Wax Deposition Model Research Based On Heat-Mass Synergy In Pipeline Process Of Crude Oil

This paper was financially supported by National Natural Science Foundation ofChina (No.51106020, No.51174042), PetroChina Innovation Foundation（2012D-5006-0610） and Youth Scholar Backbone Supporting Plan Project ofHeilongjiang General Colleges and Universities (1252G005).Waxy crude oil is a complex multi-object system consists of mixed hydrocarbons.Crude oil produced in our country mostly has characteristics of high viscosity andeasy-clotting. In such pipeline transportation process, wax deposition occurs inevitably.With temperature decreasing, oil fluidity deteriorates, amount of dissolved waxmolecules precipitate, cross-link network structure that attaches to the wall results intransport capacity decrease of pipeline, flow resistance increases leading to high costdirectly, and seriously affects the security and economic operation of the pipeline. In thispaper, through summarizing the results of previous experiments and theoretical basis,from the perspective of non-equilibrium thermodynamics, the coupling mechanism,among mass transfer, heat transfer, viscous, phase change, fluid flow, and otherirreversible phenomena in pipeline process, gets analyzed, and also the synergy effect ofconcentration gradient, temperature gradient and viscous forces on mass flux, heat fluxand momentum flux. Based on the universal the entropy production rate equation, amathematical model of entropy production rate applicable to pipeline process isestablished, thermodynamic force and flow is chosen, and the various types ofphenomenological relationships between force and flow are discussed. The pipelinewax deposition process is divided into two steps: diffusion and deposition. First, basedon phenomenological relationship between thermodynamic "force" and the "flow",linear heat-mass coupling phenomenological equations of wax molecular diffusion isderived; according to mass and energy conservation, heat-mass coupling differentialequations are gotten; and then the wax molecular diffusion rate using Laplace transformto release the kinetic reason inside. Second, in the perspective of Huang Qiyu model, waxdeposition rate calculation of irreversible heat-mass coupling is derived. Whereby, thewax deposition rate variation under different conditions is calculated. Finally, thecoupling calculation results are compared with laboratory experiments results to showthe adaptation and correctness of heat-mass coupling mechanism.