Boil-off Gas System Design for Integrated Liquefaction and Regasification Facilities

BOG system design for integrated liquefaction and re-gasification LNG facilities

Dipanjan Bhattacharya

Senior Process Engineer

Bechtel Oil, Gas, and Chemicals, Inc.

Bindu Bandari

Process Engineering Specialist

Bechtel Oil, Gas, and Chemicals, Inc.

Designing boil-off gas (BOG) system for a LNG facility that offers both liquefaction and re-gasification capabilities is inherently complex and challenging. Steady state simulation tools are commonly employed to design the BOG system for independent liquefaction or regasification facilities. But their application is limited when working with a complex network of multiple jetties, multiple LNG storage tanks, multiple boil-off gas compressors and multiple modes of operation.

This topic discusses a case study based on a dynamic simulation model of an integrated facility that is converted from an existing LNG import terminal to a bi-directional facility. The design challenges are compounded by the fact that the model has to evaluate the hydraulic adequacy of the existing systems for an entirely new operating envelope.

A well-developed integrated dynamic simulation model can be used for hydraulic analysis, compressor selection, what-if-analysis and preliminary tuning of the controllers and sizing of control valves. The what-if-analysis can be performed to evaluate transient operating conditions, system performance and response; to various operating modes - ship loading mode, normal operation and upset scenarios such as compressor trip 

This case study illustrates that a rigorous dynamic model is an effective means to analyze a complex BOG system for an integrated LNG facility.