Research On Residual Clogging Mechanism Of Nano-Emulsified Vegetable Oil In Porous Media

As a new type of slow-release carbon source,the plugging of emulsified vegetable oil in the process of in-situ remediation of groundwater pollution is the main bottleneck restricting the development of this technology.Although the nano-emulsified vegetable oil(NEVO)with optimized particle size can alleviate the physical entrapment to a certain extent,there are still retention residues,which still have an impact on the mass transfer and remediation efficiency.Hence,further research on the retention mechanism of NEVO's retention in porous media is of great significance for seeking a mitigation method for aquifer clogging during in-situ remediation.In view of the problem of NEVO residues,batch experiments,column experiments,characteristic characterization and three-dimensional reconstruction are used to characterize the process,morphology and characteristics of NEVO residue in porous media,and its control factors and mechanism are discussed.Based on the analysis of media particle size,homogeneity and flow rate,the effective measures to alleviate the adsorption residue are optimized.The main results are as follows,(1)The retention of NEVO in porous media is the result of the comprehensive effect of the properties of NEVO and media.The results showed that the capillary number(< 1),bond number(> 1),viscosity and stability determined the difference of wettability and drainage between NEVO and water phase.Pore straining,surface roughness,and interface effects play a synergistic effect on NEVO residue.Under the influence of these factors,the residual rate of NEVO in the coarse,medium and fine sands used in this experiment was 85.9%,72.2%,and 46.3%,respectively.Interface effect is the main controlling factor of NEVO residue,including solid surface and gas-liquid interface.The contribution rate is 47.33%,45.16%,and 35.63%,respectively.Among them,interfacial tension and capillary radius are the essential reasons,which are reflected by capillary rise height.(2)According to the residual results of NEVO in porous media obtained by X-ray microtractography(XMT),combined with fractal theory,this study proposed a set of quantitative recognition method for residual morphology based on natural breaks method coupled with XMT technology,which effectively solves the subjectivity and incompatibility of existing methods in the process of recognition and quantification.Four kinds of residual morphologies including cluster state(10.0~16.2%),throat and corner state(7.4~13.1%),and membrous state(0.8~1.5%)were quantitative identified when this method was applied to the coarse,medium,and fine sands in the experiment.Further analysis of the combination of porous media and residual morphological characteristics shows that: Pore,throat radius and throat length control cluste residues.Interfacial tension,pore-throat radius and shape factor determined the corner and throat residues,while the surface roughness dominated the membranous residues.The identified and quantified residual morphologies can reasonably explain their proportion and mechanism,which confirms the rationality of the method.(3)The evaluation results of NEVO residues mitigation measures show that the control of particle size,homogeneity and flow rate can effectively alleviate NEVO residues.The larger the particle size,the stronger the homogeneity and the faster the flow rate,the less the residue.The XMT scan results show that the regulation makes part of the cluster and throat residues turn into membranous and corner residues,while there is also most of the reduction.This part of the reduction is the main reason for the alleviating of NEVO residues.Considering the cost and feasibility,increasing the single flow rate parameter is the most economical and effective way to alleviate the retention of NEVO.