Thermodynamic Models Describing Systems with Mixed Gas Hydrate Formation

该项目旨在描述具有流体相和纯固相的复杂相平衡（例如，干冰、固体水）和混合水合物固相。其创新之处在于采用了高精度的多参数流体状态方程和最佳的纯固相状态方程。由于水合物形成组分在平衡的流体相中的逸度对水合物的化学势产生贡献，因此准确和一致的水合物模型取决于流体相的准确描述。一个热力学模型的八个纯天然气水合物的形成者最近已经出版。新模型的一个重要优点是它能够准确地模拟各种各样的相平衡，包括那些在宽的温度和压力范围内的纯固相。该模型仅能计算纯水合物。如果流体相包含多于一种水合物形成组分，则由混合流体相形成水合物导致混合水合物。该项目致力于将纯水合物模型增强到技术上更重要的混合水合物。 在项目第一阶段取得可喜成果的基础上，该项目第二阶段的目标基本上符合原提案中所述的概念，由于将模型扩展到混合水合物需要改变纯水合物的描述，因此有必要重新调整参数。在模型修正时，将考虑双占据的结果。在纯水合物体系中不稳定的水合物结构，可能在形成混合水合物的体系中出现。必须针对此应用开发并优化考虑此行为的稳定性分析。在第一阶段开发的初步模型已经过测试，仅为混合水合物系统含有CO2和CH 4作为水合物形成物质。在本提案所述的第二个项目阶段中，将考虑将水合物形成组分CO2、CH 4、C2 H6、C3 H8、N2和O2的二元组合扩展到水合物形成组分的二元组合。系统中抑制剂的影响在定性上预测正确;在即将到来的第二个项目阶段中，将对该主题进行更详细的研究。由此产生的算法和最终模型将在一个名为TREND的软件中实现，该软件易于由没有经验的用户操作，以确保模型的广泛分布。TREND是一个开源软件，已经被世界各地的60多个研究小组和公司使用。

This project aims to describe complex phase equilibria with fluid phases and pure solid phases (e.g., dry ice, solid water) and mixed hydrate solid phases. The innovation is to use highly accurate multiparameter equations of state for fluid phases and the best equations available for other pure solid phases. Since the fugacity of the hydrate forming components in the fluid phases in equilibrium yields a contribution to the chemical potential of the hydrate, accurate and consistent hydrate models depend on an accurate description of fluid phases. A thermodynamic model for eight pure gas hydrate formers has recently been published. An important advantage of the new model is its capability to accurately model a large variety of phase equilibria including those with pure solid phases over wide temperature and pressure ranges. This model enables the calculation of pure hydrates only. The formation of hydrates from a mixed fluid phase leads to mixed hydrates if the fluid phase contains more than just one hydrate forming component. This project addresses the enhancement of the model for pure hydrates to the technically more important mixed hydrates. Based on the promising results of the first project phase, the objectives for the second phase of this project are mostly in line with the concept described in the original proposal.Since the extension of the model to mixed hydrates required changes in the description of pure hydrates, a refit of the parameters is necessary. Results found for double occupancy will be considered in refitting the model.Hydrate structures, which are not stable in pure hydrate systems, may occur in systems forming mixed hydrates. A stability analysis taking this behavior into account has to be developed and optimized for this application. The preliminary model developed in phase one has been tested only for mixed hydrate systems containing CO2 and CH4 as hydrate forming substances. The extension to binary combinations of the hydrate forming components CO2, CH4, C2H6, C3H8, N2, and O2 will be considered in the second project phase addressed in this proposal.The influence of inhibitors in the system is predicted qualitatively correct; a more detailed study on this topic is foreseen for the upcoming second project phase. The resulting algorithms and the final model will be implemented in a software called TREND, which is easy to operate by unexperienced users, to ensure a broad distribution of the model. TREND is available as open source software and is already used by more than 60 research groups and companies all over the world.