Study On The Theory Of Electrostatic Distribution And Prevention Technology Of Electrostatic Hazard For Oil Tanks Filling System

The usage of petroleum is increasing as a result of the rapid development of industry.As an important equipment for raw material storage,liquid coordination and transportation,storage tanks play an irreplaceable role in the operation of oil processing,transportation and storage.The electrostatic charges,generated in the filling pipe,flow into the tank and accumulate during filling tanks with oil.And in the tank the electrostatic potential may reach dozens of kilovolts.Filling process is the most dangerous and also important stage for electrostatic hazards control among oil tanks filling,unloading and washing processes.Therefore,it is necessary to study on the theory of the distributions of electrostatic charges and potential in oil tanks as well as prevention measures for electrostatic hazards during filling process.The oil in the pipe must flow into a certain container(it means storage tank in this paper),and the oil in the tank must be filled through filling pipe.However,in current researches the electrostatic problems of oil tanks and filling pipes are separated,and the influence of the filling pipe on the electrostatic charge and potential in oil tanks is ignored.In this paper,the oil,filling pipe and oil tank are considered together and defined as oil tanks filling system.In order to prevent the electrostatic hazard,the distributions of the electrostatic charges and potential for the oil tanks filling system are studied.The detail researches are carried out as follows:(1)Experiment on electrostatic charge and potential for oil tanks filling system.An experiment platform for electrostatic measurement of oil tanks filling system was established.The dissipation current on the pipe wall and the electrostatic potential in the tank during filling process were measured with different filling patterns,filling pipes,filling oils and filling rates.The law of the generation and dissipation of electrostatic charges for the oil tanks filling system was explored.And the influence of filling patterns and some other factors on the electrostatic potential in the tank were analyzed.(2)Distribution of electrostatic potential in oil tanks based on static distribution of electrostatic charges.The dissipation functions of electrostatic charges in oil tanks during filling process for oils with different conductivities are deduced based on the theories of exponential and hyperbolic dissipation equations.Calculation model for the distribution of electrostatic potential in oil tanks during filling process based on the static distribution of electrostatic charges is established.The boundary conditions for solving the calculation model with the filling patterns of bottomfilling and top-filling are proposed.The distribution of electrostatic potential in oil tanks with the influence of filling pipe is explored.And the decrease effect of the filling pipe on the electrostatic potential is quantitively evaluated.(3)Theoretical study on the dynamic distribution of electrostatic charges and potential in oil tanks during filling process subjected to multi-field coupling.The theory model of the dynamic distribution of electrostatic charges and potential in oil tanks subjected to the flow-concertation-electrostatic field coupling is established.The electrostatic charges flowing into the oil tank through filling pipe are transported by convection,diffusion,conduction and dissipation forces.Considering these forces acting on the electrostatic charge,the equation of motion of the electrostatic charge is proposed and the dynamic distribution of electrostatic charges can be obtained.The operation of filling tanks with oil is simulated by the gas-liquid two-phase flow model,which can provide the distribution of flow velocity and the location of gas-oil interface.And the dynamic distribution of electrostatic potential is obtained by solving the Laplace and the Poisson equations.(4)Simulation study on the dynamic distribution of electrostatic charges and potential in oil tanks during filling process subjected to multi-field coupling.A finite element model of two-dimensional axial-symmetric oil tanks filling system is established,and then the dynamic distribution of electrostatic charges and potential in oil tanks during filling process subjected to the flow-concertation-electrostatic field coupling is conducted.The comparison between the simulation and experimental results is provided.The distribution of electrostatic charges and the distribution of electrostatic potential based on this electrostatic charge distribution are analyzed.The impacts of the dissipation time,the diffusion coefficient and some other factors on the distributions of the electrostatic charges and potential are discussed.(5)Sedimentation electrification in oil tanks after filling process.According to the mechanical balance of the impurity particle in the oil during sedimentation process,the calculation methods of sedimentation velocity and sedimentation field are put forward.The space in the tank is divided into three parts,the gas space,the oil space with impurity particles and the oil space without impurity particles.The relationships of the electrostatic fields and potentials among these spaces are established,and then the function of surface potential can be obtained.The influence of the concentration of impurity particles,the height and filling fraction of the tank on the electrostatic potential in the tank are analyzed.(6)Prevention technology of electrostatic hazard for oil tanks filling system.The fire and explosion accident chain caused by electrostatic discharge for oil tanks filling system is built.And applying the mechanism of the mitigation accident by cutting the accident chain,the prevention measures are analyzed.Based on the research results from chapter 2 to chapter 6,the quantitative prevention technologies of the controlling of flow velocity,the choosing of grounding resistance and the determining of standing time are proposed.And according to the formation process of electrostatic ignition source,these prevention technologies can reduce the generation,accumulation of electrostatic charges and the possibility of electrostatic discharge,respectively.