LNG Liquefaction Cycle With Integrated Fractionation and Cold Reflux
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Current LNG production methods, particularly in large land-based systems, are inefficient and complex, making them unsuitable for offshore applications, and they often result in the production of unwanted hydrocarbons that are difficult to store and transport safely.
Innovation Solution
A method employing a closed gas expansion process with a fractionation column and heat exchanger system that separates and recirculates a cold reflux to maximize ethane, propane, and butane content in LNG, while minimizing heavier hydrocarbons, using a gas expansion cycle for efficient liquefaction suitable for offshore installations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If a mixed refrigerant cycle is used in large land-based LNG systems, then liquefaction efficiency is improved, but system complexity increases and suitability for offshore applications deteriorates
Solution Approach 1:
The patent extracts the fractionation function from a separate external unit and integrates it within the gas expansion cycle system. The fractionation column is positioned to receive feed gas directly from the gas source and return separated streams to the cycle, eliminating the need for external fractionation equipment while maintaining separation efficiency.
Solution Approach 2:
The patent merges the fractionation process with the gas expansion liquefaction cycle into a single integrated system. The overhead fraction from the fractionation column is fed into the gas expansion cycle, and the bottom fraction is recycled back to the fractionation column, combining two previously separate functions into one unified process.
2Stability of the object's composition
If heavier hydrocarbons are removed from LNG product, then product stability is improved, but energy efficiency deteriorates due to additional separation requirements
Solution Approach 1:
The patent performs preliminary fractionation of the feed gas before it enters the main liquefaction process. The fractionation column separates the feed gas into overhead and bottom fractions, with the overhead fraction (containing lighter hydrocarbons) being processed further in the gas expansion cycle. This preliminary separation prevents heavier hydrocarbons from entering the LNG product stream, ensuring stability without requiring additional energy-intensive separation steps later in the process.
3Reliability
If external pre-cooling is used for overhead fraction, then liquefaction process reliability is improved, but system complexity and energy consumption increase
Solution Approach 1:
The patent implements self-service cooling where the gas expansion cycle itself provides the cooling for the overhead fraction. The expanded cold gas from the expander is used to cool the overhead fraction in a heat exchanger, eliminating the need for external pre-cooling equipment. The system uses its own internal cold stream to perform the pre-cooling function, reducing external energy requirements while maintaining process reliability.
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 increases energy efficiency, maximizes LNG production, and minimizes the production of unstable hydrocarbons, allowing for safer storage and transport, and reduces energy consumption by optimizing the separation of light and heavy hydrocarbons.
Implementation Method 1
a gas expansion cycle for efficient liquefaction suitable for offshore installations
Implementation Method 2
the overhead gas is partially condensed
Implementation Method 3
a heat exchanger system for cooling down and partially condensing the overhead gas stream
Implementation Method 4
the feed gas is led through a fractionation column where it is cooled and separated into an overhead fraction with reduced content of hexane (C6) and heavier components
Data Source
AI summary
A method and system for optimizing the efficiency of an LNG liquification system of the gas expansion type, wherein an incoming feed gas is first separated in a fractionation column by counter current contact with a cold reflux fluid, and a gaseous stream introduced into the heat exchanger system at a reduced temperature such that an intermediate pinch point is created in the warm composite curve.