Experimental and numerical investigation on the heat and mass transfer performance of tar rich coal in-situ pyrolysis

On ground experiments are conducted firstly to simulate the multi-physics underground pyrolysis of tar rich coal and find out the kinetic parameters of the reaction. And then multi-physics simulation is performed by coupling heat transfer, fluid flow and chemical reactions. Three pyrolysis models are compared and it's found that the convective flow of heat carrier in coal seam plays an important role in heat transfer although the flow velocity is low. Then the effects of permeability, inlet mass flow rate on heat and mass transfer are investigated for two geometric models with homogeneous and inhomogeneous permeability. It's found that increasing the permeability is beneficial for fast production of tar. For the homogeneous permeability model, the pyrolysis reaction can be completed in only 140 days when the permeability is 1000 md while for the non-homogeneous permeability model, increasing the inlet mass flow rate can improve the heat and mass transfer performance only in the early stage when the pyrolysis occurs mainly in the fractured zone with higher permeability. The pyrolysis reaction time when the inlet mass flow rate is 0.174 kg/s is 22 days shorter than that of 0.054 kg/s. But in the later stage the inlet mass flow rate has little effect on the reaction rate and brings about a higher pressure drop. The pyrolysis under different well patterns is also compared and the results indicate that four-well heating and sixwell heating modes can improve the uniformity and the reaction conversion rate with the same total inlet mass flow rate during the same time. For the six-well heating mode, the pyrolysis reaction can be completed in about 100 days, which is 60 days shorter than the single-well heating mode.