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Improving Natural Gas Quality in Mexico

PEMEX was injecting nitrogen into its Cantarell field to maintain pressure and increase production. This led to increased nitrogen content in the sales gas as the field depleted. Costain was engaged to develop a solution and designed a nitrogen rejection unit (NRU) to help PEMEX maintain their sales gas quality.

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Advisory and Concept Development
Specialist Design
Technology Integration
Complex Project Delivery


630 MMSCFD nitrogen rich gas

treated to reduce the content to 1.2% required by gas quality specification

Largest NRU in the world

designed and installed

Costain supplied patented nitrogen rejection technology for PEMEX at their Ciudad Pemex Gas Plant in Tabasco, Mexico. We conducted an initial conceptual process study for the facility and developed this through front end engineering design. The solution involved:

  • Design of the largest NRU in the world
  • A gas pre-treatment unit upstream of nitrogen rejection to remove potential contaminants
  • Two parallel cryogenic nitrogen rejection units, using Costain’s proprietary gas processing technology
  • Three parallel gas turbine-driven gas export compressor trains to bring sales gas up to export pressure
  • An export gas blending and metering system

The design was optimised to minimise the whole project lifecycle costs and acheived low hydrocarbon emissions from equipment.

The success of the concept and FEED studies resulted in Costain receiving the contract to progress into detailed engineering, procurement and construction (EPC). In addition to this we provided commissioning support to PEMEX to bring the facility online safely and efficiently.

Our solution is the largest plant of its type in the world. The NRU is able to handle feed nitrogen content ranging from 5.5-19.1% and brings this content down to 1.2%. This processed gas is blended with unprocessed gas to give sales gas which meets calorific value specifications. The rejected nitrogen is vented to the atmosphere. 

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