Semi-Submersible Offloading Unit for LNG Vessels
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Solution Overview
Problem
The high costs and operational challenges associated with constructing and maintaining marine LNG terminals, particularly due to the need for long vapor return lines and the difficulty in safely and efficiently connecting tubing to LNG carriers in inclement weather conditions, have hindered efficient and reliable offloading and loading of LNG.
Innovation Solution
A semi-submersible unit equipped with lifting and handling devices, reels for tubing extension, and seabed-anchored flexible members allows for the connection of tubing between a cargo vessel and a recipient, enabling offloading or loading of LNG while accommodating dynamic sea conditions and reducing the need for extensive terminal infrastructure.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a traditional marine LNG terminal with long jetty and breakwater is constructed, then calm conditions suitable for offloading/loading are provided, but construction costs become very significant
Solution Approach 1:
A floating connection unit serves as an intermediary between the LNG carrier and shore-based facilities. This unit provides a stable platform for connecting tubing while eliminating the need for expensive fixed infrastructure like long jetties and breakwaters, thereby reducing construction costs while maintaining operational reliability
Solution Approach 2:
The floating connection unit is designed to be self-positioning and self-stabilizing, using its own buoyancy and positioning systems to maintain operational conditions without requiring extensive fixed infrastructure, thus reducing overall terminal construction requirements
2Reliability
If a long vapor return line is installed between onshore storage tanks and the LNG carrier, then vapor return functionality is provided, but construction costs increase
Solution Approach 1:
The floating connection unit acts as an intermediary that hosts vaporization equipment and storage tanks closer to the LNG carrier. This eliminates the need for long vapor return lines by providing a localized solution on the floating unit, thereby reducing construction costs while maintaining vapor return functionality
Solution Approach 2:
The solution moves the vaporization and storage functionality from the shore-based dimension to a floating offshore dimension, allowing the vapor return system to be much shorter and more cost-effective while still serving the LNG carrier
3Adaptability or versatility
If conventional moorings are used for LNG carriers at sea, then the vessel can be positioned away from shore, but rolling motions increase under wave, wind and current loads
Solution Approach 1:
The floating connection unit serves as a stable intermediary platform that is better suited for offshore conditions than conventional ship-to-shore moorings. It provides a stable connection point for tubing while the LNG carrier maintains its position through dynamic positioning, allowing offshore operation without excessive rolling
Solution Approach 2:
The system uses dynamic positioning of the LNG carrier combined with a floating connection unit that can move with sea conditions. This dynamic approach allows the carrier to maintain position while the floating unit adapts to wave, wind and current loads, providing stability for offloading operations
4Ease of manufacture
If a semi-submersible floating connection unit is used, then terminal construction costs are reduced, but challenges remain in safely connecting tubing under dynamic loads
Solution Approach 1:
The floating connection unit incorporates shock-absorbing mechanisms and flexible connections that are designed in advance to handle dynamic loads from sea conditions. This beforehand cushioning protects the tubing connection during the connection process and during offloading operations, ensuring safety while using a cost-effective floating platform
Solution Approach 2:
The system uses flexible tubing and flexible connection mechanisms that can accommodate relative movements between the floating unit and the LNG carrier. These flexible elements absorb dynamic loads and maintain safe connections under varying sea conditions, enabling cost-effective offshore operations
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This solution enhances operational uptime, safety, and efficiency by facilitating reliable fluid communication between LNG carriers and recipients, even in harsh weather, and reduces the costs associated with traditional terminal construction and maintenance.
Implementation Method 1
a semi-submersible unit equipped with lifting and handling devices, reels for tubing extension
Implementation Method 2
at least one lifting and handling device capable of lifting an end of the first portion of the tubing onto the cargo vessel
Data Source
AI summary
Offloading cargo from a cargo vessel and delivering the cargo to a cargo recipient, or loading cargo onto the cargo vessel from a cargo supplier, may be performed using a cargo vessel which is spread moored at sea to a plurality of mooring points for mooring the cargo vessel in a desired orientation. Alternatively, the cargo vessel may be rotatably moored. Tubing may be provided and configured to be connected to the vessel for fluid communication between the vessel and the cargo recipient or the cargo supplier, and may comprise a first portion configured to be connected to the cargo vessel and a second portion configured to be connected to the cargo recipient or the cargo supplier. A semi-submersible unit may be operable to travel across the sea and carry part of the tubing from a stand-by location to a position adjacent to the cargo vessel, so as to allow an end of the first portion of the tubing to be connected the cargo vessel for offloading or loading the cargo. The unit may have at least one lifting and handling device, which when the unit is positioned adjacent to the cargo vessel, may be operable for arranging the end of the first portion of the tubing at or near a manifold on the cargo vessel for connection thereto.