Oil & Gas: Natural Gas Processing: Pretreatment

MEI Maverick Engineering has extensive experience in the pre-treatment processes in natural gas processing facilities. These processes are discussed further below.

Slug Catchers

A large volume of liquid exiting a pipeline is referred to as a “slug”. If not contained or captured, this liquid can cause process problems and very costly mechanical repairs.

Slug catchers therefore have two primary functions: the efficient separation of gas and liquid, and providing storage capacity for the separated liquids. The slug catcher is simply a vessel with sufficient volume and retention time that allows the gas stream to expand, thereby providing the area for the liquids to slow down and settle. As the volumetric flowrates of gas and the liquid loadings contained therein increase, the design of the slug catchers get larger and more complex, such as the HARP designs. MEI Maverick Engineering has experience working on all sizes and types of slug catchers, including the HARP.

Click here to see MEI contributions to the world’s largest HARP.


Dew Point Control

As with wellhead facilities, it is desired to further treat the inlet natural gas to remove heavy hydrocarbon liquids. This is accomplished through the use of JT plants or straight refrigeration.

The JT plantrelies on the Joules-Thompson effect, whereby the gas is expanded across a pressure-reducing valve, thus cooling the stream. This causes the gas liquids to condense and can be separated in a gravity separator downstream.

Another method of dew point control is straight refrigeration. Refrigeration cools the gas, dependent on design and economics, from 20o Fto -30o F. This temperature falls below the dew point of the some of the gas liquids, allowing condensation and recovery  downstream in a separator. The refrigeration media is typically Freon or propane for straight refrigeration processes.

  • Pressure drop on the gas stream is limited thereby often eliminating the need for residue gas compression
  • Ideal for remote locations where a liquid pipeline is unavailable.

Condensate Stabilizers

The process of increasing the quantity of intermediate (C3 to C5) and heavy (C6+) components in gas condensate is called condensate stabilization. The main purpose of this process is to reduce the vapor pressure of the condensate liquids to prevent the production of vapor phase upon flashing the liquid to atmospheric storage tanks. On the other hand, the scope of this process is to separate very light hydrocarbon gases, methane and ethane in particular, from the heavier hydrocarbon components (C3+).

There are two methods for stabilizing gas condensates:

  • flash vaporization
  • fractionation

The more efficient process is fractionation, and it also provides better control over vapor pressure for safer storage and transport. Fractionation also reduces the emissions of volatile hydrocarbons (VOCs) to the atmosphere. Non-refluxed fractionation is simpler, but less efficient. Since an external cooling source is not required, it makes it a better process for remote locations, such as wellheads.