LNG REGASIFICATION CONCEPTUAL DESIGN

BACKGROUND

Colbún S.A. and AES Gener required the supply and operation of an offshore LNG Regasification terminal at Oxiquim Port, Quintero Bay, Chile. The terminal was to utilise an FSRU to store LNG and export Natural Gas via a pipeline to the local network when required.

The FSRU was to be supplied with LNG from LNGCs and a jetty required to facilitate the transfer of Natural Gas from the FSRU to the pipeline. Two main options for the transfer of LNG from the LNGC to the FSRU were offered:

1) Utilise a single-berth jetty to moor the LNGC against the FSRU.  Transfer operations shall then be conducted in a double-banked arrangement.

2) Provide a double-berthed jetty against which both the FSRU and LNGC can be moored and LNG transferred across using unloading arms.

PROJECT OVERVIEW

Two options were put forward for further consideration: the Double-Jetty option and the Ship-to-Ship option. Some key elements of the design were common to both options:

• The FSRU has a capacity between 138,000m3 and 170,000m3.
• The required Compressed Natural Gas (CNG) Unloading capacity is 10,000,000Sm3/d (approx. 350MMSCFD).
• The export pressure of the CNG at the FSRU flange is between 75barg and 80 barg with the maximum allowable pressure at 85 to 90barg. The minimum CNG temperature at the FSRU flange is 6°C and 3°C at the exit of the subsea pipeline.
• The Subsea pipeline is 3.5km in length with a diameter between 18” and 22”.

KEY ASPECTS OF DELIVERY

The output of the study was to make a comparison between the two options using a selection matrix of a number of ranking criteria.  These were Technical Suitability, safety risk, cost and schedule.

Key features of the Ship-to-Ship option:

• Only the FSRU moors against the Jetty. LNGC moored in a double-banked arrangement to the FSRU.
• LNG ship-to-ship transfer with hoses
• Vapour return for ship-to-ship transfer
• Spare Arms
• Utilities and Services

DOUBLE-JETTY OPTION

Key features of the Double-Jetty option:

• Twin berths where both the LNGC and FSRU are moored
• Cross jetty transfer using hard arms
• Vapour return lines to and from the jetty
• Spare arms
• Jetty LNG Drum to collect LNG drainings all equipment and pipework
• Utilities and Services

CLEVER THINKING

Conventional comparison techniques were used to make an assessment of the two options against each other and to make sure the common elements were identified.  The use of tried and tested ship to ship transfer techniques with hoses in a jetty location rather than open sea provided the opportunity for a much more cost effective solution.

BENEFITS TO CLIENT

This design and assessment exercise resulted in the development of a feasible and safe solution for the modification of the existing LNG unloading system to allow the use of hoses to transfer LNG, in the event that the existing hard arm system became unusable in the event of an earthquake.

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