Removing hydrates for gas

The formation of hydrates in natural gas processing facilities and pipelines is a critical issue as hydrates can plug equipment, instruments, and restrict or interrupt flow in pipelines. Generally, hydrates will form when the temperature is below the hydrate formation temperature, normally with “free” water present, depending on the gas composition and pressure. 

In general, hydrates can be prevented by:-

1. Maintaining the system temperature above the hydrate formation temperature by using a heater and/or insulation or compression the gas.

2. Dehydration of the gas to prevent the condensation of a free water phase.

3. Injection of thermodynamic inhibitors to suppress the hydrate formation temperature in the free water phase. Methanol (MeOH) is widely used as an inhibitor in natural gas pipelines, particularly in cold climate facilities (e.g., Canadian environments). In these difficult environments, methanol injection is the most economical solution for preventing hydrate formation and is often the only option.The challenge

The determination of methanol injection rate can be a very challenging task for engineers -mainly because of methanol partitioning: the injected MeOH may partition into three phases: (a) the aqueous phase, (b) the vapor phase and (c) the hydrocarbon phase. \

Criteria:

GPSA: Folow the chapter

Aspen Hysys:

Do not use the Peng Robinson package 

This month (May 2015), Aspentech released HYSYS v8.8 with the addition of the Cubic-Plus-Association (CPA) fluid property package. The new CPA PP can more accurately model methanol phase behaviors, especially in the modelling of liquid-liquid equilibria (LLE) including the prediction of the partitioning of methanol between water and hydrocarbons in the hydrocarbon phase.