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The Expanded Fluid (EF) viscosity correlation was used to model the viscosity of mixtures commonly encountered in natural gas processing. This correlation provides viscosity values as a function of fluid density and characterizes each pure compound with three fluid-specific parameters: c2, ρ s o and c3, when using experimental densities (Version 1) and two parameters, c2 and ρ s o , when using a cubic equation of state (Version 2). In particular, the original EF correlation for hydrocarbons was adapted for non-hydrocarbon components, including: carbon dioxide, hydrogen sulfide, nitrogen, helium, water, methanol, ethylene glycol, diethylene glycol and triethylene glycol. A temperature dependency was introduced for parameter c2 for components with significant hydrogen bonding such as water and methanol. For all other components, a fixed c2 was found to be adequate. Both versions of the correlation were fit to experimental data for the non-hydrocarbon components with overall average absolute relative deviation (AARD) below 6%. The viscosities of several sweet and sour natural gas mixtures were predicted with overall AARDs of 6.3% and 5.1% for Versions 1 and 2, respectively. The viscosities of aqueous solutions both of methanol and of glycols were also modeled. A binary interaction parameter was required to fit the data for all aqueous mixtures in Version 2 but only for mixtures of water and methanol in Version 1. The overall AARDs of the calculated viscosities of the aqueous solutions of methanol and glycols by Versions 1 and 2 were 6% and 8.7%, respectively. |
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