Research on coal-geothermal collaborative exploration system in deep mines

Under the trend of deep mining of coal resources, the problem of high temperature heat damage in mines is becoming increasingly serious, the heat source that causes high temperature heat damage in mines is actually sustainably used geothermal energy, extracting and utilizing geothermal energy from deep mines while mining coal is an innovative way to build green mines and reduce mine carbon dioxide emission. This paper summarizes the current situation of deep mineral and geothermal energy collaborative exploration at China and abroad, analyzes the feasibility in terms of processes and key equipment and finally proposes a system of coal-geothermal collaborative exploration. The system adopts closed cycle mode, including ground heat utilization system and underground extracting system, drilling horizontal holes and installing coaxial casing heat exchangers at the coal to extract the heat, and utilization of the extracted low-grade geothermal energy through the heat pump on ground. Adhering to the principle of “mining heat first and then mining” in terms of time and space coordination, the thermal mining face is divided in front of the mining work in advance, and two modes of sequential and alternating thermal mining are proposed to ensure that the thermal mining process does not interfere with the coal mining process. Analyzed key technologies including spatial collaborative design, coal seam drilling, efficient heat extraction, and intelligent monitoring and control. Conducted underground spatial collaborative design for coal mining and geothermal energy extraction, proposed a coaxial casing heat exchanger layout process based on coal seam water injection. Multiple combinations of quick assembly coaxial casing heat exchangers can be used to achieve efficient heat extraction. Building an intelligent monitoring and control platform and proposed relevant optimization models, building a heat extraction calculation model and propose an intelligent control heat extraction method. Simplify the heat transfer process of coal formations, construct a heat transfer model for heat extraction from coal to calculate and evaluate the heat capacity of the mining face based on its actual situation and the outlet airflow parameters. According to the heat transfer model, the initial temperature of coal, the coal transportation volume, and the outlet air flow temperature through mining face are the key parameters that determine the heat extraction from the coal. The heat extraction is the maximum when the moisture content of the air flow of the working face remains unchanged and the equivalent temperature of the air flow at the outlet of the working face is not higher than 28 ℃. The application of this system will converting heat damage of deep mine to useful resources, which not only solves the problem of heat damage of coal mining, but also realizes the comprehensive utilization of geothermal energy in deep mine.