A new approach to investigate hydrate deposition in gas-dominated flowlines

摘要

A new model describing the mechanism of the hydrate deposition based on the most recent particle dynamics theories is developed. The model splits the motion of the particle into two main regions: the turbulent and the sublayer regions. A novel approach is used to define the particle migration and attachment in the sublayer region. Depending on the ratio of the particle diameter relative to the thickness of the sublayer, the particle will either travel as a result of the force balance acting on the particle (lift, adhesion, gravity, and drag) or as it may experience bouncing process. The proposed model employs the following three main components to simulate the hydrate deposition: (a) computational fluid dynamics (CFD) technique is used to configure the flow field; (b) nucleation and growth models are incorporated in the simulation to predict the incipient hydrate particles size and growth rate; and finally (c) a novel approach of particle migration and deposition is used to determine how particles deposit and adhere to the walls of flow conduit. The results predicted by the model show that the distance of the deposition decreases as the particle size increases. However, after certain size of particle, there is no impact on the deposition distance. This critical particle size is called "deposition critical size". The experimental tests are shown to be in good agreement with the model predictions in terms of the following criteria: 1) Formation of hydrate particles are observed to be poly-dispersed since different sizes of particles are formed; 2) Studying the influence of the Reynolds number and pipe diameter, the deposition distance is found to be linearly corresponded to both.