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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). The CFZ technology also has the ability to process natural gas with a wide range of impurities. Through 2040, natural gas is anticipated to grow more than any other energy source, largely due to electrical power generation growth and its carbon footprint being substantially lower than that of coal. The application of the CFZ technology at a global scale could therefore expand the pool of affordable clean-burning natural gas resources.

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, CO is melted and further distilled to recover valuable methane. This CO2 can then be injected underground 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 as a low pressure vapor and must be re-compressed 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 lower the cost of carbon capture and storage.

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
  • Cost advantages 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 injected underground for use in enhanced oil recovery or into geological formations for permanent storage for sequestration
  • Replaces compression with pumping technology, reducing energy and equipment requirements for acid gas injection or enhanced oil recovery 

Alternative to sulfur recovery plants

  • Removes 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.

However, following a downturn in the industry and due to the abundant supply of low acid gas content, more economical natural gas resources, development activities were suspended until about 2005.

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 and commissioning, ExxonMobil conducted a formal test program from March 2012 through November 2013.

CFZ commercial demonstration plant, LaBarge

The CDP successfully processed a wide range of sour gas feeds (8 to 71 percent CO2 and as much as 36 percent H2S). Natural gas pipeline specifications (<2 percent CO2 and <4 ppm H2S) were easily met thanks to CFZs effective and efficient separations. 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, dry, non-corrosive stream, ideal for use in enhanced oil recovery or dedicated storage. Competing technologies must undergo costly re-compression starting with a wet, corrosive vapor to achieve comparable results.

The results of the CDP testing clearly unveiled a significant benefit of the technology for CO2 feed concentrations above 20 percent. A standardized facility could be designed, focused on the valuable methane product rate. Great flexibility for handling a wide range of CO2 content, from 20 to 75 percent, could be provided by simply adding feed refrigeration to condense the excess CO2. This provides significant benefits when the CFZ technology is deployed in EOR applications in which the CO2 concentration in the associated gas rises over time, when comingling fields with higher acid gas content or when the acid gas content of a reservoir being produced increases over time. Further, standardized units allow the phased development of large resources.

The CFZ technology is ready for commercial use.

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