Thermal Energy Storage Mechanism And Method In Underground Energy-Stored Functional Backfilled Stopes

As one of the most typical green mining technologies,backfilling mining technology has been successfully adopted in mining coal resources,with phenomenal control effects on strata movement,surface subsidence and mining pressure,which also shows obvious technical privileges in keeping underground space stable.Meanwhile,the properties of man-made materials backfilled into the goafs could be selected depending on specific objectives,which provides favorable conditions for multiple development and utilization of underground spaces.Based on the above analyses,the concept of Energy-Stored Functional Backfilling Technology is proposed to combine backfilling technology with underground space utilization in coal mines,which aims to store and extract thermal energy with higher efficiency in underground backfilling stopes.To this end,heat transfer behaviors in underground backfilling stopes,and thermal energy storage and extraction mechanism,are the key scientific problems to be investigated.By developing the Energy-Stored functional backfilling material,revealing thermal energy storage and extraction behaviors,and selecting appropriate thermal energy storage stratigraphy,the following main innovations are achieved:(1)The concept of Energy-Stored Functional Backfilling Technology is proposed to combine backfilling technology with underground space utilization in coal mines,as well as the system configuration and layout of thermal energy storage and extraction in backfilled stopes.By systematically elaborating the technical principle and key technologies in Energy-Stored Functional Backfilling Method,the most influencing parameters on energy injection and extraction performances in underground backfilling stopes is derived.(2)Energy-Stored functional backfilling material is developed by integrating ground control and energy storage functions.The effects of mix proportion parameters,as well as the moisture and stress environment,on the thermal conductivity of backfilling materials are revealed.The prediction model for thermal conductivity of backfilling materials is established based on the experiment results,and the enhancing effects of quartz sand,graphite and steel fiber on thermal conductivity of backfilling materials are investigated.(3)By developing a self-designed platform for testing thermal energy storage and extraction performances in backfilling materials,the experimental studies on the thermal energy storage and extraction behaviors in different scenarios are conducted.The temperatures of outlet water and backfilling materials during heat storage and extraction are monitored to reveal the heat transfer behaviors between fluid in the heat exchange tube and backfilling materials.A numerical model is developed in Fluent and then validated with the experimental results,to investigate the heat storage and extraction characteristics in underground backfilled stopes.By revealing the the effects of thermal conductivities,mass flow rate of fluid and layout of tubes on the thermal energy storage and extraction performances,thermal energy storage and extraction mechanism in underground backfilling stopes is unfolded.(4)Heat transfer model of multilayer rocks-backfill-water during thermal energy storage and extraction in backfilling stopes is established.The analytical solutions to the temperature of multilayer rock strata,energy stored and energy extracted with the periodic temperatures changes in boundary condition is derived by laplace transform method.The relationship between thermal energy extraction and the composition of rock strata is established,from which thermal energy storage stratigraphy selection in Energy-Stored Functional Backfilling Technology is proposed.Based on above studies,the engineering design method of thermal energy storage system in underground backfilled stopes is proposed.There are 113 figures,17 tables and 205 references in this dissertation.