Effects of secondary reaction of primary volatiles on oil/gas yield and quality in oil shale pyrolysis

Abstract

The reaction behaviors of primary volatiles from oil shale pyrolysis were investigated using a two-stage reactor under different in-situ thermal reaction conditions. The reaction parameters of secondary reactor, such as, reactor temperature, atmosphere and residence time, were studied for their effects on the pyrolysis oil/gas yield and quality. The results showed that the reaction temperature had profound influence on the oil and gas yield. The pyrolyzed shale oil and gas yield reduced by 15% and increased by 20% (mass) respectively, with the temperature of 2nd stage reactor increasing from 600 to 650°C under optimized reaction condition of 1st stage. Comparing with nitrogen atmosphere, the liquid oil yield could be enhanced by 5% when steam was added as the reaction atmosphere in the second stage, and the corresponding oil was mainly concentrated in the gasoline and diesel distillations (that is, boiling point <350°C). The GC-MS analysis illustrated that the secondary reaction at the residence time of 0–3 s was mainly pyrolysis while the presence of steam could increase the content of aromatics in the oil and meanwhile suppress the condensation of aromatics. When the residence time was greater than 3–5 s, the secondary reaction was mainly condensation of poly-aromatics, which led to the increase of coke. Meanwhile, the gasoline and diesel oil yield remained stable, and the VGO fractions decreased by about 30%.