Noncatalytic gas-solid reactions in a vertical pneumatic transport reactor

Abstract

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 ...