Low-temperature co-current oxidizing pyrolysis of oil shale: Study on the physicochemical properties, reactivity and exothermic characters of semi-coke as heat generation donor

Abstract

Low-temperature co-current oxidizing pyrolysis is a new oil shale conversion process with low-energy-input and high shale oil recovery. However, due to the extreme complexity of oil shale decomposition, this method is far from being fully understood. In this study, we focus on the evolution characteristics of physicochemical properties and reactivity of semi-coke as heat generation donor, especially trying to further verify the feasibility of the conversion method through the investigation of its exothermic ability. The results show that as the increase of retorting temperature, the increase in pore numbers and the enhancement of pore connectivity make the oil shale with “dense and low permeability” transform to “porous and high permeability”, which will effectively enhance the heat transfer and the migration of pyrolytic products. And the thermal analysis experiments indicates that the reactivity and exothermic characteristics of semi-coke have been significantly weakened with the increase of retorting temperature. Meanwhile, the decline of heat and mass transfer performance caused by the increase of heating rates and sample masses have an obvious negative effect on the reactivity and combustibility of semi-coke. The combustion kinetic study reveals the apparent activation energy of semi-coke gradually increases and the reactivity decreases with the increase of retorting temperature. Though the heat loss caused by retorting is as high as 67.2% (SC500), the heat in semi-coke is still 2.89 times of that required for complete thermal decomposition of oil shale, which provides necessary data support for the further application of this conversion method.