First-Stage Purpose

Liquid propane from depropanizer or recovery contains dissolved lighter components. First flash at elevated pressure removes bulk vapor reducing load on downstream stages. Captures most volatile components in single step before fine polishing in subsequent flashes.

Operating Pressure

First stage typically 8-15 bar providing initial pressure drop from upstream equipment. Higher pressure than downstream stages minimizes propane loss to vapor while removing substantial light ends. Pressure selection balances separation efficiency versus vapor handling.

Drum Configuration

Horizontal vessel with liquid propane inlet, large vapor space handling high flash gas volume, vapor outlet to compression or refrigeration, liquid outlet to second stage flash, and level control. Sizing accommodates significant vapor generation from pressure reduction.

Vapor Volume

First flash generates largest vapor quantity containing mainly ethane and methane with some propane. Vapor routes to recovery compression, refrigeration system suction, or fuel gas depending on facility configuration and economics.

Material Selection

Carbon steel construction suitable for propane service. Design pressure accommodates first-stage conditions with safety margin. Temperature typically 10-40C depending on upstream process and ambient conditions.

Separation Efficiency

Single-stage flash removes 70-85% of dissolved light ends. Remaining lighter components require second and possibly third stage for specification propane. Efficient bulk removal reduces downstream equipment sizing and costs.

Applications

Gas plant propane recovery after depropanizer overhead, refinery LPG separation, NGL fractionation light ends removal, and any multi-stage propane purification system requiring initial high-pressure flash.

Flash Dynamics

Pressure drop from 15-30 bar upstream to first flash pressure vaporizes light components. Flash equilibrium depends on inlet composition, pressure, and temperature. Proper conditions maximize light ends removal while minimizing propane losses.

Level Control

Maintains liquid inventory for steady flow to second stage. High-level prevents vapor carryover. Low-level indicates upstream feed problems. Controllers coordinate with overall flash train operation.

Vapor Recovery

High vapor volume justifies compression recovery in most facilities. Recompressed gas returns to process or routes to sales. Economic recovery improves overall plant efficiency versus flaring valuable hydrocarbons.

Construction Standards

Design per ASME Section VIII for operating pressure. Materials for propane and light hydrocarbon service. Relief sizing per API 520 for fire exposure. Complete documentation with flash equilibrium calculations.

ERGIL propane first flash drums initiate multi-stage separation removing bulk light ends in gas processing LPG recovery operations.