Natural Gas Nitrogen Removal Using Dividing-Wall Rectification
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Solution Overview
Problem
Existing methods for separating hydrocarbon-rich, nitrogen-containing feed fractions in natural gas, such as those using double-column processes, face challenges with carbon dioxide freezing and require complex prepurification or refrigerant management, limiting carbon dioxide tolerance and efficiency.
Innovation Solution
A method involving a separation column with a dividing wall, where a carbon-dioxide-poor stream is taken off in the middle region to serve as a refrigerant, expanded, and used to cool nitrogen-enriched streams, allowing for efficient separation without external refrigerants and reducing carbon dioxide content to prevent freezing, thereby enhancing carbon dioxide tolerance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a double-column process is used for nitrogen removal, then nitrogen separation efficiency is improved, but carbon dioxide tolerance deteriorates due to freezing risks in low-temperature sections
Solution Approach 1:
The invention extracts the harmful carbon dioxide component from the feed gas before it enters the low-temperature rectification section. By removing carbon dioxide in advance through a dedicated removal unit, the feed gas entering the nitrogen separation column has reduced carbon dioxide content, preventing freezing in the cold process sections while maintaining efficient nitrogen separation
Solution Approach 2:
The invention performs preliminary carbon dioxide removal before the main nitrogen separation process. The carbon dioxide removal unit operates ahead of the rectification column, preparing the feed gas by depleting carbon dioxide to safe levels before it enters the low-temperature nitrogen separation section, thus preventing freezing problems downstream
2Object-affected harmful factors
If complex prepurification by amine scrubbing is applied, then carbon dioxide content is reduced to prevent freezing, but device complexity increases
Solution Approach 1:
The invention segments the gas treatment process into distinct functional units: a carbon dioxide removal unit separated from the nitrogen separation column. This segmentation allows each unit to be optimized independently - the carbon dioxide removal unit handles CO2 depletion while the rectification column focuses on nitrogen separation, simplifying the overall system compared to integrated amine scrubbing approaches
3Object-affected harmful factors
If pressure is kept high in carbon-dioxide-containing streams, then carbon dioxide tolerance is improved, but temperature increases reducing refrigeration efficiency
Solution Approach 1:
The invention dynamically adjusts pressure conditions for different process streams. The carbon dioxide-containing bottom-phase product is maintained at high pressure (20-30 bar) to prevent freezing and enable high carbon dioxide tolerance, while a portion is expanded to low pressure (2-10 bar) to generate refrigeration effect for overhead cooling, optimizing both temperature and pressure conditions for different functional requirements
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 eliminates the need for complex refrigerant management and prepurification, maintaining high carbon dioxide tolerance while reducing energy requirements and preventing carbon dioxide solids precipitation, allowing for efficient separation of nitrogen and hydrocarbons without amine scrubbing.
Implementation Method 1
the feed fraction is at least in part liquefied and divided by rectification into a nitrogen-enriched fraction and a hydrocarbon-rich, nitrogen-depleted fraction
Implementation Method 2
the nitrogen-enriched fraction is cooled and partially condensed, applied at least in part to the rectification as reflux
Implementation Method 3
a carbon-dioxide-poor stream which serves for cooling the nitrogen-enriched substream is taken off and expanded upstream of the heat exchange with the nitrogen-enriched stream that is to be cooled
Implementation Method 4
expanded upstream of the heat exchange with the nitrogen-enriched stream that is to be cooled
Data Source
AI summary
The invention relates to a method for the separation of a hydrocarbon-rich, nitrogen-containing feed fraction (1, 101), preferably natural gas, wherein the feed fraction (1, 101) is at least in part liquefied (E1, E2) and divided by rectification (T1) into a nitrogen-enriched fraction (14, 110) and a hydrocarbon-rich, nitrogen-depleted fraction (11, 111) and wherein, in the upper region of the rectification (T1), a nitrogen-enriched stream (14) is taken off, cooled (E3) and applied (20) at least in part to the rectification (T1) as reflux and/or the nitrogen-enriched fraction (110) is cooled and partially condensed (E3), applied at least in part to the rectification (T1) as reflux (115) and the remaining stream (116) of the nitrogen-enriched fraction (110) is subjected to a double-column process (T3). According to the invention, in the middle region of the rectification (T1), a carbon-dioxide-poor stream (13, 113) which serves for cooling (E3) the nitrogen-enriched substream (14) and/or cooling (E3) the nitrogen-enriched fraction (110) is taken off and the feed fraction is rectified (T1) in a separation column (T1) having a dividing wall (W), wherein the dividing wall (W) is arranged at least in the region of the separation column (T1) in which the feed fraction (2, 4, 5, 102, 104, 105) is fed to the separation column (T1) and the carbon-dioxide-poor stream (13, 113) is taken off.