| Oil shale,as an unconventional oil and gas resource,is an important supplement and alternative to oil and natural gas resources in China.The Jimsar oil shale retort plant is one of the major projects for oil shale development and utilization in China.Investigating the pyrolysis characteristics of Jimsar oil shale and the influence of pyrolysis parameters on the yield and component distribution of shale oil and pyrolysis gas,to obtain the optimal conditions for the retorting process.Meanwhile,exploring the thermal characteristics of gas full circulation retort technology,revealing the flow heat transfer thermal properties and the escape process of different pyrolysis product components in the retort,which can promote the development of Jimsar oil shale retort industry.Hence,this work presented a study of oil shale and gas full circulation retort in the Jimsar region of Xinjiang,exploring the fundamental properties,pyrolysis mechanism and hydrocarbon characteristics of Jimsar oil shale.A CFD（Computational Fluid Dynamics）and DEM（Discrete Element Model）model of the gas full circulation retort,coupled with a heat transfer model and a kinetic model of multi-component product generation,were established to study the flow,heat and mass transfer characteristics of the dry distillation furnace,and to obtain the flow,heat and mass transfer patterns of the circulating gases and the oil shale particles in the retort.The main research contents and findings include:（1）The fundamental characteristics and pyrolysis mechanism of Jimsar oil shale were investigated.The results revealed that the Jimsar oil shale consisted of a layered structure formed by minerals such as quartz,silica-aluminate,carbonate and pyrite,and a strip structure formed by a tight,smooth and porous organic matter with 70.50%aliphatic carbon（dominated by methylene structure）and 29.31%aromatic carbon.The pyrolysis process was complex and occurs in multiple steps,with different reaction mechanism observed at different conversion ranges.The generation models of pyrolysis products（C=C,-CH2,-CH3,CH4,CO,and,CO2）primarily involved chemical reaction models（F2and F3）and diffusion models（D3）.（2）The mechanism of Jimsar oil shale pyrolysis was studied through low-temperature experiments,to examine the effects on the properties of pyrolysis products by three heating parameters,including heating rate,final temperature and residence time.The survey showed that the shale oil derived from Jimsar oil shale was composed of aliphatic and aromatic groups,with the carbon source being methylene-based aliphatic carbon in the oil shale.The relative content of alkanes and alkenes in the aliphatic group accounted for more than 50%of the total content,while the content of aromatics was relatively lower.The content of aromatics increased when there was an increase in the content of alkenes and cycloalkanes within the aliphatic group.Additionally,the increase in all three heating parameters contributes to the formation of aromatics.The maximum yield of shale oil was 6.32 wt%at a final temperature of 520℃,a heating rate of 5℃/min and a residence time of 20 min,and a comprehensive analysis showed that this parameter was the best parameter for oil shale pyrolysis.（3）The influence of particle size（0-5 mm,5-10 mm,10-15 mm,15-25 mm,25-35 mm,35-50 mm）and accumulation height（10 mm,30 mm,50 mm,70 mm）on the component distribution of pyrolysis products was explored.The shale oil and pyrolysis gas may change caused by the reactions of long-chain alkane cracking,cycloalkane aromatization,alkyl side chain breakage of aromatics,monocyclic aromatic condensation,polycyclic aromatic cracking or coking and cycloalkane ring opening may occur at different particle sizes and accumulation heights due to the influence of mass transfer resistance and residence time.It was found that the content of alkane compounds in shale oil was the lowest at particle size 0-5 mm and accumulation height of 50 mm（46.33%and 50.38%）,and showed a trend of decreasing and then increasing with the increase of accumulation height.The pyrolysis gas mainly consists of CH4,CO2,CO,H2,C2H6,C2H4,C3H8,C3H6,C4H10,C4H8,C5H12,C5H10.The temperature,particle size and accumulation height mainly affected the changes of CH4,CO2,H2,C2H6,C2H4,C3H8,and C3H6.（4）A CFD model of 300 t/d gas full circulation retort based on a two-fluid model framework for porous media,coupled with a heat transfer model and multi-component product generation kinetic model,was established to investigate the heat transfer characteristics and the generation process of different pyrolysis product components in the retort.The results showed that the simultaneous application of Gunn gas-solid heat transfer model,solid-phase radiation and gas-phase DO radiation made the error between the numerical simulation results and the actual working conditions less than 15%.The temperature of gas phase and solid phase in the preheating section and retort section were reduced from the wall to the center at the same level.The main pyrolysis area was the upper part of the retorting section where the supporting structure and the retort wall were divided into three areas.The total generation rate of pyrolysis products(Shale Oil,H2O,CH4,H2,CO2,CO,C2H6,C2H4,C3H8,C3H6,C4H10,C4H8,C5H12,C5H10)and the single generation rate showed an irregular V-shaped profile,and the total generation rate at the bottom of the V-shape is greater than 0.14 kg/（m3·s）.（5）A DEM model of the material flow in the gas full circulation retort was established and combined with cold simulation tests to investigate the material flow characteristics.The establishment of a CFD-DEM multi-coupling mathematical model for the gas full circulation retort was proposed to further optimize the flow-heat-mass transfer characteristics in the gas full circulation retort.The results showed that the flow rate of oil shale particles near the wall increased gradually from the wall region to the central region along the radius of the retort due to the frictional effect with the wall.The conical and triangular structure made the oil shale particles heated more evenly in the retort area,increased the frequency of 0-200 N interaction between oil shale particles from 48.38%to 62.78%,and reduced the accumulated contact energy on the central pillar and support structure,thus reducing the wear of refractory brick structure in the retort.Coupled CFD-DEM simulation can visualize the flow and heat transfer pattern of recycled gas and oil shale particles compared with CFD simulation.And the results of the particle flow law in DEM simulation and the temperature of oil shale particles and recycled gas in the retorting section in CFD simulation decreased from the wall to the center at the same level were verified. |
PDF Full Text Request