Flash Operation

Rich amine leaves the contactor at high pressure saturated with H₂S, CO₂, and dissolved light hydrocarbons. Flash tank pressure typically 50-100 psig causes hydrocarbon vaporization. Released gas contains 60-80% hydrocarbons with some H₂S and CO₂. Partially degassed amine flows to regenerator with lower contaminant load.

Vessel Design

Vertical drum with high-pressure inlet, flash section at intermediate pressure, vapor outlet to fuel gas or compression, liquid outlet to regenerator feed, level control, and temperature monitoring. Inlet device breaks momentum promoting vapor release. Mist eliminator prevents amine carryover in overhead vapor.

Hydrocarbon Removal

Light ends absorbed in high-pressure contactor would otherwise vaporize in regenerator consuming reboiler heat without releasing acid gas. Flash tank removes these hydrocarbons before regeneration. This saves 10-20% reboiler fuel and prevents hydrocarbons from contaminating acid gas sent to sulfur recovery.

Pressure Selection

Flash pressure balances hydrocarbon removal against acid gas loss. Too low wastes H₂S to flash gas. Too high leaves hydrocarbons in amine. Typical 50-100 psig optimizes separation. Some systems use two-stage flash for maximum efficiency.

Material Selection

Carbon steel handles most rich amine service. Stainless steel for high acid gas loading or corrosive conditions. Materials per NACE standards for H₂S environments. Flash tank sees less severe service than regenerator due to lower temperature.

Gas Handling

Flash gas routes to fuel system after H₂S concentration verification. High H₂S content requires amine treating or flaring. Some plants compress flash gas back to contactor inlet recovering H₂S. Economic choice depends on gas composition and facility fuel balance.

Temperature Effects

Rich amine temperature affects flash efficiency. Warmer amine releases more vapor. Heat exchange with hot lean amine before flash increases hydrocarbon removal but also flashes some acid gas. Design balances these factors based on amine type and treating conditions.

Control Systems

Level transmitter controls amine flow to regenerator maintaining tank inventory. Pressure control on vapor outlet manages flash conditions. Temperature monitoring tracks performance. Integration with regenerator feed system coordinates operation.

Applications

Natural gas sweetening with rich gas containing heavy hydrocarbons, refinery hydrogen purification units, associated gas treating, and any amine system where hydrocarbon contamination affects regeneration. Essential in gas plants processing condensate-rich streams.

Performance Benefits

Cuts regenerator reboiler duty 10-20% through hydrocarbon removal. Reduces fuel gas make from regenerator overhead. Prevents hydrocarbon contamination of acid gas to sulfur plant. Simple pressure vessel with fast payback from energy savings.

Construction Standards

Design per ASME Section VIII with NACE materials for sour service. Pressure rating accommodates operating conditions with safety margin. Relief valve protects against blocked outlets. Complete documentation with flash calculations and material certifications.

ERGIL rich amine flash tanks reduce regeneration costs and improve acid gas quality by removing hydrocarbons before amine stripping.