Amine Unit

Unit Operation Description

The primary objective of the amine unit involves the removal of acid contaminants, predominantly H₂S, but also addressing CO₂, COS, CS₂, and others from gaseous hydrocarbon streams. This removal of acidic gases is accomplished through a straightforward absorption-desorption process (refer to Figure 1), employing a range of alkanolamine-based solvents. For in-depth insights into amine reactions, solvent selectivity, and overall process conditions, please consult the Amine Corrosion in Damage Mechanisms section.

Corrosion concerns within the amine unit predominantly stem from Amine Corrosion, Wet H₂S Damage (H₂ Blistering/HIC/SOHIC/SSC), and NH₄HS Corrosion, particularly when sufficient NH₃ is present in the treated gas. At times, instances of flow-accelerated corrosion manifest in regions of high turbulence, such as tees, bends, and weld protrusions. This occurrence is notably observed in the hot lean amine stream, especially when surpassing HSAS (heat stable amine salts) limits. Corrosion within the amine unit is well-documented, and extensively described in numerous publications that cover major issues and mitigation measures in both rich and lean amine streams. For further details, please refer to the Amine Corrosion and Monitoring sections.

Potential Damage Mechanisms

Figure 1 Amine Unit diagram with typical damage mechanisms.^{after API RP 571}

Legend: 2 - Wet H₂S Damage (H₂ Blistering/HIC/SOHIC/SSC); 7 – NH₄HS Corrosion; 20 - Erosion / Erosion-Corrosion; 22 - Amine Stress Corrosion Cracking; 45 – Amine Corrosion; 57 - Titanium Hydriting;

Integrity Operating Windows (IOWs)

The Amine Unit list of Integrity Operating Windows (IOWs) focuses on process parameters that are routinely controlled under standard operating conditions, aiming to reflect real-world practices rather than wishful thinking or a “nice-to-have” approach. As a result, the list does not fully align with API RP 584 recommendations, excluding parameters such as NH₄HS concentration, chloride levels in amine, or the detailed quantification of ionic species in Heat Stable Amine Salt analyses. Although these parameters are important, they are not monitored frequently or consistently, and any changes observed may not represent the actual state of the system.

The categorization of Amine Unit IOWs into Standard or Informational reflects a pragmatic approach, consistent with corrosion rate levels typically observed in industrial operations. No Critical IOWs have been identified, as rapid degradation is not expected upon excursions of the selected parameters. Therefore, operators and other relevant parties have sufficient time to implement mitigating actions—either through process adjustments or by refining and tightening the inspection regime.

Table 1 List of typical IOWs for amine unit. I - Informational IOW, S - Standard IOW, C - Critical IOW

General

Absorber

Regenerator

Filters