Research on Effect of Liquid Carbon Dioxide Injection on Three Zones of Coal Spontaneous Combustion Based on the 3-D of Goaf Porosity in CFD Modeling

ABSTRACT

The formation of pores due to the spontaneous combustion of coal in the goaf, as well as the damage to the surrounding rock caused by high-temperature roasting, can lead to surface subsidence and even collapse. In addition, incomplete combustion of coal can result in the production of various harmful gases, which may escape into the atmosphere through these cracks and seriously pollute the air. This pollution can exacerbate topsoil subsidence, degrade soil properties, harm surface vegetation, and contaminate surface water and groundwater. As a solution to these issues, liquid carbon dioxide fire prevention and extinguishing technology are being utilized for theoretical analysis of overburden movement in goaf. A three-dimensional distribution model of porosity in caving areas has been constructed. Based on this model, dynamic changes in temperature field and oxygen concentration field during liquid carbon dioxide perfusion are being explored. The rapid vaporization of liquid carbon dioxide into inert gas within the goaf inhibits coal oxidation and heating by forming an inert belt within its diffusion range. Simulation results indicate that injecting liquid carbon dioxide at a 90° angle into the oxidation zone (where oxygen concentration is 7–12%) at a volume of 750 m3h-1 best balances cost considerations with effective injection in mining goafs. Industrial testing has shown that after 65 h of perfusion, CO gas concentration decreased from 790ppm to 41ppm – proving significant fire prevention effects from liquid carbon dioxide application.

KEYWORDS:

• Coal spontaneous combustion
• porosity
• temperature field
• liquid carbon dioxide
• oxidation zone

Acknowledgements

The authors gratefully acknowledge the financial support from the National Natural Science Foundation of China (5217042662) and on-site technical guidance and treatment of problems from technical staff in Coal and Transportation Industry Management Department, China Energy Investment Group.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Additional information

Funding

The work was supported by the National Natural Science Foundation of China [5217042662].