Extraction and resource utilization of heat and humidity in mine ventilation

Massive low-grade thermal energy and water vapor are stored in the hot and humid airflow of mines, typically resulting in a poor underground working environment and posing threats to worker safety and health. The direct discharge of exhausted ventilation air causes an enormous waste of resources as well as pollution problems to the surrounding environment. Therefore, the extraction and utilization of mine ventilation heat and humidity have become some of the most important ways to solve thermal damage problems in deep mines, thereby boosting their low-carbon transformation development. Affected by the changes in the surface atmospheric and downhole heat and humidity sources, the hot and humid airflow parameters in mines change with time. Real-time determination of the hot and humid airflow characteristics in mines is key to extracting low-grade thermal energy from the underground environment efficiently. In this paper, the distribution law and variation characteristics of key heat and humidity joints are determined based on the real-time calculation of the hot and humid air network. A calculation model of condensation heat and humidity extraction is established, and the technology of low-grade condensation waste heat extraction from heat and humidity airflow is also developed, which, in composition, forms a low-grade heat in situ utilization system combined with refrigeration and dehumidification. Furthermore, the centralized and distributed thermal and humidity extraction and resource utilization methods of coal mine ventilation are put forward. The effects of heat extraction and water recovery are also analyzed using examples. The results show that around 224 t of moisture is wasted every day in ventilation air emission, whose recycling has economic benefits. Thousands of kilowatts of thermal energy are stored in the ventilation air emission, which can be used as direct heat energy or converted electricity. An approximately linear relationship is revealed between the temperature decrease and theoretical moisture recovery from ventilation air emission, providing a rapid way for engineering estimation. The analysis of the heat recovery shows that heat extraction is favored by high initial temperature and humidity due to high values and efficiencies. The application of heat–moisture recovery in underground nodes can effectively moderate the in situ working environment and simultaneously recover some energy as a supply to running costs. This work provides significant construction ideas and a theoretical basis for the extraction and utilization of low-level thermal energy and heat damage control in mines.