Numerical simulations of the evolutionary patterns of multi-physical fields during the in-situ pyrolysis of tar-rich coals
[Objective]The in-situ pyrolysis of tar-rich coals,an emerging technology for coal resource utilization char-acterized by cleanliness,high efficiency,and safety,is still in its initial development stage.This technology is greatly in-fluenced by the evolutionary patterns of multi-physical fields and critical process parameters.[Methods]A numerical simulation model involving multi-physical fields was established by coupling fluid flow,heat transfer,and chemical re-actions,and its reliability was verified by comparing the numerical simulation results with the pyrolysis experimental results of cylindrical coal samples.Based on the pilot test conditions,the impacts of permeability,heat-carrier flow rate,and fracture zone height on the heat and mass transfer in the pyrolysis process were investigated using homogeneous and`heterogeneous permeability models.[Results and Conclusions]The results indicate that increasing the permeability can facilitate the rapid production of coals.For the homogeneous permeability model,the pyrolysis reaction can be com-pleted in only 38 days under permeability of 1 μm2,and impact-induced fracturing is recommended to achieve coal seam permeability of a Darcy level.For the heterogeneous permeability model,increasing the heat-carrier flow rate in the pre-heating stage can enhance the mass and heat transfer rates.Under a heat-carrier flow rate of 0.12 kg/s,the pyrolysis reac-tion in the central high-permeability zone was completed in only about 12 days.In the later stage,the reaction and seep-age rates decelerated as the pyrolysis of coals in the central high-permeability zone was completed,and increasing the heat-carrier flow rate produced minor impacts on the reaction rate.Therefore,it is recommended that a high heat-carrier flow rate(0.12 kg/s)be adopted in the early production stage to accelerate the pyrolysis in the high-permeability zone and produce tar more quickly and that the heat-carrier flow rate be reduced in the later stage to save costs.Increasing the fracture zone height can enhance the pyrolysis reaction rate.With a fracture zone height of 6 m,the pyrolysis reaction can be completed in about 130 days.Additionally,it is necessary to consider the costs of impact-caused fracturing and pyrolysis time in actual production.
tar-rich coalsin-situ pyrolysisnumerical simulationmulti-physical field
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