Abstract:

During the last decade, reports on the topic of the kinetics of hydrate formation have been appearing focusing on the batch reactor or horizontal pipe. However, there are still less studies on this topic applying in the vertical special-shaped tube, for example internal spiral-grooved tube (ISGT).To investigate such multi-component gas (natural gas)-water-surfactant system during the hydrate formation process, CFD method combining with population balance model (PBM) was utilized to simulate gas-liquid mass transfer coefficient in the ISGT, based on the solute permeation model and Kolmogorov isotropic turbulence theory. The hydrate formation kinetics model in ISGT was modelled after extending the classical hydrate nucleation and growth theory proposed by Kashchiev and Firoozabadi for a single component gas-water system to the multi-component gas (natural gas)-water-sodium dodecyl sulfate system. According to the classical crystallization theory, the hydrate growth model was modified by the simulated gas-liquid mass transfer coefficient. The averaged gas-liquid mass transfer coefficients for natural gas in the water at hydrate production conditions are determined by CFD simulation. Furthermore, Microsoft Visual C++ software was utilized to obtain data of the natural gas hydrate formation kinetics. The results show that the nucleation rate of natural gas hydrate decreases sharply with the increase of the effective surface energy of the reaction system, while the driving force and growth rate of hydrate nucleation are not affected by the effective surface energy. Meanwhile, the hydrate growth rate increases with the increase of the flow rate and reaction pressure, the decrease of the temperature. The nucleation rate increases with the increase of the pressure and the decrease of the temperature. The results are promising to pave ways to further experimental and theoretical investigation on hydrate formation.

Key words: internal spiral-grooved tube, population balance model, gas-liquid mass transfer coefficient, natural gas hydrate, formation kinetics

摘要：

针对多组分气体（天然气）-水-表面活性剂体系在螺旋内槽管内的水合物生成过程，首先采用CFD方法结合群体平衡模型（PBM），基于溶质渗透模型和Kolmogorov各向同性湍流理论对螺旋内槽管内气液传质系数进行了模拟；其次基于Kashchiev和Firoozabadi的经典水合物成核和生长理论，将其体系从单组分-水系统扩展到多组分气体（天然气-水-十二烷基硫酸钠）系统，同时结合经典结晶理论利用传质系数对水合物生长模型进行了修正，建立了适用于螺旋内槽管流动体系内天然气水合物生成动力学模型。通过模拟计算，获得不同水合物生产条件下天然气在水中的平均传质系数；进而利用Microsoft Visual C++编程计算得到不同条件下水合物生成动力学数据，在考察范围内，天然气水合物的成核速率随着反应体系有效表面能的增大而锐减，而水合物生成驱动力和生长速率未受影响，同时水合物生长速率随着流速和反应压力的增大及温度的降低而增大，成核速率随着压力的增大和温度的降低而增大。

关键词: 螺旋内槽管, 群体平衡模型, 气液传质系数, 天然气水合物, 生成动力学