Molecular Characterization And Distillation Model Construction Of Petroleum

Effective separation and processing of oil products is the key to maximize the utilization of oil resources in petroleum processing.The current popular process simulation software such as Aspen plus,Aspen HYSYS and Pro II generally use the pseudocomponent method to simulate separation processes,while the molecules in oil are the internal factors that determine the macroscopic properties,oil processing processes and product properties.Driven by the concept of molecular management,how to characterize petroleum fractions at the molecular level and perform simulation of separation processes such as distillation is an important problem to be solved at present.In this paper,petroleum fractions are characterized at the molecular level,the thermodynamic calculation engine of petroleum molecules is developed,the calculation modules of isothermal flash and adiabatic flash with single equilibrium level and the distillation tower of complex molecular system with multiple equilibrium stages are built,so as to realize the development and application of molecular thermodynamic and separation models of petroleum.Firstly,the separation model of vapor-liquid phase equilibrium is established based on cubic equation of state.In this study,the calculation engine of thermodynamic parameters related to phase equilibrium is developed based on PR equation of state,which can solve the compression factor,fugacity coefficient and vapor-liquid enthalpy for complex system with high accuracy.By investigating the principle of vapor-liquid phase equilibrium,isothermal flash evaporation and adiabatic flash evaporation unit models are developed on the Matlab platform.The vaporization fraction and temperature of the system are calculated by Newton-Raphson method,and the phase equilibrium process of single equilibrium stage is calculated.Based on this,the molecular distillation tower model is developed based on bubble point calculation,which can realize the multiple equilibrium calculation of simple hydrocarbon systems.Subsequently,based on SU-BEM mixed framework,the molecular characterization of the gasoline fraction of Saudi Arabian intermediate crude oil is carried out,and 124 gasoline molecules are obtained by screening the core molecules and expanding the side chains in this study.The molecular composition model of gasoline is obtained by constraining the molecular content of gasoline with appropriate combination of probability density functions,and the macroscopic properties,distillation curve,molecular composition and distribution of the final composition model are basically consistent with the experimental values.Finally,from the molecular level,the models of isothermal flash evaporation,adiabatic flash evaporation and molecular distillation tower are applied by using the gasoline fraction,and the predicted results are compared with the simulation results of Aspen HYSYS.The vaporization fraction,equilibrium temperature and vapor-liquid molar flow rate of the final flash evaporation model are basically consistent with the simulation results of Aspen HYSYS,and the calculation results of tray temperature and vapor-liquid molar flow rate of the molecular distillation tower are also consistent with the simulation results of Aspen HYSYS,thus realizing the strict calculation of single equilibrium stage and multiple equilibrium stage of complex molecular systems.The thermodynamics and separation model of petroleum molecular established in this study is expected to provide basic models and data for the subsequent petroleum processing process and the optimization of molecular plan in the whole process.