富油煤原位热解多物理场演化规律数值模拟研究

Numerical simulations of the evolutionary patterns of multi-physical fields during the in-situ pyrolysis of tar-rich coals

【目的】富油煤原位热解是一种具有清洁、高效、安全等优势的煤炭资源新兴利用技术,尚处于起步阶段,多物理场演化规律及关键工艺参数对富油煤原位热解过程具有重要影响。【方法】通过构建耦合流体流动、传热以及化学反应的多物理场数值模型,并与富油煤圆柱煤样热解实验的结果对比分析,以验证多物理场耦合模型的可靠性。根据先导试验条件,采用均质/非均质渗透率模型研究了渗透率、热载体流量以及致裂区高度对热解过程中传热传质的影响。【结果和结论】结果表明,增大渗透率有利于快速生产,对于均质渗透率模型而言,当渗透率为1μm2时热解反应仅需38 d即可完成,建议对煤层进行冲击致裂使得煤层渗透率达到达西级别。而对于非均质渗透率模型,在加热前期增大热载体流量可以提高传质传热速率。热载体流量为0.12 kg/s时,高渗区域热解反应完成仅需12 d左右。后期当中心高渗区域煤热解完成后,反应及渗流速率变慢,提高热载体流量对反应速率的影响较小。实际生产中建议前期选择较大的热载体流量(0.12 kg/s)促进高渗区域快速热解,更快产生焦油;后期可减小热载体流量节省成本。增大致裂区高度可提高热解速率,致裂区高度为6 m时,热解反应仅需130 d左右即可完成。实际应用中需综合考虑冲击致裂成本以及热解时间成本。

[Objective]The in-situ pyrolysis of tar-rich coals,an emerging technology for coal resource utilization characterized by cleanliness,high efficiency,and safety,is still in its initial development stage.This technology is greatly influenced 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 reactions,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 completed in only 38 days under permeability of 1μm2,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 preheating stage can enhance the mass and heat transfer rates.Under a heat-carrier flow rate of 0.12 kg/s,the pyrolysis reaction in the central high-permeability zone was completed in only about 12 days.In the later stage,the reaction and seepage 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.