Study Explores Carbon-Capture Options for Gas-Processing Facilities

For operators of gas-processing facilities seeking to decarbonize their operations through carbon capture, one significant challenge stands out: identifying the optimal point for recovering a high-purity CO₂ stream suitable for sequestration. By conducting a comprehensive technoeconomic assessment of principal capture points within the gas-processing methodology, this paper aims to provide insights into addressing this challenge.

CO2 Removal in Gas-Treating Plants

Acid-Gas-Removal Units (AGRU). The natural gas fed to an AGRU is at high pressure (between 10 and 120 barg). This results in high partial pressure of the acid gases, enabling easier removal of the acid gases in a solvent-based AGRU. This contrasts with the processing units downstream of the AGRU.

In a scenario wherein the AGRU feed gas has high CO₂ and low hydrogen sulfide (H₂S), the AGRU produces a CO₂-rich stream as acid gas suitable for sequestration. The CO₂ captured from a high-pressure AGRU is low-cost compared with options wherein CO₂ is to be captured from processing facilities downstream of the AGRU. CO₂ capture from AGRU is not further evaluated in the paper.

Acid-Gas-Enrichment Units (AGEU), Tail-Gas-Treating Units (TGTU), and Incinerator Outlets. Although CO₂ capture from AGRU is attractive from a cost perspective, it must be realized that not all gases are sweet. The majority of the natural gas in the Middle East is sour, which means that the AGRU can produce an acid gas that is a mix of H₂S and CO₂. Identifying the optimal CO₂ capture point in such scenarios requires an evaluation of CO₂ capture locations.

The operator has studied two real-world operational gas plants, Cases A and B, wherein the AGRUs produce acid gas feeding the downstream sulfur recovery unit (SRU). Case A is representative of a rich acid gas (high H₂S/CO₂), while Case B is representative of a lean acid gas (low H₂S/CO₂). The SRUs in both cases operate with a sulfur recovery efficiency of approximately 99% and incinerator-stack sulfur dioxide (SO₂) emissions on the order of approximately 1,000–2,000 ppm by volume.

Study Objectives

The objectives of this study include the following:

• Lower SO₂ emissions into the atmosphere to less than 250 ppm by volume.
• Capture CO₂ available in the natural gas
• Determine the net present value and unit cost of CO₂ capture for each process configuration

Acid-Gas Quality.