Tail Gas

Tail Gas: The Residual Gas in Sulfur Recovery

In the oil and gas industry, "tail gas" refers to the residual gas stream exiting a sulfur recovery unit (SRU). This gas, while significantly depleted of its sulfur content, still contains a small percentage of hydrogen sulfide (H₂S) and other sulfur-containing compounds. It's essentially the "leftover" gas after the SRU has extracted as much sulfur as possible.

Understanding Tail Gas:

Tail gas is a crucial aspect of SRU operations. Its composition and treatment significantly impact the environmental performance and efficiency of the overall sulfur recovery process.

Composition:

• Hydrogen Sulfide (H₂S): While significantly reduced compared to the feed gas, tail gas typically contains a small amount of H₂S. This residual sulfur is often measured in parts per million (ppm).
• Other Sulfur Compounds: Besides H₂S, tail gas may contain other sulfur-containing compounds like carbonyl sulfide (COS), carbon disulfide (CS₂), and mercaptans.
• Inert Gases: Tail gas also includes inert gases like nitrogen (N₂) and carbon dioxide (CO₂), which are not involved in the sulfur recovery process.

Importance of Tail Gas Treatment:

The presence of sulfur compounds in tail gas necessitates further processing. Uncontrolled release of tail gas can result in significant environmental pollution and regulatory non-compliance.

Tail Gas Treatment Options:

Various technologies are employed to treat tail gas and minimize its sulfur content, including:

• Claus Tail Gas Treating (TGT) Unit: This unit typically uses a combination of processes like amine scrubbing and Claus reaction to further remove H₂S.
• Sulfur Recovery Units (SRUs) with Increased Efficiency: Modern SRU designs often incorporate technologies that enhance sulfur recovery efficiency, reducing the H₂S concentration in tail gas.
• Selective Oxidation: This process selectively oxidizes H₂S to elemental sulfur, further reducing its concentration in the tail gas.

Environmental Considerations:

The final treatment of tail gas is crucial for minimizing its environmental impact. Tail gas can be:

• Ventured to Atmosphere: After stringent treatment, tail gas with low sulfur content may be vented to the atmosphere.
• Used as Fuel: Tail gas, especially with higher hydrocarbon content, can be utilized as fuel for various processes within the plant.

Summary:

Tail gas represents the residual gas stream after sulfur recovery. While significantly depleted of sulfur, it still requires careful treatment to minimize environmental impact. Proper tail gas management is crucial for optimizing sulfur recovery efficiency and ensuring environmental compliance.