The Process Regulation And Mechanism Analysis Of Oil Shale Pyrolysis For Producing High-quality Oil And Gas

Oil shale is an unconventional solid fossil fuel with a vast resource reserve.Pyrolysis can extract the inherent oil and gas components containing in oil shale,which is the core technology for high-value utilization of oil shale resource.Improving the yield and quality of pyrolysis oil is important for the development of pyrolysis process.Experiments and industrial applications have found that the pursuit of pyrolysis oil yield often leads to lower quality and more difficulties for subsequent oil processing.In this paper,the factors such as reaction temperature,reaction atmosphere,residence time,additives and other factors affecting oil yield and quality are investigated.Based on the basic analysis of the secondary transformation law of primary pyrolysis products from oil shale,the reaction mechanism and control scheme were deduced.The thermogravimetric analyzer was first used to determine the suitable temperature for oil production,finding that 450-650?was chosen for the oil shale pyrolysis.Fixed bed reaction device was then used to get the appropriate reaction temperature?i.e.,600??for fast pyrolysis,with the carrier gas velocity to be 1 L/min.The water vapor and inert quartz sand were used as two-stage gas and bed materials respectively when the effect of water vapor on the transformation of secondary reaction under different temperature and residence time was studied.The analysis results illustrated that the secondary reaction was mainly cracking at the residence time of 0³s while the presence of steam could increase the content of aliphatic hydrocarbons in the oil and meanwhile suppressed the condensation of aromatics.When the residence time was greater than 3⁵s,the secondary reaction was mainly condensation of poly-aromatics.Meanwhile,the gasoline and diesel oils yield remained stable,and the VGO fractions decreased by about 30%.When further studying different additives as bed materials in the 2^nd stage,the results showed that in comparison with FCC catalyst,the shale ash possessed relatively moderate activity for adjusting the secondary reaction of pyrolysis volatiles in the applied range of residence time.In general,the liquid yield of oil shale pyrolysis over shale ash was about1.8 times?by mass,the same hereinafter?as that of FCC catalyst.Using steam as the reaction atmosphere could further enhance the liquid yield by 5%and meanwhile suppressed the C2^C3 hydrocarbons in the cracked gas.The heavy oil fractions,such as vacuum gas oil?VGO,>350??,could be converted into light oil fractions via the catalytic effects of shale ash,and correspondingly the boiling range of pyrolysis oil tended to be lighter with higher residence time.The mechanism of secondary transformation was thus proposed and the corresponding control result was derived via evaluating the coupling effects of different carrier gas,additives and residence time,which could also provide some reference for the actual process design.The combustion characteristics of ex-situ and in-situ char were finally investigated using the thermogravimetric analyzer.The results showed that when the oxygen concentration decreased from 20%to 5%,the activation energy of ex-situ char was reduced by nearly 18%.It means that the oxygen concentration has a significant influence on the combustion process of char.Comparing with the activation energy of ex-situ char combustion at 5%oxygen concentration,we found that combustion activation energy of in-situ char can be significantly reduced by 32%.It thus justified that the higher reactivity of in-situ char can promote the process of char combustion and utilization.