Diffusivity of porous-oxide-gel?Derived catalyst particles

The reduction of iron oxide fines to wustite between 590°C and 1000°C with a CO-CO 2 gas mixture of low reducing potential was studied. The reduction kinetics and the dominating reaction mechanism varied with the temperature, extent of reduction, and type of iron oxide. Reduction from hematite to wustite proceeded in two consecutive reaction steps with magnetite as an intermediate oxide. The first reduction step (hematite to magnetite) was fast and controlled by external gas mass transfer independently of the oxide type and the temperature employed. The second reduction step (magnetite to wustite) was the overall reaction-controlling step, and the reduction mechanism varied with the temperature and the oxide type. Moderately porous oxide fines followed the uniform internal reaction for the temperature range studied. For highly porous oxides, the second reduction step was controlled by external gas mass transfer above 700°C. Below that temperature, a mixed regime that involves external gas mass transfer and limited mixed control, which comprises pore diffusion and chemical reaction, takes place. The rate equations for this mixed control reaction mechanism were developed, and the limited mixed control rate constant (k lm ) was computed. For denser oxides under uniform internal reaction, the product of the rate constant and pore surface area (kAES) was calculated.

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“…D e can be estimated roughly by the correlation of Weisz and Schwartz [30] in which only molecular diffusion (D m ) is taken into account.…”

Section: Apparent Reaction Rate Constantsmentioning

confidence: 99%

Reduction of Iron Oxide Fines to Wustite with CO/CO2 Gas of Low Reducing Potential

Corbari

Fruehan

2009

Metall Mater Trans B

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“…• 3.0 for a network of randomly interconnected uniform diameter cylindrical pores with no dead ends (Johnson and Stewart, 1965). • 5.0 ( = √ 3/ P ,macro ) for an array of cells that are visualised as cubes or spheres with a fraction P ,macro of their surface open to the neighbouring cell (Weisz and Schwartz, 1962).…”

Section: Discussion On the Magnitude Of Each Intrapellet Structural Pmentioning

confidence: 99%

Macropore diffusion dusty-gas coefficient for pelletised zeolites from breakthrough experiments in the O2/N2 system

Todd

Webley

2005

Chemical Engineering Science

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“…It is a complex entity constantly changing with variations in the characteristics of the pore network such as pore shape, pore size, and pore size distribution, and with variations in the physical conditions such as temperature and pressure. For gaseous diffusion in porous particle, experimental studies have revealed that the ratio of effective diffusivity to ordinary diffusivity, is changed proportional to c 1 3 when bulk diffusion is predominate (Currie, 1960) and proportional to €2-3 when Knudsen diffusion is predominant (Weisz and Schwartz, 1962). Furthermore, the micropore model (Wakao and Smith, 1962) asserts that the effective diffusivity is proportional to €2 if the existence of micropores prevails in the system.…”

Section: The Modelmentioning

confidence: 96%

Noncatalytic gas‐solid reactions in a vertical pneumatic transport reactor

et al. 1984

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A heterogeneous model is developed to account for noncatalytic gas-solid reactions in a vertical pneumatic transport reactor. The model takes into consideration both the positive and negative variations of the solid porosity and the variation of the gas diffusivity with the reaction. The method of lines utilizing the second order centered finite difference scheme for the spatial discretization is employed fo obtain the model solution.Experiments utilizing a vertical pneumatic transport reactor of a laboratory scale are performed to study the reaction between limestone and sulfur dioxide generated from coal combustion. The reactor is of 16.2 cm ID and 610 cm in length. The experimental data for sulfur retention are reported for various superficial gas velocities and calcium-sulfur molar ratios. Verification of the model with experimental data is conducted. The agreement between the model prediction and experimental data is satisfactory. LIANG-SHIH SCOPEThe vertical pneumatic transport reactor has been widely utilized for catalytic fluid reactions and noncatalytic fluid-solid reactions. Reported modeling efforts on the reactant conversion in the reactor have been mainly concerned with the catalytic fluid reactions. Little modeling effort, however, has been placed on the noncatalytic fluid-solid reactions in the reactor. Furthermore, little experimental information is available on the reactor performance for either catalytic fluid reactions or noncatalytic fluid-solid reactions in the literature.In this paper, a heterogeneous model for a noncatalytic gassolid reaction in the vertical pneumatic transport reactor is developed. The model takes into account the empirical correlations for the hydrodynamic properties, gas-film diffusion around the solid particle and variation of the gas diffusivity in the particle during the reaction. The effects of various operating parameters of the reactor on the reactant conversion are analyzed. Experiments utilizing a vertical pneumatic transport reactor are also carried out to study the noncatalytic gas-solid reaction. The reaction selected for the study is the sulfation reaction between limestone and sulfur dioxide which is generated from coal combustion. Model verification with the experimental data is conducted. CONCLUSIONS AND SIGNIFICANCEA heterogeneous model for a noncatalytic gas-solid reaction in the vertical pneumatic transport reactor is developed. Numerical simulation is made of the effects of various operating parameters on the conversion of the gas and solid reactants. The results indicate that the gas reactant conversion increases with the increase of the solid flow rate, the decrease of the gas superficial velocity, and the increase of the reaction rate constant. Increasing the particle diameter would either increase or decrease the gas reactant conversion, depending on the rate of diffusion in the particle.Experiments are conducted using a 16.2 cm ID and 610 cm in length vertical pneumatic transport reactor in which limestone is reacted with SO2 generated from coal ...

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Diffusivity of porous-oxide-gel?Derived catalyst particles

Cited by 89 publications

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Reduction of Iron Oxide Fines to Wustite with CO/CO2 Gas of Low Reducing Potential

Reduction of Iron Oxide Fines to Wustite with CO/CO2 Gas of Low Reducing Potential

Macropore diffusion dusty-gas coefficient for pelletised zeolites from breakthrough experiments in the O2/N2 system

Noncatalytic gas‐solid reactions in a vertical pneumatic transport reactor

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