Almost all oil and gas production facilities route gases separated during processing to flare systems for safe disposal. While flaring is necessary for operational safety, it also results in the loss of potentially valuable gases. To recover more of these flared gases, operators install flare gas recovery (FGR) systems. This article discusses the key components and functioning of such FGR setups.

Separator and Compressor Systems

The starting point for any FGR system is the gas-liquid separator installed after primary production separators. These large vessels allow additional separation of hydrocarbon gases from residual liquid fractions. The gases are then routed to compressors that boost the pressure to pipeline specifications. Centrifugal, reciprocating, and screw compressors are commonly used depending on throughput requirements. Multiple compressor trains may be installed in stages to achieve higher pressures.

Operating Modes and Controls

Flare Gas Recovery System units can operate in different modes depending on facility needs. During normal production, recovered gases join the sales line directly. In upset conditions, a recycle loop returns gases from the FGR system inlet to upstream of the separators. Automatic controls switch between modes based on inlet pressure. Blowdown silencers and scrubbers mitigate noise from compressor vents during transitions.

Gas Processing and Dew Point Control

Depending on pipeline specifications, recovered gases may need processing to remove impurities. Commonly used systems include molecular sieve or glycol dehydrators to lower water content. Cooling and refrigeration can further reduce hydrocarbon dew points if needed. Control valves modulate throughput to these units based on continuous analyzer readings.

Fuel Gas System Integration

Most FGR compressors run on a portion of recovered fuel gas. Fuel handling involves metering, pressure regulation and safety accessories like relief valves. Dual fuel configurations allow diesel or electric startup if fuel supply fails. Electronic controllers manage automated transfers between fuel sources. Some operations reuse volatile gases as blending components for fuel improvement.

Piping, Valves and Instrumentation

Reliable piping, valves and controls are essential for smooth FGR plant functioning. Carbon steel is typically used with cathodic protection in sour gas environments. Control valves modulate flows while check valves prevent backflows. Instruments continuously monitor pressures, flows, temperatures and hydrocarbon analyses. Leak detection equipment identifies fugitive emissions for maintenance.