The formation of hydrates in processing facilities and pipelines has been a problem to the natural gas industry. Whether the problem occurs in transportation or processing, hydrate formation can cause shutdowns and even destruction of valuable equipment. Because of these devastating and often costly consequences of hydrate formation, methods have been applied to prevent hydrate development in gas streams. The conditions that tend to promote hydrate formation include: low temperature, high pressure, and a gas at or below its water dew point temperature with "free" water present.  The formation of hydrates can be prevented by using any of the following techniques; (a) maintaining the temperature above and pressure below the hydrate formation condition, which may not be practically possible due to economical and/or operational reasons, (b) dehydrating a gas stream with solid desiccant or glycol dehydration to prevent a free water phase, and (c) impeding hydrate formation in the free water phase by injection of an inhibitor.  The most common inhibitors are methanol (MeOH), monoethylene glycol (MEG) and diethylene glycol (DEG). Typically, methanol is used in a non-regenerable system while MEG and DEG are used in regenerable processes. With the use of inhibitors, the injected inhibitor may distribute into three possible phases: (a) the vapor hydrocarbon phase, (b) the liquid hydrocarbon phase and (c) the aqueous phase in which the hydrate inhibition occurs and the inhibitor has an effect on hydrate formation inhibition. Therefore, calculating the inhibitor concentration in aqueous phase is important.

The injection rate is a function of feed gas temperature, pressure, relative density (composition), hydrate formation temperature depression, and lean solution concentration. Recently, Moshfeghian and Taraf proposed a shortcut/graphical method to predict the required MEG or MeOH weight percent and flowrate for a desired depression in hydrate temperature of natural gas mixtures.

In this Tip of the Month (TOTM), we will demonstrate how these diagrams can be used to determine the concentration of MeOH in the rich solution and the required total injection rate for a desired hydrate formation temperature.
To learn more about this Tip and past Tips of the Month, visit JMC Tip of the Month.

Check it out, interesting conversation going on on process safety.