The power of cryogenic distillation

Nitrogen is a naturally occurring component of many natural gas reservoirs and is present in varying concentrations across producing basins worldwide. While small amounts are typically passed through to pipeline customers, elevated nitrogen content cannot be, and it has become an increasingly important issue in several US producing regions, particularly in the Permian Basin. As gas production has expanded and diversified, the industry has encountered a growing proportion of lower-quality gas streams that require treatment before they can meet pipeline or LNG specifications.

The increasing importance of LNG exports has further amplified the issue. LNG facilities require tighter specifications, making even moderate nitrogen concentrations problematic. As a result, nitrogen that may once have been tolerable in domestic markets is now a constraint in global gas supply chains.

Among the available technologies for nitrogen removal, cryogenic distillation has emerged as a key solution for processing large volumes of high-nitrogen gas. This article provides a technical overview of why nitrogen removal matters, the principal technologies available for nitrogen rejection, and the advantages of cryogenic distillation as a separation method.

Why nitrogen removal in natural gas matters

Nitrogen is an inert gas and does not contribute to the heating value of natural gas. Its presence introduces several technical and economic challenges. Most pipeline systems limit nitrogen content to approximately 3 - 4%. LNG specifications are often stricter (typically around 1%). Gas exceeding these limits must be treated before sale or transport.

High nitrogen content in natural gas can lead to reduced recovery of valuable hydrocarbons if separation is inefficient, as well as increased flaring or venting if methane is lost during treatment, and higher processing costs and capital expenditure.

Nitrogen presents challenges in LNG production because it lowers liquefaction efficiency, it occupies capacity in liquefaction trains, and it complicates storage and boil-off management.

Low nitrogen concentration in LNG (<1% mol) is a specification needed to prevent ‘rollover,’ which can cause a surge of vapour generation and pressure in LNG storage tanks. Nitrogen in LNG can cause stratified layers to form because nitrogen is more volatile and less dense than methane. Over time, heat ingress will result in a density change as nitrogen prefers to boil out of solution. When the density difference between layers diminishes to a critical point, rapid mixing can occur, triggering rollover. As LNG demand grows, nitrogen removal becomes increasingly critical to maintaining throughput and product quality as well as safe operations.

Read the article online at: https://www.hydrocarbonengineering.com/special-reports/06072026/the-power-of-cryogenic-distillation/