreover, the addition of cuprous oxide (Cu2O) could further decrease the total smoke production and carbon monoxide production. The analysis of char residues and evolved gases indicated that Cu2O was beneficial to enhance the formation amount, intumescent degree, and compactness of char. The protective layer of intumescent char residue could hinder the decomposition of EP and diffusion of gaseous products, such as hydrocarbons, aromatic compounds and carbon monoxide (CO). In addition, Cu2O also played a role in conversion of CO to CO2 through a redox cycle, involving the reduction of Cu2+—Cu+—Cu0 by CO and the oxidation of Cu0—Cu+—Cu2+ by O2. The possible flame retardant, smoke suppression, and CO oxidation mechanisms were proposed.

Concept of Variable Activation Energy and Its Validity in Nonisothermal Kinetics

The concept of variable activation energy in solid-state kinetics under nonisothermal conditions has been suffering from doubt and controversy. Rate equations of nonisothermal kinetics of solid decomposition, which involve the factors of thermodynamics conditions, pressure of gaseous product, structure parameters of solid, and/or extent of conversion, are derived from the models of the interface reaction, the diffusion of gaseous product, and the nuclei growth of the solid product, respectively. The definition of the validity function in the rate equations represents the influence of the factors on the reaction rate. A function of variable activation energy depending on the validity function is also developed. The changing trend and degree of activation energy are extrapolated from the function of variable activation energy and based on the data of nonisothermal thermal decomposition of calcium carbonate. It is shown that the concept of variable activation energy is meaningfully applicable to solid-state reactions under nonisothermal conditions.

Improve the Applicability of Rate Equation Based on the Model of Diffusion under Non-isothermal Conditions

Rate equation of non-isothermal kinetics of solid decomposition involving the factors of the pressure of gaseous product, the equilibrium pressure, temperature and structure parameters of solid is deduced according to the model of the diffusion of gaseous product. A validity function in the rate equation of non-isothermal kinetics is defined which represents the influence of these factors on the diffusion rate. The effect of the validity function on the diffusion rate are studied, based on the results of thermal analysis of decomposition of calcium carbonate at different heating rates. It is shown that it is possible to improve the validity of the rate equation of non-isothermal kinetics if the effect is taken into account.

Diffusion of gaseous products through a particle surface layer in a fluidized bed reactor

This paper examines a solid conversion process during hydrolysis and decomposition of cupric chloride in a thermochemical copper–chlorine (Cu–Cl) cycle of hydrogen production. Reaction rate constants and the time required for complete solid conversion are determined by a shrinking-core model. Diffusion of gaseous reactant occurs through a film surrounding the particle, after which the reactant penetrates and diffuses through a layer of ash to the surface of the unreacted core. The shrinking-core model for spherical particles predicts the reaction of gaseous reactant with solid at the particle surface, and diffusion of gaseous products through the ash, back to the exterior surface of the solid. The hydrolysis reaction is also analyzed with respect to chemical equilibrium conversion and required heat input. Effects of varying operating parameters are examined, including the temperature, pressure, excess steam, inert gas and hydrogen chloride (HCl) in the steam. At a temperature of 375 °C, complete conversion of CuCl 2 can be achieved by controlling the excess steam, operating pressure and inert gas supply. Addition of HCl in the steam supply increases the excess steam requirement for conversion of cupric chloride solid, and the upper limit for HCl concentration increases with temperature and inert gas composition. The addition of inert gas may also reduce the excess steam requirement, thereby reducing the heat requirement. These new results have valuable utility for equipment scale-up in the thermochemical Cu–Cl cycle of hydrogen production.

Study of oxidation of pitch fibres

The studies conducted led to the following conclusions: effective oxidation of pitch fibres begins at a temperature slightly above the flow temperature of the starting pitch; oxidation is limited by diffusion of gaseous products so that it is expedient to use initial fibres with a diameter of ≈ 10 µm and to conduct the process in conditions of effective blowing with air.

An approach to the solution of the inverse kinetic problem in the case of complex processes: Part 4. Chemical reaction complicated by diffusion

The complex process comprising chemical reaction and diffusion is analysed by means of the previously proposed approach. It is suggested that such processes be considered as the consecutive reactions representing the formation of the surface layer and the diffusion of gaseous products through it. Using both the model and experimental data, it is shown that the proposed approach identifies the hypothetical scheme of the process, reveals the limits of its proceeding in a kinetic or diffusion regime, and estimates their kinetic parameters.