Shuyuan Li

Pyrolysis characteristics of a North Korean oil shale

Pyrolysis characteristics of a North Korean oil shale and its pyrolysates were investigated in this paper. The pyrolysis experiments were conducted below 600 °C at a heating rate of 10, 15, 20 and 25 °C/min, respectively. The kinetics data were calculated using both integral and differential methods with the assumption of first order kinetics. The results show that the averaged oil content of the North Korean oil shale is about 12.1 wt% and its heat value is 13,400 kJ/kg. The oil yields at different retorting temperatures show that the higher the retorting temperature the greater the oil and retorting gas yields. The optimal retorting temperature for the North Korean oil shale is about 500 °C. The properties of the North Korean shale oil including density, viscosity, flash point and freezing point are found to be relatively low compared with those of shale oil from FuShun, China. The gasoline fraction, diesel fraction and heavy oil fraction account for 11.5 wt%, 41.5 wt% and 47 wt%, respectively. The major pyrolysis gases are CH4 (the most abundant), H2, CO2, H2S, CO, and C2–C5 hydrocarbons. The heat value of retorting gas is more than 900 kJ/mol, and the retorting gas has high sulfur content.

Heat transfer of oil shale in a small-scale fixed bed

Heat transfer experiments on Longkou oil shale were carried out in a fixed-bed reactor. Temperatures at different positions in the reactor were determined. With increasing heating rate, the temperature difference between center and exterior of the reactor increased, the time needed to get to constant temperature decreased, while the time needed to reach final pyrolysis temperature decreased. A pseudo-homogeneous one-dimensional heat transfer model was developed, and analytical expressions were obtained on the basis of mathematical derivation. It was found that the coefficient of heat conductivity is a polynomial function of temperature. The Longkou oil shale could be seen as a poor heat conductor because of its low coefficient of heat conductivity. Usually, there are many factors to affect coefficient of heat conductivity, including the composition, density, moisture content, temperature, particle size and particle size distribution. Reasonable values of heat conductivity in different temperature ranges were determined using the developed model. The calculated results using heat transfer model for Longkou oil shale are reasonably agreed with actually measured temperature.

Reaction mechanism and kinetics of pressurized pyrolysis of Chinese oil shale in the presence of water

A study of reaction mechanisms and chemical kinetics of pressurized pyrolysis of Chinese Liushuhe oil shale in the presence of water were conducted using an autoclave for simulating and modeling in-situ underground thermal degradation. It was found that the oil shale was first pyrolyzed to form pyrobitumen, shale oil, shale gas and residue, then the pyrobitumen was further pyrolyzed to form more shale oil, shale gas, and residue. It means that there are two consecutive and parallel reactions. With increasing temperature, the pyrobitumen yield, as intermediate, first reached a maximum, then decreased to approximately zero. The kinetics results show that both these reactions are first order. The activation energy of pyrobitumen formation from oil shale is lower than that of shale oil formation from pyrobitumen.

Internal heat transfer characteristics of large-particle oil shale during pyrolysis

A 2D cylinder transient heat transfer model was developed for single-particle oil shale pyrolysis in the fixed-bed reactor. Variations of physical properties of oil shale were considered in this model. The developed model was solved using ANSYS after determining boundary conditions. And then intraparticle temperature distribution was obtained during oil shale pyrolysis. Moreover, effects of particle size and heating rate on intraparticle temperature distribution were investigated. The radius of 30-mm oil shale and pyrolysis time were divided into ten equal intervals to calculate temperature at any time and any position during the sample pyrolysis. The calculated results reasonably agreed with actually measured temperature.