Influence of particle grain size on the yield and composition of products from the pyrolysis of oil shales

Oil shales from two regions of Pakistan have been pyrolysed in a fixed bed reactor in relation to particle grain size. Five size ranges were investigated, <0.5, 0.5-1.0, 1.0-1.7, 1.7-2.8 and 6.0-10 mm. The pyrolysis system consisted of a 200 cm(3) stainless steel fixed bed reactor externally electrically heated. The samples were heated to 520 degrees C at 10 K min(-1) and the oil shale sample was continuously purged with nitrogen to remove the pyrolysis products from the reactor and to minimise secondary reactions. The gases were analysed for their content of CO, CO2, H-2, CH4 and other hydrocarbons up to C-4. The derived pyrolysis oil was condensed in a series of cold traps and the total oil yield determined. In addition, experiments were carried out on a thermogravimetric analyser using the three smallest particle grain sizes under identical heating conditions to the fixed bed reactor. It was found that increasing the particle size up to the largest size used of 10 mm resulted in an increase in oil yield. The total gaseous yield was decreased, reflecting a decrease in concentration for H-2, CO, CO2 and the majority of the hydrocarbon gases. The raw oil shale samples of various particle size ranges were analysed to determine the elemental composition and surface area to determine their influence on the compositional changes in oil and gaseous yield with particle size range. (C) 1998 Elsevier Science B.V. All rights reserved.