Study On Remediation Of High Concentration Oil-contaminated Soil By Fluidized Counter-current Solvent Extraction

Solvent extraction is an ex-situ separation and concentration process in which anonaqueous liquid reagent is used to remove organic and inorganic contaminants fromwastes, soils, sendiments, sludges, or water. With the purpose of remedying highconcentration oil-contaminated soil, a suit of continuous solid-liquid fluidizedcounter-current extraction plant has been established. Hydromechanics and masstransfer of the process have been investigated by experiment and numericalsimulation.In order to find out the relationship between solid hold-up and flow rate of bothsolid and liquid, three different narrow-sized spherical particles have been contactedcounter-currently with solvent separately in the plant and then solid hold-up havebeen measured at several different heights of the column. Results show that: solidhold-up decreases with the diameter of the particles when the operating parametersare fixed as constants; For a certain solid flow rate, a vertical gradient of the solidhold-up from bottom to top appeases within the top part of the column near thefeeding point, which means a inverse pressure difference.In order to make a deeper understanding of the experiment results, amathematical model of the counter-current two-phase flow of the particles and thefluid in the extraction column was set up. A commercial CFD package FLUENT hasbeen adopted to simulate the solid-liquid counter-current fluidization in extractioncolumn. Simulation results show that no matter how the operating parameter changes,there exists one-to-one correspondence between the slip velocity and solid hold-upprovided that flooding point has not been reached. This relationship can be depicted interms of a function between Uslip/Utand ? which can be called the hold-up functionf (?). f (?)has got a form of fraction power function according to the simulationresults. Additionally?particle velocity Upalso follows a certain rules. All of thenormally-operating spots(??Up)fall within a “triangle” region in the U-? diagramswhile others which fall out of the “triangle” region are flooding points. The “triangle”region is so called the feasible operation area of counter-current fluidization.Moreover?additional simulation have been carried out of the count-current fluidization occurs in the extraction column with expanded tower head. Results showthat expanded tower head enlarges the “triangle” region and plays an important part inpreventing the column from flooding.At last, a set of experiments of the solvent-extraction-based remediation of theoil-contaminated soil have been carried out with lab-scaled stirring devices. A soventcalled TU-A has been chosen through the screening tests. The process of extractionfollows the Henry or Langmuir model of desorption according to the equilibriumexperiments. Important parameters which influence the oil-removing rates such asoperating temperature, soil moisture content, extracting time, have been alsoinvestigated by stirring experiments at the lab scale.