LNG Technical Glossary

Understand the term. Then follow it into the plant.

Definitions connect directly to the LNG University body of knowledge so acronyms and technical concepts lead into systems, equipment, drawings and safeguards.

Curriculum Explorer Digital LNG Plant

Storage & Vapor

Boil-Off Gas (BOG)

Natural-gas vapor generated as heat enters LNG storage or transfer systems and a portion of the liquid changes phase.

Controls & Protection

Emergency Shutdown System (ESD)

A protective system designed to bring defined parts of a facility to a safer state by initiating actions such as isolation, equipment shutdown or transfer interruption.

Safety Instrumented System (SIS)

An instrumented protection layer that performs defined safety functions independently of normal process control when specified hazardous conditions occur.

Distributed Control System (DCS)

The primary process-control environment used to monitor variables, execute control loops, present alarms and support operator interaction with the facility.

Pressure Protection

Pressure Safety Valve (PSV)

A self-actuated mechanical device that opens at a defined pressure to protect equipment or piping from overpressure.

Blowdown Valve (BDV)

An actuated valve used to depressurize process equipment or piping to a disposal system under defined operating or emergency conditions.

Isolation

Emergency Shutdown Valve (ESDV)

An actuated isolation valve that moves to a defined safe position when an emergency shutdown function is triggered.

Engineering Documents

Process Flow Diagram (PFD)

A system-level engineering drawing showing major equipment, principal process streams and key operating information.

Piping & Instrumentation Diagram (P&ID)

A detailed engineering drawing that shows process piping, valves, equipment, instruments, control relationships and important utility or protection connections.

Cause & Effect Chart

A matrix or logic document that connects initiating conditions with alarms, trips, valve actions, equipment shutdowns and other protective responses.

Compression

Anti-Surge Control

A fast-acting compressor protection function that maintains sufficient flow through a centrifugal compressor by opening recycle when operation approaches the surge region.

Dry Gas Seal (DGS)

A non-contacting gas seal arrangement commonly used on centrifugal compressors to limit process-gas leakage along the shaft.

BOG & Regasification

Recondenser

A vessel or contactor used to absorb or recondense boil-off gas into subcooled LNG by direct contact under suitable pressure and temperature conditions.

Regasification

Open Rack Vaporizer (ORV)

A vaporizer that uses seawater flowing over heat-exchange panels to warm and vaporize high-pressure LNG.

Submerged Combustion Vaporizer (SCV)

A vaporizer that uses hot combustion gases bubbled through a water bath to provide heat for LNG vaporization.

Liquefaction

Main Cryogenic Heat Exchanger (MCHE)

The principal cryogenic heat exchanger in many liquefaction processes where treated natural gas is cooled, condensed and subcooled using refrigeration streams.

Storage

LNG Rollover

A rapid mixing event between stratified LNG layers that can produce a sudden increase in boil-off gas generation.

LNG Stratification

The formation of LNG layers with different densities or compositions inside a storage tank.

Marine & Commercial

Custody Transfer

The measurement and accounting process used to establish the quantity and quality of LNG transferred between commercial parties.

Marine & Transfer

Vapor Return

The controlled movement of vapor between ship and shore during LNG transfer to manage displacement vapor and pressure.

Process Safety

Hazard and Operability Study (HAZOP)

A structured multidisciplinary review that uses guidewords to identify process deviations, causes, consequences and safeguards.

Layer of Protection Analysis (LOPA)

A semi-quantitative risk-analysis method that evaluates initiating-event frequency and the risk reduction provided by independent protection layers.

Commissioning

Inerting

The displacement or dilution of oxygen-containing atmosphere with an inert gas such as nitrogen to reduce flammability risk before hydrocarbon introduction.

Cooldown

The controlled reduction of equipment and piping temperature before or during introduction of cryogenic LNG.