Assessment of Nucleation Kinetic Mechanisms in Gas Hydrate Crystallization Processes

توضیحات

ABSTRACT

Nucleation is one of the most important steps in the process of crystallization of gas hydrates. In the present work the nucleation mechanism  of gas hydrate formation process using the propane as a sII gas hydrate former is investigated at isothermal operating conditions. Effects of  variations of supersaturation and impeller speed on the kinetics of hydrate nucleation are also presented. Differente expressions for   dependence of induction time with degree of supersaturation are employed. The accuracy of the predicted induction times for the case of progressive nucleation are always much higher than those obtained through instantaneous nucleation assumption at all ranges of impeller  speeds. It is found that the heterogeneous progressive nucleation is the most probable nucleation mechanism at the early stages of gas  hydrate formation processes.

INTRODUCTION

Studies on the kinetics of the process of gas hydrate crystallization are at a relatively early stage of development despite notable work of  various authors in the last three decades . Issues related to the nucleation and growth processes, including the supersaturation, the  nucleation and growth rates and the induction time, have not been sufficiently clarified . Recently, a mechanistic kinetic model for description  of gas hydrate formation processes has also been presented by ZareNezhad et al.  and the secondary nucleation mechanisms due to crystal- crystal and crystal-impeller contacts are theoretically described for the first time. Nucleation is one of the most challenging steps regarding the  crystallization of gas hydrates. Depending on where and how nucleation occurs and how is schematic of clusters, there are different  influencing mechanisms such as homogeneous nucleation (HON), heterogeneous nucleation (HEN), and instantaneous nucleation (IN) and  progressive nucleation (PN). In the present study, different mechanisms of hydrate primary nucleation have been investigated at different  supersaturations and impeller speeds. The expressions for dependence of induction time with degree of supersaturation are employed and the  arameters of model are determined by mathematical optimization. Kashchiev and Firoozabadi in their thermodynamic analysis of hydrate  formation defined that the driving force for the formation of a new phase is the chemical potential difference between the old phase and the  new one .

Year: 2013

Publisher :  2nd National Iranian Conference on Gas Hydrate (NICGH)

By :  Bahman. ZareNezhad , Mona Mottahedin, Farshad Varaminian

File Information: English Language/ 7 Page / size: 252 KB

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سال : 1392

ناشر : دومین کنفرانس ملی هیدرات گاز (NICGH)

کاری از : بهمن زارع نژاد، مونا متاهدین، فرشاد ورامینین

اطلاعات فایل : زبان انگلیسی / 7 صفحه / حجم : KB 252

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