Migration behavior of typical pollutants from underground coal gasification

The control of groundwater contamination is the key technology in underground coal gasification ( UCG) since the potential contamination risk has become the bottleneck for UCG commercialization. In this study,based on the drilling exploration of a field test of UCG,the samples of coal,char,ash,slag and rock along the drilling boreholes were obtained,then the leaching experiment of samples were performed. Moreover,the migration behavior of the typical pollution indicators,volatile phenols,ammonia nitrogen and COD were analyzed,and the migration path of pollutants was also discussed. The results show that the migration of typical pollutants mainly occurs in the center of gasification zone and their vertical migration along the roof are found. The caving zone and fractured zone in the roof provide the main channel for contaminant migration. The tendency of pollutants migration toward the floor rock through permeation is very low. Near the gasification boundary,no migration path is formed in the roof of the coal seam,and the pollutant migration is not detected. The scientific site selection of the gasification coal field is the most important step for UCG pollution control.