Study On Apparent Viscosity Characteristics Of Gas-solid High-density Separation Fluidized Bed And Low-quality Oil Shale Upgrading

With the increasing energy demand and the consumption of conventional energy sources such as coal and oil,the development and utilization of oil shale have become a research hotspot in the past few decades.However,due to the structure of oil shale and its resource distribution characteristics,conventional wet separation technology has been greatly limited in the oil shale separation.Air dense medium fluidized bed dry separation technology is a method of waterless separation of minerals,which has good application prospects in arid and water-deficient areas and provides the possibility for oil shale desilication and upgrading.However,unlike coal,the fluidized separation of low-quality oil shale belongs to the category of high-density separation.With the increase of separation medium density,the apparent viscosity becomes a key issue in fluidized separation,and its impact on the separation performance of the fluidized bed and mineral separation becomes the main contradiction.Therefore,in this study,ferrosilicon powder and oil shale particles were used as binary dense media to investigate the fluidization characteristics and the spatial distribution of apparent viscosity in gas-solid high-density fluidized bed,and a mixed dense media apparent viscosity control mechanism was constructed.Based on the above research,the effects of various factors on the mineral separation of low-quality oil shale were explored,laying a foundation for efficient separation and upgrading of low-quality oil shale.In response to different media compositions,the mixing effects of high-density binary media were investigated,and the optimal ratio of different-sized oil shale particles was obtained.The results show that the mixing behavior of Geldart D oil shale particles is better than that of Geldart B oil shale particles.The critical fluidization velocity of different binary media compositions was determined,and the variation characteristics of the critical fluidization velocity with the particle properties of the binary mixing media were discussed.Based on this,the spatial distribution characteristics and stability of bed density were studied in depth,revealing the density control performance of high-density fluidized beds and expanding the bed density control range of gas-solid high-density fluidized beds to 2.2-3.1 g/cm~3.In addition,the expansion and collapse of the bed were investigated through bed expansion and collapse experiments to explore the expansion law and phase distribution characteristics of the high-density media system.The influence of gas velocity,particle properties and composition of the media,and bed spatial position on the bed apparent viscosity was explored in detail using the rotation method,and the spatial distribution characteristics of the apparent viscosity were investigated.The results showed that the particle properties and composition of the medium had a significant impact on the uniformity and stability of the apparent viscosity spatial distribution,and an increase in the mass fraction of oil shale and fluidization velocity intensified the instability of the apparent viscosity spatial distribution.In addition,as the bed height increased,the standard deviation of the apparent viscosity radial distribution increased from 0.02 Pa·s to 0.05 Pa·s.Based on the binary heavy oil mixing behavior and the spatial distribution characteristics of the apparent viscosity in high-density media,it was determined that the optimal mass fraction of Geldart D and Geldart B oil shale should be less than 12%and 4%,respectively.The control performance of bed apparent viscosity in high-density medium systems was investigated,and a mechanism for controlling apparent viscosity in gas-solid high-density fluidized beds was constructed.The control range of bed apparent viscosity in gas-solid high-density fluidized beds was expanded to 0.425 Pa·s-1.781Pa·s.Based on the spatial distribution characteristics and stability of bed apparent viscosity,low and high apparent viscosity regions were determined.The bed apparent viscosity in the low apparent viscosity region exhibited high stability and low sensitivity to changes in fluidization velocity.The high apparent viscosity region covered a range of oil shale content greater than 12%and showed more pronounced fluctuations in apparent viscosity.Based on the two-phase theory of gas-solid fluidized beds and combined with experimental data,a prediction model for the gas phase bubble volume fraction in gas-solid high-density fluidized beds was corrected.The model prediction is in good agreement with experimental results,with a Pearson correlation coefficient of 0.9877.On this basis,a prediction model for the apparent viscosity of gas-solid high-density separation fluidized beds was constructed.When the mass fraction of oil shale is less than 12%,the model prediction error is controlled within±10%,indicating excellent prediction accuracy of the model.Based on the mechanism of controlling the apparent viscosity in binary dense media mineral fluidization,experiments were conducted on the separation of low-quality oil shale,exploring the effects of feed particle size and apparent viscosity on the separation efficiency of low-quality oil shale.The results showed that the apparent viscosity significantly affects the separation efficiency and effectiveness of oil shale minerals.Under low apparent viscosity conditions,the role of bubbles in the settling behavior of small-sized minerals became significant.When the bed apparent viscosity was 1.781 Pa·s,the settling time of the three sizes of oil shale minerals not only increased significantly but also could not be completely separated.The possible deviation of the separation of low-quality oil shale decreased first and then increased with the increase of fluidization velocity and increased with the decrease of the feed particle size of oil shale.For-50+6 mm low quality oil shale minerals,the best possible separation deviation value is 0.060 g/cm~3,the fine mineral yield is 40.71%,and the oil content is 9.56%.The dissertation consists of 74 figures,8 tables,and 134 references.