Surge Function

Fractionation columns produce LPG at varying rates depending on feed composition and operating conditions. Loading terminals, pumps, and pipelines require steady flow for efficient operation. The surge drum decouples upstream separation from downstream handling by storing liquid inventory. Level control manages inflow and outflow rates, absorbing production fluctuations and preventing process upsets. Typical residence times provide 5-30 minutes holdup at design flow rates.

Vessel Design

Horizontal or vertical pressure vessels sized for required surge volume typically 500 to 10,000 gallons. Operating pressures 150-300 psig contain LPG vapor pressure at ambient temperature. Carbon steel construction per ASME Section VIII handles hydrocarbon service. Internal baffles prevent vortexing at outlet connections. Nozzles positioned for vapor space, liquid inlet/outlet, drain, and instrumentation access.

Pressure Control

LPG exists as liquid under pressure but vaporizes if pressure drops below saturation. Pressure control systems maintain vessel pressure above LPG bubble point preventing flashing. Back-pressure regulation on vapor space or compression of boil-off gas maintains stable conditions. Relief valves protect against overpressure from external heat input or pump shutoff scenarios.

Level Management

Level transmitters monitor liquid inventory with controls adjusting downstream pump speed or valve position maintaining target levels. High-level alarms prevent overflow into vapor space piping. Low-level protection stops pumps preventing cavitation and gas breakthrough. Sight glasses provide visual verification where transparent sections are code-compliant.

Applications

Gas processing plants between depropanizer and propane storage, fractionation units separating mixed LPG into propane and butane products, terminals buffering rail car or truck loading operations, and pipeline injection points smoothing flow variations. Handles commercial propane, butane, or propane-butane mixes meeting HD-5 or other specifications.

Safety Features

Pressure relief valves sized per API 521 for fire exposure and other scenarios. Emergency isolation valves enable remote shutdown. Flame arresters on atmospheric vents where applicable. Grounding connections prevent static accumulation. Design and installation per NFPA 58 and 59 for LPG handling. Hazardous area electrical classification for instrumentation.

Construction Standards

ASME pressure vessel code with U-stamp certification. Full radiographic examination of welds. Hydrostatic testing at 1.5x design pressure. Material impact testing for low-temperature service. Corrosion allowances and protective coatings. Foundation design for vessel weight plus liquid inventory and seismic loads.

Operational Benefits

Smooth production despite upstream variations. Steady downstream flow optimizes loading and pipeline operations. Inventory visibility enables production planning. Simple reliable operation with proven technology. Minimal maintenance requirements beyond periodic inspection.

ERGIL LPG surge drums provide essential flow buffering ensuring reliable product handling between separation and distribution systems.