Pyrolysis of low rank Canadian coals

Abstract

A bench scale fluidized bed reactor with a continuous feed rate of 15–30 g/h has been developed to study the flash pyrolysis of coal at atmospheric pressure. The pyrolysis behaviour of four low rank Canadian coals has been investigated at 0.44 s apparent vapour residence time over a temperature range of 500–800°C. Conditions for maximum liquid yield have been determined for each of the coals. Material balances on all products were generally satisfactory. Variation of vapour residence time from 0.2 to 1.4 s showed that the maximum liquid yield was obtained at the minimum residence time. Use of different particle sizes indicated that an optimum size probably exists for a given set of reaction conditions. Use of a hydrogenation catalyst did not increase liquid yields and the nature of the reaction atmosphere had only a minor effect on liquid yields. The H C ratio of both the pyrolysis oil and the char decreased with increasing temperature. The maximum tar yields from lignite can be approximately correlated with the atomic H C ratio of the parent coals.