The law of pollutant enrichment and migration in underground coal gasification in Wangcun mine

In order to understand the aggregation and migration of pollutants in the process of underground coal gasification, as one of the bases for assessing the impact of underground gasification methods on the ecological environment, a model test was carried out on the underground gasification of meager lean coal in Wangcun Coal Mine, and a gasification model test bench was built to simulate the actual underground gasification process. In order to study the precipitation of pollutants, the contents of COD, ammonia nitrogen and volatile phenols under different oxygen concentrations were determined by dichromate method, Nessler reagent spectrophotometry and direct spectrophotometry, The results show that when the oxygen concentration is higher than 60%, the emission of pollutants decreases with the increase of oxygen concentration. When the oxygen concentration is 80%, the concentration of volatile phenols, ammonia nitrogen and COD are 105 mg / L, 2.09×103 mg/L and 1.11×104 mg /L respectively; In order to study the migration law of pollutants, the permeability coefficient of water in the bottom slate layer under different temperatures was determined by the RTR-1000 high temperature and high pressure comprehensive rock test system. The results show that the permeability coefficient of water in floor rock is 4.4169×10-8 cm/s at room temperature, 5.023 8×10-7 cm/s at 100 ℃; the permeability coefficient of gas in floor rock is between 1.373×10-9 and 1.059×10-8 cm/s at room temperature and 500 ℃; After that, the experimental data and geological and coal quality parameters obtained before are taken as boundary conditions and parameters and use Visual Modflow 4.1 to simulate the pollutant migration which the simulation calculation period is 50 years. The results show that the pollutant migration mainly occurs within 10 years after gasification. The maximum area of pollutant migration is 3 515.73 m2, the horizontal maximum migration distance is 10.3 m, the vertical diffusion distance is 5.4 m, and the vertical maximum penetration depth of pollutant to the floor is 1.37 m.