Progress and technology of underground coal gasification

The research history of underground coal gasification(UCG) at home and abroad is introduced. The charac- teristics and research results of UCG technology are summarized. The technological problems and application prospects are presented. The results show that during more than 100 years’ development and research,three types of UCG tech- nologies have been developed including:① Long-wall airflow gasification technology,which the inlet and outlet points are fixed,locating at both ends of the gasification channel,one well for air inlet and the other well for gas outlet. The airflow velocity is used to control the movement of the gasification working surface. ② Osmotic gasification technology, which uses natural or artificial fissures in the coal seam as the gasification channel. ③ Controlled retraction injection point(CRIP)gasification technology,which the injection air pipe is set in the gasification channel,and continuous or intermittent retracement of injection pipe is used to realize the continuous or intermittent backward movement of the injection air point. However,the UCG technology has not yet achieved large-scale industrialization,and it is necessary to further strengthen basic research and technological development. The basic researches should include geological evalu- ation,combustion,pyrolysis,gasification,the penetration characteristics of solid coal seams and evolution of character- istic fields in gasification process,the thermal properties change and caving of coal seam overlying rock mass under high temperature,and the enrichment and migration law of UCG pollutants in the cavity. The technologies should in- clude the underground gasifier structure and construction of large-scale production,the continuous stability control of UCG,the control equipment of injection air point movement,UCG safety,pollutant monitoring,cavity management,low- cost fire area detection and gasification process analysis,and UCG multi-production. UCG technology can recover aban- doning coal resources in old coal mines and exploit deep coal resources,which is of great strategic significance for en- suring energy security.