Date of Award

1982

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Chemical Engineering

Abstract

The effect of variable solid properties on the kinetics of the reaction of spherical calcium oxide pellets with nitrogen dioxide (in the presence of excess oxygen) was studied. Experimental kinetic data was collected on a thermogravimetric analyzer, which measured weight change in a single pellet during reaction as a function of time. Reactions were carried out at temperatures of 150(DEGREES) to 550(DEGREES)C for gas streams containing 0.5 to 1.8 mole percent nitrogen dioxide and 8.7 mole percent oxygen. No reaction occurred at 600(DEGREES)C. At 150(DEGREES) and 250(DEGREES)C the conversion was found to proceed at a slow but steady rate with overall fractional conversions less than 0.15 after one hour of reaction time. At higher temperatures (350(DEGREES), 450(DEGREES), and 550(DEGREES)C) severe reaction die-off was observed with die-off fractional conversion increasing with temperature. A variable property grain model (VPGM) which allowed for radial solid property variations due to reaction was used to analyze the experimental data. Four resistances were considered in the model: external mass transfer, pore diffusion, grain diffusion, and intrinsic chemical reaction. Parameters characterizing mass transfer, pore diffusion and chemical reaction were developed from literature correlations and independent measurements so that only a single parameter, the grain diffusion coefficient, had to be determined by numerical analysis. The experimental time-conversion data was compared to the predictions of both the constant property grain model (CPGM) and the VPGM. At 150(DEGREES) and 250(DEGREES)C, the CPGM and VPGM were approximately equal in matching experimental data. However, at 350(DEGREES) and above, the VPGM was vastly superior since the CPGM cannot predict reaction "die-off". The predictions of VPGM were further improved by modifying the expression for the particle effective diffusivity employed in the model.

Pages

419

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