Enhanced pyrolysis of Huadian oil shale at high temperature in the presence of water and air atmosphere

The liquid water injected at a high temperature combined with oxygen pyrolysis of oil shale is firstly studied. The pyrolysis was conducted at different temperatures and water to oil shale mass ratios (W/OS) in a self-reformed Fischer Assay retort under an air atmosphere to identify the effect of water on the distribution and characteristics of the oil shale products. The shale oil yield at a W/OS ratio of 0.5:10 was higher than that of the no water case under an air atmosphere and the highest yield was approximately 450 °C. With the same shale oil yield as that obtained from the Fischer Assay, the pyrolysis temperature decreased by approximately 78 °C with a W/OS of 0.5:10 under an air atmosphere. Pyrolysis of oil shale with different W/OS ratios significantly increased the shale oil yield from 17.03% to 20.00% and decreased the semicoke yield from 68.42% to 68.20% with an increasing W/OS from 0:10 to 1.5:10 under an air atmosphere at 450 °C. As the W/OS increased to 0.75:10, the alkane and alkene contents increased, while the aromatic hydrocarbon content decreased. Water increased the content of the heavy fractions in the shale oil by weakening the adsorption of macromolecular compounds on the minerals and prompting oil migration. The presence of water slightly increased the H/C and S contents in the shale oil but reduced the content of N. The effect of water on the distribution and characteristics of the products was caused by multiple control mechanisms in the pyrolysis process, including chemical, migration, the interaction with oxygen effect. • The high-temperature injecting water reduced the pyrolysis temperature. • The water significantly increased the shale oil yield from 17.03% to 20.00%. • The water injected at high temperature increased the heavy fractions and aliphatic hydrocarbon in the shale oil. • The possible mechanisms of water enhancing oil shale pyrolysis were discussed.