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Controlled Freeze Zone™ (CFZ) technology

ExxonMobil scientists invented and patented the Controlled Freeze Zone™ technology, a breakthrough process that more efficiently removes impurities from natural gas.

The CFZ™ technology could also make carbon capture and storage more affordable and efficient in reducing greenhouse gas emissions. The technology is fully developed and qualified for commercial application.

This proprietary CFZ™ technology targets the significant portion of today’s world gas resources which contain large amounts of carbon dioxide (CO2). While conventional technologies are unable to efficiently process natural gas with large concentrations of CO2, the CFZ™ technology has the ability to process natural gas with a wide range of impurities. The application of the CFZ™ technology at a global scale could therefore expand the pool of affordable clean-burning natural gas resources for development and delivery to consumers.

The CFZ™ technology efficiently removes impurities from natural gas and is less expensive than existing technologies, requiring fewer processing steps and equipment. This increases its attractiveness, especially for offshore and remote applications.

The CFZ™ technology works by removing CO2 and hydrogen sulfide (H2S) from natural gas in a specially-designed section of a distillation tower, where CO2 is allowed to freeze in a controlled manner.

Next, CO2 is melted and further distilled to recover valuable methane. It can then be pumped safely for injection into dedicated wells — either for sequestering or for use in enhanced oil recovery. The remaining natural gas now contains the desired level of purity.

In conventional methods, CO2 is discharged at very low pressure and must be compressed — at significant costs — for injection into underground storage. In contrast, the CFZ™ technology discharges the CO2 as a high pressure liquid, offering a strong commercial advantage. As a result, the CFZ™ technology could make carbon capture and storage more economical.

The benefits of CFZ™ technology

The CFZ™ technology offers the following advantages relative to conventional gas treating processes for the removal of CO2 and H2S in natural gas:

Single step processing

  • Meets natural gas pipeline quality requirements without additional polishing
  • Requires no solvent regeneration, additive recovery or downstream dehydration facilities

No limit on CO2 or H2S content

  • Handles highly sour gases with ease
  • Easily accommodates increases in feed concentration of sour gas components over the life of the facility
  • Its cost advantage over competing technologies expands with increasing acid gas content

High pressure operation

  • Discharges acid gas as a dry non-corrosive high pressure liquid that can be pumped for sequestration or use in enhanced oil recovery
  • Reduces compression horsepower and equipment requirements for acid gas injection or enhanced oil recovery 

Alternative to sulfur recovery plants

  • Discharges H2S and other sulfur compounds with the CO2 for disposal
  • Provides an attractive alternative to building expensive, high operating cost sulfur plants

Overall cost savings

  • Simplifies process and lowers equipment count, making the CFZ™ technology a low cost alternative
  • Reduces fuel gas consumption, allowing greater gas sales revenue — Allows efficient integration of gas treatment, acid gas injection, and/ or power generation operations  

The global commercialization of CFZ™ technology

The Clear Lake Pilot Plant, near Houston, Texas, first demonstrated the CFZ™ technology concept in 1986. The pilot plant processed natural gas with high levels of CO2 (as high as 65 percent), and at rates up to 600,000 standard cubic feet per day. The successful separation yielded an overhead gas product stream with as low as 300 ppm of CO2, and a liquid CO2 stream with as low as 0.5 percent methane.

In 2008 ExxonMobil moved closer to commercializing CFZ™ technology by constructing a Commercial Demonstration Plant (CDP) at its Shute Creek Treatment Facility in LaBarge, Wyoming — a facility with the capacity to process up to 14 million standard cubic feet per day. After completing construction in 2010, ExxonMobil conducted a formal test program from March 2012 through November 2013.

The CDP successfully processed a wide range of sour gas feeds (8 to 71 percent CO2 and as much as 36 percent H2S). Effective and efficient separations allowed it to easily meet pipeline specifications (<2 percent CO2 and <4 ppm H2S). Under some conditions the methane product met LNG feed quality of <50 ppm CO2. The project also demonstrated another key advantage of the CFZ™ technology through integration with the Shute Creek Acid Gas Injection facility — the ability to separate CO2 and H2S from natural gas into a high-pressure stream, ideal for use in sequestration or in enhanced oil recovery, and reinject it. Competing technologies must undergo costly re-compression to achieve comparable results.

Based on the success at LaBarge, the CFZ™ technology is now ready for commercial use.