Experimental investigation of spontaneous combustion of anthracite controlled by the chemical deposition of two-phase (hydroxide and CO2) aerosols

Abstract

To explore an efficient and sustainable approach to prevent coal spontaneous combustion in underground goaf, chemical deposits produced by a reaction of two-phase aerosols (CO2 and hydroxide) were utilized to prevent the spontaneous combustion of anthracite. A Henan anthracite sample (0.18 mm-0.25 mm) was treated with aerosols continuously. Ba(OH)2-CO2, Ca(OH)2-CO2, Na2SiO3-CO2 and NaAlO2-CO2 aerosols flowed through the surface of the coal sample simultaneously. After 50–55 s, in addition to Ca(OH)2-CO2, white deposits or transparent colloidal deposits appeared and accumulated gradually. After 20 mins, the weight of the produced deposits (dry mass) reached 0.95%-5.10% of the original weight of the samples. According to the results of scanning electron microscope, X-ray diffraction, thermogravimetry and differential scanning calorimetry, physical experiments and quantum chemistry simulations, we inferred that the two-phase aerosols formed dense ultrafine columnar or flocculent coatings on the coal surface. The main components of the deposits were BaCO3, CaCO3, H2SiO3, Al(OH)3, hydrates, etc. The number of residues after the combustion of the coal samples increased by 6.57%-16.12%, and the maximum exothermic peak decreased to 69.0%-86.2% of the raw coal. Ba2+ in the aerosol formed two-ligand, three-ligand and four-ligand complexes with the characteristic structure containing S in the coal samples. It can be concluded that the two-phase aerosols exhibit excellent barrier-crossing ability and a higher inhibitory effect on re-ignition for extinguishing fires.