Study On The Thermochemical Treatment Of Fine Argillaceous Heavy Oil Sludge

The oil sludge is produced in the process of crude oil exploitation,storage,transportation and refining.The production and storage of oily sludge in China are huge and need to be treated.Liaohe Oilfield produces more than 180,000 tons of sludge annually,including about 60,000 tons of ground sludge and about 80,000 tons of tank sludge.They are all sludge with small particle size,and has a high content of resin/asphaltene and extremely stable state.The treatment of those sludge is the key and difficult point of sludge treatment in Liaohe Oilfield.At present,the treatment of oil sludge in Liaohe Oilfield is mainly based on the thermochemical treatment method,but the treatment effect is general.The cleaning efficiency of oil sludge needs to be improved because,on the one hand,there is currently insufficient understanding of the stability mechanism and adsorption mechanism of sludge.On the other hand,there is no clear basis for the screening of agents.In response to this situation,In this paper,thermochemical treatment combined with the characteristics of sludge with small particle size is used.Then the stability mechanism and adsorption mechanism of sludge are discussed.And then,based on the oil-water interfacial tension,two effective detergent formulations are optimized and biosecurity evaluation is carried out.In the first part of this paper,the physical properties of tank sludge and ground sludge in Liaohe Oilfield are described,and find that the average particle size is between 11-90 ?m,the shape of the solid particles is irregular and the main component is clay mineral montmorillonite.The tank sludge has high oil content(>65%),and solid particles in sludge can be removed before the mud cleaning.The ground sludge has a relatively low oil content(<25%)and high water content for direct cleaning.The stability mechanism of oil,water and solid particles in tank sludge is discussed by measuring the viscosity,the strength of the interface film and observing its microscopic morphology.It is found that in the tank sludge,the water is uniformly dispersed in the oil phase to form a W/O emulsion,and the large size solid particles are distributed in water and oil phases,and the small size particles are closely arranged at the oil-water interface to form a stable interface film,which strongly increase the viscosity of the system and the strength of the interfacial film and finally strengthen the stability of the emulsion.The simulated adsorption experiments was carried out to discuss the adsorption mechanism of ground sludge.It is found that the adsorption of most crude oil on the solid surface conforms to the Frindlich adsorption model,which belongs to the physical adsorption of multi-molecular layers.The small amount of heavy components of the crude oil is chemically adsorbed on the solid surface.The chemically adsorbed mechanism to the sludge is farther discussed.According to the analysis results of the residual oil phase components on the solid surface after cleaning,we select two representative organic matters with carbonyl(C=O)and amide groups(O=C-NH2)and a linear alkane to simulate molecular dynamics using density functional theory calculation and XPS characterization.As the result shows,in addition to physical adsorption and hydrogen bonding adsorption of organic matter,carbonyl oxygen or amino nitrogen form a strong coordination bond with Al atoms in the crystal lattice.It shows that in the process of sludge formation,the components containing special functional groups in resin/asphaltene will be firmly combined with the metal elements on the solid surface through coordinate bonds.In the second part of the paper,according to the physical properties and stability mechanism of the tank sludge,a separation agent is optimized and screened.The ingredients of separation agents are suspending agent(Na2SO4:6%),flow agent(Kerosene:5%),cationic surfactant(DODMAC:1%)and chelating agent(HMDTMPA:0.5%).Cationic surfactant is used to replace the solid particles adsorbed on the interface because of the good interfacial activity,through which the stability of the emulsion is reduced and the solid and water phases are released.Chelating agent is used to clean sludge by competitive adsorption of carboxylic acid and oil phase on solid surface.The solids content in the oil is reduced to less than 2%,while the crude oil recovery rate is over 90%and the residual oil of sludge to about 16%after the process of separation.The biosafety evaluation result of separation agent showes that it is a micro-toxic agent which is easy to be biodegraded.In the third part of the paper,based on the adsorption mechanism of the ground sludge,a cleaning agent is screened innovatively by interfacial tension(IFT)method.The mixture of sodium carbonate,fatty alcohol ethoxylate(AEO-9),and rhamnolipid with a ratio of 5:1:0.5 is found that has the lowest IFT.At the same time,the optimum condition for thermochemical cleaning is as follows:2%cleaning agent dosage,solid-liquid ratio of 3:1,500 r/min agitated water washing at 50? for 30 minutes.After two cleaning processes,the value of Total Petroleum Hydrocarbons(TPH)of ground sludge can be reduced to 0.25%.After a cleaning process,the TPH of solids seperation from tank sludge can be reduceed to 1.56%,meetingthe requirements of some local standards for oil content<2%.The biosafety evaluation result of separation agent showes that it is a micro-toxic agent which is easy to be biodegraded.