Phenomenological Research Based On Heat-Mass Synergy In Pipeline Irreversible Process Of Crude Oil

Most crude oil produced in our country is waxy crude oil which is a complicated mixture system mainly consisted of aromatic hydrocarbons, paraffin wax, asphaltene,colloid, light hydrocarbon constituent and other components. The crude oil represented by the DaQing oilfield belong to low sulfur paraffin based crude oil which generally contains more than 50% alkanes.And this kind of oil has the characteristics of high pour point, high wax content, high viscosity. Therefore, wax deposition occurs inevitably in the crude oil pipeline transportation process. The effective flow area of pipeline is decreased, the delivery value is reduced and the flow resistance is increased when wax deposition occurs.The possibility of coagulation tube is increased and plugging accident of pipeline shutdown and restart is happened when wax deposition is more serious.Wax deposition process of waxy crude oil in pipeline is regarded as irreversible process in this paper. The mechanism coupled heat and mass transfer in waxy crude oil pipeline process is analyzed by the theoretical, and the heat transfer process and mass transfer process in waxy crude oil pipeline are discussed respectively. Taking the thermodynamic equilibrium theory as the method of researching the organic solid phase precipitation mechanism in crude oil, then the thermodynamic criterion of multiphase equilibrium is deduced. Thermodynamic model of liquid-solid phase equilibrium in waxy crude oil is established by proposing the regular solution theory and the binary mixture system is solved by using Newton-Raphson iteration method. Based on the nonequilibrium thermodynamic theory, simplified assumptions in the pipeline process is proposed. The entropy balance equation is deduced according to the basic field balance equation. Furthermore, the entropy production rate equation is obtained. On the basis of the entropy production rate equation,phenomenological equations is established which described heat and mass transfer process in the pipeline correctly. And then the mathematical expressions of each phenomenological coefficient during the heat and mass coupled process in waxy crude oil pipeline is gained.Numerical calculation for each phenomenological coefficient and analysis of temperature effects on each coefficient is made. The driving force of temperature gradient and concentration gradient are obtained by numerical calculating the heat and mass transfer process in the waxy crude oil pipeline. Coupling mechanism of heat and mass transfer process in pipeline is deeply analyzed by calculating the heat flux density and solid-phase mass flow density which can provide theoretical basis on depth study for wax deposition issues in the waxy crude oil pipeline process.