Stage Separation Purpose

First-stage separation at high pressure removes bulk liquids but leaves dissolved light hydrocarbons in gas. Reducing pressure to second stage causes additional condensation. Lower pressure also allows lighter components to remain liquid rather than vaporizing. Staged separation increases total liquid recovery 10-30% versus single-stage.

Operating Pressure

Second stage typically operates 50-150 psig versus 300-1500 psig first stage. Pressure differential drives additional liquid dropout. Too low wastes gas flashing from liquids. Too high leaves recoverable liquids in gas. Optimization depends on gas composition and economics.

Vessel Design

Horizontal or vertical separator with gas inlet from first stage, liquid space for condensate and water collection, gas outlet to compression or dehydration, oil outlet to storage, and water outlet to treatment. Three-phase separation handles oil, water, and gas using density stratification.

Liquid Recovery

Pressure drop from first to second stage condenses C5+ hydrocarbons. Cooler operating temperature enhances condensation. Recovered liquid has API gravity 50-70, more valuable than heavier first-stage condensate. Some operations use refrigeration between stages maximizing recovery.

Material Selection

Carbon steel handles sweet condensate and gas. Sour service needs NACE materials resisting H₂S. Internal coatings protect against CO₂ corrosion and produced water. Design accommodates pressure and temperature cycling during operations.

Applications

Production facility staged separation, gas plant inlet processing, gathering system liquid recovery, wellhead production optimization, and any operation where staged separation improves liquid recovery economics. Common in gas condensate fields with rich gas.

Level Control

Interface control maintains oil-water boundary. Liquid level instruments regulate discharge maintaining inventory. Dump valves send liquids to storage or treatment. High-level protection prevents carryover to gas outlet. Controllers coordinate with first-stage operation.

Gas Quality

Second-stage gas typically enters compression, dehydration, or sales lines. Further cleanup removes remaining liquids and meets pipeline specifications. Some systems add third stage at near-atmospheric pressure maximizing recovery before compression.

Performance Benefits

Increases condensate recovery improving field economics. Provides cleaner gas to downstream equipment reducing fouling and operational issues. Separates water from condensate simplifying treatment. Proven staged separation approach used worldwide.

Integration

Second stage coordinates with first-stage pressure control and downstream compression. Gas from second stage may combine with other sources before treatment. Liquids route to stabilization or storage. System design optimizes overall facility performance.

Construction Standards

Design per ASME Section VIII for pressure service. Materials suitable for condensate, water, and gas composition. Relief protection sized for both gas and liquid scenarios. Complete documentation with separation calculations and material specifications.

ERGIL second-stage separators maximize liquid recovery and gas quality through staged pressure reduction in production and gas processing operations.