Experimental Study On Fly-ash Gel Foam For Preventing And Controlling Spontaneous Combustion Of Coal

Coal is a kind of important energy in China,however,threats such as coal spontaneous combustion often occur during the mining process.In order to control coal spontaneous combustion,various fire-fighting technologies have been proposed,two of which are hydrogel injection and three-phase foam injection.considering the three-phase foam has good fluidity and easy accumulation to high places,but with short water retention time and poor stability,and the hydrogel has poor fluidity,but the performance of water retention is excellent,a new kind of fly-ash gel foam material was developed,the material integrates the advantages of three-phase foam and hydrogel,and overcomes their respective defects,greatly improves the performance of fire prevention and control.Through theoretical analysis and experimental research,this paper carried out a systematic study on the experimental preparation and relevant properties of fly-ash gel foam,and obtained the following research results:?1?The formation process of fly-ash gel foam was revealed,including three stages:adsorption of surfactants at gas-liquid interface and solid-liquid interface,collision and adhesion between hydrophobically modified particles and bubbles,and the delayed cross-linking of gelling agent and crosslinking agent.The stability mechanism of fly-ash gel foam was summarized from the behavior of surfactant molecules at the gas-liquid interface,the wetting of fly-ash particles,and the interaction between the molecules of the gelling system.?2?The experimental preparation of fly-ash gel foam was carried out.The preparation process included:the analysis of physic-chemical parameters of solid phase medium and the determination of foam additive components,in addition,the influences of water-cement ratio,pH value and environmental temperature on foam performance were analyzed.Finally,when the anionic foaming agent A and the zwitterionic foaming agent B are compounded with a ratio of 1:1,the total concentration is 0.3%,the concentration of gelling agent G and crosslinking agent C are each 0.3%,the water-cement ratio is 5:1,and the pH value is 7-9,the fly-ash gel foam with excellent water retention and high stability could be prepared.?3?The microscopic morphology of fly-ash gel foam was studied,parameters such as the number of foam bubbles,average size and size distribution were used as evaluation indexes to verify the high stability of the fly-ash gel foam from a microscopic perspective.The macroscopic morphology of fly-ash gel foam was investigated with time,the results showed the fly-ash gel foam could form a continuous and dense fly ash membrane block after the surface moisture of foam was completely evaporated,which achieved the effect of oxygen barrier continuously.The effects of polymer concentration,expansion ratio,water-cement ratio and ambient temperature on the rheological properties of fly-ash gel foam were analyzed by rheological experiments,the results showed that the fly-ash gel foam had a characteristic of shear thinning,and the rheological constitutive model of fly-ash gel foam was established.?4?The performance of fly-ash gel foam in fire prevention and control was studied.After injecting the fly-ash gel foam,the vacuum chamber of air plugging test device maintained a stable negative pressure of-14kpa,which was about 3.5 times that before the injection of foam,significantly improved the air plugging effect.Different from the rapid temperature decline after the three-phase foam contacted with the fire source,the temperature in the center of the fire source began to plummet after a slow decline of about 300s when the fire area was covered with the fly-ash gel foam,and the extinguishing and cooling mechanism of fly-ash gel foam was revealed.After the coal was treated with fly-ash gel foam,the concentration of CO and C₂H₄ released during the low-temperature oxidation of coal decreased,moreover,the temperature of C₂H₄ to be detected was delayed by about 20°C,and the crossing point temperature increased by nearly 30°C.The fly-ash gel foam exhibited a strong inhibition to the tested coal sample.