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Cryogenic Plants

Cryogenic Plants

When higher recovery of ethane and propane is required beyond the capability of HCDPC packages, cryogenic gas processing plants are the preferred solution. In gas processing, cryogenic conditions typically refer to temperatures below -45°C. SPEC designs and supplies turnkey cryogenic systems using advanced process engineering to achieve these low temperatures for maximum recovery of natural gas liquids (NGLs).

Methods for Achieving Cryogenic Temperatures

  • Turbo Expanders
  • J-T (Joule-Thomson) Valve Expansion

J-T Valve Expansion

This method is often used for smaller gas flow applications. It provides a cost-effective and simple solution for cryogenic cooling and is easier to install and operate than turbo expander units. However, it typically results in a lower ethane recovery rate.

The process works using the Joule-Thomson effect, where the gas expands from high to low pressure and cools during the expansion. To achieve the required cryogenic temperatures, a high differential pressure is maintained across the J-T valve with sufficient heat exchange.

Process Description
The gas is first dried using molecular sieve units to reduce water concentration to below 1 ppm. The dry gas is then cooled in a heat exchanger before being expanded across the J-T valve. After expansion, the gas-liquid mixture enters a cold separator. The separated liquid is sent to a De-methanizer Tower, while the overhead gas is recycled through a heat exchanger to improve efficiency. Mechanical refrigeration can be added to enhance recovery and compensate for lower inlet gas pressures.

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Advantages

Modest ethane recovery
Simple design and operation
No rotating equipment required

Limitations

High pressure required
Lower ethane recovery compared to Turbo Expanders

Major Equipment

Molecular Sieve Dehydrators
Gas/Gas Heat Exchangers
J-T Valve
Cold Separator
De-methanizer Tower
Reboilers

Turbo Expander Process

The Turbo Expander process is the predominant method for achieving high ethane recovery. It uses a turbine to expand the gas and achieve temperatures as low as -101°C, significantly lower than those achieved by a J-T valve alone.

Process Description
Before entering the expander, the gas is dried using Molecular Sieves to reduce water content to below 1 ppm. A Gas/Gas Heat Exchanger provides initial cooling. For richer gas compositions, mechanical refrigeration may also be applied. The cooled gas then enters a Cold Separator, where liquid and gas phases are separated.

A J-T Valve and Turbo Expander work in parallel, optimizing recovery efficiency. The J-T valve handles the bottom section, while the expander processes the top gas. Both liquid streams are then directed to a De-methanizer Tower, where methane is separated at the top and NGLs are collected at the bottom.

Major Equipment

  • Gas/Gas Heat Exchanger
  • Cold Separator
  • J-T Valve
  • Turbo Expander
  • De-methanizer Tower

Why Partner with SPEC Technology

SPEC brings extensive experience in cryogenic gas processing and oil and gas technology, delivering complete turnkey project solutions from design to commissioning. Our systems are engineered for efficiency, reliability, and safety, supported by in-house EPC capabilities and global fabrication facilities.

By integrating cryogenic process technologies with precision control and automation, SPEC helps clients achieve higher NGL recovery, energy optimization, and consistent product quality across upstream and midstream operations.