LNG Nitrogen Rejection Using Dynamic Decompression and Flash Separation
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Natural gas liquefaction plants face challenges in reducing nitrogen concentration and extracting helium from LNG streams, which increases transportation costs and refrigeration needs.
Innovation Solution
A method involving passing an initial LNG stream through heat exchangers and liquid expanders for dynamic decompression, followed by flash equilibrium separation in pre-fractionation vessels and fractionation columns to separate nitrogen and helium, utilizing vapor and liquid streams for cooling and further processing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If nitrogen rejection is performed to reduce nitrogen concentration in LNG, then the heating value of natural gas is improved, but the refrigeration needs of the LNG liquefaction plant increase
Solution Approach 1:
The invention changes the thermodynamic parameters (temperature and pressure) of the LNG stream by passing it through heat exchangers and liquid expanders. The stream is cooled to approximately -161°C and pressure is reduced from high pressure to atmospheric pressure, causing nitrogen to selectively vaporize and separate from the LNG, thereby reducing nitrogen concentration without requiring additional refrigeration capacity
Solution Approach 2:
The invention utilizes phase transition of nitrogen from liquid to vapor state. By cooling the LNG to approximately -161°C and then reducing pressure through expanders, nitrogen undergoes phase change and vaporizes selectively due to its lower boiling point compared to methane, allowing separation through flash equilibrium and fractionation processes
2Quantity of substance
If helium separation is performed to extract helium from natural gas, then helium recovery is achieved, but the process complexity increases
Solution Approach 1:
The invention makes the existing LNG liquefaction and nitrogen rejection system perform multiple functions. The same heat exchangers, liquid expanders, pre-fractionation vessels, and fractionation column that are used for nitrogen rejection also simultaneously separate helium from the natural gas stream, eliminating the need for separate dedicated equipment for helium recovery
Solution Approach 2:
The invention merges the helium separation process with the nitrogen rejection process. Both separations occur in the same equipment train (heat exchangers, expanders, pre-fractionation vessels, and fractionation column), combining two separation functions into a unified process system that reduces overall 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 method effectively reduces nitrogen concentration in LNG, extracts helium, and reduces refrigeration needs by optimizing the use of cold energy, leading to cost savings and improved process efficiency.
Implementation Method 1
passing an initial LNG stream through a first heat exchanger and a first liquid expander to reduce the temperature and dynamically decompress the LNG stream
Implementation Method 2
passing the second expanded LNG stream to one or more pre-fractionation vessels for flash equilibrium separation to obtain one or more vapor streams that have increased concentration of nitrogen
Implementation Method 3
passing the one or more vapor streams and the liquid stream to a fractionation column, withdrawing from an upper portion of the fractionation column a nitrogen enriched stream
Implementation Method 4
at least a portion of one of the vapor or liquid streams from the one or more pre-fractionation vessels passes through the first heat exchanger to provide cooling to the initial LNG stream
Data Source
AI summary
Methods of reducing the concentration of low boiling point components in liquefied natural gas are disclosed. The methods involve dynamic decompression of the liquefied natural gas and one or more pre-fractionation vessels. Particular embodiments are suited for recovering helium and/or nitrogen enriched streams from a liquefied natural gas stream.