Cryogenic Nitrogen Removal Using Preseparation Column Reflux
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Solution Overview
Problem
Existing methods for separating nitrogen from hydrocarbon-rich gas fractions in natural gas liquefaction processes face issues with solids formation due to higher hydrocarbons, leading to obstructions and operational impairments in rectification columns and top condensers.
Innovation Solution
A method where a liquid fraction from the main separation column is used as reflux for the preseparation column, effectively removing higher hydrocarbons such as butane, ensuring their concentration is less than 1 ppm in the overhead product, thereby preventing obstructions in the vaporization process.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If nitrogen is separated cryogenically from hydrocarbon-rich gas fractions in a rectification column, then nitrogen separation efficiency is improved, but higher hydrocarbons (from butane) can lead to solids formation and obstructions in the top condenser
Solution Approach 1:
The invention applies preliminary action by removing higher hydrocarbons from the feed stream before it enters the main separation column. A preseparation column is used to extract higher hydrocarbons ahead of time, preventing them from causing solids formation in the top condenser while maintaining efficient nitrogen separation in the main column
Solution Approach 2:
The invention segments the separation process into two distinct columns: a preseparation column that handles higher hydrocarbon removal, and a main separation column that performs the primary nitrogen-methane separation. This segmentation allows each column to be optimized for its specific function, preventing the harmful effects of higher hydrocarbons while maintaining separation efficiency
2Ease of manufacture
If a single rectification column is used for nitrogen separation, then capital costs are reduced, but higher hydrocarbons cannot be effectively removed leading to operational impairments
Solution Approach 1:
The invention divides the single-column system into two columns: a preseparation column for higher hydrocarbon removal and a main separation column for nitrogen-methane separation. This segmentation prevents operational impairments from solids formation while maintaining relatively low capital costs compared to more complex multi-column systems
3Productivity
If higher hydrocarbons are present in the bottom-phase product of the rectification column, then vaporization in the top condenser proceeds, but solids formation occurs leading to obstructions
Solution Approach 1:
The preseparation column performs preliminary removal of higher hydrocarbons from the feed stream before it enters the main separation column. This preliminary action ensures that the bottom-phase product from the main column contains minimal higher hydrocarbons, allowing vaporization to proceed without solids formation
Solution Approach 2:
The invention converts the potentially harmful presence of higher hydrocarbons into a benefit by using the preseparation column to selectively remove them. The higher hydrocarbons that would otherwise cause obstructions are extracted and concentrated in the preseparation column's bottom product, leaving the main separation column's output clean for safe vaporization
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 ensures fault-free operation by keeping higher hydrocarbons away from the bottom-phase product of the main separation column, maintaining the integrity of the rectification process and preventing solids formation in the top condenser.
Implementation Method 1
the feed fraction is separated by rectification into a nitrogen-enriched fraction and a hydrocarbon-rich, nitrogen-depleted fraction and the separation by rectification proceeds in a rectification column
Implementation Method 2
Separating off nitrogen cryogenically from hydrocarbon-rich gas fractions, for example from natural gas or from the residual gas of a natural gas liquefaction process, clearly proceeds at very low temperatures, since the rectification of the key components, nitrogen and methane, must proceed at least in part below the critical temperature of nitrogen (−147° C.)
Implementation Method 3
the top condenser of the rectification column to be provided
Implementation Method 4
During the vaporization of the refrigerant that proceeds in the top condenser of the rectification column
Data Source
AI summary
The invention relates to a method for resolving a hydrocarbon-rich, nitrogen-containing feed fraction (1, 1′), preferably natural gas, is described, wherein the feed fraction (1, 1′) is separated by rectification (T1, T2) into a nitrogen-enriched fraction (5) and a hydrocarbon-rich, nitrogen-depleted fraction (10), and wherein the separation by rectification proceeds in a rectification column consisting of a preseparation column (T1) and a main separation column (T2). A liquid fraction (6) is taken off from the main separation column (T2) above the feed-in site(s) of the fraction (7, 7′, 7″) that is taken off from the preseparation column (T1) and fed to the main separation column (T2), and the liquid fraction (6) is applied to the preseparation column (T1) as reflux.