Prode Properties
Multi phase vapor liquid solid hydrate formation software

Title : Hydrate formation, dissociation, inhibition, software, multi phase equilibria

Download the free student edition, includes both 32 and 64 bit versions for Microsoft Windows
Documentation, includes software installation and detailed description with application examples
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Hydrates in natural gas industry

Interest for hydrates began when researchers found that natural gas hydrates can block gas transmission lines even at temperatures above the ice point, after the discovery many researchers starting from Hammerschmidt, Deaton, Frost investigated the effects of inhibitors such as salts (chloride salts...) liquids (methanol, ethanol, glycols as mono ethylene glycol MEG etc.) on hydrates, thermodynamic inhibitors lower the freezing point and thereby reduce risk of hydrate formation.

Mechanisms of gas hydrate formation and inhibition

The necessary condition for hydrate formation is the presence of water (or ice), gas hydrates can form from dissolved gas or free gas. Thermodynamic inhibitors such as methanol, ethanol, mono ethylene glycol (MEG) etc. can reduce kinectics of nucleation, other inhibitors can reduce agglomeration of hydrate crystals.

Predicting gas hydrate formation

Several methods are available to predict hydrate formation conditions, the old methods (Wilcox, Katz etc.) allow direct solutions while more recent methods based on Van der Waals and Platteeuw theory require a computer software.

Solving multi phase equilibria including hydrate phase

The multi phase flash procedure in Prode Properties solves multi phase equilibria including solid and hydrate phases, given operating conditions and compositions the procedure calculates fugacities plus derivatives of each phase and the second order solver identifies the correct solution. A phase stability step removes unstable phases. The procedure doesn't require the presence of a free water phase and can include single or mixed salts (with electrolyte models).

Accuracy

Prode Properties includes two different models for hydrate phase, a simplified method and a complex method, both based on Van der Waals and Platteeuw theory. Prode Properties allows to select differnt models for vapor, liquid and solid fugacities.
Here, errors (for about 100 points) are determined as difference in hydrate formation pressure calculated by Prode Properties with CPA-PR model vs. measured data sets.
You can contact Prode to receive the complete data set with calculated data and the reference in literature.

Excel application example : multi phase vapor liquid solid hydrate equilibria

This Excel application example shows how to use Prode Properties to solve the multiphase flash operation including hydrates and get the results directly in Excel pages.

First step: calculate multiphase equilibria with solids (hydrate formation) from Prode Properties Editor.

Open Prode Properties Editor and in Stream->Operating dialog select the stream 6 in both lists of first and second window

Prode Properties Editor allows to solve a series of predefined operations, select TP-VLSH as flash operation, then enter 277 K and 15 Bar.a as specifications and click on the button "Compute", the procedure will show the the formation of a hydrate phase

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Second step : evaluate how much methanol (or another inhibitor) is required to prevent hydrate formation at specified conditions

You can evaluate how the addition of a small amount of methanol (inhibitor) can increase the formation pressure for hydrate phase, we recalculate phase equilibria with a 0.002 mole fraction of methahol, as result we must increase the operating pressure to detect a hydrate phase, hydrate formation pressure is now about 70 Bar.
To improve the accuracy of phase equilibria in presence of inhibitors it is recommended to adopt specific BIPs calculated from SLE data points (you may contact Prode for assistance)

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You can obtain the results directly in Excel (open the example page multiphase.xls included in distribution)

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Third step : hydrate formation temperature curve and hydrate formation pressure curve in Excel

With Prode Properties you can calculate the hydrate formation temperature curve or the hydrate formation pressure curve and print a graph in Excel.

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Technical features overview (Windows version)

Typical applications