Aqueous clay suspensions stabilized by alginate fluid gels for coal spontaneous combustion prevention and control

Novel PFA-Based Inorganic Three-Phase Foam for Inhibiting Coal Spontaneous Combustion

Fire accidents caused by coal spontaneous combustion usually lead to a large loss of coal resources and casualties. Not only that, the greenhouse effect is polluted while the environment is polluted. At present, the commonly used fire-extinguishing materials such as water, inhibitors, and organic foams have the disadvantages of poor stability and short fire-extinguishing cycles. It is difficult to effectively suppress coal spontaneous combustion and quickly extinguish the fire for a long time. To suppress the spontaneous combustion of coal, the research team proposed an inorganic three-phase foam with a high foam expansion rate, good cohesiveness, and excellent stability. In the formulation, pulverized fly ash (PFA) is used as the matrix, sodium dodecyl benzene sulfonate (SDBS) and α-olefin sulfonate (AOS) are used as foaming agents, curdlan is used as the foam stabilizer, and sodium silicate is the binder. The compound foaming agent with the best performance is optimized, through the two-group compounding test. The composite foaming agent's optimal compound ratio is SDBS/AOS (3:2). The optimal ratio of inorganic three-phase foam (ITPF) components was obtained through the control variable method experiment. The water-cement ratio is 5:1, the composite foaming agent is 0.2%, the curdlan is 0.5%, and the sodium silicate is 1.6%. In addition, it has been determined by experiments that ITPF has the strongest foaming ability when the pH value is 9 and the temperature is 60 °C. The fire-extinguishing performance of the new material ITPF was investigated by thermogravimetry and coal spontaneous combustion tendency test. It has been observed that the new material has the effect of cooling down and isolating coal from contact with oxygen. The results show that the new material ITPF has the potential to prevent coal spontaneous combustion.

A Novel Highly Stable Biomass Gel Foam Based on Double Cross-Linked Structure for Inhibiting Coal Spontaneous Combustion

To enhance the stability of biomass gel foam used for inhibiting coal spontaneous combustion (CSC), a novel highly stable biomass gel foam (SA-Ca2+@TA-GF) based on a double cross-linked structure was prepared by introducing tannic acid (TA) into a gel form (sodium alginate/calcium L-lactate/composite foaming agent). FT-IR confirmed the formation of the double cross-linked structure. The effects of TA concentration on the performance of SA-Ca2+@TA-GF were analyzed, considering gelation time, half-life, film microstructure, and strength. With the addition of 1.6 wt% TA, SA-Ca2+@TA-GF forms a dense foam structure with a gelation time of 10 min. The half-life of the gel foam improves from 0.4 to 30 days and the strength increases by 72.9% compared to that of foam without TA. The inhibition experiments show that SA-Ca2+@TA-GF can asphyxiate coal, thus effectively inhibiting coal oxidation. Additionally, it can increase the temperature of coal at the rapid oxidation stage by 60 °C, and the CO inhibition rate is up to 79.6% at 200 °C. The fire-fighting experiment shows that SA-Ca2+@TA-GF can effectively cool coal and quickly extinguish fires. This study provides a simple method to prepare highly stable biomass gel foams, which is useful for improving the efficiency of gel foams in inhibiting CSC.

Experimental study on the effects of chemical composite additive on the microscopic characteristics of spontaneous combustion coal

In order to study the effects of chemical composite additive (CCA) on the microscopic characteristics of spontaneous combustion coal, atomic force microscope and Fourier transform infrared spectroscopy technology were used to study the microstructure and active groups of spontaneous combustion coal. The roughness, three-dimensional surface morphology, microscopic pore structure, infrared spectrum, and active group content of raw coal samples and coal samples treated with water or different concentrations of CCA were analyzed. The experimental results showed that compared with the raw coal, the roughness Rq and Ra of the CCA-treated coal samples decreased with increasing CCA concentration, and the surface topography of the microscopic structure tended to be flat and smooth, and the size becomes smaller and the depth becomes shallow of pore. In the raw coal samples and coal samples treated with water and CCA, the main types of active groups remained constant. However, the contents of these groups changed, and the order of the contents of main types of active groups is water-treated > raw coal (untreated) > CCA-1% treated > CCA-5% treated > CCA-10% treated > CCA-20% treated. In addition, the mechanism of the CCA inhibition of coal spontaneous combustion was discussed and analyzed.