多相体系蜡晶析出热力学预测模型

Thermodynamic Prediction Model of Wax Precipitation in Multiphase Systems

在油气输送过程中,随着热力学条件发生变化,体系中的蜡组分将析出并沉积于管壁上,对管道输送过程造成一定的阻碍,且在深水高压低温条件下的输送体系中尤为突出。采用状态方程结合UNIQUAC模型建立了多相体系中蜡晶析出热力学模型,模型建立过程中考虑到液相描述一致性、固-固转变、纯组分热力学性质、Poynting修正项处理以及活度系数计算等问题。对于模型预测计算过程中涉及到的轻组分与重组分(以C20进行划分)间二元交互系数这一重要参数,采用气-液平衡及液-固平衡数据进行反算,取为-0.0296。运用该模型对六组混合物体系进行析蜡点计算,计算结果表明:析蜡点随压力的变化趋势与实验结果一致,计算结果与实验数据绝对误差在2.40 K以内,相对误差在0.77%以内,取得了较好的预测效果。

Thermodynamic condition changes in oil and gas transportation pipeline can lead to the deposition of heavy components of the system on pipe walls, especially for deep-water systems with low temperature and high pressure, which results in pipeline blockage. The UNIQUAC model and state equation were used to establish the thermodynamic model for wax deposition. Liquid phase fugacity in vapor-liquid equilibrium and liquid-solid equilibrium, solid-solid transition, thermodynamic properties of pure components, Poynting correction term and activity coefficient were taken into account in model establishment. The binary interaction parameter（-0.0296） between the light and heavy components was determined through inverse computation of the vapor-liquid equilibrium and liquid-solid phase equilibrium data. This established model was used to calculate wax appearance temperature of six mixture systems, and the calculation results show that the model results using pressure as a parameter are consistent with the experimental results, and the absolute prediction error is less than 2.40 K and the relative error is less than 0.77%.