Very rapid coal pyrolysis

• Published in: Fuel (Guildford) 1986-02, Vol.65 (2), p.182-194
• Main Authors: Solomon, Peter R., Serio, Michael A., Carangelo, Robert M., Markham, James R.
• Format: Article
• Language: English
• Subjects: Applied sciences; coal; Constitution and properties of crude oils, shale oils, natural gas and bitumens. Analysis and characteristics; Crude oil, natural gas and petroleum products; Energy; Exact sciences and technology; FT-i.r; Fuels; pyrolysis
• ISSN: 0016-2361; 1873-7153
• DOI: 10.1016/0016-2361(86)90005-0

Considerable controversy exists concerning the rate of coal pyrolysis. At 800 °C, the reported rates derived using a single first-order process to define weight loss vary from < 1 s −1 to ≈ 100 s −1. In an attempt to resolve this controversy, a new pyrolysis experiment has been designed which allows direct measurement of coal temperature and reaction time. It uses a small-diameter electrically heated tube into which coal and helium are injected. The reaction distance is varied by moving the electrode positions. Temperature is measured inside and outside the tube with a thermocouple. Temperatures of the solids are determined at the tube exit using FT-i.r. emission and transmission spectroscopy. The transit time for a pulse of coal is measured using phototransistors at the top and bottom of the tube. Particle velocities are also determined using FT-i.r. transmission. Measurements have been made on sieved size fractions of a North Dakota lignite, Rosebud subbituminous coal and Illinois No. 6 bituminous coal in tubes up to 240 cm long at asymptotic tube temperatures of 600, 700, 800 and 935 °C. At 800 °C, primary pyrolysis was completed in a period of 14 ms, during which the maximum coal temperature was increasing from 600 to 740 °C. The results are in good agreement with a previously developed functional-group model of coal pyrolysis which employs a distribution of activation energies to describe the evolution of individual pyrolysis species. The results are also in reasonable agreement with predictions of a single first-order model for weight loss which uses a rate constant k = 4.28 × 10 14 exp(−228 500/ RT) Jmol −1 s −1. This rate, which is over 1000 s −1 at 800 °C, is inconsistent with the low rates. Reasons for discrepancies in reported rates are discussed.