Preparation and characteristic study of the hydrogel of coal spontaneous combustion environmental protection

•A new environmental protection gelling scheme was proposed and tested.•PVA, SA, TE and HB constitute a double crosslinked gel to improve stability.•Gel time is controllable, with high water retention and super-absorbency.•The addition of shell powder to the gel increases the flame-retardant effect.•Both low-temperature and high-temperature have good inhibition effect. In order to solve the problem of spontaneous combustion of coal in mined-out areas, a new type of P/S/T/H environmentally friendly hydrogel was designed by using polyvinyl alcohol, sodium alginate and di(triethanolamine) titanate diisopropyl to form a gel system and adding the environmentally friendly material hybrid shell bio-filler. The formulation of P/S/T/H gel was studied by orthogonal experiment, and the forming time was precisely controlled. The synthesis mechanism and flame-retardant properties of the gels were investigated by various experimental methods. The results show that: There are folds and three-dimensional pore structures inside the P/S/T/H gels, and the two cross-linked networks strengthen the stability of the gels. Compared with WG gel and single cross-linked network gel, P/S/T/H gel has the best water retention, water absorption/salt resistance and flame-retardant effect. The water retention rate of P/S/T/H gel is still as high as 20% after 12 h, the water-absorbing multiplicity is more than 400 after 90 min, and the salt-resistant multiplicity is 54 after 90 min. When P/S/T/H gel is added to the coal samples, the combustion end temperature lags 8.4 °C, the heat release is reduced by 19.9%, the average CO inhibition rate is 45.9%, the maximum heat release rate is reduced by 20.1 KW/m2, the total heat release rate is reduced by 36.6%, and the maximum flue gas inhibition rate is 87.1%. Therefore, the highly efficient and environmentally friendly P/S/T/H gel is expected to play an important role in the work of fire prevention in mined-out areas.