Date of Award

Spring 5-1-1987

Document Type

Thesis

Degree Name

Master of Science (MS)

Department

Chemical Engineering

Abstract

Combustion of North Dakota Beulah lignite char (82.5 microns) has been studied on a DuPont 951 Thermogravimetric analyser. Three oxygen partial pressures of 5, 10 and 20 % in nitrogen, and seven different temperatures from 598 K to 923 K were utilized in isothermal combustion experiments. Slow pyrolysis at 1023 K for 5 minutes greatly reduced the reactivity of the original char. Temperature had a definite effect on reaction rate and the higher the temperature, the greater the rate. Two distinct reaction zones were observed. At lower temperatures, chemical control dominated with an activation energy of 28 to 34 kcal/gmole, and at higher temperatures, diffusion control dominated with an activation energy of 2.8 to 7.7 kcal/gmole. Oxygen partial pressure had a definite effect on the rate, and as the pressure increased, so did the rate. The order of reaction was also measured and was 0.8 for the chemical control zone and between 0.5 to 0.8 in the diffusion zone. A theoretical model was used to compare with the actual TGA combustion data. It compared well within its limitations. The evolution of volatiles during pyrolysis was also studied. Although the exact composition was not determined, 80 to 90% of volatiles evolved in a temperature range of 530 to 1000 K, with an activation energy of 11.26 kcal/gmole.

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