架空原油管道停输期间温降及原油凝固界面推进

由于架空原油管道没有土壤的蓄热来减缓管内原油的热散失,架空原油管道的温降过程往往成为决定整条管道允许停输时间的关键。根据原油温度划分管内原油为纯液油区、凝油区和纯固油区,并假设凝油区以已凝固原油、固体骨架和液态原油为填充相的多孔介质区域,该区域随着温降过程向管心推移。考虑了凝固潜热和空气横掠管道对流换热对原油温降过程的影响,建立了空气、管道与原油相互耦合的传热模型,并进行了数值模拟,数值结果表明停输前期管内原油的温度整体下降较快;在停输中后期,由于凝固潜热的释放,凝油厚度增加使得热阻增大,大大减缓了原油温度的降低;对流换热系数沿管道周向分布不均,导致管内原油温度周向分布不均和凝固界面中心偏离管道中心。

TEMPERATURE DECREASE AND SOLIDIFICATION INTERFACE ADVANCEMENT OF OVERHEAD CRUDE PIPELINE DURING SHUTDOWN

The process of temperature decrease is the key to determine the safe time of shutdown in the whole pipeline due to overhead pipeline without soil thermal storage to slow up heat dissipation.According to oil temperature,oil in pipeline is divided into there parts: liquid oil region,solidifying region and solid oil region.Assumed that solidifying region was porous media which were made of solid oil as solid skeleton and liquid oil as packed fluid phase and advanced towards the center of pipeline with temperature decreased.The coupled heat transfer model with conservation equation of air,pipeline and oil was established with consideration of the influence of solidification latent heat and heat convection across pipeline in air on oil temperature decrease.Numerical simulation was done for pipeline during shutdown.The results show that oil temperature decreases fast in early stage of shutdown and decreases slowly in middle and late stages due to solidification latent heat release and thermal resistance increase with the increase of thickness of solidified oil.Difference of convection coefficient across pipeline results in inhomogeneous temperature distribution in circumference of pipeline and offsetting of solidification interface center in pipeline.