Study On The Foamed Gel And Its Characteristics For Preventing Coal Spontaneous Combustion

Coal spontaneous combustion, one of the natural disasters in coal mineproduction, not only can burn down or freeze a great deal of coal resources, but alsocommonly triggers severe accidents of gas explosion, causing heavy casualties andeconomic loss. At present, the major control technologies at home and abroad aregrouting, insert gas, inhibitor, gel and foam, etc. Although these techniques haveplayed an important role in preventing coal spontaneous combustion, someshortcomings are obviously existed. For instance, it is difficult to meet the needs ofcontinuous plugging and controlling wind in mine and inserting cooling for coal fire.In order to prevent coal spontaneous combustion effectively, combining with the geland foam, the technology of foamed gel is brought out to prevent the spontaneouscombustion of coal. Consequently, the formation mechanism and correlatedcharacteristics of foamed gel have been systematically studied in this thesis and a lotof results in many aspects are achieved, such as in crosslinking mechanism andforming chemical kinetics, development of foaming agent and polymer, flowcharacteristics in goaf, film forming ability, fire extinguishing and preventing propertyand field application, etc.The formation of chemical kinetics and gelatinization mechanism of foamed gelwere systematically proposed by interface chemistry, colloid chemistry, polymermaterials chemistry, etc. Foamed gel, a weak gel system between bulk gel andcolloidal dispersion gel, is a kind of polymer system formed by polymer with lowconcentration which are intermolecular crosslinking mainly and intramolecularcrosslinking auxiliarily. With the help of surfactant, the foam is formed by physicaland mechanical stirring. After foaming, the thickener and crosslinker react with eachother and form foamed gel by delayed gelation. The gelatinization mechanism is whenthe thickener dissolved in water, the helical mesh polymer or double helix cluster areformed by molecular chains, besides, active group in polymer or cluster fully collidewith that in the main chain structure of crosslinker, thereby the three-dimensionalnetwork structures are formed.According to crosslinking characteristics of foamed gel and the requirement offoaming process to crosslinking polymer, the thickener and crosslinker which aresuitable to prepare foamed gel are developed. Meanwhile, depends on the functioncharacteristics that the thickener and crosslinker have on the surfactant, a new kind of foaming agent with high foam expansion has been compounded. Experimental studywas conducted on the gelation time and stability of foamed gel. The results show thatthe gelation time of foamed gel is between10to20min, and the foam is still stableafter standing for24h. In the lab, the system used to develop the foamed gel wasestablished and its technological process was confirmed. After massive experimentalstudies, it turns out that when the mass concentration of compounded foaming agent is4‰, the thickener and crosslinking agent are both3‰, and the pH value is7to9, thefoamed gel with best performance can be formed.The rheological properties of foamed gel had also been researched. The resultsindicate that it has the shear thinning nature. That is, with the increase of shear rate,the apparent viscosity of foamed gel decreases. Depends on the analysis results of theapparent viscosity and yield stress, the curve and formula model of shear stress-shearrate are obtained respectively. On this basis, the permeability characteristic of foamedgel was studied on the porous media. The Fluent software was adopted to numericallysimulate the characteristics of flowing diffusion and accumulation in goaf withdifferent angles. And the parameters are figured out such as stack height, diffusionwidth and diffusion length.Researches had also been made on the film forming ability of foamed gel,including film micro-morphology, vapor penetrability, water absorption, radiationbarrier property and leaking stoppage, etc. AFM was employed to observe the filmmicro-morphology and the effects of different proportions of polymers on filmmorphology and characteristics were discussed. The study finds that only when thethickener and crosslinker blending used as well as their mass ratio is1:1, can theycrosslink into tight and smooth film. At the same time, the higher the concentration ofblending polymer is, the better the property of film forming is. After investigating thevapor penetrability, water absorption, radiation barrier property and leaking stoppageof film, the experimental results state that the surface film has a good performance ofwater blocking, the vapor penetrability is zero within a lasted week. After absorbingwater, the weight of film is60~70times of its own weight. Moreover, the film cansignificantly reduce the radiation from outside on the combustible, and therebydecrease the surface temperature of combustible more than40℃. Furthermore, thesurface film can bear the wind pressure of at least2500Pa, thus it has certain ability ofblock air leakage in goaf.Comprehensive studies were conducted on the fire extinguishing and preventing property of foamed gel, including temperature resistance, burn resistance, coagulationand leaking stoppage, and inhibitation, etc. The results show that the temperatureresistance of foamed gel is significantly improved comparing to two-phase foam，withthe increase of the mass concentration of thickener and crosslinker, the temperatureresistance time grows, moreover, as the increasing of foaming expansion, the time oftemperature resistance decreases. The burn resistance time is347min, which is13.88times of water’s and6.20times of two-phase foam. The proportion that the foamedgel coagulates slack coal is57%~93.8%(1d later) of the coal sample.10d later still upto13.4%~52.6%. When adding1%foamed gel, the coal sample releases CO prolong20~30℃than the original coal sample, when100℃, the inhibition rate reach up to68.89%. This thesis also carried on a research on the effectiveness of foamed gel toputting out coal fire, and it turns out that if puting out the same size of coal fire, onlyuse one ninth of the amount of common foam, less than half of the fire-extinguishingtime of two-phase foam. The time of preventing fire first decreases then increaseswith the increase of mass concentration of thickener and crosslinker, when the massconcentration is3‰, the time is the least and the fire extinguishing effectiveness isthe highest.Finally, the foamed gel was adopted to prevent and distinguish fire in goaf,top-coal falling region and other concealed locations in Xinji No.2Coal Mine. Theapplication results show that the technology of foamed gel has a significantly effectand outstanding merits in fire preventing and distinguishing and filling top-coalfalling region, which is especially suitable for unknown fire location and coalspontaneous combustion in top-coal falling region. Furthermore, it is a kind of newtype of fire extinguishing and preventing material which has wide applicationprospect and popularization value.