EFFECT OF RESIDENCE TIME ON PRODUCTS YIELD AND CHARACTERISTICS OF SHALE OIL AND GASES PRODUCED BY LOW-TEMPERATURE RETORTING OF DACHENGZI OIL SHALE

摘要

Oil shale samples from Dachengzi mine located in Huadian city, Jilin province, China, were retorted in a stainless-steel cylindrical retort under argon atmosphere to determine the influence of residence time on the products yield and characteristics of shale oil and gases. It was found that the liquid yield increased with increasing residence time from 6 to 40 min, and then leveled off as the residence time further increased. The gases yield also increased with increasing residence time, while the shale char yield decreased. When prolonging the residence time from 6 to 60 min, the atomic H/C ratio of the derived shale oils decreased from 2.007 to 1.768, both the oxygen and sulfur content also decreased, while the nitrogen content slightly increased. It was also noticed that high boiling point oils were produced in the initial stage of the retorting process and low boiling point oils in its later stages. The shale oil obtained in 20 min had the lowest quantity of heavy fractions, 52.8 wt%, whilst the shale oils produced in 40 and 60 min showed similar boiling point distribution. The produced shale oils had similar atomic H/C ratio and lower heavy oil content compared to crude oils, and could be classified as sweet and high-nitrogen oil in terms of the classification method of crude oil. Extending the residence time decreased the aliphatics content and increased the aromatics content of the produced shale oil. When the residence time was 40 min, the derived oil contained the lowest amount of asphaltenes and the highest amount of non-hydrocarbons. Moreover, the produced gases contained maximum concentrations of C1—C4 gases (except propane) and had the lowest ethene/ethane ratio and the highest propene/propane and butene/butane ratios. The alkene/alkane gases ratio increased from 0.27 to 0.65 with increasing residence time from 6 to 60 min, which reflected the increasing secondary cracking reactions during a longer residence time.