Systems and methods for removing nitrogen during liquefaction of natural gas
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Solution Overview
Problem
Natural gas streams with high nitrogen concentrations pose challenges during liquefaction, leading to difficulties in condensation, reduced heating value, and inefficient processes with slow startup, unstable operation, and high methane emissions.
Innovation Solution
Implementing a nitrogen rejection unit with upstream and downstream columns, and 3-stream or 2-stream condensers for indirect heat exchange to remove nitrogen from the liquefied gas stream, improving nitrogen separation efficiency and process stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If a two or three column configuration with auto-refrigeration system is used to lower nitrogen concentration, then nitrogen removal is achieved, but startup is slow and operation is unstable due to variable feed compositions
Solution Approach 1:
The system divides the nitrogen removal process into multiple independent columns (first nitrogen removal column and second nitrogen removal column) with separate condensers (first condenser and second condenser). Each column-condenser pair operates independently, allowing the system to handle variable feed compositions more effectively and achieve stable operation while removing nitrogen.
2Quantity of substance
If two or three column configuration is used to remove nitrogen, then nitrogen concentration is lowered, but methane emissions increase due to nitrogen vent stream containing high levels of methane
Solution Approach 1:
The system changes the operating parameters of each column and condenser independently, allowing optimization of nitrogen removal efficiency while minimizing methane content in the vent stream. By adjusting temperature, pressure, and flow rates in each independent unit, the system achieves effective nitrogen removal with reduced methane emissions.
3Quantity of substance
If large configurations with five streams are used to remove nitrogen, then nitrogen removal capacity increases, but heat integration becomes suboptimal resulting in slower startup times and transient fatigue
Solution Approach 1:
Instead of using a large single configuration with five streams, the system segments the process into multiple smaller column-condenser units. This segmentation allows for better heat integration within each unit, reduces transient fatigue, and enables faster startup times while maintaining adequate nitrogen removal capacity through the combined operation of multiple units.
4Device complexity
If nitrogen is not removed from natural gas before liquefaction, then the process is simpler, but condensation becomes difficult and heating value is greatly diminished
Solution Approach 1:
The system uses multiple nitrogen removal columns and condensers arranged in series or parallel configurations to efficiently remove nitrogen before liquefaction. This segmented approach achieves effective nitrogen removal that preserves heating value, while the modular design keeps overall process complexity manageable through standardized repeating units.
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
Enhances nitrogen removal efficiency, reduces methane emissions, stabilizes operation, and shortens startup and cool-down times, allowing for faster production and compliance with environmental standards.
Implementation Method 1
The first and second condensers are configured to at least partially condense a nitrogen-containing stream via indirect heat exchange
Implementation Method 2
Each condenser is configured to at least partially condense a nitrogen-containing stream
Data Source
AI summary
Implementations described and claimed herein provide systems and methods for removing nitrogen during liquefaction of natural gas. In one implementation, a nitrogen rejection unit is used in an LNG facility to remove nitrogen from natural gas during an LNG liquefaction process. The nitrogen rejection unit contains at least two columns and at least one 3-stream condenser, 2-stream condenser or a two 2-stream condenser.