Staged Flash Purpose

First-stage flash at higher pressure removes bulk vapor from propane liquid. Second stage at lower pressure flashes remaining dissolved light ends like ethane and methane. Staged separation improves propane purity meeting product specifications while maximizing recovery economics.

Operating Pressure

Second flash typically 3-8 bar versus 8-15 bar first stage. Lower pressure vaporizes lighter components remaining in liquid. Pressure selection balances propane purity against vapor handling costs. Too low wastes propane to vapor.

Drum Configuration

Horizontal or vertical vessel with propane liquid inlet from first stage, flash vapor space, vapor outlet to compression or refrigeration recovery, liquid propane outlet to storage or further processing, and level control maintaining inventory.

Vapor Composition

Flash vapor contains mainly ethane and methane with some propane. Higher propane content than first-stage flash. Routes to compression for recovery or refrigeration system inlet. Economic decision versus flaring depends on facility configuration.

Material Selection

Carbon steel construction suitable for propane service. Design handles operating pressure and temperature typically -10C to +30C. Relief protection against thermal expansion or blocked outlets per LPG codes.

Propane Purity

Single-stage flash leaves 5-10% lighter components in propane. Second stage reduces to 1-3% meeting commercial propane specifications. Critical for propane meeting vapor pressure limits and customer quality requirements.

Applications

Gas plant LPG recovery after depropanizer, refinery propane purification, NGL fractionation intermediate separation, and any process requiring high-purity propane with staged pressure reduction maximizing recovery.

Level Control

Maintains liquid inventory for steady downstream flow. High-level protection prevents vapor carryover. Low-level alarm indicates upstream flow issues. Simple controls integrate with LPG processing system.

Energy Integration

Lower pressure flash removes heat from propane through vaporization. Some designs use second-stage temperature drop for refrigeration duty. System integration optimizes overall energy efficiency.

Performance Benefits

Improves propane purity meeting product specifications. Recovers vapor for additional processing versus losses. Staged separation more efficient than single-stage. Simple proven technology in LPG plants.

Construction Standards

Design per ASME Section VIII for operating pressure. Materials suitable for propane and light hydrocarbons. Relief sizing per API 520/521. Complete documentation with flash equilibrium calculations.

ERGIL propane second flash drums optimize light hydrocarbon recovery through staged separation improving product purity in gas processing operations.