Direct Contact Heat And Mass Transfer Of Hydrocarbon Mixtures In Structured Packing

In the first part of this dissertation, a brief review of DCH (Direct contact heattransfer), DCC (Direct contact condensation) and falling film condensation, includingtheir related theory and the development was introduced. Published works on theresearch of vapor-liquid two phase flow, heat and mass transfer in structured packingwere also reviewed. In addition, development of CTM (Continuous ThermodynamicsMethod) was introduced.In view of the lack of prediction model for the volume heat transfer coefficientin the corrugate plate structured packing of the heat transfer area in a crude oilvacuum distillation tower, three theory models were developed and relatedexperiment researches were carried out. In the second part of this dissertation, a2-DCFD model of direct contact heat and mass transfer of a multicomponent two-phaseflow in an inclined channel at sub-atmospheric pressure was developed, in which anovel source form for heat and mass transfer based on VOF method was presented.While the form of “relaxation parameter×distance to the state of thermodynamicequilibrium” was selected, a “inner boundary condition” close to the state ofthermodynamic equilibrium was formed. Five pseudo-components were used fordescribing the hydrocarbon mixtures. Parameters of gas and liquid inlet boundaryconditions were studied. Based on the model developed in the second part, a2-D CFDmodel of direct contact heat and mass transfer of a two-phase flow coupled with CTMwas developed. According to the existing theory of vapor-liquid equilibrium andtransport equations for CTM, a novel source form base on CTM for heat and masstransfer at gas-liquid interface was presented. Parameters of gas and liquid inletboundary conditions were also studied, and the results were similar to that in thesecond part.In the fourth part of this dissertation, direct contact condensation process ofwater-steam and diesel-diesel vapor mixtures in structured packing under atmosphericand vacuum pressure was investigated experimentally. The result showed thatcondensation rate in the first layer was the highest under atmospheric andsub-atmospheric, this trend was more obviously under vacuum condition. When bothtemperature difference and liquid sprayed density were large, serious mistphenomenon occurred which made a lower local volume heat transfer coefficient inthe structured packing. The local volume heat transfer coefficients from the experimental result were an order higher than the total volume heat transfercoefficient in industrial vacuum tower.Base on the model in the third section, in the fifth part of this dissertation, amulti-scale model of heat and mass transfer in a structured packing layer or sectionwas developed. Preliminary experimental verification for the model was carried outaccording to the experimental result of diesel-diesel vapor in the fourth section. Thesimulation result of the model was in good agreement with the experimental result. Asimulation focus on the top cycle in the vacuum tower was carried out according tothe industrial data. The result showed that most condensation process of the gashydrocarbon mixtures occurred in the lower four structured packing layers and thevolume heat transfer coefficient of every packing layer decreased in an upwarddirection. Along the direction of gas flow, the molecular weight of the gashydrocarbon mixtures decreased with a lighter composition. Along the direction ofliquid film flow, the film composition was lighter first and then turned heavier. Ingeneral, the area of wet and the mass fraction of non-condensable gas were twoimportant factors which influenced the condensation rate of hydrocarbon mixtures inthe gas phase.