Air-Cooled Floating LNG Liquefaction Using Methane as Sole Refrigerant
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Solution Overview
Problem
Current methods for large-scale floating LNG production face challenges in achieving cost competitiveness and efficiency, especially when transporting natural gas over long oceanic distances, and existing technologies do not effectively utilize air cooling for maximizing liquefaction capacity on floating vessels while ensuring safety and environmental sustainability.
Innovation Solution
A method involving on-shore gas pre-processing to remove contaminants, followed by piping the gas to an offshore ship-shaped vessel for air-cooled liquefaction using methane as the sole refrigerant, with multiple parallel liquefaction trains and efficient heat exchange systems, allowing for large-scale, uninterrupted LNG production and storage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If water cooling is used for liquefaction process, then cooling efficiency is improved, but environmental harm and space requirements increase
Solution Approach 1:
The patent extracts the harmful water cooling system from the liquefaction process and replaces it with air cooling. The air coolers are positioned on deck to reject heat directly to the atmosphere, eliminating the need for large volumes of seawater and avoiding thermal pollution of marine environments while maintaining effective heat rejection for the liquefaction trains.
Solution Approach 2:
The patent introduces air as an intermediary cooling medium between the liquefaction process and the environment. Air coolers serve as the intermediary device that transfers heat from the process to the atmosphere, replacing the direct water-based heat transfer system and eliminating the harmful interactions with marine ecosystems.
2Productivity
If multiple parallel liquefaction trains are used, then production capacity is improved, but device complexity increases
Solution Approach 1:
The patent divides the total liquefaction capacity into multiple parallel trains, each with its own refrigerant compression and heat exchange system. This segmentation allows independent operation and maintenance of each train while achieving high aggregate production capacity. The modular approach manages complexity by creating identical, standardized units that can be operated independently.
Solution Approach 2:
The patent employs universal, standardized equipment across all liquefaction trains including identical air coolers, compressors, and heat exchangers. This universality reduces operational complexity through standardized procedures and spare parts while maintaining high production capacity through parallel operation of multiple identical units.
3Reliability
If nitrogen refrigerant is used, then safety is improved, but weight and space requirements increase
Solution Approach 1:
The patent applies self-service by using the liquefaction gas itself (mainly methane) as the refrigerant, eliminating the need for separate nitrogen production and storage systems. The refrigerant is taken directly from the process gas stream, reducing weight and space requirements while maintaining safety through minimal inventory and inherent process integration.
Solution Approach 2:
The patent changes the refrigerant parameter from nitrogen to the liquefaction gas itself (methane-rich natural gas). This parameter change eliminates the need for nitrogen generation equipment and reduces overall system weight and footprint, while the refrigerant safety is maintained through minimal inventory and immediate re-introduction into the liquefaction process.
4Temperature
If air coolers are mounted on cantilevers, then heat rejection efficiency is improved, but structural complexity increases
Solution Approach 1:
The patent positions air coolers on deck-mounted cantilevers that extend outward from the vessel structure, utilizing the vertical and lateral dimensions to maximize exposure to ambient air for heat rejection. This spatial arrangement improves heat transfer efficiency by optimizing air flow access while the cantilever structure provides a compact, integrated solution that minimizes additional structural complexity.
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 approach enables very large-scale, cost-competitive LNG production with enhanced safety and environmental performance, maximizing liquefaction capacity and minimizing space requirements, while maintaining operational efficiency and safety standards.
Implementation Method 1
cooling of the cooling water by heat exchange with air in air coolers
Implementation Method 2
cooling of the cooling water by heat exchange with air in air coolers
Implementation Method 3
heating the cooling water to 80° C. or higher downstream process heat exchangers
Implementation Method 4
The liquefaction gas is first cooled and liquefied by heat exchange with cold refrigerant
Implementation Method 5
The liquefaction gas is first cooled and liquefied by heat exchange with cold refrigerant and then expanded to lower pressure in one or more steps. Each step reduces the temperature
Implementation Method 6
After liquefaction nitrogen may be removed from the LNG, typically any amount that exceeds 1 mole %. This is done by flashing of the LNG at near atmospheric pressure
Data Source
AI summary
A method for large-scale, air-cooled floating liquefaction, storage and offloading of natural gas gathered from onshore gas pipeline networks. Gas gathered from on-shore pipeline quality gas sources and pre-treated to remove unwanted compounds is compressed and cooled onshore before being piped to an offshore vessel for liquefaction to produce LNG.