Study On The Theory And Properties Of Colloidal Foam For Controlling And Preventing Coal Spontaneous Combustion

Coal spontaneous combustion in goaf is one of the major natural disasters in coal mines.It not only burns a lot of coal resources,but also induces secondary disasters such as gas explosion,causing serious casualties and economic losses,which is the key and difficult point in the field mine fire prevention.The extinguishing foam material has a wide diffusion range and good stacking performance,and it can effectively control the coal spontaneous combustion in the concealed area and high point of the goaf,which is an extremely effective technical means for preventing coal spontaneous combustion in the goaf.Moreover,the water retention stability of the foam is the core content of the development of foam technology,which not only affects the fire-extinguishing effect of the foam,but also directly determines the anti-extinguishing period of the foam.However,traditional aqueous foam,fly ash foam,etc.are easily broken,poor in water retention,and short time to prevent coal fire,so hindered the promotion and application of foam technology in coal mines.In order to solve the above problems and meet the needs of long-term fire prevention in coal mines,this paper proposed a colloidal foam technology that can maintain water stability for a long time and has a cross-linking film-forming function,obtaining the following research results:The formation and decay mechanism of water-based foams were studied.A colloidal foam with the foaming agent,thickening agent and organic crosslinking agent was invented,and the colloidal foam generating device was developed.Colloidal foam is an enhanced aqueous foam by forming the three-dimensional network gel structure in the foam liquid film using chemical crosslinking,finally enhancing the water retention and stability of the foam.The anionic surfactant and the zwitterionic surfactant were used to prepare the foaming agent with good shielding effect on salt ions and excellent foaming performance.Based on the physical synergistic effect between the anionic polymer X and the nonionic polymer H,a synergistic thickening agent with was developed,which shows the best effect on stabilizing foam.And then,the multi-stage ionized and slowly released organic cross-linking agent is selected to chemically link thickening agent molecules to form a gel network structure,achieving efficient water retention and long-term stable foam.In view of the high viscosity,strong integrity and difficult foaming of the gel solution,it is proposed to use a tapered inlet channel to shear the thinning solution at high speed,to use a swirling blade to collide with the mixed gas and liquid,and to cut the refined foam by means of a porous medium.Based on the principle of shear thinning and swirling collision,a cyclone foam generator was invented,and a colloidal foam preparation system was constructed,and finally the uniform and fine foam material was prepared.The effects of the raw materials ratio on the stability and foaming ratio of the foam were studied.The effective application range of the colloidal foam was determined.The water retention characteristics of the foam were clarified,and the cross-linking mechanism of the foam was revealed.The results showed that gel network structure formed by the thickening agent and the cross-linking agent significantly enhanced the foam stability,and also increased the viscosity and the surface tension of the solution,so that decreased the move rate the of surfactant molecules in the foaming solution,which resulted in a decrease in the expansion ratio.Based on the critical conditions of expansion ratio V>5 and half-life T_1/2>120h,the effective application ranges of colloidal foam were obtained as follows:the concentration range of thickening agent was 3.4⁵.5g/L,while the concentration range of the cross-linking agent was 2.1⁴.0g/L.The high-water retention gel three-dimensional network structure formed by the chemical cross-linking reaction in the foam liquid film could stably support the entire foam system,and the foam can lock the moisture for a long time and prevent the volume from collapsing.No liquid was drained in foam before 60h,so that the foam liquid membranes of the surface layer were connected to form a cross-linked dense whole colloidal layer,which is slowly dehydrated in a stable form and completely dried to form a complete cover film.The colloidal foam showed good heat resistance and fire resistance,and it had strong wetting ability to coal.And its resistance rate to coal spontaneous combustion was much higher than that of traditional aqueous foam.The fire-extinguishing experiment showed that when the colloidal foam was used to control the fire coal pile,the high-temperature fire source point could be completely covered and wrapped,and the fire source could be quickly extinguished and cooled.Finally,a layer of colloidal oxygen barrier film was formed on the surface of the coal pile to serve as a permanent covering.The rheological law of colloidal foam was studied,and the rheological constitutive equation was established.Moreover,and the seepage and diffusion law of foam in porous media was mastered.The steady-state rheological experiment showed that the viscosity of the colloidal foam system increases gradually with the increase of the expansion ratio,and it exhibited obvious shear thinning characteristics.By fitting the shear stress-shear rate curve of the colloidal foam,it is found the fire-preventing colloidal foam was the pseudoplastic fluid with no yield value,and the rheological constitutive equation of the colloidal foam was established.The experimental model of seepage accumulation of foam fluid was built in the laboratory.The seepage diffusion and high-level accumulation test of colloidal foam fluid in porous media were carried out.It was found that the colloidal foam used the outlet of the pipeline as the coordinate origin and approximate hemispherical for seepage and diffusion.As the seepage distance increased,the seepage driving force of the foam gradually decreased.Based on the spherical diffusion theory of fluid,the formula of the diffusion radius of colloidal foam in complex three-dimensional fracture network was derived,which provided a theoretical basis for the field application of foam in the goaf area.Aiming at the serious igneous intrusions in Daxing Mine,the frequent spontaneous combustion disasters in thermal metamorphic coal seams and the poor control effect of conventional fire prevention technology,this paper proposed that using the colloidal foam technology with long-term water retention and film-forming function to wet and cool the residual coal in goaf,finally forming the colloid film to isolate oxygen.The field application showed that the colloidal foam can fully wet and cover the coal in the goaf,effectively inhibiting the metamorphic coals with low moisture content,full pore development and high oxidation active to spontaneous combustion,which had a significant effect on the prevention and control of coal spontaneous combustion in goaf.This paper contains 176 figures,24 tables and 230 references.