Development of an in-situ gel from CO2-captured complex solution and inhibiting coal spontaneous combustion: A case study in thermal engineering

Abstract

The safety of underground coal mining is threatened by coal spontaneous combustion, making it essential to develop effective inhibitors to prevent such incidents. To address this, a new in-situ gel has been proposed, which is formed in coal pores from a fire-prevention aqueous solution (FPAS) that reacts with atmospheric CO2. To determine the appropriate concentrations of polyvinyl alcohol (PVA) and sodium-metasilicate nonahydrate (SN) for FPAS, 24 groups of wire-mesh basket tests were conducted on Baiyinhua coal. The gelling mechanism and performance on fire inhibition of FPAS were then investigated using temperature-programmed tests, scanning electron microscopy, energy dispersive spectrometry, fourier transform infrared tests, thermogravimetric differential thermal analysis tests, and fire-extinguishing tests. The results indicate an inhibition rate of up to 43.3% and effective protection of active groups from oxidation. The in-situ gel demonstrated excellent fire-extinguishing properties. Additionally, the self-ignition temperatures of residual coals with varying thicknesses were estimated using the Frank-Kamenetskii theory. The combined method of CO2 injection and FPAS spraying is recommended for achieving better fire-prevention effectiveness in coal mine gob. The findings are expected to provide guidance on the application of FPAS to address thermal hazards in coal mines.