Effect of heating rate on products yield and characteristics of non-condensable gases and shale oil obtained by retorting Dachengzi oil shale

Abstract

Oil shale samples from Dachengzi mine located in Huadian city, Jilin province, China, were retorted in a stainless-steel cylindrical retort at a heating rate varied from 5 to 20 °C min-1 up to a final temperature of 520 °C under argon atmosphere. The influence of heating rate on the products yield and characteristics of shale oil and non-condensable gases was determined. It was observed that the shale oil yield first increased and then slightly diminished as the heating rate increased. The maximum shale oil yield was found to be 15.696 wt.% at a heating rate of 12 °C min-1. The non-condensable gases yield increased with increasing heating rate. There was a corresponding decrease in the shale char yield. The carbon and nitrogen weight contents of the derived shale oil increased with increasing heating rate, while those of hydrogen and oxygen decreased. The sulfur weight content was not significantly affected by increasing the heating rate. As the heating rate increased from 5 to 20 °C min-1, the atomic H/C and O/C ratios of the derived shale oil decreased from 1.918 to 1.727 and from 0.116 to 0.048, respectively. Compared to crude oils, the produced shale oil had a higher atomic O/C ratio and a similar atomic H/C ratio, as well as a higher light oil content, which showed that the properties of shale oil were superior to those of crude oil. The liquid shale oil could be classified as a sweet and high nitrogen oil in terms of the classification method of crude oil. Increasing heating rate decreased the content of saturates and aromatics and increased that of light oil, asphaltenes and non-hydrocarbons of the produced shale oil. The non-condensable gases contained high amounts of CH4 and minor concentrations of C2-C4 hydrocarbons. Increasing heating rate shifted the maximum concentration of C1-C4 hydrocarbons to higher temperature and increased the total content of C1-C4 hydrocarbons. The alkene/alkane gaes. ratio decreased from 0.45 to 0.29 with increasing the heating rate from 5 to 20 °C min-1 which was linked to secondary reactions. The lower alkene/ alkane gases ratio was possibly because the coking reactions dominated at higher heating rate. © 2013 Estonian Academy Publishers.